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[EnergyPlus_Support] Re: Warning: "Air volume flow rate per watt ... is out of range .."

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Warning: "Air volume flow rate per watt ... is out of range .."
From: "JV Dirkes II" <jvd2pe@xxxxxxx>
Date: Mon, 02 Jun 2008 15:26:37 -0000
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Dear Richard,

That's so embarrassing!  I still have some "Calculated Relative
Humidity out of range" warnings where the calculated humidity fraction
exceeds 1.0, but I suspect those are minor and a function of the
humidity calculation inaccuracy.

Thank you so much!

p.s., I'd still like to know if someone has developed curves for
larger (50 -250 US refrigeration ton) units.  Failing that, I'd like
to see an example of how the curves are developed for such a unit.

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad
<RRaustad@...> wrote:
>
> Your multi-speed coil inlet/outlet node names are incorrect. Add a "1" 
> to the end of the node names.
> 
> COIL:DX:Multispeed:CoolingEmpirical,
> ClgCoil_AH1,
> SchCpct_AlwaysOn,
> Autosize,
> 0.68,
> 2.636,
> Autosize,
> NodeOut_MA_AH1,  <-----
> NodeOut_ClgCoilAir_AH1,  <-------
> 
> 
> JV Dirkes II wrote:
> >
> > File will be uploaded shortly. Thanks!
> >
> > p.s., V2.2.026 cause the error.
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > <RRaustad@> wrote:
> > >
> > > That particular error is not supposed to occur in a simulation (it's
> > > mainly used by the model developer). You have somehow managed to
trip
> > > this error. Please upload the file that causes this error.
> > >
> > > Two-speed compressors use speed ratio and cycling ratio to
define the
> > > performance. The speed ratio determines the staging. If the
first stage
> > > compressor can not meet the load, the second stage compressor
turns on.
> > > If the load is lower than the full speed compressor capacity
(for first
> > > or second stage), the compressor will cycle. The cycling ratio
is the
> > > fraction of time the compressor is on for a given time step.
> > >
> > > JV Dirkes II wrote:
> > > >
> > > > Late-breaking developments....
> > > >
> > > > When using the Coil:DX:Multispeed:CoolingEmpirical with curves
from
> > > > the example file, I get a fatal error,
> > > >
> > > > " ** Fatal ** DX unit cycling ratio calculation failed: cycling
> > > > limits exceeded, for unit=DXAIRLOOP_AH1"
> > > >
> > > > Apparently I not only need to create a curve, but it has to comply
> > > > with some sort of test. What is the "cycling ratio calculation"? I
> > > > could not find a discussion of that in the reference docs,
other than
> > > > when it's used for chillers. Chillers seem to allow any part load
> > > > ratio at all, defaulting to the minimum specified PLR when the
> > > > calculation of PLR falls below the minimum. DX must not work that
> > way....
> > > >
> > > > Thanks again.
> > > >
> > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II"
> > <jvd2pe@>
> > > > wrote:
> > > > >
> > > > > 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 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, "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 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, "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 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, 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>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > > > > > <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>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > > > > > <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:
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> > > > > > > > > > > >
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> > > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > > > --
> > > > > > > > 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 
> > <http://www.fsec.ucf.edu>
> > > > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>
> > > > > > > >
> > > > > > > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > > >
> > >
> > > --
> > > 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
<http://www.fsec.ucf.edu>
> > >
> > > UCF - From Promise to Prominence: Celebrating 40 Years
> > >
> >
> >  
> 
> -- 
> 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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  - From: Richard Raustad
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