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Federal Register / Vol. 86, No. 151 / Tuesday, August 10, 2021 / Notices
DOE amends the test procedure to address the issues presented in a waiver, the waiver will automatically terminate on the date on which use of that test procedure is required to demonstrate compliance. 10 CFR
431.401h3.

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II. RefPluss Petition for Waiver and Interim Waiver On June 2, 2021, DOE received 5 from RefPlus a petition for waiver and interim waiver from the test procedure for walk-in refrigeration systems set forth at 10 CFR part 431, subpart R, appendix C. RefPlus, No. 1 at p. 1.6
DOE received an updated petition for waiver and interim waiver from RefPlus on July 12, 2021. RefPlus, No. 2 at p.
1. The updated petition specifies additional basic models to be considered under the waiver request.
RefPlus, No. 2 at pp. 25. Pursuant to 10 CFR 431.401b1iv, DOE has posted both petitions to the docket at, at: www.regulations.gov/docket/EERE2021-BT-WAV-0014 and has reproduced the most recent petition for waiver in this notice.7
RefPlus claims that the test conditions described in Table 15 and Table 16 of the Air-Conditioning, Heating, and Refrigeration Institute AHRI
Standard 12502009, Standard for Performance Rating of Walk-In Coolers and Freezers AHRI 12502009 for walk-in refrigerator unit coolers and freezer unit coolers tested alone, respectively, as incorporated by Appendix C with modification, cannot be achieved by the specified basic models and are not consistent with the operation of RefPluss CO2 direct expansion unit coolers. RefPlus also 84 FR 18414, 18416 May 1, 2019; See 42 U.S.C.
6293c2. In the final rule published December 11, 2020, stated that it was maintaining the 180-day grace period as proposed. 85 FR 79802, 79813. As such, were a Decision and Order issued with an alternate test procedure that differed from that required under this interim waiver, beginning 180
days following publication of the Decision and Order any representations made by the petitioner must fairly disclose the results of testing in accordance with the alternate test procedure specified by the final Order and the applicable requirements of 10 CFR part 429.
5 A petition submitted under 10 CFR 431.401 is considered received on the date it is received by DOE through DOEs established email box for receipt of waiver petitions or, if delivered by mail, on the date the waiver petition is stamped as received by DOE. 10 CFR 431.401e1iii.
6 A notation in the form RefPlus, No. 1
identifies a written submission: 1 Made by RefPlus; and 2 recorded in document number 1
that is filed in the docket of this petition for waiver Docket No. EERE2021BTWAV0014 and available at www.regulations.gov/docket?D=EERE2021-BT-WAV-0014.
7 The petition did not identify any of the information contained therein as confidential business information.

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stated that CO2 has a critical temperature of 87.8 F,8 and thus the required liquid inlet saturation temperature of 105 F and the required liquid inlet subcooling temperature of 9
F are not achievable, and that the test conditions should be more consistent with typical operating conditions for a transcritical CO2 booster system RefPlus, No. 2, p. 5.
The statements made by RefPlus reference the difference in thermodynamic properties between CO2
and other refrigerants. Many substances transition from a solid to a liquid to a gas at a given pressure as temperature increases. For example, a pure substance like water transitions from liquid to steam at a specific temperature, e.g. 212 F, at atmospheric pressure. As heat is added during a liquid to gas transition, the temperature remains constant and the substance coexists as both liquid and vapor.
Continuing to add heat converts more of the liquid to vapor at a constant temperature. The reverse occurs when heat is removed. However, the transition temperature depends on the pressure the higher the pressure, the higher the transition temperature. This is a key principle in refrigeration systems, which operate at two pressure levels associated with two temperatures. A
refrigerant absorbs heat when it is at a low temperature and pressure, converting to gas and cooling the surrounding space. At high temperature and pressure, the refrigerant transitions to a liquid while releasing heat to the environment. A compressor is used to raise a gas from lowhigh-pressure, and a throttle pressure reduction device is used to reduce the pressure once the refrigerant has been fully liquefied condensed at high pressure.
All refrigerants have a critical temperature and an associated critical pressure above which liquid and vapor phases cannot coexist. Above this critical point, the refrigerant will be a gas and its temperature will increase or decrease as heat is added or removed.
For conventional refrigerants, the critical temperature is never exceeded in typical refrigeration cycles. For example, R404A is a common refrigerant used in refrigeration systems and has a critical temperature of 161.7
8 The test procedure specifies the unit cooler refrigerant inlet condition in terms of a saturation temperature the temperature at which it completes the condensation process in a condenser and the subcooling temperature additional reduction in temperature lower than the specified saturation temperature. For CO2, the critical temperature above which there cannot exist separate liquid and gas phases is below the saturation condition specified in the test procedure, hence the specified condition cannot be achieved.

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F with an associated critical pressure of 540.8 psia.9 However, CO2 behaves differently, with a critical temperature of 87.8 F and an associated critical pressure of 1,072 psia. The refrigerant temperature must be somewhat higher than the ambient temperature in order to reject refrigeration cycle heat to the ambient environment. Ambient temperatures greater than 87.8 F are common and the performance of many refrigeration and air conditioning systems are tested using a 95 F ambient temperature, as indicated by the A test condition in AHRI 12502009 Section 5.
Above the critical temperature and critical pressure, the CO2 refrigerant is in a supercritical state and heat is transferred to the environment. Since the temperature of the CO2 refrigerant ranges from supercritical to subcritical within the system, CO2 cycles are said to be transcritical.
The transcritical nature of CO2
generally requires a more complex refrigeration cycle design to approach the efficiency of traditional refrigerants i.e., R404A, R407A, R448A, etc. during operation in high temperature conditions. To increase efficiency and prevent overheating, transcritical booster systems introduce or use multiple stages of compression and intercooling. CO2 is cooled in the gas cooler of a transcritical booster system, then expands through a high-pressure control valve and is delivered to a subcritical-pressure flash tank. In the flash tank, the refrigerant is in the subcritical phase and the liquid and vapor phases can be separated. In a CO2
booster system, subcooled liquid refrigerant from the flash tank supplies the unit cooler via expansion valves where the refrigerant is evaporated. The evaporated refrigerant is subsequently compressed up to gas cooler pressure to complete the cycle Docket EERE2021
BTWAV0014, No. 5.
As noted, RefPlus requests an interim waiver from the existing DOE test procedure. DOE will review the petition for interim waiver within 45 business days of receipt of the petition. 10 CFR
431.401e1ii. If DOE does not notify the applicant of the disposition of the petition for interim waiver, in writing, within 45 business days of receipt of the petition, the interim waiver is granted utilizing the alternate test procedure requested in the petition. Id. DOE will grant an interim waiver if it appears likely that the petition for waiver will be granted, and/or if DOE determines that it would be desirable for public policy 9 Absolute pressure is the pressure measured relative to a complete vacuum; psia represents the absolute pressure in pounds per square inch.

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