Energy Audit_Pumps JHerrera

8/4/2019 Energy Audit_Pumps JHerrera

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Energy Audit Methodology

JOSEPH L. HERRERA

Fuels and Energy DivisionITDI-DOST


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Safety margins were added to the original calculations. Several peopleare involved in the fan/ pump buying decision and each of them is afraidof recommending a fan/ pump that proves to be too small for the job.

It w as anticipated that a larger fan/ pump w ould be needed in the

future, so it was purchased now to save buying the larger fan/ pumplater on.

It w as the only fan/ pump the dealer had in stock and you needed onebadly. He might have offered you a "special deal" to take the larger size.

You took the fan/ pump out of your spare parts inventory. Capitalequipment money is scarce so the larger fan/ pump appeared to be youronly choice.

You purchased the same size fan/ pump as the one that came out of theapplication and that one was over sized also.

Oversized Pumps & Fans?


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Just think

19% of industrial motor electricity use is for pumpsTo lift 1 cubic meter (1,000 liters) of water to a height of 1meter in 1 second requires 9.81 kW of energy


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Energy Balance for a Typical Pumping System

ELECTRICITY

100%

12% LOSS

2% LOSS

24% LOSS

9% LOSS

11% LOSS

MOTOR

COUPLING

PUMPS

VALVES

PIPES

WORK DONE ON WATER42%


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Pump System Components

Pumps

Prime Movers

Piping

Valves End-Use Equipment (Heat Exchanger, Tanks and Hydraulic

Equipment)


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Centrifugal Pumps

These are dynamic devices that impart kinetic energy or

energy of motion to a liquid to the spinning motion of animpeller.


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Types of Centrifugal Pumps

Radial Flow Axial Flow

Mixed Flow


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Axial FlowRadial Flow

Mixed Flow


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Pertinent Data: Pumps/ Motors

Nameplate/settings:

Brand, model and ratedparameters of installedpumps

Pump settings

Static water levels

Motor data & efficiencies

Pipeline material and

lengths

Measurements

Flow rates (m3/hr) Discharge pressures (psi or

bars)

Flow velocities (m/s)

Pipe sizes

Shaft speed (rpm)


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Major Measuring Equipment Used in EnergyAudits

Flow meters measure flowrates (in li/s or m3/hr) aswell as velocities of flow

Power analyzers measureV, A, kW, KVA, KVAR, PF,frequency

Pressure gages measure

pressure in psi or bars Tachometers/Stroboscope

measure motor shaft speedsin rpm


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Pump Operating Point

Determined from the measured flow and the calculated

head Ideally, the operating point is the intersection of the

system curve and the pump curve at BEP

Significant deviations of the actual OP from the requiredOP indicate pump performance problems


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System and Pump Curves


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Formulas/Conversions

Pressure to Head

Psi = (head (ft) x s.g.)/2.31 Bar = (head (m) x s.g.)/10.2

Velocity Head = v2/2g


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Power Requirement & Efficiency

Hydraulic Power (Ph):

Q (m 3/ s) x Total head, hd hs (m) x (kg/m 3) x g (m/ s2)Ph = ---------------------------------------------------------------------

1000

Pump Shaft Power = Hydraulic Power/Pump Efficiency

Electrical Power Input = Pump Shaft Power/Motor Efficiency


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Location of Test Points (Pressure)


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Pump Affinity Laws

Flow:Flow:Q1 / Q2 = N1 / N2

Example:100 / Q2 = 1750/3500Q2 = 200 m3/hr

Head:Head:H1/ H2 = (N12) / (N22)

Example:100 /H2 = 1750 2/ 3500 2

H2 = 400 m

Kilowatts (kW):Kilowatts (kW):kW1 / kW2 = (N13) / (N23)

Example:

5/kW2 = 17503

/ 35003

kW2 = 40


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Particulars Design Operating

Flow, m3/h 800 576

Head, m WC 55 24 (after control valve)

Power, kW 160 124

Speed, rpm 1485 1485

SampleProblem

In a large paper plant, the following are the designed andmeasured parameters for a clear water pump.The pump deliveryhas been throttled to about 30% (closed) manually to get therequired flow rate. Normal required water flow rate is 500m3/h to700m3/h. Calculate the present operating efficiency and in youropinion what should be the optimum solution to get the requiredflow rate variation? And what would be the savings if the pump isdelivering the flow rate of 550m3/h. (Consider efficiency of motoras 93% and pump efficiency as 60%).


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Computations

Q x H x g 576 x 24 x 9.81

Present pump output = -------------------- = -------------------- = 67.51 kW3600 x p x m 3600 x 0.558

Pump input power = 124 kW

pump operating efficiency = (67.51/ 124) x 100 = 54.44%

The pump operating at a poor efficiency of 54.44% due to throttling of the flow.

Since the pump discharge requirement varies from 500m3/h to 700m3/h, the idealoption would be to operate with a VSD. According to affinity laws:

Q1/Q2 = N1/N2; H1/H2 = (N1/N2)2; P1/P2 = (N1/N2)3

For a flow rate 550m3/h, the reduced speed of pump would be:

= 550/800 = N1/1485; N1 = 1021 rpmWith the reduction in speed the reduction in terms of head would be:

= (1021/1485)2 x 5.5 = 2.6kg/cm2

The reduction in power would be:

= (1021/1485)3 x 124 = 40.3 kWthe reduction in power = 124 40.3 = 83.7kW


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Energy Efficiency Options

Give efficiency of the pump due consideration while

selecting a pump. Select pumps to match head flow requirements.

Select a motor to match the load with highest efficiency.

Optimize the piping design. Monitor all important system parameters like: motor kW,

pump head, flow temperature.

Use pumps in series and parallel so that mismatch insystem design or variations in operating conditions can behandled properly.

Use variable speed drives for variations of flow due toprocess requirement.


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In general savings through speed control would be substantial

in the following cases: Pumps supplying a system with large change in flow.

Pumps which work with a bypass. These pumps are

normally operated to deliver the maximum discharge andhence consume maximum power.

Parallel pumps which discharge into a common pipe

system. In such cases, each pump is generally switchedon or off depending on the flow required. Here, it issufficient to regulate the speed of only one of these

pumps while the other pumps are operated an on/offmode.


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If the head flow is higher than needed by 5 to 15%, (i)

The existing impeller should be trimmed to a smallerdiameter, (ii) or a new impeller with a smaller diameter isto be put. Replacing the impeller by a smaller one of the

same series: Manufacturers usually supply more than oneimpeller for the same casing, thus allowing a change inhead or flow. Depending on the specific job, this can alloweither an increase or a decrease in flow or head, typically

by 10 to 25%.

In multistage pumps, add or remove stages to the existingpump, allowing an increase / decrease in delivered head

of flow, if required.


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Analysis has revealed that except for the small scale sector,pump efficiencies have increased by 5-10% in recent years.

SOME PROJECTIONS:

Savings of 5 - 10% are also generally possible by derating orreplacing oversized pumps.

Much larger saving of 15 - 20% are available on average byminimizing piping-friction loss with typical paybacks for system

retrofit of less than three years.

High efficiency pump often cost the same as less efficient

pumps, and if there is a cost premium, it is modest (of theorder of 5 - 10%).


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PUMP OPTIMIZATION PROJECTIONS: Consider buying pumps based on efficiency and notpurchase price

Portion of a pumps total cost over its life 3% for purchase cost

74% for energy cost

A more efficient pump also has lower maintenance anddowntime cost

TYPICAL ENERGY SAVINGS:

Proper matching of pump size to load 10 to 30%

Variable Speed Drives 5 to 50%

Knowing the system needs not pumping more flow undermore pressure than needed 5 to 20%

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Energy Audit_Pumps JHerrera