Clear Glazing Research Articles

Virtual reality as a tool for evaluating user acceptance of view clarity through ETFE double-skin façades

Equipping building envelopes with an additional layer is an effective measure for improving the overall thermal and daylighting performance and reducing the energy consumption of buildings. This study investigated the user acceptance of energy-saving retrofitting measures in office buildings, reporting on the view perception and emotional response towards ETFE double-skin façades (DSF). Virtual Reality (VR) and physics-based imaging techniques were used to evaluate the user experience of a window view in an office space equipped with a pneumatic ETFE cushion as a second building skin. Three DSF scenarios with different ETFE cushions, including a clear, fritted and switchable sample, were evaluated and compared to the original single-skin façade with double-glazed windows. The physical and luminous conditions of the office space were replicated in a virtual environment with a validated physically-based imaging technique and presented to a group of volunteers (N = 22) using a virtual reality headset. While immersed in the virtual environment, participants responded to a questionnaire enquiring into their view perception and emotional states. The results revealed a preference for view clarity of clear ETFE in double-skin façades (Mdn = 5) and less satisfaction for fritted (Mdn = 4) and switchable foil cushions (Mdn = 1.75), yet double glazing was preferred in all measured parameters (Mdn = 6). Statistical significance was found for fritted in comparison to switchable ETFE in terms of spatial pleasure and control. The highest ratings were given to clear glazing across all investigated parameters of view perception and emotional response. The lowest ranking in all questions was given to the sample with the switchable ETFE cushion. The study concluded that view clarity is a major aspect for the user acceptance of ETFE double-skin façades. Overall, this study provides a better understanding of the visual and emotional implications of viewing through ETFE foil and contributes to forming criteria for the design of next-generation ETFE building envelopes.

Energy and Daylighting Evaluation of Integrated Semitransparent Photovoltaic Windows with Internal Light Shelves in Open‐Office Buildings

In modern architecture, highly glazed commercial buildings account for considerable amount of energy, specifically in cold and hot climates because of heating, cooling, and lighting energy load demand. Abatement of this high building energy is possible by employing semitransparent photovoltaic (STPV) window which has triple point advantages as they control the admitted solar gain and daylight and generates benign electricity. Integration of internal light shelves (ILS) to this STPV window assists in controlling visual comfort. Thus, this study aims to evaluate the impact of a nonuniform layout of double‐glazing (DG) low‐e STPV and DG low‐E argon‐filled clear glass integrated into a fully glazed open‐office facade combined with ILS in cardinal orientations under Riyadh, London, Kuala Lumpur, and Algiers climates. Comprehensive energetic and radiance simulations were conducted to evaluate three groups of STPV configurations. The first group replaced the glazing area with amorphous silicon (a‐Si) modules with different transparencies; the second and third groups changed only 75% and 50% of the glazing area, respectively, with STPVs integrated with the ILS. The results revealed that the integration of a‐Si modules did not meet the visual comfort requirements but obtained the maximum saving in the east‐west axis. It was also found that the optimum design on the south‐facing facade with the nonuniform facade achieved 50% of STPV10 coverage in clear glazing windows combined with ILS; the energy saving ratios comparing the reference models were 76%, 83%, 65%, and 70% in Riyadh, London, Kuala Lumpur, and Algiers, respectively. Thus, the integration of STPVs with ILS is considered a more efficient way and effective solution to reduce the possibility of glare discomfort.

Recent Developments in Solar Energy-Harvesting Technologies for Building Integration and Distributed Energy Generation

We present a review of the current state of the field for a rapidly evolving group of technologies related to solar energy harvesting in built environments. In particular, we focus on recent achievements in enabling the widespread distributed generation of electric energy assisted by energy capture in semi-transparent or even optically clear glazing systems and building wall areas. Whilst concentrating on recent cutting-edge results achieved in the integration of traditional photovoltaic device types into novel concentrator-type windows and glazings, we compare the main performance characteristics reported with these using more conventional (opaque or semi-transparent) solar cell technologies. A critical overview of the current status and future application potential of multiple existing and emergent energy harvesting technologies for building integration is provided.

Development of experimental methods for quantifying the human response to chromatic glazing

Thermochromic (TC) windows have the ability to regulate daylight and control the solar heat gains that shape a building's internal environment. They therefore offer the potential to improve indoor comfort and reduce building energy demand when used in place of traditional clear glazing systems. However, the quality of the luminous environment is affected due to their chromatic appearance (e.g. common TC coatings impart a bronze or blue hue), resulting in changes to correlated colour temperatures (CCT). Previous studies show that experiments performed under daylight conditions are difficult to be control, while those conducted under artificial lighting conditions cannot faithfully reproduce window properties. In order to investigate the influence of TC windows on visual performance and comfort of subjects in an efficient and economical way, an innovative test room cubicle was designed. It is a mock-up office lit by an artificial window, simulating luminous conditions filtered through two types of TC window (one blue tinted and one bronze tinted). Clear glazing was used as a reference. Objective visual tasks involving Landolt charts and subjective assessments made using questionnaires were used to determine subjects' response to the three different luminous conditions. Results show that the experimental method is effective at determining human response to chromatic glazing. Additionally, the method is flexible due to its small scale and its ability to artificially represent different window types.

Annual thermal evaluation of a double pane window using glazing available in the Mexican market

The annual thermal evaluation of a double pane window (DPW) is presented; the DPW is modeled using three different types of panes commercially available in Mexico. Hourly climatic data of the coldest and the warmest day of each month of 2016 were used to model the behavior of the DPW in a warm region of Mexico (Chetumal, Q. Roo). The simulations were carried out using an in-house code based on the finite volume method. To carry out the annual thermal analysis of the DPW, four cases were defined; Case C1: corresponds to single clear glazing window (reference case); Case C2: clear glass + air gap + clear glass; Case C3: clear glass + air gap + reflective glass and Case C4: clear glass + air gap + Low-ε glass. Results showed that case C3 reduces the heat flux to the inside about 72.6% regarding case C1. Besides respect to case C1, cases C2 and C4 showed an energy saving of 12 and 28.6% respectively. On the other hand, case C3 resulted to be the best option for energy savings, where a saving of $30.73 USD a year was computed with respect to case C1, with an approximate cost recovery period of 3.5 years. Hence, the use of a reflective pane in a DPW is highly recommended for warm weather conditions in Mexico.

Evaluation of the thermal and optical performance of thermochromic windows for office buildings in China

Thermochromic (TC) windows were developed as a passive building component to improve indoor comfort and building energy conservation in place of traditional clear glazing systems. Thermochromic materials have the ability to regulate daylight and solar heat gains through windows stimulated by heat. This means that when the temperature of a thermochromic window becomes higher than its transition temperature, less solar radiation, primarily in the near infrared, will be admitted inside the building, reducing over-heating on hot days. The aim of this research is to explore the potential of thermochromic glazing under various climatic conditions by modelling the energy and daylight performance of a typical office room with five different thermochromic glazing types (with varying transition temperatures ranging from 20 °C to 41.3 °C and solar transmittances ranging from 0.412 to 0.690) simulated under five climatic conditions in China, representative of different climate zones. A comprehensive analysis was conducted, including a study of the thermal and optical behaviours of the selected thermochromic glazed windows; energy use for heating, cooling and artificial lighting of the selected office; and effects of window-to-wall ratios on office performance under the selected climatic conditions. The objectives are: to thoroughly understand the characteristics of the selected types of thermochromic glazing, to find the appropriate window-to-wall ratio for the thermochromic windows, and to investigate the suitability of thermochromic glazing for particular climatic conditions to realise which could achieve energy conservation and desired daylighting simultaneously. The results showed the following: (1) Low transition temperature (i.e. 20 °C) is not essential for building energy conservation, larger modulation of solar transmittance is more desirable for most of the climatic conditions. (2) Higher solar absorptance could increase thermochromic layer temperatures, improving glazing tinting capability, but it may increase window heat gains in the form of secondary heat gains and further induce cooling energy consumption on hot days. (3) All the studied thermochromic windows led to building energy savings (up to 19.9%) and better daylighting performance (i.e. increase of the desired range of illumination, UDI500-2000lux, is up to 15.52%) when compared with traditional clear double glazing. (4) Under climates such as Harbin and Beijing with more cold days, limited types of thermochromic glazing could achieve both energy conservation and desired daylighting under a particular window size, while almost all types of thermochromic glazing are suitable to be used in climates with more hot days.

A comparison of two light-redirecting fenestration systems using a modified modeling technique for Radiance 3-phase method simulations

This paper compares two different macroscopic light-redirecting fenestration systems (LRFS) using Radiance’s three-phase method. The goal is to assess the potential of simplified daylight metrics that are less computationally expensive, such as Daylight Factor (DF), in the optimization of LRFS. This work compares a highly specular LRFS optimized for DF (Lasy_S) with a validated commercial LRFS (LightLouver) using a Double Clear Glazing window as the control case. The comparison uses two different locations representative of two different annual sky conditions: London, UK - overcast; Phoenix, AZ, USA – clear. Useful Daylight Illuminance (UDI) and annual Daylight Glare Probability (DGP) are the metrics used to evaluate daylight availability and visual comfort. To facilitate the efficient modeling of customized macroscopic LRFS in the three-phase method workflow, this work extends Radiance’s genblinds routine, making it able to generate complex venetian blinds systems based on multiple-curved sections. With the modified genblinds, the Lasy_S system is properly remodeled for the three-phase method for an accurate comparison of the different systems. The analysis shows that Lasy_S is a light-weighted and low-maintenance LRFS that outperforms LightLouver in terms of useful annual illuminance levels in both locations, being more effective in cloudier skies due to the metric used in the optimization. Nevertheless, albeit the system mitigates glare, it is not as successful as the commercial LRFS. This indicates that DF and annual horizontal illuminance metrics are unable to properly inform an optimization process on glare performance, thus being more appropriate for initial exploratory optimizations. Hence, to fully address glare, daylight optimization procedures based on DF should be complemented with more detailed glare simulations that do not require unreasonable computational resources.

Simplified field measurement and verification of global solar transmittance for glazing samples under natural clear-sky conditions

Abstract This paper presents the results of an experimental study to measure and verify on-site global solar transmittance as a function of varying angles of incidence for glazing samples under natural clear-sky conditions, including: single-pane clear, double-pane clear, and double-pane low-e glazing. Field measurements were implemented using a silicon photodiode sensor and two thermopile-type pyranometers based on an easily-assembled test box with sample glazing. Measurement results were then compared to the published data (i.e., Tsol values in the WINDOW libraries). The results indicate that silicon photodiode sensors can be used to measure and verify direct solar transmittance within an acceptable range of accuracy. However, the global (i.e., direct and diffuse) solar transmittance measured by the thermopile-type sensors was significantly higher than the Tsol values from the WINDOW program. As a result, it is recommended that such field measurements could be used to verify the on-site direct and global solar transmittance of as-built glazing since the WINDOW program currently only accounts for direct (i.e., beam) solar radiation in the reference solar spectrum (i.e., ASTM E891 ).

Experimental and Theoretical Studies of Window Glazing Materials of Green Energy Building in Indian Climatic Zones

Abstract Buildings consume plenty of power for providing thermal and visual comfort inside the buildings. This paper aims at presenting the experimental results of spectral optical properties of the most widely used window glazing materials. The window glazing materials studied include clear glazing, bronze glazing, green glazing and grey coloured glazing materials. A Matlab code employing the British standard method was developed to compute transmittance and reflectance of window glasses at normal incidence angle. This code uses experimentally obtained spectral optical property data from Perkin Elmer lambda 950 spectrophotometer for the computation of transmission and reflection of window glasses. A computer program was developed for computing the total solar radiation passing through glass materials. The heat gain through different glass windows of eight coordinal orientations such as east, west, north, south, northeast, northwest, southeast and southwest in four climatic zones of India was investigated. The solar radiation through south oriented glass was found to be the least among all other orientations studied in four Indian climatic zones. The cooling load through south oriented bronze, glass, green glass and grey glass window were reduced by 23%, 31% and 37%, respectively, as compared to the south oriented clear glass window in four climatic zones of India. The grey glass window is observed to be the most energy efficient as it reduces maximum cooling loads within the building as compared to the other considered glazing materials. The results of this paper are helpful in designing energy efficient commercial buildings for reduced cooling loads.

Potential of shading devices and glazing configurations on cooling energy savings for high-rise office buildings in hot-humid climates: The case of Malaysia

Abstract Rapid growing of energy use has raised critical concerns over energy supply difficulties and negative environmental impacts globally and among ASEAN countries. Malaysia is experiencing a high average annual energy demand growth rate of approximately 2.3% which large portion of that energy is used by office buildings. Under the hot-humid climatic conditions in Malaysia, high-rise office buildings with large or fully glazed facades are facing a major problem of overheating due to high solar radiation through the glazed facades. This has caused high cooling energy requirements. The aim of this study is to investigate the potential of three types of shading devices on cooling energy savings when applied at different facade orientations. The aim also extends to investigations on different cooling energy savings when shading devices are applied on facade glazing with different configurations and thermal performances. This was done through a case study of a high-rise office building in Kuala Lumpur, Malaysia using IES (VE) building thermal simulation software. Twenty simulation building models were applied with different shading devices at different facade orientations and with high and low performance facade glazing. The simulation results indicate that high-rise office buildings in Malaysia use approximately 45.9% of total building energy for cooling purposes. The results also suggest that use of various shading devices on low-e double glazed facades will result between 1.0% and 3.4% annual cooling energy savings, depending on the types of shading devices and facade orientations. The estimated annual cooling energy savings increase to between 5.0% and 9.9% when the shading devices are applied to all orientations of low-e double glazed facades. The estimated annual cooling energy savings further increase to between 5.6% and 10.4% when the facade glazing is replaced by single clear glazing. This study recommends prioritizing shading devices on the East and West facades for optimized annual cooling energy savings. The simulation results show that egg-crate shadings are able to produce the highest annual cooling energy savings compared to vertical shadings and horizontal shadings. It is recommended to use shading devices on low performance glazing compared to high performance glazing since the energy savings are more significant when shading devices are used on low performance glazing. In conclusion, the use of shading devices is more effective in achieving cooling energy savings compared to the use of high performance glazing under the hot-humid climate of Malaysia.

Influence of Glazing Types on the Indoor Thermal Performance of Tropical High-Rise Residential Buildings

In tropical climates, the solar radiation absorption of glazed windows results in overheated indoor environments and increased cooling energy loads during daytime. Meanwhile, situations differ during nighttime. The present study focuses on the effects of glazing type on the indoor temperature in high-rise residential buildings in the hot and humid climate of Malaysia. The primary objective of this study is to assess the effects of six glazing types on the indoor air temperature of the base case room oriented toward the southwest with a Window Wall Ratio WWR of 45% under both ventilated and unventilated conditions. The effects during daytime and nighttime are investigated separately. A computerized simulation tool (Virtual Environment by Integrated Environmental Solutions) is used to conduct the investigation. Penang is selected as the empirical background location of a hot and humid climate. The study found that reflective double glazing exhibits lower indoor air temperature throughout the day regardless of the ventilation condition, with an optimum improvement of up to 107% and 14% in unventilated and ventilated rooms, respectively, compared with single clear glazing. The study recommends the use of reflective single or double glass in regions with a hot and humid climate similar to that of Malaysia.

Three approaches to optimize optical properties and size of a South-facing window for spatial Daylight Autonomy

This study presents optimization approaches by a recent Climate-Based-Daylight-Modeling tool, EvalDRC, to figure out the necessary area for a daylight redirecting micro-prism film (MPF) while minimizing the glazing area. The performance of a window in terms of spatial Daylight Autonomy (sDA) is optimized by its geometry and optical properties. Data implemented in simulation model are gathered through on-site measurements and Bidirectional-Scattering Distribution Function (BSDF) gonio-measurements. EvalDRC based on Radiance with a data driven model of the films' BSDF evaluates the window configurations in the whole year. The case to achieve an sDA of at least 75% is a South-facing window of a classroom in Switzerland. A window zone from 0.90 m to 1.80 m height provides view to the outside. The upper zone from 1.80 m to 3.60 m is divided into six areas of 0.30 m height in three optimization approaches including the operation of sunshades as well. First, the size of the clear glazing is incrementally reduced to find the smallest acceptable window-to-wall ratio (WWR). Second, micro-prism films are applied to an incrementally varying fraction the initial glazed area to determine the minimum film-to-window ratio (FWR). Finally, both approaches are combined for a minimum FWR and WWR. With clear glazing and WWR of 75%, the sDA of 70.2% fails to meet the requirements. An sDA of 86.4% and 80.8% can be achieved with WWR 75%, FWR 1/9 and WWR 50%, FWR 1/2 respectively. The results demonstrate the films' potential to improve the performance of windows with reduced WWR.

Thermal and visual performance of real and theoretical thermochromic glazing solutions for office buildings

Thermochromic windows are able to modulate their transmittance in both the visible and the near-infrared field as a function of their temperature. As a consequence, they allow to control the solar gains in summer, thus reducing the energy needs for space cooling. However, they may also yield a reduction in the daylight availability, which results in the energy consumption for indoor artificial lighting being increased.This paper investigates, by means of dynamic simulations, the application of thermochromic windows to an existing office building in terms of energy savings on an annual basis, while also focusing on the effects in terms of daylighting and thermal comfort. In particular, due attention is paid to daylight availability, described through illuminance maps and by the calculation of the daylight factor, which in several countries is subject thresholds.The study considers both a commercially available thermochromic pane and a series of theoretical thermochromic glazing. The expected performance is compared to static clear and reflective insulating glass units. The simulations are repeated in different climatic conditions, showing that the overall energy savings compared to clear glazing can range from around 5% for cold climates to around 20% in warm climates, while not compromising daylight availability.Moreover the role played by the transition temperature of the pane is examined, pointing out an optimal transition temperatures that is irrespective of the climatic conditions.

Energy and visual performance of the silica aerogel glazing system in commercial buildings of Hong Kong

To achieve a more comfortable indoor environment while still retaining low energy consumption level is an exciting challenge for designers and owners of buildings. In this paper, a silica-aerogel filled super-insulating glazing system was proposed. A numerical study was conducted to analyze the energy performance and visual performance of the proposed glazing system. Two popular building simulation programs namely EnergyPlus and Radiance were applied in the numerical study. In the study of the energy performance, three control strategies (space temperature control, operative temperature control and PMV control) were applied to simulate the occupant’s control behavior toward the air-conditioning system in reality. The result indicated that compared with conventional single clear glazing, the silica aerogel glazing could retain a 4% longer thermally comfort period, while the energy consumption of HVAC system was reduced by 4–7%. The performance of the silica aerogel glazing was almost equal to that of the state-of-art low-e glazing. It is also concluded that as the occupant’s request on thermal comfort got stricter, the performance of the silica aerogel glazing would became better. In the visual comfort point of view, it can be concluded that the glare effect and near-window bright zone could be reduced significantly while indoor illumination level still met the requirement.

Theoretical and Experimental Research of Glazed Systems in Real Conditions of Outdoor Climate

Solar diode glazing unit utilized as a solar energy absorbent. Comparison of glazed systems. Green absorptive glass as a crucial part of heat absorption feature in the composition of solar diode glazing unit. Schemes of function for different outdoor climate conditions. Analysis of physical properties of measured samples. Measurement of heat flows in real climate utilizing a comparative method between solar diode glazing and a standard clear insulated glazing unit of the same standardized U-value. Quantification and conclusions made from the analyzed data.

The Effects of Window Film on the Performance of Window System

Window film is generally attached the glazing in buildings to improve the thermal performance of the window system by addressing a range of problems such as indoor temperature rise, indoor temperature imbalance, degraded heating and cooling load due to excessive influx of solar radiation. To evaluate the performance of window films, window films are attached to 3mm or 6mm clear glass. However, window films are generally used on existing window systems for reducing the annual energy consumption. Therefore it is necessary to evaluate the performance of window films depending on the performance of glazing such as clear double glazing or low-e double glazing. Thus the purpose of this study is to analyze the performance of window systems when window film is attached. As a result, in the case of applying window films for reducing the SHGC of buildings, it is necessary to select window films suitable for the configuration and performance of the glazing to be installed, considering the SHGC of the entire glazing system.

투광형 박막 BIPV 창호 적용에 따른 냉난방 및 조명 부하 저감에 관한 연구

The purpose of this study was to analyze the annual energy demand including heating, cooling and lighting according to kind of windows with transparent thin-film a-Si Building Integrated Photovoltaic(a-Si BIPV) for office building. The analysis results of the annual energy demand indicated that the a-si BIPV window was reduced by 8.4% than the clear gazing window. The base model A was combinate with a-Si BIPV window area of 67% and clear window area of 33% among the total exterior area. The model B is to be applied with low-e clear glass instead of clear glass of the base model A. The model B was reduced to annual energy demand of 1% more than the model A. Therefore, By using a-si BIPV solar module, the cooling energy demand can be reduced by 53%(3.4MWh) and the heating energy demand can be increase by 58%(2.4MWh) than clear glazing window in office building. Also, Model C applied to the high efficient lighting device to the model B was reduced to annual energy demand of 14.4% more than the Model D applied to the high efficient lighting device to the model A. The Model E applied with daylight dimming control system to the Model C was reduced to annual energy demand of 5.9% more than Model C.

EFFECTS OF SEMI-TRANSPARENT GLAZING ON THE EMOTIONS OF OFFICE WORKERS

The use of sunlight has always been a major goal of architects and building owners in the design and operation of commercial buildings to minimize electrical consumption when using artificial lighting. However, glazing systems that are designed to allow optimal visible light transmission also allow significant unwanted direct solar gain. Conversely, glazing systems that are designed to reflect unwanted direct solar heat gain significantly reduce the transmittance of visible light through windows. Semi-transparent window glazing reduces light transmission through windows resulting in unknown effects of the natural illumination of spaces on emotional perceptions of office workers. A survey was administered to assess the emotional effect of office spaces that use semi-transparent glazing as compared to clear glazing during daylight hours. Computer visualization software was used to create animated recordings of an office environment, and a modified lighting approach was used to compute accurate solar irradiance levels for various geographic locations. While an analysis of variance revealed significant differences in satisfaction between groups, the differences did not create negative emotional responses to glazing with lower transmittances.

Evaluating the performance of shading devices and glazing types to promote energy efficiency of residential buildings

This study presents a novel residential envelope transmittance value (RETV) performance-based approach for determining the suitable external shading devices and glazing types to improve energy efficiency in residential buildings. The approach is applied to two residential buildings types, namely, point block and slab block, for any given orientation in an entire year. In this approach, a RETV equation for residential buildings was first developed. Employing this equation, we demonstrated how the design of shading devices and the selection of glazing type impact the cooling load of high-rise residential buildings. Comparing results from the model simulations, the half egg-crate louver was found to be the most suitable shading device for residential buildings facing the north and south orientations, whereas a horizontal projection with 30° downward tilt was appropriate for facade facing the east and west orientations to reduce cooling load. In addition, simulations also indicated low-E single clear glazing to be a suitable glazing since it results in relatively economical short payback periods.

Investigation on energy performance of double skin façade in Hong Kong

Double skin façade can be defined as a building façade covering one or several stories with multiple skins. The skins may be air tight or ventilated. With sophisticated study and design, buildings constructed with double skin façade can have better thermal performance than the conventional single skin façade. This paper reports the findings on the energy performance of double skin façade applied to a typical office building under the climatic condition in Hong Kong. An experimental setup was established and the measured data were used to verify the theoretical model developed via the EnergyPlus simulation program. The validated model was then used to evaluate the energy performance of double skin façade with various configurations including glazing type (clear, absorptive or reflective glass), glazing position (inner or outer pane) and glazing layers (single or double glazing material). The results indicate that a double skin façade system with single clear glazing as the inner pane and double reflective glazing as the outer pane can provide an annual saving of around 26% in building cooling energy, as compared to a conventional single skin façade with single absorptive glazing. However, the long payback period of 81 years makes the double skin façade system economically infeasible. Support and motivation are needed from the local government in order to foster successful and widespread application of the double skin façade system in buildings.