A study of direct solar radiation transmission in asymmetrical multi-span greenhouses using scale models and simulation models

Direct solar radiation transmission inside scale models of greenhouses with different roof slopes was measured and the results compared with calculations from a simulation model. Seven different roof slopes were tested, which had symmetrical and asymmetrical roof shapes: 8degrees-18degrees; 18degrees-8degrees; 27degrees-27degrees; 27degrees-45degrees; 36degrees-55degrees; 45degrees-27degrees; 55degrees-36degrees (8degrees-18degrees denoting that the south-facing slope was 8degrees and the north-facing one was 18degrees). Radiation transmission in scale models was quantified using linear solarimeters that integrated solar radiation along the cross-section of the span. The correlation between measured and calculated hourly and daily mean transmission values was good. Minor differences were attributed to the accumulation of dust and condensation on the scale models, two conditions that were not taken into account in the simulation model. The results of the study showed that direct solar radiation transmission increased considerably as slope increased, up to a value close to 30degrees, especially in the winter months in which radiation was most limited. Assymetrical greenhouses did not always transmit more than symmetrical ones with similar slopes. In the cases studied, the scale model with 27-27degrees symmetrical roof had the highest winter transmission. The use of scale models allowed different greenhouse structures to be characterised with respect to direct radiation transmission. This method can produce considerable savings of time and money and provides a realistic simulation of radiation transmission in full-scale greenhouses. (C) 2004 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.