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Residential HVAC Filtration What Does it Do?

Residential HVAC Filtration What Does it Do?. T.J. Ptak and Chrystal Gillilan Presented at National Air Filtration Association, TECH 2009. Scope. Introduction Indoor air quality Airborne contaminants Filter performance test method Residential HVAC system

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Residential HVAC Filtration What Does it Do?

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  1. Residential HVAC Filtration What Does it Do? T.J. Ptak and Chrystal Gillilan Presented at National Air Filtration Association, TECH 2009

  2. Scope • Introduction • Indoor air quality • Airborne contaminants • Filter performance test method • Residential HVAC system • Impact of filter efficiency on indoor air • Energy cost • Conclusions

  3. Indoor Air Quality • Air pollution • Unwanted substances • Particulate matter including bioaerosols • Gaseous pollutants, radon, noise • U.S. residents spend* • 87% of time indoors • 7.2% in transit and 5.6% outdoors • Indoor and outdoor air pollutants • Indoor concentration >outdoor concentration • *R. Wilson and J. Spengler – Particles in Our Air

  4. Indoor Air Quality – Commercial Buildings • Sick Building Syndrome (SBS) • 30% office buildings suffer from SBS (64 million workers) • Indoor Air Pollution costs employees $150 billion in employee productivity • 5 -7 % productivity loses • Productivity loss $22.67/Ft2

  5. Indoor Air Quality – Residential Buildings • Over 50% of homes have at least 6 detectable allergens present • Allergic diseases affect as many as 40 -50 mln • Asthma (chronic disease) affects about : • 20 mln adult Americans • 9 mln children • Allergic asthma – allergens (dust mites, mold, animal dander, pollen) make their symptoms worse • Asthma costs USA $18 billion • Source: American Academy of Allergy Asthma & Immunology

  6. Indoor Air Quality – Health Impact • Short term and chronic exposure to particulate matter (PM) is associated with: • Relationship between mortality rate and PM2.5 concentration • Increased morbidity and mortality • Respiratory and cardiovascular disease • Pulmonary inflammation, oxidative stress, endothelial dysfunction, • Combustion PM associated with mortality • Ultrafine particles induce reactive oxygen species, oxidative stress and inflammation • Source: American Journal of Respiratory and Critical Care Medicine

  7. Indoor Air Quality – Impact of Filtration • Filtration impact on microvascular function (MVF): • 21 couples, nonsmokers • During test ( 48 hrs) participant stayed home • Concentration of particles (0.1 – 0.7 µm) was monitored • Baseline concentration 10,016 #/cm3 • Filtered 3,206 #/cm3 • MVF was measured • Results: Indoor air filtration significantly improved MVP by 8.1% • Source: American Journal of Respiratory and Critical Care Medicine

  8. Personal and Ambient • Personal and outdoor PM2.5 • Good correlation (impact of ETS) • Personal and outdoor PM10 • CPersonal = 55 + 0.6 COutdoor [µg/m3] • Weak correlation • *R. Wilson and J. Spengler – Particles in Our Air

  9. Indoor Air • Particle size - 0.005 to 500 micrometers • Sources: • Outdoor • Infiltration • Tobacco smoke, stoves, fireplaces • Occupant activities • Carpets, curtains, furniture • Emission by humans • 100,000 to 10,000,000 particles per minute • Relationship between indoor/outdoor concentration • Residence with smokers 4.4 • Residence without smokers 1.1 - 1.4 • Indoor sources – cooking 5 - 10

  10. Particle Size • Tobacco smoke 0.01 – 1 µm • Household dust 0.05 – 100 • Pet dander 0.5 – 100 • Dust mite debris 0.5 – 50 • Skin flakes 0.4 – 10 • Cooking smoke/grease 0.02 – 2 • Pollen 5 – 100 • Bacteria 0.2 – 20 • Viruses 0.005 – 0.1 • Biological agents 0.5 – 5 • Molecules < 0.001 • Settling velocity of 10 µm particle V = 1.5 fpm

  11. Household Aerosols

  12. Lung Deposition • Particle deposition in lungs • Source; J. Heyder, GSF

  13. Lung Deposition • Particle deposition in respiratory tract: • Upper, upper bronchial, lower bronchial, alveolar • Source; J. Heyder, GSF

  14. Scope • Introduction • Indoor air quality • Airborne contaminants • Filter performance test method • Residential HVAC system • Impact of filter efficiency on indoor air • Energy cost • Conclusions

  15. ASHRAE 52.2 Test Method • Filtration efficiency for particle sizes 0.3 to 10 m • Challenge aerosol KCl • Test dust ASHRAE • Initial efficiency and efficiency after dust loading • Efficiency for three particle size ranges: • E1 0.3 – 1.0 m • E2 1.0 – 3.0 m • E3 3.0 – 10 m • Minimum Efficiency Reporting Value (MERV)

  16. ASHRAE 52.2 Test Method • Air flow rate (face velocity) for testing • 118 – 246 – 295 – 374 - 492 – 630 – 748 fpm • Concept of the face velocity strongly influenced by commercial HVAC • Residential HVAC – filter tested at 295 and 492 fpm • Final resistance of filter after dust loading • Greater than twice the initial resistance • Minimum final resistance depends on MERV • Does not reflect conditions for residential HVAC • ASHRAE 52.2 and residential HVAC

  17. MERV

  18. Residential HVAC • Building as protection against outdoor contaminants • Residential HVAC systems • Indoor sources of particulate matter • Re-circulating air • Portable air cleaners • Infiltration • Recommended < 0.06 cfm/ft2 of outside area at ΔP = 0.30” H2O • Typical commercial and residential infiltration is higher

  19. Residential HVAC • Major components • Return and supply ducts • Blowers • Permanent Split Capacitor (PSC) • Brushless Permanent Magnet (BPM) • Rated at Total External Static Pressure ΔP = 0.5 in. H2O • Filters • Ideal filter ΔP < 20% TESP • Heaters • Ideal coil ΔP < 40% TESP

  20. Typical Residential HVAC • ΔPS (+)ΔPR (-) • SUPPLYRETURN • HEATING • F

  21. Flow Rate • Fan curve for PSC blower • Typical, small residential PSC blowers ⅓ HP

  22. Types of Residential Filters • Pleated and flat panel – 1 and 4” deep

  23. Residential HVAC • Residential furnace filters – typical issues • Filter bypass • Lack of seal, gaskets • Filter size does not match size of specific housing • Undersized filters for given flow rate • Filter area not fully utilized • Non-uniform air velocity • Inefficient filters • Large number of MERV 7-8 filters • Majority filters MERV 10

  24. Undersized Filters • Practical industry standards • One ton of cooling 12,000 Btu • Cooling airflow 400 cfm/ton • Heating airflow 100 – 150 cfm/10,000 Btu • Undersized filters for given flow rate • Filter Face area, [ft2] Flow rate @ 295 fpm • 16 x 25 2.47 820 • 20 x 20 2.47 820 • 20 x 25 3.47 1,024

  25. Filter Area Utilization • Change in cross section area of a return duct • Smaller inlet to the blower

  26. Test Overview • Selection of residential furnace filters • Dimensions 20 x 25 x 5 in. • Efficiency MERV 4 – 16 • Filter testing according to ASHRAE 52.2 • Laboratory testing • Filter efficiency measurement using test set up simulating a typical residential furnace • Impact of seal and filter bypass • Test house • Concentration of particulates inside test house • Power consumption – test house

  27. Laboratory Test • Blower • Permanent Split Capacitor (PSC) • ¾ HP • Test set up • Duct dimensions 28 x 12 in. 28 x 21 in. • Filter housing 21 x 28 x 7 in. • Filter dimensions 20 x 25 x 5 in. • Measurements • Air velocity • Filter efficiency

  28. Air Velocity • Air velocity across MERV 8 filter • Measurements 2 in. from the test filter • Theoretical air velocity V = 576 fpm • Turbulent flow due to sharp turns

  29. Performance of Selected Filters • Filters tested according to ASHRAE 52.2 • Filter dimensions 20 x 25 x5 in. Filter efficiency at 1200 cfm

  30. Performance of Selected Filters • Filters tested according to ASHRAE 52.2 • Filter dimensions 20 x 25 x5 in. Filter efficiency at 2000 cfm

  31. Performance of Selected Filters • Filters tested according to ASHRAE 52.2 • Filter dimensions 20 x 25 x5 in. Filter pressure drop

  32. Filter Bypass • Filter penetration, P with bypass flow, QB • Bypass flow through gaps • Efficiency decrease depends on: • Bypass flow • Filter efficiency without bypass • U-shaped 10 mm gap at ΔP = 50 Pa QB/Q ~20%

  33. Filter Efficiency • Filter initial efficiency at the flow rate of 2000 cfm • E1 efficiency for submicron particles (0.3 – 1) • Ambient aerosol • Optical particle counter • Filter MERV 8 MERV 13 MERV 16 • ASHRAE 52.2 23.0 64.3 95.0 • Test set up 20.0 59.7 91.2 • NOTE: MERV 13 filter ΔP = 0.48 in. H2O at 2000 cfm • MERV 16 filter ΔP = 0.32 in. H2O at 2000 cfm

  34. Impact of Bypass • Filter initial efficiency at the flow rate of 2000 cfm • E1 efficiency for submicron particles (0.3 – 1) • Ambient aerosol • Optical particle counter • Filter MERV 8 MERV 13 MERV 16 • Test set up 20.0 59.7 91.2 • With 5 mm gap* n/a 58.1 89.1 • NOTE: *Bypass gap 250 x 5 mm (10 x 0.25 in.)

  35. Scope • Introduction • Indoor air quality • Airborne contaminants • Filter performance test method • Residential HVAC system • Impact of filter efficiency on indoor air • Energy cost • Conclusions

  36. Cleaning Effectiveness – Particle Decay • Concentration of particles • Submicron 0.3 – 0.5 micron • E2 range 1 – 3 micron • Instrument optical particle counter • Location 36 in. above the floor • Test house • House size 2300 ft2 • Blower PSC, heating mode • Test filters • Dimensions 20 x 25 x 5 and 20 x 25 x 1 in. • Seal gasket around filters

  37. Cleaning Effectiveness – Impact of MERV • Particle decay for 0.3 – 0.5 micron particles

  38. Cleaning Effectiveness – Impact of MERV • Particle decay for 1 – 3 micron particles

  39. Cleaning Effectiveness – Filter Size Impact • Particle decay for 0.3 – 0.5 micron particles

  40. Cleaning Effectiveness – Filter Size Impact • Particle decay for 1 – 3 micron particles

  41. Cleaning Effectiveness – Filter ΔP impact • Particle decay for 0.3 – 0.5 micron particles • ΔP = 0.15 and ΔP = 0.49 in. H2O @ 1200 cfm

  42. Cleaning Effectiveness – Filter ΔP impact • Particle decay for 1 – 3 micron particles • ΔP = 0.15 and ΔP = 0.49 in. H2O @ 1200 cfm

  43. Scope • Introduction • Indoor air quality • Airborne contaminants • Filter performance test method • Residential HVAC system • Impact of filter efficiency on indoor air • Energy cost • Conclusions

  44. Life Cycle Costs • Life Cycle Costs (LCC) widely used to design energy efficient commercial HVAC systems LCC = Initial Investment + Energy Cost + Maintenance Cost + Cost of Disposal • Cost of energy during filter service life • Flow rate, average filter pressure dropand energy cost

  45. Typical Residential HVAC • ΔPS (+)ΔPR (-) • SUPPLYRETURN • HEATING • F

  46. Flow Rate • Fan curve for PSC blower • Typical, small residential PSC blowers ⅓ HP

  47. Power Consumption • Power consumption for PSC blower • Typical, small residential PSC blowers ⅓ HP

  48. Test House • HVAC System • Duct dimensions 24 x 10 in. • Blower PSC – 1/3 HP • Rated at TESP 0.50 in. H2O • Furnace 88,000Btu • Filter dimensions 20 x 25 x 5 in. • Measurements • Flow rate • Air velocity in the return duct • Filter pressure drop • Power consumption

  49. Test Results • Filter FilterΔP Flow Power ΔPRΔPS [in. H2O] [cfm] [W] [in. H2O] • NO FILTER 1232 636 -0.23 0.11 • MERV 8 0.13 1172 606 -0.22 0.10 • MERV 16 0.17 1117 600 -0.19 0.10 • MERV 16 – H 0.42 950 552 -0.13 0.07 • COMMENTS: • Flow rate without filter is comparable to the fan curve • Power usage is comparable the fan curve • Pressure drop in the return and supply ducts is significant • Filter pressure drop inside the system

  50. Impact on Heating Time • Test results • Test house 2300 Ft2 • Mode Heating • Test time 1-1.5 hr per filter • Outside temperature 30 – 35oF • During test temperature within 2oF • Test filters MERV 8 MERV16 – High • MERV 8 filter ΔP = 0.10 in. H2O @ 1200 cfm • MERV 16 – H filter ΔP = 0.49 in. H2O @ 1200 cfm

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