EP2513566A2

EP2513566A2 - Split system for heating and storing water for solar heating plants, and relative method to control operation of the system

Info

Publication number: EP2513566A2
Application number: EP10810930A
Authority: EP
Inventors: Francesco Loddo
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-12-15
Filing date: 2010-12-15
Publication date: 2012-10-24
Also published as: WO2011073921A2; WO2011073921A3; ITCA20090013A1

Abstract

There is described a system for heating and storing water comprising: a sanitary water circuit and a thermal fluid circuit; a solar thermal plant (5) in which said thermal fluid circulates; a primary boiler (B1 ) and a secondary boiler (B2), the secondary boiler having a greater capacity than the primary boiler (B1 ), said sanitary water and thermal fluid circuits passing through said primary and secondary boilers; means to control circulation of the thermal fluid configured to cause circulation of the thermal fluid in a circulation circuit (7A, 9, 12) in said primary boiler (B1 ) until reaching a first temperature of the sanitary water, and/or in a circulation circuit (7B, 1 1, 12) in said secondary boiler (B2); means to control the circulation of sanitary water configured to cause inflow (1 ) of the sanitary water to be heated in said secondary boiler (B2), passage (2, 3) into said primary boiler (B1 ) and outflow (4) from said primary boiler (B1 ) toward the user.

Description

SPLIT SYSTEM FOR HEATING AND STORING WATER FOR SOLAR HEATING PLANTS, AND RELATIVE METHOD TO CONTROL OPERATION OF THE SYSTEM Field of the invention

The present invention relates to a split system for heating and storing water for solar heating plants, and relative method to control operation of the system.

State of the art

The sanitary hot water storage tank, universally identified as boiler, is the key element of plants for heating sanitary water; the water to which the thermal energy produced by conventional or renewable sources is transferred is stored therein, so that the user can draw from this continually, making use of the maximum comfort necessary. Solar heating plants present both on the national and foreign market are not differentiated on the basis of type of storage of the sanitary hot water produced, but only according to the structural technology of the panels.

As a rule, all current installations have a single boiler with dimensions that depend directly on the total surface area of the solar panels installed, therefore the larger the absorbent surface the greater the quantity of hot water that is stored in the boiler.

At most, boilers can be equipped with layering apparatus of the sanitary hot water. Although these systems are satisfactory in summer months and on winter days with a lot of sunshine, all their limits are evident on winter days. In conditions in which sunlight is limited, the thermal fluid produced by the panels is not capable of significantly increasing the temperatures of the volumes of water present in the boiler, due to the high thermal inertia. In fact, the thermal fluid currently operates on the whole of the stored volume.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to indicate a split system for heating and storing water for solar heating plants, and relative method to control operation of the system, adapted to overcome the aforesaid disadvantages. The present invention concerns a system for heating and storing water comprising: a sanitary water circuit and a thermal fluid circuit; a solar heating plant in which said thermal fluid circulates; characterized in that it comprises: a primary boiler and a secondary boiler, the secondary boiler having a greater capacity than the primary boiler, said sanitary water and thermal fluid circuits passing through said primary and secondary boilers; means to control circulation of the thermal fluid configured to cause circulation of the thermal fluid in a circulation circuit in said primary boiler until reaching a first temperature of the sanitary water, and/or in a circulation circuit in said secondary boiler; means to control the circulation of sanitary water configured to cause inflow of the sanitary water to be heated in said secondary boiler, passage into said primary boiler and outflow from said primary boiler toward the user.

Preferably, the primary boiler is inserted inside the secondary boiler, or externally adjacent to, or in line with, the secondary boiler.

Preferably, the primary boiler and the secondary boiler comprise an internal cavity for circulation of said thermal fluid, or coil heat exchangers of the thermal fluid.

Preferably, inflow of sanitary water into the primary and/or secondary boiler takes place through one or more multi-injection systems.

Preferably, the system further comprises systems for heating the sanitary water in the primary and/or secondary boilers through heating elements in the part of the boiler containing the sanitary water, optionally supplied by a photovoltaic plant.

The present invention also concerns a method to control operation of the system.

The present invention specifically concerns a split system for heating and storing water for solar heating plants, and relative method to control operation of the system, as better described in the claims, which form an integral part of the present description.

BRI EF DESCRI PTION OF THE FIGURES

Further objects and advantages of the present invention will be apparent from the detailed description below of an example of embodiment thereof (and its variants) and from the accompanying drawings provided purely by way of non- limiting example, wherein:

Fig. 1 shows a diagram of a first example of embodiment of the split system of the invention in a vertical compact configuration;

Fig. 2 shows a diagram of a second example of embodiment of the split system of the invention in a horizontal compact configuration;

Fig. 3 shows a diagram of a third example of embodiment of the split system of the invention in a vertical extended configuration;

Figs. 4, 5 and 6 show three examples of embodiment of the boiler element of the system;

Figs. 7 and 8 show further examples of embodiment of the boiler element of the system;

Fig. 9 represents details of multi-injector type distribution elements of the system.

The same reference numbers and letters in the figures identify the same element or components.

Detailed description of examples of embodiment

The structure of the system of the invention is presented as a storage system split into two separate sections with an operating circuit and control and management systems, for example, as shown in the various examples of configurations illustrated in the accompanying figures, in which the following constituent elements can be seen (in the list below the elements are identified with a number, which appears in the figures, and relative description):

1 - Inflow of sanitary cold water to B2 ("large" or "secondary" boiler).

1 .A - Multi-injector cold water distribution pipe inside B2.

2 - Outflow of sanitary hot water, premixed, or hot, from B2.

3 - Inflow of premixed or hot water to B1 ("small" or "primary" Boiler)..

3A - Multi-injector pre-mixed and/or hot water distribution pipe inside B1 .

4.A - Outflow of Sanitary Hot Water (D.H.W.) from B1 to users.

5 - Thermal solar panel (T.S.P.). 6 - Thermal fluid delivery from T.S.P.

7. A - Normally open solenoid valve.

7.B - Normally closed solenoid valve.

8 - Thermal fluid inflow pipe to B1 .

9 - Thermal fluid outflow pipe from B1 to the collector 40.

10 - Thermal fluid inflow pipe to B2.

1 1 - Thermal fluid outflow pipe from B2 to the collector 40.

12 - Common pipe for return to the T.S.P.

13 - Heating element to B1 .

14 - Heating element to B2.

15 - Photovoltaic panel (P.P.).

16 - Remote control unit.

17 - 3-way motorized valve.

18 - Regulation thermostat probe.

19 - Temperature thermometer probe.

20 - Connection flange between B1 and B2.

21 - Electrical and electronic connection.

22 - Thermal cavity of B2.

23 - Thermal cavity of B1 .

24 - D.H.W. storage volume of B2.

25 - D.H.W. storage volume of B1 .

26 - Sanitary cold water check valve.

27 - Magnesium and/or electronic anode in B2.

28 - Magnesium and/or electronic anode in B1 .

29 - Thermometer probe in B2.

30. B1 - Metal shell in B1 .

30. B2 - Metal shell in B2.

31 - Insulation of B2.

32 - Insulation of B1 .

33 - Sanitary water connection pipe between B1 and B2.

34 - Temperature probe for thermal fluid inflow to B1 .

35 - Thermal fluid circulator. 36 - Compartment to house boiler B1 .

37 - Electrical switchboard of plant and/or house.

38 - Electronic control unit (P.L.C.).

39 - Holes for connection and temperature detection.

40 - Thermal fluid return collector.

41 - Brackets for boiler B1 .

42 - Brackets for boiler B2.

43 - Thermal insulation with functions of mechanical interconnection.

44 - Fixing support on boiler B2.

45 - Fixing support on boiler B1 .

46 - Interconnection element with quick couplings or differentiated thread at the two ends.

47 - External thermometer.

48 - Heat exchange coil boiler B1 .

49 - Heat exchange coil boiler B2.

Heat exchange between the technical fluid of the panel and the sanitary hot water can take place both through a cavity exchange (Figs. 4, 5) or alternatively with coils (Fig. 6). The system will be more efficient if heat exchange takes place in counter current.

The boiler can have a "compact" configuration (Fig. 5), with a single object comprising a primary boiler B1 inserted inside a secondary boiler B2, of greater capacity than B1 .

Otherwise, the boiler can have an "extended" configuration (Fig. 4), in which there are two separate storage volumes constituted by a primary boiler B1 adjacent to a secondary boiler B2, of greater capacity than B1 .

The reason for the existence of the system is not only to split the boiler into two separate volumes, but above all the circulation route it forces the fluids present to take.

The plant engineering structure can be obtained both through external and internal mounting, and the only differences between the different configurations of the plant are represented by the different types of insulation of the storage volumes and by the different circulation routes of the plant fluids. The compact structure described in the accompanying diagrams can be obtained by enclosing one boiler inside another or also by two boilers placed one on top of the other, kept at a distance to completely eliminate the thermal bridge caused by contact between parts (Figs. 7 and 8).

In the graphic diagrams of the plant the conceptual diagrams of the system are shown using for the compact configuration only the enclosed boilers.

The system can also be structured on several systems in parallel that implement the principle set forth above on differentiated storage volumes and according to temperature level obtainable, which can, for example, be used in:

- a tourism structure with numerous residential units, where each operates to supply the nearest taps, but in the absence of local demand, transfers the hot water to the other units through a recirculation loop;

- an industrial structure that requires water or another thermal fluid at differentiated temperatures.

The system thus provides for production of the sanitary hot water storage plant installing two separate boilers or one inside the other. In any case, one of the two will be characterized by having a much smaller volume with respect to the other. For example, of the two storage tanks present in the system, the "primary" boiler B1 has a volume that in the first instance can be assumed to be approximately 1 /3 of the total available volume, but its effective dimension will depend directly on the climatic conditions of the location in which it is to be installed.

Moreover, the primary boiler can be positioned externally to and contiguous with the secondary boiler with its axis concentric thereto (Figs. 7, 8).

The boilers preferably have a cylindrical conformation.

In the case of the compact configuration, the internal boiler can be housed inside a seat made of solid metal plate, in order to make the internal compartment fluid- tight with respect to the outer compartment, or of simple profiles assembled to form a "cage".

If the centring system is constructed in the form of a cage, i.e. without physically separating the sanitary hot water from the insulation system of B1 , this will be of a type inert to water or in any case coated with an impermeable finish.

If the boilers are positioned externally to and contiguous with one another, the thermal bridges caused by direct conduction will in fact be eliminated using the brackets on the tank (41 , 42) and a thermal insulation 43 that acts as connecting element and spacer (Fig. 7).

Alternatively, a system of spacers with threaded connection, with bayonet coupling or the like or with quick coupling can be used. The spacer can be made of thermally insulating material, or in the case of particular requirements of mechanical resistance, the resistant core will be provided with a suitable coating.

Heat exchange will take place inside each boiler and for this purpose the types of boiler can be distinguished as follows:

1) boilers each provided with cavity 22, 23 for passage of the thermal fluid (Figs. 4,

5) ;

2) boilers each provided with coil heat exchangers of the thermal fluid 48, 49 (Fig.

6) fixed or removable, with smooth or finned piping or in any case provided with systems suitable to improve heat exchange;

3) the two types described above combined, i.e. one boiler with coil and the other with cavity are coupled in the system.

The system can be installed both externally and internally to the structures; the only differences will be represented by the different protective surface finishes of the structures of the plant and by the different protective degree used for the electrical and/or electronic devices.

Depending on the position of the panels 5 that recover solar energy, the plant can be produced with natural or forced circulation.

The system also integrates well with central heating plants, through interconnection both with the sanitary hot water and thermal distribution plant, through the use of three-way valves or solenoid valves managed by control units (PLC).

The system allows the output of integrated solar systems to be improved.

An essential characteristic of the system is linked to the possibility of disassembling all the accessory parts to the boiler for maintenance and replacement operations.

In the case of the boilers inserted in the compact configuration, it is also possible to replace the internal element; this operation will be possible through an interconnection between the boilers with bolted or threaded flange 20, or through quick couplings, or other linkages of known type that allow rapid access to the boiler.

It would also be possible to produce manholes of suitable dimension on the shell 30 of each boiler, in order to allow efficient and rapid maintenance thereof, primarily for removing deposits that can occur as a result of sludge and/or limescale.

From the viewpoint of simplifying the cleaning or internal washing operations after any treatment to remove limescale, or simply to remove solids conveyed by the mains water, a drain can be provided at the bottom, optionally provided with a cock.

The boilers can be provided with different types of connections for housing various types of sensors, probes, anodes, heating elements, and various valves, as well as the interconnections to the networks to be supplied.

In particular, inflow of sanitary water into the primary and/or secondary boilers can take place through systems with multi-injectors 1 .A, 3. A (Fig. 2 for horizontal installation, Fig. 3 for vertical installation), also removable to guarantee the efficiency of the system with periodic cleaning of scale deposits or replacement of the element in more difficult cases.

More in particular, the inflow of sanitary water in each of the operating stages can be obtained with a multi-injection system 1 .A, 3. A produced on linear, curved or circular piping. Injection (Fig. 9) can take place with holes produced directly on the piping, with cylindrical hole or hole with countersunk head, or with pipes leading in four directions. This allows better layering of the temperatures, slows the outflow speed, limits the incidence of oxidation and/or calcification and also limits stirring up the deposit on the bottom.

To limit calcification and deposits on the bottom, a filter can also be mounted in the tanks, upstream of the cold water supply inlet.

A significant improvement of the output of the system, and therefore a shorter time for amortization of the investment costs, can be achieved by inserting heating elements 13 and 14 in the part of the boilers containing the sanitary water, optionally supplied by a photovoltaic system 15 that may be present in the building (Figs. 1 , 2, 3). This solution allows the temperature of the fluid mass to be increased due to the more efficient recovery of solar energy. In critical cases, it will be possible to supply the heating elements also through the mains network.

With regard to illustration of the operation, the steps relative to circulation of the fluid in the thermal fluid circuit and in the sanitary water circuit are described below.

Circulation of the fluid in the thermal circuit.

Step N ° 1

Operation does not depend on the plant layout solution adopted. During the hours of useful sunlight, the fluid contained in the solar panel circulates exiting from the T.S.P. 5 along the section of piping 6 that passes first through the solenoid valve 7. A of normally open (NA) type and immediately after through the pipe 8 enters the thermal cavity 23 of the primary boiler B1 . After heat exchange has taken place, the fluid returns directly to the solar heating panel 5 through the return piping 9, the optional thermal fluid return collector 40, the optional circulator 35, if the plant is produced with forced circulation, and the final section of common piping 12. Step N ° 2

After reaching the desired temperature of the D.H.W. contained in the primary storage volume 25, optionally preset on the thermostat 18, the thermal flow is diverted automatically, through the PLC unit of the plant 38, (entirely or in part depending on requirements) to the heat exchange cavity 22 of B2.

This configuration of capturing energy will continue until it is necessary to operate only with the thermal volume of the boiler B1 to lower the ambient temperature or as both volumes have reached the maximum allowed storage temperature or in any other desired configuration.

Thermal fluid can flow into the cavity 22 of B2 through a solenoid valve 7.B of NC (Normally Closed) type, in the piping 10.

The PLC unit can be programmed through mechanical or computerized regulation. Where wishing to limit the costs of the original equipment, only thermo-mechanical regulation systems will be used.

The thermal fluid flows out of B2 through the pipe 1 1 , into the optional collector 40, the common pipe 12 and from there returns to the T.S.P. 5 for repetition of the thermal loading cycle.

As plant layout alternative, only one three-way mixing solenoid valve 17 can be used (Fig. 1 ): therefore, the system will carry out thermal transfer on only one storage volume at a time, in this manner choosing the total supply capacity of sanitary water according to the using requirements.

In any case, the solenoid valves regulate circulation of the thermal fluid in both circuits of the primary and secondary boilers, in particular open and close the circuits according to the needs of users, so that it is also possible to close both, for example in the case of reaching temperatures that are to high to be safe.

Step N ° 3 -

In the case in which a photovoltaic plant 15 is present in parallel to the solar heating plant 5, the heating elements 13 and 14 can improve energy recovery through thermal action alone. These heating elements can be supplied by the conventional electricity network, employing the system as if it were a common boiler, as known. The heating elements can be supplied by continuous or alternating current, without distinction.

In the system, also if operating with electricity supplied only by the mains network, energy will still be saved as the boiler B1 has a limited storage volume.

The collateral effect of the D.H.W. reaching the set temperature more rapidly is also consequential.

Circulation of the fluid in the sanitary water circuit.

The sanitary cold water, coming from the plant of the building, is always conveyed to a single inlet 1 , 1 .A obligatorily located in the boiler B2, through the check valve 26.

The injection of cold water can take place as shown in Fig. 1 with a single inflow point, or as shown in Figs. 2 and 3 with the multi-injection system illustrated in the detail of Fig. 9. The multi-injection system allows the flow of fluid to be slowed, improving layering thereof.

The sanitary water is transferred from boiler B2 to boiler B1 already preheated through the piping 2 and 3, if a flanged or quick coupling separation system 33 is mounted.

The pipe 3 can also be equipped with multi-injectors so as not to upset layering of the hot water.

The end users are all supplied by the piping 4.

Further variants to the non-limiting examples of embodiment described above are possible, without departing from the scope of protection of the present invention, comprising all equivalent embodiments for those skilled in the art.

The advantages deriving from application of the present invention are clear.

The system of the invention intends to obtain an improvement of the output of solar heating plants currently in production.

The system rationalizes the process for recovery of solar thermal energy in those periods in which the plant is typically not used or, even worse, is used as electric water heater through the use of one or more heating elements that heat the whole of the storage volume.

Splitting of the storage system, a primary of limited volume and a secondary, allows at least a minimum quantity of sanitary hot water, produced entirely through the solar panels, to be provided during cold weather for the needs of the user.

A characterizing element of the system is also the absence of a thermal bridge between the two boilers. If interconnection to a photovoltaic panel is implemented, all or part of the electrical energy produced thereby will be used to increase the temperature level. Only in limited cases will the system operate purely electrically through the heating provided by the heating elements.

Therefore, in any configuration the system will allow a considerable increase in the recovery of solar thermal energy to be achieved, contributing significantly to energy saving and therefore also to decreasing the volumes of atmospheric emissions.

With the same environmental conditions, the Sanitary Hot Water (D.H.W) temperature reached in the system is much higher with respect to that of current solar plants, as these latter dilute the captured energy over the whole of the storage capacity.

The total mass that can be heated in the system in the cold weather decreases with respect to that in warm weather, but in fact this is completely usable without compromises. In the same period the boilers are used in the same way as large water heaters supplied by conventional sources and therefore with considerably high costs and high pollution factor. The technical fluid flowing out of the solar panel, in the system, during cold weather will act on the water volume housed in the second and larger boiler, only if environmental conditions permit this. This solution allows the times of use of the system to be extended significantly over the course of the year, without the use of conventional sources.

In nations characterized by very low average temperatures, it is possible to use either much smaller primary storage volumes or smaller systems mounted in series or in parallel and managed integrally by an electronic system.

On the basis of the data detected, the PLC unit of the plant will actuate the most advantageous solution for the user or in any case the solution selected by it. The use of double solar technology allows the time interval of use of the plant to be extended, contributing to greater energy efficiencies, lower amortization times of the plant, further decreases in conventional energy consumptions within the building and consequently greater reduction of atmospheric emissions.

The system for storing and using hot water does not modify the general structure of the plants connected to solar panels currently in use. In fact, the split storage system can be inserted with limited operations on the plant layout in any plant currently operating, not only in those that will be produced with the present constructional philosophy. The system can be inserted in any pre-existing plant, by replacing the boiler, optionally equipped with heating elements, updating the electronic control system, optional interconnection with the existing photovoltaic plant, and optional interconnection with the 220 V power supply plant.

The system makes the energy capturing system more efficient, considerably extending the interval of use thereof during the year. Rationalization of the production of Sanitary Hot Water (D.H.W.) and the high level of integration with the photovoltaic system cause a significant increase in the thermodynamic output of the solar energy recovery and storage system.

In colder weather, where at present the thermal output typically decreases or is non-existent, the system allows significant results to be achieved, which are even greater in the case of interconnection to a photovoltaic plant. Interconnection to the photovoltaic plant will allow the temperature of the Sanitary Hot Water (D.H.W.) in the primary and, if conditions allow, also in the secondary boiler, to be increased. The possibility of using heating elements supplied by the photovoltaic system will contribute toward decreasing the production costs of hot water with conventional energies and also the volumes of carbon dioxide related thereto. The system, by splitting the thermal storage volume, limits the thermal inertia of the water system available, supplying a first storage volume characterized by the maximum temperature possible according to the weather conditions which are present. During the most critical periods for the production of hot water, the thermal fluid, outflowing from the installed panels, will always be conveyed to the first boiler, which can therefore guarantee a reasonably high temperature to the user with much faster times than those guaranteed by current systems.

The regulation and control system will be managed automatically by PLC units, which will manage the automatic mechanisms of the plant by processing the signals received from the various probes. This system allows the plant to be adapted to changes in the weather conditions in real time. The possibility of having a remote control unit will allow the plant to be monitored and managed remotely making use of home automation technologies. Action on the secondary water volume will only take place if the weather conditions are suitable, or otherwise, if after reaching the maximum programmed temperature in the primary boiler, none of the water is drawn off. In any case, after having passed into the first cavity the thermal fluid completes its cycle by passing into the second storage volume, and transferring any residual energy possessed thereto. If however the external temperatures are too cold, it can return directly to the solar panel. In more favourable environmental conditions, the thermal fluid can pass through the two storage volumes in series or in parallel.

From the above description, a person skilled in the art is capable of implementing the object of the invention without adding further structural details.

Claims

1 . A system for heating and storing water comprising: a sanitary water circuit and a thermal fluid circuit; a solar thermal plant (5) in which said thermal fluid circulates;

characterized in that it comprises:

- a primary boiler (B1 ) and a secondary boiler (B2), the secondary boiler having a greater capacity than the primary boiler (B1 ), said sanitary water and thermal fluid circuits passing through said primary and secondary boilers;

- means to control the circulation of the thermal fluid configured to cause circulation of the thermal fluid in a circulation circuit (7A, 9, 12) in said primary boiler (B1 ) until reaching a first temperature of the sanitary water, and/or in a circulation circuit (7B, 1 1 , 12) in said secondary boiler (B2);

- means to control the circulation of the sanitary water configured to cause inflow (1 ) of the sanitary water to be heated in said secondary boiler (B2), passage (2, 3) into said primary boiler (B1 ) and outflow (4) from said primary boiler (B1 ) toward the user.

2. The system for heating and storing water as claimed in claim 1 , wherein said primary boiler (B1 ) is inserted inside said secondary boiler (B2), or externally adjacent to, or in line with, said secondary boiler (B2).

3. The system for heating and storing water as claimed in claim 1 , wherein said primary boiler (B1 ) and said secondary boiler (B2) comprise an internal cavity (22, 23) for circulation of said thermal fluid, or coil heat exchangers (48) of the thermal fluid.

4. The system for heating and storing water as claimed in claim 1 , wherein inflow of sanitary water into said primary (B1 ) and/or secondary (B2) boilers takes place through one or more multi-injection systems (1 A, 3A) .

5. The system for heating and storing water as claimed in claim 4, wherein said multi-injection systems (1 .A, 3. A) are produced on linear, curved or circular piping, injection taking place with holes produced directly on the piping, with cylindrical hole or hole with countersunk head, or with pipes leading in four directions.

6. The system for heating and storing water as claimed in claim 1 , wherein said circuits for circulation of the thermal fluid in said primary and secondary boilers comprise separate solenoid valves (7A, 7B), or a three-way mixer solenoid valve (17).

7. The system for heating and storing water as claimed in claim 1 , further comprising systems for heating the sanitary water in said primary boiler (B1 ) and/or secondary boiler (B2) through heating elements (13, 14) in the part of the boilers containing sanitary water, optionally supplied by a photovoltaic plant (15).

8. A method to control operation of the system for heating and storing water as claimed in any one of the preceding claims, comprising the steps of:

- control of the circulation of the thermal fluid to cause circulation of the thermal fluid in said primary boiler (B1 ) until reaching a first temperature of the sanitary water, and/or in said secondary boiler (B2);

- control of the circulation of the sanitary water to cause inflow (1 ) of the sanitary water to be heated into said secondary boiler (B2), passage (2, 3) into said primary boiler (B1 ), and outflow (4) from said primary boiler (B1 ) toward the user.

9. The control method as claimed in claim 7, wherein said control of the circulation of the thermal fluid causes circulation of the thermal fluid first in said primary boiler (B1 ) until reaching said temperature of the sanitary water, and then in said secondary boiler (B2).

10. The control method as claimed in claim 7, wherein said control of the circulation of the thermal fluid causes circulation of the thermal fluid in said primary boiler (B1 ) and/or in said secondary boiler (B2).