). Unlike traditional air – conditioning systems using hydrofluorocarbons (HFCs),
as a natural refrigerant has a low global warming potential (GWP), making it an environmentally friendly choice. In the transcritical cycle, when the compressor is in operation, it raises the pressure of the
refrigerant to above its critical pressure. The high – pressure, high – temperature
then flows to the gas cooler. Here, heat exchange occurs between the
and the ambient air, and the
releases heat and is cooled. Subsequently, the cooled
passes through an expansion device, where its pressure drops rapidly, causing it to cool further and enter the evaporator. In the evaporator, the low – pressure
absorbs heat from the air inside the bus, cooling the air, and then returns to the compressor to complete the cycle, continuously providing a comfortable cooling environment for passengers.
air – conditioning system. Due to the high operating pressure of the
refrigeration cycle (much higher than that of traditional refrigerants), special high – pressure – resistant compressors are required. Scroll compressors or reciprocating compressors with enhanced structural strength and sealing performance are commonly used. These compressors are designed to efficiently compress the
refrigerant, ensuring stable operation of the system and reliable refrigeration performance. They also need to have good heat dissipation capabilities to prevent overheating during long – term high – pressure operation.
refrigerant during the compression process. It is usually a fin – and – tube heat exchanger, with a large heat – transfer area to enhance the heat – exchange efficiency between the
and the ambient air. The gas cooler is often installed on the exterior of the bus, where it can directly exchange heat with the outside air. Its design must take into account the high – pressure characteristics of
and ensure good structural strength and corrosion resistance to withstand the harsh operating environment of the bus.
flowing through the evaporator absorbs heat from the warm air blown over it by the fan, thus cooling the air. The evaporator’s structure is optimized to maximize the heat – transfer surface area and improve the heat – exchange efficiency. Additionally, it needs to be designed to handle the two – phase flow of the
refrigerant (a mixture of liquid and gas) during the evaporation process, ensuring smooth operation and stable cooling performance.
refrigerant. It precisely controls the amount of refrigerant entering the evaporator, ensuring that the refrigerant evaporates completely and efficiently in the evaporator. The electronic expansion valve offers more accurate control, allowing for better adaptation to different operating conditions of the bus, such as varying passenger loads and ambient temperatures, compared to the capillary tube, which has a fixed flow – rate characteristic.
has a very low GWP (close to 1), which is far lower than that of traditional HFC refrigerants. Using
as a refrigerant significantly reduces the contribution to global warming from the air – conditioning system of the bus. Moreover,
is a natural substance, non – toxic, and non – flammable, eliminating the potential risks associated with the leakage of synthetic refrigerants, making it more environmentally and user – friendly.
refrigeration cycle has the potential for high – efficiency operation, especially in high – ambient – temperature conditions. Compared to traditional refrigeration cycles, the
cycle can maintain relatively high coefficient of performance (COP) values. This means that it can achieve the same cooling effect with less energy consumption, reducing the fuel consumption of the bus (for diesel – powered buses) or the electricity consumption (for electric buses), and thus saving operating costs and reducing emissions.
, the
bus air – conditioner can achieve a faster cooling response. When the bus starts running or when there is a sudden increase in the number of passengers, the air – conditioning system can quickly adjust and cool the interior of the bus to a comfortable temperature, improving the riding experience of passengers.
refrigeration cycle poses challenges to the materials and manufacturing processes of system components. To address this, advanced materials with high – strength and high – pressure – resistance, such as special stainless steels and high – performance alloys, are used in the manufacturing of components like the compressor, gas cooler, and evaporator. Special welding and sealing technologies are also employed to ensure the tightness and reliability of the system under high – pressure conditions.
bus air – conditioning systems are equipped with enhanced heat – rejection measures, such as additional fans, improved airflow designs around the gas cooler, or even incorporating phase – change materials to assist in heat dissipation, ensuring the stable operation of the system under various operating conditions.
