Experimental Study of Heat Extraction and Soil Recovery During Space Heating Application Using Ground Source Heat Pump System

The present research paper reports experimental results on the coupled phenomena of heat extraction and heat recovery by a double U-tube borehole heat exchanger (BHE) and its thermal performance for space heating application using a ground source heat pump (GSHP) system. Experiments were performed on a 5-ton cooling capacity GSHP system installed at Roorkee located in the northern part of India, during peak and moderate winter seasons. The heat interaction by the GSHP system with the ground is achieved by five double U-tube BHEs and one single U-tube BHE of 120 m depth each. Experimental trials were conducted for parallel and series flow of heat transfer fluid (water) in the BHE. Temperature of water and power consumption by the GSHP was monitored continuously during heat extraction for 12 h and heat recovery of soil as well. For the peak winter season, during heat extraction, a 5 °C temperature rise was observed in BHE water for series connection, which is about 10% higher than that of the parallel case. Maximum heat extraction of 14.8 kW was obtained for the series connection, which is 20% higher than the parallel one, thus resulting in a 20% higher value of the overall coefficient of performance (COP) of the system for series mode compared to the parallel mode operation during the peak winter season. However, the ground near the BHE has taken lesser time for heat recovery in parallel mode compared to the series mode.