In early 2015, the American Society of Heating, Cooling and Air Conditioning Engineers (ASHRAE) released a Position Paper on Filters and Air Purification Technologies. By searching current data, evidence and literature, including ASHRAE's own publications, the relevant committee made a comprehensive review of the effectiveness, effects on indoor health, long-term effects and limitations of eight technologies: mechanical media filtration, electric filters, adsorption, ultraviolet light, photocatalytic oxidation, air purifiers, ozone and ventilation. (The document relates only to public buildings and residences, with the exception of medical facilities.)
The position paper has two distinct points:
1. In view of the adverse effects of ozone and its reaction products on human health, ozone should not be used for air purification in residential indoor environments. Even if ozone is not used for purification, it is necessary to be on high alert if the purification device can produce a large amount of ozone during operation.
2. All filtration and air purification technologies should provide contaminant removal data based on current testing methods and, if not available, third-party evaluation.
The document describes each of the eight technologies.
1. The filtration effect of Mechanical filtration or Porousmedia particle filtration on particulate matter is very obvious, and it is beneficial to human health.
2. Evidence shows that the effect of electronic filters on the removal of airborne particles ranges from relatively ineffective to very effective, depending on a number of state parameters. Moreover, its long-term effect is related to the maintenance condition of the device. Because electric filters operate on the principle of ionization, there is a risk of ozone generation.
3. The Sorbent has an obvious removal effect on gaseous pollutants. Studies have shown that the human sense of smell has a positive evaluation on its removal effect, but there is insufficient direct evidence whether it is beneficial to health. However, physical adsorbents do not have the same effect on all pollutants. For non-polar organic matter, high boiling point, large molecular weight gaseous pollutants effect is greater. For the low concentration of molecular weight less than 50, high polarity of substances, such as formaldehyde, methane and ethanol, it is not easy to adsorption. If the adsorbent first adsorbs low molecular weight, polar and low boiling point pollutants, when it encounters non-polar organic matter, high boiling point, large molecular weight gaseous pollutants, it will release part of the previously adsorbed pollutants (desorb), that is, there is adsorption competition phenomenon. In addition, even though the physical adsorbent is reproducible, the economics are worth considering.
4. Some studies have shown that Photocatalytic oxidation is effective in decomposing organic matter and microorganisms, however, there is some evidence that it is not effective. Photocatalyst uses ultraviolet light to irradiate the surface of catalyst and promote the decomposition of harmful substances on it into carbon dioxide and water, but its effect is related to the contact time, air volume and the surface condition of catalyst. If the reaction is not complete, it may also produce ozone, formaldehyde and other harmful substances.
5. Studies have shown that ultraviolet light (UV-C) has some effect on inhibiting the activity of pollutants or killing them, but be wary of ozone that may be produced.
6. Ozone is harmful to human health. The allowable exposure concentration limit proposed by ASHRAE Environmental Health Committee in 2011 is 10ppb (1/100 million). At present, however, there is no consensus on the limit values, so in accordance with the precautionary principle, ozone-free purification technologies are used wherever possible.
7. Packaged air cleaner is a product that uses a single or multiple air purification technologies.
8, when the outdoor air quality is good, Ventilation is an effective method to remove indoor pollutants. The use of filtration and other air purification techniques can reduce the need for ventilation. The evidence suggests that current air purification technologies are limited in their ability to remove gaseous pollutants. Therefore, ventilation is still irreplaceable.
