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Air Cleaner Research
Using air cleaners to remove pollutants from indoor air is part an integrated indoor air quality strategy. Air cleaners can be used, either alone or in combination with other control options, when source control and improvements in ventilation are insufficient, impractical, or otherwise not possible. The air cleaner research program includes research on particulate and gaseous air cleaners. The objectives of research on both types of air cleaners are to:
- develop methods for determining the performance of air cleaners,
- determine the effectiveness of available air cleaners,
- provide guidance to the public on the effective use of air cleaners, and
- develop ways for improving the application of air cleaners for IAQ control.
Particulate Air Cleaners
Previous research on particulate air cleaners has indicated that a few devices
had high efficiency but that commonly used devices had very low particle collection
efficiency. Laboratory and in-room experiments and computer models have been
used to determine overall system performance; the effectiveness of commercially
available devices for removal of particles; the effects of in-room air movement
and particle properties on performance; the effects of biocontaminants on
air cleaners (growth, pressure drop, etc.); the positive or negative effects
of air cleaners on biocontaminants and potential negative side effects of
air cleaners, such as ozone generation; and the effects of operation and maintenance
on air cleaner performance. Research has been conducted to determine the effects
of air cleaners on overall HVAC system performance and costs.
A test method for determining the single-pass efficiency of ducted air cleaners over the particle diameter range of 0.01 to 10 µm has been developed. A number of commercially available air cleaners have been evaluated. Electrostatic precipitators (electronic air cleaners) and high efficiency filters were found to be very efficient over the entire range of particle diameters. Results of the tests for the various types of devices tested have been published in the journal Indoor Air.
The single-pass efficiency of typical in-duct filters is shown in Figure 1.
Figure 1. Single-pass efficiency of typical in-duct particle air cleaners.
Recent research showed that efficiency of filters with permanent electrostatic fields (electrets) drops significantly when the filters become dirty. The filters show this drop in efficiency when collecting particles in both ambient (outdoor) air and indoor air. Examples of the decrease in particle collection efficiency of these filters are shown in Figures 2 and 3. This result has led to work to develop a laboratory test method to replicate the drop in performance under laboratory conditions. The test method work is part of the Indoor Air Environmental Technology Verification (ETV) program.
Figure 2. Effect of loading on single-pass efficiency of high efficiency charged filter.
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Figure 3. Effects of dust loading on single-pass efficiency of residential charged filter.Recent work as part of the Indoor Air ETV program has shown that the particle collection efficiency of some ducted electronic air cleaners decreases with operation of the air cleaners. Work is underway to develop a test protocol for verifying the performance of these air cleaners.
IEMB plans to begin research to better understand the reasons for the reduced efficiency of charged filters and electronic air cleaners. IEMB also plans to conduct research to determine the effectiveness of particulate air cleaners.
The particle diameters of some common indoor particulate pollutants are shown in Figure 4.
Figure 4. Particle diameters of some common indoor particulate pollutants.
VOC and Gas-Phase Air Cleaners
Previous research on VOC air cleaners has been very limited. Available data
indicate that VOC air cleaners, if properly applied, could be an important
part of an overall IAQ control strategy, especially for dealing with upset
conditions where source control and ventilation are not practical. However,
data necessary to determine how to best apply VOC air cleaners are not available.
A test method for evaluating the ability of air cleaners to remove organic
vapors from indoor air, based on small-scale evaluation of the performance
of the media (activated charcoal for example) used by the device, has been
developed.
Based on these small-scale tests, it appears that the useful life of organic vapor air cleaners is a strong function of the chemical composition and indoor concentration of the organic vapors being collected and the relative humidity and temperature of the indoor environment. Lifetimes of typical commercially available air cleaners, under typical indoor conditions, are less than 1 year; under conditions of high pollutant concentration, they are less than 1 month. The data and the modeling show that air cleaners have a limited capacity for organic vapors and that the performance is greatly affected by the nature of the organic vapors being collected. The full analysis was published in the February 1995 issue of the ASHRAE Journal.
IEMB is not presently conducting research on gas-phase air cleaners.