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Federal Register / Vol. 86, No. 127 / Wednesday, July 7, 2021 / Proposed Rules
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fans into the market. If so, DOE requests comment on whether a hierarchy should be established to give precedence to a given function.
2. Modulating Controls and Thermostat Pairings DOE is aware that an increasing proportion of furnace fans employ modulating controls for heating, and constant circulation modes that allow fan speed to continuously vary as opposed to operating at a discrete speed for each function. These fans are characterized by having electrically commutated brushless permanent magnet BPM motors, which can be paired with thermostats that have the capability to provide modulating control in order to make use of the BPMs ability to vary its speed to maintain a constant airflow at various ESPs.
Because input from the thermostat is essential to the functioning of these types of systems, furnace fan performance may be dependent on the specific type of thermostat with which the system is paired as it could vary depending on the types of control signals provided by the thermostat. In field operation, modulating controls enable the furnace fan to reduce its speed to match heating demand during periods of low heating demand.
Section 8.3 of Appendix AA requires that the system operate continuously for at least 30 minutes at each discrete airflow setting, which would preclude dynamic response to thermostat signals that vary more frequently than 30
minutes. In addition, there are no specific provisions for testing the performance of the furnace fan under modulating control conditions. Further, the furnace fan test procedure relies on an assumed number of hours each year that the furnace fan is in heating mode operating at a constant fan speed. See Table IV.2, Appendix AA. A modulating furnace fan could potentially spend a portion of these hours operating at a fan speed other than the speed required by the test method, impacting the energy use during periods of lower heating demand and, consequently, reduced fan speed.
Issue 9: DOE requests information about available control features that impact fan performance. Specifically, DOE requests information and data regarding modulating control approaches currently in use or planned for future use, whether the performance differences of such modulating furnace fans are currently adequately captured by the furnace fan test procedure, and, if necessary, what new provisions could be necessary to reflect the impact of these control features in FER ratings. If
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new provisions are suggested, DOE also seeks comment on any burdens associated with those provisions.
Issue 10: DOE requests comment on the most common type of thermostats used by consumers, particularly with regards to furnace fans with modulating control strategies.
DOE has also observed that some furnace fans have a ramping profile setting that is selectable through dual in-line package DIP switch adjustments during installation.
Ramping profiles allow a modulating furnace fan to gradually ramp up or down over time to meet the target fan speed instead of immediately controlling to the target fan speed.
Ramping profiles are often marketed as providing additional benefits to users by increasing dehumidification in cooling mode, providing faster outlet temperature change in heating mode, and reducing fan noise. As noted, section 8.3 of Appendix AA requires that the system operate continuously for at least 30 minutes at each test point before steady state conditions are achieved and test parameters start to be recorded, and testing is conducted at steady-state and would not account for any ramping period.
Issue 11: DOE requests information on the prevalence of field installations for modulating furnace fans where dip switches are selected to allow for ramping behavior.
Issue 12: DOE requests information on whether ramping profiles may result in any difference in tested performance vs field performance, and whether this difference should be captured by the furnace fans test procedure.
3. ESP Requirements for AirflowControl Settings Other Than the Maximum Sections 8.6.2 and 8.6.3 of Appendix AA provide the test requirements for taking measurements in airflow-control settings other than the maximum airflow-control setting. Both sections state that their respective required operating settings be maintained until steady-state conditions are attained as specified in section 8.3, 8.4, and 8.5 of Appendix AA. Regarding ESP, sections 8.3, 8.4, and 8.5 state that stabilization is indicated by an external static pressure within the range shown in Table 1. The ESP values in Table 1, as indicated by the tables title, apply only to the maximum airflow-control setting section 8.6.1, and therefore are not applicable to sections 8.6.2 and 8.6.3. In an accompanying statement immediately below Table 1, Appendix AA directs that once the specified ESP
has been achieved, the same outlet duct
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restrictions shall be used for the remainder of the furnace fan test. As such, the test procedure specifies the ESP conditions in terms of the ductwork geometry when testing at airflow-control settings other than the maximum airflow-control setting.
Given that the ESP will vary as the airflow-control setting is changed if the outlet duct restriction remains unchanged, the ESP targets in Table 1
are not required to be met at the airflowcontrol settings other than the maximum setting. DOE is considering whether it would be helpful to instruct more directly that the Table 1 ESP
requirements are only applicable to the maximum airflow control setting; for all other airflow-control settings, the required ESP is that which results from using the same test duct restrictions as used for the maximum airflow-control setting. Further, DOE is seeking feedback on whether additional criteria is necessary to limit variability in ESP
readings for steady-state operation during the tests for airflow-control settings other than the maximum airflow setting.
Issue 13: DOE requests comment on how manufacturers are currently implementing sections 8.6.2 and 8.6.3
with respect to ESP.
Issue 14: DOE requests comments on whether it is necessary to further clarify that the specific ESP values in Table 1
are not required to be maintained for testing to sections 8.6.2 and 8.6.3.
Issue 15: DOE requests comments on whether additional direction is needed as to the ESP requirement provided in the statement accompanying Table 1, including whether additional criteria is necessary to limit variability in ESP
readings for steady-state operation during the tests for airflow-control settings other than the maximum airflow setting, and if so, what that direction should be.
4. ESP Limits for Electric Resistance Heat Kits Modular blowers are not contained in the same cabinet as a furnace or central air conditioner and are sold as standalone products that can come with a variety of sizes of heating elements.
During testing, they must be paired with the electric resistance heat kit that is likely to have the largest volume of retail sales with that basic model of modular blower. Section 6.3, Appendix AA. An electric resistance heat kit is a group of usually three to seven electric resistance coils, called elements, each of which typically is rated at five kilowatts. These heating elements can activate in stages to provide the
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