Choosing an air conditioner for a bus requires a combination of many factors.
First, the cooling capacity must be considered. Usually, the required cooling capacity is estimated based on 400kcal/h per passenger, and then an air conditioning unit close to this cooling capacity is selected. However, it should be noted that even if the air conditioning units are the same, the differences in the internal layout of different models will affect the cooling effect.
The heat load of a bus compartment comes from various sources, such as the external heat transmitted from the walls, doors and windows of the car, the solar radiation heat, the hot air infiltrating the gaps, the heat emitted by the human body, the heat transmitted from the engine room, and the heat released by the components in the compartment.
The selection of refrigeration system is very important. The refrigeration system for buses has the following characteristics: many passengers, large ventilation volume per person, and large refrigeration volume per person; the electric drive consumes a lot of battery power, which affects the driving range of electric buses; limited by the quality of the whole vehicle and the installation space, the system components vary from model to model, and it is difficult to universalize them. It requires each assembly to be reliable, compact, small, light, and easy to maintain; the height inside the car is low, the air flow distribution is difficult, and the temperature distribution is not easy; the window glass area is large, and the insulation requirements of the whole vehicle are high.
The refrigeration system is divided into four categories according to the drive form. The independent refrigeration system is equipped with a special engine to drive the refrigeration system. It works stably and reliably and is suitable for tourist and long-distance buses that are parked for a long time, but it has high cost, large curb weight, and difficult maintenance. There are two types: independent integral type and independent split type.
The air conditioning matching design must comply with relevant standard documents, such as JT/T 216-20__6 “Technical Conditions for Passenger Air Conditioning Systems”, QC/T 656-20_ “Performance Requirements for Automobile Air Conditioning Refrigeration Devices”, CJ/T 134-20__1 “Technical Conditions for Urban Public Air-conditioned Bus Air Conditioning Systems”, and DB31/T 306-20__ “General Technical Requirements for Public Buses”.
The air conditioning system adopts the principle of vapor compression refrigeration and continuously circulates refrigeration. There are also requirements for the function, performance and comfort of the air conditioning system. In terms of function, it must have basic functions such as refrigeration, ventilation, air volume and temperature adjustment, compartment temperature display and fresh air. The control panel should be intuitive and easy to understand and easy to operate. The control device should have a CAN communication interface and self-detection and diagnosis functions, and can automatically adjust the compressor and fan speeds to control the temperature error within ±1 ℃. In terms of performance, the average temperature in the car in summer should be ≤30℃, the maximum temperature difference should be ≤3℃, the wind speed at the air outlet should be uniform, and the conventional air outlet should be within the range of 3m/s～6m/s. In terms of comfort, the air volume and air outlet direction of the air outlet facing the seat passengers can be adjusted and closed, and the air outlet facing the aisle can be adjusted but not completely closed. The noise inside the car should be well controlled when idling, and the cooling-only air conditioning unit should be ≤75dB (A) in a specific location.
