Patent Publication Number: US-2021180805-A1

Title: Gas heat-pump system and method of controlling same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-0019-0168124, filed Dec. 16, 2019, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a gas heat-pump system and a method of controlling the gas heat-pump system and, more particularly, to a gas heat-pump system and a method controlling the gas heat-pump system, which are capable of utilizing waste heat from refrigerant and coolant as much as possible and improving heating performance. 
     Description of the Related Art 
     A heat-pump system is a system that is capable of performing a cooling or heating operation through a refrigeration cycle, and operates in cooperation with a hot-water supply apparatus or a cooling and heating apparatus. That is, hot water is produced, or air conditioning for cooling and heating is performed using a heat source that is obtained as a result of heat exchange occurring between cooling refrigerant in the refrigeration cycle and a predetermined heat storage medium. 
     Generally, a configuration for the refrigeration cycle requires that a compressor compressing refrigerant, a condenser condensing the refrigerant compressed by the compressor, an expansion device decompressing the refrigerant condensed by the condenser, and an evaporator evaporating the decompressed refrigerant are included. 
     The heat-pump systems include a gas heat-pump system (GHP). High capacity compressors are required for industrial use or for air conditioning in large non-residential buildings. That is, the gas heat-pump system is used as a system that, instead of an electric motor, uses an electric motor to drive a compressor compressing a large amount of refrigerant into high-temperature, high-pressure gas. 
     The gas heat-pump system includes an engine generating a motive force using a mixture of fuel and gas (hereinafter referred to as “mixed gas”), an air supply device supplying the mixed gas to the engine, a fuel supply device, and a mixer mixing the air and the fuel. 
     The engine includes a cylinder to which the mixed gas is supplied and a piston provided to be movable within the cylinder. The air supply device includes an air filter purifying air. The fuel supply device includes a zero governor supplying fuel with predetermined pressure. 
     The gas heat-pump system includes coolant cooling the engine while circulating therethrough. The coolant absorbs waste heat occurring in the engine, and the absorbed waste heat is supplied to the refrigerant circulating through the gas heat-pump system, thereby improving performance thereof. Particularly, when a heating operation is performed by the gas heat-pump system, evaporation performance of the refrigeration cycle can be improved. 
     The waste heat can be continuously produced from the engine to a degree more than is necessary for the refrigeration cycle. However, a gas heat-pump system in the related art is not configured in such a manner that the waste occurring in the engine can be additionally utilized. For this reason, surplus waste heat occurring in the engine has been discharged to the surroundings. 
     The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art. 
     SUMMARY OF THE INVENTION 
     An objective of the present disclosure is to provide a gas heat-pump system and a method of controlling the gas heat-pump system, which supplies waste heat recovered from refrigerant and coolant to a hot-water storage tank to heat water stored in the hot-water storage tank, and heats the refrigerant by utilizing high-temperature hot water stored in the hot-water storage tank, thus improving heating performance. 
     According to an aspect of the present disclosure, there is provided a gas heat-pump system including: a compressor compressing refrigerant and discharging the compressed refrigerant; an engine providing a drive force to the compressor; a radiator that cools coolant which is heated while passing through the engine; an indoor heat exchanger causing heat exchange to occur between indoor air and the refrigerant and thus cooling or heating an indoor space; an outdoor heat exchanger condensing the refrigerant; a four-way valve switching a flow direction of the refrigerant in such a manner that the refrigerant discharged from the compressor flows to the outdoor heat exchanger in a cooling operation mode and flows to the indoor heat exchanger in a heating operation mode; and a hot-water storage tank causing the heat exchange to occur between stored water and the refrigerant, and thus cooling the refrigerant in the cooling operation mode and heating the refrigerant in the heating operation mode. 
     In the gas heat-pump system, in the cooling operation mode, the hot-water storage tank may cause the heat exchange to occur between the coolant passing through the engine and the stored water and thus may cool the coolant. 
     The gas heat-pump system may further include: a hot-water storage tank refrigerant line, branching off from a main refrigerant line connecting the four-way valve and the outdoor heat exchanger to each other, passing through the hot-water storage tank for the heat exchange, and then being connected to the outdoor heat exchanger; and a first three-way valve switching the flow direction of the refrigerant in such a manner that the refrigerant passing through the four-way valve flows along the main refrigerant line or the hot-water storage tank refrigerant line. 
     The gas heat-pump system may further include: a hot-water storage tank coolant line, branching off from a main coolant line connecting the engine and the radiator to each other, passing through the hot-water storage tank for the heat exchange, and then being connected to the engine; and a second three-way valve switching a flow direction of the coolant in such a manner that the coolant passing through the engine flows along the main coolant line or the hot-water storage tank coolant line. 
     In the gas heat-pump system, the hot-water storage tank coolant line may be positioned above the hot-water storage tank refrigerant line within the hot-water storage tank. 
     The gas heat-pump system may further include: a branch refrigerant line branching off from the main refrigerant line connecting the indoor heat exchanger and the outdoor heat exchanger to each other, and being connected to the hot-water storage tank refrigerant line connecting the hot-water storage tank and the outdoor heat exchanger to each other; a three-way valve provided on a junction between of the branch refrigerant line and the hot-water storage tank refrigerant line, the three-way valve being configured to selectively connect the hot-water storage tank refrigerant line and the branch refrigerant line; and an on-off valve provided on the hot-water storage tank refrigerant line between the third three-way valve and the outdoor heat exchanger, the on-off valve being configured to open the hot-water storage tank refrigerant line in the cooling operation mode and close the hot-water storage tank refrigerant line in the heating operation mode. 
     In the gas heat-pump system, in the cooling operation mode, the third three-way valve may switches the flow direction of the refrigerant in such a manner that the refrigerant passes through the outdoor heat exchanger and then flows along the main refrigerant line or flows along the main refrigerant line through the branch refrigerant line. 
     The gas heat-pump system may further include: an auxiliary refrigerant line branching off from the main refrigerant line connecting the indoor heat exchanger and the outdoor heat exchanger to each other, passing through an auxiliary heat exchanger, and then being connected to the compressor; an auxiliary expansion valve opening and closing the auxiliary refrigerant line between the indoor heat exchanger and the auxiliary heat exchanger; an auxiliary coolant line branching off from the main coolant line connecting the engine and the second three-way valve, passing through the auxiliary heat exchanger, and then being connected to the engine; and a fourth three-way valve switching the flowing direction of the coolant in such a manner that the coolant passing through the engine flows along the main coolant line or the auxiliary coolant line. 
     The gas heat-pump system may further include; a heating line passing through an inside of the hot-water storage tank for the heat exchange with water stored in the hot-water storage tank; and a heating unit heating the water passing through the heating line. 
     In the gas heat-pump system, the heating line may be positioned below a hot-water storage tank refrigerant line within the hot-water storage tank. 
     According to another aspect of the present disclosure, there is provided a method of controlling a gas heat-pump system in a cooling operation mode, the system including: a first refrigerant circulation path along which a refrigerant that is discharged from a compressor compressing the refrigerant using a drive force of an engine is cooled in an outdoor heat exchanger, passes through an indoor heat exchanger, and then circulates to the compressor; a second refrigerant circulation path along which the refrigerant discharged from the compressor is cooled in a hot-water storage tank and then in the outdoor heat exchanger, passes through the indoor heat exchanger, and then circulates to the compressor; a first coolant circulation path along which coolant cooling an engine is cooled in a radiator and then circulates to the engine; and a second coolant circulation path along which the coolant cooling the engine is cooled in the hot-water storage tank and then circulates to the engine. 
     The method includes: determining whether or not water stored in the hot-water storage tank is in use as hot water; measuring temperature of the water stored in the hot-water storage tank and thus determining an amount of the hot water in use when the water stored in the hot-water storage tank is in use as the hot water; and determining paths along which the refrigerant and the coolant circulate in a manner that corresponds to whether or not the water stored in the hot-water storage tank is in use as the hot water or the amount of the hot water in use. 
     In the method, in the determining of the paths along which the refrigerant and the coolant circulate, when it is determined that the water stored in the hot-water storage tank is not in use as the hot water, control may be performed in such a manner that the refrigerant flows along the first refrigerant circulation path and that the coolant flows along the first coolant circulation path. 
     In the method, in the determining of the paths along which the refrigerant and the coolant circulate, when the amount of the hot water in use falls short of being within a predetermined range, control may be performed in such a manner that the refrigerant flows along the second refrigerant circulation path and that the coolant flows along the first coolant circulation path. 
     In the method, in the determining of the paths along which the refrigerant and the coolant circulate, when the amount of the hot water in use falls within the predetermined range, control may be performed in such a manner that the refrigerant flows along the second refrigerant circulation path and that the coolant flows along the second coolant circulation path. 
     In the method, in the determining of the paths along which the refrigerant and the coolant circulate, when the amount of the hot water in use exceeds the predetermined range, control may be performed in such a manner that the refrigerant flows along the second refrigerant circulation path and that the coolant flows along the second coolant circulation path, and a water heating operation of heating the water stored in the hot-water storage tank may be performed by operating a heating unit connected to the hot-water storage tank through a heating line. 
     In the method, the gas heat-pump system may further include; a third refrigerant circulation path along which the refrigerant discharged from the compressor is cooled in the hot-water storage tank, bypasses the indoor heat exchanger, and then circulates to the compressor, and in the determining of the paths along which the refrigerant and the coolant circulate, when the amount of the hot water in use falls within the predetermined range, control may be performed in such a manner that the refrigerant flows along the third refrigerant circulation path and that the coolant flows along the second coolant circulation path. 
     According to still another aspect of the present disclosure, there is a method of controlling a gas heat-pump system in a heating operation mode, the system including: a first refrigerant circulation path along which a refrigerant that is discharged from a compressor compressing the refrigerant using a drive force of an engine exchanges heat in an indoor heat exchange, is heated in an auxiliary heat exchanger, and then circulates to the compressor; a second refrigerant circulation path along which the refrigerant discharged from the compressor exchanges heat in the indoor heat exchanger is heated in a hot-water storage tank, and then circulates to the compressor; and a coolant circulation path along which a coolant cooling an engine is cooled in the auxiliary heat exchanger, and then circulates to the engine. 
     The method includes: determining whether or not a water heating operation of operating a heating unit to heat water stored in the hot-water storage tank for use as hot water is performed; determining heating performance, depending on whether or not the water heating operation is performed in a manner that satisfies a preset heating condition; and determining a path along which the refrigerant circulates in a manner that corresponds to whether or not the water heating operation is performed and the heating performance. 
     In the method, in the determining of the path along which the refrigerant circulates, when it is determined that the water heating operation is not performed, control may be performed in such a manner that the refrigerant flows along the first refrigerant circulation path. 
     In the method, in the determining of the path along which the refrigerant circulates, when the water heating operation is performed and the heating performance does not satisfy the preset heating condition, control may be performed in such a manner that the refrigerant flows along both the first refrigerant circulation path and the second refrigerant circulation path. 
     In the method, in the determining of the heating performance, it may be determined whether or not temperature of air discharged from the indoor heat exchanger is a target temperature that satisfies the reset heating condition. 
     With the gas heat-pump system and the method of controlling the gas heat-pump system according to the present disclosure, when a cooling operation is performed, waste heat recovered from the refrigerant and the coolant is supplied to the hot-water storage tank to heat the water stored in the hot-water storage tank. Thus, the advantage of saving energy can be achieved. 
     Furthermore, according to the present disclosure, when a heating operation is performed, the refrigerant is heated by utilizing high-temperature hot water stored in the hot-water storage tank. Thus, the advantage of improving heating performance can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objectives, features, and other advantages of the present disclosure will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view schematically illustrating a gas heat-pump system according to the present disclosure; 
         FIG. 2  is a view schematically illustrating a gas heat-pump system operating in a cooling operation mode according to a first embodiment of the present disclosure; 
         FIG. 3  is a view schematically illustrating a gas heat-pump system operating in the cooling operation mode according to a second embodiment of the present disclosure; 
         FIG. 4  is a view schematically illustrating a gas heat-pump system operating in the cooling operation mode according to a third embodiment of the present disclosure; 
         FIG. 5  is a view schematically illustrating a gas heat-pump system in the cooling operation mode according to a fourth embodiment of the present disclosure; 
         FIG. 6  is a view schematically illustrating a gas heat-pump system in the cooling operation mode according to a fifth embodiment of the present disclosure; 
         FIG. 7  is a view schematically illustrating the gas heat-pump system in a heating operation mode according to the first embodiment of the present disclosure; 
         FIG. 8  is a view schematically illustrating the gas heat-pump system in the heating operation mode according to the second embodiment of the present disclosure; 
         FIG. 9  is a flowchart schematically illustrating a method of controlling the gas heat-pump system in the cooling operation mode according to the present disclosure; and 
         FIG. 10  is a flowchart schematically illustrating a method of controlling the gas heat-pump system in the heating operation mode according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A gas heat-pump system and methods of controlling the gas heat-pump system according to the present disclosure will be described in more detail below to provide an understanding of features of the present disclosure. 
     It is noted that, if possible, the same constituent elements are given the same reference character throughout the accompanying drawings that are referred to for illustration and may be in use as an aid in describing the embodiments. In addition, specific descriptions of well-known configurations and functions associated with the present disclosure will be omitted when determined as making the nature and gist of the present disclosure unclear. 
     Specific embodiments of the present disclosure will be described below with reference to the accompanying drawings. 
       FIG. 1  is a view schematically illustrating a gas heat-pump system according to the present disclosure. 
       FIGS. 2 to 6  are views illustrating gas heat-pump systems operating in a cooling operation mode according to first to fifth embodiments, respectively, of the present disclosure.  FIGS. 7 and 8  are views illustrating the gas heat-pump systems in a heating operation mode according to the first and second embodiments, respectively, of the present disclosure. 
     With reference to  FIG. 1 , the gas heat-pump system  11  according to the present disclosure includes an air conditioning module, an engine module, and a cooling module. The gas heat-pump system may further include a hot-water storage tank module that recovers waste heat from refrigerant and coolant and uses the waste heat as a heat source. 
     The air conditioning module includes a plurality of components that are configured for cooling or heating an indoor space using a refrigeration cycle. 
     As an example, the air conditioning module includes a compressor  110 , a four-way valve  115 , an outdoor heat exchanger  120 , an indoor heat exchanger  140 , and a gas-liquid separator  160 . The compressor  110  compresses the refrigerant. The four-way valve  115  switches a flow direction of the refrigerant compressed in the compressor  110  in a manner that corresponds to the cooling operation mode and the heating operation mode. The outdoor heat exchanger  120  condenses the refrigerant. The indoor heat exchanger  140  causes heat exchange to occur between indoor air and the refrigerant and thus cools or heats the indoor space. The gas-liquid separator  160  separates liquid refrigerant and gaseous refrigerant from each other. The outdoor heat exchanger  120  here is installed in an outdoor air conditioning condenser unit. An outdoor fan  122  is provided in the outdoor air conditioning condenser unit. The driving of the outdoor fan  122  causes the heat exchange to occur between outdoor air and the refrigerant passing through the outdoor heat exchanger  120 , thereby cooling the refrigerant. 
     In the cooling operation mode, the air conditioning module with this configuration operates as follows. The refrigerant discharged in a compressed state from the compressor  110  is supplied by operation of the four-way valve  115  to the outdoor heat exchanger  120 . The refrigerant condensed in the outdoor heat exchanger  120  is supplied to the indoor heat exchanger  140 , exchanges heat with the indoor air, and thus evaporates, thereby cooling the indoor air. Thereafter, the evaporating refrigerant passes through the four-way valve  115  and then is separated into the liquid refrigerant and the gaseous refrigerant by the gas-liquid separator  160 . The resulting gaseous refrigerant is supplied to the compressor  110  and circulates. 
     A main expansion valve  125  for depressurizing the refrigerant is provided to the exist side of the outdoor heat exchanger  120 . A depressurizing operation by the main expansion valve  125  further cools the refrigerant passing through the outdoor heat exchanger  120 . 
     A supercooling heat exchanger  130 , a supercooling flow path  132 , and a supercooling expansion valve  135  may be further provided to the exit side of the main expansion valve  125 . The supercooling heat exchanger  130  additionally cools the refrigerant. The supercooling flow path  132  branches off from the main refrigerant line  111  connecting the outdoor heat exchanger  120  and the indoor heat exchanger  140  to each other, passes through the supercooling heat exchanger  130  and is connected to the gas-liquid separator  160 . The supercooling expansion valve  135  is provided on the supercooling flow path  132  in such a manner as to be positioned to the entrance side of the supercooling heat exchanger  130  and depressurizes the refrigerant. 
     With this configuration, a depressurizing operation by the supercooling expansion valve  135  cools the refrigerant flowing out of the supercooling flow path  132 . The cooled refrigerant is further cooled while passing through the main refrigerant line  111  in the supercooling heat exchanger  130  and then is discharged to the gas-liquid separator  160 . 
     Furthermore, in the heating operation mode, the air conditioning module operates as follows. The refrigerant discharged in the compressed state from the compressor  110  is supplied by the operation of the four-way valve  115  to the indoor heat exchanger  140 , exchanges heat with the indoor air, and is condensed, thereby heating the indoor air. Thereafter, the refrigerant exchanges heat with the coolant heated in an auxiliary heat exchanger  150  and evaporates. Thereafter, the refrigerant passes through the four-way valve  115  and then is separated into the liquid refrigerant and the gaseous refrigerant by the gas-liquid separator  160 . The resulting gaseous refrigerant is supplied to the compressor  110  and circulates. 
     To this end, the air conditioning module may further include an auxiliary refrigerant line  151  and an auxiliary expansion valve  155 . The auxiliary refrigerant line  151  branches off from the main refrigerant line  111  connecting the indoor heat exchanger  140  and the outdoor heat exchanger  120  to each other, passes through the auxiliary heat exchanger  150 , and then is connected to the compressor  110 . The auxiliary expansion valve  155  opens and closes the auxiliary refrigerant line  151  between the indoor heat exchanger  140  and the auxiliary heat exchanger  150 . The auxiliary expansion valve  155  here may operate in such a manner as to depressurize the refrigerant introduced into the auxiliary heat exchanger  150 . 
     The engine module includes a plurality of components that are configured to provide a drive force for compressing the refrigerant in the compressor  110 . 
     As an example, the engine module includes an engine  210 , a mixer  230 , an air filter  220 , a zero governor  240 , and a flow control unit  270 . The engine  210  combusts mixed gas and thus generates a motive force. The mixer  230  is arranged to the entrance side of the engine  210  and supplies the mixed gas. The air filter  220  supplies purified air to the mixer  230 . The zero governor  240  supplies fuel at a predetermined pressure or lower. The flow control unit  270  is arranged between the engine  210  and the mixer  230  and controls an amount of the mixed gas to be supplied to the engine  210 . The flow control unit  270  here is provided as a valve that employs an electronic throttle control (ETC) scheme. 
     With this configuration, the amount of the mixed gas that results from the mixer  230  mixing air supplied in a purified state by the air filter  220  and fuel supplied at predetermined pressure by the zero governor  240  is controlled by the flow control unit  270 , and then the resulting mixed gas is supplied to the engine  210 , thereby generating the motive force in the engine  210 . The motive force that is generated in this manner in the engine  210  is provided as the drive force for operating the compressor  110 . Of course, although not illustrated, a turbocharger (not illustrated) may be further provided for supplying compressed mixed gas to the engine  210 . 
     The cooling module includes a plurality of components that are configured to supply the coolant for cooling the engine  210 . 
     As an example, the coolant module includes a radiator  330  and a main coolant line  310 . The radiator  300  cools the coolant heated while passing through the engine  210 . The main coolant line  310  connects the engine  210  and a radiator  330  to each other. The radiator  330  is installed in the outdoor air conditioning condenser unit, and the outdoor fan  122  is installed in the outdoor air conditioning condenser unit. With this arrangement, the driving of the outdoor fan  122  causes the heat exchange to occur between the outdoor air and the coolant passing through the radiator  330 , thereby cooling the coolant. 
     The coolant module may further include a coolant pump  300  that is arranged on the main coolant line  310  and forces the coolant to flow into the engine  210 . 
     The coolant module may further include an exhaust gas heat exchanger  280  that is arranged on the main coolant line  310  in such a manner as to be positioned to the exhaust outlet side of the engine  210  and causes the heat exchange to occur between the coolant flowing along the main coolant line  310  and exhaust gas discharged from the engine  210 . 
     Furthermore, the coolant module may further include an auxiliary coolant line  320  and a fourth three-way valve  444 . The auxiliary coolant line  320  branches off from the main coolant line  310  connecting the engine  210  and a second three-way valve  442  to each other, passes through the auxiliary heat exchanger  150 , and then is connected to the main coolant line  310  positioned to the exit side of the radiator  330 . The fourth three-way valve  444  is provided at a point where the auxiliary coolant line  320  branches off from the main coolant line  310 . 
     The fourth three-way valve  444  switches a flow direction of the coolant in such a manner that the coolant passing through the engine  210  flows along the main coolant line  310  or the auxiliary coolant line  320 . That is, the fourth three-way valve  444  switches the flow direction of the coolant in such a manner that the coolant passing through the engine  210  flows toward the radiator  330  or the auxiliary heat exchanger  150 . 
     The hot-water storage tank module includes a plurality of components that are configured to recover waste heat from the refrigerant and the coolant or uses the waste heat as a heat source. 
     As an example, the hot-water storage tank module includes a hot-water storage tank  410 , a hot-water storage tank refrigerant line  431 , and the first three-way valve  441 . Water is stored in the hot-water storage tank  410 . The hot-water storage tank refrigerant line  431  branches off from the main refrigerant line  111  and passes through the hot-water storage tank  410 . The first three-way valve  441  is provided at a point where the hot-water storage tank refrigerant line  431  branches off from the main refrigerant line  111 . 
     The water storage tank  410  here is configured to store water that is in use as hot water. That is, in a case where a user uses the hot water, a heating unit  510  performs a water heating operation of heating the stored water. Thus, the water stored in the hot-water storage tank  410  is heated and the heated water is supplied as the hot water. At this time, an amount of hot water that can be used by the user varies according to an amount of heat supplied to the hot-water storage tank  410 . 
     A hot-water storage tank supply line  421  and a hot-water storage tank discharge line  422  are provided on the hot-water storage tank  410 . The water is supplied through the hot-water storage tank supply line  421 . The hot water produced by heating the water in the hot-water storage tank  410  is discharged to the outside through the hot-water storage tank discharge line  422 . 
     The hot-water storage tank discharge line  422  is configured to discharge the hot water produced by heating the water to the outside. The water heated in the hot-water storage tank  410  moves upward. Thus, an end portion of the hot-water storage tank discharge line  422  is desirably arranged on an upper portion of the hot-water storage tank  410 . 
     The hot-water storage tank supply line  421  is configured to supply low-temperature water to the hot-water storage tank  410 . In order to minimize an effect on the heated water moving upward, an end portion of the hot-water storage tank supply line  421  is desirably arranged on the bottom surface side of the hot-water storage tank  410  in such a manner that the low-temperature water is supplied from a bottom of the hot-water storage tank  410 . 
     The hot-water storage tank module includes the hot-water storage tank refrigerant line  431 , the first three-way valve  441 , a hot-water storage tank coolant line  433 , and a second three-way valve  442 . The hot-water storage tank refrigerant line  431  branches off from the main refrigerant line  111  connecting the four-way valve  115  and the outdoor heat exchanger  120  to each other, passes through the hot-water storage tank  410  for the heat exchange, and then is connected to the outdoor heat exchanger  120 . The first three-way valve  441  switches the flow direction of the refrigerant in such a manner that the refrigerant passing through the four-way valve  115  flows along the main refrigerant line  111  or the hot-water storage tank refrigerant line  431 . The hot-water storage tank coolant line  433  branches off from the main coolant line  310  connecting the engine  210  and the radiator  330  to each other, passes through the hot-water storage tank  410  for the heat exchange, and then is connected to the engine  210 . The second three-way valve  442  switches the flow direction of the coolant in such a manner that the coolant passing through the engine  210  flows along the main coolant line  310  or the hot-water storage tank coolant line  433 . 
     With this configuration, in the cooling operation mode, the refrigerant discharged from the compressor  110  is supplied to the hot-water storage tank refrigerant line  431  for primary condensing in the hot-water storage tank  410 , and then the resulting refrigerant is supplied to the outdoor heat exchanger  120  for secondary condensing. At this time, the water stored in the hot-water storage tank  410  is heated with the refrigerant, and thus the waste heat is recovered from the refrigerant. 
     In the cooling operation mode, the coolant with which the engine  210  is cooled is supplied to the hot-water storage tank coolant line  433  and is cooled in the hot-water storage tank  410 , and then the cooled coolant is supplied back to the engine  210 . At this time, the water stored in the hot-water storage tank  410  is heated with the coolant, and thus the waste heat is recovered from the coolant. 
     The hot-water storage tank module may further include a branch refrigerant line  432 , a third three-way valve  443 , and an on-off valve  445 . 
     The branch refrigerant line  432  branches off from the main refrigerant line  111  connecting the indoor heat exchanger  140  and the outdoor heat exchanger  120  to each other and is connected to the hot-water storage tank refrigerant line  431  connecting the hot-water storage tank  410  and the outdoor heat exchanger  120  to each other. 
     The third three-way valve  443  is provided on a junction between the branch refrigerant line  432  and the hot-water storage tank refrigerant line  431  to selectively connect the hot-water storage tank refrigerant line  431  and the branch refrigerant line  432  to each other. In the cooling operation mode, the third three-way valve  443  may switch the flow direction of the refrigerant in such a manner that the refrigerant passes through the outdoor heat exchanger  120  and then flows along the main refrigerant line  111  or flows along the main refrigerant line  111  through the branch refrigerant line  432 . 
     The on-off valve  445  is provided on the hot-water storage tank refrigerant line  431  between the third three-way valve  443  and the outdoor heat exchanger  120 . The on-off valve  445  operates to open the hot-water storage tank refrigerant line  431  in the cooling operation mode and to close the hot-water storage tank refrigerant line  431  in the heating operation mode. 
     The hot-water storage tank module includes a heating line  520  and a heating unit  510 . The heating line  520  passes through the inside of the hot-water storage tank  410  for the heat exchange with the water stored in the hot-water storage tank  410 . The heating unit  510  heats the water passing through the heating line  520 . That is, the water stored in the hot-water storage tank  410  is heated with the heating line  520  and the heating unit  510 . 
     Furthermore, the hot-water storage tank coolant line  433  of the hot-water storage tank module is arranged inside of an upper portion of the hot-water storage tank  410 , the heating line  520  of the hot-water storage tank module is arranged inside of a lower portion thereof, and the hot-water storage tank refrigerant line  431  of the hot-water storage tank module is arranged inside of the middle portion thereof at a position midway between the hot-water storage tank coolant line  433  and the heating line  520 . Of course, the present disclosure is not limited to this arrangement. The hot-water storage tank refrigerant line  431  may be arranged inside of the upper portion of the hot-water storage tank  410 , and the hot-water storage tank coolant line  433  may be arranged inside of the middle portion thereof. That is, positions in which the lines are arranged may be changed according to an operating condition that is set up by a user. 
     A method of controlling the gas heat-pump system according to the present disclosure will be described below with reference to the accompanying drawings. 
     The gas heat-pump system includes first to third refrigerant circulation paths CRC 1 , CRC 2 , and CRC 3 , and first and second coolant circulation paths CWC 1  and CWC 2 . In the cooling operation mode, according to the operating condition, the refrigerant circulates along the first to third refrigerant circulation paths CRC 1 , CRC 2 , and CRC 3 , and the coolant circulates along the first and second coolant circulation path CWC 1  and CWC 2 . 
     More specifically, with reference to  FIG. 2 , the first refrigerant circulation path CRC 1  is a path along which the refrigerant discharged from the compressor  110  circulates to the compressor  110  after being cooled in the outdoor heat exchanger  120  and then exchanging heat with the indoor air the indoor heat exchanger  140 . 
     As an example, the first refrigerant circulation path CRC 1  is configured in such a manner that the refrigerant discharged from the compressor  110  flows by the operation of the four-way valve  115  toward the first three-way valve  441  and flows by the operation of the first three-way valve  441  to the main refrigerant line  111  for being supplied to the outdoor heat exchanger  120 . Furthermore, the first refrigerant circulation path CRC 1  is configured in such a manner that the refrigerant condensed while passing through the outdoor heat exchanger  120  is cooled while passing through the main expansion valve  125 , exchanges heat in the indoor heat exchanger  140 , thereby cooling the indoor air, and then passes through the first three-way valve  441  for being supplied to the gas-liquid separator  160 , and that only the gaseous refrigerant resulting from the gas-liquid separation is supplied back to the compressor  110 . 
     With reference to  FIG. 3 , the second refrigerant circulation path CRC 2  is a path along which the refrigerant discharged from the compressor  110  is cooled in the hot-water storage tank  410  and then in the outdoor heat exchanger  120 , passes through the indoor heat exchanger  140 , and then circulates to the compressor  110 . 
     As an example, the second refrigerant circulation path CRC 2  is configured in such a manner that the refrigerant discharge from the compressor  110  flows by the operation of the four-way valve  115  toward the first three-way valve  441  and flows by operation of the first three-way valve  441  to the hot-water storage tank refrigerant line  431  for being supplied to the hot-water storage tank  410 . Furthermore, the second refrigerant circulation path CRC 2  is configured in such a manner that the refrigerant primarily condensed while passing through the hot-water storage tank  410  flows by operation of the third three-way valve  443  to the outdoor heat exchanger  120 , thereby being additionally condensed, is cooled while passing through the main expansion valve  125 , exchanges heat in the indoor heat exchanger  140 , thereby cooling the indoor air, and then passes through the first three-way valve  441  for being supplied to the gas-liquid separator  160 , and that only the gaseous refrigerant resulting from the gas-liquid separation is supplied back to the compressor  110 . 
     With reference to  FIG. 6 , the third refrigerant circulation path CRC 3  is a path along which the refrigerant discharged from the compressor  110  is cooled in the hot-water storage tank  410 , bypasses the indoor heat exchanger  140 , and then circulates to the compressor  110 . 
     As an example, the third refrigerant circulation path CRC 3  is configured in such a manner that the refrigerant discharged from the compressor  110  flows by the operation of the four-way valve  115  toward the first three-way valve  441  and flows by the operation of the first three-way valve  441  to the hot-water storage tank refrigerant line  431  for being supplied to the hot-water storage tank  410 . Furthermore, the third refrigerant circulation path CRC 3  is configured in such a manner that the refrigerant primarily condensed while passing through the hot-water storage tank  410  flows by the operation of the third three-way valve  443  to the branch refrigerant line  432 , bypasses the outdoor heat exchanger  120 , is cooled while passing through the main expansion valve  125 , exchanges heat in the indoor heat exchanger  140 , thereby cooling the indoor air, and then passes through the first three-way valve  441  for being supplied to the gas-liquid separator  160 , and that only the gaseous refrigerant resulting from the gas-liquid separation is supplied back to the compressor  110 . 
     With reference to  FIG. 2 , the first coolant circulation path CWC 1  is a path along which the coolant cooling the engine  210  is cooled in the radiator  330  and then circulates to the engine  210 . 
     As an example, the first coolant circulation path CWC 1  is configured in such a manner that the coolant cooling the engine  210  flows by the operation of the fourth three-way valve  444  and by operation of the second three-way valve  442  to the main coolant line  310  for being supplied to the radiator  330 , is cooled by the outdoor fan  122  in the radiator  330 , cools the exhaust gas in the exhaust gas heat exchanger  280  while being forced to flow by the coolant pump  300 , and then is supplied back to the engine  210 . 
     With reference to  FIG. 4 , the second coolant circulation path CWC 2  is a path along which the coolant cooling the engine  210  is cooled in the hot-water storage tank  410  and then circulates to the engine  210 . 
     As an example, the second coolant circulation path CWC 2  is configured in such a manner that the coolant cooling the engine  210  flows by operation of the fourth three-way valve  444  to the main coolant line  310 , flows by the operation of the second three-way valve  442  to the hot-water storage tank coolant line  433  for being supplied to the hot-water storage tank  410 , passes through the hot-water storage tank  410 , cools the exhaust gas in the exhaust gas heat exchanger  280  while being forced by the coolant pump  300  to flow, and then is supplied back to the engine  210 . 
     A method of controlling the gas heat-pump system in the cooling operation mode according to the present disclosure will be described below with reference to the above-described refrigerant circulation path and coolant circulation path. 
     The method of controlling the gas heat-pump system in the cooling operation mode includes a hot-water-in-use determination step S 110 , a hot-water-in-use amount determination step, and a circulation path control step. In the hot-water-in-use determination step S 110 , it is determined whether or not the water stored in the hot-water storage tank  410  is in use as the hot water. In the hot-water-in-use amount determination step, when the water stored in the hot-water storage tank  410  is in use as the hot water, temperature of the water stored in the hot-water storage tank  410  is measured, and thus an amount of the hot water in use is determined. In the circulation path control step, paths along which the refrigerant and the coolant circulate are determined in manner that corresponds to whether or not the water stored in the hot-water storage tank  410  is in use as the hot water or and the amount of the hot water in use. 
     In the circulation path control step, when it is determined that the water stored in the hot-water storage tank  410  is not in use as the hot water (NO in S 110 ), as illustrated in  FIG. 2 , control is performed in such a manner that the refrigerant flows along the first refrigerant circulation path CRC 1  and that the coolant flows along the first coolant circulation path CWC 1 . 
     That is, when the hot water is not in use, there is a need to heat the water stored in the hot-water storage tank  410 . Therefore, control is performed in such a manner that the refrigerant and the coolant circulate within the air conditioning module without flowing toward the hot-water storage tank  410  and that the indoor space is thus cooled. 
     In the circulation path control step, when the amount of the hot water in use falls short of being within a predetermined range (YES in S 130 ), as illustrated in  FIG. 3 , controls is performed in such a manner that the refrigerant flows along the second refrigerant circulation path CRC 2  and that the coolant flows along the first coolant circulation path CWC 1 . 
     That is, in a case where the amount of the hot water in use is small, the waste heat is recovered from the refrigerant in the hot-water storage tank  410 , the water stored in the hot-water storage tank  410  is heated with the recovered waste heat, and the heated water is in use as the hot water. When the water stored in the hot-water storage tank  410  is heated with the waste heat recovered from the refrigerant, the heating unit  510  is not used. Thus, energy can be saved. 
     In the circulation path control step, when the amount of the hot water in use falls within the predetermined range (YES in S 150 ), as illustrated in  FIG. 4 , the control is performed in such a manner that the refrigerant flows along the second refrigerant circulation path CRC 2  and the coolant flows along the second coolant circulation path CWC 2 . 
     That is, when the amount of the hot water in use occurs to some degree, in a state where the waste heat is recovered from the refrigerant in the hot-water storage tank  410  through the second refrigerant circulation path CRC 2 , control is performed in such a manner that the coolant flows along the second coolant circulation path CWC 2 . Thus, with this control, the waste heat is also recovered from the coolant in the hot-water storage tank  410 , thereby heating a larger amount of the water. That is, the water stored in the hot-water storage tank  410  is heated with the waste heat recovered from the refrigerant and the coolant without using the heating unit  510 . Thus, the energy can be saved. 
     In the circulation path control step, when the amount of the hot water in use exceeds the predetermined range (NO in S 150 ), as illustrated in  FIG. 5 , the control is performed in such a manner that the refrigerant flows along the second refrigerant circulation path CRC 2  and that the coolant flows along the second coolant circulation path CWC 2 . Furthermore, control is performed in such a manner that the heating unit  510  connected to the hot-water storage tank  410  with the heating line  520  operates to heat the water stored in the hot-water storage tank  410 . 
     That is, when the amount of the hot water in use is increased, only with the waste heat recovered through the second refrigerant circulation path CRC 2  and the second coolant circulation path CWC 2 , it is difficult to continuously heat and supply the water to be in continuous use. Therefore, the heating unit  510  additionally supplies heat, thereby heating the water stored in the hot-water storage tank  410 . 
     In this manner, when the hot water begins to be in use, control is performed in such a manner that the refrigerant flows along the second refrigerant circulation path CRC 2 . Furthermore, when the hot water is in continuous use, control is performed in such a manner that the coolant flows along the second coolant circulation path CWC 2 . Furthermore, when the hot water is further in continuous use, control is additionally performed in such a manner that the heating unit  510  operates. 
     Therefore, in a case where the hot water is in use, when the amount of the hot water in use falls within the predetermined range, the water stored in the hot-water storage tank  410  is heated with the waste heat recovered from the refrigerant and the coolant. Thus, the energy can be saved. 
     In addition, in the circulation path control step, when the amount of the hot water in use falls within the predetermined range, as illustrated in  FIG. 6 , control may be performed in such a manner that the refrigerant flows along the third refrigerant circulation path CRC 3  and that the coolant flows along the second coolant circulation path CWC 2 . In this manner, when the refrigerant and the coolant are allowed to flow, the coolant and the refrigerant do not flow to the radiator  330  and the outdoor heat exchanger  120 . Thus, the outdoor fan  122  does not need to be driven. Thus, the energy can be additionally saved. 
     The gas heat-pump system includes first and second refrigerant circulation paths HRC 1  and HRC 2  and a coolant circulation path HWC. In the heating operation mode, according to the operating condition, the refrigerant circulates along the first and second refrigerant circulation paths HRC 1  and HRC 2 , and the coolant circulates along the coolant circulation path HWC. 
     More specifically, with reference to  FIG. 7 , the first refrigerant circulation path HRC 1  is a path along which the refrigerant discharged from the compressor  110  exchanges heat in the indoor heat exchanger  140 , is heated in the auxiliary heat exchanger  150 , and then circulates to the compressor  110 . 
     As an example, the first refrigerant circulation path HRC 1  is configured in such a manner that the refrigerant discharged from the compressor  110  flows by the operation of the four-way valve  115  to the main refrigerant line  111  for being supplied to the indoor heat exchanger  140 , and exchanges heat with the indoor air in the indoor heat exchanger  140 , thereby being condensed. Furthermore, the first refrigerant circulation path HRC 1  is configured in such a manner that the resulting condensed refrigerant passes through the auxiliary expansion valve  155 , flows along the auxiliary refrigerant line  151  for being supplied to the auxiliary heat exchanger  150 , and absorbs heat in the auxiliary heat exchanger  150 , thereby evaporating. The first refrigerant circulation path HRC 1  is configured in such a manner that the resulting evaporating refrigerant is supplied to the gas-liquid separator  160 , and that only the gaseous refrigerant resulting from the gas-liquid separation is supplied back to the compressor  110 . 
     With reference to  FIG. 8 , the second refrigerant circulation path HRC 2  is a path along which the refrigerant discharged from the compressor  110  exchanges heat in the indoor heat exchanger  140 , is heated in the hot-water storage tank  410 , and then circulates to the compressor  110 . 
     As an example, the second refrigerant circulation path HRC 2  is configured in such a manner that the refrigerant discharged from the compressor  110  flows by the operation of the four-way valve  115  to the main refrigerant line  111  and flows to the indoor heat exchanger  140 . Furthermore, the second refrigerant circulation path HRC 2  is configured in such a manner that the refrigerant condensed after exchanging heat with the indoor air in the indoor heat exchanger  140  passes through the main expansion valve  125 , flows along the branch refrigerant line  432 , and flows by the operation of the third three-way valve  443  to the hot-water storage tank refrigerant line  431  for being supplied to the hot-water storage tank  410 . Furthermore, the second refrigerant circulation path HRC 2  is configured in such a manner that the refrigerant evaporating as a result of absorbing heat in the hot-water storage tank  410  is supplied by the operation of the first three-way valve  441  and by the operation of the four-way valve  115  to the gas-liquid separator  160 , and that only the gaseous refrigerant resulting from the gas-liquid separation is supplied back to the compressor  110 . 
     With reference to  FIG. 8 , the coolant circulation path HWC is a path along which the coolant cooling the engine  210  is cooled in the auxiliary heat exchanger  150  and then circulates to the engine  210 . 
     As an example, the coolant circulation path HWC is configured in such a manner that the coolant cooling the engine  210  flows by the fourth three-way valve  444  to the auxiliary coolant line  320  for being supplied to the auxiliary heat exchanger  150 , exchanges heat with the refrigerant in the auxiliary heat exchanger  150 , resulting in being cooled, cools the exhaust gas in the exhaust gas heat exchanger  280  while being forced by the coolant pump  300  to flow, and then is supplied back to the engine  210 . 
     A method of controlling the gas heat-pump system in the heating operation mode according to the present disclosure will be described below with reference to the above-described refrigerant circulation path and coolant circulation path. 
     The method of controlling the gas heat-pump system in the heating operation mode includes a water heating operation determination step S 210 , a heating performance determination step S 220 , and a refrigerant circulation path control step. In the water heating operation determination step S 210 , it is determined whether or not a water heating operation of operating the heating unit  510  to heat the water stored in the hot-water storage tank  410  for use as the hot water is performed. In the heating performance determination step S 220 , heating performance is determined, depending on whether or not the water heating operation is performed in a manner that satisfies a preset heating condition. In the refrigerant circulation path control step, a path along which the refrigerant circulates is determined in a manner that corresponds to whether or not the water heating operation is performed and the heating performance. 
     In the heating performance determination step, it is determined whether or not temperature of air discharged from the indoor heat exchanger  140  is target temperature that satisfies the preset heating condition. 
     As an example, in a case where the user sets the heating condition to 25° C., in order to raise indoor temperature to 25° C. within a preset time, the target temperature of the air supplied to the indoor space is set to 30° C. In this case, when the temperature of the air discharged that is heated as a result of the heat exchange in the indoor heat exchanger  140  is measured, if the temperature of the air does not reach the target temperature of 30° C., it is determined that the heating performance does not satisfy the preset heating condition. Of course, the above-described heating performance is only an example. The heating performance may be determined by various external factors, such as a size of the indoor space and the operating condition. 
     In the refrigerant circulation path control step, when it is determined that the water heating operation is not determined (NO in Step S 210 ), as illustrated in  FIG. 7 , control is performed in such a manner that the refrigerant flows along the first refrigerant circulation path HRC 1 . At this point, the coolant circulates along the coolant circulation path HWC. 
     That is, when the hot water is not in use, the water stored in the hot-water storage tank  410  is not heated and remains at low temperature. Therefore, control is performed in such a manner that the refrigerant flows along the first refrigerant circulation path HRC 1  and evaporates in the auxiliary heat exchanger  150 . 
     In the refrigerant circulation path control step, when the water heating operation is performed (YES in S 210 ) and the heating performance does not satisfy the preset heating condition (NO in S 220 ), as illustrated in  FIG. 8 , control is performed in such a manner that the refrigerant flows along both the first refrigerant circulation path HRC 1  and the second refrigerant circulation path HRC 2 . At this point, the coolant circulates along the coolant circulation path HWC. 
     That is, when the hot water is in use, the water heating operation is performed. Thus, the water stored in the hot-water storage tank  410  is heated and is stored in a high-temperature state. The reason that the heating performance does not satisfy the preset heating condition is that the heating performance cannot be achieved only with an amount of heat supplied from the auxiliary heat exchanger  150 . Therefore, it is determined that there is a need to supply an additional amount of heat to the refrigerant. 
     Accordingly, in order to supply the additional amount of heat, control is performed in such a manner that a portion of the refrigerant circulates along the second refrigerant circulation path HRC 2  and absorbs heat from the hot water, heated to high temperature, in the hot-water storage tank  410 . Thus, the heating condition can be satisfied. 
     Therefore, in a case where the heating condition is not satisfied, the heat is additionally supplied from the hot-water storage tank  410 . Thus, the heating condition can be satisfied, and the heating performance can be accordingly improved. 
     Although the specific embodiment of the present disclosure has been described 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 disclosure as disclosed in the accompanying claims.