Research on the heat transfer performance of a ground heat exchanger under the synergistic effect of nanofluid and phase change material

Abstract

A ground-coupled heat pump (GCHP) system is an energy-efficient building service device that utilizes geothermal energy for heating or cooling buildings through ground heat exchanger (GHE). Owing to its ability to accomplish energy transfer, the GHE is a vital component of GCHP system. Therefore, efforts have been made to improve the heat transfer performance of GHE in terms of material and structure. A novel GHE design, nanofluid and shape-stabilized phase change material-assisted spiral-type GHE (NF&SSPCM-SGHE) system, was conceptualized. To investigate the heat transfer performance of this novel system, a 3D transient numerical model based on the thermal dispersion model for the solving nanofluid flow and heat transfer, as well as an effective heat capacity method for the solving phase transition heat transfer process, were established and verified against the data obtained by the prototype experimental platform. Subsequently, comparative studies between the NF&SSPCM-SGHE and U-type GHE (U-GHE) systems were conducted under summer conditions in Chengdu (China). The results demonstrated that the heat transfer performance of NF&SSPCM-SGHE system was significantly improved under the synergistic effects of the spiral-type heat exchanger, SSPCM, and nanofluid, and its single borehole cooling capacity was approximately 2.35 times that of U-GHE system. Nanofluid and SSPCM, a combination of one inside and one outside, play a separate role and promote and reinforce one another. Findings of this study are anticipated to realize the innovation and development of GCHP system and provide the innovative paths and methods for the realization of the “dual carbon” goal.