U.S. patent application number 15/764354 was filed with the patent office on 2018-10-04 for gas filtration system and method.
The applicant listed for this patent is KONINKLIJKE PHILIPS N.V.. Invention is credited to JOHAN MARRA, CORNELIS REINDER RONDA, MICHAEL MARTIN SCHEJA.
Application Number | 20180283707 15/764354 |
Document ID | / |
Family ID | 57133135 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180283707 |
Kind Code |
A1 |
SCHEJA; MICHAEL MARTIN ; et
al. |
October 4, 2018 |
GAS FILTRATION SYSTEM AND METHOD
Abstract
The invention provides a filtration system for removing a target
gas from a gas to be filtered in a space. The system has different
modes of operation. Based on sensing of the current level of the
target gas, the previous history of the sensing signals and the
previous modes of operation, a degree of filter loading with the
target gas can be determined. This information and the current
sensed level of the target gas are together used to select a mode 5
of operation. In particular, the filter loading and the current
pollutant level is used to determine whether absorption/adsorption
or desorption will take place and which rates these processes will
occur, which provides the basis for deciding what operation mode
should be executed.
Inventors: |
SCHEJA; MICHAEL MARTIN;
(EINDHOVEN, NL) ; RONDA; CORNELIS REINDER;
(EINDHOVEN, NL) ; MARRA; JOHAN; (EINDHOVEN,
NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KONINKLIJKE PHILIPS N.V. |
EINDHOVEN |
|
NL |
|
|
Family ID: |
57133135 |
Appl. No.: |
15/764354 |
Filed: |
September 29, 2016 |
PCT Filed: |
September 29, 2016 |
PCT NO: |
PCT/EP2016/073285 |
371 Date: |
March 29, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 2003/1628 20130101;
F24F 3/16 20130101; F24F 11/39 20180101; F24F 2110/50 20180101;
F24F 11/30 20180101; F24F 11/65 20180101 |
International
Class: |
F24F 3/16 20060101
F24F003/16; F24F 11/39 20060101 F24F011/39 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2015 |
CN |
PCT/CN2015/091289 |
Nov 17, 2015 |
EP |
15195051.6 |
Claims
1. A filtration system for removing a target gas from a gas to be
filtered in a space, the filtration system comprising: a sensor
arrangement, which comprises a gas sensor for sensing a
concentration of the target gas in the space; a filter for
filtering the target gas from the air, wherein the filter comprises
an absorption filter or an adsorption filter; and a control system
which comprises a ventilation system for controllably driving air
through the filter, wherein the control system is adapted to
implement different modes of operation of the filtration system,
wherein the control system is adapted, based on current sensor
arrangement signals, previous sensor arrangement signals and
previous modes of operation, to: determine a degree of filter
loading with the target gas; and select a mode of operation based
on the degree of filter loading and the current sensor arrangement
signals wherein: the control system is adapted to determine from
the degree of filter loading with the target gas and the current
sensor arrangement signals when filter absorption or adsorption is
taking place and when filter desorption is taking place.
2. (canceled)
3. A filtration system as claimed in claim 1, wherein the control
system is further adapted to determine from the degree of filter
loading with the target gas and the current sensor arrangement
signals the rate of absorption or adsorption, or desorption.
4. A filtration system as claimed in claim 1, wherein the control
system comprises a heater for heating the filter.
5. A filtration system as claimed in claim 1, wherein the filter
further comprises a catalyst filter.
6. A filtration system as claimed in claim 5, wherein the catalyst
filter comprises a photo-catalytic filter and the control system
further comprises a light source for illuminating the
photo-catalytic filter.
7. A filtration system as claimed in claim 1, wherein the filter is
part of an air purifier, and the control system is adapted to
switch off the air purifier when it is determined that the
concentration is above a threshold and the filter is operating in a
desorption regime.
8. A filtration system as claimed in claim 1, wherein the control
system is further adapted to provide an output which indicates when
additional ventilation of the space with outdoor air is
desirable.
9. A filtration system as claimed in claim 1, wherein the gas
sensor comprises a formaldehyde sensor, and wherein the filter
comprises an absorption formaldehyde filter.
10. A method of controlling a filtration system for removing a
target gas from a gas to be filtered in a space, the method
comprising: sensing a concentration of the target gas in the space;
filtering the target gas from the air, wherein the filtering makes
use of an absorption filter or an adsorption filter; and
implementing different modes of operation of the filtration system,
the method comprises, based on a current sensed concentration, a
previously sensed concentration and previously adopted modes of
operation: determining a degree of filter loading with the target
gas; and selecting a mode of operation based on the degree of
filter loading and the current sensor arrangement signals wherein:
the method further comprising determining from the degree of filter
loading with the target gas and the current sensed concentration,
when filter absorption or adsorption is taking place and when
filter desorption is taking place.
11. (canceled)
12. A method as claimed in claim 10, comprising determining, from
the degree of filter loading with the target gas and the current
sensed concentration the rate of absorption or adsorption, or
desorption.
13. A method as claimed in claim 10, wherein one mode of operation
comprises heating the filter and another mode of operation
comprises illuminating a photo-catalytic filter.
14. A method as claimed in claim 10, wherein the filtering step is
carried out by an air purifier, the method further comprising
switching off the air purifier when it is determined that the
concentration is above a threshold and the filter is operating in a
desorption regime.
15. A computer program comprising code for implementing the method
of claim 10 when said program is run on a processor.
Description
FIELD OF THE INVENTION
[0001] The invention relates to methods and apparatus for filtering
gaseous pollutants from a gas to be filtered.
BACKGROUND OF THE INVENTION
[0002] Indoor air pollution presents a significant health hazard in
many urbanized areas across the world. Air pollution sources are
encountered both outdoors (e.g. from motor vehicles and industry)
and indoors (from cooking, smoking, candle burning, incense
burning, outgassing building/decoration materials, use of
outgassing waxes, paints, polishes etc.). The pollution level
indoors is often higher than outdoors, especially for volatile
organic compounds. At the same time, many people reside most of
their time indoors and may thus be almost continuously exposed to
unhealthy levels of air pollution.
[0003] One method to improve the indoor air cleanliness is by
installing an air purifier indoors which is capable of continuously
recirculating the indoor air through a cleaning unit comprising one
or more air filters. Another method to improve the indoor air
cleanliness is by applying continuous ventilation with filtered
outdoor air. In the latter case, the air filter(s) are usually
comprised in a heating, ventilation and air conditioning (HVAC)
system capable of temperature adjustment, ventilation, and of
cleaning the ventilation air drawn from outdoors by passing it
first through one or more air filters before releasing it indoors.
Ventilation with cleaned outdoor air displaces polluted indoor air
and dilutes the pollution level therein.
[0004] For removing polluting gases from air, use of often made of
activated carbon filters which are capable of
adsorbing/removing/decomposing many volatile organic hydrocarbon
gases (VOCs) and several inorganic gases (NO.sub.2, O.sub.3, radon)
from air. The activated carbon material is usually present as
granules that are contained in an air-permeable filter frame
structure.
[0005] Indoor air pollution with formaldehyde (CH.sub.2O) gas is a
particular problem affecting the health and well-being of many
people. Formaldehyde is continuously emitted from indoor sources
such as building materials, decoration material, and furniture. Its
indoor concentration can increase to well above the clean air
guideline concentrations for formaldehyde (0.05 mg/m.sup.3 at 8
hour exposure, 0.10 mg/m.sup.3 at 1 hour exposure) when the room is
poorly ventilated. High ventilation conditions achieved by opening
windows and doors are not always feasible due to outdoor weather
conditions, an uncomfortable outdoor temperature, and/or safety
considerations.
[0006] For removing formaldehyde and/or small acidic gases
(SO.sub.2, acetic acid, formic acid, HNO.sub.x) from air, activated
carbon as such is also not very effective. Instead, use can be made
of impregnated filter materials capable of chemically absorbing
these gases from air. Absorption can occur via acid-base
interactions or through a chemical condensation reaction. Activated
carbon granules can be used as the impregnation carrier, but also
hydrophilic fibrous cellulose paper, glass-fiber sheet material,
and porous ceramic honeycomb structures are suitable for this
purpose. When using such filters structures, an indoor air purifier
re-circulates the air in a given enclosure through a filter stack
comprising the absorption filter.
[0007] In absorption-based air filters, binding is usually based on
chemisorption for example using corrugated, tris-based formaldehyde
filters, or physi-sorption. Such binding represents a reversible
reaction, which means that when an absorbing filter material is
exposed to a gaseous pollutant with an affinity to the filter
substrate, not only absorption will take place, but gas molecules
already bound to the substrate can overcome the energy barrier and
desorb back into the air (desorption). Thus, when clean air is
passed through an absorption filter that is partially loaded with
absorbed gas, such as formaldehyde gas, desorption of formaldehyde
gas may occur which makes the absorption filter become a source of
formaldehyde gas itself.
[0008] In general, the desorption rate increases with increased
degree of loading (amount of gas molecules bound to the filter
material) or decreasing partial pressure of the gaseous pollutant
in the gas phase.
[0009] Since desorption requires energy to overcome the forces
responsible for holding the gaseous pollutant bound to the
substrate (e.g. Van der Waals forces, chemical bonds, etc.),
introduction of external energy into the system (e.g. in form of
heat) can increase desorption rates.
[0010] Another approach which can be used to eliminate gaseous air
pollutants is to break them down into smaller molecules via
oxidation. Oxidation occurs naturally, but at relatively low rates.
Oxidation rates can be strongly increased by using catalysts (e.g.
titanium oxide in the case of PCO). Applications include photo
catalytic oxidation (PCO) and thermal oxidation. Heating a catalyst
can also result in increased oxidation rates.
[0011] Air purifiers utilizing absorption or adsorption based
filters for the removal of gaseous pollutants from indoor air have
a number of disadvantages.
[0012] The user is often faced with the problem of manually
selecting an operation mode from a number of options without having
the required background information to make a sound decision. This
may lead to arbitrary choices and a selection of an inappropriate
mode (inappropriate can for example mean that there is a more
suitable operation mode for this situation available than the one
selected by the user).
[0013] In many products, operation modes only differ in the fan
speed. This can limit the potential of an air purifier. Absorption
or adsorption based gas filters can, under certain conditions,
release the accumulated pollutant gas. This may expose inhabitants
to potentially harmful concentrations.
[0014] Absorption or adsorption based gas filters also have a
limited capacity for their target molecules and do not make
purposive use of the possibility to regenerate, which could lead to
a longer lifetime.
[0015] US 2007/105494 A1 discloses a fume hood with a system for
monitoring filter life and an improved design for extending filter
life. Filter efficiency is determined based on data from sensors
located upstream and downstream of the filter.
[0016] CN 204593639U discloses an air purifier featuring automatic
feedback control based on the monitoring of air quality. The
purpose of CN 204593639U is to provide an air purifier which adjust
its settings automatically. Sensors inside the air purifier perform
air sensing. Based on the sensor data, settings of components of
the air purifier are adjusted.
SUMMARY OF THE INVENTION
[0017] Desirable would be a filter and filtering method which
allows the filter to be operated in an optimum operating mode in a
simple manner.
[0018] The invention is defined by the independent claims. The
dependent claims define advantageous embodiments.
[0019] Examples in accordance with a first aspect of the invention
provide a system for removing a target gas from a gas to be
filtered in a space, the system comprising:
[0020] a sensor arrangement, which comprises a gas sensor for
sensing a concentration of a target gas in the space;
[0021] an air purifier which comprises a filter for filtering the
target gas from the air; and
[0022] a control system which comprises at least a ventilation
system for controllably driving air through the filter, wherein the
control system is adapted to implement different modes of operation
of the filtration system,
[0023] wherein the control system is adapted, based on the current
sensor arrangement signals, the previous history of the sensor
arrangement signals and the previously adopted modes of operation,
to: [0024] determine a degree of filter loading with the target
gas; and [0025] select a mode of operation based on the degree of
filter loading and the current sensor arrangement signals.
[0026] This system makes an automatic selection of a mode of
operation by taking account of a degree of filter loading and a
current concentration. These two pieces of information enable the
effect of the operation of the filter to be determined. For
example, if the filter is heavily loaded, it will not be able to
perform filtering when there is already a relatively low
concentration. It will instead operate in a desorption mode.
[0027] A number of zones of the parameter space of the filter
loading and the concentration may be defined, and each may then
correspond to a different preferred mode of operation. There may
for example be between 3 and 10 such zones, each with an associated
mode of operation.
[0028] The filter for example comprises an absorption filter or an
adsorption filter. The filter may be a solid or a liquid having
chemicals for binding the target gas. There may be one or more
filters of the same or different types. At least one of the filters
has a reversible function, and will thus perform
absorption/adsorption or desorption, in dependence on the filter
loading and the prevailing concentration. The control system may be
further adapted to determine from the degree of filter loading with
the target gas and the current sensor arrangement signals when
filter regeneration (desorption) is taking place and when air
filtering (absorption or adsorption) is taking place.
[0029] Note that in this context the term "desorption" is used to
mean the reverse of both adsorption and absorption, i.e. the
release process which is the opposite of the filtering process.
[0030] The control system may comprise a heater for heating the
filter. This may be used to tune the filter function so that
different options are used in different modes.
[0031] The filter may further comprise a catalyst filter (in
addition to an air purifier absorption/adsorption filter), for
example a photo-catalytic filter and the control system then
further comprises a light source for illuminating the
photo-catalytic filter. This provides another different option for
use in a different mode. In other embodiments, a catalyst filter in
the form of a thermal-catalytic filter may be used, and the control
system then further comprises a heat source for heating the thermal
catalytic filter.
[0032] The control system is for example adapted to switch off the
air purifier when it is determined that the concentration is above
a threshold and the filter is operating in a desorption regime.
This prevents the air purifier from increasing the room
concentration.
[0033] The control system may further be adapted to provide an
output which indicates when additional ventilation of the space
with outdoor air is desirable. This enables the filter to be
regenerated for example using outdoor air when there is high
loading with indoor pollutants.
[0034] The gas sensor may comprise a formaldehyde sensor, and the
filter comprises a reversible absorption and/or adsorption
formaldehyde filter.
[0035] Note that the sensor arrangement may be an integral part of
the air purifier system, or it may be a stand-alone sensor or part
of a sensor box. In the latter case, communication means are
provided (e.g. wireless via WiFi) to allow the sensor to
communicate the measurement results to the remainder of the
system.
[0036] Examples in accordance with another aspect of the invention
provide a method of controlling a filtration system for removing a
target gas from a gas to be filtered in a space, the method
comprising:
[0037] sensing a concentration of a target gas in the space;
[0038] filtering the target gas from the air using an air purifier;
and
[0039] implementing different modes of operation of the filtration
system,
[0040] wherein the method comprises, based on the current sensed
concentration, the previous history of the sensed concentration and
the previously adopted modes of operation: [0041] determining a
degree of filter loading with the target gas; and [0042] selecting
a mode of operation based on the degree of filter loading and the
current sensor arrangement signals.
[0043] This method provides automatic selection of a mode of
operation by taking account of a degree of filter loading and a
current concentration. In this way, a safe and effective mode of
operation may be chosen without requiring user input.
[0044] The filtering may make use of an absorption filter or an
adsorption filter. The method may comprise determining, from the
degree of filter loading with the target gas and the current sensed
concentration, when filter absorption or adsorption is taking place
and when filter desorption is taking place, and optionally also the
rate of absorption or absorption, or desorption.
[0045] One mode of operation may comprise heating the filter and
another mode of operation may comprise illuminating a
photo-catalytic filter.
[0046] The air purifier may be switched off when it is determined
that the concentration is above a threshold and the filter is
operating in a desorption regime.
[0047] The method may be implemented by a computer program
comprising code for implementing an algorithm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] Examples of the invention will now be described in detail
with reference to the accompanying drawings, in which:
[0049] FIG. 1 shows a first example of a gas filtration system;
[0050] FIG. 2 shows how different operating modes can be defined by
different prevailing concentration and filter loading
conditions;
[0051] FIG. 3 shows air purifier control method; and
[0052] FIG. 4 shows a second example of a gas filtration
system.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0053] The invention provides a filtration system for removing a
target gas from a gas to be filtered in a space. The system (and
the air purifier in particular) has different modes of operation.
Based on sensing of the current level of the target gas, the
previous history of the sensing signals and the previous modes of
operation, a degree of filter loading with the target gas can be
determined. This information and the current sensed level of the
target gas are together used to select a mode of operation. In
particular, the filter loading and the current target gas level is
used to determine whether absorption or desorption will take place
and which rates these processes will occur, which provides the
basis for deciding what operation mode should be executed.
[0054] In this way, the gas filtration system, i.e. air purifier,
is capable of collecting and analyzing information relevant for the
proper choice of an operation mode.
[0055] FIG. 1 shows an air purifier, in which the air flow is from
left to right as shown by the dotted arrow. The air purifier
comprises a gas sensor 10 for sensing a concentration of a target
gas. This for example provides real time formaldehyde concentration
information. The sensor may be an integral part of the system or it
may be remote from the main housing of the air purifier and then
communicate with the remainder of the system, for example
wirelessly.
[0056] The air purifier further comprises an absorption-based gas
filter 12 (e.g. an activated carbon filter, an impregnated filter
for formaldehyde etc.) for filtering the target gas from the
air.
[0057] For some examples of filter, the effectiveness or
functionality of the filter 12 is for example dependent on the
temperature, and a heater 14 is shown for controlling the filter
temperature.
[0058] A catalyst 16 may also be used as a filter, and for a
photo-catalytic filter, the catalyst activity may then be
controlled by using a light source 18. In another embodiment, the
catalyst 16 can also be a thermal catalyst and in this case, it
activity may then be controlled by a heater 18. A sensor 20 is
provided for detecting the state of the catalyst, such as a degree
of poisoning with the target gas.
[0059] The overall system may have only an absorption based filter,
or it may have both types of filter as shown.
[0060] When use is made of a catalytic filter, the user can be
provided with information as to whether the catalytic filter needs
regeneration or needs to be replaced based on the information from
the sensor 20.
[0061] A ventilation system such as a fan 22 is provided at the
outlet.
[0062] The gas sensor 10 and catalyst sensor 20 together comprise a
sensor arrangement. Together, the heater 14, catalyst 16, light
source 18 and fan 22, as well as a master control unit, comprise a
control system. As a minimum, the control system includes the
ventilation system for controllably driving air through the filter,
and the other control devices are optional. Their use will depend
on the type or types of filter used.
[0063] The control system is adapted to implement different modes
of operation of the gas filtration system.
[0064] A master control unit in the form of a controller 24 is
provided for controlling each other element of the control system.
The controller 24 takes account of the current signals from the
sensor arrangement 10, 20, the previous history of the sensor
arrangement signals, and the previous modes of operation. Using
this information, it is possible to determine a degree of filter
loading of the absorption filter with the target gas and then to
select a suitable mode of operation. The mode may be selected based
on the degree of filter loading compared to the current
concentration of the target gas in the air space being cleaned.
[0065] The light source 14 has a controllable light intensity, and
it may be used when use is made of a photo-catalytic oxidation
filter (PCO). The heating element 14 has an adjustable output
temperature, preferably with feedback control. The fan 22 has an
adjustable speed, and the catalyst 16 may have an adjustable
humidity and/or temperature. Different combinations of these
adjustable parameters then define operating modes of the overall
control system.
[0066] Preferably the control system comprises the fan and at least
one further controllable actuator, in addition to the controller
24.
[0067] Information is needed which enables the loading state of the
absorption filter to be determined. This may be in the form of data
stored in a database 26 which is updated by, and stored on, an SoC
(System on Chip) or on an external server. The sensor 20 provides
this information in respect of a catalyst filter.
[0068] The controller 24 is responsible for collecting, analyzing
and storing information from the various sources used in the
system. Sets of pre-defined parameter values for each component are
stored to define the different operation modes. The controller 24
can then control the adjustable parameters thereby inducing the
desired operation mode.
[0069] FIG. 2 is used to explain the concept underlying the design
of the filtration system. FIG. 2 plots two important factors
determining the desorption and absorption behavior of an absorption
process-based gas filter, which are the filter Loading L (x-axis)
and the ambient concentration c in the room (y-axis). There is an
equilibrium line labeled as Leq in FIG. 2 which describes all pairs
(L, c) for which the level of absorption is equal to the level of
desorption.
[0070] All pairs (L, c) above and below this equilibrium line Leq
will lead to net absorption and net desorption, respectively. With
increasing distance from the equilibrium line Leq, the desorption
or absorption rates gradually increase.
[0071] For air purifiers with an absorption-based formaldehyde
filter and in an in-home environment, a diagram can be created
where pairs (L, c) belong to discrete zones each have specific
characteristics, as listed in Table 1 below. This table defines the
five zones shown in FIG. 2 together with the equilibrium line. In
other examples, the zones in FIG. 2 can be further subdivided.
TABLE-US-00001 TABLE 1 Effect of running purifier on Zone
Characteristic room CH.sub.2O concentration A.sub.ab2 Absorption
>> Desorption = Net Fast decrease adsorption @ high rate
A.sub.ab1 Absorption > Desorption = Net Slow decrease adsorption
@ low rate A.sub.des1 Absorption < Desorption = Net Slow
increase desorption @ low rate A.sub.des2 Absorption <<
Desorption = Net Fast increase desorption @ high rate A.sub.des3
Net desorption Increase to values > Conc..sub.critical L.sub.eq
Absorption = Desorption No change in room CH.sub.2O conc.
[0072] The definition of zones in this way may be applied to any
gas filter based on an adsorption process. In this model, every
pair (L, c) is allocated to a specific zone. The actual values for
L and c are determined by the intrinsic properties of a particular
filter.
[0073] An example is now described where the gas filter is a
formaldehyde filter and the gas sensor is thus a formaldehyde
sensor. The concept can however be applied to other gases or
combinations thereof.
[0074] Considering the above, it is clear that a CH.sub.2O filter
which is used in an in-home environment will show very different
behavior depending on the c and L value at the time the air
purifier is started. For instance, when a pair (L, c) is in the
region A.sub.ab2 in FIG. 2, the air purifier will effectively
reduce the room CH.sub.2O concentration. This gradual decrease
reduces CH.sub.2O partial pressure which results in a decreased
absorption rate. The effect on loading L during this time can be
neglected if the filter has a reasonably high capacity. Ultimately,
the pair (L, c) will move to zone A.sub.ab1, where the actual
removal rate (or real-time clean air delivery rate, CADR) becomes
significantly lower. At this time, it would make sense to increase
the removal performance for the gaseous pollutant.
[0075] This is an option since the system is able to track the
current position in the L-c-diagram and thus has an overview of the
present operating conditions by acquiring and analyzing the
relevant status information. In this example, the relevant
information is the room formaldehyde concentration and the loading
status of the gas filter.
[0076] The control system may be configured to adjust the internal
control parameters by switching from a first purification mode (P1)
to a second purification mode (P2). Each mode corresponds to a
specific set of component parameter values, including at least a
fan speed. Purification mode 1 is for example characterized by a
high fan speed, hence high flow rate (preferably in the range of
200 and 400 m.sup.3/h) and a deactivated light source 18.
Purification mode 2 uses the same flow rate as purification mode 1,
but the light source 18 is switched on. In the case of a catalyst
which works at room temperature without the need of light, a
heating element might be activated in order to increase temperature
of the catalyst.
[0077] The system does not require a catalyst filter. Without any
catalyst, the desorption rate may be adapted to the natural
ventilation in the different modes of operation. This can be done
by tuning the fan speed, taking into account the reading from the
sensor arrangement.
[0078] The aim is to increase the reaction rate of the catalyst,
hence the performance of the air purifier, compensating for the
lower absorption rate of the CH.sub.2O filter in zone
A.sub.ab1.
[0079] In all cases where the pair (L, c) is below the equilibrium
line L.sub.eq, a net release of formaldehyde from a CH.sub.2O
filter will occur. The advantage is that this filter will be
regenerated. Similar to the purification modes, it also makes sense
to look into different scenarios which will enable a design of
optimized regeneration modes and their proper choice during
operation.
[0080] Again, an air purifier is started and a pair of values (L,
c) is determined. If it falls into zone A.sub.des1 (shown in FIG.
2), a net release from the formaldehyde filter will occur. The room
CH.sub.2O concentration lies below a critical value c.sub.critical
also shown in FIG. 2 which represents a safety threshold and can be
set to e.g. 0.1 mg/m.sup.3 (WHO and GB/T safety threshold for
indoor formaldehyde concentrations) or lower.
[0081] This situation is basically well-suited to regenerate the
CH.sub.2O filter. The challenge, however, is that regeneration will
take place very slowly due to the slow desorption rate (shown in
Table 1 above).
[0082] The components of the air purifier can be operated in a mode
optimized for this scenario, regeneration mode 1 (R1).
[0083] In this mode, the heating element 14 is activated, and the
flow rate decreased (e.g. to values between 10 and 50 m3/h). The
aim is to increase the temperature of the CH.sub.2O filter. The
temperature increase of the latter will result in an increased
desorption rate (due to locally lower partial pressure of CH.sub.2O
and higher probability that CH.sub.2O molecules bound to the
substrate can overcome the energy barrier required for
dissociation), which is the desired outcome of this mode.
[0084] In another embodiment, the heating element is located
upstream of the gas filter, not downstream.
[0085] Some embodiments may use a downstream located source of
humidity such as an arrangement for generating water mist, instead
of or as well as the heating element 14. In such a case, the
delivered water will compete for the binding sites on the filter
medium and therefore accelerate desorption of the gas bound to the
filter. Thus, the operation of the source of humidity provides
another parameter which can be used differently in different modes
of operation.
[0086] Compared to zone A.sub.des1, zone A.sub.des2 is
characterized by higher desorption rates (again shown in Table 1
above) which means that heating of the CH.sub.2O filter is not
required in regeneration mode 2 (R2). Therefore, this mode is
characterized by a slow flow rate (low fan speed) and an activated
light source 18. Both aspects increase the one-pass efficacy of the
catalytic filter, which is necessary to efficiently remove the
higher amount of filter-released CH.sub.2O.
[0087] FIG. 3 shows a method of controlling an air purifier (i.e. a
gas filtration system).
[0088] In step 30, the air purifier is started. In step 32 the
ambient concentration of the target gas such as formaldehyde is
measured. In step 34 a database 38 is accessed to obtain a current
loading value of the filter used in the air purifier.
[0089] In step 36, it is determined in which zone of the diagram of
FIG. 2 the loading and concentration values are located.
[0090] In step 42, it is determined if the zone is zone Aab2, i.e.
one in which the filter is lightly loaded and there is a high
concentration. If so, a first purification mode P1 is adopted in
step 43.
[0091] In step 44, it is determined if the zone is zone Aab1, i.e.
one in which there is still sufficient concentration and loading
that the filter can still be loaded further, but with a smaller
margin. If so, a second purification mode P2 is adopted in step
45.
[0092] As mentioned above, differences between the control settings
for the different purification modes P1 and P2 may for example
include whether or not a photocatalytic catalyst is activated,
whether or not a heater is turned on (or the degree of heating),
the air flow speed, and the provision of humidity in the flow.
[0093] In step 46, it is determined if the zone is zone Ades1, i.e.
one in which the filter is more heavily loaded and there is a
comparably low concentration. If so, a first regeneration mode R1
is adopted in step 47.
[0094] In step 48, it is determined if the zone is zone Ades2, i.e.
one in which the filter is even more heavily loaded and/or there is
an even lower low concentration. If so, a second regeneration mode
R2 is adopted in step 49.
[0095] While the air purifier is operated in any of these modes,
the database is updated so that historical information about the
modes that have been used is stored. In this way, the loading of
the filter can be tracked, based on the characteristics of each
mode, the characteristics of the filter (filter identification can
be used to communicate these characteristics, either directly or by
accessing a database, e.g. over the internet) and how long they are
operational.
[0096] In step 50, it is determined if the zone is zone Ades3, i.e.
one in which the concentration exceeds the critical level, and the
filter is so heavily loaded that it cannot reduce the concentration
level. If so, a warning is provided to the user in step 52. If the
user does not provide an acknowledgement of the warning, the air
purifier is stopped in step 60. If the user does provide an
acknowledgement of the warning in step 54, a third regeneration
mode R3 is adopted in step 56 and again the database is
updated.
[0097] The air purifier continues for a given time which is
monitored in step 58. If the time is not up, the cycle is repeated
with a new measurement of the concentration and an updated value
for the filter loading. The cycle thus continues, possibly with
changes in mode, until the set time is reached, when the cycle
moves to step 60.
[0098] If step 50 does not confirm operation in the zone Ades3,
there is a check if the values correspond to the line Leq, in step
61. If so, there is no point running the air purifier and it is
stopped in step 60.
[0099] If no zone is found, there is an error, and an error message
is given in step 62 before the air purifier is stopped.
[0100] This process means that the air purifier is able to properly
deal with a situation where it is powered on at a pair of values
(L, c) in zone A.sub.des3. In this scenario, running the purifier
would increase the CH.sub.2O concentration even further above the
safety threshold c.sub.critical. This could also happen with a
catalytic filter in the filter stack, namely when its one-pass
efficacy is below 100% (which will usually be the case).
[0101] The automated mode selection eliminates this risk by
identifying this scenario and notifying the user to prepare for
regeneration mode R3.
[0102] The preparation could for instance mean that the user places
the air purifier on a balcony or simply opens the windows. Only
after confirmation by the user in step 52 or by autonomous
detection (for example a rapid change in temperature, CO.sub.2 or
formaldehyde concentration in the room) that this has been done,
the mode is executed.
[0103] If the regeneration is performed on the balcony, it is not
essential to remove the desorbed pollutant efficiently since it
will quickly dilute with the outdoor air. Therefore, the light
source 18 can be off to safe energy in this mode R3. The fan speed
can be relatively low (e.g. 20 m.sup.3/h) to save power. The
heating element 14 can be off if the regeneration takes place for
long time, e.g. during the night; or it can be on to further
accelerate desorption, hence to shorten the time required for
regeneration.
[0104] Thus, differences between the control settings for the
different regeneration modes may also include whether or not a
photocatalytic catalyst is activated, whether or not a heater is
turned on (or the degree of heating), the air flow speed, and the
provision of humidity in the flow.
[0105] If confirmation does not take place within a predefined
period of time, the purifier powers off automatically. A
corresponding notification could for example be sent to a user's
mobile device.
[0106] As discussed above, the system can overcome intrinsic
disadvantages of an absorption-based filter, leading to a purifier
with longer life time. The design of the specific operation modes
may be optimized to deal with different loadings and concentrations
and this can further improve the performance. The mode selection
can be fully automated as long as the loading and ambient
concentration is known.
[0107] Other embodiments also take additional information into
account such as room temperature, humidity, water content in the
filter etc.
[0108] The system shown in FIG. 1 can realize all of the modes
explained above. In one example, the loading information can be
obtained from a database stored on a CPU of a purifier. The storage
medium can also be an external server, provided that the air
purifier is equipped with an internet connection. This database can
be continuously updated based on information about the ambient
concentration measured by the CH.sub.2O sensor and taking account
of the operation time in each mode. External data storage and
processing can be useful in filter identification (based on
performance or by a filter identifier) in case there is more than
one filter type on the market or the performance of the filters is
improved. This enables the use of up-to-date software, for each
filter type.
[0109] Alternatively, the filter loading could be derived in
real-time through other approaches, e.g. by measuring the one pass
efficacy of the filter by adding an additional sensor directly
after the gas filter. This is shown in FIG. 4 where an additional
sensor 11 is provided.
[0110] In another embodiment, the one-pass efficacy of the catalyst
(e.g. the PCO filter in FIG. 1) is determined as well, by placing
one gas sensor in front and another gas sensor after the catalytic
filter (or PCO filter-light source unit). This information can be
used to indicate the status of the catalyst and recommend
replacement.
[0111] This invention can be applied in the area of indoor air
purification, more specifically for automated mode selection of an
air purifier.
[0112] As mentioned above, the system may also provide end of life
estimation, by monitoring over time the gas concentration, and the
modes that have been employed as well as other factors such as the
relative humidity, the temperature.
[0113] The invention is of particular interest for removing
formaldehyde gas from an indoor space. The system can be based on
known sensors and filter designs, for example as disclosed in WO
2013/008170 and U.S. Pat. No. 6,071,479. The formaldehyde sensor is
capable of selectively measuring the ambient formaldehyde gas
concentration over the course of time.
[0114] An example of a reversible formaldehyde absorption filter is
disclosed in U.S. Pat. No. 6,071,479. It features a corrugated
paper structure wherein the porous paper material is impregnated
with a mixture of a base (KHCO.sub.3), a humectant (Kformate), and
an organic amine (Tris-hydroxymethyl-aminomethane (Tris)).
Preferably, the filter impregnation is carried out with an aqueous
impregnant solution comprising:
[0115] KHCO.sub.3 at a concentration preferably chosen in the 5-15%
w/w range;
[0116] Kformate at a concentration preferably chosen in the 5-20%
w/w range;
[0117] Tris at a concentration preferably chosen in the 5-25% w/w
range.
[0118] For that purpose, a fixed volume of the impregnant solution
is incorporated in the filter's paper structure per unit filter
volume, followed by drying.
[0119] The above example is based on a reversible formaldehyde
filter. The invention may be applied to other reversible filters.
For example, an activated carbon filter or a zeolite filter may be
used for adsorbing volatile organic hydrocarbon gases (VOCs) from
air. The same system may be used for such filters. The required gas
sensor is then a VOC sensor capable a sensing (a range of) VOCs
that can be adsorbed on and desorbed from the activated carbon or
zeolite adsorbents.
[0120] Examples of VOC sensors are a photo-ionization detector
(PID), a metal-oxide semiconductor (MOX) sensor and an
electrochemical sensor.
[0121] The space in which the system is used is typically in indoor
space (i.e. inside a residential or commercial building), but the
invention may equally be applied to other spaces, such as the
enclosed space inside a car, coach, plane, train or other
vehicle.
[0122] The invention is of particular interest for indoor air
purifiers, ventilation or HVAC (heating, ventilation and air
conditioning systems) and other air handling units.
[0123] As discussed above, embodiments make use of a controller.
The controller can be implemented in numerous ways, with software
and/or hardware, to perform the various functions required. A
processor is one example of a controller which employs one or more
microprocessors that may be programmed using software (e.g.,
microcode) to perform the required functions. A controller may
however be implemented with or without employing a processor, and
also may be implemented as a combination of dedicated hardware to
perform some functions and a processor (e.g., one or more
programmed microprocessors and associated circuitry) to perform
other functions.
[0124] Examples of controller components that may be employed in
various embodiments of the present disclosure include, but are not
limited to, conventional microprocessors, application-specific
integrated circuits (ASICs), and field-programmable gate arrays
(FPGAs).
[0125] In various implementations, a processor or controller may be
associated with one or more storage media such as volatile and
non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM.
The storage media may be encoded with one or more programs that,
when executed on one or more processors and/or controllers, perform
at the required functions. Various storage media may be fixed
within a processor or controller or may be transportable, such that
the one or more programs stored thereon can be loaded into a
processor or controller. The computer can, in some embodiments, be
an external device such as a smart phone. In this case, all data
needs to be sent from the sensors/air purifier to such an external
device. This may allow to activate the disclosed functionalities
once a service (e.g. in the form of an App) is purchased after the
purchase of the air purifier.
[0126] Other variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing
the claimed invention, from a study of the drawings, the
disclosure, and the appended claims. In the claims, the word
"comprising" does not exclude other elements or steps, and the
indefinite article "a" or "an" does not exclude a plurality. The
mere fact that certain measures are recited in mutually different
dependent claims does not indicate that a combination of these
measured cannot be used to advantage. Any reference signs in the
claims should not be construed as limiting the scope.
* * * * *