JP5796619B2 - Air conditioner - Google Patents

Description

  The present invention relates to a cooling-only air conditioner used in, for example, a computer room.

  Conventionally, an air conditioner used in, for example, a computer room is known. Since this type of air conditioner performs cooling operation throughout the year, the air conditioner includes a cooling-only refrigerant circuit in which a compressor, a condenser, an expansion mechanism, and an evaporator are connected in this order (for example, Patent Document 1). In this type of refrigerant circuit, when the temperature of the outside air is low (for example, in winter), the capacity of the condenser may become excessive.

  Therefore, in order to adjust the capacity of the condenser, it is conceivable to further provide a bypass circuit in the air conditioner. This bypass circuit is a circuit that has an electric valve capable of controlling the opening degree, and sends the refrigerant discharged from the compressor to the evaporator, bypassing the condenser. When the temperature of the outside air is low, by increasing the opening of the motor-operated valve or decreasing the fan air volume, the refrigerant is stored in the condenser to reduce the capacity of the condenser, and the condensation pressure (refrigerant A means of maintaining the high pressure side pressure in the circuit in a predetermined range is conceivable.

JP 2008-076001 A

  However, in an air conditioner dedicated to cooling, when the operation of storing the refrigerant in the condenser is performed as described above when the temperature of the outside air is low, such as in winter, the refrigerator oil of the compressor is dissolved in the refrigerant in the condenser. May accumulate.

  An object of the present invention is to effectively return refrigeration oil accumulated in a condenser to a compressor in an air conditioner dedicated to cooling.

The air conditioner of the present invention is a dedicated air conditioner including a main refrigerant circuit (11), a bypass circuit (12), a fan (28), and a control unit (27). The main refrigerant circuit (11) includes a compressor (24), a condenser (25), a first valve (21) capable of opening control, and an evaporator (26). The bypass circuit (12) has a second valve (22) capable of opening degree control. The bypass circuit (12) is connected to the main refrigerant circuit (11) so that the refrigerant discharged from the compressor (24) bypasses the condenser (25) and the first valve (21). Yes. The fan (28) creates a flow of air to the condenser (25). The controller (27) controls the compressor (24), the first valve (21), the second valve (22), and the fan (28). The control unit (27) performs a normal operation and an oil return operation of the condenser. In the normal operation, the condensation pressure is adjusted by adjusting at least one of the opening degree of the first valve (21), the opening degree of the second valve (22), and the air volume of the fan (28). In the oil return operation of the condenser, when a predetermined condition is satisfied, among the control for increasing the opening degree of the first valve (21) and the control for reducing the opening degree of the second valve (22). At least the opening degree of the second valve (22) is controlled to return the refrigeration oil in the condenser (25) to the compressor (24) together with the refrigerant.

  In this configuration, during normal operation, at least one of the opening degree of the first valve (21), the opening degree of the second valve (22) and the air volume of the fan (28) is adjusted to reduce the condensation pressure (the high pressure side in the refrigerant circuit). The condensation pressure can be adjusted to a predetermined range by adjusting the pressure (hereinafter sometimes referred to as a high pressure). In addition, when the temperature of the outside air is low, such as in winter, the capacity of the condenser may become excessive. In this case, for example, the opening degree of the first valve (21) may be reduced in normal operation. The capacity of the condenser (25) is reduced by increasing the opening of the second valve (22) or decreasing the air volume of the fan (28), and the liquid refrigerant is stored in the condenser (25). Thereby, the condensation pressure can be adjusted to a predetermined range (a range of a predetermined target high pressure).

When the liquid refrigerant is accumulated in the condenser (25) by the normal operation when the temperature of the outside air is low, the refrigerating machine oil is dissolved in the liquid refrigerant accumulated in the condenser (25). ). Even if the refrigeration oil accumulates in the condenser (25) as described above, the control for increasing the opening degree of the first valve (21) and the second valve (22) when the predetermined condition is satisfied. Of the control for reducing the opening, at least the second valve (22) is controlled to reduce the opening, and the refrigerating machine oil accumulated in the condenser (25) is returned to the compressor (24) together with the refrigerant. Return operation is performed. By performing the oil return operation of such a condenser, the condenser (25) to secure the differential pressure across the (condenser (25) pressure near the inlet and the condenser pressure difference in the vicinity of the outlet (25) Securing) and condensation pressure fluctuations. Thereby, since the flow of a refrigerant | coolant can be accelerated | stimulated in a condenser (25), the refrigeration oil which accumulates in a condenser (25) can be effectively returned to a compressor (24) with a refrigerant | coolant.

  In the air conditioner, the control unit (27) controls the first valve (21) so that the opening degree of the first valve (21) is fully opened in the oil return operation of the condenser. Is preferred. In this configuration, by controlling the first valve (21) so that the opening degree of the first valve (21) is fully opened, a large fluctuation in the condensation pressure before and after the opening degree control of the first valve (21). Can be generated. Thereby, the refrigerating machine oil accumulated in the condenser can be pushed out of the condenser more effectively.

  In the air conditioner, the control unit (27) increases the operation capacity of the compressor (24) and causes the refrigerating machine oil accumulated in the gas pipe of the main refrigerant circuit (11) to the compressor (24). It is preferable to perform an oil return operation of the return gas pipe. In the gas pipe through which the gas refrigerant flows, refrigeration oil may adhere to the inner surface of the gas pipe and accumulate, but by performing an oil return operation of the gas pipe that increases the operating capacity of the compressor (24), The refrigerating machine oil accumulated in the gas pipe can be returned to the compressor (24).

  In the air conditioner, the control unit (27) performs the oil return operation of the condenser in a state where the operation capacity of the compressor (24) is maintained after performing the oil return operation of the gas pipe. Is preferred. In this configuration, the oil return operation of the condenser is performed in a state where the operating capacity of the compressor (24) raised in the oil return operation of the gas pipe is maintained, that is, in a state where the refrigerant circulation amount in the refrigerant circuit is increased. In the oil return operation of the condenser, the amount of refrigerant flowing through the condenser can be increased. Thereby, the refrigerating machine oil collected in the condenser can be pushed out of the condenser more effectively.

  In the air conditioner, the predetermined condition includes, for example, a condition that the amount of oil sump is equal to or greater than a predetermined reference amount. The amount of oil reservoir and the degree of lack of refrigerating machine oil in the compressor (24) are related to each other. Therefore, the oil return operation of the condenser is more reliably performed when the oil return is required by determining whether or not the oil return operation is necessary based on the above-mentioned condition regarding the oil sump amount as in this configuration. Can do.

  In the air conditioner, the predetermined condition includes, for example, a condition that an opening degree of the first valve (21) is equal to or less than a predetermined reference opening degree. When the opening degree of the first valve (21) is equal to or less than a predetermined reference opening degree, the refrigerating machine oil tends to accumulate in the condenser (25). Further, when the opening degree of the first valve (21) is equal to or less than a predetermined reference opening degree, the fluctuation range of the opening degree of the first valve (21) (the increase amount of the opening degree) in the oil return operation of the condenser. Can be increased. Therefore, the oil return operation of the condenser is performed when the oil return is required by determining whether or not the oil return operation is necessary based on the above-described conditions regarding the opening degree of the first valve (21) as in this configuration. This can be executed more reliably, and a large fluctuation of the condensation pressure can be caused before and after the opening control of the first valve (21).

  In the air conditioner, the predetermined condition includes, for example, a condition that an outdoor air temperature is equal to or lower than a predetermined reference temperature. When the temperature of the outside air is low, the refrigerant is stored in the condenser during normal operation and the condensation pressure is adjusted to a predetermined range, so that the amount of oil pool increases. Therefore, the oil return operation of the condenser is more reliably executed when the oil return is required by determining whether or not the oil return operation is necessary based on the above-described conditions relating to the outdoor air temperature as in this configuration. Can do.

  In the air conditioner, the predetermined condition includes, for example, a condition that a state where the operation capacity of the compressor (24) is equal to or less than a predetermined reference value continues for a predetermined time. When the motor of the compressor (24) is operated at a low frequency (number of rotations), since the amount of refrigerant circulating in the refrigerant circuit is small, the refrigeration oil is not easily pushed out of the condenser and tends to accumulate in the condenser. is there. Therefore, by determining whether or not the oil return operation is necessary based on the above-described conditions relating to the operating capacity of the compressor (24) as in this configuration, the oil return operation of the condenser can be further performed when the oil return is required. It can be executed reliably.

  In the air conditioner, the control unit (27) may perform control to reduce the air volume of the fan (28) in the oil return operation of the condenser. In this configuration, in the oil return operation of the condenser, not only the opening control of the first valve (21) and the second valve (22) but also the control for reducing the air volume of the fan (28) is performed. The condensation pressure can be increased by reducing the air volume of the fan (28). Therefore, in the configuration in which the opening degree control of at least one of the first valve (21) and the second valve (22) and the air volume control of the fan (28) are performed, it is larger than the case where only the opening degree control of the valve is performed. Variations in condensation pressure can occur. Thereby, the refrigerating machine oil collected in the condenser can be pushed out of the condenser more effectively.

  In the air conditioner, the condenser (25) is a water-cooled heat exchanger, and the control unit (27) is configured to supply water flowing into the condenser (25) during oil return operation of the condenser. Control for reducing the flow rate may be performed. In this configuration, in the oil return operation of the condenser, not only the opening degree control of the first valve (21) and the second valve (22) but also the control for reducing the flow rate of the water flowing into the condenser (25) is performed. The condensing pressure can be increased by reducing the flow rate of water flowing into the condenser (25). Therefore, in the configuration in which the opening control of at least one of the first valve (21) and the second valve (22) and the flow rate control of water are performed, a larger condensation pressure can be obtained as compared with the case of performing only the valve opening control. Variations can occur. Thereby, the refrigerating machine oil collected in the condenser can be pushed out of the condenser more effectively.

  ADVANTAGE OF THE INVENTION According to this invention, in the air conditioner only for cooling, the refrigerating machine oil collected in the condenser can be effectively returned to a compressor.

1 is a schematic configuration diagram of an air conditioner according to an embodiment of the present invention. It is a control block diagram in the air conditioner according to the embodiment. It is a flowchart which shows the control example 1 of the air conditioner which concerns on the said embodiment. It is a flowchart which shows the control example 2 of the air conditioner which concerns on the said embodiment. It is a schematic block diagram of the air conditioner which concerns on the modification of the said embodiment. (A)-(C) are the graphs for demonstrating the fluctuation | variation of the differential pressure before and behind the condenser in the oil return operation | movement of a condenser.

  Hereinafter, an air conditioner according to an embodiment of the present invention will be described with reference to the drawings.

[Configuration of air conditioner]
As shown in FIG. 1, the air conditioner 1 which concerns on this embodiment is an air conditioner only for a refrigerant | coolant. The air conditioner 1 includes a refrigerant circuit 10 and cools the room by performing a vapor compression refrigeration cycle operation. When the object of cooling is a computer room such as a server room, for example, the air conditioner 1 continuously performs a cooling operation for adjusting the room to a predetermined temperature range throughout the year.

  An air conditioner 1 according to this embodiment includes a heat source unit (outdoor unit) 2 installed outdoors, a utilization unit (indoor unit) 3 installed indoors, and a refrigerant communication tube 4 that connects these units. And 5. The refrigerant circuit 10 includes a main refrigerant circuit 11 and a bypass circuit 12.

  The main refrigerant circuit 11 includes a compressor 24, a condenser 25, a first valve 21 capable of opening degree control, and an evaporator 26. The main refrigerant circuit 11 is provided in the heat source unit 2 and forms a part of the main refrigerant circuit 11, and the heat source side main refrigerant circuit 11 a that forms a part of the main refrigerant circuit 11 and the use side that forms a part of the main refrigerant circuit 11 in the use unit 3. Main refrigerant circuit 11b. In this embodiment, the condenser 25 and the first valve 21 are provided in the heat source side main refrigerant circuit 11a, and the compressor 24 and the evaporator 26 are provided in the use side main refrigerant circuit 11b. Not limited to. For example, the compressor 24 may be provided in the heat source side main refrigerant circuit 11a.

  The bypass circuit 12 has a second valve 22 capable of opening degree control. The bypass circuit 12 is connected to the main refrigerant circuit 11 (more specifically, the heat source side main refrigerant circuit 11a) so as to bypass the refrigerant discharged from the compressor 24 through the condenser 25 and the first valve 21. .

  The compressor 24 has a function of sucking low-pressure refrigerant, compressing it, and discharging it as high-pressure refrigerant. The compressor 24 is driven by a compressor motor 24M. The compressor motor 24M is driven by receiving electric power via an inverter device. The compressor 24 is a compressor whose operating capacity can be changed by changing the frequency (that is, the rotation speed) of the compressor motor 24M. The suction side of the compressor 24 is connected to the outlet of the evaporator 26, and the discharge side of the compressor 24 is connected to the inlet of the condenser 25 via the refrigerant communication pipe 4.

  As the condenser 25, for example, a cross fin type heat exchanger constituted by a heat transfer tube and a large number of fins can be used, but is not limited thereto. The condenser 25 has a function of condensing the high-pressure refrigerant using outdoor air as a heat source. The outlet of the condenser 25 is connected to the utilization unit 3 (more specifically, the third valve 23) via the first valve 21, the refrigerant regulator 30, the supercooling heat exchanger 31, and the refrigerant communication pipe 5. Yes. The inlet of the condenser 25 is connected to the utilization unit 3 (more specifically, the discharge side of the compressor 24) via the refrigerant communication pipe 4.

  As the evaporator 26, for example, a cross fin type heat exchanger constituted by a heat transfer tube and a large number of fins can be used, but is not limited thereto. The evaporator 26 has a function of evaporating the low-pressure refrigerant and cools indoor air. The inlet of the evaporator 26 is connected to the third valve 23. The outlet of the evaporator 26 is connected to the suction side of the compressor 24.

  In the present embodiment, the first valve 21 is an electric valve (expansion valve) capable of opening degree control, but is not limited thereto. The first valve 21 is mainly used when performing control (high pressure control) for maintaining the condensation pressure (high pressure) in a predetermined range. The second valve 22 is an electric valve (expansion valve) capable of opening degree control, but is not limited thereto. The second valve 22 is mainly used when performing the above-described high pressure control. In the present embodiment, the main refrigerant circuit 11 has a third valve 23 capable of opening degree control. The third valve 23 is an electronic expansion valve capable of opening degree control, but is not limited thereto. The third valve 23 is mainly used when the refrigerant cooled in the condenser 25 of the heat source unit 2 is decompressed. The third valve 23 is provided in the use side main refrigerant circuit 11 b and is connected to the heat source side main refrigerant circuit 11 a via the refrigerant communication pipe 5.

  In the present embodiment, the main refrigerant circuit 11 includes a refrigerant regulator (receiver) 30, a supercooling heat exchanger 31, and an oil separator 32. The refrigerant regulator 30 is provided on the downstream side of the condenser 25, and is configured by a container that absorbs fluctuations in the refrigerant amount in the evaporator 26 due to load fluctuations. The supercooling heat exchanger 31 further cools the refrigerant liquefied in the condenser 25, and cools it below its saturation temperature. The oil separator 32 is for separating a part of the refrigerating machine oil from the refrigerant discharged from the compressor 24. A part of the refrigerating machine oil discharged together with the refrigerant from the compressor 24 is separated from the refrigerant in the oil separator 32 and returned to the suction side of the compressor 24 through the oil return circuit 13 provided with the capillary tube 33. In the present embodiment, the third valve 23 and the oil separator 32 are provided in the use side main refrigerant circuit 11b, and the refrigerant regulator 30 and the supercooling heat exchanger 31 are provided in the heat source side main refrigerant circuit 11a. However, it is not limited to this.

  The heat source unit 2 includes a heat source side fan 28 that forms a flow of air to the condenser 25. The heat source side fan 28 sucks outdoor air from the suction port into the heat source unit 2, exchanges heat with the refrigerant in the condenser 25 accommodated in the heat source unit 2, and then blows it out as outdoor air from the air outlet. The air flow is formed. The heat source side fan 28 is driven by a fan motor 28M. In the present embodiment, the fan motor 28M is driven by receiving electric power via an inverter device. The heat source side fan 28 can change the air volume by changing the frequency (that is, the rotation speed) of the fan motor 28M.

  The usage unit 3 includes a usage-side fan 29 that forms an air flow to the evaporator 26. The usage-side fan 29 sucks room air into the usage unit 3 from the suction port, exchanges heat with the refrigerant in the evaporator 26 accommodated in the usage unit 3, and then blows it out into the room as supply air from the blow-out port. The air flow is formed. The use side fan 29 is driven by a fan motor 29M.

  The air conditioner 1 is provided with various sensors. For example, the heat source unit 2 is provided with an outdoor temperature sensor 41 that detects the temperature of outdoor air. Further, the utilization unit 3 is provided with a suction pressure sensor 42 for detecting the suction pressure of the compressor 24, a discharge pressure sensor 43 for detecting the discharge pressure of the compressor 24, and the like.

  The air conditioner 1 includes a control unit 27 that controls the operation of the air conditioner 1. The control unit 27 may be provided in the heat source unit 2, may be provided in the utilization unit 3, or may be provided in both of them. The control unit 27 includes, for example, a microcomputer and a memory.

  FIG. 2 is a control block diagram of the air conditioner 1 according to the present embodiment. The control unit 27 can capture signals corresponding to state quantities (pressure value, temperature, etc.) detected by various sensors such as the sensors 41, 42, and 43. And the control part 27 controls operation | movement of the compressor 24, the 1st valve 21, the 2nd valve 22, the 3rd valve 23, the heat-source side fan 28, the utilization side fan 29, etc. based on these signals.

[Air conditioner operation]
In the air conditioner 1 according to the present embodiment, the control unit 27 performs a normal operation and an oil return operation of the condenser. The air conditioner 1 may further perform an oil return operation of the gas pipe. Hereinafter, the normal operation and the oil return operation will be specifically described.

(Normal operation)
In normal operation, the temperature of the indoor air that is the object of cooling is adjusted to a predetermined range, and the condensation pressure (high pressure) is adjusted to a predetermined range in order to maintain the reliability of the compressor 24. Specifically, in the normal operation, the control unit 27 determines that the condensing pressure is within a predetermined target high pressure range based on the high pressure in the refrigerant circuit 10 (for example, the discharge pressure of the compressor 24 detected by the discharge pressure sensor 43). The refrigerant circuit 10 is controlled to enter.

  In the normal operation, when the compressor 24, the heat source side fan 28, the use side fan 29, and the like are activated, the refrigerant circuit 10 performs the following refrigeration cycle operation. First, the low-pressure refrigerant is sucked into the compressor 24 of the usage unit 3 and compressed to become a high-pressure refrigerant. The high-pressure refrigerant discharged from the compressor 24 is sent to the heat source unit 2 via the refrigerant communication pipe 4, and is cooled by exchanging heat with outdoor air supplied by the heat source side fan 28 in the condenser 25. Then, the high-pressure refrigerant cooled in the condenser 25 is sent to the utilization unit 3 via the first valve 21 and the refrigerant communication pipe 5. At this time, the opening degree of the first valve 21 provided in the main refrigerant circuit 11 and the opening degree of the second valve 22 provided in the bypass circuit 12 are controlled as follows, for example.

  When the normal operation is performed when the temperature of the outside air is relatively high, the load of the cooling operation is large, so the capacity of the condenser 25 needs to be increased. In this case, for example, the control unit 27 performs control to increase the opening degree of the first valve 21, reduce the opening degree of the second valve 22, or increase the air volume of the heat source side fan 28. Specifically, when the cooling operation load is large, for example, the opening degree of the first valve 21 is set to a fully open state, while the opening degree of the second valve 22 is set to a fully closed state, for example. Not limited to this.

  Further, when the normal operation is performed when the temperature of the outside air is low, such as in winter, the cooling operation load is small, so that the condensation pressure is maintained within a predetermined range while maintaining the indoor air within a predetermined temperature range. Therefore, it is necessary to reduce the capacity of the condenser 25. In this case, for example, the control unit 27 performs control to reduce the opening degree of the first valve 21, increase the opening degree of the second valve 22, or reduce the air volume of the heat source side fan 28. Specifically, when the cooling operation load is small, the opening degree of the first valve 21 can be reduced while the opening degree of the second valve 22 can be fully opened, but is not limited thereto. .

  The high-pressure refrigerant sent to the usage unit 3 is reduced in pressure by the third valve 23 to become a low-pressure gas-liquid two-phase refrigerant and sent to the evaporator 26, and is supplied by the usage-side fan 29 in the evaporator 26. Heat is exchanged with air. As a result, the refrigerant evaporates into a low-pressure gas refrigerant. The low-pressure gas refrigerant heated in the evaporator 26 is again sucked into the compressor 24.

(Oil return operation)
Next, the oil return operation will be described. When the normal operation is performed, in the gas pipe of the refrigerant circuit 10 through which the gas refrigerant flows, the refrigerating machine oil of the compressor 24 may adhere to the inner surface of the gas pipe and accumulate. Further, if the liquid refrigerant is accumulated in the condenser 25 in the normal operation when the temperature of the outside air is low, the refrigerating machine oil may be accumulated in the condenser 25 in a state of being dissolved in the liquid refrigerant.

  Therefore, in the air conditioner 1 according to the present embodiment, the oil return operation of the gas pipe for returning the refrigeration oil accumulated in the gas pipe to the compressor 24 and the refrigeration oil accumulated in the condenser 25 are returned to the compressor 24. The oil return operation of the condenser is performed. In the oil return operation of the gas pipe, in order to return the refrigeration oil adhering to the inner surface of the gas pipe to the compressor 24, the operation capacity of the compressor 24 is increased and the flow rate of the refrigerant flowing through the refrigerant circuit 10 is increased. Thereby, a part or all of the refrigerating machine oil accumulated in the gas pipe can be returned to the compressor 24. In the oil return operation of the condenser, in order to return the refrigeration oil dissolved in the liquid refrigerant in the condenser 25 to the compressor 24, the control for increasing the opening degree of the first valve 21 and the second valve 22 At least one of the controls for reducing the opening is performed to increase the flow rate of the refrigerant flowing through the condenser 25. Thereby, the refrigerating machine oil can be returned to the compressor 24 together with the liquid refrigerant in the condenser 25.

  The oil return operation of the gas pipe and the oil return operation of the condenser may be performed at different times or may be performed continuously. Specifically, a mode in which only the condenser oil return operation is performed independently as in Control Example 1 described later, and the oil in the condenser is immediately after the oil return operation of the gas pipe is performed as in Control Example 2 described later. Although the form etc. which perform a return operation can be illustrated, it is not restricted to these forms.

  The air conditioner 1 according to the present embodiment continuously performs a cooling operation for adjusting a room to a predetermined temperature range throughout the year. Therefore, the operation of the compressor 24 is easy to be stabilized and it is easy to maintain a certain state. That is, since it is easy to maintain the state where the rotation speed of the compressor 24 is low, the refrigerating machine oil tends to accumulate particularly in the gas pipe and the condenser 25.

(Control example 1)
FIG. 3 is a flowchart showing a control example 1 of the air conditioner 1 according to the present embodiment. As shown in FIG. 3, in step 1, the control unit 27 controls the refrigerant circuit 10 so that a normal operation for adjusting the indoor air temperature to a predetermined temperature range is performed.

  In step S <b> 2, the control unit 27 determines whether a start condition for the oil return operation of the condenser is satisfied. If the start condition is not satisfied, the process returns to the process of step S1 and the normal operation is continued. If the start condition is satisfied, the process proceeds to the process of step S3 to change from the normal operation to the condenser. Switch to the oil return operation.

The conditions for starting the oil return operation of the condenser are conditions determined in advance in the air conditioner 1. Examples of the start condition include the following conditions (A), (B), (C), and (D), but are not limited to these, and other conditions may be employed. The start condition for the oil return operation of the condenser may be, for example, one of the conditions (A), (B), (C), (D), and the conditions (A), (B) , (C), (D) may be combined.
(A) The amount of oil sump is equal to or greater than a predetermined reference amount (B) The opening degree of the first valve 21 is equal to or less than a predetermined reference opening degree (C) The operating capacity of the compressor 24 is predetermined. (D) The outdoor temperature is equal to or lower than a predetermined reference temperature. The reference amount for condition (A) and the reference open for condition (B). The reference value of the condition (C) and the reference temperature of the condition (D) are stored in the memory of the control unit 27. These criteria may be changeable by the user as needed.

  In the condition (A), the amount of oil pool is, for example, the amount of refrigerating machine oil contained in the refrigerant discharged from the compressor 24 and the refrigerant separated in the oil separator 32 and supplied to the compressor 24 through the oil return circuit 13. It can be obtained by integrating the returned oil return amount.

  When the condition (A) is employed, in step S2, the control unit 27 determines whether or not the accumulated oil sum is equal to or greater than a reference value. When the oil sum is less than the reference value, the process returns to step S1 to continue normal operation. When the oil sum is equal to or greater than the reference value, the process proceeds to step S3 and the normal operation starts. Switch to condenser oil return operation.

  When the condition (B) is employed, in step S2, the control unit 27 determines whether or not the opening degree of the first valve 21 is equal to or less than the reference opening degree. When the opening degree of the first valve 21 exceeds the reference opening degree, the process returns to step S1 to continue normal operation. When the opening degree of the first valve 21 is equal to or less than the reference opening degree, step S3 is performed. The process is switched to the normal operation and the condenser oil return operation. In addition, this condition (B) is good also as the state where the opening degree of the 1st valve 21 is below a predetermined reference opening degree continuing for the predetermined time. Thereby, the judgment precision of the necessity for oil return operation can be raised more.

  When the condition (C) is employed, in step S2, the control unit 27 determines that the operating capacity of the compressor 24, specifically, the frequency (that is, the rotation speed) of the compressor motor 24M is equal to or less than a predetermined reference value. It is determined whether or not this state continues for a predetermined time. If the start condition is not satisfied, the process returns to the process of step S1 and the normal operation is continued. If the start condition is satisfied, the process proceeds to the process of step S3 and the condenser is changed from the normal operation to the condenser. Switch to the oil return operation.

  When the condition (D) is employed, in step S2, the control unit 27 determines whether or not the outdoor air temperature detected by the temperature sensor 41 is equal to or lower than a predetermined reference temperature. If the outdoor temperature exceeds a predetermined reference temperature, the process returns to step S1 to continue normal operation. If the outdoor temperature is equal to or lower than the predetermined reference temperature, the process of step S3 is performed. And switch from normal operation to condenser oil return operation. In addition, this condition (D) is good also as the state where the outdoor temperature is below a predetermined reference temperature for a predetermined time. Thereby, the judgment precision of the necessity for oil return operation can be raised more.

  In step S3, the control unit 27 performs an oil return operation of the condenser. Specifically, the control unit 27 returns the refrigeration oil in the condenser 25 to the compressor 24 together with the refrigerant, for example, the first valve 21 so that the opening degree of the first valve 21 is larger than that during normal operation. To control. In the oil return operation, the opening degree of the first valve 21 is not particularly limited as long as it is larger than that in the normal operation, but it is preferable that the first valve 21 is fully opened, for example.

  FIG. 6A is a graph for explaining fluctuations in the differential pressure across the condenser 25 during the oil return operation of the condenser. In step S3, as shown in FIG. 6A, when the opening of the first valve 21 is made larger than that during normal operation (for example, when the opening of the first valve 21 is fully opened), condensation occurs. The amount of refrigerant flowing into the condenser 25 increases, and the refrigerant in the condenser 25 is pushed by the refrigerant that has flowed in, so the pressure HP near the inlet of the condenser 25 temporarily (instantaneously) increases. As a result, the differential pressure ΔP across the condenser 25, that is, the difference ΔP between the pressure HP near the inlet of the condenser 25 and the pressure LP near the outlet of the condenser 25 temporarily increases. Since the refrigerant flow is promoted in the condenser 25 by such a differential pressure ΔP, the refrigerating machine oil accumulated in the condenser 25 is pushed out of the condenser 25 together with the refrigerant.

  Further, in step S3, the opening degree of the second valve 22 in the oil return operation may be maintained as shown in FIG. 6A, and the opening degree of the second valve 22 in the normal operation may be maintained. ) May be changed so as to be smaller than the opening of the second valve 22 during normal operation.

  Specifically, when the temperature of the outside air is low and the cooling operation load is small, such as in winter, the opening of the first valve 21 is reduced in the normal operation of step S1, while the second valve 22 The opening is fully open. In the control example shown in FIG. 6A, in the oil return operation in step S3, the opening degree of the first valve 21 is, for example, fully open while the opening degree of the second valve 22 is maintained, for example, in a fully open state. Is done. Thus, when the opening degree of the second valve 22 is maintained in the fully opened state when the opening degree of the first valve 21 is in the fully opened state, the fluctuation range of the pressure in the condenser 25 is increased, The pressure fluctuation of the entire refrigerant circuit 10 can be suppressed.

  Further, as in the control example shown in FIG. 6B, in the oil return operation in step S3, the opening degree of the first valve 21 is changed to be larger than the opening degree of the first valve 21 in the normal operation step S1. And when the opening degree of the second valve 22 is changed to be smaller than the opening degree of the second valve 22 during the normal operation in step S1 (for example, when the opening degree of the second valve 22 is fully closed). As compared with the case where the opening degree during normal operation is maintained in the second valve 22 as in the control example shown in FIG. 6 (A), before and after the opening degree control of the first valve 21 and the second valve. Since a larger fluctuation of the condensation pressure can be caused, the refrigerating machine oil accumulated in the condenser 25 can be pushed out of the condenser 25 more effectively. In the control example shown in FIG. 6B, the control for increasing the opening degree of the first valve 21 and the control for decreasing the opening degree of the second valve 22 may be slightly different in time, but preferably Should be done at the same time.

  In step S3, as shown in FIG. 6C, the opening degree of the second valve 22 is made smaller than that in the normal operation, while the opening degree of the first valve 21 is maintained in the normal operation state. May be. In this case, in the oil return operation, the opening degree of the second valve 22 is not particularly limited as long as it is smaller than that in the normal operation. For example, the second valve 22 is fully closed, and the first valve 21 is opened. The degree is not at least fully closed.

  In step S3, as shown in FIG. 6C, when the opening degree of the second valve 22 is made smaller than that during normal operation (for example, when the opening degree of the second valve 22 is fully closed), Since the refrigerant in the condenser 25 is pushed temporarily (instantaneously), the pressure HP near the inlet of the condenser 25 temporarily (instantaneously) increases. As a result, the differential pressure ΔP across the condenser 25, that is, the difference ΔP between the pressure HP near the inlet of the condenser 25 and the pressure LP near the outlet of the condenser 25 temporarily increases. Since the refrigerant flow is promoted in the condenser 25 by such a differential pressure ΔP, the refrigerating machine oil accumulated in the condenser 25 is pushed out of the condenser 25 together with the refrigerant.

  Further, the air volume of the heat source side fan 28 in the oil return operation may be maintained so that the air volume of the heat source side fan 28 during the normal operation may be maintained, and may be changed to be smaller than the air volume of the heat source side fan 28 during the normal operation. Also good. That is, in the oil return operation of the condenser, the frequency (rotation speed) of the fan motor 28M may be changed to be smaller than the frequency (rotation speed) during normal operation. When the air volume of the heat source side fan 28 in the oil return operation is changed to be smaller than the air volume of the heat source side fan 28 in the normal operation, the condensation pressure can be increased, so that the air volume in the normal operation is maintained. In comparison with this, a larger fluctuation of the condensation pressure can be caused. Thereby, the refrigerating machine oil accumulated in the condenser 25 can be pushed out of the condenser 25 more effectively.

  In step S3, the timing for reducing the air volume of the heat source side fan 28 may be before the opening degree of the first valve 21 or after the opening degree of the first valve 21 is increased. However, when the opening degree of the first valve 21 is increased, a larger fluctuation of the condensation pressure can be caused. Similarly, in step S <b> 3, the timing for reducing the air volume of the heat source side fan 28 may be before the opening of the second valve 22 is reduced, or when the opening of the second valve 22 is reduced. However, when the opening degree of the second valve 22 is decreased, a larger fluctuation of the condensation pressure can be caused.

  Next, in step S4, the control unit 27 determines whether or not an end condition for the oil return operation of the condenser is satisfied. If the end condition is not satisfied, the process returns to step S3 and the oil return operation is continued. If the end condition is satisfied, the process returns to step S1 and the normal operation from the oil return operation is resumed. Switch to operation.

  The condition for ending the oil return operation of the condenser is a predetermined condition in the air conditioner 1. Examples of the end condition include a condition that the elapsed time from the start of the oil return operation in step S3 reaches a predetermined time, but is not limited to this, and other conditions can also be adopted.

(Control example 2)
FIG. 4 is a flowchart showing a control example 2 of the air conditioner 1 according to the present embodiment. This control example 2 is different from the control example 1 in that not only the condenser oil return operation but also the gas pipe oil return operation is performed.

  In the control example 2 shown in FIG. 4, step S11 is the same as step S1 of the control example 1. In step S <b> 12, the control unit 27 determines whether a start condition for the oil return operation of the gas pipe is satisfied. If the start condition is not satisfied, the process returns to step S11 to continue the normal operation. If the start condition is satisfied, the process proceeds to step S13 and the normal operation is changed to the gas pipe. Switch to the oil return operation.

  The start condition of the oil return operation of the gas pipe in step S12 is a condition determined in advance in the air conditioner 1. Examples of conditions for starting the oil return operation of the gas pipe include the conditions (A), (B), (C), and (D) in Control Example 1, but are not limited to these, and other conditions are adopted. You can also The start condition of the oil return operation of the gas pipe may be one of the conditions (A), (B), (C), (D), and the conditions (A), (B), A condition combining a plurality of (C) and (D) may be used.

  In step S13, the control unit 27 performs an oil return operation of the gas pipe. In the oil return operation of the gas pipe, the control unit 27 performs control to increase the operating capacity of the compressor 24 compared to that during normal operation in order to return the refrigeration oil in the gas pipe to the compressor 24. Specifically, the compressor motor 24M is driven so that the frequency (that is, the rotation speed) of the compressor motor 24M is larger than that in the normal operation. As a result, the amount of refrigerant circulating in the refrigerant circuit 10 increases, so that part or all of the refrigerating machine oil adhering to the inner surface of the gas pipe is returned to the compressor 24.

  In step S <b> 14, the control unit 27 determines whether an end condition for the oil return operation of the gas pipe is satisfied. If the end condition is not satisfied, the process returns to the process of step S13 and the oil return operation of the gas pipe is continued. If the end condition is satisfied, the process proceeds to step S15 and the gas is returned. Switch from the oil return operation of the pipe to the oil return operation of the condenser.

  The end condition of the oil return operation of the gas pipe is a condition predetermined in the air conditioner 1. Examples of the end condition include a condition that the elapsed time from the start of the oil return operation in step S13 reaches a predetermined time, but is not limited to this, and other conditions can also be adopted.

  In step S15, the control unit 27 performs an oil return operation of the condenser. The operation capacity of the compressor 24 in the oil return operation of the condenser in step S15 may be changed from the operation capacity of the compressor 24 in the oil return operation of the gas pipe in step S13, but the compression in the oil return operation of the gas pipe The operating capacity of the machine 24 is preferably maintained. In Step S15 of Control Example 2, the oil return operation of the condenser is performed in the same manner as Step S3 of Control Example 1.

  Since step S16 of the control example 2 is the same as the step S4 of the control example 1, detailed description thereof is omitted. During the oil return operation of the condenser, the condensation pressure may fluctuate from the condensation pressure during the normal operation. Therefore, the oil return operation of the condenser is preferably completed in a short time. Therefore, when the condition that the elapsed time from the start of the oil return operation reaches a predetermined time is adopted as the end condition of the oil return operation of the condenser in step S16, the operation of the oil return operation of the condenser is adopted. The time is preferably set shorter than the operation time of the oil return operation of the gas pipe.

[Summary of Embodiment]
In the present embodiment, in normal operation, the condensation pressure is adjusted to a predetermined value by adjusting at least one of the opening degree of the first valve 21, the opening degree of the second valve 22, and the air volume of the fan 28. Can be adjusted to range. Further, for example, when the temperature of the outside air is low, such as in winter, the capacity of the condenser may become excessive. In this case, in normal operation, for example, the opening degree of the first valve 21 may be reduced, The capacity of the condenser 25 is reduced by increasing the opening degree of the two valves 22 or by reducing the air volume of the fan 28, and the liquid refrigerant is stored in the condenser 25. Thereby, the condensation pressure can be adjusted to a predetermined range.

When the liquid refrigerant is accumulated in the condenser 25 by normal operation when the temperature of the outside air is low, the refrigeration oil is accumulated in the condenser 25 in a state of being dissolved in the liquid refrigerant accumulated in the condenser 25. Specifically, for example, when the differential pressure across the condenser 25 (the difference between the pressure near the inlet of the condenser 25 and the pressure near the outlet of the condenser 25) is small, In some cases, the refrigerant and the refrigerating machine oil do not circulate and accumulate in the flow path. Even if the refrigeration oil accumulates in the condenser 25 in this way, when the predetermined condition is satisfied, the control and the second valve for making the opening degree of the first valve 21 larger than the opening degree during the normal operation. Among the controls for making the opening degree of 22 smaller than the opening degree during normal operation, at least the opening degree of the second valve 22 is controlled to return the refrigeration oil accumulated in the condenser 25 to the compressor 24 together with the refrigerant. The oil return operation of the condenser is performed. By performing such an oil return operation of the condenser, it is possible to ensure the differential pressure across the condenser 25 and to change the condensation pressure. Thereby, since the flow of a refrigerant | coolant can be accelerated | stimulated in the condenser 25, the refrigerating machine oil which accumulates in the condenser 25 can be pushed out of the condenser 25 with a refrigerant | coolant, and can be effectively returned to the compressor 24. FIG.

  Moreover, in this embodiment, it is preferable that the control part 27 controls the 1st valve 21 so that the opening degree of the 1st valve 21 may be in a fully open state in the oil return operation | movement of a condenser. In this configuration, by controlling the first valve 21 so that the opening degree of the first valve 21 is fully opened, a large fluctuation in the condensation pressure can be caused before and after the opening degree control of the first valve 21. . Thereby, the refrigerating machine oil accumulated in the condenser 25 can be pushed out of the condenser 25 more effectively.

  In the present embodiment, the control unit 27 performs an oil return operation of the gas pipe that increases the operating capacity of the compressor 24 and returns the refrigeration oil accumulated in the gas pipe of the main refrigerant circuit 11 to the compressor 24. preferable. In the gas pipe through which the gas refrigerant flows, the refrigeration oil may adhere to the inner surface of the gas pipe and accumulate, but by performing an oil return operation of the gas pipe that increases the operating capacity of the compressor 24, The refrigerating machine oil accumulated in can be returned to the compressor 24.

  Moreover, in this embodiment, it is preferable that the control part 27 performs the oil return operation | movement of a condenser in the state which maintained the operation capacity of the compressor 24, after performing the oil return operation | movement of a gas pipe. In this configuration, since the operation capacity of the compressor 24 raised in the oil return operation of the gas pipe is maintained, that is, the refrigerant circulation amount in the refrigerant circuit is increased, the oil return operation of the condenser is performed. The amount of refrigerant flowing through the condenser 25 in the oil return operation of the vessel can be increased. Thereby, the refrigerating machine oil accumulated in the condenser 25 can be pushed out of the condenser 25 more effectively.

  Further, in the oil return operation of the condenser, not only the opening degree control of the first valve 21 and the second valve 22 but also the control for reducing the air volume of the fan 28 may be performed. By reducing the air volume of the fan 28, the condensation pressure can be increased. Therefore, in the configuration in which the opening degree control of at least one of the first valve 21 and the second valve 22 and the air volume control of the fan 28 are performed, a larger variation in the condensation pressure occurs than in the case where only the valve opening degree control is performed. Can be made. Thereby, the refrigerating machine oil accumulated in the condenser 25 can be pushed out of the condenser 25 more effectively.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to these embodiment, A various change, improvement, etc. are possible in the range which does not deviate from the meaning.

  For example, in the above-described embodiment, the case where the condenser 25 is a heat exchanger that exchanges heat between the refrigerant and the outdoor air is exemplified. It may be a heat exchanger of the type. That is, as shown in FIG. 5, the water-cooled condenser 25 includes a refrigerant passage and a water passage. Circulating water (cooling water) that flows into the water passage through the water pipe 25a is configured to flow out into the water pipe 25b after exchanging heat with the refrigerant. In the oil return operation of the condenser in the control example 1 and the control example 2, the control unit 27 may perform control to reduce the flow rate of the cooling water flowing into the condenser 25.

  Moreover, in the said embodiment, although control which enlarges the opening degree of the 1st valve 21 was illustrated so that the opening degree of the 1st valve 21 might be in a fully open state in the oil return operation | movement of a condenser, it is not restricted to this. . In the oil return operation of the condenser, control may be performed to increase the opening degree of the first valve 21 so that the opening degree of the first valve 21 is smaller than the fully opened state.

  Further, in the control example 2, after the oil return operation of the gas pipe is performed, the oil return operation of the condenser is performed in a state where the operation capacity of the compressor 24 is maintained, but the present invention is not limited to this. The oil return operation of the condenser may be performed after the operation capacity of the compressor 24 is changed after the oil return operation of the gas pipe. Further, the oil return operation of the gas pipe may be performed after the oil return operation of the condenser.

  The air conditioner 1 may include a plurality of refrigerant circuit systems. That is, the present invention can be applied to an air conditioner including a plurality of vapor compression refrigerant circuit systems each having a compressor, a condenser, an expansion mechanism, and an evaporator.

  The refrigerant circuit 10 may be provided with a plurality of compressors. The air conditioner 1 is a so-called remote condenser type in which the compressor 24 is provided in the use unit 3, but may be a type in which the compressor 24 is provided in the heat source unit 2.

DESCRIPTION OF SYMBOLS 1 Air conditioner 2 Heat source unit 3 Use unit 10 Refrigerant circuit 11 Main refrigerant circuit 11a Heat source side main refrigerant circuit 11b Usage side main refrigerant circuit 12 Bypass circuit 21 1st valve 22 2nd valve 23 3rd valve 24 Compressor 24M Compressor Motor 25 condenser 26 evaporator 27 control unit 28 heat source side fan 28M fan motor

Claims (10)

A main refrigerant circuit (11) having a compressor (24), a condenser (25), a first valve (21) capable of opening control, and an evaporator (26);
The main refrigerant has a second valve (22) capable of opening control and bypasses the refrigerant discharged from the compressor (24) through the condenser (25) and the first valve (21). A bypass circuit (12) connected to the circuit (11);
A fan (28) that creates a flow of air to the condenser (25);
A controller (27) for controlling the compressor (24), the first valve (21), the second valve (22), and the fan (28), and a cooling-only air conditioner,
The control unit (27)
A normal operation for adjusting the condensation pressure by adjusting at least one of the opening degree of the first valve (21), the opening degree of the second valve (22) and the air volume of the fan (28);
When a predetermined condition is satisfied, the first valve (21) of the control and the second valve opening is increased (22) at least the second valve out of the control of the opening degree smaller of (22) An air conditioner that performs an oil return operation of the condenser that performs control to reduce the opening degree and returns the refrigeration oil in the condenser (25) together with the refrigerant to the compressor (24).   The said control part (27) controls the said 1st valve (21) so that the opening degree of the said 1st valve (21) may be in a fully open state in the oil return operation | movement of the said condenser. Air conditioner.   The control unit (27) increases the operating capacity of the compressor (24) and returns the refrigeration oil accumulated in the gas pipe of the main refrigerant circuit (11) to the compressor (24). The air conditioner according to claim 1 or 2, wherein the air conditioner is operated.   The said control part (27) performs the oil return operation | movement of the said condenser in the state which maintained the operation capacity of the said compressor (24) after performing the oil return operation | movement of the said gas pipe | tube. Air conditioner.   The air conditioner according to any one of claims 1 to 4, wherein the predetermined condition includes a condition that an oil sum is equal to or more than a predetermined reference amount.   The air condition according to any one of claims 1 to 5, wherein the predetermined condition includes a condition that an opening degree of the first valve (21) is equal to or less than a predetermined reference opening degree. Machine.   The air conditioner according to any one of claims 1 to 6, wherein the predetermined condition includes a condition that an outdoor air temperature is equal to or lower than a predetermined reference temperature.   The predetermined condition includes, as a condition, that a state in which an operating capacity of the compressor (24) is equal to or less than a predetermined reference value continues for a predetermined time. Item 1. An air conditioner according to item 1.   The air conditioner according to any one of claims 1 to 8, wherein the control unit (27) performs control to reduce an air volume of the fan (28) in an oil return operation of the condenser. The condenser (25) is a water-cooled heat exchanger;
The air conditioning according to any one of claims 1 to 8, wherein the control unit (27) performs control to reduce a flow rate of water flowing into the condenser (25) in an oil return operation of the condenser. Machine.

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