The development of advanced materials for facades aims to achieve higher energy efficiency of buildings. Successful application of these materials depends on the availability of reliable characterization data. While data derived from integrated measurements of transmission and reflection is widely available, it does not allow to characterize the angular dependence of the performance of such materials. The Bidirectional Reflection-Transmission Distribution (BRTD) can be measured by commercially available Gonio-Photometers and, complimenting integrated transmittance and reflectance, allows the assessment of facade materials and thus supports both their development and application. Validation of the obtained data is crucial to back these measurements.
Integration of validation procedures into the operation of a characterization laboratory allowing a well-defined approach to quality control is presented for a range of typical material and sample types:
* consistency checks of measurement data
* cross-checking of integrated material properties derived from BRTD data with integrating sphere measurements
* round-robin comparison between laboratories using comparable devices
The results of of these first measurements are discussed. Potential to further improve the availability of reliable angular resolved characterization data for the building sector is identified.
Shade-screens are widely used in commercial buildings as a way to limit the amount of direct sunlight that can disturb people in the building. The shade screens also reduce the solar heat-gain through glazing the system. Modern energy and daylighting analysis software such as EnergyPlus and Radiance require complete scattering properties of the scattering materials in the system.
In this paper a shade screen used in the LBNL daylighting testbed is
characterized using a photogoniometer and a normal angle of incidence
integrating sphere. The data is used to create a complete bi-directional scattering distribution function (BSDF) that can be used in simulation programs.
The resulting BSDF is compared to a model BSDFs, both directly and by
calculating the solar heat-gain coefficient for a dual pane system using Window 6.
Light scattering materials have several uses in solar energy applications, ranging from a purely aesthetic function
as a cover glass to a way of increasing the path-length of photons inside a semiconductor. Knowing the
transmittance of such elements is of essence to properly model, simulate, and design a solar energy system.
The traditional method for obtaining the transmittance is to use a spectrophotometer fitted with an integrating
sphere detector. However, it is well-known that most commercial integrating spheres underestimate the true
transmittance of thick scattering samples. This study investigates a method to obtain quantitative values of the
losses associated with measuring a scattering sample. The International Commission on Glass (ICG TC-10) is
conducting an inter-laboratory comparison (ILC) on scattering samples to improve the methodology for characterizing
such samples. A fritted glass sample similar to one in the ILC was used as an example. One side of a
clear glass sample has a highly scattering layer. The bi-directional transmittance distribution function (BTDF)
for the sample was obtained using a goniophotometer and then used as scattering function in a ray-tracing
simulation. The ray-tracer was configured to report the amount of light exiting all six surfaces of the sample as
well as through various ports defined by the integrating sphere geometry. The sample was then measured with
a commercial integrating sphere in several different configurations, verifying the accuracy of the model.
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