Table Of ContentREHVA
Air Filtration
in HVAC Systems
Jan Gustavsson (ed.)
Alain Ginestet
Paolo Tronville
Marko Hyttinen
DISCLAIMER
REHVA and the authors reserve the right not to be held responsible for the topicality,
correctness, completeness or quality of the information provided. Liability claims regard-
ing material or non-material damage caused by the use or non-use of the information pro-
vided or the use of any information that is incorrect or incomplete will therefore be re-
jected in so far as the author cannot be charged with deliberate or gross negligence.
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Copyright © 2011 by REHVA,
Federation of European Heating, Ventilation and Air–conditioning Associations
2nd revised edition
All rights reserved
No part of this publication may be reproduced or transmitted in any form or by any
means, electronically or mechanical, including photocopy recording, or any information
storage and retrieval system, without permission in writing from the publisher.
Requests for permission to make copies of any part of the work should be addressed to
REHVA Office, 40 Rue Washington, 1050 Brussels – Belgium
e-mail: [email protected]
ISBN 978-2-930521-01-5
Printed in Finland, Forssa Print 2011
ii
Member countries of REHVA
Belgium Ireland Russia
Bosnia Italy Serbia
Croatia Latvia Slovakia
Czech Republic Lithuania Slovenia
Denmark The Netherlands Spain
Estonia Norway Sweden
Finland Poland Switzerland
France Portugal Turkey
Germany Romania United Kingdom
Hungary
REHVA Task Force on Air filtration
The present work has been carried out by the REHVA task force on Air filtration.
The Task Force organized a workshop at the Clima 2007 Conference in Helsinki and Indoor Air
conference in Copenhagen, in August 2008 where the results of the work of the Task Force were
presented and discussed. The work of the Task Force was also reported to the REHVA General
Assemblies in Berlin 2008 and Amsterdam 2009.
The members of the Task Force are:
Jan Gustavsson Sweden
Alain Ginestet France
Paolo Tronville Italy
Marko Hyttinen Finland
Reviewers
The following persons have reviewed the book and made valuable suggestions for improvements.
Denis Bémer France
Carmine Casale Italy
Gian Vincenzo Fracastoro Italy
Jorma Railio Finland
Olli Seppänen Finland
Minna Väkevä Finland
Acknowledgments
The Task Force members would like to express gratitude to Derrick Braham, UK who checked
the language. This was especially welcome as the members of the Task Force are not native
English speakers. The authors also thank Jarkko Narvanne for the final layout and typesetting of
the Guidebook.
v
Member countries of REHVA
Belgium Ireland Russia
Bosnia Italy Serbia
Croatia Latvia Slovakia
Czech Republic Lithuania Slovenia
Denmark The Netherlands Spain
Estonia Norway Sweden
Finland Poland Switzerland
France Portugal Turkey
Germany Romania United Kingdom
Hungary
REHVA Task Force on Air filtration
The present work has been carried out by the REHVA task force on Air filtration.
The Task Force organized a workshop at the Clima 2007 Conference in Helsinki and Indoor Air
conference in Copenhagen, in August 2008 where the results of the work of the Task Force were
presented and discussed. The work of the Task Force was also reported to the REHVA General
Assemblies in Berlin 2008 and Amsterdam 2009.
The members of the Task Force are:
Jan Gustavsson Sweden
Alain Ginestet France
Paolo Tronville Italy
Marko Hyttinen Finland
Reviewers
The following persons have reviewed the book and made valuable suggestions for improvements.
Denis Bémer France
Carmine Casale Italy
Gian Vincenzo Fracastoro Italy
Jorma Railio Finland
Olli Seppänen Finland
Minna Väkevä Finland
Acknowledgments
The Task Force members would like to express gratitude to Derrick Braham, UK who checked
the language. This was especially welcome as the members of the Task Force are not native
English speakers. The authors also thank Jarkko Narvanne for the final layout and typesetting of
the Guidebook.
v
REHVA –
Federation of European Heating, Ventilation and Air–Conditioning Associations
REHVA, now almost 50 years old, is an matter that could accumulate on internal
organisation of European professionals in surfaces and reduce the performance of
the field of building services (heating, ven- the system.
tilating and air–conditioning). REHVA
represents more than 100 000 experts from This Guidebook presents the theory of air
28 European countries. filtration with some basic principles of the
physics of pollutants and their effects on
REHVA’s main activity is to develop and indoor quality. However, the main focus is
disseminate economical, energy efficient on practical design, installation and opera-
and healthy technology for mechanical tion of filters in air handling systems.
services of buildings. The work is super-
vised by the board of directors. REHVA It is intended for the use of designers,
Guidebook projects are coordinated by manufacturers, installers, and building
the Technology and Research Committee owners. With its theory, practical solutions
of REHVA. and illustrations it is also an excellent text-
book for the vocational training of various
Several task forces are currently working experts in building services engineering.
on REHVA Guidebooks such as: Solar
shading, Indoor air quality investigations The Guidebook on Air filtration has been
in buildings, Energy efficient HVAC sys- written by a working group of highly
tems for good indoor environments in qualified international experts represent-
schools, Control of Legionella, Radiant ing research, manufacturing, consulting
heating systems, Advanced air distribu- and design. The work is done on a volun-
tion systems. tary basis without any commercial inter-
est. The REHVA Board would like to
Cleaning of ventilation air is becoming express its sincere gratitude to the work-
more important due to the increasing ing group for this invaluable work.
pollution in urban areas. The filters in
the air handling systems are important to
protect building occupants from external Olli Seppänen
air pollution. Air cleaning is also needed REHVA Chairman of the REHVA
to protect the equipment from particulate Technology and Research Committee
iv
Scope of the Filtration Guidebook
GUIDEBOOK 50% of outdoor airborne pollutants are
This Air Filtration Guidebook will in- carried into buildings and have a large
crease the awareness of the role of air impact on the indoor air quality. Build-
filtration to improve indoor air quality, ings supply air quality is often the domi-
and to improve the design of energy effi- nant factor in exposure to air pollution
cient air filtration systems. It will help the and associated risk to health.
designer and user to understand the back-
ground and criteria for air filtration, how Air filtration has the potential to reduce
to select air filters and avoid problems the outdoor to indoor transport of pollut-
associated with hygienic and other condi- ants and to improve the health and com-
tions in the operation of air filters. The fort of occupants and the productivity.
selection of air filters requires a number
of considerations ranging from the air Regardless of perspective, effective parti-
intake to the disposal of soiled air filters. cle filtration, it is anticipated that annual
savings will significantly exceed the run-
The Guidebook is mainly applicable to air ning costs for filtration. On the other
filters in general ventilation systems. hand, sensory pollutants emitted from
However parts of it may also be useful in soiled air filters may cause substantial
applications with any kind of forced ven- extra costs, thus exceeding the annual
tilation or when air ventilating filters are economic benefits of filtration. The air
used as a part of the ventilation system in filter is one component in a system, there-
critical applications in order to protect fore it is important to design air filters
people, products or environment. and HVAC systems together in order to
minimize ill health and sensory problems
FILTRATION IN HVAC SYSTEMS caused by pollution.
Air filters for HVAC systems have al-
ways been used to protect the ventilation The filter and its energy costs are insig-
components. A filter thus selected can nificant relative to workers salaries. Good
keep fans, ducts and coils clean and avoid indoor air quality (IAQ) and high hygi-
increased pressure drop and malfunctions. enic requirement (high efficient filters
The requirement for air purity has in- replaced twice per year) will cost about
creased by virtue of the heightened 50 € per person per year or 1 € per week
awareness of indoor air quality. About per person.
vi
List of contents
1 AIR FILTRATION IN A NUTSHELL.............................................................................1
2 TERMINOLOGY...............................................................................................................9
3 USE OF AIR FILTERS...................................................................................................11
3.1 History....................................................................................................................11
3.2 Currant use of air filters...........................................................................................12
4 GENERAL ENGINEERING CRITERIA.......................................................................14
4.1 The air around us.....................................................................................................14
4.2 Health and contaminants..........................................................................................20
4.3 Energy requirements................................................................................................23
4.4 Indoor air requirements...........................................................................................24
5 PARTICULATE FILTRATION PRINCIPLES.............................................................27
6 PARTICULATE AIR FILTER TEST METHODS........................................................31
6.1 HVAC filters...........................................................................................................31
6.2 Classification of air filters.......................................................................................34
6.3 In situ tests..............................................................................................................36
7 PARTICULATE AIR FILTERS.....................................................................................38
7.1 Fibre filters..............................................................................................................38
7.2 Electrostatic precipitators (ESP)..............................................................................44
7.3 UVC........................................................................................................................45
8 GAS PHASE AIR FILTERS............................................................................................46
8.1 Adsorption...............................................................................................................46
8.2 Media for gas phase filters.......................................................................................48
8.3 Gas phase filters......................................................................................................48
8.4 Molecular filtration test methods.............................................................................49
8.5 Gas phase filter selection.........................................................................................52
9 PARTICULATE AIR FILTERS IN SERVICE..............................................................55
9.1 Laboratory assessment and actual performance.......................................................55
9.2 Particulate air filters in operation.............................................................................57
10 HYGIENIC CONSIDERATION OF AIR FILTERS.....................................................62
10.1 Perceived air quality................................................................................................62
10.2 Microorganisms.......................................................................................................64
10.3 Antimicrobial treatment of air filters......................................................................67
11 APPLICATION AND SELECTION OF AIR FILTERS...............................................68
11.1 Particulate air filters................................................................................................68
11.2 Prefilter...................................................................................................................72
11.3 Installation...............................................................................................................73
11.4 LCC (Life Cycle Cost)............................................................................................77
11.5 LCA (Life Cycle Assessment).................................................................................80
11.6 Air intake................................................................................................................80
11.7 Replacement of soiled air filters..............................................................................81
11.8 Disposal of soiled filters..........................................................................................82
12 CERTIFICATION OF AIR FILTERS...........................................................................84
13 AIR FILTRATION - CHECK LIST...............................................................................86
14 REFERENCES.................................................................................................................88
iii
1 AIR FILTRATION IN A NUTSHELL
During the last decades, the potential It is worth considering that one particle of
benefits to health have been increasingly 10 µm weighs the same as one million ul-
recognized as the primary purpose of fil- trafine particles. The total number of parti-
tration. The important criteria for selecting cles in a city can exceed 10 000 000 000
an air filtration system are based on exter- particles/m³, which a standard air filter for
nal pollutants, indoor air quality, energy 1 m³/s has to treat every second.
requirements and hygienic conditions.
It is possible to see individual particles
Pollutants down to 10 µm with naked eye. Particles
in tobacco smoke are less than 1 µm, but
can also be seen due to the high concen-
tration of the ultrafine particles. Some
common pollutant sizes are found in
Figure 1.2.
Number Volume /mass
Example of particles in exhaust air.
0,001 0,01 0,1 1 10 100
Outdoor and indoor air pollutant charac-
teristics vary greatly with place, time and Particle size [µm]
local conditions. Huge numbers of parti-
Figure 1.1 Example of number and mass size
cles of different sizes, shapes, concentra-
distribution of atmospheric aerosol. Made from
tions and toxicity are found in the air, as EPA, 2004.
well as different gases ranging from
harmless to irritating and unhealthy. Air-
Airborne particles
borne impurities differ in size and com-
Diesel particles
position, from ultrafine or nano-particles
(less than 0.1 µm) to fine particles Tobacco smoke Spores
(0.1 µm to 2.5 µm) and coarse particles Gases Virus Bacteria Pollen
(dust >2.5 µm).
0,001 0,01 0,1 1 10 100
The distribution of the particles in the at- Particle size [µm]
mospheric aerosol may be expressed in
Figure 1.2 Examples of particle size for some
different ways (see 4.1.3 Atmospheric pollutants.
aerosol). With respect to number, most of
the particles are less than 0.1 µm (nano The concentrations of many common pol-
particles). With respect to mass most par- lutants in different places or cities can be
ticles are larger than 0.1 µm (Figure 1.1). found on the government authorities web
1
REHVA Air Filtration Guidebook
pages. The selection of air filters depends EN 13779:2007 defines the requirements
on the quality of the outdoor air and the of filter classes to meet different indoor air
desired indoor air requirement. qualities with reference to the outdoor air
EN 13779:2007 defines three categories environment (see 4.4 Indoor air require-
of outdoor air, ODA 1 (pure air, except ments). This is accomplished in most cases
for temporary pollutions such as pollen) by using a two stage filtration with mini-
to ODA 3 (very dirty air with high con- mum F7 filter quality for the treatment of
centrations of both gas and particulates). outdoor air. However, as the filter classes
Four classes of indoor air, IDA 1 (high do not cover in-situ performances, the
quality) to IDA 4 (low), are used as the minimum efficiency1 according to the
basis for selecting air filters (see 4.4.2 EN 779:2002, Eurovent (rec. 18 2009) or
EN 13779:2007 Indoor air classification an independent test of in-situ operation
and requirements). should be specified (see 9.2 Particulate air
filters in operation). This will give Mini-
Indoor air requirements mum Life Efficiency (MLE) in service and
Epidemiological studies worldwide have is the only efficiency which can be guaran-
demonstrated adverse effects of even low teed and checked in the installation.
levels of air pollution on health (see 4.2
Health and contaminants). Air contami- The filters should be replaced for hygi-
nants such as particles, sulphur dioxide, enic reasons and the service intervals may
ozone and nitrogen dioxide have serious be 2 000 h for the first filter stage and
effects on health. In Europe, indoor and 4 000 h for the second filter stage (see
outdoor air pollutants are the most impor- 4.4.2 EN 13779:2007 Indoor air classifica-
tant contributory factor of diseases related tion and requirements). The filters should
to the environment. Particles are currently be replaced in the autumn after the pollen
considered the worst. There is a clear season and in demanding applications also
connection between raised pollution lev- in spring after the winter heating season to
els of fine particles below 2.5 µm and avoid organic odours. If possible, the rela-
increased mortality caused by cardiovas- tive humidity should be kept below 80% to
cular and respiratory illness. avoid microbial growth.
We spend 90 percent of our time indoors Energy requirements
and breathing healthy indoor air is a hu- The air flow resistance in air filters con-
man right and all groups, individuals or sumes fan energy and is indirectly re-
organizations associated with a building sponsible for the global climate change.
have a responsibility to work to achieve The United Nations roadmaps on cutting
an acceptable air quality (WHO 2000). emissions and the European Directives on
Air filtration may improve indoor air saving energy will encourage measures to
quality and occupants productivity as reduce the air flow resistance and the
well as reduce the costs associated with amount of energy used by air filters. This
building and HVAC cleaning (see 3.2 has to be implemented not only in the
Currant use of air filters). initial clean conditions but during the
1
Lowest efficiency in the EN 779 test including efficiency of
neutralised filter material (discharged efficiency).
2
1 AIR FILTRATION IN A NUTSHELL
whole service life of the filter. However, according to EN 15805 (see Table 7.1
at the same time the delivered air quality Face dimensions of air filters according
should not be compromised by simply to EN 15805).
lowering the efficiency of air filters. The
correct design and good maintenance of The removal of contaminating particulates
air filters is important to minimize the is usually performed by fibrous filtering
energy consumption without affecting the media. Fine fibres are the crucial factor in
removal efficiency (see 4.3 Energy re- achieving higher efficiency and glass has
quirements). been the most frequently used material to
produce fibres with diameter around 1 µm
Energy consumption is linked to the air and below. The process development has
resistance of the filter. The energy cost progressed quickly and nowadays it is pos-
operating the filter can be 80% of the sible to produce high efficiency filter media
overall cost of the filter. The rest includes sourced from various polymer substances.
filter replacement, labour and disposal If the filter material is able to hold signifi-
costs. The air flow of the filter, replace- cant electrostatic charge the initial particu-
ment intervals and pressure drops are the late efficiency can be much improved.
parameters to be chosen based on accept-
able air flow changes in the system
(11.1.2), life cycle costs (11.4) or life cy-
cle assessments (11.5). About 80% of the
filters environmental load results from the
energy used to overcome the air flow re-
sistance during operation.
To meet the directives of a low energy
future and lower Specific Fan Power it is
necessary to reduce air flow resistance of
the filters by optimising the design and
the operation of the filter. Most air han-
dling units today are designed for a face
velocity of 2 to 3 m/s, but reducing final
pressure drop and air flow per filter, con-
siderably savings in energy and costs can
be achieved (see 11.1.2 Pressure drop).
Air filter in air handling unit.
Air filtration
The filter design has to be a compromise The overall fractional particle efficiency of
between the construction and amount of an air filter is the result of the sum of dif-
media to meet costs, stability, air flow ferent filtration mechanisms (diffusion, in-
resistance and service life. Today there terception, inertia and electrostatic forces.
are thousands of different filter sizes and See 5 PARTICULATE FILTRATION
to improve the situation it is recom- PRINCIPLES). There is a specific particle
mended to use only a few standard sizes size which is the most difficult to collect in
3
