[Bldg-sim] Exhaust, outside air and infiltration for LEED

Paul Riemer Paul.Riemer at dunhameng.com
Fri Nov 7 13:36:52 PST 2008

This is a fascinating convergence of issues.

Appendix G's requirement for the same minimum ventilation rate in the baseline as the proposed is true but also a bit incomplete when considering a design of a 100% OA VAV systems serving fume hoods.

We have a similar scenario of a small building with likely VAV hoods, possibly lower flow, likely served by a 100% outside air system BUT with my favorite added complexity of district heating and cooling.

Alas, while I was scratching my head, the client abandoned their LEED goal.

So I have not fully solved it for myself and cannot solve for it your project but I do suggest the following actions:
1) Read the 90.1-2004 prescriptive requirements for certain systems serving fume hoods to be VAV or have heat recovery.
2) Read the 90.1-2004 Appendix G base system selection section
3) Now read those same sections in 90.1-2007 and ponder which changes represent revisions and which ones represent clarifications of original intent
4) And maybe read the User's Manuals too
5) Consider the exceptional calculation method as the venue to claim energy savings, that you consider real but are not explicitly allowed or defined by the document, for consideration by the LEED reviewer
6) Research the existing CIR's
7) Before spending numerous hours on an approach that may or may not be accepted, buy a CIR and propose your tact to the USGBC itself. If they reject yours they almost certainly will dictate a new tact that their reviewer would be obligated to accept for your project.

And lastly, do not wade too much further through this on a Friday afternoon unless you have to do so. For me, tasks like this should be tackled early in the day and early in the week.

Good luck,


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Brandon Nichols
Sent: Friday, November 07, 2008 2:47 PM
To: Michael Tillou
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Exhaust, outside air and infiltration for LEED

My two cents...

The same OSA for baseline vs as-designed makes sense for occupant-required OSA, such that there is no reward for compromising occupant health to gain LEED points.

However, that fraction of the fumehood OSA over and above occupancy-required is process OSA, an opportunity where LEED should be encouraging savings.  Now I'm not saying they do, just that they should...

And after rereading the requirements it shakes out that LEED really doesn't give credit for reducing process outside air loads, keep the parametric run in your model -- the local utility may see things differently, and 'recognize you' with a big fat rebate check.


Brandon Nichols
BW Nichols PE
Seattle WA

On Fri, Nov 7, 2008 at 11:53 AM, Michael Tillou <michael.tillou at gmail.com<mailto:michael.tillou at gmail.com>> wrote:
You are correct that Appendix G requires outside air to be the same for both as-designed and baseline models.  You would not be able to claim savings for reduced ventilation airflow from a more efficient fume hood.   Similarly you cannot claim credit for reduced ventilation airflow on displacement ventilation and UFAD systems.

However I see no reason why you wouldn't be able to claim the fan energy savings associated with a more efficient fume hood.


Michael Tillou, PE, LEED
Tillou Engineering, LLC
Williamstown, MA 01267
P: 413-458-9870 C: 413-652-1087
From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Bishop, Bill
Sent: Friday, November 07, 2008 9:04 AM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Exhaust, outside air and infiltration for LEED

The mechanical engineer for a campus laboratory building with 100% OA wants to claim energy savings for reduced exhaust from more efficient fume hoods. (Established design practice uses hoods with 100 fpm flow - they are installing 70 fpm hoods. This reduces peak exhaust from 700 to 490 CFM per hood.) My approach has always been to keep outside air, exhaust and infiltration flows identical between the proposed and baseline models (except for DCV). (This was not easy for this model with proposed VAV and baseline constant volume packaged rooftops.)

Has anybody successfully claimed OA/exhaust/infiltration savings for a LEED project?



William Bishop, EIT, LEED(r) AP | Pathfinder Engineers LLP

Mechanical Engineer

3300 Monroe Ave., Suite 306
Rochester, NY  14618

TEL (585) 218-0730 Ext. 114
FAX (585) 218-0737

bbishop at pathfinderengineers.com<mailto:bbishop at pathfinderengineers.com>


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