ASHRAE Journal - September 2021 - 43

TECHNICAL FEATURE
various bacteria, fungi and viruses.33 Studies have
shown that AgNP concentrations between 10 ppm and
100 ppm have antiviral effect.33 Jeremiah, et al., found
that concentrations between 1 ppm and 10 ppm were
able to inhibit SARS-CoV-2.33 Regulations for AgNP are
still in development with the current NIOSH recommended
exposure limit for silver metal dust and soluble
compounds at 10 µg/m3 as an eight-hour time-weighted
average airborne concentration.34,35 This limit was
developed to protect against argyria and argyrosis.34
Additional Methods
In addition to the methods listed above, several other
methods have been proposed that still need to be vetted
for applicability and performance. A few are below.
Vacuum UV (VUV) has been proposed as a method
to inactivate airborne viruses. A study by Kim, et al.,
showed a 90% inactivation effi ciency for MS2 viruses
under a VUV irradiation time of 0.009 seconds using a
photocatalysis process.36 It should be noted that VUV
produces ozone that would have to be mediated.
Enzyme fi lters can eradicate microbes by attacking the
microbial cell membrane if they come into close contact
with the microbes. However, the adhesion of particles
over time on the fi lter surface can prevent the close
contact between the enzymes and microbes on the fi lter
and reduce its performance.37 Preliminary studies have
shown little difference in performance between fi lters
with and without enzymes.37
Desiccant rotors have been adapted for indoor air cleaning.
Silica gel rotors were shown in testing to provide high
air cleaning effi ciency (94% or higher for VOCs), which
could be applied to virus mitigation as well.37
Research on essential oils and their effect on microbes
has been a topic of study for many years. However,
ambiguity in the research makes the reproducibility of
many of these tests diffi cult.38 Brochot, et al., found that
an essential oil blend produced a 99% reduction in H1N1
and HSV-1 with a 60-minute contact time.39 Since some
of these essential oils may also be toxic to human cells or
cause hypersensitivity reactions in some occupants, further
research needs to be done.37
Conclusions
This series of articles in the March, April, August41-43
and this issue of ASHRAE Journal has looked at viruses and
their release into a space, the effect of environmental
factors such as temperature and humidity, the effect of
the air distribution system on the propagation of droplet
nuclei and several common and less common mitigation
techniques applicable to single zone systems. Traditional
approaches to virus mitigation like ventilation and fi ltration
generally have the most research in favor of their
effi cacy. However the operational and maintenance
cost of these approaches have made many people look
toward other technologies for answers. It is clear that
more research and innovation are still needed in many
of these cases to determine effi cacy in the actual space
and the long-term health benefi ts and risks when using
this technology.
References
1. ASHRAE. 2021. " Filtration/Disinfection. " ASHRAE. www.
ashrae.org/technical-resources/fi ltration-disinfection
2. AHAM. 2020. ANSI/AHAM AC-1-2020: Method for Measuring
Performance of Portable Household Electric Room Air Cleaners.
Association of Home Appliance Manufacturers.
3. Shaughnessy, R.J., R.G. Sextro. 2006. " What is an
effective portable air cleaning device? A review. " Journal of
Occupational and Environmental Hygiene 3(4):169 - 181. https://doi.
org/10.1080/15459620600580129
4. EPA, Indoor Environments Division. 2018. " Residential Air
Cleaners-A Technical Summary: Portable Air Cleaners Furnace
and HVAC Filters. 3rd Ed. " EPA 402-F-09-002. United States
Environmental Protection Agency. https://tinyurl.com/byrzytdh
5. Foarde, K. 1999. " Methodology to perform clean air
delivery rate type determinations with microbiological
aerosols. " Aerosol Science and Technology 30(2):235 - 245. https://doi.
org/10.1080/713834074
6. Miller-Leiden, S., C. Lobascio, W.W. Nazaroff, J.M. Macher.
1996. " Effectiveness of in-room air fi ltration and dilution
ventilation for tuberculosis infection control. " Journal of the Air &
Waste Management Association 46(9):869 - 882. https://doi.org/10.1080
/10473289.1996.10467523
7. Qian, H., Y. Li, H. Sun, P.V. Nielsen, et al. 2010. " Particle
removal effi ciency of the portable HEPA air cleaner in a simulated
hospital ward. " Building Simulation 3:215 - 224. https://doi.
org/10.1007/s12273-010-0005-4
8. Reed, N.G. 2010. " The history of ultraviolet germicidal
irradiation for air disinfection. " Public Health Reports 125(1):15 - 27.
https://doi.org/10.1177/003335491012500105
9. Brickner, P.W., R.L. Vincent, M. First, E. Nardell, et al.
2003. " The application of ultraviolet germicidal irradiation
to control transmission of airborne disease: bioterrorism
countermeasure. " Public Health Reports 118(2):99 - 114. https://doi.
org/10.1093/phr/118.2.99
10. Zhu, S., J. Srebric, S.N. Rudnick, R.L. Vincent, et al. 2013.
" Numerical investigation of upper-room UVGI disinfection effi cacy
in an environmental chamber with a ceiling fan. " Photochemistry and
Photobiology 89(4):782 - 791. https://doi.org/10.1111/php.12039
11. Beggs, C.B., E.J. Avital. 2020. " Upper-room ultraviolet air
disinfection might help to reduce COVID-19 transmission in
buildings: a feasibility study. " PeerJ 8:e10196. https://doi.org/10.7717/
peerj.10196
S E P T E M B E R 2 0 2 1 ashrae.o rg ASHRAE JOURNAL
43

http://www.ashrae.org/technical-resources/filtration-desinfection http://www.ashrae.org/technical-resources/filtration-desinfection https://doi.org/10.1080/15459620600580129 https://doi.org/10.1080/15459620600580129 https://www.tinyurl.com/byrzytdh https://doi.org/10.1080/713834074 https://doi.org/10.1080/713834074 https://www.doi.org/10.1080/10473289.1996.10467523 https://www.doi.org/10.1080/10473289.1996.10467523 https://doi.org/10.1007/s12273-010-0005-4 https://doi.org/10.1007/s12273-010-0005-4 https://www.doi.org/10.1177/003335491012500105 https://doi.org/10.1093/phr/118.2.99 https://doi.org/10.1093/phr/118.2.99 https://www.doi.org/10.1111/php.12039 https://www.doi.org/10.7717/peerj.10196 https://www.doi.org/10.7717/peerj.10196 http://ashrae.org

ASHRAE Journal - September 2021

Table of Contents for the Digital Edition of ASHRAE Journal - September 2021