Given that Australian buildings face a distinct combination of climate extremes, bushfire smoke and forced-air heating and cooling systems, the risks posed by airborne viral particles indoors differ meaningfully from what’s typically reported in US or UK facility management coverage. Claire Bird, laboratory director at Litmus, says local conditions create underrepresented challenges.
“A larger proportion of Australian cities experience milder cold seasons than those in the UK or the northern US,” Bird says. “In Australia, local buildings are designed to remain sealed to cool the air. In humid climates, the HVAC often has insufficient enough capacity to manage high outdoor air latent load and so cannot remove enough moisture from the air to prevent mould growing in buildings.”
Further, the levels of moisture in the HVAC system becomes very high for long periods of time, allowing biofilm to grow which can protect and harbour pathogens on cooling coils, drip pans and air delivery components.
Auto mode is not air cleaning
Many facility managers assume a running HVAC system is automatically removing airborne viral particles, but Bird says this misconception carries real risk.
“In reality, ‘auto’ usually means the fan operates only when there is a demand on the system for heating or cooling. Once the thermostat is satisfied, airflow may rapidly and substantially reduce or even stop. This will happen even when the room remains occupied and an occupant may have an infective illness,” she asserts. “Depending on the system, the fan may also be simply recirculating indoor air through a relatively low-efficiency filter, with little or no outdoor-air supply. In this case the reduction in risk of infection spread is very small if not negligible. Air movement is not the same as air cleaning.”
She also adds a caution about humidity control, stating, “Another common misconception is that setting an HVAC system to cooling mode will adequately dehumidify the air. Moisture is removed when air is cooled below its dewpoint, however, conventional cooling control responds primarily to temperature but rarely to humidity. The system may cycle off once the setpoint is reached while the indoor moisture load remains.”
Verified clean air over installed technology
Looking ahead, Bird expects the industry conversation to move away from which technology is installed and toward measurable outcomes.
“The main question will be shifting from inquiring about what technology is installed, or should we fit, to how much verified clean air are we delivering to the breathing zone of occupants under real operating conditions.”
She points to thermal destratification as a genuine aid in large-volume spaces, with an important caveat. “Thermal destratification and improved air mixing will probably become more common in large-volume spaces such as warehouses, halls and atria. These systems are designed to reduce stagnant air zones and hence allow aerosols to move more freely, increasing the effectiveness of ventilation or air filtration. However, destratification and increased air movement will not remove viral particles, simply improve the removal processes provided by other devices.”
