Problems Faced by Electric Bus Air Conditioners and Effective Solutions

In southern China, it is unthinkable that city buses do not have air-conditioning. But if the air conditioner is turned on from the morning to the night, its cruising range will usually drop by more than 30%, and some will reach 50%.

At present, the electrification of buses is accelerating, and the pressure to increase the specific energy of power batteries is very large. At the same time, a brand-new subject has been proposed for bus air-conditioning manufacturers. It is the author who took these questions to share with colleagues the experience after learning from the engineers and technicians of electric bus air-conditioning manufacturers.

1. The insufficiency of air-conditioning in fuel vehicles

As the “big energy consumer” of the automobile assembly, the air conditioner of fuel vehicles accounts for 20% of the engine power. The development of the automobile industry and consumption upgrades have made people increasingly demanding air conditioners. Therefore, the basic trend of engine configuration for fuel passenger cars is high-power and diesel. In the context of increasingly stringent fuel limits, how to reduce the power consumption of bus air-conditioning systems and make fuel vehicles more economical will be a huge challenge. It is not suitable for the development requirements of electric vehicles if only simple electrification of the traditional fuel vehicle air conditioner is carried out.

The evolution from engine cars to electric cars is an inevitable trend. There is no engine on the electric bus, and the air-conditioning power comes from the steering on-board battery. In fact, the specific energy of the current power battery is far from the basic requirements of the car's cruising range. Under this premise, automotive electric air conditioners must be highly efficient and low energy consumption. In other words, the level of automotive electric air-conditioning is also one of the bottlenecks in the development of electric vehicles, and the redevelopment of new products is a must.

1. The basic principles of current electric bus air conditioners

The basic design requirements of the electric bus air conditioning system are:

1) High efficiency, compact structure, light weight, low cost and low noise;

2) Equipped with both cooling and heating devices, which can work under various climatic conditions;

3) The key issue is to save limited on-board electric energy.

1. Air-conditioning assemblies for electric buses currently on the market

Figure 3 shows the composition of an electric bus air-conditioning assembly on the market.

The main changes are: the electric air conditioning compressor is frequency conversion, electronic expansion valve, battery thermal management system interface, cooling (heating) dual purpose.

4, the development of electric buses triggers new changes in air-conditioning technology

1) Energy-saving and emission-reduction technology is a basic requirement;

2) With different heating methods, the design, structure, and concept of air conditioners have also undergone major changes. How to deal with them?

3) Heat pump technology will be a major trend in automotive air conditioners, and there are many technical problems to overcome;

4) The complexity of the control system will greatly increase, how to achieve a higher utilization rate?

5) How to recover the integrated energy for my use?

6) Thermal management will definitely be the basic function of the future air-conditioning system, which is to put the air-conditioning system and the powertrain together in an overall design to become the thermal management system of the entire vehicle. The thermal management system will be more and more closely related to the vehicle, and its importance will be highly prominent;

7) How to combine vehicle thermal management system and power battery thermal dynamic management? The general trend is integration.

5, the main technical problems facing the development of electric bus air conditioners

The condenser has undergone major changes and needs to be developed separately. The main problems are:

1) When the heat pump is used for heating, the original function of the condenser has changed, that is, it should be used as a condenser when cooling;

2) When heating, it should be used as an evaporator, which results in a completely different heat exchange structure and flow channel layout from before.

3) High voltage is introduced, and its insulation requirements and control become more complicated;

4) The two issues of EMC and EMI are particularly sensitive to electric buses. The development of air conditioners for electric buses must attach great importance to this issue.