[EnergyPlus_Support] Autosizing dx cooling coil is under sizing minimum flowrate at maximum load

["Jean marais" <jeannieboef@xxxxxxxxx>]

Dear Group,
Is anyone else experiencing this:
Autosizing dx cooling coil is under sizing minimum flowrate at maximum load

Here is an example of my coil:

Coil:Cooling:DX:SingleSpeed,
    118443 AHU Cooling Coil, !- Name
    SchCpct_LowTempClgOFF,   !- Availability Schedule Name
    autosize,                !- Rated Total Cooling Capacity {W}
    autosize,                !- Rated Sensible Heat Ratio
    3.81,                    !- Rated COP {W/W}
    autosize,                !- Rated Air Flow Rate {m3/s}
    ,                        !- Rated Evaporator Fan Power Per Volume Flow Rate {W/(m3/s)}
    118443 AHU Gas Heating Coil Outlet,  !- Air Inlet Node Name
    118443 Unitary Unit Outlet,  !- Air Outlet Node Name
    118443 AHU DX Coil Cap-FT,  !- Total Cooling Capacity Function of Temperature Curve Name
    118443 AHU DX Coil Cap-FF,  !- Total Cooling Capacity Function of Flow Fraction Curve Name
    118443 AHU DX Coil EIR-FT,  !- Energy Input Ratio Function of Temperature Curve Name
    118443 AHU DX Coil EIR-FF,  !- Energy Input Ratio Function of Flow Fraction Curve Name
    118443 AHU DX Coil PLF,  !- Part Load Fraction Correlation Curve Name
    1000,                       !- Nominal Time for Condensate Removal to Begin {s}
    1.5,                       !- Ratio of Initial Moisture Evaporation Rate and Steady State Latent Capacity {dimensionless}
    1,                       !- Maximum Cycling Rate {cycles/hr}
    45,                       !- Latent Capacity Time Constant {s}
    118443 AHU Cooling Coil Condenser Inlet,  !- Condenser Air Inlet Node Name
    AirCooled,               !- Condenser Type
    0,                       !- Evaporative Condenser Effectiveness {dimensionless}
    ,                        !- Evaporative Condenser Air Flow Rate {m3/s}
    0,                       !- Evaporative Condenser Pump Rated Power Consumption {W}
    0,                       !- Crankcase Heater Capacity {W}
    10;                      !- Maximum Outdoor Dry-Bulb Temperature for Crankcase Heater Operation {C}

********************************

Reporting the output temps on a timestep basis at 60 steps per hour, I see wildly fluctuating temps from minute to minute by more than 2 deg C, although the Setpoint is Constant.

This is causing all sorts of error messages. For example:

** Warning ** CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed "118288 AHU COOLING COIL" - Full load outlet air dry-bulb temperature < 2C. This indicates the possibility of coil frost/freeze. Outlet temperature = 1.53 C.
   **   ~~~   **  ...Occurrence info = KITA, 03/27 12:36 - 12:37
   **   ~~~   ** ... Possible reasons for low outlet air dry-bulb temperatures are: This DX coil
   **   ~~~   **    1) may have a low inlet air dry-bulb temperature. Inlet air temperature = 17.430 C.
   **   ~~~   **    2) may have a low air flow rate per watt of cooling capacity. Check inputs.
   **   ~~~   **    3) is used as part of a HX assisted cooling coil which uses a high sensible effectiveness. Check inputs.

*****************************and
 ** Warning ** SolveAirLoopControllers: Maximum iterations (50) exceeded for 118320 AHU, at KITA, 01/01 00:17 - 00:18
*****************************and
** Warning ** SimHVAC: Maximum iterations (100) exceeded for all HVAC loops, at KITA, 01/21 13:35 - 13:36
   **   ~~~   ** The solution for one or more of the Air Loop HVAC systems did not appear to converge
   **   ~~~   ** ...use Output:Diagnostics,DisplayExtraWarnings;   to show more details on each max iteration exceeded.
**********************

My minimum airflow rates are autosized to meet sensible load.

Any comments please.

Jean








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