Heat-pump system

1. A heat-pump system comprising:

a first outdoor unit comprising a first compressor, a first outdoor heat exchanger, a first switch value, a first expansion device, a first common suction line of said first compressor and a first oil separator;

a second outdoor unit comprising a second compressor, a second outdoor heat exchanger, a second switch valve, a second expansion device, a second common suction line of said second compressor and a second oil separator;

a compressor side oil balance pipe coupled to the first compressor, said compressor side oil balance pipe extends from the first compressor and is fluidly coupled to the second common suction line of second compressor, the compressor side oil balance pipe allowing oil in the first compressor to be recovered by the second compressor; and

an oil separator side oil balance pipe coupled to the second oil separator, said oil separator side oil balance pipe extends from the second oil separator and is fluidly coupled to the first common suction line of the first compressor,

wherein the first compressor includes a first oil balance hole formed in a casing, one end of the compressor side oil balance pipe being coupled to the first oil balance hole so as to recover the oil above a height of the first oil balance hole that is stored in the first compressor to the second outdoor unit, and

wherein the second oil separator includes a second oil balance hole formed in an oil separation casing, one end of the oil separator side oil balance pipe being coupled to the second oil balance hole so as to recover the oil above the height of the second oil balance hole that is stored in the second oil separator to the first outdoor unit.

2. The heat-pump system according to claim 1 , wherein the first outdoor unit includes a first gas-liquid separator provided at an inlet side of the first compressor, wherein the first gas-liquid separator separates gaseous refrigerant from refrigerant and supplies the gaseous refrigerant to the first compressor; and

a first gas-liquid separation, oil balance pipe extended from the first gas-liquid separator to the first common suction pipe.

3. The heat-pump system according to claim 1 , further comprising a first valve device located in the compressor side oil balance pipe for regulating a flow of oil in the compressor side oil balance pipe.

4. The heat-pump system according to claim 1 , wherein the second outdoor unit includes a gas liquid separator provided at an inlet side of the second compressor, wherein the gas-liquid separator separates gaseous refrigerant from refrigerant and supplies the gaseous refrigerant to the second compressor; and

a gas liquid separation oil balance pipe extended from the gas liquid separator to the second common suction pipe.

5. The hexa pump system according to claim 1 , further comprising a valve device located in the oil separator side oil balance pipe for regulating a flow of oil in the oil separator side oil balance pipe.

6. The heat-pump system according to claim 1 , wherein the first outdoor unit includes a first oil separation pipe extending from the first oil separator to the first compressor, and

wherein the second outdoor unit includes a second oil separation pipe extending from the second oil separator to the second compressor.

7. The heat-pump system according to claim 6 , wherein the first outdoor unit in a first oil separation pipe valve located in the first oil separation pipe for regulating a flow of oil in the first oil separation pipe, and

wherein the second outdoor unit includes a second on separation pipe valve located in the second oil separation pipe for regulating a flow of oil in the second oil separation pipe.

8. The heat-pump system according to claim 1 , wherein the first compressor is an electromotive compressor, and wherein the second compressor is a gas engine compressor.

9. The heat-pump system according to claim 1 , further comprising:

the first common suction of refrigerant to the first compressor, the oil separator side oil balance pipe being coupled to the first common suction pipe;

a first gas-liquid separator provided at an inlet side of the first compressor, the first gas-liquid separator being configured to separate gaseous refrigerant from refrigerant and supply the gaseous refrigerant to the first compressor;

a first gas-liquid separation oil balance pipe extended from the first gas-liquid separator to the first common suction pipe;

the second common suction pipe guiding suction of refrigerant to the second compressor the compressor side oil balance pipe being coupled to the second common suction pipe;

a second gas-liquid separator provided at an inlet side of the second compressor, the second gas-liquid separator being configured to separate gaseous refrigerant from refrigerant and supply the gaseous refrigerant to the second compressor; and

a second gas-liquid separation oil balance pipe extended from the second gas-liquid separator to the second common suction pipe.

10. The heat-pump system according to claim 9 , further comprising:

a first valve device located in the compressor side oil balance pipe for regulating a flow of oil in the compressor side oil balance pipe;

a second valve device located in the oil separator side oil balance pipe for regulating a flow of oil in the oil separator side oil balance pipe;

a first oil separation pipe extending from the first oil separator to the first compressor;

a first oil separation pipe valve located in the first oil separation pipe for regulating a flow of oil in the first oil separation pipe;

a second oil separation pipe extending from the second oil separator to the second compressor; and

a second oil separation pipe valve located in the second oil separation pipe for regulating a flow of oil in the second oil separation pipe.