FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
REFRIGERANT RECOVERY IN MULTI-AIR CONDITIONER SYSTEM;
BLUE STAR LIMITED A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS KASTURI BUILDINGS, MOHAN T. ADVANI CHOWK, JAMSHETJI TATA ROAD, MUMBAI - 400 020, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION:
The invention relates to multi-air conditioner system, and more particularly to refrigerant recovery from OFF Outdoor Unit in multi-air conditioner system.
BACKGROUND OF THE INVENTION:
Generally, multi-air-conditioner system comprises a refrigerant circuit comprising of a plurality of indoor units connected to one or more outdoor units. The outdoor unit comprises a compressor, an outdoor heat exchanger, and the indoor unit comprises of an indoor heat exchanger and an expansion valve for each indoor unit. The outdoor unit and the indoor unit are connected to each other via common liquid refrigerant and gas refrigerant piping for circulation of refrigerant in the system.
When the multi-air conditioner system is switched ON, all outdoor units start at a particular capacity to recover the refrigerant from the indoor units. Once the predetermined level of refrigerant is in circulation, system starts in normal mode. Immediately, after the refrigerant is in circulation and at start of normal mode if there is a requirement of all outdoor units to be driven, all outdoor units are ON and complete system refrigerant is in circulation.
However, if there is a requirement of only one outdoor unit to be driven immediately after the refrigerant is in circulation, then the refrigerant of that particular outdoor unit which is ON will be in circulation, and the other outdoor units which are in OFF condition will have refrigerant stored which is not in circulation. Due to this the system has a refrigerant shortage, and subsequently expansion valves of the indoor units open fully for need of more refrigerant. This condition is dangerous from system reliability point of view as refrigerant shortage increases

motor winding temperature and thus it is not advisable to run the system for a long time with shortage of refrigerant.
In view of the above, there is a need in the art to compensate for the refrigerant shortage in multi-air conditioner systems.
SUMMARY OF THE INVETION:
Accordingly, the present invention in one aspect provides a multi-air conditioning system for maintaining refrigerant level in the multi-air conditioning system, the system comprising: a refrigerant circuit having at-least two outdoor units connected to a plurality of indoor units, each indoor unit having an expansion valve; a recovery valve for recovering refrigerant from an OFF outdoor unit; and a control means for actuating and de-actuating the recovery valve to recover refrigerant from the OFF outdoor unit based upon opening of the expansion valve connected to one of the indoor units and/or temperature difference between gas temperature and liquid temperature of the indoor unit.
In another aspect, the present invention provides a method for refrigerant recovery in a multi-air conditioner system, the method comprising the steps of detecting refrigerant shortage in the system; actuating a recovery valve for recovering refrigerant from an OFF outdoor unit to mix with the refrigerant in circulation, and de-actuating the recovery valve once the refrigerant is recovered.

BRIEF DESCRIPTION OF THE DRAWINGS:
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 is a schematic illustrating environment of a multi-air conditioner system according to the present invention.
Figure 2 shows flowchart of a method for refrigerant recovery in a multi-air conditioner system according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION:
The present invention provides a multi-air conditioner system capable of refrigerant recovery, wherein the system maintains optimum level of refrigerant required for the air-conditioner to run without reduction in its cooling capacity, increase in discharge temperature, etc.
Figure 1 illustrates environment of a multi-air conditioner system 100 according to the present invention. The multi-air conditioner system comprises a refrigerant circuit 102 having at-least two outdoor units 104 connected to a plurality of indoor units 106, a recovery valve 108 and a control means 110. Each indoor unit has an expansion valve 112 for allowing refrigerant from outdoor unit to be circulated in the indoor unit. The recovery valve 108 is connected to each outdoor unit, for recovering refrigerant from an OFF outdoor unit.
According to the present invention, the outdoor units 104 and indoor units 106 are connected to each-other through a common liquid refrigerant and gas refrigerant piping, and the

outdoor units 104 are connected to a common suction line. The expansion valve 112 is provided at inlet of each indoor unit and the recovery valve 108 is provided at outlet of each outdoor unit 104 on the common liquid refrigerant and gas refrigerant piping.
According to the present invention, the expansion valve 112 is capable of opening and closing based upon refrigerant level in the indoor unit 106. The expansion valve 112 has a range of control steps from a fully close position to fully open position. According to the present invention, during refrigerant recovery, the expansion valve 112 moves between the range of 100% open i.e. fully open and 95% open i.e. partially closed. During a refrigerant shortage, the expansion valve 112 is in fully open position, and once the refrigerant is recovered, the expansion valve 112 moves to partially close position
The recovery valve 108 is provided at outlet of each outdoor unit in the refrigerant circuit connecting the outdoor unit to a suction line 114 in the refrigerant circuit. According to the present invention, the recovery valve 108 is a solenoid valve, and is capable of actuating and de-actuating based upon opening and closing of the expansion valve 112 connected to one of the indoor units 106. According to the present invention, the recovery valve 108 is actuated when the expansion valve 112 is in the fully open position, and the recovery valve 108 is de-actuated when the expansion valve 112 is in partially closed position. The recovery valve 108 when actuated allows the refrigerant from one of the OFF outdoor units 104 to mix with the refrigerant in circulation as shown in figure 1 thereby allowing additional refrigerant to compensate for shortage in refrigerant in the air conditioner system.
According to the present invention, the control means actuates the recovery valve 108 to recover refrigerant from the OFF outdoor unit. The control means includes a sensor (not shown) to detect refrigerant level in the system and accordingly actuate the recovery valve 108. The sensor according to the invention can be a liquid temperature sensor and a gas temperature

sensor. The sensor is employed to detect the temperature difference between the gas temperature and liquid temperature. In this regard, when the refrigerant level is less, the difference between the gas temperature and liquid temperature increases. The sensor detects this temperature difference and the control means opens the expansion valve 112. Depending upon the opening of the expansion valve 112, the recovery valve 108 of the OFF outdoor unit is actuated by a control signal by the control means to recover the refrigerant. Subsequently as the recovery valve 108 is actuated, the expansion valve 112 begins to close i.e. it partially closes, and the, the recovery valve 108 is de-actuated.
In the environment illustrated in figure 1, when the air conditioner system is in running condition, at-least one outdoor unit 104 is in OFF condition while at-least one outdoor unit 104 is in ON condition when at-least one of the indoor units 106 are in ON condition. During operating condition when the refrigerant level in the ON indoor unit 106 reduces, the expansion valve 112 of the indoor unit 106 starts opening. The control means will actuate the recovery valve 108 of the OFF outdoor unit 104 depending on opening of the expansion valve 112. Once the recovery valve 108 is actuated, refrigerant from the outdoor unit 104 in OFF condition starts flowing through the common liquid refrigerant and gas refrigerant piping and mixes with the refrigerant in circulation.
Figure 2 shows a flow-chart illustrating a method for refrigerant recovery in a multi-air conditioner system according to the present invention. As shown, the system will detect refrigerant shortage in one of the ON indoor units of the system. The refrigerant shortage is detected by sensing the temperature difference between gas temperature and liquid temperature and/or opening of an expansion valve of the indoor unit. On detecting the temperature difference exceeding 5°C, the expansion valve opens. Depending upon the opening of the expansion valve, a recovery valve of an OFF outdoor unit is actuated. The recovery valve on actuation allows refrigerant from a heat exchanger of the OFF outdoor unit to

start flowing through the common liquid refrigerant and gas refrigerant piping to mix with the refrigerant in circulation thereby allowing additional refrigerant to compensate for shortage in refrigerant in the air conditioner system. Further, the refrigerant recovery is stopped once the expansion valve closes to partially close position and the recovery valve is de-actuated.
Advantageously the present invention prevents failure of the air-conditioner system due to refrigerant shortage, maintains cooling temperature, and ensures system reliability.
While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

WE CLAIM:
1. A multi-air conditioning system for maintaining refrigerant level in the multi-air
conditioning system, the system comprising:
a refrigerant circuit having at-least two outdoor units connected to a plurality of indoor units, each indoor unit having an expansion valve;
a recovery valve for recovering refrigerant from an OFF outdoor unit; and
a control means for actuating and de-actuating the recovery valve to recover refrigerant from the OFF outdoor unit based upon opening of the expansion valve connected to one of the indoor units and/or temperature difference between gas temperature and liquid temperature of the indoor unit.
2. The system as claimed in claim 1, wherein the control means includes a sensor to detect the refrigerant level in the indoor unit.
3. The system as claimed in claim 1, wherein the recovery valve is provided on the outlet of each outdoor unit in the refrigerant circuit connecting the outdoor unit to a suction line in the refrigerant circuit
4. The system as claimed in claim 1, wherein the expansion valve is provided on the inlet of each indoor unit in the refrigerant circuit, and the expansion valve is capable of moving between a fully open position to a partially close position.
5. The system as claimed in claim 4, wherein refrigerant recovery is started when the expansion valve connected to one of the indoor units is in the fully open position and/or temperature difference between gas temperature and liquid temperature of indoor unit exceeds a predetermined range.
6. The system as claimed in claim 5, wherein refrigerant recovery is stopped when the expansion valve is in the partially closed position.
7. The system as claimed in claim 1, wherein the recovery valve is a solenoid valve.
8. A method for refrigerant recovery in a multi-air conditioner system as claimed in claim 1, the method comprising the steps of:
detecting refrigerant shortage in the system;

actuating a recovery valve for recovering refrigerant from an OFF outdoor unit to mix
with the refrigerant in circulation, and
de-actuating the recovery valve once the refrigerant is recovered.
9. The method as claimed in claim 8, wherein step of detecting refrigerant shortage comprises sensing temperature difference between gas temperature and liquid temperature of the indoor unit and/or opening of the expansion valve of the indoor unit.
10. The method as claimed in claim 8, wherein the recovery valve is actuated when the expansion valve is in a fully open position.
11. The method as claimed in claim 8, wherein the recovery valve is de-actuated once the expansion valve is in a partially closed position, and refrigerant from the OFF outdoor unit flows into circulation.