Combined effects of daylight transmitted through coloured glazing and indoor temperature on thermal responses and overall comfort
Building and Environment. 2018-08-22. Vol. 144, p. 583-597.
DOI : 10.1016/j.buildenv.2018.08.045.
This study investigates the effect of daylight transmitted through three coloured glazing types (blue, orange and neutral) on thermal responses and overall comfort, at three temperature levels (19 °C, 22 °C and 26 °C). The goal is threefold: (i) understand whether the colour can affect a perception other than the visual (i.e., the thermal); (ii) study whether colour interacts with temperature influencing thermal responses; (iii) examine the combined effect of colour and temperature on overall comfort. A total of 75 participants took part in a controlled experiment. Thermal responses were estimated with questionnaires about subjective thermal estimation and physiological measurements (skin temperature, heart rate and skin conductance). Statistical analyses revealed that daylight transmitted through coloured glazing affected participants' thermal responses, mainly psychologically rather than physiologically, resulting in a colour-induced thermal estimation. With a blue glazing, people felt colder and less comfortable than with a neutral one. With an orange glazing, people felt warmer and more comfortable than with a blue one. Results were independent of temperature levels, but occurred mainly at temperatures perceived as comfortable (26 °C) or close-to-comfortable (22 °C). Overall comfort was also affected, both at the beginning of the colour exposure by only the glazing's colour, and at the end of the exposure by both colour and temperature. Given the significance of effects for the short exposure time and for temperature ranges that are realistic indoors, these findings should be taken into consideration in practice for both comfort and energy savings purposes, especially in transitional spaces.
Development and test application of the UrbanSOLve decision-support prototype for early-stage neighborhood design
Building and Environment. 2018-03-31. Vol. 137, p. 58-72.
DOI : 10.1016/j.buildenv.2018.03.033.
The need for adequate instruments to support practitioners toward achieving sustainable and energy-efficient architectural and urban design has long been acknowledged. Motivated by identified shortcomings of building performance assessment tools for conceptual neighborhood-scale design, this paper proposes a novel workflow to enable practitioners to efficiently explore a space of design alternatives and compare them in terms of their energy and daylight performance. The workflow includes a multi-criteria optimization algorithm, which is coupled to a performance assessment engine based on predictive mathematical models. To get some insight on the potential added value for design and the usability of this approach in practice, the workflow has been implemented as a plug-in to an existing 3D modeling software and subsequently tested by practitioners during workshops, notably on real projects provided by the participants. Outcomes from the workshops, which include responses from the participants to a pre- and post-test survey, are presented. Results highlight the relevance of the proposed workflow for informing decisions about early-stage building massing on the basis of the considered performance criteria. Improvements envisioned for both the workflow and its implementation are highlighted and discussed.
An integrative approach for embodied energy: Towards an LCA-based data-driven design method
Renewable and Sustainable Energy Reviews. 2018-02-27. Vol. 88, p. 123-132.
DOI : 10.1016/j.rser.2018.02.036.
The built environment is one of the major contributors of greenhouse gas (GHG) emissions. To tackle climate change, global targets have been set for this sector. Although life-cycle assessment (LCA) methods are typically used to evaluate a building project's embodied energy in its final stages of development, this evaluation would be especially valuable at early design stages, when the opportunity to modify the design is greatest. In this paper, an extensive review of methods to improve the usability of LCA at the early design stage is presented. Three major issues regarding the application of LCA arose from this analysis at this stage: its time consumption, the lack of design details, and the non-reproducibility of results. Moreover, LCA makes it possible to assess environmental performance, but does not provide design alternatives, which are crucial to introduce environmental targets into an iterative design process. To that end, existing techniques that can address the major LCA issues were identified, together with their respective limits. These include some promising tools that provide and explore design alternatives and their respective environmental performances. Among these tools are exploration methods, which have not been applied to LCA insofar as it is not possible to do so in a reasonable computational time. To bridge this gap, the paper outlines the structure of an LCA-based data-driven design method, which uses a combination of LCA, parametric analysis, data visualization, sensitivity analysis, and target cascading techniques.
Life cycle efficiency ratio: A new performance indicator for a life cycle driven approach to evaluate the potential of ventilative cooling and thermal inertia
Energy Build.. 2018.
DOI : 10.1016/j.enbuild.2017.12.010.
Correspondence: Investigation of Evalglare software, daylight glare probability and high dynamic range imaging for daylight glare analysis
Lighting Res. Technol.. 2018.
DOI : 10.1177/1477153518758612.
A toolkit for multi-scale mapping of the solar energy-generation potential of buildings in urban environments under uncertainty
Solar Energy. 2018.
DOI : 10.1016/j.solener.2018.08.017.
Many municipalities and public authorities have supported the creation of solar cadastres to map the solar energy-generation potential of existing buildings. Despite advancements in modelling solar potential, most of these tools provide simple evaluations based on benchmarks, neglecting the effect of uncertain environmental conditions and that of the spatial aggregation of multiple buildings. We argue that including such information in the evaluation process can lead to more robust planning decisions and a fairer allocation of public subsidies. To this end, this paper presents a novel method to incorporate uncertainty in the evaluation of the solar electricity generation potential of existing buildings using a multi-scale approach. It also presents a technique to visualise the results through their integration in a 3D-mapping environment and the use of false-colour overlays at different scales. Using multiple simulation scenarios, the method is able to provide information about confidence intervals of summary statistics of production due to variation in two typical uncertain factors: vegetation and weather. The uncertainty in production introduced by these factors is taken into account through pairwise comparisons of nominal values of indicators, calculating a comprehensive ranking of the energy potential of different spatial locations and a corresponding solar score. The analysis is run at different scales, using space- and time-aggregated results, to provide results relevant to decision-makers.
Review of Factors Influencing Discomfort Glare Perception from Daylight
LEUKOS. 2018. p. 1-38.
DOI : 10.1080/15502724.2018.1428617.
Because well-being is becoming a major challenge in construction alongside energy efficiency, there is an increasing need to be able to quantify discomfort in buildings. In the case of discomfort glare, the kind of glare provoking an irritating or distracting effect, no current indices can properly explain the high variability existing between individuals’ discomfort glare perceptions. This is due to the fact that some of the factors influencing discomfort glare perception are still unknown and the mechanism behind the discomfort glare process is not well understood. Therefore, this article aims to review the factors potentially influencing discomfort glare perception from daylight. Every factor having been studied at least once for its potential influence on discomfort glare perception has been listed, described, and analyzed. Furthermore, this study categorizes the influence of these factors on discomfort glare by introducing an influence indicator based on the number of studies having investigated the factor, the sample size of these studies, and the agreement between them. The suggested categories rate a factor influence as “almost certain,” “more likely,” “somewhat likely,” “inconclusive,” “somewhat unlikely,” “less likely,” or “almost certainly null.” Tables summarize the main information about the studies and the influencing factors. As expected, factors almost certainly influencing discomfort glare perception are the luminance of the glare source, adaptation level, contrast effect, and size and position of the glare source. In contrast, factors that almost certainly do not influence discomfort glare perception are the gender and optical correction of the observer. All other factors from the list of 30, such as the attractiveness of the view through the window or the culture of the observer, require additional studies to determine whether or not they influence discomfort glare perception.
Adequacy of Immersive Virtual Reality for the Perception of Daylit Spaces: Comparison of Real and Virtual Environments
LEUKOS. 2018. p. 1-24.
DOI : 10.1080/15502724.2017.1404918.
This article presents a novel experimental method that uses a virtual reality (VR) headset, aiming to provide an alternative environment for the conduction of subjective assessments of daylit spaces. This method can overcome the difficulty of controlling the variation of luminous conditions, one of the main challenges in experimental studies using daylight, and its novelty lies in the implementation of physically based renderings into an immersive virtual environment. The present work investigates the adequacy of the proposed method to evaluate five aspects of subjective perception of daylit spaces: the perceived pleasantness, interest, excitement, complexity, and satisfaction with the amount of view in the space. To this end, experiments with 29 participants were conducted to compare users’ perceptions of a real daylit environment and its equivalent representation in VR and test the effect of the display method on the participants’ perceptual evaluations, reported physical symptoms, and perceived presence in the virtual space. The results indicate a high level of perceptual accuracy, showing no significant differences between the real and virtual environments on the studied evaluations. In addition, there was a high level of perceived presence in the virtual environment and no significant effects on the participants’ physical symptoms after the use of the VR headset. Following these findings, the presented experimental method in VR seems very promising for use as a surrogate to real environments in investigating the aforementioned five dimensions of perception in daylit spaces.
Qualité architecturale et durabilité: de longues fiançailles
Magazine Bilan . 2017-08-30. Vol. Editorial, num. supplement “Habitat”, p. 2.
Discomfort glare perception in daylighting: influencing factors
Cisbat 2017 International Conferencefuture Buildings & Districts - Energy Efficiency From Nano To Urban Scale. 2017. Vol. 122, p. 331-336.
DOI : 10.1016/j.egypro.2017.07.332.
The mechanism behind the discomfort glare phenomenon, the kind of glare provoking an irritating or distracting effect, is not well understood. Since some of the factors influencing this phenomenon are still unknown, no current indices can properly explain the high variability existing between individuals' discomfort glare perception. A list of potential factors influencing the degree of perceived discomfort glare in daylighting has been established from existing literature. In addition to the physical quantities commonly used in glare indices, other variables, whether psychological, physiological, related to light or to the context, could influence the degree of perceived discomfort glare. (C) 2017 The Authors. Published by Elsevier Ltd.
“Our Inherent Desire for Control”: a Case Study of Automation’s Impact on the Perception of Comfort
Energy Procedia. 2017. num. 122, p. 925-930.
DOI : 10.1016/j.egypro.2017.07.414.
To investigate the relationship between occupants’ perception of control over building elements and their comfort, we conducted a study where two prototype office rooms were compared: while the first room allowed occupants to open or close the window and configure the shading, the second one was fully automated. The quantitative analysis of collected data a) supports the existing results in the literature reporting higher satisfaction where manual control is maintained, and b) uncovers a new impact of highly automated systems: lower control over building elements can increase the occupant’s consciousness of the environmental factors and the saliency of comfort parameters.
The effects of vegetation on indoor thermal comfort: the application of a multi-scale simulation methodology on a residential neighborhood renovation case study
Energy and Buildings. 2017. Vol. 146, p. 1-11.
DOI : 10.1016/j.enbuild.2017.04.022.
Despite the acknowledged positive effects of vegetation at urban, neighborhood and building scales, there are still only limited comprehensive design tools for multi-scale evaluation of the microclimate and thermal benefits of plants and building-integrated vegetation (BIV) systems. The paper describes a case study in the city of Palermo (Italy) that applied simulation methodology to quantitatively assess the microclimate effects of different neighborhood and building retrofit scenarios where vegetation plays a main role. The simulation workflow moves from a micro-urban to a building scale assessment by linking the ENVI-met software to the building energy simulation program EnergyPlus. The study takes two complementary directions. Firstly, it analyses the influence of plants on urban microclimates to enhance outdoor and indoor temperatures. Secondly, it assesses the benefits of different technical solutions applied to buildings, including BIV systems and windows substitutions, to further improve their thermal behavior. The results of the simulations show a significant reduction in outdoor and indoor temperatures, questioning traditional urban renovation practices and drawing attention to the importance of multi and inter-scale approaches for high-accuracy investigations into buildings’ thermal performances.
Predictive models for assessing the passive solar and daylight potential of neighborhood designs: A comparative proof-of-concept study
Building and Environment. 2017. Vol. 116, p. 1-16.
DOI : 10.1016/j.buildenv.2017.01.018.
Despite recent developments, neighborhood-scale performance assessment at the early-design phase is seldom carried out in practice, notably due to high computational complexity, time requirement, and perceived need for expert knowledge, ultimately limiting the integration of such a task into the design process. In this paper, we introduce a predictive modeling approach to rapidly obtain an estimate of the performance of early-design phase neighborhood projects, from simple geometry- and irradiation-based parameters. The performance criteria considered are the passive solar and daylight potential, respectively quantified by the energy need for space heating and cooling (given certain assumptions) and the spatial daylight autonomy at the ground-floor level. Two predictive models, or metamodels, are developed following distinct techniques: a multiple linear regression function and a Gaussian Processes regression model. These are developed from a reference dataset acquired through the parametric modeling and simulation of neighborhood design variants. When tested on designs provided by professionals, the metamodels with the highest accuracy within the compared types (MLR versus GPs) portray a prediction error below 10% in 87% (respectively 60%) of the cases for the passive solar (resp. daylight) potential. Results show this approach to be a promising alternative to running detailed simulations when comparing early-design variants.
A human-centric approach to assess daylight in buildings for non-visual health potential, visual interest and gaze behavior
Building and Environment. 2017. Vol. 113, p. 5-21.
DOI : 10.1016/j.buildenv.2016.09.033.
This paper introduces a novel approach for the assessment of daylight performance in buildings, venturing beyond existing methods that evaluate 2-dimensional illumination and comfort within a fixed field-of-view in order to predict human responses to light concerning non-visual health potential, visual interest, and gaze behavior in a visually immersive scene. Using a 3D rendered indoor environment to exemplify this coordinated approach, the authors assess an architectural space across a range of view directions to predict non-visual health potential, perceptual visual interest, and gaze behavior at the eye level of an occupant across an immersive field-of-view. This method allows the authors to explore and demonstrate the impact of space, time, and sky condition on three novel daylight performance models developed to predict the effects of ocular light exposure using a human-centric approach. Results for each model will be presented in parallel and then compared to discuss the need for a multi-criteria assessment of daylight-driven human responses in architecture. A parallel and comparative approach can allow the designer to adapt the architectural space based on the program use and occupants needs.
Contrast measures for predicting perceptual effects of daylight in architectural renderings
Lighting Research and Technology. 2017. Vol. 49, num. 7, p. 882–903.
DOI : 10.1177/1477153516644292.
Daylit architecture is perceived as a dynamic luminous composition, yet most existing performance metrics were designed to evaluate natural illumination for its ability to adequately illuminate a two-dimensional task surface and avoid glare-based discomfort. It may be argued that task-driven approaches based on surface illumination and glare ignore the likelihood that contrast can provide positive impacts on our visual perception of space. Advances in these metrics to accommodate climate-based sky conditions and occupant behavior have improved our ability to evaluate task illumination and glare, yet the same attention has not been paid to evaluating positive perceptual responses to daylight. Existing studies have attempted to link subjective ratings of composition to simple global contrast metrics without reaching consensus. More advanced metrics have been developed in computational graphics and vision fields, but have not been applied to studies in qualitative lighting research. This paper introduces the results from an online experiment where subject ratings of daylight composition are compared to quantitative contrast measures across a series of renderings. This paper will identify which measures correlate to subjects’ ratings of visual interest, and introduces a modified contrast algorithm, which can be used as a novel prediction model for visual interest in daylit renderings.
Gaze and discomfort glare, Part 1: Development of a gaze-driven photometry
Lighting Research and Technology. 2017. Vol. 49, num. 7, p. 845–865.
DOI : 10.1177/1477153516649016.
Discomfort glare is a major challenge for the design of workplaces. The existing metrics for discomfort glare prediction share the limitation that they do not take gaze direction into account. In order to overcome this limitation, we developed a ‘gaze-driven’ method for discomfort glare assessment. We conducted a series of experiments under simulated office conditions and recorded the participants’ gaze using mobile eye tracking and the luminance distributions using high dynamic range imaging methods. The two methods were then integrated in order to derive ‘gaze-centred’ luminance measurements in the field of view. The existing ‘fixed-gaze’ and the newly developed ‘gaze-driven’ measurement methods are compared. Our results show that there is a significant difference between the two methods. In this paper the procedure for integrating the recorded luminance images with the recorded gaze dynamics for obtaining gaze-centred luminance data is described. This gaze-centred luminance data will be compared to the subjective assessment of glare in Part 2 of this study.
Le confort, raison d’être de la maison
Le Nouvelliste. 2016. p. 12.
S’il est aujourd’hui courant de discuter de l’efficacité énergétique de sa maison, il reste nettement moins facile d’évaluer le confort qu’elle procure. Essentiel dans tous les aspects de notre vie, le confort est à l’origine de l’existence même de nos bâtiments : sans besoin de confort, pas besoin de maison. Nous avons tendance à penser qu’être confortable consiste à être à l’aise. Mais c’est bien plus que cela. Imaginez-vous installé dans une pièce bien éclairée avec des luminaires, dont la température est stable à 21°C, avec renouvellement d’air, mais sans bruit, et décorée à votre goût… mais sans fenêtre. Combien de temps serez-vous «à l’aise» dans un tel espace ?
Unified framework to evaluate non-visual spectral effectiveness of light for human health
Lighting Research and Technology. 2016.
DOI : 10.1177/1477153516655844.
The discovery of a novel non-rod, non-cone photoreceptor in the mammalian eye that mediates a range of ‘non-visual’ responses to light has required reexamination of how lighting needs for human health are characterized and evaluated. Existing literature provides useful information about how to quantify non-visual spectral sensitivities to light but the optimal approach is far from decided. As more is learned about the underlying biology, new approaches will continue to be published. What is currently lacking is a flexible framework to describe the non-visual spectral effectiveness of light using a common language. Without a unified description of quantities and units, much of the value of scientific publications can be lost. In this paper, we review the existing approaches by categorizing the proposed quantities depending on their application. Based on this review, a unified framework is provided for use in evaluating and reporting the spectral effectiveness of light for human health. The unified framework will provide greater flexibility to model the non-visual responses to light and is adaptable to a wide range of lighting solutions of interest to researchers, designers and developers. A new visualization tool, the SpeKtro dashboard, is available to explore the unified framework on-line at spektro.epfl.ch.
Occupants’ behaviour in energy simulation tools: lessons from a field monitoring campaign regarding lighting and shading control
Journal of Building Performance Simulation. 2015. Vol. 8, num. 5, p. 338-358.
DOI : 10.1080/19401493.2014.953583.
Previous studies have shown that the choice of the behavioural model for the control of lighting and shading devices has important implications in the energy performance assessment of office buildings and directly influences the comparison of design alternatives for control systems as well as for the façades (shading or glazing). Since many behavioural models exist for the same purposes, and in most cases there is no consensus on which ones are more representative of the reality, it is important to perform more real-world observations and draw lessons from them. This study appears in this context and explores the results of a field campaign that continuously monitored occupants’ behaviour regarding manual control of electric lighting and shading devices of eight real-world single offices under normal operation. Detailed measurements and observations were performed over two months in each office with the aim of assessing the level of agreement between existing behavioural models and actual occupants’ behaviour. Findings from this study enabled refining the hypothesis regarding realistic modelling of occupants’ behaviour when considering currently available whole building simulation (BS) software; moreover, needed improvements to increase the reliability of the results in whole BS were identified.
Building occupants in the spotlight
D/A Daylight & Architecture Magazine. 2015. Vol. 24, p. 68-71.
Daylighting brings together questions relevant to architectural design and building engineering, but also to human physiology and behaviour. This magazine article presents a shortened version of a more comprehensive scientific paper published in the Fifty Year Anniversary Golden Issue for Building and Environment.
Review and critical analysis of early-design phase evaluation metrics for the solar potential of neighborhood designs
Building and Environment. 2015. Vol. 92, p. 679-691.
DOI : 10.1016/j.buildenv.2015.05.012.
The energy performance of a building is strongly influenced by its level of solar exposure, in turn affected by the climate, built context, and building morphological characteristics. Since these are typically fixed at the early- design phase, performance assessment methods based on solar considerations at the urban scale are essential to support early decision-making. As the adaptation of the well-developed building performance simulation methods to the urban scale lead to complexity issues, it is of interest to verify whether simpler metrics can act as performance indicators, as is often done at the building level with quantities such as form factor. This paper first presents a review of existing methods that aim at evaluating aspects such as passive heating and photovoltaic potential. We classify each evaluation metric based on its level of complexity, before choosing a representative subset to be further examined. The goal is to test whether simple metrics fulfill their role as performance indicators when applied to neighborhoods. To do so, the selected metrics, including geometrical parameters (e.g. compactness) and solar exposure levels (e.g. annual irradiation), are compared with simulation results (e.g. heating need), taken as reference values. This is done for two sets of designs: six distinct typologies and a large number of variants from a base case typology. Results, which show various levels of correlation between simple metrics and the reference values, highlight the limitations of using any one metric and indicate a need to revise the definition and evaluation metrics of various performance criteria for neighborhood designs.
Unweaving the human response in daylighting design
Building and Environment. 2015. Vol. 91, p. 101-117.
DOI : 10.1016/j.buildenv.2015.03.014.
Daylighting as a research topic situates itself at the interface between psycho-physiological and environmental factors, bringing together questions relevant to architectural design and building engineering, but also to human physiology and behavior. While daylighting has a strong impact on human health and well-being, and an undeniable association with (subjective) emotional delight and perceived quality of a space, it is also highly dynamic and variable in nature, based on a combination of predictable (sun course) and stochastic (weather) patterns. This makes it both a challenging and essential aspect of how “performative” a space can be considered. This paper aims to discuss selected research developments regarding how architectural engineering and other domains of science could be more strongly bridged to address the need for meaningful decision support in daylighting design: how can we better integrate the complexity of human needs in buildings into effective design strategies for daylit spaces? As a basis for discussion and to illustrate this overview, it describes a unified goal-based approach in an attempt to address the multiplicity of perspectives from which daylighting performance can – and should – be evaluated in building design. Through five very different perspectives ranging from task-driven illumination or comfort to human-driven health and perception, it proposes a simulation and visualization framework in which one can start approaching these from an integrated approach.
Visualizing Perceptual Dynamics in Architecture
Phoenix, Bauen im Bestand. 2015. Vol. 1, p. 62-67.
When it comes to value how magnificent buildings are experienced, most designers believe that sunlight is essential. Although architecture is a technical discipline, it lacks a consensus about what quantity and what quality of light are required to make a space efficient.
Dagslys og døgnrytme-relevante behov - Rapport fortæller om ny metode til vurdering af dagslyset i boliger og dets betydningen for vore døgnrytme-relevante behov
Dagslys. 2014. num. LYS 03-2014, p. 10-11.
Les mécanismes de lumière naturelle: analyse des bibliothèques d'Alvar Aalto. (Prix IBE-BIV 2013, Institut Belge de l'éclairage, affilié à la CIE)
Revue E tijdschrift, Revue d'électricité et d'électronique industrielle - Tijdschrift voor elektriciteit en industriele elektronica. 2014. Vol. 130ème année / 130ste jaargang, num. 2-2014, p. 51-55.
Today, the challenges of sustainable development require revisiting all the parameters of architectural design. According to the International Energy Agency , in 2005, 19% of the electricity produced in the world was consumed for lighting. We know that the benefits of natural photons are much better than the blue light of the fluorescent lamps, or the bad chromatic rendering of the LEDs. Daylighting is an aspect which must not be overlooked to face the challenges of sustainable development. To this is added the human dimension of natural light, as a factor of well- being and social cohesion, when it is associated with the concept of "light-space." It is not only a matter of capturing more natural light , but also a matter of distributing by giving it a spatial dimension. By lack of knowledge and data, approaches allowing to simulate the lighting level of a building take only limited account of the spatial and human qualities of natural light. This research aims to articulate natural lighting and architectural design through the analysis of major examples of architecture. Therefore , libraries of the modernist Finnish architect Alvar Aalto, located along a north- south axis, from Germany to Finnish Lapland were studied in detail. These are characterized by high quality lighting scenes, despite the low sunlight under these latitudes. The subtle play of direct and indirect lighting installs some virtual boundaries, creating static and dynamic spaces, which are favorable places for activities and intergenerational meetings, under the light. For the first time, light levels have been measured extensively in a typology of Alvar Aalto's buildings, renowned for his mastery of space and light. This approach allows to consider the design of high performance lighting devices, both from a quantitative and qualitative point of view, and proves to be a relevant point of departure for the analysis of "light-spaces".
Origin and nature of measurement bias in catadioptric parallel goniophotometers
Journal of the Optical Society of America a Optics and Image Science. 2014. Vol. 31, num. 5, p. 1084-7529.
DOI : 10.1364/JOSAA.31.001040.
We briefly categorize and compare parallel goniophotometers, which are instruments capable of simultaneously measuring the far-field distribution of light scattered by a surface or emitted by a source over a large solid angle. Little is known about the accuracy and reliability of an appealing category, the catadioptric parallel goniophotometers (CPGs), which exploit a curved reflector and a lens system. We analyzed the working principle common to all the different design configurations of a CPG and established the specifications implicitly imposed on the lens system. Based on heuristic considerations, we show that the properties of a real (thick) lens system are not fully compatible with these specifications. This causes a bias to the measurements that increases with the acceptance angle of the lens system. Depending on the angular field, the measured sample area can be drastically reduced and shifted relative to the center of the sample. To gain insights into the nature and importance of the measurement bias, it was calculated with our model implemented in MATLAB for the CPG configuration incorporating a lens system with a very large acceptance angle (fisheye lens). Our results demonstrate that, due to the spatio-angular-filtering properties of the fisheye lens, this category of CPGs is so severely biased as to give unusable measurements. In addition, our findings raise the question of the importance of the bias in the other types of CPGs that rely on a lens system with a lower acceptance angle.
Measuring the Dynamics of Contrast & Daylight Variability in Architecture: A Proof of Concept Methodology
Building and Environment. 2014.
DOI : 10.1016/j.buildenv.2014.06.012.
Unlike artificial light sources, which can be calibrated to meet a desired luminous effect regardless of latitude, climate, or time of day, daylight is a dynamic light source, which produces variable shadow patterns and fluctuating levels of brightness. While we know that perceptual impacts of daylight such as contrast and temporal variability are important factors in architectural design, we are left with an imbalanced set of performance indicators – and few, if any, which address the positive visual and temporal qualities of daylight from an occupant point-of-view. If visual characteristics of daylight, such as contrast and spatial compositions, can be objectively measured, we can contribute to a more holistic analysis of daylit architecture with metrics that complement existing illumination and comfort-based performance criteria. Using image processing techniques, this paper will propose a proof-of-concept methodology for quantifying contrast-based visual effects within renderings of daylit architecture. Two new metrics will be proposed; Annual Spatial Contrast and Annual Luminance Variability. Using 56 time step instances (taken symmetrically from across the day and year) this paper will introduce a method for quantifying local contrast values within a set of rendered images and plot those instances over time to visualize hourly and seasonal fluctuations in contrast composition. Using the same 56 instances, this paper will also introduce a method for quantifying variations in luminance (brightness) between instances to measure fluctuations in brightness. This paper pre-validates each of the proposed methods by calculating annual spatial contrast and annual luminance variability across ten abstract digital models and comparing those results to the authors’ own intuitive ranking.
A framework for predicting the non-visual effects of daylight – Part II: The simulation model
Lighting Research and Technology. 2014. Vol. 46, num. 4, p. 388-406.
DOI : 10.1177/1477153513491873.
This paper describes a climate-based simulation framework devised to investigate the potential for the non-visual effects of daylight in buildings. It is part 2 of a study where the first paper focused on the formulation of the photobiological underpinnings of a threshold-based model configured for lighting simulation from the perspective of the human nonvisual system (e.g. circadian response). This threshold-based model employs a static dose-response curve and instantaneous exposure of daylight at the eye to estimate the magnitude of the non-visual effect as a first step towards a simulation framework that would establish a link between light exposure at the eye in an architectural context and expected effects on the non-visual system. In addition to being highly sensitive to the timing and duration of light exposure, the non-visual systems fundamentally differs from the visual system in its action spectrum. The photosensitive retinal ganglion cells that communicate light exposure to the brain is known to be shifted to the blue with respect to the photopic sensitivity curve. Thus the spectral character of daylight also becomes a sensitive factor in the magnitude of the predicted non-visual effect. This is accounted for in the model by approximating `yellow' sunlight, `grey' skylight and `blue' skylight to three distinct CIE illuminant types, and then tracking their `circadian-lux' weighted contributions in the summation of daylight received at the eye. A means to `condense' nonvisual effects into a synthesised graphical format for the year, split by periods of the day, is described in terms of how such a format could inform design decisions. The sensitivity of the simulation model's predictions to prevailing climate and building orientation is demonstrated by comparing results from eight European locations.
Das Smart Living Lab in Freiburg: Ein Gebäude der Zukunft wird Realität
Die Volkswirtschaft. 2013. num. 11, p. 26-27.
Nach der Schliessung der Brauerei Cardinal haben der Kanton und die Stadt Freiburg beschlossen, das Gelände in ein Innovationsquartier namens «Blue Factory» umzuwandeln. Am Projekt beteiligt ist auch die Eidg. Technische Hochschule Lausanne, die den Akzent auf die technologischen Innovationen am Bau legen will. Das daraus hervorgegangene Projekt «Smart Living Lab» soll ein nationales Kompetenzzentrum werden, das verschiedene Akteure und Institutionen aus dem Bereich der Wohntechnologien von morgen zusammenbringt und den Kern eines internationalen Netzwerks rund um diese Thematik bildet.
Le projet SLL à Fribourg: un bâtiment du futur en site réel
La Vie Economique. 2013. p. 26-27.
Suite à la fermeture de la brasserie Cardinal, le canton et la ville de Fribourg ont décidé de transformer le site en un quartier d’innovation (pôle technologique et d’innovation), appelé Blue Factory. L’École polytechnique fédérale de Lausanne (EPFL), associée au projet, a souhaité mettre l’accent sur les innovations technologiques dans le bâtiment. Le projet Smart Living Lab (SLL), qui en a résulté, doit déboucher sur la création d’un centre d’envergure nationale réunissant plusieurs institutions ainsi que d’autres acteurs spécialisés dans les technologies du bâtiment de demain. Il devra également attirer les représentants de la construction et de l’énergie, et fédérer un réseau international autour de cette thématique.
Interactive expert support for early stage full-year daylighting design: a user’s perspective on Lightsolve
Automation in Construction. 2013. Vol. 35, p. 338-352.
DOI : 10.1016/j.autcon.2013.05.014.
Designing spaces that are able to balance illumination, glare and solar gains over a year is a real challenge, yet a problem faced every day by building designers. To assist them, a full year, climate-based daylighting simulation method, called Lightsolve, was developed, providing guided search based on the variation of daylight performance over the year by combining temporal performance visualization with spatial renderings. This paper focuses on the user’s perspective for Lightsolve. After a summary of its foundational concepts, it discusses the results of several pilot and more formal user studies conducted in educational contexts. As a core element of the paper, the method and results of an original, design-oriented user study on Lightsolve’s expert system are discussed. It was conducted to determine how well its decision-making algorithm would work when independent human interactions were included. It demonstrated that the expert system is generally successful as a performance-driven design tool respectful of the non-deterministic nature of the design process itself, and as a method for educating designers to improve daylighting performance.
Modelling 'non-visual' effects of daylighting in a residential environment
Building and Environment. 2013. Vol. 70, p. 138-149.
DOI : 10.1016/j.buildenv.2013.08.018.
The importance of light not only as a therapeutic tool but as an essential element of healthy living has been highlighted by the recent discovery of a specialized photoreceptor in the eye responsible for synchronizing our internal circadian pacemaker. This pigment, melanopsin, differs from visual receptors in several characteristics, here simplified into a blue-shifted spectral sensitivity and a dose-response curve established from night-time studies. While a vast range of tools has been developed to simulate the amount of light in lux or lumens falling on a static, horizontal surface, corneal exposure estimates are needed for modelling the biological responses to light in space, which require a vertical sensor that can rotate and translate as a human eye does. This paper examines the effects of housing design upon the amount of daylight available for maintaining synchronization of the human circadian system considered in conjunction with human movement, using historic Boston row houses as a case study. Based on a series of simulations taking into account the two above-mentioned characteristics of the non-visual system, this paper proposes a preliminary workflow for suggestions regarding lighting restoration and opens new perspectives on future variables to include. This study found that even modest renovations like painting the space a lighter colour have a noticeable impact on the light received by a moving sensor. More aggressive design choices, such as not using the basement floor of the house for apartments, raise the amount and timing of light received to nearly the level of the best-case scenario.
Occupants interaction with electric lighting and shading systems in real single-occupied offices: Results from a monitoring campaign
Building and Environment. 2013. Vol. vol. 64, p. pp. 152-168.
DOI : 10.1016/j.buildenv.2013.03.015.
This study presents the results of a monitoring campaign aiming to further our understanding of occupants' behavior regarding the manual control of electric lighting in combination with shading control. It was performed on eight single-occupied offices in the city of Porto, Portugal during periods ranging from 28 to 60 days per office. A wide range of environmental variables including workplane illuminance, window and background luminance and transmitted solar radiation was measured with high frequency (20 min time steps). The study aimed to address a set of key research questions regarding typical illuminance ranges, luminance distribution and occupancy patterns found in offices and their relationship to electric lighting or shading control actions. It also enabled to compare observed behavior with predictions from benchmarking behavioral models found in the literature. The main findings were that electric lighting and shading control were influenced more by occupational dynamics (arrival and departure) than by the environmental conditions experienced over the day (daylight workplane illuminance or transmitted solar radiation), though with a large degree of variability between occupants and/or offices. It also revealed that while most of the behavioral models analyzed for comparison purposes were in qualitative agreement with field observations (e.g. more lighting switch-on actions at arrival for lower daylight illuminances), only one model (Pigg's model) predicted the frequency of observed lighting switch-off events. These findings strongly support the need for more numerous (and geographically more broadly distributed) office behavior monitoring campaigns to increase the robustness of such models.
Assessing Gaps and Needs for Integrating Building Performance Optimization Tools in Net Zero Energy Buildings Design
Energy and Buildings. 2013. Vol. 60, p. 110-124.
DOI : 10.1016/j.enbuild.2013.01.016.
This paper summarizes a study undertaken to reveal potential challenges and opportunities for integrating optimization tools in net zero energy buildings (NZEB) design. The paper reviews current trends in simulation-based building performance optimization (BPO) and outlines major criteria for optimization tools selection and evaluation. This is based on analyzing user's needs for tools capabilities and requirement specifications. The review is carried out by means of a literature review of 165 publications and interviews with 28 optimization experts. The findings are based on an inter-group comparison between experts. The aim is to assess the gaps and needs for integrating BPO tools in NZEB design. The findings indicate a breakthrough in using evolutionary algorithms in solving highly constrained envelope, HVAC and renewable optimization problems. Simple genetic algorithm solved many design and operation problems and allowed measuring the improvement in the optimality of a solution against a base case. Evolutionary algorithms are also easily adapted to enable them to solve a particular optimization problem more effectively. However, existing limitations including model uncertainty, computation time, difficulty of use and steep learning curve. Some future directions anticipated or needed for improvement of current tools are presented.
Achieving informed decision-making for net zero energy buildings design using building performance simulation tools
Building Simulation. 2013. Vol. 6, num. 1, p. 3-21.
DOI : 10.1007/s12273-013-0105-z.
Building performance simulation (BPS) is the basis for informed decision-making of Net Zero Energy Buildings (NZEBs) design. This paper aims to investigate the use of building performance simulation tools as a method of informing the design decision of NZEBs. The aim of this study is to evaluate the effect of a simulation-based decision aid, ZEBO, on informed decision-making using sensitivity analysis. The objective is to assess the effect of ZEBO and other building performance simulation tools on three specific outcomes: (i) knowledge and satisfaction when using simulation for NZEB design; (ii) users’ decision-making attitudes and patterns, and (iii) performance robustness based on an energy analysis. The paper utilizes three design case studies comprising a framework to test the use of BPS tools. The paper provides results that shed light on the effectiveness of sensitivity analysis as an approach for informing the design decisions of NZEBs.
Influence of shading control patterns on the energy assessment of office spaces
Energy and Buildings. 2012. Vol. 50, p. 35-48.
DOI : 10.1016/j.enbuild.2012.03.019.
This work reviews existing models of control patterns for occupant-shading interactions in office buildings, and studies their influence in terms of energy demand when comparing transparent façade alternatives. It starts by establishing a review of visual comfort criteria in office buildings and of the conditions that prompt occupants to interact with shading devices and electric lighting. Given the large variety of parameters identified as primary variables in the existing literature–hence the variety of conditions considered comfortable depending on the chosen reference–a sensitivity study was carried out based on dynamic simulations. The aim of the study was to characterize the impact of choosing a given shading control model (pattern or strategy) on the calculated overall energy demand for heating, cooling and lighting, as well as the impact on choosing the best-performing transparent façade option for a single-occupant office. The results show that both the calculated energy performance and the ranking of transparent façade alternatives (glazing and shading) often vary very significantly with control patterns considered for the occupant-shading interaction. They further show that, amongst the eleven control strategies that were considered, the behavioral model based on a glare acceptability threshold (expressed as DGI > 20) is the one that, when considered individually, would most reliably express an average ranking from all considered strategies. The implications of these findings are discussed in view of their applicability to energy performance-based façade design choices evaluation as well as to façade design choices.
Comprehensive Annual Daylight Design through a Goal-Based Approach
Building Research & Information. 2012. Vol. 40, num. 2, p. 154-173.
DOI : 10.1080/09613218.2012.641301.
Decisions affecting building form and orientation and choices regarding opening size, type and positioning have a great effect on the building’s access to daylight and are typically made during the earliest stages of architectural design. Computer simulations of daylight performance have become a powerful tool for making design decisions, especially since the diurnal and seasonal changes in daylight necessitate an annual, climate inclusive performance analysis because of the strong influence of climate conditions on daylight accessibility. However, the amount and complexity of information generated by an annual analysis can be overwhelming, so a need exists for appropriate, user-friendly methods to process and communicate these data to the designer. To address this problem, an alternative approach to traditional daylight analysis is explored here to develop appropriate goal-based metrics and annual graphic display formats which present illuminance, glare and solar heat gain data with a focus on time variations. Graphic outputs are created using the temporal map format to improve understanding of daylight performance as it varies over the year, and to enable comparisons to be made between spatial and non-spatial quantities. In particular, a consistent and intuitive triangular colour scale is proposed to express goal compliance, so as to enhance further comparability between dissimilar quantities and thereby assist with critical choices and performance tradeoffs during the design process.
A framework for predicting the non-visual effects of daylight – Part I: photobiology-based model
Lighting Research and Technology. 2012. Vol. 44, num. 1, p. 37-53.
DOI : 10.1177/1477153511435961.
This paper investigates the formulation of a modelling framework for the nonvisual effects of daylight, such as entrainment of the circadian system and maintenance of alertness. The body of empirical data from photobiology studies is now sufficient to start developing preliminary non-visual lighting evaluation methods for lighting design. Eventually, these non-visual effects have the potential to become a relevant quantity to consider when assessing the overall daylighting performance of a space. This paper describes the assumptions and general approach that were developed to propose a modeling framework for occupant exposure to non-visual effects of light, and presents a novel means of visualizing the ‘circadian potential’ of a point in space. The proposed approach uses current outcomes of photobiology research to define – at this point static – threshold values for illumination in terms of spectrum, intensity and timing of light at the human eye. These values are then translated into goals for lighting simulation, based on vertical illuminance at the eye, that – ultimately – could become goals for building design. A new climate-based simulation model has been developed to apply these concepts to a residential environment. This will be described in Part 2 of this paper.
A Generative Façade Design Method Based on Daylighting Performance Goals
Journal of Building Performance Simulation. 2012. Vol. 5, num. 3, p. 141-154.
DOI : 10.1080/19401493.2010.549572.
Successful daylighting design is a complex task which requires the designer to consider numerous design elements and their effects on multiple performance criteria. Facades in particular include many variables which may dramatically impact daylighting performance. Genetic algorithms (GAs) are optimization methods which are suitable for searching large solution spaces such as those presented by design problems. This paper presents a GA-based tool which facilitates the exploration of facade designs generated based on illuminance and/or glare objectives. The method allows the user to input an original 3d massing model and performance goals. The overall building form remains the same while facade elements may change. Ten parameters were considered, including materials and geometry of apertures and shading devices. A simple building data model is used to automatically generate a 3d model of each solution. Results from single and multi-objective case studies are presented to demonstrate a successful goal-driven design exploration process.
An Interactive Expert System for Daylighting Design Exploration
Building and Environment. 2011. Vol. 46, num. 11, p. 2351-2364.
DOI : 10.1016/j.buildenv.2011.05.016.
Architects increasingly use digital tools during the design process, particularly as they approach such complex problems as designing for successful daylighting performance. However, while simulation tools may provide the designer with valuable information, they do not necessarily guide the user towards design changes which will improve performance. This paper proposes an interactive, goal-based expert system for daylighting design, intended for use during the early design phase. The expert system consists of two major components: a daylighting knowledge-base which contains information regarding the effects of a variety of design conditions on resultant daylighting performance, and a fuzzy rule-based decision-making logic which is used to determine those design changes most likely to improve performance for a given design. The system gives the user the ability to input an initial model and a set of daylighting performance goals in the form of illuminance and daylighting-specific glare metrics. The system acts as a “virtual daylighting consultant,” guiding the user towards improved performance while maintaining the integrity of the original design and of the design process itself. Two sets of case studies are presented: first, a comparison of the expert system results to high performing benchmark designs generated with a genetic algorithm; and second, an evaluation of the expert system performance based on varying levels of aesthetic constraints. The results of these case studies indicate that the expert system is successful at finding designs with improved performance for a variety of initial geometries and daylighting performance goals.
A daylighting knowledge-base for performance-driven facade design exploration
LEUKOS - The Journal of the Illuminating Engineering Society of North America. 2011. Vol. 8, num. 2, p. 93-101.
DOI : 10.1582/LEUKOS.2011.08.02.001.
Heuristics and simple design guides are important tools for designers who wish to incorporate daylighting into the early design process. This paper describes a simulation-based method for generating simple rules for facade design, based on specific climate data. This approach uses the Design of Experiments methodology to populate a detailed daylighting knowledge-base. To enable consideration of both visual performance and visual comfort, the knowledge-base contains information about whole-year, climate-based illuminance and glare metrics. The design parameters considered include window and shading device geometry and glazing materials. This approach is valuable for both design and educational uses by providing a simple way to approach daylighting early in the design process and by educating designers about how various design elements affect daylighting performance.
Using Digital Imaging to Assess Spectral Solar-Optical Properties of Complex Fenestration Materials: A New Approach in Video-Goniophotometry
Solar Energy. 2010. Vol. 84, num. 4, p. 549-562.
DOI : 10.1016/j.solener.2009.02.005.
A large variety of angularly selective fenestration systems have been developed in the past two decades and show great potential in improving visual comfort while reducing energy consumption, especially when combined with spectrally selective properties. Such systems include light-redirecting glazing, shading, film coatings, reflectors and others. To assess the potential of these systems accurately and reliably, one needs to be able to predict in detail how they modify the energy, direction and spectral make-up of solar radiation. For this assessment, spectral (wavelength-dependent) Bidirectional Transmission or Reflection Distribution Functions are used, usually referred to as BTDFs or BRDFs, or more generally BSDFs for Scattering Functions.
Transmission Illuminance Proxy HDR Imaging: A New Technique to Quantify Luminous Flux
Lighting Research & Technology. 2009. Vol. 41, num. 1, p. 27-49.
DOI : 10.1177/1477153508097670.
A technique to measure arbitrarily complex luminous fluxes across large areas is presented. The technique is founded on high-dynamic range (HDR) imaging technology and can be achieved using a standard consumer digital camera and everyday materials such as printer-grade white paper. The same approach can also be used to determine the direct and diffuse components of illuminance. The technique has been named transmission illuminance proxy - high dynamic range imaging or TIP-HDRI.
Using Digital Cameras as Quasi-Spectral Radiometers to Study Complex Fenestration Systems
Lighting Research & Technology. 2009. Vol. 41, num. 1, p. 7-25.
DOI : 10.1177/1477153508094651.
This work discusses the use of digital cameras fitted with absorption filters as quasi-spectral radiometers. By filtering incident light into selected wavelength intervals, accurate estimates of radiances can be made for unknown spectra. This approach is being employed as part of a new video-projection goniophotometer to study the properties of angularly and spectrally selective complex fenestration systems. Complex fenestration systems are increasingly being used to distribute solar radiation purposefully in buildings. They can be utilized to optimize energy performance and enhance daylighting. Radiance estimates from calibrated digital cameras enable the assessment of quasi-spectral, bi-directional scattering distribution functions of total radiance transmitted or reflected by a fenestration system over desired wavelength intervals. A silicon and an indium gallium arsenide digital camera are used to enable measurements across a 380 to 1700 nm wavelength interval.
Estimating Spectral Information of Complex Fenestration Systems in a Video-Goniophotometer
Lighting Research & Technology. 2008. Vol. 40, num. 4, p. 269-285.
DOI : 10.1177/1477153508092003.
The effective use of complex fenestration systems in buildings requires knowledge of their optical spectral and directional properties. While the directional properties are commonly assessed by the measurement of bidirectional transmission or reflection distribution functions, the addition of spectral information would significantly aid in the design and analysis of such systems. This paper describes the development of a spectral estimation method that reconstructs reflectance and transmittance spectra of unknown complex fenestration samples in the Heliodome, an innovative video-goniophotometer. The estimation method relies on the digital output of a tri-chromatic charge-coupled device camera in eight filterbands to reconstruct a sample's spectrum using the truncated generalised singular value decomposition. This method is validated by comparing estimated spectra with documented reflectance and transmittance spectra of reference samples. In most spectrally selective materials, the method achieved average improvements of 50% over the Heliodome's previous quasi-spectral assessment method.
An intuitive daylighting performance analysis and optimization approach
Building Research And Information. 2008. Vol. 36, num. 6, p. 593-607.
DOI : 10.1080/09613210802243159.
The effective integration of daylighting considerations into the design process requires many issues to be considered simultaneously, such as daily and seasonal variations, illumination, and thermal comfort. To address the need for early integration into the design process, a new approach called Lightsolve has been developed. Its key objectives are to support the design process using a goal-oriented approach based on iterative design improvement suggestions; to provide climate-based annual metrics in a visual and synthesized format; and to relate quantitative and qualitative performance criteria using daylighting analysis data in various forms. This methodology includes the development of a time-segmentation process to represent weather and time in a condensed form, the adaptation of daylight metrics that encompass temporal and spatial considerations, and the creation of an interactive analysis interface to explore design options and design iterations. This system relies on optimization techniques to generate these suggestions. Lightsolve allows the designer to explore other design alternatives that may better fulfil the objectives and to learn about appropriate strategies to resolve daylight or sunlight penetration issues. It offers architects and building engineers support for daylighting design that can be employed interactively within the existing design process.
Graphical Representation of Climate-Based Daylight Performance to Support Architectural Design
LEUKOS – The Journal of the Illuminating Engineering Society of North America. 2008. Vol. 5, num. 1, p. 39-61.
DOI : 10.1582/LEUKOS.2008.05.01.003.
Many conventional daylighting design tools are limited in that each simulation represents only one time of year and time of day (or a single, theoretical overcast sky condition). Since daylight is so variable - due to the movement of the sun, changing seasons, and diverse weather conditions - one moment is hardly representative of the overall quality of the daylighting design, which is why climate-based, dynamic performance metrics like Daylight Autonomy (DA) and Useful Daylight Illuminance (UDI) are so needed. Going one step further, the annual variation in performance (condensed to a percentage by DA and UDI) is also valuable information, as is the ability to link this data to spatial visualizations and renderings. Trying to realize this combination of analytical needs using existing tools would become an overly time-consuming and tedious process. The challenge is to provide all information necessary to early design stage decision-making in a manageable form, while retaining the continuity of annual data. This paper introduces a climate data simplification method based on a splitting of the year into 56 periods, over which weather conditions are "averaged" and simulated using Perez's ASRC-CIE sky model, while information on sun penetration is provided at a greater resolution. The graphical output of the produced data in the form of "Temporal Maps" will be shown to be visually, and even numerically, comparable to reference case maps created using short time step calculations and based on illuminance data generated by Daysim.
Preliminary Method for Prospective Analysis of the Circadian Efficacy of (Day)Light with Applications to Healthcare Architecture
LEUKOS – The Journal of the Illuminating Engineering Society of North America. 2008. Vol. 5, num. 1, p. 1-26.
DOI : 10.1582/LEUKOS.2008.05.01001.
Recent studies have attempted to link environmental cues, such as lighting, with human performance and health, and initial findings seem to indicate a positive correlation between the two. Light is the major environmental time cue that resets the human circadian pacemaker, an endogenous clock in the hypothalamus that controls the timing of many 24-hour rhythms in physiology and behavior.
Interactive Selection of Optimal Fenestration Materials for Schematic Architectural Daylighting Design
Automation In Construction. 2008. Vol. 17, num. 7, p. 809-823.
DOI : 10.1016/j.autcon.2008.01.002.
Complex fenestration systems, such as prismatic and laser cut panels, are emerging as attractive options in architectural design thanks to their high potential to assist in energy and comfort issues. These systems can be used to redirect intense illumination from the sun but have complex transmissive properties that in turn depend on continuously changing illumination conditions due to the dynamic nature of natural light. The resulting non-intuitive interactions with the built environment make it necessary to develop tools that adequately represent these systems' behavior to the architect. The method presented in this paper enables simulation of the direct and indirect illumination from the sun and sky throughout each day for different months Preprint submitted to Automation in Construction 17 December 2007 of the year. The user can interactively explore the high-dimensional configuration space to select optimal materials early in the design process, using both qualitative and quantitative design criteria to make adjustments. (C) 2008 Elsevier B.V. All rights reserved.
Goniophotometry and assessment of bidirectional photometric properties of complex fenestration systems
Energy And Buildings. 2006. Vol. 38, num. 7, p. 836-848.
DOI : 10.1016/j.enbuild.2006.03.009.
This paper seeks to provide an overview of the currently available assessment tools for bidirectional transmission or reflection distribution functions (BTDFs and BRDFs) of complex fenestration systems (CFS). In the first part of the paper, the existing experimental devices (goniophotometers) developed specifically for CFS measurement are described. All but two are based on a scanning process to investigate the emerging light flux distribution, the alternative approach being based on digital imaging techniques. A critical analysis of their advantages and shortcomings is proposed to provide both researchers interested in replicating them and more generally potential users of BTDF or BRDF data with a lucid idea of the available options.
Validation of the performance of a new bidirectional video-goniophotometer
Lighting Research & Technology. 2006. Vol. 38, num. 4, p. 295-313.
DOI : 10.1177/1477153506071332.
An accurate knowledge of the directional optical properties of advanced fenestration materials is necessary for them to be adequately integrated in buildings. These properties are expressed by the Bidirectional Transmission (or Reflection) Distribution Functions (BTDF, BRDF) of such elements, which are measured by specifically designed measuring equipment: an innovative, time-efficient bidirectional goniophotometer, based on digital imaging techniques, was designed and set up for that purpose. In this paper, the in-depth validation used for the bidirectional measurements performed with this apparatus is presented. It is based on different approaches including experimental error estimation, comparisons to analytical or ray-tracing based models and to other measured data, and calculation of the directional-hemispherical transmittance (reflectance) gauged against measurements of the same systems with Ulbricht (integrating) spheres. The high accuracy and reliability of this novel device were confirmed by this detailed investigation, and led to a maximum error for BT(R)DF data of only 10%.
Experimental validation of simulation methods for bi-directional transmission properties at the daylighting performance level
Energy and Buildings. 2006. Vol. 38, num. 7, p. 878-889.
DOI : 10.1016/j.enbuild.2006.03.008.
The objective of this paper is to assess the capability of existing lighting simulation methods to predict the performance of Complex Fenestration Systems (CFS), whose potential in daylight and sunlight control make them an increasingly popular alternative to conventional glazing. The research was conducted in two phases. First, collect reliable reference data by taking illuminance measurements inside a black-box under a measured and controlled external luminance distribution, the black-box's only aperture being covered with a complex glazing sample. Two types of materials were used: a Serraglaze™ element and a Laser Cut Panel (LCP). Several simulation methods were then investigated and validated against this reference case. For the first method, measured BTDF for both material samples were integrated into different simulation tools to determine the resulting indoor lighting conditions under the external luminance distribution chosen for the reference case. The same method was then applied with calculated BTDF data, based on ray-tracing calculations. Finally, one of the CFS (the LCP) was modeled using the backward ray-tracer RADIANCE so that the inside illuminance distribution could be deduced without requiring BTDF data. The comparison between the experimental reference data and the simulation results showed that the effect of the CFS on the room's illumination could be predicted with acceptable accuracy for most of the tested methods (generally within 10–20%). The simplicity of the testing scenarios allowed error sources related to simulation to be highlighted and helped determine the extent to which an accurate physical description of the samples could influence the results. Based on this study, recommendations were made for a better use of existing simulation methods.
Development and validation of a Radiance model for a translucent panel
Energy and Buildings. 2006. Vol. 38, num. 7, p. 890-904.
DOI : 10.1016/j.enbuild.2006.03.006.
Abstract This study describes the development and validation of a Radiance model for a translucent panel. Using goniophotometer data combined with integrating sphere measurements, optical properties of the panel were derived and converted into a Radiance model using the trans and transdata material types. The Radiance model was validated in a full-scale test room with a facade featuring the translucent panel material. Over 120,000 desktop and ceiling illuminances under 24,000 sky conditions were measured and compared to simulation results using the Perez sky model and a Radiance-based daylight coefficient approach. Overall mean bias errors (MBE) below 9% and root mean square errors (RMSE) below 19% demonstrate that translucent materials can be modeled in Radiance with an even higher accuracy than was demonstrated in earlier validation studies for the plastic, metal, and glass material types. Further analysis of results suggests that the accuracy of around ±20% currently reached by dynamic Radiance/Perez/daylight coefficient calculations for many material types is sufficient for practical design considerations. A procedure is described showing how goniophotometer and integrating sphere measurements can be used to accurately model arbitrary translucent materials in Radiance using transdata function files.
Un outil numérique au service de l’éclairage naturel (A simulation tool to support natural lighting)
TRACÉS – Lumière urbaine (Invited paper). 2005. num. 01/02, p. 15-19.
La protection de l’environnement fait aujourd’hui partie des préoccupations majeures de notre société ; dans ce contexte, la nécessité de réduire la consommation énergétique dans le bâtiment se place comme une priorité. Dans le domaine de l’éclairage, et plus spécialement de la lumière naturelle, des recherches poussées cherchent à optimiser l’utilisation de la lumière du jour pour économiser de l’énergie et mettre à profit ses qualités dans le domaine du confort et du bien-être.
Design of a time-efficient video-goniophotometer combining bidirectional functions assessment for transmission and reflection
Solar Energy Materials And Solar Cells. 2005. Vol. 88, num. 1, p. 97-118.
DOI : 10.1016/j.solmat.2004.10.009.
A detailed knowledge of the light distribution characteristics through advanced window systems is required to improve the visual comfort of the building's occupants while controlling the propagation of daylight in rooms and the solar gains. An innovative bidirectional goniophotometer has recently been set up for this purpose, using digital image capture and the projection of the emerging light on a diffusing screen. It therefore provides a continuous investigation of the bidirectional transmission figures in a time-efficient way. This instrument was converted into a double-purpose device, allowing both transmission and reflection measurements, which induced several strong constraints due to the conflict of incident and emerging light flux in reflection mode: on one hand the incident beam had to be restricted to the sample area only; on the other hand, as the screen obstructed the incoming light flux in some positions, a special opening in the latter was required. The practical answer to these constraints, detailed in this paper, proved to be reliable, appropriate and efficient. (c) 2004 Elsevier B.V. All rights reserved.
Bi-directional transmission properties of Venetian blinds: experimental assessment compared to ray-tracing calculations
Solar Energy. 2005. Vol. 78, num. 2, p. 187-198.
DOI : 10.1016/j.solener.2004.06.005.
An accurate evaluation of daylight distribution through advanced fenestration systems (complex glazing, solar shading systems) requires the knowledge of their Bidirectional light Transmission (Reflection) Distribution Function BT(R)DF. An innovative equipment for the experimental assessment of these bi-directional functions has been developed, based on a digital imaging detection system. An extensive set of BTDF measurements was performed with this goniophotometer on Venetian blinds presenting curved slats with a mirror coating on the upper side.
Inclusion of the specular component in the assessment of bidirectional distribution functions based on digital imaging
Solar Energy. 2005. Vol. 79, num. 2, p. 159-167.
DOI : 10.1016/j.solener.2004.11.012.
To describe complex fenestration systems such as novel solar blinds, new glazing or coating materials, daylight and sunlight-redirecting devices, a detailed description of their optical properties is needed, given by their Bidirectional Transmission (or Reflection) Distribution Functions (commonly named BTDFs and BRDFs). These functions are angle-dependent at both the incidence and the emission levels, and are defined as the ratio of the luminance of a surface element in a given direction (after diffuse transmission or reflection) to the illuminance on the sample. However, these functions are capable of describing the specular as well as the diffuse components of emerging light, and their mutual knowledge is necessary to properly assess a glazing or shading system’s daylighting performances and benefit from their potential as energy-efficient and users’ comfort strategies. Although the analytical expression of a BT(R)DF differs whether it is related to specular or diffuse light, a simultaneous assessment of the two components can be achieved under certain conditions. These conditions are analyzed for the particular data acquisition procedure developed for a novel type of bidirectional goniophotometer, based on digital imaging.
Comparing daylighting performance assessment of buildings in scale models and test modules
Solar Energy. 2005. Vol. 79, num. 2, p. 168-182.
DOI : 10.1016/j.solener.2005.01.011.
Physical models are commonly used to assess daylighting performance of buildings using sky simulators for purpose of research as well as practice. Recent studies have pointed out the general tendency of scale model assessments to overestimate the performance, usually expressed through work plane illuminance and daylight factor profiles, when compared to the real buildings. The cause of the discrepancy between buildings and scale models is due to several sources of experimental errors, such as modelling of building details, mocking-up of surface reflectances and glazing transmittance, as well as photometer features. To analyse the main sources of errors, a comparison of a full scale test module designed for experimentation of daylighting systems and its 1:10 scale model, placed within identical outdoor daylighting conditions, was undertaken. Several physical parameters were studied in order to determine their impact on the daylighting performance assessment. These include the accurate mocking-up of surface reflectances, the scale model location, as well as the photometric sensor properties. The experimental study shows that large discrepancies can occur between the performance figures. They lead, on average, to a relative divergence of + 60 % to + 105 % in favor of the scale model for different points located in the side lit room. Some of these discrepancies were caused by slight differences in surface reflectances and photometer cosine responses. These discrepancies were reduced to a + 30 % to + 35 % relative divergence, by putting in the effort to carefully mock up the geometrical and photometrical features of the test module. This included a sound calibration of photometric sensors, whose cosine-response appeared at the end to be responsible for the remaining relative divergence observed between the daylighting performance figures.
Matrix-based analysis of digital images: application to goniophotometric measurements with variable referential
Optics and Lasers in Engineering. 2005. Vol. 43, num. 3-5, p. 419-435.
DOI : 10.1016/j.optlaseng.2004.03.011.
Digital video-based luminance mapping systems require the establishment of a precise relation between the considered spatial referential and the associated pixel coordinates on the image. Such a relation may vary with the measurement conditions, and an adjustment of the geometric calibration therefore becomes necessary. In this paper, a methodology for adapting the image calibration according to the referential transformations is proposed, based on the use of a set of matrices individually associated to each spatial coordinate. These matrices are modified with analytical conversions in order to define the actual measurement situation. The description of this approach is given through an application example on a recent bidirectional goniophotometric device, based on digital imaging, proving the consistency of the adopted methodology.
Generalization of the direct sky component calculation to openings of arbitrary tilt angle
LEUKOS - The Journal of the Illuminating Engineering Society of North America. 2004. Vol. 1, num. 2, p. 39-55.
DOI : 10.1582/leukos.2004.01.02.002.
Among the three components of daylight affecting a surface's illumination inside a room, the direct component, due to light flux reaching the surface element directly from the sky, (also called sky factor) is the most significant one. Its estimation must therefore be as accurate as possible when assessing the daylighting performances of a building.
BTDF measurements and ray-tracing simulations comparisons for prismatic glazing
International Daylighting RD&A newsletter, University of Sydney, Australia (Invited paper). 2003. Vol. 5, p. 11-14.
Marilyne Andersen, Solar Energy and Building Physics Laboratory, EPFL, Switzerland, presents a detailed validation approach for bi-directional properties of complex fenestration systems.
Comparison between ray-tracing simulations and bi-directional transmission measurements on prismatic glazing
Solar Energy. 2003. Vol. 74, num. 2, p. 157-173.
DOI : 10.1016/S0038-092X(03)00115-4.
Evaluation of solar heat gain and daylight distribution through complex window and shading systems requires the determination of the bi-directional transmission distribution function (BTDF). Measurement of BTDF can be time-consuming, and inaccuracies are likely because of physical constraints and experimental adjustments. A general calculation methodology, based on more easily measurable component properties, would be preferable and would allow much more flexibility. In this paper, measurements and calculations are compared for the specific case of prismatic daylight-redirecting panels. Measurements were performed in a photogoniometer equipped with a digital-imaging detection system. A virtual copy of the photogoniometer was then constructed with commercial ray-tracing software. For the first time, an attempt is made to validate detailed bi-directional properties for a complex system by comparing an extensive set of experimental BTDF data with ray-tracing calculations. The results generally agree under a range of input and output angles to a degree adequate for evaluation of glazing systems. An analysis is presented to show that the simultaneously measured diffuse and direct components of light transmitted by the panel are properly represented. Calculations were also performed using a more realistic model of the source and ideal model of the detector. Deviations from the photogoniometer model were small and the results were similar in form. Despite the lack of an absolute measurement standard, the good agreement in results promotes confidence in both the photogoniometer and in the calculation method.
Light distribution through advanced fenestration systems
Building Research & Information. 2002. Vol. 30, num. 4, p. 264-281.
DOI : 10.1080/09613210210132937.
Most energy-saving applications of advanced fenestration systems, e.g. solar blinds, novel types of glazing and daylight redirecting devices, require a precise knowledge of their directional light-transmission features. These photometric properties are described by a Bi-directional Transmission Distribution Function (BTDF), which is experimentally assessed by a bi-directional photogoniometer. As such a function represents a heavy amount of data, there is a need for a synthetic and intuitive visualization of a system's transmission behaviour. For this purpose, four kinds of graphical representations have been created and are presented in this paper. These are based on bi-directional data assessed by a novel digital imagingbased photogoniometer, whose measurement principle allows a continuous knowledge of the whole transmission space, and therefore an appreciable liberty in data processing. The geometric properties of the different representations are described, together with the corresponding image operations. The information extraction from these graphical visualizations is given through a comparison example between a conventional venetian blind and an optimized prototype. La plupart des mesures d'économie d'énergie appliquées aux systèmes de fenêtrage de pointe, comme les stores pare-soleil, les nouveaux types de vitrage et les dispositifs de réorientation de l'éclairage naturel, exigent une connaissance précise des caractéristiques de la transmission directionnelle de la lumière. Ces propriétés photométriques correspondent à la fonction bidirectionnelle de transmission (BTDF) qui est évaluée expérimentalement par un photogoniomètre bidirectionnel. Une telle fonction représentant un très grand volume de données, une visualisation synthétique et intuitive du comportement de la transmission d'un système devient nécessaire. A cet effet, quatre types de représentations graphiques ont été créés et sont présentés dans cet article. Ils reposent sur des données bidirectionnelles évaluées par un nouveau photogoniomètre à imagerie numérique dont le principe de mesure permet une connaissance continue de l'ensemble de l'espace de transmission permettant ainsi une liberté appréciable dans le traitement des données. Les propriétés géométriques des différentes représentations sont décrites avec les opérations appliquées aux images. L'extraction d'information de ces visualisations graphiques est donnée par un exemple de comparaison entre un store vénitien classique et un prototype optimisé.
Experimental assessment of bi-directional transmission distribution functions using digital imaging techniques
Energy & Buildings. 2001. Vol. 33, num. 5, p. 417-431.
DOI : 10.1016/S0378-7788(00)00103-1.
Many daylighting applications require a precise knowledge of the directional transmission features of advanced fenestration materials. These photometric properties are described by a bi-directional transmission distribution function (BTDF), whose experimental assessment requires an appropriate equipment. A novel bi-directional photogoniometer, based on digital imaging techniques, has been designed and developed for that purpose. The main advantages of this device are the significant reduction of the time required for data measurement and its capability to assess an almost continuous BTDF function. These features can be achieved only through detailed and accurate calibration procedures of the bi-directional photogoniometer, which are described in this paper, together with digital image and data processing. Several experimental results, obtained for different fenestration materials, are used to illustrate the capabilities of this novel equipment.
Bi-directional Photogoniometer for advanced glazing materials based on digital imaging techniques
International Daylighting, newsletter, University of Sydney, Australia (invited paper). 1999. Vol. 2-99, num. 8, p. 12.
The photogoniometer is composed of a computer-controlled movable mechanical support, presenting two main rotation axes that are powered by DC motors. It uses an accurate and reliable gear technology (harmonic drivers) and is controlled by a micro-computer. The light source is placed 6 meters above. It consists of a short-arc discharge lamp (2.5 kW HMI) combining high luminous efficiency (96 lumen/Watt) with a daylight-close spectum (5600 K); it is placed in a floodlight projector equiped with a hyperbolic mirrored reflector, Fresnel lens and an optical conic element to enhance beam uniformity. A high illuminance uniformity is observed on the sample (better than 3%).