A team of physicists and materials scientists from the University of Colorado has developed a method to better insulate double-glazed windows by adding a transparent airgel.
In a paper published in the journal Nature Energy, the group describes how airgel is made and the increased energy efficiency that can be expected from windows that use it. Nature Energy also published a research summary in the same issue of the journal describing the work carried out by the team.
Since most homeowners prefer to have windows that allow them to see outside, heat loss is inevitable. In recent decades, heat loss through windows has been improved by adding a second pane of glass.; the two panes are generally separated by an insulating air gap.
However, these windows do not offer the same degree of insulation as insulated walls. In this new approach, the Colorado team has devised a way to improve the insulating properties of double glazing.
To make the airgel (a gel with air pockets), the team soaked cellulose nanofibers extracted from wood with water. Then, the wood nanofibers were removed and immersed in an ethanol solution. Once saturated, the nanofibers were heated in a pressure oven, causing the bags of ethanol to be replaced with air. The nanofibers, which were transparent, were then coated with a water-repellent material to prevent condensation when placed between the crystals.
The final product filled the space between the crystals. The researchers note that in addition to providing more insulation, the new method makes it possible to increase the distance between the crystals, which adds even more insulation. The tests showed that a 1 inch gap provided the same degree of insulation as an insulated wall.
The research team also notes that tests have shown that the airgel had a visible light transmission of 97% to 99%, which is better than glass. It also had a haze factor of less than 1%.
Eldho Abraham et al, Highly transparent silanized cellulose aerogels to boost the energy efficiency of glazing in buildings, Nature Energy (2023). DOI: 10.1038/s41560-023-01226-7
Transparent aerogels reduce energy loss through building windows, Nature Energy (2023). DOI: 10.1038/s41560-023-01229-4