design of water supply for plumbing

7/30/2019 Design of Water Supply for Plumbing

1/23

Design of WATER SUPPLYFOR plumbing system inbuilding

Engr. Fortunato H. Amosco,fnampap,ce,pme,pee

PSPE-National President


2/23

DESIGN OF WATER SUPPLY SYSTEM

An Application of the Requirements of

Uniform Plumbing Code and or Revised

National Plumbing Codes of the Phils.

DESIGN OBJECTIVES:

The most important design objective in sizing thewater supply system is the satisfactory supply ofpotable water to al fixtures at all times, and atproper pressure and flow rate for normal fixtureoperation. This may be achieved only if adequatesizes of pipes and appurtenances are provided.

The sizes established must be large enough toprevent occurrence of negative pressures in anypart of the system during periods of peak demandinorder to avoid hazard of water supply


3/23

contamination due to backflow andbacksiphonage from potential sources of

pollution. Hence the sizing of building

water supply systems is a matter of vital

concern in protecting health and must be

regulated by codes. Other important

objectives in the design of water supply

system are:


4/23

to achieve economical sizing of piping andeliminate over design.

To provide against potential supply failure dueto gradual reduction of pipe bore with the

passing of time such as may result fromdeposits of corrosion or hard water scale in the

piping. To avoid erosion-corrosion effects and potential

pipe failure or leakage conditions owing tocorrosive characteristics of the water and/or to

excessive design velocities of flow. To eliminate water hammer damage and

objectionable whistling noise effect in thepiping due to excessive design velocity of flow.


5/23

The water supply system should be designed inaccordance with the minimum pressure available at

the public water main, or other source of watersupply pressure, and the minimum pressurerequired at all time at water outlets of the system,

where the pressure at the water main in insufficientto maintain the minimum required at the highest

water outlet of the system, a pressure booster pumpsystem, approved as to the capacity and reliability,or an automatically controlled water supply tank oreither the hydro pneumatic pressure type or the

elevated gravity type should be provided.

As a general rule, the minimum pressurerequired at the ordinary faucet of plumbing

fixture is 8 psi.


6/23

PRELIMINARY INFORMATION

REQUIRED FOR SIZING A SYSTEM:

First, obtain the necessary or all information forestablishing a proper basis for sizing the

building water supply system, such as:

1. The kinds of piping materials to be installed inthe system should be determined. This is a

matter of selection by the ownerof the building

or an authorized representative, who maybe an

Engineer, an architect or a contractor, for anexperienced person who will select the piping

materials, has knowledge and experience about.


7/23

THE SIGNIFICANT

CHARACTERISTICS WHICH MAY BE

APPLIED TO INDICATE WATERCORROSIVELY AND SCALE

TENDENCY FORMING SUCH AS:

pH value CO2 content

dissolved air content

carbonate hardness

Langelier index, and ryznar index


8/23

THE MOST APPROPRIATESOURCE OF THEABOVE MENTIONED IS THE LOCAL WATERAUTHORITY HAVING JURISDICTION OVER

THE SYSTEM SUPPLYING WATER.

2. Location and size of the water supply

3. Developed length of the system

4. Pressure data relative to source of supply

5. Elevations6. Minimum pressure required to the highest outlet


9/23

MANUFACTURERS RECOMMENDATIONS

FOR AVOIDING EROSION-CORROSION:

Velocity limits recommended by pipe manufacturersto avoid accelerated deterioration of their piping

materials due to erosion-corrosion should be

observed. Recent studies have shown that extreme

turbulence accompanying high flow velocities is animportant factor causing erosion-corrosion and that

it is especially prone to occur where the water supply

has high carbon dioxide content (in excess of 10

ppm) and where it has been softened to zero

hardness. Another important factor is very high

temperature (in excess of 150F).


10/23

TO CONTROL EROSION-CORROSION

EFFECTS IN COPPER WATER TUBES, AND

COPPER AND BRASS PIPE, MANUFACTURERS

RECOMMENDATIONS ARE AS FOLLOWS:

Where the water supply has a pH value higher that

6.9 and a positive scale-forming tendency, such as

may be shown by a positive Langelier index, velocityshould be limited to no more than 8 fps. (2.4 mps)

Where water has a pH value lower than 6.9 and may

be classified as aggressively corrosive or where water

supply has been softened to zero hardness by passagethrough a softener, velocity should be limited to no

more than 4 fps (1.2 mps)


11/23

The 4 fps (1. 2mps) velocity limitshould be applied to all not water

piping conveying water at atemperature above 150oF because ofthe accelerated rate of corrosion at such

temperature. q = 60.8 d 21.2 x (P/L)1/2 for across and cover

piping

d = inside dia. If pH value < 6.9 velocity not more than 4bp

pH > 6.9 velocity not more than 6 bps


12/23

Problem No. 1

Given:

WCWater Closet URUrinal

All WC are 1.6 GPF

All UR are 1.0 GPF

Static pressure at meter74 psi

Distance from meter to most remote outlet150ft.

Elevation of highest outlet above meter40ft.

All pipe is L Copper Design velocity per standard8 ft/sec.

Note: Lavatory group and drinking fountains were not

includes in the design as their demands are minimal.


13/23

From Chart: Revised National Plumbing Code of the

Philippines

Tabulation per sample diagram of Sizing Water System


14/23

DRAWING


15/23

Solution: The demand for this system is computed from the

fixture:

1. Unit values given in the tables

Therefore: 15 x 8 fu = 120 fixtures units13 x 5 fu = 65 fixture units

Total demand = 185 fixture units

2. Distance from meter to most remote fixture = 150 ft

3. Elevation of highest outlet above meter = 40 ft

4. Minimum pressure at the meter = 74 psi

5. From table, 185 f.u = 88 GPM; show tabulated

for all pipe runs etc.

6. Determine the total pressure available for friction loss in pound persq.

inch (psi) per 100 feet or pipe

a. Flushometric valve requires a minimum available pressure of 15 psito operate properly.


16/23

Therefore:

Minimum pressure to be maintained =15 psi

b. Total static pressure loss (head loss)This isdetermined by multiplying the elevation distance by 0.433

Therefore:

40 ft x 0.433 psi/ft = 17.2 psi

c. Pressure loss through meter, filters, reducing valves,backflow preventers, etc. In this illustration, we have

chosen a 2 disc meter.This meter has a pressure loss

of 6.5 psi at 85 gpm.

Therefore: Meter loss = 6.5 psi

Total Pressure Loss = 38.7 psi


17/23

Therefore: (minimum static pressureTotal pressure loss)

= 74 psi38.7 psi = 35.3 psi

NOTE:The remaining pressure of 35.3 psi is the maximumamount of pressure we have available for pressure loss dueto

friction in our system while maintaining the minimumpressure of 15 psi at the highest outlet. However, this 35.3psi

of pressure must be distributed throughout the total lengthof the system, which in this case has a total length of 150ft.

Determine now the pressure loss per 100 ft of pipe. Thetotal loss is 35.3 psi for 150 ft. of pipe, we calculate this way:

(100 x 35.3) divided by 150 = 23.53 psi loss per 100 ft of pipe.


18/23

7. From the Copper tubing chart project 23.53

psi up until it intersect with GPM horizontalline as demand. Note that it intersect above

line of velocity of 15 ft/sec., which is almost

16.5 ft/sec. as their rated flow.a. Since recommended velocity is 8ft/sec.,

however, good Engineering practice would

further reduce this to between 4-6 ft/sec. but

since our design call for 8ft/sec, we movefurther along the 8 GPM line until it intersect

with 8 ft./sec.


19/23

b. Note that the intersection of our new point isanother pipe size line. This will be our newstarting point which is pipe size 21/2 dia at 8

ft/sec. the GPM capacity will be 120 GPM.Going down to our 8 ft/sec transverse line as itintersect with the 2 line, the maximum GPMis:

2 pipe = 73 GPM

1 = 42 GOM

1 = 10 GPM

3/2 = 12 GPM

Note that as we follow the line to below 1 there

are three dotted lines.


20/23


21/23


22/23

These represent wall thicknesses ofsmaller pipes.

Please note that the charts and tables are

also found in the Uniform Plumbing

Code, and also in our Revised Phil.National

Plumbing Code, however there is no

problem similar or problem with solutionlike what I have discussed today.


23/23

Thank you. Good day!

God Bless Us!

design of water supply for plumbing

Documents