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Refrigerant selection is an important factor in bus air conditioning system design. For bus OEMs and fleet operators, the refrigerant used in an HVAC system can affect environmental compliance, operating performance, maintenance requirements and long-term system compatibility.
Bus air conditioning systems generally use a vapour compression refrigeration cycle. In this process, the compressor compresses low-pressure refrigerant gas into high-temperature, high-pressure gas. The refrigerant then passes through the condenser, where heat is released outside the vehicle and the refrigerant changes into liquid form. The liquid refrigerant moves through the expansion valve, where pressure drops and the refrigerant becomes a low-temperature mixture. Finally, in the evaporator, the refrigerant absorbs heat from the passenger compartment and vaporizes, helping to cool the cabin.
Two environmental indicators are commonly used when comparing refrigerants. ODP, or Ozone Depletion Potential, measures the potential impact on the ozone layer. Modern mainstream refrigerants used in bus air conditioning systems generally have ODP = 0. GWP, or Global Warming Potential, measures the climate impact of a refrigerant over a defined period. Lower GWP values are increasingly important as regulations such as the EU F-Gas framework and the Kigali Amendment continue to limit high-GWP refrigerants.
R134a is widely used in traditional diesel bus air conditioning systems. It has ODP = 0 and is non-toxic and non-flammable, but its GWP is above 1000. The refrigerant benefits from mature system design, established service knowledge and broad availability for maintenance. However, its high GWP means that its use is increasingly restricted in several regions, especially for newly launched vehicles.
R407C has been used in some earlier small new energy bus air conditioning systems. It is a blended refrigerant with ODP = 0 and high cooling capacity, but it also has a relatively high GWP. It can be relevant for older systems or specific applications, but its long-term use may be limited by regional environmental regulations.
R410A is used in several new energy bus air conditioning systems, especially where higher cooling and heating performance is required. It has ODP = 0 and offers stable cooling and heat pump performance. It can be applied in electric bus HVAC systems using high-voltage vehicle power supply architectures, including DC 420 to 720 V systems. Compared with R134a, R410A operates at higher pressure, so installation, servicing and refrigerant handling require trained technicians and appropriate equipment.
Refrigerant safety and service procedures are important for all bus HVAC systems. Different refrigerant types must not be mixed, as this can cause compressor failure, pipeline blockage or system damage. Refrigerant recovery, replacement and filling should be carried out by qualified maintenance personnel using the correct tools and procedures.
For bus OEMs and fleet operators, refrigerant selection should be based on vehicle type, powertrain, regional regulations, operating climate, service availability and HVAC system design. Diesel buses, electric buses, school buses, coaches and special vehicles may require different air conditioning configurations.
TCHAIN applies different refrigerants across its bus air conditioning portfolio, including diesel bus air conditioners, new energy bus air conditioners and built-in bus HVAC systems. The company states that refrigerant type, filling amount and system parameters can be adapted according to vehicle requirements and regional conditions, subject to project confirmation.
As environmental regulations continue to evolve, refrigerant selection will remain an important part of bus HVAC development. Lower-GWP refrigerants, safe servicing procedures and compatibility with electric bus platforms will become increasingly relevant for OEMs and fleet operators planning future vehicle projects.
