Environmental simulation chamber and respective method of operation

Abstract

Environmental simulation chamber (100) comprising a refrigeration apparatus (1) equipped with a refrigeration device (10) having a closed circuit (C) within which a refrigerant fluid circulates, said closed circuit (C) being equipped with at least one compressor (2), cooling means (3) for said refrigerant fluid, expansion means (4) for said refrigerant fluid and evaporation means (5), said chamber (100) further comprising an insulated space (20) into which a specimen (21) to be tested is inserted and wherein said evaporation means (5) are adapted to regulate the internal temperature of said insulated space (20), said simulation chamber being characterised in that said refrigerant fluid is carbon dioxide.

Description

FIELD OF THE INVENTION

[0001] The present invention concerns an environmental simulation chamber and a respective method of operation.KNOWN PRIOR ART

[0002] It is known that there are environmental simulation chambers which comprise a refrigeration apparatus equipped with refrigeration device having a closed circuit within which a refrigerant fluid circulates. This closed circuit is equipped with at least one compressor, cooling means for the refrigerant fluid, expansion means for the refrigerant fluid and evaporation means. This chamber further comprises an insulated space within which a specimen to be tested is inserted and in which the evaporation means, in cooperation with the expansion means, are adapted to regulate the internal temperature of the insulated space in order to test the behaviour of the specimen under various environmental, even extreme, conditions. Still according to known art, the refrigerant fluid is normally known as R449.

[0003] However, this refrigerant fluid is not devoid of drawbacks.

[0004] In fact, although the refrigeration device using this gas allows to achieve a very precise and rapid temperature control within the insulated space of the environmental simulation chamber, the R449 gas turns out to have a fairly high GWP. It should be specified that a refrigerant should have a relatively low CO2 equivalent. In practice, its relative Global Warming Potential or GWP should be as low as possible, so as to avoid indirect damage to the environment in case of refrigerant release. GWP measures the defined amount of mass of a greenhouse gas that contributes to global warming. Such value is established by considering carbon dioxide as a reference, which, therefore, is the reference value. GWP therefore describes the average warming effect over a specific time interval, 100 years in this context, of a given gas or gas mixture. As regards the definition of the CO2 equivalent, or its respective GWPs, reference will be made herein and hereinafter to (EU) Regulation No. 517 / 2014 of the European Parliament and Council.

[0005] Therefore, the higher the GWP value associated with a gas, the greater the risk to the environment if that gas is released into the atmosphere.

[0006] Environmental simulation chambers are known which operate with gases having very low GWPs.

[0007] For example, the patent WO2021 / 124135 in the name of ATT describes an environmental simulation chamber that operates with a gaseous mixture having an extremely low GWP value, even lower than 380 over 100 years.

[0008] In any case, the trend is to identify a gas for environmental control chambers that has an even lower GWP value than the already extremely low GWP value of the refrigerant mixture described in document WO2021 / 124135 in the name of the Applicant.

[0009] The document US2019 / 093926 in the name of Haack Christian describes an air-conditioning test chamber comprising a test space that serves to receive the test material and that can be closed off from the surrounding environment and that is thermo-insulated, and a temperature-controlling device to control the temperature of the test space. The temperature-controlling device allows to establish a temperature in a temperature range of −80° C. to +180° C., preferably from −100° C. to +200° C., to be established inside the test space. In addition, the temperature-controlling device is equipped with a cooling device comprising a cooling circuit with a refrigerant, a heat exchanger arranged in the test space, a compressor, a condenser and an expansion element.

[0010] The document JP2007132545 in the name of TAIKISHA refers to an air-conditioning system and, more particularly, it includes an air cooler for an air-conditioned area that acts as an evaporator in a refrigeration circuit and controls the system components, including the air cooler to bring the air-conditioned area up to a target temperature. This solution described in document JP2007132545 refers in particular to an air-conditioning system with controlling means for regulating humidity conditions.

[0011] Therefore, object of the present invention is to make an environmental simulation chamber that is capable of working with refrigerant fluid having extremely low GWP, tending to be close to zero.

[0012] Further object of the present invention is to make an environmental simulation chamber that is even less energy-intensive than those existing today.

[0013] In addition, object of the present invention is to make an environmental simulation chamber that also allows to increase the level of safety of current chambers.

[0014] Finally, object of the present invention is to make a method for operating a chamber according to the invention, that allows to reach high levels of efficiency and safety and, in any case, higher than those of the simulation chambers existing today.SUMMARY OF THE INVENTION

[0015] These and other objects are achieved by means of an environmental simulation chamber according to claim 1.

[0016] In particular, this environmental simulation chamber comprises a refrigeration apparatus equipped with a refrigeration device having a closed circuit within which a refrigerant fluid circulates, said closed circuit being equipped with at least one compressor, cooling means for said refrigerant fluid, expansion means for said refrigerant fluid and evaporation means, said chamber further comprising an insulated space into which a specimen to be tested is inserted and wherein said evaporation means are adapted to regulate the internal temperature of said insulated space, said simulation chamber being characterised in that said refrigerant fluid is carbon dioxide. This solution allows to achieve the proposed objects. In fact, thanks to the presence of carbon dioxide as a refrigerant fluid, it is possible to have a GWP close to zero, i.e. equal to 1 over 100 years.

[0017] In addition, this closed circuit further comprises an expansion reservoir for said carbon dioxide, which is arranged operatively along a first length arranged between said evaporation means and said at least one compressor, and means for allowing the filling of refrigerant fluid from said first length to said expansion reservoir and the release of refrigerant fluid from said expansion reservoir to said first length.

[0018] This solution, as will become clearer thanks to the method described below, allows to operate with a compressor in intermittent operation, i.e. turned off for part of the operation of the simulation chamber, especially in the event of partial operation of the chamber, i.e. in the event that a non-excessive level of refrigeration is required. This is achieved by reducing the opening of the expansion means and, therefore, allowing a lower carbon dioxide flow rate to pass through them than that sucked by the same compressor.

[0019] In practice, said compressor operates intermittently in the event of partial loads. Said expansion reservoir is in fact sized to contain pressure fluctuations at the outlet of said evaporation means below a certain pressure, preferably below 8 bars, depending on the partial-load openings of said expansion means for temperature control.

[0020] According to the proposed solution, this simulation chamber comprises a control unit which, on the basis of said internal temperature to be regulated within said insulated space, turns the compressor on or off, in which said refrigerant fluid present in said expansion reservoir feeds said closed circuit or is filled by said closed circuit. According to a first variation of the invention, said filling and releasing means comprise a connecting conduit. This way, the expansion reservoir has no control over the inflow and outflow of carbon dioxide therein but depends on the pressures that are along the first length of the closed circuit and, therefore, the refrigerant fluid upstream of the same compressor.

[0021] In a further embodiment, this connecting conduit comprises a first shut-off valve; preferably, said control unit allows or disallows the inflow / outflow of said refrigerant fluid into / from said expansion reservoir depending on the pressure at the outlet of the evaporation means.

[0022] Alternatively, said filling / releasing means comprise a by-pass circuit arranged along said first length between said evaporation means and said at least one compressor; said by-pass circuit comprises a first inlet branch from said first length to said expansion reservoir and a second outlet branch from said expansion reservoir to said first length. Said filling / releasing means further comprises a first shut-off valve arranged along said first branch, a second shut-off valve arranged along said second outlet branch and at least one third shut-off valve arranged along said first length between said first inlet branch and said second outlet branch. This second embodiment of the invention allows to achieve a finer control of the expansion reservoir filling / emptying and, therefore, a more accurate operation of the environmental simulation chamber.

[0023] Furthermore, said circuit further comprises a storage reservoir of said refrigerant fluid in liquid form, which is arranged in a second length of said closed circuit between said cooling means and said expansion means.

[0024] In accordance with a further embodiment of the invention, the closed circuit comprises at least one auxiliary line which directly or indirectly connects said closed circuit to said insulated space; said auxiliary line is provided with an inlet section for said refrigerant fluid, which is arranged along a first length of said closed circuit between said evaporation means and said at least one compressor, and an outlet section for said refrigerant fluid. This outlet section is connected to said insulated space for the inflow into said insulated space of carbon dioxide in gaseous form.

[0025] This solution, which in a particular embodiment of the invention, may exist even in the absence of the expansion reservoir, allows carbon dioxide to be introduced into the insulated space which is capable of extinguishing a fire should one occur.

[0026] In particular, said auxiliary line comprises an opening / closing valve arranged along said auxiliary line to allow or prevent the passage of said refrigerant fluid along said auxiliary line.

[0027] In addition, according to a preferred embodiment of the invention, the simulation chamber further comprises detecting means for detecting the ignition of a fire within said insulated space; said detecting means are operatively connected to said opening / closing valve to control its opening or closing. This solution allows a possible fire present inside the insulated space to be extinguished without the need for an operator to control the intervention, but automatically.

[0028] In a further embodiment of the invention, the refrigeration apparatus comprises a further refrigeration device having a further closed circuit within which a further refrigerant fluid circulates; this further closed circuit is equipped with at least one further compressor, further cooling means for cooling said refrigerant fluid, further expansion means for said refrigerant fluid and further evaporation means adapted to operate in cooperation with said cooling means of said refrigeration device. This further refrigeration device operates in a higher temperature range than the one at which said refrigeration device operates. In this case, the refrigerant fluid which circulates in the closed circuit, i.e. carbon dioxide, operates under sub-critical conditions.

[0029] In another embodiment, the refrigerant fluid can also operate under transcritical conditions but, in this case, the closed circuit is devoid of the further refrigeration device and, in addition, the cooling means no longer operate as a condenser. In this embodiment, the closed circuit comprises, in addition to said at least one compressor, a second high-pressure compressor in series to said at least one compressor, a bypass circuit for said cooling means, wherein this bypass circuit has at least one control valve for operating said bypass circuit, an intermediate throttling valve downstream of said storage reservoir and a condensation pressure control valve.

[0030] In particular, said closed circuit further comprises a heat exchanger operatively connected to a third length of said closed circuit between said at least one second compressor but downstream of said bypass circuit, and said refrigerant fluid storage reservoir and means for regulating the flow rate of refrigerant fluid entering said heat exchanger. Said heat exchanger is arranged within said insulated space; preferably said heat exchanger and said evaporation means are arranged in two separate compartments present within said insulated space.

[0031] This way, it is possible to both refrigerate and heat the insulated space by taking advantage of the same refrigeration device.

[0032] The objects are also achieved by a method for operating an environmental simulation chamber according to one or more of claims 1 to 12, comprising the steps of:

[0033] a) setting at least one temperature, or at least one temperature range, to be achieved within said insulated space;

[0034] b) activating said at least one compressor to circulate said refrigerant fluid within said closed circuit of said refrigeration device;

[0035] c) regulating the opening / closing of said expansion means in such a way as to vary the flow rate of refrigerant fluid passing through said evaporation means depending on said at least one temperature, or said temperature range, required within said insulated space;

[0036] wherein said refrigerant fluid is carbon dioxide.

[0037] In particular, the method further comprises the step d) of filling said expansion reservoir at least partially with said refrigerant fluid.

[0038] Furthermore, in the event that in said step c) said expansion means operate at partial load and said at least one expansion reservoir is sized to contain fluctuations of pressures at the outlet of said evaporation means, which are lower than a certain pressure, preferably lower than 8 bar, said method comprises the step e) of making said compressor work intermittently. In practice, the method of operation of the environmental simulation chamber works advantageously, especially when the expansion means operate at partial load, i.e. the flow rate of refrigerant passing through the expansion means is reduced compared to the flow rate that is sucked by the compressor. This takes place when the refrigeration load within the insulated space is not at the limit of the refrigeration apparatus' capacities, but a temperature preferably higher than −20° C. is requested by the user. In these conditions, thanks to the presence of the expansion reservoir, it is possible to let the compressor work intermittently, i.e. by turning it off and on again, while still maintaining an extremely efficient level of cooling control within the insulated space. In simulation chambers of known art, such as e.g. the patent WO2020012348 in the name of the applicant, the compressor is rather kept turned on at all time, with considerable electrical energy consumption for its operation.

[0039] Furthermore, said step e) comprises step e1) of reducing the flow rate of the refrigerant fluid passing through said expansion means to a value lower than that sucked by said at least one compressor in such a way as to reduce the suction pressure of said at least one compressor to such a pressure value to cause it to turn off, the step e2) of feeding said expansion reservoir by means of said fluid flowing out of said evaporation means until the pressure of said expansion reservoir has risen to a first pressure value determined depending on the temperature, or the temperature range, required within said insulated space and equal to the suction pressure at which said at least one compressor, in said step e1), starts sucking refrigerant fluid from said expansion reservoir, and step e3) of reactivating the operation of said compressor upon exceeding said first pressure value within said reservoir, said steps e1), e2) and e3) repeating cyclically. This solution offers the advantage of being able to operate with intermittently operating compressor with still excellent temperature control capabilities within the insulated space.

[0040] It should be mentioned that, with the compressor turned off, the refrigerant flow is prevented from passing through the same compressor and that, therefore, the refrigerant fluid, which continues to pass through the expansion means and thus also through the evaporation means, builds up downstream of these, thus increasing the pressure within the expansion reservoir.

[0041] The operation described above of the simulation chamber allows to save energy in the overall operation of the environmental simulation chamber.

[0042] This operation mode is achieved by the solution shown in FIG. 1.

[0043] As an alternative to the method of operation described above, with a solution in which said filling / releasing means comprise a first shut-off valve arranged along said first branch, a second shut-off valve arranged along said second outlet branch and at least one third shut-off valve arranged along said first length between said first inlet branch and said second outlet branch, i.e. with the embodiment shown in FIG. 2, said step e) comprises the step e1′) of reducing the flow rate of the refrigerant fluid through said expansion means to a value lower than that sucked by said at least one compressor, the step e2′) of closing said third shut-off valve and said first shut-off valve and opening, or keeping open, said at least one second shut-off valve upon reaching a first suction pressure for said compressor which is determined depending on the temperature, or temperature range, required within said insulated space and equal to the pressure at which said at least one compressor, in said step e1′), starts sucking refrigerant fluid from said expansion reservoir, the step e3′) of turning off said at least one compressor upon reaching such a pressure value that causes it to turn off. The method further comprises the step e4′) of reopening said first shut-off valve if, during said steps e2′) and / or e3′), the pressure of the refrigerant fluid between said first shut-off valve, or said third shut-off valve, and said evaporation means is higher than at a second suction pressure for the compressor 2, which is higher than said first suction pressure, the step e5′) of closing the first shut-off valve if during steps e2′) and / or e3′) the pressure of the refrigerant fluid between the first shut-off valve, or the third shut-off valve, and the evaporation means drops to a value lower than the first suction pressure for the compressor, and the step e6′) of reactivating the compressor at least when the pressure within the expansion reservoir is higher than said first pressure. Finally, the steps e1′)- e6′) are repeated in a cyclical manner.

[0044] This solution ensures a higher level of control than can be achieved with a closed circuit devoid of bypass circuit for said expansion reservoir and the three shut-off valves described above.

[0045] Furthermore, still in the event of a solution in which said filling / releasing means comprise a first shut-off valve arranged along said first branch, a second shut-off valve arranged along said second outlet branch and at least one third shut-off valve arranged along said first length between said first inlet branch and said second outlet branch, the method thus comprises the step f) of keeping open said second shut-off valve and said third shut-off valve and keeping closed said first shut-off valve, such that, at least when the flow rate sucked by said at least one compressor is equal to that which passes through said expansion means (i.e. in the event of full load of the simulation chamber), or for the environmental simulation chamber turned off (null load), the refrigerant fluid present in said expansion reservoir balances the specific volume increase of the refrigerant gas present in said closed circuit and / or allows to reduce any undesired pressure increase within said closed circuit.

[0046] Furthermore, still in the event of solution in which said filling / releasing means comprise a first shut-off valve arranged along said first branch, a second shut-off valve arranged along said second outlet branch and at least one third shut-off valve arranged along said first length between said first inlet branch and said second outlet branch, said step a) comprises the step al) of rapidly increasing the requirement of required refrigeration load (i.e. booster operating condition); in this event, said method further comprises the step h) of reducing the pressure within said expansion reservoir to a minimum pressure value, preferably equal to the minimum suction pressure value of said at least one compressor, and subsequently to said step h) of opening and keeping open said first shut-off valve and said expansion means.

[0047] In addition, in the event of solution wherein said filling / releasing means comprise a first shut-off valve arranged along said first branch, said step a) comprises the step a1) of rapidly increasing the requirement of required refrigeration load (i.e. booster operating condition); in this case, said method further comprises the step h) of reducing the pressure within said expansion reservoir to a minimum pressure value, preferably equal to the minimum suction pressure value of said at least one compressor, wherein said step h) is prior to said step a1), and subsequent to said step h) and simultaneously with said step a1), the method comprises the step r) of keeping open said first shut-off valve and said expansion means.

[0048] Furthermore, said step r) continues until the temperature in said insulated space reaches a value higher than the evaporation temperature of the refrigerant fluid within said evaporation means, preferably said temperature within said chamber is 10K (Kelvin) higher than said evaporation temperature, or the suction pressure for said at least one compressor has reached the maximum operating conditions expected for the operating condition of said at least one compressor and said at least one first shut-off valve and / or said at least one second shut-off valve are closed, o is closed; said storage reservoir of the refrigerant fluid and said expansion reservoir are sized in such a way that, during said step r), said liquid-phase refrigerant fluid is not depleted.

[0049] In the event of a circuit in which a refrigerant fluid circulates under transcritical conditions, then, at the same time as said step h) or independently of said step h), the step 1) of flowing refrigerant fluid along said heat exchanger is carried out.

[0050] Furthermore, the method further comprises also the step m) of controlling the opening of said opening / closing valve for the passage of said refrigerant fluid along said auxiliary line, and the step n) of fluidically connecting said closed circuit to said insulated space by means of said auxiliary line, wherein said auxiliary line is provided with an inlet section for said refrigerant fluid, which is arranged along a first length of said closed circuit between said evaporation means and said at least one compressor, and an outlet section for said refrigerant fluid; said outlet section is connected to said insulated space for the inflow into said insulated space of carbon dioxide in gaseous form.

[0051] Furthermore, said step m) is preceded by the step o) of detecting the ignition of fire within said insulated space.DESCRIPTION OF THE FIGURES

[0052] Some particular embodiments of the present invention will now be described only by way of non-limiting example, with reference to the accompanying figures, in which:

[0053] FIG. 1 is a schematic view of the environmental simulation chamber according to the invention, in accordance with a first embodiment of the invention, in which the refrigerant fluid works under sub-critical conditions;

[0054] FIG. 2 is a schematic view of the environmental simulation chamber in accordance with a second embodiment of the invention, in which the refrigerant fluid works under sub-critical conditions.

[0055] FIG. 3 is a schematic view of the environmental simulation chamber in accordance with a third embodiment of the invention, in which the refrigerant fluid works under transcritical conditions;

[0056] FIG. 4 is a schematic view of the environmental simulation chamber in accordance with a further embodiment of the invention, in which the refrigerant fluid works under sub-critical conditions.DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION

[0057] FIG. 1 shows, in a simplified manner, an environmental simulation chamber 100 which comprises a refrigeration apparatus 10 equipped with a refrigeration device 1 having a closed circuit C within which a refrigerant fluid circulates. This closed circuit C1 is equipped with a compressor 2, in particular with pistons, cooling means 3 for the refrigerant fluid, expansion means 4 for the refrigerant fluid and evaporation means 5. It should be noted that an embodiment which comprises two or more compressors in series, or arranged in stages, would nevertheless fall within the scope of protection of the present invention.

[0058] The chamber 100 further comprises an insulated space 20 into which a specimen 21 to be tested is inserted and in which the evaporation means 5, in cooperation with said expansion means 4, are adapted to regulate the internal temperature of the insulated space 20. Advantageously, the refrigerant fluid used within the refrigeration apparatus 1 is carbon dioxide.

[0059] This solution allows the GWP value of such an environmental simulation chamber 100 to be reduced to 1, thus allowing to achieve enormous environmental benefits.

[0060] Still according to the first embodiment described herein and shown in FIG. 1, the closed circuit C further comprises an expansion reservoir 30 for the carbon dioxide, operatively arranged along a first length T positioned between the evaporation means 5 and the compressor 2 and means 6 for allowing the refrigerant fluid to be filled from the first length T to the expansion reservoir 30 and the release of the refrigerant fluid from the expansion reservoir 30 to the first length T.

[0061] In particular, thanks to the presence of this expansion reservoir 30, the compressor 2 operates intermittently in case of partial loads. This expansion reservoir 30 is in fact sized to contain pressure fluctuations at the outlet of the evaporation means 5 below a certain pressure, preferably lower than 8 bars, depending on the partial-load openings of the expansion means 4 for temperature control.

[0062] In particular, the chamber 1 comprises a control unit which, on the basis of the internal temperature to be regulated within the insulated space 20, turns on and off the compressor 2. The refrigerant fluid present in the expansion reservoir 30, therefore, feeds the closed circuit C or is fed by the closed circuit C, as it is filled by the expansion means 5 during the intermittent operation of the compressor 2.

[0063] Still according to the embodiment described in FIG. 1, the filling and releasing means 6 comprise a connecting conduit 61 between the expansion reservoir 30 and the above-mentioned first length T positioned between the evaporation means 5 and the compressor 2.

[0064] The presence of the pressure reservoir 30 allows the compressor 2 to operate intermittently in the event of partial loads, if it is specially sized to contain limited pressure fluctuations on the evaporation means 4, preferably not higher than 8 bars, depending on the partial-load openings of the expansion means 4 for temperature control, up to a maximum of 50%, without exceeding the number of activations / minute allowed by the manufacturer of the compressor 2. In conventional environmental simulation chambers with conventional refrigerants, due to limitations of the load, the compressor always remains in motion and the operation of the refrigeration device is achieved through the so-called hot gas bypass conduit, or line (see also the description below).

[0065] It should be emphasised that “compressor 2 operating at partial load” means that, within the insulated space 20, a temperature to be used is sought, which is not the maximum lowest limit achievable by the refrigeration device 10 but which results, e.g., in a maximum opening of 50% of the expansion means 4. The expansion means 4 provide, e.g., for the presence of a throttling valve that controls, with its opening, the flow rate of refrigerant fluid reaching the evaporation means 5 and that, therefore, ultimately allows the temperature present within the insulated space 20 to be modulated. A partial loads' operation, therefore, means an operation which allows to reach temperatures higher than that of the lowest limit achievable.

[0066] The presence of the refrigerant fluid, such as carbon dioxide, on the other hand, allows the use of an expansion reservoir 30 that has limited dimensions compared to those that, on the contrary, would have an expansion reservoir used in a closed circuit within which a known refrigerant such as, e.g., R449 circulates. In fact, with this refrigerant, the specific gas volumes would be much higher than those resulting when using carbon dioxide and, therefore, an expansion reservoir in these systems with R449 would take up an exaggeratedly large amount of space to guarantee similar operating conditions. For this reason, in the refrigeration devices of known art, i.e. operating with R449, such expansion reservoirs are never used.

[0067] Moreover, FIG. 1 also shows, along the closed circuit C, the hot-gas bypass line 35 with the respective valve 36, which allows, in case of partial load operation of the refrigeration device 1, the passage of refrigerant fluid flow through this line 35 instead of through the expansion means 4 and the evaporation means 5. In this case, the compressor 2 operates without interruptions, i.e. continuously and the temperature within the insulated chamber 20 is close to the minimum value.

[0068] Still with reference to FIG. 1, the chamber comprises at least one auxiliary line 50 which directly connects the closed circuit C to the insulated space 20. This auxiliary line 50 is provided with an inlet section 51 for the refrigerant fluid, which is arranged along a first length T of the closed circuit C between the evaporation means 5 and the compressor 2, an outlet section 52 for the refrigerant fluid and an opening / closing valve 55 to allow or not allow the passage of carbon dioxide along the auxiliary line 50. The outlet section 52 is connected to the insulated space 20 for the inflow into the insulated space 20 of carbon dioxide in gaseous form. This solution therefore allows to make a real fire extinguisher always connected inside the insulated space 20. It should be noted that this auxiliary line 50 could also be connected indirectly to the circuit C if connected, e.g., to the evaporation reservoir 30.

[0069] In another embodiment not shown herein, the chamber 100 may comprise the auxiliary line 50 but the refrigeration device 1 could be devoid of the expansion reservoir 30, without thereby departing from the protection scope of the present invention. In addition, the chamber 100 further comprises means 80 for detecting the ignition of a fire within the insulated space 20. Specifically, these detecting means 80 are operatively connected to the opening / closing valve 55 for controlling its opening or closing. This way, in the event that a fire, or the onset of a fire, is detected within the insulated space 20, the opening of the valve 55 would be controlled immediately so as to allow part of the carbon dioxide flow rate, which circulates in the closed circuit C, to reach the insulated space 20 and thus extinguish the fire.

[0070] Still according to this first embodiment, the refrigeration apparatus 1 comprises a further refrigeration device 10′ having a further closed circuit C′ within which a further refrigerant fluid circulates. This further closed circuit C′ is equipped with a further compressor 2′, further cooling means 3′ for the refrigerant fluid, further expansion means 4′ for the refrigerant fluid and further evaporation means 5′ adapted to work in cooperation with the cooling means 3 of the refrigeration device 10 of the closed circuit C of the refrigeration apparatus 1. The further refrigeration device 10′ operates in a range of temperatures higher than that at which the refrigeration device 10 operates. In addition, the refrigerant fluid used in this further refrigeration device 10′ is R449.

[0071] In this situation, the refrigerant fluid of the refrigeration device 10, i.e. carbon dioxide, operates under sub-critical conditions, typically with refrigerant fluid having temperature lower than 20° C. In this case, the cooling means 3 operate in the same way as a condenser normally operates.

[0072] In the embodiment of FIG. 2, the only difference from the embodiment of FIG. 1 is that the filling / releasing means 6 this time comprise a bypass circuit C1 arranged along the first length T between the evaporation means 5 and the compressor 2. This bypass circuit C1 comprises a first inlet branch 41 from the first length T to the expansion reservoir 30 and a second outlet branch 42 from the expansion reservoir 30 to the first length T. The filling / releasing means 6 further comprise a first shut-off valve 43 arranged along the first branch 41, a second shut-off valve 44 arranged along the second outlet branch 42 and a third shut-off valve 45 arranged along the first length T between the first inlet branch 41 and the second outlet branch 42.

[0073] This bypass circuit Cl together with the presence of the shut-off valves 43, 44 and 45 allows to finely control the operation of the refrigeration device 10 depending on the temperature control requirements inside the insulated space 20, as will be however clear from the method of operation of the chamber 100, which is set forth below. In the embodiment of FIG. 4, the difference from the embodiment of FIG. 1 is that the filling / releasing means 6 comprise a connecting conduit 61 which, in turn, comprises a first shut-off valve 43. This control unit is adapted to open or close the first valve 43 in order to allow or not allow the inflow / outflow of the refrigerant fluid into / from the expansion reservoir 30, depending on the pressure at the outlet of the evaporation means 5.

[0074] In the embodiments described above and shown in FIGS. 1, 2 and 4, the circuit C further comprises a storage reservoir 70 of the refrigerant fluid in liquid form and arranged in a second length T2 of the closed circuit C (operatively) between the cooling means 3 and the expansion means 4.

[0075] In the event, however, of operation of the refrigerant fluid circulating in the circuit C under transcritical conditions, the further refrigeration device 10′ is absent and the cooling means 3 no longer operate as in a condenser. In this embodiment shown in FIG. 3, with respect to the circuit C shown in FIGS. 1, 2 and 4, a second high-pressure compressor 110, a bypass circuit 112 for the cooling means 3 which is equipped with a control valve 113 for activating the bypass circuit 112, an intermediate throttling valve 114 arranged downstream of the storage reservoir 70 and a condensation pressure control valve 115 are additionally present in a known manner. The second compressor 110 is also preferably of the piston type.

[0076] The intermediate throttling valve 114 is operatively arranged between the storage reservoir 70 and the second high-pressure compressor 110 and, analogously to the hot-gas bypass line 35 and the respective valve 36, allows the passage of the refrigerant flow through this line instead of through the expansion means 4 and the evaporation means 5, in the event of partial-load operation of the refrigeration device 1. In addition, the condensation pressure control valve 115, which is arranged upstream of the storage reservoir 70 and downstream of said cooling means and the bypass circuit 112, has the function of allowing the throttling of the refrigerant fluid with consequent regulation of the condensation pressure inside the storage reservoir 70.

[0077] The bypass circuit 112 allows to bypass the cooling means 3 so that the refrigerant fluid is not cooled but kept at a temperature necessary for other applications, as will be evident in the following paragraphs.

[0078] In this embodiment, the closed circuit C further comprises a heat exchanger 200 operatively connected to a further length T3 of the closed circuit C between the second high-pressure compressor 110, but downstream of the bypass circuit 112, and the storage reservoir 70. The closed circuit C further comprises means 205, 206 to regulate the flow rate of refrigerant fluid entering the heat exchanger 200. This heat exchanger 200 is arranged within the insulated space 20.

[0079] These regulating means comprise a three-way valve 205 to divert the flow of refrigerant gas, i.e. carbon dioxide, coming from the second high-pressure compressor 110 in the direction of the exchanger 200 and a non-return valve 206 exiting the exchanger 200. The three-way valve is arranged operatively downstream of the bypass circuit 112. At the time when the three-way valve 205 for the passage of the high-temperature refrigerant fluid within the heat exchanger 200 is operated, the control valve 113 for operating the bypass circuit 112 is simultaneously activated, in such a way that the cooling means 3 are bypassed.

[0080] Furthermore, still in the embodiment shown in FIG. 3, the heat exchanger 200 and the evaporation means 5 are arranged in two separate compartments present within the insulated space 20.

[0081] It should be noted that, although the embodiment of the simulation chamber 100 shown in FIG. 3 provides the presence of filling / releasing means 6 of the type shown in FIG. 2, i.e. in which a bypass circuit C1 arranged along the first length T between the evaporation means 5 and the compressor 2 is provided and where the bypass circuit C1 comprises a first inlet branch41 and a second outlet branch 42 from the expansion reservoir 30 to the first length T and in which the filling / releasing means 6 further comprise a first shut-off valve 43 arranged along the first branch 41, a second shut-off valve 44 arranged along the second outlet branch 42 and a third shut-off valve 45 arranged along the first length T between the first inlet branch 41 and the second outlet branch 42, however, an embodiment in which these filling / releasing means 6 are of the type shown in FIG. 1, in which the presence of a conduit 61 is provided, or of the type shown in FIG. 4, in which this conduit 61 comprises a first shut-off valve 43, in any event, would fall within the scope of protection of the present invention.

[0082] The operation modes of the chambers 100 shown in FIGS. 1 to 4 will be described hereinbelow.

[0083] In particular, this method for the operation of the environmental simulation chamber 100 comprises the steps of:

[0084] a) setting a temperature, or a temperature range, to be achieved within the insulated space 20;

[0085] b) activating the compressor 2 to circulate the refrigerant fluid within the closed circuit C of the refrigeration device 10;

[0086] c) regulating the opening / closing of the expansion means 4 in such a way as to vary the flow rate of refrigerant fluid passing through the evaporation means 5 depending on the temperature, or the temperature range, required within said insulated space 20; wherein the refrigerant fluid circulating within the circuit C is carbon dioxide.

[0087] In particular, the method comprises step d) of filling at least partially the expansion reservoir 30 with the refrigerant fluid in such a way as to compensate for any rapid requests by the user for temperature variations or to allow the chamber 100 to be operated while keeping the compressor 2 idle for part of its operation. This activity could not be carried out with the use of a refrigerant fluid of known art, such as e.g. R449, because, as mentioned above, this gas of known art has specific volume values far greater those of carbon dioxide, with the result that any expansion reservoir should be too large and such that it could not be used.

[0088] Furthermore, in the event that in said step c) said expansion means 4 operate at partial load and the expansion reservoir 30 is sized to contain pressure fluctuations at the outlet of the evaporation means 5 below a certain pressure, preferably lower than 8 bars, the method comprises the step e) of letting the compressor work intermittently, i.e. by continuously turning off and on the compressor 2 upon reaching certain thermodynamic conditions of the refrigerant fluid. Therefore, the expansion reservoir 30 is filled and emptied depending on both the temperature to be maintained within the insulated space 20 and the characteristics of the compressor 2, i.e. the minimum working pressure it can reach and the number of activations / deactivations per minute that this compressor can withstand without risking malfunctions.

[0089] It should be emphasised that “expansion means 4 operating at partial load” means that within the insulated space 20, a temperature to be used is sought, which is not the maximum lowest limit achievable by the refrigeration device 10 but which results, e.g., in a maximum opening of 50% of the expansion means 4. The expansion means 4 provide, for example, the presence of a throttling valve that controls, with its opening, the flow rate of refrigerant fluid reaching the evaporation means 5 and that, therefore, ultimately allows to modulate the temperature present within the insulated space 20. In particular, in the event of the embodiment of FIG. 1, therefore devoid of the bypass circuit C1, the step e) of the method comprises the step e1) of reducing the passage flow rate of the refrigerant fluid through the expansion means 4 to a value lower than the flow rate value of refrigerant fluid sucked by the compressor 2, in such a way as to reduce the suction pressure of the compressor 2 to such a pressure value Ps to cause it to turn off, the step e2) of feeding the expansion reservoir 30 by the fluid flowing out of the evaporation means 5 until the pressure of the expansion reservoir 30 has risen to a first pressure value PI determined depending on the temperature, or the temperature range, required within the insulated space 20 and equal to the suction pressure at which the compressor 2, in step e1), starts sucking refrigerant fluid from the expansion reservoir 30, and the step e3) of reactivating the operation of the compressor 2 upon exceeding the first pressure value P1 within the expansion reservoir 30. Steps e1), e2) and e3) can be repeated in a cyclic manner.

[0090] The turning off of the compressor 2 and, in any case, the normal operation of the chamber 100 allows to enormously save on the energy costs of the chamber 100, not to mention the fact that the compressor 2 would work much less than it normally does, thereby also reducing the wear and tear on this component.

[0091] In practice, once the temperature within the insulated space 20 has been determined / set / selected, e.g. −15° C. (which corresponds approximately to −25° C. as the evaporation temperature of the refrigerant fluid within the evaporation means 4), thus operating at partial load, i.e. under non-extreme conditions, this implicitly determines the operating step e1) of the method. At this point, the flow rate of refrigerant fluid passing through the expansion means 4 is less than that fed by the compressor 2, therefore, the pressure of the refrigerant fluid begins to decrease more and more downstream of the evaporation means 4. During this step, the flow rate of refrigerant fluid coming out of the evaporation means 4 reaches the compressor 2 up to a certain pressure. It should be recalled, in fact, that once the test temperature has been set within the insulated space 20, the thermodynamic pressure values of the refrigerant fluid across the circuit C are known, in particular the pressure PI at the inlet of the compressor 2 (while sucking). The pressure P1, or first pressure, is therefore uniquely determined by the temperature sought in the insulated space 20. For example, in the example provided herein, with a temperature of the insulated space 20 of −15° C., then the first pressure P1 corresponds to 17 bars.

[0092] The pressure value Ps for turning off the compressor 2 is determined once the same compressor has been selected. In this case, e.g., the suction pressure for turning off the compressor 2 is 8.5 bars.

[0093] During step e1), therefore, if the pressure of the refrigerant fluid upstream of the compressor 2 drops still below the value of the first pressure P1 (determined—as mentioned—once the pressure has been set within the insulated space 20 and, therefore, variable depending on this value), the compressor 2 continues to suck refrigerant gas at this point, instead of from the outlet of the evaporation means 5, mainly from the expansion reservoir 30 which is at a pressure greater than the gas pressure at the outlet of the evaporation means 5. The compressor 2 does not stop until the pressure drops below the value Ps (e.g. 8.5 bars).

[0094] If the compressor 2 has reached the turning-off value Ps, until the pressure of the expansion reservoir 30 has gradually risen to the value of the first pressure PI due to the action of the openings of the expansion means 4, the chamber 100 can continue to operate with excellent regulating characteristics with the compressor 2 turned off, resulting in clear energy savings compared to conventional chambers of more than 50%.

[0095] The expansion reservoir 30 of the refrigerant fluid is however sized in accordance with the dimensions of the storage reservoir 70 of the refrigerant fluid in liquid form, in order to prevent a lack of liquid refrigerant fluid supply to the expansion means 4 when the compressor 2 is turned off.

[0096] As soon as the pressure within the expansion reservoir 30 rises above the first pressure P1 (step e3), the compressor 2 restarts. The cycle of turning on and off is then continuously repeated.

[0097] Clearly, the number of cycles of turning on and off the compressor 2 cannot exceed the limit value specified by the manufacturer, otherwise the compressor 2 may be subject to failure.

[0098] In the case of the embodiment of FIG. 2, the filling / releasing means comprise a first shut-off valve 43 arranged along the first branch 41, a second shut-off valve 44 arranged along the second outlet branch 42 and a third shut-off valve 45 arranged along the first length T between the first inlet branch 41 and the second outlet branch 42. In this situation, keeping the same pressure P1, Ps and temperature values as in the previous example, i.e. 17 bars, 8.5 bars and −15° C. within the insulated space 20, the step e) of the method comprises this time the step e1′) of reducing the passage flow rate of the refrigerant fluid through the expansion means 4 to a value lower than that sucked by the compressor 2, the step e2′) of closing the third shut-off valve 45 and the first shut-off valve 43 and opening, or keeping open, the second shut-off valve 44 upon reaching a first suction pressure P1′ (which corresponds to the same first pressure P1 as in the previous case, i.e. 17 bars) for the compressor 2, which is determined depending on temperature, or temperature range, required within the insulated space 20 and equal to the pressure at which the compressor 2, during step e1′), starts to suck refrigerant fluid from the expansion reservoir 30 (instead of the expansion means 5), and the step e3′) of turning off the compressor 2 upon reaching a pressure value Ps that causes it to turn off. The method further comprises the step e4′) of reopening the first shut-off valve 43 if during steps e2′) and / or e3′), the pressure of the refrigerant fluid between the first shut-off valve 43, or the third shut-off valve 45, and the evaporation means 5 is higher than at a second suction pressure P2′ (e.g. 17.5 bars) for the compressor 2, which is higher than the first suction pressure P1′ (i.e. 17 bars), the step e5′) of closing the first shut-off valve 43 if, during steps e2′) and / or e3′), the pressure of the refrigerant fluid between the first shut-off valve 43, or the third shut-off valve 45, and the evaporation means 5 drops to a value lower than the first suction pressure P1′ for the compressor 2, and the step e6′) of reactivating the compressor 2 at least when the pressure within the expansion reservoir 30 is higher than the first pressure P1′, i.e. than 17 bars. Finally, the steps e1′)-e6′) are repeated in a cyclical manner.

[0099] Additionally, still in the embodiment of FIG. 2, in the event of steady-state, i.e. full-load, operation, the method comprises the step f) of keeping open the second shut-off valve 44 and the third shut-off valve 45 and keeping closed the first shut-off valve 43 in such a way that, at least when the flow rate sucked by the compressor 2 is equal to that passing through the expansion means 4, or with the environmental simulation chamber 100 turned off (therefore, the compressor 2 is turned off), the refrigerant fluid present in the expansion reservoir 30 compensates for the specific volume increase of the refrigerant gas present in the closed circuit C and / or allows to reduce any unwanted pressure increase within the closed circuit C. This operation takes place when precisely the step e) of the above-mentioned method is not required, i.e. to intermittently operate the compressor 2 as a result of the fact that the required loads of flow rate of the refrigerant fluid are only partial, therefore, the required temperature within the insulated space 20 is not extreme (i.e. less than −20° C.).

[0100] A particular mode of operation of the chamber 100 shown in FIG. 2, therefore, in which the filling / releasing means comprise a first shut-off valve 43 arranged along the first branch 41, a second shut-off valve 44 arranged along the second outlet branch 42 and a third shut-off valve 45 arranged along the first length T between the first inlet branch 41 and the second outlet branch 42, provides that the step a) of the method comprises the step a1) of rapidly increasing the requirement of required refrigeration load, the so-called condition known to the person skilled in the art as “booster”, and that the method further comprises the step h) of reducing the pressure within the expansion reservoir 30 to a minimum pressure value, preferably equal to the minimum suction pressure value Ps of the compressor 2, and subsequently to step h) of opening and keeping completely open the first shut-off valve 43 and the expansion means 4. Furthermore, a further mode of operation of the chamber 100 shown in FIG. 4, therefore in which the filling / releasing means comprise a first shut-off valve 43 arranged along the connecting conduit 61, provides that the step a) of the method comprises the step a1) of rapidly increasing the requirement of required refrigeration load, the so-called condition known to the person skilled in the art as “booster”, and that the method further comprises the step h) of reducing the pressure within the expansion reservoir 30 to a minimum pressure value, preferably equal to the minimum suction pressure value Ps of the compressor 2. This step h) is prior to step a1), i.e., of preparing the “booster” step, i.e., of quickly requesting temperature drop within the insulated space 20. Subsequent to step h) and simultaneously with step a1), the method comprises the step r) of keeping open the first shut-off valve 43 and the expansion means 4.

[0101] According to this “booster” operation mode, the step r) continues until the temperature in the insulated space 20 reaches a value higher than the evaporation temperature of the refrigerant fluid within the evaporation means 5, preferably this temperature within the insulated space 20 is 10° C. higher than the evaporation temperature, or the suction pressure for the compressor 2 has reached the maximum operating conditions provided for the operating condition of the same compressor 2 and the first shut-off valve 43 (in the event of the embodiment shown in FIG. 4) closes or the first shut-off valve 43 and the second shut-off valve 44 close (in the event of the embodiment shown in FIG. 2). In this case, in order for this step r) to take place, it is necessary that the storage reservoir of the liquid refrigerant 70 and the expansion reservoir 30 must be sized in such a way that during the step r), the liquid-phase refrigerant fluid is not exhausted in order to prevent a lack of liquid refrigerant fluid at the expansion means 4 during the booster effect.

[0102] In the event of the embodiment shown in FIG. 3 and in the event of a booster request by the refrigeration device 10, it is the case that, at the same time as step h) or independently of step h), the step 1) of flowing refrigerant fluid along the heat exchanger 200 is performed.

[0103] In any one of the embodiments described above and shown in FIGS. 1 to 4, the method comprises the step m) of controlling the opening of the opening / closing valve 55 for the passage of the refrigerant fluid, i.e. of carbon dioxide, along the auxiliary line 50 and the step n) of fluidically connecting the closed circuit C to the insulated space 20 by means of the auxiliary line 50. This auxiliary line 50 is provided with an inlet section 51 for the refrigerant fluid, arranged along a first length T of the closed circuit C between the evaporation means 5 and the compressor 2, and an outlet section 52 for the refrigerant fluid. This outlet section 52 is connected to the insulated space 20 for the inflow of carbon dioxide in gaseous form into this insulated space 20.

[0104] Additionally, the step m) is preceded by step o) of detecting the ignition of fire within the insulated space 20 as a condition for step m) to take place.

[0105] It should be noted that these steps m), n) and o) can operate independently of steps e)-h) and in combination with steps a) to d) of the method.

Claims

1. Environmental simulation chamber (100) comprising a refrigeration apparatus (1) comprising a refrigeration device (10) having a closed circuit (C) within which a refrigerant fluid circulates, said closed circuit (C) comprising at least one compressor (2), cooling means (3) for said refrigerant fluid, expansion means (4) for said refrigerant fluid and evaporation means (5), said chamber (100) further comprising an insulated space (20) adapted to receive a specimen (21) to be tested therein and wherein said evaporation means (5) are adapted to regulate an internal temperature of said insulated space (20) and said refrigerant fluid is carbon dioxide.

2. The environmental simulation chamber (100) according to claim 1, wherein said closed circuit further comprises an expansion reservoir (30) for said carbon dioxide, said expansion reservoir (30) arranged operatively along a first length (T) arranged between said evaporation means (5) and said at least one compressor (2), and filling and releasing means (6) for allowing the filling of refrigerant fluid from said first length (T) to said expansion reservoir (30) and the release of refrigerant fluid from said expansion reservoir (30) to said first length (T).

3. The environmental simulation chamber according to claim 2, wherein said compressor (2) has intermittent operation in case of partial loads.

4. The environmental simulation chamber according to claim 2 or 3, further comprising at least one control unit that, based on said internal temperature to be regulated within said insulated space, turns on or off said compressor (2), said refrigerant fluid present in said expansion reservoir (30) feeding said circuit (C) and / or being filled by said circuit (C).

5. The environmental simulation chamber (100) according to claim 4, wherein said filling and releasing means (6) comprise a connecting conduit (61).

6. The environmental simulation chamber (100) according to claim 5, wherein said connecting conduit (61) comprises a first shut-off valve (43) and said control unit opens or closes said first valve (43) to allow or disallow the inflow / outflow of said refrigerant fluid into / from said expansion reservoir (30) depending on the pressure at an outlet from the evaporation means (5).

7. The environmental simulation chamber (100) according to claim 2 wherein said closed circuit (C) further comprises a storage reservoir (70) of said refrigerant fluid in liquid form, which is arranged in a second length (T2) of said closed circuit between said cooling means (3) and said expansion means (4).

8. The environmental simulation chamber (100) according to claim 1, further comprising at least one auxiliary line (50) which directly or indirectly connects said closed circuit (C) to said insulated space (20), said auxiliary line (50) having an inlet section (51) for said refrigerant fluid arranged along a first length (T) of said closed circuit (C) between said evaporation means (5) and said at least one compressor (2), an outlet section (52) for said refrigerant fluid, and an opening / closing valve (55) for allowing or preventing passage of said refrigerant fluid along said auxiliary line, said outlet section (52) connected to said insulated space (20) for the inflow of carbon dioxide in gaseous form into said insulated section (20).

9. The environmental simulation chamber (100) according to claim 8, further comprising detecting means (80) for detecting an ignition of a fire within said insulated space (20), said detecting means (80) operatively connected to said opening / closing valve (55) to control its opening or closing.

10. The environmental simulation chamber (100) according to claim 1, wherein said refrigeration apparatus (1) comprises a further refrigeration device (10′) having a further closed circuit (C′) within which a further refrigerant fluid circulates, said further closed circuit (C′) comprising at least one further compressor (2′), further cooling means (3′) for said refrigerant fluid, further expansion means (4′) for said refrigerant fluid and further evaporation means (5′) adapted to operate in cooperation with said cooling means (3) of said refrigeration device (10), said further refrigeration device (10′) operating in a temperature range higher than that at which said refrigeration device (10) operates.

11. The environmental simulation chamber (100) according to claim 1, wherein said closed circuit (C) further comprises at least one second high-pressure compressor (110) arranged in series to said at least one compressor (2), a bypass circuit (112) for said cooling means (3) having at least one control valve (113) for operating said bypass circuit (112), an intermediate throttling valve (114) downstream of said storage reservoir (70) and a condensation pressure control valve (115), said intermediate throttling valve (114) operatively arranged between said storage reservoir (70) and said second compressor (110).

12. The environmental simulation chamber (100) according to claim 11 wherein said closed circuit further comprises a heat exchanger (200) operatively connected to a third length (T3) of said closed circuit (C) between said at least one second compressor (110), downstream of said bypass circuit (112), and said storage reservoir of the refrigerant fluid (70) and means (205, 206) for regulating the flow rate of refrigerant fluid entering said heat exchanger, said heat exchanger (200) disposed within said insulated space (20), said heat exchanger (200) and said evaporation means (5) disposed in two separate compartments present within said insulated space (20).

13. A method for operating an environmental simulation chamber according to claim 2, comprising the steps of:a) setting at least one temperature, or at least one temperature range, to be obtained within said insulated space (20);b) activating said at least one compressor (2) to circulate said refrigerant fluid within said closed circuit (C) of said refrigeration device (10); andc) regulating the opening / closing of said expansion means (4) to vary flow rate of refrigerant fluid passing through said evaporation means (5) depending on said at least one temperature, or said temperature range, required within said insulated space (20);wherein said refrigerant fluid is carbon dioxide.

14. The method according to claim 13, further comprising step d) filling at least partially said expansion reservoir (30) with said refrigerant fluid.

15. The method according to claim 14, wherein, if in said step c) said expansion means operate at partial load and said at least one expansion reservoir (30) is sized to contain fluctuations of pressures at the outlet of said evaporation means which are lower than 8 bars, said method further comprises step e) making said compressor work intermittently.

16. The method according to claim 15, wherein said step e) comprisesstep e1) reducing the flow rate of the refrigerant fluid passing through said expansion means (4) to a value lower than that sucked by said at least one compressor (2) in such a way as to reduce the suction pressure of said at least one compressor to such a pressure value (Ps) to cause it to turn off,step e2) feeding said expansion reservoir (30) by said fluid flowing out of said evaporation means until the pressure of said expansion reservoir (30) has risen to a first pressure value (P1) determined depending on the temperature or the temperature range required within said insulated space (20) and equal to the suction pressure at which said at least one compressor (2), in said step e1), starts sucking refrigerant fluid from said expansion reservoir (30), andstep e3) reactivating operation of said compressor upon exceeding said first pressure value (P1) within said reservoir,said steps e1), e2) and e3) repeating cyclically.

17. The method according to claim 13, wherein said filling and releasing means (6) comprise a first shut-off valve (43) arranged along said connecting conduit (61), wherein said step a) comprises step a1) rapidly increasing the requirement of required refrigeration load, and wherein said method further comprises step h) reducing the pressure within said expansion reservoir (30) to a minimum pressure value equal to a minimum suction pressure value (Ps) of said at least one compressor (2),wherein said step h) takes place prior to said step a1) and, subsequent to said step h) and simultaneous with said step a1), the method further comprises step r) keeping open said first shut-off valve (43) and said expansion means (4).

18. The method according to claim 17, wherein said step r) continues until the temperature in said insulated space reaches a value 10° K higher than said evaporation temperature, or the suction pressure for said at least one compressor (2) has reached the maximum operating conditions expected for the operating condition of said at least one compressor (2) and said at least one first shut-off valve (43) is closed, said storage reservoir of the refrigerant fluid (70) and said expansion reservoir (30) being sized so that during said step r) said liquid-phase refrigerant fluid is not depleted.

19. The method according to claim 13, wherein said refrigerant fluid circulates within said closed circuit under transcritical conditions, and further comprising step l) of flowing refrigerant fluid along said heat exchanger (200), said step l) carried out simultaneously with said step h) or independently of said step h).

20. The method according to claim 13, further comprising step m) controlling the opening of an opening / closing valve (55) for passage of said refrigerant fluid along said auxiliary line, and step n) fluidically connecting said closed circuit (C) to said insulated space (20) by means of said auxiliary line (50), said auxiliary line (50) including an inlet section (51) for said refrigerant fluid arranged along a first length (T) of said closed circuit (C) between said evaporation means (5) and said at least one compressor (2), and an outlet section (52) for said refrigerant fluid, said outlet section (52) connected to said insulated space (20) for the inflow of carbon dioxide in gaseous form into said insulated space (20).

21. The method according to claim 20, wherein said step m) is preceded by step o) detecting ignition of fire within said insulated space (20).

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