Glazing Units Research Articles

Assessment of window performance in classrooms by long term spatial comfort metrics

Providing good environmental conditions for educational buildings has always been critical because of the negative influence of thermal and visual discomfort on students’ learning and performance. Unsatisfactory conditions mostly caused by overheating and glare due to the presence of direct solar radiation, could be compensated by appropriate window configurations. Since occupants are obligated to sit in defined positions in classrooms, spatial analysis of the thermal and visual field are necessary in addition to temporal evaluations. This paper applies both spatio-temporal thermal and visual comfort metrics, to assess the effect of window design on comfort by dynamic simulations in a south and north faced classroom model in Tehran’s Climatic condition. The SolarCal method, which considers the direct effect of solar radiation on occupants, validated by field measurements, is used to assess local thermal comfort. A solution space, presented in graphs has been defined for each orientation by the defined comfort targets. These graphs could be used to select the optimum glazing properties based on the desired window wall ratio. The defined solution areas are larger in the south orientation and could be extended by considering shadings. Results show that low U-values and low Solar Heat Gain Coefficient (SHGC) are needed in both north and south faced classrooms to decrease the overheating risk. Also the use of double glazing units is not always required or the most favorable option for all window sizes. Based on the results the most effective factors for window design in regard to spatio-temporal thermal comfort are Window Wall Ratio (WWR), glazing SHGC and window shadings, orientation, and window U-value respectively. However, WWR, orientation, and glazing Visual Transmittance (VT) and shadings have almost equal effect on spatio-temporal visual comfort.

Determination of critical breakage conditions for double glazing in fire

Double glazing unit normally demonstrates better fire resistance than single glazing, but the knowledge on its thermal behavior and heat transfer mechanism during fire is limited. In this work, nine double glazing units were heated by a 500×500mm2 pool fire. The incident heat flux, temperature on four surfaces, breakage time and cracking behavior were obtained. The critical breakage conditions for interior and exterior panes were determined through gradually decreasing the glass-burner distance from 750mmto 450mm. It is established that in double glazing the pane at ambient side can withstand significantly more time than the pane exposed to fire. The critical temperature difference for interior pane is 60°C; the critical temperature of exterior pane breakage is much higher due to no frame-covered area. In addition, the heat flux at the time of crack initiation is 6kW/m2 for the pane at fire side, while more than 25kW/m2 for ambient side pane. To reveal the heat transfer mechanism in glazing-air-glazing, theoretical and numerical investigations are also performed, which agrees well with the experimental results.

Testing terracotta in the United States: early testing practices and modern conservation

ABSTRACTCracks, spalls and efflorescence are unsightly, but what do they say about the service life of a terracotta unit? And what analytical tests can we perform to help us define its life span? Unfortunately, in the case of architectural terracotta, determining if a deteriorated unit has nearly reached the end of its useful life is not entirely straightforward. Simply looking at the surface of a terracotta unit does not provide sufficient information to characterize its durability, nor does repairing the surface guarantee its survival.The large-scale manufacturing of architectural terracotta in the US began in the 1870s. By 1876, magazines such as American Architect and Building News marketed terracotta as a good, ‘durable’ material for use on cornices. Within two decades, however, concerns about the performance of the building material were raised with respect to glaze adhesion, spalling, and physical strength.Extensive research was undertaken by the author on architectural terracotta testing practices and manufacturing methods used historically throughout the US. With literally hundreds of tests carried out and published between 1899 and 1961, it seemed that no one test was able to fully address the complex question of durability.In an effort to understand the relationship between physical characteristics and durability, several historic glazed terracotta units, all taken from buildings constructed before 1938, were subjected to microscopic examination, water vapor transmission (WVT) measurement, freeze thaw testing and glaze adhesion. The article examines the results, the limits of the individual tests, and how a variety of evaluation techniques are required – in combination – to understand the structure and condition of the material. There is also a brief discussion of modern repair techniques and whether these repairs are appropriate or even worthwhile.

Electricity yield simulation for the building-integrated photovoltaic system installed in the main building roof of the Fraunhofer Institute for Solar Energy Systems ISE

The generated electricity of a rather complex building-integrated photovoltaic system, installed in the main building of the Fraunhofer Institute for Solar Energy Systems, is analyzed in detail. For this purpose, the measured irradiance on the tilted surface, the temperatures of the PV modules, the DC power and the AC power are compared with the results of an advanced electricity yield simulation program that has been developed at the institute. The chosen building-integrated photovoltaic (BIPV) system allows detailed investigation of complex shading patterns, improved electrical cell connection and the temperature characteristics of building-integrated photovoltaic modules when they simultaneously function as insulating glazing units with a low U value. The comparison of simulated and measured AC power shows that the consequences of partial shading, the consequences of the integration as a thermally insulating component of the building envelope and the electrical properties of the PV system are understood well.

New Possibilities of Sun and Glare Protection with a Structured Switchable Glazing

Glazing units used for architectural applications have an enormous potential for optimization. Currently, daylight management as well as solar and shading control can be provided only through a combination of various individual elements, such as glass panes, venetian blinds and additional glare protection elements. This combination of several separate elements not only leads to a higher consumption of resources, as well as higher production costs. It also entails additional maintenance costs. In order to overcome these shortcomings, the authors have developed a switchable glazing unit with adjustable light and energy transmission properties. This unit uses an anisotropic liquid. The functional component consists of a liquid crystal layer enclosed between two coated glass substrates, thus it is an integral part of the glazing unit. Due to the structure of the conductive layer, it is possible to subdivide the glazing unit into small areas (so-called pixels) that can be switched individually. The transparency of each pixel can be controlled independently. The glazing unit itself can be used as an effective daylight and shading control. This integral approach opens the door for new architectural applications. The authors currently focus their research on the development and tests for control strategies of the switching process itself. These control strategies are numerically validated and then tested at the ILEK facade test facility. The paper presents the first results of a performance analysis based on numerical simulations.

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.

Influence of Spacer Frames for Wooden Roof Windows on the Formation of Surface Condensation

This study reports the thermal characteristics of windows installed in the roof cladding of a block of flats in the second temperature zone of the Czech Republic, with boundary conditions for the design value θse = - 15 °C, according to the national standard CSN 73 0540-3 (2005). The thermal behaviour of these elements was evaluated with regard to the condensation on roof windows, with four different types of spacer frames and the given boundary conditions, for maintenance of the thermal and technical humidity comfort of the interior. The tests of the surface temperatures of the diagnosed glazed roof units at the glazing of the wooden windows demonstrated that the SGG composite spacer was the best from a thermal perspective. The spacer frames based on aluminum, stainless steel, and a combination of stainless steel and plastic (TGI) did not provide adequate thermal insulation characteristics for usage in roof windows under the given climatic conditions, and condensation occurred on the glass surfaces.

Simulation aided optimization of a historic window’s refurbishment

A recurring problem in retrofitting historic windows is that most traditional means of improving their energy efficiency, e.g. the use of IG units, is often unavailable due to structural and esthetic concerns. Through a refurbishment project of traditional Central-European box windows we aim to investigate the possibility of using less intrusive methods to improve the windows’ heat balance with comparable results. Many different approaches to calculating the energy balance of windows in historic buildings are reviewed and various modelling assumptions and algorithms analyzed to highlight the depth of modelling needed for fenestration heat balance calculation in a historic context. We introduce our new research program for the task: EPICAC-BE, a MATLAB based dynamic energy simulation software. After a validation with the BESTEST suite it is used to compare different retrofit options for a prototype window with and without controlled shading devices. Results indicate the use of double glazing units is not always required or the most favorable. Utilizing the dynamic window concept by combining higher U value with higher solar transmittance with automatic interpane shading can achieve better overall results. Simulations should have a key role as they can lead to designs better satisfying both energy saving and conservational requirements.

Experimental measurement and numerical simulation of the thermal performance of a double glazing system with an interstitial Venetian blind

Venetian blinds, which were originally designed to provide sun shading and privacy, also have the potential to reduce heat transfer caused by internal and external temperature difference when integrated within the cavity between the two panes of a double glazing unit. In this paper, the thermal performance of a glazing system with and without a Venetian blind with various slat orientation angles under different temperature conditions is investigated through both experiment (undertaken in a large climate chamber) and numerical simulation (obtained via Computational Fluid Dynamic modelling). The thermal resistance of a Venetian blind glazing system varies with the change of slat inclination angle, and it also highly depends on the mean temperature of the glazing and the temperature difference between the indoor and outdoor environment. Inclusion of a Venetian blind modifies both the absolute and relative strengths of convection and radiation. Vertically oriented slats showed the most significant contribution to increasing radiative thermal resistance, which led to the best overall thermal performance. The system achieved up to 28% improvement of U-value when compared with a glazing unit without a Venetian blind. Empirical correlations generated based on simulations could be used for future building energy simulation.

Thermal performance of a PCM-filled double glazing unit with different optical properties of phase change material

Phase change material (PCM) applied in the glazing structure can decrease building energy consumption and improve indoor thermal comfort by enhancing its thermal energy storage capacity. In the present work, thermal performance of a PCM-filled double glazing unit with different optical properties of phase change material was investigated numerically. The results show that optical properties of PCM play an important role in the thermal performance of double glazing unit filled with PCM, and effect of PCM phase is also strong. Effect of refractive index of PCM on the temperature of double glazing unit is weak, but the effect of extinction coefficient of PCM on the temperature and transmitted energy of double glazing unit is strong. Compared 200m−1 with 5m−1 of extinction coefficient, time to the highest temperature is 30 and 300min earlier in liquid and solid PCM of double glazing unit, and time to the highest transmitted energy is delayed 40min in liquid PCM double glazing unit, but is nearly same in solid PCM double glazing unit.

Accelerated ageing and durability of double-glazed sealed insulating window panes and impact on heating demand in buildings

A crucial property for double-glazed sealed insulating window panes is to maintain their thermal insulating properties and thus low U-values. However, degradation and thus subsequent reduction or loss of low-conductance gas concentration may occur in the sealed glazing units by their exposure to outdoor climate.The choice of spacers is important to keep as low thermal transport through the window panes as possible, i.e. low U-value. In addition, the type of spacers may also influence their durability and resistance towards ageing, which hence may be characterized by the low-conductance noble gas concentration, e.g. argon, krypton or xenon. Ageing and degradation of window panes may lead to a decreased or total loss of noble gas concentration and hence subsequent increased heating energy demand in buildings.Thus, several double-glazed sealed insulating window panes, with aluminium spacers and Super Spacers, have been subjected to accelerated ageing by climate ageing and elevated temperature ageing. The durability and ageing of the sealed window panes have been studied and characterized by their spacer type and gas concentration. Furthermore, the decrease of gas concentration in sealed insulating window panes and the impact on the energy performance and in particular heating demand of buildings have been investigated.

A Model to Determine Thermal Performance of a Non-ventilated Double Glazing Unit with PCM and Experimental Validation

Phase change material (PCM) applied in the double glazing unit can decrease energy consumption and improve indoor thermal comfort by improving its thermal energy storage capacity. In the present work, a model to determine thermal performance of a non-ventilated double glazing unit with PCM and experimental validation was developed. The result shows that the developed model in present work can solve the coupled heat transfer problem between phase change and solar heat transfer in the double glazing unit filled with PCM.

Sustainable cultivation of microalgae by an insulated glazed glass plate photobioreactor.

Microalgae growth in closed photobioreactors is greatly inhibited by elevated temperatures caused mainly by the infra-red portion of light. Current passive evaporative cooling systems for temperature control in outdoor photobioreactors are neither economical nor sustainable. Here we built a novel flat plate photobioreactor with its illumination surface customized with insulated glazing units (IGP). The IGP design enabled transmission of more than 50% of visible light while blocking 90% of ultraviolet and infrared radiations. The growth and productivity of Nannochloropsis sp. (MUR 267) in the IGP was compared against conventional flat plate photobioreactors subjected to the full spectrum (HLP) and also externally modified spectrum (CLP) of halogen lights. High temperature (up to 42°C) resulted in no growth in the HLP. Biomass productivities of Nannochloropsis sp. grown in the CLP was significantly higher than the IGP due to higher light transmission and lower temperature profiles recorded in the CLP. Lipid content of Nannochloropsis was highest in the CLP (60.23%) while protein was highest in the IGP (42.43%). All photosynthesis parameters were negatively affected in the HLP. The IGP's ability to remove infrared (heat) makes this newly developed photobioreactor a promising and sustainable cultivation system for mass algal production especially for high value products.

Optical performance of single and double glazing units in the wavelength 337–900 nm

Optical properties of glazing units play an important role in the quantificational analysis of solar ray and thermal transfer process in single and double glazing units. In the present work, a spectroscopic method was developed to determine the optical constants of float glass material including refractive index and absorption coefficient based on the transmittance spectra modeling. The transmittance spectrograms of single float glass glazing units at normal incidence with different glass thicknesses in the wavelength 337–900nm were measured. Then the optical properties of single and double glazing units were numerically investigated. The results show that the optical performance of glazing units reveals a considerable difference in the measured wavelength region. The spectrum profiles of glazing units are very similar in shape, and the shapes of the spectra are not relevantly affected by the glass thickness. However, the thicker the glass layer, the weaker the transmittance and reflectance, and the stronger the absorptance.

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.

Moisture in Multi-Layer Windows

There is an increasing interest in development of coupled multi-layer window structures. This is to optimize thermal properties and to develop systems with a better climate protected solar shading system. The risk of condensation on the inside of the exterior glass layer in a multi-layer window structure might be a challenge and is often questioned. The risk of condensation will depend on both window properties and indoor and outdoor climate conditions. The air gap between the inner and outer part have to be ventilated with outdoor air to give the window a “drying out” capacity. The U-value of the window and the moisture condition in the air gap both depend on the ventilation of the air gap. Reducing the ventilation improves the U-value, but increases the time of desiccation.Net long-wave radiation from the glass surface to the atmosphere during cloudless night-time will cause exterior glass temperatures lower than the outdoor air temperature, and hence increase the risk of condensation on both sides of the exterior glass. The aim of this work has been to assess for which climate conditions there will be a risk of condensation on the exterior glass layer and what might be the optimal ventilation of the outermost air gap. Simulations of the temperature on the exterior surface of the glazing including the long-wave radiation during night- time have been done and compared to measurements. An assessment has been made studying the risk of condensation and the drying out rate for climate conditions for two locations in Germany. A spreadsheet-based model calculating the U-value of a multilayer glazing unit according to ISO 15099 [1] has been further developed including airflow from exterior openings through the air gap.

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).

Perspective of aerogel glazings in energy efficient buildings

The application perspective of aerogel glazings in energy efficient buildings has been discussed by evaluating their energy efficiency, process economics, and environmental impact. For such a purpose, prototype aerogel glazing units have been assembled by incorporating aerogel granules into the air cavity of corresponding double glazing units, which enables an experimental investigation on their physical properties and a subsequent numerical simulation on their energy performance. The results show that, compared to the double glazing counterparts, aerogel glazings can contribute to about 21% reduction in energy consumptions related to heating, cooling, and lighting; payback time calculations indicate that the return on investment of aerogel glazing is about 4.4 years in a cold climate (Oslo, Norway); moreover, the physical properties and energy performance of aerogel glazings can be controlled by modifying the employed aerogel granules, thus highlighting their potential over other glazing technologies for window retrofitting towards energy efficient buildings. The results also show that aerogel glazings may have a large environmental impact related to the use of silica aerogels with high embodied energies and potential health, safety and environment hazards, indicating the importance of developing guidelines to regulate the use of aerogel glazings.

Optical properties of a liquid paraffin-filled double glazing unit

Based on the transmittance spectra modeling, spectroscopic methods were developed to determine the optical properties of a liquid paraffin-filled double glazing unit, including reflectance and absorptance. The transmittance spectrograms of paraffin-filled double glazing units at normal incidence with different thicknesses in the wavelength 240–900nm were measured by a TU-19 FTIR spectrometer. These values were introduced into spectroscopic methods to calculate the reflectance and absorptance of paraffin-filled double glazing units. The results showed the transmittances of glazing unit that are filled with paraffin in most area are enhanced compared with the empty glazing unit. The absorption and reflectance profiles with different paraffin thicknesses are very similar in shape and are relevantly affected by the paraffin thickness.

Comparative study of simulation and experimentation for the U-value of double-glazed windows with inter-pane blinds

This article applies the Taguchi design on a simulation as well as on an experimentation technique to determine the thermal transmittance (U-value) of a double-glazed window with inter-panes blinds so as to explore its performance potential for a particular Indian climate. Environmental parameters are selected per the composite climate in India. Simulated results show a maximum of 20% variation when compared with experimental ones. Analysis of results shows that Taguchi methods are effective in ranking the effect of various parameters on the U-value of identified glazing units. The low-emissivity glazing system ranks first, followed by slat angle, temperature difference, pane spacing, and temperature of hotplate (representing climatic conditions). The analysis of means is also carried out to identify the best combination of levels of various parameters.