PRACTICAL EXPERIENCE IN VENTILATION DESIGN FOR

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The ventilation system shall automatically be controlled as a function of the following. parameters,1 2 CO meter units 150 m after the portals. 2 2 visibility turbidity meter units 150 m after the portals. 3 1 longitudinal air velocity and airflow direction meter in the middle of the tunnel. 4 43 manual fire alarm call points divided into 10 zones. The following operation modes have to be foreseen,a program control. b manual control controlled by operator, c automatic control controlled by VI CO air speed levels. d full notch control controlled by maximum level of air quality meter. e smoke exhaust control controlled by fire alarm program. The block diagram below indicates the interplay of the different parameters and operation. zone indication control mode,fire response program. program control,manual control,automatic control,full notch control.
AS direction smoke exhaust,J F 1 to 10 start command. south north off,attenuation, CO max calculation of JF stage maximum selection of JF stage. CO 2 selection stage due to CO and direction selection of fan. 1 1 1 1 feedback of JF no,1 to 10 south,north off failure. operating hour,VI max c alculation of,VI 2 selection JFstage due to VI. CO 1 2 Legend,Air quality 1 parameter input,monitoring.
CO VI alarms stage 1 2,VI 1 2 JF Jet Fan,AS Air speed. 1 2 Metering unit,Fig 2 Block diagram for the ventilation control. 1 1 Approach, A one dimensional time dependent simulation model was used because this leads to a. minimum calculating time with reasonable and convincing results The goal was to create. different ventilation stages and strategies for different conditions traffic and meteorological. As the pressure gradients are small it was assumed that the density is almost constant. therefore the model have been linearized, International Conference Tunnel Safety and Ventilation 2004 Graz. The result of the simulation was the ventilation control procedure for normal and fire. operation Under normal operation depending on the actual CO and turbidity different fan. stages will be activated,Fig 3 Simulation interface.
The main goal of the fire response programs was to reduce the spreading of smoke to a. minimum During the evacuation phase the air flow velocity should not exceed a value of. more than 1 5 to 2 m s in order to maintain stratification of the hot smoke This will help to. enable evacuation of people trapped in the tunnel on both sides of the fire. For each of the 10 zones a fire response program have been created The selection of the. respective fire response program depends on the tunnel section in which the fire alarm has. been initiated The rotating direction of the jet fans was chosen in such a way that the smoke. extraction direction of the respective fire response program was supported. air velocity JF1 JF2 JF3 JF4 JF5 JF6 JF7 JF8 JF9 JF10 air flow. 2 5 off off off off off off on south on south on south on south. 1 5 2 5 off off off off off off off off off on south. 0 5 1 5 off off off off off off off off off off, 0 0 0 5 off off off off off off off off on south on south. direction south, 0 5 0 0 off off off off off off off off on south on south. 1 5 0 5 off off off off off off off off off off, 2 5 1 5 off off off off off off off off off on north. 5 0 2 5 off off off off off off on north on north on north on north. 5 0 off off off off on north on north on north on north on north on north. Fig 4 Fire response program for zone 1 and 2, The marked jet fans JF are located in the affected zone and not allowed to be started. International Conference Tunnel Safety and Ventilation 2004 Graz. 1 2 Test procedures, To verify all these results measurements and tests on site ha ve been necessary.
For checking the ventilation control software for normal operation the following tests. procedures have been performed, measuring of the basic air flow without any jet fans in operation. testing of the different fan stages by simulating the output signal of the CO VI meter at. the first clamp using a calibrator, checking the time frames for starting and stopping of the jet fans. measuring of the air velocities achieving with the different fan stages. measuring of the air flow rise, The air velocity was measured using a air velocity transducer To get the average air velocity. within the tunnel profile a grid of several different points 16 was used For one fan stage all. points have been measured under stable conditions Using these results a correction factor was. calculated for a reference point This reference point was used to get the results for all other. stages The tests has been performed at different natural air flow levels 0 8 3 2 and 4 5 m s. During the tests the air flow direction To achieve a low air speed it was necessary that the. north portal partially have been covered using tarpaulins This results that the air speed drops. down to 0 8 m s,ANEMOMETER 7400,TRANSMITTER,VI CO METER. 16 ANEMOMETER,15 14 13 12 11,10 9 8 7 6,Fig 5 Tunnel cross section with metering points.
The main result given by these tests have been that the difference between the average air. flow speed installed in the tunnel cross section and the one measured with the air flow meter. is about 40 There are only minor deviations within the different air speed levels. To collect information s and data on the achieved air flow inside the tunnel caused by the use. of the jet fans various tests have been done The jet fans have been started single and in pairs. to see the influence in the air flow increase as well as in the air flow decrease These effects. have been simulated by operating the fans first in and second opposite the existing air flow. direction All tests have been carried out using a minimum of 10 minutes time between each. test to reach always the na tural air flow, International Conference Tunnel Safety and Ventilation 2004 Graz. Summarizing these test results it was found out that by operation in air flow direction the use. of one jet fan accelerates the air about 1 5 m s The increase of the jet fan number leads. always to a rise of about 1 m s, All these results have been used to check the simulation conclusions The comparison for one. scenario is depicted in the next figure,site measurement. simulation, Fig 6 Comparison of the site measurement and simulation results. The course of the fire response program have been checked starting the program using the. respective button on the SCADA system in the control room This was in accordance with the. normal operation as the fire response program always will be released manually The fire. alarm will be activated by pressing the manual fire buttons inside the tunnel which leads to an. alarm in the control room The operator will check the fire zone using the CCTV installation. and start the program manually, To verify if the recommended course of the jet fan operation given in the fire response matrix.
leads to the desired result keeping the air flow in between 1 and 2 m s to guarantee optimal. conditions for a smoke stratification tests have been made using the natural air flow as. starting condition As the meteorological conditions most of the time caused air flow. velocities between 2 and 5 m s these tests have been done under realistic operation. conditions In tunnels used with bi directional traffic the air flow velocities are very seldom. higher in the majority of cases the air speed should be within this range. The first tests done showed that in some cases the given jet fan operation parameters did not. fulfil this criterion Therefore the fire response matrix have been adjusted to the local. conditions The first issue of the fire response matrix includes 10 different types After the. changes the types and steps have been reduced to 5 The reason why a further reduction was. not possible is the arrangement of the jet fans The jet fans arranged in the concerned zone or. close to this zone are not operated due to the turbulences produced by them. During all tests carried out after the adaptation the automatic control system was able to. reduce the starting velocity within 1 to 2 5 minutes and settled the air flow velocity in a range. between 1 and 2 m s The duration of all these tests have been more then 10 minutes. No change of the predominated air flow direction or turbulences have been observed inside. the tunnel, International Conference Tunnel Safety and Ventilation 2004 Graz. The next figure depicts the printout of the SCADA system for the test of the fire response. program in zone 9, Fig 7 Result of the fire response program test in zone 9. 2 SEMI TRANSVERSE VENTILATION SYSTEM, For tunnel of a length between 3 and 5 kilometres a semi transverse ventilation system often. have been applied The usual way for a semi transverse ventilation system is blowing fresh air. via an air duct and continuous openings into the traffic area Most of theses systems have. been designed as reverse operation system which means that in case of a fire the fan could be. operated in reverse mode and suck air out of the tunnel This system is efficient and proper for. normal operation but in case of a fire it is no more corresponding with the increasing. philosophy of safety The time to reverse the air flow and reach the maximum exhaust. capacity often needs more than 3 to 4 minutes This leads to the decision within Austria that. older systems of this type should be changed to exhaust systems Therefore in the year 2001. the Austrian tunnel ventilation guideline RVS 9 261 have been changed It was defined that. semi transverse system are only allowed as exhaust system. Below you can see the scheme of a fresh air supply system under normal operation including. the characteristics of the air flow speed u The fresh air is blown into the traffic area via. regular openings therefore the air speed in the duct will be reduced linear The exhaust air. will be blown out through the portals based on the pressure increase in the traffic area. Fig 8 Semi transverse system fresh air type, International Conference Tunnel Safety and Ventilation 2004 Graz. The next figure depicts the principle of an exhaust system under normal operation again. including the characteristics of the air flow speed u Fresh air have to be sucked into the. tunnel via the portals and will be taken out of the traffic area at the end of the air duct. Fig 9 Semi transverse system exhaust type, Using the same assumptions for both systems leads to a higher necessary power consumption.
for the exhaust system The reason is that the pressure loss in the air duct is significant higher. based on the air flow characteristic, But the main advantage is the essential improved extraction volume of smoke The system is. combined with electrical adjustable dampers which will be closed in the zones not affected. and opened close to the fire zone,Fig 10 System operation in case of a fire. The operation in case of fire for both systems is shown in Figure 10 Due to the high amount. of fresh air leakage through the inlet openings the efficiency of the smoke extraction at. supply systems is reduced Therefore the spread of smoke at supply systems is more than at. exhaust systems This could be seen during fire tests at adapted systems. The operation experience with an exhaust system demonstrated that the control of the system. under normal operation needs a higher amount of air quality measurements One of the reason. for that conclusion is that the influence of the traffic on the tunnel air speed is much more. higher This yields to a higher necessary number of metering instruments. To improve the exhaust system it should be foreseen to install a damper which allows to. connect both air ducts together This leads to a higher amount of air exhaust in case of a fire. and in addition to that you do have the possibility to operate your system in a reduced way at. a fan breakdown, International Conference Tunnel Safety and Ventilation 2004 Graz. 3 CONCLUSION, Simulation is a good tool to get an idea of the main effects of the ventilation operation. Several scenarios can be calculated and experience will be gained without having any real. accidents or high operation costs It will help to save time and money to find answers and. solutions But as start up tests and tests runs demonstrates the aspect of practical experience. is still necessary and important, International Conference Tunnel Safety and Ventilation 2004 Graz.
The design of tunnel ventilation systems is in theory described in many documents and papers But as it is often the case theory and practice do have small differences Today a lot of different tools are offered to calculate air demands fan layout or the necessary number of fans Using a one dimensional time dependent model you will reach

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