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[EnergyPlus_Support] Re: Warning: "Air volume flow rate per watt ... is out of range .."
Thanks, Richard.
This looks very promising, since this object is intended for VAV
systems and the COIL:DX:COOLINGBypassFactorEmpirical object is
intended (I now see) for single zone DX systems.
After reading the IO Reference and looking at some manufacturer
literature, a couple things are apparent:
1) The example file indicates that its curves are applicable to a
small system, which I guess to be smaller than 15 US refrigeration tons
2) it looks like a somewhat daunting task to create these curves for
larger systems from manufacturer literature, since I have no
experience at creating biquadratic curve fits.
That said, is anyone in the forum
a) aware of references which have information on this topic for
systems larger than 20 tons? (with multiple compressors in
combinations up to, say, 200 tons)
b) familiar with easy to use, inexpensive curve-fitting software that
would be applicable for this purpose?
c) aware of a refrigeration manufacturer who has curves already
prepared for their equipment?
Thank you!
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Richard Raustad"
<RRaustad@...> wrote:
>
> I sent an earlier email, but I don't see it. Here is a brief summary
> of the previous email.
>
> Use the 2-speed DX coil model Coil:DX:Multispeed:CoolingEmpirical to
> estimate the performance. First stage is about 1/3 capacity with an
> EIR curve set to 1 (or close to that). Second stage is full capacity
> with DX cooling coil EIR curves that replicate an unloading
> compression system. If you don't have the data, use the typical DX
> cooling coil EIR curves. Check with manufacturers for performance
> data to more closely model the energy input for unloading compressors
> at part load.
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "JV Dirkes II"
> <jvd2pe@> wrote:
> >
> > 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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