[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [EnergyPlus_Support] warning about "COOLING TOWER:VARIABLE SPEED"
Try using the single-speed or two-speed cooling tower models unless you
specifically want to use a variable-speed cooling tower. You should also
read the Engineering Reference to understand the model and it's
limitations if you intend to perform simulations with the variable-speed
cooling tower.
The warnings identify when the empirical model inputs are outside the
range used to develop the model coefficients. The variable speed tower
models are more useful when actual performance data is available and
model coefficients can be developed for specific cooling towers.
For instance, the first warning shows a tower range temperature (water
inlet minus water outlet temperature) of 0.10416 C. This is a very small
load and these specific model coefficients were not developed with a
data set with such small loads. This warning can be disregarded in most
cases if the simulation results look reasonable (i.e. tower load versus
tower water temperature difference). You can eliminate this warning by
changing the minimum range temperature input from 1.1111C to 0.01C in
the Cooling Tower:Variable Speed:YorkCalc Model Coefficients object. But
be warned that the model will then be extrapolating the original model
range for this model input.
The third warning shows that the liquid to gas ratio (water to air flow
ratio) is also out of range at 11.17 with an allowed maximum of 8. This
warning can usually be disregarded if the liquid to gas ratio is not
much higher than 8. This warning can also be eliminated by increasing
(e.g. from 8 to 12) the maximum liquid to gas ratio in the Cooling
Tower:Variable Speed:YorkCalc Model Coefficients object. But using
values greater than 8 is not recommended. And similar to other messages,
be warned that the model will then be extrapolating the original model
range for this input.
The second warning states that the air flow rate ratio calculation
failed at Twb=13.07, Trange=0.41, Tapproach=16.93, and water flow rate
ratio = 3.34. This error is harder to eliminate since it is based on the
original empirical model inputs. Increasing the free convection capacity
can reduce the number of warnings here since the error is most likely
due to low load conditions. Change the fraction of tower capacity in
free convection regime from 0.125 to 0.2 (maximum) in the Cooling
Tower:Variable Speed object. The fraction of tower capacity in the free
convection regime is usually around 0.1 (10%).
tjutw wrote:
>
> Hi all,
>
> I try to run the example file "CoolingTower_VariableSpeed.idf". It is
> OK if this just did two design days. After I changed run period from
> two days to the whole year, there are 6783 warning.
>
> I am not sure whether these warnings are serious.
> Any suggestions would be greatly appreciated.
>
> Thanks a lot.
>
> Tj Ywh
>
> "
> ** Warning ** COOLING TOWER:VARIABLE SPEED "CENTRAL TOWER" - Tower
> range temperature is outside model boundaries at 0.10.
> ** ~~~ ** ...Valid range = 1.11 to 22.22. Occurrence info =
> CHICAGO IL USA TMY2-94846 WMO#=725300, 04/01 07:00 - 07:01
> ** ~~~ ** ...Tower range temperature passed to the model =
> 0.10416
> ** ~~~ ** ...Range temperatures outside model boundaries may
> not adversely affect tower performance.
> ** ~~~ ** ...This is not an unexpected occurrence when
> simulating actual conditions.
> ** Warning ** COOLING TOWER:VARIABLE SPEED "CENTRAL TOWER" -
> Cooling tower air flow rate ratio calculation failed
> ** ~~~ ** ...with conditions as Twb = 13.07, Trange = 0.41,
> Tapproach = 16.93, and water flow rate ratio = 3.34
> ** ~~~ ** ...a solution could not be found within the valid
> range of air flow rate ratios
> ** ~~~ ** ...Valid air flow rate ratio range = 0.20 to 1.0.
> Occurrence info=CHICAGO IL USA TMY2-94846 WMO#=725300, 04/03 11:45 - 11:47
> ** ~~~ ** ...Consider modifying the design approach or design
> range temperature for this tower.
> ** Warning ** COOLING TOWER:VARIABLE SPEED "CENTRAL TOWER" - Liquid
> to gas ratio (L/G) is out of range at 11.17.
> ** ~~~ ** ...Valid maximum ratio = 8.00. Occurrence info =
> CHICAGO IL USA TMY2-94846 WMO#=725300, 04/03 12:30 - 12:45
> *************
> ************* ===== Recurring Error Summary =====
> ************* The following recurring error messages occurred.
> *************
> ************* ** Warning ** COOLING TOWER:VARIABLE SPEED "CENTRAL
> TOWER" - Tower range temperature is out of range error continues...
> ************* ** ~~~ ** This error occurred 4742 times.
> ************* ** ~~~ ** Max=1.110559 Min=5.492994E-002
> *************
> ************* ** Warning ** COOLING TOWER:VARIABLE SPEED "CENTRAL
> TOWER" - Cooling tower air flow rate ratio calculation failed error
> continues.
> ************* ** ~~~ ** This error occurred 526 times.
> *************
> ************* ** Warning ** COOLING TOWER:VARIABLE SPEED "CENTRAL
> TOWER" - Liquid to gas ratio is out of range error continues...
> ************* ** ~~~ ** This error occurred 1512 times.
> ************* ** ~~~ ** Max=16.058515 Min=8.001353
> *************
> ************* EnergyPlus Completed Successfully-- 6783 Warning; 0
> Severe Errors; Elapsed Time=00hr 00min 47.60sec
> "
>
>
--
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
1679 Clearlake Road
Cocoa, FL 32922-5703
Phone: (321) 638-1454
Fax: (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu
UCF - From Promise to Prominence: Celebrating 40 Years
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are not allowed -- please post any files to the appropriate folder in the Files area of the Support Web Site.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
mailto:EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
mailto:EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/