ASHRAE Journal - March 2022 - 48

COLUMN RESIDENTIAL APPLICATIONS
occupants avoided cooking or other
activities likely to increase PM2.5
from indoor sources. Peak measured
concentrations during this period
reached over 700 mg/m3 outdoors
and 400 mg/m3 indoors. During the
days with the highest outdoor PM2.5
concentrations, the mean indooroutdoor
ratio (I/O) was 0.5, indicating
significant penetration of PM2.5 from
outdoors. The team added a portable
air cleaner (with a flow of 160 cfm
[76 L/s] through a HEPA filter and colocated
in a 150 ft2 [14 m2] room with
the sensor) to the room with the air quality monitor,
which lowered the I/O ratio to a mean of 0.2 (Figure 1),
highlighting the benefits of portable air cleaning during
high smoke events.
However, even with the air cleaner, the indoor concen600
400
200
Sep
13
Sep 15
Sep 17
Time (UTC)
FIGURE 2 PNNL data scientist setting up an outdoor air quality station in
Portland, Ore.
trations of PM2.5 were still at unhealthy levels, stressing
the need for further research and development of air
cleaning technologies and the application of other strategies
to limit the entry of smoke. The absolute numbers
reported here for the low-cost sensors are likely biased
as reported in Delp and Singer 202028 and Holder, et
al. 2020,36 but agreed with data from a research instrument
when seeing the same particle concentrations, so
the I/O ratio is considered reliable.
Wildfire smoke enters residential buildings through
natural ventilation, mechanical ventilation systems and
infiltration of outdoor air through the building enclosure.
During high-smoke events, the U.S Environmental
Protection Agency and Centers for Disease Control recommend
that people stay indoors and create a " clean
room " by limiting smoke entry, keeping cool and using
portable air cleaners to filter the air.37 Whole-house air
filtration can be accomplished by installing a high MERV
filter in a central HVAC system and ensuring the fan
operates continuously. Ductless HVAC systems should
be coupled with additional filtration systems or properly
sized portable air cleaners.
Window and portable AC should be avoided; when
they are operated, it should only be in recirculation
modes. Older homes with leaky enclosures have a higher
risk of increased particulate matter concentrations due
to infiltration.27 Efforts to increase wildfire resiliency in
housing can be tied to enhanced energy performance of
48
ASHRAE JOURNAL ashrae.o rg M A R CH 2022
the housing stock, particularly in low-income communities,
which suffer additional burdens associated with
energy insecurity and exposure risk. Weatherization
measures such as air sealing coupled with increased
filtration efficiency can help limit particulate exposures
in homes, and high-performing HVAC systems will help
reduce the electricity demand during the hot summer
months.
Mitigating occupant exposure to outdoor pollutants
associated with wildfire smoke is an important public
health issue that ASHRAE can address by completing
Guideline 44 for commercial buildings and by developing
a best practices guide for residential buildings.
References
1. Burke, M., A. Driscoll, J. Heft-Neal, J. Xue. 2021. " The changing
risk and burden of wildfire in the United States. " Proceedings of the
National Academy of Sciences 118(2).
FIGURE 1 PM2.5 concentrations measured outside and inside. The black vertical
line indicates the time when the portable air cleaner was turned on and remained
on.
Inside
Outside
Sep 19
Sep 21
Concentration PM2.5 (mg/m3)
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