Bus heating system and method of controlling the same

A method of heating an interior of a vehicle by controlling a main heater unit configured to heat an internal bottom area of the vehicle and an auxiliary heater unit configured to heat an internal roof area of the vehicle, the method comprising:

• starting to heat the interior of the vehicle;
• and
• controlling, by a controller, operations of the main heater unit and the auxiliary heater unit in conjunction with each other based on a set target internal temperature (Ttarget), a measured outside air temperature (Toutside), a measured internal temperature (Troom), and a main-heater-unit refrigerant temperature (Trefrigerants),
• wherein the controlling operations of the main heater unit and the auxiliary heater unit includes:
• implementing a first mode in which the main heater unit is turned on and the target internal temperature (Ttarget) is compared with the measured internal temperature (Troom) based on the measured outside air temperature (Toutside) to control whether to operate the auxiliary heater unit;
• implementing a second mode in which the main heater unit is turned off when the measured internal temperature (Troom) reaches the target internal temperature (Ttarget)+α° C. in a state where the main heater unit and the auxiliary heater unit are ON in the first mode, wherein the α is a real number, wherein the second mode is implemented by the controller only once for a first time;
• implementing a third mode in which the auxiliary heater unit is turned off when the measured internal temperature (Troom) reaches the target internal temperature (Ttarget)+β° C. in the second mode, and the auxiliary heater unit is turned on when the measured internal temperature (Troom) reaches the target internal temperature (Ttarget)+α° C. in a state where the auxiliary heater unit is OFF where the α is smaller than β, wherein the β is a real number, wherein ON and OFF operations of the auxiliary heater unit are alternately repeated while the measured internal temperature (Troom) is maintained within a predetermined range in response to a condition of the measured internal temperature (Troom) and the target internal temperature (Ttarget);
• and
• implementing a fourth mode in which the main heater unit is turned on when the main-heater-unit refrigerant temperature (Trefrigerants) is 30° C. or less in the third mode, and the main heater unit is turned off when the main-heater-unit refrigerant temperature (Trefrigerants) is 40° C. or higher in a state where the main heater unit is ON, wherein ON and OFF operations of the main heater unit are alternately repeated while the main-heater-unit refrigerant temperature (Trefrigerants) is maintained within a predetermined range in response to the main-heater-unit refrigerant temperature (Trefrigerants).