[Equest-users] System-Level Exhaust??? How?

[Carol Gardner]

I'd leave it this way; You would be recovering heat from your exhaust and
maybe a bit from your return air, It's all good. Just be sure to add the
extra sp in at the return level to account for the ERV.

Carol

On Wed, Mar 17, 2010 at 7:43 AM, Nick Caton <ncaton at smithboucher.com> wrote:

>  Brian/Carol, thanks very much for your replies!
>
>
>
> I’d like to spell out a simple example to both illustrate the concept and
> verify my understanding:
>
>
>
> *Starting System Flows (CFM):*
>
> 1,000 Supply Air
>
> 300 Outside Air
>
> 200 Exhaust Air, specified at a the zone(s) level.
>
> 800 Return Air
>
>
>
> To correctly model energy recovery with this system, we need to remove the
> 200 CFM zonal-specified exhaust, and add it to the return air stream.
>
>
>
> *Energy-recovering System, corrected:*
>
> 1,000 Supply Air
>
> 300 Outside Air
>
> 1000 Return Air
>
>
>
> Am I understanding this correctly?
>
>
>
> Thanks again!
>
>
> ~Nick
>
>
>
> [image: cid:489575314 at 22072009-0ABB]**
>
> * *
>
> *NICK CATON, E.I.T.***
>
> PROJECT ENGINEER
>
> 25501 west valley parkway
>
> olathe ks 66061
>
> direct 913 344.0036
>
> fax 913 345.0617
>
> *Check out our new web-site @ *www.smithboucher.com* *
>
>
>
> *From:* Brian Fountain [mailto:bfountain at greensim.com]
> *Sent:* Tuesday, March 16, 2010 10:10 PM
> *To:* Nick Caton
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] System-Level Exhaust??? How?
>
>
>
> Nick,
>
> DOE-2 enforces a mass balance at the system level.  Whatever OA that is not
> exhausted at the zone level must be returned to the central system and
> exhausted through your heat recovery device. By defining the OA volume flow
> rate, you are also defining the exhaust volume flow rate.
>
> Nick Caton wrote:
>
> I need have an ERV which moves all the exhaust and supplies conditioned OA
> to 2 of 3 FPVAV air handlers.  I’ve specified the appropriate enthalpy wheel
> specifics at the two affected PIU systems, maintaining identical efficiency
> properties and breaking down CFM’s and fan/auxiliary power figures by
> weighting each by the supplied OA amount.
>
>
>
> I understand from the help files that zonally-specified exhaust air does
> not play into heat-recovery, when we specify energy recovery at the system
> level (help section is copied below and highlighted for reference).
>
>
>
> I take it then I’m supposed to zero out all zonally entered exhaust air
> flows, sum up the flows and add at the system level… but then *how/where
> do I specify system-level exhaust CFM rates*?
>
>
>
> I’ve tried to enter     EXHAUST-FLOW     = #### under the systems in
> question in the .inp file, but it introduces the following error:
>
>
>
> *13131*    EXHAUST-FLOW     = 2550
>
> *ERROR********* ============
> *****************************************************************UNKNOWN
> KEYWORD or PREVIOUS .. MISSING
>
>
>
> More errors ensue, and a long string of things appear to be defaulted/lost
> when I continue to open the file… something is obviously wrong with this
> approach.
>
> * *
>
> [image: cid:489575314 at 22072009-0ABB]
>
> * *
>
> *NICK CATON, E.I.T.*
>
> PROJECT ENGINEER
>
> 25501 west valley parkway
>
> olathe ks 66061
>
> direct 913 344.0036
>
> fax 913 345.0617
>
> *Check out our new web-site @ *www.smithboucher.com* *
>
>
>
> *EXHAUST-FLOW*
>
> Flow rate of the zone's exhaust fan. This entry can be omitted if there is
> no exhaust from the zone, if there is only central exhaust by way of the
> system return, or if the exhaust tracks the supply flow (see
> AIRFLOW-TRACKING). If specified, EXHAUST-STATIC should also be entered. The
> exhaust fan may be either constant flow or variable flow.
>
> If exhaust air make-up is via the air handler (EXHAUST-SOURCE =
> AIR-HANDLER), then the exhaust fan can operate only only when the system
> supply and return fans operate (see SYSTEM:FAN-SCHEDULE or
> SYSTEM:EXHAUST-FAN-SCH).
>
> The SYSTEMS program simulates heat recovery from central exhaust only, not
> from zone exhaust. If heat is to be recovered, zone exhaust should not be
> entered but rather allowed to default to the central system. Return fan
> static should be adjusted, on a weighted average basis, to reflect zone
> exhaust fan conditions.
>
> The program will not allow SYSTEM:MIN-OUTSIDE-AIR to be less than the sum
> of EXHAUST-FLOWs for all zones divided by the sum of supply flows for all
> zones. That is, MIN-OUTSIDE-AIR will not restrict the operation of exhaust
> fans. The exception is when EXHAUST-SOURCE = INFILTRATION, in which case
> zonal exhaust does not affect air handler outside air requirements.
>
>
>
>
>
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>
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