Our project features a building that has an open concept with glazing all along the exterior. The interior offices are typically encased in glazing to further allow access to natural light. When calculating the Daylight Factor for these interior offices I am considering using the following method I have seen described else where:
Use the visible light transmittance of the exterior glass and multiply it times the visible light transmittance of the interior glass of the interior room.
Then use the area of glass of the room with the borrow light glass in it just as if it was on an outside wall. This should reduce the amount of useful light in the internal room receives due to the day light's passage through exterior glass and then interior glass.
A sample of the calculation would be as assuming fairly high visible light transmittance
glazing:
• Visible light transmittance, exterior double glass (possibly low-e, untinted) = 0.69
• Visible light transmittance, interior single glass, clear = 0.81
• Useful visible light transmittance (of internal room) = 0.69 x 0.81 = 0.56.
can anyone advise if this is an acceptable approach?
Alan D'Souza
The Weidt Group, Inc.9 thumbs up
January 22, 2010 - 10:54 am
If I understand this correctly, your calculation does not account for the fall-off of light between the exterior and interior walls: simply put there is much less light incident on the interior wall than on the exterior wall.
How are you accounting for the distance of the interior wall from the exterior source of light?
Adolfo Silva
PrincipalEcovert Corporation
63 thumbs up
January 22, 2010 - 11:57 am
This is a good point....so if we were to use a combined total area which would include the interior office space plus the area from it to the perimeter windows and see if it meets the min 2% daylight factor and if so then the actual square footage of the interior office can be used in to support the credit. Thoughts?
Ryan Zizzo
Green Building Project AssociateHalsall Associates
3 thumbs up
August 17, 2010 - 4:38 pm
Adolfo, I'm assuming this reply comes too late to help - but that method would provide a conservative value. It uses the combined Tvis value for the interior space (obtained by multiplying both exterior and interior Tvis values together) for the entire area - however this value is only applicable to the interior zone (not the perimeter zone).
To accurately calculate this scenario, one would need to apply the exterior Tvis value for the perimeter space, and then the combined Tvis value for the interior space only, and somehow account for the fall-off between these areas as Alan rightly pointed out. I am unaware of any "hand-calculations" that can account for this. It is my understanding that a daylighting simulation would be required.
Jonathan Weiss
Jacobs Buildings & Infrastructure215 thumbs up
October 26, 2010 - 9:31 am
this thread is really about Daylight, not Views, right? Can it be moved on LEED User so people looking on 8.1 will find it?
Tristan Roberts
RepresentativeVermont House of Representatives
LEEDuser Expert
11477 thumbs up
October 29, 2010 - 4:21 pm
Jonathan, we can't move the thread. Maybe you can post a link on the IEQc8.1 forum, noting what you think is particularly useful about this thread? Here's the direct link to it:http://www.leeduser.com/credit/NC-2009/IEQc8.2#comment-903