One passenger freezes while another swelters. The “ideal” temperature on a train is a constant subject of debate. Especially when the air conditioning isn’t doing what it’s supposed to. Luckily, this happens far less frequently than many passengers might think. A look at the figures and how SBB’s climate control system operates dispels misconceptions and shows just how sophisticated air conditioning on trains actually is.

Today, around 9,100 air-conditioning units ensure that 98% of SBB’s passenger trains are air conditioned. Some older coaches, such as those used on the additional trains deployed during peak hours on the Zurich S-Bahn for example, and some coaches used for long-distance services have heating and year-round ventilation, but no cooling system. From May to September, trains without air conditioning are marked with a corresponding pictogram in the online timetable at sbb.ch and in the SBB Mobile app.

One of the factors that determines the temperature on board a train is the exterior temperature, which is measured by temperature sensors on the outside of the vehicle. The number of sensors depends on the length of the train. For example, a six-coach train will have twelve external temperature sensors. The average measurement is used to determine the target interior temperature (which is also measured by temperature sensors in the passenger areas) and the supply of fresh air to the interior. An air-conditioned double-deck train is equipped with around 62 interior temperature sensors.

• In addition to the exterior temperature, numerous other factors have an impact on air conditioning:
• Whether the train is stationary or moving, and its speed
• Sunlight conditions
• Air humidity
• How full the train is
• The amount of heat emitted by the lighting and other electrical equipment on board
• How long the doors stay open when the train stops
• Whether the train is driving in the open or through a tunnel

The values for each of these factors, which, of course, change constantly during a journey, are fed into the automated air conditioning controllers to calculate the temperature inside the coaches.

The electronic controllers for the air conditioners are programmed to maintain the interior temperature three to ten degrees lower than the exterior temperature during hot weather. This complies with the European standards that railway companies in other countries also follow. However, if the air in the coach is perceived as too hot or too cold, train crews can manually increase or decrease the temperature by up to two degrees. SBB does not lower the temperature any further than this in order to avoid unpleasant temperature shocks for passengers entering and leaving the train and to limit energy consumption.

SBB logs an average of 600 air conditioning malfunctions per month involving heating, ventilation or cooling. This means that, on average, around 20 air conditioning units per day malfunction. With around 9,100 air conditioning units deployed fleetwide, this corresponds to a fault rate of just 0.24%.

The causes of the faults are as varied as the vehicles in the SBB fleet. They range from faulty sensors or defective air-conditioning units, cooling compressors, fans, heating elements or electrical switching elements to faulty controllers or bugs in the control

First of all, keep your cool. To ensure that faulty systems can be located and repaired as quickly as possible, we encourage passengers to report the fault directly using the contact form on SBB’s “Claims and complaints” page. Go to this page and select “My train journey.” followed by “Temperature. Air conditioning / heating.”