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Re: [EnergyPlus_Support] Warnings in the HVAC simulation


I think your coil is sizing with massive flowrates and that during the simulation you only have tiny flowrates. The off-coil temps of -59.99ºC are just plain alarming. This must be the DX model's limit! I suggest looking at the outputs for the design flowrates. If I were a betting man, I would bet that you should have set your Sizing:Plant object to size on "Ventilation Requirement" and not "Sensible Load". Somewhere later, you then limited your fan flow capacity manually, but the coils still get autosized using the massive flowrate from the Sizing:Plant object set to size on sensible load.


2014-05-15 14:29 GMT+02:00 <mailto:luca.guj@xxxxxxxxx>luca.guj@xxxxxxxxx [EnergyPlus_Support] <<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx>:
>  
> I'm currently running a model where there are 4 different small building served by the 4 different portable AC.

> I have translated the specs of the AC into the following single speed coil model:

> 
> 
> Coil:Cooling:DX:SingleSpeed,

>     OS:Coil:Cooling:DX:SingleSpeed 1 Concrete Coated,  !- Name

>     Always On Discrete 2,    !- Availability Schedule Name

>     2491,                    !- Rated Total Cooling Capacity {W}

>     0.68,                    !- Rated Sensible Heat Ratio

>     0.38392,                 !- Rated COP {W/W}

>     0.10031,                 !- Rated Air Flow Rate {m3/s}

>     773.3,                   !- Rated Evaporator Fan Power Per Volume Flow Rate {W/(m3/s)}

>     Node 16,                 !- Air Inlet Node Name

>     Node 10,                 !- Air Outlet Node Name

>     OS:Curve:Biquadratic 1,  !- Total Cooling Capacity Function of Temperature Curve Name

>     OS:Curve:Quadratic 1,    !- Total Cooling Capacity Function of Flow Fraction Curve Name

>     OS:Curve:Biquadratic 2,  !- Energy Input Ratio Function of Temperature Curve Name

>     OS:Curve:Quadratic 2,    !- Energy Input Ratio Function of Flow Fraction Curve Name

>     OS:Curve:Quadratic 3,    !- Part Load Fraction Correlation Curve Name

>     ,                        !- Nominal Time for Condensate Removal to Begin {s}

>     ,                        !- Ratio of Initial Moisture Evaporation Rate and Steady State Latent Capacity {dimensionless}

>     ,                        !- Maximum Cycling Rate {cycles/hr}

>     ,                        !- Latent Capacity Time Constant {s}

>     ,                        !- Condenser Air Inlet Node Name

>     AirCooled,               !- Condenser Type

>     0,                       !- Evaporative Condenser Effectiveness {dimensionless}

>     ,                        !- Evaporative Condenser Air Flow Rate {m3/s}

>     ,                        !- Evaporative Condenser Pump Rated Power Consumption {W}

>     0,                       !- Crankcase Heater Capacity {W}

>     0,                       !- Maximum Outdoor Dry-Bulb Temperature for Crankcase Heater Operation {C}

>     ,                        !- Supply Water Storage Tank Name

>     ,                        !- Condensate Collection Water Storage Tank Name

>     0,                       !- Basin Heater Capacity {W/K}

>     10;                      !- Basin Heater Setpoint Temperature {C}

> 
> 
> The analysis is running till the end and it provides meaningful results. But it shows many warnings like the ones that follows:

> 
> 
> ** Warning ** CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed "OS:COIL:COOLING:DX:SINGLESPEED 2 CONCRETE NON COATED" - Full load outlet air dry-bulb temperature < 2C. This indicates the possibility of coil frost/freeze. Outlet temperature = -59.99 C.
> 
> **   ~~~   **  ...Occurrence info = RUN PERIOD 1, 01/01 00:00 - 00:15

> **   ~~~   ** ... 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 = 23.000 C.

> **   ~~~   **    2) may have a low air flow rate per watt of cooling capacity. Check inputs.

> 
> 
> ** Warning ** Enthalpy out of range (PsyTsatFnHPb)              

> **   ~~~   **   This error occurred 1203204 total times;        

> **   ~~~   **   during Warmup 0 times;                          

> **   ~~~   **   during Sizing 0 times.                          

> **   ~~~   **   Max=-128504.325865 J/kg  Min=-533236.819662 J/kg

> 
> ** Warning ** Calculated Humidity Ratio invalid (PsyWFnT
**   ~~~   **   This error occurred 759968 total times; 
**   ~~~   **   during Warmup 0 times;                  
**   ~~~   **   during Sizing 0 times.                  
**   ~~~   **   Max=-3.602886E-002 []  Min=-0.205414 [] 
> ** Warning ** CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed="OS:COIL:COOLING:DX:SINGLESPEED 3 ALUMINUM COATED" - Air volume flow rate per watt of rated total cooling capacity is out of range error continues...
**   ~~~   **   This error occurred 14856 total times;        
**   ~~~   **   during Warmup 0 times;                                                                                     
**   ~~~   **   during Sizing 0 times.      
**   ~~~   **   Max=1.479412E-006  Min=1.445607E-006                                                                                                                                                           
what is the reason for these warnings?
> Moreover I have read through some old topic and the a proposed solution for this type of warning was to use humidity control, i.e. ZoneControl:Thermostat:TemperatureAndHumidity. Is this the correct way to go?
> Thanks in advance for your support.
> Luca 
 
> 
> 
> 
> 
> 
> 
> 




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