Determining Off-Cycle Fuel Economy Benefits of 2-Layer HVAC Technology

Eric Wood, Matthew Moniot, Forrest Jehlik, Netsanet Chevers, Hidekazu Hirabayshi, Yuanpei Song, Masahiro Nomura

Research output: Contribution to conferencePaperpeer-review

5 Scopus Citations


This work presents a methodology to determine the off-cycle fuel economy benefit of a 2-Layer HVAC system which reduces ventilation and heat rejection losses of the heater core versus a vehicle using a standard system. Experimental dynamometer tests using EPA drive cycles over a broad range of ambient temperatures were conducted on a highly instrumented 2016 Lexus RX350 (3.5L, 8 speed automatic). These tests were conducted to measure differences in engine efficiency caused by changes in engine warmup due to the 2-Layer HVAC technology in use versus the technology being disabled (disabled equals fresh air-considered as the standard technology baseline). These experimental datasets were used to develop simplified response surface and lumped capacitance vehicle thermal models predictive of vehicle efficiency as a function of thermal state. These vehicle models were integrated into a database of measured on road testing and coupled with U.S. typical meteorological data to simulate vehicle efficiency across seasonal thermal and operational conditions for hundreds of thousands of drive cycles. Fuel economy benefits utilizing the 2-Layer HVAC technology are presented in addition to goodness of fit statistics of the modeling approach relative to the experimental test data.

Original languageAmerican English
Number of pages14
StatePublished - 2018
Event2018 SAE World Congress Experience, WCX 2018 - Detroit, United States
Duration: 10 Apr 201812 Apr 2018


Conference2018 SAE World Congress Experience, WCX 2018
Country/TerritoryUnited States

Bibliographical note

Publisher Copyright:
© 2018 SAE International; Argonne National Laboratory; National Renewable Energy Laboratory.

NREL Publication Number

  • NREL/CP-5400-70780

Other Report Number

  • SAE Paper No. 2018-01-1368


  • 2-layer technology
  • cabin heating
  • off-cycle credits
  • real-world fuel economy


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