A numerical study on the sustainability and efficiency of borehole heat exchanger coupled ground source heat pump systems. (5th May 2016)

• Record Type: Journal Article
• Authors: Hein, Philipp; Kolditz, Olaf; Görke, Uwe-Jens; Bucher, Anke; Shao, Haibing
• Is Part Of: Applied thermal engineering. Volume 100(2016:May)
• Page Start: 421
• Page End: 433
• Publication Date: 2016-05-05
• Subjects: Ground source heat pump (GSHP) -- Borehole heat exchanger (BHE) -- Long-term sustainability and efficiency -- Recovery of shallow geothermal reservoir -- OpenGeoSys (OGS); Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2016.02.039
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: A numerical BHE model was enhanced to include heat pumps characteristics. Surface temperature and geothermal gradient are necessary for realistic simulation. The benefit of groundwater flow and injection of excess heat is quantified. Usage of thermally enhanced grout materials will always result in financial benefit. It was found that BHE coupled GSHP systems are extremely sensitive to design errors. Abstract: To utilize shallow geothermal energy, ground source heat pump systems (GSHPS) are often coupled with borehole heat exchangers (BHE). In recent years, some GSHPSs are experiencing a gradual decrease in BHE outflow temperatures and thus have to be shut down. In this work, a comprehensive numerical model was constructed to include flow and heat transport processes, together with the dynamics of heat pump efficiency. The model parameters are based on local conditions in the Leipzig area. Different scenarios were simulated to observe the evolution of BHE outflow and soil temperatures subject to various factors of influence. In the first year, the recovery of shallow geothermal energy only accounts for about 89% of the energy extracted. Over the following years, outflow and soil temperature will gradually drop until they reach a quasi-steady-state. It was also found that groundwater flow and using BHE for cooling will be beneficial to the energy recovery and efficiency of the heat pump. In comparison to other factors, the soil heat capacity and thermal conductivity are considered to have a minor impact on the sustainability of the system. In contrast, it is very likely that undersized systems are the cause of strong system degradation.