Air-conditioning system including a master and slave configuration

1. An air conditioning system comprising:

air conditioners each including a refrigerant circuit configured to achieve a refrigeration cycle and a corresponding one of internal controllers configured to control operation; and

external controllers provided one by one correspondingly to the air conditioners and each communicably connected to one of the internal controllers in a corresponding one of the air conditioners, wherein

each of the external controllers is configured to execute a command generating operation of individually generating an operation command to the corresponding one of the air conditioners,

each of the internal controllers in each of the air conditioners is configured to control operation of a corresponding one of the air conditioners in accordance with the operation command received from one of the external controllers connected to the corresponding one of the internal controllers,

the external controllers are configured to communicate with each other to constitute an external control system,

the external control system is configured to

cause one of the external controllers to function as a master controller configured to execute the command generating operation and transmit the operation command generated through the command generating operation to the corresponding one of the internal controllers in the corresponding one of the air conditioners and remaining ones of the external controllers, and

cause the remaining ones of the external controllers, other than the one of the external controllers functioning as the master controller, to function as sub controllers, each configured to, without executing the command generating operation, transmit the operation command received from the one of the external controllers functioning as the master controller to the corresponding one of the internal controllers in the corresponding one of air conditioners,

the external control system is further configured to,

upon satisfaction of a predetermined malfunction condition indicating that any of the external controllers functioning as the sub controllers cannot receive the operation command,

cause one of the external controllers functioning as the sub controllers to switch to become the master controller, and

cause remaining ones of the external controllers, other than the one of the external controllers functioning as the master controller upon satisfaction of the malfunction condition and the one of the external controllers switched to the master controller due to satisfaction of the malfunction condition, to remain functioning as the sub-controllers, and

cause the switched master controller to execute the command generating operation and transmit the operation command generated through the command generating operation to the remaining ones of the external controllers functioning as the sub controllers, and

cause each of the remaining ones of the external controllers functioning as the sub controllers to transmit the operation command received to the corresponding one of the internal controllers in the corresponding one of air conditioners, wherein

each of the external controllers functioning as the sub controllers is configured to determine whether or not the malfunction condition is satisfied.

2. The air conditioning system according to claim 1 , wherein

the external controllers are configured to store unique identification numbers, and

the external control system is configured to cause one storing a smallest one of the identification numbers out of the external controllers functioning as the sub controllers, upon satisfaction of the malfunction condition, to switch to become the master controller.

3. The air conditioning system according to claim 1 , wherein

each of the external controllers is configured to

acquire operation data indicating an operating state of the corresponding one of the air conditioners from the corresponding one of the internal controllers in the corresponding one of the air conditioners, transmit the operation data thus acquired to the remaining ones of the external controllers, and

execute, when functioning as the master controller, the command generating operation with use of the operation data acquired from the corresponding one of the internal controllers in the corresponding one of the air conditioners and the operation data received from the external controllers functioning as the sub-controllers.

4. The air conditioning system according to claim 1 , wherein

in the external control system, each of the external controllers transmits and receives information via wireless communication, to achieve wireless communication between the one of the external controllers functioning as the master controller and the external controllers functioning as the sub-controllers.

5. The air conditioning system according to claim 2 , wherein

each of the external controllers is configured to

acquire operation data indicating an operating state of the corresponding one of the air conditioners from the corresponding one of the internal controllers in the corresponding one of the air conditioners, transmit the operation data thus acquired to the remaining ones of the external controllers, and

execute, when functioning as the master controller, the command generating operation with use of the operation data acquired from the corresponding one of the internal controllers in the corresponding one of the air conditioners and the operation data received from the external controllers functioning as the sub-controllers.

6. The air conditioning system according to claim 2 , wherein

each of the external controllers is configured to

transmit a corresponding identification number to the remaining ones of the external controllers upon the malfunction condition being satisfied, and

compare the corresponding identification number with the identification numbers received from the remaining ones of the external controllers to determine whether to operate as the master controller or as one of the sub controllers.