Why is it crucial to maintain a slight positive pressure in commercial HVAC systems?

Maintaining a slight positive pressure in commercial HVAC systems is primarily crucial to prevent the entry of contaminants. Positive pressure helps ensure that airflows into the building rather than allowing unconditioned air—often laden with pollutants, dust, and allergens—from infiltrating through gaps, cracks, or openings in the structure. This controlled environment is especially important in settings like hospitals, laboratories, and cleanrooms, where air quality is critical for health and safety.

By keeping the pressure slightly higher inside the building compared to the outside, the system effectively acts as a barrier. This is particularly beneficial in areas that require stringent air quality standards, as it helps to mitigate issues related to indoor air pollution. The focus on air cleanliness and occupant health underscores why maintaining positive pressure is a key aspect of HVAC system design and operation.