Air conditioner and control method

Abstract

This air conditioner 100 includes an outdoor unit 20 and a plurality of indoor units 10a to 10c. The air conditioner 100 is configured to transition to a thermo OFF state in response to the corresponding room temperature reaching a first temperature during a thermo ON state for each indoor unit 10a to 10c, and to transition to the thermo ON state in response to the corresponding room temperature reaching a second temperature that is higher or lower than the first temperature during the thermo OFF state. The air conditioner 100 comprises a control unit 26 for performing a control so that an indoor unit having the corresponding room temperature between the first temperature and the second temperature among the plurality of indoor units 10a to 10c is transitioned to the thermo ON state in response to an index value related to the current capability provided by the plurality of indoor units 10a to 10c having satisfied a condition.

Description

Air conditioner and control method

[0001] The present invention relates to an air conditioner and a method for controlling an air conditioner.

[0002] Conventionally, air conditioners equipped with a thermostat-off function are known that prevent further changes in temperature, etc., when the indoor temperature reaches a set value. In air conditioners equipped with a thermostat-off function, when the indoor air conditioning load is low, the indoor unit maintains the room temperature near the set temperature by repeatedly turning the thermostat on and off to prevent the room temperature from deviating too far from the set temperature. In this case, if all connected indoor units turn the thermostat off, the outdoor unit stops its compressor. Therefore, when the air conditioning load is low, the outdoor unit operates its compressor intermittently. However, to improve compressor reliability, it is desirable to avoid intermittent operation as much as possible and maintain continuous compressor operation.

[0003] The present disclosure has been made in consideration of the above points, and aims to provide an air conditioner and a control method for an air conditioner that makes it possible to avoid intermittent operation of a compressor in an air conditioner that includes multiple indoor units, and ultimately improves the reliability of the compressor.

[0004] In view of the above, the present disclosure provides an air conditioner including an outdoor unit and multiple indoor units and having the following characteristics. The air conditioner is configured to transition each indoor unit to a thermo-off state in response to the corresponding room temperature reaching a first temperature while in a thermo-on state, and to transition each indoor unit to a thermo-on state in response to the corresponding room temperature reaching a second temperature that is higher or lower than the first temperature while in the thermo-off state. The air conditioner includes a control unit that controls an indoor unit among the multiple indoor units whose corresponding room temperature is between the first temperature and the second temperature to transition to the thermo-on state in response to an index value related to the current capacity provided by the multiple indoor units satisfying a condition.

[0005] Other problems and solutions disclosed in the present application will be made clear in the detailed description and drawings.

[0006] With the above configuration, in an air conditioner including a plurality of indoor units, it is possible to avoid intermittent operation of the compressor, and ultimately to improve the reliability of the compressor.

[0007] FIG. 1 is a diagram illustrating an example of the configuration of an air conditioner according to an embodiment of the present invention. FIG. 2 is a diagram explaining thermo-on / thermo-off switching control performed by an air conditioner according to an embodiment of the present invention. FIG. 3 is a flowchart illustrating thermo-on / thermo-off switching control during cooling operation performed by an air conditioner according to an embodiment of the present invention. FIG. 4 is a flowchart illustrating thermo-on / thermo-off switching control during heating operation performed by an air conditioner according to an embodiment of the present invention. FIG. 5 is a graph showing (A) the change in room temperature over time, (B) the thermo-on / off state of the indoor unit, and (C) the change in compressor frequency over time as a result of simulating thermo-on / thermo-off switching control during heating performed by an air conditioner of the prior art. FIG. 6 is a graph showing (A) the change in room temperature over time, (B) the thermo-on / off state of the indoor unit, and (C) the change in compressor frequency over time as a result of simulating thermo-on / thermo-off switching control during heating performed by an air conditioner according to an embodiment of the present invention.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the embodiments of the present invention are not limited to the specific embodiments described below. In the drawings, the same reference numerals indicate the same or corresponding parts.

[0009] The present disclosure is directed to an air conditioner and a control method for the air conditioner. An air conditioner according to an embodiment of the present invention includes an outdoor unit and multiple indoor units. The air conditioner is configured to transition each indoor unit to a thermo-off state in response to the corresponding room temperature reaching a first temperature (lower or higher than a set temperature) while in a thermo-on state, and to transition each indoor unit to a thermo-on state in response to the corresponding room temperature reaching a second temperature (higher or lower than the first temperature and the set temperature) while in the thermo-off state. The air conditioner includes a control unit that controls an indoor unit among the multiple indoor units whose corresponding room temperature is between the first temperature and the second temperature to transition to the thermo-on state in response to an index value related to the current capacity provided by the multiple indoor units satisfying a condition.

[0010] As a result, when the number of indoor units in the thermo-on state decreases, indoor units in the thermo-off state that do not meet the thermo-off conditions (i.e., indoor units that have not reached the first temperature and will not immediately switch to thermo-off even if they switch to the thermo-on state) can be switched to the thermo-on state, allowing the compressor to operate continuously. This reduces the frequency of compressor shutdowns, improving the reliability of the air conditioner. Additionally, this avoids high-speed operation at startup to ensure reliability and pump-down operation before shutting down the compressor, improving energy conservation.

[0011] In a preferred embodiment, the index value related to the current capacity may be the number of indoor units in the thermo-on state among the multiple indoor units, the ratio of the sum of the rated capacities of one or more indoor units in the thermo-on state among the multiple indoor units to the rated capacity of the outdoor unit, or the compressor operating frequency of the outdoor unit according to the operating state of one or more indoor units in the thermo-on state among the multiple indoor units. By using such index values, it is possible to easily evaluate the current capacity provided by the multiple indoor units and to detect a state in which the frequency of compressor stoppages can be reduced by transitioning to the thermo-on state under relaxed conditions.

[0012] In a specific embodiment, when the air conditioner operates in cooling mode, the first temperature is a temperature lower than the set temperature, and the second temperature is a temperature higher than the first temperature. In this specific embodiment, the control unit can preferably select, from among the multiple indoor units, an indoor unit whose corresponding room temperature is between the first temperature and the second temperature, an indoor unit whose corresponding room temperature is equal to or higher than a third temperature that is higher than the first temperature and lower than the second temperature.

[0013] In a specific embodiment, when the air conditioner operates in heating mode, the first temperature is a temperature higher than the set temperature, and the second temperature is a temperature lower than the first temperature. In this specific embodiment, the control unit can preferably select, from among the multiple indoor units, an indoor unit whose corresponding room temperature is between the first and second temperatures, an indoor unit whose corresponding room temperature is less than a third temperature that is greater than the second temperature and less than the first temperature, and greater than or equal to the second temperature.

[0014] In a specific embodiment, the outdoor unit is configured to start operation of the compressor when at least one of the multiple indoor units changes from a state in which all of the multiple indoor units are in thermo-off to a state in which the thermo is on, and to stop operation of the compressor when at least one of the multiple indoor units changes from a state in which the thermo is on to a state in which all of the multiple indoor units are in thermo-off.

[0015] A method for controlling the above-described air conditioner according to an embodiment of the present invention is also provided.

[0016] Hereinafter, with reference to FIGS. 1 to 6, an air conditioner 100 including a plurality of indoor units 10 and outdoor units 20 will be described as an example of an air conditioner and a control method thereof according to an embodiment of the present invention.

[0017] 1 is a diagram showing an example of the configuration of an air conditioner 100 according to an embodiment of the present invention. The air conditioner 100 is configured to include a plurality of indoor units 10, each installed indoors in a house, building, etc., and an outdoor unit 20 installed outdoors. The air conditioner 100 may include an operating device (remote controller) installed in the room where the indoor units 10 are installed, which communicates wirelessly with the indoor units 10 and operates the indoor units 10.

[0018] Although FIG. 1 shows three indoor units 10a to 10c as the multiple indoor units 10, the number of indoor units 10 is not particularly limited and may be two, four or more. The multiple indoor units 10 may be installed in the same room, or all of the multiple indoor units 10 may be installed in different rooms, or one or more of the multiple indoor units 10 may be arranged in any combination in each of the multiple rooms. Hereinafter, when referring to a specific indoor unit, it will be referred to as "indoor unit 10a," for example, and when referring to any indoor unit or all indoor units collectively, it will be referred to as "indoor unit 10." The same applies to the internal configuration of the indoor units.

[0019] Each indoor unit 10 and outdoor unit 20 are connected by two pipes 30, 31 through which a refrigerant circulates as a heat medium. For example, a hydrofluorocarbon such as R410a or R32 is used as the refrigerant. The indoor unit 10 and outdoor unit 20 are connected by a communication line to communicate with each other. The indoor unit 10 and outdoor unit 20 are not limited to being connected by a wired communication line, but may also be connected wirelessly.

[0020] During operation, the indoor unit 10 takes in indoor air, exchanges heat between the taken-in air and a refrigerant supplied from the outdoor unit 20, and blows out cooled or heated air to cool or heat the room to a set temperature. To this end, the indoor unit 10 is equipped with a heat exchanger 11 that exchanges heat between the indoor air and the refrigerant, and a blower (fan) 12 that takes in indoor air into the heat exchanger 11 and blows out the air that has undergone heat exchange by the heat exchanger 11.

[0021] The indoor unit 10 includes a room temperature sensor 13 that detects the indoor temperature and notifies the outdoor unit 20 of the indoor temperature. The indoor unit 10 also includes an indoor expansion valve 14 that expands the refrigerant and adjusts the flow rate of the refrigerant flowing through the heat exchanger 11.

[0022] When the indoor unit 10 is used for cooling, the heat exchanger 11 functions as an evaporator, and the refrigerant flows into the heat exchanger 11 in a two-phase flow state (liquid refrigerant) where liquid and gas are mixed. The refrigerant exchanges heat with air taken in by the fan 12 in the heat exchanger 11, causing the liquid component to evaporate, and the refrigerant is discharged from the heat exchanger 11 as gas refrigerant and sent to the outdoor unit 20. The liquid component evaporates at a certain temperature (saturation temperature) corresponding to the pressure inside the heat exchanger 11, and is discharged from the heat exchanger 11 at the saturation temperature or a temperature higher than the saturation temperature.

[0023] The outdoor unit 20 starts up in response to a command from the control device and begins operation in an operation mode set by a remote control or the like. The operation modes include cooling mode, heating mode, and fan mode. The outdoor unit 20 controls the temperature, pressure, flow rate, and the like of the refrigerant according to the set temperature, indoor temperature, pipe temperature, and the like. The outdoor unit 20 also stops operation in response to a command from the control device. Note that, although a single outdoor unit 20 is typically assumed, this does not preclude a configuration in which multiple outdoor units are installed. For example, when multiple outdoor units are connected in parallel to a single refrigerant system, the present control may be applied within that refrigerant system. Alternatively, when there are multiple refrigerant systems, the present control may be applied to each of the refrigerant systems.

[0024] The outdoor unit 20 is connected to a plurality of indoor units 10 (10a to 10c in FIG. 1) via pipes 30 and 31, and circulates a refrigerant. To this end, it is equipped with a compressor 21 that circulates the refrigerant. The refrigerant gas compressed by the compressor 21 exchanges heat with air taken in by a fan 23 in a heat exchanger 22, and becomes a high-pressure liquid refrigerant. The outdoor unit 20 also has a four-way valve 25 that reverses the direction of refrigerant flow to enable heating operation. An outdoor expansion valve 24 is provided to convert the high-pressure refrigerant during heating into a low-temperature, low-pressure refrigerant and to adjust the flow rate of the refrigerant.

[0025] The flow rate of the refrigerant can be changed by changing the operating frequency of the compressor 21. Increasing the operating frequency of the compressor 21 increases the amount of refrigerant supplied, thereby increasing the air conditioning capacity. Conversely, decreasing the operating frequency of the compressor 21 decreases the amount of refrigerant supplied, thereby decreasing the air conditioning capacity.

[0026] The outdoor unit 20 is equipped with a control device 26. The control device 26 controls the operating frequency of the compressor 21 and the opening degree of the outdoor expansion valve 24 based on the indoor temperatures detected by the room temperature sensors 13a to 13c of the multiple indoor units 10a to 10c, the set temperature, the pipe temperature, and the operating mode. The control device 26 also switches the four-way valve 25 according to the set operating mode.

[0027] When the indoor air conditioning load is low, the indoor unit 10 repeatedly switches between thermo-on and thermo-off to maintain the indoor temperature within a predetermined range centered on the set temperature, in order to prevent the room temperature from deviating too far from the set temperature. More specifically, the air conditioner 100 is configured so that the control unit controls each of the multiple indoor units 10a to 10c to transition between the thermo-on state and the thermo-off state so that the indoor temperature is maintained between the two temperatures.

[0028] Here, a specific indoor unit 10 being in the thermo-off state refers to a state in which the supply of refrigerant to the specific indoor unit 10 is stopped or reduced to a low level by controlling the opening / closing and opening degree of the indoor expansion valve 14 of the specific indoor unit 10, and does not necessarily refer to a state in which the compressor 21 is stopped. On the other hand, if all connected indoor units 10a to 10c transition to the thermo-off state, the outdoor unit 20 stops the compressor 21 because it cannot operate at or below the minimum operating frequency. For this reason, when the air conditioning load is small, all connected indoor units 10a to 10c are likely to enter the thermo-off state, and the outdoor unit 20 will operate the compressor 21 intermittently. However, to improve the reliability of the compressor 21, it is desirable to operate the compressor 21 continuously.

[0029] Therefore, in the air conditioner 100 according to an embodiment of the present invention, the control unit is further configured to monitor index values ​​relating to the current capacity provided by the plurality of indoor units 10a to 10c, and in response to the index values ​​satisfying the conditions, perform control to transition an indoor unit 10 among the plurality of indoor units 10a to 10c that satisfies a predetermined temperature condition (an indoor unit 10 that does not satisfy the thermo-off condition but is still in the thermo-off state) to the thermo-on state.

[0030] As a result, when the number of indoor units 10 in the thermo-on state decreases, indoor units 10 that do not meet the conditions for thermo-on under normal control but meet the specified temperature conditions are switched to the thermo-on state, making it possible to operate multiple indoor units 10 as much as possible while maintaining the room temperature within a specified temperature range, and to maintain continuous operation of the compressor 21 as much as possible. Since the frequency of compressor 21 shutdowns can be reduced, the reliability of the air conditioner 100 can be improved. In addition, high rotation speed operation at startup to ensure reliability and pump-down operation before compressor shutdown can be avoided, thereby improving energy conservation. Details of this will be described below.

[0031] FIG. 2 is a diagram illustrating thermo-on / thermo-off switching control executed by the air conditioner 100 according to the embodiment of the present invention.

[0032] FIG. 2(A) illustrates the operation of the air conditioner 100 during cooling operation. Hereinafter, with reference to FIG. 2(A), the operation of thermo-on / thermo-off switching control during cooling operation will be described. As shown in FIG. 2(A), in cooling operation, a first temperature and a second temperature are set around the set temperature for thermo-on / thermo-off switching control. The first temperature is a temperature lower than the set temperature, and the second temperature is a temperature higher than the set temperature. The air conditioner 100 according to an embodiment of the present invention is configured to transition each indoor unit 10 to the thermo-off state in response to the corresponding room temperature reaching the first temperature while in the thermo-on state, and to transition to the thermo-on state in response to the corresponding room temperature reaching the second temperature while in the thermo-off state. Here, the set temperature, the first temperature, and the second temperature may be set commonly to all indoor units 10, individually to each indoor unit 10, or for each group consisting of one or more indoor units 10.

[0033] The following description will be given assuming that the cooling operation is started when the room temperature is higher than the set temperature. For simplicity, the description will focus on one indoor unit 10. In this case, the indoor unit 10 starts with the thermostat on, and the room is cooled, gradually decreasing in temperature. Even after reaching the set temperature, the room temperature continues to decrease, and when the first temperature is reached or exceeded, the thermostat is switched to off. The room temperature then gradually increases due to the temperature difference with the outside air and the heat source within the room. Even after exceeding the set temperature, the room temperature continues to increase. However, when the second temperature is reached or exceeded, the thermostat is switched to on, and the room is cooled again. Thereafter, the same operation is repeated.

[0034] In the described embodiment, the air conditioner 100 further controls the indoor units 10a-10c whose corresponding room temperatures are between a first temperature and a second temperature, as indicated by the thick dotted arrow in FIG. 2A, to transition to the thermo-on state in response to the index values ​​related to the current capacity provided by the indoor units 10a-10c satisfying the condition. In a more preferred embodiment, a third temperature greater than the first temperature and less than the second temperature is set, and the indoor units 10 whose corresponding room temperatures are greater than or equal to the third temperature and less than the second temperature, as indicated by the thick solid arrow in FIG. 2A, can be selected as the indoor units 10 to transition to the thermo-on state. In a preferred embodiment in which an indoor unit 10 whose corresponding room temperature is greater than or equal to the third temperature and less than the second temperature is selected, the indoor unit 10 is less likely to transition to the thermo-off state after transitioning to the thermo-on state, thereby reducing the likelihood of frequent thermo-on / thermo-off switching. The third temperature can also be set for all indoor units, for each indoor unit, or for each group of indoor units.

[0035] FIG. 2(B) illustrates the operation of the air conditioner 100 during heating operation. Hereinafter, the operation of thermo-on / thermo-off switching control during heating operation will be described with reference to FIG. 2(B). As shown in FIG. 2(B), in the case of heating operation, a fourth temperature and a fifth temperature are set around the set temperature for thermo-on / thermo-off switching control. The fourth temperature is a temperature lower than the set temperature, and the fifth temperature is a temperature higher than the set temperature. The air conditioner according to an embodiment of the present invention is configured to transition each indoor unit to the thermo-off state in response to the corresponding room temperature reaching the fifth temperature while in the thermo-on state, and to transition to the thermo-on state in response to the corresponding room temperature reaching the fourth temperature while in the thermo-off state.

[0036] The following description will be given assuming that the heating operation is started when the room temperature is lower than the set temperature. For simplicity, the description will focus on one indoor unit 10. In this case, the indoor unit 10 starts with the thermostat on, and the room is heated, causing the room temperature to rise. After reaching the set temperature, the room temperature continues to rise, and when it reaches or exceeds a fifth temperature, the thermostat is switched to off. The room temperature then begins to gradually drop due to the temperature difference with the outside air. Even after it falls below the set temperature, the room temperature continues to drop, and when it reaches or exceeds a fourth temperature, the thermostat is switched to on, causing the room to be heated again. Thereafter, the same operation is repeated.

[0037] In the described embodiment, in response to the current capacity index values ​​provided by the indoor units 10a-10c satisfying a condition, the air conditioner 100 controls the indoor units 10a-10c whose corresponding room temperatures are between the fourth and fifth temperatures, as indicated by the thick dotted arrows in FIG. 2B, to transition to the thermo-on state. In a more preferred embodiment, a sixth temperature is set, which is greater than the fourth temperature but less than the fifth temperature. The indoor units 10 to transition to the thermo-on state can be selected whose corresponding room temperatures are less than the sixth temperature but greater than or equal to the fourth temperature, as indicated by the thick solid arrows in FIG. 2B. In a preferred embodiment in which an indoor unit 10 less than the sixth temperature but greater than or equal to the fourth temperature is selected, the indoor unit 10 is less likely to transition to the thermo-off state after transitioning to the thermo-on state, thereby reducing the likelihood of frequent thermo-on / thermo-off switching. The set temperature, fourth temperature, fifth temperature, and sixth temperature can be set for all indoor units, for each indoor unit, or for each group of indoor units.

[0038] Here, the index value for which the condition is set and monitored is, as described above, an index value related to the current capacity provided by the multiple indoor units 10a-10c. More specifically, the index value may be the number of indoor units among the multiple indoor units 10a-10c that are in the thermo-on state. In this case, the condition is determined to be met when the number of indoor units in the thermo-on state is equal to or less than a predetermined threshold number. The index value may alternatively be the ratio of the sum of the rated capacities of one or more indoor units among the multiple indoor units that are in the thermo-on state to the outdoor unit rated capacity. In this case, the condition is determined to be met when the ratio of the sum of the rated capacities of one or more indoor units in the thermo-on state to the outdoor unit rated capacity is equal to or less than a predetermined threshold. The index value may also be the compressor operating frequency of the outdoor unit 20, which reflects the operating status of one or more indoor units among the multiple indoor units 10a-10c that are in the thermo-on state. In this case, if the compressor operating frequency is equal to or lower than a predetermined frequency, it is determined that the condition is met.

[0039] Hereinafter, the thermo-on / thermo-off switching control during cooling operation and heating operation performed by the air conditioner 100 according to the embodiment of the present invention will be described in more detail with reference to FIGS. 3 and 4. FIG.

[0040] Fig. 3 is a flowchart showing the thermo-on / thermo-off switching control during cooling operation. The control shown in Fig. 3 starts from step S100 in response to a transition to cooling operation. Note that the control shown in Fig. 3 is described as being executed by the control device 26 of the outdoor unit 20, but the control device included in one of the indoor units 10 may execute this processing, or a control device provided separately from the indoor unit 10 and the outdoor unit 20 may execute this processing.

[0041] Steps S101 to S106 are repeated for each of the multiple indoor units 10a to 10c. In step S102, the control device 26 determines whether the indoor unit 10 being judged is in the thermo-off state and the corresponding room temperature is equal to or higher than a second temperature. If it is determined in step S102 that the indoor unit 10 is in the thermo-off state and the corresponding room temperature is equal to or higher than the second temperature (YES), control proceeds to step S103. In step S103, the control device 26 transitions the indoor unit 10 being judged to the thermo-on state, and control proceeds to step S104. On the other hand, if the indoor unit 10 is already in the thermo-on state or the corresponding room temperature is less than the second temperature (NO) in step S102, control proceeds directly to step S104.

[0042] In step S104, the control device 26 determines whether the indoor unit 10 being judged is in the thermo-on state and the corresponding room temperature is equal to or lower than the first temperature. If it is determined in step S104 that the indoor unit 10 is in the thermo-on state and the corresponding room temperature is equal to or lower than the first temperature (YES), control proceeds to step S105, where the control device 26 transitions the indoor unit 10 to the thermo-off state, and control proceeds to step S106. On the other hand, if the indoor unit 10 is already in the thermo-off state or the corresponding room temperature exceeds the first temperature (NO) in step S104, control proceeds to step S106.

[0043] After the processing of steps S101 to S106 is repeated for each of the indoor units 10a to 10c, the control proceeds to step S107.

[0044] In step S107, the control device 26 determines whether the current index value is less than a threshold value. As described above, the index value may be the number of indoor units in the thermo-on state among the multiple indoor units 10a-10c, the ratio of the sum of the rated capacities of one or more indoor units in the thermo-on state among the multiple indoor units to the outdoor unit rated capacity, the compressor operating frequency of the outdoor unit 20, or a combination of these. If it is determined in step S107 that the current index value is not less than the threshold value (NO), control returns to step S101. On the other hand, if it is determined that the current index value is less than the threshold value (YES), control proceeds to step S108. Here, if the index value is less than the threshold value, it is determined that the condition is satisfied.

[0045] In step S108, the control device 26 further determines whether there is an indoor unit 10 that satisfies the predetermined conditions indicated by the thick dotted or solid arrows in FIG. 2A. If it is determined in step S108 that there is an indoor unit 10 that satisfies the conditions (YES), control proceeds to step S109. In step S109, the indoor unit 10 that satisfies the conditions is transitioned to the thermo-on state, and control returns to step S101. Note that if there are multiple indoor units 10 that satisfy the conditions, one of them may be selected and transitioned to the thermo-on state, or, depending on the system size, a predetermined number (two or more) of the multiple indoor units 10 that satisfy the conditions may be selected and transitioned to the thermo-on state. Furthermore, when selecting indoor units 10 that satisfy the conditions, priority may be given to selecting indoor units 10 whose indoor temperatures are closest to the second temperature (those that are closest to the thermo-on temperature conditions). Thereafter, control is repeated until the cooling operation is terminated. Note that a predetermined time may be waited before returning to step S101 shown in FIG. 3.

[0046] 4 is a flowchart showing the thermo-on / thermo-off switching control during heating operation. The control shown in FIG. 4 starts from step S200 in response to transition to heating operation. Note that the control shown in FIG. 4 will also be described as being executed by the control device 26 of the outdoor unit 20.

[0047] Steps S201 to S206 are repeated for each of the multiple indoor units 10a to 10c. In step S202, the control device 26 determines whether the indoor unit 10 being judged is in the thermo-off state and the corresponding room temperature is equal to or lower than a fourth temperature. If it is determined in step S202 that the indoor unit 10 is in the thermo-off state and the corresponding room temperature is equal to or lower than the fourth temperature (YES), control proceeds to step S203, where the control device 26 transitions the indoor unit 10 being judged to the thermo-on state, and control proceeds to step S204. On the other hand, if the indoor unit 10 is already in the thermo-on state or the corresponding room temperature exceeds the fourth temperature (NO) in step S202, control proceeds directly to step S204.

[0048] In step S204, the control device 26 determines whether the indoor unit 10 being judged is in the thermo-on state and the corresponding room temperature is equal to or higher than the fifth temperature. If it is determined in step S204 that the indoor unit 10 is in the thermo-on state and the corresponding room temperature is equal to or higher than the fifth temperature (YES), control proceeds to step S205. In step S205, the control device 26 transitions the indoor unit 10 to the thermo-off state, and control proceeds to step S206. On the other hand, if the indoor unit 10 is already in the thermo-off state or the corresponding room temperature is less than the fifth temperature (NO) in step S204, control proceeds to step S206.

[0049] After the processing of steps S201 to S206 is repeated for each of the indoor units 10a to 10c, control proceeds to step S207.

[0050] In step S207, the control device 26 determines whether the current index value is less than the threshold value. The index value is the same as in the case of cooling. If it is determined in step S207 that the current index value is not less than the threshold value (NO), control returns to step S201. On the other hand, if it is determined that the current index value is less than the threshold value (YES), control proceeds to step S208.

[0051] In step S208, the control device 26 further determines whether there is an indoor unit 10 that satisfies the predetermined conditions indicated by the thick dotted or solid arrows in FIG. 2(B). If it is determined in step S208 that there is an indoor unit 10 that satisfies the conditions (YES), control proceeds to step S209. In step S209, the indoor units 10 that satisfy the conditions are switched to the thermo-on state, and control returns to step S201. Note that the number of indoor units 10 that are switched to the thermo-on state at one time and the method for selecting the indoor units 10 that are switched to the thermo-on state when multiple conditions are satisfied are the same as in the case of cooling. Thereafter, control is repeated until cooling operation is completed.

[0052] In the above description, it has been described that the first and second temperatures are set around the set temperature in cooling operation, or that the fourth and fifth temperatures are set around the set temperature in heating operation. However, this is not limited to the above configuration. In other embodiments, for example, in cooling operation, when comfort is emphasized, the first and second temperatures can both be set lower than the set temperature. In heating operation, as in cooling operation, the fourth and fifth temperatures can both be set higher than the set temperature. In still other embodiments, for example, in cooling operation, when energy conservation is emphasized, the first and second temperatures can both be set higher than the set temperature. In heating operation, as in cooling operation, the fourth and fifth temperatures can both be set lower than the set temperature.

[0053] 5 and 6 show simulated results of thermo-on / thermo-off switching control during heating in a conventional air conditioner and an air conditioner 100 according to an embodiment of the present invention. FIGS. 5(A) and 6(A) show the change in room temperature over time in a conventional air conditioner and an air conditioner 100 according to an embodiment of the present invention. The horizontal axis represents time [minutes], and the vertical axis represents temperature (°C) (specific values ​​are omitted). The thermo-on and thermo-off thresholds are indicated on the graphs. FIGS. 5(B) and 6(B) show the change in the thermo-on / thermo-off status of the indoor units over time in a conventional air conditioner and an air conditioner 100 according to an embodiment of the present invention. The horizontal axis represents time [minutes], and the vertical axis is shifted for each indoor unit. For each indoor unit, HIGH represents the thermo-on state, and LOW represents the thermo-off state. FIGS. 5(C) and 6(C) are graphs showing the change in compressor frequency over time in a conventional air conditioner and an air conditioner 100 according to an embodiment of the present invention. The horizontal axis represents time [minutes], and the vertical axis represents the compressor operating frequency [Hz] (specific numerical values ​​are omitted).

[0054] 5 and 6 show the results of a dynamic simulation of a system connected to five indoor units 10. The conventional air conditioner and the air conditioner 100 according to the embodiment of the present invention share the same thermo-on / thermo-off room temperature-based control. That is, the outdoor unit 20 starts operating its compressor when one or more indoor units 10 are thermo-on after all indoor units 10 are thermo-off. The operating compressor 21 determines the required refrigerant supply amount and compressor frequency based on the indoor unit 10 room temperature, set temperature, indoor fan airflow setting, and outdoor temperature using the outdoor unit control device 26, and operates at the determined operating frequency. When all indoor units 10 are thermo-off, the outdoor unit 20 stops operating its compressor 21. The fourth and fifth temperatures are common to the conventional air conditioner and the air conditioner 100 according to the embodiment of the present invention, and the same values ​​are used in all indoor units.

[0055] In the air conditioner 100 according to the embodiment of the present invention shown in Figure 6, in addition to the above-mentioned thermo-on / thermo-off control based on room temperature, the number of indoor units that are in the thermo-on state among multiple indoor units is set as an index value, and thermo-on control is performed based on this index value. Note that the condition for the threshold number of units is two or less (less than three), and indoor units that meet the condition are switched to thermo-on one by one.

[0056] As shown in Fig. 5(B), in conventional control, at time t = 50, only the indoor unit (1) is thermo-on, but the indoor unit (1) is immediately thermo-off due to excess capacity, so all indoor units 10 are in the thermo-off state and the compressors 21 are stopped as shown in Fig. 5(C). In contrast, in the control according to the embodiment of the present invention, as shown in Fig. 6(B), after time t = 50, the indoor unit (5) that is thermo-off is thermo-on, thereby avoiding excessive supply of refrigerant, and it is possible to prevent the compressors 21 from stopping as shown in Fig. 6(C).

[0057] Furthermore, from time t=100 onwards, in addition to the indoor units (2) and (3) continuing to be thermo-on, the indoor unit (5) thermo-on responds to the indoor unit (1) thermo-off, which reduces the number of operating units, or conversely, the indoor unit (1) thermo-on responds to the indoor unit (5) thermo-off, which reduces the number of operating units, thereby avoiding an excessive supply of refrigerant and preventing the compressor 21 from stopping. As a result, during the 280-minute period of the simulation shown in Figures 5 and 6, the number of times the compressor stopped was six under control using the conventional technology, but was reduced to two under control according to the embodiment of the present invention.

[0058] As explained above, according to the above-described embodiment, it is possible to provide an air conditioner and a control method thereof that can avoid intermittent operation of the compressor in an air conditioner configured to include multiple indoor units, and thereby improve the reliability of the compressor.

[0059] It should be noted that the embodiments of the present invention are not limited to the above-described embodiments and may include various modifications. For example, the above-described embodiments have been described in detail for ease of understanding, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0060] Furthermore, some or all of the above-described configurations, functions, processing units, processing means, etc. may be realized in hardware, for example, by designing them as integrated circuits. Furthermore, some or all of the above-described configurations, functions, etc. may be realized by computer-executable programs written in legacy programming languages ​​such as assembler, C, C++, C#, Java (registered trademark), or object-oriented programming languages, in which a processor realizes each function. Information such as programs, tables, and files that realize each function may be stored on device-readable recording media such as storage devices such as HDDs (Hard Disk Drives), SSDs (Solid State Drives), ROMs, EEPROMs, EPROMs, and flash memories, flexible disks, CD-ROMs, CD-RWs, DVD-ROMs, DVD-RAMs, DVD-RWs, Blu-ray Discs, SD (registered trademark) cards, and MOs, or distributed via telecommunications lines.

[0061] Furthermore, some or all of the above configurations, functions, etc. can be implemented on a programmable device (PD) such as a field programmable gate array (FPGA), and the circuit configuration data (bitstream data) downloaded to the PD to realize the above functional units on the PD, or data written in HDL (Hardware Description Language), VHDL (Very High Speed ​​Integrated Circuits Hardware Description Language), Verilog-HDL, or the like for generating the circuit configuration data can be distributed on a recording medium. Furthermore, the control lines and information lines shown are those considered necessary for explanation, and do not necessarily represent all control lines and information lines in the product. In reality, it can be assumed that almost all configurations are interconnected.

[0062] 10... indoor unit, 11... heat exchanger, 12... fan, 13... indoor temperature sensor, 14... indoor expansion valve, 20... outdoor unit, 21... compressor, 22... heat exchanger, 23... fan, 24... expansion valve, 25... four-way valve, 26... control device, 30, 31... piping

Claims

1. An air conditioner comprising an outdoor unit and a plurality of indoor units, configured to transition each indoor unit to a thermo-off state in response to the corresponding room temperature reaching a first temperature while in a thermo-on state, and to transition to a thermo-on state in response to the corresponding room temperature reaching a second temperature higher or lower than the first temperature while in the thermo-off state, and further comprising a control unit that controls an indoor unit among the plurality of indoor units whose corresponding room temperature is between the first temperature and the second temperature to transition to the thermo-on state in response to an index value related to current capacity provided by the plurality of indoor units satisfying a condition.

2. The air conditioner according to claim 1, wherein the index value relating to the current capacity is the number of indoor units among the plurality of indoor units that are in the thermo-on state, a ratio of the sum of the rated capacities of one or more indoor units among the plurality of indoor units that are in the thermo-on state to the rated capacity of the outdoor unit, or a compressor operating frequency of the outdoor unit according to the operating state of one or more indoor units among the plurality of indoor units that are in the thermo-on state.

3. An air conditioner as described in claim 1, wherein, when the air conditioner operates in cooling mode, the first temperature is lower than a set temperature and the second temperature is higher than the first temperature.

4. The air conditioner described in claim 3, wherein the control unit selects an indoor unit from among the plurality of indoor units whose corresponding room temperature is between the first temperature and the second temperature, the indoor unit having a corresponding room temperature equal to or greater than a third temperature that is greater than the first temperature and less than the second temperature, and less than the second temperature.

5. The air conditioner of claim 1, wherein, when the air conditioner operates in heating mode, the first temperature is higher than a set temperature and the second temperature is lower than the first temperature.

6. The air conditioner described in claim 5, wherein the control unit selects an indoor unit from among the plurality of indoor units whose corresponding room temperature is between the first temperature and the second temperature, the indoor unit having a corresponding room temperature that is less than a third temperature that is greater than the second temperature and less than the first temperature, and is equal to or greater than the second temperature.

7. The air conditioner according to claim 1, wherein the outdoor unit is configured to start operation of the compressor when at least one of the plurality of indoor units changes from a thermo-off state to a thermo-on state, and to stop operation of the compressor when at least one of the plurality of indoor units changes from a thermo-on state to a thermo-off state.

8. A control method for an air conditioner consisting of an outdoor unit and a plurality of indoor units, wherein a control unit of the air conditioner executes, for each indoor unit, a step of transitioning to a thermo-off state in response to the corresponding room temperature reaching a first temperature while in a thermo-on state, and a step of transitioning to a thermo-on state in response to the corresponding room temperature reaching a second temperature higher or lower than the first temperature while in the thermo-off state, and the control unit further executes a step of transitioning to a thermo-on state any of the plurality of indoor units whose corresponding room temperature is between the first temperature and the second temperature, in response to an index value related to the current capacity provided by the plurality of indoor units satisfying a condition.

9. The control method according to claim 8, wherein the index value relating to the current capacity is the number of indoor units among the plurality of indoor units that are in the thermo-on state, a ratio of the sum of the rated capacities of one or more indoor units among the plurality of indoor units that are in the thermo-on state to the rated capacity of the outdoor unit, or a compressor operating frequency of the outdoor unit according to the operating state of one or more indoor units among the plurality of indoor units that are in the thermo-on state.

10. The control method of claim 8, wherein when the air conditioner operates in cooling mode, the first temperature is lower than a set temperature and the second temperature is higher than the set temperature.

11. The control method according to claim 8, wherein, when the air conditioner operates in heating mode, the first temperature is higher than a set temperature and the second temperature is lower than the set temperature.

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