Hydrosanitary Desing

Question

Hello well, now I have to make an hydro sanitary design for a bus station. I have some toilets, sinks and urinals, etc with flowmeter in the zone of public bathroom especially. The problem is that, for this zone I need to work in a close network to guarantee the right functioning of the system and I know that it is possible to do with watercard program, there is a way to make the water network design inside of an edification with watercard, some calibration tips? Thank you for your time.

Tom Walski · Accepted Answer

Pedro, 
 
As long as the system has no loops, no pumps and minimal elevation changes, you don't really need a model. You can just ... 
 
1. Count the fixture units upstream of each pipe 
2. Convert fixture units to max flow with curves 
3. Pick a design velocity 
4. Calculate diameter using Q = AV 
5. Round diameter to next larger commercial size 
 
If you want to do a better job and know the actual pressures throughout the system, you can use WaterCAD. Lay out the piping systems. Create a number of scenarios based on which specific toilets and sinks are running. Run the model and view pressures, flows and velocities. It is best to use pressure dependent demand calculations in this type of system. WaterCAD doesn't use the fixture unit method. It calculates actual flow and pressure. 
 
In any calculations, be sure to account for the head loss through any backflow preventers and flow meters. The key input is the Hydraulic grade you can expect from the supply system. Use a conservative value.

Sushma Choure · Answer

Hello Pedro, 
 
 Here is the technote on modeling closed loop system, which may help you, 
 http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/8066.modeling-a-closed-loop-system 
 You can introduce minor loss coefficients in the pipes, to consider the losses.

Tom Walski · Answer

What exactly do you mean by a "closed system". Are you talking about a system with no storage tank or are you talking about circulating water with no water consumption? 
 
Can you explain more abut what you're trying to accomplish?

Tom Walski · Answer

From reading between the lines in your original question, it sounds as if you have a system with consumption. 
 
You need to size the pipes based on a reasonable peak demand. The usual way of doing this is the "Fixture unit method" where you total the fixtures downstream of any point and use "Hunter's Curve" or some similar approach to determine peak flow. 
 
We discuss this a bit in Advanced Water Distribution Systems Modeling and Management (pages 399-401). You can find even better references to it in many other places such as AWWA Manual M22 "Sizing Service Liens and Meters". 
 
You are no longer in the area of water distribution design so much as building plumbing. Just do an internet search on fixture unit method.

Tom Walski · Answer

In many water distribution problems, you can ignore minor losses and just compensate with slightly increased pipe roughness during calibration. 
 
If you want to model minor losses more exactly, in WaterCAD, we provide you with a list of suggested values for K in the engineering libraries. Go to Components > Engineering Libraries > Minor Loss Libraries and select the appropriate values for each type of fitting.