ASHRAE Journal - July 2019 - 64
COLUMN IEQ APPLICATIONS
Jovan Pantelic
HVAC Source Strength and Air Distribution
Designing for Airborne
Infection Control
BY JOVAN PANTELIC, PH.D., ASSOCIATE MEMBER ASHRAE
The estimated total annual cost of hospital-acquired infections in the United States, is
~$7 billion, with airborne transmission contributing 10% to 20%.1 This is a significant
issue and these numbers increase when we consider commercial and transportation
indoor environments. However, the proper design of the HVAC system can mitigate
airborne infection transmission and help to control these costs. This article reviews
ASHRAE's HVAC Design Manual for Hospital and Clinics and HVAC from the perspective of
infectious source strength and air change rate, one of the key parameters in healthcare design.
Transmission occurs when infectious aerosols are
emitted in the environment and expose the susceptible
person. Exposure has to be above the disease specific
infectious dose to cause an infection. HVAC systems
can help to control airborne transmission by influencing dilution, exposure time and airflow patterns.2 At
the moment, air change rates for different environments are designed per ANSI/ASHRAE/ASHE Standard
170-2017, Ventilation of Health Care Facilities, considering
thermal requirements and necessary air exchange
rates, but without considering the emission of infectious aerosols, nor concentration of infectious aerosols
in respect to the infectious dose. Knowledge about
the emitted quantity of infectious aerosols combined
with well-mixed environment assumption enable
calculation of airflow rate that can sufficiently dilute
infectious aerosols and reduce exposure below the
infectious dose. Studies that quantify infectious source
64
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strength used epidemiological data to deduce information about infectious source emissions from the
epidemiological outcomes in terms of quanta or using
known dose-response relationships.3 Both of these
approaches based on epidemiological outcomes have
inherent uncertainties, and beyond research papers,
the developed methods did not find their way into the
design guideline.
One challenge in conducting this research and using
it to make design recommendations is that accurate
estimation of the infectious source strength requires
an aerosol sampling device that does not restrict respiratory activities, collects aerosol with high efficiency,
and preserves virus culturability.4 The device with
these characteristics was not available until the development of the G-II aerosol sampler. The G-II enables
Jovan Pantelic, Ph.D., is assistant professional researcher at the Center for the Built
Environment (CBE) at University of California, Berkeley.
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ASHRAE Journal - July 2019
Table of Contents for the Digital Edition of ASHRAE Journal - July 2019
Contents
ASHRAE Journal - July 2019 - Intro
ASHRAE Journal - July 2019 - Cover1
ASHRAE Journal - July 2019 - Cover2
ASHRAE Journal - July 2019 - 1
ASHRAE Journal - July 2019 - Contents
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ASHRAE Journal - July 2019 - Cover3
ASHRAE Journal - July 2019 - Cover4
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