HVAC System and Area

When you apply an exception from G3.1.1 the square footage of that area comes off the total which is then used to re-enter Table G3.1.1A. This is how that issue is currently being applied in LEED reviews as I understand it.

Personally I do not agree with this method. I think you should enter the table with the full building square footage, select the appropriate system, then apply an exceptions without it affecting the predominant condition. This way the predominant condition determines the majority system and the exception gets applied to only the appropriate spaces.

I would love to hear from the forum - which method sounds right to you?

I've contacted ASHRAE to get their interpretation of this issue. I'm hoping to have word from the subcommittee chair soon. I personally feel that the intent of the exception is to divide spaces and assign systems to those spaces as they would normally be designed. So that a space with a different occupancy, operating schedule, or peak thermal load isn't lumped in one system together. Therefore each space should be considered separately with regard to Table G3.1.1A. I know you're saying the predominant space is the only one that follows the table, and all others follow the exception (meaning CAV DX). But this doesn't make sense to me either. I can understand small areas being designated as CAV DX, like the examlpe says a Server Room. But just because a space is 5,000 sqft less than another (which allows for "games" to be played in boundary lines) doesn't mean than it should be CAV DX. Would you every make an office CAV DX just because it's 50,000 sqft and the attached warehouse is 55,000 sqft? So, I understand it, but I think it should be addressed by ASHRAE and rules should be made for maximum space allowed for the exception. But still allow for the baseline of the other spaces to be considered on their own if they have different occupancy, operating, or peak loads. I think exception A could be expanded beyond residential/non-residential or heating, to also include exception B or C so that a 20,000 sqft cutoff is established for CAV DX.

You could make the same argument about any "boundary" level established in the standard.

I agree that it should be addressed by ASHRAE so let us know if you hear anything.