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Federal Register / Vol. 86, No. 232 / Tuesday, December 7, 2021 / Proposed Rules
successive measurements on Axes B, C, and D. If using four fixed sensor arms, the readings for all four axes are measured simultaneously. See Steps 4
and 5 of section 3.3.22 of appendix U.
The team has observed that valid results are generally attained more quickly using the four-arm setup because measurements are taken simultaneously in all four axes and stability can be achieved in fewer runs i.e., a complete set of air velocity measurements for all axes. However, a four-arm setup is more expensive because it requires at least 4 times as many sensors. This setup is typically used by laboratories that primarily test LSSD fans which require low airflow to be measured or laboratories that test large quantities of fans, for which a faster throughput is important. A single-arm setup is less expensive and is typically used by laboratories that test mostly high-speed ceiling fans or test very few ceiling fans.
The single-arm setup requires the rotation of the arm every 100 seconds, which disrupts the air, often increasing the time to achieve stability. Assuming it takes 3 cycles to reach stability for the low-speed test i.e., average air velocity across all sensors for cycles 2 and 3
meet the stability criteria, the test length would be around 16 minutes for the four fixed arm unit and around 41
minutes for the single rotating arm unit.23 During round robin testing, DOE
personnel noted that laboratories using the single rotating sensor arm waited approximately 30 seconds for arm vibration to dissipate before starting data collection at the new position, adding a minimum of 1 minute 30
seconds to each test cycle.
During round-robin testing, laboratories with single-arm setups were able to achieve stability for 75 percent of fans tested, as compared to 96 percent for laboratories using four-arm setups.
To address stability issues in a singlearm setup, DOE proposes, based on observations from the round robin testing, to provide explicit instruction for setups that require arm rotation to stabilize the arm and allow 30 seconds between test runs for any residual turbulence to dissipate prior to data collection after each rotation. While this additional instruction would increase testing time of each axis, based on observation through round robin testing, DOE has initially determined that this requirement could further contribute to more accurate and stable airflow measurements during testing. In some 23 These time frames were determined in the round robin report, found in the rulemaking docket EERE2013BTTP0050. www.regulations.gov/
docket/EERE-2013-BT-TP-0050.

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cases, this could reduce overall testing time by avoiding the need to retest to meet the required air velocity stability criteria section 3.3.21 of appendix U.
As an alternative to the singleand four-arm setup options, DOE also proposes to allow laboratories to rely on test setups with two arms, so that the system would need to be rotated only once to collect data for all four axes. A
two-arm setup would require less time to collect the necessary data than a 1arm setup and would therefore reduce testing burden for laboratories currently using a 1-arm setup. It would also require fewer sensors than a four-arm setup, and could therefore provide a cost-effective approach to achieve stability conditions more easily at low speed. DOE proposes to amend sections 3.2.24 and 3.3.2 of appendix U to accommodate the use of a two-arm setup.
DOE seeks comment on the proposed requirement to add 30 seconds between test runs for a rotating arm setup either single-arm or two-arm.
DOE seeks comment on its proposal to permit the use of a two-arm setup, as well as any data to confirm that a 2-arm option produces comparable results to the existing 1-arm and 4-arm options.
G. Air Velocity Sensor Mounting Angle Section 3.2.2 of appendix U does not specify the applicable mounting angle of the sensors on the sensor arm.
Air velocity is most accurately measured by aligning the velocity sensor perpendicular to the airflow path, as this is the orientation for which the airflow through the openings of the sensor is smooth and free of turbulence.
However, during recent round robin testing, the team noted that some air velocity sensors were not aligned perpendicular to the path of airflow. A
misaligned velocity sensor could produce inaccurate air velocity measurements. Therefore, to ensure consistent air velocity alignment, DOE
proposes to include explicit instructions in section 3.2.26 of appendix U to align the air velocity sensors perpendicular to the direction of airflow. DOE could also consider updating Figure 2 of appendix U which would be renumbered as Figure 3 in this proposal, or adding a new figure, to depict more clearly the alignment of the velocity sensors perpendicular to the direction of airflow.
DOE requests comment on its proposal to specify aligning the air velocity sensors perpendicular to the airflow. DOE also requests comment on whether it should revise Figure 2 of appendix U, and/or provide an additional figure, to depict more clearly
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the alignment of the velocity sensors perpendicular to the direction of airflow.
H. Instructions To Measure Blade Thickness Sections 1.8 and 1.13 in appendix U
incorporate a fan blade thickness threshold of 3.2 mm within the definitions of HSSD ceiling fan and LSSD ceiling fan, respectively. Blade edge thickness is used to distinguish product classes because it relates to safety considerations that, in turn, relate to where a ceiling fan is likely to be installed. Commercial and industrial ceiling fans are typically installed in locations with higher ceilings, and therefore thin leading edges on the blades do not present the safety hazard that thin leading edges would present on ceiling fans that are installed at lower heights, i.e., residential ceiling fans.
Appendix U currently does not provide instruction for how to measure fan blade thickness. In the September 2019 NOPR, DOE proposed that blade edge thickness for small diameter fans be measured at the leading edge of the fan blade i.e., the edge in the forward direction with an instrument having a measurement resolution of at least a tenth of an inch. DOE also proposed the following instructions for measuring blade edge thickness to ensure test procedure reproducibility, given potential variations in blade characteristics: 1 Measure at the point at which the blade is thinnest along the radial length of the fan blade and is greater than or equal to one inch from the tip of the fan blade, and 2 Measure one inch from the leading edge of the fan blade. 84 FR 51440, 51450.
DOE has subsequently become aware of a rolled-edge blade design on a residential ceiling fan for which the thickness of the body of the blade is less than 3.2 mm, but that has a curled shape along the leading edge, with the curl having an outer thickness greater than 3.2 mm. For such a rolled-edge blade, the blade thickness measurement procedure proposed in the September 2019 NOPR would indicate a thin blade despite the thicker leading edge, resulting in the fan being classified as an HSSD, which as discussed are generally non-residential fans.
Conversely, measuring the thickness at the rolled edge less than one inch from the leading edge would result in the fan being classified as an LSSD, which are generally residential fans. In order to measure blade thickness for rollededge, flat, tapered, and other ceiling fan blade types in a manner that will consistently classify ceiling fans with
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