CondenserLoop Coincident sizing is larger than NonCoincident sizing

My model is the same as this post, but let me post a different question.

I have a problem with Coincident plant sizing for CondenserLoop. I tried both Coincident sizing and NonCoincident sizing, but the weird thing is that the autosized condenser loop (Cooling towers and condenser water pumps) by Coincident sizing is much larger than that by NonCoincident sizing. It does not happen in PlantLoop (chillers and chilled water pumps). I think my Coincident sizing settings are appropriate.

Below are the sizing results of cooling towers. Autosized condenser water flow rate by Coincndent sizing is 0.164097m3/s, which is more than 2 times larger than the autosized condenser water flow rate of 0.072678m3/s by NonCoincident sizing. Does anyone know why?

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I think the "Initial" values in the html file are the correct ones which are autosized by Coincident sizing. The "Design" values are incorrect. However, this is not just a reporting issue. I also ran annual simulations. The pump end use with Coincident sizing became much larger than that with NonCoincident sizing NonCoincident sizing. EnergyPlus uses the "Design" values.

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Is this a bug? Or am I missing something? My settings related to Coincident sizing are as follows. Any suggestions would be appreciated.

    SimulationControl,
        Yes,                     !- Do Zone Sizing Calculation
        Yes,                     !- Do System Sizing Calculation
        Yes,                     !- Do Plant Sizing Calculation
        Yes,                     !- Run Simulation for Sizing Periods
        No,                      !- Run Simulation for Weather File Run Periods
        Yes,                     !- Do HVAC Sizing Simulation for Sizing Periods
        1;                       !- Maximum Number of HVAC Sizing Simulation Passes

    Sizing:Parameters,
        1.25,                    !- Heating Sizing Factor
        1.15;                    !- Cooling Sizing Factor

    Sizing:System,
        VAV_3,                   !- AirLoop Name
        Sensible,                !- Type of Load to Size On
        autosize,                !- Design Outdoor Air Flow Rate {m3/s}
        autosize,                !- Central Heating Maximum System Air Flow Ratio
        30,                      !- Preheat Design Temperature {C}
        0.0033,                  !- Preheat Design Humidity Ratio {kgWater/kgDryAir}
        11,                      !- Precool Design Temperature {C}
        0.008,                   !- Precool Design Humidity Ratio {kgWater/kgDryAir}
        15,                      !- Central Cooling Design Supply Air Temperature {C}
        22,                      !- Central Heating Design Supply Air Temperature {C}
        Coincident,              !- Type of Zone Sum to Use
        No,                      !- 100% Outdoor Air in Cooling
        No,                      !- 100% Outdoor Air in Heating
        0.008,                   !- Central Cooling Design Supply Air Humidity Ratio {kgWater/kgDryAir}
        0.008,                   !- Central Heating Design Supply Air Humidity Ratio {kgWater/kgDryAir}
        DesignDay,               !- Cooling Supply Air Flow Rate Method
        0,                       !- Cooling Supply Air Flow Rate {m3/s}
        ,                        !- Cooling Supply Air Flow Rate Per Floor Area {m3/s-m2}
        ,                        !- Cooling Fraction of Autosized Cooling Supply Air Flow Rate
        ,                        !- Cooling Supply Air Flow Rate Per Unit Cooling Capacity {m3/s-W}
        DesignDay,               !- Heating Supply Air Flow Rate Method
        0,                       !- Heating Supply Air Flow Rate {m3/s}
        ,                        !- Heating Supply Air Flow Rate Per Floor Area {m3/s-m2}
        ,                        !- Heating Fraction of Autosized Heating Supply Air Flow Rate
        ,                        !- Heating Fraction of Autosized Cooling Supply Air Flow Rate
        ,                        !- Heating Supply Air Flow Rate Per Unit Heating Capacity {m3/s-W}
        ZoneSum,                 !- System Outdoor Air Method
        1.0,                     !- Zone Maximum Outdoor Air Fraction {dimensionless}
        CoolingDesignCapacity,   !- Cooling Design Capacity Method
        autosize,                !- Cooling Design Capacity {W}
        ,                        !- Cooling Design Capacity ...

(more)

Keigo

asked 2022-10-09 16:15:55 -0500, updated 2022-10-12 21:24:52 -0500

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I tried changing Maximum Number of HVAC Sizing Simulation Passes from 1 to 2, 3, 4 and 5, but the results did not change at all.

Keigo (2022-10-09 21:51:05 -0500) edit

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Self-resolved! If we want to do Coincident plant sizing for both chilled water loop and condenser water loop, we should choose Coincident for chilled water loop and NonCoincident for condenser water loop. This setting provides Coincident sizing results of cooling towers and condener water pumps.

Sizing:Plant,
    CHWloop Chilled Water Loop,  !- Plant or Condenser Loop Name
    Cooling,                 !- Loop Type
    6.7,                     !- Design Loop Exit Temperature {C}
    6.3,                     !- Loop Design Temperature Difference {deltaC}
    Coincident,              !- Sizing Option
    ,                        !- Zone Timesteps in Averaging Window
    None;                    !- Coincident Sizing Factor Mode

Sizing:Plant,
    CHWloop Condenser Water Loop,  !- Plant or Condenser Loop Name
    Condenser,               !- Loop Type
    29,                      !- Design Loop Exit Temperature {C}
    5.6,                     !- Loop Design Temperature Difference {deltaC}
    NonCoincident,           !- Sizing Option
    ,                        !- Zone Timesteps in Averaging Window
    None;                    !- Coincident Sizing Factor Mode

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