Investigating the effects of different diameter ratios on medium deep coaxial borehole heat exchanger

In this paper, open source finite element simulation software OpenGeoSys is used to establish a three-dimensional heat transfer model for the medium deep coaxial borehole heat exchanger (DCBHE). Then the thermal performance test and energy consumption analysis of the DCBHE coupled heat pump heating system with different diameter ratios are investigated. Results show that with the increase of the diameter ratios of DCBHE, the heat extraction performance and the outlet temperature of DCBHE has an improvement, along with higher heating pump consumption and circulation pump consumption. Besides, there is a growth of average COP of heat pump and an obvious drop of average pump power with the increasing diameter ratios. Therefore, it can be concluded that it is necessary to comprehensively consider and choose the appropriate diameter ratio to achieve the best performance of the DCBHE.