Quantifying energy savings in daylight responsive systems: The role of dimming electronic ballasts

The application of lighting control technologies with photosensors has led to an increase in public interest. Although these technologies have been promoted during the last years their successful use in buildings has been accomplished in a small percentage of new projects. One reason is the difficulty in quantifying the energy savings and thus the subsequent payback period. Daylight responsive dimming systems consist of three basic components: photosensor, controller, and dimming unit. Electronic dimming ballast (EDB) is one substantial component of these lighting control systems which can adjust the light output due to the transferred signal from the photosensor and lighting controller. The aim of this study is to quantify energy savings among different EDBs. Eighteen commercial EDBs were selected and various sets of electrical and illuminance measurements were taken for different dimming levels, in order to develop polynomial functions between light output and consumed power. Using the measured data, a set of simulations were performed for a photosensor with an ideal cosine spatial sensitivity distribution installed in a typical office room using two control algorithms, closed loop and integral reset, trying to quantify the relative differences in energy savings.     

The role of spectral response of photosensors in daylight responsive systems

Lighting control technologies using photosensors have a great potential for energy savings in areas with high levels of daylight. Although the proper application of these controls can exploit this potential, unfortunately, it has been accomplished in a small percentage of new projects. One reason is the difficulty in justification of energy savings, which in turn, is directly linked with the simulation of the behaviour of these lighting controls. The core of these systems is the photosensor, which adjusts the electric light output in proportion to the amount of the daylight that detects, using its spatial and spectral response. The aim of this study is to quantify the impact of photosensor spectral response on its illuminance values, by taking into account various daylight spectra as these are modified due to various types of coloured glazing. Five commercial photosensors were selected and their spectral response was measured. In addition, spectral transmittance of 16 commercial types of glazing was measured as well. Using these data, a set of simulations were performed using three colour channels in a typical office room and the relative differences in illuminance – and thus energy savings – among the photosensors are presented. The results show that differences are significant ranging from 36 to 118%, a fact that can affect the estimated payback period of a lighting control system.     

Performance of integrated systems of automated roller shade systems and daylight responsive dimming systems

Daylight responsive dimming systems have been used in few buildings to date because they require improvements to improve reliability. The key underlying factor contributing to poor performance is the variability of the ratio of the photosensor signal to daylight workplane illuminance in accordance with sun position, sky condition, and fenestration condition. Therefore, this paper describes the integrated systems between automated roller shade systems and daylight responsive dimming systems with an improved closed-loop proportional control algorithm, and the relative performance of the integrated systems and single systems. The concept of the improved closed-loop proportional control algorithm for the integrated systems is to predict the varying correlation of photosensor signal to daylight workplane illuminance according to roller shade height and sky conditions for improvement of the system accuracy. In this study, the performance of the integrated systems with two improved closed-loop proportional control algorithms was compared with that of the current (modified) closed-loop proportional control algorithm. In the results, the average maintenance percentage and the average discrepancies of the target illuminance, as well as the average time under 90% of target illuminance for the integrated systems significantly improved in comparison with the current closed-loop proportional control algorithm for daylight responsive dimming systems as a single system.     

Developments in tubular daylight guidance systems

Tubular daylight guidance systems are linear devices that channel daylight into the core of a building. They consist of a light transport section with, at the outer end, some device for capturing natural light and, at the inner end, a means of distributing the light within the interior. This technology is examined in terms of performance, cost, design issues and governance (codes) for the different generic types of systems. Gaps in the knowledge on a range of issues, particularly operational human factors, are identified as key determinants delaying the wider implementation of this technology.     

German developments in guidance systems: an overview daylight

An overview is provided of recent developments in different daylighting systems. The systems range from a simple adaptation of venetian blinds for a better use of daylighting, to specially developed daylight-guiding venetian blinds, mirror louvers, optical mirror elements, ADO-Toplight, holographic optical elements, prismatic systems, Micro-Grates, Plexiglas Daylight, transparent insulation material, moveable glass louvers, a three-layer pipe-grid system and the ‘light sculptor’ in the cupola of the German Parliament. Most of these technologies are available in the market. Others, e.g. the ‘light sculptor’, were designed for a unique application.

Cet article présente les grandes lignes des développements récents en matière de systèmes d'éclairage naturel. Ces systèmes vont de la simple adaptation de stores vénitiens pour un meilleur usage de la lumière naturelle jusqu'à des stores vénitiens de conception spéciale à commande par la lumière du jour, en passant par des rideaux à lattes miroirs, des éléments de miroirs optiques, le système ADO-Toplight, des éléments optiques holographiques, des systèmes prismatiques, des microgrilles, des systèmes d'éclairage naturel en plexiglas, des matériaux isolants transparents, des systèmes à lattes de verre amovibles, un système à grille tubulaire à trois couches et le “sculpteur de lumière” qui équipe la coupole du Parlement allemand. La plupart de ces technologies sont disponibles sur le marché. D'autres, comme le “sculpteur de lumière” ont été conçus pour une application unique.     

Prospective techniques of effective daylight harvesting in commercial buildings by employing window glazing, dynamic shading devices and dimming control—a literature review

Over a few decades, daylighting has been perceived to possess good potential for energy conservation. In this perspective, there have been significant advances in research methodologies and technologies for optimizing energy consumption through daylight harvesting in commercial buildings. In light of this, a thorough understanding of the application of available technology is very important for daylighting practices for building energy management. The objective of this paper is to examine the status of published research on three key building parameters: window glazing area, dynamic shading devices, and daylighting controls playing a rule on energy conservation. This article may serve as a coherent literature survey that would provide better understanding of the subjacent issues and possibly rejuvenate research interest in this immensely potential field of energy engineering.     

Theoretical and experimental analysis of daylight performance for various shading systems

The daylight coefficient approach is used for the theoretical analysis of various shading systems. Once a set of these coefficients has been calculated, it is very easy to calculate illuminance in the interior of a room under various sky luminance distributions. The present paper examines a method based on daylight coefficients to evaluate daylight in the interior of a room. The method is compared with existing radiosity and ray-tracing methods. The examined method is experimentaly validated using measurements obtained in a PASSYS test-cell equipped with shading devices.     

Efficient calculation of daylight coefficients for rooms with dissimilar complex fenestration systems

The daylight coefficient (DC) method is a powerful and efficient method to perform annual daylight illuminance simulation. A set of coefficients are calculated for a given room space and static fenestration systems prior to simulation start. Time series of indoor daylight illuminances are obtained by only knowing the sky luminance. However, for rooms with dissimilar dynamic complex fenestration systems (such as windows with movable shadings) whose optical behaviour (transmission, reflection and scattering) may change during simulation, the efficiency of the DC method may be compromised as another whole set of coefficients must be re-calculated. This study presents the development of a new methodology to compute the DC set for rooms with dissimilar complex fenestration components only once prior to simulation start. A validation study is carried out, in which the daylight illuminances in an office space equipped with a clear window and internal Venetian blinds are compared using predictions from the present model, the Radiance program, as a benchmark model employing detailed optical model of Venetian blinds, and the Daysim program employing a simple engineering blinds model. Findings from the validation study show that the present model yields overall accurate results when compared with the benchmark model for any window orientation, although some local illuminance differences are observed in areas under direct sunlight exposure.     

A computer model for predicting the daylight performance of complex parallel shading systems

In tropical areas where the exclusion of solar heat from buildings is a paramount consideration, shading systems consisting of adjustable parallel multiple slats have evolved which exclude direct solar radiation whilst permitting some daylight penetration. The modelling of daylight illuminance from these systems is not easy using conventional graphical or computational quantitative techniques. This paper sets out a computer-based model for the analysis of the general case of parallel shading systems. The model is illustrated by reference to the Rowshan shading system used in the Hedjazi architecture of Saudi Arabia.     

Analysis of the performance of prism daylight redirecting systems with bi-directional scattering distribution functions

Building Simulation - Simulation with two types of bi-directional scattering distribution function (BSDF) was used to model the prism daylight redirecting fenestration (PDRF) in the indoor luminous...     

LED自动调光系统的研究与设计

介绍基于STC89C52单片机的LED自动调光系统,对系统各模块硬件进行研究与设计,并给出系统的软件控制流程图。采用基于专家知识的多传感器数据融合技术,应用先进的PWM调光技术,根据照明环境情况的不同对LED照明进行自动调节。系统具有节能、高效和环保的作用,实现节能减排的目的,有较高的使用价值。     

边界温度周期波动下块石的温度变化规律

将块径为 6～ 8cm、4～ 6cm和 2～ 4cm的块石分别装入直径为 15cm、高度为 5 9cm的有机玻璃筒内 ,进行了边界温度周期波动条件下块石体中一维温度场的测试 ,以考察多孔块石体中温度变化规律。试验表明 ,开放系统条件下 ,块石体温度随时间变化具有不对称性 ;温度随深度变化不符合基于热传导理论的傅立叶第一定律 ,具有迟缓性 ;块石体中的平均温度经过几个周期会低于其表面平均温度 ,说明其中存在对流换热机制。封闭系统条件下 ,三种块径的块石体的温度变化均无上述规律 ,表明其中对流换热机制尚不存在或十分微弱。     

The costs and benefits of using daylight guidance to light office buildings

Daylight guidance systems are linear devices that channel daylight into the core of a building. This paper analyses costs and benefits of using the two main classes of daylight guidance to light offices as an alternative to conventional electric lighting. The work demonstrates that daylight guidance is generally not economical using conventionally accepted measures of both cost and benefit. It is shown that if intangible benefits associated with the delivery of daylight to offices are included in an analysis, a more favourable balance of cost and benefit is obtained. The implications of this for practical use of the systems are discussed.     

Pre-versus post-occupancy evaluation of daylight quality in hospitals

The purpose of this study is to examine the effect of space occupancy on indoor daylight quality in hospitals. It assesses the effect of various design variables on the indoor daylight quality in King Abdullah University Hospital (KAUH) in Jordan. By conducting a comparative study on the indoor daylight quality of pre- and post-occupancy in patient wards, it was found that hospital occupancy is highly correlated with indoor daylight quality.     

Attitudes of school children to daylight and fenestration

The behaviour and attitudes towards their visual environment of 350 primary school children were studied in 11 schools of varying design, with particular attention to factors associated with fenestration and daylight. The investigation included social factors, personality characteristics of the children and the varying visual characteristics of the buildings including photometric studies. A significant proportion of children choose to sit or work near windows, the chief factor being the amount of daylight. View out, view content and nature are important. The most popular children occupy favoured window places. Space and comfort both visual and thermal are important. Sex separation is natural.     

自然光作为设计元素在设计过程中的应用原则

对自然光设计在剖面设计、设计策划等方面进行了分析，提出了自然光作为设计元素在设计过程中应注意的关键问题，并提出在设计前期和中期的具体解决方法。     

A validation of the Radiance three-phase simulation method for modelling annual daylight performance of optically complex fenestration systems

A new capability that enables annual simulation of optically complex fenestration systems has been added to Radiance. The method relies on bidirectional scattering distribution function (BSDF) input data, which are used in an efficient matrix calculation to compute time-step performance given TMY data. The objective of this study was to explain the value of this capability to designers and developers of innovative daylighting systems and to demonstrate its speed and accuracy via comparisons of simulated to measured illuminance data for a daylight-redirecting optical louver system. The method was shown to provide valid results that accurately replicate real-world conditions with an absolute mean bias error below 13% and a root mean square error below 23%. Routine application of this new capability will not be hindered by slow computational speed for illuminance calculations. Instead, the capability will be dependent on the availability of BSDF data for daylighting, shading and fenestration systems.     

Assessment of daylight in rooms with different architectural features

Results are presented from a parametric study that assessed the amount of daylight in rooms with different architectural features: the orientation, window size and visible glazing transmittance, room depth, external obstruction angle and site. Annual lighting simulations were run in order to understand how the daylight availability within a space changes as a function of the architectural features. A sub-dataset of the full result database is examined in detail for north- and south-facing rooms in Turin, north-west Italy, with a visible glazing transmittance of 70%. Each feature is analysed for its influence on the daylighting conditions. A simple graphical tool is presented to promote an easier reading of the results. This was developed to provide a synthesis of information to the design team. It shows the influence of preliminary design solutions on the amount of indoor daylight. This allows a design team to assess indoor daylighting from the earliest design phases onwards and to determine which combinations of architectural features are able to provide high, acceptable or low daylight levels within a room.