JPH0894072A - Combustion state deciding method for hot water feeder - Google Patents

Abstract

PURPOSE: To detect worsening of a combustion state from the change of the control state of a combustion amount without using a sensor by a method wherein it is decided that the combustion state of a hot water feeder is worsened when a feedback control amount attains the limit value of a controllable range or the vicinity of a limit value. CONSTITUTION: A control device for a hot water feeder comprises an FF computing part 15 to compute an FF combustion amount according to which feedforward(FF) control of a gas proportional valve 13 is effected, and an FB computing part 16 to compute an FB combustion amount according to which feedback(FB) control of the gas proportional valve 13 is executed. An output combustion amount is decided based on an FF combustion amount and an FB combustion amount by a combustion amount setting part 17. Further, a deciding part 28 to store a limit value of an FB combustion amount is provided and an FB combustion amount inputted thereto is compared with a limit value. When an FB combustion amount attains a limit value, transfer to safety operation is effected to close an on-off valve 12, and control is executed so that combustion of a gas burner is forcibly stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a combustion state of a water heater. Specifically, it relates to a method for determining deterioration of a combustion state due to fin clogging of a heat exchanger used in a water heater.

[0002]

2. Description of the Related Art In a water heater, the gas burned by a gas burner and water are heat-exchanged by a heat exchanger to heat the water by the combustion heat of the gas. However, since the gas contains water, when the water heater is used for a long time at low temperature hot water, dew is condensed on the fins of the heat exchanger and the fins are corroded by the dew condensation. As a result, the heat exchanger is clogged with fins, the exhaust of the air that is forcibly supplied from the gas burner side to the heat exchanger deteriorates, and the combustion state of the gas burner deteriorates due to the exhaust blockage of the can body. There is a problem.

As a measure against the deterioration of the combustion state due to the fin clogging, the deterioration of the combustion state is detected by measuring the harmful components in the exhaust gas with a CO (carbon monoxide) sensor or the like. It has been proposed that the combustion of the gas burner is stopped when the deterioration exceeds a certain limit.

[0004]

However, the method of detecting the deterioration of the combustion state due to the fin clogging in this way is not widely used because of the problem in the reliability of the sensor. Further, since the sensor and its processing circuit are required, there is a drawback that the product cost increases.

The present invention has been made in view of the drawbacks of the above-mentioned conventional examples, and an object thereof is to use a sensor or the like to change the control state of the combustion amount and to change the combustion state due to fin clogging or the like. Is to be able to detect the deterioration of.

[0006]

A method for determining a combustion state of a water heater according to the present invention is such that a controllable range of a feedback control amount is preset in a water heater in which feedback control is used in combination with feedforward control to control the combustion amount. It is characterized in that it is set in advance, and when the feedback control amount reaches the limit value of the controllable range or near the limit value, it is determined that the combustion state of the water heater has deteriorated.

For example, when the feedback control amount reaches the limit value of the controllable range, combustion can be stopped.

Further, when the feedback control amount reaches the vicinity of the limit value of the controllable range, preliminary processing such as fan speed correction and display of deterioration of combustion state may be performed.

[0009]

Operation Even if the water heater is initially feed-forward controlled, if the fins of the heat exchanger are clogged, the heat exchange efficiency will decrease and the outlet water temperature will decrease. When the outlet heated water temperature decreases, feedback control is added to the feedforward control to control the heated outlet water temperature to match the set temperature. When the fin clogging further proceeds, the feedback control amount increases in order to discharge the hot water having the set temperature.

According to the present invention, in such a water heater, the controllable range of the feedback control amount is set in advance. For example, the controllable range of the feedback control amount can be determined corresponding to the allowable combustion state by experimentally examining the relationship between the combustion state and the feedback control amount, which gradually deteriorate due to fin clogging. Therefore, when it reaches the limit value or near the limit value of this controllable range, it can be determined that the combustion state of the water heater is deteriorated, and the combustion of the water heater can be stopped according to the determination result. It is possible to correct the fan rotation speed and output a display indicating deterioration of the combustion state.

[0011]

FIG. 1 is a schematic configuration diagram showing a water heater A according to an embodiment of the present invention. The heat exchanger 1 is housed in a can body 2, and a gas burner 3 is provided below the heat exchanger 1 in the can body 2.
Is provided. Further, a fan 4 for forcibly supplying combustion air to the gas burner 3 is provided at the bottom of the can body 2, and an exhaust port 5 is opened at the upper surface of the can body 2. Then, the water flowing through the heat exchanger 1 is heated by exchanging heat with the combustion gas burned by the gas burner 3, and is discharged as hot water. The fan 4 rotates at a predetermined fan rotation speed so that the gas burner 3 burns at an optimum air-fuel ratio, and the combustion air supplied from the fan 4 is heated by the gas burner 3 and the fins of the heat exchanger 1 together with the combustion gas. It passes between 1a and is exhausted to the outside from the exhaust port 5.

A water inlet pipe 6 connected to the water inlet side of the heat exchanger 1.
Is provided with a water amount sensor 7 for detecting the incoming water flow rate Q and an incoming water temperature sensor 8 such as a thermistor for detecting the incoming water temperature T _C , and a hot water outlet pipe 9 connected to the hot water outlet side of the heat exchanger 1. The discharge temperature T _H of the hot water heated in the heat exchanger 1 is
A hot water temperature sensor 10 for detecting the temperature is provided.

A gas supply pipe 11 connected to the gas burner 3.
An on-off valve 12 and a gas proportional valve 13 are provided in the engine 1. By controlling the opening of the gas proportional valve 13, the combustion amount of the water heater A, that is, the combustion amount of the gas burner 3 can be controlled. There is.

As shown in FIG. 1, the control device 14 receives the respective detection signals of the water amount sensor 7, the incoming water temperature sensor 8 and the hot water outlet temperature sensor 10, and inputs them to the fan motor 26, the on-off valve 12 and the gas proportional valve 13. A control signal is output to control the fan 4, the on-off valve 12, and the gas proportional valve 13.

FIG. 2 is a block diagram showing the configuration of the control device 14 in detail. The controller 14 uses the gas proportional valve 13
FF calculation unit 15 for calculating the FF combustion amount G _FF for feed-forward (hereinafter referred to as FF) control, and FB combustion amount G _FB for feedback (hereinafter referred to as FB) control of the gas proportional valve 13 It has a FB calculation unit 16 for calculating a combustion amount setting unit 17 based on the FB combustion quantity G _FB calculated in FF combustion amount GF _F and FB calculation unit 16 calculated by the FF operation unit 15 The output combustion amount G ₀ is determined.
The FF calculation unit 15 includes a flow rate detection circuit 18 of the water amount sensor 7.
From the water quantity sensor 7 detected by the water quantity sensor 7, the water temperature T _C detected by the water temperature sensor 8 from the water temperature detection circuit 19 of the water temperature sensor 8, and the remote controller from the temperature setting circuit 20 of the remote controller. The respective signals indicating the set temperature T _S thus set are input, and the FF calculation unit 15 calculates the FF combustion amount G _FF = ρ (T _S −T _C ) Q on the basis of these data Q, T _C , and T _S. Is calculated and the value of the FF combustion amount G _FF is output to the combustion amount setting unit 17. Here, ρ is the heat exchange efficiency of the heat exchanger 1, and a predetermined value (constant value) is used. Also, FB
The arithmetic unit 16 includes a water inlet flow rate Q detected by the water amount sensor 7 from the flow detection circuit 18, a hot water temperature T _H detected by the hot water temperature sensor 10 from the hot water temperature detector 21 for the hot water temperature sensor 10, temperature setting Each signal indicating the set temperature T _S set by the remote controller is input from the circuit 20, and the FB calculation unit 16 calculates the FB combustion amount G _FB by the proportional integral calculation based on these data Q, T _H , and T _S. Is calculated. That, FB calculation unit 16 calculates the _{G FB = K P (T S} -T H) Q + (1 / K I) S (T S -T H) Q · dt FB combustion quantity G _FB by ....... Where K _P and K _I
Are a proportional constant and an integral constant of proportional-integral (PI) control, respectively. Further, S ... · dt is an integral symbol. The FB calculation unit 16 outputs the value of the FB combustion amount G _FB thus calculated to the combustion amount setting unit 17. In the combustion amount setting unit 17, FF
FF combustion amount G _FF calculated by the calculation unit 15 and FB calculation unit 1
The FB combustion amount G _FB calculated in 6 is added to obtain the output combustion amount G ₀ = G _FF + G _FB . When the combustion amount setting unit 17 obtains the set amount,
The signal is output to the proportional valve current setting unit 22 and the fan motor rotation speed setting unit 23. In the proportional valve current setting unit 22,
Set the value of proportional valve current according to the value of output combustion amount G ₀ ,
A proportional valve current having a set value is flown from the proportional valve drive circuit 24 to the gas proportional valve 13 to control the gas proportional valve 13, and the gas burner 3 is burned at a set output combustion amount G ₀ to generate hot water having a set temperature T _S. Let the hot water come out. On the other hand, the fan motor rotation speed setting unit 23
Then, the fan motor rotation speed is set according to the value of the output combustion amount G ₀ , and the fan motor drive circuit 25 causes the fan motor 26 to rotate at the set fan rotation speed so that the gas burner 3 has the optimum air-fuel ratio. Supply combustion air.
Reference numeral 27 denotes a rotation speed detection circuit that detects the rotation speed of the fan motor 26, and the fan motor drive circuit 25 uses a feedback signal from the rotation speed detection circuit 27 so that the fan motor rotation speed becomes equal to the set value. It has feedback control.

A water heater A having such a control device 14
In the normal state (or the ideal state), the combustion amount is controlled only by the FF control, and the output combustion amount G ₀ = G _FF . That is, the FF shown in FIG.
In the relationship between the combustion amount G _FF and the output combustion amount G ₀ , the straight line G ₀ = G
_The output combustion amount G ₀ is controlled on _FF . However, if the heat exchanger 1 is clogged with fins, the heat exchanger 1
Heat exchange efficiency ρ used in the above equation
Value (default value), and the hot water outlet temperature T _H becomes lower than the set temperature T _S only by FF control. Therefore,
In such a case, the FB control comes to operate in addition to the FF control, and the set temperature T _{S is} controlled by the FF control and the FB control.
Now, the control state is straight line G _{0 in} FIG.
= G _FF deviates from above. In this way, as the fin clogging of the heat exchanger 1 progresses and the combustion state deteriorates, the FB control gradually becomes stronger and the FB control in the output combustion amount G ₀ is increased.
The ratio of the combustion amount G _FB is increasing and the control state is shown in Fig. 3.
The straight line G ₀ = G _{FF is} getting farther away.

As described above, the degree of deterioration of the combustion state due to the fin clogging of the heat exchanger 1 and FB in the output combustion amount G ₀
Since a certain relationship is recognized with the magnitude of the combustion amount G _FB , it is possible to experimentally determine the controllable range (normal range) corresponding to the safe and allowable combustion state. For example,
If the FB combustion amount G _FB becomes larger than G _FB max (> 0), it becomes a dangerous state, and if it becomes smaller than G _FB min (<0), it becomes a dangerous state. It is possible to set G _FB min <G _FB <G _FB max or G _FF + G _FB min <G ₀ <G _FF + G _FB max ........, which is the shaded area in FIG.
In this case, the limit values of the controllable range are G ₀ = G _FF + G _FB max (or G _FB = G _FB max) ...... G ₀ = G _FF + G _FB min on the upper limit side and the lower limit side, respectively. (Or G _FB = G _FB min) ...... Further, in the vicinity of the upper side of the limit value _{G 0 = G FF + G FB} max and the lower limit of the limit value _{G 0 = G F F + G} FB min is a limit value close G ₀ = G _FF + G for each preprocessing _FB u (or G _FB = G _FB u) ... G ₀ = G _FF + G _FB d (or G _FB = G _FB d). However, G _FB min <G _FB d <0 <G _FB u <G _FB max. In FIG. 3, this limit value G ₀ = G _FF + G _FB m
The ax and G ₀ = G _FF + G _FB min are represented by a solid line, and the near limit values G ₀ = G _FF + G _FB u and G ₀ = G _FF + G _FB d are represented by a chain line. Since the FB combustion amount G _FB gradually increases, only the upper limit value G ₀ = G _FF + G _FB max needs to be set. However, as shown in the equation or FIG. If a limit value is set on the side, for example, combustion abnormality when the fuel gas with a higher calorie than planned is supplied or when the FF combustion amount G _FF becomes excessive due to abnormality such as misadjustment of the gas proportional valve Will also be detectable.

In order to determine whether the control state is near the limit value or exceeds the limit value, the output combustion amount G ₀ output from the combustion amount setting unit 17 is monitored, and this output combustion amount G ₀ is
It may be compared with a limit value or a value near the limit defined by the formula. However, it is easier to monitor the FB combustion amount G _FB output from the FB calculation unit 16 and compare this FB combustion amount G _FB with the limit value or the limit vicinity value defined by the expression in the parentheses of ~. Therefore, the judgment processing efficiency is improved. Therefore, in the control device 14 shown in FIG. 2, the limit values G _FB max and G _FB min of the FB combustion amount G _{FB and} the values of the limit neighboring values G _FB u and G _FB d are stored in the determination unit 28 in advance. . This determination unit 28 has F
The value of the FB combustion amount G _FB calculated by the B calculation unit 16 is input, and the input FB combustion amount G _FB is set to the limit value G _FB ma
The values are compared with x, G _FB min and the near limit values G _FB u, G _FB d.
When the FB combustion amount G _FB reaches the limit neighborhood value G _FB u or G _FB d, the display unit (not shown) of the remote controller
An error message is displayed on the screen to prompt the user to repair and inspect the water heater A, and the fan rotation speed calculation formula (fan rotation speed calculation table) of the fan motor rotation speed setting unit 23 is corrected to compensate for the air shortage due to fin clogging. . Furthermore, FB combustion amount G
_{When FB} reaches the limit value G _FB max or G _FB min, the safe operation is started, the on-off valve 12 is closed, and the combustion of the gas burner 3 is forcibly stopped.

FIG. 4 is a flow chart showing a procedure for determining the combustion state by the control device 14 and performing necessary processing. First, when water flows through the water heater A, it is determined whether the minimum operating flow rate (MOQ) is on (that is, the water flow rate Q ≧ MOQ) or off (that is, the water flow rate Q <MOQ) (S3).
1) If the MOQ is off, the water heater A is maintained in the combustion stopped state or the combustion is stopped (S32). If the MOQ is on, it is checked whether or not the gas burner 3 is in steady combustion (S33). If it is not in steady combustion, the ignition sequence is executed to make the gas burner 3 steady combustion (S3).
4). During the steady combustion, the combustion amount setting unit 17 outputs the output combustion amount G ₀ = G _FF from the FF combustion amount G _FF calculated by the FF calculation unit 15 and the FB combustion amount G _FB calculated by the FB calculation unit 16.
+ G _FB is calculated (S35), and the gas proportional valve 13 is controlled based on this to control the combustion amount. Then, the determination unit 28
Determines whether the FB combustion amount G _FB has reached the limit neighboring value G _FB u or G _FB d (S36), and the controllable range inside the limit neighboring value (G _FB d <G _FB <G _FB u) If it is, the flow from the original step S31 is repeated. In contrast,
When the control state exceeds the limit value, G _FB ≧ G _FB u or G _FB ≦
When it is determined that G _FB d, FB combustion amount G
_It is determined whether _FB has reached the limit value G _FB max or G _FB min (S37), and the controllable range (G _FB mi
In the case of n <G _FB <G _FB max), the combustion state is maintained after correcting the fan rotational speed calculation formula and displaying an error (S38). On the other hand, when the control state exceeds the limit value and it is determined that G _FB ≧ G _FB max or G _FB ≦ G _FB min, the on-off valve 12 is closed to combust compulsorily (S39).

FIG. 5 is a diagram showing how to set another limit value and another value near the limit according to the method of the present invention. In FIG. 3, the values of the FB combustion amount limit values G _FB max and G _FB min and the limit neighboring values G _FB u and G _F Bd are constants that do not depend on the FF combustion amount G _FF , but in FIG. 5, G _FB max, G _F Bmin, G _FB u, and G _FB d are F
Since it is a function of the F combustion amount G _FF , more delicate determination can be made possible. For this purpose, it is necessary to transmit the calculated value of the FF combustion amount G _FF to the determination unit 28 also from the FF calculation unit 15 as shown by the broken line in FIG. Further, as shown in FIG. 5, a plurality of sets of limit neighborhood values G ₀ = G _FF + G _FB u and G ₀ = G _FF + G _FB d are set, and different limit neighborhood values G ₀ = G _FF +
The fan rotation speed may be corrected stepwise for each G _FB u and G ₀ = G _FF + G _FB d. Alternatively, the fan speed is corrected with the inner limit neighboring values G ₀ = G _FF + G _FB u and G ₀ = G _FF + G _FB d, and the outer limit neighboring values G ₀ = G _FF + G _FB u.
And G ₀ = G _FF + G _FB d may be displayed as an error.

[0021]

According to the present invention, the controllable range of the feedback control amount is set, and the combustion state of the water heater deteriorates when the limit value of this controllable range or the vicinity of the limit value is reached. To determine. Therefore, it suffices to set a controllable range on a program and monitor whether or not the feedback control amount has reached its limit value or near the limit value. As in the conventional method, a sensor such as a CO sensor or a sensor It is possible to monitor the combustion state of the water heater at an inexpensive cost without the need for the processing circuit of FIG.

Further, since it does not depend on the sensitivity or reliability of the sensor such as CO sensor, the deterioration or abnormality of the combustion state can be accurately detected and the reliability can be improved.

For example, when the feedback control amount reaches the limit value of the controllable range, incomplete combustion of the water heater can be prevented by stopping the combustion, and the safety of the water heater can be improved. Further, when the feedback control amount reaches the vicinity of the limit value of the controllable range, it is possible to improve the deteriorated combustion efficiency by performing the fan rotation speed correction. Alternatively, it is possible to prevent the deterioration of the combustion state to the limit by prompting the user for repair and inspection by outputting a display indicating the deterioration of the combustion state.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a water heater according to the present invention.

FIG. 2 is a block diagram showing a configuration of the above control device and its surroundings.

FIG. 3 is an explanatory diagram illustrating a method for detecting fin clogging according to the method of the present invention.

FIG. 4 is a flow chart showing a procedure for detecting fin clogging by the above method and performing necessary processing.

FIG. 5 is an explanatory diagram illustrating another method of the present invention.

[Explanation of symbols]

1 heat exchanger 1a fin 3 gas burner 4 fan 15 feed forward (FF) calculation unit 16 feedback (FB) calculation unit 17 combustion amount setting unit 28 determination unit G ₀ output combustion amount G _FF FF combustion amount G _FB FB combustion amount G _FB max, G _FB min Limit value of FB combustion amount G _FB u, G _FB d Near limit value of FB combustion amount

Claims (3)

[Claims] 1. In a water heater in which feedback control is used in combination with feedforward control to control the combustion amount, a controllable range of the feedback control amount is set in advance, and the feedback control amount is a limit value of the controllable range. Alternatively, a method for determining the combustion state of the water heater, which determines that the combustion state of the water heater is deteriorating when the temperature reaches the vicinity of the limit value. 2. The method for determining a combustion state of a water heater according to claim 1, wherein when the feedback control amount reaches a limit value of the controllable range, combustion is stopped. 3. When the feedback control amount reaches the vicinity of the limit value of the controllable range, preliminary processing such as fan speed correction and display of combustion state deterioration is performed. The method for determining the combustion state of the heat exchanger according to claim 1 or 2.