[Bldg-sim] Exhaust, outside air and infiltration for LEED
Fred Porter
FPorter at archenergy.com
Mon Nov 10 07:21:33 PST 2008
Interesting. We recently decided not to "take credit" for substantial cascade/transfer air in a restaurant EAc1 app (i.e. the transfer air from dining to kitchen/hood was included in the baseline model). Our experience is that this mode has been extremely common for many, many years in commercial and school kitchens. (And it's very inexpensive, sometimes decreasing construction costs.) We felt taking credit for it did not meet the spirit of the PRM. Maybe if one needed to build all kinds of transfer ducting in a hotel, then it might seem like an improvement worthy of recognition...
I could go on with a rant about the opacity of the credit review process, loopholes, "consensus" standards, etc. But actual work beckons.
Fred
>>> "Andrew Craig" <AndrewC at InterfaceEng.Com> 11/7/2008 3:42 PM >>>
We have successfully taken credit for reduced OSA rates in a number of applications where a "cascading" make-up air system has been designed. In a kitchen hood application for instance, the traditional design might bring in 100% OSA to offset the hood exhaust from a separate intake or unit. In certain projects (schools come to mind), this make-up air can be transferred into the space via adjacent spaces with high OSA requirements (i.e. commons), thus saving all or a portion of the mechanical energy to heat/cool this air. We have always taken the path of the exceptional calculation for LEED purposes because this is definitely a grey area as far as Appendix G is concerned.
-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org on behalf of Mitchell Dec
Sent: Fri 11/7/2008 1:50 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(r) Accredited Professional
<http://www.glumac.com/>
________________________________
320 SW Washington, Suite 200
Portland, OR 97204-2640
T. 503.227.5280 F. 503.274.7674
Thinking. Inside the building.
www.glumac.com <http://www.glumac.com/>
<http://www.glumac.com/>
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(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
www.pathfinderengineers.com
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