RP878 Radiant Heating Book From Climate Master 108 Pages

8/18/2019 RP878 Radiant Heating Book From Climate Master 108 Pages

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inlet

flange bolt

flange

impeller

stator

rotor

rotor can

outlet

junction box

volute

ceramic bushing

ESSENTIALS OF HYDRONICSFOR GSHP PROFESSIONALS


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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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2

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 distribu-

tion systems for heating and cooling. It will show you how to create reliable and efficient hydronic systems sup-plied by geothermal heat pumps that will provide years of comfort. The applications shown represent state-of-the-

art 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 possi-

ble. This can be both good and bad. Good in the sense that an experienced designer can modify an establishedsystem 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 latterthat 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 cre-ate 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 allapplicable 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 codeswithin 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 flow-ing 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 itsowner.

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 heatis released from the heat emitter depends on several things, including the water temperature, the room tempera-

ture, 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 sys-tems. The water they contain is sealed in and maintained under slight pressure. Ideally, the same water recircu-lates 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 thatwarms 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 par-ticular building. Those same heat sources can also provide the building’s domestic hot water, heat the swimmingpool, 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 nearlyall types of homes and commercial buildings — comfort so good that the occupants might literally forget it is win-

ter 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

circulatorwater flow

heat emitter

heat released

heat emitter

heat

source


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4

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 hydronicheating.

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 thesame 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.

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 signifi-cantly 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

14" x 8" duct

3/4" tube

this cut would destroy the load-carrying

ability of the floor joists

2 x

1 2

j o i s t


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too large to be routed through holes in floor framing. These force compromises, such as suspending the duct-

ing from the bottom of framing, as shown in figure 1-4, or concealing it behind valences or soffits that are visiblewithin 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 heat-ing 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, aesthet-ic 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 thebuilding 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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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 airbornepollutants 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 centralforced-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-

c o m p r e s s o r

refrigerant piping

thermal

expansion

valve

reversing

valve

f r o m g

r o u n d l o o

p

t o g r o u n d l o o p

e v a p o r a t o r

c o n d e n s e r

WATER-TO-WATER HEAT PUMP

horizontal earth loop configuration shown

high density polyethylene tubing

zoned hydronic

space heatingdistribution system

diverter valve

buffer tank

make-up water assembly

expansion

tank

air handler

(for chilled water cooling)

purge valves

purge valve

purge valve

expansion tank

variable speed circulator

air separator


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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 environmentshave a matchless value of their own. They offer a place to relax, read, write or enjoy quality music. Why shouldany 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 occu-

pied areas of a home. The loudest device in the system is typically the heat source, and with proper installationits 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 theheating 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 inunoccupied areas. They also allow the comfort level of rooms to be adjusted to suit individual tastes and activitylevels.

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 with-out elaborate or expensive hardware. In some systems, room-by-room zoning can be provided by non-electricthermostatic 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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thermostatic

radiator valves

(TRV) on each

radiator

variable-speed

circulator

TRV

TRV

TRV

TRV

TRV

TRV

manifold station

flexible PEX tubing

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 heatloss 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 losswill be about 16 times greater than that of the tube when operated at the same surface temperature and sur-

rounding conditions. This is especially important in situations where the ducting or tubing must pass throughsemi-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 possibleto distribute sufficient water flow to a typical 2,500-square-foot house using no more than 25 watts of electri-

cal power. A blower providing an equivalent rate of heat delivery could use several hundred watts of electricalpower.

• Hydronic systems also lower energy use by discouraging or even eliminating room air stratification (e.g., thetendency 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 significantlyincrease 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 condu-cive to thermal comfort. In many cases, occupants can lower thermostat settings in buildings with floor heatingwhile still maintaining very suitable comfort levels.

• Hydronic systems are highly adaptable to renewable energy sources such as heat pumps, solar thermal sys-

tems, waste heat recovery devices and biomass burning boilers. Equipping buildings with a well-designed anddurable 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-airheat 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 show-ing 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 prod-

ucts and design concepts will vie for their attention as the market grows and more people demand the benefitsthat 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 widevariety of systems.

Figure 2-1 shows the fundamental components of a single circuit hydronic system.

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 inmany residential and commercial hydronic systems. However, the versatility of hydronics allows many other pos-

sibilities, 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 tem-

perature or flow rates. Some can only be used with specific types of heat emitters. The cost and local availabilityof 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.

expansion

tank

heat emitter

heat released to building

circulator flow

checkair

separator

purging

valve

make-up water

assembly

room

thermostat

pressure

relief

valve backflow preventer

pressure reducing valve

heat source


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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 direc-tion, 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 toits inlet port.

Water always flows from an area of higher pressure to an area of lower pressure. The higher pressure water leav-

ing a circulator wants to get back to that circulator’s inlet. It will do so through any available pathway. The funda-mental 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 hydronicsystems. This type of circulator is more specifically categorized as a “wet-rotor circulator.” Such circulators arecooled and lubricated by the fluid passing through, and do not require oiling as do some earlier generation circula-

tors which couple the impeller assembly to a separate air-cooled motor. Wet-rotor circulators have been in usefor 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 flowon the load side of the system.

Many current generation wet-rotor circulators can operate at three different speeds. The circulator’s speed switchis 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 aventing device where they are ejected from the system. Many different types of air separators are currently avail-able. 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 airseparator is shown in figure 2-4. You will see several schematics throughout this publication that show proper us-

age 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 thesystem, while cool water “wants” to move downward. This movement is caused by slight differences in the den-

sity 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 migra-tion,” 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 thisphenomenon 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 weightedmetal plug or spring that holds the valve closed until a slight forward opening pressure (typically 1/4 psi) is pres-

ent. This forward opening resistance is sufficient to stop heat migration, but still allows the valve to instantly openas soon as the circulator in the associated portion of the system turns on. These valves will also prevent reverseflow.

Many current generation hydronic circulators are now supplied with internal spring-loaded check valves. Thesecirculators eliminate the need to install a separate flow-check or spring-loaded valve in each circuit, and theygenerally 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 sealedinternal chamber filled with pressurized air. This air is separated from the system water by a flexible rubber dia-

phragm. As the water expands, the sealed air volume behind the diaphragm is partially compressed, and systempressure 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 systemsused 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 sys-tem 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 equippedwith 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 liftedto 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 buildingloses 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 buildingby 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 wouldremain 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 agiven 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 thesystem. 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. Multiplewater 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 resethigh 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 watertemperature.


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A manual-reset temperature limit control.

There are also many electronic controllers available to handle specific tasks within hydronic systems. Theyinclude controllers to manage a multiple heat source system, operate mixing devices or oversee operation ofseveral 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 ofthese 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 dropsbelow 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 backflowpreventer 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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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. Oneexample 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 anyway. Thermal radiation is simply infrared light. It behaves similar to visible light, but our eyes can’t see it. It trav-els 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 surfaceswithin 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 cool-ing 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 thesystem. Rigid, type M (thinner wall) copper tubing is often used within the mechanical room to maintain a neatappearance 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. Itmay also be joined using one of several “press fit” fittings systems now on the market. The latter use a special-

ized fitting with o-rings that is mechanically compressed to create a pressure-tight joint. An example of coppertubing 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 from1/2” up to 3” nominal inside diameter. Larger sizes of copper water tube are available, but may not be economi-

cally 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 thistubing 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 dif-fusion barrier. This layer prevents oxygen molecules from diffusing through the tube wall and reaching the waterwithin 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 commonlyused in hydronic heating systems. It can withstand temperatures as high as 200ºF with simultaneous pressuresup 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 PEXtubing 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 sys-tems. 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 higherthan 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 diffusionbarrier. It also allows the tubing to retain its shape when bent, as shown in figure 2-17. In addition, the aluminumlayer 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 thiswill change in the near future. Like PEX, PEX-AL-PEX tubing is a thermoset polymer and cannot be joined by fu-

sion 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 thepolypropylene 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 andfittings 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.


22/108

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 irre-versible. 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 thepiping 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 re-quirements, 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,


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22

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 andsteel, as well as to attenuate vibration along the pipe. This method of support is highly versatile. It can accommo-

date 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, PEX-AL-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 expan-sion movement. However, long, straight runs of tubing should have either flexible supports or an inline expansioncompensator 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 asframing or subflooring.


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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. Themore 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 ofheat 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 changephase (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. Itcertainly 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).

It’s important to understand that the rate of heat transfer into or out of a stream of fl uid depends on both the temperature change and the fl ow 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 followingexamples.

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


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24

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 whereit 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 othercomponents in this circuit would not feel “hot” to the touch. That’s because skin temperature is usually in the mid-

80ºF 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?

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 sub-

stantially 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 theflow rate.There’s more to heat transfer than meets the finger tips!

90 ºF

78 ºF

heat

pump

9 gpm

9 gpm heat

emitter

water @ 0.5 gpm

T in =180ºF T

out =165ºF


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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 fromoutside 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 refriger-

ant 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.

Basic refrigeration components in a “heating only” water-to-water heat pump.

Let’s exam the refrigerant cycle, beginning in the evaporator. Refrigerant enters the evaporator as a low-tem-perature, low-pressure liquid. It passes across the surface of copper or steel tubing through which water or amixture 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 quitehot (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 warmerthan the water, heat moves from the gas to the water. This causes the refrigerant gas to condense back to a liq-uid, but still remain at a relative high pressure. Finally, the liquid refrigerant goes from the condenser to the ther-

mal expansion valve (TXV). Here its pressure is reduced, and its temperature immediately drops. The refrigerantis 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 varyfrom one manufacturer to another. However, the goal is always the same: To move heat from the low-tempera-ture “source” to the higher temperature “sink” using as little electrical energy as possible to operate the compres-

sor.

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 themto provide heated water or chilled water. The latter can be used for building cooling or for other chilled water

compressor

refrigerant piping

thermal expansion

valve

warm liquidcold liquid

heat input

hot gas

cool gas

condenser

heat output

to load

from loadfromground

loop

toground

loop

electricalenergyinput

evaporator

1

2

3

4

compressor

refrigerant piping

thermal expansion

valve

warm liquidcold liquid

heat input

hot gas

cool gas

condenser

heat output

to load

from loadfromground

loop

toground

loop

electricalenergyinput

evaporator


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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 tempera-ture 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.

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 4-5shows this effect for a ClimateMaster TMW036 unit operating with a source water flow rate of 9 gpm and 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 sideof 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.

20

25

30

35

40

45

20 25 30 35 40 45 50 55 60 65 70

H e a t i n g

c a p

a c i t y

( B t u / h r )

Entering source water temperature (ºF)

(source water flow rate = 9 gpm)

ELWT = 80ºF

ELWT = 100ºF

ELWT = 120ºF

ClimateMaster TMW036 W/W

20

25

30

35

40

45

20 25 30 35 40 45 50 55 60 65 70

H e a t i n g

c a p a c i t y

( B t u / h r )


(SOLID LINES: source water flow rate = 9 gpm)

(DASHED LINES: source water flow rate = 5 gpm)

ELWT = 80ºF

ELWT = 100ºF

ELWT = 120ºF


ELWT = 80ºF

ELWT = 100ºF

ELWT = 120ºF

source

flow rate

= 9 gpm

source

flow rate

= 5 gpm


29/108

28

Coefficient of Performance:

The thermal performance of many hydronic heat sources is expressed as an “efficiency.” It is a means of indicat-

ing 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 operatethe 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 theCOP formula is:

For example: Assume the input power to operate a heat pump was 2,000 watts. The heat pump’s heating capac-

ity 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 ofelectrical input energy. If the COP of a heat pump is 3.5, it provides 3.5 units of heat output per unit of electricalenergy 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 elec-tric resistance heat. For example, if electrical resistance heat is 100% efficient, then by comparison, a heat pumpwith 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.


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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 itsflow rate). A graph showing how the COP of a ClimateMaster TMW036 heat pump varies as a function of enteringsource water temperature and entering load water temperature is shown in figure 4-7.

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 aspossible, while at the same time keeping the required operating temperature of the hydronic distribution system aslow 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-

heat input heat output

to load

from loadfromground

loop

toground

loop

Qe=3500 watt = 11,946 Btu/hr

Qg=36,054 Btu/hr Qo=48,000 Btu/hr

Qoutput =Qground +Qelectrical

COP =heat output rate(Btu/hr)

electrical input (watt) 3.413

COP =ground heat input rate + electrical heat input rate (Btu/hr)

electrical input (watt) 3.413

COP =heat output rate(Btu/hr)

electrical input (watt) 3.413=

48,000

3500 3.413= 4.0


2

2.5

3

3.5

4

4.5

5

5.56

6.5

7

20 25 30 35 40 45 50 55 60


(source water flow rate = 9 gpm)

H e a t i n g

C O P

ELWT = 80ºF

ELWT = 100ºF

ELWT = 120ºF


31/108

30

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.

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 chill-ers. The cold water they produce can be used for cooling and dehumidifying both residential and commercialbuildings.

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 heatpumps 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 affectedby the temperature of the fluid streams passing through the evaporator and condenser. To a lesser extent, it’salso 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.

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100

H e a t i n g

C O P

Di erence between entering source

and leaving load water temperature


32/108

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 thatincreasing 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 (EnergyEfficiency 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.

Like COP, the EER of a water-to-water heat pump is a function of the source and load water temperature, as wellas the source and load water flow rate. This variation is shown in figure 4-10.

EER (Energy Efficiency Ratio) vs. entering load water temperature.


20

25

30

35

40

45

50 55 60 65 70 75 80 85 90

t o t a l c o o l i n g

c a p a c i t y

( B t u / h r )

Entering load water temperature (ºF)

ESWT = 50ºF

ESWT = 70ºF

ESWT = 90ºF


0

5

10

15

20

25

30

35

50 55 60 65 70 75 80 85 90 E E R

( E n e r g y E c i e n c y R a t i o

) B t u / h r / w a t t

Entering load water temperature (ºF)

ESWT = 50ºF

ESWT = 70ºF

ESWT = 90ºF


33/108

32

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), thehigher 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 han-dler 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 otherhydronic heating hardware to produce systems for both heating and cooling.


34/108

Section 5: Thermal Equilibrium

All hydronic systems exhibit certain behaviors regardless of the type of heat source used. One of the most impor-

tant and universal behaviors is the concept of thermal equilibrium. This section describes this, as well as ways touse 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 con-

trols, every hydronic system would eventually stabilize at a supply water temperature where this “thermal equilib-rium” 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 manipu-late the steady state supply water temperature at which the system “wants” to operate. When properly done, thisallows 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 mayattempt 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 tempera-tures, which reduced the required surface area of heat emitters. The reasoning was simple: Why pay for 10 feetof fin-tube baseboard in a room if 6 feet could do the job using a higher water temperature? This is why you’ll findthermal output ratings for fin-tube baseboard that go up to at least 220ºF. This made sense in a pre-OPEC, pre-

AFUE, 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 Coef fi cient of Performance of the heat pump.

Where Will Thermal Equilibrium Occur? A fundamental principal in sizing any type of hydronic heat emitter is thatheat output is approximately proportional to the difference between supply water temperature and room air tem-

perature. 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 distri-

bution system.

For example, imagine a building where all the heat emitters (operating as a group) release 100,000 Btu/hr into a70ºF space when the distribution system is supplied with water at 170°F. The value of the “c” in formula 5-1 canbe found as follows:


35/108

34

This mean that this distribution system releases 1,000 Btu/hr into the space for each ºF the water supply tem-

perature exceeds the room air temperature. Thus, if the water temperature supplied was 130ºF, and the space airtemperature 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 sys-

tem releases heat into the space being heating.

Anything that makes the driving delta T larger (i.e., increasing supply temperature and/or decreasing space airtemperature) 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 previ-ous example.

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 distributionsystem at one supply water temperature and the associated indoor air temperature. Subtract the indoor air tem-perature 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. Extendthe 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 sys-

tem. The larger the surface area of the heat emitters, the steeper the slope of the graph (see figure 5-2).

0

20000

40000

60000

80000

100000

H e a t o u t p u t ( B t u / h r )

0 10 2 0 30 4 0 50 60 7 0 80 9 0 100

(Ts -Tr) (ºF)


36/108

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 ef fi ciency ofground 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 improvesboth the heating capacity and COP of ground source water-to-water heat pumps. Radiant heating design soft-ware can be used to determine the supply temperature needed for a given rate of heat output from a panel of

specific construction.

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 outputgraph.” Figure 5-4 is an example. Here, the desired indoor air temperature of 70ºF has been added to the num-

bers on the horizontal axis of figure 5-1.

0

20000

40000

60000

80000

100000

H e a t o

u t p u t ( B t u / h r )

DECREASING surface area

of heat emitters requires higher

driving delta T for given

rate of heat delivery

INCREASING the surface area

of heat emitters lowers

driving delta T for given

rate of heat delivery

0 10 2 0 30 4 0 50 60 7 0 80 9 0 100

(Ts -Tr) (ºF)

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

U p w a r d h e a t o u t p u t ( B t u / h r / s q

f t )

(Ts-Tr) (ºF)

6-inch spacing

9-inch spacing

12-inch spacing

18-inch spacing

1/2" PEX-AL-PEX tubing

in 4-inch bare concrete


37/108

36

0

20000

40000

60000

80000

100000

70 80 90 100 110 120 130 140 150160170

H e a t o

u t p u t

( B t u / h r )

Supply water temperature (ºF)

(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 itintersects the sloping line. Finally, draw a line straight down to the horizontal axis to read the water supply tem-perature 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 forthis, the heat dissipation ability of the distribution system should be increased. If the system used radiant floorheating, 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 heatemitters 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, eventuallyreaching 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 dissipatedby 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 aheat source with a fi xed rate of heat output. It can even occur under design load conditions in systems having anoversized 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 re-duced 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-


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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 outputto maintain comfort, and that the heat source is not damaged by operating at lower water temperatures. The lat-

ter 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 fromthe standpoint of comfort. Large surface area heat emitters improve comfort by increasing the mean radiant tem-

perature of the room. The lower the supply water temperature to the distribution system, the greater the COP of awater-to-water heat pump.


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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 inhydronic systems.

Most general purpose valves fit into two categories based to their intended application:

1. Component Isolation2. 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 creat-ing 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 flowresistance. 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 inter-

nal design forces fluid through a sinuous path that creates relatively high flow resistance. They should not beused 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 ofcirculators. Globe valves should always be installed with their flow arrow — which is cast into the side of thevalve — pointing in the direction of flow.


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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 andcreate 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 cavi-tation noise and eventual erosion of the internal surfaces. Special types of ball valves are available for highduty 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 sys-tems. 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 tocover the opening through the valve. Swing-checks must be mounted in an upright position in horizontal pip-

ing. Be sure the arrow on the body is pointed in the intended direction of flow.

Swing-check valve with soldered connections.


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• 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 thehydronic 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 set-ting, 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 valveto 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 differ-ent 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 poweris applied. Other zone valves use a geared motor and can fully open in only two or three seconds after power isapplied. 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 controlsystem that a zone is calling for heat.


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44

The friction between a fl uid and the objects it fl ows past dissipates mechanical energy from the fl uid. This energy

is called “head”. Every piping component causes some loss of head from the fluid flowing through it. The onlyexception 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-poundby pound, you get just plain foot. Head expressed in feet is therefore the amount of mechanical energy eachpound of fluid contains.

The hydronics industry has typically used 2.31 feet of head = 1 psi as a conversion factor. This is the conversionfor 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 inwater 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 fl uid fl owing 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 toconvert 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 fl ow rate through it. The relationship, for circuits construct-

ed 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 sizeand 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)

Value of “a” for formula 7-3 (for water).

Value of “c” for formula 7-3.

0.04

0.045

0.05

0.055

0.06

0.065

50 75 100 125 150 175 200 225 250

V a l u e

o f ( a )

Water temperature (ºF)

Tube (size & type) C value

3/8” type M copper 1.016



1” type M copper 0.01776

1.25” type M copper 0.006808

1.5” type M copper 0.0030668


2.5” type M copper 0.0002977


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” P EX-AL-PEX (I.D. = 0.79”) 0.07016

1” PEX-AL-PEX (I.D. = 0.98”) 0.0252


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46

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 pipingcircuit 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 becalculated 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.

Example of a system head loss curve,

This graph is called the system head loss curve for that piping system. Every clo

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RP878 Radiant Heating Book From Climate Master 108 Pages