8.8-i APPENDIX 8.8. POWER CONSUMPTIO N OF BC/ECM+ BLOWER MOTORS
TABLE OF CONTENTS

8.8.1 INTRODUCTION

................................................... 8.8-1 8.8.2 SHAFT POWER AND STATIC PRESSURE AT CONSTANT SPEED

......... 8.8-2 8.8.3 BLOWER AT OTHER SPEEDS AND AIRFLOWS

........................ 8.8-3 8.8.4 OTHER SIZE BLOWERS

............................................. 8.8-4 8.8.5 SYSTEM EFFECT FACTOR (SEF) OF BLOWERS IN FURNACES

.......... 8.8-5 8.8.6 BLOWER SPEED AND SHAFT POWER AS FUNCTION OF FURNACE STATIC PRESSURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.8-6 8.8.7 ECM 4.0 MOTOR EFFICIENCY

....................................... 8.8-9 8.8.8 BC/ECM+ BLOWER MOTOR ELECTRICITY CONSUMPTION

........... 8.8-10

LIST OF TABLES Table 8.8.2.1 Coefficients for Shaft Power and Static Pressure at Constant Speed

...... 8.8-3 Table 8.8.4.1 Scalars for Airflow and Shaft Power for the Backward-Inclined Blowers . . 8.8-4 Table 8.8.5.1 SEF for BC/ECM+ Blowers in Virtual Model Furnaces

................ 8.8-6 Table 8.8.6.1 Coefficients for Blower Speed Equation

............................ 8.8-8 Table 8.8.6.2 Coefficients for Blower Shaft Power Equation

....................... 8.8-9

LIST OF FIGURES Figure 8.8.2.1 Pressure and Shaft Power versus Airflow at Constant Speed

............ 8.8-2 Figure 8.8.5.1 SEF Versus Nominal Airflow for Virtual Model Furnaces

............. 8.8-6 Figure 8.8.7.1 Efficiencies and Operating Range of Prototype Motor

................ 8.8-108.8-1 APPENDIX 8.8. POWER CONSUMPTIO N OF BC/ECM+ BLOWER MOTORS

8.8.1 INTRODUCTION General Electric Industrial Systems (GE) has developed a prototype backward-inclined blower impellor for use in residential furnace and air handlers. 1 Backward-inclined blowers have significantly wider blades and must rotate at higher speeds to provide the same static pressure rise as forward-curved blowers of the same size. As part of this project, GE also developed a new, smaller diameter, motor, ECM 4.0, which is able to drive the new blower at higher speeds. The Department developed the equations to predict blower motor electrical power consumption for the BC/ECM+ design option based on this prototype. From a plot of efficiencies and pressure s versus airflow of the GE prototype, DOE developed equations for shaft power and static pre ssure as functions of airflow. These equations, combined with the fan laws, allowed the Department to determine shaft power and static pressure for any speed and airflow for this prototype blower. The Department developed modifications of these equations to estimate the performance of blowers of other sizes to cover virtual model furnaces of other nominal maximum airflow capacities. The GE prototype is designed to provide airflow for a furnace built to accommodate a 3- ton air conditioner. The Department assumed it would be matched to a furnace designed to have a system effect factor (SEF) giving a static pr essure rise across the furnace of 0.5 in.w.g. at an airflow of 1200 cfm. The ratio of the SEF for other size furnaces to the SEF of this furnace was assumed to follow the pattern seen in furnaces with forward-curved blowers. Furnaces with these backward-inclined blowers are intended to operate at constant airflow, regardless of the static pressure. Once the equations based on airflow were developed, the Department applied them to determine the blower speeds required to provide nominal airflow across a range of static pressures. Shaft power was determined at these same operating points to fit equations of blower speed and shaft power aspolynomial functions of furnace static pressure. GE reported the efficiency of the ECM 4.0 at two operating conditions. The two points had almost identical efficiencies. The points roughly span the intended operating range of the motor in a furnace with a nominal airflow capacity of 1200 cfm. Based on this, the Department assumed the new motor would operate at constant efficiency. The shaft power of the BC/ECM+ blower in generic model furnaces divided by this efficiency gives the blower motor electrical power consumption. The following sections in this appendix provide the details of these calculations and assumptions.8.8-2 8.8.2 SHAFT POWER AND STATIC PRESSURE AT CONSTANT SPEED The GE topical report on the development of the prototype blower and motor includes a plot of efficiencies and pressures versus airflow at a constant speed. 1 The Department measured the values from one and a half dozen points on the curves on this plot. It then converted the values of these points to units of cfm for airflow and in.w.g. for pressure using a guide for SI units from ASTM. 2See Figure 8.8.2.1.

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0 500 1000 1500 2000 Q, Airflow (CFM)P, Static Pressure (in.w.c)

0 50 100 150 200 250H, Shaft Power (W) P H

N = 1290 RPM

Figure 8.8.2.1 Pressure and Shaft Power versus Airflow at Constant Speed The Department fit these points to equations for shaft power and static pressure at constant blower speed as polynomial functions of airflow. The equations are:


### ( ) PQ C C Q C Q C Q C Q = +×       + ×       + ×       + ×       0 1 1000 2 1000 2 3 1000 3 4 1000 4



### ( ) HQ C C Q C Q C Q = +×       + ×       + ×       0 1 1000 2 1000 2 3 1000 3

where: = static pressure rise across blower (in.w.g.), 

### P = airflow (cfm), 

### Q = blower shaft power (W), and 

### H8.8-3 C

0,C 1 ,C 2,C 3,C 4 = empirical coefficients from curve fitting. The coefficients for these equations are shown in Table 8.8.2.1. Table 8.8.2.1 Coefficients for Shaft Power and Static Pressure at Constant Speed Static Pressure (P) Shaft Power (H) C 0 0.91982 46.32071 C 1 0.34136 127.57380 C 2 -0.11357 -13.27624 C 3 -0.32487 -7.27523 C 4 0.08524

8.8.3 BLOWER AT OTHER SPEEDS AND AIRFLOWS These equations, combined with the fan laws, allowed the Department to determine shaft power and static pressure for any speed and airflow for this prototype blower. To do this requires finding the equivalent airflow at the test speed, and then scaling the pressure to new speed. 3 The equations for this are:
Q equiv Q Ntest N = × 

## ( ) 

# ( ) PNQ P test Q equiv N Ntest , = ×       2


## ( ) 

# ( ) HNQ H test Q equiv N Ntest , = ×       3

where: = static pressure rise across blower (in.w.g.), 

### P = blower speed (rpm), 

### N = blower speed during test (rpm), Ntest = equivalent airflow at test speed (cfm), Q

equiv = static pressure rise across blower at test speed (in.w.g.), P

test = shaft power of blower (W), and 

### H = shaft power of blower at test speed (W). H test8.8-4 8.8.4 OTHER SIZE BLOWERS The prototype blower developed by GE wa s thought to be designed for only one size furnace, with a nominal airflow of 1200 cfm. Wider blowers provide more airflow and require more shaft power to develop the same static pressure. The Department examined the airflow for four forward-curved blowers of the same diameter with different widths (Lau Industries blowers DD10-7A, DD10-8A, DD10-9A, and DD10-10A) when operating at 1075 rpm, the nominal speed for PSC motors they are usually driven with. 4The ratio of average airflows for these blowers across a representative range of pressures, roughly scaled as the ratio of widths raised toa power of 0.795. The Department assumed that the shaft power and airflow wider backwardinclined blowers would scale with width at this same rate. The assumed width ratios and resulting scalars for airflow and shaft power fo r the backward-inclined blowers for the four airflow capacities of the generic model furnaces are shown in Table 8.8.4.1.
Table 8.8.4.1 Scalars for Airflow and Shaft Power for the Backward-Inclined Blowers

nominal airflow (cfm) 800 1200 1600 2000 generic model forward-curved blower size 9×8 10×8 10×10 11×10

width ratio 0.875 1 1.25 1.5 scalar 0.89932 1 1.19402 1.38018 Using these assumptions, finding the pressure for a given airflow for a different width blower means finding the equivalent airflow to cal culate the pressure for the prototype blower at the test speed. This is a modification of the techniques used in section 8.8.3, Blower at Other Speeds and Airflows. The equations to find the equivalent airflow and scaled shaft power are:

Qequiv Q Ntest N W W =× × 1


# ( ) 

# ( ) HW N Q H test Q equiv N Ntest W , = ×       ×

3 1

where: = blower speed (rpm), 

### N = blower speed during test (rpm), Ntest = airflow of wider blower (cfm), 

### Q W = equivalent airflow at test speed (cfm), Q

equiv = shaft power of wider blower (W), and 

### H W = shaft power of blower at test speed(W). H test8.8-5 The equation to calculate pressure is the then same as in section 7.8.3 with the new Qequiv

.
8.8.5 SYSTEM EFFECT FACTOR (SEF) OF BLOWERS IN FURNACES The SEF is the reduction in pressure from the blower operating by itself compared to when the blower is operating in a furnace. The SEF accounts for the effect of obstructions to the airflow and the inlet and outlet geometry of the blower enclosure of the furnace. The Department made the assumption that the fractional change in SEF for every 400 cfm change of nominal airflow in the virtual model furnaces would also apply for the BC-ECM+ blowers in the virtual model furnaces. The Department fit the SEF of the virtual model furnaces to an exponential function of nominal airflow. Figure 8.8.5.1, shows values and the fit equation for forward-curved blowers and PSC motors. The equation for SEF as a function of nominal airflow is:

SEF b m Q nom = × where = system effect factor, 

### SEF = 1.227249 x10 6, 

### b = 0.999039, and 

### m = nominal airflow of blower(cfm). Q

nom The SEF was calculated independently for the BC-ECM+ at a nominal airflow of 1200 cfm. The equation is: 

# ( ) SEF P blower P furn Q

nom = − 2

where = system effect factor, 

### SEF = static pressure of blower, 0.781 (in.w.g.), calculated at 1290, P

blower rpm and 1200 cfm, = static pressure of furnace, 0.5 (in.w.g.), and P

furn = nominal airflow of blower, 1200 (cfm). Q

nom8.8-6 0.E+00 1.E-07 2.E-07 3.E-07 4.E-07 5.E-07 6.E-07 7.E-07

800 1200 1600 2000 Nominal Airflow (CFM)SEF (in.w.g./CFM2) Exponential Fit Generic Model Furnaces

Figure 8.8.5.1 SEF Versus Nominal Airflow for Virtual Model Furnaces

To get the SEF for the other virtual model furnaces with BC/ECM+ blowers, DOE calculated the ratio of SEF for the other nominal maximum airflow virtual furnaces to the SEF for this furnace. This was done using the exponential function of SEF versus nominal maximum airflow of the virtual model furnaces. The resulting ratios are shown in Table 8.8.5.1.
Table 8.8.5.1 SEF for BC/ECM+ Blowers in Virtual Model Furnaces Nominal Airflow (CFM) 800 1200 1600 2000 SEF ratio 1.468938 1 0.680764 0.463439 SEF (in.w.g./CFM 2 ) 2.86931E-07 1.953E-07 1.32975E-07 9.05245E-08

8.8.6 BLOWER SPEED AND SHAFT POWER AS FUNCTION OF FURNACE STATIC PRESSURE For furnaces with improved ECM motors and backward-inclined impellors in the blower, the Department determined the airflow and static pressure at the operating conditions from the intersection of the fan curve of the furnace and the system curve of the ducts. This is done in the same way as for standard PSC motors. However, furnaces with these motors are programmed to provide a constant airflow regardless of static pressure. Thus, the fan curves for these furnaces are a vertical line of constant airflow.8.8-7 The Department evaluated the furnace static pressure at the nominal air flow for each of the virtual model furnaces with BC/ECM+ blowers for a range of blower speeds. 

## ( ) P

furn P blower Q N SEF Q = −× , 2

where = furnace static pressure (in.w.g.), P

furn = static pressure across blower alone (in.w.g.), P

blower = airflow (cfm), 

### Q = motor speed (rpm), and 

### N = system effect factor as explained in Appendix 7.4, Furnace Fan SEF Curves, section 7.4.1, General Air Speed and Airflow Relationship. From these static pressures, the Department developed an equation for blower speed as a function of static pressure at the nominal airflows of the virtual model furnaces. 

# ( ) N P furn CCP furn C P furn = +× + × 01 2 2

where = motor speed (rpm), 

### N = furnace static pressure (in.w.g.), and P

furn C

0,C 1 ,C 2 = empirical coefficients from curve fitting. The coefficients for the equations of blower speed as a function of furnace static pressure for virtual furnaces with improved ECM motors and forward-curved impellors is shown in Table 8.8.6.1.8.8-8 Table 8.8.6.1 Coefficients for Blower Speed Equation Q C 0 C 1 C 2 Cooling

2 ton 800 771.297930225 779.26756805 -139.008728615 3 ton 1200 1004.4257405 612.718105072 -82.3858179298 4 ton 1600 1115.11438648 556.374528078 -66.4367804917 5 ton 2000 1186.32793032 524.106011654 -58.6030844866 High Fire 2 ton 640.0 620.504604012 933.280077841 -205.025304436 3 ton 960.0 805.339732049 744.862082929 -126.832574748 4 ton 1280.0 893.475264237 679.413794851 -103.848338196 5 ton 1600.0 950.264980926 641.197789459 -91.9907933216 Low Fire

2 ton 533.3 521.413603686 1068.28226839 -271.834021254 3 ton 1200 673.447604033 866.36860443 -175.654364949 4 ton 1066.7 746.403441995 793.875638502 -145.692110892 5 ton 1333.3 793.449632938 751.002693796 -129.8241 For the same air flow and speeds that were used to evaluate furnace static pressure, DOE evaluated the blower shaft power using the equations explained earlier in this appendix. From these results, the Department developed an equation for blower shaft power as a function of static pressure at the nominal airflows of the virtual model furnaces.

H P furn CCP furn C P furn C P furn ( ) = +× + × + × 01 2 2 3 3

where = blower shaft power (which is also the motor output power) H (W), = furnace static pressure (in.w.g.), and P

furn C

0,C 1 ,C 2,C 3 = empirical coefficients from curve fitting. The coefficients for the equations of blower shaft power as a function of furnace static pressure for virtual furnaces with ECM motors and forward-curved impellors is shown in Table 8.8.6.2.8.8-9 Table 8.8.6.2 Coefficients for Blower Shaft Power Equation Q C 0 C 1 C 2 C 3 Cooling

2 ton 800 34.7637865629 101.257496416 30.819237206 -4.393198813 3 ton 1200 86.8964114725 149.648658529 24.686091998 -1.351144007 4 ton 1600 142.379224744 199.258007379 25.830716411 -0.75624128 5 ton 2000 199.168681228 247.410917528 26.886578305 -0.163068387 High Fire 2 ton 640 17.7814395418 81.4599546929 36.760753941 -6.820695201 3 ton 960 44.4918524165 119.54001273 31.765403864 -3.666136066 4 ton 1280 72.9202558294 159.014401208 33.753367048 -2.927933696 5 ton 1600 101.991203084 197.482373726 35.406395106 -2.130855013 Low Fire

2 ton 533.3 10.2554469313 68.6525919364 41.182715094 -8.986586445 3 ton 800 25.7529563782 99.6988982718 37.766224552 -6.017676309 4 ton 1066.7 42.197172414 132.467356467 40.800818335 -5.419757563 5 ton 1333.3 59.0319912122 164.29823146 43.598086888 -4.793958254

8.8.7 ECM 4.0 MOTOR EFFICIENCY The GE topical report listed the efficiency of the prototype ECM 4.0 motor at two operating conditions. 1 The two points, which roughly span the intended operating range of the prototype motor, are at the target operating condition and at the maximum operating conditions. The motor efficiencies at these two operating conditions were 86.0% and 84.7%, respectively. Figure 8.8.7.1, shows these data points against the targeted operating range of the motor. Based on this, the Department assumed the new motor would operate at constant efficiency of 85%.8.8-10 

### 84.7%

86.0%
1200 1300 1400 1500 1600 1700 1800

100 150 200 250 300 350 400 450 500 H, Shaft Power (W)N, Speed (RPM)

ECM+ Max ECM+ SEER Operating Range

Figure 8.8.7.1 Efficiencies and Operating Range of Prototype Motor

8.8.8 BC/ECM+ BLOWER MOTOR ELECTRICITY CONSUMPTION The shaft power of the BC/ECM+ blower in virtual model furnaces divided by efficiency gives the blower motor electrical power consumption.

BE Hw N QW motor = (, ) η
where = blower speed at operating static pressure of furnace (rpm), 

### N = airflow of wider blower at operating static pressure of furnace QW (cfm), = shaft power of wider blower (W), and H W = motor efficiency. η

moto r8.8-11 REFERENCES 1. Wang, S. and H. Wiegman, Topical Progress Report for the Variable Speed Integrated Intelligent HVAC Blower, November 14, 2001, GE Corporate Research and Development. Niskayuna, NY. 2. American Society for Testing and Materials, Standard Practice for Use of the International System of Units (SI) (the Modernized Metric System) , 1992. Philadelphia, PA. PCN 03-543-092-34

. Report No. E 380-92. 3. Air Movement and Control Association International Inc., Fans and Systems , in AMCA Publication 201-90 . 1990: Arlington Heights, IL. 4. Lau Industries, Whirl Wind IV, Version 4.0, Fan Application Software . 2000. http://www.lau-ind.com/whirlwind.htm