Cooling or heating apparatus and method

Abstract

The present invention relates to a method of cooling or heating, comprising the steps of: (a), (b), and (c). Step (a) comprises providing a first pressure cell comprising a vessel containing a first barocaloric material, wherein the first pressure cell is connected by a first set of heat-exchangers to a heat source and a heat sink, and providing a second pressure cell comprising a vessel containing a second barocaloric material, wherein the second pressure cell is connected by a second set of heat-exchangers to the heat source and the heat sink. Each barocaloric material is capable of undergoing a heating and cooling cycle upon pressurisation and depressurisation of the respective pressure cell. Each pressure cell further comprises a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material, and each pressure cell further comprises a flexible housing between the vessel and the barocaloric material and separating the barocaloric material from the pressure-transmitting medium. The flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material. Step (b) comprises applying hydrostatic pressure to each of the first and second pressure cells, and releasing the applied pressure, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles. Step (c) comprises permitting heat flow to or from the first and second pressure cells to the heat sink or heat source. Also provided is a modular heating or cooling apparatus, and use thereof.

Description

[0001] COOLING OR HEATING APPARATUS AND METHOD

[0002] Technical Field

[0003] This invention provides methods of barocaloric cooling or heating. The invention also provides for barocaloric cooling or heating apparatuses, and use of the apparatuses for cooling or heating.

[0004] Background

[0005] Foodstuffs, beverages, medical products and medical samples, electronics, and populated spaces such as offices, all require cooling. Heating systems are also needed, such as for buildings and homes. Current refrigeration units, air-conditioning units and heat pumps rely primarily on the compression and expansion of environmentally harmful fluids, and there is strong interest in developing cooling systems that avoid such fluids.

[0006] Recent developments in the cooling and heating field have looked at solid materials that display magnetically, electrically and mechanically driven phase transitions near room temperature. Magnetocaloric and electrocaloric devices respond to an applied magnetic or electric field, for example, by changing temperature, and are able to supply heat to, or absorb heat from, their surroundings. However, the temperature changes that are displayed by magnetocaloric and electrocaloric materials under applied conditions that are considered practical are small, and the amounts of heat they are able to exchange with their surroundings are relatively small (per kg of caloric material). Devices employing these materials are currently generally found only in a few specialist laboratory applications.

[0007] These materials typically need a regenerator to amplify the temperature changes due to the innately low temperature spans otherwise achieved by these systems.

[0008] Barocaloric materials are a distinct and newer class of caloric materials with the potential to provide cooling and / or heating via pressure changes, rather than changes in electric or magnetic fields. Barocaloric materials possess some attractive potential benefits over present fluid refrigerants in that they do not pose the risk of release of potent greenhouse gases into the atmosphere, and that they may be able to achieve higher efficiencies than are possible with present refrigerant gases.

[0009] The application of pressure to a barocaloric material leads to entropy changes which generally cause a release of heat, and conversely an absorption of heat if the external pressure is subsequently reduced. Some barocaloric materials display an “inverse barocaloric effect”, where they absorb heat upon the application of pressure and release heat on the release of the applied pressure.

[0010] 008844177 Known heating or cooling devices employing barocaloric materials typically need to use a regenerator design to provide useable temperature spans, in order to employ pressures of the same order as those used in conventional refrigeration systems. This comes at the expense of heating or cooling power (i.e. the number of watts flowing to or from the system to the outside), and results in relatively low heating / cooling powers, and therefore the utility of this approach is limited.

[0011] There is a need for new improved methods and systems for barocaloric cooling or heating, in particular those that allow for higher cooling and / or heating power, while allowing for large temperature spans.

[0012] Summary of the Invention

[0013] At its most general, the present invention relates to a modular cooling or heating system comprising at least two pressure cells each containing a barocaloric material which are operated out of phase with one another in their respective heating and cooling cycles.

[0014] In a first aspect there is provided a method of cooling or heating, comprising the steps of:

[0015] (a) providing a first pressure cell comprising a vessel containing a first barocaloric material, wherein the first pressure cell is connected by a first set of heatexchangers to a heat source and a heat sink, and providing a second pressure cell comprising a vessel containing a second barocaloric material, wherein the second pressure cell is connected by a second set of heat-exchangers to the heat source and the heat sink, and wherein each barocaloric material is capable of undergoing a heating and cooling cycle upon pressurisation and depressurisation of the respective pressure cell,

[0016] (b) applying hydrostatic pressure to each of the first and second pressure cells, and releasing the applied pressure, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles; and

[0017] (c) permitting heat flow to or from the first and second pressure cells to the heat sink or heat source.

[0018] In the method, preferably, each pressure cell further comprises a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material, and each pressure cell further comprises a flexible housing between the vessel and the barocaloric material and separating the barocaloric material from the pressure-transmitting medium, wherein the flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material.

[0019] In known barocaloric cooling systems, a single pressure cell containing a barocaloric material is pressurised and depressurised to provide a cooling output. This is described for example in Cirillo et al., 2023, Qian et al., 2024 and Dai et al., 2024. By contrast, the

[0020] 008844177 present invention involves use of at least two pressure cells each comprising a barocaloric material, which materials are operated out of phase with one another in their respective heating / cooling cycles. The first and second pressure cells are arranged in parallel between an external heat source and an external heat sink. The first and second pressure cells may be independently pressurised and depressurised, and the heat source and heat sink may be a common heat source and a common heat sink. This improves the cooling or heating output, by providing a more continuous output.

[0021] In the methods of the invention, the pressure cells are operated such that the first and second barocaloric materials are at different stages of their respective heating and cooling cycles for some or all of the time. For example, the first barocaloric material may be absorbing heat (i.e. in a cooling phase of a complete heating / cooling cycle) while the second barocaloric material is releasing heat (i.e. in a heating phase of a complete heating / cooling cycle). By using two or more barocaloric materials out of phase in this way, the intermittency of the cooling or heating output is reduced or eliminated.

[0022] A heating and cooling cycle refers to a cycle comprising, in either order, a heating phase (which may be driven by pressurisation or depressurisation of the pressure cell) and a cooling phase (which may be driven by depressurisation or pressurisation of the pressure cell). A heating and cooling cycle may begin with a heating phase followed by a cooling phase, or a heating and cooling cycle may begin with a cooling phase and a heating phase. References herein to a heating and cooling cycle also encompass a cooling and heating cycle.

[0023] Barocaloric materials undergo a cycle of heating and cooling (or cooling and heating) when hydrostatic pressure is applied and subsequently released from the material. By “out of phase”, it is meant that two barocaloric materials are not simultaneously at the same stage of their respective cycles throughout a full cycle of heating and cooling. The barocaloric materials in two cells may be operated out of phase to one another by 10° or more, such as 20° or more, such as 40° or more, such as 60° or more, such as 90° or more, such as 120° or more, such as 180°. When two barocaloric materials are operated out of phase by 180°, they may also be referred to as being in anti-phase with one another, and their cycles may offset by half of a complete heating and cooling cycle. In some embodiments, the first barocaloric material is out of phase with the second barocaloric material by 10° to 180°, such as by 90° to 180°, such as by 120° to 180°, such as by 120° or by 180°.

[0024] The first and second pressure cells are arranged in parallel, with each pressure cell being thermally connected via a respective set of heat-exchangers to a common heat source and a common heat sink. Typically, the first and second pressure cells are not arranged in series, and preferably the first and second heat-exchangers are independent from one another.

[0025] 008844177 A set of heat-exchangers is capable of independently connecting a pressure cell to a heat source and a heat sink, respectively. A set of heat-exchangers may be a pair of heatexchangers, such as a first heat-exchanger for connecting the pressure cell to a heat sink, and a second heat-exchanger for connecting the pressure cell to a heat source. A set (or pair) of heat-exchangers may be separate units, for example units that do not share any common portions, or they may be a single unit sharing a common portion, such as a portion embedded within the barocaloric material with valves to control heat-flow between the pressure cell and heat source or heat sink at different parts of a heating and cooling cycle. Typically, the heat source and heat sink do not directly exchange heat with each other, and each set of heat-exchanger connected to a pressure cell comprises two heat-exchanger circuits with one between the heat source (e.g. external zone to be cooled) and the pressure cell, and one between the heat sink (e.g. external zone to be heated) and the pressure cell. A set of heat-exchangers may also be referred to as a heat-exchanger, provided that it is capable of independently connecting the pressure cell to the heat source and the heat sink.

[0026] The method may comprise pressurising the first pressure cell while depressurising the second pressure cell. Herein, pressurisation refers to the application of hydrostatic pressure unless stated otherwise. For example, the first pressure cell may be partially pressurised while the second pressure cell is partially or fully depressurised. The methods may comprise cyclic application and release of hydrostatic pressure to each of the first and second pressure cells, where the cyclic application and release of hydrostatic pressure is out of phase between the first and second pressure cells. The method may comprise sequentially pressurising the first and second barocaloric materials.

[0027] The first and second barocaloric materials may be the same, or they may be different.

[0028] In some embodiments, both the first and second barocaloric materials are capable of releasing heat upon pressurisation, and may be referred to as conventional barocaloric materials. A conventional barocaloric material is in a heating stage of a (complete) heating and cooling cycle during the application of hydrostatic pressure, and may therefore undergo a cycle of heating and cooling upon pressurisation and depressurisation of the pressure cell. The first and second barocaloric materials may be conventional barocaloric materials which are the same, or they may be different conventional barocaloric materials.

[0029] In other embodiments, both the first and second barocaloric materials are capable of absorbing heat upon pressurisation, and may be referred to as inverse barocaloric materials. An inverse barocaloric material is in a cooling stage of a (complete) heating and cooling cycle during the application of hydrostatic pressure, and may therefore undergo a cycle of cooling and heating upon pressurisation and depressurisation of the pressure cell. The first and second barocaloric materials may be inverse barocaloric materials which are the same, or they may be different inverse barocaloric materials.

[0030] 008844177 When the first and second barocaloric materials are both conventional barocaloric materials, or both inverse barocaloric materials, step (b) preferably comprises out of phase pressurisation and depressurisation of the first and second pressure cells.

[0031] In some embodiments, one of the barocaloric materials, such as the first barocaloric material, is capable of releasing heat upon pressurisation (conventional barocaloric material), and the other one of the barocaloric materials, such as the second barocaloric material, is capable of absorbing heating upon pressurisation (inverse barocaloric material). In these methods, step (b) may comprise simultaneously pressurising and depressurising the first and second pressure cells such that the first barocaloric material is releasing heat while the second barocaloric material is absorbing heat, and vice versa, during a full pressurisation and depressurisation cycle.

[0032] The first and second barocaloric materials each have a phase transition that occurs at a transition temperature or over a transition temperature range. In some embodiments the phase transition temperature or temperature range of the first barocaloric material differs from the phase transition temperature or temperature range of the second barocaloric material. In this way, the barocaloric materials may be suitable for operation over different temperature ranges at the same pressure, or over different temperature and pressure ranges. In other embodiments, the first and second barocaloric materials have substantially the same transition temperature or transition temperature range.

[0033] The methods may comprise a combination of pressurising and depressurising two or more pressure cells out of phase with one another which contain the same type of barocaloric material (e.g. both conventional or both inverse), and pressurising and depressurising two or more pressure cells simultaneously (i.e. in phase, where the method comprises at least one pressure cell with a conventional barocaloric material and at least one pressure cell with an inverse barocaloric material).

[0034] The hydrostatic pressure applied in step (b) may be an external hydrostatic pressure. By “external hydrostatic pressure” it is meant energy that is supplied from an external source, such as external to the first and second pressure cells and / or external to an apparatus described herein. In some embodiments, one or more pressure cells comprise a hydrostatic pressuriser for pressurising the barocaloric material contained within the pressure cell.

[0035] The applied hydrostatic pressure during step (b) may be up to 1.0 GPa, such as up to 0.5 GPa, such as up to 0.2 GPa, such as up to 0.1 GPa. The applied hydrostatic pressure may be at least 0.1 MPa, such as at least 0.5 mPa, such as at least 5.0 MPa. The applied hydrostatic pressure may have upper and lower limits described above, such as from 0.1 MPa to 1.0 GPa.

[0036] 008844177 In some embodiments, step (b) comprises applying hydrostatic pressure to a first group of pressure cells and a second group of pressure cells, and releasing the applied pressure, such that the barocaloric materials in the first group of pressure cells are out of phase with the barocaloric materials in the second group of pressure cells in their respective heating and cooling cycles. A group of pressure cells may be a single pressure cell, or a plurality of pressure cells. For example, the first group of pressure cells may be the first pressure cell and the second group of pressure cells may be the second pressure cell. Alternatively, each of the first and second group of pressure cells may independently be two or more pressure cells, and step (a) may comprise providing three or more pressure cells as described herein, each comprising a barocaloric material and being connected via a respectively set of heatexchangers to the heat-source and heat-sink.

[0037] In some embodiments, step (a) comprises providing one or more further pressure cells, in addition to the first and second pressure cells, wherein each further pressure cell comprises a vessel containing a barocaloric material as described herein. Each further pressure cell is connected by a respective set of heat-exchangers to the heat source and the heat sink.

[0038] Step (b) may comprise applying hydrostatic pressure to each pressure cell and releasing the applied pressure, such that the barocaloric materials in a first group of pressure cells is out of phase with the barocaloric materials in a second group of pressure cells in their respective heating and cooling cycles.

[0039] In some embodiments, step (a) comprises providing three pressure cells containing first, second and third barocaloric materials, respectively, and step (b) comprises applying hydrostatic pressure to each pressure cell and releasing the applied pressure such that the first barocaloric material is in phase with the third barocaloric material, and both of these are out of phase with the second barocaloric material in their respective heating and cooling cycles. In these embodiments, the first and third pressure cells may be the first group of pressure cells, and the second pressure cell may be the second group of pressure cells. Preferably, the first and third barocaloric materials are the same, and these are optionally different from the second barocaloric material.

[0040] In some embodiments, step (a) comprises providing one or more further pressure cells, in addition to the first and second pressure cells, wherein each further cell comprises a vessel containing a barocaloric material and is connected to a respective set of heat-exchangers as described herein, and step (b) comprises applying hydrostatic pressure to each of the pressure cells and releasing the applied pressure, such that a third group of pressure cells is out of phase with the each of the first and second group of pressure cells in their respective heating and cooling cycles. In some embodiments, step (a) comprises providing three pressure cells containing first, second and third barocaloric materials, respectively, and step (b) comprises applying hydrostatic pressure to each pressure cell and releasing the applied pressure such that the first, second and third barocaloric material are out of phase with each other in their respective heating and cooling cycles. Optionally, a fourth, fifth, sixth

[0041] 008844177 or more group of pressure cells may be provided wherein the barocaloric materials contained in any two pressure cells are out of phase in their respective heating and cooling cycles.

[0042] In some embodiments, step (a) comprises providing first and second pressure cells (or groups thereof), and step (b) comprises applying hydrostatic pressure to the first and second pressure cells and releasing the applied pressure, such that the first barocaloric material is in antiphase with the second barocaloric material. In some embodiments, step (a) comprises providing first, second and third pressure cells (or groups thereof), and step (b) comprises applying hydrostatic pressure to the pressure cells and releasing the applied pressure. The first and second barocaloric materials may be out of phase with each other by 120°, and the second and third barocaloric materials are out of phase with each other by 120°.

[0043] The first and second pressure cells, and optionally each further pressure cell, is provided with a set of heat-exchanger connecting said pressure cell to the heat source and the heat sink. In use, the set of heat-exchangers independently allows for heat flow from the pressure cell to the heat sink, and heat flow to the pressure cell from the heat source. In some embodiments, the set of heat-exchangers associated with each pressure cell is partially embedded within and in thermal contact with the barocaloric material contained in that pressure cell. The set of heat-exchangers may be a single unit, such as where the partially embedded portion is shared, thereby joining a pair of heat-exchangers. The heat-exchanger may comprise a heat-exchange fluid that is capable of being circulated to a heat source or heat sink, such that in use, heat is extracted from or supplied to the barocaloric material during pressurisation or depressurisation of the pressure cell. The heat source may be an external heat source, such as an external zone to be cooled. The heat sink may be an external heat sink, such as an external zone to be heated.

[0044] The heat-exchange fluid may be a liquid or a gas, such as water, and is preferably isolated from the barocaloric material, such as where the heat-exchanger comprises a pipe or tube containing the heat-exchange fluid.

[0045] A pressure cell may comprise a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material. The barocaloric material may be provided within the pressure-transmitting medium. Suitable pressure-transmitting mediums include liquids and solids, such as conventional hydraulic fluids, alkoxy silane materials or alumina powder.

[0046] A pressure cell may comprise a flexible housing disposed between the vessel and the barocaloric material for separating the barocaloric material from the pressure-transmitting medium, wherein the flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material. The flexible housing may prevent physical or chemical interactions between the pressure-transmitting medium and the barocaloric material.

[0047] 008844177 A pressure cell may comprise a thermally insulating material between the vessel and the barocaloric material. In some embodiments, the thermally insulating material may be the flexible housing described herein. By thermally insulating the barocaloric material in this way, the cooling or heating performance may be increased. In other embodiments, the pressure cell comprises a thermally insulating material and a flexible housing described herein, where the thermally insulating material and flexible housing are different.

[0048] In some embodiments, at least one of the first and second pressure cells is thermally connected to one or more further pressure cells arranged in series to provide a cascade of pressure cells, wherein each pressure cell comprises a vessel containing a barocaloric material, such that the energy released upon pressurisation or depressurisation of the first pressure cell in the cascade is used for heating or cooling an adjacent pressure cell. For example, the first pressure cell is thermally connected to a first further pressure cell, or a first series of (plurality of) further pressure cells, such as by the first set of heat-exchangers; and / or the second pressure cell is thermally connected to a second further pressure cell, or a second series of (plurality of) further pressure cells, such as by the second set of heat-exchangers. An arrangement of pressure cells in this way may be referred to as a barocaloric cascade, whereby in use, heat flows successively between the thermally connected pressure cells. In use, the first pressure cell in the cascade is preferably pressurised in anti-phase with the adjacent pressure cell, and each further pressure cell, where present, is pressurised in anti-phase with the neighbouring pressure cells. By cascading barocaloric cells in this way, the temperature span of cooling or heating can be increased.

[0049] In a second aspect, there is provided a modular cooling or heating apparatus, comprising: a first pressure cell comprising a vessel containing a first barocaloric material, a first set of heat-exchangers for connecting the first pressure cell to a heat source and a heat sink; a second pressure cell comprising a vessel containing a second barocaloric material; a second set of heat-exchangers for connecting the second pressure cell to the heat source and the heat sink; and a hydrostatic pressuriser for pressurising and depressurising the first pressure cell out of phase with the second pressure cell, such that in use for cooling or heating, the first barocaloric material is partially or fully pressurised when the second barocaloric material is partially or fully depressurised.

[0050] Preferably, each pressure cell of the modular cooling or heating apparatus further comprises a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material, and each pressure cell further comprises a flexible housing between the vessel and the barocaloric material and separating the barocaloric material from the pressure-

[0051] 008844177 transmitting medium, wherein the flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material.

[0052] When the apparatus is in use for cooling or heating, the first barocaloric material is partially or fully pressurised when the second barocaloric material is partially or fully depressurised, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles, thereby providing heat flow to or from the heat sink or heat source. In use, the first and second pressure cells are connected via their respective set of heat-exchangers to a common heat sink or heat source to provide a cooling or heating input. The apparatus allows for a more continuous cooling or heating output from the system to its surroundings, compared to use of a single pressure cell for cooling or heating.

[0053] In a third aspect, there is provided a modular cooling or heating apparatus, comprising: a first pressure cell comprising a vessel containing a first barocaloric material, wherein the first barocaloric material is capable of releasing heat upon pressurisation; a first set of heat-exchangers for connecting the first pressure cell to a heat source and a heat sink; a second pressure cell comprising a vessel containing a second barocaloric material, wherein the second barocaloric material is capable of absorbing heat upon pressurisation; a second set of heat-exchangers for connecting the second pressure cell to the heat source and the heat sink; and a hydrostatic pressuriser for pressurising and depressurising the first and second pressure cells.

[0054] Preferably, each pressure cell of the modular cooling or heating apparatus further comprises a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material, and each pressure cell further comprises a flexible housing between the vessel and the barocaloric material and separating the barocaloric material from the pressuretransmitting medium, wherein the flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material.

[0055] When the apparatus is in use for cooling or heating, the first and second pressure cells may be simultaneously pressurised and depressurised, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles, thereby providing heat flow to or from the heat sink or heat source. This allows a more continuous cooling or heating output, compared to use of a single pressure cell for example.

[0056] Preferences for the first aspect apply equally to the second and third aspects.

[0057] 008844177 A hydrostatic pressuriser may be any means for pressurising each of the first and second pressure cells, and any further pressure cells where present. A hydrostatic pressuriser may be configured to pressurise and depressurise each of the pressure cells such that the first pressure cell is out of phase with the second pressure cell in a pressurisation and depressurisation cycle, or the hydrostatic pressuriser may be configured to simultaneously pressurise the first and second pressure cells. A hydrostatic pressuriser may be a means for independently pressurising each pressure cell, such as where the hydrostatic pressuriser comprises a pressurising component for each pressure cell and a control unit.

[0058] The apparatuses described herein may further comprise a heat recovery means for transferring the energy released upon pressurisation or depressurisation of a pressure cell to another part of the apparatus, or externally to the apparatus. In this way, thermal energy generated by the system can be recovered and reused.

[0059] Each pressure cell may be associated with a heat-exchanger for transferring heat to and from the barocaloric material. The heat-exchanger may be suitable for transferring heat for a barocaloric transition with a latent heat, |Q0|, that is at least 1.0 kJ kg-1, such as at least 5.0 kJ kg-1, such as at least 10.0 kJ kg-1, such as at least 25.0 kJ kg-1, such as at least 50.0 kJ kg-1, such as at least 100.0 kJ kg-1, such as at least 150.0 kJ kg-1, such as at least 200 kJ kg-1.

[0060] In some embodiments, the apparatus comprises one or more further pressure cells, wherein each further pressure cell comprises a vessel containing a barocaloric material, and the hydrostatic pressuriser is configured such that in use, the further pressure cell is fully pressurised while the first pressure cell is partially pressurised and the second pressure cell is partially or fully depressurised. In these embodiments, in use during cooling or heating, any two pressure cells are out of phase with each other in their respective heating and cooling cycles.

[0061] In a fourth aspect, there is provided use of a modular cooling or heating apparatus as described herein for cooling and / or heating.

[0062] Preferences for the first to third aspect apply equally to the fourth aspect.

[0063] Summary of the Figures

[0064] The present invention is described with reference to the figures listed below.

[0065] Figure 1 shows a typical pattern of temperature variation of a barocaloric material over time when subject to pressurisation / depressurisation cycles for heating or cooling.

[0066] 008844177 Figure 2 shows a plot of the typical useful output from a barocaloric material when used for cooling below a threshold temperature.

[0067] Figures 3A and 3B show the system output of apparatuses according to the invention, where two barocaloric materials (Figure 3A) or three barocaloric materials (Figure 3B) are operated in pressurisation and depressurisation cycles out of phase with each other.

[0068] Figure 4 shows an apparatus according to an embodiment of the invention with two pressure cells arranged in parallel that are each connected independently via a heat-exchanger to a heat source and a heat sink.

[0069] Figure 5 shows an apparatus according to an embodiment of the invention with two cascades of pressure cells, which can be operated out of phase with one another. The pressure cells within each cascade are connected by a heat-exchanger and to the heat source and the heat-sink.

[0070] Detailed Description of the Invention

[0071] At its most general, the present invention relates to a modular cooling or heating system comprising at least two barocaloric materials that are operated out of phase with one another in their respective heating and cooling cycles, and are connected in parallel between an external heat source to be cooled and an external heat sink to be heated.

[0072] The system enables a smoother and more continuous cooling (of the external heat source) or heating output (to the external heat sink) compared to a system where a single barocaloric material is pressurised and depressurised, because the latter results in an intermittent cooling or heating output.

[0073] Cirillo et al., 2023 describe a barocaloric cooling system that includes a pressure cell containing a piston, and acetoxy silicone rubber as a barocaloric material, which is provided within the piston headspace. The pressure cell is cycled between adiabatic loading where the barocaloric material rises in temperature, and an adiabatic unloading where the barocaloric material drops in temperature.

[0074] Qian et al., 2024 describe a prototype cooling device where a rigid vessel containing bulk neopentylglycol (NPG) as a barocaloric cooling agent is subjected to pressurisation and depressurisation cycles. Dai et al., 2024 describes a solid-state barocaloric refrigeration system using neopentylglycol (NPG) as a refrigerant.

[0075] The cooling output of the devices described in Cirillo et al., Qian et al. and Dai et al. is typically intermittent. The present inventors have surprisingly found that by using two or more pressure cells and operating these such that the barocaloric materials are out of phase

[0076] 008844177 with one another in their respective heating and cooling cycles, it is possible to provide a more continuous cooling or heating output and thereby improve cooling or heating performance. This can be achieved by staggering pressurisation of two or more pressure cells such, and / or by using a conventional barocaloric material together with an inverse barocaloric material.

[0077] Modular Apparatus

[0078] The apparatuses described herein comprise first and second pressure cells that each comprise a barocaloric material, and a hydrostatic pressuriser for applying and removing hydrostatic pressure to and from the pressure cells. The pressure cells are arranged in parallel, and each pressure cell is connected via a respective set of heat-exchangers to a heat-sink and a heat-source.

[0079] In some aspects, the invention provides a modular cooling or heating apparatus, comprising: a first pressure cell comprising a vessel containing a first barocaloric material; a first set of heat-exchangers for connecting the first pressure cell to a heat source and a heat sink; a second pressure cell comprising a vessel containing a second barocaloric material; and a second set of heat-exchangers for connecting the second pressure cell to the heat source and the heat sink; and a hydrostatic pressuriser for pressurising and depressurising the first pressure cell out of phase with the second pressure cell, such that in use for cooling or heating, the first barocaloric material is partially or fully pressurised when the second barocaloric material is partially or fully depressurised.

[0080] In use for cooling or heating, the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles as described herein. Pressurisation and depressurisation of the pressure cells results in heat flow to or from the heat sink or heat source. The first and second set of heat-exchangers may independently be connected to the heat source and the heat sink, which is typically a common heat source and a common heat sink.

[0081] In some aspects, the invention provides a modular cooling or heating apparatus, comprising: a first pressure cell comprising a vessel containing a first barocaloric material, wherein the first barocaloric material is capable of releasing heat upon pressurisation; a first set of heat-exchangers for connecting the first pressure cell to a heat source and a heat sink; a second pressure cell comprising a vessel containing a second barocaloric material, wherein the second barocaloric material is capable of absorbing heat upon pressurisation;

[0082] 008844177 a second set of heat-exchangers for connecting the second pressure cell to the heat source and the heat sink; and a hydrostatic pressuriser for pressurising and depressurising the first and second pressure cells.

[0083] In use, the hydrostatic pressuriser may simultaneously pressurise and depressurise the first and second pressure cells, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles as described herein. Pressurisation and depressurisation of the pressure cells results in heat flow to or from the heat sink or heat source, via a portion of each set of heat-exchanger.

[0084] Pressure Cell

[0085] A barocaloric material is provided in each pressure cell. The barocaloric material is contained within a vessel, which may also be referred to as an outer vessel. By “contained” it is meant that the barocaloric material is housed or provided within the vessel. The barocaloric material may be in direct contact with one or more walls of the vessel, or the barocaloric material may be contained within another structure in the vessel, such as to separate the barocaloric material from the vessel walls.

[0086] A pressure cell is not particularly limited in size or dimension as long as it suitably contains the barocaloric material and is capable of transmitting hydrostatic pressure. In some embodiments, a pressure cell may be cylindrical.

[0087] A pressure cell may comprise a piston, and the barocaloric material may be provided within the piston headspace, such as in the presence of a pressure transmitting medium. The piston may be operably connected to a hydrostatic pressuriser as described herein for pressurising the pressure cell and optionally one or more other pressure cells. In other embodiments, the pressure cell may comprise a hydrostatic pressuriser or a component thereof as described herein.

[0088] Barocaloric material

[0089] A “barocaloric material” as described herein is a material suitable for use as a barocaloric cooling or heating agent. A barocaloric material has a phase transition that can be driven and undriven with the application and removal of pressure, and the phase transition involves heat exchange. The phase transition may be a first order phase transition. Without wishing to be bound by theory, a first-order phase transition displays a shift of transition temperature with pressure due to a change in volume at the transition, which results in a substantial heat exchange and gives rise to a barocaloric effect. A second-order phase transition may also give rise to a barocaloric effect, but generally does not display a change in volume or a change in entropy and there is no shift of transition temperature with pressure. A first-order

[0090] 008844177 phase transition may release or absorb latent heat. Therefore, a first-order phase transition may be preferred for use in barocaloric cooling or heating. In some embodiments, the barocaloric material has a first-order phase transition that can be driven by the application or removal of hydrostatic pressure. In other embodiments, the barocaloric material has a second-order phase transition.

[0091] It is necessary for a barocaloric material to have a reversible phase transition in order to be used as a barocaloric cooling or heating agent. In this way, the barocaloric material can cycle between two phases, such as over two or more cycles, such as three or more cycles. An irreversible phase transition is typically not suitable for use in barocaloric cooling or heating agent.

[0092] A barocaloric material according to the invention may be capable of releasing heat upon application of hydrostatic pressure, and absorbing heating upon release of the applied pressure. These materials may be referred to as conventional barocaloric materials. A barocaloric material may be capable of absorbing heat upon application of hydrostatic pressure and releasing heat upon release of the applied pressure, and these materials may be referred to as inverse barocaloric materials.

[0093] Each barocaloric material for use according to the invention may independently be a conventional or an inverse barocaloric material. The first and second barocaloric materials may both be conventional barocaloric materials, or they may both be inverse barocaloric materials. One of the first and second barocaloric materials may be a conventional barocaloric material, and the other one may be an inverse barocaloric material.

[0094] Preferably, each barocaloric material independently comprises a first-order phase transition where an applied hydrostatic pressure at or near the first-order phase transition temperature causes a reduction in volume and release of heat (conventional barocaloric effect) or a reduction in volume and absorption of heat (inverse barocaloric effect).

[0095] The first and second barocaloric materials may be the same material. The first and second barocaloric materials may be different materials, such as where the first and second barocaloric materials have different transition temperatures, such as where the operating temperatures of the first and second barocaloric materials are different, or where one is a conventional barocaloric material and the other is an inverse barocaloric material.

[0096] Suitable barocaloric materials are known in the art. Examples include organic materials and inorganic materials.

[0097] Organic materials displaying barocaloric effects (conventional or inverse) include: plastic crystals, such as neopentane and adamantane derivatives, such as neopentylglyol and 1 -adamantanol.

[0098] 008844177 liquid crystals, such as a non-lyotropic liquid crystal including 4-(trans-4- pentylcyclohexyl)benzonitrile (PCH5), or a lyotropic material, including phospholipids. alkyl carboxylate salts.

[0099] Organic barocaloric materials and their use as barocaloric cooling or heating agents are described in WO 2018 / 069506, Cirillo et al. 2023, Qian et al., 2024 and Dai et al., 2024, the contents of which are incorporated herein.

[0100] Inorganic materials displaying barocaloric effects (conventional or inverse) include MnsGaN and ammonium sulfate.

[0101] A barocaloric material may be provided with a thermally conductive material distributed within the barocaloric material. Any suitable material that is thermally conductive may be used, as long as it enhances heat conductivity from the barocaloric material, such as a conductive filler or metal wool.

[0102] Pressure-transmitting medium

[0103] A pressure cell may comprise a pressure-transmitting medium for transmitting an applied hydrostatic pressure to the barocaloric material. The pressure-transmitting medium may be a pressure-transmitting fluid, and may be contained within a piston head space that is in contact with the barocaloric material. The barocaloric material may be provided within the pressure-transmitting medium, such as where the barocaloric material is surrounded by the pressure-transmitting medium.

[0104] The pressure transmitting medium is not essential. In some embodiments, pressure may be applied directly to the barocaloric material, such as where the barocaloric material is in a liquid phase.

[0105] Pressure-transmitting media are well known in the art, including those described in WO 2018 / 069506. A pressure-transmitting medium may be a liquid or a solid.

[0106] Examples of a pressure-transmitting liquid include alkoxy silane materials, such as DW-Therm, available from Huber Kaltemaschinenbau GmbH.

[0107] An example of a pressure-transmitting solid is alumina powder.

[0108] In some embodiments, the pressure-transmitting medium is not water.

[0109] Where the pressure-transmitting medium is present, the barocaloric material may be separated from direct contact with the pressure-transmitting medium. In some embodiments, the pressure cell comprises a flexible housing containing the barocaloric

[0110] 008844177 material (which is provided within the vessel), where the pressure-transmitting medium is provided outside the flexible housing, such as surrounding, the flexible housing. The flexible housing separates the barocaloric material from the pressure-transmitting medium to avoid chemical interactions between these components, for example. The flexible housing is able to transmit the pressure from the pressure-transmitting medium to the barocaloric material, and is preferably a bag, or a separating membrane or other flexible structure. In some embodiments, the flexible housing comprises deformable corrugations (for example, fluted corrugations) or wrinkles. The flexible housing may be made of a polymer, such as polyethylene, polyvinyl chloride (PVC) or polyurethane.

[0111] By providing the flexible housing separating the pressure-transmitting medium and the barocaloric material, it is possible to transfer pressure between the barocaloric material and pressure-transmitting medium whilst eliminating, for example, dissolution of the barocaloric material in the pressure transmitting medium and the transport of particles of barocaloric material out of the pressure cell by the pressure transmitting medium. In this way, the lifetime and overall effectiveness of the heating or cooling apparatus comprising the barocaloric material is improved.

[0112] In other embodiments, the pressure-transmitting fluid is provided as a mixture with the barocaloric material. These components may form a slurry, which may enhance pressure transmission to the barocaloric material.

[0113] Thermally insulating material

[0114] The pressure cell may comprise a thermally insulating material for preventing the barocaloric material from direct contact with the vessel. The thermally insulating material may be disposed between the walls of the vessel and the barocaloric material, and may form a thermal barrier between the barocaloric material and the vessel wall(s).

[0115] Any low thermal conductivity material may be used as the thermally insulating material, such as a polymer such as polyetheretherketone (PEEK); or an aerogel. The thermally insulating material may be provided in the form of a bag, such as a polymer bag, such as a polyetheretherketone (PEEK) bag.

[0116] In some embodiments, the thermally insulating material is the flexible housing described herein. In other embodiments, the pressure cell comprises a thermally insulating material for separating the barocaloric material from the vessel walls, and a flexible housing, wherein the thermally insulating material differs from the flexible housing.

[0117] In some embodiments, the thermally insulating material is a pressure-transmitting medium as described herein, or comprises the pressure-transmitting medium. In other embodiments, the pressure cell comprises a thermally insulating material for separating the barocaloric

[0118] 008844177 material from the vessel walls, and a pressure-transmitting medium, wherein the thermally insulating material differs from the pressure-transmitting medium.

[0119] Heat-Exchanger

[0120] An apparatus described herein comprises a heat-exchanger. A heat-exchanger transfers heat from one medium to another.

[0121] A heat-exchanger may comprise a heat-exchange fluid. In some embodiments, the heat-exchanger comprises a heat-exchange fluid enclosed in a pipe or tube.

[0122] A heat-exchange fluid may be a liquid or gas, and preferably is a liquid. Suitable liquids as the heat-exchange fluid include water, ethylene glycol, propylene glycol and silicone oil. In some embodiments, the heat-exchange fluid comprises a mixture of water and another liquid, such as a mixture of water and ethylene glycol.

[0123] A pressure cell, such as the first pressure cell, second pressure cell, and each further pressure cell where present, may be provided or associated with a set of heat-exchangers capable of independently connecting said pressure cell to a heat source and a heat sink. A set of heat-exchangers may be a pair of heat-exchangers, such as a first heat-exchanger for connecting the pressure cell to a heat sink, and a second heat-exchanger for connecting the pressure cell to a heat source. Typically, the heat source and heat sink do not directly exchange heat with each other, and each set of heat-exchanger connected to a pressure cell comprises two heat-exchanger circuits with one between the heat source (e.g. external zone to be cooled) and the pressure cell, and one between the heat sink (e.g. external zone to be heated) and the pressure cell.

[0124] A set (or pair) of heat-exchangers may be separate units, for example units that do not share any common portions or share a common heat-exchanger circuit. A set of heat-exchangers may also be referred to as a heat-exchanger set.

[0125] A set of heat-exchangers may be a single heat-exchanger, such as having a common portion that is embedded within the barocaloric material within the pressure cell. In these embodiments, the heat-exchanger may be provided with valves to control heat-flow between the pressure cell and the heat source or the heat sink at different parts of a heating and cooling cycle to enable independent heat flow to or from the heat source and the heat sink.

[0126] A set of heat-exchangers may also be referred to as a (single) heat-exchanger, provided that it is capable of independently connecting the pressure cell to the heat source and the heat sink.

[0127] Preferably, the heat-exchanger (or set of heat-exchangers) comprises a portion that is in direct contact with the barocaloric material. For example, the heat-exchanger may comprise

[0128] 008844177 a heat-exchange fluid provided in a pipe or tube, part of which may be embedded within the barocaloric material.

[0129] Each heat-exchanger is for thermally connecting the associated pressure cell to a heat source or heat sink, such that in use, heat is extracted from or supplied to the barocaloric material during pressurisation or depressurisation of the pressure cell to the heat sink or heat source. A pressure cell is preferably provided with a pair of heat-exchangers, one connecting the pressure cell to the heat sink and the other connecting the pressure cell to the heat source. The pair of heat-exchangers may be connected, or more share a common portion.

[0130] A heat-exchanger that is partially embedded in the barocaloric material may comprise a heat-exchange fluid, which may be enclosed in a pipe or tube or network thereof, with an entry and exit point in the pressure cell. The pressure cell comprises a barocaloric material between the entry and exit points, and the pipe or tube or network thereof is embedded within and is in thermal contact with the barocaloric material. The heat-exchange fluid is typically not in direct contact with the barocaloric material, as long as a portion of the internal heat-exchanger, such as a pipe or tube or a portion thereof, is in direct contact with the barocaloric material.

[0131] The entry and exit points for a heat-exchanger within the cell may be thermally insulated. The pressure cell may comprise a thermally insulating material around the entry and exit points, such as a pressure-resistant sleeve. The thermally insulating material may be a ceramic, such as where the thermally insulating material comprises alumina, zirconia or silicon nitride. The thermally insulating material may have a lower thermal conductivity compared to steel or stainless steel, for example.

[0132] A heat-exchanger may be for transferring heat from a pressure cell to a location for cooling or heating, such as an external zone. By “external zone”, it is meant a zone that is external to the apparatus and / or a pressure cell or arrangement of pressure cells. In some embodiments, a portion of the heat-exchanger is embedded within the barocaloric material of a pressure cell, and another portion is exposed to a heat source or heat sink. The heatexchanger may comprise a heat-exchange fluid that can be circulated from the pressure cell to the heat source and / or heat sink. A valve may be provided between the pressure cell and heat source and / or heat sink, which may be adjusted in use to allow heat flow during a heating and cooling cycle.

[0133] A heat-exchanger may thermally connect one pressure cell to another pressure cell, such as where the heat-exchange fluid can be transferred between the two pressure cells. A heatexchanger may thermally connect two or pressure cells in a cascade as described herein. A valve may be suitably arranged between two pressure cells, and optionally between a

[0134] 008844177 pressure cell and a heat source or heat sink, which may be adjusted in use to allow heat flow during a heating and cooling cycle.

[0135] A heat-exchanger may be suitable for transferring heat for a barocaloric transition with a latent heat, |Q0| , that is at least 1 kJ kg-1, such as at least 5 kJ kg-1, such as at least 10 kJ kg-1, such as at least 25 kJ kg-1, such as at least 50 kJ kg-1, such as at least 100 kJ kg-1, such as at least 150 kJ kg-1, such as at least 200 kJ kg-1.

[0136] In some embodiments, the barocaloric material is mixed with a thermally conductive material for improving thermal conduction between the barocaloric material and the heat-exchanger, such as a conductive filler or metal wool as described herein. This allows temperature excursions of the cells to be minimised during each cycle and thereby maximises temperature swings.

[0137] Hydrostatic Pressuriser

[0138] A hydrostatic pressuriser may be provided for pressurising and depressurising each of the first and second pressure cells, such that in use during cooling or heating, the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles.

[0139] A hydrostatic pressuriser may be for pressurising and depressurising a first and second portion of the total pressure cells, such as that in use during cooling or heating, the barocaloric material in the first portion of pressure cells is out of phase with the barocaloric materials in the second portion of pressure cells. A portion of the total pressure cells may comprise the first or second pressure cells, and optionally one or more further pressure cells. A portion of the total pressure cells may comprise some or all of the pressure cells arranged in a cascade descried herein.

[0140] A hydrostatic pressuriser may be any means of applying hydrostatic pressure to each of the first and second pressure cells, and optionally to one or more further pressure cells, where present. In some embodiments, in use for cooling or heating the hydrostatic pressuriser is configured to partially or fully pressurise the first barocaloric material while partially or fully depressurising the second barocaloric material, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles. In some embodiments, in use for cooling or heating the hydrostatic pressuriser is configured to partially pressurise the first barocaloric material while partially or fully depressurising the second barocaloric material. In other embodiments, in use for cooling or heating the hydrostatic pressuriser is configured to fully pressurise the first barocaloric material while partially or fully depressurising the second barocaloric material.

[0141] 008844177 A barocaloric material may be fully pressurised when hydrostatic pressure is applied, such as where a phase transition of the material is driven. A barocaloric material may be fully depressurised when an applied hydrostatic pressure is released, such as where the phase transition is reversed. A barocaloric material may be partially pressurised or depressurised when a pressure lower than that necessary to drive a phase transition is applied, such as up to 90%, such as up to 80%, such as up to 75%, such as up to 50%, such as up to 25%.

[0142] Where the apparatus comprises one or more further pressure cells, the hydrostatic pressuriser may be for (e.g. suitable for, or configured for) pressurising and depressurising each further pressure cell in use during cooling or heating, such that the barocaloric materials in a first group of pressure cells are partially or fully pressurised when the barocaloric materials in a second group of cells within the apparatus are partially or fully depressurised. Each group of pressure cells may independently be a single pressure cell or a plurality of pressure cells. Where a group of pressure cells is a plurality of pressure cells, typically the barocaloric material in said group are operated in phase with each other. For example, in use half of the pressure cells (a first group) may be partially pressurised, while half of the pressure cells (a second group) may be partially depressurised. Alternatively, in use a first and third pressure cell may be in phase with one another, and out of phase with a second pressure cell.

[0143] Where the apparatus comprises one or more further pressure cells, the hydrostatic pressuriser may be configured such that in use for cooling or heating, the barocaloric material in one or more of the further pressure cells is out of phase with each of the first and second barocaloric materials in their respective heating and cooling cycles. In some embodiments, the apparatus comprises a third pressure cell, or a third group of pressure cells, each comprising a third barocaloric material, wherein in use for cooling or heating, the hydrostatic pressuriser is configured such that the third barocaloric material is out of phase with the first and second barocaloric materials in their respective heating and cooling cycles. In some embodiments, the apparatus further comprises a fourth pressure cell, or fourth group of pressure cells, each comprising a fourth barocaloric material, wherein in use for cooling or heating, the hydrostatic pressuriser is configured such that the fourth barocaloric material is out of phase with each of the first, second, third and fourth barocaloric materials in their respective heating and cooling cycles.

[0144] In some embodiments, the hydrostatic pressuriser is for sequentially pressurising the first pressure cell, the second pressure cell, and one or more further pressure cells where present. In these embodiments, the pressure applied to the first cell may be released after pressurisation of the last cell is initiated, or before depressurisation of the last cell is initiated.

[0145] In other embodiments, the hydrostatic pressuriser is configured to simultaneously pressurise or depressurise the first and second pressure cells, and optionally one or more further pressure cells where present. Preferably, where the barocaloric materials in two pressure

[0146] 008844177 cells are different, such as where one is a conventional barocaloric material and the other is an inverse barocaloric material, the hydrostatic pressuriser is configured to simultaneously pressurise the two pressure cells containing those barocaloric materials.

[0147] The hydrostatic pressuriser may be configured for simultaneously pressurising a plurality of cells (such as a mixture of cells containing conventional and inverse barocaloric materials), and pressurising another plurality of cells out of phase with one another (such as a group of cells all comprising either a conventional or inverse barocaloric material).

[0148] The hydrostatic pressuriser may comprise two or more component parts, such as two or more pressurising means which act out of phase (such as sequentially) on the first and second pressure cells. The hydrostatic pressuriser may comprise a component part for pressurising and depressurising each pressure cell in the apparatus independently, such as two or more component parts, such as three or more component parts, such as four or more component parts.

[0149] The hydrostatic pressuriser may comprise two or more intensifiers or two or more high-pressure pumps, and a control system which operates the intensifiers or high-pressure pumps. An intensifier or high-pressure pump may be provided as part of a pressure cell. The hydrostatic pressuriser may comprise valves, which may be arranged in a programmed sequence in use.

[0150] The hydrostatic pressuriser may be configured to apply, or may be suitable for applying, hydrostatic pressure at a level sufficient to induce a phase transition in the barocaloric material. The hydrostatic pressure may be at most 1.0 GPa, such as at most 0.5 GPa, such as at most 0.2 GPa, such as at most 0.15 GPa, such as at most 0.10 GPa, such as at most 0.09 GPa, such as at most 0.07 GPa, such as at most 0.06 GPa, such as at most 0.05 GPa, such as at most 0.04 GPa, such as at most 0.03 GPa, such as at most 0.02 GPa, such as at most 0.01 GPa. The hydrostatic pressure may be at least 0.1 MPa, such as at least 0.5 MPa, such as at least 1.0 MPa, such as at least 5.0 MPa. The pressure applied may be a hydrostatic pressure in a range with the lower and upper limits selected from the values given above. For example, the hydrostatic pressure may be a pressure in the range 1.0 MPa to 0.1 GPa.

[0151] The hydrostatic pressuriser may be configured to apply, or may be suitable for applying, pressure to each pressure cell to move the transition temperature of the barocaloric material to a temperature that is in an ambient temperature, such as a temperature from -20 °C to 50 °C, such as 0 °C to 35 °C, such as 5 °C to 35 °C, such as 10 °C to 30 °C (corresponding to 253.15 K to 323.15 K, such as 273.15 to 308.15 K, such as 278.15 to 308.15 K, such as 283.15 to 303.15 K).

[0152] 008844177 The hydrostatic pressuriser may be configured to pressurise and depressurise the first pressure cell, the second pressure cell, and optionally one or more further pressure cells, over different pressure ranges and / or different pressurisation and depressurisation cycles.

[0153] Out of phase cooling or heating

[0154] The invention provides a modular apparatus comprising two or more cells described herein. In use during cooling or heating, a first barocaloric material of the apparatus is out of phase with a second barocaloric material in their respective heating and cooling cycles.

[0155] Barocaloric materials undergo a heating and cooling cycle when pressure is applied and then released from the material. Each complete cycle comprises a heating phase, whereby the application of pressure, for example, causes the barocaloric material to release heat, and a cooling phase, whereby the release of the pressure, for example, causes the barocaloric material to absorb heat. Where two barocaloric materials are “out of phase”, it is meant that one barocaloric material is at a different stage of its complete heating and cooling cycle compared to another barocaloric material for at least part of the cycle. For example, a first barocaloric material may be in a heating stage, while the second barocaloric material is in a cooling stage.

[0156] In some embodiments, the first and second barocaloric materials, and optionally the barocaloric materials in any two pressure cells, may be out of phase by 10° or more, such as 20° or more, such as 40° or more, such as 60° or more, such as 90° or more, such as 100° or more, such as 120° or more, such as 180°. The first and second barocaloric materials, and optionally the barocaloric materials in any two pressure cells, may be out of phase by less than 180°, such as less than 120°, such as less than 100°, such as less than 90°, such as less than 60°, such as less 40°. Two barocaloric materials may be out of phase by a value in a range with upper and lower limits described above, such as from 10° to 180°, including from 90° to 180°, such as from 120° to 180°. Two barocaloric materials may be out of phase by 120° or by 180°.

[0157] In some embodiments, the apparatus comprises first and second barocaloric materials contained in first and second pressure cells (or sets thereof) which are operated out of phase by 180° to each other in their respective heating and cooling cycles. In some embodiments, the apparatus comprises first, second and third barocaloric materials contained in first, second and third pressure cells (or groups thereof) which are operated out of phase by 120° to each other in their respective heating and cooling cycles.

[0158] The barocaloric materials may be operated out of phase in their respective heating and cooling cycles by out of phase application and release of hydrostatic pressure. The pressure

[0159] 008844177 may be monitored by any conventional means, such as manual gauges or electronic pressure transducers.

[0160] Where two barocaloric materials are out of phase by 180° they may also be described as being in anti-phase with one another. In these cases, at any given time one material may be in a cooling stage while the other is in a heating stage, and the cooling stage of one material may begin as the heating stage of the other material begins. The use of a (electro)caloric material in antiphase is described in Meng et al., 2020, for example, the contents of which are incorporated herein. In some embodiments, the pressure cells and heat-exchange fluid, which may a water circuit, may be controlled independently. By operating pressurisation and depressurisation of the pressure cells independently from the flow of a heat-exchange fluid through the heat-exchangers, this optimises cooling or heating power and improves temperature lift.

[0161] In some embodiments, the barocaloric materials may have cooling and heating cycles of different lengths. These barocaloric materials may be in anti-phase where start of a cooling phase of one material may be occur simultaneously with the start of a heating phase of the other material. The peak temperature in one cell may be reached at a different time to the other cell.

[0162] Barocaloric cascade

[0163] In some embodiments, at least one of the first pressure cell or the second pressure cell is thermally connected to a further pressure cell, or a plurality of further pressure cells, such as by a heat-exchanger. In some such cases the first pressure cell is thermally connected to a first further pressure cell or a first series of (plurality of) further pressure cells, such as by a heat exchanger or set thereof; and the second pressure cell is thermally connected to a second further pressure cells or a second series of (plurality of) further pressure cells, such as by a heat-exchanger or set thereof.

[0164] These thermally connected pressure cells are arranged in series, to provide a cascade of pressure cells. In use for cooling or heating, the energy released upon pressurisation or depressurisation of the first pressure cell in the cascade is used directly for heating or cooling a further pressure cell that the pressure cell is thermally connected to.

[0165] By “arranged in series”, it is meant that the thermally connected pressure cells are arranged in a linear chain. Two or more pressure cells, such as three, four or five pressure cells, may be connected in this way such that energy can be transferred sequentially between the further pressure cells. This forms a barocaloric cascade, wherein the heat generated from a first pressure cell in the cascade is used for heating or cooling each downstream pressure

[0166] 008844177 cell. Heat flow may be controlled by valves arranged with in one or heat-exchangers connecting all of the pressure cells within a cascade.

[0167] In use for cooling or heating, a first pressure cell may be anti-phase with an adjacent pressure cell in the cascade in their respective cooling and heating cycles. Any two further pressure cells that are adjacent and thermally connected to one another may be operated in anti-phase.

[0168] Each further pressure cell may have the features of a pressure cell as described herein, and may include a vessel, a barocaloric material, a flexible housing, a thermally insulating material and an internal heat-exchanger.

[0169] The pressure cells in a cascade may all be of the same material and / or dimensions, or they may be of a different material and / or dimension. In some embodiments, a first cascade of pressure cells (e.g. comprising the first pressure cell) and a second cascade of pressure cells (e.g. comprising the second pressure cell) is provided, where the first cascade of pressure cells is larger in size than the second cascade of further pressure cells. In some embodiments, the pressure cells within a cascade may be of different sizes to each other, such as where the pressure cells in the cascade are successively smaller in size. This helps to enhance efficiency, and the size of the pressure cells may be adapted to the cooling load.

[0170] Cascades of caloric materials are described in WO 2016 / 096509 where magnetocaloric materials are provided as a sequence of layers with decreasing Curie temperatures.

[0171] Meng et al. 2020 describe a cascade electrocaloric cooling device, and Bai et al. 2023 describe a cascade electrocaloric cooling tube.

[0172] Methods

[0173] The present invention provides methods of barocaloric cooling or heating using two or more pressure cells that are operated out of phase in their respective heating and cooling cycles.

[0174] The methods of the invention include a cycling step of applying hydrostatic pressure to the barocaloric materials in two or more pressure cells and releasing the hydrostatic pressure. This provides for a complete heating and cooling cycle (or cooling and heating cycle).

[0175] Each barocaloric material may be used within a cycling step within a Brayton cycle, an Ericsson cycle or a Carnot cycle, to provide cooling or heating as required. The barocaloric material may be used in an alternative thermodynamic cycle to provide cooling or heating.

[0176] Where the cycling step is a part of a Brayton cycle, for example, the pressure may be applied adiabatically, with, for example, a consequential heating of the barocaloric material. Subsequent heat flow allows the barocaloric material to return to its original temperature. In

[0177] 008844177 a further part of the cycling step, pressure may be released adiabatically with, for example, a consequential cooling of the barocaloric material, and subsequent heat flow allows the barocaloric material to return to its original temperature.

[0178] Where the cycling step is a part of the Ericsson cycle, for example, the pressurisation and depressurisation steps are performed isothermally. Thus, the barocaloric material is maintained at a substantially constant temperature, with heat transfer occurring, and not subsequent to, the pressurisation and depressurisation steps.

[0179] The method of the invention may be performed in an environment at ambient temperature, such as a temperature from -20 °C to 50 °C, such as from 0 °C to 35 °C, such as 5 °C to 35 °C, such as 10 °C to 30 °C (corresponding to 253.15 K to 323.15 K, such as 273.15 to 308.15 K, such as 278.15 to 308.15 K, such as 283.15 to 303.15 K). The methods of the invention allow for the generation of cooler and warmer localised regions within the environment as part of the barocaloric cooling process. For example, the barocaloric material may become warmer or cooler than the ambient environment in the methods of the invention.

[0180] The methods of the invention allow for the use of barocaloric materials displaying conventional barocaloric effects or inverse barocaloric effects.

[0181] The methods may be used within a heat pump cycle or a refrigeration cycle to provide heating or cooling, respectively.

[0182] In some embodiments, a sufficient pressuring force is applied to move the transition temperature of the barocaloric material to a temperature that is in an ambient temperature, such as a temperature from -20 °C to 50 °C, such as 0 °C to 35 °C, such as 5 °C to 35 °C, such as 10 °C to 30 °C.

[0183] In some aspects, the invention provides a method of cooling or heating, comprising the steps of:

[0184] (a) providing a first pressure cell comprising a vessel containing a first barocaloric material, wherein the first pressure cell is connected by a first set of heat-exchangers to a heat source and a heat sink, and providing a second pressure cell comprising a vessel containing a second barocaloric material, wherein the second pressure cell is connected by a second set of heat-exchangers to the heat source and the heat sink, and wherein each barocaloric material is capable of undergoing a heating and cooling cycle upon pressurisation and depressurisation of the respective pressure cell;

[0185] (b) applying hydrostatic pressure to each of the first and second pressure cells, and releasing the applied pressure, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles; and

[0186] (c) permitting heat flow to or from each pressure cell to the heat sink or heat source.

[0187] 008844177 Steps (a) to (c) may be performed in order.

[0188] Step (a) may comprise providing a modular apparatus as described herein.

[0189] The first and second barocaloric materials may independently be a conventional barocaloric material or an inverse barocaloric material. In some embodiments the first and second barocaloric materials are both conventional barocaloric materials. In other embodiments, the first and second barocaloric materials are both inverse barocaloric materials. In other embodiments, the first barocaloric material is a conventional barocaloric material and the second barocaloric material is an inverse barocaloric material.

[0190] In some embodiments, step (b) comprises pressurising the first pressure cell while depressurising the second pressure cell. In these embodiments, the first and second barocaloric material may be of the same type, for example both conventional barocaloric materials (which may be the same or different) or both inverse barocaloric materials (which may be the same of different.

[0191] During step (b) the first pressure cell may be partially or fully pressurised, while the second pressure cell is partially or fully depressurised. For example, the first pressure cell may be partially pressurised while the second pressure cell is partially depressurised at a given time point during a pressurisation / depressurisation cycle, or the first pressure cell may be partially pressurised while the second pressure cell is fully depressurised. In this way, the pressure cells are out of phase with one another in their respective pressurisation-depressurisation cycles. In these embodiments, the first and second barocaloric materials are preferably both conventional barocaloric materials, or both inverse barocaloric materials. The pressure cells are preferably in anti-phase with one another in their respective heating and cooling cycles.

[0192] In some embodiments the first barocaloric material is a conventional barocaloric material and the second barocaloric material is an inverse barocaloric material. Step (b) may comprise simultaneously pressuring and depressurising the first and second pressure cells such that the first barocaloric material is releasing heat while the second barocaloric material is absorbing heat. Here the pressure cells may be in phase with one another in their respective pressurisation-depressurisation cycles, provided that the first and second barocaloric materials are out of phase in their respective heating and cooling cycles. For example, when a conventional barocaloric material as the first barocaloric material is being pressurised (partially or fully), it is in a heat-release phase, and when an inverse barocaloric material as the second barocaloric material is being pressurised (partially or fully), it is in a heat-absorption phase. Simultaneously pressurising these materials results in the first and second barocaloric materials being out of phase with one another in their respective heating and cooling cycles.

[0193] 008844177 In other embodiments, the first barocaloric material is a conventional barocaloric material and the second barocaloric material is an inverse barocaloric material, and step (b) comprises pressurising and depressurising the first and second pressure cells out of phase with one another. In these embodiments the first and second pressure cells may not be in anti-phase with one another in their respective pressurisation-depressurisation cycles.

[0194] In the methods of the invention, the hydrostatic pressure applied in step (b) is typically near a transition temperature of the barocaloric material. For example, the hydrostatic pressure is applied at a temperature that is within 150 K, within 100 K, within 50 K, within 20 K, within 15 K, within 10 K, such as within 5 K, such as within 2 K, such as within 1 K, such as within 0.5 K of the transition temperature, which is the transition temperature of the barocaloric material absent the applied hydrostatic pressure (for example, the transition temperature under ambient pressure).

[0195] The hydrostatic pressure may be applied at a level sufficient to induce the phase transition. The hydrostatic pressure may be at most 1.0 GPa, such as at most 0.5 GPa, such as at most 0.2 GPa, such as at most 0.15 GPa, such as at most 0.10 GPa, such as at most 0.09 GPa, such as at most 0.07 GPa, such as at most 0.06 GPa, such as at most 0.05 GPa, such as at most 0.04 GPa, such as at most 0.03 GPa, such as at most 0.02 GPa, such as at most 0.01 GPa. The hydrostatic pressure may be at least 0.1 MPa, such as at least 0.5 MPa, such as at least 1.0 MPa, such as at least 5.0 MPa. The pressure applied may be a hydrostatic pressure in a range with the lower and upper limits selected from the values given above. For example, the hydrostatic pressure may be a pressure in the range 1.0 MPa to 0.1 GPa.

[0196] The pressurising force is the change in pressure applied to the barocaloric material in a cell described herein. Typically, the change in pressure is to or from ambient (atmospheric) pressure, such as to or from about 101 kPa.

[0197] The application of hydrostatic pressure typically comprises applying hydrostatic pressure to the barocaloric material contained within a pressure cell. The pressure cell may comprise a pressure-transmitting medium as described herein, which may transmit the applied pressure to the barocaloric material.

[0198] The method may comprise providing more than two pressure cells, wherein each further pressure cell is configured as described for the first and / or second pressure cells.

[0199] The method may comprise providing a first group of pressure cells and a second group of pressure cells, and step (b) comprises applying hydrostatic pressure to each group of pressure cells and releasing the applied pressure, such that the barocaloric materials in the first group of pressure cells is out of phase with the barocaloric materials in the second group of pressure cells in respective heating and cooling cycles. A “group” of pressure cells

[0200] 008844177 may be a single pressure cell, or a plurality of pressure cells. That is, a portion of the total number of pressure cells is out of phase with at least another portion of the total number of pressure cells in their respective heating and cooling cycles.

[0201] In some embodiments, step (a) comprises providing a first, second, third and fourth pressure cell, and step (b) comprises applying hydrostatic pressure to each pressure cell and releasing the applied pressure, such the barocaloric material in the third cell is in phase with the first barocaloric material (and out of phase with the second barocaloric material), and the barocaloric material in the fourth cell is in phase with the second barocaloric material (and out of phase with the first and third barocaloric materials).

[0202] Step (a) may comprise providing one or more further pressure cells, and step (b) may comprise applying hydrostatic pressure to each pressure cell and releasing the applied pressure, such that a third group of pressure cells is out of phase with each of a first and second group of pressure cells in respective heating and cooling cycles. Step (a) may further comprise providing a fourth, fifth, sixth or more pressure cells (or group thereof), and step (b) may comprise applying hydrostatic pressure to each of the pressure cells and releasing the applied pressure such that each of the third, fourth, fifth and sixth pressure cells is out of phase with each other and each of the first and second group of pressure cells in respective heating and cooling cycles.

[0203] Where the method comprises three or more pressure cells (or group of pressure cells), hydrostatic pressure may be applied sequentially to each pressure cell (or group of pressure cells) such that the barocaloric material contained in each pressure cell (or group of cells) is out of phase in a heating and cooling cycle with the barocaloric material in each other pressure cell (or group of cells). For example, the method may comprise providing three, four, five or six pressure cells (or group of cells) where during step (b) the barocaloric material in each pressure cell (or group of cells) is in a different phase of a complete heating and cooling cycle.

[0204] The application of hydrostatic pressure during step (b) may be by use of a hydrostatic pressuriser as described herein.

[0205] The heat flow in step (c) may be a total heat flow to and from the plurality of pressure cells to a shared heat source and heat sink via respective heat-exchangers.

[0206] A pressure cell for use in step (a) may be part of a barocaloric cascade as described herein. For example, the first and / or second pressure cell may independently be thermally connected to a further pressure cell or a series of further pressure cells, wherein the method comprises using the thermal energy released upon pressurisation or depressurisation of the first and / or second pressure cell for heating or cooling an adjacent further pressure cell in the cascade.

[0207] 008844177 Uses

[0208] The invention also provides use of a modular heating or cooling apparatus as described herein for cooling or heating.

[0209] The methods of the invention may be for use in cooling foodstuffs or beverages.

[0210] The methods of the invention may be for use in cooling medicines.

[0211] The methods of the invention may be for use in cooling biological samples, such as tissues.

[0212] The methods of the invention may be for use in cooling electronic devices, such as devices for analytical measurements.

[0213] The methods of the invention may be used to cool air, such as air within building and vehicles.

[0214] Definitions

[0215] A “barocaloric material” is a material suitable for use as a barocaloric cooling or heating agent. A barocaloric material preferably has a first-order phase transition that can be driven and undriven by the application and release of hydrostatic pressure. A barocaloric material exhibits a temperature change in response to an applied hydrostatic pressure.

[0216] A “conventional barocaloric material” is a barocaloric material that releases heat upon application of hydrostatic pressure, and absorbs heat upon release of the applied pressure.

[0217] An “inverse barocaloric material” is a barocaloric material that absorbs heat upon application of hydrostatic pressure, and releases heat upon release of the applied pressure.

[0218] “Hydrostatic pressure” may also be described as isotropic stress. Hydrostatic pressure differs from uniaxial stresses that are applied to materials for use in elastocaloric cooling, for example. Unless stated otherwise, references herein to “pressure” refer to hydrostatic pressure, and references to “pressurisation” refer to the application of a hydrostatic pressure.

[0219] “Out of phase” may refer to the operation of two barocaloric materials with respect to their respectively heating and cooling cycles. When two barocaloric materials are out of phase in their respectively heating and cooling cycles, they do not simultaneously release and absorb heat at the same time. The barocaloric materials may both release heat at a given time, or both absorb heat at a given time, provided they do not do so simultaneously throughout a

[0220] 008844177 complete pressurisation and depressurisation cycle. Out of phase cooling or heat cycles include those that are in antiphase (180°), and more or less than 180°, such as 120°, such as 90°.

[0221] “Out of phase” may be used to describe the pressurisation and depressurisation of two pressure cells. When two pressure cells are out of phase in their respective pressurisationdepressurisation cycles, they are not simultaneously pressurised and depressurised. The two pressure cells may both be pressurised (such as partially or fully) at a given time, or the two pressure cells may both be depressurised (such as partially or fully) at a given time, provided that they are not simultaneously pressurised and depressurised throughout a complete heating and cooling cycle. Out of phase pressurisation-depressurisation cycles include those that are in antiphase (180°), and more or less than 180°, such as 120°, such as 90°.

[0222] A “group” of pressure cells refers to a single or a plurality of pressure cells described herein.

[0223] An “external zone” is a zone external to an apparatus or an arrangement of first and second pressure cells. An external zone may be an external zone to be heated, such as a heat sink. An external zone may be an external zone to be cooled, such as a heat source. An external zone may be thermally connected to an apparatus or a component thereof by a heat-exchanger.

[0224] A “heat-exchanger” is a means for transferring heat from one medium to another. A heatexchanger may comprise a heat-exchange fluid, which may be capable of being circulated to a heat source or heat sink, such that in use, heat is extracted from or supplied to the barocaloric material during pressurisation or depressurisation of the pressure cell. A pressure cell described herein is preferably connected to a set of heat-exchangers, with one heat-exchanger configured to connect the pressure cell to a heat source and another heatexchanger configured to connect the pressure cell to a heat sink. Each set of heatexchangers may be a single unit, or two units for example.

[0225] Other Embodiments

[0226] Each and every compatible combination of the embodiments described above is explicitly disclosed herein, as if each and every combination was individually and explicitly recited. Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0227] “and / or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example “A and / or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

[0228] 008844177 Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.

[0229] Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures described above.

[0230] Examples

[0231] Figure 1 shows the temperature variation of a barocaloric material when subjected to repeated cycles of pressurisation and depressurisation over a period of time. The useful output of this arrangement when used for cooling below a threshold temperature is intermittent, as shown in Figure 2.

[0232] A modular apparatus according to the invention may comprise two pressure cells, operated in 180° out of phase (in anti-phase) to one another. An example of the output of this modular apparatus is shown in Figure 3A. In this embodiment, in use one pressure cell is pressurised whilst the other pressure cell is depressurised. Therefore, one pressure cell may be providing a heat output whilst the other pressure cell may be absorbing heat (i.e. providing a cooling output). Superimposing the outputs from (or inputs to) each cell gives the system output as a whole, as illustrated in Figure 3A. This shows that more continuous heating above, or cooling below, a certain threshold level can be achieved compared to where a single pressure cell is used (see Figure 2 for comparison).

[0233] In another embodiment, the modular apparatus comprises three pressure cells, each operated at 120° out of phase to the others, providing a further smoothing of the overall heating (or cooling) output from the system as a whole. An illustration of the superimposed outputs from (or inputs to) each cell is shown in Figure 3B. This provides more continuous heating above, or cooling below, a certain threshold level.

[0234] In alternative embodiments the apparatus may have more than three pressure cells, which may be operated at other phase shifts from one another in terms of their pressurisation / depressurisation cycles so as to provide smoother and more continuous heating and / or cooling. In yet other embodiments, the apparatus may comprise two pressure cells where one contains a conventional barocaloric material and one contains an inverse barocaloric material, and the pressure cells are pressurised and depressurised at the same time (i.e. in phase). This also improves the heating or cooling output in an analogous way as described above.

[0235] An embodiment of an apparatus according to the invention is shown in Figure 4. A first pressure cell (cell 1) is shown at the top of Figure 4, which is connected via a pair (or set) of

[0236] 008844177 heat-exchangers and associated valves to an external zone to be cooled (e.g. the left-hand zone) and an external zone to be heated (e.g. the right-hand zone). In this embodiment, the pair of heat-exchangers share a common portion, which is embedded within the barocaloric material. Valves are provided between the embedded portion and the external zone to be cooled / heated, so that the two parts of the heat-exchanger can be configured to act independently of each other during a heating and cooling cycle. A second pressure cell in a corresponding arrangement is shown at the bottom (cell 2). In use, cells 1 and 2 may be pressurised and depressurised out of phase with each other, thereby producing a more continuous cooling output to the external zone to be cooled, and correspondingly a more continuous heating output to the external zone to be heated.

[0237] One or more pressure cells may be provided as part of a barocaloric cascade, as shown in Figure 5. In this example a first row of cells (shown at top of figure) is arranged within a cascade where pressure cell 1 is thermally connected to an adjacent pressure cell 2 by a heat-exchanger, thereby allowing heat extracted from cell 1 , for example, to provide heat input to cell 2. The heat-exchanger is provided with valves which can be operated in a chosen sequence. Specifically, the heat-exchange fluid that is heated or cooled by one pressure cell can be passed on to another pressure cell for further heating or cooling. A second row of cells (shown at bottom of Figure 5) is arranged in a similar way, comprising cells 3 and 4 which are thermally connected by another heat-exchanger.

[0238] In use the first and second rows of pressure cells each form a barocaloric cascade, which can be operated out of phase with each other (e.g. by out of phase pressurisation and depressurisation) to provide more continuous heating / cooling as well as having improved temperature span. Cells 1 and 3, for example, may be operated out of phase to each other, such as in anti-phase, where one cell is set to absorb heat at the same time that the other cell is set to output heat, and the heat extracted from these cells are used as input to cells 2 and 4, respectively.

[0239] In other embodiments, more than two pressure cells could be connected in series in this way, so as to provide greater overall temperature spans. For example, a further cell (cell 5) may be provided between cell 2 and the external zone to be heated. In such embodiments, different barocaloric materials with distinct barocaloric characteristics may optionally be used in different cells, so as to optimise the operating temperature range of each cell in such a system to the barocaloric characteristics of the material therein. Optionally the pressure ranges for different cells may differ, to optimise the operating characteristics of each cell to the barocaloric contained within.

[0240] In a specific example, a modular apparatus comprises a cylindrical pressure cell containing a volume of a barocaloric material, in which is embedded a pipe, or network of pipes containing the heat-exchange medium (e.g. fluid, e.g. water), and a pressurising-transmitting medium between the barocaloric material and the pressure cell wall. The embedded internal

[0241] 008844177 pipe (or pipe network) is optimised for size, spacing, high thermal conductivity and low heat capacity, thereby providing a large surface area with a small volume of pipe and heatexchanger fluid material.

[0242] The entry and exit points for the pipe (or network of pipes) in the cell may optionally be thermally insulated from the cell with a thermally insulating pressure-resistant sleeve material. An additional insulating material, such as a low thermal conductivity polymer, may be provided between the cell wall and the barocaloric material. This may be a flexible bag containing the barocaloric material. Alternatively, thermal insulation between the barocaloric material and the cell wall may be provided by the pressure-transmitting fluid.

[0243] In other examples, a mixture or slurry of the barocaloric material with a pressurise- transmitting fluid is provided in the cell. This helps to enhance pressure transmission to the barocaloric material.

[0244] In other examples, a conductive filler and / or metal wool is distributed within the barocaloric material to further enhance thermal conductivity to and from the heat-exchange.

[0245] References

[0246] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0247] Bai et al., Next Materials 2020, 1 (1)

[0248] Cirillo et al., Energies, 2023, 16, 6436

[0249] Dai et al., Energy 2024, 294, 130800

[0250] Meng et al., Nat. Energy 2020, 5, 996-1002

[0251] Qian et al., Cell Rep. Phys. Sci. 2024, 5, 101981

[0252] WO 2016 / 096509

[0253] WO 2018 / 069506

[0254] 008844177

Claims

Claims:

1. A method of cooling or heating, comprising the steps of:(a) providing a first pressure cell comprising a vessel containing a first barocaloric material, wherein the first pressure cell is connected by a first set of heat-exchangers to a heat source and a heat sink, and providing a second pressure cell comprising a vessel containing a second barocaloric material, wherein the second pressure cell is connected by a second set of heat-exchangers to the heat source and the heat sink, wherein each barocaloric material is capable of undergoing a heating and cooling cycle upon pressurisation and depressurisation of the respective pressure cell, wherein each pressure cell further comprises a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material, and wherein each pressure cell further comprises a flexible housing between the vessel and the barocaloric material and separating the barocaloric material from the pressure-transmitting medium, wherein the flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material;(b) applying hydrostatic pressure to each of the first and second pressure cells, and releasing the applied pressure, such that the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles; and(c) permitting heat flow to or from the first and second pressure cells to the heat sink or heat source.

2. The method of claim 1 , wherein step (b) comprises pressurising the first pressure cell while depressurising the second pressure cell.

3. The method of claim 1 or claim 2, wherein: the first barocaloric material and the second barocaloric material are each capable of releasing heat upon pressurisation; or the first barocaloric material and the second barocaloric material are each capable of absorbing heat upon pressurisation.

4. The method of claim 1 , wherein the first barocaloric material is capable of releasing heat upon pressurisation, and the second barocaloric material is capable of absorbing heat upon pressurisation, and wherein step (b) comprises simultaneously pressurising and depressurising the first and second pressure cells in their respective heating and cooling cycles such that the first barocaloric material is releasing heat while the second barocaloric material is absorbing heat.0088441775. The method of any one of claims 1 to 4, wherein step (a) comprises providing one or more further pressure cells each comprising a vessel containing a barocaloric material capable of undergoing a heating and cooling cycle upon pressurisation and depressurisation of the respective pressure cell, wherein each further pressure cell is connected by a respective set of heat-exchangers to the heat source and the heat sink, and wherein step (b) comprises applying hydrostatic pressure to each pressure cell and releasing the applied pressure, such that the barocaloric materials in a first group of pressure cells is out of phase with the barocaloric materials in a second group of pressure cells in their respective heating and cooling cycles.

6. The method of claim 5, wherein step (b) comprises applying hydrostatic pressure to each pressure cell, and releasing the applied pressure, such that the barocaloric materials in a third group of pressure cells is out of phase with the barocaloric materials in each of the first and second group of pressure cells in their respective heating and cooling cycles.

7. The method of any one of claims 1 to 4, wherein step (a) comprises providing one or more further pressure cells each comprising a vessel containing a barocaloric material capable of undergoing a heating and cooling cycle upon pressurisation and depressurisation of the respective pressure cell, wherein each further pressure cell is connected by a respective set of heat-exchangers to the heat source and the heat sink, and wherein step (b) comprises applying hydrostatic pressure sequentially to the first pressure cell, the second pressure cell, and one or more of the further pressure cells such that any two barocaloric materials are out of phase with each other in their respective heating and cooling cycles.

8. The method of any one of claims 1 to 7, wherein the applied hydrostatic pressure is at most 1.0 GPa, such as at most 0.5 GPa, such as at most 0.2 GPa, such as at most0.1 GPa.

9. The method of any one of claims 1 to 8, wherein the applied hydrostatic pressure is at least 0.1 MPa, such as at least 0.5 mPa, such as at least 5.0 MPa.

10. The method of any one of claims 1 to 9, wherein in step (b) the first barocaloric material is out of phase with the second barocaloric material in their respective heating and cooling cycles by 10° to 180°, such as from 90° to 180°, such as from 120° to 180°.

11. A modular cooling or heating apparatus, comprising: a first pressure cell comprising a vessel containing a first barocaloric material, a first set of heat-exchangers for connecting the first pressure cell to a heat source and a heat sink; a second pressure cell comprising a vessel containing a second barocaloric material;008844177a second set of heat-exchangers for connecting the second pressure cell to the heat source and the heat sink, wherein each pressure cell further comprises a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material, and wherein each pressure cell further comprises a flexible housing between the vessel and the barocaloric material and separating the barocaloric material from the pressure-transmitting medium, wherein the flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material; and a hydrostatic pressuriser for pressurising and depressurising the first pressure cell out of phase with the second pressure cell, such that in use for cooling or heating, the first barocaloric material is partially or fully pressurised when the second barocaloric material is partially or fully depressurised.

12. The method or apparatus of any of claims 1 to 11 , wherein the first and second barocaloric materials are the same.

13. The method or apparatus of any of claims 1 to 11 , wherein the first and second barocaloric materials are different, such as where the first and second barocaloric materials each have a phase transition at different transition temperatures.

14. The apparatus of any of claims 11 to 13, comprising: one or more further pressure cells each comprising a vessel containing a barocaloric material, wherein each further pressure cell is provided with a respective set of heat-exchangers for connection to the heat source and the heat sink; and wherein the hydrostatic pressuriser is for pressurising and depressurising each further pressure cell, such that in use for cooling or heating, the barocaloric materials in a first group of pressure cells are partially or fully pressurised when the barocaloric materials in a second group of cells within the apparatus are partially or fully depressurised.

15. The apparatus of claim 14, wherein the hydrostatic pressuriser is for pressurising and depressurising each further pressure cell, such that in use for cooling or heating, the barocaloric material in one or more further cells is out of phase with the first and second barocaloric materials in their respective heating and cooling cycles, and optionally wherein in use, any two barocaloric materials are out of phase with each other in their respective heating and cooling cycles.

16. A modular cooling or heating apparatus, comprising: a first pressure cell comprising a vessel containing a first barocaloric material, wherein the first barocaloric material is capable of releasing heat upon pressurisation;008844177a first set of heat-exchangers for connecting the first pressure cell to a heat source and a heat sink; a second pressure cell comprising a vessel containing a second barocaloric material, wherein the second barocaloric material is capable of absorbing heat upon pressurisation; a second set of heat-exchangers for connecting the second pressure cell to the heat source and the heat sink; and a hydrostatic pressuriser for pressurising and depressurising the first and second pressure cells, wherein each pressure cell further comprises a pressure-transmitting medium for transmitting hydrostatic pressure to the barocaloric material, and wherein each pressure cell further comprises a flexible housing between the vessel and the barocaloric material and separating the barocaloric material from the pressure-transmitting medium, wherein the flexible housing is capable of expansion and compression to allow changes in the pressure of the pressure-transmitting medium to be transmitted to the barocaloric material.

17. The method or apparatus according to any one of claims 1 to 16, comprising a thermally insulating material, wherein the flexible housing is the thermally insulating material.

18. The method or apparatus according to any one of claims 1 to 17, wherein the flexible housing comprises deformable corrugations or wrinkles.

19. The method of apparatus according to any one of claims 1 to 18, wherein the pressure cells and heat-exchange fluid are controlled independently.

20. The method or apparatus according to any one of claims 1 to 19, wherein one or more heat-exchangers are partially embedded within and in thermal contact with the barocaloric material, wherein the heat-exchanger comprises a heat-exchange fluid capable of being circulated to the heat source or the heat sink, such that in use, heat is extracted from or supplied to the barocaloric material during pressurisation or depressurisation of the pressure cell.

21. The method or apparatus of claim 20, wherein the heat-exchange fluid comprises water.

22. The method or apparatus of any one of claims 1 to 21 , wherein at least one of the pressure cells is thermally connected to one or more further pressure cells arranged in series to provide a cascade of pressure cells, wherein each further pressure cell comprises a vessel containing a barocaloric material, such that in use during heating or cooling, the energy released upon pressurisation or depressurisation of a first pressure cell in the cascade is used for heating or cooling an adjacent pressure cell, such as wherein the first008844177pressure cell is thermally connected to a first series of further pressure cells, and / or wherein the second pressure cell is thermally connected to a second series of further pressure cells.

23. The method or apparatus of claim 22, wherein in use during cooling or heating, the first and / or second pressure cell is in anti-phase with an adjacent further pressure cell in their respective heating and cooling cycles.

24. The method or apparatus of any of claims 1 to 23, wherein each pressure cell further comprises a thermally insulating material between the vessel and the barocaloric material.

25. The apparatus of any one of claims 11 to 24, further comprising a heat recovery means to transfer the energy released upon depressurisation or pressurisation of a pressure cell to another part of the apparatus, or external to the apparatus.

26. Use of a modular cooling or heating apparatus according to any one of claims 11 to 25, for cooling or heating.008844177

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