Refrigeration cycle device and method for controlling same

Abstract

A refrigeration cycle device (100) comprises a refrigeration cycle circuit. The refrigeration cycle circuit comprises: a compressor (1); a gas-liquid separator (2) disposed on the suction side of the compressor (1); and a condenser (3) that condenses refrigerant discharged from the compressor (1). The refrigeration cycle circuit circulates a mixed refrigerant containing a plurality of types of refrigerant each having a different evaporation temperature. The refrigeration cycle device (100) comprises, in the refrigeration cycle circuit, a heating device (4) that heats the refrigerant on the suction side of the compressor (1). The refrigeration cycle device (100) includes a control device (17). The control device (17) carries out control in which the control device: determines whether or not the internal temperature of the gas-liquid separator (2) is no more than a threshold value; and if the internal temperature is no more than the threshold value, executes heating using the heating device (4).

Description

Refrigeration cycle device and control method thereof

[0001] The present invention relates to a refrigeration cycle device and a control method thereof.

[0002] To prevent global warming, there is a continuous demand for a shift from refrigerants with high global warming potential (GWP) to refrigerants with low GWP. Among various refrigerants, ethylene-based fluorocarbon refrigerants such as R1123, R1132(E), and R1132a are known for their high performance. These ethylene-based refrigerants are known to undergo disproportionation reactions (autolysis reactions) under high-temperature and high-pressure conditions when used alone. Therefore, they are often mixed with higher-boiling refrigerants, such as R1234yf, to reduce the risk of disproportionation reactions. Examples of such mixed refrigerants include R474B refrigerant, which has a component composition of R1132(E) / R1234yf=31.5 / 68.5. R474B refrigerant is non-toxic and has a GWP AR4 (Fourth Assessment Report) value of approximately 3 and a GWP AR6 value of approximately 0.34. It is expected to be a next-generation low-GWP refrigerant.

[0003] International Publication No. 2015 / 140884 (Patent Document 1) is known in relation to disproportionation reactions. Patent Document 1 discloses a technology aimed at providing a safe and high-performance refrigeration cycle system by preventing conditions under which a refrigerant that undergoes a disproportionation reaction is placed in the refrigeration cycle system, even when the refrigerant is used as one of non-azeotropic refrigerant mixtures in which a disproportionation reaction occurs. The prior art disclosed in Patent Document 1 is a refrigeration cycle system that uses a non-azeotropic refrigerant mixture containing a first refrigerant and a second refrigerant having a higher boiling point than the first refrigerant at the same pressure as the working refrigerant. The first refrigerant has a characteristic that causes a disproportionation reaction. In the initial state after startup of the compressor, the temperature or pressure of the refrigerant discharged from the compressor is suppressed compared to normal operation based on the amount of liquid refrigerant in the gas-liquid separator. Patent Document 1 also discloses a configuration in which a refrigerant pipe passes through the accumulator, heating the liquid refrigerant with the heat of the gas refrigerant in the pipe, or a heating means such as an electric heater attached to the outer surface of the accumulator.

[0004] In the prior art of Patent Document 1, in order to avoid the risk of disproportionation reactions, the compressor is operated at a low speed and the accumulator is heated using discharge gas after startup. Therefore, the prior art of Patent Document 1 can mitigate the refrigerant property conditions that make disproportionation likely to occur immediately after startup. However, the prior art of Patent Document 1 does not address cases where the refrigeration cycle circuit is stopped for a long period of time. That is, when the refrigeration cycle circuit is stopped for a long period of time, the temperature in the gas-liquid separator drops when the compressor is started, and the refrigerant property inside the gas-liquid separator is already biased. In this case, the prior art of Patent Document 1 returns the refrigerant directly to the compressor, which can become an ignition source, upon startup, which is insufficient in addressing the risk of disproportionation reactions.

[0005] International Publication No. 2015 / 140884

[0006] The present disclosure has been made in consideration of the above points, and aims to provide a refrigeration cycle device and a control method for the refrigeration cycle device that can further reduce the risk of disproportionation reactions caused by imbalances in refrigerant properties due to a decrease in the internal temperature of a gas-liquid separator when the refrigeration cycle circuit is stopped for an extended period of time.

[0007] In order to solve the above-mentioned problems, the present disclosure provides a refrigeration cycle apparatus having the following characteristics. The refrigeration cycle apparatus includes a compressor, a gas-liquid separator provided on the suction side of the compressor, and a condenser that condenses refrigerant discharged from the compressor, and includes a refrigeration cycle circuit in which a mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures circulates. The refrigeration cycle apparatus also includes a heating device that heats the refrigerant on the suction side of the compressor in the refrigeration cycle circuit. The refrigeration cycle apparatus further includes a control device that determines whether the internal temperature of the gas-liquid separator is equal to or lower than a threshold value, and controls the heating device to heat the refrigerant if the internal temperature is equal to or lower than the threshold value.

[0008] The above configuration makes it possible to further reduce the risk of disproportionation reactions caused by deviations in the physical properties of the refrigerant due to a drop in the internal temperature of the gas-liquid separator when the refrigeration cycle circuit is stopped for an extended period of time.

[0009] In addition, a control method executed by the above-described refrigeration cycle apparatus is provided.

[0010] Fig. 1 is a diagram showing the overall configuration of a refrigerator according to an embodiment of the present disclosure. Fig. 2 is a diagram showing the configuration of a gas-liquid separator in a refrigeration cycle circuit of a refrigerator according to an embodiment of the present disclosure. Fig. 3 is a flowchart showing startup control performed by a refrigerator according to an embodiment of the present disclosure. Fig. 4 is a flowchart showing periodic control performed by a refrigerator according to an embodiment of the present disclosure. Fig. 5 is a flowchart showing startup control performed by a refrigerator according to another embodiment of the present disclosure.

[0011] One or more embodiments of the present disclosure will be described below with reference to the drawings, but the embodiments of the present disclosure are not limited to the specific embodiments described below. Note that the same reference numerals throughout the drawings indicate the same or corresponding parts.

[0012] The present disclosure relates to a refrigeration cycle apparatus and a control method thereof. A refrigeration cycle apparatus according to an embodiment of the present disclosure includes a refrigeration cycle circuit, which includes a compressor, a gas-liquid separator provided on the suction side of the compressor, and a condenser for condensing refrigerant discharged from the compressor. A mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures circulates (under the same pressure). The refrigeration cycle apparatus also includes a heating device for heating the refrigerant on the suction side of the compressor in the refrigeration cycle circuit. The refrigeration cycle apparatus further includes a control device, which determines whether an internal temperature of the gas-liquid separator is equal to or lower than a threshold value, and controls the heating device to heat the refrigerant if the internal temperature is equal to or lower than the threshold value.

[0013] As described above, in a refrigeration cycle circuit in which a mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures circulates, if the circuit is stopped for a long period of time, a temperature drop may cause a deviation in the refrigerant properties inside the gas-liquid separator before the compressor takes it in. The above configuration further reduces the risk of a disproportionation reaction caused by a deviation in the refrigerant properties due to a drop in the internal temperature of the gas-liquid separator when the circuit is stopped for a long period of time.

[0014] In a preferred embodiment, the control device further evaluates the stop time during which the refrigeration cycle circuit is stopped and determines whether or not the evaluation result of the stop time satisfies a condition in addition to the internal temperature being equal to or lower than a threshold value. By using the evaluation result of the stop time during which the refrigeration cycle circuit is stopped as a condition in addition to the internal temperature as a condition, it is possible to reliably condition the state inside the gas-liquid separator that requires action.

[0015] In a preferred embodiment, the heating device is provided in the gas-liquid separator and configured to heat a lower portion of the gas-liquid separator. In a specific embodiment, at least one type of refrigerant in the mixed refrigerant is a refrigerant that undergoes a disproportionation reaction, and the heating device heats the oil stored in the gas-liquid separator, thereby changing the (local) refrigerant composition in the gas-liquid separator.

[0016] Oil is stored inside the gas-liquid separator, and some of the refrigerant dissolves in the stored oil. The mixed refrigerant inside the gas-liquid separator has a set composition (concentration) when the refrigeration cycle circuit is operating. However, if the refrigeration cycle circuit is shut down for an extended period of time, the difference in vapor pressure between the various refrigerants in the mixed refrigerant can change the way the refrigerant dissolves in the oil, resulting in changes to the composition of the gas refrigerant inside the gas-liquid separator, potentially resulting in imbalances in the refrigerant properties over time and temperature ranges. This can increase the ratio of refrigerants with low evaporation temperatures and refrigerants that undergo disproportionation reactions. If the refrigeration cycle circuit is started up while the ratio of refrigerant properties that cause disproportionation reactions is elevated, disproportionation reactions are more likely to occur even at low pressures and temperatures after the compressor starts up. By heating the oil stored in the gas-liquid separator using a heating device, the refrigerant composition inside the gas-liquid separator is adjusted to a composition closer to the set concentration, thereby further reducing the risk of disproportionation reactions.

[0017] In a specific embodiment, the refrigeration cycle device includes a timer that accumulates time since operation has stopped. The stop time of the refrigeration cycle circuit is evaluated based on the accumulated time accumulated by the timer. The above-mentioned condition includes a time threshold value for the accumulated time.

[0018] In another specific embodiment, the refrigeration cycle device includes an outside air temperature sensor that measures the outside air temperature and a refrigerant temperature sensor that measures a refrigerant temperature associated with the refrigeration cycle circuit (e.g., the internal temperature of a gas-liquid separator). The stop time of the refrigeration cycle circuit is evaluated based on the temperature difference between the outside air temperature and the refrigerant temperature. The condition includes a temperature difference threshold for the temperature difference. This is because, as the stop time of the refrigeration cycle circuit increases, the refrigerant temperature of the refrigeration cycle circuit gradually approaches the outside air temperature from the temperature range of the operating state, and therefore the difference between the refrigerant temperature and the outside air temperature is a good indicator of the stop time of the refrigeration cycle circuit.

[0019] In a preferred embodiment, the control device determines whether the temperature is equal to or lower than the threshold before starting the compressor, and after heating by the heating device, starts the compressor at a speed lower than the normal speed. After starting the compressor at the low speed, the control device stops heating the gas-liquid separator by the heating device and switches the compressor to normal operation. This makes it possible to appropriately adjust the imbalance in the refrigerant properties inside the gas-liquid separator when the compressor starts.

[0020] In a particular embodiment, the control device performs a threshold-based determination regardless of whether the compressor is started, and the heating device is turned off if the internal temperature of the gas-liquid separator exceeds a target value.

[0021] In a specific embodiment, the capacity C of the heating device satisfies the following relational expression (1): 8.16[W / L]×V[L]≦C[W], where V is the container volume of the gas-liquid separator. By satisfying this condition, in standard usage, it is possible to prevent liquid refrigerant from accumulating in the gas-liquid separator during long-term shutdown, and to reliably gasify the liquid refrigerant accumulated in the gas-liquid separator.

[0022] In a specific embodiment, the refrigeration cycle apparatus includes a bypass circuit that returns refrigerant from the discharge side of the compressor to the inlet of the gas-liquid separator, bypassing the condenser. When the internal temperature is equal to or lower than a threshold, the control device further controls to open the bypass circuit (in addition to heating by the heating device). Opening the bypass circuit causes refrigerant to flow from the bypass circuit into the gas-liquid separator, thereby changing the (local) refrigerant composition in the gas-liquid separator.

[0023] As described above, when the refrigeration cycle circuit is stopped for an extended period of time, the refrigerant properties may become unbalanced over time or at certain temperatures due to differences in vapor pressures of the multiple refrigerants in the mixed refrigerant. In addition to heating by the heating device, opening the bypass circuit to allow refrigerant to flow from the bypass circuit into the gas-liquid separator makes it easier to adjust the refrigerant composition in the gas-liquid separator to a composition closer to the set concentration.

[0024] According to an embodiment of the present disclosure, there is also provided a control method executed by a refrigeration cycle apparatus. The refrigeration cycle apparatus includes a refrigeration cycle circuit and a control device, and a mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures circulates (under the same pressure) through the refrigeration cycle circuit. The control method includes a step in which the control device determines whether an internal temperature of a gas-liquid separator provided on the suction side of a compressor in the refrigeration cycle circuit is equal to or lower than a threshold. The control method also includes a step in which the control device heats the refrigerant on the suction side of the compressor in the refrigeration cycle circuit using a heating device when the internal temperature is equal to or lower than the threshold.

[0025] The above configuration makes it possible to further reduce the risk of disproportionation reactions caused by deviations in refrigerant properties due to a decrease in the internal temperature of the gas-liquid separator when the system is not in operation for a long period of time.

[0026] In a specific embodiment, the determining step includes a step of evaluating a stop time during which the refrigeration cycle circuit is stopped and a step of determining whether the evaluation result of the stop time satisfies a condition. The opening step and the starting step are performed when the internal temperature is equal to or lower than a threshold and the evaluation result of the stop time satisfies the condition. By using the evaluation result of the stop time during which the refrigeration cycle circuit is stopped in addition to the internal temperature as a condition, it is possible to reliably condition the state inside the gas-liquid separator that requires action.

[0027] In a specific embodiment, the control method further includes a step of causing the control device to operate a timer that accumulates time in response to a command to stop operation. The evaluating step includes a step of evaluating a stop time of the refrigeration cycle circuit based on the accumulated time accumulated by the timer in response to a command to start operation. The condition includes a time threshold for the accumulated time.

[0028] In a preferred embodiment, the step of determining whether the refrigerant temperature is equal to or lower than the threshold value is performed before starting the compressor. The control method further includes the steps of: starting the compressor at a speed lower than the normal speed range after heating by the heating device; and, after starting the compressor at the low speed range, stopping heating of the gas-liquid separator by the heating device and transitioning the compressor to normal operation. This makes it possible to appropriately adjust the imbalance in the refrigerant properties inside the gas-liquid separator when the compressor is started.

[0029] In a preferred embodiment, the step of determining whether the internal temperature of the gas-liquid separator is equal to or less than the threshold is performed regardless of whether the compressor is started. In the control method, the control device stops heating by the heating device when the internal temperature of the gas-liquid separator exceeds a target value. This makes it possible to preferably adjust the imbalance in the refrigerant properties inside the gas-liquid separator in preparation for future start-up of the compressor.

[0030] Hereinafter, a refrigeration cycle apparatus and a control method thereof according to an embodiment of the present disclosure will be described in more detail with reference to FIGS.

[0031] 1 is a diagram showing the overall configuration of a refrigerator 100 as a refrigeration cycle apparatus according to an embodiment of the present disclosure. The refrigerator 100 is also called a condensing unit.

[0032] First, a refrigeration cycle circuit of the refrigerator 100 shown in Fig. 1 will be described below. In Fig. 1, the refrigeration cycle circuit of the refrigerator 100 is indicated by solid lines, and the flow of refrigerant is indicated by solid arrows. As shown in Fig. 1, the refrigerator 100 includes a compressor 1 that draws in refrigerant gas, compresses the drawn refrigerant, and discharges the compressed refrigerant, and a condenser 3 into which the refrigerant discharged from the compressor 1 flows.

[0033] The compressor 1 is a compressor of any type, such as a screw type, scroll type, reciprocating type, rotary type, or turbo type. The condenser 3 is a heat exchanger that condenses the refrigerant discharged from the compressor 1 by exchanging heat with a fluid such as air. The condenser 3 shown in Fig. 1 is an air-cooled heat exchanger, and the refrigerator 100 is provided with a blower 9 for blowing air to the condenser 3. The blower 9 blows air drawn in from the outside toward the condenser 3, or draws air from the outside through the condenser 3, thereby blowing air to the condenser 3.

[0034] 1 further includes a subcooler 5 into which the condensed refrigerant from the condenser 3 flows and which subcools the refrigerant that has flowed in. The subcooler 5 is provided with a subcooling expansion valve 6, and a portion of the refrigerant is decompressed by the subcooling expansion valve 6 and enters the subcooler 5, where it exchanges heat with the refrigerant from the condenser 3 to subcool the refrigerant from the condenser 3, and is then returned to the compressor 1.

[0035] The refrigerator 100 further includes an evaporator 12 and an expansion valve 13. The refrigerant delivered from the condenser 3 and supercooled by the supercooler 5 is decompressed by the expansion valve 13, which serves as an expansion mechanism, and supplied to the evaporator 12. In the evaporator 12, the refrigerant absorbs heat from a fluid, such as air, and evaporates. The refrigerant gas is then discharged from the evaporator 12 to the compressor 1. The refrigerator 100 shown in FIG. 1 also includes a blower 14 for blowing air to the evaporator 12. The blower 14 blows air drawn in from the outside toward the evaporator 12, or draws air from the outside through the evaporator 12 to blow air to the evaporator 12. The fluid is not limited to air and may be water. In the configuration shown in FIG. 1, the evaporator 12 and expansion valve 13, enclosed by dotted lines, are typically external components of the refrigerator 100 that are prepared by the user and constitute a showcase, refrigerator / freezer, unit cooler, chiller, ice maker, or the like.

[0036] The embodiment shown in FIG. 1 further includes a gas-liquid separator 2 provided between the evaporator 12 and the compressor 1, which separates the refrigerant liquid mixed in the gas refrigerant and allows only the gas refrigerant to be sucked into the compressor 1.

[0037] In the embodiment shown in Fig. 1, as described above, the gas-liquid separator 2, compressor 1, condenser 3, expansion valve 13, and evaporator 12 are connected in sequence to form a refrigeration cycle circuit. In the example shown in Fig. 1, a pressure shutoff valve HP is provided on the discharge side of the compressor 1, and a check valve V1 is provided between the compressor 1 and the condenser 3. In addition, a strainer S1 is provided on the inlet side of the gas-liquid separator 2, and a valve V2 is provided between the gas-liquid separator 2 and the evaporator 12.

[0038] A mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures is circulated through the refrigeration cycle circuit under the same pressure. The refrigerant used in the refrigerator 100 can be a mixture of a first refrigerant capable of undergoing a disproportionation reaction and a second refrigerant with a higher boiling point and evaporation temperature than the first refrigerant. The first refrigerant is not particularly limited, but can be an ethylene-based fluorohydrocarbon refrigerant such as 1,1,2-trifluoroethylene (R1123), trans-1,2-difluoroethylene (R1132(E)), 1,1-difluoroethylene (R1132a), cis-1,2-difluoroethylene (R1132(Z)), or fluoroethylene (R1141). The second refrigerant with a high boiling point can be a propylene-based fluorohydrocarbon refrigerant such as 2,3,3,3-tetrafluoropropene (R1234yf). By using a mixture of a first ethylene-based refrigerant and a second refrigerant with a higher evaporation temperature, the risk of disproportionation reactions of the ethylene-based refrigerant can be reduced. The mixed refrigerant is not particularly limited, but is preferably a two-type mixed refrigerant. Known examples of such two-type mixed refrigerants include R474B refrigerant, which has a component composition of R1132(E) (boiling point = -52.5°C) / R1234yf (boiling point = -30°C) = 31.5 / 68.5. Using a refrigerant with a low GWP (Global Warming Potential) can reduce the impact on global warming caused by refrigerant leakage from a refrigerator.

[0039] The above-described chiller 100 may further include a bypass circuit 7 in addition to the above-described refrigeration cycle circuit, which returns refrigerant from the discharge side of the compressor 1 to the suction side of the compressor 1, bypassing the condenser 3. In the embodiment shown in Fig. 1 , the bypass circuit 7 includes a pipe that bypasses from the discharge side of the compressor 1 to the inlet side (before the strainer S1) of the gas-liquid separator 2 provided on the suction side of the compressor 1, and an electromagnetic valve 8 provided in the pipe for opening and closing the bypass circuit. Note that the bypass method of the bypass circuit 7 is not particularly limited, and may be a bypass to the inlet side of the gas-liquid separator provided before the suction port of the compressor 1 as shown in Fig. 1 , a bypass to the outlet of the evaporator 12, or a bypass to the inlet of the evaporator 12.

[0040] The chiller 100 further includes various sensors, various actuators, and a control device 17. More specifically, the various sensors include a temperature sensor 15 that measures the temperature inside the gas-liquid separator 2 and an outside air temperature sensor 16 that is provided in the condenser 3. The various actuators include blowers 9, 14 and a solenoid valve 8. In addition, the chiller 100 shown in FIG. 1 is provided with a high-pressure side pressure sensor PSH on the discharge side of the compressor 1, and a low-pressure side pressure sensor PSL on the inlet side of the gas-liquid separator 2.

[0041] The control device 17 performs overall control of the chiller 100. Based on signals from various sensors, the control device 17 controls the rotation speed of the compressor 1, the rotation speed of the blower 9, the opening degree of the expansion valve 13, or the rotation speed of the blower 14 of the evaporator 12. Based on signals from the various sensors, the control device 17 also controls the drive of the motor of the blower 9 to control the volume of air sent to the condenser 3. Based on signals from the various sensors, the control device 17 also controls the drive of the motor of the blower 14 to control the volume of air sent to the evaporator 12.

[0042] As described above, when a refrigeration cycle circuit in which a mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures is used, if the refrigeration cycle circuit is stopped for an extended period of time, a deviation in the physical properties of the refrigerant may occur in the portion before the intake of the compressor 1, more specifically, in the gas-liquid separator 2 provided between the evaporator 12 and the compressor 1. Such a deviation in the physical properties of the refrigerant may cause a disproportionation reaction under lower temperature and pressure conditions.

[0043] 2 is a diagram illustrating the configuration of a gas-liquid separator 2 in a refrigeration cycle circuit of a refrigerator 100 according to an embodiment of the present disclosure. The gas-liquid separator 2 includes a housing 2a serving as a container, a pipe 2b connected to the evaporator 12 side, and a U-shaped tube 2c connected to the compressor 1 side. A mixed gas refrigerant G is present inside the gas-liquid separator 2, and refrigeration oil O is also stored therein. A small hole 2d is provided at the bottom of the internal U-shaped tube 2c, and liquid is returned to the compressor 1 little by little through the small hole 2d.

[0044] In the gas-liquid separator 2, the mixed gas refrigerant G inside has a set composition (concentration) when the refrigeration cycle circuit is operating. However, if the refrigeration cycle circuit is stopped for an extended period of time, the temperature drops below that of the operating state. Due to differences in vapor pressure between the various refrigerants, the dissolution rate of the refrigerant into the refrigeration oil O varies. This changes the composition of the mixed gas refrigerant G inside the gas-liquid separator 2, potentially resulting in deviations in the refrigerant properties over time and at different temperatures. Because ethylene-based refrigerants are mixed with refrigerants with high boiling points, the proportion of ethylene-based refrigerants, which have relatively low evaporation temperatures, may increase if the refrigerant cools down after a long period of shutdown. When the compressor 1 starts, the mixed gas refrigerant G inside the gas-liquid separator 2 is drawn into the compressor 1. Therefore, disproportionation reactions are more likely to occur immediately after the compressor starts, even at low pressures and temperatures.

[0045] Therefore, in the refrigerator 100 according to an embodiment of the present disclosure, a heating device 4 is provided in the refrigeration cycle circuit on the suction side of the compressor 1 to heat the refrigerant. More specifically, as shown in FIG. 2 , the heating device 4 is provided below the oil reservoir in the gas-liquid separator 2 to heat the lower portion of the gas-liquid separator 2. In a specific embodiment, before starting the compressor 1, the control device 17 determines whether the internal temperature of the gas-liquid separator 2 measured by the temperature sensor 15 is equal to or lower than a threshold value. If the internal temperature is equal to or lower than the threshold value, the control device 17 controls the heating device 4 to heat the gas-liquid separator 2. In a specific embodiment, the control device 17 controls the compressor 1 to start at a speed lower than the normal range. More preferably, in order to more reliably detect a state requiring action due to a long-term shutdown, the control device 17 can evaluate the shutdown time during which the refrigeration cycle circuit is stopped and determine whether the evaluation result of the shutdown time satisfies a condition in addition to whether the internal temperature is equal to or lower than the threshold value.

[0046] If necessary, the oil stored in the gas-liquid separator 2 is heated by the heating device 4. This may change the refrigerant composition in the gas-liquid separator 2 to a composition closer to the set concentration. By warming the oil, both refrigerants with different evaporation temperature ranges are evaporated, thereby adjusting the composition of the mixed gas refrigerant G in the gas-liquid separator 2 to approach the set composition. This alleviates the condition in which disproportionation reactions are likely to occur in the low-pressure, low-temperature range when the refrigeration cycle circuit is started with an elevated ethylene-based refrigerant property ratio, and further reduces the risk of disproportionation reactions due to imbalances in the refrigerant properties during long-term shutdown. In certain embodiments, starting the refrigeration cycle circuit at a speed slower than normal operation further reduces the risk of disproportionation reactions due to imbalances in the refrigerant properties during long-term shutdown.

[0047] Here, the normal region for operation of the compressor 1 refers to a possible region (range) of the frequency or rotation speed of the compressor 1 when performing an operation in which the rotation speed of the compressor 1, the rotation speed of the blower 9, the opening of the expansion valve 13, or the rotation speed of the blower 14 of the evaporator 12 is controlled so as to achieve a target discharge refrigerant temperature and pressure corresponding to the target capacity of the chiller 100. Starting at a speed lower than normal operation means starting at a rotation speed lower than the rotation speed region of such normal operation.

[0048] Regarding the state of the refrigeration cycle circuit, since the risk is due to differences in the way the oil dissolves due to the temperature being lower than in the operating state, first, it is determined whether the internal temperature of the gas-liquid separator 2 measured by the temperature sensor 15 is equal to or lower than a threshold value. If the internal temperature of the gas-liquid separator 2 is lower than the predetermined threshold value, the bypass circuit described above is not opened.

[0049] In addition, in order to more reliably determine the condition that requires action in response to a long-term shutdown, it is determined whether the evaluation result of the shutdown time of the refrigeration cycle circuit satisfies the condition in addition to whether the internal temperature is below a threshold. The shutdown time of the refrigeration cycle circuit can be evaluated using several methods.

[0050] The first method is to directly measure the stop time. As shown in FIG. 1 , the control device 17 includes a timer function 18. The timer function 18 is used to accumulate the time since the operation has been stopped. For example, a timer may be activated when the operation is stopped to measure the time, or time information at the time of the operation stop (such as the time on a real-time clock (RTC) or the time elapsed since a reference time) may be recorded and compared with the current time information when the compressor 1 is started to evaluate the stop time. In this way, the stop time of the refrigeration cycle circuit may be evaluated based on the accumulated time accumulated by the timer. When determining whether the condition is satisfied, if the accumulated time exceeds a predetermined time threshold, it can be evaluated as a time stop requiring action.

[0051] The second method is to indirectly evaluate the shutdown time based on the difference between the readings of the temperature sensor 15 in the refrigeration cycle circuit and the readings of the outside air temperature sensor 16. As the shutdown time of the refrigeration cycle circuit increases, the refrigerant temperature of the refrigeration cycle circuit gradually approaches the outside air temperature from the operating temperature range. Therefore, the temperature difference between the refrigerant temperature and the outside air temperature is a good indicator of the shutdown time of the refrigeration cycle circuit. The temperature difference is calculated and compared with a preset temperature difference threshold. If the temperature difference between the refrigerant temperature and the outside air temperature falls within a certain range, it can be evaluated that the refrigeration cycle circuit has been shut down for a period of time requiring action. In this way, the shutdown time of the refrigeration cycle circuit may be evaluated based on the temperature difference between the outside air temperature and the refrigerant temperature.

[0052] After the heating device 4 is heated and the compressor 1 is started in the low-speed state, the heating device 4 can be stopped at an appropriate timing, and the compressor 1 can be switched to operating in the normal range. For example, the control device 17 may stop the heating device 4 and operate the compressor 1 in the normal range after a predetermined time has elapsed. Alternatively, the heating device 4 may be stopped and the compressor 1 may be operated in the normal range in response to the internal temperature of the gas-liquid separator 2 exceeding a target value. The start of heating by the heating device 4 and the start of the compressor 1 in the low-speed state can also be delayed by a predetermined delay time.

[0053] Also, in the above description, in a specific embodiment, when the compressor 1 is started, a determination is made before the compressor 1 is started as to whether heating by the heating device 4 is necessary, and if necessary, heating is performed by the heating device 4. However, in other embodiments, the above determination may be made periodically regardless of the start of the compressor 1, and if it is determined that the refrigeration cycle has been stopped for a long period of time, the oil stored in the gas-liquid separator 2 may be heated. Note that the embodiment in which the determination is made when the compressor 1 is started can be more suitably applied in cases where periodic measures cannot be taken, such as when restoring operation after repairs.

[0054] The heating device 4 may be, for example, a resistance heater such as an electric heater, which generates Joule heat by passing an electric current through it. The capacity of the heating device 4 may be any appropriate one. However, from the viewpoint of preventing liquid refrigerant from accumulating during long-term shutdown and ensuring that the liquid refrigerant accumulated in the gas-liquid separator 2 is gasified, it is preferable that the capacity of the heating device 4 be appropriate depending on the volume capacity of the gas-liquid separator. In a preferred embodiment, the capacity of the heating device 4 is C, the container volume of the gas-liquid separator 2 is V, and the following relationship (Equation 2) is satisfied: 8.16 [W / L] × V [L] ≦ C [W]. By satisfying this condition, it is possible to prevent liquid refrigerant from accumulating in the gas-liquid separator during long-term shutdown and ensure that the liquid refrigerant accumulated in the gas-liquid separator is gasified during standard usage.

[0055] FIG. 3 is a flowchart showing the startup control executed by the control device 17 provided in the refrigerator 100 according to this embodiment.

[0056] 3 starts from step S100. At this point, the compressor 1 is not operating and the refrigeration cycle circuit is in a stopped state.

[0057] In step S101, the control device 17 receives an instruction to start operation. Here, the instruction to start operation may be issued manually by a user such as an administrator of the chiller 100, or may be issued according to a schedule set in advance by the administrator.

[0058] In step S102, the control device 17 measures the temperature inside the gas-liquid separator 2 using the temperature sensor 15. In step S103, the control device 17 acquires the accumulated time since the previous shutdown using the timer function 18. Here, it is assumed that the timer recorded time information when the refrigeration cycle circuit was previously shut down. In this case, in step S103, the control device 17 acquires current time information and calculates the accumulated time from the difference between the recorded time information at the time of shutdown and the current time information.

[0059] In step S104, the control device 17 determines whether the internal temperature is equal to or lower than the temperature threshold and whether the stop time is equal to or higher than the time threshold. If it is determined in step S104 that the internal temperature is equal to or lower than the temperature threshold and the stop time is equal to or higher than the time threshold (YES), control branches to step S105. In step S105, the control device 17 starts energizing the heating device 4 (heater) attached to the gas-liquid separator 2 to start heating by the heating device 4. In step S106, the control device 17 starts operation of the compressor 1 at a low rotation frequency to circulate the refrigerant at low pressure. A predetermined delay time may be provided between steps S105 and S106 to allow the refrigerant in the gas-liquid separator 2 to be sufficiently heated so as to reduce the risk of disproportionation reaction, assuming operation at the designed low rotation frequency.

[0060] In step S107, the control device 17 shifts the rotational frequency of the compressor 1 to the normal region, and in step S108, the operation shifts to normal operation. At this time, the control device 17 stops the supply of electricity to the heating device 4 (heater) and stops heating by the heating device 4. In addition, between steps S106 and S107, a predetermined delay time is provided so that the refrigerant in the gas-liquid separator 2 can be sufficiently heated to reduce the risk of disproportionation reaction, assuming operation at a frequency in the designed normal region.

[0061] On the other hand, if it is determined in step S104 that the internal temperature is not equal to or lower than the temperature threshold value, or that the stop time is not equal to or higher than the time threshold value, or both (NO), the control proceeds directly to step S108. In step S108, the control device 17 sets the rotation frequency of the compressor 1 to the normal region, starts the operation of the compressor 1, and transitions to normal operation in step S108.

[0062] After the transition to normal operation, the timer will be reset as necessary in response to an instruction to stop operation, and will be operated again and time information will be recorded.

[0063] FIG. 4 is a flowchart showing periodic control executed by the control device 17 included in the refrigerator 100 according to another embodiment, which periodically executes the above-described determination regardless of the activation of the compressor 1 described above.

[0064] 4 starts from step S200. In step S201, the control device 17 receives an instruction to stop operation and starts accumulating the shutdown time. In step S202, the control device 17 measures the temperature inside the gas-liquid separator 2 using the temperature sensor 15. In step S203, the control device 17 uses the timer function 18 to obtain the accumulated time since the previous shutdown.

[0065] In step S204, the control device 17 determines whether the internal temperature is equal to or lower than the temperature threshold and whether the stop time is equal to or higher than the time threshold. If it is determined in step S204 that the internal temperature is equal to or lower than the temperature threshold and that the stop time is equal to or higher than the time threshold (YES), control branches to step S205. In step S205, the control device 17 starts energizing the heating device 4 (heater) attached to the gas-liquid separator 2, and starts heating by the heating device 4. In step S206, the control device 17 measures the internal temperature of the gas-liquid separator 2 using the temperature sensor 15 and determines whether the internal temperature has reached or exceeded the target temperature. If it is determined in step S206 that the internal temperature has not yet reached or exceeded the target temperature (NO), control returns to step S205, where energization to the heating device 4 continues. On the other hand, if the internal temperature has reached or exceeded the target temperature (YES), control proceeds to step S207.

[0066] In step S207, the control device 17 stops the heating device (heater) 4 and resets the accumulated time. In step S208, the control device 17 restarts the timer, and in step S209, the control ends.

[0067] On the other hand, if it is determined in step S204 that the internal temperature is not equal to or lower than the temperature threshold, or that the stop time is not equal to or higher than the time threshold, or both (NO), the control proceeds directly to step S208. In step S208, the control device 17 restarts the timer, and ends this control in step S209.

[0068] After the timer is restarted in step S208, the flow shown in FIG. 4 is executed again after a certain time has elapsed.

[0069] As in the control flow shown in Figure 4, regardless of whether compressor 1 is started, it may be determined periodically whether heating is necessary, and if it is determined that the refrigeration cycle has been stopped for a long period of time, the oil stored in gas-liquid separator 2 may be warmed. In this way, in preparation for future start-up of compressor 1, a state can be created in advance that further reduces the risk of disproportionation reaction by detecting that the refrigeration cycle has been stopped for a long period of time and adjusting the physical properties of the refrigerant in gas-liquid separator 2. Note that the threshold value for the cumulative time in the start-up control performed when starting the compressor shown in Figure 3 and the periodic control shown in Figure 4 may be the same or different.

[0070] In the above-described embodiment, the heating device 4 is used to eliminate imbalances in the refrigerant properties in the gas-liquid separator 2. However, the present invention is not limited to using only the heating device 4. For example, in a specific embodiment, the bypass circuit described above can be used in combination with heating using the heating device 4 to further reduce the risk of a disproportionation reaction caused by imbalances in the refrigerant properties due to a decrease in the internal temperature of the gas-liquid separator during a long period of shutdown. More specifically, the control device 17 may perform control to heat the gas-liquid separator using the heating device 4 and open the bypass circuit 7 when the internal temperature is equal to or lower than a threshold value.

[0071] FIG. 5 is a flowchart showing the startup control executed by the control device 17 included in the refrigerator 100 according to another embodiment.

[0072] The control shown in Fig. 5 starts from step S300. At this point, the compressor 1 is not operating, and the refrigeration cycle circuit is in a stopped state. Also, the bypass circuit 7 is closed if it was open the previous time the compressor was stopped, and is therefore in a closed state at this point. Steps S301 to S304 are the same as steps S101 to S104 described in Fig. 3, and therefore will not be described here.

[0073] If it is determined in step S304 that the internal temperature is equal to or lower than the temperature threshold and the stop time is equal to or higher than the time threshold (YES), control branches to step S305. In step S305, the control device 17 starts energizing the heating device 4 (heater) attached to the gas-liquid separator 2 to start heating by the heating device 4, and also opens the electromagnetic valve 8 of the bypass circuit 7 to open the bypass circuit 7. In step S306, the control device 17 starts operating the compressor 1 at a low rotation frequency to circulate the refrigerant at a low pressure. A predetermined delay time may be provided between steps S305 and S306.

[0074] In step S307, the control device 17 shifts the rotation frequency of the compressor 1 to the normal region, and in step S308, the operation shifts to normal operation. At this time, the control device 17 stops the supply of electricity to the heating device 4 (heater) to stop heating by the heating device 4. The control device 17 may also close the electromagnetic valve 8 and close the bypass circuit 7. A predetermined delay time is provided between step S306 and step S307.

[0075] On the other hand, if it is determined in step S304 that the internal temperature is not equal to or lower than the temperature threshold value, or that the stop time is not equal to or higher than the time threshold value, or both (NO), the control proceeds directly to step S308. In step S308, the control device 17 sets the rotation frequency of the compressor 1 to the normal region, starts the operation of the compressor 1, and transitions to normal operation in step S308.

[0076] After the transition to normal operation, the process is the same as that of the embodiment described with reference to FIG. 3, but in addition, the timer is reset as necessary to operate again and record time information.

[0077] In this way, by opening the bypass circuit 7 in addition to heating by the heating device 4, the refrigerant is caused to flow from the bypass circuit 7 into the gas-liquid separator 2. This may change the refrigerant composition in the gas-liquid separator 2 to a composition closer to the set concentration. This refrigerant that flows in is in a state where the refrigeration cycle circuit has been stopped for a long period of time, so there is no difference in the temperature range, but it is in a relatively high-pressure state on the discharge side of the compressor 1. By flowing in such a relatively high-pressure refrigerant, the composition of the mixed gas refrigerant G inside the gas-liquid separator 2 is changed to approach the set composition.

[0078] In the above-described embodiment, both heating by the heating device 4 and the inflow of the refrigerant by opening the bypass circuit 7 are uniformly performed. In other embodiments, by setting multi-stage conditions, it is possible to set both a condition for performing either heating by the heating device 4 or the inflow of the refrigerant by opening the bypass circuit 7, and a condition for performing both heating by the heating device 4 and the inflow of the refrigerant by opening the bypass circuit 7.

[0079] As described above, according to an embodiment of the present disclosure, a refrigeration cycle device and a control method thereof are provided that can further reduce the risk of disproportionation reactions caused by imbalances in refrigerant properties due to a decrease in the internal temperature of the gas-liquid separator when the refrigeration cycle circuit is stopped for an extended period of time.

[0080] As described above, in a refrigeration cycle circuit in which a mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures circulates, if the circuit is stopped for an extended period of time, a temperature drop can cause an imbalance in the composition of the gas refrigerant inside the gas-liquid separator before the compressor is suctioned, due to differences in the ease of dissolving the refrigerant in oil caused by differences in evaporation temperatures.The above configuration further reduces the risk of disproportionation reactions caused by imbalances in the refrigerant physical properties due to a drop in the internal temperature of the gas-liquid separator during an extended period of time of shutdown.

[0081] At first glance, the operation of heating the gas-liquid separator 2 may seem contradictory to the objective of preventing the disproportionation reaction (because the disproportionation reaction is likely to occur under high temperature and high pressure conditions). However, in a configuration with a high pressure ratio, such as the chiller 100, or in a configuration in which the amount of liquid refrigerant supplied to the compressor is small due to the structure of the gas-liquid separator, the temperature may become excessively high even if liquid accumulates in the gas-liquid separator 2. In such a configuration, opening the expansion valve 13 on the evaporator 12 side is not very effective in preventing high temperatures, and the risk of autolysis reaction due to liquid accumulation in the gas-liquid separator 2 increases. For this reason, heating the gas-liquid separator 2 reduces the risk.

[0082] The conventional technology of Patent Document 1 mentioned above discloses measures to be taken after the compressor is started, but such a configuration cannot deal with a situation in which the temperature inside the gas-liquid separator drops when the compressor is started, such as when the refrigeration cycle circuit is stopped for an extended period of time, and the physical properties of the refrigerant inside the gas-liquid separator have already become unbalanced.

[0083] In the above-described embodiment, the refrigerator 100 has been described as an example of a refrigeration cycle apparatus according to an embodiment of the present disclosure. However, the refrigeration cycle apparatus is not limited to a refrigerator and may include what is also called a refrigeration air-conditioning apparatus. Here, the term refrigeration air-conditioning apparatus collectively refers to devices that use a refrigerant and a refrigeration cycle, such as the refrigerator described above, air conditioners, and refrigerators. More specifically, examples of refrigeration air-conditioning apparatus include heat source equipment such as the refrigerator and chilling unit described above, air conditioners such as package air conditioners and multi-air conditioners for buildings, commercial refrigerators such as showcases, refrigerator-freezers, unit coolers, and ice makers, transportation refrigeration equipment such as car air conditioners, and heat pump water heaters.

[0084] It should be noted that the embodiments of the present invention are not limited to the above-described embodiments and may include various modifications. For example, the above-described embodiments have been described in detail for ease of understanding, and are not necessarily limited to those including all of the described features. Furthermore, some of the features of one embodiment may be replaced with features of another embodiment, or features of one embodiment may be added to features of another embodiment. Furthermore, some of the features of each embodiment may be added to, deleted from, or replaced with other features.

[0085] 100...refrigerating machine, 1...compressor, 2...gas-liquid separator, 3...condenser, 4...heating device, 5...subcooler, 6...expansion valve, 7...bypass circuit, 8...solenoid valve, 9, 14...blower, 12...evaporator, 13...expansion valve, 15...internal temperature sensor, 16...outside air temperature sensor, 17...control device, 18...timer function

Claims

1. A refrigeration cycle device comprising: a refrigeration cycle circuit including a compressor, a gas-liquid separator provided on the suction side of the compressor, and a condenser for condensing refrigerant discharged from the compressor, in which a mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures circulates; a heating device for heating the refrigerant on the suction side of the compressor in the refrigeration cycle circuit; and a control device for determining whether an internal temperature of the gas-liquid separator is equal to or lower than a threshold value, and for controlling heating by the heating device if the internal temperature is equal to or lower than the threshold value.

2. The refrigeration cycle device according to claim 1, wherein the control device further evaluates the stop time during which the refrigeration cycle circuit is stopped, and determines whether the evaluation result of the stop time satisfies the condition in addition to the internal temperature being below a threshold value.

3. The refrigeration cycle apparatus according to claim 1, wherein the heating device is provided in the gas-liquid separator and configured to heat a lower portion of the gas-liquid separator.

4. The refrigeration cycle device of claim 1, wherein at least one type of refrigerant in the mixed refrigerant is a refrigerant that undergoes a disproportionation reaction, and the oil stored in the gas-liquid separator is heated by the heating device, thereby changing the refrigerant composition in the gas-liquid separator.

5. The refrigeration cycle device according to claim 2, further comprising a timer that accumulates time since operation has stopped, wherein the stop time of the refrigeration cycle circuit is evaluated based on the accumulated time accumulated by the timer, and the condition includes a time threshold value for the accumulated time.

6. A refrigeration cycle device as described in claim 2, further comprising: an outside air temperature sensor that measures the outside air temperature; and a refrigerant temperature sensor that measures the temperature of a refrigerant associated with the refrigeration cycle circuit, wherein the stop time of the refrigeration cycle circuit is evaluated based on a temperature difference between the outside air temperature and the refrigerant temperature, and the condition includes a temperature difference threshold for the temperature difference.

7. The refrigeration cycle device of claim 1, wherein the control device determines whether the temperature is below the threshold before starting the compressor, and after heating by the heating device, starts the compressor at a speed lower than the normal range, and after starting the compressor at the low speed, stops heating the gas-liquid separator by the heating device and transitions the compressor to operation in the normal range.

8. The refrigeration cycle device of claim 1, wherein the control device determines whether the internal temperature of the gas-liquid separator is below the threshold value regardless of whether the compressor is started, and the heating device is stopped when the internal temperature of the gas-liquid separator exceeds a target value.

9. The refrigeration cycle apparatus according to claim 1, wherein the capacity C of the heating device satisfies the relational expression 8.16 [W / L] × V [L] ≦ C [W], where V is the container volume of the gas-liquid separator.

10. The refrigeration cycle device according to claim 2, further comprising a bypass circuit that returns refrigerant from the discharge side of the compressor to the inlet of the gas-liquid separator, bypassing the condenser, and the control device further controls to open the bypass circuit when the internal temperature is equal to or lower than a threshold value.

11. A control method executed by a refrigeration cycle device, the refrigeration cycle device including a refrigeration cycle circuit in which a mixed refrigerant containing multiple types of refrigerants with different evaporation temperatures circulates, and a control device, the control method including the control device executing the steps of: determining whether the internal temperature of a gas-liquid separator provided on the suction side of a compressor in the refrigeration cycle circuit is below a threshold; and, if the internal temperature is below the threshold, heating the refrigerant on the suction side of the compressor in the refrigeration cycle circuit by a heating device.

12. A control method as described in claim 11, wherein the determining step includes a step of evaluating a stop time during which the refrigeration cycle circuit is stopped, and a step of determining whether or not the evaluation result of the stop time satisfies a condition, and the exceeding step and the starting step are executed when the internal temperature is equal to or lower than a threshold value and the evaluation result of the stop time satisfies the condition.

13. The control method according to claim 11, wherein the heating device is provided in the gas-liquid separator and configured to heat a lower portion of the gas-liquid separator.

14. The control method according to claim 12, further comprising a step in which the control device operates a timer that accumulates time in response to a stop of operation, and the evaluating step comprises a step in which, in response to an instruction to start operation, the control device evaluates the stop time of the refrigeration cycle circuit based on the accumulated time accumulated by the timer, and the condition includes a time threshold value for the accumulated time.

15. A control method as described in claim 11, wherein the step of determining whether the pressure is equal to or lower than the threshold value is performed before starting the compressor, and the control method further includes the steps of: the control device starting the compressor at a speed lower than the normal range after heating by the heating device; and the control device stopping heating of the gas-liquid separator by the heating device after starting the compressor at the low speed range, and transitioning the compressor to operation in the normal range.

16. The control method according to claim 11, wherein the step of determining whether the internal temperature of the gas-liquid separator is equal to or lower than the threshold value is performed regardless of whether the compressor is started, and the control method further includes a step in which the control device stops heating by the heating device when the internal temperature of the gas-liquid separator exceeds a target value.

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