How does geothermal work?
You already have a heat pump in your home -- your refrigerator. If you put your hand behind it, you'll feel the heat that has been pumped from the inside and from its contents. It's the same principle that the geothermal heat pump uses to move heat to and from the home and earth.
In the summer, the heat pump extracts heat from the conditioned space and sends it out to the earth loop to warm the relatively cool ground, or pond, if it's an aqua loop.
In the winter, this process is reversed. The heat pump extracts heat from the relatively warm ground, usually warmer than the outdoor cold air, and pumps this heat into the conditioned space.
The result is the need for far less energy than the conventional air source heat pump system for year-round conditioning. Even in the winter, it is more efficient than conventional natural gas or oil heating systems.