Whether residential accommodation, office complex or factory building – each building has its specific requirements for ventilation. One of the special challenges here are underground and multi-story car parks, where, due to the exhaust gases, the air is severely contaminated with carbon monoxide, nitrogen oxide and LPG (liquefied petroleum gas). Depending on the concentration and the length of time spent in the car park, this is a great danger for the users. Therefore, the polluted air needs to be extracted quickly and safely. However, the duct systems which are often used for this take-up a lot of space and often cross other services such as electrical or water lines. This is reflected in the investment and installation costs. In the modern car park ventilation method the conventional ventilation has been replaced by the Jet Fans Ventilation System. This system system has been developed to ventilate the underground car parks for both CO Removal during the Normal condition and as well as smoke extraction in the emergency scenario such as fire.
The complete system consist of Jet Fans, Main Supply and Exhaust Fans, CO detection sensors and a control panel. The system is based on placing a set of axial impulse fans all along the parking area, which operates in a similar way to a ducted system, when installed on the ceiling, they move the air towards the exhaust area, by effectively creating a continuous flow, thus, avoiding the creation of stagnant zones where air gets trapped.
The fans only operates for the particular zone when the CO detectors detect a level of pollution higher than the threshold value for the zone. In case of fire or in high CO levels, the control system need to switch on the fans on full speed after getting the signal from heat/smoke sensors. In addition to switching jet fans on high speed on fire floor, the control system also switches off the fresh air fans as it contains oxygen, which is liable to spread fire. The Control system also regulates the main supply/exhaust fans on demand or signal from the respective sensors in addition to jet fans, quickly and effectively until the complete smoke is removed from the basement car park.
CFD analysis can simultaneously predict airflow, heat transfer and contaminant transport inside the parking garage. The specific aim is to find the optimal location, number and configuration of the jet fans required for the ventilation of the car park, for the given positions of inlets and exhausts, such that it meets the tenability requirements of CO exposure limit set by health and safety regulations.
The parking lot of the analyzed business center consists of 8 floors, including PB1, PB2A, PB2, PB3, PB4, PB5, PB6 and PB7. This parking lot has been divided into specific zones and the CFD simulation has been performed as if these zones are separate parking lots.
The exhaust fans are working with a single exhaust shaft from PB2A to PB7.
5-air-exchanges has been used for the Daily Emission Ventilation and 10-air exchanges has been used for the Emergency Mode, according to ASHRAE 's HVAC standards.
All jet fans are set to perform daily emission
ventilation (NPV) and they start in all zones at the same time to
perform 5 air exchanges per hour.
The floor height is accepted as 3m on an average in the calculation of these values.
The aim of this study is to perform analysis and interpretation of daily emission ventilation system design in indoor parking lot with jet fans with the help of CFD. In the study, ventilation of 8-story parking lot of a major business center in Istanbul with jet fans have been carried out, and the analysis on one story of this parking lot is provided as a case study.
The airflow in all the regions of parking lot has been examined, the most suitable jet fan placements have been determined for daily emission and fire ventilation, and accuracy of this placement has been proved through the analysis with this study. The performed CFD analysis enables us to see correct placement of the jet fans and decide the best placement of them. The ultimate purpose of the ventilation system is to discharge harmful gases as soon as possible or to rarefy their ratio in the environment.
Basement Car Park, Jet Fans, Ventilation, Contaminant Transport, Smoke Extraction, Carbon Monoxide, CFD
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