Daylight Simulation for LEED

[swalton240189]

I'm experimenting with the 3D max Daylight Simulation for LEED 2009 Design and Construction. Acording to the LEED requirements I need to do a CIE clear sky at 9am and 3pm on march. or sept. 21st. My issue is that I don't know what to put in as values for the Diffuse Horizontal Illuminance or the Direct Normal Illuminance. Do you know of any charts where I can look those up? I can use a weather file to get the numbers in the ballpark, but I want to use the correct CIE Clear Sky. does anyone know those values for Pittsburgh,PA?

I found this but on first glance it is kind of intimidating. Maybe I just need to go for it and start plugging in numbers to the big formula.
http://www.esim.ca/2002/documents/Proceedings/other2.pdf

Thanks

[swalton240189]

On closer reading it doesn't have to be the CIE clear sky it just says "a clear sky condition" But I guess my question still remains what are good numbers for direct and diffuse illuminance?

[stusic]

You're post hasn't gone unnoticed, I just don't rightly know the answer. There has to be another way than that formula (ugh!) - a chart or something out there... I tried looking a bit, but only got big formulas...

Just asking, but when you assembled this scene, you made it geographically correct (i.e., you set up the sun for Pittsburgh)?

[swalton240189]

Just asking, but when you assembled this scene, you made it geographically correct (i.e., you set up the sun for Pittsburgh)?

Thanks for getting back to me...Yeah I set the geographic location to Pittsburgh. It came in that way through the Revit to FBX.

Using the weather files from the DOE ( http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data3.cfm/region=4_north_and_central_america_wmo_region_4/country=1_usa/cname=USA#PA )you can get a pretty good idea ow whether it is sunny or cloudy based on the ratio between the direct and diffuse but it would be nice if the USGBC gave a more explicit definition of a clear sky condition.

[pierre-felix.breton]

. My issue is that I don't know what to put in as values for the Diffuse Horizontal Illuminance or the Direct Normal Illuminance.

LEED 8.1 requires daylight factors using a CIE Overcast sky. By definition, the CIES overcast sky implies that the direct normal illuminances are set to 0. THe diffuse illuminances can be pretty much anything since the daylight factors will normalize the results on a 0 to 1 scale.

You can take the design sky demonstrated in this website:

http://squ1.org/wiki/Design_Sky

Hope this helps

[swalton240189]

LEED 8.1 requires daylight factors using a CIE Overcast sky. By definition, the CIES overcast sky implies that the direct normal illuminances are set to 0. THe diffuse illuminances can be pretty much anything since the daylight factors will normalize the results on a 0 to 1 scale.

You can take the design sky demonstrated in this website:

http://squ1.org/wiki/Design_Sky

Hope this helps

That is true for pre-2009 LEED calculations. The new 2009 LEED Design and Construction asks for the following:

Demonstrate through computer simulations that 75% or 90%(extra point for schools) or more of all regularly occupied spaces achieve daylight illuminance levels of a minimum of 25 fc and a maximum of 500 fc in a clear sky condition on Sept. 21 at 9am and 3pm; areas with illuminance levels below or above the range do not comply. However, designs that incorporate view preserving automated shades for glare control may demonstrate compliance for only the minimum 25 fc illuminance level.

Does the calculator from square1 work for clear sky?

[lhanyok]

We are starting a project using LEED 2009, and I am currently researching how to simulate the daylighting requirements in IEQ Credit 8.1 as discussed below. We will be starting with a Revit model, and then exporting out to an FBX and importing into Max. Is this the most effective way to do the daylighting simulation from a Revit model? If so, I have the same question regarding the clear sky.

[Mike Sealander]

I've been bringing a Revit model into Max, and then fetching the weather file in Max. The CIE design sky values populate automatically. I'm at about 44.5 degrees north latitude, and the diffuse horizontal comes in at about 923 footcandles, the direct comes in at 10,000 fc. I believe these are valid numbers for diffuse and direct for my latitude. Daylight factor is percent light intensity indoors versus outdoors, so a DF of 2 corresponds to interior fc values that are 2% of exterior fc values.
The trick with the LEED calculations regarding 9/21 at 9 am and 3 pm is to minimize east and west glazing that will produce interior glare: fc levels above 500. In Max, it appears you can ratchet down direct sunlight glare through very low visible light transmittance glazing. I've been experimenting with high reflectance (which I believe is the opposite of transmittance) Autodesk glass, with some good results.

[josephvalentinetti689899]

You're post hasn't gone unnoticed, I just don't rightly know the answer. There has to be another way than that formula (ugh!) - a chart or something out there... I tried looking a bit, but only got big formulas...