CO2 SENSOR REFERENCE VALUE CALIBRATION APPARATUS AND METHOD FOR CALIBRATING REFERENCE VALUE OF CO2 SENSOR

Abstract

A controller as a CO.sub.2 sensor reference value calibration apparatus calibrates a reference value of the CO.sub.2 sensor in the following manner. Introduction of outside air is started after a person is not detected. A CO.sub.2 concentration, which is acquired when a preset first waiting time elapses, is set as a provisional reference value. The carbon dioxide concentration, which is acquired when a preset second waiting time elapses, is compared with the provisional reference value. In a case where a change rate of the carbon dioxide concentration is out of a preset allowable range, the carbon dioxide concentration is acquired when the second waiting time elapses after newly setting the acquired carbon dioxide concentration as the provisional reference value. In a case where the change rate of the carbon dioxide concentration is in the allowable range, the currently set provisional reference value is set as the reference value.

Claims

1. A CO.sub.2 sensor reference value calibration apparatus comprising: a person detection unit configured to detect a person in an object space; a CO.sub.2 sensor configured to acquire, as a relative value with respect to a preset reference value of the CO.sub.2 sensor, a carbon dioxide concentration in the object space; a clock unit configured to measure a time; and a calibration unit configured to calibrate the reference value, wherein the calibration unit is configured to start introduction of outside air after a person is not detected in the object space, the calibration unit is configured to set, as a provisional reference value, a carbon dioxide concentration acquired when a preset first waiting time elapses after starting the introduction of the outside air, the calibration unit is configured to compare a carbon dioxide concentration, which is acquired when a preset second waiting time elapses after the setting of the provisional reference value, with the provisional reference value, the calibration unit is configured to repeatedly acquire the carbon dioxide concentration, when the second waiting time elapses after newly setting the acquired carbon dioxide concentration as the provisional reference value, in a case where a change rate of the carbon dioxide concentration is out of a preset allowable range, and the calibration unit is configured to set a currently set provisional reference value as the reference value in a case where the change rate of the carbon dioxide concentration is in the allowable range.

2. The CO.sub.2 sensor reference value calibration apparatus according to claim 1, wherein the calibration unit is configured to compare the carbon dioxide concentration, which is acquired when the preset second waiting time elapses after the setting of the provisional reference value, with the provisional reference value, the calibration unit is configured to repeatedly acquire the carbon dioxide concentration, when the second waiting time elapses after the setting of the acquired carbon dioxide concentration as a new provisional reference value, in a case where the acquired carbon dioxide concentration is lower than the provisional reference value and where the change rate of the carbon dioxide concentration is negative, and the calibration unit is configured to set the currently set provisional reference value as the reference value in a case where the acquired carbon dioxide concentration is equal to or greater than the provisional reference value and where the change rate of the carbon dioxide concentration is positive.

3. The CO.sub.2 sensor reference value calibration apparatus according to claim 1, wherein the calibration unit is configured to set, as the provisional reference value, a value acquired by correcting the acquired carbon dioxide concentration based on a preset error correction value.

4. The CO.sub.2 sensor reference value calibration apparatus according to claim 1, wherein the first waiting time is set based on a maximum allowable value of the carbon dioxide concentration with respect to a living space and based on an amount of ventilation air defined in advance with respect to the living space.

5. The CO.sub.2 sensor reference value calibration apparatus according to claim 1, wherein the first waiting time is set based on the carbon dioxide concentration when starting the introduction of the outside air and based on the preset amount of ventilation air with respect to the living space.

6. A method for calibrating a reference value of a CO.sub.2 sensor, the CO.sub.2 sensor configured to acquire a carbon dioxide concentration in an object space, the carbon dioxide concentration being a relative value with respect to a preset reference value, the method comprising: detecting a person in the object space; starting introduction of outside air after a person is not detected in the object space; setting, as a provisional reference value, a carbon dioxide concentration acquired when a preset first waiting time elapses after the starting of the introduction of the outside air; and calibrating the reference value of the CO.sub.2 sensor by: starting the introduction of the outside air after a person is not detected in the object space; setting, as the provisional reference value, a carbon dioxide concentration acquired when the preset first waiting time elapses after the starting of the introduction of the outside air; comparing a carbon dioxide concentration, which is acquired when a preset second waiting time elapses after the setting of the provisional reference value, with the provisional reference value; acquiring the carbon dioxide concentration when the second waiting time elapses after newly setting the acquired carbon dioxide concentration as the provisional reference value, in a case where a change rate of the carbon dioxide concentration is out of a preset allowable range; and setting a currently set provisional reference value as the reference value in a case where the change rate of the carbon dioxide concentration is in the allowable range.

7. A method for calibrating a reference value of a CO.sub.2 sensor, the CO.sub.2 sensor configured to acquire a carbon dioxide concentration in an object space, the carbon dioxide concentration being a relative value with respect to a preset reference value, the method comprising: detecting a person in the object space; starting introduction of outside air after a person is not detected in the object space; setting, as a provisional reference value, a carbon dioxide concentration acquired when a preset first waiting time elapses after the starting of the introduction of the outside air; comparing a carbon dioxide concentration, which is acquired when a preset second waiting time elapses after the setting of the provisional reference value, with the provisional reference value; acquiring the carbon dioxide concentration when the second waiting time elapses after newly setting the acquired carbon dioxide concentration as the provisional reference value, in a case where a change rate of the carbon dioxide concentration is out of a preset allowable range; and setting a currently set provisional reference value as the reference value in a case where the change rate of the carbon dioxide concentration is in the allowable range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

[0022] FIG. 1 is a diagram schematically illustrating a configuration of an air conditioning system according to an embodiment;

[0023] FIG. 2 is a flowchart showing a reference value calibration process implemented by a calibrating apparatus;

[0024] FIG. 3 is a graph showing an example of change in a CO.sub.2 concentration over time;

[0025] FIG. 4 is a graph showing an example of change in the CO.sub.2 concentration over time according to another embodiment; and

[0026] FIG. 5 is a graph showing an allowable range.

DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present disclosure will be described with reference to FIG. 1 to FIG. 3. As shown in FIG. 1, an air conditioning system 1 of the present embodiment is provided with an air conditioning unit 2 and a controller 3. A well-known configuration may be employed as the air conditioning unit 2. Therefore, the detailed description of the air conditioning unit 2 is omitted. The air conditioning unit 2 includes a blower fan 5, an introduction-side damper 6, a function unit 7, and/or the like. The blower fan 5 is for introducing air. The introduction-side damper 6 is configured to adjust an introduction amount of the introduced air by controlling its opening degree. The function unit 7 adjusts temperature and humidity of the introduced air.

[0028] The controller 3 functions as an operation input unit for inputting an operation with respect to the air conditioning system 1 by a user. The controller 3 may be generally provided on a wall in the object space 4. The controller 3 includes a control unit 10, a calibration unit 11, a human sensor 12, a timer 13, a CO.sub.2 sensor 14, a display unit 15, and a switch 16. The controller 3 functions as a reference value calibration apparatus.

[0029] The control unit 10 is configured with a microcomputer including, for example, a CPU, a ROM, and a RAM which are not shown in the drawings. The control unit 10 controls the controller 3 by executing a program which is stored in the ROM and/or the like. Specifically, the control unit 10 displays a temperature of the object space 4 on the display unit 15. In addition, the control unit 10 controls the air conditioning unit 2 based on an instruction input from the switch 16. Furthermore, the control unit 10 adjusts the amount of air introduced into the object space 4 by controlling the opening degree of the introduction-side damper 6. Hereinafter, for the sake of convenience, the amount of air introduced into the object space 4 is referred to as an introduction amount of the air.

[0030] The control unit 10 is provided with the calibration unit 11. In the present embodiment, the calibration unit 11 enables the calibration with the program executed by the control unit 10. That is, the calibration unit 11 is in a form of software. The calibration unit 11 calibrates the reference value of the CO.sub.2 sensor 14 based on the CO.sub.2 concentration (carbon dioxide concentration) in the object space 4. Details of the calibration will be described below. Note that, the calibration corresponds to correction.

[0031] The human sensor 12, which detects a person in the object space 4, functions as a person detection unit. The human sensor 12 detects a person in the object space 4 by infrared, ultrasonic wave, visible light, or a combination thereof. That is, the human sensor 12 detects the presence of the person in the object space 4.

[0032] The timer 13, which measures a time, functions as a clock unit. In the present embodiment, as the timer 13, a so-called real time clock is employed. The timer 13 has so-called a calendar function of specifying the date and the time. In addition, the timer 13 is also configured to measure the time that has elapsed from a certain point of time. The timer 13 may be built in the control unit 10.

[0033] The CO.sub.2 sensor 14 acquires the CO.sub.2 concentration in the object space 4. The CO.sub.2 sensor 14 acquires the CO.sub.2 concentration as a relative value with respect to a preset reference value. The display unit 15 includes, for example, a liquid crystal panel and/or the like. The display unit 15 displays the temperature in the object space 4, a current operation state, and/or the like. The switch 16 includes, for example, a mechanical switch and/or a touch panel which is provided corresponding to the display unit 15. A user manipulates the switch 16 to provide an instruction of a set temperature, an instruction for turning-on to start the operation, and an instruction for turning-off to stop the operation.

[0034] Next, operation of the above-described configuration will be described. As described above, the CO.sub.2 sensor 14 acquires the CO.sub.2 concentration as a relative value with respect to the preset reference value. For this reason, in a case where the reference value is deviated, the acquired CO.sub.2 concentration is also deviated from the actual concentration. Thus, it is required to correctly reset the reference value, that is, it is required to calibrate the CO.sub.2 sensor. In consideration of the deviation of the reference value due to the aging, the reference value is desirably calibrated at a frequency of about, for example, once several months or once a year. In addition, it is considered that the calibration of the reference value of the CO.sub.2 sensor 14 is preferably performed in a test environment at the CO.sub.2 concentration which is deemed to be a reference value.

[0035] However, in a case where the air conditioning system 1 is installed in, for example, general homes or offices in a building, it is difficult to prepare the above-described test environment. In this regard, in the present embodiment, the reference value of the CO.sub.2 sensor 14 is calibrated in a way described below. Note that, the following processes may be performed by the calibration unit 11 or the like; however, in the embodiment, the controller 3 is described as a main component for the sake of simplicity of explanation.

[0036] The controller 3 performs the reference value calibration process illustrated in FIG. 2. The reference value calibration process shows the flow of a reference value calibration method. The controller 3 determines whether or not it is a time for the calibration of the reference value (S1). Herein, the time for the calibration represents a preset date and time or represents a certain point of time at which a predetermined time period has elapsed from the previous calibration. In the present embodiment, it is assumed that the calibration is performed once a year. In addition, the time for the calibration may be set to be midnight, at which time a person is not present in the object space, so as to easily perform the process after step S2 described below. When it is determined that it is not the time for the calibration (S1: NO), the controller 3 completes the process.

[0037] On the other hand, when it is determined that it is the time for the calibration (S1: YES), the controller 3 determines whether or not a person is present in the object space (S2). In a case where a person is not present in the object space (S2: NO), the controller 3 completes the process. The reason is as follows. In a case where a person is present in the object space, CO.sub.2 (carbon dioxide) is emitted as the person's breathing, and thus it is concerned that the reference value cannot be appropriately calibrated.

[0038] In contrast, when it is determined that a person is not present in the object space (S2: YES), the controller 3 determines that a condition for appropriate calibration of the reference value is made. Thus, the controller 3 starts the introduction of the outside air into the object space 4 (S3). At this time, the controller 3 introduces the outside air into the object space 4 by driving the blower fan 5 and adjusting the opening degree of the introduction-side damper 6. In other words, the controller 3 ventilates the inside of the object space 4 such that the state in the object space 4 becomes the same as that of the outside air.

[0039] FIG. 3 illustrates a graph G as an example of change in the CO.sub.2 concentration over time in the object space 4 after starting the introduction of the outside air. FIG. 3 illustrates a state where the introduction of the outside air at the time (t0) is started and where the CO.sub.2 concentration at the time (t0) is at the point P0. In this case, it is expected that the CO.sub.2 concentration in the object space 4 is basically decreased as the time elapses after the outside air is introduced. In addition, it is considered that the CO.sub.2 concentration in the object space 4 is continually at a constant value so as to be almost the same as the CO.sub.2 concentration of the outside air at the time point at which the ventilation of the inside of the object space 4 is completed, that is, at the time point at which the inside of the object space 4 is sufficiently ventilated and thus the state in the object space 4 is the same as that of the outside air.

[0040] For this reason, it is considered to calibrate the reference value in a state where the CO.sub.2 concentration in the object space 4 is the same as the CO.sub.2 concentration of the outside air, thereby to appropriately match the reference value with the CO.sub.2 concentration of the outside air. That is, in that state, the reference value can be appropriately calibrated. Meanwhile, in a case of general homes or offices in a building, it is expected that many people come in and go out frequently. In this case, the amount of CO.sub.2 emission is changed depending on the number of people. From this aspect, in the configuration to simply wait until determination is made that the inside of the object space 4 is sufficiently ventilated, it is necessary to set a sufficiently long ventilation time, during which ventilation is continued, in order to cope with the change in the number of people.

[0041] It is considered, in the configuration to simply wait until a predetermined time has elapsed, that as the ventilation time becomes longer, it is highly likely that people come in and go out. Consequently, it is highly likely that the calibration of the reference value is not appropriately performed due to the people coming in and out. For this reason, the reference value of the CO.sub.2 sensor 14 is desirably calibrated in a short time.

[0042] In addition, it is conceivable to set a long ventilation time in order to ventilate the inside of the object space until determination is made that the ventilation is sufficiently performed. In this case, it may be also considered that the inside of the object space has been already ventilated before elapsing the long ventilation time. Consequently, in this case, unnecessary power consumption is likely to be caused. In addition, in a configuration where the CO.sub.2 concentration is repeatedly acquired after starting the introduction of the outside air and where the ventilation state is determined based on the change in the CO.sub.2 concentration, the CO.sub.2 concentration may be acquired even in a state where the ventilation is not sufficiently performed. In this case, unnecessary power consumption is likely to be caused.

[0043] In consideration of this, the controller 3 waits until determination is made that the ventilation is performed to some extent after starting the introduction of the outside air. Subsequently, on the basis of the change in the CO.sub.2 concentration, the controller 3 determines whether or not the state of air in the object space 4 is the same as that of the outside air. The time, which is for waiting until determination is made that the ventilation is performed to some extent, corresponds to a first waiting time. In the present embodiment, the first waiting time is set as follows.

[0044] In a case of the United States, the amount of ventilation air is determined to be 0.54 m.sup.3/h*m.sup.2 based on ASHRAE standard 62.2. For this reason, ventilation is performed by 0.54 m.sup.3/h per unit area with respect to a general living space. Further, the maximum allowable value of the CO.sub.2 concentration with respect to a living space such as general homes is defined as 2000 ppm. That is, in a case where the living space is set to be an object, the maximum value of the CO.sub.2 concentration is presumed to be 2000 ppm. Note that, the ventilation of the inside the object space 4 having a large amount of ventilation air can be performed in a short time under the condition that the object spaces 4 have the same size.

[0045] On that bases, it can be determined that the ventilation of the inside of the object space 4 is completed to some extent by performing the ventilation of 0.54 m.sup.3/h per unit area and by waiting until the CO.sub.2 concentration changes from 2000 ppm to be the same as that of the outside air. That is, the first waiting time can be set based on the maximum allowable value of the carbon dioxide concentration with respect to a living space. The amount of ventilation air which is defined in advance with respect to the living space.

[0046] Further, the required time until it can be determined that the ventilation is completed is changed depending of the size of the object space 4. It is noted that, in a case where the object space 4 has a standard size, such as a living room of general homes, the time for the ventilation is estimated to be approximately 80 minutes, for example. That is, it is estimated that when the ventilation is performed for 80 minutes in a state where a person is not present, the air in the object space 4 is replaced with the outside air.

[0047] As such, in the present embodiment, the first waiting time is set based on the maximum allowable value of the CO.sub.2 concentration (here, 2000 ppm) with respect to a living space and the amount of ventilation air (here, 0.54 m.sup.3/h*m.sup.2) which is defined in advance with respect to the living space. In consideration that living spaces are in different sizes in reality, the first waiting time of the present embodiment is set to be 120 minutes with a sufficient margin.

[0048] Meanwhile, when the introduction of the outside air is started in step S3 of the reference value calibration process as shown in FIG. 2, the controller 3 determines whether or not the above-described first waiting time (T1, refer to FIG. 3) has elapsed (S4). When it is determined that the first waiting time (T1) has not elapsed yet (S4: NO), the process proceeds to step S4, and the controller 3 waits until the first waiting time has elapsed. In addition, in a case where a person is detected during the first waiting time (T1), the controller 3 stops the reference value calibration process. Further, the first waiting time (T1) and a second waiting time (T2, refer to FIG. 3) described below are counted by the timer 13.

[0049] On the other hand, when it is determined that the first waiting time (T1) has elapsed (S4: YES), the controller 3 acquires the CO.sub.2 concentration (S5). In step S5, the controller 3 acquires the CO.sub.2 concentration based on the preset reference value. At this time, the acquired CO.sub.2 concentration corresponds to a value at the point P1 at the time (t1) illustrated in FIG. 3. In addition, the controller 3 sets the CO.sub.2 concentration acquired in step S5 as a provisional reference value (S6). Note that, in the present embodiment, the acquired CO.sub.2 concentration is set as the provisional reference value as it is.

[0050] Subsequently, the controller 3 determines whether or not the second waiting time (T2) has elapsed (S7). In the present embodiment, the second waiting time is the preset value and is set to be 8 minutes which is 1/10 of the first waiting time. Note that, the second waiting time is not limited to the 8 minutes and may be properly set to be in a range of several minutes to several tens of minutes.

[0051] When it is determined that the second waiting time has not elapsed yet (S7: NO), the process proceeds to step S7 at which the controller 3 waits until the second waiting time has elapsed. In a case where a person is detected during the second waiting time (T2), the controller 3 stops the reference value calibration process.

[0052] On the other hand, when it is determined that the second waiting time has elapsed (S7: YES), the controller 3 determines the CO.sub.2 concentration based on the provisional reference value, which is set in step S6, as a reference (S8). In addition, the controller 3 determines whether or not the CO.sub.2 concentration acquired in step S8 is smaller than the provisional reference value set in step S6 (S9). That is, the controller 3 determines whether or not the change rate of the CO.sub.2 concentration is negative. In addition, in the present embodiment, the change rate of the CO.sub.2 concentration is calculated by establishing the following expression.

Change rate of CO.sub.2 concentration=provisional reference value−acquired CO.sub.2 concentration  (1)

[0053] In this case, in a case where the acquired CO.sub.2 concentration is smaller than the provisional reference value, that is, in a case where the change rate of CO.sub.2 concentration is negative, it is considered that the CO.sub.2 concentration is still decreased. For this reason, when it is determined that the CO.sub.2 concentration is smaller than the provisional reference value (S9: YES), the process proceeds to step S6. The controller 3 sets the acquired CO.sub.2 concentration as a new provisional reference value (S6). Subsequently, the controller 3 waits until the second waiting time has elapsed (S7). Such a situation corresponds to time (t2) and time (t3) as shown in FIG. 3. In other words, the CO.sub.2 concentration at the point P2 is smaller than the CO.sub.2 concentration at the point P1 which is set as an initial provisional reference value. In addition, the CO.sub.2 concentration at the point P3 is smaller than the CO.sub.2 concentration at the point P2 which is set as a new provisional reference value.

[0054] In contrast, when it is determined that the CO.sub.2 concentration is not smaller than the provisional reference value, that is, when it is determined that the CO.sub.2 concentration acquired in step S8 is equal to or greater than the currently set provisional reference value (S9: NO), the controller 3 sets the currently set provisional reference value as a reference value (S10). The present situation corresponds to the point P4 as shown in FIG. 3. The CO.sub.2 concentration at the point P4 is equal to or greater than the CO.sub.2 concentration at the point P3 which is set as the provisional reference value. That is, when it is determined that the change rate of CO.sub.2 concentration is positive, the controller 3 sets the currently set provisional reference value as the reference value.

[0055] In step S10, the CO.sub.2 concentration at the minimum value is set as the reference value among the acquired CO.sub.2 concentrations, which are acquired until the CO.sub.2 concentration becomes continually at an almost constant value after starting the introduction of the outside air. In the present configuration, the CO.sub.2 concentration, in a state where the CO.sub.2 concentration in the object space 4 is continually at an almost constant value, is set as the new reference value. That is, the CO.sub.2 concentration, which is almost matched with that of the outside air, is set as the new reference value. In this way, the controller 3 calibrates the reference value of the CO.sub.2 sensor 14 by setting the CO.sub.2 concentration, when it is determined that the air in the object space 4 is almost matched with the outside air, as the new reference value.

[0056] According to the above-described embodiment, the following effects can be acquired. The controller 3 starts the introduction of the outside air after a person is not detected in the object space 4 any longer. The controller 3 sets the CO.sub.2 concentration, which is acquired when the preset first waiting time has elapsed after starting the introduction of the outside air, as the provisional reference value. In the present configuration, acquiring of the CO.sub.2 concentration is started in a state where the ventilation is performed to some extent. In other words, the CO.sub.2 concentration is not acquired during a period in which the CO.sub.2 concentration is assumed to be obviously decreased. Thus, in the present configuration, unnecessary power consumption can be reduced.

[0057] In addition, the controller 3 acquires the CO.sub.2 concentration when the preset second waiting time has elapsed after setting the provisional reference value. The controller 3 compares the acquired CO.sub.2 concentration with the provisional reference value. In a case where the acquired CO.sub.2 concentration is smaller than the provisional reference value, that is, in a case where the change rate of the CO.sub.2 concentration is negative, the controller 3 sets the acquired CO.sub.2 concentration as a new provisional reference value. The controller 3 further acquires the CO.sub.2 concentration again when the second waiting time has elapsed.

[0058] On the other hand, in a case where the acquired CO.sub.2 concentration is equal to or greater than the provisional reference value, that is, in a case where it is determined that the change rate of CO.sub.2 concentration is positive, the controller 3 sets the currently set provisional reference value as the reference value. In the present configuration, erroneous calibrations can be avoided while the CO.sub.2 concentration is decreased. Thus, the reference value of the CO.sub.2 sensor 14 can be calibrated in the state where the decrease in the CO.sub.2 concentration has ceased, that is, in a state where the state in the object space 4 is the same as that of the outside air.

[0059] Accordingly, the reference value of the CO.sub.2 sensor 14 can be accurately matched with the CO.sub.2 concentration in the atmosphere.

[0060] The controller 3 sets the first waiting time based on the maximum value of the CO.sub.2 concentration, which is allowable for a living space, and the preset amount of ventilation air with respect to the living space. In the present configuration, even in a case where the object space 4 has a different size, the first waiting time at the same value can be used. Thus, the versatility can be improved.

[0061] In addition, when the reference value of the CO.sub.2 sensor 14 is calibrated by using the reference value calibration method as shown in FIG. 2, as described above, the reference value of the CO.sub.2 sensor 14 can be accurately matched with the CO.sub.2 concentration in the atmosphere.

Other Embodiments

[0062] The present disclosure is not limited to the configuration exemplified in the above-described embodiments, and can be optionally modified or expanded without departing from the scope.

[0063] In the embodiment, an example, in which the reference value is calibrated in the case where it is determined that the change rate of the CO.sub.2 concentration is positive, is described. It is noted that, even in a case where the change rate of the CO.sub.2 concentration is negative, the reference value may be calibrated as long as the change rate is in a preset allowable range. For example, as shown in FIG. 4, it is assumed that the introduction of the outside air is started at the time (t10). Subsequently, the initial provisional reference value is set at the time (t11) when the first waiting time has elapsed. Subsequently, the CO.sub.2 concentration is acquired at the time (t12) when the second waiting time has elapsed. In addition, on the basis of the CO.sub.2 concentration at each point, the allowable range of the change amount of the CO.sub.2 concentration is set in a range of ±δ. That is, the allowable range of the change rate of CO.sub.2 concentration is set in a range of δ/T2. Note that, the value δ may be set in consideration of an accuracy of the CO.sub.2 sensor 14, the size of the object space 4, and/or the like.

[0064] As shown in FIG. 4, the CO.sub.2 concentration at the point P12 is below the allowable range at the point P11. That is, the CO.sub.2 concentration at the point P12 is out of the allowable range which is set with respect to the provisional reference value at the point P11, that is, at the current point. For this reason, the controller 3 sets a range of ±δ as a new allowable range based on the CO.sub.2 concentration at the point P12. In addition, the controller 3 waits until the second waiting time has elapsed and acquires the CO.sub.2 concentration which is indicated at the point P13 at the time (t13).

[0065] At this time, the CO.sub.2 concentration at the point P13 is within the allowable range at the point P12. For this reason, the change rate between the values of the CO.sub.2 concentration at the two continuous measurement points is in the allowable range. Therefore, the controller 3 sets the CO.sub.2 concentration at the point P13 as the reference value. In the present configuration, the reference value can be calibrated in a state where the change rate of the CO.sub.2 concentration is small, that is, in a state where it can be determined that the CO.sub.2 concentration is almost the same as that of the outside air.

[0066] In addition, the allowable range is set, and thus the reference value can be restricted from being erroneously calibrated. That is, the allowable range is set based on the accuracy of the CO.sub.2 sensor 14, the size of the object space 4, and/or the like, as described above. In other words, the allowable range is considered in a range, in which air in the object space 4 is assumed to fluctuate in a natural state, and is considered in an error range of the CO.sub.2 sensor 14.

[0067] For example, as shown in FIG. 5, it is considered that a case where the CO.sub.2 concentration is at the point P21 at the time (t21), which is beyond the allowable range with respect to the CO.sub.2 concentration at the point P20 at the time (t20). FIG. 5 shows a state where the distribution of the CO.sub.2 concentration in the object space 4 is deviated, that is, a state where the ventilation is not sufficiently performed. Therefore, even when the change rate of the CO.sub.2 concentration is positive, in a case where the CO.sub.2 concentration is beyond the allowable range, the reference value is not set based on the above-described change rate of the CO.sub.2 concentration. In this case, the CO.sub.2 concentration is obtained again after the second waiting time has elapsed such that the error caused by the air fluctuation and/or the like can be absorbed.

[0068] In addition, in a case where the CO.sub.2 concentration is at the point P22, which is below the allowable range at the time (t21), it is considered that the CO.sub.2 concentration in the object space 4 is still decreased or that the distribution of the CO.sub.2 concentration in the object space 4 is deviated. In this case, the CO.sub.2 concentration may be acquired again after the second waiting time has elapsed without setting the reference value based on the above-described CO.sub.2 concentration. Note that, even in a case where the change rate of CO.sub.2 concentration is negative, the reference value may be calibrated on condition that the absolute amount, which is the change amount in the CO.sub.2 concentration, is in a range of −δ, that is, on condition that the change rate of the CO.sub.2 concentration is, for example, within a predetermined range.

[0069] In the embodiment, an example, in which the acquired CO.sub.2 concentration is set as the provisional reference value, is described. It is noted that, a value acquired by calibrating the acquired CO.sub.2 concentration based on a preset error correction value may be set as the provisional reference value. In consideration of the accuracy of the CO.sub.2 sensor 14 as described above, a low value may be erroneously detected. In a case where the value is a minimum value, the minimum value, which is smaller than an appropriate value supposed to be the reference value, may be set as the reference value. In this regard, the error correction value may be preset in consideration of the accuracy of the CO.sub.2 sensor 14, and/or the like. In this case, the CO.sub.2 concentration, which is corrected by using the error correction value, may be set as the provisional reference value.

[0070] In the present configuration, the deviation of the distribution of the CO.sub.2 concentration, which is caused by the air fluctuation, and an error of the accuracy of the CO.sub.2 sensor 14 can be absorbed, and thereby the reference value can be restricted from being largely deviated. In this case, the error correction value may be statically determined or may be dynamically set based on a difference value between the previously acquired CO.sub.2 concentration and the currently acquired CO.sub.2 concentration and/or based on a moving average value of the acquired CO.sub.2 concentrations.

[0071] In the embodiment, an example, in which the first waiting time is set based on the maximum value of the carbon dioxide concentration allowable for a living space and based on the preset amount of ventilation air with respect to the living space, is described. It is noted that, the first waiting time may be set based on the carbon dioxide concentration at the time of starting the introduction of the outside air and based on the preset amount of ventilation air with respect to the living space.

[0072] For example, in a case where a person is not present in the object space 4 at the time for the calibration, it is considered that the CO.sub.2 concentration in the object space 4 is not the allowable maximum value. In this case, it is considered that the time required for the ventilation of the object space 4 is shorter as compared with a time required in a case of performing the ventilation in a state where the CO.sub.2 concentration is maximum as described in the embodiment. In this case, the time for the calibration process can be shortened.

[0073] In the embodiment, an example in which the first waiting time is set based on ASHRAE standard 62.2. It is noted that, the first waiting time may be set based on other standards.

[0074] In addition, in the embodiment, the first waiting time is set in consideration of the area of the living space. It is noted that, it is considered that the first waiting time becomes longer in a specific space, which is larger than a general living space, such as a stairwell. For this reason, in a case where the first waiting time is calculated at, for example, 80 minutes, the first waiting time may be set with more sufficient margins such as at 160 minutes.

[0075] In addition, the first waiting time may be variously set by a user. For example, in a case of Japan, multiple first waiting times can be selectively set so as to correspond to the size of the object space 4 having, for example, 6 mats or 14 mats. In this case, the first waiting time may be set based on the maximum allowable value of the carbon dioxide concentration with respect to the living space or the carbon dioxide concentration at the time of starting the introduction of the outside air and based on the amount of ventilation air which is set in advance with respect to the living space.

[0076] In the embodiment, the second waiting time is set at a constant value. It is noted that, the second waiting time may be modified in response to the change rate and the change amount of CO.sub.2 concentration. For example, in a case where the change rate is large, that is, in a case where the difference between the previous provisional reference value and the current provisional reference value is large, the CO.sub.2 concentration is not completely decreased. In this case, the CO.sub.2 concentration is expected to be further decreased after the second waiting time has elapsed again. For this reason, in this case, the subsequent second waiting time can be set at a longer period. In the present configuration, the power consumption can be reduced.

[0077] The time to calibrate the reference value may be set based on days and times as well. For example, it is considered that in a case of general homes or offices in a building, it is highly likely that a person is not present at midnight. In this case, it is considered that it is less likely that the reference value calibration process is interrupted, and thus there is no need to restart the reference value calibration process.

[0078] In the embodiment, in the case where a person is detected during the first waiting time (T1) or during the second waiting time (T2), the reference value calibration process is stopped. Herein, in the case where the reference value calibration process is stopped, the reference value calibration process may be performed again after a person is not detected any longer. Alternatively or in addition, the reference value calibration process may be performed again in the following day. Alternatively or in addition, the calibration of the reference value may be skipped once.

[0079] The object space 4 has a certain degree of size as a matter of course, and thus the air state may be different depending on the place. That is, it is likely that the distribution of the CO.sub.2 concentration in the object space 4 is deviated. In addition to the above-described spatial factors, the acquired CO.sub.2 concentration may be different due to an installation height of the controller 3 or the like. For this reason, the first waiting time may be set based on the calculated value as described above and based on the expected time required to make the air in the object space 4 uniform. In this case, the expected time can be acquired by, for example, a diffusion model of air.

[0080] The human sensor 12 and the CO.sub.2 sensor 14 may be provided separately from the controller 3. The numerical values exemplified in the embodiment are merely one example, and the present disclosure is not limited thereto.

[0081] The present disclosure is not limited to the air conditioning system 1 exemplified in the embodiment. For example, various configurations may be employed in the present disclosure configured, which is to introduce the outside air into the object space 4, that is, configured to make the state in the object space 4 the same as the state of the outside air. For example, a discharge-side damper for discharging the air from the object space 4 may be provided. That is, the configuration described in FIG. 1 of the embodiment is merely one example, and the present disclosure is not limited thereto.

[0082] It should be appreciated that while the processes of the embodiments of the present disclosure have been described herein as including a specific sequence of steps, further alternative embodiments including various other sequences of these steps and/or additional steps not disclosed herein are intended to be within the steps of the present disclosure.

[0083] While the present disclosure has been described with reference to preferred embodiments thereof, it is to be understood that the disclosure is not limited to the preferred embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, which are preferred, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.