[Bldg-sim] Modeling fume hood exhausts

Tue Aug 31 15:09:42 PDT 2010

Thanks for all the help. Here is another angle I am coming from.

Assuming the base case were to be a traditional fume hood exhaust system
which used constant volume fans in order to create the 3000 fpm
discharge velocity. If the fume hoods have sash control the there is an
outside air by-pass on the fan header, so down stream VAV and upstream
constant volume exhaust fans.  I know these constant volume fans can be
staged to form a 'quasi' variable exhaust. So if this were the base case
then one could apply the list of various innovations on how to apply
variable exhaust flow to the proposed model.

The ASHRAE 90.1 6.5.7.2 isnt really a solution, however Aleka you
mention Lab 21, have you had any luck in getting this accepted by the
LEED meanies?

Peter Simmonds,Ph.D.
Senior Associate

IBE Consulting Engineers
14130 Riverside Drive, Suite 201
Sherman Oaks, CA 91423 
p: (818) 377-8220 x246 f: (818) 377-8230

www.ibece.com <http://www.ibece.com/> 
Ideas for the built environment

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From: Aleka Pappas [mailto:APappas at enermodal.com] 
Sent: Tuesday, August 31, 2010 2:41 PM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Modeling fume hood exhausts

I just spent a while digging through all the latest docs on modeling
labs for a LEED analysis (90.1-2004, 90.1-2007, addenda, & Labs 21).
This is my interpretation:

*	If the building has fume hood exhaust over 15,000 cfm, the
Baseline system is VAV, and exhaust is turned down to at least 50% for
unoccupied hours.  I am modeling the unoccupied turn down rate the same
in the Baseline as in the Proposed models, because how low it can go at
night depends on the type of lab (ie: the project doesn't get more
credit for turning down to 20%).  This is from Labs 21, and 90.1 (2004
or 2007) section 6.5.7.2.
*	A project can claim energy savings for demand controlled fume
hoods during occupied hours if the controls are automatic (Labs21 has
some schedules for guidance in modeling this).
*	Energy recovery is not modeled in the Baseline (see 90.1-2007
G3.1.2.10 Exception h).

Let me know if you have a different interpretation....I don't think all
these issues are laid out in detail for modelers yet.

Aleka Pappas

Building Energy Engineer 

ENERMODAL ENGINEERING, INC.
Inspiring energy and resource efficient buildings.
www.enermodal.com <http://www.enermodal.com/> 
1325 E. 16th Ave.
Denver, CO 80218
APappas at enermodal.com
Office: 303.861.2070/ Direct: 720.221.1082

On 8/31/2010 12:35 PM, varun kulkarni wrote: 

I think it also depends on the software you are using to model a fume
hood. Because if exhaust is specified more than the supply  due to the
hood, the software  may disregard the lower supply and equate the higher
value of exhaust to the supply. I am also trying to  model a VAV exhaust
fume hood and facing a lot of problems doing it. So you have to figure
out a way to control you exhaust by altering your VAV supply.

If you know some other way, please let me know also :)

On Tue, Aug 31, 2010 at 2:23 PM, Sami, Vikram
<Vikram.Sami at perkinswill.com> wrote:

I think that depends on the total volume of exhaust. I don't have it in
front of me, but I think if your exhaust is more than a certain amount
you have to have either energy recovery to fifty percent or vav flow.

Sent from a mobile device

 -----Original Message-----
From:   Peter Simmonds [mailto:peter.simmonds at ibece.net]
Sent:   Tuesday, August 31, 2010 12:09 PM Central Standard Time
To:     bldg-sim at lists.onebuilding.org
Subject:        [Bldg-sim] Modeling fume hood exhausts

Can anyone tell me when modeling a lab system with fume hoods as to
whether the baseline systems are to be modeled as constant volume?

(subsequent alternatives will have variable volume fume hoods).

Peter Simmonds,Ph.D.
Senior Associate

IBE Consulting Engineers
14130 Riverside Drive, Suite 201
Sherman Oaks, CA 91423
p: (818) 377-8220 x246 f: (818) 377-8230

www.ibece.com <http://www.ibece.com/>  <http://www.ibece.com/>
Ideas for the built environment

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Thanks and Best Regards,

Sincerely,

Varun Kulkarni , M.S. , EIT

RMF Engineering

5520, Research Park Drive, Suite 300

Baltimore, MD - 21228

Office : 410-576-0505 ext. 5352

Mobile: (+1)405-385-1928

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