Simple index for onsite operation management of ground source heat pump systems in cooling-dominant regions

• Published in: Renewable energy Vol. 127; pp. 182 - 194
• Main Authors: Kindaichi, Sayaka, Nishina, Daisaku
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2018
• Subjects: Borehole-type ground heat exchangers; Cooling-dominant regions; Ground source heat pump systems; Operational management; Variable temperature penalty; Operational management; Borehole-type ground heat exchangers; Ground source heat pump systems; Variable temperature penalty; Cooling-dominant regions
• ISSN: 0960-1481; 1879-0682
• DOI: 10.1016/j.renene.2018.04.065

In ground source heat pump (GSHP) systems, large imbalances between cooling and heating loads cause a rise or decline in ground temperature because of thermal interference between multiple ground heat exchangers (GHEs). To evaluate annual changes in ground temperature, we applied a variable temperature penalty, which was simply obtained using measured data without computer simulation. First, we examined measured data for 3 years after completion of a hybrid GSHP system that had 70 borehole-type GHEs, combined with an air source heat pump unit. In the hybrid system, the GSHP showed high efficiency (coefficient of performance > 5.0) throughout the year and had a variable contribution between years with regard to cooling/heating output and time of operation. The amount of heat rejected to the ground by cooling reached ∼4.8 times that of heat extracted from the ground by heating after 3 years of operation. This imbalance produced ground temperature increases of ∼3 °C in an internal borehole. The variable temperature penalty reproduced the measured temperature increase, suggesting that the index is appropriate for assessing long-term ground temperature changes in the operation phase. This simple index allows operational improvement onsite and will aid the sustainable operation of GSHP systems in cooling-dominant regions. •System performance of a GSHP with much greater cooling than heating is reported.•Hybrid use of GSHP and ASHP can be a solution in cooling-dominant regions.•A GSHP with 70 boreholes showed excellent COP >5 over years.•Seasonal thermal imbalance resulted in a ground temperature increase of 2.9 °C.•A simple index based on temperature penalty is applied for sustainable operation.