Patent Publication Number: US-2007111655-A1

Title: Air conditioning system and controlling method thereof

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an air conditioning system and a method of controlling the air conditioning system, and more particularly, to an air conditioning system that automatically performs air cleaning and ventilation using a pollutant sensor, and a method of controlling the air conditioning system.  
      2. Description of the Related Art  
      When a living thing breathes in a closed space, carbon dioxide increases with time, and thus it becomes more difficult for the living thing to breathe in the closed space. Therefore, closed spaces, such as an office where a lot of people works together or the interior of a car, should be periodically ventilated. A ventilation system can be generally used for this purpose.  
      Such a ventilation system is generally installed on a floor or a ceiling to allow inflow of outdoor air and outflow of indoor air. The ventilation system is useful, particularly for places where natural ventilation is poor or many persons stay.  
      However, only an air cleaning unit or ventilation device is provided in the related art ventilation system. Therefore, for example, when the ventilation device operates in winter, heating efficiency is deteriorated since cold outdoor air is directly introduced into an indoor area.  
      Further, since the air cleaning unit does not have a ventilation function, an indoor area cannot be ventilated using the air cleaning unit. In addition, air cleaning and ventilation are not automatically performed based on the pollution level of indoor air.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to an air conditioning system and a method of controlling the air conditioning system that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
      An object of the present invention is to provide an air conditioning system that can perform ventilation and air cleaning simultaneously or individually for maintaining indoor air clean, and a method of controlling the air conditioning system.  
      Another object of the present invention is to provide an air conditioning system that can perform automatic mode for automatically providing ventilation and air cleaning functions simultaneously or individually and perform manual mode for providing ventilation and/or air cleaning functions in response to an instruction inputted by a user.  
      Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
      To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an air conditioning system including: a controller for selecting an operation mode or an air volume rate; an air cleaning unit including a signal receiving portion receiving an instruction inputted using the selection key, a control portion receiving the instruction from the signal receiving portion, and a driving portion actuating a fan motor or other components according to the instruction inputted to the control portion; and a ventilation unit including a control portion receiving a signal from the control portion of the air cleaning unit, and a driving portion actuating a fan motor or other components according to an instruction from the control portion of the ventilation unit.  
      In another aspect of the present invention, there is provided a method of controlling an air conditioning system, the method including: turning on the air conditioning system and operating the air conditioning system in ventilation/cleaning combined mode; determining an operation mode of the air conditioning system in response to a mode-switching instruction and operating the air conditioning system in the determined operation mode; and turning off the air conditioning system or switching the air conditioning system to another operation mode, in response to a stop instruction or another mode-switching instruction.  
      In a further another aspect of the present invention, there is provided a method of controlling an air conditioning system, the method including: selecting an operation mode of the air conditioning system according to a mode selecting instruction inputted by a user or a predetermined program; operating the air conditioning system in the selected operation mode for providing ventilation and/or air-cleaning; switching the air conditioning system to another operation mode according to a mode switching instruction inputted by a user; operating the air conditioning system in the switched operation mode; and terminating the operation of the air conditioning system when the user inputs a stop instruction or a scheduled operation time arrives.  
      In a still further another aspect of the present invention, there is provided a method of controlling an air conditioning system, the method including: setting the air conditioning system to an automatic mode; measuring a pollution level of indoor air using at least one pollutant sensor; determining an air volume rate of a fan of the air conditioning system based on the pollution level measured by the pollutant sensor; and driving the fan at a speed corresponding to the determined air volume rate.  
      It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
       FIG. 1  is a perspective view of an air cleaning unit included in an air conditioning system according to the present invention;  
       FIG. 2  is an exploded perspective view of the air cleaning unit depicted in  FIG. 1 ;  
       FIG. 3  is an exploded perspective view showing an air flow of the air cleaning unit in ventilation mode;  
       FIG. 4  is a perspective view showing an air flow of the air cleaning unit in cleaning mode;  
       FIG. 5  is a perspective view of an air conditioning system according to the present invention;  
       FIG. 6  is a sectional view showing a schematic air flow of the air conditioning system shown in  FIG. 5 ;  
       FIG. 7  is a plan view of a controller of an air conditioning system according to the present invention;  
       FIG. 8  is a block diagram of an air conditioning system according to the present invention;  
       FIG. 9  is a flowchart illustrating a method of controlling an air conditioning system according to the present invention;  
       FIG. 10  is a flowchart illustrating a process of determining the air volume rate of a fan when an automatic mode is selected for the air conditioning system according to the present invention;  
       FIG. 11  is a flowchart illustrating a process of determining a pollution level using a VOC sensor when the air conditioning system operates in automatic mode according to the present invention;  
       FIG. 12  is a flowchart illustrating a process of determining a pollution level using a gas sensor when the air conditioning system operates in automatic mode according to the present invention;  
       FIG. 13  is a flowchart illustrating a process of determining a pollution level using a CO2 sensor when the air conditioning system operates in automatic mode according to the present invention; and  
       FIG. 14  is a flowchart illustrating a process of determining the air volume output of a fan when the air conditioning system operates in automatic mode according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
       FIG. 1  is a perspective view of an air cleaning unit  10  included in an air conditioning system according to the present invention, and  FIG. 2  is an exploded perspective view of the air cleaning unit  10 .  
      Referring to  FIGS. 1 and 2 , the air cleaning unit  10  includes: a front cover  11  having an air suction hole in a center portion; a cover guide  12  on which the front cover  11  is mounted; a grill  14  having cleaned air discharge holes on lateral sides and on which the cover guide  12  is slidably mounted; a filter  13  disposed in a lower portion of the grill  14  to remove impurities and odors from air; a control box  19  coupled to a lower edge of the grill  14 ; a control panel  21  detachably coupled to a lower portion of the cover guide  12 ; and a shield member  23  selectively shields screening the cleaned air discharge holes formed on the lateral sides of the grill  14 . In detail, a main printed circuit board (PCB) substrate is disposed in the control box  19  for controlling the operation of the air cleaning unit  10 , and a display PCB substrate is mounted on one side of a rear surface of the control panel  21  for display the operational state of the air cleaning unit  10 . When the air cleaning unit  10  is installed between a wall and a ceiling, the cleaned air discharge holes of the grill  14  facing the wall is screened by the shield member  23 . In this case, air is discharged through the discharge holes located on a front and an opposite side of the grill  14 .  
      The air cleaning unit  10  further includes a fan  15  disposed above the filter  13  for drawing indoor or outdoor air into the air cleaning unit  10 , a shroud  145  detachably coupled to a lower portion of the grill  14  for guiding the air drawn by the fan  15 , a fan motor  20  driving the fan  15 , and a rear panel  16  having one side connected to an exhaust duct and a supply duct. The fan motor  20  is mounted on the rear panel  16 .  
      The air cleaning unit  10  further includes a base panel  22  mounted on a top surface of the rear panel  16  for strengthen the rear panel  16 , an installation case  17  coupled to one side of the rear panel  16  for allowing the rear panel  16  to be easily connected to the exhaust duct and the supply duct, and installation bars  18  detachably coupled to a top portion of the rear panel  16  for allowing the rear panel  16  to be easily mounted on a wall or a ceiling. In detail, the installation case  17  includes a suction hole allowing inflow of indoor air and an exhaust hole  172  for expelling indoor air to an outdoor area. The rear panel  16  includes a suction hole  163  and an exhaust hole that are formed in correspondence with the suction hole  173  and the exhaust hole  172  of the installation case  17 . Therefore, indoor air and outdoor air can flow into and out of the air cleaning unit  10  through the suction holes  163  and  173  and the exhaust holes  162  and  172 .  
      Hereinafter, an air flow throughout the air cleaning unit  10  installed in an indoor area will be described with reference to the accompanying drawings according to ventilation mode and cleaning mode of the air cleaning unit  10 .  
       FIG. 3  is an exploded perspective view showing an air flow throughout the air cleaning unit  10  in ventilation mode.  
      Referring to  FIG. 3 , the air cleaning unit  10  is mounted on a ceiling, and the suction and exhaust holes  173  and  172  of the installation case  17  are connected to a duct member  30  running through a wall. Here, the air cleaning unit  10  can be F connected to a duct member running through a ceiling by using differently-shaped installation case. Description of the differently-shaped installation case will be omitted.  
      In detail, the duct member  30  includes a supply duct  31  allowing indoor air to flow into the air cleaning unit  10  and an exhaust duct  32  allowing indoor air to flow to an outdoor area.  
      In more detail, in ventilation mode, outdoor air is introduced from the supply duct  31  into the air cleaning unit  10  through the suction hole  173  of the installation case  17  and the suction hole  163  of the rear panel  16 . Next, the outdoor air is cleaned while passing through the filter  13  disposed inside the grill  14  in a bottom-to-top direction of the filter  13 . The cleaned outdoor air further flows between the grill  14  and the rear panel  16 . Then, the cleaned outdoor air is horizontally discharged by the fan  15  to an indoor area through a discharge grill  141  formed on side portions of the grill  14 .  
      Meanwhile, in the ventilation mode, indoor air is sucked into the air cleaning unit  10  through an exhaust grill  148  formed on a corner portion of the grill  14 . The exhaust grill  148  is formed at a position corresponding to the exhaust hole  162  of the rear panel  16  and bent along an edge of the exhaust hole  162 . The indoor air sucked into the air cleaning unit  10  through the exhaust grill  148  is expelled to an outdoor area through the exhaust holes  162  and  172  and the exhaust duct  32 .  
       FIG. 4  is a perspective view showing an air flow throughout the air cleaning unit  10  in cleaning mode.  
      Referring to  FIG. 4 , in cleaning mode of the air cleaning unit  10 , outdoor air and indoor air do not flow through the supply duct  31  and the exhaust duct  32  since a heat recovery ventilator (described later) connected to the duct member  30  is not operated in the cleaning mode. The heat recovery ventilator will be described later in detail.  
      Specifically, in the cleaning mode, indoor air is sucked into the air cleaning unit  10  through the indoor air suction hole  111  formed in the front cover  11 . The sucked indoor air is cleaned while passing through the filter  13 . Then, the indoor air is discharged back to an indoor area through the discharge grill  141  of the grill  14 .  
      More specifically, when the cleaning mode is selected, indoor air is taken by the fan  15  into the air cleaning unit  10  through the indoor air suction hole  111 . The sucked indoor air is cleaned while passing through the filter  13  and flows to the fan  15  through the orifice  143 . Then, the cleaned indoor air is pushed by the fan  5  in a horizontal direction and guided by an air guide  144  (refer to  FIG. 2 ) to the discharge grill  141  where the indoor air is discharged back to the indoor area.  
       FIG. 5  is a perspective view of an air conditioning system according to the present invention, and  FIG. 6  is a sectional view showing a schematic air flow of the air conditioning system shown in  FIG. 5 .  
      Referring to  FIGS. 5 and 6 , the air conditioning system of the present invention includes an air cleaning unit  10 , a ventilation unit such as a heat recovery ventilator  40  connected to the air cleaning unit  10  through a duct member  30 , and a controller  90  connected to the air cleaning unit  10  via radio waves or a cable.  
      In detail, the duct member  30  includes a supply duct  31  and an exhaust duct  32 . On end of the duct member  30  is connected to a suction hole  173  and an exhaust hole  172 , and the other end of the duct member  30  is connected to the heat recovery ventilator  40 . A supply duct connecting tube  33  and an exhaust duct connecting tube  34  are disposed between the connecting member  30  and the heat recovery ventilator  40 , such that the heat recovery ventilator  40  can be securely connected to the duct member  30 .  
      In the heat recovery ventilator  40 , outdoor air to the air cleaning unit  10  exchanges heat with indoor air from the air cleaning unit  10 . Therefore, the temperature of an indoor area is not rapidly fluctuated by the outdoor air supplied from an outdoor area to the indoor area. For example, when the indoor temperature is higher than the outdoor temperature, heat is transferred from the indoor air discharged from the air cleaning unit  10  to the outdoor air to decrease temperature difference between the indoor area and the outdoor air supplied to the indoor area, thereby preventing temperature fluctuation in the indoor area.  
      Specifically, the heat recovery ventilator  40  includes an exhaust inlet  42  formed on one side, a supply outlet  43  formed at a predetermined distance from the exhaust inlet  42 , an exhaust outlet  44  formed on the opposite side to the exhaust inlet  42 , a supply inlet  45  formed on the opposite side to the supply outlet  43 , and an heat exchanger  41 .  
      More specifically, in the heat exchanger  41 , heat exchanging occurs between inflow of outdoor air and outflow of indoor air but mixing does not occur between the outdoor air and the indoor air.  
      The heat recovery ventilator  40  further includes an exhaust fan  47  installed in a tube between the exhaust inlet  42  and the exhaust outlet  44 , and a supply fan  46  installed between a tube between the supply inlet  45  and the supply outlet  43 .  
      In detail, the exhaust inlet  42  and the supply outlet  43  are formed on the same side of the heat recovery ventilator  40 , and the exhaust outlet  44  and the supply inlet  45  are formed on the same side of the ventilator  40 . However, the positions of the exhaust inlet  42  and the supply outlet  43  or the exhaust outlet  44  and the supply inlet  45  can be changed according to the type of the heat recovery ventilator  40 .  
      In more detail, the exhaust inlet  42  is connected to the exhaust duct connecting tube  34  to allow inflow of indoor air from the air cleaning unit  10 , and the supply outlet  43  is connected to the supply duct connecting tube  33  to supply outdoor air to the air cleaning unit  10 .  
      A user or an operator can use a button of the controller  90  to operate the air cleaning unit  10  and the heat recovery ventilator  40  individually or in conjunction with each other. In other words, when a user selects ventilation mode, the air cleaning unit  10  operates together with the heat recovery ventilator  40 , such that an indoor area can be ventilated. When the user selects cleaning mode, only the air cleaning unit  10  operates. In this case, outdoor air is not introduced into the indoor area but indoor air is cleaned by the air cleaning unit  10  and discharged back to the indoor area from the air cleaning unit  10 .  
      A CO 2  sensor or a volatile organic compounds (VOC) sensor is installed in the air cleaning unit  10 . In detail, as a way of evaluating air pollution, the CO 2  sensor is used to measure the CO 2  level of an indoor air. The VOC sensor measures the VOC level of the indoor air for determining how much harmful substances are contained in the indoor air. Here, the term VOC (volatile organic compounds) is used to denote all kinds of organic compounds that are contained in air in gas phase. The VOC can be in solid or liquid state under room temperature/pressure. High VOC level causes painful symptoms or diseases such as respiratory diseases, allergic diseases, and headaches. In addition, a gas sensor can be installed in the air cleaning unit  10  or on a wall for sensing other harmful gases except the VOC. The gas sensor can be connected to a control portion of the air cleaning unit  10  via radio waves. The pollution level of the indoor air can be measured using sensor signals from the sensors, and the air cleaning unit  10  can be automatically operated in ventilation mode and/or cleaning mode based on the measured pollution level.  
      An air flow of the air conditioning system will now be described.  
      When ventilation mode is selected by a user or automatically in response to a sensor signal, the fan  15  of the air cleaning unit  10 , and the supply and exhaust fans  46  and  47  of the heat recovery ventilator  40  are driven. Outdoor air is sucked into the heat recovery ventilator  40  by the operation of the supply fan  46 , and indoor air is sucked into the heat recovery ventilator  40  by the operation of the exhaust fan  47 . The sucked outdoor air and indoor air exchange heat with each other while passing through the heat exchanger  41  installed in the heat recovery ventilator  40 . Then, the outdoor air is introduced into the air cleaning unit  10  through the supply duct  31  and cleaned by the filter  13  installed in the air cleaning unit  10 . After that, the outdoor air is discharged to an indoor area through the discharge grill  141  of the grill  14 .  
       FIG. 7  is a plan view of the controller  90  of the air conditioning system according to the present invention.  
      Referring to  FIG. 7 , the controller  90  is connected to the air cleaning unit  10  via a cable or radio waves.  
      In detail, the air cleaning unit  10  includes a remote signal receiver on a front side for receiving manipulation/instruction signals from the controller  90 . The remote signal receiver sends the received signals to a control portion of the air cleaning unit  10 . The control portion can control components of the air cleaning unit  10  such as the fan  15  according to instructions contained in the signals.  
      In more detail, the controller  90  includes a display window  96  for showing operational states of the air conditioning system, a power key  91  for receiving start and stop instructions from a user, a scheduler key  92  for scheduling the operation of the air conditioning system, a mode selection key  93  for selecting ventilation mode or cleaning mode, a air volume control key  94  for controlling air volume outputs of the fans installed in the air cleaning unit  10  and the heat recovery ventilator  40 , and a fast/power-saving selection key  95  for selecting a fast operation or a power-saving operation.  
      The fast operation function selectable using the fast/power-saving selection key  95  is provided for two purposes. For a first purpose, the supply fan  46  is driven at a higher speed than the exhaust fan  47  to introduce a larger amount of air from an outdoor area into an indoor area than the amount of air discharged from the indoor area to the outdoor area, such that the chance of polluted outdoor air flowing directly into the indoor area through other passages such as a window can be reduced. For a second purpose, the exhaust fan  47  is driven at a higher speed than the supply fan  46  to discharge a large amount of air to the outdoor area than the amount of air introduced from the outdoor area into the indoor area, such that polluted indoor air can be rapidly discharged to the outdoor area.  
      A user can operate the air conditioning system using the power key  91  and select cleaning mode, ventilation mode, or a combination mode of the cleaning mode and the ventilation mode using the mode selection key  93 . Further, the user can control the speeds of the fans installed in the air conditioning system.  
      In detail, a user can select a desired operating mode between cleaning mode, ventilation mode, and automatic mode by pressing the mode selection key  93  one or more times. In other words, when the power key  91  is first pressed, the air conditioning system starts operation in cleaning mode (default mode). The cleaning mode can be changed into the automatic mode by pressing the mode selection key  93  two times. Although the cleaning mode, ventilation mode, and the automatic mode are selected in this order, they can be selected in different orders.  
      The air volume outputs of the fans can be selected between strong, very strong, and slow using the air volume control key  94 . The order of the selectable air volume output options can be changed.  
       FIG. 8  is a block diagram of the air conditioning system according to the present invention.  
      Referring to  FIG. 8 , the air conditioning system of the present invention is configured with the air cleaning unit  10 , the controller  90 , and the heat recovery ventilator  40  as described above.  
      In detail, the air cleaning unit  10  includes a signal receiving portion  101  receiving instruction signals from the controller  90 , a control portion  102  receiving instructions from the signal receiving portion  101 , and a driving portion  103  controlled by the control portion  102 . The driving portion  103  drives the fan motor  20  in response to a control signal. A CO 2  sensor  104 , a VOC sensor, and a gas sensor  106  are connected to the control portion  102 , such that signals regarding pollution level detected by the sensors  104 ,  105 , and  106  can be transmitted to the control portion  102 . The control portion  102  automatically controls the air volume outputs of fans using the sensor signals.  
      The heat recovery ventilator  40  includes a control portion  401  receiving control signals from the control portion  102  of the air cleaning unit  10 , and a driving portion  402  controlled by the control portion  401 . The driving portion  402  drives a fan motor  403  in response to a control signal. The fan motor  403  includes fan motors installed in the heat recovery ventilator  40  to drive the supply fan  46  and the exhaust fan  47 .  
      In this configuration, when a user inputs an operating instruction through the controller  90 , an instruction signal is transmitted to the signal receiving portion  101  of the air cleaning unit  10 . The instruction signal is transmitted from the signal receiving portion  101  to the control portion  102 . The control portion  102  controls the driving portion  103  according to the instruction signal. The driving portion  103  drives the fan motor  20  or other devices according to the control of the control portion  102 . The control portion  102  of the air cleaning unit  10  can be connected to the control portion  401  of the heat recovery ventilator  40  via a cable or radio waves for signal communication. Further, the controller  90  can be connected to the control portion  102  of the air cleaning unit  10  via a cable or radio waves, as would be apparent to those of skill in the art.  
      Meanwhile, when a user inputs an instruction using the controller  90  for operating the air cleaning unit  10  in conjunction with the heat recovery ventilator  40 , the control portion  102  of the air cleaning unit  10  transmits an operating instruction to the control portion  401  of the heat recovery ventilator  40 . Then, the control portion  401  controls the driving portion  402  to drive the fan motor  403 .  
      Hereinafter, a method of controlling the air conditioning system will be described in detail with reference to the accompanying flowcharts, with regard to an individual operation of the air cleaning unit  10 , a combined operation of the air cleaning unit  10  and the heat recovery ventilator  40 , and an automatic operation using a pollution sensor signal.  
       FIG. 9  is a flowchart illustrating a method of controlling the air conditioning system according to the present invention.  
      Referring to  FIG. 9 , when a user presses the power key  91  of the controller  90 , the air cleaning unit  10  and the heat recovery ventilator  40  are powered on (S 110 ).  
      Here, when the power key  91  is pressed to operate the air conditioning system, ventilation/cleaning combined mode is performed as default mode (S 120 ). Therefore, when the air conditioning system is powered on by a user, the air cleaning unit  10  and the heat recovery ventilator  40  are operated in conjunction with each other (S 120 ). Alternatively, the air conditioning system can be set for a user to select desired mode when the user starts up the air conditioning system. In detail, a user can power on the air conditioning system and select combined mode, individual operation mode, or automatic mode using the mode selection key  93 .  
      The control portion  102  of the air cleaning unit  10  determines whether a mode-switching instruction is input using the mode selection key  93  of the controller  90  (S 130 ). If so, the control portion  102  determines whether an individual cleaning mode is selected by the mode-switching instruction (S 140 ). If the individual cleaning mode is selected, the air conditioning system switches to the individual cleaning mode (S 150 ). If the individual cleaning mode is not selected, the air conditioning system switches to automatic mode (S 141 ).  
      Meanwhile, if a mode-switching instruction is not input in operation S 130  or the air conditioning system switches from the ventilation/cleaning combined mode to the individual cleaning mode in operation S 150 , the control portion  102  determines whether an air volume rate is selected (S 160 ).  
      If so, a fan of the air conditioning system is driven at the selected air volume rate (S 170 ). If not, the fan is driven at a default air volume rate (S 161 ). Here, the default air volume rate is a rate set in the default ventilation/cleaning combined mode (S 120 ).  
      If the air conditioning system switched to the automatic mode in operation S 141 , the air volume rate of the fan is automatically set according to a pollution level detected by sensors installed inside or outside the air cleaning unit  10  (S 142 ).  
      While the fan is driven, the control portion  102  monitors whether the air conditioning system is powered off (S 180 ). In case where the operation time of the air conditioning system is preset, the control portion  102  automatically terminates the operation of the air conditioning system after the preset operation time.  
      If the air conditioning system is powered off, the operation of the air conditioning system is terminated. If not, the control portion  102  determines whether a mode-switching instruction is input (S 181 ).  
      If a mode-switching instruction is not input, the air conditioning system continues to operate at the selected air volume rate in the selected mode. On the contrary, if a mode-switching instruction is input, other modes except the selected mode are displayed on the display window  96  of the controller  90  (S 182 ). One of the displayed modes can be selected by pressing the mode selection key  93  one or more times (S 183 ). If one of the displayed modes is selected, the air conditioning system switches to the selected mode (S 184 ). Then, the control portion  102  goes back to operation S 180  to monitor whether the air conditioning system is powered off.  
      With the above-described method, a user can select the individual cleaning mode or the ventilation/cleaning combined mode according to the pollution level of indoor air. Further, the user can select the automatic mode in which sensor signals are utilized. Therefore, indoor air can be comfortably maintained.  
       FIG. 10  is a flowchart illustrating a process of determining the air volume rate of a fan when an automatic mode is selected for the air conditioning system according to the present invention.  
      Referring to  FIG. 10 , a user presses the power key  91  of the controller  90  to power on the air conditioning system (S 120 ). An automatic mode is selected by a user using a key or default settings (S 211 ). In the automatic mode, the fan and the pollutant sensor of the air cleaning unit  10  and the heat recovery ventilator  40  are operated (S 212 ). Here, it is preferable that ventilation and air cleaning be performed in conjunction with each other and the fan be driven at a predetermined RPM under default settings in the automatic mode. Alternatively, when the air conditioning system is powered on, the fan can be driven at a speed selected using a sensor signal.  
      Meanwhile, when the air conditioning system is powered on, the CO 2 , VOC, and gas sensors measure pollutant levels of indoor air (S 213 ). The measured pollutant levels are transmitted to the control portion  102  of the air cleaning unit  10 . The control portion  102  determines the pollution level of indoor air using the received pollutant levels (S 214 ). Then, the control portion  102  determines the air volume rate of the fan using the determined pollution level of the indoor air (S 215 ). In detail, the control portion  102  stores a data table containing air volume rates with respect to pollution levels for determining the air volume rates of the fan.  
      The speed of the fan is set based on the determined air volume rate, and the fan is driven at the set speed (S 216 ). The control portion determines whether a power-off instruction is input (S 217 ). The power-off instruction may be input automatically after scheduled operating time is over or manually by a user using the power key  91 . If a power-off instruction is input, the air conditioning system stops operation. If the power-off instruction is not input, operation S 213  is repeated again for measuring pollutant levels. Then, operations S 214 , S 215 , S 216 , and S 217  are repeated.  
       FIG. 11  is a flowchart illustrating a process of determining a pollution level using a VOC sensor when the air conditioning system operates in automatic mode according to the present invention.  
      Referring to  FIG. 11 , when the air conditioning system starts operation in automatic mode, the VOC sensor is powered on (S 220 ).  
      The VOC sensor measures the VOC level of indoor air for determining the pollution level of the indoor air (S 221 ).  
      The pollution level of the indoor air can be expressed using a ratio of a currently measured VOC level to a previously measured VOC level.  
      In detail, a current VOC level is determined as the average of measured VOC levels of the indoor air at intervals of 10 seconds for 2 minutes. Then, the current VOC level (average VOC level) is compared with a reference level to evaluate the pollution level of the indoor air and determine the air volume rate of the fan using the evaluated pollution level. Here, the VOC level of the indoor air is measured using the resistance of the VOC sensor that varies according to the VOC level.  
      For example, the resistance values of the VOC sensor are measured at intervals of 10 seconds for 2 minutes, and the average of the measured resistance values is calculated as an initial VOC sensor resistance R 0 . Then, in the same way, the resistance values of the VOC sensor are measured, and the average of the measured resistance values is calculated as a current VOC sensor resistance R s . After that, a pollution level of the indoor air is determined by comparing a ratio of R s /R 0  with a reference value. It is considered that the pollution level of the indoor air becomes lower as the ratio of R s /R 0  increases.  
      Referring to Table 1 below, it is determined whether the ratio of R s /R 0  is equal to or larger than 0.9 (S 222 ). If so, the pollution level of the indoor air is determined to be low (S 226 ). If not, it is determined whether the ratio of R s /R 0  is within a range equal to or larger than 0.8 but smaller than 0.9 (0.8≦R s /R 0 &lt;0.9) (S 223 ). If so, the pollution level of the indoor air is determined to be medium (S 227 ). If not, the pollution level of the indoor air is determined to be high (S 224 ). The determined pollution level grade is stored in the control portion  102  (S 225 ).  
                               TABLE 1                                   R s /R 0     Pollution level grade   Pollution level                          0.9 ≦ R s /R 0     Low   ≦38           0.8 ≦ R s /R 0  &lt; 0.9   Medium   ≦65           R s /R 0  &lt; 0.8   High      65&lt;                      
 
       FIG. 12  is a flowchart illustrating a process of determining a pollution level using a gas sensor when the air conditioning system operates in automatic mode according to the present invention.  
      Referring to  FIG. 12 , when the air conditioning system starts operation in automatic mode, the gas sensor is powered on (S 230 ).  
      The gas sensor measures the harmful gas level of indoor air (S 231 ). A ratio of R s /R 0  is calculated using the measured gas level in the same way as shown in  FIG. 11 , and the pollution level of the indoor air is determined using the calculated R s /R 0  ratio. Like the process of determining the pollution level of indoor air using the VOC sensor, it is considered that the pollution level of the indoor air becomes lower as the ratio of R s /R 0  increases.  
                               TABLE 2                                   R s /R 0     Pollution level grade   Pollution level                          0.88 ≦ R s /R 0     Low   ≦38           0.76 ≦ R s /R 0  &lt; 0.88   Medium   ≦65           R s /R 0  &lt; 0.76   High      65&lt;                      
 
      Referring to Table 2, it is determined whether the ratio of R s /R 0  is equal to or larger than 0.88 (S 232 ). If so, the pollution level of the indoor air is determined to be low (S 236 ). If not, it is determined whether the ratio of R s /R 0  is within a range equal to or larger than 0.76 but smaller than 0.88 (0.76≦R s /R 0 &lt;0.88) (S 233 ). If so, the pollution level of the indoor air is determined to be medium (S 237 ). If not, the pollution level of the indoor air is determined to be high (S 234 ). The determined pollution level grade is stored in the control portion  102  (S 235 ).  
       FIG. 13  is a flowchart illustrating a process of determining a pollution level using a CO 2  sensor when the air conditioning system operates in automatic mode according to the present invention.  
      Referring to  FIG. 13 , when the air conditioning system starts operation in automatic mode, the CO 2  sensor is powered on (S 240 ). The CO 2  sensor measures the CO 2  level of indoor air (S 241 ). The pollution level of the indoor air is determined using the CO 2  level measured by the CO 2  sensor.  
                           TABLE 3                                   CO 2  level (ppm)   Pollution level grade                          500 ≦ CO 2  &lt; 700   Low           700 ≦ CO 2  &lt; 900   Medium           900 ≦ CO 2     High                      
 
      Referring to Table 3, it is determined whether the measured CO 2  level is within a range equal to or larger than 500 ppm but lower than 700 ppm (S 242 ). If so, the pollution level of the indoor air is determined to be low (S 246 ). If not, it is determined whether the CO 2  level is within a range equal to or larger than 700 ppm but lower than 900 ppm (S 243 ). If so, the pollution level of the indoor air is determined to be medium (S 247 ). If not, the pollution level of the indoor air is determined to be high (S 244 ).  
      The pollution level grade of the indoor air determined in the above-described manner is stored in the control portion  102  (S 245 ).  
       FIG. 14  is a flowchart illustrating a process of determining the air volume rate of a fan when the air conditioning system operates in automatic mode according to the present invention.  
      Referring to  FIG. 14 , When the air conditioning system is operated in automatic mode, a cleaning operation or a cleaning/ventilation combined operation is performed by the air cleaning unit  10  or a combination of the air cleaning unit  10  and the heat recovery ventilator  40  according to the pollutant levels of indoor air measured by the CO 2  sensor, the gas sensor, and the VOC sensor.  
      Specifically, in the automatic mode, pollution level grades of indoor air are determined using pollutant levels measured by the CO 2  sensor, the gas sensor, and the VOC sensor (S 250 ). The pollution level grades of the indoor air, which are respectively determined using the pollutant levels measured by the three sensors, are compared with data, which are stored in the control portion  102  and containing air volume rates with respect to pollution level grades, in order to determine the air volume rate of a fan.  
                                   TABLE 4                                   CO 2     GAS   VOC   FAN                          High   High   High   Strong           High   High   Medium   Strong           High   High   Low   Strong           High   Medium   High   Strong           High   Medium   Medium   Strong           High   Medium   Low   Strong           High   Low   High   Strong           High   Low   Medium   Strong           High   Low   Low   Strong           Medium   High   High   Strong           Medium   High   Medium   Strong           Medium   High   Low   Strong           Medium   Medium   High   Strong           Medium   Medium   Medium   Medium           Medium   Medium   Low   Medium           Medium   Low   High   Strong           Medium   Low   Medium   Medium           Medium   Low   Low   Medium           Low   High   High   Strong           Low   High   Medium   Strong           Low   High   Low   Strong           Low   Medium   High   Strong           Low   Medium   Medium   Medium           Low   Medium   Low   Medium           Low   Low   High   Strong           Low   Low   Medium   Medium           Low   Low   Low   Low                      
 
      Referring to Table 3, pollution level grades obtained using the three sensors are used to determine the air volume rate of the fan.  
      In detail, the control portion  102  of the air cleaning unit  10 , which is connected to the three sensors, determines whether at least one of the pollution level grades is high (S 251 ). If so, the air volume rate of the fan is set to strong (S 255 ). If not, the control portion  102  determines whether at least one of the pollution level grades is medium (S 252 ). If so, the air volume rate of the fan is set to medium (S 256 ). If not, the air volume rate of the fan is set to low (S 253 ). The air volume rates of the fans of the air cleaning unit  10  and the heat recovery ventilator  40  are set to the determined rate (S 254 ). Thus, the fans are driven at the set air volume rate.  
      In the above-described method, when a user selects automatic mode of the air conditioning system, the pollution level of indoor air is measured in real time to determine an optimized air volume rates of the fans, so that indoor air can be maintained at an optimal state.  
      As described above, according to the present invention, ventilation and air cleaning can be provided at the same time or individually.  
      Further, a user can select operation mode of the air conditioning system using the controller, or the operation mode can be automatically selected depending on the air pollution level of indoor air for performing ventilation and air cleaning.  
      Furthermore, when air is supplied from an outdoor area to an indoor area, the amount of outdoor air can be properly controlled by the control portion depending on the temperature difference between indoor area and the indoor area, thereby decreasing heat loss.  
      In addition, the controller is connected to the air conditioning system via a cable or radio waves, so that the air conditioning system can be easily operated from a remote location.  
      According to the air conditioning system and the method of controlling the air conditioning system of the present invention, ventilation and air cleaning can be provided at the same time or individually. Further, the ventilation and air cleaning can be automatically performed according to the pollution level of the indoor air. Therefore, the present invention can be applied to various fields.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.