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Smoke and Heat Exhaust Ventilation System in Garage: CFD Analysis

underground parking

It was yet another beautiful evening on July 26, 2016 in St. Louis, US. Around 8.15 pm started the fire in a downtown parking garage in which multiple vehicles were involved and smoke engulfed a complete floor of the garage.

Fortunately, no one was injured and another lucky fact was that the garage had enough surrounding ventilation, as it wasn’t underground. 

Fire Accident - St Louis

Source: FOX 2 NEWS

There were 4 such parking garages accidents only in the year 2016. The consequences might be higher if a similar occurrence happens  in an underground parking garage, but this can’t be a reason to avoid them, as underground parking can reduce the emissions about 40% compared to kerbside parking [1].

Air quality in a closed environment is growing to be a great concern. Apart from smoke and fire, it is even the carbon monoxide (CO) and particle-bound polycyclic aromatic hydrocarbons (pPAH) levels that need to be looked into [2]. Some studies point out that 13 to 18% of the blood is CO saturated in parking garage employees [3].

There are many research papers which bring out the pollution effects in underground parking garages. So how do we achieve proper ventilation in them and find a solution to this problem? In this regard, there are two occurrences that need to be addressed:

  • Study of smoke or contaminant propagation.
  • Clearance of smoke or contaminant from the underground garage through a SHEV (Smoke and Heat Exhaust Ventilation System)


Smoke Propagation in Underground Garage

Why is this study significant? A small round of discussion can help us understand how the ventilation affects the propagation of smoke or any other contaminant in a closed environment. The simulations are carried out in an underground parking garage with different combinations for smoke and heat exhaust ventilation systems. Look at the two images below. In both cases, we have smoke coming out of a particular source and it is critical to understand how it circulates in the environment. The term ‘scalar ratio’ is one where the value 1 refers to smoke and 0 refers to air, and the term ‘smoke ratio’ refers to the percentage of smoke present in the entire domain. So lesser the value of ‘smoke ratio’, better ventilation in the closed space.

Case 1: The average smoke ratio in this instance is 0.754, which represents that 75.4% of the garage is covered by smoke. This can be seen from the fact that a larger area in the domain is covered by red.

Steady state - Case 1

Case 2: The same setup is altered only by changing the inlet and outlets. The results are obtained after the same time, around 30 minutes in these trials, in order to compare them. In this case, the smoke ratio is 0.417, which goes to say that this setup has less smoke by a third than the previous one.

Steady state - Case 2

What is that we infer from this study? There are regions which are less prone to the effects of pollution, so some emergency zones could be made in these areas where people can occupy during such accidents to minimize the health hazards.


Smoke Clearance: Choosing a Good Smoke and Heat Exhaust Ventilation System

The next round of analysis is to find an efficient smoke and heat exhaust ventilation system to clear a contaminated room. In the following analyses, the room is initialized to have a scalar ratio of 0.5, i.e. the room is contaminated by pollutants up to 50%.

Case 1: The domain has its inlets and outlets as shown below in the figure. The average smoke ratio is 0.166 after passing in air for about 1.5 hours.

Clearing of smoke simulation though Smoke and Heat Exhaust Ventilation

Case 2: The comparable smoke ratio in this configuration is 0.123 after the same duration. This explains that case 2 has better purification capabilities than the previous one.

Clearing of smoke simulation ventilation Smoke and Heat Exhaust Ventilation

These are just a few examples of smoke propagation or clearance through smoke and heat exhaust ventilation systems (SHEVS) and help us understand the importance of engineering simulation (in this case mainly CFD) while designing proper ventilation systems.

In actual design methods, all possible combinations should be tried out, also assuming the source of pollution to be at different points of the garage – we never know which car / vehicle or other occurrences can initiate the issue/fire. The argument can also be extended to find the most energy efficient way for ventilation. Hence simulation study proves to be a very simple way of saving money, time and a lot of lives.

The following video by SimScale contains a webinar session on smoke propagation and clearance. The project can be found here, which can be copied and worked upon to understand how engineering simulation works!


Want to learn more? Download this free white paper: How to Optimize HVAC Systems Designs with CFD


References:

[1] Paul G. Höglund, Parking, energy consumption and air pollution, Science of The Total Environment, Volumes 334–335, 1 December 2004, Pages 39-45, ISSN 0048-9697.

[2] Sung R. Kim, Francesca Dominici, Timothy J. Buckley, Concentrations of vehicle-related air pollutants in an urban parking garage, Environmental Research, Volume 105, Issue 3, November 2007, Pages 291-299, ISSN 0013-9351.

[3] James M., Ramsey MS., Carboxyhemoglobinemia in Parking Garage Employees, Archives of Environmental Health: An International Journal, Volume 15, Number 3, 1967, Pages 580-583.

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