Experimental investigation of a vertical earth-to-air heat exchanger system

Abstract

A vertical earth-to-air heat exchanger system (VEAHE) system was proposed in this study. Compared to conventional EAHE systems, it has smaller land use and higher geothermal energy utilization efficiency. To validate its thermal and economic feasibility, an experimental setup was established to examine the variation of its outlet air temperature, air temperature along the tube and soil temperature. Also, the energy metrics of the proposed system were calculated for its economic assessment. Results showed that the outlet air temperature of this system ranged from 22.4 °C to 24.4 °C in summer and from 16.0 °C to 18.0 °C in winter. A detailed air temperature profile along the whole tube revealed that, the air temperature difference under 5 m in deep soil was more than twice as many as that from the inlet to 5 m. For the soil temperature at different depths, its recovery rate approximately equaled to the corresponding changing rate at the same depth during operation. For the proposed system, its energy payback time was calculated as 8.2 years, and its CO2 emission mitigation potential and total carbon credits were calculated as 7170.42 kg and $203.43 respectively, given an economic lifespan of 20 years. In addition, its monetary payback period was calculated as 17.5 years. The above results demonstrate the feasibility and effectiveness of the proposed system in exploiting deep ground soil as a natural heat sink/source in summer/winter. Meanwhile, the energy metrics analysis indicates that the proposed system is economically viable.