Indoor and Outdoor Comparisons of Particle Sizes and Concentrations

Transcription

1 Indoor and Outdoor Comparisons of Particle Sizes and Concentrations Professor Shelly Miller Mechanical Engineering University of Colorado at Boulder

2 Main Points of Today s Talk Particles inside commercial buildings are generally lower than outdoors High efficiency filters for AHUs compared to standard filters decrease submicron particles Costs and resistance similar Clinical effects not yet clear, does show increase mental activity Issues include biological contamination and decrease in perceived air quality, mental performance with used filters

3 An idealized particle removal efficiency as a function of particle size for a typical fibrous filter Fraction particles deposited diffusion ultrafine fine Filter efficiency curve coarse Impaction and interception diameter D p, mm

4 Particles in Commercial Buildings Indoor concentrations often lower than outdoor because of filtration systems, particle deposition onto surfaces, not as many strong indoor sources In 38 buildings, 70% of measured indoor PM2.5 mass concentrations lower than outdoor concentrations (Turk et al. 1989) In office buildings, indoor submicron counts 40% less than outdoors (Jamriska et al. 1996) In 4 buildings, over 4 seasons, indoor submicron counts lower than outdoor, typical I/O ratio = 0.55 (Miller et al. 2007)

5 MERV ASHRAE Standard 52.2 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size Single-pass efficiency test Residential, commercial minimum, measure particle equipment counts protection upstream and downstream Industrial workplaces, commercial Generate particles better in the required size range from standard synthetic ASHRAE dust Superior, residential better, Lowest ratio of downstream-to-upstream particle commercial buildings counts over six test cycles Smoke removal, hospitals and healthcare superior, commercial buildings

6 Standard vs High Efficiency Filters Measurements in telecommunications building showed MERV reduced I/O counts by 50% for particles larger than 0.5 microns, 40% for larger than 1 micron compared to a 5-8 MERV (Krzyzanowski et al., 1990) Modeling studies showed MERV 12 compared to MERV 9 reduced I/O for RSP by 11-86% depending on pressurization (Herlin, 1997)

7 Standard vs High Efficiency Filters Measurements in sealed air-conditioned office building showed a MERV 16 reduced indoor submicron particles by 72-94% compared to a MERV 8 (Fisk et al 2000) Similar flow resistance, no change in supply airflow rates

8 Cost Issues (Fisk et al. 2002) Increasing filter efficiency above ~MERV results in only modest predicted incremental decreases in indoor particles

9 Cost Issues (Fisk et al. 2002) Estimated energy costs similar for filtration using filters with a wide range of efficiency ratings Total estimated filtration costs of $ $1.80 per person per month are comparable or less relative to salaries, rent or health insurance costs

10 Health Impacts (Mendell et al. 2002) Study of enhanced particle filtration in office building resulted in lower particle and bioaerosol concentrations, but no reduced symptoms performance-related mental states improved as did measures of environmental dissatisfaction Lower temperatures improved symptoms

11 Clean vs. Used Filters (Wargocki et al. 2004) Intervention study in telephone call center Replacing used filter with clean filter reduced talktime by ~10% at high ventilation rate (2.8 1/h) but had no significant effect at the low rate (0.28 1/h) Increasing outdoor air supply rate reduced talktime by 6% with a new filter in place but increased talk-time by 8% with a used filter in place The interventions also had significant effects on some SBS symptoms and environmental perceptions

12 ASHRAE STUDY OF ULTRAFINE PARTICLE PENETRATION INTO MECHANICALLY VENTILATED BUILDINGS

13 Project Goals Monitor indoor & outdoor ultrafine particulate matter at 4 mechanically ventilated buildings with standard filtration Sample all 4 seasons, 1 week each Obtain size as well as chemical species information Compare day/night, weekday/weekend, summer/winter Establish factors influencing indoor/outdoor ratio Fresh air supply rate HVAC operation

14 Instrumentation Aerodyne Aerosol Mass Spectrometer (AMS) Aerodynamic aerosol inlet, aerodynamic particle size determined via particle time-offlight Thermal vaporization, electron impact ionization Measures SO 4, NH 4, NO 3, and organic mass concentrations Measures particles from 20 nm up to 2 mm

15 Instrumentation Particle Metrics, Inc. Ultra High Sensitivity Aerosol Spectrometer Optical-scattering laser-based method to size particles from 55 nm to 1 micron Real-time size distribution Easy to operate and calibrate Resolution down to 2 nm bins Semiconductor-diode-pumped ND 3+ :YLF solid-state laser, 1kW

16 Sampling Setup Sample at each building with three 50 ft 0.5-in copper tubes: 2 routed inside and 1 outside

17 Sampling Locations Two in Boulder, CO. ITL Laboratory at the University of Colorado, Boulder Eisenhower Elementary School

18 Stairwell location Integrated Teaching and Learning Laboratory University of Colorado, Boulder Main laboratory level

19 Eisenhower Elementary School Boulder, CO Teachers lounge Music room

20 Sampling Locations And two in Denver. Denver School of the Arts (near commerce city) Fowler, Schimberg and Flanagan, Professional Corporation (downtown Denver)

21 Denver School of the Arts Denver, CO Science room Hallway location

22 Fowler, Schimberg and Flanagan, Professional Corp. Denver, CO

23 Description of of the Air Handling Unit in in each Building Building AHU type Supply Capacity (CFM) Denve r School of Arts Variable Air Volume 32,000 Grant building Dual-duct NA Eisenhowe r Elementary Constant Volume 16,450 Integrated Teaching and Learning Laboratory Variable Air Volume 48,300 Characteristics of of the Filters used at at each Building Building Filter type Rated Avg. Efficiency* MERV rating** Denve r School of the Arts 4 pleated polyester pads 35 % NA Grant building 2 pleated, pinch frame % 8 Eisenhowe r Elementary 2 pleated, high capacity % 7 Integrated Teaching and 2 pleated, high Learning Laboratory capacity % 8 * Rated Average Efficiency as described by ASHRAE standard 52.1 ** Minimum Efficiency Reporting Value (MERV) as described by ASHRAE standard 52.2.

24 Air Exchange Rates Sample Location Denve r School of the Arts Eisenhowe r Elementary (teacher s loung e) Eisenhowe r Elementary (music room) Eisenhowe r Elementary (music room at night) Air Exchange Rate (ACH) Air Supply Flow (ACFM) Interior Volume (ft 3 ) , ,443 3, ,057 7, Grant building ,000 Integrated Teaching and 4.0* 20, ,000 Learning Laboratory * This value is based on a rough estimate of the interior volume. Figure 1: Air exchange rate plot for Eisenhowe r Elementary School at night.

25 Averaged Mass Concentration Averaged mass concentrations peak at nm Indoor/outdoor ratio ranges between 0.45 and 0.60

26 Average Number Concentration Averaged number concentrations not that different indoors compared to outdoors

27 Denver air worse than Boulder air, both inside and out.

28 Seasonal Variations Winter and fall have highest outdoor concentrations Summer and spring have highest I/O ratios

29 Day vs. Night, Weekday vs. Weekend I/O similar for each period of the week, when averaged over all seasons and buildings weekend-nighttime I/O did not increase as particle size increased for diameters nm, which might be because there were no indoor sources during this time period Increase in nm particles during the other time periods may be because there are more indoor sources of particles, such as people in the building working or cleaning

30 I/O Ratio vs. Fresh Air Intake Indoor/outdoor ratio increases with fresh air intake, but not always and not exclusively

31 I/O Ratio vs. Fresh Air Intake Eisenhower Elementary, Boulder Denver School of the Arts ITL Laboratory, Boulder Grant Street, Denver

32 Indoor/outdoor ratios averaged over all ITL Laboratory datasets, separated by HVAC usage HVAC usage brings more particulate matter into the building The increase in the indoor/outdoor ratio at diameters closer to 1 micron may have been due to resuspension from building occupants or other various indoor activities

33 Indoor-Outdoor Regression Analysis Indoor particle concentration I t = S t + ao t Indoor particle sources Outdoor particle concentration a = pl k + l p=penetration factor l = air exchange rate k = deposition rate Regression analysis performed between the measured indoor particulate matter concentrations (12-min averages) and outdoor values The slope of the regression line provided an estimate of a, the y- intercept an estimate of the average indoor source contribution two sets of the described data were studied: nm (ultrafine) and nm (fine).

34 Lag Times Indoor PM concentrations correlate linearly with outdoor values Applying appropriate lag times increase correlations This lag time gives an indication of the time it takes for outdoor particles to come indoors

35 Lag times at the ITL Laboratory Lag times at the by ITL HVAC Laboratory usage by HVAC usage Particles take roughly 80 minutes to enter building with HVAC off, compared to 10 minutes with HVAC on

36 Regression Slopes for ITL Laboratory by HVAC Usage After lag time correction, indoor levels More similar to outdoor levels for ultrafines, HVAC on

37 Correlation Coefficients for ITL Laboratory by HVAC Usage Correlation between indoor and outdoor particles better for HVAC on, ultrafines

38 Ambient Chemical Makeup for Denver School of Arts in Winter

39 Nitrate Events Measured indoor ammonium nitrate concentrations lower than they would be based on penetration and deposition losses alone Extra reduction due to transformation indoors of ammonium nitrate into nitric acid and ammonia gases due to relative humidity and temperature changes (Lunden et al. 2003)

40 Nitrate Events Indoor outdoor ultrafine PM correlation difference for high ammonium nitrate event at DSA in winter

41 Nitrate Events Average AMS size distribution for DSA in winter

42 Acknowledgments ASHRAE Professors Shelly Miller and John Zhai Professor Darin Toohey Joshua Droege, Iain Elliott, Nick Ortiz Boulder Valley Public School District Denver Public Schools Facilities Management at CU Boulder All the people in the testing sites Particle Metrics, Inc. James Allen, Manchester University

43 References Fisk WJ et al. (2000). Particle concentrations and sizes with normal and high efficiency air filtration in a sealed air-conditioned office building, AS&T 32: Fisk WJ et al. (2002). Performance and costs of particle air filtration technologies, Indoor Air 12: Jamriska M et al. (2000). Effect of ventilation and Filtration on Submicrometer Particles in an Indoor Environment Indoor Air 10(1):19-26 Krzyzanowski ME (1990) Proceedings of Indoor Air 90, Vol 2, pp Mendell MJ et al. (2002). Indoor particles and symptoms among office workers: results from a double-blind cross-over study, Epidemiology 13: Miller et al (2007). Identification, Classification, and Correlation of Ultrafine Indoor Airborne Particulate Matter with Outdoor Values, Final Report ASHRAE 1281-RP Turk BH et al. (1989). Commercial building ventilation rates and particle concentrations, ASHRAE Transactions 95(1): Wargocki P et al. (2004). The performance and subjective responses of call-center operators with new and used supply air filters at two outdoor air supply rates Indoor Air 14 (s8), 7 16.