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 doesn’t sound like much to worry about.
Finally, the “Max = 5, Min = 5” text doesn’t make much sense to me unless you’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: Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
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