EPANET inlet/outlet pipe for tank, water level in tank

[boedekek]

Hello everyone

I am new to EPANET and am trying to run a water quality simulation within a network of piping. I have an older tank that has a single pipe connected to it. This pipe functions as an inlet/outlet pipe between the tank and the network (water flows out of tank when demand is required in the network and towards the tank to ensure the water level in the tank stays within the optimal range). What method should I use so that the pipe connected to the tank is able to flow in either direction depending on the water level within the tank? Should I use a control-based rule controlling the behavior of a pump and/or valve located on the pipe connected to the tank? Are there alternative ways? The final question I had pertained to the required initial, min, and max water levels parameters you must insert into the tank editor window. Are these levels the actual water level in the tank or the water level + the base elevation of the tank?

Thanks for any help
Kent Boedeker

 

[fel3]

Unless there are control valves on the tank inlet/outlet, it's just a regular pipe and one that doesn't care which direction the flow is moving.

All other things being equal and assuming just the one tank, when system demands exceed source flows, water will flow out of the tank to make up the difference. When source flows exceed system demands, water will flow into the tank to make up the difference. This is simply conservation of mass. In the first case, the HGL at the sources may or may not exceed the water level in the tank, but there will have to be at least one area in between with lower HGLs to act as an "energy sink". In the second case, at least one source point must have a higher HGL than the tank level so as to drive flow into the tank. If none of your sources can produce an HGL that exceeds the water level in the tank, then it is impossible to fill the tank to that level and this becomes a business development opportunity.

If you have a hydraulic and/or remotely controlled valve on the I/O, then you must account for it in your model. In addition, if you have pumps that are controlled by tank water level (as I suspect that you do), then this also needs to be accounted for in your model. As much as possible, model what actually exists in the system and only introduce fictitious elements or control schemes rarely and for very good reasons. I can't think of any "very good reasons" here.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[boedekek]

Thank you for the response fel3. But do you know what the initial level within the tank is. Epanet defined it as the height in feet (meters) of the water surface above the bottom elevation of the tank at the start of the simulation. Would this just be the water level in the tank or the water level + the base elevation of the tank?

 

[fel3]

In Epanet, "Elevation" is based on your survey datum, while "Level" is height above the "Elevation." That is, "Elevation" converts to zero for defining "Level." This is the same thing as when I set a finished floor of a building at a particular elevation and the architect converts my survey datum to zero for the building datum. The architect does NOT say FF = 100.000 m, 1st level = 103.500 m, 2nd level = 107.000 m, etc. Instead, the architect says FF = 100.000 m => Bldg Datum = 0.000 m, then 1st level = 3.500 m, 2nd level = 7.000 m, etc. One big benefit here is that if I need to adjust the FF elevation the architect doesn't have to change anything but the one note that converts the datums.

Closer to home, let's presume the bottom of your tank (per a survey or a topographic map) is at elevation 300.000 m. It would not be unreasonable for the Minimum Level to be, say, 0.300 m (bottom of a simple stubbed-in tank outlet; with other designs it could be lower). If your tank shell is 10.000 m high, your Maximum Level might be 9.000 m (to provide sufficient room for sloshing during an earthquake; the overflow should be slightly higher). As in the building example above, you would NOT use Min = 300.300 m and Max = 309.000 m. The Initial Level is simply the depth of water in the tank at which you choose to begin your simulation. It must be between the Maximum and Minimum Levels, but otherwise you get to pick the number.


==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill