The absorption of solar radiation/energy (47% of the sun’s energy that reaches the Earth) by the ground is the renewable energy source of geoexchange systems. In most localities across the globe, depths of greater than two to three metres provide a stable temperature environment that is the approximate equivalent of average annual air temperature for that location.
One is only required to enter an underground cave or wine cellar to experience this temperature stability first hand. These stable temperatures are typically present in the top 100m or more of the ground. The rare exceptions to the rule are unique geological regions such as those present in Rotorua, New Zealand and elsewhere that geothermal heat is present at shallow temperatures.
For example, the ground temperature in Perth, Adelaide, Melbourne, Sydney and Canberra is approximately 16-18C while in Brisbane it is 22-23C. In contrast, Darwin has a ground temperature of approximately 31C and Hobart approximately 14C.
In essence, geoexchange systems utilise this solar energy stored within the earth for heating buildings in winter (earth as a heat source) and as heat rejection in summer (earth as a heat sink). Both internationally and in Australia, the technology has been applied at the residential, commercial and district scales.
During the heating cycle, a geoexchange system uses the earth loop to extract heat from the ground. As the system pulls heat from the loop it distributes it through a conventional duct system as warm air (water to air). The same heat energy can also be used for a radiant floor system, swimming pools and spas (water to water).
In the cooling mode, a geoexchange system air conditions your home by reversing the heating process. Instead of extracting heat from the ground, it is extracted from your home and either moved back into the earth loop, or used to preheat the water in your hot water tank. Once the heat is removed from the air by being passed through the loop, it is distributed through the duct system in your home.