Multi-Source Heating Strategy Boosts Range in Extended-Range EVs
As winter temperatures drop, electric vehicle owners often face a familiar challenge: reduced driving range due to high energy demands for cabin heating. Traditional resistive heaters, while reliable, consume significant battery power, directly impacting the vehicle’s overall efficiency and usability in cold climates. In response to this critical issue, a team of researchers from Chongqing University of Technology and Ningbo Shenglong (Group) Co., Ltd. has developed an innovative, multi-source heating strategy for extended-range electric vehicles (EREVs) that dramatically improves energy efficiency and reduces cabin heating energy consumption, especially in sub-zero conditions.
The study, led by Dr. Yong Luo and his colleagues, introduces a comprehensive thermal management system that intelligently integrates four distinct heat sources: engine waste heat, electric drive system waste heat, positive temperature coefficient (PTC) heaters, and ambient air via a heat pump. This integrated approach marks a significant advancement in vehicle thermal management, moving beyond conventional single-source heating methods to create a dynamic, adaptive system that selects the most energy-efficient heating mode based on real-time operating conditions.
Extended-range electric vehicles, which combine a battery-powered electric drivetrain with a small internal combustion engine (ICE) acting solely as a generator, present a unique opportunity for advanced thermal management. Unlike pure battery electric vehicles (BEVs), EREVs have access to waste heat from the engine and electric powertrain components, which can be harnessed to warm the cabin. The research team recognized that this combination of available heat sources—engine heat, motor and inverter heat, ambient air, and supplemental electric heating—creates a rich landscape for optimization. Their goal was to design a system that could seamlessly switch between these sources to minimize total energy consumption while maintaining passenger comfort.
The core of their solution is a sophisticated control strategy that prioritizes heat sources based on their coefficient of performance (COP), a measure of heating efficiency. The system operates on a clear hierarchy. When the vehicle is running and the engine is warm—typically above 80°C—the system first utilizes engine waste heat. This method is highly efficient because it recovers energy that would otherwise be dissipated through the radiator. Since no additional electrical energy is required to generate this heat, the effective COP is very high, significantly reducing the load on the battery. This mode is particularly effective during the charge-sustaining (CS) phase of EREV operation, when the engine is actively generating electricity.
If the engine is not running or is not yet warmed up, the system turns to the next best option: waste heat from the electric drive system. Components like the motor, inverter, and generator generate substantial heat during operation. The researchers designed a heat pump loop that extracts this low-grade heat (typically from coolant around 30°C) and upgrades it to a temperature suitable for cabin heating. This “electric drive waste heat recovery heat pump” mode leverages the thermodynamic principles of a vapor-compression cycle to amplify the available thermal energy, achieving a much higher COP than direct electrical heating. This mode is ideal during the initial charge-depleting (CD) phase when the vehicle is operating in pure electric mode.
In situations where no waste heat is available—such as a cold start with a cold engine and cold powertrain—the system relies on ambient air and the vehicle’s heat pump. The air-source heat pump extracts heat from the outside air, even in cold conditions, and transfers it into the cabin. This method is highly efficient in mild winter conditions, typically above -10°C, where the temperature difference between the outside air and the desired cabin temperature is manageable. The heat pump can achieve a COP of 2 to 4, meaning it delivers two to four times more heat energy than the electrical energy it consumes, a stark contrast to the COP of 1.0 for a PTC heater.
Finally, when the ambient temperature falls below a critical threshold—determined by the research to be -10°C—the air-source heat pump becomes inefficient due to the low availability of thermal energy in the air and the physical limitations of the refrigerant. In these extreme cold conditions, the system defaults to the PTC heater. While this is the least efficient option, it is the most reliable and ensures that the cabin can be heated when no other viable source is available. The strategic use of PTC only as a last resort is key to the system’s overall energy savings.
To validate their design, the research team constructed a sophisticated joint simulation model using AMESim and Simulink. AMESim was used to model the complex physical systems—the engine, battery, electric motors, and the multi-loop thermal management system with its intricate network of valves, pumps, heat exchangers, and coolant flows. Simulink was used to develop the control algorithms that govern the system’s decision-making process. This co-simulation approach allowed for a highly realistic assessment of the system’s performance under various driving cycles, including the New European Driving Cycle (NEDC), and across a range of ambient temperatures from -20°C to 0°C.
The simulation results were compelling. The multi-source integrated heating strategy consistently outperformed both a baseline system using only a PTC heater and a system using only an air-source heat pump. At an ambient temperature of -20°C, the integrated strategy reduced heating energy consumption by 32.1% compared to a PTC-only system and by a remarkable 50.7% compared to an air-source heat pump system. This dramatic reduction in energy use translates directly into extended driving range, a crucial factor for consumer acceptance of electric vehicles in colder regions.
The researchers also analyzed the system’s coefficient of performance (COP) over time. The data showed a dynamic shift in operating modes that perfectly aligned with their control strategy. In the coldest scenario (-20°C), the system began in PTC mode, switched to the electric drive waste heat recovery heat pump as the powertrain warmed up, and then transitioned to the highly efficient engine waste heat recovery mode once the engine was running and hot. This seamless transition, managed by a series of solenoid and three-way valves, demonstrated the robustness of the control logic.
One of the key insights from the study is the importance of mode-switching logic and hysteresis. To prevent frequent and inefficient toggling between modes, the researchers incorporated a 10°C temperature hysteresis into the control strategy. For example, the system might switch from air-source heat pump to PTC at -10°C but would not switch back until the temperature rose to -0°C. This prevents the system from oscillating between modes during minor temperature fluctuations, ensuring stable cabin temperatures and reducing wear on the components.
The practical implications of this research are significant. For automakers, this integrated thermal management system provides a blueprint for improving the winter performance of their EREV models. By recovering and utilizing waste heat that is often ignored, manufacturers can offer vehicles with longer effective range and lower energy costs for consumers. For fleet operators, the reduced energy consumption can lead to lower operating expenses over the vehicle’s lifetime. For drivers, it means greater confidence in their vehicle’s ability to handle long winter commutes without the fear of being stranded due to a depleted battery.
The study also highlights the broader trend in automotive engineering toward system-level integration and optimization. Modern vehicles are no longer just a collection of independent subsystems; they are complex, interconnected networks where data and energy flow in multiple directions. The success of this multi-source heating strategy depends on the tight integration of the powertrain, battery, and climate control systems, all governed by a central control unit that makes real-time decisions based on a wide array of sensor inputs.
This research builds upon a growing body of work in the field of vehicle thermal management. Previous studies have explored the use of heat pumps in BEVs and the recovery of waste heat from fuel cell systems. However, the unique advantage of the EREV platform is the consistent availability of a high-grade heat source—the engine—when needed. The work by Luo and his team effectively leverages this advantage to create a system that is both highly efficient and highly adaptable.
The findings have direct relevance to current industry challenges. As governments around the world push for electrification of transportation, the performance of vehicles in cold climates remains a significant barrier to adoption. Solutions like this multi-source heating strategy can help to overcome “range anxiety” and make electric vehicles a more viable option for a larger portion of the global population. It also aligns with the broader goals of energy conservation and carbon reduction, as every kilowatt-hour of electricity saved means less demand on the power grid and fewer emissions from power generation.
The research methodology is also noteworthy. The use of joint simulation with AMESim and Simulink is a powerful tool for automotive engineers, allowing them to test complex control strategies in a virtual environment before committing to expensive physical prototypes. This approach accelerates the development cycle and reduces risk, enabling faster innovation and more reliable final products.
Looking ahead, this work opens several avenues for future research. The integration of battery thermal management into the same system could create an even more holistic approach, where waste heat from the engine is also used to warm a cold battery, further improving its efficiency and longevity. The use of advanced refrigerants with better low-temperature performance could potentially lower the threshold for effective heat pump operation, reducing the need for PTC heating even further. Additionally, the incorporation of predictive algorithms that use weather forecasts and route information could allow the system to pre-heat the cabin or manage the engine warm-up phase more intelligently.
In conclusion, the multi-source heating strategy developed by the team at Chongqing University of Technology represents a significant step forward in the quest for more efficient and practical electric vehicles. By intelligently combining engine waste heat, electric drive waste heat, a heat pump, and a supplemental PTC heater, they have created a system that dramatically reduces energy consumption for cabin heating. This not only extends the vehicle’s driving range but also enhances passenger comfort and contributes to the overall sustainability of electric transportation. As the automotive industry continues its transition to electrification, innovations like this will be critical in ensuring that electric vehicles are not just environmentally friendly but also practical and desirable for consumers in all climates.
Yong Luo, Hao Li, Long Zhang, Xiaobin Qiu, Lisha Li, Qiang Sun, Chongqing University of Technology, Journal of Chongqing University of Technology (Natural Science), doi:10.3969/j.issn.1674-8425(z).2024.11.008