Air cleaners and HVAC filters in Homes
PORTABLE AIR CLEANERS
To filter particles, choose a portable air cleaner that has a clean air delivery rate (CADR) that is large enough for the size of the room or area in which you will use it. The higher the CADR, the more particles the air cleaner can filter and the larger the area it can serve. Most air cleaner packaging will tell you the largest size area or room it should be used in. Portable air cleaners often achieve a high CADR by using a high-efficiency particulate air (HEPA) filter.
FURNACE AND HVAC SYSTEM FILTERS
Furnace and HVAC filters work to filter the air only when the system is operating. In most cases, HVAC systems run only when heating or cooling is needed (usually less than 25% of the time during heating and cooling seasons). In order to get more filtration, the system would have to run for longer periods. This may not be desirable or practical in many cases since longer run times increase electricity costs and may also result in less reliable humidity control during the cooling season.
https://health.ri.gov/covid/indooraircirculation/
Use a portable air purifier.
A portable air purifier with a HEPA filter can be used in rooms when you cannot open windows or use fans. If you use an air purifier, follow these recommendations:
Get a purifier that is the right size for the room where you are going to use it. A typical classroom (30 feet by 30 feet) would need two purifiers that provide 300 cfm (510 m3/h) of HEPA-filtered air to get to 4 ACH. If there is already an HVAC system providing outdoor or filtered air to the room, one air purifier might be enough additional clean air in that room. The volume of these systems is measured with a clean air delivery rate (CADR). If the air purifier’s CADR is listed in cubic meters per hour, multiply the CADR by 0.589 to get the CADR in cfm.
Follow the manufacturer’s directions for maintenance, including how often the machine’s filter should be replaced.
Do not buy an air purifier with extra features, such as ozonation. There is no evidence that these extra features make the air purifier remove more particles, and they can produce gasses that can cause lung irritation.
Put the air purifier as close to the center of the space as possible. Try to keep the sides and top of the machine at least two feet from furniture and other objects so the air flow is not blocked.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7340613/
However, using air purifiers without considering the heating, ventilation, and air conditioning (HVAC) system of the facility may expose call center workers to new risks. The use of air purifiers is not an appropriate approach to control COVID-19 at call centers for the following reasons.
First, air purifiers use a dilution ventilation method, which reduces the concentration of harmful substances in the air, while diluting particulate matter (such as fine dust) or gaseous substances (such as volatile organic compounds). Diluted ventilation is widely used due to its low toxicity, low emission rate, and high effectiveness for gaseous substances, and it is used when the substances are produced uniformly over time or when the installation of a local exhaust ventilation system is difficult. The virus that causes COVID-19 is a highly contagious, small, and a biological hazard that is still not fully understood. Therefore, air purifiers employing dilution ventilation are unsuitable. Methods of controlling biological hazards such as COVID-19 are, from most to least effective, elimination, substitution, isolation, engineering control (ventilation), administrative measures, and the use of personal protective equipment (PPE). To prevent community infection, the most feasible option is to recommend the use of PPE, even though this is less effective than other methods; however, call centers can be adequately managed through the proper application of isolation and ventilation.
The second challenge is posed by the air dispersion methods of such air purifiers. Most air purifiers function by directing pollutant-containing air downwards to capture it, passing the air through a filter, and discharging the purified air back into the surroundings. Since the purified air must be discharged at a greater distance from the purifier than its intake, the wind speed is stronger at the outlet than at the inlet. Therefore, since relatively strong air flow is present at the outlet, the pressure difference causes the air to rise and disperse into the surroundings at a location farther away or positioned higher than the inlet.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7424318/
This paper describes an innovative temporary anteroom in addition to a portable air purifier unit to turn a general patient room into an isolation space. Using an aerosolization system with a surrogate oil-based substance, we evaluated the effectiveness of the temporary plastic anteroom and the portable air purifier unit. Moreover, the optimal location of the portable unit, as well as the effect of negative pressurization and door opening on the containment of surrogate aerosols were assessed. Results suggested that the temporary anteroom alone could prevent the migration of nearly 98% of the surrogate aerosols into the adjacent corridor. Also, it was shown that the best location of a single portable air purifier unit is inside the isolation room and near the patient's bed. The outcome of this paper can be widely used by hospital facilities managers when attempting to retrofit a general patient room into an airborne infection isolation room.
