Hello, I am using WaterCad and trying to write a control set that will control five items: 2 pumps and 3 pipes. Pipe #1 comes from the city's water supplier, and it opens during a certain time interval and in response to ground storage tank levels in the city's system. Pipes #2 and #3 feed the ground storage tanks, and they are open as long as those tanks' pumps are off and Pipe #1 is open. The pumps are downstream of the ground storage tanks, and come on in response to the elevated tank level. All of this is part of the same control set. When I run the simulation, the results in the properties dialogue boxes indicate that the pumps are controlled (Controlled?-True) but that the pipes are not controlled (Controlled?-False). Is there a particular way to write controls for pipes or to ensure that they will function or any obvious mistakes I might be making? Thanks for your help.
Dave
You might want to post a screenshot of your controls, or alternatively send your model to tech support: http://appsnet.bentley.com/srmanager/addcall.aspx
If you were able to get the pump controls going, then you should be able to get the pipe controls going also - there is no real trick for pipes. The logic does seem a little bit complicated though (eg. IF pumps are off AND Pipe#1 open THEN Pipe#2 open, etc) so there could be an issue in the way you set up the control logic.
One thing to note about tanks in WaterCAD though is that they have built in valves that close the inlet/outlet pipe when the tank is full or empty. So you might want to check that your ground storage tank isn't getting to 100% full or 0% full during the simulation (and therefore causing confusion). You might also want to simplify the control setup by removing the controls on the pipes feeding the ground storage tanks.
I actually don't see the need for controls on pipes #2 and #3 anyway, so simplifying those controls might make sense. Why is it that Pipe#2 is only open as long as the pumps are off?
One final note - perhaps the problem is just the reporting in the 'Controlled?' field. Do the pipes open and close as expected even though 'Controlled' = FALSE?
Regards,
Mal Sharkey
Mal,
Without burdening you with all of the details, what I suspect is happening in my model is that the pumps downstream of the storage tanks are recirculating water through the tanks and that this water is not going into the rest of the system. I have simplified the control logic as far as I see possible:
IF {"T-1" Hydraulic Grade <= 688.50 ft} THEN {"PMP-4" Pump Status = On } IF {"T-2" Hydraulic Grade <= 655.00 ft} THEN {"PMP-4" Pump Status = On } IF {"T-3" Hydraulic Grade <= 816.76 ft} THEN {"PMP-2" Pump Status = On } IF {"T-3" Hydraulic Grade <= 811.76 ft} THEN {"PMP-1" Pump Status = On }
Where T-1 and T-2 are GSTs, T-3 is the elevated tank, and PMP-4 is the supplier's pump.
Under this scenario, T-3 empties within 8 hours and all the pumps run constantly, which provides a flow that far exceeds the actual system demands. The inlets to the tanks do not seem to be closing according to the tanks' setpoints, but rather remain open all the time. The GSTs are always within 5' of full, but the elevated tank never fills. Any thoughts?
Thanks,
Dave Grote
If the elevated tank empties even though the pumps are always on, then it is certainly possible that pumps are recirculating water through the ground storage tanks. You should be able to check this by looking at the flow arrows on the pipes downstream of the pumps and following where the flow goes. (Alternatively there is a good tool in Network Navigator for tracing flow - go to "View"..."Network Navigator"...">" ... "Network Trace"..."Trace Downstream".)
Note that the tank inlets will only close automatically when the tank is completely full or completely empty. If you want them to close at other times, you will need an explicit control, like: IF {"T-xx" Hydraulic Grade < 999 ft} THEN {Pipe-yy" Pipe Status = Closed}.
If in the real system these pipes are closed to prevent recirculation, then the fact that the tank inlets never close is likely to be causing your system issues, although other possible sources of error are:
1. System demands are too high (should be easy to check by comparing the "Flow Demanded" on the calculation summary to what your system demands should be 2. Pump curves are not correct (again should be easy to check - just look at the pump flow and head or pump curves) 3. Pipe diameters or roughnesses are not right (might be more time consuming to check if you have a lot of pipes)
Unfortunately it's a bit hard to figure out without seeing the model, so if you still have issues I would recommend sending your model to tech support so they can help further.
Mal