Principle of operation
Nowadays expression 'heat pump' is widely used by people although many of them do not exactly know what it means.
Heat pumps are units that are able to extract (or 'pump out') heat from low-temperature environment so that this heat could be used at a higher temperature. In other words: consuming electical energy, heat pumps extract some heat energy from cold media (like soil, air, water) and transform it to higher temperature so that it can be used for heating.
Translations:
A hőszivattyú - heat pump; Hőcserélő (elpárologtató) - Heat exchanger (evaporator)
Kompresszor - compressor; Hőcserélő (kondenzátor) - Heat exchanger (condenser)
Elektromos energia - electrical energy; Szabályozó szelep - expansion valve
Környezeti hő - heat source; Előremenő meleg víz - Hot water flow; Visszatérő hideg víz - Cold water return flow
In these units a refrigerant circle (1) is built in, which is filled with special gas that has liquid physical condition at very low temperatures (-10-15°C). If we have other media with higher temperature that can heat up this liquid gas, it will very quickly evaporate, i.e. the liquid will be transformed into vapor (2). Of course, the temperature of the heating media will decrease since its heat is partly transferred to the gas.
This is the first step of the refrigeration cicle in the heat pump when the gas gains some extra heat energy at low temperature.
At this moment the temperature of the gas itself is also low and cannot be employed for heating but the most important thing is that it has physical condition of vapor. Why is it important? Because from now it can be compressed.
During the second step of the circle the vaporized gas is compressed by the compressor (3) and consequently its temperature increases. The gas gets hot. This is the most important moment in the circle because the extra heat gained during the evaporation becomes usable for heating, i.e. 'temperature transformation' is carried out.
The compressor needs some electrical energy (6). During the compressing process this electrical energy is partly transformed into heat that participates in the heating process and increases its efficiency.
During the third step of the circle the hot gas warms up the heating water (4). The hot gas gives over part of its extra heat to the water.
The fourth step in the circle is when the hot gas has to be cooled down so that it could gain extra heat from the heat source again.
For this purpose there is a subsystem in the heat pump that can cool down the gas to very low temperature so, that it could become liquid again (5) until it meets the heat source. At this moment the whole circle begins again.
The main technical parameter of heat pumps is the coefficient of performance (COP) that shows how many units of heating power (for example in kW) can one unit of electrical input power produce (for example, if the heat pump's compressor consumes 2 kW of electrical power and it produces 8 kW of heating output, the COP is 4).
