SOLAR DEVICE FOR AUTONOMOUS REFRIGERATION BY SOLID-GAS SORPTION

Abstract

A device is provided for the autonomous production of refrigeration approximately 40 C. lower than ambient temperature from a low-temperature solar thermal source, the device including: (i) a reactor arranged to cool and/or heat the solid reagent; (ii) a condenser; (iii) a first tank for storing the liquid refrigerant at ambient temperature; (iv) an enclosure arranged to store a phase-change material and also including an evaporator; (v) a second tank for storing the liquid refrigerant at a low temperature; (vi) apparatus for conveying the refrigerant and (vii) apparatus for controlling the flow of the refrigerant.

Claims

1. An autonomous device for the production of refrigeration from a low-temperature solar thermal source between 50 C. and 130 C., said refrigeration being produced with a temperature difference 5 C. to 40 C. lower than ambient temperature and said device implementing a method for the thermochemical sorption of a refrigerant by a solid reagent, said device comprising: a reactor arranged to contain the solid reagent and comprising at least one heat exchanger to cool and/or heat said reactor; a condenser capable of liquefying the gaseous refrigerant coming from the reactor; a first tank for storing the liquid refrigerant produced by the condenser at ambient temperature; an enclosure arranged to store a phase-change material and also comprising an evaporator in direct contact with said phase-change material and capable of evaporating the liquid refrigerant; a second tank for storing the liquid refrigerant at a temperature lower than ambient temperature, connected to the first tank on the one hand and the evaporator and the reactor on the other hand; at least one means of conveying the refrigerant arranged to circulate said refrigerant in liquid or gaseous form between the reactor, the first tank, the second tank and the evaporator; and at least one means of controlling the flow of the refrigerant acting on the means of conveying the refrigerant, said at least one control means being arranged to regulate the flow of the refrigerant independently as a function of the pressures prevailing in the reactor, the first and second tanks, the condenser and the evaporator.

2. The device according to claim 1, characterized in that the enclosure and/or the second tank are thermally insulated.

3. The device according to claim 1, characterized in that the evaporator is supplied with liquid refrigerant from the second tank by the difference in the density of said refrigerant between the inlet and outlet of said evaporator.

4. The device according to claim 1, characterized in that the reactor also comprises an isothermal housing arranged to contain the heat exchanger and/or the reactor and capable of reducing the heat losses of said reactor.

5. The device according to claim 1, characterized in that the reactor is made up of a plurality of tubular elements comprising the solid reagent and connected to each other by said means of conveying the refrigerant.

6. The device according to claim 5, characterized in that the plurality of tubular elements is coated with a solar-absorbing coating to improve the thermal efficiency of the plurality of tubular elements, said coating being in close contact with the wall of the plurality of tubular elements.

7. The device according to claim 6, characterized in that the solar-absorbing coating has low infrared emissivity.

8. The device according to claim 5, characterized in that the reactor also comprises at least one covering element transparent to solar radiation, arranged to reduce the heat losses and enhance the solar collection efficiency, said at least one covering element extending beyond the surface of the reactor exposed to the sun.

9. The device according to claim 5, characterized in that at least one of the surfaces of the reactor not exposed to the sun is thermally insulated in order to reduce the heat losses.

10. The device according to claim 5, characterized in that the reactor also comprises actuation means in order to orient the plurality of tubular elements of the reactor in a plane substantially perpendicular to the direction of the sun and thus present the maximum possible solar-absorbing area.

11. The device according to claim 8, characterized in that the night-time cooling of the reactor is provided by natural circulation of the air in the reactor.

12. The device according to claim 11, characterized in that the reactor also comprises at least one flap for the ventilation of the plurality of tubular elements, said at least one flap being located at the top and/or bottom of said reactor.

13. The device according to claim 12, characterized in that the at least one ventilation flap is arranged to seal the reactor when it is in the closed position.

14. The device according to claim 12, characterized in that the at least one ventilation flap also comprises drive means to open and/or close it.

15. The device according to claim 14, characterized in that the drive means consists of a low-power electric motor.

16. The device according to claim 15, characterized in that the electric motor is powered by an electricity production and/or storage device.

17. The device according to claim 14, characterized in that the drive means consists of a rack and pinion device actuated by a compressed air rotary jack connected to a compressed air reserve.

18. The device according to claim 17, characterized in that the compressed air reserve is refilled by an air compressor powered by photovoltaic panels.

19. The device according to claim 14, characterized in that the drive means consists of a rack and pinion device actuated by a single-acting hydraulic linear jack controlled by a thermostat bulb in thermal contact with an absorbing plate exposed to the sun.

20. The device according to claim 11, characterized in that the plurality of tubular elements also comprises a plurality of circular fins the base of which is in close thermal contact with the wall of the tubular elements in order to enhance the heat exchanges.

21. The device according to claim 20, characterized in that the plurality of fins is covered with a solar-absorbing coating to enhance the heat exchanges.

22. The device according to claim 11, characterized in that the plurality of tubular elements is arranged horizontally in order to improve the flow of air around said tubular elements.

23. The device according to claim 11, characterized in that the condenser is of the finned tube exchanger type and cools, during the day, by natural air convection around said finned tubes.

24. The device according to claim 5, characterized in that the night-time cooling of the reactor is provided by a heat pipe loop operating as a thermosyphon and comprising: a working fluid capable of performing thermodynamic work, said working fluid propagating in the heat pipe loop by means of at least one means of conveying; a so-called heat pipe evaporator, working in conjunction with the plurality of tubular elements of the reactor and arranged to evaporate the working fluid and absorb the heat released by the reactor; a so-called heat pipe condenser, working in conjunction with the evaporator and the reactor, said condenser being arranged to liquefy the working fluid and perform a heat transfer with the outside air; a working fluid tank arranged to store said liquid working fluid and enable the optimum filling of the at least one tubular element of the reactor with working fluid; a passive, autonomous device for controlling the flow of the working fluid in the heat pipe loop comprising: a first working fluid flow control means, located between the working fluid tank and the bottom of the at least one means of conveying the working fluid, said first control means being arranged to control the liquid working fluid supply to the at least one means of conveying the working fluid; and a second working fluid flow control means, located between the outlet of the heat pipe evaporator and the heat pipe condenser, arranged to control the movement of the gaseous working fluid in the at least one means of conveying the working fluid.

25. The device according to claim 24, characterized in that it also comprises a valve for starting the heat pipe loop, arranged to fill said heat pipe loop with working fluid and/or drain it.

26. The device according to claim 24, characterized in that the heat pipe evaporator comprises at least one means of conveying the working fluid arranged inside the plurality of tubular elements of the reactor and in close thermal contact with the solid reagent, said at least one means of conveying the working fluid associated with each tubular element being connected to each other by manifolds at the top and bottom.

27. The device according to claim 24, characterized in that the heat pipe condenser is made up of at least one finned tube connected to each other by means of conveying the working fluid.

28. The device according to claim 27, characterized in that the at least one finned tube of the heat pipe condenser are arranged substantially horizontally at the rear of the reactor, with a slight tilt to enable the gravity flow of the liquefied working fluid to the working fluid tank.

29. The device according to claim 24, characterized in that the working fluid tank is arranged to maintain a minimum working fluid level in the means of conveying said working fluid of between one third and three quarters of the height of a tubular element of the reactor.

30. The device according to claim 24, characterized in that the working fluid tank is arranged to evaporate the working fluid and also comprises the refrigerant condenser arranged to liquefy said refrigerant.

31. The device according to claim 24, characterized in that the device for controlling the flow of working fluid in the heat pipe loop also comprises at least one autonomous control means, arranged to respectively open and close the first and second working fluid flow control means.

32. The device according to claim 31, characterized in that the at least one autonomous control means of the first and second working fluid flow control means comprises: an absorbing plate capable of absorbing solar radiation and emitting in the infrared, said absorbing plate being arranged to heat by means of day-time solar radiation and cool during the night; a thermostat bulb in thermal contact with the absorbing plate, comprising a fluid capable of expanding under the effect of a temperature variation; and a connecting element working in conjunction firstly with the thermostat bulb and secondly with the first and/or second working fluid flow control means, said connecting element being arranged to open or close said working fluid flow control means.

33. The device according to claim 5, characterized in that it consists of a modular architecture made up of: a plurality of first assemblies each comprising: the reactor made up of a plurality of tubular elements and comprising the heat exchanger; the condenser capable of liquefying the refrigerant; the tank for storing the refrigerant at ambient temperature, the volume of which corresponds to the volume of the plurality of tubular elements of said first assembly; refrigerant flow control means; a second assembly comprising: the enclosure arranged to store a phase-change material and comprising thermal insulation; the second tank for storing the liquid refrigerant at a temperature lower than ambient temperature and comprising thermal insulation; the evaporator for evaporating the refrigerant, located in the enclosure and working in conjunction with the second tank; first means of controlling the flow of refrigerant between the evaporator and the second tank; and second means of controlling the flow of refrigerant to ensure the connection between the second assembly and the plurality of first assemblies.

34. The device according to claim 33, characterized in that the evaporator is of the flooded type and comprises at least one tubular element arranged to circulate the refrigerant by thermosyphon with the second tank.

35. The device according to claim 33, characterized in that the second assembly comprises a tight isolation valve, arranged to fill the device with refrigerant and/or drain it.

36. The device according to claim 1, characterized in that the refrigerant is ammonia.

37. Use of the device according to claim 1 to produce refrigeration.

38. Use of the device according to claim 1 to produce water.

39. The use of the device according to claim 38, characterized in that water is produced by condensing water vapour contained in the air on a wall kept cold by the device according to claim 1.

Description

DESCRIPTION OF THE FIGURES AND EMBODIMENTS

[0099] Other advantages and characteristics of the invention will become apparent from the following description and from several embodiments given as non-limitative examples with reference to the attached schematic drawings, in which:

[0100] FIG. 1 shows a Clausius-Clapeyron diagram of the thermodynamic states of the components of the device according to the invention over the course of the two main phases,

[0101] FIG. 2 shows a schematic diagram of the thermochemical refrigeration device according to the invention,

[0102] FIG. 3 shows the day-time phase of the operation of the device according to the invention, consisting of a solar regeneration and energy production phase,

[0103] FIG. 4 shows the night-time phase of the operation of the device according to the invention, consisting of a refrigeration phase,

[0104] FIGS. 5a and 5b respectively show side and front diagrams of a reactor comprising the heat exchanger of the device according to the invention in a first embodiment wherein the night-time cooling is provided by natural convection,

[0105] FIG. 6 shows a particular method of autonomous control of a ventilation flap for the day-time heating and night-time cooling of the reactor according to the invention,

[0106] FIG. 7 shows a diagram of a reactor comprising the heat exchanger of the device according to the invention in a second embodiment wherein the night-time cooling is provided by a heat pipe loop,

[0107] FIGS. 8a and 8b respectively show the day-time state and the night-time state of an autonomous control means of the first and second means for controlling the flow of the working fluid in the heat pipe loop,

[0108] FIGS. 9a, 9b and 9c respectively show front, side and detailed diagrams of a particular embodiment of a reactor comprising the heat exchanger according to the invention and cooled by a heat pipe loop,

[0109] FIG. 10 shows a particular embodiment of the invention wherein the autonomous refrigeration device has a modular design,

[0110] FIG. 11 shows a diagram of the refrigeration module of the device according to the invention,

[0111] FIGS. 12a, 12b and 12c respectively show front, longitudinal cross-sectional and transverse cross-sectional views of an evaporator of the modular device according to the invention.

[0112] The embodiments which will be described below are in no way limitative; it is possible in particular to imagine variants of the invention comprising only a selection of characteristics described below in isolation from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art. This selection comprises at least one, preferably functional, characteristic without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art.

[0113] In particular, all the variants and all the embodiments described can be combined together if there is no objection to this combination from a technical point of view.

[0114] In the figures, the elements common to several figures retain the same reference.

The Refrigeration Method

[0115] The method for intermittent solar refrigeration described below and the object of the present invention is a thermochemical sorption thermal method the principle of which is based on the combination of a liquid/gas change of state of a refrigerant G and a reversible chemical reaction between a solid reagent and this refrigerant:

S.sub.1+G.sub.(Gas)S.sub.2Q.sub.R and G.sub.(Liq)+Q.sub.LG.sub.(Gas)

[0116] In the case of the synthesis reaction of the solid S.sub.2 from left to right, the refrigerant gas G reacts with the refrigerant-lean salt reagent S.sub.1 to form the refrigerant-rich salt S.sub.2. This reaction is exothermic and releases heat of reaction Q.sub.R. Furthermore, the gas G absorbed by S.sub.1 is produced by evaporation of the refrigerant liquid G by absorbing the latent heat Q.sub.L.

[0117] In the reverse direction from right to left, the endothermic decomposition reaction of the solid S.sub.2 requires the thermal gain Q.sub.R so that the reagent S.sub.2 releases the refrigerant gas G again. It is then condensed by releasing latent heat Q.sub.L.

[0118] These processes are implemented in two connected tanks that exchange the refrigerant gas G, thus forming a thermochemical dipole wherein the first tank, made up alternately of the evaporator or the condenser, is the seat of the change of state of the refrigerant G. The second tank is made up of the reactor and contains the solid reagent salt reacting reversibly with the refrigerant G.

[0119] The physico-chemical processes implemented in such a thermochemical method are monovariant and, with reference to FIG. 1, the thermodynamic equilibria implemented over the course of the two main phases of the method according to the invention can be represented by straight lines in a Clausius-Clapeyron diagram:

Ln(P)=f(1/T)

[0120] Each of the straight lines shown in FIG. 1 describes the change in temperature T and pressure P at the thermodynamic equilibrium of each element forming the device according to the invention (reactor, condenser, tanks, evaporator) that will be described in the paragraphs below.

[0121] The step of regeneration of the thermochemical dipole takes place at high pressure Ph imposed either by the reactor heating conditions during decomposition or by the refrigerant condensation conditions. Conversely, the refrigeration step takes place at low pressure Pb imposed by the reactor cooling conditions during synthesis and the refrigeration temperature Tf produced at the evaporator.

Description of the Device According to the Invention

[0122] To implement this thermochemical method with a solar thermal source, the simplest device according to the invention comprises the following elements, listed with reference to FIG. 2: [0123] a reactor 202 in which the solid reagent is confined, equipped with at least one heat exchanger 201 for the heating and cooling of the reactor 202 and comprising means 203 of conveying the refrigerant to the condenser 207 or the evaporator 212; [0124] a condenser 207 equipped with a first tank 208 storing the condensed liquid refrigerant 217 at ambient temperature; [0125] an evaporator 212 supplied for example by thermosyphon, i.e. by the difference in density of the refrigerant between the liquid inlet 218 and the two-phase outlet 219 of said evaporator 212, by means of a second tank 209 that can be thermally insulated from the external environment and contains the liquid refrigerant at the temperature of the refrigeration produced. The evaporator 212 is placed in an enclosure 215 that is also thermally insulated; [0126] refrigerant flow control means 204, 205 and 206, such as for example check valves, enabling the autonomous management of the refrigerant flows. The control means 204, 205 on the one hand and 206 on the other hand respectively make it possible to regulate the flow of the refrigerant in gaseous form on the one hand and liquid form on the other hand. If there is a pressure difference upstream and downstream of said control means 204 to 206, then the valves are open. By way of example, for the so-called gaseous valves 204 and 205, a pressure difference of less than 100 mbar can be preferable to ensure, in the day, slightly higher pressure in the reactor 202 relative to the condenser 207, and, at night, slightly lower pressure in the reactor 202 relative to the evaporator 212. Conversely, for the valve 206 installed on the liquid connection between the first 208 and second 209 tanks, a pressure difference corresponding to the difference between the refrigerant condensation pressure and evaporation pressure can preferably be chosen. By way of example, this pressure difference can be in the region of 5 to 10 bar lower.

Operation of the Device

[0127] The solar refrigeration device 200 according to the invention thus involves the transformation of a consumable solid reagent arranged in a reactor 202 and operates according to an intrinsically discontinuous method. It comprises two main phases that are described below with reference to FIGS. 3 and 4: [0128] a day-time regeneration phase (FIG. 3) during which the reactor 202 is connected to the condenser 207. This phase consists of heating the reactor 202 to a so-called high temperature Th, by means of the incident solar thermal energy, thus making it possible to decompose the charged salt S2 during the day. The refrigerant gas G released by this reaction first condenses in the condenser 207 at ambient temperature To and is then stored in the first tank 208 in liquid, preferably condensed, form; [0129] a night-time refrigeration phase (FIG. 4) during which the reactor 202 is connected to the evaporator 212. This phase consists of cooling the reactor 202 to ambient temperature To. The evaporator 212 is the seat of the refrigerating chemical reaction, pumping heat to the environment to be cooled on the one hand and releasing the refrigerant gas G on the other hand. The salt S1 contained in the reactor 202 then reabsorbs the gas G coming from the evaporator 212 by releasing heat of reaction to the environment at ambient temperature To. The refrigeration produced then enables the solidification of a phase-change material 213. By way of non-limitative examples, this can for example be the production of ice or the solidification of a paraffin. The phase-change material 213 thus makes it possible to store the refrigeration produced at night in order to redeliver it on demand throughout the day.

[0130] The operation of said autonomous solar refrigeration device 200 will now be described in detail over a daily cycle.

[0131] At the start of the day, the reactor 202 is at a temperature close to the outside ambient temperature To and at a so-called low pressure Pb (point S in FIG. 1). It is then connected to the evaporator 212 (point E in FIG. 1) producing refrigeration at a so-called cold temperature Tf and steam that is absorbed by the reactor 202. As the pressure in the reactor 202 is then slightly lower than the pressure in the tank 209 and the evaporator 212, the pressure difference is slightly greater than the pressure of the valve 205. As day breaks, the reactor 202 is gradually exposed to the sun and its temperature increases: it then starts to desorb the refrigerant gas G by decomposition of the reagent. The pressure in the reactor 202 then increases and the pressure difference between the evaporator 212 and the reactor 202 decreases. When the pressure difference becomes lower than the opening pressure of the check valve 205, it closes and no longer allows this steam to transfer to the reactor 202. The closing of the check valve 205 makes it possible for the pressure in the reactor 202 to increase more quickly (movement from point S to point D of the reactor along the straight line of equilibrium in FIG. 1). The benefit provided by the check valve 205 is that it makes it possible to maintain the cold temperature of the enclosure to be refrigerated by preventing the steam desorbed by the reactor 202 under the action of the exposure of the reactor 202 to the sun from condensing in the evaporator 212 and increasing the temperature thereof again.

[0132] When the pressure in the reactor 202 becomes slightly higher than the pressure prevailing in the first tank 208 of condensed liquid at ambient temperature To, the valve 204 opens in order to cool and condense the desorbed gas leaving the reactor 202 to the temperature Th in the condenser 207. The condensed gas is then stored throughout the day at the day-time ambient temperature To in the first tank 208 (corresponding to point C in FIG. 1).

[0133] When, at dusk, the solar radiation is no longer sufficient, the temperature prevailing inside the reactor 202 starts to decrease, then leading to a reduction in the internal pressure of the reactor 202. The pressure differential between the reactor 202 and the condenser 207 decreases and, beyond a certain threshold, then becomes lower than the opening pressure of the valve 204. The valve then closes and isolates the reactor 202, thus preventing it from reabsorbing the steam contained in the first tank 208 at ambient temperature To. The reactor 202 is cooled to ambient temperature To, also leading to a reduction in the internal pressure thereof in accordance with its thermodynamic equilibrium (corresponding to migration from point D to point S in FIG. 1).

[0134] Depending on the equilibria and thresholds chosen, the refrigeration temperatures Tf produced and the outside ambient temperature To, two different embodiments for the cooling of the reactor 202 are proposed and described in the paragraphs below.

[0135] As the reactor 202 cools down, the pressure thereof then also becomes lower than the pressure prevailing in the second tank 209. Advantageously, this can be thermally insulated from the outside in order to maintain the liquid refrigerant 218 contained in the tank 209 at a temperature lower than ambient temperature during the day, thus preventing the temperature of the refrigerant contained in the evaporator 212 from increasing over the course of the day. As a result, the pressure prevailing in the thermally insulated second tank 209 is lower than the pressure prevailing in the uninsulated first tank 208. The pressure decrease then enables the valve 205, when a certain pressure difference corresponding to the valve opening threshold is reached, to open, thus permitting the reactor 202 to take in and chemically absorb the gas coming from the second tank 209.

[0136] The pressure then decreases in the second tank 209 and, when the pressure difference with the first tank 208 of condensed liquid is sufficient, for example in the region of a few bar (typically 1 to 10 bar), the valve 206 opens and supplies the second tank 209 with liquid at the night-time temperature To, until all of the condensed liquid refrigerant contained in the first tank 208 has been decanted into the second tank 209 via the valve 206. As the reactor 202 continues to absorb the steam produced by evaporation of the liquid contained in the second tank 209, the decanted liquid cools until the temperature thereof is lower than the temperature of the refrigerant contained in the evaporator 212 maintained at a higher temperature by the PCM 213.

[0137] Thereafter, circulation of the refrigerant is triggered naturally, by thermosyphon, using the difference in density of the liquid refrigerant between the evaporator 212 and the second tank 209. The evaporator 212 is then supplied from the bottom 218 with liquid refrigerant that is denser than at its diphasic outlet 219. The refrigerant leaving the evaporator 212 through the diphasic outlet 219 is made up of both a liquid phase and a gaseous phase, which makes it less dense than the solely liquid refrigerant entering the evaporator 212. The steam produced in the evaporator 212 is then sucked into the second tank 209 and absorbed by the reactor 202 via the valve 205. The refrigeration is thus produced in the evaporator 212 throughout the night until sunrise, when the reactor starts to heat up; the refrigeration produced during the night is stored in the phase-change material 213 to be delivered according to the refrigeration requirements during the day.

Solar Heating of the Reactor

[0138] To achieve efficient heating, the heat exchanger 201 of the reactor 202 must have the largest possible solar absorption area. According to a particular embodiment, the optimum orientation is obtained by aligning the heat exchanger 201 with the direction normal to the sun, i.e. for example tilted relative to the ground at an angle preferably corresponding to a latitude close to the latitude of the site for optimum refrigeration production throughout the year.

[0139] Such a heat exchanger 201, arranged to utilise solar radiation, will now be described with particular reference to FIGS. 5a and 5b.

[0140] To utilise solar radiation to maximum effect, and according to a particular embodiment, the heat exchanger 201 is coupled to the reactor 202 and is made up of a set of tubular elements 501 comprising the solid reagent material 502. The tubular elements 501 are distributedpreferably evenlyin an isothermal housing 503, and are connected to each other by means of conveying 504for example manifoldsand linked to the condenser 207 and/or the evaporator 212.

[0141] According to a particular embodiment, the tubular elements 501 are covered with a solar-absorbing coating 505, if possible selective, in close contact with the wall of the tubular elements 501. The solar-absorbing coating 505 has high solar absorptivity and, advantageously, low infrared emissivity.

[0142] A cover that is transparent to solar radiation 506 covering the front surface of the heat exchanger 201 exposed to the sun makes it possible to reduce heat losses by convection. Preferably, it can also reduce radiation losses and enhance the greenhouse effect, by blocking the infrared radiation emitted by reactors heated to a high temperature. Ultimately, the solar collection efficiency is maximized.

[0143] Advantageously, thermal insulation 507for example using rock wool or glass woolcan be applied to the rear surface of the heat exchanger 201 in order to reduce heat losses by conduction and/or convection to the external environment.

Night-Time Cooling of the Reactor

[0144] The night-time cooling of the reactor 202 can be achieved according to two embodiments described below, the selection of which depends on the solid reagent 502 used in the reactor 202, the temperature of the refrigeration Tf to be produced and the night-time ambient temperature To: [0145] the first embodiment for cooling the reactor consists of natural circulation of air in said reactor 202, by external cooling of the tubular elements 501. This first embodiment can be implemented when the solid reagent 502 makes it possible to obtain a sufficiently large operating temperature difference (typically greater than 20 C.) between the night-time outside air temperature To and the stagnation temperature of the reaction at the pressure imposed by the evaporation of the refrigerant at Tf in the evaporator; [0146] the second embodiment for cooling the reactor 202 consists of a heat pipe loop operating as a thermosyphon; it is selected when cooling by natural air circulation cannot be implemented.

[0147] Each of these two embodiments, together with all of the variants of which they are comprised, are compatible with any one of the embodiments of the invention set out above or below.

First Embodiment: Reactor Cooling by Natural Convection

[0148] FIGS. 5a and 5b respectively show side and front diagrams of a reactor 202 comprising the heat exchanger 201 of the device 200 according to the invention and according to this first embodiment of night-time cooling of said reactor 202 provided by natural air convection.

[0149] This cooling thus uses the air circulation caused by the stack effect in the reactor 202 by means of opening the ventilation flaps located at the top 509 and bottom 508 of the reactor 202.

[0150] Advantageously, to improve the heat exchanges and heat removal, the tubular elements 501 are equipped with fins 510, for example circular, the base of which is in close thermal contact with the wall of the tubular elements 501 of the reactor 202.

[0151] Advantageously, they can be arranged horizontally in order to improve the heat convection coefficient by promoting an air flow substantially perpendicular to the direction of the tubular elements 501 in the reactor 202.

[0152] Finally, in order to absorb the solar radiation more efficiently, the fins 510 can be covered with a solar-absorbing coating in a similar way to the coating that can cover the tubular elements 501.

[0153] In this first embodiment for cooling the reactor 202, the reactive gas condenser 207 can be of the finned tube type and placed at the rear or said reactor 202. It is then cooled during the day by natural convection of the air on the finned tubular elements.

[0154] Each ventilation flap 508, 509 comprises a plate 511 arranged to be airtight on the frame of the reactor 202 during the day, and a rotating rod actuated in particular at daybreak to close said flap 508, 509 and at nightfall to open said flap 508, 509.

[0155] According to an advantageous variant, the ventilation flap 508, 509 can also comprise drive means 600 arranged to rotate it by means of various devices, controlled for example as a function of the detection of daybreak or nightfall, a temperature increase (thermostat device) or a solar irradiance threshold.

[0156] Different variants of these drive means 600 are proposed and described in the paragraphs below. They are all compatible with any one of the embodiments of the invention set out above or below.

First Variant of the Ventilation Flap Drive

[0157] The ventilation flap 508, 509 can be driven using a low-power electric motor that is, according to an advantageous variant, supplied by an electric battery recharged by a photovoltaic collector. Typically, the power requirements are sufficiently low and brief for the area of said photovoltaic collector to be less than one square metre.

Second Variant of the Ventilation Flap Drive

[0158] The ventilation flap 508, 509 can also be driven using a rack and pinion device that can for example be actuated by a double-acting compressed air -turn rotary jack. The rotary jack is then connected to a compressed air reserve (typically 6 bar) via a 5/3 or 4/3 monostable spool valve that is actuated over a short period (momentary control lasting approximately ten seconds) as a function of the solar irradiance. The closing of the ventilation flap is actuated when the irradiance is above a first threshold (obtained close to the moment when the sun rises) and the opening of the flap is actuated when the irradiance is below a second threshold (obtained close to the moment when the sun sets). Advantageously, the first closing threshold can be greater than the second opening threshold of said flaps.

[0159] The compressed air reserve can be refilled periodically by an air compressor powered by photovoltaic panels.

Third Variant of the Ventilation Flap Drive

[0160] The ventilation flap 508, 509 can also be driven using the device 600 described in FIG. 6. It is a rack and pinion device 601/602 actuated by a single-acting hydraulic linear jack 605 ultimately controlled by a thermostat bulb 611 in thermal contact with an absorbing plate 612 exposed to the sun.

[0161] The thermostat bulb 611 contains a fluid 613 that is sensitive to temperature variations. More particularly, the fluid 613 is capable of vaporizing over a temperature range that is preferably between To and Th and corresponds to a pressure range compatible with the opening and closing of the ventilation flap 508, 509 that it controls. The vaporization of the fluid 613 makes it possible to pressurise the hydraulic liquid 606 contained in the hydraulic linear jack 605 by means of an accumulator 608 containing a deformable bladder 609, working in conjunction with the thermostat bulb 611 and deformed by the fluid 613.

[0162] The hydraulic liquid 606 pressurized in this way makes it possible to move both the piston 604 of the jack 605 and the rack 601, thus rotating the rod 620 of the ventilation flap 508, 509 by means of the drive pinion 602.

[0163] A return spring 603 makes it possible to push the hydraulic liquid 606 back towards the accumulator 608 when the pressure in the thermostat bulb 611 decreases following reduced exposure of the solar-absorbing plate 612.

[0164] The quantity of fluid 613 contained in the thermostat bulb 611 is defined as a function firstly of the volume of the bladder 609 pressurizing the hydraulic liquid 606 of the jack 605, and secondly of the maximum pressure to be reached to actuate the ventilation flap 508, 509, which must also correspond to an intermediate temperature Ti between To and Th and at which there is no more fluid 613 to be vaporized.

[0165] The device according to this particular embodiment is entirely passive, autonomous and automatically controlled by the intensity of the solar radiation.

Second Embodiment: Reactor Cooling by Heat Pipe Loop

[0166] In this embodiment, the reactor 202 is cooled at night and/or the refrigerant condenser is cooled during the day by a heat pipe loop. It is thus possible to transfer heat, firstly by evaporating a working fluid that has absorbed the heat released by the reactor 202 during the night-time refrigeration production phase or by the condenser 207 during the day-time reactor 202 regeneration phase, and secondly by condensing said working fluid, thus releasing the heat previously absorbed directly to the outside air via the heat pipe condenser 702.

[0167] During the night, a heat pipe evaporator 701, incorporated into the tubular elements 501, is supplied with liquid working fluid and thus cools the reactor 202 by evaporation of the liquid working fluid. The steam produced in this way condenses at night-time ambient temperature in a heat pipe condenser 702. The working fluid liquefied in this way flows by gravity into the tank 705 by means of the connection via the tubing 707 between said tank 705 and the inlet of the heat pipe condenser 702.

[0168] During the day, the heat pipe evaporator 701 incorporated into the reactor 202 is inactive due to the closing of two valves 703, 704 placed between the evaporator 701 and the condenser 702 of the heat pipe loop. The first, 703, makes it possible to control the flow of the working fluid through a liquid connection located at the bottom, while the second, 704, makes it possible to control the flow of the working fluid through a gas connection located at the top.

[0169] Thus, when the reactor 202 is heated by the sun during the regeneration phase, the pressure in the heat pipe evaporator 701, isolated in this way, increases and causes the draining of the working fluid from the bottom of the evaporator 701 in liquid form. It is then stored in a working fluid tank 705 by means of a drain line 709. Preferably, the working fluid tank 705 is arranged to store the liquid working fluid during the draining of the evaporator incorporated into the reactor. The reactor 202 is thus arranged to increase in temperature and perform its regeneration during the day.

[0170] With reference to FIGS. 7 and 9, the heat pipe loop for cooling the reactor 202 thus comprises: [0171] a heat pipe evaporator 701 preferably comprising a tube 701 arranged inside the tubular elements 501 of the reactor 202 and advantageously in close thermal contact with the solid reagent material 502. The tubular elements 501 of a reactor 202, tilted vertically, each comprise an evaporator tube 701 connected by manifolds at the bottom and top; [0172] a fluid condenser 702 of the heat pipe loop, preferably comprising a set of finned tubes connected to each other by manifolds and exchanging directly with the outside ambient air. These finned tubes are preferably arranged horizontally at the rear of the reactor 202, advantageously with a slight tilt enabling the condensed working fluid to flow to a condensed liquid working fluid tank 705; [0173] a condensed liquid working fluid tank 705 the position of which advantageously enables satisfactory filling of the evaporator tubes 701 of the heat pipe loop with working fluid. According to a particular embodiment, the working fluid is preferably maintained at a minimum liquid working fluid level in the evaporator tubes 701 of between one third and three quarters of the height of the tube 701. According to another embodiment, the liquid working fluid tank 705 also comprises the condenser 207 to condense the reactive gas released during the day by the reactor 202 heated in the sun. The working fluid tank 705 thus acts as an evaporator during the day. The working fluid steam produced by the condensing of the reactive gas is then conveyed to the condenser 702 via the pipe 707; [0174] a device for regulating the flow of the working fluid in the heat pipe loop, activated passively at the start and end of the day and comprising: [0175] a valve 704 between the liquid outlet 708 of the working fluid tank 705 and the liquid inlet at the bottom of the evaporator tubes 701, thus making it possible to supply them with working fluid throughout the night and prevent them from filling during the day; [0176] a valve 703 placed on the steam pipe of the heat pipe loop, between the steam outlet of the evaporator 701at the topand the steam inlet of the condenser 702, thus making it possible, at the start of the day, to block the passage of the steam formed in the evaporator tubes 701 and cause a pressure increase therein. This pressure increase makes it possible to flush the working fluid contained in the evaporator tubes 701 more efficiently and drain them by means of a drain pipe 709 that opens into the expansion space of the tank 705. This then enables a faster temperature increase of the reactors 202 at the start of the day and therefore more efficient heating of said reactors 202. [0177] a valve 710 for starting the heat pipe loop (evacuation and/or filling with working fluid).

[0178] According to a particular embodiment, the steam 703 and liquid 704 valves close at the start of the day and open at the start of the night independently due to the action of autonomous control means the operation of which is described with reference to FIGS. 8a and 8b.

[0179] The autonomous control means of the valves 703 and 704 consists of a thermostat bulb 801, heated during the day and cooled at night by an absorbing plate 802 that has high solar absorptivity, high infrared emissivity and low thermal mass. The absorbing plate 802 is preferably exposed to the sky to utilise both heating by solar radiation during the day and radiative cooling at night. The thermostat bulb 801 contains a fluid that is arranged, under the action of solar radiation, to increase the pressure in a bellows 803 and move a needle 804 on the seat of the port of the valve 703 or 704, thus closing off the passage of the working fluid. When the pressure drops in the thermostat bulb 801, by radiative cooling at the start of the night, the bellows 803 reduces in volume under the action of a spring 805 the stiffness of which can be adjusted by an adjusting screw 806. The needle 804 rigidly connected to the bellows 803 detaches from the seat of the valve 703 or 704 and then allows the working fluid to flow into the heat pipe loop.

Alternative Embodiment of the Device According to the Invention: a Modular Design

[0180] According to a particular variant of the invention, compatible with any one of the embodiments set out in the paragraphs above, and in order to facilitate the implementation and installation of the device according to the invention, a modular design of the device according to the invention is proposed.

[0181] With reference to FIGS. 10, 11 and 12, such a modular device comprises at least two easily connectable assemblies: [0182] a first assembly 1001 made up of several reactor modules 202, 201 as described above and each comprising the tubular elements 501 exposed to the sun, the condenser 207preferably of the ammonia typeand the first tank 208 the volume of which corresponds to the capacity of the module, the device for cooling the tubular elements 501 and the condenser 702, and the means making it possible to control the flows of reactive gas over the course of the day (valves 703, 704, 204, 205, solar devices for controlling the ventilation flaps and/or the heat pipe loop 706), [0183] a second assembly 1002 incorporating the elements necessary for refrigeration: [0184] a cold chamber 215 comprising thermal insulation; [0185] a liquid refrigerant tank 209 the volume of which preferably corresponds to the daily refrigeration requirements of the cold chamber 215. This tank comprises thermal insulation 210 in order to limit the thermal gain during the night-time refrigeration phase, and liquid 1003 and steam 1005 connections comprising connecting valves 1004 to the evaporator 212 placed in the cold chamber 215. Connections 1006 and 1007 to the valves 206 and 205 provide the connection to the first assembly 1001; [0186] an evaporator 212, preferably of the flooded type, and advantageously supplied with refrigerant by thermosyphon from the second liquid refrigerant tank 209 placed above. The evaporator 212 is made up of tubes that are vertically tilted and supplied with refrigerant from the bottom by a manifold 1008. The steam produced is collected by a second manifold 1009 placed in a higher position than the manifold 1008, so that the steam produced enables the conveyance and natural circulation of the refrigerant in the evaporator 212; [0187] a phase-change material 213 that makes it possible to store the refrigeration produced and redeliver it on demand over the course of the following day; [0188] a connection equipped with a tight isolation valve 1010 that makes it possible to start the whole device (evacuation and filling with reactive gas).

[0189] The modularity of such a device makes it possible to connect a plurality of first elements 1001 to at least one second element 1002.

[0190] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without exceeding the scope of the invention. In particular, the different characteristics, forms, variants and embodiments of the invention can be combined with one another according to various combinations inasmuch as they are not incompatible or mutually exclusive. In particular all the variants and embodiments described previously can be combined with each other.