Insulating Glass Units Research Articles

Hybrid ultrasonic technique for non-invasive evaluation of argon gas content in insulated glass units

At present, the heat loss of energy-efficient buildings through transparent partitions, i.e. curtain walls and windows, make more than 40 % of the total heat loss. Since most of area of these partitions (70–80%) are covered by the insulating glass units (IGU), it accounts for the largest part of the building’s heat losses. These losses increase with the lifetime of the building as the heat transfer coefficient of the IGU increases with decreasing argon gas concentration in a cavity of glass unit, due to the ageing of the surrounding seals. While the content of Ar gases decreases, a soft low-E coating of glass is oxidizing, decreasing insulation of the radiant heat flux which determines for about 50 % of the total heat flux through the IGU. In order to make targeted decisions on replacing of degraded IGUs their insulation properties have to be evaluated using reliable in-situ measurement method. In this paper, non-invasive adaptive ultrasonic technique for assessment of Ar gas content in the gas mixture of IGU was proposed. The technique is based on the sound velocity measurements and is combined with electromagnetic field phase measurement methods for precise estimation of the thickness of IGU at any spatial position. The technique was verified on the IGU samples with known Ar gas concentrations and compared with commercial systems and gas chromatography in range of 27–93% of Ar content. It was estimated, that technique is capable of measuring Ar concentration with accuracy of ± 3.15%, which exceeds the current industry standards.

Deflections and Stresses in Rectangular, Circular and Elliptical Insulating Glass Units.

Insulating glass units (IGUs) are construction elements that react to climatic loads in a specific way. Under the influence of changes in atmospheric pressure and temperature, as well as the effect of wind, the gas closed in the tight gap between the glass panes changes its pressure, which affects the resulting static quantities of the loaded IGUs. The calculation models described in the literature mostly concern rectangular units, however, other shapes are being implemented more and more often in modern architecture. The aim of the article was to propose analytical and numerical models of circular and elliptical IGUs and to compare their results in terms of deflections and stresses with static values for square and rectangular units. Calculation examples were presented for various dimensions of IGUs loaded with changes in atmospheric pressure and an external wind effect. For elliptical IGUs, only the numerical calculations were presented, as it is not possible to formulate an applicable deflection function practically. The results were summarized in the form of tables and graphs, which illustrate the percentage differences between the deflection and stress values for the rectilinear and curvilinear shapes of IGUs for various dimensions and types of loads. It was found that in a single circular glass pane the maximum deflection is 4.2% greater, and the maximum stress is 13% greater than in a square unit of the same dimension. Meanwhile, in a circular, symmetrically loaded double-glazed IGU, the deflection in the circular IGU is smaller by 8–9% than in the square unit and the stress is practically identical.

Engineered calculation of the uneven in-plane temperatures in Insulating Glass Units for structural design

Engineered calculation of the uneven in-plane temperatures in Insulating Glass Units for structural design

Gas interaction in insulating glass units in the case of elastic support of component glass panes

Gas interaction in insulating glass units in the case of elastic support of component glass panes

On the thickness determination of rectangular glass panes in insulating glass units considering the load sharing and geometrically nonlinear bending

The number and size of windows has increased in large cruise ships, especially on the top decks. They have therefore become a weight and stability-critical component of the structure. Their thickness is determined according to the classification rules which are generalized for all type of passenger ships. That is, the provided formulae are based on linear-elastic, small deformation, plate theory and therefore more suitable for smaller windows in non-weight critical applications. However, majority of the windows are large insulating glass units (IGUs) that exhibit two effects that the rules do not currently consider: development of membrane stresses in the glass panes at large deflections due to the von Kármán strains (geometric nonlinearity) and interaction of the glass panes due to the internal cavity pressure between them (load sharing). Both increase the load bearing capacity of the IGUs. Therefore, extension to the thickness determination is needed for achieving the lightweight design. This paper uses nonlinear Finite Element Method to study the IGUs static response under uniformly distributed load considering the effects. The response consists of principal stress and deflection of the panes, and the cavity pressure. Validation is carried out by experimental results from scientific literature. Case study on typical panes from cruise ships indicate that considering the two beneficial effects, the thickness of the glass panes in the IGUs may potentially be reduced between 26–54 % with respect to the classification rule-based design. That is, by using the same allowable principal stress criterion between the linear and nonlinear predictions.

Maximum Transparency – Messeturm Frankfurt

The Messeturm in Frankfurt/Main is currently adjusted to the requirements of a modern office building. The lobby area has been enlarged by a highly transparent facade consisting of oversized insulating glass (IG) units. The IG units are curved and have a size of up to 17 m x 2.8 m. The IG units are supported by tapered stainless steel fins. Inclined steel beams connect the top of the facade fins with the tower structure creating a rounded roof. The facade with its glass roof allows maximum transparency for people inside the lobby as well as for people passing by.

Twisted Tower – A Feasibility Study for Cold‐Bent Insulating Glass Units with an Elastic Edge Seal

This paper describes a case study of cold bent insulating glass units (IGUs) for use in facades or roofs using the example of a demonstrator called the “Twisted Tower”. Modern designs often try to combine a curved shape with transparency. Cold bending IGUs is a cost efficient method to achieve both. In such applications the bending angles are often limited by the allowable deformations of the primary seal which ensures the gas tightness of the IGU. This investigation shows IGUs with much more acute bending angles than in standard applications were achieved using a flexible yet durable thermoplastic spacer ensuring superior gas tightness. This work investigates the geometry, the deformations and fixing options for the bent IGU form. The results demonstrate the advantages of using such spacer systems for these applications.

Insulation glass units made of thin glass‐polycarbonate composite panels

The combination of brittle thin glass with ductile polycarbonate leads to innovative composite panels. Two outer thin glass panels with one or more inner polycarbonate sheets represent an alternative to conventional laminated safety glass as security safety glazing with a resistance against manual attack. Following development to multi‐pane insulation glazing presents the additional advantages of the composite panel to thermal insulation. This study documents the design of single thin‐glass polycarbonate composite panels as security glazing to multi‐pane insulation glazing with the highest resistance class P8B against manual attack. The paper describes the evolution of the insulation glass unit and the experimental research to reach the defined values of resistance class, heat transfer coefficient and energy transmission. This results in slighter single composite panels and insulation glazing as an innovative alternative to common laminated safety glass as security glazing.

In situ U g-value measurement on three different glazing types

This study presents in situ monitoring data of three different glazing systems over a period of one year. An insulated glass unit (IGU), a Vacuum Insulated Glass hybrid unit (VIG-hybrid) and an opaque architectural insulation module (AIM) were monitored under the equivalent environmental condition in this study. Different issues were observed and analyzed. It was found that the Ug-value cited by the manufacturers agrees with the Ug-values derived from the measured data, to within less than 5 % for the IGU and the VIG-hybrid. The consistency of the Ug-value of each glazing types one year after the start of monitoring was validated for similar environmental conditions. Depending on the magnitude of the resistance to heat flow, an increasing Ug-value was observed for a higher temperature difference between the inside and outside environments. The effect is much more significant for the glazing type with the largest Ug-value (IGU) and less significant for the glazing types with a high thermal resistance (VIG-hybrid, AIM).

Combining thermal insulation and mobile communication in buildings: influence of laser-treated glazing on microwave propagation

With the purpose of reducing the heating energy in buildings, it is common practice to install energy-efficient windows to increase the thermal insulation of a façade. These insulating glass units (IGIJ) include a thin silver coating acting as an infrared mirror which reduces the thermal losses that occur through radiation, but at the same time reflects the microwaves for mobile communication. To address this drawback, a specific laser treatment is performed on the silver coating which strongly improves the transmission of microwaves through the window. In this study, the attenuation of microwaves signal was analyzed inside the SolAce unit in the "NEST" research building at the Swiss Federal Laboratories for Materials Science and Technology (EMPA) in Dübendorf. Two configurations (with and without laser-treated glazing) were carried out by interchanging two hinged windows. The results showed a significant improvement in signal strength in the configuration with laser-treated IGUs. A transmission loss contour plot of the SolAce unit showed a highly directional propagation of the wave which suggests that more than two windows should be treated to achieve better mobile communication in the entire unit. The novel patterned coating is thus especially valuable in the building sector to increase the microwave signal for mobile communication. To the best of our knowledge, this is the first implementation and testing of laser-treated coating for energy-efficient glazing in the building sector.

An analytical method for calculating the stress-strain state of PVC window profiles under thermal loading

Introduction. The practical operation of modern PVC windows in the climate of the Russian Federation has proven that due to thermally induced deformations of window elements cold air enters premises and window frames freeze. Presently, there is no engineering method for calculating the temperature deformations of windows, that takes account of the key features of their structure: the composite structure of window sections, the rigidity of insulating glass units, fittings, etc. An important task is to develop a method for calculating temperature deformations of PVC window elements, that takes account of nonlinear temperature distribution over their cross-sections.
 Materials and methods. A three-dimensional finite element model of a standard PVC window was developed using the COMSOL Multiphysics software, and its temperature field was calculated. The analysis of the calculation results allowed to identify the nature of the temperature distribution over the cross sections of PVC window profiles and propose a method for their analytical calculation. Using the basic equations of solid mechanics and methods of mathematical analysis, the bending of PVC window elements was described on the basis of their actual temperature fields.
 Results. The obtained equations were tested by comparing the results of the manual calculation with the results of the finite element modeling.
 Conclusions. The obtained equations, describing temperature deformations of individual window elements, serve as the starting point for an integrated method of calculating the structural behavior of PVC windows under thermal loading. The further development of the presented method will encompass the analysis of the influence of the reinforcing core on the structural behavior of PVC elements and the exploration of the structural behavior of the entire window structure.

A Method of Reducing the Distorting Curvature of Insulated Glass Units Due to Partial Rarefaction in Interglass Space

Currently, insulated glass units (hereinafter abbreviated as IGU) are the main type of translucent filling used in curtain walls. Under the influence of climatic loads in IGU, the thickness of the inter-glass space changes, leading to the deformation of the glasses. Deformations of glass lead to optical distortions on curtain walls. The paper considers the technical solutions used in the existing engineering practice to reduce the distorting curvature of IGU: the use of more rigid external glasses as part of IGU, the use of double-skin facades with external independent single glass, the use of vacuum IGUs. A new method is proposed to reduce the distorting curvature of IGUs by fixing the thickness of the interglass space. It is achieved by installing other point or linear supports between the panes. The introduction of other supports solves the problem of reducing deformations only when IGU is compressed. When the interglass space is expanded, the supports are turned off from operation and the glass is freely deformed. Therefore, to avoid such deflections, it is necessary to pre-compress the IGU under a load equivalent to the climatic load on the IGUs operating in the construction area of the object. Calculations show that for the climatic conditions of the city of Moscow, the required degree of rarefaction the interglass spaces is only 5 % of the absolute atmospheric pressure.

Phase separation of VO2 and SiO2 on SiO2-Coated float glass yields robust thermochromic coating with unrivalled optical properties

Vanadium dioxide displays thermochromic properties based on its structural phase transition from monoclinic VO2 (M) to rutile VO2 (R) and vice versa, and the accompanying reversible metal-insulator transition. We developed a single layer coating comprising VO2 (M) and SiO2. We applied the coating from an alcoholic solution comprising vanadium(IV) oxalate complex and pre-oligomerized tetra ethoxy silane to SiO2-coated float glass using dip coating, and thermally annealed the dried xerocoat in a two-step process. The addition of SiO2 as coating matrix resulted in non-scattering coatings with low surface roughness and random distribution of VO2 nanodomains (≤200 nm). Furthermore, the formation of the coating, comprising a phase separation yielding SiO2 and VO2 nanodomains during the thermal anneal, was studied in detail. The coating displays unrivalled optical properties, combining high visible light transmission Tvis > 60% and large solar modulation ΔTsol ≥ 10%. When applied in insulating glass units, the coating has a positive impact on energy savings for heating and cooling of buildings in intermediate climates, which we demonstrated through building energy simulations. For a typical house in the Netherlands, energy savings up to 24% were obtained. In addition, we demonstrate a coating stability comparable to current energy-efficient window coatings during processing into and in insulating glass units through (accelerated) life time tests.

Ug-value and edge heat loss of triple glazed insulating glass units:A comparison between measured and declared values

Triple glazed low-e coated insulating glass units with argon filling of five different suppliers on the European market with a declared thermal transmittance in the undisturbed centre of glass (Ug-value) of 0.6 W/m2K have been purchased from resellers and tested in a guarded hot plate at vertical position. The measured results showed deviations towards higher values for all 5 types. These have been analysed by recurring to the determination of the two main factors namely the gas mixture in the two cavities and the emissivity of the coated glass panes. Non-destructive measuring methods for gas mixture analysis and standardized calculation methods for the Ug-value have been used to analyse the influence of these two factors. In a further step the edge heat loss due to the spacer of the insulating glass units has been measured by using two “halves” of each glazing type with a double edge running through the middle of the measured sample. This was done following a standardized test method for the determination of the edge heat loss of Vacuum Insulation Panels (VIP). Finally, pieces of the coated glass panes were cut out of the glazing units and their emissivity measured with both an infrared spectrometer and an emissiometer. Results showed an increased emissivity value for the coated surfaces leading to higher Ug values than measured. This is partly due to the exposure to air and the possible degradation of the coating. The investigation shows non-destructive emissivity determination is needed to get more accurate in-situ emissivity values of the coatings.

Polyisobutylene and Silicone in Warm Edge Glazing Systems—Evaluation of Long-Term Performance

This article describes the characteristics of one type of sealing system used in warm edge glazing units and analyses the possible causes of damage. Attention was focused on the performance of the dual seal, PIB/silicone system. This type of glazing is widely used for modern curtain walls and roofs of office buildings and shopping centres. Study was focused on PIB displacement defects, which affects both the appearance and thermal performance of the curtain wall system. Wide-ranging field surveys were conducted to examine the problems identified in some office buildings. The information gathered in this way was used to identify the critical areas and causes of seal displacement in the analysed insulating glass units (IGUs). Laboratory tests were conducted on PIB and silicone seals retrieved from the removed defective units. The properties of these materials were determined and used to evaluate the applied edge sealing system and build a representative numerical model. Due to the problems encountered in deriving accurate analytical formulas, finite element (FE) approximation was used as a problem solving tool. The generated FE model and strain analysis were the key parts to obtaining a true representation of the actual behaviour of IGUs subjected to various environmental loads, taking into account the influence of the air cavity. Results of computer simulations and laboratory tests were compared for model validation. The effect of changes in ambient pressure was examined, showing the development of tensile strains in the silicone and PIB, which can lead to debonding. The greatest principal strains occur at the silicone/butyl rubber interface and this location should be considered to be the most susceptible to failure. The observations are summarised in the final conclusions. Additionally, as field study showed, after ten years in service, the percentage of damaged units is considerable. More frequent IGUs inspection should cover both appearance and thermal imaging to detect unsealed panels. From the standpoint of both durability and appearance, dual silicone/PIB should be phased out in favour of modern seal systems.

Material Selection and Characterization for a Novel Frame-Integrated Curtain Wall.

Curtain walls are the façade of choice in high-rise buildings and an indispensable element of architecture for a contemporary city. In conventional curtain walls, the glass panels are simply supported by the metal framing which transfers any imposed load to the building structure. The absence of composite action between glass and metal results in deep frames, protruding to the inside, occupying valuable space and causing visual disruption. In response to the limited performance of conventional systems, an innovative frame-integrated unitized curtain wall is proposed to reduce structural depth to one fifth (80%) allowing an inside flush finish and gaining nettable space. The novel curtain wall is achieved by bonding a pultruded glass fiber reinforced polymer (GFRP) frame to the glass producing a composite insulated glass unit (IGU). This paper selects the candidate frame and adhesive materials performing mechanical tests on GFRP pultrusions to characterize strength and elasticity and on GFRP-glass connections to identify failure module and strength. The material test results are used in a computer-based numerical model of a GFRP-glass composite unitized panel to predict the structural performance when subjected to realistic wind loads. The results confirm the reduction to one fifth is possible since the allowable deflections are within limits. It also indicates that the GFRP areas adjacent to the support might require reinforcing to reduce shear stresses.

The Changes in Thermal Transmittance of Window Insulating Glass Units Depending on Outdoor Temperatures in Cold Climate Countries

Windows, which have a U-value that is governed by an insulating glass unit (IGU) U-value, must be a building’s only enclosure element, which has no design value concept. The declared U-value, which is calculated or measured with 0 °C of external ambient temperature, is used instead of the design value. For most of a building’s elements, its thermal transmittance with a decrease in the external temperature diminishes a little, i.e., improves. However, for modern window IGUs with Low-E coatings, it is the opposite: the thermal transmittance with a lowering external temperature increases. Therefore, for calculating the peak power for the heating of buildings it is necessary to pay attention to this phenomenon and, therefore, it would be wise to introduce the concept of design U-value for windows, recalculation rules, or affix their declared U-values. This is especially the case in modern times with the prevailing architectural tendencies for enlargement of transparent building elements. For IGUs with Low-E coatings and inert gas fillers, the thermal transmittance depends on the temperature difference between warm and cold environments. When the external temperature is −30 °C instead of 0 °C, the thermal transmittance of the IGU can increase by up to 35%. This study presents the thermal properties of windows’ IGUs depending on the changes in outdoor temperatures by using guarded a hot box climate chamber and presents the proposed simplified methodology for determining the thermal properties of windows’ glass units. The accuracy of the composed simplified methods, comparing the calculated thermal transmittances of IGUs with those measured in the “hot box”, were up to 1.25%.

Temperature and Humidity Regime of Roof Space in Buildings with Glass Roofs

The paper analyzes the temperature and humidity conditions of the roof space of buildings with translucent roofs in the winter period of operation. The work is based on the generalization of data from a number of field observations and monitoring of translucent roofs of atrium buildings in Moscow. It is established that the temperature and humidity regime of the sub-roof space of atrium buildings with translucent roofs in the winter period of operation has a significant impact on the load-bearing capacity and durability of the translucent filling of coatings (insulated glass units), as well as snow loads on translucent roofs. At the same time, an analysis of existing approaches to the design and calculation of translucent roofs atrium buildings has shown that the issue considered in this work is often not taken into account when assigning their design solutions, which further complicates their normal operation. It is established that when performing strength calculations of roof insulated glass units it is necessary to take into account the design conditions of the transitional spring-winter period, which is characterized by low outdoor temperatures and high solar activity. The thermal regime of translucent roofs of atrium buildings also has a significant impact on the formation of snow cover on similar structures, which is manifested in a different nature of the distribution of snow loads on translucent roofs, as well as on the amount of snow loads, which are several times less than the loads on similar deaf insulated roofs.

Experimental mechanical analysis of traditional in-service glass windows subjected to dynamic tests and hard body impact

The large use of glass in buildings, and especially the presence of fenestrations and facade systems, represents a potential critical issue for people safety. The brittle nature of glass (with limited elastic deformation and resistance) is often enforced by its use in combination of several secondary components, whose reciprocal interaction and potential damage should be properly assessed. In the case of windows, accordingly, a special care should be spent for glass members but also for the framing system and possible adhesive or mechanical connections. This study aims at exploring the dynamic response and damage sensitivity of traditional glass window systems, based on the experimental derivation of few key material properties and mechanical parameters. To this aim the attention is focused on traditional, in-service windows that belongs to existing residential buildings and are typically sustained by timber frames, through a linear flexible connection. In doing so, major advantage is taken from experimental analysis, both in the static and dynamic field, for whole window assemblies of single components. For comparative purposes, selected window specimens including plastic (PVC) frame members and Insulated Glass Units (IGUs) are also taken into account in the paper. The static characteristics of the windows components are first preliminary derived. The dynamic performance of such a kind of systems is then experimentally explored with the support of modal analysis techniques and hard body impact procedures, including the experimental derivation of stiffness parameters for the frame members and the glass panels. Further assessment of experimental outcomes is finally achieved with the support of Finite Element numerical analyses.

Test and analysis of window vibration for anti-laser-eavesdropping

Windows are obvious targets for laser eavesdropping and can be easily eavesdropped. However, studies on the window vibration characteristics and associated anti-laser-eavesdropping measures are relatively scarce. To reduce the window vibration and decrease the eavesdropping risk, this study investigates the influence of the glass thickness, glass size, and number of window layers on glass vibration by carrying out theoretical analysis, full-scale testing, and finite element analysis. To begin, the effect of the window size and thickness on voice-induced vibration is investigated using elastic thin plate theory. It is found that the vibration is relatively low if the window’s natural frequency exceeded 500 Hz. Then, a full scale test is conducted to investigate the effect exerted by the number of window layers, and it is found that the glass vibration in the double-pane (Insulated Glass Unit) window is 74% less than that in the single-pane window. To further investigate the multi-layer window characteristics, a refined finite element model that considers acoustic-structural coupling is established in ABAQUS and validated by the test results. The analysis results reveal that only 1% of the glass vibration is transmitted by the window frames, and the two glasses in the Insulated Glass Unit(IGU) have similar vibration magnitude and characteristics when the total glass thickness is the same. Additionally, when the windows have the same glass thickness, the vibration of the IGU is 55% less than that of the single-pane window, and 40% less than that of the triple pane window. Hence, when the size and glass thickness are the same, IGU windows are the best option for reducing the glass vibration and prevent laser eavesdropping.