Other, more drafty or leaky buildings may require up to 300 CFM. Some buildings require as little as 45 CFM per 1000 SqFt. Same concept – more suction/blowing power is needed to pull more air through more filters or finer filters.Īnd how tight or leaky a building is will determine the amount of air per cubic foot per minute to inflate the building envelop (balloon). Now, let’s imagine a person sucking the same milkshake through a very large straw. This is like sucking a milkshake through a straw with a tiny diameter. So the more robust the HVAC system will need to be. The more fine the filter media the more force required to pull the air across it. HVAC systems pull air from a fresh air duct and through various types of filters. Since it is not being pulled from undesirable sources like unfiltered air via doors and windows – it must be pulled from an outside source across a filtration system. To keep a building pressurized requires air to be drawn into the building to create the positive pressure. Keeping the air fresh in a positive pressure building requires precise engineering. These particles entering the building and affect the people working in the building and the general cleanliness of the building. That unfiltered air brings with it pollen, dust, dirt, biological and chemical particulates, etc. The problem with negative pressure is that once a door or window is opened – any exterior air is permitted to enter the building. If the air pressure in the building is greater than the air pressure outdoors, it is called a “positive pressure room” or “positive air pressure building.” Conversely, if the pressure inside the building is less than the pressure outdoors, the room or building is said to have “negative pressure.” Generally it is not desirable to have negative pressure inside a building. This air moving into or out-of a building is due to the pressure differential. That air can be likened to deflating a balloon – the pressure in the balloon seeks to deflate to an area of lower pressure – so the balloon air rushes out. In most commercial buildings, when the automatic door opens you typically feel a rush of air exiting the building. You probably experience this when you enter a commercial building. It ensures that dust, dirt and debris introduced into a building is “pushed” back out once a door or window is opened. In short, this means there is greater or “higher” pressure inside the building than that of the outside atmospheric resting pressure. Most buildings attempt to maintain an environment of positive air pressure. Poor Building Air Pressurization = Poor Air Quality In any case, the inability to create or maintain a homeostatic building pressurization can cause a multitude of issues. Even something as simple as not changing air filters in the HVAC blowers can affect the pressurization of a building. Natural degradation of building materials and/or poorly functioning HVAC systems is another albeit this may take years to be noticible. Abnormal foot traffic patterns, causing doors to be opened more than anticipated is one of the more obvious ways. There exists many unaccounted for variables that affect a buildings air pressure which can cause it to function much differently than the way it was originally designed or engineered. The reason for this is simply that, there are a lot of variables that can affect a building’s air pressure that can not be accounted for. In commercial construction, one often overlooked aspect of planning and design is keeping a building in a homeostatic state in terms to air pressurization.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |