The invention relates to an improved filter unit, a kitchen hood comprising such a filter, an air filter comprising such a filter unit and a method for filtering air.

Filter units are known from practice and are used in a wide variety of applications including kitchen hoods, air conditioning units and air filtering units. In general, a distinction is made between passive filter units and active filter units.

Passive filter units, such as a high efficiency particulate air (HEP A) filter, are based on a number of consecutively placed filter mats or gazes for filtering the air, such as for example (glass)fiber mats and carbon mats. The air is filtered by means of guiding the air through the (passive) filters.

Active filter units include air ionizing filters and plasma filters, which use active compounds to filter the air in the filter unit. Air ionizing filters for example apply an electrostatic charge to ionize and capture particles in an air stream. Plasma filters generate plasma that includes ozone, which removes pollution by means of a chemical reaction between the ozone and the pollution. Such filters are known to be highly effective in removing pollution. It is however also known that ozone, especially in a higher concentrations, is a potent respiratory hazard for people.

A disadvantage of many known filters is that the amount of ozone released therefrom is, under some circumstances, too high. The invention is aimed to obviate or at least significantly reduce this disadvantage.

To that end, the present invention provides a filter unit for filtering and/or purifying air, the filter unit comprising:

- a housing comprising an air inlet and an air outlet, wherein the air inlet, the housing and the air outlet define an air flow path;

- a number of filter components arranged in the housing, the components including:

- an electrostatic discharge (ESD) filter comprising a first gaze acting as a first electrode and a second gaze acting as a second electrode, wherein the second gaze is positioned at a distance from the first gaze;

- a plasma filter configured to provide plasma comprising ozone;

- a carbon filter configured for capturing excess ozone;

- a control unit that is configured to control the electrostatic discharge filter and the plasma filter; and

- a fail-safe module that is configured to temporarily and/or permanently disable power supply to the electrostatic discharge filter and/or the plasma filter. It is preferred that the fail-safe module is configured to operate independently from the control unit. This provides the advantage that the filter unit is, either temporarily or permanently, shut down even if the control unit is disabled and/or malfunctioning.

An advantage of the filter unit according to the invention is that excess generation of ozone is substantially prevented, which obviates the risk of ozone being released from the filter unit to the environment.

Another advantage of the filter unit according to the invention is that the power supply to the filter unit can either be temporarily or permanently be disabled, while the static filter components of the filter unit remain operational. Any excess ozone may therewith be captured by the carbon filter even after shut down of the filter unit by the fail-safe module.

In an embodiment according to the invention, the fail-safe module may comprise a hardware component and/or a software component.

The fail-safe module may, in addition to the software component and/or a hardware component, be provided with a measuring component . It is preferred that the fail-safe module is provided with both a software and a hardware component.

An advantage of the fail-safe module with a software component is the software component can be used for a restart or reboot of the filter unit, and specifically of the control unit of the filter unit. This is for example most expedient in case the control unit is subject to a (software) error, or in case (removable) external circumstances occur that influence the operational nature of the filter unit. This may for example be a temporary fluctuation, water intake, etc. The software component may than be configured to subject the control unit to a restart in order to provide a correction to the previous error and reboot the operation to normal circumstances.

An advantage of the fail-safe module with a hardware component is that it provides an excellent protection against serious damage or errors in the filter unit (for example of permanent nature). In other words, a user will not be able to restart a malfunctioning or damaged filter unit, which reduces the risk of (unintentional) restart of ozone generation and, thus, health risks.

It is preferred that the fail-safe module comprises both a software and a hardware component in order to provide a two-stage fail-safe against both removable and permanent damage or malfunctioning.

In an embodiment of the filter unit according to the invention, the fail-safe module comprises both a hardware and a software component, wherein, in case of failure of the filter unit, the software component is configured to activate before the hardware component. Moreover, it is preferred that the hardware component is only activated if the activation of the software component has not been able to remove the failure in the filter unit. The advantage of such a combination of both fail-safe components is that minor errors, for example programming errors and the like, may be resolved using a ‘soft’ solution by a softwarecomponent initiated restart of the filter unit, whereas serious health risks will permanently be obviated by the hardware component. This for example occurs if a restart of the software component does not resolve the issue, thus requiring a (permanent) shut-down of the filter unit.

In an embodiment of the filter unit according to the invention, the hardware component is configured to permanently disable power supply to the electrostatic discharge filter and/or the plasma filter, whereas the software is configured to temporarily disable power supply to the electrostatic discharge filter and/or the plasma filter.

An advantage of this embodiment is that such a combination of both fail-safe components is that minor errors, for example programming errors and the like, may be resolved using a ‘soft’ solution by a software-component initiated restart of the filter unit, whereas serious health risks will permanently be obviated by the hardware component. This for example occurs if a restart of the software component does not resolve the issue, thus requiring a (permanent) shut-down of the filter unit.

In an embodiment according to the invention, the software component comprises a COP timer component that is connected to, or preferably embedded in, the control unit, wherein, during use, the COP timer is configured to reset in response to a timer reset signal from the control unit, and wherein the COP timer is further configured to, after a predetermined period of time, reset the filter unit if no timer reset signal is received from the control unit.

It is noted that the term COP timer component is, for the purpose of this application, equivalent to the term watchdog component and/or the term computer operating properly timer component.

An advantage of the software component comprising a COP timer is that the filter unit is continually subjected to a fail-safe control action by the periodic timer reset signal. In other words, as soon as an error or fault occurs, the COP timer will not receive a COP timer reset signal and the filter unit will be (preferably temporarily) be disabled.

Another advantage is that the software component operates independently from other components of the filter unit, such as the control unit and the active filters, which increases reliability of the fail-safe module.

It is noted that the COP timer component in an embodiment is a component configured to establish a restart of the filter unit, and specifically including the control unit, the plasma unit and the electrostatic filter unit, when a hardware fault or software error occurs in the filter unit. In order to do so, the COP timer component comprises a first and a second timer that are placed sequentially. During use, the control unit is configured to periodically send a timer reset signal to the first timer to reset the first timer in order to prevent the first timer from elapsing. If no timer reset signal is received by the first timer, the first timer is configured to elapse and send an enabling signal to the second timer to start a time-out time of the second timer. The second timer is configured to, after elapsing, send a signal to the control unit to initiate a reboot of the filter unit.

In an embodiment according to the invention, the first timer may additionally be configured to, after elapsing, send a (preferably non-maskable) interrupt signal to the control unit to indicate that a filter unit reset is imminent and to allow the control unit to record status information during the time-out period of the second timer.

An advantage of notifying the control unit of an upcoming imminent reset is that the control unit may be able to record the status of the filter unit and/or information that has led to the error or fault in the operation of the filter unit. Such information could, in a later stage, be transferred from the filter unit to an external storage or device in order to be analyzed. Not only will this information be helpful in determining the source of the error, it will also be possible, by using this information, to determine whether this error or fault has occurred in multiple filter units. This in turn will allow the filter unit to be adapted if necessary.

In an embodiment according to the invention, the hardware component is positioned between a power supply of the filter unit and the filter components and/or the control unit and comprises a current detector, a threshold timer and a circuit breaking component. The current detector is configured to measure current from the power supply to the filter components and/or the control unit. The threshold timer is configured to compare the measured current with a threshold value over a predetermined time period (i.e. the timer-period). For completeness sake, it is noted that a threshold timer in this application is a device configured to measure a value, in this case a current value, over a predetermined period of time to establish whether the (integrated) value over that time period exceeds the threshold value. The threshold timer according to the invention thus measures a time period (which may be fixed or may be adjustable) and in addition measures a value, in this case a current value, over that time period. This may be an integrated value or a summed value.

The circuit breaking component, preferably a fuse, is positioned between power supply and the current detector, and is configured to disable the electrical connection between the power supply of the filter unit and the filter components and/or the control unit. During use, the threshold timer is configured to, if the measured current exceeds a current threshold value of the threshold timer over the predetermined time period, generate and send a disable signal to the circuit breaking component to disconnect the power supply to the filter components and/or the control unit.

In other words, the current detector in this embodiment is configured to measure current from the power supply to the filter components and/or the control unit. Subsequently, the threshold component is configured to receive a measured current from the current detector and to determine if the current measured by the current detector exceeds a predetermined threshold value over the predetermined time period and/or to determine if the current intensity over a predetermined period of time exceeds a predetermined current intensity threshold, and to generate a disable signal when either threshold is exceeded. The circuit breaking component is configured to, in response to the disable signal, permanently disconnected the power supply from the filter components and/or the control unit.

An advantage of this embodiment is that the hardware component is independent of other components of the filter unit including the control unit and the (active) filters. Moreover, by positioning the hardware component before the control unit, the control unit will be unable to perform any action on the hardware component. This ensures that the hardware component disables power supply if an error or malfunctioning of the filter occurs.

Another advantage of the hardware component is that it permanently disables the filter unit to prevent the malfunctioning filter unit to be activated again. Therewith it is prevented that ozone is generated using a malfunctioning filter unit.

In an embodiment according to the invention, the plasma filter includes a plasma filter power control unit that is configured to switch the plasma filter between an operative state in which plasma is generated and an inoperative state in which no plasma is generated, and is configured to, in the operative state, control the amount of plasma generated by the filter by measuring and controlling an amount of power provided to the plasma filter.

An advantage of having a separate plasma filter power control unit, preferably one that is controlled by the (main) control unit, is that the plasma filter is controllable independently from the other filters. This allows a more detailed control over the amount of plasma, and thus ozone, generated by the plasma filter.

Another advantage of the plasma filter power control unit is that it also allows the plasma filter to be shut off, while the other components/filters of the filter unit remain operational.

In an embodiment according to the invention, the electrostatic filter includes an electrostatic filter power control unit that is configured to switch the electrostatic filter between an operative state and an inoperative state, and is configured to, in the operative state, measure and control an amount of power provided to the electrostatic filter.

An advantage of having a separate electrostatic filter power control unit, preferably one that is controlled by the (main) control unit, is that the electrostatic filter is controllable independently from the other filters. This allows a more detailed control over the filter and is helpful to reduce the amount of ozone and particulates. Another advantage of the electrostatic filter power control unit is that it also allows the electrostatic filter to be shut off, while the other components/filters of the filter unit remain operational.

Yet another advantage is that a separate electrostatic filter control unit, preferably combined with a separate plasma filter control unit, is that the (active) filter capacity can be adapted to the composition of the air to be filtered by increasing or decreasing the amount of power to each of the filters.

In an embodiment according to the invention, the plasma filter comprises a one or more plasma generators, and wherein, when the plasma filter comprises more plasma generators, the plasma generators are preferably used sequentially.

An advantage of having multiple plasma generators is that the generators can be used sequentially to increase lifetime of the generators.

Another advantage is that the plasma filter, even when one of the plasma generators malfunctions or breaks down, the remaining plasma generators are capable of continuing operation of the filter unit. This allows the plasma filter (and thus the filter unit as a whole) to remain operational.

In an embodiment according to the invention, the plasma filter comprises a voltage booster that is configured to temporarily increase the amount of ozone in the plasma to remove pollutants from the one or more plasma generators, wherein the voltage booster preferably increases the voltage above 3.5 kV AC, more preferably above 4 kV AC and most preferably to around 4.5 kV AC.

An advantage of temporarily increasing the amount of ozone is that the plasma filter is subjected to a self-cleaning operation, which removes any pollution that may have attached itself in or near the filter. Such a cleaning operation is only periodically required, wherein the period is in the range of once per week to once per year, preferably once per month. It is noted that the cleaning operation sequence strongly depends on the operational time, air flow to be filtered and other circumstances and may also be outside the preferred range for certain circumstances.

In an embodiment according to the invention, the filter unit comprises a communication component, preferably a wireless communication component and more preferably a WIFI component, wherein the communication component is operatively connected to the control unit.

An advantage of providing a communication component, preferably WIFI-based, is that the filter unit may be, to a certain extent, be remotely controlled and/or updated. This is particularly advantageous to provide software updates and/or receive maintenance information about the filter unit. This allows the producer and/or seller to proactively react to maintenance needs for the user. Another advantage of the communication component is that status information may be exchanged, for example during a malfunctioning of the filter unit, which allows a remote software reset and/or the retrieval of error information about the malfunctioning.

In an embodiment according to the invention, the control unit is configured to, via the communication component, send information to and/or receive information from an external communication device such as a computer, including one or more of: send filter unit status, receive firmware updates, send error information including critical failure information and send data containing operational information of the filter unit.

An advantage of providing a communication component, preferably WIFI-based, is that the filter unit may be, to a certain extent, be remotely controlled and/or updated. This is particularly advantageous to provide software updates and/or receive maintenance information about the filter unit. This allows the producer and/or seller to proactively react to maintenance needs for the user.

Another advantage of the communication component is that status information may be exchanged, for example during a malfunctioning of the filter unit, which allows a remote software reset and/or the retrieval of error information about the malfunctioning.

In an embodiment according to the invention, the filter unit comprises an airflow sensor that is positioned near the air inlet of the housing in the air flow path, wherein the airflow sensor is configured to, during use, at least measure a quantity of air that is flowing through the air filter.

An advantage of the embodiment is that the control unit is capable of anticipating the operational status of the filter by adapting the filter operation parameters to the quantity of air that is provided to (and guided through) the filter unit to obtain even better cleaning of the air stream.

In an embodiment according to the invention, the filter unit comprises one or more sensors that are configured for measuring and/or detection one or more of: particulate content of the airflow, (volatile) inorganic compounds, (volatile) organic compounds, undesired particles, such as fine dust, fungi, viruses, bacteria, wherein the control unit and/or control units associated with one or more of the filters are configured for receiving the measurement and/or detection data.

An advantage of the embodiment is that the control unit is capable of adapting the filter operations to the specific content of the filter unit to even further improve the cleaning of the air stream through the filter unit.

In an embodiment, the housing is manufactured from metal, preferably stainless steel or aluminium, plastic, carbon-based materials or a combination thereof.

In an embodiment according to the invention, the filter unit comprises an additional ESP (electrostatic precipitator) that, when viewed in a downstream direction, is positioned near or before the inlet opening of the housing of the filter unit. An advantage of providing an additional ESP filter as pre-filter is that particles will be removed before entering the other filters of the filter unit, which reduces pollution therein. Preferably, the ESP is provided as an exchangeable pre-filter that can easily be removed from the filter unit to be replaced. More preferably, the ESP is provided with a plug-and-play type connector to allow it to be connected in a simple and efficient way.

In an embodiment according to the invention, a voltage applied in the additional ESP filter is in the range of 6 - 10 kV and preferably is around 8 kV, and wherein the voltage applied to a feed of the additional ESP filter preferably is in the range of 12 - 24 V and more preferably is in the around 24 V.

An advantage of providing an operational voltage of around 8 kV to the additional ESP is that it provides an enhanced separation and (thus) filtering of dangerous components and substances, and in particular germs, bacteria and viruses. Moreover, by providing the operational voltage of around 8 kV, an increased removal and/or purification of aerosols is provided.

In an embodiment according to the invention, the additional ESP filter comprises a number of wires or threads that are positioned near an inlet and/or outlet opening of the additional ESP- filter, and a number of plates or louvres that extend parallel to each other in an inner ESP space.

An advantage of providing both wires and louvres is that an increased efficiency is achieved with the additional ESP filter.

In an embodiment according to the invention, the voltage applied to the wires or threads is in the range of 6 - 10 kV and preferably is around 8 kV, and wherein the voltage applied to the plates or louvres is in the range of 3 - 6 kV, and preferably is in the range of 4 - 4,5 kV.

An advantage of providing different voltages to the wires and louvres allows, especially in combination with the particular positioning of these components, is that the particles are very efficiently charged (by the wires) and subsequently removed from the air stream with the louvres.

In an embodiment according to the invention, the additional ESP filter is connected to the control unit and is configured to be controlled by the control unit, wherein the control comprises one or more of: controlling on/off switching, controlling the input voltage over the power input of the additional ESP, controlling the output voltage to the wires and/or the louvres.

An advantage of providing the control over the additional ESP filter from the control unit is that the entire filter unit is controlled from a single control unit, which increases efficiency of the filter unit and reduces complexity of the control unit.

Another advantage is that the fail-safe module, by virtue of the control of the additional ESP via the control unit, is also capable of temporarily or permanently disabling the additional ESP filter. This increases safety and reliability of the filter unit. An even further advantage is that the additional ESP-filter has a lower constructive complexity due to the fact that a control unit, that is specifically dedicated to the ESP-filter, can be obviated.

Yet another advantage is that the input voltage to the ESP-filter unit, which at least partially controls the operational voltage applied in the air stream, can be monitored and controlled by the control unit. In an embodiment, the control unit is configured to provide a input voltage to the additional ESP of 24 V.

It is however also possible to connect the ESP-filter to other components, such as the plasma filter, in which case the plasma filter and the ESP-filter are operated in tandem with each other. This may for example mean that the ESP-unit is controlled by a plasma filter control unit.

In an embodiment according to the invention, the plasma filter and/or the one or more plasma generators of the plasma filter may be removably provided in the housing and may preferably be pluggable in the housing.

An advantage of providing the plasma filter and/or the plasma generators thereof as removable, or preferably pluggable, units is that these units can easily be replaced in case of failure and/or during maintenance.

Another advantage is that a more sustainable filter unit is achieved, because the components, such as the housing, may be re-used.

In an embodiment according to the invention, the control unit may be configured to, during use of the filter unit, regulate an air flow through the air filter, in dependence of a determined COz- level in the airflow and/or a determined COz-level in ambient air of the filter unit.

An advantage of providing a COz-based control is that the air flow is adapted to a number of people in a room in which the filter unit is provided. In other words, if the number of people in a room in which the filter unit is provided increases, the volume of the air flow through the filter unit may be increased to a constant filtration level per person that is independent of the number of people in the room. This is especially interesting when filtering spaces, rooms or locations in which the accumulation of harmful particles, such as viruses, is to be prevented.

Another advantage is that, for example when the plasma and/or electrostatic filter are controlled based on the air flow, the quantity of CO2 provides a direct control link to the other components of the filter unit. In particular, an increasing airflow may than lead to a higher amount of plasma being generated by the plasma filter.

It is noted that this particular COz-based control may also be provided in combination with existing filter units, in which it may in some cases be retrofitted. In an embodiment according to the invention, the dependency of the COz-level comprises increasing the air flow with an increasing COz-level and decreasing the air flow with a decreasing air flow.

An advantage of increasing the air flow with an increasing COz-level is that the filter unit automatically adapts its operation to an increasing number of people in a space, room or location in which the filter unit is placed (or with which it is operatively connected to filter the air).

It is preferred that the control unit is configured to adapt the operation based on a predetermined formula or logic that is based on an average amount of CO2 that is exhaled by a person during breathing. This predetermined formula may be adapted to the type of activity to be expected in the room of which the air is or needs to be filtered by the filter unit.

In an embodiment according to the invention, the filter unit further comprises at least one COz-sensor that is configured to, during use, measure a quantity of CO2 in the air flow through the filter unit, preferably through the air inlet, and/or measure a quantity of CO2 in the ambient air of the filter unit, and wherein the control unit is configured to, during use, regulate a volume of the air flow through the filter unit based on the quantity of CO2 measured by the CCh-sensor.

An advantage of providing at least one CXX-scnsor is that it allows an effective means to measure a quantity of CO2 or a CCh-level. This information can be used by the control unit to control the filter unit and in particular the air flow thereof.

In an embodiment according to the invention, the filter unit further comprises a fan that is positioned in or adjacent the air inlet and that is configured to generate an air flow through the filter unit, and preferably wherein the control unit is configured to regulate a fan operating speed in dependence of CCh-measument data generated by the CXT-scnsor.

The control of the air flow through the filter unit may for example be provided by means of a fan, which may be positioned in the filter unit or even may be positioned outside the filter unit and be operatively connected therewith.

In an embodiment according to the invention, the filter unit further may comprise a fan that is configured to, during use, generate an air flow through the filter unit, and wherein the control unit is configured to, based on the measured quantity of CO2, regulate a rotation speed of the fan to regulate the volume of the air flow through the filter unit.

This embodiment, by virtue of the CXX-scnsor and the fan, provides a direct relation between the air flow through the filter unit and the CO2 present in the air flow and/or the ambient air. An advantage thereof is that an effective control is provided.

In an embodiment according to the invention, the control unit is further configured to, during use of the filter unit, at least provide a minimum air flow through the filter unit that is independent of a measured CCh-level. An advantage of providing a minimum air flow is that the control unit may also be controlled separately from the COz-level. In other words, even if a low amount of CO2 is present, the filter unit still is operable to filter the air.

In an embodiment according to the invention, the control unit is configured to, during us eof the filter unit, provide at least a predetermined minimum fan operating speed, wherein the control unit is configured to provide the predetermined minimum fan operating speed if the measured amount of CO2 is below a predetermined CO2 threshold value.

An advantage of providing a minimum air flow is that the control unit may also be controlled separately from the CCh-level. In other words, even if a low amount of CO2 is present, the filter unit still is operable to filter the air.

In an embodiment according to the invention, the control unit is operable in three modes, which include: a low throughput mode, in which the control unit controls the filter unit to provide a predetermined volume of air flow through the filter unit; a high throughput mode, in which the control unit controls the filter unit to provide a predetermined volume of air flow through the filter unit that is higher than in the low throughput mode; and a CCh-mode, in which the control unit controls the filter unit based in a quantity of CO2 in the ambient air and/or the air flow in the air inlet.

The invention also relates to a kitchen hood comprising a filter unit according to the invention.

The kitchen hood according to the invention has similar advantages and effects as the filter unit according to the invention. The kitchen hood according to the invention may be used in conjunction with a filter unit according to any or a plurality of the embodiments as described in relation to the filter unit according to the invention.

An advantage of a kitchen hood comprising the filter unit according to the invention is that the kitchen hood may be provided as a recirculation unit rather than a unit comprising an external air discharge. This reduces heat losses in the building and/or the room thereof, and simultaneously, by use of the filter unit, increases air quality when used.

The filter unit according to the invention is, when applied in a kitchen hood, preferably applied as a plug-and-play unit that can be easily introduced in a kitchen hood.

Another advantage is that the filter unit according to the invention may easily replace an existing filter unit to provide an upgrade to the kitchen hood according to the invention.

The invention also relates to a kitchen hood conversion kit, the conversion kit comprising:

- a filter unit according to the invention; - an adaptor flange to connect the filter unit to the existing filter unit opening and/or a closure configured to close an existing opening from the kitchen hood to an external environment of the building in which the kitchen hood is placed.

The kitchen hood conversion kit according to the invention has similar advantages and effects as the filter unit and the kitchen hood according to the invention. The kitchen hood conversion kit according to the invention may be used in conjunction with a filter unit according to any or a plurality of the embodiments as described in relation to the filter unit according to the invention.

The invention also relates to an air filter, the air filter comprising:

- a base; and

- a filter unit according to the invention that is operatively connected to the base.

The air filter according to the invention has similar advantages and effects as the filter unit according to the invention. The air filter according to the invention may be used in conjunction with a filter unit according to any or a plurality of the embodiments as described in relation to the filter unit according to the invention.

An advantage of the filter unit according to the invention is that it provides an efficient, safe and reliable way to increase (indoor) air quality and reduce bacteria, viruses and other airborne contaminants.

Another advantage of the air filter according to the invention is that it reduces aerosols in the air stream that is provided to the filter, which additionally reduces the risk of airborne contaminants being transferred between people. It has been found that the reduction in airborne contaminants may be up to 98%. This is especially relevant with for example viruses, since according to research aerosol transmission may contribute to the transfer of such viruses between people.

Yet another advantage of the air filter according to the invention is that it may also advantageously be used in buildings and/or locations in which a high amount of (harmful) particulates and/or substances is released, such as spray booths, (car) workshops or tunnels. Moreover, the air filter according to the invention may also be used in for example cars, buses and/or other transportation units to reduce harmful emissions therefrom.

In an embodiment of the air filter according to the invention, the air filter comprises an additional HEPA-filter that, when viewed in a downstream direction, is positioned near or before the inlet opening of the housing of the filter unit.

An advantage of providing an additional HEPA filter as pre-filter is that course particles will be removed before entering the other filters of the air filter, which reduces pollution therein. Preferably, the HEPA filter is provided as an exchangeable pre-filter that can easily be removed from the air filter to be replaced.

In an embodiment of the air filter according to the invention, the air filter comprises an elongated housing that extends from the base upwardly in a first direction, wherein the housing comprises an inlet opening, an outlet opening and the filter unit. The inlet opening is positioned near the base, whereas the outlet opening is positioned at or near an end opposite the base, wherein the outlet opening is preferably positioned at a distance of 0.75 m - 2.0 m from the base, and more preferably is positioned at around 1.5 m from the base. The filter unit is positioned between the inlet opening and the outlet opening within the housing.

In an embodiment of the air filter according to the invention, the housing of the filter unit is an elongated housing that extends from the base in a first, preferably upward direction, wherein the air inlet is positioned near the base, and wherein the air outlet is positioned at a distance of 0.75 m - 2.0 m from the base, and more preferably is positioned at around 1.5 m from the base.

In this embodiment, the filter unit is configured such that the housing of the air filter and the filter unit are one and the same. This reduces the amount of material required to manufacture the air filter, therewith reducing the cost and the environmental impact of the air filter.

An advantage of the abovementioned embodiment is that a downwardly directed air flow is induced by the filter unit, in which harmful particulates and/or viruses exhaled by people are forced downwardly in the room towards the inlet of the filter unit. This air flow is, in most cases, oppositely directed to circulation by ventilation and/or heating installations, which provide an upward air flow in a room.

It has been found that providing a downward flow decreases the amount of aerosols, and viruses contained therein, at average ‘head level’ of people and therewith decrease the chance that people get infected. The invention also relates to a method for cleaning and/or purifying air, the method comprising:

- providing a filter unit according to the invention; and

- guiding air through the air filter.

The method according to the invention has similar advantages and effects as the filter unit, the kitchen hood and/or the air filter according to the invention. The method according to the invention may be used in conjunction with a filter unit according to any or a plurality of the embodiments as described in relation to the filter unit according to the invention.

An advantage of the method according to the invention is that it provides a safe, reliable and effective manner of filtering air in a room or building. Due to the fail-safe module, the risk of accidental release of ozone into the room or building (i.e. the environment in which the filter unit is placed) is substantially obviated. This can not be achieved with the known filter units, since the known filter units only have a passive filter, which is a carbon filter, to reduce excess ozone. Such a carbon filter however has a (very) limited life-time and is thus not capable of providing the required security with regard to ozone release. This is obviated by the fail-safe module that regulates (and strictly controls) the release of ozone during the entire life-time of the filter unit.

In an embodiment of the method according to the invention, the method further may comprise one or more of the steps described below. The step of temporarily disabling power supply to the plasma filter and/or the electrostatic filter by the software component of the fail-safe module if a measured current has exceeded a current and/or time period threshold. The step of permanently disabling power supply to the plasma filter and/or the electrostatic filter by the hardware component of the fail-safe module if a measured current has exceeded a current and/or time period threshold. The step of, if the plasma filter comprises multiple plasma generators, alternatingly using the multiple plasma generators to generate plasma. The step of controlling, by the plasma power control unit, the amount of plasma generated in an operative state of the plasma filter and/or controlling, by the electrostatic filter control unit, the amount of power supplied to the electrostatic filter and/or a voltage between the first and second gaze of the electrostatic filter. The step of activating and/or deactivating, by the control unit, the ESP. The step of communicating by the control unit, via the communication unit, on one or more of: filter unit status information, firmware updates, error information including critical failure information and data containing operational information of the filter unit.

The step of activating the hardware component only after the software component has been activated, wherein the time period threshold of the hardware component exceeds the time period threshold of the software component.

The invention also relates to the use of a filter unit according to the invention, a kitchen hood according to the invention, an air filter according to the invention and/or a conversion kit according to the invention.

The use of the filter unit according to the invention has similar advantages and effects as the filter unit, the kitchen hood and/or the air filter according to the invention.

Further advantages, features and details of the invention are elucidated on the basis of a preferred embodiment thereof, wherein reference is made to the accompanying drawings, in which:

Figure 1 A-B shows a perspective view of an example of filter unit 2 according to the invention;

Figure 2 shows an example of electrical connections in filter unit 2 according to the invention;

Figure 3 shows an example of a software component of the fail-safe module according to the invention; Figure 4 shows an example of a hardware component of the fail-safe module according to the invention;

Figure 5 shows an example of a kitchen hood according to the invention; and

Figure 6A-B shows an example of an air filter according to the invention;

Figure 7 shows a partial view of another example of an air filter according to the invention; Figure 8 shows an detailed view of a part of the example of figure 7;

Figure 9 shows a cross-section of the example of figure 7 along the line IX-IX.

In an example filter unit 2 (see figure 1) comprises a filter housing 4 with inlet 6, conical body 8, and outlet surface 10. Inlet 6 is in this example provided with grate 6a, which provides additional strength to housing 4 and prevents people from accessing inner space 5 of filter housing 4. It is noted that grate 6a is however not necessary to operate filter unit 2. In addition, conical body 8 is in the illustrated embodiment provided with ribs 12, although it will be understood that ribs 12 can be omitted from conical body 8 to provide a conical body having a smooth outer wall. Filter unit 2 is further provided with plasma filter 14, electrostatic discharge filter 16 (or simply ESD filter 16 or electrostatic filter 16) and active carbon filter 18. Plasma filter 14 is connected to outer side of conical body 8 and is configured to produce plasma containing ozone that is provide to an air stream in inner space 5 of housing 4. Plasma filter 14 comprises a single ozone plate 20, whereas it is also possible to provide multiple ozone plates 20 which can be simultaneously or alternatively be activated. Electrostatic filter 16 comprises first gaze 22 and second gaze 24, which in this example are spaced apart at distance D from each other and are separated by insulation 26. Active carbon filter 18 is provided on an outer side of electrostatic filter 16 and surrounds electrostatic filter 16.

Filter unit 2 further comprises control unit 28, which in this example is provided as printed circuit board 28 on conical body 8. Control unit 28 in this example comprises microprocessor or chip 86, which is optional as control unit 28 may be provided in various other ways as well. Printed circuit board 28 is in this example further connected with sensors 30, which are provided on the during use downwardly directed side. Sensors 30 may also be provided on control unit 28. Sensors 30 may for example be used to measure the air flow in filter unit 2 or measure other or additional parameters, such as pollution level and/or presence of substances and/or particles in the air flow or stream. Filter unit 2 further comprises fail-safe module 33, which in this example comprises software component 32, which is positioned on printed circuit board 28, and hardware component 34, which is positioned between control unit 28 and external power supply connecter 36 (see also figure 2).

Filter unit 2 further comprises communication component 80, which may be provided in or on a side wall of filter unit 2. Communication component 80 preferably is connected to, or integral with, control unit 28 and may for example be controlled by microprocessor 86 of control unit 28. Communication component 80 may for example comprise a WiFi component 82, a display and/or buttons 84 or both. These communication components allow a user to communicate with and/or control filter unit 2. WiFi-component 82 for example may allow wireless communication by control unit 28 with external source 88 to send and/or receive data, such as for example firmware updates, security updates etc. It is noted that communication component 80 and/or control unit 28 are unable to control fail-safe module 33, which operates independently from control unit 28.

As can be seen in figure 2, plasma filter 14 and electrostatic filter 16 are both connected to control unit 28, which in this example is printed circuit board 28. Control unit 28 is integrally provided with software component 32 of fail-safe module 33, which connects hardware component 34 with plasma unit 14 and electrostatic filter 16. Optionally, plasma filter 14 may be provided with plasma filter power control unit 38 and/or electrostatic filter 16 may be provided with electrostatic filter power control unit 40. In this example, control unit 28 is configured to provide overall control of active components 14, 16 of filter unit 2 including power control, which is safeguarded by integrally provided software component 32 of fail-safe module 33.

Software component 32 of fail-safe module 33 comprises a COP timer with first stage timer 42 and second stage timer 44 (see figure 3), which are sequentially connected. First stage timer 42 is connected to control unit 28. In use of filter unit 2, control unit 28 under normal operating conditions periodically sends a timer reset signal (TRI) to first stage timer 42, which restarts the timer period of first stage timer 42. If control unit 28 fails to provide a timer reset signal (TRI) to first stage timer 42, for example due to a software error or another failure in filter unit 2, first stage timer 42 times out and provides a timer enable signal (TR2) or enabling signal (TR2) to second stage timer 44 to start a time-out period of the second stage timer 44. After the time-out period of second stage timer 44, second stage timer 44 is configured to send a filter unit reset signal (FUR) to control unit 28 to initiate a reboot of filter unit 2. Optionally, first stage timer 42 may be configured to, after elapsing, send a (preferably non-maskable) interrupt signal (ESS) to control unit 28 to indicate that a filter unit reset is imminent and to allow control unit 28 to record status information during the time-out period of second stage timer 44. This allows error status information to be retrieved at a later moment.

Hardware component 34 of fail-safe module 33 comprises current detector 48 that is configured to measure current from the power supply (provided via power supply connector 36) to plasma filter 14 and electrostatic filter 16 and control unit 28. Current detector 48 is connected to threshold timer 50, which is configured to compare the measured current A with a threshold value. This may include the actual current value A, an average current intensity over a predetermined period of time or both. Current detector 48 and threshold timer 50 are both connected to circuit breaking component 46, which in this example is fuse 46, which is positioned between power supply connector 36, current detector 48 and threshold timer 50. Circuit breaking component 46 is configured to disable the electrical connection between power supply connector 36 and current detector 48, therewith effectively breaking the electrical connection between filter unit 2 and its power supply. This substantially immediately shuts down plasma filter 14 and electrostatic filter 16.

In use of filter unit 2, electrical power is provided from power supply connector 36 via permanent circuit breaker 46 to current detector 48. Current detector 48 measures the actual value of the current A and provides these actual values to threshold timer 50. Threshold timer 50 continually or periodically compares the measured current A against a predetermined current threshold. If measured current A exceeds the predetermined current threshold value of threshold timer 50, threshold timer 50 generates and sends a disable signal (DS) to circuit breaking component 46 to disconnect the power supply connector 36 from current detector 48 and therewith filter unit 2. Upon receiving disable signal (DS), circuit breaking component 46 permanently disables the electrical connection to power supply connector 36.

Optionally, threshold timer 50 may, in use, continually or periodically integrate the current value over a predetermined period of time to obtain an integrated average current value or average current intensity. Threshold timer 50 subsequently compares the average current intensity with a predetermined average current intensity threshold and, upon determining that the average current intensity exceeds the predetermined average current intensity threshold, sends disable signal (DS) to circuit breaking component 46.

In an example kitchen hood 100 is provided with filter unit 102 and with a pre filter in the form of electrostatic precipitator 156 or electrostatic pre-filter 156, which reduces the amount of particles in the air stream to filter unit 102. Kitchen hood 100 is further provided with motor 154, which provides air to be cleaned to electrostatic precipitator 156 and filter unit 102.

In an example of air filter 200 according to the invention, air filter 200 comprises air filter housing 260 that extends from base 262 in upward direction z towards housing outer end 264. Air filter housing 260 (see figures 6a, 6b) is provided with side walls 266, all of which are in this example provided with a single inlet opening 268 that is positioned near base 262. Air filter housing 260 is near or, in this case at, housing outer end 264 provided with outlet opening 270. Within air filter housing 260, air filter 200 is provided with several different components. Air filter 200 comprises, when viewed in a direction of an air stream through air filter 200, subsequently HEPA-filter 252, air transport unit 254, which in this example is a fan 254, electrostatic precipitator 256 or electrostatic pre-filter 256, and filter unit 202, which may be comparable with filter unit 2 as shown in figures 1 - 4. Air filter 200 in this example further comprises outlet grate 272 and on/off switch 274, which in this example is positioned near base 262.

In use of air filter 200, air stream F is generated by fan 254, which enters air filter 200 through inlet openings 268 in housing walls 266 and is sucked through HEPA-filter 252 towards fan 254. Fan 254 subsequently provides air flow or stream F to electrostatic precipitator 256 or electrostatic pre-filter 256, and filter unit 202 before expelling the cleaned air through outlet an air filter according to the invention opening 270. Herein HEPA-filter 252 serves to separate larger particles, such as having a size larger than about 5 pm. Electrostatic precipitator 256 serves as a pre-filter for filter unit 202 and removes some particulates/particles in the range of 0.1 pm - 10.0 pm. Filter unit 202 subsequently filters gases, volatile organic compounds (VOCs), bacteria and particulates, in which the plasma filter is primarily used for removing or disabling gases, volatile organic compounds (VOCs) and bacteria, which all have a size in the range of 0.1 pm - 10.0 pm, whereas the electrostatic filter is primarily use for removing VOCs and particulates, most of which also have a size in the range of 0.1 pm - 10.0 pm. The active carbon filter of filter unit 202 is used to remove odours from air stream F, before air stream F is expelled from outlet opening 270.

Experiments have shown that the removal of contaminants, including bacteria, viruses, smoke particles and other harmful contaminants from air flow F is effective up to more than 95%, and even up to almost 100%. By incorporating the fail-safe module, it is at the same time achieved that the contaminant removal is performed without expelling ozone from outlet opening 270. Therewith, a safe and reliable air filter is achieved.

In another example, device 302 (see figures 7 - 9), comprises conical body 308 that is insertable in an inner space of a housing. Conical body 308 is provided with two plasma filters 318, each of which is provided with plasma generator 320. Plasma filters 318 are removably connected to conical body 308, which removable connected in this example comprises a click-and- release system. Thereto, plasma filter 320 is provided with connecting element 321, which is provided as projection 323 that extends away from the surface of plasma filter 320. Projection 320 cooperates with opening 325 of conical body 308 to click plasma filter 320 in place. By pushing connection element 321 in a direction opposite the extension direction of projection 323 (in figure 8 in a downwards direction), projection 323 is released from opening 325 and plasmna filter 318 is released from conical body 308. It is noted that other connections may be used to the same effect as well.

The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.