WO2008114952A1

WO2008114952A1 - Multi-unit air conditioning system and controlling method for the same

Info

Publication number: WO2008114952A1
Application number: PCT/KR2008/001375
Authority: WO
Inventors: Tae-Hee Kwak; Il-Nahm Hwang; Ho-Jong Jeong; Seung-Yong Chang; Kyung-Won Seo; Chi-Woo Song; Jin-Ha Choi; Won-Chul Kang
Original assignee: Lg Electronics Inc.
Priority date: 2007-03-16
Filing date: 2008-03-11
Publication date: 2008-09-25
Also published as: KR20080084482A; EP2137467A1; KR100885566B1; EP2137467A4

Abstract

Provided are a multi-unit air conditioning system and a controlling method thereof for reducing differences in discharged temperatures from a plurality of compressors operating in heating-only operation. The controlling method is able to reduce unbalance between discharged temperatures and concentration of refrigerant between outdoor units.

Description

MULTI-UNIT AIR CONDITIONING SYSTEM AND CONTROLLING METHOD FOR THE SAME

Technical Field

[1] The present embodiments relate to a multi-unit air conditioning system and a controlling method of the system. Background Art

[2] In general, an air conditioner is an apparatus that cools or heats an indoor environment such as a building.

[3] Today, in order to more efficiently cool or heat an indoor environment partitioned into a plurality of separate rooms, multi-unit air conditioners are continually being developed. Such air conditioners have materialized due to consumer demand for a system that allows an indoor unit installed in each of a plurality of rooms to be operated independently in a different mode from those in the other rooms.

[4] Such multi-unit air conditioners can be divided into single type systems having one outdoor unit connected to a plurality of indoor units, and series type systems having a plurality of outdoor units connected to a plurality of indoor units.

[5] Also, multi-unit air conditioners may be divided according to refrigerant circulation into switching and simultaneous supply types. That is, the switching type system switches all indoor units from cooling mode to heating mode, or vice- versa. Conversely, the simultaneous type system can operate a portion of the indoor units in cooling mode and another portion in heating mode simultaneously.

[6] With the simultaneous type system, each outdoor unit can perform a heating- dedicated operation or a cooling-dedicated operation. A heating-dedicated operation is where the outdoor heat exchangers of all the outdoor units function as evaporators, and the cooling-dedicated operation is where the outdoor heat exchangers of all the outdoor units function as condensers.

[7] In simultaneous, series type multi-unit air conditioning systems of the related art with a plurality of outdoor units connected to a plurality of indoor units, which are capable of operating simultaneously in both heating mode and cooling mode, the heat load during heating mode operation is substantial, so that the number of compressors operating must be increased. If the number of operating compressors is increased, a discrepancy of discharged pressures between the respective operating compressors arises. Such non-uniformity of discharged pressures causes severe disparity between discharged temperatures of the respective compressors. In other words, due to nonuniform pressure between the plurality of compressors, refrigerant can be concentrated to one of the outdoor units, whereupon the difference in discharged temperatures of refrigerant discharged from the compressors becomes substantial.

[8] In particular, non-uniformity of discharged temperatures is more prevalent at lower heating temperatures, so that a particular compressor will be unable to attain a level of discharging heat and thus remain in a liquid compression state. That is, low temperature, low pressure refrigerant enters through the inlet of the compressor to reduce efficiency or damage the inner components of the compressor. Disclosure of Invention Technical Problem

[9] Embodiments provide a multi-unit air conditioning system with a plurality of indoor units connected to a plurality of outdoor units, and a method of controlling the air conditioning system that are capable of negating the limitation of reduced level of intake heat caused by low pressure heating, during simultaneous operation in cooling and heating modes.

[10] Embodiments also provide a multi-unit air conditioning system and a method of controlling the air conditioning system that are capable of negating the limitations of refrigerant concentrating at a particular outdoor unit of a plurality of outdoor units that have non-uniform pressures, and non-uniform discharged temperatures caused by the concentrating of refrigerant. Technical Solution

[11] In one embodiment, a method for controlling a multi-unit air conditioning system includes: operating a plurality of indoor units connected to a plurality of outdoor units; sensing discharged temperatures from a plurality of compressors provided respectively to the outdoor units; deriving a difference between a maximum value and a minimum value of the discharged temperatures; and bypassing a portion of discharged gas to a compressor when the difference is greater than a predetermined value.

[12] In another embodiment, a multi-unit air conditioning system includes: a plurality of outdoor units including at least one or more compressors, a four-way valve, an outdoor heat exchanger, and an accumulator connected to an inlet of the compressor; a plurality of indoor units connected to the outdoor units and including an indoor heat exchanger, and an expansion member provided at an outlet of the indoor heat exchanger; a distribution unit connecting the outdoor units and the indoor units, for distributing refrigerant from the outdoor units to the indoor units and supplying refrigerant from the indoor units to the outdoor units; a bypass pipe having one end connected to a pipe at an outlet of the compressor and the other end connected to a pipe connecting the accumulator and the compressor, the bypass pipe for bypassing gas discharged from the compressor to another compressor; and a flow regulator provided at one end of the bypass pipe.

Advantageous Effects

[13] According to the provided embodiments, the multi-unit air conditioning system and the method for controlling the system can negate the limitation of lowered intake temperatures that can occur in a multi-unit air conditioning system with a plurality of indoor units connected to a plurality of outdoor units.

[14] Also, the present embodiments can negate the limitation of refrigerant concentrating at a particular outdoor unit, especially during low temperature heating, and the limitation of non-uniformity in discharged temperature between a plurality of outdoor units caused by the refrigerant concentrating.

[15] Furthermore, by reducing the non-uniformity of discharged temperatures between compressors, a level of discharging heat can be sufficiently attained by each compressor. Because the level of discharging heat is sufficiently attained, damage to compressors can be prevented and system reliability can be attained. Brief Description of the Drawings

[16] Fig. 1 is a system diagram of a multi-unit air conditioning system capable of simultaneous cooling/heating according to present embodiments.

[17] Fig. 2 is a system diagram of an outdoor unit configuring a multi-unit air conditioning system according to present embodiments, showing the flow of refrigerant with a flow regulator closed during heating mode operation of the outdoor unit.

[18] Fig. 3 is a system diagram of the outdoor unit in Fig. 2 showing the flow of refrigerant with the flow regulator open, under the otherwise same conditions. Mode for the Invention

[19] Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. However, it should be understood that the present disclosure is not limited to embodiments disclosed herein, and that numerous other modifications and embodiments can easily be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.

[20] Fig. 1 is a system diagram of a multi-unit air conditioning system capable of simultaneous cooling/heating according to present embodiments.

[21] Referring to Fig. 1, a multi-unit air conditioning system capable of simultaneous cooling/heating according to present embodiments is shown in heating-dedicated operation.

[22] In detail, the simultaneous cooling/heating multi-unit air conditioning system according to present embodiments includes a plurality of outdoor units 101, 102, and 103, a distribution unit 200, and a plurality of indoor units 301, 302, 303, 304, 305, and 306.

[23] In detail, the plurality of indoor units 301, 302, 303, 304, 305, and 306 may be provided as an integer multiple of the plurality of outdoor units 101, 102, and 103. Also, one 101 of the outdoor units 101, 102, and 103 may be designated as a main outdoor unit, and the remainder 102 and 103 may be designated as auxiliary outdoor unit.

[24] The plurality of outdoor units 101, 102, and 103, the distribution unit 200, and the plurality of indoor units 301, 302, 303, 304, 305, and 306 may be controlled by a controller (not shown).

[25] Provided respectively between the outdoor units 101, 102, and 103 are a compressor

111 for compressing refrigerant to a high temperature and high pressure gaseous state, a 4- way valve 112 provided at the discharging end of the compressor 111 to selectively direct the refrigerant discharged from the compressor 111 to an outdoor heat exchanger or the distribution unit 200, an outdoor heat exchanger 113 for performing heat exchange between refrigerant flowing from the compressor 111 or an indoor unit and outdoor air, and an accumulator 114 for separating the refrigerant returning to the compressor 111 into gas and liquid. Also, the compressor may be a constant speed compressor or an inverter compressor, and in some embodiments, the main outdoor unit may be provided with both an inverter compressor and a constant speed compressor, while the auxiliary outdoor units may only have a constant speed compressor.

[26] An electronic expansion valve (EEV) 116, a solenoid valve 117, and a check valve

118 are disposed on the refrigerant pipe at the discharging end of the outdoor heat exchanger 113.

[27] Accordingly, when the main outdoor unit 101 operates in heating mode, as shown in

Fig. 1, the refrigerant discharged from the outdoor heat exchanger 113 flows along a refrigerant pipe on which the solenoid valve 117 and check valve 118 are installed. Here, the EEV 116 is closed.

[28] Conversely, in cooling mode, the flow direction of refrigerant is in the opposite direction to that of the heating mode, and the refrigerant enters the outdoor heat exchanger 113 after passing through the EEV 116.

[29] Fig. 1 shows 2 compressors 111 disposed at each outdoor unit 101, 102, and 103; however, the outdoor units 101, 102, and 103 may respectively have 1 or 3 or more compressors disposed thereon. Here, an outdoor fan for blowing outdoor air has been omitted from the outdoor heat exchanger 113.

[30] A branch pipe 119 extends from one side of a refrigerant pipe connecting the outlet of the compressor 111 and the inlet of the 4- way valve 112. The branch pipe 119 is also connected to a high pressure pipe 121 through which high temperature and high pressure gaseous refrigerant flows. A refrigerant pipe at the outlet of the outdoor heat exchanger 113 is connected to a liquid pipe 122 through which high temperature and high pressure liquid refrigerant flows. Also, a low pressure pipe 123, through which low temperature and low pressure second-stage refrigerant flows, is connected to the refrigerant pipe between the outlet of the 4- way valve 112 and the inlet of the accumulator 114.

[31] A bypass pipe 124 branches from a point on the liquid pipe 122 and connects to the inlet of the accumulator 114. An EEV 126 is provided at a side of the bypass pipe 124, allowing low temperature and low pressure second-phase refrigerant to flow to the accumulator 114.

[32] In detail, the bypass pipe 124 may be configured to exchange heat with the liquid valve 122. For example, portions of the bypass pipe 124 and the liquid pipe 122 extending from the outlet of the outdoor heat exchanger 113 may be made to exchange heat by means of a first sub cooling unit 510.

[33] In further detail, the first sub cooling unit 510 may form a double-layered pipe structure together with the liquid pipe 122 and the bypass pipe 124 by contacting the outer peripheries thereof. Alternately, one of the liquid pipe 122 and the bypass pipe 124 may be configured to pass through the inside of the other. In this case, the bypass pipe 124 and the liquid pipe 122 may be disposed so that the respective directions of refrigerant flowing therein will flow oppositely to each other.

[34] Through the above configuration, refrigerant flowing through the liquid pipe 122 will transfer heat to the low temperature and low pressure second-phase refrigerant flowing through the bypass pipe 124, and thus be reduced in temperature. Conversely, the refrigerant flowing through the bypass pipe 124 receives transferred heat so that it becomes higher in quality, and then flows to the inlet of the accumulator 114.

[35] Temperature sensors (not shown) are provided at the outlets of the compressors 111 of each outdoor unit 101, 102, and 103, in order to sense the temperature of discharged refrigerant passing through the compressors 111.

[36] The discharged temperatures of the compressors 111 are sensed to determine whether the difference between the maximum temperature and minimum temperature exceeds a preset value, and a bypass pipe 422 is provided at the inlet of the 4- way valve 112 to allow bypassing of refrigerant. Specifically, the bypass pipe 422 branches from the inlet of the 4- way valve 112 and is connected to the inlet of the compressor 111. Also, a flow regulator 400 is provided at one side of the bypass pipe 422, enabling refrigerant to selectively flow. The flow regulator 400 may include one of an ON/OFF valve, a solenoid valve, and a pulse modulation valve (PMV). Therefore, if the difference between the maximum temperature and minimum temperature exceeds the preset value, the flow regulator 400 is opened, and the flow regulator 400 is closed when the preset value is not exceeded.

[37] The high pressure pipe 121, the liquid pipe 122, and the low pressure pipe 123 are connected to the distribution unit 200. That is, the distribution unit 200 includes a distribution part 210 storing high temperature and high pressure gaseous refrigerant, a second distribution part 220 storing high temperature and high pressure liquid refrigerant, and a third distribution part 230 storing low temperature and low pressure second-phase refrigerant. The second distribution part 220 and the third distribution part 230 are connected through an overcooling part 240. An EEV 241 is provided between the second distribution part 220 and the overcooling part 240.

[38] An end of the high pressure pipe 121 is connected to the first distribution part 210, an end of the liquid pipe 122 is connected to the second distribution part 220, and an end of the low pressure pipe 123 is connected to the third distribution part 230.

[39] The first, second, and third distribution parts 210, 220, and 230 are connected to the indoor units 301, 302, 303, 304, 305, and 306 through a plurality of branch pipes.

[40] A solenoid valve 314 and a capillary tube 600 are disposed on a pipe connecting the first distribution part 210 and the third distribution part 230. Thus, a portion of refrigerant stored in the first distribution part 210 expands while passing through the capillary tube 600, and flows into the third distribution part 230.

[41] The respective indoor units 301, 302, 303, 304, 305, and 306 include an indoor heat exchanger 311. An EEV 312 is disposed at one side of each indoor unit, and a plurality of valves 313 and a plurality of solenoid valves 314 are disposed at the other side of each indoor unit.

[42] Specifically, the EEVs 312 connected to the indoor heat exchangers 311 control the amount in which they are opened during cooling mode, to allow refrigerant supplied from the second distribution valve 220 to expand and then flow into the indoor heat exchangers 311. Conversely, in heating mode operation, the EEVs 312 are completely opened, to allow refrigerant supplied from the first distribution valves 210 to flow to the indoor units 311 without any changes in temperature and pressure.

[43] In more detail, the third distribution part 230 and the second distribution part 220 are connected in-line to an end of the indoor heat exchanger 311, and are controlled in aperture through the solenoid valve 313. Also, the second distribution part 220 is connected at the other end of the indoor heat exchanger 311, and controlled by the solenoid valve 313 in opening aperture. The directions of the inlets and outlets are shifted according to the operating mode. That is, in cooling mode, refrigerant stored in the second distribution part 220 flows to expand in the EEV 312, after which it flows to the third distribution part 230. Conversely, in heating mode, high temperature and high pressure gaseous refrigerant stored in the first distribution part 210 flows into the indoor heat exchanger 311, passes through the indoor heat exchanger 311, and flows to the second distribution part 220. Here, the EEV 312 is completely opened, so that there is no change in temperature and pressure. While the refrigerant passes through the indoor heat exchanger 311, through exchange of heat, it converts from a gaseous state to a liquid state.

[44] Also, a portion of the pipe connecting the second distribution part 220 and the EEV

312 of the indoor heat exchanger 311 has a second sub cooling unit 520 provided thereon.

[45] In detail, the second sub cooling unit 520 may be a separate pipe, or may be a portion of the pipe connecting the EEV 312 of the indoor heat exchanger 311 and the second distribution part 220.

[46] A number of branch pipes 242 are provided at the discharging end of the overcooling part 240 corresponding to the number of indoor heat exchangers 311.

[47] In detail, the distribution pipes 242 pass through the second sub cooling unit 520, and then combine into a single pipe - that is, a combined pipe 221. Specifically, a portion of the distribution pipes 242 passes through the second sub cooling unit 520 and attains a higher quality by absorbing heat. That is, the parts per unit of gas in the refrigerant rises.

[48] Also, the combined pipe 221 passes through the second distribution part 220 as a double pipe, and connects to the third distribution part 230. Accordingly, the refrigerant that absorbs heat in a first stage while passing through the second sub cooling unit 520, combines at the combined pipe 221, and then absorbs heat in a second stage while passing through the second distribution part 220, and is converted to a second- phase refrigerant close to a gaseous, low temperature and low pressure state.

[49] Referring to Fig. 1, various valves depicted solidly in black are valves turned OFF to close refrigerant pipes, and the various valves that are depicted as empty are turned ON to open refrigerant pipes.

[50] A brief description of the operation of a multi-unit air conditioning system configured as above will be given.

[51] As shown in Fig. 1, the main outdoor unit 101 is operated in cooling mode, and the sub outdoor units 102 and 103 are operated in heating mode. One 102 of the sub outdoor units 102 has a flow regulator in an open state, and the other 103 is in a closed state.

[52] To describe the operation of the main outdoor unit 101, a portion of high temperature and high pressure gaseous refrigerant discharged from the compressor 111 flows along the branch pipe 119 to the high pressure pipe 121, and the remaining portion flows through the 4- way valve 112 to the outdoor heat exchanger 113. The refrigerant that passes the outdoor heat exchanger 113 passes the solenoid valve 117 and the check valve 118 to flow into the liquid pipe 122. Here, the refrigerant passing through the outdoor heat exchanger 113 passes through the solenoid valve 117 without expansion. That is, the gaseous refrigerant only converts to liquid refrigerant while passing through the outdoor heat exchanger 113. The refrigerant that passes through the check valve 118 loses heat as it passes through the first sub cooling unit 510, so that its quality is lowered through heat exchange. That is, the refrigerant is phase-changed to a state close to a saturated liquid.

[53] A portion of the refrigerant passing through the first sub cooling unit 510 is branched to the bypass pipe 124, and converts to a second-phase refrigerant with a high temperature and high pressure while passing through the EEV 126. Also, refrigerant that changes to a low temperature and low pressure passes through the first sub cooling unit 510, and absorbs heat while exchanging heat with refrigerant that passes through the check valve 118. The second-phase refrigerant of low temperature and low pressure that is passed through the first sub cooling unit 510 flows to the inlet of the accumulator 114. The refrigerant flowing through the low pressure pipe 123 also flows to the inlet of the accumulator 114.

[54] In the case of the outdoor units 102 and 103 operating in heating mode, refrigerant that passes through the compressor 111 flows in its entirety to the branch pipe 119, and flows to the high pressure pipe 121. Here, when the flow regulator 400 is opened, a portion of the refrigerant flows to the bypass pipe 422.

[55] A portion of refrigerant flowing through the liquid pipe 122 is branched and flows toward the outdoor heat exchanger 113. The refrigerant that flows toward the outdoor heat exchanger 113 expands and converts to a low temperature and low pressure second-phase refrigerant as it passes through the EEV 116, and then absorbs heat (exchanges heat with outdoor air) as it passes through the outdoor heat exchanger 113 to attain a higher quality. The second-phase refrigerant that has passed through the outdoor heat exchanger 113 passes through the 4-way valve 112 and flows to the accumulator 114. Here, a portion of the refrigerant branching from the liquid pipe 122 loses heat while passing through the first sub cooling unit 510, and then flows toward the EEV 116. Another portion of branched refrigerant is branched again at the inlet of the first sub cooling unit 510, and expands to second-phase refrigerant of low temperature and low pressure as it passes the EEV 126. Then, the refrigerant flows through the bypass pipe 124 and attains a higher quality as it absorbs heat while passing through the first sub cooling unit 510. The higher quality second-phase refrigerant flows to the inlet of the accumulator 114.

[56] The high temperature and high pressure refrigerant flowing through the high pressure pipe 121 concentrates at the first distribution part 210. A portion of the refrigerant concentrated at the first distribution part 210 is branched and flows to the heat exchanger 113 of the indoor unit to perform heating. The refrigerant that performs heating flowing to the indoor heat exchanger 113 is lowered in temperature while passing the indoor heat exchanger 113, and then flows to the second sub cooling unit 520. The refrigerant passes the second sub cooling unit 520 and concentrates at the second distribution part 220.

[57] The high temperature and high pressure refrigerant flowing through the liquid pipe

122 and the second sub cooling unit 520 concentrates at the second distribution part 220, and a portion of the refrigerant concentrated at the second distribution part 220 is branched and flows toward the indoor heat exchanger 311 operating in cooling mode.

[58] In detail, the refrigerant flowing to the indoor heat exchanger 311 operating in cooling mode expands to a second-phase low temperature and low pressure refrigerant as it passes through the EEV 312, and then flows into the indoor heat exchanger 311. Then, the second-phase refrigerant that passes the indoor heat exchanger 311 concentrates at the third distribution part 230. From the above description, it will be apparent that the flow direction of refrigerant flowing through the inside of the indoor heat exchanger 311 operating in heating mode and the flowing direction of refrigerant flowing through the inside of the indoor heat exchanger 311 operating in cooling mode will be opposite to one another.

[59] A portion of the refrigerant concentrated at the second distribution part 220 is discharged toward the overcooling part 240.

[60] In detail, the discharged refrigerant first expands to a low temperature and low pressure second-phase refrigerant as it passes through the EEV 241, and then branches and flows through a plurality of branch pipes 242. Refrigerant flowing through each branch pipe 242 exchanges heat with refrigerant inside the second sub cooling unit 520. That is, the refrigerant absorbs heat in a first stage from high temperature and high pressure refrigerant flowing through the second sub cooling unit 520. The refrigerant that passes through the second sub cooling unit 520 combines at the combined pipe 221. As it flows through the combined pipe 221, the refrigerant absorbs heat in a second phase as it passes the second distribution part 220. Thus, through this dual stage heat absorption process, refrigerant that passes through the EEV 241 converts to second-phase refrigerant that is close to saturated gaseous refrigerant. The refrigerant that passes the second distribution part 220 flows through the combined pipe 221 and flows to the third distribution part 230.

[61] A portion of refrigerant at the first distribution part 210 passes through the capillary pipe 600 and the solenoid valve 314, and flows to the third distribution part 230.

[62] Fig. 2 is a system diagram of an outdoor unit configuring a multi-unit air conditioning system according to present embodiments, showing the flow of refrigerant with a flow regulator closed during heating mode operation of the outdoor unit, and Fig. 3 is a system diagram of the outdoor unit in Fig. 2 showing the flow of refrigerant with the flow regulator open, under the otherwise same conditions.

[63] Referring to Figs. 2 and 3, in the heating operation of the multi-unit air conditioning system, the compressor 111 of the outdoor unit 102 can be low in pressure, in which case it is burdened with a large load.

[64] Especially when performing low temperature heating, if the pressure at the inlet of the compressor 111 becomes low and the pressure at the outlet becomes too low, concentrating of refrigerant can occur. When pressure at the inlet becomes too low, the temperature at the inlet becomes too low, resulting in a low temperature of gas discharged from the compressor.

[65] Accordingly, to obviate this limitation, the temperature of discharged gas from a plurality of compressors 111 is measured. If the measured temperature values exceed a predetermined range between a maximum temperature and a minimum temperature, the flow regulator 400 is opened, as shown in Fig. 2, to bypass a portion of discharged gas through the bypass pipe 422 toward the compressor 111. The remaining portion of refrigerant is sent to the high pressure pipe 121, and heating is performed. Here, for controlling the amount of heat at the inlet of the compressor, an expansion valve 420 may be further provided at the outlet of the flow regulator 400.

[66] When high temperature and high pressure discharged gas is returned through the above bypass pipe 422 to the compressor 111 to create high pressure refrigerant, a reduction in compression ratio and an inlet temperature increase can be realized. Therefore, concentration of refrigerant or a resultant disparity in discharged temperatures, through pressure differences between outdoor compressors, can be reduced.

[67] After the discharged temperatures at the compressors 111 are detected, when the difference between the maximum temperature and the minimum temperature falls to below a predetermined value, as shown in Fig. 3, the flow regulator 400 has its valve closed, to allow the discharged gas to flow in its entirety to the high pressure pipe 121.

[68] In further detail, when operated with all the flow regulators 400 for each outdoor unit closed, the discharged temperatures are controlled by opening a flow regulator 400 of a low pressure compressor. Conversely, when operated with all the flow regulators 400 installed on the respective outdoor units opened, the discharged temperatures are controlled by closing a flow regulator 400 of a high pressure compressor. The flow regulators may be opened or closed one at a time, or may be opened or closed as a portion of the combined total.

[69] When operating with a portion of the flow regulators 400 closed, and the remainder of the flow regulators 400 open, when the difference between the maximum temperature and the minimum temperature exceeds a predetermined value, the flow regulator 400 at the compressor with the highest temperature may be closed, and the flow regulator at the compressor with the lowest temperature may be opened. [70] Table 1 shows the discharged temperatures of compressors according to a controlling method for a related art multi-unit air conditioning system, and Table 2 shows the discharged temperatures of compressors according to a controlling method for the multi-unit air conditioning system according to embodiments of the present disclosure.

[71] Table 1 [Table 1] [Table ]

[72] Table 2 [Table 2] [Table ]

[73] When a multi-unit air conditioning system is operated in heating mode, outdoor units may become low in pressure and be subject to high loads. [74] Referring to Table 1, in the related art, compressors 1, 4, and 5 have low discharged temperatures of 66, 41, and 37

O

C, respectively, and are subjected to high loads. Also, the difference between the maximum value and the minimum value for discharged temperatures is as high as 60

O

C.

[75] On the other hand, referring to Table 1, in the controlling method according to the present disclosure, the difference between the maximum and minimum values of discharged temperatures from the compressors can be maintained at only 5

C.

[76] That is, by sensing the temperatures of gas discharged from the compressors overall, and bypassing refrigerant to compressors by opening flow adjustors when the difference between the maximum temperature and the minimum temperature exceeds a preset temperature, the difference between discharged temperatures of compressors can be substantially reduced.

[77]

Claims

[1] A method for controlling a multi-unit air conditioning system, the method comprising: operating a plurality of indoor units connected to a plurality of outdoor units; sensing discharged temperatures from a plurality of compressors provided respectively to the outdoor units; deriving a difference between a maximum value and a minimum value of the discharged temperatures; and bypassing a portion of discharged gas to a compressor when the difference is greater than a predetermined value.

[2] The method according to claim 1, wherein the bypassing of the discharged gas is performed through opening and closing of flow regulators connected respectively to the compressors.

[3] The method according to claim 2, wherein heated temperatures of the compressors are controlled by a refrigerant expansion member provided at an outlet of the flow regulator.

[4] The method according to claim 2, wherein when all the flow regulators provided at the outdoor units are closed, a flow regulator provided at a compressor having a low discharged temperature is opened to control the discharged temperature.

[5] The method according to claim 2, wherein when all the flow regulators provided at the outdoor units are opened, a flow regulator provided at a compressor having a high discharged temperature is closed to control the discharged temperature.

[6] The method according to claim 2, wherein when the difference between the maximum and minimum values of the discharged temperatures is greater than a predetermined value, a flow regulator provided at a compressor having a low discharged temperature is opened.

[7] A multi-unit air conditioning system comprising: a plurality of outdoor units including at least one or more compressors, a four- way valve, an outdoor heat exchanger, and an accumulator connected to an inlet of the compressor; a plurality of indoor units connected to the outdoor units and including an indoor heat exchanger, and an expansion member provided at an outlet of the indoor heat exchanger; a distribution unit connecting the outdoor units and the indoor units, for distributing refrigerant from the outdoor units to the indoor units and supplying refrigerant from the indoor units to the outdoor units; a bypass pipe having one end connected to a pipe at an outlet of the compressor and the other end connected to a pipe connecting the accumulator and the compressor, the bypass pipe for bypassing gas discharged from the compressor to another compressor; and a flow regulator provided at one end of the bypass pipe.

[8] The multi-unit air conditioning system according to claim 7, wherein the bypass pipe and the flow regulator are respectively installed for each outdoor unit.

[9] The multi-unit air conditioning system according to claim 7, wherein the flow regulator comprises one of a solenoid valve, an ON/OFF valve, an EEV (electronic expansion valve), and a PMV (pulse modulation valve).

[10] The multi-unit air conditioning system according to claim 7, wherein the distribution unit comprises: a first distribution part at which a high temperature and high pressure gaseous refrigerant discharged from the compressor collects; a second distribution part at which a high temperature and high pressure liquid refrigerant passing through the outdoor heat exchanger collects, when the outdoor units are operated in cooling mode; and a third distribution part at which a low temperature and low pressure second- phase refrigerant passing through the indoor heat exchanger collects, when the indoor units are operated in cooling mode.

[11] The multi-unit air conditioning system according to claim 10, wherein the refrigerant collected at the first distribution part is transferred to the indoor heat exchanger during heating operation, and the refrigerant collected at the second distribution part is transferred to the indoor heat exchanger during cooling operation.

[12] The multi-unit air conditioning system according to claim 10, further comprising: a high pressure pipe connecting the outlet of the compressor to the first distribution part; a liquid pipe connecting the outdoor heat exchanger to the second distribution part; and a low pressure pipe connecting the accumulator to the third distribution part.

[13] The multi-unit air conditioning system according to claim 12, wherein when the flow regulator is closed, refrigerant gas discharged from the compressor flows entirely to the high pressure pipe.

[14] The multi-unit air conditioning system according to claim 7, wherein one of the plurality of outdoor units operates as a main outdoor unit, the main outdoor unit comprising a constant speed compressor and an inverter compressor, and the remaining outdoor units comprising a constant speed compressor.