Glazing Units Research Articles

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.

Vacuum glazed units – energy efficient glazing

The article summarizes the prerequisites for the improvement of translucent structures in terms of energy conservation. It is noted that there is a high potential of application of vacuum glazed units. On the basis of EN 673 and the application of numerical methods, a research was made to calculate the theoretical thermal resistance on the pillars and between them, and a thermal resistance of a central part of a vacuum glazed unit taking into account a heterogeneity. To compare with theoretical values, experimental laboratory examinations on a model vacuum glazed unit and a conventional single-chamber glazed unit were conducted using methods of GOST 26602.1-99. The data obtained from measuring sensors of temperature and thermal flux was processed using thermal imaging. The areas of pillars influence and the given resistance of the central part of the vacuum glazed unit were calculated. The results obtained from practical and theoretical studies showed high convergence. The accuracy of the experiment is confirmed by taking simultaneous measurements of the vacuum, and the conventional single-chamber glazed unit. It should be noted that confirmed high thermal qualities of vacuum glazed units can be compared with the required heat conductance values of Moscow for non-translucent wall constructions. A brief economic analysis is done to determine the practicability of application of vacuum glazed units.

Experimental performance characterisation of a Hybrid Photovoltaic/Solar Thermal Façade module compared to a flat Integrated Collector Storage Solar Water Heater module

A modular Hybrid Photovoltaic/Solar Thermal (HyPV/T) Façade technology that utilizes Integrated Collector Storage (ICS) solar technology, providing cost effective solar PV and thermal energy collection for direct use in the building, whilst providing significant thermal insulation has been developed and evaluated experimentally at Ulster University. The HyPV/T system, based upon a patented ICS solar thermal diode concept and shaped into a flat modular profile incorporating PV cells/module can provide space heating, domestic water heating and power generation. The complete system is designed to be compatible with traditional façade structures and fenestration framing arrangements, facilitating direct integration into new and retrofit building applications.The experimental performance of HyPV/T unit has been determined and compared with a flat Integrated Collector Storage Solar Water Heater (ICSSWH) under constant indoor solar simulated conditions. The daily thermal collection efficiencies for the ‘traditional’ flat ICSSWH units performed better than the unglazed HyPV/T, by 5–10%. However, when the additional electrical power produced by the HyPV/T is included, the overall system collection efficiencies are more equal. The heat retention performance shows that's the unglazed (bare) ICS unit had a retention efficiency of 8.3% whilst the ICS unit with a single transparent cover was 23.6% and double glazed unit was 28%. The HyPV/T heat retention efficiencies were approximately 65% over the same cool-down period.

Analysis of a non-calorimetric method for assessment of in-situ thermal transmittance and solar factor of glazed systems

The performance of glazing systems is usually assessed through the thermal transmittance and the solar factor, two metrics characterised either through calorimetric laboratory tests or calculations. In this paper, the analysis of the performance of a non-calorimetric method for obtaining the in-situ thermal transmittance and solar factor of glazing systems is presented. This method, developed as a trade-off between accurate (and expensive) laboratory tests (which characterise the systems under standardised, “averaged” conditions), and easy and less expensive tests on systems installed in real buildings (under real operative conditions), has been previously adopted for the characterisation of different glazed systems, but never presented and discussed in full detail.The method, suitable for full-scale glazing systems installed in buildings or in test cells, is based on the acquisition of temperature, heat flux, and solar irradiance values. Experimental data are then processed through simple equations and linear regressions to determine the thermal transmittance and the solar factor under real boundary conditions. In this paper, a detailed description of the method, the experimental test rig, and the related expected accuracy is reported. The method is then applied to a case study (a conventional double glazed unit) to give an example of the proposed procedure and to validate it.The results of the case study show the capability of the assessed in-situ thermal transmittance and solar factor to replicate the thermophysical behaviour of the glazing system within a satisfactory degree of accuracy. An in-depth discussion on the observed outcomes from the case study deepens the understanding of the method’s performance and the results’ significance.

A systematic workflow for retrofitting office façades with large window-to-wall ratios based on automatic control and building simulations

Fully glazed façades are still preferred by many architects due to their aesthetic features. Although this choice offers opportunities for daylighting and view contact with the outside, it can lead to overheating and glare problems if climate is not taken into account in the design. This paper presents a workflow for retrofitting that can be applied to different office façades with large window-to-wall ratios. The workflow consists of analysing the space from the point of view of the functions of its façade and then applying a retrofitting strategy based on state-of-the-art building simulations and automated shading control. The proposed workflow is illustrated by a case study at an office in Malaga (Spain), in which the originally installed, manually-controlled interior vertical blinds are replaced with automatically controlled interior roller blinds with a metallized reflecting surface facing towards the glazing unit. A full optical characterization of the roller blinds is presented. A simulation-based control strategy is applied to the motorized roller blinds in order to maximize view contact with the outside and daylighting while controlling glare and overheating.

Modeling of facade elements with switchable U-value

In this contribution, a new model of switchable insulation element is introduced. This element essentially consists of a double glazing unit with a translucent insulating panel mounted inside. Switching of the U-value is achieved by control of an internal convective flow around the insulation panel. The element can be in an insulating state with a low U-value, or in a conducting state with a high U-value. First the new model of the element, based on numerous thermal, hydraulic and optical assumptions, is introduced. The airflow rate is calculated by balancing the pressure drops and the buoyancy driving force. The model is validated against U-value measurements, showing a reasonable accuracy. Finally, the model is used for a parametric analysis, where the influence of different thermophysical properties on the U-value and g-value of the element in insulating and conducting state is investigated.

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.

Material Selection for Cable Gland to Improved Reliability of the High-hazard Industries

The sealed cable glands (SCG) are available to ensure safest connection sheathed single wire for the hazard production facility (nuclear power plant and others) the same as pilot cable, control cables, radio-frequency cables et al. In this paper, we investigate the specifics of the material selection of SCG with the express aim of hazardous man-made facility. We discuss the safe working conditions for cable glands. The research indicates the sintering powdered metals cables provide the reliability growth due to their properties. A number of studies have demonstrated the verification of material selection. On the face of it, we make findings indicating that double glazed sealed units could enhance reliability. We had evaluated sample reliability under fire conditions, seismic load, and pressure containment failure. We used the samples mineral insulated thermocouple cable.

Energy performance of an electrochromic switchable glazing: Experimental and computational assessments

This paper describes the results of experimental tests and computer simulation modelling aimed at evaluating the performance of an electrochromic (EC) window with respect to solar radiation control and the relative impact on the energy consumption of buildings of the residential type for two typical Italian climates. The research is carried out by a test-cell equipped with a small area EC double glazing unit and by a simulation program of buildings’ energy behaviour in transient regime. The experimental results show that EC devices which modulate solar radiation mainly by absorption, like the one investigated in this paper, generate secondary solar heat gains which entails a 20% decrease of the maximum potential energy flux reduction. Also, this effect could rise the temperature of the internal glass pane of the glazing to levels for which risk of thermal discomfort for the occupants may occur. The computer simulation modelling involves a residential building unoccupied during a large fraction of daytime in weekdays. The savings potential of the investigated EC window are calculated relative to a conventional clear float double glazing unit. Results show that the EC glazing may lead to a considerable decrease of the cooling energy demand (and of the total building energy consumption) in cooling dominated climates. The energy saving benefits become less marked in heating dominated climates and, for low values of the window-to-wall ratio, can be overcame by the increase in lighting and heating energy requirements that results in an increase of the total building energy demand.

Experimental investigation of optical and thermal performance of a PCM-glazed unit for building applications

In present work, optical and thermal performances of a PCM-glazed unit were experimentally investigated compared with that filled with air, and the influences of solar irradiance, melting temperature and PCM layer thickness on three parameters were analyzed including the transmittance, the temperature difference between upper and bottom surfaces, and the interior surface temperature of the glazed unit. The results show that the thermal performance of glazed unit filled with PCM is improved compared with that of air, and transmittance of glazed unit is 50% when the PCM is liquid. Solar irradiance and PCM layer thickness both have effects on the optical and thermal performance of glazed unit, but the effect of melting temperature on thermal performance can be neglected. Increasing the PCM thickness can effectively decrease the heat loss of glazed unit filled with PCM, but the PCM thickness in the glazed unit is not beyond 16mm considering the optical performance of glazed unit.

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.

Experimental study on fire response of double glazed panels in curtain walls

Double glazing is increasingly employed in glass curtain walls, but very little is known about its thermal response under fire conditions. In this work, a total of twenty seven 600 × 600 mm2 double glazing units, with 6 mm, 9 mm and 12 mm air spacings, were tested. Three different installation types were adopted: 1) exposed frames, 2) horizontal-hidden frames and 3) vertical-hidden glass in order to study their potential effects on the glazing breakage behavior. A 500 × 500 mm2n-heptane pool fire was used to heat the glass panes. The breaking time, surface temperature, total heat flux, heat release rate, and crack and fallout morphology were measured and analyzed. The test result suggests that different installation types have a significant effect on the fracture behavior of double glazing, especially for glass panes located at the fire side. Glass in exposed framing is more prone to cracks than those in semi-exposed frame, but fallout may more easily occur in semi framing façades. When no, or very limited fallout occurs at the fire side pane, thicker air space leads to a longer breakage time of ambient glass panes, thus improving the unit's integrity during fire. The experimental results obtained in this study is valuable for the development of practical guidelines for fire safety design.

Experimental Characterization and Energy Performances of Multiple Glazing Units with Integrated Shading Devices

Modern architecture is characterized by the use of large glazed surfaces. New technologies ensure thermal insulation by multiple glazing units so that, maintaining good solar gains, highly glazed buildings can achieve good energy performance during the heating season. More complicated is the management of the energy performance during the cooling season due to high permeability to solar radiation. External shading devices are a suitable solution but they are often neglected for functional and aesthetic reasons. Solar protection devices can be, however, introduced in the air gap of multiple glazing units, providing solar protection without interfering with the building envelope. Solar and thermal properties of several solution of glazing units with in-gap shading devices were measured with advanced experimental set-up, to be compared with conventional systems. Numerical analyses were also performed to estimate the impact of this technology on the energy performance of office buildings.

Effect of PCM thickness and melting temperature on thermal performance of double glazing units

The phase change material (PCM) applied in the glazing unit is an effective approach to decrease the building energy consumption and improve the utilization efficiency of solar energy, which makes a better thermal performance of glazing. In the present work, thermal performance of a PCM-filled double glazing unit with different thickness of phase change material in winter was investigated numerically in the cold area of Northeast China with the melting temperature 14–16°C, 16–18°C and 18–20°C. The validation of the calculation model with experimental data was accomplished, and a good agreement of the temperature field between simulations and experimental data can be found. Then effect of thickness and melting temperature of PCM on thermal performance of double glazing units was investigated and the relevant parameters were analyzed. The results show that the interior surface temperature increases by 158.7%, the total transmitted energy decreases by 109.1% and the transmitted solar energy decreases by 86.1% when PCM thickness is 50mm, compared with its thickness 4mm. With the increasing of PCM melting temperature, its utilization decreases. When the thickness increases from 4mm to 30mm, the liquid fraction increases, but the condition is reverse when it continues to increase to 50mm. So considering all parameters, the thickness 12–30mm and the melting temperature 14–16°C is recommended in Northeast China.

Phase Change Materials in Glazing: Implications on Light Distribution and Visual Comfort. Preliminary Results

Abstract The visual comfort concerned witha technology with PCM embedded into a double glazing unit was analyzed, using the Daylight Probability Glare and the ‘Useful Illuminance’ (percent of workplane with an illuminance in the range 100-3000 lx). A sample office room was modeled using Radiance, under a clear sky and with the facade facing south. The visible transmittance of PCM was measured in laboratory and used as input in Radiance. The simulations were carried out for the two solstices and the Autumn equinox (four hours per day), for three sites (Ostersund, 63.2°N; Turin, 45.2°N; Abu Dhabi, 24.4°N), considering the solid state of the PCM only.

Smart windows—Dynamic control of building energy performance

This paper explores the potential of thermotropic (TT) windows as a means of improving overall building energy performance. Capitalising on their ability to dynamically alter solar and visible light transmittance and reflectance based on window temperature, they have the ability to reduce solar heat gains and subsequently reduce cooling loads when the external conditions exceed those required for occupant comfort. Conversely when the external conditions fall short of those required for comfort, they maintain a degree of optical transparency thus promoting opportunities afforded by passive solar gains. To test their overall effectiveness, thermotropic layers made of varying hydroxypropyl cellulose (HPC) concentrations (2wt.%, 4wt.% and 6wt.%) were firstly synthesised and their optical properties measured. Building performance predictions were subsequently conducted in EnergyPlus for four window inclinations (90°, 60°, 30° and 0° to the horizontal) based on a small office test cell situated in the hot summer Mediterranean climate of Palermo, Italy. Results from annual predictions show that both incident solar radiation and outdoor ambient temperature play a significant role in the transmissivity and reflectivity of the glazing unit. If used as a roof light, a 6wt.% HPC-based thermotropic window has a dynamic average Solar Heat Gain Coefficient (SHGC) between 0.44 and 0.56, this lower than that of 0.74 for double glazing. Predictions also show that in the specific case tested, the 6wt.% HPC-based thermotropic window provides an overall annual energy saving of 22% over an equivalent double glazed unit. By maintaining the thermotropic window spectral properties but lowering the associated transition temperature ranges, it was found that the lowest temperature range provided the smallest solar heat gains. Although, this is beneficial during periods where cooling may be needed, in those periods where heating may be required, opportunities gained through passive solar heating are limited. In addition, with lower solar heat gain, there is a possibility that artificial lighting energy demand increases resulting in additional energy consumption.

Study on Thermal and Optical Properties and Influence Factors of Aerogel Glazing Units

Aerogel glazing units (AGUs) is a high-performance building glazing which can effectively reduce energy consumption due to its thermal and optical performance. In this paper, the effect on thermal and optical properties of AGUs with different particle sizes and filling thicknesses were investigated. The results indicated that visible light transmittance and solar direct transmittance of AGUs palpably increased as the particle size increased from 0.41mm to 0.93mm, while it lightly changed as the particle size continued to increase from 0.93mm. The heat transfer coefficient decreased by about 15% when the particle size was reduced from 2.7mm to 0.41mm. In conclusion, the increase of the thickness of aerogel can effectively decrease visible light transmittance, solar direct transmittance and heat transfer coefficient. Finally, color rendering index(CRI)the AGUs with different particle sizes and filling thicknesses were investigated and AGUs show good color performance.

Correlations for glazing properties and representation of glazing types with continuous variables for daylight and energy simulations

In daylight and energy simulations, fenestration products are characterized by their visible transmittance (VT) and solar heat gain coefficient (SHGC) that are both dependant on the angle of incidence, as well as by their U-value. In this work, 18 typical fenestration products suitable for the Canadian context were chosen and correlations between their actual properties were developed. First, it is shown that variations from a “standard” angular dependency curve for VT and SHGC are relatively small in such a way that the angular dependency can be approximated either by an average relation for all fenestration types, or by more precise correlations involving a linear combination of solutions with the use of a weigh coefficients. Then, relationships between values of normal VT, U-value and normal SHGC are established. In the end, it was possible to deduce the detailed behavior of all insulated glazing units (IGU) from only one continuous variable. A more precise approach with three continuous variables was also developed. A test case is presented to illustrate how to use the correlations to generate different types of IGUs in simulations.