JPH0370154B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a refrigeration system, and particularly to improvement of defrosting performance using hot gas.

[Prior Art] FIG. 2 is a refrigerant system diagram showing an example of a conventionally commonly used refrigeration system equipped with a plurality of compressors. In the figure, two large-capacity compressors 1 and small-capacity compressors 2, in which the rated capacity ratio of the compressors is selected to be approximately 1:2, are connected to a water-cooled condenser 3 or an air-cooled condenser (not shown). The refrigerant discharge pipes 4 and suction pipes 5 of each compressor 1 and 2 are connected in parallel to each other.

Note that 6 is a pressure equalizing oil pipe that connects the crank chambers of the compressors 1 and 2 with each other. Further, the operation of the compressors 1 and 2 is configured to be controlled individually.

Further, 7 is a first evaporator, 8 is a second evaporator,
9, 9a are liquid pipes, and these liquid pipes 9, 9
a communicates with the first electromagnetic valve 10, and the other end of the liquid pipe 9 communicates with the water-cooled condenser 3.

On the other hand, the first evaporator 7 communicates with the liquid pipe 9a via the second solenoid valve 14 and the first throttle device 12, and the second evaporator 8 communicates with the third solenoid valve 15 and the first throttle device 12. It communicates with the liquid pipe 9a via the second throttle device 13.

A check valve 11 is provided in parallel with the first throttle device 12 and the second solenoid valve 14 for the first evaporator 7, and this check valve 11 is located at the inlet 7a of the first evaporator 7.
This allows only the flow of refrigerant from the liquid pipe 9a to the liquid pipe 9a.

The first evaporator 7 and the second evaporator 8 are connected in parallel and connected to the suction side of each of the compressors 1 and 2 through a suction pipe 5. Outlet 7 of first evaporator 7
A low pressure side solenoid valve 16 is provided at b. 18
is a bypass circuit that bypasses the condenser 3 and the first throttle device 12 during defrosting operation and supplies hot gas from the compressors 1 and 2 to the first evaporator 7; It connects the outlet 7b of the container 7 and the refrigerant discharge pipe 4, and a high-pressure side solenoid valve 19 is provided in the middle thereof.

Further, 20 is a control section that controls the operation of the compressors 1 and 2 according to an output signal from a pressure detection section 21 that detects the refrigerant pressure on the low pressure side of the compressors 1 and 2. 22 and 23 are the control unit 2, respectively.
Electromagnetic contactors 24 and 25 provided on the power line connecting the compressors 1 and 2 are overcurrent relays similarly provided in series with the power line.

In the conventional refrigeration system configured as described above, when the power switch (not shown) is turned on during cooling operation, the electromagnetic contactors 22 and 23 are closed and AC power is supplied to the motors of the compressors 1 and 2. and compressors 1 and 2 are driven. As the compressors 1 and 2 operate, the discharged high-temperature refrigerant gas passes through the refrigerant discharge pipe 4 and enters the water-cooled condenser 3, where it is condensed and liquefied.

The liquid refrigerant that has exited the water-cooled condenser 3 passes through a liquid pipe 9 and a first solenoid valve 10, and is divided into two systems at the liquid pipe 9a.
Passes through the first expansion device 12, becomes low temperature and low pressure,
The first evaporator 7 absorbs heat from the surroundings and evaporates to form a gas, which is sucked into the compressors 1 and 2 through the low-pressure side electromagnetic valve 16 and the suction pipe 5.

In addition, the second system is connected to the second evaporator solenoid valve 1.
5. It passes through the second throttle device 13, becomes low temperature and low pressure, takes heat from the surroundings in the second evaporator 8, evaporates into gas, and flows into the suction pipe 5.

In this case, the high pressure side solenoid valve 19 provided in parallel with the low pressure side solenoid valve 16 at the outlet of the first evaporator 7 is closed.

Also, as shown in Figure 3, the normal pressure region is
A capacity up signal is sent to the control unit 20 based on three values: a capacity up pressure value, a capacity down pressure value, and a low pressure cut value.If the area is above the capacity up pressure value, a capacity down signal is also sent to the control unit 20. Region C where the pressure is equal to or higher than the capacity down pressure value and less than the capacity up pressure value is not output, and region B where the volume is lower than the capacity down pressure value where a capacity down signal is issued to the control unit 20, and a stop signal is issued to the compressors 1 and 2. It is divided into four areas: (a) a region below the low pressure cut value;

Here, when the cooling load decreases, the refrigerant pressure on the low pressure side of the refrigeration cycle decreases, and the level of the pressure detection signal output from the pressure detection section 21 to the control section 20 also decreases accordingly. Since the control unit 20 has a comparison circuit that compares the pressure detection signal with a reference value (capacity up pressure value or capacity down pressure value), if the pressure detection signal is lower than the capacity down pressure value, that is, In the case of area B,
The control unit 20 lowers the cooling capacity by controlling the capacities of the compressors 1 and 2 to decrease. When the cooling capacity is lowered in this way, the refrigerant pressure on the low pressure side of the refrigeration cycle increases and converges to region C, and the operation becomes stable.

Further, when the cooling load is high, the refrigerant pressure on the low pressure side of the refrigeration cycle increases, and the level of the pressure detection signal output from the pressure detection section 21 to the control section 20 increases accordingly. As a result, when the pressure detection signal is higher than the capacity up pressure value, that is, in the case of region 2, the control unit 20 controls the capacity of the compressors 1 and 2 to increase, thereby increasing the cooling capacity. When the cooling capacity increases in this way, the refrigerant pressure on the low pressure side of the refrigeration cycle decreases and converges to region C, and the operation becomes stable.

Note that when the refrigerant pressure on the low-pressure side of the refrigeration cycle falls below the low-pressure cut value, that is, in region A, the compressors 1 and 2 are immediately stopped.

For example, if the required power to obtain the required refrigerating capacity for the refrigerating load of the evaporators 7 and 8 is 15 HP, the rated capacity of one compressor 1 is
The rated capacity of the other compressor 2 is selected to be 10HP, and the rated capacity of the other compressor 2 is 5HP.

On the other hand, the refrigerating load on the evaporators 7 and 8 varies greatly from 0 to 100% depending on the usage conditions.

In response to such refrigeration load fluctuations, the refrigeration load is 33
% or less, only compressor 2 with a rated capacity of 5 HP is operated independently. Also, the refrigeration load is 33
In the range of ~66%, only compressor 1 with a rated capacity of 10 HP is operated independently.

Furthermore, when the refrigeration load becomes 66 to 100%, compressors 1 and 2 are operated in parallel at the same time. The transition of this capacity control operation is shown in Fig. 4.

In other words, as shown in Fig. 4, by selectively controlling the operation and stopping of large and small compressors whose rated capacity ratio is approximately 1:2, 0, 33, 66 , 100% capacity control operation can be performed in four stages.

Next, when defrosting of the first evaporator 7 is started, the first solenoid valve 10 and the low pressure side solenoid valve 16 are closed, and the high pressure side solenoid valve 19 is opened.

As a result, a portion of the high-temperature, high-pressure gas discharged from the compressors 1 and 2 flows into the first evaporator 7 through the pipe 18 and the high-pressure side electromagnetic valve 19. The remaining discharged gas passes through the discharge pipe 4 and is liquefied into the condenser 3.

The high temperature and high pressure gas that has flowed into the first evaporator 7 is
Heat is radiated to the surroundings and condensed, at which time the first evaporator 7
melt the frost that has adhered to it. The liquid refrigerant condensed in the first evaporator 7 flows into the liquid pipe 9a through the check valve 11 that bypasses the first throttle device 12 and the second throttle device 14 for the first evaporator 7. .

The liquid refrigerant flowing into the liquid pipe 9a passes through the second evaporator electromagnetic valve 15 and the second expansion valve 13, becomes low temperature and low pressure, and takes heat from the surroundings in the second evaporator 8 and evaporates to become gas. The air is sucked into the compressors 1 and 2 through the suction pipe 5.

[Problem that the invention seeks to solve]

In the above-mentioned refrigeration system, the cooling load during hot gas defrosting is always smaller than the load during normal cooling operation, and in the example shown in FIG. 2, it is approximately 1/2.
Therefore, during hot gas defrosting, the compressor is operated in response to a small cooling load, which reduces the suction pressure of the compressor, which not only causes poor operating efficiency, but also prevents the refrigerant from evaporating. However, it had the disadvantage of causing a liquid backlash phenomenon. In addition, there were cases where the suction pressure fell below the compressor's lower limit of use, causing the low pressure switch, which serves as a protection device, to operate. In order to prevent these, conventional refrigeration equipment as described above is a multi-type refrigerator capable of low-load operation, performs capacity control operation, and bypasses the high-pressure side and low-pressure side during defrosting operation using hot gas. However, it cannot cope with sudden changes in cooling load during defrosting operation, resulting in poor defrosting, long defrosting times, and a tendency for the temperature inside the refrigerator to rise. There were problems in that the device became complicated and the operating efficiency further deteriorated.

This invention solves the above-mentioned conventional problems, and can always supply sufficient hot gas to the evaporator, shorten the defrosting time, and
It is an object of the present invention to provide a refrigeration device that can minimize the temperature rise inside the refrigerator.

[Means for solving problems]

The refrigeration system according to the present invention includes a refrigeration cycle configured by connecting two compressors, a condenser, a throttle device, and an evaporator with different rated capacities in a closed loop, and a bypass circuit that bypasses a condenser and a throttle device and supplies hot gas from the compressor to the evaporator; a pressure detection section that detects refrigerant pressure on the low pressure side of the refrigeration cycle and generates a pressure detection signal; a defrost start device that generates a defrost start signal; , when starting defrosting operation when both of the above compressors are stopped,
The defrost start signal of the defrost start device is input to start the operation of the large capacity compressor independently, and during the defrost operation, the defrost signal of the defrost start device is input, so that the above The above objective is achieved by configuring the refrigeration system by providing a compressor capacity setting unit that allows the small capacity compressor to operate independently even if a signal to stop both of the compressors is input from the control unit. It is something to do.

[Effect]

In the refrigeration system according to the present invention, the control unit causes the refrigerant pressure on the low pressure side of the refrigeration cycle to converge to a predetermined value, and when the defrost signal is input, the compressor capacity setting unit operates at least a small-capacity compressor. controlled to do so. In addition, when starting defrosting operation when both compressors are stopped, the large-capacity compressor starts operating independently, so it is possible to prevent sudden changes in the refrigeration load during defrosting. Since sufficient hot gas can be supplied to the evaporator, the defrosting time can be shortened and the temperature rise inside the refrigerator can be minimized.

[Embodiments of the invention]

FIG. 1 is a block diagram showing an embodiment of a refrigeration system according to the present invention, and the same parts as those in FIG. 2 are designated by the same reference numerals. In the figure, 26 is a defrost starting device such as a timer that generates a defrost signal. 17 is a compressor capacity setting unit provided downstream of the control unit 20, and when starting defrosting operation from a state where both compressors 1 and 22 are stopped, the defrosting starting device 26 is When the defrost signal is input, the large-capacity compressor 1 starts operating independently, and the defrost starting device 2 is activated during the defrosting operation.
By inputting the defrosting signal No. 6, even if a signal to stop both the compressors 1 and 2 is input from the control unit 20, the small capacity compressor 2
This allows the vehicle to operate independently.

Therefore, when the first evaporator 7 starts defrosting, if the internal temperature of the second evaporator 8 is around the lower limit of the set internal temperature, the second evaporator 8 starts evaporating. The control function of the second expansion valve 13 works to reduce the amount of refrigerant circulating, and as the refrigerant circulation amount decreases, the refrigerant pressure on the low-pressure side decreases, reaching a region B below the capacity down pressure value, and the compressor 1 and 2, but when the defrost signal is input from the defrost start device, the function of the compressor capacity setting section 7 is activated, and even if the capacity down pressure value is below, the compressor 2 is stopped. As a result, sufficient hot gas is always supplied to the first evaporator 7.
defrost time can be shortened and temperature rise inside the refrigerator can be minimized.
Note that when the refrigerant pressure on the low-pressure side falls into a region A below the low-pressure cut value, the compressor 2 is immediately stopped.

In addition, when starting defrosting using hot gas when both compressors 1 and 2 are stopped, the compressor capacity setting section 17 is activated by inputting a defrosting signal from the defrosting start device 26. Function,
Since operation is now started with only large-capacity compressor 1 operating independently, if the time required to change the capacity of the compressor is 3 minutes, conventionally, two compressors 1 and 2 are operated separately. 6 by the time I drive
It used to take 3 minutes, but now it only takes 3 minutes, and it only takes 3 minutes to switch to the independent operation of small capacity compressor 2. It can respond to sudden changes in defrost load, and the compressor stops due to a drop in suction pressure. can be prevented. In the above embodiment, the case of two systems, the first evaporator 7 and the second evaporator 8, was shown, but the case of three or more systems may be used.

By the way, in this embodiment, the case where multiple evaporators are installed has been described, but even when there is only one evaporator, such as thermobank type defrost, reverse type defrost, etc., when defrosting starts, the low pressure drops rapidly and the compression However, the controller 20 operates the compressors 1 and 2 without stopping, supplies enough hot gas to the evaporator, and defrosts the refrigerator in a short time. Temperature rise can be minimized.

〔Effect of the invention〕

As explained above, the refrigeration system according to the present invention has two compressors, a condenser, and a
A refrigeration cycle configured by connecting a throttling device and an evaporator in a closed loop, and a bypass that bypasses the condenser and throttling device during defrosting operation and supplies hot gas from the compressor to the evaporator. A circuit, a pressure detection unit that detects the refrigerant pressure on the low pressure side of the refrigeration cycle and generates a pressure detection signal, and controls the operation of the compressor according to the pressure detection signal, thereby controlling the refrigerant pressure on the low pressure side. and a defrosting start device that generates a defrosting signal, and when starting defrosting operation from a state where both of the compressors are stopped, The defrost signal of the defrost start device is input to start operation of the large capacity compressor independently, and during the defrost operation, the defrost signal of the defrost start device is input to control the above. The refrigeration system is configured by providing a compressor capacity setting section that allows the small capacity compressor to operate independently when a signal to stop both of the compressors is input from the section. , it is possible to prevent the compressor from stopping due to a drop in suction pressure, and it is also possible to follow sudden changes in the refrigeration load.As a result, sufficient hot gas can always be supplied to the evaporator, making it possible to defrost. Not only can the time be shortened, but also the rise in temperature inside the refrigerator can be minimized.

[Brief explanation of drawings]

FIG. 1 is a refrigerant system diagram showing an embodiment of the refrigeration system according to the present invention, FIG. 2 is a refrigerant system diagram showing a conventional refrigeration system, FIG. 3 is a diagram showing the refrigerant pressure region on the low pressure side, and FIG. The figure is an explanatory diagram of the capacity control operation of the refrigeration system of FIG. 2. 1... Large capacity compressor, 2... Small capacity compressor, 3... Condenser, 7, 8... Evaporator, 12,
13... Throttle device, 17... Compressor capacity setting section,
18...Bypass circuit, 20...Control unit, 21...
. . . Pressure detection unit, 26 . . . Defrost starting device. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A refrigeration cycle consisting of two compressors, condensers, throttling devices, and evaporators each with different rated capacities connected in a closed loop, and the condenser and throttling device being connected to the side during defrosting operation. a bypass circuit that supplies hot gas from the compressor to the evaporator; a pressure detection section that detects refrigerant pressure on the low pressure side of the refrigeration cycle and generates a pressure detection signal; A defrosting start device includes a control unit that converges the refrigerant pressure on the low pressure side to a predetermined set value by controlling the operation of the compressor, and generates a defrosting signal; When starting defrosting operation from a stopped state, the defrosting signal of the defrosting start device is input and operation is started by independent operation of the large capacity compressor. A compressor capacity setting unit that allows a small capacity compressor to operate independently even if a signal for stopping both compressors is input from the control unit in response to input of a defrosting signal from a starting device; A refrigeration device characterized by comprising: