US20170328621A1 - Air-conditioning system - Google Patents

Abstract

An air-conditioning system capable of suppressing power consumption and maintaining the indoor temperature at a constant level includes a refrigerant circuit in which a compressor, a heat source-side heat exchanger, an expansion device, and a load-side heat exchanger are sequentially connected via a pipe, an inverter that drives the compressor, an indoor temperature sensor that detects an indoor temperature, and a controller that receives a thermostat ON signal and a thermostat OFF signal and controls the inverter according to the thermostat ON signal and the thermostat OFF signal. The controller assumes, upon receipt of the thermostat OFF signal, that the indoor temperature detected at that time is a target temperature, and regulates an output frequency of the inverter so as to maintain a difference between the indoor temperature and the target temperature in a predetermined range.

Description

CROSS REFERENCE TO RELATED APPLICATION
• This application is a U.S. national stage application of International Application No. PCT/JP2015/054357, filed on Feb. 18, 2015, the contents of which are incorporated herein by reference.
TECHNICAL FIELD
• The present invention relates to an air-conditioning system.
BACKGROUND
• Some of existing air-conditioning systems are configured to control a compressor with an inverter so as to bring the indoor temperature close to an optimal temperature. In such an air-conditioning system, a target temperature is specified, and the operation of the compressor is controlled on the basis of the indoor temperature, outlet temperature, and suction pressure and discharge pressure of the compressor. To be more detailed, the conventional air-conditioning system is configured to detect at least one of the outlet temperature, and the suction pressure and discharge pressure of the compressor, in addition to the indoor temperature, and the operation of the compressor is controlled so as to bring the detected values close to predetermined target values. Here, normally the target temperature is set through operation of a remote controller, and the target temperature, the indoor temperature, the outlet temperature, and the suction pressure and discharge pressure of the compressor are processed into signals in a controller of the air-conditioning system, and then the controller outputs an inverter control signal to the compressor.
• While many of the air-conditioning systems popularly utilized in Japan are configured to perform the inverter control of the compressor as above, the air-conditioning systems popularly utilized in the North America are generally controlled by a thermostat, which is a remote controller having a controller function (hereinafter, local thermostat), sold separately from the air-conditioning system. The local thermostat is configured to detect the indoor temperature, compare the detected indoor temperature with the target temperature, and output a signal to turn the compressor on or off to the controller according to the comparison result.
• However, in the North American air-conditioning system controlled by the local thermostat, the local thermostat only outputs the signal to turn the compressor on or off, which is insufficient to appropriately control the compressor. Accordingly, an air-conditioning system has been proposed that is configured to control the compressor according to the switching frequency of the signal to turn the compressor on or off output from the local thermostat (see, for example, Patent Literature 1).
PATENT LITERATURE
• Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2008-116068
• In the air-conditioning system according toPatent Literature 1, the local thermostat only transmits the signal to turn the compressor on or off to the controller that controls the operation of the compressor. Accordingly, the local thermostat frequently transmits the signal to turn the compressor on or off to bring the indoor temperature close to the target temperature, and hence the compressor is repeatedly activated and stopped, which leads to an increase in power consumption of the air-conditioning system. In addition, it is difficult to maintain the indoor temperature at a constant level by repeatedly activating and stopping the compressor, and therefore the comfort of the space is degraded.
SUMMARY
• The present invention has been accomplished in view of the foregoing problem, and provides an air-conditioning system capable of suppressing power consumption and maintaining the indoor temperature at a constant level.
• In an aspect, the present invention provides an air-conditioning system including a refrigerant circuit in which a compressor, a heat source-side heat exchanger, an expansion device, and a load-side heat exchanger are sequentially connected via a pipe, an inverter that drives the compressor, an indoor temperature sensor that detects an indoor temperature, and a controller that receives a thermostat ON signal and a thermostat OFF signal, and controls the inverter according to the thermostat ON signal and the thermostat OFF signal. The controller assumes, upon receipt of the thermostat OFF signal, that the indoor temperature detected when the thermostat OFF signal is received is a target temperature, and regulates an output frequency of the inverter so as to maintain a difference between the indoor temperature and the target temperature in a predetermined range.
• According to the present invention, the air-conditioning system configured as above, the controller that controls the compressor assumes, upon receipt of the thermostat OFF signal, that the indoor temperature at that time is the target temperature, and controls the output frequency of the inverter so as to maintain the difference between the indoor temperature and the target temperature in the predetermined range. Therefore, the power consumption of the air-conditioning system can be suppressed, and the indoor temperature can be maintained at a constant level.
BRIEF DESCRIPTION OF DRAWINGS
• FIG. 1 is a schematic circuit diagram showing an example of a circuit configuration of an air-conditioning apparatus according toEmbodiment 1 of the present invention.
• FIG. 2 is a schematic circuit diagram showing a refrigerant flow in a cooling operation mode of the air-conditioning apparatus according toEmbodiment 1 of the present invention.
• FIG. 3 is a schematic circuit diagram showing a refrigerant flow in a heating operation mode of the air-conditioning apparatus according toEmbodiment 1 of the present invention.
• FIG. 4 is a graph showing transition of the indoor temperature under conventional local thermostat control.
• FIG. 5 is a flowchart showing a control operation performed by a controller under the local thermostat control ofFIG. 4.
• FIG. 6 is a graph showing transition of the indoor temperature under local thermostat control and an inverter control according toEmbodiment 1 of the present invention.
• FIG. 7 is a flowchart showing a control operation performed by a controller under the local thermostat control and the inverter control ofFIG. 6.
• FIG. 8 is a graph showing a relationship between a difference between the outdoor temperature and the indoor temperature and a predetermined operation time according toEmbodiment 2 of the present invention.
DETAILED DESCRIPTION
• Hereafter, Embodiments of the air-conditioning system of the present invention will be described with reference to the drawings. The configurations of the constituents illustrated in the drawings are merely exemplary, and not intended to limit the present invention to those configurations. In the drawings referred to hereafter, in addition, the constituents of the same reference numeral are identical or corresponding ones, which is to be applied throughout the description. Further, relations in size among constituents illustrated in the drawings may differ from actual ones.
Embodiment 1[Configuration of Air-Conditioning System100]
• FIG. 1 is a schematic circuit diagram showing an example of a circuit configuration of an air-conditioning apparatus according toEmbodiment 1 of the present invention. As shown inFIG. 1, the air-conditioning system100 includes anoutdoor unit1 and anindoor unit2, and is configured to control a compressor5 with alocal thermostat20. Theoutdoor unit1 and theindoor unit2 are connected to each other via a refrigerantmain pipe3 and a refrigerant main pipe7.
[Configuration of Outdoor Unit1]
• Theoutdoor unit1 includes the compressor5, a switching valve8 such as a four-way valve, and a heat source-side heat exchanger6, which are connected to each other via a refrigerant pipe4. Theoutdoor unit1 also includes an air-sending device9 and anoutdoor temperature sensor15. The compressor5 sucks low-temperature and low-pressure refrigerant and compresses the sucked refrigerant into high-temperature and high-pressure, and is constituted of, for example, an inverter compressor with variable capacity. The air-sending device9 is located in the vicinity of the heat source-side heat exchanger6, to supply air to the heat source-side heat exchanger6. The heat source-side heat exchanger6 acts as condenser in a cooling operation and acts as evaporator in a heating operation, to exchange heat between the air supplied from the air-sending device9 such as a fan and the refrigerant. The switching valve8 switches the flow of the refrigerant between a cooling operation mode and a heating operation mode to be subsequently described. Theoutdoor temperature sensor15 is constituted of a thermistor for example, and detects the temperature of outdoor air.
[Configuration of Indoor Unit2]
• Theindoor unit2 includes an air-sending device12, a load-side heat exchanger10, anexpansion device11, acontroller13, anindoor temperature sensor14, and aninverter16. Theindoor unit2 is connected to theoutdoor unit1 via the refrigerantmain pipe3 and the refrigerant main pipe7, so that the refrigerant flows in and out. Thus, the compressor5, the heat source-side heat exchanger6, theexpansion device11, and the load-side heat exchanger10 are sequentially connected via the pipe, and constitute a refrigerant circuit of the air-conditioning system100.
• The load-side heat exchanger10 exchanges heat between the air supplied from the air-sending device12 such as a fan and the refrigerant, to thereby generate air for heating or air for cooling to be supplied to an indoor space. Theexpansion device11 has a function of a reducing valve or expansion valve, which depressurizes and expands the refrigerant, and is preferably constituted of a device with variable opening degree, such as an electronic expansion valve. Theindoor temperature sensor14 is constituted of a thermistor for example, and detects the temperature of indoor air.
• Thecontroller13 is constituted of a microcomputer for example, and acquires indoor temperature information from theindoor temperature sensor14 and outdoor temperature information from theoutdoor temperature sensor15. Thecontroller13 also controls theinverter16 in accordance with an instruction from thelocal thermostat20 to be subsequently described, to control the output frequency of the compressor5 and the rotation speed of the air-sending device9 provided for the heat source-side heat exchanger6. Further, thecontroller13 controls the switching of the switching valve8 and the opening degree of theexpansion device11, to thereby perform the cooling operation mode and the heating operation mode to be subsequently described. Theinverter16 drives the compressor5 in accordance with an instruction from thecontroller13.
[Local Thermostat20]
• First, an air-conditioning system that employs the conventional remote controller instead of thelocal thermostat20 will be described. The conventional remote controller transmits, upon being activated, a target temperature specified in the remote controller to the controller. The controller calculates the difference between the indoor temperature detected by the indoor temperature sensor and the target temperature, and causes the inverter to control the output frequency of the compressor to bring the indoor temperature close to the target temperature. Such an operation of the controller to control the operation frequency of the compressor according to the target temperature will hereinafter be referred to as inverter control. Here, the outdoor unit constituting a part of the air-conditioning system may be provided with the controller and the inverter for controlling the compressor, and the controller of the outdoor unit and the controller of the indoor unit may communicate with each other.
• Now, thelocal thermostat20 is a device having the functions of the remote controller and the thermostat, as well as a control function of the compressor5. When a user specifies a target of the indoor temperature in thelocal thermostat20, thelocal thermostat20 compares the indoor temperature detected by the thermostat with the target temperature. Thelocal thermostat20 then transmits an ON or OFF signal with respect to the compressor5 to thecontroller13, depending on the comparison result. Thecontroller13 activates the compressor5 upon receipt of the ON signal for the compressor5, and turns off the compressor5 upon receipt of the OFF signal for the compressor5. Such a control operation of thelocal thermostat20 to activate and turn off the compressor5 will hereinafter be referred to as local thermostat control.
• Thelocal thermostat20 does not transmit the information of the target indoor temperature to thecontroller13 in the local thermostat control, and therefore thecontroller13 is unable to acquire information on the magnitude of the air-conditioning load. Accordingly, thecontroller13 can only cause the compressor5 to perform the maximum frequency operation (MAX-Hz operation) upon receipt of the ON signal for the compressor5, or turn off the compressor5 upon receipt of the OFF signal for the compressor5. Here, the ON signal for the compressor5 corresponds to the thermostat-ON signal in the present invention. The OFF signal for the compressor5 corresponds to the thermostat-OFF signal in the present invention.
[Cooling Operation Mode]
• FIG. 2 is a schematic circuit diagram showing the refrigerant flow in the cooling operation mode of the air-conditioning apparatus according toEmbodiment1 of the present invention. As shown inFIG. 2, in the cooling operation mode the switching valve8 is set such that afirst port8aand asecond port8bcommunicate with each other and athird port8cand afourth port8dcommunicate with each other. Accordingly, the refrigerant flows as indicated by solid line arrows inFIG. 2.
• In the cooling operation mode, the low-temperature and low-pressure refrigerant is compressed by the compressor5 thus to be turned into high-temperature and high-pressure gas refrigerant, and discharged from the compressor5. The high-temperature and high-pressure gas refrigerant discharged from the compressor5 flows into the heat source-side heat exchanger6 through the switching valve8. The high-temperature and high-pressure gas refrigerant which has entered the heat source-side heat exchanger6 is condensed by transferring heat to the outdoor air, thereby turning into high-pressure liquid refrigerant. Then the high-pressure liquid refrigerant which has flowed out of the heat source-side heat exchanger6 flows out of theoutdoor unit1 and into theindoor unit2, through the refrigerant main pipe7.
• The high-pressure liquid refrigerant which has entered theindoor unit2 is depressurized by theexpansion device11 into low-temperature and low-pressure two-phase refrigerant, and then flows into the load-side heat exchanger10 acting as evaporator. Then the low-temperature and low-pressure two-phase refrigerant removes heat from the indoor air thereby cooling the indoor air, and turns into low-temperature and low-pressure gas refrigerant. The low-temperature and low-pressure gas refrigerant which has flowed out of the load-side heat exchanger10 flows into theoutdoor unit1 through the refrigerantmain pipe3. The refrigerant which has flowed into theoutdoor unit1 is sucked into the compressor5 through the switching valve8. With such circulation of the refrigerant, the cooling operation is performed.
[Heating Operation Mode]
• FIG. 3 is a schematic circuit diagram showing the refrigerant flow in the heating operation mode of the air-conditioning apparatus according toEmbodiment 1 of the present invention. As shown inFIG. 3, in the heating operation mode the switching valve8 is set such that thefirst port8aand thethird port8ccommunicate with each other and thesecond port8band thefourth port8dcommunicate with each other. Accordingly, the refrigerant flows as indicated by solid line arrows inFIG. 3.
• In the heating operation mode, the low-temperature and low-pressure refrigerant is compressed by the compressor5 thus to be turned into high-temperature and high-pressure gas refrigerant, and discharged from the compressor5. The high-temperature and high-pressure gas refrigerant discharged from the compressor5 flows into theindoor unit2 through the switching valve8 and the refrigerantmain pipe3. The high-temperature and high-pressure gas refrigerant which has entered theindoor unit2 transfers heat to the indoor air in the load-side heat exchanger10, thereby turning into high-pressure liquid refrigerant and flows into theexpansion device11. Then the high-pressure liquid refrigerant is depressurized by theexpansion device11 into low-temperature and low-pressure two-phase refrigerant, and flows out of theindoor unit2 and into theoutdoor unit1, through the refrigerant main pipe7.
• The low-temperature and low-pressure two-phase refrigerant which has entered theoutdoor unit1 removes heat from the outdoor air in the heat source-side heat exchanger6, thereby turning into low-temperature and low-pressure gas refrigerant. The low-temperature and low-pressure gas refrigerant which has flowed out of the heat source-side heat exchanger6 is sucked into the compressor5 through the switching valve8. With such circulation of the refrigerant, the heating operation is performed.
• FIG. 4 is a graph showing the transition of the indoor temperature under conventional local thermostat control. The air-conditioning system100 is configured to perform the cooling operation mode and the heating operation mode, out of which the local thermostat control of the air-conditioning system100 in the cooling operation mode will be described as an example. Referring toFIG. 4, the vertical axis represents the indoor temperature, and the horizontal axis represents the time. Here, the target temperature A1 and a reference temperature A2 which serves as threshold for transmitting the ON signal for the compressor5 are specified in thelocal thermostat20.
• Between a time point T0 and a time point T1, thecontroller13 is receiving the ON signal for the compressor5 from thelocal thermostat20, and is hence driving the compressor5 to perform the maximum frequency operation. With such operation of the compressor5, the indoor temperature drops from A2 to the target temperature A1. Between the time point T1 and a time point T2, thecontroller13 is receiving the OFF signal for the compressor5 from thelocal thermostat20, and hence turns off the compressor5. Because the compressor5 is off, the indoor temperature is heated by the outdoor air, and rises from the target temperature A1 to the temperature A2. Then between the time point T2 and a time point T3, thecontroller13 is receiving the ON signal for the compressor5 from thelocal thermostat20, and is hence driving the compressor5 to perform the maximum frequency operation. With such operation of the compressor5, the indoor temperature drops from A2 to the target temperature A1.
• As described above, in the case of the local thermostat control, although the indoor temperature once reaches the target temperature A1, the compressor5 is turned off at this point and therefore the indoor temperature again rises to the temperature A2. Accordingly, the indoor temperature is unable to be constantly maintained at the target temperature A1. Therefore, after the indoor temperature reaches the target temperature A1, it is desirable to perform the inverter control to be hereafter described, to thereby maintain the indoor temperature at the target temperature A1.
• FIG. 5 is a flowchart showing a control operation performed by thecontroller13 under the local thermostat control ofFIG. 4. Hereunder, the control operation of thecontroller13 will be described following the steps specified inFIG. 5, while referring also toFIG. 1.
(Step S11)
• Thecontroller13 activates the compressor5, and then proceeds to step S12.
(Step S12)
• Thecontroller13 receives the ON signal for the compressor5, and causes the compressor5 to perform the maximum frequency operation. Then thecontroller13 proceeds to step S13.
(Step S13)
• Thecontroller13 decides whether the indoor temperature has reached the target temperature A1. In the case where the indoor temperature has reached the target temperature A1, thecontroller13 proceeds to step S14. Otherwise, thecontroller13 proceeds to step S13.
(Step S14)
• Thecontroller13 receives the OFF signal for the compressor5, and turns off the compressor5. Then thecontroller13 proceeds to step S15.
(Step S15)
• Thecontroller13 decides whether the indoor temperature has reached the temperature A2. In the case where the indoor temperature has reached the temperature A2, thecontroller13 proceeds to step S12. Otherwise, thecontroller13 proceeds to step S15.
• FIG. 6 is a graph showing the transition of the indoor temperature under the local thermostat control and the inverter control according toEmbodiment 1 of the present invention. The air-conditioning system100 is configured to perform the cooling operation mode and the heating operation mode, out of which the local thermostat control of the air-conditioning system100 in the cooling operation mode will be described as an example. Referring toFIG. 6, the vertical axis represents the indoor temperature, and the horizontal axis represents the time. Here, the target temperature A1 and the reference temperature A2 which serves as threshold for transmitting the ON signal for the compressor5 are specified in thelocal thermostat20.
• Between the time point T3 and a time point T4, thecontroller13 is receiving the ON signal for the compressor5 from thelocal thermostat20, and hence controls theinverter16 so as to cause the compressor5 to perform the maximum frequency operation. With such operation of the compressor5, the indoor temperature drops from A2 to the target temperature A1.
• At the time point T4, the indoor temperature reaches the target temperature A1, and hence thecontroller13 receives the OFF signal for the compressor5 from thelocal thermostat20. Upon receipt of the OFF signal, thecontroller13 shifts to the inverter control from the local thermostat control, and continues with the inverter control up to a time point T5. More specifically, thecontroller13 controls theinverter16 to control the output frequency of the compressor5, so as to maintain the difference between the indoor temperature and the target temperature A1 within a predetermined range, during the period between the time point T4 and the time point T5. Here, the operation of the compressor5 at the output frequency set in this case will hereinafter be referred to as minimum frequency operation (min-Hz operation). Although thecontroller13 is unable to acquire the information of the target temperature A1 from thelocal thermostat20, thecontroller13 can perform the inverter control by acquiring the indoor temperature information from theindoor temperature sensor14 and assuming that the indoor temperature at the time of receiving the OFF signal for the compressor5 is the target temperature A1.
• Then at the time point T5, thecontroller13 shifts from the inverter control to the local thermostat control. The inverter control is shifted to the local thermostat control when one of the following three conditions is satisfied. A first condition is that the indoor temperature exceeds a range defined by a permissible temperature difference Au from the target temperature A1. A second condition is that the time during which the inverter control has been performed exceeds a predetermined operation time ΔT. A third condition is that thelocal thermostat20 transmits the ON signal to thecontroller13. Here, the permissible temperature difference Au and the predetermined operation time ΔT are stored in advance in thecontroller13.
• As described above, thecontroller13 shifts from the inverter control to the local thermostat control at the time point T5. After entering the local thermostat control, thecontroller13 turns off the compressor5 upon receipt of the OFF signal for the compressor5, and drives the compressor5 at the maximum frequency upon receipt of the ON signal for the compressor5. Between the time point T5 and a time point T6 thecontroller13 is receiving the OFF signal for the compressor5 from thelocal thermostat20, and hence controls theinverter16 to turn off the compressor5. Accordingly, the indoor temperature rises from A1 to A2, and at the time point T6 where the indoor temperature reaches A2 thelocal thermostat20 transmits the ON signal for the compressor5 to thecontroller13. Then between the time point T6 and a time point T7, thecontroller13 is receiving the ON signal for the compressor5 from thelocal thermostat20, and hence controls theinverter16 to cause the compressor5 to perform the maximum frequency operation. With such operation of the compressor5, the indoor temperature drops from A2 to A1.
• FIG. 7 is a flowchart showing the control operation performed by thecontroller13 under the local thermostat control and the inverter control ofFIG. 6. Hereunder, the control operation of thecontroller13 will be described following the steps specified inFIG. 7, while referring also toFIG. 1.
(Step S21)
• Thecontroller13 activates the compressor5, and then proceeds to step S22.
(Step S22)
• Thecontroller13 receives the ON signal for the compressor5, and causes the compressor5 to perform the maximum frequency operation (starts the local thermostat control). Then thecontroller13 proceeds to step S23.
(Step S23)
• Thecontroller13 decides whether the indoor temperature has reached the target temperature A1. In the case where the indoor temperature has reached the target temperature A1, thecontroller13 proceeds to step S24. Otherwise, thecontroller13 proceeds to step S23.
(Step S24)
• Thecontroller13 receives the OFF signal for the compressor5, and causes the compressor5 to perform the minimum frequency operation (starts the inverter control). Then thecontroller13 proceeds to step S25.
(Step S25)
• Thecontroller13 decides whether the indoor temperature is within the range defined by the permissible temperature difference Au from the target temperature A1. When the indoor temperature is within the range defined by the permissible temperature difference Δα from the target temperature A1, the controller proceeds to step S28. Otherwise, thecontroller13 proceeds to step S26.
(Step S26)
• Thecontroller13 turns off the compressor5, and proceeds to step S27.
(Step S27)
• Thecontroller13 decides whether the indoor temperature has reached A2. In the case where the indoor temperature has reached A2, the controller proceeds to step S22. Otherwise, thecontroller13 proceeds to step S27.
(Step S28)
• Thecontroller13 decides whether the time during which theinverter16 has been in operation has exceeded the predetermined operation time ΔT. In the case where the time during which theinverter16 has been in operation has exceeded the predetermined operation time ΔT, the controller proceeds to step S26. Otherwise, thecontroller13 proceeds to step S29.
(Step S29)
• Thecontroller13 decides whether thelocal thermostat20 has transmitted the ON signal to thecontroller13. In the case where thelocal thermostat20 has transmitted the ON signal to thecontroller13, thecontroller13 proceeds to step S22. Otherwise, thecontroller13 proceeds to step S25.
• As described above, the air-conditioning system100 assumes that the temperature information acquired from theindoor temperature sensor14 is the target temperature A1, and shifts to the inverter control from the local thermostat control. Such an arrangement prevents the compressor5 from being frequently turned on and off, thereby suppressing the power consumption and enabling the indoor temperature to be maintained at a constant level, thus to maintain the comfort in the room.
• In addition, setting the foregoing three conditions for shifting from the inverter control to the local thermostat control provides the following three advantageous effects. First, even when the indoor temperature deviates from the range defined by the permissible temperature difference4afrom the target temperature A1, the indoor temperature can be promptly brought back to the target temperature A1 by shifting to the local thermostat control from the inverter control. Second, even when the target temperature A1 is changed through thelocal thermostat20 during the inverter control, the operation is shifted to the local thermostat control after the predetermined operation time ΔT has elapsed, and therefore the air-conditioning system100 can be operated on the basis of the modified target temperature A1. Third, in the case where thecontroller13 receives the ON signal for the compressor5 during the inverter control, it can be assumed that the target temperature A1 has been modified, or the indoor temperature has exceeded the range defined by the permissible temperature difference4afrom the target temperature A1. Therefore, the operation can be shifted to the local thermostat control, so as to bring the indoor temperature close to the target temperature A1.
• Although the local thermostat control and the inverter control of the air-conditioning system100 in the cooling operation mode has been described inEmbodiment 1, the present invention is not limited to such operation, and the similar control can be performed also in the heating operation mode. In addition, although the air-conditioning system100 according toEmbodiment 1 is configured to perform both the cooling operation and the heating operation, the air-conditioning system100 may be configured to perform only either of the cooling operation and the heating operation. The above also applies toEmbodiment 2 described hereunder.
Embodiment 2
• The air-conditioning system100 according toEmbodiment 2 is configured basically in the same way as the air-conditioning system100 ofEmbodiment 1, and thereforeEmbodiment 2 will be described primarily focusing on the difference fromEmbodiment 1. The difference ofEmbodiment 2 fromEmbodiment 1 is that the former is configured to vary the predetermined operation time ΔT during which the inverter control is performed.
• FIG. 8 is a graph showing a relationship between the difference between the outdoor temperature and the indoor temperature and the predetermined operation time according toEmbodiment 2 of the present invention. The air-conditioning system100 is configured to perform the cooling operation mode and the heating operation mode, out of which the setting of the predetermined operation time ΔT in the air-conditioning system100 in the cooling operation mode will be described as an example.
• Referring toFIG. 8, the vertical axis of the graph represents the predetermined operation time ΔT, and the horizontal axis represents the difference between the outdoor temperature and the indoor temperature. When the difference between the outdoor temperature detected by theoutdoor temperature sensor15 and the indoor temperature detected by theindoor temperature sensor14 is C0, the predetermined operation time ΔT is set to B1. In contrast, when the difference between the outdoor temperature detected by theoutdoor temperature sensor15 and the indoor temperature detected by theindoor temperature sensor14 is C1, the predetermined operation time ΔT is set to B2. Thus, thecontroller13 prolongs the predetermined operation time ΔT as the difference between the outdoor temperature and the indoor temperature increases. It is desirable, however, to specify an upper limit B2 of the predetermined operation time, so as to allow the operation to be shifted to the local thermostat control when the target temperature A1 is modified through thelocal thermostat20.
• The predetermined operation time ΔT during which the inverter control is performed is prolonged along with the increase of the difference between the outdoor temperature and the indoor temperature is set accordingly, thereby the impact of the outdoor temperature on the indoor temperature is minimized.

Claims (5)

1. An air-conditioning system comprising:

a refrigerant circuit in which a compressor, a heat source-side heat exchanger, an expansion device, and a load-side heat exchanger are sequentially connected by piping;

an inverter configured to drive the compressor;

an indoor temperature sensor configured to detect an indoor temperature;

a controller configured to regulate an output frequency of the inverter to control the compressor in accordance with the indoor temperature detected by the indoor temperature sensor, and

a local thermostat configured to compare a temperature detected by the thermostat with a target temperature, and transmits a thermostat ON signal and a thermostat OFF signal to the controller,

wherein, during a first time point, the controller is configured to assume, upon receipt of the thermostat OFF signal from the local thermostat, that an indoor temperature detected by the indoor temperature sensor at a first time point when the thermostat OFF signal is received is the target temperature, and regulates the output frequency of the inverter so as to maintain a difference between the indoor temperature and the target temperature in a predetermined range, during the point between the first time point and a second time point, wherein the second time point is later than the first time point.

2. The air-conditioning system ofclaim 1,

wherein the controller is configured to finish controlling the inverter regulated at the output frequency when the indoor temperature exceeds a permissible temperature difference from the target temperature, and turn off the compressor or cause the compressor to perform at a maximum frequency.

3. The air-conditioning system ofclaim 1,

wherein the controller is configured to finish controlling the inverter regulated at the output frequency when the thermostat ON signal is input, and turn off the compressor or cause the compressor to perform at a maximum frequency.

4. The air-conditioning system ofclaim 1,

wherein the controller is configured to finish controlling the inverter regulated at the output frequency when a time during which the inverter is controlled at the output frequency exceeds a predetermined operation time, and turn off the compressor or cause the compressor to perform at a maximum frequency.

5. The air-conditioning system ofclaim 4, further comprising an outdoor temperature sensor that detects an outdoor temperature and transmits the outdoor temperature to the controller,

wherein the controller is configured to determine duration of the predetermined operation time depending on a difference between the indoor temperature and the outdoor temperature.

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