Shallow subterranean ventilation of earth-to-air heat exchanger (EAHE) system can improve renewable utilisation, decrease CO ₂ emission and promote carbon-neutral transition. However, the conventional EAHE system has drawbacks, e.g., large occupied land area, low energy-usage efficiency, small falling gradient for buried pipe and fluctuated outlet air temperature. This study proposes a vertical EAHE integrated with annular PCM with advantages, including less occupied floor space, higher energy efficiency, better centralised discharge of air condensate water and more stable outlet air temperature. An experimental test-rig was established for online testing and the real-time monitored data was for modelling calibration to characterise the sophisticated heat transfer in phase change process. Afterwards, multivariant analysis on thermo-physical PCM parameters was conducted on cooling capacity and outlet air temperature fluctuation. A dimensionality reduction approach from redundant experiments was adopted for multivariant optimization and sensitivity analysis. Results show that PCM fusion temperature and latent heat of PCM dominate the cooling capacity with percentage contribution of 37.61% and 28.91%, respectively. PCM thickness and melting temperature dominate the temperature fluctuation with percentage contribution of 31.27% and 26.18%, respectively. This study provides benchmark and guidelines on PCM thermo-physical parameters’ selection with an efficient dimensionality reduction approach, paving path for application of the vertical EAHE integrated with PCMs in buildings.

A novel vertical air-soil heat exchanger (VASHE) is proposed, coupling with diversified energy storage components, i.e., both annular and tubular phase change material (PCM) components. Compared to traditional air-soil heat exchanger systems, advantages of the new VASHE include the space-saving, higher energy efficiency, centralized discharge of condensate water and smaller fluctuation of outlet air temperature. An enthalpy-based model is developed to characterise the underlying heat transfer mechanism of the sophisticated sensible and latent heat transfer in PCMs. An experimental platform is thereafter constructed for the calibration of the developed enthalpy-based numerical model. Systematic parametrical analysis has been conducted on PCM types, PCM structure and PCM locations. Research results indicated that, the developed enthalpy-based model was accurate to predict the system performance with the maximum relative error at 1.98%. Systematic parametric analysis indicates that, within various PCM types, the RT 20 in the tubular PCM is the most promising with the smallest outlet temperature amplitude. Furthermore, accurate PCM location is an effective solution to the contradiction between daily cooling storage capacity and outlet temperature amplitude. This study demonstrates a novel air-soil heat exchanger with diversified energy storage components, which can provide concrete guidance and pave path for the geothermal energy utilisation.