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Performance analysis of a single underground thermal storage borehole using phase change material

Bayomy, A. M.
Nguyen, Hiep V.
Wang, Jun
Dworkin, Seth B.

Ground source heat pumps (GSHP) are used to provide both heating and cooling to a given system. These heat pumps transfer heat efficiently between the system and the ground. Despite this high efficiency, there has been a low adoption rate for GSHPs owing to limited usage in commercial structures and buildings primarily due to high installation costs, but also due to a lack of drilling space and unbalanced heating/cooling loads. Phase change materials (PCMs) can absorb, store and release large amounts of latent heat over a defined narrow temperature range while the material changes phase or state. The main goal of this paper is to be able to predict numerically the performance of a single borehole with the effect of implementing PCMs. In order to successfully proceed with the discussion, two main objectives for this paper are presented. The first objective is to establish a finite element model of a single borehole with accurate assumptions in order to achieve an accurate prediction over four years of operation for a GSHP. Then, the second objective of the paper is to investigate the effect of using PCM in the borehole of GSHP to help maintain a more stable ground temperature range. Two scenarios of different PCM volumes and melting temperatures are presented. It was found that the performance enhancement due to PCMs reaches up to 35% in monthly average COP. In addition, PCMs show great potential to smooth the ground thermal response.