A heat pump is a device that allows the increase of the temperature drained from the soil. The concept of this process is the so called Carnot cycle, developed by the French scientist Sadi Carnot in 1824. It is based on the fact that different aggregate phases can be set with alternating pressure and temperature values in a closed circulatory system by using compression, condensation, expansion and decompression. This cycle is adapted in a heat pump. A heat pump consists of a refrigerant circuit, composed of four main components: compressor, condenser, expansion valve and evaporator. The centerpiece of a heat pump is the compressor. Modern pumps use a robust and reliable version: the so called scroll compressor. The concept is based on two helixes rotating within each other, sucking the gas and compressing it. These devices are known to operate more smoothly, quietly and reliably than conventional compressors. Unlike pistons, the orbiting scroll's mass can be perfectly counterbalanced, with simple masses, to minimize vibration. The scroll's gas processes are more continuous. Additionally, a lack of dead space gives an increased volumetric efficiency. Another component of the refrigerant circuit is the condenser. It is here that the refrigerant supplies its heat energy to the heating network. The heat transfer is based on the counter-current principle: the hot refrigerant and the water for heating are separated by a plate that transfers the heat from one to the other. The heat exchanger consists of several soldered plate layers. The third component in the refrigerant circuit is the evaporator, another heat exchanger consisting of several plate layers. It transfers the heat from the geothermal probe circuit to the decompressed refrigerant. The decompression is done by the fourth important component, the expansion valve. The expansion valve can be thought of as a nozzle head of a spray can; the control of the valve adapts automatically to the required performance. The circuit has to be filled with a special gas, the so called refrigerant. This gas is artificially produced and meets the technical requirements of the heat pump; it is a mixture of hydrocarbons, fluor methane and fluor ethane. The components are non-toxic and do not harm the environment and ozone layer. Modern refrigerants are environmentally friendly and harm neither the surrounding world nor the used materials. They are marked with the letter R for refrigerant and numerial codes, e.g. R407c or R134a. So the Carnot cycle allows the use of geothermal energy from the soil to heat up water utilising the heat pump circuit. The advantages of a heat pump are the minimal emissions and its low operating and maintenance costs reguarding other forms of heating systems. It can be used for heating during the winter months and for cooling in the summer, reduces the required primary energy by up to 75% and only 25% of the heat output must be used for its electric drive.