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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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.@en