Filters for Heating, Ventilation, and Air Conditioning (HVAC) system

Filters for Heating, Ventilation, and Air Conditioning (HVAC) system

High-level summary for basic understanding of HVAC filter classes used in the pharmaceutical, biopharmaceutical, and medical device industry


The Heating, ventilation, and air conditioning (HVAC) system filters used in pharmaceutical and healthcare facilities have an essential role to play. They filter pollen, dust lice, Industrial-dust, spores, molds, smoke removal, bacteria, viruses, and other small particles out of the air you introduce in your pharmaceutical, biopharmaceutical, or medical device manufacturing facility. These particles are trapped in the filter to prevent them from being recirculated throughout your facility. The higher the arrestance, the more effective the filter will be.

Filters also play an important part in preventing cross-contamination, keeping equipment and instrument free from larger particles that could malfunction it. Therefore, engineers and quality assurance want to make sure that the correct type of filters is used in the facility, clean it, and change it when necessary depending on the types of filters. Here we will discuss what filtration is, the filtration mechanism, different types of filters available for HVAC systems, different standards available to classify the filters, applicable test methods, and high-level comparison between different classes.

What is air filter?

The filter is a mechanical device that removes contaminants from the air stream.

What are the different mechanisms of particulate air filtration?

Following are four mechanisms of particulate air filtration.

Filtration Mechanisms

Mechanisms of particulate air filtration

i. Inertial impaction: Impaction/ collision of particle occur with a fiber.

ii. Interception: Interception of a large particle because of its size.

iii. Diffusion: Diffusion of the particle occurs because of Brownian motion or random motion. Because of that, the particle contact with a fiber.

iv. Electrostatic attraction: Retention of the particle using electrostatic magnetism or attraction. In this mechanism, the particles are collected on the filter fibers by an electrostatic force.

[Reference – i]

What are the most commonly used standards for selection of air filtration for HVAC system?

i. EN779 ‘Particulate Air Filters For General Ventilation – Determination of the Filtration Performance’. EN 779 relates to Coarse (G) filters, Medium (M) filters, and Fine (F) filters of filter classes G1 to F9.

ii. EN1822 ‘High Efficiency Air Filters (EPA, HEPA & ULPA) – Part 1: Classification, Performance Testing, Marking’. It describes the testing of filtration attributes for absolute filters in the filter production company, which are Efficient Particulate Air filter (EPA), High Efficiency Particulate Air filter (HEPA), and Ultra Low Penetration Air filter (ULPA). EN 1822 relates to filter classes E10 to U17.

iii. ISO 29463-1:2017 ‘High efficiency filters and filter media for removing particles from the air – Part 1: Classification, performance, testing and marking’

iv. ASHRAE ‘The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) is an American professional association seeking to advance heating, ventilation, air conditioning and refrigeration systems design and construction’. Minimum Efficiency Reporting Values, or MERVs, report a filter’s ability to capture larger particles between 0.3 and 10 microns (µm). The rating is derived from a test method developed by the ASHRAE.

What are the different protection levels of cleanroom class? What are the recommended filters for different protection levels of cleanroom class?

Depending on the operations to be carried out in the area, the level of protection is defined as follows:

Filters according to the required protections
Level Location Examples locations Filtration required/ filters
1 Common area Location or area where general cleanliness and maintenance required.

No possibility of material contamination. E.g., stores

Primary:

Filtration level –  EN779-G4

2 Area where protection requires Packing area (secondary), warehouse to store raw materials Primary and secondary-filtration – EN779-G4 plus F8 or F9
3 Specialized controlled condition Area where product exposed to the environment, granulation area, tablet compression, coating, raw material dispensing etc Three level of filtration i.e.  Primary and secondary and final filtration (with HEPA)

EN779 G4-plus, F8-plus EN1822 H13-filters

[Reference – ii]

Filter classes according EN 779 and EN 1822 and its description.

Filter classes according EN 779 and EN 1822 are explained as follows:

EN class

Description

Filter
Class

EN 779

Coarse (G) filters

G1 to G 4

EN 779

Medium (M) filters

M5 to M6

EN 779

Fine (F) filters

F7 to F9

EN 1822

EPA Filter (Efficient Particulate Air filter)

E10 to E12

EN 1822

HEPA Filter (High Efficiency Particulate Air filter)

H13 to H14

EN 1822

ULPA Filter (Ultra Low Penetration Air filter)

H15 to H16

Explanation and comparison of HEPA filter classes according to EN 1822 and ISO 29463:

Comparison of HEPA filter classes according to EN 1822 and ISO 29463 are explained as follows:

Description

EN
1822

ISO
29463

EPA Filter (Efficient Particulate Air filter)

E10 to E12

ISO 15 E – ISO 30 E

HEPA Filter (High Efficiency Particulate Air filter)

H13 to H14

ISO 35 H – ISO 45 H

ULPA Filter (Ultra Low Penetration Air filter)

H15 to H16

ISO 50 U – ISO 75 U

What is difference between the leakage test methods specified in the two standards, ISO 29463:2017 Part 1 and EN 1822 Part 1?

Difference between the leakage test methods specified in the two standards, ISO 29463:2017 Part 1 and EN 1822 Part 1 is summarized in the following table.

ISO 29463

EN 1822

Scan leak test

Scan leak test

Oil thread leak test

Oil thread leak test

Efficiency leak test
for 0.3 µm to 0.5 µm

Efficiency leak test
for 0.3 µm to 0.5 µm

Aerosol photometer leak test

PSL leak test

Comparison of different filter classes used for clean rooms:

Following is the comparison of different filter classes used for clean rooms. The test standard correlations are approximate. Designing HVAC system and selection of filter should be based on user requirement and efficiency of filtration level required.

Eurovent 4/5 rating  (superseded)

EN 779 & EN 1822
MPPS integral overall efficiency (%)

EN rating as per EN 779 & EN 1822

ISO 29463

ASHRAE 52.2
Merv rating

Eurovent 4/5 ASHRAE 52.1 BS6540 Part
1
Average arrestance Am (%)

Eurovent 4/5 ASHRAE 52.1 BS6540 Part
1
Average dust spot efficiency Em (%)

Particle
size
range, μm

Application

EU 1

G1 (EN 779: 2012)

Merv 1

< 65%

< 20%

>10

Residential light pollen, dust mites

Merv 2

65.70%

< 20%

EU 2

G2 (EN 779: 2012)

Merv 3

70.75%

< 20%

Merv 4

> 75%

< 20%

EU 3

G3 (EN 779: 2012)

Merv 5

80.85%

< 20%

3.0 – 10

Industrial, dust, molds, spores

Merv 6

> 90%

< 20%

EU 4

G4 (EN 779: 2012)

> 90%

30

Merv 7

> 90%

20.25%

Merv 8

> 95%

25.30%

EU 5

M5 (EN 779: 2012)

Merv 9

> 95%

40.45%

1.0 – 3.0

Industrial, Legionella, dust

Merv 10

> 95%

50.55%

Merv 11

> 98%

60.65%

EU 6

M6 (EN 779: 2012)

> 96%

70%

Merv 12

> 98%

70.75%

EU 7

>98 %

80%

F7 (EN 779: 2012)

Merv 13

> 98%

80.90%

0.3 – 1.0

Hospitals, smoke removal, bacteria

EU 8

F8 (EN 779: 2012)

Merv 14

> 98%

90.95%

EU 9

F9 (EN 779: 2012)

Merv 15

> 98%

~95%

EU 9

85

E10 (EN 1822: 2009)

Merv 16

> 98%

> 95%

EU 10

95

E11 (EN 1822: 2009)

15E

EU 11

99.5

E12 (EN 1822: 2009)

25E

EU 12

99.95

H13 (EN 1822: 2009)

35E

Merv 17

<0.3

Clean rooms, surgery, chem-bio, viruses

EU 13

99.995

H14 (EN 1822: 2009)

45E

Merv 18

EU 14

99.9995

U15 (EN 1822: 2009)

55E

Merv 19

99.99995

U16 (EN 1822: 2009)

65E

Merv 20

99.999995

U17 (EN 1822: 2009)

75E

MPPS – Most Penetrating Particle Size

Merv – Minimum Efficiency Reporting Value

Note: The test standard correlations above are
approximate. Designing HVAC system and selection of filter should be
based on user requirement and efficiency of filtration level required.

Explain filter types used in clean rooms, filter media or Material of Construction (MoC), efficiency, initial and final pressure drop.

Filter types

Media

Filtration Rating

Initial Pressure Drop

Final Pressure Drop

Pre filter

HDPE or non-woven synthetic media stitched with
one layer of G.I. and crimped to required depth to provide larger filtration
area

Up to 90% down to 10 µm

2.5 mm WC at rated flow

7.5 mm WC



Fine filter

Compressed woolen felt or synthetic needle felt
supported by G.I. wire netting stitched together and crimped to required
depth to provide larger filtration area

Up to 99% down to 5 µm

6 mm WC at rated flow

18 mm WC

HEPA

(high-Efficiency
Particulate Air OR High-Efficiency Particulate Absorbing OR

High-Efficiency
Particulate Arrestance)

Polypropylene or fiberglass (boron silicate fiber) with
diameters between 0.5 and 2.0 micrometers that
cause contaminants to stick to them through electrostatic attraction and
other physical mechanisms.

Minimum particle collection efficiency of 99.97%
for particles 0.3 microns in diameter

Less than 25 mm WC

Up to 75 mm WC

ULPA

(Ultra
Low Particulate Air OR

Ultra Low Penetration Air filter)

HEPA and ULPA filters are made of glass
fiber material. It is possible to manufacture ULPA filters made from Teflon
(PTFE), because glass fiber material contains approximately 10% boron that in
the presence of moisture or hydrogen fluoride (HF) can be released.

ULPA filter has an efficiency of 99.999% for
particles 0.12 micron or larger size at the specified media velocity.

As rated by manufacturer

As rated by manufacturer

SULPA (Super ULPA)

At an efficiency of 99.9999% these filters are
based on the same standard as the ULPA filters

As rated by manufacturer

As rated by manufacturer

Ultimate ULPA

At an efficiency of 99.9999999% these filters are
based on the same standard as the ULPA filters.

As rated by manufacturer

As rated by manufacturer

References

i. Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks, Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, April 2003

ii. WHO, Working document QAS/02.048/Rev.2

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