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[EnergyPlus_Support] Re: Multiple chillers

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Multiple chillers
From: "berlinclownfish" <SPlamp@xxxxxxxxxxxxxxxx>
Date: Thu, 25 Jun 2009 06:32:02 -0000
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To all,

I was finally able to work out these issues by further experimenting with the entries made in the 'PlantEquipmentList'. Previous attempts considered a separate 'PlantEquipmentList' object for each chiller (e.g. Chiller#1, Chiller#2, etc). Current results suggest that all chillers must be condensed into a single 'PlantEquipmentList' object. The cooling load based operation as defined in class 'PlantEquipmentOperation:CoolingLoad' of the four chillers may very well be described as a separate object for each chiller. Unfortunately I am currently unable to derive an alternating operation sequence as specified by assigning priorities in class 'PlantEquipmentOperationSchemes' (e.g. Chiller#1 followed by Chiller#3 followed by Chiller#2 etc.). Well, there may still be a misunderstanding of the functionality of each object and my modeling approach may be flawed. For now I am quite happy to see an impact onto the different loads imposed onto each of the four chillers when selecting a different 'Plant Loop Demand Calculation Scheme'.

Replacing a simple 'Coil:Cooling:Water' with the detailed model 'Coil:Cooling:Water:DetailedGeometry' also forced the headered constant speed chilled water pump to deliver the exact amount of water as demanded and diverted the appropriate amounts through the evaporator of the chillers being requested per specifications above at any point in time.

This is fantastic to watch! Great job team!!!

Sandro

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "berlinclownfish" <SPlamp@...> wrote:
>
> Hello,
> 
> I am curious to learn whether this issue has been resolved. I am also experiencing the identical issue with no impact of my choice of load distribution scheme selected for the plant loop other than specifying rather inflexible bounds in my cooling load based operating scheme.
> 
> Thank you,
> 
> Sandro
> 
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "beyangj" <beyangj@> wrote:
> >
> > Hi,
> > 
> > Thanks for your reply.I submitted the file in the Department: General
> > in the support center, its name is "Chiller 1", and the Ticket ID is 362.
> > 
> > I'm using EnergyPlus V2.1.0.023, and the weather file of Hong Kong
> > from E+ website is used.
> > 
> > Thanks a lot for your help!
> > 
> > Young 
> > 
> > 
> > 
> > 
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Don Shirey <shirey@> wrote:
> > >
> > > Please send your input data file (idf) to the EnergyPlus helpdesk at
> >  http://energyplus.helpserve.com
> > > 
> > > 
> > > You'll also need to specify which version of EnergyPlus you are
> > using to perform the simulations... and please indicate which weather
> > file you are using.
> > > 
> > > 
> > > The definitions of the output variables are provided in the
> > EnergyPlus Input Output Reference.  Differences between Plant Loop
> > Cooling Demand [W] and Chiller Evap Heat Trans Rate [W] (for all four
> > chillers) could be due to unmet loads (e.g., the chillers were unable
> > to meet the loop chilled water set point temperature, or the chillers
> > overcooled the loop below the set point temperature because of some of
> > your inputs).
> > > 
> > > 
> > > beyangj wrote:
> > > > Dear All,
> > > >
> > > > I¡¯d like to explain more about the questions. 
> > > >
> > > > For example, PlantLoopCoolingDemand:HVAC, namely the Total Water
> > > > Cooling Coil Energy of all zones, is 2272.7kw, but all the 4 chillers
> > > > operated at the same Chiller Part Load Ratio 0.425, and Chiller Evap
> > > > Heat Trans Rate for every chiller is 586.3kw, the full load chiller
> > > > capacity for every chiller is 1512 kw in this model. According to the
> > > > reality, only two chillers can provide the system cooling demand
> > > > 2272.7kw, why the 4 chillers operate together?  The sum of the Chiller
> > > > Evap Heat Trans Rate of the 4 chillers (2345.6 kw)  are not equal to
> > > > the system cooling demand 2272.7kw. What make the difference? The Load
> > > > Distribution Scheme is set as Sequential.
> > > >
> > > > According to the report variable for Chiller Evap Heat Trans Rate and
> > > > Chiller Part Load Ratio, the value of Chiller Evap Heat Trans Rate
> > > > over Chiller Part Load Ratio is not equal to the maximum chiller
> > > > capacity, why this happened?  Chiller Evap Heat Trans Rate is the
> > > > chiller capacity?  Why the Chiller Evap Water Outlet Temp[C] is not 7¡æ
> > > > as expected?
> > > >
> > > > In addition, CHILLED WATER LOOP CHILLED WATER LOOP:Plant Loop Cooling
> > > > Demand is 7730.5kw, CHILLED WATER LOOP CHILLED WATER LOOP:Plant Loop
> > > > Unmet Demand is 175.3kw. Why the Plant Loop Unmet Demand is not zero?
> > > >  The Minimum Unloading Ratio is set as 0.25. What¡¯s the relationship 
> > > > between the Plant Loop Cooling Deman and the Total Water Cooling Coil
> > > > Energy of all zones?  
> > > >
> > > >
> > > > I appreciate your help!
> > > >
> > > > Young
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "beyangj" <beyangj@> wrote:
> > > >   
> > > >> Dear all,
> > > >>
> > > >> I have some questions about the model of multiple chillers. There are
> > > >> four water-cooled centrifugal chillers in the model, and their
> > > >> capacity are the same. The chillers are controlled as SEQUENTIAL.
> > > >>
> > > >> The first question is what's the relationship between  Plant Loop
> > > >> Cooling Demand [W] and Chiller Evap Heat Trans Rate [W]? When I
> > change
> > > >> the reference capacity in Chiller:Electric:EIR, the Plant Loop
> > Cooling
> > > >> Demand[W] also changed, why this happened?
> > > >>
> > > >>
> > > >> The second question is that the Reference Leaving Chilled Water
> > > >> Temperature is set as 7¡æ,  and Leaving Chilled Water Lower
> > Temperature
> > > >> Limit is set as  5¡æ. But in the outputs, the Chiller Evap Water
> > Outlet
> > > >> Temp[C] is 5¡æ in all outdoor conditions, why the Chiller Evap Water
> > > >> Outlet Temp[C] is  not 7¡æ as expected?
> > > >>
> > > >> When the cooling capacity of three chillers satisfied the cooling
> > > >> demand, but all the 4 chillers operated, and all the chiller operated
> > > >> on low part load ratio, even all less than 0.3,  and Chiller Evap
> > Heat
> > > >> Trans Rate [W] of the first three chillers are the same, why no
> > > >> chillers can operate at full load capacity? And why the fourth
> > chiller
> > > >> operates even there is no need for it to operate?  If three chillers
> > > >> can provide enough cooling capacity, they can operate at even load
> > > >> sharing without operating the 4th chiller? 
> > > >>
> > > >>
> > > >> Thanks in advance.
> > > >>
> > > >>
> > > >> Young
> > > >>
> > >
> >
>




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References:
- [EnergyPlus_Support] Re: Multiple chillers
  - From: berlinclownfish

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