JPH0343542B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a combustion control method for achieving combustion in a gas-fired water heater, etc. while rationally utilizing the capacity of the water heater, and in particular to a method for calculating the required combustion amount. Concerning improvements in methods.

<Prior Art> Recently, water heaters that use gas or the like as fuel and have a conceptual configuration as shown in FIG. 2 have been actively developed.

When the user opens the faucet 2, the water that flows in from the input flow path 6 is heated by the heat exchanger 3 heated by the gas burner 4, and is turned into hot water and output from the hot water flow path 7 through the faucet 2. Ru.

At this time, on the input flow path 6 side, the water amount sensor 8
The water amount (water supply amount or hot water output amount) S _w is detected by the water supply temperature sensor 9, and the water supply temperature T _c is detected by the water supply temperature sensor 9.
The information S _w and T _c are sent to the microcomputer 5 as a main control circuit. However, the water amount S _w can also be detected on the hot water outlet flow path 7 side.

On the other hand, an output flow path 7 leading from the heat exchanger 3 to the faucet 2
During the process, the outlet hot water temperature T _p is detected by the outlet hot water temperature sensor 10, and this is also fed back to the microcomputer 5.

In addition to these various sensor information, another piece of information given to the microcomputer 5 is set temperature information _Ts for specifying the user's preferred temperature.

In such a device configuration, the microcomputer 5 controls the air amount regulator 11 using the air amount control signal Sa and the gas proportional valve 12 using the gas amount control signal Sg so that optimal combustion can be carried out at any given time. , depending on the selected control method,
The required combustion amount F required at that time is calculated.

However, conventionally, the most common control methods for this purpose are feedforward control (FF control) and proportional control, as disclosed in Japanese Patent Application Laid-open No. 55-75156 and Japanese Patent Application Laid-open No. 57-33749. Therefore, in this case, the calculation formula for the required combustion amount F is as follows, assuming that the feed forward amount is “F _F ” and the proportional control amount is “F _P ”. It was becoming like that.

F = F _F + F _P = (Set temperature T _s - Water supply temperature T _c ) x Water amount S _w + (Set temperature T _s - Output water temperature T _p ) x Water amount S _w ... Here, in particular, the feed forward amount F _F
is also used to control the water flow valve 1 via the water flow valve control signal S _i , independently of the opening degree of the faucet 2, in order not to exceed the capacity of the water heater and to maximize the capacity. It will be done.

On the other hand, it is natural to consider a method that incorporates so-called proportional, integral, and differential control (PID control).
In that case, the calculation formula for the required combustion amount F is as follows, where the integral control amount is newly set as " _FI " and the component control amount is "F _D ".

F=F _P +F _I +F _D = (Set temperature T _s - Output hot water temperature T _p ) x Water amount S _w x K _P + Σ (Set temperature T _s - Output hot water temperature T _p ) x K _I + (Previous hot water temperature -
Current hot water temperature ₎ This is a method that uses forward (FF) control, proportional (P), and integral control (I) together.

Therefore, in this FF+PI control, the calculation formula for the above-mentioned required combustion amount F is defined as the following formula.

F=F _F +F _P +F _I = (Set temperature T _s - Hot water supply temperature T _c ) x Water amount S _w + (Set temperature T _s - Output hot water temperature T _p ) x Water amount S _w x K _p + Σ (Set temperature
T _s − Hot water temperature T _p ) × K _I ... <Problems to be solved by the invention> If we look only from the static characteristics, each of the above calculation formulas ~
Regardless of which control method is adopted, a stable outlet temperature T _p can be obtained.

However, first, the method that uses the above formula to calculate the required combustion amount, that is, FF + P control, PID control,
There are some disadvantages compared to FF+PI control according to the above calculation formula.

FF+P control has the disadvantage that the residual deviation is large and the outlet temperature T _p tends to deviate from the set temperature T _s . PID control tends to have a complicated calculation system and takes a long time to process. The disadvantage is that the effective response for use in water heaters is poor, and it is not as good as it should be based on the principle.

On the other hand, the FF+PI control which calculates the required combustion amount F according to the above formula has the least amount of the above-mentioned drawbacks.

However, the dynamic characteristics, that is, the transient characteristics, remained unsatisfactory, and the convergence time for the hot water temperature T _p to reach the set temperature T _s was still not sufficiently short, especially when the maximum capacity of the water heater was exceeded. The convergence time was considerably long when changing from combustion near maximum capacity to minimum combustion.

The present invention aims to further improve the FF+PI control according to the above formula, which is considered to be relatively superior among the conventional examples, in order to eliminate or alleviate all of the drawbacks of the conventional examples.

<Means for Solving the Problems> In order to achieve the above object, the present invention devises a method for calculating the required combustion amount and provides a method for controlling a water flow valve for a water heater having the following configuration.

It has a sensor that detects the water supply temperature, water flow rate, and hot water temperature, and based on these information and the set temperature information set by the user, it calculates the temperature required at any given time based on feed forward control, proportional control, and integral control. A combustion control method in a water heater that calculates the required combustion amount;
α is defined as ……, and the above required combustion amount is (set temperature – water supply temperature) × (water amount) × (set temperature – hot water temperature) ×
α + (Set temperature - hot water temperature) x (Water amount) x K _P + Σ (Set temperature -
A combustion control method in a water heater characterized by determining the temperature of hot water discharged) x K _I ...

<Operations and Effects> According to the above configuration of the present invention, it is obvious that the first term representing the feed forward amount F _F in the required combustion amount calculation formula in the conventional FF + PI control mentioned above is improved. and as shown in the above formula,
The feed forward amount obtained by the present invention with respect to the conventional feed forward amount F _F
F _F ′ is F _F ′ = F _F (set temperature - hot water temperature) x α
...' is written.

Therefore, when the set temperature rises and the outlet temperature decreases due to an increase in the flow rate, the value of the corrected product term in the above equation or '' formula, (set temperature - outlet temperature) x α...... is the set temperature. As the difference between the temperature and the outlet temperature increases, the value of the required combustion amount F expressed by the formula also becomes sufficiently large transiently, improving the start-up characteristics.Similarly, when the set temperature falls, When the temperature of the hot water rises due to a decrease in the flow rate, the required combustion amount F quickly decreases, and the falling characteristic also improves.

In this way, the FF+PI control in which the correction product term (set temperature - outlet hot water temperature) x α... is added to the feed forward amount calculation in the required combustion amount calculation formula according to the present invention is different from the conventional FF+PI control. This has the effect of further improving the characteristics of water heaters, making it extremely desirable as a control method for this type of water heater, which is expected to be widely used in the future.

Further, generally, the feed forward amount is used to control the water flow valve 1 shown in FIG. 2, but in this case also, according to the present invention, the feed forward amount _F If this is adopted, when it is necessary to raise the hot water temperature, the water flow valve is quickly operated in the closing direction to quickly reduce the amount of hot water, and then as the hot water temperature rises, it is reversely operated in the open direction, and then stopped. In exactly the same way, when it is necessary to lower the hot water temperature, the water flow valve is quickly moved in the open direction to quickly increase the hot water flow, and then
It can be moved in the closing direction and then stopped.
Therefore, it is possible to control not only the tapped water temperature T _p but also the tapped hot water temperature, thereby further aiding and improving the rise and fall characteristics of the tapped hot water temperature.

Note that the selection constant terms K _P and K _I in the above formula
has traditionally been set in design and experimentally as usual in this type of automatic control system, but in exactly the same way, the amount of feed forward
Among the newly added correction product terms to the operational terms of F _F ′,
The constant α can also be set to an appropriate value experimentally or by design.

<Example> FIG. 1 shows an example of the operation of FF+PI control using the required combustion amount F calculated according to the above-mentioned arithmetic expression in the present invention.

To state in advance, in each transition period in FIG. 1, the curves marked by solid lines a, b, c, and d correspond to the case according to the present invention, and the curves marked by virtual lines e, f, and g is the feed forward amount F _F according to the formula
Each case is shown using conventional FF + PI control to find .

As shown at time T ₁ , the amount of hot water (water amount) S _w
When the faucet 2 shown in Fig. 2 is opened from a state of zero and the _water suddenly starts flowing at a certain flow _rate , the main In the system in which the control method of the invention is adopted, in the formula for calculating the feed forward amount _F Initially, the value of the required combustion amount F obtained by the formula also becomes sufficiently large transiently due to the influence of this term. Therefore, as shown by the solid line a in the figure, the set temperature T _s at that time Depending on the situation, the water heater's maximum capacity can be reached quickly, and as a result, the hot water temperature _Tp rises quickly enough to slightly overshoot, as shown by curve b.
The temperature converges to the set temperature T _s in a short convergence time.

On the other hand, in the conventional method that does not have the correction product term according to the present invention, the transient value of the required combustion amount F cannot become that large, as shown by the virtual line e, and therefore the virtual line As shown by the curve f, the rise of the outlet temperature T _p is also poor, and the set temperature T _s
The convergence time will also be longer.

Furthermore, as shown after time T ₂ , the water amount S _w
However, if the set temperature T _s is changed by the user, the value of the corrected product term increases transiently according to the present invention (the set temperature T _s and the outlet temperature T _p (the difference becomes transiently large at this point T ₂ )
Therefore, as shown by curves a and b, curves of changes in the required combustion amount F with a steep rise and a short convergence time and the accompanying changes in the hot water temperature T _p are obtained, but in the case of the conventional method, As shown by curves e and f, the temperature rises slowly due to the influence of the integral term and takes a long time to converge to the set temperature.

These characteristic trends are exactly the same in the negative direction. For example, when the user suddenly lowers the set temperature T _s as shown at time T ₃ , according to the control method of the present invention, the A curve a with a sharp fall is obtained, so the outlet hot water temperature T _p responds quickly and drops to the set temperature T _s in a short convergence time.
When using the conventional method, as shown by curves e and f, the required combustion amount F falls slowly and the convergence time becomes long, so the time it takes for the outlet temperature T _p to drop to the set temperature T _s also increases. It will be long.

On the other hand, as shown after time T ₄ , when the user narrows the faucet 2 and the water volume S _w decreases, the required combustion volume F is similarly calculated to decrease in response quickly and in a short time. In order to converge to the required combustion amount F that satisfies the set temperature T _s in the convergence time, the outlet temperature
There is no need for large changes or fluctuations in temperature level or time at T _p .

On the other hand, when using the conventional method, as shown by the imaginary curve f, the range of temporary temperature change in the outlet hot water temperature T _p increases, which tends to cause discomfort to the user. It is.

As described above, according to the present invention, it is possible to quickly respond to various transient changes, or to minimize unpleasant temperature fluctuations. If the feed forward amount F _F ′ obtained by the calculation formula is also used to control the water flow valve, the hot water flow characteristics can be improved, which also contributes to the hot water temperature characteristics, which is figuratively desirable. We can expect a positive feedback phenomenon.

For example, a water flow valve control method involves setting a threshold at a predetermined width above and below the water heater's capacity, and when the feedforward amount is below the lower threshold, the water flow valve is activated. The water flow valve continues to operate in the open direction, and conversely continues to operate in the close direction when the water flow rate exceeds the upper threshold, and stops the water flow valve when the feed forward amount is between the upper and lower thresholds. “Constant threshold method” and ()
"Constant threshold method with hysteresis" in which the upper and lower thresholds are different depending on the direction of increase and decrease in the amount of feed forward; Operation commands in the opening direction and stop commands are issued alternately according to the duty ratio, and operation commands in the closing direction and stop commands are issued alternately according to the same constant duty ratio between the upper threshold value and the hot water supply function. There is a "constant threshold value fixed duty control method", etc., and as a new method newly developed by the applicant, as will be filed separately, ()
There is also a "constant threshold value variable duty control method" in which the duty ratio is made variable in accordance with the absolute value difference between the feed forward amount and the hot water supply function at that time when the duty control region is entered.

In particular, the "constant threshold value variable duty control method" disclosed by the present applicant mentioned at the end can always set the opening of the water flow valve at a position extremely close to the capacity of the water heater, and in practice, each The fact that the water flow valve is essentially an electromechanical element and has a limited response speed can be used to deal with fluctuations in the amount of feed forward due to flow fluctuations near the threshold and hot water supply function. Since it is possible to automatically create a dead zone, this method is superior in that it can avoid the risk of hunting, which tends to occur with the other conventional water flow valve control methods mentioned above.

However, regardless of which of these water flow valve control methods is used, the response characteristics can be improved by using the feed forward amount calculation formula of the present invention as the feed forward amount calculation formula for that purpose. Furthermore, as a result, the hot water temperature characteristics can also be improved.

In particular, for example, in _FIG.
As shown in , when the value of the correction product term in the calculation formula for the required combustion amount F increases transiently as the set temperature T _s changes, the corresponding feed forward amount F _F ′ also increases at this moment, Therefore, when the water flow valve is controlled by the feed forward amount F _F ', the water flow valve is operated in the closing direction for a short period of time as shown by symbol c in FIG. Therefore, as shown by the symbol d, the amount of hot water discharged is reduced, and therefore the hot water temperature T _p increases faster, but as the hot water temperature T _p increases, there is a slight overshoot within the desired range. Conversely, after operating in the opening direction, it is possible to perform an operation of receiving a stop command and entering a stable flow rate.

On the other hand, when the control is performed according to the feed forward amount F _F calculated by the conventional method, as shown in the virtual line curve indicated by the symbol g in Fig. 1,
There is no change in the amount of hot water dispensed, and therefore it cannot be expected to use this change in hot water temperature to quickly draw the hot water supply temperature T _p to the set temperature T _s . In addition, in this example, it is assumed that a limiter is applied to the required combustion amount exceeding the maximum capacity of each water heater, as has already been adopted in this type of water heater, but if In the absence of such a limiter, the waveform related to the required combustion amount at the time _T2 will be a curve a' shown by a dashed-dotted line according to the above-mentioned arithmetic expression.

The present invention has been explained above, but as mentioned earlier in the section of operation, in the calculation formula for the required combustion amount F defined by the present invention, the constant terms K _I , K _P , α in each term are can be set to appropriate values both by design and experiment.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an example of an application operation of the combustion control method in a water heater constructed according to the present invention, and FIG. 2 is a conceptual diagram of a water heater to which the present invention can be applied.
It is. In the figure, 1 is a water flow valve, 2 is a faucet, 3 is a heat exchanger, 4 is a gas burner, 5 is a microcomputer, 8 is a water flow sensor, 9 is a water supply temperature sensor, 10 is a hot water temperature sensor, S _w is a flow rate, and T _s is the set temperature, T _c is the water supply temperature, and T _p is the hot water temperature.

Claims (1)

[Claims] 1. It has a sensor that detects each of the water supply temperature, water volume, and hot water temperature, and performs feed forward control and proportional control based on these information and set temperature information set by the user.
A combustion control method in a water heater that calculates the required combustion amount at any given time based on integral control; - Hot water temperature)×
The above required combustion amount is defined as (set temperature - water supply temperature) x (water amount) x (set temperature - hot water temperature) x
α + (Set temperature - hot water temperature) x (Water amount) x K _P + Σ (Set temperature -
A combustion control method in a water heater, characterized in that it is determined by (outlet hot water temperature) x K _I.