When it comes to seat ventilation, the automotive industry is at a turning point: should it remain a luxury option or become an integral part of the air conditioning system? What helps OEMs make the transition to fully integrated solutions are miniaturized digital humidity sensors and the associated automation of air conditioning control.

Ventilated seats can be found on most luxury cars. The fact that they are also starting to appear in mid-range models shows a trend towards wider adoption. In most cases, they are integrated as an accessory: This means that an extra button serves to switch on the seat ventilation, typically with the option of different fan speed levels. In some cases, seat ventilation and seat heating are controlled by the same button, allowing only the one or the other feature to be used at a time. But will future customers accept such limited functionality only to simplify control?

Looking at more recent vehicles, the control integration is different: Conventional dashboards with physical buttons are being replaced by touch screens. In such solutions, access to the ventilated seat control might be hidden under a couple of menu layers. This might result in scenarios where drivers can only change the settings when it is safe to take their eyes off the road. Furthermore, complex control processes prevent many people from using the full benefits of the feature. For example, instead of increasing the seat ventilation they reduce the air conditioning temperature, which consumes more energy. Others do not even know about the feature, that probably is switched off by default.

Targeted approach reduces energy consumption

Ventilated seats make people perspire less and have the potential to make automotive climate control systems consume less energy at comparable comfort levels. Whereas the air conditioning system in a conventional car consumes about 6 % of the energy, heating and cooling the interior can consume 10 to 40 %[1] in electric vehicles (due to multiple factors). In this case, the amount of the on-board energy is being reduced noticeably. Since currently range is the biggest pain-point for electric vehicle adoption, automotive OEMs and authorities have a strong incentive to optimize the climate systems of these cars.

Another point that speaks for controlled ventilated seats is the more targeted way of reaching a state of comfort, compared to warm or cold air flowing towards the driver and passenger. While the air from the HVAC indiscriminately conditions the entire cabin including windows, trim and unoccupied seats, the seat is “in direct contact” with the person. Consequently, developers are using heated seats, steering wheels and surfaces more frequently as they allow to warm specific body parts by conduction.

Similarly, seat ventilation establishes comfort more efficiently by removing or adding air behind and underneath the person, rather than just on the front. While an EU study[2] has found that seat ventilation is one of the comfort technologies that can significantly save energy in electric vehicles, a US study[3] demonstrated that ventilated seats allow a 7 % reduction in air conditioning power for the same comfort level.

The AC reaches the front half of a person, but it also wastes air by bypassing them, while seat ventilation opens up a whole other level of comfort.

Humidity must be considered as a factor

One may think that ventilated seats are suitable for cooling only – a simplification that is easily encouraged by the supposedly juxtaposition of the seat heating control. But seat ventilation is primarily for removing humidity that already exists or may build up between the seat and the person due to perspiration or wet clothing. It is important to mention that perspiration does not necessarily occur on a warm day, but also in a stressful traffic moment. In this case, humidity is not correlated with the outdoor temperature or sun load and can only be detected by a dedicated humidity sensor.

Generally, seat ventilation removes humidity noticeably faster than passive diffusion through the seats, leading to an evaporative cooling effect that may be desirable on a warm day. However, if cooling is not wanted, seat heating and seat ventilation may be used simultaneously to “dry” the driver and passenger. The relation between temperature and humidity is visualized in the following diagram, along with the possibilities for taking action by using seat ventilation and seat heating. It shows clearly that temperature alone is not a sufficient information to control seat ventilation.

Humidity is more important than temperature for controlling seat ventilation.

Early warning allows proactive control

Another factor that plays an important role in how effective seat ventilation works is its immediate timing. In a manual control scenario, people usually reach a certain level of discomfort before they take corrective action: They switch on the ventilation only after they have realized that they are perspiring. This is too late, not only because of the intermediate state of discomfort, but also because the person might reduce the cabin temperature setting, leading to an increased energy consumption. To make matters worse, switching on the ventilation late may cause an overshoot of the cooling effect, akin to wind-chill, when there is already built-up humidity.  This requires further manual intervention to reduce the ventilation level.

Sensirion’s engineers have developed a new generation of miniaturized humidity and temperature sensors with stunning characteristics: even when imperceptibly integrated under the cover of a car seat, the Sensirion Automotive Climate Seat Sensor (SACS) is sensitive enough to measure even the smallest increase in humidity on the seats before people notice discomfort. The sensor’s functionality was extensively tested by study subjects at Sensirion and at the first automotive OEMs that rely on this new technology. The benefits: Sensirion's new humidity and temperature sensor enables proactive control of seat ventilation, which maintains comfort in the interior without having to resort to the air conditioning system.
 

The Sensirion Automotive Climate Seat Sensor (SACS), ready for integration.

It is obvious that the future lies in automated seat ventilation being a part of a car’s climate control system. Advanced humidity and temperature sensors built into the seat provide the necessary information to maintain comfort in a timely and energy efficient way, under all conditions. Thus, drivers and passengers no longer have to think about comfort, because it is always there.

[1] https://www.nrel.gov/docs/fy17osti/67672.pdf

[2] https://www.domus-project.eu/wp-content/uploads/2021/09/D4.2_final_PubSum.pdf

[3] https://www.nrel.gov/docs/fy07osti/40986.pdf