drainage fixture unit conversion to flow rate 2

[someguy79]

I am trying to design a sanitary wastewater sump pump system. At the outlet from each of two buildings will be a sump with a grinder pump to transfer waste to a wastewater treatment system. Only kitchen, bathroom and shower waste will be included in this system. The treatment system is vendor supplied.

I have been trying to use the Uniform Plumbing Code 1997 edition. I have found the sections on drainage fixture units (DFU). I intend to use these for estimating peak flow rate into the sump. The trouble is, once I count up the sinks, toilets, showers, etc. I'm out of the range listed on the little table 7-4. Further, there is no conversion from DFU to gpm or a similarly useful flow rate.

I need a good estimate of this flow rate so I can figure out pump capacity and sump size.

How should I convert DFU to gpm? (Linear, 1 DFU = 7.5 gpm?)
Is there a better reference to use?

 

[bimr]

Maybe this link will assist you:

http://www.hawsedc.com/peakfact.php

 

[PEDARRIN2]

I use a document called "Design and Construction of Sanitary and Storm Sewers" which was prepared in 1969 by ASCE.

It has a nice graph that relates peak discharge to fixture units.

A copy was given to me by a fellow engineer and when I went to look to see if there had been any updates, it was tied into another document by ASCE.

I am not a member and did not want to pay the fee to access it so if you belong or have access to their documents, you might look at that.

 

[Hoagie]

Bimr, do you know anything about the paper or the author?

 

[bimr]

Not familiar with the author. His contact number is listed.

The paper seems to be a collection and comparison of standards.

 

[mwalshpe]

I'm having the same problem. I need to design a pump station for a large 25,000 sft. home with a total of 124 dfu. There will only be five individuals living in the home, but at some point, I'm certain they'll have a large party with perhaps 300 guests.

Does anyone know of a good method for estimating the flow for a grinder station design that will not result in a sanitary sewer overflow during the party? At the same time, the station should be reasonably sized for normal use.

(7.5gpm/dfu x 124dfu) = 930 gpm seems excessive. Depending on the head conditons, I might need a 10 hp pump!

Any advice would be greatly appreciated.

 

[bimr]

It is not reasonable or feasible to design a residential service for periodic use by 300 people.

If you had such a design, the system would be seriously during normal time and probably would not function properly.

The solution would be rental of portable toilets for an event of that nature.

 

[mwalshpe]

Someone else also suggested the use of portable toilets. This would eliminate the load from the toilets, but there's a locker room, whirl pool tubs, and dishwashers to contend with as well.

 

[someguy79]

I'm guessing someone who builds a 25,000 sq-ft house does not want to be told they need honey buckets on the lawn.

You might try a different way of looking at the problem. Have you considered sizing your sump for the maximum expected waste generated?

You may be able to estimate how much wastewater the average resident guest generate during a high use timeframe. From that you can get an idea of the sump size needed. There is some guidance for this in UPC and IPC.

The drainage fixture units are really only going to be good for sizing the lines between points of water drainage, and the sump.

There is some guidance for this in UPC and IPC, but local codes may trump them. So, check on the local plumbing codes.

 

[nackra]

consider dual pump stations
one for "normal" flows with second for PEAK (party) flows
discuss with an engineer from grinder pump manufacturer
confirm electric power feed is available in panelboard

 

[PEDARRIN2]

There is an EPA document that I have used.

Type "EPA 625/R-00/008-Chapter 3" into Google and look at it.

It is a study of residential (and commercial) uses which you might be able to glean some useful information.

 

[Spartan5]

I'm having the same problem. I need to design a pump station for a large 25,000 sft. home with a total of 124 dfu. There will only be five individuals living in the home, but at some point, I'm certain they'll have a large party with perhaps 300 guests.

Does anyone know of a good method for estimating the flow for a grinder station design that will not result in a sanitary sewer overflow during the party? At the same time, the station should be reasonably sized for normal use.

(7.5gpm/dfu x 124dfu) = 930 gpm seems excessive. Depending on the head conditons, I might need a 10 hp pump!

Any advice would be greatly appreciated.

Is this waste going into a municipal sewer system or is it being treated on site?

 

[Spartan5]

And while we're on the subject, it seems that all of the standards for estimating flow were developed years ago and fail to account for the Energy Policy Act of 1992 which put in place improved fixture efficiency standards.

For instance, the link bimr provided earlier states:

A low-flow water closet uses 3.5 gallons per flush, and flushes in 5 to 10 seconds. A typical shower produces a flow of 5 gpm (7200 gpd) for 5 to 10 minutes.

Per EPAct92, toilets are limited to 1.6 gallons per flush and showerheads 2.5 gpm.

Has anyone ever come across modern criteria for estimating flow that take into account the use of the higher efficiency fixtures in modern construction?

 

[PEDARRIN2]

In a word, NO.

And with LEED, the fixtures are going lower. I am having to deal with water closets at 1 gpf, showers at 1.5 gpm, and 0125 gpf or waterless urinals.

Pretty soon we will be able to spit more than the fixtures flush.

This is a recurring plumbing issue for the inside work. We are working with data that is at least 50 years old.

We make allowances for it, but the base data is very old.

Nobody wants to pay to do research into this.