PUMP
HEAD CALCULATION
Pumps are the heart of a water supply
system which conditions the flow of the fluid from ,one place to another which
have a head to overcome.
Pumps basically act as a catalyst which
enhances the process of the fluid transfer within shortest period of time.
Before taking pump into consideration it
is necessary to understand what is head and why it is necessary ….?
Well lets understand the concept of pump
head…
Well head is the height of space, where the
fluid is to transfer.
Basically if we want to submit the fluid
from ground to top of a building we measure the vertical height of the pipe fluid
which has to be lifted that measured height may called as head.
Well lets understand the head deeply
Suction head : well
this is the height which is measured as shown in the figure from centerline of
the pump till the rim of water in the tank.
Discharge or Delivery Head: height
from centerline of the pump to the rim of the tank which has to be discharged
as shown in the figure.
Well this the plant layout of pumps
BASICALLY THERE TWO PUMPS
PRIMARY PUMP
´ THE PUMP WHICH SUCKS THE WATER FROM AHU/FCU TO THE
CHILLER UNIT.
´ THIS PUMPS SUPPLIES HEAT ABSORBED WATER FROM AHU AND
SUPPLY TO CHILLER UNIT .
SECONDARY PUMP
´ THE PUMP WHICH SUCKS THE WATER FROM CHILLER AND SUPPLY
TO AHU/FCU .
´ THIS PUMPS SUPPLIES CHILLED WATER FROM CHILLER TO AHU
FOR COOLING EFFECT.
CONDENSOR
PUMP
´ THE PUMP WHICH SUCKS THE WATER FROM CHILLER AND SUPPLY
TO COOLING TOWER .
´ THIS PUMPS SUPPLIES CONDENSENED WATER FROM COOLING TOWER
TO CHILLERS.
I hope we are clear with this diagram
so let’s move forward
Before that we should take the
note of the formula which will surely help us to find the capacity of pump
which is required for the application.
PUMP HP
FLOW RATE (GPM) X
HEAD (FT.WG) X SPECIFIC GRAVITY OF WATER/3960 X EFFICIENCY OF THE PUMP
SP.GRAVITY OF
WATER:1
EFFICIENCY OF PUMP
:55 % TO 65%( assume )
So this formula will conclude
with how much amount of capacity does the system requires to uplift the fluid .
Well everything is known in
the formula except the head , head calculation is bit lengthy so lets take dive
into it.
From the figure of pump plant
room lets understand some terminology for calculation of head.
PUMP DISCHARGE LINE
PUMP DISCHARGE HEADER
CHILLER SUCTION HEADER
CHILLER SUCTION LINE
This is the line through which
water get discharged from pump and passed to the chiller.
CHILLER DISCHARGE LINE
CHILLER DISCHARGE HEADER
BYPASS LINE
PUMP SUCTION LINE
This is the line through which
water get discharged from chiller and passed to the pump.
So lets understand the requirement
of calculation
DIAMETER
FLOW
STRAIGHT LENGTH IN FEET
VALVES AND FITTINGS
HEAD LOSS FITTING(FT) OF
FITTINGS
So we will tabulate the
requirement for better understanding.
So lets start with pump discharge
line head calculation
So to calculate the head we
need diameter of pipe which is 10 inches(calculated by pipe design)
Flow rate of the pipe in GPM
which is obtained from the capacity of chiller say 2160 GPM.
Next is straight length of discharge
line in feet say 12 feet.
Valve and fitting have
different head loss assumption from reference books
So head loss are the loss of
heat which takes place due to obstacles in the flow of water which is valves
and fittings.
So adding both head loss due
to fittings and length of discharge line we will get total head .
HEAD LOSS IN FT./100FT so to
find this we will use a pipe sizer software.
Well after putting the pipe
size 10 inches
GPM flow rate we get head loss
2.13ft/100
Head loss or friction loss for
total head
2.13 x 344/100 =7.4 feet
Hope you got it similarly we
have to do it for others and we will get the following data.
This is the line through which
water get discharged from pump and passed to the chiller.
This is the line through which
water get discharged from chiller and passed to the pump.
After that we have to add the
friction head loss and multiply it by 15% safety factor.
We will get head loss in feet
of w.g
Now as we are known with the
head we can use the following formula to calculate pump HP calculation.
PUMP HP
FLOW RATE (GPM) X
HEAD (FT.WG) X SPECIFIC GRAVITY OF WATER/3960 X EFFICIENCY OF THE PUMP
So we will get the capacity required
for fluid to be lifted to desired point using following method.
This is only for primary pump
in the same way we have to calculate for secondary pump system..
Hope this post was useful for
you…
HVAC INTRODUCTION,APPLICATION,DESIGNING,EXECUTION,ENGINEERING,HEAT LOAD CALCULATION,PIPE SIZING,CHILLED WATER SYSTEM,AC,CONTROL ,DUCT DESIGN,etc
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