Residential Indoor Air Quality
Air Quality Trends in the United States
Across the past decade we have made great strides to increase the air quality across the United States. Through environmental regulations and better technologies air quality is rarely a concern for many states. However, this trend of increasingly healthy air does not extend to the North-Western states. The primary cause for this is a natural disaster unique to the dry and mountainous region: wildfires. Between the months of July and September wildfires burn millions of acres of land. While these fires are dangerous, they are often remote and can be contained with effort. However, the smoke produced by these fires can spread freely affect much larger areas than the fire alone.
US particulate matter air quality improves except in wildfire-prone areas Crystal D. McClure, Daniel A. Jaffe Proceedings of the National Academy of Sciences Jul 2018, 115 (31) 7901-7906; DOI: 10.1073/pnas.1804353115
What's worse is that things are escalating. In recent years heat waves, droughts and human activity have led to record breaking wildfires. The 2021 fire season is an excellent example of this. Here in the west, smoke concentrations can reach incredibly elevated levels. In Sacramento they have exceeded nine times the safe shot term exposure levels outlined by the World Health Organization. This enough smoke created in just 3 months to skew an entire year's worth of increasing air quality statistics. As a final example of scale, the bootleg fire in Oregon burned hot enough to produce its own weather patterns can carry smoke to affect population centers on the east coast, over 3000 miles away.
The primary reason we are concerned with wildfire smoke is because it contains large amounts of fine particulate matter measuring 2.5 microns and smaller. These particulates are one of the primary indicators of poor air quality and contribute to the nasty brown haze we get during fire season. These particles are fine enough to be inhaled deep into your lungs and absorbed by the bloodstream causing significant health concerns. Exposure to particular matter has been linked to stroke, heart disease, lung cancer, respiratory diseases and premature death.
EPA.gov: Size comparisons for PM particles
During last years fire season Boise State professor Brian Wiley was seeking a way to protect his children and pregnant wife from the smoke. Brian lives in a mid-century suburban ranch house with standard construction and ventilation practices, about as common as it gets. And like homeowners in similar situations, Brian was offput by the high price tag of retrofitting his home with dedicated air quality systems. He set out to develop his own answer. A system that is simple, made from readily available parts and could effectively protect his family.
The result of this effort was the first prototype of a device dubbed the “EasiAir”. The EasiAir uses a convenient window mount design similar to air conditioners, to allow installation in any room with an operable window. This also means there is no need to hire a specialist to do expensive work like tampering with the building envelope or existing HVAC systems, massively increasing accessibility. To compliment this the EasiAir is constructed out of very simple materials, insulation board, some plywood, a few nuts and bolts, and a simple fan. Almost everything can be found in your local hardware store or made from the scraps of other projects.
A very simple solution that has also been shown to work well. Brain installed the device in his home and monitored the air quality index or AQI within and outside of his home using a separate IQair device. The photo below was taken 3 hours into a continuous operation stress test during the heart of fire season. For context an AQI of 8 is well below the United States 2020 average AQI of 40. On the other-hand 150 is the start of the “unhealthy for all groups” range. Further testing in the direction of minimum operation revealed that the device needs only 15 minutes every hour to maintain health levels throughout the day.
Encouraged by his success Brian reached out to the University of Idaho’s Integrated Design Lab to explore the device and its place in the built environment, as well as graciously allowed his device to be used as the inspiration for this capstone project, as well as a project from last semester.
As part of an independent study on building energy efficiency, Tais Mitchell and Jason Talford entered into the department of energy’s JUMP into STEM competition. With the EasiAir as inspiration they prepared a research paper to submit it to the Equal Access to Healthy Indoor Air track. They were selected as the finalist for that track and were invited to virtually present our findings at the competitions final event. What follows is research conducted on the EasiAir device and its place in residential indoor air quality.
Need for Clean Air
Certain demographics disproportionately lack access to healthy indoor air. Agricultural and rural communities are often required spend long days out in the smoke even when it is recommended to shelter indoors. These communities as well as Low-income households tend to live in older homes with higher-than-average occupancies. Over time the houses settle and cracks in the envelope can develop allowing smokey air into the house. Renters are another group that has a unique dilemma. In addition to issues faced by leaky constructions, landlords are responsible for the maintenance and decisions concerning HVAC equipment, meaning renter often have zero say on the systems that affect their health. During fire season these groups live every day in buildings offer little to no protection from smoke. In fact, even with smoke events indoor air can be even worse than outside.
Hazardous conditions for Agricultural workers during fire season.
Standard construction practice for these demographics uses exhaust ventilation. For these systems exhaust is provided by range hoods and bathroom fans which need to be operated 24/7 in order to meet ASHRAE 62.2. This is almost never the case as these are noisy and require manual operation. Options for quieter all hour exhaust do exist, but this method of ventilation is often designed to meet minimum requirements meaning those systems rare.
This means that homes with exhaust ventilation are prone to the buildup of contaminants over time. Especially those with additional occupants where generation from cooking and cleaning are much larger. Make up air for exhaust ventilation relies on leaky construction as well as open windows to provide unfiltered "fresh" air from outside even when exhaust fans aren’t being manually operated.
Infiltration, the seepage of air through attics and crawlspaces can bring a series of additional contaminates such as dust, mold, or hantavirus from pests. Many of these contaminants are mild or rare but some deserves special attention. The first of these is radon. Radon is a radioactive noble gas produced by naturally occurring radioactive decay of elements in the earth’s crust. It seeps up through cracks in the ground slowly enough there's not high enough concentrations to be a problem even in the northwest.
In the context of a home, unless proper measures are taken and, more importantly, maintained radon can pulled in by infiltration through cracks in the foundation. When there is not adequate ventilation the gas can build up inside a building to dangerous levels. Radon is currently the second leading cause of lung cancer in the United States, first for non-smokers and causes over 21000 deaths annually.
Another contaminant that deserves attention is carbon dioxide. For a long time CO2 has been used as a stand in to measure if a space has enough ventilation simply because it was closely connected to when people felt a space was stuffy. CO2 as a contaminant is a more recent development, research is still ongoing but the impacts of CO2, but high concentrations have been linked to significant and measurable reductions in decision making, initiative, sleep quality and other metrics.
It is deceptively easy to reach these levels. One person in a home with poor ventilation can easily pass 2500 ppm of CO2 during overnight hours. Homes with additional occupants can climb even higher and remain elevated throughout the day. The combination of these hazards suggests a situation that is quite bleak. Occupants are tired, struggle to focus, and make more mistakes they’re less motivated. Continued exposure can complicate existing sensitivities and can even cause the emergence of new medical conditions including cancer. They get sick more often and for longer periods. Medical bills can pile up and become crippling. Requiring more and more sacrifices to stay afloat.
Alternative Ventilation Options
With this expanded context it can be better understand how the EasiAir fits into a residential setting. Its operation resembles the existing technology of supply ventilation where fresh air is pumped into the building rather than out and this comes with several benefits. Firstly, the air is pulled from a specific area rather than everywhere there happens to be a crack or opening. This offers the ability to properly filter incoming air to remove particulate matter such as pollen, dust, and smoke. The next benefit of supply ventilation is that it contributes positive pressure to the space This can reduce infiltration from negative pressure differences and potentially even reverse infiltration through the building's envelope.
By effectively changing the direction of a fan, pollen, smoke, mold, and radon contaminants can no longer be drawn into a living space or pushed outward though the envelope, preventing them from entering the home in the first place. In addition, positive pressure in the home can displace contaminants generated inside the living space.
Issues and Energy Implications
Now there are some reasons we don’t see supply ventilation much especially in the more humid northwest. When warm humid air brought into a cold space can cause problems with condensed moisture, but with the control of the incoming air a dehumidification process can be added. Another issue is the temperature of the incoming air. For exhaust ventilation the air has some time to warm up as it approaches the living space.
Thankfully the expected operation of the device takes place during late summer months where the outdoor temperature is often within comfortable levels. Especially in regions such as Sacramento, California, where the weather is nice during nearly the whole fire season. But even regions with hotter summers shouldn’t expect much impact. Anecdotally during Brian Wileys testing he reported no more than a 3˚F to 4˚F increase limited to the room the EasiAir was operating in.
In order to get some perspective some on the applications for other target demographics, particularly renters the building energy optimization tool (BEopt) was used to model energy impacts. A simple shoebox model of a 4000 ft2 4-unit multifamily building was built using a typical meteorological year weather for Boise Idaho. Within in the program a custom mechanical ventilation case was created to reflect the operation of the EasiAir device.
Using the fraction of ASHRAE 62.2 and fan power the program calculated values of 120 cfm and 18 W per unit which corresponds to about half of the rated capacities of inline duct fan. This is a good mark because about half power is the reported as the most comfortable to use from a temperature and noise standpoint.
The rest of model was left at standard settings with the exception of a leakage value of 15 ACH50. This setting means the volume of the building cycled 15 times in an hour when under a 50-pascal pressure difference. This is quite a high value and reflects the worst-case scenario that our target demographics might be living in.
From the chart, the left column shows the baseline energy usage with no supply ventilation and the column on the right is with the addition of our custom supply ventilation case, and as you can see there is barely any increase in heating.
Moving more towards the hardware, the EasiAir uses a HEPA grade shop vac filter attached to the outside of the device, which is quite the benefit for this application. For some context most home HVAC systems use a MERV-8 filter which only filters 85% of particles between 10 to 3 microns. This is about the same scale as your run of the mill shopvac filter. Since the onset of covid there has been a shift towards better filters, the top of which being High Efficiency Particulate Air filter or HEPA which can remove 99.97 of particles down to 0.3 microns. Meaning a $30 shop vac filter from the local hardware store is providing cleaner air than the majority of dedicated HVAC filters. Lastly these types of filters are expected to have a lifespan of 12-18 months but with our limited operation window this could easily extend out to 3 of 4 times that duration.
The other major piece of hardware is the fan. The EasiAir currently has the Raxial 6inch inline duct booster by AC infinity. Rated at 265 cfm and 37 W It plugs right into a typical wall outlet and has a variable speed controller built in. Using the 15 minutes of operation for every hour to maintain good indoor air quality across a day, the operator expect 0.22 kWh of energy every day or 19 kWh for a whole fire season. This is at its max setting meaning the device really doesn’t add much to the power costs for the building. With Idaho power rates this is less than $2 dollars every year to have dramatically improved air quality.
The more interesting information from the fan however is how its airflow compares to that of a building. As this is a third-party addition, the EasiAir is essentially fighting against the buildings natural leakiness. Following the wisdom of an industry expert Jerry Peterson we used typical values of 10 ACH for a leaky home and 5 for a slightly tighter envelope. Both of these measured values taken at 50 pascals using a blower door test. In order to get a proper comparison, These values are converted to ACH natural or the air changes under naturally occurring conditions. Using the Infiltration Equations & Conversions sheet from the IDLs design tools the two natural ACH targets are calculated at 0.465 and 0.232 respectively.
With ACH targets set the fans performance can be compared. The fan has a rated flow of 265 cfm, but this doesn’t account for losses due to the fittings and filter. Using a flow hood provided by the IDL’s Energy Resource Library the air flow was measured at 55 cfm at maximum setting. Assuming a typical 2,000 ft2 house with 10 ft ceilings this works out to about 0.165 ACH at natural pressure. Not quite enough to completely offset the buildings natural infiltration but still a sizable reduction in negative pressure that will significantly reduce the amount of contaminates brought into the living space. This number suggests that the EasiAir’s as it is currently is best used in small spaces such as a bedroom. However, it is expected that the EasiAir can do much better than this with only one minor adjustment.
The fitting used to attach the filter (left) reduces the 6-inch duct quite significantly. This restricts the already reduced airflow through the filter. By removing the restriction, the EasiAir can produce much improved air flow perhaps even exceeding a buildings natural leakage. This is also a great chance to adjust the overall construction of the device. With the filter attached (right) assembly hangs below the level of the windowsill and can easily be blocked by exterior finishes.
Finally with a more complete picture of the EasiAir device some comparisons can be drawn to exiting solutions to indoor air quality. Pricewise the Easiair is in a great spot, even accounting for some price increases due to redesign and finishing materials, the device is $100 to $400 less than a standalone air purifier. From an operating perspective the EasiAir has the potential for an excellent position over an air purifier. If the air flow can be brought to match or exceed the buildings negative internal pressure it can entirely prevent the entry of many contaminants including gasses that an air filter will never catch. Even for scenarios where the negative pressure can’t be completely offset infiltration the EasiAir will greatly reduce the majority of contaminants and is a great option to have for a bedroom.
Even with its limitations the EasiAir device provides an effective answer the need for easy access to healthy indoor air. Its operation can significantly reduce contaminants in a home, or the case of smaller areas and tighter envelopes actively displace contaminants. During fire season and when the climate permits the EasiAir’s effects on contaminants in the indoor environment leads to better health better decisions, better productivity, more agency, and a better standard of living.
Jason graduated from Boise State University with a bachelor's degree in mechanical engineering with an emphasis on energy efficiency systems. He is excited to keep his roots in the treasure valley by pursuing a masters of mechanical engineering with the University of Idaho in Boise and is looking forward to a career focused on the communities he calls home.