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[EnergyPlus_Support] Re: Unitary System Problem
Charles:
1) As the name suggests, Furnace:Blowthru:HeatCool is a "blowthru"
fan arrangement with the fan being upstream of the cooling and heating
coils. In addition, The IO Reference Section for
Furnace:Blowthru:HeatCool has a large grey box immediately after the
description of all input fields that says:
"Note: the furnace's fan, heating coil, cooling coil and optional
reheat coil must be connected in the air loop according to the
configuration shown above (Figure 80 or Figure 81). In addition, the
volumetric air flow rate specified in the direct air unit for the
controlling zone should properly reflect the fractional volumetric air
flow rate specified in the furnace object. Furthermore, the DX cooling
coil operation mode must be specified consistently with the furnace
operating mode (e.g., with CycFanCycCoil for Furnace operating mode,
the DX cooling coil operation mode must be CycFanCycComp)."
2) You are incorrect on item #2 below. The IO Reference clearly
states that Furnace:Blowthru:HeatCool and Unitary
System:Blowthru:HeatCool can have cooling coil type
COIL:DX:CoolingBypassFactorEmpirical or COIL:DX:
CoolingHeatExchangerAssisted.
3) You can't send attachments via the yahoogroups e-mail. You must
upload your files to the "Files" area of the yahoogroups site.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Charles Bartlett
<bartlettbmw@y...> wrote:
> 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 in 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@g...> 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@g...
> >
> > 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 VolumeFl
owperRatedTotalCapacity=
> > > [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@g...
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