Tubular daylighting devices—Development and validation of a thermal model (1415-RP)

This article presents the development and validation of a simplified model to compute the thermal characteristics (solar heat gain coefficient and thermal conductance (U-factor)) and surface temperatures of tubular daylighting devices. The model takes into account the three modes of heat transfer: conduction, convection, and surface-to-surface radiation. A one-dimensional heat conduction model is applied to tubular daylight device glazing layers. The convective heat transfer from tubular daylight device surfaces to their adjacent air spaces uses existing correlations for natural flows in enclosed air cavities and free stream air spaces. A zonal model, in which the pipe air space is divided into a number of thermally stacked zones, is used to predict the vertical average temperature distribution in the air cavity and wall surface of pipe. Thermal radiation exchange among surfaces uses the formulation of the form factor applied to the aforementioned zonal model. An iterative sequential procedure is proposed...