energy management in pumps

8/12/2019 Energy Management in Pumps

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Energy Management in PumpsEnergy Management in PumpsPumping is the process of addition of kineticand potential energy to a liquid for the

purpose of moving it from one point to another.

This energy will cause the liquid to do work

such as flow through a pipe or rise to a higherlevel.


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Energy Management in PumpsEnergy Management in PumpsThe most critical aspect of energy efficiency ina pumping system is matching of pumps to

loads.

Hence, even if an efficient pump is selected,

but if it is a mismatch to the system then thepump will operate at very poor efficiencies.


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Energy Management in PumpsEnergy Management in PumpsIn addition, efficiency drop can also beexpected over time due to deposits in the

impellers.

Performance assessment of pumps would

reveal the existing operating efficiencies inorder to take corrective action.


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Purpose of Performance TestPurpose of Performance Test1. To find out pump efficiency during the

operating condition

2. To obtain system resistance and theoperating duty point of the pump and

compare the same with design.


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Terms and DefinitionsTerms and Definitions

1.1. Pump Capacity (Q)

Q = Volume of liquid delivered by pump perunit time (m3/hr or m3/sec).

Q is proportional to N,where N- rotational speed of the pump


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2.2. Total developed head (H)Total developed head (H)

Total developed head, H = difference ofdischarge and suction pressure.

The pump head represents the net work doneon unit weights of a liquid in passing frominlet of the pump to the discharge of the pump.


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There are three heads in common use inpumps namely

(i) Static head(ii) Velocity head(iii) Friction head.


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The frictional head in a system of pipes, valvesand fittings varies as a function (roughly asthe square) of the capacity flow through the

system.


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3.3. System ResistanceSystem Resistance

The sum of frictional head in resistance & totalstatic head.


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Pump efficiencyPump efficiency

4.4. Pump efficiencyPump efficiency


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How to obtain pump efficiency?How to obtain pump efficiency?

To determine the pump efficiency, three keyparameters are required:(i) Flow,

Field Testing & Pump efficiencyField Testing & Pump efficiency

(ii) Head(iii) Power.


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The following are the methods for flowmeasurements: Tracer method BS5857


Ultrasonic flow measurement Tank filling method Installation of an on-line flowmeter


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(i) Tracer method BS5857It suitable for cooling water flow measurementbecause of their sensitivity and accuracy.


This method is based on injecting a tracer intothe cooling water for a few minutes at an

accurately measured constant rate. A series ofsamples is extracted from the system at a pointwhere the tracer has become completely mixed

with the cooling water.


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qcw = q1 x C1/C2

where qcw = cooling water mass flow rate, kg/sq1 = mass flow rate of injected tracer, kg/sC1 = concentration of injected tracer, kg/kg


= wposition during the 'plateau' periodof constant concentration, kg/kg

The tracer normally used is sodium chloride.


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(ii)(ii) Ultrasonic Flow meter(a) Operates under doppler effect principle(b) these meters are non-invasive, meaning

measurements can be taken without disturbingthe system.


Disadvantage:

Scales and rust in the pipes are likely to impact the

accuracy.


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(ii) Ultrasonic Flow meter

1. Ensure measurements are taken in a sufficientlylong length of pipe free from flow disturbancedue to bends, tees and other fittings.

2. Th i i n wh r m r m n i


taken should be hammered gently to enablescales and rusts to fall out.

3. For better accuracy, a section of the pipe can be

replaced with new pipe for flow measurements.


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(iii) Tank filing method

In open flow systems such as water getting pumped

to an overhead tank or a sump, the flow can bemeasured by noting the difference in tank levels for a

ifi ri rin whi h h l fl w fr m h


tank is stopped.


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(iv) Installation of an on-line flowmeter



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Determination of total head (H)

() ()



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Determination of total head (H)

() ()

This is taken from the pump discharge side


pressure gauge.

Installation of the pressure gauge in the

discharge side is must.


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Measurement of motor input power (Pm)

The motor input power Pm can be measuredby using a portable power analyser.



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Pump shaft power (Ps)

The pump shaft power (Ps) is calculated bymultiplying the motor input power (Pm) bymotor efficiency at the existing loading.


Ps = Pm x


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Pump efficiency:-

This is arrived at by dividing the hydraulicpower by pump shaft power.


= s


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Measured DataPump flow, Q : 0.40 m3/ s

Power absorbed, P : 325 kWSuction head(Tower basin level), h1 :+1 M

ExampleExample--11

Delivery head (h2) : 55 MHeight of cooling tower : 5 MMotor efficiency :88 %

Type of drive Direct coupledDensity of water :996 kg/ m3


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Calculate

() () ()

() ()

ExampleExample--11

)( ghhQP sdh

=

() ()

()


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Measured DataVoltage=415 V, I=75 A, PF=0.9

Pump flow, Q : 200 m3

/ hPower absorbed, P :Suction head

ExampleExample--22

(Tower basin level), : 1 mDelivery head (h2) : 3 kg/cm2

Motor efficiency :88 %

Type of drive Direct coupledDensity of water :996 kg/ m3


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Calculate

() () ()

() ()

ExampleExample--22

)( ghhQP sdh

=

() ()

()

energy management in pumps

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