Simulation of the thermal comfort conditions of urban areas: a case study in Kyiv
Abstract
Formulation of the problem. Studies of bioclimate of a territory are aimed at determining the favorable and adverse impacts of various climatic factors and their combinations on the human body. Complex urban morphology has a significant impact on microclimate and, accordingly, on thermal comfort of a person in such an environment. The height of buildings, street orientation, and distance between buildings alter the solar energy inlet, affect thermal regime, transform the wind speed and direction at the street level. Studies of the bioclimatic conditions of urban areas during the warm season are highly relevant as they provide an opportunity to evaluate human thermal sensations in the city, as well as the potential effectiveness of adaptation measures to heat stress (architectural measures and measures based on the use of green areas and water
bodies).
The purpose of the article. The aim of this research is to simulate the bioclimate of an urban environment to determine the human thermal load in summer months based on modern bioclimatic indices and software.
Methods. For the purpose of this study, a part of the territory of the Osokorky residential area of Kyiv was selected. To get values of the main meteorological parameters of the researched area, a three-dimensional, prognostic, microscale model ENVI-met was used. ENVI-met pertains to the CFD-models (computation fluid dynamics model) and is designed for microscales with a horizontal resolution from 0.5 to 10 m and with a time step of 10 seconds as maximum. The PET calculation was performed using the RayMan model.
Results. A clear hot summer day (04 August 2017) was chosen for the simulation. The simulation was performed from 6:00 EEST on 4 August till 6:00 EEST the next day (output interval – 1 hour). The simulation results show that the values of the main meteorological parameters (air temperature and humidity, wind characteristics) and physiologically equivalent temperature differ significantly within urban spaces, even across small areas. The amplitudes of PET value were maximum in the daytime and made 12°–15°C. The decrease in the amplitude of the air temperature within the researched area in the evening and night hours led to a notable decrease in the PET amplitude to 2°–3°C. The analysis of the simulated PET values for the researched area confirmed that the residents of the urban areas experience the most intense heat stress while staying in the open asphalted areas during the daytime. The duration of the period with comfortable conditions during the researched day was very short – from 22:00 EEST through midnight. The range of the daily course of PET values at different points of the researched area varied from 19.4° (at point No. 7) to 37.1°C (at point No. 5 located in the well courtyard).
Based on the PET values simulated for the researched area and for CAWS Kyiv was found the significant differences between thermal comfort conditions within the complex urban spaces and at the weather station. Therefore, the values of bioclimatic indices simulated based on the weather station data can not be applied with any approximation to solve scientific and applied tasks that require information on the bioclimate at particular points in the urbanized environment. To solve such tasks, it is recommended to apply modern methods – ENVI-met and RayMan models.
Scientific novelty and practical significance. For the first time in Ukraine, microclimate and thermal comfort conditions within the complex urban environment has been simulated using ENVI-met and RayMan models. The results of such simulation can be used to choose heat adaptation measures which would help to increase the comfort of the urban areas. The simulation of microclimate and thermal comfort conditions of some parts of the city territory is important stage of design of the buildings, in order to choose the optimal location for buildings and trees and to create the most comfortable conditions for people.
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References
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