ISHS Acta Horticulturae 456: II Modelling Plant Growth, Environmental Control and Farm Management in Protected Cultivation
LIGHT TRANSMISSION OF ZIGZAG-SHAPED MULTISPAN GREENHOUSES |
| Author: | J.A. Stoffers |
| Keywords: | Selfsupporting, orientation freedom, smooth-switch, ray- or bandtracing, physical properties |
| Abstract:
The light transmission of greenhouses can be improved by either reducing or avoiding construction parts or modifying the covering material itself (e.g. coatings) or modifying the shape of the material. The ideal greenhouse cover does not need construction parts, is self-supporting and of course light transmission and orientation freedom is high. A solution could be the use of pyramidal shaped or zigzag-corrugated cladding material, since light transmission as well as stiffness might increase. To investigate the light transmission (reflection) of multispan greenhouses cladded with zigzag-shaped materials as well as the transmission (reflection) of multispan greenhouses with large slopes (slope > 45 deg.) a model (ZIGZAG.PAS) based on the tracing of R A Y S was developed. An other programme, suitable for flat material, one or more (different) layers and for slopes smaller than 45 degrees, was used for verification. This programme, (BUMBLE_BEAM.PAS), based on tracing B A N D S of light, allows the computation of transmissivity (reflectivity, absorptivity) of arbitrary linear polarised light. Both programmes allow a regressive computation of transmissivity and reflectivity, just by using smooth, averaged values in stead of the actual values determined by the geometry of polarisation. This has a small influence on the computation results as far as tranmissivity for diffuse radiation is concerned. The influence increases when the number of layers or the slope increases. With a proper design greenhouse transmission values for diffuse light of more than 90% can be achieved. | |
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