Residential heat pumps in Europe are heating-only devices, most commonly integrated into hydronic systems. To simplify integration and to improve the SPF, a research project on inverter-driven heat pumps is ongoing in Graz.

With inverter-driven heat pumps, cycling losses as well as mixing losses caused by the mismatch of heat pump outlet temperatures and necessary supply temperatures can be reduced. However, additional losses occur, caused by the inverter, particularly at low speeds, and by the compressor at high speeds. SPF modeling based on measured performance characteristics of heat pumps has shown that, in case of monovalent operation, units with inverter are preferable: Cycling and mixing losses can be reduced remarkably; predominant operation is at moderate speed, maximum speed is needed for peak load only. Further advantages are that the components of the unit become smaller and that integration into hydronic systems is simplified.

Units: Dual