22 May 2008

THERMAL ANALYSIS OF GEOTHERMAL HEAT EXCHANGERS IN GROUND-COUPLED HEAT PUMP SYSTEMS


A ground-coupled heat pump (GCHP) system utilizes the ground as a heat
source/sink for heating and air-conditioning of buildings. The geothermal heat exchanger
(GHE) is devised for extraction or injection of thermal energy from/into the ground in such systems. This paper summarizes the advances in heat transfer modeling of the GHEs that
the authors have achieved in recent years. Taking the fluid axial convective heat transfer and thermal “short-circuiting” among U-tube legs into account, a quasi-3-D model has been
solved for heat transfer inside boreholes. An explicit solution of the transient 2-D temperature response in a semi-infinite medium with a line-source of finite length has also been derived for analysis of heat conduction outside boreholes. In order to investigate the impact of groundwater advection on the performance of GHEs, an analytical solution of the transient
heat transfer is obtained for a line heat source in an infinite porous medium with groundwater advection. These explicit expressions have more solid theoretical basis, and can be easily
incorporated into computer programs for thermal analysis and engineering design of the vertical GHEs.