Glazing Units Research Articles

Synthesis of Antennas for Active Glazing Unit with Photovoltaic Modules

The problem considered in the paper concerns the synthesis process of antennas for autonomous semi-passive RFID transponder/sensors dedicated to active glazing units. Glazing units are frequently used in modern multi-storey buildings to create amazing facades. When they are integrated with photovoltaic (PV) modules, active units are obtained. It is desirable, mainly for economic reasons and in order to ensure the high efficiency of a micro-photovoltaic power plant, that active glazing units are equipped with a system for monitoring their operating parameters. In connection with this, design problems occur that fall within the fields of sensor technology and radio communications. The main purpose of the presented study was to prepare appropriate input data for design tools used in the synthesis of antenna systems in the UHF band. Many important issues are considered including: proximity to structural elements of the building facade and PV cells, which disturbs the shape of the radiation pattern and affects the impedance parameters of the antenna system; the need to ensure easy integration of the RFID sensor and the specified object, without significant interference in the production of glazing units; appropriate shaping of the radiation pattern in order to enable reading and writing of the RFID tag from both inside and outside the building; impedance matching to the selected RFID chip in the broadest possible frequency range, etc.

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 ($/m 2 ) 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 $/m 2 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 $/m 2 . The findings of this paper demonstrate the significance of triple-glazing design approaches from an economic and environmental point of view. • Reflective triple glazing design strategies for reduced air-conditioning costs. • Diurnal illumination levels through reflective triple glazing systems. • Operational energy and net annual cost savings of reflective triple glazing systems. • Color rendering index and quality of daylight through triple glazing systems.

Conventional and Advanced Glazing Technologies for Enhancing Thermal and Lighting Performance

Glass is one of the oldest man-made material that is widely used in architecture. As it is a translucent material, it permits a full penetration of direct sunlight but may also increase the internal space temperature and then increasing cooling loads and energy consumption. As the need for energy optimization is very important and glazing is considered a weak point in any building, the selection of glazing assumes tremendous significance. This paper reviews the different types of glazing which can be categorized into conventional and advanced to optimize the thermal and the lighting performance according to their properties and insulation values. Conventional glazing includes the clear glazing whether it is single double or triple, the tinted glazing, the reflective glazing, and the low-E glazing. Advanced glazing which is mainly the insulated glazing unit such as the gas filled glazing, the vacuum glazing, the aerogel glazing and the phase change material glazing.

Study on dynamic thermal behavior of double glazing unit filled with phase change materials

Glazing units are indispensable for a variety of buildings and their thermal behavior has significant effects on improving indoor thermal comfort and decreasing energy consumption. Recently, the double glazed windows that are filled with phase change material (PCM) have been considered as potential glazing units. Therefore, the dynamic thermal behavior of the PCM-filled double glazing unit is investigated in this work. A three-layer glass-PCM-glass model considering coupled conduction-solar radiation-phase change is established. Effects of physical parameters of the PCM on the thermal behavior of the PCM-filled glazing unit are examined thoroughly. The results indicate that the filling of PCM can affect heat transfer within the glazing unit significantly by reducing solar energy entering the indoor room through the window. When the glass-PCM-glass model is adopted, the transmitted solar energy can be reduced by 78.82 W/m2. Optical parameters (especially absorption coefficient) of the PCM have significant impact on the thermal behavior of glazing units: the larger the absorption coefficient is, the less solar energy will enter indoors, and the larger will be the temperature fluctuation. For different absorption coefficients, the maximum temperature difference on the interior surface can reach 3.57°C. Thermal properties of the PCM also have significant impact on the thermal behavior of glazing units. Decreasing the thermal conductivity or increasing the latent heat of the PCM can reduce the temperature fluctuation of the glazing windows. Selecting a reasonable melting temperature can make full use of the heat storage capacity of PCM. Thus, this study can provide a reference for how to apply PCM into a transparent envelope in buildings.

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.

Dynamic thermal stress analysis of PCM-glazed unit under intermittent solar irradiation

ABSTRACT In this study, a multi-physics coupled mathematical model was established on thermal stress distribution of double-glazed units with phase-change material (PCM-glazed) for the transient temperature fields and non-uniform intermittent solar irradiation, and the mathematical calculations are in good agreement with the experimental results, which shows that the developed model in present work can solve the coupled thermal stress distribution problem between phase change and intermittent solar irradiation in the PCM-glazed. A case that is the thermal stress distribution on the surface of glazed unit filled with paraffin under the outdoor variable temperature and non-uniform intermittent solar irradiation was studied in autumn in cold region of China. The results show that the stress produced on the surface of glazed unit filled with paraffin varies obvious, PCM layer between the glass panes significantly affects the stress values at different time, which can, respectively, reach up to about 4.59MPa and down to −3.9MPa for tensile and compressive strains once the paraffin in liquid state, due to improved thermal conductivity of PCM throughout phase transition to liquid. Additionally, the frame is the key factor causing temperature gradient of PCM-glazed unit, and the biggest tensile stress appears at the edge. The influence range of the frame on the surface temperature and stress of the PCM-glazed unit is limited and different, and the largest influence distance of the surface temperature and stress from the edge is 0.1 m and 0.03 m, respectively.

Thermal stress performance of glazed units contained phase change material

The low heat transfer and high energy storage performance of phase change material (PCM) will improve the thermal performance of the PCM-glazed units. However, decreasing the heat transfer results in uneven thermal load on the surface of the PCM-glazed units, which is an important cause of thermal stress in such units, because the glass in glazed units is a fragile material, and then large thermal stress can result in cracks and possible fallout of the glazed units. To study the thermal stress distribution of PCM-glazed units, a method combined numerical simulation and experimental analysis was conducted. First, the heat transfer performance and thermal stress distribution of PCM-glazed units with PCM thicknesses between 3 and 11 mm were experimentally investigated. Results showed that the thermal performance of a glazed unit was improved by adding PCM, and the variation of thermal strain on its surface with a PCM-layer thickness of 7 mm was the smallest in five test facilities. Then, the thermal stress was numerically investigated regarding the PCM height and the aspect ratio of the PCM-glazed unit. The higher the PCM height, the greater the maximum strain. An aspect ratio of PCM-glazed units of 1.5 was recommended.

Thermal-energy and lighting performance of aerogel glazings with hollow silica: Field experimental study and dynamic simulations

The excellent thermal insulation properties of aerogel glazing systems make them an interesting building solution, especially in cold climates. When aerogel glazing systems provide less solar heat gain factor, they could be useful in warm and hot regions (such as Tokyo, Rome and so on) because buildings in such areas are often designed to minimize cooling energy demands. If a sort of opaque powder is mixed with aerogel granules, able to stick to each granule and to cover the aerogel surface discontinuously, the mixture can thus reduce solar transmittance, contributing to daylight usage with less glare risks and cooling energy demand reduction, without shade or blinds, keeping as high thermal performance as aerogel. This innovation is examined in the present paper, by presenting the following solution: a double glazing unit with a mixture of silica granular aerogel and hollow silica powder in the gap (AGS), in order to reduce the solar factor. The solution is tested through in-field experimental campaigns and numerical analyses, making available a set of data not found in literature, where mixtures of aerogel and powder were never studied. The air temperatures in the test Room with AGS, especially the peak values, are lower than the ones in the reference one with installed a standard glazing system (SGS). The same behaviour is observed in several experimental campaigns in different seasons: in mid-season 1 the highest differences are of about 6–7 °C, whereas in summer they reach 12–16 °C. Significant differences in terms of illuminance are also observed: the calculated Useful Daylight Illuminance (UDI) shows AGS values 57% higher than SGS, highlighting the aerogel ability to diffuse light and to reduce glare. Experimental data were used for energy analyses of a reference building in Tokyo. AGS outperforms a low-e glazing in terms of heating energy demand: the reduction varies in the 22% (North) − 62% (South) range. The lighting energy demand is quite similar: electricity demand increases in the 3–6% range. Finally, the internal shade on the reference glazing has a significant impact on the estimated energy demand, both for cooling and heating.

Numerical analyses of the sound transmission at low frequencies of a calibrated Insulating Glazing Unit

The acoustic performances of building elements such as windows are carried out in laboratory according to standards. In addition to the high cost of the experimental tests, the measurements at low frequencies face some difficulties such as the lack of reproducibility, the rooms’ modal behaviour effect and the diffuseness of the acoustic field. To separately study each source of deviation from the ideal experimental situation, four numerical configurations, based on experimental conditions, are proposed to characterize the transmission loss (TL) of an Insulation Glazing Unit (IGU) below 500 Hz. The effect of the emitting and receiving rooms with a comparison to the ideal configuration which has a free field on both sides of the IGU are investigated. The numerical model used for the IGU is calibrated from an Experimental Modal Analysis. As expected, TL results show that there is a significant effect of the modal behavior and the acoustic properties of the rooms at low frequencies. Numerical results are compared to those obtained from experimental tests and a good agreement in the all frequency range of interest is observed. In addition, parametric studies are carried out to investigate the influence of the variation of some properties of the studied structure such as the structural damping and the panel’s thickness.

Thermal performance testing of triple-glazing water flow window in cooing operation

Water flow window is an energy efficient multi-glazing system with water flowing in the window cavity. Proper thermal insulation is crucial to enhance the related energy and cost saving. In this paper, the insulation performance of vacuum glazing (VG) and insulated glazing unit (IGU) in triple-glazing water flow window is explored. Experimental testing was completed during cooling season of Chengdu, China. The benefit of water application in window is also analyzed based on the testing results.The insulation performance of VG and IGU is found comparable when applied to water flow window in air-conditioned space. The additional water stream is quite effective in lowering the glazing surface temperature. Comparing water flow window and those without water supply, the reduction can be as large as 4.81 °C for inner glazing and reaches 10 °C for outer glazing. Also, the inner glazing surface temperature fluctuation can be narrowed with water flow window, and the performance of VG insulation water flow window (VWFW) is more favorable comparing to IGU insulated water flow window (TWFW). Thermal performance of water flow window as thermal collector is also promising. The daily thermal efficiency of VWFW and TWFW are in the ranges of 24.69–45.95% and 21.9–36.13% respectively.

Energy Efficient Smart Plasmochromic Windows: Properties, Manufacturing and Integration in Insulating Glazing

Abstract Dual band electrochromic windows enable selective spectral control of the incoming solar radiation in buildings and can therefore efficiently respond to their ever-changing lighting, heating and cooling requirements. They allow indeed to selectively filter out near-infrared solar radiation passing through the window, thus blocking solar heat gain during hot summer days and increasing it over sunny winter days, whilst regulating the amount of daylight in an independent manner. We herein present advancements in the manufacturing and the performance of screen-printed dual-band electrochromic devices (herein referred as “plasmochromic”) embodying stable gel electrolytes. Particularly three different sets of polymeric hosts, respectively based on PMMA/PEO-, PVB- and PVDF, are characterized for such integration. Most suitable formulations have been adopted to manufacture and test up to 30 x 30 cm2-large smart window prototypes. Based on the values of TLUM, TSOL, and total solar heat gain coefficient (g-value) calculated from the measured transmittance and reflectance spectra, a preliminary assessment of the device optical and thermal performances for architectural integration in insulated glazing units is carried out, compared with the performances of competing commercially available solar control and smart glazing IGU. The results demonstrate the potential of the proposed “plasmochromic” technology in reducing the energy consumption and maximizing both visual and thermal comfort in architectural glazing systems.

Study on the influence of key parameters of exterior window structure on building energy saving effect

On account of the problem which was related to the negative effect of exterior windows energy saving in current residence building, we constructed a single energy-saving building with same structure and different exterior windows. Meanwhile, taking indoor temperature field and building energy consumption as entry points, the key parameters of the energy saving effect of the exterior window were compared and analyzed to study the indoor temperature field and the building thermal load and cooling load in the heating, cooling and transition season of energy-saving buildings which had exterior window structures (standard external windows, blue heat-absorbing glass windows, thermal reflection glass with high light transmission, ordinary hollow glass windows, low-E insulating glazing units, low-E high through glass windows, ordinary 3mm glass windows) with different window frames under the same climate environment. In addition, the grey theory and regression analysis were used to get the correlation degree and matrix equation between the energy-saving effect (the indoor temperature in heating season, the indoor temperature in refrigeration season, the indoor temperature in transition season, the annual cumulative heat load index, the annual cumulative cooling load index, the heating season heat load index, the air-conditioning season cooling load index) and key parameters (the glass thickness, the air layer thickness, the glass layer number, the heat transfer coefficient, the solar heat gain coefficient, the shading coefficient, the solar transmittance, the solar reflectance, the visible light transmittance, the visible light reflectance) in energy-saving buildings.

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.

Thermal efficiency of PCM filled double glazing units in Egypt

Recent research has been focusing on using various media in glazing cavities to minimize heat transfer through translucent elements of buildings. During this study, the thermal efficiency of a Phase change material (RT28HC) glazed unit was experimentally investigated compared with that filled with air in dry arid region. Then, the effect of PCM thicknesses on the thermal efficiency of double-glazing unit (DGU) was investigated using Fluent software including internal temperature, temperature time lag, total transmitted energy, and liquid fraction. The results indicated that the effect of using PCM on room temperature is high. The internal layer's peak temperature time lag in PCM-filled DGU was around 5 h than common DGU. Also, increasing the PCM thickness can effectively improve thermal performance parameters till thickness 30 mm, and more thickness can reverse the variation trend. Hence, these outcomes could contribute to the thermal regulation of highly glazed buildings in dry arid region of Egypt.

Thermal performance of hybrid vacuum glazing installed in the wood-aluminium frame

The current development in building energy efficiency towards nearly zero energy buildings (nZEB) represents a number of new challenges to design and construction. One of these major challenges is lowering the need for heating by means of highly insulated glazing units, unique glazing technologies, such as vacuum glazing (VG) or hybrid vacuum glazing (HVG). Hybrid vacuum glazing combines vacuum glazing with double glazing technology by adding one low-emissivity glass to the vacuum glazing using a thermally-improved spacer profile to eliminate the thermal bridge at the edge of the vacuum glazing. The gap between the vacuum glazing and the low-emission glass is filled with the inert gas Argon. The thermal performance of a hybrid vacuum glazing was tested using the guarded hot box method developed in accordance with the requirements of ISO 8990. Hybrid vacuum glazing has thermal transmittance about 0.43 W.m−-2.K−1.

Green’s functions for the load sharing in multiple insulating glazing units

Insulating Glazing Units (IGUs) are glass panes held together by structural edge seals, entrapping a gas for thermal and acoustic insulation. The bending of one pane induces pressure variations in the cavities, which produce the load sharing through the gas with the other panes. Under mild hypotheses, the whole IGU behaves as a linear elastic system. Hence, for IGUs with panes and cavities of any number, shape, size and edge constraints, the Green’s functions can be defined for the pressure variations and the pane displacements, so that these quantities can be expressed as convolution integrals with any applied load. The proposed Green’s functions are calculated with a tailored used of Betti’s reciprocal work theorem, referred to as Betti’s Analytical Method (BAM), here generalized to multiple IGUs with N panes. Remarkably, the Green’s functions for the pressure variations in the cavities are completely determined by the deformation field of a simply-supported plate, with the same shape of the IGU, under uniform pressure: this represents the universal expression, possibly tabulated, covering all possible cases. The proposed approach is validated through comparisons with prescriptions by standards and numerical simulations. Parametric analyses show the effect of the IGU geometry on the load sharing.

Is the thermal transmittance of air-filled inclined multi-glazing windows similar to that of vertical ones?

By focusing on the effect of inclination angle on the thermal transmittance of glazing systems, this paper investigates the flow structure and heat transfer of air-filled uncoated multi glazed windows since the design of inclined windows are mostly considered as vertical ones in the construction sector. Revealing the influences of tilt angle on the energy saving performance of these type of window units is one of the main objectives of this study in which the examined parameters are not limited to inclination angle, which is considered from θ = 0 to 90°, but also includes air layer thickness ranging from L = 6 to 18 mm and number of panes (namely, double, triple and quadruple pane window units, without considering the window frames and edge seals). The outcomes of the computations are presented by streamline and isotherm contours which give a solid opinion about the flow and heat transfer inside the gap of the glazed windows, and also U-values which provide a quantitative understanding. The results showed that the air layer thickness optimized for vertical glazing units can be considered for inclined installation on condition that θ ≥ 45°. However, at lower inclination angles the air layer thickness should be optimized considering the inclination angle and number of panes as increasing the layer thickness above L > 9 mm may increase the thermal transmittance of glazing unit. The risk of increasing U-value with larger air layer applied to inclined surface reduces by using more panes.

Influence of sunspace on energy consumption of rural residential buildings

In this work, a detailed investigation is carried out to evaluate the effects of using sunspace on heating energy consumption of a rural house by considering utilized sunspace glazing type, the filling gas type and the gas layer thickness. In the first part of the study, the effect of a sunspace on the energy consumption of a typical rural building located in a severe cold region of China is investigated. The results showed that the sunspace having single pane reduces the energy consumption by about 4.6% with respect to the reference building considering the coldest month, January. In addition, sunspace with double glazed unit is investigated and compared with the singleglazed. It is observed that a larger amount of energy (11.3%) is saved compared to the reference building in January, and the optimum air layer thickness of double glazed sunspace is determined as 12 mm. In the second part, different filling gasses (air, argon and krypton) are taken into account to optimize the gas layer thickness with respect to filling gas. It is found that the thickness of gas layer resulting in the minimum energy consumption significantly depends on the type of filling gas. The optimum gas layer thickness values are found as 12, 15 and 9 mm for air, argon and krypton, respectively. It is concluded that the sunspace with 9 mm thickness of double glazed unit filled with krypton can be suggested for the highest energy saving. Also, the results revealed the importance of comprehensive analyses on sunspaces regarding various parameters.

Theoretic analysis and experimental evaluation of the spectrum transmission coefficient of a multilayer photovoltaic vacuum glazing

Abstract This paper introduces an innovative thin film PV vacuum glazing (PV-VG) technology. In addition to electricity generation, the PV-VG glazing can also reduce heat loss from the building in winter and reduce heat gain in summer. In building integrated photovoltaics application, optical characterization of the PV glazing is important in determining the solar ray transmission and thermal transfer process of the glazing. This paper discusses the optical properties of the PV-VG glazing by considering the different layers of the glazing unit that includes a self-cleaning glass, a thin film PV glass and a low-e vacuum glazing. Based on the optical transfer matrix, the transmission coefficients of different film layers were deduced. The theoretical calculations were then validated against the transmission coefficient experiment of the PV-VG using an EDTM SS2450 Solar Spectrum Meter. The calculation error of the transmission coefficient of the single-layer glazing is generally within 5%, the calculation error of the transmission coefficient of the integrated PV-VG glazing is about 6%. The results show that the average visible light transmission coefficient, the average infrared light transmission coefficient and the overall transmission coefficient of PV-VG glazing are 19%, 16% and 12%, respectively. The study is important to optimize the visible light transmission of the PV-VG glazing; the optical model obtained above lays a solid foundation for further study of transmission coefficient analysis of different functional coating of PV-VG glazing.

Modelling analyses of the thermal property and heat transfer performance of a novel compositive PV vacuum glazing

This paper proposes an integrated photovoltaic vacuum glazing unit with an intermediate air cavity and a calibrated modelling approach to quantify its thermal properties and evaluate the heat transfer performance. Theoretical analyses of the heat transfer process are conducted with reasonable hypotheses and traceable boundary conditions. Three-dimensional heat transfer models are then established and cross-validated against previous publications. The detailed validation demonstrates the reliability of the developed complex models under different circumstances. Furthermore, four photovoltaic vacuum glazing configurations are compared in terms of the temperature distribution and overall heat transfer coefficient (i.e. U-value). Simulation results show that the photovoltaic vacuum double glazing can achieve the optimum performance among the four configurations based on simultaneous consideration of the PV module temperature and U-value. Sensitivity analyses of glazing design factors are also conducted for the U-value, which is found to be greatly reduced by decreasing the density and diameter of vacuum pillars as well as the glass thermal conductivity. A lowest U-value of 0.23 W/(m2·K) is achieved for the photovoltaic-vacuum double glazing and can be further improved with future design optimizations. This research can provide guidance to design improvement of PV vacuum glazing systems and promote their integration with building modelling tools.