8.6-i

APPENDIX 8.6. FURNACE AIRFLOW CAPACITY TESTING

TABLE OF CONTENTS

8.6.1 SUMMARY ........................................................ 8.6-2

8.6.2 BACKGROUND .................................................... 8.6-2

8.6.3 INTRODUCTION ................................................ 8.6-3

8.6.3.1 Objectives of the Furnace and Blower Airflow Testing ................ 8.6-3

8.6.3.2 How is Airflow Tested Now .................................... 8.6-3

8.6.3.3 Who Did the Testing? ......................................... 8.6-3

8.6.3.4 Which Furnaces and Blowers were Tested? ........................ 8.6-3

8.6.3.5 What Data are Provided in the Carrier Furnace Literature for the Installer? . 8.6-4

8.6.3.6 How was the Testing Conducted? ............................... 8.6-5

8.6.3.7 Basic Description of PSC and ECM Motors ........................ 8.6-5

8.6.3.8 Furnace Circulating-Air Blowers ................................. 8.6-5

8.6.3.9 Testing with AMCA 210 ...................................... 8.6-5

8.6.3.10 How did ESL do the testing? ................................... 8.6-5

8.6.3.11 Differences from a Typical Blower Curve Test by ESL ................ 8.6-6

8.6.3.12 Instrumentation and Test Setup .................................. 8.6-6

8.6.4 RESULTS .......................................................... 8.6-7

8.6.4.1 Should AMCA 210 be Used to Measure Airflow to More 

Accurately Measure Furnace Electrical Energy Use? .................. 8.6-8

8.6.4.2 Are There Energy Savings Benefits Possible for Furnace Blowers? ...... 8.6-10

8.6.5 BLOWER SPEED AND AIRFLOW .................................... 8.6-11

8.6.6 DISCUSSION OF RESULTS ......................................... 8.6-12

8.6.7 CONCLUSIONS ................................................... 8.6-12
8.6-ii

LIST OF FIGURES

Figure 8.6.3.1 Schematic of Airflow Apparatus – from Figure 12 of AMCA 210 ........ 8.6-6

Figure 8.6.3.2 Airflow Measurement Apparatus at Energy System Laboratory ......... 8.6-7

Figure 8.6.4.1 Airflow versus Static Pressure for Three Motor/Blower Combinations at 

Highest Speed .............................................. 8.6-9

Figure 8.6.4.2 Comparison with Manufacturer's Reported Airflow versus Static Pressure 

Data at the Highest Blower Speed .............................. 8.6-10

Figure 8.6.4.3 Airflow Efficiency versus Static Pressure at Highest Blower Speed Setting . 8.6-11

Figure 8.6.5.1 Blower Speed versus Airflow .................................. 8.6-12
8.6-2

APPENDIX 8.6. FURNACE AIRFLOW CAPACITY TESTING

8.6.1 SUMMARY

This Appendix provides a discussion of the task of testing various circulating-air blowers in a

common-size furnace to assess the applicability of using the Air Movement and Control Association

test standard 210 (AMCA 210) as a method of determining the airflow capacity of a furnace

circulating-air blower.

8.6.2 BACKGROUND

Furnace manufacturers already use and report a measure of furnace electrical energy—the

annual auxiliary electrical energy (EAE) parameter. One method of setting a maximum level of electrical

energy consumption without requiring extensive revision to the furnace test procedure could be to set

limits on EAE. However, the maximum EAE limit should depend on the maximum airflow of the

circulating-air blower. The Department needs to take into consideration the maximum airflow capacity

of the furnace because some furnaces of the same input—such as furnaces coupled with larger splitsystem air conditioners—require larger airflow-capacity circulating-air blowers to accommodate the

larger cooling function. When a furnace is intended to be installed with a larger air conditioner, it is

manufactured with a larger circulating-air blower. If a furnace is designed to provide more airflow, then

it will necessarily use more electricity. The Department thus needed to determine a method of

measuring the maximum circulating blower airflow capacity. 

To simplify the test procedure, the Department to considered maximum air-flow capacity at 0.5

inches water gauge (in.w.g.) of external static pressure (ESP). Manufacturer literature typically

categorizes the cooling capacity that a furnace is designed to handle based on the amount of airflow the

furnace can deliver at 0.5 in.w.g. In the product literature of their furnaces, manufacturers provide

tables of airflow at a range of ESPs, including airflow at 0.5 in.w.g. If the furnace has multiple settings

to provide different amounts of airflow, the product literature will include tables of airflow by ESP for

every setting. 
8.6-3

8.6.3 INTRODUCTION

8.6.3.1 Objectives of the Furnace and Blower Airflow Testing

The objectives of the furnace blower testing were to:

C gauge the appropriateness of using AMCA 210 for measuring furnace airflow and identify

potential testing difficulties, and to 

C identify any potential issues with regard to testing different types of motor and blower

combinations.

8.6.3.2 How is Airflow Tested Now

It is the Department’s understanding that the airflow and static pressures reported in product

literature are typically determined using a “code tester,” i.e., an airflow-measurement apparatus based

on the existing test procedure ANSI/AMCA 210-99/ASHRAE 51-1999. However, DOE only found

anecdotal information on how furnace airflow is determined. 

Furnaces with electronically commutated motor (ECM) blower motors are often designed to

provide constant airflow across the entire range of external static pressures. A consultant reported that

at least one manufacturer uses a modified AMCA 210 method to determine air flow of furnaces with

ECM blower motors. The motor controller are bypassed and the motor is set to run at specific speeds. 

Data collected based on the AMCA 210 test method is recorded at each motor speed. These results

are then used, along with the motor control algorithm, to determine the power consumption at various

static pressures for constant cubic-feet-per-minute (cfm) operation. The procedure used by this

manufacturer may not be the same for all manufacturers. 

8.6.3.3 Who Did the Testing?

To test the blowers for this task, Lawrence Berkeley National Laboratory (LBNL) contracted

with the Energy Systems Laboratory (ESL), which is affiliated with Texas A&M University and has a

long history of testing blowers. In fact, ESL was previously an official test facility of AMCA, which

now does all of its certification at its own laboratory.

8.6.3.4 Which Furnaces and Blowers were Tested?

The Department selected two furnaces for testing that were as similar as possible, except for

their blower-motor types. The furnaces have 88 kBtu input and are designed for use with up to a fourton air conditioner. The entire project at ESL consisted of testing the following three combinations of

motors and blowers in the same size furnace:
8.6-4

1. Permanent split capacitor (PSC) motor with forward-inclined blower wheel 

(Carrier 58CTA090-14, 88 kBtuh, 3.5 ton AC, 10x8 Blower Size);

2. GE ECM 2.3 motor with forward-inclined blower wheel 

(Carrier 58CVA090-16, 2-stage, 88 kBtuh, 1.5- 4 Ton AC, 10x8 Blower Size); and

3. GE ECM 4.0 prototype motor combined with a prototype backward-inclined blower wheel. 

(GE supplied the sample motor / blower / blower wheel to DOE. See memorandum Integrated

Intelligent Blower , November 1, 2002; Project DE-FC26-00NT40993 for a complete

description of the prototype. It was installed into the Carrier 58CVA090-16 furnace housing.)

ESL tested each of the above blower-motor combinations, both installed in a furnace and as a

blower unit alone.

8.6.3.5 What Data are Provided in the Carrier Furnace Literature for the Installer?

Details on the tested furnaces can be found at the manufacturer web sites below.

Owners Manuals

C http://www.commercial.carrier.com/details/0,1240,CLI1_DIV12_ETI3757,00.html?S

MSESSION=NO

C http://www.commercial.carrier.com/wcs/literature_model_search/0,,CLI1_DIV12_ETI

499,00.html?SMIDENTITY=NO

Product Drawings

C http://www.residential.carrier.com/products/gas_furnaces/58cva_cvx.htm

For the ECM motor, the airflow is given in cfm, at static pressures from 0.1 to 1.0 ESP, for

each operation mode. The static pressure includes the resistance of an air filter. Operating modes

include low heat, high heat, air-conditioning capacities from 1.5 ton to 4 ton, and maximum airflow. 

For the PSC motor, the cfm is given for ESPs of 0.1 to 1.0 in. wg. for four speeds: low, medlow, med-high, and high.

The GE blower, ECM 4.0 is a prototype and did not come with a manual.
8.6-5

8.6.3.6 How was the Testing Conducted?

ESL performed the furnace tests without an air conditioner evaporator coil. Gas was not

connected, so the furnace was not providing heat during the test. ESL measured airflow as specified by

AMCA 210-99 Figure 12, to produce a fan curve. ESL performed testing for high speed, and

reported both actual and standard (adjusted to standard temperature and pressure) airflow data. In

addition, ESL measured blower motor power consumption at each point measured for airflow.

8.6.3.7 Basic Description of PSC and ECM Motors

PSC motor - Permanent split capacitor single-phase induction motor. The majority of

residential furnaces currently use PSC motors. 

ECM motor - The electrically-commutated motor is a permanent-magnet, brushless directcurrent (DC) motor (go to www.GEindustrial.com, enter keyword: ECM). In furnaces, ECM motors

typically are combined with controls that allow the installer to set the airflow desired. The blower will

then vary the speed and torque of the motor to achieve the desired airflow, regardless of the external

static pressure drop.

8.6.3.8 Furnace Circulating-Air Blowers

Most residential circulating-air blowers use a blower wheel with forward-curved blades. The

GE 4.0 Prototype has a backward inclined blower.

8.6.3.9 Testing with AMCA 210

The method of test, AMCA 210, provides several procedures for testing blowers. It also

specifies the equations to correct to standard conditions. However, even with this test standard, there

can be differences on some of the testing details, since the tester is given a choice of test apparatus

configurations. The Department based the tests reported in this Appendix on Figure 12 of the AMCA

210 test procedure. In this test configuration, the blower or furnace inlet is open to air and the outlet is

connected to the airflow apparatus.

8.6.3.10 How did ESL do the testing?

AMCA 210 is written as a test procedure for blowers. ESL tested the air flow with the

blowers installed in the furnace. In addition, ESL tested the PSC blower outside of the furnace. ESL

measured the furnace airflow with the filter housing installed, but without the air filter installed (so as not

to create another variable in determining airflow)—thus increasing the repeatability of the tests. The

primary output of fan testing is a plot of static pressure versus airflow. Watts are also plotted versus
8.6-6

airflow on the same chart. The Department corrected the data plotted as per AMCA 210 equations,

although ESL also made available the original uncorrected data.

8.6.3.11 Differences from a Typical Blower Curve Test by ESL

Typically, ESL tests airflow at ten points, including complete airflow shutoff. This is done in

equal increments of airflow quantity (cfm). In this case, the Department instructed ESL to instead

measure ten data points based on even increments of static pressure at the furnace outlet. The original

plan was to start at 0 in. wg static pressure and increase the airflow in 0.1 in. wg increments. Typically,

the data points are connected by a smooth curve based on airflow affinity laws.

The departure from normal test point selection was due to how ECM motors are used in a

furnace. Unlike PSC motors, an ECM motor combined with furnace control circuitry is designed to

provide constant airflow, regardless of the external static pressure. It accomplishes this by controlling

the speed and torque of the motor.

8.6.3.12 Instrumentation and Test Setup

Figure 8.6.3.1 is a schematic of the airflow test apparatus. (See AMCA 210 Figure 12 for a

detailed explanation.)

Figure 8.6.3.1 Schematic of Airflow Apparatus – from Figure 12 of AMCA 210
8.6-7

Figure 8.6.3.2 is a photograph of the apparatus used for the test. Note that the photograph is

in the opposite orientation from the schematic shown in Figure 8.6.3.1 (AMCA schematic Figure 12). 

The inlet, where the furnace or blower would be mounted, is on the right side of the photograph. The

airflow exit and variable speed blower that sets the static pressure are on the left.

Figure 8.6.3.2 Airflow Measurement Apparatus at Energy System Laboratory

8.6.4 RESULTS

The testing results provided additional information in the following areas:

• Should AMCA 210 test procedure be used to measure furnace airflow?

• Are there energy savings benefits possible for furnace blowers?

• What are the characteristics of blower curves at other than the highest speed?
8.6-8

8.6.4.1 Should AMCA 210 be Used to Measure Airflow to More Accurately Measure

Furnace Electrical Energy Use?

The Department measured airflow against various static pressures to determine if there are any

problems with using the AMCA 210 test methods for measuring the airflow of furnaces, especially at

0.5 in. wg ESP, which is used as a reference point during cooling season operation. Figure 8.6.4.1

shows static pressure-versus-airflow results for PSC, ECM2.3, and ECM4.0 motor types at high

speed.

While it was possible to measure airflow at 0.1 in. wg for the PSC blower, 0.5 in. wg pressure

was the lowest possible ESP at which ESL could obtain results for blowers with ECM motors. It is not

obvious why this was a problem, since manufacturer literature reports airflow measurements down to

0.1 in. wg. The ESL airflow testing with the ECM motors/blowers showed that, as the static pressure

was decreased below about 0.5 in. wg, the speed would also decrease. This was an even greater

problem when the blower was tested outside of the furnace. Because of this discrepancy between the

ESL test results and the manufacturer-reported data, the Department concluded that the AMCA 210

test procedure, as it is, can not be used for testing blowers with ECM motors.

As expected, Figure 8.6.4.1 also shows that there is less variation in airflow with a change in

static pressure for the ECM motor blowers. In the case of ECM 4.0 and ECM 2.3 motors (blower

with backward-inclined blades and forward-inclined blades), as ESP goes down, cfm increases. In the

case of PSC motors (blower with forward-inclined blades), as ESP goes down, cfm increases.
8.6-9

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

600 800 1000 1200 1400 1600 1800

Airflow (CFM)

External Static Pressure (in.w.g.)

ECM4.0

ECM2.3

PSC

Figure 8.6.4.1 Airflow versus Static Pressure for Three Motor/Blower

Combinations at Highest Speed

Figure 8.6.4.2 compares static-pressure-with-airflow curves for ESL test data and data

published by the manufacturer in the product literature, at the highest airflow. Note that, for the case of

a PSC motor, the tested airflow was greater than the manufacturer’s reported airflow, whereas for the

ECM motor, the tested airflow was lower than what the manufacturer reported. Additional research is

needed to explain the observed differences between the manufacturer’s results and ESL test results.
8.6-10

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

600 800 1000 1200 1400 1600 1800

Airflow (CFM)

Static Pressure (in. w.g.)

ECM 2.3

MFR ECM2.3

PSC

MFR PSC

PSC

PSC 

manufacturer

ECM 2.3

ECM 2.3 

manufacturer

Figure 8.6.4.2 Comparison with Manufacturer's Reported Airflow versus Static

Pressure Data at the Highest Blower Speed

8.6.4.2 Are There Energy Savings Benefits Possible for Furnace Blowers?

Figure 8.6.4.3 shows that, at a given static pressure, the cfm per watt is higher for the ECM

motors than for the PSC motor. These results contradicted the Department’s expectations that the

ECM 4.0 motor with the backward-inclined blower wheel blades would use less energy than the ECM

2.3 motor. Because the ECM 4.0 motor was installed in a standard blower scroll in an un-optimized

prototype assembly, its performance may be less than could normally be achieved. One factor

decreasing performance could be the larger prototype motor blocking more of the airflow at the blower

inlet. Also, the outlet area of the prototype blower may have been restricted more than it needed to be. 

Adjusting the furnace so the blower outlet area is not blocked off (as it needs to be for forward-inclined

blowers) should increase the blower efficiency. This could be optimized in furnaces manufactured at

high production volumes.
8.6-11

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.5 1.0 1.5

Static Pressure (in. w.g.)

Airflow per Unit Power Input

(cfm / Watt)

ECM4.0

ECM2.3

PSC

Figure 8.6.4.3 AirflowEfficiency versus Static Pressure at HighestBlower Speed

Setting

8.6.5 BLOWER SPEED AND AIRFLOW

The ECM motor/blowers can be set to a specific airflow by controlling the blower speed. 

Figure 8.6.5.1 demonstrates blower speed versus airflow for all three tested blower/motor

combinations. The speed and torque are controlled by an electronic control board. The ECM blowers

are designed to attempt to keep the airflow constant regardless of the external static pressure. Note

that the ECM 4.0 speed is much higher than the speed for the ECM 2.3 and PSC motor/blowers. The

higher speed is a requirement of using backward-inclined blades, instead of forward-curved blades, on

a blower.
8.6-12

600

800

1000

1200

1400

1600

1800

2000

2200

600 800 1000 1200 1400 1600 1800

Airflow (CFM)

Speed (RPM)

ECM4.0

ECM2.3

PSC

Figure 8.6.5.1 Blower Speed versus Airflow

8.6.6 DISCUSSION OF RESULTS

The ESL tests for furnaces with ECM motors do not report measurements below 0.5 in.w.g.

ESP. This is because, during the testing of the three furnace blower/motor combinations, as the static

pressure was decreased the motors would slow down and start to rotate in the opposite direction. In

some cases, if the furnace was set at a lower-than-maximum blower speed, it was impossible to

measure the airflow at static pressures as low as 0.5 in.w.g. This means that, for some furnace designs,

it may not be possible to test airflow at 0.5 in.w.g. static pressure with the current AMCA 210

protocol. Possible solutions to this issue should be examined.

8.6.7 CONCLUSIONS

Testing has determined that simply referencing the AMCA 210 test procedure to measure

furnace blower airflow at 0.5 in.w.g. ESP is insufficient. The Department found differences between

the AMCA 210 test results and the manufacturer’s reported data. These may be due to differences in

the test setup or in the testing methods. Measurement of airflow in furnaces using ECM motors

requires further investigation.