Hi All,
I have an interesting situation and would really appreciate any suggestions you have. On my project we are actually going over the allowable light levels when multiplying the WFR (window to floor area ratio) with the Tvis of the glass in many locations. (LEED CI 2009 states that it must be between .15 and .18) This is mainly due to workstations on the window wall that are only 1 bay deep in some instances. (And a Tvis of 70% which comes to .7 for calculation purposes.) I've been told that I can only include the actual workstation, and not the circulation area between, thus making my ratio of glass to floor area too close.
My question is: in the reference guide it states that I can use a combination of compliance paths and the first one mentions that the use of view-preserving automated shades demonstrates a minimum of 25 footcandles of illuminance. (which would, theoretically negate my calculations that are above 0.18). Is there a way to demonstrate for the areas that go above 0.18 that we are using shading devices so the higher than allowed light levels will not be an issue?
Thank you
Leslie
David Posada
Integrated Design & LEED SpecialistSERA Architects
LEEDuser Expert
1979 thumbs up
August 19, 2010 - 4:19 pm
I was under the impression that circulation areas in open offices would be considered part of the regularly occupied space. Given the additonal glare control provided by the shades, including the circulation area in this case may be consistent with the credit intent. Often there's a temptation to gerrymander the regularly occupied area because there's not enough daylight, which doesn't appear to be the case here. I'm interested to hear how others would interpret this!
Eddy Santosa
Director of SustainabilityDBR Engineering Consultants
376 thumbs up
August 23, 2010 - 11:58 am
In my knowledge, the prescriptive method has many inaccuracies. Therefore it will be difficult to discuss. You may see my discussion with Christina Agudelo in same credit in LEED NC 2009.
Regarding your question, I will see the only method is by doing daylight simulation.
TODD REED
Energy Program SpecialistPA DMVA
LEEDuser Expert
888 thumbs up
September 7, 2010 - 3:02 pm
The prescriptive path does not allow for the consideration of exterior or interior shading devices. If you truly want daylight to be a part of the project and you are not just chasing LEED points, it is highly suggested that simulation methods be used to provide occupants the best quantity and quality of daylight. There are alot of free daylight simulation programs available.
David Lam
LEED AP BD&CEckert-Wordell Architects
4 thumbs up
January 4, 2011 - 8:36 am
Todd, could you tell me where I can find these free daylight simulation programs? My project is in Revit 2010, would that be a problem for the daylight programs?
Leslie -
I am also having trouble with WFR (window to floor ratio). I have a tenant fit-out and each of my offices have two standard size windows in them (approx. 3' X 6') and my offices are average size offices. However they do not fall within the .15 and .18 requirement. I seem to not have enough floor area for my windows. It seems very contradictory for the intent of the daylighting credit. I have both fixed exterior shading devices and interior roller shades. We meet all the energy requirements so I'm having a hard time figuring this out as well. What did you end up doing?
Don't get me wrong, I understand why they have the WFR requirement but in situations like these, I don't understand why the square footages of the offices can't count at all. Please any input would help. Thanks.
TODD REED
Energy Program SpecialistPA DMVA
LEEDuser Expert
888 thumbs up
January 4, 2011 - 9:16 am
David,
The free programs out the there are Daysim, SPOT at www.archenergy.com, and Radiance. In your situation with a Revit model, importation into Daysim and Radiance would require another program, Ecotect. Daysim by itself does have a learning curve as does Radiance, I would suggest that you use google sketchup to build a simple model of your spaces, then use the plugins for Daysim for importation. These plugins can be found on the sketchup website, it is a little tricky. If you have 3D Sudio max, importation from Revit is not a big issue, and the daylight simulation in Max is a good one to use. SPOT has been around for awhile, and takes in consideration electric lighting. It is limited with its modeling but the results are relevant.
The current prescriptive path is not a means to help a project provide daylighting to a space. We have projects the have earned 8.1, has an average daylight autonomy of over 50%, has been verified with simulation and actual measurements that illuminance levels at the work surface under worst sky scenarios(overcast for the climate) are above 25 fc for 65% of the space. But, using the prescriptive path, we would not earn the daylight credit.
The path is formula that really is intended for projects that are not looking at using daylight effectively to ensure that spaces are not overly daylit, which is worse than not enough daylight.
Designing spaces and even building them and then looking at whether they meet the daylight requirements (let alone any credit or standard) is not good design. Its the same with using actual measurements, it is taking a chance that you actually meet the requirements. Both scenarios only look at quantitative issues and not the qualitative aspects that are, if not more important.
Good Luck