Efficiency of vertical U-tube under varied soil moisture content conditions: Laboratory experiments

Ground Source Heat Pumps (GSHPs) are important renewable energy systems to reduce the usage of conventional HVAC systems in residential and commercial heating and cooling, and can be installed almost anywhere in the United States. However, high initial cost often deters the implementation of these systems. In order to avoid potentially lengthy payback period due to inadequate installation, it is critical to ensure the installed systems perform reliably and economically. Soil water content is known to affect thermal conductivity of soil, which can alter the heat exchanging efficiency of the GSHPs. In an effort to reduce costs to build and operate, the pipe length and flow rate must be optimized based on water table height and temperature input. In this study, a series of bench-scale experiments were performed in order to show how water table elevation can affect the efficiency of a vertical U-tube heat exchanger.