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Designing Home Ventilation Systems to Stop Pollution at the Source
Reading time: 7 minutes
Safety
Newer residential homes are becoming tighter thanks to improved insulation material and new insulation practices such as the utilization of spray foam.
This creates a nearly airtight envelope to better hold preconditioned air, which in turn lowers heating or air conditioning costs.
For the home to breathe, mechanical ventilation, such as fresh air appliances, is needed to bring fresh air in and exhaust stale air out, while optimizing the energy required to do so by tempering the incoming air with the energy of the outgoing air.
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During periods when the air quality is less than favorable, such as areas impacted by wildfire smoke or by ozone pollution (normally seen in cities because of industrial and vehicle pollution), we all should take action to protect ourselves and our loved ones.
Homebuilders can ensure future homeowners have a quality solution to this problem before the home is even finished by choosing properly equipped mechanical ventilation appliances.
This article will dive into what the experts say to do during an air quality alert, as well as detail how to make a wildfire smoke readiness plan and discover the different types of methods to stop air infiltration.
What Do the Experts Say?
For impacted individuals, it seems the best course of action is to listen to the experts at the U.S. EPA (Environmental Protection Agency), or the Canadian government. A few main warnings both sides tell those who are or may become impacted include:
Sealing windows and doors and keeping them closed when the temperature is comfortable.
Installing the best quality air filter that your ventilation system can handle based on manufacturers’ recommendations.
Ensuring you have at least one functioning carbon monoxide alarm in your home.
The EPA echoes these warnings. ASHRAE goes one step further; as in 2021, they created framework to guide homeowners and building owners alike to develop a smoke readiness plan. Within this 17-page guide, they cover a topic titled “Optimization of System Airflows”. This topic considers how airflow moves in and out of the home/building. The section states,
“…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, CO2 levels, and maintains a positive building pressure consistent with building and HVAC system design…”
While this guide does not exactly point to homeowners, they can use and take tips from this guide when developing their wildfire smoke readiness plan.
What Type of Events Cause an Air Quality Alert?
Different types of air quality alerts exist in the US: the EPA measures the highest of the pollutants that day and ranks them on a scale of 0–500 (0 meaning “good”, 500 meaning “hazardous”). The Canadian government chooses to bunch all the outdoor air pollutants measured on a singular day and rank them on a scale of 1-10 (1 meaning a “low health risk”, 10 meaning a “very high health risk”).
Below is a list of common EPA Air Quality Events one might see in the US. It is important to note that in Canada during any of these potential warnings, it would be noted as a “4” and up:
Ozone Action Day
Issued when ground-level ozone concentrations are forecasted to reach unhealthy levels. This alert often recommends reducing outdoor activities and taking measures to minimize air pollution.
Particulate Matter (PM) Alert
Issued when fine particulate matter, such as PM2.5 (fine particulate matter of 2.5 microns or less) or PM10 (coarse particulate matter of 10 microns or less), exceeds national air quality standards. These alerts advise sensitive individuals to limit outdoor exposure and suggest the use of air purifiers or masks.
Air Quality Index (AQI) Alerts
The AQI is a scale used by the EPA to measure air quality and provide associated health risks. Alerts may be issued for various categories, including Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, and Hazardous.
Wildfire Smoke Advisories
During periods of significant wildfires, the EPA or the Canadian government may issue alerts for areas affected by smoke. These advisories provide information on the potential health impacts and recommend actions to reduce exposure to smoke.
Industrial or Chemical Spill Alerts
In the event of a significant industrial accident or chemical spill, the EPA may issue alerts to inform the public about potential air pollution risks, evacuation orders, or precautions to be taken.
How to Operate a Fresh Air Appliance during an Air Quality Alert
The importance of bringing in fresh air to help a tight home breathe has been stated, but during an air quality alert, what is a homeowner to do?
It is best to include ways to stop ventilation in homes during the planning phase; especially in areas prone to air quality alerts.
There are three different methods designers can implement for homeowners so they can quickly act during an air quality alert:
Implement an appliance with an OFF or Standby function.
Add accessories to this appliance to ensure a tighter air seal, such as a powered shut-off damper and an external louver.
Implement an appliance that has recirculation capability with a built-in powered shut-off damper and automatically control it with homeowner preferences in an all-in-one touch control.
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Good: Setting the Appliance in the OFF or Standby Position
This is the easiest course of action for appliances without a recirculation function. Take the ATMO™ 150 Fresh Air Appliance, for example, which can be shut down or placed in the Standby position to eliminate the possibility of air infiltration (if the house has a neutral or positive pressure scheme). This can be done easily through the external wall control (like the ECO-Touch® Auto IAQ).
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Better: Adding Accessories to an ATMO
To ensure the appliance is not drawing air into the air handling unit while off, consider adding a powered shut-off damper on the supply side of the appliance. During an air quality alert, the damper will close automatically as soon as the appliance is placed in off/standby mode.
Another recommended accessory is an external louver exhaust. The end of the louver has a flap with a hinge. When ventilating, the louver opens to allow exhaust air to pass through. If the fresh air appliance is ever placed in standby mode, the louver’s flaps fall preventing any air infiltration. This is a passive form of protection that homeowners may forget about but will never have to manually operate.
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Best: Using an Appliance with Recirculation Capability with a Whole-house HEPA System
For appliances with an integrated shut-off damper, setting the appliance into standby will ensure the damper shuts. Additionally, some appliances, like the HERO® 150H Fresh Air Appliance, are capable of recirculation that can be initiated by the ECO-Touch® Auto IAQ. During an air quality alert, putting the appliance in recirculation mode can keep the air moving while filtering it and will also shut the integrated shut-off damper to separate indoor and outdoor air streams.
With both the integrated shut-off damper closed and the appliance in recirculation mode, homeowners can conclude the air they breathe inside is much healthier than the currently polluted outdoor air. Additionally, adding MERV filters to the appliance (MERV 6, 8, and 13) will strain the air of pollutants better; thus, providing cleaner air throughout the home.
For an even stronger solution, add a whole-house HEPA ventilation system into the equation. The HERO® HS300 HEPA System uses a three-stage filtration system: the MERV8 prefilter, a carbon filter, and a HEPA filter to capture 99.97% of particles 0.3 microns and larger.
When air is pulled through the HEPA system, it passes through the MERV8 prefilter to catch particles 1.0–3.0 microns in size while the carbon filter traps odors like smoke and stops them from entering the home. Air then continues through the system and past the HEPA filter to provide the entire home with clean air.
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The Verdict
Using an appliance with a powered shut-off damper for the supply side and an external louver for the exhaust side (and/or an appliance with a plastic exhaust damper built-in) is generally more effective than not using either to protect homeowners against wildfire smoke and air pollution.
By closing off both the exhaust side and supply side of the fresh air appliance, one might think turning the appliance off totally would be fine. This is true, but keeping the appliance on will assist the air-forced system with air circulation.
All our fresh air appliances come with two MERV3 filter screens that can help with filtration, and if the appliance has a MERV8 or a MERV13 filter the filtration process becomes even stronger.
Adding a MERV8 or 13 filter to the fresh air appliance is a good step towards protecting homeowners from air pollution. And while it will not stop wildfire smoke, it will protect against other larger air particles such as mold spores, lint, pollen, legionella, and more.
However, what will remove up to 85% of particles from wildfire smoke is a HEPA filter. If you or your client lives in an area susceptible to smoke from grass or forest fires, use a whole-house HEPA filtration system alongside a fresh air appliance with a MERV8 or higher filter.
For soon-to-be-built homes in areas with frequent air quality alerts, the responsible recommendation is to include built-in powered shut-off dampers with recirculation functionality or add dampers as an accessory to the fresh air appliance. For the exhaust side, use an external louver to create a tight seal so the negative pressure pulls the flaps shut to stop smoke from infiltrating the home.
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