Experimental Performance Estimations of Horizontal Ground Heat Exchangers for GSHP System

摘要

Horizontal ground heat exchanger in ground source heat pump systems is susceptible to ground surface variations thus affecting its thermal performance. However, this configuration is desirable due to low installation costs as it mainly involved burying pipes in shallow trenches. In this study, experimental investigation of thermal performance for slinky horizontal ground heat exchangers (GHEs) in several operation conditions were conducted. The slinky type horizontal ground heat exchangers (HGHEs) in two orientations were considered such as reclined (parallel to ground surface) and standing (perpendicular to ground surface). Copper tube with outer surface coated using low-density polyethylene was considered for GHEs pipes. The GHEs were buried in 1.5 m depth of the ground. Ground temperature distribution was monitored up-to 10 m depth by placing T-type thermocouples at different depth position. During the operation, performance of GHEs decreases with operation time because of ground temperature was reaching to the circulated water temperature. From the test results, the higher heat exchange rate of the standing GHE than reclined GHE is due to the greater amount of backfilled sand which has higher thermal conductivity than site soil. The dominating parameter for the performance difference between two GHEs was backfilled sand conductivity. The average heat transfer rate increased about 21.7% for standing GHE and 17.5% for reclined GHE when flow rate increases from 1 l/min to 2 l/min. The results also indicate that the seasonal change of the surrounding ground temperature of GHE has a significant effect on the overall performance of GHE. The ground temperatures very close to the ground surface is highly affected by ambient temperature and fluctuate strongly. Ground temperature fluctuation decreases with increase in depth and below a certain depth (5 m) remains relatively constant, 18 °C at 10 m depth for example.