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Design and Experimental Validation of an Urban Microclimate Tool Integrating Indoor-Outdoor Detailed Longwave Radiative Fluxes at District Scale

Marie-Hélène Azam, Julien Berger, Edouard Walther, Sihem Guernouti

TL;DR

This work develops a district-scale microclimate tool that tightly couples inside-building long-wave radiative exchanges with outside radiative and conductive processes using 1D wall/soil conduction and radiosity-based radiation. It employs a two-loop fixed-point coupling within an implicit Euler framework and validates the approach against both a theoretical reference (Chebfun) and a reduced-scale experimental demonstrator (ClimaBat), achieving improved accuracy over a state-of-the-art tool in predicting surface and indoor temperatures. The methodology advances the ability to analyze how urban microclimate and mitigation strategies affect indoor thermal comfort and energy use, by providing more faithful representations of long-wave fluxes and interior heat transfer. The results show RMSE improvements on surface temperatures and indoor air temperature predictions, enabling more reliable assessment of district-scale mitigation measures.

Abstract

Numerical simulation is a powerful tool for assessing the causes of an Urban Heat Island (UHI) effect or quantifying the impact of mitigation solutions on outdoor and indoor thermal comfort. For that purpose, several models have been developed at the district scale. At this scale, the outside surface energy budget is detailed, however building models are very simplified and considered as a boundary condition of the district scale model. This shortcoming inhibits the opportunity to investigate the effect of urban microclimate on the inside building conditions. The aim of this work is to improve the representation of the physical phenomena involved in the building models of a district model. For that purpose, the model integrates inside and outside fully detailed long-wave radiative flux. The numerical model is based on finite differences to solve conduction through all the surfaces and the radiosity method to solve long-wave radiative heat fluxes inside and outside. Calculated temperatures and heat fluxes are evaluated with respect to \textit{in situ} measurements from an experimental demonstrator over 14 sensors and a 24-day period. Results are also compared to state-of-the-art models simulation tool show improvement of the RMSE of $0.9 \ \mathsf{^{\,\circ}C}$ to $2.1 \ \mathsf{^{\,\circ}C}$ on the surface temperature modeled.

Design and Experimental Validation of an Urban Microclimate Tool Integrating Indoor-Outdoor Detailed Longwave Radiative Fluxes at District Scale

TL;DR

This work develops a district-scale microclimate tool that tightly couples inside-building long-wave radiative exchanges with outside radiative and conductive processes using 1D wall/soil conduction and radiosity-based radiation. It employs a two-loop fixed-point coupling within an implicit Euler framework and validates the approach against both a theoretical reference (Chebfun) and a reduced-scale experimental demonstrator (ClimaBat), achieving improved accuracy over a state-of-the-art tool in predicting surface and indoor temperatures. The methodology advances the ability to analyze how urban microclimate and mitigation strategies affect indoor thermal comfort and energy use, by providing more faithful representations of long-wave fluxes and interior heat transfer. The results show RMSE improvements on surface temperatures and indoor air temperature predictions, enabling more reliable assessment of district-scale mitigation measures.

Abstract

Numerical simulation is a powerful tool for assessing the causes of an Urban Heat Island (UHI) effect or quantifying the impact of mitigation solutions on outdoor and indoor thermal comfort. For that purpose, several models have been developed at the district scale. At this scale, the outside surface energy budget is detailed, however building models are very simplified and considered as a boundary condition of the district scale model. This shortcoming inhibits the opportunity to investigate the effect of urban microclimate on the inside building conditions. The aim of this work is to improve the representation of the physical phenomena involved in the building models of a district model. For that purpose, the model integrates inside and outside fully detailed long-wave radiative flux. The numerical model is based on finite differences to solve conduction through all the surfaces and the radiosity method to solve long-wave radiative heat fluxes inside and outside. Calculated temperatures and heat fluxes are evaluated with respect to \textit{in situ} measurements from an experimental demonstrator over 14 sensors and a 24-day period. Results are also compared to state-of-the-art models simulation tool show improvement of the RMSE of to on the surface temperature modeled.

Paper Structure

This paper contains 27 sections, 30 equations, 13 figures, 4 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Methods
  3. Heat transfer in the building wall
  4. Heat transfer in the ground soil
  5. Inside air temperature
  6. Short-wave radiative heat fluxes
  7. Long-wave radiative heat fluxes
  8. Inside long-wave radiative heat fluxes
  9. Outside long-wave radiative heat fluxes
  10. Algorithm implementation
  11. Assessment methodology
  12. Building model verification case studies
  13. Description
  14. Results
  15. Model Validation with experimental data
  16. ...and 12 more sections

Figures (13)

  • Figure 1: Schematic representation of the different mathematical models of a microclimat simulation tool at district scale and the mesh.
  • Figure 2: Case study set up : boundary conditions, and mesh selection criterion for the model.
  • Figure 3: Comparison of surface temperatures calculated by the model and the reference solution
  • Figure 4: Comparison of air temperature and inside temperature profile calculated by the model and the reference solution
  • Figure 5: Location of thermocouples on the geometry studied.
  • ...and 8 more figures