JPH0450498B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the outlet temperature of hot water in a water heater.

[Conventional technology]

The conventional method for controlling the outlet temperature of a water heater is to install a temperature detector on the outlet side of the heat exchanger, and adjust the fuel flow control valve based on the deviation between the outlet temperature detected by the temperature sensor and the set temperature set by the temperature setting device. Feedback control, which adjusts the opening, was the mainstream. However, since the feedback control does not detect the amount of water, it has the drawback of poor response characteristics when starting up the water heater and when changing the amount of water. Therefore, in recent years, a water flow sensor has been installed in the water passage in the water heater to detect the water flow, and a temperature sensor has also been installed on the inlet side of the heat exchanger to detect the incoming water temperature. Feedforward control is performed to calculate a value proportional to , and adjust the opening degree of the fuel flow rate control valve.

F1=K・W・(Ts−TI) ……(1) F1: Value proportional to required heat amount W: Water amount Ts: Set temperature Ti: Inlet water temperature K: Constant This feedback control is generally based on the above feedback. It is used in conjunction with control.
FIG. 3 shows a diagram of the operating principle of a water heater that controls the temperature of hot water through feed forward control and feedback control. The water passage 1 is equipped with a water amount detector 2 and an inlet water temperature detector 3 on the upstream side of the heat exchanger 4, and an outlet hot water temperature detector 5 on the downstream side. The fuel passage 6 is equipped with an electromagnetic valve 7 and a heat flow control valve 8, and the fuel is guided to the bar T9 and combusted.

FIG. 4 shows a conventional hot water temperature control method for the water heater shown in FIG. Water amount W detected by water amount detector 2
and the inlet water temperature Ti detected by the inlet water temperature detector 3,
The hot water temperature To detected by the hot water temperature detector 5,
Using the set temperature Ts set by the temperature setting device 10 as an input signal, F1, which is a value proportional to the required amount of heat, is calculated using equation (1) above. Next, in the first control system (feed forward control system), F1 is used as an input signal. Outputs a value F2 proportional to F1. The opening degree of the fuel flow control valve 8 is then set based on the value of F2. On the other hand, in the second control system (feedback control system), the set temperature Ts
Deviation ΔT = Ts − To, which is obtained from the hot water temperature To
A feedback amount is determined based on the deviation, and a signal B2 is outputted to correct the opening degree of the fuel flow rate control valve 8 set by the first control system so that the deviation becomes smaller. Through the above control, the opening degree of the fuel flow rate control valve 8 was controlled so that the outlet hot water temperature matched the set temperature.

[Problems to be solved by the present invention]

FIG. 5 shows an example of hot water discharge characteristics under conventional feedforward and feedback control. Here, feedback control is performed using only integral control, and the response characteristics are shown when the set temperature is changed from 42°C to 50°C. When the set temperature is changed, the first control system (feed forward control system)
It inputs F1 calculated from Ts, Ti, and W, and outputs F2. The second control system (feedback control system) inputs the deviation ΔT obtained from Ts and To and outputs B2. By the way, since the water pipes of the heat exchanger 4 of the water heater have a length of 1 to 2 m, there is a dead time when the hot water temperature does not change even if an appropriate amount of fuel is input at the start of change, and the heat exchanger 4 Because of the heat capacity it has, the temperature of the hot water rises slowly.

Therefore, in the conventional control method, the opening degree of the fuel flow rate control valve 8 is set to point A by the output F2 from the first control system, and the hot water discharge is set by the output B2 from the second control system. While the temperature is below the set temperature, the fuel flow control valve 8 is driven in the direction of opening. By the way, as mentioned above, dead time and delay occur in the response of the outlet temperature when the set temperature changes, so when the set temperature starts changing, the value of ΔT increases, and as a result, B2 increases, so the fuel flow control valve The opening degree at point 8 increases to point B. Next, when the hot water outlet temperature exceeds the set temperature, the value of ΔT becomes negative and B2 also becomes negative, driving the opening of the fuel flow control valve in the direction of closing. However, the wasted time and response delay in response to the hot water outlet temperature Therefore, overshoot as shown in the figure occurs in the hot water outlet temperature, and it takes time for the hot water outlet temperature to stabilize. In addition, the feedback control system of the conventional control method shown in Fig. 4 controls only the deviation between the set temperature and the hot water temperature, and does not include data on water volume, so when the water volume is large, it is relatively dependent on feedback. When the correction value is small and the amount of water is small, the correction value due to feedback becomes relatively large, so especially when the amount of water is small, the overshoot becomes large, causing discomfort to the user.

[Means for solving problems]

FIG. 1 shows a control method of the present invention for solving the problems of the prior art.

First, from the water amount W detected by the water supply amount detector 2, the inlet water temperature Ti detected by the inlet water temperature detector 3, and the set temperature Ts set by the temperature setting device 10, F1 is calculated by formula (1).
Calculate. Further, B1 is calculated from the set temperature Ts, the hot water outlet temperature To detected by the hot water outlet temperature detector 5, and the water amount W using the following equation.

B1=K×W×(Ts-To)...(2) Here, B1 is calculated in the same manner as in the following equation.

B1=F1-K×W×(To-Ti)...(3) Next, multiply B1 by the constant C1 and take the sum with F1 to obtain F2=F1+C1×B1...(4).

F1, B1, obtained using equations (1), (2), (or (3)), and (4) above,
The following control is performed using F2.

The first control system receives F2 as an input and outputs F3, which is a function of F2, as shown in FIG. here
F3 can be considered to be a value obtained by adding proportional control of feedback to feedforward. Further, the second control system receives B1 as an input and outputs a feedback amount B2. And if the change amount DF1 of F1 per unit time is less than a certain value C2,
Within a certain period of time C3 after F1 changes, the output of the second control system is set to B2=0, and the opening degree of the fuel flow rate control valve 8 is controlled by F3, which is the output of the first control system.
After a certain period of time C3 has elapsed, the opening degree of the fuel flow control valve 8 is adjusted using both the F3 and B2 signals. That is, compared to conventional control systems, it has the following features.

(1) Conventionally, the signal output from the first control system when the load changes (when the water amount or set temperature changes) is a feedforward value, but the present invention uses a feedforward value and a feedback (proportional control) value.

(2) Conventionally, the input of the second control system was simply ΔT=Ts
-To, but in the present invention, a term for the amount of water is added to this to form equation (2).

(3) When the load changes, in the conventional control method, the fuel flow control valve 8 is driven by the output of the second control system and the output of the first control system immediately after the load change. The output of the second control system was set to O during a certain period of time.

[Effect]

The hot water temperature characteristics in the control method according to the present invention are
As shown in the figure. The conditions are the same as in FIG. First, when the set temperature is changed from 42° C. to 50° C., the output B2 of the second control system becomes 0 for a certain period of time, so the opening degree of the fuel flow control valve 8 is set by the output F3 of the first control system.
By the way, F3 is determined as a value proportional to F2 as shown in FIG. 1, and F2=F1+C1×B1.
When the set temperature changes, F1 changes to a certain value and then remains constant, but B1 is large while the difference between the hot water outlet temperature To and the set temperature Ts is large, and gradually decreases as the hot water outlet temperature To approaches the set temperature Ts. . That is, the movement of the fuel flow rate control valve 8 due to F3 increases in opening degree when the load changes, and gradually decreases in opening degree, as shown in FIG. Therefore, the slope of the rising temperature of the hot water when the set temperature changes becomes large, and the temperature tends to quickly approach the set temperature. Next, after a certain period of time has elapsed, the output B2 of the second control system is added to the output F3 of the first control system, and since B2 is a value based on B1 determined by equation (2), appropriate feedback can be achieved. Since the opening degree of the fuel flow rate control valve 8 can be controlled by the amount, there is no overshoot as shown in FIG. 5, and the stabilization time of the outlet temperature can be shortened.

〔Effect of the invention〕

According to the present invention, there is no overshoot or undershoot in the hot water output temperature even when the set temperature changes or the water amount changes, and a stable hot water temperature characteristic can be achieved, so that the user can immediately obtain hot water in the amount and temperature desired by the user. Therefore, usability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a hot water outlet temperature control method according to the present invention, FIG. 2 is a diagram showing an example of hot water outlet characteristics in the hot water outlet temperature control method according to the present invention, and FIG. 3 is a diagram showing feed forward control and feedback. Fig. 4 is a diagram showing the operating principle of a water heater with a control system, and Fig. 4 is a diagram showing conventional feedforward control and feedback control methods.
The figure is a diagram showing an example of hot water discharge characteristics according to the control method shown in FIG. 4. Explanation of symbols, 1...Water passage, 2...Water amount detector, 3...Water inlet temperature detector, 4...Heat exchanger, 5
... Hot water temperature detector, 6 ... Fuel passage, 7 ... Solenoid valve, 8 ... Fuel flow rate control valve, 9 ... Burner, 1
0...Temperature setting device, 11...Control circuit.

Claims (1)

[Claims] 1 The water passage passing through the heat exchanger is equipped with a water quantity detector, an inlet water temperature detector, and an outlet water temperature detector, and the fuel passage leading to the burner is equipped with a fuel quantity control valve, and a valve for setting the outlet water temperature. In a water heater equipped with a temperature setting device and a control circuit, a value F1 is obtained by multiplying the difference between the set temperature set by the temperature setting device and the incoming water temperature detected by the incoming water temperature detector by the amount of water detected by the water amount detector, Calculate the value C1 x B1 by multiplying the value B1, which is the difference between the set temperature and the hot water temperature detected by the hot water tap sensitivity detector by the water volume, by a certain constant C1, and use the sum value F2 = F1 + C1 x B1 as input. It has a first control system that outputs a value F3 proportional to that, and a second control system that outputs a value B2 that is an integral of the value of B1.If the amount of change in F1 per unit time is larger than a certain value, F1 F3 as B2=O for a certain period of time from the start of change of
A water heater control method characterized in that the opening degree of the combustion flow rate control valve is controlled using only the signal F3 and the opening degree of the fuel flow rate control valve after a certain period of time has elapsed, using both F3 and B2 signals.