US20180100676A1

Movatterモバイル変換

Info

Publication number: US20180100676A1
Application number: US15/560,115
Authority: US
Inventors: Driss Stitou; Sylvain Mauran; Nathalie Mazet
Original assignee: Centre National de la Recherche Scientifique CNRS
Current assignee: Centre National de la Recherche Scientifique CNRS
Priority date: 2015-03-23
Filing date: 2016-03-23
Publication date: 2018-04-12
Also published as: WO2016151017A1; CN107407511B; FR3034179B1; EP3274639B1; CA2980400A1; FR3034179A1; CN107407511A; HRP20190555T1; ES2717331T3; JP2018514735A; EP3274639A1

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.

Description

TECHNICAL FIELD

The present invention relates to a solar device for autonomous refrigeration.

The present invention lies in the fields of self-contained solar air conditioning and self-contained solar cooling.

STATE OF THE PRIOR ART

The use of solar energy for refrigeration is particularly suitable for refrigeration on isolated sites in regions with hot climates and/or that do not have access to the power grid and/or where energy supply is costly.

A number of techniques are known that enable the production of refrigeration either concomitant with the availability of day-time solar energy, or out of phase, during the night.

The current solutions are mainly based on compressor technologies, which consume large amounts of electricity and use refrigerants with high greenhouse warming potential. For isolated sites, these solutions result, for example, in electricity being produced by generators that use a fuel stored in tanks, or in electricity produced during the day by photovoltaic panels being stored in a fleet of batteries. These solutions require, as appropriate, large amounts of maintenance, frequent replenishment of fuel (weekly to monthly), periodic replacement of the battery fleet (every two to five years), and sophisticated electronic control and command devices (controllers, inverters, etc.).

More particularly, a first technique for producing refrigeration during the day consists of converting solar radiation either into electricity via photovoltaic collectors or into work via a thermodynamic engine cycle such as for example an organic Rankine engine cycle, in order then to supply a reverse thermodynamic cycle for refrigeration by expansion (Stirling cycle) or vaporization of a refrigerant (reverse Rankine cycle).

A second method consists of directly using solar radiation in thermal form to supply a gas sorption method of the liquid/gas absorption type, which requires the circulation of a binary or saline solution, such as the ammonia/water or water/lithium bromide solutions conventionally used. Such devices are for example described in U.S. Pat. No. 4,207,744 and U.S. Pat. No. 4,184,338.

These techniques are however relatively complex and costly to implement and require in particular sophisticated control and command procedures for said refrigeration method, particularly circulation pumps and compressors to circulate the working fluids, and/or require low ambient temperatures (below 35° C.) to refrigerate efficiently. These constraints affect the reliability and robustness of these methods.

Another technique is based on methods for the sorption of a gaseous refrigerant by an active solid. These are for example thermochemical methods or adsorption methods. The drawback of such methods lies in the solid nature of the sorbent materials used; they operate discontinuously and lead to intermittent refrigeration, as described for example in U.S. Pat. No. 4,586,345, U.S. Pat. No. 4,993,234 and WO 86/00691.

The object of the present invention is to at least overcome a large number of the problems set out above and also to result in other advantages.

Another purpose of the invention is to solve at least one of these problems by means of a new refrigeration device.

Another purpose of the present invention is autonomous production of refrigeration.

Another purpose of the present invention is to reduce the costs of refrigeration.

Another purpose of the present invention is to reduce the pollution associated with refrigeration.

Another purpose of the present invention is to produce refrigeration more reliably and robustly.

Another purpose of the present invention is to reduce the maintenance demands associated with refrigeration.

DISCLOSURE OF THE INVENTION

At least one of the aforementioned aims is achieved with a device for autonomous 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 the ambient temperature of the outdoor environment 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 the 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, and working in conjunction with 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,
- 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.

Preferably, the refrigeration produced by the device according to the invention is at a temperature of between −10° C. and 20° C.

The device according to the invention and the variants thereof described below make it possible to efficiently achieve both the solar heating of the reactor and the cooling of the condenser during the course of the day, and the cooling of the reactor during the course of the night.

The completely autonomous management of the day-time and night-time phases without active control is a promising solution for meeting refrigeration requirements on isolated sites in regions with hot climates that do not have access to the power grid. The device according to the invention also makes it possible to reduce production costs as there is no costly external energy supply. Furthermore, as it does not use any consumables, the maintenance of the device—which is limited to occasional cleaning of the collectors—is greatly reduced and inexpensive.

The device according to the invention also makes it possible to reduce the pollution associated with refrigeration as it can use a refrigerant that has no impact on the ozone layer or global warming. Furthermore, the device does not generate greenhouse gases or deplete fossil energy resources as it only uses thermal solar energy, which is a widely available renewable energy. Furthermore, the device according to the invention is completely silent, which is a significant advantage in urban environments or in exceptional and/or protected areas.

Finally, the device according to the invention does not have any moving mechanical parts, which thus makes it possible to reduce both the operating sound level and the wear on the components and risk of fluid leaking from dynamic sealing gaskets; the device according to the invention is more reliable.

It is also more robust due to its entirely autonomous operation that automatically adjusts to the external insolation and temperature conditions. As it does not have any control/command and/or electronic control components, it has a very long service life; the reactive composites used in the reactors of the device according to the invention have been tested over more than 30,000 cycles (corresponding to approximately 80 years of daily operation) without any loss of performance being observed.

By way of non-limitative examples, the refrigerant can be selected from water, ammonia, ethylamine, methylamine or methanol, and the solid reagent can be selected for example from calcium chloride (CaCl₂), barium chloride (BaCl₂) or strontium chloride (SrCl₂). More generally, the device according to the invention preferably uses a refrigerant other than hydrochlorofluorocarbons and chlorofluorocarbons, which deplete the ozone layer and contribute to global warming.

The phase-change materials used in the present invention to efficiently store the refrigeration produced by solidifying are preferably organic or inorganic compounds. By way of non-limitative examples, they can for example be water, an aqueous solution or a paraffin.

The means for controlling the flow of the refrigerant advantageously make it possible to regulate said flow passively, solely as a function of the pressure differences prevailing between the reactor, the condenser, the evaporator and the first and second tanks during the day-time regeneration and night-time refrigeration phases.

Advantageously, the enclosure and/or the second tank can be thermally insulated in order to reduce the energy requirements necessary to maintain the temperature inside and maintain a liquid refrigerant temperature lower than the ambient temperature during the day, thus preventing the temperature of the refrigerant contained in the evaporator from increasing over the course of the day.

Preferably, the evaporator can be supplied with liquid refrigerant from the second tank by the difference in density of said refrigerant between the inlet and outlet of said evaporator. This thermosyphon operation makes it possible generate a flow of refrigerant between the second tank and the evaporator without a pump and without an external energy supply, thus enhancing the autonomy of the device according to the invention.

Preferably, the reactor can also comprise an isothermal housing arranged to contain the heat exchanger and/or the reactor and capable of reducing the heat losses of said reactor, particularly by conduction. The insulation may be obtained by any known insulating means that withstands the temperature variations to which the reactor is subjected during the course of the night and the day, such as for example glass wool or rock wool.

Advantageously, the reactor can be made up of a plurality of tubular elements comprising the solid reagent and connected to each other by said means of conveying the refrigerant in order to make maximum use of the solar radiation and optimise the heating of the reactor. It is advantageous to maximise both the solar absorption area and the orientation of said reactor in relation to the sun. The tubular element configuration thus makes it possible to maximise both the active area of the reactor and the direct incidence of the sun on said reactor.

Preferably, the plurality of tubular elements can be 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.

By way of non-limitative examples, the coating can be a simple solar paint or a metal film (copper, aluminium, etc.) with good thermal conductivity, placed in thermal contact with the wall of the tubular elements and on which a selective thin layer can be deposited.

Advantageously, the solar-absorbing coating can have low infrared emissivity.

According to a particular embodiment, the reactor can also comprise at least one covering element transparent to solar radiation, arranged to reduce heat losses and maximise solar collection efficiency, said at least one covering element extending beyond the surface of the reactor exposed to the sun.

Optionally, the at least one covering element can also be opaque to infrared radiation in order to enhance the greenhouse effect.

Preferably, at least one of the surfaces of the reactor not exposed to the sun can be thermally insulated to reduce heat losses. The insulation may be obtained by any known insulating means, such as for example glass wool or rock wool.

According to a particular embodiment, the reactor can also comprise 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, in order to optimise the orientation of the reactor and maximise the solar collection efficiency and the associated heat exchanges.

According to a first version of the device according to the invention, the night-time cooling of the reactor is provided by natural circulation of the air in the reactor, thus making it possible to achieve cooling in a totally passive manner.

Advantageously for this first version, the reactor can also comprise 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.

Preferably, the at least one ventilation flap can be arranged to seal the reactor when it is in the closed position in order to enhance the heat exchanges inside said reactor.

Advantageously, the at least one ventilation flap can also comprise drive means to open/close it.

According to a first variant, the drive means can consist of a low-power electric motor.

Advantageously, the electric motor can be powered by an electricity production and/or storage device, optionally powered by photovoltaic panels.

According to a second variant, the drive means can consist of a rack and pinion device actuated by a compressed air rotary jack connected to a compressed air reserve.

Preferably, the compressed air reserve can be refilled by an air compressor powered by photovoltaic panels.

According to a third variant, the drive means can consist 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. This last variant is entirely passive, autonomous in terms of energy and automatically controlled.

Preferably, the plurality of tubular elements can also comprise 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.

Advantageously, the plurality of fins can be covered with a solar-absorbing coating to enhance the heat exchanges.

Advantageously, the plurality of tubular elements can be arranged horizontally in order to improve the flow of air around said tubular elements.

Preferably, the condenser can be of the finned tube type and cooled, in the day, by natural convection of the air around said finned tubes.

According to a second version of the device according to the invention, the night-time cooling of the reactor can be provided by a heat pipe loop operating as a thermosyphon and comprising:

- a working fluid capable of performing thermodynamic work,
- 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 supply of liquid working fluid to the at least one means of conveying the working fluid,
  - 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.

This second version of the cooling of the device according to the invention thus makes it possible to efficiently achieve both the heating of the reactor during the day and the cooling of firstly the reactor during the night and secondly the gaseous refrigerant flooded condenser in the working fluid tank of the heat pipe loop.

Preferably, the working fluid is selected from those fluids that have a boiling temperature at atmospheric pressure of between 0 and 40° C. and that have a pressure of between 1 and 10 bar in the temperature range from 20 to 100° C. By way of non-limitative example, it can be a type C4, C5 or C6 paraffinic hydrocarbon (such as butane, methylpropane, pentane, methylbutane, dimethylpropane, hexane, methylpentane, dimethylbutane, etc.), an HFC type working fluid conventionally used in organic Rankine cycles (R236fa, R236ea, R245fa, R245ca, FC3110, RC318, etc.), an inorganic fluid (ammonia, water), or an alcohol (methanol, ethanol, etc.).

Advantageously, the device according to this second embodiment can also comprise a valve for starting the heat pipe loop, arranged to fill said heat pipe loop with working fluid and/or drain it.

Preferably, the heat pipe evaporator can comprise 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.

Advantageously, the plurality of tubular elements of the reactor can be inclined vertically in order to facilitate the movement of the working fluid by simple gravity.

Advantageously, the heat pipe condenser can be made up of at least one finned tube connected to each other by means of conveying the working fluid.

Preferably, the at least one finned tube of the condenser can be 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.

Preferably, the working fluid tank can be 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.

The working fluid tank can also be arranged to evaporate the refrigerant and also comprises the refrigerant condenser arranged to liquefy said refrigerant.

Advantageously, the device for controlling the working fluid flow in the heat pipe loop can also comprise at least one autonomous control means, arranged to respectively open and close the first and second working fluid flow control means, for example at the start of the night and the start of the day.

Preferably, the at least one autonomous control means of the first and second working fluid flow control means can comprise:

- 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,
- 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.

According to another embodiment of the invention compatible with each of the previous variants, the device according to the invention can consist of a modular architecture comprising:

- 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,
  - second means of controlling the flow of refrigerant to ensure the connection between the second assembly and the plurality of first assemblies.

This modular arrangement makes it possible to facilitate the implementation and installation of the device.

Advantageously, the evaporator can be of the flooded type and comprise at least one tubular element arranged to circulate the refrigerant by thermosyphon with the second tank.

Preferably, the second assembly can comprise a tight isolation valve, arranged to fill the device with refrigerant and/or drain it.

Preferably, the refrigerant can be ammonia.

According to another aspect of the invention, it is proposed that the device according to the invention be used to produce ice.

Alternatively, the device according to the invention can also be used to produce water.

Advantageously, water can be produced by condensing the water vapour contained in the air on a wall that is kept cold by the device.

DESCRIPTION OF THE FIGURES AND EMBODIMENTS

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:

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,

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

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,

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

FIGS. 5aand 5brespectively 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,

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,

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,

FIGS. 8aand 8brespectively 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,

FIGS. 9a, 9band 9crespectively 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,

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

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

FIGS. 12a, 12band 12crespectively show front, longitudinal cross-sectional and transverse cross-sectional views of an evaporator of the modular device according to the invention.

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.

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.

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

The Refrigeration Method

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:

S₁+G_(Gas)⇄S₂Q_RandG_(Liq)+Q_L⇄G_(Gas)

In the case of the synthesis reaction of the solid S₂from left to right, the refrigerant gas G reacts with the refrigerant-lean salt reagent S₁to form the refrigerant-rich salt S₂. This reaction is exothermic and releases heat of reaction Q_R. Furthermore, the gas G absorbed by S₁is produced by evaporation of the refrigerant liquid G by absorbing the latent heat Q_L.

In the reverse direction from right to left, the endothermic decomposition reaction of the solid S₂requires the thermal gain Q_Rso that the reagent S₂releases the refrigerant gas G again. It is then condensed by releasing latent heat Q_L.

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.

The physico-chemical processes implemented in such a thermochemical method are monovariant and, with reference toFIG. 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)

Each of the straight lines shown inFIG. 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.

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

To implement this thermochemical method with a solar thermal source, the simplest device according to the invention comprises the following elements, listed with reference toFIG. 2:

- areactor202 in which the solid reagent is confined, equipped with at least oneheat exchanger201 for the heating and cooling of thereactor202 and comprisingmeans203 of conveying the refrigerant to thecondenser207 or theevaporator212;
- acondenser207 equipped with afirst tank208 storing the condensed liquid refrigerant217 at ambient temperature;
- anevaporator212 supplied for example by thermosyphon, i.e. by the difference in density of the refrigerant between theliquid inlet218 and the two-phase outlet219 of saidevaporator212, by means of asecond tank209 that can be thermally insulated from the external environment and contains the liquid refrigerant at the temperature of the refrigeration produced. Theevaporator212 is placed in anenclosure215 that is also thermally insulated;
- refrigerant flow control means204,205 and206, such as for example check valves, enabling the autonomous management of the refrigerant flows. The control means204,205 on the one hand and206 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 means204 to206, then the valves are open. By way of example, for the so-calledgaseous valves204 and205, a pressure difference of less than100 mbar can be preferable to ensure, in the day, slightly higher pressure in thereactor202 relative to thecondenser207, and, at night, slightly lower pressure in thereactor202 relative to theevaporator212. Conversely, for thevalve206 installed on the liquid connection between the first208 and second209 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

Thesolar refrigeration device200 according to the invention thus involves the transformation of a consumable solid reagent arranged in areactor202 and operates according to an intrinsically discontinuous method. It comprises two main phases that are described below with reference toFIGS. 3 and 4:

- a day-time regeneration phase (FIG. 3) during which thereactor202 is connected to thecondenser207. This phase consists of heating thereactor202 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 thecondenser207 at ambient temperature To and is then stored in thefirst tank208 in liquid, preferably condensed, form;
- a night-time refrigeration phase (FIG. 4) during which thereactor202 is connected to theevaporator212. This phase consists of cooling thereactor202 to ambient temperature To. Theevaporator212 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 thereactor202 then reabsorbs the gas G coming from theevaporator212 by releasing heat of reaction to the environment at ambient temperature To. The refrigeration produced then enables the solidification of a phase-change material213. By way of non-limitative examples, this can for example be the production of ice or the solidification of a paraffin. The phase-change material213 thus makes it possible to store the refrigeration produced at night in order to redeliver it on demand throughout the day.

The operation of said autonomoussolar refrigeration device200 will now be described in detail over a daily cycle.

At the start of the day, thereactor202 is at a temperature close to the outside ambient temperature To and at a so-called low pressure Pb (point S inFIG. 1). It is then connected to the evaporator212 (point E inFIG. 1) producing refrigeration at a so-called cold temperature Tf and steam that is absorbed by thereactor202. As the pressure in thereactor202 is then slightly lower than the pressure in thetank209 and theevaporator212, the pressure difference is slightly greater than the pressure of thevalve205. As day breaks, thereactor202 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 thereactor202 then increases and the pressure difference between theevaporator212 and thereactor202 decreases. When the pressure difference becomes lower than the opening pressure of thecheck valve205, it closes and no longer allows this steam to transfer to thereactor202. The closing of thecheck valve205 makes it possible for the pressure in thereactor202 to increase more quickly (movement from point S to point D of the reactor along the straight line of equilibrium inFIG. 1). The benefit provided by thecheck valve205 is that it makes it possible to maintain the cold temperature of the enclosure to be refrigerated by preventing the steam desorbed by thereactor202 under the action of the exposure of thereactor202 to the sun from condensing in theevaporator212 and increasing the temperature thereof again.

When the pressure in thereactor202 becomes slightly higher than the pressure prevailing in thefirst tank208 of condensed liquid at ambient temperature To, thevalve204 opens in order to cool and condense the desorbed gas leaving thereactor202 to the temperature Th in thecondenser207. The condensed gas is then stored throughout the day at the day-time ambient temperature To in the first tank208 (corresponding to point C inFIG. 1).

When, at dusk, the solar radiation is no longer sufficient, the temperature prevailing inside thereactor202 starts to decrease, then leading to a reduction in the internal pressure of thereactor202. The pressure differential between thereactor202 and thecondenser207 decreases and, beyond a certain threshold, then becomes lower than the opening pressure of thevalve204. The valve then closes and isolates thereactor202, thus preventing it from reabsorbing the steam contained in thefirst tank208 at ambient temperature To. Thereactor202 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 inFIG. 1).

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 thereactor202 are proposed and described in the paragraphs below.

As thereactor202 cools down, the pressure thereof then also becomes lower than the pressure prevailing in thesecond tank209. Advantageously, this can be thermally insulated from the outside in order to maintain theliquid refrigerant218 contained in thetank209 at a temperature lower than ambient temperature during the day, thus preventing the temperature of the refrigerant contained in theevaporator212 from increasing over the course of the day. As a result, the pressure prevailing in the thermally insulatedsecond tank209 is lower than the pressure prevailing in the uninsulatedfirst tank208. The pressure decrease then enables thevalve205, when a certain pressure difference corresponding to the valve opening threshold is reached, to open, thus permitting thereactor202 to take in and chemically absorb the gas coming from thesecond tank209.

The pressure then decreases in thesecond tank209 and, when the pressure difference with thefirst tank208 of condensed liquid is sufficient, for example in the region of a few bar (typically 1 to 10 bar), thevalve206 opens and supplies thesecond tank209 with liquid at the night-time temperature To, until all of the condensed liquid refrigerant contained in thefirst tank208 has been decanted into thesecond tank209 via thevalve206. As thereactor202 continues to absorb the steam produced by evaporation of the liquid contained in thesecond tank209, the decanted liquid cools until the temperature thereof is lower than the temperature of the refrigerant contained in theevaporator212 maintained at a higher temperature by thePCM213.

Thereafter, circulation of the refrigerant is triggered naturally, by thermosyphon, using the difference in density of the liquid refrigerant between theevaporator212 and thesecond tank209. Theevaporator212 is then supplied from the bottom218 with liquid refrigerant that is denser than at itsdiphasic outlet219. The refrigerant leaving theevaporator212 through thediphasic outlet219 is made up of both a liquid phase and a gaseous phase, which makes it less dense than the solely liquid refrigerant entering theevaporator212. The steam produced in theevaporator212 is then sucked into thesecond tank209 and absorbed by thereactor202 via thevalve205. The refrigeration is thus produced in theevaporator212 throughout the night until sunrise, when the reactor starts to heat up; the refrigeration produced during the night is stored in the phase-change material213 to be delivered according to the refrigeration requirements during the day.

Solar Heating of the Reactor

To achieve efficient heating, theheat exchanger201 of thereactor202 must have the largest possible solar absorption area. According to a particular embodiment, the optimum orientation is obtained by aligning theheat exchanger201 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.

Such aheat exchanger201, arranged to utilise solar radiation, will now be described with particular reference toFIGS. 5aand5b.

To utilise solar radiation to maximum effect, and according to a particular embodiment, theheat exchanger201 is coupled to thereactor202 and is made up of a set oftubular elements501 comprising thesolid reagent material502. Thetubular elements501 are distributed—preferably evenly—in anisothermal housing503, and are connected to each other by means of conveying504—for example manifolds—and linked to thecondenser207 and/or theevaporator212.

According to a particular embodiment, thetubular elements501 are covered with a solar-absorbingcoating505, if possible selective, in close contact with the wall of thetubular elements501. The solar-absorbingcoating505 has high solar absorptivity and, advantageously, low infrared emissivity.

A cover that is transparent tosolar radiation506 covering the front surface of theheat exchanger201 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.

Advantageously,thermal insulation507—for example using rock wool or glass wool—can be applied to the rear surface of theheat exchanger201 in order to reduce heat losses by conduction and/or convection to the external environment.

Night-Time Cooling of the Reactor

The night-time cooling of thereactor202 can be achieved according to two embodiments described below, the selection of which depends on thesolid reagent502 used in thereactor202, the temperature of the refrigeration Tf to be produced and the night-time ambient temperature To:

- the first embodiment for cooling the reactor consists of natural circulation of air in saidreactor202, by external cooling of thetubular elements501. This first embodiment can be implemented when thesolid reagent502 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;
- the second embodiment for cooling thereactor202 consists of a heat pipe loop operating as a thermosyphon; it is selected when cooling by natural air circulation cannot be implemented.

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

FIGS. 5aand 5brespectively show side and front diagrams of areactor202 comprising theheat exchanger201 of thedevice200 according to the invention and according to this first embodiment of night-time cooling of saidreactor202 provided by natural air convection.

This cooling thus uses the air circulation caused by the stack effect in thereactor202 by means of opening the ventilation flaps located at the top509 andbottom508 of thereactor202.

Advantageously, to improve the heat exchanges and heat removal, thetubular elements501 are equipped withfins510, for example circular, the base of which is in close thermal contact with the wall of thetubular elements501 of thereactor202.

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 thetubular elements501 in thereactor202.

Finally, in order to absorb the solar radiation more efficiently, thefins510 can be covered with a solar-absorbing coating in a similar way to the coating that can cover thetubular elements501.

In this first embodiment for cooling thereactor202, thereactive gas condenser207 can be of the finned tube type and placed at the rear or saidreactor202. It is then cooled during the day by natural convection of the air on the finned tubular elements.

Each

ventilation flap

508,509 comprises aplate511 arranged to be airtight on the frame of thereactor202 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.

According to an advantageous variant, the

ventilation flap

508,509 can also comprise drive means600 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.

Different variants of these drive means600 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

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

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 ¼-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.

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

Third Variant of the Ventilation Flap Drive

The

ventilation flap

508,509 can also be driven using thedevice600 described inFIG. 6. It is a rack andpinion device601/602 actuated by a single-acting hydrauliclinear jack605 ultimately controlled by athermostat bulb611 in thermal contact with an absorbingplate612 exposed to the sun.

Thethermostat bulb611 contains a fluid613 that is sensitive to temperature variations. More particularly, the fluid613 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 fluid613 makes it possible to pressurise thehydraulic liquid606 contained in the hydrauliclinear jack605 by means of anaccumulator608 containing adeformable bladder609, working in conjunction with thethermostat bulb611 and deformed by thefluid613.

Thehydraulic liquid606 pressurized in this way makes it possible to move both thepiston604 of thejack605 and therack601, thus rotating therod620 of the

ventilation flap

508,509 by means of thedrive pinion602.

Areturn spring603 makes it possible to push thehydraulic liquid606 back towards theaccumulator608 when the pressure in thethermostat bulb611 decreases following reduced exposure of the solar-absorbingplate612.

The quantity offluid613 contained in thethermostat bulb611 is defined as a function firstly of the volume of thebladder609 pressurizing thehydraulic liquid606 of thejack605, 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 fluid613 to be vaporized.

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

In this embodiment, thereactor202 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 thereactor202 during the night-time refrigeration production phase or by thecondenser207 during the day-time reactor202 regeneration phase, and secondly by condensing said working fluid, thus releasing the heat previously absorbed directly to the outside air via theheat pipe condenser702.

During the night, aheat pipe evaporator701, incorporated into thetubular elements501, is supplied with liquid working fluid and thus cools thereactor202 by evaporation of the liquid working fluid. The steam produced in this way condenses at night-time ambient temperature in aheat pipe condenser702. The working fluid liquefied in this way flows by gravity into thetank705 by means of the connection via thetubing707 between saidtank705 and the inlet of theheat pipe condenser702.

During the day, theheat pipe evaporator701 incorporated into thereactor202 is inactive due to the closing of two

valves

703,704 placed between theevaporator701 and thecondenser702 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.

Thus, when thereactor202 is heated by the sun during the regeneration phase, the pressure in theheat pipe evaporator701, isolated in this way, increases and causes the draining of the working fluid from the bottom of theevaporator701 in liquid form. It is then stored in a workingfluid tank705 by means of adrain line709. Preferably, the workingfluid tank705 is arranged to store the liquid working fluid during the draining of the evaporator incorporated into the reactor. Thereactor202 is thus arranged to increase in temperature and perform its regeneration during the day.

With reference toFIGS. 7 and 9, the heat pipe loop for cooling thereactor202 thus comprises:

- aheat pipe evaporator701 preferably comprising atube701 arranged inside thetubular elements501 of thereactor202 and advantageously in close thermal contact with thesolid reagent material502. Thetubular elements501 of areactor202, tilted vertically, each comprise anevaporator tube701 connected by manifolds at the bottom and top;
- afluid condenser702 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 thereactor202, advantageously with a slight tilt enabling the condensed working fluid to flow to a condensed liquid workingfluid tank705;
- a condensed liquid workingfluid tank705 the position of which advantageously enables satisfactory filling of theevaporator tubes701 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 theevaporator tubes701 of between one third and three quarters of the height of thetube701. According to another embodiment, the liquid workingfluid tank705 also comprises thecondenser207 to condense the reactive gas released during the day by thereactor202 heated in the sun. The workingfluid tank705 thus acts as an evaporator during the day. The working fluid steam produced by the condensing of the reactive gas is then conveyed to thecondenser702 via thepipe707;
- 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:
  - avalve704 between theliquid outlet708 of the workingfluid tank705 and the liquid inlet at the bottom of theevaporator tubes701, thus making it possible to supply them with working fluid throughout the night and prevent them from filling during the day;
  - avalve703 placed on the steam pipe of the heat pipe loop, between the steam outlet of theevaporator701—at the top—and the steam inlet of thecondenser702, thus making it possible, at the start of the day, to block the passage of the steam formed in theevaporator tubes701 and cause a pressure increase therein. This pressure increase makes it possible to flush the working fluid contained in theevaporator tubes701 more efficiently and drain them by means of adrain pipe709 that opens into the expansion space of thetank705. This then enables a faster temperature increase of thereactors202 at the start of the day and therefore more efficient heating of saidreactors202.
- avalve710 for starting the heat pipe loop (evacuation and/or filling with working fluid).

According to a particular embodiment, thesteam703 and liquid704 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 toFIGS. 8aand8b.

The autonomous control means of the

valves

703 and704 consists of athermostat bulb801, heated during the day and cooled at night by an absorbingplate802 that has high solar absorptivity, high infrared emissivity and low thermal mass. The absorbingplate802 is preferably exposed to the sky to utilise both heating by solar radiation during the day and radiative cooling at night. Thethermostat bulb801 contains a fluid that is arranged, under the action of solar radiation, to increase the pressure in abellows803 and move aneedle804 on the seat of the port of the

valve

703 or704, thus closing off the passage of the working fluid. When the pressure drops in thethermostat bulb801, by radiative cooling at the start of the night, thebellows803 reduces in volume under the action of aspring805 the stiffness of which can be adjusted by an adjustingscrew806. Theneedle804 rigidly connected to thebellows803 detaches from the seat of the

valve

703 or704 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

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.

With reference toFIGS. 10, 11 and 12, such a modular device comprises at least two easily connectable assemblies:

- afirst assembly1001 made up ofseveral reactor modules202,201 as described above and each comprising thetubular elements501 exposed to the sun, thecondenser207—preferably of the ammonia type—and thefirst tank208 the volume of which corresponds to the capacity of the module, the device for cooling thetubular elements501 and thecondenser702, and the means making it possible to control the flows of reactive gas over the course of the day (valves703,704,204,205, solar devices for controlling the ventilation flaps and/or the heat pipe loop706),
- asecond assembly1002 incorporating the elements necessary for refrigeration:
  - acold chamber215 comprising thermal insulation;
  - aliquid refrigerant tank209 the volume of which preferably corresponds to the daily refrigeration requirements of thecold chamber215. This tank comprisesthermal insulation210 in order to limit the thermal gain during the night-time refrigeration phase, and liquid1003 andsteam1005 connections comprising connectingvalves1004 to theevaporator212 placed in thecold chamber215.Connections1006 and1007 to thevalves206 and205 provide the connection to thefirst assembly1001;
  - anevaporator212, preferably of the flooded type, and advantageously supplied with refrigerant by thermosyphon from the secondliquid refrigerant tank209 placed above. Theevaporator212 is made up of tubes that are vertically tilted and supplied with refrigerant from the bottom by amanifold1008. The steam produced is collected by asecond manifold1009 placed in a higher position than the manifold1008, so that the steam produced enables the conveyance and natural circulation of the refrigerant in theevaporator212;
  - a phase-change material213 that makes it possible to store the refrigeration produced and redeliver it on demand over the course of the following day;
  - a connection equipped with atight isolation valve1010 that makes it possible to start the whole device (evacuation and filling with reactive gas).

The modularity of such a device makes it possible to connect a plurality offirst elements1001 to at least onesecond element1002.

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.