Control method of clothes dryer

A dryer comprising:

• a main body that defines an input port configured to receive laundry;
• a drum rotatably installed in the main body;
• a driving motor configured to provide rotation power to the drum;
• a fan configured to cause flow of air to the drum;
• a heat pump system configured to heat air and to supply heated air to the drum, the heat pump system comprising a condenser, an evaporator, and a compressor;
• an outer air temperature sensor configured to detect an outer air temperature outside of the dryer;
• and
• a control unit configured to control operation of the dryer,
• wherein the control unit is configured to:
• receive a selection of an operation mode among a plurality of operation modes, the plurality of operation modes corresponding to a plurality of initial driving frequencies of the compressor that are different from one another,
• compare the outer air temperature to a reference temperature,
• based on the outer air temperature being greater than or equal to the reference temperature, determine that a driving environment of the dryer corresponds to a room temperature environment,
• based on a determination that the driving environment corresponds to the room temperature environment, perform the selected operation mode;
• based on the outer air temperature being less than the reference temperature, determine that the driving environment of the dryer corresponds to a low temperature environment, and
• based on a determination that the driving environment corresponds to the low temperature environment, perform a first mode among the plurality of operation modes, the first mode corresponding to a highest initial driving frequency among the plurality of initial driving frequencies of the compressor.