Heat pumps heat the house (or apartment) in a climate-friendly manner without gas or fuel oil. You only need electricity for the pump operation. The heat comes from the ground or from the air. Even at sub-zero temperatures.

But how does a heat pump actually work? Often read: like a refrigerator. Or: vice versa like a refrigerator. In fact that is true. But how does it work? the actually?

How is a heat pump constructed?

You may have noticed that a refrigerator heats up at the back as the food inside cools. Very warm even. Simply put, it pulls the heat out of the fridge to make it cooler inside. It then conducts the heat outside and dissipates it on the back. A heat pump works in the same way, but consists of two parts: outside the house it absorbs heat from the environment, inside the house it returns the heat to the heating system.

Does the principle and the image above remind you of anything? If you now say, “Air conditioning!”, you are not wrong. Split air conditioners also consist of two parts and they dissipate heat from the inside to the outside. However, the principle can also be reversed, so that you can heat with it even in winter – like with a heat pump. Real However, heat pumps are significantly more efficient heating systems than air conditioning systems.

There are different types of heat pumps. With air-water heat pumps, there is usually a container in the garden. The part of the heat pump that is outside the house can also be underground.

Pipes conduct the heat from the outside into the boiler room. This is where the second part of the heat pump is located, which returns the heat to the heating system.

The existing heating then distributes the heat as usual via the heating pipes in the walls to the radiators in the respective rooms.

How does a heat pump work?

A refrigerator works with a coolant that is in a closed circuit. Heat is added and removed by compression and condensation. I explained this in detail in the article Why it gets warmer in the room when the fridge door is open.

The refrigerator extracts heat from the inside to release it outside. The heat pump works in reverse: it extracts heat from the ground or the outside air to heat the house or apartment inside.

A refrigerant evaporates in the outdoor section of the heat pump. During this process, it absorbs heat – from the ground or from the air. So the coolant heats up. A compressor then compresses the vapor, making it even hotter. The refrigerant has such a low evaporation point that this also happens at very low temperatures.

The steam condenses in the house, making it liquid again. This process releases heat that heats the water in the stove via a heat exchanger, which then circulates throughout the house.

A choke is required as the fourth element in the circuit. This is usually an expansion valve. There, the refrigerant evaporates again and cools down so much that it can absorb heat again outside.

What temperatures does a heat pump generate?

The structure of the house determines how much to heat the water in the boiler room:

1. How well is the house insulated? – So: how much heat does it lose?
2. What is the surface of the radiators? – So: how well can the heating transfer heat to the room air?

A well-insulated house with extensive underfloor heating only requires a low supply temperature. This is what is called the temperature of the water flowing through the pipes and radiators.

Therefore, in many new buildings, a low-temperature heating system is installed, which only heats the water to heat the rooms to 30 degrees. The large area of ​​underfloor heating is sufficient to heat the rooms even at such low temperatures.

For a normally insulated apartment, where part of the heat is permanently lost through windows and only moderately insulating walls, the water in the stove is heated to 40-50 degrees. A heat pump can do that too, but with a higher electricity consumption, so with more costs.

In an uninsulated old building, which still contains old convectors and radiators, 65 degrees may also be necessary. It is more expensive, but in principle doable. Modern heat pumps can certainly heat lukewarm water up to 70 degrees.

Conclusion: Heat pumps also heat old buildings

A heat pump and a refrigerator work on the same principle. So the comparison is correct. Yet the difference is large, because installing a heat pump requires an existing home to be adapted in several places.

Both inside and outside must be part of the heat pump installed shall. In addition, these must be connected to each other with pipes so that a cycle is created.

The heat pump works climate-friendly and at low cost, best in a well-insulated house. However, highly efficient heat pumps can also generate temperatures to heat a poorly insulated old building. However, then the benefits for the environment and the wallet diminish.