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SOLWEIG 1.0 – Modelling spatial variations of 3D radiant fluxes and mean radiant temperature in complex urban settings

Abstract

The mean radiant temperature, Tmrt, which sums up all shortwave and longwave radiation fluxes (both direct and reflected) to which the human body is exposed is one of the key meteorological parameters governing human energy balance and the thermal comfort of man. In this paper, a new radiation model (SOLWEIG 1.0), which simulates spatial variations of 3D radiation fluxes and Tmrt in complex urban settings, is presented. The Tmrt is derived by modelling shortwave and longwave radiation fluxes in six directions (upward, downward and from the four cardinal points) and angular factors. The model requires a limited number of inputs, such as direct, diffuse and global shortwave radiation, air temperature, relative humidity, urban geometry and geographical information (latitude, longitude and elevation). The model was evaluated using 7 days of integral radiation measurements at two sites with different building geometries – a large square and a small courtyard in Göteborg, Sweden (57°N) – across different seasons and in various weather conditions. The evaluation reveals good agreement between modelled and measured values of Tmrt, with an overall good correspondence of R 2 = 0.94, (p < 0.01, RMSE = 4.8 K). SOLWEIG 1.0 is still under development. Future work will incorporate a vegetation scheme, as well as an improvement of the estimation of fluxes from the four cardinal points.

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Acknowledgements

Financial support for this project was provided by FORMAS, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning in their key action area Urban Public Places. Thanks to Ingegärd Eliasson and Sven Lindqvist who supervised the project, and to Alexander Walther for programming support.

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Correspondence to Fredrik Lindberg.

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Lindberg, F., Holmer, B. & Thorsson, S. SOLWEIG 1.0 – Modelling spatial variations of 3D radiant fluxes and mean radiant temperature in complex urban settings. Int J Biometeorol 52, 697–713 (2008). https://doi.org/10.1007/s00484-008-0162-7

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Keywords

  • Digital elevation model
  • Integral radiation modelling
  • Mean radiant temperature
  • Göteborg
  • Outdoor thermal comfort