Multi-unit air conditioner and method for controlling the same

Abstract

 Disclosed herein is a simultaneous cooling and heating operation controlling method of a multi air conditioner system comprising a plurality of indoor units connected in parallel to an outdoor unit. The simultaneous cooling and heating operation controlling method comprises differently setting a cooling and heating reference range to decide main operation mode of the multi air conditioner system based on outdoor temperature, measuring the outdoor temperature to select the cooling and heating reference range based on the outdoor temperature, summing capacities of the indoor units where a cooling or heating operation is set to calculate cooling and heating ratio, and identifying part of the cooling and heating reference range corresponding to the cooling and heating ratio to decide the main operation mode of the multi air conditioner system.

Description

[0001] The present invention relates to an air conditioning system comprising an outdoor unit, a plurality of indoor units, a refrigerant circuit including control valves and control means configured for controlling the control valves to configure the refrigerant circuit for mainly cooling operation and mainly heating operation modes in dependence on the current operational heating and cooling capacities of the indoor units.

[0002] Generally, a multi air conditioner system comprises an outdoor unit, a plurality of indoor units connected in parallel to the outdoor unit, a branch unit having a plurality of high-pressure and low-pressure gas valves to control the flow rate of refrigerant, introduced into the indoor units, and high-pressure and low-pressure gas pipes connected between the outdoor unit and valves of the branch unit. An example of such an air conditioner system is disclosed in JP-A-1 993-099525.

[0003] The conventional multi air conditioner system is capable of performing a cooling operation, a heating operation, a mainly cooling operation and a mainly heating operation based on a heating ratio (or a cooling ratio). As shown in Figure 1, the cooling operation is performed when the heating ratio is 0 % (i.e., when the indoor unit(s) in operation are operated in cooling mode), the heating operation is performed when the heating ratio is 100 % (i.e., when the indoor unit(s) in operation are operated in heating mode), the mainly cooling operation is performed when the heating ratio is greater than 0 % and less than 50 % (i.e., when the total capacity of the indoor unit(s) in cooling operation is greater than the total capacity of the indoor unit(s) in heating operation), and mainly heating operation is performed when the heating ratio is greater than or equal to 50 % and less than 100 % (i.e., when the total capacity of the indoor unit(s) in cooling operation are less than or equal to the total capacity of the indoor unit(s) in heating operation). The heating ratio means the ratio of the capability of indoor unit(s) performing the heating operation to the total capability of the indoor unit(s) in operation.

[0004] When the multi air conditioner system is operated in the mainly heating mode or the mainly cooling mode, the high-pressure gas valve(s), connected to the indoor unit(s) in heating operation, are opened and the low-pressure gas valve(s), connected to the indoor unit(s) in heating operation, are closed. Also, the high-pressure gas valve(s) connected to the indoor unit(s) where the cooling operation is set are closed, and the low-pressure gas valve(s) connected to the indoor unit(s) where the cooling operation is set are opened. As a result, high-temperature gas refrigerant is introduced into the indoor unit(s) for heating operation and low-temperature gas refrigerant is introduced into the indoor unit(s) for cooling operation, so that cooling and heating operations can be performed concurrently by different indoor units.

[0005] In the conventional multi air conditioner system, describe above, however, the mainly cooling or heating operation is identified on the basis of the heating ratio and, therefore, mainly heating or cooling operation modes may be set inappropriately some cases.

[0006] When the heating ratio is 53 %, for example, mainly heating operation is performed irrespective of outdoor temperature. If the outdoor temperature is high at this time, the temperature of an outdoor heat exchanger of the outdoor unit is high and, therefore, the pressure of the outdoor heat exchanger is relatively high. Consequently, the temperature of the indoor heat exchangers of the indoor units, connected to the outdoor heat exchanger through a four-way valve, is increased and, therefore, the cooling efficiency of the indoor units performing cooling operation is reduced.

[0007] Since the temperature of the outdoor heat exchanger is high, the discharge pressure of the system's compressor is also increased. For this reason, the compression capacity of the compressor must be reduced to protect the compressor. If the compression capacity of the compressor is reduced, however, the heating efficiency of the indoor units performing heating operation as well as the cooling efficiency of the indoor units performing the cooling operation is reduced.

[0008] When the total capacity of the indoor units in cooling operation is less than or equal to approximately 20 % of the total capacity of the indoor units and the heating ratio is 40 %, for example, the mainly cooling operation is performed. If the interior temperature of a room being cooled is decreased, the temperature of the indoor heat exchanger of the indoor unit performing the cooling operation is also decreased. As a result, the indoor heat exchanger of the indoor unit performing the cooling operation becomes frozen. The compression capacity of the compressor must be reduced in order to prevent the indoor heat exchanger of the indoor unit performing the cooling operation from being frozen and, therefore, the heating and cooling efficiencies of the respective indoor units are lowered. In the above case, the capabilities of the outdoor heat exchanger and the indoor units in heating operation are greater than the capability of the indoor units in cooling operation. As a result, it is difficult to form high pressure at the outlet side of the compressor and, therefore, the heating efficiency of the indoor unit(s) performing the heating operation is also lowered.

[0009] An air conditioning system, according to the present invention, is characterised by an outdoor air temperature sensor and the control means being configured for controlling to control valve to configure the refrigerant circuit for mainly cooling operation and mainly heating operation modes additionally in dependence on the output of said temperature sensor.

[0010] Preferred and optional features of the invention, and corresponding method aspects, are set forth in claims 2 to 15 appended hereto.

[0011] An embodiment of the present invention will now be described, by way of example, with reference to Figures 2 to 7 of the accompanying drawings, in which:

Figure 1 illustrates the combined heating and cooling operation modes of a conventional multi air conditioner system;

Figure 2 is a refrigerant circuit diagram of a multi air conditioner system according to the present invention;

Figure 3 is a block diagram showing the construction of the multi air conditioner system shown in Figure 2;

Figure 4 illustrates a combined heating and cooling operations modes of a first embodiment of the present invention;

Figure 5 is a flowchart illustrating the simultaneous cooling and heating operation of the first embodiment of the present invention;

Figure 6 illustrates combined heating and cooling operations modes of a second embodiment of the present invention; and

Figure 7 is a flowchart illustrating the simultaneous cooling and heating operation of the second embodiment of the present invention.

[0012] Referring to Figure 2, a multi air conditioner system comprises: an outdoor unit 10, first to fourth indoor units 20a, 20b, 20c, 20d, connected in parallel to the outdoor unit 10, and a mode switching unit 30 for switching the indoor units 20a, 20b, 20c, 20d between their heating and cooling modes.

[0013] The outdoor unit 10 comprises a four way valve 12 to control the flow direction of refrigerant discharged from a compressor 11, an outdoor heat exchanger 13 to perform heat exchange with outdoor air introduced into the outdoor unit 10, an outdoor motor-operated valve 14 to expand the refrigerant and a receiver tank 15 and an accumulator 16 for separating gaseous refrigerant and liquid refrigerant from each other. The indoor units 20a, 20b, 20c, 20d are connected to the outdoor unit 10 by a high-pressure gas pipe 17, a low-pressure gas pipe 18 and a high-pressure liquid pipe 19, through which refrigerant is supplied from the outdoor unit 10 to the indoor units 20a, 20b, 20c, 20d.

[0014] The low-pressure gas pipe 18 is connected to the inlet of the compressor 11 of the outdoor unit 10, the outdoor motor-operated valve 14 is connected in series with the outdoor heat exchanger 13 and the high-pressure liquid pipe 19 is connected to the outdoor motor-operated valve 14 via the receiver tank 15. To the outdoor motor-operated valve 14 are connected, in parallel, a bypass valve 41 a serving as a flow rate control valve and a non-return valve 41b so that liquid refrigerant discharged from the outdoor heat exchanger 13 passes through the bypass valve 41 a and the non-return valve 41b during a cooling operation, and refrigerant passes through the outdoor motor-operated valve 14 when the bypass valve 41a is closed during a heating operation.

[0015] Between the four-way valve 12 and the high-pressure liquid pipe 19 is disposed a high-pressure branch pipe 42, which braches off from the high-pressure gas pipe 17. On the high-pressure branch pipe 42 are mounted a high-pressure branch pipe electromagnetic valve 43a, serving as an on/off valve, and a non-return valve 43b to prevent refrigerant back-flow from the high-pressure gas pipe 17. Between the four-way valve 12 and the high-pressure gas pipe 17 is mounted another non-return valve 44 to prevent refrigerant backflow. On the high-pressure liquid pipe 19 are mounted switching unit pipe electromagnetic valves 24a, 24b to control the flow rate of refrigerant flowing from the mode switching unit 30 to the high-pressure liquid pipe 19.

[0016] The first to fourth indoor units 20a, 20b, 20c, 20d comprise first to fourth indoor heat exchangers 21 a, 21 b, 21c, 21d, first to fourth indoor motor-operated valves 22a, 22b, 22c, 22d connected in series with respective ones of the first to fourth indoor heat exchangers 21a, 21 b, 21c, 21d and first to fourth temperature sensors 37a, 37b, 37c, 37d mounted between respective indoor units 20a, 20b, 20c, 20d and the mode switching unit 30.

[0017] The mode switching unit 30 comprises first to fourth heating valves 31a, 31 b, 31c, 31d mounted on first to fourth high-pressure gas branch pipes 33a, 33b, 33c, 33d, which branch off from the high-pressure gas pipe 17 and first to fourth cooling valves 32a, 32b, 32c, 32d mounted on first to fourth low-pressure gas branch pipes 34a, 34b, 34c, 34d, which branch off from the low-pressure gas pipe 18. The first heating and cooling valve set is connected to a first refrigerant pipe 35a, which is connected to the first indoor heat exchanger 20a. Similarly, the second to fourth heating and cooling valve sets are connected to second to fourth refrigerant pipes 35b, 35c, 35d respectively.

[0018] When the mainly cooling operation of the multi air conditioner system is performed, a first port 12a of the four-way valve 12 communicates with a second port 12b of the four-way valve 12 and a third port 12c of the four-way valve 12 communicates with a fourth port 12d of the four-way valve 12. At the same time, the high-pressure branch pipe electromagnetic valve 43a of the high-pressure branch pipe 42 is opened. Also, heating valves of the mode switching unit 30, connected to indoor units in cooling operation, are closed and cooling valves of the mode switching unit 30, connected to indoor units in cooling operation, are open. Conversely, heating valves of the mode switching unit 30, connected to indoor units in cooling operation, are open and cooling valves of the mode switching unit 30, connected to the indoor units in cooling operation, are closed.

[0019] As a result, some of the refrigerant discharged from the compressor 11, condensed by the outdoor heat exchanger 12, is supplied to indoor units in cooling operation through the high-pressure liquid pipe 19 and is then evaporated by indoor heat exchangers to cool rooms. The refrigerant heat-exchanged by indoor heat exchangers, which is low-pressure gas refrigerant, flows to the inlet of the compressor 11 through cooling valves of the mode switching unit 30 and the low-pressure gas pipe 18.

[0020] Some of the refrigerant, discharged from the compressor 11 and passing through the four-way valve 12, is supplied to indoor units in heating operation through the high-pressure branch pipe 42, the high-pressure gas pipe 17, and heating valves of the mode switching unit 30, and is then condensed by indoor heat exchangers to heat rooms. The refrigerant, having passed through indoor heat exchangers, is supplied to the high-pressure liquid pipe 19, at which the refrigerant joins refrigerant supplied to the indoor units in cooling operation cool rooms, and then flows to the compressor 11 through the low-pressure gas pipe 18.

[0021] When mainly heating operation is performed, the first port 12a of the four-way valve 12 communicates with the third port 12c of the four-way valve 12 and the second port 12b of the four-way valve 12 communicates with the fourth port 12d of the four-way valve 12. At the same time, the high-pressure branch pipe electromagnetic valve 43a of the high-pressure branch pipe 42 is closed. Also, heating valves of the mode switching unit 30, connected to indoor units in heating operation, are opened and cooling valves of the mode switching unit 30, connected to indoor units in cooling operation are closed. Conversely, heating valves of the mode switching unit 30, connected to indoor units in cooling operation, are closed and cooling valves of the mode switching unit 30, connected to the indoor units in cooling operation, are opened.

[0022] As a result, the refrigerant discharged from the compressor 11 is supplied to indoor heat exchangers of indoor units in heating operation through the high-pressure gas pipe 17, is condensed by the indoor heat exchangers to heat rooms and is then delivered to the high-pressure liquid pipe 19 through expansion valves. Some of the refrigerant, delivered to the high-pressure liquid pipe 19, is supplied to indoor units in cooling operation, is evaporated by the indoor heat exchangers to cool rooms, and then flows to the inlet of the compressor 11 through the low-pressure gas pipe 18 and the accumulator 16.

[0023] The remainder of the refrigerant, delivered to the high-pressure liquid pipe 19, is returned to the outdoor unit 10. Specifically, the refrigerant is supplied to the outdoor heat exchanger 13 through the receiver tank 15 and the outdoor motor-operated valve 14, is evaporated by the outdoor heat exchanger 13 and then flows to the compressor 11 through the third and fourth ports 12c and 12d of the four-way valve 12 and the accumulator 16.

[0024] As shown in Figure 2, the outdoor unit 10 further comprises: an outdoor unit microcomputer 23 to control the components of the outdoor unit 10 and an outdoor temperature sensor 25 to measure the temperature of outdoor air.

[0025] The first to fourth indoor units 20a, 20b, 20c, 20d further comprise first to fourth indoor unit microcomputers 36a, 36b, 36c, 36d to control the components of respective indoor units.

[0026] The mode switching unit 30 further comprises a mode switching unit microcomputer 38 to control the first to fourth cooling valves 32a, 32b, 32c, 32d and the first to fourth heating valves 31a, 31b, 31c, 31d.

[0027] Now, a simultaneous cooling and heating operation controlling method of the multi air conditioner system of a first embodiment of the present invention will be described with reference to Figures 4 and 5.

[0028] First, the outdoor temperature is measured by the outdoor temperature sensor 25 to determine the outdoor temperature as well as the heating ratio when deciding the combined (i.e. mainly heating or mainly cooling) operation mode (50) and then the sum of the capacities of the indoor units in cooling operation and the sum of the capacities of the indoor units in heating operation are obtained to calculate the heating ratio (52).

[0029] Subsequently, it is determined whether the outdoor temperature is higher than or equal to a first reference temperature (54). The first reference temperature is preferably set to a minimum outdoor temperature, where the temperature of the outdoor heat exchanger 13 is raised in mainly heating mode reducing the cooling and heating efficiencies of the entire system. In the illustrated embodiment, the first reference temperature is 15 °C as shown in Figure 4, although the first reference temperature may be different in different systems.

[0030] If the outdoor temperature is lower than the first reference temperature, it is determined whether the heating ratio is less than or equal to a second reference value (64). If the heating ratio is less than or equal to the second reference value, the system operates in mainly cooling mode (66) and, if the heating ratio is greater than the second reference value, the system operates in mainly heating mode (68). Preferably, the second reference value is set to 50 % as shown in Figure 4, although the second reference value may be different for different systems.

[0031] If the outdoor temperature is higher than or equal to the first reference temperature in Operation 54, it is determined whether the heating ratio is less than or equal to a first reference value (56). The first reference value is preferably set to above the second reference value. As shown in Figure 4, the first reference value is 55 %. If the heating ratio is less than or equal to the first reference value, the system operates in mainly cooling mode (58) and, if the heating ratio is greater than the first reference value, the system operates in mainly heating mode (62).

[0032] When the outdoor temperature is higher than or equal to the first reference temperature as described above, the heating ratio reference value, which is a critical factor in deciding which combined operation mode to use, is set to high and, therefore, the system operates in mainly cooling mode for a portion of the heating ratio at which the system operates in mainly heating mode (when the heating ratio is 50 to 55 % in Figure 4) in the prior art. Consequently, the system operates in mainly heating mode, when the outdoor temperature is high, to prevent the cooling and heating efficiencies of the multi air conditioner system from being reduced.

[0033] If the capacities of indoor units in heating operation or the capacities of the indoor units in cooling operation are changed, while after the combined operation mode has been decided upon, Operation 50 is performed to reset the combined operation mode (60).

[0034] In the illustrated embodiment, the combined operation mode is decided upon using two different reference values according to the outdoor temperature, although the outdoor temperature may be divided to set reference values based on the divided outdoor temperature. In this case, the reference values are preferably predetermined and stored in the microcomputer.

[0035] A simultaneous cooling and heating operation controlling method of the multi air conditioner system of a second embodiment of the present invention will be described hereinafter with reference to Figures 6 and 7.

[0036] First, the outdoor temperature is measured by the outdoor temperature sensor 25 and the indoor temperatures are measured by the first to fourth temperature sensors 37a, 37b, 37c, 37d of the indoor units 20a, 20b, 20c, 20d to set the combined operation mode (70) and then the sum of capacities of the indoor units in cooling operation and the sum of capacities of the indoor units in heating operation are obtained to calculate the heating ratio (72).

[0037] Subsequently, it is determined whether the required cooling capacity is less than or equal to 20 % of the total capacity of the indoor units (74). The required cooling capacity is the sum of capacities of the indoor units in cooling operation. If the required cooling capacity is greater than 20 % of the total capacity of the indoor units, Operation 54 of Figure 5 is performed. If the required cooling capacity is less than or equal to 20 % of the total capacity of the indoor units, on the other hand, it is determined whether the temperatures of the rooms, in which the indoor units are in cooling operation, are lower than or equal to a second reference temperature (76). The second reference temperature is the maximum temperature at which the heat exchangers of the indoor units in the cooling operation may be frozen in the mainly cooling mode.

[0038] If the temperatures of the rooms, in which the indoor units are in cooling operation, are higher than the second reference temperature, Operation 54 of Figure 5 is performed. If the temperatures of the rooms, in which the indoor units are in cooling operation, are lower than or equal to a second reference temperature, it is determined whether the heating ratio is greater than or equal to a third reference value (78). The third reference value is set at a heating ratio of below 50 % as shown in Figure 6. In the illustrated embodiment, the third reference value is 30 %. Consequently, mainly heating mode is used instead of mainly cooling mode in a range where the prior art employs mainly cooling mode (i.e. 30 to 50 %) to prevent the performance of the system from being lowered due to control to prevent the indoor units from being frozen.

[0039] If the capacity of the indoor units in heating operation or the capacity of the indoor units in cooling operation are changed while the system is operating in mainly heating mode, Operation 70 is performed. If the conditions of Operations 74, 76 and 78 are not satisfied, Operation 54 of Figure 5 is performed, although the main operation mode may be set according to the conventional method as shown in Figure 1 (i.e. only based on the heating ratio).

[0040] In the first and second embodiments, the combined operation modes of the multi air conditioner system is decided upon considering both the heating ratio and other conditions, although the combined operation mode of the multi air conditioner system may be decided considering both cooling ratio and other conditions.

[0041] As apparent from the above description, the main operation mode may be decided considering the outdoor temperature as well as the heating ratio (or the cooling ratio) in combined heating and cooling operation. Consequently, the present invention can have the effect of preventing the combined operation mode from being improperly set at the specific range of the heating ratio and, therefore, preventing performance of the system from being deteriorated.

[0042] Furthermore, when the capacity of the indoor units in cooling operation is less than or equal to the reference ratio of the total capacities of the indoor units and the temperatures of the room where the cooling operation is performed is lower than or equal to the reference temperature, the relatively small heating ratio reference value is set to determine the combined operation mode. Consequently, the present invention can have the effect of preventing the combined operation mode from being improperly set at a specific range of the heating ratio and, therefore, preventing the performance of the system from being deteriorated.

[0043] Although a few 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.

Claims

1. An air conditioning system comprising:

an outdoor unit;

a plurality of indoor units;

a refrigerant circuit including control valves; and

control means configured for controlling the control valves to configure the refrigerant circuit for mainly cooling operation and mainly heating operation modes in dependence on the current operational heating and cooling capacities of the indoor units,

characterised by

an outdoor air temperature sensor; and

the control means being configured for controlling to control valve to configure the refrigerant circuit for mainly cooling operation and mainly heating operation modes additionally in dependence on the output of said temperature sensor.

2. A system according to claim 1, wherein the control means is configured to set a mode changeover reference, corresponding to a ratio of operational heating or cooling capacity to operational heating and cooling capacity, and set the operation mode in dependence on a comparison between the current operational heating or cooling capacities and the mode changeover reference.

3. A system according to claim 2, wherein the mode changeover reference is set in dependence on the output of said temperature sensor.

4. A system according to claim 3, wherein mode changeover reference is set such that changeover occurs at reduced current heating operation capacity to current heating and cooling operation capacity ratio.

5. A simultaneous cooling and heating operation controlling method of a multi air conditioner system comprising a plurality of indoor units connected in parallel to an outdoor unit, wherein the method comprises:

differently setting a cooling and heating reference range to decide main operation mode of the multi air conditioner system based on outdoor temperature;

measuring the outdoor temperature to select the cooling and heating reference range based on the outdoor temperature;

summing capacities of the indoor units where a cooling or heating operation is set to calculate cooling and heating ratio; and

identifying part of the cooling and heating reference range corresponding to the cooling and heating ratio to decide the main operation mode of the multi air conditioner system.

6. The method according to claim 5, wherein the main operation mode is main cooling mode or main heating mode, and the main cooling mode or the main heating mode is decided as the main operation mode depending upon part of the cooling and heating reference range corresponding to the cooling and heating ratio.

7. A simultaneous cooling and heating operation controlling method of a multi air conditioner system comprising a plurality of indoor units connected in parallel to an outdoor unit, wherein the method comprises:

measuring outdoor temperature;

obtaining the sum of capacities of the indoor units where a cooling operation is set and the sum of capacities of the indoor units where a heating operation is set to calculate heating ratio;

comparing the heating ratio with a heating ratio reference value set based on the outdoor temperature; and

operating the multi air conditioner system in the main heating mode when the heating ratio is greater than the heating ratio reference value, and operating the multi air conditioner system in the main cooling mode when the heating ratio is not greater than the heating ratio reference value.

8. The method according to claim 7, wherein the heating ratio reference value is set to be proportional to the outdoor temperature.

9. The method according to claim 8, wherein the heating ratio reference value is set to a first reference value when the outdoor temperature is higher than or equal to a reference temperature, and the heating ratio reference value is set to a second reference value, which is less than the first reference value, when the outdoor temperature is lower than the reference temperature.

10. A simultaneous cooling and heating operation controlling method of a multi air conditioner system comprising a plurality of indoor units connected in parallel to an outdoor unit, wherein the method comprises:

measuring outdoor temperature;

obtaining the sum of capacities of the indoor units where a cooling operation is set and the sum of capacities of the indoor units where a heating operation is set to calculate heating ratio;

comparing the heating ratio with a first reference value, when the outdoor temperature is higher than or equal to a reference temperature, to decide main operation mode of the multi air conditioner system, and comparing the heating ratio with a second reference value, which is less than the first reference value, when the outdoor temperature is lower than the reference temperature, to decide main operation mode of the multi air conditioner system

11. A simultaneous cooling and heating operation controlling method of a multi air conditioner system comprising a plurality of indoor units connected in parallel to an outdoor unit, wherein the method comprises:

measuring temperatures of spaces where the indoor units are installed;

obtaining the sum of capacities of the indoor units where a cooling operation is set and the sum of capacities of the indoor units where a heating operation is set to calculate heating ratio;

if the capacity(ies) of the indoor unit(s) where a cooling operation is set are less than or equal to predetermined percentage of the total capacities of the indoor units, and the temperature(s) of the space(s) at which the indoor unit(s) where the cooling operation is set are installed are lower than or equal to a reference temperature, comparing the heating ratio with a heating ratio reference value, which is set to be less than another heating ratio reference value set when the capacity(ies) of the indoor unit(s) where the cooling operation is set are greater than the predetermined percentage of the total capacities of the indoor units, and the temperature(s) of the space(s) at which the indoor unit(s) where the cooling operation is set are installed are higher than the reference temperature; and

operating the multi air conditioner system in main heating mode when the heating ratio is greater than the heating ratio reference value.

12. The method according to claim 11, wherein the reference temperature is the maximum temperature at which the heat exchanger(s) of the indoor unit(s) where the cooling operation is set are frozen.

13. The method according to claim 11, wherein the predetermined percentage is 10 to 30%.

14. A multi air conditioner system comprising:

a plurality of indoor units connected in parallel to an outdoor unit; an outdoor temperature sensor to measure outdoor temperature; and

a control unit to perform a controlling operation to operate the multi air conditioner system in main heating mode when heating ratio is greater than a heating ratio reference value set based on the outdoor temperature measured by the outdoor temperature sensor and in main cooling mode when the heating ratio is not greater than the heating ratio reference value.

15. A multi air conditioner system comprising:

a plurality of indoor units connected in parallel to an outdoor unit;

a plurality of indoor temperature sensors to measure temperatures of spaces

where the indoor units are installed; and

a control unit to perform a controlling operation to compare heating ratio with a heating ratio reference value when the capacity(ies) of the indoor unit(s)

where a cooling operation is set are less than or equal to predetermined percentage of the total capacities of the indoor units, and the temperature(s) of the space(s) at which the indoor unit(s) where the cooling operation is set are installed are lower than or equal to a reference temperature, the heating ratio reference value being set to be less than another heating ratio reference value set when the capacity(ies) of the indoor unit(s) where the cooling operation is set are greater than the predetermined percentage of the total capacities of the indoor units, and the temperature(s) of the space(s) at which the indoor unit(s) where the cooling operation is set are installed are higher than the reference temperature, and to decide main operation mode based on the comparison.

Drawing