COOLING SYSTEM AND ASSOCIATED OPERATING PROCEDURE

Description

technical field

[0001] The invention relates to a refrigeration system and a method of operating a refrigeration system. State of the art

[0002] State-of-the-art vapor compression systems, designed for refrigeration production or heat pumping, have four generic components: two heat exchangers, a condenser and an evaporator, a compressor and an expansion valve.

[0003] A vapor compression cycle is carried out with a liquid-vapor phase-change fluid, called a refrigerant, which is chosen according to the evaporation and condensation temperature levels.

[0004] The fluid evaporates completely in the evaporator at the system's low pressure, after expansion through the expansion valve.

[0005] The refrigerant in vapor phase is compressed to the high pressure of the system by the compressor, then it is condensed at this high pressure in the condenser and it must be completely liquid at the outlet of this condenser.

[0006] The generic operating constraint is that the expansion valve only accepts a fluid in liquid phase; the presence of gas bubbles in the liquid causes malfunctions of the expansion valve, which can lead to flow blockage.

[0007] Therefore, the refrigerant must be subcooled upstream of the expansion valve, meaning that the temperature at the outlet of the condenser must be lower than the saturation condensation temperature.

[0008] Subcooling is provided by the condenser, with approximately 10% of the condenser's volume conventionally dedicated to this subcooling. This 10% of the condenser's volume is located in its lower section.

[0009] The actual operation of the vapor compression system is variable flow, depending on the required cooling or heating capacity and the season for heat rejection conditions into the ambient environment. The refrigerant flow rate varies by a factor of 2 to 5 between the minimum and maximum.

[0010] The mass of refrigerant charged in the system must correspond to the maximum flow rate, otherwise the supply to the expansion valve would be insufficient.

[0011] The system is therefore overloaded with refrigerant when the flow rate is significantly lower than the maximum flow rate.

[0012] The practical consequence is that this excess mass must be stored by introducing a volume at the high pressure of the system.

[0013] This volume is a reservoir, either arranged in series downstream of the condenser, or integrated into the condenser.

[0014] Note that to avoid recharging the system too quickly, to compensate for small refrigerant leaks, manufacturers charge the system at least 10% to 30% above the charge required for operation at maximum flow rate.

[0015] In summary, refrigerant fluid must be stored at the high pressure of the system, in a tank integrated into the connection between the condenser and the expansion valve.

[0016] This high-pressure refrigerant stock must be subcooled up to the upstream end of the expansion valve, which is not always guaranteed, far from it.

[0017] The state of the art for ensuring the subcooling of the refrigerant has given rise, and for a long time, to numerous patents for very different solutions.

[0018] WO2014 / 035134 (Korea Energy) proposes to ensure subcooling by changing the volume of the tank.

[0019] US6378323 (Carrier) proposes to introduce an additional heat exchanger inside the high-pressure tank, to maintain subcooling.

[0020] US6170272 (Systematic refrigeration) offers subcooling of the high-pressure refrigerant, by a complementary refrigeration system, solely dedicated to subcooling.

[0021] US4862702 (Neal) proposes high-pressure control on the high-pressure receiver by regulating the injection of high-pressure vapor into the receiver, to prevent the pressure upstream of the expansion valve from becoming too low and to ensure subcooling. US4831835 (Beehler) describes a refrigeration system comprising two compressors, a condenser, a liquefied refrigerant receiver, an expansion valve, an evaporator, a receiver, and manually operated valves. The system operates in three modes. In the first operating mode, the condenser does not provide satisfactory subcooling at the condenser outlet due to a high ambient temperature, and all the liquid and gaseous refrigerant exiting the condenser is directed to the receiver.In the second operating mode, the condenser provides adequate subcooling at its outlet due to a sufficiently low ambient temperature, and the liquefied refrigerant exiting the condenser flows to the expansion valve as long as the outlet pressure remains moderate. When the refrigerant pressure at the condenser outlet becomes excessive, the refrigerant flows back into the reservoir. In the third operating mode, which occurs during selected time intervals, the system is in defrost mode, with this third operating mode being superimposed on the first and second operating modes. Objects of the invention

[0022] A first object of the invention is to propose a device and a method ensuring satisfactory subcooling of a refrigerant fluid, in a refrigeration system, making it possible to eliminate the risk of the presence of gas bubbles in the refrigerant liquid, such gas bubbles being able to cause malfunctions of the expansion valve, which can lead to the blocking of the flow.

[0023] Another object of the invention is to propose a method and a device ensuring satisfactory subcooling of a refrigerant fluid, in a refrigeration system, and allowing adaptation of the circulating mass of refrigerant fluid to variations in the flow rate of the refrigerant fluid, in a vapor compression system. General presentation of the invention

[0024] To this end, a refrigeration system is proposed, firstly, comprising a compressor, a condenser, an expansion valve, an evaporator and a refrigerant reservoir, the compressor ensuring the circulation of a refrigerant, the condenser being cooled by a cooling medium circulating in a well circuit, the evaporator cooling the medium in a source circuit, a liquid refrigerant line connecting the condenser to the expansion valve, the evaporator being placed downstream of the expansion valve and upstream of the compressor, the refrigeration system ensuring heat transfer from the medium to be cooled circulating in the source circuit of the evaporator to the cooling well circuit of the condenser, the reservoir being advantageously installed on a line connected in parallel with the liquid refrigerant line which directly connects the condenser to the expansion valve,The gaseous phase of the fluid contained in the tank is connected to the highest pressure of the refrigeration system, upstream of the condenser, the system being configured such that the tank is continuously maintained at high pressure upstream of the condenser by a capillary tube.

[0025] Advantageously, the tank is connected to the liquid refrigerant line by two conduits, a first conduit being equipped with a valve allowing the discharge of the refrigerant to the tank, and a second conduit being equipped with a valve allowing the discharge of the refrigerant to the expansion valve.

[0026] Advantageously, the refrigeration system includes meters, connected to monitoring and control means, these meters including a temperature meter on the source circuit upstream of the evaporator, a temperature meter on the source circuit downstream of the evaporator, a pressure meter on the refrigerant circuit connecting the expansion valve and the evaporator, a pressure meter on the refrigerant circuit connecting the compressor and the condenser, and a temperature meter on the well circuit downstream of the condenser.

[0027] Advantageously, the refrigeration system includes meters, connected to monitoring and control means, these meters including a temperature meter on the refrigerant circuit linking the evaporator and the compressor.

[0028] Advantageously, the valve allowing the discharge of the refrigerant to the tank, and the valve allowing the discharge of the refrigerant to the expansion valve are opened by the supervision and control means.

[0029] Depending on various implementations, the refrigerant includes ammonia, a hydrocarbon, or a fluorinated fluid, or a mixture of refrigerants.

[0030] A second aspect is proposed, a method of operating a refrigeration system as presented above, comprising maintaining a predefined subcooling of the refrigerant exiting the condenser by dynamic control of the circulating mass of refrigerant, by transferring refrigerant into or to a reservoir installed in parallel with the liquid connection between the condenser and the expansion valve, depending on the temperature difference between the condensation temperature of the saturated liquid and the outlet temperature of the condenser, the gaseous phase of the fluid contained in the reservoir being connected to the highest pressure of the refrigeration system, upstream of the condenser.

[0031] Advantageously, the saturation condensation temperature of the liquid is calculated by the refrigeration system's monitoring electronics, which have in memory the thermodynamic properties of the refrigerant charged in the refrigeration system.

[0032] Measuring subcooling and adjusting the circulating mass of refrigerant allows for maintaining a slightly variable level of refrigerant in the lower part of the condenser.

[0033] The connection between the condenser and the expansion valve is advantageously always in the liquid phase.

[0034] In some implementations, the process includes a step enabling the diagnosis of refrigerant leaks outside the refrigeration system, by relating the inlet and outlet temperatures of the cooled fluid in the evaporator. Presentation of implementation methods

[0035] Other objects and advantages of the invention will become apparent from the description of the physical cause by which prior art devices, in which a reservoir is placed in series between the condenser and the expansion valve, limit subcooling, and from the description of an embodiment, with reference to the attached drawings.

[0036] There figure 1a presents a vapor compression cycle of a refrigerant fluid, in a pressure-specific enthalpy diagram, with pressure on a logarithmic scale on the vertical axis and specific enthalpy on the horizontal axis.

[0037] There figure 1b is a view analogous to the figure 1a , the subcooling of the refrigerant being represented by the segment C1C2.

[0038] There figure 1c is a view analogous to the figure 1a, the refrigerant at condensation pressure exiting the subcooled condenser at point C2, and entering a tank installed in series on the liquid line which connects the condenser to the expansion valve, according to the state of the art.

[0039] There figure 2 represents a refrigeration system according to an embodiment of the invention.

[0040] We refer firstly to figures 1a , 1b And 1c , for a description of the physical cause by which prior art devices, including a tank connected in series between a condenser and an expansion valve, limit subcooling.

[0041] There figure 1a presents a vapor compression cycle of a refrigerant fluid, in a specific pressure-enthalpy diagram.

[0042] In figure 1a, evolution AB corresponds to the compression of the refrigerant, evolution BC to the condensation of the refrigerant, evolution CD to the expansion of the refrigerant and evolution DA to the evaporation of the refrigerant which closes the cycle.

[0043] In figure 1a , pressure is in MPa and on a logarithmic scale on the vertical axis, specific enthalpy is in kJ / kg, on the horizontal axis.

[0044] There figure 1a is a theoretical representation, because point C is exactly on the saturation curve which is the point where the last vapor bubble condenses.

[0045] The slightest pressure loss on the connection between the condenser and the expansion valve leads to the formation of bubbles, so it is actually necessary to subcool the refrigerant liquid before it exits the condenser.

[0046] This subcooling is represented in figure 1b by segment C1C2.

[0047] In figure 1b, point C3 represents the state of the refrigerant still subcooled, but at a lower pressure, due to pressure losses on the connection between the condenser and the expansion valve.

[0048] Point C4 represents the acceptable limit pressure for pressure losses, because subcooling is then zero.

[0049] What is not usually understood is the phenomenon presented on the figure 1c : the refrigerant at condensation pressure exits the subcooled condenser at point C2, it enters a tank installed in series on the liquid line which connects the condenser to the expansion valve, according to the state of the art.

[0050] The tank is always designed to be partially filled, for safety reasons, therefore it has a liquid-vapor interface.

[0051] The phenomenon that occurs is linked to the physical fact that subcooling is a non-equilibrium state, which is only ensured in a completely liquid volume.

[0052] At the liquid-vapor interface, the refrigerant can only be saturated.

[0053] The consequence is that the subcooled fluid entering the tank generates vapor within it, in order to regain the saturation pressure at the liquid-vapor interface.

[0054] On the figure 1c The steam produced corresponds to the passage from C2 to C1.

[0055] This steam production takes place within the mass of the liquid, with the entrainment of bubbles in the connecting piping between the tank and the pressure regulator.

[0056] The only possible subcooling is related to the static pressure corresponding to the geometric height of the refrigerant liquid, which is only sufficient for well-filled vertical tanks.

[0057] This height of refrigerant generally ensures a subcooling of 1°C to 2°C, which is relatively low.

[0058] This phenomenon of re-boiling of the subcooled fluid is poorly understood and is usually attributed to pressure losses.

[0059] The invention avoids these drawbacks.

[0060] According to one aspect of the invention, a method is proposed which consists of controlling the circulating mass of refrigerant by introducing or removing refrigerant from a reservoir installed in parallel with the liquid refrigerant line which connects the condenser to the expansion valve.

[0061] The tank is connected to this line by two valves, one allowing the discharge of fluid from the circuit to the tank, the other allowing the refrigerant contained in the tank to be recharged from the circuit.

[0062] Advantageously, these valves remain closed, except for the short periods of adjustment of the refrigerant charge in the circuit.

[0063] This parallel tank arrangement, with fluid transfer, ensures continuous subcooling, because the condenser outlet is directly connected to the expansion valve inlet and the line connecting the condenser and the expansion valve is advantageously completely filled with liquid, regardless of the flow rate.

[0064] This subcooling control is dynamic, as it is achieved by adjusting the circulating mass of refrigerant to the required cooling capacity.

[0065] The higher this cooling or heating capacity, the higher the refrigerant flow rate is proportionally, and the higher the circulating mass in the circuit must also be, so that the bottom of the condenser and the liquid line are completely full of liquid refrigerant.

[0066] These measures prevent gas bubbles from appearing and prevent the creation of a two-phase flow in the liquid line.

[0067] The method according to the invention makes it possible to determine the required charge of refrigerant in the circuit, according to the different operating conditions, namely, according to the required cooling or heating capacity, and the variable temperature conditions at the condenser.

[0068] Advantageously, subcooling conditions are always ensured by the complete filling of the condenser and expansion valve connection with liquid, which depends, according to the control process, on two parameters: the condensation pressure and the percentage opening of the expansion valve.

[0069] In order for these two parameters to determine the mass of refrigerant in circulation, several additional conditions are advantageously taken into account.

[0070] There figure 2 presents an embodiment of a refrigeration system according to the invention.

[0071] The refrigeration system shown in figure 2 ensures the dynamic subcooling of a refrigerant, by adapting the circulating mass of refrigerant to variations in refrigerant flow rate.

[0072] In the implementation mode of the figure 2 Device 1 is a vapor compression system.

[0073] Device 1 includes a compressor 2, equipped with a power controller 20, a wattmeter 21 and a pressure gauge 22 located at the discharge of compressor 2, and measuring the high pressure of device 1, which is the condensation pressure.

[0074] Device 1 includes a condenser 3, cooled by a cooling medium circulating in a circuit 30 referred to as the well circuit, in the remainder of this description.

[0075] The cooling flow rate is measured by a flow meter 35.

[0076] A regulating valve 34 can modulate the flow rate of the cooling medium.

[0077] The inlet and outlet temperatures of the cooling medium are measured respectively by temperature meters 32, 33.

[0078] The temperature of the refrigerant is measured at the outlet of the condenser 3, by a temperature meter 31.

[0079] In condenser 3, two internal volumes are distinguished: the two-phase liquid-vapor volume 301 and the purely liquid volume 302.

[0080] The purely liquid volume 302 typically occupies 2% to 10% of the total internal volume of the condenser 3.

[0081] Device 1 includes a regulator 4, with its control electronics 40, taking into account the measurement of low pressure by a pressure meter 41.

[0082] Device 1 includes an evaporator 5, cooling the medium of a circuit 50, referred to as the source circuit in the remainder of this description.

[0083] The flow rate of this medium to be cooled is measured by a flow meter 54.

[0084] The inlet and outlet temperatures of the medium to be cooled are measured respectively by temperature meters 52,53.

[0085] The temperature of the refrigerant at the outlet of the evaporator 5 is measured by a meter 51.

[0086] Device 1 includes a liquid line 7 providing a direct connection between the condenser 3 and the expansion valve 4.

[0087] Device 1 includes, in parallel with this liquid line 7, a refrigerant fluid reservoir 6, continuously maintained at high pressure upstream of the condenser 3 by a capillary tube 600.

[0088] This reservoir 6 is connected to the liquid line 7 by two lines 601, 602, respectively equipped with control valves 61,62 with their respective actuators 611,621.

[0089] These control valves 61, 62 are normally closed.

[0090] Device 1 includes a supervisory and control electronics 8 of the refrigeration system, which integrates all the measurements and has the thermodynamic data of the refrigerant, allowing in particular to automatically calculate the saturation temperature 81 of the saturating liquid, as a function of the condensation pressure measured by the pressure gauge 22.

[0091] Note that the refrigerant can be a pure substance, such as ammonia, a hydrocarbon such as propane, a fluorinated fluid such as R-1234ze or a mixture of refrigerants where the liquid and vapor saturation temperatures are different.

[0092] The refrigerant is put into circulation by the compressor 2, with the net thermal result being the transfer of heat from the medium to be cooled circulating in the source circuit 50 of the evaporator 5 to the cooling well circuit 30 of the condenser 3.

[0093] The thermal power rejected on the cooling circuit 30 is the sum of the thermal power extracted at the evaporator 5, called cooling power, plus the thermal power transmitted to the fluid by the compressor 2.

[0094] Refrigeration systems operate at variable power, both at the evaporator 5 (because the refrigeration requirements of the source circuit 50 can vary greatly), and at the compressor 2, because the compression power depends directly on the temperature difference and therefore on the pressure difference between the evaporator 5 and the condenser 3.

[0095] When this difference varies, the powers vary simultaneously.

[0096] Two operating situations of the refrigeration system 1 represented in figure 2 will now be presented.

[0097] The first situation is that of an increase in refrigeration demand on the source circuit 50.

[0098] This increase is manifested by a temperature at the inlet of the evaporator 5 on the source circuit 50, measured by the temperature meter 52, which is higher than at the previous time step.

[0099] The cooling capacity supplied by system 1 has not changed.

[0100] As a result, the temperature measured by the measuring device 53 on the source circuit 50 at the outlet of the evaporator 5 rises.

[0101] This parameter is processed by the electronics of the power controller 20 of compressor 2, which increases the intake flow of refrigerant, either by increasing the rotation speed of compressor 2, or by starting an additional compressor, for a multi-compressor refrigeration system.

[0102] The flow rate of refrigerant drawn in by compressor 2 increases.

[0103] The evaporation pressure measured by pressure gauge 41 is decreasing.

[0104] The control electronics 40 of the regulator 4 receiving this signal causes the passage orifice of the regulator 4 to open wider.

[0105] The liquid flow rate at the inlet of the expansion valve 4 therefore increases, which has the effect of lowering the level of the purely liquid volume 302 in the condenser 3.

[0106] Reducing the volume of pure liquid 302 in the condenser 3 reduces the heat exchange dedicated to subcooling, since the exchange surface area associated with the volume is reduced, which leads to a decrease in the gap between the temperature of the saturated refrigerant liquid 81, calculated by the supervisory electronics 8 from the measurement of the condensation pressure by the pressure meter 22 and the refrigerant outlet temperature, measured by the meter 31.

[0107] The supervisory electronics 8 then commands the opening of valve 62, to gradually increase the circulating mass of refrigerant in the circuit.

[0108] This raises the level of the purely liquid volume 302 at the bottom of the condenser 3 and, concomitantly, restores the subcooling of the refrigerant by restoring the setpoint temperature difference between the calculated saturation temperature 81 and the outlet temperature of the condenser 3 measured by the meter 31.

[0109] The rise in the level of the refrigerant liquid in the volume 302 of the condenser 3 leads to an increase in subcooling, because the increase in volume is associated with an increase in the exchange surface with the cooling fluid of the well circuit 30, and therefore with an increase in heat transfer.

[0110] The second operating situation is the opposite of the first situation: the cooling power required by the source circuit 50 decreases.

[0111] This decrease is manifested by a temperature measured by the measuring device 52 that is lower than at the previous time step.

[0112] The cooling capacity supplied by system 1 has not changed.

[0113] As a result, the temperature measured by the measuring device 53 on the source circuit 50 at the outlet of the evaporator 5 decreases and, concomitantly, the temperature at the outlet of the refrigerant from the evaporator 5 measured by the measuring device 51 also decreases.

[0114] These two temperature parameters measured by the meters 52, 53 are dealt with respectively by the electronics of the power controller 20 of the compressor 2, which lowers the flow rate of refrigerant drawn in, and by the control electronics 40 of the expansion valve 4, which reduces the passage orifice of the expansion valve 4.

[0115] The liquid flow rate at the inlet of the expansion valve 4 is therefore reduced, which has the effect of raising the level of the purely liquid volume 302 in the condenser 3, hence the difference increases between the temperature of the saturated liquid 81, calculated by the supervisory electronics 8, as a function of the condensation pressure measured by the pressure gauge 22, and the refrigerant outlet temperature, measured by the gauge 31.

[0116] Tends to increase condensation pressure as well, indicating that the purely liquid volume 302 becomes relatively too large.

[0117] The supervisory electronics 8 then controls the opening of valve 61, to gradually extract refrigerant and reduce the circulating mass of refrigerant.

[0118] This lowers the liquid level 302 to the bottom of the condenser 3 and, concomitantly, restores the subcooling to its setpoint value, thus restoring the temperature difference between the calculated saturation temperature 81 and the outlet temperature of the liquid refrigerant from the condenser.

[0119] The process according to the invention has many advantages.

[0120] The method of controlling the circulating mass of refrigerant fluid ensuring the flow rate required for the proper functioning of the expansion valve 4 is advantageously based on the decoupling of two functions which are integrated in thermostatic expansion valves, namely the control of the evaporation pressure and the control of the superheat of the refrigerant vapor, at the outlet of the evaporator 5.

[0121] The purpose of the superheat control function is to prevent liquid from entering the suction of compressor 2, in order to preserve its integrity.

[0122] Advantageously, in the process which is the subject of the invention, the expansion valve 4 has as its sole function the control of the evaporation pressure and only this control.

[0123] Advantageously, overheating is controlled by varying the power of the compressor(s) 2.

[0124] According to one aspect of the invention, in the process, the control variable of the compression power is the outlet temperature of the medium cooled by the evaporator 5 and therefore indirectly the superheat temperature of the refrigerant.

[0125] This medium is a liquid, for example water, or a gas, for example air.

[0126] When the outlet temperature of the cooled medium becomes higher than the setpoint temperature, then the compression power is increased.

[0127] Conversely, when this output temperature becomes lower than the setpoint temperature, the compression power is reduced.

[0128] Knowing the power consumed by the compression and knowing the characteristics of the compressor(s) 2, the refrigerant flow rate is known and is related or not to the mass of fluid circulating in the entire circuit.

[0129] To ensure the desired subcooling upstream of the expansion valve 4, which is a minimum of 2°C and can advantageously be from 5°C to 7°C, approximately 2% to 10% of the volume of the condenser 3 must be filled with liquid refrigerant and, as previously specified, the liquid must completely occupy the connecting volume which separates the condenser 3 from the inlet of the expansion valve 4.

[0130] Condensing pressure depends on four parameters: refrigerant flow rate, condenser 3 cooling medium inlet temperature, cooling medium flow rate, and subcooled liquid level at the bottom of condenser 3.

[0131] The computerized supervision of the refrigeration system according to the invention receives the measurement of the condensation pressure (measured by the meter 22) and those of the flow rate and the inlet temperature of the cooling medium which varies slowly with the inlet temperature of the cooling medium and the flow rate of this medium.

[0132] These parameters are taken into account by supervision 8, to define the condensation pressure levels allowing to accurately monitor the variation of the two other parameters which vary more rapidly.

[0133] If the refrigerant flow rate increases, the bottom of the condenser 3 empties of its liquid, the subcooling of the refrigerant decreases and the refrigerant outlet temperature approaches the saturation temperature 81, which is calculated by the computerized supervision 8.

[0134] This reduction of the difference between the outlet temperature and the saturation temperature 81 leads to opening the filling valve 62 of the circuit coming from the reservoir 6 installed in parallel with the liquid line 7, in order to increase the circulating mass and therefore the refrigerant leveling of the bottom of the condenser 3, and thus the restoration of subcooling.

[0135] Note that, concomitant with the decrease in subcooling associated with the increase in refrigerant flow, the expansion valve 4 opens further, to allow more flow to pass through, but if it opens fully it means that the circulating mass of refrigerant tends to become insufficient, this second parameter complements or confirms the parameter of the reduction of subcooling.

[0136] Conversely, if the required cooling capacity decreases, the refrigerant flow rate decreases, the circulating mass becomes too large, the condenser 3 fills too much and the condensation pressure becomes too high, concomitantly with a significant increase in subcooling and a reduction in the opening of the expansion valve 4.

[0137] The conditions are then met to open the 61 discharge valve of the circulating mass towards the reservoir 6, and this until the subcooling setpoint value is obtained.

[0138] The process is implemented by the supervision 8 of the refrigeration system, which is advantageously a computer programming unit storing in particular the thermodynamic table of the refrigerant allowing to calculate the liquid saturation temperature 81 corresponding to the condensation pressure of the refrigerant charged in the refrigeration system.

[0139] According to one aspect of the invention, continuity of the liquid phase in the connection between the condenser 3 and the expansion valve 4 is ensured, and the necessary adjustment of the circulating mass of refrigerant is ensured according to variations in refrigerant flow rate.

[0140] Advantageously, a transfer to tank 6 is carried out if the circulating mass is too high or, conversely, an extraction of the refrigerant to tank 6 is carried out if the circulating mass is too low.

[0141] These arrangements ensure a near-constant level of liquid at the bottom of condenser 3, allowing controlled subcooling, advantageously between 2°C and 7°C.

[0142] The implementation of the invention ensures the subcooling of refrigerants in a dynamic manner, that is to say by adapting the circulating mass of refrigerant to the variations in flow rate of the refrigerant in a vapor compression system.

[0143] Another advantage of the dynamic regulation process of the circulating mass of refrigerant fluid according to variations in refrigerant flow rate is that it also allows for the rapid diagnosis of refrigerant leaks.

[0144] Indeed, a refrigerant leak will reduce the circulating mass of refrigerant.

[0145] The first effect will be the rise in temperature, measured by temperature meter 53, while the temperature measured by meter 52 has remained constant.

[0146] Compressor 2 will accelerate, the electronic control 40 of the expansion valve 4 will open the expansion orifice further, the purely liquid volume 302 will decrease in the condenser 3.

[0147] Global monitoring will be able to diagnose that there is a demand for an increase in the circulating mass of refrigerant, while the cooling demand of the source circuit 50 has not changed.

[0148] The request for additional fluid will be granted by the supervisory electronics 8, but at the same time it will trigger an alert for leak detection.

Claims

1. A refrigerating system (1) comprising a compressor (2), a condenser (3), an expansion device (4), an evaporator (5) and a reservoir (6) for a refrigerant fluid, the compressor (2) ensuring circulation of a refrigerant fluid, the condenser (3) being cooled by a cooling medium circulating in a sink circuit (30), the evaporator (5) cooling the medium of a source circuit (50), a liquid refrigerant line (7) connecting the condenser (3) to the expansion device (4), the evaporator (5) being located downstream of the expansion device (4) and upstream of the compressor (2), the refrigerating system (1) ensuring heat transfer from the medium to be cooled circulating in the source circuit (50) of the evaporator (5) to the sink circuit (30) for cooling the condenser (3), the refrigerating system (1) where the reservoir (6) is installed on a line connected in parallel to the liquid refrigerant line (7) which directly connects the condenser (3) to the expansion device (4), the gas phase of the fluid contained in the reservoir being connected to the highest pressure of the refrigerating system (1), upstream of the condenser (3), the system being configured such that the reservoir (6) is continuously maintained at high pressure upstream of the condenser (3) by a capillary tube (600).

2. The refrigerating system (1) according to claim 1, wherein the reservoir (6) is connected to the liquid refrigerant line (7) through two ducts, a first duct being provided with a valve (61) for discharging the refrigerant fluid to the reservoir (6), and a second duct being provided with a valve (62) for discharging the refrigerant fluid to the expansion device (4).

3. The refrigerating system (1) according to claim 1 or 2, wherein it comprises meters, connected to supervision and control means (8), these meters comprising a temperature meter (52) on the source circuit (50) upstream of the evaporator (5), a temperature meter (53) on the source circuit (50) downstream of the evaporator (5), a pressure meter (41) on the refrigerant fluid circuit connecting the expansion device (4) and the evaporator (5), a pressure meter (22) on the refrigerant fluid circuit connecting the compressor (2) and the condenser (3), and a temperature meter (31) on the sink circuit (30) downstream of the condenser (3).

4. The refrigerating system (1) according to any of claims 1 to 3, wherein it comprises meters, connected to the supervision and control means (8), these meters comprising a temperature meter (51) on the refrigerant fluid circuit connecting the evaporator (5) and the compressor (2).

5. The refrigerating system (1) according to claim 3 or 4, wherein the valve (61) for discharging the refrigerant fluid to the reservoir (6), and the valve (62) for discharging the refrigerant fluid to the expansion device (4) are opening-controlled by the supervision and control means (8).

6. The refrigerating system (1) according to any of claims 1 to 5, wherein the refrigerant fluid comprises ammonia, a hydrocarbon, or a fluorinated fluid or a mixture of refrigerant fluids.

7. A method for operating a refrigerating system (1) as set forth in any of claims 1 to 6, wherein it comprises maintaining a predefined sub-cooling of the refrigerant fluid exiting the condenser (3) by dynamically controlling the circulating mass of refrigerant fluid, by transferring refrigerant fluid into or toward the reservoir (6) installed in parallel to the liquid connection (7) between the condenser (3) and the expansion device (4), depending on the temperature difference between the condensation temperature of the saturating liquid (81) and the exit temperature of the condenser (3), the gas phase of the fluid contained in the reservoir (6) being connected to the highest pressure of the refrigerating system (1), upstream of the condenser (3).

8. The method according to claim 7, wherein the temperature of the saturating condensation (81) of the liquid is calculated by the supervision electronics of the refrigerating system (8) which has in memory thermodynamic properties of the refrigerant fluid loaded in the refrigerating system (1).

9. The method according to any of claims 7 to 8, wherein it comprises a step of diagnosing refrigerant fluid leak outside the refrigerating system (1), by correlating the entry and exit temperatures of the fluid cooled in the evaporator (5).