Last updated: 15.03.2023, 12:23 p.m.
By: Ulrike Hagen
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It is not suitable for apartment buildings, is noisy and only makes sense in new buildings. There are many prejudices circulating about the heat pump. An expert clarifies the biggest misconceptions.
Munich – Heat pumps are booming – they are considered the best alternative to heating systems based on fossil fuels and contribute to the independence of heating oil and natural gas, whose wholesale prices are currently falling. Nevertheless, there is hardly any other type of heating about which there are as many prejudices as heat pumps. At the same time, the systems are neither as noisy, as vulnerable or expensive as is often assumed. We spoke to an expert.
The Federal Minister for Economic Affairs and Climate Protection, Robert Habeck (Greens), wants to enforce a general ban on oil and gas heating from 2024. In the meantime, existing facilities are also in the Vice-Chancellor's sights. This is one of the reasons why heat pumps are becoming increasingly popular as a heating option. Nevertheless, persistent misconceptions about energy-efficient heating systems still persist. We spoke with Clemens Dankwerth from the Department of Heating and Cooling Technologies at the Fraunhofer Institute ISE in Freiburg.
Heat pumps are only suitable for new buildings
It is often claimed that heat pumps are only suitable for well-insulated new buildings. That's not true. "Heat pumps work best at low flow temperatures," explains Clemens Dankwerth. This makes them ideal for tailor-made installation in new buildings and is now used in more than half of all new residential buildings.
Nevertheless, heat pumps can also be installed very well in old existing buildings, for example in the course of a renovation or when replacing the old oil or gas heating system. "Studies by Fraunhofer ISE have shown that they achieve good energy efficiency even in rather poorly insulated old buildings. It only becomes inefficient from a flow temperature of over 50 degrees," says Dankwerth. The studies achieved an average annual performance factor of 3.1 for air-to-water heat pumps. This means that 3.1 kilowatt hours of heat were emitted with every kilowatt hour of electricity.
It is not suitable for apartment buildings, is noisy and only makes sense in new buildings. There are many prejudices circulating about the heat pump. (Symbolic image) © Robert Poorten/imago
Heat pumps are noisy
Air-to-water heat pumps use fans to draw in and blow out air, which creates flow noise. The compressor can also emit an audible hum caused by the vibration of the heat pump. However, modern heat pumps are very quiet and have a sound power of less than 30 dB. This means that they are whisper-quiet in the truest sense of the word. For comparison, 30 dB corresponds to the volume of whispers, 40 dB to the volume of refrigerators.
"But acoustics are always a subjective perception," says air conditioning expert Dankwerth. "That's why it makes sense to additionally avoid noise development at certain levers – for example, by keeping a sufficient distance from walls and neighbours, with vibration dampers and soundproof hoods."
Heat pumps are expensive
"Although heat pumps seem more expensive to buy at first glance, their investment is worthwhile in the long run," says Clemens Dankwerth. Not only are heat pumps supported by government subsidies, which compensate for part of the difference in investment costs. More good news for consumers: "Compared to other heating systems, heat pumps also have by far the lowest operating costs." In the case of an average-sized single-family home, between 10,6 and 000,12 euros in running costs can be saved within 000 years – of course depending on the development of gas and electricity prices.
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Heat pumps are power guzzlers
It is true that a heat pump needs electricity to function. However, the actual power consumption is much lower than often assumed. Modern and efficient heat pumps require only about 20 percent of the electricity generated compared to the heat output generated. In other words, to generate 100 percent heat, a heat pump requires only a fraction of the electricity. "The heat pump is practically unbeatable in terms of energy balance," says Felix Doucet from the Competence Center for Renewable Energies and Energy Efficiency at the University of Applied Sciences in Hamburg. His study, which compared heating with heat pumps and hydrogen, also came to a clear conclusion.
If you have your own photovoltaic system, you can even operate the heat pump with your own green electricity.
You might also be interested in: Heat pump shortage: These manufacturers are now delivering the fastest
Heat pumps are not suitable for apartment buildings
It is a misconception that heat pumps can only be used in detached or semi-detached houses. Although they are often used in these buildings, they only cover 59 percent of the total living space in Germany. In order to achieve actual CO₂ neutrality, the other 41 percent of the living space in apartment buildings must also be ecologically heated, "which require much larger amounts of energy for heating than individual houses," says Clemens Dankwerth.
The international research project LowEx Bestand, in which the scientist was involved, has therefore developed various solutions for how heat pumps can be used sensibly in apartment buildings. For example, centralised heat pump systems for the entire building, a combination of centralised and decentralised supply, heat pumps for one residential unit or for several residential units, as well as heat pumps for individual apartments or even individual rooms are possible.
At sub-zero temperatures, heat pumps only provide enough heat as hybrid heating
Modern heat pumps are capable of supplying a house with sufficient heat on its own, and certain models are able to supply it with sufficient heat even at low outside temperatures down to minus 29 degrees. But of course, heat pumps can also be used in hybrid combinations to provide additional support during particularly cold periods. "A common method is to combine heat pumps with heating elements that are only used during peak loads," explains Dankwerth. "For the maybe 50 hours a year at minus 15 degrees outside temperature, the heating element is then switched on."
Heat pumps only work with underfloor heating
It is a persistent misconception that heat pumps are only suitable for buildings with underfloor heating. "In fact, heat pumps are compatible with underfloor heating systems as well as with almost any radiator, whereby a large surface area is an advantage," says Clemens Dankwerth. "An exception are massive radiators, which require flow temperatures of 60 or 70 degrees." Practically every house can therefore be equipped with a heat pump or retrofitted during a renovation.
Heat pumps take up a lot of space
On the contrary, instead of taking up a lot of space, heat pumps are a space-saving solution. In contrast to an oil burner or a gas boiler, they can also be installed outside the home. When selecting the size of the heat pump, the previous oil or gas consumption is taken into account, among other things, as these values can be used to determine the actual heating energy required.
Heat pumps can only heat
Heat pumps are real all-rounders. In addition to providing heating and hot water, they can also be used to cool the room in an energy-efficient way – either actively or passively. In this case, the heat pump circuit is reversed, as in the refrigerator. Expert Dankwerth advises: "For cooling, care should be taken not to fall below the dew point so that no moisture settles on floors or radiators. However, a flow temperature of at least 20 degrees ensures this."
Heat pumps have a short lifespan
A heat pump is made up of many different components, some of which have a higher life expectancy and some of which have a lower life expectancy. A sensitive part is the compressor, which is said to need to be replaced after only 10 years. In fact, however, with regular maintenance, a compressor can last about 50,000 hours of operation, which corresponds to a service life of 25 to 30 years.
However, there are differences between heat pumps, which draw most of the energy for heating from the ambient air, and geothermal heat pumps. "Compressor manufacturers now assume a service life of about 20 years," says Dankwerth, "but the geothermal appliances last longer because they are subjected to constant temperatures in the ground that are 10 degrees less stressed than air source heat pumps."