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Intelligent functional glazing with self-cleaning properties to improve the energy efficiency of the built environment

Periodic Reporting for period 4 - IntelGlazing (Intelligent functional glazing with self-cleaning properties to improve the energy efficiency of the built environment)

Okres sprawozdawczy: 2020-09-01 do 2022-05-31

The latest forecast by the International Energy Agency for the CO2 emissions of the built environment portrays a gloomy picture. It is anticipated that those emissions will reach 15.2 Gt in 2050, double their 2007 levels. Rapid urbanisation and economic development is the driving force behind this growth. Buildings consume 40% of the primary energy in developed countries with heating and cooling alone accounting for 63% of the energy spent indoors. These trends are on an ascending trajectory - for example, the energy demand for air conditioning in the EU has been growing by 17% per year on average. Counterbalancing actions are urgently required to impede the above trends.

The main objective of this project was to develop intelligent window insulation technologies that could deliver significant savings to the energy needed for regulating the indoor temperature of commercial, residential, industrial and public buildings. Recognising the different requirements between newly built and existing infrastructure, two parallel concepts were developed: i) a new class of highly-performing, energy-saving glazing for new window installations, and, ii) flexible, polymer films to retrofit existing window installations. Both solutions were enhanced with unique self-cleaning properties bringing about additional economic benefits through reducing maintenance costs and environmental benefits by removing the need for cleaning chemicals. The proposed technologies were planned around sustainable materials and scalable engineering processes intended to shorten the path from the laboratory to the market. IntelGlazing culminated in energy modelling and field testing that assessed the potential of the developed technologies under real environmental conditions.

The functional material underpinning the proposed intelligent glazing was vanadium dioxide, a sustainable thermochromic material that responds reversibly to the ambient temperature. During hot periods, our developed products rejected the majority of the Sun’s infrared radiation, significantly reducing the requirements for air-conditioning. In cold periods, the windows were semi-transparent at both visible and infrared (IR) wavelengths from the Sun while they did not allow the thermal energy generated inside the building to escape. The need for heating was thus reduced. Our solution was a generation beyond existing static solar control glazing products like low-E coatings, which transmit a constant amount of infrared radiation throughout the year. Such static products are not optimum for energy saving purposes as, for example, on cold periods the rejected IR energy should ideally have been used to heat up the buildings’ interior.
People spend over 80% of their time in indoors spaces. As a consequence, buildings require vast amounts of energy. In the EU for example, almost 40% of the primary energy generated is consumed by the built environment with heating and cooling alone accounting for 63% of this. And energy consumption goes hand in hand with CO2 emissions. According to the predictions by the International Energy Agency, building associated CO2 emissions will reach 15.2 Gt in 2050, twice their 2007 levels.

The weakest link in the insulation of a building envelope is its windows. In the Summer, glazed areas illuminated by solar radiation tend to overheat, whereas in the winter heat escapes easier through the windows leading to undesirable heating penalties. This situation is exacerbated by the fact that the key glazing properties (for e.g. solar transmittance) are fixed and cannot adapt to the needs of the buildings and their inhabitants which very by the season (heating in the winter - cooling in the summer).

IntelGlazing elegantly solved these issues by developing a “smart” window technology based on thermochromic materials i.e. materials whose optical properties respond to the ambient temperature. In particular, by applying a special coating made of vanadium-dioxide (VO2), we demonstrated windows that could self-adjust their own transmittance, achieving a remarkable solar gain modulation that exceeded 220 W/m2 (e.g. "High-Performance Planar Thin Film Thermochromic Window via Dynamic Optical Impedance Matching," ACS Appl. Mater. Interfaces 12, 8140–8145, 2020). Furthermore, we enhanced our windows with further functionalities by texturing the surface of glass with bioinspired nanostructures and demonstrated combined ultra-high transmission, negligible glare, self-cleaning and the first ever antimicrobial activity towards staphylococcus aureus bacteria (e.g. "Bioinspired Multifunctional Glass Surfaces through Regenerative Secondary Mask Lithography," Adv. Mater., 2102175, 2021). These properties opened up completely new application areas for our glass, including smart phones and personal devices for which glare, accumulated dirt, fingerprints and bacteria proliferation are persistent obstacles. Later, we discovered the universal ability of our nanostructures to repel dew and condensation, further widening the space of potential applications (e.g. "Unique and universal dew-repellency of nanocones," Nat. Commun. 12, 4–12, 2021).

And we were not limited to glass, extending our material space into Silicon and polymers, making it now possible to apply our technology to a diverse range of products from solar cells to food packaging (e.g. "A route to engineered high aspect-ratio silicon nanostructures through regenerative secondary mask lithography," Nanoscale 14, 1847–1854, 2021, "Delayed Lubricant Depletion of Slippery Liquid Infused Porous Surfaces Using Precision Nanostructures," Langmuir 37, 10071–10078, 2021, "Spacer-Defined Intrinsic Multiple Patterning," ACS Nano 14, 12091–12100, 2020).

Recognizing that most of the windows have already been installed, we developed polymer / VO2 nanoparticle composite films, to easily retrofit existing installations. In the process, we developed new methods to synthesise VO2 particles with high precision over their dimensions and switching characteristics (e.g. "Combined Effect of Temperature Induced Strain and Oxygen Vacancy on Metal-Insulator Transition of VO2 Colloidal Particles," Adv. Funct. Mater. 30, 2005311, 2020) and have embedded them in multiple polymer hosts (acrylics, polyethylene, polysiloxanes and other) demonstrating again their ability to regulate solar heat gain.

Moreoever, we made real life prototypes and have subjected them to comprehensive accelerated testing and outdoors testing proving their potential in the field. In parallel, we performed building energy modelling which showed that annual energy savings of 22% can be achieved in temperate European climates like Italy’s when our windows are installed (e.g. "Optimization of the thermochromic glazing design for curtain wall buildings based on experimental measurements and dynamic simulation," Sol. Energy 216, 14–25, 2021).
1. Demonstration of highest solar gain modulation (22%) window based on thin-film
2. Demonstration of a multifunctional glass surface that combines anti-glare, super-hydrophobic, anti-microbial and anti-condensation properties
3. Demonstration of a new class of thermal antennas whose emissivity is tuned by temperature. New methods for their modelling, synthesis and fabrication
4. Demonstration of surfaces whose heat radiation adapt to the environmental conditions. Such surfaces can be used in tuneable radiative cooling, thermal camouflage, heat sensing and more.
thermochromic window action
thermochromic window action