How to determine custom chiller performance curves with correct coefficients?

asked 2016-03-22 13:49:43 -0600

Brian C
560 ●1 ●9

updated 2016-03-22 14:53:56 -0600

I would like to know how to create a chiller curve for particular chillers in energy-plus. The two exact chillers I am trying to model are:

Standard Water-Cooled Chiller (WSC087 Std Chiller)
Magnetic Bearing Water-Cooled Chiller (WME500 MAG)

It would be helpful to have a step-by-step process of how you determine the coefficients for the three curves required. An example would be most useful, which references the energy plus documentation when needed.

Thanks, Brian

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For EnergyPlus?

__AmirRoth__ ( 2016-03-22 13:57:21 -0600 )edit

Yes, sorry I updated question details to include this

Brian C ( 2016-03-22 14:21:18 -0600 )edit

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answered 2016-03-22 15:05:58 -0600

rraustad

13804 ●79 ●12 http://www.fsec.ucf.edu/

There is a curve-fit tool distributed with EnergyPlus in the Preprocess\HVACCurveFitTool folder (e.g., C:\EnergyPlusV8-4-0\PreProcess\HVACCurveFitTool). This tool was designed for HVAC systems, but can be used to create chiller curves.

For example, the electric EIR chiller uses the same equation form as the DX cooling coil. So this tool could be used by substituting chilled water supply temperature for indoor air wet-bulb temperature and entering condenser fluid temperature for outdoor dry-bulb temperature. Then add the chiller capacity and power data and click the "Press to Generate Curves" button. On the output page will be the performance curves.

Chiller:Electric:EIR,
   A2 , \field Cooling Capacity Function of Temperature Curve Name
    \object-list BiquadraticCurves
    \note curve = a + b*CWS + c*CWS**2 + d*ECT + e*ECT**2 + f*CWS*ECT
    \note CWS = supply (leaving) chilled water temperature(C)
    \note ECT = entering condenser fluid temperature(C)

Coil:Cooling:DX:SingleSpeed,
   A5 , \field Total Cooling Capacity Function of Temperature Curve Name
    \object-list BiquadraticCurves
    \note curve = a + b*wb + c*wb**2 + d*edb + e*edb**2 + f*wb*edb
    \note wb = entering wet-bulb temperature (C)
    \note edb = dry-bulb temperature seen by the condenser (C)

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What should we do for the partload ratio curve EIRFPLR. Also can the chilled water supply temperature remain constant here for all condenser water temperatures.

kbk78 ( 2019-04-12 09:39:52 -0600 )edit

The EIRFPLR curve is really a power output versus PLR curve. So this curve looks approximately proportional to PLR (e.g., at PLR = 0.5 then power output is about 50%, plus or minus some tolerance, about 10%). You might look in the AirCooledChiller.idf or Chillers.idf dataset files to see other EIRFPLR curves. The supply water temp will remain constant as long as the chiller capacity at the condensing water temp is sufficient to meet the load, otherwise the supply water temp will rise.