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A state-of-the-art review on innovative glazing technologies
Abstract
Buildings play an important role in greenhouse gas emissions since they constitute a large proportion of the global energy demand. This dramatic scenario is usually a consequence of poor thermal insulation characteristics of building fabric. Among the elements of a typical building envelope, windows are responsible for the greatest energy loss due to their notably high overall heat transfer coefficients (U-values). About 60% of heat loss through the fabric of residential buildings can be attributed to the glazed areas. Windows are useful multifunctional devices for buildings which provide passive solar gain, air ventilation and also the ability to view the outside. However, they greatly dominate the heating and cooling demand of buildings in winter and summer, respectively. Conventional window technologies tend to have poor U-values which cause significant heat losses during the winter season and undesired heat gain in summer. Unique glazing technologies are therefore required to improve visual and thermal comfort of the occupants, whilst mitigating the energy consumption of buildings. In the present work, a comprehensive review of the latest developments in glazing technologies is presented. Currently available high performance glazing products and technologies are analyzed in detail with application examples.
... Les échanges thermiques entre la fenêtre et l'occupant se font selon trois modes de transfert, par rayonnement de GLO, par pénétration du rayonnement solaire de CLO à travers le vitrage ainsi que par les courants d'air induits par le drainage de l'air froid hors de la surface de la fenêtre [71]. ...
... En termes de transmission lumineuse, un vitrage à couche antireflet permet au bâtiment de gagner 10% de plus en énergie lumineuse [71]. ...
... Ce concept a été introduit pour la première fois par Watanable et ses collaborateurs en 1992, sur un carré de céramique revêtu d'une couche d'oxyde de titane [71]. ...
Amélioration des performances du système Barra- Costantini
Etude détaillée de la tache solaire
... There are different methods including single degree of freedom (SDOF), multi degree of freedom (MDOF) and finite element (FE) methods that are widely used to find the response of such structures. SDOF methods are always used to find the response of a single member under extreme dynamic loads like blast and impacts [65,66], while MDOF [67,68] and FE methods [69][70][71][72][73] not only can be used for single members but also can be utilised for other complicated structures where more details should be taken into consideration. Besides, engineers are always seeking simpler solutions (instead of experimental and numerical analyses) to solve problems that can provide more straightforward analytical approaches for investigating the issue. ...
... Despite their validity, these approaches still have some limitations; to overcome such issues, researches aimed at discovering new emerging solutions are existing. Some investigate the development of self-regulating window materials as an alternative to glass, such as the reversible thermochromic transparent bamboo smart windows [68], prepared by impregnating delignified bamboo (DB) with epoxy resin containing thermochromic microcapsule powders (TMP), which is colorless at high temperatures and purple at low temperatures, or the air-sandwich glazing systems [69], based on the idea of a set of plastic films, with spacers and air trapped inbetween, used as insulation. ...
... Again, some concepts concerning emerging glazing technologies are present in literature even if, to the authors' knowledge, they still do not find real development of market applications. Some of them are the Vacuum Tube Window Technology [72], described as a combination of evacuated glass tubes and a glazed frame with Argon in the air gap between them, the Water-flow window [39], originated from the concept of removing the heat stored inside IGU's air-gap thanks to water flooding; the Solarpond window [69] aimed at integrating into fenestration functions of lighting, heat collection, heat storage, heat preservation and photoperiod control, and the selfsufficient smart window [73] able to regulate the amount of light entering the buildings, varying its color from a transparent state to a blue state without adding energy electricity. ...
Façade design is a challenging task, in which multidisciplinary issues and aspects should be optimally considered and addressed. This is especially the case of building façades exposed to seismic events, impacts, or fire. Special attention and major efforts are required for the detection and application of new technologies in the generation of modern, adaptive façade systems. This book presents a selection of research contributions to provide a comprehensive overview of façade design. It discusses the experimental analysis and numerical investigation of existing or traditional façades, as well as the development and optimal application of new technologies for modern adaptive façades and building envelopes.
... Therefore, improving the thermal performance of the building envelope has been one of the preferred approaches to energy saving. In this context, utilizing thermal energy storage through phase change materials (PCM) [5,6], installing thermal insulation [7,8], preventing thermal bridges [9,10], and adopting high-performance glazing units [11,12] have been studied and applied to improve the thermal performance of building envelopes. ...
... The optimization of the melting temperature and thickness of the PCM was performed according to the objective function in Eq. (11). Here, the subscript opt means "optimized". ...
... The figure shows that the energy saving due to latent heat utilization for C1 was rather different from that for C2. For both configurations, the maximum energy saving occurred at a specific PCM thickness, meaning that an optimum PCM thickness exists based on the objective function defined in Eq. (11). For instance, in configuration C1, the energy saving reached a peak of 512.9 kJ/m 2 at 8 mm thickness (L PCM,opt ). ...
... Geographical limitations can be lifted, and the growth of the door and window sector is facilitated by imitating various climates, including indoor and outdoor environments. Ref. [16] used two analytical tools (THERM and HEAT3) for thermal assessment numerical analysis in the 2D and 3D domains, derived a method to support windows in a layer of asbestos directly, and investigated three alternative energy sources for the support structure performance. Ref. [17] used the ASHRAE area method to measure area-weighted overall U-values for LSF walls. ...
... Key Findings [16] Used THERM and HEAT3 for 2D and 3D thermal assessment, developed a method to support windows with asbestos, and investigated energy sources for the support structure. ...
This research investigates building energy consumption in the Fujian region of China, characterized by warm winters and hot summers. The study focuses on window configurations and their impact on heat exchange and solar gain management. Initially examining three aluminum alloy window frames, the study utilizes the Multi-Quality Metric Calculator (MQMC) software V1 to assess the benefits of filled insulating glass. The reference values for the heat transfer coefficient, visible transmittance, and sun shading coefficient are established. Subsequently, Ecotect software V5.6 is employed to conduct a comprehensive year-round energy consumption simulation analysis, identifying an optimal window layout tailored to Fujian’s climate. In the Fuzhou simulation, aluminum–plastic co-extruded windows exhibit the lowest cooling energy consumption, while aluminum alloy windows have the highest. Summer cooling energy consumption, comprising about 75% of the total annual energy usage in hot summer and warm winter regions, significantly influences overall energy consumption. Windows made of aluminum–plastic co-extruded material with superior thermal insulation qualities can greatly reduce building energy consumption. The results contribute valuable insights to sustainable building practices and energy-conscious designs in regions characterized by warm winters and hot summers.
... Despite their validity, these approaches still have some limitations; to overcome such issues, researches aimed at discovering new emerging solutions are existing. Some investigate the development of self-regulating window materials as an alternative to glass, such as the reversible thermochromic transparent bamboo smart windows [68], prepared by impregnating delignified bamboo (DB) with epoxy resin containing thermochromic microcapsule powders (TMP), which is colorless at high temperatures and purple at low temperatures, or the air-sandwich glazing systems [69], based on the idea of a set of plastic films, with spacers and air trapped inbetween, used as insulation. ...
... Again, some concepts concerning emerging glazing technologies are present in literature even if, to the authors' knowledge, they still do not find real development of market applications. Some of them are the Vacuum Tube Window Technology [72], described as a combination of evacuated glass tubes and a glazed frame with Argon in the air gap between them, the Water-flow window [39], originated from the concept of removing the heat stored inside IGU's air-gap thanks to water flooding; the Solarpond window [69] aimed at integrating into fenestration functions of lighting, heat collection, heat storage, heat preservation and photoperiod control, and the selfsufficient smart window [73] able to regulate the amount of light entering the buildings, varying its color from a transparent state to a blue state without adding energy electricity. ...
This chapter deals with the analysis of the potential offered by the integration of smart solutions in dynamic glass façades to improve buildings’ energy performances. Dynamic solutions are here examined with reference to dry ventilated systems, active and passive cooling, solar gain, greenhouse effect, and technologies able to react and self-regulate, according to the environmental inputs. The first part is dedicated to the state of knowledge, assessing the performance evolution of dynamic and interactive architectural envelopes (smart skins). Then, the core of the chapter is divided into clusters according to different strategies that allow the building skin to react and self-regulate according to the environmental inputs: double-layer glass façades, solar shadings, PV integration, etc. The goal is to produce a sort of “smart skin guideline” divided by requirements/strategies of intervention to investigate a range of solutions able to regulate buildings’ behavior and characterize their image: from systems that allow to transform solar gain into heat to improve buildings’ energy performance in winter season, to others that integrate passive cooling, to systems that transform the façades in a real active element of energy production, thanks to the integration of renewable energy sources.
... PV glazing structures are also found to be effective in terms of shading performance. Visible light transmittance of some commercial products in market is about 0.10, which proves this statement [14]. In another research, the aforesaid optical values are justified for solar facade applications [15]. ...
... However, the windows are the weakest part of the building envelope, primarily if implemented without considering climatic conditions. They are responsible for much of the wasted energy inside the building [53]. ...
... Energy-efficient windows are designed with specific optical and thermophysical properties for optimum performance in winter or summer, ultimately contributing to the reduction of energy consumption. The thermal efficiency of a building depends on the size and characteristics of the windows [2]. Window films are a cost-effective and efficient solution to minimize heat gain through windows. ...
Many disasters are occurring around the world in connection with global warming. Many studies are being carried out to find ways to reduce emission levels of greenhouse gases. Reducing fossil fuel consumption is the most common method used to reduce emissions. In this study, the heat gain of a model building with specific window film properties is estimated. The results are presented comparatively for three film types coated on clear and tinted glass. The heat gain estimation is performed adaptively for summer days considering geographical location, glazing, building and humidity characteristics. Estimations are made for seven types of window films. A cost analysis is carried out considering the location, temperature and façade of the sample building.
... Most of studies about passive smart windows refer to small-scale production, more at the level of laboratory experiments and prototypes, and are not yet ready for the market (Ke et al., 2019). So far, the researchers have focused mainly on the improvement of the operational performances of dynamic behaviour (Cuce & Riffat, 2015), but few real-scale applications are known due to ease of production. In addition, it is unclear the overall environmental impact of these components, which could undermine their effectiveness in decreasing the environmental impact of the building sector. ...
This paper draws attention to the environmental impact of passive smart windows, a novel high-performance glazing technologies that can change their solar transmittance to control the amount of solar gain, thus reducing cooling energy demand. Despite the large influence of building envelope technologies on overall embodied carbon in buildings, the environmental impact of passive smart windows has been inadequately addressed, with a dearth of numerical data on various impact categories beyond energy consumption and Global Warming Potential (GWP). While current literature focuses on the advantages of these technologies in terms of operational energy savings, other critical environmental considerations are currently missing. This paper aims to bridge the existing gap by introducing a novel framework for evaluating the broader environmental impact of passive smart windows through a multi-category LCA method. By analysing the life cycle of these technologies, including production, usage, and disposal, the research seeks to provide a holistic understanding of their contribution to sustainability. The framework is based on systematic literature review on current state-of-art approaches and Interviews with key stakeholders in the dynamic glazing value chain. Literature review and interview results are presented, and then the framework is demonstrated through a case study of a thermochromic technologies for an office building in the Netherlands. Preliminary results show the critical areas where improvements on the methods or on the performance of the technology are required for the achievement of holistically sustainable high-performing glazing.
... The effectiveness of a building's facade directly influences its capacity to reduce energy expenses. Inadequate insulation and excessive solar heat gain can result in overheating within the building [6]. As integral components of building envelopes, windows not only offer natural lighting and passive solar gain but also function as primary conduits for heat exchange, with windows accounting for approximately 50% of energy loss [7,8]. ...
In the context of global warming, the focus on applying and researching double–skin facade (DSF) systems to reduce energy consumption in buildings has significantly increased. However, researchers have not thoroughly examined the performance and applicability of DSFs in severe cold regions with high winter heating demands. This study aims to evaluate the potential application of DSFs in the harsh cold cities of Northwest China and investigate their role in enhancing energy efficiency in large public buildings. Through energy consumption simulation and a comprehensive evaluation using the TOPSIS entropy weight method, the effects of applying 20 DSF schemes in four cold cities in Xinjiang (Kashgar, Urumqi, Altay, and Turpan) were analyzed. The experimental results indicate that the average EUI energy–saving rates in Kashgar, Urumqi, Altay, and Turpan are 64.75%, 63.19%, 56.70%, and 49.41%, respectively. South–facing orientation is deemed optimal for DSF in Xinjiang cities, with the highest energy–saving rate reaching 15.19%. In Kashgar, the energy–saving benefits of west–facing DSF surpass those of north–facing DSF. Conversely, the order of orientation benefits for other cities is south, north, west, and east. An analysis of heating, cooling, and lighting energy consumption reveals that Box Windows exhibit superior heating energy efficiency, while Corridors are more effective for cooling. This characteristic is also evident in the optimal installation orientation of various types of curtain walls. Given the relatively higher demand for heating compared to cooling in urban areas, Box Windows yields significant benefits when facing south, west, or north; conversely, if there is a high demand for urban cooling, Corridors should be considered in these three directions. Multistorey DSF systems are suitable for east–facing buildings in Xinjiang cities. Selecting suitable DSF schemes based on specific conditions and requirements can reduce building energy consumption. The research findings offer theoretical guidance for designing and implementing DSF in diverse cities in cold regions.
... The global energy consumption of buildings is responsible for challenges in sustainability [1][2][3] . Windows, as the primary means of energy exchange between the interior and exterior environments, play a crucial role in building energy consumption, accounting for as much as 20% of HVAC (heating, ventilation and air-conditioning) energy loss 4 . ...
Electrochromic windows provide a sustainable solution for use in energy-efficient buildings as their varying optical properties in changing weather conditions allow the optimization of solar radiation heat gain and indoor thermal comfort. However, as the wavelength range of sunlight that can be used remains limited, broader implementation of this technology is hampered. Here we present an electrochromic design that combines radiative cooling of mid-infrared light and maximized utilization of both visible and near-infrared light. Our electrochromic window takes advantage of a WO3/VO2 film structure that, with a controllable lithium-ion intercalation depth, affords three active optical states to control visible and near-infrared transmittance independently. Moreover, the use of electrodes with preferred emissivity at both surfaces serves to optimize the radiative heat exchange between the indoor and outdoor environments. Field experiments and simulations show that our device exhibits higher energy savings than a commercial low-emissivity glass in most climate zones around the world. Our findings suggest ample opportunities for energy-saving window designs that can help achieve global carbon neutrality and sustainability.
... In recent years, the exterior window area of office buildings has become larger, owing to various demands such as aesthetics, lighting, and psychology [2,3]. The increase in window area is beneficial for lighting energy consumption reduction, but it can lead to a significant increase in heating and air conditioning energy consumption [4,5]. ...
As a major component of the building envelope, the energy-saving design of exterior windows is key to energy savings in office buildings. The conventional design of exterior windows mainly focused on their impact on heating and cooling energy but ignored the indoor thermal comfort problems caused by the direct solar radiation transmitted by windows and the fluctuation of their internal surface temperatures. This study analyzed the influence of exterior windows on the indoor thermal environment of office buildings by carrying out field experiments. The experiments were carried out in a typical office building in Xi’an during December and January. The impact of exterior windows on human thermal comfort was studied from two perspectives: longwave radiation from the surface of window glass and solar shortwave radiation. It was found that solar radiation was the main cause of temperature fluctuations on the internal surface of windows and created non-uniform thermal environments. The mean radiant temperature fluctuations in the near-window area could reach up to 7.8 °C due to outdoor solar radiation in winter. Solar radiation transmitted by windows directly affects thermal sensations. Since conventional thermal comfort models or indices underestimated the thermal sensations of occupants in the presence of solar radiation, the additional thermal loads caused by solar radiation needed to be taken into account. The allowable operative temperature range for maintaining thermal comfort should be reduced by 0.5 °C when occupants are exposed to solar radiation.
... Buildings with high thermal conductivity, low thermal mass, and low solar absorption in the envelope contribute to increased energy use and CO 2 emissions [31]. Windows, with approximately 60 % heat loss in residential buildings, significantly impact energy efficiency [32]. The design of glazing elements in building envelopes plays a key role in energy balance, natural light, visual comfort, and illuminance consumption [33,34]. ...
This study investigates the effectiveness of envelope regulations in mitigating climate change impact on building energy demand in different locations and Representative Concentration Pathway (RCP) scenarios. It aims to assess the building thermal performance (EP tot,nd) in compliance with main Italian energy policies (issued in 2005, 2015, 2020). It specifically examines how variations in total solar energy transmittance of glazed systems (g gl,n) impact heat regulation and overall energy efficiency. Results are variable depending on national climate zone (from A to F) and related standards. Whereas climate zone E does not show significant gains from g gl,n modifications, in zone A reducing g gl,n (from 0.67 to 0.50) enhances resilience in buildings adhering to 2005 regulation (L.D. 192/2005). In climate zone C, g gl,n reduction benefits all standards, while in zone B this adjustment affects buildings following 2020 regulation (M.D. 06/08/2020), particularly under RCP 8.5. In climate zone F, decreasing g gl,n results in higher EP tot,nd , thereby compromising resilience. It is observed that buildings designed in accordance with L.D. 192/2005, compared to other regulations, show a smaller variation of EP tot,nd over time. In particular, moving from 2020 to 2070, climate zone BSh (Koppen climate classification) is the climate zone that sees the largest EP tot,nd increases over the years, while Cfc is the only zone that shows EP tot,nd decreases in all scenarios. For the other zones, a mixed behaviour is observed, with heterogeneous variations and results. Due to climate change, increased insulation in warm areas has contributed to an increase in overall annual consumption. Effective regulatory planning requires a comprehensive future climate assessment to optimize building energy performance.
... Windows and glazed facades are crucial components of building sthat impact the energy efficiency, visual and acoustic comfort of residents as well as thermal performance. However, up to 60% of total heat loss through the building envelope can be attributed to the glazed areas due to their comparably higher overall heat transfer coefficient (U-value) [1]. Therefore, enhancing the thermal resistance (R-value) of glazed building partitions holds great potential for substantial increase of energy savings. ...
An experimental study was carried out to investigate the heat flux distributionon the external surface of triple-pane windows under various conditions including: outdoor temperatures, gas filling, emissivity of the glass surfaces, and the use of electrical heating. The measurements were conducted within a controlled climatic chamber. Two window configurations were examined: one filled with air (emissivity of ε = 0.84) and the other filled with argon (emissivity of ε = 0.17). In addition, the study also assessed the impact of a local and surface electric heating on heat loss. The key contribution of this researchlies in revealing variations in the heat flux density across different parts of the external glazing of each window, specifically the lower, central, and upper regions. These findings emphasize the importance of considering the non-uniformity of thermal resistance in different areas of windows in order to accurately determine their heat transfer coefficient.
... • High cost and fragility limit their use to fixed windows. [48,49,49,[98][99][100][101][102][103] B4-C4-E4-F4 ...
Energy efficiency and the reduction of carbon emissions have become the main climate goals for newly constructed or existing buildings. In the building sector, curtain walls (CWs) account for the majority of unwanted solar heat gain and consume most of the energy used. In this context, adaptive technologies (ATs) offer a wide range of alternative solutions to improve the perfor- mance of CWs. This study aims at developing a comprehensive framework for retrofitting CWs through the integration of ATs. Based on a comprehensive analysis of previous literature, the proposed three-stage framework provides a guide for enhancing the performance of CWs by evaluating and comparing retrofitting scenarios using ATs. The three stages include pre-retrofit survey, retrofit process, and monitoring process. To achieve this goal, curtain wall systems, ret- rofitting levels, and sub-practices are discussed. The integration ability of ATs into CW systems is assessed according to functional, structural, and technical properties. Integration scenarios are evaluated based on SWOT analysis, performance criteria, adaptive parameters, and retrofitting practices to assess their efficiency. Results show that integration scenarios of materials like electrochromic and semi-transparent photovoltaic glazing are applicable to all CW systems with remarkable performance enhancement. Phase change materials and liquid infill tunable glazing are the least applicable materials. Integration scenarios of adaptive systems involving green walls and dynamic shading devices provide the greatest functional benefits. Whereas, algae facades should only be installed in newly constructed buildings. In conclusion, the study proves that the integration of ATs into CWs offers promising potential for improving CW performance.
... All these strategies as well as the distribution of functions and program (PS11) require a proper design, that considers the local climate (e. g., air and surface temperature, humidity, air pressure), urban complex phenomena (e.g., inter-building reflections, overshadowing), and urban surfaces' thermal properties, to avoid indoor overheating and outdoor thermal stress [49,67,68]. In solar neighborhoods, municipalities should support the design process by providing house-owners with guidelines Table 3 Passive solar strategies applied to the planning and design at the neighborhood scale. ...
Planning of neighborhoods that efficiently implement active solar systems (e.g., solar thermal technologies, photovoltaics) and passive solar strategies (e.g., daylight control, sunlight access through optimized buildings' morphology, cool pavements, greeneries) is increasingly important to achieve positive energy and carbon neutrality targets, as well as to create livable urban spaces. In that regard, solar neighborhoods represent a virtuous series of solutions for communities that prioritize the exploitation of solar energy, with limited energy management systems. The ten questions answered in this article provide a critical overview of the technical, legislative, and environmental aspects to be considered in the planning and design of solar neighborhoods. The article moves from the categorization of “Solar Neighborhood” and the analysis of the state-of-the-art passive and active solar strategies to the identification of challenges and opportunities for solar solutions’ deployment. Insights into legislative aspects and lessons learned from case studies are also provided. Ongoing trends in solar energy digitalization, competing use of urban surfaces, and multi-criteria design workflows for optimal use of solar energy are outlined, emphasizing how they generate new opportunities for urban planners, authorities, and citizens. A framework is introduced to guide the potential evolution of solar neighborhoods in the next decade and to support the design of urban areas and landscapes with architecturally integrated solar energy solutions.
... Windows are an essential part of the energy-saving design of the building envelope [7]. Solar radiation enters the interior through the windows and provides natural light, while heat energy also affects the building's energy consumption [8]. ...
Global energy resources are becoming increasingly scarce, and environmental problems are becoming more serious. The construction industry significantly contributes to energy consumption, and building energy efficiency has become a global concern. A critical aspect of building energy efficiency is exterior shading, which controls sunlight exposure and heat input to the interior. By effectively reducing indoor temperature and light intensity, exterior shading provides a more comfortable learning and working environment. In particular, west-facing exterior shading is essential for building shading and heat protection. This study aims to analyze school office buildings’ light and thermal comfort performance in various climatic zones. These buildings are equipped with west-facing external shading. Numerical analyses were performed using Ladybug Tools 1.6.0 software to evaluate the light and thermal comfort performance of the building. The primary objective of this study is to enhance the light performance and thermal comfort within buildings facing west. The main focus of this research is to examine the effectiveness of four different shading devices in improving light performance and thermal comfort in school office buildings located in severe cold (SC) and cold (C) regions. By studying these specific buildings, valuable insights and recommendations can be provided for selecting suitable shading devices for typical urban buildings in similar regions. The study results demonstrate that in typical cities in SC and C regions, light and thermal comfort are significantly improved with appropriate shading devices by a factor of about 1.5 to 2.5 compared to the no-shading condition (NSC). Beijing shows the most significant improvement among the cities studied, with energy efficiency and comfort improved to 2.6 times that of NSC. At the same time, Urumqi has a relatively lower effect, with an improvement of 1.59 times that of NSC. This study provides an essential reference for selecting suitable west-facing shading devices in typical cities in SC and C regions. It is expected that this will contribute to the construction industry’s efforts to achieve more significant results in energy conservation, emission reduction, and green buildings, ultimately helping to address the energy crisis and environmental pollution problems.
... The increase in the demand for fossil fuels due to energy consumption of buildings poses challenges and concerns in the energy sector, and the transparent envelope is one of the most significant thermal loss components of buildings since it is responsible for almost 60% of the total building energy loss [1,2]. The application of alternative renewable energy sources can help this situation. ...
Dual‐band electrochromic (DBEC) smart windows are an emerging energy‐saving technology, especially those constructed from single‐component DBEC materials as they offer an easy way to independently regulate visible (VIS) and near‐infrared (NIR) light. However, the current complicated organic ligand approach used to synthesize single‐component DBEC materials necessitates a post‐annealing treatment, which may severely compromise the scalability of DBEC smart windows. Herein, one organic ligand‐free process is developed to produce well‐controlled Nb‐doped anatase TiO2 nanocrystals (NTO NCs) followed by spraying on arbitrary substrates, giving NTO rigid or flexible films with good DBEC properties and a high optical modulation over 92%. A prototype of a 20 cm × 20 cm DBEC smart window is built. The simplicity and scalability of the synthesis and fabrication process make it a scalable approach to constructing large‐area electrochromic smart windows and foils, with promising applications in fields such as buildings and automobiles.
Thermochromic smart windows have been widely developed for solar regulation to save building energy. However, most current smart windows still exhibit a single responsiveness to a specific temperature, which is not conducive to daytime energy saving or nighttime privacy protection. Herein, a low‐temperature response is achieved by pre‐initiation of the monomer acrylamide (AAm) and acrylic acid (AA) in the synthesis of P(AAm‐co‐AA). Then, N‐isopropyl acrylamide and AAm are introduced into P(AAm‐co‐AA) to form a pre‐polymerized precursor solution. The liquid precursor solution can be encapsulated within two quartz glasses and synthesized in situ to prepare smart windows, which exhibit a high visible light transmittance of 84.4%, excellent solar modulation of 69.5%, and bidirectional temperature responsiveness (cold and hot). In addition, the upper critical solution temperature and the lower critical solution temperature of the hydrogel and the light transmission interval between the two temperatures can be flexibly adjusted to adapt to different climates and individual user needs. The designed smart window maintains a high light transmission within the human body's comfort temperature range. The bidirectional temperature response window achieves the dual functions of energy saving and privacy protection, making it an ideal smart window candidate with good prospects for practical applications.
Currently, high-rise buildings construction is expanding while certain climatic considerations are not foreseen in the design and implementation and design decisions are often made similar to midrise and low-rise buildings, and one of the most important reasons is the lack of relevant specialized research in the country. The purpose of this study is to explain the climatic frameworks in order to select the optimal models in the design of high-rise buildings with the approach of reducing energy consumption in order to develop climate design criteria. In this regard, the present study by means of descriptive analytical method with a quantitative approach compares seven main indicators affecting the reduction of energy consumption including building form, opening form and its area ratio, rotation angle, canopy depth, type, and thickness of thermal insulation and exterior wall glass in different conditions by using energy simulator software to find the optimal mode in terms of energy saving. The results of data analysis show that the ratio of opening areas, glass material and canopy depth are the most influential indicators and building form, for building rotation, form and dimensions of openings are the least effective on research objectives. Also, rectangular buildings with east-west elongation and horizontal windows with horizontal awnings to a depth of 100 cm on the south and east sides and vertical awnings to a depth of 150 cm on the north and west sides have a good performance in the study climate and have minimal energy consumption.
We propose an ITO grating-based metamaterial for high visible transmittance and excellent infrared tunability (0.73 at 8–13 μm) as smart windows.
Transparent bulk glass is highly demanded in devices and components of daily life to transmit light and protect against external temperature and mechanical hazards. However, the application of glass is impeded by its poor functional performance, especially in terms of thermal isolation and impact resistance. Here, a glass composite integrating the nacre‐inspired structure and shear stiffening gel (SSG) material is proposed. Benefiting from the combination of these two elements, this nacre‐inspired SSG/glass composite (NSG) exhibits superior thermal insulation and impact resistance while maintaining transparency simultaneously. Specifically, the low thermal conductivity of the SSG combined with the anisotropic heat transfer capability of the nacre‐inspired structure enhances the out‐of‐plane thermal insulation of NSG. The deformations over large volumes in nacre‐inspired facesheets promote the deformation region of the SSG core, synergistic effect of tablet sliding mechanism in nacre‐inspired structure and strain‐rate enhancement in SSG material cause the superior impact resistance of overall panels in a wide range of impact velocities. NSG demonstrates outstanding properties such as transparency, light weight, impact resistance, and thermal insulation, which are major concerns for the application in engineering fields. In conclusion, this bioinspired SSG/glass composite opens new avenues to achieve comprehensive performance improvements for transparent structural materials.
Transparent heat mirror which allows the transmission of visible sunlight while reflects the infrared thermal energy is an effective building energy efficiency technology for hot climatic regions. In this work, a five-layer dielectric/metal/dielectric/metal/dielectric (DMDMD) coating of Si3N4/Ag/Si3N4/Ag/Si3N4 structure is proposed. The radiative properties of the five-layer coatings are theoretically investigated by transfer matrix method. The thicknesses of the layers are optimized by using particle swarm optimization method. The sample of the designed Si3N4/Ag/Si3N4/Ag/Si3N4 coating is prepared and the building energy performance when applying the DMDMD coating in a simple office room is also investigated, taking the hot weather condition of Guangzhou, China as an example. The simulated results show that the Tave + Rave value of the five-layer coating is 8% higher than that of the three-layer coating, and the long-wave emittance of the five-layer coating is 24.8% lower than that of the three-layer coating. And the application of the five-layer coatings on the glazed window could provide the highest energy saving rate of 8.9% when compared with the traditional low-e coatings.
According to a recent comprehensive study on window systems, windows account for approximately 60% of a building’s total energy loss. In this regard, much research is being conducted to reduce energy loss through windows, among them, vacuum glazing maximizes the insulation performance by sealing between two sheets of glass with a vacuum. In this study, proposes a novel strategy for fabricating vacuum glazing using microwave heating in vacuum pressure and direct glass edge sealing. By applying a process using microwaves, the energy used in the vacuum glazing fabrication process is minimized, and the structural strength of the vacuum glazing is improved by directly sealing the glass. In order to prevent arc discharge that can occur when microwaves are applied in vacuum pressure, microwave power was set as a variable, and heating experiments were conducted accordingly. The experiment enabled the analysis of the relationship between temperature and pressure change according to the power, and accordingly, a vacuum glass sample with direct sealing was fabricated. The fabricated vacuum glazing was tested for thermal transmittance (U-value) in single and double layers and confirmed to be 3.5 W/m2 K and 1.6 W/m2 K, respectively.
It remains challenging to conduct an efficient dynamic façade design. In this article authors try to address this issue introducing the façade daylighting performance improvement (FDPI) indicator aimed to evaluate the performance of a dynamic (adaptive) façade from its daylighting performance point of view. To illustrate the FDPI application the authors introduced the preliminary dynamic façade concept for an office building located in Tel Aviv (Hot-summer Mediterranean Climate Csa) with further shape modification based on the daylighting performance analysis compared to the three alternatives representative of different typologies of dynamic facades. Al Bahr, One Ocean and The University of Southern Denmark façade systems were simulated under the same weather and building conditions of the preliminary dynamic façade concept and were considered as a benchmark for the study. The final dynamic façade concept elaborated by the authors in the preliminary comparative workflow showed noticeable daylight performance improvement with respect to the case studies comparative scenarios. The FDPI metric allowed to estimate a daylighting performance improvement of 43% of the final dynamic façade concept over the case study dynamic façade that showed the best performance in the daylighting simulations.
This paper presents a novel model to evaluate the electrical performance of a silicon photovoltaic (PV) module with respect
to changes in main environmental parameters such as temperature and illumination intensity. A simple one-diode model is proposed
to estimate the electrical parameters of PV module considering the series resistance and shunt conductance. Effects of PV
module parameters on current–voltage characteristic curve are investigated. The proposed model also makes a thermodynamic
assessment concerning the effects of environmental and electrical parameters on efficiency and maximum power output of the
PV module. Kyocera KD205GH-2P 205-W high-efficiency multi-crystal PV module is used for model evaluation. Model results are
compared with the manufacturer's data report and an excellent agreement is observed.
Simulation analysis of thermal performance for vacuum glazing was conducted in this paper. The heat conduction through the support pillars and edge seal and the radiation between two glass sheets were considered. The heat conductance of residual gas in vacuum gap was ignored for a low pressure of less than 0.1Pa. Two pieces of vacuum glazing with sizes of 0.3 × 0.3 m and 1.0 × 1.0 m were simulated. In order to check the accuracy of simulations with specified mesh number, the thermal performance of a small central area (4mm×4mm) with a single pillar in the center was simulated using a graded mesh of 41×41×5 nodes. The heat transfer coefficients of this unit obtained from simulation and analytic prediction were 2.194Wm-2K-1 and 2.257Wm-2K-1 respectively, with a deviation of 2.79%. The three dimensional (3D) isotherms and two dimensional (2D) isotherms on the cold and hot surfaces of the specimens were also presented. For a validity of simulated results, a guarded hot box calorimeter was used to determine the experimental thermal performance of 1.0m×1.0m vacuum glazing. The overall heat transfer coefficients obtained from experiment and simulation were 2.55Wm-2K-1 and 2.47Wm-2K-1 respectively, with a deviation of 3.14%.
The reduction of energy consumption for heating and air conditioning and electric energy saving in illumination plants could be improved by innovative Transparent Insulating Materials (TIMs), which aim to optimize two opposite requirements: transparency and thermal insulation. Aerogel is one of the more promising for use in highly energy-efficient windows: in addition to the low thermal conductivity (0.010 W/(m K) in evacuated conditions), a high solar energy and daylight transmittance is achieved. Eight samples were manufactured, by assembling several types of glass with monolithic and granular aerogel in the interspace. Measurements of transmission and reflection properties were carried out and the energetic and luminous parameters (light transmittance (τ v), solar factor (g) and thermal transmittance (U)) were calculated. U-values slightly higher than 1 W/m 2 K were obtained for all the samples. The monolithic aerogel introduces a better light transmittance (τ v = 0.60) than granular one (τ v = 0.27), while U-values are comparable in not evacuated conditions. In order to evaluate the aerogel employing in buildings, a prototype of an aluminium frame window with granular aerogel in interspace was realized. Thermal and acoustic properties of the prototype were evaluated according to the standards. The thermal transmittance of the innovative glazing system was little lower than 1 W/(m 2 K) and it showed also good acoustic properties: the R w index was 3 dB higher than the one of a conventional window with air in interspace.
The thermal performance of a hybrid vacuum glazing (HVG) was simulated using a finite volume model (FVM) and theoretically analysed using an analytic model. HVG is the combination of a conventional double vacuum glazing (DVG) and a third glass sheet separated by a gas-filled cavity. The DVG integrated within the HVG comprises two 4 mm (0.16 in.) thick glass sheets both coated with a low-emittance (low-e) coating with emittance of 0.16, sealed around their periphery by a 6 mm (0.24 in.) wide indium based sealant and separated by an array of stainless steel support pillars with a diameter of 0.4 mm (0.02 in.), a height of 0.2 mm (0.01 in.), and spaced at 25 mm (0.98 in.) within the vacuum gap. The DVG was fabricated using the pump-out method and subsequently integrated within the HVG. No low-e coating was employed on the third glass sheet. To validate the simulation results, the thermal performance of both the DVG and HVG were analyzed using a guarded hot box calorimeter (GHBC) constructed in accordance with the requirements of ISO 8990 (ISO 1996). The simulation results showed that for the 0.4 by 0.4 m (1.31 by 1.31 ft) HVG with the configuration parameters listed above, the thermal transmission U-value at the centre-of-glazing area was 0.64 W·m-2·K-1 (0.11 Btu·h-1·ft-2·°F). Before integration with the third glass sheet, the U-value of the centre-of-glazing area of the DVG was 0.85 W·m-2·K-1 (0.15 Btu·h-1·ft-2·°F). The U-value of the HVG calculated using the analytic model was 0.63 W·m -2·K-1 (0.11 Btu·h -1·ft-2·°F,) which was in good agreement with that predicted using the FVM with a deviation of less than 1.5%. Using the GHBC, the experimentally determined U-value at the centre-of-glazing area of the HVG was 0.66 W·m-2·K-1 (0.12 Btu·h-1·ft-2·°F) which was in very good agreement with the prediction by the FVM with a deviation of 3.1%. The thermal performance of the HVG compares favorably with conventional three-pane insulating glazing systems and offers significant potential as an energy saving building component.
In this study, an experimental research concerning the effects of passive cooling on performance parameters of silicon solar
cells was presented. An aluminum heat sink was used in order to dissipate waste heat from a photovoltaic (PV) cell. Dimensions
of the heat sink were determined considering the results of a steady-state heat transfer analysis. The experiments were carried
out for different ambient temperatures and various illumination intensities up to 1 sun under solar simulator. Experimental
results indicate that energy, exergy and power conversion efficiency of the PV cell considerably increase with the proposed
cooling technique. An increase of ∼20% in power output of the PV cell is achieved at 800 W/m2 radiation condition. Maximum level of cooling is observed for the intensity level of 600 W/m2. Performance of PV cells both with and without fins increases with decreasing ambient temperature.
In this investigation, TiO2 and Ag based single and multilayer-films were deposited on microscope glass slides with varying individual layer thicknesses by radio-frequency reactive magnetron sputtering. Prior to multilayer development, single layers of Ag and TiO2 were deposited and characterized. All the films were prepared at an elevated pressure of 3 Pa at room temperature. It was found that single layer of TiO2 showed anatase polycrystalline structure. It also exhibited high visible transmittance of above 80% and higher refractive index of 2.31 at a wavelength of 550 nm. The indirect optical band gap of the TiO2 films was estimated as 3.39 eV. The Ag single layer films were found to be crystalline with a very high reflectance for IR (Infra-red) light. Finally, the multi-layers have been deposited and characterized by X-ray diffraction, UV-visible-NIR spectro-photometry, scanning electron microscopy and Auger electron spectroscopy.
www.arpnjournals.com/jeas/research_papers/rp_2010/jeas_0910_381.pdf
This article is about a study on glass window and glass window with film of different types in aspect of thermal comfort and heat transmission. Different types of glass window, clear glass, tinted glass, reflective glass, double pane glass, and low-e glass were investigated. Films with different spectral optical properties were then adhered to the glass windows of different types and studied. The analysis was done based on the outside design weather condition which selected from 12 years of Bangkok meteorological data. Predicted percentage of dissatisfied (PPD) was selected as the thermal comfort index. The relative heat gain (RHG) based on local weather condition was selected as the heat transmission index. The PPD can be subdivided into the PPD due to surface temperature effect and the PPD due to solar radiation effect. The analysis indicated that, for most of the glass windows considered except the reflective glasses, the values of PPD due to solar radiation effect were much larger than the values of PPD due to surface temperature effect. And the most discomfort condition occurred when using a clear glass as window. Adhered films to the glass windows caused the PPD due to surface temperature effect increase and cause the PPD due to solar radiation effect decrease. It was also found that the PPD values due to solar radiation effect for glass windows and glass windows with films were varied linearly with the total transmittance of glass windows and glass windows with films. The PPD values due to surface temperature effect were varied with the total absorptance of glass windows and glass windows with films in an almost linear fashion. The heat transmission index, RHG, based on chosen design weather condition can be subdivided into the RHG due to conduction effect and RHG due to solar radiation effect. The analysis indicated that the values of RHG due to solar radiation effect were larger than the values of RHG due to conduction effect for all glass windows and glass windows with films considered in this study. Adhered film to the glass windows resulted in lowering the relative heat gain due to solar radiation in the amount corresponding to the film properties. But the film had very few effect on the relative heat gain due to conduction. The relative heat gain values were varied linearly with the total transmittances of the glass windows and glass windows with films. The relative heat gain values were also varied inversely with the absorptances of glass windows and glass windows with films in a linear fashion.
The purpose of this paper is to investigate the effects of concavity level on performance parameters of a parabolic fin under the influences of natural convection and radiation. Computational fluid dynamics software (FLUENT) is used for the heat transfer analysis. Optimum fin geometry is searched in order to maximize the heat dissipation from fin to the ambient while minimizing the volume of fin. The fin profile with concavity level of 2 dissipates 14.92, 17.53, 24.33 and 26.60 percent more heat and uses 34.62, 49.64, 57.66 and 63.09 percent much material compared to the fin with concavity level of 4, 6, 8 and 10, respectively. It is also observed that the amount of heat dissipation per mass considerably increases with increasing concaveness. The research was carried out for five different concavity levels in the range of 2-10. The results can be used in passive cooling applications of PV systems. Also, heat sinks for CPU cooling can be redesigned with respect to the results obtained from the research. In this paper, effects of concavity level on performance parameters of a parabolic fin are investigated for the first time. It is observed from the numerical results that the fin profile with higher concavity levels provides a cheaper and lighter heat dissipation device so it is recommended for the applications where the weight and the cost are primary considerations such as cooling of photovoltaics.
Buildings are responsible for over 70% of the average city’s greenhouse gas emissions. As the key component of buildings, window serves very important role in architecture. In current energy efficient building practice, windows are considerably less well insulating component than other parts of the building envelope. Therefore improving windows thermal performance is an important issue to develop energy efficiency building design.
This research is carried out from the case studies of zero/low carbon buildings, in which windows were found the weakest part of building envelope. Within this work state-of-the-art window glazing types, latest best performing fenestration products in the market and advanced window technologies are reviewed. Vacuum window technology using evacauted tube pannels will be presented in this research work, as well as Thermoelectric (TEC) window system and Thermoelectric power generation window system.
The objectives of the development of novel window systems are: (1) to develop the first-of-its-kind window technology using evacuated tube panels, its thermal transmittance (U-value) will be studied; (2) In order to compare U-values data with high performance windows, thermal performance of novel designed Aerogel and argon window system will be investigated; (3) to develop novel window system by combining evacuated tube panels and thermoelectric modules, which is functioned as a heat pump device; (4) to develop window system as a power generation device by interating thermoelectric generator. Novel windows technologies would meet the requirements of the Code for Sustainable Homes and those of commercial buildings.
The study on development of novel window systems is carried on from the current window technologies and includes:
(1) Computer modelling results show U-values about 0.59 W/m2K for double wall vacuum tube window, 0.61 W/m2K for single wall vacuum tube window. Laboratory measurements are carried out to validate theoretical results. The test results show that 1.0 W/m2K and 1.1 W/m2K for double and single wall vacuum tube window respectively. Economic and environmental assessments are also analysed.
(2) Numerical model and laboratory tests have illustrated the U-values of different thickness of aerogel, argon and combination of both filled window. Comparing to standard double glazed window unit with 20mm air gap (U-value of 2.8 W/m2K), the U-value result of 6mm Aerogel-Argon window can be improved by 45% in theory and 30% according to the laboratory measurement results.
(3) Advanced glazing will become “Energy Suppliers” as well as “Energy Managers”. Novel design of thermoelectric window system may function as “a heat pump” contributing buildings’ heating load in winter. Laboratory and outdoor tests investigate the amount of heat supply under various voltage regimes and weather conditions.
(4) The electric power output of thermoelectric generator device combined with vacuum tube is examined under different experimental thermal conditions. The use of TEM has advantages of its maintainance free and can operate from any heat source. Window unit (sized1m×1m) installed such device can generate electricity approximately 70~180W.
Residential window annual energy rating systems have been developed in Canada and the U. S. These systems combine window properties of solar heat gain coefficient, U-factor, and air-infiltration into a single number representative of the energy performance for each of the heating season and the cooling season. These systems provide a simple means for designers to select the best energy performing window for low-rise residential buildings over the heating and cooling seasons, the two systems, which rank windows in the same order, give different information on optimum window design and selection than just a simple U-factor comparison. These systems show the importance of a high window SHGC in cold climates and a low SHGC in hot climates. The impact of window air infiltration is surprisingly small relative to the solar heat gain and heat conduction losses.
The determination of solar heat gain coefficient (SHGC) values for complex fenestration systems is required to evaluate building energy performance, to estimate peak electrical loads, and to ensure occupant comfort. In the past, simplified techniques have been used to calculate the values of SHGC for fenestration systems. As glazing systems that incorporate complex geometries become more common, test methods are required to evaluate these products and to aid in the development of new computational tools. Recently, a unique facility and test method for the experimental determination of SHGC values were developed and demonstrated for simple fenestration systems. The study described in this paper further applies this method to a variety of commercially available glazing and shading systems (e.g., heat-absorbing insulated glazing units (IGUs), reflective film and suspended film IGUs), and shading devices (i.e., slat blinds and shades). Testing was conducted in a solar simulator facility using a specially designed window calorimeter. The results of this study demonstrate the feasibility of the solar simulator-based test method for the evaluation of SHGC values for solar-control glazings and shading devices.
In this short communication, a theoretical attempt has been made and the analytical expression developed by Dubey, Sandhu, and Tiwari [2009. “Analytical Expression for Electrical Efficiency of PV/T Hybrid air Collector.” Applied Energy 86: 697-705.] for temperature-dependent electrical efficiency of air type PV/T collector has been corrected. The analyses have indicated that their efficiency expression only considers the effects of solar intensity. However, it is unequivocal from the governing equations that the ambient temperature is another variable that should be in the efficiency expression as an initial condition of the energy balance equation of flowing air. Although they asserted that the electrical efficiency of the system has been evaluated with respect to the variations in solar intensity and ambient temperature for a typical day in the month of April 2008 for New Delhi condition, the results clearly show that the ambient temperature has not been taken into account in their study. Their expression not including a term for ambient temperature proves our statement. In the present work, the corrected version of the efficiency expression is given.
A numerical and experimental study based on analysing the cooling effect on performance characteristics of silicon solar cells is presented. In the experiments carried out for different cell temperatures, a substantial decrease in power output with increasing cell temperature was observed depending on the decrease in exergy efficiency. In contrast to the remarkable decrease in voltage parameters, a slight increase in current parameters with increasing cell temperature was obtained. A well-known computational fluid dynamics software was utilised to evaluate the effectiveness of cooling applications in terms of enhancement of energy conversion in silicon solar cells. Air was chosen as the cooling fluid in the numerical study. The numerical study was performed for various velocities and temperatures of cooling fluid. Enhancement in energy conversion was determined for each operating condition. The results indicated that cooling applications are quite important to improve the efficiency and the maximum power output of the photovoltaic modules. These strategies can be more efficient for large-scale photovoltaic power plants.
Purpose
– The purpose of this paper is to investigate the effects of concavity level on performance parameters of a parabolic fin under the influences of natural convection and radiation.
Design/methodology/approach
– Computational fluid dynamics software (FLUENT) is used for the heat transfer analysis. Optimum fin geometry is searched in order to maximize the heat dissipation from fin to the ambient while minimizing the volume of fin.
Findings
– The fin profile with concavity level of 2 dissipates 14.92, 17.53, 24.33 and 26.60 percent more heat and uses 34.62, 49.64, 57.66 and 63.09 percent much material compared to the fin with concavity level of 4, 6, 8 and 10, respectively. It is also observed that the amount of heat dissipation per mass considerably increases with increasing concaveness.
Research limitations/implications
– The research was carried out for five different concavity levels in the range of 2-10.
Practical implications
– The results can be used in passive cooling applications of PV systems. Also, heat sinks for CPU cooling can be redesigned with respect to the results obtained from the research.
Originality/value
– In this paper, effects of concavity level on performance parameters of a parabolic fin are investigated for the first time. It is observed from the numerical results that the fin profile with higher concavity levels provides a cheaper and lighter heat dissipation device so it is recommended for the applications where the weight and the cost are primary considerations such as cooling of photovoltaics.
Building integrated photovoltaics are among the best methods for generating power using solar energy. To promote and respond to the concept of BIPVs, this study developed a type of multi-functional heat insulation solar glass (HISG) that differs from traditional transparent PV modules, providing functions such as heat insulation and self-cleaning in addition to power generation. This study also made thorough preparations for the safety of future HISG installation on curtain walls in large-scale buildings. Furthermore, this study provides a comprehensive discussion regarding the energy-saving performance of HISG and relevant practical applications. Two experimental houses were constructed, which independently employed HISG and single-layer tempered glass. Taiwan's climate was adopted as the environmental condition for the experiment, and the effects of HISG and single-layer tempered glass on indoor temperature variation and the energy consumed by air conditioners and heaters were explored. Related software was also employed to simulate, compare, and verify HISG efficacy.
Aerogel is a kind of synthetic porous material, in which the liquid component of the gel is replaced with a gas. Aerogel has specific acoustic properties and remarkably lower thermal conductivity (≈0.013 W/m K) than the other commercial insulating materials. It also has superior physical and chemical characteristics like the translucent structure. Therefore, it is considered as one of the most promising thermal insulating materials for building applications. Besides its applications in residential and industrial buildings, aerogel has a great deal of application areas such as spacecrafts, skyscrapers, automobiles, electronic devices, clothing etc. Although current cost of aerogel still remains higher compared to the conventional insulation materials, intensive efforts are made to reduce its manufacturing cost and hence enable it to become widespread all over the world. In this study, a comprehensive review on aerogel and its utilization in buildings are presented. Thermal insulation materials based on aerogel are illustrated with various applications. Economic analysis and future potential of aerogel are also considered in the study.
While the primary function of concrete is structural, its pervasiveness in our society lends it to other functions and creates the need for it to maintain its integrity and aesthetic quality. Therefore, concrete with added functionality–for example, self-cleaning characteristics and the ability to remove pollutants–is desirable. Heterogeneous photocatalysis (e.g., gas–solid or liquid–solid catalytic processes caused by light irradiation) by semiconductor particles or coatings has now reached a high level of development and is a promising technology for the reduction of global environmental pollutants. Among the various semiconductor materials, TiO2 in the form of anatase has attracted wide interest, due to its strong oxidizing power under near-UV radiation, its chemical stability when exposed to acidic and basic compounds, its chemical inertness in the absence of UV light, and the absence of toxicity. TiO2 has proved very effective in the reduction of pollutants such as NOx, aromatics, ammonia, and aldehydes. Surprisingly, the use of TiO2 in combination with cementitious materials has shown a favorable synergistic effect in the reduction of pollutants. These new materials have already found relevant applications in self-cleaning building walls and in the reduction of urban pollutants.
In this study, the impact of two different types of window glazing using two identical rooms was studied. In one experiment both rooms were furnished as an office, in another experiment as a bedroom. The only other difference between the two rooms was the glazing of the window. In one room a standard three-pane window (2+1) with 4 mm clear glass was used, in the other a super-insulated four-pane window (3+1) with two silver-based low-emittance coatings. The results showed that people were clearly able to distinguish between the two windows. The room with the four-pane window felt more enclosed, and the daylight felt less strong and clear. The four-pane window also affected colour perception, making the colours of the room and of the view look more subdued or more drab. Spectral measurements revealed that the four-pane window transmitted a relatively higher percentage of the green part of the spectrum. The results agree with what might be expected given the lower transmittance and different spectral distribution of the four-pane window. It is questioned how far one should go in reducing the daylight transmittance of windows.
This paper presents the results of a numerical and experimental study on thermally efficient windows. Experimental investigation using spectrophotometry was realized on simple and composite glass samples filled with air or phase change material. The transmittance and reflectance tests indicated large reduction in the infrared and ultraviolet radiations while maintaining good visibility. The number of glass sheets, their thickness and the gap between them were also investigated. The numerical model is based upon one-dimensional formulation of the composite window. The program was optimized and the predicted results are presented and discussed.
This paper presents a different approach for thermal effective windows, i.e. windows which reduce energy transmitted into or out of the room. The idea is to use a double-sealed glass filled with pcm whose fusion temperature is determined by solar-thermal calculations. The investigation is divided into two main parts: modeling of the heat and radiation transfer through the composite window and the optical investigation of the pcm-filled window. A one-dimensional thermal model for the composite window was developed to predict the resulting effects due to variation of the geometrical and pcm thermal properties. Optical investigations using photo-spectrometry were realized on single glass, double glass filled with air, and double glass filled with pcm. The transmittance and reflectivity tests indicate large reductions in the infrared and ultraviolet radiations while maintaining the good visibility. The effects of thickness of glass and spacing were also analyzed.
Fenestration of today is continuously being developed into the fenestration of tomorrow, hence offering a steadily increase of daylight and solar energy utilization and control, and at the same time providing a necessary climate screen with a satisfactory thermal comfort. Within this work a state-of-the-art market review of the best performing fenestration products has been carried out, along with an overview of possible future research opportunities for the fenestration industry. The focus of the market review was low thermal transmittance (U-value). The lowest centre-of-glass Ug-values found was 0.28 and 0.30 W/m2 K, which was from a suspended coating glazing product and an aerogel glazing product, respectively. However, the majority of high performance products found were triple glazed. The lowest frame U-value was 0.61 W/m2 K. Vacuum glazing, smart windows, solar cell glazing, window frames, self-cleaning glazing, low-emissivity coatings and spacers were also reviewed, thus also representing possibilities for controlling and harvesting the solar radiation energy. Currently, vacuum glazing, new spacer materials and solutions, electrochromic windows and aerogel glazing seem to have the largest potential for improving the thermal performance and daylight and solar properties in fenestration products. Aerogel glazing has the lowest potential U-values, ∼0.1 W/m2 K, but requires further work to improve the visible transmittance. Electrochromic vaccum glazing and evacuated aerogel glazing are two vacuum-related solutions, which have a large potential. There may also be opportunities for completely new material innovations, which could revolutionize the fenestration industry.
The work presented in this article aims to investigate a PV/T hybrid solar window on a system level. A PV/T hybrid is an absorber on which solar cells have been laminated. The solar window is a PV/T hybrid collector with tiltable insulated reflectors integrated into a window. It simultaneously replaces thermal collectors, PV-modules and sunshade. The building integration lowers the total price of the construction since the collector utilizes the frame and the glazing in the window. When it is placed in the window a complex interaction takes place. On the positive side is the reduction of the thermal losses due to the insulated reflectors. On the negative side is the blocking of solar radiation that would otherwise heat the building passively. This limits the performance of the solar window since a photon can only be used once. To investigate the sum of such complex interaction a system analysis has to be performed. In this paper results are presented from such a system analysis showing both benefits and problems with the product. The building system with individual solar energy components, i.e. solar collector and PV modules, of the same size as the solar window, uses 1100 kW h less auxiliary energy than the system with a solar window. However, the solar window system uses 600 kW h less auxiliary energy than a system with no solar collector.
A method based on the ASHRAE two-node comfort model has been developed for predicting the effect of windows on thermal comfort. The method embodies separate analyses for longwave (thermal infrared) radiation, induced drafts, and solar load effects. Of these three impacts, modeling results demonstrate that longwave exchange between the body and the window is the most significant except for the case where the body is in direct sun, in which case the impact of solar load can be more significant. For most residential-sized windows, draft effects exist but are typically small. Generally, windows are not the primary element affecting the comfort of a building's occupants. However, when a window is very hot or cold, the occupant is very close to the window; or other factors result in thermal conditions near the edge of the comfort zone, windows can become quite influential. Furthermore, it is believed that current methods may underpredict discomfort caused by windows. The authors discuss potential refinements to the method that might address this inaccuracy by accounting for asymmetries in radiant temperature. In the near term, the model could be used to create a simplified window comfort index. To accompany the index, they envision educational material that would educate designers and consumers on the comfort implications of glazing selection.
This paper describes an end-use analysis of the national energy requirements of US residential window technologies. The authors estimate that the current US stock of 19 billion square feet of residential windows is responsible for 1.7 quadrillion BTUs (or quads) per year of energy use--1.3 quads of heating and 0.4 quads of cooling energy--which represents about 2% of total US energy consumption. They show that national energy use due to windows could be reduced by 25% by the year 2010 through accelerated adoption of currently available, advanced window technologies such as low-e and solar control low-e coatings, vinyl and wood frames, and superwindows. The authors evaluate the economics of the technologies regionally, considering both climatic and energy price variations, and find that the technologies would be cost effective for most consumers.
The simulated triple vacuum glazing (TVG) consists of three 4 mm thick glass panes with two vacuum gaps, with each internal glass surface coated with a low-emittance coating with an emittance of 0.03. The two vacuum gaps are sealed by an indium based sealant and separated by a stainless steel pillar array with a height of 0.12 mm and a pillar diameter of 0.3 mm spaced at 25 mm. The thermal transmission at the centre-of-glazing area of the TVG was predicted to be 0.26 W m² K¹. The simulation results show that although the thermal conductivity of solder glass (1 W m¹ K¹) and indium (83.7 W m¹ K¹) are very different, the difference in thermal transmission of TVGs resulting from the use of an indium and a solder glass edge seal was 0.01 W m² K¹. This is because the edge seal is so thin (0.12 mm), consequently there is a negligible temperature drop across it irrespective of the material that the seal is made from relative to the total temperature difference across the glazing. The results also show that there is a relatively large increase in the overall thermal conductance of glazings without a frame when the width of the indium edge seal is increased. Increasing the rebate depth in a solid wood frame decreased the heat transmission of the TVG. The overall heat transmission of the simulated 0.5 m by 0.5 m TVG was 32.6% greater than that of the 1 m by 1 m TVG, since heat conduction through the edge seal of the small glazing has a larger contribution to the total glazing heat transfer than that of the larger glazing system. (author)
Solar and visual light transmittance, colour appearance and other optical properties of glazing, are according to present standards specified for (near-) normal incidence. In general however, these properties are angular dependent. Realistic computation of visual light and solar energy properties therefore requires the angular behaviour to be known.The paper gives an overview of possible strategies for the development and use of algorithms for the prediction of the angular dependency of these properties. A new type of algorithm is proposed based on an ‘exact’ Fresnel model in which the complex Fresnel equations are replaced by more simple expressions. Different candidate expressions for this pseudo–Fresnel formalism are discussed and their results compared with the exact solution. The present work has been focused on the angular dependency of the visible light transmittance of a set of coated glazing materials which covers most of the products available today on the market.The results show that the new algorithm gives an accurate description of the angular behaviour of the optical properties of coated glazing for buildings and automotive applications.
The experimental system of photovoltaic window generation was installed on the test chamber. The mathematic model of photovoltaic module, used in an integrated building simulation tool ESP-r, was verified with the measured solar power. On the basis of the model validation, Photovoltaic window generation systems, used on facades of an office building located in Beijing, Shanghai and Hong Kong, were simulated, and the relationship between the electricity output and the vertical glazing azimuth and building site value was discussed.
Spectrally selective glazing system attracts great attention for energy efficient window applications. In this study, multilayer films consisting of high/low/high (TiO2/SiO2/TiO2) refractive index materials were prepared by sol–gel synthesis and spin coating process. Film thicknesses were examined by spectroscopic ellipsometry (SE) and focused ion beam (FIB) techniques, and refractive indices of TiO2 and SiO2 single layer films were also measured by SE. The reflectance spectra experimentally measured from multilayer films were in good agreement with the theoretical calculations by incorporating variable refractive index into the transfer matrix, so it is possible to modulate reflectance of multilayer films by controlling experimental variables for energy efficient transparent window applications.
This paper gives an extract of the state of the art of the manufacturing of semitransparent crystalline silicon POWER solar cells in an industrial environment. A short introduction of the POWER devices concept (see Fig. 1) will be given followed by an insight in the applied production process. Finally, examples effecting the efficiency distribution in the cell production and their solutions are given. It is believed that the lessons we learned in optimising the manufacturing process and production line of transparent POWER solar cells can be helpful for the increasing activities in the direction of thin wafers as well as novel solar cell devices.
This paper describes the main characteristics of monolithic silica aerogel and its application in evacuated superinsulating aerogel glazing including the evacuation and assembling process. Furthermore, the energetic benefit of aerogel glazing is quantified. In evacuated aerogel glazing the space between the glass panes is filled with monolithic silica aerogel evacuated to a rough vacuum of approximately 1–10hPa. The aerogel glazing does not depend on use of low emissive coatings that have the drawback of absorbing a relatively large part of the solar radiation that otherwise could reduce the space heating demand in residential buildings. The U-value of the glazing can be designed to meet the required value by increasing the monolithic silica aerogel thickness without the need for additional layers of glass. An aerogel glazing with 20mm glass distance can reach a U-value below 0.5W/(m2K) combined with a solar energy transmittance above 0.75.
The objective of this study is to increase the visible transmittance of a low-emittance (low-e) glazing as much as possible by antireflection treatment. This has been carried out by depositing thin porous films of silicon dioxide, SiO2, on both sides of a commercial glazing with a pyrolytic low-e tin oxide-based coating. SiO2 was chosen because its refractive index makes it suitable for antireflection treatment of both the uncoated glass side and the side of the tin oxide coating. The deposition of the antireflective films was performed with a dip-coating method, where the substrate was dipped in a sol–gel of silica. Two different silica sol–gels were used, one was manufactured in the laboratory and the other one was a commercial solution with a higher porosity. An increase of the integrated visible transmittance (Tvis) by 9.8% points up to 0.915 was achieved for a coating produced with the commercial solution. Calculations of U value, g value and Tvis for window configurations were also performed.
AlN/ZrN/AlN multilayers are deposited by magnetron sputtering onto borosilicate glass wafers. ZrN films have a high reflectivity in the IR range (∼85%) and AlN films have a high transmission in the visible range (∼90%). The multilayers are analysed in situ or after air contamination by X-ray photoelectron spectroscopy. This technique is used to analyse the interfaces. We observe the influence of the nitrogen partial pressure, bias voltage and post-annealing on the properties of the films (intermixing, oxygen diffusion). Then we correlate these results with the optical properties of the coating. The negative bias voltage has a great influence on the reflection of the multilayer coatings in the IR range. The layers intermixing at the interfaces are strongly dependant on the sputtered atoms energy at the surface of the growing film. This energy is controlled by the substrate bias voltage.
Transparent low-emissivity (low-e) coatings comprising dielectrics of amorphous diamond-like carbon (DLC) and Ag-alloy films are investigated. All films have been prepared by dc magnetron sputtering. An index of refraction of the DLC film deposited in a gas mixture of Ar/H2 (4%) shows n=1.80+0.047i at 500nm wavelength. A multilayer stack of DLC (70nm thick)/Ag87.5Cu12.5-alloy (10nm)/DLC (140nm)/Ag87.5Cu12.5-alloy (10nm)/DLC (70nm) has revealed clear interference spectra with spectra selectivity. This coating performs low emittance less than 0.1 for black body radiation at 297K, exhibiting a transparent heat mirror property embedded in DLC films.
For daylighting calculations, the design criteria are often expressed in terms of average daylight factors (DFave) with the computations being based on the CIE (International Commission on Illumination) overcast sky, which is generally considered to provide the worst daylight condition. The daylight illuminance of a room is mainly influenced by the luminances and patterns of the sky in the direction of view of the window at any given time. Overcast skies may not always be the appropriate reference sky types for daylighting analysis. Recently, Kittler et al. have proposed a new range of 15 standard sky luminance distributions including five clear, five partly cloudy and five overcast sky types. These 15 sky luminance models have been adopted as the CIE General Standard Skies. This paper presents an approach to computing the DFave for the 15 standard skies. The techniques for calculating the two configuration parameters for the DFave determination, namely; (a) light received directly from the sky above the horizon on a vertical surface, and (b) light received directly from the ground below the horizon on a vertical surface are established and described. The performance of the proposed method was assessed against the results obtained by other independent calculation methods and computer simulations. It is shown that the results predicted by the proposed approach are in reasonably good agreement with those produced from the other two calculation tools. The findings provide architects and building designers with a reliable and simple method for estimating the interior daylight illuminance under various standard overcast and nonovercast sky conditions.
Daylight in buildings can save energy by reducing artificial lighting energy consumption. An accurate estimate of internal daylight availability is required for energy use predictions and to include the effect of window orientation this must be based on an adequate model of sky luminance distribution. For such energy calculations the 'average sky' (based on measurements for a wide range of real skies) is recommended as a replacement for the CIE overcast sky. This paper analyses luminance data obtained by Wegner to show that the luminance distribution of an average sky is of the form L = ae-by + c where y is the angle in degrees between the sun and the element of sky under consideration, b is approximately 0.025 and a and c are functions of solar altitude alone, and, significantly, do not depend on the altitude of the element of sky. Using this formula together with a direct solar component the paper derives expressions for horizontal and vertical illuminances, and the average illuminance inside a side-lit room; and briefly outlines further work, under way at BRS, to evaluate the model for weather conditions in the UK and to apply it to problems of daylighting design.
We have developed an innovative way to fabricate organic solar arrays for application in dc power supplies for electrostatic microelectromechanical systems devices. A solar array with 20 miniature cells interconnected in series was fabricated and characterized. Photolithography was used to isolate the individual cells and output contacts of the array, whereas the thermal-vacuum deposition is employed to make the series connections of the array. With 1 mm2 for single cell and a total device area of 2.2 cm2, the organic solar array based on bulk heterojunction structure of π-conjugated polymers and C60 derivative [6,6]-phenyl C61 butyric acid methyl ester produced an open-circuit voltage of 7.8 V and a short-circuit current of 55 μA under simulated air mass (AM) 1.5 illumination with an intensity of 132 mW/cm2. The procedure described here has the full potential for use in future fabrication of microarray with the size as small as 0.01 mm2.
The potential impacts of climate change on heating and cooling energy demand were investigated by means of transient building energy simulations and hourly weather data scenarios for the Zurich–Kloten location, which is representative for the climatic situation in the Swiss Central Plateau. A multistory building with varying thermal insulation levels and internal heat gains, and a fixed window area fraction of 30% was considered. For the time horizon 2050–2100, a climatic warm reference year scenario was used that foresees a 4.4°C rise in mean annual air temperature relative to the 1961–1990 climatological normals and is thereby roughly in line with the climate change predictions made by the Intergovernmental Panel on Climate Change (IPCC). The calculation results show a 33–44% decrease in the annual heating energy demand for Swiss residential buildings for the period 2050–2100. The annual cooling energy demand for office buildings with internal heat gains of 20–30W/m2 will increase by 223–1050% while the heating energy demand will fall by 36–58%. A shortening of the heating season by up to 53 days can be observed. The study shows that efficient solar protection and night ventilation strategies capable of keeping indoor air temperatures within an acceptable comfort range and obviating the need for cooling plant are set to become a crucial building design issue.
Based on the power balance equation, an analytical tool for the calculation of the free-run-temperature of a room has been developed and a universally valid energy-strategy derived. The description of the thermal behavior of a room is traced back in this approach to three parameters only: the generalized loss-factor K, the time constant π and the gain-to-loss ratio γ. By an appropriate inclusion of solar gains the usual definition of ‘heating-degree-days’ is extended to ‘generalized heating-degree-days’, represented graphically as a function of π and γ. These two parameters yield the ‘climate surface’ of the room under consideration. A comparison with measured data from actual buildings confirms the validity of this approach. In order to illustrate its practical value, the method of climate-surfaces is applied in this paper to generate surfaces for design-temperature differences and to deduce optimized heating, cooling and control strategies, as well as strategies for the night set back solar shading, night cooling etc.
Energy savings from the utilization of daylight will be influenced by the amount of external daylight incident on the external surface of the window plane. Therefore, savings from daylight will vary from a place to another, based on the prevailing sky conditions in the climate concerned. This paper aims to investigate the potentiality of natural light if used a source of internal illuminance in buildings in the Eastern coast of Saudi Arabia. This includes providing information about daylight performance in the area.
Energy consumption in buildings is responsible for 40% of the energy end use in Italy. Most of the thermal and solar exchanges between the building and the external environment depend on fenestration. Rating schemes are useful instruments for classifying the energy efficiency of devices in many fields. For windows a rating system is largely utilised in some countries and is under study or development in many others. In Italy, single glazed units represent 80% of the total installed windows and the percentage of high quality products can be considered negligible. An energy-rating system would encourage efficient products onto the Italian market and would accelerate technical innovations in the glass and frame industries. The aim of introducing this scheme is to greatly reduce energy end use and, as a consequence, also CO2 emissions. The methodology, implemented for the residential sector, is based on the assessment of thermal performances of three reference buildings as a function of: window properties, climatic data and architectural characteristics. More than 1000 simulations, run with a building energy performance simulation code (TRNSYS), has made it possible to evaluate specific and percental heating, cooling and total energy savings as well as the reduction in CO2 emissions for the selected buildings. The simplified algorithms, which the energy-rating scheme for both cold and hot seasons is based on, have been taken from the analysis of previous results. Examples of cost–benefits analysis are presented to stress the economical and environmental advantages of the proper application of this instrument.
This article discusses the use of transparent insulation materials in low energy dwellings in cold climates. Both aesthetic and thermal issues for the capillary type of transparent insulation material are investigated. In Lien (1995) granulated silica aerogel and multilayered material of corrugated sheets are also presented.To investigate the aesthetic qualities of the material, a scale model study is performed. The study treats the distribution of daylight, the visual contact through the materials, and the appearance of the materials. The results show, among other things, that the capillary material spreads direct daylight in a cone shape and distributes it to certain areas of the floor, walls, and ceiling of a room. The visual contact through the materials is limited and dependent on the thickness of the material, the illumination situation, the distance between the observer and the material and the object observed, and the angle of direction at which the observer looks through the material.Calculations of the energy consumption for heating and ventilation are performed for a row house with different sizes of materials. The calculations are done for two climate zones in Norway. The results show that energy savings in the order of 20% can be attained. The results are especially promising for the coldest climate zone, where the problem of overheating is small and the energy saving potential is still good.
Vacuum glazing consists of two glass sheets with a narrow internal evacuated space. The separation of the sheets under the influence of atmospheric pressure is maintained by an array of small support pillars. The thermal resistances associated with the heat flow through individual pillars, and through the pillar array, are calculated using a simple analytic method, and by more complex finite element models. The results of both approaches are in very good agreement, and are validated by comparison with experimental data. It is shown that, for many purposes, the amount of heat which flows through the pillars can be determined without incurring significant errors by assuming that the heat flow is uniformly distributed over the area of the glass. Finite element modelling, and a superposition method, are used to determine the temperature distribution on the external surfaces of the glass sheets due to pillar conduction. Again the results obtained with both approaches are in very good agreement. An approximate method is described for calculating the magnitude of these temperature non- uniformities for all practical glazing parameters.