[Bldg-sim] Exhaust, outside air and infiltration for LEED
Rosenberg, Michael I
michael.rosenberg at pnl.gov
Fri Nov 7 14:39:44 PST 2008
Mitch,
That issue was addressed in the 2007 version of Appendix G.
G3.1.2.8 Design Airflow Rates. System design supply airflow rates for the baseline building design shall be based on a supply-air-to-room-air temperature difference of 20°F or the required ventilation air or makeup air, whichever is greater
__________________________
Michael Rosenberg
Senior Commercial Buildings Energy Analyst
ENERGY & ENVIRONMENT DIRECTORATE
Pacific Northwest National Laboratory
2032 Todd Street
Eugene, OR 97405
(541) 844-1960
michael.rosenberg at pnl.gov
www.pnl.gov
________________________________
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Mitchell Dec
Sent: Friday, November 07, 2008 1:51 PM
To: Paul Riemer; Brandon Nichols; Michael Tillou
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Exhaust, outside air and infiltration for LEED
Bill, Paul, Mike, et al -
We also have not mentioned another item relative to Appendix G, which requires sizing the flow rate based on a 20-degree delta T. If the system is a 100% OSA unit, and the baseline is sized for a 20-degree space-to-coil temperature differential, what happens if the makeup air unit is not designed with a 20-degree delta-T? Then it is possible the peak CFM rates could potentially vary. So right there, we could potentially have a contradiction between 2 lines in Appendix G - (1) OSA ventilation rates are to be identical, and (2) The baseline AHU flow rate is specified by a 20-degree delta T - now, which statement in Appendix G "over rules" the other?
This seems like this should fall under the Exceptional Calculation methodology to explicitly document where the savings come from, and whether the savings are justified...
Also regarding an earlier item from this thread, that one cannot take credit for UFAD and displacement ventilation systems with reduced CFM rates - as long as the OSA CFM rates are identical, then credit can be taken from the UFAD/DV system design. You'll be providing the same OSA, but different Total CFM rates could be calculated based on the different mixed air temperatures and designed coil leaving temperatures. This can be either a positive or negative, which truly depends on the climate and the ability to maximize the economizer hours...
Mitch Dec
Senior Energy Analyst, EIT
LEED® Accredited Professional
<http://www.glumac.com/>
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T. 503.227.5280 F. 503.274.7674
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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Paul Riemer
Sent: Friday, November 07, 2008 1:37 PM
To: 'Brandon Nichols'; Michael Tillou
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Exhaust, outside air and infiltration for LEED
Bill,
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,
Paul
________________________________
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.
Cheers
Brandon Nichols
BW Nichols PE
Seattle WA
206-228-8707
On Fri, Nov 7, 2008 at 11:53 AM, Michael Tillou <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.
Mike
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] On Behalf Of Bishop, Bill
Sent: Friday, November 07, 2008 9:04 AM
To: 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?
Thanks,
Bill
William Bishop, EIT, LEED® 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
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