DarkRange55
Enlightened
- Oct 15, 2023
- 1,699
Commercial buildings are supposed to ideally always maintain 0.02 positive (air) pressure on a water column so you aren't pulling in dust, pollen, car exhaust, pollution, ect. Not too positive because then you're wasting energy: heating and cooling.
Hold a napkin against a door crack and see which way it blows or use a manometer, it's like a hose that goes under the door. If you see dust on the door jams then it's negative air pressure.
Clean rooms need to be positive pressure and have anti-rooms like airlocks.
Waste rooms like toxic waste and stuff need to be negative air pressure.
Exhaust ventilation on a high floor in a building with a lot of air leaks really doesn't even need a fan when it's cool enough outdoors.
The stack effect will pull air from the room all by itself. At the top of a tall building on a cold day, the pressure inside the building is higher than the pressure outside. At the bottom of the building, the pressure inside is negative. Those exhaust vents in bathrooms down at the bottom of the building probably don't get nearly as dirty. It's even possible air moves the wrong way through them. The driving forces are stack effect, wind, and mechanical systems.
Fans may not be an exhaust fans but just the opposite, fresh air or make up air induction systems. New codes require all air leaks into a home be sealed such as sealants on the joints where the sub flooring meets the wall rim base. Commercial buildings try to maintain slightly positive pressure. This sealing makes it necessary to bring in outside make up air to lessen the pressure differential between the inside and outside of a home. Things like range exhaust fans suck air out of a house, thus creating a negative pressure. Without make up air, the exhaust fans are less efficient. There are other appliances needing air, such as dryers, ovens, HW tanks, etc. A really good induction system is a DOAS or direct outside air exchanger where cold outside air is warmed by the outbound exhaust air before it's introduced into the house thus saving energy. The opposite is also possible that hot outside air is cooled by the outgoing exhaust air saving on cooling costs.
Some buildings don't have makeup air (apartments) and just aren't sealed very well so they are always operating at negative pressure.
You also have SMC (smoke clearing fans) AKA "fire fans," which exhausts smoke and pressurizes stairwells, this also repels smoke from entering them.
Hold a napkin against a door crack and see which way it blows or use a manometer, it's like a hose that goes under the door. If you see dust on the door jams then it's negative air pressure.
Clean rooms need to be positive pressure and have anti-rooms like airlocks.
Waste rooms like toxic waste and stuff need to be negative air pressure.
Exhaust ventilation on a high floor in a building with a lot of air leaks really doesn't even need a fan when it's cool enough outdoors.
The stack effect will pull air from the room all by itself. At the top of a tall building on a cold day, the pressure inside the building is higher than the pressure outside. At the bottom of the building, the pressure inside is negative. Those exhaust vents in bathrooms down at the bottom of the building probably don't get nearly as dirty. It's even possible air moves the wrong way through them. The driving forces are stack effect, wind, and mechanical systems.
Fans may not be an exhaust fans but just the opposite, fresh air or make up air induction systems. New codes require all air leaks into a home be sealed such as sealants on the joints where the sub flooring meets the wall rim base. Commercial buildings try to maintain slightly positive pressure. This sealing makes it necessary to bring in outside make up air to lessen the pressure differential between the inside and outside of a home. Things like range exhaust fans suck air out of a house, thus creating a negative pressure. Without make up air, the exhaust fans are less efficient. There are other appliances needing air, such as dryers, ovens, HW tanks, etc. A really good induction system is a DOAS or direct outside air exchanger where cold outside air is warmed by the outbound exhaust air before it's introduced into the house thus saving energy. The opposite is also possible that hot outside air is cooled by the outgoing exhaust air saving on cooling costs.
Some buildings don't have makeup air (apartments) and just aren't sealed very well so they are always operating at negative pressure.
You also have SMC (smoke clearing fans) AKA "fire fans," which exhausts smoke and pressurizes stairwells, this also repels smoke from entering them.
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