"It's not the heat, it's the humidity." That adage applies indoors as well as out, which is where an experimental new material comes in. It absorbs humidity within rooms, reducing the need to run power-hungry ventilation systems.
As people exhale and perspire, they release moisture into the air. Therefore, if a number of people are present in a room with little or no ventilation, all of that airborne moisture can cause the room to feel uncomfortably stuffy and humid.
To keep that from happening – particularly in hot climates – electric ventilation systems are often used throughout the day, continuously moving the moist air out of the room. Needless to say, this arrangement uses a lot of electricity.
In an effort to address that problem, Prof. Guillaume Habert and colleagues at Switzerland's ETH Zurich university have developed a hygroscopic material that passively absorbs moisture from the air throughout the day. That moisture is released back into the air when the room cools at night, at which point the ventilation system only has to run briefly in order to get the moist air out.
The material consists mainly of finely ground marble, obtained as an otherwise-unwanted waste product from quarries. In a binder jet 3D-printing process, a print head moves through a bed of that powder, depositing a liquid geopolymer made up of a mineral known as metakaolin and an alkaline solution.
That geopolymer instantly sets as it's deposited, binding the powder to which it was applied. By repeating this process over and over, three-dimensional objects can be built up in successive layers.
For the purposes of the study, the scientists printed a 20 x 20-cm (7.9 x 7.9-inch) tile of the material that was 4 cm thick (1.6 in).
Instead of just taking the form of a solid slab, though, the tile has a very porous structure. As a result, the object has nearly four times as much moisture-absorbing surface area as it would it if it were completely solid, while using a 60% lower volume of material in the process.
After measuring the performance of the tile in lab tests, the scientists calculated what would happen if the walls and ceiling of an existing Portuguese library's reading room were lined with the material. For this model, the room would be occupied by 15 people throughout its opening hours, during which time it would not be ventilated.
It was ultimately determined that the occupants' discomfort index would be reduced by 75% as compared to if the tiles weren't present. That figure climbed to 85% if the tiles were an additional 1 cm (0.4 in) thicker than the 4-cm test sample.
"We were able to demonstrate with numerical simulations that the building components can significantly reduce humidity in heavily used indoor spaces," says Asst. Prof. Magda Posani, who led the study of the material's moisture-binding properties.
A paper on the research was recently published in the journal Nature Communications.
Source: ETH Zurich