Boiler and process for heating and for producing sanitary hot water

Abstract

 A boiler (1) of the combined type for heating and for producing sanitary hot water, comprising a primary circuit (7, 8, 9) for a heating fluid, having a delivery branch (7) and a return branch (8) intended for connection to a heating system, and a secondary branch (9) which connects the delivery branch to the return branch. A circulation pump (14) operates along the return branch upstream of a primary heat exchanger (13). A secondary heat exchanger (18) which is inserted in the secondary branch (9) exchanges heat between the heating fluid in the primary circuit and the sanitary water in a secondary circuit (15). A storage vessel (22) for the heating fluid in the primary circuit, which is inserted in said secondary branch (9), is located downstream of the secondary heat exchanger (18).

Description

[0001] The present invention relates to a boiler of the combined type for heating and for producing sanitary water and to an associated process.

[0002] At present most of the boilers used for heating individual homes are also designed for the production of sanitary hot water. These boilers are referred to as being of the "combined" type since with a single energy-producing device both the water of the heating system and the water for sanitary and hygiene use are heated. The function of producing sanitary hot water takes priority over the heating function.

[0003] In order to heat sanitary water it is known to use at least three different types of combined boiler.

[0004] A first type of combined boiler envisages the use of a "bithermal" type of exchanger comprising internally both the heating water circuit or "primary" circuit and the sanitary water circuit. A circulation pump ensures circulation of the water of the primary circuit.

[0005] A three-way diversion valve selectively either directs the water of the primary circuit towards the heating system, when sanitary hot water is not required, or keeps the water inside the internal circuit of the boiler, when there is no such requirement.

[0006] Some solutions of this type do not envisage the use of the three-way diversion valve, but more simply use means which, when there is a need for sanitary hot water, intervene so as to stop the pump circulating of the water in the primary heating circuit. In boilers provided with a "bithermal" exchanger, the combustion products release heat directly to both the primary circuit and sanitary circuit at the same time.

[0007] The apparatus of this type require a relatively small number of constructional components and are therefore fairly low-cost. Moreover, they allow the sanitary water to reach rapidly the required temperature, owing to the fact that the sanitary circuit is exposed directly to the heat of the combustion products.

[0008] However, in these apparatus, the sanitary circuit becomes lined with scale very quickly, mainly on account of the constant presence in the exchanger of fresh sanitary water which is exposed to the combustion products. This results in the need for frequent maintenance operations in order to clean or even replace the primary exchanger.

[0009] A second type of combined boiler envisages the use of two exchangers: a primary exchanger, inside which water of the primary circuit circulates, and a secondary exchanger, inside which an exchange of heat occurs between the sanitary circuit and a branch, inside the boiler, of the primary circuit. This solution envisages a diversion valve which, at the moment when sanitary water is drawn, diverts the water flow of the primary circuit from the heating system circuit to the internal branch of the secondary exchanger.

[0010] This solution is commonly referred to as "indirect exchange" type for the production of sanitary hot water.

[0011] In these boilers the probability of scaling of the sanitary circuit is much smaller than in the preceding case, since the sanitary circuit is not exposed in a permanent manner to the heat of the combustion products and consequently there is also less need for maintenance in order to clean the secondary exchanger.

[0012] These boilers, however, have a relatively high manufacturing cost on account of the larger number of constructional components. A further drawback consists in the fact that the sanitary water takes a relatively long time to reach the desired temperature, mainly owing to a greater quantity of water to be heated, and therefore a greater thermal inertia, compared to the first type of combined boiler.

[0013] A third type of combined boiler envisages the use of a secondary coil exchanger which is inserted in a branch of the primary circuit inside a sanitary water storage vessel. A diversion valve, upon activation of a thermostatic probe associated with the sanitary water storage vessel, directs the water of the primary circuit selectively towards the secondary exchanger or towards the heating system. When the probe detects a temperature value which is lower than a preset value, the said probe enables the valve to divert the water flow of the primary circuit towards the sanitary exchanger since the production of sanitary hot water takes priority over the heating function.

[0014] Owing to the presence of a reserve supply of hot water, it is possible to gain access immediately to a considerable quantity of sanitary water at the desired temperature. This solution, however, certain drawbacks compared to the solutions mentioned above, both owing to the additional cost of manufacturing the sanitary water storage vessel and on account of the dimensions of the latter, with a consequent increase in the overall volume of the boiler.

[0015] In recent years there has been a particularly pressing need for combined boilers which are capable of ensuring an immediate production of sanitary hot water. This need is satisfied by a boiler of the third type mentioned above (boiler with storage vessel), but to the detriment of the dimensions and manufacturing costs. One of the main problems in this sector is therefore that of providing combined boilers which allow the immediate production of sanitary hot water and which at the same time are constructionally simple and low-cost and have small dimensions.

[0016] Recently some boilers of the "instantaneous combined" type aimed at solving the abovementioned problem have been devised, said boilers basically being elaborated versions of the combined boilers of the second type mentioned above.

[0017] It is possible to identify three constructional solutions.

[0018] A first solution envisages a small insulated storage vessel which is located downstream of the sanitary exchanger and which has sanitary hot water inside it. During the stage of production of sanitary hot water, the water contained in the storage vessel is heated by the sanitary exchanger. When there is no requirement for sanitary hot water, the water inside the storage vessel is kept at a predefined temperature by means of the use of an electric resistance which is activated by a thermostat located in the upper part of the vessel.

[0019] The storage vessel, which is located in the rear part of the boiler, does not increase the dimensions of the latter. This solution allows the immediate availability of sanitary hot water and is constructionally fairly simple.

[0020] However, in this type of boiler, there is a high probability of lime-scale deposition on the resistance and moreover, during the initial stage of drawing of sanitary hot water, the temperature of the water is not constant.

[0021] A second solution also comprises a small insulated storage vessel which contains water of the sanitary circuit and is located downstream of the sanitary exchanger. In this case the water inside the storage vessel is kept at a predefined temperature by means of a small exchange coil which is inserted in a secondary branch of the primary heating circuit and which is supplied by means of a diversion valve. In this way the sanitary water, which is immediately available, is kept at the required temperature using heat supplied by the burner, without any use of electric energy.

[0022] This solution, however, involves a certain constructional complexity as well as a high probability of lime-scale deposition.

[0023] A third solution, which has the characteristic features described in the preamble of the first claim, comprises a small vessel for storing hot water of the primary circuit, which is located downstream of the primary exchanger and inserted in a branch of the primary circuit which conveys hot water to the sanitary exchanger. This vessel, which is kept at the required temperature by the heat supplied by the burner, forms a reserve supply of immediately available energy to be supplied to the sanitary exchanger at the moment when sanitary water is drawn, so that the sanitary water is able to reach rapidly the desired temperature. A first diversion valve is located in the primary circuit inside the boiler, between the storage vessel and the sanitary exchanger. When there is no requirement for sanitary hot water, the diversion valve closes the primary water supply to the sanitary exchanger and also connects the outlet of the storage vessel to the return branch of the primary circuit upstream of the supply pump. With this arrangement, the hot water of the primary circuit does not heat unnecessarily the sanitary exchanger so that there is a considerable reduction in deposition of the lime-scale contained in the sanitary water present inside the sanitary exchanger. When the temperature inside the storage vessel falls below a preset value, a control thermostat causes ignition of the boiler and operation of a second diversion valve (located on the delivery branch of the primary circuit, at the start of the supply branch of the sanitary exchanger) so as to divert the flow of the primary water towards the storage vessel until the desired temperature is restored inside the latter.

[0024] When there is a requirement for sanitary hot water, a pressure-operated valve, which is usually located along the sanitary water inlet branch, supplies a command signal both to the burner ignition system and to the second diversion valve so as to allow the storage tank to receive the hot water supplied from the primary tank, and finally to the first diversion valve so as to allow the sanitary exchanger to receive the hot water supplied from the storage tank. During the first moments following the request for sanitary hot water, the sanitary exchanger receives primary circuit hot water supplied from the small storage vessel, resulting in sanitary hot water being immediately available. In the meantime, the burner, by means of the primary exchanger, heats the entire circuit inside the boiler and provides sanitary water which is heated by means of the whole boiler power output. This solution, however, is of a considerable constructional complexity and has a relatively high cost. Another drawback is represented by the fact that, especially during the initial stage, the production of hot water may not be continuous and regular: in fact, as soon as sanitary water starts to be drawn, the reserve supply of heat stored inside the storage vessel immediately enters into the secondary exchanger, causing a sudden increase in the temperature of the outgoing sanitary water: consequently, the electronic system for controlling and regulating the boiler, which is normally present in these boilers, causes a reduction in the boiler power output which penalises the production of sanitary hot water for a certain period of time (following the instant when there is the initial requirement).

[0025] An object of the present invention is that of overcoming the abovementioned limitations and drawbacks of the known art by means of a boiler which is constructionally simple and low-cost.

[0026] Another object of the invention in question is that of providing a combined boiler which has small dimensions and which allows the rapid production of sanitary water at the desired temperature, reducing to a minimum the risk of lime-scale deposition on the component parts of the boiler.

[0027] Another object is that of achieving a continuous and regular production of sanitary hot water during the whole period of drawing of water, in particular also during the first moments of drawing and during the period immediately following it.

[0028] These and other objects are all achieved by the boiler according to the present invention which is characterized by the contents of the claims indicated below and in particular by the fact that the boiler comprises a storage vessel located downstream of a secondary heat exchanger, between the latter and one end of the secondary branch, which connects the delivery branch to the return branch of the primary circuit, said end being situated in the vicinity of the return branch.

[0029] The storage vessel is provided with heating means which keep the heating fluid contained therein at a predefined temperature and preferably comprise an independent heat source consisting of an armoured electric resistance operating inside the storage vessel.

[0030] The present invention also relates to a process in which the heating fluid inside the storage vessel is kept at a temperature such that the reserve supply of energy provided by the heating fluid contained in the storage vessel and discharged onto the primary exchanger is substantially equivalent to an advance ignition of the burner with respect to the instant when sanitary water is first drawn.

[0031] Further characteristic features and advantages of the present invention will emerge more clearly from the following detailed description of two preferred embodiments of the invention in question, illustrated by way of a non-limiting example in the accompanying plates of drawings, in which:

• Figure 1 shows a diagram of a first example of embodiment;
• Figure 2 shows a diagram of a part of second example of embodiment.

[0032] With reference to Figure 1, 1 denotes in its entirety a boiler of the combined type for heating and for producing sanitary hot water, which comprises a conventional burner 2, preferably a gas burner, operating in a combustion chamber 3 where a hood 4 is provided for evacuation of the fumes. The burner 2 receives the fuel from a feeder line indicated by 5 on which a valve 6 is located. A primary circuit is provided for a heating fluid comprising a delivery branch 7, a return branch 8 and a secondary branch 9. The delivery branch 7 and the return branch 8 are intended for connection to a heating system, not shown, via unions 10 and 11. An NTC temperature probe 12 is provided on the delivery branch for regulating and limiting the temperature in the combustion chamber.

[0033] The heating fluid is normally water which is used as a thermal energy carrier in heating systems. The secondary branch 9 connects the delivery branch to the return branch. The boiler 1 comprises a primary heat exchanger 13 from which the delivery branch exits and into which the return branch enters, said exchanger being intended for the exchange of heat between the combustion products of the burner and the heating fluid in the primary circuit. A circulation pump 14 is provided, being located in the primary circuit 14, preferably along the return branch 8 upstream of the primary exchanger, in a section located between the primary exchanger and an outlet end 34 of the secondary branch 9.

[0034] The boiler 1 is also provided with a secondary circuit 15 for the sanitary water (having an inlet 16 and outlet 17) and a secondary heat exchanger 18 which is inserted in the secondary branch of the primary circuit and is intended for heat exchange between the heating fluid in the primary circuit and the sanitary water in the secondary circuit. The secondary circuit, located downstream of the secondary exchanger 18, is provided with a sensor 19 which detects the temperature of the water leaving the sanitary circuit and which sends an associated signal to an electronic control unit, not shown, which correspondingly regulates the boiler power output and causes activation of various boiler components, in particular the burner supply means and the circulation pump 14, in accordance with various operating parameters of the boiler itself, such as, for example, the request or otherwise for sanitary hot water and the temperatures detected in the primary and secondary circuits. A diversion valve 20, of the three-way type, forms a diversion device for diverting the flow of the heating fluid in the primary circuit either towards the heating system or towards the secondary branch.

[0035] The diversion valve may be located at one of the two ends of the secondary branch 9 of the primary circuit. In the example shown the diversion valve is located at the end 34 of the secondary branch downstream of the secondary exchanger 18, but according to a variation (not shown) may be located at the other end of the secondary branch 9, upstream of the secondary exchanger.

[0036] The diversion valve connects the intake of the circulation pump 14 selectively either to a return circuit of the heating system or to the outlet end 34 of the secondary branch 9. In the particular case shown in Figure 1 the diversion valve 3 is provided with fluid-type activating means comprising a membrane-type pressure-operated valve located at the sanitary water inlet. In the example of embodiment according to Figure 2, the diversion valve is provided with activating means of the electric type comprising an electric motor 21. In both cases the activating means of the diversion valve are connected to the secondary circuit 15 and are designed to divert the flow of the heating fluid from the heating system to the secondary branch 9 when a request for sanitary hot water is signalled. The boiler 1 also comprises a vessel 22 for storing the heating fluid in the primary circuit, which is inserted in the secondary branch 9. The storage vessel 22 is located between the secondary exchanger and one end of the secondary branch situated in the vicinity of the return branch of the primary circuit. In particular the vessel 22 is located between the secondary exchanger and the diversion valve, is well insulated in order to reduce to a minimum the dispersion of heat into the environment and is provided with heating means which keep the heating fluid contained therein at a predefined temperature. These heating means comprise a source of heat which is independent, in particular independent of the burner. In the case illustrated, the heating means comprise an armoured electric resistance 23 operating inside the vessel. The heating means are provided with control means which regulate the operation thereof in accordance with the temperature detected inside the storage vessel. In the case in question the control means comprise a fixed-calibration thermostat 24 which is located inside the storage vessel in the vicinity of the armoured resistance and which interrupts the action of the heating means when a preset temperature inside the vessel itself is reached. It is possible to envisage that the thermostat for regulating the storage vessel is calibrated so that the water stored in the vessel itself is kept at a temperature slightly higher (for example approx. 20°C) than a value preselected by the user on the external control panel of the boiler. It is thus possible, right from the first moments when sanitary hot water is drawn, to keep the temperature of the sanitary water produced by the boiler constant, i.e. at a value equal to or nearly equal to the temperature value preset on the control panel.

[0037] According to a variation of embodiment not shown, the control means may comprise PTC resistors which supply heat, automatically adjusting themselves to the desired temperature value.

[0038] The boiler also comprises other elements of the known type, such as an expansion reservoir 25 with an automatic air-breather valve 26, as well as a safety thermostat 27 for regulating and limiting the temperature of the heating fluid. It is also envisaged using: a microswitch 28 of a manostat 29 of the circulation pump, a one-way valve 30, a pressure-limiting safety valve 31, a microswitch 32 of the manostat associated with the secondary sanitary circuit, and a filling/emptying group 33.

[0039] As regards operation of the boiler, the water of the primary circuit (7, 8, 9) contained in the storage vessel is heated during the first sanitary hot water drawing cycle, following which it is kept at the required temperature by the electric resistance which has a low power sufficient to offset the dispersion of heat into the environment.

[0040] Each time sanitary hot water is freshly drawn, the pressure-operated valve which is located at the sanitary water inlet 16 (where a minimum-throughput obturator 35 with a flow limiter 36 is located) and which controls the diversion valve 20 located on the primary circuit, diverts the flow of the primary circuit from the heating system to the heat exchanger 18. Instantaneously all the hot water contained in the small storage vessel travels around the whole of the primary circuit, passing through in sequence: the diversion valve 20, the pump 14, the primary exchanger 13, the secondary exchanger 18 and the pipes which are immediately heated, finally returning to the vessel 22; this reserve supply of hot water introduced into the primary circuit exchanges heat with the sanitary water inside the secondary exchanger.

[0041] The storage vessel is located downstream (with respect to the direction of advance of the water flow circulated by the pump 14) of the secondary exchanger so that the hot water contained in the vessel itself travels through practically the whole of the primary circuit before reaching the secondary exchanger.

[0042] The introduction, into the primary circuit and into the primary exchanger, of the reserve supply of energy consisting of the hot water inside the storage vessel is substantially equivalent to an advanced ignition of the burner with respect to the instant when drawing of sanitary water starts. This avoids the risk (which exists, instead, for example in the boiler of the third solution cited above) that the probes 12 and 19 for detecting the temperatures respectively of the primary heating circuit and the sanitary secondary circuit, which are located downstream of the respective exchangers 13 and 18, may detect sudden and significant increases in temperature such as to cause the electronic control system of the boiler to reduce the boiler power output or even stop the burner momentarily. In the present boiler the production of sanitary hot water is not subject to temperature fluctuations and variations during the initial stage, but is instead uniform and regular both during the initial instants of drawing and subsequently, precisely owing to the fact that the reserve supply of thermal energy is situated downstream of the secondary exchanger.

[0043] In the boiler constructed in accordance with the invention there is no risk of lime-scale deposition in the sanitary circuit, since the reserve supply of hot water which is kept at the required temperature consists exclusively of primary circuit water, namely water which circulates in a closed circuit and which is not subject to any renewal and therefore does not give rise to lime-scale depositions.

[0044] The present boiler is moreover constructionally simple and low-cost. In particular, differently from the second constructional solution of the known art, it does not have any moving parts, but comprises only static components (a vessel and an electric resistance) which, among other things, do not require any maintenance. Moreover, the storage vessel may advantageously be made of normal carbon steel, which is relatively inexpensive, since the water of the primary circuit, as is known, normally is not corrosive.

[0045] The present boiler allows immediate production of sanitary hot water, reducing significantly the time required by the burner to overcome the thermal inertia of the water and the various components of the primary circuit, owing to the fact that, at the moment when sanitary water is drawn, the primary circuit is instantly supplied again with the reserve supply of energy contained in the storage vessel.

[0046] Moreover, the boiler has relatively small dimensions and a relatively low manufacturing cost.

Claims

1. Boiler of the combined type for heating and for producing sanitary hot water, comprising:

- a burner (2);

- a primary circuit (7,8,9) for a heating fluid, in turn comprising a delivery branch (7) and a return branch (8) intended for connection to a heating system, and also comprising a secondary branch (9) which connects the delivery branch (7) to the return branch (8);

- a primary heat exchanger (13) intended for heat exchange between the combustion products of the burner (2) and the heating fluid in the primary circuit (7,8,9);

- a circulation pump (14) located in the primary circuit;

- a secondary circuit (15) for the sanitary water;

- a secondary heat exchanger (18) which is inserted in the secondary branch (9) of the primary circuit and is intended for heat exchange between the heating fluid in the primary circuit and the sanitary water in the secondary circuit;

- a diversion device (20) for diverting the circulation of the heating fluid selectively towards said secondary branch (9) or towards the heating system;

- a storage vessel (22) for the heating fluid of the primary circuit, which is inserted in said secondary branch (9);

characterized in that the storage vessel (22) is located downstream of the secondary exchanger (18).

2. Boiler according to Claim 1, in which the vessel (22) is located between the secondary exchanger (18) and the end (34) of the secondary branch (9) situated in the vicinity of the return branch (8) of the primary circuit.

3. Boiler according to Claim 1, in which the vessel (22) is located between the secondary exchanger (18) and the diversion device (20).

4. Boiler according to Claim 1, in which the vessel (22) is located between the secondary exchanger (18) and the circulation pump (14).

5. Boiler according to Claim 1, in which the storage vessel (22) is provided with heating means (23) formed so as to keep the heating fluid contained therein at a predefined temperature.

6. Boiler according to Claim 5, in which said heating means (23) comprise an independent heat source.

7. Boiler according to Claim 5 or Claim 6, in which said heating means comprise an armoured electric resistance (23) operating inside the storage vessel (22).

8. Boiler according to any one of the preceding claims, in which the diversion device (20) is provided with activating means (21) of the electric type.

9. Boiler according to any one of the preceding claims, in which the diversion device (20) is provided with activating means of the fluid type.

10. Boiler according to Claim 5, in which said heating means (23) are provided with control and regulating means (24) which operate in accordance with the temperature of the heating fluid contained in the storage vessel (22).

11. Boiler according to Claim 10, in which said control means comprise a thermostat (24) which interrupts the heating of the storage vessel (22) when a preset temperature of the fluid inside the vessel itself is reached.

12. Boiler according to Claim 10, in which said control means comprise PTC resistors which supply heat, adjusting themselves automatically to the desired temperature value.

13. Heating process in a combined boiler for heating and for producing sanitary hot water of the type comprising at least one burner; a primary circuit for a heating fluid, connected to a heating system; a primary heat exchanger intended for heat exchange between the combustion products of the burner and the heating fluid in the primary circuit; a circulation pump located in the primary circuit; a secondary circuit for the sanitary water; a secondary heat exchanger which is inserted in a branch of the primary circuit and is intended for heat exchange between the heating fluid in the primary circuit and the sanitary water in the secondary circuit; a diversion device for diverting the circulation of the heating fluid selectively towards said branch of the primary circuit or towards the heating system; a storage vessel for the heating fluid of the primary circuit, characterized in that it envisages heating with electric means the heating fluid contained in the storage vessel so that, at the moment when sanitary water is drawn, there is immediate introduction, into the primary circuit, of the heating fluid contained in the storage vessel and therefore a quantity of energy which is exchanged in the secondary exchanger with the sanitary water, with recovery of the time needed by the burner to overcome the thermal inertia of the water and the components of the primary circuit.

14. Process according to Claim 13, in which the heating fluid inside the storage vessel is kept at a temperature such that the reserve supply of energy provided by the heating fluid contained in the storage vessel and discharged onto the primary exchanger is substantially equivalent to an advanced ignition of the burner with respect to the instant when drawing of sanitary water is started.

15. Process according to Claim 14, in which said temperature is kept at a value which is about 20°C higher than a value preset on a control panel of the boiler.

16. Process according to Claim 14, in which said temperature is kept at a predefined fixed value such as to ensure instantaneous availability of sanitary hot water at a desired temperature, preferably of about 45 °C.

17. System for heating and for producing sanitary hot water, characterized by the fact of comprising at least one boiler in accordance with any one of Claims 1 to 12 or of operating with a process according to any one of Claims 13 to 16.

Drawing