Effect of asymmetrical street aspect ratios on microclimates in hot, humid regions

Abstract

Asymmetrical street aspect ratios, i.e. different height-to-width (H1/W-H2/W) ratios, have not received much attention in the study of urban climates. Putrajaya Boulevard (northeast to southwest orientation) in Malaysia was selected to study the influence of six asymmetrical aspect ratio scenarios on the street microclimate using the Envi-met three-dimensional microclimate model (V3.1 Beta). Putrajaya Boulevard suffers from high surface and air temperature during the day due to the orientation, the low aspect ratio and the wide sky view factor. These issues are a common dilemma in many boulevards. Further, low and high symmetrical streets are incompatible with tropical regions as they offer conflicting properties during the day and at night. These scenarios are examined, therefore, to find asymmetrical streets which are able to reduce the impact of the day microclimate on boulevards, and as an alternative strategy fulfilling tropical day and night climatic conditions. Asymmetrical streets are better than low symmetrical streets in enhancing wind flow and blocking solar radiation, when tall buildings confront winds direction or solar altitudes. Therefore, mitigating heat islands or improving microclimates in asymmetrical streets based on tall buildings position which captures wind or caste shades. In northeast to southwest direction, aspect ratios of 0.8-2 reduce the morning microclimate and night heat islands yet the negative effects during the day are greater than the positive effects in the night. An aspect ratio of 2-0.8 reduces the temperature of surfaces by 10 to 14 °C and the air by 4.7 °C, recommended for enhancing boulevard microclimates and mitigating tropical heat islands.

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

“…So far, within the existing literature, the crucial role of urban morphology (i.e., the width, height, and orientation of urban canyons) on thermal comfort conditions within the built environment has been well documented [22,23,54,55,69,70,74,84,85]. Therefore, and within this section, the UCCs were utilized to identify how different morphological compositions present different thermal comfort conditions from those presented by the meteorological station during three different types of days retrieved from the |Jul 2016 | dataset.…”

“…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). Within this study, and referring to the predominant symmetry that is characteristic of Lisbon’s historical quarter, all of the modelled UCCs were symmetrically constructed.…”

Approaches to Outdoor Thermal Comfort Thresholds through Public Space Design: A Review

“… Slight Tamb reductions were identified given the increase of aspect ratio; however, changes in radiation fluxed provided a much more significant microclimatic variable for thermal comfort estimations;  Given subtropical latitudes, the thermal environment within 0.50 canyons is much more stressful independent of orientation, although East-to-West proved to be slightly worse;  Within the setting of wide streets, shading strategies through PSD must be considered;   Thermal conditions vary in street canyons with different aspect ratios;  Height, width, and orientation play an important role in the examination of specific thermal bioclimatic conditions;  Estimations and simulations results proved to have significant outputs for both basic research and that of estimating specific thermal conditions #2iv [170] 'Af' A/symmetrical (0.80 to 2.00)  Taller façades of asymmetrical canyon play an important role in enhancing V at street level;  High asymmetrical aspect ratios are ideal and are better than low symmetrical streets, and are an improvement over deep symmetrical canyons in tropical climates, since they store heat at night and block air flow;  PSD and position of boulevard components at street level such as sidewalks and vehicle lanes should take advantage of the differences between high/low buildings instead of being organised in the traditional and symmetrical fashion. North-to-South, Northwest-to-Southeast, and Northeast-to-Southwest were the canyons that presented discomfort for smaller periods of time in comparison to East-to-West canyons; Optimal areas within the canyons are adjacent to north side of the East-to-West street, the northwest side of the Northeast-to-Southwest street, and the southwest side of the Southeast-Northwest street.…”

The Impact of Tipuana tipu Species on Local Human Thermal Comfort Thresholds in Different Urban Canyon Cases in Mediterranean Climates: Lisbon, Portugal

“…Although such an approach is frequently 'presumed' when approaching H/W ratios, recent microscale bioclimatic studies [23,26] have also produced important results in asymmetrical canyons whilst also addressing urban thermal comfort conditions.…”