Experimental and computational investigation of the spiral ground heat exchangers for ground source heat pump applications

This paper investigates the thermal performance of vertical spiral ground heat exchangers (GHEs), experimentally and computationally. Experimental application area consists of nine spiral GHEs and two boreholes with U-Tube GHE. During experimental study, different configurations of spiral GHEs are tested separately for 150 h. Ground source heat pump (GSHP) system with nine spiral GHEs operates for 3 months intermittently to provide cooling demands of the building in summer. Based on the results of study, thermal performance of the nine spiral GHEs are more accurately analyzed than other configurations. To better investigate thermal behavior of the spiral GHEs, comparative analyses for various configurations of spiral GHEs are explored by using COMSOL software. Based on the validated numerical models, long term heat transfer rate (HTR) of the single and nine spiral GHEs are examined under the most critical working conditions and additionally, for nine spiral GHEs, predictive curve is verified by some actual HTR values. Furthermore, in this study most important designing tools such as, performance losses against time and distance between spiral GHEs, temperature variations in ground, thermal interactions between spiral GHEs and relative performance of spiral GHEs versus different average working fluid temperature are investigated for nine spiral GHEs configuration.