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[EnergyPlus_Support] Re: Warning: "Air volume flow rate per watt ... is out of range .."
Dear Richard,
I believe that there's a valid reason for the warning and I'm glad
it's part of E+. My goal is to find out how to tell E+ that "It's OK"
because there is hot gas bypass control on the DX system or some other
unloading control which allows operation at very low part loads?
Better yet, how do I tell E+ to model the performance of such a control?
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad
<RRaustad@...> wrote:
>
> Change your report variables to "detailed" to see the values at each
> simulation time step. The HVAC system time steps are allowed to reduce
> down to 1-minute. This message is typical of VAV systems where the air
> flow is reduced far lower than should be allowed for DX systems. VAV
> chilled water systems do not have this restriction. You can report out
> the DXSystem Part-Load Ratio to back calculate the coil outlet air
> temperature to see if the coil is near freezing.
>
> System Convergence Limits,
> 1, !- Minimum System Time Step {minutes}
> 80; !- Maximum HVAC Iterations
>
> Report Variable,
> NodeOut_MA_AH1, !- Key_Value
> System Node VolFlowRate, !- Variable_Name
> detailed; !- Reporting_Frequency
>
> Report Variable,
> *, !- Key_Value
> DXSystem Part-Load Ratio, !- Variable_Name
> detailed; !- Reporting_Frequency
>
> Using data in the csv output file at 07/15 00:11:00:
> Tout,avg = Tcoil,out(PLR)+Tcoil,in(1-PLR)
> Tcoil,out = (Tout,avg-Tcoil,in(1-PLR))/PLR
> Tcoil,out = (12.20674-20.776(1-0.348526))/0.348526
> Tcoil,out = -3.811 C
>
> Tout,avg = NODEOUT_CLGCOILAIR_AH1:System Node Temp[C]
> Tcoil,in = NODEOUT_MA_AH1:System Node Temp[C]
> PLR = DXAIRLOOP_AH1:DXSystem Part-Load Ratio
>
> The warnings are trying to convey that there is a good chance of coil
> frosting and compressor failure.
>
> JV Dirkes II wrote:
> >
> > Dear E+ Forum,
> >
> > After spending considerably more time trying to resolve this problem,
> > I'm now seeing 6700 warnings after cleaning up a few minor
> > discrepancies. I'm hoping that someone can take a look at the file I
> > uploaded to determine the cause!
> >
> > p.s., The uploaded file is called "AirFlowperWatt.zip"
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II"
<jvd2pe@>
> > wrote:
> > >
> > > Dear E+ Forum,
> > >
> > > I am looking at this warning again, trying to understand it... and
> > > failing to do so.
> > >
> > > In short:
> > > The warning occurs over 3700 times in 3 Design days; this seems
> > excessive!
> > > The warning appears to occur multiple times in a single minute
(I get
> > > multiple warning messages for the exact same time, coil and design
> > > day. I have specified 4 timesteps per hour, but the warnings
refer to
> > > minutes that are NOT timesteps.)
> > > The "air volume per watt" is an acceptable value at the timestep (It
> > > is within the acceptable range noted in the warning.)
> > >
> > > Since this warning occurs for a non-timestep minute, something seems
> > > to be going on in the background. In addition, there are no other
> > > errors or warnings which suggest a cause for this one.
> > >
> > > Thanks in advance.
> > >
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, Don Shirey
<shirey@> wrote:
> > > >
> > > > The warning can be an indication of very low supply air flow rate
> > > > compared to the coil's cooling capacity.... and very low
outdoor air
> > > > temperatures may also be contributing.
> > > >
> > > > Find the autosized air flow rate and cooling coil capacity in the
> > .eio
> > > > file ... and then look at the COIL:DX:COOLINGBypassFactorEmpirical
> > > > documentation in the IO Reference and Engineering Reference
for how
> > > that
> > > > coil model works and how the flow rate/capacity values are used.
> > > >
> > > >
> > > > JV Dirkes II wrote:
> > > > > Dear E+ Forum,
> > > > >
> > > > > The Air handler for a current E+ model (v2.2) has a
> > > > > COIL:DX:COOLINGBypassFactorEmpirical cooling coil and a hot
water
> > > > > heating coil. The model runs, but has hundreds of instances
of this
> > > > > warning or "Full load outlet temperature indicates a
possibility of
> > > > > frost/freeze...", which appears to have a similar cause. All
> > > > > capacities are autosized and I am simulating only 3 Design Days
> > with 4
> > > > > timesteps per hour (so the hundreds of warnings seem to be too
> > many!)
> > > > >
> > > > > Will someone help me understand the cause of the error and
how to
> > > > > resolve it? Thank you!
> > > > >
> > > > >
> > > > > ------------------------------------
> > > > >
> > > > > The primary EnergyPlus web site is found at:
> > > > > http://www.energyplus.gov <http://www.energyplus.gov>
> > > > >
> > > > > The group web site is:
> > > > > http://groups.yahoo.com/group/EnergyPlus_Support/
> > <http://groups.yahoo.com/group/EnergyPlus_Support/>
> > > > >
> > > > > Attachments are not allowed -- please post any files to the
> > > appropriate folder in the Files area of the Support Web Site.
> > > > >
> > > > > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf
> > > under the Documentation link and press the "search" button.
> > > > > Yahoo! Groups Links
> > > > >
> > > > >
> > > > >
> > > >
> > >
> >
> >
>
> --
> 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
>
------------------------------------
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