In the quest to make electric vehicles (EVs) more efficient and comfortable in cold weather, researchers have been tackling a persistent issue: frost buildup on heat pumps. A recent study led by Wenying Zhang from the Air Conditioning and Refrigeration Center at the University of Illinois Urbana-Champaign sheds new light on how to optimize heat pump performance under cyclic frosting and defrosting conditions. The findings, published in Energies, could significantly impact the design and control strategies of automotive heat pumps, paving the way for more efficient and reliable EV heating systems.
Heat pumps are crucial for maintaining cabin comfort in EVs, especially in cold climates. However, when temperatures drop and humidity rises, frost can accumulate on the outdoor heat exchanger, reducing system efficiency. Zhang’s team investigated how different defrost-initiation criteria and orientations of the outdoor heat exchanger affect the performance of a reversible CO2 heat pump system.
One of the key findings is that the heating capacity of the heat pump system degrades only mildly (~30%) even when the air-side pressure drop of the outdoor heat exchanger increases tenfold. This means the system can operate in heat pump mode for a longer duration before defrosting, without significantly impacting passenger comfort. “This is a significant finding,” Zhang explains, “because it shows that we can delay defrosting without compromising the heating performance, which is crucial for maintaining cabin comfort in EVs.”
The study also compared the performance of horizontally and vertically installed outdoor heat exchangers. While the horizontal orientation showed better refrigerant distribution, it had a higher pressure drop, leading to faster frost accumulation and a shorter working time in heat pump mode. On the other hand, the vertical orientation drained more water during defrosting, reducing the defrosting time by 17%.
These insights are not just academic; they have real-world implications for the automotive industry. As more countries announce bans on internal combustion engines, the demand for efficient and reliable EV heating systems is set to rise. Manufacturers could use these findings to optimize their heat pump designs, improving efficiency and reducing the frequency of defrosting cycles. This could lead to longer battery life, reduced energy consumption, and ultimately, more sustainable and cost-effective EVs.
Moreover, the study highlights the importance of considering cyclic frosting and defrosting conditions in heat pump design and control strategies. Most existing research focuses on a single frosting-defrosting period, but real-world conditions involve repeated cycles. By understanding how these cycles interact, researchers and engineers can develop more robust and efficient systems.
The research also opens up new avenues for exploring advanced defrost-initiation criteria. Instead of relying on a single parameter, future systems could use comprehensive indices or machine learning algorithms to optimize defrosting timing. This could further enhance the efficiency and reliability of EV heat pumps.
As the automotive industry continues to evolve, studies like Zhang’s will play a crucial role in shaping the future of EV technology. By addressing the challenges posed by frosting and defrosting, researchers are paving the way for more efficient, reliable, and sustainable electric vehicles. The findings, published in Energies, provide a solid foundation for further research and development in this field, bringing us one step closer to a greener, more energy-efficient future.