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Description
Overall aims and objectives of the project
A huge portion of the significant amount of energy consumed to maintain thermal comfort inside buildings is lost through windows. In contrary to conventional ones, smart (i.e. energy-efficient) windows are capable of regulating solar/heat transmission for energy efficiency and comfort. It is, therefore, imperative to use smart windows, to facilitate the reduction of energy demand and carbon footprint in the building sector. Therefore, the important aspects to consider are (i) control of the transition temperature, and (ii) increase of the increase of luminous transmittance. The control over the metal-to-insulator transition in vanadium dioxide coatings is fairly new in terms of single identifiable steps in the procedure (i.e. strain, usage of a buffer layer, doping). This collaborative attempt is part of a broader research plan, in which its long-term goal is the optimization of the vanadium dioxide based hetero structures, with a scope of their large-scale testing and implementation on architectural buildings.
The project will address the challenges by (i) investigate the microstructural changes induced in vanadium dioxide coatings as a function of their growth conditions, (ii) correlate these changes with their optical and electrical behavior, and (iii) establish rigid structure – properties relationships that will lead to tailored made vanadium dioxide materials with enhanced efficiency for thermochromic smart windows applications.
The value added of partnership resides in the fact that successful implementation of the project can only be achieved by the complementary expertise of the consortium partners. Also, the complementarity of the partners’ expertise will inevitably lead to a long-term partnership and enhance research results.
Summary of project results
Windows capable of regulating solar/heat transmission for energy efficiency and comfort are called smart. Smart windows are a type of windows that have advanced characteristics, which enable the building to reach higher energy performance levels. Smart windows that follow the passive approach can partially block the unwanted solar radiation, and this ability is controlled by the ambient temperature. In periods of cold weather, the IR transmittance increases whereas in hot weather, it decreases. The modification of the transmittance characteristics is related to the thermal and radiative properties of the smart window. Glass doesn’t have the desired characteristics. By adding a layer on the top surface of glass, the optical and thermal characteristics of the structure can be completely modified. This layer can control the incident solar heat flux and transform a window to a smart one. Hence, this smart window technology can lead to reduction of the energy consumption for heating, ventilation and air conditioning systems and the overall electricity demand of the building.
The main topic of the project was to improve the optical properties of vanadium dioxide coatings deposited on glass, in order to make possible the use of this advanced oxide material for smart windows in fenestration.
The project mobilized the knowledge, the experience and the expertise of the researchers from two Romanian institutes and one university from Norway. National Institute for Lasers, Plasma and Radiation Physics (RO) implemented the concept of obtaining thermochronic smart windows. During the project VO2 and TiO2 coatings were deposited by laser technology on various materials (glass, silicon, quart etc) in different experimental conditions and configurations (monolayer, multilayer etc). National Institute for Material Physics (RO) was in charge with the characterization of obtained coatings from electrical, optical, compositional points of view. University of Stavanger performed the structural investigations of all the coatings that were obtained during the project.
A dedicated website was developed which allows both researchers and the general public free access to the information disseminated [https://teesm.inflpr.ro/ro].
During the project, we obtained the following coating types: VO2, TiO2, TiO2/VO2 (5 pairs per sample). In case of the monolayer of VO2 (70 nm thickness) that starting with the temperature of 65 °C, the reflectivity values above 1000 nm (in the IR range) slightly increase with the temperature, as expected to a specific metal-insulator transition behaviour. This effect is even more effective in the case of the bilayer structure, starting already from 50 °C, in agreement with a lower transition temperature for the bilayer. In case of the multilayer structure, the reflectivity behaviour above 1000 nm is not concluding, in the sense that it increases slightly with temperature, in the range from 1000 to 1400 nm, but decreases with the temperature for wavelengths higher than 1400 nm. From the point of view of this functionality, this multilayer system seems to be almost not effective.
Also, the TiO2(Rutile)/VO2/TiO2(Anatase) multilayer coatings could be implemented as a smart window that combines energy saving, antifogging and self-cleaning functions ensuring a sustainable approach of the project.
The window production lines are open to new technologies that can enhance the ecological characteristics of their products. The end product of this project, VO2-based thermochronic smart windows with controlled Tc could have a great impact on the usage of energy-efficient glass. A further step can also be the incorporation of these structures to the car windshield and windows that can be used in the same manner to reduce the usage of air-conditioning.
Summary of bilateral results
The project was possible thank to financial support of Norway administration. Having partner an entity from a Norway was an excited experience for Romanian partners due to opportunity to interact with the scientific community from a recognized university and with different culture and habits. It is worth to mention that the responsible project from UiS, Andreas Delimitis, has Greek nationality and the PhD student hired by UiS, Ayushi Rai, is Indian.All the team gained experience and knowledge on growth oxide structures by laser deposition and on their characterization. Specialists in laser deposition techniques, experts on measurements for electrical and optical properties, as well as on compositional and structural characterization professionals, emerge by utilizing the high-tech equipment of the participants’ laboratories. The training activities developed during the project are particularly beneficial for the young researchers which have access to state-of-the-art equipment and cutting-edge research. Researchers at the postdoctoral level had and continue to have the opportunity to improve their independence and develop their personal capabilities, which will enable them to launch a lasting career in science and/or technology.The main results from the bilateral level:- complementary and interdisciplinary research;- employment of two female PhD students;- one PhD thesis finalized;- interacademic and cultural exchanges;- exploitation of the results by common publications and oral/poster presentation: 10 published papers in open access ISI journals, 3 book chapters published by recognized publishing houses, 7 international conference presentations.