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Federal Register / Vol. 86, No. 169 / Friday, September 3, 2021 / Proposed Rules
20202022, to allow manufacturers to use the cap of 15 g/mi if the revised definitions are met for these technologies. NHTSA is proposing to adopt these same provisions for the CAFE programs as a part of this rulemaking. No caps were established for technologies gaining credits through the petitioning or 5-cycle approval methodologies and the agency are not proposing to add caps in these areas.

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iv Proposal To Update the Menu Technology Definitions a Passive Cabin Ventilation Some manufacturers have claimed offcycle credits for passive ventilation cabin technologies based on the addition of software logic to their HVAC
system that sets the dash vent to the open position when the power to vehicle is turned off at higher ambient temperatures. The manufacturers have indicated that the opening of the vent allows for the flow of ambient temperature air into the cabin. While ensuring that the interior of the vehicle is open for flow into the cabin, by only opening the dash vent no other action is taken to improve the flow of heated air out of the vehicle. This technology relies on the pressure in the cabin to reach a sufficient level for the heated air in the interior to flow out through body leaks or the body exhausters open and vent heated air out of the cabin.
The credits for passive cabin ventilation were determined based on an National Renewable Energy Laboratory NREL study that strategically opened a sunroof to allow for the unrestricted flow of heated air to exit the interior of the vehicle while combined with additional floor openings to provide a minimally restricted entry for cooler ambient air to enter the cabin.550 The modifications NREL performed on the vehicle reduced the flow restrictions for both heated cabin air to exit the vehicle and cooler ambient air to enter the vehicle, creating a convective airflow path through the vehicle cabin.
Analytical studies performed by manufacturers to evaluate the performance of the open dash vent demonstrate that while the dash vent may allow for additional airflow of ambient temperature air entering the cabin, it does not reduce the existing restrictions on heated cabin air exiting the vehicle. Opening the dash vent primarily relies on body leaks and 550 Rugh,
J., Chaney, L., Lustbader, J., and Meyer, J., Reduction in Vehicle Temperatures and Fuel Use from Cabin Ventilation, Solar-Reflective Paint, and a New Solar-Reflective Glazing, SAE
Technical Paper 2007011194, 2007.

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occasional venting of the heated cabin air through the body exhausters for the higher temperature cabin air to be vented from the vehicle. While this does provide some reduction in cabin temperatures this technology is not as effective as the combination of vents used by the NREL researchers to allow additional ambient temperature air to enter the cabin and also to reduce the restriction of heated air exiting the cabin.
As noted in the Joint Technical Support Document: Final Rulemaking for 20172025 Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards,551 pg. 584, For passive ventilation technologies, such as opening of windows and/or sunroofs and use of floor vents to supply fresh air to the cabin which enhances convective airflow, 1.7 grams/mile for LDVs and 2.3 grams/mile for LDTs a cabin air temperature reduction of 5.7 C can be realized. The passive cabin ventilation credit values were based on achieving the 5.7 C cabin temperature reduction.
EPA and NHTSA have decided to revise the passive cabin ventilation definition to make it consistent with the technology used to generate the credit value. NHTSA supports EPAs proposal to revise the definition of passive cabin ventilation to only include methods which create and maintain convective airflow through the bodys cabin by opening windows or a sunroof, or equivalent means of creating and maintaining convective airflow, when the vehicle is parked outside in direct sunlight.
Current systems claiming the passive ventilation credit by opening the dash vent would no longer meet the updated definition. Manufacturers seeking to claim credits for the open dash vent system will be eligible to petition the agency for credits for this technology using the alternative EPA approved method outlined in 86.186912d.
b Active Engine and Transmission Warmup NHTSA, in coordination with EPA, is proposing to revise the menu definitions of active engine and transmission warmup to no longer allow systems that capture heat from the coolant circulating in the engine block prior to the opening of the thermostat to qualify for the Active Engine and Active Transmission warm-up menu credits.
551 Final Rulemaking for 20172025 Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards August 2012. NHTSA and EPA. https
www.nhtsa.gov/sites/nhtsa.gov/files/joint_final_
tsd.pdf. Last Accessed June 6, 2021.

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The agency would allow credit for coolant systems that capture heat from a liquid-cooled exhaust manifold if the system is segregated from the coolant loop in the engine block. The agency would also allow system design that captures and routes waste heat from the exhaust to the engine or transmission as this was the basis for these two credits as originally proposed in the NPRM to the 2017 to 2025 GHG rulemaking 76
FR 74854, Dec. 1, 2011.
Manufacturers seeking to utilize their existing systems that capture coolant heat before the engine is fully warmedup and transfer this heat to the engine oil and transmission fluid would remain eligible to seek credits through the alternative method application process outlined in 86.186912d. These technologies may provide some benefit, however, as noted above as these system designs remove heat that is needed to warmup the engine may be less effective than those that capture and utilize exhaust waste heat.
VIII. Public Participation NHTSA requests comments on all aspects of this NPRM. This section describes how you can participate in this process.
How do I prepare and submit comments?
Your comments must be written and in English.552 To ensure that your comments are correctly filed in the docket, please include the docket number NHTSA20210053 in your comments. Your comments must not be more than 15 pages long.553 NHTSA
established this limit to encourage you to write your primary comments in a concise fashion. However, you may attach necessary additional documents to your comments, and there is no limit on the length of the attachments. If you are submitting comments electronically as a PDF Adobe file, we ask that the documents please be scanned using the Optical Character Recognition OCR
process, thus allowing NHTSA to search and copy certain portions of your submissions.554 Please note that pursuant to the Data Quality Act, in order for substantive data to be relied upon and used by the agency, it must meet the information quality standards set forth in the OMB and DOT Data Quality Act guidelines. Accordingly, we encourage you to consult the guidelines in preparing your comments. OMBs 552 49

CFR 553.21.

553 Id.
554 Optical character recognition OCR is the process of converting an image of text, such as a scanned paper document or electronic fax file, into computer-editable text.

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