Abstract:
Disclosed herein is an air conditioner comprising a plurality of indoor units and a common outdoor unit connected to each of the indoor units. The air conditioner further includes an additional indoor unit connected to an air conditioner comprising an indoor unit and an outdoor unit connected to the indoor unit. The additional indoor unit is installed in some place other than the installation place of the indoor unit. The indoor units are selectively or simultaneously operated by means of effective distribution of coolant in the outdoor unit so that the indoor units are properly operated by means of the single outdoor unit to provide a pleasant air conditioned environment.

Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 10-2002-0072883 and 10-2003-0004896 filed in KOREA on Nov. 21, 2002 and Jan. 24, 2003, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an air conditioner comprising a plurality of indoor units and a common outdoor unit connected to each of the indoor units, and more particularly to an improved air conditioner further including an additional indoor unit connected to an air conditioner comprising an indoor unit and an outdoor unit connected to the indoor unit, wherein a plurality of the indoor units can be simultaneously or individually operated by means of effective distribution of coolant in the outdoor unit of the air conditioner. 
   2. Description of the Related Art 
   As well known to those skilled in the art, air conditioners are generally classified into a separated type air conditioner comprising an indoor unit and an outdoor unit, which are separated from each other; an integrated type air conditioner comprising an indoor unit and an outdoor unit, which are integrated with each other; a wall mounted type air conditioner and a picture frame type air conditioner, each of which is mounted to a wall of a house; a free-standing type air conditioner which is constructed to stand in a room of a house; a single-split type air conditioner having a capacity to operate a single indoor unit in a small area such as a dwelling house; a medium- or large-sized type air conditioner having a large capacity to operate an indoor unit in a medium or large area such as an office building or a restaurant; and a multi-split type having a sufficient capacity to operate a plurality of indoor units. 
   The separated type air conditioner comprises an indoor unit disposed or mounted in a room of a house for supplying warm air or cool air to a room where the air conditioning is needed, and an outdoor unit for compressing and expanding a coolant so that a sufficient heat exchange operation is carried out in the indoor unit. 
   The multi-split type air conditioner comprises a plurality of indoor units disposed or mounted in a plurality of divided areas in a building, such as a school building, for individually supplying warm air or cool air to a space where the air conditioning is needed in each of the areas, and one or more outdoor units. The indoor and outdoor units constitute together a plurality of cooling cycles. In the aforesaid multi-split type air conditioner, however, the outdoor units must have sufficient capacities to simultaneously operate all of the indoor units even when all of the indoor units are operated at their maximum outputs. In other words, when a plurality of the indoor units are operated at their maximum outputs, the outdoor units of the multi-split type air conditioner must have capacities proportional to such outputs of the indoor units. 
   The single-split type air conditioner generally comprises an indoor unit and an outdoor unit. The indoor and outdoor units together constitute a cooling cycle. The capacity of the indoor unit is proportional to that of the outdoor unit. In other words, the outdoor unit of the single-split type air conditioner has a sufficient capacity to operate the indoor unit at its maximum output. 
   Among the aforesaid various kinds of the air conditioner, the present invention is connected with the separated single-split type air conditioner. 
   In Korea, most homes are generally organized by units of a family, and a life pattern in each of the homes is generalized. Most of the air conditioners are usually operated in the afternoon, and at that time the members of the family spend their time together in a living room or the other rooms of a house. 
   The air conditioner used in such a home is the single-split type air conditioner. As described above, the single-split type air conditioner comprises an indoor unit and an outdoor unit connected to the indoor unit. The outdoor unit of the single-split type air conditioner has a sufficient capacity to operate the indoor unit at its maximum output. 
   A conventional single-split type air conditioner is shown in  FIGS. 1 and 2 . As shown in  FIGS. 1 and 2 , the single-split type air conditioner comprises an outdoor unit  10  and an indoor unit  20 . The indoor unit  20  is installed in a living room or in one of the other rooms of the house. 
   The indoor unit of the single-split type air conditioner cannot be moved from one place to another place in the house. Consequently, the indoor unit of the air conditioner must be installed only in the living room or in one of the other rooms of the house, by which the air conditioning is accomplished only in the living room where the indoor unit of the air conditioner is installed or in one of the other rooms of the house where the indoor unit of the air conditioner is installed. 
   When the single-split type air conditioner has a capacity to air condition only the living room where the indoor unit of the air conditioner is installed or only one of the other rooms of the house where the indoor unit of the air conditioner is installed, the member(s) of the family in the other rooms of the house where the indoor unit of the air conditioner is not installed cannot enjoy the benefits of the air conditioning. However, it is possible for the member(s) of the family in the other rooms of the house where the indoor unit of the air conditioner is not installed to enjoy the benefits of the air conditioning if the air conditioner has a large enough capacity to air condition all of the rooms of the house, including the living room. To this end, an air conditioner having such a large capacity must be bought, which incurs an economic burden. 
   The aforesaid single-split type air conditioner having only a single indoor unit does not harmonize with the life patterns of most of the homes in Korea. As a result, a degree of satisfaction with the air conditioner is lowered, and thus a competitive power of the air conditioner is reduced. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an improved air conditioner further including an additional indoor unit connected to an air conditioner comprising an indoor unit and an outdoor unit connected to the indoor unit, wherein pressure reduction and flow rate of a coolant in the indoor units are effectively controllable by the outdoor unit, whereby the air conditioning is effectively accomplished. 
   In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an air conditioner comprising: an outdoor unit including a plurality of compressors for compressing a coolant, an outdoor heat exchanger connected to each of the compressors for condensing or evaporating the coolant as a condenser or an evaporator during cooling or heating a room of a house, and an expander connected to the outdoor heat exchanger for expanding the coolant; and an indoor unit including an indoor heat exchanger connected to the outdoor unit for evaporating or condensing the coolant as an evaporator or a condenser during cooling or heating the room of the house, the outdoor and indoor units together constituting a cooling cycle, wherein the outdoor unit comprises: a plurality of discharging pipes connected to the compressors for discharging the coolants compressed in the compressors, respectively; a connection pipe for gathering the coolants leaving the discharging pipes to guide the gathered coolants via the condenser, the expander, and the evaporator; a plurality of introducing pipes each branched off the end of the connection pipe for introducing the coolants into the compressors, respectively; and an oil separator disposed between the connection pipe and the introducing pipes for separating oil from the coolants discharged from the compressors, and wherein the air conditioner further comprises at least one auxiliary indoor unit including an indoor heat exchanger detachably attached to the outdoor unit. 
   In accordance with another aspect of the present invention, there is provided an air conditioner comprising: an outdoor unit including a plurality of compressors for compressing a coolant, an outdoor heat exchanger connected to each of the compressors for condensing or evaporating the coolant as a condenser or an evaporator during cooling or heating a room of a house, and an expander connected to the outdoor heat exchanger for expanding the coolant; and an indoor unit including an indoor heat exchanger connected to the outdoor unit for evaporating or condensing the coolant as an evaporator or a condenser during cooling or heating the room of the house, the outdoor and indoor units constituting together a cooling cycle, wherein the outdoor unit comprises: a plurality of discharging pipes connected to the compressors for discharging the coolants compressed in the compressors, respectively; a connection pipe for gathering the coolants leaving the discharging pipes to guide the gathered coolants via the condenser, the expander, and the evaporator; a plurality of introducing pipes each branched off the end of the connection pipe for introducing the coolants into the compressors, respectively; and an oil separator disposed between the connection pipe and the introducing pipes for separating oil from the coolants discharged from the compressors, and wherein the air conditioner further comprises: at least one auxiliary indoor unit including an indoor heat exchanger detachably attached to the outdoor unit; and an expansion distributor disposed between the outdoor unit and the indoor unit and between the outdoor unit and the auxiliary indoor unit for expanding the coolants to distribute the expanded coolants into each of the indoor heat exchangers of the indoor unit and the auxiliary indoor unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a view of a conventional air conditioner showing installation of the air conditioner in a house; 
       FIG. 2  is a view of the conventional air conditioner showing connection of an indoor unit of the air conditioner to an outdoor unit of the air conditioner; 
       FIG. 3  is a view of an air conditioner according to the present invention showing installation of the air conditioner in a house; 
       FIG. 4  is a view of the air conditioner according to the present invention showing connection of indoor units of the air conditioner to an outdoor unit of the air conditioner; 
       FIG. 5  is a schematic circuit diagram of an air conditioner according to a first preferred embodiment of the present invention; 
       FIG. 6  is a perspective view of an outdoor unit of the air conditioner according to the present invention with its upper case removed; 
       FIG. 7  is a longitudinal sectional view of an oil separator of the air conditioner according to the present invention; and 
       FIG. 8  is a schematic circuit diagram of an air conditioner according to a second preferred embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3  is a view of an air conditioner according to the present invention showing installation of the air conditioner in a house, and  FIG. 4  is a view of the air conditioner according to the present invention showing connection of indoor units of the air conditioner to an outdoor unit of the air conditioner. 
   As shown in  FIGS. 3 and 4 , the air conditioner comprises an outdoor unit  50 , a first indoor unit  70 , and a second indoor unit  80 . The outdoor unit  50  is connected to the first indoor units  70 . The outdoor unit  50  is also connected to the second indoor unit  80 . In the outdoor unit  50  is disposed an expansion distributor (See  FIG. 5 ) for controlling pressure reduction and flow rate of a coolant supplied to each of the first and second indoor units  70  and  80 . The expansion distributor is operated by means of a controlling unit, which will be described later in detail. 
   The aforesaid multi-split type air conditioner includes one or more outdoor units having sufficient capacities to simultaneously operate all of the indoor units even when all of the indoor units are operated at their maximum outputs. The outdoor and indoor units constitute together a plurality of cooling cycles. In the air conditioner according to the present invention, however, the outdoor unit  50  has a capacity to operate only one of the first and second indoor units  70  and  80  when it is operated at its maximum output although the outdoor unit  50  is connected to the first indoor unit  70  as well as the second indoor unit  80 . The outdoor and indoor units together constitute a single cooling cycle. Consequently, the first and second indoor units  70  and  80  cannot be simultaneously operated at their maximum outputs. Otherwise, only one of the first and second indoor units  70  and  80  can be operated at its maximum output, or both of the first and second indoor units  70  and  80  can be simultaneously operated at their appropriate outputs. 
   The air conditioner according to the present invention further includes an additional indoor unit connected to an air conditioner comprising an indoor unit and an outdoor unit connected to the indoor unit. 
   The air conditioner with the above-stated construction according to the present invention may be usually used for a house. The first and second indoor units  70  and  80  are installed in a first air-conditioning space A and a second air-conditioning space B, respectively. The first and second indoor units  70  and  80  can be selectively or simultaneously operated to cool or warm the desired air-conditioning space(s). 
   The first and second indoor units  70  and  80  may include a living room or one of the other rooms of the house. 
     FIG. 5  is a schematic circuit diagram of an air conditioner according to a first preferred embodiment of the present invention,  FIG. 6  is a perspective view of an outdoor unit of the air conditioner according to the present invention with its upper case removed, and  FIG. 7  is a longitudinal sectional view of an oil separator of the air conditioner according to the present invention. 
   As best shown in  FIG. 5 , one of the indoor units  70  (hereinafter, referred to as the first indoor unit) is connected to the outdoor unit  50  having a capacity to operate the first indoor unit  70  at its maximum output, to which the other of the indoor units  80  (hereinafter, referred to as the first indoor unit) is also connected. That is to say, the air conditioner shown in  FIG. 5  comprises the outdoor unit  50  mounted outside the room for compressing, condensing, and decompressing the coolant, and the first and second indoor units  70  and  80  each connected to the outdoor unit  50  and individually mounted in the rooms for evaporating the coolant. 
   As shown in  FIG. 6 , the outdoor unit  50  comprises: a plurality of compressors  52  and  53  for compressing the coolant to obtain gaseous coolant having high temperature and high pressure; an outdoor heat exchanger  54  connected to the compressors  52  and  53  for condensing the coolant by heat exchange between the coolant and outdoor air to obtain liquefied coolant having intermediate pressure and high temperature; and an outdoor fan  54   a  mounted at the outdoor heat exchanger  54  for blowing the outdoor air to the outdoor heat exchanger  54 . 
   The aforesaid compressors comprise a first compressor  52  having a coolant compression capacity of X %, and a second compressor  53  having a coolant compression capacity of (100−X) %. The coolant compression capacity of the first compressor  52  is larger than that of the second compressor  53 . 
   The outdoor unit  50  of the air conditioner further comprises an expansion distributor  60  disposed between the outdoor unit  50  and the first indoor unit  70  and between the outdoor unit  50  and the second indoor unit  80  in such a manner that supply of the coolant to the first and second indoor units  70  and  80  is controlled. The expansion distributor  60  controls a degree of decompression of the coolant and flow rate of the circulating coolant. 
   Especially, the outdoor unit  50  further comprises: discharging pipes o and o′ connected to the first and second compressors  52  and  53  for discharging the coolants compressed in the first and second compressors  52  and  53 , respectively; check valves  52   a  and  53   a  in the discharging pipes o and o′ at the rear end of the first and second compressors  52  and  53  for preventing the coolant having passed through the first and second compressors  52  and  53  from flowing backward; a connection pipe c for gathering the coolants leaving the discharging pipes o and o′ to guide the gathered coolants via the condenser, the expander, and the evaporator in the cooling cycle; introducing pipes i and i′ each branched off the end of the connection pipe c for introducing the coolants into the first and second compressors  52  and  53 , respectively; and an oil separator  56  disposed between the connection pipe c and the introducing pipe i and between the connection pipe c and the introducing pipe i′s for separating oil from the coolants discharged from the first and second compressors  52  and  53 . 
   Of course, the outdoor unit  50  of the air conditioner may further comprise a pair of accumulators (not shown) for accumulating surplus coolant produced depending upon the operating capacities of the first and second compressors  52  and  53  from the coolant having passed through the oil separator  56  and for separating the liquefied coolant from the coolant flowing into the first and second compressors  52  and  53 . 
   Nevertheless, it should be noted that the oil separator  56  may be adapted to serve as the aforesaid accumulators, i.e., to separate the liquefied coolant from the coolant flowing into the compressors  52  and  53  so that the operational reliability of each of the compressors  52  and  53  can be ensured as well as to separate the oil from the coolant so that it is supplied again to the first and second compressors  52  and  53 . 
   As shown in  FIG. 7 , the oil separator  56  comprises: a hermetically sealed casing  56   a  connected between the introducing pipes i and i′ where the coolant is mixed together before the coolant is supplied to the first and second compressors  52  and  53 ; a screen mesh  56   b  mounted in the inner upper part of the casing  56   a  for filtering foreign matters from the coolant and the oil; and oil separating pipes  56   c  and  56   c ′ disposed below the screen mesh  56   b . One of the oil separating pipes  56   c  has one end placed above the height of the liquefied coolant so that only gaseous coolant is introduced into casing  56   a . The other end of the oil separating pipe  56   c  is connected to one of the introducing pipes i′ for introducing the coolant into one of the first and second compressors  52  and  53 . Similarly, the other of the oil separating pipes  56   c ′ has one end placed above the height of the liquefied coolant so that only gaseous coolant is introduced into casing  56   a . The other end of the oil separating pipe  56   c ′ is connected to the other of the introducing pipes i for introducing the coolant into the other of the first and second compressors  52  and  53 . At the lower parts of the oil separating pipes  56  and  56 ′ are formed oil collection holes  56   d  and  56   d ′ through which the oil gathered on the bottom of the casing  56   a  is introduced into the oil separating pipes  56   c  and  56   c ′ by the force of a flow of the gaseous coolant, respectively. 
   Preferably, the oil separator  56  further comprises a disc-shaped screen  56   e  interposed between the screen mesh  56   b  and the upper end of each of the oil separating pipes  56   c  and  56   c ′ for preventing the liquefied coolant from flowing into the upper end of each of the oil separating pipes  56   c  and  56   c ′; and a fixing bracket  56   f  for fixing the oil separating pipes  56   c  and  56   c ′ to the inner wall of the casing  56   a  to prevent the oil separating pipes  56   c  and  56   c ′ from shaking in the casing  56   a.    
   The first indoor unit  70  comprises a first indoor heat exchanger  72  connected to the expansion distributor  60  via a coolant pipe  75  for producing cool air by heat exchange between the coolant and indoor air and evaporating the coolant to obtain gaseous coolant having low temperature and low pressure; and a first indoor fan  72   a  disposed at the first indoor heat exchanger  72  for blowing the indoor air to the first indoor heat exchanger  72 . Similarly, the second indoor unit  80  comprises a second indoor heat exchanger  82  connected to the expansion distributor  60  via a coolant pipe  85  for producing cool air by heat exchange between the coolant and indoor air and evaporating the coolant to obtain gaseous coolant having low temperature and low pressure; and a first indoor fan  82   a  disposed at the second indoor heat exchanger  82  for blowing the indoor air to the second indoor heat exchanger  82 . 
   It is preferable that the heat exchange capacity of the first indoor heat exchanger  72  of the first indoor unit  70  is larger than that of the second indoor heat exchanger  82  of the second indoor unit  80  so that the first indoor unit  70  can handle a larger cooling load than the second indoor unit  80 . 
   Operation of the air conditioner constructed as mentioned above is controlled by a microcomputer (not shown), and the first and second compressors  52  and  53  are operated on the basis of the operations of the first and second indoor units  70  and  80 , respectively. 
   When only the first indoor unit  70  is operated, at least one of the first and second compressors  52  and  53  is operated depending upon the cooling load. When only the second indoor unit  80  is operated, the first compressor  52  is not operated, but the second compressor  53  is operated. When both of the first indoor units  70  and  80  are operated simultaneously, both of the first and second compressors  52  and  53  are operated. 
   The expansion distributor  60  comprises: an electronic expansion valve  62  disposed between the outdoor heat exchanger  54  and the first indoor heat exchanger  72  for controlling the flow rate of the coolant and decompressing the coolant; a capillary tube  64  disposed between the outdoor heat exchanger  54  and the second indoor heat exchanger  82  for decompressing the coolant; and a distributing unit disposed between the electronic expansion valve  62  and the capillary tube  64  for selectively distributing the coolant having passed through the electronic expansion valve  62  or the capillary tube  64  depending upon operations of the first and second indoor units  70  and  80 . 
   The distributing unit comprises: a connection passage  66  connected between the front end of the electronic expansion valve  62  and the rear end of the capillary tube  64  in such a manner that the coolant flows between the electronic expansion valve  62  and the capillary tube  64 ; an auxiliary capillary tube  68  disposed in the connection passage  66  for decompressing the coolant; and a shutoff valve  67  mounted at the rear end of the capillary tube  64  for allowing or preventing the flow of the coolant having passed through the capillary tube  64  and the auxiliary capillary tube  68 . 
   Preferably, the shutoff valve  67  is a solenoid valve that can be controlled by an electrical signal from the microcomputer. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
               Electronic Expansion 
               Shutoff 
             
             
                 
               Operating Indoor Unit 
               Valve 62 
               Valve 67 
             
             
                 
                 
             
           
           
             
                 
               First Indoor Unit 70 
               On 
               Off 
             
             
                 
               Second Indoor Unit 80 
               Off 
               On 
             
             
                 
               First and Second Indoor 
               On 
               On 
             
             
                 
               Units 70 and 80 
             
             
                 
                 
             
           
        
       
     
   
   When only the first indoor unit  70  is operated, the electronic expansion valve  62  of the expansion distributor  60  is opened, and the shutoff valve  67  of the expansion distributor  60  is closed, as indicated in Table 1, so that the coolant passes through the electronic expansion valve  62  and then is introduced into the first indoor heat exchanger  72 . 
   When only the second indoor unit  80  is operated, the electronic expansion valve  62  of the expansion distributor  60  is closed, and the shutoff valve  67  of the expansion distributor  60  is opened, as indicated in Table 1, so that the coolant passes through the capillary tube  64  and the auxiliary capillary tube  68  and then is introduced into the second indoor heat exchanger  82 . 
   When both of the first and second indoor units  70  and  80  are simultaneously operated, the electronic expansion valve  62  and the shutoff valve  67  of the expansion distributor  60  are simultaneously opened, as indicated in Table 1, so that the coolant passes through the electronic expansion valve  62  and the capillary tube  64 , and then is introduced into the first and second indoor heat exchangers  72  and  82 , respectively. 
   The cooling operation of the air conditioner with the above-stated construction according to the first preferred embodiment of the present invention is as follows: 
   When only the first indoor unit  70  is operated by a user, at least one of the first and second compressors  52  and  53  is operated depending upon the cooling load thereof. The electronic expansion valve  62  is opened, and at the same time the shutoff valve  67  is closed. The outdoor fan  54   a  and the first indoor fan  72   a  are operated. 
   The coolant passes through the current operating one of the first and second compressors  52  and  53  with the result that gaseous coolant having high temperature and high pressure is obtained. The coolant having passed through the first compressor  52  or the second compressor  53  passes through the outdoor heat exchanger  54 , where heat exchange is performed between the coolant and outdoor air blown by the outdoor fan  54   a  to obtain liquefied coolant having intermediate temperature and high pressure. The coolant having passed through the outdoor heat exchanger  54  passes through the electronic expansion valve  62  so that the coolant is decompressed to obtain coolant having low temperature and low pressure. The coolant having passed through the electronic expansion valve  62  passes through the first indoor heat exchanger  72 , where heat exchange is performed between the coolant and indoor air blown by the first indoor fan  72   a  to obtain gaseous coolant having low temperature and low pressure, by which cool air is produced in the space where the first indoor unit  70  is installed. The coolant having passed through the first indoor heat exchanger  72  passes through the oil separator  56 , by which oil is separated from the coolant, and the coolant containing no oil therein is introduced into the operating first compressor  52  or the operating second compressor  53 . 
   As described above, the coolant is circulated through the first compressor  52  or the second compressor  53 , the outdoor heat exchanger  54 , the electronic expansion valve  62 , the first indoor heat exchanger  72 , and the oil separator  56 , to cool the space where the first indoor unit  70  is installed. 
   The operation of the first compressor  52  and/or the second compressor  53  is determined depending upon the indoor load of the space where the first indoor unit  70  is installed and the outdoor load of the space where the outdoor unit  50  is installed. The first and second compressors  52  and  53  are simultaneously operated when the load is relatively high. One of the first and second compressors  52  and  53  is operated when the load is relatively low. The degree of opening of the electronic expansion valve  62  is also controlled on the basis of the load. 
   When only the second indoor unit  80  is operated by the user, at least one of the first and second compressors  52  and  53  is operated. The electronic expansion valve  62  is closed, and at the same time the shutoff valve  67  is opened. The outdoor fan  54   a  and the second indoor fan  82   a  are operated. 
   The coolant passes through the current operating one of the first and second compressors  52  and  53  with the result that gaseous coolant having high temperature and high pressure is obtained. The coolant having passed through the first compressor  52  or the second compressor  53  passes through the outdoor heat exchanger  54 , where heat exchange is performed between the coolant and outdoor air blown by the outdoor fan  54   a  to obtain liquefied coolant having intermediate temperature and high pressure. The coolant having passed through the outdoor heat exchanger  54  passes through the capillary tube  64  and the auxiliary capillary tube  68  so that the coolant is decompressed to obtain coolant having low temperature and low pressure. The coolant having passed through the capillary tube  64  and the auxiliary capillary tube  68  passes through the second indoor heat exchanger  82 , where heat exchange is performed between the coolant and indoor air blown by the second indoor fan  82   a  to obtain gaseous coolant having low temperature and low pressure, by which cool air is produced in the space where the second indoor unit  80  is installed. The coolant having passed through the second indoor heat exchanger  82  passes through the oil separator  56 , by which oil is separated from the coolant, and the coolant containing no oil therein is introduced into the operating first compressor  52  or the operating second compressor  53 . 
   As described above, the coolant is circulated through the first compressor  52  or the second compressor  53 , the outdoor heat exchanger  54 , the capillary tube  64  and the auxiliary capillary tube  68 , the second indoor heat exchanger  82 , and the oil separator  56 , to cool the space where the second indoor unit  80  is installed. 
   When both of the first and second indoor units  70  and  80  are simultaneously operated by the user, all of the first and second compressors  52  and  53  are operated. The electronic expansion valve  62  is opened, and at the same time the shutoff valve  67  is also opened. The outdoor fan  54   a  and the first and second indoor fans  72   a  and  82   a  are operated. 
   The coolant passes through the first and second compressors  52  and  53  with the result that gaseous coolant having high temperature and high pressure is obtained. The coolants having passed through the first compressor  52  and the second compressor  53  are mixed together and the mixed coolant passes through the outdoor heat exchanger  54 , where heat exchange is performed between the coolant and outdoor air blown by the outdoor fan  54   a  to obtain liquefied coolant having intermediate temperature and high pressure. The coolant having passed through the outdoor heat exchanger  54  is divided into two parts and the divided coolants pass through the electronic expansion valve  62  and the capillary tube  64 , respectively, so that the coolants are decompressed to obtain coolants having low temperature and low pressure. The coolant having passed through the electronic expansion valve  62  passes through the first indoor heat exchanger  72 , where heat exchange is performed between the coolant and indoor air blown by the first indoor fan  72   a  to obtain gaseous coolant having low temperature and low pressure, by which cool air is produced in the space where the first indoor unit  70  is installed. On the other hand, the coolant having passed through the capillary tube  64  passes through the second indoor heat exchanger  82 , where heat exchange is performed between the coolant and indoor air blown by the second indoor fan  82   a  to obtain gaseous coolant having low temperature and low pressure, by which cool air is produced in the space where the second indoor unit  80  is installed. The coolants having passed through the first and second indoor heat exchangers  72  and  82  are mixed again together, and the mixed coolant pass through the oil separator  56 , by which oil is separated from the coolant. The coolant containing no oil therein is divided again into two parts, and the divided coolants are introduced into the first and second compressors  52  and  53 , respectively. 
   As described above, the coolant is circulated through the first and second compressors  52  and  53 , the outdoor heat exchanger  54 , the electronic expansion valve  62  and the capillary tube  64 , the first and second indoor heat exchangers  72  and  82 , and the oil separator  56 , to cool the different spaces where the first and second indoor units  70  and  80  are individually installed. 
   At this time, the degree of opening of the electronic expansion valve  62  is controlled on the basis of the indoor load of the space where the first indoor unit  70  is installed and the outdoor load of the space where the outdoor unit  50  is installed. 
     FIG. 8  is a schematic circuit diagram of an air conditioner according to a second preferred embodiment of the present invention. 
   The air conditioner according to the second preferred embodiment of the present invention is identical to that according to the previously described first preferred embodiment of the present invention except that the expansion distributor  60  of this embodiment further comprises an auxiliary shutoff valve  69  disposed in the connection passage  66  at the rear end of the auxiliary capillary tube  68  for allowing or preventing the flow of the coolant. 
   Preferably, the shutoff valve  67  and the auxiliary shutoff valve  69  are solenoid valves that can be controlled by electrical signals from the microcomputer. 
   
     
       
             
             
             
             
             
           
         
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
                 
               Electronic 
                 
               Auxiliary 
             
             
                 
                 
               Expansion 
               Shutoff 
               Shutoff 
             
             
                 
               Operating Indoor Unit 
               Valve 62 
               Valve 67 
               Valve 69 
             
             
                 
                 
             
           
           
             
                 
               First Indoor Unit 70 
               On 
               Off 
               Off 
             
             
                 
               Second Indoor Unit 80 
               Off 
               On 
               On 
             
             
                 
               First and Second Indoor 
               On 
               On 
               Off 
             
             
                 
               Units 70 and 80 
             
             
                 
                 
             
           
        
       
     
   
   When only the first indoor unit  70  is operated, the electronic expansion valve  62  of the expansion distributor  60  is opened, and the shutoff valve  67  and the auxiliary shutoff valve  69  of the expansion distributor  60  are closed, as indicated in Table 2, so that the coolant passes through the electronic expansion valve  62  and then is introduced into the first indoor heat exchanger  72 . 
   When only the second indoor unit  80  is operated, the electronic expansion valve  62  of the expansion distributor  60  is closed, and the shutoff valve  67  and the auxiliary shutoff valve  69  of the expansion distributor  60  are opened, as indicated in Table 2, so that the coolant passes through the capillary tube  64  and the auxiliary capillary tube  68  and then is introduced into the second indoor heat exchanger  82 . 
   When both of the first and second indoor units  70  and  80  are simultaneously operated, the electronic expansion valve  62  and the shutoff valve  67  of the expansion distributor  60  are opened, and the auxiliary shutoff valve  69  of the expansion distributor  60  is closed, as indicated in Table 2, so that the coolant passes through the electronic expansion valve  62  and the capillary tube  64 , and then is introduced into the first and second indoor heat exchangers  72  and  82 , respectively. 
   The air conditioner according to the second preferred embodiment of the present invention is operated in the same manner as the air conditioner of the previously described first preferred embodiment. Accordingly, the detailed description of the operation of the air conditioner according to the second preferred embodiment of the present invention will not be given. 
   As described above, the air conditioner of the present invention further includes an additional auxiliary indoor unit connected to an air conditioner comprising an indoor unit and an outdoor unit connected to the indoor unit, the outdoor unit having two compressors mounted therein. Consequently, two indoor units can be individually installed in different spaces even though the air conditioner constitutes a single cooling cycle, whereby the two indoor units can be selectively or simultaneously operated on the basis of a life pattern of a user to effectively cool or warm the different spaces where the indoor units are individually installed. 
   As apparent from the above description, the present invention provides an improved air conditioner further including an additional auxiliary indoor unit connected to an air conditioner comprising an indoor unit and an outdoor unit connected to the indoor unit so that the indoor unit and the auxiliary indoor unit can be selectively or simultaneously operated according to the needs of a user, thereby conveniently cooling or warming the desired room(s) of a user&#39;s house. In addition, the space for installing the air conditioner is reduced since only one outdoor unit is installed, and the cost of manufacturing the air conditioner and the charge of installing the air conditioner are also reduced. 
   Furthermore, the air conditioner of the present invention further comprises an expansion distributor for controlling pressure reduction and flow rate of a coolant condensed in the outdoor unit to supply the coolant to each of the indoor units even though each of the two indoor units is connected to the single outdoor unit, thereby easily controlling the cooling/warming capacities, and thus effectively cooling or warming desired room(s) or space(s) individually or simultaneously. 
   Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.