Application Note

3 Fluke Corporation If you knew how much it cost to run that equipment
For example, a 460-volt, three-phase, standard
efficiency 100 HP motor operating under full load
for 8,760 hours per year will probably cost just
over $48,000 per year to operate at an electric
rate of $0.10 per kWh. But, what if the motor is
not operating under full load at all times? Then,
the total operating cost can drop significantly.
The only way to know for sure is to measure and
record data. Then, analyze data and determine
the true dollar value that the motor is contributing
to that utility bill. Depending on the application,
such a motor may be a candidate for large energy
savings with the use of a variable frequency drive
(VFD).
The cost of lighting
Lighting is one of the largest consumers of electri-
cal energy in most industrial and commercial
facilities. For example, annual lighting cost in a
160,000-square-foot industrial facility is approxi-
mately $85,030. Such dollar amounts can often
be quickly and significantly reduced, if you know
where to find the biggest savings. Many lighting
options are available and selecting the right ones
requires intelligent decision making.
The question becomes, “What does it cost to
keep those lights on?” Then, estimates can be
made for newer, more efficient replacement sys-
tems using published data. You can make fairly
accurate estimates by counting fixtures, identify-
ing lamp wattages and types, taking into account
ballast operation, and knowing actual hours of
which lights are on when. However, for decision
making purposes, quick and accurate data can be
achieved with simple ac clamp meter readings on
lighting circuits in question.
As an example, certain fluorescent lighting
was left on at a commercial facility for extended
periods with what was thought to be good justifi-
cation. A common misconception is that it is more
energy efficient to leave fluorescent lighting on
than it is to turn it off. This is true only to a cer-
tain extent, as savings are attributed to avoiding
the small amount of inrush current when starting
these lamps. Also, excessive switching off and on,
such as several times per day, can shorten lamp
life. The US Department of Energy general rule
of thumb is that fluorescent lighting should be
turned off if the room is left unoccupied for more
than fifteen minutes. However, in some areas of
the country this number might be as low as five
minutes if electrical rates are high.
It is easy enough to use an ac clamp meter and
measure the voltage and current supplied to a
lighting circuit to quickly obtain accurate num-
bers. You can make a quick calculation for the cost
to operate that lighting circuit. But what if you are
assuming the lights are being shut off at certain
times when, in fact, they are not? After all, you
placed a sign reminding all workers to turn off all
task lighting at workstations at the end of their
shift. You probably will not be surprised that elec-
trical current and kW do not go to zero on all such
lighting circuits at the end of each day. So, how
much are lights that someone forgot to turn off
costing you? You won’t know until you measure
it. Then put up signs showing workers the dollar
amounts associated with lighting expenses and
you are sure to create some interest.
The per-hour cost of running
equipment
Sometimes operations and facility managers
simply like to know how much it costs to run a
specific piece of equipment per hour. Such infor-
mation should be provided at 100 percent load,
90 percent load, 80 percent load, and so on.
Information can then be extrapolated by managers
to make operational decisions. “What if I run press
#5 on this project instead of press #3? Which one
allows me to make the same part for less?” A fair
question that should have a concrete answer.
It is easy to look at an electric utility bill and
know what the charge is for the month. Manag-
ing and reducing that bill is the goal of energy
management and requires the cooperation of all
facility personnel. To make intelligent decisions
you must know where that electrical energy is
going each month. You must measure and record
energy data on major pieces of electrical equip-
ment and systems. Using a power logger for at
least one plant cycle or more is best. Determine
the hourly and annual costs to operate that equip-
ment. Keep track of this data and have it readily
available and know how much it cost to run your
equipment. It is much more comfortable to make
decisions based on fact rather than on estimates
and best guesses.
Fluke Corporation
PO Box 9090, Everett, WA 98206 U.S.A.
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Eindhoven, The Netherlands
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©2010 Fluke Corporation.
Specifications subject to change without notice.
Printed in U.S.A. 10/2010 3948499A A-EN-N
Modification of this document is not permitted
without written permission from Fluke Corporation.
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