JPS6235579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to hot water temperature control for water heaters that use gas, oil, air, etc. as a heat source, and solves the conventional problem that the set hot water temperature cannot be obtained when the water supply is overloaded with a large amount of water. In order to solve the problem, the present invention aims to provide a new control device that suppresses overshoot by controlling the amount of water supplied and changing the water amount change control speed according to the controlled amount.

Hereinafter, a gas water heater that uses gas as fuel will be described as an example.

FIG. 4 is a block diagram of a conventional gas water heater, in which water is exchanged with combustion heat from a gas burner 1 serving as a heat source and water is provided by a heat exchanger 2. The temperature control device 3 takes in the signal (TWO) from the outlet hot water temperature detector 4 and the signal (TWR) from the hot water temperature setting device 5, and determines a predetermined combustion amount from the deviation between them (TER=TWR−TWO). The supply heat amount controller 6 is controlled to control the hot water temperature. Generally, a thermistor is often used as the hot water temperature detector 4, and a PiD method is often used as the hot water temperature control algorithm.

FIG. 3 is a diagram showing the relationship between the water supply amount W (horizontal axis) of the gas water heater and the temperature rise ΔT (vertical axis). The thick solid line in the figure represents the temperature rise characteristic at the maximum combustion amount Qg _MAX , that is, the capacity curve of the water heater. In other words, the maximum combustion amount Qg _MAX , the temperature rise △T, and the water supply amount W that is the load are as follows, where η is the combustion efficiency, η・Qg _MAX = W・△T (1), and further, △ It is expressed as T=η・Qg _MAX /W (2). Therefore, at each water supply amount W, there is no temperature rise greater than the solid line shown in the figure. For example, when the maximum combustion amount Qg _MAX , the amount of hot water released is
If W ₁ , the temperature rise will be ΔT ₁ as shown. The above-mentioned temperature control device 3 receives the set temperature signal TWR from the hot water temperature setting device 5 and the water supply temperature.
When the difference from TWi, that is, the value ΔT at which the temperature should be increased, is ΔT ₁ , it acts effectively in the flow rate range of water supply amount WW ₁ . However, in a load larger than W ₁ , that is, in a flow rate range of W>W ₁ , control becomes impossible, and the outlet temperature TWO will never reach the set temperature TWR no matter how long it takes.

In this way, the maximum combustion amount Qg _MAX limits the amount W of hot water that can be heated and whose hot water temperature can be controlled. It is an object of the present invention to provide a control device that eliminates such drawbacks of conventional water heaters, allows a desired hot water temperature to be obtained at all times, and reaches a set temperature in a short period of time after the start of use.

FIG. 1 is a block diagram of a gas water heater of the present invention. Devices with the same numbers as in FIG. 4 are devices having the same functions. In the control device 7, the hot water temperature detector 4
The signal TWO of the water supply temperature sensor 8 and the signal TWi of the water supply temperature sensor 8
, the signal TWR of the hot water temperature setting device 5 is taken in, and the TWR
The predetermined combustion amount is determined from the deviation TER _between In this case, the water supply amount controller 9 is used to limit the amount of water supplied (W ₁ is the maximum controllable water amount). With this method, you will always get hot water at the set temperature.

However, when changing the amount of water that can be supplied depending on the TUP mentioned above, if the amount of variation in water amount is large,
In particular, when decreasing the water temperature, the controller may not be able to follow the process response delay of the controlled object, mainly the heat exchanger, and unnecessary overshoot of the hot water temperature may occur. In contrast, in the present invention, when changing the supply water amount depending on the TUP, if the rate of change of the water amount is varied according to the amount of change (operated amount), the overshoot does not become extremely large. Moreover, it is possible to control the water supply amount as soon as possible when changing the set temperature.

FIG. 2A is an example of a case where the water supply amount is changed quickly. The upper figure shows the hot water temperature characteristics, and the lower figure shows the water supply amount characteristics. When the set temperature is changed from TUP1 to TUP2 at time t= _t0 , the third
Based on the characteristics shown in the figure, the water supply amount is limited from W ₁ to W ₂ .
If the change time at this time is _t1 , the outlet temperature changes with an overshoot ΔT, and gradually converges. Increasing the rate of change is similar to, for example, a sudden load change in a hot water faucet, and when the amount of water decreases, overshoot cannot be avoided due to controllability.

On the other hand, FIG. 2B shows an example in which the water supply amount is changed relatively slowly. Similar to A, the set temperature has been changed from TUP1 to TUP2, and the water amount has been changed from _W1 to _W2 accordingly. The changing time at this time is t ₂ (>t ₁ ), which is a changing speed that can sufficiently suppress overshoot compared to the performance of the controller. As is clear from the figure, the overshoot ΔT at this time is sufficiently smaller than A, and
It can be seen that the settling time is also shorter.

Up to now, we have described the case where the flow rate is decreased, but it goes without saying that when increasing the flow rate, undershoot can also be suppressed by setting a slow change speed in consideration of transient response.

As explained above, according to the water heater control device of the present invention, the water supply amount of the water heater is limited according to the set temperature and the hot water temperature is controlled within the capacity range, so that hot water at the desired temperature is always available. In addition, since the changing speed when limiting the water supply amount is changed according to the control amount, an excellent effect can be obtained in that overshoot due to the water supply amount restriction can be eliminated.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a gas water heater according to an embodiment of the present invention, Fig. 2 A is a characteristic diagram of hot water temperature and water supply amount when the water supply amount change rate is fast, and B is a characteristic diagram when the water supply amount change rate is slow. 3 is a characteristic diagram showing the relationship between the water supply amount and temperature rise of a gas water heater, and FIG. 4 is a configuration diagram of a conventional gas water heater. 4... Hot water temperature detector, 5... Hot water temperature setting device, 6
...Supply heat amount controller, 8...Feed water temperature detector, 9
...Water supply controller.

Claims (1)

[Claims] 1 A water supply temperature sensor, a hot water temperature sensor, a hot water temperature setting device, a supply heat amount controller, a water supply amount controller, and the deviation (TER) between the signal of the hot water temperature setting device and the signal of the hot water temperature sensor. ), the supply water amount controller is controlled depending on the difference (TUP) between the signal of the hot water temperature setting device and the signal of the water supply temperature sensor, and this control A water heater control device comprising: a control device that gently varies a rate of change in the amount of water supplied according to a change in the amount of water to be increased or decreased.