ASHRAE Journal - November 2022 - 23

COLUMN IEQ APPLICATIONS
FIGURE 1 Indoor air pollutants affect cell membranes and organs in predicatable
ways, allowing quantification of the health impact of single and combined compounds
and thermal metrics.
equation, developed in 1978 following
an outbreak of measles in
an elementary school. Based on the
concept of a " quantum of infection, "
this model predicts the number of
infectious droplet nuclei required
to infect ~63% of susceptible persons
in an enclosed space. Almost 50
years later, the model is still used to
evaluate the effi cacy of ventilation,
fi ltration, humidifi cation and air
cleaning in the removal of infectious
airborne viruses.
While limiting indoor exposure
to airborne viruses is clearly an
important step in controlling disease
transmission, it is only half of
the equation. The other key variable
is the susceptibility of the exposed
human, which is determined by the
protection by their immune system.
We now know that IAQ directly
impacts the effi cacy of immune
defenses of the respiratory system.
Beyond the current pandemic, we
know that IAQ affects the incidence
FIGURE 2 Key dimensions for a health standard include the relationships between
IAQ building microbial communities (the microbiome), overall occupant physiological
functioning and conditions passed on to our children through epigenetics.
of many acute and chronic diseases.
Because humans reside indoors
most of the time, it is essential that
building professionals manage
IAQ to support, or at least to not
harm, the physiology of building
occupants.
Thankfully, we now have tools
from medicine, microbiology and
building chemistry that can correlate
occupant health and indoor
exposure to sensible and latent
(humidity) heat, gases, inert particles
and bioaerosols. Reasonably
affordable genetic analysis tools
reveal DNA and RNA fi ngerprints of
bacteria, viruses and fungal organisms
in and on our body, as well as
on surfaces and in the air in buildings.
Electronic medical records
store patients' heartbeat rhythms,
serum chemistry panels and blood
cell counts. Building occupants can
wear nonintrusive wearable devices
to record their biometrics that indicate
physiological changes associated
with stress and some illnesses.
IAQ composition can be continuously
monitored throughout changing
seasons and climatic events. And
fi nally, computers can analyze these
large data sets and draw statistically
signifi cant and actionable conclusions
(Figure 1).
Moving from IAQ Exposures to Health
Impact Requires an IAQ Health
Standard
To accurately manage IAQ so as
to optimize immunity, decrease
infl ammation and increase learning
and productivity in occupants, we
need an IAQ health standard based
on medical data. Managing indoor
spaces for occupant health requires
combined " traditional " HVAC metrics
and medical data (Figure 2).
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ASHRAE Journal - November 2022

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