By using a heat pump, the energy can be generated from liquids such as groundwater. One property of groundwater is that it has a constant temperature. The whole year round this is approx. 10o C. Drinking water stored in clear-water basins is therefore a source of energy.
The water can be cooled a little, the temperature can be lowered by 1 – 2 degrees. This energy can be used for heating the buildings.

How does this work?
This is where the special features of water are involved. In nature, water occurs in three forms, namely ice, water and water vapour. To go from one form to another requires energy or releases energy. From ice to water and from water to water vapour requires energy. To melt ice it has to be warm and to boil water we have to put fire under it. It has to be heated, energy is required. The reverse must also apply then. If water vapour becomes water (= condensation) energy has to be released. The same applies for changing water into ice. At that moment energy is released.
Caution is necessary, however, with respect to the water quality. An increase of more than 1o C in the temperature of drinking water is often undesirable. Heat pumps are possibly a good source of green energy for water companies.

Hot or cold
In the buildings of the treatment plant and the workshop three heat pumps have been installed with a total capacity of 110 kW. The heat is generated by leading drinking water from the clean-water storage through a heat exchanger. This has double, separated circuits so that the drinking water cannot come into contact with the liquids in the heat pumps. The drinking water with a constant temperature of approx. 9.0o C is used to feed the three heat pumps. In the summer this system is deployed to cool the building. In the buildings the walls and floors are heated.