Thermal energy storage system comprising a phase change material

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 arranged and at least one fluid duct (5) comprising at least one heat exchange plate (7), the duct (5) and / or the plate (7) being in thermal contact with the container (3).

Description

THERMAL ENERGY STORAGE SYSTEM COMPRISING A PHASE CHANGE MATERIAL

[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 system which may require the storage of thermal energy, which comprise a thermal energy storage system using phase change materials.

[0003] The principle of such thermal conditioning systems is to be able to store large quantities of thermal energy, i.e. frigories or calories, in a phase change material, by means of the latter's latent heat of change of state. Thus, in the case of a phase change material of the solid-liquid type, it is necessary to supply energy, calories, to the said material, in order to make it change state, for example to make it pass from a solid state 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 medium, directly by ventilation of air in the storage element and / or by means of 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 to optimize 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 it in such thermal energy storage systems.

[0007] This way 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 extreme heat or 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 arranged 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 a possible characteristic, 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 characteristic, the storage system comprises 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 capacity between said two plates. In fact, the value of the capacity measured between the two sides of a container, in particular via the heat exchange plates, makes it possible to determine the solid / liquid ratio (water / ice) of the phase change material contained in the container, and therefore indirectly the quantity of thermal energy stored in said storage system, thus allowing better management, particularly in terms of time, of the energy stored and / or consumed.

[0011] According to another possible characteristic, said at least one container has reception housings configured to accommodate the fluid conduits and, in the mounted position, each plate comes to bear against one of the faces of said at least one container. Arranging the conduits in suitable housings, for example fitted or shaped, in the walls of the container makes it possible to optimize the transfer of the heat flow between the wall of the container of the phase change material and the heat transfer fluid circulating in the conduits, this by means of said plates and said conduits.

[0012] According to another possible characteristic, at least one of said fluid conduits comprises fins which extend radially inside said conduit. The presence of fins increases the exchange surface 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 characteristic, 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 if the phase change material does not occupy the entire internal volume of the container, in order to optimize the filling of the container according to the change in volume when the phase change material changes state.

[0014] According to another possible feature, said storage system is thermally isolated from the external environment. It is interesting to note the importance of thermal insulation of the system of storage, in order to limit thermal losses or unwanted release of thermal energy, particularly to the outside.

[0015] According to another possible characteristic, said system comprises a thermally insulating material arranged on either side of said conduits (and therefore of said container). The said thermal insulating material is for example glass wool, rock wool, cellular glass, cellular polymer, etc.

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

[0017] According to another possible characteristic, said plates are configured to form a capacitor. By arranging the plates arranged on either side of said at least one container so as to form a capacitor, thus also ensuring that the container and the phase change material act as an insulator, there is a measurable electrical capacity linked to this capacitor which depends on the physical state of the phase change material. More particularly, the electrical capacity of said capacitor changes as a function of the proportion of solid and liquid of the phase change material within said container.

[0018] According to another possible characteristic, said generator produces a voltage and / or a 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 for a capacitor depends on the permittivity of said phase-change material, said permittivity changing as a function of the physical state of said material, but also of the frequency of the voltage to which said capacitor is subjected. It is therefore necessary, in order to be able to measure an interpretable and significant quantity of the physical state of said phase-change material, that said 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 state, are very different, by presenting factors of the order 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, makes it possible to prevent the untimely development of living organisms (fungi, bacteria, etc.), while the presence of an oil with a density lower than that of water, and a solidification temperature lower than the solidification temperature of water, makes it possible to limit, or even prevent, the evaporation of the water contained in the container, and to prevent the passage of gaseous oxygen into the phase change material (in particular when the material is in liquid form). Mineral or vegetable oil, for example, has a solidification temperature lower than -10°C, mineral oil is, for example, silicone oil whose solidification temperature is, for example, lower than -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 a 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 air flow; 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 a possible characteristic, said primary circuit comprises at least one pump, called the first circulation pump, configured to circulate the heat transfer fluid at least in the primary circuit.

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

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

[0025] According to another possible characteristic, 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 frigories from the cold source to the exchanger of the secondary circuit dedicated to cooling an air flow intended to flow into the volume to be cooled, in particular by activating the first and second pumps. In addition, part of the heat transfer fluid, coming from the primary circuit, also circulates in the storage system, so that frigories are stored there.

[0026] According to another possible characteristic, 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 characteristic, said loop has a third operating mode, called “destocking mode”, said conditioning loop destocking thermal energy, in particular frigories, from the storage system to the exchanger of the secondary circuit conditioning the air flow. Thus, in the third mode of operation, the secondary circuit transfers frigories from the thermal energy storage system to the exchanger dedicated to cooling an air flow 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 characteristic, the storage system comprises conduits extending on 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 from the secondary circuit. This architecture makes it possible in particular to improve thermal transfers 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 arranged 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 covers the (upper) surface of said phase change material. Indeed, such a thin layer of oil forms on the surface of the phase change material, and limits, or even prevents, the evaporation, contamination and / or oxidation of said material.

[0030] The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of a particular embodiment of the invention, given solely for illustrative and non-limiting purposes, with reference to the appended drawings, among which: [Fig. 1], is a schematic, three-quarter front 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 mode of operation of the loop of [Fig. 3]; [Fig. 6] is a diagram representing a third mode of operation of the loop of [Fig. 3],

[0031] [Fig. 1] illustrates a schematic, three-quarter front 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 a phase change material 4 is placed (also referred to by the acronym PCM for “Phase Change Material” in English); - fluid conduits 5, for example heat transfer fluid, arranged on either side of said container 3; - heat exchange plates 7 configured to allow the transfer of calories, or frigories, between the heat transfer liquid circulating in at least one of said conduits 5 and the phase change material 4 placed in said container 3.

[0033] Advantageously, a storage system according to the invention comprises a plurality of containers 3, for example stacked on top of each 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 contain 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 water.

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

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

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

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

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

[0041] Thus, at least one conduit 5 and at least one plate 7 are a single-piece or unitary assembly, said plate 7 bearing on one of the faces main 3a or 3b when the conduit 5 is inserted into the housing 3c arranged in the container 3.

[0042] In the embodiment described herein, each assembly comprises two conduits 5 and three plates 7, one plate 7 connecting the two conduits 5 together, and two side plates extending on 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 the greater part of the surface of said faces 3a and 3b. These assemblies 5-7, and more particularly the plates 7, arranged opposite each side of the container 3 thus form a capacitor.

[0043] Furthermore, said storage system 1 comprises: - a voltage and / or current generator (not shown), preferably alternating, 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 the 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 said heat exchange plates 7. Furthermore, when the phase change material is water, the difference in dielectric permittivity being very large between water and ice, the measured capacitance value will thus have a large amplitude, and makes it possible to trace the percentage of phase change material in liquid and / or solid form, thus indicating the quantity 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, in order to stop the storage of energy if the storage system 1 is full. To do this, it was chosen in this embodiment to use the support plates 7. Indeed, the arrangement of these support plates 7 allows us to make a capacitor whose electrical capacity will depend on the gaseous, liquid or solid character of the phase change material 4.

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

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

[0049] The loop 100 comprises at least: a primary heat transfer fluid circuit 102 connected, via a heat exchanger 104, also called 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 air flow; a thermal energy storage system 1 as defined above; the primary 102 and secondary 108 circuits being interconnected via said storage system 1 and at least by a mixing valve 114.

[0050] In addition, said primary circuit 102 comprises at least one pump Pi, called the first circulation pump, configured to circulate the heat transfer fluid at least in the primary circuit 102, while said secondary circuit 108 comprises 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 comprises a single 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 comprises 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 Pi, 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] [Fig. 4], [Fig. 5] and [Fig. 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, operating mode in which said loop 100 stores thermal energy in said storage system 1 via the primary circuit 102. More particularly, in the first operating mode, the primary circuit 102 transfers frigories from the cold source 106 to the thermal energy storage system 1, this by activating the first pump P1, and by 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 frigories from the cold source 106 to the exchangers 110 and 112 of the secondary circuit 108 dedicated to the cooling of an air flow intended to open into the volume to be cooled, this in particular by activating the first and second pumps Pi and P2. In addition, a portion of the heat transfer fluid, coming from the primary circuit 102, also circulates in the storage system 1, so that frigories are stored there.

[0058] It will be noted that the regulation of the different flow rates of heat transfer fluid and / or the temperature of said fluid in the 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. In fact, 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 the loop 100, an operating mode in which said conditioning loop 100 destocks thermal energy, in particular frigories, from the storage system 1 to the exchangers 110 and 112 of the secondary circuit 108 conditioning the air flow.

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

[0061] Furthermore, as previously, the mixing valve 116 makes it possible to select the proportion of heat transfer fluid from the storage system 1 and therefore to regulate the temperature of the heat transfer fluid intended to circulate through the exchangers 110 and 112.

[0062] It will be noted that the storage system 1 comprises conduits 5 extending on opposite faces of said containers 3, thus 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

Claims [Claims 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 arranged 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). [Claims 2] 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. [Claims 3] Storage system (1) according to the preceding claim, 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), as well as a measuring device configured to measure the capacity between said two plates (7). [Claims 4] Storage system (1) according to the preceding claim, 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. [Claims 5] Storage system (1) according to any one of the preceding claims, characterized in that said at least one container (3) has reception housings (3c) configured to accommodate the fluid conduits (5) and that said plates (7) come to bear against one of the faces of said at least one container (3). [Claims 6] Storage system (1) according to any one of the preceding claims, characterized in that at least one of said conduits (5) of fluid comprises fins (5a) extending radially inside said at least one conduit (5). [Claims 7] 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). [Claims 8] Storage system (1) according to any one of the preceding claims, characterized in that said phase change material is water, said water comprising chlorine and / or a mineral or vegetable oil. [Claims 9] Thermal conditioning loop (100), said thermal conditioning loop comprising: a primary heat transfer fluid circuit (102) connected, via a heat exchanger (104), also called 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 air flow; 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 one mixing valve (114). [Claims 10] Loop (100) according to the preceding claim, characterized in that said loop (100) has a first operating mode, called “storage mode”, said loop (100) storing thermal energy in said storage system (1) via the primary circuit (102). [Claims 11] Loop (100) according to the preceding claim, characterized in that said loop (100) has a second operating mode, 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). [Claims 12] Loop (100) according to the preceding claim, characterized in that said loop (100) has a third operating mode, called “destocking mode”, said conditioning loop (100) destocking thermal energy, in particular frigories, from the storage system (1) to the exchanger (110, 112) of the secondary circuit conditioning the air flow.

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