Technical Brief. 3M Commercial HVAC Filters. Commercial HVAC Filter Efficiency Reporting Value. Abstract. Introduction

Transcription

1 3M Commercial HVAC Filters Technical Brief Commercial HVAC Filter Efficiency Reporting Value Abstract The effi ciency of fi lters utilized in the HVAC industry is characterized by the Minimum Effi ciency Reporting Value (MERV), as defi ned in the ASHRAE standard. When originally adopted in 1999, it was recognized by the standard committee that the MERV value did not predict the full drop in effi ciency of electret media in actual use in many HVAC environments. ASHRAE has adopted an improved method that more accurately predicts the drop in effi ciency of electret media in commercial and industrial environments. This improved fi lter conditioning protocol is included in as Appendix J, having a designation of MERV-A. 3M Commercial HVAC Filters A13 and A11 are specifi cally designed to provide predictable particle capture effi ciency per Appendix J. To help provide the maximum energy savings potential, 3M s innovative HVAC fi lters utilize a composite media that contains a highly engineered, proprietary electrostatically charged (electret) polypropylene microfi ber layer. 3M has successfully developed products that retain a signifi cant electret component at the effi ciency minimum determined by Appendix J. 3M s fi ltration media consists of an optimized balance of electret and mechanical fi ltration components resulting in a low pressure drop, high particle loading fi lter that is robust in commercial and industrial HVAC environments. Introduction HVAC air fi lters are critical to the effi cient operation of the air handling system of any building. They provide additional protection for the equipment within the air handling system 1 and provide an important component to an Indoor Air Quality management program. 2,3 Higher particle reduction effi ciency results in cleaner air moving through the building s air handling system. Importantly, HVAC fi lters may also contribute substantially to the energy required to move air within a building as a result of the pressure drop across the fi lter, or a bank of multiple fi lters. 4,5 The pressure drop of the fi lter increases over time as it loads with environmental debris, hence, the energy utilization correspondingly increases over time. The total energy required to move air through a fi lter is directly related to the average pressure drop over the fi lter life. The greater the ability of a fi lter to load without substantial increase in pressure drop, the greater the possible energy savings. The choice of a fi lter is in large part based upon these three fundamental attributes: effi ciency, initial pressure drop, and filter loading. 3M s design approach for the 3M Commercial HVAC brand fi lters is based on ensuring that the particle capture effi ciency meets the most stringent requirement set forth by the leading industry standard test method. This test method is rigorously defi ned by ASHRAE 52.2 (2007): Method of Testing General Ventilation Air-Cleaning Devices for Reduction Effi ciency by Particle Size (Appendix J). Filters rated by this test protocol are designated with a MERV-A reporting value (Minimum Effi ciency Reporting Value, where A designates that the testing was done per Appendix J of the standard). 3M Commercial HVAC fi lters are highly engineered to provide the optimum balance of these properties for commercial and industrial air handling systems. To provide the most value for the building owner and operator, 3M Commercial HVAC fi lters are precisely designed to minimize the total energy utilization at each effi ciency level. Energy utilization is minimized by designing a product with very low initial pressure drop and low rate of pressure drop increase as it loads in-use. This is accomplished by control and optimization of every component of the product from media to pleat structure to frame design. This requires an iterative process of media and fi lter development, design and performance testing.

2 3M s innovative fi ltration media is a composite containing a highly engineered, proprietary electrostatically charged (electret) polypropylene microfi ber layer. Each layer in this composite contributes to a fi lter having a unique balance of mechanical and electrostatic fi ltration mechanisms. Importantly, the composite media is designed to help ensure a long life from both a pressure drop and minimum effi ciency perspective. 3M s unique fi ltration media is based on advanced materials and processes that result in a stable, long life electret. By truly optimizing media structure and media charge, 3M is able to provide a fi lter that is robust in HVAC environments as validated by the challenging conditioning protocol defi ned in ASHRAE Appendix J. In-Use Particle Capture Efficiency It is well known that electrostatically charged media (electret media) provides the potential basis for a fi lter having very low initial pressure drop compared to fi lters utilizing uncharged media of the same fi lter design and effi ciency. 6 Electret media is composed of fi bers containing a bipolar distribution of positive and negative charges, yet being charge neutral overall (see following illustration) 7. Fiber with line dipole charge It is also well known that the effi ciency of electret based fi lters, including 3M s, will reduce over time to some extent in HVAC and other environments. 8,9 It is important to note that this in-use effi ciency reduction is not a result of the electret charge stability itself. The charge level on 3M s media remains essentially unchanged for years when stored in temperature and humidity conditions found in the most extreme HVAC environments. Instead, the in-use effi ciency reduction is a direct result of the initial loading of the media with particulates in the environment. This effect is an inevitable consequence of the fact that airborne particles in the environment carry a bipolar charge distribution. When a charged particle is drawn to media having an opposite charge, the effect is to shield or neutralize that charge to subsequent airborne particles. At the same time, as particles are captured the effective media fi ber area is increasing, thereby, increasing the mechanical capture effi ciency. The balance in electret and mechanical effi ciency mechanisms and how they vary over time is shown generically in the following graph. Example Particle Capture Efficiencey (%) Minimum Efficiency Electret Component at Minimum Electret Mechanical Total Time In-Use 2

3 There are many factors which impact the specifi c transient effi ciency and pressure drop behaviors. Primary among these factors is the precise chemical and mechanical structure of the fi ltration media, including the media polymer and charge additive chemistry, the media formation process, the average fi ber and size distribution, and the electret charging process. In addition, the fi lter design will impact this behavior since media face air velocity and particle loading rate are important. The environmental conditions are equally important in determining this transient particle capture behavior including particle charge, average particle size and size distribution, air fl ow velocity and humidity. These factors are all dependent on a given location and air handling system. The most important of these environmental factors is the particle size distribution challenging the fi lter. Small particles have a much greater impact on the shielding effects of the electret, particularly when considering the build-up of mechanical effi ciency. It is clear that electret fi lters can be designed to maintain an important level of charge at the point that the total effi ciency is at its minimum. However, to do so in the widest range of environments requires a highly engineered product from media to fi lter, designed specifi cally for HVAC environments. ASHRAE : Method of Testing General Ventilation Air-Cleaning Devices for Reduction Efficiency by Particle Size The performance of a fi lter, particularly an electret fi lter, is dependent on many factors, related to both design and environment. The in-use effi ciency performance for an electret will vary from that in which there is little reduction in the effective charge prior to the mechanical effi ciency increase to that in which the electret reduction is more signifi cant. The challenge is to effectively quantify the minimum in-use performance in a laboratory protocol knowing that performance will be better in many environments. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has developed such an HVAC fi lter test standard, to provide a robust basis to compare fi lters by predicting a uniform level of known performance under operating conditions with reasonable certainty. When this protocol is used a Minimum Effi ciency Reporting Value is used to characterize the fractional effi ciency from 0.3 to 10 microns and is referred to as MERV. When originally adopted in 1999 the organization clearly recognized that the initial conditioning step of the dust-loading procedure described in this standard may affect the effi ciency of the fi lter but not as much as would be observed in actual service. Therefore, the minimum effi ciency observed during testing may be higher than that achieved during actual use. To address this important shortcoming in the standard an improved fi lter conditioning protocol was adopted that more nearly represents the minimum effi ciency points in actual real-world use. This improved protocol is the result of extensive laboratory and fi eld work completed over numerous years by a number of research groups and technical experts. This optional conditioning protocol is included in Standard as Appendix J. When the test in Appendix J is used, the minimum effi ciency reporting value is referred to as MERV-A. Extensive discussion of the difference between the conditioning protocol outlined in the body of the standard and that in Appendix J is provided in ASHRAE RP The fundamental difference is the size distribution and quantity of challenge particles. In the standard conditioning, the challenge dust is 72% ISO test dust (ISO fi ne), 23% powdered carbon, and 5% milled cotton linters by weight. 12 The powdered carbon (e.g., average particle size of 100 microns) and cotton linters (e.g., 4 mm screen) particle sizes are large, compared to the ISO fi ne dust. The median particle size of ISO fi ne dust is around 7 microns by volume. The median size of the particle challenge specifi ed in Appendix J is around 350 nm by volume and 35 nm by number. 3

4 ASHARE Appendix J conditioning protocol was not inherently developed to fully discharge an electret fi lter. As discussed in the ASHRAE RP-1190, it is possible to completely discharge the electret media by various means including an isopropanol dip, as in the European EN 779 standard, or exposing the fi lter to ionizing radiation such an x-ray source. 13 However, instead of adopting one of these conventional approaches, the small particle challenge protocol in Appendix J was chosen. To ensure that electrostatic mechanisms have the potential to contribute to the total effi ciency at the conditioned minimum, a maximum exposure time has been set when either (a) the effi ciency shows no more than two percentage point drop in two or more adjacent particle size ranges relative to the minimum effi ciencies ranges measured or (b) the cumulative exposure of the fi lter reaches a value estimated to be the maximum encountered in a year. Particle size effi ciency measurements are performed similarly for both conditioning protocols in that the fractional effi ciency (i.e., the capture effi ciency in 12 channels from 0.3 microns to 10 microns) is measured following a number, or sequence, of defi ned conditioning and loading intervals. A Composite Minimum Effi ciency (CME) curve is derived from the minimum effi ciency measured at any interval in each particle size channel. From this composite minimum, a MERV level is determined from a lookup table published in the standard. For the standard conditioning with ASHRAE dust the fi rst step includes a dust loading of 30g or an increase of 0.04 in. of water pressure drop across the fi lter, whichever comes fi rst. Subsequently, the increments are determined by dust-loading steps that achieve an airfl ow resistance increase of one-quarter, one-half, and three quarters of the difference between the beginning and the maximum recommended airfl ow resistance. A CME is derived and converted into a MERV value. Dust holding capacity (DHC) and mass arrestance effi ciency are also measured during this procedure. The conditioning sequence for the Appendix J protocol is much more intensive. It consists of a series of steps of exposing the fi lter to the small particle potassium chloride challenge. The conditioning sequence is concluded based on the above criteria. This is then followed by the dust loading sequence used in the standard protocol. Again, a CME is derived and converted into, in this case, a MERV-A value, along with a DHC-A. A fi nal important note is that complete discharging was found in all electret fi lters evaluated in the development of the Appendix J protocol. However, the report discusses the potential for future long life electrets. 3M has developed such a desired long life electret fi lter based on numerous innovative advances in media chemistry and structure, as well as fi lter design. 3M Commercial HVAC Filter Performance The 3M Commercial HVAC products have been designed specifi cally for building air handling environments where predictable particle capture effi ciency, low pressure drop and potential energy savings are paramount. Low fi lter pressure drop is attained through an innovative combination of fi lter materials and processes, resulting in a highly charged stable electret media. The rate of pressure drop rise during use is minimized through a composite, lofty media ensuring that particles are captured through the depth of the media, delaying, if not preventing, face loading. These two media performance attributes are maintained in the fi nal product by optimized fi lter design and precision production. 3M Commercial HVAC Filters MERV-A13 and MERV-A11 are based on advancements in blown microfi ber (BMF) media and product design. The product performance of these 3M Commercial HVAC Filter products is provided in the following table. 3M Commercial HVAC Filter Mini-Pleat Product Comparison Testing per ASHRAE MERV-A Reporting Value Air Flow Resistance Air Flow 492 fpm ( Water) Dust Holding Capacity (grams to 1.4 Water) A A

5 The graph on the following page shows the impact of the two ASHRAE conditioning protocols when applied to the 3M Commercial HVAC MERV-A13 fi lters. In addition, the effi ciency of a clean and x-ray discharged fi lter is included for reference. The curves are the average over a number of fi lters that have been tested using 3M s ASHRAE 52.2 standard test duct combined with results obtained by an external independent test organization. The fractional effi ciencies have been averaged as defi ned in 52.2 and characterized as a reporting value in the subsequent table. The fractional effi ciency of a clean fi lter is shown as the dotted blue line. This is the effi ciency that is measured on a new fi lter. This also represents the general effi ciency characteristics that should be measured on start-up in a facility. The dashed red line shows the effi ciency upon standard conditioning with ASHRAE test dust. As anticipated the effi ciency is reduced with the resulting effi ciency reporting value of MERV-14. The average initial pressure drop for the A13 fi lter is 0.39 of water and the maximum recommended pressure for the 3M Commercial HVAC Mini-Pleat fi lter line is 1.4 of water. In all fi lters tested, the minimum effi ciency was found to be at the second loading interval or ¼ of the total dust load, or after 0.64 of water. The effi ciency drop is most pronounced for the smaller particles in the E1 range. This result is anticipated as the electrostatic force is relatively greater for small particles. The effi ciency following conditioning per the Appendix J protocol is shown as the dashed green line. The effi ciency reduction more signifi cantly impacts both the E1 and E2 ranges. The average effi ciency drops for these two ranges are 28% and 8%, respectively. The conditioning time to achieve the minimum was between 7 and 13 hours. The general transient characteristic of the effi ciency reduction was that E3 attained its minimum then began to increase fi rst while E1 and E2 continued to decline. This continued until E2 attained its minimum then began to increase while E1 continued to decrease, until its minimum was attained. The last curve shown on the graph is that for an x-ray discharged clean fi lter. This shows the effi ciency in the complete absence of the electrostatic charge attribute of the media. This protocol for discharging a fi lter is not part of the 52.2 standard. Nonetheless, this is a valuable technique in quantifying the contribution to fi lter performance provided by the electrostatic charge on the media. The drop in E2 effi ciency from a clean fi lter to discharged fi lter is 17%, while that from an Appendix J conditioned to discharged fi lter is 9%. In other words, the electret charge contributes 9% to the total E2 effi ciency at the conditioned minimum. This is an important 9% from a potential energy savings standpoint. The pressure drop of a media is the result of the mechanical structure of the fi bers in the media. It is this same mechanical structure which is responsible for the mechanical only component of the particle fi ltration. It is possible to increase the mechanical fi ltration effi ciency while maintaining pressure drop but only at the expense of dust holding capacity. These three characteristics are inter-related in a fairly complex fashion. Nonetheless, a fi lter having a mechanical only E2 effi ciency of 90% would have a substantially higher initial pressure drop, and/or substantially lower dust holding capacity, than one having 81%. The minimum E2 and E3 effi ciency requirements for a MERV-A13 fi lter is 90%. There is no requirement for the E1 effi ciency range in reporting values less than MERV-A14. As can be seen in the table below, the 3M Commercial HVAC Filter MERV-A13 has been designed for a low pressure drop while meeting these minimum effi ciency requirements following conditioning per Appendix J. 5

6 100 3M TM Commercial HVAC Filter MERV-A13 Fractional Efficiency per ASHRAE at 492 fpm KCI Efficiency (%) Clean Filter Standard Conditioning Conditioning per Appendix J Clean Filter Following X-Ray Discharge 0 0 E1 E2 E Particle Size (microns) 3M Commercial HVAC Filter A13 Average Efficiencies per ASHRAE 492 fpm Particle Size Range (micron) Clean Filter Standard Filter Conditioning Conditioning per Appendix J X-Ray Discharged E1: % 84 64% 53% E2: % 97 90% 81% E3: % % 98% MERV-14 MERV-A13 For comparison, the same performance characteristics are shown below for the 3M Commercial HVAC Filter MERV-A11 below. The general behavior is very similar to that for the A13 except that the magnitude of effi ciency drop upon conditioning is more signifi cant. The E3 effi ciency drops by 3% upon conditioning per Appendix J and 13% for a completely discharged fi lter, whereas E2 drops by 23% and 40%, respectively. The electret component remaining at the conditioned minimum is 17% for E2 and 10% for E M TM Commercial HVAC Filter MERV-A11 Fractional Efficiency per ASHRAE at 492 fpm KCI Efficiency (%) Clean Filter Standard Conditioning Conditioning per Appendix J Clean Filter Following X-Ray Discharge 0 0 E1 E2 E Particle Size (microns) From this detailed data analysis it is clear that 3M has developed a long life electret fi lter as validated by the rigorous conditioning protocol defi ned in ASHRAE Appendix J. 3M Commercial HVAC Filter A11 Average Efficiencies per ASHRAE 492 fpm Particle Size Range (micron) Clean Filter Standard Filter Conditioning Conditioning per Appendix J X-Ray Discharged E1: % 67% 33% 20% E2: % 97% 68% 51% E3: % 98% 94% 84% MERV-13 MERV-A11 6

7 1 Air-Conditioning and Refrigeration Technology Institute, Report:ARTI-21CR/ US Green Building Council (USGBC) LEED v.3 ( 3 EPA Indoor Environments Division ( 4 Avery, R.H., Air Filtration: Resistances, Energy and Service Life, Heating, Piping, Air-Conditioning,. December Also sited in NAFA Guide to Air Filtration. NAFA Certifi cation Committee, t. Washington, DC: NAFA, See for example, Energy Consumption Characteristics of Commercial Building HVAC Systems Volume II: Thermal Distribution, Auxiliary Equipment, and Ventilation ( nal_report. pdf). 6, 7 ASHRAE Report: Investigation of Mechanism and Operating Environments that Impact the Filtration Effi ciency of Charged Air Filtration Media, 1189-TRP. 8 See for example, L.I. Johnson, et. al, Effi ciency of Degraded Electret Filters: Part I and Part II, Journal of the International Society for Respiratory Protection, Vol. 20 (2003), pg ; A. Wang and KC Hofacre, Assessment of Advanced Building Air Filtration Systems, EPA/600/R-08/032 (2008), 9 Raynor, P.C. and Chae, S.J., The Long-Term Performance of Electrically Charged Filters in a Ventilation System, Journal of Occupational and Environmental Hygiene, 1: ANSI/ASHRAE Standard , Method of Testing General Ventilation Air-Cleaning Devices for Reduction Effi ciency by Particle Size. 11 Hanley, J.T. and Owen, M.K., Develop a New Loading Dust and Dust Loading Procedures for he ASHRAE Filter Test Standards 52.1 and 52.2 Final Report, ASHRAE Project No PR, August See for example commercially available ASHRAE Test Dust from Powder Technology Inc., Ewing Avenue South, Burnsville, MN ( 13 3M s preferred method for discharging the charge on an electret fi lter is x-ray exposure. Rousseau, A.D., et. al., Effects of Ionizing Radiation on the Performance of Advanced Electret Filter Media, presented at the 7th International Symposium on Protection Against Chemical and Biological Warfare Agents, Stockholm, Sweden, June (2001). 7

8 IMPORTANT NOTICE: The information in this literature is based on tests 3M Purifi cation Inc. believes are reliable. It is not and should not be relied on as a product or technical specifi cation. We do not guarantee the accuracy of this information. You are responsible for determining whether products described in this literature are fi t for a particular purpose and suitable for your application. Because there are many factors within your knowledge and control that might affect the use and performance of these products, you must evaluate these products to determine whether they are fi t for a particular purpose, are suitable for your application, and meet your performance expectations. 3M PURIFI- CATION INC. IS NOT LIABLE FOR ANY LOSS OR DAMAGES, WHETHER DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL ARISING OUT OF THE USE OF OR INABILITY TO USE ANY OF THESE PRODUCTS. CAUTION: USED FILTERS MAY CONTAIN CONTAMINANTS FROM OPERATION OF THE HVAC SYSTEM. FOR PROPER HANDLYING OF USED FILTERS, CONSULT APPLICABLE HEALTH AND SAFETY STANDARDS OR CONTACT AN INDUSTRIAL HYGIENIST. TO REDUCE RISK OF ILLNESS OR INJURY, ALWAYS USE APPROPRIATE RESPIRATORY PROTECTION AND PROTECTIVE CLOTHING WHEN REMOVING OR HANDLING USED FILTERS. DISPOSE OF USED FILTERS ONLY IN ACCORDANCE WITH FEDERAL, STATE AND LOCAL LAWS AND REGULATIONS. IMPORTANT USE RESTRICTIONS: DO NOT EXPOSE THIS FILTER DIRECTLY TO UV RADIATION FROM A UV PURIFICATION SYSTEM. EXCESSIVE UV EXPOSURE MAY LEAD TO A REDUCTION IN THE MECHANICAL INTEGRITY AND PERFORMANCE OF THE FILTER. THIS FILTER MUST NOT BE USED FOR THE FOLLOWING UNATHORIZED USES: A) ASBESTOS, LEAD OR MOLD REMEDIATION; B) BIOTERRORISM PROTECTION; C) APPLICATIONS IN BUILDING THAT REQUIRE OR ARE UNDERGOING AIR HANDLING SYSTEM REMEDIATION OF HAZARDOUS SUBSTANCES; OR D) PROTECTIVE ENVIRONMENTS PER AIA GUIDELINES. LIMITED WARRANTY: 3M Purifi cation Inc. warrants that these products will be free of defects in material and manufacture when shipped. This is the exclusive remedy for any defects in these products. This warranty does not apply to damage or defects resulting from improper use, storage or maintenance of these products. LIMITATION OF LIABILITY: User must determine whether these products are fi t for a particular purpose, suitable for user s application and meet user s performance expectations. 3M Purifi cation Inc. IS NOT LIABLE FOR ANY LOSS OR DAMAGE, WHETHER DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL, ARISING OUT OF THE SALE, USE OF, OR INABILITY TO USE ANY OF THESE PRODUCTS REGARDLESS OF LEGAL THEORY. Your Local Distributor: 3M Purification Inc. 400 Research Parkway Meriden, CT U.S.A. (800) (651) cation.com/airfi lters 3M is a trademark of 3M Company. LEED is a trademark of the U.S. Green Building Council M Company. All rights reserved. Please recycle. Printed in U.S.A REV 0214