Abstract

ESPINAL-MONTES, Verónica et al. Determination of night-time thermal gradients in a greenhouse using computational thermal dynamics. Agrociencia [online]. 2015, vol.49, n.3, pp.233-247. ISSN 2521-9766.

In regions with dry and temperate climates, such as those of central and northern Mexico, the producers of greenhouse crops face low night-time temperatures, which become more severe during certain periods of the year. In a greenhouse they can be counteracted with heating systems, but when this resource is not available, the entrance of cold air is avoided by closing windows. The objective of the present study was to develop a model based on Computational Fluid Dynamics (CFD) in order to evaluate the variations of night-time temperature and air flow in a greenhouse in two scenarios: lateral windows open and closed. The data used in the simulations were collected during the winter of 2012, in a sierra type greenhouse with polyethylene cover and an area of 1 834.65 m², located at the experimental agricultural unit of the Universidad Autónoma Chapingo. The simulations were made with the commercial program CFD ANSYS-Fluent and a 3D model. To establish the conditions of boundary and validation of the model, temperature of air, cover and soil was measured inside the greenhouse. The experimental results and simulations presented an effect of thermal inversion, in which the temperature of the greenhouse was lower than the exterior. The simulation of the greenhouse with closed windows showed an average thermal inversion of 3.1 K and the experimental data of 3.3 K; with open windows the CFD model predicted a thermal inversion of 0.8 K. The opening of windows allowed air circulation, which balanced the inside temperature with the exterior. Results showed the capacity of the CFD to simulate the microclimate of the greenhouse with precision, and therefore its application in the design and management of greenhouses.

Keywords : Numerical model; thermal inversion; CFD.