Question: Table G3.1

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Here's a brain puzzler for the list.

I'm assisting a team designing an addition (auditorium + rehearsal space) to an existing high school in Connecticut. As a public project receiving state funding, CT's High Performance Building Standard applies which requires a 21% energy cost savings (LEED for Schools Silver is also targeted for the new addition only).

The new space will have independent/new ventilation systems, but will most likely utilize the boiler and potentially chillers of the existing school building.

Buried in ASHRAE modeling guidelines, we discovered (long after project started and engineers "completed" the model) that additions and alterations that share HVAC systems with existing spaces, are required to include those spaces in their energy model. The new space is designed for a 24% reduction - but if the existing spaces (approx. 3x the sf of new space) are included performance will fall way below the required threshold.

We can't understand how other LEED projects in similar situations ever meet energy reduction requirements, has anyone dealt with this on a LEED project and found ways to circumvent? Has anyone come across a similar condition, and if so - how did you approach it?

Many Thanks in advance -

Vikram Sami, LEED AP BD+C

Sami, Vikram's picture
Joined: 2011-09-30
Reputation: -1

Hey Vik,

Sounds something like a rock and a hard place, but then I've never
pursued LEED for only an addition. It's my hope someone who has can
chime in with a tested position/approach. I'm unfamiliar with the CT
standards but it seems worth nailing down whether they share the same
interpretations as well.

I can offer a few scenarios/suggestions that may help work around the
situation instead of through it in any case:

* If your target is to achieve LEED certification for the
addition only... I've seen auditorium and periphery spaces in large
schools effectively conditioned with their own independent packaged
systems... any chance that might be considered for the design? If so
that might conveniently avoid the issue entirely, by not tying into the
existing boiler/chiller. This assumes you won't have other issues
meeting the conditions for Table G3.1, part #2.

* I have had the fortune to be involved in a similar high school
project which did not explicitly seek or require LEED certification, but
the district and design team were collectively very energy conscious and
pursued a unique approach without any such mandatory/enforced
regulations. Budgets were arranged from the beginning to encompass both
a large new building addition in addition to targeted
retrofits/replacements of existing HVAC, envelope and lighting systems.
The cohesive goal was to identify and implement the most cost-effective
means to reduce and minimize the "whole building" EUI and utility bills
- only rarely focusing on the new addition in isolation of the "big
picture." This was a very involved and satisfying process... and in the
end I think everyone came away feeling the right decisions were made for
the entire facility with the resources available. With all that in mind
- are you too far along to consider re-allocating (or expanding) your
project budget, perhaps VE-ing portions of the present design, to put
those dollars to more effective use retrofitting/improving existing

Still for what it's worth, this specific interpretation does come across
as very "by the book" and in practice unreasonably inflexible
considering LEED certification is being sought only for the addition.
On the flip side, the interpretation request language is not nearly so
clear as your more concise email just now - possibly the responder
hasn't fully grasped why you're asking. If the individual(s) providing
this clarification are open to a discussion, I would propose extending
the conversation to recognize "the whole building must be modeled" and
"the whole building must be incorporated into the performance rating" as
two importantly distinct statements - and that's the clarification
you're driving towards.

It would seem reasonable for the proposed model of a building addition
to incorporate and approximate the systems & building areas not involved
in the addition (modeling the whole building effectively), separately
meter all "existing to remain" loads and systems, and then calculate the
proposed performance rating specifically using a weighted fraction of
the energies consumed by shared & existing-to-remain systems (boilers
and chillers, in this case). All other consumptions exclusive to the
addition could then be isolated and removed from the performance rating
calculation. Adopting a procedure along these lines would have a number
of positive effects, including:

* Leveling the playing field for additions to small vs. large

* Encourage designers to consider replacing, upgrading and/or
improving the operations of existing shared systems to remain

* Not driving design teams to construct entirely independent
HVAC systems where it may make a lot more sense for the building
owner/environment to utilize existing systems of sufficient capacity.

Maybe some of this will help you plot a course with the powers that be,
though I sincerely hope there's a more definite answer/precedent to draw

Best wishes,


Nick-Caton's picture
Joined: 2011-09-30
Reputation: 805

Most existing facilities I've worked with have included an envelope upgrade.
In that light App G allows for us to use the existing envelope for the
baseline. Not sure if this will be your issue, but I find a lot of the
existing envelopes that I've dealt with are simply CMU. If the envelope is
held consistent for both the proposed and baseline case, the efficiency of
the HVAC system should shine a little brighter.

Jesse Eisenhart

Jesse Eisenhart's picture
Joined: 2011-12-21
Reputation: 0

Vikram - Is there any way the district thermal methods prescribed by LEED could help? - Don't know if it will help, just a suggestion.
Perhaps a prescriptive approach is best.

Kevin J. Kyte, PE, BEMP, LEED (r) AP

Kevin Kyte2's picture
Joined: 2011-09-30
Reputation: 2