The system head curve in water distribution networks is one of the most useful design tools we can have in any project.
They allow us to study the operating point of the system’s source under different demand conditions, and this detailed study also allows us to evaluate aspects such as the maximum demands that the water network can address for a certain energy condition at the source point, guaranteeing the minimum normative pressures.
In AQUEDUCTS, we have included among the design tools you will find in the WATER NETWORK tab, the dialog that allows you to obtain the system head curve of the water supply network.
In it you will see that the necessary information to create this system head curve is rather simple, although in another video you will see that system head curves for water networks with two source points can be also generated, as in the case of those that are fed from a pumping station and with a storage tank floating on system.
But in this video we will talk about the case in which the water network has only one source point.
You will see that in the dialog’s upper left part it is required to specify:
The minimum pressure to be guaranteed in the water network. The idea here is, as I have already mentioned, to obtain a head curve that defines the Piezometric-Flow relation necessary so that, in the most unfavorable node of the network, the pressure is always above the minimum value specified here. By default we have here 20 meters of water column, which I’ll keep for this example.
Then, since it is a curve, you are asked to define the range, with respect to the average flow and as a percentage, for which the plot will be drawn.
Here we will go from the flow corresponding to 10 percent of the average flow to that corresponding to 300 percent.
And, finally, the number of points the system curve will have. Just take into account that, as more points have the curve, its appearance (and accuracy) will be higher. I will change it to 10 points for this case.
And that’s it!
By clicking the Generate button, we obtain the system head curve of this network for the specified constraints.
You must have already seen this group of controls under the RESULTS heading.
Their function, specifically of the controls above, is that you can “interrogate,” so to speak, the obtained system head curve for some flow or piezometric condition.
Suppose I want to determine the minimum required piezometric head at the system’s source to guarantee the operation of the whole network above 20 meters of water column and, for a flow rate of 13 liters per second as current water demand.
What I do then is click this button to add a row to this table.
You will see that in the Parameter column, Flow is defined as an input parameter. I keep it and enter my reference flow, 13.
I would also like to know, from my system head curve, the inverse situation. That is, I would like to know the maximum flow I can deliver, guaranteeing the minimum pressure of 20 meters, if the piezometric head at the system’s source is 591 meters.
So I add a new row and, in parameters, I now select a piezometric head input value, entering the value.
Finally, I click the button below and we see, on the one hand, the numerical values and, in the graph, the lines defining the intersection points with the system head curve of the water distribution network.
Note that, if the source operates at a piezometric of 591 meters, the flow we could guarantee would be 16.71 liters per second.
We’ll see more about this later.
When clicking this button, you can show the table with the values of the current system head curve and, if you wish, export it to Microsoft Excel or print it.
Likewise, this button allows you to format the graphic for its presentation.
and to export it as an image or printing you can use these two buttons.
But now, let’s check what the system head curve of the water distribution network has told us.
Here, from our calculation and design of the network, we know that the maximum demand is 17,905 liters per second and, remember from previous videos, the minimum pressure we have considered for the design was 15 meters of water column and not the 20 that we have used to generate the system head curve.
Let’s edit the properties of the water network source node.
Here the current piezometric is 590, smaller, of course, than the head value obtained from the head curve of 591 meters that I will enter here now.
I close the dialog and redo the calculation of the network to see the results.
Now we see that all the nodes, except two, are above 20 meters of water column and, if you look closely, the value of these nodes is practically 20.
It is clear they are not equal to 20 meters or more because the system head curve has shown that for this piezometric head, the flow is slightly less than the maximum flow of the water network. And, of course, the network at all times demands 17,905 liters per second and not the value specified here.
Another way to understand this result is in realizing the network is not able, in strict terms, to guarantee the respective maximum demand with a piezometric of 591 meters.
Thus, in essence, we have shown the process of creating this important tool for the design of water distribution networks. As I have told you, in the next video, we will see other applications, something more specific and complex.
We hope you stay tuned.
Thanks for your attention.