Application of the energy balance model to predict transpiration and microclimate conditions inside the greenhouse using meteorological data

In recent years, increasing population and limited water and arable land in Iran have led to significant investment in greenhouse production. Due to the effect of greenhouse microclimate conditions on the quantitative and qualitative yield of the product, the use of mathematical models to study and microclimate simulation of the greenhouse is necessary. The objective of this research is to apply and analyze an energy balance model using meteorological data outside the greenhouse to simulate microclimate conditions and the transpiration in a greenhouse. The study was conducted in a commercial greenhouse with plastic cover and an area of 4333 square meters. Temperature and relative humidity data were collected inside the greenhouse with 21 data loggers. For collected meteorological data outside the greenhouse, the meteorological station installed on the roof of the greenhouse and the data of the Tuyserkan synoptic meteorological station were used. A combination of energy balance and transpiration equation was used to estimate temperature, relative humidity and crop transpiration inside the greenhouse. Estimated transpiration was modified by combining the energy balance model and the Stanghellini transpiration equation. The pattern of temporal variation of the simulated and measured values of temperature and relative humidity inside the greenhouse was similar. The root mean square error of the simulated temperature for mechanical ventilation and natural ventilation was 0.72 and 0.67, 0.83 and 0.77 daily, and 0.49 and 0.49 degrees Celsius, respectively, for the daytime and night time. The root mean square error of relative humidity for mechanical and natural ventilation was 4.4% day and night, 3.0% for daytime, and 6.0% for night time. After modifying the simulation model, four days of microclimate inside the greenhouse showed that the temperature inside the greenhouse reaches 35 °C during the day and less than 16 °C at night, which are not in the optimal temperature range for greenhouse cucumbers. Due to high temperature (35º C) and low humidity (15% to 30%), evaporative cooling will be required at some hours of the day. The total simulated transpiration was 30.2 mm. The estimated temperature was acceptable, but the estimated relative humidity at night differed from the measured values due to thermal inversion. Estimated transpiration was modified by combining the energy balance model and the Stanghellini transpiration equation. After verifying and modifying the model, the microclimate conditions of the greenhouse were simulated and analyzed for four days. The results showed that by using the energy level model before the construction of the greenhouse, it is possible to estimate the microclimate conditions of the greenhouse and the water requirement of the crop.