Cogeneration system and method for controlling the same

A cogeneration system including a pre-heater to pre-heat outdoor air blown toward the outdoor heat exchanger during a heating operation of a heat pump type air conditioner, an auxiliary evaporator to evaporate a refrigerant emerging from the outdoor heat exchanger during the heating operation of the heat pump type air conditioner, and waste heat recovering means to transfer waste heat of the engine to at least one of the pre-heater and the auxiliary evaporator. The cogeneration system exhibits a high energy efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cogeneration system and a method for controlling the cogeneration system. More particularly, the present invention relates to a cogeneration system in which waste heat of an engine is recovered, and is supplied to a heat pump type air conditioner, and a method for controlling the cogeneration system.

2. Description of the Related Art

In general, cogeneration systems include an engine, a generator to generate electricity, using a rotating force outputted from the engine, and a heat transfer means to supply waste heat of the engine to a heat consumer such as a water heater or an air conditioner.

Electricity generated from the generator is used to operate various electrical devices such as electric lamps and air conditioners.

The heat transfer means recovers waste heat of cooling water used to cool the engine and waste heat of exhaust gas discharged from the engine, and supplies the recovered waste heat to the water heater or air conditioner.

However, such a conventional cogeneration system has a problem in that the waste heat of the engine is supplied to the heat consumer in an uncontrolled manner, irrespective of ambient temperature conditions, so that it is impossible to flexibly supply heat energy, taking into consideration a variation in load depending on a variation in ambient temperature.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problems, and it is an object of the invention to provide a cogeneration system in which waste heat of an engine is used to improve the heating performance of a heat pump type air conditioner or to prevent an outdoor heat exchanger of the heat pump type air conditioner from being frosted, so that the cogeneration system exhibits a high energy efficiency.

Another object of the invention is to provide a method for controlling a cogeneration system, in which waste heat is effectively used in accordance with frost conditions of an outdoor heat exchanger included in a heat pump type air conditioner, so that it is possible to enable the cogeneration system to positively cope with ambient temperature conditions, and to maximize the heating performance of the heat pump type air conditioner.

In accordance with one aspect, the present invention provides a cogeneration system comprising: an engine; a generator connected to an output shaft of the engine to generate electricity; a heat pump type air conditioner including a compressor, a directional valve, an indoor heat exchanger, an expansion device, and an outdoor heat exchanger; a pre-heater to pre-heat outdoor air blown toward the outdoor heat exchanger during a heating operation of the heat pump type air conditioner; an auxiliary evaporator to evaporate a refrigerant emerging from the outdoor heat exchanger during the heating operation of the heat pump type air conditioner; and waste heat recovering means to transfer waste heat of the engine to at least one of the pre-heater and the auxiliary evaporator.

In accordance with another aspect, the present invention provides a cogeneration system comprising: an engine; a generator connected to an output shaft of the engine to generate electricity; a heat pump type air conditioner including a compressor, a directional valve, an indoor heat exchanger, an expansion device, and an outdoor heat exchanger; a pre-heater to pre-heat outdoor air blown toward the outdoor heat exchanger during a heating operation of the heat pump type air conditioner; an auxiliary evaporator to evaporate a refrigerant emerging from the outdoor heat exchanger during the heating operation of the heat pump type air conditioner; and waste heat recovering means to transfer waste heat of the engine to at least one of the pre-heater and the auxiliary evaporator while controlling the amount of the transferred heat in accordance with a frost condition of the outdoor heat exchanger.

The heat pump type air conditioner may use the electricity generated from the generator.

At least one of the engine, the generator, the compressor, the directional valve, the indoor heat exchanger, the expansion device, and the outdoor heat exchanger may comprise a plurality of ones.

The waste heat recovering means may comprise: an engine-cooling heat exchanger to absorb heat from cooling water used to cool the engine; an exhaust gas heat exchanger to absorb heat from exhaust gas discharged from the engine; and heat transfer means to transfer at least one of the heat of the engine-cooling heat exchanger and the heat of the exhaust gas heat exchanger to at least one of the pre-heater and the auxiliary evaporator.

The heat transfer means may comprise: a pre-heater circulation conduit to guide a heat medium to be circulated around the engine-cooling heat exchanger, the exhaust gas heat exchanger, and the pre-heater; an auxiliary evaporator circulation conduit to guide the heat medium to be circulated around the engine-cooling heat exchanger, the exhaust gas heat exchanger, and the auxiliary evaporator; and a heat medium circulation pump to pump the heat medium for circulation of the heat medium.

The heat transfer means may further comprise a control valve to control the amount of the heat medium circulated through the pre-heater circulation conduit and the auxiliary evaporator circulation conduit.

The heat transfer means may further comprise an outdoor temperature sensor to measure an outdoor temperature or a temperature of the outdoor heat exchanger. The control valve may be controlled to operate in a pre-heater circulation mode when the heat pump type air conditioner operates in a heating mode, and the temperature measured by the temperature sensor is in a heavy-frost temperature range. The control valve may also be controlled to operate in an auxiliary evaporator circulation mode when the heat pump type air conditioner operates in the heating mode, and the temperature measured by the temperature sensor is in a non-frost temperature range. The control valve may also be controlled to operate in a common mode when the heat pump type air conditioner operates in the heating mode, and the temperature measured by the temperature sensor is in a light-frost temperature range.

The cogeneration system may further comprise a radiator to discharge heat. In this case, the heat transfer means may transfer the heat of the engine-cooling heat exchanger to the radiator when the heat pump type air conditioner operates in a cooling mode.

In accordance with another aspect, the present invention provides a method for controlling a cogeneration system, comprising: a temperature measuring step of measuring an outdoor temperature or a temperature of an outdoor heat exchanger included in a heat pump type air conditioner; and a waste heat controlling step comprising steps of supplying waste heat of an engine to a pre-heater adapted to pre-heat air blown to the outdoor heat exchanger when the heat pump type air conditioner operates in a heating mode, and the temperature measured in the temperature measuring step is in a heavy-frost temperature range, supplying the waste heat of the engine to a compressor suction line heater adapted to heat a suction line of a compressor included in the heat pump type air conditioner when the heat pump type air conditioner operates in the heating mode, and the temperature measured in the temperature measuring step is in a non-frost temperature range, and supplying the waste heat of the engine to both the pre-heater and the compressor suction line heater when the heat pump type air conditioner operates in the heating mode, and the temperature measured in the temperature measuring step is in a light-frost temperature range.

The waste heat controlling step may further comprise the step of supplying, to the radiator, waste heat of cooling water used to cool the engine, which is included in the waste heat of the engine, when the heat pump type air conditioner operates in a cooling mode.

The cogeneration system according to the present invention has an advantage in that waste heat of an engine is supplied, during a heating operation of the heat pump type air conditioner, to the pre-heater arranged to pre-heat outdoor air blown toward the outdoor heat exchanger or to the auxiliary evaporator arranged to evaporate refrigerant emerging from the outdoor heat exchanger, so that the cogeneration system exhibits a high energy efficiency.

In the cogeneration system according to the present invention, the heat of exhaust gas discharged from the engine is not transferred to the radiator during a cooling operation of the heat pump type air conditioner. During a cooling operation of the heat pump type air conditioner, only the heat of cooling water used to cool the engine is transferred to the radiator so that the transferred heat is discharged from the radiator. Accordingly, there are advantages in that it is possible to minimize the size of the radiator and the amount of air blown to the radiator, and to reduce costs and noise.

In the method for controlling the cogeneration system in accordance with the present invention, waste heat is selectively transferred to the pre-heater and auxiliary evaporator in accordance with frost conditions of the outdoor heat exchanger included in the heat pump type air conditioner, so that it is possible to enable the cogeneration system to positively cope with ambient temperature conditions, and to maximize the heating performance of the heat pump type air conditioner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of a cogeneration system according to the present invention will be described with reference to the annexed drawings.

FIG. 1is a schematic diagram of a cogeneration system according to a first embodiment of the present invention, illustrating a state in which a heat pump type air conditioner included in the cogeneration system operates in a heating mode under a heavy-frost condition.FIG. 2is a schematic diagram of the cogeneration system according to the first embodiment of the present invention, illustrating a state in which the heat pump type air conditioner operates in the heating mode under a non-frost condition.FIG. 3is a schematic diagram of the cogeneration system according to the first embodiment of the present invention, illustrating a state in which the heat pump type air conditioner operates in the heating mode under a light-frost condition.FIG. 4is a schematic diagram of the cogeneration system according to the first embodiment of the cogeneration system, illustrating a state in which the heat pump type air conditioner operates in a cooling mode.

As shown inFIGS. 1 to 4, the cogeneration system includes an engine2, a generator10connected to an output shaft of the engine2to generate electricity, an engine-cooling heat exchanger20to absorb heat from cooling water used to cool the engine2, and an exhaust gas heat exchanger30to absorb heat from exhaust gas discharged from the engine2. The cogeneration system also includes a heat pump type air conditioner40, which includes a compressor41, a directional valve42, an indoor heat exchanger43, an expansion device44, and an outdoor heat exchanger45. The cogeneration system further includes a pre-heater50to pre-heat air blown toward the outdoor heat exchanger45during a heating operation of the heat pump type air conditioner40, an auxiliary evaporator60to evaporate a refrigerant emerging from the outdoor heat exchanger45during the heating operation of the heat pump type air conditioner40, and a heat transfer means70to transfer heat from the engine-cooling heat exchanger20and heat from the exhaust gas heat exchanger30to at least one of the pre-heater50and auxiliary evaporator60while controlling the amount of the transferred heat in accordance with the frost condition of the outdoor heat exchanger45.

The engine2includes a combustion chamber defined in the interior of the engine2.

A fuel tube3and an exhaust tube4are connected to the engine2. The fuel tube3is adapted to supply fuel such as liquefied gas or liquefied petroleum gas into the combustion chamber. The exhaust tube4is adapted to guide exhaust gas discharged from the combustion chamber.

The exhaust tube4is arranged between the engine2and the exhaust gas heat exchanger30.

The engine-cooling heat exchanger20is connected to the engine2via cooling water circulation conduits7and8so that the cooling water, which is heated while cooling the engine2, transfers heat to the engine-cooling heat exchanger20while passing through the engine-cooling heat exchanger20, and is then again circulated into the engine2.

A cooling water circulation pump9is connected to one of the engine2, engine-cooling heat exchanger20, and cooling water circulation conduits7and8.

The generator10may be an AC generator or a DC generator.

An inverter12is coupled to the generator10to perform DC/AC conversion on electricity generated from the generator10.

The above-described cogeneration system may be implemented to supply only the electricity generated from the generator10to the heat pump type air conditioner40or to selectively supply the electricity generated from the generator10or electricity supplied from an external electricity supply source14to the heat pump type air conditioner40. For simplicity of description, the following description will be given only in conjunction with the case in which the electricity generated from the generator10or electricity supplied from an external electricity supply source14is selectively supplied to the heat pump type air conditioner40.

An electricity supply switch16is connected to the external electricity supply source14. The electricity supply switch16has an output terminal17connected to the heat pump type air conditioner40via an electricity feed line. The electricity supply switch16also has a first input terminal18connected to the external electricity supply source14via an electricity feed line, and a second input terminal19connected to the generator10via an electricity feed line.

When the electricity supply switch16is switched to an external electricity supply mode, the electricity feed lines of the external electricity supply source14and heat pump type air conditioner40are connected by the electricity supply switch16. In this case, accordingly, the electricity from the external electricity supply source14is supplied to the heat pump type air conditioner40. On the other hand, when the electricity supply switch16is switched to a generator electricity supply mode, the electricity supply lines of the generator10and heat pump type air conditioner40are connected by the electricity supply switch16. In this case, accordingly, the electricity from the generator10is supplied to the heat pump type air conditioner40.

For convenience of description, the following description will be given only in conjunction with the case in which the electricity generated from the generator10is supplied to the heat pump type air conditioner40.

The heat pump type air conditioner40further includes an indoor fan46to blow indoor air to the indoor heat exchanger43, and an outdoor fan47to blow outdoor air to the outdoor heat exchanger45.

The indoor heat exchanger43and indoor fan46constitute an indoor unit48of the heat pump type air conditioner40. The compressor41, directional valve42, expansion device44, outdoor heat exchanger45, and outdoor fan47constitute an outdoor unit49of the heat pump type air conditioner40.

The pre-heater50is arranged upstream from the outdoor heat exchanger45with respect to a flowing direction of outdoor air O blown toward the outdoor heat exchanger45such that the outdoor air O is fed to the outdoor heat exchanger25after being pre-heated by the pre-heater50.

The auxiliary evaporator60is arranged between the outdoor heat exchanger45and the directional valve42or between the directional valve42or the compressor41such that the refrigerant, which has been evaporated while passing through the outdoor heat exchanger45, is circulated into the compressor41after being re-evaporated by the auxiliary evaporator60.

When the heat pump type air conditioner40operates in a heating mode, and the outdoor heat exchanger45is under a heavy-frost condition, the heat transfer means70transfers heat from the engine-cooling heat exchanger20and heat from the exhaust gas heat exchanger30to the pre-heater50, as shown inFIG. 1. Also, when the heat pump type air conditioner40operates in the heating mode, and the outdoor heat exchanger45is under a non-frost condition, the heat transfer means70transfers the heat from the engine-cooling heat exchanger20and the heat from the exhaust gas heat exchanger30to the auxiliary evaporator60, as shown inFIG. 2. On the other hand, when the heat pump type air conditioner40operates in the heating mode, and the outdoor heat exchanger45is under a light-frost condition, the heat transfer means70transfers heat from the engine-cooling heat exchanger20and heat from the exhaust gas heat exchanger30to the pre-heater50and auxiliary evaporator60, respectively, as shown inFIG. 3.

The heat transfer means70includes pre-heater circulation conduits71and72to guide a heat medium to be circulated around the engine-cooling heat exchanger20, exhaust gas heat exchanger30, and pre-heater50, auxiliary evaporator circulation conduits73and74to guide the heat medium to be circulated around the engine-cooling heat exchanger20, exhaust gas heat exchanger39, and auxiliary evaporator60, and a heat medium circulation pump75to pump the heat medium for circulation of the heat medium. The heat transfer means70also includes a control valve76to control the amount of the heat transfer circulated through the pre-heater circulation conduits71and72and auxiliary evaporator circulation conduits73and74, an outdoor temperature sensor78to measure outdoor temperature or the temperature of the outdoor heat exchanger45, and a controller to control the control valve76in accordance with the outdoor temperature measured by the outdoor temperature sensor78.

The auxiliary evaporator circulation conduits73and74are branched from the pre-heater circulation conduit71or72upstream from the pre-heater50such that the auxiliary evaporator circulation conduits73and74are bypassed through the auxiliary evaporator60. The auxiliary evaporator circulation conduits73and74are joined to the pre-heater circulation conduit71or72downstream from the pre-heater50.

The heat medium circulation pump75is directly connected to one of the engine-cooling heat exchanger20, exhaust gas heat exchanger30, and pre-heater circulation conduits71and72. The following description will be given only in conjunction with the case in which the heat medium circulation pump75is directly connected to the pre-heater circulation conduit71or72between the engine-cooling heat exchanger20and the exhaust gas heat exchanger40.

Although the control valve76is arranged at a branching region where the auxiliary evaporator circulation conduits73and74are branched from the pre-heater circulation conduit71or72to control the amount of the heat medium circulated through the auxiliary evaporator circulation conduits73and74or pre-heater circulation conduits71and72, in the illustrated case, such control valves may be arranged at the pre-heater circulation conduits71and72and auxiliary evaporator circulation conduits73and74, respectively, to control respective heat medium amounts circulated through the circulation conduits. The following description will be given only in conjunction with the case in which only one control valve76is arranged at a branching region where the auxiliary evaporator circulation conduits73and74are branched from the pre-heater circulation conduit71or72.

The outdoor temperature sensor78may be mounted to the outdoor unit49such that the outdoor temperature sensor78is spaced apart from the outdoor heat exchanger45, so as to measure the temperature of outdoor air. Alternatively, the outdoor temperature sensor78may be mounted to the outdoor heat exchanger45to measure the temperature of the outdoor heat exchanger45. The following description will be given only in conjunction with the case in which the outdoor temperature sensor78is used to measure the temperature of the outdoor air.

When the heat pump type air conditioner40operates in the heating mode, and the temperature measured by the temperature sensor78is in a heavy-frost or over-frost temperature range (for example, a temperature range of −5° C. to 5° C.), the control unit80controls the control valve78to operate in a pre-heater circulation mode, as shown inFIG. 1.

When the heat pump type air conditioner40operates in the heating mode, and the temperature measured by the temperature sensor78is in a non-frost temperature range (for example, a temperature range of more than 5° C.), the control unit80controls the control valve78to operate in an auxiliary evaporator circulation mode, as shown inFIG. 2.

On the other hand, when the heat pump type air conditioner40operates in the heating mode, and the temperature measured by the temperature sensor78is in a light-frost temperature range (for example, a temperature range of less than −5° C.), the control unit80controls the control valve78to operate in a common mode, as shown inFIG. 3.

Hereinafter, operation of the cogeneration system having the above-described arrangement will be described.

When fuel is supplied into the engine2via the fuel tube3, and the engine2is subsequently driven, the output shaft of the engine2is rotated, thereby causing the generator10to generate electricity.

Exhaust gas, which is discharged from the engine2, is fed to the exhaust gas heat exchanger30via the exhaust tube4, and is then discharged to the atmosphere after releasing its heat into the exhaust gas heat exchanger30.

When the cooling water circulation pump9operates during the operation of the engine2, the cooling water, which is heated while cooling the engine2, is fed to the engine-cooling heat exchanger20via the cooling water circulation conduit7, and is then circulated into the engine2via the cooling water circulation conduit8after releasing its heat into the engine-cooling heat exchanger20.

Meanwhile, the temperature sensor78measures outdoor temperature, and outputs a signal indicative of the measured outdoor temperature to the controller80.

When the heat pump type air conditioner40operates in the heating mode, and the temperature measured by the temperature sensor78is in a heavy-frost or over-frost temperature range (for example, a temperature range of −5° C. to 5° C.), the control unit80controls the control valve78to operate in the pre-heater circulation mode, as shown inFIG. 1. The control unit80also controls the heat medium circulation pump75to be driven, the directional valve42to be switched to the heating mode, and the compressor41to be driven.

When the control valve78operates in the pre-heater circulation mode, the pre-heater circulation conduits71and72are opened, and the auxiliary evaporator circulation conduits73and74are closed.

When the heat medium circulation pump75operates under the condition in which the pre-heater circulation conduits71and72are opened, and the auxiliary evaporator circulation conduits73and74are closed, the heat medium absorbs heat from the engine-cooling heat exchanger20while passing around the engine-cooling heat exchanger20, and also absorbs heat from the exhaust gas heat exchanger30while passing around the exhaust gas heat exchanger30.

After absorbing the heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30, the heat medium is fed to the pre-heater50via the pre-heater circulation conduit71, so that the heat medium transfers the absorbed heat to the pre-heater50. Thereafter, the heat medium is circulated around the engine-cooling heat exchanger20via the pre-heater circulation conduit72.

When the directional valve42is switched to a heating mode in the procedure in which the waste heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30is recovered by the heat medium, and the recovered waste heat is transferred to the pre-heater50, and the compressor41operates, the compressor41compresses low-temperature and low-pressure refrigerant gas, thereby changing the refrigerant gas into a high-temperature and high-pressure state. The high-temperature and high-pressure refrigerant gas is fed into the indoor heat exchanger43via the directional valve42, and discharges its heat into indoor air while passing through the indoor heat exchanger43, so that the refrigerant gas is condensed into a liquid state.

Subsequently, the condensed refrigerant is expanded while passing through the expansion device44, and is then fed into the outdoor heat exchanger45. The expanded refrigerant absorbs heat from outdoor air O while passing through the outdoor heat exchanger45, so that the refrigerant is evaporated.

The evaporated refrigerant passes through the auxiliary evaporator60without any heat exchange or any state change, and is subsequently circulated into the compressor41via the directional valve42.

Meanwhile, the outdoor air O blown to the outdoor heat exchanger45is heated by the pre-heater50, and then passes around the outdoor heat exchanger45to prevent the outdoor heat exchanger45from being frosted.

On the other hand, when the heat pump type air conditioner40operates in the heating mode, and the temperature measured by the temperature sensor78is in a non-frost temperature range (for example, a temperature range of more than 5° C.), the control unit80controls the control valve78to operate in an auxiliary evaporator circulation mode, as shown inFIG. 2. The control unit80also controls the heat medium circulation pump75to be driven, the directional valve42to be switched to the heating mode, and the compressor41to be driven.

When the control valve78operates in the auxiliary evaporator circulation mode, the pre-heater circulation conduits71and72are closed, and the auxiliary evaporator circulation conduits73and74are opened.

When the heat medium circulation pump75operates under the condition in which the pre-heater circulation conduits71and72are closed, and the auxiliary evaporator circulation conduits73and74are opened, the heat medium absorbs heat from the engine-cooling heat exchanger20while passing around the engine-cooling heat exchanger20, and subsequently absorbs heat from the exhaust gas heat exchanger30while passing around the exhaust gas heat exchanger30.

After absorbing the heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30, the heat medium is fed to the auxiliary evaporator60via the auxiliary evaporator circulation conduit73, so that the heat medium transfers the absorbed heat to the auxiliary evaporator60. Thereafter, the heat medium is circulated around the engine-cooling heat exchanger20via the auxiliary evaporator circulation conduit74.

When the directional valve42is switched to a heating mode in the procedure in which the waste heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30is recovered by the heat medium, and the recovered waste heat is transferred to the auxiliary evaporator60, and the compressor41operates, the compressor41compresses low-temperature and low-pressure refrigerant gas, thereby changing the refrigerant gas into a high-temperature and high-pressure state. The high-temperature and high-pressure refrigerant gas is fed into the indoor heat exchanger43via the directional valve42, and discharges its heat into indoor air while passing through the indoor heat exchanger43, so that the refrigerant gas is condensed into a liquid state.

Subsequently, the condensed refrigerant is expanded while passing through the expansion device44, and is then fed into the outdoor heat exchanger45. The expanded refrigerant absorbs heat from outdoor air O while passing through the outdoor heat exchanger45, so that the refrigerant is evaporated.

The evaporated refrigerant is further evaporated by the auxiliary evaporator60while passing through the auxiliary evaporator60, and is subsequently introduced into the compressor41via the directional valve42. Thus, circulation of the refrigerant41is achieved.

The refrigerant41introduced into the compressor41repeats the above-described circulation, so that the refrigerant41is repeatedly evaporated. As a result, it is possible to achieve an improvement in the heating performance of the indoor heat exchanger42and a reduction in the power consumption of the compressor41in accordance with the repeated evaporation of the refrigerant41.

On the other hand, when the heat pump type air conditioner40operates in the heating mode, and the temperature measured by the temperature sensor78is in a light-frost temperature range (for example, a temperature range of less than −5° C.), the control unit80controls the control valve78to operate in a common mode, as shown inFIG. 3. The control unit80also controls the heat medium circulation pump75to be driven, the directional valve42to be switched to the heating mode, and the compressor41to be driven.

When the control valve78operates in the common mode, both the pre-heater circulation conduits71and72and the auxiliary evaporator circulation conduits73and74are opened.

When the heat medium circulation pump75operates under the condition in which the pre-heater circulation conduits71and72and auxiliary evaporator circulation conduits73and74are opened, the heat medium absorbs heat from the engine-cooling heat exchanger20while passing around the engine-cooling heat exchanger20, and subsequently absorbs heat from the exhaust gas heat exchanger30while passing around the exhaust gas heat exchanger30.

After absorbing the heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30, the heat medium is distributed into the pre-heater circulation conduits71and72and auxiliary evaporator circulation conduits73and74.

Thus, a part of the heat medium is fed to the pre-heater50via the pre-heater circulation conduit71, so that the heat medium transfers the absorbed heat to the pre-heater50. Thereafter, the heat medium is circulated around the engine-cooling heat exchanger20via the pre-heater circulation conduit72. The remaining part of the heat medium is fed to the auxiliary evaporator60via the auxiliary evaporator circulation conduit73, so that the heat medium transfers the absorbed heat to the auxiliary evaporator60. Thereafter, the heat medium is circulated around the engine-cooling heat exchanger20via the auxiliary evaporator circulation conduit74.

That is, the waste heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30is partially used to prevent the indoor heat exchanger45from being frosted, and is partially used to improve the heating performance of the indoor heat exchanger42.

Meanwhile, the controller80stops the heat medium circulation pump75, irrespective of the temperature measured by the temperature sensor78, when the heat pump type air conditioner40is to operate in a cooling mode. In this case, the controller80also switches the directional valve42to a cooling mode, and also operates the compressor41.

When the directional valve42is switched to a cooling mode, and the compressor41operates, the compressor41compresses low-temperature and low-pressure refrigerant gas, thereby changing the refrigerant gas into a high-temperature and high-pressure state. The high-temperature and high-pressure refrigerant gas passes through the auxiliary evaporator60via the directional valve42without any heat exchange with the auxiliary evaporator60. The refrigerant gas is then fed into the outdoor heat exchanger45, and discharges its heat into outdoor air O while passing through the outdoor heat exchanger45, so that the refrigerant gas is condensed into a liquid state.

Subsequently, the condensed refrigerant is expanded while passing through the expansion device44, and is then fed into the indoor heat exchanger43. The expanded refrigerant absorbs heat from indoor air I while passing through the indoor heat exchanger43, so that the refrigerant is evaporated.

The evaporated refrigerant is circulated into the compressor41via the directional valve42.

On the other hand, when the heat medium circulation pump75is in a stopped state, the heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30is discharged to the atmosphere without being transferred to the pre-heater50or auxiliary evaporator60.

FIG. 5is a schematic diagram of a cogeneration system according to a second embodiment of the present invention, illustrating a state in which a heat pump type air conditioner included in the cogeneration system operates in a cooling mode.

As shown inFIG. 5, the cogeneration system includes a radiator90to radiate heat, and a heat transfer means70′ to transfer heat from the engine-cooling heat exchanger20to the radiator90when the heat pump type air conditioner40operates in a cooling mode.

The radiator90includes a radiator heat exchanger92connected to the heat transfer means70′, and a radiator fan94to blow the outdoor air O to the radiator heat exchanger92.

The heat transfer means70′ includes pre-heater circulation conduits71and72to guide a heat medium to be circulated around the engine-cooling heat exchanger20, exhaust gas heat exchanger30, and pre-heater50, auxiliary evaporator circulation conduits73and74to guide the heat medium to be circulated around the engine-cooling heat exchanger20, exhaust gas heat exchanger30, and auxiliary evaporator60, and a heat medium circulation pump75to pump the heat medium for circulation of the heat medium. The heat transfer means70′ also includes a control valve76to control the amount of the heat transfer circulated through the pre-heater circulation conduits71and72and auxiliary evaporator circulation conduits73and74, an outdoor temperature sensor78to measure outdoor temperature or the temperature of the outdoor heat exchanger45, radiator circulation conduits81and82bypassed from pre-heater circulation conduits71and72to guide the heat medium to be circulated around the engine-cooling heat exchanger20and radiator heat exchanger92, a first valve84arranged at a branching region where the radiator circulation conduits81and82are branched from the pre-heater circulation conduit71or72, to alternately open/close the pre-heater circulation conduits71and72and the radiator circulation conduits81and82, and a second valve86arranged at a joining region where the radiator circulation conduits73and74are joined to the pre-heater circulation conduit71or72, to alternately open/close the pre-heater circulation conduits71and72and the radiator circulation conduits81and82. The heat transfer means70′ further includes a controller80to control the first and second valves84and86in accordance with whether the heat pump type air conditioner40operates in a cooling mode or in a heating mode, and to control the control valve76in accordance with the outdoor temperature measured by the outdoor temperature sensor78.

The heat medium circulation pump75is directly connected to the pre-heater circulation conduit71or72between the engine-cooling heat exchanger20and the exhaust gas heat exchanger30.

The radiator circulation conduits81and82are branched from the pre-heater circulation conduit71or72between the heat medium circulation pump75and the exhaust gas heat exchanger30such that the radiator circulation conduits81and82are bypassed around the radiator heat exchanger92. The radiator circulation conduits81and82are joined to the pre-heater circulation conduit71or72upstream from the engine-cooling heat exchanger20.

During a heating operation of the heat pump type air conditioner40, the first and second valves84and86operate in a pre-heater circulation mode to open the pre-heater circulation conduits71and72and to close the radiator circulation conduits81and82. During a cooling operation of the heat pump type air conditioner40, the first and second valves84and86operate in a radiator circulation mode to close the pre-heater circulation conduits71and72and to open the radiator circulation conduits81and82.

The cogeneration system of the second embodiment has the same configuration and functions as those of the first embodiment, except for the radiator90, radiator circulation conduits81and82, first valve84and second valve86. Accordingly, the constituent elements of the second embodiment respectively corresponding to those of the first embodiment are designated by the same reference numerals, and no detailed description thereof will be given.

Hereinafter, operation of the cogeneration system having the above-described arrangement according to the second embodiment of the present invention will be described.

In the cooling operation of the heat pump type air conditioner40, the heat medium circulation pump75is driven, and the first and second valves84and86are controlled to operate in a radiator circulation mode. Also, the radiator fan94is driven, the directional valve is switched to a cooling mode, and the compressor41is driven.

When the first and second valves84and86are controlled to operate in the radiator circulation mode, and the heat medium circulation pump75is driven, the heat medium absorbs heat from the engine-cooling heat exchanger20while passing through the engine-cooling heat exchanger20. Subsequently, the heat medium is fed to the radiator heat exchanger92via the radiator circulation conduit81.

The heat medium fed to the radiator heat exchanger92transfers the heat absorbed from the engine-cooling heat exchanger20to the radiator heat exchanger92. The heat medium is then circulated around the engine-cooling heat exchanger20via the radiator circulation conduit82.

During the operation of the radiator fan94, outdoor air O is blown to the radiator heat exchanger92, so that the radiator heat exchanger92discharges heat to the blown outdoor air O.

On the other hand, when the directional valve42is switched to a cooling mode, and the compressor41is driven, the compressor41compresses low-temperature and low-pressure refrigerant gas, thereby changing the refrigerant gas into a high-temperature and high-pressure state. The high-temperature and high-pressure refrigerant gas is fed into the outdoor heat exchanger45via the directional valve42, and discharges its heat into outdoor air while passing through the outdoor heat exchanger45, so that the refrigerant gas is condensed into a liquid state.

Subsequently, the condensed refrigerant is expanded while passing through the expansion device44, and is then fed into the indoor heat exchanger43. The expanded refrigerant absorbs heat from indoor air I while passing through the indoor heat exchanger43, so that the refrigerant is evaporated.

The evaporated refrigerant is circulated into the compressor41via the directional valve42.

Meanwhile, the exhaust gas heat exchanger30discharges the heat absorbed from the exhaust gas to the atmosphere.

On the other hand, in the heating operation of the heat pump type air conditioner40, the heat medium circulation pump75is driven, and the first and second valves84and86are controlled to operate in a pre-heater circulation mode. Also, the directional valve is switched to a heating mode, the compressor41is driven, and the control valve76is controlled to operate in a pre-heater circulation mode, an auxiliary evaporator circulation mode, or a common mode in accordance with the outdoor temperature measured by the temperature sensor78or the temperature of the outdoor heat exchanger45.

When the first and second valves84and86are controlled to operate in the pre-heater circulation mode, and the heat medium circulation pump75is driven, the heat medium absorbs heat from the engine-cooling heat exchanger20while passing through the engine-cooling heat exchanger20. Subsequently, the heat medium also absorbs heat from the exhaust gas heat exchanger30while passing through the exhaust gas heat exchanger30.

The heat medium, which has absorbed the heat of the engine-cooling heat exchanger20and exhaust gas heat exchanger30, transfers the absorbed heat only to the pre-heater50, only to the auxiliary evaporator60, or to both the pre-heater50and the auxiliary evaporator60.

The switching operation of the directional valve42to the heating mode, the operation of the compressor41, and the control operation of the control valve76are the same as those of the first embodiment, so that no detailed description thereof will be given.

FIG. 6is a schematic diagram of a cogeneration system according to a third embodiment of the present invention.

As shown inFIG. 6, the cogeneration system includes a heat transfer means70″ to transfer only the heat of the engine-cooling heat exchanger20to the pre-heater50or to the auxiliary evaporator60during a heating operation of the heat pump type air conditioner40.

The heat transfer means70″ includes pre-heater circulation conduits71″ and72″, which connect the engine-cooling heat exchanger20and the pre-heater50to guide a heat medium to be circulated around the engine-cooling heat exchanger20and pre-heater50without passing around the exhaust gas heat exchanger30.

The cogeneration system of the third embodiment has the same configuration and functions as those of the first embodiment or second embodiment, except for the pre-heater circulation conduits71″ and72″. Accordingly, the constituent elements of the third embodiment respectively corresponding to those of the first embodiment or second embodiment are designated by the same reference numerals, and no detailed description thereof will be given.

The heat of the exhaust gas heat exchanger30is discharged to the atmosphere without being transferred to the pre-heater50or auxiliary evaporator60.

FIG. 7is a schematic diagram of a cogeneration system according to a fourth embodiment of the present invention.

As shown inFIG. 7, the cogeneration system includes a plurality of engines2,2′ . . . . The cogeneration system also includes a plurality of generators10,10′ . . . connected to respective shafts of the engines2,2′ . . . . The cogeneration system of the fourth embodiment has the same configuration and functions as those of any one of the first through third embodiments, except for the engines2,2′ . . . and generators10,10′ . . . . Accordingly, the constituent elements of the fourth embodiment respectively corresponding to those of any one of the first through third embodiments are designated by the same reference numerals, and no detailed description thereof will be given.

One or more of the engines2,2′ . . . operate in accordance with the load to be cooled or heated.

The cooling water circulation conduits7and8,7′ and8′ . . . are connected in parallel.

The cogeneration system of the fourth embodiment has the same configuration and functions as those of any one of the first through third embodiments, except that a plurality of engines2,2′ . . . , a plurality of fuel tubes3,3′ . . . , a plurality of exhaust gas tubes4,4′ . . . , a plurality of cooling water circulation conduits7,8,7′,8′ . . . , and a plurality of generators10,10′ . . . are used. Accordingly, the constituent elements of the fourth embodiment respectively corresponding to those of any one of the first through third embodiments are designated by the same reference numerals, and no detailed description thereof will be given.

FIG. 8is a schematic diagram of a cogeneration system according to a fifth embodiment of the present invention.

As shown inFIG. 8, the heat pump type air conditioner, that is, the heat pump type air conditioner40, which is included in the cogeneration system, is of a multi-type. That is, the heat pump type air conditioner40includes a plurality of indoor units48,48′ . . . , and a single outdoor unit49. The indoor units48,48′ . . . include indoor heat exchangers43,43′ . . . , which are connected in parallel, respectively.

The cogeneration system of this embodiment has the same configuration and functions as those of any one of the first through fourth embodiments, except that the heat pump type air conditioner40includes a plurality of indoor units48,48′ . . . , and thus, a plurality of indoor heat exchangers43,43′ . . . . Accordingly, the constituent elements of the fifth embodiment respectively corresponding to those of any one of the first through fourth embodiments are designated by the same reference numerals, and no detailed description thereof will be given.

FIG. 9is a schematic diagram of a cogeneration system according to a sixth embodiment of the present invention.

As shown inFIG. 9, the heat pump type air conditioner, that is, the heat pump type air conditioner40, which is included in the cogeneration system, includes a plurality of indoor units48,48′ . . . , and a plurality of outdoor units49,49′ . . . .

In the heat pump type air conditioner40, refrigerant conduits respectively included in the indoor units48,48′ . . . may be connected in parallel. Refrigerant conduits respectively included in the outdoor units49,49′ . . . may also be connected in parallel. The following description will be given in conjunction with the case in which each of the outdoor units49,49′ . . . are connected to an associated one of the indoor units48,48′ . . . to constitute one air conditioner set, and each air conditioner set operates independently of other air conditioner sets.

Each of the pre-heaters50,50′ . . . are arranged upstream from an associated one of the outdoor heat exchangers45,45′ . . . .

Pairs of pre-heater circulation conduits71and72,71′ and72′ . . . , which are connected in parallel, are connected to respective pre-heaters50,50′ . . . . to guide a heat medium to be circulated around the pre-heaters50,50′ . . . .

Each of the auxiliary evaporators60,60′ . . . may be arranged between an associated one of the outdoor heat exchangers45,45′ . . . and an associated one of the directional valves42,42′ . . . , or may be arranged between the associated one of the directional valves42,42′ . . . and an associated one of the compressors41,41′ . . . .

Pairs of auxiliary evaporator circulation conduits73and74,73′ and74′ . . . , which are connected in parallel, are connected to respective auxiliary evaporators60,60′ . . . to guide a heat medium to be circulated around the auxiliary evaporators60,60′ . . . .

The cogeneration system of this embodiment has the same configuration and functions as those of any one of the first through fifth embodiments, except that the heat pump type air conditioner40includes a plurality of indoor units48,48′ . . . , a plurality of outdoor units49,49′ . . . , a plurality of pre-heaters50,50′ . . . , a plurality of pre-heater circulation conduits71,72,71′,72′ . . . , a plurality of auxiliary evaporators60,60′ . . . , and a plurality of auxiliary evaporator circulation conduits73,74,73′,74′ . . . . Accordingly, the constituent elements of the sixth embodiment respectively corresponding to those of any one of the first through fifth embodiments are designated by the same reference numerals, and no detailed description thereof will be given.

The cogeneration system according to any one of the above-described embodiments of the present invention has various effects.

That is, the cogeneration system according to the present invention has an advantage in that waste heat of an engine is supplied, during a heating operation of the heat pump type air conditioner, to the pre-heater arranged to pre-heat outdoor air blown toward the outdoor heat exchanger or to the auxiliary evaporator arranged to evaporate refrigerant emerging from the outdoor heat exchanger, so that the cogeneration system exhibits a high energy efficiency.

In the cogeneration system according to the present invention, the heat of exhaust gas discharged from the engine is not transferred to the radiator during a cooling operation of the heat pump type air conditioner. During a cooling operation of the heat pump type air conditioner, only the heat of cooling water used to cool the engine is transferred to the radiator so that the transferred heat is discharged from the radiator. Accordingly, there are advantages in that it is possible to minimize the size of the radiator and the amount of air blown to the radiator, and to reduce costs and noise.

In the method for controlling the cogeneration system in accordance with the present invention, waste heat is selectively transferred to the pre-heater and auxiliary evaporator in accordance with frost conditions of the outdoor heat exchanger included in the heat pump type air conditioner, so that it is possible to enable the cogeneration system to positively cope with ambient temperature conditions, and to maximize the heating performance of the heat pump type air conditioner.