Initial air-stream adjustment is vital to the startup and successful operation of air doors and curtains. Without proper equipment adjustment, the benefits of the air door/curtain will be lost. Only air-stream adjustment and readjustment as part of proper O&M will create an effective air barrier.
When properly adjusted, the air stream will be split into two paths at floor level, one path blowing to the exterior and the other path to the interior conditioned space. It is the splitting of this air stream that creates the effective thermal barrier.
The procedure for the air stream adjustment is as follows:
Verify that there are no obstructions hindering the airflow with the air door/curtain operating and the doorway opening fully open.
Use a handkerchief to locate the air stream split, as shown in photos B and C. The air stream split is the area near the floor where the air stream from the air door is split to the inside and outside of the doorway opening. The air stream split is located by holding the handkerchief approximately 12 in. from the floor and moving the handkerchief back and forth in the doorway opening. The handkerchief will remain vertical with minimal fluttering when the air stream split is located.
Adjust the nozzles on the air curtain until the split is located approximately 3 in. outside the doorway opening.
The average angle for the discharge air stream is approximately 15 degrees.
Cleaning air doors and curtains is just as important as cleaning any other HVAC unit, if not more so for several reasons. The build up of dust and dirt will result in excessive vibration and noise and could lead to premature equipment failure. In addition to the mechanical problems from poor maintenance practices, there is also an aesthetics problem. Unlike most HVAC equipment, air doors and curtains are typically visible to the general public in a retail space. The unsightly build-up of dust and dirt from the air curtains intake grille will create a bad perception of the business.
Air doors and curtains are typically cleaned once every six months. However, if the air curtains are in an extremely dirty and dusty environment, clean them every other month.
An air door with an air stream that fails to hit the floor is the most common problem with these units. A typical cause is a weak or obstructed air stream. To solve the problem, adjust the nozzles or motor speed as described above and in parts 1 and 2 of this series.
Another typical cause of this problem is negative building pressurization. The simplest solution is to adjust the makeup air to pressurize the building.
Another common problem is excessive air movement in a doorway opening. The likely cause is an air-stream split that is not adjusted properly. If the handkerchief test determines that this is the problem, adjust the air stream to approximately 3-in. on the exterior opening as described earlier in this article.
Another possible cause of excessive air movement is that the outside air is too cold, in which case an auxiliary heat source should be added to the air door. Last month's article on air-door installation detailed why it is a good idea to equip all air doors with auxiliary heat sources.
Brad Morris, PE, is the manager of M/E/P/R engineering for AETOS Construction, a division of the Giant Eagle Corp. in Pittsburgh. He has 11 years of experience in the chemical and mechanical engineering fields. He can be reached at [email protected].