Saving energy with power infrastructure equipment
Part 3 of this 3-part series provides details on how to specify motors, transformers, and other power equipment to save on electric bills.
One of the best ways to save money on an electric bill is to reduce the amount of energy used in a facility, either through the use of more energy-efficient devices or through intelligent building-control systems. While specific energy-efficient devices directly cut costs, intelligent building controls leverage new or existing technology to reduce energy consumption through advanced load-management strategies.
Three main load types dominate electric use in commercial facilities: lighting, HVAC, and power plug loads (from office devices and computers). Combined, these three represent almost 85% of all electric energy consumed by commercial customers. According to the U.S. Energy Information Administration (2008), 39% of commercial-building energy is used for lighting, 28% for HVAC, and 33% is used for computers, office devices, refrigeration, and other electrical equipment. This third part will explore ways to save money by specifying energy-efficient motors, drives, transformers, and other power infrastructure options.
Induction motors operate by using the magnetic field of an energized stator winding to apply torque to a central rotor. While designs have not changed much since the inception of the electric-power industry, the materials and techniques used in fabrication have changed dramatically.
In 2001, the National Electrical Manufactures Association (NEMA) introduced its Premium energy-efficiency motor standard. This standard applies to low-voltage induction motors with 2, 4, or 6 poles, rated for 1 to 500 hp. Improvements over previous design standards include adding more copper to the windings, creating a longer stack, and using higher slot fill and lower loss Premium steel in the rotor.
Estimated opportunity: The prevalence of motor loads in electric-power systems led to the inclusion of NEMA Premium efficiency motors in the Energy Independence and Security Act of 2007, which mandates their use for all applications below 1 kV and 200 hp.
Return on investment (ROI): The monetary savings from using a NEMA Premium efficiency motor are immense. Energy use accounts for approximately 88% of the total lifecycle costs of a motor compared to a purchase price that is only about 3% of the cost. The other lifecycle costs include installation and maintenance.
Based on the energy savings presented by the U.S. Dept. of Energy, we can calculate the annual and lifetime monetary savings gained by using a NEMA Premium efficiency motor. Annual calculations are based on 4-pole motors operating for 8000 h/yr. The results appear in Table 1.
The low-end of life expectancy for an induction motor is 10 yr. The yearly energy savings quickly dwarfs the increase in motor cost for extremely rapid payback periods. In many situations induction motor replacement is more economical, especially if repair or rewinding is required to maintain operation. Premium efficiency motors represent an excellent way for an industrial facility to save both energy and money on a rapid basis.
As with the induction motor, transformers are also integral components in power systems. They operate by energizing a primary winding wrapped around a metal core to induce voltage on a secondary winding. NEMA Premium efficiency transformers improve the performance of dry-type transformers over previous standards by employing improved magnetic windings and core materials, drastically reducing losses. An example can be seen in Figure 5.
Estimated opportunity: NEMA Premium efficiency transformers save enormous amounts of energy. Table 2 compares savings from NEMA Premium efficiency transformers to NEMA TP-1 and a 96%-efficient classic transformer. Transformer efficiencies are based on operating for 8,000 h/yr.
ROI: The case for using a NEMA Premium efficiency transformer for new construction is obvious. Older transformers present an excellent opportunity for replacement, as the amount of energy and monetary savings incurred through the use of a NEMA Premium efficiency transformer will pay the cost back quickly.
Let’s assume that a facility is thinking about upgrading an existing 75-kVA classic transformer with a NEMA Premium efficiency unit. The cost for the new transformer is around $4,500. Given the cost savings per year, the Premium transformer will pay for itself in 7 yr and last 20 to 40 yr. However, if a NEMA TP-1 unit is already installed, it is most likely not a viable investment to upgrade.
High-efficiency uninterruptible power supplies (UPS systems)
Most commercial buildings today have some UPS units installed to protect critical loads in office and/or data centers within the facilities. For years, the justification for these battery backup systems was reliability and protection of the load; a high-efficiency UPS offers an opportunity for additional savings and justification.
Estimated opportunity: Efficiency of a newer UPS is 94% to 96% with special operating modes capable of achieving greater than 99% efficiency while still maintaining high reliability. For a typical small data center in a commercial building, the savings could be upward of $10,000/yr.
Table 4 shows an example of typical savings possible with high-efficiency and Premium efficiency UPS units.
ROI: The savings from using a new high-efficiency or Premium UPS varies by size of the UPS and depends upon the unit that the new UPS is replacing. Since the ROI of UPS units were likely not initially based upon energy savings but rather upon reliability, the energy savings go right to the bottom line. Payback is generally less than 2 yr.
Daniel J. Carnovale is a senior member of the IEEE and the manager of Eaton’s Power Systems Experience Center (PSEC), where he develops and teaches technical seminars on power systems and power-system analysis and conducts power-quality site investigations for commercial, industrial, and utility power systems. Ansel Barchowsky is a doctoral student in electrical engineering at the University of Pittsburgh, a student member of the IEEE Power Engineering Society and IEEE Power Electronics Society, and a design consultant for Eaton’s PSEC. Brianna Groden is an engineer at Eaton’s PSEC, responsible for teaching power-quality and power-distribution topics, running demonstrations, and designing and managing the installation of new demonstration projects.
Eaton is a CISA member as of 9/2/2015