Numerical simulation of a ground-coupled heat pump system with vertical plate heat exchangers: A comprehensive parametric study

Plate ground heat exchangers (GHEs) are renowned for having the highest heat transfer rate per unit land area and could be of interest when the accessible land area is limited. In this study, a 3-D numerical model is developed to investigate the thermal performance of vertical plate GHEs at the real-scale level. The proposed model accounts for ambient temperature fluctuations and building cooling load variations and is such developed to couple the GHE to the heat pump. The effects of different parameters, including GHE spacing, buried depth, the height of GHE, soil type, and climate on the thermal performance of vertical plate GHEs, are comprehensively investigated for the first time. The optimum distance between two adjacent GHEs is obtained to be about 4 m to avoid the adverse effect of thermal interference. It is demonstrated that increasing GHE spacing dramatically increases cooling load per unit GHE area for values below 4 m while decreasing cooling load per unit land area. As a case in point, increasing GHE spacing from 2 m to 4 m increases cooling load per unit GHE area by 30.1 % while lowering cooling load per unit land area by 34.9 %. It can be inferred from the simulation results that soil type has the most critical effect on the thermal performance of vertical plate GHEs, and better thermal performance can be achieved when GHEs are buried in a soil type with higher thermal conductivity as well as higher heat capacity. The results also indicate that selecting proper values for buried depth and height is in fact finding a compromise between thermal performance and excavation cost. Investigating the effect of climate reveals that the maximum cooling load per unit GHE area is decreased by 37.7 % when the GCHP system operates in Ahvaz (hot climate) rather than Tehran (mild climate). However, when the GCHP system is designed to operate in Tabriz (cold climate), the maximum cooling load improves by 17.4 %.