For homeowners, the type of windows in a house contribute significantly to the heating and cooling efficiency. Maintaining indoor temperatures consumes great amount of energy and accounts for 20 % to 40% of national energy expenditures in developed countries.
Following a research initiative undertaken at the University of Oxford and University of Pittsburgh, energy efficient windows receive a lift by proposition of a new smart window design. The design involves harvesting the sun’s energy in winter to keep the house warm and reflect the sun’s energy in summer to keep it cool.
The findings of the research is recently published in the journal ACS Photonics.
Importantly, the major progress is in the ability of the window to change according to seasonal requirements. These window absorb near infrared light from the sun in winter and convert it into heat for the inside of a building. In contrast, the sun can be reflected instead of being absorbed in summer months.
Elaborately, the film of the window is composed of an optical pile of materials less than 300 nanometers in thickness, and has a very thin active coating made of phase change materials. The material can absorb invisible wavelengths of the light of the sun and radiate it as heat. Interestingly, the same material can be switched so it converts those wavelengths of light instead.
In fact, visible light is transferred almost identically in both states to not let the change appear in the window. The aesthetic consideration is important for the adoption of such green technologies.
The phase change material could even be altered. For example, if 30 percent of the material is reflecting heat, and 70 % is absorbing and emitting this allows for more precise temperature control.