Experimental Study On Tunnel Smoke Construction Essay

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Tunnels are important links in rail and road transport infrastructure. One approach of smoke control in tunnels relies on mechanically generated longitudinal ventilation. This is used to force the smoke and hot gas to move downstream and to keep the upstream tunnel segment free of smoke.

Road tunnel is an effective way to solve urban traffic problems. Nowadays, more and more urban road tunnels are under construction in cities like Tokyo, Moscow, Beijing and so on all over the world. However, owing to the special structure of tunnels, smoke and toxic gases induced by fires, such as carbon monoxide, which are the most fatal hazard to the people, will not easily be discharged. The smoke will hamper safe evacuation of occupants and affect firefighters from extinguishing the fire. In fact, 85% of the deaths in building fires are attributed to the toxic smoke according to statistics [1].

Compared with mechanical ventilation that requires a large space of excavation for installation of ventilation equipments along with a costly maintenance and electrical energy consumption, natural ventilation using vertical shafts can avoid air fans that will reduce the tunnel section height and does not consume power in the operation process. Furthermore, natural ventilation is particularly applicable to short tunnels with a light traffic flow [2]. Shafts not only contribute to discharge of high temperature smoke and weaken its impact on lining structures and equipments, but also facilitate airflow exchange in tunnels so as to improve interior air quality at ordinary times.

Ventilation for tunnels can be provided by natural means, by the traffic induced piston effect, or by mechanical systems. Natural ventilation and traffic-induced ventilation are suitable for relatively short tunnels or tunnels with low traffic density. In the event of a fire in such tunnels, traffic would be stopped and only natural ventilation provision can be relied upon. This is one of the important underlying assumptions of the code requirement. Different requirements are setup in various countries on mechanical ventilation and on the tunnel length limits with adequate natural ventilation (PIARC, 1999; NFPA, 1998). In Hong Kong, the length limit is 230 m as approved in local Fire Services Department (FSD) code (FSD, 1998).

Ventilation of tunnels is necessary to remove pollutants emitted by vehicles and to control smoke in the event of fire. In short tunnels, the airflow induced by the moving vehicles (piston effect) is usually sufficient to drive fresh air in and push polluted air out of the tunnel

(Cooley and Turkey, 1965; Goosens et al., 1994; McCormick, 1994; Rosenhead, 1963; Naser and Murad, 2002). In long tunnels, however, mechanical ventilation systems, such as jet fans and exhaust shafts, are essential in addition to the piston effect to augment the airflow inside the tunnel to keep the levels of toxic gases within safety limits.

During the last decade, many studies had been conducted to control the smoke in subway tunnel fires. The longitudinal ventilation and natural ventilation systems have become the main ventilation methods after summarizing those studies (Huang et al., 2010; Carvel et al., 2001). Natural ventilation is as simple as the name implies. The movement of air is controlled by the buoyancy force of the smoke caused by the temperature difference between the hot smoke and the surrounding air. Another driving force is the piston effect created by moving passenger train pushing the smoke through the tunnels. However, this effect is minimized during an actual fire condition (Jojo and Chow, 2003). Natural ventilation

can only be used if the tunnel is short enough. A longitudinal ventilation system is called for in tunnels when the length of the tunnel is longer than 180 m (Federal Highway Administration and Federal Transit Administration, 2003)

Smoke from a fire can not only reduce the visibility and cause slower evacuation; toxic gases in the smoke can also fatal in duration of time. The hazards caused by a fire smoke are more critical in long tunnels that may be densely occupied by vehicles and people at times.

Hong Kong is a well known international metropolis. It is situated on China's south coast and, enclosed by the Pearl River Delta and South China Sea. With a land mass of 1,104 km2 [1] and a population of seven million people, Hong Kong is one of the most densely populated areas in the world. As much of Hong Kong's terrain is hilly to mountainous with steep slopes, less than 25% of the territory's landmass is developed, and about 40% of the remaining land area is reserved as country parks and nature reserves. The territory's population is 7.07 million. In mid-2010 Hong Kong had a birth rate of 12.5 per 1,000 population and a fertility rate of 1,108 children per 1,000 women [2]. Providing quality education to cope with the high population, school should be established to provide the needs of the students. With reference to the Environment and Conservation Fund (ECF), HKSAR, follow by the injections of $1 billion and $500 million into the ECF in early 2008 and in mid 2011 respectively, the ECF has provided funding to support over 2,200 educational, research, and other projects and activities in relation to environmental and conservation matters [3]. According to the Education Bureau, HKSAR, the numbers of secondary school are more than 520. That means more than 520 energy end-users are consuming energy at each school day. Schools are the buildings that have high density of occupant and unique yearly energy consumption profile. Most of the schools start working at 08:00 am until 18:00 pm from Monday to Friday, September to June. Energy consumption may not be varied due to the stabilization of occupant. This study makes opportunity to investigate the energy saving rate to reduce the use of total energy, and figure out that which of the green feature is the most energy efficiency.

Literature Review

Green features are not only known as renewable energy generation. It is also the method which can be reduced the use of energy. Wind energy and solar energy are two of the renewable energy source which use mostly in Hong Kong [4]. Most of the studies are based on experiment and simulation results and actual measurements are lack of study [5,6,7]. Therefore, the actual energy saving should be investigated in this study. Commercial and residential buildings with energy conservation are the main topic in previous research. This study is focusing on secondary school to figure out the actual saving.

Another green feature focus in this study is the water-cool VRV system. Simulation results show that the energy saving potentials of the VRV system is expected to 22.2% compared with the VAV system in office building [8]. This study is going to investigate the actual energy saving for the water-cool VRV system compared with the air-cool VRV system.

Objectives

The objectives of this study are as follow:

To investigate the actual energy saving of the green design school compare with a non green design school.

To investigate the most effective green feature.

Methodology

To execute the study, the methodology is developed to three different stages as follow: Site Investigation, Data Collection and Data Analysis.

Site Investigation

To carry out the study, a secondary school with green feature should be selected. To obtain the actual energy saving, another secondary school should be selected to become the reference sample. Two secondary schools should be selected carefully to complete the following study. The site area and layout of the schools should be similar. Also, the location and orientation of the schools should be close to each other to reduce the error of data collection. Envelope design and system design of both schools should be check to ensure that the collected data are comparable.

Data Collection

Energy consumption of the sample schools are the main purpose of data collection. Data should be collected to obtain the profile of the energy usage for both schools. The energy consumption should be break down to small part including the lighting system, HVAC system, etc. to analyze the actual energy saving.

Data Analysis

Analyze the collected data from two sample schools to compare the total energy consumption and the energy break down usage. To ensure the data are comparable, calculation should be carried out to identify the different between two sample schools.

Possible Deliverable/Results/Analysis

Base on the site study, data collection and analysis, energy break down of each green feature can be obtained. Compare to two sample schools, this study can be located the most effective green feature. The actual energy usage of the total energy consumption can be compared with the simulation result with reference to the literature.

Project Planning

Project Planning

Semester 1

Week 1-2:

Identify the scope of research study.

Week 3-4:

Search for related papers, journals, reports and dissertations for literature review and background of research study.

Week 5-6:

Search for appropriate school to carry out the study.

Prepare the research proposal.

Week 7:

Submit the research proposal

Week 8-11:

Carry out the site investigation and data collection

Week 12-13

Prepare the research report and oral presentation

Week 14

Submit the research report and give oral presentation

Conclusion of the Proposal

To conclude the study, actual energy saving of the green design school can be found. Base on the result analysis, the most energy efficiency green feature can be obtained. This study can be the reference for the schools which want to have energy saving in future.

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