Building a negative pressure room9/9/2023 ![]() The primary benefit of a positive pressure environment is that the location of the supply air can be controlled to prevent infiltration of air borne contaminates. Use the same process for sizing louvers and keeping doors open in a positive pressure environment. When there is too much resistance to the exhaust air flow, a potentially dangerous level of positive pressure can build causing man doors to slam open or closed. The same issues apply regarding using louvers and doors for exhaust air in a positive pressure environment as they do to providing supply air in a negative pressure environment. When the supply fans are on, they will have an effect on the building like blowing up a balloon. Positive PressureĪ positive pressure environment is created by using fans for supply air and louvers or doors for exhaust air. Another downside to negative pressure systems is they will bring in outside dust and contaminants into the building because the system is basically pulling from outside into the building. Because air will follow the path of least resistance, if there are other openings or cracks too close to the exhaust fan, the air will short circuit from the opening to the fan without providing any benefit. While it may be the intention for the supply air to come in through louvers or doors, the reality is that the air will also come in through other openings or cracks in the building. One downside to a negative pressure system is that the location of supply air can’t be absolutely controlled. The second benefit is that a negative pressure system will keep the heat and contaminants from infiltrating adjoining locker rooms, break rooms or offices. Locating the exhaust fans in the right spot can pull the heat and contaminants away from people, products, or processes. This is important when there are heat, fumes or dust generating sources inside the building. ![]() The first is that the location of the exhaust air can be controlled. One way to avoid a dangerous pressure level is to have a backdraft damper installed in the space that will relieve the pressure when all doors are closed.Ī negative pressure ventilation system has two benefits. If all doors are closed, then a potentially dangerous negative pressure level could develop. ![]() When man or truck doors are intended to be the primary source of supply air, then there should be an operating policy that requires one or more of the doors to be open when the exhaust fans are running. Most manufacturers provide charts that will show the pressure drop relative to the face velocity for their louvers. When louvers are used in the supply air openings, the amount of open area in the louver should be sized to keep the air velocity at the face of the louver below a level that causes a dangerous amount of negative pressure. Too much negative pressure may cause man doors to slam open or closed creating a risk for injury if fingers are caught in the door. The amount of negative pressure created in the building depends on the air flow resistance created by the supply openings. When the exhaust fans are on, they create a vacuum in the building which pulls air in through the supply air openings. ![]() Negative PressureĪ negative pressure environment is created by using fans for exhaust air and louvers or doors for supply air. In this week’s blog I’ll discuss the benefits of both, the factors that should be considered, and how the ventilation equipment should be sized to achieve the desired positive or negative pressure. ![]() When designing an industrial ventilation system, an important design criterion is determining whether the facility requires a positive or negative pressure environment to protect people, products, and processes. ![]()
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