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Re: [EnergyPlus_Support] Unitary System Problem
Mike,
Thanks for your help. After making the change, I was able to run several of my cases. I did have a couple of other questions though that came up as I was working with the model:
1) I noticed that in order to use the reheat with FURNACE:BLOWTHRU:HEATCOOL, energyplus required me to use FAN:SIMPLE:CONSTVOLUME, rather than FAN:SIMPLE:ONOFF. It also required me to attach the fan exit node directly to the cooling coil inlet, bypassing the heating coil. This seemed a little strange, and was not in the input/output documentation anywhere, but was in the engineering reference documentation. With these changes it appeared to work ok, and give me results.
2) I am now trying to further modify the house furnace by using a heat exchanger assisted cooling coil. I know the unitary system will not operate with this coil, so I am trying to mimic the furnace model using a fan, heating coil, and heat exchanger assisted cooling coil in the air loop. My problem is that I can not figure out how to control them properly. The SetPointManager seems to control to a supply temperature, like would be used in a VAV system of a commercial building, and not a residential model. I also have not had any luck controling the temperature with the set point manager, heating, dual setpoint, or otherwise. I was wondering if you had any suggestions. As a fallback, I modeled a heat only furnace in the air loop with constant fan, followed by a heat exchanger assisted cooling coil. Even in this mode, I can not figure out how to control it properly. The documentation seems to elude to the idea that a heat exchanger assisted cooling coil can be placed i
n the
zone loop, but the idf editor will not allow this. I have attached the file I am working with. If you had any suggestions, it would be greatly appreciated. Preferably, I would like to be able to run the system as components, fan, heating coil, cooling coil, so I can model different configurations.
Thanks,
Chuck Bartlett
"Michael J. Witte" <mjwitte@xxxxxxxx> wrote:
The problem was inconsistent fan modes. In the FURNACE:BLOWTHRU:HEATCOOL
object, the Operating Mode was set to CycFanCycCoil, but in the
COIL:DX:CoolingBypassFactorEmpirical object, the Supply Air Fan Operation Mode
was set to ContFanCycComp. Changing this to CycFanCycComp eliminates the air
flow errors. I'll post a change request (CR) to see if we can add a check for
this or at least mention this as a possible cause in the airflow warning.
Mike
On 7 Apr 2005, at 12:48, Michael J. Witte wrote:
>
> It sounds like there is a bad flow rate somewhere in the input file. Check the
> flow rate on the direct air unit, the primary air loop, and the furnace. If you
> cannot find the problem, please upload the input file to the yahoo files area or
> send as a zipped attachment to energyplus-support@xxxxxxxx
>
> Mike
>
>
> On 6 Apr 2005, at 23:20, bartlettbmw wrote:
>
> >
> >
> > I am trying to model a residential home for my Master's Degree Plan
> > B paper and am running into problems with the unitary system. I am
> > modeling the home as a single zone and using the
> > FURNACE:BLOWTHRU:HEATCOOL as the plant. I have specified the fan,
> > gas coil, and DX coil. When I run the model, I get the following
> > error (60,000 times):
> >
> > ** Warning ** COIL:DX:COOLINGBYPASSFACTOREMPIRICAL "DX COIL" - Air
> > volume flow rate per watt of rated total cooling capacity is out of
> > range.
> > ** ~~~ ** ...VolumeFlowperRatedTotCap=3.085E-006 Occurrence
> > info=CHICAGO IL USA TMY2-94846 WMO#=725300, 04/07 17:30 - 17:45
> > ** ~~~ ** Expected range for VolumeFlowperRatedTotalCapacity=
> > [3.3560E-005--6.7130E-005]
> > ** Warning ** Enthalpy out of range (PsyTsatFnHPb)
> >
> > Based on the text of the error, it appears that the airflow rate is
> > too low and the cooling coil is having problems. I think I modeled
> > everything correctly, put the unitary system on the air loop and
> > connected it to the zone using a DIRECT AIR component as described
> > in the Input/Output reference. I am modeling a 4 Ton cooling system
> > with 400 CFM/Ton. This amounts to about 14,000 Watts and 0.75 m^3/s
> > airflow rate. When I do a quick calcualtion, this should be about
> > 5.35e-5 m^3/sW (0.75/14000) and should be right in the middle of the
> > acceptable range (3.35e-5 to 6.7e-5). For some reason, the model is
> > not seeing the airflow or is incorrectly calculating the cooling
> > load. I was wondering if anyone has any suggestions, or has run
> > into this problem in the past with the Unitary system. I am using
> > the FAN:SIMPLE:ONOFF component with 0.75 m^3/s flow rate.
> >
> > I would really appreciate any suggestions/help..
> >
> > Thanks
> >
> >
> >
> >
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov
> >
> > The group web site is:
> > 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.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@xxxxxxxx
>
>
>
>
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
>
> The group web site is:
> 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.
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
The primary EnergyPlus web site is found at:
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Attachments are not allowed -- please post any files to the appropriate folder in the Files area of the Support Web Site.
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