01 September 1988

Inverter-driven Heat Pumps Analysis of Heat Pump Units and Systems

Low efficiency and high costs for inverters have been historic obstacles to the introduction of continuous capacity control in small residential heat pumps. However the rapid development in electronics within the last decade has resulted in the introduction of inverter-driven heat pump air conditioners on the Japanese market in 1982. Advantages of these units are reduced energy consumption and improved comfort because of continuous operation. This situation was the basis for the HPC Project on “Inverter-Driven Heat Pumps for Hydronic Systems” approved by the Steering Committee in May 1986 in Paris. The objective of this analysis is to investigate the interaction of inverter-driven heat pumps with hydronic systems the seasonal performance factor, the share of heat consumption covered by the heat pump, and effects on the costs compares to systems presently available on the market. The tasks carried out in this analysis study are: the comparison of heat pump units without and with inverter by means of evaluation of performance characteristics of compressors (contributed by the Japanese industry and the Graz Institute of Thermal Engineering), investigation of sizing criteria of heat pump units, dimensioning of the main components, modes of integration into hydronic systems, and SPF (seasonal performance factor) modelling of hydronic heat pump systems. Results of this analysis are: In the case of systems with high balance temperature – bivalent systems – the unit without inverter is favourable in terms of SPF. In the case of systems with low balance temperature – for example monovalent systems – the unit with inverter is the better choice.

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