Heat pump system for a vehicle

A heat pump system for a vehicle, comprising:

• a compressor configured to compress a refrigerant circulating the heat pump system;
• a heat, ventilation, and air condition (HVAC) module including an internal condenser, an evaporator connected to the compressor via a refrigerant line, and an opening/closing door configured to adjust air having passed through the evaporator to be selectively introduced into the internal condenser based on a cooling mode or a heating mode of the vehicle;
• a heat-exchanger connected to the internal condenser via the refrigerant line;
• a first expansion valve provided in the refrigerant line between the heat-exchanger and the evaporator;
• a first connection line including:
• a first end connected to the refrigerant line between the heat-exchanger and the first expansion valve, and
• a second end connected to the refrigerant line between the evaporator and the compressor;
• a chiller provided in the first connection line so as to adjust a temperature of a coolant by exchanging heat between the refrigerant and the coolant introduced selectively;
• and
• a sub-heat-exchanger provided in the refrigerant line, and configured to exchange heat between the refrigerant having passed through an internal condenser or the heat-exchanger and the refrigerant having passed through at least one of the evaporator and the chiller so as to increase a condensation amount by increasing sub-cooling of the refrigerant.