ENERGY EFFICIENT LIGHTING DESIGN FOR VENLO TYPE GREENHOUSES

Abstract

TNO has developed a Radiance software model to calculate the light distribution in the greenhouse using raytracing methods, suitable for daylight and artificial lighting. The model is based on a 3D CAD (Computer aided design) model. The objective is to maximize the efficiency of the artificial lighting system (the amount of light from the bulbs reaching the crops). Raytracing is a common method to simulate the behavior of light entering a greenhouse. The calculations are based on a CIE (International commission on illumination) overcast sky. The 3D CAD model of the greenhouse is made using a standard aluminium roof system and steel superstructure of a common Venlo Type greenhouse (bay width 4.0m, section width 5.0 m). The light distribution of the brackets is provided by Lights Interaction Agro BV, based on measurements on their Papillon bracket. The vertical and horizontal light distribution in and above the greenhouse is used to find the light interception of the greenhouse. A grid of vertical measurement points are used to find the light distribution of the lighting system (using a dark sky). Special asymmetrical Papillon brackets are used to optimize the light efficiency of the greenhouse, by minimizing the lighting level on the central pathway and by minimizing the light loss through the greenhouse facade. The light interception of the Venlo type greenhouse in the CIE overcast sky is compared to the IDT (Imag/DLV/TNO) method. The IDT method is widely used in the Netherlands to evaluate the light interception of greenhouses during the design process. The calculations of the greenhouse structure and the lighting system (dark sky) are used to optimize the lighting system. Concluded is that the IDT method is comparable with the raytracing calculations. Concerning the lighting systems a improvement of 10% in lighting efficiency can be achieved using the new Papillon bracket and the asymmetrical brackets at the greenhouse facade and at the central path.