By Rae Jane Araujo

Now, a new ventilation concept for garages that lowers the required parking garage height by about 4 feet has made its way to the U.S. from Europe, where it is used for fire and life safety. This innovation is designed to increase the number of parking spaces; reduce construction, installation and running costs; and improve air quality.

 

There are many challenges to maintaining good air quality in enclosed or underground parking garages, and most are under-ventilated. Since they are often designed with low ceiling heights, it is difficult to maintain clearances between the ceiling and cars and trucks. 

Most U.S. underground parking garages use a traditional ducted approach for ventilation, with fresh-air levels based on a given number of air changes per hour. They usually use supply-and-exhaust fans with air distribution provided by ductwork; air is extracted through the ducts and air supply is uncontrolled, resulting in poor pollution control.

What’s more, the ventilation system is run constantly, even during extended periods of low (or no) traffic or ventilation requirements, resulting in high day-to-day running costs. In addition, ducted systems usually do not provide fire or smoke isolation capability. Only about 50% of the ducts extract smoke at high levels. 

A new ventilation concept has been developed that replaces distribution ducting with a number of small ceiling-mounted impulse fans. Two alternative options are available – the Jet Thrust fan and the Induction Thrust fan. This system, widely used in Europe, was brought to the U.S. by Howden American Fan Co. 

The photo below shows the Jet Thrust fan option; note the clean and uncluttered appearance of the ceiling without the distribution ducting.

The basic principle of this ventilation system is that it uses Jet Thrust fan technology, together with the main supply-and-exhaust fans, and is thus capable of eliminating most of the problems associated with conventional ducted systems. 

The fans are properly positioned within the parking garage to control the distribution of the air within the structure. They can be used to create a flow of air at both high and low levels within the facility, resulting in a more efficient use of air than the conventional ducted systems. 

Jet Thrust units in the system act in a similar way to the traditional ducted systems, pulling air into the fan inlet (i.e., a grille/louver) and discharging at a high level toward the exhaust locations (i.e., a duct/louver/fan). 

The Jet Thrust option can provide 10 air changes an hour, double most ducted systems, making it ideal for smoke evacuation applications. These fans are reversible, which allows fire department personnel easy access to the fire source, and also lets patrons clearly view the exits. 

While this feature is currently not required in most U.S. jurisdictions, it is extremely popular in Europe and the Middle East, where fire safety systems for underground parking garages are mandatory. 

Both types – Jet and Injection – are controlled by a carbon monoxide sensor; when the presence of pollutants is indicated, the fans are activated only as needed to meet required pollution thresholds. They push the air to an exhaust port, fan, louver or ramp. The system can be zoned, so all fans do not have to operate at the same time. 

Jet/Induction Thrust fans are added to the model and positioned to distribute the airflow to all areas of the garage, ensuring removal of any stagnant areas of air. Several iterations of the model may be run to get the optimum configuration with the best airflow through the system. A detailed report of the results is produced for each project with air 

 

The new underground parking garage ventilation system includes a control unit that links all components, including the supply, exhaust and thrust fans; the carbon monoxide sensors; and the variable frequency drives (VFDs). Multiple fans can be controlled by one VFD; for example, there might be one VFD for each garage level. VFDs and CO sensors are zoned, and the fans do not have to operate 24/7. 

The Jet Thrust system has a number of benefits. In addition to its cleaner, lighter appearance, the system optimizes parking garage use, providing more parking spaces, which in turn increases revenue. 

Because the system does not require clearance for duct work, it can lower the required parking garage height by about 4 feet, reducing excavation and concrete costs and lowering overall construction costs. 

Costs for installing ductwork are eliminated, and other installation costs are also lower, because there is no more need to route around ducts. 

The system also is designed to improve system performance, due to better air distribution, and to reduce external noise levels, because lower-powered extract fans are used. Operational running costs are also reduced.