EP2362931B1

EP2362931B1 - Method for minimizing energy consumption of a storage water heater through adaptative learning logic

Info

Publication number: EP2362931B1
Application number: EP09764038.7A
Authority: EP
Inventors: Stefano Ferroni; Lucio Latini; Angelo Mancini; Roberto Sampaolesi; Alessandro Stopponi
Original assignee: Merloni Termosanitari SpA; Ariston Thermo SpA
Current assignee: Merloni Termosanitari SpA; Ariston SpA
Priority date: 2008-11-28
Filing date: 2009-11-17
Publication date: 2016-02-17
Anticipated expiration: 2029-11-17
Also published as: WO2010061264A1; PL2362931T3; ES2572359T3; IT1392118B1; EP2362931A1; ITAN20080052A1

Description

The present invention relates to a new method for the management of water maintenance 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 tapping may be larger than the volume of the storage tank as this is especially kept at a storage temperature T.acc higher than said usage temperature T_u and the water withdrawn is then used mixing it with cold water.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 T.acc high (generally 75 °C), whereas the actual usage temperature T_u, 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 meeting the largest of the expectable drawings for that specific utility keeping the storage temperature T.acc 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.
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 T.acc 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 meet 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 maximum 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 tapping times and amounts, shall be referred to as drawing profile.
If it is true that the drawing time 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, user's 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.
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 T.acc drops because the heating element is forcedly deactivated.
Those methods that allow the storage temperature T.acc 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.1, t.2, ... t.k, ... t.n is recorded by setting for each time t.k the temperature T_set.k deemed able to meet the k-th drawing P_k. A limit of the method consists in the difficulty of a correct programming, because the user cannot be aware of the actual drawing times of the hot water or of the actual 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 actual 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 scale deposits, seasonal temperature variations in the room where the water heater is placed or of the water entering the storage tank, reduction of the actual 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 T.acc 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 T.acc 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 T.acc 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 T.acc is kept, however it may not be the best one for ensuring the service in the most effective manner.
The method disclosed in US 2003/0194228.A1 detects, in a storage water heater, whether drawings are occurring calculating the speed with which the temperature varies in the tank; if drawings are detected, the time and the length of the event is memorized as well as how the heating has been activated to satisfy the drawing. Each subsequent drawing is compared with the previously memorized ones and, if a previous drawing is found similar to that occurring at the moment, to this last the same modality of heating are applied as for this previous one. Such a method in ineffective for storage water heaters accumulation since the production of thermal power at the moment in which the beginning of a drawing is detected is a tardy action since 6the thermal power of a storage water heater is insufficient to supply instantaneously the required thermal energy. As a consequence, the required drawing can not be satisfied neither using the memorized information referred to a previous similar drawing. The thermal power to be supplied is calculated considering the water temperatures read at intervals of time but even environment parameters (such as ambient temperature) and/or constructive (such as thermophysical and/or geometrical characteristics of the water heater itself) so that the managing software has to be customized for each water heater model.
The method disclosed in US 5 526 287 A detects the beginning and the end of a drawing monitoring, from the exterior, the temperature of the cold water in the inlet pipe of a storage. Such control method should be considered inadequate to detect both entity as actual duration of the drawing: the outer temperature of the inlet pipe, in fact, varies with the flowing of cold water according to modality strongly influenced by the external temperature, thermal inertia of the pipe as well as temperature of the hot water in the storage that is transmitted along the pipe. The temperature to assure to the hot water is calculated considering continuously both said temperature external to the inlet pipe and that of the outlet pipe as well as the entity of the occurring drawing, the thermal losses and the available thermal energy according to formulae that use empirically predefined constant (R, B, C) as well as water heater characteristics. Neither such method is suitable to assure the service for a storage water heater since, as for the above document, it operates too tardily.
An object of the present invention in a water heater is to keep a storage temperature T.acc thereof such as to meet 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 allow an amount of water a little higher than that consumed in the previous cycle at each drawing.
These and other objects are achieved with the method as illustrated in the following description and in the annexed claims, which constitute an integral part of the description itself.

Fig. 1 shows a schematic cross-sectional 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.

With reference to fig. 1, of a water storage heater 1, hereinafter simply referred to as water heater 1, there is shown tank 2 provided with a cold water inlet 2.1, a hot water outlet 2.2. 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.1 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; S1, S2 that sense one or more corresponding temperatures T, T1, T2 of water in their immediate vicinity inside tank 2.
If a single sensor S; S1 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.
If a further sensor S2 is provided, said sensor S1 is placed lower, 100 ÷ 200 mm away from the bottom and in any case in the proximity of the cold water inlet 2.1.
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 S1 and S2 are sufficient for a good application of the method according to the invention.
By way of an example, in an 80 litre water heater 1, with 1200 W heating element 3, 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 S1 arranged at about 190 mm from the bottom and sensor S2 at about 260 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, S1, 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 U1 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.
The data said regulator 4 is capable of acquiring allow it to process further data representing

the water heater 1 features (that is, water heating speed)
the utility features (that is, drawing amounts and times)

This takes place during a predetermined first drawing cycle (one week, in particular), said learning cycle.
Once the learning has taken place, said regulator 4 is capable of piloting the heating element 3 so that, in the drawing cycles following the first one, during which the utility behaviour is assumed to be substantially equal to that of the previous drawing cycles, the storage temperature is kept to the minimum value required to meet 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, or of the water heating speed that may require a corresponding change of the water heating start times.
Going now to the details of 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; S1, S2 during the actual utility operation.
According to the invention, by processing the same data coming from said one or more sensors S; S1, 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.1, T.2 carried out through sensors S, S1, 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 T_u 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 during the first cycle of drawings so that the service to the user is certainly ensured since the first start-up.
Let's now describe in detail the method according to the invention; it involves multiple learning and operating steps according to the parameters learnt.
It is suitable to immediately define some parameters that are used by the method.
T_m, said water temperature, generically indicates the temperature resulting from the mean of the one or more temperatures T, T1, T2 sensed by the one or more sensors S, S1, 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, T1, T2.
T_set.k indicates the P_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 meeting the largest drawing expected; afterwards, they take values calculated by regulator 4 for each of the k drawings expected.
T_set.max indicates the maximum setting temperature (generally 75 °C) that for safety reasons ensures that the water does not exceed hazardous values.
T_req.max indicates the maximum temperature required for meeting the largest drawing to be ensured for each model of water heater 1. More precisely, it is clear that the reason why models of water heaters 1 differing by capacity of the storage tank 2 and by power of the heating element 3 are manufactured, is to meet different more or less important utility categories; the largest among the various required drawings thereof is substantially known and as a consequence, said maximum temperature T_req.max required to the purpose. In conclusion, the maximum temperature required T_req.max is a known and predetermined value associated to each model of water heater 1 and to the corresponding utility category said model of water heater 1 is intended for.
By way of an example, for a standard water heater 1, a preferred value for the maximum required temperature T_req.max is 52 °C.
Said maximum required temperature T_req.max of course is lower than the maximum setting temperature T_set.max so that water heater 1 is capable of ensuring also larger drawings than those normally expected.
T_stand-by indicates the maintenance temperature to ensure at times far-off the drawings, preferably but not necessarily sufficient for allowing temperature T_m of the water to ensure small unexpected drawings; this is also a parameter with which the actual water temperature T_m is compared. The maintenance temperature T_stand-by has a predetermined value preferably equal to the usage temperature T_u and thus comprised between 35 and 45 °C; it is not subject to processing over time, but for allowing a manual correction thereof if the preset value does not meet the utility or is regarded as excessive.
T_target 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_advance before the expected drawing start time t_ik and kept for a delay time interval Δt_delay subsequent to the drawing start time t_ik itself.
ΔT_hysteresis defines the hysteresis associated to said target temperature T_target. Similar to a conventional thermostat, in fact, regulator 4 enables the heating element 3 when the water temperature T_m drops below the value T_target - ΔT_hysteresis (that is, if T_m ≤ T_target - ΔT_hysteresis) and disables it when the water temperature T_m is higher than T_target (that is, if T_m > T_target). The value of hysteresis ΔT_hysteresis 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 ΔT_hysteresis 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_hysteresis is set equal to 5 °C when the target temperature T_target is set equal to the maintenance temperature T_stand-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 T_set the value of hysteresis ΔT_hysteresis may be higher (for example 8 °C).
I_wh indicates the inertia of water heater 1 and indicates the rising speed of temperature T_m when the water heater 3 is on.
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 advance relative to the start of a 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_m1 of the water temperature T_m at a given time is recorded; this preferably matches the first start-up time of water heater 1;

the value T_m2 the water temperature T_m has reached after a predetermined measurement interval Δt is recorded; this may match the time when the water temperature T_m reached the value of the drawing temperature T_set;
the inertia I_wh value of water heater 1 is calculated by formula $I_{wh} = (T_{m 2} - T_{m 1}) / Δt$

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 inertia I_wh of water heater 1 cannot be deemed as valid and the step must be repeated.
Since different degradation factors of water heater 1 and environmental factors (for example seasonal variations in the temperature of the room water heater 1 is located in) may have significant influences on the value of inertia I_wh of water heater 1, this is preferably recalculated periodically, for example upon each start-up of water heater 1 after a deactivation period (such as during holidays) and/or whenever regulator 4 decides that the target temperature T_target must change from the maintenance temperature T_stand-by to the drawing temperature T_set.
The step of recording to drawing profile shall now be described.
The drawing profile is recorded during all of said learning cycle 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_ik of each drawing P_k 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_mfk 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).
Said step is divided into an alternating sequence of n first sub-steps at the end of which the start time t_ik of drawing P_k and the corresponding drawing start temperature T_mik are detected, followed by as many second sub-steps at the end of which the end time t_fk of drawing P_k, the corresponding drawing end temperature T_mfk are detected, and the amount of the drawing itself is assessed.
Obviously, during the learning cycle said drawing start temperature T_mik matches the initial predetermined value T_set at which the target temperature T_target is preset; this is true but for the hysteresis.
Going now to describe said first sub-steps in detail, during each of them, at sampling time intervals δt_c, the temperature T indicated by sensor S is monitored, capable, relative to all of the one or more sensors S, S1, S2, of being more influenced by temperature variations due to the inlet of cold water; generally, it is sensor S arranged in the lowest position (sensor S1 of figure 1) which is the closest to the cold water inlet 2.1.
A drawing P_k is regarded as started when, at a time t_c, at the end of a sampling interval δt_c, it is noted that the temperature T(t_c) read at said time etc has decreased compared to the value T(t_c - δt_c) read at the previous time t_c - δt_c by an amount greater than or equal to a predetermined value δT_p.
In formulas, the drawing is deemed as started if $T (t_{c} - {δt}_{c}) - T (t_{c}) \geq {δT}_{p}$
Said sampling time intervals δt_c may be quite short, preferably 10 seconds and, correspondingly, said temperature reduction δT_p is preferably equal to 0.2 °C.
More explicitly, with said numerical examples the drawing is regarded as started if the temperature decrease speed has exceeded 0.02 °C/sec.
The drawing start time t_ik, however, is not deemed as coinciding with time t_c in which said temperature reduction of more than δT_p is verified; in fact, for the thermal inertia of said sensor S, S1 and for its distance from the cold water inlet 2.1, the temperature decrease takes place with a certain delay relative to time t_ik of actual drawing start that has therefore occurred with an advance interval δt_ant relative to time t_c.
In formulas, therefore, we have $t_{ik} = t_{c} - {δt}_{ant} .$
At the same time, the temperature T_m read at time t_c itself is taken and stored drawing start temperature T_mik. However, for a higher accuracy of the method, nothing prevents the use of the real drawing start temperature as drawing start temperature T_mik, that is, the temperature T_m(t_ik) actually measured and suitably stored at the previous time t_ik.
The value of said advance interval δt_ant of course depends on the construction features of water heater 1, but experimentally it has been found, for water heaters 1 with the most common shape, that a value equal to 180 sec determines the actual drawing start time t_ik with good accuracy.
During each of the above second sub-steps that follow each of said first sub-steps, on the other hand, temperature T_m is monitored until it reaches a minimum. 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 maintenance temperature T_stand-by, this means that it is not sure that all of the drawing P_k has been met, in fact the user, at least in the final step of the drawing P_k itself, may have received not sufficiently hot water.
The temperature drop ΔT_k caused by drawing P_k is now calculated, which is equal to the difference between initial and final temperatures T_mik and T_mfk; that is ${ΔT}_{k} = T_{mik} - T_{mfk}$
The step of drawing profile recording continues for the entire cycle, alternating said first and second sub-steps 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 stored, where each drawing P_k is determined by two characteristic parameters, drawing start time t_ik and temperature drop ΔT_k produced thereby.
The methods for managing water heater 1 according to the invention shall now be described.
According to the invention, regulator 4 maintains the target temperature T_target always equal to the maintenance temperature T_stand-by but for ensuring the drawing temperature T_set at the start of each drawing P_k.
To this end, the advance time interval Δt_advance.k is calculated, starting from which the heating element 3 must be enabled for the temperature T_set of drawing P_k to actually be achieved at said expected drawing start time t_ik.
Said advance time interval Δ_advance.k is calculated by formula ${Δt}_{advance, k} = (T_{set, k} - T_{m}) / I_{wh}$
The target temperature T_target is led to the drawing P_k temperature, T_set.k if at said time t the following condition is met: $t_{ik} - {Δt}_{advance, k} < t < t_{ik} + {Δt}_{delay}$
The delay time interval Δt_delay has a predetermined value, is optional (that is, it may also be set equal to zero) and has the additional function of allowing the heating element 3 to supply additional thermal energy by which larger drawings than what allowed by the drawing temperature T_set.k are met, this being limited by the maximum setting temperature T_set.max.
The delay time value Δt_delay consequently depends on the utility type and on the model of water heater 1 that is most suitable for said utility. By way of a non-limiting example, for a standard water heater 1 such delay time Δt_delay may be of 15 minutes.
Finally, as regards the drawing temperature T_set.k, the method according to the invention sets it equal to said temperature drop ΔT_k caused by drawing P_k to which said predetermined value of the maximum temperature required T_req.max and an empirical corrective term of a value of 5 °C are added.
Then, there are the additional conditions that in any case said drawing temperature T_set.k must not be less than the maintenance temperature T_standby and not higher than the maximum setting temperature T_set.max.
In short, in formulas we have: $T_{set, k} = {ΔT}_{k} + T_{req max} + 5$
$T_{set, k} \geq T_{standby}$
$T_{set, k} \leq T_{set, \max}$
Experimentally it has been found that formula 7 ensures a reduction of thermal dispersions in the order of 10% in a standard water heater 1 while ensuring the fulfilment of the required service.

Claims

Method for the management of a storage water heater (1) wherein water is heated by a heating element (3) piloted by a regulator (4), said method comprising,
- a first step, during a sequence of drawing cycles,
- wherein information is acquired regarding a drawing profile of said sequence of drawing cycles, said information acquisition taking place during a first of said drawing cycles

- a second step,
- wherein the water temperature (T_m) is assigned the drawing temperature value (T_set.k) sufficient for ensuring said drawing at the usage temperature (T_u), said drawing temperature value (T_set.k) being inferred from the above acquired information and said water temperature (T_m) being regarded as representative of the temperature distribution within the storage tank (2) of said storage water heater (1)

- wherein the water temperature (T, T(t_c)) is measured in a zone of said storage tank (2) capable, relative to other zones, of being more influenced by temperature variations due to the inlet of cold water
characterised in that

- said drawing profile is substantially repeated unchanged for subsequent drawing cycles

- said second step takes place before the time (t_ik) of start of each drawing (P_k) of all the drawings (n) comprised in each of said drawing cycles

- said water temperature (T_m) is kept below or equal to the maximum setup temperature (T_set.max) lower than dangerous values,
and characterised in that
- said information acquisition on the drawing profile consists in calculating, for each of said drawings (k),
- the drawing start time (t_ik,)

- and 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 said water temperature (T, T(t_c)) measured in a zone of the storage tank (2) capable, relative to other zones, of being more influenced by temperature variations due to the inlet of cold water,

- from said water temperature (T_m) wherein said water temperature (T_m) is the value resulting from the average of one or more temperatures (T; T1, T2) measured at different heights (S, S1, S2) of said storage tank (2).
Method for the management of a water heater (1) according to the previous claim, characterised in that
- a drawing (P_k) is regarded as started if, at a time (tc), at the end of a sampling interval (δt_c), it is noted that the temperature (T(tc)) read at said time (tc) in said zone of the storage tank (2) more influenced by the inlet of cold water has decreased compared to the value (T(tc - δtc)) read at the previous time (tc - δtc) by an amount greater than or equal to a predetermined value of temperature reduction (δT_p), that is, when the condition T(t_c - δt_c) - T(t_c) _≥ δT_p has occurred
and in that

- said drawing start time (t_ik,) is regarded as prior to said time (tc) by a predetermined advance interval (δt_adv) and that is, it is obtained from the relation t_ik = t_c - δt_adv.
Method for the management of a water heater (1) according to the previous claim, characterised in that
said drawing (P_k) is regarded as started if the temperature decrease speed has exceeded 0.02 °C/sec.
Method for the management of a water heater (1) according to claim 2
characterised in that
said sampling interval (δt_c) is equal to 10 seconds.
Method for the management a water heater (1) according to claim 2
characterised in that
said advance interval (δt_adv) is equal to 180 seconds.
Method for the management of a water heater (1) according to any previous claim
characterised in that
- the temperature (T_mik) of water (T_m) read at the drawing start time (t_ik) is stored,

- the temperature of water (T_m) is monitored from the drawing start time (t_ik),

- the drawing is regarded as completed when said water temperature (T_m) takes a minimum value,

- such minimum value is taken as water temperature at the end of the drawing (T_mfk),

- said temperature decrease (ΔT_k) due to the drawing (P_k) is calculated as a difference between said initial and final temperatures (T_mik, T_mfk), that is, according to the relation ΔT_k = T_mik - T_mfk.
Method for the management of a water heater (1) according to the previous claim,
characterised in that
the drawing temperature value (T_set.k) sufficient for ensuring said drawing (P_k) at the usage temperature (T_u) is obtained
- adding a predetermined value of maximum temperature required (T_req.max) and a further empirical corrective term of the value of 5 °C to said temperature decrease (ΔT_k), that is, applying the formula T_set.k = ΔT_k + T_req.max + 5,

- but still keeping said drawing temperature value (T_set.k) comprised between the maintenance temperature (T_stand-by) and the maximum setup temperature (T_set.max) values,
where
- said predetermined value of maximum temperature required (T_req.max) is the value sufficient for satisfying the greatest of the drawings expectable for the types of users for which said water heater model (1) is regarded as suitable,

- said maintenance temperature value (T_stand-by) is that to be set for ensuring that little unexpected drawings may be obtained at the usage temperature (T_u).
Method for the management of a water heater (1) according to the previous claim, characterised in that
said preferred value for the maximum temperature required (T_req.max) is 52 °C.
Method for the management of a water heater (1) according to any previous claim
characterised in that
- the water temperature (T_m) is always kept equal to a target temperature (T_target) which:

- during the first of said drawing cycles wherein said information on the drawing profile are acquired, is equal to a preset value (T_set),

- during the next drawing cycles,
- is set equal to the maintenance temperature (T_stand-by) away from the drawing times

- but is brought to the drawing temperature (T_set.k) at the time of the expected drawing start (t_ik).
Method for the management of a water heater (1) according to the previous claim,
characterised in that
for the water temperature (T_m) to reach the drawing temperature value (T_set.k) at the time of the expected drawing start (t_ik),
- the value (T_m1) of the water temperature (T_m) at a given time is recorded,

- the value (T_m2) the water temperature (T_m) has reached after a predetermined time (Δt) is recorded,

- the inertia (I_wh) value of the water heater (1) is calculated by the relation I_wh = (T_m2-T_m1)/Δt

- an advance time (Δt_advance) is calculated by the relation Δt_advance.k = (T_set.k - T_m)/I_wh

- the heating element (3) is actuated with an advance equal to the advance time (Δt_advance) relative to the drawing start time (t_ik).
Method for the management of a water heater (1) according to at least claim 9
characterised in that
said target temperature (T_target) is kept equal to the value of the drawing temperature (T_set.k) for an entire delay time interval (Δt_delay) subsequent to the expected drawing start time (t_ik), where said delay time interval (Δt_delay)
- is a predetermined value for each water heater model (1),

- has such duration as to satisfy larger drawings than those allowed by the drawing temperature (T_set.k).
Method for the management of a water heater (1) according to the previous claim, characterised in that
said delay time interval (Δt_delay) is equal to 15 minutes.
Regulator (4) for a water heater (1) provided with
- means (IN, IN.1, 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, T1, T2) of the water heated in the storage tank (2) and sensed by one or more sensors (S, S1, S2)

- a memory (MEM) suitable for storing said first data received from the outside, said second temperature data received from said one or more sensors (S, S 1, 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 (U1) for sending output signals for the ON-OFF or modulating control of a heating element (3) suitable for heating water in said storage tank (2)

- any second output means (U2) for signalling the system status to the user and/or to the operator
characterised in that
it is suitable for carrying out the method of claim 1.
Water heater (1) provided with
- heating element (3)

- one or more sensors (S, S1, S2) arranged at different heights in such positions (S, S1, S2) that the temperatures (T, T1, T2) sensed thereby are representative of the temperature distribution within the tank (2)
characterised in that
it further comprises a regulator (4) according to claim 13.
Water heater (1) according to the previous claim,
characterised in that
said one or more sensors (S, S1, S2) consist in a single sensor (S, S1).
Water heater (1) according to claim 14
characterised in that
said one or more sensors (S, S1, S2) consist in two sensors (S, S1, S2) a first sensor (S, S1) being arranged low, substantially at 100 to 200 mm from the bottom of the tank and in any case in the proximity of the cold water inlet (2.1) of the storage tank (2).
Water heater (1) according to claim 14
characterised in that
more than two sensors (S, S1, S2) are provided distributed so as to sense the temperature pattern (T, T1, T2) along the vertical axis with certain accuracy.