Heat Pump: Heat from the Earth
Heat from a heat pump is not produced by the burning of fuel, but by the compression of a cooling agent. This compression produces the required temperature of the heating system.
Heat pumps are one of the most efficient systems for both space heating and hot water, since they can use year-round the heat of the sun that is stored in the surrounding air, in the soil or in the ground water. This energy from the environment provides the heat pump with approximately 75% of its heat energy. With only 25% of energy from electricity a heat pump reaches 100% heating capacity.
The ground temperature throughout the year is relatively constant. At a depth of 10m it is approximately 10 ⁰C. This is significantly lower than the required heating temperature, but it can be utilized by a physical phenomenon.
How heat pumps work
Already in 1852 William Thomson discovered the thermodynamic phenomenon that gases heat up when compressed and cool down when they expand. In heat pumps a heating agent (e.g. propane) circulates in a closed system and is cooled by expansion to a lower temperature than the surrounding temperature. This difference in temperature causes a heat flow to the heating agent. The heating agent is then led to the compressor, were the temperature is raised by compression above the required temperature of the home heating system. Heat flows from the heating agent to the heating elements. The heating agent then cools down, condensates and is expanded by a valve.