Prior to January 23, 2017, manufacturers must make any representations with respect to the energy use or efficiency of ceiling fans as specified in Section 2 of this appendix (other than hugger ceiling fans, multi-mount ceiling fans in the hugger configuration, and large-diameter ceiling fans) in accordance with the results of testing pursuant either to this appendix, or to the applicable test requirements set forth in 10 CFR parts 429 and 430, as they appeared in the 10 CFR parts 200 to 499 edition revised as of January 1, 2016. On or after January 23, 2017, manufacturers of ceiling fans, as specified in Section 2 of this appendix, must make any representations with respect to energy use or efficiency in accordance with the results of testing pursuant to this appendix.

1. Definitions:

1.1. 20% speed means the ceiling fan speed at which the blade RPM are measured to be 20% of the blade RPM measured at high speed.

1.2. 40% speed means the ceiling fan speed at which the blade RPM are measured to be 40% of the blade RPM measured at high speed.

1.3. 60% speed means the ceiling fan speed at which the blade RPM are measured to be 60% of the blade RPM measured at high speed.

1.4. 80% speed means the ceiling fan speed at which the blade RPM are measured to be 80% of the blade RPM measured at high speed.

1.5. Airflow means the rate of air movement at a specific fan-speed setting expressed in cubic feet per minute (CFM).

1.6. Belt-driven ceiling fan means a ceiling fan with a series of one or more fan heads, each driven by a belt connected to one or more motors that are located outside of the fan head.

1.7. Blade span means the diameter of the largest circle swept by any part of the fan blade assembly, including any blade attachments.

1.8. Ceiling fan efficiency means the ratio of the total airflow to the total power consumption, in units of cubic feet per minute per watt (CFM/W).

1.9. Centrifugal ceiling fan means a ceiling fan for which the primary airflow direction is in the same plane as the rotation of the fan blades.

1.10. High speed means the highest available ceiling fan speed, i.e., the fan speed corresponding to the maximum blade revolutions per minute (RPM).

1.11. High-speed small-diameter ceiling fan means a small-diameter ceiling fan that is not a very-small-diameter ceiling fan, highly-decorative ceiling fan or belt-driven ceiling fan and that has a blade thickness of less than 3.2 mm at the edge or a maximum tip speed greater than the applicable limit specified in the table in this definition.

1.12. Highly-decorative ceiling fan means a ceiling with a maximum rotational speed of 90 RPM and less than 1,840 CFM airflow at high speed, as determined by sections 3 and 4 of this appendix.

1.13. Hugger ceiling fan means a low-speed small-diameter ceiling fan that is not a very-small-diameter ceiling fan, highly-decorative ceiling fan or belt-driven ceiling fan; for which the lowest point on the fan blades is less than or equal to 10 inches from the ceiling.

1.14. Large-diameter ceiling fan means a ceiling fan that is greater than seven feet in diameter.

1.15. Low speed means the lowest available ceiling fan speed, i.e., the fan speed corresponding to the minimum, non-zero, blade RPM.

1.16. Low-speed small-diameter ceiling fan means a small-diameter ceiling fan that has a blade thickness greater than or equal to 3.2 mm at the edge and a maximum tip speed less than or equal to the applicable limit specified in the table in this definition.

1.17. Multi-head ceiling fan means a ceiling fan with more than one fan head, i.e., more than one set of rotating fan blades.

1.18. Multi-mount ceiling fan means a low-speed small-diameter ceiling fan that can be mounted in the configurations associated with both the standard and hugger ceiling fans.

1.19. Oscillating ceiling fan means a ceiling fan containing one or more fan heads for which the axis of rotation of the fan blades cannot remain in a fixed position relative to the ceiling. Such fans have no inherent means by which to disable the oscillating function separate from the fan blade rotation.

1.20. Small-diameter ceiling fan means a ceiling fan that is less than or equal to seven feet in diameter.

1.21. Standard ceiling fan means a low-speed small-diameter ceiling fan that is not a very-small-diameter ceiling fan, highly-decorative ceiling fan or belt-driven ceiling fan; for which the lowest point on fan blades is greater than 10 inches from the ceiling.

1.22. Total airflow means the sum of the product of airflow and hours of operation at all tested speeds. For multi-head fans, this includes the airflow from all fan heads.

1.23. Very-small-diameter ceiling fan means a small-diameter ceiling fan that is not a highly-decorative ceiling fan or belt-driven ceiling fan; and has one or more fan heads, each of which has a blade span of 18 inches or less.

2. Scope:

The provisions in this appendix apply to ceiling fans except:

(1) Ceiling fans where the plane of rotation of a ceiling fan's blades is not less than or equal to 45 degrees from horizontal, or cannot be adjusted based on the manufacturer's specifications to be less than or equal to 45 degrees from horizontal;

(2) Centrifugal ceiling fans;

(3) Belt-driven ceiling fans; and

(4) Oscillating ceiling fans.

3. General Instructions, Test Apparatus, and Test Measurement:

The test apparatus and test measurement used to determine energy performance depend on the ceiling fan's blade span. For each tested ceiling fan, measure the lateral distance from the center of the axis of rotation of the fan blades to the furthest fan blade edge from the center of the axis of rotation, and multiply this distance by two. The blade span for a basic model of ceiling fan is then calculated as the arithmetic mean of this distance across each ceiling fan in the sample, rounded to the nearest inch.

3.1. General instructions.

3.1.1. Record measurements at the resolution of the test instrumentation. Round off calculations to the number of significant digits present at the resolution of the test instrumentation, except for blade span, which is rounded to the nearest inch. Round the final ceiling fan efficiency value to the nearest whole number as follows:

3.1.1.1. A fractional number at or above the midpoint between the two consecutive whole numbers shall be rounded up to the higher of the two whole numbers; or

3.1.1.2. A fractional number below the midpoint between the two consecutive whole numbers shall be rounded down to the lower of the two whole numbers.

3.1.2. For multi-head ceiling fans, the effective blade span is the blade span (as specified in section 3) of an individual fan head, if all fan heads are the same size. If the fan heads are of varying sizes, the effective blade span is the blade span (as specified in section 3) of the largest fan head.

3.2. Test apparatus for low-speed small-diameter and high-speed small-diameter ceiling fans: All instruments are to have accuracies within ±1% of reading, except for the air velocity sensors, which must have accuracies within ±5% of reading or 2 feet per minute (fpm), whichever is greater. Equipment is to be calibrated at least once a year to compensate for variation over time.

3.2.1. Air Delivery Room Requirements

(1) The air delivery room dimensions are to be 20 ± 0.75 feet x 20 ± 0.75 feet with an 11 ± 0.75 foot-high ceiling. The control room shall be constructed external to the air delivery room.

(2) The ceiling shall be constructed of sheet rock or stainless plate. The walls must be of adequate thickness to maintain the specified temperature and humidity during the test. The paint used on the walls, as well as the paint used on the ceiling material, must be of a type that minimizes absorption of humidity and that keeps the temperature of the room constant during the test (e.g., oil-based paint).

(3) The room must not have any ventilation other than an air conditioning and return system used to control the temperature and humidity of the room. The construction of the room must ensure consistent air circulation patterns within the room. Vents must have electronically-operated damper doors controllable from a switch outside of the testing room.

3.2.2. Equipment Set-Up

(1) Make sure the transformer power is off. Hang the ceiling fan to be tested directly from the ceiling, according to the manufacturer's installation instructions. Hang all non-multi-mount ceiling fans in the fan configuration that minimizes the distance between the ceiling and the lowest point of the fan blades. Hang and test multi-mount fans in two configurations: The configuration associated with the definitions of a standard fan that minimizes the distance between the ceiling and the lowest point of the fan blades and the configuration associated with the definition of a hugger fan that minimizes the distance between the ceiling and the lowest point of the fan blades.

(2) Connect wires as directed by manufacturer's wiring instructions. Note: Assemble fan prior to the test; lab personnel must follow the instructions provided with the fan by the fan manufacturer. Balance the fan blade assembly in accordance with the manufacturer's instructions to avoid excessive vibration of the motor assembly (at any speed) during operation.

(3) With the ceiling fan installed, adjust the height of the air velocity sensors to ensure the vertical distance between the lowest point on the ceiling fan blades and the air velocity sensors is 43 inches.

(4) Either a rotating sensor arm or four fixed sensor arms can be used to take airflow measurements along four axes, labeled A-D. Axes A, B, C, and D are at 0, 90, 180, and 270 degree positions. Axes A-D must be perpendicular to the four walls of the room. See Figure 1 of this appendix.

(5) Minimize the amount of exposed wiring. Store all sensor lead wires under the floor, if possible.

(6) Place the sensors at intervals of 4 ± 0.0625 inches along a sensor arm, starting with the first sensor at the point where the four axes intersect. Do not touch the actual sensor prior to testing. Use enough sensors to record air delivery within a circle 8 inches larger in diameter than the blade span of the ceiling fan being tested. The experimental set-up is shown in Figure 2 of this appendix.

(7) Table 1 of this appendix shows the appropriate number of sensors needed per each of four axes (including the first sensor at the intersection of the axes) for common fan sizes.

(8) Install an RPM (revolutions per minute) meter, or tachometer, to measure RPM of the ceiling fan blades.

(9) Use an RMS sensor capable of measuring power with an accuracy of ±1% to measure ceiling fan power consumption. If the ceiling fan operates on multi-phase power input, measure the active (real) power in all phases simultaneously. Measure test voltage within 6” of the connection supplied with the ceiling fan.

(10) Complete any conditioning instructions provided in the ceiling fan's instruction or installation manual must be completed prior to conducting testing.

3.2.3. Multi-Head Ceiling Fan Test Set-Up

Hang a multi-headed ceiling fan from the ceiling such that one of the ceiling fan heads is centered directly over sensor 1 (i.e., at the intersection of axes A, B, C, and D). The distance between the lowest point any of the fan blades of the centered fan head can reach and the air velocity sensors is to be such that it is the same as for all other small-diameter ceiling fans (see Figure 2 of this appendix). If the multi-head ceiling fan has an oscillating function (i.e., the fan heads change their axis of rotation relative to the ceiling) that can be switched off, switch it off prior to taking airflow measurements. If any multi-head fan does not come with the blades preinstalled, install fan blades only on the fan head that will be directly centered over the intersection of the sensor axes. (Even if the fan heads in a multi-head ceiling fan would typically oscillate when the blades are installed on all fan heads, the ceiling fan is subject to this test procedure if the centered fan head does not oscillate when it is the only fan head with the blades installed.) If the fan blades are preinstalled on all fan heads, measure airflow in accordance with section 3.3 except only turn on the centered fan head. Measure the power consumption measurements are to be made separately, with the fan blades installed on all fan heads and with any oscillating function, if present, switched on.

3.2.4. Test Set-Up for Ceiling Fans with Airflow Not Directly Downward

For ceiling fans where the airflow is not directly downward, adjust the ceiling fan head such that the airflow is as vertical as possible prior to testing. For ceiling fans where a fully vertical orientation of airflow cannot be achieved, orient the ceiling fan (or fan head, if the ceiling fan is a multi-head fan) such that any remaining tilt is aligned along one of the four sensor axes. Instead of measuring the air velocity for only those sensors directly beneath the ceiling fan, the air velocity is to be measured at all sensors along that axis, as well as the axis oriented 180 degrees with respect to that axis. For example, if the tilt is oriented along axis A, air velocity measurements are to be taken for all sensors along the A-C axis. No measurements would need to be taken along the B-D axis in this case. All other aspects of test set-up remain unchanged from sections 3 through 3.2.2.

3.3. Active mode test measurement for low-speed small-diameter and high-speed small-diameter ceiling fans.

3.3.1. Test conditions to be followed when testing:

(1) Maintain the room temperature at 70 degrees ± 5 degrees Fahrenheit and the room humidity at 50% ± 5% relative humidity during the entire test process.

(2) If present, the ceiling fan light fixture is to be installed but turned off during testing.

(3) If present, any heater is to be installed but turned off during testing.

(4) If present, turn off any oscillating function causing the axis of rotation of the fan head(s) to change relative to the ceiling during operation prior to taking airflow measurements. Turn on any oscillating function prior to taking power measurements.

(5) The supply voltage shall be:

(i) 120 V if the ceiling fan's minimum rated voltage is 120 V or the lowest rated voltage range contains 120 V,

(ii) 240 V if the ceiling fan's minimum rated voltage is 240 V or the lowest rated voltage range contains 240 V, or

(iii) The ceiling fan's minimum rated voltage (if a voltage range is not given) or the mean of the lowest rated voltage range, in all other cases. The test voltage shall not vary by more than ±1% during the tests.

(6) Test ceiling fans rated for operation with only a single- or multi-phase power supply with single- or multi-phase electricity, respectively. Measure active (real) power in all phases continuously when testing. Test ceiling fans capable of operating with single- and multi-phase electricity with single-phase electricity. DOE will allow manufacturers of ceiling fans capable of operating with single- and multi-phase electricity to test such fans with multi-phase power and make representations of efficiency associated with both single and multi-phase electricity if a manufacturer desires to do so, but the test results in the multi-phase configuration will not be valid to assess compliance with any amended energy conservation standard.

(7) Conduct the test with the fan connected to a supply circuit at the rated frequency.

(8) Measure power input at a point that includes all power-consuming components of the ceiling fan (but without any attached light kit or heater energized).

3.3.2. Airflow and Power Consumption Testing Procedure:

Measure the airflow (CFM) and power consumption (W) for HSSD ceiling fans until stable measurements are achieved, measuring at high speed only. Measure the airflow and power consumption for LSSD ceiling fans until stable measurements are achieved, measuring first at low speed and then at high speed. Airflow and power consumption measurements are considered stable if:

(1) The average air velocity for all axes for each sensor varies by less than 5% compared to the average air velocity measured for that same sensor in a successive set of air velocity measurements, and

(2) Average power consumption varies by less than 1% in a successive set of power consumption measurements. These stability criteria are applied differently to ceiling fans with airflow not directly downward. See section 4.1.2 of this appendix.

Step 1: Set the first sensor arm (if using four fixed arms) or single sensor arm (if using a single rotating arm) to the 0 degree Position (Axis A). If necessary, use a marking as reference. If using a single rotating arm, adjust the sensor arm alignment until it is at the 0 degree position by remotely controlling the antenna rotator.

Step 2: Set software up to read and record air velocity, expressed in feet per minute (FPM) in 1 second intervals. (Temperature does not need to be recorded in 1 second intervals.) Record current barometric pressure.

Step 3: Allow test fan to run 15 minutes at rated voltage and at high speed if the ceiling fan is an HSSD ceiling fan. If the ceiling fan is an LSSD ceiling fan, allow the test fan to run 15 minutes at the rated voltage and at low speed. Turn off all forced-air environmental conditioning equipment entering the chamber (e.g., air conditioning), close all doors and vents, and wait an additional 3 minutes prior to starting test session.

Step 4: Begin recording readings. Take 100 airflow velocity readings (100 seconds run-time) and save these data. If using a rotating sensor arm, this is axis A. For all fans except multi-head fans and fans capable of oscillating, measure power during the interval that air velocity measurements are taken. Record the average value of the power measurement in watts (W).

Step 5: Similarly, take 100 air velocity readings (100 seconds run-time) for Axes B, C, and D; save these data as well. Measure power as described in Step 4. If using four fixed sensor arms, take the readings for all sensor arms simultaneously.

Step 6: Repeat Steps 4 and 5 until stable measurements are achieved.

Step 7: Repeat steps 1 through 6 above on high fan speed for LSSD ceiling fans. Note: Ensure that temperature and humidity readings are maintained within the required tolerances for the duration of the test (all tested speeds). Forced-air environmental conditioning equipment may be used and doors and vents may be opened between test sessions to maintain environmental conditions.

Step 8: If testing a multi-mount ceiling fan, repeat steps 1 through 7 with the ceiling fan in the ceiling fan configuration (associated with either hugger or standard ceiling fans) not already tested.

If a multi-head ceiling fan includes more than one category of ceiling fan head, then test at least one of each unique category. A fan head with different construction that could affect air movement or power consumption, such as housing, blade pitch, or motor, would constitute a different category of fan head.

Step 9: For multi-head ceiling fans, measure active (real) power consumption in all phases simultaneously at each speed continuously for 100 seconds with all fan heads turned on, and record the average value at each speed in watts (W).

For ceiling fans with an oscillating function, measure active (real) power consumption in all phases simultaneously at each speed continuously for 100 seconds with the oscillating function turned on. Record the average value of the power measurement in watts (W).

For both multi-head ceiling fans and fans with an oscillating function, repeat power consumption measurement until stable power measurements are achieved.

3.4. Test apparatus for large-diameter ceiling fans:

The test apparatus and instructions for testing large-diameter ceiling fans must conform to the requirements specified in sections 3 through 7 of AMCA 230-15 (incorporated by reference, see §430.3), with the following modifications:

3.4.1. The test procedure is applicable to large-diameter ceiling fans up to 24 feet in diameter.

3.4.2. A “ceiling fan” is defined as in 10 CFR 430.2.

3.4.3. The supply voltage shall be (1) 120 V if the ceiling fan's minimum rated voltage is 120 V or the lowest rated voltage range contains 120 V, (2) 240 V if the ceiling fan's minimum rated voltage is 240 V or the lowest rated voltage range contains 240 V, or (3) the ceiling fan's minimum rated voltage (if a voltage range is not given) or the mean of the lowest rated voltage range, in all other cases.

3.4.4. Test ceiling fans rated for operation with only a single- or multi-phase power supply with single- or multi-phase electricity, respectively. Test ceiling fans capable of operating with single- and multi-phase electricity with multi-phase electricity. DOE will allow manufacturers of ceiling fans capable of operating with single- and multi-phase electricity to test such fans with single-phase power and make representations of efficiency associated with both single and multi-phase electricity if a manufacturer desires to do so, but the test results in the single-phase configuration will not be valid to assess compliance with any amended energy conservation standard.

3.5. Active mode test measurement for large-diameter ceiling fans:

(1) Calculate the airflow (CFM) and measure the active (real) power consumption (W) in all phases simultaneously for ceiling fans at the speeds specified in Table 2.

(2) When testing at speeds other than high speed (i.e., X% speed where X is 80, 60, 40, or 20) for ceiling fans that can operate over an infinite number of speeds (e.g., ceiling fans with VFDs), ensure the average measured RPM is within the greater of 1% of the average RPM at high speed or 1 RPM. For example, if the average measured RPM at high speed is 50 RPM, for testing at 80% speed the average measured RPM should be between 39 RPM and 41 RPM. If the average measured RPM falls outside of this tolerance, adjust the ceiling fan speed and repeat the test. Calculate the airflow and measure the active (real) power consumption in all phases simultaneously in accordance with the test requirements specified in sections 8 and 9, AMCA 230-15 (incorporated by reference, see §430.3), with the following modifications:

3.5.1. Measure active (real) power consumption in all phases simultaneously at a point that includes all power-consuming components of the ceiling fan (but without any attached light kit or heater energized).

3.5.2. Measure active (real) power consumption in all phases simultaneously continuously at the rated voltage that represents normal operation over the time period for which the load differential test is conducted.

3.6. Test measurement for standby power consumption.

(1) Measure standby power consumption if the ceiling fan offers one or more of the following user-oriented or protective functions:

☐☐o   The ability to facilitate the activation or deactivation of other functions (including active mode) by remote switch (including remote control), internal sensor, or timer.

☐   Continuous functions, including information or status displays (including clocks), or sensor-based functions.

(2) Measure standby power consumption after completion of active mode testing and after the active mode functionality has been switched off (i.e., the rotation of the ceiling fan blades is no longer energized). The ceiling fan must remain connected to the main power supply and be in the same configuration as in active mode (i.e., any ceiling fan light fixture should still be attached). Measure standby power consumption according to sections 4 and 5.3.1 through 5.3.2 of IEC 62301-U (incorporated by reference, see §430.3) with the following modifications:

3.6.1. Allow 3 minutes between switching off active mode functionality and beginning the standby power test. (No additional time before measurement is required.)

3.6.2. Simultaneously in all phases, measure active (real) power consumption continuously for 100 seconds, and record the average value of the standby power measurement in watts (W).

3.6.3. Determine power consumption according to section 5.3.2 of IEC 62301-U, or by using the following average reading method. Note that a shorter measurement period may be possible using the sample method in section 5.3.2 of IEC 62301-U.

(1) Connect the product to the power supply and power measuring instrument.

(2) Select the mode to be measured (which may require a sequence of operations and could require waiting for the product to automatically enter the desired mode) and then monitor the power.

(3) Calculate the average power using either the average power method or the accumulated energy method. For the average power method, where the power measuring instrument can record true average power over an operator selected period, the average power is taken directly from the power measuring instrument. For the accumulated energy method, determine the average power by dividing the measured energy by the time for the monitoring period. Use units of watt-hours and hours for both methods to determine average power in watts.

4. Calculation of Ceiling Fan Efficiency From the Test Results:

(1) The efficacy of a ceiling fan is the ceiling fan efficiency (as defined in section 1 of this appendix). Calculate two ceiling fan efficiencies for multi-mount ceiling fans: One efficiency corresponds to the ceiling fan mounted in the configuration associated with the definition of a hugger ceiling fan, and the other efficiency corresponds to the ceiling fan mounted in the configuration associated with the definition of a standard ceiling fan.

(2) Calculate fan efficiency using the average of both sets of airflow and power measurements from the successive sets of measurements that meet the stability criteria.

(3) To calculate the measured airflow for HSSD and LSSD ceiling fans, multiply the average air velocity measurement at each sensor from section 3.3 of this appendix (for high speed for HSSD ceiling fans, and for high and low speeds for LSSD ceiling fans) with the sensor's effective area (explained below), and then sum the products to obtain the overall measured airflow at the tested speed. Using the airflow and the power consumption measurements from sections 3.3 and 3.5 of this appendix (for all tested settings for large-diameter ceiling fans) calculate the efficiency for any ceiling fan as follows:

Where:

CFMi = airflow at speed i,

OHi = operating hours at speed i,

Wi = power consumption at speed i,

OHSb = operating hours in standby mode, and

WSb = power consumption in standby mode.

(4) Table 3 of this appendix specifies the daily hours of operation to be used in calculating ceiling fan efficiency:

(5) Calculate the effective area corresponding to each sensor used in the test method for small-diameter ceiling fans with the following equations:

(6) For sensor 1, the sensor located directly underneath the center of the ceiling fan, the effective width of the circle is 2 inches, and the effective area is:

(7) For the sensors between sensor 1 and the last sensor used in the measurement, the effective area has a width of 4 inches. If a sensor is a distance d, in inches, from sensor 1, then the effective area is:

(8) For the last sensor, the width of the effective area depends on the horizontal displacement between the last sensor and the point on the ceiling fan blades furthest radially from the center of the fan. The total area included in an airflow calculation is the area of a circle 8 inches larger in diameter than the ceiling fan blade span (as specified in section 3 of this appendix).

(9) Therefore, for example, for a 42-inch ceiling fan, the last sensor is 3 inches beyond the end of the ceiling fan blades. Because only the area within 4 inches of the end of the ceiling fan blades is included in the airflow calculation, the effective width of the circle corresponding to the last sensor would be 3 inches. The calculation for the effective area corresponding to the last sensor would then be:

(10) For a 46-inch ceiling fan, the effective area of the last sensor would have a width of 5 inches, and the effective area would be:

4.1.1. Ceiling fan efficiency calculations for multi-head ceiling fans

To determine the airflow at a given speed for a multi-head ceiling fan, sum the measured airflow for each fan head included in the ceiling fan (a single airflow measurement can be applied to identical fan heads, but at least one of each unique fan head must be tested). The power consumption is the measured power consumption with all fan heads on. Using the airflow and power consumption measurements from section 3.3 of this appendix, calculate ceiling fan efficiency for a multi-head ceiling fan as follows:

Where:

CFMi = sum of airflow at a given speed for each head,

OHi = operating hours at a given speed,

Wi = total power consumption at a given speed,

OHSb = operating hours in standby mode, and

WSb = power consumption in standby mode.

4.1.2. Ceiling fan efficiency calculations for ceiling fans with airflow not directly downward

Using a set of sensors that cover the same diameter as if the airflow were directly downward, the airflow at each speed should be calculated based on the continuous set of sensors with the largest air velocity measurements. This continuous set of sensors must be along the axis that the ceiling fan tilt is directed in (and along the axis that is 180 degrees from the first axis). For example, a 42-inch fan tilted toward axis A may create the pattern of air velocity shown in Figure 3 of this appendix. As shown in Table 1 of this appendix, a 42-inch fan would normally require 7 active sensors. However because the fan is not directed downward, all sensors must record data. In this case, because the set of sensors corresponding to maximum air velocity are centered 3 sensor positions away from the sensor 1 along the A axis, substitute the air velocity at A axis sensor 4 for the average air velocity at sensor 1. Take the average of the air velocity at A axis sensors 3 and 5 as a substitute for the average air velocity at sensor 2, take the average of the air velocity at A axis sensors 2 and 6 as a substitute for the average air velocity at sensor 3, etc. Lastly, take the average of the air velocities at A axis sensor 10 and C axis sensor 4 as a substitute for the average air velocity at sensor 7. Stability criteria apply after these substitutions. For example, air velocity stability at sensor 7 are determined based on the average of average air velocity at A axis sensor 10 and C axis sensor 4 in successive measurements. Any air velocity measurements made along the B-D axis are not included in the calculation of average air velocity.

[81 FR 48639, July 25, 2016; 81 FR 54721, Aug. 17, 2016]