Experimental performance study of ground-coupled heat pump system for cooling and heating provision in karst region

As a renewable energy technology, the ground-coupled heat pump (GCHP) system is gaining more and more world-wide attentions due to its advantages of energy efficiency and environmental friendliness. However, experimental studies on the GCHP system are still insufficient. In order to investigate the practical performance of GCHP system, the detailed on-site experiments were applied on a GCHP test rig located in a karst region of China. Operation parameters recorded during tests mainly include the temperature distributions of borehole at different depths, the temperature, pressure and flow rate of water circulating in the heat pump as well as the GHEs, the power consumption of the heat pump as well as circulating pumps. Consequently, the GCHP system for both cooling and heating provision was investigated by using three different operation modes -- mode I (i.e. intermittent mode A), mode II (i.e. intermittent mode B) and mode III (i.e. continuous mode). Experimental results indicated that the performance of GCHP system was affected by its operation conditions and modes. Moreover, heat and cold accumulation in the ground during cooling and heating provision of the GCHP system was analyzed. The results show that the average values of COPsys for cooling and heating provision are 3.12 and 2.24, which can meet the space heating and cooling requirements of a small detached laboratory room in karst region. It is also found that the intermittent mode operation is beneficial to improving the performance of GCHP system with the fact that the COPsys increases by 23.0% when Prr (the proportion of recovery time and running time) increases from 0 to 2. The COPsys of GCHP for cooling provision is 28.6% higher than which for heating provision for the reason that the cold accumulation in ground around GHEs for heating provision is more than heating accumulation in cooling provision.