# Dimensioning of heat pump systems

Oct 26, 2020

The economic and environmental benefits of generating heat with heat pumps compared to fossil fuel systems are only significant if the systems have been carefully planned and installed, and then properly operated. In particular, the dimensioning of heat pump systems represents a bigger challenge. Errors are more serious than with traditional heating systems such as oil and gas heaters.

## Total heating demand and heating load

A misplaced heat distribution system degrades the efficiency of the heat pump and shortens its life. Errors are difficult to fix. For dimensioning of the heat pump power, it is therefore important to determine the total heating demand and the heating load of the building. The calculations must be carried out according to the latest valid standards in each country. In Germany, the DIN EN 12831 applies.

The specific heating demand per square meter of living space depends on the construction of the building

 Passive house 0.015 kW / m² New building according to ENEV 0.04 kW / m² New building with standard thermal insulation 0.06 kW / m² Renovated old building with or new building without thermal insulation 0.08 kW / m² Old building without thermal insulation 0.12 kW / m

The formula for calculating the heating demand of the building is:
Living space [m²] × specific heating demand [kW / m²] = building heating demand [kW]
Heating load: The heating load of a building is also calculated according to DIN 12831, but must not be confused with the total heating demand. The heating load of a building indicates the power a heating system must provide in order to reach the desired room temperature in freezing cold.

• Total heating demand = energy / consumption
• Heat load  = power of the heater

To determine the heating load, the climatic situation is taken into account and is included in the form of standard temperatures for the respective regions.

For example, for large parts of Bavaria these are -16°C. Towards the coast, where the winter becomes milder, the standard temperature drops to -10°C. The building materials or U-values ​​of a building are also included in the calculation, as is the building geometry.

Very often, a calculation of the heating load and the total heating demand is omitted and larger heat pumps can be chosen to allow for a safety margin. Not infrequently, the heat pump is then more than 50% larger than needed. This has a negative impact on the life span of the compressor. Particularly in the transitional period, i.e. in spring and autumn, a compressor that is too large leads to so-called "clocking", i.e. frequent but short running times - which causes faster wear and higher susceptibility to failure. If the power is too low, the electric heater often needs to heat directly. That consumes a lot of electricity.

## Certification provides accurate performance data

Even if the expected total demand of a building and, more importantly, the exact heating load required have been determined by an energy consultant, structural engineer or installer, inaccurate manufacturer information can still be a problem. Certification is then the only route to exclude this source of error and benefit from the greatest possible economic and ecological advantages of heat pumps. For example, the European Heat Pump certification from Eurovent Certita Certification guarantees that all products are tested according to the same procedure. The tests are performed by third parties under strictly defined, identical conditions. Thus, factory checks meet all requirements for competence, impartiality and independence.