Numerical Simulation of the Effect of Greenhouse Crop Size on the Thermal Gradient of Air Generated By Heating Systems

In regions where winter temperatures fall below the tolerable thermal limits for crops, it is necessary to implement emergent equipment to supply heat inside the greenhouse. The objective of this work was to evaluate numerically the effect of two heating systems and crop size on the thermal gradient inside the greenhouse. This work aimed to estimate the thermal gradient generated by the heating system as a function of the age (height) of a greenhouse tomato crop. Temperature prediction was carried out using a numerical model based on Computational Fluid Dynamics (CFD), the impact of each heating system was examined, as well as the influence of crop size on thermal homogenization. The results indicate that when using electric heaters, the temperature at 1.5 m above the ground increases in the simulated no-crop scenario. As the crop size increases, the temperature at 1.5 m from the ground decreases (difference of up to 8 °C between the scenario with and without 2 m crop). Suggests that the crop, acting as a porous medium (barrier), reduces the energy exchange between the top of the greenhouse and the crop zone. However, when having a pipe heating system, the temperature at 1.5 m from the ground is more homogeneous, and the simulated scenario with the highest temperature is the one where the crop size is the largest (2 m) with a thermal difference of up to 1.5 °C between the scenario with and without 2 m crop. In summary, we have a larger thermal difference between the simulated scenarios when using electric heaters. However, electric heaters are still the best option to increase the greenhouse temperature, increasing the air temperature by up to 3 °C in the worst simulated scenario compared to the piped system. Keywords: Simulation; CFD; tomato growth; thermal homogenization; thermal comfort.