EP2366081A2 - Method for minimising energy consumption of a storage water heater - Google Patents

Abstract

Method for managing a storage water heater (1) aimed at reducing thermal dispersions, characterised in that at short time intervals (δw), all the w drawings (P1,..., Pi,..., Pw) are taken into account, the drawing start time (ti) whereof falls within a predetermined time window (Δtw) immediately following the current time; at said drawing start times (ti) comprised in said time window (Δtw), as many fictitious drawings (P' 1,..., P'i,..., P'w) are constructed, each having a fictitious drawing start temperature (T'set.i); for each of said fictitious drawings (P'1,..., P'i,..., P'w), the fictitious heating start time (t'ONi) is calculated; upon reaching the earliest of said heating start times (t'ONi), the target temperature (Ttarget) is set to the fictitious drawing start temperature value (T'set.i) of the corresponding fictitious drawing (P'i) provided that it is not higher than the maximum setup temperature (Tset.max) whereas before said earliest heating start time (t'ONi) is reached, the target temperature (Ttarget) is kept equal to the maintenance temperature (Tstand-by). The method keeps the temperature to the minimum values required to ensure the drawings.

Description

"METHOD FOR MINIMISING ENERGY CONSUMPTION OF A STORAGE WATER HEATER"

DE S CRIP TI ON

The present invention relates to a new method for the management of water preservation temperature in a generic storage water heater controllable by an electronic control. An instant water heater can dispense a hot water flow rate strictly proportional to the thermal power installed. Installing high powers is generally difficult and this poses a limit to the dispensable flow rate.

The advantage of water storage heaters is to be able to dispense very high water flow rates while limiting the thermal power installed. The amount of water that can be dispensed at the usage temperature T_u during a single drawing may be larger than the volume of the storage tank as this is especially kept at a temperature higher than said usage temperature Tu and the water withdrawn is then used mixing it with cold water.

Since storage tanks are expensive and cumbersome it is normal to have a volume as moderate as possible while keeping the storage temperature high (generally 75 °C), whereas the effective usage temperature T₁₁, normally comprised between 35° and 40 °C, is obtained at the usage points through mixing with cold water; however, water is often distributed at higher temperatures than that of usage T_u for compensating cooling along the distribution pipes.

Generally, the selected storage volume is sufficient for fulfilling the largest of the expectable drawings for that specific utility keeping the storage temperature to the maximum possible value while the thermal power installed must be such as to restore a sufficient water reserve for the next drawing. In conclusion, various utility categories correspond to as many models of storage water heaters (hereinafter simply referred to as water heater for shortness). In order to ensure the heaviest service, that is, the largest drawing expected, it is clear that most of the time the water heater is kept to a storage temperature which is uselessly high for most of the remaining drawings.

As a consequence, as known, in storage water heaters the main cause of inefficiency is due to the thermal dispersions that can be even very high and often useless during the whole day, even far-off the drawing time. Therefore, more or less accurate methods easy to be managed by the user have been developed, in order to limit the thermal dispersions while keeping the water heater temperature to the minimum values compatible with the service fulfilment. The minimum requirement for the service to always be met is that the water heater should in any case be kept at a minimum temperature not lower than the usage temperature T_u so as to fulfil small unexpected drawings, and the storage volume should be sufficiently large to ensure the largest drawing expected for that utility while keeping the temperature to the value allowed.

Usually, the drawings have a very uneven pattern during the day, both by consumption time and rate, tending to concentrate in particular times. Hereinafter, drawing pattern, consisting in drawing times and amounts, shall be referred to as drawing profile. If it is true that the drawing profile is very uneven during the day, it is highly repetitive during predetermined time cycles that repeat, equal to one another: in particular for the one week interval. In fact, utility behaviours are little changing so that a typical drawing profile can be recognised for Mondays, Tuesdays, and so on, with, in particular, clear differences between working days and holidays, as well as, of course, for midweek holidays and for holiday periods.

This cyclic nature of the drawing profiles therefore allows expecting them with reasonable certainty and it is therefore possible to carry out methods for controlling the water heater temperature so that it is variable during the day. Each of said repetitive time intervals is hereinafter referred to as drawing cycle. The so-called "small drawings" overlap, usually in a quite random manner, especially in small utilities, to this regularity of more important drawings: small water drawings, for example for rinsing a dish or washing hands, which per se do not imply considerable energy consumptions but may have the effect, well known by the man skilled in the art, of tripping the temperature setting thermostat, with the consequence that the latter thus reaches uselessly higher values with a consequent increase of thermal dispersions.

In order to limit the dispersions, the simple method that has always been used is to enable and disable the heating element by a clock so that the desired temperatures are only ensured within the time period when drawings are expected. Another simple method, less effective from the energy point of view for the user but more economically advantageous for the same, is to actuate the heating element only during any time bands with a lower rate; the water may uselessly be too hot with a certain advance compared to the needs, but in any case it was obtained at relatively low cost. These are methods wherein the adjustment temperature of thermostat T.set is simply set to a fixed value; however, the storage temperature drops because the heating element is forcedly deactivated.

Those methods that allow the storage temperature to change over time in a scheduled manner are more effective for limiting consumptions.

The drawing profile must be known for this to be possible.

Document EP 0 866 282 provides for a device wherein it is possible to program the desired drawing sequence, that is, the drawing profile. The amount of the n drawings envisaged in the time sequence t.l, t.2, ... t.k, ... t.n is recorded by setting for each time t.k the temperature T_set.k deemed able to fulfil the k-th drawing. A limit of the method consists in the difficulty of a correct programming, because the user cannot be aware of the effective drawing times of the hot water or of the effective values T_set.k to set to obtain the desired amount of hot water at the usage temperature T_u. The programming method therefore implies a series of adjustments for tests and errors with the high probability that the user stops correcting the program when he/she assesses that the services is met, but without knowing whether he/she could obtain this with greater efficiency. Another difficulty lies in the fact that the effective time of achievement of the desired temperature depends on the heating time, difficult to assess and in any case variable over time for the same water heater for various reasons, such as scaling, seasonal temperature variations in the room where the water heater is placed, reduction of the effective thermal power of the heating element over time.

The prior document GB 2 146 797, on the other hand, acquires information on the drawing times and amounts through flow and rate sensors for each drawing, the storage temperature at an intermediate value between the minimum and maximum allowed and proportional to the expected drawing volume. The method has the disadvantage of requiring the presence of flow sensors for sensing the drawings; moreover, it does not allow for corrections, meaning that it learns the drawing variability but, assigning an unchangeable temperature to each drawing amount as it is generated by a preset formula, it is not able to correct it if it is too high or too low.

According to document EP 0 356 609, on the other hand, the sequence of the drawing times and of the corresponding desired storage temperatures are set in an electronic processor; the processor consequently determines the values that the thermostat adjustment temperature must take in each time interval. Afterwards, such adjustment temperatures are changed rising them for the intervals in which the desired storage temperatures have not been reached, and dropping them in the opposite case. A limit of the method, as in the first document mentioned, is the need of having to preset the times of the expected drawings; another limit, as in the second document mentioned, is that the desired and preset storage temperature is kept, however it may not be the best one for ensuring the service in the most effective manner.

An object of the present invention in a water heater is to keep a storage temperature thereof such as to fulfil all the drawings that may be expected by the usual behaviour of the utility while minimising thermal dispersions. A second object of the present invention is to automatically learn and store, at least for cycles of weekly drawings, the drawing profile consisting in times and amounts of the same without needing manual settings or flow detectors.

A third object of the present invention is to detect utility behaviour changes changing the learnt and stored drawing profile accordingly. A further object of the present invention is to prevent small random drawings from leading to a change of the drawing profile stored.

These and other objects are achieved with the method as illustrated in the folio wing description and in the annexed claims, which constitute an integral part of the description itself. Fig. 1 shows a schematic cross-section view of the tank of a water heater.

Fig. 2 shows a schematic view of the logical device that manages the water heater according to the methods of the invention.

Figs. 3. a, 3.b and 3.c show water temperature distributions inside a storage water heater respectively at the end of a heating step, after a drawing that has used only part of the water stored and finally, after a drawing that has used substantially all and only the water that had a sufficiently hot temperature.

Figs. 4. a, 4.b, 4.c and 4.d show the patterns of water temperature in a water storage heater over time as drawing are made and water is heated by a method according to the invention.

With reference to fig. 1, of a water heater 1, there is shown tank 2 provided with a cold water inlet 2.1, a hot water outlet 2.2, a bottom 2.3 and a dome 2.4. A heating element 3, which in the figure is schematically shown as an electrical resistor but which could consist of any other equivalent means, such as a gas combustion unit or a heat exchanger or else, is in charge of water heating.

Heat dispensing by the heating element 3, without distinction according to ON-OFF or modulating modes, is subject to enabling by regulator 4.

With ref. to fig. 2, said regulator 4 is provided with means IN suitable for introducing first data therein from the outside, for example during production through input IN.l and/or upon installation through input IN.2 and/or at a later time by the user through input IN.3.

Moreover, through input IN.4, regulator 4 receives second data from one or more sensors S; Sl, S2 that sense one or more corresponding temperatures T, Tl, T2 of water in their immediate vicinity inside tank 2.

If a single sensor S; Sl is provided, it is placed where the thermostat sensor of a water heater 1 is normally placed according to the prior art, that is, substantially 1/3 away from the bottom 2.3. If a further sensor S2 is provided, it is connected at a lower point, close to bottom 2.3. If further sensors are provided, they are all distributed so as to sense the temperature pattern along the vertical axis with certain accuracy; however, it has been found that only two sensors Sl and S2 are sufficient for a good application of the method according to the invention. By way of an example, in an 80 to 150 litre water heater I₅ vertical and with a diameter of about 400-450 mm, hereinafter referred to as standard water heater 1, there are provided two sensors S: sensor Sl arranged at about 30 mm from the bottom and sensor S2 at about 230 mm from the same bottom.

Going back to regulator 4, it is further provided with a memory MEM suitable for storing: - said first data received from the outside;

- said second data received from said one or more sensors S; Sl, S2;

- as well as further parameters that regulator 4 processes from said first and second data. Consequently, regulator 4 is provided with a processing unit UE suitable for processing said first and second data for obtaining said parameters and a clock CLOCK for associating at least some of said parameters to corresponding times.

Finally, regulator 4 is provided with first means Ul for sending output signals for the ON- OFF or modulating control of the heating element 3 besides any second output means U2 for signalling the system status to the user and/or to the operator. The output means U2, for example, may consist of a display capable of showing the storage temperature, the drawing profile and so on.

In particular, said regulator 4 is capable of processing data for constructing a profile of the effective drawings carried out by the user, which extends over a predetermined drawing cycle (one week, in particular) after which it is capable of piloting the heating element 3 so that, in the drawing cycles subsequent to the first one, during which the utility behaviour is assumed as substantially equal to that of the previous drawing cycles, the storage temperature is kept to the minimum value required to fulfil the single drawings as much as it is physically possible.

Moreover, regulator 4 is capable of detecting, as the subsequent drawing cycles run, any considerable changes of the utility behaviour that may require a corresponding change of the drawing profile sensed and stored while it disregards the irregularities of minor drawings (small drawings) that are not an indication of changes in behaviour. Going now to the method that, according to the invention, regulator 4 can carry out for obtaining what described above, upon the first start-up, water heater 1 starts operating keeping the temperature of tank 2 to values stored to memory MEM of regulator 4 after which it is capable of learning the drawing profile (that is, times and amounts of the single drawings) simply by processing data received from the one or more sensors S; Sl, S2 during the actual utility operation.

According to the invention, by processing the same data coming from said one or more sensors S; Sl, S2, regulator 4 is capable of calculating the thermal inertia of water heater 1 or better, the water heating speed characteristic of the thermal system, substantially consisting in tank 2 and in heating element 3.

In fact, it can be noticed that by the simple monitoring of the one or more temperatures T, T.I, T.2 carried out through sensors S; Sl, S2, the features and the behaviour of water heater 1 and of the utility are sufficiently detectable. For example, if the water temperature drops very slowly this must be ascribed to simple cooling by thermal dispersions while if the drop is very quick this denotes a drawing in progress, the time whereof can be deduced from the start and end time of the fast drop, whereas the temperature drop allows deducing the amount of hot water drawn. A higher final water temperature at the end of the drawing than the usage temperature T₁₁ denotes that the required drawing has been met; on the other hand, if the final temperature is lower, this means that the user has received too cold water, that is, that the required service has not been provided in full. Likewise, in the heating step, with the heating element 3 on, the temperature increase speed allows deducing the time required for changing from any first temperature to a second target temperature without the need of knowing the thermal capacity of tank 2, insulation quality and thermal power of the heating element 3.

Water heater 1, therefore, at the end of the learning of its internal features and of the utility features, is capable of maintaining the temperature of tank 2 to values that are variable over time and the lowest possible yet always sufficient for ensuring the single drawings, while the information on said temperature provided from the outside through said first data only serves for operating water heater 1 itself at least during a first period of the first cycle of drawings so that the service to the user is certainly ensured since the first start-up.

Before describing the method according to the invention in detail it is appropriate to define some parameters that are used by the method.

T_m, said water temperature, generically indicate the temperature resulting from the mean of the one or more temperatures T, Tl, T2 sensed by the one or more sensors S; Sl, S2; such mean is not necessarily an arithmetical mean but it can be a weighed mean to give more importance to one or the other of said one or more temperatures T, Tl, T2.

Tm._eff indicates the effective mean temperature of the water not necessarily coinciding with the water temperature T_m read by said S; Sl, S2, and exactly determined by laboratory tests only. Of course the effective mean temperature T_m._eff is not used by the method according to the invention and shall be hereinafter referred to only for a few explanatory considerations of the method itself.

Tse_tk indicates the K-drawing temperature, and is the temperature to ensure at the beginning of the k-th drawing P_k- Said drawing temperatures T_set._k have a predetermined initial value T_set higher than or equal to the value required for fulfilling the largest drawing expected; afterwards, they take values calculated by regulator 4 for each of the k drawings expected.

Tset.max indicates the maximum setting temperature (generally 75 °C) that for safety reasons ensures that the water does not exceed hazardous values. Tstand-by indicates the maintenance temperature to ensure at times far-off the drawings; it has a predetermined value preferably equal to the usage temperature T_u and therefore comprised between 35 and 45 ⁰C so as to ensure small unexpected drawings. It is not subject to processing over time but for allowing a manual correction thereof if the preset value does not satisfy the utility or is deemed excessive. T_targ_et indicates the target temperature. The target temperature T_target is preset equal to T_set.

Afterwards, it is set by regulator 4 equal to the maintenance temperature T_stand-by away from the drawing times but it must reach the value of the drawing temperature T_set.k with a heating advance time interval Δt_ant before the expected drawing start time tk.

ΔThy_steresi_s defines the hysteresis associated to said target temperature Ttarget- Similar to a conventional thermostat, regulator 4 enables the heating element 3 when the water temperature T_m drops below the value Ttarge_t - ΔThysteresis (that is, if T_m < T_target - ΔThysteresis) and disables it when the water temperature T_m is higher than T_taiget (that is, if T_m > T_target)- The value of hysteresis ΔThysteresi_s is predetermined; it may be very low, as in all electronic temperature regulators (for example 0.5 °C) if the heating element 3 is a group of electrical resistors piloted by regulator 4 through a TRIAC. On the other hand, if regulator 4 pilots the heating element 3 through relays, hysteresis ΔThysteresis has a considerably higher value to prevent an excessive ON-OFF switching frequency of the same relays. Preferably, in this second case, the value of hysteresis ΔT_hy_stere_sis is set equal to 5 °C when the target temperature Ttarget is set equal to the maintenance temperature T_stan_d-_by so as to ensure, with good accuracy, that the water temperature T_m actually has a useful value for the utility; on the other hand, when the target temperature T_target is set equal to the drawing temperature Tset the value of hysteresis ΔThysteresis may be higher (for example 8 ⁰C). Hysteresis ΔThystere_sis shall not be mentioned anymore hereinafter and is deemed to be implicit in the methods by which regulator 4 pilots the heating element 3. Topt indicates the optimal emptying temperature. At the end of a heating step, all the water in tank 2 substantially achieves the target temperature T_targ_et (see fig. 3. a). During a drawing, on the other hand, the water undergoes a stratification by virtue of the cold water entering from the bottom so if sensors S; Sl, S2, as usually happens, are in the proximity of the bottom, they do not sense the effective temperature of the output water anymore (see figs. 3.b, 3.c). However, a correlation exists between temperatures sensed at bottom 2.3 and those at dome 2.4 during the water change process in tank 2. The optimal emptying temperature T_opt is that sensed at bottom 2.3 when all the water has been drawn from said tank 2 at a temperature T_m higher than the usage temperature T₁₁ and only the water at dome 2.4 has stayed at the usage temperature T₁₁. Achieving the optimal emptying temperature T_opt on bottom 2.3, at the end of a drawing, therefore indicates that the required drawing has been supplied and that this happened by reaching the minimum water temperature T_m in tank 2 as compatible with the drawing itself and thus leaving tank 2 in minimum thermal dispersion conditions. The optimal emptying temperature T_opt of course depends not only on the usage temperature T_u but also on the size and proportions of tank 2. By way of an example, in the already mentioned standard water heater 1, if the usage temperature T_u is equal to 40 °C, the optimal emptying temperature T_opt is comprised between 18 and 24 and more preferably, it may be set equal to 21 °C.

VTh indicates the water heating speed when the heating element 3 is active. Having defined the main parameters used by the method according to the invention, let-s now go to the description of the learning steps involved, aimed at determining the typical parameters of water heater 1 and of the utility.

The step of measurement of inertia I_Wh of water heater 1 shall now be described, which is intended for determining the water heating speed and is used for deciding with what Δt_ant relative to the start of each drawing P_k the heating element 3 should be actuated for the water temperature T_m to reach the desired drawing temperature T_set.k- In order to carry out this step, during a period in which the heating element 3 is on:

- the value T_ml of the water temperature T_m at a predetermined time is recorded;

- the value T_m2 the water temperature T_m has reached after a predetermined measurement time Δt is recorded;

- the heating speed VT_h value is calculated by formula

VT_h = (T_m2-T_ml)/Δt (formula 1)

If a drop in the water temperature T_m is recorded in this step (indicating either a deactivation, for any reason, of the heating element 3 or a successful drawing), the calculated value of the water heating speed VT_h cannot be deemed as valid and the step must be repeated. Several phenomena may significantly affect the heating speed VT_h value, some on the long term, such as degradation factors of water heater 1 or season variations in the temperature of the room where water heater 1 is arranged, - others on the short term, such as the effect of small drawings that due to the stratification they produce, lead to significant deviations between the effective water temperature T_m._eff and that sensed by the one or more sensors S; Sl, S2. As a consequence, the heating speed VTh is preferably calculated periodically, for example each time regulator 4 actuates the heating element 3 or, even more preferably, the calculation is repeated continuously with the heating element 3 on; for example, every 15 minutes, setting said predetermined measurement time Δt equal to 15 minutes as well.

Sudden variations between the progressively calculated values may be limited using various alternative known mathematical techniques.

For example, the moving mean between a predetermined number of the last values calculated may be used, or even more preferably, the last result in order of time may be filtered with a time constant τ preferably of one hour and a half. The filter used is of the recursive type (HR, that is, with infinite impulse response) of the first order the equation whereof, as known, is of the following type: y(n) = y(n-l) + Ts / (Ts + τ) . [u (n) - y (n-1)] (formula 2) wherein, in particular, Ts is the sampling interval Δt (15 minutes), τ is the filter time constant (90 minutes), y(n) is the sample at time n*Ts of the filtered value of u(n) (that is, of the calculated heating speed VTj₁).

The step of recording the drawing profile shall now be described.

The drawing profile is recorded during all of a first drawing cycle, called learning cycle, but substantially considered as equal and representative of the following drawing cycles.

Said recording may then be repeated during the next cycles so as to keep into account any changes in the utility behaviour.

The recording may start at any time t of the cycle and the start times t_k of each drawing Pk of the n total drawings that will be comprised in the cycle (where k indicates the subsequent values from 1 to n), as well as the values T_mik and T_mf_k the water temperature

T_m has at the drawing start and end, respectively, are recorded during it.

Said times t, t_k may in any case be measured from the time taken as cycle start (for example from hours 0 of Monday if the cycle has a weekly duration, by such time meaning the time of start of the algorithm should the equipment be not provided with user interface for managing the calendar).

Said step is divided into an alternating sequence of n first substeps at the end of which, for each drawing P_k (with k ranging from 1 to n), the start time tk of the k-th drawing and the corresponding drawing start temperature T_mj_k are detected, followed by as many second substeps at the end of which the corresponding drawing end temperature T_mfk is detected, and the amount of the drawing itself is assessed. Going to describe said first substeps in a detail, the water temperature T_m is monitored during each of them, at sampling time intervals δt_c.

A drawing Pk is regarded as started when the following two conditions occur.

The first condition is that a higher water cooling speed VT_C; in absolute value, than a predetermined cooling speed VT_P must occur.

For such verification, at a time t_c, at the end of a sampling interval δt₀, it is verified whether temperature T_m (t_c) read at said time t_c has decreased compared to value T_m (t_c - δt_c) read at the previous time t_c - δt_c by an amount greater than or equal to a predetermined first reduction value δT_pl selected of such value as to exclude that said temperature drop may be ascribed to cooling for thermal dispersions_.

In formulas, since VT₀ = [T_m (t_c - δt_c) - T_m (t_c)] / δt_c and VT_P = δT_pl / δt_c, the following condition must occur

T_m (t_c - δt_c) - T_m (t_c) > δT_pl (formula 3)

It is suitable for said sampling time intervals δt_c to be quite short; preferably 60 seconds; correspondingly, said temperature reduction δT_pl is preferably equal to 0.33 °C and therefore preferably, said predetermined cooling speed VT_P is equal to 0.33 °C/minute.

Such condition, however, is not deemed sufficient; in fact, the temperature drop may be due to a small random drawing which should not be taken into account as it is not characterising of the actual cyclic drawing profile, or even to ON-OFF cycles of the heating element during the normal thermostating process, should the temperature probes be close to the heating element itself.

Therefore, the second condition set is that said first condition continues to be verified until the temperature T_m has dropped by a predetermined second reduction value δT_p2, deemed to be indicative of a neither small nor random drawing. Said second reduction value δT_P2 of course depends on the model of water heater 1 and on the type of utility it is intended for.

By way of an example, only as regards standard water heaters 1, the preferred value for said second reduction value δT_p2 is comprised between 4 and 13 °C; even more preferably, its value is 6.5 ⁰C. The drawing start time t_k may be regarded as coincident with time t_c wherein said first condition occurs and at the same time temperature Tm(t_c) read at time t_c itself is taken and stored as drawing start temperature T_mi_k, that is, in formulas tk= t_c (formula 4)

T_mik = T_m(t_c) (formula 5) However, since by the thermal inertia of said sensors S; Sl, S2 and their distance from the cold water inlet 2.1, the effective drawing start time tk may have occurred with a certain advance interval δt_ant relative to the time t_c, at which the temperature drop has been noted, according to a version of the method of the invention it is possible to keep this into account by setting tk = t_c- δtant- (formula 4) and/or also

Tmik = Tm(to- δW.) (formula 5)

The value of said advance interval δt_ant of course depends on the construction features of water heater 1; experimentally it has been found, for standard water heaters 1, that a value comprised between 60 and 180 sec determines the effective drawing start time tk with good accuracy; as a consequence, it was preferred to set said advance interval δt_ant equal to said sampling time interval δt_c this having the preferred value of 60 seconds. During each of the second substeps that follow each of said first substeps, on the other hand, temperature T_m is monitored until condition T_m (t_c - δt_c) - T_m (t₀) > δT_pl (formula 3) is not met anymore.

The achievement of such condition denotes that the drawing has stopped and therefore, such minimum value read is the water temperature T_mfk at the end of the drawing. Incidentally, if the water temperature T_mfk at the end of the drawing is lower than the optimal emptying temperature T_opt, this means that all of the drawing Pk has not been fulfilled, in fact the user, at least in the final step of the drawing Pk itself, has received not sufficiently hot water.

The drawing temperature T_set.k of drawing Pk is now calculated.

Through the temperatures read by sensors S; Sl and S2, a temperature drop ΔTk of the water temperature T_m is calculated, equal to the difference between the drawing start and end temperatures Tmik e T_mfk; that is ΔT_k = Ttnik - Tπifk (foraiula 6)

It should be noted that each predetermined drawing corresponds to a precise reduction of the energy contents of water heater 1 and thus, a precise drop of the effective mean water temperature T_m._eff irrespective of the value of such temperature at the drawing start; if said one or more sensors S; Sl and S2 were distributed along the entire height of water heater 1, said calculated temperature drop ΔT_k would then be an unchanging value for each drawing, irrespective of the initial value of said effective mean water temperature T_m.eff. In fact, it can be easily checked that, being Qp the mass of water used in the drawing, V the volume of tank 2, c_p and γ respectively specific heat and density of water and T_h the waterworks water temperature, the drop ΔT_m.eff of said effective mean temperature T_m._eff is equal to

ΔT_m._eff = Qp . cp . (T_u - Tj₁) / ( V . γ . cp) (formula 7)

(where term Qp . cp . (T_u — T₁₁) represents the thermal energy deducted from tank 2) which is independent of the same mean temperature T_m._eff although the amount of water of water heater 1 that is used for the drawing at usage temperature T₁₁ is as larger as the effective means temperature T_m.eff is lower.

Seemingly, therefore, it would simply be possible to set the drawing temperature T_set.k equal to the optimal emptying temperature T_opt increased by the above temperature drop ΔT_k; in formulas: T_set.k = T_op_t + ΔT_k (formula 8)

Such condition should ensure the drawing fulfilment bringing the temperature, at the end of the same, to the optimal emptying value T_opt.

Said one or more sensors S; Sl and S2, however, for practical reasons, are preferably arranged in the proximity of bottom 2.3 and , during the drawings, sense quite a different water temperature T_m compared to the effective mean temperature T_m._eff since (please see figs. 3.b, 3.c) the cold water in input mixes partly with the hot water almost exclusively at bottom 2.3 in a volume Vp well smaller than volume V. The drop ΔT_m sensed by sensors S; Sl, S2 therefore is at least approximately expressed by a relation of this type: ΔT_m. = Qp • cp . (Tu - Th) / (Vp . γ . cp) (formula 9) However, it should be noted that the volume Vp involved in the mixing indirectly depends on the effective mean temperature T_m,_βff. In fact, the lower is the latter, the larger will be the amount of water drawn to obtain a water mass drawing Qp at the usage temperature T₁₁, as a consequence, the higher is the volume Vp involved in the mixing and therefore, in practice, the lower is the resulting drop ΔT_m. In practice, therefore, the drop ΔT_m sensed by sensors S; Sl, S2 from the start to the end of the drawing is not constant with the same drawing, but decreases as the effective mean temperature T_m._eff drops at the drawing start, which however is not sensed if said sensors S; Sl, S2 are arranged low. To conclude, since such relation between drop ΔT_m and the effective mean temperature

is actually negligible if the drawing end temperature is relatively high (indicating not very large drawings and/or high drawing start temperature T_mj_k) whereas it is stronger if the drawing end temperature is quite low (indicating large drawings and/or low drawing start temperature T_mi_k), leading to a wrong estimate of the amount of the drawing itself, according to the invention, such wrong estimate is corrected according to a rule that when the drawing end temperature T_mfk is lower than a predetermined threshold value T₈ it adds a further term ΔT'\ to said temperature drop ΔTk = TW - T_mfk (formula 6).

Said rule and threshold value of course depend on the model of water heater 1 and on the utility features, so they must be determined empirically; a general rule is that said predetermined threshold value T₈ is comprised between 20 and 30 °C and that such corrective term ΔT"_k is at most 50% of said temperature drop ΔT_k.

A method of applying such rule, preferred for its simplicity and the good results it has given experimentally is as follows: - if the drawing end temperature T_mi_k is higher than or equal to the optimal emptying temperature T_opt (an indication, among the other things, of the fact that the drawing has been fulfilled completely), as already said, the drawing temperature T_set._k is set equal to the optimal emptying temperature T_Opt increased by the above temperature drop ΔTk; that is: Tsetk ⁼ Topt + ΔTk se T_mfk ≥T_opt (formula 10) - if, on the other hand, the drawing end temperature T_mfk is lower than the optimal emptying temperature T_opt (an indication, among the other things, of the fact that the drawing has not been fulfilled completely), such corrective term ΔT"_k, the value whereof is equal to the difference between such optimal emptying temperature T_opt and the drawing end temperature T_mfk itself, is added, that is:

ΔT"_k = + (T_Opt - T_raflc) if Tmfk < Topt (formula 11.a)

T_Set.k = Topt + ΔT_k + ΔT"_k if Tmfk < T_opt (formula 11.b)

The step of drawing profile recording continues for the entire cycle, alternating said first and second substeps that, ending automatically at the beginning and at the end of each drawing respectively, will total the same number as the drawings.

The profile of the n drawings has thus been determined and stored, where each drawing k is determined by two characteristic parameters, drawing start time t_k and temperature drop ΔT_k produced thereby. According to a version of the invention, during the drawing profile recording step in the learning cycle, a small adjustment to the actual features of utilities is already possible.

Such version, in fact, envisages that if the cycle is weekly, the initial predetermined value T_Set may be changed, bringing it equal to the maximum drawing temperature T_set.g value stored the previous day, provided this does not imply an excessive modification of the initial predetermined value T_set (for example comprised within T_set± 3 ⁰C). As a consequence, if the initial predetermined value T_set was excessive for the effective usage, its reduction already produces a limitation to the dispersions; if, on the other hand, it was insufficient for the larger drawings, performance is already improved. Of course, such version assumes that the amount of the single drawings (not necessarily their number) does not substantially vary much every day. The methods for managing water heater 1 according to the invention, once the drawing profile has been learnt during the learning cycle, shall now be described. According to the invention, the target temperature Ttarg_et

- may always be kept equal to the maintenance temperature T_stand-by away from the drawings - but is brought to a temperature T'_set._k not below the drawing temperature T_set.k with a Δtan_t relative to the drawing start time t_k sufficient to ensure said drawing. Fig. 4.a shows some points Pl, ... P4 representing as many drawings characterised by the corresponding times I₁, .. U of drawing start t_k and by the corresponding temperatures T_seu, .. T_Set.₄ of drawing T_set.k- Fig. 4.b shows, in addition, the course of temperature T_m with the rising ramps Rl, ... R4 for reaching said drawing temperatures Tl, .. T4.

Said ramps Rl, ... R4 have a course that depends on the heating speed VTh; the course, as known, is exponential but may be approximated by a rectilinear portion without appreciable errors given the order of size of the time constant of the water heater temperature (for example, well above 10⁶s for a standard water heater 1).

Seemingly, for each drawing k, the heating start time to_Nk may be calculated with the formula toNk = t_k - (Tsetk - T_nO / VTh (formula 12)

- where term (T_set._k - T_1n) / VTh expresses the heating advance interval Δtan_t relative to the drawing start time tk required for bringing temperature T_m from the current value to the drawing value T_set.k

- and wherein such calculation must be carried out at short time intervals, for example 60 seconds, taking into account the closest drawing, that is, that with the drawing start time t_k that is the closest in time. Actually, such method is unsatisfactory.

In fact, in the example fig. 4.b, it should be noted that proceeding in this direction, drawing Pl is fulfilled but at the end there is no sufficient time for bringing temperature T_m which, following the drawing, has dropped to the optimal emptying temperature T_opt, to the drawing temperature T₂ required by drawing P₂. For the same reason, drawing P₃ is not fulfilled either, whereas drawing P4, small and very far-off the previous ones, is.

In practice, it is not possible to ensure the service with a method that keeps into account, one at a time, only the closest of the drawings.

According to the invention, on the other hand, the following method called of "fictitious drawings" is applied, which in fact involves the construction of fictitious drawings. At quite short time intervals δ_w, for example 60 seconds, all the w drawings P₁, ..., Pj, ..., P_w the drawing start time whereof ti falls within a fixed and predetermined time window (hereinafter referred to as time window Δt_w) immediately subsequent to the current time, are taken into account.

At said drawing start time t _w comprised within said time window Δt_w, as many fictitious drawings are constructed P'i, ..., P'j, ..., P'_weach characterised by:

- a drawing start time t_w equal to that of the corresponding real drawing Pj

- but a fictitious drawing start temperature T'_seu obtained adding the drawing start T_seti_, T_Set2, ..., TSeKi_-1) temperatures of all the drawings comprised in said time window Δt_w and prior to the drawing Pj itself to the corresponding real drawing start temperature T_set.i, wherefrom the optimal emptying temperature T_opt has been deducted; that is, in formulas,

T'seti = Tsβti + (Tseti - T_opt) + (T_Set2 - T_opt) + ... + (T_set(i-i) - T_opt) (formula 13)

The result of such operation is shown in figs. 4.c and 4.d where the fictitious drawings P'i ,

P⁵2, P⁵3, P⁵4 are indicated on top of the corresponding real drawings P₁ , P₂, P₃, P4 . The fictitious drawing P'i coincides with the real drawing P₁ because, since it was the first one in the time window Δt_w, at its drawing start temperature T_seti, no other temperature has been added.

At this point, for each drawing P; of the w drawings comprised in the time window Δt_w, the fictitious heating start time t'o_Ni is calculated according to the formula t'oNi ⁼ ti - (T'_set.i - T_πi) / VTh (formula 12 bis) where term (T'_set.i - T_m) / VTi, expresses the heating advance interval Δt_ant relative to the drawing start time t_k required for bringing temperature T_ra from the current value to the fictitious drawing value T'_set.i.

When the more prior of said heating start times t'o_Ni is reached, the target temperature Ttarget is set to the fictitious drawing start temperature value T'_set.i of the corresponding fictitious drawing P'i, it being understood that said target temperature T_target could never exceed the maximum setting temperature T_set.maχ.

The result of such method is exemplified in fig. 4.c where the earliest of said heating start times t'o_Ni is time t'_0N3 relating to the fictitious drawing P'₃; when it is reached, the heating element 3 is actuated and temperature T_m starts increasing. Once the drawing start time t\ has been reached, temperature T_m, well above the strictly required real drawing start temperature T_set.i₅ drops suddenly by a value equal to the temperature drop ΔT1 corresponding to such drawing, then rises again reaching the drawing start time t₂ with an intermediate temperature between the real drawing start temperature T_Set.2 and the fictitious drawing start temperature T'_set.2, then it drops again and at the drawing start time t₃, it reaches exactly the real drawing start temperature T_set.₃ so that all of said three drawings Pl, P2 and P3 are fulfilled while drawing P4 has not been taken into account yet because the corresponding heating start time t'oN4 = tow is much later. The process is recursive, repeated at relatively short time intervals, for example 60 seconds, each time moving said time window Δt_w forward by an equal amount of time, so that all drawings P are taken into account and fulfilled but within the limits of power of water heater 1.

Fig. 4.d, for example, shows that ramp R is blocked in its ascent due to the fact that before reaching the drawing start time t_ls it has reached the maximum setup temperature T_set.max- This does not affect drawings Pl and P2 but drawing P3 the drawing start temperature Tset.2 whereof cannot be reached.

The width of such time window Δt_w must be reasonably larger than the intervals elapsing between multiple consecutive drawings. In detail, such time window Δt_w must be sufficiently wide as to include the drawing start time t; of all the drawings Pj the fictitious heating start times t'oNi whereof are expected to be prior to the fictitious heating start times t'oN relating to the i-1 prior drawings P₁,..., Pi_-1. For higher precision, as is clear in fig. 4.c, drawing P₃, the fictitious drawing start time t'oN3 whereof comes before fictitious times t'orø and t'oN_b would not be completely assured if its drawing start time t₃ were not already included in a time window Δt_wthat still includes the drawing start times t_\ and t₂ of the prior drawings P₁ and P2. In other words, if regulator 4 could not consider drawing P₃ at the same time as the prior drawings P₁ and P₂, it would start heating at time t'o_N2 and drawing P₃ would not be completely fulfilled. It is not difficult to determine such time window Δt_w when the type of utility the water heater 1 is intended for is known. For example, if the drawing cycle lasts one week, the time window Δt_w can cover 24 hours; moreover, the fact that there certainly is a night pause in the drawings ensures that the above set condition is met.

The method just described involves, as seen, the construction of said fictitious drawings P'i, ..., P'j, ..., P', the calculation of the corresponding fictitious drawing start temperatures T'_set, then the calculation of the corresponding heating start times t'oNi and finally, the actuation of the heating element 3 upon reaching the closest of said heating start times t'oNi setting the target temperature T_target equal to the fictitious drawing start temperature T'_set.i- This method ensures the fulfilment of the utility demands as it considers together all the drawings P; that are so close to each other that there would be no time to fulfil those following the first one P₁ of the group, if the thermal energy required were not stored in advance by actuating the heating element 3.

This is obtained thanks to the fact that the procedure calculates the fictitious heating start time t'o_Ni °f drawing P; also taking into account the heating time to be allocated to all the drawings prior to it.

It should be noted that the fictitious drawing start temperature T'_set.i is almost never actually reached because as the heating proceeds, intermediate drawings reduce the water temperature T_m- In practice, the method of "fictitious drawings" allows supplying the thermal energy strictly required for ensuring the drawings, keeping the water temperature T_m, time by time, to the minimum value required for such service and calculating the duration of the actuation periods of the heating element 3 without the need of explicitly knowing the thermal power thereof. It is almost useless to say that, to the disadvantage of the maximum energy saving obtainable but to the advantage of the service safety, said heating start times t'oni may be advanced by a little (a tolerance advance Δ_toi for taking into account deviations from the effective drawing start times (tj) relative to those recorded during the learning drawing cycle). In fact, if the drawing profile recording continues in the drawing cycles subsequent to the first learning cycle, the regulator may learn which value to assign to such tolerance advance Δtoii.

Claims

CIm. 1 Method for the management of a storage water heater (1) wherein water is heated by a heating element (3) piloted by a regulator (4), suitable for regulating the water temperature (T_m) to a changeable target temperature (Ttarget) and wherein said method comprises,

- a first step wherein information is acquired

- regarding the drawing profile which is substantially repeated unchanged for subsequent drawing cycles — and the heating speed (VTh) characteristic of said water heater (1)

- a second step wherein, before the time (t_k) of start of each drawing (P_k) of all the n drawings (P_n) comprised in each of said drawing cycles,

- the water temperature (T_m) is brought to at least the drawing temperature value (T_set.k; T'_set.i) sufficient for ensuring said drawing at the usage temperature (T_u) starting the heating at a heating start time

(tθNk; t'oNi)

- provided that in any case, said water temperature (T_m) is kept below or equal to the maximum setup temperature (T_Set._max)₅ below dangerous values, - said drawing temperature value (Tset.k;T'_set.i) and said heating start time (toN_k; t'o_Ni) being inferred from the above acquired information, characterised in that said information acquisition on the drawing profile — takes place at least during a learning drawing cycle

- and consists in calculating, for each of said n drawings (Pk)₅

- the drawing start time (t_k),

- the corresponding temperature decrease (ΔT_k)

- such calculation being carried out only by processing data obtained - from the measurement of passing time (t, t_c), - from the assessment of the water temperature (T_m) resulting from the mean of one or more temperatures (T; Tl, T2) measured at different heights (S, Sl, S2) of the tank (2).

CIm. 2 Method for the management of a water heater (1) according to claim 1 characterised in that a drawing (P_k) is regarded as started if a first and a second condition occur in a sequence,

- said first condition consisting in that, at a time (tc), at the end of a sampling interval (δt_c), it is noted that the water temperature (T_m(tc)) read at said time (tc) has decreased relative to the value (T_m(tc - δtc)) read at the previous time (tc - δtc) by an amount greater than or equal to a predetermined first value of temperature reduction (δT_pl), that is, in that the condition T_m (t_c - δt_c) - T_m (t_c) ≥ δT_pl has occurred (formula 3),

- said first temperature reduction value (δT_pl) being selected such as to exclude a cooling due to thermal dispersions,

- said second condition consisting in that said first condition continues to be verified until the temperature (T_m) has dropped by a predetermined second reduction value (δT_P2),

- said second reduction value (δT_p2) being selected such as to exclude said first condition from being verified by the effect of little drawings or thermostating that are not desired to be taken into account,

CIm. 3 Method for the management of a water heater (1) according to the previous claim, characterised in that said sampling interval (δt_c) is equal to 60 seconds, and said first temperature reduction value (δT_pl) is equal to 0.33 ⁰C. CIm. 4 Method for the management of a water heater (1) according to at least claim 2 characterised in that said second reduction value (δT_P2) is comprised between 4 and 13 °C. CIm. 5 Method for the management of a water heater (1) according to the previous claim, characterised in that said second reduction value (5Tp₂) is equal to 6.5 °C.

CIm. 6 Method for the management of a water heater (1) according to any previous claim from 2 on characterised in that the drawing start time (tø of each drawing (P_k) is regarded as prior to an advance interval (δt_adv) relative to the time (t_c) wherein said first condition occurs and that is, in formulas [tk= t_c- δtant] (formula 4). CIm. 7 Method for the management of a water heater (1) according to any previous claim from 2 on characterised in that the following steps are carried out for determining the drawing temperature value (Tsβtk) - the temperature T_m(t_c- δtadv) read at the drawing start time (tk) is stored as drawing start temperature (T_mik)

- the temperature read at the time when the water temperature (T_m) stops dropping, that is, at the time when the condition [T_m (t_c - δt_c) - T_m (t_c) > δT_pl] (formula 3) stops being satisfied, is stored as drawing end temperature (T_mfk)

- if said one or more sensors (S; Sl, S2) are arranged in the proximity of the bottom (2.3) of the water heater (1), said drawing end temperature (T_mfk) is checked to see if it is below a predetermined threshold value (T₈; T_opt),

- the temperature decrease (ΔTk) of water temperature (T_m) is assigned the value of the difference between the drawing start and end temperatures

(Tmikj Tmfk)

- if said one or more sensors (S; Sl, S2) are arranged in the proximity of the bottom (2.3) and said drawing end temperature (T_mf_k) is below said predetermined threshold value (T₅; T_opt), the temperature decrease value (ΔT_k) is modified adding a corrective term (ΔT"_k) empirically obtained for each water heater model (1) and type of users associated thereto,

- the drawing temperature (T_set._k) is finally obtained adding the temperature decrease value (ΔT_k) as optionally modified above to the optimal emptying temperature (T_opt). CIm. 8 Method for the management of a water heater (1) according to the previous claim, characterised in that

- said threshold value (T₈; T_opt) is comprised between 20 and 30 °C

- and said corrective term (ΔT"_k) is equal to 50% of the temperature decrease (ΔTk).

CIm. 9 Method for the management of a water heater (1) according to claim 7 characterised in that

- said threshold value (T_s; T_opt) is equal to the optimal emptying temperature - and said corrective term (ΔT"_k) is equal to the difference between said optimal emptying T_opt and drawing end (T_mfk) temperatures.

CIm. 10 Method for the management of a water heater (1) according to claims from 7 on, characterised in that said advance interval (δt_adv) is comprised between 0 and 180 sec.

CIm. 11 Method for the management of a water heater (1) according to claims 7 on, except 10, characterised in that said advance interval (δt_adv) is equal to said sampling interval (δt_c). CIm. 12 Method for the management of a water heater (1) according to any previous claim characterised in that said information acquisition on said heating speed (VTh)

- takes place at least during said learning drawing cycle in a period where water temperature (T_m) is uninterruptedly increasing - and envisages the following steps:

- the value (T_ml) of the water temperature (T_m) at a predetermined time is recorded,

- the value (Tπώ) the water temperature (T_m) has reached after a predetermined measurement time (Δt) is recorded,

- the heating speed (VT_h) value is obtained from formula [VTh ⁼ (T_m2- T_ml)/Δt] (formula 1).

CIm. 13 Method for the management of a water heater (1) according to the previous claim, characterised in that said information acquisition on said heating speed (VT_h) is repeated whenever the regulator (4) actuates the heating element (3). CIm. 14 Method for the management of a water heater (1) according to claim 12 characterised in that said information acquisition on said heating speed (VTh) is repeated continuously as long as the heating element (3) remains activated at intervals equal to said predetermined measurement interval (Δt). CIm. 15 Method for the management of a water heater (1) according to at least claim 12 characterised in that said predetermined measurement interval (Δt) is equal to 15 minutes.

CIm. 16 Method for the management of a water heater (1) according to at least claim 12 characterised in that said information acquisition on said heating speed (VTh) is also carried out in the drawing cycles subsequent to the learning drawing cycles. CIm. 17 Method for the management of a water heater (1) according to any claim from

13 on, characterised in that the progressively calculated values of the heating speed (VT_h) are reprocessed for reducing the extent of variations between said values found. CIm. 18 Method for the management of a water heater ( 1 ) according to claim 17 characterised in that the value taken for said heating speed (VT_h) is set equal to the moving mean among a predetermined number of the last calculated values. CIm. 19 Method for the management of a water heater (1) according to claim 17 characterised in that the value taken for said heating speed (VT_h) is the last result obtained in chronological order, filtered with a time constant (τ) preferably of one hour and a half, the filter used being of recursive type (HR).

CIm. 20 Method for the management of a water heater (1) according to any previous claim characterised in that the determination of said heating start time (toNk; t'oNi) ^^{or ensurm}g ^said drawings (Pk_; Pj) envisages the following steps _:

- at short time intervals (δ_w), all the w drawings (P₁, ..., Pi, ..., P_w) the drawing start time whereof (t;) falls within a predetermined time window

(Δt_w) immediately subsequent to the current time, are taken into account,

- wherein said time window (Δt_w) is selected based on the type of users said water heater (1) is intended for and is sufficiently wide as to include the drawing start time (tj) of all the drawings (Pj) wherein fictitious heating start times (t'oNi) are expected to be prior to the fictitious heating start times (t'o_N) relating to the i-1 prior drawings (P₁,

- at said drawing start time (t;) comprised within said time window (Δt_w) as many fictitious drawings are constructed (P' _\, ..., P'j, ..., P'_w), that have each,

- a drawing start time (t_w) equal to that of the corresponding real drawing

(Pi)₅

- a fictitious drawing start temperature (T'_set.i) obtained adding the drawing start (T_seti, T_S6t2, ..., T_set(i-i)) temperatures of all the drawings comprised in said time window (Δt_w) and prior to the drawing Pi itself to the corresponding real drawing start temperature (T_set.i), wherefrom each of the drawing start temperatures (T_seti, T_set2, ..._, T_set(i-i)) have been deducted of the optimal emptying temperature T_opt according to formula

[ T'seti = Tseti + + (T_setl - T_Opt) + (T_set2 - T_opt) + ... + (T₅Bt(I_-1) - T_opt) ] (formula 13)

- for each of said fictitious drawings (P' i, ..., P\, ..., P'_w)_t the fictitious heating start time (t'oNi) is calculated according to the formula [ t'oM ⁼ t; - (T'sβti - T_1n) /VTh Formula 12 bis),

- when the more prior of said heating start times is reached (t'o_Ni), the target temperature (Ttarget) is set to the fictitious drawing start temperature value

(T'seti) of the corresponding fictitious drawing (P';) it being understood that said target temperature (Ttarget) has as top limit the maximum setting temperature (T_set.max)

- while before to reaching said more prior heating start time (t'o_Ni), the target temperature (T_target) is kept equal to the maintenance temperature (T_stand-by).

CIm. 21 Method for the management of a water heater (1) according to the previous claim, characterised in that said short time intervals (δ_w) are equal to 60 seconds. CIm. 22 Method for the management of a water heater (1) according to the previous claims 20 and 21, characterised in that if the drawing cycle lasts one week, said time window (Δt_w) covers 24 hours. CIm. 23 Method for the management of a water heater (1) according to the previous claims from 20 on, characterised in that said heating start times (t'oni) are advanced by a tolerance advance (Δt_oi) suitable for taking into account deviations from the effective drawing start times (tj) relative to those recorded during the learning drawing cycle. CIm. 24 Method for the management of a water heater (1) according to the previous claim, characterised in that

- the drawing profile recording continues in the drawing cycles subsequent to the first learning cycle - and said tolerance advance (Δt_oi) is learnt during said cycles of the drawings subsequent to the first learning cycle.

CIm. 25 Method for the management of a water heater (1) according to claim 7 characterised in that if the drawing cycle is weekly, at the beginning of each day subsequent to the first one, the initial predetermined value of the drawing temperature (T_set) is decreased or increased by at most 3 °C to bring it closer to the maximum drawing temperature value stored on the previous day (T_set._g). CIm. 26 Method for the management of a water heater (1) according to claim 20 characterised in that said maintenance temperature (T_stand-by) is equal to the usage temperature (T₀).

CIm. 27 Regulator (4) for a water heater (1) provided with

- means (IN, IN.l, IN.2, IN.3) suitable for introducing first data therein from the outside during production and/or upon installation and/or at a later time by the user - means (IN, IN.4) suitable for introducing therein second temperature data

(T, Tl, T2) of the water heated in the tank (2) and sensed by one or more sensors (S; Sl; S2)

- a memory (MEM) suitable for storing said first data received from the outside, said second data received from said one or more sensors (S, Sl, S2) as well as further parameters processed by said first and second data,

- processing unit (UE) suitable for processing said first and second data for obtaining said parameters,

- a clock (CLOCK) for associating at least some of said parameters to corresponding times - first means (Ul) for sending output signals for the ON-OFF or modulating control of a heating element (3) suitable for heating in said tank (2)

- any second output means (U2) for signalling the system status to the user and/or to the operator suitable for acquiring information, processing the same and regulating said heating element (3) according to the methods according to one or more of claims 1 to 12. CIm. 28 Water heater (1) provided with

- regulator (4) according to claim 27

- heating element (3) - one or more sensors (S; Sl, S2) suitable for sensing corresponding temperatures (T, Tl, T2) inside the tank (2) suitable for benefiting from the methods according to one or more of claims 1 to 11.

CIm. 29 Water heater (1) according to the previous claim, characterised in that said one or more sensors (S; Sl, S2) consist in a single sensor (S; Sl) placed where the thermostat sensor of a water heater (1) is normally placed according to the prior art.

CIm. 30 Water heater (1) according to claim 28 characterised in that said water heater (1) is the standard model and said one or more sensors (S; Sl, S2) consist in a first and a second sensor

(Sl, S2) respectively placed at about 30 mm and about 230 mm from the bottom (2.3) CIm. 31 Water heater (1) according to claim 28 characterised in that more than two sensors (S; Sl, S2) are provided distributed so as to sense the temperature pattern (T, Tl, T2) along the vertical axis with certain accuracy.