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Does the Jet Fan cause extra Sprinklers to activate?
29 September 2019

Does the Jet Fan cause extra Sprinklers to activate?

As you know, when jet systems are preferred in closed parking lots, we analyze the performance of emergency ventilation by CFD (computational fluid dynamcis) method. After a video we published last week, when the jetfan came into play, the question was, could it cause more sprinkers to be activated because it carries hot air? We decided to investigate this situation and prepared a comparison scenario. Two analyzes were run, and the only difference between the two was that one had jet fans and the other had no fans.

Jetfan

For fires of parking lot, we usually complete the analyzes by accepting the fixed fire load of 4MW (with sprinkler) according to the British standard for 20 minutes. It describes the energy from the joule unit it generates when the total combustion of a vehicle is completed based on this time and load value. For parking fires, we usually complete the analyzes by taking the fixed fire load of 4MW according to the British standard for 20 minutes. It describes the energy from the joule unit it generates when the total combustion of a vehicle is completed based on this time and load value. But here we set the total analysis time to 300 seconds. We also accepted the vehicle fire load to be 2.3MW in 300 seconds. The load value of the vehicle that we burned in the simulation was compiled based on the fire load data of the Citroen BX brand. In summary, the fire load in the graph we see on the side works during the analysis.

Jetfan

The sprinkler system is located at a height of 2.7m parallel to the floor in the parking lot with a ceiling height of 3m, where sprinklers are also applied. Sprinkler placement was performed in the same way in both car parks. We have accepted the parameter Response Time Index as 75 (ms)0.5 and the activation temperature as 68 °C.

Jetfan

Using exhaust fans for ventilation, fresh air is sucked in from the ramp inlets. The axial fans (3 units) are put into operation in a totally negative pressure inside the car park, with 12 air changes per hour in this 2800 m2 area. 6 jetfans, which are red above, take 8000 cubic meters of air (each) from the openings on the right and accelerate into the exhaust vents. The outdoor and initial indoor temperatures were taken to 20 ° C. In the analysis comparisons, the videos of operating the car park with and without jet fans are as follows.

There is jet fan
There is no jet fan

In the videos above that contain the analysis results, the smoke dispersion is shown first. As you know, when jetfan systems are used; dilute the smoke. This maintains the required visibility and the required temperature for the person in charge. Therefore, the resulting images are taken at an average human height (we accepted 1.6m), 300sec. during the period. We set the upper value to 65 ° C in order to display the temperature in the section. So the places you see red temperatures at 65 ° C and above… In the section indicating the visibility, the whole area we see in blue has a minimum viewing distance of 10m. Smoke condenses on the ceiling level, accumulates by approaching the floor, reducing the visibility. Finally, the value of the cross-section is again the temperature, but this time the cross-sectional image is at 2.6m. Here, we wanted to look at the temperature distribution for the sprinklers. Also, we define the fire load. The sprinklers only affect the cooling of the air inside. So it doesn’t suppress the fire and drop the load. The fire load continues to operate as we define it throughout the analysis. In the last video we see how many sprinklers explode in two different situations. According to all the boundary conditions we have defined above, 11 sprinklers were opened at the end of 300s with Jetfan and 13 when there were no jetfans. So the answer to the question we asked in this case, no! Jetfans do not interfere with the extra sprinklers and cause uncontrolled water loss.