Peaking factor
Peaking factor
(OP)
I am designing a 50 acre industrial park. I anticipate sewage demand at 1500 gallons per day per acre. I can probably assume that this 1500 gallons per day per acre is occurring in a 8 to 10 hour (say 9) window. So that will be 1500/9/60 * 50 acres = 139 gpm. Now I need to apply a peaking factor. Normally I would use a peaking factor of 3 but since I have already decided to divide my entire flow by 9 hours instead of 24 hours have I already applied the peaking factor to this? Or should I at least I reduce the peaking factor down to 2 or 2.5? Any thoughts would be appreciated.





RE: Peaking factor
Published peaking factors are most reliable for large service areas where errors tend to average out.
Fortunately, the difference in capacity of a 10-inch pipe and an 8-inch pipe is approximately 56% while the total in place cost is less than that.
The only place "oversizing" might get you in trouble would be at the upper end of a branch line where, because of low flows, you might not be able to achieve self cleaning velocities at least once a day. There you would want to try to ensure that the pipe flow at least half full for some part of every day.
good luck
RE: Peaking factor
But, can you assume all the industries in your park will only work 5 days a week, 8 hours a day ?
Assume is a word to use with great caution.
good luck
RE: Peaking factor
Because your project is relatively small, you need a slightly larger peaking factor (than 3) as shown in the attached table:
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RE: Peaking factor
RE: Peaking factor
Good point on sizing the water mains but I still have to design my sewer lines.
Depending on my peak rate factor I need 10" or 12" sewer lines.
RE: Peaking factor
RE: Peaking factor
Look at my calculation in the first post. If I apply a peaking factor to 139 gpm then I am over 155 gpm. In my part of the world our minimum slope is .4% for an 8" sewer.
RE: Peaking factor
50 acres * 1500 gal/day = 75,000 gal/ day
75,000 gal/day over 8 hours = 156 gal/min
As RWF7437 and others have noted, you do not need to use a peaking factor on the 8 hour day since you have equated the 24 hour flow to the peak hour flow.
If you want to figure the peak using the normal 3-4:1 factor, then:
75,000 gal/ day with a peaking factor of 3.8 = 197 ga/ min
Anyway, you are using only 8" sewers.
RE: Peaking factor
In NC, the rules state that you must take hours of operation into account (as you have done) when designing the conveyance system. The resulting flow is your average daily flow. Your peaking factor (minimum of 2.5, higher for smaller populations), which accounts for diurnal fluctuations in the flow, must be applied on top of the ADF calculated above.
For example, if a restaurant has 100 seats and you assign (or are required to assign) 40 gallons/seat, the permitted flow to the treatment plant will be 4000gpd, however, in the conveyance system (gravity line or pump station), you must take hours of operation into account (assume 12 hours) to get an ADF of 5.56gpm, then you multiply that by 2.5 (minimum) to get a design peak flow rate of 13.9gpm for the conveyance system.
RE: Peaking factor
RE: Peaking factor
RE: Peaking factor
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