Exterior Lighting Power for Non-Tradable Surfaces

Appendix G does not address exterior lighting in the baseline at all. Section 9.4.5 clearly indicates that only tradable surfaces can be used for trade-off. This means that you can exceed one of the tradable categories as long as you are under for another and on balance do not exceed the total tradable allowance. The rationale for having the non-tradable identical is implied in the fact that it is not tradable. The User's Manual refers to this non-tradable allowance as a "use it or lose it" value meaning you can only claim the amount you use, not the full allowance. Since it is not available for trade-off and is limited to the amount you use it must be identical in both models.

This is how the GBCI reviewers have interpreted the standard as the rating authority referenced in Appendix G.

The non-tradable surfaces of a registered historic building can exceed the ASHRAE power allowance, right? In this case, should I model the same power densities for baseline and proposed?

Historic building are exempted from 90.1 in general. However, for LEED they must comply with the mandatory provisions and all exterior lighting is part of a mandatory provision. So no, the exterior lighting cannot exceed the allowance.

Thank you for your answer, Marcus. However, is not clear to me that the ASHRAE exceptions don't apply. Could you please tell me where I can find this statement?

It is not that all ASHRAE exceptions don't apply, just some. I am not aware of any place that specifically states that historic building are not allowed to exceed the exterior lighting provisions. You could search the LEED Interpretations for "historic" and see if you can find if any exceptions have been granted for LEED. As with many issues in 90.1 and LEED there is not a definitive statement prohibiting you from breaking the rules. To get the correct interpretation requires some connecting of the dots or applying some simple logic and knowing the rules.

Section 4.2.1.3 exception a allows historic buildings to be exempted from the requirements of the entire standard. However, if the standard does not apply at all to your project you cannot get LEED certification either. You cannot just selectively apply a provision because it is to your advantage and then not apply it when it goes against you. LEED projects must comply with the mandatory provisions of 90.1 and show sufficient savings to meet the prerequisite. I am not aware of any exceptions to those two LEED requirements (rules). Since exterior lighting is a mandatory provision, logically it follows that all LEED projects must meet this LEED, not ASHRAE, requirement.

A follow up question to this: If I have to adjust the non-tradable allowance down to match the proposed then what value do I use to calculate the 5% unrestricted allowance that gets added to the baseline model? Is it 5% of the tradable + non-tradable (original) OR 5% of the tradable + non-tradable (adjusted)? Thank you.

Adjusted - if I am understanding your terms correctly.

Thanks for clarifying. By "adjusted" I am referring to the "amount used" as you describe in your early post, not the full allowance. The example in the 90.1 users manual uses the full non-tradable + tradable budget allowance to calculated the 5% unrestricted allowance, not the "amount used."

I've also read through the User's Manual on that matter, and I tend to agree with you on using the Allowable amount and not the adjusted. Otherwise, there's a bit of a double-standard. (No pun intended)

I dug into this a bit and let me try to be clear. For the baseline you determine the total tradable and non-tradable allowances and add 5% to that total. You then make the baseline non-tradable the same as the proposed non-tradable. The remaining total is the baseline allowance used for your energy model.

So in regard to your question above it is the full allowance that is used to calculate the 5% unrestricted.

Wonderful! Thank you for clarifying.