Air-conditioner having a dual-refrigerant cycle

An air-conditioner having a dual-refrigerant cycle comprising:

• a primary refrigerant circuit which includes a first compressor, an outdoor heat exchanger connected to the first compressor and heat-exchanged with outdoor air, and an expansion valve for expanding a refrigerant;
• a secondary refrigerant circuit which includes an indoor heat exchanger heat-exchanged with indoor air, and a second compressor connected to the indoor heat exchanger for circulating the refrigerant;
• and
• a heat exchange unit disposed between the primary refrigerant circuit and the secondary refrigerant circuit to perform heat exchange therebetween,
• wherein in a cooling operation, the refrigerant in the primary refrigerant circuit, having been compressed in the first compressor, is sucked back to the first compressor for circulation sequentially via the outdoor heat exchanger, the expansion valve and the heat exchange unit,
• wherein in the cooling operation, the refrigerant in the secondary refrigerant circuit, having been compressed in the second compressor, is sucked back to the second compressor for circulation sequentially via the heat exchange unit and the indoor heat exchanger,
• wherein the refrigerant in the primary refrigerant circuit and the refrigerant in the secondary refrigerant circuit are introduced into the heat exchange unit in the same direction and discharged out of the heat exchange unit in the same direction during the cooling operation,
• wherein the primary refrigerant circuit further includes a first four-way valve connected to a discharge side of the first compressor to change a flow of the refrigerant, and the second refrigerant circuit further includes a second four-way valve connected to a discharge side of the second compressor to change a flow of the refrigerant,
• wherein in a heating operation, the refrigerant in the primary refrigerant circuit, having been compressed in the first compressor, is sucked back to the first compressor for circulation sequentially via the first four-way valve, the heat exchange unit, the expansion valve, the outdoor heat exchanger and the first four-way valve,
• wherein in the heating operation, the refrigerant in the secondary refrigerant circuit, having been compressed in the second compressor, is sucked back to the second compressor for circulation sequentially via the second four-way valve, the indoor heat exchanger, the heat exchange unit and the second four-way valve, and
• wherein the refrigerant in the primary refrigerant circuit and the refrigerant in the secondary refrigerant circuit are introduced into the heat exchange unit in the same direction and discharged out of the heat exchange unit in the same direction during the heating operation.