Conversion of the heating: heat pump also possible without renovation


Status: 11/21/2022 7:21 p.m

Heat pumps are considered the heating technology of the future. Many owners of older houses believe that a costly renovation is necessary before installation. But it does not have to be like this.

Heat pumps are made for the energy transition. Since they are electrically operated, they can use the clean electricity from wind turbines and solar panels. They are also extremely efficient: while a modern gas boiler produces 0.9 kilowatt hours of heat from one kilowatt hour of gas, the heat pump produces three to four times the amount of heat from one kilowatt of electricity. This makes it superior to any other heater. These are the Federal Government’s reasons why the heat pump should become the new number one heating system in Germany.

However, quite a few doubt their suitability for older, unrenovated houses, which still make up the majority of buildings in Germany. Energy consultants in particular therefore recommend extensive insulation of the roof and outer walls – as well as underfloor heating – before installing a heat pump in an existing building. Measures that are useful, but also very expensive. The question is therefore whether such a refurbishment is absolutely necessary for older houses, because otherwise the electricity costs for the heat pump could get out of control later.

Study for use in older houses

Or is it possible without renovation? To clarify this, scientists at the Fraunhofer Institute ISE in Freiburg carried out a field study to examine the efficiency of heat pumps in existing buildings. Extensive measuring electronics were installed in 41 older houses with heat pumps throughout Germany and all consumption values ​​were continuously recorded over a year. Marek Miara, the head of the study, summarizes the result as follows:

We have definitely found out that it works. That you can also heat old, non-refurbished buildings with heat pumps. That buildings with radiators and not necessarily with underfloor heating are also suitable for heat pumps and that prices and costs do not explode if the heat pump is not running perfectly.

Even if some of the air-water heat pumps examined in the study were quite old, they achieved an average efficiency of 3.1 over the year. This means that the heat pumps generate an average of 3 kilowatts of heat from one kilowatt of electricity. For geothermal heat pumps, the value was even 4.1.

It turned out that the age of the houses played only a minor role. Heat consumption and the radiator situation in the house were much more important. Even buildings that are 40 years old or older do not necessarily have a high heat consumption. Much more revealing is a look at the last annual heating bill, where the heat consumption is noted exactly.

Underfloor heating is not a must

Underfloor heating is also not a must for a heat pump, because in older houses the radiators used to be installed very generously – often under every window and oversized. The heat pump benefits from this situation, because it needs a large surface area of ​​heating elements so that it can also be operated at low temperatures in an energy-saving manner. New underfloor heating is therefore often not necessary. In case of doubt, the heating installer can calculate the radiators and check whether they are sufficient or whether individual ones may have to be replaced with larger ones.

Nevertheless, the heat pump expert Miara sees a limit to the installation of heat pumps in existing buildings: For houses that have an individual heating consumption of more than 150 kWh per square meter and year, one should first think about thermal renovation, even if a modern heat pump heats such houses sufficiently would. Irrespective of whether you heat with oil, gas or electricity, the heat consumption, which is clearly too high, should definitely be reduced. Otherwise, the expensive energy is literally thrown out the window.

How the individual heating consumption is calculated

The annual heating cost calculation can be used to determine how good the building’s own heat consumption is. The total heat consumption is given there. In order to be able to compare the individual heat consumption (in kilowatt hours) with other houses, it must be related to the heated area of ​​the house. The efficiency of the heating system and hot water consumption also play a role. Example: A house in which two people live on 130 square meters of living space uses around 2000 liters of oil a year. These 2000 liters correspond to approximately 20,000 kWh.

1. Consider the efficiency of the heater: Due to the efficiency of the oil heating (0.7), only part of the energy in the oil is used for heating, therefore: 20,000 KWh times 0.7 = 14,000 KWh. Installers calculate with an efficiency of 0.9 for gas heating systems.
2. Subtract hot water consumption: In order to determine the pure heating consumption, the consumption for hot water must be subtracted. That is about 1000 kWh per person and year. So 14,000 KWh minus 2000 KWh = 12,000 KWh
3. the heated living space determine: Since 10 square meters of basement are not heated in the example house, these must be deducted from the total living area. So 130 square meters minus 10 = 120 square meters
4. Relate the heat consumption to the heated area. 12,000 kWh divided by 120 square meters = 100 kWh per square meter per year. This is the individual heat consumption.

Well insulated new apartments are below 50 kWh per square meter and year. A high consumption can be 200 or more.

Simple test for possible heat pump

With a very simple test, everyone can try out for themselves whether their own house can also be heated with a heat pump without renovation: On very cold winter days, you should gradually lower the operating temperature in the heating settings and observe the temperature in the rooms.

If the rooms are still warm enough with a flow temperature of 55 degrees or less, you can usually switch to a heat pump without renovation. If not, you should seek advice. A lot can usually be achieved with just a few renovation measures, such as replacing individual radiators or old windows.

Conclusion: Thermal renovation is always better, no matter which heating system you have, because it saves energy. Nevertheless, it is not a mandatory requirement for installing a heat pump in older houses.

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