3.1. Geothermal energy

Geothermal energy is energy stored in the ground in the form of heat. It is an infinite renewable energy source and can be used for heating buildings. The bestknown technique is a heat pump used to extract heat from the rocks in soil or from underground hot water. In the physical world, heat is transferred from the warmest location to the coldest location (entropy phenomenon). A heat pump reverses this process, in the same way as refrigerators. The process is done in four steps: 
  • A very volatile liquid, at low pressure and low temperature, comes into contact with a slightly warm environment (such as the underground), absorbs its heat and evaporates.
Fig. 40 – Thermodynamical functioning principle of a heat pump
Fig. 41 – Illustration of the use of geothermy to heat

  • The low-pressure gas passes through a compressor, resulting in a high-pressure and high-temperature gas.
  • This gas is passed through a series of heating pipes, where heat is dissipated.
  • When dissipating its heat, the gas turns into a fluid, undergoes an expansion and again becomes a fluid at low pressure and low temperature.