Abstract
The ground source heat pump (GSHP) is receiving increasing attention due to the global trend of energy-saving and emission reduction. However, projects with ground heat exchangers (GHEs) buried in fractured rock bodies are scarce, and the impacts of water flow in fractures on the system performance are short of detailed investigations. In this paper, a three-dimensional model was built to study the temperature distribution underground and the relative performance of heat pumps and GHEs influenced by groundwater flow in fractures. Three factors including fluid flow velocities in fractures, the number of fractures and the distributions of fractures were taken into consideration, a range of indicators including outlet temperature of GHEs, mean temperature of “Energy Storage Rock Body” (ESRB) and heat injection rate per unit length were examined. It was found that the heat injection rate per unit length of a U-pipe in fractured rock body could be up to 78.83% higher than that of a U-pipe in integrated rock. Likewise, the coefficient of performance of cases with fractures was identified to be up to 4.50% higher than the integrated rock case. In addition, differently distributed fractures also have different impacts on the heat transfer efficiency of heat pumps and GHEs.
Highlights
The building sector is one of the largest energy-consuming sectors after the industry and transportation sectors, and a significant contributor to greenhouse gas emissions [1,2]
This study presents a detailed investigation into the heat transfer mechanism between ground heat exchangers (GHEs) and the host fractured formation, and identifies the influencing extent of the above factors
In order to evaluate the impact of fracture water flow more straightforwardly, an extreme situation was considered—the load was only in the cooling mode, which means heat was only injected into the ground but not extracted
Summary
The building sector is one of the largest energy-consuming sectors after the industry and transportation sectors, and a significant contributor to greenhouse gas emissions [1,2]. 20–50% of whole energy consumption worldwide [3] and 47% in China [4]. Renewable energy resources appear to be a prime alternative energy resources for the purpose of curbing energy consumption and emissions. Special plans have been rolled out in many nations for utilizing shallow geothermal energy to alleviate the carbon emission. As a consequence of more GSHPs installed in different regions, impacts of various geological conditions, including fractured rock bodies filling with groundwater, on the performance of GSHPs need to be well evaluated
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