The heat pump comparison
Similar to the word car, heat pump is also a generic term for heating systems that use the environment as a heat source. The numerous sources and the sophisticated technology enable home owners to always find the best heating system for them, which supplies them reliably and economically with heat. The following heat pump comparison provides an initial orientation as to when an investment in which heat pump is worthwhile.
Common features of all heat pumps
As its name suggests, this heating system generates heat by pressurising a gas, similar to an air pump. Regardless of which heat source the heating system accesses, the cooling circuit process is the heart of every heat pump. Before the ambient heat (air, geothermal energy or water) can be brought to the desired temperature, it passes through pipes to a heat exchanger through which a refrigerant flows. Due to its special material properties, the refrigerant evaporates even at low temperatures. However, the heat generated is of too low temperature to be used for heating and hot water. This is where the electric compressor comes into play and raises the temperature. You can find out how the entire process works in detail in the section How the heat pump works.
Differences between heat pumps
As mentioned above, a heat pump can extract heat not only from the ambient air but also from the ground.
Air as a heat source
Air-source heat pumps are among the most installed heat pumps in the UK. This is due on the one hand to their simple and quick installation and on the other hand to their relatively low investment costs. A conventional air-water heat pump extracts heat from the outside air and raises it to the desired temperature through the cooling cycle. Depending on the model, the devices can be set up either outside or inside. In the case of externally installed monobloc units, the cooling circuit is completely installed in the heat pump. The heat generated is transported into the building with heating water. With so-called split heat pumps, the cooling circuit is separated. The heat is transported through a refrigerant pipe to the interior of the building where the evaporator heat exchanger is located. This ensures that the outdoor unit is frost-proof even in the event of a power failure.
A special form of air-water heat pump is the so-called exhaust air heat pump. Instead of the outside air, such a heat pump uses the usually much warmer exhaust air from the rooms. This means that the compressor has to work less to reach the desired temperatures. However, the amount of air is usually limited, which means that monovalent operation is not possible. As a rule, they are used for very small heating loads.
Geothermal energy as a heat source
Compared to outside air, geothermal energy is relatively high above a certain depth. Furthermore, it remains constant even in winter, even if the upper layer of earth has already iced up. Brine-water heat pumps operate very efficiently and achieve COP values of up to 5.0. There are basically two methods available for recovering geothermal energy: geothermal probes are ideal in confined spaces. These are drilled vertically or obliquely into the ground and extract heat from the ground at a depth of 40 to 100 metres.
As an alternative to geothermal probes, ground loop collectors only need a shallow depth of about one to two metres, i.e. below the frost line. Due to their horizontal and large-area installation, they require considerably more space. You can find out how heat is generated in detail in the section on the operation of the ground source heat pumps.
Groundwater as a heat source
Groundwater is also an excellent source of heat, providing consistently high temperatures throughout the year. Two wells are required for heat generation. For the water-water heat pump to operate efficiently, the groundwater composition and the amount of water must meet minimum requirements. System owners require official approval for the construction of the well system.
Which heat pump is suitable for which house?
When it comes to finding the right type of heat pump, the heat source must not be overlooked. While air-water heat pumps are used almost everywhere, the operation of a brine-water heat pump does not make sense everywhere - and is not always permitted. Drilling is necessary for mounting the geothermal probes. In principle, deep drilling is subject to mining regulations and must be reported to the competent authority.
This also applies to geothermal probes for brine/water heat pumps, which is why the use of such a system is not suitable for every house. In addition to the heat source, it is also important to check which heating system is installed. Hybrid heat pumps, for example, are particularly suitable for radiator heaters with higher temperatures.
Ice energy storage as an alternative to brine-water heat pumps
If homeowners still want to take advantage of the benefits of a brine/water heat pump despite the lack of a drilling permit, they can switch to ground surface collectors. However, sufficient free space must be available for their installation. The exact size of the area required depends, among other things, on the condition of the ground and, of course, on the heat requirements of the house. As a rule of thumb, the collector surface should be one and a half to twice as large as the living space to be heated. Furthermore, the collector surface should not be overbuilt so that the earth can regenerate more quickly with the help of the sun and rain.
As an alternative to surface collectors, consumers can also use trench collectors which, due to their design, achieve a considerably higher extraction performance per square metre. The third option is an ice energy store. For the installation, it requires an area of about four square meters and a depth of four meters. An official building permit is not required. Thus the ice energy storage is a good alternative to a classical geothermal probe system.