ASHRAE Journal - October 2021 - 28

TECHNICAL FEATURE
Central HVAC Filtration vs. Portable Air Purifi er Filtration
Mitigating COVID-19
In Public Spaces
BY ZHIQIANG (JOHN) ZHAI, PH.D., FELLOW ASHRAE; ROBERT BAHL; KEITH TRACE; BHAVESH GUPTA; HE LI, PH.D.
What can the hospitality industry do to reduce the risk of transmission of COVID-19?
Part is recognizing that HVAC systems play a role in mitigating the risk of airborne
transmission of COVID-19.1 At the beginning of the pandemic, hospitality facilities,
including hotels and restaurants, quickly aligned with guidance from the CDC,2,3
WHO4 and other credible organizations such as ASHRAE5,6 by adjusting operating
guidelines to increase outdoor air dilution and improve fi ltration, where possible,
while maintaining guest and associate comfort. This article discusses a comprehensive
study recently conducted by the authors to investigate the effi cacy of portable air
purifi ers to improve air quality in public spaces.
Improving fi ltration can be accomplished by using
fi lters with higher MERV ratings. For instance, higheffi
ciency particulate air (HEPA) fi lters are effective
in removing " 99.97% or better for all particle sizes. " 7
However, fi lters with higher ratings may increase the
pressure drop, which may make them impractical for
some applications. And, even the most effi cient fi lters
in a centralized HVAC system potentially do not mitigate
heavier droplets or other particles that do not get
entrained into the return air vents and may fl oat around
a given space.
Increasing the amount of outdoor air the system
delivers can further dilute particle concentration and
transmission risks. However, outdoor conditions such
as temperature, humidity and air quality can limit the
amount of outdoor air that can be introduced while
maintaining occupant comfort levels.
Building codes and regulations outline the requirements
for ventilation, and hotel heating and air-conditioning
systems are designed to meet these standards.
However, they were not designed to increase this signifi
cantly. Also, hotel guest room heating and air conditioning
systems should be designed with slight positive
pressure, so air does not pass from one room to another.
Another way to increase the ventilation is by leveraging
air purifi ers to provide equivalent air exchanges
Zhiqiang (John) Zhai, Ph.D., is a professor at the University of Colorado at Boulder in Boulder, Colo. He is a member of ASHRAE TC 4.10, Indoor Environmental Modeling. Robert
Bahl is Global Vice President of Engineering & Facilities, and Keith Trace is Senior Director of Engineering & Facilities at Marriott International, Inc. Bhavesh Gupta is Director of
Engineering, Healthy Buildings and INNCOM for Honeywell International. He Li, Ph.D., is a lecturer at the University of Shanghai for Science and Technology, China.
This peer-reviewed article does not represent offi cial ASHRAE guidance. For more information on ASHRAE resources on COVID-19, visit ashrae.org/COVID19.
28
ASHRAE JOURNAL ashrae.o rg O CTO B E R 2 0 2 1

http://www.ashrae.org/COVID19 http://ashrae.org

ASHRAE Journal - October 2021

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