Does heat pumps perform energy efficiently as we expected: Field tests and evaluations on various kinds of heat pump systems for space heating

•A unified method is raised to analyze the practical performance of 32 heat pump systems for space heating with different heat sources.•Over-sized capacity design, over centralized system design, unreasonable control strategy and lack of maintaining are found universally existed in the investigated systems.•Decentralized and reasonable system design, accurate and efficient control strategies are suggested. This paper introduces continuously field test results on operational energy performance of 32 heat pump systems for space heating with various heat sources in cold region of China. Therefore, normalized energy performance index for the holistic heat pump based space heating system including compressor electricity use, circulating pumps energy use for both heat source and heat sink, were introduced to evaluate and compare between different systems or different control strategies. Results showed that over-sized heat pump capacity design and install declined heat pumps efficiency during whole heating season especially in partial load regime, and solo heat pump station with large heating distribution networks led to dramatic heat loss and hydraulic unbalance problems. In addition, complicated control strategy for both heat pumps and circulating pumps did not performed properly according to building heat demand fluctuating and heat source temperature variation during whole winter. The paper disclosed clearly that optimized design and operation of the holistic heat pump based space heating systems during the heating season are essential to ensure the actual energy performance for any kinds of heat pumps rather than believing in theoretical assumption.