Microclimatic monitoring of climber green walls and an intensive green roof in subtropical summer

Abstract

This thesis documents the pioneering research on the thermodynamics of two climber green walls and an intensive green roof in a subtropical city in summer weather. High-precision environmental monitoring sensors were deployed to gather microclimatic data from the green walls and the green roof, with adjacent bare walls and bare roof serving as control. The research examined mainly the cooling benefits provision and the underlying factors and processes. Two climber green walls, one oriented northeast and the other northwest, and an intensive green roof with woodland vegetation were monitored in Tseung Kwan O New Town, Hong Kong from June to August, 2016. Data batches of representative summer weather conditions were analyzed for green wall-induced cooling benefits. Cooling was most evident at exterior building wall surface and in sunny daytime. Wall orientation exposed to solar radiation favoured more notable cooling. Wider air-gap depth between building wall and green wall can induce more cooling. These findings have contributed to bridging the knowledge gap concerning green wall applications in subtropical urban area. Fenestration on building envelope played an important role in indoor-outdoor radiative heat transfer. Solar beam penetration through windows can discount indoor cooling benefits of vertical vegetation shield and even create indoor warming in sunny weather. But windows accelerated nighttime indoor-to-outdoor radiative heat loss to cool down the indoor environment. An innovative design of rotatable climber green wall planter has been proposed to maximize daytime cooling and nighttime heat dissipation of indoor space. This original research examined how green wall would change the occurrence of maximum of temperature and radiation parameters. Only scarce studies investigated the effect of green wall on the temporal evolution of microclimatic variables. The temporal lag values between pairs of variables were identified. The results recommended above-pedestrian-level application of green wall for maximum improvement in thermal comfort of different beneficiary sites. Remarkable surface and air cooling was observed under the woodland vegetation canopy of the intensive green roof. Weather conditions stronly influenced the magnitude of cooling. The dense and thick canopy acted as an effective filter against solar radiation. The deep substrate ushered sizeable thermal capacity to buffer against the daily thermal oscillations above substrate surface and within the substrate, thus insulating the indoor space from thermal transfer through the roof fabric. With sufficient load-bearing capacity in the roof slab, it is recommended that green roof with high biomass quantity and complexity should be implemented for thermal protection. The current research took the first step in applying Physiologically Equivalent Temperature and Universal Thermal Climate Index in the assessment of thermal comfort improvement induced by green roof. The intensive green roof suppressed multiple thermal and radiative parameters, providing observable environmental cooling as well as significantly improving human thermal comfort. Although the intensive green roof did not procure sustained period of thermal neutrality, the occurrence of extreme and very strong heat stress was markedly minimized, if not completely eliminated. It is possible for building users to utilize intensive green roof as a refuge from the scorching summer urban heat.