Efficiency analysis of utilizing phase change materials as grout for a vertical U-tube heat exchanger coupled ground source heat pump system. (5th February 2018)

• Record Type: Journal Article
• Authors: Chen, Fei; Mao, Jinfeng; Chen, Shangyuan; Li, Chaofeng; Hou, Pumin; Liao, Lu
• Is Part Of: Applied thermal engineering. Volume 130(2018)
• Page Start: 698
• Page End: 709
• Publication Date: 2018-02-05
• Subjects: GSHP system -- PCM grouts -- Efficiency analysis -- Subsurface characteristics -- Daily running mode; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2017.11.062
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: Numerical model including site conditions and dynamic loads was established. Effects of using PCMs as grout on the efficiency of GSHP system were analyzed. Applicability of PCM grouts to various subsurface characteristics was investigated. Appropriate operation mode for the PCM-backfilled GSHP system was determined. Abstract: To study the effects of using phase change materials (PCMs) as grout on the efficiency of a ground source heat pump (GSHP) system, a numerical GSHP system model was established in this study, considering both the site conditions and dynamically changing loads regulated by the heat pump. First, system efficiencies of using an ordinary grout and two other PCM grouts were investigated and compared. Second, the applicability of PCM grouts to different soil environments was investigated by analyzing the effects of subsurface characteristics on the heat exchanger efficiency. Finally, the appropriate operation mode for PCM-backfilled GSHP system was determined by comparing the effects of daily running modes with various intermittent ratios on the system performance. The results show that it is necessary to consider the effect of heat pump, especially for poor heat transfer conditions. PCM grouts with a low thermal conductivity will significantly reduce the system efficiency, whereas PCM grouts with a thermal conductivity comparable to that of an ordinary grout will improve the efficiency and operational stability of a GSHP system. A higher soil thermal conductivity and Darcy velocity improve the heat exchanger efficiency, and PCM grouts with a high thermal conductivity are more suitable for areas where the groundwater is not rich. Sufficient recovery time is necessary and important for a PCM-backfilled GSHP system to ensure operational stability and sustainability and the effectiveness of thermal radius reduction.