Intelligent Glazing

Peter,

You have three options, simulations, prescriptive, and measurements.

Simulations; if you used sims during design then you should stick with them if they were done correctly. What I mean by correctly is that you used a program which had a script which actually tinted the glass as the illuminance levels increased. Or, you used the lowest VLT the window will produce as the value for all your simulations.

Prescriptive; you would need to use the lowest VLT produced by the window in the calculations.

Measurement; since there is no specific guidelines as when and under what conditions measurement should be taken, to be truthful, I would do it under clear skies around noon.

Hopefully this helps.

Technically no, blinds should be able to block the majority of direct light entering a space. But if the glazing were able to dim to say about 10% VLT which is the same as some shades, then you have an argument that it would be.

Todd, is it mentioned in the reference that we need to use lowest VLT?
If I were the daylight consultant, I would use highest VLT and treat electrochromic capability as "blinds" for single point approach or prescriptive.

Eddy, there is nothing in v3 that I have seen or read in regards to how to handle automatic glazing. But, throughout LEED, and take the MR credits for example, when given a range of performance or recycled content, you always use the lowest value, the worst case scenario.

So is the reason you are saying to use the highest VLT is because if the electronic side fails, you will only have the properties of the glass. Or, because of the potential for over daylighting and glare/

The reason I say the lowest VLT is not only what I mentioned above, but also because if the glazing goes too dark, like mirrored glass low (.3 or lower VLT) then your daylighting zone is smaller. I use the lowest levels as worst case scenario, kind of like the worst case scenario sky conditions. If you can meet it under those conditions then you are good. Blinds will always help with glare over daylit situations.

Hi Todd,
I just assumed it looks like a regular glass with blind. We usually simulate the best case scenario without blind pulled down. Using similar assumption, I will use highest VLT and make electrochromic capability as "blinds". This approach is only for single point time.

LEED usually uses best case scenario in daylight such as sunny clear sky for single point time of time approach. In my opinion, the idea of using best case scenario is related to energy impact. Definitely, climate based approach is better such as shown in LEED v4.

This is definitely an interesting topic. I may have to dig around and see If there ever was a discussion with this. Might propose this as a question to the TAG.

Peter, one suggestion might be to propose a question to GBCI in regards to this issue. What would be the accepted methodology and documentation. I hate for you to submit a credit based on what is posted here to then have it rejected during the review. LEEDuser comments do no override GBCI requirements.

Did you propose a question to GBCI to see if this can be pushed to the TAG to provide direction in regards to this?

As Eddy had mentioned in one of the earlier posts, the VLTs of 10 and 1 could be considered your glare control. I did not know previously that your glazing could basically black out. Again, I would propose this to ensure this methodology is allowable. In my opinion, I say that since you can drop the glass that low, then it would meet the requirements of glare control. But I'm not GBCI nor your reviewer and LEEDuser comments do not set ruling precedents for LEED.

So that leaves the other two VLTs. Because the occupant can control the VLT, then I would say that the highest VLT can be used. It is the same as providing regular glass at x VLT and then having blinds that occupant can lower or adjust. There is no control over the occupants, so using 58% would be what I would use.

If you had automatically dimming glass without any occupant override, then it would be more complicated.

Hope this helps you better. I still suggest that this is run past GBCI. I have not found any rulings on this issue. An since the LI database is so small anymore, and individual project LIs don't get posted, its hard to determine how to handle some of these unique circumstances.

http://www.usgbc.org/ContactUS/

Hello Peter,
I am curious to know if you ever got a response from GBCI.
Thanks