Patent Description:
Conventional water supply and distribution systems on-board commercial aircraft comprise pipework made from rigid pipes, i.e., rigid plumbing. Through the rigid pipes potable water is supplied from a central water tank to consumer assemblies such as sinks and toilets in a lavatory or steam ovens and sinks in a galley. Such conventional supply systems offer sufficient robustness against foreign particles contained in potable water, i.e., the devices and components normally employed in such systems are not prone to damage from the concentration and size of particles contained in the water supplied to the central water tank and then delivered to the consumer assemblies. Filter units are only optionally installed in a decentral manner into monuments in order to protect sensitive consumer assemblies (in particular galley inserts GAINS), such as coffee makers or steam ovens, from being adversely affected by particles and thus to extend their service life. Thereby filter cartridges are used that have to be replaced at regular maintenance intervals (cartridges with different filter effects are available).

However, recently a high pressure water system was introduced and it is described in <CIT>. Such industry-optimized water system architecture is based on the concept of a reduction of pipe cross-sections accompanied by an increase in pressure-level as well as a change of pressurization technology, i.e., rather than employing pressurized central water tanks and centrifugal pumps, displacement pumps are used, by other types of pumps may also be used in such high-pressure systems. This adaption allows massive savings, e.g., weight, installation time, equipment cost etc., but at the same time it leads to a higher sensitivity against any kind of foreign particles or deposits. In particular, the higher sensitivity requires the implementation of a filter device upstream the high pressure section with e.g. the displacement pump. The filter device protecting the water system from particles, turbidity, etc. These substances remain on the upstream side of the filter and accumulate there.

The filter device in turn involves the following disadvantages. There is additional maintenance effort for replacing or cleaning the filter cartridges, or water filters with reduced maintenance effort have a complex design which in turn results in an increase of weight. Moreover, the system performance is continuously decreasing due to filter-cake formation which reduces the pressure and flow of water through the filter and the pump.

Thus, it is an object of the present invention to provide a method for operating an on-board water supply system in an aircraft as well as such system which allow to operate the system for a long period of time without a significant reduction in performance and the need for significant maintenance efforts.

<CIT> discloses a toilet device for a rail vehicle includes flushing water-carrying installations and waste water-carrying installations. The flushing water-carrying installations include an intermediate reservoir for storing flushing water and a supply line for supplying the intermediate reservoir with flushing water. The supply line includes a filter for filtering the flushing water supplied to the intermediate reservoir. The supply line is connected to the intermediate reservoir such that flushing water from the intermediate reservoir can be returned through the filter. A backflushing line is connected to the filter and opens into a waste water-carrying installation.

The object underlying the present invention is solved by the subject matter defined in the independent claims. Preferred embodiments are described in the dependent claims.

In particular, in a first aspect of the present invention, the above object is solved by a method for operating an on-board water supply and distribution system of an aircraft for supplying water. The system comprises a central water tank and a plurality of consumer assemblies. Each consumer assembly comprises a supply device and a buffer tank, and each consumer assembly is configured to supply water from the buffer tank via the supply device.

With regard to the consumer assemblies it is to be noted that in the method of the present invention a consumer assembly may comprise not just a sole supply device but may also be provided with a plurality of supply devices so that a sole buffer tank supplies the plurality of supply devices with water by means of a micro pump or gear pump. There is a single conduit connecting this consumer assembly with the pump of the system as further discussed in the following. Thus, the present invention is not limited to consumer assemblies where each buffer tank is associated with only a single supply device.

Further, as already indicated the system comprises a pump having an upstream side and a downstream side and being configured such that it may operate in a supply mode and a reverse mode. In a preferred embodiment the pump is configured as a positive displacement pump and further preferred as a gear pump. The downstream side of the pump is connected to the high pressure conduit system that connects the downstream side to the plurality of consumer assemblies. The conduit system being configured such that the pump, when operating in the supply mode, is capable of delivering water from its upstream side to the buffer tank of each of the consumer assemblies. When the pump is operating in the reverse mode, it is capable of conveying water from the downstream side to the upstream side.

Moreover, the system comprises a filter device which protects the water system from particles, turbidity, etc. A filter device improves the quality of water by removing or reducing the concentration of particles such as turbidity or microorganisms or other undesirable substances dissolved in the water. The filter device used may preferably be a sieve filter. More preferably, the filter device may comprise a combination of several filter stages or filter principles. In any case, the respective substances remain on the upstream side of the filter and accumulate there. The central water tank is connected to the upstream side of the pump with the filter device being arranged between the central water tank and the upstream side.

The method of the present invention comprises the following steps:.

Hence, with the method according to the present invention the system on-board an aircraft comprising a central water tank, a pump and a plurality of consumer assemblies such as sinks and toilets in a lavatory or steam ovens and sinks in a galley, is operated in the first step in a manner where the buffer tanks of the consumer assemblies are supplied with water from the central water tank, the water passing the filter device so that both the pump and the consumer assemblies are prevented from getting into contact with particles having a size larger than the pore size of the filter device. In this first step, it is preferred that the buffer tanks are filled completely or at least up to a certain level. In particular, it is preferred, that level sensors are provided in the buffer tanks which are connected with a control unit of the system so that the level up to which the buffer tanks are filled, may be controlled by the control unit.

Furthermore, in particular during time periods where there is no demand for water at the consumer assemblies and especially when the aircraft is on the ground, then the pump is operated in the reverse mode, so that water from the buffer tanks is drawn to the pump and pushed through the filter device in a direction opposite to the normal flow during the first step. In this second "backwash" step particles that have been accumulated on the upstream side of the filter device are removed and then pushed back preferably towards the central water tank or, in another preferred embodiment, to the fill / drain coupling provided in the connection between the filter device and the central water tank.

Thus, the method according to the present invention allows to clean the upstream side of the filter device after a relatively short period of normal use so that the amount of particles which have accumulated in the filter device may be kept at a relatively low level which in turn results only in a minor reduction of the performance of the system. In addition, the efforts which have to be made to clean the filter device are rather small and the cleaning step for the filter device can automatically be initiated. In particular, it is not required that any parts of the system are replaced during the aforementioned cleaning step, so that no maintenance personal has to be involved.

In a preferred embodiment, where the system is provided with a fill / drain coupling in the connection between the central water tank and the filter device, an outlet valve is provided on the fill / drain coupling, the outlet valve having a closed and an open position. When the pump is operated in the supply mode, the outlet valve is in the closed position, i.e., it is controlled such that it is in the closed position, and when the pump is operated in the reverse mode, the outlet valve is preferably in the open position, i.e., it is also controlled such that it is preferably in the open position. In this preferred embodiment water contaminated with particles from the upstream side of the filter device is automatically pushed out of the system via the fill / drain coupling, whereas when the system is operated in the normal way with the pump operating the supply mode, water from the central tank is conveyed to the consumer assemblies by the pump. However, it is also conceivable and within the scope of the present invention that in the second step where the pump is operated in the reverse mode, water which is drawn through the filter, is further conveyed into the central water tank with the outlet valve being in the closed position. This latter mode of operation in which water contaminated with the filter cake is initially stored in the main tank, is advantageous when the temperatures in the surroundings of the aircraft are so low, that ice formation would take place.

Finally, it is also to be noted that the filter device may be configured such that it comprises a separate filter outlet connected to the upstream side of the filter device so that during the backwash-step when the pump is operated in the reverse mode water containing particles accumulated on the upstream side of the filter device are expelled via the filter outlet.

In a further preferred embodiment the buffer tank of each of the at least one consumer assembly comprises an inlet being connected with the downstream side of the central pump via the high pressure conduit system, and an outlet connected the supply device of the at least one consumer assembly. The inlet is arranged at a distance in the vertical direction from a bottom of the buffer tank, whereas the outlet is arranged in the bottom of the buffer tank. Such configuration of the buffer tanks enables a complete drainage of water and a transport of sediments and particles out of the buffer tanks which is a prerequisite for a hygienic water supply. On the other hand, the arrangement of the inlet at a higher level prevents that during operation of the pump in the reverse mode sediments and particles having accumulated at the bottom of the buffer tanks are conveyed towards the downstream side of the pump and the downstream side of the filter device where they could cause damage.

In a further preferred embodiment, a signal is generated being a measure of the flow rate of water through the filter device, when the pump is operated in the supply mode, and when the signal is outside a predetermined range, the pump is switched from the supply mode to the reverse mode, so that the pump is operated in the reverse mode for the second time interval. In this preferred embodiment the flow rate across the filter device is monitored, and in case it drops below a certain threshold, the reverse mode of the pump would be activated so as to remove at least parts of the filter cake on the upstream side of the filter device and, hence, to reduce the flow resistance of the filter device.

In this regard it is to be noted, that it is not required that the flow rate is measured directly. Instead, it is sufficient that a signal is constantly monitored which is merely a measure of the flow rate, and in case the signal is outside a predetermined range that corresponds to a flow rate which is acceptable, the reverse mode of the pump is activated. Here, it is further to be noted that the activation of the reverse mode is not necessarily initiated immediately upon the detecting that the signal has left predetermined range. It is also conceivable that there is a delay between the detection and the activation of the reverse mode.

In this embodiment it is further preferred that the pressure drop is detected between the side of the filter device being connected with the central water tank, i.e., the upstream side of the filter device, and the side of the filter device being connected with the upstream side of the pump, i.e. the downstream side of the filter device, and that the signal is generated based on the detected pressure drop.

In another aspect of the present invention the above object is solved by an on-board water supply and distribution system of an aircraft for supplying water, which system comprises a central water tank, a plurality of consumer assemblies, each consumer assembly comprising a supply device and a buffer tank and each consumer assembly being configured to supply water from the buffer tank via the supply device, a pump having an upstream side and a downstream side and being configured such that it may operate in a supply mode and a reverse mode, a filter device, a high pressure conduit system, and a control unit.

As already indicated above in the system of the present invention a consumer assembly may comprise not just a sole supply device. Instead, it but may also be provided with a plurality of supply devices so that a sole buffer tank supplies the plurality of supply devices with water and a single conduit connects such consumer assembly with the pump of the system, so that the present invention is not limited to consumer assemblies where each buffer tank is associated with only a single supply device.

The central water tank is connected to the upstream side of the pump with the filter device being arranged between the central water tank and the upstream side. Further, the conduit system connects the downstream side with the plurality of consumer assemblies, with the conduit system being configured such that the pump, when operating in the supply mode, is capable of delivering water from the downstream side to the buffer tank of each of the consumer assemblies. When the pump is being operated in the reverse mode, it is capable of conveying water from the downstream side to the upstream side.

The control unit is connected to the pump and being configured such that it operates the pump in the supply mode in a first time interval so that water from the central tank is delivered to at least one of the consumer assemblies wherein the buffer tank of the at least one consumer assembly is filled, and operates the pump in the reverse mode in a second time interval different from the first time interval so that water from the buffer tank of at least one of the consumer assemblies passes through the filter device. Preferably, the control unit operates the pump in such a way that in the first time interval the buffer tank of the at least one consumer assembly is filled completely.

Hence, the system of the present invention is also configured such that it can be operated in a first mode, where the buffer tanks of the consumer assemblies are supplied with water from the central water tank, and a second mode where the pump is operated in the reverse mode so that the upstream side of the filter may be cleaned and particles accumulated thereon are removed. Thus, the system of the present invention provides for the same advantages as the above-described method. The same applies to the preferred embodiments of the system as specified in the dependent claims of the respective independent claims describing the system of the present invention.

In another preferred embodiment, the filter device comprises a filter outlet on the upstream side of the filter which in a further preferred embodiment is provided with a filter outlet valve. Further, in this preferred embodiment the filter device may be arranged such that it is at a lower level than the central pump and the central water tank when the aircraft provided with the water supply and distribution system of the invention is in a horizontal position. With this latter configuration it is achieved that any water being present in the conduits between the filter device and the central tank and the central pump, respectively, may automatically be dumped via the filter outlet without employing further pump means.

Finally, the above object is also solved by an aircraft comprising a system as described before.

In the following, the invention will be described further with regard to the exemplary embodiment shown in the drawings, wherein.

As can be taken from <FIG> and <FIG> the exemplary embodiment of a water supply and distribution system <NUM> is generally arranged on-board an aircraft <NUM> and configured such that it supplies a plurality of consumer assemblies <NUM> such as sinks and toilets in a lavatory or steam ovens and sinks in a galley, with potable water as will be described in detail below. <FIG> only schematically shows the arrangement of the system <NUM> in the aircraft <NUM>, and several types of arrangements are conceivable.

The water supply and distribution system <NUM> comprises a central water tank <NUM> which is provided with a connector <NUM> at its bottom, and the connector <NUM> being connected to a supply line <NUM> which is arranged in this exemplary embodiment in such a manner in the aircraft <NUM> that it includes an angle α with the horizontal <NUM> when the aircraft <NUM> is on the ground and in a horizontal position, and generally the supply line <NUM> is inclined downwards to a fill/drain coupling <NUM> which is provided with a valve <NUM> and which is arranged at the free end of the supply line <NUM>. The valve <NUM> is connected to a control unit <NUM> of the system <NUM> and can remotely be controlled such that it can be switched between a closed and an open position.

As can further be taken from <FIG>, the supply line <NUM> connects the fill/drain coupling <NUM> with a central pump <NUM> wherein a filter device <NUM> is arranged in the supply line <NUM> between the connection to the central water tank <NUM> and the central pump <NUM>. Preferably, the central pump <NUM> is configured as a positive displacement pump and further preferred as a gear pump. The filter device <NUM> improves the quality of water by removing or reducing the concentration of particles such as turbidity or microorganisms or other undesirable substances dissolved in the water. The filter device <NUM> may preferably in the form of a sieve filter. More preferably, the filter device <NUM> may comprise a combination of several filter stages or filter principles.

Furthermore, the central pump <NUM> is also connected to the control unit <NUM> and can be operated in a supply mode where it conveys water from its upstream side <NUM> and the supply line <NUM> to its downstream side <NUM> that is connected to a high pressure conduit system <NUM> which will be described in detail below.

The high pressure conduit system <NUM> comprises a plurality of conduits <NUM> connecting the downstream side <NUM> of the central pump <NUM> with the consumer assemblies <NUM>. Moreover, the central pump <NUM> may also be operated in a so-called reverse mode in which it draws water from its downstream side <NUM> and conveys it to its upstream side <NUM> and towards the supply line <NUM>.

The consumer assembly <NUM> shown in <FIG> is configured as a lavatory with a sink <NUM> provided with a faucet <NUM> and a toilet <NUM> as supply devices. Here, it is to be noted that other forms of consumer assemblies are conceivable such as galleys having sinks etc. and that the present invention is not limited to consumer assemblies in the form of lavatories. In particular, since galleys are provided with buffer tanks that have a larger capacity than those of lavatories, the buffer tanks of galleys may play a more important role in the method of the present invention, as will become clear below.

Furthermore, the consumer assembly <NUM> comprises a buffer tank <NUM> having an inlet <NUM> and an outlet <NUM>, the inlet <NUM> being provided with an inlet valve <NUM> which is connected to the control unit <NUM> so that the position of the valve <NUM> can be controlled by the control unit <NUM>. The outlet <NUM> is connected to the faucet <NUM> and the toilet <NUM> via a micro pump <NUM>. As can further be taken from <FIG>, in this preferred embodiment the line connecting in the outlet <NUM> with the toilet <NUM> is also inclined downwards and in this exemplary embodiment includes an angle β with the horizontal <NUM>, when the aircraft <NUM> is horizontally arranged on the ground. In general, the outlet <NUM> is arranged at a higher level than the toilet <NUM>. This ensures that when the valve of the toilet <NUM> is open, the buffer tank <NUM> may completely be emptied via the toilet <NUM>. However, it is also conceivable that when such configuration with a supply device at a lower level than the outlet of the buffer tank cannot be achieved a pneumatic drainage process is conducted, to empty the buffer tank.

Finally, the buffer tank <NUM> is provided with a level sensor <NUM> which is connected to the control unit <NUM> and configured such that it provides a signal to the control unit <NUM> indicating the fill level in the buffer tank <NUM>.

Furthermore, the inlet <NUM> of the buffer tank <NUM> is connected to the downstream side of the central pump <NUM> via the high pressure conduit system <NUM> including the conduits <NUM>. When the aircraft <NUM> is on the ground, the inlet <NUM> is arranged at a distance in the vertical direction from the bottom of the buffer tank <NUM> with the outlet <NUM>. This arrangement of the inlet <NUM> has the effect that when water is drawn out of the buffer tank <NUM> via the inlet <NUM> by means of the central pump <NUM> when being operated in the reverse mode, the buffer tank <NUM> cannot entirely be emptied and particles which have sedimented at the bottom of the buffer tank <NUM> are not drawn out of the tank <NUM> and conveyed towards the pump <NUM>. Instead, these particles can only be removed from the buffer tank <NUM> via the outlet <NUM>.

As apparent from the above the consumer assemblies <NUM> comprise not just a sole supply device. Instead, several supply devices are provided and connected with a sole buffer tank <NUM> which supplies the supply devices with water and there single conduit <NUM> connecting the consumer assembly <NUM> with the pump <NUM> of the system.

Finally, in this exemplary embodiment the filter device <NUM> is provided with a device to monitor the pressure drop between the upstream side and the downstream side of the filter device <NUM>. In this preferred embodiment the monitoring device for the pressure drop comprises a first pressure sensor <NUM> and a second pressure sensor <NUM>, the first sensor <NUM> being arranged upstream the filter device <NUM> whereas the second sensor is arranged downstream the filter device <NUM> at the side pointing towards the central pump <NUM>. Each of the sensors <NUM>, <NUM> are connected to the control unit <NUM> which is configured such that during operation of the central pump <NUM> in the supply mode, it collects the signals generated by the sensors <NUM>, <NUM> so as to generate a further signal representative of the pressure drop across the filter device <NUM> and, hence, the flow rate across the filter device <NUM>. When this further signal is outside a predetermined range representing a normal condition of the filter device <NUM> resulting in an acceptable flow rate, the control unit <NUM> will activate the reverse mode of the central pump <NUM>. However, this activation of the reverse mode may not necessarily take place immediately upon detection that the further signal has left the predetermined range. It is also conceivable that the reverse mode will be activated with a certain delay or when the aircraft <NUM> has reached a condition where no demand for water in the consumer assemblies <NUM> can be expected, e.g., when the aircraft is on the ground. However, it is also conceivable that the filter backwash step is performed during flight at time periods in which only small fresh water demands are expected.

The control unit <NUM> of the system <NUM> is configured such that it operates the system <NUM> and especially the central pump <NUM> in this exemplary embodiment in the following manner:
In a first step during a first time interval the length of which is not fixed, the central pump <NUM> is constantly or intermittently operated in the supply mode so that water from the central tank <NUM> is delivered to the consumer assemblies <NUM> and their buffer tanks <NUM>, which are connected to the downstream side <NUM> of the pump <NUM> via the high pressure conduit system <NUM>, so that the buffer tanks <NUM> of the at least one consumer assembly are filled. In particular, in this step the inlet valves <NUM> of those consumer assemblies <NUM> the buffer tanks <NUM> of which shall be filled are at the same time or a subsequently brought into its open position. The level in the buffer tanks <NUM> may be monitored by means of the level sensors <NUM>.

In this exemplary embodiment, during this first step the outlet valve <NUM> on the fill/drain coupling <NUM> is kept in the closed position by the control unit <NUM>, and the control unit <NUM> generates the further signal representative of the flow rate of water through the filter device <NUM> from the signals of the first and second pressure sensors <NUM>, <NUM>, which signals are representative for the pressure drop across the filter device <NUM> from which it can be concluded to the respective flow rate. The control unit <NUM> is further configured such that it monitors this further signal and when it is outside the predetermined range representative of an acceptable flow rate through the filter device <NUM>, it is switched, optionally with a delay, to the second step.

In this respect, it is to be noted that other criteria to initiate the second step may be applied. In particular, It is conceivable that the second step is initiated when.

In the second step the central pump <NUM> is operated in the reverse mode by the control unit <NUM> for a second time interval. When being operated in the reverse mode and when the inlet valve <NUM> of at least one of the filled buffer tanks <NUM> is being brought in the open position by the control unit <NUM>, the central pump <NUM> draws water from the buffer tanks <NUM> of the consumer assemblies <NUM> towards its downstream side <NUM> and conveys it to its upstream side <NUM>. When the level sensor <NUM> of the respective buffer tank <NUM> indicates that the level in tank is below the level of the inlet <NUM>, the inlet valve <NUM> of this tank <NUM> is closed by the control unit <NUM> and the inlet valve <NUM> of another tank <NUM> previously being filled is opened.

In the preferred embodiment described herein the water is further conveyed through the fill/drain coupling <NUM> with the valve <NUM> being brought into the open position by the control unit <NUM>. However, it is also conceivable that during the step of operating the pump <NUM> in the reverse mode, water is conveyed from the buffer tanks <NUM> to the central water tank <NUM> with the valve <NUM> being in the closed position.

In <FIG> the section with the filter device <NUM> of a second embodiment of a water supply and distribution system <NUM> for an aircraft is shown. This embodiment is almost identical to the above-described embodiment and differs only in the configuration and the arrangement of the filter device <NUM>. It can be seen in <FIG> that different from the above described embodiment the filter device <NUM> comprises a filter outlet <NUM> which connects the upstream side of the filter device <NUM> where particles etc. are accumulated and the filter cake is formed, with the outside. Further, in the conduit of the filter outlet <NUM> a filter outlet valve <NUM> is provided which is also connected to the control unit <NUM> and configured such that it can be switched between an open position and a closed position by the control unit <NUM>. Similar to the aforementioned embodiment first and second pressure sensors <NUM>, <NUM> are provided on the upstream and the downstream side, respectively of the filter device <NUM>, so that also in this embodiment the flow rate across the filter device <NUM> may be determined by the control unit <NUM>.

Furthermore, as schematically shown in <FIG> the filter device <NUM> is arranged such in the supply line <NUM>, that the sections of the supply line <NUM> connecting the filter device <NUM> with the central water tank <NUM> and the upstream side <NUM> of the central pump <NUM> are inclined, so that the filter device <NUM> is at a lower level than both the upstream side <NUM> of the central pump <NUM> and the connector <NUM> of the central water tank <NUM>. In particular, both of these sections include an angle γ with the horizontal <NUM>. With this arrangement of the sections of the supply line <NUM> it is achieved that when the filter outlet valve <NUM> is in the open position water within the sections of the supply line <NUM> connecting the filter device <NUM> with the central water tank <NUM> and the central pump <NUM> automatically flows out of the filter outlet <NUM>.

The second embodiment of a water supply and distribution system is operated almost in the same manner as the first embodiment. However, when the central pump <NUM> is operated in the reverse mode, the filter outlet valve <NUM> is controlled such by the control unit <NUM> that it is in the open position, so that in the backwash-step water containing the filter cake is expelled via the filter outlet <NUM> and not guided it to the central water tank or the fill/drain coupling <NUM>.

Thus, the method according to the present invention allows to clean the upstream side of the filter device <NUM> after relatively short periods of normal use so that the amount of particles which have accumulated in the filter device <NUM> may be kept at a relatively low level. Hence, only in a minor reduction of the performance of the system <NUM> occurs between the subsequent cleaning steps applied on the filter device <NUM>.

Claim 1:
A method for operating an on-board water supply and distribution system (<NUM>) of an aircraft (<NUM>) for supplying water, the system comprising
a central water tank (<NUM>),
a plurality of consumer assemblies (<NUM>), each consumer assembly (<NUM>) comprising a supply device and a buffer tank (<NUM>) and each consumer assembly (<NUM>) being configured to supply water from the buffer tank (<NUM>) via the supply device,
a pump (<NUM>) having an upstream side (<NUM>) and a downstream side (<NUM>) and being configured such that it may operate in a supply mode and a reverse mode,
a filter device (<NUM>), and
a high pressure conduit system (<NUM>),
wherein the central water tank (<NUM>) is connected to the upstream side (<NUM>) of the pump (<NUM>) with the filter device (<NUM>) being arranged between the central water tank (<NUM>) and the upstream side (<NUM>),
wherein the high pressure conduit system (<NUM>) connects the downstream side (<NUM>) with the plurality of consumer assemblies (<NUM>), with the conduit system (<NUM>) being configured such that the pump (<NUM>), when operating in the supply mode, is capable of delivering water from the downstream side (<NUM>) to the buffer tank (<NUM>) of each of the consumer assemblies (<NUM>),
wherein, when the pump (<NUM>) is operating in the reverse mode, it is capable of conveying water from the downstream side (<NUM>) to the upstream side (<NUM>),
the method comprising the following steps:
operating the pump (<NUM>) in the supply mode so that water from the central tank (<NUM>) is delivered to at least one of the consumer assemblies (<NUM>) in a first time interval wherein the buffer tank (<NUM>) of the at least one consumer assembly (<NUM>) is filled, and
operating the pump (<NUM>) in the reverse mode in a second time interval so that water from the buffer tank (<NUM>) of the at least one of the consumer assemblies (<NUM>) passes through the filter device (<NUM>).