EP4293307A1

EP4293307A1 - Compact storage and heat exchange system for thermal systems, relative plant and method

Info

Publication number: EP4293307A1
Application number: EP23179811.7A
Authority: EP
Inventors: Alessandro Bonolis
Original assignee: Cordivari SRL
Current assignee: Cordivari SRL
Priority date: 2022-06-16
Filing date: 2023-06-16
Publication date: 2023-12-20
Also published as: IT202200012803A1

Abstract

The present invention concerns a storage system (3) for thermal solar systems (1), which is connectable to a first circuit (50) for the circulation of a first heat transfer fluid and to a second circuit (40) for the circulation of a second primary heat transfer fluid, wherein said storage system (3) comprises:
a first tank (10) for the storage of a secondary fluid to be heated; and
a second tank (11) for the storage of said second primary heat transfer fluid, said second tank (11) being hydraulically separated from said first tank (10) and being configured to be hydraulically connected to said second circuit (40);
wherein a first heat exchange conduit (31) is arranged inside said first tank (10), said first heat exchange conduit (31) being configured to be hydraulically connected to said first circuit (50), for exchanging heat between said secondary fluid contained in said first tank (10) and said first primary heat transfer fluid;
wherein a second heat exchange conduit (32) is arranged inside said second tank (11), said second heat exchange conduit (32) being configured to be hydraulically connected to said first circuit (50), for exchanging heat between said second primary heat transfer fluid in said second tank (11) and said first primary heat transfer fluid
said storage system (3) further comprising
at least one portion (56) of said first circuit (50) hydraulically connected to the inlet and outlet of said first heat exchange conduit (31) and at least to the inlet of said second heat exchange conduit (32),
first flow diverter means (501) which are arranged in said at least one portion (56) of said first circuit (50) to divert the flow of said first primary heat transfer fluid from said first circuit (50) towards the inlet of said first heat exchange conduit (31) or towards said second heat exchange conduit (32), and vice versa, and
second flow diverter means (502) which are arranged in said at least one portion (56) of said first circuit (50), downstream of said first flow diverter means (501) and of said outlet of said first heat exchange conduit (31), said second flow diverter means (502) being adapted to divert the flow of the first primary heat transfer fluid coming from the outlet of said first heat exchange conduit (31) or from said first circuit (50) towards the inlet of said second heat exchange conduit (32) or towards said first circuit (50).

The present invention also concerns a solar thermal system (1) comprising such storage system (3) and a method for operating such system (1).

Description

The present invention concerns a storage and heat exchange system for thermal systems, in particular for thermal solar systems.
In particular, the present invention concerns a compact storage system to be used in solar thermal systems for producing domestic hot water (DHW) and in hydronic air conditioning systems, combined with a solar thermal system.
The present invention also concerns a method for operating such systems.
In fact, the term "hydronic air conditioning systems" means that such systems and the related terminals use a heat transfer fluid for transferring heat, which typically is a liquid, such as, for example, but not limited to, water, treated water, glycol water or similar.
These types of systems usually comprise:

a circuit for a first solar primary heat transfer fluid, also briefly referred to as first primary heat transfer fluid;
solar collectors, capable of absorbing solar energy and transferring it in the form of thermal energy to the first primary heat transfer fluid;
a circuit for a second primary heat transfer fluid;
further heating means for heating the second primary heat transfer fluid, in particular a heat pump generator;
a tank, in particular a storage tank, containing a secondary fluid, for example domestic water,
a first heat exchanger connected to the tank and to the circuit for the first primary heat transfer fluid, to make it possible to heat the secondary fluid in the tank by heat exchange with the first primary heat transfer fluid; and
a second heat exchanger, connected to the tank and to the circuit for the second primary heat transfer fluid, to make it possible to heat the secondary fluid in the tank by heat exchange with said second primary heat transfer fluid.

In particular, the term solar heat transfer fluid or solar fluid means a fluid heated by solar energy.
One of the necessary conditions for a heat transfer to occur is that at least one primary heat transfer fluid is at a higher temperature than the secondary fluid to which the heat is to be transferred.
In the state-of-the-art solar systems, such as those shown in Figures 1 - 2, the tank for the secondary fluid, in particular domestic hot water, and the circuits for the primary heat transfer fluids can have the following configurations.
With particular reference to Figure 1, in a first configuration of solar systems according to the prior art, these can comprise a storage system with an external casing G, inside which a first tank S1 for the storage of the secondary fluid, in particular water, and a second tank S2 for the storage of the second primary heat transfer fluid of the thermal system are contained. The second storage tank S2 is able to exchange heat with the exchanger C inside which the solar heat transfer fluid, exiting from the solar collector A, is flowing and to transfer it to the domestic water in the tank S1 for producing domestic hot water (DHW); these types of storage systems are usually called combined tanks. In the particular embodiment of Figure 1 it is shown a combined tank of the "tank-in-tank" type.
With reference to Figure 2, in a second configuration of solar systems according to the prior art, these can comprise at least one first tank S1 for the storage of the secondary fluid (in the figure a boiler, i.e. a tank for domestic hot water, also called DHW) and a second storage tank S2 (in the figure a stratified storage tank, also called stratified puffer), for the storage of the second primary heat transfer fluid coming from the air conditioning system. In particular, the second storage tank S2 provides two heat exchangers, a first one C1 in its upper portion and a second one C2 in its lower portion, for exchanging heat, first in the first exchanger C1 at the top and then, once the upper part of the tank S2 is heated, in the second lower exchanger C2 for heating the lower part of the tank S2. The solar system shown in Figure 2 also comprises a heat exchanger C arranged inside the first tank S1 storing the secondary fluid for exchanging heat with a solar primary heat transfer fluid coming from solar collectors A.
In the first prior art configuration of Figure 1, having an external casing with a "combined" tank, the overall size of the casing G and of the related system is reduced in comparison with systems with a separate double tank, such as the one shown in Figure 2. However, since in the system of Figure 1 the tank S1 for the storage of the secondary fluid is arranged inside the tank S2 for the storage of the second primary heat transfer fluid coming from the thermal generator, such fluids are necessarily at the same temperature, which must be greater than or equal to the highest operating temperature provided for the secondary fluid. In particular, in the case of domestic hot water, such temperature is usually greater than or equal to its distribution temperature, i.e. between 45÷55°C.
Therefore, in the first prior art configuration of Figure 1 having a "combined" tank, the heat generator and the solar collectors A must heat the second primary heat transfer fluid of the system at temperatures above 50°C. This leads to a lower efficiency and greater expenditure of energy, especially in the case of use of heat pump thermal generators, which in the state of the art have higher performances "at a low temperature", i.e. temperatures between 35°C and 50°C. However, such temperatures are lower than those of the domestic hot water, which, as mentioned, is normally produced and stored at 55÷70 °C and distributed in the domestic water systems at 45÷55 °C. For such reasons, the system will have a low efficiency having to heat all the second primary heat transfer fluid contained in the storage at temperatures equal to or higher than 50°.
Furthermore, if there is a heat pump generator which also operates in reverse cycle, i.e. which produces a refrigerated primary fluid, for example for the summer cooling, the "combined" storage tank in Figure 1 cannot be used as a "thermal flywheel", i.e. it is not possible to accumulate the primary fluid of the system inside it at the cooling temperature, which is typically between 7 °C and 18°C, since, as just explained, the storage temperature of the primary fluid cannot be lower than the distribution temperature of the secondary fluid, which is typically between 45 °C and 55 °C.
For such reasons, especially for the aforesaid thermal systems with "low-temperature" terminals and heat generators, operating with or without a reverse cycle, the second system configuration of Figure 2 having a double tank, also called double storage, is usually preferred.
In such configuration, if the main generator is a heat pump, the function of the tank for the storage of the primary fluid is mainly to be a "thermal flywheel" for the heat pump itself. In other words, the presence of a second tank makes it possible to increase the volume of fluid which is brought to the operating temperature by the heat pump and thus to avoid frequent switching on or modulation of the inverter (if any) of the heat pump itself, which reduce its efficiency, and furthermore it constitutes an energy reservoir to cope with demand peaks that otherwise the generator could not satisfy, unless it is "oversized", thereby increasing the purchase cost.
Therefore, in the case of double-storage solar thermal systems, such additional storage of the second primary fluid must be sized for the just described function and can thus be smaller than the storage of the secondary fluid, in particular domestic hot water.
Furthermore, compact storage systems with two separate tanks in a single casing have been recently introduced to the market.
Such compact double-tank storage systems, such as for example the one shown in the system of Figure 3, are mainly used in the field of thermal systems having "low temperature" terminals. With particular reference to Figure 3, such systems can comprise a single exchanger D arranged inside the first tank S1 for the storage of the secondary fluid, for exchanging heat between the latter and the second primary heat transfer fluid coming from a heat generator P, and a three-way diverter valve V to divert the flow of the second primary heat transfer fluid alternately into the exchanger D of the first tank S1 for the storage of the secondary fluid or into the second tank S2 for the storage of the second primary fluid.
Figure 4 shows a further prior art compact storage system, comprising a further heat exchanger C connected to a solar circuit inside the storage tank for the secondary fluid, in particular domestic hot water, for exchanging heat between the latter and the solar heat transfer fluid of the solar circuit A.
Therefore, in such configurations of Figures 3 and 4, the second tank S2 only serves the aforementioned function of "thermal flywheel" for the heat transfer fluid of the generator P.
However, the aforementioned solutions do not always make it possible to fully exploit the available solar energy, since, as mentioned, for transferring heat from the solar circuit to the secondary fluid it is necessary that the solar primary heat transfer fluid is at a higher temperature than the secondary fluid to which the heat is to be transferred. Therefore, when the solar primary heat transfer fluid is at a temperature lower than or equal to that of the secondary fluid, all the heat stored in said solar primary heat transfer fluid is not transferable and remains unused, reducing the potential efficiency of the system itself.
Furthermore, in the patent document EP 2 041 496 B1 it is described a compact storage system comprising a first tank equipped with a first heat exchange conduit and a second tank equipped with a second and third heat exchange element. In particular, said first heat exchange conduit is placed in the tank positioned at the top, in fluid contact with said third conduit in said second tank. However, such solution requires to heat the fluids in both tanks in succession ("in cascade") and does not make it possible to heat only one of the two tanks on the basis of a choice or of the conditions for operating the system, such as the temperatures of fluids in the conduits and/or in the tanks, or different operation modes, such as heating one tank and cooling the other one.
An aim of the present invention is therefore to provide a compact storage system for thermal systems, in particular solar thermal systems, which makes it possible to minimize the overall size and maximize the performance of the system itself.
In particular, an aim of the present invention is that such storage system makes it possible to optimize the use of solar energy.
A further aim of the present invention is that such storage system is particularly effective for being used in "low temperature" systems.
Furthermore, an aim of the present invention is that such storage system is safe, easy and reliable and that it involves reduced costs, both for its production and for its maintenance.
Furthermore, an aim of the present invention is to provide a thermal system optimized for the use of such storage system.
Finally, an aim of the present invention is to provide a method for operating such optimized thermal system.
Therefore, an object of the present invention is a storage system for thermal solar systems, which can be connected to a first circuit for the circulation of a first heat transfer fluid and to a second circuit for the circulation of a second primary heat transfer fluid, wherein said storage system comprises:

a first tank for the storage of a secondary fluid to be heated; and
a second tank for the storage of said second primary heat transfer fluid, said second tank being hydraulically separated from said first tank and being configured to be hydraulically connected to said second circuit;
wherein said second tank has a volume between 100 L and 250 L;
wherein a first heat exchange conduit is arranged inside said first tank, said first heat exchange conduit being configured to be hydraulically connected to said first circuit, for exchanging heat between said secondary fluid contained in said first tank and said first primary heat transfer fluid;
wherein a second heat exchange conduit is arranged within said second tank, said second heat exchange conduit being configured to be hydraulically connected to said first circuit, for exchanging heat between said second primary heat transfer fluid in said second tank and said first primary heat transfer fluid; wherein a second heat exchange conduit is arranged inside said second tank, said second heat exchange conduit being configured to be hydraulically connected to said first circuit, for exchanging heat between said second primary heat transfer fluid in said second tank and said first primary heat transfer fluid.

In particular, according to the invention, said storage system can be provided with a single casing inside which said first tank and said second tank are arranged, and wherein said two tanks can be thermally separated from each other.
Still according to the invention, said system can comprise a third heat exchange conduit arranged inside said first tank and configured to be hydraulically connected to said second circuit, for exchanging heat between said secondary fluid contained in said first tank and said second primary heat transfer fluid.
Again, according to the invention the ratio between the heat exchange surface of the second heat exchange conduit and the volume of the second tank can be between $\frac{0,65}{100} \frac{m^{2}}{l}$
and $\frac{0,9}{100} \frac{m^{2}}{l}$
.
Still according to the invention, the ratio between the heat exchange surface of said second heat exchange conduit and the volume of the second tank can be substantially between two and four times the ratio between the heat exchange surface of said first heat exchange conduit and the volume of said first tank.
A further object of the present invention is a storage system for thermal solar systems, which can be connected to a first circuit for the circulation of a first heat transfer fluid and to a second circuit for the circulation of a second primary heat transfer fluid, wherein said storage system comprises:

a first tank for the storage of a secondary fluid to be heated; and
a second tank for the storage of said second primary heat transfer fluid, said second tank being hydraulically separated from said first tank and being configured to be hydraulically connected to said second circuit;
wherein a first heat exchange conduit is arranged inside said first tank, said first heat exchange conduit being configured to be hydraulically connected to said first circuit, for exchanging heat between said secondary fluid contained in said first tank and said first primary heat transfer fluid;
wherein a second heat exchange conduit is arranged inside said second tank, said second heat exchange conduit being configured to be hydraulically connected to said first circuit, for exchanging heat between said second primary heat transfer fluid in said second tank and said first primary heat transfer fluid
said storage system further comprising
at least one portion of said first circuit hydraulically connected to the inlet and outlet of said first heat exchange conduit and at least to the inlet of said second heat exchange conduit,
first flow diverter means which are arranged in said at least one portion of said first circuit to divert the flow of said first primary heat transfer fluid from said first circuit towards the inlet of said first heat exchange conduit or towards said second heat exchange conduit, and vice versa, and
second flow diverter means which are arranged in said at least one portion of said first circuit, downstream of said first flow diverter means and of said outlet of said first heat exchange conduit, said second flow diverter means being adapted to divert the flow of the first primary heat transfer fluid coming from the outlet of said first heat exchange conduit or from said first circuit towards the inlet of said second heat exchange conduit or towards said first circuit.

Preferably according to the invention, a single casing can be provided inside which said first and second tanks are arranged, and wherein said two tanks are thermally separated from each other.
In particular, according to the invention said system can comprise a third heat exchange conduit arranged inside said first tank and configured to be hydraulically connected to said second circuit, for exchanging heat between said secondary fluid contained in said first tank and said second primary heat transfer fluid.
A further object of the present invention is a solar thermal system, comprising

a storage system according to any one of the preceding claims;
ambient air conditioning terminals;
said first circuit for the circulation of said first primary heat transfer fluid;
said second circuit for the circulation of said second primary heat transfer fluid in fluid contact with said ambient air conditioning terminals;
at least one solar collector in fluid connection with said first circuit, for heating said first primary heat transfer fluid;
at least one heat generator in fluid connection with said second circuit, for heating or cooling said second primary heat transfer fluid from or to at least said second tank, and
wherein said first means for diverting the flow of the first solar primary fluid are adapted to divert the flow of said first primary heat transfer fluid from said at least one solar collector towards said first heat exchange conduit or towards said second heat exchange conduit, and vice versa, and
wherein said second means for diverting the flow of the first solar primary fluid are adapted to divert the flow of the first primary heat transfer fluid coming from the outlet of said first heat exchange conduit or from said at least one solar collector towards said second heat exchange conduit or towards said at least one solar collector,
and wherein said system comprises at least one control unit connected to said first means for diverting the flow of the first solar primary fluid and to said second means for diverting the flow of the first solar primary fluid and configured to act on them.

Preferably according to the invention, said system can comprise temperature detection means comprising a first temperature sensor for detecting a first temperature of the first primary heat transfer fluid heated by said at least one solar collector, a second temperature sensor arranged in said first tank for detecting a first storage temperature of the secondary fluid, and a third temperature sensor arranged in said second tank for detecting a storage temperature of the second primary heat transfer fluid, wherein said at least one control unit can be configured to act on said first means for diverting the flow of the first solar primary fluid on the basis of the temperatures detected by said temperature detection means.
Furthermore, according to the invention said system can comprise a fifth temperature sensor, connected to said at least one control unit and arranged at the outlet of said first heat exchange conduit, for detecting a second temperature of the first solar primary fluid and
wherein said control unit can be configured to act on said second means for diverting the flow of the first solar primary fluid on the basis of said second temperature of the first solar primary fluid.
Still according to the invention, said second circuit can comprise means for diverting the flow of the second primary fluid connected to said control unit or to a control unit of said at least one heat generator, said flow diverter means of the second primary fluid being adapted to divert the flow of said second primary heat transfer fluid exiting from said heat generator towards said third heat exchange conduit for heating said secondary fluid in said first tank by means of said second heated primary heat transfer fluid, or towards said second tank and/or towards said ambient air conditioning terminals,

wherein said temperature detection means can comprise a fourth temperature sensor, arranged in correspondence with said first tank, for detecting a second storage temperature of the secondary fluid, and
wherein a control unit of said heat generator, or said control unit 8, can be configured to act on said primary flow diverter means on the basis of said second storage temperature of the secondary fluid.

Preferably according to the invention, said second tank can be in fluid connection with a delivery conduit of said second circuit, for receiving said second primary heat transfer fluid from said heat generator, and with said ambient air conditioning terminals, for sending and/or receiving said second primary heat transfer fluid towards and/or from said ambient air conditioning terminals.
Still according to the invention, said at least one heat generator can be a boiler or a heat pump generator.
Furthermore, according to the invention said at least one heat generator can be in fluid connection with a delivery conduit to send said second primary heat transfer fluid towards said ambient air conditioning terminals.
Again, according to the invention said at least one heat generator can be a heat pump generator and wherein said second tank can be in fluid connection with a delivery conduit to send said second primary heat transfer fluid towards said ambient air conditioning terminals.
Preferably according to the invention, a control unit of said heat pump can be configured to act on said second means for diverting the flow of the first solar primary fluid.
In addition, according to the invention said second tank can be in fluid connection with a return conduit of said second circuit, for sending said second primary heat transfer fluid towards said heat generator, and with a return conduit of said second circuit, for receiving said second primary heat transfer fluid from said ambient air conditioning terminals.
Still according to the invention, said at least one heat generator can be a heat pump generator and wherein said heat pump generator can be in fluid connection with a return conduit of said second circuit, to receive said second primary heat transfer fluid from said ambient air conditioning terminals.
A further object of the following invention is a method for operating a solar thermal system, comprising the following steps:

A. sending said first primary heat transfer fluid from said at least one solar collector towards said first heat exchange conduit, for carrying out a heat exchange with said secondary fluid in said first tank by means of said first flow diverter means or
B. sending said first primary heat transfer fluid from said at least one solar collector towards said second heat exchange conduit, for carrying out a heat exchange with said second primary heat transfer fluid in said second tank by means of said first and second flow diverter means,

F. diverting said first primary heat transfer fluid exiting from said first heat exchange conduit, towards said second heat exchange conduit by means of said second means for diverting the flow of the first solar primary fluid,
or
G. diverting said first primary heat transfer fluid exiting from said first heat exchange conduit, towards said at least one solar collector by means of said second means for diverting the flow of the first solar primary fluid,
or alternatively the following step
D. interrupting the flow of the first primary fluid in said first circuit.

Preferably, according to the invention, before, during or after said step A or B, the following step can be provided:

C1. reading the first temperature of the first primary heat transfer fluid detected by said first temperature sensor, the first storage temperature of the secondary fluid detected by said second temperature sensor and the storage temperature of the second primary heat transfer fluid detected by said third temperature sensor and
if said first temperature of the first primary fluid is greater than or equal to a threshold temperature of the solar fluid and said first storage temperature of the secondary fluid is both lower than a first threshold temperature of the secondary fluid and lower than said first temperature of the first primary fluid, carrying out said step A by diverting said first primary heat transfer fluid towards said first heat exchange conduit by means of said first means for diverting the flow of the first solar primary fluid, or
if said first storage temperature of the secondary fluid is greater than or equal to said first threshold temperature of the secondary fluid, or if it is greater than or equal to said first temperature of the first primary heat transfer fluid, and,
if said storage temperature of the second primary fluid is lower than or equal to said first temperature of the first solar fluid and is lower than or equal to a threshold temperature of the second primary fluid, carrying out said step B by diverting said first primary heat transfer fluid towards said second heat exchange conduit through said first means for diverting the flow of the first solar primary fluid.

Again, according to the invention said step F can be carried out by the action of said at least one control logic unit acting on said second flow diverter means or, in the absence of control over said second flow diverter means, by said at least one control logic unit,
and wherein said step G can be carried out by the action of said at least one control logic unit acting on said second flow diverter means.
Still according to the invention, said step B or F can be carried out if said heat pump does not operate in reverse cycle, i.e. it is not producing the second refrigerated primary fluid
and wherein said step G can be carried out if said heat generator operates in reverse cycle, i.e. if it is producing the second refrigerated primary fluid.
Preferably according to the invention, during or after said step A, the following step can be provided:

C2. reading the first temperature of the first primary heat transfer fluid detected by said first temperature sensor, the first storage temperature of the secondary fluid detected by said second temperature sensor, the storage temperature of the second primary heat transfer fluid detected by said third temperature sensor and a second temperature of the first solar primary fluid detected by said fifth temperature sensor and
if said second temperature of the first solar primary fluid is greater than or equal to said storage temperature of the second primary fluid, carrying out said step F, or
if said second temperature of the solar primary fluid is lower than said storage temperature of the second primary fluid, carrying out said step G.

Again, according to the invention before, during or after said step A or B, F or G, the following step can be provided:

C1. reading the first temperature of the first primary heat transfer fluid detected by said first temperature sensor, the first storage temperature of the secondary fluid detected by said second temperature sensor, the storage temperature of the second primary heat transfer fluid detected by said third temperature sensor,
and wherein said step D can be carried out
if said first temperature of the first primary fluid is lower than a threshold temperature of the solar fluid,
or if said first storage temperature of the secondary fluid is greater than or equal to said first threshold temperature of the secondary fluid and said step G is ongoing,
or if said first storage temperature of the secondary fluid is greater than or equal to said first temperature of the first primary heat transfer fluid, and said step G is in ongoing,
or if said first storage temperature of the secondary fluid is greater than or equal to said first threshold temperature of the secondary fluid, and said storage temperature of the second primary fluid is greater than or equal to said threshold temperature of the second primary fluid,
or if said first storage temperature of the secondary fluid is greater than or equal to said first temperature of the first primary heat transfer fluid, and said storage temperature of the second primary fluid is greater than or equal to said threshold temperature of the second primary fluid,
or if said first storage temperature of the secondary fluid is greater than or equal to said first threshold temperature of the secondary fluid, and said storage temperature of the second primary fluid is greater than or equal to said first temperature of the first primary heat transfer fluid;
or if said first storage temperature of the secondary fluid is greater than or equal to said first temperature of the first primary heat transfer fluid and said storage temperature of the second primary fluid is greater than or equal to said first temperature of the first primary heat transfer fluid.

Furthermore, according to the invention if said second storage temperature of the secondary fluid is lower than a second threshold temperature of the secondary fluid, the following step can be carried out:
E. diverting said second primary heat transfer fluid towards said third heat exchange conduit through said means for diverting the flow of the second primary fluid, for heating said secondary fluid by means of said second primary heat transfer fluid.
In addition, according to the invention said second threshold temperature of the secondary fluid can be lower than or equal to said first threshold temperature of the secondary fluid.
The invention will now be described for illustrative but non-limiting purposes, with particular reference to the drawings of the attached figures, wherein:

Figure 1 shows a first example of a prior art system comprising a storage system with a tank of the "tank-in-tank" type;
Figure 2 shows a second example of a prior art system, comprising a storage system with two separate storage tanks;
Figure 3 shows a third example of a prior art system, comprising a compact storage system;
Figure 4 shows a fourth example of a priori art system, comprising a further compact storage system;
Figure 5 shows a schematic view of a first embodiment of a system according to the present invention;
Figure 6 shows a sectional view of the storage system of the system of Figure 5;
Figure 7 shows a schematic view of a second embodiment of a system according to the present invention; and
Figure 8 shows a sectional view of the storage system of the system of Figure 7.

In the diagrams shown in Figures 5-8 described below, the thicker lines represent the hydraulic circuit conduits inside which a higher- or hot-temperature or heated fluid flows, while the thinner lines represent the hydraulic circuit conduits inside which a lower- or cold-temperature or not yet heated fluid flows.
Still in such diagrams, the aforementioned hydraulic circuit conduits, used in the reverse cycle for the summer cooling, are shown with the same thicknesses, but they are dashed.
Still in such diagrams, the thin dash-dot lines represent connections of an electric, electronic or radio type with a control unit, for example a control panel.
With particular reference to Figures 5 - 6, in a first embodiment, the numerical reference 1 will be assigned to a thermal system according to the present invention.
Such embodiment is particularly advantageous in combination with systems generating thermal energy of the "low temperature" type, for example with a second primary heat transfer fluid at a temperature between 35°C - 45 °C, for the reasons explained below.
The thermal system 1 according to the invention comprises a first thermal energy generator 2, in particular a solar thermal system comprising one or more solar collectors 2, capable of transferring thermal energy to a first primary heat transfer fluid, also called first primary fluid or simply first solar heat transfer fluid. The solar collectors 2 are in fact capable of absorbing solar energy and transferring it to said first solar heat transfer fluid.
Therefore, the thermal system 1 comprises a circulator or hydraulic pump or analogous device, connected to the solar collectors 2, for the circulation of the first primary heat transfer fluid from the solar collectors 2 towards the exchangers and vice versa. In the example embodiment of Figure 5, such hydraulic pump is arranged in a circulation group 12 external to the solar collectors 2.
In particular, the expression "solar heat transfer fluid" or "solar fluid" means a heat transfer fluid heated by solar energy, while the expression "solar circulator" or "solar hydraulic pump" means a circulator or hydraulic pump or analogous device able to move such solar fluid.
The thermal system 1 also comprises a second thermal energy generator 9, in particular a heat pump 9, or in general a low-temperature heat generator 9, able to transfer thermal energy to a second primary heat transfer fluid, also called second primary fluid.
Furthermore, the thermal system 1 comprises a storage system 3 for the heating, storage and distribution of a secondary fluid, in particular domestic hot water, and for the heat exchange, storage and distribution of said second primary fluid coming from the heat generator 9, in particular from the heat pump 9. In particular, the storage system 3 is thermally connected through heat exchangers to said solar collectors 2 and to said heat pump 9.
The thermal system 1 further comprises a first circuit 50, for the circulation of the first primary heat transfer fluid from the solar collectors 2 to the storage system 3, and vice versa.
Furthermore, the thermal system 1 comprises a second circuit 40, for the circulation of the second primary heat transfer fluid from the heat pump 9 to the storage system 3 and to ambient air conditioning terminals 7, and vice versa. In particular, said ambient air conditioning terminals 7 can be "low temperature" terminals, i.e. designed for temperatures between 35°C and 45°C, such as for example radiant bodies and fan coils.
The thermal system 1 also comprises temperature detection means 33, 34, 35, 46, for detecting the temperatures of the fluids in said hydraulic circuits 40, 50 and in said storage system 3, whose function will be better detailed below.
Finally, the thermal system 1 comprises at least one control unit 8, in particular an electronic control unit 8 for controlling the heating and temperature of the fluids in the storage system 3 on the basis of the temperatures detected by the temperature detection means 33, 34, 35, 46. In particular, the control unit 8 is connected to said at least one circulator or analogue device for the circulation of the first primary fluid, as better illustrated below.
In the example embodiment shown in Figure 5, the air conditioning system is preferably a hydronic system, i.e. adapted to exchange thermal energy using a second primary water-based heat transfer fluid, such as, for example, but not limited to, water, treated water, glycol water or similar, with a second heat pump thermal energy generator 9.
In other embodiments the control unit can be that of the heat pump 9 or they can cooperate simultaneously.
The storage system 3 comprises a first tank 10 for the storage of the secondary fluid and a second tank 11 for the storage of the second primary heat transfer fluid. The second tank 11 is hydraulically separated from the first tank 10, since, in the case shown, it is physically separated from it and an insulating layer is preferably interposed to prevent thermal continuity between the tanks 10 and 11. Preferably, said first tank 10 is positioned above said second tank 11.
Preferably, the second tank 11 has a reduced volume of between 100 L and 250 L, so as to act as an inertial tank, in other words to increase the total volume of the tank and therefore the thermal inertia of the thermal system in which it is inserted.
The storage system 3 also comprises a first heat exchanger 31, or first exchanger 31 or first heat exchange conduit 31, contained in the first tank 10 and in fluid connection with said first circuit 50 for the passage of said first primary fluid, and for exchanging heat with said secondary fluid contained in the first tank 10.
Furthermore, the storage system 3 comprises a second heat exchanger 32, or second exchanger 32 or second heat exchange conduit 32, contained in the second tank 11 and still in fluid connection with said first circuit 50, for the passage of said first primary heat transfer fluid, and for exchanging heat between it and the second primary heat transfer fluid contained in the second tank 11.
In particular, said first tank 10 and said second tank 11 are arranged inside a single casing 37.
Furthermore, the first tank 10 is in fluid connection with devices 6 for supplying the secondary fluid, in particular, for example taps for supplying domestic hot water, also known as DHW.
More specifically, the first tank 10 has an upper opening 38, arranged in the upper portion of the first tank 10, for supplying the secondary fluid at a higher temperature, in particular for supplying domestic hot water, and a lower opening 39, arranged in the lower portion of the first tank 10, for inletting the secondary fluid at a lower temperature.
The second tank 11 is in fluid contact with the second circuit 40 for the storage of the second primary heat transfer fluid heated or cooled by the second thermal energy generator 9 and for distributing it towards the ambient air conditioning terminals 7.
In particular, in the example embodiment shown in the diagrams from Fig. 5 to 8, the second tank 11 is in fluid connection with a delivery conduit 47 of the second circuit 40 for receiving the second primary fluid from said second heat generator 9. Furthermore, in the diagrams of Figures 5 and 7, the second tank 11 is in fluid connection with a return conduit 43, for receiving said second primary fluid from said ambient air conditioning terminals 7 and with a return conduit 48 of said second circuit 40 for sending said second primary fluid from said second tank 11 towards said second heat generator 9.
Furthermore, the second circuit 40 comprises a terminal delivery conduit 49, for sending the second primary heat transfer fluid to the ambient air conditioning terminals 7, which can be in fluid communication directly with the second thermal generator 9 (as in the example embodiment shown in the diagrams of Figures 5 and 7), without passing through the second tank 11. In this case, said terminal delivery conduit 49 is in fluid connection with said return conduit 43 of the ambient air conditioning terminals 7 through a differential bypass valve 403.
The second tank 11, as shown in Figures 5 - 8, has a smaller volume than the first tank 10. Instead, the second exchanger 32 can preferably have a greater heat exchange surface than the heat exchange surface of the first exchanger 31. In fact, the heat exchange in the second tank 11 typically occurs at lower temperatures and with smaller temperature differences, and therefore requires a greater exchange surface.
The volume of the first tank 10 is preferably between 100 L and 600 L.
By way of example, in a first example of storage system 3 according to the present invention, the volume of the first tank 10 may be equal to 230 L, while the volume of the second tank 11 may be equal to 135 L.
Again, by way of example, in a second example of storage system 3 according to the present invention, the volume of the first tank 10 may be equal to 415 L, while the volume of the second tank 11 may be equal to 190 L.
Furthermore, the heat exchange surface of the second exchanger 32 is preferably between 130% and 160% compared with the heat exchange surface of the first exchanger 31.
In the present case,

in the case of the first example of storage system 3, the heat exchange surface of the first exchanger 31 may be equal to 0.75 m², while the heat exchange surface of the second exchanger 32 may be equal to 1.1 m²; and
in the case of the second example of storage system 3, the heat exchange surface of the first exchanger 31 may be equal to 1 m², while the heat exchange surface of the second exchanger 32 may be equal to 1.4 m².

The ratio between storage volume and exchange surface is more performing than the one currently applied in the state of the art for domestic water heating.
In particular, the ratio between the heat exchange surface of the second heat exchange conduit 32 and the volume of the second tank 11 is preferably between $\frac{0,65}{100} \frac{m^{2}}{l}$
and $\frac{0,9}{100} \frac{m^{2}}{l}$
, compared with a ratio typically used in the state of the art in similar applications for heating the fluid contained in a tank via a solar thermal system, generally between $\frac{0,15}{100} \frac{m^{2}}{l}$
and $\frac{0,35}{100} \frac{m^{2}}{l}$
.
In particular, the ratio between the heat exchange surface of the first heat exchange conduit 31 and the volume of the first tank 10 is between 1/4 and 1/2 of the ratio between the heat exchange surface of the second heat exchange conduit 32 and the volume of the second tank 11, in particular the ratio between the heat exchange surface of the first heat exchange conduit 31 and the volume of the first tank 10 is preferably between $\frac{0,15}{100} \frac{m^{2}}{l}$
and $\frac{0,35}{100} \frac{m^{2}}{l}$
.
The temperature detection means 33, 34, 35, 46 comprise a first temperature sensor 33, for detecting the temperature T1 of the first primary fluid heated by said solar collectors 2, also called temperature of the heated solar fluid T1.
Furthermore, the temperature detection means 33, 34, 35, 46 comprise a second temperature sensor 34, for detecting the temperature T2 of the secondary fluid contained inside the first tank 10, also called first storage temperature of the secondary fluid T2.
The temperature detector means 33, 34, 35, 46 also comprise a third temperature sensor 35, for detecting the temperature T3 of the second primary fluid contained inside the second tank 11, also called storage temperature of the primary fluid T3.
Finally, the temperature detector means 33, 34, 35, 46 comprise a fourth temperature sensor 46, for detecting the temperature T5 of the secondary fluid contained inside the first tank 10, also called second storage temperature of the secondary fluid T5.
The first circuit 50 comprises a first three-way valve for diverting the flow of the solar primary fluid 501, or a first solar three-way diverter valve 501, in particular a three-way diverter valve 501 or an analogue flow diverter system, controlled by said control unit 8, for diverting the flow of the first primary fluid heated by said solar collectors 2 towards the first heat exchanger 31 of said first tank 10 or towards the second heat exchanger 32 of said second tank 11.
More specifically, said first solar three-way diverter valve 500 is in fluid connection with said solar collectors 2 and with said first and second exchangers 31, 32.
Thanks to such arrangement, the first circuit 50 can switch from a first configuration for heating the secondary fluid in the first tank 10 by heat exchange with the first primary fluid, to a second configuration for heating the second primary fluid in the second tank 11 by heat exchange with the first primary fluid, or to a third configuration, wherein the flow of the first primary fluid in the first circuit 50 is interrupted.
Such switching from the first configuration to the second or third configuration depends on the temperatures T1, T2, T3 detected by the temperature detection means 33, 34, 35 and on their comparison with predetermined threshold temperatures T1s, T2s, T3s. For example, such threshold temperatures T1s, T2s, T3s can be set and controlled by the control unit 8.
In particular, the thus described system 1 with the storage system 3 operates as follows:

the control unit 8 reads the temperatures T1, T2, T3 detected by the temperature sensor means 33, 34, 35, compares them with said predetermined threshold temperatures T1s, T2s, T3s, and
- if the temperature T1 of the first heated primary fluid is greater than or equal to a threshold temperature of the solar fluid T1s (solar set-point temperature), for example between 25° and 35°, the control unit 8 proceeds with controlling the first storage temperature of the secondary fluid T2 and the storage temperature of the second primary fluid T3, therefore,
- if the temperature T1 of the first solar primary fluid is greater than or equal to said threshold temperature of the solar fluid T1s and the first storage temperature of the secondary fluid T2 is both lower than a first threshold temperature of the secondary fluid T2s (set-point temperature of the first tank 10), for example between 50° and 65 °, and lower than said temperature of the heated solar fluid T1 in the solar collectors 2,
the control unit 8 sends a signal to the first solar circulator or to another device to activate the circulation of the first solar primary heat transfer fluid and sends a signal to the first solar three-way diverter valve 501 to switch/keep the first solar circuit 50 to/in said first configuration, wherein the first solar three-way diverter valve 501 allows the first solar primary fluid to flow from said solar collectors 2 towards said first heat exchanger 31 and vice versa, so as to make it possible to heat said secondary fluid in the first tank 10 through the use of solar thermal energy.

Instead,

if the first storage temperature of the secondary fluid T2, measured in the first tank 10, is greater than or equal to the first threshold temperature of the secondary fluid T2s, or
if the first storage temperature of the secondary fluid T2, measured in the first tank 10, is greater than or equal to the temperature of the heated solar fluid T1 in the solar collectors 2 and the second heat generator 9 is not operating in reverse cycle, i.e. it is not producing the second refrigerated primary fluid,
and
if the storage temperature of the second primary heat transfer fluid T3, measured in the second tank 11, is lower than or equal to the temperature of the heated solar fluid T1 in the solar collectors 2 and a threshold temperature of the primary fluid T3s, for example between 35° and 55°,

control unit

solar circuit

way diverter valve

solar circuit

way diverter valve

solar collectors

second heat exchanger

second tank

Finally, if none of the conditions described above occurs, i.e

if the temperature T1 of the first heated solar primary fluid is lower than said threshold temperature of the solar fluid T1s (solar set-point temperature),
or
if the first storage temperature of the secondary fluid T2, measured in the first tank 10, is greater than or equal to the first threshold temperature of the secondary fluid T2s and the second thermal generator 9 is operating in reverse cycle, i.e. it is producing a refrigerated primary fluid,
or
if the first storage temperature of the secondary fluid T2 is greater than or equal to the first threshold temperature of the secondary fluid T2s and the storage temperature of the second primary fluid T3, measured in the second tank 11, is greater than or equal to the threshold temperature of the second primary fluid T3s, or
if the temperature T1 of the first heated solar primary fluid is lower than both storage temperatures T2, T3,

control unit

solar circuit

In one embodiment, the threshold temperature of the second primary fluid T3s can be lower than or equal to the first threshold temperature of the secondary fluid T2s, in particular in the case of "low temperature" systems.
In a further embodiment, by setting a high value for the threshold temperature of the second primary fluid T3s (for example between 70°C and 85°C), the heating of the second primary fluid can occur as long as there is a difference of temperature between the two heat transfer fluids.
Furthermore, in the example of Figure 5, a third heat exchanger 44 can be provided, still arranged in the first tank 10 and in fluid connection with the second primary circuit 40, for exchanging heat between the secondary fluid contained in the first tank 10 and the second primary fluid coming from the second thermal generator 9, so that it can be used to heat the secondary fluid contained in the first tank 10.
The temperature detector means 33, 34, 35, 46 comprise a fourth temperature sensor 46, for detecting the temperature T5 of the secondary fluid contained inside the first tank 10, also called second storage temperature of the secondary fluid T5, in correspondence with the volume heated by the exchanger 44 and, preferably, used for controlling the heat generator 9 or 90.
In fact, in the systems of the examples of Figures 5 and 7 the second primary circuit 40 comprises a three-way valve for diverting the flow of the second primary fluid 400, or three-way valve for diverting the second primary fluid 400, comprising:

an outlet in fluid connection with a primary return conduit 41, which returns the second primary fluid towards said thermal generator 9,
a first inlet in fluid connection with said third exchanger 44 via a third return conduit 42, and
a second inlet in fluid connection with the return from said second tank 11 via a fourth return conduit 48 or in fluid connection with the return from the terminals 7 via a return conduit 43.

Therefore, if the second storage temperature of the secondary fluid T5, measured in the first tank 10, is lower than a second threshold temperature of the secondary fluid T5s (generator set-point temperature), for example between 45° and 60°, a control unit of the second generator 9, which may coincide with the control unit 8, or an independent unit, sends a signal to the three-way valve for diverting the second primary fluid 400, which diverts the flow of the second primary fluid from said second heat generator 9 towards said third heat exchanger 44, so as to make it possible to heat said secondary fluid in the first tank 10.
In particular, the second threshold temperature of the secondary fluid T5s (generator set-point temperature) can be lower than or equal to the first threshold temperature of the secondary fluid T2s, in particular in the case of "low temperature" systems, in order to give priority to heating through the use of solar thermal energy (which is free and eco-sustainable).
In the shown embodiment, the third heat exchanger 44 is arranged above the first heat exchanger 31. This advantageously makes it possible to heat a smaller volume by means of the second generator 9, compared with the whole volume of the first tank 10, since the remaining volume of the first tank 10 heated by the first exchanger 31 is arranged below, thus exploiting the (free) solar energy and reducing the energy consumption by the second generator 9 and, if there is sufficient solar energy, it advantageously makes it possible to heat, by thermal stratification with the first exchanger 31 arranged below, also the upper volume where the third heat exchanger 44 is arranged, making even more use of the (free) solar energy and minimizing the energy consumption by the second generator 9.
In alternative embodiments (not shown), said third heat exchanger 44 and the related conduits connected to the second primary circuit 40 may not be present.
Advantageously, with the thus described system 1, it is possible to obtain both the advantages given by the use of the prior art "combined" tanks, in particular having a reduced size, and the advantages given by having separate tanks. In fact, having two different storage temperatures for the secondary fluid and for the second primary fluid in the two tanks 10 and 11 which can be set independently of each other, it is possible to transfer heat to the secondary and primary fluids in two distinct steps.
Furthermore, as mentioned, thanks to the particular configuration of the storage system 3 with the two heat exchangers 31, 32, it is possible to transfer heat from the solar collectors 2 to the secondary fluid as long as the temperature of the heated solar fluid T1 in the solar collectors 2 is higher than the first storage temperature of the secondary fluid T2 in the first tank 10, for example for the production and/or storage of domestic hot water.
Furthermore, the system 1 is configured to continue to transfer heat from the solar collectors 2 to the second primary fluid contained in the second tank 11, even after the first storage temperature of the secondary fluid T2, measured in the first tank 10, has reached the first threshold temperature of the secondary fluid T2s (set-point temperature of the first tank 10), or when the temperature of the heated solar fluid T1 in the solar collectors is lower than said first storage temperature of the secondary fluid T2 in the first tank 10, as long as there is a temperature difference between the temperature of the heated solar fluid T1 leaving the solar collectors 2 and the storage temperature of the second primary fluid T3 in the second tank 11, which, as mentioned, for "low temperature" (typically 35÷45°C) systems is always lower than the storage and distribution temperature of the DHW (which is the secondary fluid in the first tank 10).
In this way it is possible to take full advantage of the heat absorbed by the sun by the solar collectors 2, improving the performance and efficiency of the solar system itself and ensuring greater savings in the management of the air conditioning system as a whole.
Furthermore, the second primary fluid present in the second tank 11 can be advantageously used as a thermal flywheel for the heat pump generator 9, both when it operates in "direct cycle", i.e. it produces the second heated primary fluid, and when it operates in "reverse cycle", i.e. it produces the second refrigerated primary fluid.
The thus described system 1 is particularly suitable if the threshold temperature of the second primary fluid T3s in the second tank 11 is between 35°C and 55°C, i.e. in "low temperature" systems.
Furthermore, the thus described system 1 is particularly suitable also if the heat pump generator 9 also operates in reverse cycle, i.e. it produces a second refrigerated primary fluid, for example for the summer cooling.
In fact, unlike the prior art "combined" tanks of the prior art, such as for example the one in Figure 1, both when said heat generator 9 is operating in "direct cycle", i.e. it is producing the second heated primary fluid, and when said heat generator 9 is operating in "reverse cycle", i.e. it is producing the second refrigerated primary fluid, said second tank 11 can be advantageously used as a "thermal flywheel" for the second heated or refrigerated primary fluid.
Regarding the configuration of the second primary circuit 40 it is to be understood that those skilled in the art will be able to use other system configurations without thereby departing from the relative scope of protection, as defined by the attached claims.
It is also to be understood that those skilled in the art will be able to use, in said other system configurations, different flow diverter means to arrange the circulation of the second heated or refrigerated primary fluid from and to the tank 11 in the most suitable manner known in the state of the art without thereby departing from the relative scope of protection, as defined by the attached claims.
Still with reference to Figures 5 - 6, said first solar three-way diverter valve 501, controlled by said control unit 8, is in fluid connection with the delivery conduits 54, 55 and 56 of the first primary fluid towards said first and second exchanger 31, 32 and with the outlet of said first heat exchanger 31. Preferably in the configurations of Figures 5 and 6 said first solar diverter three-way valve 501 comprises

a first inlet in fluid connection with a delivery solar conduit 54, for receiving the first primary fluid heated by said solar collectors;
a second inlet in fluid connection with the outlet of said first exchanger 31; and
an outlet, in fluid connection with said second exchanger 32 by means of a second delivery conduit 56, for sending the first primary fluid heated by said first solar three-way diverter valve 501 towards the second exchanger 32.

In particular, said first solar three-way diverter valve 501 can be positioned at said inlet of said first exchanger 31 or at said outlet of said first exchanger 31.
The delivery solar conduit 54 is also in fluid connection with a first delivery conduit 55 for sending the first primary fluid towards the first exchanger 31, at a junction point 503. The junction point 503 is upstream of the first solar three-way diverter valve 501, referring to the direction of flow of the first primary fluid towards said second exchanger 32.
Therefore, depending on the state of the first solar three-way diverter valve 501, the second delivery conduit 56 can receive the first primary fluid from the outlet of the first exchanger 31 or from the delivery solar conduit 54.
In fact, when the first solar circuit 50 is in said first configuration, the first solar three-way diverter valve 501 has said first inlet closed, said second inlet open and said outlet open. Instead, when the first solar circuit 50 is in said second configuration, said first solar three-way diverter valve 501 has said first inlet open, said second inlet closed and said outlet open.
The first solar circuit 50 also comprises a second solar three-way diverter valve 502 or an analogue flow diverting system, in fluid connection with said second exchanger 32.
In particular, the second solar three-way diverter valve 502 is controlled by said control unit 8 to divert the flow of the first primary fluid from the first solar three-way diverter valve 501 towards the second exchanger 32 or towards the return conduit 53 to said solar collectors 2. This feature makes it possible to control the flow of the first primary fluid between said first exchanger 31 and/or said second exchanger 32 and/or said solar collectors 2.
In particular, said second solar three-way diverter valve 502 can be positioned at said inlet of said second exchanger 32 or at said outlet of said second exchanger 32.
More specifically, said storage system 3 provides a hydraulic connection conduit, which in the specific embodiment coincides with the second delivery conduit 56, which hydraulically connects the inlet and outlet of said first heat exchange conduit 31 and at least the inlet of said second heat exchange conduit 32. Said first flow diverter means 501 are arranged in said hydraulic connection conduit 56 and said second flow diverter means 502 are always arranged in said hydraulic connection conduit 56 downstream of said first flow diverter means 501, preferably at the inlet of said second heat exchange conduit 32. Such hydraulic connection conduit 56 turns out to be a portion of the first circuit 50. In other embodiments said first and second flow diverter means 501 and 502 can be arranged in other portions of the first circuit 50, provided that they are hydraulically connected to the inlet and outlet of said first heat exchange conduit 31 and at least to the inlet of said second heat exchange conduit 32 and provided that the second flow diverter means 502 are arranged downstream of the first flow diverter means 501. In the present text the indications "downstream" and "upstream" are meant with respect to the direction of circulation of the fluid inside its respective circuits. Specifically, they are meant with respect to the circulation of the first primary heat transfer fluid in the first circuit 50 from the first heat exchange conduit 31 to the second heat exchange conduit 32.
Preferably in the configuration of Figures 5 and 6, said second solar diverter three-way valve 502 has an inlet in fluid connection with said second delivery conduit 56, a first outlet in fluid connection with the inlet of said second exchanger 32 and a second outlet in fluid connection with a fifth return conduit 57 to said solar collectors 2, through a junction point 504 with said return conduit 53.
Since the first circuit 50 is a closed circuit, the diversion of the flow to and from the exchangers 31, 32 can be made indifferently in correspondence with the conduits at the inlet or at the outlet of said exchangers 31, 32; therefore, in alternative embodiments (not shown in the figures), the solar three- way diverter valves 501 and 502 can be replaced by analogue flow diverter means, or arranged in different points of the first circuit 50, such as for example in place of the junction points 503 and 504, respectively, which in turn would be arranged in their place, without thereby departing from the relative scope of protection, as defined by the attached claims.
Thanks to such arrangement, the first heated primary fluid can be sent from the solar collectors 2 alternatively to the first exchanger 31 of the first tank 10 or to the second exchanger 32 of the second tank 11, or from the solar collectors 2 towards the first exchanger 31, and, "in cascade" from the first exchanger 31 towards the second exchanger 32, using the following "alternative or cascade" method for heating two tanks by means of a solar thermal system.
If the temperature of the first heated primary fluid T1 exiting from the solar collectors 2 is higher than a threshold temperature of the first primary fluid T1s (solar set-point temperature) and the first storage temperature of the secondary fluid T2 in the first tank 10, the control unit 8 sends a signal to the first solar circulator or to another device to activate the circulation of the first primary heat transfer fluid in the first solar circuit 50 and sends a signal to the first solar three-way diverter valve 501 to arrange the first solar circuit 50 in said first configuration, wherein the first solar three-way diverter valve 501 allows the first primary fluid to pass from the solar collectors 2 to the first exchanger 31.
In this first configuration, the control unit 8, or other control means, sends a signal to the second solar three-way diverter valve 502, to divert the flow of said first primary heat transfer fluid exiting from the first exchanger 31 towards the inlet of the second exchanger 32 of the second tank 11.
In this case, the first primary fluid returns to the solar collector 2 through the second return conduit 53, which is in fluid connection with the outlet of the second exchanger 32 at a junction point 504 arranged downstream of said second solar three-way diverter valve 502.
Said signal is sent by the control unit 8, or other control means, to the second solar three-way diverter valve 502 to divert the flow of said first primary heat transfer fluid exiting from the first exchanger 31 towards the inlet of the second exchanger 32 of the second tank 11, if the second thermal generator 9 is not operating in reverse cycle, i.e. it is not producing a refrigerated primary fluid.
Thanks to the presence of the two three- way diverter valves 501, 502, it is therefore advantageously possible to heat the second primary fluid by heat exchange with the first primary fluid even when the first solar circuit 50 is in said first configuration, carrying out a heat exchange "in cascade" between the first primary heat transfer fluid coming from the solar collectors 2 and both fluids present in the two tanks 10, 11.
Otherwise, the control unit 8, or other control means, sends a signal to the second solar three-way diverter valve 502, for diverting the flow of said first primary heat transfer fluid exiting from the first exchanger 31 in order to direct it straight towards the solar collectors 2, the first primary fluid returns to the solar collector 2 through the conduit 57 and then by means of the second return conduit 53, without exchanging heat between the first primary heat transfer fluid and the fluid present in the tank 11.
In the embodiment shown in Figures 5 and 6, said signal is sent by the control unit 8, or other control means, to the second solar three-way diverter valve 502 for diverting the flow of said first primary heat transfer fluid exiting from the first exchanger 31 in order to direct it straight towards the solar collectors 2, preferably if the second heat-pump thermal generator 9 is operating in reverse cycle, i.e. it is producing a refrigerated primary fluid.
With particular reference to Figures 7 and 8, in a second embodiment of the system 1 according to the present invention, the temperature detection means comprise a fifth temperature sensor 36, for detecting a temperature of the first primary fluid T4 coming from the outlet of the first exchanger 31 or from the delivery solar conduit 54, in correspondence with said second delivery conduit 56.
If the temperature of the first heated primary fluid T1 exiting from the solar collectors 2 is higher than a threshold temperature of the first primary fluid T1s (solar set-point temperature) and the first storage temperature of the secondary fluid T2 in the first tank 10, the control unit 8 sends a signal to the first solar circulator or to another device to activate the circulation of the first primary heat transfer fluid in the first solar circuit 50 and sends a signal to the first solar three-way diverter valve 501 to arrange the first solar circuit 50 in said first configuration, wherein the first solar three-way diverter valve 501 allows the first primary fluid to pass from the solar collectors 2 to the first exchanger 31.
In this first configuration, if the temperature of the first primary fluid T4 exiting from said first exchanger 31, detected by the further temperature sensor 36, is greater than or equal to the storage temperature of the second primary fluid T3 contained in the second tank 11 and the second heat pump thermal generator 9 is not operating in reverse cycle, i.e. it is not producing a second primary refrigerated fluid, the control unit 8, or other control means, sends a signal to the second solar three-way diverter valve 502, to divert the flow of said first primary heat transfer fluid exiting from the first exchanger 31 towards the inlet of the second exchanger 32 of the second tank 11.
In this case, the first primary fluid returns to the solar collector 2 through the second return conduit 53, which is in fluid connection with the outlet of the second exchanger 32 at a junction point 504 arranged downstream of said second solar three-way diverter valve 502.
Said signal is sent by the control unit 8, or other control means, to the second solar three-way diverter valve 502 to divert the flow of said first primary heat transfer fluid exiting from the first exchanger 31 towards the inlet of the second exchanger 32 of the second tank 11, if the temperature of the first primary fluid T4 exiting from said first exchanger 31, detected by the further temperature sensor 36, is greater than the storage temperature of the second primary fluid T3 contained in the second tank 11 and if said storage temperature of the second primary fluid T3 is lower than a threshold temperature of the second primary fluid T3s.
Thanks to the presence of the two three- way diverter valves 501, 502, it is therefore advantageously possible to heat the second primary fluid by exchanging heat with the first primary fluid even when the first solar circuit 50 is in said first configuration, carrying out a heat exchange "in cascade" between the first primary heat transfer fluid coming from the solar collectors 2 and both fluids present in the two tanks 10, 11.
Otherwise, if the temperature of the first primary fluid T4 exiting from said first exchanger 31 is lower than the storage temperature of the second primary fluid T3, or the second heat pump thermal generator 9 is operating in reverse cycle, i.e. it is producing a primary refrigerated fluid, the control unit 8, or other control means, sends a signal to the second solar three-way diverter valve 502, for diverting the flow of said first primary heat transfer fluid exiting from the first exchanger 31 in order to direct it straight towards the solar collectors 2, the first primary fluid returns to the solar collector 2 through the conduit 57 and then through the second return conduit 53, without exchanging heat between the first primary heat transfer fluid and the fluid present in the tank 11.
Said signal is sent by the control unit 8, or other control means, to the second solar three-way diverter valve 502 for diverting the flow of said first primary heat transfer fluid exiting from the first exchanger 31 in order to direct it straight towards the solar collectors 2, if the temperature of the first primary fluid T4 exiting from said first exchanger 31, detected by the further temperature sensor 36, is lower than or equal to the storage temperature of the second primary fluid T3 contained in the second tank 11 or if said storage temperature of the second primary fluid T3 is greater than or equal to a threshold temperature of the second primary fluid T3s.
Instead,

if the first storage temperature of the secondary fluid T2 in the first tank 10 is greater than or equal to the first threshold temperature of the secondary fluid T2s, or it is greater than or equal to the temperature of the first heated primary fluid T1 in said solar collectors 2, and
if the second heat pump thermal generator 9 is not operating in reverse cycle, i.e. it is not producing a refrigerated primary fluid, and
if the temperature of the first heated primary fluid T1 in the solar collectors 2 is greater than or equal to said threshold temperature T1s and the storage temperature of the second primary fluid T3 in the second tank 11,

control unit

solar circuit

way diverter valve

solar circuit

way diverter valve

solar collectors

way diverter valve

second heat exchanger

second tank

If none of the above conditions are met, i.e.

if the temperature of the first heated primary fluid T1 is lower than said threshold temperature of the first primary fluid T1s (solar set-point temperature), or
if the first storage temperature of the secondary fluid T2 is greater than or equal to said temperature of the first heated primary fluid T1 or it is greater than or equal to said first threshold temperature of the secondary fluid T2s and the heat pump generator 9 is operating in reverse cycle, i.e. it is producing a refrigerated primary fluid, or
if the additional temperature sensor is present and if the first storage temperature of the secondary fluid T2 is greater than or equal to said temperature of the first heated primary fluid T1 or it is greater than or equal to said first threshold temperature of the secondary fluid T2s and said temperature of the first primary fluid T4 exiting from said first solar three-way diverter valve 501 is lower than said storage temperature of the second primary fluid T3, or again
if said temperature of the first heated primary fluid T1 is lower than both said storage temperatures T2 and T3,

control unit

solar circuit

Such system 1 is particularly suitable in the case of low temperature systems and, moreover, particularly suitable also if the second heat pump thermal generator 9 also operates in reverse cycle, i.e. it produces the second refrigerated primary fluid, for example for the summer cooling, making it possible to advantageously use the second tank 11 as a "thermal flywheel" for the second refrigerated primary fluid.
Advantageously, the storage system of the solar thermal system according to the invention is very compact and at the same time makes it possible to carry out the heat transfer from the solar system to the fluids contained in the two tanks with a heat exchange at temperatures which are different and independent of each other.
Furthermore, advantageously the tanks and the related exchangers of the storage system according to the invention are sized and proportioned for being used with the same number of solar collectors to ensure the production of the DHW required in the summer, and a contribution to heating of the fluid of the thermal system in the other seasons.
Again, the storage system and the system according to the invention advantageously make it possible to use the energy of the first solar primary heat transfer fluid also for heating the second primary heat transfer fluid of the air conditioning system.
Again, the storage system and the system according to the invention advantageously make it possible to

use the inertial storage of the second tank as a "thermal flywheel" of the air conditioning system both in heating and cooling mode, i.e. if the second thermal generator operates in reverse cycle, i.e. it produces the second primary refrigerated fluid;
use the energy of the first solar primary heat transfer fluid to exchange heat at different and independent temperatures between the fluids contained in the two tanks;
exploit the energy of the first solar primary fluid even when the latter is at temperatures lower than the typical DHW distribution temperatures (45÷50°C);
exploit the residual energy of the first solar primary fluid, after the heat exchange with the secondary fluid contained in the storage for the DHW production and/or storage, to heat the second primary fluid of the air conditioning system; and
size all the elements of the solar system and of the thermal system, such as storage capacity and exchange surfaces for each fluid, in an optimal way.

In the foregoing, the preferred embodiments have been described and variants of the present invention have been suggested, but it is to be understood that those skilled in the art will be able to make modifications and changes without thereby departing from the relative scope of protection, as defined by the claims attached.

Claims

A storage system (3) for solar thermal systems (1), which is connectable to a first circuit (50) for the circulation of a first heat transfer fluid and to a second circuit (40) for the circulation of a second primary heat transfer fluid, wherein said storage system (3) comprises:
a first tank (10) for the storage of a secondary fluid to be heated; and

a second tank (11) for the storage of said second primary heat transfer fluid, said second tank (11) being hydraulically separated from said first tank (10) and being configured to be hydraulically connected to said second circuit (40);

wherein a first heat exchange conduit (31) is arranged inside said first tank (10), said first heat exchange conduit (31) being configured to be hydraulically connected to said first circuit (50), for exchanging heat between said secondary fluid contained in said first tank (10) and said first primary heat transfer fluid;

wherein a second heat exchange conduit (32) is arranged inside said second tank (11), said second heat exchange conduit (32) being configured to be hydraulically connected to said first circuit (50), for exchanging heat between said second primary heat transfer fluid in said second tank (11) and said first primary heat transfer fluid

said storage system (3) further comprising

at least one portion (56) of said first circuit (50) hydraulically connected to the inlet and outlet of said first heat exchange conduit (31) and at least to the inlet of said second heat exchange conduit (32),

first flow diverter means (501) which are arranged in said at least one portion (56) of said first circuit (50) to divert the flow of said first primary heat transfer fluid from said first circuit (50) towards the inlet of said first heat exchange conduit (31) or towards said second heat exchange conduit (32), and vice versa, and

second flow diverter means (502) which are arranged in said at least one portion (56) of said first circuit (50), downstream of said first flow diverter means (501) and of said outlet of said first heat exchange conduit (31), said second flow diverter means (502) being adapted to divert the flow of the first primary heat transfer fluid coming from the outlet of said first heat exchange conduit (31) or from said first circuit (50) towards the inlet of said second heat exchange conduit (32) or towards said first circuit (50).
The storage system (3) according to the preceding claim, wherein a single casing (37) is provided inside which said first tank (10) and said second tank (11) are arranged, and wherein said two tanks (10, 11) are thermally separated from each other.
The storage system (3) according to claim 1 or 2, wherein said system (3) comprises a third heat exchange conduit (44) arranged inside said first tank (10) and configured to be hydraulically connected to said second circuit (40), for exchanging heat between said secondary fluid contained in said first tank (10) and said second primary heat transfer fluid.
A solar thermal system (1), comprising
a storage system (3) according to any one of the preceding claims;

ambient air conditioning terminals (7);

said first circuit (50) for the circulation of said first primary heat transfer fluid;

said second circuit (40) for the circulation of said second primary heat transfer fluid in fluid contact with said ambient air conditioning terminals (7);

at least one solar collector (2) in fluid connection with said first circuit (50), for heating said first primary heat transfer fluid;

at least one heat generator (9; 90) in fluid connection with said second circuit (40), for heating or cooling said second primary heat transfer fluid from or to at least said second tank (11), and

wherein said first means for diverting the flow of the first solar primary fluid (501) are adapted to divert the flow of said first primary heat transfer fluid from said at least one solar collector (2) towards said first heat exchange conduit (31) or towards said second heat exchange conduit (32), and vice versa, and

wherein said second means for diverting the flow of the first solar primary fluid (502) are adapted to divert the flow of the first primary heat transfer fluid coming from the outlet of said first heat exchange conduit (31) or from said at least one solar collector (2) towards said second heat exchange conduit (32) or towards said at least one solar collector (2),

and wherein said system (1) comprises at least one control unit (8) connected to said first means for diverting the flow of the first solar primary fluid (501) and to said second means for diverting the flow of the first solar primary fluid (502) and configured to act on them.
The system (1) according to the preceding claim, wherein it comprises temperature detection means (33, 34, 35, 36, 46) comprising a first temperature sensor (33) for detecting a first temperature of the first primary heat transfer fluid (T1) heated by said at least one solar collector (2), a second temperature sensor (34) arranged in said first tank (10) for detecting a first storage temperature of the secondary fluid (T2), and a third temperature sensor (35) arranged in said second tank (11) for detecting a storage temperature of the second primary heat transfer fluid (T3), wherein said at least one control unit (8) is configured to act on said first means for diverting the flow of the first solar primary fluid (501) on the basis of the temperatures detected by said temperature detection means (33, 34, 35, 36, 46).
The system (1) according to claim 4 or 5, wherein it comprises a fifth temperature sensor (36), connected to said at least one control unit (8) and arranged at the outlet of said first heat exchange conduit (31), for detecting a second temperature of the first solar primary fluid (T4) and
wherein said control unit (8) is configured to act on said second means for diverting the flow of the first solar primary fluid (502) on the basis of said second temperature of the first solar primary fluid (T4).
The system (1) according to any one of claims 5 - 6, when said storage system (3) is according to claim 3, wherein said second circuit (40) comprises means for diverting the flow of the second primary fluid (400) connected to said control unit (8) or to a control unit of said at least one heat generator (9; 90), said means for diverting the flow of the second primary fluid (400) being adapted to divert the flow of said second primary heat transfer fluid exiting from said heat generator (9; 90) towards said third heat exchange conduit (44) for heating said secondary fluid in said first tank (10) by means of said second heated primary heat transfer fluid, or towards said second tank (11) and/or towards said ambient air conditioning terminals (7),
wherein said temperature detection means (33, 34, 35, 36, 46) comprise a fourth temperature sensor (46) arranged in correspondence with said first tank (10), for detecting a second storage temperature of the secondary fluid (T5), and

wherein a control unit of said heat generator (9; 90) or said control unit (8) is configured to act on said primary flow diverter means (400) on the basis of said second storage temperature of the secondary fluid (T5).
The system (1) according to any one of claims 4 - 7, wherein said second tank (11) is in fluid connection with a delivery conduit (47) of said second circuit (40), for receiving said second primary heat transfer fluid from said heat generator (9, 90), and with said ambient air conditioning terminals (7), for sending and/or receiving said second primary heat transfer fluid towards and/or from said ambient air conditioning terminals (7).
The system (1) according to any one of claims 4 - 8, wherein said at least one heat generator (9, 90) is a boiler (90) or a heat pump generator (9).
The system (1) according to any one of claims 4 - 9, wherein said at least one heat generator (9; 90) is in fluid connection with a delivery conduit (49) for sending said second primary heat transfer fluid towards said ambient air conditioning terminals (7).
The system (1) according to any one of claims 4 - 9, wherein said at least one heat generator (9) is a heat pump generator (9) and wherein said second tank (11) is in fluid connection with a delivery conduit (49) for sending said second primary heat transfer fluid towards said ambient air conditioning terminals (7).
The system (1) according to the preceding claim, wherein a control unit of said heat pump (9) is configured to act on said second means for diverting the flow of the first solar primary fluid (502).
The system (1) according to any one of claims 5 - 12, wherein said second tank (11) is in fluid connection with a return conduit (48) of said second circuit (40), for sending said second primary heat transfer fluid towards said heat generator (9, 90), and with a return conduit (43) of said second circuit (40), for receiving said second primary heat transfer fluid from said ambient air conditioning terminals (7).
The system (1) according to any one of claims 4 - 9 or 11, wherein said at least one heat generator (9) is a heat pump generator (9) and wherein said heat pump generator (9) is in fluid connection with a return conduit (43) of said second circuit (40), for receiving said second primary heat transfer fluid from said ambient air conditioning terminals (7).
A method for operating a solar thermal system (1) according to any one of claims 4 - 14, comprising the following steps:
A. sending said first primary heat transfer fluid from said at least one solar collector (2) towards said first heat exchange conduit (31), for carrying out a heat exchange with said secondary fluid in said first tank (10) by means of said first flow diverter means (501) or

B. sending said first primary heat transfer fluid from said at least one solar collector (2) towards said second heat exchange conduit (32), for carrying out a heat exchange with said second primary heat transfer fluid in said second tank (11) by means of said first and second flow diverter means (501, 502),
wherein during or after said step A, the following step is provided:
F. diverting said first primary heat transfer fluid exiting from said first heat exchange conduit (31), towards said second heat exchange conduit (32) by means of said second means for diverting the flow of the first solar primary fluid (502),
or

G. diverting said first primary heat transfer fluid exiting from said first heat exchange conduit (31), towards said at least one solar collector (2) by means of said second means for diverting the flow of the first solar primary fluid (502),
or alternatively the following step

D. interrupting the flow of the first primary fluid in said first circuit (50).
The method according to claim 15, when said system (1) is according to claim 5, wherein before, during or after said step A or B, the following step is provided:
C1. reading the first temperature of the first primary heat transfer fluid (T1) detected by said first temperature sensor (33), the first storage temperature of the secondary fluid (T2) detected by said second temperature sensor (34) and the storage temperature of the second primary heat transfer fluid (T3) detected by said third temperature sensor (35) and

if said first temperature of the first primary fluid (T1) is greater than or equal to a threshold temperature of the solar fluid (T1s) and said first storage temperature of the secondary fluid (T2) is both lower than a first threshold temperature of the secondary fluid (T2s) and lower than said first temperature of the first primary fluid (T1), carrying out said step A by diverting said first primary heat transfer fluid towards said first heat exchange conduit (31) by means of said first means for diverting the flow of the first solar primary fluid (501), or

if said first storage temperature of the secondary fluid (T2) is greater than or equal to said first threshold temperature of the secondary fluid (T2s), or if it is greater than or equal to said first temperature of the first primary heat transfer fluid (T1), and,

if said storage temperature of the second primary fluid (T3) is lower than or equal to said first temperature of the first solar fluid (T1) and is lower than or equal to a threshold temperature of the second primary fluid (T3s), carrying out said step B by diverting said first primary heat transfer fluid towards said second heat exchange conduit (32) through said first means for diverting the flow of the first solar primary fluid (501).
The method for operating a solar thermal system (1) according to claim 15 or 16, wherein said step F is carried out by the action of said at least one control logic unit (8) acting on said second flow diverter means (502) or, in the absence of control over said second flow diverter means (502), by said at least one control logic unit (8),
and wherein said step G is carried out by the action of said at least one control logic unit (8) acting on said second flow diverter means (502).
The method for operating a solar thermal system (1) according to any one of claims 15 - 17, when said system (1) is according to claim 11 or 12, wherein said step B or F is carried out if said heat pump (9) does not operate in reverse cycle, i.e. it is not producing the second refrigerated primary fluid
and wherein said step G is carried out if said thermal generator (9) operates in reverse cycle, i.e. if it is producing the second refrigerated primary fluid.
The method according to any one of claims 16 - 18, when said system (1) is according to claim 6 wherein during or after said step A, the following step is provided:
C2. reading the first temperature of the first primary heat transfer fluid (T1) detected by said first temperature sensor (33), the first storage temperature of the secondary fluid (T2) detected by said second temperature sensor (34), the storage temperature of the second primary heat transfer fluid (T3) detected by said third temperature sensor (35) and a second temperature of the first solar primary fluid (T4) detected by said fifth temperature sensor (36) and

if said second temperature of the first solar primary fluid (T4) is greater than or equal to said storage temperature of the second primary fluid (T3), carrying out said step F, or

if said second temperature of the solar primary fluid (T4) is lower than said storage temperature of the second primary fluid (T3), carrying out said step G.
The method according to any one of claims 15 - 19, when the system (1) is according to claim 5, wherein before, during or after said step A or B, F or G, the following step is provided:
C1. reading the first temperature of the first primary heat transfer fluid (T1) detected by said first temperature sensor (33), the first storage temperature of the secondary fluid (T2) detected by said second temperature sensor (34), the storage temperature of the second primary heat transfer fluid (T3) detected by said third temperature sensor (35),
and wherein said step D is carried out

if said first temperature of the first primary fluid (T1) is lower than a threshold temperature of the solar fluid (T1s),

or if said first storage temperature of the secondary fluid (T2) is greater than or equal to said first threshold temperature of the secondary fluid (T2s) and said step G is ongoing,

or if said first storage temperature of the secondary fluid (T2) is greater than or equal to said first temperature of the first primary heat transfer fluid (T1), and said step G is in ongoing,

or if said first storage temperature of the secondary fluid (T2) is greater than or equal to said first threshold temperature of the secondary fluid (T2s), and said storage temperature of the second primary fluid (T3) is greater than or equal to said threshold temperature of the second primary fluid (T3s),

or if said first storage temperature of the secondary fluid (T2) is greater than or equal to said first temperature of the first primary heat transfer fluid (T1), and said storage temperature of the second primary fluid (T3) is greater than or equal to said threshold temperature of the second primary fluid (T3s),

or if said first storage temperature of the secondary fluid (T2) is greater than or equal to said first threshold temperature of the secondary fluid (T2s), and said storage temperature of the second primary fluid (T3) is greater than or equal to said first temperature of the first primary heat transfer fluid (T1);

or if said first storage temperature of the secondary fluid (T2) is greater than or equal to said first temperature of the first primary heat transfer fluid (T1) and said storage temperature of the second primary fluid (T3) is greater than or equal to said first temperature of the first primary heat transfer fluid (T1).
The method according to any one of claims 16 - 20, when said system (1) is according to claim 7, wherein
if said second storage temperature of the secondary fluid (T5) is lower than a second threshold temperature of the secondary fluid (T5s), carrying out the following step:
E. diverting said second primary heat transfer fluid towards said third heat exchange conduit (44) through said means for diverting the flow of the second primary fluid (400), for heating said secondary fluid by means of said second primary heat transfer fluid.
The method according to the preceding claim, wherein said second threshold temperature of the secondary fluid (T5s) is lower than or equal to said first threshold temperature of the secondary fluid (T2s).