JP2517071B2 - Cooling device and its control method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling device for cooling all year round and a control method therefor, and more particularly to a control method for low outside air temperature.

(Prior Art) The configuration of a basic cooling device is shown in FIG. The refrigeration cycle mainly includes a compressor 1, a condenser 2, a variable opening degree expansion valve 3,
It is composed of four elements of the evaporator 4. In an air-cooled air conditioner, an evaporator is installed indoors and a condenser is installed outdoors.
A low-boiling-point medium called a refrigerant is enclosed in the refrigeration cycle, and the refrigerant circulates between the components, whereby heat inside the room can be released to the outside.

Next, the operation of this refrigeration cycle will be described. First, in the evaporator 4, the low-pressure refrigerant liquid takes heat in the room to evaporate and become gas. The refrigerant gas vaporized in the evaporator is sent to the compressor 1, is compressed into high temperature and high pressure gas, and is sent to the condenser 2. On the contrary to the evaporator, the condenser releases heat to the outside air and becomes a high-pressure liquid. This high-pressure liquid is sent to the variable opening expansion valve 3, expands and becomes a low-temperature low-pressure liquid, which is sent to the evaporator, and this cycle is repeated thereafter. That is, by the action of the compressor, the heat inside the room can be released outside by compressing the gas refrigerant whose saturation temperature is lower than room temperature into the gas whose saturation temperature is higher than the outside air.

However, when the cooling device shown in FIG. 6 is operated in the same way as when the outside air temperature is high as it is when the outside air temperature is high, the heat exchange performance in the condenser is improved and the condensation pressure, which is the refrigerant pressure in the condenser, is increased. Get lower. When the condensing pressure becomes low, the evaporation pressure, which is the refrigerant pressure in the evaporator, also decreases accordingly, so that there are problems that the evaporator is frosted or is in an over-dehumidifying operation state. Also, if the compression work in the compressor is reduced so that the evaporation pressure does not decrease even if the condensation pressure becomes low, this time, the flow rate of the refrigerant circulating in the refrigeration cycle will decrease, and the cooling capacity will decrease. Alternatively, there is a problem that the degree of superheat becomes high.

In order to solve this, conventionally, as shown in FIG. 7, a bypass path 236 is provided in the path from the compressor to the expansion valve, and the condensing pressure control valve is provided at the confluence of the path passing through the bypass path and the condenser. There was a 226. This condensing pressure control valve is a three-way valve that encloses a gas with a constant pressure inside.When the condensing pressure decreases, the opening degree of the bypass side path is automatically increased so that the condensing pressure changes to the ambient temperature. By raising the pressure to the same level as when it was high, the evaporation pressure was kept from falling and the cooling capacity was kept from falling.

However, this method misses the opportunity to operate the cooling device with less compression power because the pressure difference between the condensation pressure and the evaporation pressure is small when the outside air temperature is low, and the condensation pressure is increased to reduce the pressure difference from the evaporation pressure. It is operated at a higher pressure and a higher compression power, which is not an economical method of operation.

Further, when the problem in operating the cooling device shown in FIG. 6 when the outside air temperature is low is solved from the viewpoint of securing the refrigerant circulation amount, the opening degree of all the opening degrees of the variable opening degree expansion valve 3 is changed. There is a way to make it bigger. As a method of increasing the opening degree of the expansion valves, a method of arranging a plurality of expansion valves in parallel or an expansion valve having a larger capacity than a predetermined capacity is attached (for example, cooling capacity 5
There is a method to attach an expansion valve for cooling capacity of 10 [RT] to the air conditioner of [T]. Here, [RT] is a unit indicating the cooling capacity of the cooling device, and 1 [RT] = 3,320 [kcal / h]. By increasing the opening degree of the expansion valve, the state where the condensing pressure is low is maintained, and the operation with less compression power in the compressor can be performed.

However, this operating method also has a limit in the opening of the expansion valves, and the number of expansion valves is increased too much (3 or 4 are installed), or the expansion valves with too large capacity (cooling capacity 5 [RT] air conditioning) are used. If an expansion valve for 15 [RT] is attached to the machine), the superheat control cannot be performed accurately, and this method also has a limit. Therefore, when the outside temperature drops, the condensation pressure drops too much. Therefore, even if the expansion valve is fully opened, the refrigerant circulation amount decreases and the degree of superheat increases.

(Problems to be Solved by the Invention) The present invention has been made in view of the inefficiency of operating the air conditioner by increasing the compression power to the same extent as when the outside temperature is high in the prior art. It is an object of the present invention to provide an economical cooling device with a small compression power and a control method thereof.

(Means and Actions for Solving the Problems) The present invention relates to a cooling device that cools year-round, and in order to enable operation of an economical cooling device with low compression power, a compressor is removed from a compressor. A bypass is provided in the path leading to the expansion valve to set a means for controlling the ratio of the refrigerant flow rate of the path passing through the condenser and the flow rate of the bypass path, or air is blown to the condenser to make the capacity of the condenser variable. A means for varying the air volume of the outdoor blower is provided.

In operation, it is basically necessary to measure the degree of superheat of the refrigerant at the outlet of the evaporator and adjust the opening variable expansion valve accordingly. However, even when the variable opening expansion valve is fully opened, when the pressure difference between the condensation pressure and the evaporation pressure is small and the refrigerant flow rate in the refrigeration cycle is small and the superheat degree is high, the difference between the set superheat degree and the measured superheat degree is small. According to the above, the condensing pressure is adjusted by the means to control the degree of superheat.

When the condensation pressure decreases and the compression ratio, which is the ratio of the suction pressure to the discharge pressure of the compressor, becomes smaller than the minimum allowable compression ratio of the compressor, the condensation pressure is set to the minimum allowable compression ratio of the compressor. The feature is that the pressure is increased to the minimum pressure above.

It differs from the conventional technology in that the low condensing pressure is effectively used when the outside temperature is low, and economical operation with less compression power can be performed.

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

FIG. 1 shows an embodiment of the device according to the invention. This cooling device includes a compressor 21 having a rotation speed control means 30, and a condenser 22.
And an outdoor fan 27 that blows air to the condenser, an evaporator 24, an indoor fan 28 that blows air to the evaporator, and the compressor 21.
A path for guiding the refrigerant discharged from the condenser 22 via the condenser 22, and a bypass path 36 for guiding the refrigerant by bypassing the condenser 22.
And a first control valve 41 provided between the confluence point and the condenser 22 and a second control valve 42 provided in the bypass path 36 as a means for adjusting the flow rate ratio of both paths. A path for guiding the refrigerant from the point to the evaporator, a means for adjusting the flow rate ratio, and an opening degree variable expansion valve 23 provided in the middle of the evaporator 24,
In a refrigerant device configured with a path for returning the refrigerant flowing out from the evaporator to the compressor, a discharge pressure of the compressor 21, and a compression ratio sensor 34 for detecting a suction pressure ratio,
A superheat sensor 33 for detecting the superheat at the suction port of the compressor 21, the compression ratio sensor 34, and the superheat sensor.
It is composed of a control device section 35 which arithmetically processes two signals from 33 and sends a control signal to the variable opening expansion valve 23 and means for adjusting the flow rate ratio. 32 is a room temperature sensor.

In the embodiment of FIG. 1, the bypass path is taken from the inlet of the condenser 22. FIG. 2 is an example in which the bypass path is pulled in from the middle of the condenser. FIG. 3 is an example in which the bypass path portion performs heat exchange as the second condenser 55. FIG. 4 shows an example in which there are multiple bypass paths for heat exchange as a condenser, and each control path has a control valve.
The configurations shown in FIGS. 1 to 4 can be arbitrarily selected depending on the scale of the cooling device, installation conditions, and the like.

FIG. 5 shows an embodiment of a cooling device using an outdoor air blower 127 capable of controlling the air flow rate. In this embodiment, the control performed on the first control valve 41 and the second control valve 42 in the embodiment of FIG. 3 is performed on the outdoor blower 127. The outdoor blower 127 is composed of a single blower or a plurality of blowers whose operating speed is variable.

Although five examples of configurations have been shown above, any configuration may be used as long as the condensation pressure can be controlled at a low outside temperature. Further, the first control valve and the second control valve and the controllable outdoor fan may be simultaneously provided.

Next, a method for controlling the cooling device of the present invention will be described. When the outside air temperature is low, in the present operating method, the condensing pressure is allowed to reach the limit and the degree of superheat is controlled by opening the opening degree of the opening degree variable expansion valve 23 as much as possible. As a method of increasing the opening degree of the expansion valves, a method of arranging a plurality of expansion valves in parallel or an expansion valve having a larger capacity than a predetermined capacity is attached (for example, an air conditioner having a cooling capacity of 5 [RT] is expanded for a cooling capacity of 10 [RT]). There is a method to attach the valve). By increasing the opening degree of the expansion valve, the state where the condensing pressure is low is maintained, so that the operation with less compression power in the compressor can be performed. However, this operation method also has a limited expansion valve opening, and the number of expansion valves is increased too much (3 or 4 are installed), or the expansion valve with too large capacity (cooling capacity 5 [RT] air conditioning). If you use an expansion valve for 15 [RT] on the machine), this method has a limit because the superheat control cannot be performed accurately.

The compressor has the lowest compression ratio acceptable in relation to the refrigeration oil.

For example, when the outside temperature drops below 10 degrees Celsius, the following problems occur.

Even if the expansion valve is fully opened because the condensing pressure is too low, the refrigerant circulation amount decreases and the degree of superheat increases.

The compression ratio between the suction pressure and the discharge pressure becomes less than the allowable minimum compression ratio of the compressor.

To avoid this situation, there is no way to increase the condensing pressure. However, since the condensing pressure that can be set by the condensing pressure control valve used in the conventional device is constant, if this is used as it is, the condensing pressure becomes unnecessarily high and the compression power becomes large. Therefore, in the present invention, means for varying the condensing pressure is provided and control is performed as follows.

The operation method in the refrigeration cycle shown in FIG.
The operation will be described with reference to the operation flow charts of FIGS.

First, the degree of superheat is controlled. Superheat is a superheat sensor
Measured by 33 and compared to the set superheat. In the first stage, like the normal superheat control, if the measured superheat is higher than the set superheat, the expansion valve 23 is opened according to the difference, and conversely,
If the measured superheat is lower than the set superheat, the expansion valve 23 is closed according to the difference. However, in the second step, when the outside air temperature becomes lower and the condensing pressure becomes lower, the measured superheat degree is higher than the set superheat degree (Y) and the expansion valve 23 is fully opened (Y), the measurement is performed. Depending on the difference between the superheat degree and the set superheat degree, the openings of the first control valve 41 and the second control valve 42 are interlocked or independently adjusted to increase the flow rate of the refrigerant flowing on the bypass side to condense. Increase pressure to reduce superheat. On the contrary, when the measured superheat degree is lower than the set superheat degree (N) and the first control valve 41 is closed and the second control valve 42 is opened to flow the refrigerant to the bypass side to increase the condensation pressure. Is the first control valve depending on the difference between the measured superheat and the set superheat.
The condensing pressure is lowered and the degree of superheat is increased by interlocking or independently controlling the openings of 41 and the second control valve 42 to adjust the flow rate of the refrigerant flowing through the bypass side to decrease. By this method, even when the expansion valve 23 cannot control the superheat degree, the first control valve 41 and the second control valve 42 can control the superheat degree.

The above is the basic control, but if the following problems occur in the compression ratio of the compressor after this control, the following control is performed.

The compression ratio, which is the ratio between the suction pressure and the discharge pressure of the compressor 21, is detected by the compression ratio sensor 34 and compared with the stored minimum allowable compression ratio. Here, if the measured compression ratio is smaller than the minimum allowable compression ratio (Y), the opening degree of the first control valve 41 and the second control valve 42 is changed according to the difference between the measured compression ratio and the minimum allowable compression ratio. Are adjusted in conjunction with each other or independently to adjust the flow rate of the refrigerant flowing on the bypass side to increase the condensing pressure so that the compression ratio becomes equal to or higher than the allowable minimum compression ratio. However, if the measured compression ratio is more than the allowable minimum compression ratio (N) and it is too large, for example, even if the allowable minimum compression ratio is 2.0, the set condensing pressure is increased to operate at the compression ratio of 3.0. In that case, the compression power becomes large and the operation becomes uneconomical. Therefore, when the measured compression ratio is larger than the allowable minimum compression ratio, conversely according to the difference,
By adjusting so that the flow rate of the refrigerant flowing through the bypass side is reduced, the condensing pressure is lowered, and the cooling device is always operated at a compression ratio near the minimum allowable compression ratio. When the outside temperature is high,
The first control valve 41 is fully opened and the second control valve 42 is fully closed.

The control regarding the allowable minimum compression ratio is based on the fact that the present compressor can operate only at a certain compression ratio or more, and is unnecessary if this problem is solved in the compressor.

Room temperature sensors 32, 232 shown in FIGS. 1 to 5 and 7.
Compares the room temperature with the set temperature, and the difference is the controller unit 3
It is fed back to the rotation control means 30, 230 of the compressor 21, 221 via 5, 235. That is, if the room temperature is higher than the set temperature, the rotation speeds of the compressors 21 and 221 are increased, and if the room temperature is lower than the set temperature, the rotation speed is decreased. Such control is control generally performed in the cooling device.

Next, the operation method in the configuration shown in FIG. 5 will be described with reference to the operation flowcharts of FIGS. 9 (a) and 9 (b).

The control in the first stage is the same as the configuration in FIG. As the second stage, when the measured superheat is higher than the set superheat (Y) and the expansion valve 23 is fully opened (Y), the outdoor side that can be controlled according to the difference between the measured superheat and the set superheat. Blower 127
The condensing pressure is raised and the superheat degree is lowered by reducing the air volume of. On the contrary, when the measured superheat degree is lower than the set superheat degree (N) and the air volume of the controllable outdoor fan 127 is reduced (Y) to increase the condensing pressure, the measured superheat degree and the set superheat degree are Outdoor blower 12 that can be controlled according to the difference
By increasing the air volume of 7, the condensing pressure is lowered and the degree of superheat is increased. When superheat control cannot be performed by the expansion valve 23 by this method, the superheat control can be performed by adjusting the controllable air volume of the outdoor blower 127.

When the outdoor blower is composed of a plurality of blowers, a part of the operation may be intermittently performed to adjust the air volume.

The control of the compression ratio is the same as the control method in the configuration of FIG. 1, and when the measured compression ratio is smaller than the minimum allowable compression ratio (Y), it depends on the difference between the measured compression ratio and the minimum allowable compression ratio. The condensing pressure is increased by reducing the amount of air that can be controlled by the outdoor blower 127 so that the compression ratio becomes equal to or higher than the allowable minimum compression ratio. However, if the measured compression ratio is more than the allowable minimum compression ratio (N) and it is too large, for example, even if the allowable minimum compression ratio is 2.0, the set condensing pressure is increased to operate at the compression ratio of 3.0. In that case, the compression power becomes large and the operation becomes uneconomical. Therefore, when the measured compression ratio is larger than the allowable minimum compression ratio, the condensing pressure is reduced by increasing the air volume of the outdoor blower 127 that can be controlled according to the difference, and the cooling device is always used with a compression ratio near the allowable minimum compression ratio. To drive.

When the outside air temperature is high, the controllable outdoor fan 127 operates at the maximum air volume.

(Effects of the Invention) From the above description, the following effects can be obtained from the present invention.

When operating the cooling device when the outside air temperature is low, by using the condensing pressure adjusting device, even if the expansion valve is fully opened and the refrigerant circulation flow rate is low and the superheat degree is high, the refrigerant flow rate bypassing the condenser can be controlled. The superheat degree can be controlled by adjusting or by adjusting the amount of air blown to the condenser, and the condensing pressure can be suppressed to the necessary minimum pressure, which enables energy-saving operation.

FIG. 10 shows a comparison of operating efficiency (COP) between the present invention and the prior art shown in FIG. COP is defined as follows.

With the configuration and control method of the present invention, the outside air temperature is 20
There is a clear difference in efficiency below [℃], and the outside temperature is 5
Below [° C], the efficiency is about 1.9 times that of the conventional method.

FIG. 11 is a performance diagram of an air conditioner to which the control method of the present invention is applied. Indoor dry-bulb temperature is 27 [℃ DB], wet-bulb temperature is 1
9.5 [℃ WB], solid line, dash-dotted line, and dotted line are outside air temperature and CO when the compressor is operated at 78Hz, 54Hz, and 32Hz, respectively.
The relationship between P, cooling capacity and power consumption is shown. From the figure, in the control method of the present invention, when the outside air temperature is low, compared with when the outside air temperature is high, even with the same compressor operating frequency, the cooling capacity increases, and at the same time, the power consumption decreases and efficient operation can be performed. I understand.

When operating the cooling device when the outside air temperature is low, even if the ratio between the suction pressure and the discharge pressure becomes smaller than the allowable minimum compression ratio of the compressor, the refrigerant flow rate bypassing the condenser is adjusted or the condenser is bypassed. The condensing pressure can be set to the minimum required pressure by adjusting the amount of air blown to the compressor, which enables energy-saving operation while protecting the compressor.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention using two control valves as condensing pressure control means, and FIG. 2 is a configuration using the condensing pressure control means of FIG.
The figure which shows the Example of this invention at the time of pulling a bypass path | route from the middle of a condenser, FIG. 3 is a structure using the condensation pressure adjusting means of FIG.
The figure which shows the Example of this invention when a bypass path part is performing heat exchange as a condenser, FIG. 4 is a structure using the condensation pressure adjusting means of FIG.
FIG. 5 is a diagram showing an embodiment of the present invention when there are multiple bypass paths for heat exchange as a condenser, and FIG. 5 is an embodiment of the present invention using a controllable outdoor blower as the condensation pressure adjusting means. Fig. 6, Fig. 6 is a diagram showing the configuration of a basic cooling device, Fig. 7 is a diagram showing the configuration of a conventional cooling device, and Fig. 8 uses two control valves as condensing pressure control means. 10 is a flow chart showing an example of the operation of the cooling device of the present invention, and FIG. 9 is a flow chart showing an example of the operation of the cooling device of the present invention using a variable rotation speed outdoor fan as the condensation pressure adjusting means. The figure shows the case where the cooling device is controlled by the conventional method,
The figure which compares the efficiency (COP) when controlling a cooling device by this invention, FIG. 11 is a performance figure of the air conditioner to which the control method of this invention is applied. 1,21,221… Compressor, 2,22,222… Condenser, 3,23,223… Variable opening expansion valve, 4,24,224… Evaporator, 226… Condensing pressure control valve, 7,27,227… Outdoor blower, 8,28,228… Indoor side blower, 30,230 ... Rotation control means, 32,232 ... Room temperature sensor, 33,2
33 ... Superheat sensor, 34 ... Compression ratio sensor, 35, 235 ... Control device section, 41 ... First control valve, 42 ... Second control valve, 55 ... Second
Condenser, 127 ... Controllable outdoor blower.

Claims (8)

(57) [Claims] 1. A compressor, a condenser, an outdoor blower for blowing air to the condenser, an evaporator, an indoor blower for blowing air to the evaporator, and a refrigerant from the compressor to the condenser. A first path for guiding, a second path for guiding the refrigerant from the condenser to the evaporator, a bypass path for guiding the refrigerant from the compressor to the second path by bypassing the condenser, and on the second path And a first control valve provided between the converging point and the condenser, a second control valve provided in the bypass path, and the second control valve. A variable opening degree expansion valve provided between the confluence point and the evaporator in the path, a third path for guiding the refrigerant from the evaporator to the compressor, and a degree of superheat of the refrigerant in the third path. And a compression ratio sensor for detecting the ratio between the discharge pressure and the suction pressure of the compressor. If the detected value of the superheat sensor is higher than a predetermined set value, the opening degree of the opening degree variable expansion valve is increased according to the difference, and the bypass path for the refrigerant flow rate of the condenser is provided. The first to increase the ratio of the refrigerant flow rate
Of the control valve and the second control valve, and if the opening is lower than the predetermined set value, the opening of the variable opening expansion valve is reduced according to the difference, and the opening is adjusted with respect to the refrigerant flow rate of the condenser. The minimum compression for adjusting the opening of the first control valve and the second control valve so as to reduce the proportion of the refrigerant flow rate in the bypass path, and for the detected value of the compression ratio sensor to enable the compressor to operate. If it is lower than the allowable compression ratio which is the ratio, it is controlled so as to increase the refrigerant flow rate of the bypass path with respect to the refrigerant flow rate of the condenser according to the difference, and if the detected compression ratio is higher than the allowable compression ratio, A cooling device having a control unit that controls to reduce the ratio of the refrigerant flow rate of the bypass path to the refrigerant flow rate of the condenser according to the difference. 2. The cooling device according to claim 1, wherein a bypass path bypassing the condenser passes through a part of the condenser. 3. The cooling device according to claim 1, further comprising another condenser in a bypass path that bypasses the condenser. 4. A compressor, a condenser, an outdoor blower capable of controlling the amount of air blown to the condenser, an evaporator, an indoor blower that blows air to the evaporator, and a refrigerant from the compressor. A first path leading to the condenser, a second path guiding the refrigerant from the condenser to the evaporator, an opening degree variable expansion valve provided in the middle of the second path, and a refrigerant from the evaporator are provided. A third path leading to the compressor, a superheat sensor for detecting a superheat degree of the refrigerant in the third path, and a compression ratio sensor for detecting a ratio between a discharge pressure and a suction pressure of the compressor are provided. Further, if the detected value of the superheat sensor is higher than a predetermined set value, the opening degree of the opening degree variable expansion valve is increased according to the difference, and control is performed so as to reduce the air flow rate of the outdoor blower, If the detected degree of superheat is lower than the predetermined set value, the opening degree is determined according to the difference. Control is performed such that the opening degree of the variable degree expansion valve is reduced and the amount of air blown by the outdoor blower is increased, and the detected value of the compression ratio sensor is the minimum compression ratio for the compressor to operate. When it is lower than the ratio, the air volume of the outdoor blower is reduced according to the difference, and when the detected compression ratio is higher than the allowable compression ratio, the air volume of the outdoor blower is increased according to the difference. A cooling device having a control device section for controlling. 5. A compressor, a condenser, an outdoor blower for blowing air to the condenser, an evaporator, an indoor blower for blowing air to the evaporator, and a refrigerant from the compressor to the condenser. A first path for guiding, a second path for guiding the refrigerant from the condenser to the evaporator, a bypass path for guiding the refrigerant from the compressor to the second path by bypassing the condenser, and a second path on the second path. In a confluence point where the bypass path is guided, a first control valve provided between the confluence point and the condenser, a second control valve provided in the bypass path, and in the second path. A variable opening expansion valve provided between the confluence point and the evaporator, a third path for guiding the refrigerant from the evaporator to the compressor, and the third path.
A superheat sensor for detecting the superheat of the refrigerant in the path, a compression ratio sensor for detecting the ratio between the discharge pressure and the suction pressure of the compressor, based on signals from the compression ratio sensor and the superheat sensor. A method for controlling a cooling device, comprising: a variable opening expansion valve; and a control device section that adjusts the opening amounts of the first control valve and the second control valve, wherein a detection value of the superheat sensor is predetermined. If it is higher than the preset value, the opening degree of the variable opening expansion valve is controlled so as to increase, and even if the variable opening expansion valve is fully opened, if the degree of superheat is higher than the predetermined set value, The openings of the first control valve and the second control valve are adjusted so as to increase the ratio of the refrigerant flow rate of the bypass path to the refrigerant flow rate of the first path, and the detected value is lower than the predetermined set value. Depending on the difference, The opening degree of the first control valve and the second control valve is adjusted so as to reduce the opening degree of the expansion valve and reduce the ratio of the refrigerant flow rate of the bypass path to the refrigerant flow rate of the condenser. Control method for cooling device. 6. A compressor, a condenser, an outdoor blower capable of controlling the amount of air blown to the condenser, an evaporator, an indoor blower that blows air to the evaporator, and a refrigerant from the compressor. A first path leading to the condenser, a second path guiding the refrigerant from the condenser to the evaporator, an opening degree variable expansion valve provided in the middle of the second path, and a refrigerant from the evaporator are provided. A third path leading to the compressor, a superheat sensor for detecting a superheat degree of the refrigerant in the third path, a compression ratio sensor for detecting a ratio between a discharge pressure and a suction pressure of the compressor, A control method for a cooling device, comprising: a controller for controlling the opening of the variable opening expansion valve and the air volume of the outdoor blower based on signals from a ratio sensor and the superheat sensor, If the detection value of the degree sensor is higher than the preset value, The opening degree of the variable opening expansion valve is controlled so as to increase, and when the detected value is higher than the predetermined set value even when the variable opening expansion valve is fully opened, the amount of air blown by the outdoor blower is changed. If the detected value is lower than the predetermined set value, the air volume of the outdoor blower is increased according to the difference, and if the detected value is lower than the set value even if the outdoor blower has the maximum air volume, the open value is set. A method for controlling a cooling device, which comprises reducing the opening degree of a variable expansion valve. 7. A compressor, a condenser, an outdoor blower for blowing air to the condenser, an evaporator, an indoor blower for blowing air to the evaporator, and a refrigerant from the compressor to the condenser. A first path for guiding the refrigerant from the condenser to the evaporator; a bypass path for guiding the refrigerant from the compressor to the second path by bypassing the condenser; A converging point on which a bypass path is guided, a first control valve provided between the converging point and the condenser, a second control valve provided on the bypass path, and the first control valve. A variable opening expansion valve provided in the middle of the confluence point and the evaporator in two paths, a third path for guiding the refrigerant from the evaporator to the compressor, and overheating of the refrigerant in the third path. And a compression ratio sensor for detecting the ratio between the discharge pressure and the suction pressure of the compressor. A cooling device including a controller for adjusting the opening of the opening variable expansion valve and the opening of the first control valve and the second control valve based on signals from the compression ratio sensor and the superheat sensor. In the control method of the above, if the detection value of the compression ratio sensor is smaller than the allowable compression ratio that is the minimum compression ratio for the compressor to operate, the bypass path for the refrigerant flow rate of the condenser is determined according to the difference. Of the first control valve and the second control valve so as to increase the refrigerant flow rate, and when the detected value is larger than the allowable compression ratio, the refrigerant flow rate of the condenser is changed according to the difference. A method for controlling a cooling device, wherein the opening degrees of the first control valve and the second control valve are adjusted so as to reduce the ratio of the refrigerant flow rate in the bypass path. 8. A compressor, a condenser, an outdoor blower capable of controlling the amount of air blown to the condenser, an evaporator, an indoor blower that blows air to the evaporator, and a refrigerant from the compressor. A first path leading to the condenser, a second path guiding the refrigerant from the condenser to the evaporator, a variable opening expansion valve provided in the middle of the path, and a refrigerant compressing the refrigerant from the evaporator. Path leading to the compressor, a superheat sensor for detecting the superheat degree of the refrigerant in the third path, a compression ratio sensor for detecting the ratio between the discharge pressure and the suction pressure of the compressor, and the compression ratio sensor. And a control method of a cooling device comprising a controller for controlling the opening of the variable opening expansion valve and the amount of air blown by the outdoor blower based on a signal from the superheat sensor, wherein the compression ratio The value detected by the sensor is the minimum compression ratio for the compressor to operate. When the detected value is higher than the allowable compression ratio, the amount of air blown by the outdoor blower is increased according to the difference when the detected value is smaller than the allowable compression ratio. A method for controlling a cooling device.