Air Source Heat Pumps

Air Source heat pumps use the energy contained in the water vapour (humidty) of air and because the air source is replenished immediately, it maintains the same efficiency regardless of how much energy is being extracted. The prinicpal advantage of Air Source pumps is that no expensive earth or bore holes are required. However, because no energy is stored from Summer to Winter (as would be the case with a large Ground-loop), the COP (efficiency) suffers during cold weather.

Also the unit itself is slightly more expensive than the ground-source types, however when the cost of earth works is factored in, the air source is the most competitive option for most applicaptions.