ES2609769T3 - Procedure to minimize the energy consumption of an accumulation water heater - Google Patents

Abstract

Procedure for managing an accumulation water heater (1) in which the storage water is heated by means of a heating element (3) governed by a regulator (4) capable of regulating the water temperature (Tm) up to a variable target temperature (Ttarget) and in which said procedure comprises, - a first stage in which information is captured - in relation to the extraction profile (P1, ..., Pk, ..., Pn) that is repeated substantially invariably during the subsequent extraction cycles - and the heating rate (VTh) characteristic of said storage water heater (1) - a second stage in which, before the start time (tk) of each extraction (Pk) of all the n extractions (Pn) included in each of said extraction cycles, - the water temperature (Tm) is brought to at least the value of the extraction temperature (Tset.k; T'set.i) sufficient to guarantee that said extraction at use temperature (Tu) starts heating at a heating start time (tONk; t'ONi) - provided that, in any case, said water temperature (Tm) remains less than or equal to the maximum set temperature (Tset.max), less than the dangerous values, - deducting said value from extraction temperature (Tset.k; T'set.i) and said heating start instant (tONk; t'ONi) based on the previously captured information, characterized in that said information capture on the extraction profile - takes place by during at least one extraction cycle for collection - and consists of calculating, for each of said n extractions (Pk), - the extraction start instant (tk), - the extraction temperature (Tset.k) performing said calculation solely by processing the data obtained from the analysis of the water temperature (Tm) obtained from the average of one or more temperatures (T; T1, T2) measured at different heights (S; S1, S2) of the tank (2) at time intervals (δtc) and characterized in that the determination of said heating start instant (tONk; t'ONi) to guarantee these extractions (Pk; Pi) takes into account the following steps: - with short intervals (δw), all w extractions (P1, ..., Pi, ..., Pw), are it takes into account the extraction start instant whose (ti) is within a fixed and predetermined interval (Δtw) immediately after the current instant. - wherein said time window (Δtw) is selected based on the type of users for which said storage water heater (1) is intended and is wide enough to include the extraction start instant (ti) of all draws (Pi) for which the false heating start times (t'ONi) are expected to be earlier than the false heat start times (t'ON) corresponding to the previous i-1 draws (P1, ..., Pi-1), - at said extraction start instant (ti) included within said time window (Δtw), the corresponding false extractions (P'1, ..., P'i, ..., P'w) that each present, - an extraction start instant (tw) equal to the corresponding real extraction (Pi), - a false extraction start temperature (T'set.i) obtained adding the starting temperatures of the extractions (Tset1, Tset2, ..., Tset(i-1)) of all the extractions included in said time window (Δtw) and prior to the extraction Pi itself to the actual starting temperature (Tset.i) corresponding, from where each one of the starting temperatures (Tset1, Tset2, ..., Tset(i-1)) has been deduced from the optimum emptying temperature Topt according to the formula [T'set. i>=Tset.i++(Tset1-Topt)+(Tset2-Topt)+...+(Tset(i-1)-Topt)] - for each of said false extractions (P'1, ..., P'i, ..., P'w), the false heating start instant t'ONi is calculated according to the formula [t'ONi>=ti - (Tset.i-Tm)/VTh],

Description

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an extraction of a mass of water Qp at the temperature of use Tu and, consequently, the greater the volume Vp involved in the mixture and, therefore, in smaller practice is the resulting decrease ∆Tm.

Therefore, in practice, the decrease ∆Tm detected by the sensors S; S1, S2 from the beginning to the end of the extraction is not constant with the extraction itself, but decreases as the effective average temperature Tm.eff drops at the beginning of the extraction, which however is not detected if said sensors S ; S1, S2 are arranged at a low level.

Finally, since this relationship between the decrease ∆Tm and the average effective temperature Tm.eff

- it is really insignificant if the final temperature of the extraction is relatively high (which indicates not very large extractions and / or a high starting temperature of the Tmik extraction)

- while it is more important if the final temperature of the extraction is quite low (which indicates large extractions and / or a start temperature of the Tmik extraction low), which causes an erroneous estimate of the amount of the extraction itself ,

according to the present invention, said erroneous estimate is corrected according to a rule whereby when the final temperature of the extraction Tmfk is lower than a predetermined limit value T, an additional term ∆T * "is added to said temperature decrease ∆Tk = Tmik-Tmfk (formula 6).

Of course, said rule and limit value depend on the model of the water heater 1 and the characteristics of the equipment, so they must be determined experimentally. A general rule is that said predetermined limit value Ts is between 20 and 30 ° C and that said correction factor ∆T "k is at most 50% of said temperature decrease ∆Tk.

A procedure for applying said rule, preferred for its simplicity and the good results it has provided experimentally, is as follows:

- if the final extraction temperature Tmfk is greater than or equal to the optimum emptying temperature Topt (an indication, among other things, that the extraction has been completely carried out), as already mentioned, the extraction temperature Tset.k it is set equal to the optimum emptying temperature Topt increased with the decrease of the previous temperature ∆Tk; that is to say:

Tset.k = Topt + ∆Tk se Tmfk ≥Topt (formula 10)

- if, on the other hand, the final extraction temperature Tmfk is lower than the optimum emptying temperature Topt (an indication, among other things, that the extraction has not been completely performed), said correction factor ∆T "is added k, whose value is equal to the difference between said optimal topt emptying temperature and the final extraction temperature Tmfk, that is:

∆T "k = + (Topt - Tmfk) if Tmfk <Topt (formula 11.a)

Tset.k = Topt + ∆Tk + ∆T "k if Tmfk <Topt (formula 11.b)

The registration stage of the extraction profile continues throughout the cycle, alternating said first and second sub-stages which, when automatically finished at the beginning and at the end of each extraction, respectively, will be the same number as the extractions.

In this way the profile of the n extractions has been determined and stored, and each extraction k is determined by two characteristic parameters, the moment of start of extraction tk and the decrease in temperature ∆Tk produced by it.

According to a version of the present invention, during the registration stage of the extraction profile in the collection cycle, a small adjustment to the actual characteristics of the equipment is already possible.

In fact, this version foresees that if the cycle is weekly, the initial default value Tset can be changed, which equals the maximum extraction temperature Tset.g, value stored the previous day, provided that this does not imply an excessive modification of the initial default value Tset (for example, included in Tset ± 3 ° C).

As a consequence, if the initial default value Tset was excessive for effective use, its reduction already results in a limitation of dispersions. On the other hand, if it was insufficient for larger extractions, the performance had already been improved. Of course, this version assumes that the amount of individual extractions (not necessarily their number) does not vary substantially much each day.

The procedures for managing the water heater 1 according to the present invention will be described below, once the extraction profile has been captured during the collection cycle.

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According to the present invention, the Ttarget target temperature

-It can always remain the same as Tstand-by maintenance temperatures away from extractions -but it takes up to a temperature Tset.k not lower than the extraction temperature Tset.k with a relativotant relative to

Tk extraction start time sufficient to guarantee such extraction.

Figure 4.a shows some points P1, ... P4 that represent the same extractions characterized by the corresponding moments t1, ... t4 of the start of the extraction tk and the corresponding temperatures Tset.l, .. Tset.4 of the Tset.k.

Figure 4.b also shows the evolution of the temperature Tm with the ascending slopes R1, ... R4 to reach said extraction temperatures T1, .. T4.

Said slopes R1, ... R4 have an evolution that depends on the heating rate VTh. The evolution, as it is known, is exponential but can be approximated by a rectilinear part without appreciable errors given the order of size of the time constant of the water heater temperature (for example, much greater than 106 s for a heater of standard water 1).

It is assumed that for each extraction k, the start time of heating tONk can be calculated with the formula

tONk = tk - (Tset.k - Tm) / VTh (formula 12)

- in which the term (Tset.k-Tm) / VTh expresses the heating advance interval ∆tant with respect to the start time tk required for the temperature Tm to pass from the current value to the extraction value Tset.k

- and in which said calculation must be carried out in short intervals, for example 60 seconds, taking into account the closest extraction, that is, with the start time of extraction tk closest in time.

In reality, this procedure is unsatisfactory.

In fact, in the example of Figure 4.b, it should be noted that proceeding in this direction, the extraction P1 has been carried out but in the end there is not enough time for the temperature to reach Tm which, following the extraction, has decreased to Optimum topt emptying temperature, up to the T2 extraction temperature required by the P2 extraction. For the same reason, the P3 extraction is also not performed, although the P4 extraction, small and far from the previous ones, is carried out.

In practice, it is not possible to guarantee the service with a procedure that takes into account, one at a time, only the closest of the extractions.

On the other hand, according to the present invention, the following procedure called "false extractions" is applied, which actually involves the creation of false extractions.

With a fairly short intervals δw, for example 60 seconds, all w extractions P1, ..., Pi, ..., Pw, take into account the start time of extraction whose ti is within a fixed interval and default (referred to hereinafter as a ventanatw time window) immediately after the current instant.

At said extraction start time tw within said time window ∆tw, the corresponding false extractions P'1, ..., P'i, ..., P'w each characterized by:

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 a start time of extraction tw equal to the corresponding actual extraction Pi

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 but a false start temperature of the extraction T'set.i obtained by adding the start temperatures of the extractions Tset1, Tset2, ..., Tset (i-1) of all the extractions included in said time window has been deduced ∆tw and prior to the actual extraction Pi at the corresponding actual start temperature Tset.i, from which the optimum emptying temperature Topt has been deduced. That is, in formulas,

T'set.i = Tset.i + (Tset.i - Topt) + (TSet2 - Topt) + ... + (Tset (i-1) - Topt) (formula 13)

Figures 4.c and 4.d show the result of this operation in which the false extractions P'1, P'2, P'3, P'4 are indicated above the corresponding real extractions P1, P2, P3 , P4. The false extraction P'1 coincides with the real extraction P1 because, since it was the first in the time window ∆tw, at its starting temperature Tset.1, no other temperature has been added.

At this point, for each extraction Pi of the w extractions included in the time window ∆tw, the start time of the false heating t'ONi is calculated according to the formula

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This is achieved thanks to the fact that the procedure calculates the start time of the false heating t'ONi of the Pi extraction, also taking into account the instant of heating to be assigned to all the previous extractions.

5 It should be noted that the start temperature of the false extraction T'set.i is almost never reached since as the heating takes place, the intermediate extractions decrease the temperature of the water Tm.

In practice, the "false extractions" procedure allows to supply the thermal energy strictly necessary to guarantee the extractions, maintaining the temperature of the water Tm, at every moment, at the value

10 minimum required for said service and calculating the duration of the operating periods of the heating element 3 without explicitly knowing the thermal power thereof.

Needless to say, with the inconvenience of the maximum energy savings that can be obtained but with the advantage of service safety, these instants of t'Oni heating start can be advanced a little (a

15 tolerance advance ∆tol to take into account the deviations of the effective moments of start of extraction (ti) with respect to those registered during the extraction of the extraction cycle). In fact, if the registration of the extraction profile continues in the extraction cycles after the first collection cycle, the regulator can capture what value to assign to said tolerance advance ∆toll.

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Claims (1)

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