WO2016147106A1

WO2016147106A1 - Active insulation panel

Info

Publication number: WO2016147106A1
Application number: PCT/IB2016/051441
Authority: WO
Inventors: Jacques De Ruyck
Original assignee: Integrate Bvba
Priority date: 2015-03-13
Filing date: 2016-03-14
Publication date: 2016-09-22
Also published as: BE1022871A1; BE1022871B1

Abstract

Multilayered panel (10), comprising thermally conductive layers (11, 12) on opposite sides (101, 102) of the panel, with, in between, an inner layer (13) made from a thermally insulating material and several members (15) made from a thermally conductive material, extending transversely through the inner layer (13), with the members having a cross section with a total surface area (nS _cond) connected in series with several thermoelectric elements (16), characterised in that the ratio between the total surface area (nS _cond) of the cross sections of the members (15) and the surface area of the panel is at least five times the ratio between the thermal conduction coefficient (λ_ins) of the thermally insulating material and the thermal conduction coefficient (λ_cond) of the thermally conductive material of the members (15).

Description

ACTIVE INSULATION PANEL

[0001] The present invention relates to a multilayered panel having an insulating inner core, comprising thermoelectric elements to improve the insulating properties of the panel. Such panels are referred to as active insulation panels.

[0002] Such panels are known from JP 2004-21 1916, which, in Fig.

12, shows an insulation panel with opposite heat-transferring surfaces and a thermally insulating core layer in between. Through the thermally insulating core layer, a Peltier element is provided which is thermally connected in series with a coupling material, which together bridge the distance between the two heat- transferring surfaces.

[0003] Other, more or less similar construction elements are described in NL 1000729 and WO 2010/029217.

[0004] By applying a voltage difference to such thermoelectric elements, such as for example Peltier elements, a temperature difference between the opposite sides of the element is created, as a result of which it becomes possible to collect heat losses through the insulation and feed them via the thermoelectric element back to the source. It is thus potentially possible to improve the insulating properties of the panel. However, it is known that the efficiency of thermoelectric elements with regard to the heat transfer/required electrical power ratio (COP, coefficient of performance) is poor, as a result of which such active insulation panels are expensive in terms of usage costs and thus of no interest from an economic point of view.

[0005] It is an aim of the present invention to provide active insulation panels of the abovementioned kind which have an improved energy efficiency and are consequently more interesting from an economic point of view.

[0006] Thus, according to a first aspect of the invention, a multilayered panel is provided, as set out in the appended claims.

[0007] Multilayered panels according to aspects of the invention comprise a first thermally conductive layer and a second thermally conductive layer, provided on opposite sides of the panel, and an inner layer which is made from a thermally insulating material and arranged between the first thermally conductive layer and the second thermally conductive layer. The panels furthermore comprise several members made from a thermally conductive material and arranged between the first thermally conductive layer and the second thermally conductive layer, extending transversely through the inner layer, wherein the members have a cross section with a total surface (nScond), and several thermoelectric elements, arranged between the first layer and the members. This arrangement is such that a thermal bridge is advantageously formed between, on the one hand, the thermoelectric elements, the members and the second thermally conductive layer and, on the other hand, the thermoelectric elements and the first thermally conductive layer.

[0008] According to aspects of the invention, the ratio between the total surface area (nScond) of the cross sections of the members and the surface area of the panel is at least five times, advantageously 6.66 times, advantageously 10 times the ratio between the thermal conduction coefficient (Ains) of the thermally insulating material of the inner layer and the thermal conduction coefficient (A_COnd) of the thermally conductive material of the members. If these conditions are taken into account when designing a panel, the result is that, on the one hand, it is ensured that all heat lost through the panel can be returned through the members and, on the other hand, it is ensured that the temperature difference across the thermoelectric elements is limited. As a result, the thermoelectric elements can be operated under optimum conditions, so that a high efficiency is achieved.

[0009] According to a second aspect of the invention, an assembly of a multilayered panel according to the first aspect and a control unit for this multilayered panel, as set out in the appended claims, is provided.

[0010] According to a third aspect of the invention, a method for controlling or activating the multilayered panel according to the first aspect and/or of the assembly according to the second aspect, as set out in the appended claims, is provided.

[001 1 ] Aspects of the invention will be described in more detail below with reference to the following figures. [0012] Figure 1 shows an exploded view of a panel according to an aspect of the invention.

[0013] Figure 2 shows a cross section of the panel of Fig. 1 .

[0014] Figure 3 shows a cross section of a panel according to a further aspect of the invention.

[0015] Figure 4 shows a cross section of a panel according to a further aspect of the invention.

[0016] In the present description, reference is made to a thermal conduction coefficient λ. The value thereof is assumed at a temperature of 293 K.

[0017] With reference to Fig. 1 , a panel 10 according to aspects of the invention is composed of several layers. Thermally conductive layers 1 1 ,12 are provided on the two outer faces (front side 101 and rear side 102, respectively) of the panel 10. These thermally conductive layers preferably extend across the entire panel surface and are arranged at a distance from one another.

[0018] As will become clear below, the front side 101 of the panel refers to the side which faces the warmer of the two environments which are separated by the panel. If the panel is used to separate a relatively warm interior space from a relatively cold environment, the panel will be installed in such a way that the front side 101 faces the interior space (inner side) and the rear side 102 faces the environment. If, however, the panel is used to separate a relatively cold interior space from a relatively warm environment, the front side 101 will face the relatively warm environment (outer side).

[0019] A thermally insulating layer 13 extends between the two thermally conductive layers 1 1 , 12. This thermally insulating layer 13 preferably bridges the distance between the two thermally conductive layers 1 1 ,12. The multilayered panel 10 thus assumes the shape of a sandwich panel, in which a thermally insulating core layer 13 is arranged between two thermally conductive layers 1 1 , 12.

[0020] Preferably, the core layer 13 is crossed in several locations by a number of heat-returning elements 14, which have the function of feeding the heat which is lost through the core layer 13 back. The heat-returning elements 14 preferably bridge the entire distance between the thermally conductive layers 1 1 and 12, and thus preferably have the same thickness as the core layer 13.

[0021] Each of these heat-returning elements 14 comprises a thermally conductive member, e.g. in the form of a bar 15, which is thermally connected in series with a thermoelectric element 16. At one end 151 , bar 15 is thermally coupled to thermally conductive layer 12, and preferably extends from layer 12 in the direction of layer 1 1 . Thermoelectric element 16 is preferably provided at the opposite end 152 of bar 15 and is thermally coupled thereto. Preferably, the thermoelectric element 16 bridges the distance between bar 15 and layer 1 1 .

[0022] Thermoelectric element 16 is preferably a Peltier element.

Thermoelectric element 16 extends between a first side 161 , called cold side, and a second opposite side 162, called warm side. By applying an electrical voltage to the thermoelectric element 16, a thermoelectric effect is produced between the cold side 161 and the warm side 162. In this case, heat is extracted from the cold side 161 and supplied to the warm side 162. The thermoelectric effect is generally known, and thermoelectric elements which can be applied in panels according to the invention are also known.

[0023] Preferably, thermoelectric element 16 is arranged in the panel 10 in such a way that the cold side 161 is thermally coupled to bar 15 whereas the warm side 162 is thermally coupled to layer 1 1 . Due to the fact that bar 15 is thermally coupled to layer 12 at end 151 , it is possible for the heat present in layer 12 to be passed through bar 15 and emitted to the cold side 161 of the thermoelectric element 16. By applying an electrical voltage, the thermoelectric element 16 can transfer the heat from the cold side 161 to the warm side 162 and beyond to layer 1 1 .

[0024] Bar 15 may be an element with a preferably high thermal conductivity, e.g. a so-called "heat pipe", made from a completely closed tube which is filled with a working fluid, which, in use, occurs in the tube both in a liquid phase and in a gas phase. Alternatively, bar 15 may optionally be solid and made from a thermally conductive material, preferably a metal, e.g. aluminium or copper. Bar 15 may possibly be coated by a thermally insulating shell, such as e.g. a vacuum tube, or a material different from the material of core layer 13 (except at ends 151 , 152). The cross section of bar 15 may have any desired shape, e.g. round, polygonal or rectangular.

[0025] As mentioned above, layer 1 1 will always be turned towards the warmer of the two environments which are separated by the panel. The heat which is then lost through insulating layer 13 from layer 1 1 to layer 12, can be recovered in this way via bar 15 and thermoelectric element 16. Layer 12 which preferably extends across the entire panel surface serves to be able to absorb all heat losses through insulating layer 13. The thickness and the material of layer 12 are preferably chosen such that the temperature of this layer is as uniform as possible across the layer. Similarly, layer 1 1 serves to be able to emit the recovered heat as well as possible to the interior space. The thickness and the material of layer 1 1 are preferably selected in such a manner that an even temperature can be maintained across this layer.

[0026] The inventors found that two factors are important to achieve an efficient and thus economical operation of such active insulation panels. Firstly, it has to be ensured that all heat which is lost through insulating layer 13 can be returned via bars 15. This means that a temperature difference has to be maintained between the ends 151 and 152 of the bars 15. In this case, it has to be noted that the heat flux through the bar will be proportional to this temperature difference. Secondly, it is important to be able to use the thermoelectric elements 16 as efficiently as possible. For this reason, the temperature difference between the cold side 161 and the warm side 162 of these elements must not be excessively high. After all, it is known that the thermoelectric elements can operate at a higher COP at small temperature differences.

[0027] The inventors have succeeded in coming up with a design for an active insulation panel which reconciles these two apparently contradictory aspects. In this case, the bars 15 have to meet a requirement regarding their minimum cross section, which is based on the choice of material for the panel. According to an aspect of the invention, the ratio between the cross sections of all bars 15 and the surface of the panel is at least five times, preferably at least 6.66 times, preferably at least 10 times the ratio between the thermal conduction coefficient of the material of core layer 13 and the thermal conduction coefficient of the material of the bars 15. If a panel 10 is designed with these requirements in mind, the result is a panel which ensures, on the one hand, that any lost heat can be returned through the bars 15 and, on the other hand, that the temperature difference across the thermoelectric elements is limited to at most 120%, preferably at most 1 15%, preferably at most 1 10% of the temperature difference across the panel 10 (i.e. the temperature difference between layers 1 1 and 12). Obviously, if the core layer 13 and/or the bars 15 are made from several materials, e.g. are of a layered design, an equivalent thermal conduction coefficient has to be used.

[0028] This condition can be derived in the following manner.

[0029] The heat flux Q_loss which is lost through the insulating core layer 13 can be determined as follows:

Qloss - ^T^ins ^T¹ 0 )

in which AT is the temperature difference between layer 1 1 and layer 12, Ai_ns is the thermal conduction coefficient of the material of the core layer 13, Sins and dins are the surface area and the thickness of the core layer 13, respectively. For the sake of simplicity, the surface area Sins of core layer 13 is assumed to be equal to the surface area Spanei of the panel 10. This results in a small overestimation of the heat losses:

Qloss - Τλ_ίη5 JS sL (2) uins

As previously indicated, according to an aspect of the invention, it is a condition that the heat losses through the insulating core layer 13 are at least compensated by the heat which is pumped through the thermoelectric elements 16. This leads to the following equation:

Qioss < nQ_TE (3) in which Q_TE is the heat flux which is pumped through a thermoelectric element 16, and n is the number of thermoelectric elements. In this case, it is assumed, for the sake of simplicity, that all thermoelectric elements are identical, although the invention is not limited thereto.

[0030] The heat flux which is pumped through a thermoelectric element 16 may depend on the properties of the chosen thermoelectric element (e.g. a Peltier element), the electrical power applied (voltage and electricity) and the temperature difference across the thermoelectric element. The COP of the thermoelectric element will increase at relatively low temperature differences across the thermoelectric element. According to an aspect of the invention, the temperature difference across the thermoelectric element is therefore limited to: AT_TE = (1 + χ)ΔΓ (4) in which ΔΤΤΕ is the temperature difference across the thermoelectric element (between cold side 161 and warm side 162). The temperature difference across the thermoelectric element 16 has to be greater than the temperature difference across the entire panel 10 by a fraction x. This is necessary in order to be able to generate a heat flux through the bars 15 which is caused by a temperature difference:

AT_cond = xAT (5) in which A Tcond is the temperature difference between the ends 151 and 152 of the bars 15.

[0031] The heat flux through a thermoelectric element 16 has to be transported through a bar 15:

Q_TE = xAT _cond -^S ^ (6) uins

in which A_COnd is the thermal conduction coefficient of the material of the bar 15 and Scond is the surface area of the cross section of the bar 15. For the sake of simplicity, it is assumed that the thickness of the thermoelectric element 16 is negligible compared to the thickness dins of the insulating core layer 13, so that the thickness of the bar 15 in equation (6) is assumed to be equal to the thickness of the core layer 13.

[0032] Combining equations (2), (3) and (6) results in:

Spanel ^x ^cond

The right-hand part of equation (7) denotes a lower limit for the ratio between the sum of the cross-sectional area of the bars 15 and the total panel surface. This lower limit turns out to be a dimensionless number and depends on the temperature difference to which the thermoelectric element is subjected, and on the material properties of the insulating core layer 13 and the bars 15.

[0033] The value for x is preferably 0.2, preferably 0.15, preferably

0.1 . The lower x is chosen to be, the higher the COP of the thermoelectric element will be. Of course, the choice of x also depends on the type of thermoelectric element which is chosen.

[0034] With nScond, equation (7) gives the total cross-sectional area of all bars 15 of the panel 10. Even though this equation (7) was derived based on the assumption of n identical bars and thermoelectric elements, it will be clear that the equation remains valid if the bars and thermoelectric elements are not all identical. In fact, equation (7) imposes a condition for the cross-sectional area of the total of the heat-returning elements 14 of the panel 10.

[0035] Equation (7) implicitly comprises the fact that all heat which is lost is returned through the bars 15 and the thermoelectric elements 16. This is ensured by requiring the bars to have a minimum cross section. This minimum cross section additionally ensures that the thermoelectric elements are used as efficiently as possible by limiting the temperature difference across them.

[0036] The insulating core layer 13 is preferably formed by a material having a thermal conduction coefficient Ai_ns which is 0.1 W/mK or less, preferably 0.08 W/mK or less, preferably 0.06 W/mK or less, preferably 0.05 W/mK or less. The material of insulating core layer 13 may, for example, be made of polyurethane, polystyrene, mineral wool, glass wool, cellular glass (Foamglass®) or other insulating materials which are customary in the building industry. The bars 15 and/or the thermally conductive layers 1 1 and 12 are preferably made from a material having a thermal conduction coefficient A_COnd which is at least 50 W/mK, preferably at least 100 W/mK, preferably at least 150 W/mK, preferably at least 200 W/mK. Bars 15 may, for example, be made from aluminium or copper.

[0037] For example, with a panel according to the invention in which the bars 15 are made from aluminium (λ = 209 W/mK) and core layer 13 is made from polyurethane foam (λ = 0.02 W/mK), the total cross-sectional area of all bars should be approximately 0.5 thousandths of the panel surface in order to limit the temperature difference across the thermoelectric elements to 120% of the temperature difference across the panel. For a 1 m² panel, this means that the total cross-sectional area of the bars has to be at least 5 cm². With a core layer made of mineral wool or cellular glass (λ = 0.04 W/mK), the total cross-sectional area of the bars has to be at least 10 cm² per square metre of panel surface. If, for example, nine evenly distributed heat-returning elements 14 are provided per square metre of panel surface, the bar of each heat-returning element advantageously has to have a cross section of at least 1 .1 cm².

[0038] Advantageously, the cross section of the bars of the heat- returning elements is chosen not to be too large, if not the thermally insulating properties of core layer 13 will be lost. Preferably, the ratio between the cross section of the bars and the panel surface is further limited by:

n^Scond ns ^

Spanel ^cond

whereby y = 1000, preferably y = 750, preferably y = 600, preferably y = 500, preferably y = 300, preferably y = 200, preferably y = 100, preferably y = 50. With reference to the above examples, condition (8) where y = 500, for example, amounts to a total cross-sectional area of the bars of at most 500 cm² per square metre of panel surface for the combination of aluminium/polyurethane foam, or at most 1000 cm² per square metre of panel surface for the combination of aluminium/mineral wool or cellular glass.

[0039] Advantageously, the heat transfer is improved further by bringing the cross section of the bars 15 and the surface of thermoelectric elements 16 in agreement with one another. Advantageously, the surface of the thermoelectric element 16 which corresponds to a bar 15 (and is thus thermally coupled thereto) is at least 70% of the cross-sectional area of this bar 15, preferably at least 80%, preferably at least 90%. Obviously, the thermoelectric element 16 may consist of several relatively small thermoelectric elements which are electrically connected to each other and which are all thermally coupled to one same bar 15.

[0040] The number of heat-returning elements 14 per unit area of panel is not limited. In order to ensure that the temperature on the two sides of the panel 10 is as uniform as possible, at least nine spaced-apart heat-returning elements 14 per m² of panel are advantageously provided, evenly distributed across this surface, advantageously at least twelve heat-returning elements per m² of panel.

[0041] The thermally conductive layers 1 1 and 12 on the outer faces of the panel 10 may have a constant thickness di and d2, respectively, as illustrated in Fig. 2. Advantageously, the thicknesses di and d2 are chosen such that a uniform temperature prevails across the surfaces of the layers 1 1 and 12. Of course, these thicknesses also depend on the heat-conducting properties of the material from which the layers are made. Advantageously, the thicknesses di and 02 are at least 0.5 mm, possibly at least 1 mm, possibly at least 1 .5 mm. The material from which the layers 1 1 and 12 are made may be identical. Alternatively, the layers 1 1 and 12 may be made from a different material.

[0042] With reference to Fig. 3, the thermally conductive outer layers of the panel may be of varying thickness. The panel 20 illustrated in Fig. 3 only differs from panel 10 by the shape of the outer layers. On the outer faces, being the front side 201 and rear side 202, panel 20 comprises a thermally conductive layer 21 and 22, respectively. At the location of the heat-returning elements 14, these layers 21 , 22 advantageously have a thickness d3, d₄ which is greater than the thickness ds, d6 of these layers between the heat-returning elements. For example, the outer faces (side 201 and 202, respectively) of layers 21 and 22 have a corrugated or ribbed profile with peaks of the waves or the ribs located at the location of the heat-returning elements 14 (bars 15 or thermoelectric elements 16). Such a profile advantageously makes it possible for the heat to spread as well as possible across the entire surface while at the same time limiting the amount of material and therefore the weight. Obviously, it is possible to provide merely one of the two layers 21 , 22 with such a corrugated profile instead of both.

[0043] The panels according to the invention may be constructed, for example, as is illustrated in Fig. 4. In panel 30, the thermally conductive bar 15 is attached to the thermally conductive layer 12 by means of a possibly thermally conductive screw 31 . On the opposite side, the bar 15 is connected to thermally conductive layer 1 1 , by means of a thermally insulating screw 32. The thermally insulating screw 32 may, for example, be made of nylon. This screw also ensures that the thermoelectric element 16 can be enclosed between the bar 15 and the layer 1 1 . As is illustrated in the figure, the screws 31 and 32 may be arranged eccentrically with respect to the axis of the bar 15. This makes it possible to arrange the thermoelectric element 16 next to the screw 32, which makes it possible to choose a thermoelectric element which has a simple shape, for example square, rectangular or disc-shaped. A thermally insulating supporting connection 33 may be provided opposite screw 32, with respect to thermoelectric element 16. As an alternative (not shown), a thermoelectric element may be provided which is arranged in an annular manner around screw 32. In addition, the interfaces 34 between the thermoelectric element 16 and layer 1 1 and bar 15 and between bar 15 and layer 12 may be provided with a thermally conductive adhesive connection. The construction of Fig. 4 makes it possible to attach the heat-conducting bars to the thermally conductive outer layers 1 1 , 12 and to the thermoelectric elements 16 before filling the intermediate space with an insulating core layer 13, for example by spraying. It should be noted that other ways of attachment are possible between the bars 15 and the layers 1 1 and 12, for example solely by gluing.

[0044] Figs 2 and 3 show that the thermoelectric elements 16 are electrically connected to each other, e.g. by placing them in an electrical circuit 17. Such an electrical connection may place the thermoelectric elements electrically in parallel, in series or in a combination of parallel and series connection. Advantageously, the thermoelectric elements 16 of the panel are placed electrically in series in the circuit 17. This reduces the amount of electrical cables required.

[0045] Advantageously, the power through the electrical circuit 17 is controlled by a control unit 18, as illustrated in Fig. 3. The same control unit 18 may also be placed in Fig. 2, but has not been shown for the sake of simplicity.

[0046] Control unit 18 may be configured to control the power in circuit 17 by controlling the voltage level. Alternatively, the electric current through circuit 17 may be controlled or a combination of both. The electrical power in circuit 17, and consequently supplied to the thermoelectric elements 16, is advantageously controlled on the basis of a temperature difference. This temperature difference may be a difference in temperature between the outer faces 101 and 102, or 201 and 202 of the panel 10, 20. An alternative possibility is to measure (or to determine) the difference in temperature between the cold side 161 and the warm side 162 of one or several thermoelectric elements 16. It is also possible to use the difference in temperature between, for example, the interior space which is delimited by the panel 10, 20 and the outside environment as temperature difference for the control unit. In other words, temperature probes may be provided at various locations and connected to the connection terminals 181 of the control unit 18.

[0047] Based on the measured temperature difference, the control unit 18 may be configured to determine a voltage level and/or a current level in the circuit 17. This may be achieved by means of a look up table which is provided in control unit 18, e.g. stored or programmed in a storage or memory medium of control unit 18. Such a table may, for example, comprise, for each temperature difference, a certain value for the voltage level and/or current level which advantageously corresponds to an operating state of the thermoelectric elements 16 which is as efficient as possible, in other words, corresponds to a COP which is as high as possible.

[0048] The control unit 18 may advantageously be programmed in such a manner that the electrical power in circuit 17 is controlled in such a manner that the temperature difference between the cold side 161 and the warm side 162 of one or several of the thermoelectric elements 16 is not more than 120% of the temperature difference between the outer faces of the panel, preferably not more than 1 15%, preferably not more than 1 10%. This result may be achieved, on the one hand, by an appropriate control of the electrical power in circuit 17 and, on the other hand, by the specific construction of the panel 10, 20, as described above, or by a combination of both.

[0049] Advantageously, the circuit 17 comprises means for measuring the electrical voltage across a thermoelectric element 16 separately, or across a (sub)group of thermoelectric elements separately. Additionally or alternatively, these means are configured to measure the electrical current through the thermoelectric element separately, or across a (sub)group of thermoelectric elements separately. The expression a group of thermoelectric elements is understood to mean several thermoelectric elements, the number of which is smaller than the total number of thermoelectric elements of the panel 10, 20. The panel comprises in such case several advantageously non-overlapping groups of thermoelectric elements. The groups can be distinguished by the way of switching in the electrical circuit 17, and/or by the way of configuring the means for measuring voltage and/or current. [0050] Advantageously, these means for measuring voltage and/or current are connected to the control unit 18, which is configured to control the voltage across or the current through a thermoelectric element or group separately on the basis of the measured values for voltage and/or current determined by the means. To this end, the control unit 18 may comprise one or more voltage regulators or current regulators. Advantageously, such a control arrangement takes into account the energy that has to be pumped, which can be determined on the basis of the above-described measurement of the temperature difference. In other words, the control unit 18 may be configured to control the electrical power which has been supplied to a thermoelectric element 16 or the electrical power supplied to different groups of thermoelectric elements separately, on the basis of the measurement of an advantageously local temperature difference and/or on the basis of the measurement of the electrical voltage across and/or the current through the thermoelectric element or the group of thermoelectric elements. By controlling the thermoelectric elements in groups or separately, the control unit can respond more efficiently to local temperature differences, resulting in greater efficiency.

[0051] The control unit 18 may also comprise additional operating states for the thermoelectric elements. For example, the thermoelectric elements 16 may also be used for actively heating or actively cooling an interior space. That is to say that the thermoelectric elements will be actuated in such a way that they will not only recover the lost heat or cold, but will produce additional heat or cold. For example, after a window in the interior space of a building has been open, the control unit 18 may actuate the thermoelectric elements 16 in such a way that they briefly generate additional heating or cooling.

[0052] The above description shows that panels can be used accordingly for both heat insulation (insulating an interior space with a view to keeping the interior space warmer than the environment), and for cold insulation (insulating an interior space with a view to keeping the interior space colder than the environment). However, installation of the panel differs between the two cases. In the case of heat insulation, the side on which the thermoelectric elements are provided (front side 101 , 201 or layer 1 1 , 21 ) faces the interior space, whereas this side faces the outside environment in the case of cold insulation.

Claims

1. Multilayered panel (10, 20, 30), comprising:

a first thermally conductive layer (1 1 , 21 ), provided on a first side (101 , 201 ) of the panel,

- a second thermally conductive layer (12, 22), provided on a second side (102, 202) of the panel, opposite the first side,

an inner layer (13), made from a thermally insulating material and arranged between the first layer (1 1 , 21 ) and the second layer (12, 22),

several members (15), made from a thermally conductive material and arranged between the first layer (1 1 , 21 ) and the second layer (12, 22), extending transversely through the inner layer (13), wherein the members have a cross section with a total surface area (nScond) and

several thermoelectric elements (16), arranged between the first layer (1 1 , 21 ) and the members (15), so that a thermal bridge is formed, on the one hand, between the thermoelectric elements, the members and the second thermally conductive layer and, on the other hand, between the thermoelectric elements and the first thermally conductive layer,

characterised in that the ratio between the total surface area (nScond) of the cross sections of the members and the surface area of the panel is at least five times the ratio between the thermal conduction coefficient (Ai_ns) of the thermally insulating material of the inner layer (13) and the thermal conduction coefficient (Acond) of the thermally conductive material of the members (15).

2. Multilayered panel according to Claim 1 , wherein the ratio between the total surface area (nScond) of the cross sections of the several members and the surface area of the panel is at least 6.66 times the ratio between the thermal conduction coefficient (Ai_ns) of the thermally insulating material of the inner layer and the thermal conduction coefficient (A_COnd) of the thermally conductive material of the members.

3. Multilayered panel according to Claim 1 or 2, wherein the ratio between the total surface area (nScond) of the cross section of the several members and the surface area of the panel is at least ten times the ratio between the thermal conduction coefficient (Ai_ns) of the thermally insulating material of the inner layer and the thermal conduction coefficient (A_COnd) of the thermally conductive material of the members.

4. Multilayered panel according to any one of the preceding claims, wherein the thermal conduction coefficient (Ai_ns) of the thermally insulating material of the inner layer is 0.1 W/mK or less.

5. Multilayered panel according to any one of the preceding claims, wherein the thermal conduction coefficient (A_COnd) of the thermally conductive material of the members (15) is at least 50 W/mK.

6. Multilayered panel according to Claim 5, wherein the thermal conduction coefficient (A_COnd) of the thermally conductive material of the members (15) is at least 200 W/mK.

7. Multilayered panel according to any one of the preceding claims, wherein the ratio between the total surface area of the cross sections {nScond) of the several members and the surface area of the panel is smaller than or equal to 1000 times the ratio between the thermal conduction coefficient (Ai_ns) of the thermally insulating material of the inner layer and the thermal conduction coefficient (A_∞nd) of the thermally conductive material of the members.

8. Multilayered panel according to any one of the preceding claims, wherein one or more of the thermoelectric elements (16) thermally coupled to a corresponding member, takes up a surface area which is at least 70% of the cross section of the corresponding member.

9. Multilayered panel according to any one of the preceding claims, having at least nine separate and spaced-apart members (15) per square metre of panel surface.

10. Multilayered panel (20) according to any one of the preceding claims, wherein the first (21 ) and/or the second thermally conductive layer (22) has a varying thickness, with a greater thickness (d3, d₄) at the location of the members (15) and/or of the thermoelectric elements (16), and a smaller thickness (ds, de) in between.

1 1. Assembly comprising at least one multilayered panel (10,

20, 30) according to any one of the preceding claims and a control unit (18) configured to be electrically connected to the thermoelectric elements (16) of the multilayered panel, wherein the control unit is programmed to control an electric energy supply of the thermoelectric elements on the basis of a temperature difference.

12. Assembly according to Claim 1 1 , wherein the temperature difference is a difference in temperature between two sides (101 , 102) of the multilayered panel (10, 20).

13. Assembly according to Claim 1 1 , wherein the temperature difference is a difference in temperature between the cold side (161 ) and the warm side (162) of one of the thermoelectric elements (16).

14. Assembly according to any one of Claims 1 1 to 13, wherein the control unit (18) comprises an operating state, in which the temperature difference between the cold side (161 ) and the warm side (162) of the thermoelectric element (16) is smaller than or equal to 120% of the temperature difference between the first thermally conductive layer (1 1 , 21 ) and the second thermally conductive layer (12, 22) of the multilayered panel (10, 20).

15. Assembly according to any one of Claims 1 1 to 13, wherein the control unit (18) comprises an operating state, in which the temperature difference between the cold side (161 ) and the warm side (162) of the thermoelectric element (16) is smaller than or equal to 1 15% of the temperature difference between the first thermally conductive layer (1 1 , 21 ) and the second thermally conductive layer (12, 22) of the multilayered panel (10, 20).

16. Assembly according to any one of Claims 1 1 to 13, wherein the control unit (18) comprises an operating state, in which the temperature difference between the cold side (161 ) and the warm side (162) of the thermoelectric element (16) is smaller than or equal to 1 10% of the temperature difference between the first thermally conductive layer (1 1 , 21 ) and the second thermally conductive layer (12, 22) of the multilayered panel (10, 20).

17. Assembly according to any one of Claims 1 1 to 16, wherein the control unit (18) comprises a connection terminal (181 ) configured for connecting a temperature sensor.

18. Assembly according to any one of Claims 1 1 to 17, wherein the control unit (18) comprises a look up table, containing a list of values indicative of an electrical power associated with the temperature difference.

19. Assembly according to any one of Claims 1 1 to 18, comprising means for determining an electrical voltage across and/or electric current through a thermoelectric element (16) or group of thermoelectric elements separately, wherein the group comprises several thermoelectric elements, the number of which is smaller than the total number of thermoelectric elements of the multilayered panel (10, 20).

20. Method for controlling an active insulation, comprising: providing a multilayered panel (10, 20) according to any one of Claims 1 -

10,

- connecting the thermoelectric elements (16) of the multilayered panel to a source of electrical energy,

measuring a temperature difference between two sides (101 , 102) of the multilayered panel (10, 20) and/or between the cold side (161 ) and the warm side

(162) of one of the thermoelectric elements (16),

- controlling the electrical power supplied to the thermoelectric elements (16) on the basis of the temperature difference.

21. Method according to Claim 20, wherein controlling of the electrical power is effected by means of looking up in a table.