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Chiller IPLV Calculation

asked 2022-10-03 13:49:05 -0600

Keigo's avatar

updated 2022-10-12 21:24:21 -0600

I want to adjust IPLV of Chiller:Electric:EIR. I referred to Engineering Reference and calculate the IPLV in Excel before running simulation, which can avoid iterating simulation many times. When I change the coefficients of three chiller performance curves in the Excel, I can get the IPLV instantly.

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However, the calculated IPLV (6.62) in the Excel is approximately 1.5% larger than the reported IPLV (6.52) in the html file. I did a sizing run to output the html file.

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I saw this post, and I have already fixed the Minimum Value of y. IPLV calculating conditions are within the Minimum/Maximum value of x/y. (When Chiller:Electric:EIR is generated from HVACTemplate, the default Minimum Value of y for Curve:Biquadratic is 24 which is higher than the entering condenser water temperature of 18.3degC at 25% load, which should be fixed.)

Minimum Unloading Ratio of Chiller:Electric:EIR is set to 0.1 which is lower than 0.25, so I think the degradation coefficient does not affect the IPLV calculation.

What is causing this difference? I can't identify it. Is it due to the significant figures? Or are the numbers in Engineering Reference different from numbers actually used in EnergyPlus?

The excel, html file and the idf file (V9-6-0) are here. I want to calculate IPLV accurately in Excel to avoid running simulation again and again. Any suggestions would be appreciated.

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answered 2022-10-04 09:35:59 -0600

Keigo's avatar

updated 2022-10-05 01:55:10 -0600

I found two causes.

- Evaporator leaving water temperature and Condenser entering water temperature are different between Engineering Reference and actual code of EnergyPlus.

I summarised in the table below. The code says it follows AHRI 551/591-2011, but actually Evaporator leaving water temperature and Condenser entering water temperature at 75% load are different from AHRI 551/591.

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The code on lines 341 and 342 is weird. I think this is a bug.

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- Part Load Ratio

This is my mistake. It's confusing that there are two different parameters: ReducedPLR and PartLoadRatio . ReducedPLR is 100%, 75%, 50% and 25%. PartLoadRatio = ReducedPLR / ChillerCapFT.

I revised my excel calculation according to the current code. The calculated IPLV became very close to the reported IPLV, but still there is a slight difference (Hundredth's place is sometimes different). I'm still waiting for suggestions. image description


When I changed the coefficients of two Biquadratic curves from the default centrifugal chiller to the default screw chiller, the difference between the calculated IPLV and the reported IPLV exceeded 1% again. My excel is not perfect...

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answered 2022-10-03 17:03:33 -0600

Maybe it's because the cooling towers are not achieving the entering condenser water temperatures at the PLRs in that table? It looks like the condenser water is using SetpointManager:FollowOutdoorAirTemperature, which may not achieve the entering CW temperatures listed in your Excel calculation at the respective PLRs.

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A few thoughts: 1) 1.5% difference is small and I wouldn't worry as long as it's consistently small. It might be rounding error. 2) I suspect the IPLV is calculated at the AHRI conditions independently of the actual condenser water temperature (at least, I think it should be done that way) 3) As it happens, I developed a DX coil IPLV / IEER calculation several years ago and am halfway through making an equivalent for a chiller's IPLV. Are you willing to exchange those procedures?

Jim Dirkes's avatar Jim Dirkes  ( 2022-10-04 09:32:28 -0600 )edit

@ericmartinpe Thank you for your advice. I agree with @Jim Dirkes 's opinion, i.e., IPLV is calculated at the AHRI conditions independently of the actual condenser water temperature.

Keigo's avatar Keigo  ( 2022-10-04 09:42:57 -0600 )edit

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Asked: 2022-10-03 13:49:05 -0600

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Last updated: Oct 05