Heat exchange: How to heat heat pumps optimally

In the future, several million heat pumps will be installed in Germany – as a climate-friendly replacement for oil and gas heat. For the heat generator to work properly, homeowners need to consider a few things when switching. Otherwise there is a risk of high electricity costs.

It shows the information program Zukunft Altbau funded by the Ministry of the Environment of Baden-Württemberg. Large radiators or surface heat and a building shell with low heat loss are particularly important. Experts should also carry out a hydraulic balancing of the heating system so that the heat is evenly distributed to all radiators. If the housing is not suitable enough for the sole operation of a heat pump, the existing fossil boiler can be combined with a heat pump. However, it only makes sense for a transitional period until the building has been energetically renovated.

Heat pumps are a climate-friendly and future-proof alternative to oil and gas heating. They use geothermal energy, groundwater or ambient air as a heat source. Using electricity, the appliances raise the environmental energy to a higher temperature level and thus provide heat for heating and hot water. The electricity from the grid is increasingly coming from wind energy and solar cell systems – by 2030, the share of green electricity must be 80 percent. It makes the technology more and more climate friendly year after year. There are three types of heat pumps: ground, groundwater and air source heat pumps.

The energy level of the house is important for economical operation

Appropriate framework conditions are particularly important for the efficient operation of heat pumps. “This includes above all the energetic state of the house,” says Frank Hettler of Zukunft Altbau. “Adequate insulation of the external components reduces the building’s heat loss and thus the required temperature level in the heating system.” This is crucial for heat pumps: In order for energy-saving heating to take place, the temperature difference between the environmental energy source and the heating system must be as small as possible. Heat pumps require so little power for heating. Therefore, the location of the building, in addition to the type of heat pump and the energetic condition of the house, is also important. For example, if you live in the warmer Rhindal, it is easier to cope with an air source heat pump than someone in the upper Black Forest.

The flow temperature of the heater is particularly important. This corresponds to the temperature of the heating water when it leaves the heat pump before it is pumped to the radiators. It should be at most in the range of 55 degrees Celsius, better below. “Therefore, there is often no way around renovation measures for individual poorly insulated parts of the building,” explains Dr. Martin Pehnt from the Department of Energy and Environmental Research Heidelberg (ifeu). “Anyone who has a heat pump installed should not only use an improved climate screen, but also large heating surfaces such as underfloor heating, wall or ceiling heating.” These heating surfaces usually cope with flow temperatures below 40 degrees Celsius. However, conventional large area radiators are also possible.

Hydraulic balancing contributes to efficient heating

Careful specialist planning, including good integration into the heating system, is also important for efficient operation. Among other things, a hydraulic balancing of the heating is required. It should certainly be determined using calculation method B. Experts use this method to calculate the exact heat load for each room and each radiator. With the result, the heating system can be optimized and the precise performance requirements for the heat pump can be clarified. This enables a particularly efficient and cost-saving operation.

If you own a house, you can read the actual efficiency of the heat pump based on the annual performance factor (SPF). JAZ describes the relationship between the amount of heat generated and the electricity consumed. It should not fall below a certain value. The number can be calculated as follows: First, measure the amount of heat given off by the heat pump with a heat meter. If there is no meter in the heat pump, it must be installed during installation. A meter is mandatory for state-subsidized heat pumps anyway.

Then you determine the heat pump’s power consumption including operating current and any direct heater. The value can be read on the electricity meter for the heat pump. When the power consumption and the amount of heat are registered, the generated kilowatt hours of heat are divided by the consumed kilowatt hours or the like. To determine a meaningful value, one should use an entire year as a period. With a good air source heat pump, JAZ should reach a value of around 3.5. With good groundwater heat pumps and geothermal heat pumps, the value can also be 4.5 and above.

Hybrid heat pumps: plan B for houses to catch up

If you want to heat more climate-friendly with heat pumps in the future, but have not yet insulated the climate screen in your house sufficiently, you can combine the existing oil or gas heating with a heat pump. Experts are talking about hybrid heat pumps. The majority of the heat demand is covered by the heat pump, the peak load proportion for particularly cold winter days with oil or gas. Alternatively, there are new hybrid systems completely ex works.

If e.g. basement ceiling and roof or facade are later insulated, allowing the heating system’s lower flow temperatures so exclusive operation of a heat pump. This is climate friendly and makes you completely independent of fossil fuels.

The appropriations for heat pumps are high

Buying heat pumps is not cheap. However, the state subsidy reduces these costs enormously: If, for example, you install a heat pump when replacing an oil boiler and at the same time show supported building energy advice, the state reimburses up to 50 percent of the investment costs.

Source: Future Altbau

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