The principle of using a current of air as an invisible “barrier” between hot and cold zones in entrance areas originally comes from Europe where advanced heated duct systems are constructed using powerful blower fans in the ceiling and extraction grids in the floor. These systems are often energy inefficient, expensive to install and operate. Enershield Air Barriers have evolved this concept to give maximum efficiency, minimal costs and simple installation.
An Enershield Air Barrier creates an effective seal on the doorway by re-circulating facility air in a smooth laminar flow, preventing the penetration of outdoor air. The air velocity from the Air Barrier must be great enough that the resulting air velocity is directed downwards. The Air Barrier should be set so that a small part of the air stream is directed out of the opening, while the rest blows into the premises. In this way, the cold outside air is kept out, while the warm indoor air is kept inside.
The energy loss through an open door depends on
- the pressure difference between outside and indoor
- the temperature difference between outside and indoor
- the wind forces on the door opening
In premises where ventilation systems are installed, it is vital that the system is balanced (same amount of air taken out as put in) in order to reduce the pressure difference over the door openings.
The less-dense indoor air and the denser outdoor air generate a pressure distribution (b). The cold air flows in through the lower part of the door while the warm air out through the upper part. The overall airflow increases according to the temperature difference. When the wind blows against the door, air flows into the building in a current that is equally large in the whole opening (a). The total airflow through the door is the sum of these effects (c).
How An Air Barrier Works
Air Barriers have a fan that generates a large airflow that blows across an open doorway. The kinetic energy in the moving air generates a barrier, like a waterfall, that prevents leakage of air between two areas with different pressure and climate. The more laminar (smooth) this airflow, the harder it is for the outside air to penetrate the air steam. The strength of the Air Barrier follows the formula: mass times the velocity squared. Therefore an Air Barrier that blows at twice the speed has four times the wind stopping capability at the same air volume.
Approx. 10-15 % of the airflow should be directed outwards into the open air. This “loss” is necessary to prevent cold draught by the floor as illustrated (c). Air velocity by the floor should be approx. 800 ft/min (3-4 m/s). Use a handkerchief to determine the split location as illustrated in the diagram below.
Approx. 10-15 % of the airflow should be directed outwards in order to prevent cold draught by the floor. To find the airflow’s split location hold a handkerchief by the corner approximately 2-3 inches above the floor and move it gently back and forth in the doorway. The split location should be in the middle of the doorway or a little outside.
Savings and Comfort
Open doors account for a considerable amount of energy loss in a building. A correctly installed Air Barrier can reduce heat loss through the door as much as 90 %. An Air Barrier prevents cold draught that allows facilities to keep their doors open for extended periods in wintertime, creating a more comfortable work environment thus saving a substantial amount of energy. It has also proved beneficial in certain situations to enhance manufacturing processes where atmosphere and temperature are critical.
In the summertime, Air Barriers can be used in order to keep hot air, dust and insects out. These units are often installed in connection with refrigerated rooms and coolers.
Enershield offers a series of models specially made for these various applications.