JP3922792B2 - Water heater and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water heater that can change a set temperature during hot water discharge.
[0002]
[Prior art]
Conventional water heaters control the amount of gas supplied to the combustion section by feedforward control based on the incoming water temperature, set temperature, etc. for a few seconds after the start of tapping, and then perform feedback control and feedforward based on the tapping temperature. The gas amount was controlled by a control method used in combination with the control.
[0003]
[Problems to be solved by the invention]
However, there is a certain time delay until the change in the gas amount appears as a change in the tapping temperature, and even if the gas amount is changed in steps, the tapping temperature gradually changes according to a predetermined time constant. If the set temperature is changed to, feedback control will be too effective. For this reason, the hot water temperature overshoots or undershoots the set temperature until it stabilizes at the changed set temperature, and it takes time for the hot water temperature to stabilize at the changed set temperature. There was a problem.
[0004]
The present invention has been made paying attention to such problems of the conventional technology, and when the set temperature is changed during tapping, overshoot and undershoot with respect to the set temperature after the change are suppressed to a short level. It is an object of the present invention to provide a water heater and a control method therefor that can stabilize the tapping temperature to the set temperature after the change.
[0005]
[Means for Solving the Problems]
The gist of the present invention for achieving the object lies in the inventions of the following items.
[1] In a water heater that can change the set temperature during hot water,
A first combustion control means (21) for feedforward controlling the amount of gas supplied to the combustion section (11), and a predetermined control method involving feedback control of the amount of gas supplied to the combustion section (11) based on at least the tapping temperature. The second combustion control means (22) controlled by the control of the first combustion control means (21) and the second combustion control means (22) control the amount of gas supplied to the combustion section (11). The switching means (23) for switching which of the control means to perform, and the amount of gas when the first combustion control means (21) feeds the amount of gas supplied to the combustion section (11). Change characteristic setting means (25) for setting the change characteristic,
The switching means (23) switches the control means for the amount of gas to be supplied to the combustion section (11) to the first combustion control means (21) when the set temperature is changed during tapping, and then a predetermined amount When the return condition is satisfied, the gas amount control means is returned to the second combustion control means (22),
When the set temperature is changed during tapping, the change characteristic setting means (25) exceeds the target gas amount in the direction in which the target gas amount for steady operation from the current gas amount to the set temperature after the change exists. The gas amount changed in this way is set as an initial value, and a characteristic that gradually changes from the initial value so as to approach the target gas amount is set as a change characteristic of the gas amount,
The first combustion control means (21) supplies the amount of gas supplied to the combustion section (11) in accordance with the change characteristic set by the change characteristic setting means (25) from the time when the set temperature is changed during tapping. Feed-forward control ,
A hot water heater characterized by appropriately combining feedback control and feedforward control so that the hot water temperature can be stabilized at the set temperature after the change in a short time .
[0006]
[2] The water heater according to [1], wherein the change characteristic setting means (25) sets the change characteristic based on a temperature difference between a set temperature before the change and a set temperature after the change.
[0007]
[3] The switching means (23) supplies an amount of gas supplied to the combustion section (11) assuming that the return condition is satisfied when a predetermined time has elapsed since switching to the first combustion control means (21). The hot water heater according to [1] or [2], wherein the control means is returned to the second combustion control means (22).
[0008]
[4] The switching means (23) determines that the return condition is satisfied when the difference between the gas amount supplied to the combustion portion (11) and the target gas amount is within a predetermined value. The hot water heater according to [1] or [2], wherein the control means for the amount of gas supplied to 11) is returned to the second combustion control means (22).
[0009]
[5] The change characteristic setting means (25) sets the change characteristic of the gas amount so that the hot water temperature reaches the set temperature most quickly without overshooting or undershooting [1]. , [2], [3] or [4].
[0010]
[6] In a method for controlling a water heater capable of changing a set temperature during hot water,
When the set temperature is changed during tapping, a predetermined gas amount that has been changed beyond the target gas amount in the direction of the target gas amount for steady operation from the current gas amount to the changed set temperature is initialized. And a feed-forward control based on a change characteristic that gradually changes from the initial value so as to approach the target gas amount, and when a predetermined return condition is satisfied, (11) A method for controlling a water heater, wherein the control of the amount of gas supplied to (11) is returned from the feedforward control to a predetermined control accompanied by feedback control based on at least the hot water temperature.
[0011]
The present invention operates as follows.
The present water heater has a first combustion control means (21) for feedforward control of the amount of gas supplied to the combustion section (11), and feedback control based on at least the tapping temperature for the amount of gas supplied to the combustion section (11). And a second combustion control means (22) controlled by a predetermined control method, and feedback control by the second combustion control means (22) in a steady state after the start of pouring and after the hot water temperature has stabilized. The amount of gas is adjusted by combustion control with
[0012]
When the set temperature is changed during the hot water discharge in the steady state, the switching means (23) switches the control means for the amount of gas supplied to the combustion section (11) to the first combustion control means (21). In addition, when the set temperature is changed during tapping, the change characteristic setting means (25) sets the target gas amount in the direction in which the target gas amount for steady operation at the set temperature after the change exists from the current gas amount. The gas amount change characteristic when the first combustion control means (21) performs feedforward control on the characteristic that changes from the initial value to the target gas amount gradually with the gas amount changed beyond the initial value. Set as.
[0013]
The first combustion control means (21) feeds forward the amount of gas supplied to the combustion section (11) according to the change characteristic set by the change characteristic setting means (25) from the time when the set temperature is changed during tapping. Then, the switching means (23) returns the gas amount control means to the second combustion control means (22) when a predetermined return condition is satisfied.
[0014]
In this way, the gas amount is adjusted by feedforward control until a certain period of time elapses from when the set temperature is changed, and the gas amount at that time is initially set to the target gas amount corresponding to the changed set temperature. Since it is changed so that it gradually approaches the target gas amount after it is fluctuated up to a value exceeding the value, the hot water temperature can be stabilized at the changed set temperature in a short time without overshooting or undershooting. .
[0015]
The change characteristic of the gas amount during the feedforward control is set based on the temperature difference between the set temperature before the change and the set temperature after the change. Thereby, an optimal change characteristic can be set according to the temperature difference before and after the change, and the tapping temperature can be made to quickly follow the set temperature after the change regardless of the change width of the set temperature.
[0016]
When the predetermined time has elapsed since switching to the first combustion control means (21), the switching means (23) serves as a second combustion control means (22) for controlling the amount of gas supplied to the combustion section (11). Return to. Thus, since the elapsed time is used as a reference, it is possible to easily switch to the second combustion control means (22).
[0017]
The switching means (23) also supplies the gas to be supplied to the combustion section (11) when the difference between the gas amount supplied to the combustion section (11) and the target gas quantity is within a predetermined value, assuming that the return condition is satisfied. The quantity control means is returned to the second combustion control means (22). For example, when the difference between the supplied gas amount and the target gas amount falls within 5% of the difference between the gas amount before changing the set temperature and the target gas amount, the second combustion control means (22) Switch.
[0018]
In this way, when the temperature approaches the target gas amount, the tapping temperature is also approaching the set temperature after the change, so that even after switching to combustion control with feedback control, the tapping temperature will fluctuate greatly thereafter. There is no such thing. Further, since feedback control is applied at a stage where the target gas amount is almost approached, the actual tapping temperature can be made to coincide with the set temperature early and reliably.
[0019]
The change characteristic setting means (25) sets the gas quantity change characteristic so that the tapping temperature reaches the set temperature the fastest without overshooting or undershooting.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Each figure shows an embodiment of the present invention.
As shown in FIG. 2, the water heater 10 includes a burner 11 and a heat exchanger 12 disposed above the burner 11. A water supply pipe 13 is connected to the heat exchanger 12 on the inlet side. A hot water supply pipe 14 is connected to the outlet side of the exchanger 12. A water tap (not shown) is attached to the tip of the hot water supply pipe 14.
[0021]
In the middle of the water supply pipe 13, a flow sensor 15 for detecting the presence / absence of water flow and a flow rate of water and an incoming water temperature sensor 16 for detecting the temperature of water before heating flowing into the heat exchanger 12 are attached. Further, a hot water temperature sensor 17 that detects the hot water temperature after being heated by the heat exchanger 12 is provided in the vicinity of the heat exchanger 12 in the hot water supply pipe 14. A gas proportional valve 19 for adjusting the amount of gas supplied to the burner 11 is attached in the middle of the gas supply pipe 18 leading to the burner 11.
[0022]
The water heater 10 has a control unit 20 on which various circuit components for controlling the hot water supply operation are mounted. In addition to the flow sensor 15, the incoming water temperature sensor 16, the outgoing hot water temperature sensor 17, the gas proportional valve 19, etc., the control unit 20 includes operations such as setting the outgoing hot water temperature and turning on / off the operation of the water heater 10 itself. A remote control 40 is connected to accept.
[0023]
FIG. 1 shows an outline of the circuit configuration of the control unit 20. The control unit 20 controls the amount of gas supplied to the burner 11 by using both the first combustion control means 21 that controls the amount of gas supplied to the burner 11 by feedforward control and the feedforward control and feedback control. 2 combustion control means 22, and a switching means 23 for switching which of the first combustion control means 21 and the second combustion control means 22 controls the amount of gas supplied to the burner 11. is doing.
[0024]
The switching means 23 controls the gas amount by the first combustion control means 21 for a predetermined time after the start of the hot water and for a predetermined period after the set temperature is changed during the hot water, and the second combustion control for the other time. These control means are switched so that the gas amount is controlled by the means 22. That is, the switching means 23 selects the first combustion control means 21 when the required heat quantity changes greatly, and the second combustion control means 22 during the steady operation where the required heat quantity does not change much. The switching means 23 is connected to a timer 24 for measuring the elapsed time since switching to the first combustion control means 21.
[0025]
The change characteristic setting means 25 connected to the first combustion control means 21 indicates how the burner 11 should change the gas amount by feed-forward control when the set temperature is changed during tapping. It is a circuit part that determines the change characteristics. When the set temperature is changed, the change characteristic setting unit 25 selects a change characteristic corresponding to the change width of the set temperature before and after the change. In the data storage unit 26, change characteristics for each change width are registered in advance.
[0026]
The remote controller 40 has a temperature setting switch 41 for changing the set temperature. In addition, the remote controller 40 includes various operation switches (not shown) and a display unit for displaying a set temperature, an operating state, error information, and the like.
[0027]
FIG. 3 is a graph showing a part of the change characteristic data stored in the data storage unit 26 of the change characteristic setting means 25. The horizontal axis of the figure shows the time after the set temperature is changed, and the vertical axis shows the change amount of the gas amount when the gas amount (GF1) immediately before the set temperature is changed is used as a reference.
[0028]
The change characteristic 51 indicated by the solid line indicates that the change width of the set temperature is + 10 ° C., the change characteristic 52 indicated by the dotted line indicates that the change width is + 8 ° C., and the change characteristic 53 indicated by the two-dot broken line indicates the change width. In the case of + 6 ° C., the change characteristic 54 indicated by a one-dot broken line indicates a case where the change width is + 4 ° C. The gas amounts 51a to 54a when the change characteristics 51 to 54 are substantially parallel to the horizontal axis are the gas amount (target gas amount GF2) necessary for steady operation at the changed set temperature and the gas immediately before the change. The difference from the quantity (GF1) is shown.
[0029]
As described above, since the change characteristic is stored using the change width of the set temperature as a parameter without depending on the absolute temperature, the amount of data to be stored can be reduced. These gas amount change characteristics are specified so that when the set temperature is changed during tapping, the tapping temperature transitions to the new set temperature in the shortest time without overshoot or undershoot. This is obtained by repeating the driving test. Although FIG. 3 shows the case where the set temperature is raised, the change characteristics when the set temperature is lowered have a shape that is substantially symmetrical with respect to that shown in FIG. 3 about the time axis.
[0030]
Next, the operation will be described.
FIG. 4 shows a flow of operations performed by the control unit 20 when the set temperature is changed during hot water. The gas amount is controlled by the first combustion control means 21 until a certain time has elapsed from the start of the hot water, and thereafter, the hot water temperature is stabilized and the required heat amount does not change significantly. Therefore, the second combustion control means 22 The amount of gas is controlled. When the set temperature is changed after entering the steady hot water state in this way (step S101; Y), the change characteristic setting means 25 indicates how much the set temperature has been changed in either the up or down direction (change). The width ΔTsp) is obtained, the data storage unit 26 is referred to, and a change characteristic corresponding to the change width is acquired (step S102).
[0031]
After the change characteristic acquired by the change characteristic setting means 25 is set in the first combustion control means 21, the switching means 23 changes the control means for the amount of gas supplied to the burner 11 from the second combustion control means 22 to the first combustion control means 21. Switching to the combustion control means 21 (step S103). Thereby, the control of the gas amount is switched from the combination of the feedback control and the feedforward control to the feedforward control alone.
[0032]
FIG. 5 shows the change in the set temperature, the change in the tapping temperature, and the change in the amount of gas supplied to the burner 11 when the set temperature is raised from Tsp1 to Tsp2. When the set temperature is increased from Tsp1 to Tsp2 as shown in FIG. 5A, the control of the gas amount is shifted to the feedforward control as shown in FIG. 5C, and the initial gas amount 61 is The value is set to a value larger than the target gas amount GF2 at the time of steady operation at the set temperature Tsp2 after the change. Thereafter, as indicated by the solid line b in FIG. 5C, the gas amount is gradually lowered toward the target gas amount GF2 (step S104).
[0033]
When the difference ΔGF between the gas amount supplied by the feedforward control and the target gas amount GF2 becomes smaller than a predetermined reference value (step S105; Y), the switching unit 23 changes the gas amount control unit to The control is switched to the second combustion control means 22 (step S106), and thereafter, the gas amount is controlled by combustion control using both feedforward control and feedback control. Here, the value of the reference value ΔGF is determined by the following equation.
ΔGF = ABS (GF2−GF1) × 0.05 (2) where ABS indicates an absolute value.
[0034]
After the set temperature is changed, by controlling the gas amount as described above, the tapping temperature does not overshoot as shown by the solid line b in FIG. Reach set temperature. When combustion control with feedback control is executed even after the set temperature has been changed as in the prior art, the gas amount changes as indicated by the dotted line a in FIG. 5C, and the tapping temperature is the dotted line in FIG. 5B. As shown by a, it changes so as to reach the set temperature after change while overshooting or undershooting.
[0035]
Even if the gas amount is changed, there is a certain delay time until the change appears in the hot water temperature as shown in FIG. 5B, and the hot water temperature is present even after the change starts to appear. Since it changes gradually according to the time constant, if the feedback control that keeps the tapping temperature close to the set temperature is continued when the set temperature is changed, the gas amount will be changed more than necessary, and the tapping temperature will eventually change. Overshoot. Further, if it is detected that the tapping temperature exceeds the set temperature after the change and this is fed back, the amount of gas is drastically reduced, so that an undershoot appears this time.
[0036]
The change characteristic set by the change characteristic setting means 25 is determined so that the tapping temperature shifts to the set temperature after the change without causing overshoot in consideration of such time delay and time constant. By performing feedforward control according to the change characteristic, it is possible to smoothly shift the tapping temperature to the target temperature.
[0037]
In addition, since the initial value of the gas amount in the change characteristic is rapidly changed to a value exceeding the target gas amount GF2 corresponding to the changed set temperature, the tapping temperature is rapidly changed toward the changed set temperature. It is possible. Further, after that, the amount of gas to be supplied is gradually brought closer to the target gas amount GF2, so that the tapping temperature can be stabilized at the changed set temperature without overshooting or undershooting.
[0038]
FIG. 6 shows the change in the set temperature, the change in the tapping temperature, and the change in the amount of gas supplied to the burner 11 when the set temperature is lowered from Tsp1 to Tsp2. Even when the set temperature is lowered from Tsp1 to Tsp2 as shown in FIG. 6A, the control of the gas amount is shifted to the feedforward control as shown in FIG. Is set to a value that is even smaller than the target gas amount GF2 for steady operation at the set temperature Tsp2 after the change. Thereafter, as indicated by a solid line b in FIG. 6C, the gas amount is gradually increased toward the target gas amount GF2.
[0039]
When the difference ΔGF between the gas amount supplied by the feedforward control and the target gas amount GF2 becomes smaller than the reference value, the gas amount control means is switched to the second combustion control means 22, and thereafter The amount of gas is controlled by combustion control using both feedforward control and feedback control.
[0040]
Thus, when a change to lower the set temperature is made, by controlling the gas amount as described above, the tapping temperature does not undershoot as shown by the solid line b in FIG. The changed set temperature is reached within a short time. In addition, if control with feedback control is performed even after setting temperature is changed like the past, the amount of gas will change as shown by the dotted line a of FIG.6 (c), and tapping temperature will change in FIG.6 (b). As indicated by the dotted line a, the temperature changes so as to reach the set temperature after the change while overshooting or undershooting.
[0041]
In the embodiment described above, the reference value ΔGF is set to 5 percent of the absolute value of the difference between GF1 and GF2, but the value of ΔGF is not limited to this. Further, the timing for returning from the feedforward control to the combustion control with feedback control is determined based on the gas amount (ΔGF). However, when a predetermined time has elapsed after switching to the first combustion control means 21, You may make it return to the combustion control accompanied by the feedback control by the 2 combustion control means 22. For example, the elapsed time after switching to the feed-forward control by the first combustion control means 21 is measured by the timer 24 of FIG. 1, and the second combustion control means 22 is obtained when a predetermined time such as 5 seconds elapses. You may make it return control to.
[0042]
【The invention's effect】
According to the water heater and the control method thereof according to the present invention, the gas amount is adjusted by feedforward control over a certain period from the time when the set temperature is changed during tapping, and the gas amount at that time is changed after the change. After changing the temperature to a value that exceeds the target gas amount corresponding to the set temperature, it is changed so that it gradually approaches the target gas amount, so the hot water temperature can be changed in a short time without overshooting or undershooting. The set temperature can be stabilized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a circuit configuration of a water heater according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a configuration of a water heater according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram illustrating an example of a gas amount change characteristic stored in a data storage unit of a change characteristic setting unit;
FIG. 4 is a flowchart showing a flow of operations performed when the set temperature is changed during hot water discharge by the water heater according to the embodiment of the present invention.
FIG. 5 is an explanatory view showing a change in set temperature, a change in tapping temperature, and a change in the amount of gas supplied to the burner when the set temperature is raised from Tsp1 to Tsp2.
FIG. 6 is an explanatory diagram showing a change in set temperature, a change in tapping temperature, and a change in the amount of gas supplied to the burner when the set temperature is lowered from Tsp1 to Tsp2.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Hot water heater 11 ... Burner 12 ... Heat exchanger 13 ... Water supply pipe 14 ... Hot water supply pipe 15 ... Flow sensor 16 ... Incoming water temperature sensor 17 ... Hot water temperature sensor 18 ... Gas supply pipe 19 ... Gas proportional valve 20 ... Control part 21 ... 1st combustion control means 22 ... 2nd combustion control means 23 ... Switching means 24 ... Timer 25 ... Change characteristic setting means 26 ... Data storage part 40 ... Remote control 41 ... Temperature setting switch

Claims (6)

In a water heater that can change the set temperature during hot water,
First combustion control means for feedforward control of the amount of gas supplied to the combustion section, and second combustion control means for controlling the amount of gas supplied to the combustion section by a predetermined control method involving at least feedback control based on the tapping temperature. Switching means for switching between the first combustion control means and the second combustion control means for controlling the amount of gas supplied to the combustion section, and the first combustion control A change characteristic setting means for setting a change characteristic of the gas amount when feedforward control is performed on the amount of gas supplied to the combustion unit by the means,
The switching means switches the control means for the amount of gas supplied to the combustion section to the first combustion control means when the set temperature is changed during tapping, and then when the predetermined return condition is satisfied, Returning the control means to the second combustion control means;
The change characteristic setting means, when the set temperature is changed during tapping, changes the current gas amount from the current gas amount to the direction in which the target gas amount for steady operation at the changed set temperature exists exceeds the target gas amount. The gas amount is set as an initial value, and a characteristic that gradually changes from the initial value so as to approach the target gas amount is set as a change characteristic of the gas amount,
The first combustion control means performs feedforward control on the amount of gas supplied to the combustion section according to the change characteristic set by the change characteristic setting means from the time when the set temperature is changed during tapping ,
A hot water heater characterized by appropriately combining feedback control and feedforward control so that the hot water temperature can be stabilized at the set temperature after the change in a short time . The hot water heater according to claim 1, wherein the change characteristic setting means sets the change characteristic based on a temperature difference between a set temperature before the change and a set temperature after the change. The switching means supplies, to the second combustion control means, a control means for controlling the amount of gas to be supplied to the combustion section assuming that the return condition is satisfied when a predetermined time has elapsed since switching to the first combustion control means. The hot water heater according to claim 1 or 2, wherein the water heater is returned. The switching means includes means for controlling the amount of gas supplied to the combustion section on the assumption that the return condition is satisfied when the difference between the amount of gas supplied to the combustion section and the target gas quantity falls within a predetermined value. The hot water heater according to claim 1 or 2, wherein the hot water heater is returned to the second combustion control means. The said change characteristic setting means sets the change characteristic of the said gas amount so that the tapping temperature reaches the set temperature fastest without overshooting or undershooting. The listed water heater. In the control method of a water heater that can change the set temperature during hot water,
When the set temperature is changed during tapping, the predetermined gas amount that has been changed beyond the target gas amount in the direction of the target gas amount for steady operation at the set temperature after the change from the current gas amount is initialized. And feedforward control based on a change characteristic that changes the amount of gas supplied to the combustion section so as to gradually approach the target gas amount from the initial value, and supplies the combustion section when a predetermined return condition is satisfied A method for controlling a water heater, wherein the control of the gas amount is returned from the feedforward control to a predetermined control accompanied by feedback control based on at least a hot water temperature.

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