Design recommendations for the rehabilitation of an urban canyon in a subtropical climate region using aerial thermography and simulation tools

Abstract

Outdoor public space is the setting for everyday social interaction where activities take place in order to satisfy collective urban needs. It is important to achieve climate-friendly urban design in order to ensure acceptable urban thermal comfort, especially in over-urbanised city centres during summer periods. In this research, an urban canyon street located in the historical centre of the subtropical city of Huelva (Spain) was analysed. After a survey carried out by in situ meteorological sensors and airborne infrared sensors (equipped on an unmanned aerial vehicle, UAV), the current thermal comfort was analysed in terms of PMV and PPD at different times of a typical summer day (11:00 h, 15:00 h and 19:00 h) with the aim of formulating design recommendations to improve its performance in terms of urban comfort. Then, thermal comfort was evaluated in different scenarios where feasible mitigation strategies (replacement of materiality, addition of vegetation and sun shading elements) were applied to classify them according to their effectiveness using the ENVI-met simulation tool. The results of the current scenario showed that, due to its N-S orientation and its aspect ratio (H/W), the urban comfort depends drastically on the day hour variation. A comfortable thermal environment is achieved at all points of the urban canyon as a result of the shade generated by the buildings during the morning and afternoon. However, in the central hours of the day the feeling of thermal discomfort was alarming (PMV values of +3 and PPD values above 90%). The proposed mitigation measures showed a considerable improvement in urban thermal comfort, with the addition of vegetation being the most effective solution (with an improvement in PMV value of 42% and a reduction in PPD value of 43%). The combination of all the proposed measures in a single scenario showed encouraging results in the rehabilitation of public spaces in use.