CFD Simulation of HVAC Systems on Trains Makes Rail Travel More Comfortable

Every time I travel in Europe, I enjoy riding the fast, comfortable trains. Riding from city center to city center without long security lines and tight uncomfortable airplane seats (worse for me because I’m tall!) can even make travel pleasant. But, I’ve always taken that comfort for granted. Were trains not always that way? Then, I found out about the challenges that Siemens engineers face as they design passenger coaches. Now I have huge respect for those engineers. Read on to find out how CFD is making their lives easier while giving me the comfort I love.


While sometimes it seems that maintaining a comfortable temperature is impossible even in a non-moving office space, train passengers in Europe are guaranteed a pleasant ride by European Standard 13129 (EN13129). This standard sets out strict requirements for controlling air temperature, relative humidity and air speed within passenger compartments. It even specifies how many degrees the temperature can vary from the setpoint vertically and horizontally throughout a train car, and how warm or cool the walls, ceilings, windows and floors can be. To meet these tough standards, Siemens Mobility in Germany uses ANSYS CFD solutions to simulate airflow and thermal conditions for the HVAC systems in new ICE 4 passenger coaches.

Previously, engineers had to spend four months testing passenger train coaches in a wind tunnel to fine tune the HVAC systems to meet the standards. For these tests, they needed to install up to 800 sensors throughout a single passenger coach, and put heating pads in the seats to represent the heat output of passengers. Even with all this physical testing, the designers still could not be confident the coach would pass the standard until just before delivery. Looking for ways to improve this lengthy and costly process, Siemens climate control engineers used their experience with computational fluid dynamics (CFD) simulation — and the availability of high-performance computing (HPC) — to develop an alternative method.

Instead of building and testing a physical prototype first and using CFD to verify the findings, Siemens engineers performed CFD digital prototyping up front. Running CFD simulations enabled the engineers to predict the thermal conditions throughout the passenger car — including the heat contribution coming from the passengers themselves. These predictions showed that the ICE 4 coach met the EN13129 standards for railway passenger comfort.

Simulation model of ICE 4 trains

Afterward, to prove that the software was accurate the first time through, they built a physical model of the coach and tested it in a wind tunnel. Because the physical measurements agreed so well with the CFD predictions in this proof-of-concept trial run, Siemens engineers in the future will be able to rely on CFD simulations and dispense with much of the physical testing in demonstrating compliance with EN13129. Siemens estimated that simulation will save them up to 50 percent in reduced time and testing in the future.

To read more about using CFD for climate control in challenging conditions, read the full article in the latest issue of ANSYS Advantage magazine.

You might also be interested in our white paper “ANSYS Fluent with PRIMERGY HPC: HVAC for Built Environment,” which deals with how CFD has been used to design more efficient, comfortable and safer buildings.