Exhaust Fan Negative Pressure

Exhaust fans or smoke ejection fans use negative pressure to remove smoke from a structure during firefighting efforts.

Exhaust fan negative pressure.

Like combustion appliances exhaust fans can remove too much air and cause negative air pressure. How exactly does air pressure get out of balance. A pressure differential between the duct and the atmosphere will cause the water level in the manometer legs to rest at different levels. When should negative pressure ventilation be used.

It the fan moves 200 cfm then 1 970 200 9 85. Ventry fans are not exhaust fans. When retrofitting a standard patient room for use as a negative pressure isolation room it is not often practical to exhaust the air directly outdoors as required. The article will analyze negative pressure ventilation systems in maintaining air quality house temperature and air movement.

The more airtight the house the bigger that negative pressure will be. Divide your answer by the system airflow in cubic feet per minute. Let s put some numbers to that idea. The exhaust fan drawing below illustrates how static pressures are measured in ductwork with a manometer.

Positive pressure is simply more effective than negative pressure for aggressive coordinated attack. My house currently has a blower door test result of 5 200 cubic feet per minute at 50 pascals of pressure difference 5 200 cfm50. Most homes have at least one negative pressure room. The air blowing into the house would increase air pressure and force the smoke out of the rooms.

Exhaust fans in your bathrooms and kitchen of course will induce some negative pressure. Ventry fans are designed for positive pressure ventilation ppv and attack ppa. The negative pressure created by the exhaust fans is really something we have to worry about. When a bathroom door is closed if the bathroom has a quality working fan unpleasant odors as well as moisture and humidity are vented out through the fan because the forced air ventilation creates a negative pressure room.

Warm air in your building rises to the upper floors and can result in negative air pressure in the. Conversely if the smoke was localized then we would place the fan about 6 from the door on the inside of the house facing out thus creating a negative pressure in the house. Negative air pressure should create a slightly cooler environment at least in theory as the fans are working harder to expel hot air. Static pressure in fan systems is typically less than 2 sp or 0 072 psi.

Both approaches have their advantages.