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

2. Filter performance test method Residential HVAC system
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 and outdoor air pollutants
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 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 outdoor PM2.5 Personal and outdoor PM10
Personal and Ambient
Personal and outdoor PM2.5
Good correlation (impact of ETS)
Personal and outdoor PM10
CPersonal = COutdoor [µg/m3]
Weak correlation
*R. Wilson and J. Spengler – Particles in Our Air

9. Relationship between indoor/outdoor concentration
Indoor Air
Particle size 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
Residence without smokers
Indoor sources – cooking

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

11. PARTICLE SIZE, MICROMETERS
Household Aerosols
PARTICLE SIZE, MICROMETERS
0.01
0.1 1 10
100
Pet Dander
Dust Mite Debris
Skin Flakes
Can
Tobacco Smoke
Cooking smoke
Pollens
Bacteria
Hair

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

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

14. Filter performance test method Residential HVAC system
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. Filtration efficiency for particle sizes 0.3 to 10 m
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:
E – 1.0 m
E – 3.0 m
E – 10 m
Minimum Efficiency Reporting Value (MERV)

16. ASHRAE 52.2 and residential HVAC
ASHRAE 52.2 Test Method
Air flow rate (face velocity) for testing
118 – 246 – 295 – – 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. Building as protection against outdoor contaminants
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. Major components Residential HVAC 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 (-)
SUPPLY RETURN
HEATING F

21. Fan curve for PSC blower
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 furnace filters – typical issues
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. Practical industry standards
Undersized Filters
Practical industry standards
One ton of cooling 12,000 Btu
Cooling airflow cfm/ton
Heating airflow – 150 cfm/10,000 Btu
Undersized filters for given flow rate
Filter Face area, [ft2] Flow 295 fpm
16 x
20 x
20 x ,024

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

26. Selection of residential furnace filters
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. Blower Test set up Measurements Air velocity Laboratory Test
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 penetration, P with bypass flow, QB Bypass flow through gaps
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 initial efficiency at the flow rate of 2000 cfm
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
Test set up
NOTE: MERV 13 filter ΔP = 0.48 in. H2O at 2000 cfm
MERV 16 filter ΔP = 0.32 in. H2O at 2000 cfm

34. Filter initial efficiency at the flow rate of 2000 cfm
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
With 5 mm gap* n/a
NOTE: *Bypass gap 250 x 5 mm (10 x 0.25 in.)

35. Filter performance test method Residential HVAC system
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 – 0.5 micron
E2 range 1 – 3 micron
Instrument optical particle counter
Location 36 in. above the floor
Test house
House size 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 cfm

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

43. Filter performance test method Residential HVAC system
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. LCC = Initial Investment + Energy Cost + Maintenance Cost +
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 drop and energy cost

45. Typical Residential HVAC
ΔPS (+) ΔPR (-)
SUPPLY RETURN
HEATING F

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

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

48. HVAC System Measurements Test House Duct dimensions 24 x 10 in.
Blower PSC – 1/3 HP
Rated at TESP 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. Filter Filter ΔP Flow Power ΔPR ΔPS [in. H2O] [cfm] [W] [in. H2O]
Test Results
Filter Filter ΔP Flow Power ΔPR ΔPS [in. H2O] [cfm] [W] [in. H2O]
NO FILTER
MERV
MERV
MERV 16 – H
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. Test results Impact on Heating Time Test house 2300 Ft2 Mode Heating
Test time 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 cfm
MERV 16 – H filter ΔP = 0.49 in cfm

51. Average heating time for each filter was measured
Impact on Heating Time
Average heating time for each filter was measured
Heating time for high ΔP filter
Ratio =
Heating time for low ΔP filter

52. Blower electrical energy High ΔP filter Low ΔP filter
Impact on Heating Time
Blower electrical energy
High ΔP filter Low ΔP filter
Power usage, [W]
Corrected for time
Annual heating 2080 hrs 1231 kWh kWh
$0.10/kWh, [$]
Furnace – natural gas
Annual energy, [therm]
Corrected for time
$1.30/therm, [$]
TOTAL COST, [$]

53. Summary
Literature data support link between exposure to submicron particles and health issues
Performance of residential filters in real life conditions does not correlate well with the laboratory testing according to ASHRAE 52.2 due to lower test face velocity (295 fpm), flow conditions, leaks, duct construction
Low grade residential HVAC filters (MERV ≤ 10) do not provide sufficient protection against airborne particles
In order to decrease cardiovascular risk and other health hazards associated with exposure to air pollution, high efficiency residential filters such as MERV 14 – 16 should be used

54. Summary
Energy cost to operate residential HVAC system during heating mode is higher for high resistance filters
Residential HVAC systems with PSC blowers and installed high pressure drop filters require:
Longer time to heat specific space resulting in higher operational cost
Longer time to reduce concentration of airborne particles due to reduced flow rate