Electrochromic Glazing Research Articles

Decision-making process for thermal comfort and energy efficiency optimization coupling smart-window and natural ventilation in the warm and hot climates

Many studies were conducted to reduce energy demand and consumption in buildings related to HVAC systems, mainly in warm and hot climates, where heat gain from the envelope is relevant. In this context, the window is the component that demands more attention as it usually shows a low thermal performance and represents the weakest component in the building envelope. This work proposes a method to evaluate window performance considering operation strategies regarding dynamic solar control and passive cooling in commercial buildings in subtropical and tropical climates. Parametric simulations were run for three Brazilian cities testing three windows compositions – laminated, insulated, and electrochromic glazing – with hybrid ventilation. Personalized codes were developed to establish rules for window control and prioritize actions to meet energy-saving and thermal comfort for five electrochromic and five hybrid ventilation controls. It was proposed the Pareto-optimal frontier to obtain the optimal set of solutions. The results showed that electrochromic windows reached an energy saving of up to 6.1% to 8.6% in the studied cities. The most influential variables were solar radiation incidence, external illuminance level, and outdoor air temperature. The method is adequate to establish guidelines for window controlling in warm and hot climates, especially coupling different techniques.

Electronic properties and ion migration of “in vacuo” lithiated nanoporous WO3:Mo thin films

Electrochromic (EC) glazing helps manage daylight and solar heat gains in building, thereby allowing a reduction in energy consumption caused by heating, cooling, and artificial lighting. This study relates the optical and electronic properties of nanoporous amorphous molybdenum-doped tungsten trioxide thin films (WO3:Mo) in the pristine state and upon lithiation. When such a film is used as a cathode in EC devices, the color neutrality can be improved with respect to pure WO3, and electrochromic transmission control can be achieved in the full spectral range of solar radiation. In situ x-ray photoelectron spectroscopy reveals that the coloration mechanism is related to the reduction of W6+ to W5+ and Mo6+ to Mo5+. In the initial stages of lithiation, Mo is preferably reduced followed by the reduction of W. Ultraviolet photoelectron spectroscopy highlights systematic trends in the position of the valence band edge and in work function. The occurrence of peaks at 2.2 and 0.8 eV is observed and is related to the formation of partially delocalized Mo5+ and W5+ midgap states. Visible/near-infrared spectrophotometry shows initial absorption mainly in the visible spectral range, followed by absorption in the near infrared. Both absorption bands can be associated with the midgap states due to the occurrence of Mo5+ and W5+, respectively. Lithiation of bilayers composed of WO3:Mo and WO3 shows that the Mo5+ states, which are energetically lower, trap preferentially the transferred charges. Furthermore, our results suggest that lithium ions diffuse rather freely in the direction perpendicular to the substrate. These findings pave the way to next-generation EC devices with color neutral and broadband modulation of spectral transmission and in principle also with dual-band modulation of visible and near-infrared light.

ENERGY PERFORMANCE OF BUILDINGS USING ELECTROCHROMIC SMART WINDOWS WITH DIFFERENT WINDOW-WALL RATIOS

ABSTRACT The electrochromic (EC) smart window is a promising intelligent technology for improving the energy performance of a building. When applying a new glazing material, the window-wall ratio (WWR) is regarded as a significant factor related to daylight and building energy losses. However, there have not been any studies examining the relationship between the efficiency of the EC smart window and the WWR. The aim of this study is to provide strategies for mitigating energy losses and environmental impacts from window elements in an office building. It focuses on optimizing the WWR of EC smart windows to increase building energy efficiency. Double EC, low-emissivity (low-E), and clear glazing materials are simulated combined with five WWRs from 0% to 80% with an interval of 20%, four window orientations, and humid subtropical and Mediterranean climates. The results show that a 40% WWR in a southern-facing building façade using a humid subtropical climate setting provides the optimum energy performance of EC glazing among all the configurations tested. Since it was also found that EC glazing reduces the cooling load, it is more suitable for climate conditions characterized by a hotter temperature with greater solar irradiation. Future research should consider the impact of WWR when balancing thermal, lighting and ventilation requirements, and the properties of EC glazing.

ENERGY PERFORMANCE OF BUILDINGS USING ELECTROCHROMIC SMART WINDOWS WITH DIFFERENT WINDOW-WALL RATIOS

ABSTRACT The electrochromic (EC) smart window is a promising intelligent technology for improving the energy performance of a building. When applying a new glazing material, the window-wall ratio (WWR) is regarded as a significant factor related to daylight and building energy losses. However, there have not been any studies examining the relationship between the efficiency of the EC smart window and the WWR. The aim of this study is to provide strategies for mitigating energy losses and environmental impacts from window elements in an office building. It focuses on optimizing the WWR of EC smart windows to increase building energy efficiency. Double EC, low-emissivity (low-E), and clear glazing materials are simulated combined with five WWRs from 0% to 80% with an interval of 20%, four window orientations, and humid subtropical and Mediterranean climates. The results show that a 40% WWR in a southern-facing building façade using a humid subtropical climate setting provides the optimum energy performance of EC glazing among all the configurations tested. Since it was also found that EC glazing reduces the cooling load, it is more suitable for climate conditions characterized by a hotter temperature with greater solar irradiation. Future research should consider the impact of WWR when balancing thermal, lighting and ventilation requirements, and the properties of EC glazing.

Transmittance thresholds of electrochromic glazing to achieve annual low-glare work environments

A recent study on the glare protection performance of electrochromic (EC) glazing showed that visible transmittance levels lower than 0.6% are necessary to achieve comfortable situations for sun positions, that were close to the central field of view. However, the question that arises is how often such situations occur throughout the year and how the glare protection performance of EC systems is for typical office situations for different climates and orientations. This study aims to quantify the annual performance for such configurations by applying improved simulation methods to conduct annual glare simulations and comparing them to the EN17037 classifications. The enhancement of the simulation method compared to existing methods was necessary to correctly consider the blurring effect in the lens of the eye – neglecting this would lead to an overestimation of glare.We found that for mid and north European climates the extreme situations do not occur such often, so that the ECglazing systems being able to switch to transmittance levels of 1% can mitigate glare throughout the year reasonably well for typical office situations and reaches typically the highest glare protection category according to EN17037 for a viewing direction, that is parallel to the facade. For more sunny climates such as Rome, slightly lower transmittance levels (around 0.5%) would be necessary to achieve a similar glare protection level.The study also revealed that tables E.7 and E.8 of EN17037 with pre-calculated 95-percentile Daylight Glare Probability (DGP) values should be re-calculated.

Human-plant centric shading control: Considering the impact of shading systems on both occupants’ and plants’ requirements

Traditionally, control strategies are applied to automate switchable electrochromic glazing systems (EC) to save energy and provide comfort for occupants indoors. In addition, the plants’ minimum requirements and the consequences of active shading on the supplemental artificial lighting for plants should be considered when designers want to embrace Biophilic design. This paper introduces a simulation workflow to evaluate the impact of shading activation on both human and plant requirements year-round using combined climate-based daylight (Radiance) and building energy simulation tool (TRNSYS). Finally, the simulated total electricity demand for supplemental lighting for plants in a prototypical office room in temperate climate condition are presented and discussed under different control strategies.

Controlling Switchable Electrochromic Glazing for Energy Savings, Visual Comfort and Thermal Comfort: A Model Predictive Control

Dynamic façades play an important role in enhancing the overall performance of buildings: they respond to the environmental conditions and adjust the amount of transmitted solar radiation. This paper proposes a simulation-based framework to evaluate the energy and comfort performance of different control strategies for switchable electrochromic glazing (EC). The presented method shows the impact of a model predictive control (MPC) on energy savings and on visual and thermal comfort for different orientations compared to other strategies. Besides manual operation and conventional rule-based controls, the benchmark in this study was a simulation-based control (multi-objective penalty-based control) with optimal performance. The hourly results of various control cases were analyzed based on the established performance indicators and criteria. The cumulative annual results show the capabilities and limitations of each control strategy for an EC glazing. For a temperate climate (Mannheim, Germany), results showed that an MPC for EC glazing provides visual and thermal comfort while saving energy of up to 14%, 37%, 37%, and 34% respectively for facing north, east, south, and west relative to the base-case.

Behind electrochromic glazing: Assessing user's perception of glare from the sun in a controlled environment

The adaptable transmittance of electrochromic glazing allows to control the solar radiation entering buildings, yet the level of transmittance needed to protect from glare is still an unanswered question. To bridge this gap, this study evaluates the level of visible light transmittance (τv) required for blue-tinted low transmittance glazing to prevent discomfort glare when the sun is visible through the glazing. Twenty participants were exposed to four visual scenarios with varying viewing directions and window transmittance. Results indicate that when the sun is close to the central field of view, a normal-hemispherical transmittance, τv, n-h of 0.6% prevents disturbing glare for most users but does not provide a comfortable situation (this condition corresponds to a “seen” sun disc’s luminance of 4.8 M cd/m2). To achieve comfortable situations, a τv, n-h of 0.14% was found suitable. For non-critical viewing directions, τv n-h of 0.6% is sufficient to achieve visually comfortable space for most participants. This study also examined the reliability of five discomfort glare metrics by comparing their objective output to subjective responses for the tested conditions. The contrast-based metrics (Daylight Glare Probability, CIE Glare Index, Unified Glare Probability, Daylight Glare Index) possess a valid positional sensitivity and show higher Spearman’s rank correlations (ρ – 0.56–0.59) compared to solely saturation-based metrics as the vertical illuminance (Ev) (ρ – 0.44).

Impact of active façade control parameters and sensor network complexity on comfort and efficiency: A residential Italian case-study

Extensive literature exists on the use of dynamic shading devices for the control of visual and thermal comfort in non-residential buildings, however research in the residential sector is far less widespread. Several control strategies and thresholds are utilised in literature, yet it is unclear how these should be chosen. The aim of this work is to evaluate the impact of several control strategies and parameters on three Key Performance Indicators (KPIs) (adaptive overheating, useful daylight illuminance and heating demand) in a case-study apartment near Bologna, Italy, modelled in TRNSYS 18 and Radiance. Multiple levels of complexity were tested to evaluate the extent of the benefits of each sensor (temperature, irradiance and occupancy). Three commercially available solar control devices were simulated: external and integrated Venetian blinds and electrochromic (EC) glazing. The study has shown that occupancy-based controls can greatly reduce overheating, while irradiance sensors are only beneficial for certain orientations. The cut-off angle’s limited effectiveness was revealed, as fully closing blinds led to significant additional overheating reductions. Complex controls did not always outperform simpler controls. Heating demand was found to be easy to minimise, while the trade-off tends to be between overheating risk and daylighting availability. Each control parameter’s impact on the KPIs has been evaluated. Optimal solutions are identified which yield near-best performance for all three KPIs, however such ‘optimal’ solutions may not represent the wishes of all users, therefore more studies are required to calibrate the control to the user experience.

Subjective assessment of visual comfort in a daylit workplace with an electrochromic glazed façade

Electrochromic (EC) glazing is increasingly employed in building façades to achieve better visual comfort for the occupants. EC glazing can modulate the light entering through the façade by varying the solar transmittance of the glass and therefore can work as a shading strategy to minimize solar heat gains or glare. However, it also alters the spectrum and distribution of light entering through the façade, which influences certain visual attributes associated with a space. This user assessment study evaluates some of these attributes including the colour perception of the elements inside and outside the room, the uniformity of daylight distribution, the clarity of the view through the glazing and the perception of glare when the sun is in the field of view. Results indicate a visual transmittance (τv) of 0.6% is sufficient to control glare when the sun is in the peripheral field of view (FOV) while τv,n-n of 0.14% is required to control glare when the sun is close to the central FOV. Most of the participants did not perceive the colours of outdoor environment as natural when seen through EC glazed window. The majority of participants also desired to change the glazing configuration by adding an additional shading device.

Electrochromic window integration in adaptive building envelopes in different climates: a genetic optimization of switchable glazing parameters to reduce energy consumptions in office buildings

During last decades, many efforts have been made to address challenges regarding building energy consumption. A particularly interesting and effective field of development in the building domain is represented by responsive technologies applied to transparent envelopes. Among these technologies, the electrochromic (EC) glazing is one of the most developed solutions thanks to its capability to dynamically modulate daylight and thermal radiation, simply applying a controlled external voltage. The aim of this study is to provide a methodology to analyse smart responsive technologies and optimize the properties of an ideal switchable glazing to find the best configuration for a medium office in different climatic zones. The genetic optimization considers a 5-elements genome, constituted of the following genes: i) solar heat gain coefficient in bleached (SHGCB) and ii) coloured state (SHGCC), iii) visible light transmittance in bleached (VLTB) and iv) coloured state (VLTC) and v) thermal transmittance (U). Moreover, different European cities were selected as representative of different climatic zones and results obtained give a set of ideal EC glazing configurations in the case of EC window controlled by daylighting sensors.

Enhancing energy efficiency and comfort in buildings through model predictive control for dynamic façades with electrochromic glazing

Reducing building energy consumption while ensuring indoor comfort conditions is driving the building envelope transition from static to responsive . In this context, electrochromic windows represent a promising solution to manage optical and thermal requirements in response to changing boundary conditions or user requirements, and control strategies play a central role in the exploitation of this technology. The present paper proposes a Hybrid Model Predictive Control strategy for the online operation optimization of an electrochromic-based active façade . The controller was implemented and tested on a simulated case study. This was achieved by co-simulating the optimal controller which used reduced data-driven grey-box model, with a high accuracy white-box physical model. This setup enabled to close the control loop and to perform an accurate performance benchmarking. Results showed that the proposed Hybrid Model Predictive Control strategy outperformed two baseline Rule Based Controllers, reducing simultaneously energy consumption, peak power and percentage of discomfort hours by up to 82%, 71% and 51% respectively. In comparison with the two baseline controllers and considering all the scenarios, the overall energy consumption could be reduced by approximately 40%–60% on average. In addition the work demonstrates how tuning the Hybrid Model Predictive Control weights adds flexibility to the controller, significantly changing its behaviour to meet the requirements of the designer. • A test cell equipped with a switchable electrochromic window was modelled. • A grey-box model of the zone and window was developed and calibrated. • A Hybrid Model Predictive Control strategy was formulated for the window control. • A comprehensive controller performance benchmarking was performed.

Study of Electrochromic (EC) and Gasochromic (GC) Glazing for Buildings in Aspect of Energy Efficiency

Abstract The paper analyzes the impact of switchable glazing: electrochromic (EC) and gasochromic (GC) on the energy efficiency of the building. Using the analytical and comparative method, the energy-relevant EC and GC glazing features were defined. Secondly, experimental studies on the energy-saving role of EC and GC glazing in various climatic zones were analyzed. The paper aims to define this role. The analyzes were referred to the thermal and lighting aspects. Comparisons were made between the EC and GC technologies, as well as with traditional - “static” types of glazing. The analysis showed differences in the technical characteristics of both technologies. Despite the differences, the results prove a beneficial effect of EC and GC glazing on the reduction of usable energy consumption in the building. The impact is most significant in terms of relieving the cooling and air conditioning systems. In this field, EC glazing was determined a more favorable technology. Further detailed research is required, focusing mainly on the lighting aspect for moderate and cold climate zones. The research was summarized with a collective evaluation of the energy-related role of EC and GC glazing.

Energy consumption of hybrid smart water-filled glass (SWFG) building envelope

Thermal properties have significant impact on ecological footprint and life-cycle assessment of buildings. This is even more crucial aspect for glass buildings, which have been criticised as major factors in climate change around the world. Recent debates on glass facades, which culminated in plans for a “glass building ban” in New York City highlighted the importance of innovation in glass construction.The current solutions for mitigating energy consumption for glass facades are improving insulation (U-value) and solar heat gain coefficient (SHGC) with advanced glazing or using shading devices. A fourth approach is the recent technology of water-filled glass (WFG), which utilizes water layer to improve thermal comfort and energy performance of the façade.This paper introduces Smart Water-filled Glass (SWFG) control method, which enables the change of the opacity of the façade element by colouring the fluid over a year regarding seasonal changes. The impact of changing transparency of water layer on cooling and heating energy demand is evaluated by simulating and analysing the energy performance of a reference office room with large glazing facade in different climates.The significance of this energy evaluation is that a water-filled glass with switchable transparency is simulated and assessed here for the first time. The paper analyses the performance in seven cities from all relevant major climatic regions using LBNL WINDOW and TRNSYS (v.18) As a novel approach, the simulation study makes it possible to evaluate the overall performance of two proposed operational methods (insolation-based & storage-based) for adjusting water layer settings depending on climate conditions and reusability of the captured heat in water layer. Moreover, seven different base cases are presented in this study to compare the performance of proposed system, including conventional solutions (e.g. double or triple glazing with/without shading) and a state-of-the-art switchable technology (e.g. electrochromic glazing or EC).The results verify the hypothesis that the impact of SWFG compared to WFG varies depending on the climate with 0%-5.28% for hot climates and 0.25–3.39% for climates with heating demand. The discussion includes comparison with standard glass facades, where SWFG shows 47.41%-78.01% energy savings depending on climate. The climate-based approach of SWFG and WFG offers a significant shift in façade design that sees glass buildings as an opportunity for sustainability rather than liability for climate change.

Life cycle cost analysis on three high-performance glazing systems for an office building in New Cairo, Egypt

ABSTRACT In the hot desert climate zones, the energy consumption of fully glazed office buildings is too high due to the heavy cooling loads. This problem forced architects to use the High-Performance Glazing Systems (HPGSs) which reduce the solar heat gain and save energy. Despite the high initial cost, the HPGSs are supposed to be economically feasible in the long term. This study investigates and compares the economic feasibility of three HPGSs for an office building in New Cairo. In terms of life cycle cost (LCC), the Low-E, Electrochromic, and Photovoltaic glazing systems are compared to the Clear Double-Glazing as a conventional system. Furthermore, the three economic indicators; Net Present Value (NPV), Internal Rate of Return (IRR), and Payback Period (PBP) are analysed. In conclusion, the Low-E Glazing System has the lowest LCC because of the low disposal cost. Moreover, the Low-E glazing has the highest NPV, IRR, and the shortest PBP (15 years). Due to the high initial and maintenance costs, the Photovoltaic Glazing System has a higher LCC. The Electrochromic Glazing System is not economically feasible due to the highest LCC, the lowest NPV, the lowest IRR, and the longest PBP which exceeds 30 years.

A comparative life cycle assessment of three high-performance glazing systems for office buildings in a hot desert climate zone

In hot desert climates, the office buildings with high-performance glazing systems (HPGSs) provide better indoor thermal and visual comfort to the occupants due to the advanced coatings which prevent the undesired heat gain and daylight. However, these systems save energy in the use phase; it could consume more energy in the pre-use and post-use phases. Furthermore, the use of advanced materials may have negative impacts on the environment. Therefore, this paper selected the comparative life cycle assessment method as an environmental measuring tool to compare the energy consumption and the environmental impacts of three HPGSs with that of the conventional clear double-glazing system. The results show that the photovoltaic glazing system (PVGS) has the lowest energy consumption and the lowest environmental impacts, followed by the electrochromic glazing system (ECGS) and the low-E glazing system. In the use phase, both PVGS and ECGS achieved the highest energy savings, 87% and 25%, respectively. The use phase has a major contribution to the energy consumption and environmental impacts, while the pre-use and post-use phases have insignificant contributions in this study. The results could support decision-makers in choosing the most environmentally friendly HPGS for their projects.

Multi-criteria selection of high-performance glazing systems: A case study of an office building in New Cairo, Egypt

The energy consumption of fully glazed office buildings is very high due to the heavy cooling loads in summer. Therefore, building designers resort to the High-Performance Glazing System (HPGS) solutions to reduce solar heat gain and save energy. However, the selection of most sustainable HPGS is considered a complicated process because the one criterion decision method - which building designers still tend to use - cannot solve this complexity. Multi-Criteria Decision Making (MCDM) analysis can solve this problem and rank the alternatives. In this paper, the Analytic Hierarchy Process (AHP) - one of the MCDM methods - is applied by SuperDecisions software to rank three proposed HPGS alternatives for an existing office building in New Cairo, Egypt as a case study in a hot desert climate zone. Four criteria of sustainability (energy, environmental impacts, cost, and occupant comfort) are assessed and a new weighting method is applied based on LEED rating system to prioritize the alternatives. The ranking results show in the first place the Photovoltaic glazing system followed by the Low-E and Electrochromic glazing systems, respectively with a negligible difference. The Life cycle cost criterion is the major influencer on the ranking results according to the applied sensitivity analysis.

Multi-Season Assessment of Occupant Responses to Manual Shading and Dynamic Glass in a Workplace Environment

The quality and controllability of the building façade can significantly contribute to building indoor environmental quality (IEQ) as well as the building’s energy efficiency. Advanced technologies that support a façade’s dynamic response to climatic changes, such as electrochromic (dynamic) glazing, have emerged as smart systems for IEQ and environmental sustainability. This research summarizes a four-season study of office workers moving from a floor with conventional blinds to work environments equipped with smart dynamic glazing which changes tint in response to weather condition to control daylighting levels. Multiple occupant environmental satisfaction surveys were conducted over one year to investigate differences in environmental and psychological responses to office settings with manual, and often static, facades as compared to offices with dynamic glazing. This research confirms that dynamic glazing significantly affected occupants’ environmental satisfaction—enhancing individuals’ environmental perceptions and psychological health—as compared to manual blinds. It reveals that the occupants in work environments with dynamic glazing reported 21.7% higher productivity gains, 24.8% increased ability to relax, 12.7% improved concentration, 25.3% better moods and 29.4% greater alertness than when they were in offices in the same building with manual shading devices. Also, the dynamic feature of the smart glazing showed a significant contribution to perceived work productivity while enhancing positive emotional responses by an average of 26%.

Optimal control parameter for electrochromic glazing operation in commercial buildings under different climatic conditions

Electrochromic glazing can dynamically control solar heat gains of windows depending on the indoor and outdoor environments. This means that the energy performance of buildings with the electrochromic glazing window systems are affected by control parameters and climatic conditions. This study proposes an optimized electrochromic glazing control parameter and value to improve the energy performance and sustainability of medium-sized commercial building in different climates. It characterized the annual heating and cooling energy consumption of a typical building model with the window systems for different potential control parameters, such as outdoor air temperature, room air temperature, solar radiation incident on the window, and global horizontal solar irradiance. A pattern search algorithm was applied to derive the optimal control value of each parameter for four window orientations in six different climatic conditions. Our results show that for the electrochromic glazing window operation, outdoor air temperature is the most effective control parameter for reducing both cooling and heating energies in all window orientations and climatic conditions. When the electrochromic glazing window on three sides of building is controlled at the optimal outdoor air temperature, the cooling coil size of the air handling unit decreased by 16.5% on average under different climatic conditions. Furthermore, the daily peak cooling loads reduced by an average of 11.8%. The annual heating and cooling energy consumption decreased by 46.1kWh (17.4%) on average per unit window area compared with the typical static window case under six different locations.

The Potential of Smart Glazing for Occupant Well-Being and Reduced Energy Load in a Central-Mediterranean Climate

The ever-increasing aesthetically driven demand for fully glazed façades poses a design challenge; not least in controlling the cooling demand and occupant well-being of such buildings, especially in a central Mediterranean climate. This paper outlines the ever-important need to design for occupants and for designers to keep in mind, first and foremost, occupant well-being rather than aim solely to create energy-efficient buildings. The original objective of buildings was to provide shelter. Today however, the need for occupant comfort and its direct effect on productivity cannot be ignored. This need, therefore, ought to feature a central role in any building design. Studies show that occupant well-being is directly related to a range of environmental factors, particularly daylight distribution, glare and indoor air temperature. The use of external shading devices and more commonly, indoor blinds are often the adopted approaches to attempt to achieve indoor occupant comfort, often to the detriment of views. Adaptive facades seek to address the need to somehow strike a balance between occupant comfort and energy efficiency. These facades range from exterior and interior shading devices with varying control strategies, to the different forms of adaptive/switchable glazing technologies intended to control the visual light transmittance and solar radiation transmitted into a building’s interior. In the opinion of the authors, electrochromic glazing has a great potential in a cooling-dominated central Mediterranean climate, to achieve a compromise between occupant visual and thermal comfort whilst retaining unobstructed outdoor views at all times. Research shows that the potential benefits of electrochromic glazing have not yet been studied enough in real-life scenarios,and this paper further introduces the objectives for field study within two identical offices, having a South-South-East orientation, located in a central Mediterranean climate.