THERMAL ENERGY STORAGE SYSTEM COMPRISING A PHASE CHANGE MATERIAL AND A THERMAL CONDITIONING LOOP COMPRISING SUCH A SYSTEM

Abstract

The present invention relates to a thermal energy storage system (1) for a thermal conditioning loop, said system (1) comprising at least one container (3) in which a phase-change material is disposed and at least one fluid conduit (5) comprising at least one heat exchange plate (7), said conduit (5) and / or said plate (7) being in thermal contact with said container (3). [Fig. 1]

Description

Title of the invention: THERMAL ENERGY STORAGE SYSTEM COMPRISING A PHASE CHANGE MATERIAL AND THERMAL CONDITIONING LOOP INCLUDING SUCH A SYSTEM

[0001] The present invention relates to the field of thermal conditioning, for example of a volume, such as a room, a building, etc. More specifically, the present invention relates to the field of thermal conditioning in which a thermal energy storage system comprising phase-change materials is used.

[0002] The invention thus relates to thermal conditioning loops, or other types of systems that may require the storage of thermal energy, which include a thermal energy storage system involving phase change materials.

[0003] The principle of such thermal conditioning systems is to be able to store large quantities of thermal energy, i.e., cooling or heating, in a phase-change material, by means of the latent heat of phase change of that material. Thus, in the case of a solid-liquid phase-change material, it is necessary to supply energy, or heating, to said material in order to make it change state, for example, to change it from a solid to a liquid state.

[0004] Once the change of state has taken place, energy is therefore stored inside said phase change material, it is therefore possible to reuse it in due time to thermally condition a desired environment, directly by air ventilation in the storage element and / or via a heat transfer fluid, such as water or a water / glycol mixture without limitation with an exchanger external to the storage element.

[0005] Currently, electrical energy, particularly renewable energy, presents a problem of instability in terms of production and demand. Indeed, electrical energy is difficult and expensive to store, for example in batteries, and demand varies greatly depending on the time of day, weather conditions, etc., making it difficult to reduce, or at least optimize, electrical energy consumption.

[0006] One solution for optimizing the use of electrical energy is the use of a thermal energy storage system comprising a phase-change material. Indeed, it is possible to convert electrical energy from renewable sources, such as wind turbines and / or photovoltaic panels, into thermal energy and store this in such thermal energy storage systems.

[0007] This method of storing thermal energy makes it possible in particular to use electrical energy when it is in excess and / or very cheap, and to use this thermal energy when necessary, among other things at night or during periods of the day without sun or wind, or during periods of high energy demand resulting in high pricing, for example during the day, during periods of high heat or extreme cold.

[0008] The invention is thus a thermal energy storage system for a thermal conditioning loop, said system comprising at least one container in which a phase change material is disposed and at least one fluid conduit comprising at least one heat exchange plate, said conduit and / or said plate being in thermal contact with said container.

[0009] According to one possible feature, the storage system comprises at least two fluid conduits, each comprising a heat exchange plate, said conduits and / or plates being arranged on either side of said container, and preferably in thermal contact with opposite faces of said container.

[0010] According to another possible feature, the storage system includes a generator, advantageously high frequency, of voltage and / or current connected to two heat exchange plates located on opposite faces of the container, as well as a measuring device configured to measure the capacitance between said two plates. Indeed, the value of the capacity measured between the two faces of a container, in particular via the heat exchange plates, makes it possible to determine the solid / liquid (water / ice) ratio of the phase change material contained in the container, and therefore indirectly the amount of thermal energy stored in said storage system, thus allowing better management, particularly temporal, of the energy stored and / or consumed.

[0011] According to another possible feature, said at least one container has housings configured to accommodate fluid conduits and, in the mounted position, each plate rests against one of the faces of said at least one container. Placing the conduits in suitable housings, for example fitted or shaped, within the container walls optimizes the flow transfer thermal between the wall of the phase change material container and the heat transfer fluid circulating in the ducts, this via said plates and said ducts.

[0012] According to another possible feature, at least one of said fluid conduits comprises fins which extend radially inside said conduit. The presence of fins increases the exchange surface area between the heat transfer fluid and the duct, thus promoting heat transfer between the heat transfer fluid and the wall delimiting said duct.

[0013] According to another possible feature, said phase-change material occupies at least 85% of the internal volume of said at least one container, and preferably, between 85% and 95% of the internal volume of said at least one container. It is advantageous for the phase-change material not to occupy the entire internal volume of the container, in order to optimize the filling of the container according to the change in volume during the phase change of the material.

[0014] According to another possible feature, said storage system is thermally insulated from the external environment. It is worth noting the importance of thermal insulation of the storage system, in order to limit heat loss or unwanted release of thermal energy, particularly to the outside.

[0015] According to another possible feature, said system comprises a thermally insulating material arranged on both sides of said ducts (and therefore of said container). Said thermally insulating material is, for example, glass wool, rock wool, cellular glass, a cellular polymer, etc.

[0016] According to another possible feature, said at least one container is made of an electrically insulating material.

[0017] According to another possible feature, said plates are configured to form a capacitor. By arranging the plates on either side of at least one container to form a capacitor, thus ensuring that both the container and the phase-change material act as insulators, there is a measurable electrical capacitance associated with this capacitor that depends on the physical state of the phase-change material. More specifically, the electrical capacitance of the capacitor varies according to the proportion of solid and liquid phase-change material within the container.

[0018] According to another possible characteristic, said generator produces a voltage and / or current having a frequency of at least 500 kHz, and preferably at a frequency of at least 800 kHz, and for example a frequency between 1 MHz and 10 MHz.

[0019] It should also be noted here that the capacitance of a capacitor depends on the permittivity of the phase-change material, said permittivity varying according to the physical state of the material, but also according to the frequency of the voltage to which the capacitor is subjected. Therefore, in order to measure an interpretable and meaningful quantity of the physical state of the phase-change material, it is necessary that the capacitor be subjected to a voltage at a defined frequency at which the relative permittivity values ​​of the phase-change material, in the solid and liquid states, are very different, by factors of at least 3, and preferably 10.

[0020] According to another possible characteristic, said phase-change material is water, said water comprising chlorine (generally in the form of chlorine bromide) and / or a mineral or vegetable oil. The presence of chlorine, for example at concentrations between 0.5 and 2 mg / L, helps prevent the uncontrolled growth of living organisms (fungi, bacteria, etc.), while the presence of an oil with a lower density than water and a freezing point lower than water's freezing point limits, or even prevents, the evaporation of water from the container and prevents the passage of oxygen gas into the phase-change material (especially when the material is in liquid form). Mineral or vegetable oil, for example, has a freezing point below -10°C; silicone oil, for instance, has a freezing point below -20°C.

[0021] The invention also relates to a thermal conditioning loop comprising at least: - a primary heat transfer fluid circuit connected, via a heat exchanger, also called the first heat exchanger, to a cold source, for example a heat pump type circuit, - a secondary heat transfer fluid circuit comprising at least one heat exchanger configured to thermally condition an airflow; - a thermal energy storage system as defined above; the primary and secondary circuits being interconnected via said thermal energy storage system and at least by a mixing valve.

[0022] According to one possible feature, said primary circuit includes at least one pump, called first circulation pump, configured to circulate the heat transfer fluid at least in the primary circuit.

[0023] According to another possible feature, said secondary circuit includes at least one pump, called second circulation pump, configured to circulate the heat transfer fluid at least in the secondary circuit.

[0024] According to another possible feature, said loop has a first mode of operation, called "storage mode", said loop storing thermal energy in said storage system via the primary circuit. Thus, in the first operating mode, the primary circuit transfers cooling from the cold source to the thermal energy storage system by activating the first pump and reducing, or even preventing, the circulation of heat transfer fluid in the secondary circuit.

[0025] According to another possible feature, said loop has a second operating mode, called "hybrid cooling mode", in which the primary and secondary circuits are interconnected in such a way that the heat exchanger of the secondary circuit is connected, via the mixing valve, to the cold source of the primary circuit. Thus, in the second operating mode, the primary circuit transfers cooling energy from the cold source to the heat exchanger of the secondary circuit, which is dedicated to cooling an airflow destined for the volume to be cooled. This is achieved by activating the first and second pumps. Furthermore, a portion of the heat transfer fluid from the primary circuit also circulates in the storage system, allowing cooling energy to be stored there.

[0026] According to another possible feature, in the second operating mode, the heat transfer fluid from the primary circuit is mixed, via the mixing valve, with the heat transfer fluid from the secondary circuit.

[0027] According to another possible feature, said loop has a third operating mode, called "destocking mode", said conditioning loop destocking thermal energy, in particular cooling, from the storage system to the exchanger of the secondary circuit conditioning the airflow. Thus, in the third operating mode, the secondary circuit transfers cooling from the thermal energy storage system to the heat exchanger dedicated to cooling an airflow intended to control the temperature of the volume to be cooled, by activating the second pump and deactivating the first pump.

[0028] According to another possible feature, the storage system includes conduits extending over opposite faces of said containers; thus, in all or part of the operating modes of said loop, said conduits are traversed respectively by the heat transfer fluid from the primary circuit or the secondary circuit. This architecture notably improves heat transfer between the heat transfer fluid and the thermal storage system.

[0029] The invention may also relate to the use of a mineral or vegetable oil in a phase-change material (for example, one placed in a container of a storage system according to the invention), said oil having a density lower than the density of the phase-change material, so that the oil coats the (upper) surface of said phase-change material. Indeed, such a thin layer of oil thus forms on the surface of the phase-change material and limits, or even prevents, evaporation, contamination, and / or oxidation of said material.

[0030] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of a particular embodiment of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings, among which: - Fig. 1 is a schematic, three-quarter perspective view of a thermal energy storage system according to the invention; - [Fig.2] is a schematic, cross-sectional view of a thermal storage system according to the invention; - [Fig.3] illustrates a hydraulic diagram of a thermal conditioning loop according to the invention comprising a thermal storage system of [Fig.1]; - [Fig.4] is a diagram representing a first mode of operation of the loop of [Fig.3]; - [Fig.5] is a diagram representing a second operating mode of the loop of [Fig.3]; - [Fig.6] is a diagram representing a third operating mode of the loop of [Fig.3].

[0031] [Fig.1] illustrates a schematic, three-quarter perspective view of a thermal energy storage system 1 according to the invention, while [Fig.2] is a cross-sectional view of the storage system 1 of [Fig.1].

[0032] The storage system 1 is thus configured to be able to store and / or release thermal energy, calories or frigories, and includes among other things at least: - a container 3 in which is placed a phase change material 4 (also designated by the acronym PCM for "Phase Change Material" in English); - 5 fluid conduits, for example heat transfer fluid, arranged on either side of said container 3; - 7 heat exchange plates configured to allow the transfer of heat, or cooling, between the heat transfer fluid circulating in at least one of said conduits 5 and the phase change material 4 disposed in said container 3.

[0033] Advantageously, a storage system according to the invention comprises a plurality of containers 3, for example stacked one on top of the other to form a wall, while conduits 5 and plates 7 are arranged on either side of such a wall formed of containers 3.

[0034] The container 3 is thus a container configured to hold the phase-change material 4, such as water, acetic acid, phenol, etc. Said phase-change material 4 preferably occupies at least 85% of the internal volume of said at least one container 3, and preferably between 85% and 95% of the internal volume of said at least one container 3.

[0035] When the phase change material is water, it contains chlorine, in sufficient quantity to prevent the development of fungi and / or bacteria, but without altering the melting / solidification temperature of the water.

[0036] It should be noted that the term phase change material (or PCM) means any material capable of changing its physical state, for example solid-liquid, within a restricted temperature range, particularly around 0°C.

[0037] The container 3 can be made of an electrically insulating material, for example a plastic material, such as high-density polyethylene (or HDPE), or even glass, ceramic, etc. The container 3 advantageously has a polygonal shape, for example parallelepiped, cubic, etc., comprising at least two opposing principal faces 3a and 3b, generally opposite faces having the largest surfaces and extending substantially parallel to the principal extension plane of the container 3.

[0038] Thus, said container 3 has housings 3c for the conduits 5, housings 3c advantageously arranged or formed in the walls of the container 3, a conduit 5 being for example forced into one of the housings 3c.

[0039] The conduits 5 are, for their part, made of a thermally conductive material, for example of metal, such as steel, aluminum, etc. Said conduits 5 may have passage sections of various shapes, but advantageously include fins 5a which extend radially inside the conduit 5, in order to increase the exchange surface between the heat transfer fluid circulating in said conduit 5 and the constitutive walls of said conduit 5.

[0040] The heat exchange plates 7 are also made of a thermally conductive material, for example a metal such as steel, aluminum, etc., and are thermally connected to at least one of said conduits 5. Thus, at least one plate 7 is positioned in contact with each of the faces opposite 3a and 3b of container 3 and thermally connected to a fluid conduit 5.

[0041] Thus, at least one conduit 5 and at least one plate 7 are a single unit, or unit, said plate 7 bearing against one of the main faces 3a or 3b when the conduit 5 is inserted into the housing 3c fitted in the container 3.

[0042] In the embodiment described herein, each assembly comprises two conduits 5 and three plates 7, a plate 7 connecting the two conduits 5, and two lateral plates extending from each free side of said conduits 5. A conduit-plate assembly 5 and 7 is thus in contact with each of the faces 3a and 3b and covers most of the surface of said faces 3a and 3b. These 5-7 assemblies, and more particularly the plates 7, arranged opposite each other on each side of the container 3, thus form a capacitor.

[0043] In addition, said storage system 1 comprises: - a voltage and / or current generator (not shown), preferably alternating current, connected to at least one of said plates 7; - a device for measuring an electrical quantity (not shown) indicative of the physical state of the phase change material, for example a capacitance meter configured to measure the (electrical) capacitance of the plates 7 forming a capacitor.

[0044] Said generator produces for example an alternating voltage and / or current having a frequency of at least 500 kHz, and preferably at a frequency of at least 800 kHz, and advantageously between 1 MHz and 100 MHz.

[0045] Thus, the electrical capacitance measured by the measuring device is a function of the physical state of the phase-change material located in the container 3, between the heat exchange plates 7. Furthermore, when the phase-change material is water, the difference in dielectric permittivity between water and ice being very significant, the measured capacitance value will therefore exhibit a large amplitude, and will allow the percentage of phase-change material in liquid and / or solid form to be determined, thus indicating the amount of energy stored by said phase-change material.

[0046] In order to avoid wasting energy, it is necessary to know the physical state of the phase-change material 4 inside the container 3, so that energy storage can cease if the storage system 1 is full. To achieve this, support plates 7 have been chosen in this embodiment. Indeed, the arrangement of these support plates 7 allows us to create a capacitor whose electrical capacitance will depend on whether the phase-change material 4 is gaseous, liquid, or solid.

[0047] Said storage system is thermally insulated from the external environment, for example by means of an insulating material arranged on either side of said conduits, such as glass wool, rock wool, etc.

[0048] Fig. 3, meanwhile, illustrates a schematic view of a thermal conditioning loop 100 which includes a storage system 1 according to the invention.

[0049] Loop 100 comprises at least: - a primary heat transfer fluid circuit 102 connected, via a heat exchanger 104, also called the first heat exchanger, to a cold source 106, for example a heat pump type circuit, - a secondary heat transfer fluid circuit 108 comprising at least one heat exchanger 110 and 112, and preferably at least two, configured to thermally condition an airflow; - a thermal energy storage system 1 as defined above; the primary circuit 102 and secondary circuit 108 being interconnected via said storage system 1 and at least by a mixing valve 114.

[0050] Furthermore, said primary circuit 102 includes at least one pump Pb, called the first circulation pump, configured to circulate the heat transfer fluid at least in the primary circuit 102, while said secondary circuit 108 includes at least one pump P2, called the second circulation pump, configured to circulate the heat transfer fluid at least in the secondary circuit 108.

[0051] In addition, the primary circuit 102 advantageously includes a simple valve 116 (or "on-off" valve) placed downstream of the first pump Pi (or directly at the outlet of said first pump), in order to be able to interrupt the circulation of heat transfer fluid in the primary circuit 102, in particular depending on the operating modes of said loop 100.

[0052] Furthermore, the mixing valve 114 is a three-way valve which includes an outlet connected to the inlet of the second pump P2 (for example directly downstream of said second pump), and two inlets, one inlet connected to the storage system 1 and to the outlet of the first pump PH and another inlet connected to the outlet of said exchangers 110 and 112 of the secondary circuit 108 and to the storage system 1 (each of the inlets of the mixing valve being connected to an opposite end of said storage device).

[0053] Furthermore, the mixing valve 114 is configured so that the heat transfer fluid intended for or coming from the exchangers 110 and 112 can be mixed in selected proportions, in order to more finely regulate the temperature of the heat transfer fluid circulating in said exchangers 110 and 112 of the secondary circuit 108.

[0054] Figs. 4, 5 and 6 are schematic views of the different operating modes of the thermal conditioning loop 100, respectively the first, second and third operating modes.

[0055] Thus, [Fig.4] illustrates the first operating mode, called "storage mode", of the loop 100, an operating mode in which said loop 100 stores thermal energy in said storage system 1 via the primary circuit 102. More specifically, in the first mode of operation, the primary circuit 102 transfers cooling from the cold source 106 to the thermal energy storage system 1, by activating the first pump PI, and preventing any circulation of heat transfer fluid in the secondary circuit 108, in particular by closing the mixing valve 114 and by not activating the second pump P2.

[0056] Fig. 5 illustrates the second operating mode, called "hybrid cooling mode", of the loop 100, an operating mode in which the primary circuit 102 and secondary circuit 108 are interconnected in such a way that the heat exchangers 110 and 112 of the secondary circuit 108 are connected, via the mixing valve 114, to the cold source 106.

[0057] Thus, in the second operating mode, the primary circuit 102 transfers cooling energy from the cold source 106 to the heat exchangers 110 and 112 of the secondary circuit 108, which is dedicated to cooling an airflow intended to enter the volume to be cooled, notably by activating the first and second pumps Pi and P2. In addition, a portion of the heat transfer fluid from the primary circuit 102 also circulates in the storage system 1, so that cooling energy is stored there.

[0058] It should be noted that the regulation of the different flow rates of heat transfer fluid and / or of the temperature of said fluid in the heat exchangers 110 and 112 is controlled by the flow rate of the pumps Pi and / or P2, as well as by the mixing valve 114. Indeed, the heat transfer fluid from the primary circuit 102 is mixed, via the mixing valve 114, with the heat transfer fluid from the secondary circuit 108.

[0059] Fig. 6 illustrates the third operating mode, called "destocking mode", of loop 100, operating mode in which said conditioning loop 100 destocks thermal energy, in particular cooling, from the storage system 1 to the exchangers 110 and 112 of the secondary circuit 108 conditioning the airflow.

[0060] Thus, in the third operating mode, the secondary circuit 108 transfers cooling from the thermal energy storage system 1 to the heat exchangers 110 and 112 dedicated to cooling an airflow intended to control the temperature of the volume to be refreshed, this by activating the second pump P2, deactivating the first pump Pb and closing the simple valve 116.

[0061] In addition, as before, the mixing valve 116 allows the proportion of heat transfer fluid from the storage system 1 to be selected and thus the temperature of the heat transfer fluid intended to circulate through the exchangers 110 and 112 to be regulated.

[0062] It will be noted that the storage system 1 includes conduits 5 extending over opposite faces of said containers 3, so in all or part of the operating modes of said loop 100, said conduits 5 are traversed respectively by the heat transfer fluid from the primary circuit 102 or from the secondary circuit 108.

Claims

Demands

1. Thermal energy storage system (1) for thermal conditioning loop, said system (1) comprising at least one container (3) in which a phase change material is disposed and at least one fluid conduit (5) comprising at least one heat exchange plate (7), said conduit (5) and / or said plate (7) being in thermal contact with said container (3), characterized in that said storage system (1) comprises a voltage and / or current generator connected to two heat exchange plates (7) located on opposite faces of the container (3), and a measuring device configured to measure the capacitance between said two plates (7).

2. A storage system (1) according to the preceding claim, characterized in that the storage system (1) comprises at least two fluid conduits (5), each comprising a heat exchange plate (7), said conduits (5) and / or plates being arranged on either side of said container, and preferably in thermal contact with opposite faces of said container

3. Storage system (1) according to claim 1, characterized in that said generator produces a voltage and / or a current, oscillating at a frequency of at least 500 kHz, and preferably at a frequency of at least 800 kHz.

4. Storage system (1) according to any one of the preceding claims, characterized in that said at least one container (3) has housings (3c) configured to accommodate the fluid conduits (5) and that said plates (7) bear against one of the faces of said at least one container (3).

5. Storage system (1) according to any one of the preceding claims, characterized in that at least one of said fluid conduits (5) comprises fins (5a) extending radially inside said at least one conduit (5).

6. Storage system (1) according to any one of the preceding claims, characterized in that said phase-change material occupies at least 85% of the internal volume of said at least one container (5).

7. Storage system (1) according to any one of the preceding claims, characterized in that said change material phase is water, said water comprising chlorine and / or a mineral or vegetable oil.

8. Thermal conditioning loop (100), said thermal conditioning loop comprising: - a primary heat transfer fluid circuit (102) connected, via a heat exchanger (104), also referred to as the first heat exchanger, to a cold source (106); - a secondary heat transfer fluid circuit (108) comprising at least one heat exchanger (110, 112) configured to thermally condition an airflow; - a thermal energy storage system (1) according to any one of the preceding claims; the primary and secondary circuits (102, 108) being interconnected via said thermal energy storage system (1) and at least by a mixing valve (114).

9. Loop (100) according to the preceding claim, characterized in that said loop (100) has a first mode of operation, called "storage mode", said loop (100) storing thermal energy in said storage system (1) via the primary circuit (102).

10. Loop (100) according to the preceding claim, characterized in that said loop (100) has a second mode of operation, called "hybrid cooling mode", in which the primary (102) and secondary (104) circuits are interconnected in such a way that the heat exchanger (110, 112) of the secondary circuit (108) is connected, via the mixing valve (114), to the cold source of the primary circuit (102).

11. Loop (100) according to the preceding claim, characterized in that said loop (100) has a third mode of operation, called "destocking mode", said conditioning loop (100) destocking thermal energy, in particular cooling, from the storage system (1) to the exchanger (110, 112) of the secondary circuit conditioning the airflow.

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