A Case Study of Space Heating using a Downhole Heat Exchanger in China

Abstract

Since the closed loop heat exchangers subsurface have no disturbance on the level of ground water, they are becoming popular in many countries over the world. However, most of the installations so far are of Borehole Heat Exchangers (BHE) for ground coupled heat pump systems, which have been increasing remarkably in the last five years in China. There was not yet a real application of Downhole Heat Exchanger (DHE) designed for space heating in China. In this paper, we introduce a demonstration project of space heating by using a DHE together with a heat pump. The project was carried out in Shacheng, Hebei Province. The building to be heated was a dinning hall, which has a floor area of about 1028 m2. The DHE was installed in a shallow well 115m in depth and 11 inches in diameter. The maximum reservoir temperature was found at the bottom of the well, which is about 64oC, and there are two main permeable zones having a temperature of 51 oC. The transient heat transfer tests were conducted for the U-shaped DHE with different circulating flow rates and inlet temperatures. The heat transfer performance outside of the DHE was analyzed by correlating the experimental data. It is demonstrated that a combination of DHEs with heat pumps could extend the uses of DHEs in locations without high geothermal gradient, with a relative high heat transfer performance.