ASHRAE Journal - January 2021 - 24

TECHNICAL FEATURE

of COVID-19 suspected or confirmed patients, especially
when aerosol generating procedures (e.g., intubation)
are performed.13 For the general public, however, the
CDC describes SARS-CoV-2 transmission as primarily
by droplets from coughs or sneezes, which " land in the
mouths or noses of people who are nearby or possibly
inhaled into the lungs. " 14
Because of this, facilities beginning to reopen aren't
likely to need a heavy investment in air cleaning technologies for central air-handling units, beyond ensuring
filters are rated at MERV 13 or above. The most necessary
investment may simply be a strategy for maximizing
the amount of outdoor air within the capacity of the airhandling unit.15
The growing science16 around far-field aerosol transmission essentially negates the need for in-duct or air
system control technologies such as UV lights. While
these products and services may serve a useful function, in most applications, they may not meet the specific need that's called for in mitigating the hazards of
SARS-CoV-2.
Of course, specialized applications may exist where
added levels of in-space or in-room protection may be
useful, most notably in health-care and long-term or
senior-care facilities. For example, portable HEPA units
are very effective in filtering airborne pathogens from
the air before recirculating essentially particle-free air
back into areas in which they are used.17 Properly sized
and mounted portable HEPA units can also be used to
establish directional flows in various settings ranging
from temporary surge rooms in health-care facilities to
nurses' rooms in school buildings.
In this type of application, potentially contaminated
air can be extracted from an inner, physically isolated
zone by the HEPA filtration system, where it is cleaned
of pathogens and then discharged into an adjacent outer
zone. This type of application not only cleans the air but
helps maintain a negative pressure relationship to the
inner, potentially infectious zone relative to adjacent
areas.18

Exceptions to Air Cleaning Recommendations
Despite the broad recommendation that supplementary air treatment isn't required, certain circumstances
may exist in which some level of HVAC disinfection is
warranted. Generally speaking, this will involve specialized locations that could be considered higher-risk
24

ASHRAE JOURNAL

ashrae.org

JAN UARY 2021

areas. These could be specific areas of health-care
facilities, such as ER waiting rooms, treatment facilities
where there is a risk of aerosol production or ICUs;19
elderly care facilities; or transportation terminals for
airlines, buses or trains.20
In addition, some areas in commercial buildings could
require greater effective air exchange rates via air cleaning technologies, such as upper room UV or localized
higher-efficiency filtration. These include areas that see
high densities of people or where increases in outdoor
air cannot be achieved for increased air dilution.

The Real Challenge of Reopening
Does this mean that building engineers can rest easy
knowing there's no action to take to protect building
workers? Not exactly. However, the risk that comes with
reopening may not be where most building owners are
focusing. (See Reference 1, the ASHRAE Epidemic Task
Force's " Building Readiness " guide, for additional guidance on reopening.)
Many office, retail and institutional buildings looking
to reopen have operated at low or nearly no HVAC load
for several months. As these buildings come back online,
many are increasing the amount of outdoor air coming
in, or they are returning to full operation to condition
air for what may be a fraction of typical building occupancy levels. These dramatic shifts can lead to significant maintenance issues and operational concerns.
HVAC systems haven't been truly challenged in
months. Bringing these systems online and expecting
them to perform as they did on the building's last day
of normal occupancy is a big demand. For buildings
reopening today, it's best to address HVAC systems as if
this were the first day of operation, following ASHRAE/
ACCA Standard 180-2018, Standard Practice for Inspection
and Maintenance of Commercial Building HVAC Systems.
If maintenance challenges aren't enough to convince
building owners to reevaluate the mechanical systems in their building, they also need to consider that
system control sensors may have failed or gotten out
of calibration. The remedy for this condition is to go
through a retro-commissioning process to make sure
that all systems are running as intended and to check,
repair and adjust as necessary all control sensors. See
ASHRAE Guideline 1.2-2019, Technical Requirements for
the Commissioning Process for Existing HVAC&R Systems and
Assemblies,21 for guidance.
https://www.ashrae.org/
ASHRAE Journal - January 2021

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