JP2015111020A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner for performing efficient air conditioning operation independently of the amount of refrigerant circulating in a refrigerant circuit.SOLUTION: A compressor 3, a condenser, a restrictor, and an evaporator are connected to form the refrigerant circuit. When a large amount of refrigerant circulates in the refrigerant circuit, suction superheat control is performed to allow the operation of the restrictor on the basis of the suction temperature of the refrigerant sucked into the compressor 3. When a small amount of refrigerant circulates therein, the suction superheat control is performed until a refrigeration cycle is stabilized and then discharge superheat control is performed to allow the operation of the restrictor on the basis of the discharge temperature of the refrigerant discharged from the compressor 3 after the refrigeration cycle is stabilized.

Description

  The present invention relates to an air conditioner capable of adjusting a circulating refrigerant amount and performing stable air conditioning operation.

  In an air conditioner, a compressor, a condenser, a throttling device, and an evaporator are connected to form a refrigerant circuit, and the refrigerant circulates through the refrigerant circuit, whereby air conditioning operations such as cooling, heating, and dehumidification are performed. Here, the opening degree of the expansion valve as the expansion device is controlled according to the degree of superheat of suction obtained from the temperature of the evaporator and the outlet temperature of the evaporator. Thereby, the refrigerant | coolant amount which circulates is adjusted appropriately, and efficient air-conditioning driving | operation is performed.

  As another control of the expansion valve, in Patent Document 1, the difference between the discharge temperature of the compressor and the temperature of the condenser is calculated as the discharge superheat degree, and the expansion valve is based on the calculated temperature difference and the target discharge temperature difference. Is controlled. The target discharge temperature difference is calculated from the rotation speed of the compressor. The amount of refrigerant to be circulated is determined according to the rotational speed of the compressor. By controlling the opening degree of the expansion valve based on the discharge temperature difference determined in accordance with the rotation speed of the compressor, the amount of circulating refrigerant is appropriately adjusted.

JP 2011-122756 A

  In the control of the expansion valve based on the discharge superheat degree, even if the operation is started, the discharge temperature is not stable until the compressor is warmed. For this reason, it takes time until the discharge temperature is stabilized, and the expansion valve cannot be controlled. During this time, the air conditioner must perform an inefficient operation.

  On the other hand, in the control of the expansion valve based on the suction superheat degree, the discharge temperature is quickly stabilized. However, when the amount of circulating refrigerant is small and the most efficient operation is performed, the temperature difference between the temperature of the evaporator and the suction temperature of the refrigerant sucked into the compressor is small. Therefore, the suction superheat degree is small, and it becomes difficult to control the expansion valve.

  In view of the above, an object of the present invention is to provide an air conditioner capable of quickly and efficiently performing an air conditioning operation regardless of the amount of refrigerant circulating.

  The air conditioner of the present invention includes a control device that controls the operation of the throttle device in accordance with the amount of refrigerant circulating in the refrigerant circuit by connecting a compressor, a condenser, a throttle device, and an evaporator to form a refrigerant circuit. It is a thing. The control device judges the operating state and operates the throttle device based on the suction superheat degree control for operating the throttle device based on the refrigerant suction temperature sucked into the compressor and the refrigerant discharge temperature discharged from the compressor Switch the superheat control to be performed and perform optimal air conditioning operation.

  That is, the control device performs suction superheat control that operates the expansion device based on the suction temperature of the refrigerant sucked into the compressor when the amount of refrigerant circulating is large, and discharges from the compressor when the amount of refrigerant circulating is small. Discharge superheat degree control for operating the expansion device based on the discharge temperature of the refrigerant to be performed is performed.

  The control device determines the operating state based on the amount of circulating refrigerant. The superheat control is switched according to the amount of refrigerant circulating in the refrigerant circuit, and the suction superheat control is performed when the amount of refrigerant circulating is large, so that the refrigeration cycle is stabilized quickly. When the amount of refrigerant circulating is small, the difference between the suction temperature and the evaporation temperature is small, so that superheat control based on the suction temperature becomes difficult. Therefore, the discharge superheat control is performed when the amount of refrigerant circulating is small, so that the superheat control can be performed reliably, and an efficient air conditioning operation can be performed regardless of the amount of refrigerant circulating.

  The control device preferably performs suction superheat control until the refrigeration cycle is stabilized when the amount of refrigerant circulating is small, and performs discharge superheat control after the refrigeration cycle is stabilized. In this way, when the air-conditioning operation is started, the suction superheat degree control is performed first, so that the refrigeration cycle is quickly stabilized. Since discharge superheat degree control is performed in a state where the refrigeration cycle is stable, efficient air-conditioning operation can be performed even if the amount of circulating refrigerant is small.

  The control device preferably performs the suction superheat control when the refrigeration cycle becomes unstable while performing the discharge superheat control. In this way, if the discharge superheat control is continued when the refrigeration cycle becomes unstable, the time until stabilization becomes longer. At this time, the refrigeration cycle is quickly stabilized by switching to suction superheat control.

  It is preferable that the control device determines whether or not the refrigeration cycle is unstable by comparing the target suction superheat degree with the actual suction superheat degree. In this way, when the refrigeration cycle becomes unstable, the fluctuation of the suction superheat degree becomes significant, so that it can be quickly detected that it has become unstable.

  The control device preferably determines that the refrigeration cycle is stable when the actual suction superheat varies around the target suction superheat. If it does in this way, when the state where the actual suction superheat degree is hunting continues, it cannot be determined that it is stable forever. Thus, when it is in such a state, it can be promptly switched to the discharge superheat degree control by determining that it is stable.

  The control device performs discharge temperature control that operates the throttle device so that the discharge temperature approaches the set temperature as superheat degree control when the amount of circulating refrigerant is large, determines the operating state based on the discharge temperature, and depends on the discharge temperature It is preferable to switch between discharge temperature control and suction superheat control. In this way, when the discharge temperature control is performed, the discharge temperature can be prevented from becoming high.

  The control device preferably performs discharge temperature control when the discharge temperature is high, and performs suction superheat degree control when the discharge temperature is low. In this way, if the suction superheat control is performed when the discharge temperature is low, the suction superheat can be brought close to the target suction superheat, and an efficient air conditioning operation can be performed. When the discharge temperature increases in this state, the discharge temperature control is performed. By switching superheat degree control in this way, it is possible to prevent the discharge temperature from becoming high while performing efficient air conditioning operation.

  The control device performs discharge temperature control when the difference between the target suction superheat degree and the actual suction superheat degree is small, and performs the suction superheat degree control when the difference between the target suction superheat degree and the actual suction superheat degree is large. preferable. In this way, if the suction superheat degree control is performed when the difference between the target suction superheat degree and the actual suction superheat degree is large, the difference between the two becomes small, and the discharge temperature control is performed. Thereby, the air conditioning operation can be performed so that the discharge temperature does not become high while the actual suction superheat degree is maintained close to the target suction superheat degree.

  The determination formula of the discharge temperature is determined by the evaporation temperature, the condensation temperature, and the suction superheat degree, and the control device performs the discharge temperature control based on the discharge temperature calculated from the determination formula so that the discharge temperature does not exceed the upper limit value. Is preferred. In this way, by performing the discharge temperature control based on the discharge temperature obtained from the discriminant, the discharge temperature can be controlled so that the actual discharge temperature does not exceed the upper limit of the discharge temperature.

  Preferably, the control device performs discharge temperature control when the discharge temperature calculated from the determination formula is high, and performs suction superheat degree control when the discharge temperature calculated from the determination formula is low. In this way, it is possible to prevent the discharge temperature from rising excessively by performing the discharge temperature control when the discharge temperature is high.

  In order to reduce the air conditioning capacity when the compressor operates at the minimum rotation speed, the target discharge superheat degree for the minimum rotation speed of the compressor is set lower than the normal target discharge superheat degree, and the control device sets the target It is preferable to perform discharge superheat control based on the discharge superheat.

  In this way, the discharge superheat degree control is performed so that the discharge superheat degree becomes the target discharge superheat degree, but since the target discharge superheat degree is set low, the compressor is operating at the minimum rotation speed. When it becomes difficult to obtain the target discharge superheat degree. Therefore, the air-conditioning capability when the compressor is operating at the minimum rotation speed is reduced.

  According to the present invention, the superheat degree can be brought close to the target superheat degree regardless of the amount of refrigerant circulating in the refrigerant circuit, and an efficient air conditioning operation can always be performed.

Schematic configuration diagram of the refrigeration cycle of the air conditioner of the present invention Air conditioner control block diagram Flowchart of air conditioning operation by superheat degree control of the first embodiment Flow chart of determination process for suction superheat degree control and discharge superheat degree control Flow chart of suction superheat control Flow chart of discharge superheat control Flowchart of air conditioning operation by discharge superheat degree control of the second embodiment Flow chart for determining the stability of the refrigeration cycle Flowchart of determination of stability of refrigeration cycle when there is hunting according to the third embodiment Flowchart when the refrigeration cycle becomes unstable during execution of the discharge superheat degree control of the fourth embodiment The flowchart when determining superheat degree control based on the refrigerant | coolant amount which circulates of 5th Embodiment. Flow chart of determination process for suction superheat control and discharge temperature control Flow chart of discharge temperature control Flowchart of determination processing for suction superheat control and discharge temperature control of the sixth embodiment Flowchart of discharge temperature control of the seventh embodiment Flowchart of discharge temperature control of the eighth embodiment Flowchart of discharge temperature control of the ninth embodiment Flowchart of discharge temperature control according to the tenth embodiment Flowchart of discharge temperature control of the eleventh embodiment Flowchart of discharge temperature control of the twelfth embodiment The figure which shows the relationship between the rotation speed and discharge superheat degree of the conventional compressor The figure which shows the relationship between the rotation speed of the compressor of 13th Embodiment, and discharge superheat degree.

  The air conditioner of 1st Embodiment is shown in FIG. The air conditioner is configured by connecting an outdoor unit 1 and an indoor unit 2 by piping and wiring. The outdoor unit 1 includes a compressor 3, a four-way valve 4, an outdoor heat exchanger 5, an expansion valve 6, and an outdoor fan 7. The indoor unit 2 includes an indoor heat exchanger 8 and an indoor fan 9. The compressor 3, the four-way valve 4, the outdoor heat exchanger 5, the expansion valve 6, and the indoor heat exchanger 8 are connected by piping to form a refrigerant circuit. In order to connect the piping of the indoor unit 2 and the piping of the outdoor unit 1, a two-way valve 10 and a three-way valve 11 are provided in the outdoor unit. A two-way valve 10 is interposed in a pipe connecting the expansion valve 6 and the indoor heat exchanger 8, and a three-way valve 11 is interposed in a pipe connecting the four-way valve 4 and the indoor heat exchanger 8.

  When the compressor 3 is driven, the refrigerant circulates through the refrigerant circuit. The opening of the expansion valve 6 is adjusted stepwise by driving the stepping motor, and functions as a throttle device that adjusts the pressure of the circulating refrigerant and the amount of refrigerant. As the refrigerant circulates through the refrigerant circuit, a refrigeration cycle is formed. In the refrigeration cycle during cooling, the refrigerant circulates in the order of the compressor 3, the four-way valve 4, the outdoor heat exchanger 5, the expansion valve 6, and the indoor heat exchanger 8. The outdoor heat exchanger 5 functions as a condenser, and the indoor heat exchanger 8 functions as an evaporator. In the refrigeration cycle during heating, the refrigerant circulates in the order of the compressor 3, the four-way valve 4, the indoor heat exchanger 8, the expansion valve 6, and the outdoor heat exchanger 5. The indoor heat exchanger 8 functions as a condenser, and the outdoor heat exchanger 5 functions as an evaporator. Note that a capillary tube or the like may be used instead of the expansion valve 6 as the expansion device, and the amount of circulating refrigerant can be adjusted by changing the combination of a plurality of capillary tubes.

  As shown in FIG. 2, the air conditioner includes a control device 12 that controls the refrigeration cycle and performs air conditioning operations such as cooling, heating, and dehumidification. The air conditioner also includes a room temperature detector 13, an outside air temperature detector 14, a discharge temperature detector 15 that detects the discharge temperature of the refrigerant discharged from the compressor 3, and a suction temperature (suction) of the refrigerant sucked into the compressor 3. A suction temperature detector 16 for detecting the temperature), a first temperature detector 17 for detecting the temperature of the outdoor heat exchanger 5, and a second temperature detector 18 for detecting the temperature of the indoor heat exchanger 8. Each temperature detector 13 to 18 uses a temperature sensor such as a thermistor.

  As the second temperature detector 18, a temperature detector that detects the temperature of the refrigerant flowing through the pipe between the expansion valve 6 and the indoor heat exchanger 8 is used. The second temperature detector 18 is disposed between the expansion valve 6 and the two-way valve 10, and all other temperature detectors except the room temperature detector 13 are provided in the outdoor unit 1. The temperature of the refrigerant flowing through the indoor heat exchanger 8 during the cooling operation is the same as the temperature of the refrigerant passing through the expansion valve 6. Therefore, instead of providing a temperature detector that detects the temperature of the indoor heat exchanger 8, the temperature of the refrigerant is detected by a temperature detector provided between the expansion valve 6 and the indoor heat exchanger 8, thereby The temperature of the exchanger 8 can be detected.

  Based on the temperature detected by each of the temperature detectors 13 to 18, the control device 12 determines the rotational speed (operation frequency) of the compressor 3, the opening degree of the expansion valve 6, and the outdoor fan 7 according to the instructed operation mode. And the rotation speed of the indoor fan 9 are respectively controlled. The control device 12 includes an indoor control unit provided in the indoor unit 2 and an outdoor control unit provided in the outdoor unit 1. The indoor control unit and the outdoor control unit are connected so as to be communicable with each other, and both cooperate to control operations of the indoor unit 2 and the outdoor unit 1. The outdoor control unit collectively transmits detection signals input from the plurality of temperature detectors 14 to 18 to the indoor control unit, and manages the temperature information detected by the indoor control unit.

  The operating frequency of the compressor 3 is controlled stepwise based on the frequency code (FD). A plurality of frequency codes are set for each operation frequency. The higher the frequency code, the higher the operating frequency. The number of rotations corresponds to each frequency code. The control device 12 selects a frequency code according to the control temperature determined from the room temperature and the set temperature, and outputs the frequency code to the driver of the compressor 3. The driver drives the compressor 3 at an operation frequency corresponding to the frequency code. When the control device 12 issues a command to the expansion valve 6, the expansion valve 6 has a specified opening degree. The amount of refrigerant passing through the expansion valve 6 is varied according to the opening.

  The control device 12 determines the rotation speed of the compressor 3 based on the set temperature set by the user or the preset temperature set in the automatic operation mode and the detected load such as the room temperature and the outside temperature. Then, the rotational speed of the indoor fan 9 is determined in accordance with the rotational speed of the compressor 3. The control device 12 controls the compressor 3 at a determined rotational speed, changes the rotational speed of the compressor 3 in accordance with the room temperature, and based on the rotational speed in accordance with the rotational speed of the compressor 3, the indoor fan 9. To control. Further, the control device 12 determines the opening degree of the expansion valve 6 according to the determined rotation speed of the compressor 3.

  When the air conditioning operation is performed, an amount of refrigerant according to the rotation speed of the compressor 3 circulates in the refrigerant circuit. During the cooling operation, the first temperature detector 17 detects the temperature of the outdoor heat exchanger 5 that is a condenser, that is, the condensation temperature, and the second temperature detector 18 is the temperature of the indoor heat exchanger 8 that is an evaporator, That is, the evaporation temperature is detected. During the heating operation, the first temperature detector 17 detects the evaporation temperature, and the second temperature detector 18 detects the condensation temperature.

  In order to realize an efficient refrigeration cycle, the air conditioner controls the refrigeration cycle so as to achieve a target superheat degree corresponding to the amount of refrigerant circulating in the refrigerant circuit. That is, when the control device 12 controls the opening degree of the expansion valve 6 according to the degree of superheat, the amount of circulating refrigerant is adjusted, and the degree of superheat becomes the target degree of superheat.

  Here, the control device 12 determines the operating state, and controls the degree of suction superheat to operate the expansion valve 6 based on the suction temperature of the refrigerant sucked into the compressor 3 and the discharge temperature of the refrigerant discharged from the compressor 3. Is switched to discharge superheat degree control for operating the expansion valve 6 to perform the air conditioning operation. The control device 12 controls the opening degree of the expansion valve 6 so that the temperature difference between the suction temperature and the evaporation temperature approaches a predetermined value in the suction superheat degree control. In the discharge superheat degree control, the control device 12 sets the discharge temperature and the condensation temperature. The opening degree of the expansion valve 6 is controlled so that the temperature difference approaches a predetermined value.

  The suction superheat degree is a difference between the suction temperature and the evaporation temperature, and the target suction superheat degree is set to a suction superheat degree set according to the amount of circulating refrigerant. When the temperature difference between the suction temperature and the evaporation temperature approaches a predetermined value, the suction superheat degree calculated during the air conditioning operation approaches the target suction superheat degree. The discharge superheat degree is a difference between the discharge temperature and the condensation temperature, and the target discharge superheat degree is a discharge superheat degree set in accordance with the amount of refrigerant circulating. When the temperature difference between the discharge temperature and the condensing temperature approaches a predetermined value, the discharge superheat calculated during the air conditioning operation approaches the target discharge superheat.

  And the control apparatus 12 judges an operating state based on the refrigerant | coolant amount which circulates through a refrigerant circuit, and switches each superheat degree control according to the refrigerant | coolant amount which circulates. Suction superheat control can immediately respond to changes in the refrigeration cycle, and can stabilize the refrigeration cycle quickly. On the other hand, since the change in the temperature of the refrigerant is small when the amount of refrigerant circulating is small, it is difficult to control the refrigeration cycle with the suction superheat control. That is, when the amount of circulating refrigerant is large, suction superheat control is suitable. When the amount of circulating refrigerant is small, discharge superheat control is suitable.

  As shown in FIG. 3, when the air-conditioning operation is performed, the control device 12 determines the rotation speed of the compressor 3 based on the load such as the difference between the set temperature and the room temperature, the outside air temperature, and the like (S1). The rotation speed of the compressor 3 corresponds to the amount of refrigerant circulating in the refrigerant circuit. The higher the rotation speed of the compressor 3 is, the more refrigerant is circulated, and the lower the rotation speed is, the less refrigerant is circulated. The control device 12 performs a determination process for determining superheat degree control to be executed from the determined rotation speed of the compressor 3 (S2). When the rotation speed of the compressor 3 is high, that is, when the amount of circulating refrigerant is large, the control device 12 performs suction superheat degree control (S3). When the rotation speed of the compressor 3 is low, that is, when the amount of circulating refrigerant is small, the control device 12 performs discharge superheat degree control (S4).

  In the determination process, as shown in FIG. 4, the control device 12 checks whether or not the determined rotation speed of the compressor 3 is equal to or higher than a preset first rotation speed (S5). That is, it is checked whether or not the circulating refrigerant amount is greater than or equal to the first set amount. When the rotational speed is equal to or higher than the first rotational speed (the circulating refrigerant amount is equal to or higher than the first set amount), the control device 12 selects the suction superheat degree control (S6). When the rotational speed is lower than the first rotational speed (the circulating refrigerant amount is smaller than the first set amount), the control device 12 selects the discharge superheat degree control (S7). The first rotation speed (first set amount) is experimentally determined in advance and is set for each air conditioner.

  When the air conditioning operation is started, the control device 12 performs an initial operation in which the compressor 3 is driven for a predetermined time at a rotational speed lower than a predetermined rotational speed. Thereby, a refrigerant | coolant spreads to a refrigerant circuit and the operation | movement of the compressor 3 can be stabilized quickly. After the initial operation, the control device 12 drives the compressor 3 at a rotational speed determined based on the load, and sets the opening degree of the expansion valve 6 to a predetermined opening degree.

  When the air conditioning operation by the suction superheat degree control is performed, as shown in FIG. 5, during the initial operation, the control device 12 determines the target suction superheat degree from the rotation speed of the compressor 3 corresponding to the circulating refrigerant amount ( S11). The target suction superheat degree is experimentally obtained in advance, and the target suction superheat degree is stored in the nonvolatile memory of the control device 12 for each rotation speed of the compressor 3. The target discharge superheat degree is similarly stored in the memory. The control device 12 reads out the target suction superheat degree corresponding to the determined rotation speed of the compressor 3 from the memory.

  When the compressor 3 is driven at the determined rotation speed, the control device 12 acquires the actual suction superheat degree (S12). By subtracting the evaporation temperature detected by the first temperature detector 17 or the second temperature detector 18 from the actual suction temperature detected by the suction temperature detector 16, the actual suction superheat degree is calculated. When the cooling operation is performed, the control device 12 uses the temperature detected by the second temperature detector 18 as the evaporation temperature. When the heating operation is performed, the control device 12 uses the temperature detected by the first temperature detector 17 as the evaporation temperature.

  The control device 12 compares the target suction superheat degree with the acquired actual suction superheat degree (S13). When the actual suction superheat degree is larger than the target suction superheat degree, the control device 12 controls to increase the opening degree of the expansion valve 6 (S14). The expansion valve 6 is opened by a predetermined opening degree from the current opening degree. As the opening degree of the expansion valve 6 increases, the amount of refrigerant passing through the expansion valve 6 increases, the amount of liquid refrigerant that evaporates in the evaporator increases, and the temperature of the refrigerant discharged from the evaporator decreases. As a result, the suction temperature decreases, the actual suction superheat degree decreases, and the actual suction superheat degree approaches the target suction superheat degree.

  When the actual suction superheat degree is smaller than the target suction superheat degree, the control device 12 performs control so as to reduce the opening degree of the expansion valve 6 (S15). The expansion valve 6 is closed by a predetermined opening degree from the current opening degree. When the opening degree of the expansion valve 6 is reduced, the refrigerant passing through the expansion valve 6 is reduced, the liquid refrigerant evaporating in the evaporator is reduced, and the temperature drop of the refrigerant exiting the evaporator is suppressed. As a result, the suction temperature rises, the actual suction superheat degree increases, and the actual suction superheat degree approaches the target suction superheat degree. When the actual suction superheat degree is equal to the target suction superheat degree, the control device 12 does not change the opening degree of the expansion valve 6.

  When the air conditioning operation by the discharge superheat degree control is performed, as shown in FIG. 6, the control device 12 determines the target discharge superheat degree from the rotation speed of the compressor 3 corresponding to the circulating refrigerant amount (S21). When the compressor 3 is driven at the determined rotational speed, the control device 12 acquires the actual discharge superheat degree from the detected discharge temperature and the detected condensation temperature (S22).

  The control device 12 compares the target discharge superheat degree with the acquired actual discharge superheat degree (S23). When the actual discharge superheat degree is larger than the target discharge superheat degree, the control device 12 controls to increase the opening degree of the expansion valve 6 (S24). The expansion valve 6 opens by a predetermined opening degree. As the opening degree of the expansion valve 6 increases, the refrigerant passing through the expansion valve 6 increases, the liquid refrigerant evaporated in the evaporator increases, and the temperature of the refrigerant sucked into the compressor 3 decreases. As a result, the discharge temperature of the refrigerant discharged from the compressor 3 decreases, the actual discharge superheat degree decreases, and the actual discharge superheat degree approaches the target discharge superheat degree.

  When the actual discharge superheat degree is smaller than the target discharge superheat degree, the control device 12 performs control so as to reduce the opening degree of the expansion valve 6 (S25). The expansion valve 6 is closed by a predetermined opening degree. As the opening degree of the expansion valve 6 decreases, the amount of refrigerant passing through the expansion valve 6 decreases and the amount of liquid refrigerant that evaporates in the evaporator decreases. As a result, the temperature drop of the refrigerant sucked into the compressor 3 decreases, the discharge temperature rises, the actual discharge superheat degree increases, and the actual discharge superheat degree approaches the target discharge superheat degree.

  When the air conditioning operation is performed by the superheat degree control as described above, the room temperature changes. When the room temperature approaches the set temperature, the number of revolutions of the compressor 3 is reduced, and the amount of circulating refrigerant changes. The control device 12 selects the superheat degree control to be executed based on the rotation speed of the compressor 3 after the change, and performs any one of the selected superheat degree controls. One of the selected superheat control is performed until the air-conditioning operation is stopped.

  As described above, by performing suction superheat control during air conditioning operation with a large amount of circulating refrigerant, the refrigeration cycle can be stabilized quickly, and efficient air conditioning operation can be performed quickly. However, at the time of air conditioning operation with a small amount of circulating refrigerant, it is difficult to adjust the amount of refrigerant by suction superheat control. Therefore, by performing the discharge superheat control during the air conditioning operation with a small amount of circulating refrigerant, the refrigerant amount can be appropriately adjusted, and an efficient air conditioning operation is performed. Therefore, efficient air-conditioning operation can always be performed regardless of the amount of circulating refrigerant.

  By the way, since the compressor 3 is not warmed for a while after the air-conditioning operation is started, the discharge temperature is not stable. When controlling the opening degree of the expansion valve 6 in the discharge superheat degree control, the opening degree of the expansion valve 6 is frequently changed according to the discharge temperature, and the refrigeration cycle is not stable. Therefore, the expansion valve 6 must be operated slowly, and the time until the refrigeration cycle is stabilized becomes long.

  Therefore, the air conditioner of the second embodiment switches the superheat degree control when performing the air conditioning operation with a small amount of circulating refrigerant, performs the suction superheat degree control first, and then performs the discharge superheat degree control. The suction superheat degree control is suitable for the superheat degree control at the start of operation where the temperature rise of the refrigerant is large because it can immediately respond to the change in the refrigerant temperature. Therefore, the control device 12 performs suction superheat degree control until the refrigeration cycle is stabilized when the amount of refrigerant circulating is small, and performs discharge superheat degree control after the refrigeration cycle is stabilized. Other configurations are the same as those in the first embodiment.

  As shown in FIG. 7, when the air conditioning operation is started, the control device 12 determines the rotation speed of the compressor 3 based on a load such as a difference between the set temperature and the room temperature, an outside air temperature, and the like. At this time, the rotation speed of the compressor 3 is set to be lower than the first rotation speed. Therefore, the control device 12 determines superheat degree control to be performed as discharge superheat degree control based on the determined rotation speed of the compressor 3 (S31).

  The controller 12 first performs suction superheat control (S32), and determines whether the refrigeration cycle is stable (S33). If it determines with the refrigerating cycle having been stabilized, the control apparatus 12 will switch from suction superheat degree control to discharge superheat degree control, and will perform discharge superheat degree control (S34).

  The determination of the stability of the refrigeration cycle is made based on the suction temperature. As shown in FIG. 8, the control device 12 confirms that the rotational speed of the compressor 3 is low during execution of the suction superheat degree control, and determines whether the detected actual suction superheat degree approaches the target suction superheat degree. Check (S35). When the state where the rotation speed of the compressor 3 is smaller than the first rotation speed and the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree is smaller than the stability determination value continues for a certain time, that is, continuously for a certain time. , | Target suction superheat degree−actual suction superheat degree | <A, the control device 12 determines that the refrigeration cycle is stable (S36). The stability determination value A is determined in advance by a test or the like.

  Although the rotation speed of the compressor 3 is smaller than the first rotation speed, the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree is greater than or equal to the stability determination value, or the target suction superheat degree and the actual suction superheat degree When the state where the absolute value of the difference is smaller than the stability determination value does not continue for a certain period of time, the control device 12 determines that the refrigeration cycle is not yet stable. At this time, the control device 12 continues the suction superheat control until the refrigeration cycle is stabilized. In addition, when the rotation speed of the compressor 3 becomes more than 1st rotation speed, the control apparatus 12 continues suction superheat degree control, without performing discharge superheat degree control.

  As described above, by performing the suction superheat control first, even when the amount of circulating refrigerant is small, it is possible to quickly cope with the temperature change of the refrigerant and to quickly stabilize the refrigeration cycle. By switching to discharge superheat control after stabilization, efficient air-conditioning operation can be performed quickly when the amount of circulating refrigerant is small.

  Here, the suction superheat degree control is performed at the start of operation, whereby the actual suction superheat degree approaches the target suction superheat degree. For example, when the target suction superheat degree is low, the actual suction superheat degree is close to the target superheat degree, but if the actual suction superheat degree is not stable and hunting, the difference between the two superheat degrees may become smaller or larger. is there. In this case, the determination that the refrigeration cycle is stable cannot be made.

  Therefore, as another embodiment in determining the stability of the refrigeration cycle, the air conditioner of the third embodiment considers that the refrigeration cycle is stable when the actual suction superheat degree is hunting near the target superheat degree. That is, when the actual suction superheat degree varies up and down around the target suction superheat degree such that the actual suction superheat degree becomes greater than or less than the target suction superheat degree, the control device 12 Is determined to be stable. Other configurations are the same as those in the first and second embodiments.

  As shown in FIG. 9, when the air-conditioning operation with a small amount of circulating refrigerant is started, the control device 12 performs suction superheat degree control (S41). The control device 12 confirms that the rotational speed of the compressor 3 is low, and checks whether the detected actual suction superheat degree approaches the target suction superheat degree (S42). When the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree is equal to or greater than the stability determination value, the control device 12 continues the suction superheat degree control and checks again.

  Here, when the control device 12 detects that the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree is smaller than the stability determination value, the actual suction superheat degree is not hunting with respect to the target suction superheat degree. (S43). When the actual suction superheat is continuously hunting for a certain time, the control device 12 determines that the refrigeration cycle is stable (S44), switches from the suction superheat control to the discharge superheat control, and discharge superheat control. (S45).

  When the actual suction superheat degree is not hunting or when the actual suction superheat degree is hunting but does not continue for a certain time, the control device 12 calculates the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree. Is smaller than the stability determination value, it is confirmed whether or not it continues for a certain time (S46). When this state continues for a predetermined time, the control device 12 determines that the refrigeration cycle is stable (S44), and performs discharge superheat degree control (S45). When the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree is not smaller than the stability determination value for a certain period of time, the control device 12 determines that the refrigeration cycle is not stable and performs suction until it is stable. Continue superheat control.

  As described above, when the actual suction superheat degree is close to the target suction superheat degree, when the unstable state continues, by determining that the refrigeration cycle is stable, the suction superheat degree control is quickly performed. It is possible to shift to discharge superheat degree control. Therefore, when the amount of circulating refrigerant is small, an efficient and efficient air conditioning operation can be performed.

  Next, when the air-conditioning operation by the discharge superheat degree control is performed, the rotation speed of the compressor 3 or the rotation speed of the indoor and outdoor fans changes according to changes in the outside air temperature, room temperature, and the like. The driving state changes. When such a change occurs when the amount of circulating refrigerant is small, the degree of superheat changes greatly and the refrigeration cycle becomes unstable. When the discharge superheat degree control is continued, it takes time for the refrigeration cycle to be stabilized, and the inefficient air-conditioning operation is performed for a long time. In order to quickly eliminate the instability of the refrigeration cycle, the air conditioner according to the fourth embodiment switches superheat degree control when the refrigeration cycle becomes unstable.

  That is, when the refrigeration cycle becomes unstable during the air conditioning operation by the discharge superheat degree control, the control device 12 switches from the discharge superheat degree control to the suction superheat degree control, and performs the suction superheat degree control. When the refrigeration cycle is stable, the control device 12 continues the discharge superheat degree control. Other configurations are the same as those in the first to third embodiments.

  When the air conditioning operation by the discharge superheat degree control is performed, as shown in FIG. 10, the control device 12 determines the target discharge superheat degree and the target suction based on the circulating refrigerant amount, that is, the current rotation speed of the compressor 3. The degree of superheat is determined (S51). The target discharge superheat degree and the target suction superheat degree are determined each time the rotation speed of the compressor 3 is changed.

  Then, the control device 12 acquires the actual discharge superheat degree and the actual suction superheat degree (S52). The actual discharge superheat degree is calculated from the discharge temperature and the condensation temperature detected by each temperature detector, and the actual suction superheat degree is calculated from the suction temperature and the evaporation temperature.

  The control device 12 compares the target suction superheat degree with the acquired actual suction superheat degree (S53). When the difference between the target suction superheat degree and the actual suction superheat degree is equal to or less than a preset stability reference value, the control device 12 determines that the refrigeration cycle is stable and continues the discharge superheat degree control. In this case, the control device 12 compares the target discharge superheat degree with the acquired actual discharge superheat degree (S54).

  When the actual discharge superheat degree is larger than the target discharge superheat degree, the control device 12 controls to increase the opening degree of the expansion valve 6 (S55). The expansion valve 6 opens by a predetermined opening, the refrigerant passing through the expansion valve 6 increases, the liquid refrigerant that evaporates in the evaporator increases, and the temperature of the refrigerant sucked into the compressor 3 decreases. As a result, the discharge temperature of the refrigerant discharged from the compressor 3 decreases, the actual discharge superheat degree decreases, the actual discharge superheat degree decreases, and the target discharge superheat degree approaches the target discharge superheat degree.

  When the actual discharge superheat degree is smaller than the target discharge superheat degree, the control device 12 performs control so as to reduce the opening degree of the expansion valve 6 (S56). When the expansion valve 6 is closed by a predetermined opening, the refrigerant passing through the expansion valve 6 is reduced, and the liquid refrigerant evaporated in the evaporator is reduced. As a result, the suction temperature rises, the discharge temperature rises, the actual discharge superheat degree increases, and the actual discharge superheat degree approaches the target discharge superheat degree.

  When the operating state changes due to environmental changes, in S53, the difference between the target suction superheat degree and the actual suction superheat degree becomes larger than the stability reference value. At this time, the control device 12 determines that the refrigeration cycle is unstable, switches from discharge superheat degree control to suction superheat degree control, and performs suction superheat degree control (S57).

  After shifting to the suction superheat degree control, the control device 12 compares the target suction superheat degree with the actual suction superheat degree to check whether the refrigeration cycle is stable (S58). When the difference between the target suction superheat degree and the actual suction superheat degree is larger than the stability reference value, the control device 12 determines that the refrigeration cycle is unstable, and continues the suction superheat degree control. When the difference between the target suction superheat degree and the actual suction superheat degree is equal to or less than the stability reference value, the control device 12 determines that the refrigeration cycle is stable, switches from suction superheat degree control to discharge superheat degree control, and discharge superheat. Degree control is performed (S59).

  As described above, if the refrigeration cycle becomes unstable when air-conditioning operation using discharge superheat degree control is performed, switching to suction superheat degree control quickly stabilizes the refrigeration cycle, resulting in inefficient air-conditioning operation. Prolonging can be prevented.

  Here, examples of the refrigerant used in the air conditioner include R407C and R410A. Further, R32 and R1234yf are refrigerants having a global warming potential smaller than those of these refrigerants. In an air conditioner using such a refrigerant, when the superheat control is performed so that the superheat degree as described above approaches the target superheat degree, the discharge temperature becomes high, for example, 110 to 120 ° C. When components constituting the refrigeration cycle such as the compressor 3 are exposed to such a high temperature, the components may be damaged. In particular, when a refrigerant such as R32 is used, the discharge temperature tends to be high and parts having high heat resistance must be used.

  Therefore, the air conditioner of the fifth embodiment performs discharge temperature control so that the discharge temperature does not become high. The discharge temperature control is performed when the discharge temperature is high, and the control device 12 controls the refrigeration cycle according to the actual discharge temperature so that the discharge temperature does not exceed a predetermined temperature. Moreover, discharge temperature control and suction superheat degree control are switched and performed. That is, the discharge temperature control is performed when the amount of circulating refrigerant is large. Other configurations are the same as those in the first to fourth embodiments.

  When the air conditioning operation is started, the control device 12 performs suction superheat control until the refrigeration cycle is stabilized. When the refrigeration cycle is stabilized, as shown in FIG. 11, the control device 12 determines the rotation speed of the compressor 3 based on the current load (S61), and the determined rotation speed of the compressor 3, that is, the circulating refrigerant. Control to be executed based on the amount is determined from discharge superheat control, suction superheat control, and discharge temperature control (S62). Here, the control device 12 determines the operating state based on the circulating refrigerant amount and the discharge temperature, and selects the superheat degree control to be executed.

  When the rotation speed of the compressor 3 is lower than the first rotation speed, the discharge superheat degree control is selected (S63). When the rotation speed of the compressor 3 is equal to or higher than the first rotation speed, either suction superheat control or discharge temperature control is selected (S64, S65).

  As a determination process between the suction superheat degree control and the discharge temperature control, as shown in FIG. 12, the control device 12 determines whether the rotation speed of the compressor 3 is equal to or higher than a second rotation speed set in advance according to the current load. Confirm (S66). The second rotation number is a higher rotation number than the first rotation number.

  When the rotation speed of the compressor 3 is lower than the second rotation speed, the control device 12 performs suction superheat degree control (S67). When the rotation speed of the compressor 3 is equal to or higher than the second rotation speed, the control device 12 compares the detected discharge temperature (Td) with the determined discharge temperature (Ta) (S68). When the detected discharge temperature is higher than the determination discharge temperature, the control device 12 performs discharge temperature control (S69). For example, when the suction control superheat degree is performed, the discharge temperature control is performed when the discharge temperature becomes high.

  When the detected discharge temperature is equal to or lower than the determination discharge temperature, the control device 12 performs suction superheat degree control (S68). Even if the rotation speed of the compressor 3 is high, that is, the amount of circulating refrigerant is large, when the discharge temperature is not high, the discharge temperature is less likely to become high during the air conditioning operation. Therefore, even if normal suction superheat control is performed, the air-conditioning operation can be performed so that the discharge temperature does not become high.

  When the air conditioning operation by the discharge temperature control is performed, the control device 12 controls the opening degree of the expansion valve 6 based on the detected discharge temperature so that the discharge temperature does not exceed the upper limit discharge temperature. As shown in FIG. 13, the control device 12 determines a target discharge temperature (Taim) from the rotational speed of the compressor 3 (S71). The target discharge temperature is set according to the refrigerant to be used. When the air conditioning operation is started, the discharge temperature detector detects the discharge temperature (Td) (S72). The control device 12 compares the target discharge temperature with the actual discharge temperature (S73).

  When the actual discharge temperature is higher than the target discharge temperature (Td> Taim), the control device 12 increases the opening of the expansion valve 6 (S74). The refrigerant passing through the expansion valve 6 increases, the degree of superheat decreases, and the discharge temperature from the compressor 3 decreases. As a result, the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is lower than the target discharge temperature (Td <Taim), the control device 12 decreases the opening degree of the expansion valve 6 (S75). The refrigerant passing through the expansion valve 6 decreases, the degree of superheat increases, and the discharge temperature increases. As a result, the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is the same as the target discharge temperature (Td = Taim), the control device 12 does not change the opening degree of the expansion valve 6 (S76). The actual discharge temperature is maintained at the target discharge temperature.

  As described above, by controlling the degree of superheat so that the discharge temperature approaches the target discharge temperature, the actual discharge temperature can be prevented from exceeding the upper limit discharge temperature. As a result, even if R32, which tends to be high in temperature, is used as the refrigerant, the refrigerant can be prevented from becoming high temperature, so that failure of parts such as the compressor 3 can be reduced, and the use of heat-resistant parts is eliminated.

  As another form of the determination process of the suction superheat degree control and the discharge temperature control, the air conditioner of the sixth embodiment adds the actual suction superheat degree to the rotation speed and the discharge temperature of the compressor 3, and performs the suction superheat. Select either degree control or discharge temperature control. Here, the operating state is determined based on the circulating refrigerant amount, the discharge temperature, and the suction superheat degree. Other configurations are the same as those of the first to fifth embodiments.

  When the air conditioning operation is performed and the refrigeration cycle is stabilized, as shown in FIG. 14, the control device 12 confirms that the rotation speed of the compressor 3 determined according to the current load is equal to or higher than the second rotation speed. (S66), it is confirmed whether the detected discharge temperature is higher than the determination discharge temperature (S68). When the detected discharge temperature is higher than the determination discharge temperature, the control device 12 compares the target suction superheat degree with the actual suction superheat degree (S70).

  When the difference between the target suction superheat degree and the actual suction superheat degree is large, that is, when the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree is equal to or larger than a predetermined criterion value, the control device 12 Degree control is performed (S67). When the suction superheat degree control is performed, the actual suction superheat degree approaches the target suction superheat degree.

  When the difference between the target suction superheat degree and the actual suction superheat degree is small, that is, when the absolute value of the difference between the target suction superheat degree and the actual suction superheat degree is smaller than the determination reference value, the control device 12 performs discharge temperature control ( S69). When the difference between the actual suction superheat degree and the target suction superheat degree is small, the actual suction superheat degree is close to the target suction superheat degree. Since it is not necessary to set the suction superheat degree as a control target, the control device 12 controls the refrigeration cycle so that the discharge temperature does not rise too much with the discharge temperature as the control target.

  When the discharge temperature control is being performed, the control device 12 monitors the suction superheat degree and checks the difference between the target suction superheat degree and the actual suction superheat degree. If the difference between the target suction superheat degree and the actual suction superheat degree becomes large, the control device 12 switches from the discharge temperature control to the suction superheat degree control. When the actual suction superheat degree approaches the target suction superheat degree by executing the suction superheat degree control, the control device 12 switches to the discharge temperature control and performs the discharge temperature control. In this way, it is possible to prevent the discharge temperature from becoming high while performing an efficient air conditioning operation.

  During execution of the discharge temperature control, the load changes due to a change in room temperature or the like. Accordingly, the rotational speed of the compressor 3 is changed, the amount of refrigerant circulating in the refrigerant circuit is also changed, and the degree of superheat varies. The air conditioner according to the seventh embodiment switches between discharge temperature control and suction superheat degree control in accordance with the amount of circulating refrigerant so that it can quickly cope with the fluctuation in the degree of superheat. Other configurations are the same as those in the first to sixth embodiments.

  When the discharge temperature control is being performed, the control device 12 selects the discharge temperature control and the suction superheat degree control according to the rotation speed of the compressor 3 when changing the rotation speed of the compressor 3 based on the load. . As shown in FIG. 15, the control device 12 detects the rotational speed of the compressor 3 during the air-conditioning operation and checks whether there is a change in the rotational speed (S77).

  When the rotation speed of the compressor 3 has not changed, the control device 12 continues the discharge temperature control (S71 to S76). When the rotational speed of the compressor 3 is changing, the control device 12 confirms whether the rotational speed has decreased. When the rotational speed is decreasing, the control device 12 switches from the discharge temperature control to the suction superheat degree control (S78). When the rotation speed of the compressor 3 decreases, the amount of circulating refrigerant decreases and the suction superheat degree increases. Since the difference between the actual suction superheat degree and the target suction superheat degree becomes large, the actual suction superheat degree can be brought close to the target suction superheat degree by performing the suction superheat degree control.

  During the execution of the suction superheat degree control, the control device 12 checks whether the suction superheat degree control can be switched to the discharge temperature control (S79). That is, the control device 12 confirms the rotation speed of the compressor 3 and checks the difference between the discharge temperature or the actual suction superheat degree and the target suction superheat degree. When the rotational speed of the compressor 3 increases, the discharge temperature becomes higher than the determination discharge temperature, or the absolute value of the difference between the actual suction superheat degree and the target suction superheat degree falls below the determination reference value, The control device 12 performs discharge temperature control by switching from suction superheat degree control to discharge temperature control.

  In S77, when the rotation speed of the compressor 3 is increasing, the control device 12 continues the discharge temperature control without switching the superheat degree control. When the rotation speed of the compressor 3 increases, the discharge temperature may increase. Therefore, when this change occurs, the discharge temperature is controlled so that the discharge temperature does not become high.

  As another form of discharge temperature control that prevents the discharge temperature from becoming high, the air conditioner of the eighth embodiment performs discharge temperature control so that the discharge temperature falls within a predetermined temperature range. As the discharge temperature control, the control device 12 controls the expansion valve 6 according to the discharge temperature. Other configurations are the same as those in the first to seventh embodiments.

  As shown in FIG. 16, when the discharge temperature control is being performed, the control device 12 determines the target discharge temperature and the target suction superheat degree from the current rotational speed of the compressor 3 (S81). The control device 12 acquires the detected discharge temperature and the actual suction superheat degree (S82). An upper limit discharge temperature Th and a lower limit discharge temperature Tl are set in advance. For example, the upper limit discharge temperature is 100 ° C., and the lower limit discharge temperature is 95 ° C. The control device 12 determines the detected discharge temperature (S83). That is, the control device 12 compares the actual discharge temperature Td with the set discharge temperature.

  When the discharge temperature Td is higher than the upper limit discharge temperature Th (Td> Th), the control device 12 increases the opening degree of the expansion valve 6 (S84). The expansion valve 6 is opened by a predetermined opening from the current opening. By opening the expansion valve 6, the degree of superheat is lowered and the discharge temperature is also lowered. Thereby, the discharge temperature falls within a predetermined temperature range.

  When the discharge temperature Td is lower than the lower limit discharge temperature Tl (Td <Tl), the control device 12 decreases the opening of the expansion valve 6 (S85). The expansion valve 6 is closed by a predetermined opening degree from the current opening degree. By closing the expansion valve 6, the degree of superheat increases and the discharge temperature rises. Thereby, the discharge temperature falls within a predetermined temperature range.

  When the discharge temperature Td is between the upper limit discharge temperature Th and the lower limit discharge temperature Tl (Tl ≦ Td ≦ Th), the control device 12 compares the actual suction superheat degree with the target suction superheat degree (S86). When the actual suction superheat degree is equal to or lower than the target suction superheat degree, the control device 12 does not change the opening degree of the expansion valve 6 (S87). The discharge temperature is maintained within a predetermined temperature range.

  When the actual suction superheat degree is larger than the target suction superheat degree, the control device 12 switches from the discharge temperature control to the suction superheat degree control, and performs the suction superheat degree control (S88). In this suction superheat degree control, since the actual suction superheat degree is larger than the target suction superheat degree, the control device 12 increases the opening degree of the expansion valve 6. When the expansion valve 6 is opened more than the current opening degree, the temperature of the refrigerant coming out of the evaporator is lowered, the suction temperature is lowered, and the actual suction superheat degree is reduced. Thereby, the actual suction superheat degree approaches the target suction superheat degree while the discharge temperature is maintained within a predetermined temperature range.

  In each of the above embodiments, in the discharge temperature control, the discharge temperature is controlled by controlling the expansion valve 6 so that the discharge temperature does not become high and the discharge temperature is within a predetermined temperature range. The The air conditioner of the ninth embodiment controls the compressor 3 so that the discharge temperature does not become high. Other configurations are the same as those in the first to seventh embodiments.

  The control device 12 controls the rotation speed of the compressor 3 based on the discharge temperature. As shown in FIG. 17, when the discharge temperature control is being performed, the control device 12 determines a target discharge temperature (Taim) from the rotational speed of the compressor 3 (S71). When the air conditioning operation is started, the discharge temperature detector detects the discharge temperature (Td) (S72). The control device 12 compares the target discharge temperature with the actual discharge temperature (S73).

  When the actual discharge temperature is higher than the target discharge temperature (Td> Taim), the control device 12 decreases the rotational speed of the compressor 3 (S91). The rotational speed of the compressor 3 is lower than the current rotational speed by a predetermined rotational speed. Although the amount of refrigerant circulating in the refrigerant circuit is reduced, the discharge pressure from the compressor 3 is lowered, so that the discharge temperature is lowered. As a result, the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is lower than the target discharge temperature (Td <Taim), the control device 12 increases the rotation speed of the compressor 3 (S92). The rotation speed of the compressor 3 is higher than the current rotation speed by a predetermined rotation speed. Although the amount of circulating refrigerant increases, the discharge pressure from the compressor 3 increases, so the discharge temperature increases. As a result, the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is the same as the target discharge temperature (Td = Taim), the control device 12 does not change the rotation speed of the compressor 3 (S93). Thereby, the actual discharge temperature is maintained at the target discharge temperature.

  The air conditioner of the tenth embodiment controls the indoor and outdoor fans 7 and 9 so that the discharge temperature does not become high. Other configurations are the same as those in the first to seventh embodiments.

  The control device 12 controls the driving of the indoor fan 9 or the outdoor fan 7 based on the discharge temperature. As shown in FIG. 18, when the discharge temperature control is being performed, the control device 12 determines a target discharge temperature (Taim) from the rotational speed of the compressor 3 (S71). When the air conditioning operation is started, the discharge temperature detector 15 detects the discharge temperature (Td) (S72). The control device 12 compares the target discharge temperature with the actual discharge temperature (S73).

  When the actual discharge temperature is higher than the target discharge temperature (Td> Taim), the control device 12 increases the rotational speed of the indoor fan 9 or the outdoor fan 7 (S94). It is good to raise the rotation speed of the fan with respect to the heat exchanger used as a condenser in air-conditioning driving | operation. That is, the rotational speed of the outdoor fan 7 is increased when the cooling operation is performed, and the rotational speed of the indoor fan 9 is increased when the heating operation is performed. The rotational speed of the fan is higher than the current rotational speed by a predetermined rotational speed. Heat exchange in the condenser is promoted, and the amount of liquid refrigerant flowing out of the condenser increases, so that the amount of circulating refrigerant increases. As a result, the discharge temperature decreases and the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is lower than the target discharge temperature (Td <Taim), the control device 12 decreases the rotational speed of the indoor fan 9 or the outdoor fan 7 (S95). It is good to reduce the rotation speed of the fan with respect to the heat exchanger used as a condenser in air-conditioning operation. That is, the rotational speed of the outdoor fan 7 is reduced when the cooling operation is performed, and the rotational speed of the indoor fan 9 is decreased when the heating operation is performed. The rotational speed of the fan is lower than the current rotational speed by a predetermined rotational speed. Since the heat exchange in the condenser is suppressed and the liquid refrigerant flowing out of the condenser is reduced, the amount of circulating refrigerant is reduced. As the amount of refrigerant that evaporates in the evaporator increases, the degree of suction superheat increases. As a result, the discharge temperature rises and the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is the same as the target discharge temperature (Td = Taim), the control device 12 does not change the rotational speeds of the indoor and outdoor fans 7 and 9 (S96). Thereby, the actual discharge temperature is maintained at the target discharge temperature.

  You may change the rotation speed of the fan with respect to an evaporator with the rotation speed of the fan with respect to a condenser. That is, both the rotation speed of the indoor fan 9 and the rotation speed of the outdoor fan 7 may be changed. The controller 12 decreases the rotational speed of the fan relative to the evaporator when increasing the rotational speed of the fan relative to the condenser, and increases the rotational speed of the fan relative to the condenser when decreasing the rotational speed of the fan relative to the condenser.

  The air conditioner of the eleventh embodiment controls at least one of the compressor 3, the expansion valve 6, and the indoor and outdoor fans 7 and 9 so that the discharge temperature does not become high. Other configurations are the same as those in the first to tenth embodiments.

  The control device 12 controls at least one of the rotational speed of the compressor 3, the opening degree of the expansion valve 6, the rotational speed of the indoor fan 9, and the rotational speed of the outdoor fan 7 based on the discharge temperature. As shown in FIG. 19, when the discharge temperature control is being performed, the control device 12 determines a target discharge temperature (Taim) from the rotation speed of the compressor 3 (S71). When the air conditioning operation is started, the discharge temperature detector detects the discharge temperature (Td) (S72). The control device 12 compares the target discharge temperature with the actual discharge temperature (S73).

  When the actual discharge temperature is higher than the target discharge temperature (Td> Taim), the control device 12 decreases the rotation speed of the compressor 3, increases the opening degree of the expansion valve 6, and changes the rotation speed of the indoor fan 9. Any one or a combination of changing the number of rotations of the outdoor fan 7 is performed (S97). In addition, regarding the control of each fan 7 and 9, the rotation speed of the fan with respect to the heat exchanger used as a condenser is raised. As a result, the discharge temperature decreases and the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is lower than the target discharge temperature (Td <Taim), the control device 12 increases the rotation speed of the compressor 3, decreases the opening degree of the expansion valve 6, and changes the rotation speed of the indoor fan 9. Any one or a combination of changing the number of rotations of the outdoor fan 7 is performed (S98). In addition, regarding the control of each fan 7 and 9, the rotation speed of the fan with respect to the heat exchanger used as a condenser is raised. As a result, the discharge temperature rises and the actual discharge temperature approaches the target discharge temperature.

  When the actual discharge temperature is the same as the target discharge temperature (Td = Taim), the control device 12 does not change the operations of the compressor 3, the expansion valve 6, and the indoor and outdoor fans 7, 9, and keeps the current state. (S99). Thereby, the actual discharge temperature is maintained at the target discharge temperature.

  Here, the compressor 3 has the largest influence on the discharge temperature, and the expansion valve 6 and the fans 7 and 9 are in this order. Therefore, when the discharge temperature suddenly increases, the control by the compressor 3 is selected, and when the change in the discharge temperature is slow, the control by the fans 7 and 9 is selected. Furthermore, this control may be combined with other controls. However, the combination of the compressor 3, the expansion valve 6, and the fans 7 and 9 is arbitrary.

  As another form of the discharge temperature control for preventing the discharge temperature from becoming high, the air conditioner of the twelfth embodiment uses a determination formula relating to the discharge temperature, so that the discharge temperature does not become high and a predetermined temperature range. The superheat control is performed so that Other configurations are the same as those in the first to eleventh embodiments.

The discriminant relating to the discharge temperature shown below is created based on the condensation temperature, evaporation temperature, and suction superheat degree.
Td = αTc + β-Te + SH
Td: discharge temperature, Tc: condensation temperature, Te: evaporation temperature, SH: suction superheat degree 1 <α <2, 0 <β <10
α and β are experimentally determined in advance.

  The discharge temperature obtained from this equation is almost equal to the theoretical value, and the discharge temperature can be controlled by using this equation. Therefore, the control device 12 performs superheat degree control based on the discharge temperature obtained from the discriminant so that the discharge temperature does not become high. As the superheat degree control, at least one of the number of rotations of the compressor 3, the opening degree of the expansion valve 6, the number of rotations 9 of the indoor fan, and the number of rotations of the outdoor fan 7 is controlled.

  The control device 12 performs discharge temperature control when the discharge temperature calculated from the determination formula is high, and performs suction superheat degree control when the discharge temperature calculated from the determination formula is low. That is, the control device 12 compares the detected discharge temperature (Td) with the determined discharge temperature (Ta). When the detected discharge temperature is higher than the determination discharge temperature, the control device 12 performs discharge temperature control. For example, when the suction control superheat degree is performed, the discharge temperature control is performed when the discharge temperature becomes high. When the detected discharge temperature is equal to or lower than the determination discharge temperature, the control device 12 performs suction superheat degree control.

  When the discharge temperature control is performed, as shown in FIG. 20, the control device 12 determines the target suction superheat degree from the current rotation speed of the compressor 3 (S101). The control device 12 acquires the actual suction superheat degree based on the detected condensation temperature and evaporation temperature, and further calculates the discharge temperature from the discriminant (S102). The control device 12 determines the calculated discharge temperature based on the preset upper limit discharge temperature and lower limit discharge temperature (S103). For example, the upper limit discharge temperature Th is 100 ° C., and the lower limit discharge temperature Tl is 95 ° C. That is, the control device 12 compares the discharge temperature Td obtained from the discriminant with the set discharge temperature.

  When the discharge temperature Td is higher than the upper limit discharge temperature Th (Td> Th), the control device 12 decreases the rotation speed of the compressor 3, increases the opening degree of the expansion valve 6, and changes the rotation speed of the indoor fan 9. Any one or a combination of changing the number of rotations of the outdoor fan 7 is performed (S104). As a result, the discharge temperature decreases, the actual discharge temperature becomes lower than the upper limit discharge temperature, and falls within a predetermined temperature range.

  When the discharge temperature Td is lower than the lower limit discharge temperature Tl (Td <Tl), the control device 12 increases the rotation speed of the compressor 3, decreases the opening degree of the expansion valve 6, and changes the rotation speed of the indoor fan 9. Any one or a combination of changing the number of rotations of the outdoor fan 7 is performed (S105). Thereby, the discharge temperature rises, the actual discharge temperature becomes higher than the lower limit discharge temperature, and falls within a predetermined temperature range.

  When the discharge temperature Td is between the upper limit discharge temperature Th and the lower limit discharge temperature Tl (Tl ≦ Td ≦ Th), the control device 12 compares the actual suction superheat degree with the target suction superheat degree (S106). When the actual suction superheat degree is equal to or lower than the target suction superheat degree, the control device 12 does not change the operations of the compressor 3, the expansion valve 6, and the indoor and outdoor fans 7, 9, and keeps the current state (S107). As a result, the actual discharge temperature is maintained within a predetermined temperature range.

  When the actual suction superheat degree is larger than the target suction superheat degree, the control device 12 switches from the discharge temperature control to the suction superheat degree control, and performs the suction superheat degree control (S108). In this suction superheat degree control, since the actual suction superheat degree is larger than the target suction superheat degree, the control device 12 decreases the rotation speed of the compressor 3 and increases the opening degree of the expansion valve 6. Or changing the number of rotations of the outdoor fan 7 or any combination thereof. Thereby, the actual suction superheat degree approaches the target suction superheat degree while the actual discharge temperature is maintained within a predetermined temperature range.

  Even if the difference between the discharge temperature obtained from the discriminant and the actual discharge temperature is large, the actual discharge temperature approaches the discharge temperature obtained from the discriminant as time elapses. That is, the trend of the discharge temperature can be predicted. For example, when the actual discharge temperature is lower than the discharge temperature obtained from the discriminant, it can be predicted that the discharge temperature further increases. In such a case, if the discharge temperature control is performed based on the discharge temperature obtained from the discriminant, it is possible to prevent the discharge temperature from rising excessively.

  In the air conditioner of each of the above embodiments, when R32 is used as a refrigerant, the refrigerant has characteristics such as a low pressure loss and a large amount of heat exchange per mass flow rate compared to other refrigerants such as R410. Have. Therefore, the minimum air conditioning capability is higher than other refrigerants. By the way, when the amount of refrigerant circulating through the refrigerant circuit is small, the discharge superheat degree control is performed, but the discharge superheat degree becomes smaller as the rotation speed of the compressor 3 is lower, and the compressor 3 is driven at the minimum rotation speed. The minimum air conditioning capability. However, when the refrigerant is R32, even if the compressor 3 is driven at the minimum number of rotations, the air-conditioning capability is increased, and thus the operating temperature range is narrowed.

  Therefore, the air conditioner of the thirteenth embodiment reduces the air conditioning capability when the compressor 3 operates at the minimum rotation speed. Therefore, the target discharge superheat degree is set lower as the rotation speed of the compressor 3 is lower, and the control device 12 performs the discharge superheat degree control based on the set target discharge superheat degree. Other configurations are the same as those in the first to twelfth embodiments.

  The minimum rotation speed of the compressor 3 is lower than the rotation speed when the frequency code is FD1. And the target discharge superheat degree with respect to the minimum rotation speed is set lower than the target discharge superheat degree with respect to FD1. As shown in FIG. 21, the normal target discharge superheat degree with respect to the minimum rotation speed is set to the superheat degree on the line connecting the target discharge superheat degree with respect to FD1 of the frequency code and the target discharge superheat degree with respect to the intermediate rotation speed. Yes.

  On the other hand, as shown in FIG. 22, the target discharge superheat degree with respect to the minimum rotation speed when performing the discharge superheat degree control is set to a superheat degree lower than the normal target discharge superheat degree. The target discharge superheat degree of the minimum rotation speed is lower than the line connecting the target discharge superheat degree for FD1 and the target discharge superheat degree for the intermediate rotation speed.

  When the discharge superheat degree control is performed, the control device 12 performs the discharge temperature control aiming at the target discharge superheat degree. At this time, the control device 12 controls the opening degree of the expansion valve 6 according to the difference between the target discharge superheat degree and the actual discharge superheat degree. When the actual discharge superheat degree is larger than the target discharge superheat degree, the target discharge superheat degree is set low, so that the difference between the target discharge superheat degree and the actual discharge superheat degree becomes large. The control device 12 makes the opening degree of the expansion valve 6 larger than the normal opening degree.

  When the compressor 3 is operating at the minimum number of rotations, the opening degree of the expansion valve 6 is larger than normal. Since it becomes difficult to take the target discharge superheat degree, the air-conditioning capacity is lowered. By reducing the air conditioning capability at the minimum rotation speed, it is possible to prevent the load on the compressor 3 from being reduced and the compressor 3 from being stopped. Thereby, even if the compressor 3 operates at a low speed, the compressor 3 does not stop, so that the air conditioning operation can be continued, and the user's comfort is not impaired. As described above, since the air conditioning capability can be lowered, an air conditioning operation at a low operating temperature is possible, and an air conditioner that can cope with a wide operating temperature range can be realized.

  As described above, in the air conditioner of the present invention, the compressor 3, the condenser, the throttle device, and the evaporator are connected to form a refrigerant circuit, and the operation of the throttle device is controlled according to the amount of refrigerant circulating in the refrigerant circuit. The control device 12 is provided. The control device 12 performs suction superheat degree control for operating the expansion device based on the suction temperature of the refrigerant sucked into the compressor 3 when the amount of refrigerant circulating is large, and from the compressor 3 when the amount of refrigerant circulating is small Based on the discharge temperature of the discharged refrigerant, discharge superheat control for operating the expansion device is performed.

  When the amount of circulating refrigerant is large, suction superheat control with good responsiveness to changes in superheat is suitable, and when the amount of refrigerant circulating is small, discharge superheat control that can cope with small changes in superheat is suitable ing. Appropriate superheat control can be performed according to the amount of circulating refrigerant, and efficient air-conditioning operation can be performed.

  When the amount of refrigerant circulating is small, the control device 12 performs suction superheat degree control until the refrigeration cycle is stabilized, and performs discharge superheat degree control after the refrigeration cycle is stabilized.

Since the suction superheat degree control can stabilize the refrigeration cycle quickly, efficient air conditioning operation can be performed quickly by sequentially performing the suction superheat degree control and the discharge superheat degree control.

  The control device 12 controls the opening degree of the throttle device so that the temperature difference between the suction temperature and the evaporation temperature approaches a predetermined value in the suction superheat degree control, and in the discharge superheat degree control, the temperature between the discharge temperature and the condensation temperature. The opening degree of the expansion device is controlled so that the difference approaches a predetermined value.

  When the refrigeration cycle becomes unstable while performing the discharge superheat control, the control device 12 performs the suction superheat control. By switching to the suction superheat control when the refrigeration cycle becomes unstable, the refrigeration cycle stabilizes quickly, so that the time until returning to the discharge superheat control can be shortened.

  The control device 12 compares the target suction superheat degree with the actual suction superheat degree to determine whether or not the refrigeration cycle is unstable. That is, when the difference between the target suction superheat degree and the actual suction superheat degree is large, the control device 12 determines that the refrigeration cycle is unstable, and the difference between the target suction superheat degree and the actual suction superheat degree is small. When it is determined that the refrigeration cycle is stable.

  When the refrigeration cycle becomes unstable, the change in suction superheat is greater than the change in discharge superheat, so by judging based on the suction superheat, it quickly detects that the refrigeration cycle has become unstable. be able to.

  The control device 12 determines that the refrigeration cycle is stable when the actual suction superheat degree varies around the target suction superheat degree. Thereby, it can switch to suitable superheat degree control quickly.

  The air conditioner includes a control device 12 that controls the operation of the throttle device according to the amount of refrigerant circulating in the refrigerant circuit by connecting the compressor 3, the condenser, the throttle device, and the evaporator to form a refrigerant circuit. The control device determines the operating state and operates the expansion device based on the suction temperature of the refrigerant sucked into the compressor, and the expansion device based on the discharge temperature of the refrigerant discharged from the compressor Switch the superheat control to operate the, and perform the optimal air conditioning operation.

  That is, the control device 12 controls the degree of suction superheat to operate the throttle device based on the suction temperature of the refrigerant sucked into the compressor 3 according to the operation state determined by the amount of circulating refrigerant, etc., and discharges from the compressor 3 One of the superheat degree control for operating the throttle device based on the discharged refrigerant temperature and the discharge temperature control for operating the throttle device so that the discharge temperature approaches the set temperature is performed.

  Appropriate superheat control is selected from the three superheat control depending on the amount of refrigerant to be circulated, the discharge temperature, and the suction superheat, and optimal air conditioning operation can be performed.

  When the amount of refrigerant circulating is large, the control device 12 performs discharge temperature control that operates the throttle device so that the discharge temperature approaches the set temperature, and switches between discharge temperature control and suction superheat degree control according to the discharge temperature. By performing the discharge temperature control, the discharge temperature can be prevented from exceeding a predetermined temperature.

  The control device 12 performs discharge temperature control when the discharge temperature is high, and performs suction superheat degree control when the discharge temperature is low. When the suction superheat degree becomes close to the target suction superheat degree and the discharge temperature becomes high, the discharge temperature can be prevented from exceeding a predetermined temperature.

  The control device 12 performs discharge temperature control when the difference between the target suction superheat degree and the actual suction superheat degree is small, and performs suction superheat degree control when the difference between the target suction superheat degree and the actual suction superheat degree is large.

  By switching between the suction superheat degree control and the discharge temperature control according to the difference between the target suction superheat degree and the actual suction superheat degree, it is possible to prevent the discharge temperature from becoming high while performing an efficient air conditioning operation.

  The determination formula of the discharge temperature is determined by the evaporation temperature, the condensation temperature, and the suction superheat degree, and the control device 12 performs the discharge temperature control based on the discharge temperature calculated from the determination formula so that the discharge temperature does not exceed the predetermined temperature. .

  Since the trend of the discharge temperature can be predicted from the judgment formula, the discharge temperature can be controlled so as not to exceed the predetermined temperature.

  The control device 12 performs discharge temperature control when the discharge temperature calculated from the determination formula is high, and performs suction superheat degree control when the discharge temperature calculated from the determination formula is low.

  Thereby, the suction superheat degree approaches the target suction superheat degree, and the discharge temperature can be prevented from exceeding the predetermined temperature.

  The control device 12 controls at least one of the rotational speed of the compressor 3, the opening degree of the expansion device, and the rotational speed of the heat exchanger fan according to the target value of the discharge temperature and the calculated discharge temperature. .

  By appropriately combining the three control objects according to the difference in the discharge temperature, it is possible to ensure that the discharge temperature does not exceed the predetermined temperature and is within the predetermined temperature range.

  When controlling the discharge temperature, the control device 12 increases the opening degree of the expansion device according to the discharge temperature so that the discharge temperature does not exceed a predetermined temperature, decreases the rotation speed of the compressor 3, and sets the fan for the heat exchanger. Either one of increasing the number of rotations, in particular, increasing the number of rotations of the fan with respect to the condenser, or a combination of two or more.

  In order to reduce the air conditioning capability when the compressor 3 operates at the minimum rotation speed, the target discharge superheat degree with respect to the minimum rotation speed of the compressor 3 is set lower than the normal target discharge superheat degree, and the control device 12 The discharge superheat degree control is performed based on the target discharge superheat degree.

  Since the air conditioning capability when the compressor 3 operates at the minimum rotation speed is reduced, the compressor 3 can operate without stopping even at a low operating temperature. Thereby, an air-conditioning operation can be performed in a wide operating temperature range.

  The control device 12 determines whether the amount of refrigerant circulating is large or small depending on the number of rotations of the compressor 3, and when the number of rotations of the compressor 3 is higher than a predetermined number, the amount of refrigerant circulating is large and the rotation of the compressor 3 When the number is lower than the predetermined number, it is determined that the amount of circulating refrigerant is small. If the rotation speed of the compressor 3 changes according to the load during the air conditioning operation, the superheat degree control is switched.

  In addition, this invention is not limited to the said embodiment, Of course, many corrections and changes can be added to the said embodiment within the scope of the present invention. In the suction superheat control and the discharge superheat control, not only the expansion valve 6 but also the compressor 3 and the indoor and outdoor fans 7 and 9 may be controlled.

  As the second temperature detector 18, a temperature detector may be provided for the indoor heat exchanger 8. The second temperature detector 18 directly detects the temperature of the indoor heat exchanger 8.

DESCRIPTION OF SYMBOLS 1 Outdoor unit 2 Indoor unit 3 Compressor 4 Four-way valve 5 Outdoor heat exchanger 6 Expansion valve 7 Outdoor fan 8 Indoor heat exchanger 9 Indoor fan 10 Two-way valve 12 Controller 13 Room temperature detector 14 Outdoor temperature detector 15 Discharge temperature Detector 16 Suction temperature detector 17 First temperature detector 18 Second temperature detector

Claims (12)

A compressor, a condenser, a throttle device, and an evaporator are connected to form a refrigerant circuit, and an air conditioner including a control device that controls the operation of the throttle device according to the amount of refrigerant circulating in the refrigerant circuit, The control device judges the operating state and operates the throttle device based on the suction superheat degree control for operating the throttle device based on the refrigerant suction temperature sucked into the compressor and the refrigerant discharge temperature discharged from the compressor An air conditioner characterized by switching the superheat degree control to be performed and performing optimal air conditioning operation. The control device performs suction superheat control that operates the expansion device based on the suction temperature of the refrigerant sucked into the compressor when the amount of refrigerant circulating is large, and is discharged from the compressor when the amount of refrigerant circulating is small The air conditioner according to claim 1, wherein discharge superheat degree control is performed to operate the expansion device based on the discharge temperature of the refrigerant. 3. The air conditioner according to claim 1, wherein when the amount of refrigerant circulating is small, the control device performs suction superheat control until the refrigeration cycle is stabilized, and performs discharge superheat control after the refrigeration cycle is stabilized. Machine. The air conditioner according to any one of claims 1 to 3, wherein the control device performs suction superheat control when the refrigeration cycle becomes unstable while performing discharge superheat control. The air conditioner according to claim 3 or 4, wherein the control device compares the target suction superheat degree with the actual suction superheat degree to determine whether or not the refrigeration cycle is unstable. The air conditioner according to any one of claims 3 to 5, wherein the control device determines that the refrigeration cycle is stable when the actual suction superheat degree varies around the target suction superheat degree. The control device performs discharge temperature control that operates the throttle device so that the discharge temperature approaches the set temperature when the amount of circulating refrigerant is large, and switches between discharge temperature control and suction superheat degree control according to the discharge temperature. The air conditioner according to any one of claims 1 to 6, wherein 8. The air conditioner according to claim 7, wherein the control device performs discharge temperature control when the discharge temperature is high, and performs suction superheat degree control when the discharge temperature is low. The control device performs discharge temperature control when the difference between the target suction superheat degree and the actual suction superheat degree is small, and performs the suction superheat degree control when the difference between the target suction superheat degree and the actual suction superheat degree is large. The air conditioner according to claim 7 or 8, characterized in that The determination formula of the discharge temperature is determined by the evaporation temperature, the condensation temperature, and the suction superheat degree, and the control device performs the discharge temperature control based on the discharge temperature calculated from the determination formula so that the discharge temperature does not exceed the predetermined temperature. The air conditioner according to any one of claims 1 to 9. The air conditioning according to claim 10, wherein the control device performs discharge temperature control when the discharge temperature calculated from the determination formula is high, and performs suction superheat degree control when the discharge temperature calculated from the determination formula is low. Machine. In order to reduce the air conditioning capacity when the compressor operates at the minimum rotation speed, the target discharge superheat degree for the minimum rotation speed of the compressor is set lower than the normal target discharge superheat degree, and the control device sets the target The air conditioner according to any one of claims 1 to 11, wherein discharge superheat degree control is performed based on the discharge superheat degree.

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