The impact of changing solar screen rotation angle and its opening aspect ratios on Daylight Availability in residential desert buildings

In desert sunny clear-sky regions solar penetration can become excessive. This can cause non-uniform daylight distribution, glare and high solar heat gain, affecting both visual and thermal comfort. Shading devices, such as solar screens, were usually used to diffuse and prevent direct solar penetration into spaces. This paper investigates the impact of changing solar screen axial rotation angle and screen opening aspect ratio on daylighting performance in a typical residential living room space under the desert sunny clear-sky. The larger aim is to arrive at efficient solar screen designs that suit the different orientations.The study was divided into three consecutive phases. In phase one, the effect of the two parameters on Daylight Availability was tested. The solar screen was axially rotated by three different angles at 10° increments. Also, the aspect ratio of the screen opening in both horizontal and vertical directions was changed systematically. Simulation was conducted using the annual Daylight Dynamic Performance Metrics (DDPMs). In phase two, the Annual Daylight Glare Probability (DGP) metric was evaluated for the cases that were found adequate in phase one. In the third phase, the annual solar energy transmittance through the screen was calculated for the cases that achieved acceptable performance in the two previous phases in order to identify the more energy efficient screens.Solar screens with openings having horizontal aspect ratios were found to be the most effective, while those with vertical aspect ratios were achieved the lowest performance. In the North orientation, since almost all the cases that were tested in this research provided acceptable daylighting performance, the designer now have a variety of options to choose from. Preference should be given to screen openings of horizontal aspect ratios, especially the 12:1 and 18:1 (H:V) screens that achieved the best performance where 92% of the space was “daylit” in comparison with only 53% of the base case. In the East orientation, it is advisable to use the 12:1 (H:V) screen opening ratio, as it was found acceptable in the two daylighting testing phases and achieved the best performance in regards to annual transmittance of solar radiation. For the South orientation, there were also many acceptable choices. However, the 3:1 screen aspect ratio is recommended as it assists in saving energy by reducing the annual transmitted solar radiation (60% reduction) while achieving acceptable daylighting performance.     

不同电池宽度半透明光伏窗天然采光分析

为了模拟不同太阳电池宽度对半透明光伏窗采光性能的影响,提出将非透光电池和透光玻璃间隙分开模拟的新方法,并使用实验数据验证新方法和模型的准确性。通过与实验结果的差异分析,采用新方法模拟所得到的照度和眩光可能性（DGP）的准确性均明显优于传统方法。采用新方法对太阳电池覆盖率相同但电池宽度分别为2.5、5.0以及7.5 mm的3种半透明光伏窗的天然采光特性进行模拟研究,并采用全天然采光时间百分比（DA）、有效天然采光照度（UDI）、天然光眩光指数（DGI）、眩光可能性（DGP）等指标对不同电池宽度光伏窗的采光和眩光性能进行对比分析。结果表明,随着电池宽度增加,室内平均DA和UDI逐渐减小,产生眩光的可能性增加,室内视觉舒适度下降。该文提出的方法使得研究不同电池宽度条件下半透明光伏窗的采光和眩光性能变为可能,且利用该方法得出相同电池覆盖率下最佳的电池宽度。     

Lighting and energy performance of solar film coating in air-conditioned cellular offices

In subtropical Hong Kong, the principal objectives of fenestration design include eliminating direct sunlight and decreasing cooling loads. To avoid the problems of glare, excessive brightness and thermal discomfort, occupants may block the windows with internal shading devices, resulting in poor daylighting performance and very small amount of electric lighting energy savings. Recently, the advances in thin film coatings for window glass products provide a means of substantially reducing heat gain without proportionally reducing daylight transmittance. It has been suggested that film coatings together with photoelectric lighting control systems could minimise the electric lighting and cooling requirements without causing undue visual and thermal discomfort to the occupants. This paper presents field measurements on solar control film coatings in fully air-conditioned offices in Hong Kong. Solar heat gains, indoor illuminance levels and the electricity consumption by the fluorescent luminaires were systematically recorded and analysed. Measurements were made for two cellular offices, one with solar control film coating on the window glass and the other without. The findings showed that the solar film coating could cut down energy expenditures for air-conditioned buildings, especially for spaces with large glazing areas subject to substantial amount of direct sunlight. Results are presented and the design implications discussed.     

Efficient venetian blind control strategies considering daylight utilization and glare protection

This paper presents the development of new venetian blind control strategies considering daylight provision, lighting energy use and visual comfort. A hybrid ray-tracing and radiosity method is used to calculate transmission through the window-blind system and interior illuminance distributions taking into account specular and diffuse material properties. Work plane illuminances are used to extract daylighting metrics, while directional light distribution and respective luminance values are used to calculate glare potential. Four types of control strategies were evaluated – a cut-off angle control, a daylight-redirecting control, and two glare protection control modes. Using the common “cut-off” angle may result in a strong second reflection that might significantly affect visual discomfort depending on view direction and profile angle. Proper rotation of the tilt angle and consideration of specular characteristics can minimize this effect and redistribute daylight deeper into the space, although glare problems cannot be eliminated in some cases. Moreover, two additional control strategies were developed based on glare probability and sky conditions: the first is a model-based control derived from real time glare simulation results. The second is a “simplified” control that uses pre-calculated correlations between glare probability and transmitted illuminance to establish binary set points that can be used in model-predictive control algorithms.A detailed daylighting analysis was performed in order to evaluate set points for blind control actions, annual daylighting metrics, lighting energy use and daylight glare probability and duration. Different room sizes, glazing properties, blind material characteristics and orientations were studied. The results showed that diffuse blinds do not reduce the risk of glare when light redirection is desired; double-sided slats with a diffuse top and a specular bottom surface are better in this regard. Fixed angles at 60° or higher provide satisfactory results for most cases, although there is a penalty in daylighting efficiency. The two glare protection control algorithms proved to be efficient in providing high daylight autonomy values without the risk of glare for all studied cases.     

Daylighting performance evaluation of a bottom-up motorized roller shade

This paper presents an experimental and simulation study for quantifying the daylighting performance of bottom-up roller shades installed in office spaces. The bottom-up shade is a motorized roller shade that opens from top to bottom operating in the opposite direction of a conventional roller shade, so as to cover the bottom part of the window, while allowing daylight to enter from the top part of the window, reaching deeper into the room. A daylighting simulation model, validated with full-scale experiments, was developed in order to establish correlations between the shade position, outdoor illuminance and work plane illuminance for different outdoor conditions. Then, a shading control algorithm was developed for application in any location and orientation. The validated model was employed for a sensitivity analysis of the impact of shade optical properties and control on the potential energy savings due to the use of daylighting. The results showed that Daylight Autonomy for the bottom-up shade is 8–58% higher compared to a conventional roller shade, with a difference of 46% further away from the façade, where the use of electric lighting is needed most of the time. The potential reduction in energy consumption for lighting is 21–41%.     

The availability of daylight from tropical skies—a case study of Malaysia

In Malaysia, no long-term daylight data are measured. It was only recently that the need to measure the availability of daylight became urgent when the importance of daylighting in buildings was rediscovered. The hourly daylight availability has been simulated for the Malaysian sky using daylight modelling techniques based on empirical and measured solar irradiation and cloud cover data. This paper presents the techniques involved in producing exterior illuminance data. These data were then compared with measured illuminance at Shah Alam and Bangi, Malaysia. The global illuminance levels are generally high, with values exceeding 80,000 lux at noon during the months when solar irradiation is highest. Even during the months when the ground receives less solar irradiation, the peak illuminance can reach 60,000 lux. Applications and uses of such data are in daylighting design, both for visual and thermal comfort, task illuminance and energy-conscious design of buildings. Recommendations are made at the end of the paper on the various climatic data that are required to be measured for overall daylighting design applications.     

Predicting daylight illuminance on inclined surfaces using sky luminance data

Daylight illuminance, particularly on vertical surfaces, plays a major role in determining and evaluating the daylighting performance of a building. In many parts of the world, however, the basic daylight illuminance data for various vertical planes are not always readily available. The usual method to obtain diffuse illuminance on tilted planes would be based on inclined surfaces models using data from the horizontal measurements. Alternatively, the diffuse illuminance on a sloping plane can be computed by integrating the luminance distribution of the sky ‘seen’ by the plane. This paper presents an approach to estimate the vertical outdoor illuminance from sky luminance data and solar geometry. Sky luminance data recorded from January 1999 to December 2001 in Hong Kong and generated by two well-known sky luminance models (Kittler and Perez) were used to compute the outdoor illuminance for the four principal vertical planes (N, E, S and W). The performance of this approach was evaluated against data measured in the same period. Statistical analysis indicated that using sky luminance distributions to predict outdoor illuminance can give reasonably good agreement with measured data for all vertical surfaces. The findings provide an accurate alternative to determine the amount of daylight on vertical as well as other inclined surfaces when sky luminance data are available.     

Science of daylighting in buildings

The materials characterisation requirements for accurate yet practical simulation of daylighting in buildings is examined for a range of emerging and existing technologies which seek to raise the contribution of daylighting to overall lighting requirements. Algorithms based on underlying physical models can be established from analysis of data on bi-directional transmission and reflection. Demonstrations of effects in simulation relevant to glare, view and illuminance are given.     

Solar radiation calculation methodology for building exterior surfaces

The present article shows a new methodology of calculation of the direct, diffuse and reflected incident solar radiation, in all type of surfaces, either in open urban environments or inside buildings. This methodology is applicable in problems related to solar access (space heating in buildings, shadowing of open spaces), solar gains (space cooling in buildings), and daylighting. Solar radiation is the most important contribution to the surface and volumetric energy balance during the daytime. Particularly, solar radiation is the main contributor to heat gains in buildings, especially in residential buildings, where internal gains are very low. Utilization of daylight in buildings may result in significant savings in electricity consumption for lighting while creating a higher quality indoor environment. Additional energy savings may also be realized during cooling season, when reduction of internal heat gains due to electric lighting results in a corresponding reduction of cooling energy consumption.The analysis of the existing calculation methods and proposed in the scientific bibliography for the calculation of the solar radiation in problems of solar access in winter, solar gains in summer, and daylighting, takes us to the necessity of outlining a new and complete methodology. This new methodology is applicable to all these problems with a great accuracy and calculation speed.     

A review of daylight illuminance determinations and energy implications

Daylighting is recognized as an important element in architecture and a useful strategy in energy-efficient building designs. Daylight gives a sense of cheeriness and brightness that can have a significant positive impact on the people. There is a scope for integrating daylight with electric light to reduce building energy use. The amount of daylight entering a building is mainly through window openings, which create in the indoor environment a more attractive and pleasing atmosphere, in addition to maximise visual access to the pleasant views of the outside world. Determinations of the exterior and interior daylight and lighting energy savings are key issues to demonstrate the benefits based on daylighting designs. This paper provides a review of daylight illuminance determinations and the lighting energy reductions due to daylighting schemes. The study includes daylight measurements, prediction of daylight illuminance under various sky conditions and potential electric lighting energy savings from daylight-linked lighting controls. The article aims at providing building professionals, practitioners and researchers more information and a better understanding of daylight for promoting effective daylighting designs and evaluations.     

Automated demand response system in lighting for optimization of electricity cost

Daylighting is an important factor in improving visual comfort and energy efficiency. Lighting control using daylighting can reduce energy consumption in buildings. This thesis proposes an automatic demand response system for lighting based on wireless sensor networks (WSN) in order to reduce the peak electricity demand according to the stage of electricity rate with real-time pricing (RTP), time of use pricing (TOUP), and critical peak pricing (CPP). The proposed system automatically controls the slat angle of the venetian blind with a cut-off angle according to the altitude of the sun, automatically executing light dimming according to measured current luminance to remove an unpleasant glare caused by daylighting. The target illuminance of area at this time is set at a minimum illuminance required for the work execution in the office during the time zone where the electricity load is high to save the lighting energy cost, while a maximum illuminance is set during the time zone where the electricity load is low according to the real-time electricity pricing stages obtained through the advanced metering infrastructure (AMI) in order to improve the work efficiency of the occupants. In this study, two testbeds having the same environments, as well as a control system targeting a fixed illuminance per price system, were established. The illuminance energy consumption and cost were then measured and the effect of the proposed illuminance system was evaluated.     

Passive solar systems for heating, daylighting and ventilation for rooms without an equator-facing facade

Spaces without northerly orientations have an impact on the ‘energy behaviour’ of a building. This paper outlines possible energy savings and better performance achieved by different zenithal solar passive strategies (skylights, roof monitors and clerestory roof windows) and element arrangements across the roof in zones of cold to temperate climates typical of the central and central-southern Argentina. Analyses were undertaken considering daylighting, thermal and ventilation performances of the different strategies. The results indicate that heating, ventilation and lighting loads in spaces without an equator-facing facade can be significantly reduced by implementing solar passive strategies. In the thermal aspect, the solar saving fraction reached for the different strategies were averaged 43.16% for clerestories, 41.4% for roof monitors and 38.86% for skylights for a glass area of 9% to the floor area. The results also indicate average illuminance levels above 500 lux for the different clerestory and monitor arrangements, uniformity ratios of 0.66–0.82 for the most distributed arrangements and daylighting factors between 11.78 and 20.30% for clear sky conditions, depending on the strategy. In addition, minimum air changes rates of 4 were reached for the most extreme conditions.     

Daylighting and energy analysis of private offices with automated interior roller shades

This paper presents a comprehensive analysis to study the balance between daylighting benefits and energy requirements (control of solar gains) in perimeter private office spaces with interior roller shades taking into account glazing properties, shading properties and control together with window size, climate and orientation in an integrated daylighting and thermal manner. Daylight autonomy and useful daylight illuminances were computed as a function of façade design parameters. A thermal simulation module using the explicit finite difference thermal network approach runs at the same time step and calculates heating, cooling and lighting source energy consumption as well as surface temperatures and operative temperature. Based on the daylighting results, lighting internal gains (continuous dimming control) are simultaneously input to the thermal module. The model also considers the air in the gap between shade and interior glass as a separate thermal node.Detailed results for Chicago and Los Angeles showed that windows with visible transmittance higher than 50% have the ability to allow enough daylight into the space for all locations and orientations for window-to-wall ratios higher than 50%. Useful daylight illuminances between 500 and 1000 lux were considered in detail – it was found that this index can be maximized for specific window-to-wall ratios and that depends on the glazing properties and fabric properties for each orientation. Moreover, the complex interactions of the studied parameters and their impact on the heating, cooling and lighting energy performance revealed an interesting result: windows occupying 30–50% of the façade can actually result in lower total energy consumption for most cases with automated shading. This illustration of daylighting benefits can be realized only if the integration of daylighting and thermal climate-based analysis is modeled efficiently and depends on glazing and shading properties and control. Finally, best designs for each orientation and location were pointed out based on both daylighting and thermal results.     

An analysis of lighting energy savings and switching frequency for a daylit corridor under various indoor design illuminance levels

Visual comfort and electric lighting energy issues are essential criteria to justify daylighting schemes. The evaluation of energy efficiency due to daylight linked lighting control systems is best demonstrated by case studies. This paper presents field measurements on daylighting for a fully air-conditioned daylit corridor. Artificial lighting load, brightness of the fluorescent luminaires, daylight availability for various switching illuminance levels were systematically recorded and analyzed. The general features and characteristics of the findings including the number of switching operations and electric-lighting energy savings are presented and discussed. Daylighting theories, using cumulative frequency distribution of outdoor illuminance and regression models based on brightness of light output, outdoor illuminance and electric light power to estimate daylight-linked lighting control savings, have been developed and assessed. It has been found that data from both approaches show reasonably good agreements with measured results. The findings from this study provide some operational and energy information, which would be useful and applicable to other interior spaces with similar architectural designs.     

Easing high brightness and contrast glare problems in universal space design studios in the UAE: Real models testing

The new building of the department of architectural engineering at UAE University introduces a rare form for such a type of function, especially in desert climate. This created an incentive to investigate its performance with regard to daylighting. The study depends mainly on experimental research approach under actual sky using scaled architectural physical models. Based on previous study by the author, it was decided to test two design modifications. These are the adding of external reflective light shelf (in different slopes) to improve the daylighting level and visual comfort in the back space of the first floor studio and the replacement of the current transparent glazing in the existing skylights with a diffusing translucent glazing to improve visual comfort in the third floor studio. Quantitative analysis was conducted based on measurements taken using lighting photometric sensors that were distributed in several locations inside the model. Qualitative analysis was also conducted to assess the visual environment and the presence of glare inside the studio spaces using photography.     

Evaluation of a large dish‐type concentrator solar lighting system for underground car park

To utilize solar energy more efficiently and reduce lighting power consumption in underground public spaces such as car park, a large dish‐type concentrator solar lighting system is put forward along with its evaluation, which is a unique design to apply a laminated layer of beam split thin‐film coating and thin‐film solar cells onto the dish reflector. The collected sunlight is split into 2 parts, one being reflected into a fiber optical bundle and transmitted for daylighting, while the rest being absorbed by solar cells for electricity generation as the other way to replenish daylighting. A set of 4 solar lighting systems using 3.28‐m diameter dish are designed to meet the lighting requirement in a 1771‐m² underground car park. A mathematical model is adopted to calculate the output power and conversion efficiency of solar cells distributed on the parabolic dish surface. The indoor illuminance distribution is given by lighting simulation. The results indicate that the average daylight illuminance in the car park can vary between 62.7 and 284 lx on February 25, 2016 and between 62.7 and 353 lx on August 17, 2016 for 2 chosen days, respectively. For the presented design, the electricity produced by solar cells is just enough to power light‐emitting diodes for lighting meeting a criterion at night. Considering about 19% conversion efficiency of solar cells and the efficacy of 129.5 lm/W of light‐emitting diodes, the hybrid solar lighting system can have about 40% utilization ratio of solar energy, so it can be concluded that a sufficient lighting provision can be provided by the proposed large dish‐type concentrator solar lighting system for applications in underground car park.     

Implementing the partial daylight factor method under a scanning sky simulator

Architects need support for the evaluation of the daylighting performance of their buildings. As experimental tools, sky simulators, used in conjunction with scale models, allow a concrete and intuitive approach to the problem. Yet conventional artificial skies and their measurement technology are of limited use, because they are usually not able to evaluate building performance under a non-standard sky luminance distribution (CIE sky models). The Partial Daylight Factor (PDF) method presented in this paper addresses this problem. It is applied to a scanning sky simulator in conjunction with a methodology of experimental research (experimental plans of Hadamard). Scale model experimental simulations carried out with the scanning sky simulator and the PDF method offer an evaluation of the daylighting performance of a building for any luminous configuration of the sky vault. Coupled to a climatic database, they allow an evaluation of daylighting performance indicators such as daylight sufficiency and average or cumulated illuminance for all types of overcast, intermediate and clear skies, including CIE standard models. Moreover, new concepts, such as the Partial Illuminance Factor (PIF), allow a better knowledge and comprehension of the daylighting strategy.     

Energy and cost analysis of semi-transparent photovoltaic in office buildings

Solar energy conversion systems and daylighting schemes are important building energy strategies to produce clean energy, reduce the peak electrical and cooling demands and save the building electricity expenditures. A semi-transparent photovoltaic (PV) is a building component generating electricity via PV modules and allowing daylight entering into the interior spaces to facilitate daylighting designs. This paper studies the thermal and visual properties, energy performance and financial issue of such solar facades. Data measurements including solar irradiance, daylight illuminance and output power for a semi-transparent PV panel were undertaken. Using the recorded results, essential parameters pertaining to the power generation, thermal and optical characteristics of the PV system were determined. Case studies based on a generic reference office building were conducted to elaborate the energy and cooling requirements, and the cost implications when the PV facades together with the daylight-linked lighting controls were being used. The findings showed that such an integrated system could produce electricity and cut down electric lighting and cooling energy requirements to benefit the environmental, energy and economic aspects.     

办公建筑遮阳产品综合性能模拟与评价

该文旨在探究卷帘对夏热冬冷地区办公建筑采光和能耗的综合影响并确定影响卷帘综合性能的关键参数。首先，选取影响卷帘性能的6个参数：太阳辐射透过率、太阳辐射反射率、红外透射率、外侧发射率、内侧发射率和导热系数；组合得到560种遮阳产品，并利用EnergyPlus软件和Radiance软件对其进行全年动态能耗模拟和全年采光模拟；其次，通过调查问卷获得考虑办公建筑人员行为的遮阳时间表以及室内人员对眩光、自然采光和能耗的关注度占比；最后，综合考虑能耗、眩光和自然采光，创新性地提出综合性能指标（ED）对卷帘进行综合评价。基于该指标，确定影响卷帘性能的关键参数。研究结果表明，在夏热冬冷地区，太阳辐射透过率和太阳辐射反射率是影响卷帘综合性能的关键参数，当太阳辐射透过率在0.01～0.10范围内变化时，其对卷帘综合性能有积极影响。     

Parametric definition of the daylight climate

Solar radiation and sunlight are the universal and free sources of renewable energy available everywhere and the survival of life and health as well as the conditions of environmental comfort and prosperity are dependent on their effective utilisation.Several parameters are used nowadays to characterise the sunlight and skylight conditions and their connection with the solar radiation climate. A complex concept linking the sky luminance patterns with the resulting skylight, that is, diffuse illuminance levels as well as usually coexisting sunlight illuminance is needed to express the exact definition of possible real cases either measured or predicted in a set of relevant parameters. Evaluation of measured data gathered by current IDMP (International Daylight Measurement Programme) stations presents also problems of parametrisation necessary for their study and general formulation of prediction and mutual comparison. This contribution tries to show various problems and solutions linking the radiation and daylight climate specification with the new set of sky types proposed for the CIE standardisation.