Patent Description:
Hot water storage devices known from prior art comprise a tank configured to store water, wherein the tank has a bottom wall, a top wall and a side wall extending between the bottom wall and the top wall. Hot water storage devices known from prior art further comprise a heating unit positioned at a first distance from the bottom wall, wherein the heating unit is configured to heat the water stored within the tank, namely in such a manner that water heated by the heating unit rises up within the tank such that the heated water is stratified above unheated water within the tank. Hot water storage devices known from prior art further comprise a temperature sensor positioned at a distance from the bottom wall, the temperature sensor being configured to measure a water temperature of the heated water. Hot water storage devices known from prior art further comprise a controller being configured to control the heating unit and thereby the water temperature of the heated water stored within the tank. Heating of the water within the tank may be initiated when the temperature of the water within the tank falls under a respective threshold.

<CIT>, <CIT>, <CIT>, <CIT> and <CIT> disclose hot water storage devices.

Controllers of a hot water storage devices known form prior art keep permanently a defined water volume within the tank of the hot water storage device at a defined hot water temperature, either <NUM> hours per day and <NUM> days per week or according to a daily ON/OFF schedule of the hot water storage device when the hot water storage device is in the ON status. Keeping the defined water volume within the tank of the hot water storage device permanently at a defined hot water temperature is energy inefficient and creates carbon emissions when no actual hot water demand is present.

<CIT> and <CIT> disclose further prior art.

Against this background a novel method to operate a hot water storage device as defined in claim <NUM> and a novel controller of a hot water storage device as defined in claim <NUM> as well as a novel hot water storage device as defined in claim <NUM> are provided that allow an energy efficient operation of a hot water storage device with lower carbon emissions.

The method according to claim <NUM> determines from a water temperature measurement signal provided by the at least one temperature sensor a water usage profile, said water usage profile providing for defined time intervals of a day and/or for defined days of a week a nominal temperature and a nominal volume of the heated water to be stored within the tank.

The method according to claim <NUM> operates the heating unit in such a manner that for each defined time interval of a day and/or for each defined day of a week the actual temperature and the actual volume of the heated water stored withing the tank corresponds automatically to the respective nominal value of the water usage profile.

According to claim <NUM>, for each respective time interval of each respective day a confidence factor associated with the nominal temperature and the nominal volume of the heated water to be stored within the tank is determined, wherein the confidence factor depends on the frequency and from the amount of a hot water demand in the respective time interval of the respective day. Based on the confidence factor the nominal value pair used for the operation of the hot water storage device may be changed.

According to a first alternative, the at least one water temperature measurement signal provided by the at least one temperature sensor is provided to a database like a cloud-database, wherein the database determines the water usage profile providing for each respective time interval of a respective day of a week the nominal temperature and the nominal volume of the heated water to be stored within the tank, and wherein the controller operates the heating unit of basis of said water usage profile provided by the database to the controller. In the first alternative, the functionality of the method is split up between the database and the controller.

According to a second alternative, the at least one water temperature measurement signal provided by the at least one temperature sensor is provided to the controller, wherein the controller determines the water usage profile providing for each respective time interval of a respective day of a week the nominal temperature and the nominal volume of the heated water to be stored within the tank, and wherein the controller operates the heating unit of basis of said water usage profile. In the second alternative, the functionality of the method is provided by the controller only.

The controller of the hot water storage device according to claim <NUM> is configured to determine from a water temperature measurement signal provided by the at least one temperature sensor of the hot water storage device a water usage profile, said water usage profile providing for defined time intervals of a day and/or for defined days of a week a nominal temperature and a nominal volume of the heated water to be stored within the tank.

The controller of the hot water storage device according to claim <NUM> is configured to operate the heating unit of the hot water storage device in such a manner that for each defined time interval of a day and/or for each de-fined day of a week the actual temperature and the actual volume of the heated water stored withing the tank of the hot water storage device corresponds automatically to the respective nominal value of the water usage profile.

The controller of the hot water storage device according to claim <NUM> is configured to determine for each respective time interval of each respective day a confidence factor associated with the nominal temperature and the nominal volume of the heated water to be stored within the tank, wherein the confidence factor depends on the frequency and the amount of a hot water demand in the respective time intervals of the respective day.

The method as well as the controller of the hot water storage device according to the present disclosure allow an energy efficient operation of a hot water storage device with lower carbon emissions. The water usage profile is determined from the water temperature measurement signal provided by the at least one temperature sensor. Said water usage profile provides for each respective time interval of a day and for each respective day of a week the nominal temperature and the nominal volume of the heated water to be stored within the tank. So, the water usage profile does not only provide a nominal value for the water temperature but also a nominal value for the volume of the heated water to be stored within the tank.

Preferably, the water usage profile is determined from a first water temperature measurement signal provided by a first temperature sensor positioned at a second distance from the bottom wall of the tank and from a second water temperature measurement signal provided by the second temperature sensor positioned at a third distance from the bottom wall of the tank and/or from an average water temperature signal of the first water temperature measurement signal and the second water temperature measurement signal, wherein said second distance is greater than said first distance and said third distance is greater than said second distance. This allows an even more precise control of the temperature and of the volume of the heated water within the tank to provide an energy efficient operation of a hot water storage device with lower carbon emissions.

Preferably, the water usage profile is determined as a function of a change rate of the at least one water temperature measurement signal in the respective time interval of the respective day and/or as a function of a frequency and as a function of an amount of a hot water demand in the respective time interval of the respective day. This allows to determine the water usage profile in a reliable and simple manner.

Preferably, the water usage profile is determined in such a manner that for each respective time interval of each respective day of a week a nominal value pair comprising the nominal temperature and the nominal volume of the heated water to be stored within the tank is determined, namely a nominal value pair N of a set of nominal value pairs comprising at least the following nominal value pairs: pair <NUM>: first nominal volume and first nominal temperature, pair <NUM>: first nominal volume and second nominal temperature, pair <NUM>: second nominal volume and first nominal temperature, pair <NUM>: second nominal volume and second nominal temperature, wherein the second nominal volume is greater than the first nominal volume, and wherein the second nominal temperature is greater than the first nominal temperature. The set of nominal value pairs on basis of which the water usage profile for each respective time interval of each respective day of a week is determined may comprise the following additional nominal value pair: pair <NUM>: third volume and second nominal temperature, wherein the third nominal volume is greater than the second nominal volume. The set of nominal value pairs on basis of which the water usage profile for each respective time interval of each respective day of a week is determined may comprise the following additional nominal value pair: pair <NUM>: fourth volume and fourth nominal temperature, wherein the fourth nominal volume is smaller than the first nominal volume and the fourth nominal temperature is smaller than the first nominal temperature. Pair <NUM> may correspond to on OFF status or STANDBY status of the hot water storage device <NUM>. Pairs <NUM> to <NUM> all belong to an ON status of the hot water storage device <NUM>. With pairs <NUM> to <NUM> a respective volume of heated water is stratified above unheated water within the tank. With pair <NUM> the tank may become de-stratified such that the full volume of the tank is filled with heated water. This allows an simple and reliable, energy efficient operation of a hot water storage device with lower carbon emissions using a limited number of nominal value pairs defining the nominal temperature and the nominal volume of the heated water to be stored within the tank.

Preferably, the confidence factor of a respective time interval is increased if the frequency of hot water demands and/or the amount of a hot water demand in the respective time interval is above a respective upper threshold within the respective time interval of the respective day. The confidence factor of a respective time interval is decreased if the frequency of hot water demands and/or the amount of a hot water demand in the respective time interval is below a respective lower threshold within the respective time interval of the respective day. The confidence factor of a respective time interval remains unchanged if the frequency of hot water demands and/or the amount of a hot water demand in the respective time interval is above a respective lower threshold and below the respective upper threshold. A change of the confidence factor of a respective time interval of a respective day may affect the confidence factor of time intervals adjoining the respective time interval in which the confidence factor has changed. Such a confidence factor allows a simple and reliable change of the nominal value pair used in a respective time interval to control temperature and volume of heated water stored within the tank of the hot water storage device and to provide an energy efficient operation of a hot water storage device with lower carbon emissions.

Preferably at an initial state or at an initialization state of the hot water storage device, the water usage profile of each time interval of each day is initialized with the pair N (N=<NUM> or <NUM> or <NUM>) of the nominal value pairs, preferably with pair <NUM>. If the confidence factor of the respective time interval of the respective day is below a lower limit, then the water usage profile of the respective time is changed to pair N-<NUM> of the nominal value pairs. If the confidence factor of the respective time interval of the respective day is above an upper limit, then the water usage profile of the respective time interval is changed to pair N+<NUM> of the nominal value pairs. If the confidence factor of the respective time interval of the respective day is above the lower limit and below the upper limit, then the water usage profile of the respective time interval remains at pair N of the nominal value pairs. This allows an simple and reliable change of the nominal value pair used in a respective time interval to control temperature and volume of the heated water within the tank to provide an energy efficient operation of a hot water storage device with lower carbon emissions.

Further on, a hot water storage device as defined in the claim <NUM> having such a controller is provided.

Preferred developments of the invention are provided by the dependent claims and the description which follows. Exemplary embodiments are explained in more detail on the basis of the drawing, in which:.

<FIG> shows a hot water storage device <NUM>. The water hot storage device <NUM> comprises a tank <NUM> configured to store water. The tank <NUM> of the hot water storage device <NUM> has a bottom wall <NUM>, a top wall <NUM> and a side wall <NUM> extending between the bottom wall <NUM> and the top wall <NUM>.

The hot water storage device <NUM> further comprises a heating unit <NUM> positioned at a first distance from the bottom wall <NUM> of the tank <NUM>. The heating unit <NUM> is configured to heat the water stored within the tank <NUM> in such a manner that water heated by the heating unit <NUM> rises up within the tank <NUM> such that the heated water is stratified above unheated water within the tank <NUM>.

<FIG> shows a pipe <NUM> through which heated water can be taken out of the tank <NUM> in order to provide the heated water to a hot water consumer <NUM>. The pipe <NUM> is connected to the top wall <NUM> or to the side wall <NUM> adjacent to the top wall <NUM>. <FIG> further shows a pipe <NUM> through which unheated water can be provided to the tank <NUM> in order to replace the volume of water which has been taken out of the tank <NUM> through the pipe <NUM>. The pipe <NUM> is connected to the bottom wall <NUM> or to the side wall <NUM> adjacent to the bottom wall <NUM>.

The hot water storage device <NUM> further comprises at least one temperature sensor <NUM>, <NUM> positioned at a distance from the bottom wall <NUM>, wherein the at least one temperature sensor <NUM>, <NUM> is configured to measure a water temperature of the heated water stored within the tank <NUM>.

In the preferred embodiment shown in <FIG>, the hot water storage device <NUM> comprises a first temperature sensor <NUM> positioned at a second distance from the bottom wall <NUM> of the tank <NUM>, said second distance being greater that said first distance, and a second temperature sensor <NUM> positioned at a third distance from the bottom wall <NUM> of the tank <NUM>, said third distance being greater that said second distance. Both temperature sensors <NUM>, <NUM> are assigned to the side wall <NUM> of the tank. Both temperature sensors <NUM>, <NUM> are configured to measure a water temperature of the heated water stored within the tank <NUM>.

The hot water storage device <NUM> further comprises a controller <NUM>. The controller <NUM> is configured to control the heating unit <NUM> and thereby the water temperature of the water stored within the tank <NUM>.

The controller <NUM> provides a control signal to the heating unit <NUM> in order to control the operation of the heating unit <NUM> of the hot water storage device <NUM>.

The controller <NUM> is configured to receive a respective water temperature measurement signal from the respective temperature sensor <NUM>, <NUM>.

<FIG> further shows an optional recirculation pipe <NUM> extending between the pipe <NUM> and the tank <NUM>. A pump <NUM> is assigned to the recirculation pipe <NUM>. The pump <NUM> and recirculation pipe <NUM> may be used to recirculate the heated water taken out of the tank <NUM> through the tank <NUM>. The recirculation pipe <NUM> is connected to the bottom wall <NUM> or to the side wall <NUM> adjacent to the bottom wall <NUM>. With the pump <NUM> the water within the tank <NUM> may be de-stratified.

Controllers of a hot water storage device known form prior art keep permanently a de-fined water volume within the tank of the hot water storage device at a defined hot water temperature, either <NUM> hours per day and <NUM> days per week or according to a daily ON/OFF schedule of the hot water storage device when the same is in the ON status. Keeping the defined water volume within the tank of the hot water storage device permanently at a defined hot water temperature is energy inefficient and creates carbon emissions when no actual hot water demand is present.

According to the present disclosure, the controller <NUM> of the hot water storage device <NUM> is configured to determine from a water temperature measurement signal provided by at least one temperature sensor <NUM>, <NUM> a water usage profile, said water usage profile providing for defined time intervals of a day and/or for defined days of a week a nominal temperature and a nominal volume of the heated water to be stored within the tank <NUM> of the hot water storage device <NUM>.

Preferably, the controller <NUM> is configured to determine from a first water temperature measurement signal provided by the first temperature sensor <NUM> and from a second water temperature measurement signal provided by the second temperature sensor <NUM> and/or from an average water temperature signal of the first water temperature measurement signal and the second water temperature measurement signal the water usage profile providing for defined time intervals of a day and/or for defined days of a week the nominal temperature and the nominal volume of the heated water to be stored within the tank <NUM> of the hot water storage device <NUM>.

The controller <NUM> according to the present disclosure is configured to operate the heating unit <NUM> of the hot water storage device <NUM> in such a manner that for each defined time interval of a day and/or for each defined day of a week the actual temperature and the actual volume of the heated water stored withing the tank <NUM> of the hot water storage device <NUM> corresponds automatically to the respective nominal value of the water usage profile.

The controller <NUM> of the hot water storage device <NUM> according to the present disclosure allows an energy efficient operation of a water storage device with lower carbon emissions.

If the controller <NUM> is configured to determine the water usage profile, the functionality of the present disclosure is provided by the controller <NUM> only. In this case the at least one water temperature measurement signal provided by the at least one temperature sensor <NUM>, <NUM> is provided to the controller <NUM>, wherein the controller <NUM> determines the water usage profile providing for each respective defined time interval of a respective day of a week the nominal temperature and the nominal volume of the heated water to be stored within the tank, and wherein the controller <NUM> operates the heating unit <NUM> of basis of said water usage profile.

Alternatively, the functionality of the present disclosure may be split up between the controller <NUM> and a database <NUM> like a cloud database. In this alternative, the at least one water temperature measurement signal provided by the at least one temperature sensor <NUM>, <NUM> is provided to the database <NUM> preferably through the controller <NUM>, wherein the database <NUM> determines the water usage profile providing for each respective defined time interval of a respective day of a week the nominal temperature and the nominal volume of the heated water to be stored within the tank, and wherein the controller <NUM> operates the heating unit <NUM> of basis of said water usage profile provided by the database <NUM> to the controller <NUM>.

<FIG> shows the tank <NUM> in different conditions, The conditions can be provided with the method and controller <NUM> of the present disclosure.

In condition I of <FIG>, the tank <NUM> stores a first volume V1 of heated water being stratified above unheated water within the tank <NUM>. In condition I of <FIG>, the volume V1 has a size that the first, lower temperature sensor <NUM> measures the temperature of the unheated water and the second, upper temperature sensor <NUM> measures the temperature of the heated water. The second, upper temperature sensor <NUM> measures the temperature of the heated water of volume V1 in a lower section of volume V1, preferably adjacent to or abutting a lower boundary surface of volume V1. In condition I of <FIG>, the heated water being present at the first volume V1 may have a first, relative low temperature T1 of example given <NUM> or a second, relative high temperature T2 of example given <NUM>.

In condition II of <FIG>, the tank <NUM> stores a second volume V2 of heated water being stratified above unheated water within the tank <NUM>. The second volume is greater than the first volume. In condition II of <FIG>, the volume V2 has a size that the first, lower temperature sensor <NUM> and the second, upper temperature sensor <NUM> both measure the temperature of the heated water. The first, lower temperature sensor <NUM> measures the temperature of the heated water of volume V2 in a lower section of volume V2, preferably adjacent to or abutting a lower boundary surface of volume V2. In condition II of <FIG>, the heated water being present at the first volume V2 may have the first, relative low temperature T1 of example given <NUM> or the second, relative high temperature T2 of example given <NUM>.

In both conditions I and II of <FIG>, the heated water of the respective volume V1, V2 is stratified above unheated water within the tank <NUM>.

In condition III of <FIG>, the tank <NUM> stores a third volume V3 of heated water occupying the entire volume of the tank <NUM>. In condition III of <FIG>, no unheated water is present within the tank <NUM> and the tank <NUM> is de-stratified. In condition III of <FIG>, the first, lower temperature sensor <NUM> and the second, upper temperature sensor <NUM> both measure the temperature of the heated water. In condition III of <FIG>, the heated water being present at the first volume V3 has the second, relative high temperature T2 of example given <NUM>.

Depending on the above combination of the volumes V1, V2, V3 of the heated water within the tank <NUM> and the temperatures T1, T2 the tank <NUM> may have different conditions in case the hot water storage device <NUM> is in an ON status. A sixth condition may be the OFF status of hot water storage device10.

The controller <NUM> of the hot water storage device10 may be configured to determine the water usage profile as a function of the change rate of the at least one water temperature measurement signal in the respective time interval of the respective day. The controller <NUM> may further be configured to determine the water usage profile as a function of a frequency and as a function of an amount of a hot water demand in the respective time intervals of the respective day.

The controller <NUM> of the hot water storage device <NUM> may be configured to determine the water usage profile in such a manner that for each respective time interval of each respective day of a week a nominal value pair comprising the nominal temperature and the nominal volume of the heated water to be stored within the tank <NUM> is determined, namely a nominal value pair of a set of nominal value pairs comprising at least:.

The second nominal volume of the heated water to be stored in the tank <NUM> is greater than the first nominal volume of the heated water to be stored in the tank <NUM>. The second nominal temperature of the heated water to be stored in the tank <NUM> is greater than the first nominal temperature of the heated water to be stored in the tank <NUM>.

Pairs <NUM> and <NUM> may be used to provide condition I of <FIG>, namely pair <NUM> a first volume V1 of heated water having the first temperature T1 and pair <NUM> a first volume V1 of heated water having the second temperature T2.

Pairs <NUM> and <NUM> may be used to provide condition II of <FIG>, namely pair <NUM> a second volume V2 of heated water having the first temperature T1 and pair <NUM> a second volume V2 of heated water having the second temperature T2.

The nominal value pairs on basis of which the water usage profile for each respective time interval of each respective day of a week is determined may comprise the following additional nominal value pair:
Pair <NUM>: third nominal volume and second nominal temperature.

The third nominal volume is greater than the second nominal volume.

Pair <NUM> may be used to provide condition III of <FIG>, namely a third volume V3 of heated water having the second temperature T2.

The second nominal volume and thereby the second volume V2 is greater than the first nominal volume and thereby the first volume V1. A ratio R2/<NUM> between the second nominal volume and thereby the second volume V2 and the first nominal volume and thereby the first volume V1 may be from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>. The third nominal volume and thereby the third volume V3 is greater than the first and second nominal volume and thereby the first volume V1 and second volume V2. A ratio R3/<NUM> between the third nominal volume and thereby the third volume V3 and the first nominal volume and thereby the first volume V1 may be from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>. In any case the ratio R3/<NUM> is greater than the ratio R2/<NUM>. In an embodiment the ratio R2/<NUM> may be <NUM>:<NUM> and the ratio R3/<NUM> may be <NUM>:<NUM>. These ratios are of exemplary nature.

The nominal value pairs on basis of which the water usage profile for each respective time interval of each respective day of a week is determined may comprise the following additional nominal value pair:
Pair <NUM>: fourth nominal volume and fourth nominal temperature.

The fourth nominal volume is smaller than the first nominal volume and fourth nominal temperature is smaller than the first nominal temperature.

Pair <NUM> may be used to provide as sixth condition of the hot water storage device10 corresponding preferably to the OFF status or STANDBY status of hot water storage device <NUM> in which no heated water in stored with the tank <NUM> of the hot water storage device <NUM>.

The water usage profile based on nominal value pairs may also be determined by the database <NUM>.

The controller <NUM> of the hot water storage device <NUM> is configured to determine for each respective time interval of each respective day a confidence factor associated with the nominal temperature and the nominal volume of the heated water to be stored within the tank <NUM>.

The confidence factor depends on the frequency and from the amount of a hot water demand in the respective time interval of the respective day. The amount of a hot water demand corresponds to the duration of the same or to the volume of heated water taken out of the tank <NUM> in connection with the respective hot water demand. The amount of the hot water demand may be determined on basis of the time needed to replace the heated water taken out of the tank, namely to recover the hot volume and temperature of the water within the tank according to the nominal volume and nominal temperature.

The controller <NUM> of the hot water storage device <NUM> is configured to increase the confidence factor of a respective time interval if the frequency of hot water demands and/or the amount of a hot water demand in the respective time interval is above a respective upper threshold.

The controller <NUM> of the hot water storage device <NUM> is configured to decrease the confidence factor of a respective time interval if the frequency of hot water demands and/or the amount of a hot water demand in the respective time interval is below a respective lower threshold.

The controller <NUM> of the hot water storage device <NUM> is configured to remain the confidence factor of a respective time interval unchanged if the frequency of hot water demands and/or the amount of a hot water demand in the respective time interval is above a respective lower threshold and below the respective upper threshold.

The confidence factor of the respective time intervals may also be determined by the database <NUM>.

A change of the confidence factor of a respective time interval of a respective day may affect the confidence factor of time intervals adjoining the respective time interval in which the confidence factor has changed on basis of a weight factor. Example give, if the confidence factor of a time interval may change by <NUM>%, the confidence factor of time intervals adjoining said respective time interval may change by <NUM>% if a weight factor of <NUM>% is used or by <NUM>% if a weight factor of <NUM>% is used.

At an initial state or at an initialization state of the hot water storage device <NUM>, the water usage profile of each time interval of each day is initialized with the pair N (N=<NUM> or <NUM> or <NUM>) of the nominal value pairs. Preferably, the water usage profile of each time interval of each day is initialized with the pair <NUM>, meaning that for each time interval of each day the controller <NUM> would use the second nominal volume and the second nominal temperature to control the volume and temperature of the heated water within the tank <NUM>.

During operation of the hot water storage device <NUM> the confidence factor is determined as described above as a function of the frequency and as a function of the amount of a hot water demand in the respective time intervals of the respective day. The amount depends on the change rate of the respective water temperature measurement signal and preferably the time to recover the heated water within the tank <NUM> according to the nominal volume and nominal temperature.

If the confidence factor of the respective time interval of the respective day is below a lower limit, the water usage profile of said time interval is changed from pair N to pair N-<NUM>. In other words, if the initialized nominal value pair or actual nominal value pair of a respective time internal is pair <NUM> but the confidence factor of said respective time interval is below the lower limit, pair <NUM> is used as new nominal value pair for said respective time internal. If there is no pair N-<NUM> available, the actual pair is preferably remained unchanged. There may be a factor in the above learning algorithm that provides a time-based decay or forgetfulness. This would allow the confidence factor to reduce over time if there is no water usage over a certain time frame. A rate of memory loss produced by this decay or forgetfulness may depend on the implementation of the hot water storage device <NUM> in the field.

If the confidence factor of the respective time interval of the respective day is above an upper limit, the water usage profile of said time interval is changed from pair N to pair N+<NUM>. In other words, if the initialized nominal value pair or actual nominal value pair of a respective time internal is pair <NUM> but the confidence factor of said respective time interval is above the upper limit, pair <NUM> is used as new nominal value pair for said respective time internal. If there is no pair N+<NUM> available, the actual pair is remained unchanged.

If the confidence factor of the respective time interval of the respective day is above the lower limit and below the upper limit, the water usage profile of said time interval is remained at pair N. In other words, if the initialized nominal value pair or actual nominal value pair of a respective time internal is pair <NUM> and the confidence factor of the respective time interval of the respective day is above the lower limit and below the upper limit, pair <NUM> is kept unchanged as nominal value pair for said respective time internal.

<FIG> shows a detail of a water usage profile <NUM> for six individual time intervals <NUM> of the water usage profile <NUM>. In <FIG>, each time interval has a duration of <NUM> minutes. The time intervals <NUM> may have a longer or shorter duration than <NUM> minutes. <FIG> further shows actual nominal value pairs <NUM> for each of the time intervals <NUM> defining the nominal temperature and the nominal volume of the heated water to be stored within the tank <NUM>. Pair <NUM> is valid for time intervals 31a, 31b. Pair <NUM> is valid for time intervals 31c, 31d, 31e. Pair <NUM> is valid for time intervals 31c. <FIG> further shows actual confidence factors <NUM> determined for each time intervals <NUM>. For time interval 31a the confidence factor of <NUM>% as been determined which may cause a subsequent change to pair <NUM> for time interval 31a. For time interval 31f the confidence factor of <NUM>% as been determined which may cause a subsequent change to pair <NUM> for time interval 31f.

<FIG> shows an average water temperature signal <NUM> determined from said first and second water temperature measurement signals provided by said first and second temperature sensors <NUM>, <NUM>. At times t1, t2 the respective change rate of the average water temperature signal <NUM> is relatively small but higher that a change rate caused by thermal losses of the tank <NUM>. This is determined as a relatively small amount of a hot water demand in the respective time interval of the respective day. At time t3 the respective change rate of the average water temperature signal <NUM> is relatively high. This is determined as a relatively large amount of a hot water demand in the respective time interval of the respective day. Depending on the amount and frequency of such water demands the confidence factor <NUM> is determined for each time interval <NUM>. The amount of a water demand may be determined on basis of the time needed to recover the water within the tank according to the nominal volume and nominal temperature.

The controller <NUM> defines both the temperature and volume of the heated water within the tank <NUM> of the water storage device on basis of the determined water usage profile. At a peak demand (corresponding to nominal value pair <NUM>) the water of the whole volume V3 of the tank <NUM> is heated up to temperature T2 using the pump <NUM>. This state elevates the thermal energy stored within the tank <NUM> above the normal maximum capacity of the tank <NUM>. This state may be initiated by external factors like communicated energy tariffs from the cloud.

At time intervals with a small hot water demand a smaller volume V1 at the first temperature T1 is sufficient (corresponding to nominal value pair <NUM>). The hot water storage device <NUM> minimizes the energy required to heat the water and minimizes heat loss over time as well as an energy inefficient operation of the hot water storage device <NUM>. The hot water storage device <NUM> can be operated very energy efficiently with lower carbon emissions. Based on the detected water usage (see <FIG>) which influences the confidence factor <NUM> a learned pattern of nominal value pairs <NUM> is built up which is used to operate the hot water storage device <NUM> over time.

Claim 1:
Method to operate a hot water storage device (<NUM>), the hot water storage device (<NUM>) comprising
a tank (<NUM>) configured to store water,
a heating unit (<NUM>) positioned at a first distance from a bottom wall (<NUM>) of the tank (<NUM>), the heating unit (<NUM>) being configured to heat the water stored within the tank (<NUM>) such that heated water rises up within the tank (<NUM>) and is stratified above unheated water within the tank (<NUM>),
at least one temperature sensor (<NUM>, <NUM>) positioned at a distance from the bottom wall (<NUM>) of the tank (<NUM>) being greater than said first distance,
a controller (<NUM>) configured to control the heating unit (<NUM>),
the method comprising the following steps:
determine from a water temperature measurement signal provided by the at least one temperature sensor (<NUM>, <NUM>) a water usage profile, said water usage profile providing for defined time intervals of a day and/or for defined days of a week a nominal temperature and a nominal volume of the heated water to be stored within the tank, wherein the water usage profile is determined on basis of a frequency and of an amount of a hot water demand in the respective time intervals of the respective day,
operate the heating unit (<NUM>) in such a manner that for each defined time interval of a day and/or for each defined day of a week the actual temperature and the actual volume of the heated water stored withing the tank corresponds automatically to the respective nominal value of the water usage profile,
characterized by the following step:
determine for each respective time interval of each respective day a confidence factor associated with the nominal temperature and the nominal volume of the heated water to be stored within the tank, wherein the confidence factor depends on the frequency and the amount of a hot water demand in the respective time intervals of the respective day.