University of Colorado, Boulder (CU-Boulder)

Numerous U.S. buildings have single-pane windows that do not insulate the building or its occupants as well as double-pane units or other advanced windows. Single-pane windows are also inferior in condensation resistance and occupant comfort. However, complete replacement of single-pane windows with efficient, modern windows is not always desirable or feasible due to cost, changes in appearance, and other concerns. Retrofitting, rather than replacing, single-pane windows can reduce heat loss and save roughly the amount of electricity needed to power 32 million U.S. homes each year. Transparent adhesive products that can be applied directly onto existing windows could increase window energy efficiency and other qualities without substantially affecting the window’s appearance.

The University of Colorado, Boulder (CU-Boulder) with its partners will develop a flexible window film made of nanostructured cellulose. The film can be applied onto single-pane windows to improve their energy efficiency without compromising transparency. The team will be able to economically harvest cellulose needed for the films from food waste using a bacteria-driven process. The cellulose will self-assemble into liquid crystal type structures that selectively reflect infrared light (or heat) while transmitting visible light. The technology is related to liquid crystals that are used in display screens ranging from smart phones to flat-panel HDTVs. The optical properties of these crystals arise from fine-tuning the arrangement of the individual molecules and nanostructures that compose the crystals. Engineering the liquid crystals to be transparent to visible light but able to reflect infrared light will allow heat retention in building spaces, similar to low-emissivity glass.

If successful, CU-Boulder’s innovations will enable energy-efficient retrofits for the substantial remaining stock of single-pane windows in the United States. Retrofitting single-pane windows could produce significant economic and environmental benefits. These technologies could help reduce building energy consumption and save money for homeowners and businesses. Consumers adopting these retrofits could also benefit from improved window performance, including greater comfort and condensation resistance in cold weather and better soundproofing. Finally, by consuming less electricity, natural gas, and/or heating oil to warm a building, these technologies reduce the greenhouse gas emissions associated with using these energy sources.