JP4989507B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus, and particularly to a low-temperature refrigeration apparatus used in a refrigeration warehouse.

  As a refrigeration apparatus having a main refrigerant circuit in which a compressor is arranged in two stages, a low stage and a high stage, a subcool circuit having an intermediate expansion valve (external equality, capillary, etc.) and an intermediate heat exchanger is provided, Some refrigerants exchange heat with the main expansion valve and introduce refrigerant from the subcool circuit into the high-stage suction side of the compressor (see, for example, Patent Document 1).

Japanese Patent No. 3599996

In the refrigeration apparatus as described above, if the high-stage suction side superheat degree is small, liquid back is easy, and if the superheat degree is large, the high-stage discharge temperature becomes abnormally high. For this reason, conventionally, it has been necessary to adjust the intermediate expansion valve (also referred to as an intermediate pressure expansion valve) in accordance with the local operating conditions.
Moreover, since it is controlled by the high-stage suction superheat degree, the high-stage discharge temperature changes depending on the operating conditions, and the amount of refrigerant bypassed to the intermediate circuit changes. There is also a problem that power consumption increases as the amount of bypass refrigerant increases.

The present invention has been made to solve the above-described problems, and a first object thereof is to eliminate the trouble of adjusting the intermediate expansion valve in accordance with the on-site operating conditions. In addition, another object of the present invention is to provide a refrigeration apparatus with improved quality by preventing liquid back on the high suction side and preventing abnormal discharge temperature.
Another object of the present invention is to save energy by setting the discharge gas temperature on the high stage side to an optimum value so that the amount of bypass refrigerant is the most efficient under any operating condition.

The refrigeration apparatus of the present invention includes a main refrigerant circuit in which a plurality of compressors arranged in series in multiple stages, a condenser, a main expansion valve, and an evaporator are connected in order, the condenser, and the main expansion valve. And a bypass refrigerant circuit connected between the plurality of compressors via an intermediate expansion valve and an electronic device whose opening degree is linearly controllable. A controller that controls the opening of the electronic expansion valve in accordance with the temperature information of the refrigerant in the main refrigerant circuit; and a discharge temperature of a final stage compressor among the plurality of compressors. 1 temperature detector, the control device predicts an expected temperature Tt after t seconds from the detected temperature of the first temperature detector, and according to the difference between the expected temperature Tt and a predetermined target temperature Tp Thus, the opening degree of the electronic expansion valve is controlled.

According to the refrigeration apparatus of the present invention, since the intermediate expansion valve is a linearly controllable electronic expansion valve, the opening degree of the electronic expansion valve is changed to the temperature information of the refrigerant in operation or the temperature information and the pressure information. Since it can be controlled linearly, the adjustment that was performed according to the operating conditions in each place is not required, and the workload during installation work can be reduced.
Further, since the opening degree of the intermediate expansion valve can be controlled linearly, it is possible to prevent the occurrence of liquid back on the high-stage suction side and abnormal discharge temperature.
Further, by setting the discharge gas temperature on the high stage side to an optimum value, the most efficient bypass refrigerant amount can be achieved under any operating condition, and energy saving can be achieved.

Embodiment 1 FIG.
FIG. 1 is a refrigerant circuit diagram of a refrigeration apparatus according to Embodiment 1 of the present invention. This refrigerant circuit includes a plurality of compressors (two-stage configuration of a first compressor 1 and a second compressor 2 here) arranged in series in multiple stages, a condenser 3, a liquid receiver 4, refrigerant / refrigerant heat. It has a main refrigerant circuit in which an exchanger (intermediate heat exchanger) 5, a main expansion valve 6, an evaporator 7, and a gas-liquid separator 8 are connected in order. Here, the compressor 1 is also referred to as a low stage compressor or a first stage compressor, and the compressor 2 is also referred to as a high stage compressor or a second stage compressor .

  Then, between the condenser 3 and the main expansion valve 6 (in this example, there are the liquid receiver 4 and the refrigerant / refrigerant heat exchanger 5), an electronic that can be linearly controlled as an intermediate expansion valve. A bypass refrigerant circuit (subcool circuit) 10 is connected to the main refrigerant circuit between the discharge side of the compressor 1 and the suction side of the compressor 2 via the expansion valve 9.

Furthermore, the refrigerant circuit includes a first temperature detector 11 that detects the discharge temperature of the compressor 2, a second temperature detector 12 that detects the suction temperature of the compressor 2, and a third temperature that detects the discharge temperature of the compressor 1. The temperature detector 14, the fourth temperature detector 16 that detects the suction temperature of the compressor 1, the first pressure detector 13 that detects the suction pressure of the compressor 2, and the second pressure detection that detects the suction pressure of the compressor 1 The control device 20 that receives temperature information and pressure information from the detector 15 and the detectors and controls the opening degree of the electronic control valve 9 based on the information is provided.
In FIG. 1, the temperature detectors and pressure detectors used in various control modes described below are all provided in advance, but specific temperature detectors and pressure detectors are used according to the respective control modes. Therefore, only a necessary temperature detector or pressure detector may be provided according to the control mode to be applied.

  The refrigeration apparatus having the refrigerant circuit performs the following basic operation. That is, the refrigerant is compressed by the compressors 1 and 2 and then enters the condenser 3 to be condensed. Thereafter, the refrigerant passes through the liquid receiver 4 and the refrigerant / refrigerant heat exchanger 5 and is depressurized by the main expansion valve 6. Thereafter, the refrigerant returns to the compressor 1 through the gas-liquid separator 8. At this time, the state of the refrigerant flowing through the main refrigerant circuit is detected by the temperature detectors 11, 12, 14, 16 and the pressure detectors 13, 15 described above.

  Although several control modes of the electronic control valve 9 by the control device 20 are conceivable, the discharge temperature is based on the temperature information of the first temperature detector 11 that detects the discharge temperature ((A) part temperature) of the compressor 2. Controlling the electronic expansion valve 9 so that is within a predetermined range is one preferred control mode. Hereinafter, the control mode will be described based on the flowchart of FIG.

When the operation of the refrigeration apparatus starts (S1), the control device 20 causes the first temperature detector 11 to detect temperature at, for example, a constant interval and receives the temperature information T4 (S2). Subsequently, an expected temperature Tt of (a) part after t seconds is predicted based on the temperature information T4 (S3). When the absolute value of the difference between the predicted temperature Tt and the predetermined target temperature Tp is within a predetermined value α (about 1 to 3 ° C.), the opening degree of the electronic expansion valve 9 is maintained (S5). ) When the difference between the predicted temperature Tt and the target temperature Tp is less than −α, the opening degree of the electronic expansion valve 9 is decreased (S6), and the difference between the predicted temperature Tt and the target temperature Tp is greater than + α. In this case, the opening degree of the electronic expansion valve 9 is increased (S7).
In the above, by predicting the temperature information T4 (expected temperature Tt) after t seconds, the convergence to the target value can be improved. For example, when the opening degree of the electronic expansion valve is controlled by the current temperature information T4 and the target value Tp, the temperature change gradient is ignored. On the other hand, by predicting the temperature information T4 after t seconds, an element of the temperature change gradient can be taken into the control, and the convergence to the target value can be improved. “T seconds” is, for example, 15 to 30 seconds. Of course, you may control the opening degree of an electronic expansion valve with the present detection temperature.

In the above control, the target temperature Tp is about 100 to 115 ° C. It is desirable to make Tp as high as possible. This is because if the Tp is set too low, the amount of refrigerant flowing through the electronic expansion valve 9 increases, the work amount of the compressor 2 increases, and the efficiency deteriorates. However, if the value is set too high, deterioration of the refrigerating machine oil in the compressor is promoted and the reliability of the refrigerant circuit is lowered. Therefore, Tp is preferably set to about 100 to 115 ° C.
The value α is about 1 to 3 ° C. This is because if α is too small, the electronic expansion valve 9 hunts and the stability of the refrigerant circuit deteriorates. On the other hand, if α is too large, the control is stopped before the temperature reaches the target temperature, and it is difficult to reach the target temperature.
Further, when the superheat degree (SH) on the suction side of the compressor 2 which is a high-stage compressor becomes 0 to 3 k or less, the opening degree of the electronic expansion valve 9 is reduced regardless of the target temperature Tp. The liquid back to the compressor 2 is prevented. Conversely, when Tt exceeds 120 ° C. to 130 ° C., the expansion valve opening can be temporarily increased in order to prevent deterioration of the oil.

3 is a Mollier diagram showing a refrigeration cycle of the refrigeration apparatus according to Embodiment 1. FIG. Note that (A) to (F) in FIG. 3 correspond to the positions (A) to (F) in FIG. Further, T _{1 to} T ₄ in FIG. 3 represent temperatures at the positions (D), (A), (C), and (A) in FIG. As shown in FIG. 3, in the first embodiment, the conditions used in the actual market and customer are that the refrigerant condensation temperature CT is about 45 ° C. and the refrigerant evaporation temperature ET is about −60 ° C. It is thought that there are many. In the figure, the portion indicated by the wavy line is that of the conventional device, and is often set so that the temperature of T4 is low, so the amount of bypass refrigerant needs to be increased. In particular, since the intermediate expansion valve is set at a high evaporation temperature that requires the highest flow rate, it is often overflowed at a low evaporation temperature.

According to the refrigeration apparatus of Embodiment 1 controlled as described above, the opening degree of the electronic expansion valve 9 that is an intermediate expansion valve is set according to the temperature information of the refrigerant in operation, or the temperature information and pressure information of the refrigerant. Therefore, it is not necessary to adjust the intermediate expansion valve, which has been performed in advance according to the local operating conditions.
Moreover, since the opening degree of the electronic expansion valve 9 can be controlled linearly, the occurrence of abnormal discharge temperature can be prevented. Furthermore, if the suction side superheat degree of the compressor 2 is monitored by, for example, the suction pressure and the suction gas temperature, and the opening degree of the electronic expansion valve 9 can be adjusted according to the superheat degree, the refrigerant is supplied to the compressor 2. Liquid back can also be prevented.
In addition, by setting the discharge gas temperature on the high stage side to the optimum value, the most efficient bypass refrigerant amount can be achieved under any operating condition, and energy saving can be achieved.

  FIG. 4 is an explanatory diagram of the effect of the refrigeration apparatus according to Embodiment 1. As shown in FIG. 4, in the case of the refrigeration apparatus of Embodiment 1 by the above control, an efficiency increase of 20 to 40% was achieved at a low evaporation temperature compared to the conventional refrigeration apparatus. This is because the degree of opening of the electronic expansion valve 9, which is an intermediate expansion valve, is linearly controlled according to the temperature information of the refrigerant in operation or according to the temperature information and pressure information of the refrigerant. This is because an excessive flow of the bypass refrigerant amount is prevented. In particular, in the conventional machine, since the opening degree of the electronic expansion valve is adjusted in the high evaporation temperature range, the amount of bypass refrigerant increases in the low temperature range, leading to a reduction in efficiency.

The control of the electronic expansion valve 9 may be performed as shown in the following (a) and (b) instead of the above control based on the discharge temperature of the compressor 2.
(A) The opening degree of the electronic expansion valve 9 is controlled so that the degree of superheat that is the difference between the saturation temperature of the detected pressure of the first pressure detector 13 and the detected temperature of the second temperature detector 12 becomes constant. According to this, since the gas refrigerant with a constant superheat degree is always sucked into the second compressor 2, it is possible to prevent the compressor from sucking the liquid refrigerant.
(B) The opening degree of the electronic expansion valve 9 is controlled so that the degree of superheat, which is the difference between the saturation temperature of the detected pressure of the second pressure detector 15 and the detected temperature of the fourth temperature detector 16, becomes constant. According to this, like (a), while being able to prevent the liquid return to the 2nd compressor 2, the liquid return to the 1st compressor 1 can also be prevented.

Embodiment 2. FIG.
FIG. 5 is a refrigerant circuit diagram of the refrigeration apparatus according to Embodiment 2 of the present invention. 5, the same reference numerals as those in FIG. 1 denote the same or equivalent components. The difference in circuit configuration from FIG. 1 in FIG. 5 is that the bypass refrigerant circuit 10 is branched into the first refrigerant circuit 10a and the second refrigerant circuit 10b in the middle of the flow path of the refrigerant / refrigerant heat exchanger 5. It is a point. That is, the first refrigerant circuit 10a branches from the middle of the bypass side heat exchange flow path of the refrigerant / refrigerant heat exchanger 5 and is connected between the compressors 1 and 2 via the first electromagnetic valve (open / close valve) 21. The second refrigerant circuit 10b is connected between the compressors 1 and 2 via the second electromagnetic valve (open / close valve) 22 through the end of the bypass side heat exchange flow path of the refrigerant / refrigerant heat exchanger 5. Yes.
The same effect can be obtained by using the two separate refrigerant / refrigerant heat exchangers instead of branching the heat exchange flow path of the refrigerant / refrigerant heat exchanger 5 in the middle. It is done.

Also in the refrigeration apparatus of FIG. 5, the control device 20 controls the electronic expansion valve 9 as described in the first embodiment.
In the second embodiment, in addition to that, the control device 20 performs control so as to switch between opening and closing of the first electromagnetic valve 21 and the second electromagnetic valve 22 in accordance with the temperature detected by the first temperature detector 11. That is, under conditions where the temperature detected by the first temperature detector 11 is likely to rise, only the first solenoid valve 21 is opened, and the amount of heat exchange of the refrigerant in the main refrigerant circuit is reduced. On the other hand, in the condition where the temperature detected by the first temperature detector 11 tends to decrease, only the second electromagnetic valve 22 is opened, and the amount of heat exchange of the refrigerant in the main refrigerant circuit is increased.
The condition that the detected temperature of the first temperature detector 11 is likely to rise is when the pressure difference between the high pressure and the low pressure is large, for example, when the evaporation temperature is set low in summer. The detected temperature of the first temperature detector 11 is also used when the degree of superheat of the expansion valve constituting the expansion device 6 is set large and the refrigerant temperature sucked into the first compressor 1 is very high. Is easy to go up.
On the other hand, the condition that the temperature detected by the first temperature detector 11 is likely to decrease is when the pressure difference between the high pressure and the low pressure is small, for example, when the evaporation temperature is set high in winter. Further, even when the refrigerant temperature sucked into the first compressor 1 is very low, the temperature detected by the first temperature detector 11 tends to decrease.
Even if the control of the electronic expansion valve 9 is not sufficient by performing the opening / closing control of the first electromagnetic valve 21 and the second electromagnetic valve 22 in addition to the opening degree control of the electronic expansion valve 9, to the compressor 2. Prevention of liquid back, increase in the capacity of the refrigeration apparatus, and reduction in power consumption.

Embodiment 3 FIG.
FIG. 6 is a refrigerant circuit diagram of the refrigeration apparatus according to Embodiment 3 of the present invention. 6, the same reference numerals as those in FIG. 1 denote the same or equivalent components. 6 is different from the circuit configuration of FIG. 1 in that the bypass refrigerant circuit 10 of FIG. 1 includes a first bypass refrigerant circuit 10A and a second bypass refrigerant circuit 10B. The first bypass refrigerant circuit 10A includes the first electronic expansion valve 9A, and may be regarded as a heat exchange portion removed from the bypass refrigerant circuit 10 of the first embodiment. On the other hand, the second bypass refrigerant circuit 10B can be regarded as a newly added bypass circuit separately from the bypass refrigerant circuit 10 of the first embodiment, and branches from the main refrigerant circuit on the inlet side of the refrigerant / refrigerant heat exchanger 5. The second electronic expansion valve 9B and the refrigerant / refrigerant heat exchanger 5 are connected to the input side of the compressor 1 via the bypass side heat exchange flow path.

Also in the refrigeration apparatus of FIG. 6, the control device 20 controls the electronic expansion valve 9A as described in the first embodiment.
In the third embodiment, in addition to that, the control device 20 controls the difference between the detected temperature of the fifth temperature detector 23 and the detected temperature of the sixth temperature detector 24 to be constant. Thereby, the subcool (SC) on the outlet side of the refrigerant / refrigerant heat exchanger 5 in the main refrigerant circuit becomes constant, and fluctuations in the refrigerating capacity can be reduced.
Further, since the refrigerant injection amount to the compressor 2 can be adjusted without being influenced by the heat exchange amount in the refrigerant / refrigerant heat exchanger 5, the stability of the discharge temperature of the compressor 2 can be achieved and the reliability can be improved.

Embodiment 4 FIG.
In each of the above embodiments, description has been made based on an example in which the compressor has a two-stage configuration. However, the present invention can also be applied to a case of a configuration of a multistage compressor having two or more stages. FIG. 7 is a refrigerant circuit diagram corresponding to FIG. 1 having a three-stage compressor. In addition, you may provide the part of the heat exchanger enclosed with the dotted line separately from another part. Further, the parts omitted in FIG. 7 may be regarded as the same configuration as in FIG.
In this case, in basic control, the opening degree of one electronic expansion valve 9 is determined based on the temperature detected by the first temperature detector 11, and the other electronic expansion valve 26 is detected by the third temperature detector 14. The opening degree is determined based on the temperature.
Further, in applied control, one electronic expansion valve 9 determines its opening degree so as to make the degree of superheat calculated from the detection values of the second temperature detector 12 and the first pressure detector 13 constant, The other electronic expansion valve 26 determines its opening degree so that the degree of superheat calculated from the detection values of the seventh temperature detector 27 and the third pressure detector 28 is constant.
By controlling the electronic expansion valves 9 and 26 as described above, the effects described in the first embodiment can be obtained even in the refrigeration apparatus having the three-stage compressor.

In each embodiment, natural refrigerants such as CO ₂ can be used in addition to HFC and HCFC refrigerants such as R22, R404A, and R410A.

2 is a refrigerant circuit diagram of the refrigeration apparatus according to Embodiment 1. FIG. 3 is a flowchart showing an example of control of the refrigeration apparatus according to Embodiment 1. The Mollier diagram of the refrigeration apparatus which concerns on Embodiment 1. FIG. Explanatory drawing of the effect of the freezing apparatus which concerns on Embodiment 1. FIG. FIG. 4 is a refrigerant circuit diagram of a refrigeration apparatus according to Embodiment 2. FIG. 6 is a refrigerant circuit diagram of a refrigeration apparatus according to Embodiment 3. FIG. 6 is a refrigerant circuit diagram of a refrigeration apparatus according to Embodiment 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st compressor, 2nd 2nd compressor, 3 condenser, 4 liquid receiver, 5 refrigerant | coolant / refrigerant heat exchanger (intermediate heat exchanger), 6 expansion apparatus, 7 evaporator, 8 gas-liquid separator , 9 Electronic expansion valve (intermediate expansion valve), 9A First electronic expansion valve, 9B Second electronic expansion valve, 10 Bypass refrigerant circuit (subcool circuit), 10A First bypass refrigerant circuit, 10B Second bypass refrigerant circuit, 11 DESCRIPTION OF SYMBOLS 1 temperature detector, 12 2nd temperature detector, 13 1st pressure detector, 14 3rd temperature detector, 15 2nd pressure detector, 16 4th temperature detector, 20 control apparatus, 21 1st solenoid valve, 22 2nd solenoid valve, 23 5th temperature detector, 24 6th temperature detector, 25 3rd compressor, 26 Electronic expansion valve, 27 7th temperature detector, 28 3rd pressure detector.

Claims (5)

A plurality of compressors arranged in series in multiple stages, a condenser, a main expansion valve, a main refrigerant circuit in which an evaporator is connected in order, and a branch from between the condenser and the main expansion valve, In a refrigeration apparatus comprising a bypass refrigerant circuit connected between the plurality of compressors via an expansion valve,
The intermediate expansion valve is an electronic expansion valve whose opening degree can be controlled linearly,
A control device that controls the opening degree of the electronic expansion valve in accordance with the temperature information of the refrigerant in the main refrigerant circuit, and a first temperature detector that detects the discharge temperature of the last stage compressor among the plurality of compressors And
The controller predicts an expected temperature Tt after t seconds from the temperature detected by the first temperature detector, and opens the electronic expansion valve according to a difference between the expected temperature Tt and a predetermined target temperature Tp. A refrigeration apparatus characterized by controlling the degree . 2. The refrigeration apparatus according to claim 1, wherein when the predicted temperature Tt exceeds 120 ° C. to 130 ° C., the opening degree of the electronic expansion valve is temporarily increased . When the superheat degree on the suction side of the final stage compressor becomes 0 to 3 k or less, the opening degree of the electronic expansion valve is reduced regardless of the target temperature Tp, and the liquid to the compressor is reduced. The refrigeration apparatus according to claim 1 or 2, wherein back-up is prevented . There are two flow paths, and one flow path is arranged between the branch portion of the bypass refrigerant circuit and the main expansion valve between the condenser and the main expansion valve, and the other flow path is the bypass refrigerant. It has a refrigerant / refrigerant heat exchanger that forms part of the circuit,
The bypass refrigerant circuit branches from the middle of the flow path of the refrigerant / refrigerant heat exchanger and is connected between the plurality of compressors via a first on-off valve; and the refrigerant / refrigerant heat A second refrigerant circuit connected between the plurality of compressors via a second on-off valve from a terminal portion of the flow path of the exchanger,
Said controller, in response to the detected temperature of the first temperature detector, any one of claims 1 to 3, wherein the controller controls to switch the opening and closing of the first on-off valve and the second on-off valve The refrigeration apparatus according to item . A refrigerant / refrigerant heat exchanger disposed between the branch of the bypass refrigerant circuit between the condenser and the main expansion valve and the main expansion valve, the first flow path having two flow paths;
Branching on the inlet side of the refrigerant / refrigerant heat exchanger, and suctioning the first stage compressor of the plurality of compressors through the second electronic expansion valve and the other flow path of the refrigerant / refrigerant heat exchanger A second bypass refrigerant circuit connected to the side;
A fifth temperature detector and a sixth temperature detector provided at the inlet and outlet of the refrigerant / refrigerant heat exchanger of the main refrigerant circuit,
The control device controls the opening degree of the second electronic expansion valve so that a difference between a temperature detected by the fifth temperature detector and a temperature detected by the sixth temperature detector is constant. The refrigeration apparatus according to any one of claims 1 to 3 .

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