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Weng M.,Chongqing University | Yu L.,Chongqing University | Liu F.,Chongqing University | Liu F.,Chongqing Three Gorges University | Liu F.,National Center for International Research of Low Carbon and Green Buildings
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2014

Fire smoke flow characteristics in an underground metro tunnel were researched by full-scale experiments and numerical simulation in program FDS (fire dynamic simulation), and the tunnel is 349 m in length with one end connected to an underground metro station and the other end opened to outside in Chongqing, China. Smoke spread velocity, maximal smoke temperature and smoke temperature distribution in the longitudinal direction of the metro tunnel were analyzed on the conditions of different heat release rates with the combustion source in the middle of the tunnel, effects of mechanical smoke exhaust mode and air supply mode through the emergency vent were compared, and the sectional shape factor of a tunnel was introduced. The results show that smoke spread rate is affected by longitudinal air velocity and chimney effect, smoke spread rate is small in the upstream area of combustion source, backflow distance is shorter than calculated by the empirical equations acquired from the tunnel with two open ends, the excess maximal temperature rise in tunnel is lower than that predicted by Kurioka, smoke temperature distribution in the longitudinal direction on the top area of the metro tunnel obeys exponential decay laws, and further correction can be added to Kurioka model when the sectional shape factor of tunnel is less than 1. In case of a fire breakout in the metro tunnel, mechanical smoke exhaust mode or air supply mode through the emergency vent is working, and smoke in the tunnel can be exhausted effectively. Mechanical ventilation volume and mode are related to factors including geography information of the tunnel, fire heat release, evacuation route and etc. Source


Yao R.,Chongqing University | Yao R.,University of Reading | Shahrestani M.,University of Reading | Han S.,University of Reading | And 3 more authors.
ASHRAE Transactions | Year: 2016

Buildings account for over 40% of carbon dioxide (CO2) emissions in the United Kingdom and around 25% in China. In an attempt to mitigate global warming and reduce green-house gas emissions, the UK government is committed to reducing its greenhouse gas emissions by 80% below thel 990s level by 2050; China pledged a 40% to 45% decrease in CO2 emissions per gross domestic product (GDP) by 2020 against 2005 levels. One efficient way to improve building energy efficiency and the associated CO2 emissions is building retrofitting. This study aims to assess two levels of deep retrofit plans in typical office buildings to evaluate the potential energy savings that can be achieved. These retrofit scenarios are assessed using numerical simulation of prototypical buildings in five climate zones in China as well as London and Aberdeen in the UK. Numerical simulations have been conducted using EnergyPlus software. The outcomes of this study reveal that deep retrofits in office buildings can potentially achieve the target of 50% energy reduction compared with the source energy consumption of buildings designed in the 1980s. However, economic factors should also be considered in the process of decision making to choose the most appropriate building retrofit strategies. © 2016 ASHRAE. Source


Weng M.C.,Chongqing University | Yu L.X.,Chongqing University | Liu F.,Chongqing University | Liu F.,Chongqing Three Gorges University | And 2 more authors.
Tunnelling and Underground Space Technology | Year: 2014

Three full-scale model experiments were conducted in a unidirectional tube, which is a part of a metro tunnel with one end connected to an underground metro station and the other end opened to outside in Chongqing, PR China. Three fire HRRs, 1.35. MW, 3. MW and 3.8. MW were produced by pool fires with different oil pan sizes in the experiments. Temperature distributions under the tunnel ceiling along the longitudinal direction were measured. At the same time, CFD simulations were conducted under the same boundary conditions with the experiments by FDS 5.5. In addition, more FDS simulation cases were conducted after the FDS simulation results agreed with the experimental results. The simulation results show that the smoke temperature and the decay rate of the temperature distribution under the tunnel ceiling along the longitudinal direction increase as HRR increases. The smoke exhausts effectively from the tunnel under mechanical ventilation system, whether the emergency vent is activated as a smoke exhaust or an air supply vent. The operation mode of the mechanical ventilation system depends on the evacuation route. © 2014 Elsevier Ltd. Source


Yu W.,Chongqing University | Yu W.,National Center for International Research of Low Carbon and Green Buildings | Li B.,Chongqing University | Li B.,National Center for International Research of Low Carbon and Green Buildings | And 3 more authors.
Renewable Energy | Year: 2015

Store buildings usually have distinct characteristics of significant depth, high human density and heat-emitting sources, a high simultaneity usage coefficient for the air conditioning system, etc. The aim of this paper is to develop a rational rating method for green stores. By comparing the commonly used evaluation methods of green buildings, an assessment method for green store buildings in China has been developed. This method references the rating requirements set by the "China Green Building Evaluation Standard" and weighted credits for each category. This method attempts to avoid the effect of "imbalanced performance" when labeling green buildings. The Expert Group Decision AHP method has been used to develop the weighting system for green store buildings. The weight distributions highlight the importance of indoor environmental quality, energy efficiency and operation management within store buildings. © 2014 Elsevier Ltd. Source


Weng M.-C.,Chongqing University | Weng M.-C.,Chongqing Three Gorges University | Weng M.-C.,National Center for International Research of Low Carbon and Green Buildings | Lu X.-L.,Chongqing University | And 4 more authors.
Applied Thermal Engineering | Year: 2016

The critical velocity and the backlayering length of smoke in tunnel fires are the two most important parameters in longitudinal ventilation design. This paper deduced the dimensionless expression of backlayering length and critical velocity of smoke in tunnel fires using the dimensional analysis method. The sectional coefficient ζ (ζ = A/H2) was introduced to describe the geometrical characteristic of the tunnel section, and the characteristic hydraulic diameter of the tunnel H¯ replaced the tunnel height H. Then, CFD simulations were conducted in nine tunnels with different cross sectional shapes using the proprietary software Fire Dynamic Simulator (FDS), version 5.5. With the FDS simulations, prediction models for backlayering length and critical velocity modified by the sectional coefficient ζ and the tunnel slope were proposed. Meanwhile, complementary experiments were carried out in a 1/10 scale tunnel in order to provide a verification. The experimental results show a good agreement with the numerical simulations. Moreover, the prediction models for critical velocity on different slopes were compared with the prediction models proposed by others. © 2015 Elsevier Ltd. All rights reserved. Source

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