Right Fit Options
Installation and Operation
Make sure the ASHP is installed properly by a program participating 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 trained on 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 (see the Department of Energy article on Operating and Maintaining Your Heat Pump). Two families living in identical houses can have different utility bills, with one family paying 50% less based on proper operation of the heating and cooling system. Remember to change your filter monthly; you could save 5% on your heating cost.
Select the Right Equipment
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 furnace integrated 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, and two or more indoor, wall mounted air-handling units installed in key locations in the home.
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 home. Minnesota Power and participating utilities offer rebates on both the furnace integrated and mini-split ductless heat pumps for electrically heated homes. (Heat pumps must meet specific requirements to qualify for the rebate.)
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% of your total home energy costs are related to heating and cooling.
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% of installed cooling equipment may have incorrect refrigerant levels, which can reduce system capacity and efficiency by 20% 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.
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.
ASHP refrigeration systems consist of a compressor and two coils made of copper tubing which are surrounded by aluminum fins to aid heat transfer.
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.
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 2% or more on heating energy usage for every degree you reduce the temperature in your home, so if you keep the temperature at 70° rather than 72°, you could save about 4% on heating usage. There is a similar relationship for cooling your home. If you keep your home at 78° rather than 76°, you could save about 4% on your cooling costs.