JPH11141866A - Combustion device, and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To periodically clean a detection element irrespective of presence/ absence of the combustion operation without obstructing the detection action during the combustion by the cleaning action. SOLUTION: A combustion condition-monitoring part 52 monitors the concentration of the prescribed gases contained in the exhaust gas by operating a CO-sensor 40 during the combustion, and an indoor environment monitoring parts 53 monitors the indoor air condition during the non-combustion by operating the CO-sensor 40. A low service frequency period judging part 55 finds the period of low probability where the combustion of a combustion device is in operation during the period with the predetermined period (e.g. one day) as a period, based on the past operation history, a cleaning control part 54 removes the pollution of the CO-sensor 40 at least once for each period, in a period of low probability of the combustion found out by the low service frequency period judging part 55.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion device provided with a detecting element for detecting the concentration of a predetermined gas contained in exhaust gas.

[0002]

2. Description of the Related Art A conventional combustion apparatus is generally provided with a CO sensor for detecting the concentration of carbon monoxide (CO), which is operated during combustion operation to monitor the presence or absence of incomplete combustion. ing. As a CO sensor, catalytic combustion that covers the element surface with a catalyst that reacts with carbon monoxide and detects the CO concentration by utilizing the fact that the resistance value of a resistor placed inside is changed by the reaction heat generated by the catalyst Formulas are commonly used.

In such a CO sensor, it is necessary to keep its surface clean at all times in order to ensure detection accuracy. Therefore, in the conventional combustion device, dirt is removed at the start of the combustion operation or at the end of the combustion operation.

[0004]

The time required from the start of the cleaning of the CO sensor to the return to the state where the concentration of carbon monoxide can be normally detected is about 40 seconds in the case of the catalytic combustion type. . Therefore, if cleaning is performed at the start of combustion, there is a problem that the exhaust state at the start of combustion, where incomplete combustion is likely to occur, cannot be monitored.

[0005] By the way, it is conceivable to use the CO sensor of the combustion device for monitoring the indoor air when the combustion operation is stopped. In this case, the CO sensor is extended without performing the combustion operation. A state in which time driving is continued may occur. For this reason, in the conventional technology in which the CO sensor is cleaned on the condition that the combustion starts or the combustion ends, the CO sensor remains in a dirty state, and the concentration of carbon monoxide contained in the indoor air is appropriately monitored. The problem arises that you cannot continue.

The present invention has been made in view of such problems of the prior art, and the cleaning operation does not hinder the detection operation during the combustion operation, and the cleaning operation is performed periodically regardless of the presence or absence of the combustion operation. It is an object of the present invention to provide a combustion device capable of cleaning a sensing element and a control method thereof.

[0007]

The gist of the present invention to achieve the above object lies in the following inventions. [1] In a combustion device provided with a detection element (40) for detecting the concentration of a predetermined gas contained in exhaust gas, a cleaning means (54) for removing dirt attached to the detection element (40), and a low use amount Frequency period determining means (55, 57), wherein the low usage frequency period determining means (55, 57) is provided.
Finds, based on a past operation history, a period during which the combustion device has a low probability of being burned in a predetermined period, based on a past operation history. Frequency period determination means (55, 5
A combustion device characterized in that the detection element (40) is cleaned during a period in which the probability of performing the combustion operation found in (7) is low.

[2] In a combustion device provided with a detecting element (40) for detecting the concentration of a predetermined gas contained in exhaust gas, a cleaning means (54) for removing dirt attached to the detecting element (40). , Low usage frequency period determining means (55, 57), combustion state monitoring means (52), and indoor environment monitoring means (53). The combustion state monitoring means (52) During the operation, the detection element (40) is operated to monitor the concentration of a predetermined gas contained in the exhaust gas, and the indoor environment monitoring means (53)
When the combustion device is not performing the combustion operation, the state of the indoor air is monitored by operating the detection element (40), and the low use frequency period determining means (55, 57) determines the predetermined period of time. The cleaning means (54) finds a period during which the combustion device has a low probability of being burned in the cycle based on the past operation history, and the cleaning means (54) determines the low use frequency period determining means (55, 57). A combustion device characterized in that the detection element (40) is removed of dirt prior to the operation of the indoor environment monitoring means (53) during a period in which the probability of performing the combustion operation is low.

[3] In a combustion device provided with a detecting element (40) for detecting the concentration of a predetermined gas contained in exhaust gas, a cleaning means (54) for removing dirt attached to the detecting element (40); , Low usage frequency period determining means (55, 57), combustion state monitoring means (52), and indoor environment monitoring means (53). The combustion state monitoring means (52) During the operation, the detection element (40) is operated to monitor the concentration of a predetermined gas contained in the exhaust gas, and the indoor environment monitoring means (53)
When the combustion device is not performing the combustion operation, the state of the indoor air is monitored by operating the detection element (40), and the low use frequency period determining means (55, 57) determines the predetermined period of time. The cleaning unit (54) finds a period during which the combustion device has a low probability of performing the combustion operation in the cycle based on the past operation history, and the cleaning unit (54) removes the contamination of the detection element (40). This is performed at least once every cycle, and this is performed in preference to the operation of the indoor environment monitoring means (53) during a period in which the probability of performing the combustion operation found by the low use frequency period determination means (55, 57) is low. A combustion device characterized by performing.

[4] In a combustion apparatus provided with a detecting element (40) for detecting the concentration of a predetermined gas contained in exhaust gas, a cleaning means (54) for removing dirt attached to the detecting element (40). A reservation unit (58) for receiving a reservation of a time at which cleaning of the sensing element (40) is to be performed, wherein the cleaning unit (54) comprises:
Each time the reserved time arrives, the detection element (4
0) A combustion device for removing dirt.

[5] In a control method of a combustion device provided with a detection element (40) for detecting a concentration of a predetermined gas contained in exhaust gas, a combustion operation is performed in a predetermined period as a period. A method for controlling a combustion apparatus, comprising: finding a period during which the probability of performing a combustion operation is low based on a past operation history; and removing dirt on the detection element (40) during a period during which the probability of performing a combustion operation is low.

The present invention operates as follows. The low use frequency period discriminating means (55, 57) finds a period in which the combustion device has a low probability of performing a combustion operation in a cycle of a predetermined period based on a past operation history, and performs cleaning. The means (54) removes dirt on the sensing element (40) during the period in which the probability of performing the combustion operation found by the low use frequency period determining means (55, 57) is low.

For example, the number of times the combustion operation is performed for each time zone in a cycle of one day is cumulatively stored, and the detection element (40) is cleaned during a period when the frequency of the combustion operation is low.
Since the detection element (40) is cleaned during the period in which the probability of performing the combustion operation found based on the past operation history is low, the concentration of carbon monoxide and the like contained in the exhaust gas from the start of the combustion operation. Can be detected. In addition, you may make it find a low usage frequency period with a cycle of one week or one month.

The combustion state monitoring means (52) activates the detection element (40) when the combustion device is performing a combustion operation to monitor the concentration of a predetermined gas contained in the exhaust gas. ) Monitors the state of indoor air by operating the detection element (40) when the combustion device is not performing a combustion operation. The cleaning means (54) has a higher priority than the operation of the indoor environment monitoring means (53) during the period in which the probability of performing the combustion operation found by the low usage frequency period determining means (55, 57) is low. Remove dirt.

Thus, during the non-combustion operation, the detection element (4
Even when the detection element (4) is operated for monitoring the indoor environment, the detection element (4) is set in a period in which the combustion operation is unlikely to be performed (the period is usually a period in which the indoor environment monitoring operation is to be performed).
Since the cleaning of 0) is performed prior to the monitoring operation of the indoor environment, even if the detection element (40) is also used for monitoring the indoor environment, the cleaning element such as carbon monoxide contained in the exhaust gas from the start of the combustion operation. The density can be detected. In addition, since the concentration of carbon monoxide and the like does not change suddenly in the indoor environment as in the combustion operation, even if the cleaning operation is performed prior to the indoor environment monitoring operation, the monitoring operation is hardly affected. .

Further, the cleaning means (54) removes dirt from the detection element (40) at least once in a predetermined cycle, and removes the same from the combustion detected by the low use frequency period discriminating means (55, 57). Perform during periods when the probability of driving is low. As described above, since the cleaning operation is performed at least once in each cycle, even if the combustion operation is not performed for a long time, the detection element (40) is not left in a state where the detection element (40) is still dirty.

In addition, when the cleaning operation is performed at a reserved time, for example, if a time when there is almost no possibility of performing the combustion operation such as at night is reserved, the cleaning operation can be performed without competing with the combustion operation. It can be carried out.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Each drawing shows an embodiment of the present invention. Water heater 10 as a combustion device according to the present embodiment is installed indoors, takes in the air in the room into the appliance, supplies air to burner 22, and discharges exhaust air to the outside through an exhaust pipe. FE) is adopted.

As shown in FIG. 2, a housing 11 which is a main body of the water heater 10 has a box shape, and an air supply port 12 for taking indoor air into the appliance is provided on a right side surface thereof.
Has been established.

A combustion chamber 21 is provided at a substantially central portion in the housing 11, a burner 22 is provided at a lower portion thereof, and a heat exchanger 23 is provided at an upper portion for heating water by heat from the air supply port 12. Is arranged.

At the lower left end of the combustion chamber 21, there is provided a combustion fan 24 for feeding air taken in from the air supply port 12 to the burner 22, and an exhaust port 25 is provided at the center of the upper surface of the combustion chamber 21. . An exhaust pipe (not shown) communicating with the outside is connected to the exhaust port 25. At the upper right end of the combustion chamber 21, a CO sensor 40 for detecting a concentration of carbon monoxide (CO) and the like is attached. C
The location of the O sensor 40 is a location where the wind from the combustion fan 24 does not directly hit and where the exhaust does not stop.

The CO sensor 40 detects the concentration of carbon monoxide contained in the exhaust gas during the combustion operation for burning the burner 22, and operates the combustion fan 24 at a low speed when the combustion operation is not performed. When rotated, the indoor air is taken into the apparatus, and the CO sensor 40 is used for monitoring the indoor environment for monitoring the concentration of carbon monoxide and methane contained in the indoor air.

A gas supply path 26 leading to the burner 22 has a source gas solenoid 27, a gas solenoid valve 28, a gas proportional valve 29,
Various valves such as a gas capacity switching valve 30 are attached. In addition, adjacent to the burner 22, the igniter electrode 3
1 and a frame rod electrode 32 are arranged.

Water supply pipe 3 leading to the inlet of heat exchanger 23
In the middle of 3, an incoming water thermistor 34 for detecting the supply water temperature
And a water amount sensor 35 for detecting the flow rate at the time of tapping. Hot water supply pipe 36 extending from the outlet side of heat exchanger 23
Is provided with a flow control valve 37 for controlling the total flow rate of hot water to be discharged, and the water supply pipe 3 bypassing the heat exchanger 23.
A flow control valve 39 for controlling a bypass ratio is provided in a bypass passage 38 connecting the hot water supply pipe 3 and the hot water supply pipe 36.

An operation section 13 provided with an operation switch for receiving various operations such as temperature setting of hot water and a small liquid crystal display is provided at a lower front portion of the housing 11. The operation unit 13 includes an alarm lamp 15 and an alarm buzzer 16 for notifying when the concentration of carbon monoxide or methane contained in the indoor air exceeds the allowable upper limit.

At the upper right end in the housing 11, a control board 50 for controlling various controls in the water heater 10 is arranged. The control board 50 mainly includes a CPU (Central Processing Unit) (not shown), a ROM for storing programs and various fixed data, a RAM for temporarily storing data required for executing the programs, and the like. It is composed of a circuit as a unit.

FIG. 3 shows the configuration of the CO sensor 40. The CO sensor 40 is obtained by connecting a detection element 41 of a contact combustion type and a comparison element 42 for temperature compensation in series.
The detection element 41 and the comparison element 42 are arranged close to each other.

The contact combustion type detecting element 41 includes a resistor 43
Is wrapped in a ceramic 44 and its surface is covered with a catalyst 45 that generates heat in response to a combustible gas such as carbon monoxide. The resistance value of the internal resistor 43 is changed by heat generated by the reaction of the catalyst 45 on the surface with the combustible gas in the atmosphere. The comparison element 42 includes the resistor 4
6 is covered with a ceramic 47. The detection of the concentration of carbon monoxide or the like is performed based on the voltage (Vsns) across the detection element 41 by driving the detection element 41 and the comparison element 42 at a constant current. In practice, the voltage across the detection element 41 is equal to the voltage across the comparison element 42 (Vre
The temperature is compensated by f), and the voltage across the sensing element 41 after the temperature compensation indicates the concentration of carbon monoxide or the like.

The CO sensor 40 is driven at a constant current of about 170 mA when detecting carbon monoxide, and is driven at a constant current of 200 to 220 mA when detecting the concentration of methane. When removing dirt adhering to the surface of the sensing element 41, a current of about 240 milliamperes is passed through the CO sensor 40 to raise the temperature of the element surface to remove dirt. Such a heat cleaning is performed in a state where the concentration of carbon monoxide or the like can be detected again after the heat cleaning is started, that is, until the temperature of the element surface decreases to a temperature that reacts with carbon monoxide or the like.
It takes seconds.

FIG. 1 shows a control board 50 of the water heater 10.
Represents a functional configuration. Although not shown, various components related to the control of the water heater 10, such as the combustion fan 24 and the gas solenoid valve 28, are electrically connected to the control board 50.

The control board 50 is provided with a hot water supply operation control section 51 for performing overall control of hot water supply operations such as ignition and extinguishing of the burner 22 and adjustment of the amount of supplied gas. When the water heater 10 is performing a combustion operation, the combustion state monitor 52
This is a circuit part for monitoring the carbon monoxide contained in the exhaust gas by operating the CO sensor 40. The indoor environment monitoring unit 53 is a circuit portion that monitors the state of indoor air by operating the CO sensor 40 when the water heater 10 is not performing a combustion operation. The combustion state monitoring unit 52 and the indoor environment monitoring unit 53
Based on the state information from the hot water supply operation control unit 51, it is determined whether or not the water heater 10 is burning.

The cleaning control unit 54 includes the CO sensor 4
0 is a circuit part for removing dirt adhering to the element surface by driving at a constant current of 240 mA for several tens of seconds.
The low-frequency period discriminating unit 55 is a part that performs a function of finding a period during which the water heater 10 has a low probability of performing the combustion operation in the cycle based on a predetermined operation period based on a past operation history. . Here, the operation is performed so as to find a time zone in which the probability of performing the combustion operation in one day is low with a cycle of one day.

The clock section 56 is a circuit section for counting the current date, day of the week, and time, and the operation history storage section 57 is a section for storing the history of the combustion operation. The reservation unit 58 uses CO
This is a circuit part for registering a reservation time as a time at which a dirt removal operation of the sensor 40 is performed.

The hot water supply operation control section 51 outputs a signal indicating whether or not the water heater 10 is performing a combustion operation.
Stores the time at which the combustion operation is started and the time at which the combustion operation is ended based on the signal and the time information from the clock unit 56. More specifically, the day is divided into 48 time zones of 30 minutes, and the number of times the water heater 10 has been operated for combustion is accumulated and stored for each time zone.

The cleaning control unit 54 sets the CO sensor 40 every time the time set in the reservation unit 58 comes.
And the CO sensor 4 at the time designated by the low frequency period discriminating section 55.
And a low frequency period priority mode for performing heat cleaning of 0. The initial value of the reserved time is set in advance at 2 o'clock in the night or the like, and the time can be changed to a desired time through the operation unit 13.

When the appliance is initially installed, it operates in the reserved time priority mode. When a predetermined amount of data (for example, data for one week from the start of energization after installation) is stored in the low frequency period discriminating section 55, the low The mode is switched to the frequency period priority mode. The reservation time priority mode and the low frequency period priority mode can be arbitrarily switched from the operation unit 13.

Next, the operation will be described. The water heater 10 emits the CO sensor 40 by the combustion state monitor 52 until the burner 22 is ignited, the burner 22 is extinguished, and then the post-fan operation for discharging the exhaust gas in the combustion chamber 21 to the outside is terminated. To monitor the concentration of carbon monoxide contained in the exhaust gas. On the other hand, when the combustion operation is not being performed as described above, the indoor environment monitoring unit 53 monitors the state of indoor air.

When monitoring the state of indoor air, the indoor environment monitor 53 drives the combustion fan 24 at a low speed to take indoor air into the appliance, and uses the CO sensor 40 to measure the concentration of carbon monoxide. The methane concentration is monitored alternately at predetermined intervals. That is, the period during which the CO sensor 40 is driven at a constant current of 170 mA and the CO sensor 40
Periods of constant current driving at 0 to 220 mA are alternately provided.

Here, the detected carbon monoxide concentration is 2
Over 100 ppm and when the methane concentration is 1.2
When it exceeds 5%, it is notified through the alarm lamp 15 and the alarm buzzer 16 that an abnormality has occurred in the indoor environment. Further, when such an alarm condition occurs, the combustion fan 24
Is driven at a high speed to exhaust the indoor air to the outside to perform ventilation.

The operation history storage unit 57 stores the hot water supply operation control unit 5
Status information indicating whether the combustion operation is in progress or not and the clock unit 56
The time when the combustion operation was started and the time when the combustion operation was ended are stored in an internal memory based on the time information from. The operation history storage unit 57 includes 48 storage areas in which a day is divided every 30 minutes, and accumulates and stores the number of times the combustion operation is performed for each time period.

FIG. 4 shows the contents stored in the operation history storage unit 57. In this example, a time zone 61 from 6:30 to 8:00 and a time zone 62 from 11:00 to 12:30.
The combustion operation is performed in a time zone 63 from 16:30 to 19:30. Then, a time zone 64 from 8:30 to 11:00, a time zone 65 from 12:30 to 16:30, and a time zone 6 from 19:30 to the next day.
The combustion operation is not performed in the time period 66 until 1:30. Here, based on the history of the combustion operation in the past week, the distribution of the use frequency for each time zone as shown in FIG. 4 is created.

The low frequency period discriminating section 55 finds a low usage frequency period in which the probability of performing the combustion operation is low, based on the combustion operation history stored in the operation history storage section 57.
In the example shown in FIG. 4, the time zones 64 to 66 are low usage frequency periods. Further, the low frequency period determination unit 55 sets the CO sensor 40
To determine when to heat clean. For example, a low usage frequency period is preferentially selected in descending order of unused periods, and a time at the center of the selected time zone is determined as a heat cleaning start time. In the example of FIG. 4, since the low usage frequency period 66 at night is the longest, the time at the center, 1:00 of the night, is set as the heat cleaning start time.

Alternatively, a low use frequency period 66 appearing after the time zone 63 in which the combustion operation is performed most frequently is selected.
The heat cleaning start time is set to the time at the center or the time when a predetermined time (for example, one hour) has elapsed from the beginning of the low usage frequency period 66. By performing the heat cleaning as early as possible while securing a certain margin after entering the low use frequency period, the clean state of the CO sensor 40 can be ensured for a long time.

In addition, the number of times of performing the heat cleaning may be increased according to the length of the combustion operation time per day. At this time, a plurality of heat cleaning start times are selected according to the above criteria. Alternatively, the start times may be selected such that a plurality of heat cleaning start times are evenly distributed in each low usage frequency period.

Even if the combustion operation is not performed at all for one or several days and the time period corresponds to the low-use frequency period, the low-frequency period discriminating unit 55 performs at least once a day. Set the start time so that cleaning is performed. Conversely, even when the combustion operation is being performed throughout the day, a time zone that is relatively infrequently used is selected.

When the heat cleaning start time determined by the low frequency period determination unit 55 has arrived, the cleaning control unit 54 temporarily suspends the indoor air monitoring operation by the indoor environment monitoring unit 53 and causes the CO sensor 40 to operate. The flowing current is increased to 240 mA to perform the heat cleaning operation. As described above, since the heat cleaning of the CO sensor 40 is performed during the time period in which the probability of performing the combustion operation is low, the concentration of carbon monoxide or the like can be detected immediately from the start of combustion. Further, since the heat cleaning is performed at least once a day even if the combustion operation is not performed, even if the period during which the CO sensor 40 is used only for the monitoring operation of the indoor environment continues for a long time, the CO sensor 40 is always operated. The surface can be kept clean.

If the combustion operation is being performed at the time when the heat cleaning start time has arrived, the heat cleaning operation is performed after the completion of the combustion operation. On the other hand, when the combustion operation starts during the heat cleaning operation, the heat cleaning operation is continuously performed. Alternatively, whether or not to interrupt the heat cleaning may be selected according to how far the heat cleaning operation has progressed and the combustion operation has been started.

The cleaning control unit 54 sets the CO sensor 40 every time the time set in the reservation unit 58 comes.
And the CO sensor 4 at the time designated by the low frequency period discriminating section 55.
And a low frequency period priority mode for performing heat cleaning of 0. The initial value of the reservation time is set in advance at 2:00 at night, and the reservation time can be changed to a desired time through the operation unit 13.

Also, here, when the appliance is installed, it operates in the reserved time priority mode, and when a predetermined amount of data (for example, data for one week from the start of energization after installation) is stored in the low frequency period discriminating unit 55. Then, the mode is switched to the low frequency period priority mode. The reservation time priority mode and the low frequency period priority mode can be arbitrarily switched from the operation unit 13.

In the embodiment described above, the history of the combustion operation is obtained on a cycle of one day to find the low use frequency period. However, as shown in FIG. Then, the heat cleaning start time may be determined based on the usage frequency distribution for each day of the week.

For example, the frequency of use for each time period in one day shown in FIG. 4 is individually accumulated for each day of the week, and the heat cleaning start time and the number of times of heat cleaning for the day of the week are accumulated according to the operation history of each day of the week. To be set. That is, when used for business in restaurants and the like, the frequency of combustion operation varies depending on weekdays, weekends, holidays, etc., so every weekday or weekday, Saturday, Sunday,
If the frequency of use is managed for each holiday, etc., heat cleaning can be performed at a more appropriate timing and frequency.

In addition, in the embodiment, both the operation in the reservation time priority mode and the operation in the low frequency period priority mode are provided, but the operation is performed in only one of these modes. Is also good. For example, only a function to perform heat cleaning according to the reservation time is provided,
The heat cleaning may be performed every day at 2 o'clock at night.

The storage format of the operation history is not limited to the one exemplified in the embodiment. Further, the heat cleaning start time may be determined based on fuzzy logic or various learning functions.

[0054]

According to the combustion apparatus and the control method thereof according to the present invention, a period in which the probability of combustion operation is low is found based on the past operation history, and the sensing element is cleaned during the low use frequency period. It is possible to detect the concentration of carbon monoxide and the like contained in the exhaust gas from the start of the combustion operation.

Further, even when the detection element is operated for monitoring the indoor environment during the non-combustion operation, the cleaning of the detection element is performed prior to the operation for monitoring the indoor environment during a period in which the probability of the combustion operation is low. Even if the detection element is also used for monitoring the indoor environment, the concentration of carbon monoxide and the like contained in the exhaust gas can be detected from the start of the combustion operation.

Further, at least one for every predetermined cycle
Since the sensor is cleaned at the time, the combustion operation is not performed, and even if the sensor is used for a long time only for monitoring the indoor environment, it is not left as it is in a dirty state, It is possible to accurately monitor the indoor environment.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a combustion device according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a combustion device according to one embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a contact combustion type detection element according to one embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an example of a time-based distribution of a frequency at which a combustion operation is performed.

FIG. 5 is an explanatory diagram showing an example of the distribution of the frequency at which a combustion operation is performed for each day of the week.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Hot water supply 12 ... Air supply port 13 ... Operation part 15 ... Warning lamp 16 ... Warning buzzer 21 ... Combustion chamber 22 ... Burner 23 ... Heat exchanger 24 ... Combustion fan 25 ... Exhaust port 40 ... CO sensor 50 ... Control board 51 ... hot water supply operation control unit 52 ... combustion state monitoring unit 53 ... indoor environment monitoring unit 54 ... cleaning control unit 55 ... low frequency period discrimination unit 56 ... clock unit 57 ... operation history storage unit 58 ... reservation unit

Claims (5)

[Claims] 1. A combustion device provided with a detecting element for detecting a concentration of a predetermined gas contained in exhaust gas, comprising: a cleaning means for removing dirt attached to the detecting element; and a low use frequency period determining means. The low use frequency period determining means finds a period in which the combustion device has a low probability of performing a combustion operation in a cycle of a predetermined period based on a past operation history, and the cleaning means. The present invention relates to a combustion apparatus, wherein a dirt on the detection element is removed during a period in which the probability of performing the combustion operation found by the low use frequency period determination means is low. 2. A combustion apparatus comprising a detecting element for detecting a concentration of a predetermined gas contained in exhaust gas, wherein a cleaning means for removing dirt attached to the detecting element, a low-use frequency period determining means, State monitoring means, and an indoor environment monitoring means, wherein the combustion state monitoring means monitors the concentration of a predetermined gas contained in exhaust gas by operating the detection element when the combustion device is performing a combustion operation; The indoor environment monitoring unit monitors the state of indoor air by operating the detection element when the combustion device is not performing a combustion operation, and the low use frequency period determining unit periodically cycles a predetermined period. In the cycle, a period during which the combustion device has a low probability of being burned is found based on a past operation history, and the cleaning unit looks at the low use frequency period determining unit. Combustion apparatus, characterized in that the low probability of being issued the combustion operation interval in preference to operation of the indoor environment monitoring means to remove dirt of the detection device. 3. A combustion device having a detection element for detecting a concentration of a predetermined gas contained in exhaust gas, wherein a cleaning means for removing dirt attached to the detection element, a low-use frequency period discriminating means, State monitoring means, and an indoor environment monitoring means, wherein the combustion state monitoring means monitors the concentration of a predetermined gas contained in exhaust gas by operating the detection element when the combustion device is performing a combustion operation; The indoor environment monitoring unit monitors the state of indoor air by operating the detection element when the combustion device is not performing a combustion operation, and the low use frequency period determining unit periodically cycles a predetermined period. The cleaning means finds a period during which the combustion device has a low probability of being burned in the cycle based on the past operation history, and the cleaning means removes dirt from the detection element every cycle. At least performs once, combustion apparatus, which comprises carrying out in preference it to the operation of the indoor environment monitoring means during periods of low probability of the being-burn operation has been found by the low frequency of use period determination means. 4. A combustion device provided with a detecting element for detecting a concentration of a predetermined gas contained in exhaust gas, a cleaning means for removing dirt attached to the detecting element, and a time when the detecting element should be cleaned. A combustion unit, wherein the cleaning unit removes dirt from the detection element every time the reserved time arrives. 5. A control method for a combustion device provided with a detection element for detecting a concentration of a predetermined gas contained in exhaust gas, wherein a probability of performing a combustion operation in a predetermined period is set as a period. A method for controlling a combustion apparatus, comprising: finding a low period based on a past operation history; and removing dirt on the detection element during a period in which the probability of performing the combustion operation is low.