Application Note

Application Note
From the Fluke Digital Library @ www.fluke.com/library
Core components of
energy
If you haven’t measured energy
before, take a minute to under-
stand how it differs from volts
and current. When we talk
about the “energy” supplied by
the utility, we’re talking about
two primary components: power
and demand.
Power, kW, is commonly
measured in Watts, which indi-
cate the rate at which energy
is expended in one second.
Watt-hours describe the total
energy expended over other
time periods, such as a month,
as recorded for ac energy use
by our electrical utilities. Watt-
hours measure actual work, such
as heating or cooling buildings,
moving objects or liquids, etc.
Demand, kVA, measures the
total requirement that a cus-
tomer places on the utility to
deliver voltage and current,
without regard to the efficiency
of that delivery or whether or
not it does actual work.
Now let’s start measuring. Use
a regular digital multimeter with
an accessory current probe to
measure the voltage and then
How do you
measure energy
consumption?
the current, and then multiply
the two values to get demand—
kiloVoltAmperes (kVA.)
This works for a simple single
phase circuit where the load
remains stable for the period
of the two measurements. For
a real-life load, we need to
account for a few other elements.
Power factor, imaginary
power, and harmonics
Power factor. If the circuit is
operating at 100 % efficiency
(which rarely happens), then
demand is also a measure of
power. In reality, power (kW) is
usually less than demand (kVA).
The difference, kW/kVA, is
called power factor (PF). Utilities
often collect a penalty charge
if PF falls below 0.95. Some
utilities are setting the bar even
higher. Remember: Low power
factor is bad; high power factor
is good.
The typical industrial or com-
mercial facility uses three phase
energy distribution, and then
uses that energy in a number
of ways—to provide heating,
operate three phase motors and
motor drives, or handle single
With energy costs high, and getting higher, many
facilities are trying to reduce their energy consumption.
Most have not previously analyzed their monthly energy
usage, traced it to operational components, or broken
out the utility fees. And until you understand how you’re
using energy, it’s hard to make smart decisions on how
to reduce consumption.
With power, demand… and a power quality tool
Using a Fluke 1735 Power Logger to log power consumption at a
chiller to determine equipment efficiency.