GREENHOUSE TRANSMISSIVITY COMPUTATIONS BASED ON A GLOBAL RADIATION TRANSFER MODEL

The distribution of the incident solar energy across different spectrum regions (i.e. UV, PAR, NIR) on the surfaces inside a greenhouse plays a major role in its energy balance and also affects basic plant physiological processes, as well as pathogen, weed and insect development. In this paper a global radiation transfer model is used, along with a solar energy model and various well-established computer graphics techniques, in order to implement an algorithm, which computes the greenhouse global solar transmissivity. The algorithm can compute the transmissivity for greenhouses of arbitrary geometric complexity, based on the greenhouse position and orientation, its CAD model, and the optical properties of its surfaces. Multiple reflections and transmissions, based on surface-to-surface visibilities are computed on a finite-element mesh of the greenhouse surfaces, in order to compute a physically correct and accurate irradiance distribution. A number of simulation tests are presented, which indicate that the proposed method provides physically sound results. As a case study, the daily average of a greenhouse’s (clear sky) global transmissivity was computed on winter solstice, for E-W and N-S orientations. In accordance to published experimental results, the spatially-average transmissivity was found to be higher for the E-W orientation, accompanied though by a higher standard deviation (non-uniformity).