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Re: [EnergyPlus_Support] Re: unit ventilator woes
Hi Richard;
Thanks for your help; while trying to answer your questions, I found my
error: there is, in actually, no flow imbalance, because I neglected to
consider the UNIT VENTILATOR's relief node. Intuitively, I was thinking that
if the unit was drawing 100% outside air, flow from the zone exhaust node
and to its relief node would both be zero. However, what's happening
(judging by looking at the node flowrates and temperatures) is that the unit
is taking air from the zone exhaust node and sending it all to its relief
node, while also taking air from its OA node and sending that air through
the unit's fan and coil and into the zone. So, it actually is working
alright, it just didn't look like I though it would.
Thanks a lot for your help in helping me to get to the bottom of this.
Josh
On Jan 25, 2008 1:54 PM, Richard Raustad <RRaustad@xxxxxxxxxxxx> wrote:
> What is the zone return node flow rate compared to the zone supply node
> and zone exhaust node flow rates? If there is any flow rate on the zone
> return node, and you are bringing in 100% OA, then the relief air node
> flow rate will equal the zone return node flow rate (for 1 zone models,
> for multiple zone you will have to add up all the return node flow rates).
>
> If your zone exhaust fan has a larger flow rate than the zone supply
> node flow rate, then the return node flow rate will be zero and the zone
> will be negatively pressurized, and you will see the warnings.
>
> Report out all 3 zone nodes, Return, Supply, and Exhaust. Also report
> out the outside air node and relief air node flow rates.
>
> If (Zone Supply - Zone Exhaust) flow rate is <= 0 and the Zone Return
> node flow rate is > 0, upload your file to the _Problem_Submittals
> folder in the files area.
>
> http://tech.groups.yahoo.com/group/EnergyPlus_Support/files/_Problem_Submittals/
> and I'll check for a bug.
>
> Here's the point, if you do see an outside air system relief air flow
> rate (when you think you shouldn't) and it is equal to the zone supply
> air flow rate. then just put in the zone exhaust fan at the same flow
> rate and let E+ calculate the power for you. The extra exhaust flow
> leaving the outside air system's relief node will not affect the heat
> balance calculations. Even if E+ thinks the zone is at negative
> pressure, the simulation will not add infiltration to compensate.
>
>
> Josh K wrote:
> >
> > Hi Richard;
> >
> > Thanks for the reply. It's good to know that I can ignore the error,
> > but it
> > seems like this could possibly be a bug in the software. When a UNIT
> > VENTILATOR is drawing 100% outside air, it doesn't seem like the zone
> > exhaust node that it is connected to should be showing any flow...
> >
> > Also, I had a second issue that remains a problem: that of the UNIT
> > VENTILATOR not running in a COOLING/NO COIL/FIXED AMOUNT scenario.
> > Specifically: my UNIT VENTILATOR uses an outside air control type of
> FIXED
> > AMOUNT, and has only a heating coil and no cooling coil. On the summer
> > design day, when there is no heating load, the UNIT VENTILATOR in my
> model
> > isn't turning on when its component availability schedule is > 0 as the
> > documentation suggests that it should be. Can you think of a reason
> > why this
> > is happening?
> >
> > Thanks a lot for your help,
> >
> > Josh
> >
>
> --
> Richard A. Raustad
> Senior Research Engineer
> Florida Solar Energy Center
> University of Central Florida
> 1679 Clearlake Road
> Cocoa, FL 32922-5703
> Phone: (321) 638-1454
> Fax: (321) 638-1439 or 1010
> Visit our web site at: http://www.fsec.ucf.edu
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
>
>
--
Josh Kjenner, EIT, LEED AP
Manasc Isaac Architects Ltd.
10225 100 Avenue :: Edmonton, AB T5J 0A1
780.429.3977
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