Models to estimate daily diffuse irradiation inside polyethylene greenhouses lined east-west and north-south

摘要

In this work is shown simple linear equations to estimate daily diffuse radiation inside and outside of two polyethylene (100 mu m of thickness) tunnel greenhouses, oriented at East-West and North-South directions. During the years of 1997 and 1998, diffuse irradiances (W.m~(-2)) were measured using an Eppley-PSP piranometer, shaded by a ring. Irradiance values were integrated to find the daily values of diffuse irradiation. It was found that, for relatively high values of diffuse outside the greenhouse, the corresponding inside values were always lower while the converse occurred when the outside values were relatively low. Is was concluded that, under the climatic conditions of Botucatu/SP-Brazil and for greenhouse with constructive characteristics similar to those used in this experiment, monthly average daily diffuse solar radiation inside the greenhouse were not dependent on the greenhouse orientation but a function of the sky condition. It was also concluded that a simple linear equation can be used, with good accuracy, in the estimation of daily diffuse radiation inside the greenhouse from measurements taken outside.