Daylight In Buildings Research Articles

Core Sunlighting System, a New Approach to Daylighting in Buildings

The building industry recognizes the importance of incorporating daylighting into the illumination of buildings to improve energy performance and lighting quality. There are several well-known methods that building designers use to increase the daylighting level in buildings, including windows and skylights. However, these methods are usually not capable of illuminating the core of the building, and may increase the energy usage of the building due to reduced insulation. There are other systems designed for illuminating the core of buildings with daylighting, but all have some limitations that have impeded widespread adoption.An alternate daylighting system described here offers a novel approach to illuminating the core of buildings. This system consists of active and passive optical components that capture sunlight outside multi-floor buildings and transfer it to the dark core. Active sunlight redirectors, mounted at roof level on the edge of the building, track the sun throughout the day and redirect the sunlight towards building façades at a certain angle. Passive concentrator elements mounted on the façades of the building capture and concentrate the light and direct it into light guides. The sunlight is then distributed within the building via interior light guides to efficiently illuminate the building.

A framework for predicting the non-visual effects of daylight – Part II: The simulation model

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 non-visual 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 system differs fundamentally from the visual system in its action spectrum. The photosensitivity of the 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 Commission Internationale de l'Eclairage (CIE) illuminant types, and then tracking their ‘circadian-lux’ weighted contributions in the summation of daylight received at the eye. A means to ‘condense’ non-visual 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.

Measurement and Evaluation of Annual Daylighting Performance of an Exist School in Hot and Arid Regions of Iran

Daylighting is one of the important environmental factors that its proper design not only can drastically reduce energy consumption, but also creates healthier learning environments that may result in increased attendance and improved grades. Both the quantity and the quality of daylight in building are important parameters that designer must consider. The aim of this research is to develop an extended daylighting evaluation in educational spaces of the school buildings in hot and arid region of Iran. In this paper a survey of observation, geometric determination of devices and the results of measurements of daylight levels in classrooms in "Kashan" that are coordinated by “Iran school Organization of renovation and development” typical form, are mentioned. All the research analyses have been done based on the classrooms models comparison through the computational simulations. Finally the problems were determined and comparison of results was discussed.

Estimation of Daylight Availability and Illuminance on Vertical South Facing Surfaces in Tehran

To effectively design daylight in buildings, daylight availability data are necessary. Although there is a great potential of daylight energy in Iran, its use is hindered by absence of measured data. In this paper the illuminance data on vertical south facing surfaces of Tehran were estimated using IESNA model. For this propose an illuminance measuring set was used for measuring vertical illuminances for standard times over 20 days at one minute intervals from 9 a.m. to 4 p.m. Then the measured data were compared with IESNA model calculated data. A regression model between measured and calculated data was developed which showed an acceptable linear correlation (r2=0.9535). Also mean hourly and monthly vertical illuminance was obtained from the new equation between measured and calculated data for a whole working year. To estimate daylight availability, frequency curves for vertical illuminance on south facing surfaces were created.

Exploring the Spatial Preferences of Plant Landscape Dynamics around the Buildings in the Humble Administrator’s Garden, China

The Humble Administrator’s Garden is not only the topmost classical private garden south of the Yangtze River in China, but a member of the World Culture Heritage List. Its rich plant landscape patterns around housings have valuable effects on today’s building environment. This study tried to explore the spatial preferences of plant landscape dynamics of the garden. The 13 sample plots, each of which centered about a building and 12m outward radiation, were investigated in February and August 2010. We recorded totally 53 tree species and 325 individuals. Tree height, defoliation, direction (relative to building) and spacing (distance from building) were divided into levels of 6, 2, 8 and 4 respectively. Each level was encoded in order. Thus a tree had a four-digit code including the four factors. There were 4 evergreen gymnosperms which had only a little effect on building daylighting. Both the defoliation ratio of 0.69 and dominant species of most deciduous species showed primary deciduous trees were valuable to realize the balance of daylighting, ventilation and seasonal beauty. The result of small evergreen trees and large deciduous trees is valuable for both sunshine and green in winter as well as shading in summer. Most small trees on the west can be barrier against the hot sun on summer afternoon. Most large trees on the south are beneficial to southern shading and ventilation. Finally, the open space before window is necessary for daylighting and ventilation.

Illuminance Level in the Urban Fabric and in the Room

The decisions made on the urban planning level could influence the building design at later stages. Many studies have shown that the utilisation of daylight in buildings would result in significant savings in electricity consumption for lighting, while creating a higher quality indoor environment. The surroundings of a building have a great influence on the indoor environment of that building. A major factor is the shading that the surrounding buildings could provide, blocking and diminishing the available amount of daylight in nearby buildings. This paper reports a study that combine the effect of the exterior illuminance levels on façades with the interior illuminance levels on the working plane. The paper also explains an easy to use tool (EvUrban-plan) developed by the authors, which was applied to their findings in the early stages of urban planning to ensure daylight optimisation in the buildings.

Opinion: Daylighting prescriptions: Keep taking the pills?

The role that daylight evaluation plays in the design process has acquired a new impetus as the need to demonstrate compliance with various ‘performance indicators’ becomes ever more pressing. Two of the most used rating systems are BREEAM and LEED which originated in the UK and US respectively, though they are both used world-wide. Until recently, the majority of codes worldwide were founded on the daylight factor. First proposed in the UK in the early 1900s, and formalised into building standards over fifty years ago, the daylight factor is simply the ratio of internal illuminance to unobstructed horizontal illuminance under standard CIE overcast sky conditions (usually expressed as a percentage). One of the key standards documents for daylight in buildings is British Standard 8206-2 ‘‘Lighting for buildings - Part 2: Code of practice for daylighting’’, and many guidelines refer to that. BS 8206-2 recommends that ‘‘the average daylight factor should be at least 2%’’. A slightly more exacting recommendation has featured in LEED: ‘‘75% of all critical visual task occupied space must achieve a Daylight Factor of 2%’’. Since maximum daylight factor values are rarely specified, the prescription of minimum daylight factor values in the majority of guidelines has inevitably led to a perception that ‘more is better’. The Carbon Trust have recommended ‘‘not less than 4%, preferably 6%’’ daylight factor. And one can find statements such as the following in various good practice guidelines for schools: ‘‘Maximise daylight factor to improve student performance (5% or more)’’. Compliance ‘chasing’ is now a major driver in building design and expert daylight designers rarely have any input. Fundamental design parameters that have enormous consequences for overall building performance are being selected on the basis of daylight factor evaluations - a climate and orientation insensitive metric that takes no account of sun. Consequently, the elusive balance between good daylight provision and effective solar control is often not achieved. Among the problems discovered in a detailed review by the Commission for Architecture and the Built Environment (CABE) of forty proposed designs for schools across England were classrooms which are too dark or prone to overheating on sunny afternoons. Extending the basis of the daylight factor approach by incremental means has proved problematic. Recent ‘clear sky’ options in LEED and ASHRAE provide no guidance on normalising the sky output, a significant omission since absolute values are now the

Illuminance-based slat angle selection model for automated control of split blinds

Venetian blinds play an important role in controlling daylight in buildings. Automated blinds overcome some limitations of manual blinds; however, the existing automated systems mainly control the direct solar radiation and glare and cannot be used for controlling innovative blind systems such as split blinds. This research developed an Illuminance-based Slat Angle Selection (ISAS) model that predicts the optimum slat angles of split blinds to achieve the designed indoor illuminance. The model was constructed based on a series of multi-layer feed-forward artificial neural networks (ANNs). The illuminance values at the sensor points used to develop the ANNs were obtained by the software EnergyPlus™. The weather determinants (such as horizontal illuminance and sun angles) were used as the input variables for the ANNs. The illuminance level at a sensor point was the output variable for the ANNs. The ISAS model was validated by evaluating the errors in the calculation of the: 1) illuminance and 2) optimum slat angles. The validation results showed that the power of the ISAS model to predict illuminance was 94.7% while its power to calculate the optimum slat angles was 98.5%. For about 90% of time in the year, the illuminance percentage errors were less than 10%, and the percentage errors in calculating the optimum slat angles were less than 5%. This research offers a new approach for the automated control of split blinds and a guide for future research to utilize the adaptive nature of ANNs to develop a more practical and applicable blind control system.

Optimal tree design for daylighting in residential buildings

Urban reforestation is advocated as an efficient countermeasure to the intensification of urban heat islands. The greening and beautification of residential quarters is one of the main concerns of residents, while lighting and ventilation are two main energy-consuming building services. Hence, the tree layout in green space between buildings is important, and it is necessary to determine the relationships between trees and buildings. This study takes Shanghai as a case study to optimize tree design between residential buildings and meet good daylighting requirements. Models were made using software such as AutoCAD and SketchUp. The relationships between maximum tree height and building separation were determined. For the same building layout, there were different tree height limits according to crown shape; the order of decreasing height limits was cylindrical, conical, spherical, and inverted conical crowns. Three cases having different green space between building layouts were studied. Their maximum tree heights differed. Overall, our model helps us realize good daylighting of a building environment. The formula allows us to determine which trees to plant between buildings in that we can predict the effects of future tree growth on building daylighting.

Automated blind control to maximize the benefits of daylight in buildings

Venetian blinds are a common type of shading device and are increasingly operated automatically to overcome the limitations of manual operation. Automated blinds need to be controlled to maximize benefits of daylight in the point of occupant comfort and energy consumption. However, the previous control methods are focused on minimizing negative impacts of daylight, so they might fail to maximize positive impacts of daylight. They may often overpredict a blind's position, resulting in the undesirable blockage of daylight. In this paper, we propose a new control method for automated venetian blinds to maximize occupant comfort. The proposed control method can not only protect occupants from direct solar glare but also maximize daylight penetration into buildings based on occupants' preferences on daylight. The proposed control method is designed to allow the occupants to define the zone they want protected from direct sunlight. It can control the blinds to protect only the defined zone; therefore, more daylight can be introduced to the other areas, excluding the predetermined zone. A control method for the case of one blind with one zone was developed and then extended for the case of multiple blinds with multiple zones.

Assessment of building façade performance in terms of daylighting and the associated energy consumption in architectural spaces: Vertical and horizontal shading devices for southern exposure facades

This paper examines the effect of vertical and horizontal shading devices on the quality of daylight in buildings and the associated energy saving. Excessive daylight in architectural spaces contributes negatively to the energy consumption in buildings. Blinds and shading devices are good solutions to attenuate the surplus amount of daylight in spaces. Accordingly, this study evaluates the effect of shading devices on the amount of light flux and the associated solar energy in buildings. It estimates the energy consumption attributed to lighting spaces for three common positions of shading devices. Computer simulation strategy was undertaken to correlate the illuminance level in spaces with room geometry and architectural shading elements. The Holophane model for lighting calculations was used to estimate the average illuminance level on workplane and correlate it with the expected saving energy in buildings. The study concluded that there is an optimal orientation for shading devices that keeps the internal illuminance level within the acceptable range with minimum amount of solar heat gain.

Knowledge in the making

This project began when one of my research colleagues, a civil engineer, pointed to his very thorough study of daylighting in buildings and said: ‘Here is all that architects need to know about light – why don't they use it?’ A discussion followed about what kind of knowledge is relevant, when, and for whom. It ended with the questions: ‘What kind of knowledge do architects really use in their design process?’ and ‘How can we as researchers provide the different kinds of knowledge that are useful for practice?’ These questions became the basis of a research project and this paper reports on its studies and discussions.

Electrochromic device with a redox electrolyte

Electrochromic glazing allows the solar energy gain and daylighting in buildings and cars to be controlled. Here we report new results about a special type of electrochromic device. It consists of an electrochromic layer (WO 3) on a transparent electrode, an electrolyte containing Li + cations and a redox system (I −/I 3 −), and a catalyst (Pt) on a second transparent electrode. The electrolyte is based on gelled ionic liquids. The change in the transmittance is extremely high; the visible (solar) transmittance can be switched between 63% (46%) and 1.2% (0.7%). A segmented 30×30 cm 2 sample with conductor paths reduces the transmittance by a factor of 10 in 8 s.

Daylight for Energy Savings and Psycho-Physiological Well-Being in Sustainable Built Environments

Natural light is a vital force for human beings. Successful daylighting in buildings requires trade-offs and optimization between competing design aspects (e.g. light distribution, glare, solar gains, views, etc.), whilst also including consideration of façade layout, space configuration, internal finishes and choice/operation of shading devices. However, to design energy-sustainable built environments which are conducive to human health, these variables have necessarily to be related also with biological and behavioural factors such as metabolic rhythms, psychological stimulation and occupants’ preferences. Basing on a multidisciplinary review of existing literature, this paper looks at the relationship between quantitative physical measures of the luminous environment (e.g. horizontal and vertical illuminance, luminance ratio, correlated colour temperature), qualitative aspects of vision (e.g. uniformity, distribution), and psycho-physiological human response to natural light. The aim of the study consists in defining a framework to implement existing daylighting practices basing not solely on photopic requirements but also containing awareness of the demands for psychological and photobiological stimulation, so as to positively influence the health of occupants whilst enhancing energy savings.

Estimating depth of daylight zone and PSALI for side lit office spaces using the CIE Standard General Sky

The use of daylight has energy saving implications. But to harness daylight in buildings requires detailed analysis into its penetration. The paper predicts the depth of daylight zone and Permanent Supplementary Artificial Lighting of Interiors (PSALI) in a generalized high-rise office space in Kuala Lumpur, Malaysia. Using CIE Standard General Skies, two experiments are conducted to find the probable upper and lower limits of daylight penetration throughout the year. As CIE Standard General Skies are not widely incorporated into simulation software, therefore, a combination of Daylight Coefficient method and Waldram Diagrams is used for daylight calculation. The lowest daylight penetration is taken as the depth of daylight zone while the difference between the lowest and highest daylight penetration is considered for the depth of PSALI zone.

Frequency Distribution of CIE Standard General Skies for Subang, Malaysia

Standard skies are very important in analysing the daylight climate of a particular region or country. Studies of their frequency distribution can help in identifying the most reccurring typologies, which can then be used by researchers in modelling daylight in buildings. The paper describes the process of determining the occurrence of CIE Standard General Skies for Subang, Malaysia, utilizing the daylight coefficient method and global illuminance values converted from global irradiance measurements available for the location.

Estimation of Luminous efficacy of daylight and exterior illuminance for composite climate of Indore city in Mid Western India

Daylighting is one of the basic components of passive solar building design and its estimation is essential. In India there are a few available data of measured illuminance as in many regions of the world. The Indian climate is generally clear with overcast conditions prevailing through the months of June to September, which provides good potential to daylighting in buildings. Therefore, an analytical model that would encompass the weather conditions of Indore was selected. Hourly exterior horizontal and slope daylight availability has been estimated for Indore using daylight modeling techniques based on solar radiation data.

Useful daylight illuminances: A replacement for daylight factors

This paper describes the application of a new paradigm, called useful daylight illuminance (UDI), to assess daylight in buildings. The UDI paradigm is designed to aid the interpretation of climate-based analyses of daylight illuminance levels that are founded on hourly meteorological data for a period of a full year. Unlike the conventional daylight factor approach, a climate-based analysis employs realistic, time-varying sky and sun conditions and predicts hourly levels of absolute daylight illuminance. The conventional approach produces a single number – the daylight factor as a percentage – for each evaluation point in the space. In contrast, a climate-based analysis results in an illuminance prediction for every daylight hour of the year for each point considered. The UDI paradigm offers a way to reduce the voluminous time-series data to a form that is of comparative interpretative simplicity to the daylight factor method, but which nevertheless preserves a great deal of the significant information content of the illuminance time-series. The UDI paradigm informs not only on useful levels of daylight illuminance, but also on the propensity for excessive levels of daylight that are associated with occupant discomfort and unwanted solar gain. In a conventional analysis of daylight provision and solar penetration, the two phenomena are assessed independently using methods that are idealised (daylight factor) and qualitative (shadow patterns). The UDI paradigm offers a simple methodology whereby daylight provision and levels of solar exposure are quantified using a single evaluative schema. Thus, it is also well-suited for teaching purposes. Application of the UDI paradigm is demonstrated using an analysis of design variants for a deep-plan building with a light-well. Comparison is made with the conventional daylight factor approach, the LEED daylight credit and measures of daylight autonomy.

Daylight Dividends Case Study: Smith Middle School, Chapel Hill, N.C.

Abstract Daylight Dividends is a three-year research program facilitating the widespread implementation of daylight in buildings. The “dividends” include human comfort and performance and energy savings. Daylight Dividends is run by the Lighting Research Center at Rensselaer Polytechnic Institute on behalf of the project sponsors. The Daylight Dividends program was established to build market demand for daylighting as a means of improving indoor environmental quality; to overcome technological barriers to effectively reap the energy savings of daylight; and to inform and assist state and regional market transformation and resource acquisition program implementation efforts. In 2004, Daylight Dividends published a case study on the R. D. & Euzelle P. Smith Middle School, part of the Chapel Hill-Carrboro City School District in Chapel Hill, North Carolina. The school embraced an environmentally conscious attitude and continues to exemplify good daylighting practice since it opened its doors in 2001. The cas...

Assessing Daylighting Performance of Buildings Using Orthographically Projected Area of Obstructions

Recently the Hong Kong Government has issued a performance-based code governing daylighting in buildings to supplement its prescriptive code. The performance-based method uses the vertical daylight factor (VDF) at the centre of the window pane in the specification of the performance standards. However, the calculation of VDF is not an easy task and is especially not suitable in the early design stage when designers may need to evaluate the daylighting performance quickly using simple sketches and limited data. In view of this, the current performance-based code allows the use of a simplified alternative method called the unobstructed vision area (UVA) method. In this paper, a review of the UVA method is first given. Then a method based on the orthographically projected area (OPA) of all obstructions above the reference point is presented. The OPA can be determined with similar efforts as determining the UVA. Case studies comparing the performance between the OPA and UVA methods are presented. Results show that the OPA method predicts the VDF reliably and therefore is truly a simplified performance-based method.