ASHRAE Journal - March 2021 - 42

COLUMN IEQ APPLICATIONS

or windows are open, air filters are degrading or HEPA
room air purifiers should be turned on. Make a plan
for how the data from the monitor will be accessed and
the actions that will be taken during a smoke event.
9. Determine How to Create Temporary Cleaner Air
Spaces. Determine how to create temporary cleaner
air spaces within the building prior to fire season. Use
portable room air cleaners of the appropriate size for the
room with HEPA filters (or other high efficiency filters)
and other methods to clean the air (see discussion
below). Some portable air cleaners come with indicators
that change color as the air quality improves. If the
cleaner does not come with an indicator function, it
may be helpful to purchase a low-cost air monitor to
determine whether the air is being cleaned. A lowcost air monitor may also help verify that the air is in
fact cleaner in the cleaner air space relative to other
spaces in the building. Avoid models of air cleaners that
produce ozone or generate ions (see list on California Air
Resources Board website).7
10. Anticipate Sources of Indoor PM2.5. Cooking,
vacuum cleaning, use of printers or copiers and
smoking are examples of activities that increase indoor
PM2.5 levels.8 Understanding potential sources in the
building can assist in the reduction of these sources
during wildfire or prescribed burn events.
The planning framework includes a full checklist to
determine whether the building HVAC system is ready
for smoke. A few issues include: Are outdoor dampers
working correctly? Is the outdoor air economizer working and can it be shut off? Can the HVAC system use
MERV 13 filters?

Pay Special Attention to Economizers
The planning framework urges special attention to
economizers. Most rooftop units and larger HVAC systems are equipped with an outdoor air economizer. To
save energy, the economizer uses outdoor air to replace
the mechanical cooling system when temperatures
allow. This can bring large amounts of smoke and particulate matter into a building during wildfire season. The
economizer control also maintains a minimum outdoor
air damper position for ventilation, controls relief fans
and may close the outdoor damper when the building is
unoccupied. Care and regular maintenance are recommended to ensure the economizer operates as intended.
Numerous manufacturers and control schemes exist
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ASHRAE JOURNAL

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MARCH 2021

for economizers. Finding effective work-arounds to
temporarily limit the economizer damper operation in
response to wildfires is challenging. This framework recommends investigating what actions are needed to limit
operations; this may include adding switches and control relays. Other work-arounds may also be required,
such as placing the outdoor air damper in manual control and setting the position to allow the minimum air
required for ventilation.

SARS-CoV-2
The planning framework recognizes that SARS-CoV-2
raises additional challenges. While HVAC filtration and
air cleaning recommendations for smoke and SARSCoV-2 are similar due to comparable respirable particle
sizes, a low ventilation rate may be desirable for smoke
control9 and, in contrast, a high ventilation rate may
be needed to remove SARS-CoV-2 virus particles.10 The
building manager's challenge is to monitor system components and indoor conditions and change system settings as outdoor air quality changes to balance potential
trade-offs between smoke and SARS-CoV-2 exposure.
Portable air cleaners with a HEPA filter may be helpful in
removing virus as well as smoke particles.

Portable Air Cleaners
If the HVAC system is not able to reduce the PM2.5
concentrations sufficiently throughout the building or
trade-offs are made to reduce potential SARS-CoV-2
exposures, a cleaner air space is needed. A portable air
cleaner with a HEPA filter (or other high efficiency filter), appropriately sized for the space, is recommended.
Multiple devices may be needed for larger rooms. The
Association of Home Appliance Manufacturers has
developed a rating system and room size recommendations for portable air cleaners. The smoke clean air
delivery rate (CADR) is the rating for 0.09 to 1.0 micron
particles and represents the amount of clean air delivered on the high-speed setting. Units with HEPA filters
(or other high efficiency filters) and low noise ratings are
recommended.11
While do-it-yourself room air cleaners using a box fan
and a MERV 13 furnace filter provide air cleaning similar to a small room (100 ft2 [9 m2]) air cleaner, they are
noisier and should not be left unattended or placed near
water.12 The framework also recommends reading and
following the fan safety instructions.

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