A numerical model of a vertical earth-to-air heat exchanger (VEAHE) system was developed for the first time. Compared to conventional EAHE system models, the developed model considered the vertical distribution of soil temperature and thermal conductivity. The model validation against experimental data showed a good agreement. A parametric study was then conducted to investigate the effects of tube parameters, insulation parameters, mass flow rates and soil types. Results indicate that a system with a smaller tube diameter provides more thermal capacity with a fixed air mass flow rate, while a larger tube diameter can enhance the system's COP. An increase in tube depths causes the outlet air temperatures to decrease/increase in summer/winter, with a smaller daily oscillation. Compared to PVC and PE, stainless steel can be recommended as the most appropriate tube material, taking into account both heat exchange and soil pressure. Polyurethane, rubber or rock wool as insulation materials can be used as thermal barriers to shield the undesirable heat gains from the shallow soil with the almost same insulation effects. A thickness of 30 mm and a length of from 4 to 5 m can be recommended as the most appropriate insulation parameters for this proposed system.

In this study, a new vertical earth-to-air heat exchanger (VEAHE) system coupled with tubular phase change material (PCM) components was proposed. The proposed system has smaller occupied areas and higher geothermal energy use efficiency than traditional EAHE systems. Moreover, the tubular PCM component enables the system's air temperature at the outlet to be more stable, thereby enhancing the system's thermal performance. In particular, the tubular components' simple geometry, easy fabrication, convenient assembling-disassembling and low-cost facilitate their usage in practical applications. To explore the system's thermal performance, an experimental set-up was established and its numerical model was developed. Then the model was verified through a comparison between the system's simulated and monitored air temperatures at the outlet. The verification produced acceptable results with the maximum absolute relative error of 1.33%. Based on this model, the influences of the tubular PCM component, tube depth, PCM conductivity and container length on the proposed system's thermal performance were investigated. Results indicated that the tubular PCM components can effectively reduce the VEAHE system's air temperature peak and fluctuation at the outlet, and increase its average cooling capacity. For the proposed system, as the tube depths increase from 12 to 24 m, the air temperature peak and fluctuation at the outlet decrease from 25.74 °C and 3.59 °C to 21.01 °C and 0.62 °C, respectively. Different thermal conductivity of PCM has almost same influences on the system's air temperature at the outlet as the container diameter is 50 mm. Such influences, however, become apparent and require to be considered as the container diameter increases to 150 mm. The air temperature fluctuation at the outlet decreases as the container lengths increase, and 12 m can be considered as an appropriate length for the proposed system. Additionally, the system's static payback period was calculated as 18.03 years.