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Modeling mean radiant temperature in outdoor spaces: A comparative numerical simulation and validation study
Dalarna University, School of Technology and Business Studies, Energy Technology.ORCID iD: 0000-0003-4573-0026
2018 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Cities are increasingly under pressure to address the challenges of climate change. One of the most pressing and unifying issue in this respect is the maintenance of comfortable outdoor conditions despite rising air temperatures and increasing extreme heat events. As a means to inform urban planner and city officials, the assessment of outdoor thermal comfort conditions—either via numerical modeling or field measurements—have gained popularity over the past decade. While measurements can deliver highly accurate data, they are expensive and time-consuming endeavors that can only inform us about the conditions in an existing environment on a specific day and time of the year. In contrast, numerical modeling allows us to evaluate alternative urban design scenarios as well as to grasp the spatial and temporal variability of outdoor human thermal comfort conditions.

Given the advantages of numerical modeling and the increasing computational power of personal computers, several tools have emerged with an aim to assess the microclimate and human thermal comfort impacts of urban planning and design decisions. 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, in one way or another. Mean radiant temperature (Tmrt), the driving parameter of human thermal comfort in outdoor spaces, requires the modeling of both short- and long waver radiation fluxes. While different calculation methods exist to deriving this parameter, most models also introduce some kind of numerical simplification to increase computational speed. The multitude of numerical approaches in deriving Tmrt, coupled with the high spatial and temporal variability of this parameter, can result in a range of values delivered by these tools. Given both the growing importance of improving the outdoor thermal environment of cities and the role these tools play in it, reporting on their performance is of high importance.

The aim of this study is to assess popular microclimate models in their ability to reproduce the complex radiative environment of cities, as indicated by Tmrt, and to inform to the research and design community about their performance, compared to integral radiation measurement derived filed data. While the documentation of some numerical simulation tools is lacking or incomplete, this paper will nevertheless attempt to shed lights on the reasons behind the disparities in the derived Tmrt values. Initial results indicate that most microclimate models have a tendency to underestimate nighttime Tmrt together with daytime values when the location is exposed to the sun. In contrast, when the locations become shaded, Tmrt values are generally overestimated. In general, these errors indicate issues with surface temperature parametrization and point to the greatest challenge of the numerical simulation community.

Place, publisher, year, edition, pages
2018.
National Category
Climate Research
Research subject
Energy, Forests and Built Environments
Identifiers
URN: urn:nbn:se:du-28469OAI: oai:DiVA.org:du-28469DiVA, id: diva2:1246425
Conference
10th International Conference on Urban Climate jointly with 14th Symposium on the Urban Environment, New York, NY, USA, 6-10 August 2018
Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2018-09-10Bibliographically approved

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Gál, Csilla V

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