A heat pump for an old building? It pays off much more often than you think!
In new builds, the heat pump has already arrived as a fossil-free and environmentally friendly alternative to gas and oil heating. According to the German Federal Statistical Office, heat pumps were already installed as the primary heating system in 50.6% of residential buildings completed in 2021. However, heat pumps will also play an increasingly important role in the energy modernization of old buildings thanks to new, efficient technologies. In this guide, we give you an overview of the state of the art and explain when retrofitting a heat pump in existing buildings makes economic and energy sense.
The requirements for a heat pump in an old building
It is not possible to make a general statement as to whether you can replace your old oil or gas heating system in an old building with a heat pump without further information. The decisive factor is not the age of your building, but the quality of the insulation of the windows, doors, facades and roof as well as the condition of the existing heating system. If the heating load is low, you can also heat your old building efficiently with a heat pump – ideally combined with a sensible renovation of the building envelope.
What are the advantages of heat pumps in old buildings?
- Heat pumps draw around three quarters of their energy from the environment. If the electricity for operating the compressor is also generated from renewable sources, e.g. via photovoltaics on the roof, you are investing in a climate-friendly, resource-saving heat source.
- A heat pump makes you independent of fossil fuels. A small bonus on the side: your heating system no longer produces any emissions through combustion and you save the costs for the chimney sweep.
- With a heat pump, you can make yourself independent of rising heating costs and prices for operating oil and gas heating systems.
- With a heat pump, you can rely on a future-proof heating system that meets all legal requirements with regard to the use of renewable energies as a heat source.
- The heat pump is not only good for the climate and the environment, it also sustainably increases the value of the property. This is because the use of a modern and energy-efficient heating system, ideally in combination with a solar system or solar thermal system, also improves the building's energy performance certificate.
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What flow temperatures does the heat pump need in an old building?
A field study by Freiburg-based Fraunhofer ISE, which was also supported by the ait Group, provided a surprising answer to this question: not as high as expected. according to the above-mentioned study, the maximum flow temperatures required for room heating in existing buildings averaged just under 44 degrees Celsius. The electricity consumption of the heating element, which ensures the heating output (measured in kWh) in extremely cold weather, was also negligible over the year. As the majority of heat pumps available on the market are designed for flow temperatures below 55 degrees Celsius, the chances are very good that you can retrofit a heat pump in your home.
The flow temperature, i.e. the temperature at which the heating water flows from the heat generator of the heating system into the radiators, is decisive for the efficiency of any heating system - depending on the heating system design. The lower the outside temperatures, the higher the flow temperature must be, i.e. the more energy is required to heat a building. In our latitudes, however, days with temperatures of minus 10 degrees Celsius and below are the exception rather than the rule.
Which radiators are suitable for heat pumps in old buildings?
Underfloor heating systems have larger surfaces for heat transfer, which means that the flow temperature required to heat the rooms is correspondingly lower. Underfloor heating systems, as well as wall and ceiling heating systems, are therefore ideal for the efficient operation of a heat pump. As they mainly emit heat via radiation, the room climate is usually perceived as particularly pleasant and the room temperature can be set lower.
Many existing buildings are already equipped with so-called panel radiators. They consist of several hollow elements arranged one behind the other, through which the heating water flows. In many cases, convection plates are arranged between them to increase the heating surfaces. As panel radiators also emit a large proportion of the heat energy via radiation, they are more efficient than classic finned radiators – provided they have been dimensioned accordingly – and can therefore be operated together with a heat pump in many cases.
Ribbed radiators, also known as sectional radiators, consist of several ribs through which heating water flows. They mainly heat the room air and only emit a small amount of radiant heat. To generate a comfortable room temperature, they require high flow temperatures of up to 70° Celsius and therefore more energy due to their small surface area.
Whether it is possible and economical to replace your old radiators with panel heating in an old building depends on your building and should be assessed by a heating engineer. In general, the market for radiators is extremely dynamic at the moment. Wall and ceiling heating systems are available as complete drywall systems with insulation and significantly increase heating efficiency. Special products with a low installation height are available for retrofitting underfloor heating. Alternatively, you can consider purchasing low-temperature radiators that have been specially developed for low flow temperatures and therefore for operation with heat pumps.
With a simple test, you can find out whether your existing radiators can be operated with a heat pump. On a very cold day, lower the flow temperature to 50 degrees Celsius. Depending on whether the heating output is sufficient, you should talk to your heating engineer about installing a heat pump with or without replacing the radiators.
Which heat pumps for old buildings?
The choice of the right heat pump for the renovation depends on the heating output, the efficiency expressed in the predicted seasonal performance factor and, last but not least, the available space. To install a brine/water heat pump or a groundwater heat pump, for example, the ground must be dug up. The installation of an air/water heat pump, on the other hand, is much less complicated and installation and transportation are possible with suitable heat pumps, even where space is limited.
If you are planning to renovate your old building in stages, hybrid heating is also an option. In this case, you use a heat pump to generate heat and hot water for most of the year and have your conventional oil or gas-fired heating system as a backup.
High-temperature heat pumps such as the Hybrox air/water heat pump from alpha innotec, which can be connected to the existing heating system, are now available especially for old buildings that are not optimally insulated. They can be operated with excellent efficiency at flow temperatures of 70 degrees Celsius and are designed for a heating output of up to 8 kW at low outside temperatures. They can also switch to active cooling mode if required. As they work with the natural refrigerant R290 (propane), they are both climate-friendly and powerful.