Daylight Coefficients Research Articles

Application of Building Information Modelling (BIM) Six Dimension (6D) in Green Buildings: A Case Study of Sunshine and Daylight Analysis

Although a considerable amount of research has been focused on how building information modeling (BIM) helps improve sustainable construction, BIM(6D) model validation and efficient data analysis methods are still lacking. This study aims to provide the more effective research method and analytical method. The Greenjiansville Sunshine analysis software Sun2020 and daylight analysis software Dali2020 were used for 6D modeling and simulation and real simulation of a building outside the daylight range and time. The daylight coefficients, outdoor visual field observation rate, and daylight quality were calculated for the rooms inside the building. The results show that single the daylight statistics and analysis color map can not accurately analyze whether the actual daylighting meets the demand, but combined with Power BI comprehensive analysis can get fast and accurate results. This paper provides important guidance for building researchers and practitioners to better align BIM development with green building development in the future.

Uncertainty in daylight calculations

There is uncertainty in every daylighting calculation, an inherent and unavoidable imprecision which exists in addition to any error due to inaccuracy in a numerical model. It occurs because neither the future state of a building nor the future luminance pattern of the sky can be predicted with certainty. This paper examines the propagation of error in a daylight coefficient calculation and concludes that the overall effect of uncertainty in the various parameters is significant and must be taken into account in practice. The theory of daylight coefficients is extended. The daylight factor under a uniform sky is shown to be equal to twice the mean of the daylight coefficients, making it possible to compare criteria used in climate-based simulation with older daylighting standards. Simple examples are used as illustrations, with theoretical working and numerical experimentation. Guidelines are given for good practice.

An out-of-core photon mapping approach to daylight coefficients

Climate-based daylight modelling (CBDM) is an effective means of assessing the performance of daylight redirecting components (DRCs) with highly directional scattering to determine their impact on daylight availability and visual comfort. Such a simulation imposes significant computational demands on commodity hardware as it requires high density luminance samples obtained by forward raytracing. We propose an out-of-core photon mapping method within the Radiance framework to compute high quality daylight coefficients as a basis for CBDM. The method is particularly suited to angularly selective DRCs exhibiting strong redirection in conjunction with non-uniform sky luminance distributions with high resolution subdivisions. Our implementation is a work in progress and currently accommodates up to 4.3G photons on disk, while optimizing the in-core memory footprint by loading only photons which actually contribute flux to sensor points. We also leverage the fact that photon paths are independent through parallelization.

Evaluating daylighting potential and energy efficiency in a classroom building

In this paper, we analyze the possibility of using daylight as the main source of light for learning and teaching activities in a classroom building of the Universidade Tecnológica Federal do Paraná, in Curitiba, Brazil. Beginning with a survey on light bulb and luminaire types used in the building and on the potential of daylighting in such environments, six different classroom types with different solar orientations were selected for analysis. The research methods included the estimation of daylighting potential from obtained daylight coefficients (DCs) for periods of the year and sky conditions, other than those of the onsite measurements; the evaluation of conformity of the lighting system to the Brazilian RTQ Code (Regulamento Técnico de Qualidade), an energy consumption rating system, aimed at reducing electric energy consumption in office buildings; the estimation of electric energy demand for a combined use of daylighting and lighting system; the proposal of an efficient lighting system; and cost assessment using payback analysis. Results suggest energy savings of up to 94% when integrating daylight with the artificial lighting system, a payback within the range of 22–60 months for a complete substitution of the existing lighting system for a more efficient one.

Efficient calculation of daylight coefficients for rooms with dissimilar complex fenestration systems

The daylight coefficient (DC) method is a powerful and efficient method to perform annual daylight illuminance simulation. A set of coefficients are calculated for a given room space and static fenestration systems prior to simulation start. Time series of indoor daylight illuminances are obtained by only knowing the sky luminance. However, for rooms with dissimilar dynamic complex fenestration systems (such as windows with movable shadings) whose optical behaviour (transmission, reflection and scattering) may change during simulation, the efficiency of the DC method may be compromised as another whole set of coefficients must be re-calculated. This study presents the development of a new methodology to compute the DC set for rooms with dissimilar complex fenestration components only once prior to simulation start. A validation study is carried out, in which the daylight illuminances in an office space equipped with a clear window and internal Venetian blinds are compared using predictions from the present model, the Radiance program, as a benchmark model employing detailed optical model of Venetian blinds, and the Daysim program employing a simple engineering blinds model. Findings from the validation study show that the present model yields overall accurate results when compared with the benchmark model for any window orientation, although some local illuminance differences are observed in areas under direct sunlight exposure.

Standard daylight coefficient model for dynamic daylighting simulations

Daylight coefficients are normalized contributions from discretized sky or ground segments, or preset solar positions, to solar quantities calculated at various building sensor points. Once generated, daylight coefficients can be folded against luminance efficacy and distribution models to calculate, for instance, time series of illuminances. Over about the last 25 years several daylight coefficient models have been published. The objective of this paper is to propose a standard daylight coefficient model for dynamic daylighting simulations (DDS), consolidating previously published methods. This entails the definition of a standard daylight coefficient data format and accompanying software concepts for dynamic simulation purposes; dynamic in this context meaning variable with time due to changing sky conditions and shading device settings, in contrast to static modelling concepts such as daylight factors. The DDS standard model defines daylight coefficient data independent of building location and scene orientation, and generated using either simulation or measurement. It provides functionality to take into account independently controlled daylighting sources (e.g. windows and skylights) and to query different daylighting quantities in a simulation context (e.g. illuminance at one or more sensors, annual daylight performance metrics). A Radiance-based intermodel comparison shows that DDS-based software outperforms the original validated Daysim approach, upon which DDS is based, notably in cases where sensors are subjected to sudden changes in solar exposure, e.g. in an urban canyon or for sensors located far from a window. The proposed DDS standard daylight coefficient model, including the data format and accompanying software concepts, can be adopted by daylighting and energy-simulation software as a common mechanism for efficiently sharing daylight coefficient data for simulation purposes. Les coefficients d'éclairage diurne sont des contributions normalisées provenant de segments de ciel ou de sol discrétisés, ou de positions solaires prédéfinies, pour des quantités solaires calculées en divers points au sein d'un bâtiment. Une fois générés, les coefficients d'éclairage diurne peuvent être couplés à des modèles d'efficacité et de distribution de luminance pour calculer, par exemple, des séries temporelles de niveaux d'éclairement. Plusieurs modèles de coefficients d'éclairage diurne ont été publiés au cours des 25 dernières années. L'objectif de cet article est de proposer un modèle de coefficient d'éclairage diurne standard pour des simulations dynamiques d'éclairage diurne (DDS) qui consolident les méthodes publiées anterieurement. Cela implique la définition d'un format de données standard pour les coefficients d'éclairage diurne, et des concepts logiciels complémentaires pour la simulation dynamique; dynamique, dans ce contexte, signifiant une variabilité dans le temps due à des conditions changeantes du ciel et à des réglages de dispositifs d'occultation, en contraste aux concepts de modélisation statique comme les facteurs d'éclairage diurne. Le modèle standard DDS définit des coefficients d'éclairage diurne indépendants de l'emplacement des bâtiments et de l'orientation de la scène, et qui peuvent être générés à partir soit de simulations soit de mesures. Ce modèle intègre les fonctionnalités nécessaires pour tenir compte de sources d'éclairage diurne contrôlées indépendamment les unes des autres (par exemple, fenêtres et lanterneaux) et d'étudier différentes quantités d'éclairage diurne dans un contexte de simulation (par exemple, niveau d'éclairement parmi un ou plusieurs capteurs, indices de performance d'éclairage diurne annuel). Une comparaison entre modèles basés sur Radiance permet d'établir la supériorité de DDS sur l′approche Daysim, notamment lorsque les capteurs sont sujets à des changements brusques d'exposition au soleil, par exemple dans un canyon urbain ou lorsque les capteurs sont loin d'une fenêtre. Le modèle standard de coefficient d'éclairage diurne DDS proposé, y inclus le format de données et les concepts logiciels complémentaires, peut être adopté par des logiciels d'éclairage diurne et de simulation d'énergie comme mécanisme commun pour le partage efficace de données de coefficient d'éclairage diurne à des fins de simulation. Mots Clés: coefficient d'éclairage diurne, éclairage diurne, énergie, Industry Foundation Class (IFC), simulation

Validation of dynamic RADIANCE-based daylight simulations for a test office with external blinds

The study encompasses the validation of the dynamic, RADIANCE-based daylight simulation method DAYSIM, which uses the concept of daylight coefficients and the Perez sky model to predict the short-time-step development of indoor illuminances. Measured and simulated illuminances have been compared under 10,097 sky conditions in a full-scale test office with a double glazing and external venetian blinds. The additional planning effort for the designer compared to a conventional daylight simulation is addressed. It has been found that the treatment of direct sunlight strongly influences the accuracy of the daylight coefficient method. Three different simulation modes for the direct sunlight are investigated. The simulation results prove that indoor illuminances can be modeled with comparable accuracy for various blind settings under arbitrary sky conditions. Daylight autonomies are predicted with an accuracy below 2% points, where simulation errors stem with roughly equal parts from the raytracing and the sky model.

The simulation of annual daylight illuminance distributions — a state-of-the-art comparison of six RADIANCE-based methods

The present work discusses simulation results of annual indoor illuminance distributions for two office geometries situated in Freiburg, Germany, calculated with six different RADIANCE-based daylight simulation methods. These methods are the ubiquitous daylight factor method [P.J. Littlefair, Predicting annual lighting use in daylit buildings, Building and Environment 25 (1990) 43–54.], ADELINE 2.0 [M. Szerman, J. Stoffel, ADELINE 2.0, Radlink Technical Manual, IEA Solar Heating and Cooling, Task 12.], the classified weather data according to Herkel and Pasquay [S. Herkel, T. Pasquay, Dynamic link of light and thermal simulation: on the way to integrated planing tools, 5th Int. IBPSA Conf., Prague, Sept., 8–10, 1997, Vol. II, pp. 307–312.] and two simulation procedures based on daylight coefficients according to Tregenza, namely ESP-r version 9 series [J.A. Clarke, M. Janak, Simulating the thermal effects of daylight-controlled lighting, Building Performance (BEPAC), (1) (Spring 1998).] and a new accelerated method developed by the authors. The new method calculates 145 diffuse and three ground daylight coefficients in a single raytracing run which considerably reduces the required calculation times for an annual daylight simulation. An explicit calculation of the indoor illuminances under all 4703 annual hourly mean sky luminance distributions from the Freiburg test reference year (TRY) serves as a reference case against which the other methods are tested. The simulation results reveal that the accuracy of an annual daylight simulation method is not necessarily coupled with the required simulation time. The quality of an annual simulation rather depends on the underlying sky luminous efficacy model and whether the method considers the hourly mean direct and diffuse illuminances for each time period explicitly. The two methods relying on daylight coefficients exhibit the lowest relative root mean square errors (RMSEs) for the straightforward office geometry. The results for the advanced office show that internal illuminance contributions due to external ground reflections are only considered by the new method.

Theoretical and experimental analysis of daylight performance for various shading systems

The daylight coefficient approach is used for the theoretical analysis of various shading systems. Once a set of these coefficients has been calculated, it is very easy to calculate illuminance in the interior of a room under various sky luminance distributions. The present paper examines a method based on daylight coefficients to evaluate daylight in the interior of a room. The method is compared with existing radiosity and ray-tracing methods. The examined method is experimentaly validated using measurements obtained in a PASSYS test-cell equipped with shading devices.

Daylighting computation: Radiosity method using triangular patches

Room surfaces, windows and external obstructions are subdivided into triangular patches for radiosity calculations, and initial daylight illuminances are calculated from daylight coefficients. The paper describes procedures in which both the form factors for computing inter-reflection and the daylight coefficients are determined by recursively subdividing the spherical triangles subtended by triangular patches. This permits analysis of hidden surfaces and gives also a procedure for tracing specular reflections. An appendix to the paper describes a geometrical framework for the computation.

Daylight coefficients for practical computation of internal illuminances

The daylight coefficient approach developed by Tregenza and Waters relates the luminance of an element of sky to the illuminance it produces at a point in a room. Its use can speed up daylight calculations. Once a set of daylight coefficients has been computed, it is possible to find daylight illuminances under a large number of sky luminance distributions with minimal extra effort. Because it relates to a point source of light the daylight coefficient technique can also be used for the calculation of reflected sunlight; and it is especially suitable for innovative daylighting systems with complex optical properties. This paper describes computer programming strategies to make effective use of daylight coefficients. It outlines the practical implementation of such a program to calculate year-round internal illuminances. To realise the efficiency benefits of the technique, it is important to calculate as few individual daylight coefficients as possible. This can be done by using Gaussian integration and by separating out the calculation of direct sunlight and internally reflected light. The paper describes the interface between the sky modelling technique and simulation of internal reflection, and the modelling of blinds and innovative daylighting systems. The special problems of external obstructions and ground-reflected light are also discussed.

Daylight measurement in models: New type of equipment

Standard laboratory methods for predicting daylight illumination in buildings involve model testing in large artificial skies. Usually only one sky luminance distribution can be simulated. In the equipment described in this Note, the sky is divided into a large number of zones, and the daylight coefficients are measured. The illuminance beneath any sky luminance distribution can then be found by multiplying the coefficients by the appropriate sky luminance values. The equipment serves also as a computer-controlled heliodon which permits measurement of building illuminance under direct sunlight.

Predicting daylight from cloudy skies

The authors describe the concept of daylight coefficients, which are functions relating the luminance of the sky to the illuminance at a point within a room. The coefficients are presented first in the context of standard daylight calculations, and then as finite element matrices. Graphs of the functions enable the effects of sky luminance changes to be appreciated qualitatively. Use of the coefficients in a computer program gives an efficient method for calculating daylight from a number of sky brightness distributions in succession.

Daylight coefficients

The concept of daylight coefficients is introduced, mathematical functions that relate the luminance distribution of the sky to the illuminance at a point in a room. They are illustrated first in the context of standard daylight calculations, and then in the form of finite element matrices. Graphs of the functions enable effects of sky luminance changes to be appreciated qualitatively; use of the coefficients in computer programs gives an efficient method for calculating daylight from a number of sky brightness distributions in succession.

Electrocardiographic changes and peripheral nerve palsies in toxic diphtheria: Burkhardt, Edward A., Eggleston, Cary, and Smith, Lawrence W.: Am. J. M. Sc. 195: 301, 1938

The present work discusses simulation results of annual indoor illuminance distributions for two office geometries situated in Freiburg, Germany, calculated with six different RADIANCE-based daylight simulation methods. These methods are the ubiquitous daylight factor method [P.J. Littlefair, Predicting annual lighting use in daylit buildings, Building and Environment 25 (1990) 43–54.], ADELINE 2.0 [M. Szerman, J. Stoffel, ADELINE 2.0, Radlink Technical Manual, IEA Solar Heating and Cooling, Task 12.], the classified weather data according to Herkel and Pasquay [S. Herkel, T. Pasquay, Dynamic link of light and thermal simulation: on the way to integrated planing tools, 5th Int. IBPSA Conf., Prague, Sept., 8–10, 1997, Vol. II, pp. 307–312.] and two simulation procedures based on daylight coefficients according to Tregenza, namely ESP-r version 9 series [J.A. Clarke, M. Janak, Simulating the thermal effects of daylight-controlled lighting, Building Performance (BEPAC), (1) (Spring 1998).] and a new accelerated method developed by the authors. The new method calculates 145 diffuse and three ground daylight coefficients in a single raytracing run which considerably reduces the required calculation times for an annual daylight simulation. An explicit calculation of the indoor illuminances under all 4703 annual hourly mean sky luminance distributions from the Freiburg test reference year (TRY) serves as a reference case against which the other methods are tested.The simulation results reveal that the accuracy of an annual daylight simulation method is not necessarily coupled with the required simulation time. The quality of an annual simulation rather depends on the underlying sky luminous efficacy model and whether the method considers the hourly mean direct and diffuse illuminances for each time period explicitly.The two methods relying on daylight coefficients exhibit the lowest relative root mean square errors (RMSEs) for the straightforward office geometry. The results for the advanced office show that internal illuminance contributions due to external ground reflections are only considered by the new method.