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Re: [EnergyPlus_Support] Re: Electric Chiller: air cooled



Mr. Morrissey,

Problem #1:

You have set the pumps to be on at all times regardless of load. Change 
the Pump Control Type to INTERMITTENT for both cooling and heating. The 
pumps will run at a constant speed when there is a call for either 
cooling or heating. The "average" flow rate in a single time step will 
be proportional to the Part Load Ratio of the equipment (if equipment 
cycles on half the time, the flow rate will be half of the maximum). 
Turn on the report variable for Chiller Evap Heat Trans Rate and compare 
this value to the maximum chiller capacity to verify this.

PUMP:CONSTANT SPEED

Field: Pump Control Type

This is a choice field of CONTINUOUS or INTERMITTENT.  The operation of 
a constant speed pump is fairly straightforward.  If the user designates 
a constant speed pump that is operating continuously, the pump will run 
regardless of whether or not there is a load.  This may have the net 
effect of adding heat to the loop if no equipment is turned on.  If the 
pump is constant speed and operates intermittently, the pump will run at 
its capacity if a load is sensed and will shut off if there is no load 
on the loop.


Problem #2:

There is no load in Zone 2. No occupants, no equipment, no lights. Only 
infiltration. This is not enough to require cooling. The zone 
temperature never rises above the cooling set point, therefore, the 
cooling coil is sized to 0. For a design day, you would want to add 
occupants, lighting, and equipment to reflect what might happen 
throughout the year. Certainly someone will enter this zone and turn on 
lights at some point. You would want your HVAC system to be able to 
handle this. Although I agree that autosizing the equipment should allow 
the set point to be met on the design day, this seems to be an issue 
with Energy+ at this time. I added lighting (copied zone 3 to zone 2) to 
force a cooling load.

This did not completely fix the problem of meeting the set point 
temperature during the summer design day. I had to take one more step.

In the Sizing Parameters object, you are using an averaging window of 4 
time steps (1 hour). This effectively reduces the capacity of the 
equipment so as not to inadvertently oversize during pull down periods 
on a summer or winter morning. You would actually want the system to 
fully turn on and gradually approach the set point instead of meeting 
the set point in a single time step. I first tried increasing the sizing 
factor (to 1.5) but this did not seem to help, I am not sure why. To fix 
the problem, I changed the time steps in averaging window to 1 and the 
set point was then met (with a lighting object in zone 2).

SIZING PARAMETERS,
    1,                       !- sizing factor
    1;                       !- time steps in averaging window

 From the I/O Reference Manual:

Sizing Parameters

This object allows the user to specify a global sizing ratio. This ratio 
will be applied at the zone level to all of the zone heating and cooling 
loads and air flow rates. These new loads and air flow rates are then 
used to calculate the system level flow rates and capacities and are 
used in all of the component sizing calculations.

The user can also specify the width (in load timesteps) of a moving 
average window which can be used to smooth the calculated zone design 
flow sequences. The use of this parameter is described below.


        Field: sizing factor

The global sizing ratio applied to all of the zone design load and air 
flow rates.


        Field: time steps in averaging window

The number of load timesteps in the zone design flow sequence averaging 
window. The default is 1, in which case the calculated zone design flow 
rates are averaged over the load time step.

The zone design air flow rate calculation is performed assuming a 
potentially infinite supply of heating or cooling air at a fixed 
temperature. Thus the calculated design air flow rate will always be 
able to meet any load or change in load no matter how large or abrupt. 
In reality air flow rates are limited by duct sizes and fan capacities. 
The idealized zone design flow calculation may result in unrealistically 
large flow rates, especially if the user is performing the sizing 
calculations using thermostat schedules with night setup or setback. The 
calculated zone design flow rates are always averaged over the load 
timestep. The user may want to perform a broader average to mitigate the 
effect of thermostat setup and setback and prevent the warm up or cool 
down flow rates from dominating the design flow rate calculation.. 
Specifying the width of the averaging window allows the user to do this.

For example, if the load calculation timestep is 15 minutes and the user 
specifies the time steps in averaging window to be 4, the zone design 
air flows will be averaged over a time period of 1 hour. Specifying 8 
would result in averaging over a 2 hour period.



Elmer Morrissey wrote:

> Hi Richard,
>
> I checked that out and I am still getting all the same problems.
> I've subbitted the file called in CC.idf  to the problems submittals
> section. I really appreciate the help.
>
> Kind regards
>
> -Elmer
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad
> <RRaustad@...> wrote:
> >
> > Even a constant volume plant should shut down when there is no
> call for
> > cooling. Are you sure there is no flow through any of the cooling
> coils?
> > Is the demand side bypass pipe flow rate EQUAL to the supply side
> flow
> > rate at these times? If there is no flow through any cooling coils
> and
> > the demand bypass is equal to the supply flow rate (these are the
> first
> > checks to be verified), then submit your file to the EnergyPlus
> Support
> > Group for further study.
> >
> > Elmer Morrissey wrote:
> >
> > > Hi,
> > >
> > > That makes sense. I had a constant volumetric flow rate, so even
> > > though the unit was not required to do any work (the cooling
> coil's
> > > operations was never requested), the system WAS requesting 7C at
> the
> > > outlet of the loop year round.
> > >
> > > I scheduled this loop to off during the winter months. This took
> > > care of the errors however I noticed that there is still a flow
> > > through the system!!!? Any idea why this would remain operating?
> > >
> > > However, I still have two issues with the system.
> > >
> > > (1) In the summer, the system is not pulling the cooling coil air
> > > outlet node temp to 12C. It gets close, but never all the way
> during
> > > peak times. The system if fully autosized..
> > >
> > > (2) The .err file says that "Loads Initialization did not
> Converge
> > > (CheckWarmupConvergence)"
> > >
> > > I've tried increasing the warmup days to 40 but this doesn't
> seem to
> > > have an effect.
> > >
> > > Kind regards
> > >
> > > -Elmer
> > >
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad
> > > <RRaustad@> wrote:
> > > >
> > > > The message is warning you that an "air cooled" chiller is
> > > operating
> > > > when outdoor temperatures are below 0C. This type of operation
> > > could
> > > > freeze the chiller barrel and damage the unit. Good thing it is
> > > only a
> > > > simulation. What type of loads are in your building that
> require
> > > cooling
> > > > when it is 0C outside? How about scheduling you chiller off in
> the
> > > > winter and using an economizer.
> > > >
> > > >
> > > > Elmer Morrissey wrote:
> > > >
> > > > > Hello all,
> > > > >
> > > > > I'm am getting the following error from an electric chiller
> (air
> > > > > cooled) which supplies the cool water at 7C for the cooling
> coil
> > > in
> > > > > the AHU...
> > > > >
> > > > > ElectricChillerModel:Air Cooled Condenser Inlet Temperature
> > > below 0C
> > > > > continues
> > > > >
> > > > > Can anyone point me where I would remove this error?
> > > > >
> > > > > My chiller definition looks like this
> > > > >
> > > > > CHILLER:ELECTRIC,
> > > > >     Z1:Plant1,               !- Chiller Name
> > > > >     AIR COOLED,              !- Condenser Type
> > > > >     autosize,                !- Nominal Capacity {W}
> > > > >     3.2,                     !- COP
> > > > >     Z1:Plant1In,             !- Plant_Side_Inlet_Node
> > > > >     Z1:Plant1Out,            !- Plant_Side_Outlet_Node
> > > > >     ZC1:Plant1In,            !- Condenser_Side_Inlet_Node
> > > > >     ZC1:Plant1Out,           !- Condenser_Side_Outlet_Node
> > > > >     0,                       !- Minimum Part Load Ratio
> > > > >     1,                       !- Maximum Part Load Ratio
> > > > >     0.65,                    !- Opt Part Load Ratio
> > > > >     35,                      !- Temp Design Condenser Inlet
> {C}
> > > > >     2.778,                   !- Temp Rise Coefficient
> > > > >     6.67,                    !- Temp Design Evaporator
> Outlet {C}
> > > > >     autosize,                !- Design Evaporator Volumetric
> > > Water
> > > > > Flow Rate {m3/s}
> > > > >     autosize,                !- Design Condenser Volumetric
> Water
> > > > > Flow Rate {m3/s}
> > > > >     0.9949,                  !- Coefficient1 of the capacity
> > > ratio
> > > > > curve
> > > > >     -0.045954,               !- Coefficient2 of the capacity
> > > ratio
> > > > > curve
> > > > >     -0.0013543,              !- Coefficient3 of the capacity
> > > ratio
> > > > > curve
> > > > >     2.333,                   !- Coefficient1 of the power
> ratio
> > > curve
> > > > >     -1.975,                  !- Coefficient2 of the power
> ratio
> > > curve
> > > > >     0.6121,                  !- Coefficient3 of the power
> ratio
> > > curve
> > > > >     0.03303,                 !- Coefficient1 of the full load
> > > ratio
> > > > > curve
> > > > >     0.6852,                  !- Coefficient2 of the full load
> > > ratio
> > > > > curve
> > > > >     0.2818,                  !- Coefficient3 of the full load
> > > ratio
> > > > > curve
> > > > >     5,                       !- Temp Lower Limit Evaporator
> > > Outlet
> > > > > {C}
> > > > >     ConstantFlow;            !- Chiller Flow Mode
> > > > >
> > > > > I've attempted reducing the design inlet temperature into the
> > > > > condenser but it doesn't appear to be making a difference.
> Also
> > > the
> > > > > cooling coil is not reducing the temperature of the outlet
> air
> > > > > stream to the desired temp of 12C. It gets close (13C) but
> never
> > > > > quite down there at peak times.
> > > > >
> > > > > I appreciate the help, kind regards
> > > > >
> > > > > -Elmer
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > The primary EnergyPlus web site is found at:
> > > > > http://www.energyplus.gov
> > > > >
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> > > > >
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> > > and
> > > > > press the "search" button.
> > > > >
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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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> > > >
> > > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > >
> > > >
> > > >
> > > > [Non-text portions of this message have been removed]
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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
> >
> > UCF - From Promise to Prominence: Celebrating 40 Years
> >
> >
> >
> > [Non-text portions of this message have been removed]
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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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