Geothermal district heating

Technical Description

A Geothermal district heating (DH) plant extracts heat from subsurface water reservoirs. Each plant consists of several wells and installations on the surface. Hot water (called the brine) is pumped from deep subsurface natural occurring reservoirs. The brine has a temperature below 100 °C and the heat is extracted using a heat exchanger and possibly a heat pump. Afterward, the heat-depleted brine is returned to the reservoir..

Recent definitions of geothermal energy include all heat from the ground. The geothermal potential of a well can be expressed by two key factors: The temperature of the reservoir and the permeability of the sedimentary layers found in the reservoir.

In the typical system, warm geothermal water is pumped to the surface from one or more production wells, where heat is extracted via heat exchangers and possibly a heat pump. the heat-depleted brine is pumped back into the source reservoir via one or more injection wells to maintain the pressure. As shown in figure, a certain lateral spacing in the reservoir between production and reinjection wells is necessary. This can be obtained with deviated well trajectories (as the figure shows) or, from a drilling point of view simpler, with vertical wells and a horizontal transmission pipe on the surface.

The heat from deep reservoirs can be utilized directly through a heat exchanger if the demanded temperature is lower than the temperature of the reservoir. Likewise, the use of heat pumps increases production capacity by cooling the brine before reinjection. The geothermal water has a high content of salt - often 10-20% (weight-%) - and various other minerals.

The principle of a doublet system geothermal plant producing into a DH system [1]

Technology Flowchart


Example of a geothermal system with an absorption heat pump. The numbers indicate the energy flows relative to the extracted amount of geothermal heat from the reservoir, which is set at 100 energy units [2]

Technology requirements and operating conditions

Technology requirements and operating conditions of a Geothermal plant, electric heat pump, 1200 m, dh temp 80/40 degree

Documentation (Links, References)

  1. Danish Energy Agency, Technology Data for Generation of Electricity and District Heating, February 2024,