Solar radiation transmissivity of a single-span greenhouse through measurements on scale models

The solar transmissivity of a single-span greenhouse has been investigated experimentally using a scale model, of dimensions 40 cm width and 80 cm length. The solar transmissivity was measured at 48 positions on the "ground" surface of the scale model using 48 small silicon solar cells. The greenhouse model was positioned horizontally on a specially made goniometric mechanism. In this way, the greenhouse azimuth could be changed so that typical days of the year could be simulated using different combinations of greenhouse azimuth and the position of the sun in the sky. The measured solar transmissivity distribution at the "ground" surface and the average greenhouse solar transmissivity are presented and analysed, for characteristic days of the year, for winter and summer for a latitude of 37 degrees 58' (Athens, Greece). It is shown that for the latitude of 37 degrees 58' N during winter, the E-W orientation is preferable to the N-S one. The side walls, and especially the East and West ones for the E-W orientation, reduce considerably the greenhouse transmissivity at areas close to the walls for long periods of the day when the angle of incidence of the solar rays to these walls is large. (C) 1998 Silsoe Research Institute.