Energy Efficient Motor Drive Systems

Motor Electricity Use • Motors consume about 75% of all the electricity used by industry.

• Their popularity is a testament to their reliability, versatility and efficiency. • Despite these attributes, the cost of powering motor driven systems in the US is over $90 billion per year. • Thus, increasing the efficiency of motor drive systems can lead to significant savings.

Motors: The Nature of Wealth    James Watt observed that a horse pulling 180 pounds of force walked at 181 feet per minute. Thus, the horse generated 33,000 ft. lbs. per minute, which Watt called one “horsepower”.

Generating 1 hp required: – 1,000 lb horse – 6 ft tall – costs $5,000 /yr to board  Today, generating 1-hp requires: – 32 lb motor (30x less) – 4 x 6 inches (12x less) – costs $250 /year (20x less)

Inside Out Approach to Energy Efficient Motor Drive Systems    End Use – Turn off motors when not in use – Move motor use to off-peak shift Distribution – Motor drives Primary Energy Conversion – Right size motors – Purchase ‘Premium Efficiency’ motors

Turn Off Motors When Not In Use!  Stamping press motors – 80% loaded while stamping – 65% loaded during idle – 65% of power dissipated as heat due to friction!

 Example: Turn off 50-hp stamping press for 2,000 hr/yr.

– 50 hp x .65 x .75 kW/hp x 2,000 hr/yr x $0.10 /kWh = $4,875 /yr

Turn Off Motors When Not In Use!  Hydraulic system motors – 8 kW while loaded – 5 kW while unloaded – Draws 63% of loaded power when unloaded.

 Example: Turn off 20-hp hydraulic motor for 2,000 hr/yr.

– 5 kW x 2,000 hr/yr x $0.10 /kWh = $1,000 /yr

Move Motor Operation to Off-Peak Shift  Motor used only during first shift  Move motor use from 1 st to 2 nd shift to reduce electrical demand  Example: Move use of 50-hp, 80% loaded, 90% efficient, grinder to off-peak shift – 50-hp x 0.75 kW/hp x 80% / 90% = 33 kW – 33 kW x $14 /kW-mo x 12 mo/yr = $5,544 /yr

Inside Out Approach to Energy Efficient Motor Drive Systems    End Use – Turn off motors when not in use – Move motor use to off-peak shift Distribution – Motor drives Primary Energy Conversion – Right size motors – Purchase ‘Premium Efficiency’ motors

Replace Smooth with Notched V-belts

Notched V-belts

– 3% more efficient than smooth belts – Last 50% to 400% longer than smooth belts – Cost only 30% more than smooth belts

Example

– 25-hp motor, 91% efficient, 75% loaded – Savings = 25 hp x 0.75 kW/hp x 75% / .91 x (1/.92 - 1/.95 ) = 0.5 kW – Savings = 0.5 kW x 6,000 hours/yr = 3,000 kWh/year – Savings = 3,000 kWh/year x $0.10 /kWh = $300 /year h = 92% h = 95%

Inside Out Approach to Energy Efficient Motor Drive Systems    End Use – Turn off motors when not in use – Move motor use to off-peak shift Distribution – Motor drives Primary Energy Conversion – Down size under-loaded motors – Purchase ‘premium efficiency’ motors – Replace rather than repair older failed motors

Down-size Under-loaded Motors Efficiency declines at low loads Power factor declines at low loads

Motors: Energy Cost >> Purchase Cost 150,000 120,000

($)

90,000 60,000 30,000 0

Purchase and Energy Costs (20 hp motor at 8,000 hours/year over 20 years)

Purchase Energy • 20-hp, 93% eff, 75% loaded, 8,000 hrs/year, $0.10 /kWh, cost = $1,161 • Annual energy cost = 20 hp x 75% x .75 kW/hp / 93% x 8,000 hr/yr x $0.10 /kWh = $9,677 /yr • Over 1 yr, energy cost is 8x greater than purchase cost • Over 12-yr life, energy cost is 100x greater than purchase cost!

Purchase Premium Efficiency Motors Consider – 15 hp motor, 80% loaded, 6,000 hr/yr, $0.10 /kWh – Standard Eff = 0.91 = $889 Premium Eff = 0.93 = $1,010 Cost of electricity – Savings = 15 hp x .8 x .75 kW/hp x 6,000 hr/yr x $0.10 /kWh x (1/.91 – 1/.93) – Savings = $127 /yr Incremental Cost of Premium Efficiency Motor – $1,010 - $889 = $121 Simple Payback – $127 / $121 /yr = 1 year

Replace or Repair Older Failed Motor?

Size (hp) 1 5 10 15 20 30 50 60 75 100 150 200 250 300 500 Efficiency Rewound 73 82 84.7

85.5

87.3

88.2

90.6

90.8

91 91.2

91.8

92.3

92.9

93.1

92.8

Cost Rewound ($) 220 330 500 550 600 760 980 1,116 1,320 1,650 2,400 2,650 2,860 3,080 4,400 Efficiency Engy Eff 84.6

89.8

91.7

92.6

93 93.8

94.4

94.8

95.3

95.4

95.5

95.7

95.8

96.1

96.6

Assuming 80% loaded, 6,000 hr/yr, $0.10 /kWh Cost Engy Eff ($) 275 432 686 911 1,071 1,553 2,482 3,280 4,476 5,645 8,624 10,680 13,043 14,084 25,725 Rew-Rep ($/yr) 68 191 324 484 505 731 800 1,004 1,339 1,738 2,279 2,771 2,933 3,621 7,630 Rep-Rew ($) 55 102 186 361 471 793 1,502 2,164 3,156 3,995 6,224 8,030 10,183 11,004 21,325 S. P.

(yr) 0.8

0.5

0.6

0.7

0.9

1.1

1.9

2.2

2.4

2.3

2.7

2.9

3.5

3.0

2.8

10 9 8 7 6 5 4 3 2 1 0 0 Replace Rather than Rewind Motors

Operating Hours: 8,000 hrs/year

$0.05 /kWh $0.08 /kWh $0.11 /kWh 50 100

Motor HP

150

Source: US DOE Motor Master+ 4.0

200 250

U.S. D.O.E. Motor Master Software       Over 25,000 motors from 18 manufacturers Rapid data entry, sorting by condition, and rewind/replace recommendations.

Technical data to help optimize drive systems, such as: – Motor part-load efficiency, power factor – Full-load speed, locked-rotor, breakdown, and full-load torque.

Motor purchasing information, including list prices, warranty periods, etc.

Capability to calculate savings, payback, return-on-investment, etc.

http://www1.eere.energy.gov/industry/bestpractices/software.html#mm

Employ Energy Efficient Flow Control

Inefficient Flow Control Fan w/ Inlet Vanes By-pass loop (No savings) By-pass damper (No savings) Throttling valve (Small savings) Inlet vanes (Moderate savings)

Efficient Flow Control Close Bypass Valve dP Trim impellor for constant-flow pumps Slow fan for constant-flow fans VFD VFD for variable-flow pumps or fans

Power and Flow Control 100% 80% 60% 40% 20% 0% 0% 20% 40% 60% 80% By-pass Variable Inlet Vane

Volume Flow Rate (%)

Outlet Damper Variable Frequency Drive 100%

Case study: Large Cooling Towers

Large Cooling Loop Pumps

Worlds Largest Bypass Pipe

For Constant Flow Pumping: Trim Pump Impellor and Open Throttling Valve

For Constant Flow Fan: Slow Fan Speed by Increasing Pulley Diameter

For Variable Flow: Install VFD & Control with Difference Pressure cooling tower bypass / pressure relief valve dP • W 2 = W 1 (V 2 /V 1 ) 3 city water make-up 7.5 hp pump reservoir warm water cool water 25 hp pump VSD cooling water to process loads • Reducing flow by 50% reduces pumping costs by 87% process water return