How a heat pump works and what it consists of

How a heat pump works and what it consists of

The operation of a heat pump is based on two physical processes. First, when a substance evaporates, it absorbs heat; when it condenses, it releases heat. Second, the evaporation temperature of a substance rises as pressure increases.

To understand how a heat pump transfers heat to a home heating system, it is useful to look at its main circuits and components: the external circuit, evaporator, compressor, condenser and expansion valve.

What circuits does a heat pump system include?

A heat pump system consists of an external circuit that collects heat from the environment and an internal circuit that transfers this heat to the home heating system.

• External circuit: transfers heat from the ground, water or air to an antifreeze liquid — brine. It usually consists of pipework and a circulation pump.
• Internal circuit: transfers the collected heat energy to the heating system, domestic hot water system or another heat consumer inside the house.

How does a heat pump work?

A heat pump works in a closed cycle: the brine collects low-grade heat from the environment, the refrigerant absorbs this heat in the evaporator, the compressor raises its temperature, and the condenser transfers the heat to the heating system.

• As the antifreeze mixture — brine — flows through the pipes of the external circuit, it is heated to approximately 1–10 °C.
• In the evaporator, the brine transfers the collected heat energy to the internal refrigerant circuit.
• The refrigerant has a low boiling point, so in the evaporator it absorbs heat from the brine and changes from liquid to gas.
• The gaseous refrigerant enters the compressor. There it is compressed, its pressure rises, and its temperature rises together with the pressure.
• The hot refrigerant enters the condenser, where it transfers heat to the heating system. After that, it cools down and returns to a liquid state.
• The expansion valve lowers the refrigerant pressure before it returns to the evaporator. Then the cycle repeats.

What does the compressor do in a heat pump?

The compressor is one of the key components of a heat pump. It compresses the gaseous refrigerant, increases its pressure and temperature, and makes it possible to transfer heat to the home heating system.

Most of the electricity consumed by a heat pump is used to operate the compressor and circulation pumps. At the same time, a large share of the heat delivered to the house comes not from the electrical grid, but from the surrounding environment.

What does the COP of a heat pump mean?

COP, or coefficient of performance, shows how efficiently a heat pump operates. It describes the ratio between the electricity consumed by the system and the amount of heat energy delivered to the heating system.

If the COP is 3, it means that for every 1 kW of electricity consumed, the heat pump can deliver approximately 3 kW of heat energy. Under favorable conditions, this value may be higher and reach 4–5 or more.

The COP depends on the heat source temperature, the heating system temperature, compressor operating mode, installation quality and correct equipment selection. The smaller the temperature difference between the heat source and the heating system, the more efficiently the heat pump works.

Why is a heat pump considered an energy-efficient heating system?

A heat pump is energy-efficient because electricity is used mainly to run the compressor and pumps, while most of the heat comes from the ground, water or air. This allows the system to deliver more heat energy than the electrical energy it consumes.

Compared with many conventional heat generators, a heat pump can provide lower operating costs, especially in a well-insulated house with a low-temperature heating system, such as underfloor heating.

The efficiency of a heat pump depends not only on the equipment itself, but also on the heat loss of the house, the heating temperature regime, the heat source and the quality of the overall system design.

Conclusion

A heat pump is a system that transfers heat from the environment into a house using an external circuit, evaporator, compressor, condenser and expansion valve. Its efficiency depends not only on the equipment, but also on proper calculation, installation and operating conditions.

Read more articles about heat pumps.