Abstract
A thermally comfortable design of outdoor spaces favors social interaction and outdoor activities and thus contributes to the overall well-being of urban dwellers. To assess such a design, obstacle-resolving models (ORM) combined with thermal indices may be used. This paper reviews existing thermal indices to identify those suitable for thermal comfort assessment with ORMs. For the identification, 11 criteria and six index features are derived from literature analysis focusing on the characteristics of human environmental heat exchange, of outdoor urban environments, and of ORMs. An air temperature weighted world population distribution is calculated to derive the minimal air temperature range; a thermal index should cover to be applicable to 95% of the world population. The criteria are applied to 165 thermal indices by reviewing their original publications. Results show that only four thermal indices are suitable to be applied globally in their current form to various outdoor urban environments and also fulfill the requirements of ORMs. The evaluation of the index features shows that they differ with respect to the comprehensiveness of the thermophysiological model, the assessed human response, the treatment of clothing and activity, and the computational costs. Furthermore, they differ in their total application frequency in past ORM studies and in their application frequency for different climatic zones, as a systematic literature analysis of thermal comfort studies employing ORMs showed. By depicting the differences of the thermal indices, this paper provides guidance to select an appropriate thermal index for thermal comfort studies with ORMs.
Highlights
Urban system models aim to describe the urban system consisting of individuals, society, morphology, and environmental stressors with its complex relations to model, for instance, health-related urban wellbeing
Considering the large number of proposed indices and the characteristics of obstacle-resolving models (ORM), this study addresses the overall question: which thermal indices can be used globally in their current form to evaluate the outdoor thermal environment in ORM applications? The term Bin ORM applications^ in this paper refers to an evaluation of the thermal situation simulated by the ORM by thermal indices, both online during the simulation and offline using model output
The assessment criteria derived in BThermal indices and application demands^ section are applied using the method described in BEvaluation procedure for suitable indices^ section in order to identify suitable thermal indices for ORM applications
Summary
Urban system models aim to describe the urban system consisting of individuals, society, morphology, and environmental stressors (von Szombathely et al 2017) with its complex relations to model, for instance, health-related urban wellbeing. In the section BThermal indices and application demands,^ the principles of thermal indices are introduced, and the characteristics of human environmental heat exchange of outdoor urban environments and of ORMs are summarized from a literature analysis. Based on those characteristics, criteria for suitable thermal indices are determined. Buzan et al (2015) showed for global simulations that infrequent model output can cause an underestimation of thermal stress experienced To avoid this effect in ORMs, the output needs to be frequent enough to reflect the changing air temperature and wind conditions (e.g., about 20 min). Applied thermal indices allow for a comparison of thermally comfortable designs in different climatic zones
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