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Thread: Pump Controls

  1. #1

    Pump Controls

    Hi there,

    I am modeling a water treatment plant which has three wells pumping to a clearwell. In the model, I have set up three fixed reservoirs (the wells) which each individually go to a pump (well pump). The discharge from these three well pumps combine into one and then flow into a tank (clearwell).

    In reality, the clearwell fluctuates between 51 ft and 54 ft. (I have set the size, level of the tank in the model to match the clearwell size in reality).

    I want the well pumps to turn on/off given the clearwell level. i.e., the well pumps should TURN ON when the clearwell level falls BELOW 51 ft, and then should TURN OFF when the clearwell level goes ABOVE 54 ft.

    I have set the following as my controls on these well pumps (T5000 is my clearwell):
    Pump Controls.JPG

    Each of the three well pumps has these same controls. The initial status for each of the well pumps is CLOSED and the initial level of my clearwell is 54 ft.

    When I run the model, I am not seeing the results I expect to see for how these well pumps should be turning on/off.

    Here is what my clearwell (T5000) is doing:
    Clearwell Level.JPG
    As you can see, the initial level is 54 ft. The lowest the clearwell gets is 51.21 ft. My impression of my controls is that this means none of the well pumps should turn on. They will only turn on if the level goes below 51 ft. Once it goes below 51 ft, the well pumps should stay on until the tank level goes above 54 feet again, at which point they would turn off. (Please correct my understanding if it is wrong).

    However, the following is what one of my well pumps is doing (representative of all three well pumps):
    Well Pump.JPG
    The well pump is turning ON at Hour 1, and then it turns back off again. As the level in the tank never goes below 51 ft (as we saw above), I am mystified as to why the pump would turn on at all.

    Any help/suggestions are much appreciated!

    Thanks

  2. #2
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    Cassandra,

    It is difficult to say with certainty without seeing the model, but what is most likely occurring is that in between your reporting hours the tank is reaching the "on" and "off" levels and therefore turning the pumps on and off.

    If you are unsure if this is happening or not just reduce your reporting timestep to like 5 minutes or so and rerun your model. This will increase the reporting points and you should be able to see why the controls are actually coming on. When using 1 hour reporting intervals, it may not always be 100% clear that the control levels are being reached, but the tank levels have to reach the specified levels to turn on and off, but 5 minute intervals will usually clear up any confusion occuring.

    If you are using a full Hydraulic status report in the Report options you will be able to see the intermediate time step runs that initiated the pump controls coming on and turning off at timesteps that were in between the hour reporting intervals as well, but it is often more useful to increase your reporting interval and to see it occur graphically, but both should tell you the same thing. You want to look for statements that say "TIME Z: Pump X changed by Tank Y control" where Time Z is the run elapsed time the change occured. At the end of the simulation for that specific time it will say something like "TIME Z: Pump X changed from closed to open" or "TIME Z: Pump X changed from open to closed" as confirmation of what change was actually made. The change occurred at elapsed simulation time at Time Z.

    The only other thing that can occur is that you may have unexpected rule based controls that are turning the pumps on and off as well that may not be obvious., Rule based controls can be seen in the InfoWater menu under Edit- Rule Based Controls. If you get a pop-up that says name a new rule based control, this tells you there are no rule based controls currently in use in the model, but may be worth checking as well to make sure.

    Patrick Moore

    Quote Originally Posted by albrechtc View Post
    Hi there,

    I am modeling a water treatment plant which has three wells pumping to a clearwell. In the model, I have set up three fixed reservoirs (the wells) which each individually go to a pump (well pump). The discharge from these three well pumps combine into one and then flow into a tank (clearwell).

    In reality, the clearwell fluctuates between 51 ft and 54 ft. (I have set the size, level of the tank in the model to match the clearwell size in reality).

    I want the well pumps to turn on/off given the clearwell level. i.e., the well pumps should TURN ON when the clearwell level falls BELOW 51 ft, and then should TURN OFF when the clearwell level goes ABOVE 54 ft.

    I have set the following as my controls on these well pumps (T5000 is my clearwell):
    Pump Controls.JPG

    Each of the three well pumps has these same controls. The initial status for each of the well pumps is CLOSED and the initial level of my clearwell is 54 ft.

    When I run the model, I am not seeing the results I expect to see for how these well pumps should be turning on/off.

    Here is what my clearwell (T5000) is doing:
    Clearwell Level.JPG
    As you can see, the initial level is 54 ft. The lowest the clearwell gets is 51.21 ft. My impression of my controls is that this means none of the well pumps should turn on. They will only turn on if the level goes below 51 ft. Once it goes below 51 ft, the well pumps should stay on until the tank level goes above 54 feet again, at which point they would turn off. (Please correct my understanding if it is wrong).

    However, the following is what one of my well pumps is doing (representative of all three well pumps):
    Well Pump.JPG
    The well pump is turning ON at Hour 1, and then it turns back off again. As the level in the tank never goes below 51 ft (as we saw above), I am mystified as to why the pump would turn on at all.

    Any help/suggestions are much appreciated!

    Thanks

  3. #3
    Hello,

    I am now taking a closer look at the Hydraulic status report, and have also made my reporting time step 5 minutes, as you recommended.

    I still believe there is something else going on in my model, as the tank level does not ever go below 51 ft - I can tell this from the graph (below).
    Tank Level.JPG

    The closest it gets is at Hours 0.75, ~2.25, and ~5.25. The lowest value is 51.03 ft.

    If I read the hydraulic status report, the first mention of anything happening to my pumps (Pumps U7010, U7012, and U7014) is at Time 0:43:34. (approximately 0.75 hours).
    Here is the report information I get:
    Hydraulic Report.JPG
    You can see that the three pumps are changed by my tank (clearwell) at this time - they all go from closed to open.

    I still cannot reconcile this with the graph I am seeing, unless some very funky rounding down is happening. Because my control says that the clearwell must be BELOW 51, i.e. it would have to be 50.99 ft. That means that 51.03 feet should not cut it...

    Am I correct in these assumptions?
    I have checked for rule-based controls - there were a couple, but they were not associated with these pumps or the tank. Nevertheless, I deleted them, but am still receiving this same result.

    Do you agree that there be some other factor affecting how my model is running? I'm hoping we can get to the bottom of this issue.

    Thank you!

  4. #4
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    Cassandra,

    If you have controls set to be on at 51 and off at 54, your tank appears to be doing just that. If you are unsure, just decrease your output report timestep to 1 minute or if still not convinced to as low as 1 second and rerun it.

    You will find that the pumps are actually turning on at exactly when the tank falls to below 51.00 ft and off at when it is greater than 54.00 ft exactly even though on a graph they may appear to be just above 51 and just below 54 ft as the point at which the control happens as you could see from the run report you posted.

    The graph is ONLY going to show the tank level at the EXACT time of the reporting run and will "connect the dots" between all the points which could make the graph appear to show the tank level never reaches the minimum or the maximum, when it really is. The output graphs are not displaying every output point it calculated in the runs, but simply the results requested as the reporting period.

    For example say at 40 minutes and 45 minutes you have reporting but the tank level reaches 51 at 43 minutes. The graph could show 51.5 at 40 and 51.4 at 45 and 51.9 at 50 minutes. This would "appear" to look in the graph like the low point was 51.4, when in reality the low was 51, but the time period at 51 was not "shown" in the graph.

    This is where reducing the reporting down until you feel convinced you really know what is occuring can be helpful. I have had models where I reduced the reporting to every 1 second to find an unusual behavior (very very rare) or even to 1 minute just to see better in the graph more clearly what was really occurring.

    The good news is that results will actually calculate as expected on the exact values specified even if the reported values could somewhat hide this from you if you use a large reporting period like 1 hour that most models do.

    If you need to convince yourself, please do reduce your reporting period until you can see it as this is a useful thing to actually see, ok it really is doing what I asked it to do.

    Once you have that confidence you generally can trust the hour results better, but if you need convincing, that is the only real way to fully convince yourself, then by all means, take the time to do it. It really is helpful to see that and understand how the reporting and the model works once in a while. If one minute reporting is not clear enough, definitely go down as small as 1 second reporting (Note: you may want to reduce your run length if you go this small of reporting though or your run might take a long time). This is one of the nice ways to "see it" if needed.

    Please feel free to contact us at support@innovyze.com as well if you need more detailed assistance.

    Patrick Moore



    Quote Originally Posted by albrechtc View Post
    Hello,

    I am now taking a closer look at the Hydraulic status report, and have also made my reporting time step 5 minutes, as you recommended.

    I still believe there is something else going on in my model, as the tank level does not ever go below 51 ft - I can tell this from the graph (below).
    Tank Level.JPG

    The closest it gets is at Hours 0.75, ~2.25, and ~5.25. The lowest value is 51.03 ft.

    If I read the hydraulic status report, the first mention of anything happening to my pumps (Pumps U7010, U7012, and U7014) is at Time 0:43:34. (approximately 0.75 hours).
    Here is the report information I get:
    Hydraulic Report.JPG
    You can see that the three pumps are changed by my tank (clearwell) at this time - they all go from closed to open.

    I still cannot reconcile this with the graph I am seeing, unless some very funky rounding down is happening. Because my control says that the clearwell must be BELOW 51, i.e. it would have to be 50.99 ft. That means that 51.03 feet should not cut it...

    Am I correct in these assumptions?
    I have checked for rule-based controls - there were a couple, but they were not associated with these pumps or the tank. Nevertheless, I deleted them, but am still receiving this same result.

    Do you agree that there be some other factor affecting how my model is running? I'm hoping we can get to the bottom of this issue.

    Thank you!

  5. #5
    Patrick,

    Okay. That all makes much more sense. I did actually go ahead and move the time step to 1 minute - I still could not see where it went below 51 ft, but this helped me to understand that not all points are going to be shown properly on the graph if the reporting time step is 1 hour. With a 1 minute time step I saw that there were more points, and the level did get closer to 51 feet than it had with an hour time step.

    Your explanation is very helpful. Thank you for all the detail!

    Cassandra

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