JPH0573983B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a refrigeration system, and particularly to a refrigeration system that ensures the freshness of objects to be cooled and effectively returns oil mixed in a refrigerant to a compressor. The present invention relates to a refrigeration device configured as described above.

[Conventional technology]

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. Reference numeral 26 denotes a compressor independent operation time integration unit that integrates the time during which only one of the compressors 1 and 2 is operating. Further, when the compressor independent operation time accumulating section 26 reaches a predetermined time, 17 stops both the compressors 1 and 2 for a certain period of time, and the accumulated time of the compressor independent operating time accumulating section 26 reaches zero. This is a compressor capacity setting unit that starts the operation of the two compressors 1 and 2, which have different rated capacities.

Reference numerals 22 and 23 indicate electromagnetic contactors provided in the power lines connecting the control unit 20 and compressor capacity setting unit 17 with the compressors 1 and 2, and 24 and 25 indicate overcurrent relays provided in series with the power supply lines. It is.

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 in a liquid pipe 9a. It passes through the device 12, becomes low temperature and low pressure, takes heat from the surroundings in the first evaporator 7, evaporates, and becomes a gas.
The compressor 1 is connected to the low pressure side solenoid valve 16 and the suction pipe 5.
and 2.

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 the capacity up pressure value, capacity down pressure value, and low pressure cut value.The area above the capacity up pressure value and the control unit 2
0, a region C where the pressure is above the capacity down pressure value and below the capacity up pressure value where neither a capacity down signal nor a capacity up signal is output; It is divided into four areas: 1, 2, and 2, a region where the voltage is below the low pressure cut value, where a stop signal is issued.

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, when 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. In addition, the refrigeration load is 33~
In the 66% range, only compressor 1 with a rated capacity of 10 HP is operated independently.

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

In other words, as shown in Fig. 4, by selectively operating and stopping large and small compressors whose rated capacity ratios are selected to be approximately 1:2, 0.33, 66, 100 % capacity control operation can be performed.

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 in the condenser 3.

The high temperature and high pressure gas that has flowed into the first evaporator 7 is
The heat is radiated to the area and condensed, and at this 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 first throttle device 12 for the first evaporator 7 and the check valve 11 that bypasses the second electromagnetic valve 14. .

The liquid refrigerant that has flowed into the liquid pipe 9a passes through the third solenoid valve 1.
5 and a second expansion valve 13, the gas becomes low temperature and low pressure, and in the second evaporator 8, it absorbs heat from the surroundings and evaporates into gas, which is sucked into the compressors 1 and 2 through the suction pipe 5.

In general, in compressors that compress refrigerant to high temperature and high pressure, the lubricating oil of the compressor is added to the refrigerant in terms of weight ratio.
Mix 0.5-1%. This mixed lubricating oil mixes well with the refrigerant when the refrigerant is in a liquid state, but when the refrigerant is vaporized, it does not mix with the refrigerant and separates. Therefore,
In conventional refrigeration systems, lubricating oil mixed into the refrigerant does not return to the compressor, as will be explained next, and the lubricating oil in the compressor sometimes decreases.

In a conventional refrigeration system, for example, evaporators 7 and 8 are installed in each of a plurality of parts to be cooled, such as a show case.
In refrigeration equipment equipped with a refrigeration system, each case is equipped with a temperature controller and a liquid line solenoid valve that controls the flow of refrigerant to control the temperature of each case. . In this case, for example, in a refrigeration system that has two cases and controls the two cases individually, only one evaporator 7 may be operated for a long time due to load reduction at night. At this time, the load has been reduced, so the refrigeration system is operated by the evaporator 7.
It will be operated with the evaporation temperature of
The refrigerant gas flow rate in the suction pipes of compressors 1 and 2 is reduced. When the refrigerant gas flow rate decreases, the lubricating oil separated from the refrigerant gas will have difficulty returning to the compressors 1 and 2, and the lubricating oil in the compressors 1 and 2 will decrease, causing burning of sliding parts such as compressor bearings. There was a fear that it would happen. In addition, in anticipation of reducing the load on operating one of the evaporators 7, the suction pipe diameter of the compressors 1 and 2 is made smaller to secure refrigerant gas. When under load, the refrigerant gas flow rate becomes very high, and the pressure loss in the suction pipes of the compressors 1 and 2 becomes extremely large. As a result, the pressure capacity of the compressors 1 and 2 is reduced, resulting in a reduction in the refrigerating capacity of the refrigeration system.

In order to eliminate these drawbacks, as mentioned above, the capacity of the refrigeration system is changed according to the refrigerant pressure on the low-pressure side of the refrigeration cycle, and the evaporation temperature on the suction side is kept constant, so-called capacity control operation. , the time during which only one of the compressors 1 and 2 is operated due to a decrease in suction side pressure due to a reduction in load is accumulated by the compressor independent operation time integration unit 26, and when the value reaches a predetermined time, , by the compressor capacity setting section 17,
Both the compressors 1 and 2 are stopped for a certain period of time, and the compressor independent operation time integration unit 26
The cumulative time is set to 0, and the two compressors 1 and 2 having different rated capacities start operating. That is, by stopping the compressors 1 and 2 for a certain period of time, the liquid refrigerant on the high pressure side returns to the low pressure side, increasing the refrigerant pressure on the low pressure side, and by restarting the operation of the compressors 1 and 2, the refrigerant gas in the suction pipe is reduced. The flow rate increases and the lubricating oil accumulated in the suction pipes during low-load operation is returned to the compressors 1 and 2 all at once, thereby preventing the lubricating oil in the compressors 1 and 26 from decreasing.

[Problem that the invention seeks to solve]

Conventional refrigeration equipment is configured as described above, so when only one compressor is operating for a predetermined period of time, both compressors stop, regardless of the operating state, and the The drawback was that the freshness of the food was not maintained.

This invention was made to solve the above-mentioned conventional problems, and it reduces the time during which the compressor is stopped as much as possible to maintain the freshness of the cooled material and to prevent the buildup in the suction pipe. It is an object of the present invention to provide a refrigeration system that effectively returns lubricating oil to a compressor.

[Means to solve the problem]

A refrigeration system according to the present invention has a refrigeration cycle configured by connecting two compressors, a condenser, a throttle device, and an evaporator in a closed loop, each having a suction pipe and a discharge pipe connected in parallel. a bypass circuit that bypasses the condenser and throttle device during defrosting operation and supplies hot gas from the compressor to the evaporator; and a bypass circuit that detects refrigerant pressure on the low pressure side of the refrigeration cycle and generates a pressure detection signal. A pressure detection unit that generates a defrosting start signal, and 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 according to the pressure detection signal, and a defrosting start signal is provided. When the accumulated time of the defrosting starting device that occurs, the compressor independent operating time integrating unit that integrates the time during which only one compressor is operating, and the compressor independent operating time integrating unit reaches a predetermined time, a compressor capacity setting unit that stops both of the compressors for a certain period of time, sets the cumulative time of the compressor independent operation time cumulative unit to 0, and starts the operation of the two compressors; The above object is achieved by configuring a refrigeration system by providing a compressor independent operation time correction section that inputs a defrosting signal of the device and sets the integrated time of the compressor independent operation time integration section to 0.

[Effect]

In the refrigeration system according to the present invention, the integrated time of the compressor independent operating time accumulating section becomes 0 by the function of the compressor independent operating time correction section when the defrosting signal of the defrosting starting device is input, so the compressor is stopped. The cooling time can be made as short as possible, the freshness of the object to be cooled can be maintained, and the lubricating oil accumulated in the suction pipe can be effectively returned to the compressor.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a refrigeration system according to the present invention, and the same parts as in FIG. 2 are designated by the same reference numerals. In the figure, 28 is a defrost starting device such as a timer that generates a defrost signal. 27 is a compressor independent operation time correction section;
When the defrosting signal from the defrosting starting device 28 is input, it has a function of setting the accumulated time of the compressor independent operation time accumulating section 26 to 0.

Next, the operation will be explained. The compressor independent operation time accumulating section 26 accumulates the operating time of only one of the compressors 1 and 2, and when it reaches 48 minutes, for example, the compressor capacity setting section 17 selects the operating time of the compressors 1 and 2. Both compressors 1 and 2 are stopped for a certain period of time, for example, 3 minutes, and the cumulative time (48 minutes) of the compression independent operation time cumulative section 26 is set to 0, and the two compressors 1 and 2 with different rated capacities are operated in parallel. People are starting to start driving more. By the way, when the defrosting signal of the defrosting start device 28 is inputted by the compressor independent operation time correction section 27, even if the accumulated time of the compressor independent operation time accumulation section 26 reaches 43 minutes, the above-mentioned The cumulative time of the compressor independent operation time cumulative unit 26 is reset to 0, and the cumulative time is calculated from 0.

Therefore, the time during which the compressor is stopped is kept as short as possible to maintain the freshness of the cooled material, and by stopping the compressors 1 and 2 for a certain period of time, the liquid refrigerant on the high pressure side returns to the low pressure side, and the low pressure By increasing the refrigerant pressure on the side and restarting the operation of compressors 1 and 2, the flow rate of refrigerant gas in the suction pipe increases,
By returning the lubricating oil accumulated in the suction pipes to the compressors 1 and 2 at once during low-load operation, it is possible to prevent the lubricating oil in the compressors 1 and 2 from decreasing.

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. Further, in this embodiment, a case has been described in which a plurality of evaporators are installed, but even in a case where there is only one evaporator, that is, a thermobank type defrost, a reverse type defrost, etc.
Equivalent functionality can be obtained by inputting the defrost signal of In addition, in the above embodiment, capacity control is performed using two compressors, but even when controlling the capacity of the compressor by changing the output frequency of the inverter, the oil mixed in the refrigerant can be effectively compressed. In order to return the compressor to the compressor, the output frequency of the compressor is accumulated for a predetermined value, for example, 40 Hz or less, and when that value reaches a predetermined value, for example, 48 minutes, the compressor is operated for a predetermined time, for example, 48 minutes. After stopping for 3 minutes, the two compressors start operating in parallel. However, when the defrost signal from the defrost start device is input, the low frequency operation time correction section of the compressor sets the accumulated time of the compressor low frequency operation time integration section to 0, and the same effect can be obtained. .

〔Effect of the invention〕

As explained above, the refrigeration system according to the present invention has 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 defrosting operation. a bypass circuit that sometimes bypasses the condenser and throttle device and supplies hot gas from the compressor to the evaporator; and a pressure detection section that detects refrigerant pressure on the low pressure side of the refrigeration cycle and generates a pressure detection signal. and a control unit that controls the operation of the compressor according to the pressure detection signal to converge the refrigerant pressure on the low pressure side to a predetermined set value, and generates a defrost signal. , a compressor independent operation time accumulating section that accumulates the time during which only one compressor is operating; and when the compressor independent operating time accumulating section reaches a predetermined time, both compressors are operated on a fixed axis. a compressor capacity setting unit that stops the pipe, sets the cumulative time of the compressor independent operation time cumulative unit to 0, and starts the operation of the two compressors with different rated capacities; and a defrosting start device. It is equipped with a compressor independent operation time correction section that takes the frost signal as input and sets the accumulated time of the compressor independent operation time accumulation section to 0, so the time during which the compressor is stopped can be shortened as much as possible, and the cooling object can be The freshness of the oil is maintained, and the lubricating oil accumulated in the suction pipe can be effectively returned to the compressor.

[Brief explanation of the drawing]

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. In these figures, 1 is a compressor, 2 is a compressor, 3 is a condenser, 7 and 8 are evaporators, 12 and 13 are throttle devices, 17 is a compressor capacity setting section, 18 is a bypass circuit, and 20 is a control section , 21 is a pressure detection section, 2
Reference numeral 6 indicates a compressor independent operation time integration section, 27 indicates a compressor independent operation time correction section, and 28 indicates a defrosting starting device.
In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A refrigeration cycle configured by connecting two compressors, a condenser, a throttle device, and an evaporator in a closed loop, each having a suction pipe and a discharge pipe connected in parallel, and the above-mentioned during defrosting operation. 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 starting device that generates a defrost signal, comprising 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 according to the pressure detection signal; When the compressor independent operation time accumulating section which accumulates the time during which only one compressor is operating, and the compressor independent operating time accumulating section reach a predetermined time, both of the compressors are stopped for a certain period of time. and a compressor capacity setting unit that sets the cumulative time of the compressor independent operation time cumulative unit to 0 and starts the operation of the two compressors, and a defrosting signal of the defrosting start device is input to the compressor A refrigeration system comprising: a compressor independent operation time correction section that sets the accumulated time of the independent operation time accumulation section to 0.