Post by Nadica (She/Her) on Aug 30, 2024 3:23:26 GMT
Do-It-Yourself Portable Air Cleaners
Introduction
There are three main approaches for improving indoor air quality: (i) reducing sources of indoor air pollution, (ii) dilution ventilation, and (iii) air cleaning. Air cleaners are generally used to reduce contaminant concentrations in buildings. Different technologies are employed to target different types of indoor air contaminants, such as media filtration for removing particles, sorbents for reducing the indoor concentration of organic and inorganic gas-phase pollutants, and ultraviolet germicidal irradiation (UVGI) for inactivating bio-aerosols and microorganisms. Therefore, the types of air contaminants which an air cleaner can mitigate depends on the technologies that it uses.
Air cleaners relying on media filtration are commercially available and commonly used for reducing the concentration of airborne particulate matter in residential, commercial, and industrial environments. Particulate matter is known to cause a range of health issues, including irregular heartbeat, decreased lung function, exacerbation of asthma symptoms, coughing, and decreased cognitive function. Studies that examined particle filtration interventions reported improvements in health outcomes from the use of portable air cleaners. Even for those without underlying health conditions, portable air cleaners can be used daily to reduce adverse respiratory health effects by lowering the indoor concentrations of particulate matter that result from regular activities. For example, cooking generates large amounts of airborne particles, which is especially problematic if one does not have or operate a directly-exhausting range hood. A portable air cleaner can be an effective tool to lower particle concentrations and improve health outcomes while still allowing occupants to engage in regular activities. Moreover, residential heating, ventilation, and air conditioning (HVAC) systems typically run for only a small portion of the day — one study found a median runtime of 18%. Consequently, even if your building has an HVAC system with filtration, you will only benefit from improved indoor air quality during the limited time when the system is actively operating. A portable air cleaner allows you to decouple from the central HVAC system and provide targeted, on-demand air cleaning in the most regularly occupied spaces. Beyond everyday use, portable air cleaners can help reduce the transmission of infectious diseases, such as COVID-19. They also offer essential protection from extreme weather events such as wildfires, which increasingly threaten indoor air quality and public health. In this article we’ll discuss the basics of air cleaners and teach you how to make your own portable air cleaner.
What is CADR?
Portable air cleaner performance is commonly reported as a Clean Air Delivery Rate (CADR) in cubic feet per minute (cfm). The CADR is the product of 1) the fraction of airborne particles removed by the filter as air passes through it one time, which is called the “single-pass filtration efficiency,” and 2) how quickly air passes through the filter, which is called the “airflow rate.” This means that the CADR can be improved with higher efficiency filters and/or a higher airflow rate. A higher CADR means more particles can be removed from the air, or in other words, a higher CADR yields a better air cleaning effectiveness. When purchasing a commercially available/off-the-shelf portable air cleaner, the rated CADRs can be compared across units. If you’re building your own do-it-yourself (DIY) portable air cleaner, there are some steps that you can take to increase your air cleaner’s CADR.
Steps to improve the CADR of a DIY Air Cleaner
You can begin to improve your DIY air cleaner’s CADR by purchasing the right supplies for building it:
Select a fan with a high airflow rate. The fan’s rated airflow is usually based on the its highest speed, so note that airflow rates will be lower in practice if the fan is run on a lower speed setting.
Select high efficiency filters. Look for MERV 13 or higher.
Air Filter Performance
You might be wondering just how much airflow resistance and filter area will impact the performance of your unit. Without testing each unit, it is hard to say for certain, since there will be variation across filter types, brands, and DIY air cleaner configurations and construction. Nonetheless, one investigation found that installing a 1” MERV 13 filter to a box fan reduced the measured air speed by close to 60% compared to fan operation without a filter. When a single MERV 13 filter of greater depth was used, the air speed improved: a single 2” MERV 13 filter and a single 4” MERV 13 filter resulted in ~50% and ~40% reductions in measured air speed compared to the fan operation without a filter attached, respectively. Beyond filter depth, increasing the filter area by incorporating five filters resulted in a much lower reduction in air speed of ~25%. Adding air filters can improve airflow: as shown in the figure below, using two air filters in a prism configuration yields faster airflow than using one air filter in parallel configuration. Overall, increasing filter area, either through increasing filter depth or increasing the number of filters, should improve the airflow rate through the filters and thus improve the resulting CADR.
Do-It-Yourself Instructions
Now we’ll walk you through three DIY options that can cost less and be as or more effective than some commercially available air purifiers. The DIY options are also helpful during events when the availability of off-the-shelf air cleaners is limited, like the COVID-19 pandemic or the 2023 forest fires in Maui, Hawaii. All three DIY options involve some variation on attaching one or more pleated media air filters to a commercially available box fan. The DIY air cleaners can be used in a variety of indoor spaces, such as schools, offices, or personal residences, and provide targeted airborne particle removal. Note that since media filtration is the only technology implemented in these DIY air cleaners, they only remove airborne particles (including bio-aerosols, which can contain viruses). These devices will not remove gaseous pollutants and they will not inactivate microorganisms.
Across the three DIY options, there is a trade-off between (1) air cleaning effectiveness (i.e., CADR) and (2) the resources (e.g., time, money, and materials) required to build the unit. As shown below, options with a higher CADR require more effort and resources to build.
Once you’ve decided on which of the three DIY air cleaners you intend to build, you can follow the instructions below. We’ve included all the steps within each DIY air cleaner’s instructions, so don’t worry about reading all three sections if you already know which cleaner you’re going to build. If you’re unsure, you can always start with the Parallel option and then purchase more filters and upgrade to one of the higher CADR options at a later time. If you are interested in further increasing your unit’s performance, see the “Extra Considerations” section that follows the DIY instructions.
OPTION 1: PARALLEL
The simplest of all three DIY air cleaners is the Parallel air cleaner. It requires the fewest materials and is the easiest to build — it basically involves taping a filter to the back of a box fan. However, it has the lowest CADR of all three options, since it has the lowest filter area and thus the lowest airflow rate too.
Option 2: Prism
The Prism will take more time and resources to build than the Parallel unit, but it should also offer a higher effectiveness since it incorporates a second air filter and therefore has a higher filter area.
Option 3: Cube (Corsi Box)
The final DIY option is the Cube, or the “Corsi box.” The Cube requires the most effort to build, but it should also have the highest CADR since it incorporates five air filters and thus has the largest filter area!
Extra Considerations
If you’re interested in improving the operation and CADR of your DIY air cleaner even further, there are a few more steps you can take.
Maintenance
Like filters in a central HVAC system, filters in an air cleaner also require maintenance and replacement. The filter you purchased should have replacement guidance on the package or manufacturer’s website. It would also be wise to keep an eye on the unit to see how “loaded” the filters are (i.e., how much dust has accumulated on the filters). A heavily loaded/soiled filter can negatively impact performance and should be replaced. It is good practice to use personal protective equipment, such as gloves and a mask, and to ensure the device is off when replacing the filters. Keep in mind that wildfires impact filter performance, so make sure to replace filters after wildfire events.
Acoustics
Regardless of which DIY air cleaner option you build, particles are only being removed from the air when the fan is on. Therefore, it’s important to understand how considerations of comfort, such as fan noise, could impact how often the air cleaner is actually used. The fan will typically be louder when operated at higher speeds, so it is also a good idea to review information about the fan’s noise (look for a “decibel (sound) rating” on the fan specifications). This is particularly important if the air cleaner will be used in a space where distractions could be especially problematic, or if individuals are highly sensitive to noise. Fortunately, sound produced by the DIY air cleaners can be comparable to or even quieter than some commercially available units. Note that like CADR, the noise produced by DIY units depends on the materials used and construction methods. Please refer to the images below and follow these links to see how the noise produced by Parallel and Cube DIY air cleaners compares to commercially available units.
Airflow
To further improve airflow through the filter area:
Consider using weather-stripping in between connections (e.g., filter-filter, filter-cardboard, and/or filter-fan) before taping, and adding zip-ties to ensure a tighter seal. This will help reduce pathways for air to bypass the filter and ensure air flows through those high efficiency filters instead of around them.
Consider incorporating a “fan shroud” to improve the airflow rate. A fan shroud is basically a frame in front of the box fan which prevents backwards airflow around the fan’s corners, improving the effectiveness of your unit. You could incorporate a fan shroud either by using a fan with a built-in shroud or by making a DIY fan shroud.
We hope this guide has been helpful in providing you with an overview of portable air cleaner basics and assisting you in building your own DIY air cleaner. If you’re interested in reading more about any of the topics discussed, see the hyperlinks throughout this blog or refer to the resources below.
References
ASHRAE. (2017). ANSI/ASHRAE Standard 52.2-2017: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. www.ashrae.org/File%20Library/Technical%20Resources/COVID-19/52_2_2017_COVID-19_20200401.pdf
Butz AM, Matsui EC, Breysse P, et al. (2011). A Randomized Trial of Air Cleaners and a Health Coach to Improve Indoor Air Quality for Inner-City Children With Asthma and Secondhand Smoke Exposure. Arch Pediatr Adolesc Med. 165(8):741–748. doi:10.1001/archpediatrics.2011.111
Chao J. (2013). Pollution in the Home: Kitchens Can Produce Hazardous Levels of Indoor Pollutants. newscenter.lbl.gov/2013/07/23/kitchens-can-produce-hazardous-levels-of-indoor-pollutants/
Davison G, Barkjohn KK, Hagler GSW, Holder AL, Coefield S, Noonan C and Hassett-Sipple B. (2021). Creating Clean Air Spaces During Wildland Fire Smoke Episodes: Web Summit Summary. Front. Public Health 9:508971. doi: 10.3389/fpubh.2021.508971
Fisk, W.J. (2013). Health benefits of particle filtration. Indoor Air, 23: 357-368. doi.org/10.1111/ina.12036
Gao X., Coull B., Lin X. et al. (2021). Short-term air pollution, cognitive performance and nonsteroidal anti-inflammatory drug use in the Veterans Affairs Normative Aging Study. Nat Aging 1, 430–437. doi.org/10.1038/s43587-021-00060-4
Grundig T., Köksal N., Sing A. (2021). Is an $800 purifier best to clean your home’s air? Marketplace tested5 top brands and their claims. www.cbc.ca/news/business/portable-air-purifier-tests-marketplace-1.5900782
Harriman L., Stephens B., Brennan, T. (2019). New Guidance for Residential Air Cleaners. ASHRAE 61 (9): 14–23. www.ashrae.org.
Militello-Hourigan R.E., Miller S.L. (2018). The impacts of cooking and an assessment of indoor air quality in Colorado passive and tightly constructed homes.
Building and Environment. 144: 573-582. doi.org/10.1016/j.buildenv.2018.08.044
Ray K. (2019). Filters in Our Lives, Decreasing Our Exposure to Wildland Smoke. www.epa.gov/sites/production/files/2019-07/documents/ray_filters_in_our_lives_decreasing_our_exposure_ray_tagged.pdf.
Rosenthal J. (2020). A Variation on the ‘Box Fan with MERV 13 Filter’ Air Cleaner. www.texairfilters.com/a-variation-on-the-box-fan-with-merv-13-filter-air-cleaner/.
Rosenthal J. (2020). Comparing Filters for Resistance and Efficiency. www.texairfilters.com/comparing-filters-for-resistance-and-efficiency/
Sacks JD., Wichers Stanek L., Luben TJ., Johns DO., Buckley BJ., Brown JS., Ross M. Particulate Matter-Induced Health Effects: Who Is Susceptible? Environmental Health Perspectives. 119(4): 446-454. doi:10.1289/ehp.1002255
Salimifard P., Jones E., Allen J. (2020). Portable Air Cleaners: Selection and Application Considerations for COVID-19 Risk Reduction. schools.forhealth.org/wp-content/uploads/sites/19/2020/08/Harvard-Healthy-Buildings-Program-Portable-Air-Cleaners.pdf#page=4.
Snel, P. (2020). Air filtration a COVID-19: Indoor air quality expert explains how to keep you and your building safe. civmin.utoronto.ca/air-filtration-and-covid-19-indoor-air-quality-expert-explains-how-to-keep-you-and-your-building-safe/
Siegel JA. (2016). Primary and secondary consequences of indoor air cleaners. Indoor Air. 26(1):88-96. doi: 10.1111/ina.12194. Epub 2015 Mar 14. PMID: 25689321.
Stephens B., Novoselac A., Siegel JA. (2010). The Effects of Filtration on Pressure Drop and Energy Consumption in Residential HVAC Systems (RP-1299). HVAC&R Research, 16:3, 273-294, DOI: 10.1080/10789669.2010.10390905
Talheim T. (2020). $70 DIY Purifier Effectiveness Better than $1,000 IQAir. Smart Air. smartairfilters.com/en/blog/diy-purifier-effectivness/
Talheim T. (2013). Measuring Air Purifier Noise. Smart Air. smartairfilters.com/en/blog/china-english-noise/
Touchie, MF, Siegel, JA. (2018) Residential HVAC runtime from smart thermostats: characterization, comparison, and impacts. Indoor Air. 28: 905– 915. doi.org/10.1111/ina.12496
US. Environmental Protection Agency. Health and Environmental Effects of Particulate Matter (PM). www.epa.gov/pm-pollution/health-and-environmental-effects-particulate-matter-pm.
U.S. Environmental Protection Agency. (2018). Residential Air Cleaners – A Technical Summary. www.epa.gov/sites/production/files/2018-07/documents/residential_air_cleaners_- _a_technical_summary_3rd_edition.pdf.
Zhang J., Huntley D., Fox A., Cerhardt B., Vatine A., Cherne J. (2020). Study of Viral Filtration Performance of Residential HVAC Filters. www.ashrae.org/file%20library/technical%20resources/covid-19/zhang_digital-first.pdf
Introduction
There are three main approaches for improving indoor air quality: (i) reducing sources of indoor air pollution, (ii) dilution ventilation, and (iii) air cleaning. Air cleaners are generally used to reduce contaminant concentrations in buildings. Different technologies are employed to target different types of indoor air contaminants, such as media filtration for removing particles, sorbents for reducing the indoor concentration of organic and inorganic gas-phase pollutants, and ultraviolet germicidal irradiation (UVGI) for inactivating bio-aerosols and microorganisms. Therefore, the types of air contaminants which an air cleaner can mitigate depends on the technologies that it uses.
Air cleaners relying on media filtration are commercially available and commonly used for reducing the concentration of airborne particulate matter in residential, commercial, and industrial environments. Particulate matter is known to cause a range of health issues, including irregular heartbeat, decreased lung function, exacerbation of asthma symptoms, coughing, and decreased cognitive function. Studies that examined particle filtration interventions reported improvements in health outcomes from the use of portable air cleaners. Even for those without underlying health conditions, portable air cleaners can be used daily to reduce adverse respiratory health effects by lowering the indoor concentrations of particulate matter that result from regular activities. For example, cooking generates large amounts of airborne particles, which is especially problematic if one does not have or operate a directly-exhausting range hood. A portable air cleaner can be an effective tool to lower particle concentrations and improve health outcomes while still allowing occupants to engage in regular activities. Moreover, residential heating, ventilation, and air conditioning (HVAC) systems typically run for only a small portion of the day — one study found a median runtime of 18%. Consequently, even if your building has an HVAC system with filtration, you will only benefit from improved indoor air quality during the limited time when the system is actively operating. A portable air cleaner allows you to decouple from the central HVAC system and provide targeted, on-demand air cleaning in the most regularly occupied spaces. Beyond everyday use, portable air cleaners can help reduce the transmission of infectious diseases, such as COVID-19. They also offer essential protection from extreme weather events such as wildfires, which increasingly threaten indoor air quality and public health. In this article we’ll discuss the basics of air cleaners and teach you how to make your own portable air cleaner.
What is CADR?
Portable air cleaner performance is commonly reported as a Clean Air Delivery Rate (CADR) in cubic feet per minute (cfm). The CADR is the product of 1) the fraction of airborne particles removed by the filter as air passes through it one time, which is called the “single-pass filtration efficiency,” and 2) how quickly air passes through the filter, which is called the “airflow rate.” This means that the CADR can be improved with higher efficiency filters and/or a higher airflow rate. A higher CADR means more particles can be removed from the air, or in other words, a higher CADR yields a better air cleaning effectiveness. When purchasing a commercially available/off-the-shelf portable air cleaner, the rated CADRs can be compared across units. If you’re building your own do-it-yourself (DIY) portable air cleaner, there are some steps that you can take to increase your air cleaner’s CADR.
Steps to improve the CADR of a DIY Air Cleaner
You can begin to improve your DIY air cleaner’s CADR by purchasing the right supplies for building it:
Select a fan with a high airflow rate. The fan’s rated airflow is usually based on the its highest speed, so note that airflow rates will be lower in practice if the fan is run on a lower speed setting.
Select high efficiency filters. Look for MERV 13 or higher.
Air Filter Performance
You might be wondering just how much airflow resistance and filter area will impact the performance of your unit. Without testing each unit, it is hard to say for certain, since there will be variation across filter types, brands, and DIY air cleaner configurations and construction. Nonetheless, one investigation found that installing a 1” MERV 13 filter to a box fan reduced the measured air speed by close to 60% compared to fan operation without a filter. When a single MERV 13 filter of greater depth was used, the air speed improved: a single 2” MERV 13 filter and a single 4” MERV 13 filter resulted in ~50% and ~40% reductions in measured air speed compared to the fan operation without a filter attached, respectively. Beyond filter depth, increasing the filter area by incorporating five filters resulted in a much lower reduction in air speed of ~25%. Adding air filters can improve airflow: as shown in the figure below, using two air filters in a prism configuration yields faster airflow than using one air filter in parallel configuration. Overall, increasing filter area, either through increasing filter depth or increasing the number of filters, should improve the airflow rate through the filters and thus improve the resulting CADR.
Do-It-Yourself Instructions
Now we’ll walk you through three DIY options that can cost less and be as or more effective than some commercially available air purifiers. The DIY options are also helpful during events when the availability of off-the-shelf air cleaners is limited, like the COVID-19 pandemic or the 2023 forest fires in Maui, Hawaii. All three DIY options involve some variation on attaching one or more pleated media air filters to a commercially available box fan. The DIY air cleaners can be used in a variety of indoor spaces, such as schools, offices, or personal residences, and provide targeted airborne particle removal. Note that since media filtration is the only technology implemented in these DIY air cleaners, they only remove airborne particles (including bio-aerosols, which can contain viruses). These devices will not remove gaseous pollutants and they will not inactivate microorganisms.
Across the three DIY options, there is a trade-off between (1) air cleaning effectiveness (i.e., CADR) and (2) the resources (e.g., time, money, and materials) required to build the unit. As shown below, options with a higher CADR require more effort and resources to build.
Once you’ve decided on which of the three DIY air cleaners you intend to build, you can follow the instructions below. We’ve included all the steps within each DIY air cleaner’s instructions, so don’t worry about reading all three sections if you already know which cleaner you’re going to build. If you’re unsure, you can always start with the Parallel option and then purchase more filters and upgrade to one of the higher CADR options at a later time. If you are interested in further increasing your unit’s performance, see the “Extra Considerations” section that follows the DIY instructions.
OPTION 1: PARALLEL
The simplest of all three DIY air cleaners is the Parallel air cleaner. It requires the fewest materials and is the easiest to build — it basically involves taping a filter to the back of a box fan. However, it has the lowest CADR of all three options, since it has the lowest filter area and thus the lowest airflow rate too.
Option 2: Prism
The Prism will take more time and resources to build than the Parallel unit, but it should also offer a higher effectiveness since it incorporates a second air filter and therefore has a higher filter area.
Option 3: Cube (Corsi Box)
The final DIY option is the Cube, or the “Corsi box.” The Cube requires the most effort to build, but it should also have the highest CADR since it incorporates five air filters and thus has the largest filter area!
Extra Considerations
If you’re interested in improving the operation and CADR of your DIY air cleaner even further, there are a few more steps you can take.
Maintenance
Like filters in a central HVAC system, filters in an air cleaner also require maintenance and replacement. The filter you purchased should have replacement guidance on the package or manufacturer’s website. It would also be wise to keep an eye on the unit to see how “loaded” the filters are (i.e., how much dust has accumulated on the filters). A heavily loaded/soiled filter can negatively impact performance and should be replaced. It is good practice to use personal protective equipment, such as gloves and a mask, and to ensure the device is off when replacing the filters. Keep in mind that wildfires impact filter performance, so make sure to replace filters after wildfire events.
Acoustics
Regardless of which DIY air cleaner option you build, particles are only being removed from the air when the fan is on. Therefore, it’s important to understand how considerations of comfort, such as fan noise, could impact how often the air cleaner is actually used. The fan will typically be louder when operated at higher speeds, so it is also a good idea to review information about the fan’s noise (look for a “decibel (sound) rating” on the fan specifications). This is particularly important if the air cleaner will be used in a space where distractions could be especially problematic, or if individuals are highly sensitive to noise. Fortunately, sound produced by the DIY air cleaners can be comparable to or even quieter than some commercially available units. Note that like CADR, the noise produced by DIY units depends on the materials used and construction methods. Please refer to the images below and follow these links to see how the noise produced by Parallel and Cube DIY air cleaners compares to commercially available units.
Airflow
To further improve airflow through the filter area:
Consider using weather-stripping in between connections (e.g., filter-filter, filter-cardboard, and/or filter-fan) before taping, and adding zip-ties to ensure a tighter seal. This will help reduce pathways for air to bypass the filter and ensure air flows through those high efficiency filters instead of around them.
Consider incorporating a “fan shroud” to improve the airflow rate. A fan shroud is basically a frame in front of the box fan which prevents backwards airflow around the fan’s corners, improving the effectiveness of your unit. You could incorporate a fan shroud either by using a fan with a built-in shroud or by making a DIY fan shroud.
We hope this guide has been helpful in providing you with an overview of portable air cleaner basics and assisting you in building your own DIY air cleaner. If you’re interested in reading more about any of the topics discussed, see the hyperlinks throughout this blog or refer to the resources below.
References
ASHRAE. (2017). ANSI/ASHRAE Standard 52.2-2017: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. www.ashrae.org/File%20Library/Technical%20Resources/COVID-19/52_2_2017_COVID-19_20200401.pdf
Butz AM, Matsui EC, Breysse P, et al. (2011). A Randomized Trial of Air Cleaners and a Health Coach to Improve Indoor Air Quality for Inner-City Children With Asthma and Secondhand Smoke Exposure. Arch Pediatr Adolesc Med. 165(8):741–748. doi:10.1001/archpediatrics.2011.111
Chao J. (2013). Pollution in the Home: Kitchens Can Produce Hazardous Levels of Indoor Pollutants. newscenter.lbl.gov/2013/07/23/kitchens-can-produce-hazardous-levels-of-indoor-pollutants/
Davison G, Barkjohn KK, Hagler GSW, Holder AL, Coefield S, Noonan C and Hassett-Sipple B. (2021). Creating Clean Air Spaces During Wildland Fire Smoke Episodes: Web Summit Summary. Front. Public Health 9:508971. doi: 10.3389/fpubh.2021.508971
Fisk, W.J. (2013). Health benefits of particle filtration. Indoor Air, 23: 357-368. doi.org/10.1111/ina.12036
Gao X., Coull B., Lin X. et al. (2021). Short-term air pollution, cognitive performance and nonsteroidal anti-inflammatory drug use in the Veterans Affairs Normative Aging Study. Nat Aging 1, 430–437. doi.org/10.1038/s43587-021-00060-4
Grundig T., Köksal N., Sing A. (2021). Is an $800 purifier best to clean your home’s air? Marketplace tested5 top brands and their claims. www.cbc.ca/news/business/portable-air-purifier-tests-marketplace-1.5900782
Harriman L., Stephens B., Brennan, T. (2019). New Guidance for Residential Air Cleaners. ASHRAE 61 (9): 14–23. www.ashrae.org.
Militello-Hourigan R.E., Miller S.L. (2018). The impacts of cooking and an assessment of indoor air quality in Colorado passive and tightly constructed homes.
Building and Environment. 144: 573-582. doi.org/10.1016/j.buildenv.2018.08.044
Ray K. (2019). Filters in Our Lives, Decreasing Our Exposure to Wildland Smoke. www.epa.gov/sites/production/files/2019-07/documents/ray_filters_in_our_lives_decreasing_our_exposure_ray_tagged.pdf.
Rosenthal J. (2020). A Variation on the ‘Box Fan with MERV 13 Filter’ Air Cleaner. www.texairfilters.com/a-variation-on-the-box-fan-with-merv-13-filter-air-cleaner/.
Rosenthal J. (2020). Comparing Filters for Resistance and Efficiency. www.texairfilters.com/comparing-filters-for-resistance-and-efficiency/
Sacks JD., Wichers Stanek L., Luben TJ., Johns DO., Buckley BJ., Brown JS., Ross M. Particulate Matter-Induced Health Effects: Who Is Susceptible? Environmental Health Perspectives. 119(4): 446-454. doi:10.1289/ehp.1002255
Salimifard P., Jones E., Allen J. (2020). Portable Air Cleaners: Selection and Application Considerations for COVID-19 Risk Reduction. schools.forhealth.org/wp-content/uploads/sites/19/2020/08/Harvard-Healthy-Buildings-Program-Portable-Air-Cleaners.pdf#page=4.
Snel, P. (2020). Air filtration a COVID-19: Indoor air quality expert explains how to keep you and your building safe. civmin.utoronto.ca/air-filtration-and-covid-19-indoor-air-quality-expert-explains-how-to-keep-you-and-your-building-safe/
Siegel JA. (2016). Primary and secondary consequences of indoor air cleaners. Indoor Air. 26(1):88-96. doi: 10.1111/ina.12194. Epub 2015 Mar 14. PMID: 25689321.
Stephens B., Novoselac A., Siegel JA. (2010). The Effects of Filtration on Pressure Drop and Energy Consumption in Residential HVAC Systems (RP-1299). HVAC&R Research, 16:3, 273-294, DOI: 10.1080/10789669.2010.10390905
Talheim T. (2020). $70 DIY Purifier Effectiveness Better than $1,000 IQAir. Smart Air. smartairfilters.com/en/blog/diy-purifier-effectivness/
Talheim T. (2013). Measuring Air Purifier Noise. Smart Air. smartairfilters.com/en/blog/china-english-noise/
Touchie, MF, Siegel, JA. (2018) Residential HVAC runtime from smart thermostats: characterization, comparison, and impacts. Indoor Air. 28: 905– 915. doi.org/10.1111/ina.12496
US. Environmental Protection Agency. Health and Environmental Effects of Particulate Matter (PM). www.epa.gov/pm-pollution/health-and-environmental-effects-particulate-matter-pm.
U.S. Environmental Protection Agency. (2018). Residential Air Cleaners – A Technical Summary. www.epa.gov/sites/production/files/2018-07/documents/residential_air_cleaners_- _a_technical_summary_3rd_edition.pdf.
Zhang J., Huntley D., Fox A., Cerhardt B., Vatine A., Cherne J. (2020). Study of Viral Filtration Performance of Residential HVAC Filters. www.ashrae.org/file%20library/technical%20resources/covid-19/zhang_digital-first.pdf