TECHNICAL BULLETIN Electrostatic Filtration Separating Fact & Fiction

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1 TECHNICAL BULLETIN Electrostatic Filtration Separating Fact & Fiction Air filters serve a variety of purposes and each filter type has a place. In this bulletin we will address electrostatic filtration whose principle of operation requires a direct electrical connection. The basis for any air filter comparison must always begin with basic particle capture principles 1. Mechanical Principle Particle Capture Media air filters operate through a combination of mechanical particle capture principles. These principles include; straining, inertia, interception and diffusion. Straining is the process of removing larger particles or agglomerations thereof, where diffusion and interception remove smaller sub-micron size particles. It is important to note that each principle shows some efficiency across the total range of airborne particle sizes. Electrostatic Particle Attraction A non-mechanical principle of particle removal requires the addition of an electric charge to the filtering medium to capture particles. These units are referred to as electrostatic precipitators (ESPs). The original ESP was invented by Dr. Frederick Cottrell in In the 1960 s Dr. Gaylord Penny developed the two-stage design that is the basis for most ESP HVAC level designs that we see today. ESP filters operate on the principle that positive-charged and opposing negative-charged objects attract to each other and similarly charged objects repel. For air filters, as particles move through the airstream a charge is imparted on a particle as it moves through an ionization zone. As it Mechanical principles of air filtration do not require outside forces of enhancement to operate in HVAC application. Media filters use a combination of these principles to provide consistent MERV performance throughout the life of the filter. The filtration principle of electrostatic attraction requires a constant source of charge (electric) to maintain filter efficiency and filter loading can insulate the particle from the charge. moves through the filtering system it encounters an area of similar or opposing charge that move the particle toward the opposing charge collection surface where it is captured and held there by the opposing forces. Media Type Air Filters Media filters are highly dependent upon the fiber size of the filter media fiber, the smaller the filter fiber the higher the filter efficiency. The operative fiber size is smaller as efficiency increases in MERV 8 filters through MERV 16 filters commonly used in HVAC systems. The finest filter fiber sizes are used in high efficiency particulate air (HEPA) filters which are the most efficient air filters available. These filters are used in clean rooms, hospital operating suites and other areas where ultra-clean air for the protection of people or processes is required.

2 A media type air filter s efficiency remains constant in the sub-micron to 2 micron range and increases slightly when larger particles are considered. A MERV 14 air filter, using fine fiber media, will maintain its efficiency throughout the life of the filter providing MERV 14 performance upon installation, and MERV 14 performance when removed from the system for filter change 2 or 3 years thereafter. Similarly MERV 8 media air filters maintain their efficiency over time although their performance is only considered applicable above 3 microns. Some media type air filters use larger fibers that are enhanced with an electrostatic charge during manufacturer or the fibers are designed with an irregular surface that encourages a slight level of electrostatic attraction when forced air moves across the filter surface. When captured particles start to blind the fibers during filter operation, they start to decrease in particle capture efficiency. This decrease continues over time. The American Society of Heating, Refrigeration and Air- Conditioning Engineers address this phenomenon in their Standard , Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size in Appendix J with the results being published as MERV-A to the filter test reviewer. Size Matters Removal of Smaller Particles is Our Concern Air filters should always be selected based upon the size of the contaminants of concern. Authorities 1 have noted that 0.3 micron to 0.7 micron is a critical range for considering lung damaging particles and is related to the lung pore opening size of 0.5 micron. These particles can enter the opening and create health problems. Particles less than 0.3 micron in size are not considered a concern as they aerodynamically are not respirable. They act similar to gases in that are constantly moving in random patterns not relative to the airflow. The principle is defined as defined as Brownian Motion 2. Gaseous contaminates are not considered with either media type or ESP filters as gases are typically less than micron in size. When gaseous contaminants are a concern they are usually removed from the air by adsorbent media air filters or oxidized by other filters available for that purpose. When considering protecting building occupants from particulate contaminants of concern MERV 13 or MERV 14 filters should be the basis of design based upon their respective 50-80% efficiency in the 0.3 micron range. As an example, MERV 14 air filters are required in critical care areas of hospitals to remove particles that could exasperate the health of individuals that already have compromised immune-systems. These filters also protect visitors and employees. The MERV 14 efficiency is based upon healthbased research dating back to the 1950 s relating to specific size airborne contaminants In the most critical areas of hospitals, HEPA filters are applied as they are the most efficient particle removal filters available. Electrostatic air filters are manufactured in a variety of configurations ranging from large built-up systems used in industrial applications to panel-type filters typically applied in v-bank configurations in commercial HVAC systems. The electrical requirements for industrial systems can be very high while panels typically use step-down 24 volt transformers.

3 By definition HEPA filters are at least 99.97% efficient on 0.3 micron size particles. There are ULPA filters which have a particle capture efficiency of % on particles 0.1 micron in size which are typically applied in manufacturing clean rooms where the cleanliness levels required are extreme. Filters with MERVs of less than 9 are used primarily for the protection of equipment or as prefilters to more expensive final filters removing larger particles that can compromise the second stage high efficiency filter life. ESPs can initially remove particles from 0.01 to 1 micron in size effectively. This initial efficiency across this broad range may be as high as 99.9%. Some factors that can affect particle capture performance include: Particle size An ESP collects particles most easily when the particle size is larger. The generation of the charging corona in the charging area may be suppressed if the airstream has too many small particles (less than 1 micron). Very small particles ( micron) are the most difficult to collect because the charging mechanism may be overwhelmed by diffusional forces or cross-particle charging due to random collisions and exchange of free ions. Particle Resistivity - Resistivity is resistance to electrical conduction. As the filter particle collection surface becomes coated with particles the surface becomes resistive making it harder for a particle or the collection surface to react to an electrostatic charge. Resistivity may also be influenced by the composition of the air stream, temperature and high relative humidity. Another interesting side effect of charged particle filtration is what can happen to charged particles that escape through the collection area that was supposed to remove them. These particles can move downstream, back into the occupied area of the building, and find a surface of opposing charge where they can be attracted to and stick to an unintended surface. In one unusual severe instance, in a large arena where a circus had an extended stay, agglomerated particles with a charge moved through the filtration system and attached themselves to the walls of the arena. The agglomerated particles included adsorbed odors related to the circus animals. The cleaning bill was extensive and the ESP air filtration system was removed in favor of HVAC media filters. An additional negative side-effect of electrostatic precipitation devices is the production of toxic ozone and NOx which can adversely affect health of building occupants. Particle contact with the collection surface can cause an electrical arc and overloaded collection areas may also produce arcing which can generate ozone. Two stage systems (charging section ahead of collecting section) can minimize ozone production, but in any system where the exchange of ions is induced, arcing can occur. In ESPs, power supplies are designed to provide voltage to the electrical field (or bus section) at the highest possible level. The voltage is controlled in most commercial systems to avoid causing sustained arcing or sparking between the charging areas and collecting surfaces but physics dictates that arcing cannot be completely eliminated. As a precaution to this phenomenon an automatic voltage control is supposed to vary the power to the transformer-rectifier in response to signals received from sensors in the precipitator and the transformer-rectifier itself. It monitors the electrical conditions inside the precipitator, protects the internal components from arc-over damages, and protects the transformer-rectifier and other components in the primary circuit. The ideal automatic voltage control would protect the system by holding the operating voltage of the precipitator at a level just below the spark-over level. However, this level cannot be achieved given that conditions change from moment to moment. Instead, the automatic voltage control increases output from the transformer-rectifier until a spark occurs. Then the control resets to a lower power level, and the power increases again until the next spark occurs which can be conducive to the production of ozone and NOx.

4 Resistance to Airflow Any component added to a system that is designed to move air creates resistance to airflow, which directly translates to an energy factor as more power is required of the fan. Although ESPs generally offer a lower resistance to airflow the decrease in particle capture efficiency and resultant poor air quality is a poor trade-off. An HVAC media type filter will maintain or increase in particle removal efficiency, and since that is the sole purpose of an air filter, energy savings or any other side effects of the filtration system becomes moot if the minimum particle removal efficiency is not maintained. Through the years, manufacturers of media type filters have improved filter designs and added additional media area to the filter to lower resistance values. Most media filters will operate within 20% of their initial rated resistance through 80% of the filter s life in an HVAC system. When life-cycle operational techniques are applied, as through Camfil s Life-Cycle Cost (LCC) Green Software, energy costs associated with air filtration can be acutely minimized. The only recognized Standard for evaluating air filters in North America is ASHRAE Standard Standards are prescribed procedures where each step of the procedure needs to be followed to provide results for product comparison. Camfil Farr not only supplies the main page of the report, but also includes all of the required base information to allow in-depth filter performance evaulation..

5 Marketing Beyond the Facts Some of the claims that we have seen published by ESP manufacturers include: 75-95% efficiency on micron size particles including an emphasis on tobacco smoke. Virtually every cognizant authority has condemned the use of tobacco products in areas of human habitation. In fact, most regulations even require smoking areas that are outdoors, far removed from the buildings, based upon concerns of contaminant re-entrainment. In the case of gambling casinos, there is a strong financial concern for keeping people comfortable at the tables even though smoking may be allowed comfortable people will continue to spend money. Some localities have even made code exceptions due to the economic impact. Most local codes in casino areas require a high level (up to 100%) of ventilation air or a filtration system capable of removing the contaminants of concern. The contaminant particle sizes of concern with regard to tobacco smoke are in the 0.01 to 1.0 micron range, having a mass mean diameter of 0.3 micron. Camfil recommends a filter efficiency of MERV 14 with increased air changes to the area of concern with the additional consideration of HEPA filters as the final filter in series. To address the over 4000 gaseous contaminants associated with tobacco smoke, gaseous filters that include carbon and selected oxidizers should be installed. Gaseous contaminants cannot be addressed with any level of efficiency with either media filters or ESPs. Manufacturers that attempt to address smoking with particulate filters alone leave the building owner open to liabilities defined to our legal system through the wealth of knowledge available on the subject. Additionally, the sustained efficiency of media type filters ensures that the filters will continue to remove the most critical particle range of contaminants throughout the life of the filter. References to MERV as an efficiency value or substitution of a conditioning method. By definition, a Standard needs to be followed completely in order for the results to have value to the end user. Standards are developed by recognized industry experts as defined by the cognizant authority which in this case is the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE). When the original ASHRAE 52.2 air filter testing Standard was developed manufacturers of ESPs were voting members of the Standard forming ASHRAE committee and they were specifically tasked with developing a method that would facilitate the testing of ESPs. They repeatedly refused to provide a method that would be acceptable and as such wrote themselves out of the Standard. This inability to address ESP shortcomings has opened the door to their adapting the test Standard to make their products appear superior to conventional media filtration. The results are misleading and often erroneous. Additionally the test dust used in the ASHRAE Standard includes carbon black which can dissipate a charge. MERVs are not applicable to ESPs based upon their principle of particle capture, effectively shortcircuited by the dust. There have been references in some manufacturer s literature to a term MERV-NC. There is no such term defined by any cognizant standard writing body. Originally conceived as a marketingoriented adaptation by an independent testing lab, it involves providing a MERV without doing the dust loading The loading is a key requirement of the Standard. Standards are written through a consensus process by recognized industry professionals to help guide the users of products. Picking and choosing which parts of a document that you wish to meet is not meeting the Standard. MERV-NC is not a part of ASHRAE Testing without dust loading changes the basic intent of the Standard and trying to justify this behavior with an undefined term (MERV-NC), is misleading at best. In these tests they note that they perform only the first part of a two part test as they claim that it is all that is required to obtain a MERV for the filter under test.

6 The particle size versus efficiency levels used in the ASHRAE Standard (PSE) are a set of 12 data points that are a measurement of the filter s ability to remove particulate from the air based on the size of those particulates. The twelve different particle size ranges are between 0.3 micron and 10.0 micron and are specifically defined in the Standard. To meet the Standard there must be a total of six PSE evaluation data sets. The resultant MERV is a composite of these six PSE data sets. The Dust Holding Capacity (DHC) is measured by the amount of ASHRAE dust the filtration device will hold to a set final resistance to airflow. PSE measurements are taken before any loading (clean filter), and at four stages throughout the loading process (to see how the filter performs during the loading) and then there is a final PSE measurement after the loading is completed. The composite PSE data from each of these 6 PSE data sets is used to determine the filter s MERV value. Thus, the complete set of PSE data has to be measured to be able to determine the MERV per ASHRAE Thus, it is not a 2 part test, but an integral test of alternating efficiency measurements and loading steps to determine the filter performance characteristics. In some manufacturer s published graphs within sales literature, the manufacturer notes the use of SAE fine dust instead of ASHRAE Test Dust. SAE fine is a dust that is used for evaluating dust collection equipment and automotive air filters. The corresponding proportion of sizes between the two different dusts is more than 3 to 1, totally unacceptable when making comparisons between products and certainly not applicable to the basis of filter comparisons, ASHRAE Standard A graph is also presented to compare relative ESP life to media bags and box filters. A missing plot value is the ESPs particle size versus efficiency over time this time period; this level of loading severely insulates the charge associated with particle capture and misleads the reader with this lack of information. The Standard was also designed to compare filters of similar construction when levels of dust holding capacity are defined as a matter of filter-to-filter comparison with the published caveat that the published value has nothing to do with how long a filter will last in actual application. ESPs were intentionally left out of the Standard based upon the ESPs principles of performance. If the complete Standard criteria were applied, the ESPs results would be at a severe disadvantage for comparison to other filters. Likewise, ESP manufacturers cannot pick and choose which sections of the Standard apply to their product or adapt the Standard in principle by using a different loading dust. Additional concerns include: There is no recognized Standard as published by an independent cognizant authority for substantiating claims. All historical data relating to ESP performance in commercial building HVAC applications, indicates that ESP filters drop in efficiency over time. Camfil s testing labs also confirm reduced ESP efficiency over time. As dust accumulates on the filters the airborne particles moving through the system become insulated from the charge which is designed to attract them. To avoid efficiency degradation an ESP system requires frequent cleaning. ESP systems require proprietary replacement components. Media type air filters are produced by a variety of manufacturers and are designed to be installed in universally-accepting filter holding mechanisms, filters can commonly be interchanged between manufacturers. ESPs require return to the single-source supplier. When costs are evaluated over time the expense can be prohibitive. As the technology of filtration evolves towards improved performance, the ease of design upgrade becomes apparent. The average media type air filter pressure drop has decreased over 50% in the last ten years based upon improved product designs. Based upon current research, the trend towards more energy-efficient filters and higher filter efficiencies,

7 new concepts will fit in existing filter holding mechanisms. Graphs of data used to portray performance variance are incomplete, with missing velocity values, dust feeding rates, or any reference to any recognized testing Standard. Any data representative of the performance of a product should note all the parameters used in the evaluation. As an example, reducing the airflow in a test from 500 feetper-minute to 300 feet-per-minute can skew the results by as much as 300%. Media filters will show radical improvement, especially in terms or energy usage. With both types of filters, there may even be an increase in particle capture efficiency. That is why there are Standards published by cognizant authorities, to ensure a baseline of equivalent evaluation. Published statements relating to a germicidal or detrimental effect on organisms (bacteria, viruses) or removal of gaseous contaminants by ESPs. References to the above, relating an ESPs effectiveness on these items, are oblique at best. In a properly run HVAC system these items become inert as moisture and nutrients that support their proliferation are removed. This is consistent with any filter that may be installed in a properly operating HVAC system. Reference to the removal of gaseous contaminants. The reaction of ozone, a byproduct of ESPs will breakdown other gaseous contaminants. However, when some of the affected contaminants are separated into sub-contaminants from an original source, the result can be of more concern than the original base contaminant. If there is no ozone production as some ESP manufacturers note, then the only gaseous contaminant capture would be the gases that have adsorbed into the particulates, not an inherent benefit of one particulate filter over another. In real world application particulate air filters should not be considered as gaseous contaminant removal filters; the levels of removal efficiency are insignificant. Any statement to the contrary does not withstand scientific scrutiny. Targeting of the health care industry. The health care industry has defined air filtration requirements based upon their concerns for the protection of patients, employees and visitors. The most commonly defined requirement is a MERV 8 filter upstream of the coil because of coil wetting, and a MERV 14 filter downstream of the coil as the common final barrier to particles of concern for common hospital areas. A single stage of air filtration is not acceptable, and any filter that has even a remote chance of not meeting the continued contaminant capture efficiency is not acceptable. The historical efficiency loss of ESPs is recognized by cognizant authorities and some design guidelines specifically prohibit ESPs as the base for contaminant control in hospitals. Local codes require a UL rating for electrically-connected components. Most localities require UL Certification for any electrical component installed in an HVAC system. Reference to ASHRAE 62.1 Indoor Air Quality Procedure. The indoor air quality procedure (IAQP) as defined in ASHRAE 62.1 requires the designer to address both particulate and gaseous contaminants. One ESP manufacturer states in reference to using their product per the IAQP The air-cleaning used to clean the recirculated air should be designed to reduce particulate and, where necessary and feasible, gaseous contaminants. This is a totally inaccurate statement as the gaseous contaminants of concern must be defined up front including those that may exist in the outside air, and those that may be produced during building occupancy. At that point the specific method of control, based upon those identified gaseous contaminants must be defined, as well as the prescribed adsorbent filter s efficiency on those specific contaminants. Reference to a LEED Credit for using a specific air filtration technology. The United States Green Building Council in their Leadership in Energy and Environmental Design program does not offer a 1 point credit for the use of a specific air filtration product. The minimum

8 TECHNICAL BULLETIN Electrostatic Filtration Separating Fact & Fiction requirement for any building for LEED certification is that a MERV 13 filter be the basis of design, any MERV 13 filter. Since there are no specific tests for ESPs, and Standard 52.2 specifically excludes ESPs, they cannot meet the minimum basis of design and the building should not receive LEED Certification. MERV is not applicable to an ESP. Additional references to Indoor Air Quality Credits or Reduced Energy Credits in LEED require the design engineer to demonstrate applied technologies above and beyond what would be considered normal design. These concepts may be applied using technology from media or ESP manufacturers with no product advantage one way or the other. It should be pointed out that there are applications that support all types of air filters and every filter has a place. At the same time, some filters are marketed as a cure-all for any or every air quality concern when the physics and principles of filtration do not support these claims. 1 American Society of Heating and Air-Conditioning F Handbook, HVAC Systems and Equipment Chapter 29 2 American Society of Heating and Air-Conditioning F Handbook, Fundamentals, Chapter 11, and Health and Environmental Effects of Particulate Matter, U.S. Environmental Protection Agency; and Indoor Air Pollution Fact Sheet, American Lung Association; 3 Brownian Motion: Additional document references: ASHRAE , Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size, ASHRAE, 1791 Tullie Circle, N.E. Atlanta, GA 30329, The Modern Problems of Electrostatics with Applications in Environment Protection, NATO Science Series, Inculet, Tanasecu and Camariuc Camfil Laboratory Report: ASHRAE Testing of Dynamic Air Cleaner by Environmental Dynamics Group ESP Patent Reference 4,351,648 Dr Gaylord Penny, Beachler, D. S., J. A. Jahnke, G. T. Joseph andm.m. Peterson Air Pollution Control Systems for Selected Industries-Self-Instructional Guidebook. (APTI Course SI:431). EPA 450/ U.S. Environmental Protection Agency Bethea, R. M Air Pollution Control Technology-an Engineering Analysis Point of View. New York: Van Nostrand Reinhold Katz, J The Art of Electrostatic Precipitators. Munhall, PA: Precipitator Technology Nichols, G. B. 1976, September. Electrostatic Precipitation. Seminar presented to the U.S. Environmental Protection Agency. Research Triangle Park, NC Richards, J.R Control of Particulate Emissions-Student Manual. (APTI Course 413). U.S. Environmental Protection Agency, Turner, J. H., P. A. Lawless, T. Yamamoto, D. W. Coy, G. P. Greiner, J. D. McKenna, and W.M. Vatavuk Electrostatic precipitators. In A. J. Buonicore and W. T. Davis (Eds.), Air Pollution Engineering Manual (pp ). Air and Waste Management Association. New York: Van Nostrand Reinhold U.S. Environmental Protection Agency Air Pollution Engineering Manual. 2d ed. AP-40 U.S. Environmental Protection Agency Operation and Maintenance Manual for Electrostatic Precipitators. EPA 625/1-85/017 White, H. J Electrostatic precipitation of fly ash. APCA Reprint Series. Journal of Air Pollution Control Association. Pittsburgh, PA Copyright 2013 Camfil - ESP Technical Bulletin