Patent Publication Number: US-2022214068-A1

Title: Air-conditioning device and air-conditioning system

Description:
TECHNICAL FIELD 
     The present disclosure relates to an air-conditioning device and an air-conditioning system that perform indoor air conditioning. 
     BACKGROUND ART 
     In some air-conditioning device that includes a refrigerant circuit, a compressor has been often provided to an outdoor unit. In such a case, if the air-conditioning device stops in an environment where the outside air temperature is low, a phenomenon called “stagnation” may occur where refrigerant condenses and stagnates in the compressor and a heat exchanger provided to the outdoor unit. In particular, in the case where refrigerant stagnates in the compressor, refrigerating machine oil in the compressor is diluted and hence, there is a possibility that malfunction occurs, such as seizure of the shaft of the compressor. 
     As a typical method for reducing stagnation of refrigerant in the compressor, there is a known technique where, during a period in which the operation of the compressor is stopped, refrigerant in the compressor is caused to evaporate by heating the compressor by a heater or by performing a stagnation prevention control referred to as a constraint energization control. The constraint energization control is a control of energizing a motor winding to heat the compressor without driving a motor in the compressor. Patent Literature 1 discloses a method where the amount of energization of a heater or the voltage of the constraint energization control is adjusted depending on the outside air temperature to reduce power consumption at the time of heating the compressor to cause refrigerant in the compressor to evaporate. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 7-167504 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in some air-conditioning device, when to start the operation cannot be determined during a period in which the operation of the compressor is stopped and hence, the stagnation prevention control is always performed. Accordingly, there is a problem in that power consumption increases during the period in which the operation of the compressor is stopped. 
     The present disclosure has been made in view of the above-mentioned problem of the known technique, and it is an objective of the present disclosure to provide an air-conditioning device and an air-conditioning system that can reduce power consumption during a period in which the operation of the compressor is stopped. 
     Solution to Problem 
     An air-conditioning device according to one embodiment of the present disclosure is an air-conditioning device that includes an outdoor unit and an indoor unit, the outdoor unit including a compressor, the indoor unit being connected to the outdoor unit, the air-conditioning device including a heating means provided to the compressor, and configured to heat refrigerant in the compressor, and a controller configured to control the heating means. The controller includes a heat load learning unit configured to learn a heat load based on temperature data and air conditioning data, a stagnation prevention control start timing estimation unit configured to estimate a stagnation prevention control start timing based on the heat load obtained by learning, the stagnation prevention control start timing being a timing at which a stagnation prevention control of heating the compressor is started, and a device control unit configured to control the heating means such that the stagnation prevention control is performed by the heating means at the stagnation prevention control start timing estimated. 
     An air-conditioning device according to another embodiment of the present disclosure is an air-conditioning device that includes an outdoor unit and an indoor unit, the outdoor unit including a compressor, the indoor unit being connected to the outdoor unit, the air-conditioning device including a heating means provided to the compressor, and configured to heat refrigerant in the compressor, and a controller configured to control the heating means. The controller includes an outside air temperature learning unit configured to learn an outside air temperature for a set time interval based on a current outside air temperature, a stagnation prevention control required time period calculation unit configured to calculate, based on the outside air temperature obtained by learning, a stagnation prevention control required time period indicating a time period required for a stagnation prevention control of heating the compressor, and a device control unit configured to derive, based on a set time and the stagnation prevention control required time period, a stagnation prevention control start timing at which the stagnation prevention control is started, and configured to control the heating means such that the stagnation prevention control is performed by the heating means at the stagnation prevention control start timing derived for the stagnation prevention control required time period calculated. 
     An air-conditioning system according to still another embodiment of the present disclosure is an air-conditioning system including at least one air-conditioning device that includes an outdoor unit and an indoor unit, the outdoor unit including a compressor, the indoor unit being connected to the outdoor unit, and a management device configured to manage the at least one air-conditioning device. The at least one air-conditioning device includes a heating means provided to the compressor, and configured to heat refrigerant in the compressor, the management device includes a controller configured to control the heating means, and the controller includes a heat load learning unit configured to learn a heat load based on temperature data and air conditioning data, a stagnation prevention control start timing estimation unit configured to estimate a stagnation prevention control start timing based on the heat load obtained by learning, the stagnation prevention control start timing being a timing at which a stagnation prevention control of heating the compressor is started, and a device control unit configured to control the heating means such that the stagnation prevention control is performed by the heating means at the stagnation prevention control start timing estimated. 
     An air-conditioning system according to yet another embodiment of the present disclosure is an air-conditioning system including at least one air-conditioning device that includes an outdoor unit and an indoor unit, the outdoor unit including a compressor, the indoor unit being connected to the outdoor unit, and a management device configured to manage the at least one air-conditioning device. The at least one air-conditioning device includes a heating means provided to the compressor, and configured to heat refrigerant in the compressor, the management device includes a controller configured to control the heating means, and the controller includes an outside air temperature learning unit configured to learn an outside air temperature for a set time interval based on a current outside air temperature, a stagnation prevention control required time period calculation unit configured to calculate, based on the outside air temperature obtained by learning, a stagnation prevention control required time period indicating a time period required for a stagnation prevention control of heating the compressor, and a device control unit configured to derive, based on a set time and the stagnation prevention control required time period, a stagnation prevention control start timing at which the stagnation prevention control is started, and configured to control the heating means such that the stagnation prevention control is performed by the heating means at the stagnation prevention control start timing derived for the stagnation prevention control required time period calculated. 
     Advantageous Effects of Invention 
     According to an embodiment of the present disclosure, the stagnation prevention control is started at the estimated stagnation prevention control start timing and hence, the stagnation prevention control is performed appropriately. Accordingly, power consumption can be reduced during a period in which the operation of the compressor is stopped. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram showing one example of a configuration of an air-conditioning device according to Embodiment 1. 
         FIG. 2  is a function block diagram showing one example of a configuration of a controller shown in  FIG. 1 . 
         FIG. 3  is a hardware configuration diagram showing one example of the configuration of the controller shown in  FIG. 2 . 
         FIG. 4  is a hardware configuration diagram showing another example of the configuration of the controller shown in  FIG. 2 . 
         FIG. 5  is a schematic view showing one example of a model of machine learning performed by a heat load learning unit shown in  FIG. 2 . 
         FIG. 6  is a flowchart showing one example of a flow of learning performed by the heat load learning unit shown in  FIG. 2 . 
         FIG. 7  is a flowchart showing one example of a flow of stagnation prevention control performed by the air-conditioning device according to Embodiment 1. 
         FIG. 8  is a function block diagram showing one example of a configuration of a controller according to Embodiment 2. 
         FIG. 9  is a flowchart showing one example of a flow of learning performed by an outside air temperature learning unit shown in  FIG. 8 . 
         FIG. 10  is a flowchart showing one example of a flow of stagnation prevention control performed by an air-conditioning device according to Embodiment 2. 
         FIG. 11  is a circuit diagram showing one example of a configuration of an air-conditioning system according to Embodiment 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, Embodiments of the present disclosure will be described with reference to drawings. The present disclosure is not limited to the following Embodiments, and various modifications are possible without departing from the gist of the present disclosure. Further, the present disclosure includes any combination of the configurations that can be obtained by combining configurations shown in the following respective Embodiments. In the respective drawings, components given the same reference signs are identical or corresponding components, and the reference signs are common in the entire description. 
     Embodiment 1 
     An air-conditioning device according to Embodiment 1 will be described. The air-conditioning device according to Embodiment 1 performs air conditioning of an air-conditioned space by causing refrigerant to cycle through a refrigerant circuit. 
     [Configuration of Air-Conditioning Device  1 ] 
       FIG. 1  is a circuit diagram showing one example of a configuration of the air-conditioning device according to Embodiment 1. As shown in  FIG. 1 , an air-conditioning device  1  includes an outdoor unit  10 , an indoor unit  20 , and a controller  30 . The outdoor unit  10  and the indoor unit  20  are connected with each other via refrigerant pipes. 
     The outdoor unit  10  includes a compressor  11 , a refrigerant flow passage switching device  12 , an outdoor heat exchanger  13 , an expansion valve  14 , and an outside air temperature sensor  15 . The indoor unit  20  includes an indoor heat exchanger  21  and an indoor temperature sensor  22 . In the air-conditioning device  1 , the compressor  11 , the refrigerant flow passage switching device  12 , the outdoor heat exchanger  13 , the expansion valve  14 , and the indoor heat exchanger  21  are sequentially connected via refrigerant pipes to form the refrigerant circuit through which refrigerant cycles. 
     (Outdoor Unit  10 ) 
     The compressor  11  suctions refrigerant of low temperature and low pressure, compresses the suctioned refrigerant into a high temperature and high pressure state, and then discharges the refrigerant. The compressor  11  is an inverter compressor where capacity, which is the delivery amount per unit time, is controlled by changing the operating frequency. The operating frequency of the compressor  11  is controlled by the controller  30 . 
     The refrigerant flow passage switching device  12  is a four-way valve, for example. The refrigerant flow passage switching device  12  switches between a cooling operation and a heating operation by switching flow directions of refrigerant. During the cooling operation, the refrigerant flow passage switching device  12  is switched to a state shown by solid lines in  FIG. 1 , that is, a state where the discharge port of the compressor  11  and the outdoor heat exchanger  13  are connected. During the heating operation, the refrigerant flow passage switching device  12  is switched to a state shown by broken lines in  FIG. 1 , that is, a state where the suction port of the compressor  11  and the outdoor heat exchanger  13  are connected. Switching of flow passages performed by the refrigerant flow passage switching device  12  is controlled by the controller  30 . 
     The outdoor heat exchanger  13  is a fin-and-tube heat exchanger, for example. The outdoor heat exchanger  13  exchanges heat between refrigerant and outdoor air supplied by a fan or other similar device not shown in the drawing. During the cooling operation, the outdoor heat exchanger  13  is used as a condenser that rejects heat of refrigerant to outdoor air to condense the refrigerant. During the heating operation, the outdoor heat exchanger  13  is used as an evaporator that evaporates refrigerant to cool outdoor air by the heat of vaporization from the evaporation of the refrigerant. 
     The expansion valve  14  causes refrigerant to expand by reducing the pressure of the refrigerant. The expansion valve  14  is a valve whose opening degree can be controlled, such as an electronic expansion valve, for example. The opening degree of the expansion valve  14  is controlled by the controller  30 . The outside air temperature sensor  15  is provided in the vicinity of the outdoor heat exchanger  13  to detect outside air temperature. The outside air temperature detected by the outside air temperature sensor  15  is supplied to the controller  30 . 
     In Embodiment 1, a heating means  16  is provided to the compressor  11 . With the control from the controller  30 , the heating means  16  heats and evaporates refrigerant having stagnated in the compressor  11  during a period in which the compressor  11  is stopped. 
     Specifically, a heater attached to the periphery of the compressor  11 , such as a belt heater, is used as the heating means  16 , for example. When the heater is energized by a control from the controller  30 , the compressor  11  is heated. To perform a constraint energization control, the heating means  16  may also be, for example, an energization control device that controls energization of the compressor  11 . The constraint energization control is a control where any two phases of three phases of power supplied to the compressor  11  are intermittently energized to heat the compressor  11  without driving a motor in the compressor  11 . 
     (Indoor Unit  20 ) 
     The indoor heat exchanger  21  exchanges heat between refrigerant and indoor air supplied by a fan or other similar device not shown in the drawing. With such heat exchange, cooling air or heating air to be supplied to an indoor space is generated. During the cooling operation, the indoor heat exchanger  21  is used as an evaporator, and cools the air-conditioned space by cooling the air of the air-conditioned space. During the heating operation, the indoor heat exchanger  21  is used as a condenser, and heats the air-conditioned space by heating the air of the air-conditioned space. 
     The indoor temperature sensor  22  is provided in the vicinity of the indoor heat exchanger  21  to detect temperature of indoor air. The indoor temperature detected by the indoor temperature sensor  22  is supplied to the controller  30 . 
     (Controller  30 ) 
     The controller  30  controls separate units provided to the outdoor unit  10  and separate units provided to the indoor unit  20 . In particular, in Embodiment 1, based on data including, for example, the outside air temperature detected by the outside air temperature sensor  15  and the indoor temperature detected by the indoor temperature sensor  22 , the controller  30  controls the heating means  16  for the compressor  11  to perform stagnation prevention control. The stagnation prevention control is a control of causing refrigerant having stagnated in the compressor  11  to evaporate by the heating means  16  provided to the compressor  11 . 
       FIG. 2  is a function block diagram showing one example of a configuration of the controller shown in  FIG. 1 . As shown in  FIG. 2 , the controller  30  includes a data acquisition unit  31 , a heat load learning unit  32 , a stagnation prevention control start timing estimation unit  33 , a device control unit  34 , and a data holding unit  35 . The controller  30 , for example, is an arithmetic device, such as a microcomputer, that implements various functions by executing software, or is hardware, such as a circuit device, that corresponds to the various functions. In  FIG. 2 , only components for functions relating to Embodiment 1 are illustrated, and the illustration of the other components will be omitted. 
     The data acquisition unit  31  acquires various pieces of data. Specifically, the data acquisition unit  31  acquires outside air temperature detected by the outside air temperature sensor  15  and indoor temperature detected by the indoor temperature sensor  22  as temperature data. The data acquisition unit  31  also acquires set temperature set for the indoor unit  20  by a user or other person and operating frequency of the compressor  11  as air conditioning data. The data acquisition unit  31  supplies the acquired temperature data and the acquired air conditioning data to the data holding unit  35 . 
     The heat load learning unit  32  learns the heat load of the air-conditioning device  1  by machine learning by using various pieces of data, such as temperature data and air conditioning data that are held in the data holding unit  35 . Specifically, the heat load learning unit  32  learns an amount of heat processed by the air-conditioning device  1  from current time, outside air temperature, indoor temperature, set temperature, and operating frequency of the compressor  11 , for example. In Embodiment 1, the air-conditioning device  1  has only the amount of heat processed by the air-conditioning device  1  as data relating to heat load. In such a case where an amount of heat is thought to be equal to the heat load in an air-conditioned space, the air-conditioning device  1  can obtain the heat load of the air-conditioned space. Accordingly, the heat load learning unit  32  relatively learns the heat load of the air-conditioned space by learning the amount of heat processed by the air-conditioning device  1 . Learning of the heat load will be described later. The heat load learning unit  32  also derives the heat load based on temperature data and air conditioning data by using the learning results obtained as described above. 
     The stagnation prevention control start timing estimation unit  33  estimates, based on the heat load obtained by learning by the heat load learning unit  32 , a stagnation prevention control start timing by using an estimation means, such as a timing estimation formula set in advance. The stagnation prevention control start timing is a timing at which the stagnation prevention control is started. To allow the indoor temperature to reach a set temperature at a set time, such as an operation start time set by a user, the stagnation prevention control start timing is a time prior to a start-up time at which the air-conditioning device  1  is caused to start up. 
     The device control unit  34  generates and outputs a stagnation prevention command signal for controlling the heating means  16  at the estimated stagnation prevention control start timing based on the estimation result from the stagnation prevention control start timing estimation unit  33 . 
     The data holding unit  35  holds various pieces of information used by the separate units of the controller  30 . In Embodiment 1, for example, the data holding unit  35  holds various pieces of data including the temperature data and the air conditioning data that are acquired by the data acquisition unit  31  and that are used when learning is performed by the heat load learning unit  32 . 
       FIG. 3  is a hardware configuration diagram showing one example of the configuration of the controller shown in  FIG. 2 . In the case where the various functions of the controller  30  are executed by hardware, as shown in  FIG. 3 , the controller  30  shown in  FIG. 2  is a processing circuit  41 . In the controller  30  shown in  FIG. 2 , the respective functions of the data acquisition unit  31 , the heat load learning unit  32 , the stagnation prevention control start timing estimation unit  33 , the device control unit  34 , and the data holding unit  35  are implemented by the processing circuit  41 . 
     In the case where the respective functions are executed by hardware, for example, the processing circuit  41  corresponds to a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination of the above. The controller  30  may implement each of the functions of the respective units, that is, the data acquisition unit  31 , the heat load learning unit  32 , the stagnation prevention control start timing estimation unit  33 , the device control unit  34 , and the data holding unit  35 , by the processing circuit  41 , or may implement the functions of the respective units by one processing circuit  41 . 
       FIG. 4  is a hardware configuration diagram showing another example of the configuration of the controller shown in  FIG. 2 . In the case where the various functions of the controller  30  are executed by software, as shown in  FIG. 4 , the controller  30  shown in  FIG. 2  includes a processor  51  and a memory  52 . In the controller  30 , the respective functions of the data acquisition unit  31 , the heat load learning unit  32 , the stagnation prevention control start timing estimation unit  33 , the device control unit  34 , and the data holding unit  35  are implemented by the processor  51  and the memory  52 . 
     In the case where the respective functions are executed by software, in the controller  30 , the functions of the data acquisition unit  31 , the heat load learning unit  32 , the stagnation prevention control start timing estimation unit  33 , the device control unit  34 , and the data holding unit  35  are implemented by software, firmware, or the combination of the software and the firmware. The software or the firmware is described as a program, and is stored in the memory  52 . The processor  51  reads and executes the program stored in the memory  52  to implement the functions of the respective units. 
     As the memory  52 , for example, a nonvolatile or volatile semiconductor memory is used, such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable and programmable ROM (EPROM), and an electrically erasable and programmable ROM (EEPROM). Further, as the memory  52 , for example, a detachable recording medium may be used, such as a magnetic disk, a flexible disk, an optical disc, a compact disc (CD), a mini disc (MD), and a digital versatile disc (DVD). 
     [Action of Air-Conditioning Device  1 ] 
     Next, the action of the air-conditioning device  1  having such a configuration will be described together with the flow of refrigerant with reference to  FIG. 1 . In  FIG. 1 , solid lines show a state of the refrigerant flow passage switching device  12  when the air-conditioning device  1  performs the heating operation. The air-conditioning device  1  can perform both the cooling operation and the heating operation. However, in Embodiment 1, the action of the air-conditioning device  1  during the heating operation will be described, and the description for the action of the air-conditioning device  1  during the cooling operation will be omitted. 
     (During Heating Operation) 
     A case where the air-conditioning device  1  performs the heating operation will be described. When the compressor  11  is driven, refrigerant in a gas state at high temperature and high pressure is discharged from the compressor  11 . The gas refrigerant of high temperature and high pressure discharged from the compressor  11  flows into the indoor heat exchanger  21 , which is used as a condenser, via the refrigerant flow passage switching device  12 . In the indoor heat exchanger  21 , heat exchange is performed between the gas refrigerant of high temperature and high pressure that flows into the indoor heat exchanger  21  and indoor air supplied by an air-sending device not shown in the drawing. With such heat exchange, the gas refrigerant of high temperature and high pressure is condensed, thus becoming high-pressure liquid refrigerant. 
     The high-pressure liquid refrigerant that flows out from the indoor heat exchanger  21  expands in the expansion valve  14 , thus becoming refrigerant in a two-phase state where low-pressure gas refrigerant and low-pressure liquid refrigerant are in a mixed state. The refrigerant in a two-phase state flows into the outdoor heat exchanger  13 , which is used as an evaporator. In the outdoor heat exchanger  13 , heat exchange is performed between the refrigerant in a two-phase state that flows into the outdoor heat exchanger  13  and outdoor air supplied by an air-sending device not shown in the drawing. With such heat exchange, liquid refrigerant evaporates from the refrigerant in a two-phase state, so that the refrigerant becomes low-pressure gas refrigerant. The low-pressure gas refrigerant that flows out from the outdoor heat exchanger  13  flows into the compressor  11  via the refrigerant flow passage switching device  12 , and is compressed, thus becoming gas refrigerant of high temperature and high pressure. Then, the gas refrigerant is discharged from the compressor  11  again. Hereinafter, this cycle is repeated. 
     [Stagnation Prevention Control] 
     Next, the stagnation prevention control performed by the air-conditioning device  1  according to Embodiment 1 will be described. In a typical air-conditioning device, operation schedule, such as an operation start time and an operation stop time can be set in advance by a user. In this case, to allow the indoor temperature to reach a set temperature at the set time that is set in advance, it is necessary to start up the air-conditioning device at a start-up time prior to the set time. 
     During a period in which the operation of the air-conditioning device is stopped, as also described in Background Art, “stagnation” may occur where refrigerant condenses and stagnates in the compressor. Therefore, even when the air-conditioning device starts up at the start-up time in a state of stagnation occurring, the compressor is not normally activated and hence, it is difficult to allow the indoor temperature to reach the set temperature at the set time. 
     In view of the above, in the air-conditioning device  1  according to Embodiment 1, a stagnation prevention control start timing, at which stagnation prevention control is started, is estimated such that the air-conditioning device  1  starts up at a start-up time prior to the set time set by a user in a state where stagnation is eliminated. The air-conditioning device  1  starts the stagnation prevention control at the estimated stagnation prevention control start timing. 
     In estimating the stagnation prevention control start timing, a heat load processed by the air-conditioning device  1  is used. To acquire such a heat load, in Embodiment 1, learning of the heat load is performed by the heat load learning unit  32  of the controller  30 . 
     (Learning of Heat Load) 
     Learning of a heat load performed by the heat load learning unit  32  will be described. To acquire a heat load used in estimating a start timing for the stagnation prevention control by the stagnation prevention control start timing estimation unit  33 , the heat load learning unit  32  performs learning of a heat load processed by the air-conditioning device  1 . Machine learning is used for learning a heat load. 
       FIG. 5  is a schematic view showing one example of a model of machine learning performed by the heat load learning unit shown in  FIG. 2 . In the machine learning model shown in  FIG. 5 , preprocessing is performed on input data. A heat load is estimated from the data, on which preprocessing is performed, by using a learning model, and the heat load is output. 
     In this case, outside air temperature, indoor temperature, set temperature, and action capability, for example, are used for input data. Temperature data detected by the outside air temperature sensor  15  is used for the outside air temperature. Temperature data detected by the indoor temperature sensor  22  is used for the indoor temperature. The set temperature is a temperature set for the indoor unit  20 , and air conditioning data held in the data holding unit  35  is used for the set temperature. The action capability may be operating frequency of the compressor  11 , for example, and air conditioning data held in the data holding unit  35  is used for the action capability. For alternative data for the outside air temperature or the indoor temperature, data from the weather forecast, for example, may be used. 
     In the preprocessing, processing set in advance, such as optimization of input data and reduction in input dimensions, is performed. More specifically, in the case where temperature data is input as input data, in the preprocessing, for example, processing set in advance, such as derivation of a differential value between a set temperature and an indoor temperature and normalization, is performed on the input data. 
     The learning model may be, for example, a heat load calculation formula that derives a heat load as output data that correspond to input data. The learning model is formed by using learning with a teacher, for example. An example of the learning model is not limited to the above, and a neural network, deep learning, or other similar technique may be used depending on the required accuracy and computational capacity. 
     Each time a plurality of data are input, parameters included in the heat load calculation formula of the learning model are updated. Specifically, for example, in the case where the learning model is formed by learning with a teacher, the learning model outputs output data by using the heat load calculation formula based on input data. The output data is input in an evaluation function together with teacher data. The evaluation function evaluates validity of the heat load calculation formula, which is the learning model, based on the output data and the teacher data. Then, the heat load learning unit  32  updates the parameters of the heat load calculation formula such that the output data calculated from the heat load calculation formula approach the teacher data. 
       FIG. 6  is a flowchart showing one example of a flow of learning performed by the heat load learning unit shown in  FIG. 2 . In step S 1 , the data acquisition unit  31  of the controller  30  acquires an outside air temperature detected by the outside air temperature sensor  15  and an indoor temperature detected by the indoor temperature sensor  22  as temperature data. The acquired temperature data are held in the data holding unit  35 . In step S 2 , the data acquisition unit  31  acquires a set temperature set for the indoor unit  20  and operating frequency of the compressor  11  as air conditioning data. The acquired air conditioning data are held in the data holding unit  35 . 
     In step S 3 , the heat load learning unit  32  determines whether it is a learning timing. The learning timing here is determined to be set to an arbitrary timing set in advance. When it is the learning timing (YES in step S 3 ), the heat load learning unit  32  performs learning of the heat load of the air-conditioning device  1  by using the temperature data and the air conditioning data that are held in the data holding unit  35 . In contrast, when it is not the learning timing (NO in step S 3 ), the process returns to step S 1 . Hereinafter, processing in step S 1  to step S 4  is cyclically repeated with a fixed period. 
     (Estimation of Start Timing for Stagnation Prevention Control) 
     Next, estimation of a start timing for the stagnation prevention control performed by the stagnation prevention control start timing estimation unit  33  will be described. The stagnation prevention control start timing estimation unit  33  estimates, by using the heat load derived by the heat load learning unit  32 , a timing at which the stagnation prevention control, which is performed prior to a start-up time, is started. For example, the stagnation prevention control start timing estimation unit  33  estimates the stagnation prevention control start timing such that the higher the derived heat load is, the earlier the stagnation prevention control is started. 
     (Stagnation Prevention Control) 
       FIG. 7  is a flowchart showing one example of a flow of the stagnation prevention control performed by the air-conditioning device according to Embodiment 1. In step S 11 , the data acquisition unit  31  acquires the outside air temperature detected by the outside air temperature sensor  15  and the indoor temperature detected by the indoor temperature sensor  22  as temperature data. The acquired temperature data are supplied to the heat load learning unit  32 , and are held in the data holding unit  35 . In step S 12 , the data acquisition unit  31  acquires, as air conditioning data, a set temperature and an operation start time that are set for the indoor unit  20  and action capability, such as the operating frequency of the compressor  11 . The acquired air conditioning data are supplied to the heat load learning unit  32 , and are held in the data holding unit  35 . Processing in step S 11  and step S 12  is performed arbitrary time period prior to the set time, such as the operation start time. 
     When the temperature data and the air conditioning data are input, the heat load learning unit  32  derives a heat load in step S 13 . In step S 14 , the stagnation prevention control start timing estimation unit  33  estimates a stagnation prevention control start timing by using an estimation means, such as a timing estimation formula, based on the heat load derived in step S 13 . At this point of operation, the stagnation prevention control start timing estimation unit  33  estimates the stagnation prevention control start timing such that the higher the heat load is, the earlier the stagnation prevention control is started. 
     In step S 15 , the device control unit  34  determines whether it is a time indicated by the stagnation prevention control start timing. When it is the stagnation prevention control start timing (YES in step S 15 ), the device control unit  34  generates a stagnation prevention command signal and outputs the stagnation prevention command signal to the heating means  16  in step S 16 . The stagnation prevention control is performed by the heating means  16  in this manner. In this case, the stagnation prevention control is performed for a fixed time period that is fixedly set. 
     In contrast, when it is not the stagnation prevention control start timing (NO in step S 15 ), the process returns to step S 15 , and the processing in step S 15  is repeated until the stagnation prevention control start timing is reached. 
     As described above, the air-conditioning device  1  according to Embodiment 1 learns a heat load based on temperature data and air conditioning data, and estimates a stagnation prevention control start timing based on the heat load obtained by learning. Then, the air-conditioning device  1  performs the stagnation prevention control of heating the compressor  11  at the estimated stagnation prevention control start timing. 
     In the air-conditioning device  1 , the stagnation prevention control is started at the estimated stagnation prevention control start timing in this manner and hence, unlike a known technique, there is no possibility that the stagnation prevention control is always performed during a period in which the operation of the compressor  11  is stopped. Therefore, it is possible to reduce power consumption during a period in which the operation of the compressor  11  is stopped. 
     At this point of operation, the controller  30  acquires the outside air temperature detected by the outside air temperature sensor  15  and the indoor temperature detected by the indoor temperature sensor  22  as temperature data. The controller  30  also acquires the operating frequency of the compressor  11  as air conditioning data. The controller  30  may acquire the set temperature set for the indoor unit  20  as air conditioning data. 
     In the air-conditioning device  1  according to Embodiment 1, a heater attached to the periphery of the compressor  11  may be used for the heating means  16 . With such a configuration, when the stagnation prevention control is performed, the heater is energized, thus heating the compressor  11 . 
     An energization control device that controls energization of the compressor  11  may also be used for the heating means  16 . With such a configuration, when the stagnation prevention control is performed, the compressor  11  is energized such that the constraint energization control is performed and hence, the compressor  11  can be heated. 
     Embodiment 2 
     Next, Embodiment 2 will be described. Embodiment 2 differs from Embodiment 1 in that the time period required for the stagnation prevention control is calculated. In Embodiment 2, components identical to the corresponding components in Embodiment 1 are given the same reference signs, and the detailed description of such components will be omitted. 
     An air-conditioning device  1  according to Embodiment 2 is substantially equal to the air-conditioning device  1  according to Embodiment 1 shown in  FIG. 1  except for the configuration of the controller  30  and hence, the detailed description of the air-conditioning device  1  according to Embodiment 2 will be omitted. 
     [Configuration of Controller  30 ] 
     In the same manner as Embodiment 1, the controller  30  controls separate units provided to the outdoor unit  10  and separate units provided to the indoor unit  20 . In Embodiment 2, in addition to the functions of the controller  30  according to Embodiment 1, the controller  30  estimates outside air temperatures for set time intervals, set in advance, based on the outside air temperature detected by the outside air temperature sensor  15 , and calculates the time period required for the stagnation prevention control based on the estimation result. 
       FIG. 8  is a function block diagram showing one example of a configuration of the controller according to Embodiment 2. As shown in  FIG. 8 , the controller  30  includes the data acquisition unit  31 , the device control unit  34 , the data holding unit  35 , an outside air temperature learning unit  36 , and a stagnation prevention control required time period calculation unit  37 . The controller  30  may be, for example, an arithmetic device, such as a microcomputer, that implements various functions by executing software, or may be hardware, such as a circuit device, that corresponds to the various functions. In  FIG. 8 , only components having functions relating to Embodiment 2 are illustrated, and the illustration of the other components will be omitted. 
     The outside air temperature learning unit  36  learns outside air temperatures for the set time intervals by machine learning by using the outside air temperature included in temperature data held in the data holding unit  35 . Learning of outside air temperature will be described later in detail. Further, the outside air temperature learning unit  36  derives, by using the above-mentioned learning results, the outside air temperatures for the set time intervals based on a current outside air temperature detected by the outside air temperature sensor  15 . 
     The stagnation prevention control required time period calculation unit  37  calculates a stagnation prevention control required time period based on the outside air temperatures obtained by learning by the outside air temperature learning unit  36 . The stagnation prevention control required time period is the minimum time period required for the stagnation prevention control to evaporate refrigerant in the compressor  11 . The stagnation prevention control required time period calculation unit  37  calculates a stagnation prevention control required time period by using a predetermined calculation formula based on the current outside air temperature and the outside air temperatures for the set time intervals obtained by learning. 
     Based on the calculation result from the stagnation prevention control required time period calculation unit  37 , the device control unit  34  derives a start timing for the stagnation prevention control from a set time and the stagnation prevention control required time period such that the stagnation prevention control is performed for the stagnation prevention control required time period. Then, the device control unit  34  generates and outputs a stagnation prevention command signal. In Embodiment 2, the stagnation prevention command signal includes information indicating a start timing for the stagnation prevention control and information indicating an execution time period for the stagnation prevention control. 
     In the same manner as Embodiment 1, the data holding unit  35  holds various pieces of information used by the separate units of the controller  30 . In Embodiment 2, for example, the data holding unit  35  holds various pieces of data including the temperature data and the air conditioning data that are acquired by the data acquisition unit  31  and that are used when learning is performed by the heat load learning unit  32  and the outside air temperature learning unit  36 . 
     [Stagnation Prevention Control] 
     Next, the stagnation prevention control performed by the air-conditioning device  1  according to Embodiment 2 will be described. In the case where stagnation of refrigerant occurs in the compressor  11 , the amount of refrigerant condensed varies with the outside air temperature. Therefore, the time period required for the stagnation prevention control of heating refrigerant in the compressor  11  varies with the outside air temperature. 
     In this case, if a time period during which the stagnation prevention control is performed is fixedly determined, there is a possibility that the stagnation prevention control is not performed for an appropriate time period depending on the degree of stagnation. For example, in the case where the amount of condensed refrigerant is relatively large, it is necessary to set a long time period for the stagnation prevention control. In contrast, in the case where the amount of condensed refrigerant is relatively small, it is sufficient to set a short time period for the stagnation prevention control. 
     In view of the above, in Embodiment 2, the stagnation prevention control required time period, which is a time period required for the stagnation prevention control, is calculated such that a stagnation prevention control time period during the stagnation prevention control is an appropriate time period depending on the state of stagnation. The air-conditioning device  1  performs the stagnation prevention control for the calculated stagnation prevention control required time period. 
     When the stagnation prevention control required time period is calculated, the outside air temperatures for the set time intervals are used. To obtain such outside air temperatures, in Embodiment 2, learning of outside air temperature is performed by the outside air temperature learning unit  36  of the controller  30 . 
     (Learning of Outside Air Temperature) 
     Learning of outside air temperature performed by the outside air temperature learning unit  36  will be described. The outside air temperature learning unit  36  performs learning of outside air temperatures for the set time intervals to acquire outside air temperatures that are used for estimating a required time period for the stagnation prevention control by the stagnation prevention control required time period calculation unit  37 . In the same manner as the heat load learning unit  32  in Embodiment 1, machine learning is used for the learning of outside air temperatures. 
     For a model of machine learning performed by the outside air temperature learning unit  36 , a machine learning model shown in  FIG. 5  is used. In this case, outside air temperature is used for input data, for example. As alternative data for outside air temperature, data from the weather forecast, for example, may be used. 
       FIG. 9  is a flowchart showing one example of a flow of learning performed by the outside air temperature learning unit shown in  FIG. 8 . In step S 21 , the data acquisition unit  31  of the controller  30  acquires an outside air temperature detected by the outside air temperature sensor  15  as temperature data. The acquired temperature data is held in the data holding unit  35 . 
     In step S 22 , the outside air temperature learning unit  36  determines whether it is the learning timing. The learning timing here is determined to be set to an arbitrary timing set in advance. When it is the learning timing (YES in step S 22 ), the outside air temperature learning unit  36  performs learning of outside air temperatures for the set time intervals by using temperature data held in the data holding unit  35 . In contrast, when it is not the learning timing (NO in step S 22 ), the process returns to step S 21 . Hereinafter, processing in step S 21  to step S 23  is cyclically repeated with a fixed period. 
     (Calculation of Required Time Period for Stagnation Prevention Control) 
     Next, calculation of the required time period for the stagnation prevention control performed by the stagnation prevention control required time period calculation unit  37  will be described. The stagnation prevention control required time period calculation unit  37  calculates a required time period for the stagnation prevention control by using the outside air temperatures derived by the outside air temperature learning unit  36 . For example, the stagnation prevention control required time period calculation unit  37  calculates the stagnation prevention control required time period such that the higher the derived outside air temperatures are, the shorter an execution time period for the stagnation prevention control becomes. 
     (Stagnation Prevention Control) 
       FIG. 10  is a flowchart showing one example of a flow of the stagnation prevention control performed by the air-conditioning device according to Embodiment 2. In  FIG. 10 , processing that is common to processing for the stagnation prevention control in Embodiment 1 shown in  FIG. 7  is given the same reference sign, and the repeated description of such processing will be omitted. 
     The data acquisition unit  31  acquires temperature data in step S 11  and air conditioning data in step S 12 . The acquired temperature data and air conditioning data are supplied to the outside air temperature learning unit  36 , and are held in the data holding unit  35 . 
     After the temperature data are input, the outside air temperature learning unit  36  derives outside air temperatures for set time intervals in step S 31 . The outside air temperature learning unit  36  extracts an outside air temperature having the lowest temperature from the derived outside air temperatures for the set time intervals. In step S 32 , the stagnation prevention control required time period calculation unit  37  calculates a stagnation prevention control required time period based on the outside air temperature extracted in step S 31  and the outside air temperature held in the data holding unit  35 . 
     In step S 15 , the device control unit  34  determines whether it is the time indicated by the stagnation prevention control start timing. The stagnation prevention control start timing is derived by calculating backward from a start-up time by the calculated stagnation prevention control required time period. When it is the stagnation prevention control start timing (YES in step S 15 ), the device control unit  34  generates a stagnation prevention command signal and outputs the stagnation prevention command signal to the heating means  16  in step S 33 . With such a configuration, the stagnation prevention control is performed by the heating means  16  for the stagnation prevention control required time period. 
     In contrast, when it is not the stagnation prevention control start timing (NO in step S 15 ), the process returns to step S 15 , and the processing in step S 15  is repeated until the stagnation prevention control start timing is reached. 
     As described above, in the air-conditioning device  1  according to Embodiment 2, the controller  30  learns outside air temperatures for the set time intervals based on outside air temperature, and calculates the stagnation prevention control required time period based on the outside air temperatures obtained by learning. The controller  30  derives the stagnation prevention control start timing based on a set time and the stagnation prevention control required time period. The controller  30  controls the heating means  16  such that the stagnation prevention control is performed at the derived stagnation prevention control start timing for the calculated stagnation prevention control required time period. 
     With such a configuration, in the same manner as Embodiment 1, it is possible to reduce power consumption during a period in which the operation of the compressor  11  is stopped. Further, in Embodiment 2, the time period required for the stagnation prevention control is calculated and hence, the stagnation prevention control is performed for an appropriate time period depending on the amount of refrigerant condensed in the compressor  11 . Therefore, an unnecessary stagnation prevention control can be reduced and hence, power consumption can be reduced more appropriately during a period in which the operation of the compressor  11  is stopped. 
     Embodiment 3 
     Next, Embodiment 3 will be described. In Embodiment 3, the description will be made for an air-conditioning system where a function of the controller  30  that performs the stagnation prevention control is provided to a device different from the air-conditioning device. In Embodiment 3, components identical to the corresponding components in Embodiments 1 and 2 are given the same reference signs, and the detailed description of such components will be omitted. 
     [Configuration of Air-Conditioning System  100 ] 
       FIG. 11  is a circuit diagram showing one example of a configuration of the air-conditioning system according to Embodiment 3. As shown in  FIG. 11 , an air-conditioning system  100  includes one or a plurality of air-conditioning devices  110  and a management device  120  connected to each of the air-conditioning devices  110 . 
     In the same manner as the air-conditioning device  1  of Embodiments 1 and 2 shown in  FIG. 1 , each air-conditioning device  110  includes the outdoor unit  10  and the indoor unit  20 , and the outdoor unit  10  includes the compressor  11  to which the heating means  16  is provided. The air-conditioning device  110  has a configuration obtained by excluding the function of performing the stagnation prevention control from the controller  30  of the air-conditioning device  1  shown in  FIG. 1 . 
     The management device  120  manages the one or the plurality of air-conditioning devices  110  connected to the management device  120 . In Embodiment 3, the management device  120  receives temperature data and air conditioning data from each of the air-conditioning devices  110 , and performs the stagnation prevention control on the corresponding one of the air-conditioning devices  110  based on the received temperature data and air conditioning data. 
     The management device  120  includes a controller  130 . The controller  130  has a function of performing the stagnation prevention control performed by the controller  30  shown in  FIG. 1 . That is, the controller  130  has a configuration substantially equal to the configuration of the controller  30  according to Embodiment 1 or 2. 
     In the case where the controller  130  has the configuration substantially equal to the configuration of the controller  30  according to Embodiment 1, as shown in  FIG. 2 , the controller  130  includes the data acquisition unit  31 , the heat load learning unit  32 , the stagnation prevention control start timing estimation unit  33 , the device control unit  34 , and the data holding unit  35 . In the case where the controller  130  has a configuration substantially equal to the configuration of the controller  30  according to Embodiment 2, as shown in  FIG. 8 , the controller  130  includes the data acquisition unit  31 , the heat load learning unit  32 , the stagnation prevention control start timing estimation unit  33 , the device control unit  34 , the data holding unit  35 , the outside air temperature learning unit  36 , and the stagnation prevention control required time period calculation unit  37 . 
     As described above, the air-conditioning system  100  according to Embodiment 3 has the configuration where the function of performing the stagnation prevention control for the air-conditioning device  1  described in Embodiments 1 and 2 is provided to the management device  120 , which is different from the air-conditioning devices  110 . 
     As described above, in the air-conditioning system  100  according to Embodiment 3, the controller  130  that performs the stagnation prevention control is provided to the management device  120  that manages the one or the plurality of air-conditioning devices  110 . With such a configuration, in the same manner as Embodiments 1 and 2, it is possible to reduce power consumption during a period in which the operation of the compressor  11  of the air-conditioning device  110  is stopped. Further, in Embodiment 3, the controller  130  is provided separately from the air-conditioning devices  110  and hence, the stagnation prevention control can also be performed on an air-conditioning device that is already installed. 
     REFERENCE SIGNS LIST 
       1 ,  110 : air-conditioning device,  10 : outdoor unit,  11 : compressor,  12 : refrigerant flow passage switching device,  13 : outdoor heat exchanger,  14 : expansion valve,  15 : outside air temperature sensor,  16 : heating means,  20 : indoor unit,  21 : indoor heat exchanger,  22 : indoor temperature sensor,  30 ,  130 : controller,  31 : data acquisition unit,  32 : heat load learning unit,  33 : stagnation prevention control start timing estimation unit,  34 : device control unit,  35 : data holding unit,  36 : outside air temperature learning unit,  37 : stagnation prevention control required time period calculation unit,  41 : processing circuit,  51 : processor,  52 : memory,  100 : air-conditioning system,  120 : management device