- Email: [email protected]
Indoor air filtration: Why use polymer based filter media?
Here Thomas Carlsson of Sea&filter
AB, Sweden, reminds us all
why synthetic fibres remain the materials of choice when looking to develop innovative media for indoor airfiltration applications.
ver a ten-year
period
l
there has been a
l
considerable
l
change in
what filter media are
l
used in ventilation applications.
Up until about 30 years ago,
almost all such filters were based on glass
environmental
impact;
methods:
process considerations; resistance
and
polymer
to microorganisms. satisfy these performance
specifications?
High Filtration
Polymer based
material
Efficiency
being used.
Low Pressure
effective way of optimising
The efficiency
share. To find the reason(s)
separated in a filter is primarily
calculation
determined
variety of equipment
change, the requirements for ventillation
applications
that filter media need to satisfy
must be considered. The performance
with which particles
of a
are
by fibre size. Polymer fibres
can now be produced in a wide range of sizes. The most commonly
specification
the meltblow-n process, polymers
used method is
which involves
filter medium suitable for use as a class
extruding
G 1 -F9 filter is based upon the following
and temperature
parameters:
stream. By varying the process parameters,
l
l
filtration
efficiency;
in diameter
from 0.1 pm-100
pressure drop;
Conversely,
the average fibre diameter
mechanical
for a class F7 glass fibre material is
strength;
-
pm
1 I-‘m VI. Polymer
[ 11.
LCC = Investment LCCIvlaintrnance
+
+ LCCtncrgv +
’
LCCDispoaal
As an example,
consider a class F7 filter
with the following cost breakdown: Investment Energ?
+ LCCMaintcnsnrp= =
18.5%
81% =
0.5%
[4].
A low pressure drop is an important
affects energy running costs. From
technnique
which
Figure 1 it can be seen that energy
can further
increase
running costs account for 8 1% of the total
Thus, this ability makes them preferable
cost. Using polymer fibres, the structure
(Figure 2). By using different fibre sizes, a fibres
filter web can be constructed
that cannot be
open structure
charged.
Several
the larger particles,
methods
of charging
gressively finer structure
materials
have been
developed
of
the material can be varied and controlled
to
conventional
2OOl
In the case of a filter, the life cycle cost can be calculated as follows:
down because the pressure drop directly a
filter efficiency.
March
including filters,
fans, pumps, etc.
element in keeping total running costs
charging,
30
Several methods of
fibres
electrostatic
Investment Energy E Disposal
an
the total cost
have been developed for
LCCDispo\al
suited for
n
of an installation.
LCC
are also ideally
n
in order
under high pressure
into a high velocity air-
it is possible to produce fibres that range
l
Drop
to achieve a low life cycle cost (LCC),
materials now hold the major market behind this
of
on the type of
A low pressure drop is important
fibre. Today, glass fibre only accounts for 40% of the market.
effect and the
and the choice
method is dependent
How well do present day polymer based materials
the triboelectric
corona treatment,
fire resistance;
and
with an
on the inlet face, to catch followed by a proas you move
towards the centre of the web to capture the smaller particles. This means that
refined over recent
the increase in pressure drop with time
years. There are
can be kept low, which in turn lowers the
essentially
LCC.
two
Filtration+Separation
It can be seen from Table 1 that the tensile strength of the polymer based material is nearly twice that of a glass fibre material. The combination of high tensile strength and good elongation to break guards against the polymer based fibres breaking during use.
Environmental Impact
Mechanical Strength An important parameter for an)' f i l t e r material is its mechanical strength. Pulvmer based fibres possess a combination of high tensile strength and good strain resistance, even under high humidity conditions. High tensile strength and good elongation performance are important, not only when the filter is being fitted but also during operation. Materials, with a low strength can, for example, be torn by sharp metal edges when being fitted. The elongation performance of polymer based fibres give the material good resistance to tearing, and therefore reduces the risk of it becoming damaged during installation.
A life cycle assessment (LCA) evaluates the environmental impact of a product by taking into consideration the total environlnental impact of a product during Inanufacturc, operation and disposal, i.e. a cradle to grave approach. The energy requirement of the various processes provides an important indicator of the environmental impact of a product. In terms of energy use during the manufacture and disposal, a polymer based filter material, with a plastic frame, is said to have the least environmental impact of any commercial filter currently available on the market [3]. If the energy used hv or in connection with a polymer based filter, with a plastic frame is given the index 1, then other filters have indices in the range 2-4.5.
P o l y m e r based m a t e r i a l
Ultimate tensile strength* (N)
Glass fibre m a t e r i a l
99
58
* m e a s u r e d in a c c o r d a n c e w i t h ISO 5081:1977
The greatest energy demand of a filter occurs when overcoming the pressure drop that happens {luring normal operations [4]. In order to achieve a low pressure drop, and therefore a low energy demand, the filter needs to have a high dust loading capacity. a common error when assessing dust loading capacity is to compare the surface areas of the filters. However, a filter having a large surface area does not necessarily have a high dust loading capacity. Using polymer fibres, it is possible to vary the fibre sizes throughout the thickness of the medium (Figure 2), so that dust is loaded in the interior of the medium, rather than on the surface. This gives a low pressure drop across the filter, resulting in good running costs. In addition, ~ hen manutacturing polymer based filter media, it is possible to some extent (up to 30 %) to use recycled fibres, e.g. from polyethylene terephthalate (PET) bottles, giving these fibres a further environmental edge.
Microorganism Resistance Outdoor air contains thousands of naturally occurring microorganisms (bacteria, mould spores, fungi, ctc). They are separated in the filter and, together with the other })articles, form a dust cake on the filter. Unfortunately, this {lust cake can provide a source of nutrients for the microorganisms. The Freie Univ~irsit~it Berlin, Germany, carried out an investigation [5] to determine the di[Ii~rences in bacteria anti mould growth patterns between a polymer based anti a glass fibre filter. The two filters were installed in the same plant and exposed to outdoor air. The biological activity on them was measured once a week. The results of the study are shown in Figure 3. Bacteria
Moulds 4000000
6000000
•
• Micro glass . . . . . Polymer fibres
%
!
4000000
M i c r o glass
......... P o l y m e r fibres 3000000
"E 2000000
~D
0
2000000
.... J - ~ ...... 1000000
i 0
i
2
. . . . . .
[
i 4 Week
Filtration+Separation
_
I 4 Week
6
March 2001
31
Smoke Emission
Output Heating Effect --
300
Micro glass Polymer fibres
250 200 150 100 50 50
20
40
60
100
80
1
Set
See
etc) to produce a tailor-made
filter media
for a specific application.
Conclusions
Air in air @ration &at of%rs a wide r&e
The development
of glass and synthetic media for prim&,
secondary and final. WEPA filtration levels, as we11 as filters for special apphahions. Over the course of the past year Russel Mcleod has been focussing its business on clean air filtration applications through several acqusitions. Early in 2000 it purchasedvokes Invensys plc, creatingvokes of high technology
air filtration, i.e. cleanrooms
and the pharmaceutical
based at Interfilta’s site in Burnley (FiZtrution+Separotion,
The recent acquistions
in Switzerland
industry. It is
January/February
More recently, Russel Mcleod acquired Eurpoean filter technology which is headquartered
from
Air Filtration, which is a well known name within the fields 2000, p.4).
company, Luwa,
(Filtrotion+Separation, January/February
have had the result of significantly
position in the Euopean clean air filtration
It was found that the growth of both
strengthening
2001).
Mcleod Russel’s
market.
performance environments.
In fact, even manufacturers
which previously concentrated of glass fibre materials to appreciate materials:
the advantages of these
fibres, with the mechanical process potentials
1. CiachT.
2000.
structures:
growth in the glass fibre material. The
filter not only incrcascs the risk of damage
manufacturing,
layered polymer)
material (multi-
appears more suitable for
use in heating, ventilation conditioning
to the rest of the ventilation system, but also
that ‘the new
& air
of spreading the fire. In addition, the amount of smoke released by the glass tibre filter was sufficiently high that any electrical
(HVAC) systems because the
material itself appears able to reduce the growth or survival of microorganisms.’
Fire Resistance
component
exposed to it would have to be
completely replaced.
Deep bed filtration
Properties
Filtration Congress, Brighton, 10/93 3. Maria Eriksson, Technology,
miljiibediimning
innemiljii’
[Alrjilters:
environmental
One particular benefit of polymer based
environment].
4. Eurovent/Cecomaj: Recommendation
that is less prone to distortion.
calculation
generation
are the possible
there is no need to add any binder to the
of toxic gases and how much
product, as the fibres are bound together
heat is released. These characteristics investigated
were
for a polymer based and a
either thermally or by friction. Therefore, concerns regarding potentially toxic binders
glass fibre filter. The filters were installed
being dissolved by moisture and distributed
in the same ventilation
through the ventilation system by the supply
plant for a period
of five months, after which they were tested at the Fire Testing Laboratory
of the
It is also possible, when using polymer based filter media, to incorporate
Institute,
with varying characteristics
Sweden. The heat and fire
gas release results obtained in the study are
resistant,
shown in Figure 4.
tensile strength,
32
March
2OOl
1999,
concerning
of life cycle cost for air
filters. 5. Kemp P C. 1999. Comparison
of
microorganism
loading from two air
filter materials.
Indoor Air,
6. Gustafsson J, Camfil. Energi &MiJjc, 2/00
air are eliminated.
Swedish National Testing and Research Boris,
och
technical qualities,
assessment and the indoor
ensures airtight joints, and produces a filter
taken into consideration
University
tekniska
kvaliteter,
Process Considerations
In addition,
Chalmers
Luftfilter:
materials is their ability to be welded, which
The factors that need to be
UK.
2. Gustafsson J, Camfil. Energy &Wjb’,
From a safety point of view the fire important.
and
ProceedInS 8th World
resistance
of a filter medium is very
fibres have
161.
References
gases. The high heat output of the glass fibre
of air filtration
charged
strength and
of svnthetic
future prospects’
material was less than the corresponding [5] concludes
on the use
are now beginning
‘fine electrostatically
releases considerably more heat and fire
report
filter with different
levels to satisfy a variety of
bacteria and mould in the polymer based
generation
rapidly, making it
possible to customisc
excellent It can bc seen that the glass fibre filter
of new polymer based
fibrcs is progressing
fibres
(flame
bactericide-containing, good elongation
For more mformatmn contact: Thomas Carlson, R&D Director, Scan$Jter Sweden. Tel: f46
325
AB. 512 85 SvenJjup,
66 16 00;
high
Fax: f46
to break,
Webnte: www.scandfiJter.com
325 6 1 14 90;
Filtration+Separation
of
AB, Sweden, reminds us all
why synthetic fibres remain the materials of choice when looking to develop innovative media for indoor airfiltration applications.
ver a ten-year
period
l
there has been a
l
considerable
l
change in
what filter media are
l
used in ventilation applications.
Up until about 30 years ago,
almost all such filters were based on glass
environmental
impact;
methods:
process considerations; resistance
and
polymer
to microorganisms. satisfy these performance
specifications?
High Filtration
Polymer based
material
Efficiency
being used.
Low Pressure
effective way of optimising
The efficiency
share. To find the reason(s)
separated in a filter is primarily
calculation
determined
variety of equipment
change, the requirements for ventillation
applications
that filter media need to satisfy
must be considered. The performance
with which particles
of a
are
by fibre size. Polymer fibres
can now be produced in a wide range of sizes. The most commonly
specification
the meltblow-n process, polymers
used method is
which involves
filter medium suitable for use as a class
extruding
G 1 -F9 filter is based upon the following
and temperature
parameters:
stream. By varying the process parameters,
l
l
filtration
efficiency;
in diameter
from 0.1 pm-100
pressure drop;
Conversely,
the average fibre diameter
mechanical
for a class F7 glass fibre material is
strength;
-
pm
1 I-‘m VI. Polymer
[ 11.
LCC = Investment LCCIvlaintrnance
+
+ LCCtncrgv +
’
LCCDispoaal
As an example,
consider a class F7 filter
with the following cost breakdown: Investment Energ?
+ LCCMaintcnsnrp= =
18.5%
81% =
0.5%
[4].
A low pressure drop is an important
affects energy running costs. From
technnique
which
Figure 1 it can be seen that energy
can further
increase
running costs account for 8 1% of the total
Thus, this ability makes them preferable
cost. Using polymer fibres, the structure
(Figure 2). By using different fibre sizes, a fibres
filter web can be constructed
that cannot be
open structure
charged.
Several
the larger particles,
methods
of charging
gressively finer structure
materials
have been
developed
of
the material can be varied and controlled
to
conventional
2OOl
In the case of a filter, the life cycle cost can be calculated as follows:
down because the pressure drop directly a
filter efficiency.
March
including filters,
fans, pumps, etc.
element in keeping total running costs
charging,
30
Several methods of
fibres
electrostatic
Investment Energy E Disposal
an
the total cost
have been developed for
LCCDispo\al
suited for
n
of an installation.
LCC
are also ideally
n
in order
under high pressure
into a high velocity air-
it is possible to produce fibres that range
l
Drop
to achieve a low life cycle cost (LCC),
materials now hold the major market behind this
of
on the type of
A low pressure drop is important
fibre. Today, glass fibre only accounts for 40% of the market.
effect and the
and the choice
method is dependent
How well do present day polymer based materials
the triboelectric
corona treatment,
fire resistance;
and
with an
on the inlet face, to catch followed by a proas you move
towards the centre of the web to capture the smaller particles. This means that
refined over recent
the increase in pressure drop with time
years. There are
can be kept low, which in turn lowers the
essentially
LCC.
two
Filtration+Separation
It can be seen from Table 1 that the tensile strength of the polymer based material is nearly twice that of a glass fibre material. The combination of high tensile strength and good elongation to break guards against the polymer based fibres breaking during use.
Environmental Impact
Mechanical Strength An important parameter for an)' f i l t e r material is its mechanical strength. Pulvmer based fibres possess a combination of high tensile strength and good strain resistance, even under high humidity conditions. High tensile strength and good elongation performance are important, not only when the filter is being fitted but also during operation. Materials, with a low strength can, for example, be torn by sharp metal edges when being fitted. The elongation performance of polymer based fibres give the material good resistance to tearing, and therefore reduces the risk of it becoming damaged during installation.
A life cycle assessment (LCA) evaluates the environmental impact of a product by taking into consideration the total environlnental impact of a product during Inanufacturc, operation and disposal, i.e. a cradle to grave approach. The energy requirement of the various processes provides an important indicator of the environmental impact of a product. In terms of energy use during the manufacture and disposal, a polymer based filter material, with a plastic frame, is said to have the least environmental impact of any commercial filter currently available on the market [3]. If the energy used hv or in connection with a polymer based filter, with a plastic frame is given the index 1, then other filters have indices in the range 2-4.5.
P o l y m e r based m a t e r i a l
Ultimate tensile strength* (N)
Glass fibre m a t e r i a l
99
58
* m e a s u r e d in a c c o r d a n c e w i t h ISO 5081:1977
The greatest energy demand of a filter occurs when overcoming the pressure drop that happens {luring normal operations [4]. In order to achieve a low pressure drop, and therefore a low energy demand, the filter needs to have a high dust loading capacity. a common error when assessing dust loading capacity is to compare the surface areas of the filters. However, a filter having a large surface area does not necessarily have a high dust loading capacity. Using polymer fibres, it is possible to vary the fibre sizes throughout the thickness of the medium (Figure 2), so that dust is loaded in the interior of the medium, rather than on the surface. This gives a low pressure drop across the filter, resulting in good running costs. In addition, ~ hen manutacturing polymer based filter media, it is possible to some extent (up to 30 %) to use recycled fibres, e.g. from polyethylene terephthalate (PET) bottles, giving these fibres a further environmental edge.
Microorganism Resistance Outdoor air contains thousands of naturally occurring microorganisms (bacteria, mould spores, fungi, ctc). They are separated in the filter and, together with the other })articles, form a dust cake on the filter. Unfortunately, this {lust cake can provide a source of nutrients for the microorganisms. The Freie Univ~irsit~it Berlin, Germany, carried out an investigation [5] to determine the di[Ii~rences in bacteria anti mould growth patterns between a polymer based anti a glass fibre filter. The two filters were installed in the same plant and exposed to outdoor air. The biological activity on them was measured once a week. The results of the study are shown in Figure 3. Bacteria
Moulds 4000000
6000000
•
• Micro glass . . . . . Polymer fibres
%
!
4000000
M i c r o glass
......... P o l y m e r fibres 3000000
"E 2000000
~D
0
2000000
.... J - ~ ...... 1000000
i 0
i
2
. . . . . .
[
i 4 Week
Filtration+Separation
_
I 4 Week
6
March 2001
31
Smoke Emission
Output Heating Effect --
300
Micro glass Polymer fibres
250 200 150 100 50 50
20
40
60
100
80
1
Set
See
etc) to produce a tailor-made
filter media
for a specific application.
Conclusions
Air in air @ration &at of%rs a wide r&e
The development
of glass and synthetic media for prim&,
secondary and final. WEPA filtration levels, as we11 as filters for special apphahions. Over the course of the past year Russel Mcleod has been focussing its business on clean air filtration applications through several acqusitions. Early in 2000 it purchasedvokes Invensys plc, creatingvokes of high technology
air filtration, i.e. cleanrooms
and the pharmaceutical
based at Interfilta’s site in Burnley (FiZtrution+Separotion,
The recent acquistions
in Switzerland
industry. It is
January/February
More recently, Russel Mcleod acquired Eurpoean filter technology which is headquartered
from
Air Filtration, which is a well known name within the fields 2000, p.4).
company, Luwa,
(Filtrotion+Separation, January/February
have had the result of significantly
position in the Euopean clean air filtration
It was found that the growth of both
strengthening
2001).
Mcleod Russel’s
market.
performance environments.
In fact, even manufacturers
which previously concentrated of glass fibre materials to appreciate materials:
the advantages of these
fibres, with the mechanical process potentials
1. CiachT.
2000.
structures:
growth in the glass fibre material. The
filter not only incrcascs the risk of damage
manufacturing,
layered polymer)
material (multi-
appears more suitable for
use in heating, ventilation conditioning
to the rest of the ventilation system, but also
that ‘the new
& air
of spreading the fire. In addition, the amount of smoke released by the glass tibre filter was sufficiently high that any electrical
(HVAC) systems because the
material itself appears able to reduce the growth or survival of microorganisms.’
Fire Resistance
component
exposed to it would have to be
completely replaced.
Deep bed filtration
Properties
Filtration Congress, Brighton, 10/93 3. Maria Eriksson, Technology,
miljiibediimning
innemiljii’
[Alrjilters:
environmental
One particular benefit of polymer based
environment].
4. Eurovent/Cecomaj: Recommendation
that is less prone to distortion.
calculation
generation
are the possible
there is no need to add any binder to the
of toxic gases and how much
product, as the fibres are bound together
heat is released. These characteristics investigated
were
for a polymer based and a
either thermally or by friction. Therefore, concerns regarding potentially toxic binders
glass fibre filter. The filters were installed
being dissolved by moisture and distributed
in the same ventilation
through the ventilation system by the supply
plant for a period
of five months, after which they were tested at the Fire Testing Laboratory
of the
It is also possible, when using polymer based filter media, to incorporate
Institute,
with varying characteristics
Sweden. The heat and fire
gas release results obtained in the study are
resistant,
shown in Figure 4.
tensile strength,
32
March
2OOl
1999,
concerning
of life cycle cost for air
filters. 5. Kemp P C. 1999. Comparison
of
microorganism
loading from two air
filter materials.
Indoor Air,
6. Gustafsson J, Camfil. Energi &MiJjc, 2/00
air are eliminated.
Swedish National Testing and Research Boris,
och
technical qualities,
assessment and the indoor
ensures airtight joints, and produces a filter
taken into consideration
University
tekniska
kvaliteter,
Process Considerations
In addition,
Chalmers
Luftfilter:
materials is their ability to be welded, which
The factors that need to be
UK.
2. Gustafsson J, Camfil. Energy &Wjb’,
From a safety point of view the fire important.
and
ProceedInS 8th World
resistance
of a filter medium is very
fibres have
161.
References
gases. The high heat output of the glass fibre
of air filtration
charged
strength and
of svnthetic
future prospects’
material was less than the corresponding [5] concludes
on the use
are now beginning
‘fine electrostatically
releases considerably more heat and fire
report
filter with different
levels to satisfy a variety of
bacteria and mould in the polymer based
generation
rapidly, making it
possible to customisc
excellent It can bc seen that the glass fibre filter
of new polymer based
fibrcs is progressing
fibres
(flame
bactericide-containing, good elongation
For more mformatmn contact: Thomas Carlson, R&D Director, Scan$Jter Sweden. Tel: f46
325
AB. 512 85 SvenJjup,
66 16 00;
high
Fax: f46
to break,
Webnte: www.scandfiJter.com
325 6 1 14 90;
Filtration+Separation
of