The nanoscale technology could elevate the thermal performance of single-pane windows to that of double-pane.
Researchers from the Penn State University have recently developed a nanoscale technology that could help to elevate the thermal performance of single-pane windows to that of double-pane windows in winter.
By sandwiching a layer of insulating air, double-pane windows allow to improve energy efficiency over single-pane windows, although replacing them can be expensive or technically challenging. A more economical but less effective alternative would be to coat single-pane windows with translucent metallic films capable of absorbing some solar heat in winter without compromising clarity of the glass. However, the solution developed by the researchers may now improve the coating’s efficacy.
“Near-infrared light — a portion of solar light that humans cannot see but can feel as heat — can activate unique light-to-heat effects on certain metallic nanoparticles, enhancing how heat flows inward through a window. We were interested in understanding how these effects could be helpful in saving energy in buildings, particularly during the winter season,” stated Julian Wang, associate professor of architectural engineering and affiliated with the College of Art and Architecture’s Department of Architecture and the Materials Research Institute at Penn State.
The study
The research team first developed a model to estimate how much heat from sunlight would be reflected, absorbed into or transferred through a window coated with metallic nanoparticles. They selected the photothermal compound because of its ability to absorb the sun’s near-infrared light while allowing for ample visible light transmission at the same time. The model predicted that the coating would reflect less near-infrared light or heat, thus absorbing more of it through the window than most of other coating types.
Then, by testing a single-pane window coated with the nanoparticles under simulated sunlight in the laboratory, the researchers confirmed the predictions that had been made by the simulation: there was a significant rise in temperature on the side of the window coated with the nanoparticles, indicating that the coating could pull heat from the sunlight inside, in order to compensate for internal heat lost through a single-pane window.
The researchers then implemented their data into a larger-scale simulation to analyse the energy savings for an entire building with coated windows across different climates. Compared to a commercially available single-pane window’s low-emissivity coating, the photothermal coating absorbed much of the light in the near-infrared region of the spectrum while the conventionally coated window reflected it outside. This near-infrared absorption resulted in a roughly 12% to 20% reduction in heat loss compared to the other coatings and an overall building energy saving potential of up to around 20% when compared to a building with no coatings on single-pane windows.
To account for seasonal changes, the researchers also implemented awnings into their building-scale simulation, blocking the more direct rays of sunlight that heat the environment in summer, largely negating the undesirable heat transfer and any associated cooling costs.
“As demonstrated by this study, we can still improve the overall thermal performance of single-pane windows to be similar to double-pane windows in the winter season at this research stage. These findings challenge our conventional solution of using more layers or insulation materials to retrofit single-pane windows for energy savings,” added Wang.
The results of the study have been published here.