Negative and positive pressures in a building
Pressure problems in buildings are often caused by adding exhaust to remove contaminants and not providing adequate outdoor air to make up the exhaust air quantities.
Essentially the building is being put into a vacuum by the exhaust. The outside air is introduced uncontrolled through any cracks within the building structure. Cold drafts in the office, factory and warehouse spaces are then prevalent.
Outside man doors are harder to open and can become a hazard. Additionally when overhead and mandoors are opened a sudden surge of outdoor air will come into the building adding to the cold drafts.
Exhaust air is reduced when the building is closed up for the winter causing a potential health concern from the reduced air volumes to remove contaminants.
Boiler, furnace, unit heater, and process heating equipment flue gases could potentially be drawn into the space.
Installing a temperature and pressure controlled make-up air unit will bring in the right amount of air to properly pressurize with heated and/or cooled air.
You’ll be in control of your temperature and pressue while eliminating the problems assciated with negative pressure.
Positive pressures on the other hand need additional exhaust or a way of relieving the pressure. This mainly occurs when buildings are cooled with an outdoor air economizer or have 100% outside air units.
With high positive pressure, doors could open by themselves to relieve the building pressure.
Additional information to follow in the future.