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Re: [EnergyPlus_Support] Re: Precooling chilled water return



EnergyPlus plant loops only support one splitter/mixer on the supply side (or 
demand side) of the loop.  So you will need to arrange the components as 
follows:

1. Inlet branch with pump
2. Splitter
3a.  Small chiller branch
3b.  Bypass
4. Mixer
5. Large chiller branch which is the supply side outlet

This might work, but it might have flow resolution errors.  The large chiller 
and the pump must both be constant flow or both variable flow, because there is 
no place to put a second bypass around the large chiller.

Mike


On 31 Jan 2008 at 11:01, Richard Raustad wrote:

> I thought you wanted them in series, I see now you were asking about a 
> bypass around the smaller chiller. I can't say for sure if that will 
> work correctly. You will just have to try it and see. I think you need 
> the same number of splitters and mixers, so put a splitter at the inlet 
> (return) of the small chiller and a mixer at the outlet (supply) of the 
> small chiller and connect with a bypass pipe. Let us know if this works 
> correctly.
> 
> zhaicq98 wrote:
> >
> > Thanks Richard. I donot quite understand when you said both chillers
> > will operate at the same evaporator volumeric flowrate. Can I bypass
> > some of the chilled water flow around the small chiller? In this
> > way, the big chiller can have a higher flow and the small chiller
> > has a lower flow.
> >
> > Thanks again,
> > Chaoqin
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > <RRaustad@...> wrote:
> > >
> > > This should work in E+. You would need to use constant flow
> > chillers and
> > > the chillers should not be auto-sized (or at least the smaller
> > one). The
> > > only problem I see is that you can not have a significant
> > difference in
> > > the capacities of the series chillers. The reason is that both
> > chillers
> > > will operate at the same evaporator volumetric flow rate (and the
> > > performance curves should account for off-design flow rates).
> > There is
> > > an upper (and lower) limit to the water velocities through a
> > chiller's
> > > heat exchanger. Above the upper limit, erosion of heat exchanger
> > will be
> > > excessive (and so will the pressure drop). Below the lower limit
> > there
> > > is a chance of freezing the heat exchanger or reducing oil
> > transport
> > > through the refrigeration system. Of course this will not hurt the
> > > simulation, but you want to be as close to reality as possible.
> > And if
> > > you actually built a chiller with an over-sized heat exchanger,
> > you
> > > would not have this problem. Check with manufacturers for
> > appropriate
> > > ranges of water flow rates through the evaporators for your type
> > of
> > > chiller. The same holds true for the condenser heat exchangers,
> > but you
> > > could pipe the condensers in parallel.
> > >
> > > zhaicq98 wrote:
> > > >
> > > > I have a big and a small water cooled vapor compression chiller
> > in the
> > > > system. They are configured in series, but the chilled water
> > flowrate
> > > > of the
> > > > big chiller is much greater than the small one. The small
> > chiller is
> > > > used to
> > > > pre-cool a portion of the chilled water return to the big
> > chiller.
> > > >
> > > > I wonder if EnergyPlus is able to handle this system. Thanks for
> > your
> > > > help.
> > > >
> > > > -Chaoqin
> > > >
> > > >
> > >
> > > --
> > > 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 <http://www.fsec.ucf.edu>
> > >
> > > UCF - From Promise to Prominence: Celebrating 40 Years
> > >
> >
> >  
> 
> -- 
> 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
> 
> 
> 
> 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.
> 
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 


========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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