CALCULATION METHOD OF INTERIOR ILLUMINANCE FROM VENETIAN BLIND SYSTEM : Part 2 Case of sun-lit blind system

Abstract

In Part 2 the slats of blind system are uniformly illuminated by the direct sunlight on the critical condition of precisely shading it with slats. On this incident condition numerical solutions of the integral equations give the average luminances of downward and upward surfaces of slats, and from these results the transmittances of blind system of downward and upward light to interior are calculated. When comparing these values with those of flat slats louver system, it is recognized that the differences of both data are not so remarkable. Effects of regular reflection of direct sunlight on the slat surfaces are investigated on the direct and indirect illuminances on the working plane in interior. The first regular reflection on the upward surface of slat adds to direct illuminance. A calculation method of this component is introduced and numerical examples are compared with illuminance due to the diffuse reflection of direct sunlight on the upward slat surfaces. An additional transmittance by the first reqular reflection is also calculated as downward and upward fluxes. It becomes clear that the more regular reflections than twice are negligible for transmittances of blind system. As a result, effects of regular reflection of slat surface are not important as far as Venetian blind system is usually used in the normal slat angle of inclination. Thus, the calculation method of flat slats louver system can be available to get direct and indirect illuminances from Venetian blind system in normal condition.