Final report of the "OptiPower" research study - Swiss Building Simulation Association

The oversizing of heating and cooling systems is a well-known problem among experts, but there has been no comprehensive study of this in Switzerland to date.

The SPF Institute for Solar Technology and the IET Institute for Energy Technology at OST - Ostschweizer Fachhochschule have now analysed over 500 apartment blocks and ten office buildings with regard to the oversizing of their heating and cooling systems. The comprehensive study shows:

The oversizing of heat and cooling generators, which is assumed in practice, was confirmed. For residential buildings, the median is +40% and for administrative buildings between +100% and +300%. There is a need for action in both types of building, but it is very high in administrative buildings.

Oversizing can be reduced in residential buildings with a simple plausibility check method developed in the project during the planning phase. For administrative buildings, the application of the new standard SIA 380/2:2022 (Dynamic building simulation) is recommended. The additional costs of overdimensioning exceed the additional costs of a dynamic building simulation many times over.

Oversizing does not necessarily have to impair the efficiency of the system operation; the efficiency of brine-to-water heat pumps can also increase. However, these increases in efficiency are accompanied by high additional costs, meaning that oversizing is still not recommended.

The advantages of inverter control in particular can be counteracted by oversizing. This is particularly critical for air-to-water heat pumps, which have a steeper performance curve. Therefore, especially in these cases, the heat pump should be designed carefully and rather tightly so that the advantages of inverter control can be realised.

These and other results can be found in the final report of the project, which can be accessed via the following link: Downloads

SPF was involved in the project: Igor Bosshard, Krisztina Kelevitz, Marcel Troxler and Amina Guliyeva.