Hello, My project is located in a building from the 1960's, the project is not going to have any window treatment such as tints or films, what would be a valid VTS value for the exterior windows (clear glass), .90 would be ok?

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TODD REED

Energy Program Specialist

PA DMVA

LEEDuser Expert

626 thumbs up

Fri, 07/26/2013 - 12:18

One way to determine an unknown VLT is to use a light meter. If you can open the windows, or take a reading outside, and then a reading on the interior side of the window right away, should give you a reasonable VLT. Not quite sure if a building, and I'm assuming a US building, would have a VLT of 90%. The amount of iron used in glass manufacturing at the time might put it a lower value, maybe at 80%. The other option is to use the default VLT that is used in energy modeling for an unknown glass. I had posted on this option awhile ago and will search for that post as to the specific ASHRAE document that sets these defaults.

TODD REED

Energy Program Specialist

PA DMVA

LEEDuser Expert

626 thumbs up

Fri, 07/26/2013 - 12:34

ASHRAE 90.1 2007 table A8.2 sets default VLTs depending on the window construction. This could be used if you don;t use a light meter to try an establish a reasonable VLT.

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