As well as trialling 100% electric buses in 2015, transport authority RTM, which governs the bus, train and tram networks in Marseille, has turned to the environmentally friendly refrigerant CO2 to increase energy efficiency and reduce its carbon emissions.
Konvekta’s CO2 philosophy is already echoed by much of the German automotive industry as well as national environmental body Deutsch Umwelt Hilfe (DUH), who have both urged a swift transition to eco-friendly CO2 air conditioning on buses.
Now it has other European regions in its sight. RTM represents Konvekta’s first foray into France and regularly turns over 40-50 buses per year. Following winter testing, the authority has also ordered six fully electric buses for its drivers to test in 2015.
The virtues of R744 in MAC have been promoted by the automotive industry for a number of reasons. Firstly, it contributes 1,400 times less greenhouse gas emissions than R134a, can be more cost efficient by consuming less fuel (25%) in bus and train MAC applications, and requires significantly less service and maintenance as there is no necessity to recover or dispose of excess refrigerant after repair. Konvekta insists that several years of fault-free operation is possible due to the construction and design of the system and its components.
According to the The German NIAG Group (Niederrheinische Verkehrsbetriebe Aktiengesellschaft), Konvekta’s CO2 MAC systems are simpler to inspect and require around one third of the service costs demanded by a standardised R134a system.
MAC Directive and safety issues
The European Commission issued a directive in 2006 enforcing the phase out of R134a in MAC systems in personal vehicles and its replacement by refrigerants with a GWP of no higher than 150. As of 2011, a total ban on R134a was applied to all new models, and as of 2017, to all passanger vehicles. Currently this restriction does not extend to public transport, meaning RTM implemented the use of R744 for purely environmental and efficiency reasons rather than legislative obligations.
The elephant in the room is HFO R1234yf, which a number of car manufacturers opted for in 2009 given its relatively low GWP compared to R134a. However, due to safety and flammability concerns, one manufacturer Daimler resisted the transition to 1234yf, and with the backing of German authorities, automotive giants Audi, Volkswagen, Porsche and BMW soon followed suit. Daimler’s position has remained unchanged with the company since opting for CO2 MAC systems, which are expected to be rolled out in 2017.
Konvekta MAC Technology
The system achieves energy savings due to CO2’s superb thermodynamic properties, high volumetric cooling performance and good thermal transmission efficiency. Due to the higher pressures of CO2 in an air conditioning unit, the system and all its components require a customised design optimised for CO2.
Dual functionality it supplied via a thermal heat pump for heating the interior of the bus, which further reduces the consumption of the air-conditioning unit.
In addition, Konvekta’s CO2 climate technology utilises a heat pump, prologing the life of the sensitive and expensive batteries in electric buses by allowing them to operate at an optimal temperature range in terms of power output by taking over the temperature control. In effect, this also extends the buses’ operating distance by 40%.