Thermal performance of a ground heat exchanger in a cold climate: a CFD study

The thermal performance of a ground heat exchanger (GHE) depends on many parameters, particularly the relation of the working fluid, pipe diameter, and fluid velocity. The effect of these parameters on the pressure drop is rarely addressed in the thermal performance calculations. The present study bridges this knowledge gap with the investigation of the thermal performance of a GHE that is supplied with other working fluids than typical air. A 3D computational fluid dynamics simulation of the performance of a GHE has been carried out by using the realizable k-ε turbulence model. The thermal performance of a segment of a GHE system with different pipe diameters at a wide range of Reynolds number (5,000–50,000) is investigated for different working fluids (air, propylene glycol, and ethylene glycol) which are thermally validated with a 3D model. The numerical results show that ethylene glycol as the working fluid has a higher temperature increment rate comparing to other working fluids. The maximum temperature difference between the inlet and outlet sections of the GHE is calculated as 13.3 K at Re = 30,000 for ethylene glycol. The Euler number decreases as the Reynolds number increases. The highest Euler number is approximately 10.4 using ethylene glycol and is seen at Re = 5,000 which is 7.7% and 46.5% higher than that when using propylene glycol and air as working fluid, respectively.