Types of battery thermal management systems
Different battery thermal management methods involve different numbers of parts, structures, and layouts. Different types of thermal management systems are selected based on vehicle development costs, vehicle weight, and layout space requirements. The main technical routes are the following five types:
1. Direct cooling type
Referred to as battery direct cooling technology, the direct cooling system is a built-in refrigeration evaporator inside the battery, which is connected to the air conditioning system through a pipeline. When the battery needs to be cooled, the compressor is used to send the compressed refrigerant into the evaporator inside the battery, and then take away the heat inside the battery to achieve the cooling effect. The system has the advantages of compact structure, good cooling effect, small number of parts (only one inlet and one outlet refrigeration pipeline is required), light weight, etc. However, the disadvantage of this system is that it cannot heat the battery under sub-zero low temperature conditions, the condensed water generated during the refrigeration process is unprotected, and the temperature uniformity of the refrigerant is difficult to control. The refrigeration system has a short life and low reliability, and often refrigerant leakage, insufficient refrigeration capacity and other faults occur. This is the latest battery cooling technology, with a relatively low maturity. It has been applied in mass-produced models such as BYD and Tesla on the market. It is a major technical route in the future, as shown in Figure 1.
2. Radiator water cooling type
The radiator cooling circuit is an independent circuit, which consists of a radiator, an electronic water pump, a heater, etc., with antifreeze as the medium. The antifreeze comes out of the radiator, passes through the heater to the battery, and finally returns to the radiator. This circulation method is used to cool and heat the battery. The system has the advantages of simple structure, low cost, and energy saving in a perennial low temperature environment. However, the system has low heat dissipation efficiency, and the water temperature is high in a high temperature climate environment in summer, which cannot meet the use conditions in a high temperature environment, as shown in Figure 2.
3. Direct cooling and water cooling type
This system is integrated on the basis of direct cooling and water cooling, and bridges the air conditioning system and the water cooling system through the battery cooler Chiller (also called heat exchanger). This system avoids the shortcomings of the first two cooling methods and is one of the most commonly used battery thermal management systems. The system has more components than the first two, the system is more complex, and the required component layout space is relatively large. The compressor load is large during operation, which consumes a lot of energy for the whole vehicle and has poor economy. In addition, when the air conditioning system fails partially, the battery cooling demand cannot be fully met, as shown in Figure 3.
4. Water-cooled hybrid type
This system is based on the direct cooling water cooling system, and adds a radiator water cooling system. The two are arranged in parallel circuits. By controlling the solenoid valve, different circuits are used to cool the battery under different conditions. In low temperature environments, only the radiator water cooling system needs to work. When in a high temperature environment, switch to the direct cooling water cooling system. Under harsh working conditions, the two systems can work at the same time, and the battery can also obtain maximum cooling capacity, which can basically cover all usage environments. This cooling system is extremely complex and costly, and has high requirements for the layout space of the whole vehicle. The control strategy of the system is complex, and stability and reliability are a challenge. This system is also used in most hybrid PHEV models on the market and has mature technology, as shown in Figure 4.
5. Air cooling type
This system directly guides the cold air from the passenger compartment to the battery through a pipe, and uses the cold air to cool the battery. The advantages of this system are simple structure, controllable cold air temperature, and low system cost. However, it also has the disadvantages of the direct cooling system. The system has no heating function, and the condensed water generated on the battery surface is not easy to dry, which has the risk of erosion and contamination to the inside of the battery. This type of thermal management method is generally not recommended, see Figure 5.
