Energy savings of block-scale facade greening for different urban forms

Abstract

Many studies investigated the energy savings of buildings with green facades for different facade orientations and structures, whereas few studies have analyzed the influence of the urban form. This study evaluates the summer cooling energy savings of full-scale facade greening at blocks with different urban forms, using an integrated simulation with ENVI-met and EnergyPlus. Six idealized urban blocks (IUBs), each with two green-facade scenarios and one baseline bare-facade scenario, are established. The hourly output cooling loads of the bare- and green-facade scenarios are used to estimate the daily energy-saving rate (DER) and daily energy savings per m2 of green facades (DES). The results show that the block-scale facade greening provides a DER of 3.2–11% and a DES of 123–347 Wh/m2, representing a summer cooling energy reduction of 11–31 kWh for every m2 of the green facade. Among the six IUBs, the high-rise high-density site (HH) has the lowest DER and DES, and the mid-rise low-density site (ML) has the highest. A higher greening ratio (65%) results in a cumulative effect and a higher DER and DES than in the buildings with a lower greening ratio (35%). Shading provided by plants and substrates is the primary reason for the DES, whereas cooling and humidifying have relatively small influences, and a trade-off effect between the two is observed. The findings of this research can shed light on green-facade practices and building energy conservation in humid subtropical cities.