Pumps and Systems, June 2009
The pump industry is the largest purchaser of electric motors in the United States. According to the U.S. Department of Energy (DOE), electric motors consume more 50 percent of all electrical energy in the United States and more than 85 percent of industrial production electrical energy. Electric motors account for roughly $85 out of every $100 of a manufacturing/process plant's electrical bill.
Here is a breakdown of how much one 200 hp, 1,800 rpm and 460 V TEFC motor costs in power in a calendar year (7,200 hours of operation):
- Average cost of power in the United States: $.068/kWh
- Annual Power Cost: $70,669
- Initial Purchase Price: Slightly more than $10,000
Considering the above factors, one 200 hp pump motor running 6 days a week for 50 weeks a year will cost more than $70,000 dollars at the end of one year. Interestingly enough, most end-users spend more time negotiating the initial purchase price of a motor than understanding the true cost for operating that motor. According to the DOE, the average life of an electric motor is 20 years. During the life of an electric motor the initial purchase price represents just 1 percent of the total cost of owning and operating it. The largest cost of operating an electric motor is the power cost. DOE estimates the power cost to be 90 percent during the electric motor's 20-year life (see Figure 1).
To help reduce the power cost for pump motors, end-users need to understand the motor industry's terminology. The DOE and National Electrical Manufacturers Association (NEMA) have defined two motor efficiency levels. With the Energy Policy Act of 1992, the U.S. government mandated minimum efficiencies for all electric motors up to 200 hp (3,600, 1,800 or 1,200 rpm) that can be purchased in the United States. In adherence to this act, any motor made since 1997 is referred to as EPACT and must meet the act's mandates.
NEMA has created the second category for electric motor efficiency. These electric motors are called NEMA premium efficient. NEMA premium efficient electric motors range up to 500 hp (3,600, 1,800, 1,200 and 900 rpm). Figure 2 shows the differences in the two types of electric motors.
When selecting a new application for a pump motor, a buyer has two choices for electric motor efficiency: EPACT efficiency or NEMA premium efficiency. For overall performance and lowest operating cost, consider purchasing a NEMA premium efficiency motor from a supplier. Figure 2 shows that NEMA premium efficiency motors have larger rotors and stators. These larger rotors and stators have more copper and electrical steel than the EPACT or standard efficiency motors. With more inert materials (cooper and electrical steel), NEMA premium efficiency electric motors have a high motor efficiency and cost tens of thousands less to operate through the years than EPACT efficiency and standard efficiency electric motors.
If an existing electric pump motor needs to be replaced because of a failure, a buyer should consider the repair cost versus the potential cost savings of switching to a NEMA premium efficiency electric motor. Consider buying a NEMA premium efficiency motor under the following conditions:
- If the pump motor operates more than 4,000 hours annually, contact an electric motor supplier to review energy payback analysis and potentially reduce operation cost.
- Check with the local electric utility company because many electric companies offer rebate programs to help offset the cost of a new NEMA premium efficiency motor for replacement. Electric companies typically pay end-users a fixed dollar amount per electric motor horsepower.
- If the motor is an older electric motor, contact an electric motor supplier to review an energy payback analysis. Older electric motors are defined as standard efficiency motors more than 20 years old.
- If the plant is developing a preventive maintenance or energy conversation program, a NEMA premium efficiency motor might fit into the new program scheme.
To be proactive in reducing power costs at a manufacturing/process plant, review the electric motors in operation. Contact a local electric motor supplier and ask them to perform an electric motor energy audit of the facility. An audit will list the types of electric motors in operation and gauge their energy efficiency. Generally, electric motor energy audits are performed for free. An electric motor energy audit will reveal:
- Which electric motors are costing the most in terms of power cost and whether and when to change to a NEMA premium efficiency motor.
- When to repair or replace an electric motor when and if it fails.
- How the local electric motor supplier can help by adjusting its motor inventory to suit the facility's current and future needs.
The DOE provides a guide to selecting electric motors based on hours of operation and the cost for electric power (see Figure 3).
Since the largest cost to a manufacturing/processing plant is the cost of electric power, the key to lowering electrical cost is reducing the highest energy-consuming motors in the plant. The highest energy users in the plant are likely the electric motors that run pumps, air compressors, HVAC systems, etc. Whether the facility uses a few large horsepower electric motors or multiple smaller horsepower electric motors, the motors can be more energy efficient and save tens of thousands in utility costs.
