Class goal: feel good and save energy with KNX, CO2 measurement and multi-sensors


  • Extension to a primary and community school with newly designed ventilation to improve indoor air quality and energy efficiency



  • Presence detector (multi-sensor) thePrema P360 KNX Multi with integrated room air sensor for light control and ventilation control


"The last one turns off the lights" and "Close the windows, we're not heating the street," such appeals have long been the only known energy efficiency measures in schools. The effect was limited. Modern and largely automated building technology is more promising. An extension to the school in Hirrlingen proves that this is feasible even on a tight budget. Multi-sensors from Theben and cleverly programmed automation ensure the economical use of energy and at the same time a child-friendly feel-good climate.

In autumn 2022, the primary and community school in Hirrlingen in the Tübingen district was able to inaugurate a 775 m2 extension (Fig. 1). Despite the pandemic and its effects, the school was built within the planned timeframe and was even 2% cheaper than planned. In addition to three classrooms, it also offers four rooms for core time care. Architect Frank Schillinger from Schillinger Architekten in Rottenburg, who was able to convince the municipality of his firm's design in a competition, describes the requirements: "From our point of view, the extension building should fit into the small-scale village structure, fit within the existing space and offer potential for expansion" This resulted in an L-shaped building form with a terrace and the potential for adding two more classrooms.


A warm welcome instead of a jump into cold water

Architect Schillinger attached importance to a friendly, warm atmosphere: "When six-year-olds enter their new school for the first time, they are excited or may have some anxiety," he says, describing the situation from the children's perspective. "With warm materials and calm acoustics, the transition to a new living space  can happen gently and improve motivation. First impressions like that are strong." Despite the cost pressure that all public buildings are subject to, Schillinger managed to set an example. The colour scheme and materials are reminiscent of a deciduous forest at different times of the year. Sound-absorbing ceilings, some with an open, spacious roof design, provide quiet acoustics and a spacious room experience. A special feature, among others, is the floor made of solid oak planks, an unusual covering for a school, but economical in the long run. It can be sanded several times, while a floor made of rubber must be completely replaced. This is also convincing for a community like Hirrlingen with just 3,000 inhabitants, for whom such a building is a major financial outlay. Luxury and gimmicks would be out of place here, but the people of Hirrlingen are happy to invest in solid, durable building fabric.

In keeping with the sustainable architecture, Schillinger also used every opportunity to save energy in the building technology. In addition to a control system for lighting and shading, this also includes a ventilation system. It offers significant advantages, especially in the cold season. The air quality in the rooms remains excellent even without regular boost ventilation. The ventilation kicks in when theCO2 levelin the classroom exceeds a preset value. At the same timea great deal of energy can be saved through heat recovery. A PV system on the roof normally generates more energy than the ventilation system needs. The surplus goes to the old building. This eliminates the need for battery storage or complex processes for feeding electricity into the public grid.


Building automation taken literally

“When the teacher comes into the room, has picked up a few latecomers along the way, has to get the class into their chairs and wants to start the lesson, they can't also spend time operating the ventilation and the blinds,” says Schillinger, describing the school day. "Everyone involved has put a lot of effort into designing the building automation so that users don't have to intervene. If everyone switches something, with so many people, it won't work. We have had lecture rooms at institutes where the users were overwhelmed with three lighting scenarios. If the automation system regulates as much as possible, it ensures stress free operation and it has the the most efficient energy consumption.”

Automation should include lighting, shading, and ventilation of classrooms and restrooms. The company Elektro-Zug from nearby Rottenburg am Neckar was commissioned with the installation and programming of the system . Long-time employee and partner Lorenz Hoch oversaw the project. He also took care of the selection of components and found a particularly interesting solution at Theben.


One connection, two detectors

In his search for the right sensor technology, Lorenz Hoch approached Theben: "We have had a good relationship for a long time. Theben offers very good support and can deliver reliably, probably due to the manufacturing in Haigerloch," he explains. The Theben sales representative, Holger Wagner, suggested suitable products to him: "We discussed the various positions for the presence detectors on site. It turned out that air quality should also be measured in the rooms. For this, of course, our multisensor was ideal." We are talking about the product thePrema P360 KNX AP Multi WH. This KNX multisensor, consists of a passive infrared presence detector with square detection area and a room air sensor that detectsCO2 concentration, relative humidity, temperature and air pressure (Figure 4). This ring-shaped sensor also serves as a base on which the presence detector is mounted. This is even possible later as a retrofit solution. In combination, the sensors form two bus participants, but only require one KNX connection - a solution that also appeals to Schillinger: "As an architect, I would prefer a clear ceiling without any detectors at all," he points out the aesthetic aspects. "With such a multifunctional sensor, we can make the room more beautiful. We don’t take up the whole ceiling.”

The sensors from Theben also meet these design requirements in other places, as Wagner explains: "Our presence detectors thePassa are installed in the hallways. The design is similar to thePrema, but the coverage area is 5m x 30m. This allows me to cover a long hallway with just one detector. That means fewer outlets, less installation work and a cleaner ceiling appearance."

Presence detectors and sensors for humidity in the sanitary areas complete the system.


When in doubt, the teacher is right …

… or, of course, the teacher. Schillinger attached great importance to the technology working automatically as far as possible, but not patronizing the users. This means that lighting and shading can be controlled manually at any time, independently of the automation system, if, for example, the room needs to remain dark for a film screening or the full morning sun needs to shine into the room to wake you up. With the sensor technology from Theben, this could also be implemented without any restrictions, as Hoch reports: "We had some problems with manual override at the beginning. To do this, we wanted to lock the sensor. But when and how should it be unlocked again? We contacted Theben and quickly got a solution: thePrema can be parameterized in such a way that it can be easily overridden directly. It detects the manual command and then stops sending control commands as long as it detects presence. Each presence signal starts an adjustable follow-up time. We have set it to 20 min. Only when this has expired does the detector go back to automatic."


Automatic operation every day of the year

But the control system not only ensures that forgotten lights are switched off after a short time, it also adjusts to different times of the year, school and vacations. In winter, the ventilation in one room ramps up, as soon as the CO2-Detector goes off. If the presence detector detects absence, the ventilation stops after a follow-up time of two hours.

In summer operation, the system is used for night cooling. If the temperature difference outside / inside is large enough, the ventilation runs. Thus, the classrooms are pleasantly cool in the morning. At outdoor temperatures below 22 °C, the ventilation also starts if theCO2 valuesare too high. At higher temperatures - only then is manual operation still required - the teachers open the windows on the side of the room facing away from the sun as needed. To achieve this, Schillinger planned all the rooms to have windows on several sides.

The ventilation is supported by the time-of-day-dependent blind control. Depending on the position of the sun and the temperature, the shading provides cool rooms or captures solar heat if needed in winter. Of course, the priority is always the presence of people in the room or the higher authority - manual control.

In general, the automation system is designed in such a way that it is not even necessary to switch manually during the vacations. Without human presence, the plant goes into minimal operation.


Minimalist operation for central functions and pandemics

Even the best automation system cannot do without a control panel. It is located in the teachers' lounge and displays conditions such as the air quality in the rooms or malfunctions. Central functions, such as switching the entire lighting system on and off, are also stored here.

Especially worth mentioning is the pandemic function. On the touchscreen, the system can be set to pandemic mode by pressing a button. The ventilators in classrooms and sanitary facilities then run constantly when present, regardless of theCO2 content. Only when the outside temperatures are too high, the windows must be opened according to the legally prescribed cycles. The ventilation would otherwise bring too much warm air into the classrooms.
Overall, the concept offers maximum energy efficiency and comfort with a manageable investment.

Theben product used


Electrical installation

Elektro Zug, Rottenburg


Schillinger Architekten, Rottenburg