JPH0144977B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a water heater with a temperature control device, which reduces transient temperature changes, especially rapid temperature rises, and dramatically improves the safety and comfort of showers, etc. It is something to do.

A conventional water heater with a temperature control device and its temperature control characteristics will be explained with reference to FIGS. 1 to 5.

Figure 1 shows the most common gas water heater control system. Water is supplied from water supply pipe 2 to heat exchanger 1
and then to the faucet 6. Gas enters through a gas pipe 3, passes through a proportional control valve 4, and is combusted in a burner 5, which is a heat source, to heat water in a heat exchanger 1. The proportional control valve 4 continuously controls the gas flow rate by varying the magnetic force by, for example, the amount of current flowing through the coil and moving the valve up and down. The outlet temperature is detected by the second temperature sensor 7, and compared with the set temperature determined by the temperature setting device 9 in the control circuit 8, and the proportional control valve 4 is driven according to the difference to control the combustion amount. This is to maintain the hot water temperature at the set value. However, in this case, the problem with closed-loop control is that there is a delay in the heating of the main unit, which does not appear as an immediate change in the temperature of hot water, especially when the amount of hot water dispensed is variable, resulting in poor control stability and the characteristics shown in Figure 2. become. The vertical axis T is the hot water temperature, and the horizontal axis t is the elapsed time, To
is the set temperature, Ti is the initial temperature, and as shown in the figure, damped oscillation occurs with the set temperature To as a boundary. In severe cases, the shower vibrates permanently, causing discomfort when using the shower and creating a risk of burns.

Therefore, as shown in FIG. 3, the inventors of the present invention detect the water supply temperature with the first temperature sensor 11, detect the amount of hot water with the flow rate sensor 10, and control the control circuit 12 by (set temperature - water supply temperature) x output. We have proposed a method in which the amount of hot water is calculated and the result is sent to the proportional control valve 4 to determine the amount of combustion, but since it is an open loop control, a deviation ΔT from the set temperature To inevitably occurs, as shown in Figure 4. Undesirable. The cause of the deviation ΔT is due to variations in the linear variation of mechanical parts such as the heat exchanger 1, proportional control valve 4, and burner 5, and circuit parts such as the sensor 7 and control circuit 8. is indeterminate (for example, when the amount of combustion is large, it takes a negative value, and when the amount of combustion is small, it becomes a positive value)
Therefore, when using a shower in the summer, it often happens that the water suddenly comes out hotter than expected.

Further, as another conventional example, a system as shown in FIG. 5 is known. The control circuit 13 processes the hot water temperature detected by the second temperature sensor 7, the hot water amount detected by the flow rate sensor 10, and the temperature set value determined by the temperature setting device 9, and The calculation result is output to the proportional control valve 4 to control the combustion amount. However, since this method does not have a factor for supply water temperature, its control characteristics change depending on the season, resulting in the situation shown in FIG. 2. The reason for this is that even with the same temperature setting and the same change in hot water output, unless the change in combustion rate is small when the water supply temperature is high (summer) and the combustion rate is large when the water supply temperature is low (winter), transient This is due to the inability to keep changes small.

The present invention solves the above-mentioned drawbacks of the conventional technology, and one embodiment thereof is shown in FIG. The present invention includes a controller 100, which controls the outlet hot water temperature detected by the second temperature sensor 7 and the temperature setting device 9.
A closed loop control means 8 compares the temperature set by the temperature setting device 9 and outputs an output according to the temperature difference, and a closed loop control means 8 compares the temperature of the water detected by the first temperature sensor and the temperature set by the temperature setting device 9 and outputs an output according to the temperature difference. Open loop control means 14 performs the calculation shown in the following formula by multiplying the amount of hot water detected by the flow rate sensor 10, and outputs the value ((set temperature - water supply temperature) x amount of hot water released)
output reduction control means 101 that reduces the output of the open loop control means to a predetermined value; and output reduction control means 101 that combines the output of the output reduction control means and the output of the closed loop control means and controls the burner 5, which is a heat source, according to the combined output. Output synthesis control means 102 that controls the combustion amount
It is composed of In a water heater using this controller, only the advantages of open-loop control and closed-loop control are brought out, and the disadvantages are offset and minimized, so the hot water output characteristics are as shown in Figure 7. This provides nearly ideal control characteristics for a water heater, in that transient undershoots and especially dangerous overshoots are eliminated, and a temperature always equal to the set temperature is obtained. Until the time tp, the temperature is rapidly raised to the vicinity of the set temperature To mainly by the open loop control output, but the value is determined by taking into account the variation of each component and output reduction control means 1.
01, the set temperature To
It never exceeds. Furthermore, since the amount of hot water that does not reach the set temperature is quickly corrected by the closed loop control output, hot water at the set temperature To can be reliably obtained.

The specific reason why the above-mentioned undershoot/overshoot becomes small is, for example, when the hot water output amount is decreased, (set temperature - water supply temperature) x hot water output x decrease value - however, decrease value < 1.0 - or (set temperature The open-loop control output, which is expressed as - water supply temperature) × hot water output amount - decrease value, immediately changes to output a value that is close to the required output but does not exceed the required output even if deviation variations are included, and with this output, the hot water output temperature is rapidly moved to a low value almost close to the set temperature, and this open-loop control output stably exists as a fixed output that is not affected by changes in the tapped water temperature, that is, a bottom-up output.
Furthermore, minute negative deviations between the hot water outlet temperature and the set temperature are automatically corrected by the closed loop control output, so the hot water outlet temperature always matches the set temperature and works as a correction for minute deviations. The change in the closed loop control output inevitably becomes a small value, and as a result, the cause of transient undershoot/overshoot is removed and the value becomes small. The fact that the change in the closed-loop control output described above inevitably becomes a small value is an effect that only occurs when open-loop control and closed-loop control are combined. It can be stably demonstrated almost unaffected by the size of the object.

A concrete example of this control circuit is shown in FIG. 7′
is a negative temperature-sensitive resistance element (hereinafter referred to as a thermistor) of the second temperature sensor 7 that detects the temperature of the tapped water. 11' is a thermistor of the first temperature sensor 11 that detects the temperature of the water supply. 10' is a pressure sensitive resistance element of the flow rate sensor 10 that detects the amount of hot water dispensed;
For example, the flow rate is converted into differential pressure, and that pressure causes a change in resistance value. 9' is temperature setting device 9
This is a double variable resistor used in 4' is a coil of the proportional control valve 4. 20 and 33 are operational amplifiers, and 32 is a power supply for the circuit.

First, the open loop control means 14 will be explained. Resistors 16, 17, temperature setting variable resistor 9',
A bridge is formed by a thermistor 11' for detecting the supply water temperature, and the difference in midpoint potential is compared and amplified by an operational amplifier 20. The resistor 15 is for linearizing the thermistor change. The amplification factor of this circuit is determined by the ratio of the resistor 18 to the parallel composite value of the flow rate sensor 10' and the resistor 19. Resistor 19 linearizes the variation in flow rate sensor 10'. With the above circuit configuration, the output of the operational amplifier 20 is a value proportional to (set temperature - water supply temperature) x amount of hot water dispensed as the output of the open loop control means 14 .

Next, the output reduction control means 101 will be explained. The output of the operational amplifier 20 is divided by resistors 34 and 35,
The midpoint is set as the output of the output reduction control means 101. For example, if the outlet temperature does not rise too much when driven at 80% of the calculated value, taking into account variations and fluctuations, the objective can be achieved by setting the ratio of resistors 34 and 35 to 2:8. In this example, the calculated value is reduced by multiplying it by a constant ratio of 0.8, but there are many other possible configurations such as subtracting a constant value or making that value a certain function value. In order to quickly match the set temperature, it is natural that the decrease value should be as small as possible, and for this reason, for example, parallel resistors 15, 19, 21, etc. are connected to promote linearization of each sensor. It is something.

Next, the closed loop control means 8 will be explained. Resistors 22, 23, temperature setting variable resistor 9'
and the thermistor 7' for detecting the hot water temperature, forming a bridge, and the difference between the midpoint potentials is compared and amplified by the operational amplifier 33. The resistor 21 is for linearizing the change in the thermistor 7'. The amplification factor of this circuit is determined by the ratio of the resistors 24 and 25, and since the integrating capacitor 26 is connected, integration is performed as long as there is a difference between the set temperature and the detected temperature.
The output of the operational amplifier 33 is changed, and this becomes the output of the closed loop control means 8. The output synthesis control means 102 drives the base of the transistor 30 via resistors 27 and 28 to adjust the current flowing through the proportional control valve coil 4'. ' is a diode for absorbing induced voltage.

The effects of the present invention are summarized below.

(1) Since the output of the open-loop control means is reduced to a predetermined value by the output reduction control means, it is possible to avoid errors caused by variations in mechanical parts or circuit parts or variations in linear variation. There is no danger that the temperature will be higher than the set temperature, and in addition, any temperature that has not reached the temperature due to the output of the open-loop control means is quickly corrected by the output of the closed-loop control means, so hot water is reliably delivered at the set temperature. can be obtained.

(2) The open-loop control output exists stably as a bottom-up output, and on top of that, the minute negative deviation between the tapped water temperature and the set temperature is automatically corrected by the closed-loop control output. The change in the closed loop control output that acts as a correction for minute deviations inevitably becomes a small value, and as a result, the cause of transient undershoot/overshoot is removed and the value becomes small.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a conventional example, Fig. 2 is a diagram showing its temperature control characteristics, and Fig. 3 is a configuration diagram of another conventional example.
Fig. 4 is a diagram showing its temperature control characteristics, Fig. 5 is a block diagram of another conventional example, Fig. 6 is a block diagram of the water heater of the present invention, and Fig. 7 is a diagram showing its temperature control characteristics. , FIG. 8 is a circuit diagram showing an embodiment of the control circuit. 1... Heat exchanger, 2... Water supply pipe, 4... Proportional control valve, 5... Heat source (burner), 7... Second temperature sensor,
8... Closed loop control means, 9... Temperature setter, 10... Flow rate sensor, 11... First temperature sensor, 14... Open loop control means, 100... Controller, 101... Output reduction control means, 102... Output combination control means.

Claims (1)

[Claims] 1 a heat source, a heat exchanger that transfers heat from the heat source to water, and a first device that detects the temperature of the water heading toward the heat exchanger.
a second temperature sensor that detects the temperature of the hot water coming out of the heat exchanger, a flow rate sensor that detects the flow rate of the water, and a temperature sensor that is detected by the first temperature sensor. open loop control means that compares the temperature of the heated water with a set temperature and outputs a multiplied value obtained by multiplying the temperature difference by the flow rate detected by the flow rate sensor; and the outlet temperature detected by the second temperature sensor and the set temperature. closed-loop control means for comparing the temperature and outputting the output according to the temperature difference; output reduction control means for reducing the output of the open-loop control means to a predetermined value; and the output of the output reduction control means and the closed-loop control means. and a controller comprising an output synthesis control means for synthesizing the outputs of and controlling the heat source according to the synthesized output.