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Research Papers

A Simplified Method for Calculating the Effective Solar Optical Properties of a Venetian Blind Layer for Building Energy Simulation

[+] Author and Article Information
N. A. Kotey

Department of Mechanical Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canadanakotey@engmail.uwaterloo.ca

M. R. Collins, J. L. Wright

Department of Mechanical Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada

T. Jiang

 BC Hydro, Power Smart Engineering, 8th Floor, 4555 Kingsway, Burnaby, BC V5H 4T8

J. Sol. Energy Eng 131(2), 021002 (Mar 24, 2009) (9 pages) doi:10.1115/1.3090822 History: Received November 12, 2007; Revised May 05, 2008; Published March 24, 2009

The use of venetian blinds to control solar gain through windows is common in both residential and commercial buildings, and their potential for reduction in peak cooling load and energy consumption is recognized to be large. As such, there is a strong need for models that allow a venetian blind to be included in glazing system analysis. A simplified method of calculating the “effective” solar optical properties of a venetian blind is presented. The solar optical properties of the entire blind are determined based on slat geometry and the optical properties of the slat material, and on the direction and nature (beam or diffuse) of incident radiation. The slat material optical properties are assumed to be independent of the angle of incidence, and are assumed to transmit and reflect beam radiation diffusely. As a first approximation, the slats are assumed to be flat with negligible thickness. A correction is then developed and applied that accounts for the curvature of the slat. The results of the flat and curved slat models are compared with experimental data for commercially available venetian blinds. Both models demonstrate excellent agreement with experiments, except when the profile and slat angles are aligned. In that case, the flat slat model predicts blind transmissions that are too large. The models developed in this study provide useful input to multilayer glazing/shading models used for rating or for building energy simulation.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Enclosure geometry for calculating venetian blind layer optical properties: (a) incident beam radiation (four-surface model), (b) incident beam radiation (six-surface model), and (c) incident diffuse radiation

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Figure 2

Differing effects of slat curvature on blockage of irradiation

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Figure 3

Angular conditions under which slat curvature is a factor

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Figure 4

Locations of intermediate points

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Figure 5

Irradiation cases considered in original model (top-lit only)

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Figure 6

Effective solar optical properties versus profile angle of incident beam radiation: (a) front optical properties and (b) back optical properties

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Figure 7

Effective solar optical properties versus slat angle for incident diffuse radiation

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Figure 8

The BAI-IS and the experimental model

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Figure 9

Comparison between experimental data, flat slat model, and curved slat model for three slat angles: (a) ϕ=0 deg, (b) ϕ=30 deg, and (c) ϕ=60 deg

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