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Numerical Simulation of Borehole Heat Transfer with Phase Change Material as Grout

Ground source heat pumps (GSHP) have been widely used in recent years. The heat transfer between borehole heat exchanger (BHE) and earth is the key factor impacting on the performance of GSHP. However, in order to setup BHE, a large amount of area of land is necessary, since the heat capacity of earth is limited. In this paper, phase change materials (PCMs) are used as grout instead of common materials. Thus, the heat capacity of soil has been improved, but the heat transfer characteristic of BHE has also changed. To prove its feasibility, the 3-dimensional numerical heat transfer simulation has been carried for three models which grout are respectively soil, PCMs, and PCMs with heat transfer enhancement measures. The characteristics of heat transfer and the land areas used of the three models are compared. The results show that the land area can be reduced effectively with PCMs as backfilling, while heat transfer enhancements must be adopted because the conductivity of PCM is small.