Refrigeration system

Abstract

A refrigeration system includes a refrigeration circuit having a compression device, a heat rejection heat exchanger, an expansion device, and a heat absorption heat exchanger. The refrigeration system includes: one or more sensors configured to measure a pressure associated with the heat rejection heat exchanger; and a controller configured to compare the pressure measured by the one or more sensors with a predicted pressure and control the expansion device based on the comparison.

Description

Technical Field

[0001] The present invention relates to a refrigeration system and a method of operating a refrigeration system. Background Art

[0002] Refrigeration or heating can be provided by a refrigeration system that utilizes a refrigeration cycle in which a refrigerant fluid is compressed, cooled, expanded, and then heated.

[0003] In the case of using a refrigeration system to meet a cooling load, the cooling of the refrigerant fluid can be accomplished by discharging heat to the atmosphere via a heat rejection heat exchanger, and the heating of the refrigerant fluid can be accomplished by absorbing heat from an object to be cooled (such as a refrigerated space for cryogenic storage or the interior of a building) via a heat absorption heat exchanger. In this way, even when the interior is colder than the atmosphere, the refrigeration system can transfer heat from inside the refrigerated space or building to outside the refrigerated space or building.

[0004] Alternatively, the refrigeration system can be used as a heat pump to meet a heat demand. In this case, the heat absorption heat exchanger can be used to absorb heat from a low-temperature source, where the refrigeration circuit then discharges the heat to a higher-temperature object to be heated. Again, for example, this could be the interior of a building.

[0005] The applicant believes that there is still room for improvement in refrigeration systems. Summary of the Invention

[0006] The present invention provides a refrigeration system comprising:

[0007] a refrigeration circuit comprising a compression device, a heat rejection heat exchanger, an expansion device, and a heat absorption heat exchanger;

[0008] one or more sensors configured to measure a pressure associated with the heat rejection heat exchanger; and

[0009] a controller configured to compare the pressure measured by the one or more sensors with a predicted pressure and to control the expansion device based on the comparison.

[0010] Controlling the expansion device based on a comparison between the measured pressure associated with the heat rejection heat exchanger and the corresponding predicted pressure can improve the functionality of the refrigeration system, specifically by stabilizing the operation of the refrigeration system, broadening the conditions under which the system can operate (i.e., expanding its operating range), and increasing the efficiency of the refrigeration system.

[0011] The applicant has recognized that the liquid slug (or "slug flow") phenomenon (and similar instabilities) of the refrigerant fluid within the heat rejection heat exchanger of the refrigeration circuit can cause the refrigeration system to be unstable, thereby reducing the conditions under which the system can operate reliably and reducing its efficiency.

[0012] The applicant also recognizes that the presence (or absence) of slug flow (or similar instabilities) in the heat rejection heat exchanger of the refrigeration circuit can be detected by comparing the measured pressure with the corresponding predicted pressure. Specifically, as will be described in more detail below, the maximum pressure in a heat rejection heat exchanger without slug flow (or similar instabilities) can be (and in various embodiments is) calculated based on various operating parameters of the refrigeration system that can be easily measured and / or determined (in addition to the measured pressure). The measured pressure reaching or exceeding this predicted pressure can indicate the presence of slug flow (or similar instabilities).

[0013] The applicant also recognizes that slug flow phenomena (and similar instabilities) can be controlled (e.g., eliminated or reduced) by controlling the expansion device based on the comparison. For example, when slug flow is detected (based on the comparison), the expansion device can be controlled to increase the flow rate of the refrigerant through the refrigeration circuit, thereby flushing the refrigerant from the heat rejection heat exchanger and eliminating or reducing the slug flow phenomenon.

[0014] Therefore, it will be recognized that the present disclosure provides an improved refrigeration system.

[0015] The refrigerant fluid can be provided within the refrigeration circuit. The refrigerant fluid can include any suitable refrigerant fluid, such as a two-phase refrigerant having a mixture of a liquid phase and a gas phase, e.g., such as R410A, R454B, or R134A refrigerants, etc. In various specific embodiments, the refrigerant fluid includes R32 refrigerant. An oil such as lubricating oil can also optionally be provided into the refrigeration circuit together with the refrigerant fluid.

[0016] The compression device can be any suitable device for increasing the pressure of the refrigerant fluid and can thus be a compressor. The compression device can have an inlet connected to the fluid path from the heat absorption heat exchanger and an outlet connected to the fluid path leading to the heat rejection heat exchanger.

[0017] The heat rejection heat exchanger can be a condenser. The heat rejection heat exchanger can include a microchannel heat exchanger (MCHE). The heat rejection heat exchanger can have an inlet connected to the fluid path from the compression device and an outlet connected to the fluid path leading to the expansion device.

[0018] The expansion device can be any suitable device for reducing the pressure of the refrigerant fluid, such as an expansion valve, or a separator having an expansion function. The expansion device can be arranged to provide a controllable degree of expansion, such as by using a valve with a controllable opening degree. The expansion valve can be an electronic expansion valve. The opening degree of the expansion valve can be controlled by a controller. The expansion device can have an inlet connected to the fluid path from the heat rejection heat exchanger and an outlet connected to the fluid path leading to the heat absorption heat exchanger.

[0019] The heat-absorbing heat exchanger can be an evaporator. The heat-absorbing heat exchanger can be a brazed plate heat exchanger (BPHE). The heat-absorbing heat exchanger can have an inlet connected to a fluid path from an expansion device and an outlet connected to a fluid path leading to a compression device.

[0020] One or more sensors can include one or more pressure sensors configured to measure a pressure associated with the heat-rejecting heat exchanger, such as the pressure of a refrigeration fluid. One or more sensors can be configured to measure the pressure of the refrigeration fluid within the heat-rejecting heat exchanger or a pressure indicative of the pressure of the refrigeration fluid within the heat-rejecting heat exchanger. One or more sensors can include a pressure sensor located near the inlet of the heat-rejecting heat exchanger, i.e., between the compression device and the heat-rejecting heat exchanger.

[0021] One or more sensors can be configured to (in operation) measure (the pressure of the refrigeration fluid) substantially continuously or periodically. The system can be configured such that information indicative of the pressure measured by one or more sensors is sent to (and received by) a controller.

[0022] The controller can be configured to calculate (predict) a predicted pressure. In operation, the controller can be configured to calculate (predict) the predicted pressure substantially continuously or periodically.

[0023] The predicted pressure can (approximately) be the maximum pressure of the refrigeration fluid that would be possible (e.g., within) in the absence of slug flow (or similar instabilities) associated with the heat-rejecting heat exchanger.

[0024] It will be appreciated that this pressure can vary, for example, depending on the particular operating conditions of the refrigeration system. Accordingly, the controller can be configured to use one or more measured and / or determined parameters of the refrigeration system (in addition to the measured pressure) to calculate the predicted pressure.

[0025] Correspondingly, the system can be configured to measure and / or determine one or more or each of the one or more parameters. In operation, the system can be configured to measure and / or determine one or more or each of the one or more parameters substantially continuously or periodically.

[0026] One or more parameters can include: (i) outdoor air temperature; (ii) a temperature associated with the heat-absorbing heat exchanger, such as the temperature of the heat-absorbing heat exchanger; (iii) the capacity (tonnage) of the compression device; (iv) an area associated with the heat-rejecting heat exchanger, such as the area of the heat-rejecting heat exchanger; (v) a pressure ratio associated with the refrigeration circuit; and / or (vi) fan speed. The applicant has recognized that these parameters can be used to calculate a suitable predicted pressure.

[0027] One or more or each of these parameters can be used to calculate a predicted pressure. At least one or more or each of these parameters can be measured and / or determined (in real time) by the refrigeration system. However, one or more of these parameters can be constant (in which case the system need not measure or determine the parameter, but can instead use an appropriate constant value, e.g., which can be stored in memory).

[0028] The controller is configured to compare the measured pressure with the predicted pressure. In operation, the controller can be configured to compare the measured pressure with the predicted pressure substantially continuously or periodically.

[0029] The controller is configured to control the expansion device based on the comparison. The controller can be configured to control the degree of expansion of the expansion device based on the comparison. The controller can be configured to control the opening of the expansion valve of the expansion device based on the comparison.

[0030] When the measured pressure is less than the predicted pressure, the controller can control the expansion device so as to maintain a desired refrigerant flow rate through the refrigeration circuit. This can include the controller controlling the expansion valve so as to maintain its opening at a first value.

[0031] When the measured pressure is greater than or equal to the predicted pressure, the controller can control the expansion device so as to temporarily increase the refrigerant flow rate through the refrigeration circuit. This can include temporarily increasing the opening of the expansion valve. During some relatively short time period, such as a period of several seconds or dozens of seconds, the opening of the expansion valve can be increased to, for example, approximately 2 or 3 times.

[0032] Increasing the opening of the expansion device in this way will have the effect of increasing the flow rate of the refrigerant through the refrigeration circuit, thereby flushing the refrigerant from the heat rejection heat exchanger and eliminating or reducing the slug flow phenomenon. By only temporarily increasing the opening of the expansion device during some relatively short time periods, this can be done in a way that does not significantly affect the function of the refrigeration system, i.e., does not significantly affect the refrigeration (or heating) provided by the refrigeration system.

[0033] Accordingly, when the measured pressure is greater than or equal to the predicted pressure, the controller can control the expansion valve so as to temporarily increase its opening from a first value to a second value, where the second value is greater than the first value. The controller can control the expansion valve so as to maintain its opening at the second value for a period of time and then (after that period of time) can control the expansion valve so as to return its opening to the first value (or some other desired value).

[0034] In various embodiments, the ratio of the second value to the first value may be, for example, (i) ≥ 1.5; (ii) ≥ 2; (iii) ≥ 2.5; (iv) ≥ 3; (v) ≥ 3.5; or (vi) ≥ 4. In various embodiments, the time period may be, for example, (i) 1 - 10 seconds; (ii) 10 - 20 seconds; (iii) 20 - 30 seconds; (iv) 30 - 40 seconds; (v) 40 - 50 seconds; (vi) 50 - 60 seconds; or (vii) > 60 seconds.

[0035] The present invention also provides a method of operating a refrigeration system that includes a refrigeration circuit having a compression device, a heat rejection heat exchanger, an expansion device, and a heat absorption heat exchanger, the method comprising:

[0036] measuring a pressure associated with the heat rejection heat exchanger;

[0037] comparing the measured pressure with a predicted pressure; and

[0038] controlling the expansion device based on the comparison.

[0039] The method may include transferring refrigerant fluid from the heat absorption heat exchanger to the compressor, transferring refrigerant fluid from the compressor to the heat rejection heat exchanger, transferring refrigerant fluid from the heat rejection heat exchanger to the expansion device, and / or transferring refrigerant fluid from the expansion device to the heat absorption heat exchanger. The method may include the compression device increasing the pressure of the refrigerant fluid and / or the expansion device decreasing the pressure of the refrigerant fluid.

[0040] Measuring a pressure associated with the heat rejection heat exchanger may include measuring the pressure of the refrigeration fluid within the heat rejection heat exchanger or a pressure indicative of the pressure of the refrigeration fluid within the heat rejection heat exchanger.

[0041] Measuring a pressure associated with the heat rejection heat exchanger may include measuring the pressure associated with the heat rejection heat exchanger substantially continuously and / or periodically.

[0042] The method may include calculating a predicted pressure. This may be done substantially continuously and / or periodically. One or more measured and / or determined parameters of the refrigeration system (other than the measured pressure) may be used to calculate the predicted pressure. The method may include continuously and / or periodically measuring one or more parameters.

[0043] One or more parameters may include: (i) outdoor air temperature; (ii) a temperature associated with the heat absorption heat exchanger, such as the temperature of the heat absorption heat exchanger; (iii) the capacity (tonnage) of the compression device; (iv) an area associated with the heat rejection heat exchanger, such as the area of the heat rejection heat exchanger; (v) a pressure ratio associated with the refrigeration circuit; and / or (vi) fan speed. The applicant has recognized that these parameters can be used to calculate a suitable predicted pressure.

[0044] Comparing the measured pressure with the predicted pressure may include comparing the measured pressure with the predicted pressure substantially continuously and / or periodically.

[0045] The expansion device may include a valve with a controllable opening degree, and the method may include controlling the opening degree of the expansion valve based on the comparison.

[0046] The method may include controlling the expansion device to maintain a desired refrigerant flow rate through the refrigeration circuit when the measured pressure is less than the predicted pressure. This may include controlling the expansion valve to maintain its opening degree at a first value.

[0047] The method may include controlling the expansion device to temporarily increase the refrigerant flow rate through the refrigeration circuit when the measured pressure is greater than or equal to the predicted pressure. This may include: when the measured pressure is greater than or equal to the predicted pressure, temporarily increasing the opening degree of the expansion valve from the first value to a second value, where the second value is greater than the first value. The method may include controlling the expansion valve to maintain its opening degree at the second value for a period of time and then (after that period of time) controlling the expansion valve to return its opening degree to the first value (or some other desired value).

[0048] The ratio of the second value to the first value may be approximately (i) ≥1.5; (ii) ≥2; (iii) ≥2.5; (iv) ≥3; (v) ≥3.5; or (vi) ≥4. The first period of time may have a period of approximately (i) 1 - 10 seconds; (ii) 10 - 20 seconds; (iii) 20 - 30 seconds; (iv) 30 - 40 seconds; (v) 40 - 50 seconds; (vi) 50 - 60 seconds; or (vii) > 60 seconds.

[0049] The refrigeration system may be used to meet a cooling load. In this case, the cooling of the refrigerant fluid may be accomplished by discharging heat to the atmosphere through a heat rejection heat exchanger, and the heating of the refrigerant fluid may be accomplished by absorbing heat from an object to be cooled (such as a refrigeration space for cryogenic storage or the interior of a building) through an endothermic heat exchanger.

[0050] Alternatively, the refrigeration system may be used as a heat pump to meet a heat demand. In this case, the endothermic heat exchanger may be used to absorb heat from a low - temperature source, where the refrigeration circuit then discharges the heat to a higher - temperature object to be heated (such as a heating space or the interior of a building). BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Certain preferred embodiments of the present invention will now be described by way of example only with reference to the following drawings, in which:

[0052] Figure 1 is a schematic diagram of a refrigeration system according to various embodiments;

[0053] Figure 2 is a graph showing the measured pressure change over time of a refrigeration system operating without the technology of various embodiments;

[0054] Figure 3 is a flowchart showing a method of operating a refrigeration system according to various embodiments; and

[0055] Figure 4 is a graph showing the measured pressure change over time of a refrigeration system operating according to various embodiments. Detailed Description

[0056] As Figure 1 shown, the refrigeration system includes a compression device 12, a heat rejection heat exchanger 14, an expansion device 18, and an endothermic heat exchanger 16 that together form a refrigeration circuit. The refrigeration circuit contains a refrigerant fluid, and the circulation of the refrigerant fluid through the compression device 12 enables the refrigeration system to utilize a refrigeration cycle (or heat pump cycle) to meet a cooling (or heating) load.

[0057] In this example, the compression device 12 is a compressor 12 for compressing the gaseous refrigerant fluid, the heat rejection heat exchanger 14 is a condenser for at least partially condensing the refrigerant fluid, the expansion device 18 is an expansion valve for expanding the refrigerant fluid, and the endothermic heat exchanger 16 is an evaporator for at least partially evaporating the refrigerant fluid. The refrigeration system can be arranged such that the fluid is completely condensed at the condenser 14 and completely evaporated at the evaporator 16.

[0058] Also as Figure 1 shown, the system further includes a controller 20 that can receive various inputs from the refrigeration system, and the controller can be configured to control various parts of the refrigeration system. The controller can include a suitable control circuit configured to operate the refrigeration system in the manner of various embodiments described herein. The controller can include a suitable processing circuit configured to perform any one or more or all of the necessary processing operations for the various embodiments described herein. In various embodiments, the controller can include a suitable computing device (computer), a microprocessor system, a programmable FPGA (field programmable gate array), etc.

[0059] As Figure 1 shown, the controller 20 can receive as an input a pressure measurement from a pressure sensor 22 disposed at the inlet of the heat rejection heat exchanger 14. As will be further described below, the controller can be configured to receive other inputs from the refrigeration system ( Figure 1 not shown herein).

[0060] The controller can also be configured to control the expansion device 18 by controlling the opening degree of the expansion valve. The controller can be configured to control other elements of the refrigeration system (Figure 1 not shown).

[0061] The heat rejection heat exchanger 14 may include a microchannel heat exchanger (MCHE). Generally, these heat exchangers have been operated using R410A or R134a refrigerants.

[0062] By introducing the R32 refrigerant, the applicant has recognized that the liquid slug (or "slug flow") phenomenon of the refrigerant fluid within the heat rejection heat exchanger 14 may cause the refrigeration system to be unstable, thereby reducing the conditions under which the system can operate reliably and reducing its efficiency. This is thought to be due to the new refrigerant / oil mixture having a lower refrigerant density but a higher oil viscosity. A similar phenomenon may also occur when other high-pressure refrigerants (such as R32, R410A, R454B, etc.) are used with a microchannel heat exchanger (MCHE).

[0063] Figure 2 is a graph showing the variation of the pressure measured by the sensor 22 over time in a refrigeration system operating without controlling the expansion device 18 in a manner based on a comparison of various embodiments. Figure 2 Also shown is the variation of the opening degree of the expansion valve 18 over time.

[0064] In this example, the system initially operates in a "normal" state, whereby the expansion valve 18 operates at a desired opening degree, which in this example is approximately 7%. However, in this example, slug flow occurs within the heat rejection heat exchanger 14, and thus the pressure measured by the sensor 22 increases over time until the maximum allowable operating pressure is reached. When the maximum allowable operating pressure is reached, the controller 20 shuts down the refrigeration system by fully closing the expansion device 18.

[0065] This disadvantageously causes interference to the user because when the system is operating at a dangerous high pressure, the system stops operating due to the controller 20 shutting down the system.

[0066] According to various embodiments, the controller 20 is provided with additional logic in order to eliminate or reduce the problems associated with slug flow.

[0067] Specifically, the controller 20 may be configured to calculate the maximum pressure value that is expected to be measured by the sensor 22 in the absence of the slug flow phenomenon. This calculation may be done using the operating parameters of the refrigeration system (other than the measured pressure), which can be easily measured and / or determined. The measured pressure reaching or exceeding this predicted pressure may indicate the presence of slug flow (or a similar instability).

[0068] In this regard, the applicant has recognized that a suitable predicted maximum pressure value can be determined based on outdoor air temperature, evaporator temperature, compressor tonnage, heat exchanger area, pressure ratio, and fan speed. Specifically, the predicted pressure value can be determined using the following equation:

[0069] .

[0070] In this equation, "Tons per coil" can be the number of compressors turned on divided by the number of coils in the circuit; "OAT" can be the outdoor air temperature (which can be measured by a temperature sensor); "SST" can be the saturated suction temperature of the circuit (which can be measured by a pressure sensor, e.g., on the suction pipe); "P discharge / P suction " can be the ratio of the discharge pressure to the suction pressure of the circuit (which can be measured by pressure sensors, e.g., on the discharge pipe and the suction pipe); and "Rpm fan " can be the fan frequency of the circuit (which can be determined from software). It should be noted that all of these parameters can be measured or determined using sensors that may already exist in the refrigeration system, so additional sensors may not be required.

[0071] The various coefficients a, b, c, d, and e can be set for the needs of the specific refrigeration system under discussion, e.g., depending on calibration and / or varying operating conditions. For example, they are set to take into account contamination of the coils, etc.

[0072] The controller 20 can be configured to compare the pressure measured by the sensor 22 with the calculated predicted pressure value.

[0073] If the pressure value measured by the sensor 22 is greater than the calculated predicted value, the controller 20 can control the expansion valve 18 to increase its opening degree, so as to instantaneously increase the mass flow rate of the refrigerant through the refrigeration circuit, thereby reducing the pressure in the discharge heat exchanger 14 and stopping or reducing the slug flow in the discharge heat exchanger 14.

[0074] The controller 20 can control the expansion valve 18 to increase its opening degree within a sufficiently short time period and at a sufficiently low opening degree such that the impact of the pressure wave on the operation of the refrigeration system is insignificant, meaning it cannot be detected by the user.

[0075] Figure 3 is a flowchart showing the programming logic of the controller 20 for controlling the expansion valve 18.

[0076] As Figure 3As shown, the controller receives information indicating the pressure measured by sensor 22 ("discharge pressure"). The pressure measurement is compared with the maximum system pressure, which is calculated using the equation described above. Controller 20 can be configured to receive readings from sensor 22 continuously or periodically to continuously or periodically calculate the maximum system pressure and continuously or periodically compare the measurement with the maximum system pressure.

[0077] If the pressure measurement approaches the maximum system pressure, controller 20 activates its "clean coil logic" by opening expansion valve 18 for a specific amount of time and at a specific opening to eliminate any slug flow from the system.

[0078] Figure 4 is a graph showing the variation of the pressure measured by sensor 22 over time in a refrigeration system operating in controlling expansion device 18 in a manner based on various embodiments.

[0079] In this example, the system initially operates in a "normal" state, whereby expansion valve 18 operates at a desired opening, which in this example is approximately 7%. However, in this example, slug flow occurs within the discharge heat exchanger 14, and thus the pressure measured by sensor 22 increases over time.

[0080] However, at the same time, the system continuously calculates the maximum pressure in the manner described above. Once the measured pressure reaches or exceeds the calculated maximum pressure, the opening of expansion valve 18 is increased within a short amount of time (a few seconds or tens of seconds) and to a specific opening percentage (in this example approximately 18%), thereby reducing the pressure of the refrigerant fluid within discharge heat exchanger 14 and eliminating and / or removing any slug flow.

[0081] This process repeats continuously during the operation of the refrigeration system such that the pressure never reaches the maximum allowable operating pressure.

[0082] Advantageously, this results in continuous operation of the refrigeration system without causing interference to the user. This can also expand the operating range of the refrigeration system and improve its efficiency.

[0083] For example, under some specific conditions, a low proportion of liquid slug can provide higher efficiency by creating additional subcooling. The efficiency improvement under low load conditions is estimated to be up to 5%.

[0084] It will be appreciated that the various embodiments provide an algorithm that can detect the slug flow phenomenon and can act to ensure stable operation under various possible operating conditions. The pressure of heat exchanger 14 is continuously monitored and the theoretical coil pressure is continuously evaluated.

[0085] When the pressure of the heat exchanger 14 is higher than the theoretical coil pressure, the cleaning coil logic is activated. The cleaning coil logic involves opening the expansion device 18 at a specific time period and open position to clean the coils of the heat exchanger 14 by flushing the liquid mixture for a few seconds, thereby significantly increasing the refrigerant flow.

[0086] The various embodiments advantageously provide a more stable operation of the system, without any visible effect on the refrigeration provided, broaden the operating range of the system, and improve its efficiency.

Claims

1. A refrigeration system, comprising: A refrigeration circuit, which includes a compression device, a heat rejection heat exchanger, an expansion device, and a heat absorption heat exchanger; One or more sensors configured to measure the pressure associated with the heat rejection heat exchanger; And A controller configured to compare the pressure measured by the one or more sensors with a predicted pressure and control the expansion device based on the comparison, and wherein the predicted pressure is the maximum predicted pressure of the refrigerant fluid without slug flow phenomenon.

2. The refrigeration system according to claim 1, wherein The controller is configured to continuously and / or periodically compare the measured pressure with the predicted pressure.

3. The refrigeration system according to claim 1 or claim 2, characterized in that, The controller is configured to continuously and / or periodically calculate the predicted pressure using one or more measured parameters.

4. The refrigeration system according to claim 3, characterized in that, The one or more measured parameters include: (i) outdoor air temperature; (ii) temperature associated with the heat absorption heat exchanger; (iii) capacity of the compression device; (iv) area associated with the heat rejection heat exchanger; (v) pressure ratio associated with the refrigeration circuit; and / or (vi) fan speed associated with the refrigeration circuit.

5. The refrigeration system according to claim 1 or claim 2, characterized in that, The expansion device includes an expansion valve, and wherein the controller is configured to control the opening degree of the expansion valve based on the comparison.

6. The refrigeration system according to any one of claims 5, characterized in that, The controller is configured to control the expansion device based on the comparison by temporarily increasing the opening degree of the expansion valve when the measured pressure is greater than or equal to the predicted pressure.

7. The refrigeration system according to claim 6, wherein The controller is configured to temporarily increase the opening degree of the expansion valve to (i) ≥1.5; (ii) ≥2; (iii) ≥2.5; (iv) ≥3; (v) ≥3.5; or (vi) ≥4 times.

8. The refrigeration system according to claim 6 or claim 7, characterized in that, The controller is configured to temporarily increase the opening degree of the expansion valve within a time period of (i) 1 - 10 seconds; (ii) 10 - 20 seconds; (iii) 20 - 30 seconds; (iv) 30 - 40 seconds; (v) 40 - 50 seconds; (vi) 50 - 60 seconds; or (vii) >60 seconds.

9. A method of operating a refrigeration system, the refrigeration system including a refrigeration circuit, the refrigeration circuit including a compression device, a heat rejection heat exchanger, an expansion device, and a heat absorption heat exchanger, the method comprising: Measuring the pressure associated with the heat rejection heat exchanger; Comparing the measured pressure with a predicted pressure; And Controlling the expansion device based on the comparison; And Wherein the predicted pressure is the maximum predicted pressure of the refrigerant fluid without slug flow phenomenon.

10. The method according to claim 9, characterized in that, Including continuously and / or periodically measuring the pressure, and continuously and / or periodically comparing the measured pressure with the predicted pressure.

11. The method according to claim 9 or claim 10, characterized in that Further comprising: Continuously and / or periodically measuring one or more parameters; And Continuously and / or periodically calculating the predicted pressure based on the one or more parameters.

12. The method according to claim 9 or claim 10, characterized in that, The expansion device includes an expansion valve, and wherein controlling the expansion device based on the comparison includes: temporarily increasing the opening degree of the expansion valve when the measured pressure is greater than or equal to the predicted pressure.

13. The method according to claim 12, wherein Controlling the expansion device based on the comparison includes: when the measured pressure is greater than or equal to the predicted pressure, temporarily increasing the opening degree of the expansion valve from a first value to a second value, where the ratio of the second value to the first value is (i) ≥ 1.5; (ii) ≥ 2; (iii) ≥ 2.5; (iv) ≥ 3; (v) ≥ 3.5; or (vi) ≥ 4.

14. The method according to claim 12, wherein Controlling the expansion device based on the comparison includes temporarily increasing the opening degree of the expansion valve within a time period of (i) 1 - 10 seconds; (ii) 10 - 20 seconds; (iii) 20 - 30 seconds; (iv) 30 - 40 seconds; (v) 40 - 50 seconds; (vi) 50 - 60 seconds; or (vii) > 60 seconds.

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