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

[Nick Caton]

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

 

 

 

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.

 



 

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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