15 September 2011


The popularity of air/water heat pumps (A/W-HPs) has continually increased as a common heating system in residential buildings. However, the potential for improvements in efficiency remains large. Theoretical and experimental analyses indicate that the exergetic efficiency of common A/W-HPs operating in an on/off control mode becomes smaller as the ambient temperature increases. A substantial increase in efficiency requires the adaption of the generated heating capacity to the required one using an appropriate continuous power control of the compressor and the fan. In this contribution, universally valid design and
planning criteria for the realisation of efficient and economic A/W-HPs with continuous capacity control are presented. The optimal control strategy and the achievable efficiency strongly depend upon the part load characteristics of the compressor and the fan. Experiments with a prototype confirm the great potential of such capacity control. The seasonal performance factor (SPF) can be increased by approximately 10% to 60%
compared to on/off operation. The application of these design guidelines and this control strategy can significantly reduce the primary energy consumption and the associated CO2
emissions of A/W-HPs as well as the operating costs.