A heat pump is one of the most efficient heating systems available on the market, provided that the system is properly matched to the building and operates in a relatively well-insulated property. Its heart is the compressor, which is responsible for the correct course of the entire heat extraction process. The efficiency, performance and reliability of the unit depend on the quality of this component. What exactly is a heat pump compressor and why does it play such an important role?
The compressor is a key component of the heat pump's refrigeration circuit. Without it, the heat pump would be useless for heating homes, because it is thanks to the compressor – and the process of compressing the refrigerant gas – that the heat pump can generate the temperatures needed to heat a house or domestic hot water.
As many people know, a refrigerant circulates inside the heat pump (that's its name, although it is actually responsible for transferring heat). We have certainly come across refrigerants many times, but usually under specific names – as there are various types, e.g. R134a, R410a or the recently very popular R32. This refrigerant initially extracts thermal energy from the so-called lower heat source, i.e. from the air (in the case of an air-to-water heat pump), from groundwater (in the case of a ground source heat pump), etc. However, this is not the end of the process, and there is still not enough thermal energy. For the heat pump to be sufficiently efficient to heat a house – this process needs to be further enhanced. And this is where the heat pump compressor comes in.
The task of the heat pump compressor is to compress the refrigerant which is in a gaseous state – that is, to squeeze and press it together (using both terms very loosely). The pressure increases, and as a result of the pressure increase, the temperature of the refrigerant also rises, making it possible to transfer thermal energy to the building's heating system. After leaving the compressor, the refrigerant is hot and can be directed to the condenser, where it releases heat to the water that heats the building.
Without a properly functioning compressor, the process of transferring heat from the lower source (air, ground or water) to the central heating system would be impossible.
The compressor's operation begins with it drawing in the refrigerant in the form of a gas at low pressure. The compressor then increases its pressure, causing a significant rise in temperature. The hot refrigerant goes to the condenser, where it releases heat to the heating system. The condenser is essentially a gas-to-water heat exchanger, where on one side we have the hot refrigerant and on the other side water, which absorbs thermal energy from it – in simpler terms, it heats up.
After releasing thermal energy in the condenser, the refrigerant passes through the expansion valve, lowering its pressure and temperature, and then returns to the evaporator, where the whole cycle begins anew. The cooled refrigerant can once again absorb energy from the lower source, only to return to the compressor again.
This is, in a simplified way, the entire operating cycle of a heat pump – in which the compressor plays a fundamental role.
The heat pump compressor is a device driven by an electric motor, which draws electrical energy and uses it to operate, compressing the refrigerant. Hence, it is worth pausing here for a moment.
As we know, heat pumps consume relatively large amounts of electricity, and they consume even more when operating at high temperatures. Heat pumps working in buildings with underfloor heating, which is supplied with a low temperature of around 28-35 degrees Celsius, consume relatively little power. They are energy-hungry, however, in the case of old houses – with old heating systems and old radiators requiring supply temperatures as high as 55-60 degrees – which often makes investing in a heat pump in such a house basically unprofitable, at least before replacing the heating system and carrying out thorough thermal modernization.
Why is this the case? Why does a heat pump work more efficiently and cheaply at low temperatures – and what does this have to do with the compressor? Well, when the heat pump operates at low temperatures, the compressor works for a shorter time, because the refrigerant reaches the required temperature more quickly during compression. It is easier and faster for the compressor to raise the refrigerant temperature to, say, 35 degrees than to 50 degrees Celsius. Therefore, compressors in low-temperature systems work for shorter periods and less intensively. And this translates directly into low energy consumption.
Incidentally, it is also worth noting another aspect. The compressor in a low-temperature heat pump system, as it works much less intensively, wears out much more slowly and the risk of potential failure is also much lower than in high-temperature systems. A heat pump – is essentially a device designed to work in low-temperature supply systems, in well-thermally-insulated buildings.
Modern heat pumps essentially use several types of compressors. The most popular are rotary, scroll and piston compressors.
Scroll compressors are particularly highly regarded due to their high efficiency, quiet operation and long service life. They are widely used in both domestic and commercial heat pump installations. Rotary compressors, on the other hand, are distinguished by their compact design and good energy efficiency.
More and more manufacturers are using inverter technology in heat pumps. This means that the compressor can smoothly adjust its power according to the building's current heat demand. The inverter ensures that the compressor does not only work in ON/OFF mode but modulates its operation.
Unlike traditional ON/OFF solutions, an inverter compressor does not have to constantly start up and shut down. As a result, it consumes less electricity, operates more quietly and has greater durability.
Despite their high durability, compressors can sometimes suffer damage. The most common causes of failure include incorrect installation, improper refrigerant charge, contaminants in the system and electrical supply problems.
Frequent start-stop cycles of the unit are also dangerous, at least from the perspective of long-term use. That is why it is so important to properly match the heat pump's capacity to the building's needs and to carry out regular servicing.
Regular maintenance can significantly extend the compressor's lifespan. It is advisable to carry out periodic technical inspections, monitor the unit's operating parameters and check the condition of the electrical installation. This is the basics.
Professional servicing can also verify the refrigerant level and detect any irregularities before they lead to an expensive breakdown. It is probably not worth doing this yourself, especially since most refrigerants in use require special certification.
The compressor is one of the most expensive components of a heat pump. The cost of its replacement depends on the type of unit, the manufacturer and the heating capacity. For domestic heat pumps, the price of a new compressor including installation can range from €700 to as much as €4,000.
For this reason, it is worth investing in equipment from reputable manufacturers and regularly servicing the installation to avoid premature wear of this key component.
To a large extent, yes. The efficiency of the compressor directly affects the COP and the seasonal efficiency SCOP of the entire unit. Modern inverter compressors allow very high performance parameters to be achieved while limiting electricity consumption.
When choosing a heat pump, it is worth paying attention not only to the unit's output but also to the type of compressor used. After all, it is this component that is responsible for the reliability, cost-effectiveness and comfort of using the heating system for many years.
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