ARCHIVED - Motors and Drives

Motors are used to run HVAC systems, elevators and other equipment, and can account for up to 50 percent of your facility's overall energy use. Over a typical 10-year operating life, a motor can consume electricity valued at 50 times the original cost of the equipment. Using this calculation, a $1,000 motor running continuously for a decade could cost you up to $50,000 in electricity.

• Energy-efficient motors are good investments. Even if they yield only 2 to 8 percent in energy savings, these motors generally achieve incremental paybacks in 2.5 to 5.0 years compared with buying less-efficient replacement motors.

• Adjustable-speed drives (ASDs)   sometimes referred to as variable-speed drives (VSDs) and variable-frequency drives (VFDs)   regulate motor speeds according to the amount of work required. Reducing motor speed by 10 percent can cut power consumption by 27 percent, and a 20 percent speed reduction can cut consumption by 49 percent. These drives are particularly useful when combined with high-efficiency motors since they tend to run faster than conventional motors. An added benefit is their ability to reduce noise   an important consideration near guest rooms and small meeting rooms. These drives can save on your facility's total energy consumption, but tend to be expensive, with approximate paybacks between two and eight years.

The Vocabulary of Motors

Motors are classified as AC (alternating current from outlets), DC (direct current, usually from a battery) or universal (operating as either AC or DC). A motor's mechanical power is measured in either kilowatts or horsepower (1 hp = 0.746 kW). The two factors that determine power are torque (measured in newton metres or pound feet) and speed (measured in revolutions per minute [rpm]). The slower a motor operates, the more torque it must produce to deliver the same amount of power. A motor's efficiency is a measure of the energy it delivers (output) relative to the energy it uses (input).

• Power-factor correction capacitors are devices that store electrical charges and reduce the consumption of reactive power that motors need to generate magnetic fields. These are important only if you have demand charges on your electricity bills (see How to Read Your Energy Bill in Step 1).

• Energy-efficient drive belts have teeth or longitudinal grooves that improve grip, reduce slippage and are only slightly more expensive than standard V-belts. Ensure that drive-belt inspections are performed every few months as part of regular maintenance, and replace the belts when they wear out.

• Choose the right motor for the job. Oversizing is the inefficient practice of employing a larger motor than required for a task. This is a particular concern if the motor is loaded under 50 percent.