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.
•Current Climate-Based Daylight Modelling methods treat sunlight very differently.•Metrics based on direct sunlight are very sensitive to the choice of method.•Benchmarking systems should guide future development of methods and metrics.
Display omitted
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.
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.
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 ( Formula omitted. 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.
Abstract
User experience and satisfaction with the facade play a significant role in user comfort and energy efficiency of buildings. This paper explores the concept of User-Facade archetypes to ...inform the user-centred design of shading devices based on the perceived level of importance of different environmental domains at the workplace. A questionnaire was developed to collect data on users’ perceived level of importance of different environmental domains, user characteristics and other preferences. Based on the associated level of importance of the domains affected by shading devices (thermal conditions, access to daylight, access to outdoor view, privacy and glare mitigation), users were then clustered into eight different archetypes, which associated different “weights” to each comfort domain. The study also found a significant correlation between the associated level of importance and the reported frequency of interaction with shadings because of thermal comfort, glare mitigation or privacy. Overall, users that associated high levels of importance to several environmental domains also reported high perceived levels of importance for personal control at the workplace. Only one archetype reported low importance for personal control at the workplace. Further work is required to validate these archetypes by capturing actual user behaviour and preferences in real workplaces. However, these findings provide preliminary and valuable insights into the possibility of clustering users on their preferences and using this for informing a more user-centred design or operation of shading devices.
PDF
