JP2510534B2 - Control equipment for refrigeration equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a control device for refrigeration equipment used for air conditioning,
In particular, the present invention relates to a refrigeration facility control device that can be controlled appropriately even when the load is low and that can simplify the control device.

(Prior Art) FIG. 5 shows a schematic system diagram of a refrigeration facility and a control device therefor, which are conventionally used for air conditioning and the like.

In FIG. 5, the refrigerant gas in the evaporator 1 is sucked into and pressurized by the centrifugal compressor 2, becomes high-pressure and high-temperature gas, is cooled in the condenser 3 and is liquefied, and this liquid passes through the float valve 4. The low-pressure refrigerant gas is ejected to the low-pressure evaporator 1 and heat is taken from the surroundings (cold water) to be evaporated, and the evaporated low-pressure refrigerant gas is sucked into the centrifugal compressor 2 again, thus constituting the refrigeration equipment.

The centrifugal compressor 2 compresses the refrigerant gas by the rotation of the impeller and is generally driven by the squirrel cage induction motor 5.

Generally, in order to rotate the centrifugal compressor 2 at a high speed of about 10,000 rpm, the electric motor 5 is operated at about 3000 rpm and is connected to the centrifugal compressor 2 by a speed increasing gear 26.

The basic refrigeration cycle is shown in FIG. 6 using the Mollier diagram. Point A is a state where it leaves the evaporator 1 and enters the centrifugal compressor 2,
It is on the saturated vapor line. If this refrigerant gas is adiabatically compressed, it changes as A → B. When the compressed refrigerant is cooled in the condenser 3, the pressure remains unchanged, only the enthalpy decreases, and when all the refrigerant becomes liquid, the point C on the saturated liquid line is reached. When this refrigerant liquid is adiabatically expanded through the throttle of the float valve 4, the refrigerant state shifts from C to D. After that, it enters the evaporator 1 and takes heat from the surroundings to increase the enthalpy, and when it completely increases, it reaches the point A. The amount of heat used for freezing in this cycle is the difference in enthalpy between points A and D. The refrigeration capacity is represented by the product of this enthalpy difference and the refrigerant circulation amount.

In actual operation, (1) refrigeration capacity control for adjusting the refrigeration capacity according to heat load, (2) current control for preventing overload of the motor (3) start-up for limiting start-up current at start-up It is operated and controlled by a device. These controls will be described below.

(1) Refrigeration capacity control As shown in FIG. 5, cold water exiting the refrigeration equipment is supplied to the cooler 6 of the air conditioner at a substantially constant temperature (for example, 7 ° C.),
The heat load raises the temperature and returns to the refrigeration equipment. But,
The heat load on the cooler 6 of the air conditioner changes depending on the weather, equipment usage conditions, etc., and the chilled water temperature returning to the refrigeration equipment is not always constant.

That is, in the rated operation, the cold water (eg, 7 ° C.) exiting the refrigerating equipment rises in temperature (eg, 5 ^deg ) due to the heat load of the cooler 6 of the air conditioner, and ^reaches a high temperature (in this case, 12 ° C.).
℃) and return to the freezer. In the refrigeration equipment, the cold water is cooled again (5 ^{deg in} this case) to ^reach the outlet water temperature. The refrigerant is
It circulates in an amount suitable for cooling cold water.

If the heat load on the cooler 6 of the air conditioner decreases and the temperature rise of the cold water becomes small (for example, 3 ^deg ), the cold water returns to the refrigeration facility at a temperature lower than the rated time (10 ° C. in this case).
Here, if the refrigerant circulation amount in the refrigerating equipment is the same as that at the time of rating, the cold water outlet temperature becomes lower than the initial value (7 ° C. in this case), which is not preferable.

Therefore, in order to keep the cooling outlet temperature constant, the temperature of the cold water is measured by the temperature measuring device 7, and the controller 25 operates the suction vane 21 and the bypass valve 24 to reduce the refrigerant circulation amount to reduce the refrigerator capacity. It is supposed to be controlled.

The suction vane control and the bypass valve control will be described in detail below.

i) Suction vane control In suction vane control, a rectifying blade (vane) is provided at the suction port of the centrifugal compressor, and the angle (opening) of the vane is changed to change the characteristics of the centrifugal compressor and control the refrigerant circulation amount. To do.

Suction vane control is used from rated capacity to most of the partial capacity. However, if the suction vane control is closed below a certain opening degree, surging will occur and operation will be impossible, so the control range is limited.

The relationship between the refrigerant capacity and pressure of the centrifugal compressor is shown in FIG. The pressure of the extension H is a pressure corresponding to the pressure difference between the condenser 3 and the evaporator 1, and the curve T is a pressure loss (device resistance curve) generated when the refrigerant circulates in the refrigerator. Curve A is a compressor characteristic curve at the rated capacity, and intersects with the device resistance curve T on the line of the rated refrigeration capacity.

The state in which the refrigerating capacity is controlled and the suction vane 21 is closed is the curve B, the intersection with the device resistance curve T has moved to the left, and the refrigerating capacity has decreased from the rated value.

When the suction vane 21 is further closed, the compressor characteristic curve becomes
It enters the surging area and becomes inoperable on curve C.

The control range of suction vane control is just before entering the surging area.

ii) Bypass valve control Bypass valve control is used to control the refrigeration capacity within the control range of the suction vane control.

In order to reduce the capacity of the refrigeration equipment, the circulation amount of the refrigerant must be further reduced. However, if the total circulation amount is further reduced by the suction vane 21, it enters the surging region described above, so that the amount of refrigerant in the centrifugal compressor 2 is kept at a low amount that does not enter the surging region, and the evaporation action in the evaporator 1 is reduced. Bypass valve control is designed to reduce the refrigeration capacity to be used.

That is, by bypassing a part of the high-pressure refrigerant gas of the condenser 3 to the evaporator 1 by the bypass valve 24, the condenser 3
The amount of the refrigerant condensed by is reduced and the amount of the refrigerant ejected to the evaporator 1 is reduced.

The capacity of the refrigeration equipment can be controlled by adjusting the amount of refrigerant to be bypassed.

Most refrigeration equipment has a capacity of 100% to about 5% by combining suction vane control and bypass control.
It is possible to control in the range of.

If the heat load is further reduced and the capacity of the refrigeration equipment must be reduced to less than about 5%, the refrigeration capacity cannot be controlled even by the combination of the suction vane control and the bypass valve control, and the chilled water outlet temperature becomes Gradually lowers. If the chilled water temperature is lowered as it is, the chilled water freezes, which causes a serious inconvenience to the refrigerator. Therefore, when the chilled water outlet temperature falls below a certain level (for example, 6 ° C), the operation of the compressor is stopped. After stopping and the chilled water temperature becomes high again (for example, 12 ° C), the ON-OFF control operation is performed to restart.

 Next, the current control will be described.

(2) Current control Refrigeration capacity control is performed by vane control and bypass control so as to maintain the chilled water outlet temperature at the set value as described above.

Here, when the chilled water temperature is higher than the set value, such as at the beginning of operation of the refrigeration equipment, as the refrigeration capacity control,
In order to quickly bring the cold water temperature close to the set value, the suction bay 21 is opened further than the opening at the rated capacity to increase the refrigeration capacity. The specific weight of the refrigerant is larger than that in normal operation.

As a result, the centrifugal compressor 2 may have an unrated performance, and the induction motor 5 may overwhelm. Therefore, a current measuring device 11 is provided on the feeder line of the induction motor 5, the current value is measured and input to the controller 25, and when the current value exceeds the rated value so as not to cause overload, the refrigeration capacity control is performed. The suction vane 21 and the bypass valve 24 are preferentially operated to control to reduce the current value. After that, if the current value falls below the rated value, the refrigeration capacity control is performed again.

 Next, the starting device will be described.

(3) Starter As the induction motor 5, an induction motor having a capacity of more than 75 kW is used according to the refrigerating equipment capacity. Since the starting current of the squirrel-cage induction motor 5 is large in the full-voltage starting, the starting device 22 and the operating switch 23 such as star-delta starting and reactor starting are used in facilities where the amount of power receiving equipment is limited.

(Problems to be Solved by the Invention) A conventional control device for refrigeration equipment controls the suction vane 21 and the bypass valve 24, and requires the suction vane 21 and the bypass valve 24. There is a problem.

In other words, the suction vane 21 has a precise and complicated structure and there is a risk of failure, and the suction vane 21 and the bypass valve 24
The operating mechanism of (1) penetrates the pressure boundary and thus requires a special airtight device. In addition, confidential devices require regular inspection and replacement of parts.

In addition, since the conventional control is performed by combining the vane control and the bypass control, a dedicated controller is required, the control method is complicated, and the setting and adjustment also requires skill. Also, ON
Frequent OFF control operation is not preferable because a large current flows at the time of starting the motor, which causes problems such as removal of heat generation at startup, fatigue due to a large load applied to each part of the motor, and fatigue of the switch. Therefore, generally start up
It is controlled not to exceed once every 20 minutes to 1 hour (continuous restart prevention control).

As a result, when the heat load is about 5% or less, the cold water temperature becomes low, the cold water temperature becomes high again after the compressor stops, and even if the restart temperature is reached, continuous restart prevention is prevented. It is conceivable that the control cannot be activated and the temperature of the chilled water further rises, causing an inconvenience on the air conditioner side. Further, it is desirable that the power consumption be proportional to the refrigerating equipment capacity, but since the bypass valve control is performed in the low heat load region, the work of the centrifugal compressor 2 does not change, and the efficiency tends to deteriorate.

Further, the conventional control equipment for refrigeration equipment requires the starter 22 when the capacity of the power receiving equipment is limited, and not only the equipment cost and installation space of this starter but also the need for maintenance and inspection have arisen.

In order to solve such a problem, it has been proposed to control the refrigeration capacity by adjusting the rotation speed of the centrifugal compressor 2.

FIG. 8 is a special drawing showing the relationship between the refrigerating capacity and the pressure of the centrifugal compressor 2 when the rotational speed of the centrifugal compressor 2 is controlled. The pressure at the point H is that of the condenser 3 and the evaporator 1. The pressure corresponds to the pressure difference, and the curve T is the pressure loss (device resistance curve) generated when the refrigerant circulates in the refrigerator. Curve A is a compressor characteristic curve at the rated capacity, and intersects with the device resistance curve T on the line of the rated refrigeration capacity. The state in which the refrigeration capacity is controlled and the rotational speed of the centrifugal compressor 2 is reduced is the curve B,
The intersection with the device resistance curve T has moved to the left, and the refrigeration capacity has decreased from the rated value.

By controlling the rotation speed of the centrifugal compressor 2 in this way, the refrigerating capacity of the refrigerating equipment can be controlled.

However, the characteristics of the centrifugal compressor 2 are that the refrigeration capacity is proportional to the number of revolutions and the pressure is 2
It has the property of being reduced in proportion to the power.

Therefore, if the rotation speed of the compressor is further reduced in order to further reduce the refrigeration capacity, a curve C is obtained, and the condenser 3
It becomes impossible to circulate the refrigerant while maintaining the pressure difference (pressure above the point H) between the evaporator and the evaporator 1.

Therefore, it is not possible to control the refrigeration capacity over a wide range, especially when the load is low, simply by adjusting the rotation speed.

Further, since the ON-OFF control operation has the above-mentioned problems, it is not suitable to be widely used as a control method.

The present invention has been made in consideration of the above points, and an object thereof is to provide a control device for a refrigeration facility that can be appropriately controlled even under a low load and can simplify the control device. And

[Structure of Invention]

(Means for Solving Problems) The present invention includes a rotation speed controller that generates a rotation speed signal according to a heat load, and controls a rotation speed of a centrifugal compressor to control a refrigerating capacity of a refrigeration facility. When the control device is a low heat load that cannot control the continuous rotation speed of the centrifugal compressor, the control method is switched from continuous rotation speed control that follows the process amount (heat load amount in this case) to pulsation rotation control, The rotation speed controller alternately generates a high rotation speed signal that causes a pressure equal to or higher than the pressure difference between the condenser and the evaporator, and a low rotation speed signal that causes a pressure equal to or lower than the pressure difference, and performs centrifugal compression. It is characterized by controlling the rotation speed of the machine.

(Operation) Continuously operate the electric motor during refrigerator operation, and during high heat load, control the continuous rotation of the centrifugal compressor according to the rotation speed according to the load, and rotate at low heat load where continuous rotation control of the centrifugal compressor is not possible. The rotation speed of the centrifugal compressor is generated by the number controller alternately generating a high rotation speed signal that produces a pressure greater than the pressure difference between the condenser and the evaporator and a low rotation speed signal that produces a pressure less than this pressure difference. By controlling the number, the refrigerating capacity can be appropriately controlled in this way, and theoretically, continuous capacity control of 0 to 100% becomes possible.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 are views showing an embodiment of a control device for refrigeration equipment according to the present invention. In FIG. 1, the evaporator 1
The refrigerant gas inside is sucked into the centrifugal compressor, pressurized, becomes a high pressure and high temperature, is cooled in the condenser 3 and is liquefied, and this liquid is jetted to the low pressure evaporator 1 through the float valve 4 and the surrounding (cold water )
The heat is taken away from the refrigerant to evaporate, and the evaporated low-pressure refrigerant gas is sucked into the centrifugal compressor 2 again, and the refrigeration equipment is configured in this way. The centrifugal compressor 2 compresses the refrigerant by rotating the impeller, and is driven by the squirrel cage induction motor 5. Further, a check valve 15 is provided on the discharge side of the centrifugal compressor 2.

A switch 14 and a power adjustment device 10 are sequentially connected between the power source and the squirrel cage induction motor 5, and an operation switch 13 is connected to the switch 14.

Further, a rotation speed controller 9 is connected to the power adjustment device 10, and the rotation speed controller 9 receives a measurement signal from a temperature measurement device 7 attached to the chilled water outlet of the refrigeration equipment. Are connected. In this way, the rotation speed controller 9
Is configured to generate a rotation speed signal according to the heat load measured by the temperature measuring device 7 and transmit the rotation speed signal to the power adjusting device 10. Further, the rotation speed controller 9 is connected to a current controller 12 to which the current value signal of the squirrel cage induction motor 5 from the current measuring device 11 is input.

The rotation speed controller 9 comprises two main functions, a rotation speed control function 29 and a time control function 30, and a continuous rotation / pulsation rotation switching function 28 for switching these.

(1) Rotation speed control function When the continuous rotation speed control of the centrifugal compressor can be performed under the condition that the high heat load is continuously stable, the rotation speed is adjusted so that the motor continuously operates at the rotation speed according to the load. Send a signal.

(2) Time control function When the continuous rotation speed control of the centrifugal compressor cannot be performed under the condition that the low heat load is continuously stable, the electric motor generates a pressure higher than the pressure difference between the condenser 3 and the evaporator 1. Depending on the load, the high rotation speed (r ₁ ) and the low rotation speed (r ₂ ) that produces a pressure less than this pressure difference may be switched alternately. ₁ ) Adjust the signal transmission time and the low rotation speed (r ₂ ) signal transmission time to transmit alternately. That is, the adjustment is performed in a unit of time (cycle time), and the total of the time of operating at a high rotational speed (r ₁ ) and the time of operating at a low rotational speed (r ₂ ) within a unit time is constant and the load is The operating time of high rpm (r ₁ ) and low rpm (r ₂ ) is adjusted accordingly. For example, if the unit time is 10 seconds and the operation at high rotation speed (r ₁ ) is 8 seconds and the operation at low rotation speed (r ₂ ) is 2 seconds, the average refrigeration capacity is high rotation speed (r ₁ )
It can be reduced to 4/5 of the refrigeration capacity during continuous operation.

In this way, the average refrigeration capacity can be reduced by reducing the operating time at high rotational speed (r ₁ ) (increasing the operating time at low rotational speed (r ₂ )). Here, the high rotation speed (r ₁ ) and the low rotation speed (r ₂ ) are not adjusted by the change of the process amount (heat load), but the condensation pressure, the evaporation pressure, the special centrifugal compressor, etc. It is predetermined by mechanical factors.

Next, the operation of this embodiment having such a configuration will be described.

When starting the electric motor, by operating the operation switch 13,
The switch 14 is closed to supply electricity to the electric power adjusting device 10, and the electric power adjusting device 10 supplies electric power to the electric motor 5 while limiting the current value. Until the electric motor 5 reaches a predetermined rotation speed,
The signal from the rotation speed controller 9 is bypassed.

During operation of the centrifugal compressor 2, the temperature measuring device 7 measures the chilled water outlet temperature and sends a signal to the temperature controller 8 so as to keep the chiller outlet chilled water temperature constant even if the heat load changes. The temperature controller 8 compares the input signal with the set value, and sends an adjustment signal corresponding to the deviation to the rotation speed controller 9. The rotation speed controller 9 converts into a control signal for operating the centrifugal compressor 2 at a rotation speed that provides a refrigeration capacity commensurate with the adjustment signal, and a power adjustment device.
Control 10 The power adjusting device 10 adjusts the voltage and frequency of the supplied power and supplies the voltage to the induction motor 5,
Is operated at a predetermined rotation speed.

 This rotation speed control will be described with reference to FIGS.

(1) At rated capacity When there is a rated heat load, the temperature controller 8 receives a signal from the temperature measuring device 7, and the refrigerating capacity is rated (100%) (A
100% signal is sent to the rotation speed controller 9 so as to be (point).

Since the rotation speed controller 9 receives the 100% signal, the rotation speed controller 9 controls the power adjusting device 10 so as to continuously operate the electric motor at a rotation speed r _A (for example, 2800 rpm) commensurate with the rated capacity.

(2) High heat load (continuous rotation control) (for example, capacity 90
%) If the heat load is reduced to 90% of the rated value, the temperature controller 8 receives a signal from the temperature measuring device 7 and the refrigerating capacity is reduced.
A 90% signal is sent to the rotation speed controller 9 so that it becomes 90% (point B). Since the rotation speed controller 9 receives a 90% signal, the rotation speed r _B (for example, 2650 rpm) corresponding to the refrigeration capacity of the motor is 90%.
Controls the electric power adjustment device 10 so as to operate in continuous rotation. This control method is performed up to point C (for example, refrigeration capacity 80%), and the rotation speed at that time is r ₁ (for example, 2500 rpm).

r ₁ is the minimum number of rotations that produces a pressure equal to or higher than the pressure difference between the condenser 3 and the evaporator 1.

(3) Low heat load (pulsation rotation control) (for example, capacity 40
%) If the heat load is further reduced to 40% of the rating,
The temperature controller 8 receives the signal from the temperature measuring device 7 and sends a 40% signal to the rotation speed controller 9 so that the refrigerating capacity becomes 40% (point D).

Since the rotation speed controller 9 receives a 40% signal, if the rotation speed is lowered (for example, 1800 rpm) so that the motor operates at a rotation speed commensurate with the refrigeration capacity of 40%, the rotation speed will be the same when a high heat load is applied. Then, the minimum rotation speed r ₁ (in this case 2500 rp) that produces a pressure equal to or higher than the pressure difference between the condenser 3 and the evaporator 1.
m) lower, making it impossible to circulate the refrigerant,
The freezing capacity becomes zero. Therefore, the rotation speed controller 9
Then, switch from continuous rotation control to pulsation rotation control
Number of revolutions r ₁ that produces a pressure greater than the pressure difference between the
And a rotational speed r ₂ (for example, 2000rp
m) and are switched alternately, depending on the input signal, r ₁ ,
r ₂ Adjust each operation time.

That is, when a signal of a refrigeration capacity of 40% is received, the operation is performed so that the operation time at r ₁ and the operation time at r ₂ are substantially the same as shown in FIG.

If the heat load is further reduced to, for example, 25% of the rating (point E), the refrigerating capacity is smaller than the point D, so the operating time of r ₁ is shorter than that of r ₂ as shown in Fig. 4. Drive less.

In this way, the rotation speed controller 9 receives a linear signal from the temperature controller 8 and controls the rotation speed within a range where continuous rotation control can be performed, and r ₁ within a range where continuous rotation control cannot be performed. operating time, it is possible to control the refrigeration capacity is almost 100% to 0% by controlling the driving time in the r _2.

The number of rotations of the electric motor with respect to the refrigerating capacity, the operating time in alternate operation, etc. will be determined when designing the individual refrigerators.

The determination of the number of rotations for switching between continuous rotation control and pulsation rotation control depends on the design, and a differential pressure measuring device 27 for measuring the pressure difference between the suction and discharge of the centrifugal compressor 2 is provided and the signal is rotated. It is also possible to input it to the number controller 9 and compare it with a preset value.

That is, when the heat load decreases, the refrigerating capacity is reduced, and therefore the rotation speed controller 9 controls to reduce the rotation speed of the electric motor. As a result, the pressure difference between suction and discharge generated in the centrifugal compressor is also reduced. Therefore, the continuous rotation control is switched to the pulsation rotation control immediately before the pressure difference is about to become smaller than the pressure difference between the condenser 3 and the evaporator 1. Further, it can be seen that when the differential pressure of r ₂ becomes smaller than the differential pressure between the condenser 3 and the evaporator 1, it is unnecessary to further reduce the rotational speed.

When the rotational speed reaches r ₂ during the operation with the pulsating rotation control, the pressure generated in the centrifugal compressor 2 becomes a pressure equal to or lower than the pressure difference between the condenser 3 and the evaporator 1, and therefore at the rotational speed r ₁ . Pressurized and conveyed refrigerant flows backward from the condenser to the evaporator, contrary to the usual
It is possible that a normal refrigeration cycle cannot be constructed.

A backflow prevention valve 15 is provided on the discharge side of the centrifugal compressor to prevent the backflow of the refrigerant.

When the chilled water temperature is higher than the set value at the beginning of operation of the refrigeration equipment, the control based on the chilled water temperature requires that the chilled water temperature be faster than the rated capacity in order to bring the chilled water temperature closer to the set temperature. Acts to enhance.
Further, the specific weight of the refrigerant is larger than that during normal operation. As a result, the centrifugal compressor 2 may work above the rated value and the electric motor 5 may be overloaded. In this case, in order to prevent overload, the current value to the induction motor 5 is measured by the current measuring device 11 and a signal is sent to the current controller 12. The current controller 12 compares the input signal with the set value and sends an adjustment signal corresponding to the deviation to the rotation speed controller 9. In the rotation speed controller 9, the signal from the current controller 12 is prioritized over the signal from the temperature controller 8 to control the power regulator 10.

That is, the current measuring device 11 and the current regulator 12 constantly measure the input current to the motor, and the current value is 100% of the rated current value.
When it exceeds, the rotation speed controller 9 should reduce the current value.
An instruction signal is issued to reduce the number of revolutions controlled by the signal from the temperature controller 8.

The rotation speed controller 9 stops the control by the signal from the temperature controller 8 and gradually lowers the rotation speed.
Control 10

If the number of revolutions of the electric motor is lower than the rated current value (for example, 95%), the current regulator 12 stops the instruction signal. The rotation speed controller 9 again controls the rotation speed according to the signal from the temperature controller 8.

As described above, according to this embodiment, when the electric motor is started, the electric power adjusting device 10 can rotate the electric motor 5 while limiting the current value, and it is not necessary to provide a special starting device. Further, during operation of the electric motor, when the load on the centrifugal compressor 2 cannot be controlled continuously, the rotation of the centrifugal compressor 2 is controlled by pulsating rotation that alternately switches the rotational speed r ₁ and the rotational speed r _2. Therefore, the suction vane 21 and the bypass valve 24 having a complicated structure are unnecessary. Further, the current value signal measured by the current measuring device 11 is sent to the current regulator 12, and the current regulator 12 prevents the induction motor 5 from overloading.

〔The invention's effect〕

As described above, according to the present invention, at the time of low heat load where the continuous rotation control of the centrifugal compressor cannot be performed, the rotation speed controller generates a high rotation speed that produces a pressure equal to or higher than the pressure difference between the condenser and the evaporator. The signal and a low speed signal that produces a pressure less than this pressure difference are alternately generated to control the speed of the centrifugal compressor and thus to control the refrigeration capacity appropriately. Therefore, since a bypass valve and a suction vane having a complicated structure are not required, the control device is simplified and the capacity control of 0 to 100% is possible.

[Brief description of drawings]

1 to 4 are views showing an embodiment of a control device for refrigerating equipment according to the present invention. FIG. 1 is a schematic system diagram thereof, and FIG. 2 shows refrigerating capacity and rotational speed of a centrifugal compressor. FIG. 3 is a diagram showing the relationship, FIG. 3 and FIG. 4 are diagrams showing the relationship between the elapsed time and the rotational speed of the centrifugal compressor when the centrifugal compressor is operated in pulsating rotation, and FIG. Schematic diagram of
FIG. 6 is a diagram showing a basic refrigeration cycle using a Mollier diagram, FIG. 7 is a diagram showing a relationship between refrigeration capacity and pressure of a centrifugal compressor when suction vane control is performed, and FIG. 8 is a rotation speed control. It is a figure which shows the relationship between the refrigerating capacity and pressure of a centrifugal compressor in the case of performing. 1 ... Evaporator, 2 ... Centrifugal compressor, 3 ... Condenser, 4 ...
... Float valve, 5 ... Induction motor, 6 ... Cooler, 7 ...
… Temperature measuring instrument, 8 …… Temperature controller, 9 …… Rotation speed controller, 10 …… Power regulator, 11 …… Power meter, 12 …… Current regulator, 13 …… Operation switch, 14 …… Switch, 15 ……
Check valve.

Claims (1)

(57) [Claims] 1. A controller for refrigeration equipment, comprising a rotation speed controller for generating a rotation speed signal according to a heat load, for controlling the rotation speed of a centrifugal compressor to control a refrigerating capacity. At a low heat load that cannot control the rotation speed, the rotation speed controller generates a high rotation speed signal that generates a pressure equal to or higher than the pressure difference between the condenser and the evaporator, and a low rotation speed signal that generates a pressure that is equal to or lower than the pressure difference. To control the number of revolutions of the centrifugal compressor.