Residential Air Filtration
1
Residential Issues

Cleaner Air
– Removal of Particulates
– Removal of Odors
Maintain Airflow
 Customers Change Filters

2
Principles of Air Filtration
Particulate Phase
Straining
 Impingement (Inertial Impaction)
 Interception
 Diffusion
 Electrostatic Attraction
 Electrostatic Precipitation

3
Straining
Airflow
Particle
Airstream
Very large
particles
are captured
between two
fibers.
Fiber
Airflow
4
Impingement
Airflow
Fiber
Particle
Airstream
Airflow
Larger
particles
do not move
around
the fiber with
the
airstream
and are
carried into
the
fiber due to
their
momentum.
5
Spun Fiberglass Filters
Picture provided by Glasfloss Industries, Inc.
6
Interception
Airflow
Fiber
Airstream
Particle
Airflow
Midsize
particles
move along
with
airstream lines
and contact a
fiber when
they are just
close enough.
7
Electrostatic Attraction
Airflow
Fiber
Particle
Airstream
Airflow
Particles are
pulled to the
fiber due to
electrostatic
attraction
(charge) of the
fiber that is
opposite of the
particle
charge.
8
Electrostatic Attraction
Airflow
Fiber
Particle
Airstream
Airflow
Particles are
pulled to the
fiber due to
electrostatic
attraction
(charge) of the
fiber that is
opposite of the
particle
charge.
9
Electrostatic Precipitation
Electronic Air Cleaner
www.fedders.com
Particles past
through an
ionizing
section
and receive a
strong
positive
charge. These
particles are
then collected
on charged
plates.
Connected to
10
a
Residential Air Filter Standard
ASHRAE 62.2 “…has three primary
sets of requirements…whole-house
ventilation, local exhaust and source
control..”
11
Residential Air Filter Standard

Ventilation – Minimum Filtration – “MERV 6 or
better..”
MERV = Minimum Efficiency Reporting
Value from ASHRAE 52.2-1999
12
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.”
13
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
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
Copyright National Air Filtration Association
2006 Rev. 2
ASHRAE 52.2
Test Duct Configuration
Outlet
Filters
Exhaust
ASME
Nozzle
Downstream Mixer
Room Air
Inlet
Filters
Blower
Flow
Control
Valve
Aerosol
Generator
Upstream
Mixer
OPC
Device
Section
Backup Filter
Holder (Used
When Dust loading)
Typical 52.2 Complete Loading
Test Data Report
Size
Range
(micron)
Fractional Efficiency (%) at Resistance (in
H20)
0.28
0.32
0.46
0.64
0.82
1.00
Composit
e
Minimum
0.3 to 0.4
2.7
6.7
17.2
29.4
37.1
37.9
2.7
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
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
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
Composit
e
Average
E1 = 9.8
E2 = 27.2
E3 = 44.8
Minimum Efficiency Reporting Value is 6 at 492 fpm
17
Composite Minimum Curve
Minimum Efficiency Reporting Value
Particle Size Removal
Efficiency %
100
80
60
40
20
0
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
18
Table 7.2.1
Minimum
Efficiency
Reporting
Value
Composite Average Particle Size Efficiency
(%)
0.3 to 1.0
E1
1.0 to 3.0
E2
3.0 to 10
E3
1
n/a
n/a
E3 < 20
2
n/a
n/a
3
n/a
4
Average
Arrestance
by ASHRAE
52.1
Minimum Final Resistance
Pa
In Water
Aavg < 65
75
0.3
E3 < 20
65 ≤ Aavg <
70
75
0.3
n/a
E3 < 20
70 ≤ Aavg <
75
75
0.3
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
19
Table 7.2.1
Minimum
Efficiency
Reporting
Value
Composite Average Particle Size Efficiency
(%)
0.3 to 1.0
E1
1.0 to 3.0
E2
3.0 to 10
E3
1
n/a
n/a
E3 < 20
2
n/a
n/a
3
n/a
4
Average
Arrestance
by ASHRAE
52.1
Minimum Final Resistance
Pa
In Water
Aavg < 65
75
0.3
E3 < 20
65 ≤ Aavg <
70
75
0.3
n/a
E3 < 20
70 ≤ Aavg <
75
75
0.3
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
9
n/a
E2 < 50
E3 ≥ 85
n/a
10
n/a
50 ≤ E2 < 65
E3 ≥ 85
n/a
11
n/a
65 ≤ E2 < 80
E3 ≥ 85
n/a
12
n/a
E2 ≥ 80
E3 ≥ 90
n/a
13
E1 < 75
E2 ≥ 90
E3 ≥ 90
n/a
14
75 ≤ E1 < 85
E2 ≥ 90
E3 ≥ 90
n/a
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
E1 = 9.8%
150
250
E2 = 27.2%
250
250
E3 = 44.8%
250
350
MERV
350 6
0.6
1.0
1.0
1.0
1.0
1.4
1.4
MERV

MERV then is an efficiency number for
particle removal…

Gas-phase removal numbers are not
mentioned in the standard…
21
Gaseous Contaminant Removal
Principle Methods
 Physical
– Adsorption
– Activated carbons
 Chemical
- Chemisorption
– Chemically treated activated carbons
– Potassium permanganate
impregnated media
22
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.
23
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
24
Gas Phase Contaminants

Where in the home?
– Bathroom
– Kitchen - biggest
– Laundry room
– Garage
– Trash storage area
– Pet area
– Smoking household
25
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
26
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

27
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
28
Filters Used
Filter #1 – 1” standard fiberglass
throwaway
Filter 1 0.35” w.g.
842 cfm
29
Filters Used

Filter #2 - 1” mini-pleated extended
surface filter
Filter 2 0.50” w.g.
798 cfm
30
Filters Used

Filter #3 - 5” Extended surface unitmounted filter
Filter 3 0.40” w.g.
811 cfm
31
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
32