JPS6235580B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to temperature control of water heaters that use gas, oil, electricity, etc. as a heat source. It is an object of the present invention to provide a control device that reduces the time required to converge to a target hot water temperature and suppresses deviations in hot water temperature from a set value as much as possible by controlling from a predetermined heat supply value when starting.

Here, the effects of the present invention will be explained using an example of a gas instantaneous water heater that uses gas as fuel.

FIG. 1 shows the configuration of the water heater. gas burner 1
The combustion heat is replaced with water in the heat exchanger 2 and supplied as hot water. The temperature controller 3 inputs the signal TWO ₂ from the hot water temperature detector 4 and the signal TWR from the temperature setting device 5, and calculates the temperature deviation TER=
A predetermined combustion amount is determined from TWR-TWO ₂ , and the supply heat amount controller 6 is controlled to control the hot water temperature. Generally, a thermistor or thermocouple is used as the hot water temperature detector, and proportional, integral, and differential control (PiD method) or a combination thereof is used as the hot water temperature control algorithm. 7 indicates a hot water supply port.

In FIG. 2, the hot water temperature control system of FIG. 1 is shown in blocks. 8 is the gain of the controller (arithmetic control using PiD method, etc.), 9 is the gain mainly for the heat exchanger which is a process, and 10 is the block that shows the response and gain of the hot water temperature detector, and the hot water temperature deviation TER is input. The controller gives an output TC (corresponding to the amount of combustion) to the process,
As a result, the water temperature is expressed as TWO. TWO ₂
is the outlet hot water temperature input via the outlet hot water temperature detector 4, and includes an element of response delay with respect to TWO.

FIG. 5 shows the outlet temperature characteristics of a conventional temperature controller. a is the hot water temperature, b is the water supply amount, and c is the time characteristic of the controller output and the integral term. Steady state combustion continues until t<t ₁ , at which time the water supply amount is W ₁ and the controller output is TC ₁ . In the PiD method, which does not leave a steady deviation in temperature,
The controller output in steady state is equal to the value of the integral term. In other words, the integral amount is the balance point with the load. If hot water supply is stopped at t= _t1 , instantaneous water heaters will immediately stop combustion and no additional combustion will occur. In other words, the controller output TC becomes zero. When water starts flowing again from the hot water supply port at t=t ₂ ,
The hot water temperature TWO that is heated by the heat capacity of the equipment that has accumulated in the water heater first appears (Tov ₁ ), and then the hot water that is heated from the water temperature according to combustion control appears. T _DW1 is an undershoot and is greatly influenced by the control output. c's
VTi indicates the integral amount in the controller, and this VTi
The output of the PiD method that includes is TC.
In the conventional method, when re-igniting, the same control as when starting to use the water heater is performed, so the calculation of the integral term starts from zero. In electronic circuits, charging and discharging a capacitor corresponds to an integral amount. For this reason, a large undershoot T _DW1 occurs as shown in Figure a, which is a problem when using the water heater by frequently opening and closing the hot water supply opening.

FIG. 6 shows another conventional example, in which the amount of water supplied at the time of re-ignition at t=t ₂ is W ₃ −W ₂ , which is smaller than the flow rate before the water flow is stopped. When the flow rate at the time of re-ignition is small in this way, the absolute value of the overshoot amount T _OV2 , which depends on the capacity of the heat exchanger, becomes large. Furthermore, when the set temperature WTR ₂ is high, the output hot water may reach a dangerous temperature Tx (for example, 95°C) for a water heater. In this case as well, in the conventional method, a large undershoot T _DW2 is generated after the overshoot.
is occurring. For this reason, the settling time is also becoming longer.

It is an object of the present invention to eliminate such conventional drawbacks, suppress undershoot, and supply high-quality hot water that converges quickly.

With reference to FIG. 3, the hot water temperature control of the present invention will be explained. a,
b and c are the time characteristics of the hot water temperature, water supply amount, and controller output, respectively, and as in Fig. 5, t = t ₁
This represents a mode in which hot water supply is stopped at t= _t2 and hot water supply is restarted at t=t2. The overshoot T _OV5 after re-ignition due to restarting hot water supply depends on the heat capacity, set temperature, and hot water supply amount of the water heater, and if the hot water amount at the time of re-heating is W ₁ as in Figure 5, it will be different from the conventional method. There is no difference. However, as shown in c, the integral amount set at time t ₂ is the integral amount in the steady state just before the water flow is stopped.
If the integral operation is started as TC ₁ (as described above, the controller output in a steady state can be considered as the integral quantity itself), the undershoot T _DW5 will almost disappear as shown by a. At t>t ₂ of c
The slight drop in VTi is due to the effect of overshoot.

In this way, if the hot water supply port is frequently opened and closed, undershoot can be prevented by restarting combustion control from the integral amount set for re-ignition TC ₁ within a predetermined time after water flow is stopped. It is possible not only to suppress this, but also to accelerate convergence to the target value. c's
Tix indicates the upper limit of a predetermined range of integral quantity,
The effect will be explained next.

FIG. 7 shows the response when the predetermined range of the integral amount is not provided. Similar to the hot water supply amount mode in FIG. 6, this is an example where the temperature setting is high at TWR ₂ and the hot water supply amount W ₃ at the time of re-ignition is smaller than the hot water supply amount W ₂ before water flow is stopped. At this time, if the integral amount set at the time of re-ignition is set to the steady state value TC ₂ , the deviation area after overshoot T _OV3 will increase, and the time to exceed Tx will become longer, making it less convenient to use and more dangerous. Become. Tix of c represents the upper limit value of the above-mentioned integral. TC ₃ is the steady state controller output at W ₃ .

Therefore, the present invention aims to reduce the risk of continuing overshoot and shorten the convergence time by determining the range of integration dependent on the set temperature as shown in FIG. a, b, c in Figure 4
are characteristic diagrams similar to a, b, and c in FIG. 3 above.
At the time of re-ignition, if the integral amount to be set exceeds the upper limit value Tix, Tix is used as the integral set value. As at time t=t ₂ in c, TC ₂ >
When Tix, let Tix be the integral set value and
It has time characteristics similar to VTi. By regulating it within this predetermined range, the overshoot T _OV
The over-deviation area after ₄ has been significantly reduced, and undershoot T _DW4 has also been suppressed.

By the way, when the set temperature is TWR ₂ and the amount of hot water supplied after re-ignition operation is equal to W ₃ ≒ W ₂ ,
By limiting TC ₂ to Tix, the undershoot will be larger than the characteristics shown in Figure 4, but in systems that do not have a means to immediately detect the amount of hot water, it is necessary to take into account the risk of high temperature in the flow rate change mode. do
It is better to set an upper limit like Tix. Furthermore, by making Tix compatible with TWR, even more precise control of water temperature becomes possible.

Moreover, although the upper limit value of the predetermined range has been described in the above description, undershoot can be suppressed by limiting the lower limit value to a predetermined value based on the relationship between the controller output and the process response. This is particularly effective when, contrary to the above, the flow rate during re-ignition is increased compared to when water flow is stopped.

As explained above, according to the water heater control device of the present invention, the undershoot at the time of re-ignition can be significantly suppressed or eliminated, and the settling time can be shortened. Furthermore, by providing a predetermined range of the integral amount depending on the signal TWR of the temperature setting device, it is possible to reduce the risk of abnormally high water temperature especially when the temperature is set to high temperature, and it is possible to realize a significant improvement in hot water supply performance. It should be noted that the present invention is sufficiently effective even for equipment that does not have a pilot burner.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a gas instantaneous water heater, Fig. 2 is a block diagram of temperature control, and Figs. 3 a, b, and c are hot water temperature characteristic diagrams of a water heater control device according to an embodiment of the present invention. Figures 4a, b, and c are characteristic diagrams showing other embodiments of the present invention; Figures 5a, b, and c are hot water temperature characteristic diagrams using a conventional control device; Figures 6a, b, and c are conventional FIGS. 7a, b, and c are characteristic diagrams showing other examples of comparison characteristics in the case where a predetermined range of integration is not provided. 3... Temperature controller, 4... Hot water temperature detector, 5
...Temperature setting device, 6...Supply heat amount controller, Tix...
...The upper limit of a predetermined range of integrals.

Claims (1)

[Claims] 1. A hot water temperature detector of a water heater, a temperature setting device,
a temperature controller that outputs a signal for controlling the amount of heat supplied by the water heater depending on the difference between the signal of the temperature setting device and the signal of the hot water temperature detector; and a supply amount of heat controller that responds to the output of the temperature controller. It maintains the temperature controller output value immediately before the heat supply is stopped due to hot water supply, and also maintains the upper limit and undershoot of the temperature controller output to prevent the hot water temperature from overshooting into the dangerous range when hot water supply is resumed. A water heater control device that controls the amount of heat to be supplied from the temperature controller output value held within a predetermined range indicated by the lower limit value of the temperature controller output that does not excessively increase the temperature. 2. The water heater control device according to claim 1, which holds the integral value of the temperature controller output immediately before the heat supply is stopped, and starts the integral operation from the held integral value within a predetermined range when hot water supply is resumed. . 3. The water heater control device according to claim 2, wherein the predetermined range is varied according to the temperature setting value.