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Type: Artigo de evento
Title: A Method To Identify The Solar Absorptance Of Opaque Surfaces With A Low-cost Spectrometer
Author: Dornelles K.
Roriz M.
Abstract: The factor with major influence over solar heat gains of a building is the solar absorptance of its external surfaces defined as the ratio of the solar energy absorbed by the surface to the total of the incident solar energy. For several cases, particularly in low latitudes, these gains can represent more than 50% of the building total thermal load, with great influence over its indoor temperatures. For opaque surfaces, the absorptance corresponds to the difference between its reflectance and the unity. Currently, the most accurate process used to identify the solar absorptance of a sample is to measure its reflectance using a spectrophotometer, a very expensive equipment rarely available for specialists or designers. For these reasons, they use simplified tables based only on the object colours. This paper presents a method to identify, with very satisfactory accuracy, solar absorptances of opaque surfaces using the ALTA II, a low-cost spectrometer that measures reflectances correspondent to radiations at eleven different wavelengths, from 470 to 940 nm. Firstly, reflectances of painted samples with different colours were measured using the ALTA, and they were compared with correspondent determined values using a spectrophotometer. After this, based on ALTA II data, equations were developed to calculate reflectances for the visible range (380 to 780 nm) of the solar spectrum, the near-Infrared range (780 to 2500 nm), and for the total solar spectrum (380 to 2500 nm). The main contribution of this work is to indicate a reliable and accessible procedure to specialists, which will be useful as an alternative to usual techniques to obtain reflectances and absorptances.
Rights: fechado
Identifier DOI: 
Date Issue: 2006
Appears in Collections:Unicamp - Artigos e Outros Documentos

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