Passive cooling of greenhouses in extreme climates through spectral control film
Yanpei Tian, Lei Yue, S. Zeng, Yue He, Chi Feng, Qiang Li, Rebekah Waller, Qiaoqiang Gan
Abstract
A warming climate poses a major threat to agriculture globally, necessitating technological solutions to mitigate frequently occurring extreme heat stress. Greenhouses in hot regions can provide suitable growth environments throughout the year by active cooling systems such as pad-and-fan systems or heat pumps; however, this practice comes with significant water and/or energy costs. In this study, we demonstrate a solution for passive thermal regulation in greenhouse environments utilizing the combination of a spectrally selective cover and a radiative cooling ground film. The cover consists of a polyethylene film infused with cesium tungsten oxide nanoparticles (PCsW), which block near-infrared sunlight to reduce solar heating while maintaining a high mid-infrared transmittance of 0.74, effectively dissipating radiative heat flux. The ground layer is a biodegradable cellulose mulch with a solar reflectance of 0.93 and a high mid-infrared emittance of 0.95, facilitating sunlight redistribution and efficient radiative cooling. Field trials conducted in a hot desert climate demonstrated that the combination of the cover and ground film led to a remarkable 25.1°C reduction in soil temperature within the greenhouse compared with the control, resulting in an increased germination rate, an optimized thermal environment for crops during their most vulnerable early growth stages, and enhanced yield of the experimental Chinese cabbage. This innovative passive cooling approach with zero water or energy input can extend growing seasons while significantly reducing the environmental footprint of greenhouse agriculture, especially in hot regions. Furthermore, the biodegradable nature of the cellulose mulch offers a sustainable alternative to conventional plastic films.