EP2529159B1 - Flat water heater with reduced capacity storage tanks - Google Patents

Description

• The object of the present invention is a storage water heater known as flat.
• In this description, the following terms have the following meaning:
• by "standard storage water heater" or simply "standard water heater" it is meant a storage water heater provided with a single cylindrical tank;
• by "predetermined storage temperature Tacc" or simply "storage temperature Tacc" it is meant the maximum storage temperature at which the thermostatic adjustment means allow to maintain the water stored in the water heater; the storage temperature Tacc is a typical parameter of each model of water heater, generally equal to 60 - 75 °C and lower by at least 10 - 15 °C than the storage temperature compatible with the safety standards;
• by "set temperature Timp" it is meant the optional water temperature that may be set by the user which can at most be equal to the storage temperature Tacc;
• by "usage temperature Tu" it is meant the temperature at which the hot water is deemed as used by the utilities (generally Tu = 40 °C); the utility obtains this temperature by mixing the water it receives from the water heater with the cold water coming from the waterworks at a temperature Th (generally Th = 15 °C);
• by "capacity Vc" it is meant the overall volume of water contained in the tanks one water heater is provided with;
• by "useful water volume Vu" it is meant the maximum volume of water at usage temperature Tu obtainable in a single drawing from a water heater maintained at the maximum temperature allowed by the manufacturer;
• "equivalent" are two storage water heaters that are characterised by the same volume of useful water Vu;
• by "flat storage water heater" or, more briefly, "flat water heater", it is meant a storage water heater that has one of the three dimensions, in particular the distance between front face and back face, that is the thickness, significantly reduced compared to the corresponding one of an equivalent standard water heater.
• While with the same capacity Vc, a flat water heater has a larger outside dispersing surface and a higher cost than a standard water heater, such equipment is more appreciated as it has a more pleasant appearance and is less cumbersome in the room it is installed in.
• The considerably smaller thickness of flat water heaters compared to that of an equivalent standard water heater is due to the use of a flat tank and/or to the use of two or more tanks with a reduced thickness compared to the diameter of the single tank of the standard water heater.
• When two or more tanks are provided, the "upstream" one receives the cold water to be heated and the "downstream" one sends it hot to the utilities.
• For an exemplary flat water heater with two tanks, see document US 2004/0079749 .
• Hereinafter, the term "flat water heater" will denote flat water heaters using two or more tanks, preferably but not necessarily cylindrical, because the present invention refers to them, excluding those using a single flat tank. As regards the heating system, it may be either electrical or by fuel without distinction.
• An advantage of such flat water heaters is that it is quite simple to heat only a part of the stored water, when this is sufficient for the expected consumptions, heating only the water contained in the downstream tank (or tanks).
• The so-called "mixing" phenomenon is well known in storage water heaters, which may substantially be synthesised in that the cold water, entering the tank, upon each drawing of hot water mixes with the stored hot water, making a part that had already exceeded the minimum temperature required (equal to the usage temperature Tu) drop below the same, thus reducing the volume of useful water Vu compared to that theoretically possible for that tank volume. In substance, with the same volume of hot water desired for a reserve, the stronger the "mixing" phenomenon, the larger the storage tank volume, must be compared to that theoretically required.
• Two storage water heaters having the same capacity Vc and where water is maintained at the same storage Tacc (that is, with the same enthalpic contents) may not be equivalent, according to the meaning given herein to this term, because in one the mixing phenomenon may be stronger than in the other. In other words, with the same thermal energy stored, the volume of useful water Vu may be very different.
• Documents IT 1345007 and IT 1345037 propose means for pre-heating, to the expense of the thermal energy already stored in the water heater, the cold water coming from the waterworks before it mixes with the water in the tank. With the teachings of such documents, the negative effects of mixing are reduced as the amount is reduced for the water that, after reaching a temperature higher than or equal to, that of usage Tu, returns to be unusable as it has already cooled below such level by the effect of mixing with the incoming colder water. The means indicated in these two documents are effective, however they require additional heat exchangers the cost whereof is not always justified. Going back to the flat water heaters as defined above, the effects of mixing are more reduced than in a standard water heater with the same storage volume because, with the same rate of incoming cold water, the phenomenon is increasingly less strong as the tank passage section becomes smaller, that is, the section substantially orthogonal to the water flow direction. In fact, the mass of cold water entering the upstream tank, as the passage section of the same becomes smaller, increasingly behaves as a sort of piston, pushing the overlying mass of hot water without making the two masses particularly mixed.
• As a consequence, a flat water heater has a smaller capacity Vc than that of an equivalent standard water heater; such reduction substantially depends, with the same storage temperature Tacc, on the passage section of the upstream tank.
• The object of the present invention is to indicate methods and means for further reducing the water volume contained in a flat water heater compared to that of the equivalent standard water heater.
• This object is achieved, according to the present invention, by a flat water heater according to the claims herein appended.
• The features of the present invention will appear more clearly from the following description of a preferred embodiment thereof, according to the patent claims and illustrated, by way of a non-limiting example, in the annexed figure 1, consisting in the cutaway view of the tanks of a flat water heater according to the invention.
• With reference to figure 1, reference numeral 1 globally indicates the essential parts of the flat water heater according to the preferred version.
• Within the chassis and the thermal insulation (not shown in the figure) there are seated two storage tanks 2.M and 2.V connected in series; the upstream tank 2.M receives the cold water to be heated and the downstream tank 2.V distributes the hot water to the utilities. The preferred version of the invention, shown in fig. 1 and whereto the following description refers, provides for said storage tanks 2.M and 2.V to have the same dimensions, be cylindrical with diameter substantially equal to half that of the tank of an equivalent standard water heater and connected in series to one another.
• For both tanks 2.M and 2.V, reference numeral 3 indicates a flange suitable for closing the bottom opening and reference numeral 4 indicates a sheath wherein one or more sensors of thermo-regulators TR.M, TR.V (not shown) may be seated, which keep each tank 2.M and 2.V to the set temperature, by actuating/deactivating the heating bodies 5, herein represented by electrical resistances 5.
• Reference numeral 6 indicates the inlet tube of cold water from the waterworks whereon a flow baffle 7, per se known, is fitted, shaped so as to minimise the turbulences upon the entrance of water into the tank, so as to reduce the negative effects of mixing.
• Reference numeral 8 indicates the outlet tubes of the hot water drafted at the dome of tanks 2.M and 2.V; more precisely, tube 8 of tank 2.M directs the water stored therein towards tank 2.V, through a connecting union 9, whereas tube 10 of tank 2.V directs the water stored therein towards the utilities.
• According to the invention, said thermo-regulators TR.M and TR.V are calibrated so as to keep the water in the upstream tank 2.M at a higher temperature TM, which is equal to the storage temperature Tacc of the downstream tank 2.V increased by an overtemperature ΔTacc which is preferably comprised between 8 and 12 °C and even more preferably, is equal to 10 °C.
• Using such adjustment method for the storage temperatures TM and Tacc, in fact, the mixing effect is reduced since a smaller part of the water of the upstream tank 2.M, kept at storage temperature TM, is cooled to a lower temperature than the usage temperature Tu when it mixes with the incoming cold water.
• Of course, also in a standard water heater the increase in the storage temperature Tacc compared to the currently used values would increase the useful water volume Vu but would also considerably increase thermal dispersions. On the contrary, it will be seen that such device has a negligible effect, which may even be eliminated without increasing costs, if only applied to the upstream tank 2.M of a flat water heater.
• Numerical examples may help to understand the advantages of the invention.
• The theoretical useful water volume Vu.teor that may be obtained in a single drafting at the usage temperature Tu from a water heater having capacity Vc and storage temperature Tacc, if Th is the temperature of the incoming cold water, is provided by the formula: $$\mathrm{Vu}\mathrm{.}\mathrm{teor}=\mathrm{Vc\; x}\left(\mathrm{Tacc}-\mathrm{Th}\right)/\left(\mathrm{Tu}-\mathrm{Th}\right)$$

  
• Let us consider a standard reference water heater, herein indicated with SCB.rif, having a cylindrical tank with diameter of 412 mm, capacity Vc = 76 litres and storage temperature Tacc = 65 °C.
• If Tu = 40 °C and Th =15 °C, we have: $$\mathrm{Vu}\mathrm{.}\mathrm{teor}=76x\left(65-15\right)/\left(40-15\right)=152\mathrm{litres}\mathrm{.}$$

  
• Actually, by the effect of mixing, the useful water volume Vu actually obtained in laboratory tests is equal to 126 litres.
• It is possible to define a usability coefficient Cu equal to the ratio between the useful water volume Vu and the theoretical useful water volume Vu.teor, that is $$\mathrm{Cu}=\mathrm{Vu}/\mathrm{Vu}\mathrm{.}\mathrm{teor}\mathrm{.}$$

  
• In the example, in fact, it is Cu = 0.83.
• Now, let us consider a flat water heater provided with two equal cylindrical tanks and with diameter substantially equal to half the previous one (220 mm) and having the same storage temperature Tacc = 65 °C in both tanks.
• Such flat water heater (herein indicated with FLAT.1) is equivalent to the previous standard water heater, if its two tanks have a volume of 36 litres each (that is, a capacity Vc equal to 72 rather than 76 litres, with a 5% volume reduction).
• In fact, for this size the useful water volume Vu in laboratory is also equal to 126 litres. Since the theoretical useful water volume Vu.teor of FLAT.1 is equal to 144 litres, the usability coefficient Cu goes up to 0.88.
• Finally, let us consider a flat water heater always provided with two equal cylindrical tanks and with the same diameter as in FLAT.1 but now having, according to the invention, a storage temperature TM of the upstream tank 2.M equal to = 75 °C and storage temperature Tacc in the downstream tank 2.V equal, as in the previous example, to 65 °C. A flat water heater with such storage temperatures (herein indicated with FLAT.2) is equivalent to the standard water heater if its tanks have a volume of 33 litres each (that is, a capacity Vc equal to 66 rather than 76 litres, with a 13% volume reduction compared to the standard reference water heater); in fact, for such volumes the useful water volume Vu in laboratory is always equal to said 126 litres.
• The theoretical useful water volume Vu.teor of FLAT.2 is equal to 145 litres and the usability coefficient Cu becomes 0.87; substantially the same as FLAT.1.
• Always remaining at the same numerical examples, it can be shown that the adoption of storage temperatures Tacc, TM according to the invention only causes a very small increase in the thermal dispersions compared to FLAT.1, which can also be easily eliminated.
• The flat water heater FLAT.1 may be constructed with an overall surface SE.1 of the outer shell equal to 1.8 m² using the currently used thicknesses of insulating material; using the same thicknesses, since the flat water heater FLAT.2 has a reduced size, it has an overall surface SE.2 of the outer shell equal to 1.69 m² (with a 6% reduction compared to the FLAT.1).
• Since the thermal dispersions may be deemed as proportional to the average inside temperature of the water heater and to the surface of the outer shell, it is easy to check that if the temperature of the room where the flat water heaters FLAT.1 and FLAT.2 are installed is 20 °C, FLAT.2 has thermal dispersions of just 4% higher than those of FLAT.1; said slight increase in the dispersions may be totally eliminated by slightly increasing the thickness of the thermal insulation (substantially a 4% thickness increase) while obtaining a flat water heater with a considerably lower production cost than the FLAT.1 thanks to the 13% reduction in the tank volume and substantially 6% of the outer shell.
• Thus, the numerical example has shown that using the setting system for the storage temperatures Tacc, TM according to the invention, it is possible to reduce costs and overall dimensions of a flat water heater while maintaining the same performance as regards useful water volume Vu and energy consumption.
• According to a version of the invention, said thermo-regulators TR.M and TR.V may be devices of any known type, electromechanical or electronic, physically separate or in any case, independent of one another.
• In this case, while thermo-regulator TR.V is calibrated for maintaining a predetermined temperature Tacc in tank 2.V, thermo-regulator TR.M is calibrated so as to maintain the upstream tank 2.M at a storage temperature TM equal to Tacc + ΔTacc.
• If one or more of said thermo-regulators TR.V, TR.M are of the user-adjustable type, they are such as not to accept the setting of higher temperatures, respectively, than Tacc and TM.
• As an alternative, said thermo-regulators TR.M and TR.V can advantageously consist of a single electronic device TR provided with data processing capabilities that ensures the thermo-regulation of both tanks 2.M and 2.V and that optionally, is in turn part of an electronic control unit suitable for performing further functions.
• In that case, when the user is allowed to adjust the water heating temperature, the set temperature Timp selected by the user is assigned to the downstream tank 2.V whereas a storage temperature TM equal to Timp + ΔTacc is automatically assigned to the upstream tank 2.M.
• It is understood that in any case, the maximum acceptable temperature Timp is such that Timp + ΔTacc is compatible with the safety standards.
• However, it is easier for the user if he/she is given the possibility of selecting the amount of desired hot water at the usage temperature Tu, rather than the heating temperature in the water heater. For each amount selected, of course, the electronic device TR determines and sets the minimum heating temperatures Timp required so as to ensure in both tanks, and only when the required amount of water is so large to require the elimination of the mixing effects, the storage temperature TM of the upstream tank 2.M is set equal to Timp + ΔTacc.
• The invention has been described with reference to a flat water heater provided with two storage tanks 2.M and 2.V having the same dimensions, cylindrical with diameter substantially equal to half that of the tank of an equivalent standard water heater and connected in series to one another.
• More in general, however, the invention relates to flat water heaters using two or more tanks, not necessarily cylindrical nor having the same volume, with heating either electrical or by fuel without distinction and where the cold water is received by an upstream storage tank 2.M and hence sent to subsequent tanks 2.V, without distinction connected to one another in series or parallel.

Claims (10)

1. Method for managing the heating temperature (Timp, Tacc, TM) of a flat water heater (1) provided with two or more storage tanks (2.M, 2.V) communicating with one another,

   - wherein one upstream tank (2.M) receives cold water from the waterworks and delivers it to one or more downstream tanks (2.V)

   - and wherein thermo-regulators (TR.M, TR.V; TR) ensure that said heating temperatures (Timp, Tacc, TM) are maintained by actuating/deactivating heating bodies (5)
   characterised in that
   the maximum volume (Vu) of water at usage temperature (Tu) obtainable in a single drawing from said flat water heater (1) is ensured by keeping the water in the downstream tank(s) (2.V) at a predetermined storage temperature (Tacc) and, in the upstream tank (2.M), at a higher temperature (TM) which is

   - equal to said predetermined storage temperature (Tacc) increased by a predetermined over-temperature (ΔTacc)

   - and compatible with the safety standards.
2. Method for managing the heating temperature (Timp, Tacc, TM) of a flat water heater (1) according to claim 1,
   characterised in that
   the user is given the possibility of adjusting the temperature

   - in said downstream tank(s) (2.V) up at most to said predetermined storage temperature (Tacc)

   - and in the upstream tank (2.M) up to said higher temperature (TM).
3. Method for managing the heating temperature (Timp, Tacc, TM) of a flat water heater (1) according to claim 1,
   characterised in that
   the user is given the possibility of adjusting the temperature in said downstream tank(s) (2.V) up at most to said predetermined storage temperature (Tacc), whereas in the upstream tank (2.M) the temperature is automatically set to said higher temperature (TM).
4. Method for managing the heating temperature (Timp, Tacc, TM) of a flat water heater (1) according to claim 1,
   characterised in that

   - the user is given the possibility of selecting the amount of desired hot water at the usage temperature (Tu),

   - the minimum heating temperatures required for ensuring said amount of hot water are automatically selected for both said upstream tank (2.M) and for said downstream tanks (2.V)

   - and only when said required amount of water is so high as to require the elimination of the mixing effects, the storage temperature of the upstream tank (2.M) is automatically set to said higher temperature (TM).
5. Method for managing the heating temperature (Timp, Tacc, TM) of a flat water heater (1) according to any previous claim,
   characterised in that
   said predetermined storage temperature (Tacc) is comprised between 60 and 75 °C.
6. Method for managing the heating temperature (Timp, Tacc, TM) of a flat water heater (1) according to any previous claim,
   characterised in that
   said over-temperature (ΔTacc) is comprised between 8 and 12 °C.
7. Flat water heater (1) provided with two or more storage tanks (2.M, 2.V) communicating with one another,

   - wherein one upstream tank (2.M) receives cold water from the waterworks and delivers it to one or more downstream tanks (2.V)

   - and wherein thermo-regulators (TR.M, TR.V; TR) ensure that two or more storage tanks (2.M, 2.V) are maintained at heating temperatures (Timp, Tacc, TM) settable by the user and/or predetermined,
   characterised in that
   said thermo-regulators (TR.M, TR.V; TR) allow keeping the water

   - in the downstream tank(s) (2.V) at a temperature not higher than a predetermined storage temperature (Tacc),

   - and in the upstream tank (2.M), at a higher temperature (TM) which is

   - equal to said predetermined storage temperature (Tacc) increased by a predetermined over-temperature (ΔTacc)

   - and compatible with the safety standards.
8. Flat water heater (1) according to the previous claim,
   characterised in that
   said thermo-regulators (TR.M, TR.V; TR) are each individually adjustable by the user.
9. Flat water heater (1) according to the previous claim,
   characterised in that
   said thermo-regulators (TR.M, TR.V; TR) consist of a single thermo-regulator (TR) provided with data processing capability

   - wherein the user can only set the temperature (Timp) selected for the one or more downstream tanks (2.V),

   - whereas in the thermo-regulator (TR) itself, it automatically assigns a higher temperature (TM) to the upstream tank (2.M), equal to said selected temperature (Timp) increased by said over-temperature (ΔTacc).
10. Flat water heater (1) according to claim 7,
    characterised in that
    said thermo-regulators (TR.M, TR.V; TR) consist of a single thermo-regulator (TR) provided with data processing capability

    - wherein the user can set the amount of desired water at the usage temperature (Tu),

    - whereas the thermo-regulator (TR) itself has computation means suitable for determining and setting, in all downstream and upstream tanks (2.V, 2.M), the minimum heating temperatures (Timp, TM) required for ensuring the desired amount of water

    - and when the required amount of water is so large as to require the elimination of the mixing effects, the storage temperature (TM) of the upstream tank (2.M) is set equal to the temperature of the remaining tanks (2.V) increased by said over-temperature (ΔTacc).

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