The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Steve Sharples - One of the best experts on this subject based on the ideXlab platform.
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The assessment of vertical Daylight Factors across the walls of atrium buildings, Part 1: Square atria
Lighting Research & Technology, 2011Co-Authors: Jiangtao Du, Steve SharplesAbstract:This study investigated the impact of well geometry and surface reflectance on the vertical Daylight Factors of walls in atria with square plan forms under a CIE standard overcast sky. Artificial sky scale model measurements were used to validate predicted values of vertical Daylight Factors using the software package Radiance. More simulated vertical Daylight Factors data for a much wider range of square atrium geometries and surface reflectances were then produced. From the results the variations of the vertical Daylight Factor on the walls of square atria were assessed and explained and some empirical functions derived. Some guidelines for supporting design are presented.
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surface reflectance distributions and their effect on average Daylight Factor values in atrium buildings
Architectural Science Review, 2004Co-Authors: Swinal Samant, Steve SharplesAbstract:The aim of this research was to study parametrically the effect of different distribution patterns of atrium wall reflectances on average Daylight Factor (ADF) values in the well of a square, four-sided, top-lit atrium model that was placed inside an artificial sky. The artificial sky replicated the luminance distribution of a CIE overcast sky. To achieve the variability in reflection distribution the atrium surfaces were painted in alternating bands of white and black horizontal stripes. For each of the experiments the widths of these bands were altered but the overall split between white and black bands was always maintained at 50 % white and 50% black. Experiments were also conducted for atrium wall surfaces painted all black (0% wall reflectance) and all white (100% wall reflectance). This study was able to investigate the impact on ADF values in atria of more realistic distributions of light reflecting surfaces. Results from the study showed that the ADF values on the floor of the atrium, compared to...
Danny H.w. Li - One of the best experts on this subject based on the ideXlab platform.
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study of residential thermal transfer values rttv and vertical Daylight Factor vdf for hong kong
IOP Conference Series: Materials Science and Engineering, 2019Co-Authors: Ernest K.w. Tsang, Danny H.w. LiAbstract:In Hong Kong, over one-quarter of the total electricity use was consumed by residential buildings. Recently, the Hong Kong Government issued a practice note namely Design and Construction Requirements for Energy Efficiency of Residential Buildings. This practice note set out the Residential Thermal Transfer Values (RTTV) of building envelopes. To enhance energy efficiency of residential buildings, the RTTV of wall (RTTVwall) and roof (RTTVroof) should not exceed 14 and 4 W/m2, respectively. Being one of the most densely populated cities in the world, most of building developments in Hong Kong are high-rise blocks located in densely built zones. The shading effects due to surrounding buildings could substantially restrict the diffuse light coming from the sky. In 2003, a practice note on lighting and ventilation requirements was issued. Referring to the performance-based approach, the note adopted the vertical Daylight Factor (VDF) to specify the Daylighting performance of the building. The VDF should not be less than 8% for habitable rooms and 4% for domestic kitchens. This paper presents the energy performance of recently designed building fulfills the RTTV requirements. It found that VDF is a good indicator to shows the lighting elecricty consumption in buildings. For most of the bedroom, about 40% of air conditioning and 3 % lighting energy can be saved.
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a review of calculating procedures on Daylight Factor based metrics under various cie standard skies and obstructed environments
Building and Environment, 2017Co-Authors: Danny H.w. Li, Amirhosein Ghaffarianhoseini, Khalid A AlshaibaniAbstract:Abstract Prediction of the Daylight level for any point within an indoor space is important in Daylighting analysis. Recently, the International Commission on Illumination (CIE) has adopted a range of 15 standard skies covering the whole probable spectrum of usual skies found in the world. In densely-built urban cities, the exterior obstructions may substantially reduce the amount of Daylight entering to the building interior. Through exhaustive investigations, we proposed various Daylight computation tools for buildings under different obstructed overcast and non-overcast skies. This paper reviews the Daylight Factor (DF) based metrics and gives an overview of the latest dynamic Daylight metrics, and generalizes the calculation procedures for estimating the internal Daylight under the unobstructed and obstructed 15 CIE Standard Skies. The merits and limitations of the calculating procedures on DF-based metrics are discussed. The findings could be globally adopted and useful to students and building professions conducting Daylighting studies and designs.
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An analysis of Daylighting performance for office buildings in Hong Kong
Building and Environment, 2008Co-Authors: Danny H.w. Li, Ernest K.w. TsangAbstract:Daylighting has often been recognized as a useful source of energy savings and visual comforts in buildings. Occupants expect good Daylight in their working spaces. The quality and quantity of natural light entering a building depend on both internal and external Factors. In Hong Kong, commercial building accounts for the major building energy use and electric lighting is one of the major electricity-consuming items. This paper studies the Daylighting performance and energy implications for office buildings. A total of 35 commercial buildings have been selected in the survey. Key building parameters affecting Daylighting designs are presented. Two typical office blocks were further analysed based on a lighting simulation program. The Daylighting performance was evaluated in terms of Daylight Factor, room depth and glare index. It has been found that the Daylighting performance for office buildings is quite effective. About one-third of the office areas that are near the perimeter regions have an average Daylight Factor of 5%. For inner region of deep plan offices, some innovative Daylighting systems such as light redirecting panels and light pipe could be used to improve the Daylighting performance. In general, the office building envelop designs are conducive to effective Daylighting and proper Daylight linked lighting controls could save over 25% of the total electric lighting use. © 2008 Elsevier Ltd. All rights reserved.
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Average Daylight Factor for the 15 CIE standard skies
Lighting Research and Technology, 2006Co-Authors: Danny H.w. Li, G. H.w. CheungAbstract:For Daylighting calculations, the design criteria are often expressed in terms of average Daylight Factors (DFave) with the computations being based on the CIE (International Commission on Illumination) overcast sky, which is generally considered to provide the worst Daylight condition. The Daylight illuminance of a room is mainly influenced by the luminances and patterns of the sky in the direction of view of the window at any given time. Overcast skies may not always be the appropriate reference sky types for Daylighting analysis. Recently, Kittler et al. have proposed a new range of 15 standard sky luminance distributions including five clear, five partly cloudy and five overcast sky types. These 15 sky luminance models have been adopted as the CIE General Standard Skies. This paper presents an approach to computing the DFave for the 15 standard skies. The techniques for calculating the two configuration parameters for the DFave determination, namely; (a) light received directly from the sky above the horizon on a vertical surface, and (b) light received directly from the ground below the horizon on a vertical surface are established and described. The performance of the proposed method was assessed against the results obtained by other independent calculation methods and computer simulations. It is shown that the results predicted by the proposed approach are in reasonably good agreement with those produced from the other two calculation tools. The findings provide architects and building designers with a reliable and simple method for estimating the interior Daylight illuminance under various standard overcast and nonovercast sky conditions.
John Mardaljevic - One of the best experts on this subject based on the ideXlab platform.
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Examples of Climate-Based Daylight Modelling
2020Co-Authors: John MardaljevicAbstract:The Daylight Factor persists as the dominant evaluation metric because of its simplicity rather than its capacity to describe reality. The Daylight Factor is insensitive to both the prevailing local climate and building orientation. The drive towards sustainable, low-energy buildings places increasing emphasis on detailed performance evaluation at the early design stage. Recent advances in lighting simulation techniques have demonstrated that reliable predictions founded on hourly climatic data are attainable. The first part of this paper describes the application of climate-based Daylight modelling to recent projects in New York and St. Petersburg. A climate-based Daylighting metric to replace Daylight Factors is described. The second part of the paper is a discussion on the origins and practice of “traditional” Daylight modelling.
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‘Climate connectivity’ in the Daylight Factor basis of building standards
Building and Environment, 2017Co-Authors: John Mardaljevic, Jens ChristoffersenAbstract: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.
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Rethinking Daylighting and compliance
2013Co-Authors: John MardaljevicAbstract:Daylight in buildings is the natural illumination experienced by the occupants of any man-made construction with openings to the outside. Our attempts to formulate some measure of Daylight provision in buildings can be traced back over a century, and the Daylight Factor as we know it today is over 50 years old. Still the most common measure found in guidelines and recommendations worldwide, the Daylight Factor is used routinely and, it is fair to say, often rather uncritically. The consideration of Daylight in buildings has received a new impetus from the accumulation of evidence on the wider benefits of Daylight exposure. But it is continuing to prove difficult to advance beyond Daylight Factors towards a more realistic quantification of Daylighting performance that would allow us to accommodate these new considerations in an evaluative schema. This paper examines the basis of current practice with respect to Daylight evaluation, and suggests a few ways in which it can be improved with relatively modest additional effort. The paper also critiques some of the recent attempts to advance Daylight evaluation by incremental means using so-called “clear sky options”.
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Opinion: Daylighting prescriptions: Keep taking the pills?:
Lighting Research & Technology, 2011Co-Authors: John MardaljevicAbstract: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
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Useful Daylight illuminances: A replacement for Daylight Factors
Energy and Buildings, 2006Co-Authors: Arsalane Nabil, John MardaljevicAbstract: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.
K. Alshaibani - One of the best experts on this subject based on the ideXlab platform.
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average Daylight Factor for the iso cie standard general sky
Lighting Research & Technology, 2016Co-Authors: K. AlshaibaniAbstract:The average Daylight Factor is one of the most widely used methods for predicting the internal illuminance due to Daylight. It is a simple tool that can be used in the early stages of design and can give information about the luminous environment inside a room. This method is supposed to be used under overcast sky conditions. Expanding the use of the average Daylight Factor to other sky conditions will encourage the use of Daylight in buildings. Several methods have been proposed for the prediction of Daylight based on the CIE Standard General Sky. However, most of these methods aimed for a detailed estimation of the internal illuminance pattern. This paper aims to investigate the potential for using the average Daylight Factor method under the ISO/CIE Standard General Sky.
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Average Daylight Factor for the ISO/CIE Standard General Sky
Lighting Research and Technology, 2016Co-Authors: K. AlshaibaniAbstract:The average Daylight Factor is one of the most widely used methods for predicting the internal illuminance due to Daylight. It is a simple tool that can be used in the early stages of design and can give information about the luminous environment inside a room. This method is supposed to be used under overcast sky conditions. Expanding the use of the average Daylight Factor to other sky conditions will encourage the use of Daylight in buildings. Several methods have been proposed for the prediction of Daylight based on the CIE Standard General Sky. However, most of these methods aimed for a detailed estimation of the internal illuminance pattern. This paper aims to investigate the potential for using the average Daylight Factor method under the ISO/CIE Standard General Sky.
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average Daylight Factor for clear sky conditions
Lighting Research & Technology, 1997Co-Authors: K. AlshaibaniAbstract:An average Daylight Factor is proposed for sunny climates on the basis of two assumptions. The first is that the illuminance on the external plane of a vertical window (as a result of direct skylight, reflected skylight and reflected sunlight) is approximately equal to the horizontal diffuse illuminance as a worst condition, where direct sunlight is not included in either quantity. Although the illuminance on the vertical window plane may vary considerably from the diffuse illuminance, such an assumption reduces the complexity of estimating the illuminance on the window under clear sky conditions. The second assumption is a new equation to predict the average internal illuminance on the working plane as a proportion of the illuminance on the external surface of the vertical window plane.
Khalid Alshaibani Arch B Mbdgsc - One of the best experts on this subject based on the ideXlab platform.
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a Daylight Factor for clear sky conditions
Architectural Science Review, 1999Co-Authors: Khalid Alshaibani Arch B MbdgscAbstract:This paper describes a method for estimating the Daylight Factor under clear sky conditions. The internal illuminance is divided into two components; light received directly form the window, as a diffuse source, and light reflected from the internal surfaces of the room. The method intended to estimate the internal illuminance as a relative value from the vertical illuminance on the external surface of the vertical window plane. A comparison against computer simulation is used to validate the proposed method. The purpose of this method is to provide a simple technique that can be used at the early design stages, which can give a preliminary information about Daylight performance inside a room.
