Energy & Cost Impacts: High Efficiency Motors
The United States Department of Energy (DOE) as well as the California Energy Commission (CEC) specify minimum motor efficiency requirements and, depending on the application, the ability to modulate the speed of the motor. These stipulations were established mainly to reduce greenhouse gas emissions and make the electrical grid more reliable. For the end users, these requirements also result in significant energy and cost savings.
When people consider the cost of a motor, they often only look at the price tag. While this is a significant portion of the overall cost, it does not tell the entire story. When considering the cost of a motor, three things should be accounted for:
- Purchase Cost
Many premium efficiency motors have a purchase cost that is higher than standard efficiency motors. This is because efficient motors have newer design, often with more costly materials. Internal components of highly efficient motors are also held to higher standards and may have a more thorough quality assurance process at the factory. As premium efficiency motors are on the market longer, and development costs have been covered, these higher costs are likely to decrease.
- Operational Cost
Operating cost savings are directly related to the energy saved from improved motor efficiency. Often the cost of the energy saved can pay for the higher purchase price quickly. The US Department of Energy has developed a simple way to estimate the annual dollar savings when using an efficient motor:
For example, consider a 7.5 HP motor running at 80% of peak load for 8000 hours a year with an average energy cost of 0.13 $/kWh. If a premium-efficiency motor has an efficiency of 80% as opposed to 78%, it would save $149.20 a year in this application. The simple payback in years can be calculated by dividing the price premium (purchase price difference between the premium motor and the standard motor) by the annual dollar savings. Continuing with this example, if the premium efficient motor cost $450 more than the standard motor the simple payback would be roughly 3 years. After the 3 year payback, the motor would continue to provide additional savings for the life of the motor.
- For more detailed savings information, a simulation of motor use was performed using the DOE’s EnergyPlus software. This model was applied to DOE’s stand-alone retail reference building, which is representative of a commercial building that has four roof-top units (RTUs) to provide heating and cooling. The results for each motor simulated can be found on their respective product pages: https://energyproductevaluations.org/product_categories/motors/
- Maintenance and Replacement Cost
Most premium efficiency motors have a longer life and require less maintenance than standard efficiency motors. This should be accounted for when considering the overall cost of using a motor for a specific application. As stated above, the long-term cost savings of choosing a motor of this type is not often accounted for in the purchasing phase of a project.