Triple Glazed Unit Research Articles

Closed cavity façade, an innovative energy saving façade

In its simplest form, a Closed Cavity Façade (CCF) consists of a double or triple glazing unit (DGU or TGU) on the inner layer and single glazing on the outer one, forming a sealed non-ventilated cavity with an automated shading device in between. Given its dynamic behaviour, this technology can dynamically control the flow of solar energy and light penetrating the building. Using EnergyPlus and IDA ICE, several CCF configurations were investigated and compared to the baseline (TGU). MATELab, an office-like test facility at the University of Cambridge, was used as the model, which was beforehand experimentally validated. The results show extensive benefits of CCFs compared to traditional TGU systems, in terms of thermal performance and occupants’ comfort. The CCF configurations investigated led to an improvement of energy performance in the range of 18–37% compared to the traditional TGU, depending on the CCF configuration and the climate while a previous study, using CCF configurations with DGU as inner skin, revealed an improvement of energy performance in the range of 22–41% compared to the conventional DGU. Further investigation showed that glass coatings and solar shading characteristics play an important role in cutting down overheating phenomenon while increasing occupants’ comfort. Practical application: Governments are making ever more stringent energy regulations for the building industry aiming to reduce energy consumption and carbon emissions. At the same time, building owners and architects are looking at cost-effective solutions for the long-term performance of buildings while tenants/occupants are more than ever aware of the fact that building comfort increases well-being and productivity. In all these regards, this work focuses and accentuates that substantial improvements can be achieved by designing and using suitable configurations of the innovative Closed Cavity Façade according to the climatic conditions of each location. The results presented indicate that there is much potential in improving the energy and comfort performance of a building, raising awareness to help deploy innovative glazing technologies.

Dynamic coupled heat transfer and energy conservation performance of multilayer glazing window filled with phase change material in summer day

Windows as indispensable for buildings play an important role in decreasing building energy consumption and improving indoor thermal comfort. However, the conventional windows made of the pure glazing units fail to meet the requirements of energy conservation for buildings due to poor thermal insulation. Recent researches found that the application of phase change materials (PCM) can improve the heat transfer performance of glazing unit and the PCM-filled glazing units have advantage in reducing building energy consumption and improving indoor thermal comfort. Therefore, the dynamic coupled heat transfer and energy conservation performance of PCM-filled multilayer glazing unit are investigated numerically in this work. A transient coupled heat transfer model considering conduction, phase change and solar radiation transfer in glazing unit is established, and the energy conservation performance is analyzed based on the heat transfer calculation. Results show that the PCM-filled multilayer glazing unit can significantly reduce energy consumption compared with pure glazing unit, and the energy saving rates are 14.55% for double glazing unit, 33.89% for triple glazing unit and 50.71% for four glazing unit, respectively. In addition, the effects of optical and thermal parameters of PCM on thermal performance of glazing units are investigated thoroughly. It is found that the PCM-filled multilayer glazing unit has advantages in thermal insulation which is good choice for transparent envelope in the building fields.

Sustainable reflective triple glazing design strategies: Spectral characteristics, air-conditioning cost savings, daylight factors, and payback periods

Buildings with conventional glazing systems are responsible for excessive cooling and heating costs. Sustainable use of energy in building environments requires the use of high-performing opaque and windowed walls. Triple glazing units attenuate solar heat gain/loss compared to single- and double-glazing assemblies, thus reducing air-conditioning costs and greenhouse gas emissions. The optical, energy, economic and environmental performances of a glazing unit are strictly correlated with each other. An improvement of optical properties leads to higher glazing energy performance, cost savings, and greenhouse gas emission mitigations. This work aims to suggest and define an energy-efficient triple glazing unit for lowering cooling and heating costs in buildings while experimentally testing the spectral performance of reflective glasses and assessing heat gains/losses. In this regard, bronze, green, grey, sapphire blue, and gold reflective glasses were considered and settled in sixty different triple glazing combinations. Spectral characteristics of reflective glasses were measured experimentally using a spectrophotometer over the entire solar spectral range (300–2500 nm). For the aims of this investigation, a numerical model was developed to assess the net annual cost saving ($/m2) and the payback period of the examined glazing units for the eight cardinal directions (N, N-E, E, S-E, S, S–W, W and N–W). The results confirmed that the TWG35 window glass unit in the S-E orientation was the most energy-efficient glazing in terms of alleviating this critical challenge (air-conditioning cost-saving 16.72 $/m2 among all other studied window glass units), while a payback period of 2.2 years was revealed. On the other hand, the TWG33 window glass unit has led to the optimal-lowest payback period (2.1 years), with a net annual cost saving of 16.55 $/m2. The findings of this paper demonstrate the significance of triple-glazing design approaches from an economic and environmental point of view.

Dynamics of Melting Process in Phase Change Material Windows Determined Based on Direct Light Transmission

Detailed analyses of melting processes in phase change material (PCM) glazing units, changes of direct transmittance as well as investigation of refraction index were provided based on laboratory measurements. The main goal of the study was to determine the direct light transmittance versus time under constant solar radiation intensity and stable temperature of the surrounding air. The experiment was conducted on a triple glazed unit with one cavity filled with a paraffin RT21HC as a PCM. The unit was installed in a special holder and exposed to the radiation from an artificial sun. The vertical illuminance was measured by luxmeters and compared with a reference case to determine the direct light transmittance. The transmittance was determined for the whole period of measurements when some specific artefacts were identified and theoretically explained based on values of refractive indexes for paraffins in the solid and liquid state, and for a glass. The melting process of a PCM in a glass unit was identified as a complex one, with interreflections and refraction of light on semi layers characterized by a different physical states (solid, liquid or mushy). These optical phenomena caused nonuniformity in light transmittance, especially when the PCM is in a mushy state. It was revealed that light transmittance versus temperature cannot be treated as a linear function.

Time-Temperature Dependency of Laminated Glass Subjected to Blast Load – A Numerical Study

The behavior of laminated glass has strong time-temperature dependency. Viscoelastic material models are often employed to define mechanical properties of Polyvinyl Butyral (PVB), the most common interlayer for structural glass applications. However, it is an apparent notion to simplify the high complexity of such material models, as only specific software is capable of considering this behavior. Most studies in blast design of laminated glass have focused on room temperature condition and recommend the use of elastic material models for PVB with high modulus of elasticity for simplification. The main purpose of this study is to develop an understanding of time and temperature dependency of interlayers in real building application. On the basis of empirical weather data, a range of interlayer temperatures is proposed to be considered for blast design situation in Germany for vertical double glazed and triple glazed units in accordance with Eurocode 0 and Eurocode 1. The results obtained from this analysis are further investigated within a transient structural parametric study of laminated glass to identify the effect of winter interlayer temperature and summer interlayer temperature in difference to simplified monolithic glass approach. As a result, significant increase of maximum principal glass stress and maximum deformation is observed for laminated glass subjected to blast load under summer temperature condition.

Parametric analysis on the heat transfer, daylight and thermal comfort for a sustainable roof window with triple glazing and external shutter

Roof windows are widely used in northern European countries, contributing positively by giving daylight, passive solar heat and view to the outside. In order to improve their thermal property, triple glazing unit together with external shutter are more and more common on the market. Additionally, the junction part between window and roof is also important since it greatly influences the linear thermal transmittance (LTT) along edges of the window and the daylight level of the room. This research presents a parametric analysis for roof windows with triple glazing unit and external shutter from perspectives of energy, daylight and thermal comfort. The investigation can be described in two parts:•Analysis of thermal and comfort performance for triple glazing unit with an external shutter.•Analysis of combined performance of daylight level and LTT for roof windows.Performances of energy and thermal comfort of triple glazing unit with external shutter can be influenced by different properties, including the width of the cavity between shutter and external pane, air penetration rate through the cavity between shutter and external pane, the tilt angle of the window. The study conducts analysis on the energy and comfort performances of the window by calculating U-value of the entire window and internal surface temperature of the glazing. The calculations are performed by a model developed via state-space modelling using Simulink/MATLAB. The results reveal that the external shutter improves both the thermal and comfort performances of the window.The ways of installing windows on a roof and cutting on the internal wall along window edges also have great influences on the combined performance of daylight level and LTT along the edge between window and roof. Therefore, daylight and LTT are also evaluated with different parameters, including the thickness of roof insulation, installation level of windows on the roof, cutting of lining and extra insulation around the perimeter of windows. The analysis is conducted using DIVA/Rhino and Flixo. The calculations show that the lower installation level and extra insulation around the window frame can decrease linear thermal transmittance of the entire window by more than 60%.

Influence of Pressure Equalisation Elements on the Quality of Insulating Glass Units

Abstract Continuous increase of expectations concerning improvement in quality of building partitions by means of increasing their thermal insulation properties brings, among others, a need of modification in standards that have been applied to the double glazed windows so far. Triple-glazed and quadruple-glazed IGUs are used more and more often. Such elements have better thermal properties, but they are more prone to deflection and stress resulting from climatic load, i.e. changes in temperature, atmospheric pressure and wind load. Due to the above certain concepts occurred that consist in equalising gas pressure in the gas-filled gaps with the atmospheric pressure. The article contains assessment of such solutions in the context of providing suitable technical parameters of glass panes: thermal insulation and susceptibility to climatic load. It was stated that the pressure-equalizing elements (capillaries) can result in a significant reduction in the quality of the glass partition in the event of the argon purging chamber or damage to the low-E emissions. The lower risk of using required thermal properties occurs when periodically active valves are used, they operate only in case of extreme pressure level differences. Further analysis concerned the idea of pressure equalisation between the gaps of a triple-glazed unit, as that can be done by using an edge spacer of appropriate design. On the basis of comparative analysis of static values it was shown that it is a reasonable solution. Such a unit maintains the properties of a tight unit, while the possibility of gas exchange between the gaps leads to relief of the central glass pane in the unit, thus allowing for decreasing its thickness to 2 mm.

Determination of total solar and visual radiation transmitted through triple glazing component with PCM layer

Modification of a glazing unit by application of PCM layer can lead to the increase of the heat capacity of the component and effective control of solar heat gains in buildings. The purpose of this study was to investigate the effect of the PCM layer on total solar and visual transmittance in solid, mushy (transition) and liquid state of PCM. The experiment was conducted in laboratory scale using triple glazed window unit sample and artificial sun as a source of solar radiation. The transmittance (total and visual) was calculated based on the results from pyranometers and illuminance meters taking into account the intensity of solar radiation at the level of 1000 W/m2. Measurements revealed that the component is almost blind in the solid state why in the liquid the transmittance is lower than for empty - traditional triple glazing. The transmitted radiation (total and visible) depends on the location of PCM layer (internal or external window chamber). The registered total solar radiation obtained in solid state was even 0 W/m2 (when material was on the inner side), while the maximum values for liquid was 142 W/m2 (material is located on the outer side). The light transmittance for more transparent case was around 1.6 klx and ten times higher in liquid than solid state.

A photochromic single glass pane

The transmittance of a photochromic (PC) window is reduced in sunlight but returns to its original value in the dark similar to photo-sensitive sun glasses. A 30 cm × 30 cm double glazed window containing a PC multi-layer coating on a single glass pane has been developed. A single PC glass pane can be used to build a window with a low heat transfer coefficient, e.g. double or triple glazed unit, using existing technology. To develop the PC glass with a multi-layered coating that combines chromogenic and photoactive materials we employed sol-gel chemistry approaches and up-scaled the synthesis. Double glazed windows have been assembled using PC glass with two different layer configurations. The transmittance (Tvis) was reduced from 76% to 35% under outdoor solar radiation (750 W/m2) within 15 min.

Phase Change Materials in Transparent Building Envelopes: A Strengths, Weakness, Opportunities and Threats (SWOT) Analysis

Building envelopes can play a crucial role in building improvement efficiency, and the adoption of Phase Change Materials (PCMs), coupled with transparent elements, may: (i) allow a better control of the heat flows from/to the outdoor environment, (ii) increase the exploitation of solar energy at a building scale and (iii) modulate light transmission in order to prevent glare effects. Starting from a literature review, focused on experimental works, this research identifies the main possible integrations of PCMs in transparent/translucent building envelope components (in glazing, in shutters and in multilayer façade system) in order to draw a global picture of the potential and limitations of these technologies. Transparent envelopes with PCMs have been classified from the simplest “zero” technology, which integrates the PCM in a double glass unit (DGU), to more complex solutions—with a different number of glass cavities (triple glazed unit TGU), different positions of the PCM layer (internal/external shutter), and in combination with other materials (TIM, aerogel, prismatic solar reflector, PCM curtain controlled by an electric pump). The results of the analysis have been summarised in a Strengths, Weakness, Opportunities and Threats (SWOT) analysis table to underline the strengths and weaknesses of transparent building envelope components with PCMs, and to indicate opportunities and threats for future research and building applications.

Responsive glazing systems: Characterisation methods, summer performance and implications on thermal comfort

In recent years, there have been several experimental and numerical researches on transparent envelope components that integrate phase change materials (PCMs). To address some of the drawbacks of these systems, new prototypes were created and their summer performance was monitored under Cfa climatic conditions (Turin, Italy). The proposed glazing system comprises a triple glazing unit with a thermotropic layer placed on the outer side, acting as a switchable shading system capable of regulating the phase transition of the PCM. The PCM is tested in both the inner and the outer cavity of the glazing, alternately. In this paper, the summer performance of these responsive glazing systems is reported, complementing the assessment of their performance under winter conditions, which was previously presented in another paper (Bianco et al., 2017). Two additional systems were also tested in parallel for reference purposes: a triple glazing unit with a thermotropic layer only, and a reference triple glazing unit. Direct solar transmission was assessed, and the correlation between glazing temperature and solar transmission coefficient of the thermotropic layer, when coupled with the triple glazing unit, was derived. The solar transmission as a function of the external surface temperature of the PCM glazing units was also evaluated. The energy performance was assessed by means of a long-term evaluation in addition to daily analyses during cloudy and sunny days. The capability of the aforementioned technologies to improve indoor thermal comfort was investigated, with the effect of the transmitted solar radiation impinging on the occupants also taken into account. The results highlight that the integration of a thermotropic layer in a triple glazing unit allows the cooling load through the transparent component to be reduced by one third when compared to a traditional triple glazing unit. The overall energy performance was found to be primarily affected by the position of the PCM; not only during winter season, but especially in summer, the PCM completed the phase transition only when placed in the outermost cavity. The thermal comfort conditions were improved, when evaluated in terms of traditional PMV, regardless of the position of the PCM layer. However, when the influence of the direct solar radiation impinging on the occupants was taken into account, the solution with the PCM layer located in the inner cavity presented a better performance.

Renovation of existing glass facade in order to implement energy efficiency and media facade

Modern cities and their architectural structures undergo significant functional and physical changes. In recent years, the interventions on building envelopes have increased. Therefore, it is necessary to analyse potential remodeling of glass facades, along with applying the concept of smart technologies, in order to increase energy efficiency of the existing buildings. This paper analyses the modernization process of devastated glass façade of the tall Slavija hotel, built in 1960s in Belgrade, Serbia, taking into consideration some positive examples of transformation and reskinning of buildings, where the aspect of medialization is an active part of urban renewal. The subject of this paper is the analysis of research findings about the improved thermal comfort of this building, after performing the replacement of its glass façade and converting the hotel building into an office building. Special attention was paid to the implementation of media technologies and final effects on energy balance of the newly designed facade.The proposed solution is supposed to evaluate the improved thermal comfort that was achieved by a radical renovation of the facade and by replacing the existing facade with a new single façade (double and triple glazed units), with media elements as well as without them. The research results are presented as proposals for improving EE public buildings by implementing the latest system of curtain walls in order to increase the value of the buildings. One of the most important criteria included in the process of energy refurbishment is technological improvement of the existing buildings, along with the presentation of media facades. The case study is based on EnergyPlus simulations.

Responsive glazing systems: Characterisation methods and winter performance

Responsive envelope components are promising technologies for improving the energy and indoor comfort performance of buildings. As far as the transparent envelope is concerned, several experimental and numerical researches have been carried out in recent years, focusing on the integration of Phase Change Materials (PCM) in glazing systems. To overcome some limitations highlighted during previous experimental campaigns, a new concept was prototyped, and the energy and comfort performance of a full-scale prototype was experimentally assessed in an outdoor test cell facility. In this paper, the focus is placed on the evaluation of the cold-season behaviour. The proposed glazing system comprises a triple-glazed unit with a PCM-filled cavity and a thermotropic glass placed on the outer side. The thermotropic glass acted as a switchable shading system capable of regulating the phase transition of the PCM by modulating the amount of solar radiation impinging on the PCM layer. The thermophysical and optical behaviour of the technology was monitored with the PCM alternately placed in the inner or the outer cavity of the triple-glazed unit and compared against a reference triple-glazing unit. In parallel to the measurements on the glazing with PCM and thermotropic glass, a triple-glazed unit equipped with a thermotropic glass was also monitored, giving a total of three different glazing systems under analysis. Representative days were selected in order to analyse the performance of the proposed technologies under significant and comparable boundary conditions. The equivalent thermal conductance of each technology was evaluated. The energy performance was assessed by means of both a long-term analysis and daily analyses on cloudy and sunny days. In addition, the visible transmittance of the three technologies was estimated through hourly measurements of vertical illuminance performed during a cloudy and a sunny day. Moreover, implications on thermal comfort conditions were evaluated ex-post by means of numerical simulations based on experimental data. The results showed that, during cloudy winter days, the position of the PCM did not influence the overall performance of the prototype since it never changed phase. On the other hand, during sunny winter days, the glazing with the PCM in the outer position underwent phase transition and presented a slightly better performance.

Thermal Induced Climatic Loads of Insulated Glazed Units in Energy Efficient Facades

Climatic loads on Insulated Glazed Units (IGU) have been investigated since the early 1990s. Beginning in 1996 a German technical guideline defined the procedure to respect climatic loads in static design of IGUs. Furthermore the required values of climatic changes and thermal changes of Double Glazed Units (DGU) have been determined. In practice, those values have been applied to other systems like Triple Glazed Units (TGU) as well as Double Skin Facades (DSF). In the last two decade’s those values haven not changed. This paper presents the results of a study on IGU’s in summer conditions, evaluating the thermal performance recent constructions. The upgrade from DGU to TGU causes a significant change of the thermal behavior. By adding a third glass layer, the middle glass gets insulated on both sides. In case of solar radiation the middle glass layer absorbs energy and is disabled to release energy. As a result, higher temperatures can be reached on TGU. By considering ventilated or not ventilated DSF’s, external or internal shading devices can influence further changes in the thermal behavior. This paper shows the development of an iterative calculation model by including present European standards. The model is able to deal with factors mentioned above. The results of different facade studies are shown and compared to the DIN 18008 standard. Furthermore the ongoing changes through European prestandards were discussed. Over all the study shows that a more sophisticated approach is necessary to determine correct temperature and climatic loads.

Thermal and Optical Properties of a Thermotropic Glass Pane: Laboratory and In-Field Characterization

Switchable windows are glazing technologies that exhibit dynamic optical properties and may thus be used to improve the energy performance of buildings. A window system based on a thermotropic glass pane was tested both in the laboratory and by means of an outdoor test cell facility.In this paper the full optical and thermal characterization of this glazing technology is presented. Experiments and data analysis led to the characterization of the behaviour of the thermotropic glazing both when this technology is used alone (single glass pane) and when it is integrated in a multilayer fenestration (a triple glazed unit).

Experimental Analysis of an External Dynamic Solar Shading Integrating PCMs: First Results

This paper presents the first results of an experimental analysis on dynamic translucent solar shadings with PCM, aimed at demonstrating its potential on reducing internal solar heat gains. The study is focused on the assessment of the thermal performance of the prototype panel during the solid phase of the PCM through an experimental campaign in a test cell facility. The total daily solar heat gains were reduced by more than 50% compared to the non-shaded reference triple glazing unit and the internal surface temperature of the glazing decreased of more than 6°C during the maximum external incident solar radiation.

Novel hybrid vacuum/triple glazing units with pressure equalisation design

Vacuum glazing units (VGUs) are thought to be a type of glazing system with superior effective insulation performance. However, the differential pressure between the outside and the inner spaces and the supporting pillars create a high pre-existing stress field in the constituent glass during fabrication and hence make the units highly susceptible to breakage, even under small applied loads. In order to address this problem, a novel hybrid vacuum/triple glazing system with a pressure equalisation design has been devised and is reported in this paper. In this system, a VGU is enclosed by two glass panels to form a triple glazing unit system. This new design creates an equalised air pressure on both sides of the VGU hence subjects the VGU to no additional loads apart from the inherent fabrication stresses. This results in a high thermal and sound insulation as well as a more durable safety performance of the hybrid glazing component. Pressure tests were undertaken on the novel glazing system to confirm its reliability. Results show that under various loading levels, the stresses and deflections in the VGU of this novel glazing system always remain at a marginal level, and hence the likelihood of breakage for VGUs can be reduced significantly.

Experimental Analysis of an Advanced Dynamic Glazing Prototype Integrating PCM and Thermotropic Layers

Glazing components are the most challenging element of the building envelope system. The insertion of a Phase Change Material coupled with a thermotropic layer is herewith proposed as an innovative solution aimed at improving the energy performance of the fenestration. The intention is to increase the dynamic features of glazing systems and to enhance their capability of exploiting solar energy – a crucial feature in nearly Zero Energy Buildings.The paper presents the experimental analysis of two prototypes of such a glazing concept and the assessment of their energy performance during the warm season. The samples are installed on an outdoor thermostatic cell facing south, together with a reference triple glazed unit, and continuous measurements of temperatures, irradiances and heat fluxes are performed. In the summer season, when the aim of the glazing system is to reduce the solar gain and to allow daylighting the energy performance is very promising. When compared to the reference technology, both the prototypes are able to reduce to a great extend the direct transmitted solar energy, as well as to smooth the peak indoor surface temperature of the glazing. In particular, one of the two configurations lowers down the solar energy gain under all boundary conditions, while the other configuration presents a slightly worse performance than the other prototype when high solar irradiation occurs. An attempt to measure the thermal transmittance was also carried out and it is shown that the insertion of PCM does not increase the U-value of the component.

Heat Transfer Performance of Glazed Units in Dual Airflow Windows

The purpose of this paper is to derive a new method to research heat transfer performance of special glazed units in dual airflow windows because of their special structure and function. The equivalent height has been defined to conduct the analysis of this specificity. Two models names ISO and EN have been built and tested by experiment. The results calculated by the models are compared to ensure the conclusions are correct. Meanwhile two models lead to better understanding the rules of heat transfer in a triple glazed unit.

Performance of coupled novel triple glass unit and pcm wall

Abstract A PCM wall includes phase change material (PCM) as a heat storage medium. In the current project, the south facade of a test room was constructed using PCM walls that were made of (from inside to outside) insulation, brick, plaster (including PCMs), an air gap and a novel triple glazing unit (TGU). Although the annual behaviour of the PCM walls were investigated in the project, the current paper covers an evaluation of the performance of PCM walls in the summer only. The solar transmittance of the TGU decreased approximately 100% during summer compared to winter. There were no overheating problems observed for the PCM wall during the summer.