H.khaled, Khaled

Khaled K., Berardi U., Schlaf M., Soldatov D.V.

Khaled K., Berardi U.

Khaled K., Berardi U., Schlaf M., Soldatov D.

Windows are considered the least efficient elements in the building envelope, leading to high cooling and heating costs. Coating the glazed areas not only reduces operational costs but also enhances occupant comfort. In particular, chromogenic coatings with variable thermo-optical properties attracted strong interest from the scientific community. Among the various technologies, thermochromic coatings are the most promising due to their passive temperature-responsive nature. Vanadium Dioxide (VO2) based thermochromic coatings have been candidates for extensive research due to VO2’s reversible semiconductor-metal phase transition from near-infrared transmitting to blocking states. In this article, VO2 structures were synthesized hydrothermally, and the effects of several experimental parameters, including tungsten (W+6) doping level, reaction time and temperature, reductant type, vanadium concentration, and precursor pH, were investigated. The synthesized structures were subsequently ball-milled and spin-coated on glass substrates, and their thermo-optical properties were measured. The results show that a reaction temperature of 280 ℃ for 72 h combined with tungsten-doping are critical to synthesizing VO2 (M/R) structures via a one-step hydrothermal synthesis without annealing. Furthermore, using tartaric acid as a reductant yielded particles with higher crystallinity; however, V6O13 was present. Similarly, a 1% tungsten doping level and doubling the vanadium concentration yielded particles with higher crystallinity while still exhibiting a phase transition temperature of 41 ℃ and a narrow hysteresis of 4 ℃, suitable for window applications. Further work aims to improve the solar modulation ability by overcoating the ground particles with SiO2 shells while enhancing the sensitivity of the films through the inclusion of photothermal nanoparticles.

Khaled K., Berardi U.

Windows play a critical role in driving the heating and cooling energy loads of buildings, especially in older buildings with outdated windows. While replacing existing windows with high-performance products can significantly boost building energy efficiency, the associated costs can be prohibitive. Consequently, retrofit technologies that utilize existing glass panes and frames offer a compelling solution. This paper investigates the energy performance of two innovative window retrofit technologies at the BeTOP outdoor test cell facility in Toronto, Ontario, a continental location with warm summers and cold winters. The evaluated technologies include a near-infrared-absorbing liquid-applied nano-coating and a peal-and-stick photochromic window film with dynamic absorptance to visible radiation. These technologies are applied directly to the interior glazing surface, allowing for swift installation with minimal occupancy interruption. Since the studied retrofit technologies primarily target cooling energy savings, they may contribute to greater heating energy consumption in a heating-dominated climate. Hence, the study focused on evaluating the in-situ winter performance of the retrofit technologies against a clear reference under identical conditions. While the considered retrofit technologies did not significantly amplify the heating consumption, a noticeable increase in the interior glazing surface temperature was driven by the retrofit coatings' solar absorbing property. Hence, the studied retrofit technologies could potentially show enhancements in thermal comfort aspects in the winter without significant heating penalties. This suggests potential for effective year-round energy savings. Further work is planned to evaluate the cooling and annual performances as well as the daylight performances for different sky conditions.

Khaled K., Berardi U.

Driven by their low thermal resistance and static transmittance to solar radiation, existing static clear windows are often considered the least-efficient components in the building envelope, driving the heating and cooling demands and compromising the thermal and visual comfort of building occupants. Hence, window retrofit technologies that utilize innovative coatings are critical for enhancing energy efficiency and indoor daylight quality in the existing building stock. In particular, dynamic photochromic window films that reversibly modulate solar gains responding to the abundance of ultraviolet radiation are promising but received little attention. In this paper, five commercial flexible photochromic window films were experimentally characterized, and their energy and daylighting performance were numerically and parametrically evaluated in a representative office with different window configurations and orientations across six representative cities with a diverse range of climates. This is one of the first works dealing with photochromic window films as a retrofit technology. The results show that the films exhibit excellent colour-rendering and cyclic stability with rapid switching/bleaching rates. In addition, annual energy savings in the 1% − 4% range were observed for low window-wall ratios, reaching 10% − 14% in cooling-dominated climates with lower latitudes using PC-1, which resulted in the most significant cooling energy savings. Although the film influenced the quantity of light, resulting in lower daylight autonomy, improvements in the useful daylight illuminance and significant reductions in discomfort glare levels were the major benefits of retrofitting existing double-glazed clear windows with the photochromic film.

Khaled K., Berardi U., Liao Z.

Windows are considered the least-efficient components in the thermal envelope driven by their low thermal resistance and static transmittance to solar gains. Thermochromic coatings are promising to address the latter. Nevertheless, current building energy simulation (BES) tools were not originally developed for the performance assessment of adaptive facades. Hence, in this paper, a previously developed 1-D transient heat transfer model was utilized to evaluate the annual heating and cooling energy performance of two thermochromic glazing systems, including commercial Ligand-Exchange (LET) and industrial Vanadium Dioxide (VO2) thermochromic coatings, and compare their performance to reference low-E coated glazing in the cold climate of Toronto, ON. Contrary to current BES, the model accounts for spectral-selectivity, gradual transmittance change, hysteresis, and switching time of thermochromic coatings. A representative room’s annual energy performance was evaluated for different glazing configurations and several exposures. The results show that the VO2 thermochromic glazing is the most energy-efficient configuration in Toronto, driven by low solar transmittance and increased near-infrared reflectance at higher coating temperatures. Furthermore, increasing the switching time and hysteresis width have less significant effects for VO2 glazing.

Berardi U., Khaled K.

Building fenestration, of which glass constitutes a crucial component, is often considered a weak link in the building envelope due to its low thermal resistance and static solar transmittance. Hence, modern glazing technologies aim to optimize thermal and optical performance to improve building energy efficiency and occupant comfort. In particular, coatings have emerged as promising means to transform windows from energy liabilities to assets through radiation control. In this chapter, several coating technologies with static and dynamic optical properties are discussed, and new material developments are presented. The review indicates that static and dynamic technologies are often complementary in enhancing glazing performance. Low-emissivity coatings effectively reduce thermal gains and losses, while solar control coatings exhibit superior performance in reflecting near and far infrared radiation. To further improve heating performance, electrothermal coatings actively enhance glazing thermal resistance by Joule-heating, while photothermal coatings achieve this passively through absorption and efficient conversion of ultraviolet and near-infrared radiation into heat directed inwards. Additionally, photothermal coatings can be utilized for absorption-based solar control by emitting heat outwards. To further enhance the cooling performance, dynamic coatings can modulate the transmission of solar radiation by switching between solar transmitting and blocking states in response to external stimuli. Active dynamic coatings, including electrochromic and gasochromic, offer superior modulation abilities but are hindered by high fabrication and building-integration costs and the need to develop effective operational strategies. In contrast, photochromic and thermochromic coatings are more accessible passive technologies that shift the focus to optimizing intrinsic material properties. Selecting a suitable coating technology depends on various factors, including building use, location, climatic conditions, window-wall ratio, orientation, and ultimately payback periods. Nevertheless, multi-functional coatings that combine low-emissive, dynamic solar modulation, and anti-reflective properties are particularly promising for high-performance advanced glazing applications.

Khaled K., Berardi U.

Windows are considered the weakest components in the building envelope, driven by their low thermal resistance and static transmittance to solar gains. Consequently, innovative coatings are often proposed to promote energy saving performance of windows. This article investigates several flexible photochromic window films capable of reversibly modulating solar gains based on the abundance of ultraviolet radiation. The peel-and-stick films are applied to the internal glazing surface, making them suitable for window retrofits without interrupting building occupancy. The optical properties of the photochromic films are experimentally characterized at various solar radiation intensities. The results are then used to numerically evaluate the energy-saving potential of the different films for a representative room in a high-rise office building located in Tokyo’s warm climate. The results of the experimental and numerical investigations are discussed to show the potential of photochromic films for window-retrofit applications.

Khaled K., Berardi U., Liao Z.

• Climate-responsive coatings adjust their thermo-optical properties in response to boundary conditions. • A transient heat transfer model was developed in MATLAB/Simulink. • Annual heating and cooling energy performance of commercial thermochromic coatings are assessed. • Spectral-selectivity, gradual transmittance change, hysteresis , and switching time are considered. • Results are more promising during cooling seansons, but are evident yearound in continental climates. Windows are often considered the weakest components in the thermal envelope driven by their low thermal resistances and static transmittances to solar gains. While low-E coatings improve the former, climate-responsive coatings that adjust their thermo-optical properties in response to changing boundary conditions are promising to address the latter. In particular, thermochromic films are passive technologies that rely on intrinsic material properties to adapt to varying ambient conditions and are more accessible with simpler structures than their active counterparts; hence, they prevail for solar control applications. However, the nature of current building energy simulation tools imposes limitations on evaluating their performance. In this article, a 1-D transient heat transfer model was developed in MATLAB/Simulink to evaluate the annual heating and cooling energy performance of thermochromic glazing while overcoming several limitations of current building energy simulation tools by accounting for spectral-selectivity, gradual transmittance change, hysteresis behaviour, and delayed switching time. The model was benchmarked against EnergyPlus, and the annual energy performance of a representative room was then evaluated for several double-glazing configurations, window-wall ratios, and exposures in the cold and hot climates of Toronto, ON and Abu Dhabi, UAE, respectively, while quantifying the effects of varying the hysteresis width and switching time. The results showed that commercial thermochromic glazing outperformed clear and low-E windows for both climate conditions. In particular, for a window-wall ratio of 80 % and compared to clear reference glazing, annual energy use intensity reductions up to 6.3 kWh/m 2 and 12 kWh/m 2 were realized in Toronto and Abu Dhabi, respectively, utilizing a glazing configuration that combined exterior thermochromic and interior low-E coated panes, where the latter helped in increasing the former’s temperature causing it to switch at lower ambient temperatures.. While the typical 30-minute switching time of thermochromic coatings was found to increase the annual energy use intensity by up to 0.5 kWh/m 2 , a 5 °C hysteresis reduced the annual cooling energy use intensity by up to 0.2 kWh/m 2 in Abu Dhabi. Less significant effects and savings were found for lower window-wall ratios, particularly in Toronto, where the coating rarely reached temperatures higher than 45 °C.

Khaled K., Berardi U.

• A review of the state-of-the-art coating technologies for glazing applications is reported. • Static coating technologies with fixed optical properties are compared to dynamic coatings. • Electrothermal coatings and photothermal coatings are compared. • Recent evolution in electrochromic and gasochromic coatings is reported. • An ideal passive dynamic hybrid photo-thermochromic coating on flexible films is presented. This paper presents a comprehensive review of the current state-of-the-art coating technologies for glazing applications. The main objective is to collect and present current commercially available technologies on today's market and future research prototypes to identify the most promising coating technologies. Several static coating technologies with fixed optical properties are compared, including low emissivity, electrothermal and photothermal coatings. Low-E coatings are the current industry standard and have almost reached their full energy-saving potential. Hence, electrothermal coatings that convert electricity to heat by the Joule effect are discussed, together with their limitations of needed power supply. To overcome these issues, photothermal coatings have been proposed to improve the glazing thermal performance by absorption of ultra-violet and near-infrared radiation. On the other hand, dynamic coatings can modulate solar gains by switching between clear and tinted states in response to external stimuli. Electrochromic and gasochromic coatings are still limited by high costs. In comparison, photochromic and thermochromic coatings are more accessible and less complex passive technologies, although photochromic coatings are still hindered by low bleaching rates and poor cyclic stabilities. In comparison, thermochromic coatings are more mature, especially those based on vanadium dioxide. This review shows that both static and dynamic technologies thrive to enhance optical and thermal performances while providing an opportunity for the realization of durable next-generation dynamic windows. In particular, the development of passive dynamic hybrid photo-thermochromic coatings seems the most promising trajectory.

Khaled K., Richman R.

One of the key improvements in EIFS/ETICS is the addition of geometrically-defined drainage cavities at the rear of the continuous insulation layer to allow water that has penetrated the outer EIFS lamina to drain out by gravity to the exterior; and to provide an opportunity for enhancing the convective drying ability of the wall assembly by introducing air flow and moisture exchange between the cavities and the exterior environment. EIFS assemblies with such cavities can be either vented or ventilated depending on the vents size, location and distribution. The integration of these cavities has raised questions regarding their impacts on the thermal performance of wall assemblies constructed of EIFS with such cavities. The principal objective of this research was to evaluate the reduction in the whole-assembly's effective thermal resistance due to the use of vented EIFS in lieu of face-sealed EIFS. Thermal numerical simulations were conducted on models that were validated against experimental results of full-scale field tests conducted in the cold climate of southern Ontario. Reductions in the thermal resistances of vented EIFS assemblies were observed in the range of 1.4–5.3% and 0.1–4.6% for south and north facing walls, respectively. Reducing the spacing between the cavities further reduced the thermal resistances due to increased ventilation. It was also found that the thermal resistances of the lightly and medium insulated south-facing EIFS were lower than their northern counterparts, mainly due to the thermal storage ability of the construction materials. However, heavily insulated EIFS reduces this flux of heat and eventually the south-facing walls' thermal resistances overcome their northern counterparts.

Berardi U., Tomassoni E., Khaled K.

The current energy inefficiencies in relocatable temporary camps of the Armed Force troops create logistic challenges associated with fuel supply. The energy needs of these camps are primarily satisfied by diesel engine generators, which imply that a significant amount of fuel needs to be continuously provided to these camps, often built in remote areas. This paper presents an alternative solution, named Smart Hybrid Energy System (SHES), aiming towards significantly reducing the amount of fuel needed and minimizing transportation logistics while meeting camp energy demands. The SHES combines the existing diesel generators with solar power generation, energy storage, and waste heat recovery technologies, all connected to a microgrid, ensuring uninterrupted electricity and hot water supplies. All components are controlled by an energy management system that prioritizes output and switches between different power generators, ensuring operation at optimum efficiencies. The SHES components have been selected to be easily transportable in standard shipping 20 ft containers. The modularity of the solution, scalable from the base camp for 150 people, is designed according to available on-site renewable sources, allowing for energy optimization of different camp sizes in different climates.

You Y., Yang X., Xu Z., Cui C., Shi F., Hong X.

Khaled K., Berardi U., Schlaf M., Soldatov D.V.

Teixeira H., Rodrigues A.M., Aelenei D., Gomes M.G.

Tahmasbi F., Khdair A.I., Aburumman G.A., Tahmasebi M., Thi N.H., Afrand M.

Wijewardane S., Santamouris M.

Zhang G., Qin X., Wang D., Li J., Pan W., Yin J.

The utilization of heat-shielding glazing technologies can efficiently promote carbon emission reductions and energy savings by decreasing solar irradiation into buildings. Although a variety of glazing technologies have been created for solar glazing, either the heat-shielding performance is low, the thermal stability is poor, or the cost is high. Here, we report a thermally stable heat-shielding coated glass for solar glazing in a simple way via direct calcination of Ce and Sb co-doped SnO2 nanoparticles with polysilazane (PSZ) coatings in air. The resulting coated glass has transmittances of 4.7% at 250–380 nm, 59.3% at 380–780 nm, and 9.7% at 780–2500 nm; excellent environment stability under accelerated aging conditions over 350 h; and also a ca. 50-fold lower fixed cost than commercial low-E glass. Moreover, a coated glass with a high pencil hardness of 9H was also fabricated via further spraying and calcinating of a PSZ coating as the cover layer, which is also the hardest coated solar glaze to our knowledge. The high solar-shielding performance and unprecedented low cost of the Ce and Sb co-doped SnO2-coated glass, as well as the simplicity of its fabrication, exhibit great potential in energy-saving buildings and cars.

You Y., Yang X., Deng X., Shi F., Wang C., Hong X.

Li X., Sun Y., Wu Y.

Zakirullin R.

Khaled K., Berardi U.

Fasi M.A., Budaiwi I.

Ong H.L., Ji Z., Haworth L., Guo Y., del Moral J., Jacob S., Borras A., Gonzalez‐Elipe A.R., Zhang J., Zhou J., McHale G., Fu Y.

Fogging, icing, or frosting on optical lenses, optics/photonics, windshields, vehicle/airplane windows, and solar panel surfaces have often shown serious safety concerns with hazardous conditions and impaired sight. Various active techniques, such as resistive heating, and passive techniques, such as icephobic treatments, are widely employed for their prevention and elimination. However, these methods are not always suitable, effective, or efficient. This review provides a comprehensive overview of the fundamentals and recent advances of transparent thin‐film surface acoustic wave (SAW) technologies on glass substrates for monitoring and prevention/elimination of fogging, frosting, and icing. Key challenges related to fogging and icing on glass substrates are discussed, along with fundamental mechanisms that establish thin‐film SAWs as optimal solution for these issues. Various types of thin‐film acoustic wave technologies are discussed, including recent wearable and flexible SAW devices integrated onto glass substrates for expanding future applications. The focus of this review is on the principles and strategies for hybrid or integrated de‐fogging/de‐icing and sensing/monitoring functions. Finally, critical issues and future outlooks for thin‐film‐based SAW technology on glass substrates in industry applications are presented.

Khaled K., Berardi U., Schlaf M., Soldatov D.

Windows are considered the least efficient elements in the building envelope, leading to high cooling and heating costs. Coating the glazed areas not only reduces operational costs but also enhances occupant comfort. In particular, chromogenic coatings with variable thermo-optical properties attracted strong interest from the scientific community. Among the various technologies, thermochromic coatings are the most promising due to their passive temperature-responsive nature. Vanadium Dioxide (VO2) based thermochromic coatings have been candidates for extensive research due to VO2’s reversible semiconductor-metal phase transition from near-infrared transmitting to blocking states. In this article, VO2 structures were synthesized hydrothermally, and the effects of several experimental parameters, including tungsten (W+6) doping level, reaction time and temperature, reductant type, vanadium concentration, and precursor pH, were investigated. The synthesized structures were subsequently ball-milled and spin-coated on glass substrates, and their thermo-optical properties were measured. The results show that a reaction temperature of 280 ℃ for 72 h combined with tungsten-doping are critical to synthesizing VO2 (M/R) structures via a one-step hydrothermal synthesis without annealing. Furthermore, using tartaric acid as a reductant yielded particles with higher crystallinity; however, V6O13 was present. Similarly, a 1% tungsten doping level and doubling the vanadium concentration yielded particles with higher crystallinity while still exhibiting a phase transition temperature of 41 ℃ and a narrow hysteresis of 4 ℃, suitable for window applications. Further work aims to improve the solar modulation ability by overcoating the ground particles with SiO2 shells while enhancing the sensitivity of the films through the inclusion of photothermal nanoparticles.

Jain H.

AbstractTo address the multifaceted aspects of indoor environmental sciences, this review paper critically investigates the optimization of thermal comfort and the development of heat-resilient indoor environments. Drawing on knowledge from a wide range of disciplines, such as chemistry, microbiology, public health, psychology, epidemiology, engineering, and toxicology, among others, it provides an extensive overview of recent study findings. The paper examines solutions targeted at reducing the negative impacts of heat stress while improving thermal comfort levels indoors, highlighting the complex link between indoor environment, human health, and comfort. Using both theoretical frameworks and actual data, the study assesses a variety of cutting-edge methods, such as behavioral interventions, heating, ventilation, and air conditioning (HVAC) systems, passive design strategies, and adaptable building materials. The statement underscores the importance of interdisciplinary cooperation in tackling the intricate problems related to interior thermal comfort and resistance to heat waves. The review attempts to offer practical insights for practitioners and researchers looking to optimize interior settings for human health and well-being by looking at the synergistic impacts of several treatments. Additionally, the research emphasizes how crucial it is to consider the larger context of climate change and its effects on interior spaces. To improve our understanding of thermal comfort optimization and heat-resilient design techniques, it suggests new research directions and knowledge gaps and advocates for ongoing interdisciplinary inquiry. In the end, the review adds to the continuing conversation about designing livable, sustainable, and healthful interior spaces in the face of changing weather patterns.

Khaled K., Berardi U.

Windows play a critical role in driving the heating and cooling energy loads of buildings, especially in older buildings with outdated windows. While replacing existing windows with high-performance products can significantly boost building energy efficiency, the associated costs can be prohibitive. Consequently, retrofit technologies that utilize existing glass panes and frames offer a compelling solution. This paper investigates the energy performance of two innovative window retrofit technologies at the BeTOP outdoor test cell facility in Toronto, Ontario, a continental location with warm summers and cold winters. The evaluated technologies include a near-infrared-absorbing liquid-applied nano-coating and a peal-and-stick photochromic window film with dynamic absorptance to visible radiation. These technologies are applied directly to the interior glazing surface, allowing for swift installation with minimal occupancy interruption. Since the studied retrofit technologies primarily target cooling energy savings, they may contribute to greater heating energy consumption in a heating-dominated climate. Hence, the study focused on evaluating the in-situ winter performance of the retrofit technologies against a clear reference under identical conditions. While the considered retrofit technologies did not significantly amplify the heating consumption, a noticeable increase in the interior glazing surface temperature was driven by the retrofit coatings' solar absorbing property. Hence, the studied retrofit technologies could potentially show enhancements in thermal comfort aspects in the winter without significant heating penalties. This suggests potential for effective year-round energy savings. Further work is planned to evaluate the cooling and annual performances as well as the daylight performances for different sky conditions.

Khaled K., Berardi U.

Teixeira H., Moret Rodrigues A., Aelenei D., Ferreira I., Gomes M.G.

de Oliveira C.C., Catão Martins Vaz I., Ghisi E.

Teixeira H., Gomes M.G., Moret Rodrigues A., Aelenei D.

The application of films on conventional glazing aims at increasing the glazing performance by reducing energy needs and increasing indoor comfort. Photochromic films in particular can alter their optical properties due to a chromatic change in response to solar radiation, allowing for reduced glare levels and solar heat gains. However, despite the potential of application, this refurbishment solution is still poorly explored. Therefore, the main purpose of this work was to experimentally evaluate the thermal and luminous performance of a double glazing with and without a photochromic film installed, using two office rooms in Lisbon as case study. An extended field experimental campaign was conducted simultaneously in both offices, where temperature, solar radiation and illuminance levels were collected. The key contribution and novelty of this research lies on the experimental assessment of the thermal and visual comfort conditions with the photochromic film under real-occupancy. Even though the photochromic film significantly increased the surface temperatures of the glazing, the indoor air temperature was not negatively affected, with an increase up to 14% of working hours with comfortable temperature during the heating period. Illuminance levels on vertical/horizontal plane were reduced by 24/36% in the presence of the photochromic film, when compared to the clear glazing without film, resulting in an increase of 7% of working hours with useful illuminance during the heating period, and large areas in the office room with imperceptible daylight glare levels when facing the glazing system. The impact of the film was less noticeable during the cooling period.

Martinho H., Loonen R., Hensen J.

Adaptive solar shading systems offer a dynamic solution to balance daylight availability and glare control in buildings. While building performance simulation methods are useful to understand the potential of these systems to improve daylight conditions in indoor spaces, it is unclear if established practices such as the use of hourly averaged climate data are sufficient to accurately estimate the benefits of adaptive solar shading in real-world conditions. This study investigates how the time resolution of irradiance data in simulation models affects the predicted performance of adaptive solar shading systems. To that end, a series of simulations for models with time resolutions from 1 to 60 min are run, and the results are compared to quantify the variation in daylight metrics between different resolutions. The outcome of this comparison study reveals that while hourly averaged irradiance data generally suffices for daylight performance estimations, it is also likely to overlook short-term periods of glare discomfort that would be present in high-resolution irradiance data. In the context of adaptive shading design, capturing these discomfort periods can be key to providing solutions that achieve specific visual comfort goals. This suggests that the need for high-resolution irradiance data is project-specific, which emphasizes the need for more tailored approaches in the representation of adaptive shading systems in early building design.

Liyanage D.R., Hewage K., Hussain S.A., Razi F., Sadiq R.

Energy retrofitting for buildings has gained great attention in recent years due to the significant benefits of reducing environmental impacts and costs. Generally, retrofit planning involves considering criteria such as energy savings, emissions savings, and cost savings. However, the rapid transition of climate and extreme climate forces integrate climate adaptation into retrofit practices. This study examines strategies and modifications necessary to transform the current climate mitigation-based retrofit processes into frameworks that simultaneously improve climate mitigation and adaptation. A comprehensive literature review is conducted on building energy retrofit studies based on climate adaptation. It was found that future climate events are anticipated to be more related to overheating than under-cooling in many regions. Passive retrofit strategies can reduce overheating risks substantially, while the dependency on active cooling is unavoidable in warm climatic regions in future climates. Retrofit strategies designed based on traditional approaches may not be effective and may even worsen the risks of overheating in the future climate due to drastic climate change. Climate resiliency criteria must be adapted to the building retrofit field. Climate modelling and energy simulation have a substantial role in designing retrofits, and yet significant research and development is required to penetrate the current retrofit practices. The synthesis of the findings guides the systematic and careful designing and implementation of building energy retrofits. These findings offer valuable insights to policymakers, urban planners, and researchers seeking to improve buildings' energy performance and resiliency and act as a guideline to implement climate change adaptation strategies.

Shu L., Mo Y., Zhao D.

The trajectory of sustainable urban development evolves with the integration of intelligent technologies, extending beyond individual buildings to encompass entire communities interwoven with smart systems. Energy retrofits at smart and connected communities are crucial for sustainable urban renewal, yet they present distinct challenges from individual home retrofitting. However, a comprehensive understanding of the emerging research scopes and technologies in large-scale energy retrofits is lacking. To address this problem, this research systematically reviews journal publications in this field from 2000 to 2023. Results disclose four research scopes: building construction, mechanical systems and equipment, electrical systems and computing, and human-centered design and connectivity, suggesting a new landscape for energy retrofit research, which largely extends beyond the traditional field of the built environment (e.g., heating, cooling, lighting, and structure) to advanced computing, renewable energy, and human-centered connectivity. Results also delineate a new paradigm of retrofit technologies with three focused areas: within-building optimizations (heating and air conditioning, envelope, engineering design, and smart technology), between-building connections (power grid, district energy, and integrated energy system), and whole-community integrations. They represent the nodes, ties, and interplay within community networks. Eight retrofit focuses and their specific technologies and computational techniques are summarized and examined. Notably, the approach of simulation and computational modeling is prevalent, with evolutionary algorithms featured in computational techniques. The review suggests five gaps and proposes a roadmap to advance future research in energy retrofits, specifically emphasizing the integration of intelligent technologies and multidisciplinary collaborations.

Ghosh A., Hafnaoui R., Mesloub A., Elkhayat K., Albaqawy G., Alnaim M.M., Mayhoub M.S.

Globally building sector consumes a significant amount of fossil fuel-generated grid energy which emits a considerable level of carbon emissions. These scenarios can be an obstacle to sustainable or smart city developments. In a building which consists of various components, windows are the most influential to contribute to this energy consumption. To abate the excessive amount of building energy consumption, an alternative glazing system is paramount. Among the other available energy-efficient glazing, an active smart switchable is promising as it can be altered based on occupant choice. In this work, four active smart switchable glazings have been studied (electrochromic, suspended particle device, liquid crystal and gasochromic) based on their operating principle, glazing factors and energetic application. It is evident that EC has more material aspect investigation and overall energetic application for PLDC, SPD and EC needs more study. Gasochromic which can be a potential in future is not explored in higher order. However, these types of windows integration in buildings and how they will have an impact on urban heat islands, part of smart buildings, smart cities and digital twins have also been discussed.

Khaled K., Berardi U.

Driven by their low thermal resistance and static transmittance to solar radiation, existing static clear windows are often considered the least-efficient components in the building envelope, driving the heating and cooling demands and compromising the thermal and visual comfort of building occupants. Hence, window retrofit technologies that utilize innovative coatings are critical for enhancing energy efficiency and indoor daylight quality in the existing building stock. In particular, dynamic photochromic window films that reversibly modulate solar gains responding to the abundance of ultraviolet radiation are promising but received little attention. In this paper, five commercial flexible photochromic window films were experimentally characterized, and their energy and daylighting performance were numerically and parametrically evaluated in a representative office with different window configurations and orientations across six representative cities with a diverse range of climates. This is one of the first works dealing with photochromic window films as a retrofit technology. The results show that the films exhibit excellent colour-rendering and cyclic stability with rapid switching/bleaching rates. In addition, annual energy savings in the 1% − 4% range were observed for low window-wall ratios, reaching 10% − 14% in cooling-dominated climates with lower latitudes using PC-1, which resulted in the most significant cooling energy savings. Although the film influenced the quantity of light, resulting in lower daylight autonomy, improvements in the useful daylight illuminance and significant reductions in discomfort glare levels were the major benefits of retrofitting existing double-glazed clear windows with the photochromic film.

Berardi U., Soudian S.

Proposing new materials and systems to improve the performance and energy efficiency of buildings is often followed by performance evaluation to monitor how they perform and contribute. Experimental performance characterization of new and existing building materials and systems is crucial to understanding their behaviour in relation to indoor environmental and conditional changes, in addition to outdoor environmental changes. Full-scale experimental test cell facilities have been at the forefront of experimental performance evaluation in building-related research, as they can provide a realistic representation of buildings, which includes environmental conditions, building structure, and operational characteristics. In this paper, the new test cell facility of BeTOP, located in the city of Toronto, Ontario, is introduced as a full-scale experimental facility with the capability of multiple practical tests simultaneously. This paper describes the characteristics of this test cell, including structure details, testing capabilities, system details, previous testing campaigns, and future testing potential. The design of such a full-scale testing facility is shown to be crucial in a continental climate, such as Toronto, to observe the long-term performance of new systems under variable boundary conditions with cold winters and hot and humid summer seasons.

Berardi U., Khaled K.

Building fenestration, of which glass constitutes a crucial component, is often considered a weak link in the building envelope due to its low thermal resistance and static solar transmittance. Hence, modern glazing technologies aim to optimize thermal and optical performance to improve building energy efficiency and occupant comfort. In particular, coatings have emerged as promising means to transform windows from energy liabilities to assets through radiation control. In this chapter, several coating technologies with static and dynamic optical properties are discussed, and new material developments are presented. The review indicates that static and dynamic technologies are often complementary in enhancing glazing performance. Low-emissivity coatings effectively reduce thermal gains and losses, while solar control coatings exhibit superior performance in reflecting near and far infrared radiation. To further improve heating performance, electrothermal coatings actively enhance glazing thermal resistance by Joule-heating, while photothermal coatings achieve this passively through absorption and efficient conversion of ultraviolet and near-infrared radiation into heat directed inwards. Additionally, photothermal coatings can be utilized for absorption-based solar control by emitting heat outwards. To further enhance the cooling performance, dynamic coatings can modulate the transmission of solar radiation by switching between solar transmitting and blocking states in response to external stimuli. Active dynamic coatings, including electrochromic and gasochromic, offer superior modulation abilities but are hindered by high fabrication and building-integration costs and the need to develop effective operational strategies. In contrast, photochromic and thermochromic coatings are more accessible passive technologies that shift the focus to optimizing intrinsic material properties. Selecting a suitable coating technology depends on various factors, including building use, location, climatic conditions, window-wall ratio, orientation, and ultimately payback periods. Nevertheless, multi-functional coatings that combine low-emissive, dynamic solar modulation, and anti-reflective properties are particularly promising for high-performance advanced glazing applications.

Pu J., Shen C., Wang J., Zhang Y., Zhang C., Kalogirou S.A.

In the past decades, spectrally selective windows, such near-infrared absorbing (NIR) glazings, low-e glazings, and various smart windows, have been widely studied, developed, and applied in different climatic conditions for building energy-saving purposes. One major pathway of the spectrally selective glazings to achieve energy savings is through solar radiation control, either by NIR reflection or absorption. This review concerns the NIR absorbing glazings with the limited subset of ion-based and nanoparticle-based glazings. In detail, each category’s spectral absorbing materials are further distinguished into sub-categories, and then their underlying mechanisms of spectral selectivity were elaborated, as well as their application status in terms of manufacturing, cost, and commercialization popularity. To further advise the application in the building sector, we comparatively evaluated the performance of each kind of glazing in terms of the light and heat decoupling ability and visual qualities (i.e., color rendering). Finally, the challenges and future directions of the NIR absorbing glazings to bridge the gap between lab research and large-scale practical applications are illustrated.

Li Q., Deng S., Li D., Yang J., Jin H., Li J.

Cesium tungsten bronze (CsxWO3), a unique energy-saving material, has attracted great interest because of its excellent visible transmittance and near-infrared absorption. In order to improve its optical properties, the Ti doping modification was carried out in this work, and a series of Ti-doped CsXWO3 (Ti-CsxWO3) nanopowders were synthesized by a solvothermal reaction and post-annealing. The 1.71 at. % of Ti dopants achieved remarkable enhancement of both integral visible transmittance (Tlum, 380–780 nm) and near-infrared shielding efficiency (ΨNIR, 780–2500 nm) of CsxWO3. The Tlum and ΨNIR of the 1.71 at. % Ti-CsxWO3 polymer film reaches 63.87 % and 76.90 %, respectively, higher by 51.88 % and 65.00 % than those of the CsxWO3 film. The improvement of Tlum is attributed to the broadening of band gap and smaller size of the nanoparticles induced by Ti doping, and the enhanced ΨNIR would result from the increased free electron concentration and energy levels of impurities. The incorporation of Ti elements renders CsxWO3 a promising application in the field of energy saving.

Yang X., Zou J.

The facile fabrication of VO2 thermochromic film with outstanding solar modulation ability along with high luminous transmittance is still challenging for the large-scale practical application of VO2 films. The dispersity of VO2 in polymer matrix can determine the optical performance of VO2 thermochromic film to some content. Herein, the VO2 nanoparticles were prepared by one-step hydrothermal method and directly dispersed in polyurethane (PU) sol with different viscosity to cast the VO2 composite film. The solar modulation ability (ΔTsol) almost increased linearly with the logarithm of viscosity for PU sol, and ΔTsol can be enhanced to 14.5% from 6.6% while maintaining a high Tlum beyond 54% only by changing the content of thickener. The ΔTsol increased further to 20.0% for the three layers film. The enhanced optical performances might be attributed to the good dispersity of VO2 nanoparticles and pore structure in PU matrix. This study provides a novel strategy in preparing VO2 film for the applications in smart windows.

Santos A.J., Martin N., Outón J., Blanco E., García R., Morales F.M.

Vanadium dioxide (VO2) is considered as one of the most promising materials for the next generation of energy-efficient smart glazing since it experiments a reversible metal-to-insulator transition at near room temperature. Nevertheless, the complexity and high cost associated to the fabrication of VO2-based nanostructures limit the transfer of this technology to the industrial scale. Aware of this opportunity, we present a simple and advantageous method for the fabrication of VO2 coatings on glass substrates which comprises the initial sputtering of vanadium thin films at glancing angles and the subsequent very fast oxidation of such systems in open air atmosphere. Relying on the accurate control of the thermal treatment parameters, as well as the enhanced reactivity of the high surface-to-volume porous deposited structures, thermochromic VO2 coatings were achieved and then characterized by means of scanning electron microscopy, grazing incidence X-ray diffraction, variable temperature UV-vis-NIR spectrophotometry, and resistivity measurements. These investigations allowed us to determine the key role that oxidation temperatures and times not only play in modulating the optical performance of the film, but also in the surprising and advantageous decrease in the transition temperature (up to 12 °C lower than the standard value for pure VO2), which is attained without incorporating doping agents. This fact, together with the remarkable values of luminous transmittance (∼50 %) and solar modulation ability (5–10 %) accomplished for our best samples, opens up an alternative and simpler pathway towards the large-scale manufacturing of VO2 coatings for smart window applications, reaching, on a preliminary basis, similar or even better performances than those obtained so far for single and undoped VO2 films.