KR20070097333A - Control method for absorption refrigerator - Google Patents

Abstract

A control method for an absorption freezer is provided to stabilize cold water temperature at rating operation by allowing width of the dead-band to be large when change speed of cold water temperature is rapid, and the width of the dead-band to be small when the change speed of the cold water temperature is slow. A control method for an absorption freezer setting opening degree of a fuel valve of a burner of a high temperature regenerator as operation amount(M) and performing the operation amount by PID control using a sum of a proportional term, an integration term and a differential term comprises the steps of: deciding dead-band in a plus direction of the operation amount(100%) at rating operation(S5); and making width of the dead-band to be changed corresponding to the proportional term, so that the width of the dead-band is large when change speed of cold water temperature is rapid, and the width of the dead-band is small when the change speed of the cold water temperature is slow.

Description

Control Method for Absorption Refrigerator

1 is a schematic configuration diagram (first embodiment) of an absorption type refrigerator according to the present invention.

Fig. 2 is a control flowchart (first embodiment) in the case of varying the deadband width according to the present invention.

Fig. 3 is a control flowchart (first embodiment) in the case of fixing the deadband width according to the present invention.

<Explanation of symbols for main parts of the drawings>

1: high temperature regenerator

2: burner

3: low temperature regenerator

4: condenser

5: evaporator

6: absorber

7: low temperature heat exchanger

8: high temperature heat exchanger

9 to 11: Absorbing liquid tube

12: absorbent pump

13 to 15: refrigerant pipe

16: refrigerant pump

17: cold water pipe

19: gas supply pipe to the gas burner (2)

20: fuel valve

21: temperature detector

22: control unit

[Document 1] Japanese Patent Application Laid-open No. Hei 10-170088

TECHNICAL FIELD This invention relates to the technique which carries out operation control of an absorption refrigerator by PID control which is control by the sum of a proportional term, an integral term, and a derivative term.

When the operation control for controlling the cold water temperature, which is the output of the absorption chiller, to the set water temperature performs the opening degree of the fuel valve of the burner of the high temperature regenerator as the operation amount M, the operation amount M in a range where the current water temperature is sufficiently higher than the set water temperature. ) Is 100%, the manipulated value M is set to 0% in a sufficiently low range, and the response is delayed when any disturbance occurs when control is performed in which the manipulated value M is proportional to the current water temperature. There is a problem and it is known to employ PID control to solve this problem (for example, document 1).

This document 1 discloses that when PID water is designed to take out the cold water at the set water temperature in a state of about 100% (state of about 100% of the rated output) when the operation amount M is about 100%. Since there is a problem of poor controllability due to lack of the manipulated variable (M), in order to solve this problem, the correction coefficients A, B, and C determined from the relationship between the current water temperature and the set water temperature, respectively, in the proportional term, the integral term, and the derivative Multiply by

Thus, in order to control the cold water temperature which is the output of an absorption chiller to set water temperature, the opening degree of the fuel valve of the burner of a high temperature regenerator is made into operation amount M, and this operation amount M is made into the proportional term, the integral term, and the derivative term. When performing by PID control which is control by the sum, the speed of change of the cold water temperature which is an output differs according to the installation situation of an absorption refrigerator, etc. If the change rate is high, the heat input control (burner fuel valve opening degree control) is also performed quickly to follow the load fluctuations, while the heat input control (even at a slight cold water temperature change at the rated operation) Control of the opening of the fuel valve of the burner) causes a problem that the cold water temperature fluctuates up and down and is not stable.

In view of the above, the present invention provides a dead zone in the positive direction of the control amount (100%) during rated operation, whereby a slight change in the cold water temperature at around 100% can be absorbed to stabilize the cold water temperature. It is to be. In this case, the width of the dead zone is varied in accordance with the set value of the control speed, so that the case where the change rate of the cold water temperature is fast or slow can be coped with.

In the absorption chiller control method according to the first aspect of the invention, in order to control the cold water temperature, which is the output of the absorption chiller, to the set water temperature, the opening degree of the fuel valve of the burner of the high temperature regenerator is set as the operation amount M, and the operation amount M is proportional term. In the control method performed by PID control which is control by the sum of the integral term, the integral term, and the derivative term, a dead zone is set in the positive direction of the operation amount M (100%) at the rated operation, and the change rate of cold water temperature is quick. In the case where the width of the dead zone is large, and when the rate of change of the cold water temperature is slow, the width of the dead zone is varied in response to the proportional term P so that the width of the dead zone decreases. to be.

In the absorption chiller control method of the present invention, in order to control the cold water temperature, which is the output of the absorption chiller, to the set water temperature, the opening degree of the fuel valve of the burner of the high temperature regenerator is set as the operation amount M, and the operation amount M is a proportional term and an integral. In the control method performed by PID control which is control by the sum of a term and a derivative term, when a dead zone is set to the positive direction of the operation amount M (100%) at the time of rated operation, and a change rate of cold water temperature is fast, When the width of the dead zone is large and the rate of change of the cold water temperature is slow, the width of the dead zone is varied according to the proportional term P so that the width of the dead zone becomes small. It describes below.

<First Embodiment>

Next, an embodiment of the absorption chiller of the present invention will be described. 1 is a schematic configuration diagram of an absorption type refrigerator according to the present invention, FIG. 2 is a control flowchart when the deadband width is variable according to the present invention, and FIG. 3 is a control flowchart when the deadband width is fixed according to the present invention.

An embodiment of the present invention will be described. 1 shows a schematic configuration diagram of an absorption chiller using water as a refrigerant and lithium bromide (LiBr) as an absorption liquid. The high temperature regenerator 1 is configured to heat the lean solution in which the absorbent liquid and the refrigerant are mixed by the thermal power of the gas burner 2 that uses city gas as a fuel to evaporate the refrigerant and separate the absorbent liquid and the refrigerant. 3 is a low temperature regenerator, 4 is a condenser, 5 is an evaporator, 6 is an absorber, 7 is a low temperature heat exchanger, 8 is a high temperature heat exchanger, 9-11 is an absorption liquid pipe, 12 is an absorption liquid pump, 13-15 is a refrigerant tube, 16 Is a refrigerant pump, 17 is a cold water pipe, 18 is a cooling water pipe, 19 is a gas supply pipe to the gas burner 2, 20 is a fuel valve for controlling the gas supply amount to the gas burner 2, 21 is an outlet of the cold water pipe 17 The temperature detector 22 that detects the temperature is a controller that controls the degree of opening of the fuel valve 20 based on the temperature detection of the temperature detector 21. The control unit 22 controls the opening degree of the fuel valve 20 by comparison control between the setting data stored in the data storage unit and the data based on the temperature detection of the temperature detection unit 21.

The control method for controlling the outlet temperature (hereinafter referred to as cold water temperature) of the cold water pipe 17, which is the output of the absorption chiller of the present invention, to a set water temperature includes a fuel valve of the gas burner 2 of the high temperature regenerator 1 The opening degree of 20) is the manipulated value M, and the manipulated value M is performed by PID control, which is a control by the sum of the proportional term, the integral term, and the derivative term, which is described in Document 1 (Japanese Patent Application Laid-Open No. 10). As described in Japanese Patent Application Laid-Open No. 170088), the manipulated variable M is represented by [Equation 1] or [Equation 2]. In addition to the above, the control unit 22 includes a program required for microcomputer control, a set temperature data, an operation amount M calculated on the basis of the temperature detection of the temperature detection unit 21, and various data necessary for performing a control operation. It also has a memory for storing.

[Equation 1]

M: manipulated value (%)

P: Proportional band (℃)

Ti: Integral time (seconds)

Td: derivative time in seconds

τ: sampling time (seconds)

e _n : deviation between nth target water temperature and current water temperature

e _{n -1} : Deviation between n-1th target water temperature and current water temperature

[Equation 2]

A, B, C: correction factor

M: manipulated value (%)

P: Proportional band (℃)

Ti: Integral time (seconds)

Td: derivative time in seconds

τ: sampling time (seconds)

e _n : deviation between nth target water temperature and current water temperature

e _{n -1} : Deviation between n-1th target water temperature and current water temperature

In this way, when the operation amount M is executed by PID control, which is control by the sum of the proportional term, the integral term, and the derivative term, the rate of change of the output cold water temperature varies depending on the installation condition of the absorption refrigerator. When the change rate is high, the control of heat input (control of the opening degree of the fuel valve 20 of the burner 2) is also performed quickly so that it can follow the load fluctuation quickly, while the slight cold water temperature at the time of rated operation Even with the change, the control of heat input (control of the opening degree of the fuel valve of the burner) acts, and there is a problem that the cold water temperature fluctuates up and down and is not stable.

Normally, it is designed to take out cold water at the set water temperature from the outlet of the cold water pipe 17 in a state where the operation amount M is 100% (at a state of 100% of rated output), but at the time of rated operation (at 100% of the rated output). Even if the cold water temperature is slightly changed in the state of the control amount (the operation amount M is 100%), the opening degree control of the fuel valve 20 of the burner 2 is performed accordingly, and it swings around the 100% rated operating state. A phenomenon is exhibited and it becomes a state which cannot control stable rated operation (control amount M of 100%).

In order to eliminate this shaking phenomenon, a dead zone is provided in the positive direction of the control amount (100%) during rated operation, whereby a slight change in the cold water temperature at around 100% can be absorbed and the cold water temperature can be stabilized. There is a way to control. In this method, as shown in Fig. 3, the temperature detection unit 21 detects the current water temperature (step S1), reads the value Mc of the current manipulated variable M from the memory (step S2), and sets in advance. Calculation based on the operation amount M calculated from the outlet water temperature (called the set water temperature) of the cold water pipe 17 and the PID set values (proportional term, integral term, and derivative term) and the water temperature detected by the temperature detector 21. The operation amount M and the difference ΔM are calculated (step S3), and the value Mc of the new operation amount M is calculated by adding this ΔM to the value Mc of the current operation amount M (step S4). ).

As an example, the width of the dead zone is set to 20. For this reason, when the value of this new operation amount Mc is 0 or less, it is made into 0 (step S5), and when the value of this new operation amount Mc is 120 or more, determination control is made to be 120 (step S6). The value of the new operation amount Mc is stored in the memory (step S7). The operation amount Mt, which is the target opening degree of the fuel valve 20, is calculated from this new operation amount Mc (step S8), and it is determined whether Mc is 100 or less or 100 or more, and if Mc is 100 or less, Mt = If Mc is set to 100 or more, Mc is set to Mt = 100, these are stored in the memory (step S9), and the control unit 22 outputs the output signal so that the opening degree of the fuel valve 20 is Mt. (Step S10).

In this manner, by repeatedly performing the above calculation, when the current operation amount Mc is 100, Mt is 100, and the opening degree Mt of the fuel valve 20 at this time is Mt = 100, that is, 100% output state. The combustion state in the burner 2 is 100%. When the calculated ΔM is +5, for example, the new operation amount Mc becomes 105, and after this, Mc is calculated up to 120, but the opening degree Mt of the fuel valve 20 is 100. Therefore, the 100% output state is maintained, and even if the outlet water temperature of the cold water pipe 17 varies, the opening degree of the fuel valve 20 is maintained at 100%, and the combustion state at the burner 2 is 100%. In the rated output state, even if there is slight fluctuation in the outlet water temperature of the cold water pipe 17, fluctuation in the opening degree of the fuel valve 20 does not occur accordingly, resulting in a feeling of insensitivity, and a stable state is obtained.

That is, although the output value which changes the opening degree of the fuel valve 20 is 0 to 100%, for example, when the width of the dead zone of 20 is provided, the calculated value of the operation amount M is 100 or more (range of 100 to 120). ), The output value of varying the opening degree of the fuel valve 20 is 100%. For this reason, even if the outlet water temperature of the cold water pipe 17 rises slightly, the shaking phenomenon in the vicinity of 100% of the rated output can be avoided, and the change of the outlet water temperature of the cold water pipe 17 in the vicinity of 100% is slightly changed. Absorbs water and stabilizes the outlet water temperature of the cold water pipe 17. Although the width of the dead zone is fixed to 20 in the above, the width of the dead zone may be 10 or 15, and the appropriate width may be determined by a prior test.

Here, although the current operation amount Mc is based on 100, it is determined based on Mc = 98 to determine whether Mc is 98 or less or 98 or more, and the fuel valve 20 is opened at Mc = 98 or more. You may make it 100%. In this case, when Mc = 98 or more, it becomes the operation state of the rated output 100%, and even if the exit water temperature of the cold water pipe 17 falls slightly or rises, the shaking phenomenon in the vicinity of the rated output 100% can be avoided. It is possible to absorb a slight change in the outlet water temperature of the cold water pipe 17 in the vicinity of 100%, and stabilize the outlet water temperature of the cold water pipe 17.

In the above, although the width of the dead zone is fixed to, for example, a constant 20, the present invention employs a variable value according to the set value of the control speed. In particular, even when the change rate of the outlet water temperature of the cold water pipe 17 is fast, In addition, it is also possible to cope with slow cases.

That is, when the P set value changes from 1 to 20 in a state in which the P set value (proportional term), which is the set value of the proportional band width of the PID control, is variable, and the width of the fixed dead band is set to an integer 20 as described above. For example, calculate the width of the deadband by 20 / P (20 divided by P). The P setting value is a value which is changed by the operation manager of the absorption chiller or the like operating the remote controller operation unit. For this reason, based on the temperature detection of the temperature detection part 21, the operation manager etc. visually confirm the temperature change of the temperature display part displayed by operation | movement of the control part 22, and the temperature of the exit water temperature of the cold water pipe 17 If the change is slow, increase P accordingly. As a result, the width of the dead zone decreases. In addition, when the outlet water temperature of the cold water pipe 17 changes rapidly, P is appropriately reduced. As a result, the width of the dead band increases. In this way, control corresponding to the change rate of the outlet water temperature of the cold water pipe 17 can be performed, and even when the outlet water temperature change of the cold water pipe 17 is fast or slow, it is possible to cope with it. The cold water temperature at the time of operation can be stabilized. Also in this case, the constant 20 which is a molecule of 20 / P is a case where the fixed width 20 of the dead band is set, and what is necessary is just to set it to an appropriate value by the prior test like the above.

2 shows a control flow related thereto. In this case, steps S1 to S4 are the same as those in FIG. In step S5, the maximum width Mm of Mc is calculated from P setting value (proportional term) of PID control (for example, Mm = 20 / P). Then, when Mc calculated in step S4 is 0 or less (step S6), when the value of this new operation amount Mc is 100 + Mm or more, determination control is performed to 100 + Mm (step S7), The value of this new operation amount Mc is stored in the memory (step S8). The operation amount Mt, which is the target opening degree of the fuel valve 20, is calculated from this new operation amount Mc (step S9), and it is determined whether Mc is 100 or less or 100 or more, and if Mc is 100 or less, Mt = If Mc is 100 and M is 100 or more, Mt = 100, these are stored in the memory (step S10), and the control unit 22 outputs the output signal so that the opening degree of the fuel valve 20 is Mt. (Step S10).

In this manner, by repeatedly performing the above calculation, when the current operation amount Mc is 100, Mt is 100, and the opening degree Mt of the fuel valve 20 at this time is Mt = 100, that is, 100% output state. The combustion state in the burner 2 is 100%. And if Mc calculated in step S4 is 0 or less, it sets to 0, and when the value of this new operation amount Mc is 100 + Mm or more, it controls to 100 + Mm, and therefore exit water temperature of the cold water pipe 17 is carried out. The control according to the change speed can be performed, so that even if the outlet water temperature change of the cold water pipe 17 is fast or slow, it can cope.

This invention is not limited to the said embodiment, The piping diagram of an absorption type refrigerator is applicable to either of the forms of each figure of the literature 1 described in the prior art, and is applied to various aspects, unless it deviates from the technical scope of this invention. You can do it.

According to the first aspect of the invention, even when the change rate of the output cold water temperature is different due to the installation situation of the absorption chiller or the like, when the change rate of the cold water temperature is fast, the width of the dead band is large and the change rate of the cold water temperature is slow. By decreasing the width of the dead zone, it is possible to cope with the case where the change rate of the cold water temperature is fast or slow, and the cold water temperature at the rated operation of the absorption chiller can be stabilized.

Claims (1)

In order to control the cold water temperature, which is the output of the absorption chiller, to the set water temperature, the opening degree of the fuel valve of the burner of the high temperature regenerator is set as the operation amount M, and this operation amount M is obtained by the sum of the proportional term, the integral term, and the derivative term. In the control method performed by PID control which is control, when the dead zone is set to the positive direction of the operation amount M (100%) at the time of rated operation, and the change rate of cold water temperature is fast, the width of the dead zone is large and cold water When the temperature change rate is slow, the width of the dead zone is varied in response to the proportional term (P) so that the width of the dead zone becomes small.

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