ASHRAE Journal - July 2021 - 8

LETTERS
Epidemic Task
Force Core
Recommendations
I expected more specifics
and evidence-based recommendations
from the Epidemic
Task Force (ETF) than noted in
May's IEQ Applications column,
" ASHRAE Epidemic Task Force
Core Recommendations: Reducing
Airborne Infectious Aerosol
Exposure " by William Bahnfleth,
Ph.D., P.E., and Jason DeGraw, Ph.D.
Without specifics, I am afraid
these will lead to more misuse than
benefit. For example, without more
specifics on wavelengths and caution,
I am afraid anyone with any
ultraviolet lamp will claim it works.
Or, since many HVAC-grade filters
are charged, at a minimum
they should be tested per ASHRAE
Standard 52.2 Appendix J. Besides,
since most IAQ systems are recirculating
air, the effect of upgrading
filters rated for single pass will not
be appreciable.
I hope ASHRAE is not adding to
the noise on this subject instead of
being the brain trust the HVAC market
depends on. I look forward to
more specifics for nonexperts.
R. Vijayakumar, Ph.D., Fellow ASHRAE, Liverpool, N.Y.
The Authors Respond
We thank Dr. Vijayakumar for
his comments. We agree the Core
Recommendations are not complete
in themselves, but they were not
intended to be, as our column stated.
The column's first paragraph notes
the Core Recommendations are a
" concise summary of the most current
task force recommendations. "
Those recommendations and their
application are detailed in nearly
8
400 pages of detailed and widely
referenced guidance that can be
found at the ASHRAE COVID-19
resources page (www.ashrae.org/
COVID19). It is based as much as
possible on good practice for airborne
infection control and our currently
incomplete knowledge about
SARS-CoV-2.
To address the specific issues
raised in the letter, first, the Core
Recommendations clearly state that
only air cleaners for which there
is clear evidence of effectiveness
and safety should be used. Further
discussion of what this means
can be found in task force guidance
on filtration and disinfection,
the " ASHRAE Position Document
on Filtration and Air Cleaning "
(https://tinyurl.com/t5m4t3xn) ,
and-specifically for ultraviolet air
disinfection equipment-ASHRAE
Standards 185.1 and 185.2.
Likewise, the task force Filtration
and Disinfection (https://tinyurl.
com/jyfyvuw) and Building
Readiness (https://tinyurl.
com/899sfp7s) guidance documents
include extensive discussion of
mechanical filter ratings according
to ASHRAE Standard 52.2-2017 and
other guidance for effective application
of enhanced filtration.
We are unclear about the meaning
of the comment on recirculation.
The only reason filters in central air
distribution systems have potential
to reduce exposure to infectious
aerosols is that indoor air recirculates
through them. Without
recirculation, filters in air-handling
units only remove particulate matter
of outdoor origin, and their total
removal increases as the indoor
air recirculated through them
increases.
ASHRAE JOURNAL ashrae.org J U LY 2021
It is straightforward to estimate
the effect of a filter of known
single-pass efficiency in a recirculating
system. The combined
effect of outdoor air, filtration
and air cleaning can be estimated
using a spreadsheet tool for which
a link is provided in the previously
referenced Building Readiness
guidance.
We hope this response clarifies
that the Core Recommendations
are a point of entry into the extensive
guidance developed by the task
force. To date it has proved a useful
tool for explaining the key points to
a variety of audiences.
William Bahnfleth, Ph.D., P.E., Presidential Member/Fellow
ASHRAE, State College, Pa.; Jason DeGraw, Ph.D.,
Member ASHRAE, Knoxville, Tenn.
Virus Transmission
Modes and Mitigation
Strategies
We read with great interest " Virus
Transmission Modes and Mitigation
Strategies, Part 1 and Part 2 " by
Jonathan Burkett, P.E., in the March
and April issues.
In minimizing airborne transmission,
ventilation provision is the
most important. The ventilation
requirement expressed in terms
of the number of air changes per
hour (ach) was worked out based
on acceptable CO2 levels for general
applications and the CO concentration
for parking lots or vehicular
tunnels.
On the other hand, ventilation
design guides on virus control
indoors can be developed using the
Wells-Riley model.1,2 The probability,
P, of infection risk for a susceptible
is expressed in terms of the air
change rate, Q, through a parameter,
A, by:
http://www.ashrae.org/COVID19 http://www.ashrae.org/COVID19 https://www.tinyurl.com/t5m4t3xn https://tinyurl.com/jyfyvuw https://tinyurl.com/jyfyvuw https://tinyurl.com/899sfp7s https://tinyurl.com/899sfp7s http://www.ashrae.org

ASHRAE Journal - July 2021

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

Contents
ASHRAE Journal - July 2021 - Intro
ASHRAE Journal - July 2021 - Cover1
ASHRAE Journal - July 2021 - Cover2
ASHRAE Journal - July 2021 - 1
ASHRAE Journal - July 2021 - Contents
ASHRAE Journal - July 2021 - 3
ASHRAE Journal - July 2021 - 4
ASHRAE Journal - July 2021 - 5
ASHRAE Journal - July 2021 - 6
ASHRAE Journal - July 2021 - 7
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ASHRAE Journal - July 2021 - Cover3
ASHRAE Journal - July 2021 - Cover4
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