How to Confirm the Performance of Car park Ventilation System by Using CFD..?
Updated: Sep 29, 2019
Developing a ventilation system and confirming the air quality and ensuring the efficient removal of high contaminant concentrations in a Car Park is one the main tasks that any Engineering Design Office have to conduct.
Qatar Design Consortium (QDC) had carried out to design the new DPS School in Qatar. With almost 7,700 sqm car park, a main mission was to verify the performance of the mechanical ventilation system in case of fire, as it a mandatory requirement for Qatar Civil Defense Department (QCDD) for the any Car Park Ventilation System by Jet Fans.
NabtakerEngineering Carried it Out To Get QCDD Approval
NabtakerEngineering had been retained by QDC to conduct a CFD Simulation for the car park. It has a success percentage with 100% to take the approval form the 1st revision.
The objective of this project was to check and confirm the performance of Mechanical Ventilation System; if the smoke produced by fire is evacuated within 30 mins by using CFD analysis as per QCDD Requirements. The acceptance results must be met with Qatar Civil Defence Department within 20 mins.
2 Scenarios are Required
First Scenario; in case the fire is happened in the LEFT SIDE of the car park, fans in the left side will be acted as exhaust points.
Second Scenario; in case the fire is happened in the RIGHT SIDE, fans in the right side will be acted as exhaust points.
· Fire Dynamic Simulator Tool (FDS) is used to carry out CFD simulation.
· Large Eddy Simulation (LES) turbulence model is used.
· Mass and Species Transport model is used to model the smoke propagation.
· Discrete Ordinates Model to model radiation.
· Combustion and radiation are introduced into the governing equations via the source
terms in the energy transport equation.
(2m X 5m) Fire Block burns at 4 MW. The time necessary to reach a 4 MW is set to be as fast with respect to NFPA 204.
The fire location is proposed to be the onerous as per QCDD Requirements. The proposed fire location will be in the center of the car park as it will be onerous to exhaust fans in both scenarios.
In both simulation scenarios process is designed to act as per the following:
Time = 0 Sec (0 mins): The smoke is generated by 4 MW and Fresh air from Fresh Air Fans is introduced into the car park. Main Exhaust Fans will operate at high speed and will provide an air change rate of 10 ACH.
Time = 120 Sec (2 mins): With time delay of 120 Seconds all jet fans will be run at high speed.
Time = 1800 Sec (30 mins): The computation is stopped after physical 30 minutes of simulation time.
10 Days to Get Results ONLY..!
After 10 days, two separate simulations had been conducted. It was noticed that jet fans play an important role in driving and orienting the smoke to the exhaust louvers. They also reduce the ability to find a considered dead zone. Moreover, the visibility was 10 meters in the same mentioned area, which give a clear sign that it will be a safe path for occupants to be evacuated through it and for fire brigade to get access at any time to the car park. All. The visibility was also above the tenability criteria at 1.8 m in upstream area within 20 mins.