Do Air Cleaners Work

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Information about Do Air Cleaners Work

Published on November 19, 2007

Author: Kestrel


Do Air Cleaners Really Work?:  Do Air Cleaners Really Work? Professor Shelly Miller Mechanical Engineering University of Colorado at Boulder Motivation and Background:  Motivation and Background Slide3:  Adverse health effects due to exposure to airborne particulate matter could be more significant than effects due to exposure to many other airborne pollutants (Vedal, 1997) Slide4:  An idealized particle size distribution, showing coarse, fine, and ultrafine particles. Also shown are major formation and growth mechanisms, example compositions, and lung deposition efficiency upon inhalation. Airborne particles come in many different sizes and composition. ultrafine fine coarse DV/DlogDp (mm3/cm3) diameter Dp, mm 2.5 0.1 10 0.01 mechanically generated Lung deposition efficiency curve Fraction particles deposited OK, so how bad are the health effects?:  London Fog Donora, PA Chimney sweeps And now, we are looking into fine particles (a.k.a. PM2.5) OK, so how bad are the health effects? Slide6:  Across the board, fine particles are associated with increased risk A 10 mg/m3 increment is associated with an increase in overall mortality risk of 1.06, cardiopulmonary mortality of 1.09, and lung cancer of 1.14. For a US city these increased risks are roughly equivalent to the risk associated with being moderately obese. NOTE: The increase in overall mortality associated with being a smoker is 2.58, cardiopulmonary mortality is 2.89, and lung cancer is 14.80. Slide7:  People spend >85% of their time inside and 3/4 of that time is at home. Long et al., 2001 Indoor Particle Dynamics:  Indoor Particle Dynamics Slide9:  Factors governing indoor particle concentrations include: Slide10:  Factors governing indoor particle concentrations include: Emissions from indoor sources Slide11:  Factors governing indoor particle concentrations include: ventilation supply from outdoor air Slide12:  Factors governing indoor particle concentrations include: Operating portable air cleaners Slide13:  Factors governing indoor particle concentrations include: deposition onto indoor surfaces Slide14:  Factors governing indoor particle concentrations include: Removal by ventilation Air Cleaning:  Air Cleaning In-duct air cleaners, designed to be integrated with a forced-air heating/cooling system Air follows a single pass through particle removal technology Unducted air cleaners which are portable and designed primarily for cleaning in one room Air is multi-pass, recirculated through particle removal technology Consumers bought 3.4 million portable air cleaners in 2001, 70% more than in 2000 Do you have forced-air?:  Do you have forced-air? If so, then get best results from in-duct air cleaning, since so much air is circulated through the heating/cooling system Furnace filters are not adequate, need a filter with a higher efficiency (usually rated with a Min Effic Reporting Value or MERV) Portable Air Cleaners:  Portable Air Cleaners Slide18:  Fan draws particle-laden air through a fibrous filter media Fan draws particle-laden air through an electrical field Filters Electrostatic precipitators Charged particles are deposited on oppositely charged collector plates NOTE: some ESPs have no fan (for example, Sharper Image) Slide19:  An idealized particle removal efficiency as a function of particle size for a typical fibrous filter. Remember the particle size distribution? diameter Dp, mm 2.5 0.1 10 0.01 Filter efficiency curve Fraction particles deposited Impaction and interception diffusion Air cleaner standards :  Air cleaner standards Currently there are no standards for testing/rating portable air cleaners Many air cleaners certified by the Association of Home Appliance manufacturers in a widely accepted voluntary program ( Quantifying air cleaner performance:  Quantifying air cleaner performance 1. Effectiveness 2. CADR Effectiveness, E:  Effectiveness, E Quantifies improvement in indoor air quality that is associated with the technology’s use E can range between 0 and 1 E = 1 represents ideal performance E = 0 indicates complete lack of improvement Determining Effectiveness:  Determining Effectiveness Measure particle concentrations both with and without air cleaner operating and compare Particle #/ m3 No air cleaner air cleaner Fire study:  Fire study Experimental Design:  Experimental Design Locate wildfire producing smoke that will impact local residents Monitor indoor and outdoor PM2.5 concentrations at both homes during fire Install air cleaners in one of the 2 homes Instruct residents to keep windows closed Air Cleaner:  Air Cleaner PRE-FILTER catches larger particles IONIZING CELL electrically charges particles when they pass through an electric field COLLECTOR PLATES immediately attract "charged" particles ACTIVATED CARBON FILTER removes most common odors and fumes 3 tests performed on the air cleaners in a test chamber to measure Clean Air Delivery Rate (CADR) We measured an average CADR of 420 m3/ h Agrees with CADR of 325-370 m3/ h that is published by Association of Home Appliance Manufacturers Friedrich C-90a Electrostatic Precipitator Slide27:  Air cleaners effective at reducing particle concentrations inside from fire smoke outside Slide28:  Keeping windows and doors closed not very effective at reducing particle concentrations inside from fire smoke outside Clean air delivery rate:  Clean air delivery rate single-pass efficiency of the device (fractional removal of pollutants from the air stream as it passes through the device) multiplied by the airflow rate through the device (Nazaroff, 2000) airflow rate that represents the effective amount of particle-clean air produced by the air cleaner (Offermann et al., 1985) The Association of Home Appliance Manufacturers (AHAM) has published method ANSI/AHAM AC-1-2002, which determines the CADR for three types of particulate matter—dust, tobacco smoke, and pollen (AHAM, 2002). Clean air delivery rate:  Clean air delivery rate Determining CADR experimentally:  Determining CADR experimentally Generate particles continuously until concentration in room reached suitable level for detection. Stop generation, turn on air cleaner. Concentration within the room will decrease over time. Sample during decay. Mixing fans should be on to ensure well-mixed conditions. Experiment repeated with air cleaner off. Particle #/ m3 No air cleaner air cleaner Determining CADR analytically:  Determining CADR analytically Apply mass-balance indoor air quality model, which assumes indoor environment represented as a single, well-mixed zone. Ventilation Q Outdoor conc Co Q Indoor conc C Emissions E Deposition rate k CADR Indoor air quality model:  Indoor air quality model The indoor particle concentration as a function of time is given by (Miller and Macher, 2000): Using model to interpret experimental data:  Using model to interpret experimental data Concentration of particles measured sequentially during the decay period are statistically fit to the log form of model equation using linear regression: With air cleaner Using model to interpret experimental data:  Using model to interpret experimental data Slope of fit gives sum of rates for experiment with and without air cleaner and subtractions gives rate of particle removal due to air cleaner: Air Cleaner CADR study:  Air Cleaner CADR study Objectives:  Objectives To quantify the CADR of two currently portable air cleaners, which contain UV-C lamps Air cleaners challenged with pure cultures of airborne microorganisms UV-C lamp performance was evaluated by estimating the percentage of captured bacteria and fungi that were inactivated on the filter surface Aerosolized Mycobacteria and Fungi:  Aspergillus versicolor Mycobacterium parafortuitum Aerosolized Mycobacteria and Fungi Aspergillus versicolor, fungus, diameter ranges 5-7 mm, spores can be used as subpathogenic surrogates Mycobacteriumparafortuitum, bacterium, diameter around 1 mm, has a structure and environmental sensitivity similar to the bacteria that causes tuberculosis Determining UV Lamp Performance:  Determining UV Lamp Performance Load filter media with bioaerosol. Expose sections of media to UV irradiation for varying lengths of time. Extract exposed organisms and assay using culturing UV-C lamp performance defined as fraction of culturable bacteria, normalized to total number of bacteria, that survive with UV-C lamp turned on compared to without UV-C lamp operating Slide40:  Ionic Breeze (Sharper Image) manufacturer specified flow rate 46 m3 h-1, ~$500 Jaguar (Shaklee) manufacturer specified flow rate 425 m3 h-1, prototype Slide41:  The CADRm for A. versicolor was statistically the same as CADRm for M. parafortuitum provided by both Jaguar and Ionic Breeze. This finding suggests that when these units are operated in multi-pass fashion, in which indoor air laden with biological particles passes through the air cleaner multiple times, the difference in particle size is not a larger factor in performance. A. versicolor aerosol contains larger particles (>5 m) compared to the M. parafortuitum aerosol (on the order of 1 m). Ionic Breeze and Jaguar averaged clean-air delivery rates for mycobacteria and fungi Slide42:  Jaguar UV-C Lamp performance for inactivating captured M. parafortuitum and A. versicolor expressed as percentage inactivated Inactivation due to UV (%) UV-C lamp inactivated captured organisms within 60-120 minutes FUNGI BACTERIA How big of a room can the air cleaner clean?:  How big of a room can the air cleaner clean? Another way of looking at data is to predict volume of space that can be adequately cleaned -- defined as reducing concentration by 80% -- by the air cleaner The Jaguar can clean a 30 m3 room and the Ionic Breeze can clean a 4 m3 room 30 m3 4 m3 SO, Do Air Cleaners Really Work?:  SO, Do Air Cleaners Really Work? Yes, they DO!:  Yes, they DO! If you have respiratory problems, or are concerned with episodic elevated exposures (i.e.fires), you will benefit from using an air cleaner If its an option, use forced-air system, with efficient filters If not, choose an air cleaner that’s AHAM certified and designed to cover an area somewhat larger than the one you need to treat Example of air cleaners that work: Friedrich C-90A, (see Consumer Reports, 2003) Acknowledgements:  Acknowledgements US EPA Region 8 Firefighters and families Shaklee and Jay Julos Elmira Kujundzic Fatimah Matalkah Cody Howard David Henderson Mark Hernandez

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