Thusitha SugathapalaDepartment of Mechanical Engineering

University of Moratuwa

26th JANUARY 2011

Lecture Series on Energy Efficienct Building Codes

Organized by Lanka Association of Building Services Engineers

Energy Conservation in Fluid Machinery (Pumps and Fans)

OVERVIEW

INTRODUCTION

ELECTRIC MOTORS

– Selection & Sizing of Motors

– Motor Control

– Preventive & Predictive Maintenance

Pumps

– Basics

– Performance Characteristics

FLUID FLOW SYSTEMS

– System Performance

– Energy Conservation in Fluid Flow Systems

INTRODUCTION

Fluid machinery, including pumps, and drive systems

consume considerable amount of energy

Electric motor and drive systems typically account for

over 50% of electricity used in building systems

– A large proportion of which is used to drive fluid machinery such

as pumps, fans and chillers.

In industries, the drive systems may consume up to 90%

of the factory demand for electricity

Pumps are used in many applications:

– water supply and distribution in domestic & commercial sectors

and for industrial processes

– pumping of variety of liquids, and slurry

– waste/sewage pumping etc.

In total, about 200 GWh per year of electricity is used for

powering pumps,

– equivalent to about 3% of Sri Lanka's entire electricity use.

In addition, fans and blowers are used in commercial

and industrial sectors

- equivalent to about 2% of Sri Lanka's entire electricity use.

Fluid Machinery offer substantial and varied

opportunities for:

– energy efficiency gains

– energy cost savings, and

– improving environmental conditions within the facility.

INTRODUCTION

Energy Conservation Opportunities

– Motor Sizing - Motors can be correctly sized to match the load

they are expected to drive.

– Motor Selection - High efficiency motors, with improved

efficiency ratings can be substituted for

standard construction motors.

– Motor Controls- When the driven equipment have to meet a

variable demand, controls can be used to

reduce capacity and improve efficiency.

– Maintenance - Proper care of motors can prolong their service

life and avoid the electrical and mechanical

problems, which contribute to lower energy

efficiency.

ELECTRIC MOTORS

0.75 HP

7.5 HP

75 HP

Efficiency of a motor depends on

– the design

– the voltage level and voltage balance of the power supply

– the load at which it operates

– its kW rating, and

– its synchronous speed

0

10

20

30

40

50

60

70

80

90

100

0 25 50 75 100 125 150

% of Rated Load

Effi

cie

ncy

(%

)

ELECTRIC MOTORS

Load Factor:

– Load factor is one of the key parameter which determines the

running efficiency of an electric motor.

ELECTRIC MOTORS

Motor Speed:

– For the same kW rating, motors with higher speeds generally have

a higher efficiency at rated load than motors with lower speeds.

ELECTRIC MOTORS

ELECTRIC MOTORS

High Efficient Motors (HEMs)– HEMs are designed to minimize the inherent losses of motors

PUMPS

A machine in which energy is transmitted to a liquid is

known as a pump

Pumps are usually driven by electric motors

Classification

– Rotor-dynamic pumps

– Positive displacement pumps

Rotor-dynamic Pumps:

– Most commonly used pumps

– Consist of rotating impeller

– Centrifugal pumps (Axial, Mixed, Radial flow)

Positive Displacement Pumps:

– Operate due to change of volume occupied by the fluid within

the machine

– Vane, Gear, Piston, Diaphragm, Screw, Lobe

Positive Displacement Pumps:

PUMPS

Rotor-dynamic Pumps:

FANS AND BLOWERS

Devices that cause flow of a gas by creating a pressure

difference are known as fans or blowers

These machines are usually driven by electric motors

Classification based on pressure levels

Blowers generate relatively higher pressure than fans

Engineering practice distinguishes fans and blowers for

low pressure and compressors for high pressure.

The gaseous fluid transported by a fan is most often air

and/or toxic fumes, whereas blowers may transport a

mixture of particulate and air

Specific ratio: The ratio of the discharge pressure over the suction pressure

Classification based on to the direction of flow through

the rotor:

– Axial Fans: Have high volume capability for large duct size

ventilation applications

– Centrifugal Fans: Have high pressure capability for applications

such as boilers, bag-houses, and conveyors.

FANS AND BLOWERS

Axial Flow FanCentrifugal Fan

PERFORMANCE CHARACTERISTICS OF Fluid Machinery

Basics …

Main operational parameters:

– Head H

– Flow rate Q

– Efficiency = Pout / Pin

Other parameters:

– Speed N

– Impeller / Rotor Diameter D

– Power Input Pin

– Hydraulic Power Output Pout = HgQ = pQ

– Net Positive Suction Head (NPSH)

Centrifugal Machines:

Efficiency

Curve

Head

Best Efficiency

Point (BEP)

Flow Rate - Q

HLower Speed

Higher Speed

.

QgHPP out

in

PERFORMANCE CHARACTERISTICS OF Fluid Machinery

Centrifugal Machines:

PERFORMANCE CHARACTERISTICS OF Fluid Machinery

Axial Flow

Radial Flow

Mixed Flow

Centrifugal Machines: Efficient Region

of Operation

PERFORMANCE CHARACTERISTICS OF Fluid Machinery

Affinity (or Similarity) Laws:

If Machine 1 and Machine 2 are from the same geometric

family and are operating at homogeneous points

.

5

1

2

3

1

2

1

2

1

2

2

1

2

2

1

2

1

2

3

1

2

1

2

1

2

D

D

N

N

P

P

D

D

N

N

H

H

D

D

N

N

Q

Q

PERFORMANCE CHARACTERISTICS OF Fluid Machinery

Dimensionless Parameters

PERFORMANCE CHARACTERISTICS OF PUMPS

.t CoefficienPower

t Coefficien Flow

t Coefficien Head

53

3

22

DN

PC

ND

QC

DN

gHC

P

Q

H

. efficiency Pump

P

gQH

C

CC

P

QH

4/1

2

1

1

2

1

1

D

D

Effects of size on efficiency

Dimensionless Parameters: Specific Speed

– Most pump applications involve a known head and discharge for

the particular system, and a speed range dictated by electric

motor speeds or cavitation requirements.

– The designer then select the best size and type for the pump.

– To help this selection, one needs a dimensionless parameter

involving speed, discharge and head but not size.

– This is realized by introducing the parameter “Specific Speed”

PERFORMANCE CHARACTERISTICS OF Fluid Machinery

4/3

2/1

4/3

2/1

4/3

2/1

formCommon

Units)(SI form essDimensionl

H

NQN

gH

Q

C

C

s

H

Q

s

s < 1 Radial-flow

1 < s < 4 Mixed-flow

s > 4 Axial-flow

Dimensionless Parameters: Specific Speed

PERFORMANCE CHARACTERISTICS OF Fluid Machinery

FLUID FLOW SYSTEMS Energy in flowing fluids:

– Energy per unit weight of a flowing fluid is given by

.Z2g

V

ρg

pH

2

Total energy

per unit weight

Pressure

energy

per unit weight

Kinetic energy

per unit weight

Potential

energy

per unit weight

Fluid machinery generate both pressure energy and kinetic energy

FLUID FLOW SYSTEMS System Components:

– Consists of

- Fluid Machinery (Pumps, Fans, Blowers, Compressors)

- Prime Mover (Electric Motor, IC Engine)

- Pipes, Ducts

- Fittings (Valves, Dampers, Grilles, Diffusers, Elbows,

Bends, Tee Junctions, Filters, Acoustic Silencers)

- End use equipments (Such as Tanks, Heat Exchangers, and

Hydraulic Equipments)

– Could be open-loop or close-loop

FLUID FLOW SYSTEMS System Components:

System Performance:

– Depends on performances of all components

– Energy Balance

- Energy Supply : Pump / Fan / Overhead Tank

- Energy Losses : Pipes; Ducts; Fittings

- Energy Gain : Static head (suction; delivery)

- Correct Balance of Energy Supply, Losses and Energy Gain: Operating Point

Pipes / Ducts:

– Function

- Efficient transmission of flow

– Sizing

- Limits on velocities, noise intensities and space availability

- Energy (Frictional) Losses: Wall Friction & Fitting

FLUID FLOW SYSTEMS

Energy Losses:– Wall Friction Losses

V Flow

A

A

B

B

V

velocityFlow

Diameter-Length;-Factor;FrictionMoody-

LossPressure

42 /πDQ/V

DLfD

2

Dfr ρV2

1

D

LfΔp

FLUID FLOW SYSTEMS

Energy Losses:– Wall Friction Losses: Moody Chart

FLUID FLOW SYSTEMS

Energy Losses:– Component Losses

FLUID FLOW SYSTEMS

Energy Losses:– Component Losses

tCoefficienLossFitting-;2

1 2 KVKpl

(a) Flow through a Pipe Bend

B

B

Eddy Zone

Eddy Zone

AA

A

A

B

B

(b) Flow through a Pipe Orifice

Eddy Zones

FLUID FLOW SYSTEMS

Energy Losses:– Component Losses: K Factors

– Total System Head

FLUID FLOW SYSTEMS

1.0Pipe Exit0.04Coupling/Union

0.5Pipe Entrance (sharp)1.8Standard T (side outlet)

5.5Gate Valve (1/2 Open)1.5180 Bend

0.2Gate Valve (Open)0.390 Smooth Bend

40Globe Valve (1/2 Open)0.4545 Standard Elbow

10Globe Valve (Open)0.990 Standard Elbow

KType of FittingKType of Fitting

1.0Pipe Exit0.04Coupling/Union

0.5Pipe Entrance (sharp)1.8Standard T (side outlet)

5.5Gate Valve (1/2 Open)1.5180 Bend

0.2Gate Valve (Open)0.390 Smooth Bend

40Globe Valve (1/2 Open)0.4545 Standard Elbow

10Globe Valve (Open)0.990 Standard Elbow

KType of FittingKType of Fitting

.2

2

002

2

12 QKHgA

QK

D

LfZZH sys

System Operating Point:

FLUID FLOW SYSTEMS

Pump Head

BEP

Flow Rate - Q

H

Efficiency

Curve

System Head

System

Operating

Point

Required

Operating

Point

Selection of Fluid Machine:

FLUID FLOW SYSTEMS

Life Cycle Cost:

– Energy cost contribute to the largest part of the lifecycle cost

Energy cost

83%

Maintenance

3%Investment

14%

Energy cost

91%

Maintenance

1%Investment

8%

10 kW Pump 130 kW Pump

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

– Numerous opportunities for energy saving

– Modern designs with higher efficiencies

– Best design practices (need “System Approach”)

- Avoid over-sizing

- Appropriate flow-control

- Multiple machines than single larger one

- Appropriate Maintenance practices

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Over-Sizing:

In many applications, fluid machines are oversized for

the load they are serving, due to a number of factors. Designers add safety factors as insurance against failure.

Designers want the ability to increase the output of driven equipment at some time in the future.

The existing load is less than the initial design load due to energy management activities and changes in building use.

Larger motors can override load fluctuations without dropping out.

Voltage imbalances in three phase power supplies can cause increases in motor losses, and so a larger machine is required to meet the duty.

However, these practices often lead to excessive loss in energy,

resulting high operating cost.

Further, larger machines cost more to buy, install and maintain.

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Flow Control:

Fluid machinery are required to perform over a range of flows

and pressures called, “The Duty Cycle”.

How the machine is controlled to achieve the required range, can

have a significant energy cost.

The type of control should be selected on the basis of cost, the

precision of control required and the frequency and magnitude

of system flow changes.

Method of Flow Control

– Flow control valve / Damper Control: High Energy Loss

– By-Pass Valve: No gain

– Blade Pitch Control

– Guide Vane Control

– Impeller Trimming

– Multiple Machines with On-off Control

– Variable Speed Drive (VSD): Most Efficient

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Throttling and By-Passing for Oversized Machines:

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Impeller Trimming for Oversized Machines:

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Flow Control With VSD:

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Flow Control With VSD:

- Comparison with throttled damper

0

5

10

15

20

25

30

35

40

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Flow Rate (m3/s)

Head

(m

)

Throttled Damper

N = 3000 rpm

N = 1500 rpm

Damper fully open

A

B

C

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Pumps in Combinations:

- Pumps in Parallel: For high flow rate applications

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8

Flow Rate Q

He

ad

H

High Flow

Rate

Demand

Low Flow

Rate

Demand

Two Pumps

Single

Pump

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Pumps in Combinations:

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5

Flow Rate Q

He

ad

H

High Head

Load

Low Head

Load

Two

Pumps

Single

Pump

- Pumps in Series: For high head applications

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

Pump Cavitation:

– Results in noise, vibration, surface damage and reduction of

performance

– Net Positive Suction Head Requirement:

Discharge pipe

Suction pipe

Location of minimum

pressure in the pump

2

1

.1S

v hzg

ppNPSH

ENERGY CONSERVATION IN FLUID FLOW SYSTEMS

CASE STUDY