Airflow in buildings can be extremely complex, with time-dependent and multi-directional variables. The operation of mechanical cooling, heating, exhaust, in addition to other ventilation systems can have an enormous impact on pressure. Still, interstitial airflow and interstitial air pressure fields are often overlooked during planning, construction and HVAC implementation.  

Proper pressurization of buildings is crucial to indoor air quality (IAQ) management, maintenance of occupant health and comfort, not to mention maximizing energy efficiency. Lack of building pressurization management can allow infiltration of moisture, constant drafts in extreme weather and difficulty with doors at entrances and exits.

Air Pressure and Building Performance

Indoor air escaping from a building can affect pressurization, as will outdoor air entering into the building. Both instances can cause changes in indoor air quality, thermal comfort, HVAC efficiency, building energy costs and more. 

Infiltration and Exfiltration  

When a building’s internal pressure is less than the external pressure, it becomes possible for untreated outdoor air to infiltrate, or leak into, the building. Typically control strategies are implemented to prevent infiltration, thereby minimizing HVAC loads and reducing related operating costs. A small amount of infiltration in winter can help reduce moisture condensation. However, during the cooling season, infiltration of warm, moist air can increase latent loads and negative pressure can become excessive. 

When the indoor pressure is greater than the pressure outside, it becomes possible for conditioned indoor air to exfiltrate, or leak out of, the building. Exfiltration in summer months of cool, dehumidified indoor air can provide some benefit to the building by keeping the envelope dry. However, excessive positive pressure can impede supply airflow, cause imbalances in building temperatures and encourage noisy, high-velocity airflow around apertures (in addition to condensation on cold surfaces inside walls during the heating season).  

While excessive building pressure should be avoided whenever possible, a neutral pressure level (NPL), can be almost impossible to achieve, since building pressurization is a result of the combined effect of weather, wind and HVAC operation.

Are the System Controls Easy to Use?

The user experience is crucial and should be considered part of the design. Ideally, lighting will be fully automated and connected to the building management system. Using the Internet of Things (IoT), sensors can track usage and efficiency and complete predictive maintenance to help keep your system working at optimal capacity.