When sustainability meets efficiency: MAN Lion’s City E with CO2 air-conditioning technology

MAN has committed itself to significantly reducing the CO₂ emissions of the vehicles sold by 2030. As one measure to achieve this, the company has implemented a CO₂ air-conditioning system in the MAN Lion’s City E after an intensive development phase. In addition to its environmental friendliness, this system is also characterised by impressive efficiency.
 
The topic of sustainability is a key focus at MAN Truck & Bus. The company has set itself the goal of drastically reducing CO₂ emissions from the fleet vehicles sold. By 2030, the aim is to reduce greenhouse gas emissions per kilometre driven by sold trucks, buses and vans by 28 percent compared with 2019. MAN wants to achieve greenhouse gas neutrality by 2050 at the latest – in other words, net zero emissions along the entire value chain. In order to meet this goal, MAN is driving forward the electrification of drives in the various series – as well as the use of sustainable refrigerants for the air-conditioning systems. HVAC (Heating, Ventilation & Air Conditioning) systems based on synthetic R134a as a refrigerant are still largely common in all bus segments. However, this refrigerant can amplify the greenhouse effect due to its high GWP value (Global Warming Potential) of 1430.
 
Conversion of HVAC systems requires a great deal of development and validation work. Consequently, intensive scientific analyses were carried out at MAN Truck & Bus SE to determine the future refrigerant strategy. Based on a subdivision into natural and synthetic refrigerants, these analyses examined the natural refrigerants R744 (CO₂) and R290 (propane) as well as the synthetic refrigerant R1234yf, which is now widely used in the automotive industry. In addition to the environmental compatibility of the refrigerant, the analyses focused in particular on improving the efficiency of the HVAC system. For buses in particular, HVAC technology has a great influence on how efficiently a vehicle can be operated. The high interior volume of electrically powered buses means that the energy consumption of the air-conditioning system in heating and cooling mode is decisive for the range.
 
Analysis of the different refrigerants – the results obtained by the MAN experts

The synthetic refrigerant R1234yf can generally be regarded as a successor to R134a, but its use for the MAN Lion’s City E would not offer any significant benefits either in terms of environmental friendliness or efficiency. In addition, the future viability of the refrigerant is currently not certain due to possible legal requirements. From today’s perspective, its use is therefore expedient only as a temporary alternative to R134a – should there be significant price increases for R134a in the future. However, as MAN sees a clear long-term trend towards natural refrigerants and is also driving this forward, the synthetic refrigerant R1234yf was not analysed in further detail.
 
However, the natural refrigerant propane was analysed intensively. The physical properties of this refrigerant generally promise high efficiency in both winter and summer due to a comparatively low system pressure and a low GWP of 3. On closer examination, however, there were some system-related challenges: propane is classified as A3, for example, and is therefore highly flammable. As a result, some system adaptations are essential in order to achieve approval by the German Technical Inspection Agency (TÜV). However, from today’s perspective, these challenges can definitely be solved technically. With optimal implementation, another HVAC option with natural refrigerant could thus develop in a few years. However, there is currently no sufficiently powerful propane system available for MAN bus applications and it is therefore not yet possible to offer this system for series production. However, MAN Truck & Bus will continue to pursue the development of this technology.
 
CO₂ technology promises a significant improvement in efficiency compared with conventional HVAC systems

Ultimately, the decision of the MAN experts was taken to use the natural R744 (CO₂). There are also some challenges to overcome for this refrigerant due to the high system pressures. However, these are now completely controllable, and corresponding systems are already being used successfully by some manufacturers in the e-mobility sector. However, in order to be able to exploit the full potential of the refrigerant, particularly in the colder months of the year, MAN has worked with a system partner to further develop and refine the system technology as well as the control system and integration into the overall system. The final winter tests in the far north have shown that the performance of the system technology available since May 2022 even exceeds the original project goals in terms of efficiency and increased range. The aim of the development was to heat exclusively using a highly efficient heat pump as far as possible, even in very cold regions – and to be able to largely dispense with the support of electric heaters. As a result, CO₂technology requires the support of electric heaters only in very cold outdoor temperatures, which represents a significant improvement in efficiency compared with conventional HVAC systems.
 
Following extensive monitoring of market developments and an intensive development phase, the MAN Lion’s City E is now available with a CO₂air-conditioning system. In addition to the changeover to the climate-friendly refrigerant CO_2,, the new technology focuses on the following areas in particular:

• High performance

Thanks to the development of an innovative and highly efficient air-conditioning system concept, the MAN Lion’s City E guarantees optimum performance in all temperature ranges. The system provides sufficient heating power even in the winter months that are critical for electric vehicles – without negatively affecting energy consumption and thus range.

• Efficient thermal management

In addition to prioritising the use of the efficient heat pump of the CO₂air-conditioning system, all environmental influences are utilised with the help of an intelligent control in order to optimise heating and cooling operation. In order to further increase energy efficiency, all energy sources and their contribution to the energy balance were also tested and intelligently integrated into the system. 

• Integration of an sVF controller (smart vehicle function)

With the help of the sVF controller (smart vehicle function), the vehicle adapts to individual customer use by calculating the respective optimum energy deployment. The first test runs for this have already been started.
 
Investments were also made in the development of the digital control system (over the air – OTA) and the intelligence of the heating, ventilation and air conditioning. For vehicle preconditioning – in other words, ideal temperature control of the passenger area and circuit filling before the start of the journey – the existing communication channels via charging stations and the MAN backend were optimised by investigating numerous test cases. The aim of all these measures was and remains to bring an environmentally friendly and at the same time highly efficient air-conditioning system to market. This is what the MAN Lion’s City E family now offers for the international market with its innovative and award-winning e-buses in three lengths. Nevertheless, the overall system will be continuously developed over the next few months and years in order to exploit the potential for further optimisation in the best possible way.