Climate-Based Daylight Modelling (CBDM) methods have been validated against long-term measurements in laboratory settings and found to exhibit errors small enough to make such assessments useful for daylight performance prediction. However, real occupied spaces are affected by a higher number of uncertainties than laboratory or controlled conditions. This study aims at validating CBDM methods against measurements collected in an occupied classroom space, where a monitoring system based on High Dynamic Range Imaging was installed. Four vertical regions were identified on two of the room's walls, and mean illuminance was calculated for these regions at every time step, both from HDR images and from simulated results. Two simulation methods were evaluated: the 2-phase and the 4-component methods. Sun and sky conditions for the simulations were derived from simultaneous monitored irradiation measurements. Both simulation methods led to moderate over-prediction of HDR-derived results, when considering instantaneous illuminance means and when looking at long-term metrics (cumulative irradiation and Useful Daylight Illuminance). Wall regions exposed to more direct sky- and sunlight were characterised by smaller systematic errors (rMBE = 4%) but similar variance (r² = 0.83) than regions situated at the back of the room (rMBE = 17–34% and rMAE = 27–37%). Further studies are needed to identify and separate the sources of such errors.

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Aperture-based daylight modelling (ABDM) is a new building simulation paradigm founded on measures of an aperture's 'connectedness' to the sun and the external environment. At the planning level, there currently does not exist anywhere an evaluative schema which is equally applicable to measures of solar energy potential (for PV performance, overheating risk, etc) and measures of sunlight/daylight amenity (for daylight, well-being, connectivity/view, etc). ABDM addresses that shortcoming. This paper describes the latest development of ABDM which is the addition of an airmass factor in the computation of the sunlight beam index (SBI). This enhancement preserves the 'geometrical purity' of ABDM, but now airmass SBI can serve as a reliable proxy for direct sun irradiation totals derived from weather files.

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The responsiveness of buildings to prevailing local climate plays an important role if the dual aspects of occupant comfort and low energy demand are to be met. This study takes as example the State of Kerala in India where the Government - as part of the project titled “Livelihood Inclusion and Financial Empowerment (LIFE) mission” - plans to build more than 750, 000 houses across the State, using a uniform design, irrespective of the location or climate. A previous study has identified regions with different climatic characteristics within Kerala using a method based on adaptive thermal comfort model. This study aims to understand how the building design influences occupant comfort in the different adaptive climate zones by performing an uncertainty analysis on the output metrics. The thermal comfort was assessed based on the hours requiring heating/cooling while visual comfort was assessed based on the Useful Daylight Illuminance metric. A sensitivity analysis was also carried out to identify design parameters that influence occupant comfort. The results of this study will serve as a reference for practitioners during the early stages of design to achieve thermal and visual comfort for high performance residential buildings.

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A new set of CIBSE weather files for building performance simulation was recently developed to address the need for better quality solar data. These are essential for most building performance simulation applications, particularly for daylighting studies and low-energy building design, which requires detailed irradiation data for passive solar design and overheating risk analysis. The reliability of weather data becomes paramount when building performance is pushed to its limits. Findings illustrate how principles of good window design can be applied to a case study building, built to the Passivhaus standard, and how its expected performance is affected by the quality of solar irradiation data. Analyses using test reference years were most affected by changes in the solar radiation model (up to 8.3% points), whereas for design summer years the maximum difference was 1.7% points. Adopting the new model caused overheating risk to be classified as more severe using test reference years than design summer years, prompting a discussion on the design summer year selection method. Irradiance data measured on-site were used as a benchmark to evaluate the new solar radiation model, which was found to significantly improve the accuracy of irradiance data within weather files and so the reliability of overheating assessments. Practical application : CIBSE weather files are widely used for compliance verification of building performance in the UK context. This paper tests how the introduction of a new solar radiation model in weather files will affect daylighting and overheating simulation results. Examples are given on how low-energy building design considerations driven by advanced simulation techniques can help reaching indoor visual and thermal comfort requirements.

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The latest advancements in glazing technology are driving facade design towards complex and adaptive fenestration systems. Accurate simulation of their optical properties and operational controls for building daylight performance evaluation requires advanced modelling techniques, such as climate-based daylight modelling (CBDM). At the same time, computational efficiency is key to quickly simulate this complex performance over a full year. Over the years, several CBDM techniques were developed to answer these two main challenges, but they were never systematically benchmarked against each other. This paper compares state-of-the-art RADIANCE-based simulation techniques in terms of annual daylight performance metrics required by national guidelines and international green building rating schemes. The comparison is performed on three different shading systems: diffuse Venetian blinds, specular Venetian blinds, and perforated solar screens. Findings show that simulation methods are characterised by significant differences in their implementation and visual rendering, but most annual daylight metrics result in consistent values (within ± 20%). A notable exception is Annual Sunlight Exposure, which is highly sensitive to the chosen simulation method, with differences of up to 47 percentage points. Additional outcomes from the present work are used to compile a list of generalised recommendations for designers and policy makers.

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Climate-Based Daylight Modelling (CBDM) gives designers the possibility to evaluate complex, long-term luminous environment dynamics. This complexity can be challenging to simulate, and even more challenging to communicate effectively through the use of performance metrics. A multiplicity of CBDM techniques and metrics has been developed over the last two decades, but these were rarely assessed against each other. This paper reviews four state-of-the-art techniques based on the Radiance raytracing engine and systematically compares them against a benchmark CBDM method. Four classroom spaces are used to carry out an inter-model comparison between performance metrics commonly used for compliance verification obtained from all analysed techniques. Additional sensitivity analyses assessed how changes in input variables influence such metrics. Results from the inter-model comparison showed that the representation of direct sunlight is markedly different between the various CBDM techniques, and that metrics based on horizontal direct sunlight are very sensitive to the choice of simulation method. This led to differences in predicted Annual Sunlight Exposure up to 39 percentage points. Metrics that consider both direct and inter-reflected light were found to be more robust, with variations from benchmark results within ±15%. The analysis of the input variables showed that sensor grid spacing and time-step interpolation do not significantly affect any of these metrics. Changes in orientation and sky discretisation scheme had different effects depending on the metric and technique considered. The need for authoritative benchmarking systems when introducing new performance metrics for compliance verification or new simulation methods is also discussed.

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Classification of climate zones for building design and energy assessment purposes plays a vital role in aiding building engineers and architects in achieving energy efficiency in buildings using building performance simulation. Previous studies highlighted the need for climate assessments at higher resolutions for the purpose of climate classification but failed to infer the resolution requirement. In this study, climate zones of Kerala (one of the 29 States in India) are defined and delineated with climate data from grid resolutions of 10, 15, 20 and 25 km. The delineated zones are then assessed by comparing them with the thermal performance of a building representative of building typology of Kerala to identify the grid resolution necessary for zone delineation.

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This paper investigated the uncertainty introduced in Climate-Based Daylight Modelling (CBDM) by two solar radiation and one luminous efficacy models, chosen among those often found in Building Performance Simulation (BPS) tools. Analyses were carried out for two locations, Camborne, UK, and Sonnblick, Austria. Irradiances and CBDM metrics were found to be more accurately predicted by the model used for IWEC climate files, as such model can be optimised for each specific location. The model used within CIBSE climate files was found to be less accurate. In both cases, the direct component prediction exhibited significant errors.

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The insertion of climate-based daylight metrics as a requirement in several design guidelines calls for a better understanding of their effectiveness. This paper draws attention to the sensitivity of annual daylight metrics to changes in input reflectance values. The uncertainties related to the choice of guidelines and of simulation techniques were also considered. Total Annual Illumination (TAI) showed the most consistent correlation and the highest sensitivity to variations in reflectance (up to ±60% from the benchmark), independently of the geometrical characteristics of the space. Other annual metrics were less sensitive, or showed a poorer correlation. The deviations among different simulation techniques varied with the chosen metric too (NRMSD ≤ 15% for TAI), but all techniques were equally affected by variations in reflectance. The results highlighted the importance of selecting appropriate metrics for annual climate-based daylight evaluations.

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This paper analyses two main renovations of a University building façade retrofit from the viewpoint of annual daylighting improvement. Currently, this building consists of some teaching rooms connected by a hall but it is expected that this arrangement will change in order to accommodate two open-plan spaces for architecture students. The renovated design will increase the height of the North-East windows and introduce shading devices on the South-West facade. These renovations were explored to determine if the internal luminous conditions will maintain adequate levels. Five degrees of visual screening (100, 90, 70, 45 and 34%) and two slats positions (horizontal and vertical) were evaluated in relation to the building with no screens. Climate-based daylight modelling (CBDM) was carried out by using Diva-for-Grasshopper. The study revealed that effectiveness of convergence testing depends strongly on the choice of CBDM metrics employed as a diagnostic - an important consideration when modelling light transfer through louvres. Results recommended using louvred panels with no more than 70% of visual screening as higher percentages decrease useful illuminances over the range 300-3000 lux (UDI-a), to less than 50% of the occupancy time. Furthermore, vertical louvres were better suited to increase UDI-a than horizontal slats.@en

The evolution of building facades towards increasingly smarter and more complex fenestration systems required an evolution in simulation capabilities too. While simulation software can reliably reproduce the system's optical behaviour, the climate-based daylight evaluation of entire buildings needs to efficiently combine accuracy and computation speed. Five state-of-the-art Climate-Based Daylight Modelling (CBDM) techniques to evaluate a space with fixed Venetian blinds are compared with each others. Multiple options to apply these techniques are also considered. The use of annual metrics based on global illumination led to a good agreement between all methods, while evaluating only direct sunlight exposed some profound differences between simulation techniques.

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The recent development of climate-based daylight modelling (CBDM) and its application in various commercial tools, as well as its introduction in building simulation guidelines, created the need of more common procedures and quality checks on input values. Between these, the optical properties to be assigned to the modelled building can be very influential on the final results and on the building performance evaluation. In this study, the reflectance values of the opaque surfaces are analysed in detail, taking as a case study the model of a real classroom and performing the evaluations with various methods, all based on the Radiance lighting simulation system but employing significantly different procedures. A Sensitivity Analysis (SA) is carried out to rank the outputs, expressed with both traditional and CBDM metrics.@en