T OF ENERGY

DEPARTMEN

U

E

NITED STAT S OFA ERICA

M

An Office of Industrial Technologies 

Bimonthly Publication Focusing on

Energy Efficiency Opportunities for Today

www.oit.doe.gov

www.motor.doe.gov

March/April 2000

Issue Focus: 

Adjustable Speed Drive 

(ASD) Technologies

IN THIS ISSUE

Putney Paper Becomes More 

Energy Efficient . . . . . . . . . . . . . . . . . . . . . . . . 1

Learning to Use Bifocals . . . . . . . . . . . . . . . . 2

Guest Column . . . . . . . . . . . . . . . . . . . . . . . . . 3

Performance Optimization Tips . . . . . . . . . . . 4

Maximize Your ASD Application

with ASDMaster . . . . . . . . . . . . . . . . . . . . . . . . 6

Adjustable Speed Drive Application

Workshops . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Soliciting Help . . . . . . . . . . . . . . . . . . . . . . . . . 6

Mark Your Calendar for . . . . . . . . . . . . . . . . . . 6

Go Online for Extra News and Updates. . . . . 7

Coming Events. . . . . . . . . . . . . . . . . . . . . . . . . 8

A major rebuild of your processing plant may seem like a daunting endeavor, but Putney Paper

Company did just that and is

now saving energy and money.

The Vermont-based paper-recycling mill upgraded many of its

older motors and installed variable frequency drives (VFDs) on

its pump and agitator system.

The upgrade also entailed rerouting water flow, which eliminated

the use of one pumping system.

The project is saving the company 400,000

kWh of electricity, or $30,000 annually.

To offset costs and increase efficiency,

Putney took advantage of technical assistance and rebates from its electric utility,

Green Mountain Power Corporation (GMP),

an OIT Allied Partner. 

Using original equipment installed in

the 1930s was costing Putney Paper Company a heavy price in high energy bills. In

an effort to lower costs, in the early 90s,

Putney learned of energy efficiency incentives offered by GMP and replaced 27

motors with high efficiency ones that meet

or exceed EPAct requirements. The positive

results led to further upgrades and opportunities to work with GMP on the recent

major plant rebuild.

By 1997, Putney planned to rewind

about 13 of the plant’s motors driving the

mill’s pumping process. GMP’s review of

the plans led to the mill changing the project plan. Instead of rewinding, Putney

decided to replace the motors and include

upgrades to the agitator systems. “Putney

was already committed to upgrading their

older equipment to improve productivity.

What we were able to bring were recommendations for getting the maximum possible energy savings out of the upgrades,” said

Dan Gaherty, Green Mountain Power Corporation. GMP provided MotorMaster+ software to help Putney analyze motor

replacement options. As a result, Putney

installed 15 premium efficient motors and

2 VFDs to operate its pump system. Putney

also changed the routing of tray water from

the paper machine. The rerouting enabled

the company to shut down one pump and

use gravity flow in its place, which offered

more reliability and cost reductions. 

Benefits

In addition to cost savings and energy efficiency, the upgrade has other benefits. For

instance, the VFDs have given the operators more control of the process. “We’re

saving energy by using inverters [VFDs] to

achieve the pumping capacity we need.

We’ve eliminated valves and the waste

associated with throttling back,” said Don

Sellarole, plant engineer at Putney. Without

throttling back, the operating life of the

pump is extended. Also, pressure adjustments have been converted to a digital

mode, which allows greater precision and

saves time on maintenance. The only drawback is the more complicated drive system

that requires greater technical knowledge

and expertise to run effectively. To address

this, Putney has provided staff training in

maintenance and troubleshooting.

Incentives from GMP for the two VFDs

reduced payback time from 1.2 years to

less than a year. 

Working together, Putney Paper and

GMP prove that energy efficiency, lower

costs, and technological advancement can

be affordable realities.

Regenerative drive system on #4 rewinder.

Putney Paper Company Becomes More Energy Efficient 

with Help from Green Mountain Power 

INSERT:

Combined Heat and Power Supplement
ENERGY MATTERS

is published bimonthly by the

U.S. Department of Energy’s

(DOE) Office of Industrial

Technologies. 

Information contained in the

newsletter can be reproduced

without permission provided due

acknowledgement is given (the

U.S. Department of Energy’s

Energy Matters newsletter) and a

copy of the publication is 

supplied to the editor.

■

EDITORIAL BOARD

Rob Boteler, representing

National Electrical Manufacturers

Association

Lynda Butek, representing 

Electrical Apparatus Service 

Association

Don Casada, Oak Ridge National

Laboratory

Keith Davidson, Onsite Sycom

Energy

Bob Gemmer, U.S. DOE,

Process Heat

Glenn Hahn, Spirax Sarco

Fred Hart, U.S. DOE, Steam 

Challenge

Chris Hunter, Johnson & Johnson

Roy Jones, representing

Compressed Air and Gas Institute

Aimee McKane, Lawrence

Berkeley National Laboratory,

Compressed Air Challenge

Rick Payton, Rockwell 

Automation/Reliance Electric

Bill Stafford, Technical 

Association of the Pulp and Paper

Industry

Chuck Whelan, DuPont

■

COMMENTS? 

Contact: 

Julia Oliver, DOE, at 

(510) 637-1952, or e-mail

julia.oliver@oak.doe.gov

Michelle Mallory, 

Energy Matters Editor, at 

(303) 275-3627, or e-mail 

michelle_sosa-mallory@nrel.gov

1617 Cole Blvd., MS 1713

Golden, CO 80401

2 Energy Matters, March/April 2000

Learning to Use Bifocals

By Don Casada and John Kueck, Oak

Ridge National Laboratory (ORNL)

Both of the authors of this article are learning to use bifocal glasses. The general idea

with bifocals is that they provide two general zones of focus—the lower portion for

close up (e.g., reading) and the upper for

distance. Leaning your head back while

driving or looking out the bottom part of

your glasses while descending stairs are

recipes for disaster.

There are many demerits associated

with our condition (not the least of which

are egotistical factors), but like most of

life’s difficulties, the lessons we learn here

have analogs in other arenas. 

Take the case of adjustable speed drives, for example. We’d like to discuss two

common aspects of drives from a couple of

different focal lengths.

Efficiency or Power?

A common way of comparing device A

with device B in the energy domain is to

compare efficiencies. After all, efficiency is

a sort of universal standard that is used in

everything from hog farming to haute cuisine, defining the value of the product in

proportion to the cost of the input.

Figure 1 shows typical combined drive

and motor1 efficiencies for a new, pulsewidth-modulated (PWM) drive and an older

eddy-current (EC) drive when connected to

a centrifugal load, such as a pump or fan.

There is obviously a dramatic difference in

drive efficiency at reduced speeds.

Consider a situation where we have a

fan load that operates at full speed 75% of

the time and at half speed 25% of the time.

Table 1 shows the combined motor and

drive efficiencies at those speeds and calculates an average efficiency.

Table 1. Motor and Drive Efficiency Comparison

Drive Full-speed Half-speed Average 

Type efficiency efficiency efficiency2

PWM 86% 77% 84% 

EC 86% 38% 74% 

The average electromechanical efficiency with the EC drive is only 88% of

that with the PWM drive, certainly a noteworthy difference. 

Now let’s extend our point of focus to

include the electric meter. Does our electric bill include an average efficiency term?

Of course not—we pay for energy3. Let’s

assume that the fan requires 50-hp shaft

output power at full speed and behaves

according to the centrifugal load affinity

laws (flow rate is proportional to speed,

and power is proportional to the speed

cubed). For this assumed load, the electric

input power vs. speed shown in Figure 2

applies.

(continued on page 7)

Speed, %

90

80

70

60

50

40

30

50 60 70 80 90 100

Efficiency, %

PWM

EC

Figure 1. Combined motor and drive 

efficiency vs. speed.

Speed, %

50

40

30

20

10

0

50 60 70 80 90 100

Power, kWe

PWM

EC

Figure 2. Electric power vs. speed.
Energy Matters, March/April 2000 3

Guest Column

Using ASDs with Variable

Torque Applications 

By John Malinowski, Baldor

Electric Company, Fort Smith, AR

Operating energy costs continue to be a

major concern for plant managers. Recent

studies of electric motor applications show

that pumps require 31% of the energy

used, 18% for compressors, 18% for blowers and fans, and about 14% for conveyors. 

Variable torque applications are the best

candidates for adding an adjustable speed

drive (ASD) to save energy. Centrifugal

pumps and fans are variable torque loads

where the amount of power required drops

off by the cube of the speed decrease.

Thus, the actual savings come from reducing the motor speed, resulting in lowering

the motor’s power requirements. Constant

torque applications such as conveyors

often use ASDs, but generally this is not for

reasons of energy savings, rather it is for

production flow improvements. 

Let’s look at a pump application with

varying flow requirements. Typically, control

valves are used to regulate flow from a

pump with the motor and pump operating

at fixed speed with the motor driven

directly from the power line. As the valve is

closed, the amount of energy that is wasted

is increased. If instead of throttling, an AC

inverter (a type of ASD) is employed, considerable savings can be achieved. To illustrate, assume we have a centrifugal pump

that requires 100 hp at design flow. Let’s

further assume an electrical cost rate of

$0.07/kWh, an equipment and installation

cost of $8,800, and required flow rate that

varies from 40% to 90% of design capacity,

per Table 1.

Table 1. Load Profile

% of flow rate % of year

40 10

50 20

60 40

70 15

80 10

90 5

As shown in Figure 1, the purchase and

installation costs would be recovered from

energy savings in less than 5 months, with

annual savings of about $22,000.

Caution needs to be taken in this

inverter retrofit. Inverters not only reduce

the speed by adjusting the voltage and frequency, the motor can also be made to

operate above its base speed. Since horsepower requirements on a centrifugal 

pump increase by the cube of the speed

change, it doesn’t take much more speed

to overload the motor and risk premature

failure.

Operation of an AC induction motor

from a pulse-width-modulated (PWM)

inverter causes extra

motor heating due to

harmonics. The signal of the inverter to

the motor is an artificial sine wave.

Motors operating

from inverters may

experience extra

heating resulting in

premature failure.

Newer high efficiency (EPAct) and

premium efficiency

motors often have

low temperature

rise. A rule of thumb

is that for every

10°C cooler a motor

operates, its insulation life is doubled.

Newer motors will

also have insulation

capable of handling

the higher temperatures at which the motor operates when

powered from an inverter. Many new

motors have a Class F (155°C) insulation

system whereas older motors may only be

Class B (130°C). Most inverter-ready

motors have a Class H system rated for

180°C operation.

Although the inverter will operate any

three-phase AC induction motor, it is wise

to purchase a motor with an insulation system that will handle the troublesome voltage spikes, which may be 1600 volts or

more in applications with long motor-feeder

cables. New inverter spike-resistant magnet

wire provide more than 100 times more

resistance to high-voltage spikes than 

standard magnet wire. Long wiring runs

between the motor and inverter increase the

high-voltage spikes by a condition called

“voltage ring-up”. To mitigate this situation,

line reactors or harmonic filters can be

placed between the motor and control.

NEMA addresses operation of inverterfed motors in its MG 1-1998 standards. Part

31 discusses specific-purpose motors for

inverter-fed power supplies. It would be

wise to select a motor that complies to MG

1-1998, Part 31.4.4.2 for voltage spikes as

a minimum requirement.

Addition of inverters to power motors

may provide reduced maintenance and

production improvements as well. Instead

of starting the motor across the line, the

inverter will “soft-start” the motor. By

increasing the speed gradually, mechanical

stresses on the motor, pump, couplings, and

pipes are reduced. Any water hammer

(heard as a banging noise in the piping system) should be eliminated. If required, the

inverter speed may be adjusted automatically via a process control loop, providing a

more precise flow of water from the pump

as required by the production process.

(continued on page 4)

$8,800

544,923 228,450

$38,145 $15,991

$22,153

4.8

Figure 1. On variable torque applications, ASDs can offer significant

energy savings and quick payback periods.
4 Energy Matters, March/April 2000

Performance 

Optimization Tips

Field Measurements in

Pumping Systems—

Practicalities and Pitfalls

By Don Casada,

BestPractices Motor

Systems, Oak Ridge

National Laboratory 

This article is the 4th

in a series dealing

with practical considerations and pitfalls of field measurements needed to understand pumping

systems.

One by one, we’re addressing the individual elements critical to understanding

pumping system operation. But remember

the importance of maintaining a system

perspective, not just elements in isolation.

In the words of Robert Browning (from A

Grammarian’s Funeral):

“Image the whole, then execute the parts—

Fancy the fabric

Quite, ere you build, ere steel strike fire

from quartz,

Ere mortar dab brick!”

Does Your Car Have a Speedometer?

I recently led a PSAT1 workshop, and

we discussed a scenario where no flow

instrumentation was installed. Tom Angle,

Director of Technology for Envirotech

Pump, offered this insightful simile: “A

pumping system without a flow meter is

like a car without a speedometer.” 

Tom further noted that we wouldn’t buy

a car without a speedometer, but we routinely see pumping systems without flow

meters. To see how out of whack this is,

let’s do an operating cost comparison

between a mid-size car and a small industrial pump. 

Energy Cost Comparison

Automobile 25-hp pump 

Fuel unit cost $1.40/gallon 5 ¢/kWh 

Annual 15,000 6,132 hours 

usage miles 

Power source 25 miles 93% (motor 

effectiveness per gallon efficiency) 

Annual cost $840 $6,150 

Quite a contrast! If I doubled the gas

mileage of my automobile to 50 miles per

gallon, I’d save only a third of what I’d

save if I dropped my pump load from 25

down to 20 horsepower. Doubling my

car’s gas mileage would be a challenge,

but a 20% improvement is often achievable in pumping systems—if system performance and requirements are well

understood. 

I suspect that 99% of the time you use

your speedometer simply to avoid getting

the “blue light special.” Consider how big

a fine you pay to the local electric utility

every day because you don’t know your

pumping system’s speed.

I’m Appalled—No Meter’s Installed!

Pumping systems with no flow meters are

very common, even in large industrial systems. Because energy costs usually overwhelm capital costs for pumping systems,

the wisdom of building an unmetered system may be questionable. But given this

reality, we’ll identify alternative

approaches to estimating flow rate in such

systems2. Beginning with this issue, we’ll

discuss three methods:

1) Use of head-capacity curve.

2) Volume change rate measurement.

3) Velocity head deduction.

As we begin to discuss these techniques,

here is one final automobile analogy. 

With my car on cruise control, I occasionally compare my odometer-indicated

distance and speedometer-indicated speed

with the distance and speed deduced from

mileage markers and my wristwatch.

Doing this, I can verify that my speed and

mileage indications are reasonably accurate (assuming that my watch and the

mileage markers are dependable). 

Similarly, these flow-estimating techniques, though far from perfect, are worth

considering, even when a flow meter is

installed. 

(continued on page 5)

Guest Column

continued from page 3

Since most variable torque applications

are similar, HVAC installations offer similar

savings. 

Constant torque applications such as

conveyors don’t offer the same energy savings as variable torque applications

because power is only linear with speed.

Again production improvements may be

seen with the addition of ASDs. Changing

out older, less efficient motors to current

premium efficiency designs will reduce

energy usage. 

Many older conveyors are already

adjustable speed, but powered by DC

motors and SCR (thyristor) controls. Typically these DC drive systems have efficiencies in the 80-85% range compared to

newer AC drives with efficiencies in the

mid-90s. Power factor on DC drives may

be in the 50% range whereas power factor

for AC drives is approaching unity. Changing an older DC SCR system to an AC Vector Drive can provide better performance

than the old DC drive. The AC Vector with

encoder feedback can provide constant

torque from base speed all the way to zero

speed. Besides the energy savings, the

maintenance required by the brushes and

commutator of the DC motor is eliminated

(downtime and costs). A larger motor is

sometimes required for low-speed, constant-torque applications.

Energy savings translate directly to the

bottom line of any manufacturing facility.

All of these technologies are proven, in use

for 10 years or more. Many different suppliers build inverters, vector drives, and

inverter-ready motors. Most difficulties

encountered are simple and easily resolved.

Local distributors can help estimate savings and initial investment in equipment

costs. Most manufacturers also have free

cost/analysis software available to help calculate these savings. These computer programs calculate payback details based on

the actual motors you have in your plant,

duty cycles, and energy costs.

For questions or comments, contact John

Malinowski at (501) 648-5909 or send email to John_Malinowski@baldor.com.
Energy Matters, March/April 2000 5

continued from page 4

Using the Head-Capacity Curve

Pump manufacturers develop headcapacity curves for generic pump models,

based on test performance data. These

curves are useful in selecting a pump for a

particular service; they can also be used to

estimate flow rate based on measured

head. 

Consider the pump configuration in 

Figure 1, and the head-capacity curve in

Figure 2.

If this system is handling ambient temperature water, the 68-psig discharge pressure and the 3-ft elevation difference from

the vented suction tank to the discharge

pressure gauge equates to a developed

head difference of about 160 ft. From Figure 2, the flow rate deduced would be

about 2400 gpm.

Pretty straightforward, right? 

But What About?...

Now let’s flag a few assumptions inherent in this approach:

1) This pump’s original performance curve

is identical to the generic curve.

2) The field performance is identical to the

test facility performance.

3) Pump performance is not degraded

from service wear or foreign material.

4) The actual rotating speed is 1750 rpm.

How many of these assumptions are

likely to be valid?

For the first assumption, consider the

Hydraulic Institute’s (HI) acceptance test

tolerances for a pump in this general category3, which allows the measured head to

be up to 8% above that specified at the

rated flow rate. Alternatively, the flow rate

can be up to 10% above that specified at

the rated head. This tolerance range alone

gives an indication of the potential variability from pump to pump, and highlights

the value of a certified test curve for the

specific pump.

Field and test facility performance can

differ for a variety of reasons; in this example, the discharge pressure is measured

downstream of an expander and discharge

header tee. There are losses across these

components that would need to be

accounted for.

The potential effects of service wear can

be extremely variable, but the longer a

pump has been in service, the less likely it

will perform like new.

Fortunately, speed equality can be

checked (for example, with a strobe light as

shown in Figure 3) and accounted for, if different. We’ll illustrate how speed can be

accounted for with ASDs. This is important,

even when operating on a fixed speed motor.

Assume we find the rotational speed of

the pump is 1780 rpm. Using pump affinity

laws, the head-capacity curve can be

adjusted upwards, as in Figure 4.

The flow rate at 160 ft on the 1780 rpm

curve is 2570 gpm, about 7% more than

estimated from the 1750 rpm curve. If the

measured head had been 200 ft, the speedrelated error would be dramatically

greater—over 75% (700 vs. 1240 gpm)!

One last potential “gotcha” in using

pump head to estimate flow rate is that the

velocity head component must be

included. But since the velocity head can

only be determined once the flow rate is

known, we must use an iterative solution4.

In this case, the velocity head component

is small (about 0.7 ft), but that is not

always the case.

In the next issue, we will cover the

other two methods of estimating flow rate

in unmetered systems.

Comments/questions welcome by e-mail:

a85@ornl.gov

1 PSAT– Pumping System Assessment Tool, a DOE software product available as a free download at:

http://public.ornl.gov/psat.

2 Clamp-on, ultrasonic flow meters are available that

are non-intrusive. My experience with externally

mounted ultrasonic meters has been mixed. I’m not

aware of a report on independent testing of such flow

meters under real-world conditions, but encourage

readers to provide feedback in this regard.

3 See ANSI/HI 2.6-1994, Vertical Pump Tests, Section

2.6.5.3.

4 There is a way to avoid the iteration – but we’ll leave

that for a future column.

P = 68 psig

3'

12"

Figure 1. Example pump configuration.

Figure 3. Strobing pump shaft speed.

Flow rate, gpm

220

200

180

160

140

120

100

0 1000 500 1500 2000 2500 3000

Head, ft

Figure 2. Generic head-capacity curve (1750

rpm).

Flow rate, gpm

220

200

180

160

140

120

100

0 1000 500 1500 2000 2500 3000

Head, ft

1780

1750

Figure 4. Head-capacity curves for 1750 rpm

and 1780 rpm.
6 Energy Matters, March/April 2000

Mark Your Calendar for...

...the 4th OIT Industrial Energy Efficiency

Symposium and Exposition. Set for February 19-22 in 2001, this event will help U.S.

industry prepare to compete globally.

Learn from recognized experts who will

share their perspectives on the competitive

challenges awaiting U.S. manufacturers

and hear their potential solutions for success in global markets. The exhibit hall will

feature over 150 booths highlighting technologies under development, emerging

cutting-edge processes, and other results of

collaborative partnerships. Join other manufacturers, government R&D managers,

corporate R&D directors, university

researchers, national laboratory scientists,

representatives from the financial community and many more at this exciting Expo,

to be held in Washington, D.C.

How to Register

You may register online at www.oitexpo4.

com or call (877) OIT-7967 to obtain a 

registration form.

Soliciting Help

OIT’s Industrial Assessment Center (IAC)

program is soliciting ABET accredited engineering schools across the country to help

small and medium size manufacturers save

money and improve productivity. The

Industrial Assessment Centers, at present,

are located at 30 universities across the

country. Teams of engineering faculty and

students from the centers conduct, at no

cost, industrial assessments and provide

recommendations to small and medium

size manufacturers to help them identify

opportunities to improve productivity,

reduce waste, and save energy. Recommendations from industrial assessments

have averaged about $55,000 in potential

annual savings for these manufacturers. 

Solicitations will be sent to the Department Heads and Deans of Engineering at

all ABET accredited schools. Call Gwen

Looby at (215) 387-1535, ext. 221, for

more information.

Control of process equipment using electronic adjustable speed drives (ASDs) offers

significant opportunity to save energy and

improve operations. However, the

effects of ASDs on process systems

are not always well understood. To

simplify the process of learning about,

analyzing, and specifying an ASD application, the Electric Power Research Institute (EPRI) Adjustable Speed Drive

Demonstration Office (ASDO), in cooperation with the Bonneville Power Administration, developed the ASDMaster software.

Designed with the layperson in mind,

ASDMaster provides a suite of educational

materials and software tools for people

with little or no experience applying ASDs,

to experienced ASD application engineers

looking for accurate, user friendly analysis

software. 

How Does it Work?

ASDMaster is a windows-based software package consisting of six different

modules designed to educate and assist

users in the proper application of ASDs. A

software instruction module and text are

included to educate users on the process

effects, technology, and power quality

issues associated with ASDs. Analysis tools

assist users in the accurate, total systemsbased analysis of the energy and production benefits associated with ASDs. A

simultaneous analysis is performed on constant speed controls for comparison. ASDMaster also contains a specification tool

that assists users in writing a solid performance specification for an ASD, just by

answering the appropriate questions and

filling in the blanks. Finally, ASDMaster’s

database module directs users to manufacturers with ASDs that can meet their needs,

generating a bid-list and contact information with just a few button-clicks. 

Where to Get Your Copy

To order your copy of ASDMaster, or to

receive more information about the product, call the EPRI ASDO today at 1-800-

982-9294. 

Adjustable Speed Drive Application Workshops

If you are an end user, utility, or motor manufacturer, the Adjustable Speed Drive

Application workshops can help you in your job. These workshops address the fundamentals of ASDs and offer a demonstration of the ASDMaster software. The workshops

are offered in co-sponsorship with OIT Allied Partners.

Attend one of the following:

■ April 25 in Marlboro, MA, MA Toxics Use Reduction Institute. 

Call Ann Berlin Blackman at (978) 934-2124.

■ May 9 in Greensburg, PA, PA DEP Allegheny Power. 

■ May 23 in Manchester, NH, State of NH Wastecap Resource Conservation Network. 

Call Erin Wheeler at (360) 754-1097, ext.104.

Maximize Your ASD Application with ASDMaster 
Energy Matters, March/April 2000 7

Learning to Use Bifocals

continued from page 2

Table 2 shows the power for the two

load conditions, and annual electrical

energy and expense, assuming an energy

cost of $.05/kWh.

Table 2. Power, Energy, and Cost Comparison

Full- Half- Annual 

Drive speed speed Annual cost,

Type kWe kWe MWh $1000 

PWM 43 6 296 $14.8 

EC 43 12 309 $15.4 

The energy consumed by the PWM drive is

only 4% less than the EC drive. Why is

this? The simple reason is that the affinity

laws are the dominant factor—the shaft

power required at 50% fan speed is only

1/8 of what it was at full speed. With this

load profile, it would be very difficult to

justify replacing a functional, less efficient

EC drive with a new PWM drive. A different conclusion might be reached with a

different load profile; the point is that efficiency comparisons don’t tell the whole

story.

Beyond the Affinity Laws

Now that we’ve shown why the affinity

laws tend to dominate the picture in centrifugal loads, it is worth extending our

focal length a bit more to see a system picture. A very common mistake made in

developing rough estimates of energy

reduction by applying adjustable speed

drives is to simply use the affinity laws. 

Assume we have a pump that is operated simply to fill a tank. The tank supplies

the system (by gravity) continuously, but

the pump only has to run 12 hours a day to

keep the tank full. According to the affinity

laws, if we slowed the pump down to 50%

speed, the flow rate would drop to half and

the power would drop by a factor of eight.

If we ran the pump at half speed for 24

hours a day instead of at full speed for 12

hours a day, the energy consumption

would go down by a factor of four, right?

Wrong.

If the system had no static head, the

logic would be fine; but in many pumping

systems, static head is a significant part of

the overall system head. For example, as

shown in Figure 3, the pump operates at

about 3350 gpm and 50 ft of head when

operated at full speed. However, when it is

slowed to half speed, the flow rate is 0

gpm; in other words, the pump function

has switched from a water mover to a

water heater. The simple reason is that the

system has static head—in this case, about

half of the head at full speed is static.

Looking Out the Top of the Lens

In many industrial operations,

adjustable speed drives can be beneficial.

There are many details that must be considered in implementing drives. But these

examples have illustrated how too narrow

a focus on individual component performance and the failure to see the system as

a whole can lead to significant errors. 

While the examples used here are just

that—examples—they are in their essentials identical to situations that are commonly encountered. Don’t be misled by

the details—look out the upper part of the

lens and see the system as a whole.

1 The PWM data for Figure 1 is average performance of

three drives tested with an older, standard efficiency,

50-hp motor at ORNL. The eddy current efficiency

curve assumes 3% loss at all speeds combined with

measured direct, across-the-line efficiency for the same

motor (full-load motor efficiency was 89%).

2 Weighted according to the percentage of time operated at the two speeds.

3 Some electric billing structures also include demand

charges and/or power factor penalties; PWM drives do

improve power factor.

Find more articles and resources on this

issue’s theme—ASD Technologies—by visiting the Energy Matters Extra Web site.

From here, you can also link to a Webbased Combined Heat and Power (CHP)

analysis tool to screen a potential CHP site.

Then, access the Office of Industrial Technologies’ (OIT’s) new online discussion

database to post your comments or questions about CHP. Universities will find a

new solicitation announcement with the

details on applying for participation in

OIT’s Industrial Assessment Center program. Go to Energy Matters Extra at www.

motor.doe.gov/emextra.

Flow rate, gpm ÷ 1000

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Figure 3. Electric power vs. speed. Go Online for Extra News and

Updates

MORE COVERAGE OF ENERGY EFFICIENCY OPPORTUNITIES FOR YOUR INDUSTRY

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Letters to the Editor

Energy Matters welcomes

your typewritten letters and

e-mails. Please include your

full name, address, association, and phone

number, and limit comments to 200 words.

Address correspondence to:

Michelle Mallory, Letters to the Editor

NREL, MS 1713

1617 Cole Blvd.

Golden, CO 80401 

e-mail: michelle_sosa-mallory@nrel.gov

We publish letters of interest to our

readers on related technical topics, comments, or criticisms/corrections of a technical nature. Preference is given to letters

relating to articles that appeared in the previous two issues. Letters may be edited for

clarity, length, and style.

NAMING NAMES

David Gaw of the Washington State University Energy Program took the Name Game

Challenge (November/ December issue of

Energy Matters Extra) and correctly identified

19 of the 25 historical energy champions

hidden within a story by Don Casada. Our

thanks and congratulations to Mr. Gaw for

his effort. Check out the answers in the current edition of Energy Matters Extra—and

watch for other energy-related quizzes in

future editions. 
Coming Events 

INFORMATION

CLEARINGHOUSE

Do you have questions about 

using energy-efficient process

and utility systems in your industrial

facility? Call the OIT Information Clearinghouse for answers, Monday through

Friday 9:00 a.m. to 8:00 p.m. (EST).

Fax: (360) 586-8303, or access our

homepage at www.motor.doe.gov

HOTLINE: (800) 862-2086

DOE Regional Support Office 

Representatives

■ Tim Eastling, Atlanta, GA, 

(404) 347-7141

■ Scott Hutchins, Boston, MA, 

(617) 565-9765

■ Julie Pollitt, Chicago, IL, 

(312) 886-8571

■ Gibson Asuquo, Denver, CO, 

(303) 275-4841

■ Julia Oliver, Seattle, WA, 

(510) 637-1952

■ Maryanne Daniel, Philadelphia, PA, 

(215) 656-6964

This document was produced for the Office 

of Energy Efficiency and Renewable Energy at

the U.S. Department of Energy (DOE) by the

National Renewable Energy Laboratory, a DOE

national laboratory.

DOE/GO-102000-0985 • March/April 2000

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Printed with a renewable-source ink on paper

containing at least 50% wastepaper, including

20% postconsumer waste

FUNDAMENTALS OF COMPRESSED AIR SYSTEMS

■ April 19, in Northhampton, MA, New England Electric, MA Electric.

Call Anita Hagspiel at (508) 421-7221.

ADJUSTABLE SPEED DRIVE APPLICATION TRAINING

■ April 25 in Marlboro, MA, MA Toxics Use Reduction Institute. 

Call Ann Berlin Blackman at (978) 934-2124.

■ May 9 in Greensburg, PA, PA DEP Allegheny Power. 

■ May 23 in Manchester, NH, State of NH Wastecap Resource Conservation Network. 

Call Erin Wheeler at (360) 754-1097, ext.104.

PUMP SYSTEMS/PUMPING SYSTEM ASSESSMENT TOOL WORKSHOP

■ April 26 in Marlboro, MA, MA Toxics Use Reduction Institute. 

Call Ann Berlin Blackman at (978) 934-2124.

■ May 1 in Westbrook, CT, BJM Corp. 

Call Anna Maksimova at (360) 754-1097, ext. 100.

NC STATE UNIVERSITY, INDUSTRIAL EXTENSION SERVICE WORKSHOPS

■ Cooling Tower Operations, April 25 in Atlantic Beach, NC.

■ Energy-Efficient Lighting, April 26 in Atlantic Beach, NC.

■ Preventive Maintenance, April 27 in Atlantic Beach, NC.

■ Energy-Efficient Motors, May 5 in Atlantic Beach, NC.

■ Certified Energy Manager, May 8-9 in Raleigh, NC. (2 days, 8:30 a.m.-4:00 p.m.)

All events last from 9:00 a.m. till 4:00 p.m. For more information, contact Jim Parker at 

(919) 515-5438, or at jim_parker@ncsu.edu.

U.S. Department of Energy

c/o NREL

1617 Cole Blvd.

Golden, CO 80401

Bulk Rate

U.S. Postage

PAID

Permit No. 258

Golden, Colorado