Air Source Heat Pump
Do Air-to-Air Heat Pumps really work in cold climates like Montana, and what do the terms SEER and HSPF mean?
15 years ago when I started AirWorks, I would have gently guided my customers away from Air-to-Air Heat Pumps (also called Air Source Heat pumps). They just could not keep up with our coldest weather and running the supplemental heat could get very expensive. But over the years the technology has evolved significantly and we can get much higher energy performance from air source heat pumps at colder temperatures. This is primarily due to advancements in refrigerants, variable speed blowers, improved coil design and surface area, and two-speed/variable compressor designs.
The heat pump works by absorbing heat outside and transferring it inside during the heating season. This process is reversed during the cooling season. The amount of heat the system can supply indoors is dependent on the outdoor temperature. As the outdoor temperature drops, so does the capacity of the heat pump to absorb enough heat to maintain indoor comfort. The outdoor temperature at which the heat pump capacity equals the heat loss of the house is called the outdoor ambient balance point temperature. When the outdoor temperature falls below this point, supplemental heat is needed to keep the indoors comfortable. This supplemental heat is typically electric resistance heat but can be a gas furnace as well (this is called a Dual Fuel system).
SEER stands for Seasonal Energy Efficiency Ratio and represents the efficiency of the heat pump (or air conditioner) operating in the cooling mode. HSPF stands for Heating Seasonal Performance Factor and rates the operating efficiency in the heating mode. A higher number, in both cases, means greater efficiency. The minimum SEER value allowed in new systems is 13. AirWorks has ductless heat pumps that rate as high as SEER 26. In our climate the HSPF is more important, as our cooling load is rather low, and heating is where it is at. The HSPF can range from 7.7 – 10. Energy Star tax credits and utility rebates require an HSPF of at least 8.2-8.5 to qualify (depending on the type of system installed: ductless, split, or packaged).
So, the short answer is, yes, today’s high efficiency air source heat pumps work great in our climate. And while we do experience days of extreme cold, the majority of our heating hours, fall well within the effective range of air source heat pumps.