Abstract:
An air conditioning apparatus and control method thereof is provided, in which two-stage variable-capacity compressors are connected in parallel with each other to control capacities of the two stage variable-capacity compressors according to indoor air conditioning loads. A pair of two-stage variable-capacity compressors are used in the air conditioning apparatus to be cost competitive and can obtain an effect in which the pair of two-stage variable-capacity compressors are controlled as if a large-scale variable-capacity compressor with a capacity the same as a total capacity of the two compressors were linearly controlled.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims the benefit of Korean Application No. 2002-33223, filed Jun. 14, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to an air conditioning apparatus and control method thereof, in which two-stage variable-capacity compressors are connected in parallel with each other.  
           [0004]    2. Description of the Related Art  
           [0005]    Generally, a single air conditioning apparatus in which one indoor unit is connected to one outdoor unit does not have a large indoor air conditioning load (required capacity), so a fixed-capacity compressor is installed in the outdoor unit.  
           [0006]    On the contrary, a multi-unit air conditioning apparatus in which a plurality of indoor units are connected to one outdoor unit is designed such that each of the indoor units independently copes with an air conditioning load of a corresponding indoor space. In such a multi-unit air conditioning apparatus, since air conditioning loads of respect indoor units are different and vary at any time, a variable-capacity compressor is installed in an outdoor unit, and a flow of refrigerant is controlled by ascertaining loads and operating states using communication between each the of indoor units and the outdoor unit. Further, the variable-capacity compressor is controlled by a microcomputer of the outdoor unit. The outdoor unit microcomputer checks the air conditioning requirements with respect to a corresponding indoor space, a temperature condition of the corresponding indoor space, etc. based on information received from each of the indoor units, and controls a capacity of the compressor according to the checked information.  
           [0007]    However, since a conventional multi-unit air conditioning apparatus employs a construction in which a plurality of indoor units are connected to one outdoor unit, a compressor installed in the outdoor unit must be designed to endure a maximum indoor air conditioning load. Further, in order for a compressor to endure the maximum indoor air conditioning load, significant difficulty arises in the production of the compressor. That is, a plurality of performance tests must be carried out so as to increase the capacity of the compressor.  
           [0008]    A high-capacity compressor produced by the above process is problematic in that the high-capacity compressor is very expensive, relative to a conventional compressor.  
           [0009]    In the prior art, a manner in which a variable-capacity compressor and a fixed-capacity compressor are mixed to cope with indoor air conditioning loads is used in consideration of the above problem.  
           [0010]    As shown in FIG. 1, a compressor  10 , which operates at a capacity varied according to a frequency of an inverter circuit, and a fixed-capacity compressor  20 , which operates at a constant capacity, are connected in parallel with each other. Further, an outdoor unit microcomputer (not shown) controls capacities of the variable-capacity compressor  10  and the fixed-capacity compressor  20  according to indoor air conditioning loads (required capacities) received from respective indoor units. Referring to FIG. 2, if the indoor air conditioning loads are 0% to 50%, the outdoor unit microcomputer controls the capacity of the variable-capacity compressor  10 . In this case, the microcomputer controls the capacity of the variable-capacity compressor  10  by varying a frequency outputted to the variable-capacity compressor  10  from an inverter circuit within a predetermined range R1 according to the indoor air conditioning loads (required capacities) received from the respect indoor units. Further, if the indoor air conditioning loads are 50% to 100%, the outdoor unit microcomputer controls the capacities of the variable-capacity compressor  10  and fixed-capacity compressor  20 . In this case, the microcomputer copes with an insufficient capacity by controlling the capacity of the inverter-type variable-capacity compressor  10  operated according to a frequency of the inverter circuit within a predetermined range R2 after activating the fixed capacity compressor  20 .  
           [0011]    However, if the conventional air conditioning apparatus is used for facilities such as large buildings, a capacity, which must be provided by a variable-capacity compressor, inevitably becomes large. Further, to produce such a high-capacity compressor as an independent device is difficult and expensive, even though an independent device can be produced, thus causing an economic burden by increasing a price of the compressor.  
           [0012]    Therefore, in the multi-unit air conditioning apparatus, a method is required of effectively coping with a large-scale indoor air conditioning load (required capacity). Further, a method of accommodating requirements for the large-scale air conditioning capacity while using a conventional compressor is seriously required.  
         SUMMARY OF THE INVENTION  
         [0013]    Accordingly, an air conditioning apparatus and control method thereof is provided, in which two-stage variable-capacity compressors are connected in parallel with each other to cope with indoor air conditioning loads, thus realizing the compressors at a low price.  
           [0014]    Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
           [0015]    In order to accomplish the above and other aspects, an air conditioning apparatus is provided, comprising a first compressor controlled to operate at one of a first minimum capacity and a first maximum capacity; a second compressor connected in parallel with the first compressor and controlled to operate at one of a second minimum capacity and a second maximum capacity; and a control unit controlling the capacities of the first and second compressors such that a total capacity of the first and second compressors is controlled in multiple stages according to indoor air conditioning loads.  
           [0016]    Further, an air conditioning apparatus, comprising a plurality of indoor units; and an outdoor unit connected to the plurality of indoor units is provided, comprising a first compressor controlled to operate at one of a first minimum capacity and a first maximum capacity, a second compressor connected in parallel with the first compressor and controlled to operate at one of a second minimum capacity and a second maximum capacity, and an outdoor control unit controlling the capacities of the first and second compressors such that a total capacity of the first and second compressors is controlled in multiple stages according to indoor air conditioning loads required by the indoor units.  
           [0017]    Further, a method of controlling an air conditioning apparatus, the air conditioning apparatus is provided having a plurality of indoor units connected to an outdoor unit comprising a first compressor operating at one of a first minimum capacity and a first maximum capacity, and a second compressor for operating at one of a second minimum capacity and a second maximum capacity, comprising calculating an air conditioning capacity required by corresponding indoor units; and controlling the capacities of the first and second compressors such that a total capacity of the first and second compressors is controlled in multiple stages according to the calculated required air conditioning capacity, wherein the first maximum capacity of the first compressor is equal to the second minimum capacity of the second compressor, and the second maximum capacity of the second compressor is two times greater than the second minimum capacity of the second compressor.  
           [0018]    The air conditioning apparatus uses a pair of two-stage variable-capacity compressors connected in parallel with each other, wherein each of the two-stage variable-capacity compressors operates at two different capacities. One of the compressors operates at a first minimum capacity and a first maximum capacity, and the other operates at a second minimum capacity and a second maximum capacity. In this case, the first maximum capacity is equal to the second minimum capacity and corresponds to a half of the second maximum capacity. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    These and other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:  
         [0020]    [0020]FIG. 1 is a view showing a construction of a conventional air conditioning apparatus in which a variable-capacity compressor and a fixed-capacity compressor are connected in parallel with each other;  
         [0021]    [0021]FIG. 2 is a graph showing an operation of controlling capacities of the compressors of FIG. 1;  
         [0022]    [0022]FIG. 3 is a view showing a construction of an air conditioning apparatus in which two-stage variable-capacity compressors are connected in parallel with each other according to an embodiment of the present invention;  
         [0023]    [0023]FIG. 4 is a view showing a construction in which an oil equalization tube is connected to the compressors according to the embodiment of the present invention;  
         [0024]    [0024]FIG. 5 is a graph showing the operation of controlling capacities of the compressors according to a second embodiment of the present invention;  
         [0025]    [0025]FIG. 6 is a flowchart of a method of controlling the air conditioning apparatus according to the second embodiment of the present invention; and  
         [0026]    [0026]FIG. 7 is a block diagram showing a multi-unit air conditioning according to the embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Reference will now made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
         [0028]    [0028]FIG. 3 is a view showing a construction in which of an air conditioning apparatus in which two-stage variable-capacity compressors are connected in parallel with each other according to an embodiment of the present invention.  
         [0029]    As shown in FIG. 3, the air conditioning apparatus comprises two compressors  30  and  40  connected in parallel with each other. The compressors  30  and  40  can be applied to a multi-unit air conditioning apparatus, as shown in FIG. 7, in which a plurality of indoor units  60  are connected to one outdoor unit  80 . In this case, the compressors  30  and  40  are installed in the outdoor unit  80 , and the capacities of the compressors  30  and  40  are under the control of an outdoor unit controller  70  (i.e., a microcomputer).  
         [0030]    The first and second compressors  30  and  40  compress refrigerant using a common method, wherein a capacity supplied by the second compressor  40  is almost two times a capacity of the first compressor  30 .  
         [0031]    The first compressor  30  is a two-stage variable-capacity compressor which has two compressing rooms P 1  and P 2  therein. If a motor in the first compressor  30  rotates in a forward direction according to a control instruction of an outdoor unit controller  70 , both the compressing rooms P 1  and P 2  perform compression of refrigerant, so the first compressor  30  is operated at 100% capacity, which is a first maximum capacity. Alternatively, if the motor in the first compressor  30  rotates in a reverse direction according to a control instruction of the outdoor unit  80  microcomputer, any one of the two compressing rooms P 1  and P 2  may perform the compression of refrigerant, so the first compressor  30  is operated at 50% capacity, which is a first minimum capacity.  
         [0032]    The second compressor  40  is a two-stage variable-capacity compressor which has two compressing rooms P 3  and P 4  therein. If a motor in the second compressor  40  rotates in the forward direction according to the control instruction of the outdoor unit controller  70 , both of the compressing rooms P 3  and P 4  perform the compression of refrigerant, so the second compressor  40  is operated at 100% capacity, which is a second maximum capacity. Alternatively, if the motor in the second compressor  40  rotates in the reverse direction according to the control instruction of the outdoor unit controller  70 , any one of the two compressing rooms P 3  and P 4  may perform the compression of refrigerant, so the second compressor  40  is operated at 50% capacity, which is a second minimum capacity.  
         [0033]    As described above, each of the first and second compressors  30  and  40  operates at one of two different capacities either a minimum capacity or a maximum capacity determined by the outdoor unit controller  70 . It is further understood that additional compressors can be added to add more capacities as needed, which operates with a total capacity characteristic which is piece-wise linear.  
         [0034]    The first maximum capacity of the first compressor  30  is equal to the second minimum capacity of the second compressor  40 , and corresponds to a half of the second maximum capacity.  
         [0035]    A device to keep oil supplied to the first and second compressors  30  and  40  with different capacities may be provided. An oil equalization tube B may be employed, as shown in FIG. 4.  
         [0036]    As shown in FIG. 4, an oil separator  50  is arranged in discharge sides of the first and second compressors  30  and  40  to separate refrigerant and oil. A capillary tube  51  is disposed between the first compressor  30  and the oil separator  50 . Further, the oil equalization tube B is disposed between the first and second compressors  30  and  40  to connect an oil storing room of the first compressor  30  with an oil storing room of the second compressor  40 .  
         [0037]    Oil separated from the refrigerant by the oil separator  50  returns to the first compressor  30  through the oil equalization tube B. In this case, an additional oil equalizing operation is not performed.  
         [0038]    Hereinafter, the operation of the air conditioning apparatus and control method thereof according to the present invention is described in detail with reference to FIGS. 5 and 6.  
         [0039]    The air conditioning apparatus is applied to a multi-unit air conditioning apparatus in which an indoor air conditioning load may be greatly varied. In this case, the multi-unit air conditioning apparatus is described, in which a plurality of indoor units  60  are connected to one outdoor unit  80 , the indoor units  60  and the outdoor unit  80  mutually communicate with each other, and an outdoor unit controller  70  controlling several compressors  30 ,  40  installed in the outdoor unit  80  controls capacities of the compressors  30 ,  40  according to indoor air conditioning loads (required capacities) received from respective indoor units  60 .  
         [0040]    First, the outdoor unit microcomputer calculates a total indoor air conditioning load (required capacity) by summing up the air conditioning loads received from corresponding indoor units  60  of the plural indoor units  60  at operation S 110 .  
         [0041]    Then, the outdoor unit controller  70  determines whether the calculated total required capacity is 0 at operation S 120 . If the total required capacity is 0, the outdoor unit controller  70  stops operations of both the first and second compressors  30  and  40  at operation S 130 .  
         [0042]    If the total required capacity is not 0 at operation S 120 , the outdoor unit controller  70  determines whether the total required capacity is equal to or less than 17% of a total capacity of the compressors  30 ,  40  at operation S 140 . If the total required capacity is equal to or less than 17% of the total capacity of the compressors  30 ,  40 , the microcomputer stops the operation of the second compressor  40 , and operates the first compressor  30  to rotate in a reverse direction so as to allow the first compressor  30  to operate at the first minimum capacity (with reference to A 1  of FIG. 5) at operations S 150  and S 160 .  
         [0043]    If the total required capacity is greater than 17% of the total capacity of the compressors  30 ,  40  at operation S 140 , the outdoor unit controller  70  determines whether the total required capacity is less than or equal to 34% of the total capacity of the compressors at S 170 . If the total required capacity is less than or equal to 34% of the total capacity of the compressors  30 ,  40 , the outdoor unit controller  70  stops the operation of the second compressor  40 , and operates the first compressor  30  to rotate in a forward direction so as to allow the first compressor  30  to operate at the first maximum capacity (with reference to A 2  of FIG. 5) at operations S 180  and S 190 .  
         [0044]    If the total required capacity is greater than 34% of the total capacity of the compressors  30 ,  40  at S 170 , the outdoor unit controller  70  determines whether the total required capacity is less than or equal to 50% of the total capacity of the compressors  30 ,  40  at operation S 200 . If the total required capacity is less than or equal to 50% of the total capacity of the compressors  30 ,  40 , the outdoor unit controller  70  operates the second compressor  40  to rotate in the reverse direction so as to allow the second compressor  40  to operate at the second minimum capacity, and to operates the first compressor  30  to rotate in the reverse direction so as to allow the first compressor  30  to operate at the first minimum capacity (with reference to A 1  and B 1  of FIG. 5) at operations S 210  and S 220 .  
         [0045]    If the total required capacity is greater than 50% of the total capacity of the compressors  30 ,  40  at operation S 200 , the outdoor unit controller  70  determines whether the total required capacity is less than or equal to 67% of the total capacity of the compressors  30 ,  40  at operation S 230 . If the total required capacity is less than or equal to 67% of the total capacity of the compressors  30 ,  40 , the microcomputer operates the second compressor  40  to rotate in the forward direction so as to allow the second compressor  40  to operate at the second maximum capacity, and stops the operation of the first compressor  30  (with reference to B 2  of FIG. 5) at operations S 240  and S 250 .  
         [0046]    If the total required capacity is greater than 67% of the total capacity of the compressors  30 ,  40  at operation S 230 , the outdoor unit controller  70  determines whether the total required capacity is less than or equal to 84% of the total capacity of the compressors  30 ,  40  at operation S 260 . If the total required capacity is less than or equal to 84% of the total capacity of the compressors  30 ,  40 , the microcomputer operates the second compressor  40  to rotate in the forward direction so as to allow the second compressor  40  to operate at the second maximum capacity, and to operate the first compressor  30  to rotate in the reverse direction so as to allow the first compressor  30  to operate at the first minimum capacity (with reference to A 1  and B 2  of FIG. 5) at operations S 270  and S 280 .  
         [0047]    If the total required capacity is greater than 84% of the total capacity of the compressors  30 ,  40  at operation S 260 , the outdoor unit controller  70  operates both the second compressor  40  and the first compressor  30  to rotate in the forward direction so as to allow the second compressor  40  and the first compressor  30  to operate at the second maximum capacity and the first maximum capacity, respectively (with reference to A 2  and B 2  of FIG. 5) at operations S 290  and S 300 .  
         [0048]    After the operations S 130 , S 160 , S 190 , S 220 , S 250 , S 280 , and S 300  are performed, a processing operation returns to a start.  
         [0049]    As described above, an air conditioning apparatus and control method thereof is provided, in which a two-stage variable-capacity compressor with large capacity and a two-stage variable-capacity compressor with small capacity are connected in parallel with each other, thus enabling the capacities of the compressors to be controlled in multiple stages according to indoor air conditioning loads. Further, the air conditioning apparatus advantageously employs two-stage variable-capacity compressors, which are inexpensive compared with a linear variable-capacity compressor, thus reducing a cost of the air conditioning apparatus. Further, a high operating efficiency advantageously can be obtained over entire operating areas because the two-stage variable-capacity compressor is higher than the linear variable-capacity compressor in operating efficiency. It is understood that additional compressors can be used, and that the micro controller can be a computer implementing the control method which is programmed on a computer readable medium or in firmware.  
         [0050]    Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.