Daylight Modelling Research Articles

Daylighting buildings: Standards and the needs of the designer

Despite widespread research on daylighting, there are insufficient data to justify a definitive statement on daylighting design criteria. This paper reviews the requirements for daylighting codes and guidelines, doing so from two different viewpoints. The first considers standards and regulations, the second is focused on development and the scope of climate-based daylight modelling.

Climate-Based Daylight Modeling (CBDM) for an atrium: An experimentally validated novel daylight performance

In the present paper, a new daylight performance metric, Daylight Illuminance Ratio (DIR) has been developed for an atrium space to take into account the direct and diffuse components (Sun and sky). The daylight performance on each inner surface of a square atrium has been investigated and validated with hourly measured experimental data under clear sky conditions. There is good agreement between theoretical and experimental values, with a correlation coefficient (r) of 0.92–0.96 and a root mean square percentage error (e) of 8.53–10.21%. Results show that the interior surface of the west and north walls receive more daylight in June (summer) and October (winter), respectively. The presented metric can be used to predict vertical illuminance at a given point on the atrium walls.

What Is the Reference? An Examination of Alternatives to the Reference Sources Used in IES TM-30-15

ABSTRACTThis article documents the role of the reference illuminant in the IES TM-30-15 method for evaluating color rendition. TM-30-15 relies on a relative reference scheme; that is, the reference illuminant and test source always have the same correlated color temperature (CCT). The reference illuminant is a Planckian radiator, model of daylight, or combination of those two, depending on the exact CCT of the test source. Three alternative reference schemes were considered: (1) either using all Planckian radiators or all daylight models, while maintaining the CCT match of the test and reference; (2) using only one of 10 possible illuminants (Planckian, daylight, or equal energy), regardless of the CCT of the test source; (3) using an off-Planckian reference illuminant (that is, a source with a negative Duv). No reference scheme is inherently superior to another, with differences in metric values largely a result of small differences in gamut shape for the reference alternatives. Though using any of the alternative schemes is more reasonable in the TM-30-15 evaluation framework than it was with the CIE Test Color Method, the differences still ultimately manifest only as changes in interpretation of the results. Reference illuminants are employed in TM-30 to provide a familiar point of comparison, not to establish an ideal source.

A novel circadian daylight metric for building design and evaluation

This paper extends the applicability of emerging frameworks for evaluating the non-visual effects of light through the development of a novel area-based daylighting metric addressing goals of human circadian stimulus and entrainment in buildings. Procedures using annual, climate-based daylight modeling of eye-level light exposures are developed to analyze and map indoor environments in regard to spatial and seasonal changes in the availability of a circadian-effective daylight stimulus. Because the biological effects of light exposure are not instantaneous, a novel approach is developed to assess the duration of an effective stimulus on a daily basis, as well as the frequency an effective stimulus is present over the course of a year. Results can be used to identify and visually examine building zones where long-term occupancy may lead to disruption of the circadian system in the absence of supplemental electrical lighting capable of effective circadian stimulus. The metric and visualization techniques are implemented in a parametric, simulation-based workflow utilizing publicly available software tools. The workflow can be used to assess and differentiate the performance of various daylighting strategies during the design phases of a project, or to examine existing spaces. The applicability of the workflow is demonstrated using two example models: a portable school classroom, and a generic open-plan commercial office floor plate.

New tools for managing daylight exposure of works of art: case study of Hambletonian, Mount Stewart, Northern Ireland

This paper describes a project to reduce the excessive daylight exposure of an oil painting, Hambletonian, Rubbing Down, displayed at Mount Stewart, Northern Ireland. Climate-based daylight modelling (CBDM) was used to understand the light exposure of Hambletonian and to assess the impact of control measures on the annual light exposure and viewing condition of the painting in the winter months. The computer model was used in conjunction with measured lux data to establish the base case light exposure and the effect of the control measures. Light control was implemented through the use of darker paint finishes on the walls and ceiling, which reduced the amount of reflected light reaching Hambletonian; and the addition of a mesh screen to the outside of the glazed dome above the painting. These interventions were cost-effective and straightforward to implement and manage. CBDM suggests the interventions reduced Hambletonian’s annual daylight exposure from 3.5 mlxhr to 0.63 mlxhr.

‘Climate connectivity’ in the daylight factor basis of building standards

This paper describes a proposal for a daylight standard for CEN countries. It is now widely accepted in the research community, and increasingly so amongst practitioners, that the standards/guidelines for daylight in buildings are in need of upgrading. The essence of the proposal is that the ‘target’ for daylight provision should be founded on the availability of daylight as determined from climate files. The proposal is in fact a refinement of an approach originally described in a CIE document from 1970, and which appears to have been largely overlooked since then. The proposal states that a design should achieve a target daylight factor at workplane height across a specified percentage of the relevant floor area for half of the daylight hours in the year, where the target daylight factor is based on the provision of 300 lux. A key feature of the refinements are the formulation of the methodology such that the likelihood for misinterpretation and ‘game-playing’ is greatly reduced, if not eliminated altogether. The method, founded on cumulative diffuse illuminance curves, could be introduced relatively swiftly since it requires only modest enhancement of existing daylight prediction tools. In addition, the proposal will provide a sound ‘footing’ for eventual progression to evaluations founded on full-blown climate-based daylight modelling.

Increased Light Harvesting by Structured Cell Interconnection Ribbons: An Optical Ray Tracing Study Using a Realistic Daylight Model

A key for increasing the module efficiency is improved light harvesting. The structuring of solar cell interconnection ribbons (CIR) is a promising option for improved light harvesting as it can easily be integrated into current module production. We perform ray tracing simulations of complete PV modules in 3D exhibiting geometric features such as profiled CIR and surface textured cells. We evaluate the increase in module performance by a light harvesting string (LHS) under realistic irradiation conditions with respect to angular and spectral distribution. Using the realistic irradiation for a location in Germany, a location at the polar circle and a location at the equator we simulate the enhancement of short-circuit current density Jsc resulting from the use of LHS. Our results show Jsc gains between 1.00% and 1.86% depending on the location and module orientation. We demonstrate the applicability of our model by comparing measurements and simulations for a one-cell module that we measure and simulate under various angles of the light incidence.

Energy analysis of the daylighting from a double-pane glazed window with enclosed horizontal slats in the tropics

Daylighting is perceived to be a potential measure for energy conservation in commercial buildings. In Thailand where the sky is highly luminous and daytime is long throughout the year, daylighting is however neglected by the use of heat reflective glasses to prevent excessive solar gain from windows. To address the issue, this paper investigates the energy performance of the daylighting from a window with horizontal slats located between two panes of glasses (slat window). The slats can shade the intense beam radiation, but allow penetration of the diffuse daylight for interior illumination. In the study, a model was developed to determine the thermal gain from the slat window. By using the thermal model together with the daylight model developed earlier, the simulations were performed and the results show that the slat window, when used with typical office room, can save 25–70% of the total electrical energy of air-conditioning and lighting in the same room equipped with heat reflective glass window.

Optimization method for perforated solar screen design to improve daylighting using orthogonal arrays and climate-based daylight modelling

This paper analyses the influence of different perforated solar screens (PSS) in annual daylight conditions expressed using climate-based daylight metrics. The PSS design require parametric studies that are often complex and time consuming due to a large number of simulations. Hence, a new methodology is proposed to optimize PSS design by applying Design of Experiments using Orthogonal Arrays (DOA). A case study from the DOA perspective has been conducted, which involves an office space in Seville, Spain. The goal is to assess the effect of the following PSS design variables in daylighting performance: perforation percentage, matrix, shape and orientation. DOA results reveal that optimized PSS can increase daylit area by 33% and reduce over lit area by 35%, compared with reference models with no PSS. DOA method reduces the number of simulations from the 256 required to 16, so it could save time during the initial stages of building design.

Dynamic coupling between a Kriging-based daylight model and building energy model

Harvesting daylight for improving building energy performance has become an important issue in recent years. Most energy simulation tools use a Daylight Factor (DF) based algorithm to capture the complexity of daylight behaviors. However, DF has a limitation for fully accounting realistic daylight conditions, and several modifications or integrations with other supporting tools were developed to compensate for this limitation.This paper uses the Kriging method to predict daylight conditions for a whole year, and couples this method with energy simulation tools. Kriging is a group of geo-statistical techniques used to interpolate the value of a random field at an unobserved location from discrete observed values at nearby locations. In previous research, the Kriging method showed promising outcomes; that result was significantly better than current daylight modeling in energy simulation tool, and very close to the results from advanced physics-based daylight simulation tool.However, Kriging also comes with certain limitations that require further investigation. One major hurdle was Kriging’s long computational time compared to current daylight models in energy simulation tools. For this reason, this paper aims to find possibilities to reduce computational time to realistic levels that can be applicable in practice. Furthermore, it proposes a method to integrate Kriging-based daylight model with an energy simulation tool that can plot hourly indoor light distribution. This proposal obtains more realistic results than current energy simulation daylight models, while reducing computational expense.

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.

Adaptation of Kriging in daylight modeling for energy simulation

Kriging is a group of geo-statistical techniques used to interpolate the value of a random field at an unobserved location from discrete observed values at nearby locations. Kriging has been very popular in oceanic research used for predicting the variance of geographical conditions. However, it has been difficult to find a similar application in the built environment. This paper aims to uncover possibilities of using Kriging for built environment studies, specifically focusing on indoor daylight modeling.Currently, most energy simulation tools use algorithms that are based on Daylight Factor (DF) [1] to capture the complexity of daylight behavior. However, DF has limitations in its ability to fully account for realistic daylight conditions. Thus, efficiently integrating the light domain with thermal calculations remains a major hurdle for building energy simulation tools [2].For this reason, the paper aims to find possibilities of using Kriging for daylight modeling. Kriging will use sample points to predict illuminance values of nearby locations. Kriging will considerably reduce the number of points needed to map indoor light intensity profiles. Furthermore, Kriging will be able to provide a more seamless daylight model for energy simulation tools. This proposed method can produce light distribution, such as illuminance (lux), while obtaining more realistic results than DF and at the same time reduce computational expense through statistical methods.The paper first investigates accuracy to determine whether Kriging modeling can interpolate the profile of illuminance from a select sample of data points. To validate the daylight model used in this paper, real indoor illuminance levels were measured for different days and compared with the daylight simulation model. Further, this paper tests Kriging predictions and compares them with both advanced physics-based light simulation and energy simulation to determine possibilities and limitations of the proposed method.In comparison with RADIANCE, this paper found that the proposed Kriging model was able to predict better than the energy simulation daylight model. The difference between Kriging and RADIANCE was 25.52lux. The Kriging model showed great promise since it was able to cut the full RADIANCE simulation time in half and proved to be much closer to RADIANCE predictions than other methods.

친환경 파사드 설계지원도구를 통한 오피스의 자연채광 최적화

Integrated sustainable design of building envelopes with optimization into the design process requires the analysis of environmental performances. With the parametric & associative design technology for assessing daylight and promoting visually comfortable spaces, a great potential exists for optimizing the performance of contemporary building façades. We investigates daylight metrics in randomized patterns of office façades with different window-to-wall ratios (WWR) and sun shading louver designs, such as vertical and horizontal devices. Climate-Based Daylight Modeling (CBDM) is applied as the assessment strategy and DIVA plug-in for Rhinoceros/Grasshopper is used for validation to effectively calculate daylight metrics based on the Radiance/Daysim engine. Useful Daylight Illuminace (UDI) and Daylight Glare Probability (DGP) are adopted as the dynamic daylight metrics to compare the design alternatives. This paper presents a parametrically driven design support system and proposes the guide matrix for optimized daylighting design. The matrix of this study suggest façades alternatives of office building in terms of daylight for the climate conditions of Incheon, Korea to reduce glare and lead to energy-saving buildings.

The impact of the software’s choice on dynamic daylight simulations’ results: A comparison between Daysim and 3ds Max Design®

Evaluating indoor daylight availability is extremely important in order to define the characteristics of an environment in terms of visual comfort and energy performances of lighting systems. The criticism of the static calculation approach based on Daylight Factor led to the development of the Climate Based Daylight Modeling (CBDM) one. Dynamic simulations are performed thanks to the use of specific software and the choice of a calculation tool or another could provide different output results. Therefore the aim of this paper is to compare results of dynamic daylight simulations carried out with two different software, Daysim and 3ds Max Design® and referred to a simple office located in 4 different cities and exposed according to the 4 main orientations. It demonstrates that differences in results are more or less significant depending on several factors: outdoor daylight conditions, window’s orientation and considered internal calculation point.

Assessing daylight performance in atrium buildings by using Climate Based Daylight Modeling

This research focuses on daylight assessment in office buildings with different atrium types, proportions and roof aperture designs. The goal is to assess and optimize atrium type and proportions to improve energy efficiency of atrium buildings. This paper investigates daylight metrics in central, attached and semi-enclosed atrium types with different proportions and roof aperture designs, such as monitor and horizontal skylight. Daylight performance is measured based on the proportions of an atrium that are defined by Well Index (WI), used to characterize atria. Climate-Based Daylight Modeling (CBDM) is applied as the assessment strategy with U.S Climate Zone 3 as the climatic setting. Spatial Daylight Autonomy (sDA) and Annual Solar Exposure (ASE) are adopted as the dynamic daylight metrics to compare the results. This study also validates DIVA for Rhino as the simulation tool by comparing daylight results of the computer simulation with the same scale-model.This research applies both scale-model and computer simulation methods to assess daylight and energy performance in atrium buildings based on Well Index. This paper then employs DIVA simulation tool to assess daylight performance based on the Well Index.The results demonstrate that Well Index is a reliable indicator to characterize atrium proportion and confirm that Well Index works with (CBDM). Having assessed the impact of design parameters, such as climate, building thickness, material reflectance, material transmittance, furniture and monitor roof glazing height, the study potentially provides architects with an atrium design database for U.S. Climate Zone 3. This database compares daylight metrics for Well Index of 0.5, 1 and 2 in central, attached and semi-enclosed atrium types using different roof aperture designs.

Unified model of radiance patterns under arbitrary sky conditions

The radiance/luminance patterns that simulate more realistic skies are urgently needed in lighting engineering applications to model daylight availability in exterior and interior spaces. Undoubtedly, the angular behavior of sky radiance/luminance is a key factor determining the daylight conditions in rooms with variable orientations and window sizes. Therefore, much effort is currently expended in search of a universal, scalable daylight model that accepts actual meteorological situations.The natural sky radiances are neither monotonic nor smooth functions of zenith/azimuth angle, primarily due to the presence of broken cloud arrays or single clouds scattered over the whole sky vault. In this paper we show how we have addressed the phenomena and developed a universal sky radiance model for a turbid, cloudy atmosphere. This model accommodates higher scattering orders, aerosol optics, surface albedo, and the statistically relevant contributions of single clouds. The radiance at ground depends on the bulk characteristics of cloud fields, such as spectral optical thickness, spectral reflectance, altitude, positions on the sky, sizes, and shapes. We have shown that single scattering approximation fails to reproduce the radiance in the circumsolar region when clouds block the direct solar beams. The single scattering concept also overestimates reflection by individual clouds. Incorporation of double scattering into a computational model generally makes the radiance patterns smooth and less steep at the edges of clouds as commonly occur in nature. The numerical demonstrations are based on UniSky Simulator (Kocifaj and Fecko, 2014) which allows for modeling of various cloud configurations and is available for public use.

Fener: A Radiance-based modelling approach to assess the thermal and daylighting performance of complex fenestration systems in office spaces

A new Radiance-based modelling approach called Fener is presented. The motivation is to be able to perform detailed analyses of complex fenestration systems (CFS) from the energetic and daylighting points of view in a computationally efficient manner, so the benefits of innovative products can be easily quantified. The model couples daylighting and thermal simulations in a time-step basis, so that shading control strategies that depend on thermal variables, such as indoor air temperature and energy load, can be simulated without iterating between full-year simulations of a thermal model and a daylighting model. Fener is a single-zone energy model that uses the three-phase method and bi-directional scattering distribution functions (BSDF) to predict the transmitted solar irradiance and indoor illuminance of office spaces with CFS. An evaluation of the model is presented. Fener is tested against EnergyPlus and classic Radiance for different fenestration systems and sky conditions. Cooling and heating energy demand, transmitted solar irradiance and indoor illuminance are compared. As an exemplary application, Fener is used to assess the performance of an innovative perforated lamella system together with a control strategy that depends on indoor air temperature.

A systematic method for selecting roller shade properties for glare protection

Currently, there is no methodical procedure for selecting solar-optical properties of roller shades, which affect the energy and indoor environmental performance of perimeter building zones. This paper presents a new systematic methodology for identifying the range of shading properties (openness factor and visible transmittance) that can significantly reduce the risk of glare. A model that calculates angular beam–beam and beam–diffuse shading optical properties using minimum inputs is used within a hybrid ray-tracing and radiosity daylighting model, validated with full-scale experiments. The temporal variation of beam and total vertical illuminance is used to define the annual visual discomfort frequency and establish a process for selecting the range of acceptable shading properties for each set of external parameters (location, orientation, glazing visible transmittance, and buffer zone). The combined impact of visible transmittance and openness factor on discomfort frequency and daylight metrics is non-linear and complex. Recommendations for openness factors and visible transmittance values are made for different scenarios. Selecting the upper limits of suggested ranges can provide more daylight into the space and reduce the probability of high contrast. These guidelines may be used for selection of shading products, followed by considerations about energy savings and provision of outside view.

Methodology for Assessing Daylighting Design Strategies in Classroom with a Climate-Based Method

Considering the importance of daylight in the performance and well-being of the students, an investigation has been carried out in daylit classrooms. The objective was applying a methodology that integrates the daylight variations to know the annual lighting performance in typologies that resulted from passive design strategies in order to compare their performance. The context of the study was three zones of Chile: north, center and south. The study was done through a climate-based daylight modelling method using Radiance software. The interior illuminance was evaluated in relation to a target illuminance value (goal-oriented assessment), for which five intervals are defined: low, too low, in range, high and too high. The aim of the goal-oriented approach is to set a target range of values and assess the percentage of time over the year where each range is reached and the percentage of spaces in a temporal map within in range during the year. To see a compliance or non-compliance indicator, a category is proposed that considers the average annual illuminance “in range” over the year identifying which one is the most efficient. Finally, it is concluded that the information obtained is based on target ranges, which allows guiding the design decisions, effectively recognizing the annual performance.

Climate-based daylight analysis of fixed shading devices in an open-plan office

Office buildings consume large amounts of energy and are responsible for large amounts of greenhouse gas emissions worldwide. Among building energy efficiency measures, solar shading plays a significant role in reducing building energy consumption for cooling. This study analysed the influence of solar protection on daylighting of an open-plan office. Climate-based daylight modelling was used to predict such metrics as daylight factor, daylight autonomy and useful daylight illuminances. The results obtained showed that overhangs, and horizontal and vertical louvres have similar behaviours and sidefins have no relevance to indoor daylight conditions. In all cases, it has been proven that excessive obstruction may yield an excessive reduction in a range of illuminances between 500 and 2000 lux, increasing lighting energy consumption.