Absortancia solar de superficies opacas : metodos de determminação e base de dados para tintas latex acrilica e PVA / Solar absorptance of opaque surfaces : a determination methods and data base for latex acrylic and PVA coatings

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Solar radiation is the main responsible factor for the thermal load of buildings, and its impact over this load depends, mainly, on the solar absorptance of the building envelope. The lack of reliable and current data implies that researchers and specialists use visual perception or adopt tables based on surface colors to quantify the solar absorptance, which enhances the concept that absorptance increases as much as colors are darker. In order to show that the human eye is not reliable indicator of how much solar energy a surface absorbs, this work presents solar absorptance data for different paint colors, which are commonly used in Brazilian façades, measured with a spectrophotometer. Based on these data, determination methods of solar absorptance are proposed and can be used by designers, researchers, and specialists. Besides the spectrophotometer, it is presented a method based on samples digital images through a scanner, in which samples were classified according to the RGB and HSL digital chromatic systems. The second method uses the reflectances of samples measured with the ALTA II spectrometer, and the third method is based on the samples surface temperatures and the absorptances of black and white reference samples. Solar absorptance data measured with the spectrophotometer were adjusted to the standard solar spectrum, because the solar energy is not constant along the solar spectrum. This correction indicated solar absorptance diminishes when submitted to different solar radiation intensities. Finally, the influence of roughness on the solar absorptance was analyzed, whose results indicated roughness linearly increases surfaces solar absorptance. The several analysis and discussions presented in this work prove that only color is not a determinant factor of the solar absorptance. Furthermore, proposed methods are very reliable to identify the solar absorptance of opaque surfaces, whose estimated values with scanner, ALTA II, and surface temperature methods presented differences under 10%, 6,8%, and 3,7%, respectively, when compared to the absorptances measured with the spectrophotometer

ASSUNTO(S)

opaque surfaces conforto termico solar absorptance calor solar construção civil coating thermal comfort tintas

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