Browse Publications Technical Papers 2020-01-1252
2020-04-14

Real-world Evaluation of National Energy Efficiency Potential of Cold Storage Evaporator Technology in the Context of Engine Start-Stop Systems 2020-01-1252

National concerns over energy consumption and emissions from the transportation sector have prompted regulatory agencies to implement aggressive fuel economy targets for light-duty vehicles through the NHTSA/EPA corporate average fuel economy (CAFE) program. Automotive manufacturers have responded by bringing competitive technologies to market that maximize efficiency while meeting or exceeding consumer performance and comfort expectations. In a collaborative effort between Toyota Motor Corporation, Argonne National Laboratory (ANL), and the National Renewable Energy Laboratory (NREL), the real-world savings of one such technology is evaluated. A commercially available Toyota Highlander equipped with two-phase cold storage technology was tested at ANL’s chassis dynamometer testing facility. The cold storage technology maintains the thermal state of air-conditioning evaporators to enable longer and more frequent engine off operation in vehicles equipped with start-stop functionality. Test results were analyzed and provided to NREL where a novel simulation framework was developed and calibrated to test data. The vehicle model was then exercised over a large set of real-world drive cycle and ambient condition data to estimate national-level fuel economy benefits. Results indicate that the cold storage evaporator provided national fuel consumption reductions of 0.11% relative to a conventional evaporator in the same vehicle. Additionally, when the cold storage evaporator engine stop/start was enabled for any temperature and the baseline was limited to the standard 80°F, a national fuel savings of 0.497% was found. Fuel savings result from a combination of extended engine-off duration during idle events and increased frequency of deceleration fuel cut off; both enabled by the ability of the cold storage evaporator to maintain thermal state in situations where air conditioning is active.

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