Thermal performance of water‐based brines as a heat carrier for ground heat exchanger under severely cold environments

The aim of the present study is to investigate the performance of water-based brine solutions in the ground heat exchanger (GHX) for space heating applications under severely cold climate conditions. The conventional ethylene glycol (EG) and propylene glycol (PG)-based water solutions have been considered for investigation. For the closed-loop vertical U-tube GHX, a mathematically built model is developed for ambient temperature below 0 degrees C. The thermal performance analysis of GHX is carried out for the variation in fluid flow rate and brine solutions for different mixture percentages of water in EG and PG. The percentage of the mixture and fluid flow rate varied from 25% to 60% and 0.2 to 0.6 LPS, respectively. GHX performance parameters, namely convective coefficient, pressure drop, borehole resistance, and GHX effectiveness are determined for both EG and PG brines. Better performance of GHX is noticed with EG brines as compared to PG brines for similar operating conditions. The drop in convective coefficient from 22% to 44% in the case of PG brines as compared to EG brines with the increase in mixture percentage from 25% to 60%, for the same operating conditions. The pressure drops decreased from 15% to 74% for EG mixture as compared to PG mixture at considered flow rate and mixture percentage. The effectiveness and overall borehole resistance were higher for EG as compared to the PG solution.