Refrigeration cycle device

Abstract

The present invention ensures reliability of a compressor at the startup of an air conditioner, and improves startup capability. The present invention comprises: a refrigerant circuit (C) in which a compressor (1), a condenser (2), a decompression mechanism (3), and an evaporator (4) are sequentially connected by refrigerant piping, and through which a refrigerant circulates; a condenser fan (21) that sends air to the condenser (2); a condensation temperature detection sensor (22) that detects the condensation temperature of the refrigerant at startup; a condenser suction air temperature detection sensor (23) that detects the temperature of the air sucked into the condenser (2); and a control device (6) that switches between startup control and normal control. The control device (6) executes the startup control at startup, and terminates the startup control and switches to the normal control when a startup temperature difference obtained by subtracting the air temperature detected by the condenser suction air temperature detection sensor (23) from the condensation temperature detected by the condensation temperature detection sensor (22) is greater than a preset temperature difference threshold value.

Description

Refrigeration Cycle Equipment

[0001] An embodiment of the present invention relates to a refrigeration cycle device.

[0002] In recent years, demand for air conditioners in cold regions has been increasing. Air conditioners used in cold regions are often operated in low outdoor temperatures, especially when heating. Generally, energy efficiency tends to decrease when operating in low outdoor temperatures, but even in such cases, improvements in energy efficiency are required.

[0003] Normally, when an air conditioner starts up (when the compressor starts operating), refrigerant is drawn into the compressor even though no refrigerant is circulating in the refrigerant circuit included in the refrigeration cycle device. Therefore, the amount of refrigerant on the low-pressure side tends to decrease during startup. Furthermore, when used in cold regions or other low outdoor temperatures, not only the compressor but also the refrigerant is cold, so the refrigerant is drawn into the compressor in a condensed state.

[0004] Furthermore, if an air conditioner is stopped for a long period of time at low outdoor temperatures, refrigerant may accumulate in the compressor. When the air conditioner is started under these conditions, the refrigerant is compressed and condensed inside the compressor, resulting in a smaller amount of refrigerant being discharged than when the outdoor temperature is high. As a result, the amount of refrigerant circulating in the refrigeration cycle is insufficient, and the amount of refrigerant drawn into the compressor is also reduced. This may cause the suction pressure of the compressor to fall below the lower limit of its specifications, raising concerns about a decrease in compressor reliability.

[0005] Therefore, in the invention disclosed in the following Patent Document 1, the refrigerant that has accumulated in the receiver while the air conditioner is stopped is released into the refrigerant circuit when the air conditioning operation is started. By increasing the amount of refrigerant circulating through the refrigerant circuit when the air conditioning operation is started in this way, the above-mentioned inconveniences are eliminated and the reliability of the compressor is ensured.

[0006] JP 2014-119144 A

[0007] However, the air conditioner disclosed in the aforementioned Patent Document 1 attempts to solve this problem by increasing the amount of refrigerant circulating within the refrigerant circuit. Therefore, the expansion valve is opened to a large degree, and the timing for terminating the startup control is set to the timing when the refrigeration cycle is stabilized. Generally, the appropriate opening of the expansion valve is set to, for example, an opening that allows the refrigerant drawn into the compressor to be in a gas phase, which is smaller than the opening during startup control. Therefore, the expansion valve is maintained at an unnecessarily large opening from the time when the suction pressure of the compressor is no longer at a risk of falling below the lower limit of the specifications until the refrigeration cycle is stabilized. This increases the time required to reach the appropriate opening, potentially resulting in poor start-up performance.

[0008] An object of the present invention is to provide a refrigeration cycle device that can ensure the reliability of a compressor when starting an air conditioner and can improve start-up performance.

[0009] A refrigeration cycle device according to one aspect of the present invention comprises a refrigerant circuit in which a compressor, a condenser, a pressure reduction mechanism, and an evaporator are connected in sequence by refrigerant piping and through which a refrigerant circulates; a condenser fan that sends air to the condenser; a condensation temperature detection sensor that detects the condensation temperature of the refrigerant when the compressor is started; a condenser intake air temperature detection sensor that detects the temperature of the air drawn into the condenser by the condenser fan; and a control device that switches between startup control that controls the opening of the pressure reduction mechanism at the start of the compressor to fix it at a preset startup opening, and normal control that controls the opening of the pressure reduction mechanism to a normal opening depending on the state of the refrigerant circulating through the refrigerant circuit. The control device performs the startup control when the compressor is started, and terminates the startup control and switches to normal control when a startup temperature difference obtained by subtracting the air temperature detected by the condenser intake air temperature detection sensor from the condenser temperature detection sensor is greater than a preset temperature difference threshold.

[0010] According to the present invention, a refrigeration cycle device is provided that can ensure the reliability of the compressor when starting up an air conditioner and can improve the start-up performance.

[0011] 1 is a refrigerant circuit diagram of a refrigeration cycle apparatus according to an embodiment of the present invention.

[0024] FIG. 2 is a graph schematically illustrating the relationship between the aperture of a pressure reducing mechanism and the pressure of a refrigerant in a refrigerant circuit over time, with respect to the control of a conventional refrigeration cycle apparatus, where FIG. 2(A) shows the relationship between the aperture of the pressure reducing mechanism and time, and FIG. 2(B) shows the relationship between the refrigerant pressure and time.

[0025] FIG. 3 is a block diagram illustrating the internal configuration of a control device for a refrigeration cycle apparatus according to an embodiment of the present invention.

[0026] FIG. 4 is a graph schematically illustrating the relationship between the aperture of a pressure reducing mechanism and the pressure of a refrigerant in a refrigerant circuit over time, with respect to the control of a refrigeration cycle apparatus according to an embodiment of the present invention, where FIG. 4(A) shows the relationship between the aperture of the pressure reducing mechanism and time, and FIG. 4(B) shows the relationship between the low-pressure side refrigerant pressure and time.

[0027] FIG. 5 is a graph schematically illustrating the relationship between the aperture of a pressure reducing mechanism and the pressure of a refrigerant in a refrigerant circuit over time, with respect to the control of a refrigeration cycle apparatus according to an embodiment of the present invention, where FIG. 5(A) shows the relationship between the aperture of the pressure reducing mechanism and time, and FIG. 5(B) shows the relationship between the low-pressure side refrigerant pressure and time.

[0028] FIG. 6 is a flowchart illustrating a basic flow of control of the aperture of the pressure reducing mechanism at the start of a refrigeration cycle apparatus according to an embodiment of the present invention. 1 is a flowchart relating to control of the opening degree of the pressure reducing mechanism at the time of start-up of the refrigeration cycle device according to an embodiment of the present invention. 2 is a flowchart relating to control of the opening degree of the pressure reducing mechanism at the time of start-up of the refrigeration cycle device according to an embodiment of the present invention. 3 is a flowchart relating to control of the opening degree of the pressure reducing mechanism during normal control of the refrigeration cycle device according to an embodiment of the present invention.

[0012] The structure of a refrigeration cycle apparatus S according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a refrigerant circuit diagram of the refrigeration cycle apparatus S according to the embodiment of the present invention. The refrigeration cycle apparatus S according to the embodiment of the present invention shown in Fig. 1 has a refrigerant circuit C in which a compressor 1, an indoor heat exchanger 2, a pressure reducing mechanism 3, and an outdoor heat exchanger 4 are connected in sequence by refrigerant piping, and through which a refrigerant circulates.

[0013] A four-way valve 5 is provided between the compressor 1 and the indoor heat exchanger 2, and between the compressor 1 and the outdoor heat exchanger 4. The four-way valve 5 switches whether the refrigerant discharged from the compressor flows to the indoor heat exchanger 2 side or the outdoor heat exchanger 4 side.

[0014] The compressor 1 draws in the refrigerant circulating through the refrigerant circuit C, compresses it, and discharges it into the refrigerant circuit C. A discharge temperature detection sensor 11 is provided on the discharge side of the compressor 1 to detect the temperature of the refrigerant discharged from the compressor 1.

[0015] The indoor heat exchanger 2 is disposed inside the indoor unit installed in the indoor space. For example, in heating operation, the indoor heat exchanger 2 exchanges heat between the refrigerant and the air flowing into the indoor unit, and supplies the heated air to the indoor space by absorbing heat from the refrigerant.

[0016] The indoor unit is also provided with an indoor fan 21. The indoor fan 21 takes in indoor air and supplies the air that has undergone heat exchange with the refrigerant into the room. Furthermore, a refrigerant temperature detection sensor 22 is also provided to detect the temperature of the two-phase refrigerant flowing through the indoor heat exchanger 2.

[0017] As the indoor fan 21 rotates in this manner, indoor air is drawn into the indoor unit (indoor heat exchanger 2). In the refrigeration cycle apparatus S according to the embodiment of the present invention, an intake air temperature detection sensor 23 is provided to detect the temperature of the air drawn into the indoor unit.

[0018] In the refrigerant circuit C, a pressure reduction mechanism 3 is provided between the indoor heat exchanger 2 and the outdoor heat exchanger 4. The pressure reduction mechanism 3 is, for example, an expansion valve, and reduces the pressure of the high-pressure refrigerant that has passed through the indoor heat exchanger 2 or the outdoor heat exchanger 4. The pressure reduction mechanism 3 is controlled by a pressure reduction mechanism control unit 65, which will be described later.

[0019] The outdoor heat exchanger 4 is disposed inside an outdoor unit that is installed outdoors. For example, during heating operation, in the outdoor heat exchanger 4, heat is exchanged between the refrigerant and the air (outdoor air) flowing into the outdoor unit, and heat of the outdoor air is absorbed by the refrigerant.

[0020] The outdoor unit is provided with an outdoor fan 41. The outdoor fan 41 takes in air into the outdoor unit and expels the air that has exchanged heat with the refrigerant to the outside. The outdoor unit is also provided with a refrigerant temperature detection sensor 42 that detects the temperature of the two-phase refrigerant flowing through the outdoor heat exchanger 4.

[0021] Furthermore, as described above, outdoor air is drawn into the outdoor unit (outdoor heat exchanger 4) by the rotation of the outdoor fan 41, and an intake air temperature detection sensor 43 is provided to detect the temperature of the air drawn into the outdoor unit. The temperature of the air drawn into the outdoor unit, acquired by the intake air temperature detection sensor 43, is the temperature outdoors where the outdoor unit is installed (outdoor air temperature).

[0022] The flow of refrigerant in the refrigerant circuit C when the refrigeration cycle apparatus S performs heating operation is as follows. During heating operation, high-temperature, high-pressure gas refrigerant discharged from the compressor 1 flows into the indoor heat exchanger 2 via the four-way valve 5. In the indoor heat exchanger 2, heat is exchanged between the refrigerant and indoor air, and heated air is supplied into the room. The high-temperature, high-pressure gas refrigerant releases heat through heat exchange as it passes through the indoor heat exchanger 2, becoming a high-pressure liquid refrigerant.

[0023] The high-pressure liquid refrigerant that flows out of the indoor heat exchanger 2 flows into the pressure reduction mechanism 3. The high-pressure liquid refrigerant is reduced in pressure as it passes through the pressure reduction mechanism 3, becoming a low-pressure two-phase refrigerant. The low-pressure two-phase refrigerant that flows out of the pressure reduction mechanism 3 then flows into the outdoor heat exchanger 4. In the outdoor heat exchanger 4, heat is exchanged between the low-pressure two-phase refrigerant and the outside air, causing the refrigerant to absorb heat and become a low-pressure gas refrigerant, which is then drawn into the compressor 1 via the four-way valve 5.

[0024] On the other hand, when the refrigeration cycle apparatus S performs cooling operation, the flow of refrigerant in the refrigerant circuit C is as follows: When cooling operation is performed, high-temperature, high-pressure gas refrigerant discharged from the compressor 1 flows into the outdoor heat exchanger 4 via the four-way valve 5. The refrigerant that has flowed into the outdoor heat exchanger 4 exchanges heat with the outside air, dissipating heat and becoming a high-pressure liquid refrigerant.

[0025] The high-pressure liquid refrigerant flowing out of the outdoor heat exchanger 4 flows into the pressure reducing mechanism 3, where it is reduced in pressure and becomes a low-pressure two-phase refrigerant. It then flows into the indoor heat exchanger 2, and exchanges heat with the indoor air as it passes through the indoor heat exchanger 2, causing the low-pressure two-phase refrigerant to absorb heat and become a low-pressure gas refrigerant. The cooled air is then supplied into the room. The low-pressure gas refrigerant flowing out of the indoor heat exchanger 2 is drawn into the compressor 1 via the four-way valve 5.

[0026] Next, the control at the time of startup of the refrigeration cycle apparatus S in the embodiment of the present invention will be described below. Note that the control content described below can be executed regardless of whether the refrigeration cycle apparatus S is performing heating operation or cooling operation. However, for convenience of explanation, the startup control when the refrigeration cycle apparatus S is performing heating operation will be described as an example.

[0027] The flow of the refrigerant when the refrigeration cycle apparatus S performs heating operation is as described above. During heating operation, the indoor heat exchanger 2 functions as a condenser, while the outdoor heat exchanger 4 functions as an evaporator.

[0028] Therefore, in the following description, the indoor fan 21 provided in the indoor unit will be referred to as the condenser fan 21. Similarly, the refrigerant temperature detection sensor 22 will be referred to as the condensation temperature detection sensor 22. Furthermore, the intake air temperature detection sensor 23 will be referred to as the condenser intake air temperature detection sensor 23.

[0029] As described above, particularly when the refrigeration cycle apparatus S is used in a cold region where the outside air temperature is low, when the operation of the refrigeration cycle apparatus S is started and the compressor 1 is activated, the amount of refrigerant discharged from the compressor 1 decreases. As a result, the amount of refrigerant circulating in the refrigerant circuit C becomes insufficient, and the amount of refrigerant drawn into the compressor 1 also decreases. To solve this problem, in the above-mentioned Patent Document 1, the opening degree of the pressure reducing mechanism 3 is maintained large to increase the amount of refrigerant circulating in the refrigerant circuit C.

[0030] However, when such control is performed and the operating mode transitions from startup control to normal control, there is a large discrepancy between the opening degree of the pressure reducing mechanism 3 in startup control and the opening degree of the pressure reducing mechanism 3 in normal control. Therefore, when feedback control in normal control is performed, the opening degree of the pressure reducing mechanism 3 gradually transitions from the opening degree of the pressure reducing mechanism 3 in startup control to the opening degree required in normal control, resulting in poor start-up performance.

[0031] Before describing the startup control in the embodiment of the present invention, the control described in the above-mentioned Patent Document 1 will be described for comparison. Figure 2 is a graph showing the relationship between the opening of the expansion valve (pressure reducing mechanism) and the refrigerant pressure in the refrigerant circuit over time. Figure 2(A) shows the relationship between the pressure reducing mechanism opening and time, and Figure 2(B) shows the relationship between the refrigerant pressure and time.

[0032] In Fig. 2(A), the vertical axis represents the opening degree of the pressure reducing mechanism, and the horizontal axis represents time. On the other hand, in Fig. 2(B), the vertical axis represents the refrigerant pressure, and the horizontal axis represents time. Note that in both Fig. 2(A) and Fig. 2(B), the point M where the horizontal axis intersects with the vertical axis represents the start time of the air conditioner (compressor).

[0033] First, using Figure 2(B), we will explain how the refrigerant pressure changes over time after the air conditioner starts operating. In Figure 2(B), the two-dot chain line shows the change in the high-pressure side refrigerant pressure, and the dashed line shows the change in the low-pressure side refrigerant pressure. When the air conditioner starts operating and the compressor starts, the high-pressure side refrigerant pressure gradually increases and becomes approximately constant at a certain point.

[0034] On the other hand, the refrigerant pressure on the low-pressure side is roughly equal to the refrigerant pressure on the high-pressure side at startup, but drops immediately after startup. This is because the amount of refrigerant flowing into the compressor decreases, as described above. In Figure 2B, a dotted line is shown parallel to and close to the horizontal axis, which indicates the passage of time. This dotted line indicates the lower limit of the specified suction pressure of the compressor.

[0035] When the compressor starts, the refrigerant pressure on the low-pressure side drops to near the lower limit of the specifications, then begins to rise and remains roughly constant. After a certain amount of time has passed since the compressor started, both the high-pressure and low-pressure refrigerant pressures are maintained at roughly constant pressures.

[0036] The refrigeration cycle is stable when the refrigerant pressures on the high-pressure side and the low-pressure side are constant. In the above-mentioned Patent Document 1, startup control of the air conditioner is performed until the refrigeration cycle is stabilized, and after the refrigeration cycle is stabilized, the operation mode is switched from startup control to normal control.

[0037] In Figures 2A and 2B, dotted lines parallel to the vertical axis are shown. These lines indicate the timing at which the air conditioner switches from startup control to normal control. As shown in Figure 2B, at the timing indicated by the dotted line, both the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure are approximately constant, so the refrigeration cycle is in a stable state to the right of the dotted line. Therefore, at the timing indicated by the dotted line, the operating mode switches from startup control to normal control.

[0038] Specifically, in the invention described in Patent Document 1, as shown in Fig. 2A, the opening of the pressure reducing mechanism is set large during startup control, and after transition to normal control, the opening of the pressure reducing mechanism is gradually reduced. However, this type of control has the following problems.

[0039] That is, as indicated by the double-headed arrow denoted by the symbol X, the opening degree of the pressure reducing mechanism is fixed for a certain period of time after the compressor is started. Therefore, while startup control is being performed, the opening degree of the pressure reducing mechanism is maintained at a value greater than necessary, which lengthens the time it takes for the opening degree of the pressure reducing mechanism to reach the appropriate opening degree. This may result in a deterioration in start-up capability.

[0040] Furthermore, when the startup control is terminated and normal control is initiated, feedback control is performed to adjust the discharge temperature to a target temperature, for example, to approach the user-specified air-conditioning operation temperature. The aperture of the pressure-reducing mechanism is controlled based on this feedback control. However, as indicated by the double-headed arrow Y in FIG. 2A , there is a large difference between the aperture of the pressure-reducing mechanism during startup control and that during normal control. This is because the appropriate aperture of the pressure-reducing mechanism during normal control is set to, for example, a value that allows the refrigerant drawn into the compressor to be in a gaseous state, and is therefore smaller than the aperture during startup control. Performing such control during normal control increases the enthalpy difference between the evaporator inlet and outlet, thereby increasing the air-conditioning capacity without unnecessarily increasing the compressor rotation speed, resulting in favorable operation in terms of energy conservation.

[0041] However, there is a large difference between the opening degree of the pressure reduction mechanism in startup control and that in normal control. Therefore, with feedback control, it takes time for the opening degree of the pressure reduction mechanism in startup control to reach the opening degree of the pressure reduction mechanism in normal control, which is required for energy-efficient operation. In other words, when the air conditioner performs heating operation, for example, it takes time for heated air to be supplied to the room, which results in a deterioration in the so-called start-up performance.

[0042] Next, a description will be given of the startup control performed in the embodiment of the present invention. In the embodiment of the present invention, the refrigeration cycle apparatus S is controlled as described below, thereby improving the startup performance while ensuring the reliability of the compressor 1 at the time of startup of the refrigeration cycle apparatus S.

[0043] First, a description will be given of each part of the control device 6. The control device 6 switches between startup control, which controls the opening degree of the pressure reducing mechanism 3 at startup, and normal control, which controls the opening degree of the pressure reducing mechanism 3 after the startup control ends.

[0044] When the startup control is executed by the control device 6, the opening degree of the pressure reducing mechanism 3 is fixed to a preset startup opening degree. By fixing the opening degree of the pressure reducing mechanism 3, a large amount of refrigerant is circulated through the refrigerant circuit C when the refrigeration cycle apparatus S is started up.

[0045] In contrast, in normal control, control is performed according to the state of the refrigerant circulating through the refrigerant circuit C. That is, the control device 6 performs feedback control using parameters indicating the states of various refrigerants so that the opening degree of the pressure reducing mechanism 3 becomes the normal opening degree.

[0046] Furthermore, when the opening degree of the pressure reducing mechanism 3 at the startup opening degree and the normal opening degree are compared, the startup opening degree is larger than the normal opening degree. That is, the opening degree of the pressure reducing mechanism 3 at the normal control is set in consideration of energy saving, and therefore is smaller than the opening degree of the pressure reducing mechanism 3 at the startup control degree.

[0047] In this way, the opening degree of the pressure reducing mechanism 3 in the startup control differs from the opening degree of the pressure reducing mechanism 3 in the normal control. Therefore, the control device 6 controls the opening degree of the pressure reducing mechanism 3 in each of the startup control of the refrigeration cycle apparatus S, the control for transitioning the operation mode from the startup control to the normal control, and the normal control.

[0048] The specific control will be described later, but when it is determined that the temperature difference between the condensation temperature detected by the condensation temperature detection sensor 22 and the air temperature detected by the condenser intake air temperature detection sensor 23 (hereinafter, this temperature difference will be referred to as the "start-up temperature difference") is greater than a predetermined temperature difference threshold, the startup control is terminated and control is switched to normal control.

[0049] 3 is a block diagram showing the internal configuration of the control device 6 of the refrigeration cycle apparatus S according to the embodiment of the present invention. The control device 6 includes an information acquisition unit 61, a calculation unit 62, a comparison unit 63, a storage unit 64, and a pressure reduction mechanism control unit 65.

[0050] In addition, the control device 6 is provided with various other functions for controlling the refrigeration cycle apparatus S. However, hereinafter, with regard to the control device 6, only the functions necessary for operation control of the refrigeration cycle apparatus S in the embodiment of the present invention will be described.

[0051] That is, the control device 6 may have a configuration in which, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input / output interface are connected via a bus, which are not shown in Fig. 3. Furthermore, the input / output interface may be connected to the above-mentioned units as well as units such as a display unit, a communication control unit, or an input unit.

[0052] The information acquisition unit 61 acquires information necessary for the control device 6 to perform startup control of the refrigeration cycle apparatus S. The information acquired by the information acquisition unit 61 includes, for example, information on the condensation temperature of the refrigerant at the time of startup of the refrigeration cycle apparatus S, which is detected by the condensation temperature detection sensor 22. Also, information on the temperature of air drawn into the indoor heat exchanger 2 serving as a condenser by the condenser fan 21, which is detected by the condenser intake air temperature detection sensor 23.

[0053] It should be noted that the information acquisition unit 61 may receive information transmitted from the condensation temperature detection sensor 22 or the condenser intake air temperature detection sensor 23 as appropriate. Alternatively, conversely, the information acquisition unit 61 may obtain information from the condensation temperature detection sensor 22 or the condenser intake air temperature detection sensor 23.

[0054] The information acquiring unit 61 acquires the condensation temperature information from the condensation temperature detection sensor 22. However, for example, the refrigerant discharge temperature acquired by the discharge temperature detection sensor 11 may be acquired as the condensation temperature information instead of the condensation temperature detection sensor 22. This is because, when the refrigeration cycle apparatus S is started, the refrigerant discharged from the compressor is in a two-phase state, and therefore the discharge temperature and the condensation temperature are approximately equal.

[0055] The calculation unit 62 calculates a value used to determine whether to shift from startup control to normal control of the refrigeration cycle apparatus S. Specifically, the calculation unit 62 calculates a startup temperature difference obtained by subtracting the air temperature detected by the condenser suction air temperature detection sensor 23 from the condensing temperature detected by the condensing temperature detection sensor 22.

[0056] The comparison unit 63 receives information about the temperature difference at startup, which is calculated by subtracting the air temperature from the condensation temperature calculated by the calculation unit 62, and compares the temperature difference at startup with a preset temperature difference threshold. Therefore, when the comparison unit 63 performs the comparison, it accesses the storage unit 64 to obtain information about the temperature difference threshold.

[0057] The storage unit 64 stores information related to the above-mentioned temperature difference threshold. Here, the "temperature difference threshold" stored in the storage unit 64 is set to a temperature difference at which the refrigerant can condense, such as 0 degrees. In addition, application programs and the like used when the control device 6 controls the refrigeration cycle apparatus S may be stored as appropriate.

[0058] When the comparison unit 63 compares the temperature difference at startup with the temperature difference threshold and finds that the temperature difference at startup is greater than the temperature difference threshold, the startup control is terminated and the control is switched to normal control. Specifically, the pressure reduction mechanism control unit 65 receives an instruction from the comparison unit 63 to set the opening degree of the pressure reduction mechanism 3 set when the startup control is performed to the opening degree of the pressure reduction mechanism 3 when normal control is performed.

[0059] The pressure reducing mechanism control unit 65 receives an instruction from the comparison unit 63 and controls the degree of opening of the pressure reducing mechanism 3. When controlling the pressure reducing mechanism 3, for example, the control is performed so that the degree of opening becomes a predetermined pulse, or so that the degree of opening becomes a predetermined opening area.

[0060] On the other hand, if the comparison by the comparison unit 63 shows that the temperature difference at startup is less than the temperature difference threshold, the above-mentioned processing is executed again based on the condensation temperature information and air temperature information acquired by the information acquisition unit 61.

[0061] The control by each part of the control device 6 described above will be explained using graphs as follows. Figure 4 is a graph that schematically shows the time course of the aperture of the pressure reducing mechanism 3 and the pressure of the refrigerant in the refrigerant circuit C in the control of the refrigeration cycle apparatus S according to an embodiment of the present invention. Figure 4(A) shows the relationship between the aperture of the pressure reducing mechanism 3 and time, and Figure 4(B) shows the relationship between the low-pressure side refrigerant pressure and time.

[0062] In the graph shown in Fig. 4, point M, which indicates the position (time) where the vertical axis and the horizontal axis intersect, indicates the timing of starting the refrigeration cycle apparatus S. In addition, in the graph of Fig. 4, a dotted line (hereinafter referred to as "dotted line O") shown parallel to the opening degree of the pressure reducing mechanism (vertical axis) indicates the timing at which the operating mode is switched in the embodiment of the present invention.

[0063] 4A, immediately after the start-up of the refrigeration cycle apparatus S, the start-up control is executed by the control device 6, and the start-up control is switched to the normal control at the timing indicated by the dotted line O. After that, the normal control is executed.

[0064] The opening degree of the pressure reducing mechanism 3 during startup control is preset. Therefore, the pressure reducing mechanism control unit 65 controls the pressure reducing mechanism 3 so that the opening degree of the pressure reducing mechanism 3 during startup control is the preset opening degree. Furthermore, while startup control is being executed, the opening degree remains fixed and is not changed.

[0065] In this way, during startup control, the opening degree of the pressure reducing mechanism 3 is adjusted to be larger than that during normal control. This is because by opening the pressure reducing mechanism 3 to a larger degree, immediately after startup of the refrigeration cycle apparatus S, emphasis is placed on start-up capability over energy saving performance, and a larger amount of refrigerant is circulated through the refrigerant circuit C.

[0066] The reason why the opening degree of the pressure reducing mechanism 3 is fixed during the startup control is as follows: As shown in Fig. 2B, the refrigerant pressure on the high-pressure side and the refrigerant pressure on the low-pressure side do not stabilize (become roughly constant) until a certain time has elapsed after the startup of the refrigeration cycle apparatus S. Also, it takes longer for the refrigerant pressure on the high-pressure side to stabilize than for the refrigerant pressure on the low-pressure side.

[0067] Furthermore, since feedback control in normal control involves adjusting the aperture of the pressure reducing mechanism 3 as needed so that the discharge temperature reaches a target temperature, for example, such feedback control cannot be performed when the refrigeration cycle is not stable. Therefore, the aperture of the pressure reducing mechanism 3 is fixed and not adjusted while startup control is being executed.

[0068] 4A also shows a dotted line indicated by the symbol P (hereinafter referred to as "dotted line P" where appropriate). The dotted line P indicates a change in the opening degree of the pressure reducing mechanism 3 accompanying a switchover from startup control to normal control in the technology disclosed in Patent Document 1, which is shown in FIG. 2A.

[0069] As can be seen from the dotted line P, in the prior art, when the control switches from startup control to normal control, the degree of opening of the pressure reducing mechanism 3 gradually decreases, and after a certain time has passed, the degree of opening of the pressure reducing mechanism 3 reaches the desired degree of opening. This is because, in normal control, feedback control is performed, and the degree of opening of the pressure reducing mechanism 3 does not immediately reach the desired degree of opening.

[0070] In other words, in the prior art, the opening degree of the pressure reducing mechanism 3 switches from startup control to normal control after both the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure have reached a substantially constant pressure, that is, after the refrigeration cycle has stabilized, as shown in Fig. 2. In other words, once the refrigeration cycle has stabilized, feedback control (normal control) becomes possible. Therefore, startup control is performed until then, and the opening degree of the pressure reducing mechanism 3 remains largely fixed.

[0071] 4A, the boundary where the opening degree of the pressure reducing mechanism 3 changes from a fixed opening degree corresponds to the timing at which the operating mode switches from startup control to normal control in the conventional technology. This switching timing is indicated by the dashed line indicated by the symbol Q (hereinafter referred to as "dashed line Q" where appropriate).

[0072] 4B, which shows the change in refrigerant pressure over time after the start-up of the refrigeration cycle apparatus S according to the embodiment of the present invention, the refrigerant pressure on the low-pressure side first drops to approximately the lower limit of the specifications of the compressor 1 when the refrigeration cycle apparatus S is started up. Thereafter, the refrigerant pressure starts to increase over time, and then stabilizes at a constant pressure, as described above with reference to FIG.

[0073] It should be noted that the low-pressure side refrigerant pressure does not necessarily decrease to the lower limit of the specifications of the compressor 1 after startup, and is depicted in this manner merely for the convenience of explaining that the low-pressure side refrigerant pressure decreases immediately after startup of the refrigeration cycle apparatus S (compressor 1). Also, Fig. 4(B) shows only the low-pressure side refrigerant pressure shown in Fig. 2(B), and does not depict changes in the high-pressure side refrigerant pressure.

[0074] That is, at startup, the refrigerant discharged from the compressor 1 is in a two-phase state. Furthermore, if the condensation temperature is lower than the condenser suction air temperature, the refrigerant cannot dissipate heat to the indoor air (for convenience, the temperature of the refrigerant in a heat exchanger that is to function as a condenser even when not condensed will hereinafter be referred to as the "condensation temperature"). Therefore, a low-density two-phase refrigerant flows into the pressure reducing mechanism 3. In this state, the refrigerant does not easily circulate inside the refrigerant circuit C (a state in which the refrigerant pressure on the low-pressure side, which is the pressure on the suction side of the compressor 1, drops).

[0075] Therefore, when the refrigeration cycle apparatus S is in this state, that is, immediately after the start-up of the refrigeration cycle apparatus S, it is necessary to increase the opening degree of the pressure reduction mechanism 3. Such an opening degree of the pressure reduction mechanism 3 is shown in Fig. 4(A), and the opening degree of the pressure reduction mechanism 3 is maintained large from the start-up to the dotted line O that separates the start-up control from the normal control.

[0076] On the other hand, if the condensation temperature becomes higher than the condenser intake air temperature, the refrigerant can dissipate heat to the indoor air. Therefore, the refrigerant in a liquid phase with a high density flows into the pressure reducing mechanism 3.

[0077] In this state, the refrigerant is more likely to circulate within the refrigeration cycle (the refrigerant pressure on the low-pressure side, which is the pressure on the suction side of the compressor 1, increases). Therefore, unlike immediately after startup, there is no need to circulate a large amount of refrigerant through the refrigerant circuit C. In this state, the refrigerant drawn into the compressor 1 is a two-phase refrigerant, and it is necessary to prevent damage to the compressor 1 due to the liquid-phase refrigerant being drawn into the compressor 1. Therefore, it is necessary to reduce (throttle) the opening of the pressure reducing mechanism 3 via the pressure reducing mechanism control unit 65.

[0078] Therefore, in the refrigeration cycle apparatus S according to an embodiment of the present invention, a startup temperature difference (condensing temperature minus air temperature) is compared with a temperature difference threshold. If the startup temperature difference is greater than the temperature difference threshold, the system switches from startup control to normal control. The timing at which the startup temperature difference exceeds the temperature difference threshold is often the timing at which the low-pressure side refrigerant pressure, which had been decreasing immediately after startup, begins to increase (the timing at which the dotted line O intersects with the dashed line representing the low-pressure side refrigerant pressure in FIG. 4B). Even if startup control is switched to normal control using feedback control after this timing, the low-pressure side pressure is unlikely to decrease.

[0079] By executing such control, the timing at which the operating mode switches from startup control to normal control can be significantly accelerated. That is, as shown by the large arrow designated by the symbol N, the timing at which the operating mode switches from startup control to normal control in the prior art, indicated by the dashed line Q, is shortened to the timing at which the operating mode switches from startup control to normal control in the embodiment of the present invention, indicated by the dotted line O.

[0080] The change in the low-pressure side refrigerant pressure after the refrigeration cycle apparatus S starts and the startup control is initiated is as described above. Therefore, in the embodiment of the present invention, the switch from startup control to normal control is performed while the low-pressure side refrigerant pressure is changing. However, as described above, even if the startup control is switched to normal control at this timing and feedback control is performed in the normal control, the low-pressure side refrigerant pressure will not drop any further and fall below the lower limit of the specifications of the compressor 1.

[0081] 4A, when the startup control is executed, the opening degree of the pressure reducing mechanism 3 is large. In contrast, in normal control, the opening degree of the pressure reducing mechanism 3 is controlled so that the refrigerant drawn into the compressor 1 is not in a two-phase state but in a gas phase state, for example, so that the quality fraction is 1. To perform such control, the feedback control is executed as described above.

[0082] By executing the feedback control in this manner, it is possible to maintain the opening degree of the pressure reducing mechanism 3 at a small level while optimizing the amount of refrigerant circulating in the refrigerant circuit C more effectively than with the startup control. Therefore, the normal control is more energy-efficient than the startup control.

[0083] In the embodiment of the present invention, the control of the aperture of the pressure reducing mechanism 3 when the operating mode is switched from startup control to normal control does not involve immediately controlling the aperture of the pressure reducing mechanism 3 by feedback control in normal control after the operating mode is switched from startup control to normal control. The aperture of the pressure reducing mechanism 3 in startup control is referred to as a "first startup aperture" as appropriate.

[0084] In the refrigeration cycle apparatus S according to the embodiment of the present invention, the aperture of the pressure reducing mechanism 3 is controlled to follow the change indicated by the solid line in the graph of Fig. 4A. During this period, from immediately after the start of the compressor 1 until the time indicated by the dotted line O, the aperture of the pressure reducing mechanism 3 during startup control is controlled to a large aperture. This is to allow a larger amount of refrigerant to flow through the refrigerant circuit C, as described above.

[0085] On the other hand, if the opening of the pressure reducing mechanism 3 is too large and the suction side of the compressor 1 enters a two-phase state, the enthalpy difference between the evaporator inlet and outlet will decrease, which may result in a decrease in the capacity of the refrigeration cycle device S. Therefore, in normal control, feedback control is performed to control the opening of the pressure reducing mechanism 3 so that the suction dryness fraction becomes 1, for example.

[0086] Therefore, the opening degree of the pressure reducing mechanism 3 under normal control is smaller than the first startup opening degree. In Fig. 4(A), the solid line drawn parallel to the horizontal axis, which represents the passage of time, at a position close to the horizontal axis, indicates the opening degree of the pressure reducing mechanism 3 adjusted as a result of feedback control under normal control.

[0087] However, there is a large difference between the first startup opening degree and the opening degree of the pressure reducing mechanism 3 under normal control. Because of this difference, when the opening degree of the pressure reducing mechanism 3 is changed by feedback control in response to a switch in the operating mode from startup control to normal control, it takes a long time for the opening degree of the pressure reducing mechanism 3 under normal control to be reached.

[0088] That is, as described above, in the conventional control of the opening degree of the pressure reducing mechanism 3 indicated by the dotted line P in Fig. 4A, feedback control is executed immediately after switching to normal control. When such control is performed, as indicated by the dotted line P, it takes time for the opening degree of the pressure reducing mechanism 3 to change from the first startup opening degree to the desired opening degree under normal control due to the execution of feedback control.

[0089] Therefore, in controlling the opening degree of the pressure reducing mechanism 3 in the embodiment of the present invention, control is performed to reduce the opening degree of the pressure reducing mechanism 3 while adjusting the first startup opening degree to the opening degree of the pressure reducing mechanism 3 in normal control. However, the opening degree of the pressure reducing mechanism 3 is not immediately changed to the opening degree executed by feedback control in normal control, but is controlled to change from the first startup opening degree to an opening degree larger than the opening degree of the pressure reducing mechanism 3 in normal control (hereinafter, this opening degree will be referred to as the "second startup opening degree" as appropriate).

[0090] As described above, Fig. 4A shows the change in the opening degree of the pressure reducing mechanism 3. Here, when the operating mode is switched from startup control to normal control, the opening degree of the pressure reducing mechanism 3 is controlled to change from a large opening degree to a small opening degree. The dotted line O in Fig. 4A shows the timing when the operating mode is switched from startup control to normal control, and the solid line indicates the change in the opening degree of the pressure reducing mechanism 3 due to this control. That is, the opening degree of the pressure reducing mechanism 3 is controlled from a first startup opening degree, which is the opening degree of the pressure reducing mechanism 3 while startup control is being performed immediately after startup of the compressor 1, to a second startup opening degree when switching from startup control to normal control.

[0091] The control for reducing the opening of the pressure reducing mechanism 3 when switching from the startup control to the normal control is performed not by feedback control but by, for example, feedforward control. Then, the opening of the pressure reducing mechanism 3 is gradually controlled to a desired opening from the second startup opening by feedback control.

[0092] By performing such control, the opening degree of the pressure reduction mechanism 3 can be adjusted more quickly from the opening degree of the pressure reduction mechanism 3 in the startup control to the opening degree of the pressure reduction mechanism 3 in the normal control. Therefore, in the normal control, the opening degree of the pressure reduction mechanism 3 can be set to an appropriate opening degree early, and the energy saving performance of the refrigeration cycle apparatus S can be improved.

[0093] In the above-described control, the degree to which the pressure reduction mechanism 3 is reduced from the opening degree in the startup control is set in advance. The pressure reduction mechanism control unit 65 reduces the opening degree of the pressure reduction mechanism 3 to the set opening degree (second startup opening degree).

[0094] That is, the second startup opening is set to the smallest opening that does not cause a new decrease in the refrigerant pressure on the low-pressure side immediately after switching from startup control to normal control. Therefore, if the second startup opening is set to a larger opening than this opening, it will take time to adjust the opening of the pressure reducing mechanism 3 to the appropriate opening for normal control, as described above, which is insufficient from the perspective of improving the energy efficiency of the refrigeration cycle apparatus S. Furthermore, setting the second startup opening to a smaller opening than this opening cannot be adopted because there is a possibility that the refrigerant pressure on the low-pressure side will fall below the lower limit of the specifications.

[0095] As described above, the opening degree of the pressure reducing mechanism 3 when the startup control is executed can be set as the first startup opening degree. This assumes, for example, a situation in which the refrigeration cycle apparatus S is installed in a cold region or the like and has been stopped for a long time. In such a situation, when the compressor 1 is started after being stopped for a long time, the temperature of the refrigerant has also dropped, making it difficult for the refrigerant to circulate within the refrigerant circuit C. Therefore, the startup control is executed by setting the opening degree of the pressure reducing mechanism 3 to a large value, such as the first startup opening degree.

[0096] On the other hand, for example, there may be a case where the compressor 1 is stopped for a short time and the refrigeration cycle apparatus S (compressor 1) is started again not long after the previous stop. In such a case, the refrigerant tends to circulate within the refrigerant circuit C, and therefore it is not necessary to set the opening of the pressure reducing mechanism 3 to a large opening (first startup opening) similar to that in the case where the compressor 1 is started after the long stop described above.

[0097] 5A and 5B are graphs showing the relationship between the opening degree of the pressure reducing mechanism 3 and the time course of the refrigerant pressure in the refrigerant circuit C in the control of the refrigeration cycle apparatus S according to the embodiment of the present invention. Fig. 5A shows the relationship between the opening degree of the pressure reducing mechanism 3 and time, and Fig. 5B shows the relationship between the low-pressure side refrigerant pressure and time.

[0098] The graph showing the change in low-pressure side refrigerant pressure over time in Fig. 5(B) is the same as Fig. 4(B). On the other hand, Fig. 5(A) is basically the same as Fig. 4(A), except that the dotted line P and dashed line Q are not drawn and a solid line R is shown at the second startup opening. The second startup opening indicated by the solid line R is the opening set in startup control when the compressor 1 is stopped for a short time and then immediately started again.

[0099] 4A, the solid line shows the change in the opening degree of the pressure reducing mechanism 3 that occurs when the operation mode is switched from startup control to normal control in the case where the opening degree of the pressure reducing mechanism 3 is set to the first startup opening degree at the start of the compressor 1. However, in FIG. 5A, the change in the opening degree of the pressure reducing mechanism 3 that was shown by the solid line is shown by a dashed line.

[0100] That is, when the compressor 1 is stopped for a short time and then started again, the refrigerant is in a state where it is easy to circulate within the refrigerant circuit C, and in such a case, it is not necessary to increase the opening degree of the pressure reducing mechanism 3 to the first startup opening degree. Therefore, in such a case, the opening degree of the pressure reducing mechanism 3 in the startup control is not set to the first startup opening degree, but is set to a second startup opening degree that is smaller than the first startup opening degree.

[0101] 3, in addition to the above-mentioned components, the control device 6 further includes a determination unit 66, a timer unit 67, and a setting unit 68. That is, the length of the stop time of the compressor 1 is measured by the timer unit 67. The timer unit 67 starts timing from the point in time when the compressor 1 stops, and measures the time until the compressor 1 starts up thereafter.

[0102] The determination unit 66 acquires information regarding the stop time of the compressor 1 measured by the timing unit 67. Then, the determination unit 66 compares the information regarding the stop time of the compressor 1 with a stop time threshold, and if the determination unit 66 determines that the stop time of the compressor 1 is equal to or greater than the stop time threshold, the determination unit 66 instructs the setting unit 68 to set the opening degree of the pressure reducing mechanism 3 to the first start-up opening degree. On the other hand, if the determination unit 66 determines that the stop time of the compressor 1 is less than the stop time threshold, the determination unit 66 instructs the setting unit 68 to set the opening degree of the pressure reducing mechanism 3 to the second start-up opening degree.

[0103] By changing the start-up opening of the pressure reducing mechanism 3 based on the stop time in this way, it is possible to prevent the start-up opening from being set smaller than necessary, causing the suction pressure of the compressor 1 to drop excessively and fall below the specified pressure range.

[0104] Furthermore, it is possible to prevent the refrigerant drawn into the compressor 1 from becoming wet (liquid refrigerant being drawn in) due to the start-up opening being set larger than necessary. By preventing these situations from occurring, it is possible to ensure the reliability of the compressor 1. Furthermore, by setting the opening of the pressure reducing mechanism 3 to the second start-up opening, it is possible to further improve the start-up capability.

[0105] The above-mentioned stop time threshold, first start opening, and second start opening are stored in advance in the storage unit 64. The stop time threshold is a value obtained through an experiment, for example, and can be set to, for example, 60 minutes.

[0106] The above describes setting the opening degree of the pressure reducing mechanism 3 during startup control based on the stop time of the compressor 1. However, when setting the opening degree of the pressure reducing mechanism 3 during startup control, the outside air temperature may also be used as the basis, instead of the stop time of the compressor 1.

[0107] That is, the temperature outdoors where the outdoor unit is installed (outdoor air temperature) is detected using the above-described intake air temperature detection sensor 43. The determination unit 66 compares the detected outdoor air temperature with a preset outdoor air temperature threshold, and, for example, if the outdoor air temperature is lower than the outdoor air temperature threshold, sets the opening degree of the pressure reducing mechanism 3 to the first startup opening degree.

[0108] This is because the lower the outside air temperature, the lower the refrigerant temperature, and therefore when the suction pressure of the refrigerant into the compressor 1 drops to the saturation pressure of the outside air temperature, the amount of refrigerant circulating in the refrigerant circuit C decreases. Also, when the outside air temperature is low, the refrigerant is more likely to stagnate in the compressor 1, which is known as stagnation.

[0109] On the other hand, when the outside air temperature is equal to or higher than the outside air temperature threshold, the refrigerant temperature is relatively high and the refrigerant easily circulates within the refrigerant circuit C. In such a case, the opening degree of the pressure reducing mechanism 3 is set to, for example, the second startup opening degree.

[0110] Here, for example, if the refrigeration cycle apparatus S is installed in a cold region or the like, it is necessary to more precisely control the opening degree of the pressure reducing mechanism 3 depending on the length of time that the refrigeration cycle apparatus S is not started. As an example of a method for doing so, when setting the opening degree of the pressure reducing mechanism 3, it is possible to combine the outside air temperature and the stop time of the compressor 1.

[0111] For example, if the opening degree of the pressure reducing mechanism 3 is set to the first startup opening degree because the stop time of the compressor 1 is equal to or greater than the stop time threshold, and if the outside air temperature is lower than the outside air temperature threshold, the set first startup opening degree can be corrected to an even larger opening degree. Conversely, if the opening degree of the pressure reducing mechanism 3 is set to the second startup opening degree because the stop time of the compressor 1 is less than the stop time threshold, and if the outside air temperature is equal to or greater than the outside air temperature threshold, the second startup opening degree can be corrected to an even smaller opening degree.

[0112] On the other hand, it is also possible to first set the opening degree of the pressure reducing mechanism 3 at the time of startup based on the outside air temperature, and then correct the set opening degree of the pressure reducing mechanism 3 using the stop time of the compressor 1. For example, if the opening degree of the pressure reducing mechanism 3 is set to the first startup opening degree because the outside air temperature is below the outside air temperature threshold, and the stop time of the compressor 1 is equal to or greater than the stop time threshold, it is also possible to correct the set first startup opening degree to an even larger opening degree.

[0113] In this case, for example, when the opening degree of the pressure reducing mechanism 3 is set to the second start-up opening degree because the outside air temperature is equal to or higher than the outside air temperature threshold, it is also possible that the stop time of the compressor 1 is less than the stop time threshold. In this case, it is also possible to correct the set second start-up opening degree to an even smaller opening degree.

[0114] By setting the aperture of the pressure reducing mechanism 3 in this manner, it is possible to set the aperture of the pressure reducing mechanism 3 in a manner that is more suited to the state of the refrigerant when performing startup control. In addition, the aperture of the pressure reducing mechanism 3 does not fall below the specified pressure, and it is possible to prevent liquid refrigerant from flowing into the compressor 1, thereby avoiding damage to the compressor 1.

[0115] Furthermore, after the operation mode is switched from startup control to normal control, the normal control method can also be controlled as described below. That is, the feedback control in the normal control performed after the refrigeration cycle has stabilized is performed based on two parameters: the temperature difference between the target value of the temperature (discharge temperature) of the refrigerant discharged from the compressor 1 detected by the discharge temperature detection sensor 11 and the current discharge temperature, and the change in the discharge temperature over time.

[0116] However, as explained above, in the startup control according to the embodiment of the present invention, the startup control is terminated and the control is switched to normal control when the refrigerant pressure on the low-pressure side starts to rise, as shown in Fig. 4(B) . At this timing when the operation mode is switched, the refrigerant has not yet completely transitioned to a gas phase state and is in a two-phase state.

[0117] In this way, if feedback control is executed as normal control when the refrigerant is in a two-phase state, the increase in discharge temperature due to the operation of the compressor 1 may be detected, and it may be determined that, of the two parameters described above, the discharge temperature in particular changes significantly over time. Therefore, although it would be desirable to control the opening of the pressure reducing mechanism 3 as small as possible in consideration of energy saving because this is normal control, there is a possibility that control may be executed to increase the opening of the pressure reducing mechanism 3 in order to make the change over time more gradual.

[0118] To avoid this, the normal control in this embodiment of the present invention performs the following control: If it is determined that the refrigerant is in a two-phase state when transitioning from startup control to normal control, the normal control uses only the difference between the target value of the discharge temperature and the current discharge temperature as the control parameter, without considering the change in discharge temperature over time, which is one of the two parameters considered when performing normal control.

[0119] The control device 6 first estimates whether the refrigerant is in a two-phase state or a gas phase state. Specifically, the determination unit 66 determines whether the temperature difference obtained by subtracting the condensation temperature detected by the condensation temperature detection sensor 22 from the discharge temperature detected by the discharge temperature detection sensor 11 is equal to or greater than a predetermined value (e.g., 0°C). This process determines whether the refrigerant is in a two-phase state or a gas phase state.

[0120] If the judgment unit 66 determines that the refrigerant is in a two-phase state, the judgment unit 66 instructs the setting unit 68 to set the opening degree of the pressure reducing mechanism 3 using the difference between the discharge temperature detected by the discharge temperature detection sensor 11 and the target discharge temperature.

[0121] On the other hand, if the judgment unit 66 determines that the refrigerant is in a gas phase, the judgment unit 66 instructs the setting unit 68 to set the opening degree of the pressure reducing mechanism 3 using the difference between the discharge temperature detected by the discharge temperature detection sensor 11 and the target discharge temperature, and the change in the discharge temperature over time.

[0122] [Operation] Next, the control of the opening degree of the pressure reducing mechanism 3 in the above-mentioned startup control and normal control will be described with reference to the flowcharts shown in Figures 6 to 9. Figure 6 is a flowchart showing a basic flow of the control of the opening degree of the pressure reducing mechanism 3 at the time of startup of the refrigeration cycle apparatus S according to the embodiment of the present invention.

[0123] When the refrigeration cycle apparatus S (compressor 1) is started, the control device 6 starts the start-up control (ST1). Then, first, the opening degree of the pressure reducing mechanism 3 in the start-up control is set to a predetermined opening degree (ST2). Note that the setting of the opening degree of the pressure reducing mechanism 3 in the start-up control will be described separately with reference to FIG. 7 etc.

[0124] The information acquisition unit 61 acquires information on the condensation temperature from the condensation temperature detection sensor 22 (ST3) and also acquires information on the condenser suction air temperature from the condenser suction air temperature detection sensor 23 (ST4).

[0125] For convenience of explanation, the condensation temperature information and the condenser intake air temperature information have been described as being acquired in this order, but the order in which these pieces of information are acquired may vary, or they may be acquired simultaneously.

[0126] The calculation unit 62 calculates the startup temperature difference by subtracting the condenser intake air temperature from the condensation temperature information, based on the condensation temperature information and the condenser intake air temperature information acquired by the information acquisition unit 61 (ST5). The calculation result is sent to the comparison unit 63 and compared with the temperature difference threshold value.

[0127] The comparison unit 63 accesses the storage unit 64 to acquire the temperature difference threshold value, and compares it with the startup temperature difference calculated by subtracting the condenser intake air temperature from the condensing temperature acquired from the calculation unit 62. The comparison unit 63 then determines whether the startup temperature difference is greater than the temperature difference threshold value (ST6).

[0128] If the comparison unit 63 determines that the temperature difference at startup is equal to or less than the temperature difference threshold value (NO in ST6), the pressure reduction mechanism 3 is in a state where the refrigerant is unlikely to circulate inside the refrigerant circuit C (a state where the refrigerant pressure on the low-pressure side, which is the pressure on the suction side of the compressor 1, is reduced), and a low-density two-phase refrigerant flows in. In this case, the process returns to step ST3, and the processes of steps ST3 to ST6 described above are repeated.

[0129] On the other hand, if the comparison unit 63 determines that the temperature difference at startup is greater than the temperature difference threshold value (YES in ST6), the startup control is terminated and the control is switched to normal control (ST7). Specifically, the pressure reduction mechanism control unit 65 changes the opening degree of the pressure reduction mechanism 3 from the opening degree in the startup control up to that in normal control (ST8).

[0130] The above is the basic control flow for the aperture of the pressure reducing mechanism 3 at the time of startup of the refrigeration cycle apparatus S. Next, the flow for setting the aperture of the pressure reducing mechanism 3 when startup control is initiated will be described with reference to Fig. 7. Fig. 7 is a flowchart relating to the control of the aperture of the pressure reducing mechanism 3 at the time of startup of the refrigeration cycle apparatus S according to an embodiment of the present invention.

[0131] 7 illustrates a case where the stop time of the compressor 1 is taken into consideration when setting the opening degree of the pressure reducing mechanism 3. That is, when the start-up control is started (ST1), the determination unit 66 first checks the stop time of the compressor 1 measured by the timer unit 67 (ST21).

[0132] The determination unit 66 then obtains a stop time threshold stored in the memory unit 64, for example, and compares it with the stop time of the compressor 1 measured by the timer unit 67 (ST22). As a result, if the determination unit 66 determines that the stop time is equal to or greater than the stop time threshold (YES in ST22), the setting unit 68 sets the opening degree of the pressure reducing mechanism 3 to the first startup opening degree (ST23). The pressure reducing mechanism control unit 65 then controls the opening degree of the pressure reducing mechanism 3 to the first startup opening degree set by the setting unit 68.

[0133] On the other hand, if the determination unit 66 determines that the stop time is less than the stop time threshold value (NO in ST22), the setting unit 68 sets the opening degree of the pressure reducing mechanism 3 to the second startup opening degree (ST24). In this case, it can be considered that the refrigerant is in a state where it is easy for the refrigerant to circulate within the refrigerant circuit C, so the opening degree of the pressure reducing mechanism 3 is set to the second startup opening degree, which is smaller than the first startup opening degree.

[0134] Thereafter, the control device 6 determines whether or not to switch the operation mode from startup control to normal control (ST3 to ST6). If the comparison unit 63 determines that the startup temperature difference is equal to or greater than the temperature difference threshold value (YES in ST6), the operation mode is switched from startup control to normal control.

[0135] At this time, the determination unit 66 checks whether the opening of the pressure reducing mechanism 3 in the startup control has been set to the first startup opening (ST25). If it has been set to the first startup opening (YES in ST25), the determination unit 66 instructs the setting unit 68 to change the opening to the second startup opening, and the pressure reducing mechanism control unit 65 changes the opening of the pressure reducing mechanism 3 from the first startup opening to the second startup opening (ST26).

[0136] 4A, there is a large difference between the opening degree of the pressure-reducing mechanism 3 in startup control and the opening degree of the pressure-reducing mechanism 3 targeted by performing feedback control in normal control. Therefore, if the opening degree of the pressure-reducing mechanism 3 in normal control is set by feedback control in conjunction with switching of the operation mode, it takes time to set the opening degree.

[0137] Therefore, by quickly changing the opening of the pressure reducing mechanism 3, which has been set to the first startup opening, to the second startup opening, and then controlling the opening of the pressure reducing mechanism 3 to that under normal control, the opening of the pressure reducing mechanism 3 can be quickly set to that under normal control, thereby ensuring start-up capability.

[0138] Thereafter, the operation mode is switched from startup control to normal control (ST7). That is, the pressure reduction mechanism control unit 65 changes the opening degree of the pressure reduction mechanism 3 from the opening degree under startup control to the opening degree under normal control (ST8).

[0139] On the other hand, if the opening of the pressure reducing mechanism 3 in the startup control was originally set to the second startup opening (NO in ST25), the process of changing the first startup opening to the second startup opening as described above is not necessary, so the startup control is ended and normal control is started (ST7). Also, the pressure reducing mechanism control unit 65 sets the opening of the pressure reducing mechanism 3 to the opening in normal control (ST8).

[0140] Next, a control flow for another setting of the aperture of the pressure reducing mechanism 3 when startup control is initiated will be described with reference to Fig. 8. Fig. 8 is a flowchart relating to control of the aperture of the pressure reducing mechanism 3 at startup of the refrigeration cycle apparatus S according to an embodiment of the present invention. Here, a flow will be described in which the aperture of the pressure reducing mechanism 3 is set based on the stop time of the compressor 1, and then the aperture of the pressure reducing mechanism 3 is corrected using the outside air temperature.

[0141] First, the flow from when startup control is started until the aperture of the pressure reducing mechanism 3 is set using the stop time of the compressor 1 is as described using steps ST1 to ST24 shown in Fig. 7. Thereafter, the information acquisition unit 61 acquires information on the outside air temperature from the intake air temperature detection sensor 43 (ST31). Then, the determination unit 66 and the setting unit 68 correct the first startup aperture and the second startup aperture in accordance with the outside air temperature (ST32).

[0142] Specifically, when the stop time of compressor 1 is equal to or greater than the stop time threshold and the opening of pressure reducing mechanism 3 is set to the first start opening, and when the outside air temperature is lower than the outside air temperature threshold, the set first start opening can be corrected to an even larger opening.

[0143] Conversely, for example, if the opening of the pressure reducing mechanism 3 is set to the second start-up opening because the stop time of the compressor 1 is less than the stop time threshold, and if the outside air temperature is equal to or higher than the outside air temperature threshold, the second start-up opening can be corrected to an even smaller opening.

[0144] The subsequent processing flow is as explained using the flowchart shown in Fig. 7 (ST3 to ST8). Therefore, in Fig. 8, the processing flow from step ST3 onwards is partially omitted and is shown by dashed lines.

[0145] By carrying out the above-described process, the opening degree of the pressure reducing mechanism 3 can be set in full consideration of the state of the refrigerant in the environment in which the refrigeration cycle apparatus S is installed.

[0146] Next, the flow of normal control after the operation mode is switched from startup control to normal control will be described with reference to Fig. 9. Fig. 9 is a flowchart relating to control of the opening degree of the pressure reducing mechanism 3 at the time of startup of the refrigeration cycle apparatus S according to the embodiment of the present invention.

[0147] First, the compressor 1 is started, and startup control is performed. After that, the process of setting the opening degree of the pressure reducing mechanism 3, which has been described so far, is performed, and the flow up to when the operating mode is switched from startup control to normal control is as described with reference to FIGS. 6 to 8 .

[0148] 9 shows the process from the point where the operation mode is switched from startup control to normal control and the pressure reduction mechanism control unit 65 sets the opening degree of the pressure reduction mechanism 3 in normal control (ST8). However, since the processing of step ST8 has already been explained, the content of this processing is indicated by dashed lines.

[0149] After transitioning to normal control, the control device 6 determines whether the refrigerant discharged from the compressor 1 is in a two-phase state (ST41). Specifically, as described above, the determination unit 66 determines whether the temperature difference obtained by subtracting the condensation temperature from the discharge temperature is equal to or greater than a predetermined value, thereby determining whether the refrigerant is in a two-phase state or a gas phase state.

[0150] If the judgment unit 66 determines that the discharged refrigerant is in a two-phase state (YES in ST41), the opening degree of the pressure reducing mechanism 3 is set (controlled) using the temperature difference between the target discharge temperature and the current discharge temperature (ST42).

[0151] On the other hand, if the judgment unit 66 determines that the discharged refrigerant is in a gas phase (NO in ST41), the opening degree of the pressure reducing mechanism 3 is set (controlled) using the temperature difference between the target discharge temperature and the current discharge temperature, and the change in the discharge temperature over time (ST43).

[0152] Then, the determination unit 66 determines again whether the refrigerant discharged from the compressor 1 is in a two-phase state (ST44). If it is determined that the refrigerant is still in a two-phase state (YES in ST44), the process returns to step ST42 and the degree of opening of the pressure reducing mechanism 3 is set (controlled) using the temperature difference between the target discharge temperature and the current discharge temperature (ST42).

[0153] On the other hand, if the judgment unit 66 judges that the refrigerant is in a gas phase state (NO in ST44), similar to step ST43, the opening degree of the pressure reducing mechanism 3 is set (controlled) using the temperature difference between the target discharge temperature and the current discharge temperature, and the change in the discharge temperature over time (ST45).

[0154] The above has described the startup control that is initiated when the compressor 1 is started, and the control of the opening degree of the pressure reducing mechanism 3 when the operation mode is switched from the startup control to the normal control. By executing such control, it is possible to ensure the reliability of the compressor when the refrigeration cycle device is started and to improve the start-up capability.

[0155] It should be noted that the present invention is not limited to the above-described embodiment, but is merely an example of the present invention. In the implementation stage, the components can be modified and embodied without departing from the spirit of the invention, and various changes and improvements can be made to the above-described embodiment. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiment.

[0156] For example, some components may be deleted from all of the components shown in the embodiments. Furthermore, components from different embodiments may be combined as appropriate, and such modified or improved forms may also be included in the present invention. Such embodiments and their modifications are included in the scope and spirit of the inventions, and are also included in the scope of the inventions and their equivalents as defined in the claims.

[0157] For example, the above explanation has been based on the assumption that if the startup temperature difference (the condensation temperature minus the condenser intake air temperature) is greater than the temperature difference threshold, the startup control immediately transitions to normal control. However, this is not necessarily the case.

[0158] That is, for example, even if the startup temperature difference is greater than the temperature difference threshold, the startup control may be controlled to be executed for a predetermined minimum time. This is because, for example, when the compressor 1 starts, it is possible that the refrigerant is not circulating in the refrigerant circuit C even if the startup temperature difference is greater than the temperature difference threshold. Therefore, for example, the minimum time is set to be the time until the refrigerant circulates once in the refrigerant circuit C after the compressor 1 starts. Furthermore, this minimum time is obtained in advance through experimentation.

[0159] The techniques described in the embodiments of the present invention may also be configured as follows: (1) A refrigeration cycle apparatus comprising: a refrigerant circuit in which a compressor, a condenser, a pressure reducing mechanism, and an evaporator are sequentially connected by refrigerant piping, and in which a refrigerant circulates; a condenser fan that sends air to the condenser; a condensation temperature detection sensor that detects a condensation temperature of the refrigerant at startup of the compressor; a condenser intake air temperature detection sensor that detects the temperature of the air drawn into the condenser by the condenser fan; and a control device that switches between startup control that controls an opening of the pressure reducing mechanism at startup of the compressor to fix it at a preset startup opening and normal control that controls the opening of the pressure reducing mechanism to a normal opening depending on the state of the refrigerant circulating in the refrigerant circuit, wherein the control device executes the startup control at startup of the compressor, and terminates the startup control and switches to the normal control when a startup temperature difference obtained by subtracting the air temperature detected by the condenser intake air temperature detection sensor from the condensing temperature detection sensor is greater than a preset temperature difference threshold. (2) The refrigeration cycle apparatus according to (1), wherein the control device comprises: an information acquisition unit that acquires the condensation temperature and the air temperature; a calculation unit that calculates the startup temperature difference by subtracting the air temperature from the condensation temperature; a comparison unit that compares the startup temperature difference with a temperature difference threshold; and a pressure reduction mechanism control unit that changes the opening of the pressure reduction mechanism from the startup opening to the normal opening when the comparison result in the comparison unit indicates that the startup temperature difference is greater than the temperature difference threshold. (3) The refrigeration cycle apparatus according to (1) or (2), wherein the condensation temperature detection sensor detects the temperature of the refrigerant discharged from the compressor. (4) The refrigeration cycle apparatus according to any of (1) to (3), wherein the control device comprises: a timer that measures a stop time during which the compressor is stopped; and a setting unit that sets the opening of the pressure reduction mechanism, and the setting unit sets the startup opening of the pressure reduction mechanism based on the stop time measured by the timer.(5) The refrigeration cycle apparatus according to (4), wherein the setting unit, when setting the startup opening, sets the first startup opening if the stop time is equal to or greater than a predetermined stop time threshold, and sets the second startup opening which is smaller than the first startup opening if the stop time is less than the stop time threshold. (6) The refrigeration cycle apparatus according to (5), wherein, when the control device switches from the startup control to the normal control, the pressure reducing mechanism control unit changes the opening of the pressure reducing mechanism so that the first startup opening becomes the second startup opening when the startup opening is set to the first startup opening and it is determined that a startup temperature difference obtained by subtracting the air temperature from the condensing temperature is greater than the temperature difference threshold. (7) The refrigeration cycle device according to (6) above, further comprising an outside air temperature detection sensor that detects an outside air temperature, wherein the setting unit, when setting the first startup opening and the second startup opening, corrects the first startup opening and the second startup opening based on the outside air temperature detected by the outside air temperature detection sensor. (8) The refrigeration cycle device according to (7) above, characterized in that the correction of the first startup opening and the second startup opening based on the outside air temperature by the setting unit is such that the lower the outside air temperature is, the larger the first startup opening and the smaller the second startup opening. (9) The refrigeration cycle device according to (1) above, further comprising a discharge temperature detection sensor for detecting the discharge temperature of the refrigerant discharged from the compressor, wherein the control device controls the opening degree of the pressure reducing mechanism so that the discharge temperature becomes a preset target discharge temperature during normal control, the control device estimates whether the refrigerant is in a two-phase state or a gas phase state, and when it is determined that the refrigerant is in the gas phase state, the control device sets the opening degree of the pressure reducing mechanism using the difference between the discharge temperature detected by the discharge temperature sensor and the target discharge temperature and the change in the discharge temperature over time, and when it is determined that the refrigerant is in the two-phase state, the control device sets the opening degree of the pressure reducing mechanism using the difference between the discharge temperature detected by the discharge temperature sensor and the target discharge temperature.

[0160] 1...Compressor, 11...Discharge temperature detection sensor, 2...Indoor heat exchanger, 21...Indoor fan (condenser fan), 22...Refrigerant temperature detection sensor (condensation temperature detection sensor), 23...Suction air temperature detection sensor (condenser suction air temperature detection sensor), 3...Decompression mechanism, 4...Outdoor heat exchanger, 41...Outdoor fan, 42...Refrigerant temperature detection sensor, 43...Suction air temperature detection sensor, 5...Four-way valve, 6...Control device, 61...Information acquisition unit, 62...Calculation unit, 63...Comparator, 64...Storage unit, 65...Decompression mechanism control unit, 66...Determination unit, 67...Timekeeping unit, 68...Setting unit, C...Refrigerant circuit, S...Refrigeration cycle device

Claims

1. A refrigeration cycle apparatus comprising: a refrigerant circuit in which a compressor, a condenser, a pressure reducing mechanism, and an evaporator are connected in sequence by refrigerant piping, and in which a refrigerant circulates; a condenser fan that sends air to the condenser; a condensation temperature detection sensor that detects the condensation temperature of the refrigerant when the compressor is started; a condenser intake air temperature detection sensor that detects the temperature of the air drawn into the condenser by the condenser fan; and a control device that switches between startup control that controls the opening of the pressure reducing mechanism to a preset startup opening when the compressor is started, and normal control that controls the opening of the pressure reducing mechanism to a normal opening depending on the state of the refrigerant circulating in the refrigerant circuit, wherein the control device executes the startup control when the compressor is started, and terminates the startup control and switches to the normal control when a startup temperature difference obtained by subtracting the air temperature detected by the condenser intake air temperature detection sensor from the condensing temperature detection sensor is greater than a preset temperature difference threshold.

2. The refrigeration cycle device of claim 1, characterized in that the control device comprises: an information acquisition unit that acquires the condensation temperature and the air temperature; a calculation unit that calculates the startup temperature difference by subtracting the air temperature from the condensation temperature; a comparison unit that compares the startup temperature difference with the temperature difference threshold; and a pressure reduction mechanism control unit that changes the opening of the pressure reduction mechanism from the startup opening to the normal opening when the comparison in the comparison unit shows that the startup temperature difference is greater than the temperature difference threshold.

3. The refrigeration cycle device according to claim 1, wherein the condensation temperature detection sensor detects the temperature of the refrigerant discharged from the compressor.

4. A refrigeration cycle device as described in any one of claims 1 to 3, wherein the control device comprises a timing unit that measures the stop time during which the compressor is stopped, and a setting unit that sets the opening degree of the pressure reduction mechanism, and the setting unit sets the startup opening degree of the pressure reduction mechanism based on the stop time measured by the timing unit.

5. The refrigeration cycle device of claim 4, characterized in that, when setting the start-up opening, the setting unit sets the start-up opening to a first start-up opening if the stop time is equal to or greater than a predetermined stop time threshold, and sets the start-up opening to a second start-up opening that is smaller than the first start-up opening if the stop time is less than the stop time threshold.

6. The refrigeration cycle device of claim 5, characterized in that when the control device switches from the startup control to the normal control, the pressure reducing mechanism control unit changes the opening of the pressure reducing mechanism so that the first startup opening becomes the second startup opening when the startup opening is set to the first startup opening and it is determined that the startup temperature difference obtained by subtracting the air temperature from the condensing temperature is greater than the temperature difference threshold.

7. A refrigeration cycle device as described in claim 6, further comprising an outside air temperature detection sensor that detects outside air temperature, and wherein the setting unit, when setting the first start-up opening and the second start-up opening, corrects the first start-up opening and the second start-up opening based on the outside air temperature detected by the outside air temperature detection sensor.

8. A refrigeration cycle device as described in claim 7, characterized in that the setting unit corrects the first startup opening and the second startup opening based on the outside air temperature, so that the lower the outside air temperature, the larger the first startup opening and the smaller the second startup opening.

9. A refrigeration cycle device as described in claim 1, further comprising a discharge temperature detection sensor for detecting the discharge temperature of the refrigerant discharged from the compressor, wherein the control device controls the opening of the pressure reducing mechanism so that the discharge temperature becomes a predetermined target discharge temperature during normal control, the control device estimates whether the refrigerant is in a two-phase state or a gas phase state, and when it is determined that the refrigerant is in the gas phase state, the control device sets the opening of the pressure reducing mechanism using the difference between the discharge temperature detected by the discharge temperature sensor and the target discharge temperature and the change in the discharge temperature over time, and when it is determined that the refrigerant is in the two-phase state, the control device sets the opening of the pressure reducing mechanism using the difference between the discharge temperature detected by the discharge temperature sensor and the target discharge temperature.

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