Urban Roughness Estimation Based on Digital Building Models for Urban Wind and Thermal Condition Estimation—Application of the SkyHelios Model

Abstract

Roughness length is a critical parameter for estimation of wind conditions, and it is therefore also relevant for the estimation of human thermal conditions in urban areas. The high density of buildings in urban areas causes large changes in land coverage, thereby increasing surface roughness. This influence atmospheric flow and also leads to a reduction in urban air ventilation, thus increasing the risk of human thermal stress. In this study, a digital building model of Tainan city was used to calculate roughness length using an approach based on Voronoi cells by applying the microclimate model, SkyHelios. The model was also used to estimate the wind conditions, including the wind speed and wind direction. For estimation of the thermal conditions, this study obtained meteorological data for air temperature, relative humidity, globe temperature, wind speed, and wind direction on two specific days (31 July 2015 and 21 January 2016). To quantify the thermal stress, the physiologically equivalent temperature (PET) was used to represent the thermal conditions. The wind conditions results obtained from the model indicate that even microscale conditions with vortices and corner flow can be represented with high precision and resolution. The thermal conditions results demonstrate that different created environments and microclimate conditions affect the thermal environment. The difference in PET can be up to 3 • C. This study confirmed that comparison of microclimate thermal conditions based on measurements and obtained from modeling using SkyHelios are in sufficient agreement and can be used in urban planning in the future.

Beyond Singular Climatic Variables—Identifying the Dynamics of Wholesome Thermo-Physiological Factors for Existing/Future Human Thermal Comfort during Hot Dry Mediterranean Summers

“…Referring to the earlier study of Lin, et al [71], the calculation of SVF was based on a classic single-point SVF (or SVF SP ) within a fixed point, so as to obtain a “fisheye view”, with a calibrated height of 1.1m (which is complacent with the gravity centre of the human body as described by Kuttler [63]). As shown in Figure 1, each fixed point (henceforth reference point (RP)) within the UCCs was tested within the SkyHelios model (Research Center Human Biometeorology; Freiburg, Germany; ) [72,73], to identify the SVF SP at each RP. Such a methodology was already utilized by numerous other studies ([23,54,69] for symmetrical canyons, and [55,74] for asymmetrical canyons).…”

Estimation of roughness and zero-displacement heights over Baghdad utilizing remote sensing and GIS techniques

“…For an array of the equivalent height of roughness element, an excess of λ P can lead to the excess of the displacement height and a reduction of the roughness of the obstacle array as λ P , tends to 1. This means that the elements are so close that they merge to form a new surface (Chen, Fröhlich, Matzarakis & Lin, 2017). The ratio of displacement height over the roughness element height is given as:…”

Study of Aerodynamic Surface Roughness for Baghdad City Using Signal-Level Measurements

“…At  =0.1, this means the elements are so close and they merge to form a new surface (9). For this method, the most important benefits are that the values of the length of roughness which can be calculated without the need for high towers, as well as their means.…”

“…Roughness lengths were also evaluated for Kalpakkam site, India, using terrain features by Jesan et al They observed maximum and minimum roughness lengths of 0.48 m to 0.26 m, respectively (8). Finally, Chen et al calculated roughness length using an approach based on digital building model of Tainan city using an approach based on Voronoi cells by applying the microclimate (9).…”