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.     

A case for ‘active’ daylighting by appropriate management of electric lighting

Understanding of how occupants of non-domestic buildings use electric lighting, gained from behavioural studies, indicates that the mere provision of daylighting is unlikely to lead to its useful uptake. It is suggested that the design of appropriate electric lighting control systems, including those requiring occupant action, can be related to occupancy patterns of space use and daylight availability in the space and that provision of such systems should be seen as ‘active daylighting’. It is also suggested that design for ‘active daylighting’ requires more accurate prediction of daylight availability in interiors.     

A comprehensive approach to the integration of daylight and electric light in buildings

Effective daylighting within an interior space depends to a large extent on the shape and size of the building. However, it is often impossible to illuminate a building exclusively by daylight. In this paper we review the past and present attitudes regarding optimal utilization of daylight in deep interiors. Such an optimal solution seems to be an integration of daylight and electric light.Various concepts of integration are examined, starting with permanent supplementary artificial lighting of interiors (PSALI), and a comprehensive list of types of integration is proposed. The preferred type for a specific design depends on activity pattern, visual requirements, location, climate, etc. Human requirements, energy saving, and cost-effectiveness are examined as determinants for optimal integration.     

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。     

Effects of daylighting options on the energy performance of two existing passive commercial buildings

Results are presented from a study of south facing roof apertures on two buildings from the U.S. Department of Energy's Non-Residential Experimental Passive Buildings Program. This study is part of a broad effort to evaluate the energy, functional and economic performance of all twenty buildings in the program based on on-site observations and physical data. The work reported here supplemented the basic building data with illumination data from physical models and from the buildings themselves, and with additional observations and measurements. Energy analyses were performed in order to examine more comprehensively the daylighting systems incorporated into the buildings, especially as they relate to (a) interaction between heating, cooling and lighting requirements; (b) integration of the electric lighting and daylighting systems and (c) functional effectiveness and occupant interaction with the daylighting system.Results of this study provide quantitative information on the energy benefits of the daylighting systems as designed and used in the two buildings examined. The daylighting strategies are shown to provide substantial energy savings over similar non-daylit buildings. In both buildings, manual control of the electric lights is used; the evaluation demonstrates that in these buildings this proves to be an extremely effective strategy. Factors contributing to this result are discussed in terms of the observed behavior of the occupants and functional requirements of the buildings.     

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.     

The daylighting dashboard – A simulation-based design analysis for daylit spaces

This paper presents a vision of how state-of-the-art computer-based analysis techniques can be effectively used during the design of daylit spaces. Following a review of recent advances in dynamic daylight computation capabilities, climate-based daylighting metrics, occupant behavior and glare analysis, a fully integrated design analysis method is introduced that simultaneously considers annual daylight availability, visual comfort and energy use: Annual daylight glare probability profiles are combined with an occupant behavior model in order to determine annual shading profiles and visual comfort conditions throughout a space. The shading profiles are then used to calculate daylight autonomy plots, energy loads, operational energy costs and green house gas emissions. The paper then shows how simulation results for a sidelit space can be visually presented to simulation non-experts using the concept of a daylighting dashboard. The paper ends with a discussion of how the daylighting dashboard could be practically implemented using technologies that are available today.     

云南地区卷烟工厂采光优化设计

卷烟工厂具有建筑面积大、室内进深大的特点。加之考虑到工艺和视觉工作要求,工厂对室内光环境要求较高。以云南某卷烟复烤联合工房为例,运用Ecotect建立原自然采光设计方案的建筑模型,导入Desktop Radiance进行采光系数计算,分析原设计方案中存在的问题,提出自然采光设计方案优化结果;分析优化方案对室内照明能耗和空调能耗的影响,同时,提供自然采光产品的性能参数指标。提出自然采光模拟分析技术在卷烟工厂采光优化设计中的研究与运用思路。     

Overview and new developments in optical daylighting systems for building a healthy indoor environment

Optical daylighting technology can deliver natural light to a space in a building where daylight is limited. This study gives an overview of two optical daylighting systems for capturing natural light: light pipe systems and mirror sunlighting systems. The literature on optical system theories and developments is identified and commercial products for optical daylighting systems on the market are described. By using a survey of major applications for optical daylighting systems, this study provides practical advice to building designers and researchers and also shows a light pipe system and a mirror sunlighting system developed from this investigation as well as an evaluation of their performance. The evaluation measured the illuminance of the two optical systems installed in a test room and a living room. This study concluded that optical daylighting systems can provide adequate visual comfort and can save energy if they are carefully designed.     

Occupant preferences and satisfaction with the luminous environment and control systems in daylit offices: a literature review

This paper presents an overview of peer-reviewed investigations of subjective issues linked to the use of daylighting in office buildings, particularly studies of preferred physical and luminous conditions in daylit office environments, and studies of occupant satisfaction and acceptance of electric lighting and window shading controls. The literature shows a consistent strong preference for daylight and a wide distribution between individuals in relation to the preferred illuminance levels in daylit offices. Existing knowledge about how people respond to daylight-linked lighting and shading controls in the workplace is very limited; therefore, this paper presents a summary of knowledge gaps in the field of daylighting and its interaction with the occupants. The resulting key directions for future research highlight issues for which a better understanding is required for the development of lighting and window shading control systems that are both energy efficient and suitable for the office occupants.     

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.     

Smart lighting system using ANN-IMC for personalized lighting control and daylight harvesting

Lighting contributes a significant portion to the overall energy consumption in an office building. It is thus important to reduce the energy consumption of lighting systems especially for Net Zero Energy Buildings( NZEB). Maximizing daylight harvesting can significantly increase the energy savings. With increase in demand for satisfying occupant preferences in visual comfort,the need for personalized lighting in the office space is also rising. In this paper,a novel lighting control system for Net Zero Energy Buildings( NZEB) is proposed which models the lighting system using Artificial Neural Netw ork( ANN) and utili-zes this model with the Internal Model Control( IMC) principle for controller design. Modeling the lighting system using ANN reduces the challenge of modeling a large and complex system with inherent process variability without the need to analyze extensive data-sets. The proposed ANN-IMC controller uses feedback from sensors on the task table to maintain desired illuminance,is easy to tune with just one parameter and is robust to process variability. The proposed control design is applicable to square systems where the number of lights and number of sensors are equal. How ever,the proposed architecture can also be extended for controlling other lighting accessories such as roller blinds. The performance of the proposed lighting control system to harvest the daylight effectively is demonstrated using both simulation results and an experimental setup in test-bed environment. The versatility of the proposed system will allow an operator to deploy personalized lighting in an office space.     

Thermal and daylighting performance of an automated venetian blind and lighting system in a full-scale private office

Dynamic envelope/lighting systems have the potential to optimize the perimeter zone energy balance between daylight admission and solar heat gain rejection on a real-time basis, and to increase occupant comfort. Two side-by-side full-scale offices in Oakland, California were built to further develop and test this concept. An automated venetian blind was operated in synchronization with a dimmable electric lighting system to block direct sun, provide the design workplane illuminance, and maximize view. The research program encompassed system design refinements, energy measurements, and human factors tests. In this study, we present lighting energy and cooling load data that were monitored in this facility over the course of a year. Significant energy savings and peak demand reductions were attained with the automated Venetian blind/lighting system compared to a static venetian blind with the same dimmable electric lighting system. Correlations between key weather parameters and cooling and lighting were used to illustrate how the dynamic system was able to simultaneously achieve optimization between lighting and cooling end uses under the full range of weather conditions of this sunny, moderate climate. Energy efficiency estimates were conservative since experience shows that conventional daylighting control systems and manually operated shading devices are rarely used effectively in real world applications.     

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。     

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.     

基于节能的办公建筑采光中庭形态优化设计

采光中庭由于其独特的空间设计给人们带来不一样的视觉感受,已在办公建筑中广泛应用,中庭结构的合理设计对建筑自然采光、建筑能耗具有很大的影响。通过Autodesk Ecotect和Ra-diance数值软件,模拟计算不同中庭平面布局、尺寸比例以及幕墙朝向对办公建筑自然采光系数、全年自然采光满足率DA、天然采光照明节能率、室内照度全年满足率的影响;在模拟分析的基础上,采用Designbuilder数值软件比较分析采光中庭形态优化设计对办公建筑人工照明、采暖空调能耗的影响。     

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.     

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.     

住宅天然光环境视知觉感受的影响因素分析

为了明确住宅天然光环境中的不同因素对视知觉感受的影响作用,该文利用SD法对相关内容进行了实验研究,并利用实验所得数据对不同个体及窗户大小、位置、形状对居住者视知觉感受的影响规律进行了分析和研究。发现不同个体之间的年龄差异对于评价结果的影响最为显著;窗户的面积、宽度、窗台高度的变化与居住者满意度之间都非简单线性的变化规律,这些结果的获得可以为设计者在设计初期提供设计参考和依据。