This document discusses residential air filtration. It begins by outlining some key residential air filtration issues like removing particulates and odors while maintaining airflow. It then describes various principles of air filtration like straining, impingement, interception, diffusion, and electrostatic attraction/precipitation that can remove particles. It provides diagrams to illustrate these principles. The document also discusses standards for residential air filters from ASHRAE and how filters are tested and assigned a Minimum Efficiency Reporting Value (MERV) rating. Finally, it considers pressure drop and airflow reduction that can occur with higher efficiency filters.

1. 1
Residential Air Filtration

2. 2
Residential Issues
 Cleaner Air
– Removal of Particulates
– Removal of Odors
 Maintain Airflow
 Customers Change Filters

3. 3
Principles of Air Filtration
Particulate Phase
 Straining
 Impingement (Inertial Impaction)
 Interception
 Diffusion
 Electrostatic Attraction
 Electrostatic Precipitation

4. 4
Straining
Fiber
Very large
particles
are captured
between two
fibers.
Airflow
Airflow
Particle
Airstream

5. 5
Impingement
Fiber
Larger
particles
do not move
around
the fiber with
the
airstream
and are
carried into
the
fiber due to
their
momentum.
Airflow
Airflow
Particle
Airstream

6. 6
Spun Fiberglass Filters
Picture provided by Glasfloss Industries, Inc.

7. 7
Interception
Fiber
Midsize
particles
move along
with
airstream lines
and contact a
fiber when
they are just
close enough.
Airflow
Airflow
Particle
Airstream

8. 8
Electrostatic Attraction
Fiber
Airflow
Airflow
Particle
Airstream
Particles are
pulled to the
fiber due to
electrostatic
attraction
(charge) of the
fiber that is
opposite of the
particle
charge.

9. 9
Electrostatic Attraction
Fiber
Airflow
Airflow
Particle
Airstream
Particles are
pulled to the
fiber due to
electrostatic
attraction
(charge) of the
fiber that is
opposite of the
particle
charge.

10. 10
Electrostatic Precipitation
Electronic Air Cleaner
Particles past
through an
ionizing
section
and receive a
strong
positive
charge. These
particles are
then collected
on charged
plates.
Connected to
a
www.fedders.com

11. 11
Residential Air Filter Standard
ASHRAE 62.2 “…has three primary
sets of requirements…whole-house
ventilation, local exhaust and source
control..”

12. 12
Residential Air Filter Standard
 Ventilation -
– Minimum Filtration – “MERV 6 or
better..”
MERV = Minimum Efficiency Reporting
Value from ASHRAE 52.2-1999

13. 13
Residential Air Filter Standard
Definition:
Acceptable indoor air quality – “air
towards which a substantial majority of
occupants express no dissatisfaction
with respect to odor and sensory
irritation and in which there are not likely
to be contaminants at concentrations
that are known to pose a health risk.”

14. ASHRAE 52.2
 A design qualification test
 A destructive test to measure minimum
efficiency reporting value (MERV)
 Efficiency test aerosol is Potassium Chloride
(KCl) particles, 0.3 to 10 micron
 Dust loading aerosol is ASHRAE Standard
Test Dust

15. Copyright National Air Filtration Association
2006 Rev. 2
ASHRAE 52.2
 Initial Resistance
 Pressure required to move air through filter
at a certain air flow written in inches water,
Pascal or millimeters water
 Final Resistance
 Pressure at which the filter would be
considered fully loaded

16. Exhaust
Room Air
Outlet
Filters
ASME
Nozzle Downstream Mixer
Blower Flow
Control
Valve
Inlet
Filters
Aerosol
Generator
Upstream
Mixer
OPC
Device
Section
Backup Filter
Holder (Used
When Dust loading)
ASHRAE 52.2
Test Duct Configuration

17. 17
Typical 52.2 Complete Loading
Test Data Report
Size
Range
(micron)
Fractional Efficiency (%) at Resistance (in
H20)
Composit
e
Minimum
Composit
e
Average
0.28 0.32 0.46 0.64 0.82 1.00
0.3 to 0.4 2.7 6.7 17.2 29.4 37.1 37.9 2.7
E1 = 9.8
0.4 to 0.55 7.8 15.9 27.7 43.3 53.2 54.6 7.8
0.55 to 0.7 11.2 30.2 46.0 60.7 70.5 71.6 11.2
0.7 to 1.0 17.6 42.6 59.3 73.7 81.3 81.8 17.6
1.0 to 1.3 20.4 51.6 70.3 80.8 83.7 85.2 20.4
E2 = 27.2
1.3 to 1.6 23.9 58.2 76.5 84.7 86.1 87.2 23.9
1.6 to 2.2 28.3 69.6 84.1 89.1 90.2 91.0 28.3
2.2 to 3.0 36.3 83.9 91.9 94.2 94.4 93.2 36.3
3.0 to 4.0 39.4 89.4 93.7 95.8 96.4 94.9 39.4
E3 = 44.8
4.0 to 5.5 42.8 90.6 95.3 96.5 97.9 95.6 42.8
5.5 to 7.0 46.5 92.3 97.1 98.0 98.4 97.9 46.5
7.0 to 10.0 50.4 94.8 97.5 98.3 100 99.2 50.4
Minimum Efficiency Reporting Value is 6 at 492 fpm

18. 18
Composite Minimum Curve
Minimum Efficiency Reporting Value
0
20
40
60
80
100
0.35 0.47 0.62 0.84 1.14 1.44 1.88 2.57 3.46 4.69 6.2 8.37 10
Particle Size - um
Particle
Size
Removal
Efficiency
%

19. 19
Table 7.2.1
Minimum
Efficiency
Reporting
Value
Composite Average Particle Size Efficiency
(%)
Average
Arrestance
by ASHRAE
52.1
Minimum Final Resistance
0.3 to 1.0
E1
1.0 to 3.0
E2
3.0 to 10
E3
Pa In Water
1 n/a n/a E3 < 20 Aavg < 65 75 0.3
2 n/a n/a E3 < 20
65 ≤ Aavg <
70
75 0.3
3 n/a n/a E3 < 20
70 ≤ Aavg <
75
75 0.3
4 n/a n/a E3 < 20 75 ≤ Aavg 75 0.3
5 n/a n/a 20 ≤ E3 < 35 n/a 150 0.6
6 n/a n/a 35 ≤ E3 < 50 n/a 150 0.6
7 n/a n/a 50 ≤ E3 < 70 n/a 150 0.6
8 n/a n/a 70 ≤ E3 < 85 n/a 150 0.6
9 n/a E2 < 50 E3 ≥ 85 n/a 250 1.0
10 n/a 50 ≤ E2 < 65 E3 ≥ 85 n/a 250 1.0
11 n/a 65 ≤ E2 < 80 E3 ≥ 85 n/a 250 1.0
12 n/a E2 ≥ 80 E3 ≥ 90 n/a 250 1.0
13 E1 < 75 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4
14 75 ≤ E1 < 85 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4
15 85 ≤ E1 < 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4
16 E1 ≥ 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4

20. 20
Table 7.2.1
Minimum
Efficiency
Reporting
Value
Composite Average Particle Size Efficiency
(%)
Average
Arrestance
by ASHRAE
52.1
Minimum Final Resistance
0.3 to 1.0
E1
1.0 to 3.0
E2
3.0 to 10
E3
Pa In Water
1 n/a n/a E3 < 20 Aavg < 65 75 0.3
2 n/a n/a E3 < 20
65 ≤ Aavg <
70
75 0.3
3 n/a n/a E3 < 20
70 ≤ Aavg <
75
75 0.3
4 n/a n/a E3 < 20 75 ≤ Aavg 75 0.3
5 n/a n/a 20 ≤ E3 < 35 n/a 150 0.6
6 n/a n/a 35 ≤ E3 < 50 n/a 150 0.6
7 n/a n/a 50 ≤ E3 < 70 n/a 150 0.6
8 n/a n/a 70 ≤ E3 < 85 n/a 150 0.6
9 n/a E2 < 50 E3 ≥ 85 n/a 250 1.0
10 n/a 50 ≤ E2 < 65 E3 ≥ 85 n/a 250 1.0
11 n/a 65 ≤ E2 < 80 E3 ≥ 85 n/a 250 1.0
12 n/a E2 ≥ 80 E3 ≥ 90 n/a 250 1.0
13 E1 < 75 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4
14 75 ≤ E1 < 85 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4
15 85 ≤ E1 < 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4
16 E1 ≥ 95 E2 ≥ 90 E3 ≥ 90 n/a 350 1.4
E1 = 9.8%
E2 = 27.2%
E3 = 44.8%
MERV 6

21. 21
MERV
 MERV then is an efficiency number for
particle removal…
 Gas-phase removal numbers are not
mentioned in the standard…

22. 22
Gaseous Contaminant Removal
Principle Methods
 Physical – Adsorption
–Activated carbons
 Chemical - Chemisorption
–Chemically treated activated carbons
–Potassium permanganate
impregnated media

23. 23
Principle Methods
 Adsorption - The process by which one
substance is attracted and held onto the
surface of another.
– It is a surface phenomena.
– Capacity is independent of particle size
– Adsorption rate is inversely proportional to
particle size.

24. 24
Principle Methods
 Chemisorption - The result of chemical
reactions on and in the surface of the
adsorbent.
– Fairly specific and depends upon chemical
nature of media and the contaminant
– Irreversible and essentially instantaneous

25. 25
Gas Phase Contaminants
 Where in the home?
– Bathroom
– Kitchen - biggest
– Laundry room
– Garage
– Trash storage area
– Pet area
– Smoking household

26. 26
Pressure–Velocity
In the attempt to increase residential air
filtration efficiency, little attention has
been paid to the problem associated
with increase pressure drop
 Lower flow rates
 Premature equipment failure
 Bypass leakage in ductwork

27. 27
Project: Test Pressure Drop with
3 Types of Residential Filters
 Test Facility – one story 1800 sq. ft.
condominium
 Unit – 3 yr. old constant speed gas/ac
unit
 Motor – 1/3 hp with max. 0.5” w.g.
external static
 Filter Grille and extended surface filter
installation

28. 28
Test Protocol
 Fan turned to the “On” position
 All filters removed
 Readings taken with calibrated
flowhood on return air grille
No filter installed: 0.30” w.g.
848 cfm

29. 29
Filters Used
Filter #1 – 1” standard fiberglass
throwaway
Filter 1 0.35” w.g.
842 cfm

30. 30
Filters Used
 Filter #2 - 1” mini-pleated extended
surface filter
Filter 2 0.50” w.g.
798 cfm

31. 31
Filters Used
 Filter #3 - 5” Extended surface unit-
mounted filter
Filter 3 0.40” w.g.
811 cfm

32. 32
Summary
Filter #1 – 1% decrease in flow 848 to 842 –
0.35 ΔP
Filter #2 – 6% decrease in flow 848 to 798 - 0.5
ΔP – starts out clean at max. ext. static
Filter # 3 – 4% decrease in flow 848 to 811 –
0.4 ΔP