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NAFA Guide To Air Filtration Fifth Edition Chapter 6 Air Cleaners presented by the National Air Filtration Association
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: 1. 2. 3. 4. 5. 6. 7. Particle Size Velocity through the filter Voltage on Ionizer and Collector Plate Spacing Collector Plate Loading Ionizer Spacing Ozone
Service Requirements § Electronic air cleaners should be designed for easy cleaning. § Important design considerations: 1. Insulators: high quality arc-resistant material and mounted out of the airstream. 2. Easy access to the ionizer and collector cells. 3. 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 C 22. 2 No. 187 -Mi 986 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 for Electronic 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: 1. It can be washed off the collector plates. 2. 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 ?