Dynamic energy balance model of a glass greenhouse: An experimental validation and solar energy analysis

摘要

Taking only the mean value of cover transmittance and cover absorbance would lead to a large error in estimating the thermal performance of a greenhouse. This paper discusses an innovative dynamic energy balance model of a glass greenhouse, incorporating dynamic cover absorbance and transmittance. Different cover absorbances and transmittances for diffuse, beam, and ground-reflected radiation are used. The model primarily comprises nine differential energy conservation equations for indoor air, seven layers of soil, and the greenhouse's cover. Greenhouse temperature trends are acquired by solving the unsteady-state equations with MATLAB. The model was verified using experimental data recorded during three non-continuous periods of 15 days each in northern China (36.08°N, 116.95°E), during which the daily maximum outdoor solar radiation flux intensity fell between 191 and 894 Wm~(-2), the outdoor air temperature fell between -12.3 ℃ and 24.5 ℃, the ground surface temperature fell between 0.6℃ and 44.3 ℃, and the indoor air temperature fell between -9.0 ℃ and 51.8 ℃. The estimates agree well with the measurements, suggesting that the dynamic model is valid. Meanwhile, the dynamic cover absorbance and transmittance, the solar radiation absorbed by the cover, the solar radiation transmitted into the glass greenhouse and the proportion of solar radiation from each surface are discussed.