Model of Spectral and Directional Radiative Transfer in Complex Urban Canopies with Participating Atmospheres

Abstract

Thermal heat transfers, including solar and infrared radiation in cities, are key processes for studying urban heat islands, outdoor human thermal comfort, energy consumption, and production. Thus, accurate radiative transfer models are required to compute the solar and infrared fluxes in complex urban geometry accounting for the spectral and directional properties of the atmosphere and city fabric materials. In addition, these reference models may be used to evaluate existing parametrization models of radiative heat transfer and to develop new ones. The present article introduces a new reference model for outdoor radiative exchange based on the backward Monte Carlo method. The integral formulations of the direct and scattered solar, and the terrestrial infrared radiative flux densities are presented. This model can take into account the ground (e.g., roads, grass), different types of buildings and vegetation (e.g., trees consisting of opaque leaves and trunks) with their spectral and directional (Lambertian and specular) reflectivity of materials. Numerical validations of the algorithm are presented against the results of a state-of-the-art model based on the radiosity method for the particular case of an infinitely long street canyon. In addition, the convergence of urban solar radiation budgets is studied for a selection of urban complex geometries including

Coupling the urban canopy model TEB (SURFEXv9.0) with the radiation model SPARTACUS-Urbanv0.6.1 for more realistic urban radiative exchange calculation

“…TEB-SPARTACUS almost perfectly corrects this shortcoming of TEB-Classical, because the LCZ9 morphology resembling cubes respects well the SPARTACUS-Urban assumption of the decreasing exponential function for p ww and p gw (Stretton et al, 2022). Similar to the findings of Caliot et al (2022), the TEB-Classical results are almost identical to the HTRDR-Urban ones for the infinitely-long street canyon, which is due to the analytical solution for the radiosity method under these conditions (vacuum and Lambertian surfaces). For γ below 5 • , QR is underestimated by both TEB-Classical and TEB-SPARTACUS, because with a uniform H build , they cannot represent shading of roofs by higher buildings.…”

“…It would therefore be difficult to attribute a potential improvement of the fluxes simulated with TEB-SPARTACUS to the better representation of urban geometry or radiative transfer physics. For this reason, in this study, the radiative observables simulated by TEB are evaluated with the Monte-Carlo-based HTRDR-Urban reference model (Caliot et al, 2022).…”

Precomputed Radiative Heat Transport for Efficient Thermal Simulation

“…Simulation of radiation often only considers direct solar radiation [ JGP12 , MPLFC13 , AYG*20 ] and employs simplified models and calculation, e.g., polygon clipping or pixel counting [ HD17 , dOM17 , dRO*19 ]. Only a few works use GPU acceleration [ JR14b , JR14a , JR15 , JR17 ] or consider indirect radiation reflected by surrounding buildings or the environment and simulate thermal radiation [ AGNA*20 , CSF*22 ].…”

“…Those most recent approaches deal with the simulation of thermography imaging [ AGNA*20 ] or computation of view‐dependent solutions or statistical aggregates [ CSF*22 ]. In contrast, we focus on the efficient computation of view‐independent results, i.e., the temperature distribution over all surfaces due to, e.g., direct and indirect solar radiation.…”

Principal Component Analysis for the Characterisation of Spatiotemporal Variations of the Solar Resource in Urban Environments

“…However, the complexity of the urban environment makes the production of solar energy challenging. The presence of buildings, vegetation and other obstacles, and the diversity of their geometrical nature *Corresponding Author: guillaume.le-gall@univ-smb.fr (e.g., shape, size, orientation and inclination) and materials optical properties (e.g., specular and/or diffuse reflectivity, transmissivity) alter solar and infrared radiative transfers [4]. Multiple reflections of solar radiations and complex dynamic overshadowing effects are taking place between structural elements [3].…”