Numerical study on the cooling performance of a novel passive system: Cylindrical phase change material-assisted earth-air heat exchanger

The application of renewable energy technologies, such as the earth-air heat exchanger (EAHE), is quite conducive to reducing the energy consumption of buildings. However, the heat transfer process of traditional EAHE may greatly change the soil temperature, which hinders the system from fully exerting its thermal performance. Based on the features of high energy density and stable output temperature in the phase change heat storage process, this paper proposes a cylindrical phase change material-assisted EAHE (CPCM-EAHE) to improve the performance of such systems. An equivalent heat capacity method based 3-D numerical model for this novel system was established on the ANSYS Fluent platform. And its calculation result was verified by an indoor experimental set-up. Under summer high-temperature meteorological conditions of Chongqing, the cooling performance of CPCM-EAHE and traditional EAHE is comparatively studied through this numerical model. The results tell that PCM does enhance the heat transfer of EAHE most of the time, as well as delay its transition from the heating mode to cooling mode but advance its transition from the cooling mode to heating mode. These changes finally make the CPCME-AHE achieve excellent cooling performance. Specifically, compared to traditional EAHE, the daily maximum cooling capacity of CPCM-EAHE is increased by 28.55%-39.74%. Even from the whole 20-day investigation period, its total cooling output is increased by 20.05% as well. Finally, this CPCM-EAHE can damp the temperature fluctuation of fresh air to approximately 1 degrees C. (C) 2019 Elsevier Ltd. All rights reserved.