How to choose a fire ventilation system?
Smoke removal from the garages can be achieved in two ways: through ducted smoke removal ventilation or through jet smoke removal ventilation. How do they differ and which one to choose in the case of underground garages?
Despite the fact that relatively many underground garages are being built, fire ventilation of these facilities is still a very difficult issue for designers and architects. Balancing between legal guidelines, scientific studies and the experience of practitioners, a given design task can still surprise. What garage fire ventilation systems exist and what factors determine the choice of system?
Fire ventilation is mandatory
What is a smoke exhaust ventilation installation? In accordance with the provisions of the Technical Conditions, it is an installation whose task is not only to remove smoke from a given room, but also to ensure safe and effective evacuation for people who are in such a room, as well as to create conditions for work rescue teams. Additionally, the smoke exhaust ventilation installation is characterized by a constant supply of outside air, which is often also referred to as compensating air.
In the case of closed garages, a smoke exhaust ventilation system activated by a smoke detection system should be used if this zone does not have a direct entrance or exit from the building or if its area exceeds 1,500 m2.
Basic elements of the smoke exhaust system
Smoke removal from underground garages can be performed in two ways. The first method is duct smoke extraction ventilation, the second method is jet ventilation.
The ducted smoke exhaust system consists of:
- smoke exhaust ducts distributed under the garage ceiling, ending with smoke exhaust grilles,
- smoke exhaust fans at the end of the duct installation,
- gravity air compensation points.
The jet smoke removal installation includes the following elements:
- main smoke exhaust and air compensation shafts, with smoke exhaust fans, with the possibility of reverse operation,
- gravity air compensation points,
- jet fans placed under the garage ceiling.
Two principles of operation
The ducted smoke exhaust system is activated immediately after a fire alarm. As a result of the operation, a layer of hot smoke is divided into a layer under the ceiling and a smoke-free layer below, safe for movement during evacuation and enabling the operation of rescue teams.
The jet smoke removal installation is turned on in two stages. In the first stage, after a fire alarm, the main smoke exhaust fans, mechanical air compensation and gravity compensation are turned on. The purpose of the installation is to ensure safe conditions for evacuation by keeping smoke under the garage ceiling. The smoke removal installation operates in this mode until the evacuation is completed. After the evacuation of all garage users, jet fans are turned on from the power supply and control center towards the smoke exhaust shaft. As a result, the smoke is kept in the area between the fire source and the smoke extraction shaft. Thanks to the operation of jet fans, rescue teams are provided with easy access to the source of the fire, while reducing the smoke temperature.
Which smoke removal system should be chosen?
The polish legislator does not specify formal requirements related to the parameters of the system used, but indicates the purpose of its use and functionality. Therefore, the designer is responsible for the correct selection and effectiveness of the system.
Therefore, when choosing to design a specific type of smoke removal installation, the designer must take into account several important factors.
Jet smoke extraction installation is best suited to garages where:
- division into smoke zones is possible,
- smoke exhaust shafts are available in each smoke zone or it is possible to install a field exhaust vent in each smoke zone.
It is best to design a ducted smoke exhaust system in garages:
- with one smoke zone,
- one smoke exhaust shaft available,
- at least 3 m high, due to large-size smoke exhaust ducts running under the ceiling.
Due to the lack of computational methods for designing a jet smoke removal installation, the designer should remember to confirm the effectiveness of the designed installation using CFD simulation. The duct installation can be designed based on existing calculation methods, therefore simulation is not required.
Good solutions
A ducted smoke exhaust system and a stream smoke exhaust system can be designed using the following devices:
mcr Monsun smoke exhaust fan
mcr Pasat smoke exhaust fan
mcr Bora jet fan
mcr Omega Pro power and control unit