The most commonly used method of sustainable heat generation is a system of heat pumps. Heat pumps can use a variety of different sources of heat: air, ground, Geothermal energy, surface and drinking water.
Heat from the ambient air
Air source heat pumps extract heat from ambient air. The heat pumps designed to extract heat from outside air are designed in such a manner that they can extract heat from cold air, i.e. even when the demand for heat is greatest.
Heat from the ground
The earth is hot, and that heat can be used. Even at depths humans can reach, the temperature is several thousands of degrees Celsius. An enormous amount of energy is stored in heat. This source of energy is permanently available, making it a useful addition to sources that are not available continually, such as solar and wind energy.
Heat from surface water
Heat pumps can be used to extract heat from surface water. This technology is well-suited for use in urban areas. Besides the presence of water, another condition is that the water must have a relatively constant temperature. The offices of Rijkswaterstaat, the Dutch Directorate General for Public Works and Water Management, in Terneuzen, described elsewhere in this publication, have a heat pump that draws heat from the canal water. A seawater system has been realised in the harbour of Scheveningen that extracts heat for approximately 800 new homes from the seawater.
Heat from drinking water
Drinking water contains heat, too. The temperature of drinking water is almost constant when it is extracted. Drawing heat from drinking water only lowers the temperature of the water by a few degrees. The heat can be drawn directly from the water at local water extraction locations (see the example of Culemborg) or directly where users have individual heat pumps.
At various locations in the Netherlands geothermal energy is extracted from deeper layers in the ground. The energy is used primarily to heat greenhouses. For more information see www.geothermie.nl.