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Ground Source Heat Pumps

Using the soil, bedrock or groundwater as the heat source

All around us are sources of energy in the form of stored solar energy, which even if they have a low temperature can provide us with heat. But how can a few degrees above zero gives us energy to heat radiators and hot water. Let us explain!

Surface soil heat

During the summer, solar heat is stored in the surface layer of the soil. Using that energy for heating is a practical approach for houses with a large plot. The amount of energy that can be extracted is greatest in soils with a high water content.

The heat is extracted from the soil by means of buried plastic tubing. An environment-friendly non-freezing liquid circulates in the tubing and delivers the collected heat to the heat pump. In the heat pump the heat is converted into high-grade heat for space heating and to produce hot water.

Heat from bedrock

Down in the bedrock there is a source of heat that stays at practically the same temperature all year round. Using heat from the rock is a secure, safe and environment-friendly way of heating all types of building, large and small, public and private.

The capital cost is relatively high, but in return you get a reliable, low-energy form of heating with an extremely long life. The coefficient of performance (COP) is good, as high as 4.8. The plant occupies little space and can even be installed on small plots. Very little reinstatement work is needed after drilling the borehole, so the effect on the nearby environment is minimal. The groundwater level is not affected, since no groundwater is used.

The heat energy can be transferred to an existing, conventional, water-borne heating system and can also be used to produce hot water.

Drilling for energy

The heat is collected from the bedrock and the groundwater through a borehole 4.5 to 6.5 inches in diameter. The depth of the borehole is determined by the amount of energy needed for heating. If the energy demand is great, several boreholes can be connected together. Two lengths of tubing connected at the bottom are passed down into the borehole. Inside the collector tubing there is a frost-resistant liquid (cooling medium, brine). The system is completely sealed, so the cooling medium never makes contact with the groundwater.

To ensure that the groundwater is not contaminated by surface water running down into the borehole, a steel liner or casing which extends a short distance down into the borehole is installed. Grouting or rubber rings should be used to form a seal between casing and bedrock.

Function of the cooling circuit

The collector liquid (cooling medium) is pumped up from the borehole in tubing and passed to the heat pump.

Another fluid circulates in the heat pump in a closed system with the most important characteristic of having a low boiling point. This fluid is called a refrigerant. When the refrigerant reaches the evaporator, which has received energy from the borehole, the refrigerant evaporates.

The vapour is fed to a compressor where it is compressed. This results in a high increase in temperature.

The warm refrigerant is fed to the condenser, which is positioned in the boiler water. Here the refrigerant gives off its energy to the boiler water, so that its temperature drops and the refrigerant changes state from gas to liquid.

The refrigerant then goes via filters to an expansion valve, where the pressure and temperature are further reduced.

The refrigerant has now completed its circuit and is once more fed into the evaporator where it is evaporated yet again due to the effect of the energy that the collector has carried from the energy source.

Save 65 – 75% of your heating costs with a NIBE heat pump

The ground source heat pumps come in 15 models from 4 kW up to 30 kW (even up to 300 kW when connected in parallel). At least 65% of the heating and hot water energy consumption of a house can be saved.

For example, the NIBE FIGHTER 1140 shown above is a ground source heat pump for heating single and multi-family houses and industrial buildings.