Abstract
The parameter governing outdoor human thermal comfort (HTC) on warm, clear-sky days is radiation. Its effect on HTC is accounted for by mean radiant temperature (Tmrt). While Tmrt differences owing to different measurement methods are well established, the impact of different computational approaches have not been systematically evaluated. This study assesses the performance of three microclimate models in their ability to estimate Tmrt values in complex urban environments. The evaluated models are RayMan Pro, SOLWEIG and ENVI-met. The model evaluation encompasses both the comparison of modeled Tmrt values with those derived from observations and model intercomparisons with analyses extending to several radiation terms and parameters that comprise or explain the resultant Tmrt. Results indicate that the models systematically underestimate nighttime Tmrt. SOLWEIG and ENVI-met tend to overestimate Tmrt during prolonged periods of shade and underestimate when the sites are sunlit. RayMan underestimates Tmrt values during most part of the day. The largest Tmrt errors occur at low sun elevations in all three models, mainly as a result of underestimated longwave emitted and shortwave reflected radiation fluxes by the adjacent facades. These errors indicate room for improvement with regards to surface temperature estimation and shortwave reflected radiation calculations in the models.
Highlights
Cities are increasingly under pressure to address the challenges of climate change
While these tools differ both in the human thermal comfort indices they deliver and in their numerical modeling approach, they all rely on the calculation of mean radiant temperature
Each figure refers to a particular site (e.g. Fig. 4 to P1, Fig. 5 to P2, and so on) and the three images within them present the results from the respective models: RayMan, SOLWEIG and ENVI-met
Summary
Given the advantages of numerical modeling and the increasing computational power of personal computers, several tools have emerged to facilitate the assessment of microclimate and human thermal comfort implications of various urban design and planning strategies (Lindberg et al, 2008; Matzarakis et al, 2010; Bruse, 2004; Musy et al, 2015; Nice et al, 2018; Huang et al, 2014). While these tools differ both in the human thermal comfort indices they deliver and in their numerical modeling approach, they all rely on the calculation of mean radiant temperature
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