Booster Fans:

When is a booster fan required?
When the duct distance to the filter exceeds 50 feet or when the exhaust from the filter exceeds 50 feet, a fan should be considered.

What is a normal booster fan installation? 
Laundries in the basement of multi-story buildings often require booster fans to lift the exhaust up many floors to exhaust onto the roof.

What type of fan is standard? 
Usually a tubeaxial round duct fan is used, one that pulls the same amount air as the total dryer exhaust.

Where is the fan usually mounted?
It is normally mounted in the duct after the filter, just before the exhaust leaves the facility to the outside.

What happens when the fan is on and several of the dryers are off? 
The higher fan pull will create negative pressure at the filter – this must be eliminated.

How can I recognize a negative pressure problem? 
The lint bag is sucked up into the filter. In normal operation, the necessary minor positive pressure “puffs” the bag out.

How can the negative pressure problem be cured? 
One way to eliminate negative pressure is to install a variable speed control on the fan that adjusts the fan speed for the number of dryers that are operating. While optimum, this is can be an expensive solution. Another solution is a simple barometric damper door just above the filter outlet that will pull in outside air to balance the reduced dryer exhaust.

What is a barometric damper?
It is a simple weighted, hinged door that opens and mixes air from the room to balance the exhaust air as dryers turn on and off. Remember, this method draws air from the laundry room that may have been heated or cooled.

Note: 
In instances where the exhaust is into a multistory common duct serving other airflow purposes the pull of the air, or the pressure of the air column can cause filter problems. This has been a problem where the air is ducted into a common duct that serves other air movement requirements. Note that on cruise ships the air is exhausted over 10 stories and the other air requirements cause major negative pressure at the filter. Notify Energenics of any of this type installation so we can work with the architect to insure optimum dryer filter performance.