This energy source can be used via ground collector or ground probes. The required area of the collectors is determined according to the soil conditions and heating requirements of the building. The ground collector consists of pipes, which are laid with a brine / water mixture just under the frost line in approx. 1.2 m. The rule of thumb is approximately 1.5 times the heated area as a collector surface. Ground probes uses the stored heat in a depth of several meters up to over 100 m. Ground probes are also filled with a brine / water mixture, thereby absorbing the stored heat of the soil and deliver it to the heat pump.