ASHRAE Journal - November 2022 - 24

COLUMN IEQ APPLICATIONS
To add to the already complex
equation, we also need to incorporate
the health consequences-both
beneficial and harmful-of the
microbes that reside in buildings.
The community of viruses, bacteria
and fungi, collectively known as the
building microbiome, is a constantly
evolving ecosystem shaped by the
use of spaces, surface materials and
IAQ. Most importantly, the building
microbiome has a direct relationship
with the human microbiome-a
cornerstone to human health or
disease. Understanding and quantifying
the interactions between
thermal metrics, indoor air pollutants
and both human and microbial
occupants is clearly not an easy task.
Nevertheless, it is now possible!
Implementing Building Management for Health
IAQ impacts human immune
protection and microbial infectivity
(Figure 3). We now know that IAQ
can support or harm the ability of
our immune system to protect us.
For example, low relative humidity
(less than 40%) impairs the ability
of our respiratory mucosa to resist
infection by harmful bacteria and
viruses.1 Often a misconception
exists that it takes hours to days
for IAQ to impact our respiratory
tract. This is wrong. In less than 15
minutes of exposure to low relative
humidity (RH less than 40%), detectable
injury to the cells lining our
sinuses, upper airways and exposed
skin occurs.2
If occupants are simultaneously
exposed to particulate matter and
other compounds such as ozone
or combustion by-products, harm
to the respiratory tract is compounded.3
To further complicate
the picture, poor IAQ can contribute
to beneficial microbes becoming
pathogenic microbes.4
And how does this work? The multitude
of good microbes in and on
each of us form a line of defense on
our skin, in our respiratory tract,
intestines and vagina (if you have
FIGURE 3 IAQ managed for human health supports protective occupant immunity
and a beneficial building microbiome. The opposite is also true: IAQ not managed
for health impairs human immunity and fosters transmission of infectious, pathogenic
microbes.
one) that protects us from invasion
by pathogenic microbes. By competing
for nutrients, secreting chemicals
and other strategies, microbes,
paradoxically, keep infectious
pathogens in check. This balance is
disrupted when, for example, we
take antibiotics. It is also disrupted
when an environmental trigger
either reduces the function of our
immune system or increases the
virulence of a specific microbe.
No single genetic or cell characteristic
differentiates families of
beneficial microbes from harmful
pathogens. Instead, microbes
adapt to their environment through
genetic mutations or alterations in
cell characteristics as they evolve
to survive changing conditions. If
an adaptation to survive in indoor
conditions results in a microbe penetrating
human tissues and bypassing
immune defenses that normally
prevent allergies or infection, the
bacteria, virus or fungi shifts from a
helpful microbe to a disease-causing
pathogen. To effectively limit microbial
adaptations that result in occupant
illness, we need to understand
and limit the indoor environmental
forces that drive this change.
Biodiversity is essential in any
ecosystem. For example, one species
may be severely harmed by an environmental
threat, but another may
not be. Therefore, a biodiverse garden-or
microbiome-will be more
stable than a low-diversity ecosystem
in the face of environmental
threats. Even if certain species are
affected, the ecosystem as a whole
can better adapt and survive.
The next question is how environmental
factors drive a decrease
in building microbiome diversity
and an increase in pathogens? An
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ASHRAE Journal - November 2022

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