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Re: [EnergyPlus_Support] Re: QUESTION ON AIR COOLED CONDENSER INLET TEMPERATURE
For some reason the chiller is operating on the winter design day. Check
the output for the winter design day to determine the reason that the
chiller is turning on. Schedules for WinterDesignDay may inadvertently
represent a much greater load than will be actually used during the
winter simulation. For example, a schedule for equipment loads may look
like this:
ELECTRIC EQUIPMENT,
North Zone, !- Zone Name
EquipmentSch, !- SCHEDULE Name
5000.0, !- Design Level {W}
0.0000000E+00, !- Fraction Latent
0.3000000, !- Fraction Radiant
0.0000000E+00, !- Fraction Lost
0; !- End-Use Category
SCHEDULE:COMPACT,
EquipmentSch, !- Name
Fraction, !- ScheduleType
Through: 12/31,
For: WeekDays,
Until: 8:00, 0.0,
Until: 18:00, 0.5,
Until: 24:00, 0.0,
For: WeekEnds,
Until: 24:00, 0.0,
For: AllOtherDays,
Until: 24:00, 1.0;
This schedule layout would simulate equipment operating at 50% capacity
from 8am to 6pm on weekdays and off on weekends during the actual
simulation. All other days (Holidays, SummerDesignDay, WinterDesignDay,
CustomDay1, CustomDay2) will operate the equipment at full capacity 24
hrs per day. A more realistic schedule would turn off the equipment on a
winter design day and turn on the equipment on a summer design day to
determine the extreme loads for adequate equipment sizing:
ELECTRIC EQUIPMENT,
North Zone, !- Zone Name
EquipmentSch, !- SCHEDULE Name
2500.0, !- Design Level {W}
0.0000000E+00, !- Fraction Latent
0.3000000, !- Fraction Radiant
0.0000000E+00, !- Fraction Lost
0; !- End-Use Category
SCHEDULE:COMPACT,
EquipmentSch, !- Name
Fraction, !- ScheduleType
Through: 12/31,
For: WeekDays,
Until: 8:00, 0.0,
Until: 18:00, 1.00,
Until: 24:00, 0.0,
For: WeekEnds,
Until: 24:00, 0.0,
For: WinterDesignDays,
Until: 24:00, 0.0;
For: AllOtherDays,
Until: 24:00, 1.0;
Make sure your schedules are not the cause for chiller operation on the
winter design day. This applies to occupancy, lighting, and equipment
schedules as well. The schedules you use for simulation are very
powerful and represent to the best of your knowledge the actual
operation of the building in question. Although the operation of
chillers during winter months is dependent on the building being
simulated, it is possible to require cooling during the colder months of
the year. An architect or engineer would then assure the proper type of
cooling equipment such that the equipment would not be damaged if
operated on these cold days (the reason for the warning you are seeing).
If the equipment actually operates during the winter months consider
switching to a water-cooled chiller or contact manufacturers to
determine the correct capacity and EIR curves for this climate (include
the impact of emergency heaters on chiller performance [you can then
disregard the warnings]). As I said before, EnergyPlus does not
currently support freeze protection for chillers and it is up to the
user to provide the correct performance curves for the specific application.
zhaicq98 wrote:
> Hi, Richard,
>
> Thanks for your response. Actually I am not really operating the
> chiller in cold days. Right now I am just running the file for winter
> and summer design days, in order to get the auto-sizing information.
> I am hoping there is be no such warning when I do the entire year
> simulation.
>
> Thanks again,
> Chaoqin
>
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad
> <RRaustad@F...> wrote:
> > Why is your chiller operating on such a cold day?
> >
> > Air-cooled chillers should not be used in cold climates without
> freeze
> > protection. Energyplus does not currently support freeze protection
> on
> > electric chillers. If you want to continue to use the air-cooled
> > electric EIR chiller, limit the minimum outdoor temperature in the
> > Cooling Capacity Function of Temperature Curve and Energy Input to
> > Cooling Output Ratio Function of Temperature Curve objects to 0C
> and
> > verify that the output makes sense (i.e. Capacity and Power at this
> low
> > temperature is reasonable). Limiting the minimum outdoor
> temperature
> > "caps" the capacity and power at 0C and simulates the use of
> heaters to
> > maintain chiller performance. This heater power will not be
> accounted
> > for in the simulation. If the output makes sense you can disregard
> the
> > warnings. Otherwise change to a water cooled chiller where the
> entering
> > condenser water temperature can be better controlled.
> >
> > zhaicq98 wrote:
> >
> > > Hi,
> > >
> > > I am simulating a system with an air-cooled electric chiller.
> However I
> > > got lots of warning messages, saying:
> > >
> > > ElectricEIRChillerModel:Air Cooled Condenser Inlet Temperature
> below 0C
> > >
> > > What should I to with regard to these warnings? I am using the
> chiller
> > > in a relatively cold climate.
> > >
> > > Thanks,
> > > Chaoqin
> > >
> > >
> > >
> > >
> > > The primary EnergyPlus web site is found at:
> > > http://www.energyplus.gov
> > >
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> > > http://groups.yahoo.com/group/EnergyPlus_Support/
> > >
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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
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> > [Non-text portions of this message have been removed]
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> Accounting software program
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> Affiliate program software
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> Program management software
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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
UCF - From Promise to Prominence: Celebrating 40 Years
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