WO2015029001A1

WO2015029001A1 - A system for heat recuperation and method for exchanging energy

Info

Publication number: WO2015029001A1
Application number: PCT/IB2014/064199
Authority: WO
Inventors: Mark SMET
Original assignee: Delta Recover
Priority date: 2013-09-02
Filing date: 2014-09-02
Publication date: 2015-03-05

Abstract

A system for heat recuperation, comprising: • - a thermally insulated chamber (6); • - a buffer tank (1), comprising a container (2) for the storage of a liquid (3), the container (2) comprising a top end and a bottom end, an internal separating element (4) which is designed to separate a top section of the container (2) in a liquid-tight manner from a bottom section, wherein the internal separating element (4) is also designed to be movable through the container (2) without losing liquid tightness between the top section and the bottom section, the relative volumes of the top section and the bottom section varying in this case; • - an external circuit arrangement (5) which connects the top end to the bottom end and which defines a further closed liquid circuit which comprises an exchange part (51) which is designed to be able to exchange heat with the thermally insulated chamber (6); • - a pressure means (7) for generating a pressure difference in a liquid present in the buffer tank (1) and the external circuit (5), for example between the upper edge and lower edge of the separating element (4), over the closed liquid circuit; • - a heat pump system (63) which is thermally coupled to the thermally insulated chamber (6) and to the exchange part (51) for exchanging heat between the thermally insulated chamber (6) and the exchange part (51).

Description

A SYSTEM FOR HEAT RECUPERATION AND METHOD FOR EXCHANGING ENERGY

Scope of the invention The present invention relates to systems and methods for recovering thermal energy, e.g. for the storage and/or discharge of thermal energy from/to a space. Aspects of the present invention may, for example, be used in the areas of cyclic drying and/or heating and/or heat treatment of a product, wood for example, in a thermally insulated chamber, but its application is not limited to this. Indeed, systems and methods according to aspects of the present invention may be used and applied in all areas where thermal energy can be recovered and re-used in a space. Another area of application may be the chemical industry, for example.

Background

It is already known in the prior art that a product, wood for example, which is transported internationally is subject to adapted temperatures, preferably a heat treatment, in order to ensure that any organisms present are killed. The drying of wood or other products is also a commonly occurring activity in industry. Typically large quantities of wood are repeatedly placed in a specially adapted container which is thermally insulated and also contains means for suitably heating the container. The wood is heated in it and then dried, whereupon the container is opened, emptied filled with the next load of wood. A large quantity of energy, particularly thermal energy, is lost during this process. It is already known in the prior art that a buffer tank, filled with a liquid, can be used to recover heat from a thermally insulated space, by coupling the buffer tank thermally to a circuit comprising pipes and other elements which enables thermal energy to be exchanged with this space.

However, the state of the art systems of the buffer tank type suffer from the problem that during heating and cooling a saturation temperature is reached reasonably quickly due to the coupling to a space whose temperature varies correspondingly. After this saturation temperature is reached there is no further heat absorption or heat discharge because the chamber is, respectively, colder than or the same temperature as, or is warmer than or has the same temperature as the temperature of the liquid in the buffer tank. A continuous heat exchange stands in the way of this. This lack of continuous heat exchange is exacerbated when such exchanges are to be used in cycles of alternating consecutive heating and cooling stages. The efficiency of the heat exchange is therefore rather limited.

In DE10 2007 047 435 A1 a device and a process are described for tempering and heat recuperation in thermally driven heat pumps and cooling machines with fixed sorption means such as adsorption cooling machines. In such a system the quantity of energy which is stored and used can be rather limited. Summary

The objective of the present invention is to reduce or solve at least one of the above- mentioned problems. This is achieved by using a system for heat recuperation according to the measures in the feature of Claim 1 and by using an associated method according to the measures in the feature of Claim 9.

When terms such as "first", "second", "third" and so on are used, this does not necessarily mean that a consecutive or chronological order must be assumed.

The terms "top" and "bottom" correspond, in this description, to a first object being "higher" and "lower" than a second object respectively, the height of an object being determined as the distance from the object to the ground surface.

It should also be noted that the characteristics stated in the description of different aspects of the invention may also be applied to the other aspects, as will be understood by a person skilled in the art. In a first aspect of the present invention a device is described, e.g. a buffer tank, comprising a container for storing a liquid (buffer medium), the container comprising a top end (e.g. at or the upper surface, e.g. comprising a second opening) and a bottom end (e.g. a or the lower surface, e.g. comprising a second opening), an internal separating element which is designed to separate a top section of the container so that it is liquid tight from a bottom section in which the internal separating element is also designed to be movable through the container without losing liquid tightness between the top and bottom section, where the relative volumes of the top and bottom section van/..

The movable separating element may, for example, be a movable divider. The separating element may, for example, assume the form of a plate or disc whose edge profile corresponds to the profile of the inner wall of the container. The liquid tightness may be achieved, for example, by means of one or a plurality of seals, e.g. one or a plurality of sealing ring(s) which are contained in the separating element, which is/are fitted to the outer edge of the separating element and which provide/s a termination of the space between the outer edge of the separating element and the inner wall of the container. The external edge of the separating element is preferably designed to connect to the inner wall of the container. If the separating element has a small thickness, the separating element should preferably have stabilisation means which are arranged on this extreme edge to guide the liquid-tight movement. For example, these stabilisation means may comprise an upright edge which cooperates with the inner edge of the container, thus preventing the separating element from tipping over during its movement through the container. A further effect of this upright edge is that its surface, i.e. the surface of the separating element directed towards the inner edge of the container, can be enlarged. One or a plurality of sealing means, such as sealing rings, e.g. rubber sealing rings, can be fitted along this surface. The fitting of such sealing rings is also simpler if more lateral surface area is available. The sealing rings should preferably be fitted in parallel. The sealing rings should also preferably contribute to the positioning and/or stabilisation of the separating element. The upright edge may, for example, extend upwards or downwards, or may, for example, extend both partially upwards and partially downwards. In preferred embodiments the container comprises, at its top end (e.g. on the upper surface) and/or bottom end (e.g. on the lower surface) a recess (e.g. annular recess) which is designed to receive the stabilisation means when the separating element approaches or reaches its extreme top or bottom position in the container. The advantage of this is that the main upper or lower surface of the separating element is able to move closer to or fully against the upper or lower surface in these extreme positions so that all the liquid (buffer medium) is able to flow properly into/out of the container in these extreme positions.

In other preferred embodiments the separating element is sufficiently thick, and in particular the outer edge of the separating element is sufficiently thick, so that the outer edge itself is designed to guide the liquid-tight movement. The outer edge can then cooperate with the inner edge of the container, thus preventing the separating element from tipping over during its movement through the container. In such embodiments the use of extra stabilisation means is less appropriate or is not necessary. One or a plurality of sealing means, e.g. sealing rings, e.g. rubber sealing rings, can then be fitted along the outer edge, for example with variants such as those described in the embodiment with the extra stabilisation means. The sealing rings should preferably be fitted in parallel. The sealing rings should also preferably contribute to the positioning and/or stabilisation of the separating element.

In preferred embodiments the separating element has a thickness which is greater than 5 cm, or greater than 10 cm, or greater than 15 cm.

In preferred embodiments the separating element has a thickness on its outermost edge which is greater than 5 cm, or greater than 0 cm, or greater than 15 cm.

In preferred embodiments the design of the separating element is of the cylinder type. The separating element comprises a cylindrical jacket which defines the outer edge and which interconnects an upper surface and/or lower surface of the separating element. The upper and/or lower surface may, for example, be flat or can be more complex in form. The upper surface and/or the lower surface should preferably be spherical. The curvature should preferably be directed outwards (convex). Both the lower surface and the upper surface should preferably be spherical and be directed outwards (convex). This design is ideal for use in combination with a container which has corresponding lower and upper surfaces. In fact, if the lower surface and/or (preferably both) upper surface of the container is/are spherical, with the curvature directed outwards (convex), the respective upper surface and/or lower surface of the separating element should preferably have a corresponding curvature which runs as parallel as possible to the respective curvature of the lower and/or upper surface (strictly speaking to the inner surface of the upper and/or upper surface of the container). The advantage of this is that there is relatively less or no dead or unused volume when the separating element is in an extreme position and in an extreme bottom and/or top position in the container.

More generally the advantage is that the lower and upper surface of the container (in particular its inner edge) and the design of the respective lower and upper surface of the separating element are matched to each other, and are, in particular, complementary, so that there is no dead or unused volume when the separating element is in an extreme position, such as in an extreme bottom and/or top position in the container.

In preferred embodiments the volumes of the top section and the bottom section are complementary. Together with the separating element they form the internal volume of the container.

In preferred embodiments the top end and the bottom end are interconnected by means of a jacket. This jacket may, for example, be cylindrical and may have a circular or elliptical diameter. Both the inner surface and the outer surface may typically be cylindrical in shape. This jacket can of course assume other shapes without detracting from the inventive aspects of the present invention, as the person skilled in the art will recognised. In preferred embodiments the buffer tank also comprises a local driving means for driving the liquid-tight movement of the separating element in the container. This local driving means may, for example, be one which is designed to exert a mechanical force upon the separating element from the cylinder. However, the presence of a local driving means is not strictly necessary since an external driving means may provide the movement of the separating element, as will be explained later.

In preferred embodiments the separating element also embodies a thermal insulation between the top and bottom sections.

In preferred embodiments the container is thermally insulated from the outside world. The use of such a tank in a system described for heat recuperation, and in a system further described in a second and third aspect of the present invention, allows a continuous exchange of energy. This ensures greater efficiency for this heat exchange than if a state of the art buffer tank were to be used. In a second aspect of the present invention a buffer tank system is described which comprises a device or buffer tank according to an embodiment of the first aspect and which also comprises a pipe or circuit device which connects the top end (for example the first opening) to the second end (e.g. the second opening), and which defines a further closed liquid circuit. The circuit device or pipe may comprise different elements which improve or make possible heat exchange with an external chamber or with a heat pump installed between (and functionally positioned between) the circuit device and the external chamber. The circuit device may, for example, incorporate a heat exchanger.

The buffer tank and buffer tank system should preferably be used completely full of buffer medium, preferably a liquid. This liquid may be water or any liquid which the person skilled in the art would use to allow efficient heat exchange and heat storage. The buffer tank system may consequently comprise a sealable feed pipe for introducing liquid into the system and/or a breather valve, as are known by the person skilled in the art.

In preferred embodiments a positive upward temperature gradient is present in the liquid in the top and/or bottom section. This gradient is formed naturally, as the person skilled in the art will recognise.

In preferred embodiments the buffer tank system also comprises a thermally insulated chamber, and the circuit device which forms the closed liquid circuit comprises an exchange part which is designed to be able to exchange heat with the thermally insulated chamber, directly, or with the heat pump, which is also designed to be able to exchange heat with the thermally insulated chamber in order, for example, to transmit heat indirectly to/extract heat from the thermally insulated chamber.

In preferred embodiments the thermally insulated chamber can be opened and closed so that a product can be received in/removed from the chamber. In preferred embodiments the separating element comprises an upper edge and a lower edge, and the buffer tank system also comprises a pressure means to generate a pressure difference in the liquid between the upper edge and the lower edge of the separating element over the closed liquid circuit. This pressure means or means of generating a pressure difference may, for example, consist of at least one pump which is installed in the circuit device or closed liquid circuit.

In preferred embodiments in which the exchange part exchanges energy directly with the thermally insulated chamber, the buffer tank system includes a means for determining the temperature of the liquid in the vicinity of the exchange part, a means for determining an internal temperature of the chamber, preferably in the vicinity of the exchange part, and a control unit which is designed to receive information from these means and for activating the pressure means so that the temperature and/or the flow rate of the liquid supplied / buffer medium supplied is controlled in the vicinity of the exchange part as a function of the temperature in the thermally insulated chamber. In preferred embodiments in which the exchange part exchanges energy directly with a thermally insulated chamber, the control unit is designed to activate the pressure means in the case of a falling temperature gradient in the chamber, so that the temperature of the liquid in the vicinity of the exchange part is always lower than the temperature of the chamber. In preferred embodiments in which the exchange part exchanges energy directly with a thermally insulated chamber, the control unit is designed to activate the pressure means in the case of a rising temperature gradient in the chamber, so that the temperature of the liquid in the vicinity of the exchange part is always higher than the temperature of the chamber. In preferred embodiments in which the exchange part exchanges energy directly with a thermally insulated chamber, the control unit is designed to keep the absolute temperature difference between the chamber and the liquid in the vicinity of the exchange part consistently lower than 10 °C, and preferably lower than 9 °C, lower than 8 °C, lower than 7 °C , lower than 6 °C, lower than 5 °C, lower than 4 °C, lower than 3 °C, lower than 2 °C, lower than 1 °C, lower than 0.5 °C or lower than 0.1 °C. In preferred embodiments in which the exchange part exchanges energy directly with the thermally insulated chamber by means of a heat pump system, the system should preferably incorporate a means for determining the temperature of a buffer medium in the vicinity of the exchange part, a means for determining an internal temperature of the thermally insulated chamber, and a control unit which is designed to receive information from these means and activate the pressure means so that the flow and/or the temperature of the liquid supplied/buffer medium supplied is controlled in the vicinity of the exchange part as a function of the temperature in the thermally insulated chamber. The control unit should preferably be designed to keep the absolute temperature difference between the thermally insulated chamber and the buffer medium in the vicinity of the exchange part consistently lower than 15 °C. The exchange part should preferably comprise a heat exchanger and the control unit should be designed to keep the absolute temperature difference between the thermally insulated chamber and the buffer medium at the output of the heat exchanger consistently lower than 15 °C. In a third aspect of this invention a system is described for heat recuperation, comprising:

- a thermally insulated chamber;

- a buffer tank, comprising a container for storing a liquid, the container comprising a top end and a bottom end, an internal separating element designed to separate an top section of the container, in a liquid-tight manner, from a lower section in which the internal separating element is also designed to be movable through the container without losing liquid tightness between the top section and the bottom section, where the relative volumes of the top section and the bottom section vary;

- an external circuit device which connects the top end with the bottom end and which defines a further closed liquid circuit which has an exchange part (e.g. heat exchanger) which is designed to be able to exchange heat with the thermally insulated chamber;

- a pressure means for generating a pressure difference in a liquid present in the buffer tank and the external circuit, for example between the upper edge and lower edge of the separating element, over the sealed liquid circuit; - a heat pump system which is thermally linked to the thermally insulated space and to the exchange part (e.g. heat exchanger) for exchanging heat between the thermally insulated chamber and the exchange part.

By making use of a heat pump system which is thermally linked to the thermally insulated space/chamber, and to the exchange part, a suitable (and necessary) temperature difference can be created so that the heat transfer between the thermally insulated space (treatment chamber) and the buffer medium is optimum. This system makes it possible to extract more than 95% or more than 99%, or 100% of the required thermal energy, from the buffer medium, then re-store it.

The thermally insulated chamber, the buffer tank, the external circuit device and the pressure means are as described, for example, for one of the embodiments of the first and second aspect.

In preferred embodiments the buffer tank system comprises a means of determining the temperature of the liquid in the vicinity of the exchange part, a means of determining an internal temperature of the thermally insulated chamber, preferably in the vicinity of the exchange part, and a control unit which is designed to receive information from these means and to activate the pressure means so that the temperature and/or the flow of the activated fluid in the vicinity of the exchange part is controlled as a function of the temperature in the thermally insulated chamber.

In preferred embodiments the control unit is designed to activate the pressure means, in the case of a falling temperature gradient in the chamber, so that the temperature in the liquid in the vicinity of the exchange part approaches the temperature of the thermally insulated chamber as closely as possible with the heat pump. This provides high efficiency for a typical heat pump system 63. It should be noted that a heat pump system 63 which is not operating efficiently can no longer perform a useful function if this heat pump system 63 does not itself consume too much energy, for example if this were to consume more energy than the energy which can be recovered.

In preferred embodiments the control unit is designed, in the case of a rising temperature gradient in the chamber, to activate the pressure means so that the temperature of the liquid in the vicinity of the exchange part approaches the temperature of the chamber as closely as possible with the heat pump.

The control unit should preferably be designed to keep the absolute temperature difference between the thermally insulated chamber and the buffer medium in the vicinity of the exchange part consistently lower than 15 °C. The exchange part should preferably comprise a heat exchanger and the control unit should be designed to keep the absolute temperature difference between the thermally insulated chamber and the buffer medium at the output of the heat exchanger consistently lower than 15 °C.

In preferred embodiments the control unit is designed to keep the absolute temperature difference between the chamber and the liquid/buffer medium in the vicinity of the exchange part consistently (e.g. at the output of the heat exchanger which incorporates the exchange part) with the heat pump consistently lower than 15 °C, and preferably lower than 14 °C, lower than 13 °C, lower than 12 °C, lower than 1 1 °C, lower than 10 °C, lower than 9 °C, lower than 8 °C, lower than 7 °C, lower than 6 °C, lower than 5 °C, lower than 3 °C or lower than 1 °C.

The presence of the heat pump also makes it possible for the quantity of energy which is extracted from the buffer tank, or which is stored therein, to be controlled and to be determined as a function of the mass of the product to be treated. This may, for example, be increased or reduced by the temperature difference between the incoming and outgoing water over the heat exchanger of the buffer tank system. Consequently more or less energy in the buffer water will be stored or extracted.

This makes it possible to vary the mass of product (e.g. wood) to be heated per drying cycle when different quantities of product are dried consecutively in the thermally insulated chamber and if energy from the thermally insulated chamber is stored from a previous drying cycle and re-used in a subsequent drying cycle, preferably one following immediately afterwards.

A fourth aspect of the present invention comprises a method for exchanging energy between a thermally insulated space with a continuously falling or continuously rising temperature gradient and a liquid in a closed liquid circuit., where the closed liquid circuit has an exchange part which is designed to be able to exchange heat with the thermally insulated space, including allowing the liquid to flow through into the exchange part. Here the temperature of the supplied liquid in the exchange part is controlled so that the temperature difference between the thermally insulated space and the supplied liquid remains lower than 10 °C. In rpfprrpH pmhnrjirnpntc t e tpmnprati irp Hiffprpnrp hotwoon thp ci innlioH lini liH in thp exchange part and the temperature in the thermally insulated space is kept constant. The term "constant temperature difference" should be interpreted here as a temperature difference which varies no more than 25%, or varies no more than 20% percent, or varies no more than 10%, or varies no more than 5%, or varies no more than 2%, or varies no more than 1 %.

A fifth aspect of the present invention comprises a method for exchanging energy between a thermally insulated space with a continuously falling or continuously rising temperature gradient and a liquid in a closed liquid circuit by means of a heat pump, where the closed liquid circuit comprises an exchange part which is designed to be to exchange heat by means of a heat pump system which is thermally coupled to the thermally insulated space and with the exchange part in order to exchange heat between the thermally insulated space and the exchange part, allowing the liquid to flow into the exchange part and controlling the temperature of the supplied liquid in the exchange part so that the temperature difference between the thermally insulated space and the supplied liquid in the vicinity of the exchange part remains as low as possible, preferably lower than 15 °C.

In preferred embodiments the controlling of the temperature of the supplied liquid in the exchange part involves supplying liquid from a top or bottom part of a buffer tank according to one of the embodiments of the first aspect to the exchange part through the closed liquid circuit, then discharging the liquid to the bottom or top of the buffer tank respectively, through the closed liquid circuit, by activating a pressure means in a controlled manger, where the buffer tank in the top and bottom part has a positive upward temperature gradient in the liquid.

In preferred embodiments the system consists of the closed liquid circuit and the buffer tank completely filled with a buffer medium, e.g. a suitable liquid. The description of aspects of the present invention is given on the basis of specific embodiments and with reference to certain figures. The figures shown are schematic only and should be considered as limiting. For example, certain elements or features may not have been presented in proportion or to scale in relation to other elements. Reference symbols in the figures have been chosen so that they are the same for comparable or the same elements or features in different figures or drawings.

Detailed description of preferred embodiments Figures 1 and 2 illustrate embodiments of the present invention. A buffer tank 1 comprises a container 2 for storing a liquid 3, water for example. The container comprises a first opening 20 near a top end or top surface 22 of the container, and a second opening 21 near a bottom end or bottom surface 23. The buffer tank also comprises an internal separating element 4 which is designed to separate a top part 24 of the container in a liquid-tight manner from a top part 25 of the container. The term 'liquid-tight' indicates that separating element 4 ensures that no liquid can be exchanged between top part 24 and bottom part 25 of the container along the contact surface between the top edge 41 of separating element 4 and inner wall 27 of the container. Separating element 4 is preferably a highly thermally insulating component, so that any heat exchange between the liquid in top part 24 and bottom part 25 of container 2 is limited as far as possible.

Buffer tank 1 is contained in a buffer tank system which, in addition to the buffer tank, also comprises a closed liquid circuit 5 which is connected at a first end to the first opening 20, at the top of the container, and is connected at its other end to opening 21 at the bottom end of the container. When in operation the buffer tank and the closed liquid circuit 5 are completely filled with the liquid. Therefore there will be little or no air present in the closed system. In this context buffer tank 1 and/or the closed liquid circuit 5 may comprise one or a plurality of breather valves, as they are known by the person skilled in the art (not shown).

The system consisting of buffer tank 1 and closed liquid circuit 5 is also thermally coupled to a thermally insulated or chamber 6. The term 'is thermally coupled' means that an energy exchange between liquid circuit 5 and insulated space 6 is made possible, and preferably that an optimum energy exchange is made possible between liquid circuit 5 and the insulated space 6. For this purpose closed liquid circuit 5 comprises at least one exchange part 51. This exchange part 51 may, for example, be installed in the thermally insulated space 6. It may be the part of closed liquid circuit 5 which runs through the thermally insulated space 6. In a typical application the thermally insulated space 6 will be filled with a product P which should undergo a temperature step, for example a drying stage or disinfection stage. Product P may be installed in and removed from the thermally insulated space 6 by means of at least one gate or door 61. The thermally insulated space 6 may also comprise one or a plurality of heating elements 64 which are adapted to heat the thermally insulated space at suitable times, for example when starting up the cyclic heating system and at other suitable times, to compensate for any energy losses suffered. The system also contains a pressure means 7 to generate a pressure difference in liquid 3, e.g. between the upper edge and lower edge of the separating element via the closed liquid circuit 5. This pressure means 7 may, for example, comprise one or a plurality of pumps. Alternatively, or as a

supplement to one or a plurality of pumps, the pressure means may comprise a local pressure means (not shown) which makes possible a mechanical drive of separating element 4, in other words which is adapted to driving the movement through container 2 of separating element 4 mechanically. It should be noted that the system shown is completely filled with a liquid during use and that this liquid will spontaneously form an upward positive temperature gradient in both bottom part 25 and top part 24 of container 2. In fact, during use, the bottom part of bottom section 25 will be colder than the top part of bottom section 25. Equally, the temperature of the liquid in the bottom part of top section 24 will be lower than the temperature in the top part of top section 24. By generating a pressure difference by means of a pressure means 7 (and/or local pressure means), separating element 4 can move downwards (Figure 1 ) or upwards (Figure 2) through the container, top edge 41 of separating element 4 remaining in constant contact with inner wall 27 of container 2. The liquid, e.g. water, which is pumped through the closed liquid circuit 5 and consequently through exchange element 51 will vary in temperature in bottom section 25 and top section 24 respectively due to the temperature gradient. By suitably controlling the pump, e.g. by means of a control unit 9, the temperature of the supplied liquid in exchange part 51 can therefore be controlled. In particular, this temperature can be controlled in such a manner that the temperature difference between the inside of the thermally insulated space 6 and exchange part 51 is constant, and/or that this temperature difference has a constant sign (being always positive or always negative), and so that the absolute value of this difference remains below a predetermined maximum value.

The naturally formed temperature distribution of liquid 3 in buffer tank 1 ensures that in this system a downward movement of separating element 4 in container 2 guarantees an initially colder, then an increasingly warmer flow of liquid into exchange part 51 when the separating element moves downwards (Figure 1). This corresponds to the scenario where heat is to be transferred to the thermally insulated space so that it heats up. On the other hand, in the scenario where thermal energy is to be transferred to the buffer tank from the thermally insulated space 6, so that the temperature in the thermally insulated space 6 drops, warmer liquid will be initially supplied followed by increasingly colder liquid due to the upward movement of separating element 4 in container 2 (Figure 2).

The person skilled in the art will recognise that the processes described above make possibly a highly efficient, continuous heat exchange between the new buffer tank and the thermally insulated space 6. Figure 3 illustrates the movement of separating element 4 through container 2 in the downward direction, where top section 24 becomes increasingly large and the complementary bottom section 25 is in this case reduced in volume.

Figure 4 illustrates the arrangement described for Figure 2, where separating element 4 moves from the bottom of container 2 to the top of container 2 in an upward direction, and where the volume of bottom section 25 steadily increases so that the volume of the complementary top section 24 decreases correspondingly.

Figures 5a and 5b illustrate embodiments of separating element 4. This separating element 4 comprises, on its outermost edge 41 , stabilisation means 42 which are designed, on this extreme edge, to guide the liquid-tight movement of separating element 4 through container 2, and in particular to prevent separating element 4 from overturning during the movement through container 2. For this purpose stabilisation means 42 may have an upright edge. This upright edge may, at one or more points and on one or more lines or surfaces, touch inner wall 27 of the container so that a tilting movement of separating element 4 is rendered impossible. A further advantage of an upright edge 42 for separating element 4 is that this creates more space for placing one or a plurality of rubber sealing rings 45 between edge 41 of separating element 4 and inner wall 27 of the container. Such sealing rings are preferably fitted parallel and above each other along outermost edge 41 of separating element 4. The upright edge may, for example, extend upwards or downwards, or may, for example, extend both partially upwards and downwards (see Figure 5b). The container comprises, at its top end (in the upper plane) and bottom end (in the lower plane) suitable recesses 28 (e.g. annular recesses 28) which are suitable for receiving the stabilisation means 42 when separating element 4 approaches or reaches its extreme top or bottom position in container 2. The advantage of this is that the top principal plane 43 or bottom principal plane 44 of separating element 4 may reach these extreme positions closer to or exactly opposite the upper plane 22 or lower plane 23, so that all liquid 3 can flow properly out of/into the container in these extreme positions.

Figure 5a shows a perspective view of such an arrangement, whilst Figure 5b shows a cross-section in which three sealing rings are visible. An important aspect of the present invention is the control of the temperature of the liquid in exchange part 51. Furthermore, the temperature of the thermally insulated space 6 is also important, as in principle this corresponds to the temperature of the product in this chamber, or is very close to it. It will be clear to the person skilled in the art that these temperatures can be determined in different ways and with different arrangements. Some embodiments of a control unit which is designed to measure and/or determine such temperatures are illustrated in Figures 6a and 6b.

In Figure 6a a control unit 9 is connected to a number of temperature sensors 8 which are installed or in or in the immediate vicinity of exchange part 51 , in or along the closed liquid circuit 5. Control unit 9 is also connected to pressure means 7, a pump for example. Based on the temperature measurements deriving from sensors 8, and the temperature measurements deriving from a further temperature sensor 62 in the thermally insulated space 6, control unit 9 can activate pressure means 7 to supply warmer or colder and/or more or less water to exchange part 51 , depending on the temperature of the thermally insulated space 6. Figure 6b illustrates an equivalent embodiment where in this case temperature sensors 8 are not fitted in or in the vicinity of exchange part 51 but in or in the immediate vicinity of a buffer tank. The control unit, e.g. a computer unit, can measure the temperature values at different points on the buffer tank, and may also determine them by means of tables and/or models and/or simulations. For example, a temperature sensor can be installed both in top section 24 and in bottom section 25 of container 2, and an extrapolation can be made to determine the temperature at a certain height and/or location in the buffer tank. For example, a temperature sensor can be installed in both top section 24 and in bottom section 25 of container 2, both at the top and bottom of the respective part. In such embodiments it may be appropriate to install a temperature sensor 8 on separating element 4. For example, the temperature sensor in the bottom part of the top section of container 2 may be installed on the upper edge of separating part 4. Temperature sensor 8, installed in the top part of the bottom section, may be fitted on the lower edge of separating part 4. This positioning of temperature sensors 8 on separating part 4 ensures a measurement of the respective temperature sensors 8 that always remains relevant e since they always move together when the respective volumes of the bottom section and the top section change complementarily as a result of a displacement of separating part 4 through cylinder 2, designed for example as a cylindrical shape. It is evident that the person skilled in the art may consider other distributions of temperature sensors over the buffer tank system that allow the temperature of the liquid fed through into exchange part 51 to be determined sufficiently accurately.

Finally, Figure 7 illustrates a further preferred embodiment of the present invention. This embodiment is very-similar to the embodiments previously described, but differs in the sense that exchange element 51 does not run directly through the thermally insulated chamber 6. In fact in this embodiment a heat pump system 63 is provided. Heat pump system 63 can be constructed in various designs, as is known to the person skilled in the art. A heat pump system is an apparatus which displaces heat by means of work. All types of heat pumps absorb heat at low temperature which is discharged again at high temperature. One or other form of work must be supplied here. The most common types of heat pumps operate by allowing liquid to evaporate at low temperature and allowing the steam to condense at high temperature. In the first case the boiling point must therefore be lowered and/or in the second case increased. The boiling point can be increased by increasing the pressure with a compressor (pump), but on the other hand the boiling point can be lowered again by allowing the pressure to drop, e.g. in a turbine or throttle valve.

The combination of evaporation, compression, condensation and expansion forms a closed circuit for the circulating coolant, the thermodynamic cycle, but not for the heat and work: net work is supplied to the system (in the compressor) and heat is displaced from the evaporator to the condenser.

A heat pump system typically comprises a closed circuit consisting, in the order given, a compressor, a condenser, a turbine/throttle valve and an evaporator. A liquid/coolant flows through the circuit in the following order: the compressor, the condenser, the turbine/throttle valve and the evaporator. The heat pump system preferably performs the following functions:

- pressure increase in the compressor: in the first stage the gaseous coolant is compressed, causing the temperature to rise above that of the space to be heated. The hot steam flows to the condenser;

- heat discharge in the condenser: in the condenser (or radiator) the steam

condenses against the relatively cold wall, thereby discharging heat. The temperature at which this takes place depends on the pressure: the higher the pressure the higher the boiling point. The liquid then flows to a throttle valve;

- pressure reduction: in the throttle valve or reducing valve the liquid flows through a narrow opening, after which the pressure is considerably lower;

- heat absorption from the surrounding area: in the evaporator the pressure is lower so that the liquid reaches boiling point. The heat which is required for this is extracted from the surrounding area. The temperature at which this takes place depends on the prevailing pressure, which is kept low by the suction effect of the compressor.

Heat pump system 63 is thermally coupled to the thermally insulated space so that heat exchange between the thermally insulated space 6 and (elements of) heat pump system 63 is made possible. Furthermore (elements of) heat pump 63 can exchange heat, in other words it is thermally coupled to exchange part 51. The condenser/evaporator may preferably be designed to be able to exchange heat with the thermally insulated space (for example it may be installed in the thermally insulated chamber) and the respective evaporator/condenser of heat pump system 63 can then be designed to be able to exchange heat with exchange part 51. In this embodiment it is important to keep the temperature difference between the supplied liquid in exchange part 51 and the thermally insulated chamber 6 as small as possible with heat pump 63 and to ensure that the temperature of the supplied liquid to be kept as close as possible to the temperature of the chamber in the vicinity of the exchange part with the heat pump, because this greatly improves the efficiency of a typical heat pump system 63. It should be noted that a heat pump system 63 that is not operating efficiently can longer perform a useful function if this water pump system 63 would consume more energy than can be re-used.

During the heating of the treatment chamber (thermally insulated space) the outgoing temperature of the heat exchanger (exchange means) of the buffer water should be lower than the incoming air of the condenser of the heat pump system installed in the treatment chamber, preferably 5 °C to 15 °C lower.

During the cooling of the treatment chamber the outgoing temperature of the heat exchanger of the buffer water should be higher than the ingoing air of the evaporator in the treatment chamber (thermally insulated space).

It should be noted that the elements "condenser" and "evaporator" of heat pump 63 are redefined (changing respective functions) when there is a switch between heating mode and cooling mode. The temperature difference between the incoming and outgoing buffer medium/buffer water over the heat exchanger is determined by the mass of product to be treated in the treatment chamber. The temperature difference may be determined as follows, for example.

During the heating cycle the air above the condenser is heated (e.g. by 10 °C). The heat pump will automatically vary the temperature difference between the evaporator and condenser in order to extract sufficient thermal energy from the buffer water and effect this heating. During the start-up the flow across the heat exchanger will be regulated in order to obtain a predetermined temperature difference (e.g. of 10 °C) of the buffer medium across the heat exchanger. If, with this temperature difference between the incoming and outgoing buffer medium in the heat exchanger and treatment chamber does not remain constant, i.e. becomes higher or lower, the flow is adjusted until this temperature difference between the outgoing buffer medium in the heat exchanger and treatment chamber remains constant.

During the cooling cycle the same operating principle can in fact be followed: the air above the evaporator is cooled (e.g. by 10 °C), the heat pump automatically varies the temperature difference between the evaporator and condenser to effect this cooling. During the start- of the cooling cycle the flow is regulated to obtain a predetermined temperature difference between incoming and outgoing buffer medium across the heat exchanger (e.g. 10 °C). If, with this temperature difference between incoming and outgoing buffer medium across the heat exchanger, the temperature difference between the outgoing buffer medium in the heat exchanger and the treatment chamber does not remain constant, the flow is adjusted until the temperature difference between the outgoing buffer medium in the heat exchanger and the treatment chamber remains constant. These methods of flow regulation automatically ensures that the extracted or discharged energy from the buffer medium is in balance with the energy required for heating or cooling the product to be treated. In the case of a larger mass to be treated the temperature difference across the heat exchanger of the buffer water will be greater and more energy will therefore also be extracted from the buffer water and a comparable quantity of energy will be recovered in cooling.

And in the case of a smaller mass to be treated a smaller quantity of energy will be extracted and recovered so that the maximum available quantity of buffer medium is used and an optimum temperature gradient is maintained in the buffer tank.

A further detailed description of a typical cycle is given below for the system as described in relation to Figures 1 and 2, without the use of heat pump 63.

The temperature values indicated below are merely examples used to confirm the theories. Before heat recuperation can occur energy should be fed into the thermally insulated space 6 when the system is first started up in order to heat this space. An internal heating means 64 or an external heating means can be used for this purpose.

The description below is based on a condition of the system in which thermal energy has already been stored in buffer tank 1 and where the thermally insulated space 6 is to be heated.

When the product heating cycle starts, partition 4 (separating element 4) is on top of buffer tank 1 (on top of container 2), and water 3 is underneath partition 4. The water in bottom section 25 has a temperature of 25 °C underneath, for example, and this temperature gradually increases to 58 °C on the top, for example.

The water on top is pumped out of the tank by means of pump 7 which is installed in the closed liquid. The water discharges heat via a heat exchanger 51 (exchange part 51) to the air which circulates in treatment chamber 6 (thermally insulated space 6). There is a difference of 3 °C, for example, across heat exchanger 51 , resulting in outgoing air of 22 °C, for example. This air circulates along the product at 13 °C, for example, which heats to 15 °C, for example. The returning air has a temperature of 17 °C, for example, and is reheated to 22 °C, for example. The outgoing water from heat exchanger 51 has a temperature of 20 °C, for example, and is pumped back on top of the same buffer tank above partition 4.

By pumping the water partition 4 is displaced downwards as a result of the pressure difference generated.

By regulating the flow from the pump it can be ensured that the temperature of the buffer water follows the heating of product P (i.e. the heating of the thermally insulated chamber). The temperature difference between the buffer water and the product and/or thermally insulated space may vary to a limited extent, for example it may increase or decrease a maximum of a few degrees during heating but generally follows the heating of the product.

At the end of the heating cycle the outgoing water from heat exchanger 51 has a temperature of 53 °C, for example.

The outgoing air has a temperature of 55 °C, for example, the incoming air 50 °C, for example, and the temperature of the product is approximately 48 °C, for example.

Partition 4 is now underneath the buffer tank and the buffer water is in top section 24 of container 2.

The temperature gradient of buffer water is now 20 °C, for example, at the bottom of top section 24, and increases gradually to 50 °C, for example, at the top of top section 24. The product, wood for example, is further heated to 65 °C, for example, via an internal or external heat bridge 64. After the heat treatment of the product, it is recooled by storing heat in the buffer tank.

The water is pumped is pumped out of the first section 24 of the tank at the top and is heated to 58 °C, for example, via heat exchanger 51. The water is pumped back into second section 25 at the bottom of the tank.

The outgoing air from the heat exchanger is at 61 °C, for example, and circulates along the product that cools down to 63 °C, for example. The returning air has a temperature of 64 °C, for example.

By activating the pump, in particular by varying the pump delivery, the temperature of the buffer water can follow the cooling of the product. The temperature difference between the buffer water and the product will vary to a limited degree and may, for example, increase or decrease a few degrees during cooling, but will follow the temperature of the product. At the end of the cooling cycle the temperature of the outgoing water from heat exchanger 51 is 25 °C, for example. The temperature of the outgoing air is 23 °C, for example, that of the incoming air is 28 °C, for example, and the product has a temperature of 30 °C, for example. Partition 4 is now on top of the tank with the buffer water underneath in bottom section 25.

The buffer water is now at a temperature of 25 °C, for example, underneath in the bottom section, and the temperature gradually increases to 58 °C, for example, at the top of bottom section 25.

The above cycle can now be repeated after the product has been removed and replaced by a fresh quantity of product.

A possible operation of a system such as that discussed in relation to Figure 7 is explained below, according to a third aspect of the present invention, comprising a heat pump system 63 thermally coupled to the thermally insulated space and to the exchange part in order to exchange heat between the thermally insulated space and the exchange part.

The description below is based on the condition of the system in which thermal energy has already been stored in buffer tank 1 and the thermally insulated space 6 is to be heated.

At the start of the product heating cycle (for example at a temperature of 13 °C), partition 4 is on top of the buffer tank, and the water is underneath partition 4 in bottom section 25.

The water underneath bottom section 25 is then at a temperature of 15 °C, for example, which gradually increases to 67 °C, for example, on top of bottom section 25.

The water is pumped out of tank 1 on the bottom and discharges heat via an evaporator (not shown) of heat pump 63, close to exchange part 51 of the closed liquid circuit 5. The outgoing water from exchange part 51 is at a temperature of 5 °C, for example, and is pumped back on top of the buffer tank into top section 25 above the movable partition 4.

By pumping water 3, partition 4 is displaced downwards due to the pressure difference. The condenser (not shown) of heat pump 63 heats the circulating air from the treatment chamber to a temperature of 22 °C, for example. The air circulates along the product at 13 °C, for example. The product heats up to 15 °C, for example. The returning air has a temperature of 17 °C, for example, and again heated in the condenser to 22 °C, for example. As product P rises in temperature, the temperature of the condenser is increased proportionately.

By regulating the delivery of pump 7 the temperature of buffer water 3 follows the heating of product P so that the temperature difference between the evaporator and the condenser is kept as small as possible for the purpose of keeping the output of the heat pump as high as possible.

At the end of the heating cycle the outgoing water from the evaporator is at a

temperature of 57 °C, for example. The outgoing air from the condenser is at 69 °C, for example, the incoming air is at 67 °C, for example, and the temperature of the product is approximately 65 °C, for example.

The partition is now underneath buffer tank 1 with buffer water 3 on top in top section 24. The temperature of the buffer water is now 5 °C, for example, at the bottom of top section 24, and gradually increases to 57 °C, for example, at the top of top section 24. After heat treatment of product P, this is recooled by storing energy/heat in buffer tank 1. Water 3 is pumped at the top out of top section 24 of the tank and is heated via the condenser to 67 °C, for example, and is pumped at the top of the tank back into bottom section 25. The outgoing air from the evaporator is at 60 °C, for example, and circulates along product P which cools down to 62 °C, for example. The returning air has a temperature of 64 °C, for example.

As the temperature of product P drops, the temperature of the evaporator is reduced proportionately. By regulating the delivery of pump 7, the temperature of the buffer water 3 follows the cooling of product P (or of the thermally insulated space 6) so that the temperature difference between the evaporator and the condenser is again kept as small as possible. At the end of the cooling cycle the outgoing water temperature from the condenser is at 15 °C, for example. The outgoing air from the evaporator is at a temperature of 8 °C, for example, the incoming air is at a temperature of 11 °C, for example, and the product has a temperature of 13 °C, for example. Partition 4 is now on top of the tank, with the buffer water underneath in bottom section 25.

The temperature of buffer water 3 is now at a temperature of 15 °C, for example, underneath the bottom section, and gradually increases to 67 °C, for example, on top of the bottom section.

In the description of certain embodiments according to the present invention, different features are sometimes grouped into one single embodiment, figure or description of it with the aim of contributing to an understanding of one or more of the different inventive aspects of the invention. This must not be interpreted as implying that all features of the group are necessarily present for solving a specific problem.

Whilst the principles of the invention above are described in connection with specific embodiments, it must be clearly understood that this description has only been given by way of an example and does not limit the scope of protection intended by the attached claims.

Claims

1. A system for heat recuperation, comprising:

- a thermally insulated chamber;

- a buffer tank, comprising a container for the storage of a liquid, the container comprising a top end and a bottom end, an internal separating element which is designed to separate a top section of the container in a liquid-tight manner from a bottom section, wherein the internal separating element is also designed to be movable through the container without losing liquid tightness between the top section and the bottom section, the relative volumes of the top section and the bottom section varying in this case;

- an external circuit arrangement which connects the top end to the bottom end and which defines a further closed liquid circuit which comprises an exchange part which is designed to be able to exchange heat with the thermally insulated chamber;

- a pressure means for generating a pressure difference in a liquid present in the buffer tank and the external circuit, for example between the upper edge and lower edge of the separating element, over the closed liquid circuit;

- a heat pump system which is thermally coupled to the thermally insulated chamber and to the exchange part for exchanging heat between the thermally insulated chamber and the exchange part.

2. A system for heat recuperation according to Claim 1 , further comprising a means ... for determining the temperature of a buffer medium in the vicinity of the exchange part, a means for determining an internal temperature of the thermally insulated chamber, and a control unit which is designed to receive information from these means and for activating the pressure means so that the flow rate and/or the temperature of the supplied buffer medium in the vicinity of the exchange part is controlled according to the temperature in the thermally insulated chamber.

3. A system for heat recuperation according to Claim 2, wherein the control unit is designed to keep the absolute temperature difference between the thermally insulated chamber and the buffer medium in the vicinity of the exchange part smaller than 15 °C at all times.

4. A system for heat recuperation according to Claim 3, wherein the exchange part comprises a heat exchanger and wherein the control unit is designed to keep the absolute temperature difference between the thermally insulated chamber and the buffer medium at the outlet of the heat exchanger smaller than 15 °C at all times.

5. A system for heat recuperation according to any one of the preceding claims, wherein the thermally insulated chamber can be opened and closed so that a product can be received in/removed from the chamber.

6. A system for heat recuperation according to any one of the preceding claims, wherein the means for generating a pressure difference comprises at least one pump which is installed in the closed liquid circuit.

7. The use of a system according to any one of Claims 1 to 6, for the cyclic drying of a product in the thermally insulated chamber.

8. The use according to Claim 7, where the product contains wood.

9. A method for exchanging energy between a thermally insulated space with a continuously falling or continuously rising temperature gradient and a liquid in a closed liquid circuit, wherein the closed liquid circuit comprises an exchange part which is designed to be able to exchange heat with the thermally insulated space by means of a heat pump system which is thermally coupled to the thermally insulated space and to the exchange part in order to exchange heat between the thermally insulated space and the exchange part, including allowing the liquid to flow through into the exchange part, controlling the temperature of the supplied liquid in the exchange part so that the temperature difference between the thermally insulated space and the supplied liquid close to the exchange part with the heat pump is smaller than 15 °C.