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Pump Head & Flow WaterGems

I need technical assistance for the attached cooling water model

KSP-Cooling Water System.wtg

Process Brief: The cold water from the elevated tank (actually a cooling tower) is pumped (fixed speed pump) through heat exchanger (chiller) and back to the tank. There are 7 cooling towers. 7 pumps and multiple heat exchangers all connected through common header arrangement. The model is attached. Now the task is to evaluate the head developed by the pump for this process.

Please provide your inputs for following:

  1. I understand that Water gems-Pump element does not have the feature to evaluate the head based on flow only.  I have to give an arbitrary pump-head co-relation in-order to finalize the pump head. Please confirm
  2. The required pump flow is 14,300 usgpm, so I had set up flow demand in the tank as 14,300 usgpm and the flow through FCV as 14,300 usgpm. The pump head is approx 35 m, which I think is not correct, because the fixed pressure drop across heat exchangers, suction diffusers (modelled as GPV) = 1.22+2.23+2.59+1.22 = 7.26 m and the static head difference between the tank initial elevation and tank top pipe inlet is 16.93-7.68=9.25 m. Therefore the total head required by the pump = 7.26+9.25+losses in the pipe = 16.51+piping pressure loss. I did a quick calculation in excel to evaluate the frictional pressure loss which is 5.5 m. Therefore the total head of the pump should not be more than 16.51+5.5= 22.01 m. Can you help in finding the error in the model.
  3. I had provided the demand for the tank as 14,300 usgpm, however in the tank result sheet I see that the flow in & flow out does not match to 14,300 usgpm

Thanks

Pratik

Parents Reply Children
  • Did you try to upload using link provided earlier? Sharing Hydraulic Model Files 

    Or you could directly upload here in your reply if the model files are not confidential or you can hover over name and send a private message with model files. 

    Regards,

    Sushma Choure

    Bentley Technical Suppport

  • I have uploaded the file in Sharing Hyraulic Model Files

  • Hello Pratik,

    In your pump definition, you have entered a design point where the flow is 14300 gpm and the head is 35 meters. Since your pump flows are all right around 14300 gpm, this is the reason that the pump head is around 35 meters. 

    If you are saying that the pump head needs to be lower, you would need to adjust the pump definition. If the pump definition is accurate, the head added by the pump is accurate as well.

    Regards,

    Scott

  • I tried udpating the pump definition, by decreasing the had to 22 m. But then the error i receive is that the FCV's cannot achive the desired flow of 14300 gpm and also the pump flow drops below 11,000 gpm (less than the design requirement of 14300 pm)

  • Hello Pratik,

    As Jesse noted in his response above, this might be a calibration issue. However, before looking into that, I would recommend reviewing the pump information you have. Are this existing pumps or are you trying to decide on the correct pump? If they are existing pumps, I would recommend getting the actual pump definition to use. 

    Otherwise this may be a calibration issue, as Jesse noted above. You have demands on the tank elements, however this will not impact the pump flow directly. Instead, the demand will come directly from the tank. The pump flow will be based on the pump definition, headlosses in the system (from pipes and valves), and the initial hydraulic grade of the tanks. Confirming that the tank elevations are accurate is the first step, but you will also want to make sure that you have pump data that is as accurate as possible. Then you can try adjusting valve headloss and pipe roughness coefficients to see if you get a better match with expected results. 

    This link has information on model calibration: Water model calibration tips. If you are using WaterCAD, you will not have access to Darwin Calibfrator, but the link includes other tips for model calibration as well.

    Regards,

    Scott