Residential Air Filtration 1 Residential Issues Cleaner Air – Removal of Particulates – Removal of Odors Maintain Airflow Customers Change Filters 2 Principles of Air Filtration Particulate Phase Straining Impingement (Inertial Impaction) Interception Diffusion Electrostatic Attraction Electrostatic Precipitation 3 Straining Airflow Particle Airstream Very large particles are captured between two fibers. Fiber Airflow 4 Impingement Airflow Fiber Particle Airstream Airflow Larger particles do not move around the fiber with the airstream and are carried into the fiber due to their momentum. 5 Spun Fiberglass Filters Picture provided by Glasfloss Industries, Inc. 6 Interception Airflow Fiber Airstream Particle Airflow Midsize particles move along with airstream lines and contact a fiber when they are just close enough. 7 Electrostatic Attraction Airflow Fiber Particle Airstream Airflow Particles are pulled to the fiber due to electrostatic attraction (charge) of the fiber that is opposite of the particle charge. 8 Electrostatic Attraction Airflow Fiber Particle Airstream Airflow Particles are pulled to the fiber due to electrostatic attraction (charge) of the fiber that is opposite of the particle charge. 9 Electrostatic Precipitation Electronic Air Cleaner www.fedders.com Particles past through an ionizing section and receive a strong positive charge. These particles are then collected on charged plates. Connected to 10 a Residential Air Filter Standard ASHRAE 62.2 “…has three primary sets of requirements…whole-house ventilation, local exhaust and source control..” 11 Residential Air Filter Standard Ventilation – Minimum Filtration – “MERV 6 or better..” MERV = Minimum Efficiency Reporting Value from ASHRAE 52.2-1999 12 Residential Air Filter Standard Definition: Acceptable indoor air quality – “air towards which a substantial majority of occupants express no dissatisfaction with respect to odor and sensory irritation and in which there are not likely to be contaminants at concentrations that are known to pose a health risk.” 13 ASHRAE 52.2 A design qualification test A destructive test to measure minimum efficiency reporting value (MERV) Efficiency test aerosol is Potassium Chloride (KCl) particles, 0.3 to 10 micron Dust loading aerosol is ASHRAE Standard Test Dust ASHRAE 52.2 Initial Resistance Pressure required to move air through filter at a certain air flow written in inches water, Pascal or millimeters water Final Resistance Pressure at which the filter would be considered fully loaded Copyright National Air Filtration Association 2006 Rev. 2 ASHRAE 52.2 Test Duct Configuration Outlet Filters Exhaust ASME Nozzle Downstream Mixer Room Air Inlet Filters Blower Flow Control Valve Aerosol Generator Upstream Mixer OPC Device Section Backup Filter Holder (Used When Dust loading) Typical 52.2 Complete Loading Test Data Report Size Range (micron) Fractional Efficiency (%) at Resistance (in H20) 0.28 0.32 0.46 0.64 0.82 1.00 Composit e Minimum 0.3 to 0.4 2.7 6.7 17.2 29.4 37.1 37.9 2.7 0.4 to 0.55 7.8 15.9 27.7 43.3 53.2 54.6 7.8 0.55 to 0.7 11.2 30.2 46.0 60.7 70.5 71.6 11.2 0.7 to 1.0 17.6 42.6 59.3 73.7 81.3 81.8 17.6 1.0 to 1.3 20.4 51.6 70.3 80.8 83.7 85.2 20.4 1.3 to 1.6 23.9 58.2 76.5 84.7 86.1 87.2 23.9 1.6 to 2.2 28.3 69.6 84.1 89.1 90.2 91.0 28.3 2.2 to 3.0 36.3 83.9 91.9 94.2 94.4 93.2 36.3 3.0 to 4.0 39.4 89.4 93.7 95.8 96.4 94.9 39.4 4.0 to 5.5 42.8 90.6 95.3 96.5 97.9 95.6 42.8 5.5 to 7.0 46.5 92.3 97.1 98.0 98.4 97.9 46.5 7.0 to 10.0 50.4 94.8 97.5 98.3 100 99.2 50.4 Composit e Average E1 = 9.8 E2 = 27.2 E3 = 44.8 Minimum Efficiency Reporting Value is 6 at 492 fpm 17 Composite Minimum Curve Minimum Efficiency Reporting Value Particle Size Removal Efficiency % 100 80 60 40 20 0 0.35 0.47 0.62 0.84 1.14 1.44 1.88 2.57 3.46 4.69 6.2 8.37 10 Particle Size - um 18 Table 7.2.1 Minimum Efficiency Reporting Value Composite Average Particle Size Efficiency (%) 0.3 to 1.0 E1 1.0 to 3.0 E2 3.0 to 10 E3 1 n/a n/a E3 < 20 2 n/a n/a 3 n/a 4 Average Arrestance by ASHRAE 52.1 Minimum Final Resistance Pa In Water Aavg < 65 75 0.3 E3 < 20 65 ≤ Aavg < 70 75 0.3 n/a E3 < 20 70 ≤ Aavg < 75 75 0.3 n/a n/a E3 < 20 75 ≤ Aavg 75 0.3 5 n/a n/a 20 ≤ E3 < 35 n/a 150 0.6 6 n/a n/a 35 ≤ E3 < 50 n/a 150 0.6 7 n/a n/a 50 ≤ E3 < 70 n/a 150 0.6 8 n/a n/a 70 ≤ E3 < 85 n/a 150 0.6 9 n/a E2 < 50 E3 ≥ 85 n/a 250 1.0 10 n/a 50 ≤ E2 < 65 E3 ≥ 85 n/a 250 1.0 11 n/a 65 ≤ E2 < 80 E3 ≥ 85 n/a 250 1.0 12 n/a E2 ≥ 80 E3 ≥ 90 n/a 250 1.0 13 E1 < 75 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4 14 75 ≤ E1 < 85 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4 15 85 ≤ E1 < 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4 16 E1 ≥ 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4 19 Table 7.2.1 Minimum Efficiency Reporting Value Composite Average Particle Size Efficiency (%) 0.3 to 1.0 E1 1.0 to 3.0 E2 3.0 to 10 E3 1 n/a n/a E3 < 20 2 n/a n/a 3 n/a 4 Average Arrestance by ASHRAE 52.1 Minimum Final Resistance Pa In Water Aavg < 65 75 0.3 E3 < 20 65 ≤ Aavg < 70 75 0.3 n/a E3 < 20 70 ≤ Aavg < 75 75 0.3 n/a n/a E3 < 20 75 ≤ Aavg 75 0.3 5 n/a n/a 20 ≤ E3 < 35 n/a 150 0.6 6 n/a n/a 35 ≤ E3 < 50 n/a 150 0.6 7 n/a n/a 50 ≤ E3 < 70 n/a 150 0.6 8 n/a n/a 70 ≤ E3 < 85 n/a 9 n/a E2 < 50 E3 ≥ 85 n/a 10 n/a 50 ≤ E2 < 65 E3 ≥ 85 n/a 11 n/a 65 ≤ E2 < 80 E3 ≥ 85 n/a 12 n/a E2 ≥ 80 E3 ≥ 90 n/a 13 E1 < 75 E2 ≥ 90 E3 ≥ 90 n/a 14 75 ≤ E1 < 85 E2 ≥ 90 E3 ≥ 90 n/a 15 85 ≤ E1 < 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4 16 E1 ≥ 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4 20 E1 = 9.8% 150 250 E2 = 27.2% 250 250 E3 = 44.8% 250 350 MERV 350 6 0.6 1.0 1.0 1.0 1.0 1.4 1.4 MERV MERV then is an efficiency number for particle removal… Gas-phase removal numbers are not mentioned in the standard… 21 Gaseous Contaminant Removal Principle Methods Physical – Adsorption – Activated carbons Chemical - Chemisorption – Chemically treated activated carbons – Potassium permanganate impregnated media 22 Principle Methods Adsorption - The process by which one substance is attracted and held onto the surface of another. – It is a surface phenomena. – Capacity is independent of particle size – Adsorption rate is inversely proportional to particle size. 23 Principle Methods Chemisorption - The result of chemical reactions on and in the surface of the adsorbent. – Fairly specific and depends upon chemical nature of media and the contaminant – Irreversible and essentially instantaneous 24 Gas Phase Contaminants Where in the home? – Bathroom – Kitchen - biggest – Laundry room – Garage – Trash storage area – Pet area – Smoking household 25 Pressure–Velocity In the attempt to increase residential air filtration efficiency, little attention has been paid to the problem associated with increase pressure drop Lower flow rates Premature equipment failure Bypass leakage in ductwork 26 Project: Test Pressure Drop with 3 Types of Residential Filters Test Facility – one story 1800 sq. ft. condominium Unit – 3 yr. old constant speed gas/ac unit Motor – 1/3 hp with max. 0.5” w.g. external static Filter Grille and extended surface filter installation 27 Test Protocol Fan turned to the “On” position All filters removed Readings taken with calibrated flowhood on return air grille No filter installed: 0.30” w.g. 848 cfm 28 Filters Used Filter #1 – 1” standard fiberglass throwaway Filter 1 0.35” w.g. 842 cfm 29 Filters Used Filter #2 - 1” mini-pleated extended surface filter Filter 2 0.50” w.g. 798 cfm 30 Filters Used Filter #3 - 5” Extended surface unitmounted filter Filter 3 0.40” w.g. 811 cfm 31 Summary Filter #1 – 1% decrease in flow 848 to 842 – 0.35 ΔP Filter #2 – 6% decrease in flow 848 to 798 - 0.5 ΔP – starts out clean at max. ext. static Filter # 3 – 4% decrease in flow 848 to 811 – 0.4 ΔP 32