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Energy efficiency comparison of air-conditioning systems in electric vehicles

A study compares the energy efficiency of conventional refrigeration systems with that of heat pumps in mobile air conditioning. R744, R134a and R1234yf are considered. Reversible heat pumps are found the most energy-efficient systems.

An article1 published by SAE International2 compares the electrical energy consumption of two mobile air conditioning systems in battery electric vehicles. In each case, CO2 (R744) was compared to another refrigerant:


  • System 1: Conventional refrigeration cycles with positive temperature coefficients (PTC). Comparison of R744 and R1234yf.
  • System 2: Reversible heat pumps. Comparison of R744 and R134a.

 

 

The study is based on a thermal vehicle simulation considering driving times between 6 AM and 24 PM and takes into account 6 different temperature ranges. The relative humidity and the solar radiation are also taken into account and they correspond to the data of 211 cities worldwide (located in Europe, Americas, Asia, Africa ...).


The simulation is based on GREEN-MAC-LCCP data. It is a model used to calculate and predict the life cycle of greenhouse gas emissions for refrigerants used in mobile air conditioning.


According to this study, the reversible heat pump system is the most energy efficient. Of the two refrigerants considered, R744 leads to a lower electric consumption (311TWh per year) than R134a (320 TWh per year). The difference would be even more significant in cold climates.


1 WESTERLOH, M. TWENHÖVEL, S. KOEHLER, J. Worldwide electrical energy consumption of various hvac systems in BEVs and their thermal management and assessment. SAE International. 2018.04. Available following this link.

2 SAE International is an organisation of automotive professionnals from more than 97 countries. It was formerly known as Society Automotive Engineers. The article was written by researchers from the University of Braunschweig and from Volkswagen AG.