Performance Analysis of an Earth–Air Heat Exchanger Integrated into an Agricultural Irrigation System for a Greenhouse Environmental Temperature-control System

Abstract In this article, an earth–air heat exchanger (EAHE) system is applied in an agricultural greenhouse temperature-control system and integrated into the existing irrigation facilities to reduce the installation cost. In addition, an annual performance study and analysis are conducted for this system, and the mathematical model is verified with the experimental results; then, the energy-saving efficiency and economic benefits of the system are evaluated from the mathematical models and experimental data. The average difference between the experimental data and mathematical models is about 2.6%. This EAHE is buried under an existing irrigation channel; the channel is supplemented by an irrigation well, and the water temperature of the channel is stabilized by the well water. Compared with the traditional EAHE system, this system can achieve sufficient performance without a deep soil layer (above 5 m) and use the system's integrated existing facilities, significantly reducing the installation cost. According to the experimental results, a cooling capacity of 1.5–4.5 kW can be provided in summer under different weather conditions, a heating capacity of 0.7–2.8 kW can be provided in winter, and the greenhouse temperature can be maintained in the required range. Compared with the traditional heat-pump system, 561.6 kWh can be saved through this EAHE system in summer (operating for 90 days), with an energy-saving benefit of 74.3%, and 177.6 kWh can be saved in winter (operating for 30 days), with an energy-saving benefit of 67.3%. Moreover, the initial equipment costs can be reduced by 35.3%.