Thermal performance evaluation of stainless steel pipe as a ground heat exchanger

Abstract

In recent years, the utilization of geothermal energy for buildings has increased significantly. Especially in growing urban areas, there is a need for supplementary research to maximize the efficiency of heat exchange in geothermal energy systems on space-restricted sites. There is currently a little research about improving the heat exchange by choice of pipe materials. Circular pipes of high-density polyethylene (HDPE) and polybutylene (PB) are commonly used as ground heat exchangers (GHEs) for convenience and cost benefit, but PB pipes, in particular, have thermal properties that do not have a favor in the heat exchange. Therefore, this paper presents the results of an experimental study on the use of annular stainless steel (STS) pipe as a GHE. Thermal response tests (TRT) were conducted to measure heat exchange rates in circular PB pipe and annular STS pipe installed in a steel box with the dimension of 5 m × 1 m × 1 m. Dry Joomunjin standard sand was used to fill the box and TRTs were performed for 30 hours to reach a steady state. As a result, the annular STS pipe showed about 9% higher heat-exchange rate (per pipe length) than did the circular PB pipe. Compared to the length of heat exchanger required under the same conditions, the annular STS pipe needed was shorter than the circular PB pipe. It is concluded that the STS pipe could be used as an efficient GHE.