ASHRAE Journal - March 2021 - 40

COLUMN IEQ APPLICATIONS

should rely on qualified HVAC staff and consultants.
Ideally, quick implementation of temporary measures
will clean the air coming into the building and limit
infiltration of wildfire smoke. Some buildings and HVAC
systems are not designed and/or maintained to accommodate the modifications recommended in the planning
framework. Appropriately sized portable air cleaners can
help create temporary cleaner air spaces. However, building managers will need to assess whether these measures
are sufficiently reducing the levels of particulate matter.
The planning framework emphasizes assistance from an
HVAC professional is generally required to assess existing
HVAC equipment capabilities and implement portions of
these recommendations.
Indoor air needs to be cleaned whether ventilating with
outdoor air or recirculating indoor air. To help building managers accomplish this, the planning framework
outlines a process for making a building smoke ready
(Figure 1). Figure 2 provides a flowchart of actions within
this process, including assessing whether these actions
have been effective in reducing indoor PM2.5 levels. The
planning framework explains how and why they should
be taken before and during wildfire smoke episodes.
The planning framework emphasizes a Smoke
Readiness Plan needs to be building-specific and
address the following:
1. Purchase Smoke Preparation Supplies. Before wildfire season, purchase materials and supplies needed for
the plan. For example, purchase portable air cleaners
and extra filters in advance, as they may become difficult to find during a smoke event. Wildfire smoke can
quickly load filters (Figure 3) and they may need to be
changed as frequently as daily.
2. Upgrade HVAC System Recirculation Filter.
MERV 13 filters are recommended during smoke
events. However, prior to wildfire season, HVAC
systems must be assessed for the ability to function
properly with the upgraded filters.
3. Maintain the HVAC System. Repair broken
dampers, actuators and HVAC controls prior to fire
season. Pay special attention to the economizer because
they can be complex and may not be installed correctly.
The economizer will need to be temporarily disabled.
4. Optimize System Airflows. Assess and maintain
adequate airflows that are protective of human health
and equipment health during smoke events. Prior to
wildfire season, determine an outdoor air intake level
40

ASHRAE JOURNAL

ashrae.org

MARCH 2021

FIGURE 3 A clean filter (left) and a filter heavily loaded with wildfire smoke (right).

FIGURE 4 MERV 13 filter installed on an intake air vent.

that controls odor, temperature, indoor contaminant
levels and maintains a positive building pressure
consistent with the building and HVAC system design.
5. Prepare to Add Supplemental Filtration. During
a smoke event, add additional filtration at the intake
air vent where possible (Figure 4). A minimum of a
MERV 13 filter on the outdoor air intakes will capture a
large fraction of the PM2.5. Prior to fire season, inspect
the air intake and make a list of filters, tape, temporary
ducting materials and other items needed to mount filters
to the air intake with minimal bypass around the filter.
6. Assess Filter Conditions. Prior to wildfire season,
add a port or pressure gauge to measure the filter
pressure drop on at least one air-handling unit. This
will simplify determining when to change filters.
7. Limit Smoke Intrusion. Prior to wildfire season,
weatherize the building envelope, including doors and
windows, to reduce infiltration by sealing and caulking
cracks. Keep doors and windows closed to limit smoke
intrusion.
8. Prepare to Monitor Indoor PM2.5. Prior to wildfire
season, purchase one or more low-cost air monitors
equipped with a PM2.5 sensor and install it in the
facility.6 These monitors will not be as accurate as
regulatory monitors but can show whether your
interventions are reducing indoor PM2.5. For example,
upward trends in PM2.5 levels can indicate that doors

http://ashrae.org

ASHRAE Journal - March 2021

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