ASHRAE Journal - November 2021 - 44

TECHNICAL FEATURE
in exposure to negative air ions and
respiratory function or asthmatic
symptom alleviation. Further, collectively,
the human experimental
studies do not indicate a significant
detrimental effect of exposure to positive
air ions on respiratory measures.
Exposure to negative or positive air
ions does not appear to play an appreciable
role in respiratory function. " 10
FIGURE 4 Agglomeration of fine particles by electrostatic attraction as applied in cleanrooms.
Ion
Ion
Ion
Ion
Airborne
Particle
Ion
Ion
Charged Atoms
Or Molecules
Power of Ions
The U.S. Environmental Protection Agency (EPA) has
identified indoor air quality as one of the environmental
risks to public health.13 The air we breathe may contain a
variety of contaminants such as viruses, bacteria, pollen,
dust, smoke and volatile organic compounds (VOCs). An
extensive body of scientific evidence demonstrates that
short- and long-term exposure to particle and gas pollution
negatively affects our health and well-being. The
world's leading health-related organizations consider
fine particulate matter (2.5 micrometers in diameter
and smaller) the most dangerous for humans because
they penetrate deep into the lungs and bloodstream
where they pose a threat to human health.14
Fine particulate existing within the indoor air may be
too small or lightweight to easily be removed from the
occupied space by the influence of air motion alone,
particularly at the relatively low air change per hour
(ach) rates typical of many residential and commercial
HVAC systems. These contaminants, therefore, can
remain suspended in the air for long periods.15 It may
include viral material and other pathogens as a part
of these airborne particles, which are the transport
mechanism for the transmission of respiratory infection
between individuals breathing this air. Traditional HVAC
ventilation and filtration strategies may have a reduced
impact on cleaning the indoor environment.16
Technologies that help remediate this problem, like
those used in cleanroom applications, may, therefore, be
worth consideration.
A simple concept is that if the harmful particles and
gases in the space can be removed, they are no longer
of concern to human occupants. Ionized air has been
demonstrated to be efficient at removing aerosol particles
from indoor environments. Studies have found
a significant reduction in concentrations of airborne
44
ASHRAE JOURNAL ashrae.o rg N O V E M B E R 2021
Ion
Ion
Agglomerated
Particles
Once the ions attach to the particle, the particle grows
larger by attracting nearby particles of the opposite
polarity, thereby increasing the filtration effectiveness.
particles due to the presence of ions.17 Ions, like those
already abundant in outdoor air, are artificially generated
within the HVAC system so that when released and
distributed throughout the building can mix with room
air and attach (electrostatically) to airborne particles.
As these charged particles are increasingly attracted
and joined to one another, their size and weight is
increased to the point where they are larger and heavy
enough to be more easily and quickly moved with the
HVAC system's airflow (Figure 4). They can now be more
effectively removed from the space to be exhausted, filtered
or treated. Air filters are more successful at removing
these larger particles from the air, while internally
mounted HVAC air purification devices can now address
the pollutants they have been tasked with remediating,
those which before had remained in the space.18
Bipolar ionization of the air has been used in cleanroom
applications to help reduce airborne particle
counts and create the clean indoor environments for
critical pharmaceutical, health-care, semiconductor,
food processing and manufacturing processes.19
Studies20 have demonstrated that air ionization is effective
at removing aerosols and particles from the environment,
providing significant reductions in particulate
concentrations. Bipolar ionization has also been studied
and shown to be effective at both increasing the filtering
rate of aerosolized pathogens as well as effectively
increasing the decay of certain viruses and pathogens in
testing.18-23
Ions in Buildings
On Nov. 11, 2020, Purdue University College of
Engineering hosted a webinar24 in which experts in the
built environment addressed a variety of issues relevant
to virus transmission and mitigation in buildings specific
to SARS-CoV-2. Discussed was the issue that viruses
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