Numerical Analysis of Heat Exchange Processes for Ground Source Heat Pump.

Ground source heat pump systems (GSHP) use ground or groundwater as a heat source. They can achieve much higher coefficient of performance (COP) than conventional air source heat pump systems because the temperature of the ground is generally much more stable than that of the air. Heat energy in the ground is then viewed as one of the renewable energy sources. GSHP has been receiving great interests among countries in North America and Western Europe, as well as some developed countries in Asia because it can potentially reduce energy consumption and greenhouse gas emission. While GSHP can inject heat from the buildings to the ground for cooling during the summer, it can pump heat stored in the ground for heating during the winter. As some physical, chemical, and biological properties of the ground and groundwater are temperature dependent, running GSHP can eventually affect groundwater quality.

The main objective of this study was to develop a model that allows predicting not only ground and groundwater temperatures but also changes in physical, chemical, and biological properties with GSHP under operation. In this particular study, we used HYDRUS software to simulate heat exchange and transfer processes in the ground for a vertical-loop closed GSHP system. HYDRUS allows one to simulate variably-saturated water flow and solute and heat transport in porous media numerically in two- and three-dimensional domains with great flexibility in defining boundary conditions. At first changes in ground temperatures measured at every 5-m in a 50-m observation well installed 3.7 m from the 50-m long heat exchange boreholes were predicted in response to Thermal Response Test (TRT) conducted at our study site. Then, heat exchange and transfer processes for the vertical closed-loop GSHP systems were simulated to predict changes in ground and groundwater temperatures using three-dimensional domains.