Sustainability, Energy and Architecture by Sayigh Ali

Author:Sayigh, Ali
Language: eng
Format: epub
ISBN: 9780123977571
Publisher: Elsevier Science
Published: 2013-09-29T16:00:00+00:00

Solar control glass can reduce daylighting as well. Therefore, selecting glazing with specific characteristics is an important step in daylighting design.

9.12.1 Glazing

The type of glazing used in a window or skylight influences the light transmittance considerably. A single sheet of glass transmits about 90% of the incident light, a double glazing with a low-e coating about 65%, and solar control double glazing from 65% to 30%. In climatic zones with significant heating demand, double or triple glazing with low-e coatings are used, to achieve low heat transmission coefficients (u-values).

In regions with significant cooling demand, double glazed units with low-e coating and external shading devices are very efficient, especially if they are adjustable for good daylighting. In buildings with large window areas or totally glazed façades, solar protective glass is often used in combination with internal glare protection. Body-tinted glass offers rather poor solar protection, as the radiation is mainly absorbed, hence increasing the temperature of the internal glass surfaces. Solar reflective coatings are more efficient. Nowadays, selectively reflective coatings are often applied, which are more effective for daylighting and solar control. These advanced materials predominantly reflect the infrared part of solar radiation, while transmitting the visible spectrum. Typical ratios of light transmittance to solar heat gain coefficient are e.g. 66% / 33% or 50% / 25%. The reflecting characteristics of these glasses also avoid the typical mirror effect of conventional solar reflective coatings.

All the coatings described do not only change the light transmittance, but also alter the spectral composition of the transmitted light. Helena Buelow-Huebe [17] has shown in detail that coatings particularly filter out the red and the blue regions of the visible spectrum (Figure 9.12). The quality of color rendering is reduced in comparison to clear, uncoated glass and, last not least, the circadian effect by wavelengths from 446 to 477 nm, too.

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