Central air source heat pumps account for about 85% of the heat pump market, in the North America. But there are other interesting types of heat pumps.
The heat pump technology includes also geothermal or ground-source heat pumps and ductless (mini-split) models, a very interesting type of heating for energy efficient single-family homes.
Air Source Heat Pumps Belong to the Air Conditioner Family
Air source heat pumps belong to the air conditioner family. They can be seen as air conditioners that are also able to move heat from the outside air, even when the temperatures are relatively low (besides being able to cool the house during the summer, like air conditioners).
Our video, comparing...
Air Source Heat Pumps and Geothermal Heat Pumps:
Air source heat pumps can provide 1.5 to 3 times more heat than the electricity they consume. Unfortunately common air source heat pumps only work properly when temperatures do not drop to very low levels (to below 40º-35ºF; 5-2ºC). At such temperatures these heat pumps have to resort to electric-resistance elements.
Fortunately, there are now new heat pumps (cold-climate heat pumps) able to overcome this limitation. They are a great alternative to gas heating equipment as long as temperatures do not drop below -20ºF...
Most air source heat pumps have split designs, that is, they are two-piece units: one located indoors and the other outdoors.
The outdoor unit (similar to the outdoor unit of air conditioners) comprises the outdoor coil, a compressor, a reversing valve and a fan. The indoor unit contains a large blower and a filter, also like conventional air conditioners.
Geothermal or Ground Source Heat Pumps Make Little Sense in Low-Energy Homes
Geothermal heat pumps can be seen as large air conditioners, with a long loop buried in the soil or submerged in a well or other body of water, designed to move heat from the ground into the house (and the reverse, in the summer).
They can provide 3, 4 or more times kWh of heat (or cold) than the electricity they consume, even when outside temperatures are freezing.
Since earth temperatures are a lot more constant then those of the outside air, they may not require auxiliary sources of heating, but their installed price is very high, which can make them non-cost competitive for average heating and cooling needs. And since energy-efficient homes are designed to have small heating needs, they do not make sense from an energy-efficiency standpoint.
Ductless Heat Pumps: Often the Best Choice for Very Energy Efficient Homes
Ductless heat pumps are relatively cheap and can be designed to heat up to four rooms, through separated air handlers and thermostats.
They allow zoning, and can be an interesting choice in homes with good insulation and sealing levels, including colder climates (there are now new high-performance mini-splits able to overcome the limitations of some years ago).
Ductless heat pumps involve an outdoor unit with the compressor and the condenser; and an indoor air-handling unit, with the blower and the filter. These two parts are connected by a conduit, housing the power cable, the suction and refrigerant tubing, and the condensate drain.
See, for details:
Ductless Heat Pumps