Building Pressurization and Indoor Air Quality

Building pressurization is the difference in air pressure between the inside and outside of a building. There are three types of pressure that we typically talk about: positive pressure, negative pressure, or stack pressure, and each has an affect on indoor air quality.

Positive pressure occurs when there is more air coming into the building than going out. This is often used in hospitals, laboratories, and other buildings where it’s important to keep the air inside clean and free of contaminants. The positive pressure helps to keep outside air from coming in, which reduces the risk of airborne diseases spreading.

Negative pressure is the opposite – there is more air going out of the building than coming in. This is often used in places like isolation rooms or public restrooms, where it’s important to keep contaminants from spreading to other parts of the building or to the outside environment.

Stack pressure is a result of the temperature difference between the inside and outside of a building. Warm air rises, so if the inside of a building is warmer than the outside, the air will rise and create a positive pressure at the top of the building. If the inside is cooler than the outside, the air will sink and create a negative pressure at the bottom of the building.

How Building Pressurization Affects IAQ

Building pressurization is important for indoor air quality and ventilation. According to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE),

“maintaining appropriate pressure relationships between spaces is critical to ensuring good indoor air quality and preventing the spread of airborne contaminants”
(source: ASHRAE Standard 62.1-2019).

Building pressurization affects ventilation and indoor air quality in several ways. When a building is positively pressurized, it helps to keep outside air from coming in. This can be helpful for reducing the amount of pollutants, allergens, and other contaminants that might be in the outdoor air. However, if a building is too positively pressurized, it can cause problems with the heating and cooling systems, and it can make it difficult to open doors and windows.

Negative pressure can help to remove contaminants from the indoor air and prevent them from spreading to other parts of the building or to the outside environment. However, if a building is too negatively pressurized, it can cause problems with the HVAC system and create drafts that can be uncomfortable for occupants.

Stack pressure is typically not something that we can control directly, but it can affect the way that air moves through a building. If a building is tall enough, stack pressure can help to create natural ventilation by drawing air in at the bottom and releasing it at the top.

WTI Pure Air Control Services has an entire Building Sciences division dedicated to testing, finding and making recommendations to fix building envelope related issues. Our scalable Building Health Check testing program investigates building pressurization and its affect on indoor air quality. Then, based on the findings, will provide solutions to improve the situation. A few common solutions include, better sealing of the building envelope and recalculating the ventilation rates provided by the mechanical systems. 

Building pressurization is an important factor in maintaining good indoor air quality and preventing the spread of contaminants. It’s something that building engineers and HVAC professionals need to consider when designing and maintaining buildings. For more info or to get started with a Building Health Check please contact us today.

Other Sources:

  • ASHRAE Handbook – HVAC Applications, Chapter 16: Laboratories
  • OSHA Technical Manual, Section III: Chapter 4 – Ventilation
  • EPA Indoor Air Quality Building Education and Assessment Model (I-BEAM)