Long-term operation analysis of a ground source heat pump with an air source heat pump as an auxiliary heat source in a warm region

Abstract

With the urgent need to achieve carbon neutrality, there are growing expectations for ground source heat pump (GSHP) systems. This study analyzed the long-term operational performance of a GSHP in combination with a modular-type ground source heat pump (ASHP) installed at a university in a warmer region of Japan. As results, in warmer regions, as the cooling load tends to be greater than the heating load and the electrical consumption heat from the GSHP is added to the rejection heat to the ground, the ground heat balance is more likely to be unbalanced than it would be in colder regions. Predominant rejection into the ground for extraction from the ground resulted in an increase in ground temperature and a decrease in the SCOP of the GSHP during cooling periods. However, a decrease in the cooling load in one season considerably reduced the ground temperature during cooling in the following season. Because the module-type ASHP was able to quickly control its thermal output, it unexpectedly reacted HVAC load fluctuations before the GSHP output control. This lowered the load factor of the GSHP and caused the ASHP to start and stop repeatedly at extremely low loads.