Industry experts are increasingly advocating for increased ventilation in buildings to reduce the airborne transmission of diseases. In technical terms, this involves increasing the air exchange rate by introducing higher volumes of outside air and exhausting it mechanically or naturally. While this effectively dilutes bioaerosols and pathogens, the implementation of such strategies carries significant technical and environmental risks if not managed with precision.

Infrastructure and Design Constraints

The ability to increase ventilation is often restricted by existing building infrastructure. Many facilities housing sensitive populations, such as school classrooms, childcare centres, and aged care facilities, rely on non-ducted reverse cycle air conditioning with no outside air component. These buildings depend on natural ventilation through the opening of doors and windows, which is difficult to regulate and entirely dependent on outdoor conditions.

Even in buildings with ducted systems, the volume of outside air is limited by the original mechanical design and the climatic region. Introducing excessive outside air can lead to:

• Substantial increases in energy consumption.
• An inability to maintain thermal comfort for occupants.
• A loss of humidity control within the occupied space.
• The introduction of outdoor pollutants, such as smoke from fires or seasonal allergens, which necessitates high-quality filtration that further increases energy costs due to higher static pressure.

The Microbial Challenge: Humidity and Condensation

The most significant risk associated with increased ventilation is the potential for widespread microbial contamination. This is particularly problematic in climatic regions with prolonged periods of high ambient humidity, including Sydney and the East Coast of Australia, Darwin, and northern regions like Karratha and Port Hedland.

When warm, humid outside air is introduced, the air conditioning plant must work significantly harder to cool the building, resulting in lower coil temperatures. This interaction creates excessive condensation. If a system lacks the capacity to remove this excess moisture, it leads to two primary failure points:

1. Condensate Carry-Over: Moisture is physically blown or sucked off the cooling coils, wetting downstream components.
2. Porous Insulation Contamination: Most internal surfaces of air handling systems and initial lengths of supply ducts use porous insulation. When this insulation becomes wet, it provides the ideal conditions for the proliferation of mould and bacteria.

Strategic Management and Monitoring

If the air conditioning system cannot effectively remove moisture from the incoming air, highly humid air passes into the building, leading to condensation and subsequent mould growth on interior surfaces and contents.

To make existing building stock safer without compromising structural integrity or indoor air quality, a smart approach is required. This involves the use of electronic sensor packages to continuously monitor air quality parameters both indoors and outdoors. By using real-time data to govern ventilation rates, building operators can balance the need for air exchange with the necessity of moisture control, preventing the systemic microbial issues that arise from unmanaged humidity.