Since more people are using heat pumps these days, even in cold climates, let’s spell out the three different types of heat that conventional heat pumps provide. Why not? We’ve just recently covered the three main sources of home heating and then stepped back and looked another group of three sources of heat for high-performance homes (as enumerated by Skylar Swinford). Now let’s zoom in a bit on heat pumps.
This is the heat you get when the compressor runs. The compressor is what drives the refrigerant through the phase-changing, heat-exchanging thermodynamic cycle that allows your heat pump to extract heat from the cold outdoor air and transfer it to your warm indoor air. This is possible because the Second Law of Thermodynamics says heat flows from warmer to cooler objects…and the refrigeration cycle makes the outdoor coil colder than the outdoor air.
This type of heat is abundantly available when it’s chilly but not real cold. As the outdoor temperature drops, so does the amount of heat available in the outdoor air. That in turn reduces the capacity of the heat pump. As long as the outdoors isn’t at absolute zero —and it’s never absolute zero anywhere — there’s still heat available. It just gets harder and harder to move it indoors.
Eventually, the amount of compressor heat available drops below the amount of heat needed inside the home. That’s when you need…
As stated above, the heating capacity of a heat pump drops as the outdoor temperature drops. At the same time, the heating load of the house increases. At some temperature, the capacity is just equal to the load, a temperature we call the balance point. Below that, the load is bigger than the capacity and you need some…
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