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NAFA Guide To Air Filtration. Chapter 6 Air Cleaners presented by the National Air Filtration Association. Fifth Edition. Air Cleaners. Different types of air cleaners - Media Electronic Air Cleaners (aka-- Electrostatic Precipitators Agglomorators Service requirements for air cleaners
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NAFA Guide To Air Filtration Chapter 6 Air Cleaners presented by the National Air Filtration Association Fifth Edition
Air Cleaners • Different types of air cleaners - Media • Electronic Air Cleaners (aka-- Electrostatic Precipitators • Agglomorators • Service requirements for air cleaners • Standards for operation
Media Air Cleaners • Most media-type air cleaners use HEPA filters and molecular (activated carbon) afterfilters to clean the air.
Media Air Cleaners • Air cleaners also come in whole-house residential styles that add-on to the existing HVAC unit
Electronic Air Cleaners Two-stage electronic air cleaners utilize: • an ionizer section • a collector section
Efficiency • The ASHRAE 52.2 filter test method has no specific procedure for testing the loading of electronic air cleaners – carbon fouls units • The efficiency is highest when the plates are clean. • Velocity and humidity sensitive.
Prefilters • Low-efficiency air filters upstream of an electronic air cleaner: • Filters will act as air distribution panels to equalize the airflow. • Will capture large particles that could bridge the plates and cause a short or arcing • excessive power consumption • snapping noise • Elimination of arcing helps control ozone generation.
Factors Affecting ESP Design & Efficiency • Their successful use depends on the following: • Particle Size • Velocity through the filter • Voltage on Ionizer and Collector • Collector Plate Spacing • Collector Plate Loading • Ionizer Spacing • Ozone
Service Requirements • Electronic air cleaners should be designed for easy cleaning. • Important design considerations: • Insulators: high quality arc-resistant material and mounted out of the airstream. • Easy access to the ionizer and collector cells. • Some provision for isolating a section in large multi-component units if one becomes defective.
Standards for Electronic Air Cleaners • UL 867 “Standard for Electronic Air Cleaners: Unites States • Covers electrical and fire safety requirements. • It makes no comment about the air-cleaning ability of electronic air cleaners • CSA C22.2 No. 187-Mi986 Canadian Standard: • Specifically states (Par.i.5) that the Standard does not specify the effectiveness of air cleaners with respect to the removal of airborne particles. • Association of Home Appliance Manufacturers Association (AHAM) AC-1-2006
Applications Not Suitable forElectronic Air Cleaners • Conditions of very high humidity • Systems where there can be a build up of explosive gases. • Unattended equipment where periodic maintenance procedures are not assured.
Dust Disposal • The removal of dust that an electronic air cleaner has captured can be accomplished in two ways: • It can be washed off the collector plates. • If it has agglomerated on the plates, it can be allowed to blow off the plates. The blow-off is then captured by a mechanical filter downstream of the agglomerator cells
Washable Electronic Air Cleaners • When the collector plates became loaded with dust so that the performance of the electronic air cleaner is reduced, the power is shut off and the plated are washed.
Washing • Removable component assemblies. • Washing tanks • Manual wash in place. • Power spray with detergent • Automatic wash in place. • Built in spray nozzles • Mobile washers. • Large installations
Agglomerator Units • Dry collector plates with a strong bond between the small dust particles and the collector plates. • The particles on the plates form agglomerates. • As the agglomerates grow larger, their attraction to the plate is reduced and finally these agglomerates may be introduced back into the airstream.
Afterfilters • Automatic Roll Filters • Capture agglomerates – larger particles • Because the face velocity is not uniform, it can cause variations in efficiency. • Extended Surface Filters • MERV 14 • More uniform air flow creates conditions for the agglomerator to operate at optimum efficiency.
Sample Questions • Electronic Air Cleaners cannot be tested for loading using the ASHRAE 52.2 test because? The carbon in the Test Dust shorts out the electrical connections of the unit. • One advantage of a self-contained ESP is? Washable cell/capture of smaller particles/good for source capture/portable
Thank you. Other Questions ?