So I have a room of 300SF with a window area (above the 30"zone) of
56 SF and a Tvis of .69 (from the window manufacturer). Basically when I complete the calculation in a LEED v2.2 sample calculator, the space passes the test. When I calculate the same information in the LEED 2009 version, it does not pass the .150 to .180 test. The window covers one wall of the 300SF space from 2'6" to 10' height above finished floor. There is nothing special about how the window is located....no overhangs....no headheight adjustment. In general, it seems as if this room would comply with the .150 to .180 test???? Any thought as to what I am overlooking in the calculation??? I have been researching all day and I can't figure out what my problem is.....a headache is building....HELP!
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Seema Pandya
Sustainability ConsultantSLP
150 thumbs up
June 25, 2010 - 11:46 am
Hi Anne, The NCv2.2 prescriptive way of calculating daylight and the 2009 version are very different from each other, which is why you may be coming up with different numbers. The daylight factor in NCv2.2 takes into account a variable number for the "window geometry". 2009 does not do this. There are completely separate compliances for side lighting and sky lighting.
Lee Dingemans
LEED APWightman & Assoc.
56 thumbs up
August 16, 2010 - 3:20 pm
If I understand this correctly you are supposed to do the following (window area / room area)* V.L.T. this should be between 0.15 and 0.18. Room area you can play around with until you have the max number that works per bay, room area does not have to be an entire room. Could someone let me know if this is correct?
Thus (56/300)*(0.69)=0.12. is out of the 0.15 to 0.18 range, and thus 300 sf does not comply with this credit. However only 225 sf (75%) has to comply to get the point (56/225)*(0.69)=0.17 so I am wondering if this room does meet the criteria?
Could someone clarify this? I would like to know if this is correct to see if I am doing my own math on my project correctly.
Thanks!
Jill Dalglish, PE
Lighting EngineerMKK Consulting Engineers
LEEDuser Expert
440 thumbs up
August 20, 2010 - 10:54 am
Hi Lee, You are doing the math correctly, at least in my understanding. The room meets the criteria only if it is the only room in your project. For your project to meet the criteria, all of the compliant area and all of the regularly occupied spaces must be evaluated together. In other words, if you back out the square footage of this room that meets the minimum 0.15, you get 257 sf to add to the total project compliant area. That way, if you are under the 75% in some areas, you can make it up in other areas.
Keep in mind your windows can't be blocked by dropped ceilings and you must have glare control devices.
Also, as a general comment about this method of compliance, many lighting and daylighting designers agree that this method is far from the best way to go about designing for daylighting. In my opinion, it greatly interrupts good thought on determining glazing visible light transmittance especially in clear sky conditions.