Not too hot, not too cold: how can we maintain the right temperature for public transport?

The climate in the metro depends strongly on the outside temperature.
For increased comfort, our networks and fleets are equipped with three different systems:

• Forced mechanical ventilation (VMF) draws air from outside using ventilators on the vehicle roof, thus providing an air current for the passengers. The vast majority of buses use this type of ventilation, supplemented by heat-reflecting windows that reduce the effect of sunlight. This equipment is efficient in terms of environmental and economic performance while limiting energy consumption and emissions.
• Refrigerated forced mechanical ventilation (VMFR) uses only outdoor air and produces a temperature a few degrees lower than outside to give passengers a feeling of freshness. The new airport and smaller-sized vehicles thus use refrigerated ventilation to offer passengers better climate comfort while consuming less energy than conventional air conditioning.
• Series/lean air conditioning: this involves cooling a mixture of inside and outside air/recycling of the inside air in a closed circuit. This is a solution that is very little used (only in some buses) because of its high energy consumption, and because natural heating from regular opening of the doors means it is not possible to obtain a low and uniform temperature.

Air conditioning is not the ideal solution for rolling stock operating underground, because it has a high environmental impact consuming a lot of energy, which reappears in the form of heat, all inevitably pushed back into the tunnels and platforms. In addition, it is not compatible with regular door opening.

Also, the installation of air conditioning underground is a problem because of the small gauge of the metro tunnels. The small space available between the tunnel and the train roof impacts the performance of the installations because of recirculation of hot air blown out and then drawn back by the fans.

If we are only equipping lines that present difficult situations, it is because of the current context of scarcity of energy resources, in accordance with our sustainable development policy. The decision is taken line by line, in agreement with Île-de-France Mobilités, the transport authority in the Ile-de-France region and legal owner of the rolling stock. This mostly concerns lines with above-ground sections or with carriages parked outside.

Some vehicles (MF67s) use natural ventilation: in this case, there is no artificial mechanism; ventilation is provided by the air currents between the inside and outside of the vehicle, created in particular by skylights on the roof.

Preventive maintenance operations are also carried out on the vehicles to avoid breakdown of the ventilation units during hot weather:

• For rail: filter changes, dust removal from evaporators and condensers, checking of air conditioners and cleaning of water outlets;
• For buses: checking of air conditioners and fans, filter changes and cleaning of cooling radiators.

Since 2009, in most of our RER line A and B trains, the heating only cuts in when the temperature drops below 15°C, compared with 18°C previously. This measure contributes to an overall energy saving of between 5% and 30% depending on the train type, while ensuring better comfort for passengers, who dress according to the outdoor weather conditions.

Overall figures for the rail network:

• 60% of the fleet is equipped with refrigerated ventilation,
• 24% of the fleet is equipped with forced mechanical ventilation,
• 16% of the fleet is equipped with natural ventilation.
   

On our metro network:

• 7 lines are equipped with natural ventilation from skylights on the roof:       and ;
• 5 lines are equipped with forced mechanical ventilation:     and part of the fleet for line ;
• 5 lines are equipped with refrigerated ventilation:     and part of the fleet for line (11 trains).

On our RER network:

• 89% of the fleet is equipped with refrigerated ventilation;
• On line : the MI09s and the MI2Ns are equipped with refrigerated ventilation;
• On line : all the refurbished MI79s (i.e. 75% of the fleet) are equipped with refrigerated ventilation. The MI84s are equipped with forced mechanical ventilation.

On our tram network:

• tram symbole tram ligne1 (35 trams),
• tram symbole tram ligne2 (60 trams),
• tram symbole tram ligne3a tram ligne3b (46 trams),
• tram symbole tram ligne5 (15 trams),
• tram symbole tram ligne6 (28 trams),
• tram symbole tram ligne7 (19 trams) and
• tram symbole tram ligne8 (20 trams).

On our bus network:

• 94% of the fleet with forced mechanical ventilation;
• 5 % of the fleet with refrigerated forced mechanical ventilation;
• 1 % of the fleet with lean air conditioning.

Climatic comfort inside buses is one of the subjects for which RATP and Île-de-France Mobilités are looking ahead, to identify and implement the best solutions that may emerge in the future, particularly in the context of the Bus2025 plan, which anticipates conversion to a 100% green fleet by 2025, mainly electric but also bio natural gas.