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Gravity Ventilation Systems

Natural draft or gravity ventilation systems represent one of the oldest and most common methods of obtaining fresh airflow to an enclosed space. Industries around the world are discovering the physical and financial advantage to free flow ventilation. Physical effects such as the temperature differential between inside and outside are, wind speed, and the height between the center of the air inlets near the floor and the ventilator at the roof level all contribute to a natural convection effect. The primary purpose of a natural flow system is to use natural forces to introduce cool outside air into the occupancy level of a building, while exhausting heated and contaminated air. When outside air is introduced into the building via louvers or fans, the heat produced within the building rises due to its reduced specific weight and Western Gravity Ventilators on the roof provide an opening for the heated air to pass through.

The widest application for Gravity Ventilation occurs in manufacturing and industrial processes which generate large amounts of heat. The metals industry is a prime example and the use of natural flow ventilation is used extensively in aluminum reduction, steel making or rolling, and heat treating operations. The glass and rubber industry, as well as fossil fueled electric generating plants, are other operations which utilize this specific type of ventilation. In addition natural flow systems have had widespread use in general manufacturing plants for both pressure relief, general building ventilation, and emergency heat and smoke venting. Before deciding to use a gravity or natural flow system, we recommend careful evaluation to insure a successful application. Items to be considered include:

• The vertical distance between the exhaust air roof opening and the center line of the intake air openings, or stack height should be more than ten feet.
• The intake air openings should be located as close to the operating floor level as possible.
• The free area of the available intake openings should be greater than the roof ventilator throat area; normally a ratio of 1.5 to 1 will be the optimum. Keeping the exhaust opening at the top of the building as the point of maximum restriction, helps to insure that a positive pressure will be created in the upper portion of the building.
• The heat released in the building should be sufficient to provide a moving force to maintain the desired change rate.
• Inlet openings should be distributed uniformly about the building and care should be taken that they are not obstructed by exterior buildings, topography, interior partitions, or equipment.

Where special building characteristics or high and concentrated heat sources exist, the Western Canwell staff will utilize the heat removal method of calculation. We would be happy to provide you with more statistical data and information pertaining to your specific ventilation requirements. We also have product specifications and drawings available upon request. Please contact us through the below listed information or by completing our online Information Request Form.