Moving to mass-based HVAC filtration metrics

Transcription

1 Moving to mass-based HVAC filtration metrics Brent Stephens, Ph.D. Associate Professor Civil, Architectural and Environmental Engineering web

2 How is filtration efficiency typically measured/reported? Filters are evaluated in laboratory tests: ASHRAE Standard 52.2 most widely used Test results: Size-resolved efficiency 0.3 to 10 µm particles Reporting metrics: MERV MPR FPR E 1 E 2 E 3 2

3 How is airborne particulate matter measured? Number concentrations (e.g., #/cm 3 ) Total counts (e.g., CPC: 10 nm to 1 µm) Size resolution (e.g., OPC/OPS, APS, SMPS, EAS, etc.) A few nm to tens of µm possible Mass concentrations (e.g., µg/m 3 ) PM 2.5 PM 10 TSP EPA 2009 Int. Sci. Assess. PM 3

4 What do we know about PM exposure and health? Associations with ambient fine particulate matter (PM 2.5 ) PM in outdoor air Concentration-Response (C-R) Function Burnett et al., 2014 EHP Pope and Dockery, 2006 J Air Waste Manage Assoc 4

5 What do we know about PM exposure and health? PM in outdoor air Typical C-R effect estimate for PM 2.5 and mortality: ~7% per 10 µg/m 3 Fann et al Risk Analysis 5

6 What do we know about PM exposure and health? PM in indoor air Fisk 2013 Indoor Air Air cleaners typically reduce indoor PM concentrations by ~50% Usually PM 2.5 Sometimes PM 10 or total number counts (TNC) (e.g. <1 µm) Documented health improvements with air cleaners include: Improvements in lung function in asthmatics Fewer asthma-related doctor visits Improvements in cardiovascular and pulmonary function 6

7 Moving to mass-based filtration metrics Almost everything we know about PM and health is from mass-based PM measurements To a (much) lesser extent: total number concentrations under a given size (e.g., 100 nm or 1 µm) So what do we need to know to move to massbased metrics? Size-resolved removal efficiencies for filters ( ) Underlying particle size distributions that filters are challenged with (?) Understanding of how aerosol density varies with size Secondary importance some decent literature on this ( ) Pitz et al ES&T; Hu et al ES&T 7

8 MASS-BASED FILTRATION METRICS FOR AMBIENT AEROSOLS 8

9 Moving to mass-based metrics: ISO Assumes 100% outdoor air (OA) Maps size-resolved efficiency to ambient size distribution Calculates PM mass concentration upstream and downstream, assuming: spherical particles constant density epm 1 and epm 2.5 urban PSD epm 10 rural PSD ISO

10 Moving to mass-based metrics: ISO Volume distributions Where did these ambient distributions come from? ISO

11 Where did the ISO ambient distributions come from? (a) Urban Stephens 2018 Atmosphere (a) Urban (b) Rural (b) Rural Seinfeld and Pandis

12 Where did the ISO ambient distributions come from? Jaenicke 1993 International Geophysics 12

13 Where did the ISO ambient distributions come from? Jaenicke 1993 International Geophysics 13

14 Where did the ISO ambient distributions come from? Rural Hobbs et al 1985 J Climate Applied Meteorology Whitby et al 1978 Atmospheric Environment Urban 14

15 Are the ISO ambient distributions still relevant? In 2014, we gathered 194 long-term average (1-year or more) outdoor particle size distributions from the literature from all over the world: Number distributions Azimi et al., 2014 Atmos Environ 15

16 Are the ISO ambient distributions still relevant? Comparing the Jaenicke (1993) distributions to Azimi et al. (2014) Number distributions Volume distributions ISO distributions clearly much greater in magnitude Number distributions: a little skewed, but reasonably close Volume distributions: Below 1-2 µm a little skewed, but not that much Above 1-2 µm can t compare (instrumentation overlap issues) Stephens 2018 Atmosphere 16

17 Are the ISO ambient distributions still relevant? Let s compare 100% ambient air epm for a few example filters Only works for epm 1 and epm 2.5 because newer measurements miss µm 4 filters Stephens 2018 Atmosphere; filter efficiency data from Hecker and Hofacre 2008 EPA Report 17

18 Are the ISO ambient distributions still relevant? Let s compare 100% ambient air epm for a few example filters Only works for epm 1 and epm 2.5 because newer measurements miss µm epm 1 : 2-6% difference (abs) epm 2.5 : 4-23% difference (abs) Stephens 2018 Atmosphere 18

19 Is the assumption of 100% OA realistic? 19

20 Is the assumption of 100% OA realistic? Outdoor particles P AER Loss Loss AER Infiltration factor: Penetration from outdoors F inf C in C out noindoor sources F inf P AER AER Loss Removal by air exchange Removal by deposition to surfaces, phase changes, or control by filters or air cleaners 20

21 Is the assumption of 100% OA realistic? Let s compare 100% ambient air epm for a few filters to ambient indoor transport Works for epm 1, epm 2.5, and epm 10 Typical residential infiltration factor (size-resolved) El Orch et al Building and Environment Stephens 2018 Atmosphere 21

22 Is the assumption of 100% OA realistic? Let s compare 100% ambient air epm for a few filters to ambient indoor transport Works for epm 1, epm 2.5, and epm 10 0% Change in removal efficiency (%) -2% -4% -6% -8% -10% -12% -14% -16% MERV 6 MERV 8 MERV 10 MERV 14 MERV 6 MERV 8 MERV 10 MERV 14 MERV 6 MERV 8 MERV 10 MERV 14 epm1 epm2.5 epm10 ISO rural -0.4% -1.2% -1.3% -1.0% -2.6% -4.9% -5.3% -2.8% -9.4% -10.9% -12.0% -4.0% ISO urban -0.3% -0.9% -0.9% -0.7% -1.8% -3.8% -4.1% -2.4% -10.4% -13.9% -15.1% -6.2% Azimi et al (100% OA) -0.2% -0.6% -0.6% -0.5% -0.5% -1.2% -1.2% -0.9% -0.7% -1.4% -1.5% -1.0% epm 1 : 0-2% difference (abs) epm 2.5 : 1-5% difference (abs) epm 10 : 1-15% difference (abs) Stephens 2018 Atmosphere 22

23 WHAT ABOUT MASS-BASED FILTRATION METRICS FOR INDOOR AEROSOLS? 23

24 What do indoor aerosol distributions look like? 24

25 Indoor particle sources Combustion processes Incense smoke, candle burning, cigarette smoke, etc. Cooking Both gas and electric stoves, toaster ovens, etc. Cleaning activities Resuspension from cleaning, walking, etc. Other indoor sources Aerosolization from tap water in humidifiers Office appliances (e.g., printers, copiers, etc.) Transport from outdoors Infiltration through leaks Delivery via mechanical ventilation 25

26 Indoor particle sources Indoor particle sources vary in size and composition Indoor emission sources are typically episodic Tend to be brief, intermittent, and highly variable Steady state rarely applies Outdoor particle levels and ventilation rates often vary with time Nazaroff 2004 Indoor Air 26

27 Indoor particle number and volume distributions I searched the literature for studies that measured indoor particle size distributions with the following criteria: Measured for at least a few days to capture a mix of indoor and outdoor sources Used an SMPS to measure nm range (e.g., µm) Used OPS/OPC or APS to measure µm range (e.g., µm) I found 2 studies in the US: 4 homes in Boston, MA 9 homes in Boston, MA Abt et al Environ Health Perspect Long et al Environ Sci Technol 27

28 Two example indoor particle volume distributions Stephens 2018 Atmosphere 28

29 How do indoor particle distributions compare to the ISO outdoor distributions? Stephens 2018 Atmosphere 29

30 How does indoor particle filtration efficiency compare to filtration efficiency for the ISO outdoor distributions? epm 1 : 0-6% difference (abs) epm 2.5 : 0-16% difference (abs) epm 10 : 1-29% difference (abs) Stephens 2018 Atmosphere 30

31 Summary of ISO comparisons The ISO urban/rural ambient distributions are from the 1970s Number concentrations are no longer realistic Shape of number distributions is reasonable, except for µm Volume distributions are difficult to compare (minimal modern data) ISO distributions overestimate efficiency for 100% OA compared to more modern ambient distributions Larger deviations for epm 2.5 than epm 1 Can t really compare epm 10 Ignoring size-resolved transformations of 100% OA into residences magnifies this overestimation Assuming filtration of indoor PM as a mix of indoor and outdoor sources: Only small overestimations for epm 1 Larger overestimations for epm 2.5 and epm 10 And ISO rural is much worse than ISO urban 31

32 What is needed to move to mass-based metrics? Need a better understanding of the number and volume distributions that filters are challenged with Ability to tailor the distribution assumptions for different use cases? Examples: 100% OA, recirculating systems in offices, schools, and homes What about PM mass (or number) below 0.3 µm? Currently this is ignored in filter testing and in resulting metrics How much does it contribute to mass concentrations? (it depends) Would need filtration efficiency measurements below 0.3 µm Possible number-based metrics below 0.3 µm Total UFPs (particles smaller than 100 nm) Total Number Counts (TNC: particles smaller than 1 µm) 32

33 What about particles smaller than 0.3 µm? Outdoor size distributions: Almost all PM (by number) is <0.3 µm MERV E 1 E 2 E 3 Azimi et al., 2014 Atmos Environ 33

34 What about particles smaller than 0.3 µm? Indoor size distributions: Almost all PM (by number) is <0.3 µm Wallace and Ott 2011 J Expo Sci Environ Epidem Wallace 2006 Aerosol Sci Technol 34

35 How are we helping? We have been making measurements of in-situ particle removal efficiency of a large number of residential HVAC filters Particles from 10 nm to 10 µm About 50 filters tested to date 35

36 In-situ fine and ultrafine particle removal efficiency Building a database of filter efficiency measurements MERV 16 5 MERV 13 2 MERV 13 1 MERV 11 4 MERV 11 2 MERV 11 2 MERV 8 4 MERV 8 1 MERV <4 1 Send me your filters! brent@iit.edu 16 x 25 x any depth Fazli and Stephens 2016 ASHRAE Conference 36

37 In-situ fine and ultrafine particle removal efficiency Mapping filtration efficiency to outdoor size distributions Azimi et al Atmos Environ 37

38 In-situ fine and ultrafine particle removal efficiency Mapping filtration efficiency to outdoor size distributions Azimi et al Atmos Environ And next we will do the same for indoor size distributions 38

39 Funding sources Acknowledgements ASHRAE: 2015 New Investigator Award and RP-1691 Kimberly-Clark Others: NAFA Foundation, US EPA, HUD, Sloan Foundation Collaborators IIT: Torkan Fazli, Parham Azimi, Dan Zhao, Haoran Zhao Jim Rosenthal, Tex-Air Filters Kevin Morrow, Kimberly-Clark Laura Kolb, EPA Lew Harriman, Mason-Grant Consulting Terry Brennan, Camroden Associates Send me your filters! Vito Ilacqua, EPA 16 x 25 x any depth Many others who donated filters 39

40 Exhibitor and Sponsor opportunities available Early bird registration is open NOW ( til Apr 15 th ) me: Brent Stephens - brent@iit.edu 40