LO-09-078 -- Thermal Modeling of Shading Devices of Windows PDF

Shading devices are important design elements of glazed façades to reduce energy consumption of buildings and improve thermal and visual comfort of occupants. Although there has been significant development in the evaluation and modeling of the thermal performance of shading devices, current methodologies are limited to a few shading products and types. Furthermore, current fenestration thermal models do not account for radiation emission and absorption throughout shading layers, and allurements for energy generation and conversion imbedded in glazing layers. This paper presents a general methodology to compute the thermal performance of fenestration systems incorporating permeable shading devices and elements for energy generation and conversion. The methodology assumes each shading layer as porous with effective radiation and thermal properties. The effective properties account for the geometrical and thermal characteristics of the shading layer, and the effect of the convective heat transfer within the layer porous structure. Using the concept of the thermal penetration length, effects of porous shading layers on the convective heat transfer from their boundary surfaces to the adjacent gas spaces are also accounted for. A validation study is carried out, in which the U-factor of a double-glazed window with between-pane Venetian blinds are compared with the available laboratory measurement. The comparison results show that the model predictions are in good agreement with the measurement.

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