Too much Window Area (WA)?

I agree with you. The calculation method is not a robust method. I will suggest to use simulation method. I think if there is no direct light in the room, the room will comply easily.

Do you have any program suggestions for the simulation method? I have been trying to figure out a couple different ones but would like some input from others that have done this before. Thank you!

Tyler, At our company we have used two software packages, Autodesk's 3d Studio Max and AGI. It seems like AGI has less of a learning curve than 3d Studio Max. What we haven't found yet is a daylighting simulation software that takes the results from 9am and 3pm and gives you the net percentage which is compliant. Any ideas anyone?

Tyler, I use Ecotect as GUI and run the calculation in Radiance engine. Additionally, I heard AGI is a good tool as well.

Carol, To address your initial question of too much window area: from your description it does sound like you have too much window area and quite a high VLT. In what way do you think that reducing your window area does not follow the purpose of the credit? A lot more information about your project is needed to assess this, for example, what is the use of the room (a classroom) ? What are the hours of the room? Is the building heating load or cooling load dominant? Are the windows on the same wall or two different walls with two different orientations? What is the height of the window head height? What is the height of the ceiling? Glare and over-glazing are the two main enemies of good daylighting. What type of shading devices are being provided? To answer the software question, first a question in reply: What kind of resources do you have to commit to purchasing, learning and using daylighting software? If you do not have roughly $1,000/2 years, at least 40-80 training hours and roughly 4-8 hours per room simulation, you are probably better off hiring a daylighting consultant or simulationist on an as-needed basis. Daylighting simulations are like any other computer software, garbage in-garbage out, so you need someone who is experienced with the output to make sure that it is accurate.

I have a similar situation. My project has a large overhang external shading, but with big windows. Simulation results show all the perimeter rooms with almost no light at Sep 21 09:00 and 15:00. However, when I attempt with the prescriptive method, my WTF ratios are too large for compliance! My Tvis is 0.83. Something is wrong here. And also is the "Daylit zone" deturmined from the 62º rule (or is that only for internally dropped ceilings), or is it 2H where H is the allowable window height for calculations, OR is it the bay depth to the back wall of the zone?

Jean, What simulation program are you running? Something appears to be wrong if simulation is showing nothing with a TVIS of 0.83 (This TVIS is typical for interior glazing or single glazing. Seems high for an exterior glazing component) and your WFR is too big. I would say you have an input error or you modeled something incorrectly. I have done projects were the WFR was too small to meet compliance, yet, both simulation and actual measurements show the project meeting the daylight requirements with a 63% VLT in north facing glazing. It is actually 63 degrees, and is used to determine your daylight zone if there is a drop ceiling that would intersect the glazing if continued across the space. If there is no ceiling that would interfere with the glazing then the depth of your daylight zone is twice the window head height.

Thanks for the reply, Actually, in my prescriptive method, I discovered a meter to foot conversion error. I just, just get 75%, but I've not limited it to 2H (we don't have any dropped ceilings under the top of the window height). That means if I recalculate with 2H...it's dead. Also, at the moment I am using a bay area that starts on the interior side of a glass vestibule (on x2 occasions)...which makes it even more dead, if this is not accepted. As for the simulation, I have simulated with energy plus using fullexterior reflections (and am rerunning with fullinterior and exterior reflections to see if it improves things), and got the same result when running the model in the new DesignBuilder v3 Daylighting simulation which uses Radiance. There are public picture up of the building here: http://www.schloss-geister.de/nachricht/items/baufortschritt-28-juni-2011/ The funny thing is, is when you look at the model and try to tell someone that it doesn't have "good enough" daylighting, they will laugh in your face.

It looks like I used the 62º Rule on the lighting through the glass vestibules which gave 0ft² conforming square meter. So I'm still in there with a chance.

Jean, I did laugh when i saw the pictures. Those spaces have to meet the daylight requirements. A far as the programs that you are using for daylighting, i do not have any experience with any of them. I will say that i probably wouldn;t rely on energy plus to calculate my daylighting. You might break down each space into multiple daylight zones. Break the spaces down so that the WFR meets the requirements. For documentation, provide a table showing the multiple zones for each space and how they meet the requirement.

One last question: Is H (for the daylit area depth) = window head height (adjusted down with 63° rule if applicable, due to underhang) to FLOOR or to the 30" above finished floor level (as used for the window area calculation)?

It would be to the floor. The 30 inches is the minimum height that can be used to calculate usable glazing. This is the same height that was used for glazing factor calculation. Basically, any glazing under 30" in height does not contribute to usable daylight on the work surface.