Operation performance test and energy efficiency analysis of ground-source heat pump systems

The improper operation of a ground source heat pump (GSHP) system is a significant cause of poor energy efficiency. Despite the increasing popularity of GSHP systems in China, few field test has been conducted on the operation of GSHP systems in the southwest and western regions of the country, and there is a lack of comprehensive comparative study. This study tested the operation performance of 26 GSHP systems in Sichuan, Chongqing, and Shaanxi under typical operation conditions. The performances indexes of the systems were calculated and investigated, including the coefficients of performance of the heat pump and system, water transfer factor of the water pump, and energy efficiency ratio of the system. These parameters were then compared and analyzed based on existing literature and relevant domestic standards concerning energy efficiency. Accordingly, suggestions were proposed for improving the operation performance of GSHP systems from the aspects of system design, construction, and operation. Results show that the average coefficient of performance (COP) of the tested systems was less than 3.0 under heating conditions, which did not meet the requirements for energy-saving operation stipulated by the national standard and fail to achieve the initial intention of saving energy in buildings by using GSHP systems. Based on the analysis, typical problems were diagnosed in GSHP systems. Specifically, the heat pumps usually operate in part-load conditions and at low efficiency for a long time; the transfer and distribution systems operate with small temperature differences and large flows; and the settings of room temperatures tend to be unreasonable. In view of the operation performance, ground-coupled heat pump (GCHP) systems are recommended for use in the western regions of China.