A THERMAL STORAGE SYSTEM AND TEMPERATURE CONTROLLED CONTAINER COMPRISING THE SAME

Abstract

Passive thermal storage systems and methods comprising at least one thermal storage module for storing thermal energy in a predetermined temperature range, are disclosed. The thermal storage module comprises an FT unit and a Heat Storage (HS) unit at least partially filled with a first Phase Change Material (PCM). The HS unit comprises a container. The thermal storage module may be in the form of a stacked structure comprising the FT unit having a first wall with a first heat exchange surface and the HS unit having a second wall with a second heat exchange surface, the first and second heat exchange surfaces being in thermal contact with each other. The thermal storage system may be used to maintain the temperature of the payload of a temperature controlled container at a predetermined value or within a predetermined range.

Description

TECHNICAL FIELD

The present invention relates to a thermal storage system arranged for storing thermal energy, which is for example suitable for maintaining a payload space at a predetermined temperature. The present invention further relates to a temperature controlled container comprising a thermal storage system according to the present invention.

BACKGROUND ART

Phase change materials (PCM) are substances that absorb and release thermal energy during the phase change. When a PCM freezes, it releases a large amount of energy in the form of latent heat at a relatively constant temperature. Conversely, when such material melts, it absorbs a large amount of heat for instance from the environment. As thermal energy carrier, PCMs are ideal for a variety of everyday applications that require temperature control. The most commonly used PCM is water/ice. Ice is an excellent PCM for maintaining temperatures at 0° C. But water's freezing point is fixed at about 0° C. (32° F.), which makes it unsuitable for thermal energy storage applications at other temperature levels. To address that limitation, PCMs have been developed for use across a broad range of temperatures, from −40° C. to more than 150° C. In contrast to water, many PCMs do not change phase at a single temperature but they change phase over a temperature range of some degrees Celsius. For instance a PCM with a peak phase change temperature of −21° C. may already start freezing at −14° C. and is completely frozen at −26° C. The phase change temperature, which is commonly reported on the data sheet of the PCM, is the peak temperature at which the highest amount of latent heat is released or absorbed. PCMs typically store 5 to 14 times more heat per unit volume than materials such as water, masonry or rock. Among various heat storage options, PCMs are particularly attractive because they offer high-density energy storage and store heat within a narrow temperature range.

PCMs have been used for the development of thermal storage systems, which can be used for maintaining a payload space at a predetermined temperature or in a predetermined temperature range for an extended period of time, without the need for using an external power supply. For example, such thermal storage systems have been used in the development of passive refrigerator units used for transporting temperature sensitive products that need to be maintained at a predetermined temperature for an extended period of time without the need of connection to an external power supply. WO2014178015 discloses an apparatus for preserving refrigerated or frozen products, particularly for thermally insulated compartments of refrigeration vehicles, refrigeration chambers or the like. The apparatus of WO2014178015 is provided with heat accumulation elements filled with a heat accumulation liquid, which is a PCM material. Each of the heat accumulation elements are provided with a heat exchanger element that can be supplied with a heat exchange fluid and that is submerged in the PCM. According to WO2014178015, the heat exchange element is immersed in the heat accumulation fluid. The heat exchanger element is arranged for charging and discharging the heat accumulation element by pumping through the heat exchanger element a heat exchange fluid. More specifically, the heat exchange fluid is a single phase refrigerant in the form of a liquid or gas arranged to be pumped in and out of the heat exchange element by means of an external system until the heat accumulation fluid is charged or discharged. Once the charging or discharging process is completed, the passive refrigerator unit is disconnected from the external system and the heat transfer fluid is removed from the heat exchanger elements.

DE102013221918A1, EP1236960A1, DE19907250A1 and U.S. Pat. No. 6,094,933A describe temperature controlled containers that include a thermal storage system with PCM material. The thermal storage system however is coupled with an active thermal system requiring an external power supply. The thermal system comprises a heat pump, employing the well-known refrigeration-type cycle, while in use moving thermal energy in the opposite direction of spontaneous heat flow and in order to perform that work it requires an external power supply, the thermal storage system allowing to change the performance of the thermal system.

DISCLOSURE OF THE INVENTION

It is an aim of the present invention to provide a thermal storage system, which is suitable for storing thermal energy at a predetermined temperature or temperature range and which can be used for example to maintain a payload space of a temperature controlled container at a predetermined temperature or temperature range for a certain period of time.

According to the present invention the term “charging” of the PCM material refers to the process of storing thermal energy in the form of “heat” or “cold” in the PCM material.

According to the present invention the term “discharging” of the PCM material refers to the process of thermal energy being released from the PCM material.

According to the invention the term “phase change temperature” of the PCM refers to the phase change temperature, which is for example commonly reported on the data sheet of the PCM, which is the peak temperature at which the highest amount of latent heat is released or absorbed. In case there is no temperature range at which the phase change occurs but only a single phase change temperature, such as for example with water when going from liquid to solid at 0° C., the single phase change temperature corresponds to the peak temperature.

This aim is achieved according to the invention with the thermal storage system showing the technical characteristics of the characterising part of the first claim.

According to a first aspect of the present invention a thermal storage system is provided, which is suitable for storing thermal energy at a predetermined temperature or temperature range. The thermal storage system is provided with at least one thermal storage module, which comprises at least one Fluid Transporting (FT) unit and at least one Heat Storage (HS) unit filled with a first Phase Change Material (PCM). The FT unit may be provided with a wall having a heat exchange surface. The at least one FT unit is provided with at least one passageway arranged for receiving a heat transfer fluid, at least one inlet port for the inflow of the heat transfer fluid to the passageway and at least one outlet port for the outflow of the heat transfer fluid from the passageway. The inlet and outlet ports of the at least one fluid transporting unit are arranged for being releasably connected to a heat transfer fluid system, such as a chiller or a boiler, which heat transfer fluid system is arranged for supplying or releasing the heat transfer fluid from the at least one fluid transporting unit passageway via the inlet and outlet ports. The at least one HS unit is filled with a first Phase Change Material (PCM), the first PCM being arranged for exchanging thermal energy by at least partially changing from a first phase to a second phase. The first PCM of the HS unit is arranged for being in thermal contact with the heat transfer fluid of the at least one FT unit such that thermal energy can be transferred between the at least one FT unit and the at least one HS unit so that the first PCM of the HS unit can change from the first to the second phase at a first predetermined phase change temperature.

According to embodiments of the present invention the at least one FT unit comprises the heat transfer fluid, the heat transfer fluid having a predetermined inlet temperature such that there is a non-zero temperature difference between the inlet temperature of the heat transfer fluid in the FT unit and the phase change temperature of the first PCM in the HS unit allowing heat transfer between the heat transfer fluid and first PCM. The heat transfer fluid may be a pumpable single phase fluid or a pumpable multi phase fluid of which at least one substance changes phase during heat transfer. Examples of such a pumpable multi phase fluid of which at least one component changes phase during heat transfer is a solid/liquid slurry or a vapour/liquid refrigerant. A solid/liquid slurry, for instance an ice slurry or a PCM slurry, is preferred due to the lower pressures compared to liquid/vapour fluids. When disconnecting the at least one FT unit from the heat transfer fluid system, the heat transfer fluid can be removed from the FT unit or the heat transfer fluid can at least partially remain in the passageway of the at least one FT unit.

It has been found that by providing the at least one FT unit with a heat transfer fluid, which is maintained in the passageway of the at least one FT unit upon disconnection of the heat transfer fluid system, a larger thermal energy density is obtained compared to the systems of the prior art. The thermal energy density is the amount of thermal energy stored in the thermal storage system per unit of volume of the thermal storage system. In the case where the heat transfer fluid is a multi phase fluid of which at least one substance changes phase during heat transfer the thermal energy density may be significantly higher due to the latent contribution during phase change of the heat transfer fluid, which is not available when using a single phase heat transfer fluid which only has a sensible heat contribution. Moreover, the heat transfer coefficient of a multi phase fluid of which at least one substance changes phase during heat transfer may also be significantly higher than the heat transfer coefficient of a single phase fluid. This may significantly increase the faster transfer of thermal energy between the first FT and HS unit, even when for example the heat transfer fluid is not maintained in the passageway of the at least one FT unit upon disconnection of the heat transfer fluid system.

According to embodiments of the present invention, the FT unit may be provided with a first wall having a first heat exchange surface and the HS unit may be provided with a second wall having a second heat exchange surface, the first and second heat exchange surfaces being in thermal contact with each other. For example, the thermal storage system may be in the form of a stacked structure, wherein the first and second walls of respectively the FT and HS unit are in thermal contact with each other. In this way, thermal energy can be exchanged between the first PCM of the HS unit and the heat transfer fluid of the FT unit. According to embodiments of the present invention, the first and second heat exchange surfaces of respectively the FT and HS unit may be in thermal contact with one another via a common wall. According to embodiments of the present invention the HS unit may be a closed volume container at least partially filled with the first PCM. For example, the HS unit may be a container with at least one opening to fill the container with PCM. After at least partially filling the container with PCM the at least one filling opening is sealed resulting in a closed volume container. Furthermore, the first and second heat exchange surfaces may be on an outer side of respectively the first and second walls of the FT and HS unit. For example, the HS unit and the FT unit may be placed on top of one another such that their respective outer heat exchanging surfaces are in thermal contact. Such a configuration has been found to allow an easier assembly of the different units into the module. Moreover, the use of a common wall allows improving the thermal contact between the HS unit and the FT unit.

According to embodiments of the present invention, the thermal storage module may be in the form of a stacked structure comprising at least two HS units, each being in thermal contact with the a respective heat exchange surface of the FT unit. The two HS units may contain a different PCM having a different phase change temperature.

According to embodiments of the present invention, the stacked structure may be provided with a plurality of alternating layers of the HS unit and the FT unit. Different HS units may contain different PCMs. By providing a stacked structure with alternating layers of HS units and the FT units the thermal energy that can be stored in the thermal storage system may significantly increase. By keeping the HS units thin, the PCM in each HS unit can rapidly be at least partially charged or discharged. The PCM charging or discharging process can further be accelerated by adding heat conducting elements to the HS unit. If at least two FT units are present in the thermal energy system their inlet and outlet ports are connected to each other realizing a certain flow path.

According to embodiments of the present invention, the HS unit and/or the FT unit may in the form of a beam like structure, such as a panel, having a predetermined shape. For example, the FT unit and/or the HS unit may be in the form of a beam like panel having a rectangular shape.

According to embodiments of the present invention the HS unit and/or the FT unit may be provided with at least one undulated heat exchange surface e.g. an outer heat exchange surface. The undulations may increase the available heat transfer surface and further increase the mechanical strength of the thermal storage module.

According to embodiments of the present invention the PCM in the HS panel may have a thickness of less than 40 mm, measured from the heat exchange surface in contact with the FT unit. For example, the HS panel may have a thickness between 1 mm and 40 mm, preferably 5 mm and 20 mm. This limited thickness of the PCM ensures a fast charging or discharging and further reduces the overall size of the thermal storage unit.

According to embodiments of the present invention, the at least one FT unit comprises an extruded profile comprising at least one passageway for the heat transfer fluid. In this way, the heat transfer fluid can efficiently be circulated in the at least one FT unit so as to reduce the time required for charging the first PCM material. The FT unit may be provided with a plurality of passageways, thereby defining a plurality of flow paths for the heat transfer fluid.

According to embodiments of the present invention, the thermal storage module comprises an extruded profile comprising the at least one passageway for the heat transferring fluid in the at least one FT unit and at least part of the at least one HS unit. Such an extruded profile provides a high mechanical strength to the thermal storage module.

According to embodiments of the present invention, the HS unit is provided with a plurality of heat conducting elements arranged for being in contact with the first PCM material. The heat conducting elements may be further in contact with at least one inner surface of the HS unit. By providing heat conducting elements a faster transfer of thermal energy can be realized from the heat transfer fluid in the FT unit to the PCM in the HS unit. In this way, the PCM is charged or discharged faster and more efficient.

According to embodiments of the present invention, the heat conducting elements may be made from a heat conducting material. For example the heat conducting elements can made of a metal having good thermal conduction properties e.g. aluminium. In this way, the thermal energy can be quickly transferred from the outer surface to the first PCM material and vice versa, thereby allowing for a faster response to a temperature change.

According to embodiments of the present invention, the heat conducting elements are in the form of a porous structure having a predetermined porosity. The volumetric porosity of this porous structure may be between 75% and 98%, preferably between 88% and 95% with respect to the volume of the porous structure. It has been found that by providing a highly porous structure the volume taken by this structure otherwise lost to add PCM is limited. For example, the porous structure is made of metal foam. Structures like metal foam allow thermal energy to be distributed more efficiently throughout the first PCM material making it possible to use the volume of the PCM material more efficiently and thus make it possible to more efficiently use the HS unit by making more use of the possibility of more efficiently transporting the thermal energy inside the first PCM material and not only of the contact surface of the HS unit. The metal foam has a surface-to-volume ratio (SVR) ranging from 300 m²/m³ to 1500 m²/m³ measured using a micro computed tomography scanning technique. The metal foam has an average cell diameter of 10 mm or smaller measured using a micro computed tomography scanning technique.

According to embodiments of the present invention, the thermal storage system may be provided with at least two thermal storage modules connected to each other via the inlet and outlet ports of their respective FT units. Furthermore, a connecting element may be provided for connecting the input and output points of each thermal storage module so as to provide a thermal storage system of a predetermined shape, e.g. by connecting two thermal storage modules at a 90 degree orientation a thermal storage system having an L-shape may be provided. It should be understood that other thermal storage configurations are possible, e.g. by connecting three thermal storage units in a 90 degree orientation a U-shaped thermal storage system may be provided. In this way different configurations of the thermal storage system may be provided, thereby allowing for the thermal storage system to be used in a variety of applications, for instance as walls of a temperature controlled container.

According to preferred embodiments of the present invention, the thermal storage system is passive. Although the thermal storage system could also be active, as opposed to passive. Passive thermal storage systems are while in use not coupled with an active thermal system and external power supply. The external power supply in active thermal storage systems usually comprise a heat pump, for example employing the well-known refrigeration-type cycle, while in use moving thermal energy in the opposite direction of spontaneous heat flow and, in order to perform that work, require an external power supply. As such the thermal storage system can continuously be charged or discharged during use. Passive thermal storage systems on the other hand while in use, i.e. for maintaining a payload space at a predetermined temperature or in a predetermined temperature range, while in use preferably do not require an external power supply moving thermal energy in the opposite direction of spontaneous heat flow. For example, such thermal storage systems can be used in the development of passive temperature controlled container units used for transporting, usually in a temperature insulated payload space, temperature sensitive products that need to be maintained at a predetermined temperature for an extended period of time without the need of connection to such external power supply. As these passive thermal storage systems cannot be charged while in use, they need to be charged before usage, and therefore require to be connected releasably to a heat transfer system. In order to optimise the logistics process this charging needs to be fast and reliable, moreover, the capacity over volume/mass ratio of the thermal storage system needs to be as high as possible.

According to embodiments of the present invention, the inlet port and/or outlet port, which are arranged for being releasably connected to the heat transfer fluid system, are in the form of a male/female connector. Such connectors have been found to allow a relatively easy way of releasably connecting the connector to the heat transfer fluid system.

According to a second aspect of the present invention a method is provided for charging the first PCM material of the at least one thermal storage system. The method comprises the following steps:

a) providing a heat transfer fluid system, such as a chiller, e.g. a liquid ice production chiller, or a boiler, with or without a reservoir for the heat transfer fluid;

b) connecting the heat transfer fluid system to the inlet and outlet ports of the thermal storage system forming a closed circuit for the heat transfer fluid;

c) operating the heat transfer fluid system such that the heat transfer fluid is supplied to the at least one FT unit passageway via the inlet ports of the at least one FT unit;

d) operating the heat transfer fluid system such that the heat transfer fluid supplied in step c) is released from the at least one FT unit passageways via the outlet ports of the at least one FT unit;

e) charging of the first PCM during a certain period of time during which the PCM at least partially changes phase depending on the desired energy content;

f) removing the heat transfer fluid from the passageways or keeping the heat transfer fluid at least partially in the passageways of the FT units of the thermal storage system before, during or after disconnecting the thermal storage system from the heat transfer fluid system.

According to embodiments of the present invention, the heat transfer fluid system comprises a hydraulic circuit arranged for supplying the heat transfer fluid to and releasing the heat transfer fluid from the thermal storage system. For example, the heat transfer fluid system may be an external system to which the thermal storage system may be connected, such as a chiller or a boiler. The heat transfer fluid system may comprise at least one reservoir for storing the heat transfer fluid pumped in and out of the at least one fluid transportation unit. The hydraulic circuit may comprise a pump arranged for pumping the heat transfer fluid in an out of the at least one fluid transportation unit. The pump may be configured for pumping the heat transfer fluid at a predetermined speed or flow rate.

According to a third aspect of the present invention a temperature controlled container may be provided, which may be arranged for maintaining a payload space at a predetermined temperature or in a predetermined temperature range. The temperature controlled container may be provided with a thermally insulated payload space arranged for receiving temperature sensitive products. Furthermore, a thermal storage system according to any one of the embodiments above may be positioned at a predetermined location in the thermally insulated payload space. The temperature controlled container may be mobile. According to preferred embodiments of the present invention, the unit of the FT unit and the HS unit having a temperature which is closest to the ambient temperature in which the temperature controlled container is kept, is put closest to the outside of the container. It has been found that such configuration limits the heat losses to the ambient environment in which the container is kept.

According to yet a third aspect of the present invention a method for providing a temperature controlled container is provided, the method comprising the steps of:

a) providing a container unit having a thermally insulating payload space arranged for receiving temperature sensitive products;

b) providing at a predetermined location in the payload space at least one thermal storage system according embodiments of the first aspect of the present invention, the thermal storage system being arranged for maintaining the payload space at a predetermined temperature or in a predetermined temperature range for a predetermined amount of time;

c) releasably connecting the inlet and outlet ports of the thermal storage system to a heat transfer fluid system, the heat transfer fluid system being arranged for forming a closed circuit with the at least one FT unit of the thermal storage system allowing circulation of the heat transfer fluid;

d) at least partially charging or discharging the first PCM material of the at least one thermal storage module according to the method for charging the thermal storage system;

f) removing the heat transfer fluid from the passageways or keeping at least partially the heat transfer fluid in the passageways of the FT units of the thermal storage system before, during or after disconnecting the thermal storage system from the heat transfer fluid system.

Then the temperature of the payload volume of the temperature controlled container remains within a predetermined temperature range for a certain period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further elucidated by means of the following description and the appended figures.

FIGS. 1 to 3 show three-dimensional views of an FT unit according to embodiments of the present invention.

FIG. 4 shows a cross-sectional view of a first exemplified thermal storage system according to embodiments of the present invention.

FIGS. 5 to 6 show side views of a second exemplified thermal storage system according to embodiments of the present invention.

FIGS. 7 to 8 show exemplified perspective views of a thermal storage system with separate FT and HS units according to embodiments of the present invention.

FIGS. 9 to 14 show exemplified perspective views of a thermal storage system comprising an extruded profile according to embodiments of the present invention.

FIGS. 15 to 17 shows exemplified embodiments of a thermal storage system having a stacked configuration.

FIG. 18 show a cross-sectional view of an exemplified thermal storage system having an L-shape according to embodiments of the present invention

FIGS. 19 to 22 show cross-sectional views of an exemplified temperature controlled container unit according to embodiments of the present inventions.

MODES FOR CARRYING OUT THE INVENTION

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the invention described herein can operate in other orientations than described or illustrated herein.

The term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

The present invention will be elucidated by means of the example embodiments shown in FIGS. 1 to 22, which will be described in more details below.

FIGS. 1 to 3 show an exemplified Fluid Transportation unit (FT) 10 according to embodiments of the present invention. The FT unit 10 is provided with an inlet port 12a and an outlet port 12b which may be in on the same side, as shown in FIG. 1, or on opposing sides, as shown in FIG. 2 or 3. The FT unit 10 is provided with at least one passageway 11 for circulating a heat transfer fluid between the inlet port 12a and the outlet port 12b. As shown in FIG. 2, the FT unit 10 may be provided with a plurality of passageways 11, which may be interconnected so as to allow the heat transfer fluid to be circulated between the inlet port 12a and the outlet port 12b. Furthermore, the FT unit 10 may be provided with a plurality of passageways, each connected to a separate inlet port 12a and outlet port 12b. The heat transfer fluid in the FT unit 10 may be circulated in the passageways 11 in the direction indicated by the arrows, but other flow direction are possible by providing different passageway configurations. The FT unit 10 may be provided with an extruded profile defining at least one passageway via which the heat transfer fluid may be circulated between the inlet and outlet ports 12a and 12b.

FIG. 4 shows a cross-sectional view of an exemplified thermal storage system 100 according to embodiments of the present invention. The thermal storage system 100 may be provided with a thermal storage module 20, which may comprise at least one FT unit 10 having at least one wall 15 with a heat exchange surface. The at least one FT unit 10 may be provided with at least one passageway arranged for circulating a heat transfer fluid, the flow of which is indicated by the arrows, between the inlet port 12a and the outlet port 12b. The inlet port 12a and outlet port 12b of the at least one FT unit 10 may be arranged for being releasably connected to a heat transfer fluid system 40, such as a chiller or a boiler, which is arranged for supplying or releasing the heat transfer fluid from the at least one FT unit 10 via the inlet and outlet ports 12a and 12b. The heat transfer fluid system 40 may comprise a docking station allowing a more easy connection of the thermal storage module to the supply of heat transfer fluid. The thermal storage module 10 may further be provided with at least one Heat Storage (HS) unit 13, which may be filled with a first Phase Change Material (PCM) 14, the first PCM 14 being arranged for exchanging thermal energy, for example as latent heat, while at least partially changing from a first phase to a second phase. The first PCM 14 of the HS unit 13 may be arranged for being in thermal contact, via the wall 15 provided with a heat exchange surface, with the heat transfer fluid circulating in the at least one FT unit 10 such that thermal energy can be transferred between the heat transfer fluid and the first PCM 14. The transferred thermal energy may then be stored in the first PCM 14, for example during the transition of the first PCM 14 between a first phase and a second phase, e.g. between solid and liquid or gas and liquid and vice versa. As shown in FIG. 4, the FT unit 10 may be provided with a wall 15 having a heat exchange surface, which may be in direct contact with the first PCM of the HS unit 13. This for example may be achieved by providing a thermal storage module 20 whereby the FT unit 10 inside the HS unit 13 such that the wall 15 of the FT unit 10 may be provided in direct contact with the first PCM 14.

According to embodiments of the present invention, the thermal storage module 20 may be provided in the form of a stacked structure, with the FT unit 10 and HS unit 13 having different dimensions, as shown in FIG. 5, or identical dimensions, as shown in FIG. 6. For example, the thermal storage module 20 may be provided in the form of a stacked structure by providing the FT unit 10 and HS unit 13 as separate units, as shown in FIG. 7. In this configuration, the separate FT and HS units 10 and 13 can be positioned on top of one another such that their respective thermal contact surfaces may be provided in thermal contact, as shown in FIG. 8. Alternatively, the thermal storage module 20 may be provide din the form of a stacked structure by extruding the FT unit 10 and the HS unit 13 as a single profile unit. For example, the extruded profile unit may be provided with openings defining the FT unit 10 passageways 11, a common wall shared between the FT unit 10 and the HS unit 13, and a number of ribs 18 defining a space 19 for positioning the first PCM of the HS unit 13, which may be covered by a plate 21, as shown in FIG. 10 In this configuration, thermal energy is transferred between the heat exchange surfaces of respectively the FT unit 10 and the HS unit 13 via the common wall. The extruded profile for the FT unit 10 and HS unit 13 may be dimensioned according to the requirements of the thermal storage module 20. For example, an extruded profile provided with two spaces 19 for positioning the first PCM may be provided, as shown in FIGS. 9 and 10. Even larger extruded profiles may be provided having a plurality of spaces 19 for positioning the first PCM or a material for holding the first PCM, and a plurality of passageways 11, as shown in FIGS. 13 and 14. The FT unit 10 may be dimensioned such that it is smaller than or substantially equal to the HS unit 13 dimensions. Furthermore, it should be understood that the FT unit 10 may be provided with larger dimensions than the HS unit 13.

According to embodiments of the present invention, the heat transfer fluid may be a pumpable multi phase fluid comprising at least one substance which changes phase while circulated through the FT unit 10. The multi phase heat transfer fluid may be a two-phase fluid arranged for changing between a solid phase and a liquid phase, which may be circulated between he inlet and outlet ports, which offers the advantages of higher heat transfer coefficient, thus faster charge/discharge, and a more constant temperature during heat transfer resulting in a better thermal matching between the temperature profiles of the heat transfer fluid and the first PCM 14. For example, the multi-phase heat transfer fluid may be a liquid with solid particles which change phase during heat transfer. This can be PCM slurry or an ice slurry. Furthermore, a portion of the heat transfer fluid circulated between the inlet an outlet ports 12a and 12b may remain in the passageways 11 upon disconnecting the thermal storage system from the heat transfer fluid system.

According to embodiments of the present invention the HS unit 13 may be provided in the form of a container having at least one wall with a heat exchange surface, e.g. a closed volume container. The HS unit 13 may be further provided with a filing port, which is not shown, which can be used for filling or extracting or replenishing or replacing the first PCM 14 of the HS unit according to the needs of the thermal storage module 20.

According to embodiments of the present invention, the thermal storage module 20 may be provided in the form of a stacked structure provided with a number of HS units 13 in thermal contact with at least one FT unit 10. For example, as shown in FIG. 15, the thermal storage module 20 may be provided with an FT unit 10 sandwiched between two HS units 13 such that their respective walls 15 and 16 are in contact with one another, thereby ensuring that thermal energy can be transferred between their respective heat exchange surfaces. As previously described the FT and HS units may be in the form of separate units, similar to the ones in FIG. 7, or in the form of an extruded profile, as explained with reference to FIGS. 9 to 14.

As shown in FIG. 7, the passageways of a rectangular cross-section. Such a cross-section has been found to provide an improved usage of the available space as the usage of the material to make up the passageways can be decreased and the volume of the fluid going through the passageways can be increased, further improving the energy density.

According to embodiments of the present invention, the thermal storage module 20 may be provided with a plurality of alternating layers of HS units 13 and the FT units 10 so as to increase the thermal energy storage. For example, as shown in FIG. 16, the thermal storage module 20 may be provided with three HS units 13 and two FT units 10 sandwiched in between the HS units 13 such that their respective heat exchange surfaces are in thermal contact with one another. Furthermore, in the case where the thermal storage module 20 is in the form of an extruded profile, the stacked structure may be realised by positioning a plurality of extruded profiles on top of one another as shown in FIG. 17.

According to embodiments of the present invention, the at least one HS unit 13 may be provided on the inside of the closed volume container with a plurality of heat conducting elements arranged for being at least partially in contact with the first PCM 14. For example, the heat conducting elements, may be made of a metal having predetermined heat conduction properties so that the thermal energy can be more efficiently exchanged between the heat exchange surface of the HS unit 13 and the first PCM 14. For example, the heat conducting elements may be made from aluminium or another suitable metal with good heat conducting properties. The heat conducting elements may be in the form of a porous structure having a predetermine porosity and which is at least partially submerged in the first PCM 14. The porous structure may be in the form of an open cell porous structure, which may have a volumetric porosity between 75% and 98%, preferably between 88% and 95% with respect to the volume of the porous structure.8. For example, the porous structure may be made from metal foam, which may have a surface-to-volume ratio (SVR) ranging from 300 m²/m³-1500 m²/m and an average cell diameter of less than 10 mm. For example, the metal foam may be provided in the form of slabs, which can be fitted in the spaces 19 provided between the ribs 18 of the thermal storage module 20 extruded profile.

According to embodiments of the present invention, the HS unit 13 and/or FT unit 10 may be provided with a substantially beam like shape with the height being significantly smaller than the width and length. For example, the HS unit 13 and/or FT unit 10 may be provided in the form of substantially rectangular panels. According to embodiments of the present invention the HS unit 13 and/or FT unit 10 may be provided with a height between 1 mm and 40 mm. The height direction 22 along which the height can be measured is for example shown in FIG. 15. It should be understood that the FT unit 10 and the HS unit 13 may be provided with different shapes depending on the requirement of the thermal storage system 100. Furthermore, the walls of the HS unit 13 and/or the FT unit may have a predetermine shape. For example, the HS unit walls 16 and/or the FT unit walls 15 may have an undulated form.

According to embodiments of the present invention, the thermal storage system 100 may be provided with a plurality of thermal storage modules 20. For example, the thermal storage system 100 may be provided with a first and a second thermal storage modules 20 which may be connected to one another via their respective inlet and outlet ports 12a and 12b, thereby forming a continuous structure having a predetermined shape, as shown in FIG. 8. A connecting element 17 may be provided for connecting the inlet and outlet ports 12a and 12b of adjacent thermal storage modules 20, as shown in FIG. 8. According to embodiments of the present invention, the connector 17 may be used for connecting a plurality of thermal storage modules 20 in a variety of shape configuration to match the needs of the payload space. For example, the connector 17 may be used to connect the thermal storage units 20 in a 90 degrees orientation, thereby providing a thermal storage system having a U-shape, an L-shape, etc. depending on the number of thermal storage modules 20 connected to one another. Furthermore, the connector 17 may be used to connect several thermal storage modules in a substantially flat configuration. The connector 17 and the corresponding inlet and outlet ports 12a and 12b can for example be in the form of cooperating male/female connectors. The connecting elements 17 can be part of a docking station.

According to embodiments of the present invention, the thermal storage system 100 may be used in a variety of applications. For example, the thermal storage system 100 may be used for storing excess “heat” or “cold” energy from a boiler or chiller which can be used at a later time when there is a heating or cooling demand. The heat or cold stored in the thermal storage system can also be used to maintain a payload space of a temperature controlled container unit 30, as shown in FIGS. 19 to 22, at a predetermined temperature or within a predetermined temperature range For example, the thermal storage system 100 may be positioned at an inner wall of a temperature controlled container 30 provided with a payload space arranged for receiving temperature sensitive goods. For example, as shown in FIG. 19 the thermal storage system 100 may be positioned, without any limitation with regards to the positioning of the thermal storage unit in the payload space, at a top inner wall of the temperature controlled container unit 30. The temperature controlled container unit 30 may be provided with a container unit connector 34, which is in contact with the inlet and outlet ports 12a and 12b of the thermal storage system 100. The temperature controlled container unit 30 may be provided with an insulated layer 32 for insulating the payload space 35. The container unit connector 34 may be arranged for releasably connecting the thermal storage unit inlet and outlet ports 12a and 12b to a heat transfer fluid system 40. The heat transfer fluid system 40 may be arranged for circulating the heat transfer fluid through the at least one FT unit 10 of the thermal storage system 100 via the at least one inlet and outlet ports 12a and 12b, so as to charge or discharge the PCM 14 of the at least one HS unit 13, as shown in FIG. 20. In the case where the thermal storage unit is provided with HS units 13 having different PCMs, the heat transfer fluid may be circulated until all PCMs are charged/discharged. For example, the heat transfer system may be provide with a hydraulic system, which may comprise a pump, arranged for pumping and releasing the heat transfer fluid from the thermal storage system 100. The heat transfer fluid system 40 may be provided with a connector 41, which may connected to the container unit connector 34 via pipes 42 and 43. In this way, the heat transfer fluid is circulated in the thermal storage system 100 so as to charge the first PCM material of the thermal storage modules 20. Once the charging process is completed the heat transfer fluid system 40 is disconnected from the connector 34, and the heat transfer fluid is at least partially maintained in the at least one passageways of the at least one FT unit 10. According to embodiments of the present invention, the thermal storage system 100 may be provided in a number of different configurations. For example, as shown in FIG. 21, the thermal storage system 100 may provided in an L-shape so as to cover two of the inner walls of the temperature controlled container. Furthermore, the thermal storage system 100 may be provided at a suitable shape to cover three walls of the container, such as U-shape, or all of the walls of the temperature controlled container 30, as shown in FIG. 22.

According to embodiments of the present invention, a method for charging the first PCM material of the at least one thermal storage system of the present invention may be provided. The method may comprise the steps of:

• • a) providing a heat transfer fluid system, such as a chiller, e.g. a liquid ice production chiller, or a boiler, with or without a reservoir for the heat transfer fluid;

b) connecting the heat transfer fluid system to the inlet and outlet ports of the thermal storage system forming a closed circuit for the heat transfer fluid;

c) operating the heat transfer fluid system such that the heat transfer fluid is supplied to the at least one FT unit passageway via the inlet ports of the at least one FT unit;

d) operating the heat transfer fluid system such that the heat transfer fluid supplied in step c) is released from the at least one FT unit passageways via the outlet ports of the at least one FT unit;

e) charging of the first PCM during a certain period of time during which the PCM at least partially changes phase depending on the desired energy content;

f) removing the heat transfer fluid from the passageways or keeping the heat transfer fluid at least partially in the passageways of the FT units of the thermal storage system before, during or after disconnecting the thermal storage system from the heat transfer fluid system.

Claims

1. A passive thermal storage system for storing thermal energy in a predetermined temperature range, the thermal storage system comprising at least one thermal storage module comprising:

a fluid transporting (FT) unit comprising: a passageway configured for circulating a heat transfer fluid therethrough; and an inlet port for the inflow of the heat transfer fluid to the passageway and the outlet port for the outflow of the heat transfer fluid from the passageway, wherein the inlet port and an outlet port of the FT unit are releasably connectable to a heat transfer fluid system, the heat transfer fluid system being configured for circulating the heat transfer fluid through the FT unit of the thermal storage system via the inlet and outlet ports; and a first Heat Storage (HS) unit at least partially filled with a first Phase Change Material (PCM), wherein the first HS unit comprises a container at least partially filled with the first PCM material; wherein the thermal storage module is in the form of a stacked structure comprising the FT unit having a first wall with a first heat exchange surface, and the first HS unit having a second wall with a second heat exchange surface, the first and second heat exchange surfaces being in thermal contact with each other such that thermal energy can be transferred between the heat transfer fluid in the FT unit and the first PCM in the first HS unit so that the first PCM of the first HS unit can at least partially change phase in the predetermined temperature range.

2. The thermal storage system according to claim 1, wherein the heat transfer fluid is a pumpable single phase fluid.

3. The thermal storage system according to claim 1, wherein the heat transfer fluid is a pumpable multi phase fluid.

4. A passive thermal storage system for storing thermal energy in a predetermined temperature range, the thermal storage system comprising a thermal storage module comprising:

a fluid transporting (FT) unit (10) comprising: a passageway configured for circulating a heat transfer fluid therethrough; and an inlet port for the inflow of the heat transfer fluid to the passageway and an outlet port for the outflow of the heat transfer fluid from the passageway; wherein the inlet port and the outlet port of the FT unit are releasably connectable to a heat transfer fluid system, the heat transfer fluid system being configured for circulating the heat transfer fluid through the FT unit of the thermal storage system via the inlet and outlet ports; and a Heat Storage (HS) unit at least partially filled with a first Phase Change Material (PCM); wherein the first PCM of the HS unit is configured for being in thermal contact with the heat transfer fluid of the FT unit such that thermal energy can be transferred between the heat transfer fluid in the FT unit and the first PCM in the HS unit so that the first PCM of the HS unit can at least partially change phase in the predetermined temperature range; wherein the heat transfer fluid is a pumpable multi phase fluid comprising a substance which changes phase while circulated through the FT unit.

5. The passive thermal storage system according to claim 3, wherein the multi phase heat transfer fluid is a two-phase fluid configured for changing between a solid phase and a liquid phase.

6. The thermal storage system according to claim 5, wherein the multi phase heat transfer fluid is in the form of an ice slurry.

7. The thermal storage system according to claim 3, wherein the multi phase heat transfer fluid is a second PCM.

8. The thermal storage system according to claim 7, wherein the second PCM has a phase changing temperature range different from the predetermined temperature range.

9. The thermal storage system according to claim 1, wherein the heat transfer fluid remains within the FT unit upon disconnecting the thermal storage system from the heat transfer fluid system.

10. The thermal storage system, according to claim 4, wherein the thermal storage module is in the form of a stacked structure comprising the FT unit having a first wall with a first heat exchange surface and the HS unit having a second wall with a second heat exchange surface, the first and second heat exchange surfaces being in thermal contact with each other.

11. The thermal storage system according to claim 1, wherein the first and second walls are substantially the same.

12. The thermal storage system according to claim 1, wherein the stacked structure comprises a second HS unit, the first HS unit being in thermal contact with the first wall of the FT unit, the second HS unit being in thermal contact with a second wall of the FT unit.

13. The thermal storage system according to claim 12, wherein the stacked structure comprises a plurality of alternating layers of the first HS unit and the FT unit being in thermal contact with each other.

14. The thermal storage system according to claim 1, wherein the first HS unit is a closed volume container.

15. The thermal storage system according to claim 1, wherein the first HS unit comprises a plurality of heat conducting elements configured for being in thermal contact with the first PCM material.

16. The thermal storage system according to claim 15, wherein each of the plurality of heat conducting elements are in the form of a porous structure having a predetermined porosity and are at least partially submerged in the first PCM.

17. The thermal storage system according to claim 16, wherein the porous structure is an open cell porous structure.

18. The thermal storage system according to claim 16, wherein a volumetric porosity of the porous structure is between 75% and 98%.

19. The thermal storage system according to claim 16, wherein the porous structure is a metal foam.

20. The thermal storage system according to claim 19, wherein the metal foam has a surface-to-volume ratio (SVR) between 300 m2/m3 and 1500 m2/m3.

21. The thermal storage system according to claim 19, wherein the metal foam has an average cell diameter of less than 10 mm.

22. The thermal storage system according to claim 1, wherein at least one of the first HS unit and the FT unit has a substantially beam like shape with a height being significantly smaller than a width and a length.

23. The thermal storage system according to claim 22, wherein at least one of the first HS unit and the FT units have a height between 1 mm and 40 mm.

24. The thermal storage system according to claim 4, wherein the FT unit comprises an extruded profile comprising the passageway for the heat transferring fluid.

25. The thermal storage system according to claim 4, wherein the thermal storage module comprises an extruded profile comprising the passageway for the heat transferring fluid.

26. The thermal storage system according to claim 4, wherein the thermal storage system comprises a second FT unit connected to the first FT unit via the inlet and outlet port ports.

27. The thermal storage system according to claim 26, further comprising a second thermal storage module comprising a second inlet port and a second outlet port, and a connecting element on the thermal storage module configured form at least part of a connection between the inlet port and the second inlet port.

28. The thermal storage system according to claim 26, wherein the thermal storage system has an L-shape or a U-shape.

29. A method for charging the first PCM of the thermal storage system according to claim 1, the method comprising the steps of:

a) providing a heat transfer fluid system, such as a chiller or a boiler;

b) connecting the heat transfer fluid system to the inlet and outlet ports of the thermal storage system to form a closed circuit for the heat transfer fluid;

c) operating the heat transfer fluid system such that the heat transfer fluid is supplied to the passageway of the FT unit via the inlet port of the FT unit;

d) operating the heat transfer fluid system such that the heat transfer fluid supplied in step c) is released from the passageways of the FT unit via the outlet port of the FT unit;

e) charging of the first PCM for a time period during which the PCM at least partially changes phase; and

f) removing at least some of the heat transfer fluid from the passageway of the FT unit before, during or after disconnecting the thermal storage system from the heat transfer fluid system.

30. The method for charging the first PCM according to claim 29, wherein the heat transfer fluid system comprises a hydraulic circuit configured to circulate the heat transfer fluid through the FT unit of the thermal storage system.

31. The method for charging the first PCM according to claim 30, wherein the hydraulic circuit comprises a pump.

32. A temperature controlled container unit comprising:

a thermally insulated payload space arranged for receiving temperature sensitive products; and

at least one thermal storage system according to claim 1, positioned in the thermally insulated payload space.

33. The temperature controlled container unit according to claim 32, wherein the temperature controlled container unit is mobile.