Control device for condensing unit, condensing unit, control method and program

Abstract

This system provides an oil return control mechanism that enables oil return even in situations where oil tends to accumulate. [Solution] In the oil return control of the condensing unit, which returns the oil discharged from the compressor together with the refrigerant back to the compressor, Swelling The system includes means for stopping the compressor, provided that the expansion valve is fully closed, and means for starting the compressor after the expansion valve is fully opened and operating it at an oil return rotation speed that allows the oil to be recovered into the compressor.

Description

Technical Field

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[0001] The present invention relates to a control device for a condensing unit, a condensing unit, a control method, and a program.

Background Art

[0002] Oil is enclosed in the compressor of the condensing unit for lubrication. This oil is discharged from the compressor together with the refrigerant and, when captured by the oil separator, is separated from the refrigerant and recovered to the compressor. If the amount of oil recovered to the compressor becomes insufficient, problems such as seizure may occur in the compressor, so it is necessary to perform oil return control so that an appropriate amount of oil is recovered. Generally, oil return control is performed by increasing the rotational speed of the compressor (for example, Patent Document 1). This is "oil return by gas flow velocity" in which the rotational speed of the compressor is increased to increase the amount of refrigerant flowing through the piping and the flow velocity of the oil to return the oil. When a large number of large-capacity loaders are connected, such as in the showcases of large stores, or when the piping length is long, there are cases where "oil return by gas flow velocity" cannot collect a sufficient amount of oil because oil accumulates on the loader side.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a need for a control method that enables oil return even in situations where oil is likely to accumulate.

[0005] Therefore, an object of this invention is to provide a control device for a condensing unit, a condensing unit, a control method, and a program that can solve the above problems.

Means for Solving the Problems

[0006] According to one aspect of the present disclosure, the control device for a condensing unit is a control device for a condensing unit in a refrigeration system including a compressor and a gas cooler, which are part of a refrigerant circuit including a compressor, a gas cooler, an expansion valve, and a utilization-side heat exchanger, and a load equipment including an expansion valve and a utilization-side heat exchanger, and comprises: means for outputting a start instruction signal to the load equipment to instruct the start of oil return control, which returns oil discharged from the compressor together with the refrigerant to the compressor, when predetermined start conditions are met; means for stopping the compressor, assuming that the load equipment fully closes the expansion valve based on the start instruction signal; and means for starting the compressor after the waiting time has elapsed since the compressor was stopped, based on a predetermined waiting time set to be longer than the time it takes for the load equipment to fully open the expansion valve after it has been fully closed, and operating the compressor by increasing its rotational speed to a predetermined oil return rotational speed that can recover the oil into the compressor.

[0007] According to one aspect of the present disclosure, the condensing unit comprises a compressor, a gas cooler for cooling the refrigerant discharged by the compressor, and the control device described above.

[0008] According to one aspect of the present disclosure, a control method is a control method for a condensing unit in a refrigeration system, which includes a condensing unit comprising a compressor and the gas cooler, and a load equipment comprising the expansion valve and the utilization-side heat exchanger, wherein when a predetermined start condition is met, a start instruction signal is output to the load equipment instructing the start of oil return control, which returns oil discharged from the compressor together with the refrigerant to the compressor; the start instruction signal is output to the load equipment instructing the start of oil return control; the start instruction signal is output to the load equipment assuming that the expansion valve is fully closed based on the start instruction signal, and the compressor is stopped; and the compressor is started after the waiting time has elapsed, based on a predetermined waiting time set to be longer than the time it takes for the load equipment to fully open the expansion valve after it has been fully closed, and the compressor is operated by increasing the rotational speed of the compressor to a predetermined oil return rotational speed that can recover the oil into the compressor.

[0009] According to one aspect of the present disclosure, the program causes a computer that controls a condensing unit in a refrigeration system, which includes a condensing unit comprising a compressor and the gas cooler, and a load equipment comprising the expansion valve and the utilization-side heat exchanger, to function as: a means for outputting a start instruction signal to the load equipment to instruct the start of oil return control, which returns oil discharged from the compressor together with the refrigerant to the compressor, when predetermined start conditions are met; a means for stopping the compressor, assuming that the load equipment fully closes the expansion valve based on the start instruction signal; and a means for starting the compressor after the waiting time has elapsed since the compressor was stopped, based on a predetermined waiting time set to be longer than the time from when the load equipment fully closes the expansion valve until it is fully open, and operating the compressor by increasing its rotational speed to a predetermined oil return rotational speed that can recover the oil into the compressor. [Effects of the Invention]

[0010] The control device, condensing unit, control method, and program of this disclosure can improve the performance of oil return. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an example of a refrigeration system according to the embodiment. [Figure 2] This figure shows an example of a control device according to the embodiment. [Figure 3] This figure illustrates the oil return control according to the embodiment. [Figure 4] This flowchart shows an example of oil return control on the condensing unit side according to the embodiment. [Figure 5] This flowchart shows an example of oil return control on the showcase side according to the embodiment. [Figure 6] This figure shows an example of the hardware configuration of the control device according to the embodiment. [Modes for carrying out the invention]

[0012] <Embodiment> Hereinafter, a refrigeration system according to one embodiment of this disclosure will be described with reference to the drawings. (composition) Figure 1 is a diagram showing an example of a schematic configuration of a refrigeration system according to an embodiment. Figure 1 shows a refrigeration system 100 including a condensing unit 1 for freezing and refrigeration and a showcase 2 for housing objects to be frozen and refrigerated. The condensing unit 1 includes a compressor 11, an oil pot 12, an oil separator 13, gas coolers 14a and 14b, intermediate pressure receivers 16a and 16b, a subcooling coil 17, an accumulator 18, a compressor accumulator 19, a control device 10, and the like. The showcase 2 includes an expansion valve 23, an evaporator 24, a control device 20, and the like. The refrigerant circuit of this embodiment is composed of the compressor 11, gas coolers 14a and 14b, expansion valve 23, evaporator 24, and piping P1 to P13 connecting them. The refrigeration system 100 shown in Figure 1 is a schematic representation of the basic configuration, and may include other components.

[0013] The compressor 11 compresses the refrigerant and supplies the compressed high-pressure refrigerant to the refrigerant circuit. The compressor 11 is a two-stage compressor having a first-stage compression section 11a and a second-stage compression section 11b. The refrigerant flowing through the discharge pipe P1 on the discharge side of the compressor 11 is supplied to the oil separator 13. In the oil separator 13, the refrigerant and the oil dissolved in the refrigerant are separated, and the refrigerant flows to the gas pipe P2. The bottom of the oil separator 13 and the side of the oil pot 12 are connected by an oil return pipe P3. The oil separated in the oil separator 13 is returned to the oil pot 12 through the oil return pipe P3. A strainer 131 is provided in the oil return pipe P3, and downstream of the strainer 131, the oil return pipe P3 is divided into two flow paths. One of the flow paths is equipped with a capillary tube 133 and a solenoid valve SV-OIL1, while the other flow path is equipped with a capillary tube 132. The amount of oil returned to the oil pot 12 is adjusted by the control device 10 opening and closing the solenoid valve SV-OIL1.

[0014] The top of the oil pot 12 is connected to the discharge side of the first-stage compression section 11a of the compressor 11 by piping. In addition to the oil flowing in from the oil return pipe P3, oil also flows into the oil pot 12 from the connecting pipe on the discharge side of the first-stage compression section 11a while the compressor 11 is operating. Furthermore, the bottom of the oil pot 12 is connected to the bottom of the compressor 11 by piping. The oil accumulated at the bottom of the oil pot 12 is returned to the compressor 11 through the piping at the bottom. A temperature sensor Tho-C1 is installed below the dome of the compressor 11.

[0015] The oil pot 12 is equipped with an OLS (oil level sensor) 12a. The OLS 12a detects the height of the oil level in the oil pot 12. When the oil level drops to a predetermined height (when the amount of oil in the compressor 11 falls below a predetermined amount), the OLS 12a outputs an oil-less signal to the control device 10 indicating a drop in the oil level.

[0016] A pipe P4 (hot gas bypass) is provided, connecting the gas pipe P2 to the return pipe P13, which is the flow path for the refrigerant returning from the load side (showcase 2). A strainer 134, a solenoid valve SVHG1, and a capillary tube 135 are provided in pipe P4. The flow of refrigerant in the hot gas bypass is controlled by opening and closing the solenoid valve SVHG1. In other words, when the control device 10 opens the solenoid valve SVHG1, the discharge side and suction side of the compressor 11 are connected, and the refrigerant flows through the hot gas bypass. During operation of the condensing unit 1, the refrigerant discharged by the compressor 11 flows through the discharge pipe P1 and gas pipe P2 without flowing through the hot gas bypass.

[0017] The high-temperature, high-pressure refrigerant discharged by the compressor 11 is supplied through the gas pipe P2 to the parallel-connected gas coolers 14a and 14b. The refrigerant supplied to the gas coolers 14a and 14b is cooled and condensed by heat exchange with the air supplied by the fans 15a and 15b. The refrigerant condensed in the gas coolers 14a and 14b passes through the strainer 141 located in the gas-liquid two-phase pipe P5, is reduced to an intermediate pressure by the expansion valve EEVG located on the inlet side of the intermediate-pressure receivers 16a and 16b, and is supplied to the intermediate-pressure receivers 16a and 16b.

[0018] Also, on the upstream side of the expansion valve EEVG in the gas-liquid two-phase pipe P5, a liquid bypass pipe P6 for returning the condensed refrigerant to the compressor 11 is connected. An expansion valve EEV-LB1 is provided in the liquid bypass pipe P6, and the control device 10 adjusts the amount of refrigerant flowing into the liquid bypass pipe P6 by controlling the opening degree of the expansion valve EEV-LB1. The liquid bypass pipe P6 is connected to an injection pipe P7 described later. The expansion valve EEV-LB1 is opened by the control device 10, for example, when the temperature on the discharge side of the compressor 11 becomes a predetermined temperature or higher. When the expansion valve EEV-LB1 opens, the refrigerant that has undergone heat exchange in the gas coolers 14a and 14b and is at a lower temperature than the discharge side of the compressor 11 is supplied through the liquid bypass pipe P6 and the injection pipe P7 to the intermediate-pressure section (the suction side of the second-stage compression section 11b) of the compressor 11, suppressing an excessive temperature rise on the discharge side of the compressor 11.

[0019] The intermediate-pressure receivers 16a and 16b separate the refrigerant in the gas-liquid two-phase state expanded by the expansion valve EEVG into a gas refrigerant, which is a gas-phase refrigerant, and a liquid refrigerant, which is a liquid-phase refrigerant. An injection pipe P7 is connected to the upper parts of the intermediate-pressure receivers 16a and 16b to send out the gas refrigerant. An expansion valve SV-INJ1 is provided in the injection pipe P7, and the control device 10 controls the pressure of the refrigerant flowing into the injection pipe P7 by controlling the opening degree of the expansion valve SV-INJ1. The intermediate-pressure gas refrigerant flowing into the injection pipe P7 is supplied to the intermediate-pressure section of the compressor 11 and recompressed by the second-stage compression section 11b. Thereby, the COP (Coefficient Of Performance) of the refrigeration cycle can be improved.

[0020] On one hand, the liquid refrigerant separated within the medium-pressure receivers 16a and 16b flows through the liquid pipe P8, passes through the strainer 161, and is cooled by the subcooling coil 17. Upstream of the subcooling coil 17, the subcooling pipe P9 is connected to the liquid pipe P8, and a part of the liquid refrigerant flowing out from the medium-pressure receivers 16a and 16b flows into the subcooling pipe P9. The liquid refrigerant flowing into the subcooling pipe P9 is depressurized by the expansion valve EEVSC for the subcooling coil to become low temperature, and in the subcooling coil 17, it cools the liquid refrigerant flowing through the liquid pipe P8 (the refrigerant supplied to the load side). The refrigerant branched into the subcooling pipe P9 flows into the accumulator 18 after passing through the subcooling coil 17.

[0021] The refrigerant flowing through the liquid pipe P8 is cooled by the subcooling coil 17, then flows out from the condensing unit 1 and is supplied to the liquid pipe P10 of the showcase 2. The refrigerant supplied from the condensing unit 1 passes through the drier 21 and the strainer 22, is depressurized by the expansion valve 23, and in the evaporator 24, cools the object through heat exchange with the air sent in by the fan 25. On the outlet side of the evaporator 24, a temperature sensor 26 for measuring the temperature of the refrigerant and a pressure sensor 27 for measuring the pressure of the refrigerant are provided. Near the evaporator 24, a temperature sensor 28 for measuring the temperature of the cooling object (showcase 2) is provided. After the heat exchange, the refrigerant returns to the condensing unit 1 through the pipe P11. In the condensing unit 1, the refrigerant returned from the load side flows into the accumulator 18 through the return pipe P12. On the upstream side of the accumulator 18 in the return pipe MP12, a temperature sensor Tho-S and a pressure sensor PSL for low-pressure measurement are provided.

[0022] The accumulator 18 separates the gas-liquid of the refrigerant. A part of the gas refrigerant separated by the accumulator 18 passes through the return pipe P13 and is supplied to the compressor accumulator 19 attached to the compressor 11. The gas refrigerant from which only the gas phase is further extracted by the compressor accumulator 19 is supplied to the suction side of the first-stage compression part 11a of the compressor 11 through the suction pipe P14.

[0023] The control device 10 of the condensing unit 1 is connected to various sensors such as the pressure sensor PSL, temperature sensor Tho-S, temperature sensor Tho-C1, various valves such as the expansion valve EEVG, and equipment such as the compressor 11. It acquires measured values ​​from each sensor and adjusts the rotation speed of the compressor 11 and the opening and closing of the expansion valve EEVG to operate the condensing unit 1. The control device 20 of the showcase 2 adjusts the opening degree of the expansion valve 23 based on the measured value of the temperature sensor 28 installed in the showcase 2 and the target temperature of the showcase 2, and works in conjunction with the control device 10 to control the temperature of the showcase 2 so that it reaches the target temperature. Furthermore, when predetermined conditions are met, the control devices 10 and 20 perform oil return control. In particular, in this embodiment, in addition to simply increasing the rotation speed of the compressor 11, it performs "coupled control with the loader expansion valve" in conjunction with the opening degree control of the expansion valve 23 of the showcase 2 to effectively return the oil accumulated in the showcase 2.

[0024] Figure 2 shows the functional block diagrams of control device 10 and control device 20. The control device 10 comprises an oil return control execution determination unit 101 and a control unit 102. The oil return control execution determination unit 101 determines whether to start oil return control and whether to end oil return control. The control device 10 and the control device 20 are connected in a communication manner, and if the oil return control execution determination unit 101 determines to start oil return control, it outputs an oil return control start signal to the control device 20. Also, if the oil return control execution determination unit 101 determines to end oil return control, it outputs an oil return control end signal to the control device 20. Examples of start and end conditions for oil return control are shown below.

[0025] <Regarding the start conditions> (1) When the set temperature of showcase 2 is higher than a predetermined value (e.g., -22 degrees Celsius) for refrigeration. The oil return control execution determination unit 101 determines to execute "coupled control with loader expansion valve" when it receives an oil-less signal from OLS12a for 100 seconds continuously. The oil return control execution determination unit 101 determines to execute "oil return by gas flow velocity" if the cumulative operating time of the compressor 11 since the last oil return control is above a threshold, or if the amount of oil coming up is above a threshold. In "oil return by gas flow velocity," the control unit 102 performs oil return control by increasing the rotational speed of the compressor 11 to the oil return rotational speed without stopping the compressor 11. The oil return rotational speed is a value that has been confirmed through experiments and calculations to be able to return oil to the compressor 11 when the compressor 11 is operated at this rotational speed. In addition, when executing "oil return by gas flow velocity," the control unit 202 maintains the state in which the expansion valve 23 is open. (2) In the case of freezing, when the set temperature of showcase 2 falls below a predetermined value. The oil return control execution determination unit 101 determines to execute "coupled control with loader expansion valve" when it receives an oil-less signal from OLS12a for 100 seconds continuously. The oil return control execution determination unit 101 determines to execute "coupled control with loader expansion valve" if the cumulative operating time of the compressor 11 since the last oil return control is above a threshold, or if the amount of oil rising is above a threshold.

[0026] <Regarding termination conditions> (1) With respect to the compressor 11, when L1 seconds (for example, 600 seconds) have elapsed since operation at a higher-than-normal oil return rotation speed began, the oil return control execution determination unit 101 determines that the oil return control should be terminated. (2) When the oil return control execution determination unit 101 determines that oil has returned and terminates the oil return control, it considers that oil return has occurred based on the superheating degree on the suction side of the compressor 11 or under the dome. For example, the oil return control execution determination unit 101 is equipped with a table that defines the relationship between the refrigerant pressure on the suction side of the compressor 11 and the saturation temperature of the refrigerant, and converts the pressure measured by the pressure sensor PSL into a saturation temperature Tc based on this table. Next, the oil return control execution determination unit 101 subtracts the saturation temperature Tc from the refrigerant temperature Td on the suction side of the compressor 11 measured by the temperature sensor Tho-S to calculate the superheating degree on the suction side of the compressor 11 (suction superheating degree). The oil return control execution determination unit 101 determines that the termination condition has been met when the suction superheating degree remains below X1 degrees for a continuous x1 second, or when the suction superheating degree remains below X2 degrees for a continuous x2 second. Alternatively, the oil return control execution determination unit 101 calculates the degree of superheating under the dome of the compressor 11 (referred to as the degree of superheating under the dome) by subtracting the saturation temperature Tc from the refrigerant temperature Te under the dome of the compressor 11 measured by the temperature sensor Tho-C1. The oil return control execution determination unit 101 determines that the termination condition has been met if the degree of superheating under the dome remains below Y degrees for y seconds. An example of X1, x1, X2, x2, Y, and y is shown below. (A) If the intake superheating degree at the start of oil return control is less than 15 degrees, X1 = 4 degrees, x1 = 12 seconds, X1 = 5 degrees, x1 = 20 seconds, Y = 7 degrees, y = 10 seconds. (B) If the intake superheating degree at the start of oil return control is 15 degrees or higher, X1 = 9 degrees, x1 = 12 seconds, X1 = 10 degrees, x1 = 20 seconds, Y = 7 degrees, y = 10 seconds.

[0027] The control unit 102 starts oil return control when the oil return control execution determination unit 101 determines that oil return control should be started, and terminates oil return control when the oil return control execution determination unit 101 determines that oil return control should be terminated. There are two types of oil return control: "oil return by gas flow velocity," which is a general type of oil return control, and "coupled control with loader expansion valve" as in this embodiment. The control unit 102 performs one of the oil return control methods (condensing unit side) based on the decision of the oil return control execution determination unit 101. The oil return control (condensing unit side) consists of starting, stopping, and controlling the rotational speed of the compressor 11.

[0028] The control device 20 comprises a signal receiving unit 201 and a control unit 202. The signal receiving unit 201 receives oil return control start signals and oil return control end signals from the control device 10. When the signal receiving unit 201 receives an oil return control start signal, the control unit 202 starts oil return control (showcase side), and when the signal receiving unit 201 receives an oil return control end signal, it terminates the oil return control. The oil return control (showcase side) is performed by controlling the opening degree of the expansion valve 23.

[0029] Next, using Figure 3, we will explain the oil return control of the "coupled control with the loader expansion valve". (1) When the oil return control execution determination unit 101 determines that oil return control should be started, the control unit 102 stops the compressor. At the same time, the control unit 202 completely closes the expansion valve 23. (2) The control unit 202 fully opens the expansion valve 23 after D seconds (for example, 120 seconds) have elapsed since the expansion valve 23 was fully closed. The period from when the expansion valve 23 is fully closed at the same time as the start of the oil return control of the "coupled control with loader expansion valve" until the expansion valve 23 is fully opened is called "control 1". (3) The control unit 102 waits for A seconds (for example, 180 seconds) with the compressor 11 stopped, then starts the compressor 11 and increases the rotational speed to the oil return speed (for example, 70 rps), and operates it at that speed until the termination condition for oil return control is met. In Figure 3, B seconds (for example, 70 seconds) is the preparation period for starting the compressor 11, and the following C seconds (for example, 120 seconds) is the period during which the compressor 11 is operated at the initial rotational speed (for example, 45 rps). After these steps, the compressor 11 is operated at the oil return speed, and when, for example, L1 seconds have elapsed (termination condition met), the control returns to normal. (4) On the other hand, with respect to the expansion valve 23, once "control 1" is completed, the control unit 202 performs normal control. For example, the control unit 202 performs superheat control. For example, the control unit 202 has a table that defines the relationship between the refrigerant pressure on the outlet side of the evaporator 24 and the saturation temperature of the refrigerant, and based on this table, the control unit 20 converts the pressure measured by the pressure sensor 27 into the saturation temperature Ta. Next, the control device 20 subtracts the saturation temperature Ta from the refrigerant temperature Tb on the outlet side of the evaporator 24 measured by the temperature sensor 26 to calculate the superheat on the outlet side of the evaporator 24 (referred to as the evaporator outlet superheat). The control unit 202 controls the opening degree of the expansion valve 23 so that the evaporator outlet superheat remains constant. Alternatively, the control unit 202 performs constant internal temperature control by controlling the opening degree of the expansion valve 23 so that the temperature measured by the temperature sensor 28 becomes the target temperature.

[0030] The values ​​exemplified above for the lengths of A-D seconds, L1 second, initial rotational speed, oil return rotational speed, etc., are examples only and are not limited to these. However, the lengths of A-D seconds are determined such that the following processing sequence is satisfied: at the start of oil return control, there is a period of time (for example, several minutes) during which the compressor 11 is stopped and the expansion valve 23 is fully closed, followed by a period of time during which the expansion valve 23 is fully open, and then the compressor 11 is started. The values ​​of A-C seconds and L1 second are registered in the control unit 102 of the control device 10, and the control unit 102 controls the compressor 11 based on these values ​​(independently and independently of the control device 20). The value of D second is registered in the control unit 202, and the control unit 202 controls the expansion valve 23 based on this value (independently and independently of the control device 10). When the compressor 11 and expansion valve 23 are coupled and controlled in this sequence, the compressor 11 is initially stopped and the expansion valve 23 is fully closed for a certain period of time. This maintains the low pressure on the compressor 11 side, and at the inlet side of the expansion valve 23, the high pressure on the discharge side of the compressor 11 and the medium pressure on the inlet side of the expansion valve 23 are equalized. As a result, the pressure at the inlet side of the expansion valve 23 becomes higher than before the oil return control began, creating a pressure difference greater than the original differential pressure before and after the expansion valve 23. Then, by fully opening the expansion valve 23, the oil accumulated in the load device is discharged to the suction side of the compressor 11 due to the differential pressure. Based on this principle, "coupled control with load device expansion valve" allows for the recovery of a larger amount of oil compared to "oil return by gas flow velocity," even when the load device is large in capacity and multiple units are connected, such as in a large store's display case, or when the piping length is long.

[0031] (operation) Next, referring to Figures 4 and 5, we will explain the flow of "coupled control with the loader expansion valve". Figure 4 is a flowchart showing an example of control on the condensing unit side according to the embodiment. The oil return control execution determination unit 101 determines whether to execute oil return control (step S1). The oil return control execution determination unit 101 determines whether the above-mentioned start conditions are met. If the start conditions are met, the oil return control execution determination unit 101 determines to execute oil return control; otherwise, it determines not to execute oil return control. If it is determined not to execute oil return control (step S1; No), the process of step S1 is repeated. If it is determined to execute oil return control (step S1; Yes), the oil return control execution determination unit 101 outputs an oil return control start signal to the control device 20 (step S2) and instructs the control unit 102 to start executing oil return control. In Figure 4, the following process is explained assuming that the start conditions for "coupled control with load expansion valve" of the two oil return controls are met. In this case, the oil return control start signal includes information instructing the execution of "coupled control with load expansion valve," and the instruction to the control unit 102 also includes information instructing the execution of "coupled control with load expansion valve."

[0032] When the control unit 102 is instructed to perform "coupled control with loader expansion valve," it stops the compressor 11 (step S3). The control unit 102 waits for a predetermined time (A seconds in Figure 3) with the compressor 11 stopped (step S4). After that, the control unit 102 starts the compressor 11 and operates it at a predetermined rotational speed (oil return rotational speed) (step S5).

[0033] The oil return control execution determination unit 101 determines whether to terminate the oil return control (step S6). The oil return control execution determination unit 101 determines whether the above termination conditions are met. If the termination conditions are met, the oil return control execution determination unit 101 determines to terminate the oil return control; otherwise, it determines not to terminate the oil return control. If it is determined not to terminate the oil return control (step S6; No), the oil return control execution determination unit 101 repeatedly executes the process in step S6 at a predetermined control cycle. If it is determined to terminate the oil return control (step S6; Yes), the oil return control execution determination unit 101 outputs an oil return control termination signal to the control device 20 (step S7) and instructs the control unit 102 to terminate the oil return control. The control unit 102 reduces the rotational speed of the compressor 11 from the oil return rotational speed and performs normal control.

[0034] Figure 5 is a flowchart showing an example of oil return control on the showcase side according to the embodiment. The signal receiving unit 201 determines whether it has received an oil return control start signal from the control device 10 (step S11). If the oil return control start signal has not been received (step S11; No), step S11 is repeated. If the oil return control start signal has been received (step S11; Yes), the signal receiving unit 201 instructs the control unit 202 to start executing the oil return control. Figure 5 describes the following process assuming that the start condition for "coupled control with loader expansion valve" has been met.

[0035] When the control unit 202 is instructed to perform "oil return control," it completely closes the expansion valve 23 (step S12). The control unit 202 waits for a predetermined time (D seconds in Figure 3) with the expansion valve 23 completely closed (step S13). After that, the control unit 202 completely opens the expansion valve 23 (step S14). After that, the control unit 202 performs normal control (step S15). For example, the control unit 202 performs superheating control and constant internal temperature control.

[0036] The signal receiving unit 201 determines whether it has received an oil return control termination signal from the control device 10 (step S16). If the oil return control termination signal has not been received (step S16; No), step S16 is repeated. If the oil return control termination signal has been received (step S16; Yes), the signal receiving unit 201 instructs the control unit 202 to terminate the oil return control.

[0037] As explained above, according to the "coupled control with the loader expansion valve" of this embodiment, even in situations where oil tends to accumulate in the loader due to the loader's specifications (capacity, number of units) and construction conditions, the oil can be reliably returned to the compressor 11, ensuring the reliability of the compressor 11. Furthermore, although the operation of the compressor 11 is temporarily stopped in the "coupled control with the loader expansion valve," the impact on the temperature of the showcase 2 can be suppressed by limiting the starting conditions. In the above embodiment, the control device 10 that controls the condensing unit 1 and the control device 20 that controls the showcase 2 are provided separately, but the control devices 10 and 20 may be implemented as a single control device.

[0038] Figure 5 shows an example of the hardware configuration of a control device according to an embodiment. The computer 900 includes a CPU 901, main memory 902, auxiliary memory 903, input / output interface 904, and communication interface 905. Control devices 10 and 20 are implemented in the computer 900. The functions described above are stored in the auxiliary memory 903 in the form of a program. The CPU 901 reads the program from the auxiliary memory 903, expands it in the main memory 902, and executes the above processing according to the program. The CPU 901 also allocates a memory area in the main memory 902 according to the program. The CPU 901 also allocates a memory area in the auxiliary memory 903 to store the data being processed according to the program.

[0039] A program for realizing all or part of the functions of control devices 10 and 20 may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be loaded into a computer system and executed to perform processing by each functional unit. Here, "computer system" includes hardware such as the OS and peripheral devices. Furthermore, if a WWW system is used, "computer system" also includes the homepage provisioning environment (or display environment). Furthermore, "computer-readable recording medium" refers to portable media such as CDs, DVDs, USBs, and storage devices such as hard disks built into the computer system. Furthermore, if this program is distributed to computer 900 via a communication line, computer 900 that receives the program may load it into main memory 902 and execute the above processing. Furthermore, the above program may be for realizing only a part of the functions described above, and may also be able to realize the above functions in combination with programs already recorded in the computer system.

[0040] Furthermore, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, without departing from the spirit of the present invention. Also, the technical scope of this invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0041] <Note> The control device, condensing unit, control method, and program for each embodiment of the condensing unit can be understood, for example, as follows.

[0042] (1) The control device 10 according to the first embodiment is a control device 10 for the condensing unit 1 in a refrigeration system 100 which includes a condensing unit 1 comprising the compressor 11 and the gas coolers (14a, 14b) of a refrigerant circuit including a compressor 11, gas coolers 14a, 14b, expansion valve 23 and utilization-side heat exchanger (evaporator 24), and a load equipment (showcase 2) comprising the expansion valve 23 and the utilization-side heat exchanger (evaporator 24), wherein when predetermined start conditions are met, the control device initiates oil return control to return the oil discharged from the compressor 11 together with the refrigerant back to the compressor 11. The system includes means (S2) for outputting a start instruction signal to the load equipment to instruct the start of the expansion valve, means (S3) for stopping the compressor, assuming that the load equipment fully closes the expansion valve based on the start instruction signal (S11, S12), and means for starting the compressor after the waiting time has elapsed, based on a predetermined waiting time (A seconds) set to be longer than the time (D seconds) from when the load equipment fully closes the expansion valve until it fully opens, and operating the compressor by increasing its rotational speed to a predetermined oil return rotational speed that allows the oil to be recovered into the compressor. This allows the oil accumulated in the load unit to be returned to the compressor, regardless of the load unit's specifications (capacity, number of units) or installation conditions.

[0043] (2) The control device according to the second embodiment is the control device according to (1), wherein the predetermined condition is one of the following: when the load equipment is refrigerated, a sensor for detecting the amount of oil in the compressor detects that the amount of oil in the compressor has decreased below a predetermined amount; when the load equipment is frozen, a sensor for detecting the amount of oil in the compressor detects that the amount of oil in the compressor has decreased below a predetermined amount; or when the load equipment is frozen, the continuous operating time of the compressor is above a predetermined threshold. The influence on the load equipment (influence due to temperature changes) can be suppressed by limiting the opportunities for oil return control that involves stopping the compressor (in the case of refrigeration where there is no margin for temperature changes, oil return control that involves stopping the compressor is performed only when no oil is detected).

[0044] (3) The control device according to the third embodiment is the control device described in Appendix (2), further comprising means for controlling the return of oil to the compressor by increasing the rotational speed of the compressor to the oil return rotational speed without stopping the compressor when the continuous operating time of the compressor exceeds a predetermined threshold when the load is refrigerated. By limiting the opportunities for oil return control that involve stopping the compressor, the impact on the load equipment (influence of temperature changes) can be suppressed.

[0045] (4) The control device according to the fourth embodiment is the control device described in any of the appendices (1) to (3), further comprising means for determining that the oil return control should be terminated when a predetermined time has elapsed since the start of the oil return control, or when the superheating level on the suction side of the compressor or the superheating level below the dome of the compressor reaches a state in which liquid back can be considered to be occurring. This allows the oil return control to be terminated.

[0046] (5) The condensing unit according to the fifth embodiment comprises a compressor, a gas cooler for cooling the refrigerant discharged by the compressor, and a control device for the condensing unit as described in any of the appendices (1) to (4). This ensures that oil is reliably returned to the compressor 11 regardless of the specifications (capacity, number) of the condensing unit's loaders or the installation conditions.

[0047] (6) A control method according to a sixth embodiment is a control method for a condensing unit in a refrigeration system, which includes a condensing unit comprising a compressor and the gas cooler, and a load equipment comprising the expansion valve and the utilization-side heat exchanger, comprising: a step of outputting a start instruction signal to the load equipment to instruct the start of oil return control, which returns oil discharged from the compressor together with the refrigerant to the compressor, when a predetermined start condition is met; a step of stopping the compressor, assuming that the load equipment fully closes the expansion valve based on the start instruction signal; and a step of starting the compressor after the waiting time has elapsed since the compressor was stopped, based on a predetermined waiting time set to be longer than the time it takes for the load equipment to fully open the expansion valve after it has fully closed, and operating the compressor by increasing its rotational speed to a predetermined oil return rotational speed that can recover the oil into the compressor.

[0048] (7) The program according to the seventh aspect causes a computer that controls the condensing unit in a refrigeration system, which includes a condensing unit comprising a compressor and the gas cooler, and a load equipment comprising the expansion valve and the utilization-side heat exchanger, to function as follows: when predetermined start conditions are met, a means to output a start instruction signal to the load equipment that instructs the start of oil return control to return oil discharged from the compressor together with the refrigerant to the compressor; a means to stop the compressor, assuming that the load equipment fully closes the expansion valve based on the start instruction signal; and a means to start the compressor after the waiting time has elapsed, based on a predetermined waiting time set to be longer than the time it takes for the load equipment to fully open the expansion valve after it has been stopped, and to operate the compressor by increasing its rotational speed to a predetermined oil return rotational speed that can recover the oil into the compressor. [Explanation of symbols]

[0049] 100...Refrigeration system, 1...Condensing unit, 11...Compressor, 12...Oil pot, 13...Oil separator, 14a, 14b...Gas cooler, 15a, 15b...Fan, 16a, 16b...Intermediate pressure receiver, 17...Supercooling coil, 18...Accumulator, 19...Compressor accumulator, 10...Control device, 101...Oil return control execution determination unit, 102...Control unit, 2...Showcase, 20...Control device, 201...Signal receiving unit, 202...Control unit, 23...Expansion valve, 24...Evaporator, 900...Computer, 901...CPU, 902...Main memory, 903...Auxiliary memory, 904...Input / output interface, 905...Communication interface

Claims

1. A control device for a condensing unit in a refrigeration system, which includes a condensing unit comprising a compressor and a gas cooler, and load equipment comprising an expansion valve and a utilization-side heat exchanger, wherein the condensing unit comprises a compressor and a gas cooler, and a load equipment comprising an expansion valve and a utilization-side heat exchanger, A means for outputting a start instruction signal to the load equipment when predetermined start conditions are met, which instructs the start of oil return control, which returns the oil discharged from the compressor along with the refrigerant back to the compressor, Assuming that the load equipment fully closes the expansion valve based on the start instruction signal, means for stopping the compressor, A means for operating the compressor by stopping it, then starting it after the waiting time has elapsed, based on a predetermined waiting time set to be longer than the time it takes for the load equipment to fully close and then fully open the expansion valve, and increasing the rotational speed of the compressor to a predetermined oil return rotational speed that allows the oil to be recovered into the compressor, A control device for a condensing unit equipped with [a specific feature].

2. The aforementioned predetermined conditions are: If the load equipment is refrigerated, and the sensor that detects the amount of oil in the compressor detects that the amount of oil in the compressor has decreased below a predetermined amount, In the case where the load equipment is refrigerated, the sensor that detects the amount of oil in the compressor detects that the amount of oil in the compressor has decreased below a predetermined amount, or in the case where the load equipment is refrigerated, the continuous operating time of the compressor exceeds a predetermined threshold. A control device for a condensing unit according to claim 1.

3. When the load equipment is refrigerated, if the continuous operating time of the compressor exceeds a predetermined threshold, assuming that the load equipment keeps the expansion valve open, a means for controlling the return of oil to the compressor by increasing the rotational speed of the compressor to the oil return rotational speed without stopping the compressor, A control device for a condensing unit according to claim 2, further comprising the above.

4. Means for determining that the oil return control will be terminated when a predetermined time has elapsed since the start of the oil return control, or when the superheating level on the suction side of the compressor or the superheating level below the dome of the compressor reaches a state in which liquid back is considered to be occurring. A control device for a condensing unit according to claim 1 or claim 2, further comprising the above.

5. Compressor and, A gas cooler for cooling the refrigerant discharged by the compressor, A control device for a condensing unit according to claim 1 or claim 2, A condensing unit equipped with [a specific feature].

6. A method for controlling a condensing unit in a refrigeration system, which includes a condensing unit comprising a compressor and a gas cooler, and load equipment comprising an expansion valve and a utilization-side heat exchanger, wherein the condensing unit comprises a compressor and a gas cooler, and a load equipment comprising an expansion valve and a utilization-side heat exchanger, When predetermined start conditions are met, a start instruction signal is output to the load equipment to instruct the start of oil return control, which returns the oil discharged from the compressor along with the refrigerant back to the compressor. The step of stopping the compressor, assuming that the load equipment fully closes the expansion valve based on the start instruction signal, The steps include: stopping the compressor and then starting it after the waiting time has elapsed, based on a predetermined waiting time set to be longer than the time it takes for the load equipment to fully close and then fully open the expansion valve, and then increasing the rotational speed of the compressor to a predetermined oil return rotational speed at which the oil can be recovered into the compressor; A control method having

7. A computer for controlling the condensing unit in a refrigeration system, which includes a condensing unit comprising a compressor and the gas cooler, and load equipment comprising the expansion valve and the heat exchanger on the utilization side, is provided. A means for outputting a start instruction signal to the load equipment when predetermined start conditions are met, which instructs the start of oil return control, which returns the oil discharged from the compressor along with the refrigerant back to the compressor. Assuming that the load equipment fully closes the expansion valve based on the start instruction signal, means for stopping the compressor, Means for operating the compressor by stopping it, starting it after the waiting time has elapsed, based on a predetermined waiting time set to be longer than the time it takes for the load equipment to fully close and then fully open the expansion valve, and increasing the rotational speed of the compressor to a predetermined oil return rotational speed at which the oil can be recovered into the compressor, A program designed to function as such.

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