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DOE/GO-102001-1113 June 2001 Air-Source Heat Pumps

There are two common types of heatpumps: Air-Source heat Pumps and geot-hermal heat Pumps (GHPs). Either onecan keep your home warm in the winterand cool in the summer. An air-sourceheat pump pulls its heat indoors from theoutdoor air in the winter and from theindoor air in the summer. A GHP extractsheat from the indoor air when it's hot out-side, but when it's cold outside, it drawsheat into a home from the ground, whichmaintains a nearly constant temperatureof 50 to 60 F. This fact sheet focuses onair-source heat Pumps , which comprisethe majority of all residential heat pumpapplications. An Air-Source heat pump can provide effi-cient heating and cooling for your home,especially if you live in a warm properly installed, an air-sourceheat pump can deliver one-and-a-half tothree times more heat energy to a homecompared to the electrical energy it con-sumes.

source heat pump uses the outdoor winter air to heat a home. Believe it or not: heat can be harvested from cold outdoor air ... This home in Austin, Texas, features an air-source heat pump. Sara Farrar, NREL/PIX05420. down to about 40°F. And this can be accomplished through a …

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Transcription of DOE/GO-102001-1113 June 2001 Air-Source Heat Pumps

1 There are two common types of heatpumps: Air-Source heat Pumps and geot-hermal heat Pumps (GHPs). Either onecan keep your home warm in the winterand cool in the summer. An air-sourceheat pump pulls its heat indoors from theoutdoor air in the winter and from theindoor air in the summer. A GHP extractsheat from the indoor air when it's hot out-side, but when it's cold outside, it drawsheat into a home from the ground, whichmaintains a nearly constant temperatureof 50 to 60 F. This fact sheet focuses onair-source heat Pumps , which comprisethe majority of all residential heat pumpapplications. An Air-Source heat pump can provide effi-cient heating and cooling for your home,especially if you live in a warm properly installed, an air-sourceheat pump can deliver one-and-a-half tothree times more heat energy to a homecompared to the electrical energy it con-sumes.

2 This is possible because a heatpump moves heat rather than convertingit from a fuel, like in combustion heatingsystems. How They Work You might be wondering how an Air-Source heat pump uses the outdoor winterair to heat a home. Believe it or not: heatcan be harvested from cold outdoor airAir-SourceHeat PumpsThis document was produced for the Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. Thedocument was produced by the Information and Outreach Program at NREL for the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiencyand Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based oninformation known to EREC and NREL at the time of printing.

3 No recommendation or endorsement of any product or service is implied if mentioned by with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer wasteDOE/GO-102001-1113FS143 June 2001 This home in Austin, Texas, features an Air-Source heat Farrar, NREL/PIX05420down to about 40 F. And this can be accomplished through a process you're probably already familiar with , a heat pump's refrigeration sys-tem consists of a compressor, and twocoils made of copper tubing, which aresurrounded by aluminum fins to aid heattransfer. The coils look much like the radi-ator in your car. Like in a refrigerator orair-conditioner, refrigerant flows continu-ously through pipes, back and forth fromthe outdoor coils.

4 In the heating mode, liq-uid refrigerant extracts heat from the out-side coils and air, and moves it inside as itevaporates into a gas. The indoor coilstransfer heat from the refrigerant as it con-denses back into a liquid (see Fig. 1below). A reversing valve, near the com-pressor, can change the direction of therefrigerant flow for cooling as well as fordefrosting the outdoor coils in winter (seeFig. 2 on page 3).When outdoor temperatures fall below 40 F, a less-efficient panel of electric resis-tance coils, similar to those in your toaster,kicks in to provide indoor heating. This iswhy Air-Source heat Pumps aren't alwaysvery efficient for heating in areas withcold winters. Fuel-burning furnaces gener-ally can provide a more economical wayto heat homes in cooler climates.

5 Types of Air-Source heat Pumps You can use a central heat pump to heatand cool a whole house. Most central heatpumps are split-systems that is, theyeach have one coil indoors and one out-doors (see Fig. 1 below). Supply andreturn ducts connect to a central fan,which is located indoors. The fan, oftencalled an air handler or blower, circulatesair throughout the house. The fan alsousually contains electric resistance coils(some units now have a gas-fired furnaceoption). The heated or cooled air circulatesfrom the fan to the supply ducts, and open-ings in the home called supply registers and ductwork return theair to the fan to be heat Pumps are packaged usually have both coils and the fanoutdoors. Heated or cooled air is deliveredto the interior from ductwork that protrudes through a wall or roof.

6 Another packaged system is the ductlessroom heat pump. These Pumps will effi-ciently heat or cool a room or small housewith an open floor plan. They are muchmore common for apartments and motelrooms than homes. They can be installedin a window or through a hole in thewall wall installations being preferablefor appearances sake. Through-the-wall2 You can use acentral heat pump toheat and cool a lv eOutdoorCoilsCompressorLiquidevaporatesi nto gasGascondensesinto a liquidFig. 1 A split-system heat pump heating cycle3 When selecting a newheat pump,it s important thatyou determine theproper size needed foryour , however, sometimes aren'twell insulated from inside to outside andcan have infiltration problems. Whenused, mini-split systems can solve theseproblems.

7 Selecting a heat PumpWhen selecting an Air-Source heat pump,consider the following three characteris-tics carefully: the energy efficiency rating,sizing, and the system's efficiency rating In the United States, we rate a heatpump's energy efficiency by how manyBritish thermal units (Btu) of heat it movesfor each watt-hour of electrical energy itconsumes. Every residential heat pumpsold in this country has an EnergyGuideLabel, which features the heat pump'sheating and cooling efficiency perfor-mance rating, comparing it to other avail-able makes and models. The Heating Seasonal Performance Factor(HSPF) rates both the efficiency of thecompressor and the electric-resistance ele-ments. The HSPF gives the number of Btuharvested per watt-hour used.

8 The mostefficient heat Pumps have an HSPF ofbetween 8 and Seasonal Energy Efficiency Ratio(SEER) rates a heat pump's cooling effi-ciency. In general, the higher the SEER, thehigher the cost. However, the energy sav-ings can return the higher initial invest-ment several times during the heatpump s life. Replacing a 1970s vintage,central heat pump (SEER = 6) with a newunit (SEER=12) will use half the energy toprovide the same amount of cooling, cut-ting air-conditioning costs in half. Themost efficient heat Pumps have SEERs ofbetween 14 and 18. You'll find the Energy Star label spon-sored by the Department of Energy(DOE) and the Environmental Protec-tion Agency (EPA) on heat Pumps withan HSPF of at least 7 and a SEER of atleast 12.

9 Many new heat Pumps exceedthese ratings, but looking for this label is agood way to start shopping for one. FanIndoorCoilsLiquidevaporatesinto gasGascondensesinto a liquidExpansionVa lv eCompressorOutdoorCoilsFig. 2 A split-system heat pump cooling cycleSizing When selecting a new heatpump, it's important that youdetermine the proper sizeneeded for your home. Biggeris not better. Oversizingcauses the heat pump to startand stop more frequently,which is less efficient andharder on the componentsthan letting it run for longercycles. A properly sized heatpump also will provide youwith better comfort andhumidity control than anoversized one. The heating and coolingcapacity of heat Pumps ismeasured in Btu per hour. Thecooling capacity is commonlyexpressed in "tons" of coolingcapacity each ton equaling12,000 Btu per hour.

10 Correctsizing procedures involve complex calcu-lations, which are best performed by anexperienced contractor, who uses sizingmethods accepted by the heat pumpindustry. Don't employ a contractor whoguesses the size of the heat pump sizing techniques are gen-erally inaccurate, often resulting in higherthan necessary purchase and annualenergy costs. System components You and your contractor should discussoptions that will help improve yourhome's comfort and the economy of yourheat pump. Regarding ducts, for example,it's important to carefully consider theirdesign and materials, as well as the properamount of space they require. Check yourhome's blueprints to see if the architectand builder have planned adequate spacefor ducts and fans.


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