LP Design is the pipe sizing method which sizes pipes to meet the pressure range for the outlets. In the sizing calculations IRRICAD also trades running cost against capital cost to select appropriate pipe sizes.
However, if the pipe retail prices are all the same, e.g., 0.00, or are not relative to the different sizes, then sizes may increase and decrease along the zone or mainline. This is correct as per the mathematical computation with the information provided. A low or zero capital cost will cause LP Design to select larger pipes as they require a smaller running cost.
To assist LP Design in selecting decreasing pipe sizes, ensure pipes contain retail prices, even if the price is simply relative to the other sizes and classes.
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Hi Dan, That is a good tip, but are you sure that will fix the LP sizing issue. I have always had retail pricing in my database, relative to the pipe size, yet still get the issue with increasing/decreasing pipes when running LP design. Mainly when there is a lot of topography. On flat ground, it seems to work well. These days I mainly use Velocity design, because of the LP bugs. Will give LP a try next time and let you know if I have any problems.
Gennaro, LP Design is a very powerful tool and finds a solution for a particular set of constraints and candidate pipe sizes which are based on the slope of the hydraulic gradeline. Unlike velocity design it takes into account the required emitter pressure envelopes and can trade off capital versus running costs to find a more optimal solution.
In most cases the use of the HGL allows LP Design to find a relatively “sensible”, as well as mathematically correct, solution. However there may still be some instances where LP design may select a larger pipe after selecting a smaller pipe. I don’t think that it is fair to say these situations necessarily represent “bugs” they are simply a consequence of the LP method. If you have a good example of this behaviour you are welcome to send it to us so we can determine the cause. Also bear in mind that you can always make manual adjustments to the selected pipes after LP design.
We do have plans for a rationalization function that will remedy any pipe telescoping anomalies, remove any short lengths of pipe, adjust pipe sizes to the nearest manufactured length and perhaps make suitable pipe class changes.
Update:
You can turn on the "Rationalization Parameters" in Design|Design Parameters|Hydraulic Parameters in V17 and later.
