Methods for Calculating the Effective Longwave Radiative Properties of a Venetian Blind Layer
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Date
2004
Authors
Yahoda, Darryl S.
Wright, John L.
Journal Title
Journal ISSN
Volume Title
Publisher
American Society of Heating, Refrigerating and Air-Conditioning Engineers
Abstract
Window solar gain can strongly influence building energy consumption, peak loads, and comfort. Shading devices are routinely used to control solar gain. The use of venetian blinds is particularly common. There is a strong need for models that can accurately simulate this type of device. As a first step, this study deals with the mechanisms of longwave radiant exchange. Methods are presented by which spatially averaged optical properties (referred to as “effective” optical proper-ties) can be calculated. An enclosure model was formulated to model the interaction of radiation with the slat surfaces. Six enclosure areas, rather than four, were used to account for the possible overlap of blind slats. This optical model allows the venetian blind to be treated as a planar, homogeneous ''black-box'' layer in a series of glazing layers and, coupled with the appropriate convection model, can be incorporated within a standard one-dimensional center-glass heat transfer analysis. Sample calculations were performed and the resulting effec-tive optical properties discussed. The model compares favor-ably with expected trends and limits. The effect of slat curvature was also examined.
Description
© 2004. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Vol. 110, Part 1. For personal use only. Additional reproduction,
distribution, or transmission in either print or digital form is not permitted without ASHRAE’s prior written permission.
Keywords
Fenestration, Venetian blind, Longwave, Model