Experimental Study on Smoke Exhaust Effect by Using Jet Fans in an Underground Garage

Construction Engineering Volume 4, 2016 www.seipub.org/ce doi: 10.14355/ce.2016.04.004

Experimental Study on Smoke Exhaust Effect

by Using Jet Fans in an Underground Garage Ren Zhang, Yanfeng Li, Lin Chang, Qiang Liang College of Architectural and Civil Engineering, Beijing University of Technology, Beijing, 100124 liyanfeng@emails.bjut.edu.cn

Abstract In order to research the technical feasibility and influence factors of impulse ventilation systems in an underground garage, full‐scale fire tests have been designed and conducted. Four testing conditions have been designed by changing jet fan combination form and opening time. The temperature and smoke layer at different distances from the fire source have been recorded. Results show that jet fan would drive smoke to the downstream exhaust port more quickly and visibility of fire source upstream would be increased. There is a significant change on smoke exhaust of jet fan combination. Series arrangement of jet fan would keep smoke layer temperature stable and smoke could be exhausted effectively. However, series‐parallel combination of jet fans could cause a high fluctuation in smoke layer temperature. It would do harm to exhaust smoke quickly in garage.

Key word Underground Garage; Jet Fan; Smoke Exhaust; Impulse Ventilation

Introduction Underground garage is a low‐rise space. Garage is characterized by a low floor height, a lot of wires and a very large area. There are dangers in fire safety. Test results show that garage fire is rapid‐velocity combustion, high temperature smoke, low visibility. Buildings above the garage will be damaged by the fire because of explosion [1‐3]. More and more underground garage install no duct induction ventilation exhaust system because of tradition ventilation on exhaust system’s weakness. Smoke exhaust mode needs to consider the smoke layer disturbance, subsidence, human evacuation, organization of the flow field and other factors. Preliminary studies at home and abroad have focused on major underground garage induction ventilation exhaust system. No systematic research on induced fan flow field characteristics and influence of space structure on induced smoke exhaust [4‐6]. The paper has been designed and conducted full‐scale fire tests in underground garage. Four testing conditions have been designed by changing jet fan combination form and opening time. Texts measurements on the temperature up‐downstream fire source, to observe changes in smoke layer. Provide a theoretical basis for the study of the impact of induced ventilation on heat release rate, research and analysis of dynamic characteristics of fire, distribution Characteristics of induced smoke layer [7‐10].

Field Test Conditions of Underground Garage Induced Ventilation

FIG.1 SCHEMATIC DIAGRAM OF UNDERGRROUND GARAGE FIELD TEXT

The test site is an underground double garage in Tianjin. The size of garage is 67m (length) X25.4m (width) X4.2m (Height). The garage is divided into a smoke control area. Garage exhaust system with using ducted exhaust has

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been installed. There aren’t ceiling beams garage. West and east have two Passageways. Passageways install insulating fire‐resisting rolling shutter. Because the high of garage floor longitudinal beam has little effect on the jet exhaust. It is advantageous for the jet exhaust test. There are two smoke vents. Each of the area is 1.5m×1m. Smoke exhaust rate is 20000m³/h. The air‐supplement area is 2.5m×1.5m. Air‐supplement rate is 32000 m³/h. Garage structure diagram is shown as Figure 1.

Test Setup Due to the experimental conditions and security considerations, the main purpose of the test is to investigate the induction of the ventilation exhaust system of operating results. Fire source power is 50kW methanol pool fire. The position of the fire source is located in the west side of entrance 28.4m. Fire source is in the center line of the garage. Field test used tobacco cake to observe smoke diffusion. There are seven jet fans as shown in Figure 2. The location of the fan on the ground 2.2m. Fan outlet size is d=400mm, speed 2830r/min, axial thrust 46N. The field test arranges string of armoured thermocouple for measuring temperature. The measurement range of 0‐1300℃, accuracy 0.1℃. Test sets thermocouple string at the fire source upstream 2m and downstream 2m, 4m. Each string arranges 6 temperature measuring points spaced 0.4m. The test uses hand‐anemometer to measure wind speed at air event. The tests have designed four conditions, and Table 1 lists the various test conditions the fan on mode.

FIG.2 SCHEMATIC DIAGRAM of JET FAN TABLE 1 TEST CONDITION [11]

Condition

Jet fan

1

1#2#3#

2

2#3#

3

3#4#5#

4

3#6#7#

Opening time

After 50s,test open all fans

After 50S test open 6# 7# fan. 30S later text open 3# and exhaust fan

Result and Discussion The Temperature at Different Distance from the f Ire Source Varies with Time.

Because mechanical exhaust temperature near the fire source has little effect, select the fire source at the upstream 4m temperature change over time. The results can be concluded. Condition 2, jet fans are arranged in series, after ignition 50s turning on the fan. It began a steady decline in the fire source upstream of the smoke layer temperature, from 30℃ dropped to about 20℃. The temperature changed gently and well. Condition 3, jet fans are arranged in parallel, after ignition 50s turning on the fan. It began a steady decline in the fire source upstream of the smoke layer temperature. The temperature change fluctuated. Jet fan arranged in parallel has better effect than arranged in series.

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FIG.3 TEMPERATURE AT 4m UPSTREAM IN No.1 TEST FIG.4 TEMPERATURE AT 4m UPSTREAM IN NO.2 TEST

The results can be concluded. Jet fans are arranged in parallel in condition 3 and condition 4. Condition 3 smoke control effect is better than condition 4. In condition 4 smoke layer temperature drops in a fluctuation and smoke is failed to exhaust smoke effectively. This is due to the arrangement of the jet fan incoherent of condition 4. Airflow cannot effectively relay. In the condition 4, the source of upstream of the fan open 30 seconds later than the source of downstream of the fan. Jet fan did not form orderly flow field in the whole garage. Smoke layer temperature fluctuates, temperature decreases slowly.

FIG.5 TEMPERATURE AT 4m UPSTREAM IN No.3 TEST FIG.6 TEMPERATURE AT 4m UPSTREAM IN No.4 TEST

Variation of Smoke Layer Height In order to better observe the variation with time of smoke layer, the test set tobacco cake above the fire source is used. Smoke layer height is recorded by manual recording and video surveillance. Figure 7 is condition 1 smoke layer changing picture. Figure 7 shows that Jet fan can speed up the smoke exhaust port to move. A substantial increase in the visibility of the fire sources upstream. At upstream smoke exist significantly less than downstream.

Jet fan assisted smoke control affects stratified smoke layer. Fire source downstream smoke layer will be faster settlement. Smoke reflux occurred in the part of the garage.

FIG.7 CONDITION 1 SMOKE LAYER AT 40s FIG.8 CONDITION 1 SMOKE LAYER AT 140s

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TABLE3 VARATION OF SMOKE LAYER HEIGHT

Condition 1

Fire source upstream 10m

Fire source downstream 10m

40s

140s

40s

140s

No smoke reflux

No smoke reflux

4.0m

3.8m

2

No smoke reflux

Little smoke reflux

4.0m

3.4m

3

No smoke reflux

No smoke reflux

4.0m

3.6m

4

No smoke reflux

large smoke reflux

4.0m

3.2m

Comparison of different fan arrangement of the impact of the smoke layer stratified jet fans series combination (condition 1) stratify smoke layer significantly. Fans mix smoke little. Fans can improve upstream visibility and quickly exhaust smoke. Jet fans parallel combination (condition 4) smoke flow is not well. The visibility in fire source upstream declines. The fans disturb smoke layer in fire source downstream.

Conclusion The paper carried out jet fan ventilation induced secondary smoke exhaust test. Conclusion follows:(1) Jet fan can accelerate movement smoke towards exhaust port, a substantial increase in the fire source upstream temperature and visibility, can be induced to a downstream smoke discharge. (2) Jet fan arranged in series, smoke layer temperature changes more ideal, smoke temperature change little, temperature decline fast. Ideal flow smoke layer, the smoke layer disturbance small. Fire source upstream have high visibility. Smoke discharge rapidly. (3) Arranged in series and parallel combinations of jet fans, the smoke layer temperature is not good. Smoke layer temperature fluctuates, temperature drop is slower. Under fan parallel case, the combined gas airflow in the form of jet fans a great impact on smoke control effect. The fire source upstream fan turn‐on delay 30s opened, affecting the smoke exhaust.

ACKNOWLEDGEMENTS

This work was supported by Beijing Natural Science Foundation (Grant No.8132019).

REFERENCES

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[10] Yu Lina. Experimental and numerical simulation on smoke movement in the fires in underground garages [D]. Xian university of architecture and technology.2011 [11] Chang Lin. Jet fan exhaust research in underground garage [D]. Beijing university of Technology.2015

Ren Zhang, born in 1990, graduated student of Beijing University of Technology, is working on city underground building fire safety.

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