Research on heat pump integrated thermal management system
for pure electric commercial vehicles
1. Traditional thermal management system
Thermal management systems commonly used in the design of pure electric commercial vehicles for the main heat sources include power battery system thermal management (BTMS), air conditioning system thermal management and motor electronic control system thermal management. The traditional decentralized thermal management system is that the three loops of battery, air conditioning and motor electronic control system are independent of each other. Each has a complete temperature control system and pipeline system. Therefore, during the operation of the car, there is an electric heating system for a certain system. At the same time, the external heat dissipation energy of another component or system is not fully utilized, which not only causes energy waste, but is also detrimental to energy conservation and environmental protection. On the other hand, due to the low integration level of the entire thermal management system, the pipelines are complex, the number of parts is high, the cost is high, and the quality of the vehicle is heavy. This also accelerates the consumption of battery power during vehicle operation and reduces vehicle life. The driving mileage has a considerable impact on the economy of the vehicle.
2. Heat pump type integrated thermal management system
On the basis of integrated thermal management systems, in order to better meet the high temperature sensitivity of batteries, the complexity and refinement of thermal management of pure electric commercial vehicles continues to increase, and some innovative applications are being added, such as heat pumps Technology is one of them. The heat pump itself does not produce heat, but is just a transporter of heat. Based on the reverse Carnot cycle principle (Figure 1), it uses a small amount of electric energy to drive the unit, circulates the working medium in a disguised phase, and absorbs, compresses, and heats low-grade heat energy before utilizing it. The main components of a heat pump include refrigerant, compressor, condenser, expansion valve and evaporator. It is a closed loop in which the medium, the refrigerant/refrigerant, is continuously compressed and expanded in the loop. Each time it is compressed and expanded (that is, each cycle of operation), the refrigerant "extracts" heat from the low-temperature environment and transfers it to the high-temperature environment. Air is not used as a refrigerant, although it does not cause pollution and is cost-free, because its thermal efficiency per cycle is quite low. The actual refrigerant used is a liquid that evaporates when absorbing heat and condenses when dissipating heat. The process of changing liquid form can greatly improve thermal efficiency in each working cycle. The heat pump system has two working modes: cooling and heating. By integrating heat pump technology with integrated thermal management systems, new heat pump-type integrated thermal management systems can be developed. The heat pump air conditioning system using this technology uses an electric air conditioning compressor and utilizes the reversible characteristics of the refrigeration cycle to integrate refrigeration and heating. It has the advantages of good versatility, compact structure, high efficiency, energy saving and environmental protection, and has become a new type of vehicle air conditioner. trend. Under winter heating conditions, the COP (Coefficient of Performance) can reach 2 to 4. The energy efficiency is many times that of the PTC heating system commonly used in the field of pure electric vehicles, which can effectively extend the driving range by more than 20%. The current types of heat pump systems mainly include direct heat pump air-conditioning systems, indirect heat pump air-conditioning systems and air-supplementing and enthalpy-increasing direct heat pump air-conditioning systems. As shown in Figure 2, they can be used for heating and cooling. In layman's terms, the use of a four-way reversing valve in a heat pump system can interchange the functions of the evaporator and condenser of the heat pump air conditioner and change the direction of heat transfer, thereby achieving the effect of cooling in summer and heating in winter.
3. Advantages and disadvantages of heat pump integrated thermal management system
The main advantages are: 1) Strong system integration: multiple thermal management subsystems are integrated into one system to achieve unified control and optimization; this helps reduce system complexity and improve management efficiency. 2) Energy efficiency By precisely controlling the temperature and heat flow of each component, energy can be used more efficiently and energy consumption can be reduced. 3) Intelligent management: Usually equipped with advanced sensors and control systems, which can monitor and adjust the operating status of the system in real time to achieve intelligent management. 4) Environmental adaptability: The operating strategy can be automatically adjusted according to environmental conditions to improve the adaptability and stability of the system. 5) Installation and maintenance: The integrated thermal management system has a compact structure and is easy to install.
The main disadvantages are: 1) High technical difficulty: multiple subsystems need to be integrated, the technical difficulty is relatively high, and professional technical support is required. 2) Large initial investment: Since integrated thermal management requires the integration of multiple subsystems, the initial investment is relatively large. 3) High maintenance costs: Due to the high complexity of the system, the maintenance costs of integrated thermal management are also relatively high. To sum up, the heat pump integrated thermal management with the purpose of improving the comprehensive performance of the vehicle, the standard of integrated design optimization, and the means of multi-system coordinated control and overall management has great advantages in energy utilization efficiency, intelligent management, environmental adaptability and long-term performance. It has significant advantages in terms of lifespan and other aspects, and these advantages are the general trend in the development of vehicle thermal management in the future.
