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.
Recent years have seen issues related to thermal comfort gaining more momentum in tropical countries. The thermal adaptation and thermal comfort index play a significant role in evaluating the outdoor thermal comfort. In this study, the aim is to capture the thermal sensation of respondents at outdoor environment through questionnaire survey and to determine the discomfort index (DI) to measure the thermal discomfort level. The results indicated that most respondents had thermally accepted the existing environment conditions although they felt slightly warm and hot. A strong correlation between thermal sensation and measured DI was also identified. As a result, a new discomfort index range had been proposed in association with local climate and thermal sensation of occupants to evaluate thermal comfort. The results had proved that the respondents can adapt to a wider range of thermal conditions.Validation of the questionnaire data at Putrajaya was done to prove that the thermal sensation in both Putrajaya and UTM was almost similar since they are located in the same tropical climate region. Hence, a quantitative field study on building layouts was done to facilitate the outdoor human discomfort level based on newly proposed discomfort index range. The results showed that slightly shaded building layouts of type- A and B exhibited higher temperature and discomfort index. The resultant adaptive thermal comfort theory was incorporated into the field studies as well. Finally, the study also showed that the DI values were highly dependent on ambient temperature and relative humidity but had fewer effects for solar radiation intensity.