THERMAL EFFECTS OF BUILDING′S EXTERNAL SURFACES IN CITY——Characteristics of Heat Flux into and out of External Wall Surfaces

This study examined the thermal effects of building′s external wall surfaces, using observational data of spatial-temporal distribution of surface temperature, air temperature, and heat flux into and out of external surface. Results indicate that external wall surface temperature and nearby air temperature vary with the change of orientation, height and season. In general, the external wall surface temperature is lower near the ground, and is higher near the roof, than nearby air temperature. But north wall surface temperature is mostly lower than nearby air temperature at the same height; south wall surface temperature during the daytime in December, and west wall surface temperature all day in August, is respectively higher than nearby air temperature. The heat fluxes into and out of external wall surfaces show the differences that exist in the various orientations, heights and seasons. In December, south wall surface at the lower sites emits heat and north wall surface at the higher sites absorbs heat. In April, all external wall surfaces, emit heat near the ground and absorb heat near the roof. In August, west wall surface all day emits heat, and other wall surfaces just show the commensurate behavior with that in April.

Numerical modeling of external light gauge steel framed wall systems exposed to bushfire flame zone conditions

Bushfire-related building losses cause adverse economic impacts to countries prone to bushfires.Building materials and components play a vital role in reducing these impacts.However,due to high costs of experimental studies and lack of numerical studies,the heat transfer behavior of building’s external components in bushfire-prone areas has not been adequately investigated.Often large-scale heat transfer models are developed using Computational Fluid Dynamics(CFD)tools,and the availability of CFD models for heat transfer in building components improves the understanding of the behavior of systems and systems of systems.Therefore,this paper uses a numerical modeling approach to investigate the bushfire/wildfire resistance of external Light gauge Steel Framed(LSF)wall systems.Both full-scale and small-scale heat transfer models were developed for the LSF wall systems.Experimental results of six internal and external LSF wall systems with varying plasterboard thickness and cladding material were used to validate the developed models.The study was then extended to investigate the bushfire resistance of seven external wall systems under two different bushfire flame zone conditions.The results illustrate the significant effects of fire curves,LSF wall components and configuration on the heat transfer across the walls.They have shown 1)the favorable performance of steel cladding and Autoclaved Aerated Concrete(AAC)panels when used on the external side of wall systems and 2)the adequacy of thin-walled steel studs’load-bearing capacity during bushfire exposures.This study has shown that most of the investigated external LSF walls could be reused with cost-effective retrofitting such as replacing the Fire Side(FS)steel cladding after bushfire exposures.Overall,this study has advanced the understanding of the behavior of external light steel framed walls under bushfire flame zone conditions.

Simulation of thermal and humid environment of rural residence envelope inner surface during the plum rains season in Changsha China

The Plum Rains Season(PRS)has the typical characteristics of outdoor air temperature dramatic changes and high air humidity in the hot summer and cold winter region in China.Even if the indoor heat source and moisture production is constant,when the outdoor air temperature rises rapidly during high air humidity PRS,the build-ing envelope temperature heats up much more slower than the indoor air temperature and therefore the wall surface temperature is lower than the indoor air dewpoint which leads to condensation phenomenon,resulting in deterioration of insulation performance,mouldy walls,deterioration of indoor air quality.At present,there is a lack of research on the factors affecting condensation in rural residence during PRS.This paper evaluates the impact of occupants’habit of window opening modes and building construction parameters on the building envelope surface condensation in Changsha during PRS.Using Designer’Simulation Toolkit(DeST)simulated and analysed the impact of key parameters such as window-to-wall ratio,exterior wall reflectivity,window opening mode(open/close),and external wall insulation on the building indoor thermal and humid environment.The condensation risk X is proposed to evaluate the condensation possibility on the building envelope’s inner sur-face.The results show that from the perspective of anti-condensation:The rural residential building in Changsha should balance the window-wall ratio against better natural lighting;Keeping windows closed during PRS can effectively alleviate the condensation problem while the insulation in the external wall layer could aggravate the condensation.