How to determine custom chiller performance curves with correct coefficients?

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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)