Title of Invention	A CONTROL METHOD IN AN ABSORPTION REFRIGERATION APPARATUS HAVING PID CONTROL FOR STABILIZING THE COLD WATER TEMPERATURE
Abstract	The present invention provides a technique of absorbing a slight change in cold water temperature near 100% of a manipulated variable M to stabilize the cold water temperature, when a cold water temperature is controlled by PID control where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator. A dead band is determined in a positive direction of the manipulated variable M (100%} in a rated operation, and a dead band width is set to be variable corresponding to the proportional term in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow.

Title of Invention

A CONTROL METHOD IN AN ABSORPTION REFRIGERATION APPARATUS HAVING PID CONTROL FOR STABILIZING THE COLD WATER TEMPERATURE

Abstract

The present invention provides a technique of absorbing a slight change in cold water temperature near 100% of a manipulated variable M to stabilize the cold water temperature, when a cold water temperature is controlled by PID control where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator. A dead band is determined in a positive direction of the manipulated variable M (100%} in a rated operation, and a dead band width is set to be variable corresponding to the proportional term in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow.

Full Text	ABSORPTION REFRIGERATION APPARATUS BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to a technique of performing operation control of an absorption refrigeration apparatus by PID control which is the control performed by the sum of a proportional term, an integral term, and a differential term 2 Description of the Related Art When operation control for controlling a cold water temperature as an output of the absorption refrigeration apparatus to be maintained at a setting water temperature is performed by a manipulated variable M which is of an opening of a fuel valve of a burner in a high-temperature regenerator, the manipulated variable M is set to 100% in the range where a current water temperature is sufficient higher than the setting water temperature, the manipulated variable M is set to 0% m the range where a current water temperature is sufficient lower than the setting water temperature, and the manipulated variable M is proportioned to the current water temperature in the range between the sufficiently lower range and the sufficiently higher range In such cases, there is a problem that response is delayed when some sort of disturbance is generated The PID control is adopted to solve the problem, (for example, see Japanese patent Laid-Open No H10-170088) 2 In the PID control disclosed in Japanese patent Laid-Open No H10-170088 which is designed to take out the cold water having the setting water temperature while the manipulated variable M is substantially 100% (rated output is substantially 100%), when the current water temperature is located near the setting water temperature, controllability becomes worsened due to little margin of the manipulated variable M In order to solve this problem, the proportional term, the integral term, and the differential term are respectively multiplied by correction coefficients A, B, and C determined from a relationship between the current water temperature and the setting water temperature Thus, in order to perform the control such that the cold water temperature which is the output of the absorption refrigeration apparatus is maintained at the setting water temperature, in the case where the manipulated variable M which is the opening of the fuel valve of the burner in the high-temperature regenerator is controlled by the PID control which is the control performed by the sum of the proportional term, the integral term, and the differential term, a cold water temperature change speed which is the output is variable depending on an installation state of the absorption refrigeration apparatus and the like In the case where the change speed is fast, heat input control (opening control of the fuel valve of the burner) can rapidly be performed to quickly follow the load change At the same time, the heat input control (opening control of the fuel valve of the burner) is performed 2A even if the cold water temperature is slightly changed during a rated operation, which results in the problem that the cold water temperature becomes unstable due to a fluctuation in cold water temperature In view of the foregoing, an object of the invention is to provide a control method in which the slight change in cold water temperature is absorbed to stabilize the cold water temperature by providing a dead band in a positive direction of a controlled variable (100%) during the rated operation In this case, a dead band width is set to be variable according to the setting value of the control speed, and thereby the dead band width can correspond to both the case where the cold water temperature change speed is fast and the case where the cold water temperature change speed is slow SUMMARY OF THE INVENTION An absorption refrigeration apparatus control method according to the invention in which a cold water temperature is maintained at a setting water temperature by PID control, the cold water temperature being an output of an absorption refrigeration apparatus, the PID control being control in which a manipulated variable M is controlled by the sum of a proportional term, an integral term, and a differential term where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator, wherein a dead band is determined in a positive direction of the manipulated 3 variable M (100%) during a rated operation, and a dead band width is set to be variable corresponding to the proportional term P in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow According to the absorption refrigeration apparatus control method of the invention, even if the change speed of the cold water temperature which is the output is variable according to the installation state of the absorption refrigeration apparatus and the like, the dead band width is increased when the cold water temperature change speed is fast and the dead band width is decreased when the cold water temperature change speed is slow Therefore, the dead band width can correspond to both the case where the cold water temperature change speed is fast and the case where the cold water temperature change speed is slow, and the cold water temperature can be stabilized during the rated operation of the absorption refrigeration apparatus BRIEF DESCRIPTION OF THE DRAWINGS Fig 1 shows a schematic configuration of an absorption refrigeration apparatus according to an embodiment of the invention, Fig 2 is a flowchart showing control according to the invention when a dead band width is variable, and 4 Fig 3 is a flowchart showing control according to the invention when the dead band width is fixed DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In an absorption refrigeration apparatus control method according to the invention, a cold water temperature which is an output of an absorption refrigeration apparatus is maintained at a setting water temperature by PID control which is the control in which a manipulated variable M is controlled by the sum of a proportional term, an integral term, and a differential term where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator In the absorption refrigeration apparatus control method according to the invention, a dead band is determined in a positive direction of the manipulated variable M (100%) in a rated operation, and a dead band width is set to be variable corresponding to the proportional term P in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow Embodiment 1 A preferred embodiment of the absorption refrigerant apparatus of the invention will be described below Fig 1 shows a schematic configuration of the absorption refrigeration apparatus of the invention. Fig 2 is a flowchart showing the 5 control according to the invention when a dead band width is variable, and Fig 3 is a flowchart showing the control according to the invention when the dead band width is fixed Fig 1 shows the schematic configuration of the absorption refrigeration apparatus m which water is used as a refrigerant and lithium bromide (LiBr) is used as an absorbing solution In a configuration of a high-temperature regenerator 1, a diluent in which the absorbing solution and the refrigerant are mixed together is heated to evaporate the refrigerant by heating power of a gas burner 2 in which a town gas or the like is used as fuel, and thereby the absorbing solution and the refrigerant are separated from each other The numeral 3 designates a low-temperature regenerator, the numeral 4 designates a condenser, the numeral 5 designates an evaporator, the numeral 6 designates absorber, the numeral 7 designates a low-temperature heat exchanger, the numeral 8 designates a high-temperature heat exchanger, the numerals 9 to 11 designate an absorbing solution pipe, the numeral 12 designates an absorbing solution pump, the numerals 13 to 15 designate a refrigerant pipe, the numeral 16 designates a refrigerant pump, the numeral 17 designates a cold water pipe, the numeral 18 designates a cooling water pipe, the numeral 19 designates a gas supply pipe to the gas burner 2, the numeral 20 designates a fuel valve which controls gas supply amount to the gas burner 2, the numeral 21 designates a temperature detection unit which detects an outlet temperature of the cold water pipe 17, and the numeral 22 designates a control unit which controls opening 6 of the fuel valve 2 0 based on the temperature detected by the temperature detection unit 21 The control unit 22 controls the opening of the fuel valve 2 0 by comparison between setting data stored in a data storage unit and data based on the temperature detected by the temperature detection unit 21 A method of controlling an outlet temperature (hereinafter referred to as cold water temperature) of the cold water pipe 17 at a setting water temperature is performed by the PID control The cold water temperature of the cold water pipe 17 is an output of the absorption refrigeration apparatus of the invention In the PID control, assuming that a manipulated variable M is an opening of the fuel valve 20 of the gas burner 2 in the high-temperature regenerator 1, the manipulated variable M is controlled by the sum of the proportional term, the integral term, and the differential term As described in Japanese patent Laid-Open No H10-170088, the manipulated variable M is expressed by the following equation 7 (1) or (2) The control unit 22 includes a memory m which a program necessary for microcomputer control, setting temperature data, the manipulated variable M computed based on the detection temperature of the temperature detection unit 21, and various kinds of data necessary to perform control operations are stored [Formula 1] P proportional band (°C) Tx integral time (second) Td differential time (second) T sampling time (second) en deviation between nth target water temperature and current water temperature en-i deviation between (n-l)the target water temperature and current water temperature [Formula 2] A, B, and C correction coefficient M manipulated variable (%) P proportional band (°C) Ta integral time (second) Td differential time (second) x sampling time (second) en deviation between nth target water temperature and current water temperature en-i deviation between (n-l)the target water temperature' and current water temperature Conventionally in the case where the manipulated variable M is controlled by the PID control which is the control performed by the sum of the proportional term, the integral term, and the differential term, a cold water temperature change speed which is the output is variable depending on an installation 8 state of the absorption refrigeration apparatus and the like In the case where the change speed is fast, the heat input control (opening control of the fuel valve of the burner) can rapidly be performed to quickly follow the load change At the same time, the heat input control (opening control of the fuel valve of the burner) is performed even if the cold water temperature is slightly changed during the rated operation, which results m the problem that the cold water temperature becomes unstable due to the fluctuation in cold water temperature Normally, the design is made to take out the cold water having the setting water temperature from the outlet of the cold water pipe while the manipulated variable M is in the state of 100% (rated output is in the state of 100%) In the state of the controlled variable (manipulated variable M is 100%) during the rated operation (rated output of 100%) , even if the cold water temperature is slightly changed, the opening control is performed in the fuel valve of the burner by following the slight change in cold water temperature, and the fluctuation phenomenon is generated around the 100% rated operation state Therefore, the control cannot stably be performed in the rated operation (control in the manipulated variable M of 100%) On the contrary, in the control method of the invention, the dead band is provided in the positive direction of the control Led variable (100%) during the rated operation in order to eliminate the fluctuation phenomenon, and thereby the slight change in cold water temperature is absorbed near 10 0% to stabilize the cold water temperature Fig 3 is a flowchart 9 showing control according to the invention Referring to Fig 3, the temperature detection unit 21 detects the current water temperature (Step S1) , and a current value Mc of the manipulated variable M is read from the memory (Step S2) In Step S3, a difference ?M is computed from the manipulated variable M, determined from a previously set outlet water temperature (hereinafter referred to as setting water temperature) of the cold water pipe 17 and a PID setting value {proportional term, integral term, and differential term), and the manipulated variable M determined based on the water temperature detected by the temperature detection unit 21 Then, the new value Mc of the manipulated variable M is computed by adding the difference ?M to the current value Mc of the manipulated variable M (Step S4) In the embodiment, the dead band width is set at 2 0 Therefore, in Step S5, it is judged whether or not the new value Mc of the manipulated variable is not more than zero When the new value Mc is not more than zero, the new value Mc is set at zero In Step S6, it is judged whether or not the new value Mc is not lower than 120 When the new value Mc is not lower than 120, the new value Mc is set at 120 Then, in Step S7, the new value Mc is stored in the memory In Step S8, a manipulated variable Mt which is of the target opening of the fuel valve 2 0 is computed from the new value Mc In Step S9, it is judged whether or not the value Mc is not more than 100 When the value Mc is not more than zero 100, the manipulated variable Mt is set at the value Mc When the value Mc is more 10 than zero 100, the manipulated variable Mt is set at 100 Then, the manipulated variable Mt is stored in the memory In Step S10, the control unit 22 outputs the signal to the fuel valve 20 such that the opening of the fuel valve 2 0 becomes the manipulated variable Mt Thus, the manipulated variable Mt is set at 100 when the current manipulated variable Mc is 100, and the opening of the fuel valve 20 is set at the manipulated variable Mt of 100 at that time That is, because the opening of the fuel valve 20 is in the output state of 100%, the combustion state becomes 100% in the burner 2 For example, when the computed difference ?M iS +5, the new manipulated variable Mc becomes 105, and the computation is continued until the manipulated variable Mc becomes 120 However, the opening of the fuel valve 20 is fixed to 100, so that the output state is maintained at 100% Therefore, even if the outlet water temperature of the cold water pipe 17 is fluctuated, the opening of the fuel valve 20 is maintained at 100% In the case where the combustion state of the burner 2 is in the rated output state of 100%, even if the slight change is generated in the outlet water temperature of the cold water pipe 17, the opening of the fuel valve 20 is not fluctuated, and the opening of the fuel valve 2 0 is stabilized The opening of the fuel valve 2 0 is variable in the range of 0 to 100% However, for example, in the case where the dead band width is set at 20 , the output value which varies the opening of the fuel valve 20 is set at 100% when the computed value of 11 the manipulated variable M is not lower than 100 (in the range of 100 to 120) Therefore, even if the outlet water temperature of the cold water pipe 17 is slightly raised, the fluctuation phenomenon can be avoided near the rated output of 100%, and the slight change in outlet water temperature of the cold water pipe 17 can be absorbed near 100% to stabilize the opening of the fuel valve 20 In the above embodiment, the dead band width is fixed to 20 However, the dead band width may arbitrarily be set, for example, 10 or 15, and the dead band width may appropriately be determined by the preliminary test In the embodiment, the judgment of the current manipulated variable Mc is made based on the value of 100 Alternatively, judgment of the current manipulated variable Mc is made based on the value of 98, it is judged whether or not the current manipulated variable Mc is not more than 98, and the opening of the fuel valve 20 can be set at 100% when the current manipulated variable Mc is more than 98 In this case, operation state becomes the rated output of 100% when the current manipulated variable Mc is more than 98, and the fluctuation phenomenon can be avoided near the rated output of 100% even if the outlet water temperature of the cold water pipe 17 is slightly lowered or raised Therefore, the slight change in outlet water temperature of the cold water pipe 17 can be absorbed near 100% to stabilize the opening of the fuel valve 20 In the above embodiment, the dead band width is fixed to 20 However, another embodiment of the invention, the dead band 12 width can be varied according to the setting value of the control speed, and thereby the opening of the fuel valve 20 can correspond to both the fast and slow outlet water temperature change speeds of the cold water pipe 17 That is, the opening of the fuel valve 2 0 is varied with respect to the P setting value {proportional term) which is the setting value of the proportional band width in the PID control, the dead band width is fixed to 20, and the dead band width is computed from 20/P (20 is divided by P) when the P setting value is changed from 1 to 20 The P setting value is a value which is varied in such a manner that an operating manager or the like of the absorption refrigeration apparatus operates a remote control operation unit On the basis of the temperature detected by the temperature detection unit 21, the operating manager or the like watches the temperature change of the temperature display unit displayed by the operation of the control unit 22, and the operating manager increases the P setting value when the outlet water temperature change of the cold water pipe 17 is slow Therefore, the dead band width is decreased On the other hand, the operating manager decreases the P setting value when the outlet water temperature change of the cold water pipe 17 is fast Therefore, the dead band width is increased Accordingly, the control can be performed according to the outlet water temperature change speed of the cold water pipe 17, and the control can correspond to both the case where the outlet water temperature is rapidly changed in the cold water pipe 17 and the case where the outlet water 13 temperature is slowly changed in the cold water pipe 17, which allows the cold water temperature to be stabilized during the rated operation of the absorption refrigeration apparatus In this case, the constant value of 20 in the numerator of 20/P is the fixed dead band width of 20 As described above, the dead band width may appropriately be determined by the preliminary test Fig 2 is a flowchart showing control according to the invention when a dead band width is variable In the flowchart of Fig 2, Steps S1 to S4 are similar to those of Fig 3 In Step S5, the maximum width Mm of the manipulated variable Me is computed from the P setting value (proportional term) of the PID control (for example, Mm=20/P) In Step S6, it is judged whether or not the manipulated variable Mc computed in Step S4 is not more than zero When the manipulated variable Me is not more than zero, the manipulated variable Mc is set at zero In Step S7, it is judged whether or not the new manipulated variable Mc is not lower than 100+Mm When the new manipulated variable Mc is not lower than 100+Mm, the new manipulated variable Mc is set at 100+Mm Then, in Step S8, the new manipulated variable Me is stored in the memory In Step S9, the manipulated variable Mt which is the target opening of the fuel valve 20 is computed from the new manipulated variable Mc in Step S10 , it is judged whether or not the manipulated variable Mc computed in Step S9 is not more than 100 When the manipulated variable Me is not more than 100, the manipulated variable Mt is set to the manipulated variable Me On the other hand, when the 14 manipulated variable Mc is not lower than 100, the manipulated variable Mt is set at 100 Then, the manipulated variable Mt is stored in the memory In Step Sll, the control unit 22 outputs the signal to the fuel valve 20 such that the opening of the fuel valve 20 becomes the manipulated variable Mt According to the absorption refrigeration apparatus control method of the invention, the manipulated variable Mt is set at 100 when the current manipulated variable Mc is 100, and the opening of the fuel valve 20 is set at the manipulated variable Mt of 10 0 at that time That is, because the opening of the fuel valve 2 0 is in the output state of 100%, the combustion state becomes 100% in the burner 2 The control is performed, such that the manipulated variable Mc is set at zero when the manipulated variable Mc computed in Step S4 is not more than zero and the manipulated variable Mc is set at 100+Mm when the new manipulated variable Mc is not lower than 100+Mm Therefore, the control can be performed according to the outlet water temperature change speed of the cold water pipe 17, and the control can correspond to both the fast and slow outlet water temperature change speeds of the cold water pipe 17 The invention is not limited to the above embodiments For example, the piping diagram of the absorption refrigeration apparatus of the invention can be applied to any modes of the drawings disclosed in Japanese patent Laid-Open No H10-170088 Various changes and modifications could be made without departing from the scope of the invention 15 We claim 16 1 An absorption refrigeration apparatus control method in which a cold water temperature is maintained at a setting water temperature by PID control, the cold water temperature being an output of an absorption refrigeration apparatus, the PID control being control in which a manipulated variable M is controlled by the sum of a proportional term, an integral term, and a differential term where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator, wherein a dead band is determined in a positive direction of the manipulated variable M (100%) during a rated operation, and a dead band width is set to be variable corresponding to the proportional term P in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow. The present invention provides a technique of absorbing a slight change in cold water temperature near 100% of a manipulated variable M to stabilize the cold water temperature, when a cold water temperature is controlled by PID control where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator. A dead band is determined in a positive direction of the manipulated variable M (100%} in a rated operation, and a dead band width is set to be variable corresponding to the proportional term in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow.

Full Text

ABSORPTION REFRIGERATION APPARATUS
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates to a technique of performing operation control of an absorption refrigeration apparatus by PID control which is the control performed by the sum of a proportional term, an integral term, and a differential term
2 Description of the Related Art
When operation control for controlling a cold water temperature as an output of the absorption refrigeration apparatus to be maintained at a setting water temperature is performed by a manipulated variable M which is of an opening of a fuel valve of a burner in a high-temperature regenerator, the manipulated variable M is set to 100% in the range where a current water temperature is sufficient higher than the setting water temperature, the manipulated variable M is set to 0% m the range where a current water temperature is sufficient lower than the setting water temperature, and the manipulated variable M is proportioned to the current water temperature in the range between the sufficiently lower range and the sufficiently higher range In such cases, there is a problem that response is delayed when some sort of disturbance is generated The PID control is adopted to solve the problem, (for example, see Japanese patent Laid-Open No H10-170088)
2

In the PID control disclosed in Japanese patent Laid-Open No H10-170088 which is designed to take out the cold water having the setting water temperature while the manipulated variable M is substantially 100% (rated output is substantially 100%), when the current water temperature is located near the setting water temperature, controllability becomes worsened due to little margin of the manipulated variable M In order to solve this problem, the proportional term, the integral term, and the differential term are respectively multiplied by correction coefficients A, B, and C determined from a relationship between the current water temperature and the setting water temperature
Thus, in order to perform the control such that the cold water temperature which is the output of the absorption refrigeration apparatus is maintained at the setting water temperature, in the case where the manipulated variable M which is the opening of the fuel valve of the burner in the high-temperature regenerator is controlled by the PID control which is the control performed by the sum of the proportional term, the integral term, and the differential term, a cold water temperature change speed which is the output is variable depending on an installation state of the absorption refrigeration apparatus and the like In the case where the change speed is fast, heat input control (opening control of the fuel valve of the burner) can rapidly be performed to quickly follow the load change At the same time, the heat input control (opening control of the fuel valve of the burner) is performed
2A

even if the cold water temperature is slightly changed during a rated operation, which results in the problem that the cold water temperature becomes unstable due to a fluctuation in cold water temperature
In view of the foregoing, an object of the invention is to provide a control method in which the slight change in cold water temperature is absorbed to stabilize the cold water temperature by providing a dead band in a positive direction of a controlled variable (100%) during the rated operation In this case, a dead band width is set to be variable according to the setting value of the control speed, and thereby the dead band width can correspond to both the case where the cold water temperature change speed is fast and the case where the cold water temperature change speed is slow
SUMMARY OF THE INVENTION
An absorption refrigeration apparatus control method according to the invention in which a cold water temperature is maintained at a setting water temperature by PID control, the cold water temperature being an output of an absorption refrigeration apparatus, the PID control being control in which a manipulated variable M is controlled by the sum of a proportional term, an integral term, and a differential term where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator, wherein a dead band is determined in a positive direction of the manipulated
3

variable M (100%) during a rated operation, and a dead band width is set to be variable corresponding to the proportional term P in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow
According to the absorption refrigeration apparatus control method of the invention, even if the change speed of the cold water temperature which is the output is variable according to the installation state of the absorption refrigeration apparatus and the like, the dead band width is increased when the cold water temperature change speed is fast and the dead band width is decreased when the cold water temperature change speed is slow Therefore, the dead band width can correspond to both the case where the cold water temperature change speed is fast and the case where the cold water temperature change speed is slow, and the cold water temperature can be stabilized during the rated operation of the absorption refrigeration apparatus
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 shows a schematic configuration of an absorption refrigeration apparatus according to an embodiment of the invention,
Fig 2 is a flowchart showing control according to the invention when a dead band width is variable, and
4

Fig 3 is a flowchart showing control according to the invention when the dead band width is fixed
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In an absorption refrigeration apparatus control method according to the invention, a cold water temperature which is an output of an absorption refrigeration apparatus is maintained at a setting water temperature by PID control which is the control in which a manipulated variable M is controlled by the sum of a proportional term, an integral term, and a differential term where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator In the absorption refrigeration apparatus control method according to the invention, a dead band is determined in a positive direction of the manipulated variable M (100%) in a rated operation, and a dead band width is set to be variable corresponding to the proportional term P in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow
Embodiment 1
A preferred embodiment of the absorption refrigerant apparatus of the invention will be described below Fig 1 shows a schematic configuration of the absorption refrigeration apparatus of the invention. Fig 2 is a flowchart showing the
5

control according to the invention when a dead band width is variable, and Fig 3 is a flowchart showing the control according to the invention when the dead band width is fixed
Fig 1 shows the schematic configuration of the absorption refrigeration apparatus m which water is used as a refrigerant and lithium bromide (LiBr) is used as an absorbing solution In a configuration of a high-temperature regenerator 1, a diluent in which the absorbing solution and the refrigerant are mixed together is heated to evaporate the refrigerant by heating power of a gas burner 2 in which a town gas or the like is used as fuel, and thereby the absorbing solution and the refrigerant are separated from each other The numeral 3 designates a low-temperature regenerator, the numeral 4 designates a condenser, the numeral 5 designates an evaporator, the numeral 6 designates absorber, the numeral 7 designates a low-temperature heat exchanger, the numeral 8 designates a high-temperature heat exchanger, the numerals 9 to 11 designate an absorbing solution pipe, the numeral 12 designates an absorbing solution pump, the numerals 13 to 15 designate a refrigerant pipe, the numeral 16 designates a refrigerant pump, the numeral 17 designates a cold water pipe, the numeral 18 designates a cooling water pipe, the numeral 19 designates a gas supply pipe to the gas burner 2, the numeral 20 designates a fuel valve which controls gas supply amount to the gas burner 2, the numeral 21 designates a temperature detection unit which detects an outlet temperature of the cold water pipe 17, and the numeral 22 designates a control unit which controls opening
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of the fuel valve 2 0 based on the temperature detected by the temperature detection unit 21 The control unit 22 controls the opening of the fuel valve 2 0 by comparison between setting data stored in a data storage unit and data based on the temperature detected by the temperature detection unit 21
A method of controlling an outlet temperature
(hereinafter referred to as cold water temperature) of the cold water pipe 17 at a setting water temperature is performed by the PID control The cold water temperature of the cold water pipe 17 is an output of the absorption refrigeration apparatus of the invention In the PID control, assuming that a manipulated variable M is an opening of the fuel valve 20 of the gas burner 2 in the high-temperature regenerator 1, the manipulated variable M is controlled by the sum of the proportional term, the integral term, and the differential term As described in Japanese patent Laid-Open No H10-170088, the manipulated variable M is expressed by the following equation
7
(1) or (2) The control unit 22 includes a memory m which a program necessary for microcomputer control, setting temperature data, the manipulated variable M computed based on the detection temperature of the temperature detection unit 21, and various kinds of data necessary to perform control operations are stored [Formula 1]

P proportional band (°C)
Tx integral time (second)
Td differential time (second)
T sampling time (second)
en deviation between nth target water temperature and
current water temperature
en-i deviation between (n-l)the target water temperature and current water temperature
[Formula 2]

A, B, and C correction coefficient M manipulated variable (%)
P proportional band (°C)
Ta integral time (second)
Td differential time (second)
x sampling time (second)
en deviation between nth target water temperature and current water temperature
en-i deviation between (n-l)the target water temperature' and current water temperature
Conventionally in the case where the manipulated variable M is controlled by the PID control which is the control performed by the sum of the proportional term, the integral term, and the differential term, a cold water temperature change speed which is the output is variable depending on an installation
8

state of the absorption refrigeration apparatus and the like In the case where the change speed is fast, the heat input control (opening control of the fuel valve of the burner) can rapidly be performed to quickly follow the load change At the same time, the heat input control (opening control of the fuel valve of the burner) is performed even if the cold water temperature is slightly changed during the rated operation, which results m the problem that the cold water temperature becomes unstable due to the fluctuation in cold water temperature
Normally, the design is made to take out the cold water having the setting water temperature from the outlet of the cold water pipe while the manipulated variable M is in the state of 100% (rated output is in the state of 100%) In the state of the controlled variable (manipulated variable M is 100%) during the rated operation (rated output of 100%) , even if the cold water temperature is slightly changed, the opening control is performed in the fuel valve of the burner by following the slight change in cold water temperature, and the fluctuation phenomenon is generated around the 100% rated operation state Therefore, the control cannot stably be performed in the rated operation (control in the manipulated variable M of 100%)
On the contrary, in the control method of the invention, the dead band is provided in the positive direction of the control Led variable (100%) during the rated operation in order to eliminate the fluctuation phenomenon, and thereby the slight change in cold water temperature is absorbed near 10 0% to stabilize the cold water temperature Fig 3 is a flowchart
9

showing control according to the invention Referring to Fig 3, the temperature detection unit 21 detects the current water temperature (Step S1) , and a current value Mc of the manipulated variable M is read from the memory (Step S2) In Step S3, a difference ?M is computed from the manipulated variable M, determined from a previously set outlet water temperature (hereinafter referred to as setting water temperature) of the cold water pipe 17 and a PID setting value {proportional term, integral term, and differential term), and the manipulated variable M determined based on the water temperature detected by the temperature detection unit 21 Then, the new value Mc of the manipulated variable M is computed by adding the
difference ?M to the current value Mc of the manipulated variable M (Step S4)
In the embodiment, the dead band width is set at 2 0 Therefore, in Step S5, it is judged whether or not the new value Mc of the manipulated variable is not more than zero When the new value Mc is not more than zero, the new value Mc is set at zero In Step S6, it is judged whether or not the new value Mc is not lower than 120 When the new value Mc is not lower than 120, the new value Mc is set at 120 Then, in Step S7, the new value Mc is stored in the memory In Step S8, a manipulated variable Mt which is of the target opening of the fuel valve 2 0 is computed from the new value Mc In Step S9, it is judged whether or not the value Mc is not more than 100 When the value Mc is not more than zero 100, the manipulated variable Mt is set at the value Mc When the value Mc is more
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than zero 100, the manipulated variable Mt is set at 100 Then, the manipulated variable Mt is stored in the memory In Step S10, the control unit 22 outputs the signal to the fuel valve 20 such that the opening of the fuel valve 2 0 becomes the manipulated variable Mt
Thus, the manipulated variable Mt is set at 100 when the current manipulated variable Mc is 100, and the opening of the fuel valve 20 is set at the manipulated variable Mt of 100 at that time That is, because the opening of the fuel valve 20 is in the output state of 100%, the combustion state becomes 100% in the burner 2 For example, when the computed difference ?M iS +5, the new manipulated variable Mc becomes 105, and the computation is continued until the manipulated variable Mc becomes 120 However, the opening of the fuel valve 20 is fixed to 100, so that the output state is maintained at 100% Therefore, even if the outlet water temperature of the cold water pipe 17 is fluctuated, the opening of the fuel valve 20 is maintained at 100% In the case where the combustion state of the burner 2 is in the rated output state of 100%, even if the slight change is generated in the outlet water temperature of the cold water pipe 17, the opening of the fuel valve 20 is not fluctuated, and the opening of the fuel valve 2 0 is stabilized
The opening of the fuel valve 2 0 is variable in the range of 0 to 100% However, for example, in the case where the dead band width is set at 20 , the output value which varies the opening of the fuel valve 20 is set at 100% when the computed value of
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the manipulated variable M is not lower than 100 (in the range of 100 to 120) Therefore, even if the outlet water temperature of the cold water pipe 17 is slightly raised, the fluctuation phenomenon can be avoided near the rated output of 100%, and the slight change in outlet water temperature of the cold water pipe 17 can be absorbed near 100% to stabilize the opening of the fuel valve 20 In the above embodiment, the dead band width is fixed to 20 However, the dead band width may arbitrarily be set, for example, 10 or 15, and the dead band width may appropriately be determined by the preliminary test
In the embodiment, the judgment of the current manipulated variable Mc is made based on the value of 100 Alternatively, judgment of the current manipulated variable Mc is made based on the value of 98, it is judged whether or not the current manipulated variable Mc is not more than 98, and the opening of the fuel valve 20 can be set at 100% when the current manipulated variable Mc is more than 98 In this case, operation state becomes the rated output of 100% when the current manipulated variable Mc is more than 98, and the fluctuation phenomenon can be avoided near the rated output of 100% even if the outlet water temperature of the cold water pipe 17 is slightly lowered or raised Therefore, the slight change in outlet water temperature of the cold water pipe 17 can be absorbed near 100% to stabilize the opening of the fuel valve 20
In the above embodiment, the dead band width is fixed to 20 However, another embodiment of the invention, the dead band
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width can be varied according to the setting value of the control speed, and thereby the opening of the fuel valve 20 can correspond to both the fast and slow outlet water temperature change speeds of the cold water pipe 17
That is, the opening of the fuel valve 2 0 is varied with respect to the P setting value {proportional term) which is the setting value of the proportional band width in the PID control, the dead band width is fixed to 20, and the dead band width is computed from 20/P (20 is divided by P) when the P setting value is changed from 1 to 20 The P setting value is a value which is varied in such a manner that an operating manager or the like of the absorption refrigeration apparatus operates a remote control operation unit On the basis of the temperature detected by the temperature detection unit 21, the operating manager or the like watches the temperature change of the temperature display unit displayed by the operation of the control unit 22, and the operating manager increases the P setting value when the outlet water temperature change of the cold water pipe 17 is slow Therefore, the dead band width is decreased On the other hand, the operating manager decreases the P setting value when the outlet water temperature change of the cold water pipe 17 is fast Therefore, the dead band width is increased Accordingly, the control can be performed according to the outlet water temperature change speed of the cold water pipe 17, and the control can correspond to both the case where the outlet water temperature is rapidly changed in the cold water pipe 17 and the case where the outlet water
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temperature is slowly changed in the cold water pipe 17, which allows the cold water temperature to be stabilized during the rated operation of the absorption refrigeration apparatus In this case, the constant value of 20 in the numerator of 20/P is the fixed dead band width of 20 As described above, the dead band width may appropriately be determined by the preliminary test
Fig 2 is a flowchart showing control according to the invention when a dead band width is variable In the flowchart of Fig 2, Steps S1 to S4 are similar to those of Fig 3 In Step S5, the maximum width Mm of the manipulated variable Me is computed from the P setting value (proportional term) of the PID control (for example, Mm=20/P) In Step S6, it is judged whether or not the manipulated variable Mc computed in Step S4 is not more than zero When the manipulated variable Me is not more than zero, the manipulated variable Mc is set at zero In Step S7, it is judged whether or not the new manipulated variable Mc is not lower than 100+Mm When the new manipulated variable Mc is not lower than 100+Mm, the new manipulated variable Mc is set at 100+Mm Then, in Step S8, the new manipulated variable Me is stored in the memory In Step S9, the manipulated variable Mt which is the target opening of the fuel valve 20 is computed from the new manipulated variable Mc in Step S10 , it is judged whether or not the manipulated variable Mc computed in Step S9 is not more than 100 When the manipulated variable Me is not more than 100, the manipulated variable Mt is set to the manipulated variable Me On the other hand, when the
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manipulated variable Mc is not lower than 100, the manipulated variable Mt is set at 100 Then, the manipulated variable Mt is stored in the memory In Step Sll, the control unit 22 outputs the signal to the fuel valve 20 such that the opening of the fuel valve 20 becomes the manipulated variable Mt
According to the absorption refrigeration apparatus control method of the invention, the manipulated variable Mt is set at 100 when the current manipulated variable Mc is 100, and the opening of the fuel valve 20 is set at the manipulated variable Mt of 10 0 at that time That is, because the opening of the fuel valve 2 0 is in the output state of 100%, the combustion state becomes 100% in the burner 2 The control is performed, such that the manipulated variable Mc is set at zero when the manipulated variable Mc computed in Step S4 is not more than zero and the manipulated variable Mc is set at 100+Mm when the new manipulated variable Mc is not lower than 100+Mm Therefore, the control can be performed according to the outlet water temperature change speed of the cold water pipe 17, and the control can correspond to both the fast and slow outlet water temperature change speeds of the cold water pipe 17
The invention is not limited to the above embodiments For example, the piping diagram of the absorption refrigeration apparatus of the invention can be applied to any modes of the drawings disclosed in Japanese patent Laid-Open No H10-170088 Various changes and modifications could be made without departing from the scope of the invention
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We claim
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1 An absorption refrigeration apparatus control method in which a cold water temperature is maintained at a setting water temperature by PID control, the cold water temperature being an output of an absorption refrigeration apparatus, the PID control being control in which a manipulated variable M is controlled by the sum of a proportional term, an integral term, and a differential term where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator, wherein a dead band is determined in a positive direction of the manipulated variable M (100%) during a rated operation, and a dead band width is set to be variable corresponding to the proportional term P in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow.

The present invention provides a technique of absorbing a slight change in cold water temperature near 100% of a manipulated variable M to stabilize the cold water temperature, when a cold water temperature is controlled by PID control where the manipulated variable M is an opening of a fuel valve of a burner of a high-temperature regenerator. A dead band is determined in a positive direction of the manipulated variable M (100%} in a rated operation, and a dead band width is set to be variable corresponding to the proportional term in such a manner that the dead band width is increased when a cold water temperature change speed is fast while the dead band width is decreased when the cold water temperature change speed is slow.

A CONTROL METHOD IN AN ABSORPTION REFRIGERATION APPARATUS HAVING PID CONTROL FOR STABILIZING THE COLD WATER TEMPERATURE

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