Air-source heat pumps operate the same way as ground-source heat pumps, but capture heat from the air rather than the ground. In the summer, they operate in reverse. That is, they strip heat from the house and dump it outside. As illustrated in Figure 4-12, the air source heat pump extracts heat from outside coils filled with refrigerant. The refrigerant absorbs heat from the air, even at very low temperatures.

How?

The refrigerant is cold, sometimes as cold as 0°F (–18°C). Because it is cooler than ambient air, the refrigerant can absorb heat from it. Figure 4-12 illustrates how this device actually operates.

Although air-source heat pump sales outstrip ground-source heat pump sales and installations, they are not as efficient as ground-source heat pumps. Nor can they be installed in as many places. As a rule, air-source heat pumps work best in warmer climates, such as that of the southeastern United States, where the cooling load exceeds the heating load. Of the two models, choose a ground-source heat pump. They use half as much HCFC as the air-source heat pumps and deliver more heat (or cooling) per unit of electricity consumed. If you’d like to learn more about heat pumps, I strongly recommend John Lynch’s article, “Heat from the Earth” in Home Power, Issue 98.

In closing, although heating oil and natural gas are heading toward extinction, we have many options to heat our homes that make sense economically and environmentally.