JPH0573982B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a refrigeration system, and particularly to a refrigeration system that maintains the freshness of objects to be cooled and that effectively removes oil mixed in the refrigerant into a compressor. The present invention relates to a refrigeration device that is designed to revert back to its original state.

[Conventional technology]

Conventionally, there has been a device of this type as shown in FIG. In Fig. 2, 1 is a parallel compression type refrigeration system, and 2 is a plurality of show cases 2a, 2b, 2c.
This is a cooling device composed of a combination of In the parallel compression refrigeration system 1, the rated capacity ratio of the compressor is selected to be approximately 2:1 on a liquid receiver connected to the downstream side of a water-cooled condenser 1a or an air-cooled condenser (not shown). Two large-capacity compressors 1b and small-capacity compressors 1c are installed in parallel, and each compressor 1b and 1c has a refrigerant discharge pipe 1d and a suction pipe 1e.
are connected in parallel with each other. Note that 1f is a pressure-equalizing oil pipe that connects the crank chambers of the compressors 1b and 1c with each other.

Further, 5 corresponds to the pressure difference between the output signal of the output detection unit 3 that detects the refrigerant pressure on the low pressure side and the refrigerant pressure set in the pressure setting unit 4 that sets the refrigerant pressure on the low pressure side to be converged. The above compressors 1b and 1
This is a control unit that individually controls the operation and stopping of the controllers c.

Reference numeral 7 denotes a compressor single-lung operating time integrating unit that integrates the operating time of only one of the compressors 1b and 1c. Further, 6 indicates that when the compressor independent operation time integrating unit 7 reaches a predetermined time, the compressor 1
Both compressors b and 1c are stopped for a certain period of time, and the cumulative time of the compressor independent operation time integrating section 7 is set to 0, and the two compressors 1 have different rated capacities.
This is a compressor capacity setting unit that starts the operation of compressors b and 1c.

Also, as shown in Figure 3, the normal pressure region is
A region above the capacity up pressure value in which a capacity up signal is sent to the parallel compression refrigeration system 1 based on the capacity up pressure value, capacity down pressure value, and low pressure cut value set by the pressure setting section 4. (2) In a region where the pressure is above the capacity down pressure value and below the capacity up pressure value in which neither a capacity down signal nor a capacity up signal is issued to the parallel compression refrigeration system 1, a capacity down signal is issued to the parallel compression refrigeration system 1. It is divided into four regions: region (b) below the capacity down pressure value, and region (b) below the low pressure cut value that issues a stop signal to the parallel compression type refrigeration system 1.

Next, the operation will be explained. For example, if the required power to obtain the required refrigerating capacity for the refrigerating load of the cooling device 2 is 15, the rated capacity of one compressor 1b is selected to be 10, and the rated capacity of the other compressor 1c is selected to be 5. be done.

On the other hand, multiple show cases 2a, 2b, 2c
In the cooling device 2, the cooling load varies greatly from 0 to 100% depending on the usage status of each case.

Here, when the refrigeration 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 3 to the control section 5 also decreases accordingly.

Since the control unit 5 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 region B, the control unit 5 controls the capacity of the parallel compression type refrigeration device 1 to decrease, thereby lowering the cooling capacity. When the cooling capacity is reduced in this way, the refrigerant pressure on the low pressure side of the refrigeration cycle increases,
It converges to region C, and 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 3 to the control section 5 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 5 controls the capacity of the parallel compression refrigeration system 1 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,
It converges to region C, and operation becomes stable. Note that the time from when the pressure detection section 3 detects the pressure in region 2 or region 2 until the capacity up signal or capacity down signal is generated from the control section 5 is the same.

Note that when the refrigerant pressure on the low-pressure side of the refrigeration cycle falls below the low-pressure cut value, that is, falls into region A, the compressors 1b and 1c are designed to immediately stop.

Therefore, with respect to the above-mentioned refrigeration load fluctuation, only the compressor 1c with a rated capacity of 5 is operated independently when the refrigeration load is at a partial load of 33% or less. In addition, when the refrigeration load is in the range of 33% to 66%, compressor 1 with a rated capacity of 10
Only b is operated independently.

Furthermore, when the refrigeration load becomes 66 to 100%, compressors 1b and 1c are simultaneously operated in parallel. The transition of this capacity control operation is shown in FIG. 4.

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

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, a cooler 2a is installed in each of a plurality of parts to be cooled, such as a case.
In a refrigeration system equipped with 2b and 2c, each case is equipped with a temperature regulator and a liquid line solenoid valve that controls the flow of refrigerant to control the temperature of each case. It was on. In this case, for example, in a refrigeration system that has three cases and controls the three cases individually, only one cooler 2a may be operated for a long time due to load reduction at night. At this time, since the load is reduced, the refrigeration system operates with the evaporation temperature of the cooler 2a lowered, and the refrigerant gas flow rate in the suction pipes of the compressors 1b and 1c decreases. When the refrigerant gas flow rate decreases, the lubricating oil separated from the refrigerant gas is transferred to the compressor 1b,
The lubricating oil in the compressors 1b and 1c decreased, and there was a risk that sliding parts such as compressor bearings would burn out.

In addition, if the suction pipe diameter of the compressors 1b and 1c is made smaller to ensure the refrigerant gas flow velocity in anticipation of a reduction in the load of operating one of the coolers 2a, eight coolers 2a, 2b, and 2c can be operated. During heavy load operation, the refrigerant gas flow rate becomes extremely high, and compressor 1
The pressure loss in the suction pipes b and 1c becomes extremely large. Therefore, there was a drawback that the compression capacity of the compressors 1b and 1c was reduced, and the refrigeration capacity of the refrigeration system was reduced.

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. , compressor 1b due to a decrease in suction side pressure due to load reduction,
The time during which only one of the compressors 1b and 1c operates is accumulated by the compressor independent operation time accumulating unit 7, and when the value reaches a predetermined time, the compressor capacity setting unit 6 controls the operation of the two compressors 1b and 1c. Both compressors 1b and 1c having different rated capacities are stopped for a certain period of time, the accumulated time of the compressor independent operation time accumulating unit 7 is set to 0, and operation is started by parallel operation of the two compressors 1b and 1c having different rated capacities. . That is, by stopping the compressors 1b, 1c 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 causing the compressors 1b, 1c to return to the low pressure side.
When the operation of the compressor 1c is resumed, the flow rate of the refrigerant gas in the suction pipe increases, and the lubricating oil accumulated in the suction pipe during low load operation is returned to the compressors 1b and 1c all at once. This prevents the internal lubricating oil from decreasing.

[Problem that the invention seeks to solve]

Conventional refrigeration equipment is configured as described above, so when only one of the two compressors is operating for a predetermined time, both compressors stop and the object to be cooled is stopped. The drawback was that the freshness of the food was not maintained.

This invention was made in order to solve the conventional problems as described above, and it reduces the time during which the compressor is stopped as much as possible to maintain the freshness of the material to be cooled, and also 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]

In this invention, the pressure detection section detects the refrigerant pressure on the low pressure side of the refrigeration cycle to generate a pressure detection signal, and the pressure setting section sets the refrigerant pressure to be converged. A controller that determines whether the refrigerant pressure is above or below the desired refrigerant pressure and generates a capacity control output signal to control the capacity of the refrigerator, and an integrated time when only one compressor is operating. When the cumulative time of the compressor independent operating time integrating section and the compressor independent operating time integrating section reaches a predetermined time, both of the compressors are stopped for a certain period of time, and the compressor independent operating time integrating section calculates the integrated time. a compressor capacity setting section that sets the time to 0 and starts the operation of the two compressors; and when the continuous parallel operation time of the two compressors reaches a predetermined time, the compressor independent operation time integration section The above object is achieved by configuring a refrigeration system by providing a compressor independent operation time correction section that sets the accumulated time to 0.

[Effect]

In the refrigeration system of the present invention, when the continuous parallel operation time of the two compressors reaches a predetermined time, the integrated time of the compressor independent operation time accumulator is reduced to 0 by the function of the compressor independent operation time correction section. Therefore, the time during which the compressor is stopped 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, 8 is a compressor independent operation time correction section, and when the parallel operation of the two compressors 1b and 1c having different rated capacities reaches a predetermined time, the compressor independent operation time integration section 7
It has a function to set the cumulative time to 0.

Next, the operation will be explained. Of the compressors 1b and 1c, the compressor independent operation time accumulating unit 7
Accumulate the time when only one vehicle is operating, and calculate, for example,
When 4 minutes have elapsed, the compressor capacity setting unit 6 sets both the compressors 1b and 1c for a certain period of time, for example, 3 minutes.
At the same time, the accumulated time (48 minutes) of the compressor independent operation time accumulating unit 7 is set to 0, and the two compressors 1b and 1c having different rated capacities start operating in parallel. ing. By the way, the compressor independent operation time correction unit 8 integrates the parallel continuous operation time of the two compressors 1b and 1c having different rated capacities, and when a predetermined time, for example, 10 minutes, is reached, the compression Machine independent operation time accumulation section 7
Even if the cumulative time has reached 43 minutes, the cumulative time of the compressor independent operation time cumulative section 7 is reset to 0.
I'm starting to accumulate more.

Therefore, the time during which the compressors are stopped is kept as short as possible to maintain the freshness of the object to be cooled, and by stopping the compressors 1b and 1c 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 when the compressors 1b and 1c restart, the flow rate of refrigerant gas in the suction pipe increases, and during low-load operation, the refrigerant gas flows into the suction pipe. The accumulated lubricating oil is transferred to the compressor 1b,
1c at once, the compressor 1
It is possible to prevent the lubricating oil in b and 1c from decreasing.

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. Then, when the continuous parallel operation time reaches a predetermined time, for example 10 minutes, the cumulative time of the low frequency operational time integrating section of the compressor becomes 0.
A similar effect can be obtained by doing so.

〔Effect of the invention〕

As explained above, the refrigeration system according to the present invention detects the refrigerant pressure on the low pressure side of the refrigeration cycle with the pressure detection section to generate a pressure detection signal,
The pressure of the refrigerant to be converged is set at the bottom, and the output signal for capacity control is determined to determine whether the pressure detection signal is above or below the refrigerant pressure to be converged, and to control the capacity of the refrigerator. a compressor independent operation time accumulation section that accumulates the time during which only one compressor is in operation; and a compressor independent operation time accumulation section that accumulates the time when only one compressor is in operation; and when the compressor independent operation time accumulation section reaches a predetermined time, A compressor capacity setting section that stops both compressors for a certain period of time, sets the accumulated time of the compressor independent operation time accumulating section to 0, and starts operation of the two compressors, and a continuous parallel operation of the two compressors. When the operating time reaches a predetermined time, the compressor independent operating time correction section sets the accumulated time of the compressor independent operating time integrating section to 0, so that the time during which the compressor is stopped can be shortened as much as possible. ,
The freshness of the object to be cooled 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 block diagram showing an embodiment of a refrigeration system according to the present invention, FIG. 2 is a block diagram showing a conventional refrigeration system, and FIG. 3 is a diagram showing a region of refrigerant pressure on the low pressure side.
FIG. 4 is an explanatory diagram of the capacity control operation of the refrigeration system shown in FIG. 2. In the figure, 1a is a condenser, 1b and 1c are compressors, 2a to 2c are coolers, 3 is a pressure detection section, 4 is a pressure setting section, 5 is a control section, 6 is a compressor capacity setting section, and 7 is a compressor 8 is a compressor independent operation time correction section. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Two compressors each having a suction pipe and a discharge pipe connected in parallel, a condenser that condenses and liquefies the refrigerant discharged from these compressors, and a cooling system that evaporates and vaporizes the refrigerant sent out from the condenser. A refrigeration circuit in which pipes are connected in sequence to form a closed circuit, detects the refrigerant pressure on the low pressure side of this refrigeration circuit,
A pressure detection unit that generates a pressure detection signal according to this refrigerant pressure, a pressure setting unit that sets a convergence pressure value of the refrigerant pressure on the low pressure side to be converged, and whether the pressure detection signal is greater than or equal to the convergence pressure value. a control unit that determines whether or not the compressor is operating, and generates a capacity control output signal for controlling the capacity of the refrigerator based on the determination result; When the cumulative time of the operating time integrating unit and the compressor independent operating time integrating unit reaches a predetermined time, both of the compressors are stopped for a certain period of time, and the cumulative time of the compressor independent operating time integrating unit is set to 0; And when the compressor capacity setting section starts the operation of the two compressors, and the continuous parallel operation time of the two compressors reaches a predetermined time, the cumulative time of the compressor independent operation time integrating section is set to 0. A refrigeration system comprising: a compressor independent operation time correction section.