Abstract:
Provided is an energy system comprising: a screw compressor; a condenser; an expansion device; an evaporator; an evaporator heat source flow path configured to provide a heating medium supplied from an outside as a heat source of the evaporator; a lubricant oil heat-exchanging unit configured to perform a heat-exchanging operation of the heating medium on an evaporator heat source flow path and lubricant oil including a refrigerant inside the screw compressor, to heat the lubricant oil by the heating medium before the screw compressor starts up, and to cool the lubricant oil by the heating medium discharged from the evaporator after the evaporator is heated by the heating medium, after the screw compressor starts up; and a controller configured to control the lubricant oil heat-exchanging unit depending on whether the screw compressor starts up.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2015-0100333, filed on Jul. 15, 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an energy system, and more particularly, to an energy system capable of protecting a compressor by heating lubricant oil and a refrigerant in a screw compressor. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, a screw compressor compresses a low-pressure refrigerant gas with a high pressure. The screw compressor cools heat of the refrigerant gas generated between two screw rotors, and lubricant oil is continuously supplied into the screw compressor so that leakage of the refrigerant gas compressed in the two screw rotors can be prevented and a bearing, etc. can be cooled and lubricated. A lubricant oil storage chamber is provided in the screw compressor, and the lubricant oil collected in the lubricant oil storage chamber is supplied to the screw rotors, the bearing, a motor, etc. via each lubricant oil supply line, and the lubricant oil mixed with a refrigerant in the screw rotors is separated and recovered from a lubricant oil separator and then is collected into the lubricant oil storage chamber again. 
         [0006]    When a system including the screw compressor stops, a liquid refrigerant is introduced into the screw compressor, and the liquid refrigerant and the lubricant oil are mixed with each other such that the lubricant oil is cooled and the concentration of the mixture is lowered and damage occurs when the screw compressor starts up. Thus, a crank heater, etc. is installed in the screw compressor for warming-up of the screw compressor. However, the crank heater consumes a large amount of power when operating such that the efficiency of the system is lowered. Also, the screw compressor should be managed at a predetermined temperature or less so as to acquire a lubricating capability while the system operates, and an additional device therefor is required. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides an energy system capable of heating a refrigerant and lubricant oil in a screw compressor before start-up and cooling the lubricant oil while operating. 
         [0008]    According to an aspect of the present invention, there is provided an energy system including: a screw compressor; a condenser; an expansion device; an evaporator; an evaporator heat source flow path configured to provide a heating medium supplied from an outside as a heat source of the evaporator; a lubricant oil heat-exchanging unit configured to perform a heat-exchanging operation of the heating medium on an evaporator heat source flow path and lubricant oil including a refrigerant inside the screw compressor, to heat the lubricant oil by the heating medium before the screw compressor starts up, and to cool the lubricant oil by the heating medium discharged from the evaporator after the evaporator is heated by the heating medium, after the screw compressor starts up; and a controller configured to control the lubricant oil heat-exchanging unit depending on whether the screw compressor starts up. 
         [0009]    According to another aspect of the present invention, there is provided an energy system including: a screw compressor; a condenser; an expansion device; an evaporator; a lubricant oil heat-exchanger configured to perform a heat-exchanging operation of lubricant oil in a lubricant oil storage portion provided in the screw compressor and a heating medium on an evaporator heat source flow path; a lubricant oil circulation flow path configured to connect the lubricant oil storage portion and the lubricant oil heat exchanger, to deliver the lubricant oil in the lubricant oil storage portion to the lubricant oil heat exchanger, and to circulate the lubricant oil heat-exchanged by the lubricant oil heat exchanger into the lubricant oil storage portion; a lubricant oil circulation pump installed on the lubricant oil circulation flow path and configured to pump the lubricant oil in the lubricant oil storage portion; an injection flow path configured to inject the lubricant oil bypassed via the lubricant oil circulation flow path and heat-exchanged by the lubricant oil heat exchanger into the screw compressor; an injection flow path opening/closing valve installed on the injection flow path; a lubricant oil discharge flow path configured to guide the lubricant oil including the refrigerant at a motor provided in the screw compressor to be discharged toward the lubricant oil storage portion; a lubricant oil discharge pump installed on the lubricant oil discharge flow path; and a controller, before the screw compressor starts up, configured to operate the lubricant oil circulation pump and the lubricant oil discharge pump and to open the injection flow path opening/closing valve, and when temperature inside the screw compressor reaches a preset temperature, configured to stop an operation of the lubricant oil circulation pump and an operation of the lubricant oil discharge pump and to close the injection flow path opening/closing valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0011]      FIG. 1  is a schematic view of a configuration of an energy system according to a first embodiment of the present invention; 
           [0012]      FIG. 2  is a view illustrating an operating state of the energy system illustrated in  FIG. 1  in which lubricant oil is heated before a screw compressor starts up; 
           [0013]      FIG. 3  is a schematic view of a configuration of an energy system according to a second embodiment of the present invention; 
           [0014]      FIG. 4  is a view illustrating an operating state of the energy system illustrated in  FIG. 3  in which lubricant oil is heated before a screw compressor starts up; 
           [0015]      FIG. 5  is a schematic view of a configuration of an energy system according to a third embodiment of the present invention; 
           [0016]      FIG. 6  is a view illustrating an operating state of the energy system illustrated in  FIG. 5  in which lubricant oil is heated before a screw compressor starts up; and 
           [0017]      FIG. 7  is a view illustrating a state in which an operation of a lubricant oil discharge pump of the energy system illustrated in  FIG. 5  stops. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
         [0019]      FIG. 1  is a schematic view of a configuration of an energy system according to a first embodiment of the present invention, and  FIG. 2  is a view illustrating an operating state of the energy system illustrated in  FIG. 1  in which lubricant oil is heated before a screw compressor starts up. 
         [0020]    Referring to  FIGS. 1 and 2 , the energy system will be described as a heat pump, for example. The heat pump includes a screw compressor  10 , a condenser  20 , an expansion device  30 , an evaporator  40 , an evaporator heat source flow path  50 , a lubricant oil heat-exchanging unit, and a controller. 
         [0021]    The screw compressor  10  includes a screw rotor  11 , a motor  12 , and a lubricant oil storage portion  13 , which are disposed inside a housing. The screw rotor  11  will be described as two twin screw rotors, for example. The two twin screw rotors  11  are connected to the motor  12 . The lubricant oil storage portion  13  may be formed below the screw rotors  11  or may be formed integrally with a lubricant oil separator (not shown) that separates lubricant oil including a refrigerant discharged from a compressive chamber including the screw rotors  11 . The inside of the housing may be partitioned off into a motor chamber  12   a  in which the motor  12  is disposed, and the compressive chamber in which the screw rotors  11  are disposed. 
         [0022]    The condenser  20  condenses the refrigerant discharged from the screw compressor  10  using an external cooling source  23 , etc. The external cooling source  23  is used as a heating medium for generating steam, etc. The condenser  20  and the screw compressor  10  are connected to each other via a compressor discharge flow path  21 . 
         [0023]    The expansion device  30  is an expansion valve that expands the refrigerant condensed by the condenser  20 . The expansion device  30  and the condenser  20  are connected to each other via a condenser discharge flow path  22 . 
         [0024]    The evaporator  40  evaporates the refrigerant expanded by the expansion device  30  using the heating medium supplied from the outside. The evaporator  40  and the expansion device  30  are connected to each other via an expansion device discharge flow path  31 . 
         [0025]    The evaporator heat source flow path  50  is connected to the evaporator  40  and supplies the heating medium supplied from the outside to the evaporator  40 , thereby providing a heat source. Here, the heating medium may use waste heat in an industrial process, etc.. The evaporator heat source flow path  50  includes an evaporator heat source supply flow path  51  in which the heat source is supplied to the evaporator  40 , and an evaporator heat source discharge flow path  52  in which the heat source is discharged from the evaporator  40  after the evaporator  40  is heated by the heat source. 
         [0026]    The lubricant oil heat-exchanging unit performs a heat-exchanging operation of the heating medium discharged from the evaporator heat source discharge flow path  52  after the evaporator  40  is heated by the heating medium, and lubricant oil including the refrigerant inside the screw compressor  10  (hereinafter, referred to as ‘lubricant oil’). The temperature of the lubricant oil may be maintained at an appropriate level so that the viscosity of the lubricant oil may be secured. The lubricant oil heat-exchanging unit includes a lubricant oil heat exchanger  64 , a lubricant oil circulation flow path  60 , and a lubricant oil circulation pump  66 . 
         [0027]    The lubricant oil heat exchanger  64  is a heat exchanger that performs a heat-exchanging operation of the heating medium on the evaporator heat source flow path  50  and lubricant oil including the refrigerant inside the screw compressor  10 . That is, the lubricant oil heat exchanger  64  is installed between the evaporator heat source discharge flow path  52  and the lubricant oil circulation flow path  60 . Before the screw compressor  10  starts up, the heating medium on the evaporator heat source discharge flow path  52  is supplied to the lubricant oil heat exchanger  64  in a state in which heat-exchanging of the heating medium and the lubricant oil is not performed in the evaporator  40 , and after the screw compressor  10  starts up, the heating medium on the evaporator heat source discharge flow path  52  is supplied to the lubricant oil heat exchanger  64  in a state in which the heat medium is discharged from the evaporator heat source discharge flow path  52  after the evaporator  40  is heated by the heating medium. Thus, the lubricant oil heat exchanger  64  may be used to heat the lubricant oil before the screw compressor  10  starts up, and after the screw compressor  10  starts up and when the screw compressor  10  operates normally, the lubricant oil heat exchanger  64  may be used to cool the lubricant oil. However, embodiments of the present invention are not limited thereto, and a bypass flow path (not shown) formed to bypass the evaporator  40  on the evaporator heat source flow path  50  is provided. Thus, the bypass flow path (not shown) may be connected to the lubricant oil heat exchanger  64  so that heat of the heating medium may also be supplied to the lubricant oil heat exchanger  64  via the bypass flow path (not shown). 
         [0028]    The lubricant oil circulation flow path  60  includes a first lubricant oil circulation flow path  61  that is connected to the lubricant oil heat exchanger  64  from the lubricant oil storage portion  13  and formed to discharge lubricant oil in the lubricant oil storage portion  13  toward the lubricant oil heat exchanger  64 , and a second lubricant oil circulation flow path  62  that is connected to the lubricant oil storage portion  13  from the lubricant oil heat exchanger  64  and formed to circulate the lubricant oil heated by the lubricant oil heat exchanger  64  into the lubricant oil storage portion  13 . 
         [0029]    The lubricant oil circulation pump  66  is installed on the first oil lubricant circulation flow path  61  and pumps the lubricant oil in the lubricant oil storage portion  13 . An operation of the lubricant oil circulation pump  66  is controlled by the controller (not shown). 
         [0030]    The controller (not shown) operates the lubricant oil circulation pump  66  before the screw compressor  10  starts up. Also, the controller (not shown) controls an operation of the lubricant oil circulation pump  66  according to the temperature inside the screw compressor  10  since the lubricant oil circulation pump  66  starts to operate. The temperature inside the screw compressor  10  is the temperature of the lubricant Oil. 
         [0031]    An operation of the energy system (the heat pump) having the above configuration according to the first embodiment of the present invention will be described as below. 
         [0032]    Referring to  FIG. 2 , the controller operates the lubricant oil circulation pump  66  before the screw compressor  10  starts up. 
         [0033]    When the lubricant oil circulation pump  66  operates, the lubricant oil in the lubricant oil storage portion  13  is introduced into the lubricant oil heat exchanger  64  via the first lubricant oil circulation flow path  61 . The lubricant oil in the lubricant oil storage portion  13  is lubricant oil including the refrigerant, and hereinafter, is referred to as lubricant oil. 
         [0034]    The lubricant oil heat exchanger  64  performs a heat-exchanging operation of the lubricant oil introduced via the first lubricant oil circulation flow path  61  and the heating medium on the evaporator heat source discharge flow path  52 . Before the screw compressor  10  starts up, a heating-exchanging operation of the heating medium on the evaporator heat source flow path  50  and the refrigerant is not performed by the evaporator  40  so that heat of the heating medium on the evaporator heat source flow path  50  may be intactly supplied to the lubricant oil heat exchanger  64 . That is, before the screw compressor  10  starts up, the temperature of the heating medium on the evaporator heat source discharge flow path  52  is higher than a room temperature so that the heating medium on the evaporator heat source discharge flow path  52  may be be provided as a sufficient heat source for heating the lubricant oil using the lubricant oil heat exchanger  64 . Thus, when the lubricant oil is heated by the heating medium using the lubricant oil heat exchanger  64  and the temperature of the lubricant oil is increased, the refrigerant in the lubricant oil is vaporized, and the viscosity of the lubricant oil may be secured. 
         [0035]    The lubricant oil heated by the lubricant oil heat exchanger  64  is circulated into the lubricant oil storage portion  13  via the second lubricant oil circulation flow path  62 . When the lubricant oil heated by the lubricant oil heat exchanger  64  is supplied to the screw compressor  10 , the temperature inside the screw compressor  10  is increased so that pressure of the entire system is increased and damage may be be prevented from occurring due to a low pressure when the screw compressor  10  starts up. Also, the lubricant oil heated by the lubricant oil heat exchanger  64  and supplied to the screw compressor  10  may absorb or vaporize a part of the refrigerant in the compressive chamber of the screw compressor  10  when the screw compressor  10  starts up so that damage caused by flooded start may be reduced. 
         [0036]    The controller (not shown) operates the lubricant oil circulation pump  66  until the temperature inside the screw compressor  10  is equal to or higher than a preset temperature. Here, the preset temperature will be about 60° for example. When the temperature inside the screw compressor  10  reaches the preset temperature, the controller (not shown) stops an operation of the lubricant oil circulation pump  66 . 
         [0037]    Subsequently, the screw compressor  10  may start up so that the energy system may operate normally. When the screw compressor  10  starts up and operates normally, the refrigerant compressed by the screw compressor  10  is condensed by the condenser  20 , and the refrigerant condensed by the condenser  20  is expanded by the expansion device  30  and then is introduced into the evaporator  40 . After the refrigerant is heated by the heating medium introduced via the evaporator heat source flow path  50  and evaporated using the evaporator  40 , the refrigerant circulates into the screw compressor  10 . 
         [0038]    While the screw compressor  10  operates normally, as described above, when the temperature of the lubricant oil in the screw compressor  10  is equal to or higher than the preset temperature, the lubricant oil circulation pump  66  may operate for cooling of the lubricant oil. 
         [0039]    When the lubricant oil circulation pump  66  operates, the lubricant oil in the lubricant oil storage portion  13  is introduced into the lubricant oil heat exchanger  64  via the first lubricant oil circulation flow path  61 . 
         [0040]    The lubricant oil heat exchanger  64  performs a heat-exchanging operation of the heating medium discharged from the evaporator  40  after the evaporator  40  is heated by the heating medium, and the lubricant oil. Because heat of the heating medium is taken when the evaporator  40  is heated by the heating medium, the temperature of the heating medium is lower than the temperature of the lubricant oil. Thus, cooling of the lubricant oil may be performed by the lubricant oil heat exchanger  64 . 
         [0041]    Thus, no additional heater, etc. for heating the lubricant oil in the screw compressor  10  is required so that there is no power consumption for driving the heater, etc. and thus efficiency may be improved. 
         [0042]    In addition, the heating medium that is not used as the heat source for the evaporator  40  is used to heat the lubricant oil before the screw compressor  10  starts up so that the efficiency of energy usage may be further improved. 
         [0043]    In addition, when the screw compressor  10  operates, the heating medium discharged from the evaporator  40  after the evaporator  40  is heated by the heating medium, is used to cool the lubricant oil so that the efficiency of energy usage may be further improved. 
         [0044]      FIG. 3  is a schematic view of a configuration of an energy system according to a second embodiment of the present invention, and  FIG. 4  is a view illustrating an operating state of the energy system illustrated in  FIG. 3  in which lubricant oil is heated before a screw compressor starts up. 
         [0045]    Referring to  FIGS. 3 and 4 , the energy system according to the second embodiment of the present invention is a heat pump. A difference between the heat pump of the second embodiment and the heat pump of the first embodiment is that the heat pump according to the second embodiment further includes an injection flow path  70  that injects lubricant oil bypassed via the lubricant oil circulation flow path  60  and heat-exchanged by the lubricant oil heat exchanger  64  into an inside of the screw compressor  10 . Thus, the difference will be described in detail. 
         [0046]    The injection flow path  70  is a flow path in which the lubricant oil bypassed via the second lubricant oil circulation flow path  62  and heat-exchanged by the lubricant oil heat exchanger  64  is directly injected into the inside of the screw compressor  10 . 
         [0047]    The injection flow path  70  includes a motor injection flow path  71  in which the lubricant oil heat-exchanged by the lubricant oil heat exchanger  64  is injected into the motor  12 , and a screw rotor injection flow path  72  in which the lubricant oil heat-exchanged by the lubricant oil heat exchanger  64  is injected into the screw rotors  11 . A nozzle may be formed at each end of the motor injection flow path  71  and the screw rotor injection flow path  72 , or an additional nozzle may be combined with each end of the motor injection flow path  71  and the screw rotor injection flow path  72 . 
         [0048]    An injection flow path opening/closing valve  73  that controls injection of the lubricant oil by controlling opening/closing of the injection flow path  70  is installed on the injection flow path  70 . 
         [0049]    An operation of the energy system (the heat pump) having the above configuration according to the second embodiment of the present invention will be described as follows. 
         [0050]    Referring to  FIG. 4 , before the screw compressor  10  starts up, the controller operates the lubricant oil circulation pump  66  and opens the injection flow path opening/closing valve  73 . 
         [0051]    When the lubricant oil circulation pump  66  operates, the lubricant oil in the lubricant oil storage portion  13  is introduced into the lubricant oil heat exchanger  64  via the first lubricant oil circulation flow path  61 . 
         [0052]    The lubricant oil heat exchanger  64  performs a heat-exchanging operation of the lubricant oil introduced via the first lubricant oil circulation flow path  61  and the heating medium on the evaporator heat source discharge flow path  52 . Before the screw compressor  10  starts up, the heat-exchanging operation of the heating medium of the evaporator heat source flow path  50  and the refrigerant is not performed by the evaporator  40  so that heat of the heating medium on the evaporator heat source flow path  50  may be intactly supplied to the lubricant oil heat exchanger  64 . That is, before the screw compressor  10  starts up, the temperature of the heating medium on the evaporator heat source discharge flow path  52  is higher than the room temperature so that the heating medium on the evaporator heat source discharge flow path  52  may be provided as a sufficient heat source for heating the lubricant oil in the lubricant oil heat exchanger  64 . Thus, when the lubricant oil is heated by the heating medium in the lubricant oil heat exchanger  64  and the temperature of the lubricant oil is increased, the refrigerant in the lubricant oil is vaporized, and the viscosity of the lubricant oil may be secured. 
         [0053]    A part of the lubricant oil heated by the lubricant oil heat exchanger  64  and discharged via the second lubricant oil circulation flow path  62  is circulated into the lubricant oil storage portion  13 , and the other part thereof is introduced via the injection flow path  70 . 
         [0054]    When the lubricant oil circulated into the lubricant oil storage portion  13  is supplied to the screw compressor  10 , the temperature in the screw compressor  10  is increased so that pressure of the entire system is increased and damage may be be prevented from occurring due to a low pressure when the screw compressor  10  starts up. Also, the lubricant oil heated by the lubricant oil heat exchanger  64  and supplied to the screw compressor  10  may absorb or vaporize a part of the refrigerant in the compressive chamber of the screw compressor  10  when the screw compressor  10  starts up so that damage caused by flooded start may be reduced. The lubricant oil introduced via the injection flow path  70  may be injected into the motor  12  and the screw rotors  11 , respectively, via the motor injection flow path  71  and the screw rotor injection flow path  72 . The lubricant oil heated by the lubricant oil heat exchanger  64  is directly injected into the motor  12  and the screw rotors  11  so that introduction of the liquid refrigerant into the compressive chamber may be reduced when the screw compressor  10  starts up later. 
         [0055]    The controller (not shown) operates the lubricant oil circulation pump  66  until the temperature inside the screw compressor  10  is equal to or higher than a preset temperature, and opens the injection flow path opening/closing valve  73 . Here, the preset temperature will be about 60° C., for example. When the temperature inside the screw compressor  10  reaches the preset temperature, the controller (not shown) stops an operation of the lubricant oil circulation pump  66  and closes the injection flow path opening/closing valve  73 . 
         [0056]    Subsequently, the screw compressor  10  may start up so that the energy system may operate normally. When the screw compressor  10  starts up and operates normally, the refrigerant compressed by the screw compressor  10  is condensed by the condenser  20 , and the refrigerant condensed by the condenser  20  is expanded by the expansion device  30  and then is introduced into the evaporator  40 . After the refrigerant is heated by the heating medium introduced via the evaporator heat source flow path  50  and evaporated using the evaporator  40 , the refrigerant circulates into the screw compressor  10 . 
         [0057]    While the screw compressor  10  operates normally, as described above, when the temperature of the lubricant oil in the screw compressor  10  is equal to or higher than the preset temperature, the lubricant oil circulation pump  66  may operate for cooling of the lubricant oil, and the injection flow path opening/closing valve  73  may be opened. 
         [0058]    When the lubricant oil circulation pump  66  operates, the lubricant oil in the lubricant oil storage portion  13  is introduced into the lubricant oil heat exchanger  64  via the first lubricant oil circulation flow path  61 . 
         [0059]    The lubricant oil heat exchanger  64  performs a heat-exchanging operation of the heating medium discharged from the evaporator  40  after the evaporator  40  is heated by the heating medium, and the lubricant oil. Because heat of the heating medium is taken when the evaporator  40  is heated by the heating medium, the temperature of the heating medium is lower than the temperature of the lubricant oil. 
         [0060]    Thus, cooling of the lubricant oil may be performed by the lubricant oil heat exchanger  64 . 
         [0061]    Thus, no additional heater, etc. for heating the lubricant oil in the screw compressor  10  is required so that there is no power consumption for driving the heater, etc. and thus efficiency can be improved. 
         [0062]    In addition, the heating medium that is not used as the heat source for the evaporator  40  is used to heat the lubricant oil before the screw compressor  10  starts up so that the efficiency of energy usage may be further improved. 
         [0063]    In addition, when the screw compressor  10  operates, the heating medium discharged from the evaporator  40  after the evaporator  40  is heated by the heating medium, is used to cool the lubricant oil so that the efficiency of energy usage can be further improved. 
         [0064]    In addition, the lubricant oil heated by the lubricant oil heat exchanger  64  is directly injected into the motor  12  and the screw rotor  11  so that introduction of the liquid refrigerant into the compressive chamber can be reduced when the screw compressor  10  starts up later. 
         [0065]      FIG. 5  is a schematic view of a configuration of an energy system according to a third embodiment of the present invention.  FIG. 6  is a view illustrating an operating state of the energy system illustrated in  FIG. 5  in which lubricant oil is heated before a screw compressor starts up.  FIG. 7  is a view illustrating a state in which an operation of a lubricant oil discharge pump of the energy system illustrated in  FIG. 5  stops. 
         [0066]    Referring to  FIGS. 5 through 7 , the energy system according to the third embodiment of the present invention is a heat pump. A difference between the heat pump of the third embodiment and the heat pump of the second embodiment is that the heat pump according to the third embodiment further includes a lubricant oil discharge flow path  80  in which a motor chamber  12   a  and the lubricant oil storage portion  13  are connected to each other so that lubricant oil including a refrigerant in the motor chamber  12   a  is discharged toward the lubricant oil storage portion  13  before the screw compressor  10  starts up, and a lubricant oil discharge pump  82  installed on the lubricant oil discharge flow path  80 . Thus, the difference will be described in detail. 
         [0067]    The lubricant oil discharge flow path  80  connects the motor chamber  12   a  and the lubricant oil storage portion  13 , thereby guiding the lubricant oil including the refrigerant in the motor chamber  12   a  to the lubricant oil storage portion  13 . A check valve  84  that prevents backflow of the lubricant oil is installed on the lubricant oil discharge flow path  80 . 
         [0068]    A water level sensor  86  is installed in the motor chamber  12   a  so as to detect the water level of the lubricant oil in the motor chamber  12   a.  The controller may stop an operation of the lubricant oil discharge pump  82  when the water level detected by the water level sensor  86  is less than a preset water level. 
         [0069]    An operation of the energy system (the heat pump) having the above configuration according to the third embodiment of the present invention will be described as follows. 
         [0070]    Referring to  FIG. 6 , before the screw compressor  10  starts up, the controller operates both the lubricant oil circulation pump  66  and the lubricant oil discharge pump  82  and opens the injection flow path opening/closing valve  73 . 
         [0071]    When the lubricant oil discharge pump  82  operates, the lubricant oil introduced into the motor chamber  12   a  is delivered to the lubricant oil storage portion  13 . Thus, the lubricant oil including the liquid refrigerant introduced into the motor chamber  12   a  may be prevented in advance from being introduced into the screw rotor  11  when the screw compressor  10  starts up later. 
         [0072]    When the lubricant oil circulation pump  66  operates, the lubricant oil in the lubricant oil storage portion  13  is introduced into the lubricant oil heat exchanger  64  via the first lubricant oil circulation flow path  61 . 
         [0073]    The lubricant oil heat exchanger  64  performs a heat-exchanging operation of the lubricant oil introduced via the first lubricant oil circulation flow path  61  and the heating medium on the evaporator heat source discharge flow path  52 . Before the screw compressor  10  starts up, the heat-exchanging operation of the heating medium of the evaporator heat source flow path  50  and the refrigerant is not performed by the evaporator  40  so that heat of the heating medium on the evaporator heat source flow path  50  may be intactly supplied to the lubricant oil heat exchanger  64 . That is, before the screw compressor  10  starts up, the temperature of the heating medium on the evaporator heat source discharge flow path  52  is temperature of about 60° C. that is higher than the room temperature so that the heating medium on the evaporator heat source discharge flow path  52  may be provided as a sufficient heat source for heating the lubricant oil in the lubricant oil heat exchanger  64 . Thus, when the lubricant oil is heated by the heating medium in the lubricant oil heat exchanger  64  and the temperature of the lubricant oil is increased, the refrigerant in the lubricant oil is vaporized, and the viscosity of the lubricant oil may be secured. 
         [0074]    A part of the lubricant oil heated by the lubricant oil heat exchanger  64  and discharged via the second lubricant oil circulation flow path  62  is circulated into the lubricant oil storage portion  13 , and the other part thereof is introduced via the injection flow path  70 . 
         [0075]    When the lubricant oil circulated into the lubricant oil storage portion  13  is supplied to the screw compressor  10 , the temperature in the screw compressor  10  is increased so that pressure of the entire system is increased and damage may be prevented from occurring due to a low pressure when the screw compressor  10  starts up. Also, the lubricant oil heated by the lubricant oil heat exchanger  64  and supplied to the screw compressor  10  may absorb or vaporize a part of the refrigerant in the compressive chamber of the screw compressor  10  when the screw compressor  10  starts up so that damage caused by flooded start may be reduced. 
         [0076]    The lubricant oil introduced via the injection flow path  70  may be injected into the motor  12  and the screw rotor  11 , respectively, via the motor injection flow path  71  and the screw rotor injection flow path  72 . The lubricant oil heated by the lubricant oil heat exchanger  64  is directly injected into the motor  12  and the screw rotor  11  so that introduction of the liquid refrigerant into the compressive chamber may be reduced when the screw compressor  10  starts up later. 
         [0077]    The controller (not shown) operates the lubricant oil circulation pump  66  and the lubricant oil discharge pump  82  until the temperature inside the screw compressor  10  is equal to or higher than a preset temperature, and opens the injection flow path opening/closing valve  73 . Here, the preset temperature will be about 60°, for example. When the temperature inside the screw compressor  10  reaches the preset temperature, the controller (not shown) stops an operation of the lubricant oil circulation pump  66  and an operation of the lubricant oil discharge pump  82  and closes the injection flow path opening/closing valve  73 . 
         [0078]    Referring to  FIG. 7 , before the screw compressor  10  starts up, the controller (not shown) stops the operation of the lubricant oil discharge pump  82  when the water level detected by the water level sensor  86  is less than the preset water level. In this case, the operation of the lubricant oil circulation pump  66  is maintained. Also, the injection flow path opening/closing valve  73  is also opened. That is, the lubricant oil discharge pump  82  operates only when the water level in the motor chamber  12   a  is equal to or higher than the preset water level. Thus, the water level of the lubricant oil in the motor chamber  12   a  may be maintained at the present water level. 
         [0079]    Subsequently, the screw compressor  10  may start up so that the energy system may operate normally. When the screw compressor  10  starts up and operates normally, the refrigerant compressed by the screw compressor  10  is condensed by the condenser  20 , and the refrigerant condensed by the condenser  20  is expanded by the expansion device  30  and then is introduced into the evaporator  40 . After the refrigerant is heated by the heating medium introduced via the evaporator heat source flow path  50  and evaporated using the evaporator  40 , the refrigerant circulates into the screw compressor  10 . 
         [0080]    While the screw compressor  10  operates normally, as described above, when the temperature of the lubricant oil in the screw compressor  10  is equal to or higher than the preset temperature, the lubricant oil circulation pump  66  may operate for cooling of the lubricant oil, and the injection flow path opening/closing valve  73  may be opened. 
         [0081]    When the lubricant oil circulation pump  66  operates, the lubricant oil in the lubricant oil storage portion  13  is introduced into the lubricant oil heat exchanger  64  via the first lubricant oil circulation flow path  61 . 
         [0082]    The lubricant oil heat exchanger  64  performs a heat-exchanging operation of the heating medium discharged from the evaporator  40  after the evaporator  40  is heated by the heating medium, and the lubricant oil. Because heat of the heating medium is taken when the evaporator  40  is heated by the heating medium, the temperature of the heating medium is lower than the temperature of the lubricant oil. 
         [0083]    Thus, cooling of the lubricant oil may be performed by the lubricant oil heat exchanger  64 . 
         [0084]    Thus, no additional heater, etc. for heating the lubricant oil in the screw compressor  10  is required so that there is no power consumption for driving the heater, etc. and thus efficiency may be improved. 
         [0085]    In addition, the heating medium that is not used as the heat source for the evaporator  40  is used to heat the lubricant oil before the screw compressor  10  starts up so that the efficiency of energy usage may be further improved. 
         [0086]    In addition, when the screw compressor  10  operates, the heating medium discharged from the evaporator  40  after the evaporator  40  is heated by the heating medium, is used to cool the lubricant oil so that the efficiency of energy usage may be further improved. 
         [0087]    In addition, the lubricant oil heated by the lubricant oil heat exchanger  64  is directly injected into the motor  12  and the screw rotor  11  so that introduction of the liquid refrigerant into the compressive chamber may be reduced when the screw compressor  10  starts up later. 
         [0088]    As described above, in an energy system according to the one or more embodiments of the present invention, a heating medium supplied to an evaporator is used to heat lubricant oil in a screw compressor before the screw compressor starts up so that the efficiency of energy usage can be further improved. 
         [0089]    In addition, no additional heater for heating the lubricant oil in the screw compressor is required so that there is no power consumption for driving a heater, etc. and efficiency can be improved. 
         [0090]    In addition, when the screw compressor operates, the heating medium discharged from the evaporator after the evaporator is heated by the heating medium, is used to cool the lubricant oil so that the efficiency of energy usage can be further improved. 
         [0091]    In addition, the lubricant oil heated by a lubricant oil heat exchanger is directly injected into a motor and a screw rotor so that introduction of a liquid refrigerant into a compressive chamber can be reduced when the screw compressor starts up later. 
         [0092]    Furthermore, the lubricant oil introduced into the motor is discharged toward a lubricant oil storage portion before the screw compressor starts up so that the liquid refrigerant can be prevented in advance from being introduced into the screw rotor when the screw compressor starts up. 
         [0093]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.