Glazing Units Research Articles

Parametric Optimization Approach to Evaluate Dynamic Shading Within Double-Skin Insulated Glazed Units for Multi-Criteria Daylighting Performance in Tropics

This research aims to support the choice of an appropriate dynamic louver shading system (DL-SS) within double-skin facade insulated glazed units (DSF-IGUs) as a high-performance integrated window system (DSF-IGUs/DL-SS) that meets both thermal and energy performance via daylight availability under a tropical climate. The research framework has developed a multi-objective optimization method to achieve research objectives via optimizing two different scenarios of the proposed system. The first scenario was optimized for daylighting availability, meanwhile, the second scenario was optimized for energy and thermal performance. For each scenario, the best solutions are selected from respective Pareto fronts according to energy efficiency criteria, thermal comfort via enhancing daylighting availability. Based on the best options resulting from both optimizations, the final step involved comparing the results of all performance indicators in the best cases to select the best solution. Overall, based on the optimizing objectives, the ranking of the best cases varied based on giving priority to the improvement objective in the optimization process. For each scenario, the best solutions are selected from the respective Pareto fronts. Overall, ranking of the best cases varied based on giving priority to the improvement objectives. Optimizing DL-SS within DSF-IGUs while giving priority to improving energy and thermal comfort while maintaining daylighting at acceptable levels is more reasonable. Thus, the DSF-IGUs/DL-SS best-case resulting from the second optimization scenario was overcome all best cases and ranked first in energy and thermal comfort. Compared to the base case, the differences of total Predicted mean vote and percentage of dissatisfied for better thermal comfort achieved were -0.35% and -1.48% with an average decreased by 22.99% and 28.72%, respectively. The differences of total energy and cooling load for better energy performance reduced by -96.84 kwh/m2. and -86.88 kwh with an average decreased by 25.33% and 26.20%, respectively. Meanwhile, the total satisfied of spatial Daylight Autonomy for better daylighting distribution and better daylighting availability of useful daylighting illuminance improvement were improved by -5.54% and +24.76% with an average percentage variation increased by 6.25% and 36.87%, respectively.

Experimental study on optical properties of various paraffin-based PCM glazing unit and radiative transfer model optimization

Experimental study on optical properties of various paraffin-based PCM glazing unit and radiative transfer model optimization

Outdoor Performance Analysis of Semitransparent Photovoltaic Windows with Bifacial Cells and Integrated Blinds

The stricter requirements for the energy performance of buildings are creating a market for several building‐integrated photovoltaic (BIPV) technologies, including photovoltaic (PV) windows. Herein, an innovative multifunctional PV window concept designed to enhance energy generation while providing overheating protection for better indoor thermal and visual comfort is presented. This concept utilizes bifacial c‐Si solar cell strips combined with venetian blinds, all embedded in a unique insulating glazing unit. The bifacial technology increases the energy yield by using the blinds as reflectors, directing more irradiance to the cells’ rear side. The goal of this study is to analyze the outdoor performance of this concept under real operating conditions. Twelve demonstrators are installed and monitored. Various measurement campaigns are conducted, examining the impact of different blind types, tilt angles, sun positions and sky conditions. The highest energy boosts occur when the blinds are fully closed at a 75° angle with their convex side facing outward. Blinds with the highest specular reflectance achieve a maximum performance increase of 25% on sunny days and a daily average increase of 12% compared to the case of no blinds.

Environmental performance of patient rooms using an integrated approach considering operational energy, daylight and comfort analysis

PurposeThe aim is to holistically assess the environmental performance of windows and analyse how their design and characteristics contribute to the overall performance of the building/space. This study focuses on the performance of windows in patient rooms hosting less mobile people.Design/methodology/approachThis study investigates the life cycle environmental impacts of different glazing types, window frames and fire safety doors at the product level. This article also presents a building-integrated environmental analysis of patient rooms that considers the multiple functionalities of windows by incorporating dynamic energy analysis, comfort and daylighting performance with a life cycle assessment (LCA) study.FindingsThe results indicate that the amount of flat glass is the main contributor to the environmental impacts of the glazing units. As for the patient rooms, global warming shows the most significant contribution to the environmental costs, followed by human toxicity, particulate matter formation and eutrophication. The key drivers for these impacts are production processes and operational energy use. This study highlights the significance of evaluating a wide range of criteria for assessing the performance of windows.Originality/valueAn integrated assessment approach is used to investigate the influence of windows on environmental performance by considering the link between window/design parameters and their effects on energy use/costs, daylighting, comfort and environmental impacts. The embodied impacts of different building elements and the influence of various design parameters on environmental performance are assessed and compared. The environmental costs are expressed as an external environmental cost (euro).

A comparison of the use of traditional glazing and a novel concentrated photovoltaic glazing (CoPVG) for building solar gain analysis using IESVE

The aim of this study is to compare the difference in solar gain for an internal space when a novel Concentrated Photovoltaic Glazing (CoPVG) unit is compared against traditional glazing modules. The CoPVG is an innovative glazing system developed by Ulster University, that takes advantage of Total Internal Reflection (TIR) to direct solar radiation into the internal space during periods of low solar altitude (around winter) harnessing the thermal contribution of solar gain and daylight. During periods of higher solar altitude (around summer), the solar radiation is mostly directed onto embedded photovoltaic cells. Previous work assessed the concept’s optical functionality, through experimental measurement and computational ray-tracing. Dynamic simulation in Matrix Laboratory (MATLAB) using a series of codes to represent the optical function of the CoPVG’s and Integrated Environmental Solutions Virtual Environment (IESVE) was validated by the experimental data. This work investigates methodologies in determining the transmissivty of the system in a dynamic simulation approach using ray tracing and Radiance in IESVE for visualisation, thereby building on the versability of this software to allow building designers and consultants to investigate energy and economic benefits of this system and systems like it in real building applications. The impact of integrating CoPVG as a replacement to traditonal glazing on a sun-facing building facade is assessed and the solar gain in the adjaciant space is compared throughout the year. During the summer months the integrated system reduces solar gain in the space by 34% but only 11% in the winter months, representing a reduction in the overall annual building energy needs. The study presents the potential economic and environmental savings provided by reduced cooling.

Long-Term Viscoelastic Behavior of Polyisobutylene Sealants before and after Thermal Stabilization.

Polyisobutylene (PIB) is commonly used as a primary sealant in multi-layer insulating glazing elements, where temperatures often exceed 100 °C. At such conditions, PIB undergoes structural changes, causing different relaxation dynamics and leading to decreased lifetime of the material. Understanding thermal behavior is therefore imperative for achieving effective insulation of these materials for long-term use in insulating application. The present study was focused on the temperature dependence of viscoelastic behavior of two commercially available polyisobutylene (PIB) materials, which are commonly used as primary sealants for energy-efficient multi-layer glazing units. The long-term viscoelastic behavior of the materials before and after thermal treatment at high temperatures was studied by using time-temperature superposition (tTS). Van-Gurp-Palmen plots were obtained directly from experimental data and enabled the study of thermally induced changes, while the relaxation time spectra were calculated from master curves and enabled the calculation of molecular weight distribution. The results showed that, after thermal treatment, the structure of PIB materials changes from linear to branched, while the molecular weight distributions transition from monomodal to bimodal. The untreated samples exhibited viscous-like behavior, while the thermally stabilized samples exhibited solid-like behavior, extending the material response for ~6 decades towards a longer timescale. Moreover, the presented results can be directly used to simulate the mechanical responses of the sealants using currently available FEM software packages to predict their functional and structural lifetime.

Vacuum insulated glazing (VIG) units under wind load—part 1: global deformation and stresses on the outer glass surfaces

This paper presents the first part of a study on the effect of wind loads on Vacuum Insulated Glass (VIG) units. The study provides background information on VIG and relevant Standards, explains the numerical modelling process, and discusses the implications of the results in relation to European and North American codes and Standards. The focus of the study is on vertical windows and façade installations in low-rise buildings (< 25 m) commonly found in residential buildings. The mechanical behaviour of VIG was analysed using the Finite Element Method (FEM) with respect to various design parameters such as glass pane size, glass thickness, surface pressure magnitude, and edge boundary conditions. The study analysed global deformation as well as the stresses on the outer glass surfaces. The VIG features such as pillar geometry and contact dynamics, and material non-linear effects, were explicitly modelled. In addition, monolithic glass plates were also modelled, and the FEM results of the monolithic cases were in reasonable agreement with an analytical solution obtained from linear thin plate theory. These results highlight the limit of linear behaviour in monolithic plate bending. The centre-of-pane deflection of the VIG was in good agreement with the FEM and analytical solutions of the equivalent thickness monolithic pane, for sample sizes below 800 × 800 mm. However, for larger glass sizes, a deviation was found, and the VIG exhibited a higher plate stiffness than the equivalent thickness monolithic pane. The simulations also showed that the stresses in the glass panes are highly dependent on the edge of glass boundary condition. Finally, the results demonstrated that with appropriate design choices, the VIG can satisfy the Standards requirements for wind load and glass design in both Europe and North America.

A Shingled Glass Envelope System Constructed from Reclaimed Insulated Glass

This paper presents a new approach to the design and construction of glazed building envelopes using salvaged insulated glazing units from demolition sites or surplus supply. Typically, Insulated Glazing Units (IGUs) are sent to landfill. Contemporary Architectural glazing is floated using virgin sand melted at 1700°C, a high energy extractive process. Obsolete architectural glass sent to recycling plants is not fed back into new float glass, rather it is downcycled to products such as glass bottles. This paper introduces a pathway for reusing obsolete and irregular Insulated Glazing Units into new curtainwalls; a pathway that currently does not exist. We demonstrate that the carbon footprint of glazed curtainwall could be halved by utilizing reclaimed IGUs. The system is a high-performance enclosure with weather tight compression gaskets and overlapping IGUs for thermal insulation and operational energy advantages over typical curtainwall systems. The system involves a computational configuration process for determining the best fit assembly of salvaged glass from a digitized inventory. The shingled glass façade system could be used in various applications, ranging from corporate offices to storefronts. This paper presents a one-to-one proof of concept, made from reclaimed IGUs of irregular size, collected in Lewes (UK).

Experimental study on thermal performance of finned tube water flow window

Water flow window is an advanced energy-saving building façade, and the design of the heat exchanger affects the thermal performance directly. A novel finned tube water flow window (FTWFW) applying a finned tube heat exchanger is proposed. Its thermal performance, with regard to energy savings and the thermal environment created under various operating conditions, is studied experimentally. The reduction in indoor heat gain reached 88.1% compared with insulated glazing unit, and the average daily water heat gain efficiency was 65.2% during the summer testing. The inner glazing surface temperature of FTWFW was more stable and closer to the comfort room temperature, especially under non-air-conditioning condition in winter, resulting in enhanced thermal comfort. Moreover, increasing the flow rate or decreasing the temperature of feed water can improve the thermal performance of FTWFW in summer. In winter, compared to increasing the feed water flow rate, raising the feed water temperature was more effective in increasing the room temperature. The advantages of FTWFW in cooling/heating energy saving, thermal collection, and thermal comfort enhancement were well demonstrated. Its large-scale application is expected to make contributions in green and low-carbon building development. The findings of this study can helpful in decision making of real projects.

A Systematic Review and Classification of Glazing Technologies for Building Façades

High-performance glazing technologies are essential for achieving the occupant comfort and building energy efficiency required in contemporary and future buildings. In real-world applications, glazing façades are selected from a steadily increasing number of glazing technologies. However, the authors could not identify a systematic and comprehensive review and classification of glazing technologies in the literature. This creates a barrier when comparing typologically different glazing technologies and combining multiple technologies in a glazing unit. This paper provides a systematic review and classification of established and emerging glazing technologies based on publications from 2001–2022 which were interpreted following the PRISMA methodology. This study reveals that the majority of high-performance glazing systems used in practice are in multi-layer glazing configurations and that the glazing system performance can focus on including additional and multiple functionalities, which aim at improving overall building performance. It was also found that there is a large potential for improvement of multilayer, evacuated, aerogels, electrochromic, and solar cell glazing by incorporating other technologies or innovative materials in multi-layer glazing units for either improving existing technologies or for the development of new ones. However, their longevity, robustness, and cost affordability should be ensured.

Thermal Performance Investigation of Greenhouse Glazing Units Containing PCM with Different Thermophysical and Optical Properties

Improved thermal storage capacity and reduced building energy consumption can be attained by utilizing phase-change materials (PCM) in glass enclosure structures, which can effectively utilize solar energy to improve the building’s thermal performance. This article investigates the thermal performance of double-layer glass filled with PCM as a function of relevant thermal physical parameters. Numerical analyses were conducted on the PCM glass units to assess the glass greenhouse thermal performance. Results indicate that the temperature distribution of the glass channel is mainly influenced by the absorption coefficient of the paraffin material. Compared to the absorption coefficient, the refractive index has a smaller impact on the temperature of the glass channel. On the other hand, the transmittance of the interior surface of the glass channel is greatly affected by solar radiation. According to the outdoor meteorological conditions of different seasons, increasing the latent heat of paraffin materials within a certain range with a reasonable density and melting temperature can greatly improve the thermal performances. Meanwhile, the thermal conductivity of paraffin materials and the change in the specific heat of paraffin materials have little impact on the improvement of thermal performance.

Experimental assessment of the energy performance of microfluidic glazing components: The first results of a monitoring campaign carried out in an outdoor test facility

Microfluidic glazing is a newly developed, adaptive, transparent component characterized by micro-channels filled with a circulating liquid, functioning as a heat exchanger and controlling the heat transfer through a façade. The performance of this glazing depends on its design and operation on site. The aim of this study is to present the results of an in-situ performance evaluation of microfluidic glazing components obtained from an experimental campaign in outdoor test cells, and to explore their potential and limitations under realistic working conditions. A case study has been conducted in Turin, Italy, in which two small south-oriented triple glazing units, upgraded with different functional elements, including a laminated semi-transparent Perovskite solar cell and microfluidic glazing, have been investigated under different operating conditions. Overall, the experimental campaign has shown a reduction in the heat exchange through the façade of about 70%. Moreover, this technology allows the temperature in the Perovskite solar cell to be decreased by as much as 10 °C, and the central glazing temperature to be reduced by as much as 41 °C, when set as the central panel, thereby effectively decreasing the risk of thermal degradation or thermal shocks. A temperature difference of 12 °C and 16 °C was recorded, depending on the modules, between the inlet and outlet temperatures.

Energy and Thermal Performance Analysis of PCM-Incorporated Glazing Units Combined with Passive and Active Techniques: A Review Study

The building envelope provides thermal comfort, an excellent visual view, and sunlight for the occupants. It consists of two parts: (i) an opaque (non-transparent) part (e.g., walls and roofs) and (ii) a transparent part (e.g., windows, curtain walls, and skylight devices). Recently, the use of fully-glazed facades, especially in large cities, has increased due to their aesthetical and structural advantages. This has led this study to review the performance of the currently passive smart glazing technologies. Phase Change Materials (PCMs) as latent energy storage material is the focus of this review, as well as other individual and combined techniques, including shading systems, solar cells (photovoltaic), and chromogenic (thermotropic and thermochromic) materials. PCM-integrated glazing systems have been extensively studied and rapidly developed over the past several decades from the standpoint of unique system designs, such as passive, active, and passive/active mixed designs, intelligent management, and sophisticated controls. In the academic literature, numerous studies on PCM-integrated building envelopes have been conducted, but a comprehensive review of PCM-integrated GUs combined with other passive and active techniques using dialectical analysis and comparing the climatic conditions of each study using Köppen-Geiger climate classification climate classification has been performed only rarely. Consequently, the primary objective of this study is to reduce this discrepancy for all types of glazing, excluding glazed roofs. This review article also contains literature tables as well as highlights, limitations, and further research suggestions at the end of each subsection.

Retrofit Proposals for Energy Efficiency and Thermal Comfort in Historic Public Buildings: The Case of the Engineering Faculty’s Seat of Sapienza University

The building sector greatly contributes to energy consumption and Greenhouse Gas emissions, relating to the whole building life cycle. Boasting a huge building heritage of historical and architectural value, Europe faces challenging retrofit perspectives, as the potential for high energy efficiency has to be exploited while preserving the buildings’ original characteristics. The present work aims to feature the influence of a passive strategy on a heritage building in a mild climate. As historical its façade cannot be modified, its large glazing areas involve multiple issues, such as an increase in the heating (QH) and cooling (QC) energy demands and the risk of thermal discomfort. Thus, window replacement was proposed for retrofitting. A dynamic simulation model in TRNSYS was validated with experimental data collected by the continuous monitoring of walls of different thicknesses and orientations. Solutions from replacement with Double Glazing Units (DGUs) with improved thermal insulation, to internal shading activation were applied. All configurations were compared in terms of QH, QC, thermal performance of the building and user comfort (Fanger). Low-e DGU enabled the saving of up to 14% of the annual energy demand, and shading also offered good results in summer, reducing QC by 19%. In summer, DGU involved a maximum PPD reduction of 10 units.

Characteristics of PCMs-filled double glazing unit under fire: A detailed thermal structural analysis

The behavior of double-glazing unit filled with paraffin wax as phase change materials (PCMs) under fire is studied in this paper. Based on the glass fracture criterion, the mathematical model of PCMs-filled double glazing unit is established, the probability failure conditions of glass fracture under fire load are reasonably set, the thermal structure characteristics of glass structure with paraffin wax layer and hollow glass unit are numerically examined, and the heat transfer characteristics of glass envelope with paraffin wax layer under fire conditions are analyzed. The thermal deformation temperature of glass envelope with paraffin wax layer reaching the fire surface under four fixed boundary conditions and the time of reaching the limit temperature at the edge are respectively delayed by 55 s and 5 s, compared to that of hollow glass unit. The outcomes reveal that the fire resistance of the double-glazing unit filled with paraffin wax is better than that of ordinary double-glazing unit. This research has important implications for the application and popularization of PCMs-filled double glazing unit in building exterior windows.

Experimental study of heat transfer characteristics of phase change material–filled glazed windows

The inclusion of phase change material (PCM) in glazing unit is an effective method to reduce energy consumption in building by absorbing a portion of the solar radiation for thermal energy storage while allowing visible light to reach the inside environment for daylighting. This results in reduction in fluctuation of temperature and improved thermal comfort for indoor occupants. There is limited published research, for calculating the heat transfer characteristics of the PCM used in the glazing units, especially under climatic conditions prevailing in India. In this work, the heat transfer characteristics of a PCM-filled double glazing unit were analysed experimentally. The heat transfer performance of the PCM-filled double glazed window unit was experimentally studied and compared with that filled with air, water, and a single glazed window. The experiment was carried out on different days for each window unit to find the temperature of inner and outer surface of glazing and also heat flux through the glazing. The result shows that PCM filled double glazing can minimize the inner surface temperature of the window by four degrees below the outer surface temperature in the morning, compared to air and water-filled double glazed windows. However, air and water-filled glazing are only capable of reducing inner surface temperature by a maximum of two degrees. Thus, a PCM-filled double glazed window can efficiently reduce the inner surface temperature than a single glazed window, air, or water-filled window.

Experimental Investigation of Thermal Bridges and Heat Transfer through Window Frame Elements at Achieving Energy Saving

Windows are responsible for significant amounts of energy loss through typical building envelopes. There have been multiple studies on heat loss through the glazing unit and frame system. This study presents an experimental investigation of a window unit and focuses specifically on the conductance between the structural elements and the frame system of a conventional house in the city of Xanthi, northern Greece. It is obvious that even a perfect window system cannot reduce heat transfer between the base of the frame and the upper surface of the floor. The experimental and simulation procedure of this project includes the installation of an insulating layer in front of the window unit for a variety of frames (solid wood, aluminum, PVC, etc.) at different distances. The main objective of this paper is to determine how effective an insulating barrier can be in respect to different types of frame, glazing, and weather conditions for the control of heat loss. Through the application of this technique, in combination with an appropriate insulating frame and window unit, designers can control the temperature inside the room at close proximity to the windows, in order to contribute to energy saving, aiming towards a building with zero energy demand.

Control of heat transfer in single-story mechanically ventilated double skin facades

This paper systematically investigates and quantifies the interplay between mechanical ventilation rate and operation of venetian blinds in determining the performance of a single-story double skin façade. The investigation covers both the supply-air mode and the outdoor air curtain mode of a mechanically ventilated double skin façade. For this experimental study, a full-scale mock-up of a single-story double skin façade was installed in a climate simulator facility and exposed to a series of steady-state regime conditions under two representative cases of temperature gradient and solar irradiance replicating the summer, and the mid-season/winter case. The study results showed the relative weights of the different variables in leading the behavior of the façade. They provided evidence that the control of the performance of a double skin façade may change with the seasons, and that airflow rates and venetian blinds can play different roles depending on the boundary conditions and target performance. Venetian blinds were far more dominant than the mechanical ventilation rate in controlling the net heat transfer in the tested summer conditions, while the opposite was seen for the dynamic insulation efficiency. In mid-season/winter conditions, while operating the façade in a supply-air operation mode, the mechanical ventilation rate was the dominant variable in controlling the net heat transfer. Recommendations for the operation of the double skin façade were also developed as a result of this study. Low and moderate ventilation rates (up to 100 m3h−1 per linear meter of façade) were found suitable to deliver enough fresh air with good preheating efficiency while provide adequate control over the net heat transfer. Higher airflow rates, even in summer peak conditions, were not found to be particularly effective in reducing the solar gain through a façade operated in an outdoor air curtain mode when the interior skin was realized with an insulated glazed unit.

Towards the scale-up of solid-state, low-emissive electrochromic films, fabricated on a single substrate with novel electrolyte formulations

This experimental work reports the activities of design, fabrication and characterization of an innovative solid-state electrochromic device, deposited on a single substrate with high transparency in the bleached conditions and a wide modulation of transmittance (ΔT of 60% at 750 nm) both in the visible and near-infrared wavelengths. A tailored formulation of the solid electrolytes, based on sulfonated tetrafluoroethylene-based fluoropolymer-copolymer dispersions and the accurate design of a suitable layer of porous tin oxide nanoparticles provided high coloration and bleaching kinetics and recovery of the pristine conditions, even after 500 complete cycles. Devices were scaled-up to 10 × 10 cm2 size, without mechanical and aesthetic defects and relevant homogeneity, throughout the coloration and bleaching processes. Furthermore, this device shows the further feature to be a low-emissivity dynamic solar control film, highly compatible with integration within insulated glazed units.

Slim Skins: Towards a New Glazed Façade System

From early 20th century architects have envisioned transparent buildings such as Mies van der Rohe’s “skin and bones” concept and his 1921 proposal for the Friedrichstrasse Skyscraper competition in Berlin. One hundred years on, there is a much better understanding of the energy consumption implications of highly glazed buildings, yet architects, developers and users are still attracted to fully transparent facades. This paper sheds some light on the challenges to build with high performing glazing façade systems (originally called curtain wall systems) while efficiently utilising resources and reducing its manufacturing embodied carbon. This can be achieved by omitting the typical frame (mullions and transoms) and making the glass work structurally. Built examples by Octatube are Triodos Bank (Netherlands) and Echo Building (TU Delft- Netherlands). A further option that will focus on sustainable unitised systems is currently being explored by Octatube and TU Delft Building Technology graduation student. This is based on an optimised unitised frame integrated in between glazed units. These different systems will be assessed and compared against each other regarding its end-of-life recovery potential, embodied carbon and visual impact.