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

[Paul Riemer]

Nick,
In your corrected you would have 300 cfm available for the heat recovery but I read your intent to be heat recovery on 200 cfm of exhaust.
Would you be better to specify 100 cfm of zone level exhaust to get a 200 cfm system level exhaust to recover from?
Check and/or manipulate your schedules and static pressures too.

Paul Riemer
Dunham




From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Wednesday, March 17, 2010 9:44 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] System-Level Exhaust??? How?

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

[cid:image001.jpg at 01CAC5B8.258A37B0]

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.

[cid:image001.jpg at 01CAC5B8.258A37B0]

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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