Patent Description:
A heat-pump system is a system that includes a heat pump cycle capable of performing a cooling or heating operation. The heat pump system may be linked to a hot water supply device or a cooling/heating device. That is, it is possible to produce hot water by using a heat source obtained through a heat exchange between refrigerant for the heat pump cycle and a certain heat storage medium or perform air conditioning for cooling and heating.

The heat pump cycle includes a compressor for compressing refrigerant, a condenser for condensing refrigerant compressed by the compressor, an expansion device for decompressing refrigerant condensed by the condenser and an evaporator for evaporating decompressed refrigerant.

The heat-pump system may be an electrical heat-pump system or a gas heat-pump system.

A compressor having a relatively small or intermediate capacity operates in the electrical heat-pump system and the compressor may operate with an electric motor.

On the contrary, the gas heat-pump system needs a compressor having a large capacity for an industrial facility or for conditioning air in a large building, rather than for a typical home. That is, in order to operate a compressor for compressing a lot of refrigerant to a gas having a high temperature and a high pressure, the gas heat-pump system may be used as a system that uses a gas engine instead of the electric motor.

The gas heat-pump system includes an engine that uses a mixture (hereinafter, referred to as "mixed fuel") of fuel and air to generate power. As an example, the engine may include a cylinder to which the mixed fuel is supplied and a piston that is provided to be capable of moving in the cylinder.

According to such a typical heat-pump system, since oil is not easily separated from refrigerant circulating during the heat pump cycle, there is a limitation in that the compressor lacks oil.

<CIT> relates to a multiroom air-conditioning apparatus, wherein refrigerant flow between plural outdoor side units is controlled so that abnormality, i.e. lack or excess, of refrigerant amount in an outdoor side unit in operation is redressed. Moreover, <CIT> discloses a heat-pump system according to the preamble of claim <NUM>.

Any references in the following description to embodiments, objects, aspects and/or examples which are not covered by the appended claims are considered as not being part of the present invention.

In an embodiment according to claim <NUM>, a heat-pump system includes a first outdoor unit including an electromotive compressor and a first oil separator; a second outdoor unit including a gas engine compressor and a second oil separator; a compressor side oil balance pipe coupled to the electromotive compressor and coupled to the second outdoor unit, the compressor side oil balance pipe allowing oil in the electromotive compressor to be recovered by the gas engine compressor; and an oil separator side oil balance pipe coupled to the second oil separator and coupled to the first outdoor unit, the oil separator side oil balance pipe allowing oil in the second oil separator to be recovered by the electromotive compressor.

The heat-pump system further includes a first common suction pipe guiding suction of refrigerant to the electromotive compressor, wherein the oil separator side oil balance pipe is coupled to the first common suction pipe.

The heat-pump system further includes a second common suction pipe guiding suction of refrigerant to the gas engine compressor, wherein the compressor side oil balance pipe is coupled to the second common suction pipe.

According to the heat-pump system of the embodiment, there is an advantage in that it is possible to easily recover oil when the compressor operates, because oil separated from the oil separator or the compressor is supplied to the common suction pipe of the compressor.

In particular, when the outdoor unit includes both the electromotive compressor and the gas engine compressor, there is an advantage in that it is possible to prevent oil from becoming excessively stored in the electromotive compressor and the gas engine compressor from experiencing a lack of oil depending on the operation state of the compressor.

Also, since the electromotive compressor includes the oil balance hole and the compressor side oil balance pipe is extended from the oil balance hole to the common suction pipe of the oil balance hole, oil having a height equal to or higher than the oil balance hole of the electromotive compressor may be effectively distributed to the gas engine compressor.

Also, since the first outdoor unit including the electromotive compressor is linked to the second outdoor unit including the gas engine compressor in order to distribute oil, there is an advantage in that it is possible to prevent oil imbalance between a plurality of outdoor units.

According to the heat-pump system of the embodiment, it is possible to easily recover oil when the compressor operates, because oil separated from the oil separator or the compressor is supplied to the common suction pipe of the compressor.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

<FIG> is a cycle diagram showing a configuration of a heat-pump system according to a first embodiment not forming part of the invention.

Referring to <FIG>, a heat-pump system <NUM> according to the first embodiment includes a plurality of parts that configure a refrigerant cycle as an air conditioning system. More particularly, the refrigerant cycle includes first and second compressors <NUM> and <NUM> compressing refrigerant and a flow switch valve <NUM> switching the direction of refrigerant compressed by the first and second compressors.

The gas heat pump system <NUM> further includes an outdoor heat exchanger <NUM> and an indoor heat exchanger <NUM>. The outdoor heat exchanger <NUM> may be arranged inside an outdoor unit arranged outdoors and the indoor heat exchanger <NUM> may be arranged inside an indoor unit <NUM> arranged indoors. Refrigerant passing through the flow switch valve <NUM> flows into the outdoor heat exchanger <NUM> or the indoor heat exchanger <NUM>.

Components of the system in <FIG> excluding the indoor heat exchanger <NUM> and an indoor expansion device <NUM> may be arranged outdoors or inside the outdoor unit. The outdoor unit and the indoor unit <NUM> may be connected by a connection pipe <NUM>.

More particularly, when the system <NUM> operates in a cooling operation mode, refrigerant passing through the flow switch valve <NUM> is condensed at the outdoor heat exchanger <NUM> and then flows toward the indoor heat exchanger <NUM>. On the contrary, when the system <NUM> operates in a heating operation mode, refrigerant passing through the flow switch valve <NUM> is condensed at the indoor heat exchanger <NUM> and then flows toward the outdoor heat exchanger <NUM>.

On one side of the outdoor heat exchanger <NUM>, an outdoor expansion device <NUM> for decompressing refrigerant is arranged. The outdoor expansion device <NUM> includes an electronic expansion valve (EEV). When the system <NUM> operates in the heating operation mode, refrigerant passing through the indoor heat exchanger <NUM> decompresses at the outdoor expansion device <NUM> and then may be evaporated from the outdoor heat exchanger <NUM>.

The system <NUM> further includes a refrigerant pipe <NUM> that connects the compressors <NUM> and <NUM>, the outdoor heat exchanger <NUM> and the indoor unit <NUM> to guide the flow of refrigerant.

A configuration of the system <NUM> is described based on a cooling operation mode.

Refrigerant compressed by the first and second compressors <NUM> and <NUM> may flow into the outdoor heat exchanger <NUM> to heat-exchange with external air (condense). An outdoor fan <NUM> moving external air is provided on one side of the outdoor heat exchanger <NUM>.

Refrigerant passing through the outdoor heat exchanger <NUM> flows toward the indoor unit <NUM>, decompresses at the indoor expansion device <NUM> and then is evaporated from the indoor heat exchanger <NUM>. The indoor expansion device <NUM> may be installed inside the indoor unit <NUM> and include the EEV.

Refrigerant evaporated from the indoor heat exchanger <NUM> flows into a secondary heat exchanger <NUM> via the flow switch valve <NUM>. The secondary heat exchanger <NUM> is a heat exchanger that may perform heat exchange between evaporated refrigerant having a low pressure and cooling water having a high temperature and include a plate-type heat exchanger.

Since refrigerant evaporated from the indoor heat exchanger <NUM> may absorb heat while passing through the secondary heat exchanger <NUM>, evaporation efficiency may be improved. A gas-liquid separator <NUM> for separating gaseous refrigerant from evaporated refrigerant is provided on the exit side of the secondary heat exchanger <NUM>.

Refrigerant passing through the secondary heat exchanger <NUM> is gas-liquid separated at the gas-liquid separator <NUM>, and separated gaseous refrigerant may branch into the first and second compressors <NUM> and <NUM> and may be suctioned into the first and second compressors <NUM> and <NUM>.

The heat-pump system <NUM> further includes a cooling-water flow path <NUM> that guides the flow of cooling water. In addition, a cooling-water pump <NUM> generating the flow of cooling water may be installed on the cooling-water flow path <NUM>.

When the cooling-water pump <NUM> operates, cooling water may flow in the cooling-water flow path <NUM> and pass through the secondary heat exchanger <NUM>. As described, cooling water may perform heat exchanger with refrigerant in the secondary heat exchanger <NUM> and thus be cooled.

The heat-pump system <NUM> may include an engine <NUM> that generates power for operating the first compressor <NUM>. The first compressor <NUM> may be a gas engine compressor that operates by the driving power of the engine <NUM>. On the contrary, the second compressor <NUM> may be an electromotive compressor that operates by an electric motor.

The cooling-water flow path <NUM> passes through the engine <NUM>. Cooling water may cool the engine <NUM> while passing through the engine <NUM>. That is, while flowing in the cooling-water flow path <NUM>, cooling water may cool the engine <NUM> and heat refrigerant in the secondary heat exchanger <NUM>.

<FIG> shows an oil recovery structure of a heat-pump system according to a first embodiment not forming part of the invention.

Referring to <FIG>, the heat-pump system <NUM> according to the first embodiment includes the gas/liquid separator <NUM> into which evaporated re- frigerant flows, the first and second compressors <NUM> and <NUM> into which gaseous refrigerant separated by the gas/liquid separator <NUM> flows, and an oil separator <NUM> that is provided on the discharge sides of the first and second compressors <NUM> and <NUM> and separates oil mixed with compressed refrigerant.

An oil separator discharge pipe <NUM> through which refrigerant having no oil due to the separation of oil by the oil separator <NUM> is discharged is extended to one side of the oil separator <NUM>.

The first compressor <NUM> is a gas engine compressor and may be coupled to the engine <NUM>. In addition, the second compressor <NUM> is an electromotive compressor and may be connected in parallel to the first compressor <NUM>.

The second compressor <NUM> is a compressor useful for dealing with low load and has an advantage in that operation efficiency is high. In addition, the first compressor <NUM> may be understood as a large-capacity compressor that may be used when load is equal to or greater than a set load.

A common suction pipe <NUM> is extended to the discharge side of the gas/liquid separator <NUM>. The common suction pipe <NUM> may branch into a first branch pipe <NUM> and a second branch pipe <NUM>. The first branch pipe <NUM> may be connected to the suction side of the first compressor <NUM> and the second branch pipe <NUM> may be connected to the suction side of the second compressor <NUM>.

Gaseous refrigerant discharged from the gas/liquid separator <NUM> may flow in the common suction pipe <NUM>, branch into the first and second branch pipes <NUM> and <NUM>, and be suctioned by the first and second compressors <NUM> and <NUM>. The common suction pipe <NUM> and the first and second branch pipes <NUM> and <NUM> may be understood as "suction flow paths" for enabling the first and second compressors <NUM> and <NUM> to suction refrigerant.

Refrigerant compressed by the first compressor <NUM> and the second compressor <NUM> may join at a first join portion <NUM> and flow into the oil separator <NUM>. The first join portion <NUM> is understood as a point at which the discharge-side pipe of the first compressor <NUM> and the discharge-side pipe of the second compressor <NUM> join.

Refrigerant flowing into the oil separator <NUM> may include oil that exists in the first and second compressors <NUM> and <NUM>. Oil mixed with the refrigerant may be separated inside the oil separator <NUM> and recovered by the first and second compressors <NUM> and <NUM>.

In addition, refrigerant separated from the oil flows to the flow switch valve <NUM> (see <FIG>) through the oil-separator discharge pipe <NUM>. In <FIG>, a refrigerant flow is indicated by dotted arrows and an oil flow is indicated by solid arrows.

An oil separation pipe <NUM> is coupled to the oil separator <NUM>, through which oil separated by the oil separator <NUM> is discharged. As an example, the oil-separator discharge pipe <NUM> is coupled to the upper part of the oil separator <NUM> and the oil separation pipe <NUM> is coupled to the lower part of the oil separator <NUM>.

A first flow regulating unit <NUM> for regulating the flow of oil flowing in the oil separation pipe <NUM> is installed at the oil separation pipe <NUM>. As an example, the first flow regulating unit <NUM> may include a capillary tube.

The oil separation pipe <NUM> may be coupled to the common suction pipe <NUM>. Thus, the oil in the oil separation pipe <NUM> flows into the common suction pipe <NUM> and may be suctioned by the first and second compressors <NUM> and <NUM> via the first and second branch pipes <NUM> and <NUM>, respectively.

A compressor's balance pipe <NUM> for discharging oil stored in the second compressor <NUM> is coupled to the second compressor <NUM>.

More particularly, the second compressor <NUM> includes a casing 112a and an oil balance hole 112b that is formed in the casing 112a. The oil balance hole 112b may be formed at a set height from the lower end of the casing 112b. The set height may be a height corresponding to the optimal height of oil.

The compressor side oil balance pipe <NUM> is coupled to the oil balance hole 112b and extended to the oil separation pipe <NUM>. That is, one end of the compressor side oil balance pipe <NUM> may be coupled to the oil balance hole 112b and the other end may be coupled to the oil separation pipe <NUM>.

A first valve <NUM> and a second flow regulating unit <NUM> for regulating the flow of oil flowing in the compressor side oil balance pipe <NUM> may be installed at the compressor side oil balance pipe <NUM>. The second flow regulating unit <NUM> may be installed on one side of the first valve <NUM>. As an example, the first valve <NUM> includes a solenoid valve enabling an on/off operation, and the second flow regulating unit <NUM> may include a capillary tube. As another example, the first valve <NUM> may include an EVV that may regulate an open/close operation.

The compressor side oil balance pipe <NUM> is coupled to a second join portion <NUM> of the oil separation pipe <NUM>.

The second join portion <NUM> is a portion of the oil separation pipe <NUM> and is understood as a point at which the compressor side oil balance pipe <NUM> is connected.

While oil stored in the second compressor <NUM> has a height equal to or higher than the oil balance hole 112b, the oil in the second compressor <NUM> is discharged to the compressor side oil balance pipe <NUM>. In addition, the flow of the oil in the compressor side oil balance pipe <NUM> is regulated in the process of passing through the second flow regulating unit <NUM>, and the oil in the compressor side oil balance pipe <NUM> and the oil in the oil separation pipe <NUM> join.

In addition, oil after joining flows into the common suction pipe <NUM> and is mixed with refrigerant discharged from the gas/liquid separator <NUM>. In addition, mixed refrigerant and oil branch into the first and second branch pipes <NUM> and <NUM> to be suctioned by the first compressor <NUM> and the second compressor <NUM>.

The gas/liquid separator <NUM> is coupled to a gas/liquid separation oil balance pipe <NUM> that guides oil stored in the gas/liquid separator <NUM> to the common suction pipe <NUM>. As an example, the gas/liquid oil balance pipe <NUM> may be coupled to the lower part of the gas/liquid separator <NUM>. On the contrary, a pipe from which gaseous refrigerant separated by the gas/liquid separator <NUM> may be coupled to the upper part of the gas/liquid separator <NUM>.

A second valve <NUM> for regulating the flow of oil is installed at the gas/liquid separation oil balance pipe <NUM>. As an example, the second valve <NUM> includes a solenoid valve enabling an on/off operation. As another example, the second valve <NUM> may include an EVV that may regulate an open/close operation.

The gas/liquid separation oil balance pipe <NUM> is coupled to the common suction pipe <NUM>. Thus, when the second valve <NUM> is open, oil stored in the lower part of the gas/ liquid separator <NUM> may be discharged to the gas/liquid separation oil balance pipe <NUM> and flow into the common suction pipe <NUM>.

When the first compressor <NUM> is a gas engine compressor and the second compressor <NUM> is an electromotive compressor, a small space (reservoir) that may store oil is formed inside the first compressor <NUM> and a relatively large space that may store oil is formed inside the second compressor <NUM>.

In this case, when the first and second compressors <NUM> and <NUM> simultaneously operate, there may be a tendency for relatively more oil to be stored in the second compressor <NUM>. As an example, the height of the oil in the second compressor <NUM> may be equal to or higher than the oil balance hole 112b. That is, there may be a limitation in that oil is excessively stored in the second compressor <NUM> and the first compressor <NUM> lacks oil.

Thus, the present embodiment provides the second compressor <NUM> with the oil balance hole 112b and extends the compressor side oil balance pipe <NUM> from the oil balance hole 112b to the oil separation pipe <NUM> so that oil stored in the second compressor <NUM> may be divided into the first and second compressors <NUM> and <NUM> and then restored.

In conclusion, the height of the oil of the second compressor <NUM> may decrease to a height corresponding to the oil balance hole 112b and a lack of oil in the first compressor <NUM> may also be solved. In the following, a control method of the heat-pump system according to the present invention is described with reference to the drawings.

<FIG> is a flowchart of the control method of a heat-pump system according to a first embodiment.

Referring to <FIG>, when the heat-pump system <NUM> according to the first embodiment operates, it is possible to recognize whether the first compressor <NUM> or the second compressor <NUM> operates. As described above, the first compressor <NUM> and the second compressor <NUM> may be selectively operated depending on an operation load.

As an example, when a desired operation load is equal to or less than a set load, only the second compressor <NUM> may operate, and when the desired operation load is equal to or more than the set load, both the first and second compressors <NUM> and <NUM> may operate.

When only the second compressor <NUM> operates, gaseous refrigerant discharged from the gas/liquid separator <NUM> flows into the second compressor <NUM> via the second branch pipe <NUM>. In addition, oil may flow into the common suction pipe <NUM> via the oil separation pipe <NUM> and the compressor side oil balance pipe <NUM> and may be recovered by the second compressor <NUM> via the second branch pipe <NUM>.

On the contrary, when both the first and second compressors <NUM> and <NUM> operate, gaseous refrigerant discharged from the gas/liquid separator <NUM> branches and flows into the first and second compressors <NUM> and <NUM> via the first and second branch pipes <NUM> and <NUM>. In addition, oil may flow into the common suction pipe <NUM> via the oil separation pipe <NUM> and the compressor side oil balance pipe <NUM> and may branch into the first and second compressors <NUM> and <NUM> via the first and second branch pipes <NUM> and <NUM> and then recovered, as shown in steps Sil and S12.

More particularly, when both the first and second compressors <NUM> and <NUM> operate, the first valve <NUM> may be open for a set time. When the first valve <NUM> is open, oil may flow into the common suction pipe <NUM> via the compressor side oil balance pipe <NUM> and the oil separation pipe <NUM> and may be divided into the first and second compressors <NUM> and <NUM> via the first and second branch pipes <NUM> and <NUM> and then recovered.

In this case, since the second valve <NUM> is also open, oil stored in the gas/liquid separator <NUM> may be recovered by the common suction pipe <NUM>.

When the set time elapses, the first valve <NUM> is turned off (closed) and thus an oil flow through the compressor side oil balance pipe <NUM> is restricted. The set time may be determined to a time sufficient to lower the height of oil stored in the second compressor <NUM> to be equal to or lower than the oil balance hole 112b in steps S13 and S14.

On the contrary, when all of the first and second compressors <NUM> and <NUM> do not operate, for example, when only the second compressor <NUM> operates, the first valve <NUM> maintains a closed state and thus recovery of oil stored in the second compressor <NUM> by the second compressor <NUM> is restricted in step S15.

<FIG> shows an oil recovery structure of a heat-pump system according to a second embodiment of the present invention.

Referring to <FIG>, the heat-pump system <NUM> according to the second embodiment of the present invention includes a plurality of outdoor units <NUM> and <NUM>.

The plurality of outdoor units <NUM> and <NUM> include the first outdoor unit <NUM> that generates an electronic heat pump cycle by the operation of an electromotive compressor and the second outdoor unit <NUM> that generates a gas heat pump cycle by the operation of gas engine compressors <NUM> and412.

The first outdoor unit <NUM> includes the electromotive compressor <NUM>, a first oil separator <NUM>, a flow switch valve <NUM>, a first outdoor heat exchanger <NUM>, a first outdoor expansion device <NUM> and a first gas-liquid separator <NUM>. Reference is made to the first embodiment for a complete understanding of the functions of these components.

The first outdoor unit <NUM> includes a first common suction pipe <NUM> that is extended from the exit side of the first gas-liquid separator <NUM> to the electromotive compressor <NUM> and guides the section of gaseous refrigerant to the electromotive compressor <NUM>.

The first outdoor unit <NUM> includes a first gas-liquid separation oil balance pipe <NUM> that is extended from the lower part of the first gas-liquid separator <NUM> to the first common suction pipe <NUM> and enables oil stored in the first gas-liquid separator <NUM> to be recovered by the electromotive compressor <NUM>.

In addition, a valve device <NUM> enabling an on/off operation in order to regulate the flow of oil may be installed at the first gas-liquid separation oil balance pipe <NUM>. The valve device <NUM> may include a solenoid valve or an electronic expansion valve.

The first outdoor unit <NUM> includes a first oil separation pipe <NUM> that is extended from the first oil separator <NUM> to the electromotive compressor <NUM>. Oil stored in the first oil separator <NUM> may be recovered by the electromotive compressor <NUM> through the first oil separation pipe <NUM>. In addition, a valve device (not shown) for regulating the flow of oil may be installed at the first oil separation pipe <NUM>.

The first outdoor unit <NUM> includes a compressor side oil balance pipe <NUM> that is extended from the electromotive compressor <NUM> to the second outdoor unit <NUM>.

More particularly, the electromotive compressor <NUM> includes a first oil balance hole <NUM> formed in a casing <NUM> and one end of the compressor side oil balance pipe <NUM> is coupled to the first oil balance hole <NUM>. In addition, the other end of the compressor side oil balance pipe <NUM> may be connected to a second common suction pipe <NUM> of the second outdoor unit <NUM>.

Thus, oil having a height equal to or higher than the first oil balance hole <NUM> among oil stored in the electromotive compressor <NUM> may be recovered by the second outdoor unit <NUM> through the compressor side oil balance pipe <NUM>.

In addition, a first outdoor unit side valve <NUM> and a first outdoor flow regulating unit <NUM> for regulating the flow of oil may be installed at the compressor side oil balance pipe <NUM>. As an example, the first outdoor unit side valve <NUM> may include a solenoid valve enabling an on/off operation and the first outdoor flow regulating unit <NUM> may include a capillary tube.

The second outdoor unit <NUM> includes a plurality of gas engine compressors <NUM> and <NUM>, a second oil separator <NUM>, a flow switch valve <NUM>, a second outdoor heat exchanger <NUM>, a second outdoor expansion device <NUM>, and a second gas-liquid separator <NUM>. Reference is made to the first embodiment for a complete understanding of the functions of these components.

The plurality of gas engine compressors <NUM> and <NUM> may be coupled to gas engines <NUM> and <NUM>, respectively, and receive driving power therefrom.

The second outdoor unit <NUM> includes a second common suction pipe <NUM> that is extended from the exit side of the second gas-liquid separator <NUM>, and first and second branch pipes <NUM> and <NUM> that branch from the second common suction pipe <NUM> and are extended to the plurality of gas engine compressors <NUM> and <NUM>.

The first branch pipe <NUM> may be connected to the suction side of the first gas engine compressor <NUM> of the plurality of gas engine compressors <NUM> and <NUM> and the second branch pipe <NUM> may be connected to the suction side of the gas engine compressor <NUM>.

The second outdoor unit <NUM> includes a second gas-liquid separation oil balance pipe <NUM> that is extended from the lower part of the second gas-liquid separator <NUM> and to the second common suction pipe <NUM> and enables oil stored in the second gas-liquid separator <NUM> to be recovered by the first and second gas engine compressors <NUM> and <NUM>.

In addition, a valve device <NUM> enabling an on/off operation may be installed at the second gas-liquid separation oil balance pipe <NUM> in order to regulate the flow of oil. The valve device <NUM> may include a solenoid valve or an electronic expansion valve. The valve device <NUM> may be called a "first gas-liquid separation valve" and the valve device <NUM> may be called a "second gas-liquid separation valve".

The second outdoor unit <NUM> includes an oil separation oil balance pipe <NUM> that is extended from the second oil separator <NUM> to the first outdoor unit <NUM>. The oil separation oil balance pipe <NUM> is connected to the first common suction pipe <NUM> of the first outdoor unit <NUM>.

More particularly, the second oil separator includes oil separation casing <NUM> and a second oil balance hole <NUM> that is formed at a set height from the lower end of the oil separation casing <NUM>.

One end of the oil separation oil balance pipe <NUM> is coupled to the second oil balance hole <NUM>, and the other end of the oil separation oil balance pipe is coupled to the first common suction pipe <NUM>. Thus, oil having a height equal to or higher than the oil balance hole <NUM> may be recovered by the first outdoor unit <NUM> through the oil separation oil balance pipe <NUM>.

In addition, a second outdoor unit side valve <NUM> and a second outdoor flow regulating unit <NUM> for regulating the flow of oil may be installed at the oil separation oil balance pipe <NUM>. As an example, the second outdoor unit side valve <NUM> includes a solenoid valve enabling an on/off operation and the second outdoor flow regulating unit <NUM> may include a capillary tube.

The second outdoor unit <NUM> includes an oil separation discharge pipe <NUM> that is extended from the second oil separator <NUM> and discharges refrigerant from which oil has been separated. The oil separation discharge pipe <NUM> is connected to the flow switch valve <NUM>.

The second outdoor unit <NUM> includes a second oil separation pipe <NUM> that is extended from the lower part of the second oil separator <NUM> and guides the discharge of oil, and first and second oil branch pipes <NUM> and <NUM> that are branched from the second oil separation pipe <NUM>.

The second oil separation pipe <NUM> may be coupled to the second oil separator <NUM> at a location lower than the second oil balance hole <NUM>.

The first oil branch pipe <NUM> is coupled to the first gas engine compressor <NUM> and guides the recovery of oil, and the second oil branch pipe <NUM> is coupled to the second gas engine compressor <NUM> and guides the recovery of oil.

In addition, an oil branch valve <NUM> and an oil branch flow regulating unit <NUM> for regulating the flow of oil may be installed at the first and second oil branch pipes <NUM> and <NUM>. As an example, the oil branch valve <NUM> may include a solenoid valve enabling an on/off operation and the oil branch flow regulating unit <NUM> may include a capillary tube.

The flow of oil under such a configuration is simply described.

When the first outdoor unit <NUM> or the electromotive compressor operates and the first outdoor unit side valve <NUM> opens, the flow of oil stored in the electromotive compressor <NUM> is regulated at the first outdoor flow regulating unit <NUM> and the oil flows into the second common suction pipe <NUM> of the second outdoor unit <NUM>.

In addition, the oil flowing into the second common suction pipe <NUM> may be recovered by the first and second gas engine compressors <NUM> and <NUM> via the first and second branch pipes <NUM> and <NUM>.

The first gas-liquid separation valve <NUM> also opens, so oil stored in the first gas-liquid separator <NUM> may be recovered by the electromotive compressor <NUM>.

When the second outdoor unit <NUM> or the first and second gas engine compressors <NUM> and <NUM> operate and the second outdoor unit side valve <NUM> opens, the flow of oil stored in the second oil separator <NUM> is regulated at the second outdoor flow regulating unit <NUM> and the oil flows into the first common suction pipe <NUM> of the first outdoor unit <NUM>.

In addition, oil flowing into the first common suction pipe <NUM> may be recovered by the electromotive compressor <NUM>.

The second gas-liquid separation valve <NUM> and the oil branch valve <NUM> also open, so oil stored in the second gas-liquid separator <NUM> and the second oil separator <NUM> may be recovered by the first and second gas engine compressors <NUM> and <NUM>.

According to such a configuration, when there is oil imbalance between the first and second outdoor units <NUM> and <NUM>, there is an effect in that oil may be recovered by the outdoor unit that lacks oil.

<FIG> is a flowchart of a control method of the heat-pump system according to the second embodiment.

Referring to <FIG>, when the heat-pump system <NUM> according to the second embodiment operates, whether the first outdoor unit <NUM> or the second outdoor unit <NUM> operates may be recognized. The first outdoor unit <NUM> or the second outdoor unit <NUM> may selectively operate depending on an operation load.

As an example, when a desired operation load is equal to or less than a set load, only the first outdoor unit operates; when the desired operation load is equal to or more than the set load, both the first and second outdoor units <NUM> and <NUM> may operate in steps S21 and S22.

More particularly, when both the first and second outdoor units <NUM> and <NUM> operate, the operation times of the first and second outdoor units <NUM> and <NUM> may be added up.

When an added time passes a set time, the first outdoor unit side valve <NUM> and the second outdoor unit valve <NUM> may open.

As the first outdoor unit valve <NUM> opens, oil having a height equal to or higher than the first oil balance hole <NUM> among the oil stored in the electromotive compressor <NUM> flows into the second common suction pipe <NUM> of the second outdoor unit <NUM> via the compressor side oil balance pipe <NUM>.

In addition, oil branches into the first and second gas engine compressors <NUM> and <NUM> and is suctioned by them.

In addition, as the second outdoor unit valve <NUM> opens, oil having a height equal to higher than the second oil balance hole <NUM> among oil stored in the second oil separator <NUM> flows into the first common suction pipe <NUM> of the first outdoor unit <NUM> via the oil separation oil balance pipe <NUM>. In addition, oil is suctioned by the electromotive compressor <NUM>.

In this case, the first and second gas-liquid separation valves <NUM> and <NUM> open and oil stored in the first and second gas-liquid separators <NUM> and <NUM> may be recovered by the compressor of each outdoor unit.

In addition, the oil branch valve <NUM> opens, and oil stored in the second oil separator <NUM> may branch into the first and second gas engine compressors <NUM> and <NUM> and be recovered by them in step S23.

Accordingly, oil present inside each outdoor unit may be easily recovered by a compressor and there is an advantage in that oil may be recovered by an outdoor unit lacking oil when there is oil imbalance between the first and second outdoor units <NUM> and <NUM>.

In step S23, when both the first outdoor unit <NUM> and the second outdoor unit <NUM> do not operate, the first outdoor unit valve <NUM> and the second outdoor unit valve <NUM> may maintain a closed state.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the invention as disclosed in the accompanying claims.

Claim 1:
A heat-pump system comprising:
a first outdoor unit (<NUM>) comprising: a first compressor (<NUM>), a first common suction pipe (<NUM>) configured to guide suction of refrigerant to the first compressor (<NUM>), and a first oil separator (<NUM>);
a second outdoor unit (<NUM>) comprising: a second compressor (<NUM>, <NUM>), a second common suction pipe (<NUM>) configured to guide suction of refrigerant to the second compressor (<NUM>, <NUM>), and a second oil separator (<NUM>);
a compressor side oil balance pipe (<NUM>) coupled to the first compressor (<NUM>) and extended to the second outdoor unit (<NUM>),
wherein the compressor side oil balance pipe (<NUM>) is coupled to the second common suction pipe (<NUM>),
wherein the compressor side oil balance pipe (<NUM>) is configured to guide oil in the first compressor (<NUM>) to be recovered by the second compressor (<NUM>); and
an oil separation oil balance pipe (<NUM>) coupled to the second oil separator (<NUM>) and extended to the first outdoor unit (<NUM>),
wherein the oil separation oil balance pipe (<NUM>) is coupled to the first common suction pipe (<NUM>),
wherein the oil separation oil balance pipe (<NUM>) is configured to guide oil in the second oil separator (<NUM>) to be recovered by the first compressor (<NUM>),
characterized in that:
the first outdoor unit (<NUM>) includes a first gas-liquid separator (<NUM>) provided at an inlet side of the first compressor (<NUM>), and
a first gas-liquid separation oil balance pipe (<NUM>) extended from the first gas-liquid separator (<NUM>) to the first common suction pipe (<NUM>),
wherein the first gas-liquid separator (<NUM>) is configured to separate gaseous refrigerant from refrigerant and configured to supply the gaseous refrigerant to the first compressor (<NUM>),
wherein the first common suction pipe (<NUM>) is extending from an exit side of the first gas-liquid separator (<NUM>) to the first compressor (<NUM>),
wherein the first compressor (<NUM>) is an electromotive compressor, and wherein the second compressor (<NUM>, <NUM>) is a gas engine compressor.