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Home > Energy Efficiency Tips & Tools > Commercial Buildings > Machines, Equipment and Motors
Machines, Equipment and Motors
Your electric motors can drive your savings program
In industry, electric motors account for about 75% of total electricity
use. In commercial and institutional buildings, it's about 50%. That includes
use in HVAC, refrigeration, elevator systems, conveyor belts, printing
presses, blowers and pumps, and manufacturing and assembly processes.
These are all opportunities for savings.
Electric motors efficiency checklist
Buy the right size motor
Before replacing a burned out electric motor, verify that the old motor
was sized correctly. Don't assume that it was the right size. Over or
under-sized units will operate at reduced efficiencies. You may need a
professional to help you determine the appropriate motor size.
Consider a high efficiency motor next time
Motors are available in standard and high efficiency models. It almost
always pays to replace a burned out standard efficiency motor with a high
efficiency motor. A high efficiency motor may cost more, but electricity
savings can quickly make up for it.
Shopping for high efficiency motors
Manufacturers use words like "high", "premium", "super",
or "extra" to describe their high efficiency models. But check
the information from the motor nameplate or the manufacturers' literature
to compare.
In addition to the horsepower rating and the nominal efficiency of each
motor, you must have estimates of how hard the motor will have to work
(mechanical load) and how many hours per year it will run. The example
shows that attention to efficiency ratings can result in significant savings
every year for a 20hp motor that runs continuously. The payback of the
extra cost for the higher efficiency motor can be very fast.
Example of a motor efficiency comparison
| Motor Rating |
20hp |
| Mechanical Load: |
85% of rating |
| Use Schedule: |
24 hrs/day, all year = 8760 hrs/yr |
| |
| |
Motor A |
Motor B |
| |
"Standard" |
"Premium" |
| Horsepower |
20 |
20 |
| Nominal Efficiency |
87% |
91% |
| |
|
| Electricity use/hr: |
| Horsepower |
20hp |
20hp |
| x load |
x85% |
x85% |
| x kW/hp |
x.746* |
x.746* |
| ÷ nom. eff. |
÷87% |
÷91% |
| = kW used |
14.58kW |
13.94kW |
| |
|
|
| Savings |
.64kW
|
| |
|
|
| Difference in electricity
use per year: |
| Electricity Saved |
.64kW
|
| x hours used/year |
x 8,760 hrs/yr
|
| = electricity saved/year |
= 5,606 kWh
|
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Adjustable speed drives and other options
Often you don't need the full power that motors can produce. To get the
motor power output that's required, you have three options: "throttling",
which lets the motor run at full speed but chokes off some of its power
output. This wastes energy.
Consider equipping the motor with an adjustable speed drive, which will
allow the motor to run at less than full speed. In some situations, the
best solution will be several smaller motors that run individually or
ganged.
Elevators and escalators
With large electric motors in many cases operating virtually continually,
elevators and escalators can consume significant amounts of electrical
energy. For lower operating costs:
- Operate only as needed. There may be some that can be shut down during
periods of little or no demand. A stopped escalator still "works"
as a flight of stairs. Make sure you or some other responsible person
knows how to use the controls.
- If your elevator motor runs continuously, consider having the controls
modified so the motor turns off automatically after a short period of
time (say, two or three minutes). A control which "puts it to sleep"
can be installed. With older elevators, a time clock can be used to
shut off the motors during unoccupied hours.
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