Solar irradiation inside a single span greenhouse with shading screens

Abstract

A model is offered which yields the solar irradiation at the ground of a single-span greenhouse fitted with screens, in terms of the outside solar irradiation, the position of the sun, the optical properties of the cladding and screening surfaces, the geometry of the screening surface and orientation of the axis of the greenhouse. The model is mathematically exact. From the physical point of view it is founded on the assumption that both the cladding and the screening surfaces are fully diffusive and the radiation diffused through the atmosphere and by the ground is fully isotropic.

The importance of the geometry and of the optical properties of the screen in blocking the admission of solar irradiation inside are indicated. It is found that the solar irradiation inside a greenhouse, with any given cladding material, with any orientation and fitted with shading screens, is mainly determined by the transmittance of the screening surface and to a lesser extent by its reflectance. The collected radiation increases with the transmittance of the screening surface and for a given transmittance, with the reflectance of both the bottom side and topside of the screen. It is also found that a screening surface forming a closed cavity with the inside ground is always more efficient in blocking the admission of solar irradiation than any other shape.