JPH0784943B2 - Water heater temperature control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention detects the temperature of hot water flowing out of a heat exchanger without providing a water temperature sensor for detecting the temperature of water flowing into the heat exchanger. The present invention relates to a temperature control device for a water heater, which is provided with only an outflow temperature sensor for feedback control, and is particularly effective in a temperature controller for a water heater having a simple structure without a flow rate sensor for detecting the flow rate of water passing through a heat exchanger. Target.

[Prior Art] In order to simplify the manufacturing process by simplifying the structure of the water heater, and to reduce the manufacturing cost, there is a temperature control device that controls the amount of heating by only the tapping temperature thermistor. In such a feedback control temperature control device, the reference heating amount is determined according to the temperature difference between the target temperature set by the temperature setting device or the like and the hot water temperature detected by the hot water temperature thermistor. Further, in the temperature control of the water heater, when the flow rate changes, it is important to quickly change the heating amount according to the change in the flow rate, and it is desirable that the change in the heating amount be synchronized with the flow rate change. ing. And in a water heater equipped with a flow rate sensor, the heating amount can be changed quickly according to the flow rate, but in the temperature control device that controls the heating amount only by the hot water temperature thermistor, the heated water is discharged. Since there is a time delay until the temperature is detected by the temperature thermistor, the heating amount cannot be changed promptly with changes in the flow rate. Therefore, in such a temperature control device, when the flow rate changes during hot water supply and the hot water temperature changes accordingly, the temperature is proportional to the differential value of the temperature detected by the hot water temperature thermistor in order to quickly correct the heating amount. The correction function is provided with the above correction amount, and the effect of the flow rate change is reduced to improve the tapping temperature characteristic.

[Problems to be Solved by the Invention] In such a conventional feedback control, for example,
When the flow rate decreases as indicated by the solid line L1 in the figure, the outlet heated water temperature detected by the outlet hot water temperature thermistor gradually changes with a time delay, as indicated by the solid line L2, so proportional control of feedback control is performed. The reference heating amount due to is changed as indicated by a broken line L8 according to the change in the tapping temperature. Therefore, the reference heating amount is also changed with a time delay from the change in the flow rate. Further, at this time, the derivative value of the outlet heated water temperature continuously appears as a substantially constant value as shown by the solid line L3 while the outlet heated water temperature is changing, and in the differential correction, as shown by the broken line L9, it is proportional to the constant. The given differential correction amount is given. For this reason, the final heating amount in the feedback control is the dashed line although it is originally desired to give the heating amount according to the flow rate such as the one-dot chain line L6 in order to obtain stable temperature characteristics even if the flow rate changes. It is corrected as a broken line L7 in which L8 and the broken line L9 are combined.

Therefore, when the conventional differential correction amount correction that is proportional to such a differential value is performed, for example, when the flow rate change is small, the heating amount is appropriate at the initial stage of the flow rate change, as indicated by the broken line L11 in FIG. If a constant is set so that the differentially corrected heating amount is given, this initial correction amount is continuously given until there is no change in the tap water temperature.
With respect to the ideal heating amount shown in 2, an excessive differential correction amount is gradually given as the change continues. For this reason, even if there is a slight change in the flow rate, excessive heating amount correction will be performed, which will cause a large change in the tapping temperature, and the stability will deteriorate.

On the contrary, in the conventional differential correction, when the flow rate change is large, the correction amount is insufficient with respect to the ideal heating amount shown by the alternate long and short dash line L14 at the beginning of the flow rate change as shown by the broken line L13 in FIG. Similarly, since an excessive amount of correction is given at the end of the correction, it takes time for the hot water temperature to stabilize.

If the constant for determining the differential correction amount is made smaller so as not to perform such excessive correction, the correction amount will be further insufficient if there is a large flow rate change. Conversely, if the constant is made larger, a small flow rate change will occur. On the other hand, excessive correction will be performed, and even for a large flow rate change, an excessive correction amount will be similarly given at the end of the correction.

As described above, as long as the differential correction amount proportional to the differential value of the outlet heated water temperature is continuously given while the differential value is obtained, the excess and deficiency of the heating amount cannot be improved together.

Therefore, since the heating amount according to the changed flow rate cannot be continuously applied while the hot water temperature is changing, the hot water temperature becomes unstable if the flow rate is changed, and excellent hot water temperature characteristics can be obtained. There is a problem that you can not.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the influence of flow rate change and obtain a stable hot water outlet temperature characteristic in a water heater temperature control device that performs feedback control based on the detected temperature of a hot water hot water thermistor.

[Means for Solving the Problem] The present invention includes a temperature setting means for setting a target temperature and a temperature sensor provided in an outflow portion of a heat exchanger, and the target temperature of the temperature setting means and the temperature sensor. In the temperature control device of the water heater for feedback controlling the heating amount of the heating means for heating the heat exchanger based on the temperature difference from the detected temperature, the heating amount of the heating means based on the differential value of the detected temperature. And a differential correction means for correcting the differential value, and the differential correction means is a technical means for setting a product of the differential value and a coefficient whose absolute value becomes smaller according to the duration of the differential value as the correction amount. To do.

[Operation] In general, in a water heater, a flow rate change from one flow rate to another flow rate occurs only during a short time when a user operates a hot water tap, for example, and once the flow rate stabilizes after the change, the flow rate changes. Is continued. In this case, assuming that the heating amount is constant, the change in the tap water temperature due to the change in the flow rate appears at a certain time after the change in the flow rate, completes with a time delay, and during that time, a substantially constant change state occurs. Show.

At this time, in the proportional control of the feedback control, the heating amount is determined according to the temperature difference between the outlet heated water temperature and the target temperature.
An inappropriate heating amount is determined while the tapping temperature is changing with respect to the changed actual flow rate. This improper heating amount error appears largely immediately after the flow rate changes, and then gradually decreases.

On the other hand, in the differential correction means of the present invention, the differential value is obtained only while the hot water temperature is changing, and the heating amount is corrected based on this differential value. At this time, the absolute value of the correction amount based on the differential value is gradually reduced according to the duration of the differential value.

Therefore, the correction amount by the differential correction means changes with time so as to respond to the change in the error of the heating amount by the proportional control that does not correspond to the flow rate, and in order to cancel the error just, the entire feedback control combining the proportional control and the differential control is performed. As a result, it is possible to determine the heating amount according to the change as well as the change of the flow rate, and to provide an appropriate heating amount according to the flow rate.

[Advantages of the Invention] In the present invention, when the hot water temperature changes due to a change in the flow rate, the heating amount of the heating means can be controlled to an appropriate heating amount according to the changed flow rate.

Therefore, the outlet heated water temperature does not largely change due to the change of the flow rate, and the stability of the outlet heated water temperature after the change of the flow rate can be improved.

[Embodiment] Next, a temperature control device for a water heater according to the present invention will be described based on an embodiment shown in the drawings.

In the combustor case 10 of the gas combustion type water heater 1 shown in FIG. 2, a burner group 11 including a plurality of burners is provided. A blower 12 for supplying combustion air to the burner group 11 is provided below the combustor case 10. Above the burner group 11 in the combustor case 10 is a water pipe type heat exchanger.
13 is provided, and the water passing through the inside is heated by the heat of combustion by the burner group 11. Burner group 11 in combustor case 11
A sparker 14 for igniting the burner group 11 and a frame rod 15 for detecting ignition of the burner group 11 are provided in the vicinity of. Further, an exhaust port 2 for discharging combustion exhaust gas to the outside is provided above the combustor case 10.

A nozzle pipe 16 for supplying fuel gas is provided below the burner group 11, and the nozzle pipe 16 is provided with a plurality of fuel ejection ports 16a for ejecting fuel gas corresponding to each burner of the burner group 11. It is provided.

The fuel pipe 20 for guiding the fuel gas to the nozzle pipe 16 has two solenoid valves 21 and 22 for passing the fuel gas when energized, and a governor for controlling the supply amount of the fuel gas by controlling the supply pressure according to the energized current. Proportional valves 23 are provided in order from the upstream side.

A water supply pipe that guides water from a water supply source (not shown) to the heat exchanger 13.
17 is an electric water amount control device for adjusting the amount of hot water supplied.
18, water flow switch 19 for detecting water passing through the heat exchanger 13
Are sequentially provided from the upstream side, and the hot water supply pipe 17a downstream of the heat exchanger 13 has a hot water outlet temperature T flowing out from the heat exchanger 13.
A hot water temperature thermistor 25 for detecting out is provided.

The control device 30 has a control circuit centered on a microcomputer, starts and stops combustion in a predetermined sequence, and based on the detection signal of the hot water temperature thermistor 25 by the functional configuration shown in FIG. Performs feedback control temperature control.

Further, the control device 30 controls the detected temperature T of the hot water temperature thermistor 25.
As a functional unit for estimating the water input temperature Tin and the water amount W into the heat exchanger 13 based on the
And a water amount estimation unit 32.

The incoming water temperature estimator 31 estimates the incoming water temperature Tin as follows according to the detected temperature T and the change state thereof, and stores it in the memory 31a.

When the start of hot water supply is detected by the water flow switch 19 (YES in step 1), if the detected temperature T of the hot water temperature thermistor 25 is changing, it is considered that hot water supply is being performed again. Therefore, when there is a temperature gradient of the detected temperature T (NO in step 2), the estimation of the incoming water temperature Tin is not performed.

When the start of hot water supply is detected and the detected temperature T is not detected (YES in step 2),
Detected temperature T of hot water temperature thermistor 25 and memory 31a already
The storage temperature Tmem stored as the input water temperature Tin is compared with the stored temperature Tmem, and the input water temperature Tin to be newly stored in the memory 31a is estimated according to the comparison result as follows.

If the detected temperature T is less than or equal to the memory temperature Tmem (step 3
YES), the detected temperature T remains unchanged and a new water temperature T
As in (step 4), the detected temperature T is stored in the memory 31a.
And the stored contents are updated (step 5).

On the contrary, when the detected temperature T is higher than the memory temperature Tmem (NO in step 3), a part of the temperature information of the detected temperature T is incorporated into the memory temperature Tmem to estimate a new water inlet temperature Tin (step 6). , And set it as the memory temperature Tmem (step 5).

In step 6, the new estimated temperature Tin is the memory temperature Tmem.
A new incoming water temperature Tin is calculated by Tin = (a * Tmem + b * T) / (a + b) from a part of the temperature information of the above and a part of the temperature information of the detected temperature T.

The water amount estimation unit 32 has respective functional units of a heating amount calculation unit 33, a heating amount storage unit 34, a heating time calculation unit 35, and a water amount calculation unit 36, and estimates the water amount W passing through the heat exchanger 13.

The temperature of the hot water flowing out of the heat exchanger 13 is
It is the result of being heated by the heating means from the inflow to the outflow. Now, assuming that it takes time t for the water of the flow rate W to pass through the heat exchanger 13 per unit time, at this time, the total heating amount involved in the temperature rise ΔT of the hot water flowing out of the heat exchanger 13. Q _T can be generally expressed by, for example, a product of a heating amount Qu per unit time and a heating time t (time t required for passing through the heat exchanger 13).
That is, it is represented by Q _T = Qu × t.

Here, Qu × t indicates an integration of the heating amount Qu per unit time during the heating time t.

Therefore, when the total heating amount Q _T is shown including the case where the heating amount changes during the heating time t from the time t1 to the time tn and the heating amount per unit time is not constant, Q _T = Qn + Qn ₋₁ + Qn _-2 + ... + Q ₂ + Q ₁ = ▲ Σ ⁿ ₁ ▼ Qt….

Here, Qn, Qn _-1 , Qn _-2 , ... Q ₂ , Q ₁ are each unit time tn,
The heating amounts at tn _-1 , tn _-2 , ..., t ₂ , t ₁ are shown.

Further, the total heating amount Q _T by the heating means can be considered to have acted on the temperature increase ΔT of the total amount U of water in the heat exchanger 13 according to the volume of the heat exchanger 13, so that Q _T = ΔT × U ... Therefore, from the equation and the equation, ΔT × U = ▲ Σ ⁿ ₁ ▼ Qt = Qn + Qn ₋₁ ＋ Qn ₋₂ ＋ ・ ・ ・ ＋ Q ₂ ＋ Q ₁・ ・ ・
As a result, when the heating amount for each unit time is integrated retroactively, a heating amount commensurate with the total heating amount Q _T that gives a temperature increase of ΔT with respect to the total water amount U in the heat exchanger 13 is obtained. If the total of the unit time until it is obtained is calculated, it can be set as the heating time t.

Further, this heating time t is a time required for water to pass through the heat exchanger 13, and between the total amount of water U in the heat exchanger 13 and the flow rate W, U = W × t ... Therefore, the flow rate W can be calculated by W = U / t.

In this case, the constant of the delay time associated with the delay in the heating response may be taken into consideration.

The heating amount calculation unit 33 detects the temperature T detected by the hot water temperature thermistor 25.
And the temperature rise ΔT estimated from the incoming water temperature estimation unit 31 and the incoming water temperature Tin stored in the memory 31a, and the total water amount U in the heat exchanger 13 due to the capacity of the heat exchanger 13 Calculate the total heating amount Q _T by.

The heating amount storage unit 34 stores the heating amount output information ΔQ for each predetermined unit time Δt by the temperature control unit 37, which will be described later, successively in areas E1, E2, ..., Area Ex shown in FIG. , The information is accumulated for a predetermined time, and the information for which the predetermined time has elapsed is sequentially deleted each time new information is given.

That is, for example, the predetermined unit time Δ by the temperature control unit 37
As shown in FIG. 5, the heating amount output information ΔQ for each t changes with time, ..., ΔQn _-4 , ΔQn _-3 , ΔQn _-2 , ΔQn _-1 ,
In the case of changes such as ΔQn, ΔQn ₊₁ , ΔQn ₊₂ , ... At time Δtn, the heating amount storage unit 34 shows the area E1 at time Δtn at time Δtn as shown in FIG. 4A. DerutaQn is, the DerutaQn _-1 at time .DELTA.tn _-1 in the area E2, ΔQn _-2 at time .DELTA.tn _-2 in the area E3 is, in the area E4 time .DELTA.tn _-3
ΔQn _-3 in FIG. ₃ is stored until area Ex, corresponding to each heating amount output information ΔQ before time Δtn corresponding to each area E.

Then, the next time .DELTA.tn _+1, as shown in FIG. 4 of B, heating amount output information DerutaQn ₊₁ is the area at the time .DELTA.tn ₊₁
Stored in E1, ΔQn in area E2, ΔQn _-1 in area E3
Then, ΔQn _-2 is in the area E4, ..., and so on until the area Ex, the heating amount output information Δ of each area E at each time Δt.
Each Q is shifted and stored.

After that, similarly, the newest heating amount output information ΔQ is always stored in the area E1 and the stored information in the area Ex is deleted so that the heating amount output information ΔQ for each predetermined unit time Δt.
Are continuously stored and accumulated.

The heating time calculation unit 35 integrates the heating amount output information ΔQ stored in the heating amount storage unit 34 in order from new information for each predetermined unit time Δt, and calculates the total amount calculated by the heating amount calculation unit 33 by the above formula. Predetermined unit time Δt when heating amount becomes equal to Q _T
Is calculated as the heating time t of the water flowing out from the heat exchanger 13.

The water amount calculation unit 36 calculates the water amount W of the water passing through the heat exchanger 13 from the above formula, based on the heating time t obtained by the heating time calculation unit 35. The water amount W calculated here is a numerical value as the average water amount W in the heating time t before each time, and when the water amount W is changed, the water amount W at each time cannot be represented. However, it is sufficiently effective to obtain the amount of hot water supply or the amount of hot water filling, or to determine the time constant of the feedback control system in the temperature control unit 37 based on the estimated amount W of water.

In addition, the water volume estimation unit 32 uses the hot water temperature thermistor at the start of hot water supply.
The water amount W in the initial stage of hot water supply is estimated from the change state of the detected temperature T of 25 and is set as the initial water amount Wp.

The temperature control unit 37 includes the target temperature Tset set by the controller 40, the outlet hot water temperature Tout detected by the outlet hot water temperature thermistor 25, and the memory 31a estimated by the incoming water temperature estimation unit 31.
The heating amount Q is determined from the input water temperature Tin stored in the table and the water amount W estimated by the water amount estimating unit 32.

Here, at the start of combustion, the target temperature Tset and the memory temperature Tm
Based on the initial water amount Wp by the em and the water amount estimation unit 32, the heating amount FF in the feedforward control is determined, and thereafter, the feedforward heating amount FF is determined based on the detected temperature T of the outlet hot water thermistor 25 and the target temperature Tset. Perform feedback control to correct.

As a functional unit in the feedback control, a proportional correction unit 37a for determining the proportional correction amount P based on the temperature difference between the detected temperature T and the target temperature Tset, and a differential correction amount D based on the differential value of the detected temperature T are determined. There is a differential correction unit 37c,
The heating amount Q in the feedback control is determined by Q = FF + P + D.

Particularly in the present embodiment, the differential correction amount D by the differential correction unit 37c
Is the time during which the differential correction is continued, that is, the detected temperature T
It is decided to gradually decrease in accordance with the time elapsed after the change of.

As a result, for example, when the amount of water changes as shown by the solid line L1 in FIG. 6 and the hot water outlet temperature Tout changes as shown by the solid line L2, the differential value d of the detected temperature T becomes the solid line L3.
, The differential correction amount D is gradually decreased with the lapse of time after the change of the detected temperature T, as shown by the solid line L4, so that the heating amount Q is shown by the solid line L5. It is decided as follows. Therefore, the heating amount Q is
The error from the ideal heating amount Qi corresponding to the change in the water amount shown in L6 is reduced, and an appropriate differential correction amount according to the water amount W is given as compared with the correction by the conventional differential correction, and the broken line L7
The heating amount corresponding to the water amount W can be given more than the conventional heating amount shown in FIG.

Therefore, when the change in the water amount W is small, the fluctuation of the hot water discharge temperature does not increase, and when the change in the water amount W is large, it takes less time to stabilize the hot water discharge temperature. There is.

In the present embodiment, when the water amount W changes, the water amount estimating unit 32 determines, based on the outlet heated water temperature Tout that changes as shown by the solid line L2 in FIG. 6, after the change as shown by the broken line L10. Regardless of the water amount W, since the water amount W is estimated by changing with the same gradient, the water amount W cannot be specified until the change of the tap water temperature T is completed. Therefore, although it is not possible to use the water amount W estimated by the water amount estimating unit 32 to cope with the change in the water amount W, the differential correction amount D by the differential correcting unit 37c can be used to change the heating amount in accordance with the water amount change. It can be changed and an appropriate heating amount can be given.

In this feedback control,
Since the time constant of the feedback control system can be set based on the water amount W estimated by 32, stable temperature control is performed and hunting or the like is prevented. Therefore, stable temperature control can be performed even when the time constant of the feedback control system changes with a change in the amount of water.

The heating amount Q of the temperature control unit 37 is the heating amount output information ΔQ.
Is sequentially stored in the above-described heating amount storage unit 34 at every predetermined unit time Δt.

The drive unit 38 drives and controls the blower 12 and the governor proportional valve 23 based on the heating amount Q of the temperature control unit 37. here,
The blower 12 supplies a voltage based on the heating amount Q by the temperature control unit 37.
The current value to the governor proportional valve 23 is energized and controlled based on the detected rotation speed of the blower 12.

Further, in the control device 30, in order to prevent the supplied water amount from exceeding the heating capacity, the opening amount of the electric water amount control device 18 is adjusted based on the detected temperature T of the hot water temperature thermistor 25 to limit the passage flow rate. To do.

The controller 40 that allows the user to arbitrarily set the target temperature Tset is installed according to the specifications of the water heater, and when the controller 40 is provided, the target temperature Tset is set according to the user's operation. Is set in the controller
Constant temperature (eg 60 ° C) if 40 is not installed
Is the target temperature Tset.

Next, temperature control in the gas combustion type water heater 1 of the present embodiment having the above configuration will be described.

When the user opens a hot water supply tap (not shown) provided downstream of the hot water supply pipe 17a, and when more water than the working water amount of the gas combustion type water heater 1 passes through the water supply pipe 17, hot water supply is detected by the water flow switch 19, Ignition control is performed in a predetermined sequence to start combustion. Further, the incoming water temperature Tin is estimated according to the detected temperature T of the hot water temperature thermistor 25, and the storage temperature Tmem of the memory 31a is updated.

When the flame rod 15 detects ignition of the burner group 11, the temperature adjustment control unit 37 determines the heating amount FF in the feedforward control, and the blower 12 and the governor proportional valve 23 are controlled based on the heating amount FF.

When the temperature of the water flowing out of the heat exchanger 13 rises to some extent due to the heating, the water amount W is estimated based on the detected temperature T of the hot water temperature thermistor 25, and the heating amount Q is corrected by the feedback control.

If the water amount W changes during hot water supply, the heating amount Q is corrected by feedback control. At this time, the differential correction unit 37
The amount of heating Q corresponding to the changed water amount is given by the differential correction amount D of c. For example, when there is a small change in the water amount, as shown by the solid line L15 in FIG. When a heating amount close to the heating amount of is given, and a large amount of water changes similarly, a heating amount close to the ideal heating amount shown by the chain line L14 is given as shown by the solid line 16 in FIG. Therefore, excessive heating and insufficient heating are less likely to occur. Therefore, the change in the outlet heated water temperature Tout due to the change in the amount of water is reduced, and stable outlet heated water temperature characteristics can be obtained.

Further, since the water amount W obtained by the water amount estimating unit 32 is used as a time constant for each predetermined unit time Δt in the feedback control, for example, when the hot water temperature changes due to a change in the flow amount, it corresponds to the change in the flow amount. Since the heating amount Q can be corrected by the time constant, hunting or the like due to the heating amount correction is unlikely to occur.

Combustion stops when the hot water supply is closed and hot water supply is stopped.

As described above, according to the present embodiment, when the water amount changes, the heating amount is changed according to the changed water amount,
A heating amount that is not excessive or insufficient with respect to the amount of water is provided. As a result, it is possible to reduce fluctuations in the outlet heated water temperature and maintain stable outlet heated water temperature characteristics. Further, since the water amount is estimated, the time constant in the feedback control can be set according to the water amount, and the heating amount can be corrected with appropriate responsiveness according to the water amount.

As a result, excellent hot water outlet temperature characteristics can be obtained, and stable hot water supply can be performed.

Further, in this embodiment, only the hot water temperature thermistor is provided as the sensor, and the flow rate sensor and the incoming water temperature sensor are not provided at the inflow portion of the heat exchanger, so that the structure of the water heater is further simplified, and the manufacturing process In addition to having a structure similar to that of a mere feedback-controlled water heater, very stable hot water temperature characteristics can be obtained.

Further, in the above-described embodiment, the correction in which the integrated value of the outlet hot water thermistor is not used in the feedback control is shown, but the correction corresponding to the integrated correction may be performed by the integrated value.

In the above embodiments, a water heater using a burner that uses gas as a fuel is shown, but a water heater including a burner using another fuel such as oil may be used. Further, the heating source is not limited to the burner, and may be an electric heating or the like.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a functional configuration of a control device for a gas combustion type water heater of this embodiment, and FIG. 2 is a schematic configuration diagram showing an outline of a gas combustion type water heater of this embodiment, and FIG. FIG. 4 is a flow chart for explaining the process of calculating the incoming water temperature in the control device of the present embodiment, FIG. 4 is an area map showing the storage contents of the storage area of the heating amount storage unit in the control device of the present embodiment, and FIG. A time chart showing changes in heating amount output information in the control device of the embodiment, FIG. 6 is a time chart for explaining temperature control of the present invention, and FIGS. 7 and 8 are changes in heating amount of the present embodiment. 2 is a time chart showing. In the figure, 11 ... Burner (heating means), 13 ... Heat exchanger, 25
...... Hot water temperature thermistor (temperature sensor), 30 ...... Control device (water heater temperature control device), 37 ...... Temperature adjustment control unit (feedback control), 37c ...... Differential control unit (differential correction means), 40 ... ... Controller (temperature setting means).

Claims (1)

[Claims] 1. A temperature difference between the target temperature of the temperature setting means and the detected temperature of the temperature sensor, comprising a temperature setting means for setting a target temperature and a temperature sensor provided at an outflow portion of the heat exchanger. In the temperature control device of the water heater for feedback controlling the heating amount of the heating means for heating the heat exchanger based on the differential temperature, there is provided a differential correction means for correcting the heating amount of the heating means based on the differential value of the detected temperature. Then, the differential correction means uses a product of a coefficient whose absolute value becomes smaller according to the duration of the differential value and the differential value as a correction amount, the temperature control device of the water heater.