[BLDG-SIM] Oh, what a tangled web we weave...

[Graham Carter & Megan Lyall]

If return air is via plenum then the volume connected to the return  
air is the same.  My guess is that EQuest/2.2 does not try to do a  
CO2 balance and is thus working off occupant density and outdoor air  
(probably from mechanical systems only) so volume may be  
inconsequential.  For large spaces with transient occupancy this  
could be inaccurate - codes in Australia allow us to take advantage  
of this large volume of unvitiated air for theatre foyers etc.  If  
EQuest/2.2 did do a transient CO2 balance then the inaccurracies of  
modelling with no plenum would be limited to transient conditions  
which for offices would be morning, evening and lunch.  In this case  
I gues your simulation would be slightly optimistic.  I assume Steve  
Gates / Jeff Hirsch can clarify anything that isn't stated in the 2.2  
Dictionary.
Regards,
Graham
On 17/07/2007, at 3:06 AM, Lynn Qualmann wrote:

> Thanks to everyone who responded to the threads that came from the  
> original question. With respect to the note immediately below, how  
> is the demand for outside air determined when DCV is modeled in  
> eQuest? I was assuming the inputs would be the number of occupants  
> (and their activity levels) and the volume of the space. If deleted  
> plenum volumes are re-assigned to occupied spaces, the CO2  
> concentration (and presumably OA fraction) should clearly be  
> reduced in a real-life DCV situation. Does the eQuest model of DCV  
> take this into account or is it more simplified?
>
> R. Lynn Qualmann, P.E.
> SBW Consulting, Inc.
> 2820 Northup Way  #230
> Bellevue, WA  98004
> Phone:  (425) 827-0330
> FAX:     (425) 822-8119
> e-mail:  rlq at sbwconsulting.com
>
> From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of  
> David S Eldridge
> Sent: Monday, July 16, 2007 8:13 AM
> To: BLDG-SIM at gard.com
> Subject: [BLDG-SIM] Oh, what a tangled web we weave...
>
> John, that is a good point if your program is modeling the CO2  
> concentration explicitly.
>
>
>
> If you (or simulation program) are using the scheduled quantity of  
> people as the surrogate for CO2 measurements then it would be the  
> same amount of OA with or without plenums.
>
>
>
> (How ironic is that?  Using number of people in the model as the  
> surrogate for CO2 measurements…which in the real building is the  
> surrogate for the number of people…)
>
>
>
> David
>
>
>
>
>
> From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of  
> Peterson, John
> Sent: Friday, July 13, 2007 8:05 AM
> To: BLDG-SIM at gard.com
> Subject: [BLDG-SIM] Oh, what a tangled web we weave...
>
>
>
> The plenums subtract from the total room volume.  If the return is  
> ducted, this makes a large difference.  Also while the plenum &  
> room may have the same or nearly the same temp/humidity,  
> ventilation rates for the room might be calculated based on a CO2  
> level difference.  The CO2 calculation is based on the room volume,  
> which relates directly with OA needed, and hence the energy to  
> condition that OA.  The plenum can mean a big difference in room  
> volume flows when extrapolated across an entire building.
>
>
>
> John Peterson, PE, LEED AP
>
> 625 N. Washington Street     Alexandria, VA  22314
>
> Tel: (703) 683-9700
>
> Fax: (703) 683-2480
>
>
>
>
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