Domestic Water Sizing with Irrigation 1

[Steven Reed P.E.]

This is a fairly typical task, but I can't find any good answers. I'm using the standard UPC tables 610.3 and 610.4 to determine required domestic water service and meter sizes. Those are sized based on WSFU's because it assumes some percentage of them are actually being utilized at a given time. We also have to connect an irrigation line, which runs one zone at a time with a known flow in GPM. In order to size the common line to both, I'm effectively adding WSFU and GPM to check velocity and pressure loss. The issue is I don't know how to convert GPM to WSFU or vice versa, because I don't know the assumed number of fixtures on at a time. There are conversions I can find online, but they seem to be limited to tank or non-tank toilets, rather than all of the fixtures. I can of course just assume that we have a reasonable velocity in the pipe and back-calculate the GPM from the WSFU, but I don't like to make those types of assumptions without knowing for sure how the calculation was done.

Does anyone have any idea how to best get combine these flows and size the common line?

Thanks,

 

[1503-44]

Use this chart.

Follow the cautions here ...

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

https://www.engineeringtoolbox.com/wsfu-gpm-d_1074.html

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Steven Reed P.E.]

That's exactly what I was looking for, thank you! And the cautions make sense, this would only work for a system where there aren't huge patterns of everyone taking a shower at once for example.

Another way I looked at doing this is to size the line per the UPC, then, based on a maximum assumed velocity of about 5-7 ft/s, back-calculate what the peak flow must be for that line. If the flow is higher than that, then the UPC is likely under-sizing the lines in the first place.

 

[1503-44]

Reverse engineering is often a pretty good sanity check.

3 to 5 fps is probably better than 5 to 7 for these small lines. Then when you do get extreme usage, it won't drop pressure so quickly.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[bimr]

Do a search of the eng tips site:

Link