Life cycle climate performance (LCCP) evaluation model for electric vehicle heat pumps and emission reduction analysis of low-GWP refrigerants

Abstract

<p indent="0mm">With the proposal of China’s carbon neutrality target and the official entry into force of the Kigali Amendment to the Montreal Protocol, the green and efficient development of the new energy vehicle heat pump is imperative, since China has the largest number of new energy vehicles in the world. The environmental-friendly heat pump with low global warming potential (GWP) is increasingly essential for the electric vehicle (EV) to save energy consumption and extend the driving range, it is beneficial to achieve the carbon neutrality from reducing both direct and indirect carbon emissions. The long-used R134a has a great climate impact due to its high GWP, researchers have been investigating heat pump systems with low-GWP refrigerants. Previously, the life cycle climate performance (LCCP) was a widely accepted metric to evaluate the carbon footprint of mobile air conditioning systems “from cradle to grave” for the classical engine vehicle, however, the new energy vehicle heat pump has significant differences from the mobile air conditioning systems, which makes the LCCP developed for MAC systems no longer applicable for the NEV heat pump system. Such LCCP analysis about EV heat pumps can hardly be found. To facilitate the EV industry and policymakers better understand the environmental impacts of those low-GWP refrigerants, this study provides a comprehensive LCCP analysis for the EV heat pumps based on the heat pump system bench test results, local climates (six cities: Beijing, Shanghai, Guangzhou, Phoenix, Fargo, and Chicago), local power supply characteristics, real-world driving patterns, vehicle cabin thermal sensation, and climate control load. Three low-GWP refrigerants, i.e., CO₂, binary blends of CO₂ and R41 (with GWP value of 49), M2 (R410A substitute with GWP value of 137), were compared against R410A and R134a. Results show that the system COPs in the energy consumption model are estimated within ±6.5%; In most regions, the heat pump can save 36%–69% of electricity for heating on electric vehicles compared to the conventional PTC heater system; The direct emissions depend on the refrigerant GWP and are almost unaffected by the climate. The indirect emissions are influenced by the climate, refrigerant type and the carbon intensity; among the indirect emissions, manufacturing and EOL disposal account for only 5% or so, while the major part is the emissions due to system operation; The R410A heat pump shows higher levels than R134a in both direct and indirect emissions, with 11%–36% increase in total; although M2 shows 2%–27% higher indirect emissions than R134a, it reduces 90% of the direct emissions. In general, it shows 3%–35% less total emissions compared to R134a for EV heat pump application; the direct emissions of the CO₂ heat pump can be neglected while the CO₂ system can reduce 7% of the indirect emissions only in cold climates such as Fargo. Thanks to its low direct emissions, the total LCCPs of the CO₂ heat pump are reduced by 6%–27% relative to R134a except in Shanghai (+20%); among the selected refrigerants, CO₂/R41 shows the lowest LCCP, reducing 5%–42% of total emissions relative to R134a in various climates, and 1%–21% less than the CO₂ system.