The use of reflectors in venetian blinds to enhance irradiance in greenhouses

Abstract

Using a venetian blind as a basis, we describe and analyse novel forms of high-gain, nonfocussed sunlight concentrators and test experimental versions. Generally, midday winter light passing mainly through the roof of an E-W single-span greenhouse is reflected downwards to the floor through the use of conventional and modified reflecting louvres in a venetian-blind assembly suspended from the greenhouse apex. Experimentally, in a 7.3-m wide compartment, a 2-m deep conventional louvre assembly produced approximately an 18% gain in the southern half of the house, but a 4% loss in the northern half. A modified louvre assembly, which directs light to both halves of the house, gave, without readjustment of the louvre angle, 16% in the southern half and 7 1 2% in the northern half. Under diffuse light conditions the blind was shown to produce an average 2% loss across the house. As a percentage of light received by the plant, as opposed to external irradiance, an average of 20% gain over the whole house width is predicted under sunny conditions if better manufacturing techniques are employed. Reasonable agreement with theoretical calculations of irradiance is also shown, and a theoretical analysis shows that full irradiance enhancement before and after midday, when oblique sunlight is incident on the reflector, will still be generally obtained.