PDD Sample Item #4

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    Benjamin Norkin

    It seems like Low-E coating is a magical material that either lets heat in or rejects heat, based on your mood for the day. But after crashing on this last night, I think:

    - It prevents conductance of heat, i.e. helps the window maintain a low U-factor.
    - It allows solar radiation, which you want for passive heating, i.e. high SHGC
    - It's very customizable, so you can block the solar radiation you don't want and allow the solar radiation you do want...all three typical bands, UV, Visible and IR.

    From one of the Lechner books on the matrix...special coatings are now available that transmit solar radiation but reflect long-wave infrared radiation. These low-e (low-emissivity)coatings are ideal for those buildings that need to reduce winter heat loss and at the same time allow the sun to shine in (i.e. passive solar). Because low-e windows reduce heat flow, they are given a higher R-Value."

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    Erica Spayd

    Benjamin is pretty spot on, these can be customized to your needs based on the specific type of coating AND the location of the coating - which face of which lite of an IGU the coating is applied to. In a colder climate where you want passive solar heating, you'd put the coating on the #3 or #4 surface. In a warmer climate where you want to limit heat gain, your put it on the #2 surface. You'd rarely coat the #1 surface, as it is exposed to the elements and could be damaged more easily. The only instance I've ever seen with the coating on the #1 surface was when bird glass was required, as the etchings were on the #2.

    Also, specifically in regards sample item 4, though an IGU with clear glass does increase visibility into the storefront, it also causes product on display in the window to fade pretty rapidly; the low-e helps keep the UV light out, protecting the product within.

    This low-e glass manufacturer's link is really helpful in breaking down the properties of low-e coatings: http://glassed.vitroglazings.com/glasstopics/how_lowe_works.aspx

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