Fire ventilation systems for enclosed garages

Limited space for investment has made constructing underground garages as part of buildings increasingly popular in our country. In particular, this is true for large city centres, where the number of parking spots in the streets is smaller than the number of drivers looking for a parking space. As a result underground and multi-storey car parks are becoming more popular.

According to Polish laws, if the area of the garage is greater than 1500 m2, automatic smoke ventilation devices must be installed.

The application of smoke ventilation should ensure that, if there is a fire, the smoke and gas products of combustion are extracted from the garage, enabling evacuation of people and minimisation of property loss.

The smoke ventilation system should also support fire fighting teams during fire suppression activities. By extracting smoke and heat from the garage, it is possible to reduce the temperature and keep better visibility, making it easier for fire fighters to locate the fire and proceed with suppression.

Apart from smoke extraction, the garage ventilation system also performs another, equally important function. During regular operation of the garage, the system should support fresh air supply and extraction of fumes and other toxic gases from the garage space. Ensuring a continuous flow of air in the garage prevents the formation of “dead zones”, where harmful substances could accumulate. This is the primary role of the ventilation system, affecting everyday user comfort.

Considering the above needs, SMAY launched new product groups for comprehensive garage protection.

First is a smoke ventilation ducting system (SDS—Smay Duct System). SDS is a system of horizontal ducts and rectangular fittings made of galvanised steel, and with maximum dimensions 2500 x 1250 mm. To enable the production of so large ducts, their structure is reinforced by a system of dedicated bracing elements.

The ducts were tested for fire resistance at the Building Research Institute (ITB), which was the basis for granting the Technical Approval for the system. Positive results of fire-rating tests were also obtained for system accessories, tested together with the ductwork according to PN-EN 12101‑7.

Tested accessories included silencers with the same dimensions as the ducts, access doors with maximum dimensions of 300 x 300 mm, as well as air supply and exhaust grilles, which may optionally be fitted with dampers that can be adjusted to the opening angle from 45 to 90o. The compensation of linear elongations, caused by temperature rise under fire conditions, is possible owing to the application of SDS-KEP joints made of special fabric stitched together with fibres resistant to high temperatures.

The SDS system also includes seals and suspensions dedicated to smoke ventilation ducts. This renders the SDS system a complete solution with ducting and all accessories necessary to install a comprehensive smoke ventilation ducting network.

In their basic version, the fans are 1850 mm long, and come in three diameter sizes: 315, 355 and 400 mm. Optionally, they may be provided with vanes to change the air supply angle from 0 to 20o, which helps bypass local hurdles, such as ceiling beams, and prevent the Coanda effect (adhesion of the air stream to the ceiling). SCF-series fans are also manufactured in the reversible version.SMAY also has on offer ventilation systems for enclosed garages, where ducted ventilation system may not be used owing to small height. New SCF (safety carpark fan) jet fans were designed for such garages.

SCF 355 jet fan

Jet fan ventilation has become a subject of discussions in Poland, as some argue it is ineffective. However, these opinions may be based on isolated cases of poor installation, which should not affect the overall evaluation of jet stream ventilation.

Problems with evaluating jet fan ventilation emerge as soon as the design concept stage. It is assumed that at this stage the performance of a designed system should be confirmed by computer simulations. However, to prepare relevant simulations, verifiable data must first be obtained.

In Poland simulations can be prepared by anyone, and there are no requirements as to their reliability assessment. On the other hand, in some countries e.g. in the United Arab Emirates, regulations stipulate that the CFD simulation report should be accompanied by a separate report with the comparison of the discharge profile specified during physical testing for a single jet fan with the profile from the CFD simulation.

Only upon obtaining a satisfactory comparison simulations may be prepared for the entire system. The requirement should also be present in Poland, but for that to happen, jet fan manufacturers should provide data concerning air discharge and airflow range behind the fan.

To meet these demands, SMAY has began testing the discharge of downstream airflow from SCF fans. The air discharge is one of the crucial details to be considered, when choosing the right fan. This is confirmed by research to date, demonstrating that two fans having the same diameter and similar parameters such as power and thrust, will have a different stream range, which results from the differences in streamflow behind the fan.

By knowing the air discharge characteristics of the streamflow behind the jet fan, it is possible to reproduce it as computer simulations, and thus achieve reliable simulation data and a system working properly upon installation.

Chart 1. Speed profile for SCF 355 jet fan axis, working in the primary direction

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