Automatic Water Flow Control

7/30/2019 Automatic Water Flow Control

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AUTOMATIC WATER FLOW CONTROL

For

HIGH RISE BUILDING

BY:

ABNER V. PAHILANGA

BSEE , BSME , MBA

P.E.E , RMP


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PUMP-PIPING SYSTEMS

System Curve When a pump is connected with a pipe system, it forms a pump-piping

system. A water system may consist of one pump-pumping system or acombination of several pump-piping system.

The speed of variables-speed pump in a variable-flow water

system is often controlled by a pressure-differentialtransmitter installed at the end of the supply main, with a set

point normally between 15 and 20 ft. WC ( 4.5 and 6 m WC )6.5 PSI AND 8.6 PSI. This represent the head loss resultingfrom the control valve, pipe fittings, and pipe friction

between the supply and return mains at the farthest branchcircuit from the variable-speed pump. Therefore, the headlosses of a pump piping system can be divided into two parts:


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Constant, or fixed, head loss Hfix, remains constant as the

water flow varies. Its magnitude is equal to the set point of

the pressure-differential transmitterHset, or the difference

between the suction and the discharge levels of the pump in

open systems Hsd [ft. WC (m WC )].

Variable head loss Hvar, which varies as the water flow

changes. Its magnitude is the sum of the head losses causedby pipe friction Hpipe,pipe fittings Hfit, equipment Heq,,

and components Hcp, all in ft WC (m WC), that is,

Hvar= Hpipe + Hfit + Heq + Hcp


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Head losses Hfix and Hvar. The relationship between thepressurelossp [ft WC (kpa)]; flow headHvar[ft WC ( m WC)]; flow

resistance of the water systemR var[ft WC/(gpm)2 (m WC.s2/m6)];and water volume flow rateVw [gpm (m

3/s], can be exprssed as

Hvar = p [ gc/pwg ]

p = Rvar

V2w

Hvar =R varV2w

Where pw ( RHO) = density of water, lb/ft3 (kg/m3)

g = gravitational acceleration, ft/s2 (m/s2)

gc = dimensional constant, 32.2lbm ft/lbfs2


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The curve that indicates between the flow head, flow resistance, and

water volume flow rate is called thesystemcurve of a pumping

system, or a water system.

SYSTEM OPERATING POINT

The intersection of the pump performance curve and water systemcurve is the operating point of this variable-flow water system as shown

by pointP. Its volume flow rate is representedby Vr[gpm ( m3/s)],and

its total head is Hp = Hfix + Hvar[ ft WC (m WC)].

Usually, the calculated head lossis over estimated,and the

selected pump is oversized with higher pump head, so thatthe actual system operation point is point P.


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Therefore, for a variable-flow water system installed with a

constant-speed pump, the design system operating point is

preferably located to the left of the region of pump maximumefficiency, because the system operating point of an oversized pump

moves into or nearer to the region of pump maximum efficiency.

COMBINATIONOF PUMP PIPING SYSTEM

When two pump-piping system 1 and 2 are connected in series, the

volume flow rate that combined pump-piping system, Vcom [ gpm

(m3/s)] is

Vcom = V1 = V2


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TWO PUMP IN SERIES

H1

H2

Ht

P1 + P2

P1

P2

Vt

R

R

R

Operating

point

Hfix


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Where V1 and V2 are the flow rate of pump-piping systems 1 and 2, gpm(m3/s). The total head lift of the combined system H

com[ ft WC (m WC)]

is

Hcom = H1 + H2

where H1

and H2 are the head of the pump-piping systems 1 and 2, ft

WC ( m WC ).

It is simpler to use one system curve to represent the wholesystem, to use a combined system curve. The system operating pointof the combined pump-piping system is illustrated by pontPwith avolume flow ofVp and head ofHp. The purpose of pump-piping

system in series is to increase the system head.


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When a pump-piping system has a parallel-connected water pimps,

its volume flow rate V[gpm (m3/s)] is the sum of the volume flow

rates of the consumed pumps V1

, V2

,etc.. The head of each

constituent pump and head of the combined pump-piping system are

equal. It is more convenient to draw a combined pump curve and

one system curve to determine their intersection, the system

operating pointP. The purpose of equipping a water system with

parallel-connected pumps is to increase its volume flow rate.


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PUMP IN PARALLEL OPERATION

P1P1

P2

P3

Q1

Q2

Q3

gpm

H

Q1

Q1 + Q2

Q1 + Q2 + Q3


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MODULATION OF PUMP-PIPING SYSTEM

Modulation of the volume flow rate of a pump-piping system can

be done by means of the following:

Throttle the volume flow by using a valve. As the valve closes is

opening, the flow resistance of the pump-piping system increases. A

new system curve is form, which results in having new systemoperating point that moves along the pump curves to the left-hand

side of the original curve, with a lower volume rate and higher total

head. Such behavior is known as riding on the curve. Using the

valve to modulate the volume flow rate of a pump-piping system

always wastes energy because of the head loss across the valveHval.


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Turn the water pumps on or off in sequence for pump-piping

systems that have multiple pumps in a parallel connection.

Modulation of the volume flow rate by means of turning waterpumps on and off often result in a sudden drop or increase in the

volume flow rate and head, as shown by system operating pointsP,

Q and T.

Vary the pump speed to modulate the volume flow and head of the

pump-piping system. When the speed of the pump is varied from n1ton2 and then to n3 , new pump curvesP2 andP3 are formed. the

system operating point will move from point Pto Q and then to T

along the system curve, with a lower volume flow rate, head, andinput pump power. The system curve become modulating curve and

approaches Hfix = Hsetis the set point of pressure-differential

transmitter,


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Ft WC ( m WC). Varying the pump speed requires the lower pump

power input in comparison with other modulatiopn methods.

METHOD OF MODULATION

GPM

INVTR

FREQ

GPM

n1

n2

n3

H

H


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PUMP LAWS

The performance of geometrically and dynamically similar

pump-piping systems 1 and 2 can be expressed as follows:

V2/V2= D32n2/ D

31n1

H2 /H1 = n22 /n21

P2/ P1 = n32/n

31

Where V = volume flow rate of pump-piping system, gpm

(m3/s)

H1 = total head lift, ft WC (m WC)

P = pump over input at shaft, hp (kW) D = outside diameter of pump impeller, ft (m)

n = speed of pump impeller, rpm


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WIRE-TO-WATER EFFICIENCY

A pump may be directly driven by a motor, or it may be driven by

a motor and belts. When the energy cost of water system isevaluated, the pump total efficiency p, the motor efficiency mot,

and the efficiency of the variable-speed drives drshould all be

considered.

The wire-to-water efficiency of a water system ww, expressed

either in dimensionless in form as a percentage, is defined as the

ratio of energy output from water to energy input to the electric wire

connected to the motor. It can calculated as

ww = p drmot


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The total efficiency of the centrifugal pump p can be obtain from

the manufacturer or calculated. The pump efficiency p depends on

the type and size of pump as well as the percentage of the designvolume flow rate during operation. Pump efficiency usually varies

from 0.7 to 0.85 at the design volume flow rate. Drive efficiency dr

indicates the efficiency of to direct drive, belt drive, and various

type of speed drives. For direct drive, dr= 1. among variable-speed

drives, an adjustable-frequency alternating-current (AC) has thehighest drive efficiency. For a 25hp (18.7-kw) motor, dr often

varies from 0.80 at 20 percent design flow. Motor efficiency mot

depends on the type and size of motor. It normally varies from 0.91

for a 10-hp ( 7.5-kw ) high efficiency motor to 0.96 for a 250-hp (

187-kw ) motor.


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MULTI ZONE APPLICATION FIRE PUMP

150psi 150psi

150psi

max

max

max

LOW ZONE

MED ZONE HI ZONE

PUMP 1PUMP 2 PUMP 3

Vp1 = Vp2 = Vp3

H1 + H2 + H3 = Htotal

LOW ZONE

P1-RUNMED ZONE P1& P2 - RUN

HI ZONE- P1& P2 & P3 - RUN


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WISDOM IS THE PRINCIPAL THING,

THEREFORE GET WISDOM.

AND IN ALL YOUR GETTING , GET

UNDERSTANDING

PROVERBS 4 : 7

GOD BLESS AND THANK YOU

Automatic Water Flow Control

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