JPH0730951B2 - Water heater - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water heater that performs switching control from feedforward control to feedback control.

[Prior Art] Generally, in a water heater, a required capacity is calculated based on a temperature difference between a set temperature and an incoming water temperature and an incoming water temperature, and a combustion fan and a gas proportional valve are operated according to the calculated value of the required capacity. When the deviation between the set temperature and the hot water temperature becomes a predetermined temperature difference during the feed-forward control in which the air amount and the gas amount are controlled to be automatically controlled, the combustion fan and the The gas proportional valve was switched to feedback control that proportionally controls the air amount and the gas amount automatically.

[Problems to be Solved by the Invention] However, in the conventional water heater, no consideration was given to a load error such as a shortage of gas amount due to variations in gas appliances such as gas proportional valves. For this reason, during feed-forward control, a prescribed combustion capacity cannot be obtained, so the outlet heated water temperature does not approach the set temperature until the difference between the set temperature and the outlet heated water temperature reaches the prescribed temperature difference, and feedback control from the feed forward control is performed. There was a problem that it was not possible to switch to.

An object of the present invention is to provide a water heater capable of switching from feedforward control to feedback control even when the outlet heated water temperature does not approach the set temperature until the deviation between the set temperature and the outlet heated water temperature reaches a predetermined temperature difference. .

[Means for Solving Problems] A water heater according to the present invention includes a burner that burns fuel, fuel supply amount control means that adjusts the amount of fuel supplied to the burner, and water that passes through the inside of the burner. A heat exchanger heated by a burner; an inlet water temperature thermistor provided upstream of the heat exchanger to detect an inlet temperature of water flowing into the heat exchanger; and a heat exchanger provided downstream of the heat exchanger. A hot water temperature thermistor for detecting the hot water temperature of the water flowing out of the exchanger, a temperature setting means for setting the hot water temperature to a desired set temperature, and a water quantity detecting means for detecting the water quantity flowing into the heat exchanger, A first calculated value that is a required capacity calculated based on the temperature difference between the set temperature and the incoming water temperature and the incoming water temperature, and a second calculated value that is calculated based on the temperature difference between the outgoing hot water temperature and the incoming water temperature and the incoming water temperature. Required capacity according to the comparison result of Any one of the same gentle heating capacity, a rapid heating capacity larger than the required capacity, and a minimum capacity smaller than the required capacity is selected, and the control state of the fuel supply amount control means is set to the selected capacity. A control circuit for executing a switching control from a feedforward control for changing the control of the fuel supply amount to a feedback control for changing the control state of the fuel supply amount control means in accordance with the deviation between the set temperature and the hot water temperature. The control circuit, during the feedforward control by the output that becomes the rapid heating capacity and the minimum capacity, when the deviation between the set temperature and the hot water temperature becomes a predetermined temperature difference, or the control time of the feedforward control. When a predetermined time, which is a function of only the amount of water input, has passed, a technical means for switching to feedback control has been adopted.

[Operation] In the water heater of the present invention, the first calculated value, which is the necessary capacity, is calculated based on the temperature difference between the set temperature and the incoming water temperature and the incoming water temperature, and the temperature difference between the outgoing hot water temperature and the incoming water temperature and the incoming water amount. The second calculated value is calculated based on And the first calculated value and the second
Depending on the result of comparison with the calculated value of, one of the slow heating capacity that is the same as the required capacity, the rapid heating capacity that is larger than the required capacity, and the minimum capacity that is smaller than the required capacity is selected. Then, the feedforward control is executed to perform control to change the control state of the fuel supply amount control means so that the selected capacity is obtained.

During the feedforward control by the output that provides the rapid heating capacity and the minimum capacity, when the outlet heated water temperature approaches the set temperature until the deviation between the set temperature and the outlet heated water temperature reaches the predetermined temperature difference, the feedforward control is switched to the feedback control. . Further, during the feedforward control with the output that provides the rapid heating capacity and the minimum capacity, even if the control time of the feedforward control elapses a predetermined time that is a function of only the water input amount, the deviation between the set temperature and the hot water output temperature becomes the predetermined value. When the outlet heated water temperature does not approach the set temperature until the temperature difference is reached, the feedforward control is switched to the feedback control.

[Effects of the Invention] The water heater of the present invention discharges hot water until the deviation between the hot water temperature and the set temperature reaches a predetermined temperature difference even after a predetermined time that is a function of only the amount of water that has entered since the feedforward control was started. Even if the temperature does not approach the set temperature, the feedforward control can be switched to the feedback control. Therefore, for example, even when a load error such as an excess or deficiency of fuel due to variations in equipment occurs, it is possible to quickly switch from feedforward control that performs rough control to feedback control that allows fine adjustment control. The responsiveness becomes faster, and the hot water temperature can be brought closer to the set temperature quickly.

[Embodiment] An embodiment of a gas combustion type water heater using fuel gas as fuel will be described with reference to the drawings.

FIG. 1 is a diagram showing a gas combustion type water heater adopting an embodiment of the present invention.

A combustor case 10 is provided in the water heater case 2 of the gas combustion type water heater 1, and a first burner 11a for combusting the fuel gas supplied by the gas supply pipe 20 is provided inside the combustor case 10.
And a dual type gas burner 11 including a second burner 11b
Is provided. In addition, the combustor case 10 has a three-phase Y
A blower that uses a brushless DC motor for connection,
A combustion fan 12 for adjusting the amount of combustion air to the gas burner 11 is provided. The gas burner 11 is provided with combustion air supplied by the combustion fan 12 and a gas supply pipe.
The combustor is a forced air combustor that combusts the fuel gas supplied from 20 at a predetermined air-fuel ratio, and the combustion gas generated by the combustion is exhausted from the exhaust port 3 to the outside.

A heat exchanger 13 connected to a water supply pipe 30 is provided above the inside of the combustor case 10, and the water passing through the inside is gas burner.
It is heated by the heat of the flame and combustion gas generated at 11.
Further, in the vicinity of the gas burner 11 in the combustor case 10, there are provided a sparker 14 which is an ignition device and a frame rod 15 which is a flame detection means.

In the gas supply pipe 20, a source solenoid valve 21 that allows the fuel gas to pass through from the upstream side when energized, a main solenoid valve 22, a fuel gas supply amount (hereinafter referred to as the gas amount) is adjusted by controlling the supply pressure. A governor-type gas proportional valve (hereinafter abbreviated as a governor proportional valve) 23 that is a supply amount control means, and a switching solenoid valve that is a fuel supply amount control means that shuts off the fuel gas to the second burner 11b according to the use state ( Each of them is provided with a switching valve (hereinafter abbreviated as 24) and supplies fuel gas to the gas burner 11 described above.

A water draining plug 32 equipped with a water filter 31 is provided at the most upstream part of the water supply pipe 30, and a water amount proportional adjusting valve by a gad motor for adjusting the amount of water entering the heat exchanger 13 is provided downstream thereof.
33 is provided, and this water amount proportional adjustment valve 33 is provided with a potentiometer 34 for detecting its opening.

The water whose inflow has been adjusted by the water amount proportional adjustment valve 33 is used as the incoming water temperature thermistor 35 which is an incoming water temperature detecting means provided immediately downstream.
The temperature is detected by the water temperature sensor, and the amount of water input is detected by a water amount sensor 36, which is a means for detecting the amount of water input further downstream, and the water amount is sent through the water supply pipe 30 to the heat exchanger 13.

The water supply pipe 30 on the downstream side of the heat exchanger 13 is provided with a hot water temperature thermistor which is hot water temperature detecting means for detecting the temperature of the heated water.
38, and a boiling prevention switch 39 that is turned on when the hot water temperature exceeds the boiling temperature, and a hot water supply plug (not shown) attached to the hot water supply place is provided at the most downstream position.

The water heater 1 having the above configuration is controlled by the control device 50.

As shown in FIG. 2, the control device 50 includes a control circuit 60 connected to an electric cord 51 connected to an outlet for wiring.
And the main controller to operate the water heater 1 remotely
A terminal that connects 54 and the sub-controller 54a and a gas type changeover switch 55 that is set according to the type of fuel gas are provided. As the type of fuel gas, a large number of gas fuels such as LP gas, city gas 13A, city gas 6C and the like, liquid fuel such as petroleum and the like can be used, and these are selectively switched by the gas type changeover switch 55.

The main controller 54 and the sub controller 54a are
This is a temperature setting means set by the user. In the present embodiment, a main controller 54 is provided near the water heater 1, and a sub controller 54a is provided at a hot water supply place such as a bathroom. The main controller 54 and the sub-controller 54a are provided with respective operation switches 56 and 56a and a hot water temperature setting switch 5 for setting the hot water temperature to a desired set temperature.
7, 57a are provided.

The control circuit 60 mainly includes a microcomputer (hereinafter referred to as CPU) 70, a sparker circuit 71, and a fan drive circuit.
72, a proportional valve control circuit 73, a gad motor drive circuit 74, a position detection circuit 75, and a water amount detection circuit 76. These circuits are CP
Predetermined control is performed by U70.

The fan drive circuit 72 rotates the combustion fan 12 according to the combustion capacity such as a set temperature, and detects the rotation speed by a Hall IC provided in a brushless DC motor with a three-phase Y connection and sends a detection signal to the CPU 70. send.

The proportional valve control circuit 73 controls the amount of electricity supplied to the governor proportional valve 23 in order to adjust the amount of fuel gas supplied so that combustion in the gas burner 11 is performed at a desired air-fuel ratio. It is a circuit that controls based on a proportional control constant according to (different). The proportional valve control circuit 73 proportionally controls the maximum value of the current to the governor proportional valve 23 in order to correct an error due to variations in the water heater 1 and a pressure loss due to gas species to obtain an appropriate amount of gas. Is equipped with.

The gad motor drive circuit 74 is a circuit for driving the gad motor of the water amount proportional adjustment valve 33 for adjusting the amount of water entering the heat exchanger 13. The gad motor drive circuit 74 does not operate when the power is off, but the sub controller 54a does not operate when the power is on. Driving switch 56a
Is set to the position of the previous set temperature regardless of whether it is ON or OFF, and the position is initialized from that position to the position corresponding to the reference temperature.

The position detection circuit 75 is a circuit for analyzing a signal from the potentiometer 34 provided for detecting the opening of the water amount proportional adjustment valve 33.

The water amount detection circuit 76 detects the amount of water input based on the rotation speed signal of the water amount sensor 36.

The CPU 70 has a storage function of storing a reference temperature preset at the time of assembling the water heater 1 or a shipping stage and a gas type of the fuel gas to be used, and a determination function of determining the main controller 54 and the sub controller 54a. , Sequence control to control the operation sequence and timing of each circuit above, feed-forward control (hereinafter referred to as FF control) to control the combustion amount and water amount based on the incoming water temperature and set temperature as the combustion capacity control, and the hot water temperature Feedback control (hereinafter referred to as FB control) that performs proportional and integral control (hereinafter referred to as PI control) of combustion amount such as automatic adjustment of gas amount, ON / OFF of switching valve 24, and adjustment of air flow of combustion fan 12 based on Is called), and FF → FM (PI) switching control for switching between FF control and FB control is performed, and in addition to this, a safety function is also provided.

The determination function is a portion that analyzes the pulse signal to perform control according to the setting states of the main controller 54 and the sub-controller 54a connected to the terminal 61 and the terminal 62 of the control circuit 60, respectively. Terminal
62 is a main controller 54 and a sub controller 54a
It is a wire-saving type two-wire terminal that can supply electricity to.

In the sequence control, when the user opens the hot water tap to obtain a water flow signal based on the water amount sensor 36, the combustion fan 12 operates, and ignition is performed after pre-purge for a predetermined time. Ignition operation is based on the original solenoid valve 21, the main solenoid valve
22, the governor proportional valve 23 and the sparker 14 are energized at the same time, and after the ignition is detected, the capacity calculation of the combustion amount is performed, and the combustion corresponding to the combustion amount is started.

On the other hand, when the water flow signal is detected based on the water amount sensor 36,
At the same time, the calculation of the combustion amount starts based on the incoming water temperature thermistor 35.However, if the incoming water temperature when water is not being supplied to the water supply pipe 30 is read, the correct incoming water temperature cannot be obtained. The input water temperature is read by the thermistor 35 after detection of the water flow signal, and the input water temperature at that time is used as the water temperature data.

In the combustion capacity control, the first calculated value (required capacity) Q calculated from the temperature difference between the set temperature and the incoming water temperature and the amount of incoming water, and the second calculated value from the temperature difference between the incoming water temperature and the outgoing hot water temperature and the incoming water amount. FF control that sets the combustion amount and water input amount according to the calculated value (current capacity in the transition period) q, and FB (PI) that corrects the combustion amount and water input amount according to the deviation between the hot water temperature and the set temperature.
Control is performed.

The FF control is performed by a first calculated value (required capacity) Q calculated from the temperature difference between the set temperature and the incoming water temperature by the main controller 54 and the sub-controller 54a and the incoming water amount, and the temperature difference between the incoming water temperature and the outgoing hot water temperature and the incoming water temperature. The most efficient capacity is calculated from the second calculated value q calculated from the water amount, and the combustion fan 12, the governor proportional valve 23, the switching valve 24, and the water amount proportional adjustment valve 33 are controlled to control the air amount, Automatically adjust the amount of gas and the amount of water input

Further, the FF control is a graph showing the relationship between the required capacity and the gas amount (fuel supply amount) in FIG. 8 according to the comparison result of the first calculated value (required capacity) Q and the second calculated value q. As described above, the slow heating capacity range A for proportionally controlling the supply voltage to the combustion fan 12 and the energizing current to the governor proportional valve 23 so that an output having the same slow heating capacity (Q × 1.0) as the required capacity Q is produced. When,
Rapid heating capacity larger than required capacity Q {Q × (Q + α) / Q}
In order to generate the output that satisfies the above condition, the rapid heating capacity range B in which the supply voltage to the combustion fan 12 and the energizing current to the governor proportional valve 23 are varied, and the minimum capacity {Q × (Q
β) / Q} is selected so that the supply voltage to the combustion fan 12 and the residual heat purge capacity range C for varying the current supplied to the governor proportional valve 23 are selected.

Further, in the present embodiment, 1/4 of the total opening degree of the governor proportional valve 23.
In the case of the water heater 1 having the governor proportional valve 23 capable of being throttled to the opening degree of, the fully open capacity 1 of the governor proportional valve 23 during the half open capacity operation in which the switching valve 24 is closed and the combustion is performed only by the first burner 11a. / 8 to 1/2 half-opening capacity control region I that performs proportional control of the gas amount, and when the switching valve 24 is in the open state, during full-opening capacity operation that simultaneously burns the first burner 11a and the second burner 11b. Full open capacity of governor proportional valve 23 Full open capacity control area II that performs proportional control of gas amount from 1/4 to 1 and full open capacity less than the maximum value of half open capacity control area (full open capacity 1/2 of governor proportional valve 23) Overlapping control range III with the minimum value of the control range (full open capacity of governor proportional valve 23 1/4) or more is set. In the FF control, the switching between the half-open capacity operation and the full-open capacity operation is performed based on the first calculated value (required capacity) Q.

In the FB control, the supply voltage to the combustion fan 12 and the energizing current to the governor proportional valve 23 are proportionally controlled according to the combustion amount calculated based on the deviation between the set temperature and the hot water temperature, and the gad motor is energized. By doing so, the air amount, the gas amount, and the water input amount are automatically adjusted.

By the FB control, when the proportional control of the supply voltage to the combustion fan 12 and the energizing current to the governor proportional valve 23 reaches near the maximum range of the half-open capacity control range I (for example, the maximum value of the half-open capacity control range I), The switching valve 24 is turned on (open) while flowing a slow ignition current to the governor proportional valve 23 to switch to full-open capacity operation.

By the FB control, when the proportional control of the supply voltage to the combustion fan 12 and the energizing current to the governor proportional valve 23 reaches near the minimum range of the full opening capacity control range II (for example, the minimum value of the full opening capacity control range II), The switching valve 24 can be operated without changing the rotation speed (supply voltage) of the combustion fan 12 and the current flowing to the governor proportional valve 23.
By turning off (valve closing) and switching to half-open capacity operation,
While maintaining a safe combustion state, smooth switching control between half open capacity operation and full open capacity operation is performed.

In the FF → FB (PI) switching control, when the deviation between the set temperature and the hot water temperature reaches a predetermined temperature difference [± y ° C = ± 5 ° C], the FF control is switched to the FB (PI) control. Alternatively, the FF control control is performed by calculating a predetermined time (τ ₁ : for example, 2 to 4 seconds) that is a function of only the amount of water input, and a predetermined time (τ ₂ : for example, 5 to 9 seconds) that is a function of only the amount of water input. Time is a predetermined time τ ₁ , τ
_{Even if 2} is exceeded, if the outlet hot water temperature does not approach the set temperature until the deviation between the set temperature and the hot water temperature reaches the predetermined temperature difference, FF
Switch from control to FB (PI) control.

Note that τ ₁ is the time that satisfies a / w. Here, a is a coefficient, for example, when the heat capacity of the heat exchanger 13 is 500 cc,
The coefficient a is 20 × 60 [l], w is the amount of water input, for example, the amount of water input w
Is 5 [l / min], τ ₁ is set to 4 seconds, and the water input w is
In the case of 10 [l / min], τ ₁ is set to 2 seconds.

Further, τ ₂ is the time that satisfies b−cw. Where b,
c is a coefficient, for example, when the heat capacity of the heat exchanger 13 is 500 cc, the coefficient b is 12.5 [seconds] and the coefficient c is 0.7 × 60 [seconds ² /
l] and w are the amount of water input, for example, when the amount w of water input is 5 [l / min], τ ₂ is 9 seconds, and when the amount w of water input is 10 [l / min], τ ₂ is 5.5 seconds. To be done.

As a safety function, if the hot water temperature exceeds the boiling temperature and continues for a predetermined time (t8 seconds: 1-10 seconds), or if continuous combustion continues for a predetermined time (t7 minutes: 40-120 minutes), When no flame is detected, each solenoid valve is closed and the operation of the water heater 1 is stopped.

The operation of the controller 50 of the water heater 1 of this embodiment will be described with reference to the flowcharts shown in FIGS. 3 to 7 and the graph shown in FIG. 3 to 5 are flowcharts showing sequence control (ignition operation), combustion capacity control, safety control and the like.

When installing the water heater 1, check the type of fuel gas used by the gas company or the seller of the water heater 1,
The reference temperature (40 ° C. in this embodiment) is set (S1). The type of fuel gas and the reference temperature are set by the water heater 1.
User does not. Further, the gas type of the fuel gas and the setting of the reference temperature are stored in the storage function of the CPU 70 regardless of whether the power supply is ON or OFF. However, when the user inputs the set temperature, the CPU 70 gives priority to the set temperature over the reference temperature, and controls the water heater 1 so that the hot water temperature approaches the set temperature.

To use the water heater 1, the power cord 51 is connected to a wiring outlet and the power is turned on (S2).

The opening degree of the water amount proportional adjustment valve 33 is set to the reference temperature (40 degrees in this embodiment).
It is determined whether or not the maximum amount of water input, which is the amount of water input according to (° C), is initially set to the maximum possible opening (S3).

Here, the water amount proportional adjustment valve 33 is the O of the sub-controller 54a.
Regardless of whether it is N or OFF, the opening is set to correspond to the set temperature (or reference temperature) when the water heater 1 was last used.
However, with a gad motor that changes the opening of the water amount proportional adjustment valve 33, if you try to adjust the opening after inputting the set temperature, it may take a few seconds to move, so there is a risk of cutting into the combustion capacity control time. , Combustion capacity control is delayed. In order to prevent this, in this embodiment, the water amount proportional adjustment valve 33 is moved prior to the start of the combustion capacity control (FF control).

Therefore, since the adjustment time of the water amount proportional adjustment valve 33 from the initially set opening amount of the water amount proportional adjustment valve 33 to the opening according to the set temperature during the FF control described later is shortened, FF
The hot water temperature can be quickly set to the set temperature during control.

The gad motor is turned off when the maximum opening is set for the combustion capacity so that the maximum amount of water can be entered (S4). When it is not set to the maximum opening that allows the maximum water input, turn on the geared motor (S5).

Here, normally, the drive time of the water amount proportional adjustment valve 33 is about several seconds even if it is displaced to the maximum, but when the water amount proportional adjustment valve 33 is frozen or mixed with foreign matter, the water amount proportional adjustment valve 33 is locked. The water amount proportional control valve 33 may not be displaced despite the energization from the drive circuit 74, so that the energization time of the gad motor becomes long and there is a risk of burning the gad motor or the gad motor drive circuit 74 due to heating. In the present embodiment, even in such a case, a predetermined energization time (t1 second: for example, 5 to 5 seconds) to the gad motor by the gad motor drive circuit 74 is prevented so that the device of the water heater 1 does not break down.
When 30 seconds have passed (S6), the gad motor is turned off.

Next, main controller 54 or sub controller 54
It is determined whether or not the operation switches 56 and 56a of a are turned on (S7), and S7 is repeated until it is turned on. When it is ON, it is determined whether or not the hot water temperature setting switches 57 and 57a set the hot water temperature to a desired set temperature (S8).

In addition, if the outlet heated water temperature has not been set to the desired set temperature even after the elapse of a predetermined time (t2 seconds: 1 second, for example) (S9), the set temperature is set to the reference temperature of 40 degrees (S10). .
Next, when the user opens the hot water tap (S11), the water amount sensor 36 detects the amount of water entering (S12).

Here, how to receive the water input change signal is as follows.
It does not accept minute changes that are not detected by, but accepts when the amount of change in the amount of water input is greater than or equal to a predetermined value compared to the current amount of water input (steady flow).

When the signal input to the water amount detection circuit 76 that reads the signal from the water amount sensor 36 is higher than a predetermined voltage, it is detected as a water-passing signal, but a reading error occurs in the water amount detection circuit 76 due to swelling of the water flow, etc. Since chattering will occur if this is set, chattering is prevented by providing a hysteresis characteristic in this embodiment,
When the water input is 2.5 l / min or more, it is detected as a water flow signal and 2.0
If it is a minute change such as less than 1 / min, it will not be detected as a water flow signal.

Normally, the amount of water input is updated every sampling time, but considering the response delay of the water amount sensor 36, the amount of water input changes even when the cumulative value within a certain time exceeds a predetermined value. Accept as.

Therefore, it is possible to detect not only the change in the amount of water input at the moment, but also the change in the amount of water input within a certain time.
The amount of gas can be adjusted according to a wide range of changes in water input.

After the amount of water entering is detected, a predetermined time (t3 seconds: for example, 10 seconds) elapses (S13), and then the incoming water temperature thermistor 35 detects the incoming water temperature (S14). Then, it is determined whether the incoming water temperature is 55 ° C or higher (S15), and when the incoming water temperature is 55 ° C or higher, the user closes the hot water tap (S16), and the operation switch 56 of the main controller 54 and the sub-controller 54a, Turn off 56a (S17). When the incoming water temperature is lower than 55 ° C, it is determined whether the incoming water temperature is below the set temperature (S18), and when the incoming water temperature is above the set temperature, the operation below S12 is repeated, and when it is below the set temperature, as shown in Fig. 4. The combustion fan 12 is turned on (S19).

Hall IC detects the rotation speed of combustion fan 12 (S2
0), it is determined whether the rotation speed of the combustion fan 12 is equal to or higher than a predetermined rotation speed (S21). When the rotation speed of the combustion fan 12 is lower than the predetermined rotation speed, the rotation speed corresponding to the combustion capacity cannot be obtained, so the original solenoid valve 21, the main solenoid valve 22, the switching valve 24, the governor proportional valve 23, the combustion Turn off all fan 12 for (S22-S2
6) The user closes the hot water tap (S27), and then turns off the operation switches 56 and 56a of the main controller 54 and the sub controller 54a (S28).

When the rotation speed of the combustion fan 12 is equal to or higher than the predetermined rotation speed, pre-purge is performed for a predetermined time (t4 seconds: for example, 0.5 to 10 seconds) (S29), the sparker 14, the original solenoid valve 21, the main solenoid valve 22, the switching valve. All 24 are turned on (S30 to S33), and the slow ignition current is supplied to the governor proportional valve 23 (S34).

The energizing current to the governor proportional valve 23 is controlled based on the rotation speed of the combustion fan 12, that is, the air volume and the gas type Kp, except at the time of ignition. In the present embodiment, in particular, the amount of slowly igniting gas at the time of ignition is set to a constant rate (initial value) with respect to the maximum value of the energizing current to the governor proportional valve 23 adjusted by the semi-fixed volume of the proportional valve control circuit 73. Therefore, an appropriate amount of gas for slow ignition can be supplied at the time of ignition.

Further, after turning on the sparker 14, after a predetermined time (t5 seconds: for example, 5 to 20 seconds) has elapsed (S35), the sparker 14 is turned on.
FF (S36). Then, the combustion flame is detected by the frame rod 15, and it is determined whether or not an electric current of IA or more is input by the frame rod 15 (S37). When the current of IA or more is not input, the operation of S22 and below is repeated because of ignition failure. When a current of IA or more is input, a slow ignition timer for a predetermined time (t6 seconds: 0.1 to 10 seconds, for example) is performed (S38), and the hot water temperature thermistor 38 discharges hot water as shown in the flowchart of FIG. Detects temperature (S3
9).

Next, after performing the combustion capacity control shown in the flowcharts of FIGS. 6 and 7 (S40), the safety control of S41 and thereafter is performed.

It is determined whether the rotation speed of the combustion fan 12 is equal to or higher than a predetermined rotation speed (S41). When the rotation speed of the combustion fan 12 is lower than the predetermined rotation speed, the operation of S22 and below is repeated, and when the rotation speed of the combustion fan 12 is the predetermined rotation speed or more, the frame rod
It is determined whether a current of IA or more is input according to 15 (S42). When an electric current of IA or more is input, continuous combustion continues for a predetermined time (t7 minutes: 40 to 120 minutes, for example) (S43), or the hot water temperature exceeds the boiling temperature (S44) for a predetermined time (t8 Seconds: For example, 1 to 10 seconds (S4)
5) Repeat the operation from S22 onward.

If the continuous combustion is less than t7 minutes and the hot water temperature does not reach the boiling temperature, enter the set temperature again (S46) and then S39.
Repeat the following operations. The operation of S46 deals with the case where the user changes the set temperature.

When a current above IA is not input, it is detected as a misfire such as blowout, and it is determined whether or not it is the first misfire during combustion (S47), and when the misfire is the second time, the operation from S22 onward is repeated. When the misfire is the first time, the original solenoid valve 21, the main solenoid valve 22,
The switching valve 24 is turned off (S48 to S50), and then the operation from S19 onward is repeated.

FIG. 6 mainly shows a flow chart of the FF control of the combustion capacity control.

After performing the operation of S39 in FIG. 5, the required capacity is calculated based on the following formulas (S100) and (S101).

Formula 1 ... 1st calculated value Q = (Tset-THin) * W = Required capacity Formula 2 ... 2nd calculated value q = (THout-THin) * W = Current capacity in transition period Tset: Set temperature THin : Inlet water temperature THout: Outlet water temperature W: Inlet water amount After calculating the first calculated value Q and the second calculated value q, FF
Whether or not control has been performed is determined (S102), and if FF control is being performed, FB (PI) control of S123 and subsequent steps shown in the flowchart of FIG. 7 is performed.

Further, it is determined whether or not a predetermined time (t9 seconds: for example, 1 second) has elapsed after the initial setting of the water amount proportional adjustment valve 33 (S10
3) After t9 seconds have elapsed, it is determined whether or not Q ≧ qx (S104). Here, x is a coefficient satisfying, for example, 1.5, and the cold start of the water heater 1 is determined based on the comparison result of the first calculated value Q and the second calculated value qsk.

When Q ≧ qx is not satisfied, it is determined whether or not Q <q (S105).

[When Q <q is not satisfied] That is, when the hot water temperature (THout) is slightly lower than the set temperature (Tset), the switching valve 24 is operated according to the required capacity Q calculated in S100.
Is controlled (ON: full open capacity operation, or OFF: half open capacity operation). Then, set the hot water temperature (THout) to the set temperature (T
fan drive circuit 72, so as to output the same slow heating capacity (Q × 1.0) as the required capacity Q in order to approach
The proportional valve control circuit 73 and the gad motor drive circuit 74 are controlled (S106). Note that 1.0 of (Q × 1.0) is a coefficient.

That is, in the operation of S106, the slow heating capacity (Q × 1.
With the required opening (gas amount) at which 0) is obtained as the control target value, the current supplied to the governor proportional valve 23 is adjusted by proportional control. Further, the rotation speed of the combustion fan 12 and the opening of the water amount proportional adjustment valve 33 are also controlled.

After that, S123 and below shown in the flowchart of FIG.
Performs FB (PI) control.

[When Q <q] That is, when the hot water temperature (THout) is higher than the set temperature (Tset), the switching valve 24 is controlled according to the required capacity Q calculated in S100 (ON: full open capacity operation Or off:
Half open capacity operation). Then, in order to bring the hot water temperature (THout) close to the set temperature (Tset), the control target value of the governor proportional valve 23 is set so that the minimum capacity smaller than the required capacity Q is output, and the fan drive circuit 72, the proportional Valve control circuit 73
And the gad motor drive circuit 74 is controlled (S107).

That is, according to the required capacity Q calculated in S100, the switching valve 24
Is turned off (half-open capacity operation), the required opening (gas amount) at which the minimum capacity of the half-open capacity control range I is obtained is the control target value, and the energizing current to the governor proportional valve 23 is proportionally controlled. Adjusted.

If the switching valve 24 is turned on (fully open capacity operation) according to the required capacity Q calculated in S100, the fully open capacity control range
The energizing current to the governor proportional valve 23 is adjusted by the proportional control with the required opening (gas amount) at which the minimum value II is obtained as the control target value. Further, the rotation speed of the combustion fan 12 and the opening of the water amount proportional adjustment valve 33 are also controlled.

Next, a predetermined time {τ ₁ = a / w that is a function of only the amount of water input
[Second]} is calculated (S108). Note that τ ₁ is the time that satisfies a / w. Here, a is a coefficient, for example, a heat exchanger.
When the heat capacity of 13 is 500cc, coefficient a is 20 x 60 [l],
w is the amount of water input, for example τ when the amount w of water input is 5 [l / min]
₁ is set to 4 seconds and τ ₁ when the water input w is 10 [l / min]
For 2 seconds.

Then, the FF control time has passed a predetermined time (τ ₁ second: for example, 2 to 4 seconds) which is a function of only the amount of water input (S109).
After that, the fan drive circuit 72, the proportional valve control circuit 73, and the gad motor drive circuit 74 are controlled so as to output the same gentle heating capacity (Q × 1.0) as the required capacity Q (S110). In addition, (Q
× 1.0) 1.0 is a coefficient.

That is, in the operation of S110, the slow heating capacity (Q × 1.
The required opening (gas amount) for obtaining 0) is used as a control target value to adjust the energization current to the governor proportional valve 23 by proportional control. Further, the rotation speed of the combustion fan 12 and the opening of the water amount proportional adjustment valve 33 are also controlled.

After that, S123 and below shown in the flowchart of FIG.
Performs FB (PI) control.

Here, when the FF control time has not passed a predetermined time (τ ₁ second: for example, 2 to 4 seconds) which is a function of only the amount of water input, the deviation between the set temperature (Tset) and the hot water outlet temperature (THout) is predetermined. It is determined whether or not there is a temperature difference (| dt | ° C = ± y ° C: ± 5 ° C, for example) (S111), and when the deviation is the predetermined temperature difference, S110 is performed and the deviation is the predetermined temperature. When there is no difference, S109 is continuously performed.

As described above, during the control with the minimum capacity of the FF control, the outlet heated water temperature becomes the set temperature until the deviation between the set temperature and the heated hot water temperature reaches a predetermined temperature difference (| dt | ° C = ± y ° C: for example ± 5 ° C). When approaching, it is switched from FF control to FB (PI) control (operations below S110). Also, the control time with the minimum capacity of FF control is
Predetermined time (τ ₁ second: eg 2
Even if (approx. 4 seconds) elapses, the deviation between the set temperature and the hot water temperature does not approach the set temperature until the difference between the set temperature and the hot water temperature reaches the predetermined temperature difference (| dt | ° C = ± y ° C: ± 5 ° C, for example). Control to FB (PI)
It is switched to control (operation after S110).

Therefore, for example, a load error such as a gas amount shortage due to variations in appliances such as the combustion fan 12 and the governor proportional valve 23, the control circuit 60, the incoming water temperature thermistor 35, the outgoing hot water temperature thermistor 38, the main controller 54 and the sub-controller 54.
In the case where there is an error in each input / output of the hot water temperature setting switches 57, 57a, etc. of a, or the calculated capacity cannot be obtained due to insufficient capacity of the water heater 1, control with the minimum capacity of FF control is started. , A predetermined time (τ ₁
Second: The deviation between the set temperature and the tap water temperature is a predetermined temperature difference (| dt | ° C = ± y ° C .: ± 5 °, for example) even after the elapse of 2 to 4 seconds.
Even when the hot water temperature does not approach the set temperature until
FB that allows fine adjustment control from FF control that performs rough control
Since (PI) control can be switched to quickly, the responsiveness becomes faster and the hot water temperature can be brought closer to the set temperature quickly.

[When Q ≧ qx] That is, when the hot water temperature does not reach the set temperature, the difference between the set temperature (Tset) and the hot water temperature (THout) is a predetermined temperature difference (| dt | ° C = ± y ° C: for example ± 5). (° C) is determined (S112), and when the deviation is the predetermined temperature difference, S106 is performed.

When the deviation is not the predetermined temperature difference, the switching valve 24 is controlled (ON: full open capacity operation or OFF: half open capacity operation) according to the required capacity Q calculated in S110. And the maximum capacity larger than the required capacity Q {rapid heating capacity: Q x (Q +
The fan drive circuit 72, the proportional valve control circuit 73, and the gad motor drive circuit 74 are controlled to output α) / Q} (S113). Note that (Q + α) / Q is a coefficient, for example, α is Q ×
When it is 3/4 kcal, it is 1.75.

That is, in the operation of S113, the energizing current to the governor proportional valve 23 is proportional to the control target value that is the required opening degree (gas amount) at which the maximum capacity {Q × (Q + α) / Q} larger than the required capacity Q is obtained. Adjusted by control. Further, the rotation speed of the combustion fan 12 and the opening of the water amount proportional adjustment valve 33 are also controlled.

At this time, for example, the water amount proportional adjustment valve 33 reads the data previously input to the CPU 70 and promptly sets the temperature (Tset).
And the opening temperature according to the deviation between the hot water temperature (THout).

However, the first calculated value Q, which is the required capacity, is updated due to the change in the amount of water input, and when the governor proportional valve 23 operates at this time, the change in the amount of gas interferes with the change in the amount of water input, affecting the hot water temperature. Since it appears, when changing the opening degree (water input amount) of the water amount proportional adjustment valve 33, the example control of the capacity (gas amount) by the governor proportional valve 23 is not performed.

Next, a predetermined time (τ ₂ = b−cw) that is a function of only the amount of water input.
[Second]) is calculated (S118). Note that b and c are coefficients,
For example, when the heat capacity of the heat exchanger 13 is 500cc, the coefficient b is 1
2.5 [sec], coefficient c is 0.7 × 60 [sec ² / l], w is the amount of water input. For example, when the amount w of water input is 5 [l / min], τ ₂ is 9 seconds, and the amount w of water input is In the case of 10 [l / min], τ ₂ is 5.5 seconds.

Then, the FF control time has passed a predetermined time (τ ₂ seconds: for example, 5 to 9 seconds) which is a function of only the amount of water input (S119).
After that, the residual heat purge capacity smaller than the required capacity {Q x (Q-
The fan drive circuit 72, the proportional valve control circuit 73, and the gad motor drive circuit 74 are controlled to output β) / Q} (S120). Note that (Q−β) / Q is a coefficient, for example, β is Q ×
When it is set to 1/4 kcal, it is set to 0.6.

That is, in the operation of S120, the governor proportional valve 23 is first throttled so that the target opening degree is obtained so that the residual heat purge capacity {Q × (Q−β) / Q} smaller than the required capacity Q is obtained. Then, the switching valve 24 is controlled according to the required capacity Q calculated in S100 (on: full open capacity operation, or off: half open capacity operation).
To be done. Further, the rotation speed of the combustion fan 12 and the opening of the water amount proportional adjustment valve 33 are also controlled.

Here, when the FF control time has not passed a predetermined time (τ ₂ seconds: for example, 5 to 9 seconds) which is a function of only the amount of water input, the deviation between the set temperature (Tset) and the hot water temperature (THout) is predetermined. Whether or not there is a temperature difference (| dt | ° C = ± y ° C .: ± 5 ° C., for example) is determined (S121), and when the deviation is the predetermined temperature difference, S120 is performed.

When the deviation is not the predetermined temperature difference, it is determined whether or not there is a change in the outlet heated water temperature that is equal to or less than the temperature difference Δy of the outlet heated water temperature within a predetermined time Δt (S122). When there is a change in the outlet hot water temperature of Δy / Δt or less, the operation of S120 is performed, and when there is no change of the tap hot water temperature of Δy / Δt or less, the operation of S119 and the following is repeated.

As described above, in the present embodiment, by comparing the first calculated value (required capacity) Q and the second calculated value q, as shown in the graph of FIG. 8 showing the relationship between the required capacity and the gas amount, A slow heating capacity range A that produces an output that is the same as the required capacity Q, a rapid heating capacity range B that produces an output that is a rapid heating capacity that is greater than the required capacity Q, and a residual heat purge capacity that is smaller than the required capacity Q. Of the residual heat purging capacity range C that produces the following output, proportional control of the combustion fan 12, the governor proportional valve 23, the water amount proportional adjustment valve 33, and the opening / closing of the switching valve 24 according to these control ranges. By controlling the valve, FF control that automatically adjusts the air amount, gas amount, and water input amount is performed.

Then, during the control in the rapid heating capacity range B of the FF control, the deviation between the set temperature and the hot water temperature is a predetermined temperature difference (| dt | ° C = ± y
When the hot water temperature approaches the set temperature until the temperature reaches, for example, ± 5 ° C., the FF control is switched to the FB (PI) control (operations below S120). In addition, even if the control time of the rapid heating capacity range B of the FF control elapses a predetermined time (τ ₂ seconds: for example, 5 to 9 seconds) that is a function of only the water input amount, the deviation between the set temperature and the hot water temperature is predetermined. When the hot water temperature does not approach the set temperature until the temperature difference (| dt | ℃ = ± y ℃: ± 5 ℃, for example) is reached, the FF control to FB
It is switched to (PI) control (operation of S120 and below).

Therefore, even if a predetermined time (τ ₂ seconds: 5 to 9 seconds, for example), which is a function of only the amount of water input, has elapsed since the control of the rapid heating capacity range B of the FF control has started, the deviation between the set temperature and the hot water output temperature Even if the hot water temperature does not approach the set temperature until the temperature difference reaches a predetermined temperature difference (| dt | ℃ = ± y ℃: ± 5 ℃)
Since it is possible to switch to FB (PI) control, load errors such as insufficient gas amount due to variations in equipment such as combustion fan 12 and governor proportional valve 23, control circuit 60, incoming water temperature thermistor 45, hot water temperature thermistor 38 、 Main controller
54 and sub controller 54a hot water temperature setting switch 5
Even if there is an error in each input / output of 7, 57a etc., it is possible to quickly switch from FF control that performs rough control to FB (PI) control that allows fine adjustment control, so responsiveness becomes faster,
The hot water temperature can be quickly approached the set temperature.

Further, in the FF control, if the required capacity Q is (set temperature-inlet water temperature) × inlet water quantity, the maximum capacity (rapid heating capacity) larger than the required capacity Q and the required capacity are required during the transition period such as cold start and capacity change. It is controlled with a minimum capacity smaller than its capacity. Here, the feedforward control based on the maximum capacity and the minimum capacity is caused by the heat capacity of the water-passing device such as the heat exchanger 13 and is an amount that need not be taken into consideration in the steady state.

Generally, the heat capacity of the water-flowing equipment such as the heat exchanger 13 is a constant amount that is directly proportional to the increase in the outlet water temperature, because the heating amount of the gas burner 11 is negatively proportional to the increase in the amount of water input,
It becomes a steady value in a time inversely proportional to the increase in the amount of water input.
Also, in the transitional period, such as a rise of the water heater 1 (cold start) or a change in the capacity of the water heater 1 due to a change in the hot water temperature (amount of water input), synthesizing the FB control with the FF control is the actual hot water temperature. The output hot water thermistor 38 delays the response, that is, even the excess or deficiency amount due to the delay time required for the detection value to rise or fall until the actual hot water temperature is reached will be output. Delays stabilization.

Therefore, the hot water temperature thermistor 38 relative to the actual hot water temperature
Since the response delay of becomes smaller as the water input increases, the FF control is performed during the predetermined time τ ₁ which is an inverse proportional function of the water input and the predetermined time τ ₂ which is a negative proportional function of the water input. Only the output is used and the FB control output is not used. Therefore, the control time of the FF control is a predetermined time (τ ₁ = a / w [second]: for example, 2 to 4 seconds), which is a function of only the water input amount,
The FF control is continued for ([tau] ₂ = b-cw [second]: 5 to 9 seconds, for example).

Further, in this embodiment, since the capacity of the water heater 1 is limited, an empirical formula (τ ₁ = a / w and τ ₂ = b−cw) considering the calculated value and the limit value of the practical range is used. The temperature is decreased and the temperature is increased. In the FF control by the maximum capacity (rapid heating capacity), since the influence of the heat capacity of water flow fixtures such as heat exchanger 13 is very large, the empirical formula (tau ₂
If the upper limit value b used in (= b−cw) is also long, the FF control by the rapid heating capability becomes long, and the outlet heated water temperature overshoots the set temperature. Also, the upper limit value b
If it is a short time, switching to FF control becomes faster, so the correction amount of the hot water temperature due to FB control becomes large, and the actual hot water temperature stabilizes slowly at the set temperature. We decided to use a negative proportional function with b.

Then, each input / output of the control circuit 60, the incoming water temperature thermistor 35, the hot water temperature thermistor 38, the main controller 54 and the sub controller 54a paste hot water temperature setting switches 57, 57a, etc. is normal, that is, if there is no error, the calculated capacity is obtained. However, if the calculated capacity cannot be obtained due to insufficient capacity of the water heater 1, the hot water temperature does not approach the set temperature even if the FF control is continued with this capacity. Therefore, a predetermined time (τ ₁ = a / w [sec]) that is a function of only the amount of water input is used as a criterion for determining that the calculated capacity cannot be obtained.
Sec), (τ ₂ = b−cw [sec]: for example, 5 to 9 seconds), and the time is set as the control time of the FF control time.

For this reason, a predetermined time (τ ₁ = a /
w [second]: for example, 2 to 4 seconds, (τ ₂ = b−cw
[Second]: The hot water temperature is set until the deviation between the set temperature and the hot water temperature reaches a predetermined temperature difference (| dt | ° C = ± y ° C: ± 5 ° C., for example) even after 5 to 9 seconds have passed. If it does not approach the temperature, it is possible to quickly switch from FF control, which performs rough control, to FB (PI) control, which allows fine adjustment control, so that the responsiveness becomes faster and the hot water temperature approaches the set temperature faster. be able to.

FIG. 7 shows a flowchart of FB (I) control.

In FB (PI) control, the set temperature (Tset) and the hot water temperature (THou
It is determined whether the deviation from (t) is + y ° C (for example, + 5 ° C) or more (S123). When the deviation is + y ° C (eg, + 5 ° C) or more, the residual heat purge capacity smaller than the required capacity Q {Q x (Q-
The fan drive circuit 72, the proportional valve control circuit 73, and the gad motor drive circuit 74 are controlled to output β) / Q} (S124). In addition, (Q-β) / Q is a coefficient, for example, β is Q ×
When it is set to 1/4 kcal, it is set to 0.6.

That is, in the operation of S124, the governor proportional valve 23 is first throttled so that the target opening degree is obtained so that the residual heat purge capacity {Q × (Q−β) / Q} smaller than the required capacity Q is obtained. Then, the switching valve 24 is controlled according to the required capacity Q calculated in S100 (on: full open capacity operation, or off: half open capacity operation).
To be done. Further, the rotation speed of the combustion fan 12 and the opening of the water amount proportional adjustment valve 33 are also controlled.

Then, after the output time of the FF control output (t10 seconds: 30 seconds, for example) has elapsed (S125), the safety control of S41 and subsequent steps shown in the flowchart of FIG. 5 is performed. If t10 seconds have not elapsed, the operation from S123 onward is repeated.

Therefore, when the deviation between the set temperature (Tset) and the hot water temperature (THout) is + y ° C (for example, + 5 ° C) or more, the output time (t10 seconds: 30 seconds, for example) set independently of the integration time T Until the time elapses, the FF control output becomes {remaining heat purge capacity: Q × (Q−β) / Q}.

When the deviation between the set temperature (Tset) and the hot water temperature (THout) is less than + y ° C (for example, + 5 ° C), the integration time (PI control output time) is calculated from the combined function of the temperature deviation function and the water input function. Calculate T (S127).

Here, the temperature deviation function F (e) is derived from the following arithmetic expression.

∴F (e) = (K ₁ −e) × K ₁ K ₁ and K ₁ are constants e = set temperature−outflow temperature In addition, the water input function G (w) is derived from the following arithmetic expression.

∴G (w) = (K ₂ −w) × K ₂ K ₂ , K ₂ is a constant, and the integration time T is derived from the following arithmetic expression.

∴T = {F (e) + G (w)} = {(155-e) × 1/8 + (80-w) × 1/8} = PI control output time Therefore, the set temperature (Tset) and hot water temperature When the deviation from (THout) is less than + y ° C (for example, + 5 ° C), the integration time (output time of PI control) T becomes shorter as the deviation (e) becomes larger or the water amount (w) becomes larger.

Further, the smaller the deviation (e) or the smaller the amount of water input (w), the longer the integration time (output time of PI control) T.

After that, the integration time (T: 150 seconds, for example) has elapsed (S12
8) After that, it is determined whether or not the temperature deviation e ≦ 1 (S129). e
≤1 o'clock, that is, the set temperature (Tset) and the hot water temperature (THou
When the deviation (e) from t) is 1 ° C. or less, the safety control from S41 onward in the flowchart shown in FIG. 5 is performed.

When e ≦ 1 is not satisfied, that is, when the deviation (e) between the set temperature (Tset) and the hot water temperature (THout) is not less than 1 ° C, the gas type Kp of the fuel gas is input (S130), and the gas type is set. The calculation formula of the PI control output of the incoming water temperature is updated so that the proportional control constant is switched to Kp, and the combustion fan 12 and the governor proportional valve 23, and the amount of water are adjusted so that the updated PI control output is obtained. The proportional adjustment valve 33 is controlled (S131).

PI control output: PN = PN-1 + e + Kp = proportional control constant PI control output variation: ΔVS = e x Kp Current PI control output: PN-1 = Q x (Q + α) / Q ∴ PI control main force: PN = PN- 1 + ΔVS That is, in the operation of S131, the PI control output (proportional control constant to the combustion fan 12 and the governor proportional valve 23) is output as a temperature deviation function so that the PI control output becomes the target rotational speed. The current supplied to the governor proportional valve 23 is adjusted by proportional control so that the supply voltage to the combustion fan 12 and the target opening degree are obtained.

However, when the water flow rate is less than the specified flow rate (5 l / min), the maximum value of the FF control output {Q × (Q + α) / Q} is brought close to the slow heating capacity (Q × 1.0) which is the same as the required capacity Q, and is very small. Improves stability at flow rate.

After that, the safety control from S41 onward in the flowchart shown in FIG. 5 is performed.

Therefore, by switching to proportional control constants according to the load such as gas type Kp, gas amount, and water input amount, the gas amount can be increased or decreased (a variable instead of a fixed value), and a wide and wide PI control output Can be updated.
The characteristics of the governor proportional valve 23 (depending on the gas type Kp)
PI control that is compatible with can be performed. Furthermore, the hot water outlet temperature can be brought closer to the set temperature quickly from the integration time T and the PI control output.

[Modification] In this embodiment, a gaseous fuel such as a fuel gas is used as the fuel, but a liquid fuel such as petroleum may be used as the fuel.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a gas combustion type water heater according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a control device of the gas combustion type water heater according to an embodiment of the present invention. 3 to 5 are flow charts of sequence control, combustion capacity control, and safety control according to one embodiment of the present invention, and FIG. 6 is a flow chart of FF control according to one embodiment of the present invention.
FIG. 7 is a flow chart of FB control according to one embodiment of the present invention, and FIG. 8 is a graph showing the relationship between the required capacity and the gas amount. In the figure, 1 ... Gas-fired water heater, 11 ... Gas burner, 13 ... Heat exchanger, 23 ... Governor proportional valve (fuel supply amount control means),
24 …… Switching solenoid valve (fuel supply amount control means), 35 …… Incoming water temperature thermistor (incoming water temperature detecting means), 36 …… Water volume sensor (incoming water amount detecting means), 38 …… Outlet temperature thermistor (outlet temperature detection) Means), 50 ... control device, 54 ... main controller (temperature setting means), 54a ... sub-controller (temperature setting means), 60 ... control circuit

Claims (1)

[Claims] 1. A burner for burning fuel, (b) a fuel supply amount control means for adjusting the supply amount of fuel to the burner, and (c) heating water passing through the inside by the burner. And (d) an inlet water temperature thermistor which is provided upstream of the heat exchanger and detects an inlet temperature of water flowing into the heat exchanger, and (e) which is provided downstream of the heat exchanger. An outlet hot water temperature thermistor for detecting the outlet hot water temperature of the water flowing out from the heat exchanger, (f) a temperature setting means for setting the hot water outlet temperature to a desired set temperature, and (g) an amount of incoming water flowing into the heat exchanger. And (h) a first calculated value that is a necessary capacity calculated based on the temperature difference between the set temperature and the incoming water temperature and the incoming water amount, and the temperature difference between the outgoing hot water temperature and the incoming water temperature, and Depending on the comparison result of the second calculated value calculated based on the water input, Note that any one of a slow heating capacity that is the same as the required capacity, a rapid heating capacity that is larger than the required capacity, and a minimum capacity that is smaller than the required capacity is selected, and the fuel supply amount control is performed to achieve this selected capacity. Switching control from feedforward control, which performs control for varying the control state of the means, to feedback control, which performs control for varying the control state of the fuel supply amount control means in accordance with the deviation between the set temperature and the hot water temperature, is executed. A control circuit, wherein the control circuit performs a feedforward control when a difference between the set temperature and the hot water temperature becomes a predetermined temperature difference during the feedforward control by the output that becomes the rapid heating capacity and the minimum capacity. The water heater, wherein the control time is switched to feedback control when a predetermined time which is a function of only the amount of water input has passed.