Cooling effects of block-scale facade greening and their relationship with urban form

摘要

Green facades in cities have great potential for facilitating climate change adaptation and mitigation due to their well-documented energy and cooling effects. Many studies have reported that a green facade can noticeably reduce the building surface temperature and cooling loads in summer. However, little is known about the extent to which large-scale facade greening cools the ambient air or the relationship between the cooling effects and urban form. This research employed the ENVI-met model to evaluate the summer cooling effects of block-scale facade greening and their relationship with urban form in Nanjing City in China. Six idealized urban blocks (IUBs) representing typical urban forms in Nanjing combined with five hypothetical facade-greening ratios generated 30 scenarios for simulation. The results revealed a distinct spatial pattern of cooling effects in each IUB. The cooling intensity decreases with increasing elevation, and it is strongest in ground spaces on the downwind side. The maximum cooling intensity is 0.96 degrees C and observed in the high-rise high-density site (HH). Among the six IUBs, the low-rise high-density block (LH) appears to be optimal for facade greening since it ranks in the top 1-3 for the four cooling-effect indicators. The threshold values were evaluated to further estimate the minimum greening ratios required to achieve corresponding energy-saving targets in each IUB. The findings can provide insights into the cool air dispersion process in urban canyons that have varying geometries. Furthermore, the results can inform vertical greening practices for the determination of appropriate sites and coverage ratios.