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Home , Air source heat pump

DOE/GO-102001-1113 FS143 June 2001 Air-Source Heat Pumps

There are two common types of heat An air-source can provide effi- pumps: air-source heat pumps and geot- cient heating and cooling for your home, hermal heat pumps (GHPs). Either one especially if you live in a warm climate. can keep your home warm in the winter When properly installed, an air-source and cool in the summer. An air-source heat pump can deliver one-and-a-half to heat pump pulls its heat indoors from the three times more heat energy to a home outdoor air in the winter and from the compared to the electrical energy it con- indoor air in the summer. A GHP extracts sumes. This is possible because a heat heat from the indoor air when it's hot out- pump moves heat rather than converting side, but when it's cold outside, it draws it from a fuel, like in combustion heating heat into a home from the ground, which systems. maintains a nearly constant of 50˚ to 60˚F. This fact sheet focuses on How They Work air-source heat pumps, which comprise You might be wondering how an air- the majority of all residential heat pump source heat pump uses the outdoor winter applications. air to heat a home. Believe it or not: heat can be harvested from cold outdoor air Sara Farrar, NREL/PIX05420 Sara Farrar, This home in Austin, Texas, features an air-source heat pump.

This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. The document was produced by the Information and Outreach Program at NREL for the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC.

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste down to about 40°F. And this can Types of Air-Source Heat Pumps be accomplished through a process You can use a central heat pump to heat you're probably already familiar and cool a whole house. Most central heat with—. pumps are split-systems—that is, they Basically, a heat pump's refrigeration sys- each have one coil indoors and one out- tem consists of a , and two doors (see Fig. 1 below). Supply and coils made of copper tubing, which are return ducts connect to a central , surrounded by aluminum fins to aid heat which is located indoors. The fan, often transfer. The coils look much like the radi- called an or blower, circulates ator in your car. Like in a refrigerator or air throughout the house. The fan also air-conditioner, flows continu- usually contains electric resistance coils You can use a ously through pipes, back and forth from (some units now have a -fired the outdoor coils. In the heating mode, liq- option). The heated or cooled air circulates central heat pump to uid refrigerant extracts heat from the out- from the fan to the supply ducts, and open- side coils and air, and moves it inside as it ings in the home called supply registers. heat and cool a whole evaporates into a gas. The indoor coils Return registers and ductwork return the air to the fan to be heated. house. transfer heat from the refrigerant as it con- denses back into a (see Fig. 1 Some heat pumps are packaged systems. below). A reversing , near the com- These usually have both coils and the fan pressor, can change the direction of the outdoors. Heated or cooled air is delivered refrigerant flow for cooling as well as for to the interior from ductwork that defrosting the outdoor coils in winter (see protrudes through a wall or roof. Fig. 2 on page 3). Another packaged system is the ductless When outdoor fall below room heat pump. These pumps will effi- 40°F, a less-efficient panel of electric resis- ciently heat or cool a room or small house tance coils, similar to those in your toaster, with an open floor plan. They are much kicks in to provide indoor heating. This is more common for apartments and motel why air-source heat pumps aren't always rooms than homes. They can be installed very efficient for heating in areas with in a window or through a hole in the cold winters. Fuel-burning gener- wall—wall installations being preferable ally can provide a more economical way for appearances sake. Through-the-wall to heat homes in cooler U.S. climates.

Compressor

Fan Liquid Gas evaporates condenses into gas into a liquid Expansion Valve Outdoor Indoor Coils Coils

Fig. 1 A split-system heat pump heating cycle

2 Compressor

Gas Liquid condenses Fan evaporates into a into gas liquid Expansion Valve Indoor Coils Outdoor Coils

Fig. 2 A split-system heat pump cooling cycle

installations, however, sometimes aren't The Seasonal Energy Efficiency Ratio well insulated from inside to outside and (SEER) rates a heat pump's cooling effi- can have problems. When ciency. In general, the higher the SEER, the When selecting a new used, mini-split systems can solve these higher the cost. However, the energy sav- heat pump, problems. ings can return the higher initial invest- Selecting a Heat Pump ment several times during the heat pump’s life. Replacing a 1970s vintage, it’s important that When selecting an air-source heat pump, central heat pump (SEER = 6) with a new consider the following three characteris- unit (SEER=12) will use half the energy to you determine the tics carefully: the energy efficiency rating, provide the same amount of cooling, cut- sizing, and the system's components. proper size needed for ting air-conditioning costs in half. The Energy efficiency rating most efficient heat pumps have SEERs of between 14 and 18. your home. In the United States, we rate a heat pump's energy efficiency by how many You'll find the Energy Star® label—spon- British thermal units (Btu) of heat it moves sored by the U.S Department of Energy for each watt-hour of electrical energy it (DOE) and the U.S. Environmental Protec- consumes. Every residential heat pump tion Agency (EPA)—on heat pumps with sold in this country has an EnergyGuide an HSPF of at least 7 and a SEER of at Label, which features the heat pump's least 12. Many new heat pumps exceed heating and cooling efficiency perfor- these ratings, but looking for this label is a mance rating, comparing it to other avail- good way to start shopping for one. able makes and models. The Heating Seasonal Performance Factor (HSPF) rates both the efficiency of the compressor and the electric-resistance ele- ments. The HSPF gives the number of Btu harvested per watt-hour used. The most efficient heat pumps have an HSPF of between 8 and 10.

3 Sizing efficiency not only depend on the selection New Energy-Efficient Heat Pumps When selecting a new heat and planning of the equipment but also on pump, it's important that you careful installation. The efficiency and performance of determine the proper size today’s air-source heat pumps is one- Consumers and home builders alike tend and-a-half to two times greater than needed for your home. Bigger to accept the lowest bid for heating and those available 30 years ago. This is not better. Oversizing air-conditioning work. This unfortunate improvement in efficiency has resulted causes the heat pump to start choice can often leave a system lacking 10 from technical advances and options and stop more frequently, to 30 percent in the materials and labor such as: which is less efficient and necessary to optimize heat-pump • Thermostatic expansion for harder on the components performance. Rather than just accepting more precise control of the refriger- than letting it run for longer the lowest bid, it's best to research the ant flow to the indoor coil cycles. A properly sized heat performance records of local contractors, • Variable speed blowers, which are pump also will provide you and get involved in the planning and more efficient and can compensate with better comfort and for some of the adverse effects of decision-making about your new heat control than an pump system. restricted ducts, dirty filters, and oversized one. dirty coils You can avoid most of the common com- • Improved coil design The heating and cooling fort and performance problems from • Improved electric motor and two- capacity of heat pumps is improper installation by following these speed compressor designs measured in Btu per hour. The guidelines: • Copper tubing, grooved inside to cooling capacity is commonly • Make your home as energy-efficient as increase surface area. expressed in "tons" of cooling you can with proper insulation, energy- capacity—each ton equaling efficient windows, and an effective air 12,000 Btu per hour. Correct barrier, etc. Then your contractor can sizing procedures involve complex calcu- install a smaller pump system with lations, which are best performed by an shorter lengths. In an energy- experienced contractor, who uses sizing efficient home, it isn’t necessary to run methods accepted by the heat pump ducts all the way out to exterior walls to industry. Don't employ a contractor who install registers near the exterior walls. guesses the size of the heat pump needed. • Install the ducts inside your home’s Rule-of-thumb sizing techniques are gen- insulation and , if possible. erally inaccurate, often resulting in higher Research shows that this strategy is a than necessary purchase and annual major energy saver. energy costs. • Insulate your ducts to R-8 if they System components must be located in an attic or crawl space beyond the home’s air barrier You and your contractor should discuss and insulation. options that will help improve your You and your • Locate the outdoor unit on the northside home's comfort and the economy of your of your home if possible. If not, pick a heat pump. Regarding ducts, for example, contractor should dis- shady spot. There should be no obstruc- it's important to carefully consider their tions within 10 feet of the sides with design and materials, as well as the proper cuss options openings and the top. amount of space they require. Check your • Specify that the measured air leakage home's blueprints to see if the architect that will help improve through your new ducts be less than and builder have planned adequate space 10 percent of your system’s airflow. for ducts and fans. Heating and cooling your home’s comfort Air leakage of 5 percent or less is possi- contractors complain that they often have ble with careful workmanship. to squeeze heating and cooling systems and the economy of • Tell your contractor that you want a into spaces that are too small, resulting in return register in every room. constricted ducts and inadequate airflow. your heat pump. • Don’t use building cavities as ducts. Except for packaged systems, you'll also Building-cavity return ducts are notori- need to select the proper type of indoor ously leaky and often cause comfort, coil for adequate summer moisture energy, and moisture problems. removal. • Pull on ductwork after installation to make sure it is fastened and sealed well. Installing a New Heat Pump (Seal duct joints with mastic.) A heat pump's performance and energy

4 Improving Performance Air-sealing ducts Poor installation, duct losses, and inade- Measurements of heat pump performance quate maintenance are more of a problem indicate that duct leakage wastes 10 to 30 for heat pumps than for combustion fur- percent of the heating and/or cooling naces. A growing body of evidence sug- energy in a typical home. It's one of the gests that most heat pumps have most severe energy problems commonly significant installation or service problems found in homes because the leaking air is that reduce performance and efficiency. 20° to 70°F warmer than indoor air in win- According to a report on research funded ter and 15° to 30°F cooler in the summer. by Energy Star‚ more than 50 percent of all Duct leakage may cause some minor com- heat pumps have significant problems fort problems when ducts are located in with low airflow, leaky ducts, and incor- conditioned areas. But when leaky ducts rect refrigerant charge. are located in an attic or crawl space, the Increasing airflow in central energy loss is often large. Some of the Measurements heat pumps worst duct leakage occurs at joints between the air handler, and the main The capacity and the efficiency of a heat supply and return air ducts. of heat pump pump depend upon adequate airflow. There should be about 400 to 500 cubic Some main return ducts use plywood or performance feet per minute (cfm) airflow for each ton fiberglass duct-board boxes. These boxes of the heat pump’s air-conditioning capac- frequently leak because their joints are indicate that duct ity. Efficiency and performance deteriorate exposed to the duct system’s highest air if airflow is much less than 350 cfm per pressures. Heating and air-conditioning leakage waste 10 to 30 ton. contractors often use wall, floor, and ceil- ing cavities as return ducts. These build- An ideal duct system has both a supply percent of the ing-cavity return ducts are often register and a return register for every accidentally connected to an attic, crawl room. Most homes, however, have only heating and/or cool- space, or even the outdoors, creating seri- one or two return registers for the entire ous air leakage. Fiberglass ducts and flex house. Air from other rooms must find its ing energy in ducts are often installed improperly. These way back to these registers to be reheated ducts may also deteriorate with age, lead- or re-cooled. Obstructions in return air are a typical home. a common air circulation problem, partic- ing to significant supply-duct leakage. ularly from closed interior doors to rooms The best heating and cooling contractors with no return-air register. have equipment to test for duct leakage. Blockage of supply or return air ducts and Testing helps locate duct leaks and indi- registers can pressurize or depressurize cates how much duct sealing is necessary. portions of the home, resulting in poor Do not use duct tape for sealing—its lifes- performance and increased air leakage pan is very short, often less than 6 months. through the . Restric- Adjusting refrigerant charge tions to airflow have the greatest impact Room heat pumps and packaged heat on the return-air side of the system, so pumps are charged with refrigerant at the repairs should start with the return ducts. factory. They are seldom incorrectly Air from every supply register must have an unobstructed pathway back to a return charged. Split-system heat pumps, on the register. You can install louvered other hand, are charged in the field, which through walls or doors, ducts between can sometimes result in either too much or rooms, and/or additional return ducts and too little refrigerant. registers to improve air circulation. Split-system heat pumps that have the Technicians can increase the airflow by correct refrigerant charge and airflow usu- cleaning the coil, increasing fan ally perform very close to manufacturer’s speed, or enlarging the ducts—especially listed SEER and HSPF. Too much or too return ducts. Enlarging ducts may seem little refrigerant, however, reduces heat- drastic but in some cases, might be the pump performance and efficiency. only remedy for poor comfort and high energy costs.

5 For satisfactory performance and effi- A defrost control tells the ciency, a split-system heat pump should when to send hot refrigerant outdoors to be within a few ounces of the correct thaw the outdoor coil during the winter. charge, specified by the manufacturer. During the 2-to-10-minute defrost cycle, When the charge is correct, specific refrig- auxiliary heat takes over, reducing the erant temperatures and pressures listed by heat pump’s overall efficiency up to 10 the manufacturer will match temperatures percent. The two most common types of and pressures measured by your service defrost controls are time-temperature technician. Verify these measurements and demand-defrost. Time-temperature with the technician. defrost controls activate defrost at regular time intervals for set time periods, If the manufacturer’s temperatures and whether there is ice on the outdoor coil or pressure’s don’t match the measured ones, not. A demand-defrost control senses coil refrigerant should be added or with- temperature or airflow through the coil, drawn, according to standards specified and only activates defrost if it detects the by the EPA. Refrigeration systems should presence of ice. Obviously, choosing a heat be leak-checked at installation and during pump with demand-defrost will pay a sig- each service call. nificant efficiency dividend. Manufacturer’s say that a technician For greater efficiency, don't locate a ther- must measure airflow prior to checking mostat near a heat source or cold draft refrigerant charge because the refrigerant The difference because they can cause a heat pump to measurements aren’t accurate unless air- operate erratically. This includes shading flow is correct. between the energy from direct sunlight. Also, do Operating a heat pump not turn the beyond the consumption of a Like combustion heating systems, you desired temperature. It will not make the control heat pumps using thermostats. heat pump heat or cool your home any well-maintained heat faster. It will only waste energy. Residents If you leave and return at regular times who duel one another over the thermostat pump and a neglected everyday, you'll save money by using settings, moving it up and down to suit automatic thermostats, which minimize their different comfort levels, cause heat one ranges from 10 energy use during the times the home is pumps to operate erratically and ineffi- unoccupied. However, choosing an auto- ciently. to 25 percent. matic thermostat’s reactivation time requires considering the duration of heat- Maintaining and Servicing pump operation necessary to restore a Heat-pump performance will deteriorate comfortable temperature. During the heat- without regular maintenance and service. ing season, some homeowners also set The difference between the energy con- their thermostats back 10°F, manually or sumption of a well-maintained heat pump automatically, when they leave home or and a severely neglected one ranges from go to bed. 10 to 25 percent. A two-stage thermostat controls the heat- Regular Maintenance ing. The first stage activates the refrigera- Either the homeowner or service techni- tion system. If it’s too cold outside for the cian can perform the following routine refrigeration system to counteract the maintenance tasks: home’s heat loss, then the thermostat’s second stage activates the electric resis- • Clean or replace filters regularly (every tance coils. An outdoor thermostat will 2 to 6 months, depending on operating prevent the less efficient electric resistance time and amount of dust in the environ- heat from coming on until the outdoor ment). temperature falls below 40°F. An outdoor • Clean outdoor coils as often as thermostat also will prevent auxiliary heat necessary (when dirt is visible on the from activating when an automatic ther- outside of the coil). mostat is warming the house after a set- back period. Use setback thermostats that • Remove plant life and debris from are only for heat pumps. around the outdoor unit.

6 • Clean evaporator coil and condensate • Verify correct refrigerant charge by mea- pan every 2 to 4 years. surement. • Clean the blower’s fan blades. • Check for refrigerant leaks. • Clean supply and return registers and • Inspect electric terminals, and if neces- straighten their fins. sary, clean and tighten connections, and apply nonconductive coating. Professional Service • Lubricate motors, and inspect belts for You should have a professional technician tightness and wear. service your heat pump at least every year. The technician can: • Verify correct electric control, making sure that heating is locked out when the • Inspect ducts, filters, blower, and indoor thermostat calls for cooling and vice coil for dirt and other obstructions. versa. • Diagnose and seal duct leakage. • Verify correct thermostat operation. • Verify adequate airflow by measurement.

Resources Fax: (703) 575-4449 E-mail: [email protected] The following are sources of additional information on Web site: www.acca.org/ heat pumps. This list is not exhaustive, nor does the mention of any resource constitute a recommendation A national, trade association of heating, ventilation, or endorsement. air-conditioning, and refrigeration contractors. Ask an Energy Expert Air-Conditioning and Refrigeration Institute (ARI) DOE’s Energy Efficiency and Renewable Energy 4301 N. Fairfax Drive, Suite 425 Clearinghouse (EREC) Arlington, VA 22203 Phone: (703) 524-8800 P.O. Box 3048 Fax: (703) 528-3816 Merrifield, VA 22116 E-mail: [email protected] 1-800-DOE-EREC (363-3732) Web site: www.ari.org/ E-mail: [email protected] Online submittal form: A national trade association representing manufacturers of www.eren.doe.gov/menus/energyex.html U.S. produced central air-conditioning and commercial refriger- Consumer Energy Information Web site: ation equipment. www.eren.doe.gov/consumerinfo/ Consortium for Energy Efficiency (CEE) Energy experts at EREC provide free general and One State Street, Suite 1400 technical information to the public on many topics Boston, MA 02109-3507 and technologies pertaining to energy efficiency and Phone: (617) 589-3949 renewable energy. Fax: (617) 589-3948 DOE’s Energy Efficiency and Renewable Energy Web site: www.ceeformt.org/ Network (EREN) A national, nonprofit, benefits corporation that promotes Web site: www.eren.doe.gov the manufacture and purchase of energy-efficient products and services. Your comprehensive online resource for DOE’s energy efficiency and renewable energy information. Organizations Contractors of America (ACCA) 2800 Shirlington Rd., Suite 300 Arlington, VA 22206 Phone: (703) 575-4477 (Continued on page 8)

7 (Continued from page 7) Further Reading Consumer Guide to Home Energy Savings, Wilson A., Eastern Heating & Cooling Council (EH-CC) Thorne J., Morrill J, American Council for an Energy- 20,000 Horizon Way, Suite 260 Efficient Economy (ACE3), Washington, DC. Mt. Laurel, NJ 08054 Available from ACE3 at (202)429-8873, E-mail: [email protected] [email protected], or online at www.aceee.org. Web site: www.eh-cc.org/ Energy Savers: Tips on Saving Energy and Money Educates consumers and contractors on properly designed at Home, DOE. Available from EREC (see Ask an Energy and installed high-efficiency heating and cooling systems. Expert above) or online in PDF and HTML at Energy Star® www.eren.doe.gov/consumerinfo/energy_savers/. DOE and EPA Geothermal Heat Pumps Make Sense for Homeowners, Phone: (888) STAR-YES (782-7937) DOE Office of Geothermal Technologies, 1998. E-mail: [email protected]/ Available from EREC (see Ask an Energy Expert above) Web site: www.energystar.gov/ or online in PDF at www.eren.doe.gov/ Provides lists of energy-efficient, Energy Star®-qualified geothermal/pdf/26161b.pdf or in HTML at products, including heat pumps. www.eren.doe.gov/erec/factsheets/ ghp_homeowners.html. Home Energy Magazine 2124 Kittredge Street, #95 Residential Energy: Cost Savings and Comfort for Berkeley, CA 94704 Existing Buildings , Krigger J., Saturn Resource Phone: (510) 524-5405 Management, Helena, MT 2000. Available from Saturn E-mail: [email protected], at (406) 443-3433. Web site: www.homeenergy.org/ A source of information on reducing energy consumption in the home.

Web Sites Heat Pumps The Energy Outlet Web site: www.energyoutlet.com/res/heatpump/

Heat Pumps for Heating and Cooling DOE Office of Building Technology, State and Community Programs Web site: www.eren.doe.gov/buildings/ ee_heatpump.html

International Energy Agency Heat Pump Centre Web site: www.heatpumpcentre.org/

Top-Rated Energy-Efficient Appliances American Council for an Energy-Efficient Economy Web site: www.aceee.org/consumerguide/2000enef.htm

Why Buy Energy-Efficient Appliances? DOE Office of Codes and Standards Web site: www.eren.doe.gov/buildings/ consumer_information/

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