WATER HEATER ENABLED TO RESPOND TO GRID CONDITIONS

Abstract

Object of the present invention is an electric water heater with a vertical development storage and upper and bottom resistive heating elements and possibly a lower heating element consisting of the condenser of a heat pump. The water to be heated enters the bottom portion and is drawn from the upper section. The water heater is configured to operate in different heating modes selectable by a user, wherein all the modes guarantee to meet a set temperature but different by control logic and consumption level and is further able to have flexible consumption depending on a condition of the power grid.

Claims

1. Water heater powered by energy from a power grid, the water heater comprising: a vertical development storage having an upper portion and a bottom portion to which are associated respective upper temperature sensor and bottom temperature sensors and at least one respective upper heating element and bottom heating element, adapted to heat the liquid in the storage, an interface for selecting one of at least two heating modes (Comfort, I-memory, Green, Fast, I-memory green, I-memory fast) differing from each other by control logic of the heating elements and which are configured to reach a thermostating temperature T.sub.target that is one of a user set temperature T.sub.set, or a temperature threshold T.sub.hp of a heating element which is a condenser of a heat pump or an optimised temperature T.sub.mem, a regulator of the heating elements, adapted to receive readings from the temperature sensors the selected heating mode (Comfort, I-memory, Green, Fast, I-memory green, I-memory fast) and to implement the control logic of the heating elements according to the selected heating mode, wherein the regulator is configured to modify the control parameters of the heating elements in response to a detected and/or estimated and/or expected condition of energy scarcity or surplus of the grid and the behaviour resulting from a response to a grid condition is a function of both the power grid condition and the heating mode selected by the user, the water heater characterised in that the regulator is further configured to modify the control parameters thereof according to a condition selected among one of scarcity or surplus condition of electrical energy and to the selected heating mode for at least some scarcity and abundance grid conditions so that at least some of the heating elements are still controlled at a thermostating temperature to be reached.

2. Water heater as in claim 1, wherein the control parameters comprise at least one of the thermostating temperature T.sub.target or a hysteresis of a heating element or a deactivation status of some of the heating elements in favour of another heating element.

3. Water heater as in claim 1, wherein the control parameters modified in response to a condition of the grid comprise at least a thermostating temperature T.sub.target common to all the active heating elements.

4. Water heater as in claim 1, wherein to the condition of energy scarcity and/or surplus of the power grid can be associated severity levels and the regulator is configured to respond in a different way to at least two of the following severity levels listed in increasing order for each condition: a first scarcity level (Load shed), a second scarcity level (Critical peak event), a third scarcity level (Grid emergency) a first surplus level (Load up), a second surplus level (Advanced load up).

5. Water heater as in claim 4 wherein the regulator is configured to set a possible new thermostating temperature T.sub.target for all the heating elements and/or a possible new hysteresis T.sub.hyst for the bottom heating elements according to the severity level detected.

6. Water heater according to claim 4, configured to respond to the first scarcity level (Load shed) by setting the thermostating temperature Ttarget to the minimum value between a comfort threshold Tconfort and the previous thermostating temperature Ttarget, in formulas:
T.sub.target=min(T.sub.confort,T.sub.target) where the comfort threshold T.sub.confort is a value comprised in the interval 40 C. to 50 C., preferably it is equal to about 42 C.

7. Water heater as in claim 6, configured to respond to the second scarcity level (Critical peak event) by implementing the response to the first scarcity level (Load shed) and in addition: if the heating elements comprise a heat pump by deactivating any resistive elements, otherwise by deactivating the at least one of the bottom resistive elements.

8. Water heater as in claim 4, configured to have a hysteresis Thyst of the bottom heating elements: in models with only bottom resistive type elements, comprised in an interval from 4 C. to 21 C. and preferably equal to 15 C., in models comprising at least one condenser of a heat pump as a bottom heating element comprised in an interval from 4 C. to 20 C. and preferably equal to 5 C., and to respond to the first surplus level (Load up), by bringing the hysteresis T.sub.k|vw of the bottom elements to a value lower than or equal to 3 C.

9. Water heater as in claim 8, configured to respond to the second surplus level (Advanced load up) by implementing the response to the first surplus level (Load up) and in addition: if provided with resistive heating elements only, by setting the thermostating temperature T.sub.t.sub.dujhw equal to a predefined maximum temperature T.sub.max, if provided with at least one heat pump and having a sustainable heating mode selected (Green; I-memory green) characterised by limiting the use of the heating elements to the heat pump only, by setting the thermostating temperature T.sub.target equal to the minimum between a maximum temperature T.sub.max provided for the thermostating temperature T.sub.target and a maximum temperature threshold T.sub.hp that may be reached by the heat pump.

10. Water heater as in claim 4 configured to receive signals (S) that the regulator is able to process and that convey a condition of the grid and optionally the severity level.

11. Water heater as in claim 4, configured to respond to an energy price hourly schedule, by associating to the lower price values the severity levels corresponding to the surplus condition, by increasing price and decreasing severity level and to the higher prices the severity levels corresponding to the scarcity condition, by increasing cost and increasing severity level.

12. Method for heating a liquid in a water heater according to claim 4, the method comprising: step 1: receiving from a user interface the selection of a heating mode (Comfort), (I-memory), (Green), (Fast), (I-memory green), (I-memory fast) that defines a control logic for each heating element, step 2: receiving a first signal (S) associated with a severity level of an energy scarcity or surplus condition of energy in the grid and a time duration, the severity level belonging to the list: a first scarcity level (Load shed), a second scarcity level (Critical peak event), a third scarcity level (Grid emergency), a first surplus level (Load up), a second surplus level (Advanced load up), step 3: according to the selected heating mode and to the severity level, setting a possible new thermostating temperature T.sub.target for all the heating elements and/or a possible new hysteresis T.sub.hyst for the bottom heating elements, in the event of a third scarcity level (Grid emergency), deactivating the heating elements, in the event of a second scarcity level (Critical peak event) if the heating elements comprise a heat pump, deactivating any resistive elements, otherwise deactivating the at least one of the bottom resistive elements, if a second signal arrives (S), repeating step 2, otherwise, if a new heating mode (Comfort), (green), (I-memory), (fast), (I-memory green) or (I-memory fast) is selected or a new temperature T.sub.set is set, continuing with step 3 with the new heating mode or the new value of set temperature T.sub.set for the remaining time duration.

13. Method for heating a liquid in a water heater according to an hourly rate schedule, wherein the water heater is according to claim 4, the method comprises the following steps: step 1: receiving from a user interface, a heating mode that defines a control logic for each heating element, step 2: reading into memory or receiving from an input or from the grid an hourly schedule of the prices, wherein the order between step 1 or 2 makes no difference, step 3: dividing the interval between minimum and maximum price into as many sub-intervals as the overall severity levels are plus a possible intermediate interval, step 4: sorting the intervals by increasing price and associating them to the severity levels by associating the lower price intervals with the energy surplus conditions by decreasing severity and increasing price order and the higher cost intervals with the decreasing severity order of scarcity conditions and decreasing price by leaving an intermediate interval not associated with any severity level, step 5: for each new time band in which the price does not belong to the intermediate interval, deactivating the heating elements and/or modifying the control parameters thereof according to the active heating mode (Comfort), (Green), (I-memory), (Fast), (I-memory green) or (I-memory fast) and to the severity level (Load shed), (Critical peak event), (Grid emergency), (Load up), (Advanced Load up).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0014] FIGS. 1.a, 1.b, 1.c, 1.d show various views of a possible embodiment of a water heater with electrical resistances;

[0015] FIGS. 2.a, 2.b and 2.c show a second possible embodiment of a water heater comprising electrical resistances and a heat pump;

[0016] FIGS. 3.a and 3.b show tables of correspondence between hourly rates and particular grid conditions;

[0017] FIG. 4 shows a table with values taken by a variable in different possible operating modes.

[0018] Further features of the present invention shall be better highlighted by the following descriptions of possible embodiments, in accordance with the claims and illustrated, purely by way of a non-limiting example, with the aid of the figures. It should be noted that the invention is not limited to the constructive details and examples and to what is illustrated in the figures; other embodiments are possible without thereby departing from the scope of the claims. The terms used in the description should not be construed as limiting. The terms receive, read, detect, sense are used in a broad sense to indicate receiving information comprising the cases of information contained in signals coming from outside, retrieved from a memory or received as input from a user interface. Similarly, communication or connection are not limited to communication via physical links or wiring.

[0019] In the figures, reference number 1 indicates a water heater comprising a vertically developing storage 10 having an upper 11 and a bottom 12 portion.

[0020] The upper portion 11 of the storage 10 comprises at least one first heating element 41, while the bottom portion 12 of the storage 11 comprises at least one second heating element 51, 61, hereinafter also referred to heating elements or elements in short. The at least one upper element 41 may comprise an electrical resistance, the at least one bottom element 51, 61 can be an electrical resistance 51 and/or a condenser 61 of a heat pump 6.

[0021] In the proximity of the respective elements 41, 51, 61, are a first temperature sensor or upper temperature sensor 42, which detects a higher temperature referred to as T.sub.dome, or also dome temperature and a second temperature sensor or bottom temperature sensor 52 which detects a bottom temperature T.sub.bottom. The temperature sensors 42, 52 may be conventional temperature sensors (for example thermistors).

[0022] A water heater 1 comprising as heating elements only resistances 41, 51 shall hereinafter be referred to as an electrical water heater or electrical model, to distinguish it from the hybrid model which also comprises a condenser 61 of a heat pump 6.

[0023] The storage 10 is configured to let cold water in in the proximity of the bottom 12 through a first opening 2, and to let heated water, directed to the user, out through a second opening 3 close to the top of the storage 10. This way, in stationary conditions, the stratification of the temperatures contributes to the fact that the water let out from the storage 10 is that at highest the temperature.

[0024] The water heater 1 also comprises a regulator 5 for regulating the operation of the heating elements 41, 51, 61.

[0025] The regulator 5 comprises memory means and is adapted to receive the temperature readings made by the temperature sensors 42, 52 and a temperature T.sub.set which can be set by the user, via a user interface 7.

[0026] The regulator 5 is configured to calculate a control temperature for each heating element 41, 51, 61. The control temperatures may be equal to the temperatures detected by the temperature sensors 42, 52 or may be equal to their weighted average. A plurality of heating elements 41, 51, 61 may share the same control temperature.

[0027] The regulator 5 may be an electronic control unit comprising: [0028] a memory with program instructions and parameters, [0029] means for executing instructions and calculations, [0030] means for controlling the heating elements and receiving signals from the outside.

[0031] The regulator 5 is configured to implement a set temperature, T.sub.set that may be set via a user interface 7. The user interface 7 may be integrated in the water heater and comprise manual input means such as buttons or knobs and/or be external and comprise means for sending input data to the regulator 5 that is configured to receive it. When integrated in the water heater 1, the user interface 7 may be assembled in a single assembly with the regulator 5, as shown in FIGS. 1.a, 1.b, 2.a and 2.b.

[0032] The upper section 11 of the storage is heated directly by the at least one upper heating element 41 and indirectly, by convection effect, by the at least one bottom heating element 51, 61. The at least one upper heating element 41 has the upper temperature T.sub.dome as control temperature or has the upper temperature T.sub.dome as the prevailing component in a weighted average of the temperatures sensed by the temperature sensors 42, 52. For the at least one bottom heating element 51, 61 the control temperature is the bottom temperature T.sub.bottom or alternatively an average temperature T.sub.avg that is obtained as the average between the dome temperature T.sub.dome and the bottom temperature T.sub.bottom. Preferably, such average is a weighted average, even more preferably the weight W.sub.dome of the dome temperature is less than the weight W.sub.bottom of the bottom temperature T.sub.bottom.

[0033] According to a preferred embodiment, the weight W.sub.dome of the dome temperature is comprised in an interval between 0.25 and 0.40, for example 0.3. At least one of the weights W.sub.dome, W.sub.bottom is a parameter stored in the memory of the regulator 5, the other being calculable accordingly or being stored as well.

[0034] A thermostating temperature T.sub.target is set for each heating element 41, 51, 61.

[0035] In a possible embodiment, the regulator 5 sets a common thermostating temperature T.sub.target at least for the electrical resistances 41, 51. The thermostating temperature T.sub.target of each heating element 41, 51, 61 is comprised in an interval between a minimum T.sub.min and maximum T.sub.max temperature (T.sub.minT.sub.targetT.sub.max).

[0036] The maximum temperature T.sub.max is a factory parameter, possibly modifiable on site, and may vary, for example, between 55 C. and 85 C. Preferably, it reaches the highest values if a thermostatic mixing valve is present.

[0037] The minimum temperature T.sub.min is one considered as acceptable to guarantee the comfort for domestic uses; it may be comprised between 37 C. and 42 C., for example around 40 C. Thermostating at temperatures higher than the minimum T.sub.min enables mixing the drawn water with cold water bringing the advantage of increasing the volume of delivered water beyond the volume of the storage.

[0038] The heating elements 41, 51, 61 are configured to be activated when the respective control temperature drops below the thermostating temperature T.sub.target minus a hysteresis value and to be deactivated at the thermostating temperature T.sub.target. The at least one upper element 41 has an upper hysteresis T.sub.hystDome (so the switch on temperature is T.sub.targetT.sub.hystDome) while the at least one bottom heating element 51, 61 has a bottom hysteresis T.sub.hyst (so the switch on is temperature T.sub.targetT.sub.hyst). In general, there may be different hysteresis for each heating element. The median value between activation and deactivation temperatures is therefore: [0039] for the upper heating element 41 T.sub.targetT.sub.hystDome/2; [0040] for the bottom heating element 51, 61 T.sub.targetT.sub.hyst/2.

[0041] By shifting all the temperature values of the amplitude of the hysteresis, the present description can be applied also to a possible embodiment in which the heating elements are activated at the thermostating temperature, T.sub.target, and are switched off at the temperature T.sub.target+T.sub.hyst, T.sub.target+T.sub.hystDome, which is when the temperature increase is equal to the hysteresis T.sub.hyst, T.sub.hystDome. In this case, the median value between activation and deactivation temperatures is therefore: [0042] for the upper heating element 41 T.sub.target+T.sub.hystDome/2; [0043] for the bottom heating element 51, 61 T.sub.target+T.sub.hyst/2.

[0044] In an embodiment schematically illustrated in FIG. 2.a, 2.b, the at least one bottom heating element 51, 61 comprises, a bottom resistance 51 and a condenser 61 of a heat pump 6.

[0045] In the illustrated example the condenser 61 comprises two sets of windings 611, 612 respectively positioned above and below the bottom resistance 51.

[0046] The heat pump 6 has a higher energy efficiency compared to the resistance 51, but may heat only up to a maximum heat pump temperature threshold T.sub.hp, hereon heat pump threshold T.sub.hp for brevity; a typical value for the heat pump threshold T.sub.hp of the pump is about 55 C. Beyond this heat pump threshold T.sub.hp, the heating function can be performed by the resistances 41, 51.

[0047] In the embodiment of FIG. 2 the bottom resistance 51 may work in relay with the condenser 61 of the heat pump 6. In the relay operation below the heat pump threshold T.sub.hp the bottom element used is the condenser 61, above the threshold T.sub.hp, the bottom element used is the resistance 51.

[0048] The relay operation between the exchanger 61 of the heat pump 6 and the bottom resistance 51 allows reducing both the instantaneous power consumption and the electrical energy consumption, because of the higher energy efficiency of the heat pump 6 compared to the resistance 51.

[0049] When the heat pump 6 and the bottom resistance 51 operate in relay, it is preferable that the control temperature for both is the average temperature T.sub.avg for a more efficient operation of the water heater 1. According to some embodiments in the water heater models 1 which comprise a condenser 61 as a unique or additional bottom heating element, for all of the bottom heating elements 51, 61 the control temperature is the average temperature T.sub.avg.

[0050] In the exclusively electrical models, for the bottom resistance 51 the control temperature is preferably the bottom temperature T.sub.bottom as measured by the bottom sensor 52.

[0051] In the preferred embodiments the upper 41 and bottom 51 resistances never activate together and even more preferably, the upper resistance 41 has priority over the bottom one 51. In other words, in these embodiments, priority is always given to heating the water contained in the upper part 11 of the storage 10, (which is the first water to be supplied).

[0052] In order to meet the contrasting needs to reduce the energy consumption and to guarantee enough hot water, the water heater 1 has at least two heating modes which may be selected according to users' need.

[0053] The heating modes, hereinafter also called modes for brevity, allow having water at a set temperature T.sub.set, but they are different for the control logic of the heating elements 41, 51, 61 and for consumption. The heating modes are preferably selectable with the user interface 7.

[0054] In a first heating mode called Manual or Comfort, the water heater 1 sets the thermostating temperature T.sub.target equal to the set temperature T.sub.set for all the resistive heating elements 41, 51 and for any heat pump 6, provided the user temperature T.sub.set is not higher than the heat pump threshold T.sub.hp. The user temperature T.sub.set varies between the minimum temperature T.sub.min and the maximum temperature T.sub.max. In the first heating mode, Comfort: [0055] the upper 41 and bottom 51 resistances are never activated together, [0056] the upper resistance 41 has priority over the bottom one 51, [0057] if a condenser 61 is present as a bottom element, the bottom resistance 51 operates in relay with the heat pump 6.

[0058] According to a possible embodiment, the heating modes further comprise a second heating mode which is an optimised mode, called I-memory. The second mode I-memory differs from the first mode, Comfort, for the thermostating temperature T.sub.target which is equal to an optimised temperature T.sub.mem that varies over time and is a function of a saved withdrawals pattern (the withdrawals pattern comprising the data of volume and temperature of withdrawals over a period). The optimised temperature T.sub.mem may vary from the minimum T.sub.min to the maximum T.sub.max temperature. Methods for calculating such optimised temperature are known; by way of an example a method is described in EP2366081B1 (the content whereof forms an integral part of the present description).

[0059] In FIG. 2, the water heater 1 comprises at least one heating element of the resistive type 41, 51 and one consisting of the condenser 61 of a heat pump 6, adapted to heat up to a maximum temperature heat pump threshold T.sub.hp.

[0060] In particular, in the embodiments herein described that include a heat pump 6, the water heater 1 may also comprise a third heating mode that is a sustainable mode called Green and/or a fourth heating mode that is a quick mode called Fast.

[0061] The third heating mode, Green, prioritizes reducing the electrical consumption, and it uses exclusively the heat pump 6, while the resistive elements 41, 51 are always deactivated. In the third mode Green, the thermostating temperature T.sub.target is equal to the minimum between the user temperature T.sub.set, and the heat pump 6 threshold T.sub.hp.

[0062] The fourth mode, Fast, prioritizes heating rapidly and differs from the first mode, Comfort, in that the bottom resistance 51 is not activated in relay, but simultaneously with the heat pump 6, with the only additional constraint that the upper resistance 41 is and remains off, while the bottom resistance 51 is on. In the fourth mode, Fast, the heat pump 6 is preferably controlled with the average temperature T.sub.avg, while the bottom resistance 51 is preferably controlled with the bottom temperature T.sub.bottom.

[0063] In the third Green and fourth Fast mode, the thermostating temperature T.sub.target is equal to the user set temperature T.sub.set. It is possible to implement a fifth mode called I-memory green which is equal to the third mode, Green, with the thermostating temperature, T.sub.target, equal to the minimum between the optimised temperature, T.sub.mem, and the heat pump temperature threshold T.sub.hp. Similarly, it is possible to implement a sixth mode called I-memory fast that is equal to the fourth mode, Fast, with the thermostating temperature T.sub.target equal to the optimised temperature T.sub.mem. This allows combining the advantages of the second mode I-memory with the third mode Green, or the fourth mode Fast. FIG. 4 shows in a table the values of the thermostating temperature T.sub.target for each heating mode.

[0064] From the above description it is clear that each heating mode is configured to reach one of a user set temperature T.sub.set, a temperature threshold T.sub.hp of a heating element which is a condenser 61 of a heat pump 6 or an optimised temperature T.sub.mem.

[0065] According to some possible variants, at least two hysteresis values are defined: an upper hysteresis T.sub.hystDome for the upper element 41 and a bottom hysteresis T.sub.hyst for the at least one bottom element 51, 61. It has been observed that adopting different hysteresis values for the upper 41 and bottom heating elements 51, 61 allows further reducing the consumption or, for the same consumption, improving comfort. Hereinafter, dome hysteresis T.sub.hystDome indicates the hysteresis of one or more upper elements, bottom hysteresis T.sub.hyst indicates that of one or more bottom elements 51.

[0066] In particular, in the embodiments of the water heater 1 with only electrical resistances 41, 51 it is advantageous having a bottom hysteresis T.sub.hyst of higher value, (for example comprised between 2 C. and 21 C., preferably between 12 C. and 18 C., in particular 15 C.) and a hysteresis at the dome T.sub.hystDome of smaller value (for example between 1 C. and 20 C., preferably between 3 C. and 9 C., in particular 5 C.).

[0067] Instead, in the embodiments in which the water heater 1 comprises a condenser 61 of a heat pump 6 as a bottom heating element, the situation is reversed and it is more convenient having a bottom hysteresis T.sub.hyst of smaller value (for example in an interval between 1 C. at 20 C., preferably between 3 C. and 9 C., in particular 5 C.) and a hysteresis at the dome T.sub.hystDome of higher value (for example an interval comprised between 2 C. and 21 C., preferably between 9 C. and 18 C., in particular 12 C.).

[0068] This is because in the embodiments in which the water heating is obtained only by means of electrical resistances, it is preferred to avoid the activation of the bottom resistance 51 for small and momentary temperature oscillations which are due to the entry of cold water caused by small withdrawals and subsequent turbulences of water. A higher value hysteresis T.sub.hyst at the bottom resistance 51, renders it more stable and less sensitive to small turbulences. To compensate for less sensitivity, it is very useful to set an upper hysteresis T.sub.hystDome at a smaller value, so as to render the upper resistance 41 very sensitive even to small turbulences so that it is promptly activated to guarantee the correct temperature at the outlet 3 of the water heater 1.

[0069] In the embodiments that also include a condenser 61 as a bottom heating element, the priority is in maximizing use of the heat pump 6 thus limiting the use of the resistances 41, 51. Herein here it is therefore advisable to activate the heat pump 6 even for small water temperature fluctuations by adopting a bottom hysteresis T.sub.hyst smaller in value than the upper hysteresis T.sub.hystDome.

[0070] Optionally, in the heat pump models the electrical model hysteresis are used when the average temperature T.sub.avg, or the thermostating temperature T.sub.target, is greater than the heat pump threshold T.sub.hp. In these conditions the heat pump 6 is unable to make a contribution and the water heater 1 may be controlled as if it were an electrical model.

[0071] According to a possible embodiment, the water heater 1 is powered by energy from a power grid and is configured to operate with at least two heating modes selected between the first mode Comfort, the second mode I-memory, the third mode Green, the fourth mode Fast, the fifth mode I-memory green, or the sixth mode I-memory fast and to receive the heating mode selection from a user interface. The regulator 5 is further configured to deactivate the heating elements 41, 51, 61 and/or modify the control parameters thereof according to a scarcity or surplus condition (detected or estimated or foreseen) of electrical energy and of the selected heating mode.

[0072] In ideal conditions, the demand for electrical energy and the energy fed into the power grid balance each other. In practice these values vary with respect to each other giving rise to imbalance conditions which cause a frequency and voltage drift. Beyond an allowed interval, the grid does not tolerate this imbalance, and to avoid damage or generalised blackouts, or in any case to comply with voltage and frequency standards, either users or generators may have to be disconnected. In what follows conditions of significant imbalance towards the energy supply will be referred to as conditions of scarcity and vice versa those of significant imbalance towards the energy fed into the grid will be referred to as conditions of surplus.

[0073] Both in the scarcity condition of the grid (imbalance towards the demand) and/or in the surplus (imbalance towards the supply) of energy, several severity levels may be defined and preferably the water heater 1 is configured to respond to at least two different severity levels (hereinafter level) for to a condition of energy scarcity and/or surplus from the grid.

[0074] In a possible embodiment, the regulator 5 is adapted to manage the following severity levels, listed in order of increasing severity: [0075] a first scarcity level that indicates a moderate imbalance towards the demand referred to as Load shed, [0076] a second scarcity level that indicates a strong imbalance towards the demand referred to as Critical peak event, [0077] a third scarcity level that indicates a very strong imbalance towards the demand with the risk of detachment referred to as Grid emergency [0078] a first surplus level that indicates a moderate imbalance towards the supply called Load up, [0079] a second surplus level that indicates a strong imbalance towards the supply referred to as Advanced load up.

[0080] It should be noted that the response of the water heater 1 does not guarantee an immediate and certain change in the consumption level, but there is a probability associated to the change in consumption and the probability increases with the severity level and with the persistence of the grid condition over time. This is because of the physical constraints of the thermodynamic system and because the regulator 5 of the water heater 1 preferably implements rules which ensure that a minimum comfort level is maintained. If several water heaters 1 exist in the same power grid, over large numbers, the overall effect to have a variation of energy demand is certain, therefore the objective of balancing the grid is achieved.

[0081] According to a first embodiment, the water heater 1 is able to receive and the regulator 5 is configured to respond to signals S, that indicate a condition of scarcity or surplus of energy in the grid, according to at least some of the five severity levels defined, first, second and third scarcity levels: Load shed, Critical peak event, Grid emergency, first and second surplus levels: Load up, Advanced load up.

[0082] Several known protocols allow a device connected to the grid to receive signals S that correspond to at least some of the listed severity levels. Some protocols include in a signal S a severity level and a duration required for the response.

[0083] By way of a non-limiting example, the water heater 1 may be configured to receive signals compatible with the protocol CTA2045. In general, similar protocols are increasingly widespread because they are functional for implementing so-called demand response services, that allow the energy supply in a period to be flexible in order to follow the demand.

[0084] The water heater 1 may receive the signals S directly from the grid or may receive them indirectly by means of other devices that receive them from the grid.

[0085] According to possible embodiments, the signals S are sent to the water heater 1 by a local device that manages the energy consumption of one or more devices.

[0086] In a second embodiment, the water heater 1 responds to an hourly schedule of the energy price and assigns one of the severity levels to price values higher or lower with respect to an average value. Without loss of generality, the hourly schedule may be preset in the water heater 1, manually updated by a user, periodically updated or received in real time by the water heater 1 that is set up to receive and manage an hourly price signal. By way of a non-limiting example, the water heater 1 may be configured to receive hourly rate signals with the protocol JA-13.

[0087] The same water heater 1 may be configured to receive signals S and to have hourly schedules set. The first, second and third scarcity level Load shed, Critical peak event, Grid emergency have priority over any other setting comprising hourly price schedules. Preferably, the response to a grid condition has priority over the hourly schedules. In general, the water heater 1 gives priority to the signals S from the grid.

[0088] The water heater 1 described above may operate as follows: [0089] receiving from a user interface the input of a heating mode Comfort, I-memory, Green, Fast, I-memory green, I-memory fast that defines a control logic for each heating element, [0090] receiving a first signal S to which one of the severity levels of a scarcity or surplus condition in the grid is associated and a time duration, the severity level being one among the list containing the first, second, third scarcity level, Load shed, Critical peak event, Grid emergency, and first and second surplus level Load up, Advanced load up, [0091] according to the selected heating mode and to the severity level, a new thermostating temperature T.sub.target is set for all the heating elements and/or a new hysteresis T.sub.hyst is set for the bottom heating elements, [0092] in the event of a third scarcity level Grid emergency, the heating elements are deactivated, [0093] in the event of a second scarcity level Critical peak event, in the heat pump model, deactivating the resistances 41, 51, in the case of an electrical water heater, deactivating the bottom resistance 51, [0094] if a second signal S arrives, going back to step 2, [0095] if a new heating mode Comfort, Green, I-memory, fast, I-memory green, I-memory fast is selected or a new temperature T.sub.set is set, continuing the step 3 with the new heating mode or the new set temperature value T.sub.set for the remaining time duration, [0096] at the end of the time duration associated with the signal S, restoring the control logic associated to the selected heating mode.

[0097] The water heater 1 may be configured to respond to an energy price hourly schedule, by associating to the lower price values the severity levels corresponding to the surplus condition, by decreasing price and increasing surplus severity level and by associating to the higher prices the severity levels corresponding to the scarcity condition, by increasing price and increasing scarcity severity level. Preferably prices that are in an intermediate level are not associated with any severity level.

[0098] A method is described for optimising the consumption according to an hourly rate schedule, using FIGS. 3.a and 3.b. The method comprises the following steps: [0099] receiving from a user interface 7 a heating mode that defines a control logic for each heating element; [0100] reading in memory or receiving from input or from the grid an hourly scheduling of the energy prices, each associated with a period of the day referred to as time band; [0101] wherein the order of execution between step 1 or 2 is indifferent: [0102] identifying the minimum and maximum price among all those associated with the various time bands; [0103] selecting the severity levels to which there is a need to respond; [0104] dividing the interval between minimum and maximum price into as many sub-intervals as the selected severity levels plus a possible intermediate interval; [0105] sorting the intervals by increasing price and: [0106] associating the lowest price intervals with the conditions of energy surplus in order of decreasing severity and increasing price; [0107] associating the higher price intervals with the energy scarcity conditions in order of decreasing severity and decreasing price; [0108] leaving the intermediate price interval not associated with any severity level; [0109] for each new time band in which the price does not belong to the intermediate level, controlling the heating elements according to the active heating mode and severity level.

[0110] FIG. 3.a shows a depiction according to a possible embodiment in which the selected severity levels are a first and second scarcity level Load shed, Critical peak event, and first surplus level Load up. FIG. 3.b shows a second possible embodiment wherein all the defined severity levels are selected.

[0111] Some preferred embodiments for changing the control parameters according to the severity levels are described below. It has been said that the water heater 1 is configured to respond to the different severity levels by modifying the control parameters; according to a preferred embodiment the control parameters comprise at least the thermostating temperature T.sub.target. Preferably the control parameters comprise also upper hysteresis T.sub.hystDome and/or bottom hysteresis T.sub.hyst.

[0112] For the first scarcity level load shed the water heater 1 sets the thermostating temperature T.sub.target to the minimum value between a comfort threshold T.sub.comfort, and the previous thermostating temperature T.sub.target, in formulas there is:

[00001]$T_{\mathrm{target}}=\min \left(T_{\mathrm{comfort}},T_{target}\right)$

[0113] The comfort threshold T.sub.comfort is a value comprised in the comfort interval that corresponds to about 40 C.-50 C., preferably it is equal to about 42 C.

[0114] In any heating mode the thermostating temperature T.sub.target may already be lower than a comfort threshold T.sub.comfort=42 C. either because the user has already set it to the minimum value or because it is set by the algorithm in case of second mode I-memory. In all the other cases an actual reduction of the consumptions is achieved.

[0115] In some possible embodiments the water heater 1 combines both the reduction of the described thermostating temperature T.sub.target, and the deactivation of the bottom resistance 51 in order to respond to the second scarcity level critical peak event, and in case of heat pump model it deactivates also the upper resistance 41, by heating only with the heat pump. This response is applicable to all heating modes.

[0116] The water heater 1, for responding to the third scarcity level Grid emergency, may deactivate all the heating elements and/or may set the thermostating temperature T.sub.target to a value just above the average temperature of the mains water, by way of a non-limiting example equal to 16 C. In this case, the functionality is no longer guaranteed; the third scarcity level Grid emergency indicates the risk of blackouts or an hourly cost of energy that the user is not willing to bear.

[0117] According to a possible embodiment, the bottom hysteresis T.sub.hyst under normal mains conditions is greater than or equal to 4 C. and the water heater 1, in order to respond to the first surplus level Load up, increases the average temperature in the bottom section with respect to the thermostating temperature T.sub.target; this is achieved by reducing the bottom hysteresis T.sub.hyst, which corresponds to increasing the temperature at which the elements are reactivated. By way of an example, the hysteresis may be reduced to a value lower than or equal to 3 C. It should be noted that in an alternative embodiment where the hysteresis defined the switch-off threshold, the hysteresis would be increased in order to obtain the same effect of average temperature increase.

[0118] In response to the second surplus level Advanced load up, in addition to increasing the average temperature in the bottom section, by reducing the bottom hysteresis T.sub.hyst, the water heater 1 may increase the thermostating temperature T.sub.target up to the maximum temperature T.sub.max. In case of third mode Green, the thermostating temperature T.sub.target maximum value has the heat pump threshold T.sub.hp as upper limit.

[0119] It should be noted that the response to the severity level maintains the essential characteristics of the heating mode, for example if in the second mode I-memory the thermostating temperature T.sub.target is 40 C., a severity level Load up causes a reduction in the bottom hysteresis T.sub.hyst (i.e. a small increase in the average temperature in the bottom section with respect to the thermostating control temperature T.sub.target) but not a thermostating increase at unnecessary temperatures.

[0120] In other words, the regulator 5 is configured so that the response to the severity level does not constitute a shift from one mode to another, but a modification within the selected heating mode. Therefore, the response to severity levels is combined with the control logic determined by the selected heating mode resulting in a modified logic that depends both on the selected heating mode and the severity level.

[0121] Any reference to a user interface is to be understood in the broad sense and includes any device able to receive an input from a user and send it to the regulator 5; in particular it includes, by way of a non-limiting example, a dedicated physical user interface 7 comprised in the water heater, or the interface of a smart phone or other devices that are not part of the water heater 1, but from which the water heater 1 is configured to receive input with any known communication technology including wireless communication or a vocal command sensor.

[0122] It is clear for the expert of the field that a system with the characteristics of water heater 1 can be used to heat other types of liquid and is not limited to water.