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Air FiltersAC units and control

Dr. Ahmed Elsaft

College of Engineering & TechnologyMechanical and Marine Engineering Dept.

Arab Academy for Science, Technology and

Maritime Transport

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Contents

Indoor air quality

urpose o ers

Types of filters

Filters selection

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Indoor air is one of the top five environmental threats to

uman ea .

According to the World Health Organization, 30% of

Syndrome (SBS).

SBS is characterized by headaches, nausea, irritated

nasal passages, itchy eyes, and skin irritation amongbuilding occupants.

,recently ranked the Number 1 management issue by the

International Facilities Management Association.

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Indoor Air ualit IA

affects the health and well-being of occupants.

How well indoor air satisfies the three basic requirements for

uman occupancy :-

a erma accepta ty

(b) Maintenance of normal concentrations of respiratory gases(c) Dilution and removal of contaminants to levels below health

or odor discomfort thresholds.

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urpose o ers

To remove particulates from air-stream. Depends on:

Particle size

Shape Mass

Construction

Electrostatic properties

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Filter Particles larger than 2.5 m are classified as coarse dust

w e a ess an . m are cons ere as ne us .

Arrestance: A standardized synthetic dust consisting of,mass fraction of the dust removed is determined.

Dust-spot efficiency: Atmospheric dust is passed into the

air cleaner, and the discoloration effect of the cleaned airon filter paper targets is compared with that of the

.

Fractional efficiency or penetration: Uniform-sized particles

are fed into the air cleaner and the percentage removed bythe cleaner is determined.

DOP: is a penetration test where Di-Octyl Phthalate (oily.

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Filter

Group I: Panel-type filters of expanded metal. (Aluminum Filter)

Group Ill: Extended-surface filters of fine glass fibers. (Bag Filter)

roup : ea e pane - ype ers o ne syn e c ers en s. yn e c er

Group IV: Extended-area pleated HEPA-type filters of ultra fine glass fiber

paper. Biological grade air filters are generally 95% DOP efficiency; HEPA

filters are 99.97% and 99.99%; and ULPA filters are 99.999%.

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Comparative Performance of Viscous Impingement and Dry-Media Filters

Group IPanel-type filters of spun glass, open cell foams, expanded metal and screens, synthetics, textile

denier woven and nonwoven, or animal hair.

Grou II

Pleated panel-type filters of fine denier nonwoven synthetic and synthetic-natural fibers blends, orall natural fibre.

Group III- ,

fibers, or wet-laid paper of cellulose- glass, synthetic, or all-glass fibers.

Group IV

Extended-area pleated HEPA-type filters of wet-laid ultra fine glass fibre paper. Biological grade air. .

99.999%.

Notes:1. Group numbers have no significance other than their use in this figure.

. .

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FilterMeasured byEfficiencyNew ClassEurovent classType

Synthetic dustweight arrestance

65, 80, 90G4EU4

40, 60, 80,

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AHU/PAU-Filters

Air filtration is an important component to achieve

an acceptable indoor air quality. Low-efficiency filters of the panel type as pre-filter

Medium- and hi h-efficienc ba t e for filterin

the air

-

removal of objectionable odors

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Test Method for Filters with different efficiency

Weight

arrestance

Dust Spot Di-Otyl

Phthalate

DOP

Particle size of test

dust

Large particles

in atmospheric

Atmospheric dust 0.3mparticles

Means to determine

dust concentration

Precision

Balance

Change in light

transmission

Particle count

Application Low efficiency

filter

Medium efficiency

filter

High

efficiency filter

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Low Efficiency Filter

Dust spot efficiency lower than 30%

Panel type

Dimension 500mm x 500mmFilter media

Corrugated metal wire mesh

Dr and reusable-n lon

Dry and disposable Glass fibre mats

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Medium Efficiency Filter

Filter efficiency between 30% to 95%

Extended surfaces such as pleated mats or bags are used to

Increase surface area of the filter media

Increase air velocity flowing through the filter media

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High Efficiency Particulate Air Filter

It remove dust particle by filtration of the passing air;

The filter media is glass fibre of submicrometer diameter

that is formed into pleated paper mats (dry and disposable).

The erformance of filter media is measured b al ha value

which is a function of penetration in % and pressure drop

(mm).

Typical size of filter is 600mm x 600mm x 300mm

Surface filter media area may be 50 times of the face area

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High Efficiency Particulate Air Filter(Contd)

Application: meet the requirement of di-octyl phthalate (DOP) 99.97%

efficiency for dust particle 0.3m

Clean room

Clean space for microelectronic industry

Pharmaceutical industry Precision manufacturing industry

Operating theatre in hospital

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Princi les of o eration

When traveling in the air stream of the ionizing

field, positively charged dust particles areattracte an attac e to t e groun p ates.

Dust particles agglomerate at the ground plates.

that they are blown off and carried away by the airstream.

Application:

Cigarettes smoke

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Electronic air cleaner(contd)

A hi h DC otential of 1.2kV is a lied to the ionizin field.

Positive ions generated from the ionizer wire charge the dust particles. After passing the ionizing section, dust particles come to a collecting section.

This section consists of several plates alternatively grounded and insulated.

A strong electric field is produced by a DC potential of 6KV is applied to these

plates. Dust particles become positively charged which are attracted and

attached to the ground plates.

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Activated carbon filter

Principles of operation: Removal by absorption.

Activated carbon has porous surface.

carbon, bond to these surfaces and come in contact with the carbon

granules.

Reactivation or regeneration required for activated carbon at the end ofits life

Construction

.

Activated carbon is placed in special tray This special tray slides easily into position to form activated carbon beds

These activated carbon beds are sealed into the cell housing by facing

plates.

Low efficiency filter is placed as pre-filter

l Refuse storage room ventilation: removal of objectionable odour and

irritating vapour of gaseous airborne particles 3nm to 6nm in size

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Activated carbon filter

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Effects of indoor air pollution

IAQ problems which affect people

fall into three general areas: (a)

and (c) chronic health effects.

Pollutants in our indoor environment

affect work productivity. Therelationship between point sources

con am nan s an suscep e

population will determine the risk

and effect of indoor air pollution,and this is often driven by

inadequate ventilation

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selection

-

2- Specific particle size range or aerosolsthat require filtration

-

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The most important

characteristics of the air

the air filters.

Particles less than 2.5micrometer in diameter

are generally reoffered to

as fine with those greaterthan 2.5 micrometer

being considered as

.

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Three operating characteristics thatdistinguish the various types of fi lters:

1-Efficiency: the ability of the filter to removeparticulate matter from an air-stream.

2-Air flow resistance: is the pressure dropacross the filter at a given air flow rate.

3-Dust-holding capacity: the amount of

particulate type of dust that filters can holdwhen it is operated at a specified air flowrate.

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A standardized synthetic dust consisting of

Dust spot efficiency :

into the filter, and the discoloration effect ofthe cleaned air filter paper targets is

com ared with that of that of the incominair.

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Fractional efficiency orenetration:

Uniform-sized particles are fed intothe filter and the percentage removedb the filter is determined b aphotometer or condensation nucleicounter

Particle size efficiency:Atmospheric dust is fed to the filterand air samples taken upstream and

downstream are drawn through aparticle counter to obtain efficiencyverses particle size

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Test Method for Filters with different efficiency

Weight

arrestance

Dust Spot Di-Otyl

Phthalate

DOP

Particle size of test

dust

Large particles

in atmospheric

Atmospheric dust 0.3mparticles

Means to determinedust concentration

PrecisionBalance

Change in lighttransmission

Particle count

Application Low efficiency

filter

Medium efficiency

filter

High

efficiency filter

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Straining.

openings that are smaller than the

particulate being removed

Direct interce tion.

The particles follow a fluid

that the particle contacts the fiber

and remains there

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Inertial deposition

Coated viscous material. Adhesivecoating, wire screen impingement filter

Diffusion

motion about their basic streamlines(Brownian motion), which contributes

to de osition on the fiber

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,

accumulating dust loadcauses pressure drop toincrease u to somemaximum recommendedvalue

Renewable media filters inwhich fresh media areintroduced into the air-stream as needed to

constant resistance andconsequently, constantefficienc

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Electronic filters, which if

maintained ro erl b re ularcleaning have relatively constant

pressure drop and efficiency

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a e o an ex en e sur ace con gura on

of deep space folds of submicron glass fiberpaper.

It must be capable of removing 99.97% of. .

s an ar or a s, c ean room, nuc ear,hospitals, semiconductor, electronics,pharmaceutical manufacturing and toxic-

articulate a lications

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ULPA filters can remove particles as

small as 0.1 microns.

Ultra low penetration air filters areextended media dry filters in a rigidframe that have a minimum particlecollection efficiency of 99.999% for

articles reater than or e ual to 0.12micron in size.

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Renewable media filters :(RMF)

1-Moving-curtain viscous

impingement filters.

2-Moving-curtain dry

media fi lters

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to remove and collectparticulate contaminants such

as dust, and smoke.

The filter consists of anionization section [small

-kV grounded] and col lectingplate section [a series ofparallel equally spaced with a

- .

Electronic fil ters should have an

indicator or alarm system toindicate when the high voltageis off or shorted out.

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Liquid sprayers:

Used to remove wettable solids contaminants, liquidcon am nan s an wa er so u e po u ng gases n

industrial

Ultra-violet lamps:

intensity 14,000 microwatt cm2. This would kill most

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Evaluation of fi lters

Degree of air cleanliness required.

Disposal of dust after it is removed from the air.

Amount and type of dust in the air to be filtered.

Operating resistance to air flow (pressure drop).

pace ava a e or ra on equ pmen .

Cost of maintaining or replacing filters.

.

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The most important characteristics

-the air filters.

Particles less than 2.5 micrometer

reoffered to as fine, with thosegreater t an .5 m e ng

.

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Three o eratin characteristics that distin uishthe various types of filters:

.

particulate matter from an air-stream.

. r ow res s ance: res s ance s e pressure

drop across the filter at a given air flow rate.

3.Dust-holding capacity: the amount of particulate

type of dust that filter can hold when it is operated

at a specified air flow rate.

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Typical Filter Applications Classified by Filter Efficiency and Type

Pre-filter Pre-filter/Filter Final Filter

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Arrestance:A standardised synthetic dust consisting of various particle sizes is fed to the filter.

A standardized atmospheric dust is passed into the filter, and the discoloration effect of

the cleaned air filter paper targets is compared with that of the incoming air.

ract ona e c ency or penetrat on:Uniform- sized particles are fed into the filter and the percentage removed by the filter isdetermined b a hotometer or condensation nuclei counter.

Particle size efficiency:

drawn through a particle counter to obtain efficiency verses particle size.

Mechanisms of particle

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Mechanisms of particle

collection:1. Straining.

Strain particles through membrane openings that is smaller than the particulate

being removed.

2. Direct interception.The particles follow a fluid streamline close enough to a fibre that the particle

contacts the fibre and remains there.

3. Inertial deposition.Coated viscous material. [adhesive coating, wire screen impingement filter]

4. Diffusion.Very small particles have random motion about their basic streamlines (Brownian

motion), which contributes to deposition on the fibre.

5. Electrostatic effects.Particles or media charging can produce changes in the collection of dust.

f f

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f fCommon filters are grouped as follows:

. , n w c e accumu a ng us oa causes pressure rop oincrease up to some maximum recommended value.

2. Renewable media filters, in which fresh media are introduced intothe air-stream as needed to maintain essentially constant resistance and

consequently, constant efficiency.

,

have relatively constant pressure drop and efficiency.

4. Panel filters, there are a variety of panel filters including viscous, y- y x - u , y

Particulate Air [HEPA] filters.

5. Viscous impingement filters, are panel filters made of coarsefibers with high porosity. Glass fibers, steel or aluminium mesh, and metal baffles

are used for filter media. The filter medium is often coated with a viscous

substance e.g. filter oil [adhesive] that causes particulates to impinge on the

.

HEPA filt

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HEPA filters: Stands for High Efficiency Particulate Air filters.

Made of an extended surface configuration of deep space folds of .

it must be capable of removing 99.97% of particles as small as 0.3microns.

These filters are the standard for labs clean room nuclear hos italssemiconductor, electronics, pharmaceutical manufacturing and toxic-particulate applications.

Stands for Ultra Low Penetration Air filters.

ers can remove par c es as sma as a ou . m crons.

Ultra low penetration air filters are extended media dry filters in a rigidframe that have a minimum particle collection efficiency of 99.999

ercent for articles reater than or e ual to 0.12 micron in size

Renewable Media Filters:

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Renewable Media Filters:

Types of RMF:

1. Movin -curtain viscous im in ement filters.

2. Moving-curtain dry media filters.

Using electrostatic precipitation to remove and collect

, .

The filter consists of an ionization section [small diam.-

plate section [a series of parallel equally spaced with a

positive DC volt of 4-10kV]. Electronic filters should have an indicator or alarm

system to indicate when the high voltage is off or

shorted out.

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.

used to remove wettable solids contaminants, liquid contaminates andwater soluble polluting gases in industrial areas such as hydrogen

sul hide, Sul hur dioxide, Nitro en oxide and carbon monoxide.

2. Activated Carbon Filter:The carbon sheath is heated to a high temperature to be activated. Oncens a e , e ac va e car on w a rac e a oms o e gases a

cause the odour. carbon will absorb as much as 50% of its weight inforeign gases. . . . ,

-- removes dangerous household chemical gases from things likecleaners, paints, solvents, carpets, furniture, and other materialcontaining chemical substances.

3. Ultra-Violet Lamps:Lamps give an electromagnetic (Ultraviolet) radiation of intensity 14,000

.seconds.

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va ua on o ers:

1. Degree of air cleanliness required.

. sposa o us a er s remove rom eair.

.

filtered..

drop).

5. S ace available for filtration e ui ment.6. Cost of maintaining or replacing filters.

7. Initial cost of the s stem.

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