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Re: [EnergyPlus_Support] Cooling Tower outlet temperature below specified minimum



Thanks Jim,

900 errors on 1008 timesteps is a lot though... That's my problem. (I've only pasted the result of a simulation over the first week of january).

I definitely have a cooling load, these serve a high-density data center. My condenser loop is defined between 5°C min and 80°C max.
I've left the Fraction of Tower Capacity in Free Convection Regime at its default value of 0.125.

The Max / Min message is because this is from the Recurring Error summary. It means (at least I think it does...) that of those 900 times, the max value was 5C and the min was 5C (so it was 5C all the time...). This seems to be confirmed if I look above in the error file to the individual error level:
   ** Warning ** CoolingTower:VariableSpeed "COOLING TOWER 1"
   **   ~~~   ** Cooling tower water outlet temperature (5.00 C) is below the specified minimum condenser loop temp of 5.00 C
   **   ~~~   **  Environment=Newark International Arpt NJ USA TMY3 WMO#=725020, at Simulation time=01/01 21:40 - 21:50

This seems like a weird rounding error thing...


Otherwise I've tried turning off the cooling towers but I made it worse for some reason... I can't figure out why or what I didn't do correctly...

Best,
Julien

--
Julien Marrec, EBCP, BPI MFBA
Energy&Sutainability Engineer
T: +33 6 95 14 42 13
www.julienmarrec.com

DoYouBuzz : www.doyoubuzz.com/julien-marrec_1
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr
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2014-07-08 13:09 GMT+02:00 Jim Dirkes jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:
 

Julien,

It sounds as though the natural drift / convection is causing enough cooling to reduce your outlet temperature to 5C.  Assuming there is actually some load, I think that turning off a couple of towers may help.  If there I no load, there may be no difference.

Also, 900 errors in a complete annual simulation doesnâ??t sound like much to worry about.

Finally, the â??Max = 5, Min = 5â?? text doesnâ??t make much sense to me unless youâ??ve defined the maximum loop temp to be 5C.  If so, consider making the max = 15.

 

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

 

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Tuesday, July 08, 2014 6:54 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Cooling Tower outlet temperature below specified minimum

 

 

Hi,

I've got a building with 4 cooling towers and a big cooling load all year, including the winter.

I'm getting the following errors (Here for one week only, in january)

   *************  ** Warning ** CoolingTower:VariableSpeed "COOLING TOWER 1" Cooling tower water outlet temperature is below the specified minimum condenser loop temp error continues...
   *************  **   ~~~   **   This error occurred 909 total times;
   *************  **   ~~~   **   during Warmup 0 times;
   *************  **   ~~~   **   during Sizing 0 times.
   *************  **   ~~~   **   Max=5.  Min=5.
   *************
   *************  ** Warning ** CoolingTower:VariableSpeed "COOLING TOWER 2" Cooling tower water outlet temperature is below the specified minimum condenser loop temp error continues...
   *************  **   ~~~   **   This error occurred 909 total times;
   *************  **   ~~~   **   during Warmup 0 times;
   *************  **   ~~~   **   during Sizing 0 times.
   *************  **   ~~~   **   Max=5.  Min=5.
   *************
   *************  ** Warning ** CoolingTower:VariableSpeed "COOLING TOWER 3" Cooling tower water outlet temperature is below the specified minimum condenser loop temp error continues...
   *************  **   ~~~   **   This error occurred 909 total times;
   *************  **   ~~~   **   during Warmup 0 times;
   *************  **   ~~~   **   during Sizing 0 times.
   *************  **   ~~~   **   Max=5.  Min=5.
   *************
   *************  ** Warning ** CoolingTower:VariableSpeed "COOLING TOWER 4" Cooling tower water outlet temperature is below the specified minimum condenser loop temp error continues...
   *************  **   ~~~   **   This error occurred 67 total times;
   *************  **   ~~~   **   during Warmup 0 times;
   *************  **   ~~~   **   during Sizing 0 times.
   *************  **   ~~~   **   Max=5.  Min=5.

My minimum condenser loop temperature is 5C. I also have a basin heater set at 2°C. Here it seems that I'm getting all these warnings (they're only for one week in January...) without much cause since Max=5. and Min=5.

Can I discard them?

Also, I'm wondering if I shouldn't just turn off 1 or 2 CTs when outside temperature is below 5°C or something like that, so I'd be closer to the needed capacity. Does that make any sense to you?
If I were to do this, should I use the "PlantEquipmentOperation:OutdoorDryBulb" object or is there a better way to do it? I've tried doing it as follows and it made things worse, temperature was below setpoint 2671 times for each tower (which I don't even understand since I'm simulating 24*7*6=1008 timesteps...) :

CondenserEquipmentList,
    Chiller 1_TowerWaterSys Equipment List,  !- Name
    COOLINGTOWER:VARIABLESPEED,  !- Equipment 1 Object Type
    cooling tower 1,         !- Equipment 1 Name
    COOLINGTOWER:VARIABLESPEED,  !- Equipment 2 Object Type
    cooling tower 2,         !- Equipment 2 Name
    COOLINGTOWER:VARIABLESPEED,  !- Equipment 3 Object Type
    cooling tower 3,         !- Equipment 3 Name
    COOLINGTOWER:VARIABLESPEED,  !- Equipment 4 Object Type
    cooling tower 4;         !- Equipment 4 Name

CondenserEquipmentList,
    Chiller 1_TowerWaterSys Equipment List 1-2 ON,  !- Name
    COOLINGTOWER:VARIABLESPEED,  !- Equipment 1 Object Type
    cooling tower 1,         !- Equipment 1 Name
    COOLINGTOWER:VARIABLESPEED,  !- Equipment 2 Object Type
    cooling tower 2;         !- Equipment 2 Name

PlantEquipmentOperation:OutdoorDryBulb,
    CT two off below 10C,   !- Name
    -70,                     !- Dry-Bulb Temperature Range 1 Lower Limit {C}
    10,                      !- Dry-Bulb Temperature Range 1 Upper Limit {C}
    Chiller 1_TowerWaterSys Equipment List 1-2 ON,  !- Range 1 Equipment List Name
    10,                      !- Dry-Bulb Temperature Range 2 Lower Limit {C}
    70,                      !- Dry-Bulb Temperature Range 2 Upper Limit {C}
    Chiller 1_TowerWaterSys Equipment List;  !- Range 2 Equipment List Name

CondenserEquipmentOperationSchemes,
    Chiller 1_TowerWaterSys Loop Operation Scheme List,  !- Name
    PlantEquipmentOperation:OutdoorDryBulb,  !- Control Scheme 1 Object Type
    CT two off below 10C,   !- Control Scheme 1 Name
    PlantOnSched;            !- Control Scheme 1 Schedule Name

(plantOnSched = 1 all times)

 

Any idea why?

 

Thanks for any help you can provide,

Best,

--
Julien Marrec, EBCP, BPI MFBA
Energy&Sutainability Engineer
T: +33 6 95 14 42 13
www.julienmarrec.com

DoYouBuzz : www.doyoubuzz.com/julien-marrec_1
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr

LinkedIn (en) : www.linkedin.com/in/julienmarrec




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Posted by: Julien Marrec <julien.marrec@xxxxxxxxx>


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