EP2150758A2

EP2150758A2 - Backup co<sb>2</sb>cooling system

Info

Publication number: EP2150758A2
Application number: EP08788178A
Authority: EP
Inventors: Olivier Pouchain; Didier Alo; Daniel Fontana; Pierre Kowalewski
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2007-04-25
Filing date: 2008-04-14
Publication date: 2010-02-10
Anticipated expiration: 2028-04-14
Also published as: WO2008142341A2; WO2008142341A3; PT2150758T; EP2150758B1; ES2713490T3; FR2915559A1; FR2915559B1

Abstract

This invention relates to a backup cooling system for a user site possessing at least one cold chamber for preserving foodstuffs or perishable products, the cold chamber being cooled by a mechanical cooling system, the user site being provided with a liquid CO2 tank used on site for a primary utilization, and the backup device comprising the following elements:- a liquid CO2 evaporation unit positioned in the cold chamber and comprising an evaporator, which is a second evaporator independent of the evaporator of the mechanical cooling system; - a line which supplies said second evaporator of the evaporation unit from said liquid CO2 tank; a discharge out of the chamber for the CO2 vaporized in said second evaporator; - a means for acquiring at least one data item representing the operation or non-operation of the mechanical cooling system; and - a data acquisition and processing system for capturing said representative data item or items and commanding the supply of CO2 to said second evaporator from said tank when the captured data item represents non-operation of the mechanical cooling system.

Description

SYSTEM OF AID IN COOLING CO ₂ The present invention relates to the sites, including the shops, restaurants etc .. requiring the presence of a cold room to preserve food or other perishable products like pharmaceuticals or biologics.

The need for cold is commonly provided by mechanical cold systems that are susceptible to breakdowns. When these occur, the stored assets are at risk if the repair does not take place quickly.

This situation is found, for example, in the fast food industry, with the consequent costs associated with the loss of the food itself and the loss due to lack of activity.

It is known that the notion of "mechanical cold system" commonly means a system for compressing, relaxing, condensing and evaporation of a refrigerant fluid. Evaporation of the refrigerant occurs in an evaporator placed in the cold room.

To limit therefore, in such cold rooms cooled by mechanical cold, the negative effects of possible breakdowns, effective maintenance, rapid intervention, is necessary. In practice, however, it is common that troubleshooting can not occur as quickly as desired and that therefore intervention times do not prevent losses.

Obviously one of the solutions would be to double the mechanical cold installation with a backup group. This uneconomic solution is in practice not implemented by this sector of activity.

Moreover, we know that some of these businesses, such as restaurants, use CO ₂ elsewhere on the site, for example for carbonating beverages in the restaurant, and thus have a reserve of CO ₂ , stored under pressure in the form of carbon dioxide. liquid and which has a cooling capacity when it is evaporated. As will be seen in more detail below, the present invention proposes to use this CO ₂ storage to compensate for failures of the refrigeration system that keeps the cold room cold. The investment of such a system is relatively low because of the presence of CO ₂ for another use. Among the cooling technologies mentioned in the literature (in the sense that a cold fluid absorbs heat from a product), there are applications using CO2 stored in liquid form and which by evaporation produces a cooling effect. Some applications use CO2 to cool or keep in cold rooms (or boxes) containing food.

The following documents can be cited as illustrative: US-6,062,030, US2002 / 0129613A, EP-0652409 A1. The peculiarity of these prior systems is the use of a cryogenic fluid to cool products and assist primary systems of mechanical cold. The applications targeted are most often in the transport of goods. In any case, it should be pointed out that none of these documents describes or suggests the benefits of implementing a liquid CO2 storage already present on the installation for another use to serve as a backup to a main installation of mechanical cooling under controlled and efficient conditions, both thermally and economically in the economic use of CO ₂ .

It is conceivable that it is insufficient to simply use a temperature measurement inside the chamber cooled by the cooling unit (mechanical cooling) as an alert and simply trigger the implementation of the liquid CO2 of backup when this temperature is below a set temperature. Indeed, as an illustration, what would serve to trigger the rescue if simply the door of the cold room was inadvertently left open, this situation is obviously not the result of a faulty fridge group.

On the other hand, as will be seen below, the "backup system" proposed by the present invention can also be considered to overcome management errors of the cold room (door remained open, products introduced into the chamber at a temperature too high). high, etc.) which would lead to a thermal load such that the mechanical cold circuit could no longer maintain an ad-hoc conservation temperature. In this case, the backup system would complement the mechanical cold system to try to maintain the desired temperature. This second case can be nevertheless considered secondary to the primary objectives of the present invention.

Furthermore, it is also conceivable that the user site may agree to use such a backup but under conditions that are not only thermally efficient (so that the liquid CO2 can effectively allow the products to be maintained under temperature conditions that are safe for the time that the problem causing the failure is solved) but also trying to save the liquid CO2 that is present on the installation for another use that must be performed also without suffering from this "CO2 deviation" for relief reasons.

The invention therefore proposes a backup system during failures of the refrigeration system of the cold room, using the CO2 storage already present on the installation for another use, for example already present for the carbonation of beverages.

As will be seen in more detail below, a control system allows the activation (manual or automatic) of the backup system and the regulation of the consumption of CO2. The system can operate as needed for several hours to maintain the cold room at the desired temperature.

The backup system then implements a line that starts from the liquid CO2 tank to feed an evaporator placed in the cold room and a vaporized CO2 evacuation (as shown schematically in the attached figure 1 which illustrates the case of a restaurant) .

The line advantageously comprises a device for regulating the CO2 flow rate and the evaporation pressure as well as safety elements to prevent excessive pressure.

The system can be regulated / controlled by one or more parameters among in particular:

- information taken at the level of the mechanical cold system to trigger the sending of liquid CO2 (for example temperature inside the chamber, temperature taken in a dummy product present in the chamber, compressor non-operating indicator, compressor suction pressure level indicator, indicator that the system is not in defrost mode when it should, for example, taking into account automatic defrosting phases provided in the operation of the room, a witness to open the door, etc.);

- information taken on the CO2 supply line and the cold room to regulate the cold produced by the backup system.

The backup system is then advantageously constituted by the following elements: the main cold room comprises a cold battery (evaporator / exchanger) provided with fans; a liquid CO2 evaporation circuit positioned in the cold chamber and comprising an evaporator, which is a second evaporator independent of the evaporator of the mechanical cooling system, a CO ₂ supply circuit of the evaporator and a cooling system; evacuation of the CO2 gas that will result from the passage of liquid CO2 in the second evaporator; a system for regulating the CO2 flow supplying this second evaporator; a triggering system in the food ie backup device in CO ₂ of the second evaporator in accordance with information taken at the cold room.

The invention thus relates to a cooling device for a user site having at least one cold room for preserving perishable goods or products, cold room cooled by a mechanical cold system, the user site being provided with a storage tank. Liquid CO2 used on the site for primary use, the backup device comprising the following:

a liquid CO2 evaporation circuit positioned in the cold chamber and comprising an evaporator, which is a second evaporator independent of the evaporator of the mechanical cold system; a line which feeds, from said liquid CO 2 reservoir, said second evaporator of the evaporation circuit, in order to carry out the evaporation of the CO 2 and thus to bring about frigories of product audits, the line being provided with a device for controlling the amount of CO2 supplying said second evaporator;

an evacuation towards the outside of the chamber of vaporized CO2 in said second evaporator;

means for acquiring at least one piece of information representative of the operation or dysfunction of the mechanical cold system; a data acquisition and processing system able to recover said at least one representative information and to trigger the supply of CO _{2 of} said second evaporator from said reservoir when the recovered information is representative of a malfunction of the system of mechanical cold.

It should be noted that preferably this second evaporator has a clean ventilation means allowing the air of the cold room to exchange with the CO2 evaporation circuit.

But according to another embodiment of the invention, said second evaporator does not have a clean ventilation means, the installation uses the ventilation means specific to the mechanical cooling system (this for advantageous reasons of saving space ).

It is conceivable that the triggering of the emergency system may be manual, for example following the observation by a person of the site of a malfunction (for example a visually controlled temperature, for example still following the hearing of an alarm temperature ...), it will be preferred according to the invention an automatic trigger according to one or more of the factors mentioned above. By way of illustrative example, the following example of implementation of the emergency system can be given under the following conditions:

- the supply pressure is fixed using an expansion valve, the flow is limited to a given and maximum flow rate; - when the temperature produced is good or the refrigeration unit is no longer in alarm, the supply of the exchanger is stopped using the CO2 backup.

By way of illustration also, typical examples of CO2 consumption are given below in connection with the table of values below.

For a cooling capacity of 1 kW, the CO2 consumption is around 12.5 kg / h at 13 bar.

At this power it compensates only the heat inputs of the cold room without taking into account the openings or a significant rise of the cold room temperature. With a tank of 180 kg if it is one third full autonomy will be less than 5 hours for a maintenance of the cold room at -20 ⁰ C. With a tank of 275kg the autonomy will be less than 7 hours.

Table 1: CO savings? depending on the cooling capacity of 1 or 2 kW depending on the remaining capacity in the tank

Other features and advantages will emerge from the following description, examples of embodiments of the invention, made in particular with reference to the appended figures.

For reasons of readability, it is not detailed in these figures the mechanical cold system. A first method implements, according to the appended FIG. 2, an electronic expander which supplies the evaporator to ensure a minimum of overheating at the outlet. When the cooling system of the cold room is in default, the backup system is started by opening the solenoid valve V1 which connects the CO2 storage to the CO2 distribution line that feeds the evaporator.

An electronic valve V2 is controlled by a regulator (R1) to regulate the flow of CO2 in the evaporator. The regulator operates the opening of V2 according to the pressure information P (of the CO2 circuit at the inlet of the evaporator) and of the temperature T (of the CO2 circuit at the outlet of the evaporator) so that the temperature T is greater than the CO2 saturation temperature, which is a function of the pressure, of a value between OK and 2OK. The regulator ensures that the CO2 output is in gaseous form with a fixed superheat.

The valve V3 makes it possible to maintain a minimum pressure in the CO2 circuit above 5.2bar (absolute), avoiding the formation of dry ice, pressure preferably between 5.5 bar and 10 bar (absolute). The safety valves S which are well distinguished in the figure are arranged along the CO2 circuit to prevent overpressure.

Thus in emergency mode, when the temperature of the cold room is higher than the temperature of the CO2 in the evaporation circuit, the heat exchanged at the evaporator vaporizes the CO2, which tends to increase its pressure in the evaporator until at the limit pressure set by the opening of the valve V3. The electronic valve controller compares the CO2 temperature at the evaporator outlet with its setpoint temperature (set to maintain overheating) and the saturation temperature at the measured operating pressure P. If the CO2 temperature is higher than the set point, the valve V2 opens a little more to increase the CO2 flow. As a result, the cooling capacity of the evaporator increases and the exit temperature of the CO2 decreases. If the CO2 temperature is lower than the setpoint, reverse actions are initiated. In this way the cooling capacity is regulated indirectly by the state of overheating of the CO2 at the outlet of the evaporator ensuring a good use of the latter.

This first method, although technically possible, will not be preferred according to the present invention because of the material cost involved.

A second method (which will now be described in connection with FIG. 3) uses a solenoid valve which opens and closes the CO2 supply of the evaporator as a function of the CO 2 exit temperature. A thermostat switches off the evaporator supply when the threshold temperature is reached.

In other words, this solution implements two nested loops. As long as the fault on the cold room persists, the solenoid valve V1 supplies the CO2 evaporation circuit placed in the cold room. The CO2 evaporates by absorbing the heat coming from the air in the cold room at a pressure higher than the minimum pressure set by the valve V3. This valve is intended to prevent the CO2 from being in solid form in the evaporation circuit by maintaining a pressure greater than a minimum pressure, for example 5.2 bar (absolute), preferably between 5.5 bar and 10 bar (absolute). . A temperature sensor T placed on the CO2 circuit at the outlet of the evaporator allows a thermostat to act on the opening of the valve V2 placed at the inlet of the evaporator. The opening and closing of V2 adjusts the CO2 flow rate in the evaporator so that the temperature at the outlet of the latter is kept close to a fixed set point, preferably between -30 ^° C. and -40 ^° C. The set temperature is set so that the CO2 at the outlet of the evaporator is completely vaporized. If the measured temperature is higher than that of the setpoint, the solenoid valve opens allowing the liquid CO2 to feed the evaporator. The cooling capacity available increases leading to decrease the CO2 output temperature. If the measured temperature is lower than that of the setpoint, the inverse actions are initiated.

Thus the cooling capacity delivered to the cold room is controlled indirectly by the CO 2 output temperature of the evaporator. An alternative to the valve V2 is to use a thermostatic expansion valve that regulates the flow of CO2 at the inlet of the evaporator according to a fixed pressure and a fixed superheat. Thus, the CO2 at the outlet of the evaporator is completely vaporized ensuring a good use of the latter.

A third method (which will be described in conjunction with Figure 4), implements a constant cooling capacity. CO2 injection is via a solenoid valve (2). The room thermostat (3) in the chamber controls the solenoid valve (2) and the evaporator fan (this is delayed when stopped).

A calibrated orifice (4) located at the evaporator outlet makes it possible to obtain a controlled flow rate of CO2 as a function of the pressure in the reservoir. Positioning it at the outlet of the exchanger makes it possible to limit the flow rate on a gaseous phase and to overcome the fluid inlet conditions in the evaporator (problem of limitation of flow on a fluid in two-phase at a low flow rate ). The flow is directly related to the tank pressure.

An overflow (5) maintains the pressure in the evaporator and in the circuit at a pressure greater than that of the triple bridge of CO2. When the solenoid valve (2) closes, the pressure drops in the evaporator (as well as the temperature) up to the regulator pressure.

The evaporation pressure in the evaporator corresponds to the storage pressure, the valves of which are conventionally regulated at around 13.6 bars (temperature of about -30 ^° C.).

It can be said that this solution is technically simple, uses conventional equipment, it limits the flow of CO2 flowing in the evaporator and therefore to know the autonomy. This method does not control the heat exchange in the evaporator. In case it (icing, ventilation impossible because of obstacles left unintentionally ..., etc.) does not allow the vaporization of CO2 can be obtained a two-phase mixture to the calibrated orifice.

The figure also shows a safety solenoid valve (1) and safety valves (6) to protect the CO2 circuit, as well as a control box for the electrical part. By way of illustration, when the chamber is perceived to be in fault (for example by using two alarm information: for example a temperature information of a dummy product (7) constituted by a temperature probe in a polyethylene block, for example in combination with other alarm information related to the operation of the refrigeration plant (8), the CO2 is then sent from the emergency storage via the solenoid valve (2), which by means of a fixed flow rate guarantees a minimum of autonomy If the temperature of the cold room is restored or if one of the two aforementioned alarms disappears, the injection of CO _{2 is} stopped.

A fourth method (described below with reference to FIG. 5) implements a variable cooling capacity.

CO ₂ injection is via a solenoid valve (2). The room thermostat (3) in the chamber controls the solenoid valve and the evaporator fan (this is delayed when stopped). A pressure regulator (6) maintains a given evaporation pressure in the evaporator, for example 8 bar. If the pressure in the tank is lower than the regulator setting pressure, it remains open. A temperature sensor (5) located at the evaporator outlet makes it possible to regulate the CO2 at a constant temperature. It is desired to ensure that the CO2 sent into it is completely evaporated (avoid in case of poor ventilation of the evaporator, that it may be necessary to evacuate to the outside at the gas outlet a two-phase mixture). An overflow (7) maintains the pressure in the exchanger and in the circuit at a pressure greater than that of the triple bridge of CO2. In case the tank reaches the pressure set at the overflow it prevents the injection of CO ₂ .

In other words, we present here the use of a control loop on the exchanger, with a threshold relay (4) and a temperature probe (5) at the outlet of the exchanger, which to the advantage of using equipment commonly used in industry, whatever the desired cooling capacity. The cooling capacity in the exchanger is directly related to the need for the cold room and the instantaneous heat exchange capacity of the exchanger.

But we do not control here a limited flow of CO2 and therefore we no longer control the autonomy of the CO2 contained in the tank (for example in the case of cold room door remained open, defrost failure, etc.).

This embodiment uses a safety solenoid valve (1) and safety valves (8) to protect the CO2 circuit a control box for the electrical part. By way of illustration, if the chamber is perceived to be in fault (for example by the temperature of a dummy product (9)) placed in a polyethylene block, for example in combination with other alarm information related to the operation of the refrigeration plant (10)), it then triggers the sending of CO2 from the emergency storage, under controlled conditions not to waste CO2 unnecessarily. If the temperature of the cold room falls below a threshold or if one of the two alarms mentioned above disappears, the injection of CO2 is stopped.

A fifth method (described below with reference to FIG. 6) is in a way the combination of the two previous solutions. That is to say, implement a variable cooling capacity to optimize the heat exchange in the evaporator and have a constant flow.

CO2 injection is via a solenoid valve (2). The room thermostat (3) inside the cold room controls the solenoid valve (2) and the evaporator fan (the latter is delayed when stopped).

A pressure regulator (6) maintains a given evaporation pressure in the evaporator, for example 8 bar.

A temperature probe (5) located at the evaporator outlet makes it possible to maintain the CO 2 temperature at the evaporator outlet and to overcome any heat exchange problem related to the conditions in which the evaporator is located (obstacles in the evaporator). the chamber preventing good ventilation, icing of the exchanger etc.). The temperature chosen at the outlet of the exchanger makes it possible to always be in the gas phase. The calibrated orifice (8) allows a controlled and limited flow of CO2.

An overflow (7) maintains the pressure in the exchanger and in the circuit at a pressure greater than that of the triple bridge of CO2. In case the tank reaches the pressure set at the overflow it will prevent CO2 injection.

In other words, we present here the use of a control loop on the exchanger, a threshold relay (4) with temperature probe (5) at the evaporator outlet, which has the advantage of use current equipment, whatever the cooling capacity desired and have a controlled flow rate of CO2 through the calibrated orifice or a control valve. Depending on the thermal exchange conditions, the CO2 flow rate will be less than or equal to that defined with the calibrated orifice.

A safety solenoid valve (1) and safety valves (9) are also used here to protect the CO2 circuit as well as a control box for the electrical part.

As an illustration, if the chamber is perceived to be in fault (for example by the temperature of a dummy product (10), for example in combination with another alarm information related to the operation of the refrigerating installation (11)), the CO2 is then sent from the emergency storage, under controlled conditions so as not to waste CO2 unnecessarily and to obtain a fixed flow rate, conditions that guarantee a minimum of autonomy.

Claims

1. A device for cooling a user site having at least one cold room for preserving perishable goods or products, cold room cooled by a mechanical cold system, the user site being provided with a liquid CO2 tank used on the site for primary use, the backup device comprising the following:

a liquid CO2 evaporation circuit positioned in the cold chamber and comprising an evaporator, which is a second evaporator independent of the evaporator of the mechanical cold system;

a line which feeds, from said liquid CO 2 reservoir, said second evaporator of the evaporation circuit, in order to carry out the evaporation of the CO 2 therefrom and thus to supply frigories to said products, the line being provided with a device for controlling the amount of CO2 supplying said second evaporator;

means for acquiring at least one piece of information representative of the operation or dysfunction of the mechanical cold system;

a data acquisition and processing system able to recover said at least one representative information and to trigger the supply of CO _{2 of} said second evaporator from said reservoir when the recovered information is representative of a malfunction of the system of mechanical cold.

2. Emergency device according to claim 1, characterized in that said second evaporator has a clean ventilation means allowing the air of the cold room to exchange with the CO ₂ evaporation circuit.

3. Emergency device according to claim 1, characterized in that said second evaporator does not have a clean ventilation means allowing the air of the cold room to exchange with the CO ₂ evaporation circuit. , the installation uses the ventilation means specific to the mechanical cold system.

4. Emergency device according to one of the preceding claims, characterized in that said at least one representative information is constituted by one or more of the following data: a temperature measurement inside the chamber, a measurement of temperature taken in a dummy product present in the chamber, a non-operating indicator of the compressor of said mechanical cold system, a witness of the level of the suction pressure of the compressor of said mechanical cold system, a witness that the system is not in defrost mode when it should, given for example automatic defrosting phases provided in the automatic operation of the cold room, a witness that the door of the cold room is in the open position .

5. Emergency device according to one of the preceding claims, characterized in that it comprises the following elements:

a solenoid valve (V1) capable of opening and closing the supply of CO2 of said second evaporator as a function of the temperature of the CO2 leaving said second evaporator;

a temperature probe (T) placed on the CO2 circuit at the outlet of said second evaporator;

- A valve (V3) placed on the CO2 circuit at the outlet of said second evaporator adapted to maintain in the evaporation circuit a pressure greater than a minimum pressure.

6. Emergency device according to one of claims 1 to 4, characterized in that it comprises the following elements:

- a room thermostat (3) located in the room; - a calibrated orifice (4) located on the CO2 circuit at the outlet of said second evaporator, adapted to provide a controlled flow rate of CO2 as a function of the pressure in the reservoir;

a solenoid valve (2) able to open and close the CO2 supply of said second evaporator as a function of the measurement made by the thermostat; - A discharger (5), located on the CO2 circuit at the outlet of said second evaporator, adapted to maintain the pressure in the evaporator and in the circuit at a pressure greater than that of the triple bridge of CO2.

7. Emergency device according to one of claims 1 to 4, characterized in that it comprises the following elements: - a room thermostat (3) located in the room;

- a solenoid valve (2) adapted to open and close the CO2 supply of said second evaporator;

a pressure regulator (6) capable of maintaining a given evaporation pressure in said second evaporator;

a temperature probe (5) located on the CO2 circuit at the outlet of said second evaporator;

- An overflow (7) located on the CO2 circuit at the outlet of said second evaporator, able to maintain the pressure in the exchanger and in the circuit at a pressure greater than that of the triple bridge of CO2.

8. Emergency device according to one of claims 1 to 4, characterized in that it comprises the following elements:

- a room thermostat (3) located in the room;

- a calibrated orifice (8) located on the CO2 circuit at the outlet of said second evaporator, adapted to provide a controlled flow rate of CO2 as a function of the pressure in the reservoir;

a solenoid valve (2) able to open and close the CO2 supply of said second evaporator as a function of the measurement made by the thermostat;

a temperature probe (5) located on the CO2 circuit at the outlet of said second evaporator able to maintain the CO2 temperature at the evaporator outlet at a given value;

a discharger (7) located on the CO2 circuit at the outlet of said second evaporator, able to maintain the pressure in the exchanger and in the circuit at a pressure greater than that of the triple bridge of CO2

9. A method of piloting emergency of a user site having at least one cold room for preserving food or perishable products, cold room cooled by a mechanical cold system, the user site being provided with a liquid CO2 tank used on the site for a primary use, according to which the following elements are available and the following steps are implemented: - There is a liquid CO2 evaporation circuit positioned in the cold room and comprising an evaporator which is a second evaporator independent of the evaporator of the mechanical cold system;

a line is provided which feeds, from said liquid CO 2 reservoir, said second evaporator of the evaporation circuit, in order to carry out the evaporation of the CO 2 therefrom and thus to supply frigories to said products, the line being provided with a device for controlling the amount of CO2 supplying said second evaporator;

there is an evacuation towards the outside of the vaporized CO2 chamber in said second evaporator;

a means is available for acquiring at least one piece of information representative of the operation or dysfunction of the mechanical cooling system;

an acquisition and data processing system capable of recovering the said at least one representative information and triggering the supply of CO _{2 of the} said second evaporator from the said reservoir when the information recovered is representative of a malfunction of the mechanical cold system; and

- following reception by the data acquisition and processing system of at least one piece of information representing a malfunction of the mechanical cold system, the supply of said second evaporator with CO2 from the storage of CO2 is triggered. liquid;

the supply of the CO2 evaporator is stopped when the said at least one piece of information which has been received by the data acquisition and processing system and analyzed as being representative of a malfunction of the mechanical cold system is again received by the data acquisition and processing system and analyzed as being representative of normal operation of the mechanical cold system.

10. Emergency driving method according to claim 9, characterized in that said at least one representative information is constituted by one or more of the following data: a temperature measurement inside the chamber, a temperature measurement taken in a dummy product present in the chamber, a non-operating indicator of the compressor of said mechanical cold system, a witness of the level of the compressor suction pressure of said mechanical cooling system, a witness that the system is not in defrosting mode when it should, taking into account, for example, automatic defrosting phases provided for in the automatic operation of the cold room , a witness that the door of the cold room is in the open position.

11. Emergency piloting method according to claim 9 or 10, characterized in that the following elements are available:

a solenoid valve (V1) capable of opening and closing the supply of CO2 of said second evaporator as a function of the temperature of the CO2 leaving the evaporator;

- A valve (V3) placed on the CO2 circuit at the outlet of said second evaporator adapted to maintain in the evaporation circuit a pressure greater than a minimum pressure. and in that the following measures are taken:

- triggering, using the solenoid valve (V1) following receipt by the data acquisition and processing system of at least one information representative of a malfunction of the mechanical cold system, the supplying said second evaporator with CO2 from the storage of liquid CO2;

the CO2 evaporates by absorbing the heat coming from the air in the cold room, at a pressure greater than the minimum pressure fixed by said valve (V3); on the basis of the information provided by said temperature probe, the amount of CO2 arriving in said second evaporator is adjusted so that the temperature at the outlet of the latter is kept close to a fixed set point value, preferably situated between -30 ^° C. and -40 ^° C., so that the CO2 escaping at the outlet of the evaporator is completely vaporized; the supply of said second CO2 evaporator is stopped when said at least one piece of information which has been received by the data acquisition and processing system and analyzed as being representative of a malfunction of the mechanical cold system is again received speak data acquisition and processing system and analyzed as being representative of normal operation of the mechanical cold system.

12. Emergency driving method according to claim 11, characterized in that said minimum pressure is in the range from 5.5 bar to 10 bar (absolute).

13. Emergency steering method according to claim 9 or 10, characterized in that the following elements are available:

- a room thermostat (3) located in the room;

- A calibrated orifice (4) located on the CO2 circuit at the outlet of said second evaporator, adapted to provide a controlled flow rate of CO2 as a function of the pressure in the reservoir;

a discharger (5) located on the CO2 circuit at the outlet of said second evaporator, able to maintain the pressure in the evaporator and in the circuit at a pressure greater than that of the triple carbon bridge, and what we do to the following measures:

- triggering, using the solenoid valve, following receipt by the data acquisition and processing system of at least one piece of information representative of a malfunction of the mechanical cold system, the power supply of the CO2 evaporator from the storage of liquid CO2;

the supply of said second CO2 evaporator is stopped when said at least one piece of information which has been received by the data acquisition and processing system and analyzed as being representative of a malfunction of the mechanical cold system is again received by the data acquisition and processing system and analyzed as being representative of a normal operation of the mechanical cold system.

14. A method of emergency driving according to claim 9 or 10, characterized in that it has the following elements: - a room thermostat (3) located in the chamber;

a pressure regulator (6) capable of maintaining a given evaporation pressure in said second evaporator; a temperature probe (5) located on the CO2 circuit at the outlet of said second evaporator;

a discharge device (7) situated on the CO2 circuit at the outlet of said second evaporator, able to maintain the pressure in the exchanger as well as in the circuit at a pressure greater than that of the triple bridge of the CO2, and in that the following measures are taken:

- triggering, using the solenoid valve, following receipt by the data acquisition and processing system of at least one information representative of a malfunction of the mechanical cold system, the supply of said second CO2 evaporator from the storage of liquid CO2;

- the CO2 evaporates by absorbing the heat coming from the air of the cold room;

the quantity of CO2 arriving in said second evaporator is adjusted on the basis of the information provided by said temperature probe so that the temperature at the outlet of the latter is kept close to a fixed setpoint, so that CO2 escaping at the outlet of said second evaporator is completely vaporized;

15. Emergency steering method according to claim 9 or 10, characterized in that the following elements are available:

- a room thermostat (3) located in the room;

- a calibrated orifice (8) located on the CO2 circuit at the outlet of said second evaporator, adapted to obtain a controlled flow rate of CO2 as a function of the pressure in the reservoir;

a pressure regulator (6) capable of maintaining a given evaporation pressure in said second evaporator; a temperature probe (5) located on the CO2 circuit at the outlet of said second evaporator able to maintain the CO2 temperature at the evaporator outlet at a given value;

- the CO2 evaporates by absorbing the heat coming from the air of the cold room; the quantity of CO2 arriving in said second evaporator is adjusted on the basis of the information provided by said temperature probe so that the temperature at the outlet of the latter is kept close to a fixed setpoint, so that the CO2 escaping at the outlet of the evaporator is completely vaporized; the supply of said second CO2 evaporator is stopped when said at least one piece of information which has been received by the data acquisition and processing system and analyzed as being representative of a malfunction of the mechanical cold system is again received by the data acquisition and processing system and analyzed as being representative of a normal operation of the mechanical cold system.