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RI07: Daylight calculation methods (2023) (pdf)
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RI07: Daylight calculation methods (2023) (pdf)

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Daylighting is a key element of sustainable building design. It is vital that workplaces and homes have good levels of daylight. Daylight calculation methods are important to enable the designer to predict the lighting environment in buildings, the resulting energy consumption for lighting, and its input into the overall thermal performance of the building.

In 2019, British Standard BS 8206-2: Lighting for buildings — Code of practice for daylighting was replaced by BS EN 17037: Daylight in buildings. The latter standard has more complex methodologies for calculating daylight provision in buildings. It makes use of climate-based daylight modelling which gives a much more sophisticated, and potentially more accurate, method to predict daylight provision and lighting use. However, the standard does not fully explain how to carry out these calculations.

A CIBSE-funded research project was carried out to investigate the daylight provision calculation methods in BS EN 17037. The overall aim of the project was to provide detailed guidance for daylighting practitioners on applying the daylight assessment methods in BS EN 17037. This report explains the project background and methodology, presents the findings from the modelling and analysis carried out, and gives recommendations for applying the daylight assessment methods in BS EN 17037.

This report explains the daylight calculation methodology in BS EN 17037 and reviews the key issues in applying the calculation methods in practice. It gives the key conclusions from an online workshop to review what is already known about these calculation issues, and to find out from daylighting design practitioners and researchers the current issues they face and any relevant experiences.


Executive summary

1         Introduction

2         Calculations in BS EN 17037

           2.1      Illuminance method (climate-based daylight modelling)

           2.2      Daylight factor method         

           2.3      Specific recommendations for daylight provision in UK dwellings

           2.4      Computational methods

3         A workshop to review calculation issues

4         Methodology

           4.1      Computational parameters

           4.2      Ground plane size

           4.3      Calculation grids

           4.4      Weather datasets

5         Main study

           5.1      Calculation results

           5.2      Results interpretation

           5.3      Comparative analysis on computational methods

6         Conclusions

Appendix A: details of case study rooms and buildings

Appendix B: Details of study on computational parameters

Appendix C: details of study on calculation grids

Appendix D: details of study on weather datasets

           D.1     Useful daylight illuminance

           D.2     Summary of statistical test results

Appendix E: details of comparative analysis on computational methods

Appendix F: details of a workshop to explore calculation issues

Appendix F: details of a workshop to explore calculation issues

Authors: Dr Cosmin Ticleanu (BRE), Gareth Howlett (BRE), Lorna Flores Villa (BRE) and Guillaume Le Gall (BRE)

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