# Calculated Savings: Driving Energy Efficiency

#### Inefficient motor-driven systems lead to the loss of power. That’s  the equivalent of losing money. Lots of money. Taking a little time to do the math can help your operations change this equation.

Tens of millions of electric motor-driven systems in operation at manufacturing facilities around the United States are not running at optimum efficiency. Why does that matter? These motor-driven systems consume 70% of all electricity used in the plants, and the energy costs companies billions of dollars.

Today, approximately one-third of the electric motors in the industrial and commercial sectors use belt drives—most of them standard V-belts. While they are popular for their low acquisition costs, wide availability and quiet performance, V-belts simply are not as energy-efficient as synchronous belt drives.

Efficiency of any power transmission system is a measure of the power loss associated with the motor, the bearings and the belt drive. It is defined by these formulas:

As these equations show, energy losses in belt drives are separated into two categories: torque loss and speed loss. These vary in V-belt and synchronous drives as a result of the belts’ inherently different physical characteristics.

Although properly maintained V-belt drives can run as high as 95-98% efficient at the time of installation, such efficiencies deteriorate by as much as 5% during operation. Poorly maintained V-belt drives may be up to 10% less efficient. Synchronous belt drives, on the other hand, remain at an energy efficiency of 98-99% over the life of the belt. A proven, viable alternative to V-belt drives and roller-chain drives, they are generating savings across a variety of industrial applications.

Here, we look at how to calculate energy costs, energy savings and payback period—all of which are important factors in realizing the value of belt-drive conversion.

The calculations
Plant maintenance managers leverage improved energy efficiency by converting V-belt drives to synchronous belt drives in one of two ways: 1) maintaining current capacity while using less power; or 2) increasing capacity slightly using the same power. For example, if the current airflow in an HVAC application is satisfactory, a synchronous drive would use less energy to do the job. If the current airflow is insufficient, a synchronous drive could increase airflow without increasing use of energy with proper attention to design.

To determine the kilowatt-hours saved when using synchronous drives instead of V-belt drives, the following formula is used:

In this equation, .746 is the conversion factor from HP to KW, and .05 is the estimated 5% energy savings gained by converting.

Short payback

Estimating potential energy savings and the payback period for a synchronous belt drive is simple with these formulas:

Consider this example: If energy costs are \$0.10 per KWh, the annual energy cost for a 40 hp motor running at 89% efficiency, 8736 hours per year, totals \$29,290.14. The annual energy savings is \$1464.51. If a new synchronous belt drive costs \$342.83, the payback period is .23 years—less than three months.

When the annual dollar savings amount is multiplied by the number of similar motors in a plant, and added to the savings from motors of all other types, a facility’s overall energy-savings impact is clear.