CFD simulation study to evaluate the economic feasibility of backfilling materials for ground-air heat exchanger system

• Published in: Geothermics Vol. 90; p. 102002
• Main Authors: Agrawal, Kamal Kumar, Misra, Rohit, Agrawal, Ghanshyam Das
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.02.2021; Elsevier Science Ltd
• Subjects: Air temperature; Backfill; Backfilling materials; Bentonite; CFD simulation; Computational fluid dynamics; Economic feasibility; Energy efficiency; Excavation; Feasibility studies; Geothermal power; Ground-air heat eexchanger; Heat exchange; Heat exchangers; Heat transfer; Initial installation cost; Installation; Installation costs; Pipe length; Pipes; Sand; Simulation; Soils; Thermal conductivity; Three dimensional models; CFD; Ground-air heat eexchanger; CFD simulation; Initial installation cost; VWC; Economic feasibility; GHE; NS; Backfilling materials; BFM(s); Pipe length; SB; HVAC; GAHE; EAHE; PVC; BHE
• ISSN: 0375-6505; 1879-3576
• DOI: 10.1016/j.geothermics.2020.102002

•Evaluated economic feasibility of backfilling materials for GAHE system.•Developed a CFD simulation model for GAHE system with backfilling materials.•Use of backfilling materials to improve the overall economics of GAHE system.•Required length of GAHE pipe is determined with different BFMs. The ground-air heat exchanger (GAHE) system is an energy-efficient system for building cooling/ heating, but its initial cost is higher due to the requirement of longer pipes to achieve the desired heat exchange between air and soil. To reduce required pipe length, secondary soil (i.e. soil of high thermal conductivity) can be used as backfilling material in the vicinity of GAHE pipe. However, due to the use of secondary soil, the installation cost of the GAHE system may increase. Therefore, the key objective of this study is to explore the economic feasibility of using backfilling materials in the vicinity of GAHE pipe. For this, a three-dimensional CFD simulation model of GAHE system with backfilling material has been developed using FLUENT 15.0, and the required length of GAHE pipe to achieve a specified drop in air temperature with backfilling materials has been determined. Based on this, the initial installation cost of the GAHE system (i.e. pipe cost, trench excavation cost, backfilling material cost) has been estimated. The study revealed that the initial installation cost of a GAHE system could be reduced by 25.7%, 32%, and 38% using dry sand-bentonite, wet sand-bentonite, and wet native soil respectively, as backfilling materials in place of dry native soil.