Optimizing HVAC for wildfire challenges: Expert advice

With unprecedented wildfires in Canada and the increased likelihood for future wildfire activity across North America, experts from Buro Happold offer advice on minimizing contaminants in buildings and effective HVAC systems strategies for AECO professionals.

To protect against smoke infiltration and reduce impacts of fine particulate matter, called PM2.5, Justin Schultz from Buro Happold’s San Francisco office, as well as John Rozeluk from the Los Angeles office, present solutions to building owners aiming to reduce health hazards on building occupants. Both engineers bring a wide experience in building decarbonization and sustainability, as well as design for wildfire and smoke impacts across the U.S.

Wildfire season considerations

Current guidance for the wildfire season is to use a large degree of recirculation for ventilation. New buildings and renovations now take this into account to provide energy-efficient, cost-effective solutions. Obstacles to maintaining a healthy internal environment include (i) clogged filters in air handler units (AHUs) and (ii) fresh air supplies polluted by smoke.

Possible interventions and example scenarios offered by Buro Happold experts include:

Unavoidable recirculation of central air

Where air recirculation cannot be avoided or reduced sufficiently, building owners should consider air scrubbers on the exhaust air and high-grade filters, known as high-efficiency particulate air (HEPA) filters rated MERV 15. Minimum efficiency reporting value (MERV) indicates an air filter’s effectiveness at decreasing airborne particles and contaminants.

Mixed-mode ventilation

A mixed-mode ventilation system is suitable for natural ventilation for most of the time. In the event of poor air quality due to wildfires, a local mechanical ventilation with heat recovery (MVHR) system can be used to provide fresh air.

Local modifications to centralized systems

Where only local modifications are possible to a centralized HVAC system, building owners can consider in-room modifications, such as forming discrete bulkheads to allow horizontal air introduction.

Displacement ventilation / UFAD

Displacement ventilation or underfloor air distribution (UFAD) introduces air at low levels with a unidirectional air path to exhaust vents located higher in the interior spaces. This washes clean air over the occupants and extracts contaminants at the ceiling.

“We need to be building resiliency and flexibility of response into our designs and engineering, in order to be appropriately responsive to whatever may occur. During the pandemic, we were trying to increase the volume of outside air and reduce recirculation, which is the opposite of what we need to shut out wildfire smoke and filter out particulates. Also, consider the demand on energy for pushing air through HEPA or MERV 15 filters is very high, when most days a MERV 13 filter is sufficient. Architects and engineers need to consider how to design ventilation systems that can be switched from a regular-use mode to settings more appropriate for given crisis conditions. This will balance healthy air quality with overall energy use and operating costs,” says Rozeluk, while responding to a query by The Construction Specifier, as to the role that architects and engineers can play in mitigating the effects of wildfires on IAQ. He added: “We should also be exploring options for managing the air pressure within a building, so that in the event of a wildfire, you can resist air incoming through the typical openings and pathways in the envelope, reducing infiltration of smoke-borne particulates.”

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2 comments on “Optimizing HVAC for wildfire challenges: Expert advice”

  1. I’ve a stand alone MUA IAQ design that provides filtering, purging, enhanced MTBF, and is very efficient.

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