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How to get VRF Performance Curve Output Value

asked 2026-03-25 23:16:38 -0500

Keigo's avatar

I would like to get the output values of VRF performnance curves for validation purpose.

I tested with an ExampleFile VariableRefrigerantFlow_5Zone.idf (V25-2-0). The output values of the following curves are -999 throughout the year, which indicates the curves are inactive or unused.

  1. Cooling Combination Ratio Correction Factor Curve
  2. Piping Correction Factor for Length in Cooling Mode Curve

FYI, the Output:Variable settings are as follows.

Output:Variable,
    COOLINGCOMBRATIO,        !- Key Value
    Performance Curve Output Value ,  !- Variable Name
    Hourly;                  !- Reporting Frequency

Output:Variable,
    CoolingLengthCorrectionFactor,  !- Key Value
    Performance Curve Output Value ,  !- Variable Name
    Hourly;                  !- Reporting Frequency

For 1, it will not be used when CR is less than 1. I reduced the heat pump's Gross Rated Total Cooling Capacity by hardsizing it, but I still got -999.

For 2, I changed the performance curve coefficients, and the cooling energy use changed. So, the curve is actualy used.

I tested all types of Reporting Frequency, but in vain.

How can I get the output of the two curves?

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answered 2026-03-26 11:45:44 -0500

@Keigo, those curves are used during initialization of the VRF system and only happens 1 time at the beginning of the simulation. Think of these as more of a sizing input for autosizing. Output of these curves is not available during the simulation.

if (CheckVRFCombinationRatio(VRFCond)) {

    if (state.dataHVACVarRefFlow->VRF(VRFCond).CoolCombRatioPTR > 0) {
        state.dataHVACVarRefFlow->CoolCombinationRatio(VRFCond) = CurveValue(
            state, state.dataHVACVarRefFlow->VRF(VRFCond).CoolCombRatioPTR, state.dataHVACVarRefFlow->VRF(VRFCond).CoolingCombinationRatio);
    } else {
        state.dataHVACVarRefFlow->CoolCombinationRatio(VRFCond) = 1.0;
    }

    CheckVRFCombinationRatio(VRFCond) = false;
}

The results of these curves is shown in the eio file:

if (state.dataHVACVarRefFlow->MyOneTimeEIOFlag) {
    static constexpr std::string_view Format_990(
        "! <VRF System Information>, VRF System Type, VRF System Name, VRF System Cooling Combination Ratio, VRF "
        "System Heating Combination Ratio, VRF System Cooling Piping Correction Factor, VRF System Heating Piping "
        "Correction Factor\n");
    print(state.files.eio, Format_990);
    state.dataHVACVarRefFlow->MyOneTimeEIOFlag = false;
}
print(state.files.eio,
      Format_991,
      cVRFTypes(state.dataHVACVarRefFlow->VRF(VRFCond).VRFSystemTypeNum),
      state.dataHVACVarRefFlow->VRF(VRFCond).Name,
      state.dataHVACVarRefFlow->VRF(VRFCond).CoolingCombinationRatio,
      state.dataHVACVarRefFlow->VRF(VRFCond).HeatingCombinationRatio,
      state.dataHVACVarRefFlow->VRF(VRFCond).PipingCorrectionCooling,
      state.dataHVACVarRefFlow->VRF(VRFCond).PipingCorrectionHeating);
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I found the results of the curves in the eio file. Thank you so much!

Keigo's avatar Keigo  ( 2026-03-26 20:06:21 -0500 )edit
1

answered 2026-03-26 09:29:36 -0500

Greg Estep's avatar

Hi Keigo, I like your thinking and understand wanting to validate curve outputs. I took a quick look at the InputOutput reference and noticed that the VRF objects don't list the curves as available outputs. The other place to look would be the eplusout.edd file and search for the curves to see if an output is available. I'm guessing you already looked in these places. Let me know what you find out. -Greg

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Thanks Greg for taking the time.

Keigo's avatar Keigo  ( 2026-03-26 20:10:21 -0500 )edit

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Asked: 2026-03-25 23:16:38 -0500

Seen: 120 times

Last updated: Mar 26