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

Abstract

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.