Components from the 3D printer improve indoor climate

Whether office buildings, showrooms or waiting areas in hospitals, doctors' surgeries and public authorities – many people come together everywhere and the air quickly becomes stuffy. People bring moisture with them, which increases humidity. To keep rooms dry and create a pleasant indoor climate, ventilation systems are often used in office and administrative buildings. Although these systems reliably dehumidify the air, they consume energy and are high-maintenance.

A research team at ETH Zurich has developed an innovative method of passively dehumidifying indoor spaces. A specially developed material in walls and ceilings absorbs excess moisture from the air and stores it temporarily. Instead of discharging the moisture to the outside as with mechanical ventilation systems, the hygroscopic material binds the moisture and releases it again later when the room is ventilated. “Our solution is recommended for heavily frequented rooms for which the installed ventilation systems are inadequate,” explains Guillaume Habert, Professor of Sustainable Building and head of the ETH research project.

Waste from marble quarrying as a basis

As reported by Informationsdienst Wissenschaft, Guillaume Habert and his research team relied on the principle of the circular economy to develop a suitable hygroscopic material. They used finely ground waste from marble quarries as a basis. To produce moisture-binding wall and ceiling elements, they combined the marble powder with a binding agent – known as a geopolymer. This class of material is created by activating metakaolin, a substance used in porcelain production, with an alkaline solution of potassium silicate and water. This reaction forms the geopolymer binder, which binds the marble powder into a solid building material. Compared to cement, this binder produces significantly less CO₂ and offers a more sustainable alternative.

The project followed on from the doctoral theses of materials scientist Vera Voney and architect Pietro Odaglia, who developed the material and the 3D printing machine at ETH. In the ETH project, the researchers developed a prototype for a wall and ceiling element with dimensions of 20×20 cm and a thickness of 4 cm. The team produced the prototype using 3D printing. They applied the marble powder layer by layer and bonded it with the geopolymer binder – a process known as binder jet printing technology. “This process can be used to efficiently produce components in a wide range of shapes,” explains Benjamin Dillenburger.

More comfort with moisture-inhibiting components

“We were able to use numerical simulations to prove that the components can significantly reduce humidity in heavily used indoor spaces,” explains Magda Posani. For the simulation, she assumed that the walls and ceilings of a reading room are completely clad with the hygroscopic building elements. The reading room is used by 15 people, and Posani calculated how often and to what extent the humidity leaves the comfort zone of 40 to 60 percent relative humidity over the course of the year. From this, she created a discomfort index that shows how much too high or too low humidity affects comfort. With the moisture-binding elements, the index fell by 75 percent compared to a conventional wall with a coat of paint. For elements with a thickness of 5 cm instead of 4 cm, the index was even reduced by 85 percent.

The hygroscopic wall and ceiling elements score points for climate friendliness: over a period of 30 years, they cause significantly fewer greenhouse gas emissions than a ventilation system that removes the same amount of moisture from the air. In the simulations, the researchers also compared the elements with traditional clay plaster, which has been used for centuries to passively regulate indoor humidity. The clay plaster performed even better than the modern components in terms of climate friendliness. However, the plaster has a lower storage capacity for water vapor than the building elements from the 3D printer.

The ETH's work proves that the combination of geopolymer and 3D printing can be used to develop wall and ceiling elements that efficiently buffer moisture. The next step will be to further develop the production process. The aim is to achieve cost-effective production on an industrial scale. At the same time, research is continuing. Together with the Polytechnic University of Turin and Aalto University, ETH Zurich is researching further production processes and construction elements that should cause less and less greenhouse gas emissions.

(usz)