Poor indoor air quality (IAQ) is a common problem faced in car parks. If the hazardous gases keep entrapping and accumulating in the car park, these hazardous gases are harmful and they affect people health. Carbon monoxide and nitrogen dioxide are the most relevant air pollutants inside car parks. Carbon monoxide blocks the absorption of oxygen by the blood and this can lead to dizziness, unconsciousness or death depending on the concentration. Nitrogen dioxide affects the lungs and can cause breathing difficulties, prompts asthma attacks and causes long term damage to the lungs. Nowadays, variety of underground car park examples can be seen in various shopping malls, buildings and hospitals. Since there are lots of cars in these areas, quantity of carbon monoxide and other polluting gases increase drastically. Evacuating these gases is done with jet fan or duct system. Another type of ventilation is natural ventilation but most cases it is not sufficient for evacuation. Because of this, mechanical ventilation is mostly obligated.
Car park ventilation systems are required to achieve two objectives-
- When a car park is in general use, it is important that the exhaust gases produced by vehicles like Carbon Monoxide, NOx are effectively removed and that there are no pockets of stagnant air.
- In the event of a fire, assistance needs to be given to the Civil Defence to clear smoke from the car park during and after the fire.
CFD modelling allows for the detailed computation of airflow in car parks, taking into account often complex geometry of individual buildings. CFD modelling has the objective of confirming the viability of the ventilation scheme.
CFD analysis to investigate the impact of changing the number of buses running and the speed of the ventilation system fans on the distribution of Carbon Monoxide distribution, air velocities and temperatures inside the bus parking area.
The public transport exchange building:
parking garage dimensions: 60 × 38 × 9 meters
Bus dimensions: 12 x 2.6 x 3.35 meters
Number of Buses: 22
Tail Pipe exhaust ports (square imprint faces on the back side of the buses) dimensions: 20 × 20 mm
Flow rate of Carbon Monoxide exiting from a diesel bus exhaust tailpipe: 20.8 g/kWh
(Exhaust emissions exiting the buses’ tailpipes are the main source of pollutants inside the garage)
Test this system with 6 scenarios:
Scenario 1: Fans at Low speed with ten buses idling
Scenario 2: Fans at low speed with 15 buses idling
Scenario 3: Fans at low speed with all buses idling
Scenario 4: Fans at high speed with all buses idling
Scenario 5: Turning one supply fan-off (To increase flow from ramps)
Scenario 6: Using Supply from both sides and exhaust from the middle
The purpose of the simulation is to compare between the performances of different ventilation schemes, the conventional low level supply, high level exhaust system and a proposed system with low level exhaust and high level supply and predict the distributions of CO mass fraction and velocities at different operating scenarios to meet the tenability criteria.
Car Park, Ventilation, Indoor Air Quality, Smoke Extraction, Carbon Monoxide, CFD
Literature & Sources
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