|Air-source heat pumps are different from boilers and furnaces in that they do not "produce" heat. Heat pumps actually "move" heat from the outside to inside of a building. Like your refrigerator, heat pumps use electricity to move heat from a cool space into a warm place (heat pumps powered by natural gas are also commercially available now). During the heating season, heat pumps move heat from the cool outdoors into your warm building; during the cooling season, heat pumps move heat from your cool building into the warm outdoors. |
Because they move rather than generate heat, heat pumps can provide up to 4 times the amount of energy they consume. If you heat with electricity, a heat pump can trim the amount of electricity you use for heating by as much as 30% to 40%.
Heat pumps use about 50% less energy than electric resistance heating units. High-efficiency heat pumps also dehumidify better than standard central air conditioners, resulting in less energy usage and more cooling comfort in summer months.
For heat pumps with capacities of five tons or less, cooling efficiency is expressed as the Seasonal Energy Efficiency Ratio (SEER) and heating efficiency is expressed as the Heating Season Performance Factor (HSPF). For larger units, cooling efficiency is expressed as the Energy Efficiency Ratio (EER) and heating efficiency is expressed as the Coefficient of Performance (COP). Since cooling efficiency and heating efficiency don’t necessarily go up and down together, when selecting a heat pump you should focus on the cooling efficiency rating if you’re in a predominantly warm climate and the heating efficiency if you’re in a predominantly cool climate.
When buying a new heat pump, make sure it has a SEER rating of 12 or higher. A heat pump with a SEER value of 12 or better will save 15% to 20% in air conditioning costs, compared to a heat pump with a SEER value of 10. Avoid purchasing an oversized heat pump, which will result in weaker energy efficiency and a shorter product life.
Although air-source heat pumps can be used in nearly all parts of the United States, they do not perform well over extended periods of sub-freezing temperatures. In regions with sub-freezing winter temperatures, it may not be cost effective to meet all your heating needs with an air-source heat pump.
A professional service technician should perform proper maintenance on a heat pump at least every other year. The service call will involve a general tune-up, inspection, and cleaning of the system. Every tune-up should include a filter change, inspection of the inside and outside coils (and cleaning if necessary) and a check for proper airflow. In addition, the first time your heat pump is serviced, the technician should check the refrigerant levels by testing something called "superheat" or "subcooling" (depending on the type of unit). Once they verify the proper refrigerant charge, no service person should attach refrigerant gauges again, unless you notice a decrease in performance or a sudden increase in your electric bills. In addition, have the technician show you how to change the filter. This should be done every month when the system is operating. A 1 inch pleated filter is recommended for most applications, as an upgrade from the cheapest fiberglass filters. "Washable" electrostatic air filters create a lot of resistance that can reduce air flow and operating efficiency.
A list of high efficiency heat pumps is available from the American Council for an Energy-Efficient Economy (ACEEE) at http://www.aceee.org/Consumer/consumer.htm. ACEEE also publishes the Guide to Energy Efficient Commercial Equipment that includes a chapter on HVAC systems as well as a heat pump product listing.
Additional Resources: US DOE, Federal Energy Management Program, Technology Brief: Air Source Heat Pumps – High Efficiency