DOE motor challenge program

Motor Challenge is a partnership program between the U.S. Department of Energy and the nation’s industries. The program is committed to increasing the use of industrial energy-efficient electric motor systems and related technologies.

This program is wholly funded by the U.S. Department of Energy and is dedicated to helping industry increase its competitive edge, while conserving the nation’s energy resources and enhancing environmental quality.

Over half of all electrical energy consumed in the United States is used by electric motors. Improving the efficiency of electric motors and the equipment they drive can save energy, reduce operating costs, and improve our nation’s productivity.

Energy efficiency should be a major consideration when you purchase or rewind a motor. The annual energy cost of running a motor is usually many times greater than its initial purchase price. For example, even at the relatively low energy rate of $0.04/kWh, a typical 20-horsepower (hp) continuously running motor uses almost $6,000 worth of electricity annually, about six times its initial purchase price.

Select a new energy-efficient motor under any of the following conditions:

• The motor is less than 40 hp.

• An energy-efficient motor is recommended according to Table 3.

• The cost of the rewind exceeds 65% of the price of a new motor.

• The motor was rewound before 1980 year

Survey your motors. Gather nameplate information and obtain field measurements (voltage, amperage, power factor, operating speed) under typical operating conditions. Initially focus on motors that exceed minimum size and operating duration criteria. Typical selection criteria include:

• Three-phase NEMA design B motor

• Non-specialty motor

• 10 to 600 hp

• At least 2000 hours per year of operation

• Constant load (not intermittent, cyclic, or fluctuating

• Older or rewound standard efficiency motors

• Easy access

• Readable nameplate.

BHP = (ρ*(Q/3600)*H)/(102*η)

BHP : Pump Power [Kw]
ρ  : Fluid Density [kg/m3]
Q   : Flow Rate [m3/hr]
H   : Total Diff' Head [m]
η  : Pump Efficiency [%]

Design Condition
ρ = 1,126 kg/m3 
Q = 173.0 m3/hr
P1 = 0.6 kgf/cm2g
P2 = 14.4 kgf/cm2g
H = (14.4-0.6)*10/(1126/1000) = 122.6 m
η = 66.5%
BHP = (1126*(173/3600)*122.6)/(102*66.5/100) = 97.8 kW

Actual Condition
ρ = 1,126 kg/m3
Q = 84.4 m3/hr
P1 = 0.6 kgf/cm2g
P2 = 14.6 kgf/cm2g
H = (14.6-0.6)*10/(1126/1000) = 124.3 m
n = 53.0%
BHP = (1126*(84.4/3600)*124.3)/(102*53.0/100) = 60.7 kW

Load Factor = Pump Operation BHP / Pump Rated BHP
            = 60.7 kW /97.8 kW = 62%
Pump Imbalance = [(Actual Q * Actual H) / (Design Q * Design H) -1] * 100%
               = ((84.4*124.3)/(173*122.6)-1)) = -51%
Flow Ratio = Actual Q / Design Q

           = 84.4 m3/hr / 173 m3/hr = 49%
Motor Load = Operation P / Rated P

           = 63.8 kW / 110 kW = 58%

If the calculation results of the four parameters calculated above meet the conditions below, energy engineer should consider an investment project to save energy consumption.

Pump Imbalance: Review below -20%
Pressure Ratio: Review when exceeding 130%
Flow Ratio: Review when below 70%
Motor Load: Review when below 40%