JPH02293563A - Refrigerating plant - Google Patents

Abstract

PURPOSE:To previously avoid liquid return upon restarting by providing superheat degree altering means for obtaining larger suction superheat degree than suction superheat degree at the time of full load operation, at the time of partial load operation. CONSTITUTION:Superheat degree altering means 7 for obtaining larger suction superheat degree than that at a full load operation, at the time of partial load operation is provided. The means 7 has temperature difference correcting means for correcting temperature difference to be detected at the inlet of an evaporator 5 to a smaller value than an actual value. A switch A is opened, a switch B is closed at the time of partial load, an inlet temperature sensor T1 is inserted in series with a quasi-resistor R, its quasi-resistance value is added to the resistance value to meet the detected inlet temperature of the sensor T1 to provide a larger apparent value than the actually detected inlet temperature and to input it to a regulator 6, and the difference (T2-T1) between the detected outlet temperature by an outlet temperature sensor T2 and the inlet temperature is corrected to a smaller value than the actual value. Thus, larger suction superheat degree than that at the time of full load is obtained, and an accident due to liquid return is prevented at the time of restarting.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a refrigeration system equipped with a capacity-controllable compressor and using an electric expansion valve as an expansion mechanism, mainly during restart during partial load operation. Concerning measures to prevent liquid packs that occur in

(Prior Art) Conventionally, an electric expansion valve is used, and the valve opening degree is adjusted based on the temperature difference between the entrance and exit of the evaporator, and the degree of superheating of the intake gas is controlled to a predetermined constant value. For example, JP-A-61
It is known from Publication No.-38671 and the like. In this way, the reason why the suction gas is always given a constant degree of superheating is to keep the suction gas returned to the compressor in a saturated state and prevent the liquid refrigerant from returning. This is to prevent mechanical damage.

(Problem to be solved by the invention) However, in ordinary refrigeration equipment, in order to perform appropriate operation according to the load such as cooling water temperature, the compressor has a bypass that bypasses a part of the gas that is being compressed to the suction side. Because it is equipped with a capacity control mechanism such as an inverter evening type that changes the number of compressions per unit time by changing the rotation speed using inverter control, it is not possible to simply control the suction superheat to a constant value. During partial load operation, which is considered to have a low capacity,
The following problem occurs.

In other words, during partial load operation, as the capacity of the compressor decreases,
Since the flow rate of refrigerant sucked into the compressor, that is, the flow rate of refrigerant flowing to the evaporator per unit time, is lower than when it is at full load, electric expansion is used to maintain the same degree of suction superheat as when it is at full load. If the opening degree of the valve was controlled, the evaporator heat transfer area needed to generate the necessary superheat for the reduced refrigerant flow rate would be small, which would reduce the number of dry heat transfer tubes and reduce the evaporator heat transfer area. Liquid refrigerant tends to accumulate in the area.

Then, when the load such as the cooling water temperature reaches the set value in this state and the compressor operation is interrupted and restarted, the liquid refrigerant that has settled in the evaporator is sucked into the compressor. As a result, excessive liquid compression due to the liquid bag may cause mechanical damage to the compressor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a refrigeration system that can avoid liquid pack caused by restart by changing the suction superheat degree secured during partial load operation to a value larger than that during full load operation.

(Means for solving the problem) Therefore, a compressor (1), a condenser (3), an evaporator (5), and the evaporator (5) that perform capacity control in response to full load and partial load are provided. In a refrigeration system equipped with an electric expansion valve (4) that controls the degree of suction superheat to a set value based on the temperature difference detected at the entrance and exit of the It was decided to provide superheat degree changing means (7) to ensure a large suction superheat degree.

In this case, as a preferable example of the superheat degree changing means (7), the changing means (7) may be set to the evaporator (5) during partial load operation.
The temperature difference correcting means corrects the temperature difference detected at the entrance/exit to a value smaller than the actual value.

Furthermore, when using the superheat degree changing means (7) by correcting the detected temperature difference, it is also effective to provide a continuous changing means that continuously changes the correction value in accordance with the continuously changing partial load factor. .

(Function) At partial load, where the flow rate of refrigerant passing through the evaporator (5) is lower than that at full load, a large degree of suction superheat commensurate with the decrease in flow rate is ensured, so that the liquid refrigerant in the evaporator (5) This reduces the amount of stagnation in the compressor (
1) The situation where a large amount of liquid refrigerant is inhaled can be avoided.

In this case, by means of correcting the detected temperature difference to a smaller value, it is possible to increase the degree of superheating at partial load without changing the set value of the suction superheating degree itself, resulting in improved controllability. It will be done.

In addition, when changing the correction value continuously, the degree of superheat to be actually adjusted can be set appropriately according to the continuously changing partial load factor, allowing fine-grained control that matches the load. .

(Example) The one shown in Fig. 2 includes a condenser (3) provided with a cooling water pipe (30) on the discharge side of the compressor (1), a valve drive motor (
40), and a cold water or brine outlet pipe (50) used as a cold source for air conditioning, etc.
A so-called refrigeration cycle is constructed by sequentially connecting the evaporators (5) provided with the evaporators (5).

The compressor (1) is equipped with a motor (11) driven by an imperter control circuit (10), and adjusts the rotation speed by changing the frequency of the power supply to the motor (11), from 100% to 0%.
This allows the operating capacity to be changed over a wide range of nearby areas.

The electric expansion valve (4) is configured so that the difference in temperature detected by an inlet temperature sensor (T1) and an outlet temperature sensor (T2) installed at the inlet and outlet of the evaporator (6) reaches a preset value of the suction superheat degree. The opening degree is adjusted via the regulator (6) so that the openings are equal. That is, the outlet temperature sensor (T
The temperature difference (T2 - TI) obtained by subtracting the detected value of the inlet temperature sensor (T1) from the detected value of 2) is the actual degree of superheating. If this is smaller than the set value, the degree of superheating is insufficient and the evaporator (5) Since the refrigerant on the outlet side becomes too wet, as shown in Figure 1, switch the changeover switch (60) of the regulator (6) to the close side and operate the expansion valve (4) to the close side. The first coil (4a) of the valve drive motor (40) is energized to reduce the opening degree of the expansion valve (4), thereby reducing the amount of refrigerant passing through the evaporator (5) and increasing the degree of superheat. On the other hand, if the temperature difference (T2-TI) is larger than the set value, the degree of superheating is too high than necessary, and the changeover switch (6o) is turned to the open side to open the expansion valve (4). The second coil (4b) is energized to increase the opening degree of the expansion valve (4), thereby reducing the degree of superheating.

In Fig. 1, (S) is a contact that is turned on during operation and turned off when stopped, and when the contact (S) is turned on during operation, the relay (Y) is energized and its break setting ( Y
-b) is opened, the forced excitation line of the first coil (4a) is opened, and the valve opening degree is adjusted exclusively by the regulator (6). On the other hand, when the engine stops, the break contact (Y-b) is closed, the first coil (4a) is forcibly excited, and the expansion valve (4) is fully closed. When the operation is resumed, the refrigerant that has accumulated on the downstream side of the fully closed expansion valve (4), that is, in the evaporator (5), is pumped down to the compressor (1), and the refrigerant is pumped down to the compressor (1), and the refrigerant is pumped down to the compressor (1). is stored in the condenser (3) etc. on the upstream side. The end of this pump-down operation is detected, for example, when the pressure of the intake gas drops below a certain value.

(PD) is a contact that turns on when the pump down operation ends, and when the contact (PD) turns on, the relay (X)
is energized to close its make contact (X-a), and the second
Establish an excitation line for the coil (4b). At the same time, the second
In the figure, a solenoid valve (SV
), and then operation follows the normal refrigeration cycle.

With the above configuration, as shown in Figure 1, during partial load operation,
Superheat degree changing means (7) is provided to ensure a suction superheat degree greater than the suction superheat degree during full-load operation. This means of change (
7) comprises a temperature difference correction means for correcting the temperature difference detected at the entrance and exit of the evaporator (5) to a value smaller than the actual value during partial load. That is, at partial load,
The first switch (A) is turned off, the second switch (B) is turned on, and the pseudo resistance (R) is applied to the inlet temperature sensor (T1).
) in series and adding the pseudo resistance value to the resistance value corresponding to the detected inlet temperature of the sensor (T1), the regulator (6) is made to appear larger than the actual detected inlet temperature.
As a result, the difference (T2-TI) between the outlet temperature and the inlet temperature detected by the outlet temperature sensor (T2) is corrected to be smaller than the actual value.

The first and second switches (A) and (B) are in a relationship such that when one is on, the other is off, and the operation of the switch is controlled by the inverter control circuit (10) that determines the operating capacity, that is, the load factor. This is done in conjunction with the Shukeyaki number setting value. By the way, when the capacity is 100% to 50%, it is considered full load operation, and A is turned on and b is turned off.When the capacity is 49% or less, it is considered to be partial load operation, and conversely, A is turned off and B is turned on. There is.

Incidentally, the pseudo resistance (R) is constituted by a variable resistor, so that the correction value can be changed. In addition, in order to correct the detected inlet and outlet temperature difference of the evaporator (5) to be smaller than the actual value, in addition to inserting this pseudo-resistance in series with the inlet temperature sensor (T1), at partial load, the outlet temperature sensor(
The same effect can be obtained by inserting a resistor in parallel with T2) to make it lower than the actual detected outlet temperature.

As a result of the above, a larger degree of suction superheat can be secured during partial load operation than during full load operation, so even if the flow rate of the refrigerant flowing through the evaporator (5) decreases, the expansion valve ( 4) is adjusted, the refrigerant is sufficiently evaporated in the evaporator (5), and the amount of liquid refrigerant that remains in the evaporator (5) can be reduced. Therefore,
After the operation of the compressor (1) is interrupted, the amount of liquid back up when the compressor (1) is restarted can be reduced, and an excessive increase in pressure due to liquid compression can be prevented.

In addition, in order to make the suction superheat degree at partial load larger than the full load, the value on the detection side is made to appear smaller than the actual value, so the suction superheat degree setting is set by one regulator (6). The value itself can be determined to be the same regardless of whether the load is full or partial, which has the advantage of improving control efficiency.

"By the way, in the above embodiment, the pseudo resistance (R) is numbered 2', but as shown in Fig. 3, a plurality of pseudo resistances are inserted, and as shown in Fig. 4, the range of change in operating capacity is changed. is divided into multiple regions (■, ■, ■, ■), and as the operating region decreases, the pseudo resistance (Rl.R2, R3) is
The number of insertions may be increased to increase the composite pseudo resistance value, and the degree of suction superheat may be increased to perform more fine-grained correction. In this case as well, each pair of switches (AI, Bl) (A2, B2) (
A3.83) enables operation in conjunction with the frequency setting value from the inverter control circuit (10) that determines the operating capacity.

Furthermore, as shown in FIG. 5, an inverter control circuit (10
), which is connected in series to the inlet temperature sensor (T1) either directly or via a frequency-to-resistance converter (16) as shown. However, as shown in FIG. 6, the insertion pseudo resistance value may be continuously increased due to the continuously changing operating capacity decrease, and may be steplessly corrected in accordance with the variously changing partial load factors. In this case, even more precise control can be achieved. still,
As the compressor (1) in the above description, various types are used, such as a rotary vane type, a reciprocating type, a scroll type, and a screw type.

Furthermore, in the embodiment described above, the inperter control circuit (1
Although the capacity control mechanism according to No. 0) was used, it goes without saying that it is also applicable to other mechanical capacity control mechanisms such as a bypass method.

(Effects of the Invention) As described above, according to the present invention, when the flow rate of refrigerant passing through the evaporator (5) is reduced compared to the time of full load, a large suction superheat degree commensurate with the decrease in flow rate is ensured. , it is possible to reduce the accumulation of liquid refrigerant in the evaporator (5), and it is possible to avoid a situation where a large amount of liquid refrigerant is sucked into the compressor (1) when restarting after the operation is interrupted, and it is possible to prevent the liquid refrigerant from rising into the liquid bag. Mechanical damage accidents can be prevented.

In this case, if the suction superheat degree at partial load is made larger than that at full load by correcting the temperature difference detected at the entrance and exit of the evaporator (5) to a small value, the set value of the suction superheat degree itself becomes It is possible to set the value to one value regardless of whether it is a load or a partial load, and it is also possible to improve controllability.

In addition, when changing the degree of superheating by correcting the detected temperature difference, and when changing the corrected value continuously according to the partial load rate, the actual The degree of superheating can be set appropriately, allowing for fine-grained control that matches the load.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment of the refrigeration system according to the present invention, FIG. 2 is a refrigerant piping system diagram, and FIG. 3 is an electric circuit diagram of main parts of the second embodiment. FIG. 4 is a diagram showing changes in correction values to explain the control, FIG. 5 is an electric circuit diagram in case of stepless control, and FIG. 6 is a diagram showing changes in correction values to explain the control. (-1)...Compressor (3)...Condenser (4)...Electric expansion valve...Evaporator...Superheat degree changing means Fig. 5 Fig. 1 Fig. 2 4 Electric large layer ki M transformation t('/c) Fukuichi round fact number tl! ．． −,l,)

Claims (1)

[Claims] 1) A compressor (1) that performs capacity control in response to full load and partial load, a condenser (3), an evaporator (5), and an inlet/outlet of the evaporator (5). In a refrigeration system equipped with an electric expansion valve (4) that controls the degree of suction superheat to a set value based on the detected temperature difference, the degree of suction superheat during partial load operation is greater than the degree of suction superheat during full load operation. A refrigeration system characterized by comprising a superheat degree changing means (7) for ensuring a certain temperature. 2) Claim 1, wherein the superheat degree changing means (7) is a detected temperature difference correction means for correcting the temperature difference detected at the entrance and exit of the evaporator (5) to a value smaller than the actual value during partial load operation. Refrigeration equipment as described. 3) The refrigeration system according to claim 2, further comprising continuous changing means for continuously changing the correction value in accordance with a continuously changing partial load factor.