In recent years, a record number of wildfires in Canada and the Western United States has sparked a renewed discussion about indoor air quality (IAQ). Building codes and ASHRAE’s Ventilation and IAQ Standards (62.1, 62.2) basis for achieving IAQ is through dilution (ventilation) and air cleaning (filtration) as well as ensuring air that enters or leaves a building in a controlled and intended manner (pressurization control). These things are essential to maintaining indoor contaminant levels generated by people, building materials, and components below thresholds.
In some instances, the contaminants outdoors may be higher than indoors, universally measured by the air quality index (AQI), and sometimes differs by country. Wildfires generate gases and particulate matter that the AQI measures; it is a good indicator to determine when the outdoor air is at risk. These contaminants can be filtered out.
The amount of removal depends on the mass removal efficiency of the filters used and the loading of the filter (how long the filter is effective) is dependent on particle size. Recent events have put the AQI within the unhealthy to hazardous levels. With the increase in wildfires and other events that release contaminants into the air, it is good practice to have a Smoke Readiness Plan that can be implemented to protect people indoors from bad outdoor air while also protecting them from contaminants generated indoors.
That is why it is essential to:
ASHRAE Journal stated one of the points on the Smoke Readiness Plan. “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 that controls odor, temperature, indoor contaminant levels and maintains a positive building pressure consistent with the building and HVAC system design.”
Filtering, ventilation, and pressure control are the foundation of maintaining a healthy building during normal operation and essential during an outdoor event such as a wildfire. Integrating airflow measuring devices into a building automation system allows ventilation rates to be automatically adjusted or manually adjusted as conditions change. In addition, it prepares the building for any future need to increase and confirm ventilation rates.
Proper outdoor air ventilation and building pressurization are necessary for controlling indoor pollution concentration. Uncontrolled or imbalanced airflow can cause unwanted air to enter a space through walls, windows, and doors; janitor closets or mechanical rooms; toilet or locker rooms; basements or underground. Installed airflow measuring solutions can also indicate when filters are becoming loaded and need replacement.
Maintenance is critical for effective operation in any mode. Testing and inspection protocols maintain IAQ during normal operation and keep systems ready for future events. It is important to inspect the HVAC system after a smoke event. Smoke may have affected the operation of components and caused the system to function improperly or inefficiently, impacting normal mode IAQ.
If you don’t measure it, you can’t control it.
When designing or upgrading a mechanical system or setting up an HVAC system, it’s essential to prioritize measurement, control, and fault alerts as the foundation for these systems. New HVAC system designs should consider adding filtration efficiency and control strategies to initiate smoke mode. This will allow the system to operate energy efficiently during normal mode and allow for additional fan capacity and the control logic needed during wildfire events. Airflow measurement and control costs in an HVAC system are minimal compared to the future impact and cost due to over ventilation, inadequate ventilation, and infiltration.
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