inlet stator rotor junction box
impeller
volute
flange bolt flange rotor can ceramic bushing outlet
ESSENTIALS OF HYDRONICS FOR GSHP PROFESSIONALS
Manual for ClimateMaster Training Course:
Essentials of Hydronics for GSHP Professionals Table of Contents Section 1: What is Hydronic Heating? Section 2: An Overview of Modern Hydronic Hardware Section 3: The Relationship between Temperature & Heat Section 4: Water-to-Water Heat Pumps: Section 5: Thermal Equilibrium Section 6: Valve Basics Section 7: Pipe Sizing and Head Loss Section 8: Circulators Section 9: Hydraulic Equilibrium Section 10: Expansion Tanks Section 11: Basic Hydronic Controls Section 12: Hydronic Heat Emitters for GSHP Systems Section 13: Air Separation and Removal Section 14: Buffer Tanks for GSHP Systems Section 15: Sample Schematics for Hydronic Systems Supplied by GSHPs
Appendix A: Piping Schematic Symbol Legend Appendix B: Heat Emitter Application Range Appendix C: Head Loss Graphs for Copper Tube abd PEX Appendix D: Additional Sources of Information on Hydronic System Design
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Welcome to the ClimateMaster Essentials of Hydronics for GSHP Professionals course manual. This course is tailored for those wanting to combine water-to-water GSHP technology with water-based distribution systems for heating and cooling. It will show you how to create reliable and efficient hydronic systems supplied by geothermal heat pumps that will provide years of comfort. The applications shown represent state-of-theart systems for both residential and light commercial buildings. Given the versatility of hydronics, there is virtually no limit to the unique system piping and control designs possible. This can be both good and bad. Good in the sense that an experienced designer can modify an established system design concept to the exact requirements of a “special needs” situation. Bad from the standpoint that some inexperienced designers might create “piping aberrations” that do not perform as expected. It’s the latter that must be avoided, and doing so is a major goal of this application manual. Although not every possible piping schematic can be shown, those that are represent well-established practices to help ensure the systems you create using the information presented will perform as expected. Topics Covered: This manual addresses the following topics: • • • • • • • • • • • • • • •
The benefits of hydronics An overview of modern hardware for hydronic systems The relationship between flow rate, temperature change and heat The concept of thermal equilibrium The concept of hydraulic equilibrium Pipe selection and sizing Valve selection and sizing Circulator performance, selection and sizing Expansion tank selection and sizing The basics of modern hydronic controllers An overview of hydronic distribution systems An overview of hydronic heat emitters The do’s and don’ts of hydronic radiant panel heating systems The concept of hydraulic separation and how to achieve it Filling and purging hydronic systems
Local Code Requirements: It is impossible to present hydronic piping systems that are guaranteed to meet all applicable codes throughout the U.S. and Canada. It is the responsibility of all those using piping or electrical schematics shown in this manual to verify that such designs meet or exceed local building or mechanical codes within the jurisdiction where the system will be installed. In some cases, local codes may require differences in design or additional safety components relative to those shown on the application drawings.
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Section 1: What is Hydronic Heating? The best way to describe a hydronic heating system is “a conveyor belt for heat.” This concept is shown in figure 1-1. Heat is “loaded” onto the water stream at the heat source, carried to where it’s needed by the water flowing through piping, and then “unloaded” at one or more heat emitters. Within this simplified general concept are thousands of options that allow hydronic heating systems to be tailored to the exact needs of the building and its owner. heat released
circulator
water flow
heat emitter
heat source
heat emitter
A very basic hydronic heating system: “A conveyor belt for heat.”
When water absorbs heat within the heat source, its temperature increases. In the systems we will discuss, the water doesn’t change from liquid to vapor as it does in a steam heating system. As warm water travels through the distribution system, a small portion of the heat it carries is released from piping and other components. As the water passes through a heat emitter, more heat is released. The rate at which heat is released from the heat emitter depends on several things, including the water temperature, the room temperature, the size of the heat emitter and the water flow rate. The vast majority of residential and light commercial hydronic heating systems are classified as closed-loop systems. The water they contain is sealed in and maintained under slight pressure. Ideally, the same water recirculates through the system over and over, year after year. Very small amounts of fresh water are added only when necessary. This reduces the potential for corrosion and allows the system to last for decades. A hydronic heating system might be as simple as a water heater connected to a loop of flexible plastic tubing that warms a bathroom floor. More sophisticated systems might use multiple boilers or heat pumps along with a wide assortment of heat emitters specifically selected to match the thermal, aesthetic and budget constraints of a particular building. Those same heat sources can also provide the building’s domestic hot water, heat the swimming pool, and even melt snow on the driveway. The versatility of hydronics makes such options available in both new construction and retrofit situations. When properly planned and installed, modern hydronic heating provides years of unsurpassed comfort in nearly all types of homes and commercial buildings — comfort so good that the occupants might literally forget it is winter as they walk in the door. Why Use a Hydronic System? Hydronic heating and cooling systems offer many benefits not available with forced-air systems. These include: Superior Comfort: Hydronic heating has long been respected for providing excellent thermal comfort. The better systems achieve 3
this by not only maintaining the desired air temperature in each room, but by warming objects in the room and the room surfaces themselves. Comfort has become the preeminent reason discriminating owners select hydronic heating.
Warm surfaces are a major benefit of hydronic radiant heating.
Unobtrusive Installation: Hydronic systems can be installed without having to drill, saw or otherwise hack out major pieces of the home’s structure. A given volume of water can absorb almost 3,500 times more heat than the same volume of air. This means that small tubing can replace large, cumbersome ducting. For example, a 3/4”-diameter flexible tube can deliver the same amount of heat as a 14” x 8” rigid metal duct when both systems are operated under typical conditions. These two heat delivery systems are shown to scale and side by side in figure 1-3.
2 x 12 joist
this cut would destroy the load-carrying ability of the floor joists
14' x 8' duct 3/4' tube A 3/4”-diameter tube carrying water can convey the same heat as a 14” x 8” duct carrying heated air.
When necessary, a tube of this size is easily routed through floor framing without drilling large holes that significantly weaken the structure. This allows the entire piping distribution system to be easily routed through and concealed within the structure of a typical wood-frame building. Accommodating ducting sized for the same heat delivery capability in the same manner, is virtually impossible. With the possible exception of wooden “I-joist” framing, or specially designed floor trusses, most ducting is simply
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too large to be routed through holes in floor framing. These force compromises, such as suspending the ducting from the bottom of framing, as shown in figure 1-4, or concealing it behind valences or soffits that are visible within living spaces.
Duct systems require more headroom than hydronic piping.
Should the aesthetics of an otherwise meticulously planned building be compromised to “shoe-horn” in a heating or cooling system? The obvious answer to this question is no, but in reality this is done quite often. In some cases, the inability to accommodate properly sized ducting leads to inadequate heating or cooling of the building. The latter is one of the chief complaints from owners of improperly sized or installed forced-air heating and cooling systems. Design Flexibility: Hydronic distribution systems offer virtually unlimited options to accommodate the comfort needs, usage, aesthetic tastes and budget constraints of just about any building. A single hydronic heat source can supply heated water to several different kinds of heat emitters, provide the building with domestic hot water, and supply specialty loads such as a swimming pool or snow-melting system. When a heat pump serves as that heat source, it’s possible to provide both heating and cooling. The latter is supplied using a chilled-water distribution system. A simplified schematic of this concept is shown in figure 1-5. These systems will be discussed in more detail later in this publication.
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air handler0001 (for chilled water cooling)
compressor
WATER-TO-WATER0001 HEAT PUMP
purge0001 valve
zoned hydronic0001 space heating distribution system diverter0001 valve
reversing0001 valve
air0001 separator
buffer0001 tank
thermal0001 expansion0001 valve
condenser
expansion0001 tank
evaporator
refrigerant piping
purge0001 valves
variable speed circulator
purge0001 valve
expansion0001 tank
to ground loop
from ground loop
make-up water assembly
horizontal earth loop0001 configuration shown high density polyethylene tubing
Concept for a heating/cooling system supplied by GSHP.
Clean Operation: Another common complaint from owners of forced-air heating systems is the amount of dust and other airborne pollutants their systems distribute throughout the building. Although often the result of poorly maintained filters, this complaint demonstrates one of the pitfalls of whole-house air circulation.
Dust and allergen dispersal are characteristic of poorly maintained forced-air systems.
In contrast, most hydronic heat emitters induce very gentle air circulation relative to that created by a central forced-air system. The hydronic heat emitters that do use fans or blowers typically create room air circulation rather than whole-house air circulation. People with allergies often appreciate the reduced symptoms experi-
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enced in building with hydronic radiant heating systems. It’s a tangible benefit that is virtually priceless to those who benefit from it. Quiet Operation: Many owners view their home as a sanctuary against the noise of the outside world. Quiet indoor environments have a matchless value of their own. They offer a place to relax, read, write or enjoy quality music. Why should any heating or cooling system compromise this enjoyment?
Owners want quiet spaces in their homes — hydronics can provide this.
A properly designed and installed hydronic system produces virtually undetectable sound levels within the occupied areas of a home. The loudest device in the system is typically the heat source, and with proper installation its sound output can be isolated to the mechanical room. Zonability: The purpose of any heating or cooling system is to provide comfort in all areas of a building throughout the year. Doing so requires a system that can adapt to the lifestyle of the occupants, as well as constantly changing thermal conditions inside and outside of a building. A heating system that attempts to maintain all parts of a building at the same temperature, at the same time, seldom accomplishes its goal, nor does it give its owner much flexibility. In most buildings it’s better to divide the heating and cooling system in smaller, independently controlled areas called zones. A separate thermostat or other room temperature-sensing device controls the temperature within each zone. Zoned systems provide the potential for reduced energy consumption by allowing for lower air temperatures in unoccupied areas. They also allow the comfort level of rooms to be adjusted to suit individual tastes and activity levels. Imagine a heating system that can automatically adjust itself as sunlight pours into some windows but not others. A system that automatically reduces heat output when several people gather in a game room or home theater, but at the same time maintains a toasty warm bathroom in which another person is taking a shower. This type of “room-by-room” zoning is easily accomplished using hydronic distribution systems, and it can be done without elaborate or expensive hardware. In some systems, room-by-room zoning can be provided by non-electric thermostatic devices fitted to individual panel radiators, as shown in figure 1-8. Such systems are also discussed later in the manual.
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TRV
TRV
thermostatic0001 radiator valves0001 (TRV) on each0001 radiator
TRV
TRV
TRV TRV
flexible PEX tubing
0001 variable-speed0001 circulator manifold station
Example of a “homerun” hydronic distribution system.
Energy Efficiency: Hydronic systems reduce energy consumption in several ways: • The small size of hydronic tubing compared to equivalent forced-air ducting greatly reduces undesirable heat loss from the heat distribution system. For example, the previously mentioned 14” x 8” duct has approximately 16 times more surface area than its hydronic equivalent: a 3/4”-diameter tube. This implies the duct’s heat loss will be about 16 times greater than that of the tube when operated at the same surface temperature and surrounding conditions. This is especially important in situations where the ducting or tubing must pass through semi-conditioned space. Even in situations where the tubing and ducting are covered with the same insulation, the larger surface area of the ducting results in significantly greater heat loss. • The electrical energy required to circulate water through a well-designed hydronic system is typically a fraction of that used to move air in a similarly sized forced-air system. Using state-of-the-art circulators, it’s possible to distribute sufficient water flow to a typical 2,500-square-foot house using no more than 25 watts of electrical power. A blower providing an equivalent rate of heat delivery could use several hundred watts of electrical power. • Hydronic systems also lower energy use by discouraging or even eliminating room air stratification (e.g., the tendency of warm air to rise to the ceiling while cool air settles to the floor). Warm air pooled against a ceiling increases heat loss to the attic. It also enhances the air leakage of the room. Both effects can significantly increase energy use during the heating season. Hydronic systems that heat the floors in a room with high ceilings can eliminate room air stratification. At the same time, they maintain “warmth” in the lower occupied areas of the room. Such conditions are highly conducive to thermal comfort. In many cases, occupants can lower thermostat settings in buildings with floor heating while still maintaining very suitable comfort levels. • Hydronic systems are highly adaptable to renewable energy sources such as heat pumps, solar thermal systems, waste heat recovery devices and biomass burning boilers. Equipping buildings with a well-designed and durable hydronic distribution system holds open the possibility of supplying that building from a wide variety of
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heat sources, including some that have not yet been invented. • Finally, as previously mentioned, zoned hydronic systems also provide the potential for unoccupied rooms to be kept at lower temperatures, which lowers heat loss and reduces fuel consumption. GeoDesigner system simulation software, by ClimateMaster, allows simulation of all types of residential heating, cooling, and domestic hot water systems including geothermal, furnaces, boilers, air conditioners, and air-to-air heat pumps. GeoDesigner provides estimated annual energy consumption (and costs) of the various systems and assists in the design of ground loops for geothermal systems. GeoDesigner generates written reports showing each system’s cost of operation and operating statistics from simple inputs including heating and cooling loads, geographical location, utility costs, thermostat set point, etc.
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Section 2: An Overview of Modern Hydronic Hardware Those who want to design quality hydronic heating systems must be committed to ongoing learning. New products and design concepts will vie for their attention as the market grows and more people demand the benefits that hydronic heating and cooling offer. Learning starts with the fundamentals. What are the basics components found in almost every type of hydronic heating system, and what are their functions? This section gives you a basic understanding of the “building blocks” used in almost every residential and light commercial hydronic system. Later sections will demonstrate the repeated usage of these components in a wide variety of systems. Figure 2-1 shows the fundamental components of a single circuit hydronic system. heat released to building circulator
air0001 separator
flow0001 check
room0001 thermostat
heat emitter pressure0001 relief0001 valve heat source
make-up water assembly backflow preventer pressure reducing valve expansion0001 tank
purging0001 valve
The basic components in a hydronic system.
• Heat Source: The starting point in a hydronic system is getting heat into the water. While it can be said that any device that heats water is a potential hydronic heat source, some options are clearly more practical than others. Boilers supplied with natural gas, propane and fuel oil arguably are the most “traditional” heat sources used in many residential and commercial hydronic systems. However, the versatility of hydronics allows many other possibilities, including geothermal water-to-water heat pumps, biomass-fuel boilers and solar collector arrays. Each of these options has strengths and limitations. Some constrain the system design in terms of operating temperature or flow rates. Some can only be used with specific types of heat emitters. The cost and local availability of certain fuels obviously has a big impact on heat source selection. In this publication we will focus on geothermal water-to-water heat pumps, such as the unit shown in figure 2-2, as the heat source for several types of hydronic systems.
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An example of a modern water-to-water heat pump. (ClimateMaster TMW series)
• Circulator: Often referred to as a pump, the circulator is what “motivates” fluid to flow through the system, in the proper direction, and at a suitable rate. The key component within a circulator is its impeller, which is rotated by an electric motor. As water flows through the spinning impeller mechanical energy called “head” is transferred to the fluid. The evidence of this added mechanical energy is higher pressure at the circulator’s discharge port compared to its inlet port. Water always flows from an area of higher pressure to an area of lower pressure. The higher pressure water leaving a circulator wants to get back to that circulator’s inlet. It will do so through any available pathway. The fundamental concept in designing a hydronic system is to create piping pathways that allow water carry heat throughout the building as it flows from the circulator’s outlet back to its inlet. Figure 2-3 shows a circulator that would be typical of those used in residential or light commercial hydronic systems. This type of circulator is more specifically categorized as a “wet-rotor circulator.” Such circulators are cooled and lubricated by the fluid passing through, and do not require oiling as do some earlier generation circulators which couple the impeller assembly to a separate air-cooled motor. Wet-rotor circulators have been in use for more than five decades and have earned a reputation for reliability and quiet operation. They are extensively used in geothermal heat pump applications for flow in the earth loop, and with water-to-water heat pumps for flow on the load side of the system. Many current generation wet-rotor circulators can operate at three different speeds. The circulator’s speed switch is set based on the circuit it is installed in, and the desired flow rate in that circuit. Circulator selection and sizing will be discussed in later portions of this manual.
A modern 3-speed wet-rotor circulator.
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• Air Separator: All closed-loop hydronic systems operate best when free of air. In some cases, flow through the piping system cannot even be established until the majority of air in the piping and components has been purged. An air separator is designed to capture air bubbles from the water flowing through it and route these bubbles to a venting device where they are ejected from the system. Many different types of air separators are currently available. All function by reducing the fluid’s flow velocity, as well as providing surfaces that air bubbles can cling to as they rise toward a venting device. Air separators function best when located near the outlet of the heat source, where the hottest water will flow through them. This is where molecules of oxygen, nitrogen and other gases are most likely to coalesce into bubbles that can be captured and ejected. An example of a high-performance air separator is shown in figure 2-4. You will see several schematics throughout this publication that show proper usage of air separators.
A high-performance air separator.
• Flow-check Valve: An often overlooked characteristic of hydronic heating systems is that hot water “wants” to move upward in the system, while cool water “wants” to move downward. This movement is caused by slight differences in the density of hot vs. cool water (the higher the water’s temperature, the lower its density). If an unblocked flow path exists between an area of heated water and an area of cool water, a slow but persistent flow will be established in an attempt to equalize these temperatures. Such a flow is often called “thermal migration,” and can occur even when all circulators in the system are off. If allowed to occur, heat migration can lead to aggravating problems by allowing heat into portions of the system where or when it is not needed. Think of this phenomenon as a “thermal leak” in the system. A flow-check valve or spring-load check valve can prevent such a situation. These valves contain a weighted metal plug or spring that holds the valve closed until a slight forward opening pressure (typically 1/4 psi) is present. This forward opening resistance is sufficient to stop heat migration, but still allows the valve to instantly open as soon as the circulator in the associated portion of the system turns on. These valves will also prevent reverse flow. Many current generation hydronic circulators are now supplied with internal spring-loaded check valves. These circulators eliminate the need to install a separate flow-check or spring-loaded valve in each circuit, and they generally reduce installation cost.
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Example of a flow-check valve.
• Expansion Tank: All fluids expand when heated. If a closed-loop hydronic system were completely filled with water, the pressure in that system would rise rapidly as the water is heated. Dangerously high pressures that could rupture piping components would quickly develop. To prevent this, all closed-loop hydronic systems must have an expansion tank. This tank contains a sealed internal chamber filled with pressurized air. This air is separated from the system water by a flexible rubber diaphragm. As the water expands, the sealed air volume behind the diaphragm is partially compressed, and system pressure increases slightly. When turned off, the pressurized air volume expands as the water shrinks back to its original volume.
Example of a diaphragm-type expansion tank.
• Pressure Relief Valve: The forces that expanding water can generate are extremely powerful. To prevent dangerously high pressures from occurring, every closed-loop hydronic system must be equipped with a pressure relief valve. Most systems used in residential or light commercial buildings have pressure relief valves rated at 30 pounds per square inch (psi). If the pressure at the relief valve location reaches this pressure, fluid is immediately released to lower system pressure.
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Pressure relief valves should always be installed with their stem in a vertical upright position, as shown in figure 2-7. Most pressure relief valves are installed on or close to the heat source. They should always be equipped with a discharge pipe that ends near a floor drain. This pipe cannot contain any type of valve or flow-restricting device, and should have minimal fittings. The lever at the top of a pressure relief valve should be periodically lifted to verify that the valve is ready for operation. This is normally done during annual maintenance checks.
A pressure relief valve.
• Control System: An ideal hydronic heating system would always deliver heat to the building at exactly the same rate the building loses heat to the outdoors. Such a system would be called “fully modulating” because it could vary heat output from zero to full capacity as necessary. Unfortunately, fully modulating heat sources such as boiler or water-to-water heat pumps are not yet available. In lieu of modulation, many hydronic control systems regulate heat output from the heat source to the building by turning the heat source and circulator(s) on and off. Heat is delivered to the building in intervals, the length of which depends on how large the load is. For example, on a very cold day, a properly sized heat source would remain on most of the time. However, during a milder day that same heat source may only be operated 10-25%of the elapsed time. The length of the on-cycle and off-cycle determines the total heat delivered to the load over a given elapsed time. A room thermostat similar to that used in other heating systems controls this on/off cycling. Hydronic heating systems also have controls that regulate the water temperature delivered to different parts of the system. For example, it’s not uncommon for a boiler to deliver 170ºF water to fin-tube baseboard heat emitters while at the same time delivering 110ºF water to a radiant floor slab in a different part of the building. Multiple water temperature distribution systems are also possible when geothermal water-to-water heat pumps serve as the heat source. Still other controls provide safety against excessive high temperatures or water loss in the system. In some (but not all) situations, these controls are required by code. A specific type of safety control called a manual reset high limit — shown in figure 2-8 —turns off the heat source and prevents it from automatically restarting if water leaving the heat source ever reaches a preset temperature. Think of this device as a “circuit breaker” for water temperature.
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A manual-reset temperature limit control.
There are also many electronic controllers available to handle specific tasks within hydronic systems. They include controllers to manage a multiple heat source system, operate mixing devices or oversee operation of several zones. Some of these controllers can communicate with similar devices and thus “share” certain devices, such as an outdoor temperature sensor. Some can even be monitored and adjusted over the Internet. Several of these more sophisticated controllers will be discussed in later sections of this manual.
A controller that adjusts boiler temperature based on outdoor temperature.
• Make-up Water Assembly: All hydronic systems experience minor pressure drops over time. Sometimes it’s caused by air being expelled from vents. Other times it’s the result of evaporation from valve packing or circulator flange gaskets. An automatic make-up water assembly feeds new water into the system whenever the system’s pressure drops below a preset value, typically in the range of 10 to 20 psi. Hence, this assembly “makes up” for minor water losses. A typical make-up water assembly consists of a backflow preventer, pressure reducing valve and shut off valve. The backflow preventer does just what its name suggests: It prevents any fluid in the hydronic system from migrating back into the building’s potable water piping. Most plumbing and mechanical codes mandate a backflow preventer on any hydronic system connected to a building’s potable water system. The pressure reducing valve in the make-up water assembly detects when the system’s pressure drops below a
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set lower limit and responds by allowing water in to restore system pressure. It’s important to understand that following their initial filling and air purging, properly functioning closed-loop hydronic systems require only minor amounts of make-up water. Large amounts of fresh water are NOT good for closed-loop systems containing iron or steel components. The dissolved oxygen in fresh water encourages corrosion and sludge formation.
An automatic make-up water assembly that maintains system pressure. (Courtesy of Caleffi North America).
• Purging Valves: When a hydronic system is put in service, it must be filled with water and cleared of air. A specialized valve called a “purging valve” is used in combination with the makeup water assembly to establish a rapid water flow through the system as it is filled. The rapid flow displaces air bubbles and pulls them along with the water. The mixture of water and air eventually exits the piping through a side port on the purging valve (see figure 2-11). This process is called purging.
Modern hydronic purging valve. (Courtesy of Webstone, Inc.)
When this exiting stream is free of air bubbles, the purging process is complete, and the side port of the purging valve is closed. The use and correct placement of purging valves is essential to properly filling the system and preparing it for operation. • Heat Emitters: All hydronic heat emitters absorb heat from water flowing through them, and deliver that heat to the building space in which they are located. However, various types of heat emitters use different forms of heat transfer to accomplish this task. Some devices, like the fin-tube baseboard (see figure 2-12) and fan-coils, rely on convective heat transfer. They
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add heat directly to room air as it passes through them. The heated air then flows into and around the room.
An example of a fin-tube baseboard convector. (Courtesy of Weil-McLain)
Other hydronic heat emitters rely on thermal radiation to deliver most of their heat output into the room. One example of such a heat emitter is a concrete slab with embedded tubing. Figure 2-13 shows tubing installed over polystyrene insulation awaiting the concrete slab.
Flexible hydronic tubing that will be embedded in a concrete floor.
Although the term “thermal radiation” sounds ominous, it refers to something that’s natural and not harmful in any way. Thermal radiation is simply infrared light. It behaves similar to visible light, but our eyes can’t see it. It travels out from the heat emitter and is quickly absorbed by objects and surfaces within the room. The instant thermal radiation strikes these surfaces it becomes heat, warming the object that absorbed it. Warm objects and surfaces within a room significantly improve comfort. Tubing Options: There is a wide variety of tubing materials and joining systems now available for use in hydronic heating and cooling systems. The most commonly used piping materials include: • Rigid copper water tubing (usually type M thinner wall) • Crosslinked polyethylene tubing (PEX) • Multi-layer composite tubing (PEX-AL-PEX)
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• Multi-layer composite tubing (polypropylene and fiberglass) • Black iron or steel tubing (typically schedule 40 wall thickness) Copper Tubing: Many residential and light commercial hydronic systems use copper water tubing for at least some portion of the system. Rigid, type M (thinner wall) copper tubing is often used within the mechanical room to maintain a neat appearance and keep the other components supported. In some systems, it is also used to construct some or all of the distribution system through the remainder of the building. In hydronic systems, copper water tubing can be joined by traditional soft soldering using a 95/5 tin/lead solder. It may also be joined using one of several “press fit” fittings systems now on the market. The latter use a specialized fitting with o-rings that is mechanically compressed to create a pressure-tight joint. An example of copper tubing joined by pressed fittings is shown in figure 2-14.
Most residential and light commercial hydronic systems can be constructed using copper water tube in sizes from 1/2” up to 3” nominal inside diameter. Larger sizes of copper water tube are available, but may not be economically competitive with other piping options now available. PEX Tubing: In the early 1980s a new type of tubing, developed in Europe, entered the North American hydronic market. Crosslinked polyethylene tubing (a.k.a. PEX) is now a staple of hydronic heating worldwide. Billions of feet of this tubing has been installed in hydronic systems. When properly applied, it has proven to be extremely durable. Most of the PEX tubing used in hydronic applications is manufactured with a special layer called an oxygen diffusion barrier. This layer prevents oxygen molecules from diffusing through the tube wall and reaching the water within the system. This in turn greatly reduces the potential for oxidation corrosion. PEX that meets the ASME F876 standard and that is equipped with an oxygen diffusion barrier meeting the DIN 4726 standard is commonly used in hydronic heating systems. It can withstand temperatures as high as 200ºF with simultaneous pressures up to 80 psi. These temperature and pressure numbers are much higher than what would be found in hydronic systems supplied by geothermal heat pumps. PEX tubing is currently available in sizes from 5/16” to 2” nominal inside diameter. Samples in sizes from 3/8” to
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3/4” are shown in figure 2-15. The smaller sizes are often used to construct radiant floor, wall or ceiling panels, as well as other types of manifold-based distribution systems (which will be discussed latter). Larger sizes of PEX tubing can be used to supply manifold stations or convey liquids over long distances at high flow rates.
PEX tubing with oxygen barrier in sizes of 3/8”, 1/2”, 5/8” and 3/4”
PEX-AL-PEX Tubing: Developed as a composite of both PEX and aluminum, PEX-AL-PEX tubing is also widely used in hydronic systems. It consists of an inner layer of crosslinked polyethylene, a center layer of welded aluminum, and an outer layer of crosslinked polyethylene (see figure 2-16). These layers are bonded together using special adhesives.
PEX-AL-PEX tubing consists of an inner and outer layer of PEX with a center layer of aluminum.
In North America, it is currently available in sizes form 3/8” to 1”. Tubing that meets the ASTM F1281 standard has a temperature rating of 210ºF with a corresponding pressure limit of 115 psi. These ratings are slightly higher than PEX tubing, and are also much higher than would be required in a hydronic system using a geothermal heat pump as the heat source. The aluminum core layer of PEX-AL-PEX tubing provides an excellent oxygen diffusion barrier. It also allows the tubing to retain its shape when bent, as shown in figure 2-17. In addition, the aluminum layer reduces expansion movement relative to standard PEX tubing.
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PEX-AL-PEX tubing is easily bent by hand and retains its shape.
PEX-AL-PEX tubing is currently available in sizes larger than 1” in Europe, but not in North America. It’s likely this will change in the near future. Like PEX, PEX-AL-PEX tubing is a thermoset polymer and cannot be joined by fusion techniques. There are several types of compression and press fittings available for joining PEX-AL-PEX. Polypropylene Composite Pipe: Another piping option of European origin now available in North America is polypropylene composite tubing. Available in a variety of sizes from 3/8” to 6”, the tubing features a fiberglass core that, in combination with the polypropylene inner and outer layers, allows operating temperatures up to 185ºF. Polypropylene composite tubing is joined by socket fusion, a process in which the mating surfaces of the tube and fittings are simultaneous heated using special tools, and then immediately forced together while held in alignment. Figure 2-18 shows a segment of 4” polypropylene composite pipe and a matching coupling being simultaneous heated in this fixture.
A 4” polypropylene composite tube and fitting being joined.
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Once the mating surfaces of the tube and fitting reach the proper temperature, the heating element is removed, and the components are forced together while held by the fixture. The resulting joint is extremely strong and irreversible. Examples of polypropylene composite tube and fittings joined by socket fusion are shown in figure 2-19.
Example of polypropylene composite tube and fittings joined by socket fusion.
The relatively low thermal conductivity of this piping material (relative to metal) and its wall thickness make the piping more resistant to surface condensation when carrying chilled water. Piping Supports: All piping used in hydronic systems should be properly supported. The support method must support the weight of the pipe and its contents, and allow the pipe to expand and contract as its temperature changes. The support requirements will vary depending on the piping material. In some cases, mechanical or plumbing codes mandate specific support-spacing and weight-bearing requirements. In the absence of specific code requirements, the following guidelines are suggested for supporting rigid copper tubing: • • • •
1/2” and 3/4” tubing — maximum support spacing = 5 feet 1” and 1.25” tubing — maximum support spacing = 6 feet 1.5” and 2” tubing — maximum support spacing = 8 feet Vertical piping maximum support spacing is every floor level or 10 feet, whichever is less.
The following support guidelines are suggested for PEX and PEX-AL-PEX tubing carrying heated fluids: • • • •
5/16” through 1/2” tubing — maximum support spacing = 2 feet 3/4” and 1” tubing — maximum support spacing = 2.5 feet 1.25” and 1.5” tubing — maximum support spacing = 3 feet 2” tubing — maximum support spacing = 4 feet
The following support guidelines are suggested for polypropylene composite tubing carrying heated fluids: • 1/2” tubing — maximum support spacing = 2 feet • 3/4” tubing — maximum support spacing = 2.5 feet • 1” tubing — maximum support spacing = 3 feet • 1.25” tubing — maximum support spacing = 3.3 feet • 1.5” tubing — maximum support spacing = 3.9 feet • 2” tubing — maximum support spacing = 4.6 feet • 2.5” tubing — maximum support spacing = 4.9 feet • 3” tubing — maximum support spacing = 5.2 feet • 4” tubing — maximum support spacing = 6.6 feet One of the most popular methods of supporting rigid tubing in mechanical rooms is with a strut/clamp system,
21
such as the one shown in figure 2-20. In this case, the strut rails are supported from the ceiling by threaded steel rod. Notice that this system used rubber-lined clamps to prevent metal-to-metal contact between the copper and steel, as well as to attenuate vibration along the pipe. This method of support is highly versatile. It can accommodate a wide range of pipe sizes, as well as serve to support electrical conduit.
Rigid piping support with strut/clamp system.
Other piping support methods include: • Wire hangers: Typically used to suspend small piping from wooden floor framing. • Clevis hangers: Used to support horizontal pipe from ceiling via threaded steel rods. • Polymer clips: Typically screws to a support surface. Tubing is then clamped into support. It’s important to allow for thermal expansion when supporting piping. This is especially true for polymer tubing, which can expand 7 to 10 times as much as metal piping as it warms. In general, it’s best to allow the PEX, PEXAL-PEX or polypropylene tubing to move through support points rather than rigidly fix the tubing in place. The relatively short, straight tubing runs in mechanical rooms, in combination with elbow fittings, help absorb expansion movement. However, long, straight runs of tubing should have either flexible supports or an inline expansion compensator to absorb tubing movement. When installing flexible PEX tubing from coils, be sure to size holes through framing at least 1/4” greater than the outside diameter of the tubing. Also try not to create situations where the tubing will rub against surfaces such as framing or subflooring.
22
Section 3: The Relationship Between Temperature & Heat Sensible Heat: Energy exists in many forms…electrical, chemical, mechanical and thermal. Energy in thermal form is what we call heat. This energy causes the molecules of the material in which it is present to vibrate back and forth. The more heat the material contains, the more vigorous these vibrations. We can’t see molecules vibrate, even under a powerful microscope. But we can detect the relative amount of heat in an object by measuring its temperature. Simply put: Temperature is how we sense the amount of heat present in an object. Although it’s possible for a material to absorb heat without changing temperature, the material has to change phase (solid to liquid, or liquid to vapor) for that to happen. The hydronic systems we will discuss do not involve materials changing phase; therefore the only type of heat we’ll examine is sensible heat. The word “sensible” implies that the heat is able to be sensed (detected) by a change in temperature. Heat Transfer and Flowing Water: In heating system design, we’re often more interested in the rate of heat transfer rather than the amount of heat. A heat pump rating of 48,000 Btu/hr describes the rate heat can be created and delivered to a stream of water. It certainly doesn’t mean the heat pump will produce 48,000 Btus and then “die” like a worn-out battery. The rate of heat transfer into or out of a stream of water is easy to calculate if you know both the flow rate and temperature change of the water as it flows through something. Formula 3-1 can be used for this calculation. Formula 3-1:
Where: Q = rate of heat transfer into or out of a stream of water (Btu/hr) f = flow rate of water (gallons/minute, abbreviated gpm) ∆T = the temperature change of water as it passes through the heat exchanging device (ºF) k = a constant based on the fluid and its approximate temperature (see table). Temperature of fluid (°F)
Water
30% propylene glycol solution
50
k=500
k=475
100
k=496
k=479
150
k=489
k=476
200
k=481
k=476
It’s important to understand that the rate of heat transfer into or out of a stream of fluid depends on both the temperature change and the flow rate. It doesn’t, for example, depend only on how hot a pipe feels at some point in the system. Many people assume that a pipe that feels hot is moving a large quantity of heat through the system, and a pipe that feels cool or “luke warm” isn’t carrying much heat. Don’t make such assumptions. Look at the following examples.
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90 ºF heat pump
9 gpm 78 ºF
heat0001 emitter
9 gpm Heat transfer from source to load.
Example 1: Water flows out of the return manifold of a radiant floor system at 78°F through a heat pump where it picks up heat. It leaves the heat pump at 90°F. The flow rate through the circuit is 9 gpm. What is the rate of heat transfer to the water stream? Solution: Since the water averages about 84, the value of the constant k will be just a bit less than 496 (say 495). Putting this and the other data into formula 1-1 yields:
This is a substantial rate of heat transfer — enough to heat an average-size house — and yet the piping and other components in this circuit would not feel “hot” to the touch. That’s because skin temperature is usually in the mid80ºF range. Example 2: Water flows from a boiler into a panel radiator at 180ºF and exits at 165ºF. The flow rate through the radiator is 0.5 gpm. What is the rate of heat transfer from the water to the radiator?
Tin = 180º F
Tout = 165º F
water @ 0.5 gpm Water flow and temperature drop across a panel radiator.
Just use formula 3-1 again, this time with the constant k having a value around 485:
Compared to the first example, this is a much smaller rate of heat transfer, even though the water involved is substantially hotter, and the piping both into and out of the radiator would feel very hot to the touch. Formula 3-1 applies regardless of whether heat is moving into or out of the stream of water. It’s a formula that can be universally applied in hydronic heating. The essential point of these examples is you should not judge the rate of heat transfer based on temperature only. Always feel (or measure) the temperature change of the water as it flows through a component and factor in the flow rate. There’s more to heat transfer than meets the finger tips!
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Section 4: Water-to-Water Heat Pumps All heat pumps move heat from an area of lower temperature to one at a higher temperature. The “source” from which the lower temperature heat is being taken can be just about anything. Many heat pumps extract heat from outside air. They are appropriately called “air-source” heat pumps. Geothermal heat pumps extract heat from the ground or water in contact with the ground. They are likewise referred to as ground source heat pumps. The heat pumps discussed in this manual use a standard vapor-compression cycle of R-22 or R-410a refrigerant. As the refrigerant moves around the cycle, it changes from vapor to liquid and vice versa in a continuous process. When liquid refrigerant evaporates, it absorbs heat from its surroundings. Conversely, when a vaporous refrigerant condenses back to a liquid, it releases heat to its surroundings. The basic components used in a water-to-water (heating only) heat pump are shown in figure 4-1. electrical energy input
cool gas
hot gas refrigerant piping compressor to ground loop
2
evaporator
condenser to load 3
1
heat output
heat input 4
from ground loop
from load
thermal0001 warm liquid expansion0001 valve Basic refrigeration components in a “heating only” water-to-water heat pump. cold liquid
Let’s exam the refrigerant cycle, beginning in the evaporator. Refrigerant enters the evaporator as a low-temperature, low-pressure liquid. It passes across the surface of copper or steel tubing through which water or a mixture of water and antifreeze is flowing. Because the liquid refrigerant is several degrees colder than the water, heat moves from the water through the copper or steel tubing wall, and is absorbed by the refrigerant. As heat is absorbed, the cold liquid refrigerant vaporizes or evaporates. The vapor collects at the top of the evaporator (shown as bubbles in figure 4-1). The cool refrigerant vapor then passes to the compressor. Here the vapor is compressed, and its temperature immediately increases. The hot gas line leaving the compressor can be quite hot (140–170ºF). The hot gas then flows to the condenser. Here it passes across another coil of copper or steel tubing carrying water that flows through a hydronic distribution system. Because the hot refrigerant gas is warmer than the water, heat moves from the gas to the water. This causes the refrigerant gas to condense back to a liquid, but still remain at a relative high pressure. Finally, the liquid refrigerant goes from the condenser to the thermal expansion valve (TXV). Here its pressure is reduced, and its temperature immediately drops. The refrigerant is now back to the same condition at which we began examining the cycle, and it is ready to enter the evaporator to begin the same process again. The materials and shapes used to construct the evaporator and condenser of a water-to-water heat pump vary from one manufacturer to another. However, the goal is always the same: To move heat from the low-temperature “source” to the higher temperature “sink” using as little electrical energy as possible to operate the compressor. Reversible Water-To-Water Heat Pumps: As with air-source heat pumps, a reversing valve can be added to water-to-water heat pumps. This allows them to provide heated water or chilled water. The latter can be used for building cooling or for other chilled water 25
industrial applications. The basic internal design of a reversible water-to-water heat pump (in the heating mode) is shown in figure 4-2. cool gas
compressor
electrical energy input
hot gas refrigerant piping
reversing0001 valve to ground loop
evaporator
condenser to load
heat input
heat output
thermal0001 expansion0001 valve
from ground loop
from load
cold liquid A reversible water-to-water heat pump (operating in heating mode).
warm liquid
When the reversing valve is activated by a 24VAC signal, refrigerant flow is reversed through the evaporator and condenser. The heat absorbed from the building’s hydronic distribution system is added to the heat generated by the compressor. The combined heat is then transferred to the water stream flowing through the condenser. In a ground source system, this heat is then carried to and dissipated into the earth or directly to ground water. The flow of refrigerant in a reversible water-to-water heat pump operating in the cooling mode is shown in figure 4-3. cool gas
compressor
electrical energy input
hot gas refrigerant piping
reversing0001 valve to ground loop
evaporator
condenser
to load
heat output from ground loop
thermal0001 expansion0001 valve
warm liquid
heat input from load
cold liquid
A reversible water-to-water heat pump (operating in cooling mode).
Dedicated Domestic Hot water Mode: The THW heat pump includes a dedicated domestic hot water mode. Its domestic hot water mode is a fullcondensing mode providing approximately three tons of domestic water heating capacity. The THW includes two degrees of internal separation between the refrigerant and the potable water, as well as a bronze internal potable water circulator. This mode can provide up to 145ºF domestic water.
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Water-to-Water Heat Pump Performance (Heating Mode): In hydronic heating system applications, there are two performance characteristics that are particularly important: • Heating Capacity • Coefficient of Performance These performance indices both vary based on the operating conditions of the heat pump. Both are affected by the distribution system the heat pump is coupled to. The heating capacity is very dependent on the temperature of the fluid entering the evaporator, and the temperature of the water returning to the condenser from the hydronic distribution system. A graph showing the variation in capacity is shown in figure 4-4. ClimateMaster TMW036 W/W
45
ELWT = 80ºF
Heating capacity (Btu/hr)
ELWT = 100ºF ELWT = 120ºF
40 35 30 25
20
20 25 30 35 40 45 50 55 60 65 70 Entering source water temperature (ºF)0001 (source water flow rate = 9 gpm)
Heating capacity of water-to-water heat pump vs. entering source water temperature.
The flow rate through the evaporator and condenser also affect the heat pump’s heating capacity. Figure 4-5 shows this effect for a ClimateMaster TMW036 unit operating with a source water flow rate of 9 gpm and 5 gpm. 45
ClimateMaster TMW036 W/W
ELWT = 80ºF
Heating capacity (Btu/hr)
ELWT = 100ºF ELWT = 120ºF
40 35 30
ELWT = 80ºF ELWT = 100ºF ELWT = 120ºF
source0001 flow rate0001 = 9 gpm
source0001 flow rate0001 = 5 gpm
25
20
20 25 30 35 40 45 50 55 60 65 70
Entering source water temperature (ºF)0001 (SOLID LINES: source water flow rate = 9 gpm)0001 (DASHED LINES: source water flow rate = 5 gpm)
Heating capacity vs. source water temperature at different flow rates.
Notice that the heating capacity decreases slightly as the flow rate through the evaporator decreases. This is also true for flow rate through the condenser. Lower flow rates reduce convection heat transfer on the water side of these heat exchangers (e.g., the evaporator and condenser). This in turn reduces the rate of heat transfer through them, and hence lowers their heating capacity. 27
Coefficient of Performance: The thermal performance of many hydronic heat sources is expressed as an “efficiency.” It is a means of indicating the ratio of a desired output divided by the necessary input.
When the units in the top and bottom of the fraction are the same, the efficiency is simply a decimal percentage. For example: Consider a boiler in constant operation that consumes 9/10 of a therm of natural gas in an hour. During that hour, the boiler delivers 78,000 Btu of heat. Its thermal efficiency could be calculated as:
A similar definition applies to the efficiency of a heat pump (e.g., the ratio of the desired output to the necessary input). The desired output is the heating capacity. The necessary input is the electrical power needed to operate the heat pump. This ratio is called the coefficient of performance of the heat pump, and is abbreviated as COP. Since the electrical power to operate the heat pump is usually expressed as wattage, the convenient form of the COP formula is:
For example: Assume the input power to operate a heat pump was 2,000 watts. The heat pump’s heating capacity under this condition was 24,000 Btu/hr. Its COP would be:
Notice that the units of watt and Btu/hr both cancel out in this formula. This means the COP is just a number with no units. The best way to think of COP is the number of units of heat output the heat pump provides per unit of electrical input energy. If the COP of a heat pump is 3.5, it provides 3.5 units of heat output per unit of electrical energy input. One could also think of COP as the number of times “better” the heat pump is at producing heat relative to an electrical resistance heating device. The COP of an electrical resistance heating device will always by 1.00. Another way to think of COP is to multiply it by 100 and use that number as a comparison to the efficiency of electric resistance heat. For example, if electrical resistance heat is 100% efficient, then by comparison, a heat pump with a COP of 3.5 would be 350% efficient. The quantities that go into making up the COP of a heat pump are shown in figure 4-6.
28
Qe=3500 watt = 11,946 Btu/hr
Qoutput = Qground + Qelectrical
to ground loop
to load
Qg=36,054 Btu/hr heat input
Qo=48,000 Btu/hr
heat output
from ground loop
from load
heat output rate(Btu/hr) electrical input (watt) 0001 3.413 ground heat input rate + electrical heat input rate (Btu/hr) COP = electrical input (watt) 0001 3.413 heat output rate(Btu/hr) 48,000 COP = = = 4.0 electrical input (watt) 0001 3.413 3500 0001 3.413 COP =
Calculating the COP of a water-to-water heat pump.
The heating capacity or COP of a water-to-water heat pump is very dependent on the operating conditions (e.g., the entering source water temperature and its flow rates, as well as the entering load water temperature and its flow rate). A graph showing how the COP of a ClimateMaster TMW036 heat pump varies as a function of entering source water temperature and entering load water temperature is shown in figure 4-7. ClimateMaster TMW036 W/W
7
ELWT = 80ºF
6.5 6 Heating COP
5.5 ELWT = 100ºF
5 4.5 4
ELWT = 120ºF
3.5 3 2.5 2
20 25 30 35 40 45 50 55 60 Entering source water temperature (ºF)0001 (source water flow rate = 9 gpm)
COP for water-to-water heat pump vs. entering source water temperature.
This graph shows that the heat pump’s COP improves with warmer source water temperatures as well as cooler load water temperatures. This means it’s best to keep the water temperature from the ground source as high as possible, while at the same time keeping the required operating temperature of the hydronic distribution system as low as possible. High source and low load operating temperatures also improve heating capacity. These are both key issues when interfacing a water-to-water heat pump with a hydronic distribution system. The relationship between the heating COP, source water temperature and load water temperature can also be ex-
29
pressed as shown in figure 4-8. Here, heating COP is plotted as a function of the difference between the entering source water temperature and leaving load water temperature. 10 9 8
Heating COP
7 6 5 4 3 2 1 0
0 10 20 30 40 50 60 70 80 90 100 Di0001erence between entering source and leaving load water temperature
COP vs. difference between leaving load and entering source water temperature.
Cooling Performance: A unique benefit of many water-to-water heat pumps is that they are reversible, and thus able to operate as chillers. The cold water they produce can be used for cooling and dehumidifying both residential and commercial buildings. Designing a chilled-water cooling system involves knowledge of how choices in the hydronic distribution system will affect operation of the heat pump. To that end, we will look at the cooling performance of water-to-water heat pumps in a manner similar to that just discussed for heating performance. The cooling performance of a water-to-water heat pump can be categorized as follows: • Cooling Capacity • Energy Efficiency Ratio (EER) Cooling capacity represents the total cooling effect (sensible cooling and latent cooling) that a given heat pump can produce while operating at specific conditions. As with heating, the cooling ability of a heat pump is affected by the temperature of the fluid streams passing through the evaporator and condenser. To a lesser extent, it’s also affected by the flow rates of these two fluid streams. The cooling capacity of a ClimateMaster TMW036 water-to-water heat pump is shown graphically in figure 4-9.
30
total cooling capacity (Btu/hr)
45
ClimateMaster TMW036 W/W ESWT = 50ºF ESWT = 70ºF ESWT = 90ºF
40 35 30 25
20
50 55 60 65 70 75 80 85 90 Entering load water temperature (ºF)
Cooling capacity vs. entering load water temperature.
As the temperature of the entering load water goes up, so does the cooling capacity. Keep in mind that lower entering load water temperature will produce better sensible and latent cooling effect. It can also be seen that increasing temperature from the earth loop decreases the cooling capacity of the heat pump. The common way to express the cooling efficiency of a water-to-water heat pump is an index called EER (Energy Efficiency Ratio), which is defined as follows:
Where: EER = Energy Efficiency Ratio Qc = cooling capacity (Btu/hr) We = electrical input wattage to heat pump The higher the EER of a heat pump, the lower the amount of electrical power being used to produce a given rate of cooling.
EER (Energy E0001ciency Ratio) Btu/hr/watt
Like COP, the EER of a water-to-water heat pump is a function of the source and load water temperature, as well as the source and load water flow rate. This variation is shown in figure 4-10. 35 30 25 20
ClimateMaster TMW036 W/W ESWT = 50ºF
ESWT = 70ºF ESWT = 90ºF
15 10 5 0
50 55 60 65 70 75 80 85 90 Entering load water temperature (ºF) EER (Energy Efficiency Ratio) vs. entering load water temperature.
31
This plot shows that EER increases as the temperature of the entering load water increases. Keep in mind that lower entering load water temperatures are better for cooling capacity. It can also be seen that the cooler the source water (such as supplied from an earth loop heat exchanger), the higher the EER. Thus, cooling performance will generally be better at the beginning of a cooling season when earth temperatures are still relatively low, compared to late summer when the earth has warmed. As was the case with heating, design decisions that reduce the difference between the source water and load water temperatures will improve the cooling capacity and efficiency (as measured by EER) of the heat pump. Water-to-water heat pumps are typically coupled with an air handler to provide cooling. The power of the air handler and any additional circulators must also be considered when determining overall system efficiency. The latter sections of this manual will show you how to combine water-to-water heat pumps with a variety of other hydronic heating hardware to produce systems for both heating and cooling.
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Section 5: Thermal Equilibrium All hydronic systems exhibit certain behaviors regardless of the type of heat source used. One of the most important and universal behaviors is the concept of thermal equilibrium. This section describes this, as well as ways to use it for both design and troubleshooting. Once turned on, every hydronic system attempts to establish operating conditions such that the rate of heat input from the heat sources is exactly the same as the rate of heat released at the heat emitters. This condition, when achieved, is called thermal equilibrium. If not for the intervention of temperature-limiting controls, every hydronic system would eventually stabilize at a supply water temperature where this “thermal equilibrium” exists. This temperature may or may not provide proper heat input to the building. Likewise, it may or may not be conducive to safe and efficient operation or long system life. By adjusting the size, number or other characteristics of heat emitters in the system, the designer can manipulate the steady state supply water temperature at which the system “wants” to operate. When properly done, this allows both the heat source and distribution system to operate at conditions that are safe, efficient, comfortable and conducive to long system life. If the principle of thermal equilibrium is disregarded, the resulting system may attempt to stabilize at a supply temperature that is either unsafe, inefficient or shortens the life of the heat source. In decades past, when fuel was cheap, the North American hydronics industry favored use of high water temperatures, which reduced the required surface area of heat emitters. The reasoning was simple: Why pay for 10 feet of fin-tube baseboard in a room if 6 feet could do the job using a higher water temperature? This is why you’ll find thermal output ratings for fin-tube baseboard that go up to at least 220ºF. This made sense in a pre-OPEC, preAFUE, pre-EPA era. Today the picture is very different, and the trend is clear: The future of North American hydronics is reduced operating temperature. This is necessary to allow boilers to operate with sustained flue gas condensation, which in turn boosts thermal efficiency from the mid-80% to mid-90% range. Low system operating temperatures are also ideal for geothermal water-to-water heat pumps. The lower the system’s operating temperature, the higher the heat output and Coefficient of Performance of the heat pump. Where Will Thermal Equilibrium Occur? A fundamental principal in sizing any type of hydronic heat emitter is that heat output is approximately proportional to the difference between supply water temperature and room air temperature. This can be written mathematically as formula 5-1: Formula 5-1
Where: Qoutput = heat output of the heat emitter (Btu/hr) c = a number dependent on the type and size of the heat emitter (Btu/hr/ºF) Ts = water temperature supplied to the heat emitter (ºF) Tr = room air temperature (ºF) This relationship is true for a single heat emitter, as well as a group of heat emitters operating as an overall distribution system. For example, imagine a building where all the heat emitters (operating as a group) release 100,000 Btu/hr into a 70ºF space when the distribution system is supplied with water at 170°F. The value of the “c” in formula 5-1 can be found as follows:
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This mean that this distribution system releases 1,000 Btu/hr into the space for each ºF the water supply temperature exceeds the room air temperature. Thus, if the water temperature supplied was 130ºF, and the space air temperature was 68ºF, this distribution system would release:
The term (Ts-Tr) in formula 5-1 is called the “driving delta T.” It determines the rate that a given distribution system releases heat into the space being heating. Anything that makes the driving delta T larger (i.e., increasing supply temperature and/or decreasing space air temperature) increases the rate of heat transfer into the space and vice versa. Formula 5-1 can also be represented by a graph. Figure 5-1 shows this for the same numbers used in the previous example.
Heat output (Btu/hr)
100000 80000 60000 40000 20000
0
0 10 20 30 40 50 60 70 80 90 100 (Ts -Tr) (ºF)
Heat output vs. driving delta-T for a hydronic distribution system
To construct this graph for a given hydronic distribution system, you need the heat output rate of the distribution system at one supply water temperature and the associated indoor air temperature. Subtract the indoor air temperature from the supply temperature to get the value of the driving delta T, (Ts-Tr), then plot that point along with the associated heat output rate. Draw a straight line from this point back to the point (0,0) on the graph. Extend the straight line in the other direction of high driving delta-T if necessary. The slope of the line is determined by the number and size of the heat emitters that make up the distribution system. The larger the surface area of the heat emitters, the steeper the slope of the graph (see figure 5-2).
34
Heat output (Btu/hr)
100000 80000
INCREASING the0001surface area0001 of heat emitters lowers0001 driving delta T for given 0001 rate of heat delivery
60000 40000 20000
0
DECREASING surface area0001 of heat emitters requires higher0001 driving delta T for given 0001 rate of heat delivery
0 10 20 30 40 50 60 70 80 90 100 (Ts -Tr) (ºF)
Steeper lines indicate distribution systems with greater heat emitter surface area.
Steeper lines mean that a given rate of heat release occurs at lower values of the driving delta T. For a given room temperature, steeper lines favor lower supply water temperature. This in turn improves the efficiency of ground source water-to-water heat pumps. For spaces heated by radiant panels, steeper lines are achieved by closer tube spacing, as shown in figure 5-3. This lowers the supply temperature at which the floor will deliver a given rate of heat output. Again, this improves both the heating capacity and COP of ground source water-to-water heat pumps. Radiant heating design software can be used to determine the supply temperature needed for a given rate of heat output from a panel of specific construction. Upward heat output (Btu/hr/sq ft)
35 6-inch spacing
30
9-inch spacing 12-inch spacing
25
18-inch spacing
20 15 10 5 0
1/2' PEX-AL-PEX tubing in 4-inch bare concrete 0
5
10
15
20
25
30
35
(Ts-Tr) (ºF) Heat output vs. driving delta T for a heated floor slab using different tube spacing.
Adding the desired room temperature to the numbers along the bottom axis makes another useful variant of this graph. The graph now shows heat delivery vs. supply water temperature, and is called a “system heat output graph.” Figure 5-4 is an example. Here, the desired indoor air temperature of 70ºF has been added to the numbers on the horizontal axis of figure 5-1.
35
Heat output (Btu/hr)
100000 80000 60000 40000 20000
0
70 80 90 100 110 120 130 140 150 160170
Supply water temperature (ºF)0001 (based on space temperature of 70 ºF) Heat output vs. supply water temperature for a specific hydronic distribution system.
You can use a system heat output graph for a given distribution system to find the supply temperature at which that system will achieve thermal equilibrium with a heat source having a given heat output rate. First, locate the output rate of the heat source on the vertical axis. Then draw a horizontal line to the right until it intersects the sloping line. Finally, draw a line straight down to the horizontal axis to read the water supply temperature at which the system wants to operate. For example: If a water-to-water heat pump having an output rate of 60,000 Btu/hr was coupled to the distribution system represented by figure 5-4, that system would seek to operate at a supply water temperature of 130ºF. This supply water temperature is higher than recommended for some water-to-water heat pumps. To correct for this, the heat dissipation ability of the distribution system should be increased. If the system used radiant floor heating, this could be done through closer tube spacing or a floor covering with less thermal resistance. If the distribution system used radiators, their size could be increased or the number of radiators could be increased. The Effect of Controls: Temperature-limiting controls sometimes interfere with a system as it attempts to natural find thermal equilibrium. Here’s how that works. If the temperature limiting control of the heat source is set below the thermal equilibrium temperature, the heat emitters in the distribution system will not get hot enough to dissipate the full (steady state) output of the heat source. The temperature of the water leaving the heat source will climb as the system operates, eventually reaching the temperature setting of the limit control. At that point, the heat source (burner, compressor, etc.) is turned off. The water temperature leaving the heat source begins to decrease as heat continues to be dissipated by the distribution system. Eventually, the temperature drops to the point where the heat source is turned back on, and the cycle repeats. This is a very common operating mode in many hydronic heating systems that use a heat source with a fixed rate of heat output. It can even occur under design load conditions in systems having an oversized heat source. If the temperature limiting control on the heat source is set above the temperature at which thermal equilibrium occurs, the water leaving the heat source will not be able to achieve that temperature setting unless the load is reduced or turned off. This explains why some systems never reach the set point of the heat source’s limit control, even after hours of operation. In simple terms, the distribution system doesn’t need to climb to the boiler limit con-
36
trol setting to dissipate all the heat the boiler can throw at it. It only climbs as high as necessary so that all boiler heat input can be released. This is generally OK, provided that the heat source is delivering sufficient heat output to maintain comfort, and that the heat source is not damaged by operating at lower water temperatures. The latter is not a concern with water-to-water heat pumps. Trend Toward Lower Temperatures: It’s certain that hydronic heating systems in North America will be designed with increasingly lower supply water temperatures. This makes sense from the standpoint of efficiency and environment. It also makes sense from the standpoint of comfort. Large surface area heat emitters improve comfort by increasing the mean radiant temperature of the room. The lower the supply water temperature to the distribution system, the greater the COP of a water-to-water heat pump.
37
Section 6: Valve Basics Many types of valves are used in hydronic heating systems. Some are the same as those used in plumbing systems; others are very specialized. This section discusses proper application of the common valves used in hydronic systems. Most general purpose valves fit into two categories based to their intended application: 1. Component Isolation 2. Flow Regulation Valves designed for component isolation should be either fully open (during normal operation) or fully closed (to isolate a component for servicing). They should not be set in a partially open position within an operating system. Noise and eventual mechanical damage to the valve will result from improper use. Valves designed for flow regulation can operate at any position between fully open and fully closed without creating excessive noise or experiencing mechanical damage. Common Valves Used in Hydronic Systems: • Gate valves are designed for component isolation service. In their fully open position, they yield very low flow resistance. They should never be operated in a partially open position.
Gate valve with threaded (FPT) connections.
• Globe valves are specifically designed to “throttle” (e.g., regulate) flow rate through a piping path. Their internal design forces fluid through a sinuous path that creates relatively high flow resistance. They should not be used as isolation valves because such use causes unnecessary head loss in a normally functioning system. Because they create pressure drop and turbulence, globe valves should never be located near the inlet of circulators. Globe valves should always be installed with their flow arrow — which is cast into the side of the valve — pointing in the direction of flow.
38
Globe valve cross-section.
• Ball valves come in both “standard port” and “full port” varieties. The full port version creates slightly less flow resistance than the standard port version. Both types are designed primarily for component isolation and create minimal flow resistance in their open position. Minor amounts of flow regulation are possible with ball valves. However, they should not be operated in an almost closed position because of the potential for cavitation noise and eventual erosion of the internal surfaces. Special types of ball valves are available for high duty cycle (motorized) applications.
Ball valve with soldered connections.
• Check valves are designed to block flow in one direction. There are several variations used in hydronic systems. The simplest is the swing-check. It contains a hinged disc that swings up and out of the path of flow in the forward direction. As soon as the flow stops, or attempts to reverse direction, the disc swings down to cover the opening through the valve. Swing-checks must be mounted in an upright position in horizontal piping. Be sure the arrow on the body is pointed in the intended direction of flow.
Swing-check valve with soldered connections.
39
Another variety of check valve is called a flow-check. It contains an internal plug that seats over the hole through the valve. The plug is sufficiently heavy to prevent the buoyancy of hot water from creating flow through the valve until the circulator turns on. This plug also blocks flow in the reverse direction. Some flow-check valves come equipped with knobs allowing them to be manually opened.
Flow-check valve with soldered connections.
Finally, there’s the spring-check valve. It uses an internal spring to force the disc of the valve to close whenever there is no flow through the valve. The spring allows the valve to be installed in any orientation. The spring also prevents buoyancy-induced flow through the valve when the circulator is off. Spring-checks should be installed with at least 10 diameters of straight pipe upstream of the valve to minimize turbulence that otherwise can cause the disc to rattle.
Spring-loaded check valve.
• Pressure relief valves — Any closed piping loop containing a heat source (be it a boiler, heat exchanger, electric element or other) must be equipped with a pressure relief valve. These spring-loaded valves are designed to open at a specific rated pressure to prevent higher pressures from developing in the piping circuits they serve. Pressure relief valves are usually located on or near the heat source. They should be mounted with their shaft in a vertical position to prevent uneven scale accumulation on their seats. They should always be equipped with a pipe that directs any discharge toward a drain and away from any occupants. Local mechanical and plumbing codes should be consulted regarding specific installation requirements of pressure relief valves.
Pressure relief valve.
40
• Pressure-reducing valves, also known as “feedwater valves,” are part of the make-up water assembly. They reduce the pressure in the cold-water service pipe to a predetermined pressure before allowing it into the hydronic system. A typical setting is around 12 psi. It can be adjusted up or down by turning the valve’s stem. Whenever the pressure on the downstream (heating system) side of the valve drops below this setting, water is allowed into the system. Some pressure-reducing valves are equipped with a built-in strainer to prevent particulates from entering the system. Some are also equipped with a low inlet pressure check valve to prevent reverse flow.
Combination of a backflow preventer and pressure-reducing valve. (Courtesy of Caleffi)
• Zone valves are electrically operated valves used to permit or prevent flow through piping circuits serving different parts of a building. The most common zone valves use a 24VAC motor to move the shaft of the valve. Some use a plug assembly that moves up and down. Others use a ball that rotates on a shaft.
Cross-section of a 2-way zone valve. (Courtesy of Caleffi)
Some zone valves use a “thermal motor” that requires about 3 minutes to reach the fully open position after power is applied. Other zone valves use a geared motor and can fully open in only two or three seconds after power is applied. Because of the relatively slow response of most heating systems, either type of motor works fine. Many zone valves come equipped with an “end switch.” It is simply an isolated normally open switch that closes when the valve stem reaches its fully open position. The closed end switch signals the other parts of the control system that a zone is calling for heat.
41
• Thermostatic Radiator Valves (TRVs) can be installed on heat emitters like baseboard and panel radiators. They have a thermostatic knob that can be set for a specific temperature. The knob senses the air temperature around it. A fluid-filled internal bellows assembly then moves the stem of the valve as necessary to try to maintain this temperature. If the thermostatic knob senses an increase in room temperature, it begins closing the valve to reduce the flow of heated water through the heat emitter, and vice versa.
Thermostatic radiator valve (valve body at bottom, thermostatic operator at top).
All motor force required to operate the TRV comes from the internal bellows. Because they are non-electric, they cannot signal other parts of the control system that heat is needed at their heat emitter. Instead, they count on constant flow of heated water through the distribution system. TRVs mounted on individual heat emitters are an excellent way to zone hydronic systems on a room-by-room basis.
42
Section 7: Pipe Sizing and Head Loss Most residential and light commercial hydronic systems use smooth tubing. Materials include: • • • • •
Copper: PEX PEX-AL-PEX Fused Polypropylene Fused Polyethylene
Selecting a Pipe Size: In hydronic systems, tubing should be sized so that the flow velocity through it will be in the range of 2 to 4 feet per second. The flow rate (in gallons per minute) that corresponds to these flow velocities is given in figure 7-1. Tubing size/ type
Minimum Flow rate (based on 2 ft/sec) (gpm)
Maximum Flow rate (based on 4 ft/ sec) (gpm)
3/8” copper
1.0
2.0
1/2” copper
1.6
3.2
3/4” copper
3.2
6.5
1” copper
5.5
10.9
1.25” copper
8.2
16.3
1.5” copper
11.4
22.9
2” copper
19.8
39.6
2.5” copper
30.5
61.1
3” copper
43.6
87.1
3/8” PEX
0.6
1.3
1/2” PEX
1.2
2.3
5/8” PEX
1.7
3.3
3/4” PEX
2.3
4.6
1” PEX
3.8
7.5
1.25” PEX
5.6
11.2
1.5” PEX
7.8
15.6
2” PEX
13.4
26.8
3/8” PEX-AL-PEX
0.6
1.2
1/2” PEX-AL-PEX
1.2
2.5
5/8” PEX-AL-PEX
2
4.0
3/4” PEX-AL-PEX
3.2
6.4
1” PEX-AL-PEX
5.2
10.4
Minimum and maximum recommended flow rates through tubing.
Flow velocities of 2 feet per second or higher allow water to “entrain” air bubbles and carry them along. This is essential in helping purge the piping system of air upon initial start up. Flow velocities of over 4 feet per second tend to create higher levels of noise. Velocities in excess of 6 feet per second can cause erosion of the copper tube wall, especially at tight turns in elbows or tees, and thus should be avoided. Friction and Head Loss: All fluids experience flow resistance as they move though piping components. Fluids with greater viscosities (like glycol antifreeze solutions) experience more flow resistance than pure water. 43
The friction between a fluid and the objects it flows past dissipates mechanical energy from the fluid. This energy is called “head”. Every piping component causes some loss of head from the fluid flowing through it. The only exception is an operating circulator, which adds head energy back into the fluid. The standard units for expressing head energy are feet of head. It results from dividing another unit of energy — called a foot-pound — by a unit of weight (pound). One Btu equals 778 foot-pounds. When you divide foot-pound by pound, you get just plain foot. Head expressed in feet is therefore the amount of mechanical energy each pound of fluid contains.
The hydronics industry has typically used 2.31 feet of head = 1 psi as a conversion factor. This is the conversion for water at 60°F. The actual conversion will depend on the temperature and type of fluid used. For example, the conversion for water at 130°F is 2.34 feet of head = 1 psi, whereas, the conversion for 50% propylene glycol in water at 90°F is 2.23 feet of head = 1 psi.
Head and Pressure Drop Are NOT the Same Thing: The “evidence” that head has been removed from a fluid flowing through a piping component is a pressure drop across that component. For example, the farther a fluid flows along a horizontal pipe, the lower its pressure becomes. It’s possible to convert a loss of head energy into an associated pressure drop, or vice versa. For horizontal piping (so there’s no change in pressure due to changes in elevation), the following formula is used: Formula 7-1:
Where: Hloss = head loss between two points on a pipe (feet of head) ∆P = pressure drop between the two points on the pipe (psi) D = density of the fluid flowing through the pipe (lb/ft3) 144 = a number based on units used The head loss a pipe creates depends strongly on the flow rate through it. The relationship, for circuits constructed of smooth tubing, such as copper, PEX and PEX-AL-PEX, can be calculated using formula 7-2: Formula 7-2
Where: Hloss = head loss of the pipe (feet of head) R = the hydraulic resistance of the pipe
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f = flow rate through the pipe (gpm) 1.75 = the exponent of the flow rate The hydraulic resistance (R) of a pipe (or other component) depends on several characteristics, including its size and length as well as the density and viscosity of the fluid flowing through it. It can be calculated using formula 7-3. Formula 7-3
Where: a = fluid properties factor (for water see figure 7-2) c = pipe size factor for tubing used (see figure 7-3) L = total equivalent length of circuit (feet) 0.065
Value of (a)
0.06 0.055 0.05 0.045
0.04
50 75 100 125 150 175 200 225 250 Water temperature (ºF)
Value of “a” for formula 7-3 (for water).
Tube (size & type)
C value
3/8” type M copper
1.016
1/2” type M copper
0.3335
3/4” type M copper
0.06196
1” type M copper
0.01776
1.25” type M copper
0.006808
1.5” type M copper
0.0030668
2” type M copper
0.00083317
2.5” type M copper
0.0002977
3” type M copper
0.0001278
3/8” PEX (I.D. = 0.36”)
2.9336
1/2” PEX (I.D. = 0.475”)
0.7862
5/8” PEX (I.D. = 0.584”)
0.2947
3/4” PEX (I.D. = 0.670”)
0.1535
1” PEX (I.D. = 0.86”)
0.04688
3/8” PEX-AL-PEX (I.D. = 0.35”)
3.354
1/2” PEX-AL-PEX (I.D. = 0.47”)
0.8267
5/8” PEX-AL-PEX (I.D. = 0.63”)
0.2056
3/4” PEX-AL-PEX (I.D. = 0.79”)
0.07016
1” PEX-AL-PEX (I.D. = 0.98”)
0.0252
Value of “c” for formula 7-3.
45
Piping components such as fittings and valves also have a hydraulic resistance. They can be treated as pipes with equivalent lengths that would create the same head loss as the component itself. This allows the entire piping circuit to be considered as a single pipe equal in length to the total length of the piping, plus the total equivalent lengths of all the piping components. The equivalent length of several common fittings and valves can be read from the table in figure 7-4.
Equivalent length of fittings and valves.
Once the hydraulic resistance of a piping circuit is known, the head loss of that circuit at different flow rates can be calculated using formula 7-2. If the head loss is calculated at several different flow rates, and the resulting numbers are plotted, the result would be a graph like that shown in figure 7-5.
head loss (feet)
15 10 5
0
0
2
4 6 8 flow rate (gpm)
10
Example of a system head loss curve,
This graph is called the system head loss curve for that piping system. Every closed-loop piping system has a system curve; it’s just a matter of calculating its exact appearance. Here’s an example: The piping circuit shown in figure 7-6 is constructed of 3/4” copper tube. It operated with water at an average temperature of 140ºF. Using the previously discussed formulas and data, determine the hydraulic resistance of this circuit and plot its system curve. 10 ft.
3 ft. globe valve
2 ft. 8 ft.
all tube & fitting are 3/4' copper
5 ft. 8 ft.
gauge 2 ft.
ball valve
ball valve
2 ft. 2 ft. Piping circuit for example calculation.
46
16 ft.
2 ft.
2 ft.
Solution: The total equivalent length of this circuit is the sum of the tubing lengths plus the equivalent lengths of all fittings and valves in the flow path: L = 62 + 6x2 + 2x3 + 1x0.4 + 1x20 + 2x2.2 = 104.8 = 105 ft. The value of (a) for water at 140ºF (from figure 7-2) is 0.0476. The value of c for 3/4-inch copper (from figure 7-3) is 0.061957. Putting these together in formula 7-3 determines the hydraulic resistance of the circuit:
Formula 7-2 can then be used to determine the head loss of this circuit at a given flow rate:
Figure 7-7 shows the results of substituting a few random flow rates into formula 7-2 and plotting the results.
HL = 0.3097 0001 f
1.75
flow rate 0001 (US gpm)
head loss 0001 (feet)
00001 30001 60001 90001 12
00001 2.110001 7.120001 14.480001 23.96
head loss (feet)
25 20 15 10 5
0
0
2
4
6
8
10
12
flow rate (gpm) Calculating values of head loss and plotting the system head loss curve.
Appendix C contains pressure drop graphs for copper tube and PEX pipe.
47
Section 8: Circulators The circulator is the heart of a hydronic circuit. It adds head to the fluid, which creates the pressure differential forcing fluid to move through the circuit. The circulators used in hydronic systems are classified as centrifugal pumps. Figure 8-1 shows a cross-section of such a pump. discharge port
inlet stator rotor
flange volute
junction box
impeller
impeller disks (2) impeller
volute impeller vanes
flange bolt flange
'eye' of impeller
rotor can ceramic bushing outlet
inlet port Components of a wet-rotor circulator.
After flowing through the inlet port, fluid is channeled through the intake volute to the “eye” of the spinning impeller. Curved vanes on the impeller push the fluid outward between two disks. This is where mechanical energy called head is transferred to the fluid. The fluid discharges from the perimeter of the impeller and is gathered up by the outlet volute (the chamber in which the impeller spins). The fluid is then routed to the discharge port, its pressure having been raised. Its flow rate, however, is still the same as when it entered. When the inlet and discharge ports are aligned along a common centerline, the circulator is called an “inline” circulator. Some circulators have their intakes parallel to the impeller shaft and are called “end suction” circulators. Most circulators used in residential and light commercial systems use the inline configuration. The end suction configuration is more common in larger floor-mounted circulators. Circulator Performance: The ability of a circulator to move fluid cannot be expressed by a single number. Instead, it’s given as a graph called a pump curve. An example is shown in figure 8-2. 25
head (feet)
20
15
10
5
0 0
2
4
6
8
10
12
flow rate (gpm) Example of a pump curve for a small wet-rotor circulator.
48
Pump curves show how much head the circulator adds to the fluid as it flows through at a specific flow rate. For example, the circulator represented by the pump curve in figure 9-2 adds 12 feet of head to a fluid flowing through it at 8 gpm. A circulator always operates at some point on its pump curve. The head added to a fluid by a given circulator operating at a specific flow rate does NOT, for all practical purposes, depend on the fluid itself. For example, a circulator pumping a 50% glycol solution at 8 gpm would add the same amount of head as it would pumping pure water at 8 gpm. However, the pressure increase of the glycol solution as it flows through the circulator will not be the same as for water. The pressure increase for either fluid can be calculated using formula 8-1: Formula 8-1
Where: ∆Prise = pressure increase due to head added by circulator (psi) Hadded = head added by circulator (feet of head) D = density of fluid (lb/ft3) The densities of water and a 30% solution of propylene glycol/water are shown in figure 8-3. 30% propylene glycol water
65
Density (lb/ft3)
64 63 62 61 60 59 58
30
80
130
180
230
280
Temperature (ºF) The density of water and a 30% solution of propylene glycol.
Because the density of a glycol solution is slightly greater than that of pure water, the pressure increase across the circulator would be slightly higher for the glycol solution than for pure water. To find the flow rate a circulator would produce in a specific pipe system, the system curve is overlaid on (drawn over) the pump curve. The intersection of the curves is where the head supplied by the circulator exactly equals the head removed by fluid friction. It’s called the “operating point”. The flow rate at the operating point is found by dropping straight down to the horizontal axis, as shown in figure 8-4. Using this method, the system curve of any piping circuit can be overlaid on the pump curve of any circulator to find what the flow rate would be if such a combination were to be used. It’s a powerful design tool that eliminates a lot of guess work.
49
25 system curve 20
head (feet)
pump curve 15 operating point 10
5
0 0
2
4
6
8
10
12
flow rate (gpm) Intersection of the pump curve and system curve.
Measuring the Flow Rate through a Circulator: Because a circulator always operates along its pump curve, it’s possible to determine the flow rate through it without using a flowmeter. All that’s required is an accurate measurement of the pressure gain across the circulator, and a copy of the circulator’s pump curve. The pressure gain across the circulator can be measured by installing accurate pressure gauges near (or directly into) the inlet and outlet flanges of the circulator, as shown in figure 8-5. The differential pressure can also be determined using a single differential pressure gauge connected to both these locations.
10 psi
differential pressure0001 across circulator
14 psi
Differential pressure measured across an operating circulator.
The procedure is as follows: 1. Measure the pressure increase across the circulator using gauges on, or very close to, the inlet and outlet flanges. Some larger circulators come with their flanges already drilled and tapped for these gauges. Another option is to install a single pressure gauge on a tee between two ball valves. The other sides of the ball valves are teed into the piping adjacent to the inlet and outlet flanges. Open one ball valve to read inlet pressure. Close it. Then open the other valve to read outlet pressure. 2. Convert this pressure increase to an equivalent amount of head gain.
Where: Hadded = head added by circulator (feet of head) ∆Prise = pressure increase due to head added by circulator (psi) D = density of fluid (lb/ft3) 144 = a constant required for the units used To use this formula, you need to estimate the density of the fluid being pumped. A graph of the density of water
50
at various temperatures is given in appendix B. You can look up the density of antifreeze solutions on technical specification sheets supplied by the manufacturer. 3. Find the calculated value of head on the vertical axis of the pump curve graph, then draw a horizontal line from that value over to the pump curve. The intersection of this line and the curve is the operating point of the circulator. 4. Finally, draw a line straight down from the operating point and read the operating flow rate on the horizontal axis. Circulator Efficiency: The efficiency at which a circulator converts the electrical energy supplied to its motor into head depends on where it operates along its pump curve. Peak efficiency occurs near the center of the pump curve (see figure 8-6). When selecting a circulator for a piping circuit, the operating point should fall within the center third of the pump curve to achieve reasonably good efficiency. pump curve efficiency maximum efficiency
0.2
16
0.15
12
0.1
8
0.05
4
0
H =head added (feet)
circulator (wire-to-water) efficiency
0.25
0 0
2
4
6
8
10 12 14 16 18
flow rate (gpm) The efficiency of a small wet-rotor circulator.
Cavitation: One thing hydronic circulators don’t handle well is when the fluid they’re trying to move flashes into a vapor as it enters their impellers. This can happen at fluid temperatures above and below 212°F, depending on the pressure in the system. Water boils whenever its drops below its vapor pressure. The vapor pockets formed when the water boils at the eye of the impeller collapse as they flow out through the impeller vanes. This collapse happens with incredible speed and can actually erode hardened metal surfaces if it persists. A pump that’s operating with severe cavitation will make rumbling and popping sounds. If left unchecked, severe cavitation can destroy the impeller and parts of the volute in a short period of time. The performance of a cavitating circulator will also be a fraction of its normal performance. Cavitation simply must be avoided in all hydronic systems. Guidelines for avoiding cavitation: • Don’t allow the system to operate with abnormally low pressure upstream of the circulator. At any given temperature, the lower the pressure, the closer the water is to boiling as it enters the circulator. Most systems should be fine if kept within the normal 10 to 20 psi (boiler pressure) operating range. Slightly higher pressures are fine as long as the relief valve doesn’t prematurely open. • Mount the circulator so it pumps away from the expansion tank connection point. This allows the pressure
51
differential created by the circulator to be added to the static pressure in the system. If the circulator pumps toward the expansion tank, its pressure differential will show up as a decrease in pressure at the worst possible spot — the eye of the impeller. This is a very cordial invitation for cavitation. • Don’t operate the system at excessively high temperatures. Personally, I seldom find any reason to operate a residential or light commercial hydronic heating system with supply temperatures in excess of 200°F. The higher the water temperature, the closer the water is to its boiling point, and hence to cavitation. • Always install the circulator with a minimum of 10 pipe diameters of straight pipe on its inlet side. This reduces turbulence entering the impeller. Never install a throttling valve or other piping component with high flow resistance near the inlet of a circulator. • All other factors being equal, lower RPM circulators are less prone to cavitation than higher RPM circulators. Circulators with “steep” pump curves that are improperly applied are also more susceptible to cavitation than circulators with relatively “flat” pump curves.
52
Section 9: Hydraulic Equilibrium As is the case with thermal equilibrium, every hydronic system always seeks to operate at a condition called “hydraulic equilibrium.” This is a condition in which the mechanical energy imparted to the fluid by the circulator(s) is exactly balanced with the mechanical energy dissipated from the fluid due to flow resistance of the piping, fittings, valves and any other components the fluid flows through. Recall from previous sections that the mechanical energy imparted to the fluid by the circulator is called “head.” The “evidence” that head energy has been added to a fluid as it moves through a circulator is an increase in pressure, as shown in figure 9-1. This increase in pressure is often called the ∆P (pronounced delta-P). The fluid flow rate does not increase across the circulator, and neither do the flow velocity or temperature. differential pressure0001 across circulator
10 psi
14 psi
An increase in pressure across the operating circulator is the evidence that head energy has been added to the water.
The exact head energy imparted to a fluid by a circulator depends on the pump curve for the circulator. An example of pump curves is shown in figure 9-2 40 'steep' pump curve0001 (high head circulator)
head added (feet)
35 30 25 20
'flat' pump curve
15 10 5 0 0
2
4
6
8
10
12
14
16
flow rate (gpm) Example of pump curves for different circulators.
Note that the curves start high and descend as the flow rate increases. Thus a circulator imparts maximum head energy to a fluid when the fluid is not actually flowing (i.e., perhaps a valve is closed elsewhere in the circuit). Although such a “dead head” condition is possible, it is not normal. As the flow rate through the circulator increases, the head energy added to each pound of fluid decreases. Every hydronic circulator has a pump curve. It’s typically shown in literature or found in the specifications at the manufacturer’s website. Also recall from previous sections that every piping system has a “head loss curve” such as the one shown in figure 9-3.
53
25
head (feet)
20
15
10
5
0 0
2
4
6
8
10
12
flow rate (gpm) Example of system head loss curve.
Hydraulic equilibrium occurs when the head energy added by the circulator exactly matches the head energy dissipation by the other components in the system. This condition, illustrated in figure 9-4, typically occurs within a few seconds after the circulator is turned on.
head energy DISSIPATION0001 due to fluid friction in0001 piping components
head energy INPUT0001 from circulator
The circulator adds head energy to fluid. All other piping components (with flow through them) dissipate head energy.
The flow rate at which a given piping circuit with a given circulator will operate at, when it achieves hydraulic equilibrium, is easy to find. Just draw the system head loss curve on the same graph as the pump curve for the circulator, and find where the curves cross (see figure 9-5).
54
25 system curve 20
head (feet)
pump curve 15 operating point 10
5
0 0
2
4
6
8
10
12
flow rate (gpm) Hydraulic equilibrium occurs where the pump curve crosses the system head loss curve.
The point where the curves cross is called the system’s “operating point.” A line drawn straight down from this point to the horizontal axis will give the flow rate where the head energy input from the circulator exactly balances the head energy dissipation by the piping circuit (e.g., the flow rate at hydraulic equilibrium). Remember, EVERY hydronic system will always achieve hydraulic equilibrium once the circulator is operating. There is no guarantee that this condition will deliver the correct amount of heat to the spaces, or that the operating condition is efficient or even safe. Nature doesn’t care about the same concerns as the hydronic system designer. It only cares that hydraulic equilibrium is achieved. A well-designed hydronic system will deliver the proper amount of heat to each space, operate with minimal sound, minimize the required pumping input power and do all these things while operating under hydraulic equilibrium.
55
Section 10: Expansion Tanks All closed-loop hydronic heating systems require an expansion tank to accommodate the increased volume of the heated fluid. Modern systems use a diaphragm-type expansion tank. Such tanks are pre-charged with air. The air is trapped between the steel shell of the tank and a flexible polymer diaphragm, which moves back and forth as water moves into and out of the tank, as depicted in figure 10-1. A Schrader valve at the bottom of the tank allows the air pressure within the tank to be adjusted.
water water
air diaphragm
air diaphragm air is compressed as expanding water pushes into tank
compressed air pushes contracting water back into system
air valve
air valve
Movement of the diaphragm as heated water enters the expansion tank.
Locating the Expansion Tank: The point where the expansion tank connects to the system piping is called the point of no pressure change (PONPC). Ideally, this point should be close to the inlet side of the circulator(s) in the system. Such placement allows the differential pressure developed by the circulator to add to the static pressure in the system. This condition helps prevent circulator cavitation and helps in air elimination. You will see this detail shown on nearly all the piping schematics in this publication. Sizing Diaphragm-type Expansion Tanks: Modern hydronic systems typically have expansion tanks in which the system fluid is separated from the enclosed air by a flexible diaphragm. When the system is installed, the pressure in the air side of the expansion tank should be adjusted to equal the static pressure of the fluid at that location in the system. This ensures the diaphragm is fully expanded against the tank’s shell before the water begins expanding due to heating (see figure 10-2).
56
cold water
diaphragm0001 (expanded against0001 tank shell) PRESSURIZED0001 AIR steel tank shell
air valve The diaphragm is fully expanded against the upper portion of the tank shell when the water is cold, and the air side of the tank is properly pressurized.
Sizing Step 1: The proper air-side pressure can be calculated with the formula 10-1: Formula 10-1
Where: Pair = the proper air-side pressure (before adding water to the system) (psi) H = the height of liquid in the system above the inlet to the expansion tank (feet) Dc = the density of the system fluid at its initial (cold) fill temperature (lb/cubic foot) 5 = an allowance for 5 psi static pressure at the top of the system. This formula can be used for systems containing either water or antifreeze solutions. It requires the density of the cold fluid used to fill the system. For water, use a value of 62.4 lbs/cubic foot. For other fluids, look up their density at 60°F in the manufacturer’s literature. The number 5 at the end of the formula assumes 5 psi of static pressure is desired at the top of the piping system to help push air out through vents, as well as to suppress vapor pocket formation in high-temperature systems. This number can be adjusted up or down. Higher values will result in larger expansion tank sizes and vice versa. The value “H” in the formula is the vertical distance from the inlet of the expansion tank to the top of the piping system (in feet). The greater this height is, the greater the static pressure on the tank, and thus the higher the airside pressurization required to ensure the diaphragm remains fully expanded when the system is filled. It’s important to calculate the air-side pressure and adjust it as necessary using the Schrader valve on the tank before adding fluid to the system. This ensures that the diaphragm will not be partially compressed when the system is filled. Sizing Step 2: Estimate the volume of liquid in the system (excluding the expansion tank). The volume of tubing can be estimated using the data in figure 10-3. The volume of the boiler and other components is typically listed on the manufacturer’s specification sheets. Add these component volumes together to get the total estimated system volume.
57
Tube type / size
Gallons/foot
3/8' type M copper
0.008272
1/2' type M copper
0.0132
3/4' type M copper
0.0269
1' type M copper
0.0454
1.25' type M copper
0.068
1.5' type M copper
0.095
2' type M copper
0.165
2.5' type M copper
0.2543
3' type M copper
0.3630
3/8' PEX
0.005294
1/2' PEX
0.009609
5/8' PEX
0.01393
3/4' PEX
0.01894
1' PEX
0.03128
1.25' PEX
0.04668
1.5' PEX
0.06516
2' PEX
0.1116
3/8' PEX-AL-PEX
0.00489
1/2' PEX-AL-PEX
0.01038
5/8' PEX-AL-PEX
0.01658
3/4' PEX-AL-PEX
0.02654
1' PEX-AL-PEX
0.04351
Volume data for different types of tubing.
Sizing Step 3: Calculate the required minimum expansion tank volume using formula 10-2: Formula 10-2:
Where: Vt = the required minimum volume of the expansion tank (gallons) Vs = the system volume (gallons) PRV = the pressure at which the pressure relief valve opens (psi) Pa = the correct air-side pressure (psi) Dh = the density of the system fluid at its final (hot) temperature (lb/cubic foot) Dc = the density of the system fluid at its initial (cold) fill temperature (lb/cubic foot) The volume of the system (Vs) was estimated in step 2. The air-side pressurization (Pa) was determined in step 1, as was the density of the fluid when the system will filled (Dc). The pressure relief valve setting (PRV) on most residential and light commercial systems is 30 psi. What remains is to look up the density of the fluid when the system is at maximum temperature. For water or 30% propylene glycol, use the graph shown in figure 10-4. For other fluids, look up the density in the manufacturer’s literature for the concentration being used.
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30% propylene glycol water
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Density (lb/ft3)
64 63 62 61 60 59 58
30
80
130
180
230
280
Temperature (ºF) Density of water and 30% solution of propylene glycol.
Example: The top of a hydronic distribution system is 20 feet above the expansion tank connection. The system is filled with 60°F water. Based on the amount of piping and boiler volume, it’s estimated that the system contains 22 gallons of water. The boiler is equipped with a 30-psi relief valve. The maximum operating temperature of the system will be 200°F. What’s the minimum expansion tank volume required? Step 1: Calculate the air-side pressurization using formula 1:
From figure 29, the density of water at 200°F is 59.9 lb/cubic foot. Putting the numbers in formula 2 yields:
This is the minimum expansion tank volume required for this system. Using a larger volume tank is fine. An oversized expansion tank reduces variations in system pressure between its temperature extremes, but also adds to cost.
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Section 11: Basic Hydronic Controls There are a wide variety of controls for modern hydronic systems. They range from standard room thermostats to a sophisticated multi-stage heat source controller to mixing devices. This section will look at the controllers and concepts most often used in residential and light commercial systems, and focus specifically on those most useful for hydronic systems using ground source heat pumps. Zoning: One of the most common control requirements for hydronics is zoning. Two common methods for zoning are: • Multiple zone circulators • Multiple zone valves Zoning with Circulators: An example of a multiple zone circulator system is shown in figure 11-1.
zone circulators0001 (w/ checks)
temperature0001 controller
supply header sensor in well
purge0001 valves
T&P0001 ports return header
earth loop0001 circulator
GSHP purging0001 valves
earth loop circuits
Zoning using circulators.
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Buffer tank
In this system, each zone of heat distribution has its own circulator. Each circulator is equipped with an integral (or external) check valve to prevent reverse flow through inactive zones when other zones are operating. All zone circulators draw heated water from a common supply header, and return cooler water to a common return header. A purging valve is located at the end of each zone circuit to expedite air removal at start-up or after servicing. Heated water is constantly available from the buffer tank. The temperature within the buffer tank is maintained by operating the GSHP. We will discuss buffer tanks in more detail later in this section. There are several ways to operate the zone circulators. One would be to use line voltage thermostats wired directly to each circulator. This is simple and it’s efficient — because there is no need for a low-voltage control circuit and its associated transformer. However, the selection of line voltage thermostats is much more limited than thermostats that operate on 24 VAC power. Another common method of controlling zone circulators is via a multi-zone relay center as shown in figure 11-2. 120 VAC L1 N
normally-closed priority contact DHW tank0001 aquastat0001 (A1)
L1
X
N
X
room0001 thermostat0001 (T2)
T1
T1
T2
C1
C1 C2
T2
room0001 thermostat0001 (T3)
room0001 thermostat0001 (T4)
room0001 thermostat0001 (T5)
room0001 thermostat0001 (T6)
T3
T3
T4
T4
T5
T5
T6
T6
C2 C3
C3
C4
C4 C5
C5
C6
C6
to boiler0001 high limit control
C1
C2
C3
C4
C5 C6 zone circulators
Internal and external views of a multi-zone relay center.
The multi-zone relay center combines all the electrical devices necessary to operate several zone circulators using 24 VAC thermostats. This includes a 24 VAC power supply for the thermostats. Multi-zone relay centers also
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have an isolated relay contact that closes whenever any one or more of the zones is active. The “X X” terminals within the relay center connect to this contact, which can be used to signal other control devices within the overall control circuit that at least one zone is active. The “X X” terminals are commonly used to signal the heat source to operate. Most multi-zone relay centers now include a “priority zone.” When enabled, this function allows one zone (usually zone #1) to take priority over all remaining zones. If the priority zone is active, all other zones are temporarily prevented from operating. A common application for this is turning off space heating during a call for domestic water heating. Priority control usually includes a “time out” feature that allows the other zones to continue operating if the priority zone has been on for a set period of time (30 minutes is common). Most currently available multi-zone relay centers are available with connections for 3, 4 or 6 zones. If more than 6 zones are needed, the system can be expanded by “daisy-chaining” additional zone relay centers together. Such systems still retain the ability to provide priority zone control. Zoning with Valves: Zoning with electrically operated zone valves is also common. This method of zone control is currently growing in popularity because of the availability of variable-speed, pressure-regulated circulators, which are ideal for such systems. An example of the same system shown in figure 11-1, only using zone valves rather than zone circulators, is shown in figure 11-3.
zone valves
temperature0001 controller
sensor in well
variable speed0001 pressure-regulated circulator purge0001 valves
T&P0001 ports
return header
earth loop0001 circulator
GSHP
Buffer tank
purging0001 valves
earth loop circuits
Zoning with a zone valve and variable speed circulator.
The only difference is that the zone circulators have been replaced with electrically operated zone valves, and a single variable-speed circulator is used to create flow.
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Zoning with valves and a variable-speed, pressure-regulated circulator will generally use significantly less electrical energy to operate the distribution system over the course of a heating season. This is due to the circulator automatically reducing speed as zone valves close, and vice versa. In this way, the pumping power is always matched to the load. Some examples of these circulators are shown in figure 11-4.
Two examples of variable-speed, pressure-regulated circulators using electronically commutated motors.
Multi-zone relay panels are also available for systems using zone valves. They offer similar priority zoning and zone expansion options to those used with zone circulators. Outdoor Reset Control: A perfect heating system would constantly adjust its rate of heat delivery to match the heat loss of a building. This would allow the indoor air temperature to remain perfectly stable regardless of outside conditions. With hydronic heating, this condition can be closely approximated using a technique called outdoor reset control (ORC). The control process that’s continually operating in an outdoor reset controller is as follows: 1. Measure outdoor temperature. 2. Calculate the ideal “target” supply water temperature for the distribution system. 3. Operate one or more devices in the system to steer the system’s supply temperature toward the target value. When properly configured, outdoor reset control is like “cruise control” for a hydronic heating system, allowing it to deliver just the right amount of heat so room air temperature doesn’t overshoot or undershoot the desired setting. In addition to stable room temperature, outdoor reset control provides the following benefits: • Improved heat source efficiency: ORC allows the water temperature supplied by the heat source to reach a temperature just hot enough to supply the current heating load. This, in turn, allows a GSHP system to operate at the minimum condenser operating temperature commensurate with the load. Doing so maximizes both COP and heating capacity of the GSHP. • Quasi-continuous circulation: Because the water is just warm enough to meet the current heating load, the distribution circulator is almost always operating. This allows heat to be continually “stirred” within the distribution system. In the case of a heated concrete slab, floor areas covered with low-resistance floor coverings tend to cool faster than areas covered by carpets. If circulation stops when the thermostat is satisfied, owners will notice differences in floor surface temperatures. However, with constant circulation, heat from warmer floor areas can be moved to cooler floor areas to minimize these differences. Continuous circulation also minimizes expansion sounds because materials within the heating system warm up and cool down at much slower rates than with on/off circulation.
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• Indoor temperature limiting: In systems not using outdoor reset control, it’s common to supply water to the heating system at a temperature high enough to meet the heating load requirement on the coldest day of the year. This allows the heating system to deliver heat much faster than necessary during partial load conditions. Occupants can set the thermostat to a high setting and simply open a window or door to control overheating. Although this sounds like a foolish practice, it’s often done in rental properties where tenants don’t pay for their utilities. However, when outdoor reset control is used, the water is just hot enough to meet the prevailing load with the windows and doors closed. • Reduced energy use: One of the most attractive features of outdoor reset control is its demonstrated ability to reduce fuel consumption in both residential and commercial buildings. Although exact savings vary from one project to another, conservative estimates of 10-15% are common. The common method for expressing what an outdoor reset control does is a graph like the one shown in figure 10-4.
Example of a reset line.
The line on the graph is called a reset line. It indicates the ideal “target” supply water temperature to the distribution system for a corresponding outdoor temperature. For example, using the reset line shown in figure 11-4, the target supply temperature when it’s 0°F outside is approximately 114°F. When it’s 40ºF outside, the target temperature is only 88ºF. The slope of the reset line is called the reset ratio. This slope is an adjustable setting on an outdoor reset controller. Steeper slopes are appropriate for higher temperature distribution systems, such as those used for fin-tube baseboard. Shallow slopes are appropriate for lower temperature systems, such as slab-type radiant floor heating. Figure 11-5 shows some representative reset lines for different types of distribution systems.
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f lo or
180 ºF
ra
di a
nt
170
sp en de d
tu be
150 130
e at
ra
a di
nt
or f lo
t ia n ad
150 ºF
or f lo 130 ºF
pl & br e oor 110 ºF b s la t fl tu hin ia n t d a br s la
su
Water supply temperature (ºF)
190
110 90
70 70 60 50 40 30 20 10 0 -10 Outdoortemperature temperature (ºF)(ºF) Outdoor
Examples of reset lines for different hydronic heat emitters.
The appropriate reset line for a given system depends upon the heat loss characteristics of the building, as well as the heat output characteristics of the hydronic distribution system. To determine the appropriate reset line, one needs to know the supply water temperature requirement of the distribution system at design load, as well as the corresponding outdoor temperature at design load. For example, imagine a radiant panel heating system has been designed to provide a design heating load of 50,000 Btu/hr when the outdoor temperature is 0ºF. To release 50,000 Btu/hr, the distribution system must be supplied with 110ºF water. The reset line for this system can be determined by plotting this condition as shown in figure 11-6. design heating load condition
105 100
lin
e
95
se t
90
re
supply water temperature (ºF)
110
85 80 75 70 70
no heat load condition 60
50 40 30 20 10 outdoor temperature (ºF)
0
The reset line goes between design load condition and no-load condition.
The reset line connects the design heating load condition (upper right) to the point 70,70 (lower left). The latter represents a no-heating load condition (e.g., when the outdoor temperature is 70ºF, and the supply water temperature is also 70ºF, there will be no heat transfer from the distribution system.) The reset ratio for a reset line is the overall difference in supply water temperature divided by the overall difference in outdoor temperature. In the case of the reset line in figure 11-6:
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Many outdoor reset controllers need to be set to the system’s proper reset ratio when the system is commissioned. When a GSHP is used as the heat source, the upper supply water temperature will typically be 120ºF for Genesis (R-22-based) systems and 140ºF for specifically engineered R-410a systems, such as the ClimateMaster THW series. Thus, distribution systems that require higher temperatures are likely not satisfactory for use in GSHP systems.
Implementing Outdoor Reset Control: There are two ways to implement outdoor reset control in hydronic heating systems: 1. Turning the heat source on and off to maintain an average supply water temperature close to the “target” temperature represented by the reset line. 2. Using a mixing device to control the target temperature to the distribution system. The second method assumes the heat source can produce water temperatures higher than required by the distribution system. Although this is possible when a GSHP serves as the heat source, it is not necessarily the most efficient approach because the heat pump’s COP is lowered by operating at temperatures higher than necessary. Thus, the first method of turning the heat pump on and off to maintain an average supply water temperature close to the target temperature is generally used in such systems.
Supply water temperature (ºF)
The variance between actual supply temperature and calculated target temperature is due to a required temperature differential between “compressor on” and “compressor off” states. Without this differential, short cycling would occur. This differential is illustrated in figure 11-7.
130 120 differential 110 contacts on reset control open 0001 (@ 1/2 differential above 0001 target temperature)0001 to turn off heat pump calculated target temperature
100 90 80 70 70 60 50 40 30 20 10
0
contacts on reset control close 0001 (@ 1/2 differential below 0001 target temperature)0001 to enable heat pump -10 -20
Outdoor temperature (ºF) The reset line along with upper and lower differential lines.
An example of an outdoor reset controller is shown in figure 11-8. Notice the dials for setting the steepness of the reset line (reset ratio), the maximum allowed supply temperature, and the differential between “compressor on” and “compressor off” (differential centered on the target temperature).
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Example of an outdoor reset controller.
The ClimateMaster THW series heat pump has a built-in outdoor reset control. With this control the installer simply needs to input four variables to establish the outdoor reset line. The four variables are the outdoor design temperature, the maximum buffer tank temperature, the building balance point temperature (the outdoor temperature at which heating is no longer needed), and the minimum buffer tank temperature. The water temperature supplied to a distribution system can also be adjusted based on outdoor reset control using a motorized mixing valve or injection-mixing controller. This action is called mixing reset control. The mixing device allows the water temperature supplied to a portion of the distribution system to be reduced below that of the other portion. An example of such a system would be a building with two different types of radiant panel heating. One of the radiant panel subsystems requires 120ºF water at design load, and the other requires 105ºF at design load. In this case, the buffer tank would be maintained to supply the higher of these temperatures, and the lower temperature system would be supplied through the mixing device (see figure 11-9).
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higher 0001 temperature0001 load0001 (120ºF @ design)
lower 0001 temperature0001 load0001 (105ºF @ design)
outdoor0001 temperature0001 sensors
integral0001 check0001 valve
supply temperature sensor
zone circulators
3-way motorized mixing valve temperature0001 controller supply header
120 ºF water0001 temperature0001 @ design load sensor in well
T&P0001 ports
check0001 valve
purge0001 valves
return header
earth loop0001 circulator
GSHP
Buffer tank
purging0001 valves
earth loop circuits
The 3-way motorized mixing valve can operate with outdoor reset control logic.
It is possible, although not always necessary, to use both on/off heat source reset and mixing reset in the same system. In such cases, the reset control results in decreased fuel use, while mixing reset control optimizes comfort. Multi-stage Heat Source Control In large residential and commercial buildings, it is common to use two or more heat sources operated in stages to better match heat output to building heating load. This “staging” control has been used for several decades with boilers and is equally applicable to GSHP systems.
heating load (Btu/hr)
Consider the load profile shown in figure 11-10a. The load begins at zero, increases steadily for several hours until reaching full design load, remains at design load for several hours, and finally decreases to half load and remains there.
design load
one stage
time (hr) 24 hr
A hypothetical heating load profile.
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heating load (Btu/hr)
Figure 11-10b shows how a single stage heat source (boiler, heat pump or other on/off heat source) would operate in an attempt to match the load. Notice there is considerable “excess” heat output whenever the load is less than design load. The heat source is on for a time, and then “coasts” through an off period in an attempt to balance heat supply with heat loss.
design load
one stage
time (hr) 24 hr
A match between the heating load profile and a single stage heat source.
heating load (Btu/hr)
Figure 11-10c shows the same load with two equal stages of on/off heat source control. Although there is still some overshoot of heat production relative to the load, as well as some “coasting” time, the overall match is definitely an improvement relative to a single stage heat source.
design load
two stages
cycling of stage 2
stage 2 on 0001 continuously stage 1 on continuously time (hr) cycling of stage 1
24 hr
A match between the heating load profile and a two-stage heat source.
heating load (Btu/hr)
Figure 11-10d shows the same load with four equal stages of heat source output. This results in further refinement of the output relative to the load. stage 4
design load
four stages
stage 3 stage 2 stage 1
time (hr) 24 hr
A match between the heating load profile and a four-stage heat source.
In theory, additional stages of heat output would further improve the match. However, the cost of adding stages doesn’t always provide a reasonable return on investment relative to the benefit. Systems with 2, 3, 4 and possibly 8 stages of on/off heat output are the most common. Figure 11-11 shows an example of a 4-stage controller. Note that dry contact outputs are used, enabling the controller to operate any on/off heat source.
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Example of a 4-stage heat source controller. (Courtesy of tekmar)
It’s also possible to use multi-unit staging control in combination with 2-stage heat pumps. A 2-stage heat pump has two compressors that can be independently operated. In such cases, the operating order would typically be: a. heat pump #1/compressor 1 b. heat pump #1/compressor 2 c. heat pump #2/compressor 1 d. heat pump #2/compressor 2 etc. An example of a system using two 2-stage water-to-water heat pumps to supply a common buffer tank is shown in figure 11-11.
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zone0001 valves 2-stage0001 w/w heat pumps
zone0001 valves
zone0001 valves
pressure-regulated0001 variable-speed0001 ECM circulator
zone0001 valves0001 (1 / stage)
zone0001 valves0001 (1 / stage)
cold water DHW electic0001 booster 0001 heater
variable speed0001 pressure-regulated circulator
pressure-regulated0001 variable-speed0001 ECM circulator
to/from0001 earth loop
to/from0001 auxiliary boiler
PRV
make-up water assembly
pressure-regulated0001 variable-speed0001 ECM circulator
buffer tank w/ large interior coils for DHW preheating
expansion0001 tank
Example of a system using two 2-stage water-to-water heat pumps to supply a buffer tank.
Staging controllers can be configured for this type of paired compressor staging. Staging controllers can also be configured to “rotate” the operating order of the heat sources so that each unit accumulates approximately the same number of run time hours. This prevents one unit from “wearing out” much soon than another. The ClimateMaster THW series heat pump has the capability to control a second-stage boiler or water-to-water heat pump. When a backup boiler or heat pump is used to supplement the heating capacity of the THW, a 24VAC output from the THW unit can be used to energize the boiler. The boiler control box simply needs a relay that can be used to interface with the THW unit.
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Section 12: Hydronic Heat Emitters for GSHP Systems As discussed in section 4, the heating efficiency (e.g., COP) and heating capacity of a water-to-water GSHP system is very dependent on the water temperature at which the distribution system operates. The lower this temperature, the better the GSHP performs. This implies that low temperature hydronic heat emitters are essential if the system is to perform well. This section discusses several heat emitter systems that can perform well when supplied by a GSHP. What NOT to Use: Fin-tube baseboard is one of the most common hydronic heat emitters in the North American market. This hydronic heat emitter was designed around boilers in an era when water temperatures of 180ºF or higher were commonly used, and thermal efficiency was not of paramount importance. Such water temperatures are much higher than can be attained with current-generation ground source heat pump systems. Fin-tube baseboard releases less heat at lower water temperatures. However, the heat output at 120ºF water temperature is only about 28% of that at 180ºF water temperature. Thus, about 3.5 times as much linear footage of baseboard would be required at 120ºF water temperature to produce equivalent heat output of baseboard operated at 180ºF water temperature. This is clearly impractical from both a space and aesthetic standpoint. Thus, the combination of fin-tube baseboard and a GSHP is NOT recommended.
Fin-tube baseboard typically requires higher water temperatures than can be generated with a geothermal heat pump.
A similar argument can be made for “plateless staple-up” radiant floor heating (see figure 12-2). Such an installation is very limited in its heat output, especially at the lower water temperatures supplied by a GSHP.
Never install floor-heating tubing like this! The required operating water temperature would be very high.
A suggested guideline is that space-heating distribution systems used with GSHPs should provide design heating load output using supply water temperatures no higher than 120ºF (other than the THW series which can operate with temperatures up to 140ºF).
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Distribution systems that supply each heat emitter using parallel piping branches rather than series configurations are also preferred because they provide the same supply water temperature to each heat emitter. Examples of space-heating systems that allow the GSHP to provide good performance include: • Heated floor slabs with low-resistance coverings • Heated thin-slabs over framed floors with low-resistance floor coverings • Generously sized panel radiator systems with parallel piping
Slab-on-grade Radiant Floor: One of the most common types of radiant panel is a heated floor slab, as shown in figure 12-3. This type of radiant panel has one of the lowest supply water temperature requirements of any hydronic heat emitter, and thus will perform well with a GSHP. edge insulation (extruded polystyrene) underslab insulation (extruded polystyrene) steel reinforcing concrete slab embedded tubing finish flooring
compacted soil polyethylene vapor barrier foundation
Cross-section of a heating slab-on-grade floor.
To keep the supply water temperature low, it’s important to: a. Keep tube spacing relatively close. b. Keep the thermal resistance of the finish floor as low as possible. The graph in figure 12-4 shows upward heat output from a heated slab based on tube spacing of 6 inches and 12 inches, and for finish floor resistances ranging from 0 to 2.0ºF • hr • ft2/Btu. The steeper the line, the better the distribution system is suited for use with a GSHP.
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upward heat output0001 (Btu/hr/ft^2)
12' tube spacing 6' tube spacing 60
Rff=0
Rff=0.5 Rff=1.0
40
Rff=1.5 Rff=2.0
20 0
0 10 20 30 40 50 60 70 80 90 100 Twater - Troom (ºF) Rff = resistance of finish flooring (ºF/hr/ft^2/Btu)
The effect of finish floor resistance on upward heat output of a heated slab floor.
Achieving an upward heat output of 25 Btu/hr/ft2 from a slab with no covering (e.g., Rff = 0) and 6” tube spacing requires the “driving ∆T” (e.g., the difference between average water temperature in tubing and room air temperature) to be about 22ºF. Thus, in a room maintained at 70ºF, the average water temperature in the circuit needs to be 92ºF. The supply water temperature to the circuit would likely be in the range of 102ºF. This is a relatively low supply water temperature, and should allow the GSHP to operate at good efficiency. However, if this same heat output is required from a slab with 12” tube spacing and a finish floor resistance of 1.0ºF • hr • ft2/Btu. The driving ∆T must be 53ºF. The average circuit water temperature required to maintain a room temperature of 70ºF would be 123ºF, and the supply temperature likely in the range of 133ºF. This supply temperature is higher than recommended for some heat pumps, although units such as the THW are capable of reaching this supply temperature. The following guidelines are suggested in applications where a heated floor slab will be used to deliver heat derived from a solar collector array: • Tube spacing within the slab should not exceed 12 inches. • Slab should have a minimum of R-10 insulation on its underside. • Tubing should be placed at approximately 1/2 the slab depth below the surface, as shown in figure 12-5. Leaving the tube at the bottom of the slab can increase the required supply water temperature several degrees Fahrenheit. This will decrease the heating capacity and COP of the heat pump. • Bare, painted or stained slab surfaces are ideal because the finish floor resistance is essentially zero. • Other floor finishes should have a Total R-value of 1.0 or less.
PEX-AL-PEX tubing and reinforcing mesh being lifted as concrete is placed for a heated slab-on-grade floor.
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Summary of heated slab-on-grade floors: • Typical water supply temperature at design load = 95° to 120°F Strengths: • Most economical installation (slab is already part of building) • Operates on low water temperatures (good match to GSHP) • Very durable • High thermal storage responds well to cold air influx Limitations: • Slow thermal response (best when loads are slow to change) • Quality control dependent on masons Always… • Verify proper preparation of subgrade • Insulate edge and underside of slab • Lift welded wire reinforcing with tubing during pour • Use proper detailing at control joints • Pressure-test circuits prior to placing concrete • Make tubing layout drawing prior to placing tubing Never… • Drive power buggies or trucks over tubing • Pressure-test with water • Cover with flooring having total R-value over 2.0°F hr/ft2/Btu
Thin-slab (Concrete) Radiant Floor: Another method of constructing a heated floor is called a “thin-slab.” It is created by placing a thin (1.5” to 2” thick) layer of concrete over tubing that has been fastened to a wooden subfloor as shown in figure 12-6. sleeper finish flooring tubing secured to subfloor concrete thin-slab 6-mill polyethylene bond breaker anti-fracture membrane (for tile flooring) walls framed after0001 thin-slab is installed
slight separation occurs as concrete cures coat edges of sleepers with mineral oil0001 to prevent concrete bonding 6-mill polyethylene bond breaker sheet crack forms above control joint strip 1'x1' PVC drywall trim angle0001 stapled to subfloor serves as0001 control joint strip
sleeper
underside insulation subfloor
plywood subfloor
concrete thin-slab
Cross-section of a concrete thin-slab heated floor.
Figure 12-7 shows tubing installed over a layer of 6-mil polyethylene sheeting. The latter serves to prevent bonding between the underside of the concrete and the wooden subfloor. This, in turn, helps reduce tensile stress in the concrete as the slab cures. The concrete will be placed to a depth of 1.5 inches above the subfloor. Slab thickness is controlled by screeded level with the top of the 2x4 and 2x6 wall plates seen in figure 12-7.
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Tubing being placed over polyethylene sheeting awaiting placement of concrete thin-slab.
Summary of thin-slab (concrete) heated floors: Typical water supply temperature at design load = 95° to 120°F Strengths: • Usually lower installed cost relative to poured gypsum thin-slab • Operate on low water temperatures (good match to GSHP) • Very durable, waterproof • Medium thermal storage tends to smooth heat delivery Limitations: • Slower thermal response (best when loads are slow to change) • Adds about 18 pounds/square foot to floor loading @ 1.5” thickness Always… • Verify load carrying ability of floor framing • Account for added 1.5 inches in floor height • Install control joints and release oil on adjacent framing • Install polyethylene bond breaker layer between subfloor and slab • Pressure-test circuits prior to placing concrete • Make tubing layout drawing prior to placing tubing • Install R-11 to R-30 underside insulation Never… • Allow concrete to freeze prior to curing • Pressure-test with water • Place tubing closer than 9 inches to toilet flanges • Cover with flooring having total R-value over 2.0°F hr/ft2/Btu • Use asphalt-saturated roofing felt for bond breaker layer • Exceed 12” tube spacing
Thin-slab (Poured Gypsum Underlayment) Radiant Floor: Another type of thin-slab is created using poured gypsum underlayment rather than concrete. A cross-section of this floor is shown in figure 12-8.
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poured gypsum seals at base of walls drywall installed prior to gypsum slab finish flooring tubing secured to subfloor poured gypsum underlayment thin-slab spray applied sealant putty holes in subfloor0001 prior to pouring slab
underside insulation subfloor
Cross-section of a poured gypsum underlayment heated floor.
As in the case of concrete, the slab thickness is typically 1.5 inches. The difference is that the poured gypsum material has a much greater flow characteristic than concrete. It is pumped into the building through a hose and is largely self-leveling as it is placed on the subfloor (see figure 12-9). No polyethylene sheet is used to break the bond between the poured underlayment and the subfloor.
Poured gypsum underlayment being placed over hydronic tubing fastened to wood subfloor.
Summary of thin-slab (poured gypsum underlayment) heated floor: • Typical water supply temperature at design load = 95° to 120°F Strengths: • Faster installation than concrete thin-slab • Operates on low water temperatures (good match to GSHP) • Excellent air sealing at wall/floor intersection • Medium thermal storage tends to smooth heat delivery • No control joints required Limitations: • Slower thermal response (best when loads are slow to change) • Adds about 14.5 pounds/square foot to floor loading @ 1.5” thickness • Not waterproof Always… • Verify load-carrying ability of floor framing
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• • • • •
Account for added 1.5 inches in floor height Pressure-test circuits prior to placing gypsum underlayment Make tubing layout drawing prior to placing tubing Install R-11 to R-30 underside insulation Use proper surface preparations prior to finish flooring
Never… • Allow gypsum to freeze prior to curing • Pressure-test with water • Place tubing closer than 9 inches to toilet flanges • Cover with flooring having total R-value over 2.0°F hr/ft2/Btu • Exceed 12” tube spacing • Install in locations that could be flooded
Above Floor Tube & Plate Radiant Floor: One final radiant floor panel that would be compatible with GSHPs (under specific circumstances) is shown in figure 12-10. This system is known as an above floor tube and plate system. Rather than concrete or poured gypsum underlayment, this system uses thin aluminum plates to conduct heat away from the tubing and spread it out across the floor surface.
hardwood floor nailed directly over plates
carpet, tile, or vinyl flooring 3/8' cover sheet (plywood / cement brd.) aluminum heat transfer plate staples, one side only tube slight gap (side opposite staples) plywood sleeper construction adhesive subfloor
construction adhesive sleeper heat transfer plate tube
Cross-section of an above floor tube and plate system.
An example of an above floor tube and plate system being covered with nail-down hardwood flooring is shown in figure 12-11.
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Hardwood flooring being nailed down over an above floor tube and plate radiant panel.
It’s important to realize that the supply water temperature to this type of system is often higher than that of slabtype systems. When used with a GSHP, the lower end of this temperature range will provide the best efficiency. • Typical water supply temperature at design load = 120° to 145°F Strengths: • Adds very little weight to floor • Operates on medium water temperatures (some potential for GSHP) • Minimizes resistance between plates and top of floor • Relatively low thermal mass for fast response • Excellent for use with nailed-down wood flooring • Doesn’t require tubing to run parallel with floor joists Limitations: • Potential to cause expansion sounds if not properly installed • Requires several “passes” over floor during installation; labor intensive • Requires considerable amount of wood fabrication Always… • Staple only one side of plate to sleeper — allow for expansion • Account for added 3/4” in floor height • Pressure-test circuits prior to covering • Make tubing layout drawing prior to placing tubing • Install R-11 to R-30 underside insulation Never… • • • • •
Place in an area where nails might penetrate tubing Pressure-test with water Place tubing closer than 9 inches to toilet flanges Cover with flooring having total R-value over 2.0°F hr/ft2/Btu Exceed 12” tube spacing
Floor Warming: In some systems, a heated floor may only provide part of the total heating load. This may be due to high loads (those in excess of 40 Btu/hr/ft2). In such cases, some other type of heat emitter, hydronic or otherwise, is used to supplement the heat output of the floor so that the space remains comfortable.
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Floor warming is also used in combination with hydronic air handlers. The heated floor may operate with surface temperatures in the range of 73º to 80ºF to cover the “base load” of the space. The air handlers then add any additional heat necessary to maintain room temperature. This approach is well suited to situations where unpredictable internal heat gains from sunlight, occupants, equipment or other sources are likely. It allows the system to adapt to these gains rapidly, and thus minimizes the potential temperature overshoot that could occur if a high-mass heated floor was the only heat emitter present. Floor warming also allows the heat pump to operate at relatively low supply water temperatures, and thus at high COPs. Radiant Wall Panels: Radiant panels can be integrated into walls and ceilings as well as floors. Two configurations that would be well suited for GSHPs both use the same aluminum plate system just described. An example of a radiant wall constructed using aluminum plates is shown in figure 12-12 and figure 12-13. crossection
wooden nailer (@ end of wall)
7/16' oriented strand board 3/4' foil-faced polyisocyanurate insulation 2.5' drywall screws 6'x24' aluminum heat transfer plates 1/2' PEX-AL-PEX tubing 1/2' drywall
fiberglass insulation
1/2' PEX-AL-PEX tubing (8-inch spacing) 6' x 24' aluminum heat transfer plates 3/4' foil-faced polyisocyanurate foam strips 7/16' oriented strand board
Elevation and cross-section of a radiant wall.
A radiant wall panel during construction.
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The radiant wall design shown has very low thermal mass relative to the floor-heating panels previous described. This makes it very responsive to changes in internal heat gains or thermostat settings. Such a characteristic is very desirable in buildings with significant solar heat gain, or situations where temperature setback schedules are used. Radiant walls can also be incorporated in areas such as stair walls (see figure 12-14), or walls under a kitchen island.
The wall around these stairs is a radiant panel with embedded tubing and aluminum plates.
The heat output of a radiant wall constructed as shown can be estimated using the following formula.
Where: Q = heat output of wall (Btu/hr/ft2) Twater = average water temperature in panel (ºF) Troom = room air temperature (ºF)
Radiant Ceiling Panels: The same type of construction shown for radiant walls can also be incorporated into ceilings, as shown in figure 12-15 and 12-16. Like the radiant wall design, this radiant ceiling panel can respond very quickly. Radiant ceilings also have the advantage of not being blocked by furniture or covered with other materials that reduce heat transfer. top side insulation
ceiling framing
tube 7/16' oriented strand board aluminum heat transfer plate 3/4' foil-faced polyisocyanurate foam strips 1/2' drywall
Cross-section of a low thermal mass radiant ceiling panel using aluminum plates.
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A radiant ceiling prior to installation of drywall.
The heat output of a radiant ceiling constructed as shown can be estimated using the following formula.
Where: q = heat output of wall (Btu/hr/ft2) Twater = average water temperature in panel (ºF) Troom = room air temperature (ºF)
Panel Radiators: Extensively used in European systems, panel radiators are becoming increasingly popular in North America. Base-model panel radiators are built of pressed steel plates, and come in a wide variety of shapes and sizes. With proper sizing (for low supply water temperatures), they can be used in combination with water-to-water GSHPs. An example of a typical panel installation is shown in figure 12-17.
A typical panel radiator installation.
The heat output of a panel radiator is very dependent on its size as well as its supply water temperature. The table in figure 2-18 lists the “reference” heat output of several common-size panels. This output is based on 180ºF average water temperature in the panel, and 68ºF room temperature. The water temperature is much higher
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than what can be attained with a GSHP. However, the reference heat output can be corrected for differences in average water temperature, as well as different room air temperatures. Use the curve or formula shown in figure 12-19 to determine a multiplier for the reference heat output to correct it for different operating conditions. length
Heat output ratings (Btu/hr)0001 at reference conditions:0001 Average water temperature in panel = 180ºF0001 Room temperature = 68ºF0001 temperature drop across panel = 20ºF
height
1 water plate
1 water plate panel thickness 16' long
24' long
36' long
48' long
64' long
72' long
24' high
1870
2817
4222
5630
7509
8447
20' high
1607
2421
3632
4842
6455
7260
16' high
1352
2032
3046
4060
5415
6091
2 water plates
2 water plate panel thickness 16' long
24' long
36' long
48' long
64' long
72' long
24' high
3153
4750
7127
9500
12668
14254
20' high
2733
4123
6186
8245
10994
12368
16' high
2301
3455
5180
6907
9212
10363
10' high
1491
2247
3373
4498
5995
6745
72' long
3 water plates
3 water plate panel thickness 16' long
24' long
36' long
48' long
64' long
24' high
4531
6830
10247
13664
18216
20494
20' high
3934
5937
9586
11870
15829
17807
16' high
3320
4978
7469
9957
13277
14938
10' high
2191
3304
4958
6609
8811
9913
Reference heat output ratings for panel radiators. 1 1.33
CF = 0.001882 ( 0001T )
0.8 0.7 reference condition
Correction factor (CF)
0.9
0.6 0.5 0.4 0.3 0.2 0.1 0
0002T=112 ºF
0
20
40
60
80
100
120
0001T (ave water temp - room air temp) (ºF) Reference condition:0001 Ave water temp. in panel = 180ºF0001 Room air temperature = 68ºF
Correction factor for adjusting the reference heat output to other operating conditions.
For example: Figure 12-18 indicates that a panel with a single water plate, measuring 24 inches high and 72 inches long, has a heat output of 8,447 Btu/hr based on the reference conditions of 180 ºF average water temperature and 68ºF room air temperature. Using the formula in figure 12-19, the correction factor with an average panel water temperature of 110ºF and room temperature of 68ºF is:
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The estimated heat output at the lower water temperature is thus:
This demonstrates that systems limiting the supply water temperature to 120ºF to retain good performance of the GSHP often require substantially larger panel radiators compared to systems with conventional heat sources that often supply much higher water temperatures.
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Section 13: Air Separation and Removal The vast majority of hydronic heating systems are designed to operate without air in the piping. Thus, it’s essential to provide the means of separating air from the water when the system is filled (e.g., purging) and preserving this deareated state throughout the life of the system. Air in hydronic systems can lead to the following problems: • • • • • • •
Noises in the piping and heat emitters Inadequate circulator performance Inadequate heat output from the heat emitters Accelerated corrosion due to oxygen in contact with ferrous metals Circulator noise or failure due to improper lubrication Poor performance of balancing valves Complete loss of flow and heat output due to large air pockets
Air exists in three forms within hydronic systems: • Stationary air pockets • Entrained air bubbles • Gases dissolved within water A well-planned air separation strategy must address all three forms. Stationary Air Pockets: Stationary air pockets are created from air that’s not expelled when the system is filled and purged. Since air is lighter than water, it migrates to high points in the system. Such points are not necessarily just at the top of the piping circuit. They can form at the top of heat emitters, even those located low in the building. Air pockets can also form in horizontal piping that eventually turns downward or piping routed up, over, down and around obstacles. Stationary air pockets can also form as air bubbles not removed during system purging merge together and migrate toward high points. This is especially likely in components with low flow velocities, where slow-moving fluid cannot push or drag the air along with it. Proper purging at startup can usually dislodge stationary air pockets to the extent that the circulator can maintain flow in the system. Further removal of air pockets can be done through a combination of air vents at system high points and microbubble absorption. Entrained Air: A moving fluid may be able to carry air bubbles along (entrain them) through a hydronic piping system. This can be beneficial when the entrainment carries the air bubble from remote parts of the system back to a central airseparating device, which can then capture and expel the air. However, if the fluid’s flow velocity through the air-separating device is too high, the entrained air cannot be efficiently separated and could end up recirculating through the system many times. The ability of a fluid to entrain air is based largely on its velocity. A minimum flow velocity of 2 feet per second is needed to entrain air bubbles within downward-flowing pipes. Microbubbles: Water has the ability to absorb the gas molecules that make up air. These molecules are interspersed with water molecules, and thus are said to be dissolved into the water. The cooler the water, and the greater the pressure on the water, the more dissolved gases it can contain. Conversely, the hotter the water, and the lower its pressure, the less dissolved gases it can contain. 85
The decreasing ability of the water to retain gas molecules in solution as the water is heated forces the “excess” molecules out of solution in the form of microbubbles. The latter are so small they cannot be seen as individual bubbles. Instead, they typically appear as a cloud in otherwise clear water. Microbubbles have very low rise velocities and are easily entrained with water flowing through a hydronic system at normal flow velocities. This makes it difficult to collect them based on the premise they will simply gather at high points where vents are located. Efficient collection of microbubbles requires a coalescing media in combination with a low-velocity chamber. The coalescing media provides a high amount of surface area with solid edges that create very localized low-pressure areas due to vortex formation. Microbubbles flowing past the coalescing media tend to cling to these edges. From there, the coalescing media provides pathways along which the microbubbles can slowly rise through the active flow zone of the separator without being pulled away from the media. Figure 13-1 shows an example of a coalescing media used in a hydronic air separator.
Coalescing media used in a microbubble air separator. (Courtesy of Caleffi North America)
Most microbubble air separators have a vertically oriented cylindrical chamber to house the coalescing media and create acceptably low flow velocities so that bubbles can rise above the active flow zone of the separator. Once above this zone, the bubbles collect at the top of the air separator, and eventually leave through a float-operated vent at the top. They are driven out of the vent by positive system pressure. An example of a modern microbubble air separator is shown in figure 13-2.
Example of a microbubble air separator.
Microbubble air separators are best placed where water is hottest and where the pressure is reasonably low. In heating systems, the preferred placement is near the outlet of the heat source. The flow velocity in the piping leading into the air separator should not exceed 4 feet per second (see figure 7-1).
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The ability of a microbubble air separator to lower the air content of hot water as it passes through allows the water to be in an “unsaturated” state as it cools while passing through the hydronic distribution system. When the unsaturated water comes into contact with air molecules in the distribution system, it will absorb them and carry them back to the heat source. When the water is reheated, the gathered air is released and quickly captured by the air separator waiting downstream. Eventually, a microbubble air separator can lower the air content of the water to about 0.4%. At that point, the system is, for all intents and purposes, air free.
Filling & Purging Hydronic Systems All hydronic systems must be filled and purged of bulk air when put into service. Beyond initial purging, they need a means to gather and expel any air bubbles that form as the water is heated. This section describes procedures and hardware for this purpose. Make-up Water Assembly: Although much of the “bulk” air in a hydronic system can be expelled when the system is first filled, it may take several days of operation to effectively separate the dissolved air molecules and rid this air from the system. During this time, it’s necessary to replace the ejected air with an equivalent volume of water. In most systems, this is done using an automatic make-up water assembly consisting of a backflow preventer, pressure-reducing valve and some ball valves, as shown in figure 13-3. connection0001 to system tank isolation valve connection0001 to cold water0001 source
backflow preventer fast fill (ball) valve pressure reducing valve expansion tank air pressure adjustment valve
Components used in an automatic make-up water system.
This assembly is connected to the cold water piping in the building. Whenever the pressure on the system side of the assembly drops below the setting of the pressure-reducing valve, water flows into the system. This typically occurs at the same time air is being ejected by the air separator. Forced Water Purging: The process of forcing air out of a hydronic system as water enters that system is called purging. Every hydronic system must be purged when it’s commissioned. In some cases, air rises upward within the piping as water is introduced lower in the system. In other cases, air is forced along the piping by a fast-moving water stream, and eventually exits through a valve. Purging is a coordinated process between the make-up water assembly and one or more purging valves. The latter is a combination of a ball valve and drain valve sharing a common body. An example of a modern purging valve is shown in figure 13-4.
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A modern hydronic purging valve. (Courtesy of Webstone, Inc.)
Figure 13-5 shows both the make-up water system and purging valve within a typical distribution system. alternative placement of 0001 make-up water assembly
air release
heat0001 source0001 (off)
make-up water assembly
distribution0001 piping0001 system
inline valve0001 closed0001 during purging
outlet valve open0001 during purging
air & water0001 exit system0001 through hose
5 gallon bucket0001 or drain
The typical relationship between the make-up water assembly and purging hardware.
Begin the purging process by opening the side port valve that connects to a drain hose. The automatic feed valve is then manually opened to allow rapid water flow into the system. The fast fill valve in parallel with the automatic feed valve should also be opened to maximize the rate of water flow to the system. Because the ball valve on the heat source inlet pipe is closed, the entering water begins filling the heat source. Air within the heat source is displaced as the water enters. It migrates up to the central air separator and exits. When the heat source is full, water flows out into the distribution system, pushing air ahead of it. The air and some water exits through the drain port of the purging valve. A hose fastened to the purge valve leads this mixture to a pail or floor drain. Purging continues until the discharge stream is running free of visible air bubbles. At this point, most of the bulk air will have been purged from the circuit. The bypass valve in the make-up assembly is closed, and the fast fill function of the automatic feed valve is turned off. Systems with two or more branch circuits should have a purge valve in each circuit. This allows each circuit to be individually purged. When the flow exiting the purge valve on a given circuit is running free of air bubbles, the next branch circuit is opened and the previous one is closed. This allows the maximum possible flow rate through each branch circuit to dislodge and entrain as much air as possible.
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Section 14: Buffer Tanks for GSHP Systems Most current-generation water-to-water heat pumps are simple “on/off” devices. When operating, they deliver the maximum amount of heating or cooling capacity possible based on their current entering source and entering load water temperatures. When such heat sources serve a zoned distribution system, there will be many times when their instantaneous heat output significantly exceeds the current heat load of the distribution system. In hydronic systems that have significant thermal mass in the heat source, this difference between heat production and heat release can be temporarily absorbed by the thermal mass. However, most GSHPs have relatively low thermal mass, and thus a very limited ability to temporarily absorb this surplus heat production. The end result will be “short cycling” of the heat source. In the case of a GSHP, the compressor will turn on for short periods of time – perhaps even less than one minute, and then turn off. This cycle will be repeated, perhaps thousands of times over the course of a heating season. Such operation strains components such as the compressor, and the compressor contactor, and therefore should be avoided. All ClimateMaster water-to-water heat pumps include a 5-minute minimum off-cycle control function. However, this does not preclude the need for a properly sized buffer tank in a zoned system. In larger systems, multi-stage heat production as discussed in section 11 can be used to improve the balance between heat production and heating load. The greater the number of stages, the better the potential match. Unfortunately, many residential systems do not have sufficient load to justify a multi-stage heat source subsystem. In these systems, the currently appropriate solution is to provide additional thermal mass between the heat pump and the distribution system. This mass typically takes the form of a buffer tank. A simple concept for such a system is shown in figure 14-1.
to / from other zones
zone valves
temperature0001 controller
sensor in well
purge0001 valves
T&P0001 ports earth loop0001 circulator
variable speed0001 pressure-regulated circulator
GSHP
Buffer tank
purging0001 valves
earth loop circuits
A buffer tank installed near a GSHP and zoned distribution system.
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The heat pump’s “responsibility” in this system is to simply keep the temperature in the buffer tank within a set temperature range so that sufficient heat can be supplied to any zone circuit that might happen to come on. This is accomplished by using a controller to monitor the temperature of the tank and turn the heat pump on and off as necessary to maintain this operating temperature range. ClimateMaster THW heat pumps include this control logic and the necessary sensors to control buffer tank temperature. The controller may be a simple set point device with a user-set “target temperature and differential.” For example, the controller might be set to a target temperature of 105ºF with a differential of 10ºF. In this case, the set point controller would turn on the heat pump when the buffer tank temperature dropped to 105-10/2=100ºF. The heat pump would continue to operate until the tank’s temperature climbed to 105+10/2 = 110ºF, at which point it would shut off. Another possibility, one that will increase the overall efficiency of the system, is to use an outdoor reset controller (as described in section 10) to operate the heat pump. Like the set point controller, the ORC has a target temperature and operating differential. The difference is that the target temperature can change in response to outdoor temperature. This allows the target temperature to drop as outdoor temperature rises. Lower load temperatures increase both the COP and heating capacity of the heat pump. Unlike more traditional zoned hydronic systems, there is no direct call from the room thermostats to the heat source. The load circuits only “see” the heated buffer tank as their source as needed. The heat pump only “sees” the buffer tank as its load. Sizing a Buffer Tank: The required volume of a buffer tank depends on the rates of heat input and release, as well as the allowed temperature rise of the tank from when the heat source is turned on, to when it is turned off. The greater the tank’s volume, and the wider the operating temperature differential, the longer the heat source cycle length. Formula 14-1 can be used to calculate the volume necessary when given a specified minimum heat source ontime, tank operating differential and rate of heat transfer: Formula 14-1
Where: v = required volume of the buffer tank (gallons) t = desired duration of the heat source’s “on cycle” (minutes) Qheat source = heat output rate of the heat source (Btu/hr) qload = rate of heat extraction from the tank (Btu/hr) ∆T = temperature rise of the tank from when the heat source is turned on to when it is turned off (ºF) For example, assume it’s desired that a heat pump operate with a minimum compressor on-cycle duration of 10 minutes. The heat pump, when on, supplies 60,000 Btu/hr. The compressor turns on when the buffer tank temperature drops to 100ºF, and off when the tank reaches 120ºF. What is the necessary tank buffer tank volume to accomplish this? Solution: Substituting the numbers into Formula 14-1 yields:
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If a tank larger than the minimum required volume is used, the on-cycle length could be increased, or the temperature differential through which the tank cycles could be reduced. The wider the temperature differential, and the greater the volume of the tank, the longer the heat source on-cycle will be. Buffer Tank Simulator: The cycling time of hydronic heating supplying a load through a buffer tank can also be simulated in software. The Buffer Tank Simulator module of the Hydronics Design Toolkit program can simulate the performance of a system containing up to 24 independently controlled loads supplied through a buffer tank. The buffer tank is located between the heat source and the loads. The user specifies the volume of the tank, the operating temperature range of the tank and the R-value of the tank’s insulation. The user also specifies the size and on/off status of each load. The module calculates the on-time and off-time of the heat source based on the specified buffer tank and current load configuration. It also calculates thermal losses from the buffer tank. A screen shot is shown in figure 14-2.
Buffer Tank Simulator software module.
Figure 14-3 shows an example of a commercially available buffer tank. This product is currently available in 30and 80-gallon sizes. This tank has 2 inches of polyurethane insulation, 4 large connection ports, an air vent at the top, and a drain valve at the bottom.
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Example of a 30-gallon buffer tank. (Courtesy of Hot Water Products, Inc.)
When placed between the heat pump and loads, a buffer tank of this design also provides hydraulic separation between the heat pump condenser circulator and the circulator(s) used in the distribution system. This is especially beneficial when the distribution system uses a variable-speed circulator.
Combined Buffer/DHW Tanks
reverse return piping shown
Another way to achieve the benefits of a buffering thermal mass is to use an indirect water heater as a buffer tank. The concept is shown in figure 14-4. zone0001 valves
cold water DHW
pressure-regulated0001 variable-speed0001 ECM circulator
very low flow resistance0001 allows for hydraulic separation0001 of circulators
booster 0001 heater
PRV
T&P0001 ports
buffer tank w/ large interior coils for DHW preheating
earth loop0001 circulator
GSHP purging0001 valves
earth loop circuits
The buffer tank also serves to heat domestic water.
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Section 15: Sample Schematics for Hydronic Systems Supplied by GSHPs This section pulls together many of the principles discussed in earlier sections. It shows several ways to combine modern hydronic principles into systems supplied by GSHPs. The following system schematics are shown: 1. 2. 3. 4. 5. 6. 7. 8.
Single zone radiant floor heating Single zone radiant floor heating with domestic water preheating Multi-zone radiant panel heating using zone valves Homerun distribution system supplying panel radiators Multiple water-to-water heat pump system supplying zoned distribution Multiple water temperature distribution system Heating using radiant panel with single zone chilled-water cooling Heating using radiant panel with multi-zone chilled-water cooling
#1. Single zone radiant floor heating: This system uses a single GSHP to supply a single radiant panel manifold station. There is no need for a buffer tank since the entire distribution system operates as a single zone. The heat pump, earth loop circulator and distribution circulator would all operate together. THIS PIPING IS ONLY APPROPRIATE FOR SINGLE ZONE SYSTEMS.
PRV
T&P0001 ports earth loop0001 circulator
air0001 separator
purging0001 valves
GSHP purging0001 valves
single zone radiant panel0001 manifold station distribution0001 circulator
make-up water assembly
expansion0001 tank
earth loop circuits
Single zone space heating. Buffer tank is not required.
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#2. Single zone radiant floor heating with domestic water preheating: This system adds a flat-plate heat exchanger as a second load to the radiant manifold station. When there is a call for domestic water heating, space heat is temporarily suspended. This allows the full output of the heat pump to be directed to domestic water heating. The heat exchanger circulator and bronze DHW tank circulator operate. Heat is transferred from the system water to potable water through a generously sized flat-plate heat exchanger. When the DHW load is satisfied, or has been active for a set period of time (i.e., 30 minutes), the space-heating load is allowed to operate. THIS PIPING IS ONLY APPROPRIATE FOR SINGLE ZONE SYSTEMS. CW DHW
anti-scald0001 tempering0001 valve
P&TRV
check0001 valves
electric0001 heating0001 element
electric0001 water heater
flat plate0001 heat exchanger
bronze or stainless0001 circulator
DHW HX0001 circulator0001 (w/ check)
PRV
T&P0001 ports earth loop0001 circulator
purging0001 valves
GSHP purging0001 valves
single zone radiant panel0001 manifold station distribution0001 circulator0001 (w/ check)
make-up water assembly expansion0001 tank
earth loop circuits
Single zone space heating plus DHW preheating via an external flat-plate heat exchanger. Buffer tank is not required.
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Another possibility is a GSHP equipped with a desuperheater. In this case, heat is extracted directly from the hot compressor discharge gas and used to heat domestic water being circulated from the DHW storage tank. A piping schematic for this option is shown in figure 15-3. THIS PIPING IS ONLY APPROPRIATE FOR SINGLE ZONE SYSTEMS. CW DHW
anti-scald0001 tempering0001 valve
P&TRV
check0001 valves
electric0001 heating0001 element
bronze or stainless0001 circulator electric0001 water heater desuperheater HX PRV
T&P0001 ports earth loop0001 circulator
air0001 separator
purging0001 valves
GSHP
purging0001 valves
single zone radiant panel0001 manifold station distribution0001 circulator
make-up water assembly
expansion0001 tank
earth loop circuits
Single zone space heating plus DHW preheating via a desuperheater. Buffer tank is not required.
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#3. Multi-zone radiant panel heating using zone valves: This system addresses one of the major benefits of hydronics: Zoning. It uses a high-efficiency variable-speed circulator to control flow through zone circuits that are in turn controlled by zone valves. The GSHP is operated by an outdoor reset controller, which maintains the target temperature of the buffer tank based on the current outdoor temperature. The reset controller is adjusted based on the supply temperature requirement of the radiant panel zones. DHW preheating is provided by a desuperheater in the heat pump, and boosted, if necessary, by the heating element in the water heater. All ClimateMaster THW series water-to-water heat pumps include this outdoor reset capability. CW DHW
anti-scald0001 tempering0001 valve
P&TRV
check0001 valves
outdoor0001 temperature0001 sensor
electric0001 heating0001 element
bronze or stainless0001 circulator
outdoor reset controller
electric0001 water heater
to / from0001 other zones zone valves supply header
desuperheater HX variable speed0001 pressure-regulated circulator temperature0001 sensor T&P0001 ports
purge0001 valves
purging0001 valves return header
earth loop0001 circulator
GSHP
purging0001 valves
Buffer tank
make-up water assembly
expansion0001 tank
earth loop circuits
A multi-zone system supplies DHW preheating and zoned space heating via zone valves and a variable-speed circulator.
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#4. Homerun distribution system supplying panel radiators: The system shown in figure 15.5 is very similar to that shown in figure 15.4. The difference is in the distribution system on the right side of the buffer tank. The system in figure 15-5 uses a “homerun” distribution system, which consists of a manifold station and individual supply/return piping to each panel radiator. This piping is flexible 1/2” PEX or PEX-AL-PEX tubing. Such tubing is easy to route through framing cavities in either new construction or retrofit applications. The heat emitters are panel radiators with individual thermostatic radiator valves the allow room-by-room temperature control. To keep the GSHP within its normal operating range, these radiators have been sized to provide design heat output at a supply water temperature of 120ºF. If a ClimateMaster THW series heat pump is used, the supply water temperature can be as high as 140ºF. Increasing the supply water temperature will decrease the size of the panel radiator needed for a given heat output The variable- speed, pressure-regulated circulator continually monitors the differential pressure between the supply and return side of the distribution system, and adjusts its speed as necessary to maintain a set differential pressure. NOTE: Radiators sized for design load output using 120 ºF water TRV
TRV
thermostatic0001 radiator valves0001 (TRV) on each0001 radiator
CW DHW
anti-scald0001 tempering0001 valve
P&TRV
check0001 valves
TRV
outdoor0001 temperature0001 sensor
TRV
TRV TRV
electric0001 heating0001 element
bronze or stainless0001 circulator
outdoor reset controller
1/2' PEX or0001 PEX-AL-PEX0001 tubing
electric0001 water heater desuperheater HX
variable speed0001 pressure-regulated circulator temperature0001 sensor T&P0001 ports earth loop0001 circulator
purging0001 valves
GSHP
purging0001 valves
Buffer tank
manifold station PRV
make-up water assembly
expansion0001 tank
earth loop circuits
Multi-zone system supplies DHW preheating and zoned space heating via panel radiators, thermostat valves and a variable-speed circulator.
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#5. Multiple water-to-water heat pump system supplying zoned distribution: This system uses multiple water-to-water heat pumps, operated by a staging controller, to maintain a specific target temperature in the buffer tank. This target temperature may be a fixed set point, or it may be based on outdoor reset control. The 3-way motorized mixing valve may or may not be needed, depending on the temperature the tank is maintained at for DHW purposes relative to the supply water temperature of the space-heating distribution system. Zone valves are used to control flow through both sides of each heat pump. They are open only when the heat pump operates. The variable speed circulator maintains a constant differential pressure across the headers serving each side of the heat pump array. This reduces pumping power when some heat pumps are not operating. The buffer tank allows for extensive zoning of the distribution systems without creating short cycling of the heat pumps. The internal copper coils in the buffer tank allow for domestic water preheating. zone0001 valve reverse return piping shown
zone0001 valve
low flow resistance headers (IMPORTANT!)
low flow resistance headers (IMPORTANT!)
pressure-regulated0001 variable-speed0001 ECM circulator
flexible reinforced hose
cold water DHW booster 0001 heater
isolation valve
on/off zone valve
isolation & purge valve
very low flow resistance0001 allows for hydraulic separation0001 of circulators
pressure-regulated0001 variable-speed0001 ECM circulator
pressure-regulated0001 variable-speed0001 ECM circulator
earth loop circuits
PRV
buffer tank w/ large interior coils for DHW preheating
make-up water assembly
expansion0001 tank
Multi-stage water-to-water heat pumps supply the zoned distribution system through a buffer tank. The tank also preheats domestic water.
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#6. Multiple water temperature distribution system: This system supplies two loads that require different water temperatures. The outdoor reset controller maintains the buffer tank close to the target temperature required by the higher temperature load. Water flows directly from the buffer tank to this load (no mixing). The lower temperature load is supplied through a 3-way motorized mixing valve, which blends in some cooler return water to achieve the lower supply temperature. The heat pump operates to maintain the tank temperature suitable for the higher temperature load. This temperature could be based on a set point or outdoor reset control. Similarly, the 3-way mixing valve operates to maintain the supply temperature needed by the lower temperature load. Again, this could be based on a set point or outdoor reset control. CW DHW
anti-scald0001 tempering0001 valve
P&TRV
check0001 valves
outdoor0001 temperature0001 sensor
electric0001 heating0001 element
bronze or stainless0001 circulator
3-way0001 motorized0001 mixing 0001 valve lower temperature0001 manifold station0001 (through mixing valve)
outdoor reset controller
electric0001 water heater desuperheater HX
circulator0001 w/ integral0001 check valve check0001 valve
temperature0001 sensor T&P0001 ports earth loop0001 circulator
purging0001 valves
GSHP
purging0001 valves
PRV
Buffer tank
purge0001 valves
higher temperature0001 manifold station0001 (no mixing)
make-up water assembly
expansion0001 tank
earth loop circuits
A two-temperature distribution system. The mixing valve is used to create a lower supply water temperature.
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#7. Heating using radiant panel with single zone chilled-water cooling: This system provides zoned heating using a variable-speed circulator and zone valves. It also provides single zone cooling using a chilled-water air handler. In the cooling mode, an electrically operated 3-way diverter valve directs the flow of chilled water, leaving the heat pump to the air handler. At the same time, it isolates flow from passing through the buffer tank. Here, the water-to-water heat pump and chilled water air handler’s capacities must be matched. chilled water air handler
insulate all chilled water piping CW DHW
anti-scald0001 tempering0001 valve
P&TRV
check0001 valves 3-way0001 diverter0001 valve
electric0001 heating0001 element
to / from0001 other zones
outdoor reset controller
zone valves
electric0001 water heater
supply header
desuperheater HX variable speed0001 pressure-regulated circulator temperature0001 sensor T&P0001 ports
purging0001 valves
purge0001 valves return header
earth loop0001 circulator
GSHP
purging0001 valves
Buffer tank make-up water assembly
expansion0001 tank
earth loop circuits
Multiple heating zones with a single chilled-water cooling zone.
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PRV
#8. Multi-zone heating with radiant panel and multi-zone chilled-water cooling: This system provides zoned heating using a variable-speed circulator and zone valves. It also provides multiple zone cooling using chilled-water air handlers. In the cooling mode, an electrically operated 3-way diverter valve directs the flow of chilled water leaving the buffer tank to the active air handlers. At the same time, it isolates flow from passing through the buffer tank. In some systems, the same variable-speed circulator that supplies the heating zones may also be used to supply the cooling zones. However, if the hydraulic characteristics of these two subsystems differ significantly, if may be necessary to select a separate circulator for each. chilled water air handler
insulate all chilled water piping0001 to prevent condensation
CW DHW
anti-scald0001 tempering0001 valve
P&TRV
check0001 valves
electric0001 heating0001 element
outdoor reset controller
electric0001 water heater
variable speed0001 pressure-regulated circulator
to / from0001 other zones zone valves
desuperheater HX
temperature0001 sensor T&P0001 ports
purging0001 valves
PRV
purge0001 valves return header
earth loop0001 circulator
GSHP
purging0001 valves
Buffer tank make-up water assembly
expansion0001 tank
earth loop circuits
Multiple heating and multiple cooling zones.
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Appendix A: Piping Schematic Symbol Legend
cast-iron circulator 0001 w/ isolation flanges 0001
3-way motorized 0001 mixing valve
cast-iron circulator 0001 w/ isolation flange 0001 and integral check valve
4-way motorized 0001 mixing valve
bronze or stainless0001 circulator w/0001 isolation flanges
microbubble0001 air separator
pressure regulated0001 circulator w/0001 isolation flanges
zone valve0001 (2 way)
swing check valve
finned-tube baseboard
spring-load0001 check valve
panel radiator with0001 thermostatic valve
purging valve
manifold station0001 serving radiant panel circuits
diverter valve
air handler0001 w/ water coil hydraulic0001 separator
gate valve
globe valves
ball valve
thermostatic0001 radiator valve0001 (straight pattern) thermostatic0001 radiator valve0001 (angle pattern) Y-strainer
hose bib0001 drain valve
pressure 0001 relief valve
P&T0001 relief valve
3-way 0001 thermostatic0001 mixing valve backflow preventer pressure reducing0001 valve
brazed plate0001 stainless steel0001 heat exchanger
manifold station0001 w/ electric valve actuators0001 and bypass valve
balancing0001 valve
thermometer
pressure gauge
cap union closely spaced tees0001 (or P/S fitting)
diaphragm-type0001 expanion tank float -type0001 air vent indirect water heater 0001 (with safety trim)
NOTES:0001 1. 2. 3. 4. 5.
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hot water storage tank 0001 (with safety trim)
Installer is responsible for all equipment selection & detailing as required by local codes0001 All piping should be sized for a maximum flow velocity of 4 feet/second0001 Install a minimum of 12 diameters of straight pipe upstream of all circulators and check valves0001 Install isolating flanges or isolating valves on all circulators0001 An anti-scald mixing valve is recommended if the DHW temperature is set above the 115ºF0001
Appendix B: Heat Emitters Suggested application range of hydronic heat emitters0001 (based on supply water temperature at design load) 90 ºF
100 ºF
110 ºF
120 ºF
130 ºF
140 ºF
150 ºF
160 ºF
170 ºF
180 ºF
190 ºF
200 ºF
180 ºF
190 ºF
200 ºF
heated floor slab heated floor thin slab heated floor top side tube& plate radiant walls radiant ceilings panel radiators fan-coils fin-tube baseboard
90 ºF
100 ºF
110 ºF
120 ºF
130 ºF
140 ºF
150 ºF
160 ºF
170 ºF
suggested range (R-22 heat pumps)
suggested range (R-410a THW heat pump)
left end REQUIRES:0001 • larger surface areas0001 • minimal if any coverings 0001 on radiant panels0001 • closer tube spacing in radiant panels0001 • lower heat loss buildings
right end ALLOWS:0001 • smaller surface areas0001 • higher resistance surface 0001 coverings on radiant panels0001 • wider tube spacing in radiant panels0001 • higher heat loss from building
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Appendix C: Heat Loss
Head loss (feet of head) versus flow rate (gpm) for copper tube and PEX tube operating with 120 ºF water0001 (curves end at nominal 4 ft/sec flow velocity limit) 3/8' copper 1/2' copper
head loss (ft head loss / 100' pipe)
10
3/4' copper
9 8
1' copper
7 6
1.25' copper
5
1.5' copper
4
2' copper
3 2 1 0
0
head loss (ft head loss / 100' pipe)
5
10 15 20 25 30 35 40 flow rate (gpm) 3/8' PEX 1/2' PEX 5/8' PEX
16 14
3/4' PEX
12 10
Head loss (per 100 ft of pipe)0001 ASTM F876 PEX tube0001 operating with 120ºF water
1' PEX
8
1.25' PEX
6
1.5' PEX
4
2' PEX
2 0
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Head loss (per 100 ft of pipe)0001 Type M copper water tube0001 operating with 120ºF water
0
5
10 15 20 flow rate (gpm)
25
30
Appendix D: Additional Sources of Information on Hydronic System Design 1. Publications: a. Plumbing & Mechanical magazine (www.pmmag.com) b. PM Engineer magazine (www.pmengineer.com) c. Contractor magazine (www.contractormag.com) d. Radiant Living magazine (www.radiantlivingmag.com) 2. Associations: a. Radiant Panel Association (www.radiantpanelassociation.com) b. Hydronics Industry Alliance (www.myhomeheating.com) c. Hydronic Heating Association (www.comfortableheat.net) 3. Other hydronic heating Web sites: a. www.hydronicpros.com b. www.heatinghelp.com c. www.healthyheating.com d. www.radiantandhydronics.com 4. Technical Reference Books: a. Modern Hydronic Heating: For Residential & Light Commercial Buildings, 2nd Edition, ISBN 0-7668-1637-0. b. Radiant Basics: A Basic Course for Radiant Panel Heating Systems, ISBN 1-932137-00-9. Published by the Radiant Panel Association. c. Radiant Precision: Advanced Design and Control of Hydronic Radiant Panel Heating Systems, 2nd Edition. Published by the Radiant Panel Association. d. Guide 2000 Residential Hydronic Heating — Installation and Design Training Manual, published by the Gas Appliance Manufacturers Association. 5. Hydronics Design Software: a. Hydronics Design Studio — Professional Edition (www.hydronicpros.com) b. LoopCAD: (www.loopcad.com) c. Wright-Suite (www.wrightsoft.com)
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