JP5583897B2 - Cooling tower and heat source system - Google Patents

Description

  The present invention relates to a cooling tower and a heat source apparatus system, and more particularly to a technique for controlling a rotation frequency of a cooling tower fan.

  For example, the cooling water heated to a high temperature by cooling the heat load with a heat source machine such as an absorption chiller / heater is led to the cooling tower through a pipe, cooled by the cooling tower, and then again through the pipe. Circulated to the heat load. The cooling tower is known as one in which high-temperature cooling water guided from a heat source device is sprayed in a casing and cooled by latent heat of vaporization by a fan provided in the cooling tower.

  By the way, in order to respond to recent energy-saving requirements, energy-saving research on a heat-source unit system including a heat-source unit and a cooling tower has been conducted, and the efficiency of the heat-source unit itself has been improved to some extent.

  However, it is not sufficient to save the energy of the heat source unit itself. For example, it is required to improve the efficiency of the power of a fan used for a pump or a cooling tower that transports cooling water between the heat source unit and the cooling tower.

  In this regard, as described in Patent Document 1, the temperature of the cooling water cooled by the cooling tower is detected, and the number of rotations of the cooling tower fan is controlled by the inverter in a variable manner according to the detected temperature. It is known to increase fan efficiency.

  That is, conventionally, the fan is driven at a frequency of 100% when the cooling water temperature becomes a certain set temperature (for example, 27 ° C.) or more, and the fan is stopped when the cooling water temperature becomes a certain set temperature (for example, 24.5 ° C.) or less. Since it was on-off control, the fan was frequently started and stopped, which was not preferable from the viewpoint of fan efficiency. On the other hand, in Patent Document 1, when the detected temperature is between the lower limit set temperature (for example, 24.5 ° C.) and the upper limit set temperature (for example, 27 ° C.), the detected temperature has a one-to-one correspondence. It is said that the number of times the fan is started and stopped can be reduced by driving the fan at a frequency set to be approximately proportional.

JP-A-5-340690

  By the way, the conventional fan frequency control technique described in Patent Document 1 does not consider the optimization of the fan frequency in consideration of the cooling load of the heat source device.

  That is, the technique described in Patent Document 1 is based on a fixed correspondence relationship regardless of the cooling load of the heat source unit because the correspondence relationship between the detected temperature of the cooling water and the fan frequency is fixed. The fan is driven at a different frequency.

  However, when the cooling load of the heat source device fluctuates, the frequency determined corresponding to the detected temperature is not always appropriate. For example, when the cooling load of the heat source device fluctuates and becomes small, the fan is driven at a frequency higher than the appropriate frequency, which is not preferable from the viewpoint of energy saving. May not be controlled.

  Accordingly, an object of the present invention is to optimize the frequency control of the fan in consideration of the cooling load of the heat source device.

  The cooling tower of the present invention sprays high-temperature cooling water returned from the heat load into the air, cools the cooling water with latent heat of vaporization caused by the air flow accompanying the rotation of the fan, and circulates and supplies it again to the heat load. The control unit is configured to detect the temperature of the cooled cooling water and control the frequency of the fan based on the correspondence relationship between the preset detection temperature of the cooling water and the frequency of the fan.

  In particular, the control means is characterized by detecting the cooling load of the heat source device and correcting the correspondence relationship between the detected temperature of the cooling water and the frequency of the fan in accordance with the detected load.

  According to this, when the cooling load of the heat source device fluctuates, the correspondence between the detected temperature of the cooling water and the frequency of the fan can be corrected to an appropriate one following the variation.

  Specifically, the control means corrects at least a part of the frequency of the fan set corresponding to the detected temperature of the cooling water as the detected load decreases. That is, when the load of the heat source device fluctuates and becomes smaller, it is preferable to drive the fan at a lower frequency than in the case of a high load to lower the cooling capacity of the cooling water. According to this, it is possible to save energy by suppressing driving of the fan at a high frequency corresponding to a load larger than the actual load, and to suppress the cooling water overcooling and to set the cooling water temperature to the target temperature. Can be controlled appropriately. On the other hand, if the detected load increases, the cooling water is appropriately cooled by increasing the cooling capacity by largely correcting the frequency of the fan set corresponding to the detected temperature of the cooling water.

  In addition, the control means can be configured to perform so-called P control that controls the frequency of the fan in proportion to the deviation between the detected temperature of the cooling water and a preset target temperature of the cooling water. In this case, the proportional gain of control may be changed according to the detected load. Specifically, the proportional gain is decreased as the detected load decreases. This proportional gain is applied to both the deviation component term and the manipulated variable when the cooling water temperature is the target temperature.

  That is, since the frequency of the fan corresponding to the detected temperature of the cooling water can be corrected by changing the proportional gain, the fan can be driven at an appropriate frequency according to the load of the heat source unit. it can.

  In addition to so-called P control, in so-called PID control that controls the fan frequency in proportion to the deviation between the detected temperature of the cooled cooling water and the target temperature, the integral component of the deviation, and the differential component of the deviation. The proportional gain may be changed according to the detected load.

  In the case where the heat source device is composed of an absorption chiller / heater, the control means is a cooling load of the heat source device, the temperature of the fluid returned from the cooling load of the absorption chiller / heater, or the regenerator of the absorption chiller / heater The amount of heat input to can be detected.

  Further, the control means continues the target temperature when the detected temperature of the cooling water continues for a preset time or longer and the fan frequency is higher than the high temperature threshold temperature at which the detected upper limit frequency is reached as the detected temperature of the cooling water rises. Can be high. In other words, the fact that the cooling water temperature is higher than the high temperature threshold temperature for a certain period of time indicates that the load of the heat source unit is high and the deviation of the detected temperature from the target temperature of the cooling water is large, and the fan is continued. Thus, it is not preferable to continue driving at the set upper limit frequency from the viewpoint of energy saving. Therefore, in this case, the target temperature is increased, in other words, the target temperature is brought closer to the current cooling water temperature, thereby reducing the deviation between the target temperature of the cooling water and the detected temperature, thereby reducing the fan frequency. , Energy saving can be achieved.

  On the other hand, when the detected temperature of the cooling water continues for a preset time or longer and the detected temperature of the cooling water drops and the fan frequency is lower than the low temperature threshold temperature that is the set lower limit frequency except when the fan is stopped The target temperature can be lowered. In this case as well, the deviation of the detected temperature with respect to the target temperature of the cooling water is large as described above. Therefore, by lowering the target temperature and reducing the deviation, the fan frequency is reduced and the fan starts and stops. Since the cooling water is stabilized by avoiding as much as possible, the entire system can save energy.

  Also, a heat source unit, a cooling tower, a pipe for guiding the high-temperature cooling water returned from the heat load of the heat source unit to the cooling tower, and a pipe for guiding the cooling water cooled by the cooling tower to the heat load of the heat source unit are provided. In the heat source system configured as described above, the frequency control of the cooling tower fan described above can be employed.

  According to the present invention, energy saving can be achieved by controlling the frequency of the fan in consideration of the cooling load of the heat source device.

  Hereinafter, embodiments of a cooling tower and a heat source system to which the present invention is applied will be described. FIG. 1 is a diagram illustrating an overall configuration of a heat source apparatus system according to the present embodiment. As shown in FIG. 1, the heat source apparatus system 100 includes a cooling tower 10, a heat source apparatus 20, and a cooling water pipe 30.

  The cooling tower 10 includes a cylindrical casing 11, an air inlet 12 is formed on the lower side surface of the casing 11, and a cooling water tank 13 is provided at the bottom. The air inlet 12 is formed in a louver shape. A filler 14 is accommodated in the casing 11 above the position of the air inlet 12, and a cooling water sprinkling nozzle 15 is disposed above the filler 14.

  An opening 16 is provided at the top of the casing 11. A fan motor 18 is fixed to the opening 16 by a fixture 17, and a fan 19 is fixed to the rotation shaft of the fan motor 18. In addition, the replenishment water of the cooling water to the water tank 13 of the cooling tower 10 is supplied from a water supply port having a ball tap or the like (not shown).

  The cooling water pipe 30 includes an outgoing pipe 31 and a return pipe 32. In the outgoing pipe 31, a cooling water pump 33 and a check valve 34 are arranged in order from the cooling tower 10 toward the heat source unit 20. The suction port of the cooling water pump 33 communicates with the vicinity of the bottom of the water tank 13. The discharge port of the cooling water pump 33 is connected via a check valve 34 to a heat exchanger (not shown) that can exchange heat with the heat load of the heat source unit 20. A cooling water temperature sensor 51 is provided between the check valve 34 of the outgoing pipe 31 and a heat exchanger (not shown) (inlet part of the heat source unit 20). An output signal of the cooling water temperature sensor 51 is provided. Is input to an operation control device 50 described later.

  The return pipe 32 is provided with an electric three-way valve 41 and a bypass pipe 42 that guides cooling water of the return pipe 32 to the water tank 13 when the electric three-way valve 41 is opened by a bypass command.

  The operation control device 50 includes a control device 53 and an inverter device 55. The control device 53 forms a frequency signal for rotating the fan motor 18 and the fan 19 at a frequency set in advance according to a temperature signal detected by the cooling water temperature sensor 51 and a gas flow rate detected by a gas flow rate sensor described later. This is given to the inverter device 55.

  Further, the control device 53 forms a bypass command signal based on the detected temperature signal from the cooling water temperature sensor 51 and gives it to the electric three-way valve 41 to bypass the cooling water. For example, when the detected temperature of the cooling water is lower than the lower limit set temperature (for example, 24 ° C.), the electric three-way valve 41 is switched to drop the return cooling water from the heat source unit 20 directly into the water tank 13 of the cooling tower 10. Prevents cooling water from being overcooled.

  In the present embodiment, for convenience of explanation, the control device 53 is provided independently of the cooling tower 10 and the heat source unit 20, but is provided attached to the cooling tower 10 as one component of the cooling tower 10. Alternatively, it can be attached to the heat source unit 20 and can be a component of the heat source unit system 100.

  Moreover, the heat source machine 20 of this embodiment is comprised with the absorption-type cold / hot water machine. As shown in FIG. 1, an absorption chiller / heater that is a heat source device 20 forms a absorption refrigeration cycle by connecting a regenerator 60, a separator 61, a condenser 62, an evaporator 63, an absorber 64, and the like. Configured. The cooling water cooled by the cooling tower 10 flows through the absorber 64 and the condenser 62 and exchanges heat with the refrigerant of the absorption chiller / heater so as to be returned to the cooling tower 10 again. It has become.

  In addition, as a characteristic configuration of the present embodiment, a gas flow rate sensor that detects the amount of heat input to the regenerator 60 in order to detect the cooling load of the absorption chiller / heater (hereinafter simply referred to simply as the load of the absorption chiller / heater). 65 is provided, and a signal detected by the gas flow sensor 65 is input to the control device 53.

  In the direct-fired absorption chiller / heater driven using the combustion heat of the burner, the gas flow rate may be detected as the amount of heat input to the regenerator 60 as in this embodiment. On the other hand, when adopting an exhaust heat type absorption chiller / heater driven using exhaust heat, a sensor for detecting the amount of heat input of exhaust heat may be used. Moreover, in order to detect the load of an absorption-type cold / hot water machine, you may detect the temperature of fluids, such as cold water, returned from the load of an absorption-type cold / hot water machine.

  Note that the heat source device 20 is not limited to the absorption chiller / heater, but may be a device that needs to cool the heat load using the cooling water cooled by the cooling tower 10. Also in this case, a sensor or the like that detects the cooling load of the heat source device 20 can be provided as appropriate, and the detected signal can be input to the control device 53.

  FIG. 2 is a block diagram showing a detailed configuration of the control device 53. The control device 53 shown in FIG. 2 includes a central processing unit 531, a storage device 532, an input signal unit 533, an output signal unit 534, and the like. The control device 53 starts to operate as the cooling tower 10 starts operating. Then, the central processing unit 531 operates based on the program stored in the storage device 532, and in advance according to the data fetched from the cooling water temperature sensor 51 and the gas flow rate sensor 65 via the input signal unit 533. A frequency signal for rotationally driving the fan motor 18 and the fan 19 at a set frequency is formed and can be supplied to the inverter device 55 via the output signal unit 534.

  By the way, in such a heat source system 100, conventionally, the rotation frequency of the fan 19 is set so that the temperature detected by the cooling water temperature sensor 51 of the cooling water is maintained at a target temperature between the lower limit set temperature and the upper limit set temperature. Be controlled. For example, the fan frequency is set to be proportional to the detected temperature so that the fan frequency is increased when the detected temperature is higher than the target temperature, and the fan frequency is decreased when the detected temperature is lower. It is known to drive the fan 19 at a frequency of

  However, in such a conventional technique, consideration is not given to optimizing the frequency of the fan 19 in consideration of the cooling load of the heat source device 20.

  That is, in the prior art, the cooling water temperature is simply detected, and the fan frequency is controlled based on the correspondence between the cooling water detection temperature fixed in advance and the fan frequency. For this reason, the fan 19 is driven at a frequency based on the fixed correspondence regardless of the cooling load of the heat source device 20.

  However, when the cooling load of the heat source device 20 fluctuates, the frequency determined corresponding to the detected temperature is not always appropriate. For example, when the cooling load of the heat source device 20 is fluctuated and becomes small, the fan is driven at a frequency higher than an appropriate frequency, which is not preferable from the viewpoint of energy saving. There is a risk of being out of control.

  The heat source machine system 100 and the cooling tower 10 of this embodiment are made to cope with such a problem. Hereinafter, the frequency control contents of the fan of the control device 53 that is a characteristic part of the heat source apparatus system 100 and the cooling tower 10 of the present embodiment will be described in detail for each example.

  The control device 53 of the present embodiment includes a deviation between a preset target temperature of cooling water (hereinafter referred to as Mp as appropriate) and a detected temperature of cooling water (hereinafter referred to as CTI as appropriate), an integral of deviation, and a differential of deviation. The frequency of the fan 19 is controlled by so-called PID control in proportion to these three elements.

The PID basic control expression is expressed by the following (Equation 1).
(Equation 1)
m (nTs) = K × (1/100) × (P component term + I component term + D component term + Mo)
Each component term in Equation 1 is expressed by the following (Equation 2) to (Equation 4).
(Equation 2)
P component term = (1 / P) × e (nTs) × 100
(Equation 3)
I component term = (1 / P) × (Ts / Ti) × Σe (iTs) × 100
(Equation 4)
D component term = (1 / P) × (Td / a × Ts) × {e (nTs) −e ((n−a) Ts)} × 100
Here, the variables in Equations 1 to 4 are as follows.
m (nTs): n-th output, K: proportional gain (total manipulated variable), P: proportional band (proportional operation range), e (nTs): n-th deviation (difference from target temperature), Ts: sampling Time (s), Ti: integration time (s), Td: derivative time (s), a × Ts: derivative period (s), e ((na) Ts): (na) th output, Mo: Amount of operation at target temperature (%)
Mo is a representative value (for example, 50%) at a specific load of the heat source device.

  For example, assuming that Mp is set to 28 ° C., the deviation of the current CTI with respect to Mp: 28 ° C. becomes the P component term (proportional component), so that the P component term increases as the deviation increases. Since the I component term (integral component) continuously integrates the deviation between Mp: 28 ° C. and the current CTI at regular intervals, the deviation increases as the time away from the target temperature increases. The larger the value, the larger the I component term. The D component term (differential component) is a component for dealing with a sudden fluctuation due to a disturbance or the like, and makes an output for correcting the sudden fluctuation.

  The control device 53 starts calculation of PID control from the point of time when the combustion signal of the regenerator 60 is input, and sequentially calculates and outputs the frequency of the fan 19 based on CTI and Formula 1 input every control cycle. The calculation is stopped by stopping the combustion. According to such PID control, it is possible to set the target temperature pinpoint, and the followability to disturbance is improved.

  In addition to this, as a feature of the present embodiment, the control device 53 has the gas flow rate to the regenerator 60 detected by the gas flow rate sensor 65, in other words, to the regenerator 60 correlated with the load of the absorption chiller / heater. Heat input amount (or combustion amount of regenerator 60, input) is input. The control device 53 changes the proportional gain (K) of the control in the above equation 1 according to the detected load of the absorption chiller / heater. This point will be described with reference to FIG.

  FIG. 3 is a diagram illustrating a correspondence relationship between the detected temperature of the cooling water of the control device 53 of the present embodiment and the frequency of the fan 19. In FIG. 3, the horizontal axis represents the cooling water inlet temperature (° C.) (hereinafter referred to as CTI as appropriate) detected by the cooling water temperature sensor 51, and the vertical axis represents the ratio when the frequency rating of the fan 19 is 100%. ing. FIG. 3 is a diagram showing the content of so-called proportional control (P control) in which the frequency of the fan 19 is controlled in proportion to the deviation between the target temperature of the cooling water and the detected temperature.

  As shown in FIG. 3, when the CTI is lower than 24 ° C., the fan 19 is turned off. When the CTI rises from less than 24 ° C. to 25 ° C., the fan 19 is activated and driven at a frequency of 50%, and when the CTI is between 25 ° C. and 26 ° C., it is uniformly driven at a frequency of 50%.

  On the other hand, when the CTI is 26 ° C. or higher, the heat input to the regenerator 60 (combustion amount of the regenerator 60, input) correlated with the load of the absorption chiller / heater is 100% and 25%, respectively. The correspondence relationship between the detected temperature of the cooling water and the frequency of the fan 19 is different. That is, by changing the value of the proportional gain (K) of the control in the above equation 1 according to the heat input to the regenerator 60, the detected temperature of the cooling water and the frequency of the fan 19 are changed as shown in FIG. Correspondence is changed.

  More specifically, the proportional gain is decreased as the amount of heat input to the regenerator 60 is decreased, and is increased as the amount of heat input is increased. Since this proportional gain is applied to both the component term and Mo as shown in Equation 1, for example, when the heat input to the regenerator 60 is 100%, the heat input is small. As a result, the frequency of the fan 19 with respect to the detected temperature of the cooling water decreases as a whole, and the inclination becomes gentle.

  3 representatively shows the case where the heat input to the regenerator 60 is 100% and 25%. In addition, the correspondence between the detected temperature of the cooling water corresponding to the heat input and the frequency of the fan 19 is shown. The relationship is determined as appropriate.

  Thus, according to the present embodiment, when the load of the absorption chiller / heater varies, the correspondence between the detected temperature of the cooling water and the frequency of the fan 19 is corrected to an appropriate one following the variation. can do.

  That is, when the load of the heat source device fluctuates and becomes smaller, it is preferable to drive the fan 19 at a lower frequency than in the case of a high load to lower the cooling capacity of the cooling water. According to the present embodiment, it is possible to save energy by suppressing driving of the fan 19 at a high frequency corresponding to a load larger than the actual load, and it is possible to suppress cooling water overcooling to reduce the cooling water temperature. Can be appropriately controlled to the target temperature.

  On the other hand, if the detected load increases, the cooling water can be appropriately cooled by increasing the cooling capacity by largely correcting the frequency of the fan set corresponding to the detected temperature of the cooling water. Further, by correcting the output value using the proportional gain, the behavior of the cooling water is improved because of a predictive movement against the disturbance.

  In this embodiment, PID control is used as basic control. However, the present invention is not limited to this. For example, P control or PI control can be used as basic control. Further, without using such a control function, for example, a plurality of tables in which the frequency of the fan 19 corresponding to the detected temperature of the cooling water is set are provided for each amount of heat input to the regenerator 60, and the regenerator 60 is provided. The frequency of the fan 19 according to the heat input amount and the CTI may be selected from a plurality of tables.

  In the present embodiment, in addition to the control of the first embodiment, control for appropriately changing the target temperature (Mp) based on CTI is performed to save energy. A description of the same parts as in the first embodiment will be omitted.

  When the CTI is continuously higher than the high temperature threshold temperature (30 ° C.) for a predetermined time or longer, the control device 53 increases the target temperature (Mp: 28 ° C.) by 1 ° C. to 29 ° C., for example.

  This makes the target temperature (Mp) variable according to the load of the absorption chiller / heater. That is, the fact that the cooling water temperature is higher than the high temperature threshold temperature continuously for a certain time or more indicates that the load of the absorption chiller / heater is high and the deviation of the detected temperature from the target temperature of the cooling water is large. It is not preferable from the viewpoint of energy saving to continue driving the fan 19 at the set upper limit frequency. Therefore, in this case, by increasing the target temperature and bringing the target temperature closer to the current cooling water temperature, the deviation between the target temperature of the cooling water and the detected temperature is reduced, thereby reducing the fan frequency. Energy saving can be achieved.

  On the other hand, when the CTI is continuously lower than the low temperature threshold temperature (26 ° C.) for a preset time, the control device 53 decreases the target temperature by 1 ° C. from 28 ° C. to 27 ° C.

  In this case, the load of the absorption chiller / heater is small, and the deviation of the detected temperature with respect to the target temperature of the cooling water is large. Therefore, as described above, by reducing the target temperature and reducing the deviation, the cooling water is stabilized by reducing the frequency of the fan 19 and avoiding the start and stop of the fan 19 as much as possible. Can be planned.

It is a figure showing the whole heat source machine system composition of this embodiment. It is a block diagram which shows the detailed structure of a control apparatus. It is a figure which shows the correspondence of the detected temperature of the cooling water of the control apparatus in the heat-source equipment system of this embodiment, and a cooling tower, and the frequency of a fan.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cooling tower 11 Casing 12 Air inlet 14 Filling material 15 Sprinkling nozzle 16 Opening 18 Fan motor 19 Fan 20 Heat source machine 30 Cooling water piping 31 Outward pipe 32 Return pipe 50 Operation control apparatus 51 Cooling water temperature sensor 53 Control apparatus 55 Inverter apparatus 60 Regenerator 65 Gas Flow Sensor 100 Heat Source System

Claims (6)

A cooling tower, a pipe for guiding the high-temperature cooling water returned from the heat load of the heat source unit to the cooling tower, and a pipe for leading the cooling water cooled by the cooling tower to the heat load of the heat source unit. Used in the heat source system
The high-temperature cooling water returned from the heat load of the heat source device is dispersed in the air, and the cooling water is cooled by the latent heat of vaporization caused by the air flow accompanying the rotation of the fan, and is circulated again to the heat load of the heat source device. And a control means for detecting the temperature of the cooled cooling water and controlling the frequency of the fan based on a correspondence relationship between a preset detection temperature of the cooling water and the frequency of the fan. In the cooling tower
The heat source machine is an absorption chiller / heater,
The control means detects, as the cooling load of the heat source device, the temperature of the fluid returned from the cooling load of the absorption chiller / heater, or the amount of heat input to the regenerator of the absorption chiller / heater, and the cooling load Detecting the cooling load of the heat source unit based on the temperature of the fluid returned from or the amount of heat input, correcting the correspondence between the detected temperature of the cooling water and the frequency of the fan according to the detected load, As the detected load decreases, at least a part of the fan frequency set corresponding to the detected temperature of the cooling water is corrected to be smaller.   The control means corrects the correspondence between the detected temperature of the cooling water and the frequency of the fan according to the detected load, and sets the detected temperature of the cooling water and a preset target temperature of the cooling water. The frequency of the fan is controlled in proportion to the deviation, and at least a part of the fan frequency set corresponding to the detected temperature of the cooling water is corrected to be smaller as the detected load becomes smaller, When the detected temperature of the cooling water continues for a preset time or longer and the frequency of the fan is higher than a high temperature threshold temperature that becomes a set upper limit frequency as the detected temperature of the cooling water increases, the target temperature is increased. The cooling tower according to claim 1, wherein:   The control means corrects the correspondence between the detected temperature of the cooling water and the frequency of the fan according to the detected load, and sets the detected temperature of the cooling water and a preset target temperature of the cooling water. The frequency of the fan is controlled in proportion to the deviation, and at least a part of the fan frequency set corresponding to the detected temperature of the cooling water is corrected to be smaller as the detected load becomes smaller, The detected temperature of the cooling water continues for a preset time or more, and the detected temperature of the cooling water decreases and the frequency of the fan is lower than a low temperature threshold temperature that becomes a set lower limit frequency except when the fan is stopped. The cooling tower according to claim 1, wherein the target temperature is lowered. The control means corrects the correspondence between the detected temperature of the cooling water and the frequency of the fan according to the detected load, and sets the detected temperature of the cooling water and a preset target temperature of the cooling water. The frequency of the fan is controlled in proportion to the deviation, and at least a part of the fan frequency set corresponding to the detected temperature of the cooling water is corrected to be smaller as the detected load becomes smaller,
The control means controls the frequency of the fan in proportion to a deviation between a detected temperature of the cooled cooling water and the target temperature, an integral component of the deviation, and a differential component of the deviation. The cooling tower according to claim 1. The control means controls the frequency of the fan in proportion to a deviation between the detected temperature of the cooling water and a preset target temperature of the cooling water,
The cooling tower according to any one of claims 1 to 4, wherein a proportional gain of the control is changed according to the detected load.   6. The cooling tower according to claim 5, wherein the control means decreases the proportional gain as the detected load decreases.

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