On any proposed water piping installation sized pursuant to subpart 9, the following conditions shall be determined:
Total number of fixture units as determined from the table of equivalent fixture units (subpart 8) for the fixtures to be installed.
Developed length of supply pipe from meter to most remote outlet, or if the pressure at the meter is unknown, use the developed length from the street main to most remote outlet.
Difference in elevation between the meter or other source of supply and the highest fixture or outlet.
Pressure in the street main or other source of supply at the locality where the installation is to be made. Calculations shall be based on not to exceed 100 psi pressure in the system.
In localities where there is a wide fluctuation of pressure in the main throughout the day, the water piping systems shall be designed on the basis of the minimum pressure available.
Knowing the available pressure at the water meter, water main, or other source of supply, and after subtracting one-half pound per square inch pressure for each foot of difference in elevation between such source of supply and the highest water supply outlet in the building or on the premises, use the "pressure range" group within which this pressure will fall. Select the "length" column which is equal to or longer than the required length. Follow down the column to a fixture unit value equal to or greater than the total number of fixture units required by the installation. Having located the proper fixture unit value for the required length, sizes of meter and building supply pipe will be found in the two left-hand columns.
The size of each branch shall be determined by the number of fixture units to be served by that branch, following the methods in subpart 2.
Branches and mains serving water closet or similar flushometer valves may be sized from subpart 9 when the following values are assigned to each flushometer valve beginning with the most remote valve on each branch:
for the first flushometer valve, 40 fixture units;
for the second flushometer valve, 30 fixture units;
for the third flushometer valve, 20 fixture units;
for the fourth flushometer valve, 15 fixture units; and
for the fifth flushometer valve, ten fixture units.
After the fifth valve on any branch, subsequent loadings may be computed using the values given in subpart 8 of this chapter. Piping supplying a flushometer valve shall not be less in size than the valve inlet.
In sizing the hot water piping or water supply systems from subpart 9, the greatest developed length of the cold water supply piping may be used and the length of the hot water piping ignored when the hot water piping friction loss is compensated for by the following method:
Compute the total hot water fixture unit demand, using those values given in subpart 8 for the combined hot and cold water use.
Assign the total demand computed as required in item A, as the fixture unit demand at the hot water heater supply branch and inlet.
Starting at the most remote outlet on the cold water piping and working back toward the water meter, compute the pipe sizing for the system from the column originally selected in subpart 9, using the fixture unit values given in subpart 8, and adding in the fixture unit demand of the hot water heater supply inlet as computed in subpart 5, at the point where it occurs. The final size of the cold water main need not be larger than the originally established size required by subpart 9 for the total building supply.
Starting at the most remote outlets on the hot water piping and working back toward the water heater, compute the pipe sizing for the system from the column originally selected in subpart 9, using the fixture unit values given in subpart 8.
|Fixture||Number of Private Use||Fixture Unit Public Use|
|Bathtub (with or without shower over)||2||4|
|Dental unit or cuspidor||--||1|
|Drinking fountain (each head)||--||1|
|Hose Bibb of sill cock (standard type)||3||5|
|House trailer (each)||6||6|
|Laundry tub or clothes washer (each pair of faucets)||2||4|
|Lawn sprinklers (standard type, each head)||1||1|
|Shower (each head)||2||4|
|Sink or dishwasher||2||4|
|Sink (flushing rim, clinic)||--||10|
|Sink (washup, each set of faucets)||--||2|
|Sink (washup, circular spray)||--||4|
|Urinal (pedestal or similar type)||--||10|
|Urinal (flush tank)||--||3|
|Water closet (flush tank)||3||5|
|Water closet (flushometer valve)||--||10|
Water supply outlets for items not listed above shall be computed at their maximum demand, but in no case less than:
* See subpart 4 for method of sizing flushometer valve installations using this subpart.
28 SR 146; L 2007 c 140 art 4 s 61; art 6 s 15; art 13 s 4
May 14, 2012
Copyright © 2012 by the Revisor of Statutes, State of Minnesota. All rights reserved.