Patent Publication Number: US-2022214059-A1

Title: Air conditioning system

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS 
     This application is the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/JP2020/003887, filed on Feb. 3, 2020, which in turn claims the benefit of Japanese Application No. 2019-081043, filed on Apr. 22, 2019, the entire disclosures of which Applications are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an air conditioning system. 
     BACKGROUND ART 
     Conventionally, a technology for improving indoor air quality has been proposed. For example, Patent Literature (PTL) 1 discloses an air cleaner that allows a user to readily recognize that the air in a room has a PM2.5 concentration that affects health. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Unexamined Patent Application Publication No. 2017-227434 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     As a general technology for improving air quality, a technology for controlling a ventilating device based on, for example, a PM2.5 concentration in a room has been known. With such a technology, a gas concentration other than the PM2.5 concentration is not considered, and thus it is difficult to sufficiently improve air quality in the room. 
     The present invention provides an air conditioning system that can effectively improve air quality in an indoor space. 
     Solution to Problem 
     An air conditioning system according to an aspect of the present invention includes: a sensor that measures air quality in an indoor space; an obtainer that obtains information indicating the air quality in the indoor space, the information being output by the sensor; and a controller that calculates an air quality index based on the information obtained, and controls a ventilator that ventilates the indoor space, based on the air quality index calculated. The air quality index is expressed by f(X n )×g(T, H), where f(X n ) denotes a function with respect to X n  that indicates at least one of a CO 2  concentration, a concentration of total volatile organic compounds (TVOC), a concentration of particulate matter (PM), an NO X  concentration, an SO X  concentration, an O 3  concentration, a mold count, or a dust count, and g(T, H) denotes a function with respect to T denoting temperature and H denoting humidity in the indoor space. 
     Advantageous Effects of Invention 
     The air conditioning system according to the present invention can effectively improve air quality in an indoor space. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a functional configuration of an air conditioning system according to an embodiment. 
         FIG. 2  is a flowchart illustrating Operation Example 1 of the air conditioning system according to the embodiment. 
         FIG. 3  illustrates values obtained by substituting gas concentrations such as a CO 2  concentration, a particulate matter (PM) concentration, and a concentration of total volatile organic compounds (TVOC) into equations for obtaining natural logarithms. 
         FIG. 4  illustrates a relation between values of a discomfort index and general body sensations. 
         FIG. 5  is a flowchart illustrating Operation Example 2 of the air conditioning system according to the embodiment. 
         FIG. 6  is a flowchart illustrating Operation Example 3 of the air conditioning system according to the embodiment. 
         FIG. 7  is a flowchart illustrating Operation Example 4 of the air conditioning system according to the embodiment. 
         FIG. 8  is a flowchart illustrating Operation Example 5 of the air conditioning system according to the embodiment. 
         FIG. 9  is a flowchart illustrating Operation Example 6 of the air conditioning system according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments with reference to the drawings. Note that the embodiments described below each show a general or particular example. The numerical values, shapes, materials, elements, the arrangement and connection of the elements, steps, and the order of processing the steps, for instance, described in the following embodiments are examples, and thus are not intended to limit the present invention. Among the elements in the following embodiments, elements not recited in any of the independent claims are described as arbitrary elements. 
     Note that the diagrams are schematic diagrams, and do not necessarily provide strictly accurate illustration. In the drawings, the same numeral is given to a substantially same configuration, and a redundant description thereof may be omitted or simplified. 
     Embodiment 
     Configuration 
     First, a configuration of an air conditioning system according to an embodiment is to be described.  FIG. 1  is a block diagram illustrating a functional configuration of the air conditioning system according to the embodiment. Air conditioning system  10  controls devices using a general air quality index, in order to improve air quality in an indoor space (a closed space) (IAQ: indoor air quality) within a building such as a house, an office, or a hospital. As illustrated in  FIG. 1 , air conditioning system  10  includes sensor  20 , control device  30 , ventilator  40 , air conditioner  50 , air cleaner  60 , activity amount measurer  70 , and server device  80 , specifically. 
     Sensor  20  includes indoor sensor  21  and outdoor sensor  22 . Indoor sensor  21  measures air quality in an indoor space, and outputs information indicating the air quality in the indoor space as a measurement result. Indoor sensor  21  can communicate with control device  30 , and transmit information indicating air quality to control device  30 . Air quality is expressed by at least one of, for instance, a gas concentration, a mold count, a dust count, temperature, or humidity in an indoor space, and indoor sensor  21  can measure at least one of those, that is, a gas concentration, a mold count, a dust count, temperature, or humidity. Specifically, indoor sensor  21  is achieved by a semiconductor gas sensor, a temperature sensor, or a humidity sensor, for instance. 
     More specifically, the gas concentration includes at least one of a CO 2  concentration, a concentration of total volatile organic compounds (a TVOC concentration), a particulate matter (PM) concentration, a nitrogen oxide (NO X ) concentration, a sulfur oxide (SO X ) concentration, or an ozone (O 3 ) concentration. 
     Outdoor sensor  22  measures air quality in an outdoor space in the surrounding of the above indoor space, and outputs information indicating the air quality in the outdoor space as a measurement result. Outdoor sensor  22  can communicate with control device  30 , and transmit information indicating air quality to control device  30 . Outdoor sensor  22  has the same configuration as that of indoor sensor  21  except that the measurement target is an outdoor space, and is achieved by, for instance, a semiconductor gas sensor, a temperature sensor, or a humidity sensor, specifically. 
     Control device  30  obtains, from sensor  20 , information that indicates air quality in an indoor space or information that indicates air quality in an outdoor space, and calculates a general air quality index based on the obtained information. Control device  30  controls ventilator  40  and air conditioner  50 , based on the calculated general air quality index. Specifically, control device  30  includes first communicator  31 , controller  32 , storage  33 , and second communicator  34 . 
     First communicator  31  is a communication module (communication circuit) for control device  30  to communicate with sensor  20 , ventilator  40 , air conditioner  50 , air cleaner  60 , and activity amount measurer  70 , via a local communication network. Communication established by first communicator  31  may be wired communication or wireless communication. A communication standard used for the communication is not limited in particular. First communicator  31  includes obtainer  35 . 
     Controller  32  calculates a general air quality index, and controls ventilator  40  and air conditioner  50 , for instance, based on the calculated general air quality index. Specifically, controller  32  is achieved by a processor, a microcomputer, or a dedicated circuit. Controller  32  may be achieved by a combination of at least two of a processor, a microcomputer, and a dedicated circuit. 
     Storage  33  is a storage device that stores, for instance, computer programs executed by controller  32  to control devices based on the general air quality index. Specifically, storage  33  is achieved by a semiconductor memory, for instance. 
     Second communicator  34  is a communication module (communication circuit) for control device  30  to communicate with server device  80  via wide-area communication network  90  such as the Internet. Communication established by second communicator  34  may be wireless communication or wired communication. A communication standard used for the communication is not limited in particular. 
     Ventilator  40  ventilates an indoor space, based on a control signal received from control device  30 . Ventilator  40  includes air supply device  41  that supplies air from an outdoor space to an indoor space, and air discharge device  42  that discharges air from the indoor space to the outdoor space. Air supply device  41  and air discharge device  42  are both achieved by blowers (fans), for example. 
     Note that air supply device  41  may include air filter  41   a . Air filter  41   a  decreases the concentration of at least one of PM, NO X , SO X , and O 3  in the air to be supplied to the indoor space. Specifically, air supply device  41  takes in air from the outdoor space, filters the air using air filter  41   a , and discharges the filtered air into the indoor space. An example of air filter  41   a  is a high efficiency particulate air (HEPA) filter. 
     Air conditioner  50  adjusts the temperature and the humidity in the indoor space, based on a control signal received from control device  30 . 
     Air cleaner  60  is an example of a removal device, and has a function of decreasing the concentration of at least one of PM, NO X , SO X , and O 3  in the indoor space. Air cleaner  60  is, for example, fan-type cleaner  60 , includes air filter  60   a , takes in the air in the indoor space, filters the air using air filter  60   a , and discharges the filtered air into the indoor space. An example of air filter  60   a  is an HEPA filter. In the following embodiments, ventilator  40  and air conditioner  50  are main targets to be controlled by control device  30 , yet air cleaner  60  may be a target to be controlled by control device  30 . Thus, control device  30  controls air cleaner  60  (causes air cleaner  60  to operate) to bring the general air quality index close to a target range. 
     Activity amount measurer  70  is a wearable activity amount measuring device that a person staying in the indoor space (for example, a resident of a house) wears. Activity amount measurer  70  may be a non-contact type activity amount measuring device achieved by a radio sensor and disposed in the indoor space. Specifically, activity amount measurer  70  measures the activity amount of a person staying in the indoor space, based on, for instance, motion of the body of the person, and outputs information indicating the activity amount. Activity amount measurer  70  can communicate with control device  30 , and transmit information indicating the activity amount to control device  30 . The activity amount can be expressed in units of metabolic equivalents (METs). 
     Server device  80  is a cloud server that collects data related to device control using the general air quality index from a plurality of control devices that include control device  30 , and manages the data. Server device  80  includes communicator  81 , data processor  82 , and storage  83 . 
     Communicator  81  is a communication module (communication circuit) for server device  80  to communicate with control device  30  via wide-area communication network  90 . Communication established by communicator  81  may be wired communication or wireless communication. A communication standard used for the communication is not limited in particular. 
     Data processor  82  performs information processing for collecting and managing data related to device control using the general air quality index. Specifically, data processor  82  is achieved by a processor, a microcomputer, or a dedicated circuit. Data processor  82  may be achieved by a combination of at least two of a processor, a microcomputer, and a dedicated circuit. 
     Storage  83  is a storage device that stores, for instance, computer programs that data processor  82  executes to process the above data. Storage  83  is achieved by a semiconductor memory or a hard disk drive (HDD), specifically. 
     Operation Example 1 
     Next, Operation Example 1 of air conditioning system  10  is to be described with reference to  FIG. 2 .  FIG. 2  is a flowchart illustrating Operation Example 1 of air conditioning system  10 . In Operation Example 1, control device  30  calculates a general air quality index based on information indicating air quality, which is obtained from indoor sensor  21  of sensor  20 , and controls ventilator  40  based on the calculated general air quality index. 
     First, the general air quality index used in Operation Example 1 is to be described. The general air quality index used in Operation Example 1 is expressed by f(X n )×g(T, H), where f(X n ) denotes a function with respect to X n  that indicates a concentration of at least one of CO 2 , TVOC, PM, NO X , SO X , or O 3  or at least one of a mold count or a dust count, and g(T, H) denotes a function with respect to temperature T and humidity H in an indoor space. More specifically, f(X n ) is expressed by (Expression 1) below. Note that f(X n ) is expressed as f(X 1 ) when n=1, and as f(X 1 , . . . , X n ) when n≥2. 
     
       
         
           
             
               
                 
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     In (Expression 1), an is a coefficient. For example, when n=3, X 1  denotes a CO 2  concentration, X 2  denotes a PM concentration, and X 3  denotes a TVOC concentration, a 1 , a 2 , and a 3  denote coefficients (or in other words, weights) for adjusting the degrees of influence exerted by a CO 2  concentration, a PM concentration, and a TVOC concentration on the general air quality index. A specific value of a n  is appropriately determined based on experience or experiments. 
     Further, In denotes a natural logarithm.  FIG. 3  illustrates values obtained by substituting gas concentrations such as a CO 2  concentration, a PM concentration, and a TVOC concentration into equations for obtaining natural logarithms. 
     In  FIG. 3 , the hatched values of gas concentrations show reference concentrations (in other words, reference values), and if a gas concentration exceeds its reference concentration in an indoor space, the gas has a harmful effect on human bodies. For example, the reference concentration of the CO 2  concentration is 1000 ppm, the reference concentration of the PM concentration is 30 ppm, and the reference concentration of the TVOC concentration is 400 μg/m 3 . In this manner, a reference concentration greatly varies depending on a type of a gas, and thus if the value of a gas concentration is used as it is to calculate the general air quality index, the degree of influence on the general air quality index greatly varies depending on a type of a gas. However, as illustrated in  FIG. 3 , if the general air quality index is calculated using natural logarithms of gas concentrations, the degrees of influence of the gas concentrations on the general air quality index can be smoothed. In other words, a difference of the degrees of influence of the gas concentrations on the general air quality index can be decreased. 
     Note that it is not essential to use a natural logarithm of a gas concentration for f(X n ) and, for example, the influence of gas concentrations on the general air quality index can be smoothed also by normalizing gas concentration X n  based on reference concentration c n . (Expression 1′) stated below expresses f(X n ) in this case. 
     
       
         
           
             
               
                 
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     On the other hand, (Expression 2) stated below expresses g(T, H). 
     
       
         
           
             
               
                 
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     In (Expression 2), α and β are coefficients. α is a coefficient that prevents the denominator of (Expression 2) from being 0, and is a positive constant. β is a positive constant that acquires balance between the degrees of influence of f(X n ) and g(T, H) on the general air quality index. 
     ABS denotes a function for obtaining an absolute value of a numerical value. DI(T, H) denotes a function for obtaining a discomfort index, and is, for example, DI(T, H)=0.81T+0.01H×(0.99T−14.3)+46.3.  FIG. 4  illustrates a relation between values of the discomfort index and general body sensations, and 67.5 in (Expression 2) is based on a value of a discomfort index (the central value) for a person to feel comfortable. 
     As can be seen from (Expression 1) above, f(X n ) has a greater value as a gas concentration in an indoor space is lower. Thus, the better the air quality of the indoor space is, the greater positive value f(X n ) has. In addition, as can be seen from (Expression 2) above, g(T, H) has a greater positive value as a person feels more comfortable. Thus, the general air quality index in Operation Example 1 expressed by a product of f(X n ) and g(T, H) has a positive value, and indicates that the air quality is higher as the value is greater, and is lower as the value is closer to zero. 
     Next, details of Operation Example 1 in which such a general air quality index is used are to be continuously described with reference to  FIG. 2 . 
     First, controller  32  of control device  30  causes ventilator  40  to operate under a provisional condition (S 11 ). Specifically, controller  32  causes first communicator  31  to transmit, to ventilator  40 , a control signal for causing ventilator  40  to operate under the provisional condition. 
     Next, obtainer  35  obtains (receives) information indicating air quality in an indoor space, which is output by indoor sensor  21  of sensor  20  (S 12 ). 
     Next, controller  32  calculates a general air quality index, based on the obtained information (S 13 ). Subsequently, controller  32  determines whether the value of the calculated general air quality index is within a target range (a range of values considered to be optimal, an optimal range) (S 14 ). The target range of the general air quality index is appropriately determined based on experience or experiments. Note that the target range of the general air quality index differs depending on a combination of gas concentrations used to calculate the general air quality index. 
     If controller  32  determines that the value of the calculated general air quality index is out of the target range (No in S 14 ), controller  32  controls ventilator  40  to bring the general air quality index close to the target range (S 15 ). Specifically, controller  32  causes first communicator  31  to transmit a control signal to ventilator  40 . For example, if the value of f(X n ) is small, controller  32  estimates that the concentration of a pollutant (such as PM, TVOC, or CO 2 ), and actively ventilates the indoor space by increasing the operating ratio of ventilator  40 . In the following, until controller  32  determines that the value of the calculated general air quality index is within the target range, the processing from steps S 12  to S 15  is repeated. 
     For example, if a large amount of warm (or cold) air flows into the indoor space or the indoor space becomes dry due to air having low humidity as a result of actively ventilating the indoor space, the value of g(T, H) then decreases, resulting in a decrease in the value of the general air quality index. Accordingly, controller  32  brings the value of the general air quality index to the target range by controlling ventilator  40  while acquiring balance between such matters. 
     On the other hand, when controller  32  determines that the value of the calculated general air quality index is within the target range (Yes in S 14 ), controller  32  causes ventilator  40  to operate under an optimal condition (for example, a setting condition for maintaining the current state) (S 16 ). 
     As described above, in Operation Example 1, ventilator  40  is controlled using the general air quality index. The air quality is considered based on a concentration of a pollutant such as PM, TVOC, or NO X , temperature, and humidity, yet ventilator  40  is generally controlled based not on the influence of a combination of such factors but on the influence of a single factor such as the magnitude of the PM2.5 concentration, for example. 
     In view of this, air conditioning system  10  controls ventilator  40 , based on the general air quality index for which the degrees of influence exerted by the concentration of a pollutant, temperature, and humidity. According to the general air quality index, whether a person is actually feeling that the air quality is pleasant in the indoor space can be quantitatively determined, and thus air conditioning system  10  can effectively improve the air quality of the indoor space. 
     Further, in Operation Example 1, the result of controlling ventilator  40  is reflected (fed back) on the general air quality index. Thus, air conditioning system  10  can steadily improve the air quality in the indoor space. 
     Operation Example 2 
     Next, Operation Example 2 of air conditioning system  10  is to be described with reference to  FIG. 5 .  FIG. 5  is a flowchart illustrating Operation Example 2 of air conditioning system  10 . In Operation Example 2, control device  30  calculates a general air quality index based on information indicating air quality, which is obtained from indoor sensor  21  of sensor  20 , and information indicating air quality, which is obtained from outdoor sensor  22  of sensor  20 , and controls ventilator  40  and air conditioner  50  based on the calculated general air quality index. 
     First, the general air quality index used in Operation Example 2 is to be described. The general air quality index used in Operation Example 2 is expressed by f(X n )×g in (T in , H in )×g out (T out , H out ). Here, g in (T in , H in ) is a function with respect to temperature T in  and humidity H in  in an indoor space, and is substantially the same as g(T, H) in Operation Example 1. Further, g out (T out , H out ) is a function with respect to temperature T out  and humidity H out  in an outdoor space, and is substantially the same as a function resulting from replacing T with outdoor temperature and H with outdoor humidity in g(T, H) in Operation Example 1. 
     Next, details of Operation Example 2 in which such a general air quality index is used are to be continuously described with reference to  FIG. 5 . 
     First, controller  32  of control device  30  causes ventilator  40  to operate under a provisional condition (S 21 ). Specifically, controller  32  causes first communicator  31  to transmit, to ventilator  40 , a control signal for causing ventilator  40  to operate under the provisional condition. 
     Next, obtainer  35  obtains (receives) first information indicating air quality in an indoor space, which is output by indoor sensor  21  of sensor  20  (S 22 ), and obtains (receives) second information indicating air quality in an outdoor space, which is output by outdoor sensor  22  (S 23 ). 
     Next, controller  32  calculates a general air quality index, based on the obtained first information and the obtained second information (S 24 ). Subsequently, controller  32  determines whether the value of the calculated general air quality index is within a target range (S 25 ). The target range of the general air quality index is appropriately determined based on experience or experiments. Note that the target range of the general air quality index differs depending on a combination of gas concentrations used to calculate the general air quality index. 
     If controller  32  determines that the value of the calculated general air quality index is out of the target range (No in S 25 ), controller  32  determines whether air conditioner  50  needs to operate (S 26 ). Specifically, controller  32  determines whether an air quality index obtained when g in (T in , H in ) is assumed to be 1 (or in other words, f(X n )×g out (T out , H out )) can be caused to reach the target range by causing only ventilator  40  to operate. For example, the value of g out (T out , H out ) is low under circumstances where a person feels uncomfortable in the outside. If the value of g out (T out , H out ) is too small (for example, if the value of g out (T out , H out ) is smaller than a predetermined value), even if ventilator  40  is caused to operate to increase the value of f(X n ), the general air quality index may not reach the target range. In such a case, it is necessary to cause the general air quality index to reach the target range by causing not only ventilator  40 , but also air conditioner  50  to operate to increase the value of g in  (T in , H in ). 
     In view of this, controller  32  determines it is necessary to cause air conditioner  50  to operate if the air quality index obtained when g in (T in , H in ) is assumed to be 1 cannot be caused to reach the target range by causing only ventilator  40  to operate (Yes in S 26 ). In this case, controller  32  controls ventilator  40  and air conditioner  50  to bring the general air quality index close to the target range (S 27 ). Specifically, controller  32  causes first communicator  31  to transmit a control signal to each of ventilator  40  and air conditioner  50 . 
     Controller  32  determines it is unnecessary to cause air conditioner  50  to operate if the air quality index obtained when g in (T in , H in ) is assumed to be 1 can be caused to reach the target range by causing only ventilator  40  to operate (No in S 26 ). In this case, controller  32  selectively controls only ventilator  40  out of ventilator  40  and air conditioner  50 , to bring the general air quality index close to the target range (S 28 ). Specifically, controller  32  causes first communicator  31  to transmit a control signal to ventilator  40 . In the following, the processing from steps S 22  to S 28  is repeated until controller  32  determines that the value of the calculated general air quality index is within the target range. 
     On the other hand, when controller  32  determines in step S 25  that the value of the calculated general air quality index is within the target range (Yes in S 25 ), controller  32  causes ventilator  40  to operate under an optimal condition (S 29 ). 
     In this manner, air conditioner  50  is controlled when necessary in Operation Example 2. Accordingly, air conditioning system  10  can efficiently improve the air quality in the indoor space. 
     Operation Example 3 
     Next, Operation Example 3 of air conditioning system  10  is to be described with reference to  FIG. 6 .  FIG. 6  is a flowchart illustrating Operation Example 3 of air conditioning system  10 . In Operation Example 3, control device  30  calculates a general air quality index based on information indicating air quality, which is obtained from indoor sensor  21  of sensor  20 , and activity amount information obtained from activity amount measurer  70 , and controls ventilator  40  based on the calculated general air quality index. 
     First, the general air quality index used in Operation Example 3 is to be described. The general air quality index used in Operation Example 3 is expressed by f(X n )×g(T, H)×h(A). Here, h(A) is a function with respect to activity amount A. For example, function h(A) has a positive value irrespective of activity amount A, decreases with an increase in activity amount A, and increases with a decrease in activity amount A. Function h(A) preferably decreases in a shape of being convex upward with an increase in the activity amount, when the horizontal axis indicates the activity amount. This is because the amount of sweat and accumulated fatigue caused due to an increase in the activity amount are low at the beginning of the activity, but rapidly increase once the activity amount exceeds a certain amount. 
     Next, details of Operation Example 3 in which such a general air quality index is used are to be continuously described with reference to  FIG. 6 . 
     First, controller  32  of control device  30  causes ventilator  40  to operate under a provisional condition (S 31 ). Specifically, controller  32  causes first communicator  31  to transmit, to ventilator  40 , a control signal for causing ventilator  40  to operate under a provisional condition. 
     Next, obtainer  35  obtains (receives) information indicating air quality in an indoor space, which is output by indoor sensor  21  of sensor  20  (S 32 ). 
     Next, obtainer  35  obtains (receives) activity amount information indicating the activity amount of a person staying in the indoor space, which is output by activity amount measurer  70  (S 33 ). 
     Next, controller  32  calculates a general air quality index, based on the obtained information indicating the air quality and the obtained activity amount information (S 34 ). Subsequently, controller  32  determines whether the value of the calculated general air quality index is within a target range (S 35 ). The target range of the general air quality index is appropriately determined based on experience or experiments. Note that the target range of the general air quality index differs depending on a combination of gas concentrations used to calculate the general air quality index. 
     If controller  32  determines that the value of the calculated general air quality index is out of the target range (No in S 35 ), controller  32  controls ventilator  40  to bring the general air quality index close to the target range (S 36 ). Specifically, controller  32  causes first communicator  31  to transmit a control signal to ventilator  40 . In the following, until controller  32  determines that the value of the calculated general air quality index is within the target range, the processing from steps S 32  to S 36  is repeated. 
     On the other hand, when controller  32  determines that the value of the calculated general air quality index is within the target range (Yes in S 35 ), controller  32  causes ventilator  40  to operate under an optimal condition (for example, a setting condition for maintaining the current state) (S 37 ). 
     As described above, the general air quality index that reflects the activity amount of a person staying in the indoor space is used in Operation Example 3. Accordingly, air conditioning system  10  can improve air quality in the indoor space, taking into consideration the activity amount of a person staying in the indoor space. 
     Operation Example 4 
     Next, Operation Example 4 of air conditioning system  10  is to be described with reference to  FIG. 7 .  FIG. 7  is a flowchart illustrating Operation Example 4 of air conditioning system  10 . In Operation Example 4, server device  80  provides a target range that is to be compared with a general air quality index. Note that the following describes, as Operation Example 4, the case where server device  80  provides the target range in Operation Example 1, but the case where server device  80  provides the target range in Operation Example 2 or 3 can also be considered as Operation Example 4. 
     First, controller  32  of control device  30  causes ventilator  40  to operate under a provisional condition (S 41 ). Specifically, controller  32  causes first communicator  31  to transmit, to ventilator  40 , a control signal for causing ventilator  40  to operate under the provisional condition. 
     Next, obtainer  35  obtains (receives) information indicating air quality in an indoor space, which is output by indoor sensor  21  of sensor  20  (S 42 ). 
     Next, controller  32  calculates a general air quality index, based on the obtained information (S 43 ). Subsequently, controller  32  causes second communicator  34  to transmit, to server device  80 , data that includes, for instance, the information indicating the air quality in the indoor space measured by sensor  20  (that is, the information obtained in step S 42 ), an operating status of ventilator  40 , and the value of the general air quality index calculated in step S 43  (S 44 ). 
     Communicator  81  of server device  80  receives the data (S 45 ), and data processor  82  determines a target range based on the received data. Server device  80  has obtained in the past similar data items from a plurality of control devices that includes control device  30 , and has stored such data items into storage  83  as big data. Thus, for example, data processor  82  identifies a case highly similar to the data received in step S 45  from among big data, and determines the target range provided in the identified case as a target range to be provided to control device  30  this time (S 46 ). 
     Note that how the target range is determined based on received data (that is, an algorithm for determining a target range) is not limited in particular. For example, server device  80  may be a trained model achieved in advance by machine learning, and determine a target range using a training model that outputs a target range using the received data as input information. 
     Data processor  82  determines the target range, and thereafter notifies control device  30  of the determined target range (S 47 ). Specifically, data processor  82  causes communicator  81  to transmit information indicating the target range to control device  30 . 
     Second communicator  34  of control device  30  receives the information indicating the target range. Thus, control device  30  receives a notification of the target range (S 48 ). Controller  32  determines whether the value of the general air quality index calculated in step S 43  is within the target range notified in step S 48  (or in other words, determined in step S 46 ) (S 49 ). 
     If controller  32  determines that the value of the calculated general air quality index is out of the target range (No in S 49 ), controller  32  controls ventilator  40  to bring the general air quality index close to the target range (S 50 ). 
     On the other hand, when controller  32  determines that the value of the calculated general air quality index is within the target range (Yes in S 49 ), controller  32  causes ventilator  40  to operate under an optimal condition (for example, a setting condition for maintaining the current state) (S 51 ). 
     As described above, server device  80  determines a target range and provides control device  30  with the target range in Operation Example 4. If server device  80  determines a target range based on, for instance, data from another control device and data received in the past by control device  30 , air conditioning system  10  can control devices such as ventilator  40 , based on a comparison between a more appropriate target range and the general air quality index. 
     Operation Example 5 
     There are a plurality of combinations of types of gases, temperature, and humidity, for instance that are used to calculate a general air quality index, yet what is given priority to control devices (cause the devices to operate) can be more considered in order to cause the general air quality index to fall within a target range. Accordingly, Operation Example 5 in which a decrease in a gas concentration is given priority over improving comfort is to be described with reference to  FIG. 8 .  FIG. 8  is a flowchart illustrating Operation Example 5 of air conditioning system  10 . 
     First, obtainer  35  of control device  30  obtains information indicating air quality in an indoor space, which is output by indoor sensor  21  of sensor  20  (S 61 ), and controller  32  calculates a general air quality index, based on the obtained information (S 62 ). The general air quality index is, for example, the same as the index used in Operation Example 1, but may be the same as the index used in Operation Example 2 or 3. 
     Next, controller  32  determines, based on the obtained information indicating the air quality, whether all the gas concentrations (that is, the gas concentrations indicated by X n ) used to calculate the general air quality index are lower than reference concentrations (S 63 ). For example, when n=3, X 1  denotes a CO 2  concentration, X 2  denotes a PM concentration, and X 3  denotes a TVOC concentration, controller  32  determines, based on the reference concentrations illustrated in  FIG. 3 , whether X 1  (CO 2  concentration)&lt;1000 ppm, and X 2  (PM concentration)&lt;30 ppm, and furthermore X 3  (TVOC concentration)&lt;400 μg/m 3 . 
     If controller  32  determines that all the gas concentrations indicated by X n  are lower than the reference concentrations (Yes in S 63 ), controller  32  causes air conditioner  50  disposed in the indoor space to operate to bring the general air quality index close to a target range (S 64 ). 
     On the other hand, if controller  32  determines that at least one gas concentration indicated by X n  is higher than or equal to the reference concentration (No in S 63 ), controller  32  causes ventilator  40  to operate (S 65 ). The processing of steps S 61  to S 63  and step S 65  is repeated until all the gas concentrations indicated by X n  are lower than the reference concentrations. After the concentration of the gas higher than or equal to the reference concentration is decreased below the reference concentration by causing ventilator  40  to operate (Yes in S 63 ), controller  32  causes air conditioner  50  disposed in the indoor space to operate to bring the general air quality index close to the target range. 
     As described above, in Operation Example 5, after the value of f(X n ) is increased (or in other words, a gas concentration is decreased), the value of g(T, H) is increased (or in other words, comfort is improved) to bring the general air quality index close to the target range. Thus, air conditioning system  10  can give priority to decreasing a gas concentration over improving comfort. 
     Operation Example 6 
     Next, Operation Example 6 in which improving comfort is given priority over decreasing a gas concentration is to be described with reference to  FIG. 9 .  FIG. 9  is a flowchart illustrating Operation Example 6 of air conditioning system  10 . 
     First, obtainer  35  of control device  30  obtains information indicating air quality in an indoor space, which is output by indoor sensor  21  of sensor  20  (S 71 ), and obtains (receives) activity amount information indicating the activity amount of a person staying in the indoor space, which is output by activity amount measurer  70  (S 72 ). 
     Next, controller  32  calculates a general air quality index, based on the obtained information indicating the air quality and the obtained activity amount information (S 73 ). The general air quality index is the same as the index used in Operation Example 3. 
     Next, controller  32  determines whether the activity amount indicated by the activity amount information is greater than or equal to a reference amount, based on the obtained activity amount information (S 74 ). When controller  32  determines that the activity amount indicated by the activity amount information is greater than or equal to the reference amount (Yes in S 74 ), controller  32  causes air conditioner  50  disposed in the indoor space to operate to decrease a temporal change rate of the general air quality index to a predetermined value or less (S 75 ). Stated differently, controller  32  stabilizes a change in the general air quality index. The predetermined value here is 20%, for example, but may be another value. After that, controller  32  causes ventilator  40  to operate to bring the general air quality index close to a target range (S 76 ). 
     On the other hand, when controller  32  determines that the activity amount indicated by the activity amount information is less than a reference amount (No in S 74 ), controller  32  causes ventilator  40  to operate to bring the general air quality index close to the target range (S 76 ). 
     As described above, in Operation Example 6, when the activity amount of a person staying in an indoor space is relatively large so that the person readily feels uncomfortable due to temperature and humidity, the value of g(T, H) is increased (or in other words, comfort is improved), and thereafter the value of f(X n ) is increased (or in other words, a gas concentration is decreased) to bring the general air quality index close to the target range. Thus, air conditioning system  10  can give priority to improving comfort over decreasing a gas concentration. 
     Advantageous Effects and Others 
     As described above, air conditioning system  10  includes: sensor  20  that measures air quality in an indoor space; obtainer  35  that obtains information indicating the air quality in the indoor space, the information being output by sensor  20 ; and controller  32  that calculates an air quality index (the general air quality index in the above embodiment) based on the information obtained, and controls ventilator  40  that ventilates the indoor space, based on the air quality index calculated. The air quality index is expressed by f(X n )×g(T, H), where f(X n ) denotes a function with respect to X n  that indicates at least one of a CO 2  concentration, a concentration of total volatile organic compounds (TVOC), a concentration of particulate matter (PM), an NO X  concentration, an SO X  concentration, an O 3  concentration, a mold count, or a dust count, and g(T, H) denotes a function with respect to T denoting temperature and H denoting humidity in the indoor space. 
     Such air conditioning system  10  controls ventilator  40  based on the general air quality index for which the degrees of influence exerted by a concentration of, for instance, a pollutant, temperature, and humidity are considered, and thus can effectively improve the air quality in the indoor space. 
     For example, f(X n ) is expressed by (Expression 1) above, where a n  denotes a coefficient, and g(T, H) is expressed by (Expression 2) above, where DI(T, H) denotes a function indicating a discomfort index, and α and β denote coefficients. 
     In this manner, if the air quality index is calculated using natural logarithms, the influence of a gas concentration and others on the air quality index can be smoothed. In other words, a difference of the degrees of influence of a gas concentration and others on the air quality index can be decreased. 
     For example, f(X n ) is expressed by (Expression 1′) above, where a n  and c n  denote coefficients, and g(T, H) is expressed by (Expression 2) above, where DI(T, H) denotes a function indicating a discomfort index, and α and β denote coefficients. 
     In this manner, if the air quality index is calculated by normalizing a gas concentration and others, the influence of, for instance, a gas concentration and others on the air quality index can be smoothed. In other words, a difference of the degrees of influence of a gas concentration and others on the air quality index can be decreased. 
     For example, controller  32  brings the air quality index close to a target range by causing air conditioner  50  disposed in the indoor space to operate when each gas concentration denoted by X n  is lower than a reference concentration. 
     Such air conditioning system  10  can improve air quality by improving comfort when the gas concentrations are relatively low. 
     For example, when at least one gas concentration denoted by X n  is higher than or equal to a reference concentration, controller  32  decreases the at least one gas concentration to a gas concentration below the reference concentration by causing ventilator  40  to operate, and thereafter causes air conditioner  50  disposed in the indoor space to operate to bring the air quality index close to a target range. 
     Such air conditioning system  10  can give priority to decreasing a gas concentration to improve air quality over improving comfort. 
     Further, air conditioning system  10  includes: sensor  20  that measures air quality in an indoor space and air quality in an outdoor space; obtainer  35  that obtains first information indicating the air quality in the indoor space and second information indicating the air quality in the outdoor space, the first information and the second information being output by sensor  20 ; and controller  32  that calculates an air quality index based on the first information obtained and the second information obtained, and controls ventilator  40  that ventilates the indoor space and air conditioner  50  disposed in the indoor space, based on the air quality index calculated. The air quality index is expressed by f(X n )×g in (T in , H in )×g out (T out , H out ), where f(X n ) denotes a function with respect to X n  that indicates at least one of a CO 2  concentration, a concentration of total volatile organic compounds (TVOC), a concentration of particulate matter (PM), an NO X  concentration, an SO X  concentration, an O 3  concentration, a mold count, or a dust count, g in (T in , H in ) denoting a function with respect to T in  denoting temperature and H in  denoting humidity in the indoor space, and g out (T out , H out ) denoting a function with respect to T out  denoting temperature and H out  denoting humidity in the outdoor space. When controller  32  determines that the air quality index obtained when g in (T in , H in ) is assumed to be 1 is to reach a target range as a result of ventilator  40  operating, controller  32  brings the air quality index close to the target range by causing ventilator  40  to operate. When controller  32  determines that the air quality index obtained when g in (T in , H in ) is assumed to be 1 is not to reach the target range as a result of ventilator  40  operating, controller  32  brings the air quality index close to the target range by causing air conditioner  50  to operate. 
     Such air conditioning system  10  controls air conditioner  50  as necessary, and thus the air quality in the indoor space can be improved effectively. 
     Further, air conditioning system  10  includes: sensor  20  that measures air quality in an indoor space; activity amount measurer  70  that measures an activity amount of a person staying in the indoor space; obtainer  35  that obtains information indicating the air quality in the indoor space, and activity amount information indicating the activity amount of the person, the information being output by sensor  20 , the activity amount information being output by activity amount measurer  70 ; and controller  32  that calculates an air quality index based on the information obtained and the activity amount information obtained, and controls ventilator  40  that ventilates the indoor space, based on the air quality index calculated. The air quality index is expressed by f(X n )×g(T, H)×h(A), where f(X n ) denotes a function with respect to X n  that indicates at least one of a CO 2  concentration, a concentration of total volatile organic compounds (TVOC), a concentration of particulate matter (PM), an NO X  concentration, an SO X  concentration, an O 3  concentration, a mold count, or a dust count, g(T, H) denotes a function with respect to T denoting temperature and H denoting humidity in the indoor space, and h(A) denotes a function with respect to A denoting an activity amount. 
     Such air conditioning system  10  can improve air quality in the indoor space, taking into consideration the activity amount of a person staying in the indoor space. 
     For example, the function denoted by h(A) has a positive value irrespective of the activity amount denoted by A, decreases with an increase in the activity amount denoted by A, and increases with a decrease in the activity amount denoted by A. 
     Such air conditioning system  10  can improve air quality in the indoor space, taking into consideration the activity amount of a person staying in the indoor space. 
     For example, when the activity amount indicated by the activity amount information is greater than or equal to a reference amount, controller  32  decreases a temporal change rate of the air quality index to a predetermined value or less by causing air conditioner  50  disposed in the indoor space to operate, and thereafter brings the air quality index close to a target range by causing ventilator  40  to operate. 
     Such air conditioning system  10  can give priority to improving comfort over decreasing gas concentrations, when the activity amount of a person staying in the indoor space is relatively large so that the person readily feels uncomfortable due to temperature and humidity. 
     For example, ventilator  40  includes air supply device  41  that supplies air to the indoor space, and includes air filter  41   a  that decreases at least one of a PM concentration, an NO X  concentration, an SO X  concentration, or an O 3  concentration in the air to be supplied to the indoor space. Air filter  41   a  is an example of a removal function. 
     Such air conditioning system  10  can decrease at least one of a PM concentration, an NO X  concentration, an SO X  concentration, or an O 3  concentration, by controlling ventilator  40 . 
     For example, air conditioning system  10  further includes: air cleaner  60  having a function of decreasing at least one of a PM concentration, an NO X  concentration, an SO X  concentration, or an O 3  concentration in the indoor space. Air cleaner  60  is an example of a removal device. 
     Such air conditioning system  10  can decrease at least one of a PM concentration, an NO X  concentration, an SO X  concentration, or an O 3  concentration, by controlling air cleaner  60 . 
     For example, air conditioning system  10  further includes: server device  80  that includes data processor  82  that determines a target range of the air quality index, based on the information indicating the air quality in the indoor space measured by sensor  20 , an operating status of ventilator  40 , and the air quality index. Controller  32  brings the air quality index close to the target range determined, by controlling at least ventilator  40 . 
     Accordingly, if server device  80  determines the target range based on, for instance, data from another control device and data received in the past by control device  30 , air conditioning system  10  can control devices such as ventilator  40 , based on a comparison between a more appropriate target range and the air quality index. 
     Other Embodiments 
     The above has described the air conditioning system according to the embodiment, yet the present invention is not limited to the above embodiment. 
     For example, in the above embodiment, the general air quality index has a positive value that increases as the air quality of the indoor space is higher, but may be a positive value that decreases as the air quality of the indoor space is higher. 
     In the above embodiment, the air conditioning system is achieved by a plurality of devices, but may be achieved as a single device. If the air conditioning system is achieved by a plurality of devices, the elements included in the air conditioning system may be distributed to the plurality of devices in any manner. 
     In the above embodiment, each of the elements may be constituted by dedicated hardware, or may be achieved by executing a software program suitable for the element. Each element may be achieved by a program executor such as a CPU or a processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory. 
     The elements may be circuits (or integrated circuits). These circuits may form one circuit as a whole, or may be separate circuits. Furthermore, each circuit may be a general-purpose circuit or a dedicated circuit. 
     A general or specific aspect of the present invention may be achieved by a system, a device, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or any combination of systems, devices, methods, integrated circuits, computer programs, or recording media. For example, the present invention may be achieved as a control device in the above embodiment (or a system corresponding to the control device). The present invention may be achieved as an air conditioning method executed by a computer such as an air conditioning system according to the above embodiment. The present invention may be achieved as a program for a computer to execute such an air conditioning method or may be achieved as a computer-readable non-transitory recording medium in which such a program is stored. 
     The processing orders of the processes in the flowcharts described in the above embodiment are examples. The processing orders of the processes may be changed, or the processes may be executed in parallel. Furthermore, a process that a particular processing unit executes may be executed by another processing unit. 
     The present invention may also include embodiments as a result of adding, to the embodiments, various modifications that may be conceived by those skilled in the art, and embodiments obtained by combining elements and functions in the embodiments in any manner without departing from the scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  air conditioning system 
               20  sensor 
               32  controller 
               35  obtainer 
               40  ventilator 
               41  air supply device 
               41   a  air filter (removal function) 
               50  air conditioner 
               60  air cleaner (removal device) 
               70  activity amount measurer 
               80  server device 
               82  data processor