Daylight Simulation at 9am and 3pm

It is both 9am and 3pm.

So lets say one space has 85% of its calculation points falling between the limits at 9am, but only 65% at 3pm. The 65% is the value of compliant square footage for that space. You'll need to submit both 9am and 3pm simulation results.

I use a spreadsheet listing all the spaces with a total square footage column, 9am and 3pm column, and then a total compliant square footage column.

Todd, I agree with you as long as the 65% at 3pm overlaps with the 85% at 9am. In other words, if the 85% at 9am is all on the left side of the room and the 65% at 3pm is all on the right side of the room and the overlap between them only covers 50% of the room, then only 50% of the room complies. At least, that is my understanding.

I think that Todd's approach is sufficient. The intent of the daylight credit is to provide 75% of the room. The daylight illuminance level pattern in the room may change every second because of the solar latitude and azimuth position. However as long as the room has 75% daylighted area, it should be OK. If the overlap method is required, it is very difficult to achieve 75%.

For some reason, I cannot find the original place where I posted this comment from the USGBC, so I'll post it here again:

I received this statement in a response from USGBC Technical Customer Service: 'The simulation needs to document compliance at both 9:00 a.m. and 3:00 p.m.. Only areas that meet the requirements at both of these times are considered complaint.'

To me, this means that you cannot take an average and you cannot evaluate the two times separately, ie. you cannot include the space in the compliant area if 75% of it meets the footcandle requirement at 9am and then also meets it at 75% at 3pm (unless that 75% overlaps.)

If the agent had said only ROOMS that comply with this requirement apply, I think that might still leave some doubt, but because they said 'area' and only area is compliant, not rooms, I can only interpret it to mean that each calculation spot must be evaluated at 9am and 3pm and applied toward the compliant area totals if there are 25 fc at that spot at both times.

I would be cautious of evaluating an interpretation on how it applies to the credit's difficulty.

I would love to hear from others who have experience with reviewers.

Update: I spoke with a colleague today who told me that she has had luck with reviewers when using the "averaging" method. The method is: calc at 9 and 3. If each of those times meet the 75% individually, take the average of those square footages and use that to enter into the reporting spreadsheet. So, once again...it all depends on what reviewer you get apparently.

I have submitted a couple of 8.1s already for 2009 using what i initially stated a year ago ( a year already) and have not had any issues.

If it were to be considered on a point being compliant at both times, then it would be required and requested to provide overlapping simulation results to verify the points and areas are calculated correctly.
Already the reviewer can only really visually determine whether the project team entered the correct compliant square footage, its based on the word of the professional. If the claimed area looks smaller than in the outputs, assuming the calc point grid is correct, then a reviewer would have reason to question it. I have yet to see that.

So, you don't use an average, right? You take the minimum % from 9am or 3pm for each space and add that up and compare it to the total. Then if that number is greater than 75% of the total, it complies?

No you don't use an average. However, as you explained how a colleaque used the average to document the credit, that is also acceptable. ( I'm assuming that this is a single space, and not the total compliant space for that time. If your colleague took the total compliant square footage for 9am and 3pm and averaged them together, they got away with one.) So lets say you have a space and at both times it has a minimum of 75%, you could average it together because it would be over 75% no matter what. Where this is could not be acceptable if this method is used to push a school project to earn two points for 90% where they would not otherwise earn it.

On my spreadsheet, ( i make my own) i have total space sq ft, 9am compliant sq ft, 3pm compliant sq ft, total compliant sq ft (which is the lowest of the two.) The total compliant sq ft column is divided by the total sq ft.