Climate Modelling of a Greenhouse with Proportional Environmental Control

Abstract

Performance of greenhouse environmental control systems can be evaluated by predictive climate models. In this work, a model for the prediction of environmental parameters such as temperature and humidity based on energy and mass balances, was developed and validated for a greenhouse controlled with a proportional environmental control system. The greenhouse is in Viveiros do Furadouro, a forestry nursery from the Altri Group, located near Óbidos, Portugal. The greenhouse under study is a Venlo greenhouse covered with glass with an area of 1632 m2 and is used for Eucalyptus globulus Labbill. vegetative propagation through minicuttings. Eucalyptus globulus is characterized by having low rooting ability and environmental control has to be very accurate and requires the use of multiple control equipments, such as heating, cooling (pad or fog), thermal/shade screens, natural and dynamic ventilation. The proportional control of each equipment, such as the fan and wet pad for cooling, is difficult and requires good knowledge of the dynamics of greenhouse environmental parameters, as well as the influence of individual equipment. However, it allows different alternatives to achieve the set points. The climate data were recorded every 8 min and were used to develop a climatic model based on energy and mass balances, to use for prediction of internal environmental parameters. Information about the activation percentage of the environmental control systems was also included. The extraction of the coefficients for the balances combines direct calculation and interaction using Microsoft Excel® SOLVER®, until reaching the minimum absolute difference between simulated and measured inside temperature and humidity. The climate model was validated by comparison between measured and simulated values for temperature and humidity. This model can be used to optimize the greenhouse environment in order to achieve the production objectives.