A simplified procedure for determining indoor daylight illuminance using daylight coefficient concept

The first step in evaluating the visual performance and energy efficiency provided by daylight requires an accurate estimation of the amount of daylight entering a building. The actual daylight illuminance of a room is mainly influenced by the luminance levels and patterns of the sky in the direction of view of the window at that time. The daylight coefficient concept, which considers the changes in the luminance of the sky elements, offers a more effective way of computing indoor daylight illuminances. Recently, Kittler et al. have proposed a new range of 15 standard sky luminance distributions including the CIE (International Commission on Illumination) standard clear sky. Lately, these 15 sky luminance models have been adopted as the CIE Standard General Skies. This paper presents a graphical method to calculate interior illuminance for the CIE standard clear sky using the daylight coefficient approach. The simplified techniques in the form of a nomograph and Waldram diagram were established and described. The performance of the proposed approach was evaluated against the results obtained by an independent calculation approach and a computer simulation program. It was shown that the daylight illuminances estimated by our graphical tool were in reasonably good agreement with those produced from the other two methods. The findings provide building professionals and students a reliable and simple alternative that incorporates the daylight coefficient concept to estimate the interior daylight illuminance and assess daylighting performance.     

A study of the daylighting performance and energy use in heavily obstructed residential buildings via computer simulation techniques

The quality and quantity of natural light entering a building depends on both internal and external factors. In Hong Kong, many buildings are high-rise blocks constructed close to each other and hence the external factor plays a significant role in daylighting designs. This paper studies the daylighting performance and energy use for residential flats facing large sky obstructions via computer simulations. Key building parameters affecting daylighting designs are presented. The daylighting performance for typical interior rooms was investigated in terms of illuminance level and daylight factor. The daylight levels of residential flats can be severely reduced by neighboring buildings and hence the externally reflected component would be the main source of natural light. The indoor daylight levels for kitchen and living/dining faced large neighboring building were found always less than the standard maintenance illuminance during daytime period. These imply that many residential flats in Hong Kong would have to rely on supplementary electric lighting.     

探索建筑采光的优化设计之道

文章阐述了一种建筑采光设计方法，重点强调了在地域性光气候条件下的采光分析以及利用参数化模型进行采光方案的比对，以上过程保证了优化方案的获得。文中以位于广州市的某给定的建筑项目为例探讨了建筑侧窗遮阳构件可能给室内采光带来的改善，设计过程可概括为：以优化的自然光环境的优化为目标，利用参数化模型技术对于方案进行了高效的择优，最终得出了兼顾遮阳效果的采光设计方案。基于课题组前提的研究成果，文章涉及的采光模拟工作均在可反映广州地区地域性光气候特征的典型天空亮度模型（CSRS）的基础上进行。     

Determination of vertical daylight illuminance under non-overcast sky conditions

In a dense urban region in which high-rise buildings are packed inside limited land areas, the daylight components reflected from ground and surrounding buildings play significant roles in daylighting design. The natural light available in an interior strongly depends on the amount of daylight reaching the window facades. Lately we proposed a calculation procedure, presented in form of simple mathematical expressions and diagrams, to determine the daylight illuminance on a vertical plane under overcast skies. This paper extends the study to non-overcast sky conditions. The performance of the proposed method was evaluated by comparison with the daylight illuminance simulated by a lighting software, namely RADIANCE, and with measurements under real skies. It was found that the data estimated by the proposed method were in good agreement both with the values simulated by RADIANCE and with the measured results. The paper offers to architects and building engineers a useful tool for estimating the daylight illuminance and in particular for determining and assessing various daylighting schemes and concepts during design and construction stages.     

An analysis of daylighting performance for office buildings in Hong Kong

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.     

Daylighting simulation in the DOE-2 building energy analysis program

A daylighting calculation has been intergrated grated into the DOE-2 building energy analysis computer program. Users can, for the first time in a widely-accepted, publicly-available program, determine the impact of daylight utilization on heating and cooling loads, energy use, energy cost, and peak electrical demand. We describe the algorithms which simulate hourly-varying interior illuminance, management of windows for sun and glare control, and the operation of electric lighting control systems. Sample DOE-2 daylighting output reports are presented and results of program validation against scale model illuminance measurements using the Lawrence Berkeley Laboratory sky simulator are discussed.     

用太阳辐射转化法计算室外照度值

针对中国光气候数据资料不足、太阳辐射数据丰富以及资金有限的现状,在分析多种光气候数据采集方法的基础上,选用太阳辐射转化法获得光气候数据.引入发光功效的概念作为室外照度值和太阳辐射量转化的基本关系,并分析对比了已有的发光功效模型,运用天空晴朗指数,以重庆1991-1992年的实测数据为基础进行拟合,建立了总发光功效模型和...     

Assessing and predicting average daylight factors of adjoining spaces in atrium buildings under overcast sky

Daylight use in an atrium is particularly beneficial as the natural light can illuminate potentially dark core areas and decrease energy consumption from electric lighting. This study has investigated, for overcast sky conditions, the horizontal daylight levels in spaces adjoining atria and the vertical daylight levels on atrium well walls in atria. The daylight levels in the rooms and on the walls were derived from scale model measurements, theoretical calculations and predictions from the lighting simulation package Radiance. A comparison of measured data and modelling has validated Radiance simulations of atrium daylighting. The simulations show generally good agreement with theory while some limitations in the calculations used in determining the daylight factors in rooms with large widow area to total wall area ratios were observed. The average daylight levels in rooms displayed a linear relationship with the vertical daylight levels on the well wall. In terms of the well geometry and well façades (decided by the ratio of window area to solid wall area) and well surface reflectance, the variations of daylight level in the adjoining rooms have been analysed and some conclusions and design strategies for supporting preliminary design decisions are presented.     

Findings from a survey on the current use of daylight simulations in building design

This paper presents findings from a web-based survey on the current use of daylight simulations in building design. The survey was administered from December 2nd 2003 to January 19th 2004. One hundred and eighty five individuals from 27 countries completed the survey. The majority of respondents worked in Canada (20%), the United States (20%), and Germany (12%). Most participants were recruited through building simulation mailing lists. Their self-reported professions ranged from energy consultants and engineers (38%) to architects and lighting designers (31%) as well as researchers (23%). They worked predominantly on large and small offices and schools.Ninety one percent of respondents included daylighting aspects in their building design. Those who did not consider daylighting blamed lack of information and unwillingness of clients to pay for this extra service. Among those participants who were considering daylighting 79% used computer simulations. This strong sample bias towards computer simulations reflects that many participants had been recruited through building simulation mailing lists. Participants named tools’ complexity and insufficient program documentation as weaknesses of existing programs. Self-training was the most common training method for daylight simulation tools. Tool usage was significantly higher during design development than during schematic design. Most survey participants used daylighting software for parameter studies and presented the results to their clients as a basis for design decisions.While daylight factor and interior illuminances were the most commonly calculated simulation outputs, shading type and control were the most common design aspects influenced by a daylighting analysis. The use of scale model measurements had rapidly fallen compared to a 1994 survey, whereas, trust in the reliability of daylighting tools has risen. While participants named a total of 42 different daylight simulation programs that they routinely used, over 50% of program selections were for tools that use the RADIANCE simulation engine, revealing the program's predominance within the daylight simulation community.     

窑洞采光因素分析及改善研究

本文通过对甘肃平凉地区窑洞采光的具体测量,分析了采光影响因素,提出了改善采光的设计方法和改造措施。首先,参考不同窑洞的照度,综合分析了光气候、窑洞朝向、口部构造、窑内空间设计、窑洞进深及窑内表面材料光反射等因素对采光量的制约。其次,完善适用于窑洞的天空照度模型,提出了窑内工作面综合照度公式,计算分析表明室外环境是影响采光的首要因素,采光口高度、透光材料及窑内表面反光材料对采光量的影响较大。最后,提出了窑洞在选址、设计、施工和室内装饰等方面的改善措施。     

A computational study on the use of balconies to reduce flame spread in high-rise apartment fires

High-rise apartment fires are perhaps the most dangerous residential fires. Within high-rise buildings, flames and smoke can travel through ductwork, between interior walls, and up elevator shafts and stairwells. One of the fastest ways a fire spreads to other floors is along the exterior of the building due to open windows. Flame spread up vertical walls has been studied experimentally and computationally for years in the US and abroad. A numerical study has been undertaken to examine the reduction of vertical flame spread due to the presence of a balcony. The depth and geometry of the balcony greatly affects the vertical movement of fire. By varying the balcony depth and geometry, the aim of this study is to find an optimum configuration that reduces vertical fire spread on the external wall.     

现代住宅与天然采光

通过科学的设计把天然光引入建筑已成为一种时尚,它不仅可以降低建筑能耗,还能利用阳光提高室内的环境质量.本文从四个方面探讨住宅建筑中的采光设计问题,包括室内天然光设计标准分析、采光窗对居室内部光环境的影响、天然采光系统主要技术手段的应用和住宅获得良好天然光的具体要求及其应注意的问题.     

广深机场天然光环境营造方式的比较研究

天然光环境更有利于人体健康与视觉舒适,这促使机场等大空间建筑对于天然采光设计的重视程度逐渐提高。比较广州新白云机场、深圳宝安机场T3航站楼两个大型机场的采光设计方案及其实际采光效果,文章旨在提出机场等大空间公共建筑采光设计应注意的问题以及设计原则。通过理论分析、现场测量、使用后评价等方法,研究两者在天然采光设计方面的优劣。经调研对比后发现开敞式大空间建筑使用集中式带型天窗不利于在整个室内实现均匀的天然光环境,而使用分散式平天窗更有利于营造均匀的天然光环境。     

Energy and visual comfort performance of electrochromic windows with overhangs

DOE-2 building energy simulations were conducted to determine if there were practical architectural and control strategy solutions that would enable electrochromic (EC) windows to significantly improve visual comfort without eroding energy-efficiency benefits. EC windows were combined with overhangs since opaque overhangs provide protection from direct sun which EC windows are unable to do alone. The window wall was divided into an upper and lower aperture so that various combinations of overhang position and control strategies could be considered. The overhang was positioned either at the top of the upper window aperture or between the upper and lower apertures. Overhang depth was varied. EC control strategies were fully bleached at all times, modulated based on incident vertical solar radiation limits, or modulated to meet the design work plane illuminance with daylight. The EC performance was compared to a state-of-the-art spectrally selective low-e window with the same divided window wall, window size, and overhang as the EC configuration. The reference window was also combined with an interior shade which was manually deployed to control glare and direct sun. Both systems had the same daylighting control system to dim the electric lighting. Results were given for south-facing private offices in a typical commercial building.     

An analysis of measured and simulated daylight illuminance and lighting savings in a daylit corridor

Lighting control integrated with daylighting is recognised as an important and useful strategy in energy-efficient building designs and operations. Prediction of the internal daylight levels is a key stage in daylighting designs. With the advances in computer technology, the computation of daylight illuminances can be conducted via lighting simulation program. This paper presents a study of the daylight coefficient (DC) approach using RADIANCE lighting software in simulating the indoor daylight illuminance of a corridor. The interior daylight illuminance data measured in the corridor were compared with the simulated results based on the computer software. It was found that the DC approach could give satisfactory results especially for the sun-shaded surface and sun-facing surface receiving a large amount of direct sunlight. Further, the daylight illuminance detected by the photosensor was also simulated in conjunction with measured daylight illuminance, dimming ratio and electric lighting power to predict the lighting energy savings. The findings suggested that the measured and predicted data showed a good agreement when large electric lighting savings resulted. The probable reasons causing the discrepancies were discussed.     

Multi-criteria analysis for the integrated performance assessment of complex fenestration systems

Complex fenestration systems (CFS) designed to collect and redirect daylight from the sky-vault are generally placed on the upper part of a window in order to improve the distribution of indoor daylight. Due to their additional function as solar protection, their use might contribute to the mitigation of the unfavourable effects that the admission of daylight signifies, especially in buildings located in prevailing sunny climates (risk of glare and overheating). An appropriate selection of the CFS that better contributes to improve the interior daylight environment would imply an integrated performance assessment taking into account relevant aspects such as indoor daylight distribution and the visual and thermal comfort of occupants. However, such an assessment implies the use of performance criteria with different targets; therefore, in order to evaluate their overall performance, a multi-criteria analysis is applied in this study. The method presented here describes a comprehensive evaluation to determine those CFS that better contribute to an improved indoor daylighting environment in a building located in a prevailing sunny climate. The CFS performance assessment was undertaken with computer simulations using their bi-directional transmission distribution function (BTDF).     

Numerical investigation of smoke contamination in atrium upper balconies at different down stand depths

Smoke contamination in upper balconies of shopping mall atriums presents a significant hazard to occupants by affecting evacuation and risking lives. Past research investigated the effects of varying balcony breadth, fire compartment opening width and fire size on smoke contamination. However, effects of varying the down stand depth at the fire compartment opening on smoke contamination have not been investigated. The down stand structure is widely used in shopping malls shops to display the trade names. This research investigates the effect of down stand depth on smoke contamination occurrence and severity in atrium upper balconies by varying the down stand depth together with the previously investigated parameters by utilizing Fire Dynamic Simulator (FDS), a computational fluid dynamics (CFD) software. Results demonstrated that the extent of smoke contamination increased with increased down stand depth. CFD simulation results showed that as down stand depth increased, from no down stand to 0.1 m in 1/10 scaled model, smoke severity increased by up to 40%. An empirical correlation was also developed to predetermine the smoke contamination height by relating the above mentioned variables in a single correlation.     

Advanced lighting simulation in architectural design in the tropics

This paper outlines a 2-year research program that the team attempted to apply one of the most powerful computational lighting simulation softwares, radiance, to assist in the daylighting design of an actual building in the tropics. The validation studies, which were carried out in the Asian Civilisation Museum (ACM) in Singapore, showed that radiance can be used to predict the internal illuminance with a high degree of accuracy under overcast sky conditions. The experimental application of radiance to daylighting investigation of the ACM further supports its capabilities as well as its accuracy. Using radiance to study two daylighting control options (curtains and louvers), it can be found that louvers are more effective than curtains as daylighting control devices, and that the angle of the louvers have more effect than their reflectance on daylight penetration and distribution.     

Simplified daylighting energy savings for non-daylighting building energy simulation programs

The California Legislature mandated the California Energy Commission (CEC) to establish and periodically update energy efficiency standards for new buildings. To this end, a sensitivity analysis was conducted by the Standards Development Office of the California Energy Commission for nonresidential buildings. The purpose of this parametric analysis was to determine which variations in building parameters actually have significant energy impacts.A “generic” building model was developed and implemented in conducting this sensitivity analysis. The generic model was used as an analytical tool in modeling the energy impact of building parameter variations, as well as architectural and mechanical energy-saving measures on the energy use of each module. It is recognized that the level of significant energy impact is equivalent to, or bounded by the accuracy of the energy analysis tools in predicting energy usage in actual buildings. For the computer program used, DOE 2.1A this accuracy is within ±5%.Since DOE 2.1A and most of the other building energy simulation programs do not have daylighting algorithms, another calculation tool was used to determine daylight availability and lighting power reduction on an hour-by-hour basis for each orientation. This is accomplished with a daylight reduction factor (DRF).Quicklite, a simplified daylighting program, calculated footcandle (lux) levels based on outdoor ambient light levels, physical room dimensions and properties. To assess the impact of the Quicklite calculated footcandle (lux) levels on artificial lighting use, a control scheme was assumed, and a DRF was calculated based on annual sky conditions by climate zone.Once the DRF values are known for each orientation, the electric lighting schedule can be modified. A new profile number, representing the proportion of installed lighting switched on at that hour, replaced the daily lighting schedules when daylighting was utilized (09:00 – 17:00). To test this methodology, a sensitivity analysis was conducted between DOE 2.1A with Quicklite modifications and DOE 2.1B which has a daylighting preprocessor. The results displayed a 3.6% variation in total energy use.We conclude that daylighting calculations for design days using simplified programs can be used to approximate daylighting energy savings in building energy simulation programs that allow zoned lighting schedules but do not calculate daylight contributions.