STULZ worldwide

Deutsche Bahn AG

Reliable, efficient air conditioning for sustainable rail transport

In Schleswig-Holstein in Germany, diesel locomotives are now being replaced by battery-powered trains over nearly 290 miles of track. The trains are charged by overhead lines at train stations, which are supplied with electricity by so-called charging substations. Special Shelter air conditioning units from STULZ are being used to ensure mission-critical and energy-efficient air conditioning of the necessary charging infrastructure.

The customer

Deutsche Bahn AG is Germany’s largest mobility and transport corporation, with railroad transport as its core business. As part of its drive toward sustainability, Deutsche Bahn is working to deliver emission-free rail transport on previously non-electrified sections of track in Schleswig-Holstein, with a length totaling nearly 290 miles. This should save roughly 10 million liters of diesel and cut 26,000 tons of CO2 a year. Battery-electric trains have an important role to play here. They are charged by overhead lines in train stations and can then cover a distance of up to 93 miles on battery power. This approach has one major advantage over conventional electric trains: it isn’t necessary to install overhead lines along the entire track, just on short sections. The overhead lines are supplied by so-called charging substations, which deliver a charging voltage of 15 kV from the local medium-voltage network. The equipment in these charging substations must be kept at a constant temperature all year round. The necessary temperatures and the fact that no components can be installed outdoors mean the required technology faces extremely exacting requirements.

The challenge
Our solution
The result
Our product

The charging substation in Heide consists of prefabricated concrete modules that sit on a shared base and are connected via a cable cellar. All the air conditioning equipment must be located inside the individual modules, and can only draw in filtered outside air through apertures with grills. A maximum room temperature of 26 degrees Celsius is required inside the modules, and reliable operation of the air conditioning units has to be guaranteed up to an outside temperature of 45 degrees Celsius.

The air conditioning units must have the following operating modes:

- Free Cooling,

- Mechanical Cooling,

- Mixed mode (Free Cooling and Mechanical Cooling), and

- Heating.

The air conditioning equipment has to have 100% redundancy and be linked to the building management system for monitoring.


Due to the particular requirements of this project, Deutsche Bahn decided to have the annual maintenance of the air conditioning equipment at the Heide charging substation performed by the experienced specialists at STULZ. For emergencies requiring an especially fast response time, STULZ’s on-call staff are available to the railroad company at any time. 

In December 2023, STULZ service engineers put the supplied air conditioning systems at the Deutsche Bahn’s charging substation in Heide into operation. In doing this, they installed a total of eight special Tel-Air3 Shelter air conditioning units from STULZ in the rooms that need cooling.

Two identical units were installed in each room and use failover and redundant switchover to ensure one hundred percent redundancy. In the connection room containing the medium-voltage system and control technology, two STULZ TXD 40 F air conditioning units were installed. Each unit has a useful cooling capacity of 4.6 kW at a room air temperature of 26 degrees Celsius and guarantees reliable operation up to an outside air temperature of 45 degrees Celsius.

In the two transformer rooms, each with a 2.5 MVA transformer, two STULZ TXD A4 F air conditioning units each with a useful cooling capacity of 12.6 kW at a maximum room temperature of 26 degrees Celsius have been installed in each room. These systems can also run at an outside temperature of up to 45 degrees Celsius.

Finally, there is another room for the installation’s own supply (AC 400V/230V, DC 110V) containing four battery enclosures each with a battery capacity of 101 Ah, control technology, and operator console of the charging substation. This room was fitted with two STULZ TXD 60 F air conditioning units each with a useful cooling capacity of 6.2 kW, also ensuring reliable operation up to an outside air temperature of 45 degrees Celsius. 

Thanks to the relatively compact dimensions of the STULZ air conditioning units, installation and start-up in a sometimes very restricted space was fast and simple. With the pure Free Cooling function and the option of Mixed mode for the installed TelAir3 units, with simultaneous Free Cooling and mechanical cooling, reduced energy consumption over a broad temperature range is guaranteed for the long term, significantly cutting operating costs. If outside temperatures are very low, an integrated electric heater pre-heats the outside air, ensuring a constant temperature in the charging substation even in winter. This is especially vital to keep the buffer batteries in the battery enclosures in perfect working order. Thanks to Ethernet interfaces and the use of common protocols, connection to the existing building management system was also possible without major expense or additional hardware.

The air conditioning equipment is serviced by specialists from STULZ once a year and continually monitored by the building management system. If there are any irregularities during operation or a fault in the systems, STULZ service engineers are on call at short notice within a set response time. This way, all Deutsche Bahn’s requirements for the air conditioning equipment for its Heide charging substation can be comprehensively met – not just at the planning stage, but in terms of implementation as well. In future, this now tried-and-tested air conditioning concept from STULZ will also be used at the charging substations in Tönning and Husum. 

TelAir 3

TelAir units are designed for telecommunication containers and equipment rooms. As the precision air conditioning units are installed indoors, noise is kept to a minimum and the units are protected against environmental influences and vandalism.


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