Air source heat pumps (ASHPs) are an energy efficient alternative to furnaces and air conditioners, even in colder climates and for those with moderate cooling needs. They’re an attractive option because they are capable of providing efficient cooling along with heating in the spring and fall, with a single piece of equipment.
When properly installed, an ASHP can deliver 1½ to 3 times more heat energy to a home than the electrical energy it consumes. As a result, these systems can provide heat for Minnesota’s shoulder seasons (fall and spring) at a higher efficiency and lower cost than electric resistance heating, oil, or propane heating systems—and in some cases, for a lower cost than gas heating as well.
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$300 Rebate on Standard Split, Furnace Integrated ASHPs
$550 Rebate on Mini Split Ductless ASHPs |
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| How Air Source Heat Pumps Work |
ASHPs use electricity to transfer energy between indoor and outdoor air. Because they move heat rather than generate heat, these systems typically consume less electricity than electric-resistance heating systems. In cooling mode, heat pumps function like an air conditioner, moving heat from inside to outside the home. In heating mode, the refrigerant flow is reversed to extract low-temperature heat from outdoors and deliver concentrated high-temperature heat to the home.
These systems typically work well to temperatures as low as 30°F. Below that, a backup or supplemental heating source is required. The backup system can be electric, fossil fuel, or a combination. Some ASHP manufacturers have a hybrid system that includes a standard split heat pump with supplemental electric heating and fossil fuel furnace in one complete package. Note: Minnesota Power’s ASHP rebate program requires electricity as a primary heating source. Minnesota Power also offers a rebate on geothermal heat pumps (GHPs). GHPs are similar to ASHPs but use ground temperature, rather than air, via buried piping or drilled wells and can provide 100 percent of the building’s heating and cooling needs. Find out more about qualifying for ASHP and GHP rebates.
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| Select the Right Equipment |
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| Mini split ductless ASHPs provide the flexibility of room
by room temperature control (wall mounted units (A))
with a centralized heating and cooling system (outside
compressor (B)). |
When retrofitting an existing building with an air source heat pump, it is important to consider the building’s heat distribution system. If the system uses forced air ducts, a standard split, ASHP is likely to be the most cost-effective option. If there are no air ducts in the home, you should select a mini split ductless heat pump. This system utilizes an outdoor compressor/condenser unit (B), and two or more indoor, wall mounted air-handling units installed in key locations in the home (A). When planning a new home, work with your builder, HVAC contractor, and local utility to determine the type of heat pump that complements the energy efficient design of your home. Heat pumps offer an energy efficient option that enhances the overall energy savings of a Triple E/ENERGY STAR® home. Minnesota Power and participating utilities offer rebates on both the standard split and mini split ductless heat pumps. Heat pumps must meet specific requirements to qualify for the rebate.
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| Choosing a Contractor |
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While ASHPs are gaining popularity in northern climates, they’re still a new technology to some Minnesota contractors. As with any job, it’s important to choose an experienced contractor who is trained and certified to install the specific product you have in mind. Ask for references to ensure the quality of the contractor’s work and make sure they meet the requirements to participate in MP’s heat pump rebate program. You must use a program trained contractor to qualify for these rebates.
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| Considerations |
| Installation and Operation |
Make sure the ASHP is installed properly by a qualified contractor. Incorrect installation can lead to higher electric bills, reduced comfort, and maintenance problems. Minnesota Power’s ASHP rebate program requires that heat pump installers be distributor trained on the proper heat pump installation and operation and on utility program requirements.
In addition, it is very important that your ASHP installer explain how to operate your heat pump to maximize energy efficiency. How you operate your heating and cooling system has a significant impact on your energy bills. Two families living in identical houses can have different utility bills, with one family paying 50 percent less based on proper operation of the heating and cooling system.
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| Efficiency |
Look for the ENERGY STAR® to find the highest efficiency air source heat pumps on the market. ENERGY STAR qualified units are rated at 14 SEER, 11.5 EER and 8.2 HSPF, compared to the federal minimum of 13 SEER and 7.7 HSPF, making these heat pumps about 8 percent more efficient than standard models. Minnesota Power’s rebate program requires that standard split ASHPs meet ENERGY STAR standards. xx Note: ENERGY STAR standards are anticipated to increase in 2009. These terms are defined at the end of this document. Mini split ductless units also need to meet specific performance requirements to qualify for an Minnesota Power rebate. Work with your program trained contractor to make sure you choose a unit that meets these standards.
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| Sizing |
Proper sizing is important. Equipment that is too large for the home will cost more, both up front and throughout the unit’s life. It will cycle on and off more frequently, reducing peak performance and resulting in temperature fluctuations. This inefficient operation will also shorten the unit’s life. On the other hand, equipment that is too small will be forced to run for long periods of time and will struggle to heat to the desired temperature. Proper heat pump size is determined by other factors, too, such as insulation levels, air tightness, and heat gain. Again, your heating and cooling selection is a key component in building energy efficiency into your new or existing home. On average, 45−55 percent of your total home energy costs are related to heating and cooling.
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| Refrigerant charge |
An air conditioner’s ability to operate at its greatest efficiency is directly dependent upon the amount of refrigerant it contains. According to the U.S. Environmental Protection Agency, recent field studies suggest that approximately 75 percent of installed cooling equipment may have incorrect refrigerant levels, which can reduce system capacity and efficiency by 20 percent or more. The level of refrigerant charge is unique to each system and is determined by every piece of equipment within that particular system, including the outdoor compressor, the indoor evaporator coil, and the refrigeration lines between them. Correct refrigerant charge and proper refrigerant line sizing will protect the compressor from possible damage, ensure efficiency, and improve performance. Refrigerant charge assessment is a requirement for proper installation of the ASHP and it’s a key component in Minnesota Power’s rebate program.
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| Airflow |
 ASHP refrigeration systems consist of a compressor and
two coils made of copper tubing which are surrounded by
aluminum fins to aid heat transfer. |
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Incorrect airflow across the indoor coil is another common problem in heat pump installations, with a subsequent impact on indoor comfort and operating costs. Low airflow affects the cooling and heating capacity and reduces the distribution efficiency of the unit, contributing to premature equipment failure. Excess airflow is a less common problem, but it can increase duct leakage, cause poor dehumidification during cooling, increase duct noise, and create drafts. Airflow assessment is a requirement for proper installation of the ASHP and it’s a key component in Minnesota Power’s ASHP rebate program.
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| Controls |
The ASHP is an integrated unit that provides high efficiency cooling along with efficient heating in the spring and fall and is capable of interfacing with your existing heating system. Because it is a refrigeration system that provides cooling and can reverse itself to provide heating, it has a defrost cycle. The ASHP is installed with controls that automatically provide supplemental heating during the defrost cycle and when the temperature gets below the balance point of 30−35°F. The controls also prevent the backup or supplemental heating system from coming on when it’s not needed or when using set-back practices.
As a rule of thumb, you can save about two or more percent on heating energy usage for every degree you reduce the temperature in your home, so if you keep the temperature at 70 degrees rather than 72 degrees, you could save about 4 percent on heating usage. There is a similar relationship for cooling your home. If you keep your home at 78 degrees rather than 76 degrees, you could save about 4 percent on your cooling costs
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| HVAC Quick Glossary |
SEER—Seasonal Energy Efficiency Ratio: An energy efficiency rating for residential air conditioners. The higher the SEER, the better the energy performance and the lower the energy costs. The U.S. Department of Energy’s established minimum SEER rating for cooling is 10.
EER—Energy Efficiency Ratio: A measure of the efficiency of cooling equipment at peak performance when the outdoor temperature is at a specific level (usually 95°F). A higher EER means greater energy efficiency.
HSPF—Heating Seasonal Performance Factor: Measures the efficiency of residential heating equipment throughout an entire heating season. Typically considered the heating equivalent of SEER. A higher HSP means higher efficiency. The U.S. Department of Energy’s minimum HSP rating is 6.8.
COP—Coefficient of Performance: Measures the efficiency of heating equipment at 17°F and 47°F. A higher COP means higher efficiency. This rating does not reflect how much energy is being used by backup heating sources.
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| For more information |
www.mnpower.com/powerofone Minnesota Power offers rebates on qualifying air source and ground source heat pumps. Information on these rebates is available at the above website.
www.energystar.gov The U.S. Environmental Protection Agency and U.S. Department of Energy’s ENERGY STAR® program provides information on energy efficient products that meet ENERGY STAR standards.
www.eere.energy.gov/consumerinfo The U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) offers a wealth of home energy tips.
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