Ventilation often accounts for 20%–40% of HVAC energy, yet most buildings verify outdoor-air supply once, i.e., at design or commissioning, rather than in the occupied zone. Too little outdoor air degrades indoor air quality and raises the risk of infection and reduced cognitive performance; too much locks in heating and cooling load for the life of the plant. Without a room-level measurement, the delivered rate is unknown, and operators gamble between waste and stale air. Humans cannot smell carbon dioxide or see respiratory aerosols, and they adapt within minutes to the odors they can detect, so occupants never generate the complaint signal that produced thermostats and smoke detectors. A century of chamber science was frozen into prescriptive per-person and per-area ventilation rates; a dedicated mammalian olfactory pathway for near-atmospheric CO₂ was lost in haplorrhine primates, and many burrowing species became tolerant of high CO₂ rather than better at metering it. A smoke-detector-class sensor in each occupied zone, coupled to dampers and to a dual performance rule, i.e., breathing-zone CO₂ together with measured ventilation energy or heat-recovery effectiveness, would close that loop. Until outdoor air is metered where people breathe, claims that a building is both efficient and healthy remain hypotheses.

During the coronavirus disease 2019 pandemic, short-range virus transmission has been observed to have a higher risk of causing infection than long-range virus transmission. However, the roles played by the inhalation and large droplet routes cannot be distinguished in practice. A recent analytical study revealed the predominance of short-range inhalation over the large droplet spray route as causes of respiratory infections. In the current study, short-range exposure was analyzed via computational fluid dynamics (CFD) simulations using a discrete phase model. Detailed facial membranes, including eyes, nostrils, and a mouth, were considered. In CFD simulations, there is no need for a spherical approximation of the human head for estimating deposition nor the "anisokinetic aerosol sampling" approximation for estimating inhalation in the analytical model. We considered two scenarios (with two spheres [Scenario 1] and two human manikins [Scenario 2]), source–target distances of 0.2 to 2 m, and droplet diameters of 3 to 1,500 μm. The overall CFD exposure results agree well with data previously obtained from a simple analytical model. The CFD results confirm the predominance of the short-range inhalation route beyond 0.2 m for expiratory droplets smaller than 50 μm during talking and coughing. A critical droplet size of 87.5 μm was found to differentiate droplet behaviors. The number of droplets deposited on the target head exceeded those exposed to facial membranes, which implies a risk of exposure through the immediate surface route over a short range.

Many common respiratory infectious diseases transmit readily among school-age children. In major epidemics, school closures and class suspensions may be implemented to attempt to control transmission in the community. However, such intervention measures have been subject to an extensive debate as well as questions of its effectiveness and adverse social impacts. In the meanwhile, engineering intervention methods are also available, but their impacts at the community level were not well studied. A better understanding of how different school interventions contribute to the airborne disease prevention can provide public health officials important information to design infection control strategies, in particular how engineering control methods such as ventilation are compared to other intervention methods. In this study a hypothetical indoor social contact network was constructed based on census and statistical data of Hong Kong. Detailed school contact structures were modeled and predicted. Influenza outbreaks were simulated within indoor contact networks, allowing for airborne transmission. Local infection risks were calculated from the modified Wells-Riley equation, and the transmission dynamics of the disease were simulated using the SEPIR model. Both school-based general public health interventions (such as school closures, household isolation) and engineering control methods (including increasing ventilation rate in schools and homes) were evaluated in this study. The results showed that among different school-based interventions, increasing ventilation rate together with household isolation could be as effective as school closure.