The future runs on propane
Sustainability is a central component of Eberspächer's vision of clean mobility. At Busworld Europe 2025, the company unveiled its first propane-based air-conditioning systems for buses. In this interview, Kuno Zeller, Head of Development of the Business Unit Bus & Coach, explains why R290 is becoming the key to sustainable mobility.
Our solutions enable existing and new vehicles to be equipped with natural refrigerants. This is a world first and a milestone for us.
Kuno Zeller, Head of Development of the Business Unit Bus & Coach
Why are alternatives to synthetic refrigerants so important for the bus industry?
30 October 2025 – There are several closely related reasons for this. One key aspect is what is known as global warming potential (GWP). This describes how much a refrigerant contributes to global warming compared to carbon dioxide (CO2). CO2 serves as a reference value with a factor of 1. The higher the GWP, the greater the impact a substance has on the climate – the lower the value, the more environmentally friendly it is. The widely used synthetic refrigerants are significantly higher in this respect: R134a, which is frequently used in bus air-conditioning, has a GWP of 1,435. This means that over a period of
100 years, a certain amount of this refrigerant contributes around one thousand five hundred times more to global warming than the same amount of carbon dioxide (CO2). Propane, for example, has a GWP of around 3 and is therefore considered to be significantly more sustainable than synthetic refrigerants. This development shows where the journey is headed. And stricter legal requirements are further accelerating the switch to natural refrigerants.
What are the specific legal conditions?
There are essentially three legal developments that are accelerating the shift towards natural refrigerants. The most important is the EU F-Gas Regulation. It is based on the international Kigali Agreement and has been signed by over 170 nations. This obliges countries to gradually reduce the use of fluorinated greenhouse gases. A phase-down curve has been defined for this purpose: since 2015, the total amount of refrigerants available has been falling continuously. In the European Union, only 25 percent of the original quantities may be placed on the market since March 2024, and by 2030 the proportion will be reduced to just five percent.
This gradual shortage means that conventional synthetic refrigerants are not only becoming more expensive but will also be virtually unavailable in the long term. At the same time, the EU is preparing to ban PFAS (per- and polyfluoroalkyl substances). These so-called “forever chemicals” are found in many refrigerants, do not degrade in the environment, and are considered potentially hazardous to health. As things stand at present, the law is set to come into force in 2029, with a transition period of around six and a half years – meaning that a complete ban will be in place by 2035 at the latest.
In practice, this means that a bus sold today with a lifespan of around 15 years will no longer be allowed to run on conventional refrigerants in about ten years' time, according to current regulations. This is why not only new, sustainable systems are in demand, but also retrofit solutions. These enable existing vehicle fleets to switch to natural refrigerants.
What solutions does Eberspächer offer to meet these new requirements?
We will also be offering our roof-mounted air-conditioning systems – the AC135 family and the AC138 EVO – with natural refrigerants in the future. Propane covers a wide temperature range from approximately -15 to +55 degrees in heating and cooling mode and is particularly suitable for warm climates and heat pump operation. For cooler regions, we rely on CO2-based systems as an efficient alternative.
In addition, we worked with several partners to develop a retrofit concept for diesel buses.
How do our systems differ from those of other manufacturers?
The biggest difference lies in the system design. Many manufacturers only use propane in an indirect system: the refrigerant first cools water, which is then fed into the passenger compartment via a heat exchanger. Although this reduces the amount of refrigerant and potential contact, it also reduces efficiency—every additional heat exchanger means energy losses. We go one step further with a direct refrigerant circuit. This means that the propane flows directly through the evaporator and condenser without a secondary medium. This eliminates an entire circuit, numerous components, and unnecessary mass. The effect is measurable: compared to indirect systems, we achieve up to 27 percent higher energy efficiency.
How does Eberspächer ensure safety with this direct approach?
Safety is our top priority. Our system concept follows proven standards based on those used in the railway industry. The system is divided into defined zones. Targeted sealing and ventilation measures ensure that even in the highly unlikely event of a leak, no refrigerant can enter critical areas of the vehicle. In addition, we conducted a comprehensive risk assessment together with customers and analyzed all conceivable scenarios. The result: the remaining risk is well below everyday comparative values.
What is behind the solution for diesel buses?
This is a milestone for us: Until now, the use of natural refrigerants in diesel buses was not technically possible because mechanically driven compressors are not available for propane or CO2. This meant that retrofitting existing vehicles was practically impossible. Together with several partners, we applied a generator that provides electrical energy and thus drives the electric compressor in the air-conditioning unit. This allows diesel buses – whether existing or new vehicles – to be equipped with natural refrigerants. A world first.
The products celebrated their premiere at Busworld Europe 2025. How was the feedback?
The response was positive. We had the opportunity to present our new systems for the first time at the trade fair, both at our own booth and directly at several vehicle manufacturers' booths. The AC138 EVO and AC135, for example, were on display on vehicles from MAN, CaetanoBus, and VDL Bus & Coach. This attracted a lot of attention.
Many visitors were impressed that we presented propane air-conditioning systems with a direct refrigerant circuit that are ready for series production and in fleet operation. For us, this is clear evidence that the market is ready to take the next step toward climate-friendly, future-proof solutions.
