Solar transmittance of honeycomb and parallel slat arrays

Abstract This paper presents generalized formulations for the calculation of the solar transmittance of symmetrical configurations like square celled honeycombs as well as for such convection suppression devices (CSDs) as parallel slat arrays, wherein propagation of the incident ray is a strong function of solar azimuthal angle. The formulations take into account refraction, scattering and absorption of radiation by vertical walls. The validity of the formulations is examined by experimental observations made with a pyranometer which show good agreement. Honeycomb and slat array transmittance to incident radiation is calculated, and results corresponding to a wide range of angles of incidence and aspect ratios are presented. It is found that a slat device made from thin transparent film may have solar transmittance in the range 0.9–0.95. However, it seems essential that the device be encapsulated for satisfactory performance.