Effect of ventilation on thermal and humidity environment of the underground utility tunnel in the plum rain season in southern China:Field measurement and CFD simulation

The underground utility tunnel(UUT)is one of the typical urban underground structures,which usually requires mechanical ventilation systems for forced ventilation.In addition to the ventilation scheme for accident scenarios,the normal operating ventilation scheme deserves equal attention as it has a great impact on the air quality as well as the thermal and humidity environment inside the UUT.In this study,a UUT located in southern China is taken as the research object,and the effect of ventilation on its internal thermal and humidity distribution is explored with a combined use of field measurements and numerical simulations.The results of field measurements show that the average temperature inside the closed UUT is 20.5℃and the average humidity ratio is 14.1 g/kgdry;both are lower than those of the external environment.In the plum rain season,if the tunnel is ventilated without any treatment of the external airflows,surface condensation tends to occur near the air inlet while the region with high relative humidity would be distributed on both sides far from the air inlet.The study also discusses the effect of different temperatures and humidity ratios of the inflow air on the humidity inside the UUT,and on this basis,the humidity control strategy for UUT in the plum rain season is proposed.

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.