TECHNICAL FIELD

[0001] The present disclosure relates to the field of energy storage and in particular to Thermo Energy Storage (TES) using a Phase Change Material (PCM). The PCM storage arrangement disclosed herein may find application e.g. at systems for heating buildings, such as residential, industrial and storage buildings.

BACKGROUND

[0002] There is often a need of storing energy. Efficient energy storage may e.g. importantly decrease the overall energy consumption of heating systems for buildings. This has over the years become increasingly important both from an environmental and an economical point of view.

[0003] By using energy storage, energy availability and demand which vary over time may be balanced thereby to decrease the overall energy consumption. For example at buildings and other applications, the heating system may be provided with a TES system for storing heat energy during periods when the externally available energy is higher than the demand and releasing heat energy at periods when the demand is higher than the availability. At heating systems comprising solar, air or ground energy harvesting means for supplying external energy, the fluctuations between energy availability and demand typically occurs over day and night and/or over a year.

[0004] Known TES system may comprise phase change materials (PCM) for the energy storage. A PCM is material that stores or releases a large amount of energy during a change in state, or "phase", e.g. crystallization (solidifying) or melting (liquefying) at a specific temperature. The amount of energy stored or released by a material during crystallization or melting, respectively, is the latent heat of that material. During such phase changes, the temperature of the material remains relatively constant. This is in contrast to the "sensible" heat, which does result in a temperature change of the material, but not a phase change.

[0005] PCMs are therefore "latent" thermal storage materials. A transfer of energy occurs when the material undergoes a phase change, e.g. from a liquid to a solid and thus helps to maintain the temperature of a system. When heat is supplied to the system in which the temperature is at the melting point of the PCM, energy will be stored by the PCM, resulting in a mediating effect on the temperature of the system. Similarly, when the temperature of the system decreases to the crystallization temperature of the PCM, the energy stored by the PCM will be released into the surrounding environment. The amount of energy stored or released by a material is a constant and is that material's latent heat value. For example, water has a latent heat of 333 J/g. Therefore, a gram of water will release 333 J of energy to its surrounding environment during crystallization (freezing), at 0° C. without changing temperature. Similarly, a gram of frozen water will absorb 333 J of energy from its surrounding environment during melting without an increase in temperature from o° C.

[0006] At previously known TES systems, water in a bore hole or a well of a ground source heat pump system may be used as a PCM for the energy storage. At other known examples, water used as a PCM is stored in a separate tank or in an elastic bladder.

[0007] US2017/0254601 Al discloses a TES system comprising encapsulated

PCMs and a heat transfer medium. At an application where the TES system is used at a building, the system comprises a solar plate collector, a building piping system for heating the building, a tank comprising encapsulated PCM and a conduit arrangement for circulating a heat transfer medium. During daytime, the heat transfer medium is circulated between the solar plate collector and the PCM tank for melting i.e. charging the PCM. During night-time, the heat transfer medium is instead circulated between the PCM tank and the piping system for freezing, i.e. discharging the PCM and heating the building.

SUMMARY

[0008] An object of the present disclosure is to provide an enhanced PCM thermal energy storage arrangement.

[0009] Another object is to provide such an arrangement which may readily be used at various buildings and other constructions.

[0010] A further object is to provide such an arrangement which is reliable in use and has a long service life.

[0011] Yet another object is to provide such an arrangement which exhibits a high energy efficiency. [0012] Another object is to provide such an arrangement which is environmentally friendly.

[0013] Still an object is to provide such an arrangement which requires low maintenance.

[0014] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0015] The term “tire derived aggregate” and its abbreviation “TDA” is used to signify a bulk material made of recycled tires, which have been shredded into pieces of varying sizes and geometries.

[0016] The term “container” is used to signify any type of enclosure or containment which, preferably sealingly, encloses the TDA material and the PCM. Examples of such containers are bags, pouches, bladders, tanks, boxes and barrels

[0017] According to a first aspect, the present disclosure provides a phase change energy storage arrangement as set out in appended claim 1. The phase change thermal energy storage arrangement comprises; a container holding a phase change material, which container is sealed from the surroundings and a conduit arranged to conduct a heat absorbing medium, which conduit comprises a heat transfer portion arranged in the container. A tyre derivate aggregate (TDA) material is embedded in the phase change material in said container.

[0018] The container being sealed from the surroundings holds the phase change material and the TDA enclosed in the container such that there is no flow of phase change material or TDA into or out from the container. By this means leakage of PCM and TDA material from the container as well as intrusion of foreign material is effectively prevented. By using a TDA embedded in the PCM in the container, a number of advantages are provided. Firstly, TDA has load carrying capacities. By this means the energy storage arrangement may be arranged in the ground beneath a building or other heavy construction such as under the building having a heating system to which the energy storage arrangement is connected. The load carrying capacity of the TDA then allows for that the walls of container need no load carrying capacity and especially that the container walls may be made flexible. Also at such non load carrying containers, the energy storage arrangement may be installed in the ground and the building constructed on top without any additional load carrying or reinforcing constructions. The energy storage arrangement may thus be applied in a space saving manner at low cost.

[0019] Secondly, TDA has elastic properties which allows for that that the expansion of the PCM occurring at phase transition to the solid or crystalline phase may be absorbed by the TDA particles without affecting the overall volume of the PCM-TDA-bed in the container. By this means, the volume of the container may be minimized to thereby minimize the space requirements.

[0020] Thirdly, the TDA embedded in the PCM provides a fixation function to the heat transfer portion of the conduit for conducting the heat absorbing media through the PCM-TDA-bed in the container. By this means the conduit is reliably held in position in the container whereby excessive movements causing wear or fatigue of the conduit is reduced.

[0021] Additionally, the TDA has heat insulating capabilities which insulate the PCM and the heat transferring portion of the conduit from the surroundings. This allows for high energy efficiency during charging, storing and discharging as well as reduces or eliminates the need of arranging additional insulating material inside or around the container.

[0022] The use of TDA material further positively contributes to the preservation of the environment and counteracts climate change. The TDA usage fulfils all three aspects of the so called “Three R Environmental Concept”; Reduce, Reuse and Recycle. Burying TDA material in the ground, e.g. under or in proximity to a building where the energy storage system is used, constitutes an efficient means of carbon capture and storage. Instead of burning the used tyres from which the TDA material is formed, using the TDA material in the energy storage arrangement effectively reduces the CO2 and other emissions otherwise caused by burning. Since the energy storage arrangement may have an expected service life of up to 100 years, this amounts to an important contribution to the preservation of the environment. [0023] Utilizing TDA embedded in the PCM such that a PCM-TDA-bed is held in the container thus provides for that the heat energy storage arrangement may be applied in a space and energy efficient manner while allowing easy installation at low cost in an environmentally friendly manner.

[0024] According to an embodiment of said first aspect, the phase change material may comprise water, preferably at least 90 % by weight. The comparatively high latent heat of water makes it suitable for energy storage. Additionally, the freezing temperature of water is o°C which makes it suitable to use as a PCM at many applications involving heating of residential and other buildings.

[0025] The water comprised in the PCM may be deionized. By this means rancidation or other deterioration of the water may be effectively prevented or reduced

[0026] According to further aspects, the porosity of said TDA material may be 50 - 80 %, preferably 60 - 70 %. Such porosity enhances the TDA’s ability to absorb expansion of the PCM when it freezes.

[0027] The mean size of the TDA particles may be 20 - 125 mm. Using TDA particles with sizes varying within this range improves the load carrying capacity and from stability of the TDA. These capacities may be enhanced further by compacting the TDA material before use.

[0028] The TDA material may be Type A TDA according to ASTM D6270 - 17.

[0029] The container may comprise at least one wall formed of a flexible sheet material.

[0030] The container may also comprise or constitute a flexible bag. By this means the container may adapt its shape to the from of the recess or cavity in the ground where it is installed. Thereby after-filling of ground material outside the container during installation may be omitted while still maintaining a high load carrying capacity after installation. Forming the container as a flexible bag also reduces the risk of piercing and other damages to the container caused by movements in the surrounding ground during and after installation.

[0031] The heat transfer portion of the conduit may be arranged as a cylindrical spiral in the container. This allows for that the heat transfer portion exhibits a large heat transferring area inside the container, to thereby enhance the total energy transfer between the heat absorbing medium and the PCM.

[0032] The phase change material may further comprise an additive for lowering the freezing point of the phase change material. This maybe favourable at some applications where it is desirable that the phase transition heat transfer occurs at some specific lower temperatures.

[0033] The porous TDA material may entirely fill the interior volume of the container. Hereby the load carrying capacity of the TDA material and the energy storage arrangement is enhanced.

[0034] The phase change material may, when in liquid form, reach up to 70-90%, preferably 80-85% of the vertical height of the container. This further enhances the ability of the energy storage arrangement to absorb expansion of the PCM at freezing without affecting the form of the container.

[0035] At one embodiment, the phase change thermal energy storage arrangement further comprises an energy harvesting device, a heat dissipating utility arrangement and conduit coupling means, wherein the conduit and the conduit coupling means are arranged to circulate the heat absorbing media selectively between the container and the energy harvesting device and/or between the container and the heat dissipating utility arrangement.

[0036] The energy harvesting device may comprise a solar thermal collector optionally combined with a photovoltaic device to form a hybrid solar thermal and electric power harvesting device.

[0037] The heat dissipating utility arrangement may comprise a heat pump, such as a liquid-to-liquid heat pump.

[0038] Further objects, advantages and aspects appear from the following detailed description and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawing (Fig. 1), which is a schematic cross section through a phase change thermal energy storage arrangement according to an embodiment. DETAILED DESCRIPTION

[0040] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

[0041] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0042] Fig. 1 schematically illustrates an embodiment of a phase change thermal energy storage arrangement 20 when applied to a building 4 provided with a heating system 10. The heating system 10 comprises an energy harvesting device in the form of a solar thermal collector 2 arranged at the roof of a building 4 to be heated and a heat dissipating utility arrangement comprising a liquid-to-liquid heat pump 6 and a radiator 8 connected to the heat pump 6 by means of a piping 9 for circulating water between the heat pump 6 and the radiator 8.

[0043] The phase change thermal energy storage system 20 comprises a container 22 holding a phase change material (PCM) 24. In the shown example the PCM is deionized water. The exemplifying PCM thus has a freezing temperature of o °C. The container 22 is sealed from the surroundings and formed of a flexible bag made of EPDM sheeting. The container 22 has a cuboid shape and is buried in the ground under the building. The container further holds a tyre derivate (TDA) material 26 which is embedded in the PCM to form a PCM-TDA-bed. Optionally, a thermally insulating layer of TDA material may be arranged below and/or above the container 22. In such cases the same TDA material may preferably be used inside and outside the container.

[0044] In the shown example, the TDA is a TDA denominated CLR LF-001, provided by Wieder Tech incorporated association. The TDA comprises vulcanised cross-linked rubber with steel and textile reinforcements obtained by shredding styrene butadien rubber (SBR) tires. The TDA has further been cleaned for eliminating small loose particles and any zinc oxide present after the shredding process. The particle size of the cleaned TDA is 20 - 125 mm, the non-compacted porosity is 65-67 % and the bulk density is approx. 360 kg / m3.

[0045] The porous TDA material 26 fills the entire interior volume of the container 22 such that it may carry the load of the building without any substantial compression or other deformation. For this purpose, the recess formed in the ground has the same volume as the flexible container the TDA material. Preferably the TDA material may be compacted, e.g. by vibration compaction during installation. When the PCM is in liquid form it occupies approx. 80% of the void space between the TDA particles in the container, such that the surface level of the PCM reaches up to approx. 80% of the height of the container.

[0046] The PCM TES arrangement further comprises a conduit 28 for conducting a heat absorbing medium. The conduit comprises a heat transfer portion 28a which is arranged in the container 22 for transferring heat through the conduit wall between the PCM and the heat absorbing medium. The conduit 28 further comprises a connection portion 28b for connecting the PCM-TES arrangement to the heating system 10. In the shown example, the connection portion 28b is connected to the heat pump 6. The heating system 10 further comprises a branch-off conduit 12 for circulating the heat absorbing medium through the solar thermal collector 2, circulating pumps 14, 16 and a closable non-return valve 18. The conduits 12, 28, the pumps 14, 16 and the valve 18 are arranged such that the heat absorbing medium, by opening the valve 18, may be circulated only between the heat pump 6 and the container 22. By closing the valve 18, the heat absorbing medium is circulated from the heat pump 6, through first the solar thermal collector 2, and thereafter through the container 22 back to the heat pump 6. Additionally, when the valve 18 is open, the pumps 14, 16 may be controlled such that a portion of the medium flow from the heat pump 6 is directed directly to the container 22 while an adjustable portion of the flow is branched off through the solar thermal collector 2 before it joins the flow directed through the container 22.

[0047] The heat transfer portion 28a of the conduit 28 is arranged inside the container and is formed as a cylindrical spiral extending vertically over the height of the container which is filled with PCM when in liquid form. The heat transfer portion 28a is embedded in the TDA material such that it is held in place by contacting the TDA particles 26 while being surrounded by the PCM 24. [0048] In use the PCM thermal energy storage arrangement 20 and the heating system 10 are operated in different modes depending on the relation between the available heat energy provided by the solar thermal collector 2 and the heat dissipated from the radiator 8 in reply to the demand in the building.

[0049] At periods when the energy provided by the solar thermal collector is higher than the demand, the system is operated in a storage charging mode where the valve is closed such that the entire heat absorbing medium flow is circulated from the heat pump 6 through the solar thermal collector 2 and therefrom through the container 22 back to the heat pump 6. Heat absorbed by the medium in the solar thermal collector is then transported to the container where at least a portion of the heat is transferred to the PCM. At instances where the PCM is originally frozen, typically at least in the vicinity to the heat transfer portion 28a, the heat transferred to the PCM then initially melts the PCM. Continuous operation of the system in charging mode then heats the PCM to temperatures above its freezing temperature. Typically, the PCM may be heated to an average temperature of approx. 20 °C.

[0050] At periods when the demand is higher that the available energy provided by the solar thermal collector 2, the system is operated in a discharge mode. At such instances the branch-off conduit 12 may be cut off or portion of the flow from the heat pump may be branched-off through the solar thermal collector 2. In any case, the temperature of the heat absorbing medium at such instances is lower than the temperature of the PCM such that the heat absorbing medium when passing through the heat transfer portion 28a in the container absorbs heat from the PCM. The so heated medium then delivers heat energy to the heat pump 6 where it contributes to heat the water in the piping 9 for being dissipated to the building through the radiator 8. At continuous operation in the discharge mode, the temperature of the PCM will gradually decrease until it reaches its freezing temperature. During the following phase transition of the PCM a comparatively high energy amount is absorbed by the medium and transported to the heat pump.

[0051] During the phase transition from liquid to crystalline form, the PCM expands and this expansion is absorbed by compression of the TDA particles. Typically, the water containing PCM first forms ice on the outer surface of the heat transferring portion 28a of the conduit 28. The ice formation then gradually grows radially out from the heat transferring portion 28a. Since ice has a comparatively high thermal conductivity heat transfer from the PCM to the heat absorbing medium continues also when ice has formed around the heat transfer portion 28a.

EXAMPLE

[0052] At the schematic exemplifying embodiment illustrated in fig. 1 and described above the parameters listed in Table 1 imay apply. In the example the energy storage system is installed under a single-family house of approx. 100 m ² , which house is located in southern Scandinavia.

Table 1

[0053] It has proven that a energy storage capacity of 2 000 kWh well suffices for providing sufficient heating energy to the heating system during periods over the year when the energy provided from the solar thermal collector is lower than the heat energy demand of such houses.

[0054] The aspects of the present disclosure have mainly been described above with reference to a few embodiments and examples thereof. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.