Articles
LIGHT TRANSMISSION OF ZIGZAG-SHAPED MULTISPAN GREENHOUSES
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.