Heat pump - Soil to water
The heat source for the soil to water heat pump is the heat stored in the ground itself. But this could be a (combination with a) water source under the ground as well. Even open-water at the surface could function as the heat source. This is a 'closed' system, refering to the fact that, in case of (ground) water as the heat source, this water is not moved and remains at its location. With closed sources, a closed circuit of hoses or pipes (usually made of plastic tubing) is introduced into the heat source. This circuit contains a mixture of water and an anti-freeze such as glycol. The mixture is pumped around and takes over the heat from the source through a heat exchanger.
A heating device must, among other things, be selected for its heating capacity. This capacity depends on (1) the degree of insulation of a building, (2) the desired interior temperature and (3) the size of the building. The largest houses are larger than the smallest buildings within the utility sector (and the other way around). This means that every heat pump that is placed in the residential sector, can also be found within the services sector. Within the latter sector, however, there are also much larger buildings; this does create a different situation with a much larger heat demand. Such buildings are often equipped with several heating appliances, which are placed in a cascade arrangement.
When the outside temperature drops further, an additional appliance will start operating. This way, electrical heat pumps are most often combined with gas fired boilers. The more efficient, but more expensive heat pump, for example, provides 80% of the heat demand, the gas boiler only assists on the coldest days in order to meet the "peak heat demand". The combination of an electric heat pumps with a gas fired boilers can be considered as a ‘hybrid cascade setup’. In a services building that reaches the level of 'nearly zero energy', a stand-alone heat pump could be sufficient, just as in a residential building.