6-i 6-3 6-5 6-5 6-7

6-5 6-6 6-6

6-7

6-4 CHAPTER 6. ENERGY USE CHARACTERIZATION

TABLE OF CONTENTS

6.1 INTRODUCTION ........................................................................................................... 6-1 6.2 ENERGY USE ANALYSIS FOR SMALL ELECTRIC MOTORS ............................... 6-1 6.2.1 Introduction .................................................................................................... 6-1 6.2.2 Motor Losses .................................................................................................. 6-1 6.2.3 Reactive Power

.............................................................................................. 6.2.4 Motor Applications

........................................................................................ 6.2.5 Loading

.......................................................................................................... 6.3 ANNUAL ENERGY USE

...............................................................................................

LIST OF TABLES

Table 6.2.1 Motor Application Market Shares

....................................................................... Table 6.2.2 Motor Operation Characteristics by Application

................................................. Table 6.2.3 Average Operating Characteristics for Small Electric Motors

............................ Table 6.3.1 Average Annual Electricity Use by Effi ciency Level for Small Electric Motors

..................................................................................................................

LIST OF FIGURES
Figure 6.2.1 Average Dependence of Motor Losses on the Square of the Motor Loading for Polyphase 1 Horsepower Motor. ...................................................... 6-2 Figure 6.2.2 Average Dependence of Reactive Power on Motor Loading for Polyphase 1 Horsepower Motor............................................................................................6-1 CHAPTER 6. ENERGY USE CHARACTERIZATION

6.1 INTRODUCTION
The U.S. Department of Energy (DOE) carried out the life-cycle cost (LCC) and payback period (PBP) calculations described in chapter 8 by determining the savings in operating cost consumers would realize from more energy e fficient products. Energy costs are the most significant component of consumer operating costs, with maintenance and repair costs the other contributors. DOE uses annual ener gy use, along with energy prices, to establish energy costs at various energy efficiency levels. This chapter describes how DOE determined the annual energy use of small electric motors.

6.2 ENERGY USE ANALYSIS FOR SMALL ELECTRIC MOTORS

6.2.1 Introduction
The energy use by small electric motors derives from three components: energy converted to useful mechanical shaft power, motor losses, an d reactive power. Motor losses consist of I 2 R losses (both stator and rotor), core lo sses, stray losses and friction and windage losses. 1 Core losses and friction and windage losses are relatively c onstant with variations in motor loading, while I 2 R losses increase with the square of the motor loading. Stray losses are also dependent upon loading. DOE models the I 2 R losses and stray losses as load-dependent losses.

6.2.2 Motor Losses
DOE’s mathematical description of energy us e separates motor losses into a constant component and a component that depends on mo tor loading. In DOE’s analysis, the design efficiency of the motor at full load determines the total losses at 100-pe rcent motor loading. DOE then estimates the fraction of these losses that is load independent and the fraction that varies as the square of the motor loading. To determine the annual energy use in kilowatt hours (kWh), DOE adjusts the full-load losses using the estimate of the motor duty factor (hours of operationper year) and loading. All losses are proportional to duty factor, and DOE approximates the loaddependent losses as proportional to both the duty factor and the square of the loading. Annual energy use E ann is represented by the following equation:

E

ann = H op × (P NL

+ P LL × L 2 )

Where:

E ann = annual energy use; H op = the annual operating hours, also known as the duty factor; P NL

= the power of load-inde pendent losses at full load; P LL = the power of load-depende nt losses at full load; and L = motor loading as a fraction of rated power.y = 67.025x + 139.39 R 2 = 0.9874

0 50 100 150 200 250

0.00 0.20 0.40 0.60 0.80 1.00 1.20 

### Square of Motor LoadingLoss (watts)

Figure 6.2.1 Average Dependence of Motor Losses on the Square of the Motor Loading for Polyphase 1 Horsepower Motor.
DOE confirmed the functional form of the dependence of motor losses on loading through a review of motor efficiency data from catalogue data available on the Internet as illustrated in figure 6.2.1 above.
For this preliminary analysis, DOE appor tioned the losses at full load equally to P NL

and P LL . For the notice of proposed rulemaking (NOP R), DOE will use a more sophisticated and potentially more precise method fo r apportioning full load losses to P NL

and P LL . While motor manufacturers do not explicitly publish motor losses as a function of load, many manufacturers do publish efficien cy as a function of motor load. This allows the estimate of motor losses as a functi on of motor loading and a mo tor-by-motor estimate of P NL

and P LL . The relationship between motor losses, effici ency and capacity is given by the following equation:
Efficiency = (P W * L)/ (P W * L + Losses)
Solving for the losses, we obtain:
Losses = (P W * L)*(1/Efficiency – 1) Where:
Efficiency = motor efficiency;

6-26-3 P W = the motor’s rated power in watts; Losses = the power of load-independent losses at full load in watts; L = motor loading as a fraction of rated power.
DOE collected from the Internet efficiency vs. loading for seve ral hundred listed motor models built in two-digit frame sizes. In some cases, on-line catalogues for at least two manufacturers had efficiency ra tings for motors at 25, 50, 75 and 100 percent loading levels.

6.2.3 Reactive Power
In an alternating current power system, the reactive power is the root mean square (RMS) voltage times the RMS current, multiplied by the sine of the phase difference between the voltage and the current. Reactive power occurs when the inductance or capacitance of the load shifts the phase of the voltage relative to the phase of the current. While reactive power does not consume energy directly, it can increase losses an d costs for the electricity distribution system. Motors tend to create reactive power because the windings in the motor coils have high inductance.
In practice, reactive power may result in onl y minor increases in energy consumption if capacitors in the electrical system compensate (i.e., mitigate) the reactive power. Also in previous analyses and standards for both sm all and medium electric motors, DOE has not considered power factor in the estimation of mo tor losses or efficiency. In this preliminary analysis, DOE assumes that, while reactive power ma y result in extra energy supply costs, actual losses before power factor compensation (through distribution system capac itor banks) are small. Actual fractional consumptive losses due to re active power are approximately equal to the fractional losses on the electrica l distribution system in gene ral. This means that actual consumptive losses due to reactive power are likely to be less than 10 percent of total reactive power. For the NOPR, DOE will use a more sophis ticated and potentially more precise method for accounting for the losses and costs due to reactive power.
While motor manufacturers do not explicitly report reactive power as a function of load, many manufacturers do publish power factor as a function of moto r load. Power factor is the ratio of the real power divided by the apparent power, where the apparent power is the sum of the real power and the reactive power. This allo ws the estimate of motor reactive power as a function of motor loading and a motor-by-motor esti mate of reactive power as a function of load. The relationship between reactive power ( PF ), efficiency, and rated power is given by the following equations:

PF =P real /P apparent
Where:

P real = (P W * L)/Efficiency

and where:P apparent = P real + P reactive

Solving for the reactive power, we obtain:

P reactive = (P W * L)*(1/Efficiency)*(1/PF-1) Where:

P real = real power in watts; P apparent = apparent power in watts; P reactive = reactive power in watts; P W = the motor’s rated power in watts; Efficiency = motor efficiency; PF = the motor’s power factor; L = motor loading as a fraction of rated power.
DOE collected from the Internet efficiency vs. loading for seve ral hundred listed motor models built in two-digit frame sizes. In some cases, on-line catalogues for at least two manufacturers had power factor and efficiency ratings for motors at 25, 50, 75 and 100 percent loading levels.

y = 413.73x + 113.35 R 2 = 0.9812

0 100 200 300 400 500 600

0.00 0.20 0.40 0.60 0.80 1.00 1.20 Motor LoadingReactive Power (watts)

Figure 6.2.2 Average Dependence of Reactive Power on Motor Loading for Polyphase 1 Horsepower Motor

6-46.2.4 Motor Applications
The annual operating hours and loading of small electric motors depends on the application. For different types of motors, the market shares of different motor applications can vary. In preparation for the determination anal ysis, DOE developed a classification of small electric motor applications and estimated shipments market shares for such motors in 2001. DOE then adjusted these market shares in the dete rmination analysis to account for newly covered products and provided adjusted application market shares in the technical support document for the small motors determination. 2 The estimates from the determination analysis provided information on only polyphase and capacitor star t motors. For this anal ysis DOE used equal application market shares for capacitor-start in duction-run (CSIR) and capacitor-start capacitorrun (CSCR) motors.

Table 6.2.1 Motor Application Market Shares

No. Application Polyphase (%) CSIR (%) CSCR (%)
1 Air and gas compressors 9.2 8.1 8.1

2 Commercial and industrial heating, ventilating, air-conditioning (HVAC)/refrigeration equipment 4.3 8.4 8.4

3 Commercial laundry machinery 0.4 1.2 1.2
4 Conveyors 18.8 11.8 11.8
5 Farm machinery 3.0 10.9 10.9
6 Food machinery 8.2 2.1 2.1
7 General industrial machinery 3.4 2.4 2.4
8 Industrial and commercial fans and blowers 5.6 5.9 5.9
9 Machine tools 7.3 1.9 1.9
10 Packaging machinery 1.0 0.3 0.3
11 Pumps and pumping equipment 33.0 41.1 41.1
12 Service industry machinery 1.5 3.0 3.0
13 Textile machinery 1.2 0.4 0.4
14 Woodworking machinery 3.1 2.4 2.4

6.2.5 Loading

To calculate the annual kWh use at each effi ciency level in each equipment class, DOE used the efficiencies and losses from the engin eering analysis, along with estimates of operating hours and motor loading from the determination anal ysis for the applications that use equipment containing small electric motors ( Table 6.2.2 ).

6-56-6 Table 6.2.2 Motor Operation Characteristics by Application

No. Application Hours/Year Motor Loading (Percent of Rated)
1 Air and gas compressors 800 85

2 Commercial and industrial heating, ventilating, airconditioning (HVAC)/refrigeration equipment 2,500 60

3 Commercial laundry machinery 2,000 60
4 Conveyors 3,000 50
5 Farm machinery 1,000 70
6 Food machinery 3,000 60
7 General industrial machinery 2,000 70
8 Industrial and commercial fans and blowers 5,000 80
9 Machine tools 2,000 60
10 Packaging machinery 3,000 60
11 Pumps and pumping equipment 3,000 65
12 Service industry machinery 1,500 60
13 Textile machinery 3,000 70
14 Woodworking machinery 2,000 35

DOE derived the distribution of values fo r operating hours and motor loading from the shares of the applications in the motor stock for each equipment class, as estimated in the determination analysis ( Table 6.2.1 ). For this preliminary analysis, DOE used point values for hours of operation and loading for each appl ication. For the NOPR, DOE may use a more sophisticated characterization of motor operating conditions by replacing these point values by distributions that have mean values that a pproximate the point values. This more precise characterization of motor operating conditions is likely to have a small effect on the mean result of DOE’s analyses, but may result in greater vari ability in the distributio n of consumer economic impacts estimated by the life-cycle cost analysis.

Table 6.2.3 shows the average values of opera ting hours and motor loading for each equipment class, weighted by the shares of each application.

Table 6.2.3 Average Operating Characteristics for Small Electric Motors

Equipment Class Annual Operating Hours Motor Loading (% of rated) Polyphase 2,665 63.2

CSIR 2,557 64.8 CSCR 2,557 64.86-7 6.3 ANNUAL ENERGY USE
Depending on the hours of operation and the loading (which are functions of the application) and depending on the efficiency of the motor (which varies with the standard level), the annual energy use varies both by effici ency level and from motor to motor. Table 6.3.1 shows the average annual energy use as a function of efficiency leve l for the three product classes. In the table, the rated capacity of the representative moto r from the product class is in parentheses in each column header. In each case, th e motors at the highest efficiency levels have losses that are approximately three times lower than the losses for the baseline designs.

Table 6.3.1 Average Annual Electricity Use by E fficiency Level for Small Electric Motors Polyphase (1 Horsepower) CSIR (0.5 Horsepower) CSCR (0.75 Horsepower) Candidate Standard

Level Efficiency (%) kWh Efficiency (%) kWh Efficiency (%) kWh

Baseline 75.8 444 62.3 410 68.6 465

CSL 1 84.0 265 70.9 278 80.2 250 CSL 2 85.5 236 73.6 243 82.1 222 CSL 3 86.5 217 75.4 220 83.3 203 CSL 4 88.0 190 78.2 189 85.2 177 CSL 5 90.0 154 81.8 151 87.6 1436-8 REFERENCES

1 National Electrical Manufacturers Associati on Standards Publication Condensed MG1-2002: Information Guide for General Purpose I ndustrial AC Small and Medium Squirrel-Cage Induction Motor Standards , NEMA, 1300 North 17 th Street, Suite 1847, Rosslyn, VA 22209, 2002. Also see http://www.nema.org

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2 U.S. Department of Energy- Office of Building Technologies. Technical Support Document: Analysis of Energy Conservation Standards for Small Electric Motors, June 2006, U.S. Department of Energy, Washington, DC. Also see http://www1.eere.energy.gov/bui ldings/appliance_standards/comme rcial/small_electric_motors. html

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