[Bldg-sim] Modeling fume hood exhausts

[Gerald Pde]

Peter,
I think as Vikram mentioned, it depends on the total exhaust (cumulative exhaust 
of all the fume hoods). If the total exhaust exceeds 15,000cfm, then  the 
baseline needs to have AT LEAST one of the following:

1. VAV hood exhaust till a 50% min turn down over the total CFM. Hence you could 
only take advantage of a lower VAV set point on the actual equipment.
2. Make-up air. Separate make-up air with supply temperature very close to room 
temperatures.
3. Heat recovery . If the building has both VAV and HR, then you should be able 
to take  full benefits of heat recovery or vise-versa.
 
Hence if your total fume hood exhaust is lower than 15,000 cfm,  then you should 
be able to take advantage of  VAV fume hood exhaust over constant volume 
exhaust.

Does this make sense?

Gerald




________________________________
From: Peter Simmonds <peter.simmonds at ibece.net>
To: Aleka Pappas <APappas at enermodal.com>; bldg-sim at lists.onebuilding.org
Sent: Wed, September 1, 2010 3:39:42 AM
Subject: Re: [Bldg-sim] Modeling fume hood exhausts

 
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 x246f: (818) 377-8230

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
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/>
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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