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Re: [EnergyPlus_Support] Re: Unrealistic ChillerEIRFPLR curves for data in the file: Chillers.idf?
It's pretty easy in a spreadsheet.
For example Output = X + X^2 + Y + Y^2 + XY
Set up columns in a spreadsheet to represent the independent variables
Column A B C D E F
Output X X^2 Y Y^2 XY
were column:
A = Output
B = X (for example leaving evaporator temp)
C = X^2
D = Y (for example entering condenser temp)
E = Y^2
F = XY
You actually multiple out the ^2 terms and cross-product in the
spreadsheet. Then perform a regression analysis on this data. Select
Output as the regression Y data (e.g., A2..A20) and "ALL independent
variables" as the X variable (e.g. B2..F20). You will get the
coefficients for B through F, there will be 1 additional coefficient if
Y does not cross the X axis at 0 (always the first coefficient). The t
Stat in the regression statistics will be greater than 2 if that
independent term is significant (i.e.., helps describe changes to the
dependent variable [Output or Y in this example]).
Example:
1.2 2 4 6 36 12
1.6 3 9 5 25 15
JV Dirkes II wrote:
>
>
>
> Dear Damian,
>
> 2-4 times the peak capacity COP sounds like a stretch for believability.
> On the other hand, improved part load COP is exactly the goal to be
> striven for, since the vast majority of operation hours are at part
> load. I suspect that the "typical" COP vs PLR values in the example
> file do not represent a specific chiller and may not represent most
> chillers. It's a good place to start, but if you can derive a curve for
> the actual chiller, that is preferred!
>
> I have not developed part load curves often enough to pretend that I am
> an expert, but most chiller manufacturers publish performance with
> varying entering water temps, delta T and condenser water temp / delta
> T. In theory, that allows you to create a performance curve which
> incorporates those variables, although it sounds challenging. I have
> not needed to do so yet, so I've put off the task. As I recall, the
> information set varies quite a bit among the major manufacturers, so
> standardization might be difficult.
>
> This, it seems, is an opportunity for the modeling community. I started
> the process a while back by setting up a standard representation of
> performance with those variables, but haven't figured out how to do the
> curve-fit for multiple variables. If you figure it out or someone else
> has already figured it out, please share the information!
>
> Actually, it would be VERY nice if the manufacturers would publish these
> curves...
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>, "d_h51@..." <d_h51@...>
> wrote:
> >
> > Hi all,
> >
> > When I plot the COP vs PLR dependence taken from the file
> 'Chillers.idf'
> > for specific chillers (please see the file COP vs PLR
> > (EnergyPlus).jpg
> >
> <http://f1.grp.yahoofs.com/v1/cA3eSXpIH0plWrUAXrH171qOeNo_sglXxA6WFL-5A1\
> \
> <http://f1.grp.yahoofs.com/v1/cA3eSXpIH0plWrUAXrH171qOeNo_sglXxA6WFL-5A1>>
> c9cj_Ewy5DotS8QUGcGAVrG8-yS_ZOkZM7K4eZBiXgSaqQ_1FPQsMlalsOvFE/_Problem_S\
> \
> > ubmittals/COP%20vs%20PLR%20%28EnergyPlus%29.jpg> ) it shows that for
> > some chillers at e.g. PLR=0.4 the COP is 4times higher than for PLR=1,
> > and for PLR =0.5 most of the chillers have 2times higher COP than at
> > PLR=1.
> >
> > For me it's unrealistic, especially when i compare these results to
> the
> > catalogue data given from the producers (where the COP/COP_ref value
> > reaches its maximum usually for PLR=0.5 and is about 1.6)
> >
> > Do I do a mistake somewhere? COP/COP_ref = 1/ChillerEIRFPLR, right?
> >
> > Or maybe this problem is related to my next question:
> > COP vs PLR performance in catalogue data is mostly rated under ARI
> > conditions, for instance for water2water chillers and PLR=1 ECWT=29.4C
> > and for PLR=0.5 ECWT=18.3C. Do the ChillerEIRPLR curves are rated for
> > constant ECWT? If yes how can I modify PLR curves rated according to
> ARI
> > standard into curves for constant ECWT?
> >
> > Thanks for any help in advance,
> > Damian
> >
>
>
--
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
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