Patent Publication Number: US-6655161-B1

Title: Air conditioner and control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 2002-27271, filed May 17, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to air conditioners, and more particularly to a system air conditioner having a plurality of indoor units and method of controlling the air conditioner. 
     2. Description of the Related Art 
     In general, air conditioners are machines that automatically and appropriately condition indoor air in residential or office buildings by controlling properties of the indoor air, such as temperature and humidity. Since residents of such residential or office buildings typically desire to accomplish different target conditions of indoor air, and atmospheric environments of the buildings frequently vary, required air conditioning capacities of the air conditioners are frequently changed. 
     A system air conditioner, in which a plurality of indoor units are connected to a single outdoor unit, is a built-in air conditioner which is planned and designed in accordance with factors such as the air conditioning capacities and locations of the indoor units during a planning or designing stage of a building. In the system air conditioner, refrigerant pipes connected to a single outdoor unit are connected in series to one another to form a single pipeline with a variety of types of indoor units having various capacities and structures, such as, for example, duct type, cassette type and/or wall mounted type indoor units. Therefore, the required air conditioning capacities of the indoor units in the system air conditioner may be different from one another. Furthermore, the indoor units of the system air conditioner are mostly operated independently such that a total required air conditioning capacity of the air conditioner calculated by summing up the individually required air conditioning capacities of the indoor units is variable. 
     As an example of variable-capacity compressors used in a variable-capacity system air conditioner, a variable-rotation number compressor has been proposed and used. The variable-rotation number compressor is designed such that its compressing capacity is controlled in accordance with a required air conditioning capacity. Thus, the variable-rotation number compressor is controlled by controlling a rotation number of a motor thereof by changing a frequency of a current applied to the motor through inverter control. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an aspect of the present invention to provide an air conditioner and control method thereof, which is capable of rapidly shutting off refrigerant supply when refrigerant is leaked out of a refrigerant pipe connected to indoor units, and restoring leaked refrigerant into an outdoor unit. 
     The foregoing and other aspects of the present invention are achieved by providing an air conditioner having an outdoor unit, at least one indoor unit and a compressor. The outdoor unit is connected to the indoor unit by a refrigerant pipe to form a closed circuit. The refrigerant pipe is divided into high and low pressure pipes. The air conditioner includes a refrigerant leakage detecting unit provided on the indoor unit to detect refrigerant leakage, a high pressure pipe shutoff valve provided on a high pressure pipe of the refrigerant pipe to shut off a flow of refrigerant between the outdoor unit and the indoor unit when the refrigerant leakage is detected, and a low pressure pipe shutoff valve provided on a low pressure pipe of the refrigerant pipe to shut off a flow of refrigerant between the outdoor unit and the indoor unit when the refrigerant leakage is detected. Refrigerant within the indoor unit is restored into the outdoor unit by dosing the high pressure pipe shutoff valve and opening the low pressure pipe shutoff valve when the refrigerant leakage is detected. 
     The foregoing and other aspects of the present invention are achieved by providing a method of controlling an air conditioner having an outdoor unit, at least one indoor unit, a compressor, an electric expansion valve, a high pressure pipe shutoff valve and a low pressure cutoff valve. The outdoor unit is connected to the indoor unit by a refrigerant pipe to form a dosed circuit. The refrigerant pipe is divided into high and low pressure pipes. The electric expansion valve is provided on the refrigerant pipe to vary pressure of refrigerant flowing into the indoor unit. The high pressure pipe shutoff valve is provided on a high pressure pipe of the refrigerant pipe, and the low pressure pipe shutoff valve is provided on a low pressure pipe of the refrigerant pipe. The method includes restoring leaked refrigerant by keeping the high pressure pipe shutoff valve dosed and the low pressure pipe shutoff valve opened for a preset period of time when refrigerant leakage is detected, and closing the low pressure pipe shutoff valve and stopping the compressor when the preset period of time elapses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects and advantages of the invention will become apparent and more appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a view showing an air conditioner employing a pulse width modulation type compressor, according to an embodiment of the present invention; 
     FIG. 2 is a block diagram showing a control system of the air conditioner of FIG. 1; 
     FIG. 3 is a flowchart showing a refrigerant leakage preventing method in a cooling mode of the air conditioner, 
     FIG. 4 is a flowchart showing a refrigerant leakage preventing method in a heating mode of the air conditioner; and 
     FIG. 5 is a flowchart showing a refrigerant leakage preventing method when the refrigerant leakage occurs while a compressor of the air conditioner is stopped. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be 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 like elements throughout. 
     As an example of the variable-capacity compressors, a pulse width modulation type compressor has been proposed and used. The air conditioner having the pulse width modulation type compressor is disclosed in Korean Patent Application No. 2000-0086775. A constant-speed compressor is adopted as the pulse width modulation type compressor. The constant-speed compressor is provided with a pulse width modulation valve to vary an amount of discharged refrigerant with an accumulated amount of discharged refrigerant varied by controlling an ON/OFF ratio of the pulse width modulation valve. For example, when the pulse width modulation valve is turned on (i.e., opened), the compressor is switched to an idle state so refrigerant is not discharged. In contrast, when the pulse width modulation valve is turned off (i.e., dosed), the amount of discharged refrigerant reaches 100% of a total amount. Thus, as described above, the accumulated amount of discharged refrigerant is varied by controlling the ON/OFF ratio of the pulse width modulation valve. 
     One characteristic of the pulse width modulation type compressor is that a variable range of a capacity of the compressor, which is determined according to loads of indoor air conditioning units, vary as widely as 10 to 100% of its rated capacity. An inverter type compressor has an available minimal capacity of about 30% of its rated capacity because of difficulty in restoring oil during its low capacity operation, whereas the pulse width modulation compressor may restore oil even during its low capacity operation because 100% of refrigerant is instantly discharged when the pulse width modulation valve is turned off. Thus, the pulse width modulation type compressor allows a low capacity operation at 10% of its rated capacity. 
     Accordingly, the system air conditioner employing the pulse width modulation type compressor may accomplish air conditioning for indoor spaces having different volumes ranging from small to large because of its ability to manage various types of indoor units and its wide capacity range of 10 to 100% of the compressor&#39;s rated capacity 
     In addition, differently from a generally small-sized air conditioner in which a ratio of a capacity of a compressor to a load of the compressor is about 1:1 and a corresponding small amount of refrigerant is supplied, the system air conditioner may manage a large capacity compressor and require a large amount of refrigerant. 
     Since the small-sized air conditioner may have a relative small amount of refrigerant for a volume of an indoor space, leaked refrigerant may be spread over a relatively wide space. Consequently, since an amount of supplied refrigerant in a building equipped with the system air conditioner is large, a large amount of refrigerant can accumulate in an indoor space. 
     FIG. 1 is a view showing an air conditioner employing a pulse width modulation type compressor, according to an embodiment of the present invention. As shown in FIG. 1, an air conditioner  100  includes a compressor  104 , an outdoor heat exchanger  106 , electric expansion valves  108  and indoor exchangers  110 , which are connected by refrigerant pipes to form a dosed circuit. Of the refrigerant pipes, a high pressure refrigerant pipe  112  connects an outlet side of the compressor  104  of the outdoor unit  116  and inlet sides of the electric expansion valves  108 . The high pressure pipe  112  guides a flow of high pressure refrigerant discharged from the compressor  104 . A low pressure refrigerant pipe  114  connects outlet sides of the electric expansion valves  108  and an inlet side of the compressor  104  of the outdoor unit  116 . The low pressure pipe  114  guides a flow of low pressure refrigerant expanded by the electric expansion valves  108 . The outdoor heat exchanger  106  is installed within the outdoor unit  116  on the high pressure pipe  112 . The indoor heat exchangers  110  are installed within indoor units of an indoor unit arrangement  118  on the low pressure pipe  114 . When the compressor  104  is operated in a cooling mode, refrigerant flows in directions indicated by the solid arrows shown in FIG.  1 . The high pressure pipe  112  is connected to a service port  158  through which refrigerant is supplemented with additional refrigerant. 
     As the air conditioner  100  of the present invention includes the outdoor unit  116  and the indoor unit arrangement  118 , the outdoor unit  116  includes the compressor  104  and the outdoor heat exchanger  106  as described above. The outdoor unit  116  also includes an accumulator  120  installed on the low pressure pipe  114  positioned upstream of the compressor  104 , and a receiver  122  installed on the high pressure pipe  112  positioned downstream of the outdoor heat exchanger  106 . The accumulator  120  collects and evaporates liquid refrigerant that has not been evaporated in the indoor heat exchangers  110  to allow the evaporated refrigerant to flow into the compressor  104 . In other words, if the liquid refrigerant is not completely evaporated in the indoor heat exchangers  110 , the refrigerant flowing into the accumulator  120  is a mixture of liquid and gas. The accumulator  120  evaporates only the liquid refrigerant such that only a gaseous refrigerant is compressed. For this reason, an inlet and outlet of the refrigerant pipe within the accumulator  120  are preferably positioned in an upper portion of the accumulator  120 . 
     If the refrigerant is not completely condensed in the outdoor heat exchanger  106 , the refrigerant flowing into the receiver  122  is a mixture of liquid and gas. The receiver  122  is configured to allow an inlet and outlet of the refrigerant pipe therein to be extended up to a lower portion of the receiver  122  so as to separate liquid refrigerant and gaseous refrigerant such that only liquid refrigerant flows out of it. 
     A vent bypass pipe  124  is provided to connect the receiver  122  and the low pressure pipe  114  positioned upstream of the accumulator  120  so that the gaseous refrigerant within the receiver  122  is bypassed. An inlet of the vent bypass pipe  124  is provided in an upper portion of the receiver  122  to allow only the gaseous refrigerant to flow into the vent bypass pipe  124 , while a vent valve  126  is provided in the vent bypass pipe  124  so as to control a flow rate of bypassed gaseous refrigerant. An arrow positioned along the vent bypass pipe  124  and indicated by a dotted line in FIG. 1 represents a direction of a flow of the bypassed gaseous refrigerant. 
     The high pressure pipe  112  extended from the receiver  122  is configured to pass through the accumulator  120  so as to evaporate the liquid refrigerant of relatively low temperature within the accumulator  120  using refrigerant of relatively high temperature passing through the high pressure pipe  112 . For the purpose of accomplishing effective evaporation in the accumulator  120 , a low pressure refrigerant pipe  121  within the accumulator  120  is formed to have a U shape, and a high pressure refrigerant pipe  123  having a U shape passes through the accumulator  120 . 
     The outdoor unit  116  further includes a hot gas bypass pipe  128  connecting the accumulator  120  to the high pressure pipe  112  between the compressor  104  and the outdoor heat exchanger  106 , and a liquid bypass pipe  130  located downstream of the receiver  122  to a pipe located downstream of the accumulator  120 . A hot gas valve  132  to control a flow rate of bypassed hot gas is provided in the hot gas bypass pipe  128 , while a liquid valve  134  to control a flow rate of bypassed liquid refrigerant is provided on the liquid bypass pipe  130 . Accordingly, when the hot gas valve  132  is opened, a portion of hot gas coming out of the compressor  104  flows in a direction indicated by a dotted arrow along the hot gas bypass pipe  128 , while when the liquid valve  134  is opened, a portion of the liquid refrigerant coming out of the receiver  122  flows in a direction indicated by a dotted arrow parallel to the liquid bypass pipe  130 . 
     A high pressure pipe shutoff valve  154  is provided on the high pressure refrigerant pipe  123  to connect the accumulator  120  and the indoor unit arrangement  118 . In case of refrigerant leakage, the high pressure pipe shutoff valve  154  is closed (turned off) such that the refrigerant discharged from the compressor  104  does not flow into the indoor unit arrangement  118 . In addition, a low pressure pipe shutoff valve  156  is provided on the low pressure pipe  114  of the outdoor unit  116  such that a flow of refrigerant between the outdoor unit  116  and the indoor unit arrangement  118  is prevented. 
     The indoor unit arrangement  118  includes a plurality of indoor units  118 ′ that are connected in parallel to one another. Each of the indoor units  118 ′ includes one electric expansion valve  108 , one indoor heat exchanger  110  and a sensor unit  152 . Thus, the air conditioner  100  of the present invention has a configuration in which a plurality of indoor units  118 ′ is connected to a single outdoor unit  116 , and the indoor units  118 ′ may be similar or different in their shapes and capacities. 
     FIG. 2 is a block diagram showing a control system of the air conditioner of FIG.  1 . As shown in FIG. 2, the outdoor unit  116  includes the compressor  104 , a pulse width modulation valve  160 , and an outdoor control unit  202  connected to the compressor  104  and the pulse width modulation valve  160 . The outdoor control unit  202  is also connected to an outdoor communication circuit unit  204  to receive and transmit data therefrom and thereto. Each indoor unit  118 ′ of the indoor unit arrangement  118  includes an indoor control unit  208 , a temperature sensing unit  210  connected to an input part of the indoor control unit  208 , a temperature setting unit  212 , a contamination detecting unit  214  and the electric expansion valve  108 , which is connected to an output port of the indoor control unit  208 . The temperature sensing unit  210  connected to an input port of the indoor control unit  208 , is a temperature sensor to sense a temperature of a room in which the′ indoor unit  118 ′ is installed. A required air conditioning capacity is calculated on the basis of the temperature sensed by the temperature sensing unit  210 . Instead of the temperature sensing unit  210 , a pressure sensor to sense a pressure of refrigerant may be used. The temperature sensor and the pressure sensor of the temperature sensing unit  210  are load sensors to calculate the required air conditioning capacity ( i.e., loads ) of the indoor unit  118 ′. 
     An oxygen concentration detecting sensor or a Freon detecting sensor to detect contamination of indoor air may be used as the contamination detecting unit  214 . When the oxygen concentration detecting sensor is used as the contamination detecting unit  214 , it is installed near an air inlet hole of the indoor unit  118 ′ to ascertain a presence of refrigerant leakage by measuring the oxygen concentration of indoor air flowing into the indoor unit  118 ′ and detecting a degree of air contamination. If Freon gas is used as. refrigerant, the Freon detecting sensor is used to ascertain a presence of refrigerant leakage by detecting whether Freon gas is included in sucked air. 
     The indoor unit  118 ′ further includes an indoor communication circuit unit  206  connected to the indoor control unit  208 . The outdoor and indoor communication circuit units  204  and  206  are connected to each other in a wire or wireless data communication manner. The above-described construction is similar for a four-way cassette type indoor unit, a one-way cassette type indoor unit, a wall mounted type indoor unit, etc. 
     The indoor control unit  208  calculates the required air conditioning capacity of the indoor unit  118 ′ based on a difference between a room temperature sensed by the temperature sensing unit  210  and a temperature preset by the temperature setting unit  212 . In addition, since the indoor control unit  208  contains information on its air conditioning capacity, it calculates the required air conditioning capacity based on its air conditioning capacity and the difference between the room temperature and the preset temperature. 
     FIGS. 3 through 5 are flowcharts showing refrigerant leakage preventing methods according to embodiments of the present invention. The refrigerant leakage preventing methods are different depending on operation modes of the compressor  104 , which are divided into a cooling mode, a heating mode, and a mode in which the compressor  104  is stopped. 
     FIG. 3 is a flowchart showing a refrigerant leakage preventing method in the cooling mode of the air conditioner. As shown in FIG. 3, when the refrigerant leakage is detected at operation  304  while the compressor  104  is operating in a cooling mode at operation  302 , the high pressure pipe shutoff valve  154  is dosed such that the refrigerant discharged from the compressor  104  does not flow into the indoor unit arrangement  118  at operation  306 . Simultaneously, the low pressure pipe shutoff valve  156  is completely opened such that the refrigerant within the indoor unit arrangement  118  flows into the inlet side of the compressor  104  at operation  308 . In this state, when the electric expansion valves  108  are completely opened, refrigerant within the indoor unit arrangement  118  is restored into the outdoor unit  116  at operation  310 . After the refrigerant restoration is carried out for a preset period of refrigerant restoration time t, all the refrigerant within the indoor unit arrangement  118  may be restored into the outdoor unit  116  at operation  312 . The preset period of refrigerant restoration time t r , which is a period of time taken to restore all refrigerant supplied to the indoor unit arrangement  118 , depends on the amount of refrigerant supplied to the air conditioner  100  and lengths of the refrigerant pipes. If the refrigerant leakage is not detected in the refrigerant leakage detecting operation S 304 , the compressor operation in operation S 302  continues until the refrigerant leakage is detected at operation S 304 . When the preset period of refrigerant restoration time relapses at operation  312 , the low pressure pipe shutoff valve  156  is closed such that a portion of the refrigerant pipe between the inlet side of the compressor  104  and the indoor unit arrangement  118  is blocked at operation  314 . Thereafter, the compressor  104  is stopped at operation  316  and the refrigerant leakage is displayed on displays (not shown) provided in indoor units  118 ′ at operation  318 . 
     FIG. 4 is a flowchart showing a refrigerant leakage preventing method in the heating mode of the air conditioner. As shown in FIG. 4, when the refrigerant leakage is detected at operation  404  while the compressor  104  is operated in the heating mode at operation  402 , the electric expansion valves  108  in the indoor units  118 ′, in which the refrigerant leakage occurs, is dosed such that a portion of the refrigerant pipe connected to the indoor units  118 ′ is blocked at operation  406 . Subsequently, after the compressor  104  is switched to a cooling mode at operation  408  to start the cooling operation of the compressor  104 , the electric expansion valves  108  are opened at operation  410 . In this state, the high pressure pipe shutoff valve  154  is dosed such that refrigerant discharged from the compressor  104  does not flow into the indoor unit arrangement  118  at operation  412 . Simultaneously, the low pressure pipe shutoff valve  156  is completely opened such that the refrigerant within the indoor unit arrangement  118  flows into the inlet side of the compressor  104  so as to restore the refrigerant into the outdoor unit  116  at operation  414 . After the refrigerant restoration is carried out for a preset period of refrigerant restoration time t r , all the refrigerant within the indoor unit arrangement  118  may be restored into the outdoor unit  116  at operation  416 . If the refrigerant leakage is not detected in the refrigerant leakage detecting operation S 404 , the compressor operation in operation S 402  continues until the refrigerant leakage is detected at operation S 404 . When the preset period of refrigerant restoration time t r  elapses at operation  416 , the low pressure pipe shutoff valve  156  is dosed such that a portion of the refrigerant pipe between the inlet side of the compressor  104  and the indoor unit arrangement  118  is blocked at operation  418 . Thereafter, the compressor  104  is stopped at operation S 420 , and the refrigerant leakage is displayed on displays (not shown) provided in the indoor units  118 ′ at operation  422 . 
     FIG. 5 is a flowchart showing a refrigerant leakage preventing method when the refrigerant leakage occurs while the compressor of the air conditioner is stopped. As shown in FIG. 5, when the refrigerant leakage is detected at operation S 504  while the compressor  104  is stopped at operation  502 , the high pressure pipe shutoff valve  154  is closed such that the outlet side of the compressor  104  is separated from the indoor unit arrangement  118  at operation S 506 . Subsequently, after the compressor  104  is operated in the cooling mode at operation S 508 , the low pressure pipe shutoff valve  156  is completely opened such that the refrigerant within the indoor unit arrangement  118  flows into the inlet side of the compressor  104  so as to restore the refrigerant into the outdoor unit  116  at operation  510 . In this state, when the electric expansion valves  108  are completely opened, the refrigerant within the indoor unit arrangement  118  is restored into the outdoor unit  116  at operation  512 . After the refrigerant restoration is carried out for a preset period of refrigerant restoration time t r , all the refrigerant within the indoor unit arrangement  118  may be restored into the outdoor unit  116  at operation  514 . If the refrigerant leakage is not detected in the refrigerant leakage detecting operation S 504 , the compressor operation in operation S 502  continues until the refrigerant leakage is detected at operation  504 . When the preset period of refrigerant restoration time t r  elapses at operation  514 , the low pressure pipe shutoff valve  156  is. dosed such that a portion of the refrigerant pipe between the inlet side of the compressor  104  and the indoor unit arrangement  118  is blocked at operation  516 . Thereafter, the compressor  104  is stopped at operation  518  and the refrigerant leakage is displayed on displays (not shown) provided in the indoor units  118 ′ at operation  520 . 
     As described above, the present invention provides an air conditioner and method of controlling the same, which is capable of rapidly shutting off refrigerant supply when refrigerant is leaked out of a refrigerant pipe connected to one or more indoor units, and restoring the leaked refrigerant into an outdoor unit. Thus, a leakage amount of refrigerant into a small indoor space is prevented, and a loss of refrigerant is minimized. 
     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 these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.