Complex Fenestration Systems Research Articles

Integrating daylight with solar thermal modeling: A dynamic calculation method for complex fenestration systems

This study developed a mathematical model named the DL-E model, which links annual dynamic daylight and solar heat gain calculations for Complex Fenestration Systems (CFSs). The DL-E model utilizes the Klems Bidirectional Scattering Distribution Function (BSDF) to characterize CFSs and can consider the shading effect of obstacles, as well as solar radiation reflected from obstacles and the ground. The DL-E model uses the Perez all-weather model to calculate transmitted solar radiation contributed by diffuse solar radiation, rather than the simplified sky model used in EnergyPlus. Results calculated with the DL-E were compared with those computed with EnergyPlus, and it was found that for most of the results, the both methods yielded closely aligned outcomes. However, for the diffuse transmitted solar radiations, reflected solar radiation from the ground in the case with a vertical obstacle, and the reflected solar radiations from the obstacle, the values calculated with DL-E showed significant differences compared to those calculated with EnergyPlus due to the use of the simplified sky model in EnergyPlus. In contrast, the values calculated with the DL-E model which used the Perez all weather sky model displayed very small difference compared to those calculated with Radiance, which means the values derived with EnergyPlus may produce significant errors. Additionally, a new workflow has been developed for calculating building load and energy for CFSs to avoid the manual conversion of the BSDF files.

Glare analysis of an integral daylighting and lighting control strategy for offices

Complex Fenestration Systems (CFSs) can significantly impact both the visual and non-visual daylight effects on the occupants as well as the energy performance of buildings. To ensure that those impacts improve the overall situation, proper control algorithms are required if the CFS can be operated. The state of the CFS directly and immediately effects the indoor lighting situation. The thermal condition of the building is usually strongly but not directly influenced by the condition of the façade system due to thermal capacities.In this study an experimental integral control strategy, called Integrated Lighting Module (ILM) is investigated in terms of it’s glare prevention capabilities and compared to a cut-off- and a simple rule based control logic. The ILM is an autonomous software package capable to run on building management hardware to control façade systems and artificial lighting in real buildings in an energetically optimised way. The adaptive sampling algorithm raytraverse is employed to calculate Daylight Glare Probability (DGP) values, which are used as a benchmark for the control strategy comparison. The other aspect of this comparison is the opening of the façade, which is evaluated as statistics how often each possible façade state is selected by each control strategy.

Comparative assessment of optical characterization of prismatic materials (PMs), using genBSDF tool for virtual simulations and a goniophotometer for physical measurements

To improve daylight availability and thermal performance of buildings, complex fenestration systems are used to redirect/distribute solar radiation indoors. We need to characterize the optical properties of these complex fenestration systems through measuring their spectral, bidirectional distribution function to evaluate their performance for energy efficiency, daylight availability, and building sustainability purposes. This paper represents the characterization of two different Prismatic Material (PM) products that apply to diverse purposes in buildings. First, we conduct two methods to measure the Bidirectional Scattering Distribution Function (BSDF) of materials; genBSDF raytracing tool of Radiance and goniophotometer measurement (goniophotometry). In the next step, we compare the genBSDF result with the results of the goniophotometry. The aim of this study is to evaluate the angular-based optical behavior of prismatic materials in distributing light and also to assess the reliability of the genBSDF tool result for further simulation of high-performance building purposes. The results demonstrate that the genBSDF raytracing tool method creates a comparable result to the goniophotometry method. Therefore, genBSDF is a robust tool for assessing the solar-optical properties of PMs.

Field validation of isotropic analytical models for simulating fabric shades

Fabric roller shades are common shading materials used in commercial and residential buildings. Accurately characterizing and modeling shades helps practitioners select the appropriate product and its control strategy based on climate and occupants' priorities, such as visual comfort and view to outdoors. Previous studies established a generalized method for modeling complex fenestration systems using data-driven tabulated bidirectional scattering distribution functions. However, deploying such a method at scale to all fabric shading products on the market is too costly and time-consuming. Analytical models that are based on a limited set of measurements (e.g., normal-normal and normal-hemispherical visible transmittance and reflectance, and directional cut-off angles) can be used to model the wide variety of shading products on the market. This study evaluates the performance of two isotropic analytical models, Roos-Wienold and Modified-Kotey, for modeling fabric roller shades, with a focus on the model's ability to predict occupant visual comfort. The performance evaluation was conducted through laboratory and field measurements and simulations. The results showed that both models are sufficient for predicting vertical illuminance at seated eye-level. Roos-Wienold model was able to predict binary visual comfort classification (glare/no-glare) under a wide range of luminance conditions, while Modified-Kotey model did not perform as well under high-contrast low-adaptation conditions. Both models are insufficient in predicting visual comfort at a four-point scale (e.g., imperceptible, perceptible, disturbing, intolerable). The two isotropic models become less accurate when the fabric exhibits high anisotropy.

Development and experimental validation of a CFD model for the thermal behaviour assessment of Complex Fenestration Systems

Complex Fenestration Systems with integrated shading systems are becoming widely used to enhance the building's envelope performance and increase the occupants' thermal and visual comfort. Their peculiarity of integrating a complex shading system makes it difficult to assess their thermal and optical performance. The complexity of the shading system itself, in addition to the interaction with the fluid flow in the window cavity, calls for the use of adequate modelling and simulation techniques. In this framework, a novel modelling approach for the thermal characterization of Complex Fenestration Systems with integrated venetian blinds at different tilt angles has been investigated and validated against onsite measurements under dynamic conditions. The numerical assessment includes a preliminary optical calculation to determine the fraction of solar radiation absorbed by the glazing system and a subsequent Computational Fluid Dynamic simulation to which the absorbed solar radiation is assigned. On the other side, the experimental characterization is based on heat flux, solar irradiance, and temperature measurements. After the model calibration - through the selection of the most appropriate models for the internal and external convective heat transfer coefficients, the numerical simulation showed a good correspondence with experimental data for all analyzed blind tilt angles with a Coefficient of Variation of the Root Mean Square Error in the open blind configuration (18° from horizontal) of 22.75%, 7.27% and 4.74% and in the intermediate blind configuration (37° from horizontal) of 21.14%, 6.02% and 2.86%, respectively for heat flux, external and internal surfaces temperatures.

Solar Angle Model for Daylight Redirection in Prismatic Panel

An advanced complex fenestration system can utilize uniform daylight. Nonetheless, an inefficient design would increase solar heat gain and indoor temperatures, besides uneven light distribution that would cause the "cave effect." Prismatic panels are widely used as complex fenestration systems, providing uniform daylight. This paper proposes a computational model that integrates optical principles like Snell's law with environmental variables and visualizes the performance of prismatic panels in terms of redirection angle while encountering the prism refractive index and geometry at the specified geographic location. The proposed model entails a prismatic panel as a daylight system for redirecting daylight. In contrast to detailed modeling needed for simulation in software programs like Radiance, this computational tool provides a more straightforward and efficient solution for the initial design of light redirection panels that rely on the principle of refraction and evaluate their annual performance based on the angle of deviation. The model's applicability has been demonstrated by utilizing various triangular prism design examples with diverse materials in Frankfurt and Helsinki.

Contrast-based evaluation of the reflected daylight glare on the blackboard in a classroom with complex fenestration systems

Visual comfort within a classroom determines students’ concentration, productivity and well-being. The existing glare-based metric (e.g. Daylight Glare Probability, DGP) cannot reveal the visual comfort level when students look at notes written on the blackboard in a daylit classroom. Contrast-based metric has been proven as a more appreciate method for evaluating the vision within the area of a blackboard. The aim of this article is to explore the applicability of a contrast-based metric in evaluating classroom daylight design. The contrast-based metric was proposed based on the statistical results of a previous study on disturbing reflections on a blackboard. The evaluation method using contrast ratios within the blackboard area was established based on RADIANCE simulation and validated against experimental measurements. Bidirectional scattering distribution function (BSDF) data was used to model the complex fenestration systems (CFS) in the studied classroom. The validation results show that the error of simulated contrast ratio is within 17%. When using the contrast-based metric for assessing the studied classroom with different fenestration designs, the simulation results indicate that applying vertically placed daylight redirecting louver can significantly improve the contrast performance while maintain the daylight availability, providing design guidance for fenestration systems of classrooms. The simulation also illustrates that using DGP in a classroom leads to an underestimation of the glare level. This study contributes to expanding the knowledge on visual environment evaluations of classrooms, demonstrating the capacity of using contrast-based metric on determining disturbing glares in a classroom daylight design.

In-situ evaluation of high-performance glazing based on illuminance and glare

High-technology glazing panes are designed to meet the need for natural light, while optimizing key functions such as reducing solar heat gain in spaces and/or redirecting daylight to the rear of the spaces. However, the actual performance in terms of both illumination and glare protection of these glazing systems is often unknown. This study aims to compare the visual comfort performance of four complex fenestration systems by means of point-in-time measurements under real sky conditions and for different seasons. The tested systems included: two glazing types with embedded seasonal solar protection, namely, MicroShade™ and Coolshade™, one prototype of daylight redirecting glazing with embedded micro-mirrors (GEMM), and one clear glazing. We conducted our tests in side-by-side nearly identical spaces in the NEST building in Dübendorf, Switzerland. Results showed a higher daylight provision for clear and daylight redirecting glazing. Discomfort glare assessment from daylight showed that MicroShade™ was substantially more efficient at addressing glare due to sunlight for high sun angles when compared to Coolshade™. The performance of the GEMM prototype was highly dependent on the glazing pane used and one pane provided a promising performance when it comes to mitigating glare risks for high sun positions. However, none of the systems were able to provide an adequate glare protection for lower sun positions. The performed measurements provide a basis for the calibration of simulation models.

Analysis of dynamic louver control with prism redirecting fenestrations for office daylighting optimization

Daylighting with redirecting complex fenestration system (CFS) may improve the indoor luminous environment. This study is to explore the strategies for controlling louver tilts of dynamic micro-prism film louvers corresponding to different solar incident angles, to optimize the work-plane illuminance (WPI) at the middle/back zone of the analyzed large-depth office, based on the simulation results of daylight filtering. To reduce the rotation frequency of the slats, several slat tilt angles were tested to adapt to the changes of different sun incident angles. The study compared the annual daylight performance and glare levels of the three CFSs with dynamic metal louvers, dynamic micro-prism film louvers, and micro-prism film, using the Five-phase method (5-PM). The results showed that the dynamic micro-prism film louvers combined with the proposed control strategy provided a better daylighting luminous environment, regarding the improved useful daylight illuminance (UDI) at inner space, and yielded less glare occurrence rates at space close to windows, compared with dynamic metal louvers and double glazing. Furthermore, the study proposed the combined dynamic louvers that consisted of micro-prism film slats and metal slats to reduce the possible glare on the premise and improve the indoor illuminance at the inner space. The simulation results showed that the combined dynamic louvers could reduce the discomfort glare occurrence rate by 68.9%, compared to the discomfort rate with double glazing at the front zone; UDI300-2000 lx of the combined louvers could be improved by 23%, compared with that of double glazing at the front zone. Compared with the metal louvers with similar low glare occurrence rate, the combined louvers could improve UDI100-300 lx at front/middle/back zones by 7.9%, 29.1%, and 2.9%, respectively, and UDI300-2000 lx by 40.0%, 11.7%, and 5.7% at these zones, respectively.

Field validation of data-driven BSDF and peak extraction models for light-scattering fabric shades

Shading and daylighting systems affect cooling, heating, and lighting energy use by modulating solar radiation through the building façade. Characterizing shading systems holistically and accurately helps designers and engineers evaluate shading systems to achieve energy and non-energy performance goals. These complex fenestration systems can be modeled using Bidirectional Scattering Distribution Functions (BSDF), which map incident radiation to hemispherical distributions of outgoing radiation. Data-driven, tabulated BSDFs are derived from interpolated goniophotometer measured data, then sampled during the raytracing calculation. A peak extraction (PE) algorithm was developed to circumvent limits in BSDF angular resolution, where the specular peak is extracted during simulation by evaluating the BSDF in the through direction and surrounding region. The objective of this study was to validate this measurement and modeling workflow using field monitored data from a full scale testbed with eleven installed fabrics of different weaves, openness factors, and colors and assess the accuracy of the workflow under different adaptation and contrast conditions. Test conditions were limited to clear sky conditions with the sun in the field of view. Results showed that, for tensor tree datasets, vertical illuminance, solar luminance (2.5° apex), and daylight glare probability (DGP) were predicted to within a mean bias error (MBE) error of −456 lx (−12.3%), −3.46e5 (−38.4%), and −0.042 (−7.8%) when full PE occurred. With a binary classification of glare/ no glare, DGP was predicted accurately with a true positive rate of 0.98 and true negative rate of 1.0 using tensor tree data and less accurately with Klems BSDF data, particularly for cases of no glare. The workflow may be of insufficient accuracy to distinguish borderline performance between fabrics using the four-point glare scale, particularly under low adaptation, high contrast daylit conditions. Errors were due to reductions in peak shape and intensity across the BSDF interpolation and data reduction workflow. Future work is needed to better preserve measurement fidelity during interpolation and sampling, which in turn will improve PE performance.

Solar energy density as a benchmark to improve daylight availability and energy performance in buildings: A single metric for a single-objective optimization

Different simulation engines are currently required to perform daylight and energy evaluations of complex fenestration systems: Radiance has been validated to evaluate complex geometries but EnergyPlus cannot deal with them, making infeasible the thermal evaluations. The Shading Coefficient method adds an extra step to overcome that limitation: it runs irradiance simulations to create shading schedules that are shared between the simulation engines. This work supports the premise that Solar Energy Density (SED) can be used as a benchmark to evaluate the dual performance of perforated screens (PS). Therefore, only irradiance calculations will be required in evaluations – instead of running three different simulations. Orthogonal Arrays and Principal Component Analysis were the statistical techniques used to select the PS sample and weight the simulation results. The resultant SED thresholds concurrently fostered the accomplishment of daylighting and energy goals, at five different orientations: they maximised the daylit area and minimised the overlit area and total energy use. This work also presents an application example of the single-metric approach to test its effectiveness to perform single-objective optimization of PS design by using Evolutionary Algorithms. The SED approach has the advantage of reducing considerably the simulation time needed to perform the parametric optimization of PS.

Calibration of DSF model for real-time control

Double Skin Façades are complex fenestration systems capable to control solar heat gain and ventilation in buildings. Due to the high flexibility of such innovative components, having energy models able to replicate the thermal behaviour of the Double Skin Facades is of utmost importance for their optimal control and integration with building automation strategies. In this context, a numerical model has been developed and validate within the experimental data. The methodological steps are presented in this work and in the last section, the potential applications of the model are discussed.

Multi-state vertical-blinds solar shading – Performance assessment and recommended development directions

The aim of this paper is to evaluate the potential of a novel multi-state sun-tracking vertical-blind (ST-VB) concept using building performance simulation (BPS). A multi-domain simulation toolchain was developed and verified to evaluate the interior vertical-blind concept. The toolchain is used to quantify whole-building performance effects of design choices in the development of the initial concept within a larger framework of functional and aesthetic requirements. Multiple control concepts are tested, including different sun-tracking approaches, utilising the double-sided blind to switch between absorbing and reflecting solar radiation, and the ability to fully retract the blinds versus rotating them into an open position. Different possible materialisations of the blind are tested by evaluating the performance sensitivity of each of the potential control strategies to varying the blinds' solar and visible reflectance. The most promising ST-VB strategies perform substantially better than a conventional automated roller-blind strategy in terms of preventing visual discomfort (8% less DGPs0.4exc0deg), the admission of daylight (75–99% higher sDA300lx/50%), allowing for views to the outdoors (8–33% more hours with a view), and energy performance (11–35% reduction in primary energy consumption for heating, cooling and lighting). This research concludes with a set of recommendations for the development of the ST-VB system and by extrapolating the ‘lessons-learned’ for future research and development into multi-state solar shading systems. The novelty of this research can be found in that automated control concepts for interior vertical blinds have thus far been largely unexplored. Additionally, this research contributes to the body of knowledge on performance modelling of complex fenestration systems and the use of BPS in the, relatively new, context of product development.

Transition Planes for Visual Comfort: Out View with Complex Fenestration System Design at Restaurants in Spain

This work deals with daylighting for quality indoor atmospheres, considering building skins. In recent years, almost all retrofit facades of restaurants are highly glazed façades, boosting glare, sun ray absorption and overheating inside. Most of the time, they are not integrated with daylight control; therefore, lighting and out view requirements are not so balanced. Taking into account this daylighting complexity, an alternative façade system is proposed to simulate by Radiance. Previously, perception simulations are compared with measured data, in order to discretize the simulations. In addition, for one point three different view are assessed as: work plane, relation plane and the out plane. Subsequently, two virtual façade models, windows combined by complex fenestration system (CFS) as prismatic film (PF) and highly glazed façade, are tested according to daylighting. For that, three indexes have been used: daylight glare probability (DGP), daylight glare index (DGI) and daylight autonomy (DA). The results show that the proposed complex façade has a good light contribution with less absorption, while maintaining the outside view. In addition, the DGI is needed to test the out plane, because DGP is more suitable for lower luminance; therefore, each visual plane should be assessed regarding different visual comfort conditions, or parameters and methods. Accordingly, the mean DGI result of window combined by CFS is approximately lower in 5% than highly glazed façade. However, the DA of highly glazed is higher in 5%, but the DA of window combined by CFS is enough, above 80%. Definitely, the complex scene at restaurant with the proposed integrated façade system improves light performance and indoor atmosphere.

A daylight-oriented multi-objective optimisation of complex fenestration systems

Complex fenestration systems (CFS) are effective daylighting strategies that improve daylight performance in indoor living spaces. Nevertheless, the design of CFS is complex as it requires specialised knowledge in optical physics and advanced building simulation. This paper presents an evaluation method (CFStrace) to optimise the CFS design in a multi-objective optimisation setting. The method takes into account both architectural and environmental conditions that maximise the effect of light redirection for complex fenestration systems to its full potential. The research aims to demonstrate a multi-objective and multi-scenario optimisation methodology for designing complex fenestration systems. The parameters of the optimisation problem can be easily changed due to the parametric nature of the modelling environment used. Thus, this gives designers the flexibility to adjust the CFS parameters and decrease their discretisation. To support the presented methodology, a case study is presented to demonstrate the design process and guide designers in selecting the best design option. The case study involves the design optimisation of a sinewave-shaped light redirecting panel by tweaking its geometrical parameters and comparing the optimised result with existing light redirecting panels. The case study results indicate that optimising a CFS according to the architectural design can improve daylight metrics (such as improving the useful daylight illuminance (UDI) by +10%). The case study reveals the importance of addressing architectural and environmental constraints when designing CFS as the optimised design can differ with changing parameters such as the room depth or panel height.

Modeling specular transmission of complex fenestration systems with data-driven BSDFs

A Bidirectional Scattering Distribution Function (BSDF) describes how light from each incident direction is scattered (reflected and transmitted) by a simple or composite surface, such as a window shade. Compact, tabular BSDFs may be derived via interpolation, discretization and/or compression from goniophotometer measurements. These data-driven BSDFs can represent any measurable distribution to the limits of their tabulated resolution, making them more general than parametric or analytical BSDFs, which are restricted to a particular class of materials. However, tabulated BSDFs present a trade-off between higher sampling loads versus lower directional accuracy during simulation. Low-resolution BSDFs (e.g., Klems basis) may be adequate for calculating solar heat gains but fall short when applied to daylight glare predictions. The tensor-tree representation moderates this trade-off using a variable-resolution basis, providing detail where needed at an acceptable cost. Independently, a peak extraction algorithm isolates direct transmission from any tabular BSDF, enabling high-resolution beam radiation and glare analysis through transmitting systems with a “vision” component. Our data-driven BSDF methods were validated with a pilot study of a fabric shade installed in an outdoor, full-scale office testbed. Comparisons between measurement and simulation were made for vertical illuminance, specular and near-specular transmission, and daylight glare probability. Models based on high resolution BSDF measurements yielded superior results when accounting for anisotropy compared to isotropic models. Models with higher resolution produced more accurate source luminance data than low-resolution models. Further validation work is needed to better characterize generality of observed trends from this pilot study.

Modeling specular transmission of complex fenestration systems with data-driven BSDFs

Modeling specular transmission of complex fenestration systems with data-driven BSDFs

CFStrace: An evaluation method to include complex fenestration systems in the façade design process

Complex fenestration systems (CFS) have proven to enhance the daylight quality inside spaces when designed correctly. While research in this area focuses on assessing CFS performance accurately, the number of CFS daylight analysis frameworks are too complex for the building designer to use for selecting a suitable CFS. Also, some CFS design frameworks focus only on light redirection efficiency without considering the spatial or environmental context. The paper demonstrates a new framework to analyse CFS considering both architectural and environmental conditions. The framework is presented as a computational tool (CFStrace), which accepts parametric geometric input and uses forward raytracing to simulate the complex optical behaviour of CFS. The framework also introduces new metrics for the assessment of CFS, which are developed to suit the forward raytracing simulation technique, that predicts the uniformity of redirected sunlight in the built environment and ensures adequate visual comfort to the occupants. A comparison study is carried out to state the effectiveness of the metrics where various CFS designs from previous literature are tested. The comparative case study revealed which CFS designs would be more suitable at the specific setting and location and provided insight on metrics that can be used to assess the feasibility of one design over the other in terms of daylight performance. The new framework will involve less technical and modelling capabilities making it “architect-friendly” encouraging building designers to include CFS in their design process, especially in the early design phase, and pave the way for new CFS designs possibilities.

Assessment of angular visual transmittance of Perforated Masonry Walls patterns employed as solar shading systems

Perforated Masonry Walls are traditional construction systems typical of the Mediterranean area, especially in existing rural buildings. Practical reasons are linked to their original employment as a separation element meant to be air permeable to promote cross-ventilation. Successively, they started to be designed for achieving architectural goals, integrating them with additional internal glazing. Moreover, due to their geometry, they can behave like real solar radiation shades, permitting daylight influx while controlling solar penetration. The implication of the use of these systems on daylighting and energy fields have not been widely analysed. This research intends to establish a starting point for their detailed daylighting analyses, considering them as Complex Fenestration Systems. To do so, brick materials were characterized through direct measurements of visual reflectance on a heterogeneous group of brick samples. Results show that reflectance values fall within the range of 0.081–0.262. Angle-dependent transmittances of seven masonry patterns were produced using Bidirectional Scattering Distribution Functions (BSDF) calculated with Radiance. For which, the highest reduction in visual transmittance values was found for solar incidence angles greater than 45°, reaching peaks approximately at 55–65°. These were tested and compared as shading systems on a test room with a South oriented glazed façade, located in Milan. Their implementation resulted in a mean indoor illuminance decay of ~15%. Lastly, the perforation ratio was confirmed not adequate to provide an insight into the visual performance of shading devices.

Evaluation of the effectiveness of a multi-sectional facade with Venetian blinds and roller shades with automated shading control strategies

Daylighting plays an important role in building design. To maintain visual comfort and provide outdoor views, designers can use multi-sectional facades to extend daylit areas by daylight-redirecting devices and minimize undesired sunlight by movable shading devices. Beyond using specially designed light-redirecting systems, a combination of common shading devices – roller shades and blinds – may be used to meet aesthetic and cost requirements. However, the evaluation and simulation of multi-sectional facades are challenging, especially when the modeling involves complex fenestration systems and automated control strategies. In this study, we evaluate the effectiveness of multi-sectional facades with a roller shade and blind combination. Two control strategies are designed for two different multi-sectional facades, with a workflow developed for the evaluation. This workflow applies Radiance’s three-phase method for each shading state to model movable shades. External scripts are adopted to describe control algorithms and to generate annual results and daylight metrics. The workflow facilitates simulations of daylighting conditions for spaces equipped with both movable shading devices and daylight-redirecting devices under any customized control algorithms. The results demonstrate that the combinations of roller shades, blinds, and proper control algorithms greatly increase daylight near a rear wall compared to cases with only controlled roller shades, and do not cause glare. The combination with fixed blinds and controlled roller shades at the top section and another controlled roller shade at the middle section works well for rear spaces with south-facing or west-facing facades in both Taipei and New York.