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Federal Register / Vol. 86, No. 58 / Monday, March 29, 2021 / Rules and Regulations
Incorporating these standards would clarify which versions of the standards are required to conduct tests according to the procedure in appendix F. 85 FR
35700, 35707 Jun. 11, 2020.
DOE received no comments on the proposal to incorporate ANSI/ASHRAE
Standard 41.12013, ANSI/ASHRAE
Standard 41.21987 RA 1992, ANSI/
ASHRAE Standard 41.32014, ANSI/
ASHRAE Standard 41.62014, and ANSI/ASHRAE Standard 41.112014 in appendix F. DOE is adopting its proposal to incorporate those industry standards appendix F.
C. Variable-Speed Room Air Conditioner Test Procedure Historically, room ACs have been designed using a single-speed compressor, which operates at full cooling capacity while the compressor is on. To match the cooling load of the space, which in most cases is less than the full cooling capacity of the compressor, a single-speed compressor cycles on and off. This cycling behavior generally introduces inefficiencies in refrigeration system performance.
Variable-speed room ACs became available on the U.S. market in 2018.
These models employ an inverter compressor that can reduce its speed to provide continuous cooling that matches the observed cooling load.
Accordingly, a variable-speed compressor runs continuously, adjusting its speed up or down as required. In addition to reducing or
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eliminating cycling inefficiencies, in a variable-speed unit operating at reduced capacity the evaporator and condenser heat exchange effectiveness are improved, since they are handling reduced loads, thereby improving compressor efficiency.
The previous DOE test procedure measured the performance of a room AC
while operating under a full cooling load; i.e., the compressor is operated continuously in its on state. As a result, the DOE test does not capture any inefficiencies due to compressor cycling. Consequently, the efficiency gains that can be achieved by variablespeed room ACs due to the avoidance of cycling losses were not measured by the previous test procedure.
In the June 2020 NOPR, DOE
presented the results of its investigative testing to quantify the impacts of cycling losses and the relative efficiency benefits of a variable-speed compressor.
85 FR 35700, 3570735708 Jun. 11, 2020. DOE compared the performance of two variable-speed room ACs from two different manufacturers, with single-speed room AC of similar capacity from the same manufacturers, under reduced cooling load conditions.12 DOE installed each room 12 The first room AC was tested under the 95 F
outdoor test condition Figure III1, the second under the 82 F outdoor test condition Figure III
2, and the change in EER and load from full-load used for each test was determined based on an appendix F test with the noted outdoor test condition.

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AC in a calorimeter test chamber, set the unit thermostat to 80 degrees Fahrenheit F, and applied a range of fixed cooling loads to the indoor chamber.13 14
The calorimeter chamber conditioning system was configured to apply a fixed cooling load rather than maintaining constant indoor chamber temperature, thereby allowing the test unit to maintain the target indoor chamber temperature by adjusting its cooling operation in response to the changing temperature of the indoor chamber.15
Figures III1 and III2 show the efficiency gains and losses for the range of reduced cooling loads tested for each unit, relative to the performance of each unit as tested using appendix F.16
13 A cooling load is applied by adjusting and fixing the rate of heat added to the indoor test chamber to a level at or below that of the nominal cooling capacity of the test unit.
14 This approach aims to represent a consumer installation in which the amount of heat added to a room may be less than the rated cooling capacity of the room AC e.g., electronics or lighting turned off, people or pets leaving the room, and external factors such as heat transfer through walls and windows reducing with outdoor temperature.
15 DOE notes that this test chamber configuration differs from the configuration used in appendix F.
Appendix F uses a constant-temperature configuration, in which the indoor chamber temperature is held fixed i.e., the indoor temperature does not drop while the room AC is operational.
16 For single-speed room ACs under appendix F, the thermostat is typically set as low as possible to ensure that the unit provides maximum cooling during the cooling mode test period.

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