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Re: [EnergyPlus_Support] Unrealistic ChillerEIRFPLR curves for data in the file: Chillers.idf?



See below.

d_h51@xxxxxxxxx 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 ) 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?
Actually this is wrong, due to a confusing feature of EIRFPLR: EIRFPLR contains a PLR factor within it. The correct formula
is  COP/COP_ref = PLR/ChillerEIRFPLR.

This also holds true for Doe-2, eQuest etc.

Here's the derivation:

COP = CoolOut/EnergyIn
PLR = CoolOut/AvailCap
EnergyIn = (AvailCap/COP_nom)*EIRFPLR*EIRFT  (this is from the EPlus code. Note the use of AvailCap on
   the right hand side of the equation, rather than what you'd expect: CoolOut =AvailCap*PLR)
So COP = (PLR*AvailCap) / ( (AvailCap/Cop_npm)*EIRFPLR*EIRFT)
and COP/COP_nom = PLR/(EIRFPLT*EIRFT)

Fred Buhl

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 ECW! T=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


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