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Conditioning Air Filters with IPA Vapor
NAFA TECH2012 Phoenix, AZ
April 19, 2012
Monroe A. Britt
Green Leaf Technologies
HVAC General Ventilation Air Filters
Medias used in air filters may contain an electrostatic charge
Charged medias may cause increase in particle size efficiency
Charged medias may decrease in efficiency over time
• charge may dissipate
• charge may become masked by dust particles
Installed filter may not be providing degree of protection as believed by user and required for intended purpose
Possible Causes for Reduced Filter Efficiency
High humidity
Sensible moisture
Elevated temperature
Atmospheric dust particles
• Cigarette smoke
• Diesel fume
Atmospheric aerosols
• Cooking oil
• General hydrocarbons
Etc. Etc, Etc
Not all charged medias response to all contaminants to same degree
Recommended Reference
ASHRAE Research Project ---- RP 1189
“Investigation of Mechanisms and Operating Environments that Impact the Filtration Efficiency of
Charged Air Filtration Media”
VTT Technical Research Centre of Finland VTT Industrial Systems
Matti Lehtimaki – Chief Research Scientist
Why “Condition” Filters?
To provide lab test results that better conform to “real life” service performance ---- better “apple-to-apple” comparisons
Same filter performance can vary greatly from site to site No one lab test method can accurately predict filter “real life” service
performance --- true for charged or un-charged medias User of filter should be made aware of the possibility of efficiency decrease and
to what extent would be expected under typical severe environmental conditions
Air filter laboratory test methods require COMPROMISE
Current Methods of Conditioning Air Filters
• ASHRAE 52.2 -- Informative Appendix J
Conducted on full size filters and establishes MERV A ranking and MERV A Dust Holding Capacity
• EN 779 -- conducted on flat sheet media or filter section , presently test data not used to assign G and F numbers
ASHRAE 52.2 KCl Conditioning Procedure
• Feed very large concentration (106 particles/cm3) of very fine KCl particles (less than 0.1 microns) until:
a. Efficiencies meet “convergence”
criteria (<2% difference in two adjacent bands), or
b. Total “particle concentration times
time” (CT) reaches pre-determined
limit (109 particles/cm3 – minute)
• Some filters may require over 24 hours of conditioning
Laskin Nozzle Sub-micron Particle Generators
Laskin Nozzle Particle Injection Into Duct
Condensation Particle Counter
Typical Conditioning Curves
EN 779-2011(E) Method of Discharge
Sample -- Flat Sheet or section of air filter
No. of samples --at least three, each with minimum area of 600 cm2 ( 93 in2)
Measure efficiency of samples at nominal velocity of 100% and 50%
Immerse in liquid isopropanol alcohol (IPA) for two minutes ---- 99.5% IPA
Place wet samples on perforated surface for drying – 24 hours - weigh after to insure samples are dry
Measure efficiency of conditioned samples at nominal velocity of 100 % and 50%
EN 779-2011(E) Influence of Discharged Flat Sheet Efficiency
IPA Vapor Conditioning of Air Filters
• ISO TC 142 WG9 --- Test Standards for Gas Turbine Intake Air Filter
• First proposed for flat sheet media conditioning method
• “Proposal on new preconditioning method”, Y. Ogaki, Japan Delegate
• “Comparisons of the dipping and fumigation methods for the discharge of electrets filtration media”, J. Cai, China Delegate
Proposed flat sheet IPA vapor method
Flat Sheet IPA vapor exposure and immersion
ISO TC 142 WG9 “Round Robin” Tests
• WG9 conducted flat sheet round robin test program
• five medias
• immersion and vapor
• 8 labs
• good agreement between labs
• IPA vapor efficiencies slightly lower than immersions.
Report --- “ISO TC 142/WG9 N91 Report on Round Robin test for IPA Methods”
Small IPA Vapor Chamber – with residential filter
Residential Filter– Small Chamber
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KCL Mean Particle Diameter - Microns
Filter Efficiency vs KCl Particle Size
New Filter 2.5 Hrs IPA Vapor Exposure
4.5 Hrs IPA Vapor Exposure 6.5 Hrs IPA Vapor Exposure
After Liquid IPA Dip
Fiber-Glass Rigid Filter – Small Chamber
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Filter Efficiency vs KCl Particle Size
New Filter 1 Hr IPA Vapor Exposure
3.5 Hrs IPA Vapor Exposure
Synthetic Rigid Filter – Small Chamber
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Filter Efficiency vs KCl Particle Size
New Filter
1 Hr IPA Vapor Exposure
3.5 Hrs IPA Vapor Exposure
Effect of IPA Chamber Size on Discharge
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Filter Efficiency vs KCl Particle Size
New Filter
1 Hr IPA Vapor Exposure - LC
7 Hr IPA Vapor Exposure - LC
1 Hr IPA vapor Exposure - SC
3.5 Hr IPA Vapor Exposure - SC
IPA Chamber with 24 x 24 x 22 Pocket Filter Installed with 12 v dc fan
Pocket filter is companion filter to the pocket filter used in initial IPA vapor testing.
Previous tests proved that filter did not discharge when placed in large chamber(LC).
Filter did discharge when folded and placed in small chamber(SC)
Pocket filter Initial efficiency tested prior to IPA exposure
Filter placed in IPA vapor chamber for 1 hour with circulating fan operating
Comparisons of Pocket Filter Test Data Using Large and Small Chambers with and w/o Circulating Fan.
New companion filter (made at same time as previous filter) did have slightly higher efficiency than previous filter.
This chart demonstrates that the previous pocket filter did not discharge in the large chamber (LC) with out a circulating fan.
The discharge of the companion filter that are discharged in the large chamber with the fan matches the discharge data of the previous filter placed in the small chamber.
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KCL Mean Particle Diameter - Microns
Filter Efficiency vs KCl Particle Size
New Filter
1 Hr IPA Vapor Exposure - LC
7 Hr IPA Vapor Exposure - LC
1 Hr IPA vapor Exposure - SC
3.5 Hr IPA Vapor Exposure - SC
New Companion Filter
Companion Filter - 1 Hr IPA Vapor LC w/Fan
IPA Vapor Chamber with 12v dc Fan Installed -- with 3 20 x 20 x 1 filters Each filter tested in 52.2 test duct for Initial efficiency prior to IPA exposure 99.% IPA liquid added to cover bottom of chamber 4 inch x 4 inch fan turned on and filters exposed to IPA vapor for 1 hour.(note fan toward bottom left inside of chamber) Fan free airflow is approximately 80 cfm Chamber volume is approximately 35 cubic feet Caution -- Use of Electric Fans and IPA/Air Mixtures Can Potentially Cause Explosions. Consult your Safety Officer and Company Policies
Initial Efficiencies of the 3 Filters before and After IPA Exposure Efficiencies of 3 filters in good agreement prior to IPA vapor exposure
After exposure, three filters have significantly different efficiencies. Resistances of filters did not change.
Filters were relocated in chamber (move middle to bottom, bottom to top, and top to middle) and IPA vapor exposure and tests repeated.
Location of filters within chamber had no effect on the results
Test Program repeated to verify conclusion.
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KCl Particle Size Removal Efficiency
Filter A - New Filter B - New
Filter C - New Filter A - Bottom - IPA
Filter B - Middle - IPA Filter C - Top - IPA
Initial Efficiency of Pocket Filter Prior to and After 1 Hour IPA Vapor Exposure with Fan
Pocket Filter did demonstrate significantly lower efficiencies after IPA vapor exposure in large chamber with air circulating fan.
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KCl Particle Size - Microns
KCl Particle Size Removal Efficiency
1 Hr IPA Vapor with Fan New Filter
Caution -- Use of Electric Fans
and IPA/Air Mixtures Can
Potentially Cause Explosions.
Consult your Safety Officer and
Company Policies
IPA Vapor Chamber with 12v dc fan Installed -- with 2 20” x 20” x 1”
filters
Each filter tested in 52.2 test duct for Initial efficiency prior to IPA exposure 99.% IPA liquid added to five (5) round trays at top of chamber. No IPA liquid in bottom of chamber. Condition 1. Filters exposed to IPA vapor for one hour with out fan operating; efficiency measured on both filters. Condition 2. Filters exposed to IPA vapor for an additional hour with fan operating; efficiency measured on both filters Condition 3. Filter located on bottom dipped in liquid IPA for two (2) minutes; efficiency measured on filter Caution -- Use of Electric Fans and IPA/Air Mixtures Can Potentially Cause Explosions. Consult your Safety Officer and Company Policies
Initial Efficiencies of the 2 filters before and after IPA exposure - w & w/o fan
Efficiencies of the 2 filters in good agreement prior to IPA vapor exposure
Condition 1. Exposure w/o fan; neither filter efficiencies were affected by IPA vapor
Condition 2. Exposure with fan; both filters affected by IPA, essentially to the same degree;
Condition 3. Bottom filter dipped in IPA liquid; filter affected to the same degree as in previous tests
Items to Resolve
Apparent simplicity and low cost of IPA vapor method
warrants further study
• Safe use of electric fan in IPA vapor/air mixture
• Proper design of IPA chamber with and without fan to re-circulate air
• Period of time for IPA vapor exposure for various style filters and medias
• Correlation of medias lab discharge vs field services
• Suggestions welcomed
Continued Verification of IPA Vapor Method
• ASHRAE 52.2 has formed Task Group to review status and recommend next actions.
• ISO TC 142/WG9 in process of round robin test program using full size filters
• ISO TC 142 WG3 has initiated process for approval to develop an ISO standard for conditioning full size air filters using the ISO vapor method.
List of Desirables
• Direct comparison data of lab IPA vapor results vs Appendix J method
• SEM Photo’s of various filter media fibers exposed to IPA vapor and IPA liquid
• Explanation of why IPA vapor “works” ,its limitations and potential problems
• Compilation of data on field service filters, IPA vapor, and IPA liquid
• Suggestions welcomed
End