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Federal Register / Vol. 86, No. 31 / Thursday, February 18, 2021 / Notices thus the required liquid inlet saturation temperature of 105 F and the required liquid inlet subcooling temperature of 9
F required in DOEs test procedure are not achievable, and that the test conditions should be more consistent with typical operating conditions for a transcritical CO2 booster system Hussmann, No. 1 at p.3.
The statements made by Hussmann reference the difference in thermodynamic properties between CO2
and other refrigerants. At modest pressures i.e. below the critical point, many substances transition from a solid to a liquid to a gas 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 the low-pressure gas to a high 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 pressure and an associated critical temperature 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 all conventional refrigerants, the critical pressure is so high that it is never exceeded in typical refrigeration cycles. For example, R404A is a common refrigerant used in refrigeration systems that has a critical pressure of 540.8 psia 6 with an associated critical temperature of 161.7 F. However, CO2
behaves differently, with a critical specified in the test procedure, hence the specified condition cannot be achieved.
6 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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pressure of 1,072 psia associated with a much lower critical temperature of 87.8
F. 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. At temperatures greater than the critical temperature, the CO2 refrigerant is in a supercritical state i.e. a condition with pressure above the critical temperature and heat is transferred to the environment. Since useful cooling is provided below the critical temperature, CO2 cycles are said to be transcritical.
The transcritical nature of CO2
generally requires 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. A unit cooler in a CO2 booster system would be supplied with liquid refrigerant from the flash tank via expansion valves where the refrigerant is evaporated. The evaporated refrigerant is subsequently compressed up to gas cooler pressure to complete the cycle Hussmann, No. 5.
Hussmann also requests an interim waiver from the existing DOE test procedure. 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 reasons to grant immediate relief pending a determination of the petition for waiver.
See 10 CFR 431.401e2.
Based on the assertions in the petition, absent an interim waiver, the prescribed test procedure is not appropriate for Hussmanns CO2 direct expansion unit coolers and the test conditions are not achievable, since CO2
refrigerant has a critical temperature of 87.8 F and the current DOE test procedure calls for a liquid inlet saturation temperature of 105 F. The inability to achieve test conditions for the stated basic models would result in economic hardship from loss of sales
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stemming from the inability of the DOE
test procedure to address the operating conditions of Hussmanns equipment.
III. Requested Alternate Test Procedure EPCA requires that manufacturers use the applicable DOE test procedures when making representations about the energy consumption and energy consumption costs of covered equipment 42 U.S.C. 6314d.
Consistency is important when making representations about the energy efficiency of equipment, including when demonstrating compliance with applicable DOE energy conservation standards. Pursuant to 10 CFR 431.401, and after consideration of public comments on the petition, DOE may establish in a subsequent Decision and Order an alternate test procedure for the basic models addressed by the Interim Waiver Order.
Hussmann seeks to test and rate specific CO2 direct expansion unit cooler basic models with modifications to the DOE test procedure. Hussmanns suggested approach specifies using modified liquid inlet saturation and liquid inlet subcooling temperatures of 38 F and 5 F, respectively, for both walk-in refrigerator unit coolers and walk-in freezer unit coolers.
Additionally, Hussmann recommends that because the subject units are used in transcritical CO2 booster systems, the calculations in AHRI 12502009 section 7.9 should be used to determine the Annual Walk-in Efficiency Factor AWEF and net capacity for unit coolers matched to parallel rack systems as required under the DOE test procedure. This section of AHRI 1250
2009 is prescribed by the DOE test procedure for determining AWEF for all unit coolers tested alone see 10 CFR
part 431, subpart R, appendix C, section 3.3.1. Finally, Hussmann also suggested that AHRI 12502009 Table 17 EER
Energy Efficiency Ratio for Remote Commercial Refrigerated Display Merchandisers and Storage Cabinets should be used to determine EER values and power consumption for the subject CO2 direct expansion unit cooler systems as required under the DOE test procedure.
IV. Interim Waiver Order DOE has reviewed Hussmanns application, its suggested testing approach, industry materials regarding CO2 transcritical booster systems, and Hussmanns consumer-facing materials, including websites and product specification sheets for the basic models listed in Hussmanns petition. Based on this review, the suggested testing approach appears to allow for the
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