HEAT TRANSFER MODELLING OF SCREENHOUSES

Abstract

Several mathematical models to represent the behavior of the inside temperature of screenhouses were developed. These models take into account different screenhouse configurations as well as the fact that the roof can be built of a single or double layer of cover. The influence of four types of commercial screens (Lumite 32 and 50, and Tildenet 32 and 50) on inside screenhouse temperatures was analyzed. The concept of cooling through water spray was mathematically represented. Experimental data on real screenhouses was obtained at the Benin station of the International Institute of Tropical Agriculture (IITA-Benin), Republic of Benin, Africa. Four small scale experimental screenhouses having different structural configurations were tested. The experiments were done for different types of screens. Three important parameters required to complete the mathematical representation (transmissivity of the cover, τ; natural ventilation, N v; and global heat transfer coefficient, U) were determined independently from experimental screenhouse data. Comparison between simulation and experimental results showed that the mathematical models were appropriate to predict inside screenhouse temperatures. The differences between experimental and predicted inside temperatures were not greater than 2°C for all the experiments tested. It can be concluded that a simple lumped approach such as the one presented in this article, can be safely used for prediction of single and double roof screenhouse inside temperatures, with and without water spray, once the values of τ, N v and U parameters have been determined.