Case Studies

Train HVAC Upgrade

Simatic S5 to S7 Upgrade for Train HVAC System

Posted in Energy and Utilities, HMI and SCADA, Manufacturing Automation and Intelligence, PLC Programming, Siemens PLC


DMC worked for a transportation company to upgrade their train car HVAC controllers from an outdated Simatic S5 platform to an S7-1200 PLC. DMC’s solution included new features such as an HMI panel, data logging, and flexible implementation ability.


DMC’s client wanted to upgrade their train car HVAC system, which was running on Simatic S5 controllers. Due to the age of the system, many of the control units had started to fail. During subpar weather conditions, these failures required the train cars to be taken out of service. To avoid car downtime and improve the reliability of the system, the customer sought DMC’s help to upgrade to a Simatic S7 solution.

In order to leverage the S7 technology fully, DMC wrote the new application from scratch, referencing the the old S5 project and its documentation as a basis for confirming specifications. DMC utilized TIA Portal's modular and reusable code development tools to create a flexible and scalable solution that could seamlessly accommodate future feature additions. DMC implemented the solution using a phased approach, by first developing and testing the software for one train unit, and then deploying the validated software to several train car control panels.

While the original HVAC system included only the controller and a handful of physical pushbuttons, DMC’s solution incorporated an integrated PLC/HMI system with custom user interface screens. The final solution included several HMI screens, robust automatic mode control, and custom user administration. Below are two of the HMI screens that DMC created based on client style requests.  

plc siemens hmi hvac

The Main Screen displays a snapshot of system status values and buttons for quick navigation. 

plc siemens hmi hvac

The Temperature Matrix Screen shows automatic mode in action, with a snapshot of relevant I/O values. 

The control solution interfaced with several HVAC hardware components including boilers, compressors, valves, and evaporators. In addition to matching the functionality of the older system, DMC’s solution included data logging, trend displays, flexible implementation options, and improved alarm diagnostic messages. DMC’s system was implemented in dozens of train cars to significantly enhance the reliability and usability of their HVAC controls.

Customer Benefits

  • Improved system reliability
  • Turnkey solution can be deployed to any number of train cars
  • Configurable for multiple train car hardware setups
  • Customized data logging and real-time chart displays
  • Improved fault handling
  • Modular code allows for rapid development of future feature additions


  • TIA Portal
  • SIMATIC S7-1200 PLC & ET200SP Remote I/O
  • WinCC Comfort Panel