1. NAFA Guide To Air Filtration
Fourth Edition
Chapter 1
Importance of Air Filtration
presented by the
National Air Filtration Association
2008

2. The Importance of Air Filtration.
Air filtration supplies the means to obtain the level of particulate cleanliness required by any definition of “air conditioning.”
An air filter (air cleaner) is a device used for the removal of particulate or gaseous (molecular) impurities from the air.

3. Comfort Air Conditioning
Is described as the process of treating air to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the requirements of the occupants of the conditioned space.

4. Air We Breathe
Slide is self explanatory

5. Aerosol - Gas
Regardless of its source, an airborne contaminant can be either an aerosol or a gas.
An aerosol is a suspension of solid or liquid particles in the air.

6. Measurement of Contaminants is in Micrometers aka Microns
It is important to understand the size of particle we are capturing in our air filters. This illustration shows how small a micrometer is in proportion to a human hair. A micrometer is millionth of a meter…for us here in America who continue to use the Inch/Pound System of measure, a micrometer is 1/25,400th of an inch.

7. 1 MICROMETER A Micrometer (µm) is 1 millionth of a
meter or in I/P - 1/25,400 of an inch
Pollen
10 to 100 micrometers
Pollen is a large particle by air filtration standards as are some of the salts.
Salt is 40 to 200 micrometers

8. Aerosols
You’ve probably been asked by your friends, “Will I have to dust less if I buy one of your higher efficiency filters?
Being in the air filter business, you have probably answered this question once or twice….

9. Particle Settling Velocities
Particle Size (µm)
100.0
50.0
10.0
5.0
1.0
.05
0.1
<0.1
Settling Velocity
59.2 feet per minute
14.8 feet per minute
7.1 inches per minute
2.5 inches per minute
5.1 inches per hour
1.4 inches per day
1.13 inches per day negligible-behave like gases
The answer is “Yes” and “No.” This chart shows that some large particles do not make it to a filter because they are so heavy, they fall to the closest horizontal surface. This accounts for the dust on your furniture. Smaller particles do get entrained in the HVAC airstream and can be removed by filtration. Other particles are so small that they do not ever make it through a filter to be removed but remain suspended in the air in a facility forever.

10. Aerosols
Fumes are solid aerosols formed by the condensation of vapors of solid materials.
Fogs are liquid aerosols formed by the condensation of water vapor in the air.
Mists are liquid aerosols formed by the atomization of liquids.
Smokes are solid or liquid aerosols formed by the incomplete combustion of organic substances.

11. Gases
A gas is any material that has the tendency to expand indefinitely and which completely and uniformly fills the container it occupies.
Vapors are gases formed by evaporation of materials that are normally liquid or solid.

12. Measuring Particle Contamination
Measured by Weight – drawing air onto a pre-weighed paper target
Counting & Sizing – either through a membrane filter (old) or using an optical particle counter (OPC).
See Chart on page 1.4 – NAFA Guide
Numbers of particles can be weighed (if the size of the particle is not a needed criteria) by using a paper target. This is one way the EPA measures contaminants in cities across the US to determine air quality. Page 1.4 in your NAFA Guide shows a list of common particulates in the air and can help you by knowing the size of a contaminant so that you can design the best filtration to remove it.

13. Size Distribution of Atmospheric Dust Sample
Percent by Particle Count
Percent by Weight
30 micron
10 micron
0.005%
28%
5.0 micron
0.175%
52%
Who knows why the sky is blue? As sunlight comes through space, it hits billions of very small particles in our atmosphere. Blue being at the shortest end of the light spectrum, is the only color not eliminated by the particles. This diagram describes the distribution of particles in the air. Most people think there are many large particles in the air but just the opposite is true – our air is 98.5% composed of particles under 1 micrometer.
11%
3.0 micron
0.25% 6%
1.0 micron
1.07%
<1.0 micron 3%
98.5%
Source: NAFA Guide to Air Filtration

14. The Importance of Air Filtration.
Air filtration supplies the means to obtain the level of particulate cleanliness required by any definition of “air conditioning.”

15. Air Filters are used for a variety of purposes:
Protecting the health and well-being of the occupants of the space by removal of airborne microorganisms and particles.
Protecting the décor of occupied spaces by removing the staining portion of airborne dust.
Reducing maintenance of building interiors by reducing the frequency of washing such items as Venetian blinds and fluorescent bulbs.

16. Protecting the contents of occupied
Protecting the contents of occupied spaces including paintings, tapestries, and other items of historic or cultural value.
Elimination of fire hazards by removing lint and other materials which might accumulate in the ductwork.
Removing airborne bacteria from operating room air to help prevent postoperative infection.

17. Filter Efficiency
Properly evaluate the size of the particulate you want to remove. And at what efficiency.
Details on filter testing will be given in the presentation on Chapter 7.
ANSI/ASHRAE 52.2 Method of Test

18. Draw-through System Detail
Filter 1
Filter 2
This slide details the draw-through system, the filters are located in the Filter #1 and #2 (in a 2-bank system) position in the drawing and are used to protect the coils and HVAC equipment. One disadvantage to this system is the plenum and ductwork are negative pressure all the way to the high side of the fan which can cause particles to bypass the air filter bank, or particles to be entrained by the blower belts and other components.

19. Blow-through System Possible Terminal Filter
A Blow-through system puts the first filter protecting the blower and/or coils while the second filter is downstream of the coils to catch anything that might come off of the coils or be entrained in the system. Terminal filters are increasingly used in hospitals because they filter the air just before it enters the space.
Possible Terminal Filter

20. Some Sample Questions 1 Millionth of a Meter is called a __________?
Micrometer or Micron
The air we breathe is composed mainly of
__________?
Nitrogen

21. Sample Questions
The size of particles in outdoor air are mainly ???% and smaller?
1 Micrometer and smaller
_____(size) particles behave like a gas, have negligible settling rates and are affected by Brownian Motion.
Particles less than 0.1 micrometers

22. Thank you.
Other Questions?