The biggest breakthrough in thermal management technology of new energy vehicles comes from the further popularization and promotion of heat pump technology.
01
What is heat pump technology?
The heat pump technology of new energy vehicles is an effective solution to solve the shortening of the winter mileage of pure electric vehicles. Using the "inverse Carnot" cycle of the air conditioner, the heat pump can "pump" the heat from the low temperature air outside the car to the relatively high temperature seat room. The use of heat pumps to heat air conditioners in winter can reduce energy consumption by 60% and increase the mileage by about 25% compared with the use of traditional PTC heating.
The refrigeration principle of traditional air conditioning is to use the change of the state of the refrigerant, from the gaseous state to the liquid state will emit heat, and from the liquid to the gaseous state will absorb heat. The "reverse Carnot" cycle used for heating in the car is contrary to the refrigeration principle of traditional air conditioning, and a "four-way electromagnetic reversing valve" can be used to realize the refrigeration cycle or heating cycle, so that the car can get cold air or hot gas. In the circulation of air conditioning refrigerant, the use of high temperature and high pressure gas in the condenser liquefaction into high pressure liquid process, will release a large amount of heat, this is the principle of heat pump exothermic heat. In winter, the directional valve can be used to change the flow direction of the air conditioning refrigerant, at this time, the evaporator acts as a condenser in the reverse cycle to exotherm, forming a "heat source". At this time, only a small part of the electrical energy is consumed, and a large amount of heat from the outside world can be transported into a pure electric vehicle and become a heat pump. However, the heating effect of the heat pump in the low temperature environment still needs to be improved.
At present, the heat pump system from the two heat exchanger circuit architecture to the three heat exchanger circuit architecture, with the intermediate heat exchanger of the gas enthalpy circuit architecture, the two-stage compression circuit has a thermal management system supplier in development, some manufacturers have passed the bench test and loaded the car, to achieve part of the mass production.
Image source: Zhihu
Such as Audi e-tron, Volkswagen iD3, Ideal Car ONE, Xiaopeng P4, SAIC Passenger Car ei5 and Marvel X, FAW Car B30EV, BYD Han, Weilan Auto ET7, GAC Aion LX, Changan Automobile C211EV4, Tesla Model Y, etc., 36% of electric vehicles have adopted heat pump technology, and it is expected to reach more than 60% in 2026.
At the same time, the integration of components is also increasing, the introduction of super kettles and 8-way valves, air conditioning ECU is integrated into the vehicle ECU architecture. Active cooling and active heating technology has become the mainstream technology choice for battery heat management, and liquid cooling technology is adopted in 74% of new energy vehicles, and liquid cooling technology has been fully adopted in medium and high-end cars.
"Octovalve" – the core of Tesla's Model Y's HVAC system
The image comes from the Internet
02
Technical difficulties of heat pump systems
At present, the thermal management system of new energy vehicles still urgently needs to solve the technical difficulties of the application of heat pump systems as follows:
1) The heat pump system needs to be further optimized and simplified for different application scenarios. The application of heat pump technology is also strongly related to the energy density of the battery, and the cost reduction rate per kWh battery and the cost reduction rate per kW of the heat pump are in competition, which also determines the application speed and depth of the heat pump technology. At present, the proposed circuit control components of the heat pump system are still more numerous, the system control is still more complex, and the system reliability is not high;
2) The integration and modularization of electric components need to be further improved. Such as the integration of electronic expansion valves and battery coolers, four-way reversing valves and system reliability and durability;
3) The system performance is further improved under the working conditions of the heat pump. Especially in the north use scenario of -30 °C, the performance of the R134a/R1234yf system is sharply reduced, the heat is not enough, the power consumption is increased, and the outdoor heat exchanger is seriously frosted under low temperature conditions such as (2 °C/1 °C ambient temperature) and the system performance deteriorates;
4) The cost of the heat pump system needs to be further reduced. Due to its complexity and more components, the heat pump system of new energy vehicles makes its cost less advantageous than that of conventional thermal management systems. On the one hand, it is necessary to further increase the promotion of heat pump systems to dilute design and development costs, and on the other hand, to reduce costs through technical improvements (such as system optimization, low-cost alternative materials, etc.) and integrated design and manufacturing;
5) The research and development of CO2 heat pump system is not enough. Under the development trend of environmental protection and heat pump, CO2 heat pump system has natural heating performance advantages, which is more and more valued in the industry, but there are still many technical problems that need to be solved urgently, such as the balance of refrigeration and heating performance, system high pressure safety issues, system key component design and matching, manufacturing system upgrade conversion and transformation, after-sales maintenance service system transformation and upgrading.
Volkswagen ID.4 co2 heat pump system analysis
Image source: CITIC Securities
03
Solutions to technical difficulties in heat pumps
For the technical difficulties of thermal management of new energy vehicles described in the second section, major automotive thermal management competitors at home and abroad are doing solutions and product development.
In terms of heat pump systems, foreign BMW, Tesla and Volkswagen have been applied to electric vehicle products, and domestic FAW Besturn B30EV, SAIC Roewe Ei5 and Roewe Marvel X, Xiaopeng Automobile P5 have been applied heat pump air conditioning systems.
Sunden has also developed compressors for heat pump systems using CO2 and installed them on Mercedes-Benz models.
Domestic BYD has developed and produced heat pump products using R410A, which can meet the heating needs of the whole vehicle in the extremely cold environment of -40 °C, COP reaches 3.5 at -10 °C, and recently, it is developing R290 heat pump air conditioners.
The three heat exchanger passenger car R134a heat pump air conditioner developed by Shanghai Jialang Songzhi can meet the use of ambient temperature -20 °C, and the COP reaches 1.8 at -10 °C, and has been successfully applied to all new energy models of JacHuai Automobile and SAIC-GM-Wuling mini EV. In addition, the ultra-low temperature R410A bus heat pump air conditioner with intermediate heat exchanger and make-up gas enthalpy refrigeration circuit has been developed and mass-produced, which can meet the ambient temperature of -30 °C, and the COP reaches 1.48 at -20 °C.
In the development of heat pump system, Tesla adopts a system coupled with air circuit, refrigerant circuit and coolant circuit, adds electric motor waste heat recovery and reuse to the heat pump system, and applies it to mass production on Model Y.
It is worth mentioning that Tesla has introduced an auxiliary heating mode that runs electric compressors and brushless fans in the non-efficiency zone, which can make full use of existing parts for auxiliary heating without adding parts, greatly improving heating capacity and heating energy efficiency, and effectively reducing the cost of system components.
Tesla ModelY heat pump system
Image source: Gaogong New Car Review
In summary, domestic and foreign competitors in the development of heat pump air conditioning technology is basically go hand in hand, each has its own advantages, covering refrigeration, heating, dehumidification, pre-cooling, preheating and a variety of mixed mode crew compartment and battery thermal management requirements. However, in the field of passenger cars, the commercialization of foreign technology is slightly earlier than that of China, and in the field of large buses, Chinese manufacturers are still relatively leading.
Source:
1. Huang Guoqiang. Development and Technology Path Exploration of Automotive Thermal Management Industry[J].Refrigeration and Air Conditioning,2022,22(03):78-83.
2. Wang Guixing, Wang Yuxuan. Principle and application of "heat pump" for pure electric vehicles[J].Automotive Repair and Maintenance, 2022(01):42-44.