An earth-air heat exchanger integrated with a greenhouse in cold-winter and hot-summer regions of northern China: Modeling and experimental analysis

Abstract

This study aimed to investigate the thermal performance of Earth-Air Heat Exchangers (EAHE) in greenhouses in northern China's cold winter and hot summer regions. The experiment was conducted in two identical greenhouses (with and without an EAHE), and a mathematical and Computational Fluid Dynamics (CFD) simulation model was established to predict the air temperature inside the greenhouse and heat exchanger outlets and verified with measured data. Parametric analysis was also performed, and the effect of long-period application was evaluated. The results showed that the data calculated by the model agreed well with the experimental data. The average differences between the inlet and outlet air temperatures of the EAHE, daily average heat exchange capacity, and coefficient of performance (COP) was 9.26 ℃, 18.86 MJ, and 22.49 in winter, respectively, while in summer, they were 10.55 ℃, 18.78 MJ, and 23.52, respectively. The night-time temperature of the greenhouse increased by 1.43 °C during winter, while the temperature during summer daytime was reduced by 2.10 ℃. An increase in the pipe length improves the heat exchange efficiency, the heat exchange mainly occurs in the first half of the horizontal pipe, and the increase in air velocity and operation time will reduce the heat exchange efficiency. In conclusion, the system was proposed as a viable auxiliary device for greenhouse heating and cooling in cold winter and hot summer regions and to reduce greenhouse gas emissions. The system is recommended to be arranged outdoors for cooling and indoors for heating.