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Brine/water heat pump – function, benefits and funding

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The earth is a huge, almost inexhaustible storage heater, and at the same time one of the most important heat sources of them all. From a certain depth, the ground has a base temperature of about ten degrees Celsius. When compared to the ambient air, that temperature is very constant. This means that even if the upper layer of earth is iced over, ground source heat pumps can continue to work efficiently because the difference between the heat source and the flow temperature remains relatively small, even in winter.  

How a brine/water heat pump works

Like all other heat pumps, a brine/water heat pump works on the same principle: First, thermal energy is extracted from the ground and then transferred to the refrigerant. This evaporates and is additionally compressed using a compressor. This not only increases its pressure, but also its temperature. The resulting heat is absorbed by a heat exchanger (condenser) and passed on to the heating system. You can learn in detail about how this process works in the article How the brine/water heat pump works.

In principle, geothermal heat can be extracted via a ground source heat pump in two ways: either via geothermal collectors that are laid close to the surface or via geothermal probes that penetrate down to 100 metres into the earth. We will look at both versions in the following sections.

Geothermal collectors are laid underground

To extract the geothermal heat, a pipe system is laid horizontally and in serpentine form below the frost line. The depth is around one to two metres below the surface of the lawn or soil. A brine medium made of frost-proof liquid circulates in the pipe system, which absorbs the thermal energy and transfers it to the heat exchanger. The size of the collector area required depends, among other things, on the heat demand of the building in question. In practice, it is 1.5 to 2 times the area that needs to be heated. Geothermal collectors absorb thermal energy from near the surface. The energy is provided by solar radiation and rainwater. Consequently, the condition of the ground plays a decisive role in the energy yield of the collectors. It is important that the area above the pipe system is not asphalted or built upon. You can read more about what needs to be taken into account when laying the geothermal collectors in the article Geothermal collectors for brine/water heat pumps.

Brine/water heat pump

[1] Vitocal brine/water heat pump
[2] DHW cylinder
[3] Heating water buffer cylinder

Geothermal probes extract heat from deeper layers of the earth

An alternative to geothermal collectors are probes. With the help of boreholes, the geothermal probes are sunk vertically or at an angle into the earth. A brine medium also flows through it, that absorbs the geothermal heat at a depth of 40 to 100 metres and passes it on to a heat exchanger. From a depth of around ten metres, the temperature remains constant all year round, so geothermal probes work efficiently even at very low outside temperatures. They also require little space when compared to geothermal collectors, and can also be used for cooling in the summer. The depth of the borehole also depends on the heat demand and thermal conductivity of the ground. As several groundwater-bearing strata are penetrated in a borehole of up to 100 metres, permits must always be obtained for drilling boreholes.

Heat from the ground (probe)

[1] Vitocal heat pump
[2] DHW cylinder
[3] Heating water buffer cylinder

Benefits of the brine/water heat pump

There are many ways to combine good with good. One of these is the operation of a brine/water heat pump. Thanks to its use of geothermal energy, a brine/water heat pump is an efficient means of heating. Geothermal energy is the thermal energy available below the earth's surface that can be used as a heat source for a ground source heat pump. In addition to the attractive subsidy programmes from the state, the benefits of a brine/water heat pump are numerous. These can be roughly divided into ecological and economic benefits:

One of the main benefits of a brine/water pump is the fact that the heat source is available virtually free of charge. The only energy you need to purchase is the power to supply the compressor. Here, a combination with a photovoltaic system is ideal, so that you can convert the solar radiation into electricity. The almost infinite heat source also helps to ensure that the price of raw materials is not subject to economic or political fluctuations. System owners are thus significantly less dependent on their fuel suppliers. A ground source heat pump can be operated economically in either mono mode or dual mode. This means that in the heating system used, either one or two different heat generators will be responsible for the heating heat and/or the domestic hot water.

Investing in a ground source heat pump also means investing in the future. This is because geothermal collectors and probes have a very long service life. The units are also extremely low-maintenance, as only a few moving components are installed. Planning and installation are usually carried out by a heating contractor, so that safe operation is guaranteed from the very outset.

In the warmer summer months, a brine/water heat pump can also be used for temperate heating. With this function, the heat of the room is transferred to the geothermal probe system via the underfloor heating. The ground then stores the heat so that it can be used in the subsequent heating period. In this mode, only the circulation pump and control unit are operational, making natural cooling an energy saving and cost effective method of cooling buildings. How this process looks in detail is explained in the section entitled Natural and active cooling.

In addition to the economic benefits, there are many ecological reasons for operating a ground source heat pump. This is because the energy required for heating is, on the one hand, climate-friendly and, on the other, available right below your own property. Long and CO₂-intensive transport routes are completely eliminated. The use of geothermal energy also means a reduction in harmful CO₂ emissions. When compared to a gas or oil heating system, up to 90 per cent fewer flue gases reach the ozone layer.

The operation of a brine/water heat pump has another positive effect in addition to the benefits already mentioned: Experts see great potential here in achieving the climate targets set by the German government. The key term here is "sector coupling", i.e. the merging of the electricity and heating markets. The background to this vision is the ever-increasing share of clean electricity. Wind and photovoltaic systems already produce so much electrical energy that they have to be temporarily shut down in order not to destabilise the power grid. Many experts are committed to finding ways of using this surplus power with the help of heat pumps.

Using a ground source heat pump from Viessmann offers numerous benefits. Among the most important are:

  • Free heat source available at any time of day  
  • Efficient operation even in winter thanks to a constant high temperature
  • Can be used for natural cooling in summer
  • Reduction in CO₂ emissions
  • High state subsidies

Brine/water heat pumps for commercial and local authority use

Brine/water heat pumps use the ground as the primary source of energy. This is done with geothermal collectors or geothermal probes, which are inserted into the ground to extract the heat that is there. The brine/water heat pumps for commercial and local authority use are characterised by their environmental responsibility and significantly reduce the costs of generating heating energy and domestic hot water.


Vitocal  300-G

Vitocal  350-G

Rated heating output

Single-stage: 21.2 to 42.8  kW; two-stage: 42.4 to 85.6  kW,

20.5 to 84.6  kW

Application area

Apartment buildings, commercial enterprises, local authorities, new build and modernisation projects

Detached houses, two-family houses, apartment buildings, commercial enterprises, local authorities, new build and modernisation projects

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