How is it possible to heat water to 35°C with air that is -5°C?
The heat pump, based on the principle of compression and expansion of the refrigerant, takes heat from the ambient air and transfers it to the circulating water in the system. It does not consume electricity directly to heat the water, but uses it only to operate the compressor and circulation pump. The heat itself is literally taken from the air, thanks to which it is possible to produce up to 5kW of heat with the consumption of 1kW of electricity.
You've probably ever inflated your bike tires with a hand pump, which got hot after a while. Compressing gas (compression) creates heat. Conversely, when releasing compressed gas from a pressure tank, you may notice that the nozzle where the gas comes out quickly becomes covered with ice because the rapid release of pressure (expansion) takes away heat.
How can this be used in practice?
Inside the heat pump, a refrigerant circulates, which is a special filling that conducts heat well and does not freeze at low temperatures. This refrigerant is compressed to high pressure by a compressor, which increases its temperature, and this heat is then transferred to the circulating heating water in the exchanger (condenser). The cooled refrigerant then travels to the expansion valve (nozzle), where it expands - reducing pressure and rapidly cooling to temperatures well below freezing, i.e. to a temperature lower than the outside air temperature. The refrigerant cooled in this way is forced through the external evaporator (visible ribbed part of the heat pump) where air from the environment is forcibly driven by a fan. Since the refrigerant has a lower temperature than the surrounding air at this point, it heats up to the air temperature and then in the compressor this temperature is raised again above the temperature of the circulating water, to which the obtained heat is transferred.
Compression is therefore used to raise the temperature of the refrigerant above the temperature of the circulating water so that heat can be transferred to it and the subsequent expansion moves the temperature below the temperature of the ambient air so that it can be heated by it. In this way, heating the refrigerant by 5°C from a temperature of -10°C to -5°C is transferred as heating the heating water by the same 5°C but in the range of 30°C to 35°C.
Why does frost form on the heat pump?
This is precisely because of the low temperature of the refrigerant, well below freezing, driven into the thin fins of the evaporator. The evaporator body cools down sharply and the air moisture begins to freeze on its surface. This frost gradually grows until it prevents the ambient air from flowing between the fins and transferring its heat to the refrigerant. The control unit monitors this condition and starts the defrosting process at appropriate intervals.
How is it possible that a heat pump can cool in the summer?
The control unit can reverse the direction of the coolant circulation, which starts the opposite process to heating. The coolant takes heat from the heating water, then travels to the compressor where it increases its temperature even more and the hot one is let into the evaporator, where it is cooled by the ambient air. Then, a sharp cooling takes place in the nozzle and the thus cooled coolant again takes heat from the heating water.
ECO vs CLASSIC (R290 vs R32)
We offer two types of pumps, the ECO series with modern refrigerant R290 and the CLASSIC series with refrigerant R32. The R290 refrigerant is currently the most environmentally friendly refrigerant on the market, if you were to leak the entire charge into the air, the carbon footprint is the same as driving 6 km by car (GWP parameter = 3). The R32 refrigerant is the second most environmentally friendly, the carbon footprint in the event of a leak would be equivalent to driving 3500 km by car (GWP = 675). For example, another available refrigerant R410 has a GWP = 2088.
However, ecology is only one factor. The modern refrigerant R290 has a better heat capacity and therefore does not require such high pressures in the system, which extends the life of the heat pump and allows it to operate up to an outlet water temperature of 70°C. In contrast, R32 has a slightly higher volumetric cooling capacity, which is why pumps with it are slightly more efficient.
From a chemical point of view, the refrigerant R290 is propane gas. Its disadvantage is flammability, which is not a problem in combination with a monoblock pump, since any leaks are only to the surrounding environment. The refrigerant R32 is difluoromethane, is non-flammable and has a slightly higher volumetric cooling capacity.
If your house has purely low-temperature heating, you can use the cheaper CLASSIC pump variant with R32 refrigerant or the slightly more expensive and more environmentally friendly ECO pump variant with R290 refrigerant. In the case of a heating system with a combination of underfloor heating and radiators, we definitely recommend only the ECO series for the possibility of higher outlet water temperatures.
