The Hohenstein Institute in Bönnigheim, Germany has developed some new tests to determine the so-called “g-value,” a measure for the energy transmittance of materials. Textile manufacturers can use the results of these tests to optimize their products with specific regard to low energy transmission. The g-value is composed of the directly-transmitted solar radiation and the secondary heat emission resulting from radiant emittance and convection on the inside of the material. A g-value of 1 corresponds to an energy transmission, or heat gain, of 100 percent. These new tests should help manufacturers choose textiles that are cool in summer and warm in winter with a minimum use of energy. The experts at the Hohenstein Institute determine the g-value based on EN 410 “Glass in building,” the European standards for the determination of the luminous and solar characteristics of glazing. Conventional uncoated glass has a g-value of around 0.85, which means that 85 percent of the incoming heat can be transmitted into the room behind the glazing. The rest is reflected or absorbed by the glass. Modern triple glazing has a value of around 0.55. In addition to the g-value, the new tests can also provide information about direct radiation transmittance, radiation reflectance, the radiation absorption factor, light transmittance, light reflectance, as well as UVA and UVB transmission.

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