Residential HVAC Filtration What Does it Do

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 gtoutdoor 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 lt 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 lt 0.06 cfm/ft2 of outside area at ?P
  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 ?P 0.5
  in. H2O
• Filters
• Ideal filter ?P lt 20 TESP
• Heaters
• Ideal coil ?P lt 40 TESP

20
Typical Residential HVAC

• ?PS () ?PR (-)
• SUPPLY RETURN
• HEATING
• F

21
Flow Rate

• Fan curve for PSC blower
• Typical, small residential PSC blowers ? 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 _at_ 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 ?P 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 ?P 0.48 in. H2O at 2000
  cfm
• MERV 16 filter ?P 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 ?P impact

• Particle decay for 0.3 0.5 micron particles
• ?P 0.15 and ?P 0.49 in. H2O _at_ 1200 cfm

42
Cleaning Effectiveness Filter ?P impact

• Particle decay for 1 3 micron particles
• ?P 0.15 and ?P 0.49 in. H2O _at_ 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 drop and
  energy cost

45
Typical Residential HVAC

• ?PS () ?PR (-)
• SUPPLY RETURN
• HEATING
• F

46
Flow Rate

• Fan curve for PSC blower
• Typical, small residential PSC blowers ? HP

47
Power Consumption

• Power consumption for PSC blower
• Typical, small residential PSC blowers ? 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 Filter ?P Flow Power ?PR ?PS
  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 ?P 0.10 in. H2O _at_ 1200 cfm
• MERV 16 H filter ?P 0.49 in. H2O _at_ 1200 cfm

51
Impact on Heating Time

• Average heating time for each filter was measured
• Heating time for high ?P filter
• Ratio ---------------------------------------
• Heating time for low ?P filter

52
Impact on Heating Time

• Blower electrical energy
• High ?P filter Low ?P filter
• Power usage, W 552 606
• Corrected for time 592 606
• Annual heating 2080 hrs 1231 kWh 1260 kWh
• Cost _at_ 0.10/kWh, 123 126
• Furnace natural gas
• High ?P filter Low ?P filter
• Annual energy, therm 790
• Corrected for time 848 790
• Cost _at_ 1.30/therm, 1102 1027
• TOTAL COST, 1225 1153

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