WO2009071849A2 - Positive cold cooling unit and devices using such unit - Google Patents

Abstract

The invention relates to a continuous-cycle storage method and device for cooling a medium or an element, in which the unit comprises: a closed circuit (2) for the flow of a refrigerant fluid; a compressor group (3) connected to the closed circuit (2) and ensuring the compression of the refrigerant fluid; a condenser (4) connected to the closed circuit (2) downstream from the compressor (3) and ensuring the condensation of the compressed refrigerant fluid; an evaporator (6) connected to the closed circuit (2) downstream from the condenser, having an exchange surface (9) with the medium or the element to be cooled, and ensuring the evaporation of the refrigerant fluid; an evaporator supply means (5) connected to the closed circuit (2), provided between the condenser (4) and the evaporator (6), and ensuring the expansion of the refrigerant fluid; characterised in that it is adapted so that, in a nominal operation mode, the temperature of the exchange surface (9) of the so-called positive-cold evaporator is strictly higher than 0°C.

Description

 POSITIVE COLD COOLING UNIT AND DEVICES USING SUCH A UNIT

The present invention relates to the technical field of cooling products or various media in particular to ensure their conservation or the cooling of a room or a cabin.

In the above field, it is known to produce cold by means of a cooling unit involving a continuous cycle of compression and expansion of a refrigerant. For this purpose, the installation generally comprises a compressor which compresses the refrigerant then directed to a condenser at which the refrigerant is cooled. The refrigerant, in the liquid state, is then conveyed to a regulator which supplies an evaporator at which the refrigerant is heated. At the outlet of the evaporator, the refrigerant in the gaseous state is redirected towards the compressor. The cooling unit thus constituted operates in a closed circuit. The evaporator of such a cooling unit is then the source of cold in contact with which the medium to be cooled is placed. Insofar as the temperature at the exchange surface of the evaporator is very much lower than 0 ^° C., the cooling unit comprises regulating means which control an intermittent operation of the compressor so as to obtain the desired temperature. at the refrigerated enclosure or the air-conditioned room.

If such cooling units give full satisfaction in obtaining the desired temperatures, they nevertheless have the drawback of generating significant condensation phenomena at the level of the evaporator. In addition, this condensation is most often accompanied by a frost deposit on the surface of the capacitor. These phenomena of condensation and icing have the disadvantage of altering the humidity of the cooled environment, which can be detrimental to the preservation of certain types of food products or to the comfort of the user. In addition, the icing of the evaporator requires a regular defrost to the extent that frost impairs the thermal performance of the evaporator. It has therefore appeared the need for a new type of cooling unit which reduces the condensation phenomena and eliminates any risk of icing at the evaporator.

In order to achieve this objective, the invention relates to a continuous cycle unit for cooling a medium or element, comprising:

a closed circuit for circulating a refrigerant,

a compressor unit which is connected to the closed circuit and ensures a compression of the refrigerant,

a condenser which is connected to the closed circuit downstream of the compressor and ensures condensation of the compressed refrigerant,

an evaporator connected to the closed circuit downstream of the condenser has an exchange surface with the medium or the element to be cooled and ensures evaporation of the refrigerant; means for supplying the evaporator which are connected to the condenser; closed circuit, being arranged between the condenser and the evaporator, and provide a relaxation of the refrigerant.

According to the invention, the cooling unit is characterized in that it is adapted so that, during a continuous continuous supply of the so-called positive cold evaporator, the temperature of the exchange surface of the positive cold evaporator, that is strictly greater than 0 ^° C.

The invention also relates to a process for continuous cycle cooling and closed circuit circulation of a refrigerant, the process comprising the following steps:

compression of the refrigerant by a compressor unit up to a compression pressure at the outlet of the compressor unit,

condensing the refrigerant compressed in a condenser; expanding the condensed refrigerant to a pressure of expansion at the outlet of the supply means;

- Supply, in expanded refrigerant, of a so-called positive cold evaporator which has an exchange surface with a medium or the element to be cooled, - evaporation of the refrigerant in the positive cold evaporator to cool the medium in contact with the exchange surface,

suction of the refrigerant by the compressor unit at the outlet of the evaporator.

According to the invention, the method is characterized in that the compression pressure and / or the expansion pressure is adapted so that, during a continuous continuous supply of the positive cold evaporator, the temperature of the exchange surface of the the positive cold evaporator is greater than 0 ^° C.

For the purposes of the invention, a prolonged continuous supply is equivalent to normal operation of the apparatus and corresponds to an uninterrupted supply of the evaporator for a period greater than one hour, or even two hours as opposed to a chopped or intermittent supply. of the evaporator. A continuous extended feeding period of the evaporator can also be defined as a period during which the positive cold evaporator operates in steady state or quasi stationary mode.

The implementation of such a positive cold evaporator has the advantage of eliminating any risk of frost or ice appearing at the exchange surface of the evaporator. In addition, the positive temperature of the exchange surface of the evaporator substantially reduces the condensation phenomena at the exchange surface of the latter, which makes it particularly suitable for use in storage enclosures of products to be kept at positive temperatures in atmospheres with a high degree of hygrometry. This lack of hygrometry also makes the cooling unit according to the invention particularly suitable for air conditioning applications of living rooms or cockpit. Thus, the positive cold evaporator is adapted so that its exchange surface is in direct contact with the medium to be cooled without interposition of insulating material. The positive cold evaporator can therefore be placed directly in the enclosure to be cooled in contact with the medium or the fluid to be cooled. According to one characteristic of the invention, the positive cold evaporator comprises at least one refrigerant circulation channel whose inner wall is connected to the exchange surface by a material or a thermally conductive material assembly. Preferably, the material or assembly of materials between the inner wall at the heat exchange surface will have a thermal conductivity greater than or equal to 1 Wm ^-1 K ^"1. More preferably, the material or the assembly material connecting the inner wall to the heat exchange surface has a thermal conductivity greater than or equal to 10 Wm ^-1 K ^"1. So, according to this characteristic, the positive temperature of the surface of exchange of the evaporator does not result from the implementation of a material with low thermal conduction between the refrigerant circulation channel and the exchange surface of the evaporator but rather the method of construction of the supplying the evaporator of the refrigerant, in particular at the pressure reached at the outlet of the supply and expansion means associated with the evaporator and possibly the compression pressure of the refrigerant. Indeed, according to the invention the design and adjustment of the cooling unit will be carried out so that the temperature of the exchange surface of the evaporator is always positive even during continuous supply phases of the relatively large positive evaporator and greater than one hour, or even two hours as opposed to a chilled or intermittent positive cold evaporator supply for very short periods of the order of minutes or less. During these phases of continuous supply of the positive cold evaporator, the compressor will also have a continuous operation.

According to another characteristic of the invention, the refrigerant used for the cooling installation is selected from carbon dioxide (CO2), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrochlorofluorocarbons (HFCs), hydrocarbons (HC) and mixtures thereof. The refrigerant may also be selected from: - trifluoromethane,

difluoroethane,

pentafluoroethane,

- Tetrafluoroethane

- isobutane - propane and mixtures thereof.

According to yet another characteristic of the invention, the cooling unit is adapted so that in a normal operating mode, the pressure of the refrigerant is: the compression pressure at the outlet of the compressor, between 7 bar and 17 bar and preferably between 8 bar and 15.5 bar in the case of the use of a refrigerant type R134a or between 15 bar and 28 bar in the case of the use of a refrigerant R404a type . - The expansion pressure at the outlet of the supply means, between 2 bar and 4 bar and preferably between 2.5 bar and 3.5 bar in the case of the use of a refrigerant type R134a or included between 5 bar and 7 bar in the case of the use of a type R404a refrigerant. The pressure values are given here in absolute bars.

The implementation of such pressures makes it possible, in particular, to reduce the electrical consumption of the compressor insofar as, according to the invention, the pressure of the refrigerant at the level of the evaporator is greater than that generally used by the compressors. installations or cooling units according to the prior art. Indeed, according to the prior art, the pressure of the refrigerant at the evaporator is at values below 2 bar and most often of the order of 1.2 bar in the case of the use of a type R134a refrigerant. This increase of the pressure at the level of the evaporator according to the invention makes it possible to reduce the pressure difference between the inlet and the outlet of the compressor and therefore the quantity of energy necessary to reach the outlet pressure of the compressor.

According to the invention, the cooling of the refrigerant at the outlet of the compressor can be carried out in any appropriate manner and thus, according to a feature of the invention, the cooling unit comprises an air condenser. According to another characteristic of the invention, the cooling unit comprises a water condenser being understood that said cooling unit can implement both a water condenser and an air condenser, or any other type of adapted condenser. for the use of the cooling unit.

According to the invention, a cooling unit can be designed to cool different types of media or food products or not.

Thus, according to one characteristic of the invention, the positive cold evaporator comprises an exchange surface adapted to cool air. The positive cold evaporator may then be in the form of a plate at which the air to be cooled will move by natural convection. In the context of the production of a compact exchanger, the exchange surface may be constituted by a series of fins.

According to a characteristic of the invention, the cooling unit also comprises forced ventilation means adapted to circulate air to be cooled at the exchange surface of the positive cold evaporator.

According to the invention, the cooling unit may also comprise an evaporator for cooling the fluid contained in a circuit. Thus, according to one characteristic of the invention, the positive cold evaporator comprises at least one circulation channel for a fluid to be cooled, an internal wall of which forms the exchange surface of the positive cold evaporator. Insofar as the temperature of the exchange surface of the positive cold exchanger according to the invention is greater than 0 ^° C., such an evaporator exchanger Liquid cooler is particularly suitable for cooling water without the need to add antifreeze products.

According to the invention, the evaporator can also be designed to provide cooling of products or elements by conduction. For this purpose, and according to another characteristic of the invention, the positive cold evaporator is adapted to ensure the cooling of elements by contact and the exchange surface is then adapted to support the elements to be cooled. Such a contact evaporator is particularly suitable for cooling foodstuffs or products which must not be subjected to freezing while having to be kept at relatively low positive temperatures, as is the case, for example, with fish.

According to another characteristic of the invention, the cooling unit further comprises a negative cold evaporator which is connected to the closed circuit downstream of the condenser and has an exchange surface with a medium or an element to be cooled. The cooling unit is then adapted so that in a normal operating mode the temperature of the exchange surface of the negative cold evaporator is less than 0 ^° C.

The invention also relates to an air conditioning device of a living room or a passenger compartment which comprises at least one cooling unit according to the invention.

According to a characteristic of the invention, the air conditioning device comprises forced ventilation means adapted to circulate air at the exchange surface of the positive cold exchanger and to direct it inside the the room or the cockpit.

According to yet another characteristic of the invention, the air conditioning device comprises means for directing a flow of air cooled by the positive cold heat exchanger to a user. Indeed, the implementation of a positive cold heat exchanger avoids too much alteration of the moisture content of the cooled air so that it can be directed directly to a person or an animal without creating a feeling of discomfort or a risk of too fast drying of the mucous membranes, such drying being generally linked to a too dry character of the air. Thus, for example, it could be envisaged to integrate the evaporation unit in a luminaire. The cooled air naturally having a downward movement within a hot air mass, it is then possible to cool the users located generally under the luminaire. This cooling can then be assisted or not by a fan. Such a combination is particularly attractive, effective and aesthetic, and also economical in energy as it directs the cold only towards users without seeking to cool their entire environment.

The invention also relates to a cooling device of a subject comprising a surface for receiving the subject, characterized in that the receiving surface is cooled by means of a cooling unit according to the invention. Indeed, the implementation of a positive cold evaporator avoids any risk of burning or discomfort in case of direct contact of the subject with the exchange surface of the positive cold evaporator forming at least part of the receiving surface of the subject. The implementation of a positive cold evaporator also allows a cooling of the receiving surface of the subject by circulating a heat transfer fluid in a closed circuit which may advantageously be water. In fact, the positive cold evaporator according to the invention eliminates any risk of frost and therefore clogging of the water circuit at the evaporator. This presents a great advantage insofar as the surface of reception of the subject may be constituted by a water mattress which can be filled at the place of use and which will not present any risk of toxicity in case of perforation and may be emptied without special precautions at the end of use. The invention also relates to a temperature-controlled storage device comprising at least one closed positive-temperature storage enclosure delimited by a peripheral wall and at least one access door. According to the invention, the storage device comprises a cooling unit according to the invention, the positive cold evaporator of which is located in relation to the positive-temperature storage chamber for cooling it.

The implementation of a positive cold evaporator makes the storage device according to the invention particularly suitable for the preservation of products or food requiring a high degree of hygrometry without it necessarily being necessary to provide means of storage. additional humidification.

According to one characteristic of the invention, the temperature-controlled storage device comprises a positive-temperature storage chamber and a negative-temperature storage chamber. The cooling unit then comprises a negative cold evaporator which is placed in relation with the negative temperature storage enclosure. Of course, in the case of such use, the negative temperature air is confined in the negative temperature storage compartment. According to one embodiment of the invention, the storage device comprises:

a cooling chamber which is separated from the positive-temperature storage enclosure by a partition and communicates with the storage enclosure by at least one opening an air suction opening and an air discharge opening, the positive evaporator being placed in the cooling chamber, and

- Forced ventilation means adapted to ensure the circulation of air between the positive temperature storage chamber and the cooling chamber.

According to a variant of this embodiment, at least some parts of the peripheral wall comprise a double wall forming peripheral channels for the circulation of cooled air which are connected to the discharge opening and open into the storage chamber at positive temperature.

The interposition of the cooled air circulation channels integrated in the thickness of the wall between the external environment and the inside of the positive-temperature storage chamber makes it possible to reduce or even cancel the temperature gradients. in certain directions. In addition, the circulation of air in these channels allows a warming of the cooled air, a heat transfer between the cooled air and the air of the enclosure as well as between the external environment and the cooled air, so as to bring the cooled air to the desired temperature before contacting the products or foods to cool or maintain at a given storage temperature.

Preferably but not necessary, the cooling chamber will be located under the positive temperature storage chamber and at least a portion of the channels will open in the upper part of the positive temperature storage chamber.

According to a variant of the embodiment above, part of the circulation channels opens at an intermediate height in the storage chamber at a positive temperature, which makes it possible to define zones having different temperatures therein. According to another variant of the above embodiment, at least some portions of the peripheral wall comprise a double wall forming peripheral air suction channels which are connected to the suction opening and comprise an inlet open air at the positive temperature storage enclosure. According to the invention, the air inlet of at least a portion of the suction channels may be located in the upper part of the storage enclosure. The air inlet of a portion of the suction channels may also be located at an intermediate height of the positive cold storage enclosure.

According to yet another variant of the embodiment above, the access door is front opening and comprises a double wall forming at least one cooled air circulation channel which is connected to the discharge opening and opens in the upper part of the storage chamber at positive temperature.

According to a characteristic of the invention, ventilation means are adapted to ensure an upward forced circulation of the air in the storage enclosure.

According to another characteristic of the invention, the ventilation means are adapted to ensure forced downward circulation of the air in the storage enclosure.

According to a characteristic of the storage device according to the invention, the positive cold heat exchanger is located at a distance from the peripheral wall. Indeed, insofar as the exchange surface of the positive cold evaporator according to the invention has a still positive temperature, it is no longer necessary to include the positive cold evaporator in the insulating walls in order to facilitate defrosting. Thus, the assembly and disassembly of the installation are greatly facilitated since the cooling unit, and more particularly its positive cold evaporator, can be separated from the wall defining the storage enclosure without risk of rupture of the circuit containing the refrigerant.

Of course, the various features, embodiments and variants of the objects of the invention may be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other.

Furthermore, various other features of the invention will emerge from the description below made with reference to the accompanying drawings which illustrate the non-limiting embodiments of various objects of the invention.

- Figure 1 is a schematic view of a cooling unit according to the invention, implemented in the context of an air conditioning device for a living room or a vehicle interior.

FIG. 2 is a schematic view of a luminaire incorporating a positive cold evaporation of a cooling installation according to the invention.

- Figure 3 is a schematic view of a cooling device of a subject by contact.

- Figure 4 is a vertical sectional view of a storage device according to the invention comprising a positive temperature storage chamber.

FIG. 5 is a diagrammatic section along the line IV-IV of FIG.

- Figure 6 is a section similar to Figure 4 showing another operating mode of the storage device illustrated in Figures 4 and 5. - Figures 7 and 8 are sections similar to Figures 4 and 5 and illustrating an alternative embodiment of the storage device represented by the latter.

- Figure 9 is a schematic vertical section of a storage device according to the invention, comprising a positive temperature storage chamber and a negative temperature storage chamber.

In these figures, the common references designate elements that are common to the various embodiments. As is apparent from FIG. 1, a cooling unit, according to the invention, designated as a whole by the reference numeral 1 comprises a closed circuit 2 inside which a refrigerant circulates in a loop in order to undergo a continuous cycle of compression therein. and relaxation. Thus, the cooling unit comprises a compressor 3 which will compress the refrigerant at a compression pressure between 7 bar and 17 bar, and preferably between 8 bar and 15.5 bar in the case of the use of a type R134a refrigerant. At the outlet of the compressor 3, the high pressure refrigerant is directed by the circuit 2 to a condenser 4 at which it will cool and liquefy. From the condenser 4, the refrigerant is conveyed by the circuit 2 to supply means 5 of an evaporator 6. The supply means 5 are adapted to relax the refrigerant so as to bring it to an expansion pressure of between 2 bar and 4 bar and preferably between 2.5 bar and 3.5 bar. The supply means 5 can then be made in any appropriate manner, for example in the form of an expansion valve or a capillary tube whose structural characteristics have been chosen to achieve the desired relaxation values. The cooling unit 1 further comprises a control unit 7 controlling the operation of the compressor 3 from the information provided by a temperature sensor 8.

According to the invention, the evaporator 6 may be of any suitable type and, according to the illustrated example, it is formed by a finned cooling evaporator (not shown). According to an essential characteristic of the invention, the cooling unit 1 and more particularly the operating points of the compressor 3 and the expander 5, are determined so that in normal operating mode corresponding to a prolonged continuous supply of the evaporator the temperature of the exchange surface 9 of the exchanger 6 is strictly greater than 0 ^° C., so as to avoid any appearance of frost at the level of the said exchange surface 9. Thus, the evaporator 6 is qualified as positive cold evaporator. This positive temperature of the exchange surface 9 makes it possible to reduce the dehydration of the air in contact with the evaporator 6 so that it is possible to blow this air directly on a user U. For this purpose, according to FIG. As illustrated, the cooling unit 1 further comprises a fan 15 ensuring a forced circulation of the air through the exchange of the positive cold evaporator 6 and the baffles 16 directing the air on the user. . The assembly formed of the cooling unit 1, the fan 15 and the deflector 16 then constitutes an air conditioning unit that can be implemented either in a room or as part of the air conditioning of a vehicle cabin.

According to the invention, and as shown in Figure 2, the positive cold evaporator can be associated with a luminaire 17, so that a user U located under a luminaire is cooled by natural convection. The use of a positive cold evaporator further has the advantage of eliminating any risk of cold burn in the event of direct contact with the exchange surface 9 of the evaporator.

Thus, it is possible to envisage using the cooling unit 1 according to the invention in the context of a device 19 for cooling a subject by contact as illustrated in FIG. 3. Such a device comprises then a receiving surface 20 of a subject S which is cooled by means of the cooling unit 1. According to the illustrated example, part of the surface 20 is constituted by the exchange surface 9 of the evaporator. positive cold 6.

Moreover, by virtue of the presence of its positive cold evaporator 6, the cooling unit according to the invention 1 is particularly suitable for the storage and preservation of products requiring a high humidity content, for example wine. .

Thus, Figures 4 and 5 illustrate a storage device more particularly suitable for the storage of wine bottles at a suitable storage temperature.

According to the illustrated example, the storage device designated as a whole by the reference 25 comprises an insulating peripheral wall 26 which delimits a positive-temperature storage enclosure 27. The enclosure 27 is open on the front and the device 25 then comprises a door 28 with front opening. Of course, the storage device 25 comprises a cooling unit 1 according to the invention, the positive cold evaporator 6 of which is placed in relation with the positive-temperature storage enclosure 27. According to the illustrated example, the evaporator positive cold 6 is placed inside a cooling chamber 29 which is separated from the storage enclosure by a partition 30 having at its center air suction openings 31 and, at its periphery , an opening device 32 discharge air. The positive cold exchanger 6 is then associated with forced ventilation means 34 such as for example a fan 34 disposed in the cooling chamber. The fan 34 is designed to ensure suction of the air from the positive temperature storage chamber 27 to bring it into contact with the exchange surface 9 of the positive cold evaporator 6. According to the illustrated example, the peripheral discharge opening 33 opens into vertical channels 35 delimited by a doubling wall 36 associated with the peripheral wall 26 and the door. The channels 35 open into the upper part of the storage chamber 27 so as to bring the cooled air down into the positive cold storage chamber 27 and then be taken up in the cooling chamber. Such an air circulation allows its heating inside the channels 35 before entering the storage chamber 27, which allows to bring it to exactly the desired temperature, while reducing or even canceling gradients of horizontal temperature within the enclosure 27. It should be noted that in such a mode of operation, the temperature within the cooling chamber will be lower than that prevailing inside the positive temperature storage enclosure 27. Thus, for example, provision may be made to adapt a drawer 50 in the cooling chamber 29 so as to store wine bottles at a service temperature, while the temperature within the enclosure of Positive temperature storage 27 will have optimum value for keeping in good wine conditions.

Such a mode of operation makes it possible to obtain, within the storage enclosure 27, a reduced vertical temperature gradient and a near zero horizontal temperature gradient. However, depending on the nature of the contents of the storage enclosure 17, it can be sought a larger vertical temperature gradient and for example of the order of 12 ° C between the top and bottom of the enclosure 27 with a horizontal temperature gradient almost zero. For this purpose, the operating mode of the storage device 25 may be modified by reversing the direction of ventilation provided by the ventilation means 34. Thus, as shown in FIG. 6, the air present, within the enclosure 27, a forced upward movement and is sucked in the upper part of the storage chamber 27 to be channeled by the peripheral channels 35 to the cooling chamber 29. The ventilation means 34 will then work at low speed. in order to induce a reduced speed of upward vertical displacement of the air in the chamber 27. According to the invention, the direction and / or the working speed of the forced ventilation means 34 can be determined at the factory or, conversely, set by the user of the storage device 25.

FIGS. 7 and 8 illustrate an alternative embodiment of the storage device shown in FIGS. 4 and 5. According to this embodiment, the channels for circulating the cooled air open through intermediate openings 37 at an intermediate height in the In addition, according to this example, the rear wall of the storage device 25 comprises a double wall 38 which forms at least one or more peripheral air suction channels 39. These peripheral channels aspiration 39 are then connected to the suction opening 33 and comprise an open air inlet at the upper part of the storage room 27 and an air inlet open at a height intermediate of the storage enclosure 27. The association of the suction channels 39 and the outlets In the case of intermediate air 37 and others, it is then possible to define in the positive-temperature storage enclosure 27 two zones A and B with different storage temperatures.

According to the invention, the storage device can also be designed to ensure the preservation of various foodstuffs. Thus, FIG. 9 illustrates a storage device comprising a negative temperature storage enclosure 40 in addition to the positive temperature storage enclosure 27. The cooling unit then comprises a negative cold evaporator 41 which is powered in such a way that the temperature of its exchange surface 42 is strictly less than 0 and the temperature inside the negative temperature storage chamber 40 is adapted to the preservation of frozen or frozen food for example.

It should be noted that according to this embodiment, the positive cold evaporator 6 is designed so that its exchange surface 9 can receive fragile foods that can be maintained at a constant low temperature greater than 0 ° as fish P Thus, according to the illustrated example, the evaporator 6 constitutes a contact cooler evaporator. Of course, it could be envisaged to complete the positive contact cold evaporator 6 by an air-cooled positive cold evaporator disposed inside the positive-temperature storage enclosure.

Of course, various other modifications can be made to the cooling unit and the cooling or air conditioning device according to the invention within the scope of the claims.

Claims

A method of continuous cycle cooling and closed circuit circulation of a refrigerant, the method comprising the steps of: - compressing the refrigerant by a compressor unit (3) to a compression pressure at the compressor unit outlet, condensation of the compressed refrigerant in a condenser (4), - Expansion of the condensed refrigerant to an expansion pressure at the outlet of the supply means (5), - supply, in expanded refrigerant, a positive cold evaporator (6) which has an exchange surface (9) with a medium or the element to be cooled, evaporation of the refrigerant in the evaporator (6) to cool the medium in contact with the exchange surface (9), - suction of the refrigerant by the compressor unit (3) at the outlet of the evaporator (6), characterized in that the compression pressure and / or the expansion pressure is adapted so that during a continuous continuous supply of the positive cold evaporator (6), the temperature of the exchange surface (9) of the positive cold evaporator (6) is greater than 0 ^° C. 2. Cooling method according to claim 1 characterized in that the exchange surface of the positive cold heat exchanger is placed in direct contact with the medium to be cooled. 3. Cooling method according to claim 1 or 2, characterized in that the refrigerant is selected from carbon dioxide (CO ₂ ), hydrocarbons (HC), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrochlorofluorocarbons (HFCs) and mixtures thereof. 4. Cooling method according to one of claims 1 to 4, characterized in that the refrigerant is selected from: - trifluoromethane, difluoroethane, pentafluoroethane, tetrafluoroethane, - isobutane - propane and mixtures thereof Cooling method according to one of Claims 1 to 3, characterized in that: the refrigerant is of the R134a type; the compression pressure at the outlet of the compressor unit (3) is between 7 bars and 17 bars, and preferably between 8 bars and 15.5 bars, and - The expansion pressure at the outlet of the supply means (5) is between 2 bar and 4 bar and preferably between 2.5 bar and 3.5 bar. Cooling method according to one of Claims 1 to 4, characterized in that: the refrigerant is of the R404a type, the compression pressure at the outlet of the compressor unit (3) is between 15 bar and 28 bar, - The expansion pressure at the outlet of the supply means (5) is between 5 bar and 7 bar. 7. Cooling method according to one of claims 1 to 6, characterized in that the positive cold evaporator (6) comprises an exchange surface (9) adapted to cool air. Temperature-controlled storage device comprising: at least one closed positive temperature storage enclosure (27) delimited by a peripheral wall (26) and at least one access door; continuous cycle cooling unit comprising: a closed circuit (2) for circulating a refrigerant, - a compressor unit (3) which is connected to the closed circuit (2) and ensures compression of the refrigerant, - a condenser (4) which is connected to the closed circuit (2) downstream of the compressor (3) and ensures condensation of the compressed refrigerant, - an evaporator (6) connected to the closed circuit (2) downstream of the condenser, has an exchange surface (9) with the medium or the element to be cooled and ensures evaporation of the refrigerant and which is located in relation with the positive temperature storage chamber (27) to cool it - means (5) for supplying the evaporator which are connected to the closed circuit (2), being arranged between the condenser (4) and the evaporator (6), and provide a relaxation of the refrigerant, characterized in that the cooling unit is adapted to implement the method according to one of claims 1 to 7 and for that during a continuous continuous supply of the evaporator (6) said positive cold, located in the enclosure positive cold storage, the temperature of the exchange surface (9) of the positive cold evaporator (6) is greater than 0 ^° C. 9. Storage device according to claim 8 characterized in that it comprises: a cooling chamber which is separated from the positive-temperature storage enclosure (27) by a partition (30) and communicates with the storage chamber by at least one air suction opening (31) and an air discharge opening (33), the positive cold evaporator (6) being placed in the cooling chamber and - forced ventilation means (34) adapted to ensure the circulation of air between the positive temperature storage chamber and the cooling chamber. 10. Storage device according to claim 9, characterized in that at least some parts of the peripheral wall comprise a double wall forming peripheral channels (35) for circulating the cooled air which are connected to the discharge opening ( 33) and open into the positive temperature storage chamber (27). 11. Storage device according to claim 10, characterized in that the cooling chamber is located under the positive temperature storage chamber (27) and in that at least part of the circulation channels (35) open in the upper part of the positive temperature storage chamber (27). 12. Storage device according to claim 10 or 11, characterized in that a portion of the circulation channels (35) open at an intermediate height in the storage chamber at positive temperature. 13. Storage device according to one of claims 9 to 12, characterized in that at least parts of the peripheral wall comprise a double wall forming peripheral channels (35) of air suction which are connected to the the suction opening (31) and comprise an open air inlet at the positive temperature storage chamber (27). 14. Storage device according to claim 13, characterized in that the air inlet of at least a portion of the suction channels is located in the upper part of the positive cold storage chamber. 15. Storage device according to claim 13 or 14, characterized in that the air inlet of a portion of the suction channels is located at an intermediate height of the positive cold storage chamber. 16. Storage device according to one of claims 9 to 15, characterized in that the access door is front opening and comprises a double wall forming at least one cooled air circulation channel which is connected to the door. discharge opening and opens in the upper part of the storage chamber at positive temperature. 17. Storage device according to one of claims 9 to 16, characterized in that ventilation means are adapted to ensure an upward forced circulation of air in the storage chamber. 18. Storage device according to one of claims 9 to 16, characterized in that the ventilation means are adapted to ensure a flow of forced downward air in the storage chamber. 19. Storage device according to one of claims 8 to 18 characterized in that the positive cold heat exchanger (6) is located at a distance from the peripheral wall of the positive cold storage chamber. 20. Storage device according to claim 8 characterized in that the positive cold heat exchanger is located in the positive cold storage chamber. 21. Storage device according to one of claims 8 to 20 characterized in that it further comprises a negative temperature storage chamber (40) and in that the cooling unit further comprises a negative cold evaporator which is connected to the closed circuit (2) downstream of the condenser (4) and placed in connection with the temperature storage enclosure, the cooling unit being adapted so that in a normal operation the temperature of the exchange surface of the negative cold evaporator is strictly less than 0 ^° C.