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Subdivision of the sky hemisphere for luminance measurements
Abstract
A scanning pattern for sky photometry is described, in which the hemisphere is divided into 151 zones in bands parallel with the horizon.
... where R1 is External Reflectance Matrix, R2 Direct Daylight from Sky-Vault Matrix, R3 calculates the Reflections in the interior of a space and C is the illuminance list from a CIE standard sky [60][61][62]. Subsequently, the Split-Flux formula divides illumination into a dot product of three components (external, internal, direct). In order to "activate" this product, the direct component (R2) must be greater than zero. ...
... The standard sky distributions for computing illuminance are derived from the CIE standard skies constants table and a Tregenza-based schematic sky vault division. This method accounts for both sky geometry and sun position [60,62]. ...
The construction industry faces a growing challenge in reducing its environmental impact through sustainable design and practices. Buildings are responsible for a significant share of CO2 emissions and pollution, with lighting alone accounting for roughly 15% of global electricity consumption according to the International Energy Agency (IEA). A key element in achieving sustainability is optimizing daylight penetration within buildings, reducing reliance on artificial lighting and associated energy demands. This research introduces a novel approach by optimizing the geometry of a building’s exterior skin fabricated with adobe by 3D-printed molds. This method aims to achieve a balance between structural integrity, improved daylight availability within the building, and the inherent sustainability benefits of using adobe, an earth-based material. The proposed design procedure starts with a 2D geometry and applies it to the building’s exterior. The framework then optimizes the geometry to maintain structural stability while maximizing daylight penetration into the interior. Importantly, this optimization considers the specific material properties of adobe walls created using 3D-printed metal molds. By integrating 3D-printed adobe molds and daylight optimization, a framework is offered with a potential path towards sustainable building design with improved energy efficiency and reduced environmental impact.
... To discretize the sky, as shown in Fig. 3, the sky vault is divided into rings with the same angular amplitude, and each ring is further subdivided into a number of elements (denoted by their azimuthal position) such that each sky patch subtends a similar solid angle, similar to the well-know approach of Tregenza [72]. Around 2300 patches are used in this study. ...
The European targets for the Energy Transition by 2030 are strongly oriented toward the massive diffusion of PV plants, both at the building level and in large-scale utility systems on land. The expected PV capacity in Europe by 2030 is 900 GW, 4.3 times the 2022 level. Bifacial modules are currently the best solution for utility-scale PV systems, offering higher solar energy yields with minimal additional costs. This paper helps improve the efficiency of bifacial PV power plants at the European scale through the optimization of tilt angles in various configurations. Typical Meteorological Year data are retrieved from the PVGIS platform for a series of 2382 points uniformly distributed across Europe according to a regular 50 km × 50 km grid. A cumulative sky radiance is built for each location and an iterative search for the best tilt angle is performed to maximize the annual energy yield (on both front and back surfaces considering direct, diffuse and reflected energy) of south-facing modules, with both ground albedo and PV row spacing taken as parameters. Latitude is the primary influencing factor for optimal tilt angles, with an average value ranging from 26 • for Greece to 36 • for Finland. The results indicate that the Ground Coverage Ratio is also a significant parameter, while albedo has only a minor effect. The study of an Alpine region with a finer grid shows that mountainous terrain leads to reduced optimal tilt angles. A free web-based tool has been developed to provide optimal tilt angles for any location in Europe.
... The discretization process involves dividing the sky hemisphere into multiple segments, each characterized by an identical solid angle (Tregenza 1987). This base division, known as the Tregenza sky, comprises 145 segments. ...
Achieving precise and scalable solar potential estimation in urban settings is challenging due to the presence of a wide variety of obstructions. To address this issue, we developed a novel urban solar potential modeling method based on an improved 2-phase daylight model. Utilizing a dynamic graph convolutional neural network semantic segmentation model to process urban point cloud data, our method distinguishes between different types of solar obstructions, assigning specific simulation hyperparameters accordingly. Demonstrated through experiments, our method significantly outperforms traditional models by avoiding the underestimation of shading impacts—by up to 60% for monthly solar irradiation potential and 40% for annual PV yield potential. Moreover, our method accurately accounts for complex solar transmission through tree canopies, avoiding underestimation of PV energy potential by up to 7% compared to its predecessor (Pyrano 1.0). These improvements offer substantial benefits for managing PV shading risks, configuring PV systems, and managing renewable resources, especially in urban areas with complex geometries and dynamically changing shading conditions. Our findings underscore the method’s potential to enhance decision-making in sustainable urban development and renewable energy integration.
... As a result, the illuminance of a sky element depends on the zenith luminance, the elevation angle of the sky element above the horizon, and the angular distance between the sky element and zenith [54]. In the second method, the sun disk is not neglected and the skydome is subdivided into parts to generate a skymesh [19,55,56]. The illuminance distribution was determined by considering the angular distance of the sky element from the sun disk and the zenith distance of the sun. ...
Conducting a rigorous evaluation of the daylight performance of buildings is essential for human health and energy efficiency. Today, there are two main methods used for analysis: the daylight factor, which has been used since the early 1900s, and the newer approach known as climate-based modelling. Both methods are employed in the EN 17037 Daylight in Buildings’ standard. Utilizing different calculation methods causes discrepancies in daylight provision performance analyses of a room. However, there is no definition or limitation for this subject in the standard. As a result, researchers prefer different calculation methods for the same location in daylighting analyses without a clear justification. Additionally, there is a lack of parametric methods that follow the guidelines of the standard. This study aims to analyse the impact of calculation methods on daylighting analyses according to different regions and generate parametric methods in compliance with the standard. In this respect, comparison calculations are conducted for a theoretical room situated in all 81 provinces of Turkey, where variant climate types occur over a year. Furthermore, parametric workflows are generated using Rhinoceros/Grasshopper following the directives of the standard. The findings indicate that the method choice affects the illumination levels in all zones, ranging from 15 to 114 %.
Innovative designs of daylighting systems effectively use solar energy and can redefine how we bring light to interiors. However, the daylighting devices fail to meet the desired lighting levels under a cloudy sky. An alternative illumination source is always desirable in order to have uninterrupted lighting levels for the visual performance of occupants. This work demonstrates a hybrid illumination method using an efficient tubular skylight design integrated with a solar panel system for solar-powered electric lighting. The position and orientation of the solar panel mounted on the daylight collector give a compact design and ensure unblocked passage for daylighting under low altitude sun. The LEDs mounted on the periphery of the exit aperture of the mirror light pipe can be turned on and dimmed through closed-loop control when daylight illuminance is inadequate. The proposed hybrid illumination system was simulated under beam sunlight and compared with a conventional tubular skylight system with a hemispherical transparent dome as a daylight collector for lighting performance. Simulation results show that the illuminance value obtained by the proposed daylight collector design was at least twice that of the conventional design light output under low altitude sun while delivering controlled light levels during the summer mid-day sun. The uniformity ratio for the entire floor ranged from 0.43 to 0.59, indicating a moderately even light distribution. Under a combination of an overcast sky and an artificial light source (LED), the luminous flux entering the room was 3220 lumens, and the average illuminance on the work plane was 192 lux. A power backup of 10.7 h, 10.15 h, and 6.4 h was concluded for a 20-W LED (~ 2000 lm) light source due to the beam sunlight incident on the solar panel system on 21st June, 23rd September and 21st December, respectively, assuming clear sky conditions.
The generalized expansion of urbanization and population requires the implementation of sustainable practices in cities, particularly in developing nations more vulnerable to climate change impacts. Blue-green infrastructures can be viable solutions to climate and sustainability emergencies in the built environment. In this context, urban areas possess the opportunity to create climate change-resilient agricultural systems in order to meet the “No Poverty” (SDG 1) and “Zero Hunger” (SDG 2) goals included in the United Nations (UN) Sustainable Development Goals (SDGs). Consequently, with 70% of the population residing in urban areas, food systems can close the gap between production and consumption to ensure local food security. The substantial growth of cities in Asia, South America, and Africa renders localized urban agriculture essential for feeding its inhabitants. As the Food and Agriculture Organization (FAO) indicates, 6,000 tons of food are imported daily to feed cities with more than 20 million residents, such as Sao Paolo or Mexico City. Food chains and imports could be drastically mitigated by utilizing existing urban surfaces (roofs, facades, and ground areas) to produce crops. For this reason, there is a rising demand for research to assist urban planners and governments in strategizing local agriculture production. This chapter addresses food security in developing cities by introducing a sunlight-based computational approach for designating the agricultural potential of three-dimensional urban surfaces according to crop-centric environmental suitability. Building-integrated agriculture (BIA) can deliver crops throughout the entire year, minimizing the externalities that endanger food production, such as climate variations (droughts and floods) and climate-induced pests (from human and soil pathogens). Critics of high-tech indoor developments in hydroponics, aeroponics, and aquaponics argue that these systems are energy-intensive. In response, hybrid lighting systems offer alternative solutions that can efficiently reduce energy requirements by integrating sunlight data analysis. Blending sunlight to optimize lighting can have remarkable energy savings of up to 70% in developing nations with constricted energy infrastructures. Therefore, the availability of an appropriate amount of solar radiation on three-dimensional surfaces is a critical factor in selecting BIA locations.
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