Building Water Supply Line Sizing

[cuels]

I have been working on sizing a building supply line. I am used to working with Public Water Distribution system designs and have been using state codes to design those systems. I am now working on a single building site and need to size a line running to the building. In the IPC I found where they provide the sizing criteria for each fixture in a building (i.e. toilet, lavatory, sink, etc.) however when I add all of these up to find the Peak Demand, it is outrageous. It makes sense to me that each fixture is not going to be used all at the same time, however, I need some way to justify this. I normally get a flow from the mechanical engineer designing the building distribution system, but in this case I have been asked to size those lines. I found a statistical approach on the Engineering Toolbox's website.

http://www.engineeringtoolbox.com/water-supply-expected-demand-formula-d_1076.html

I am unsure as to where this equation came from. Does anyone have an actual source for this type of theoretical vs. expected demand approach for sizing building water supply lines. Otherwise I am going to have to tell these people to use a 4 inch line.

 

[bimr]

Search on this site. This issue has been discussed before.

Plumbing engineers use the total fixture method to develop the water demand for buildings. This method uses a statistical probability to calculate the number of water users that will use fixtures at any one time.

You need to obtain a book such as the Piping Handbook by Nayyar

 

[PEDARRIN2]

The IPC has a method in the appendix that uses the fixture count - depending on whether you have flush tank or flush valve toilets.

Obtain the fixture unit count, use the appropriate column.

I commonly use a multiplier of .7 for this value since the table was developed in the '50s and uses fixtures of greater flow rate.

This will give you a flow rate. I size the main coming in for a maximum 3 ft/sec. and then usually upsize the pipe at least one size for future renovations.

That seems to work.