EP4130615A1

EP4130615A1 - Outdoor unit and refrigeration cycle device

Info

Publication number: EP4130615A1
Application number: EP20927414.1A
Authority: EP
Inventors: Motoshi HAYASAKA; Yusuke Arii; Tomotaka Ishikawa
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2023-02-08
Also published as: EP4130615A4; JPWO2021192292A1; JP7282258B2; WO2021192292A1

Abstract

A refrigeration cycle apparatus (1) includes a load device (3) and an outdoor unit (2). The outdoor unit (2) includes a compressor (10), a condenser (20), a heat exchanger (30), a second expansion valve (40), the second expansion valve (40), an injection flow path (101) configured to cause refrigerant to flow from a pipe (81) between an outlet of the condenser (20) and an inlet of a first passage (H1) to the compressor (10), a controller (100), and a notification device (150). The injection flow path (101) is provided with a first refrigerant flow path (91 to 94), a second refrigerant flow path (96), a receiver (73), a third expansion valve (71), and a flow rate control valve (72). When a supercritical state is reached where a discharge pressure of the compressor (10) exceeds a critical pressure of the refrigerant, the controller (100) determines whether or not the refrigerant is insufficient, based on a degree of opening of the flow rate control valve (72).

Description

TECHNICAL FIELD

The present disclosure relates to an outdoor unit and a refrigeration cycle apparatus.

BACKGROUND ART

Japanese Patent Laying-Open No. 2014-119221 (PTL 1) discloses a refrigeration apparatus including a circulation flow path (a main refrigerant circuit) in which refrigerant circulates through a compressor, a condenser, an expansion valve, and an evaporator, and an injection flow path branching from the circulation flow path. In this refrigeration apparatus, the discharge temperature of the compressor can be decreased by merging a portion of the refrigerant flowing from the condenser toward the expansion valve with the intermediate pressure refrigerant in the compressor using the injection flow path. Further, in this refrigeration apparatus, a receiver is provided midway on the injection flow path, and the amount of the refrigerant to be stored in the receiver can be adjusted by an expansion valve of an outdoor unit.
Furthermore, this refrigeration apparatus includes an economizer (a heat exchanger) configured to exchange heat between the refrigerant flowing through the circulation flow path from the condenser toward the expansion valve and the refrigerant flowing through the injection flow path. Since the refrigerant flowing from the condenser toward the expansion valve is thereby cooled by the refrigerant flowing through the injection flow path, subcooling is ensured.

CITATION LIST

PATENT LITERATURE

PTL 1: Japanese Patent Laying-Open No. 2014-119221

SUMMARY OF INVENTION

TECHNICAL PROBLEM

Some refrigeration cycle apparatuses including the heat exchanger (economizer) described above and an injection flow path provided with a receiver as described above include a flow rate control valve which adjusts the amount of refrigerant gas and the amount of refrigerant liquid to be supplied from the receiver to the economizer.
In the refrigeration cycle apparatus including the flow rate control valve described above, the amount of the refrigerant flowing from the injection flow path to the circulation flow path can be adjusted by adjusting the degree of opening of the flow rate control valve. Further, in the refrigeration cycle apparatus including the flow rate control valve described above, when the heat exchanger described above has a low temperature efficiency (a small heat exchange amount) in spite of an increased degree of opening of the flow rate control valve, it can be determined that the refrigerant filled in the entire refrigerant circuit including the circulation flow path and the injection flow path is insufficient.
However, when refrigerant that can reach a supercritical state is used, the refrigeration cycle apparatus may be operated with the refrigerant being in the supercritical state. When the refrigeration cycle apparatus is operated with the refrigerant being in the supercritical state, the relation between a saturation temperature and an outdoor air temperature changes, and thus it is difficult to determine whether or not the refrigerant is insufficient using the temperature efficiency of the heat exchanger described above.
The present disclosure has been made solve the aforementioned problem, and an object thereof is to allow, in a refrigeration cycle apparatus using refrigerant that can reach a supercritical state, determination of whether or not the refrigerant in a refrigerant circuit is insufficient, even under an operation condition in the supercritical state.

SOLUTION TO PROBLEM

An outdoor unit according to the present disclosure is an outdoor unit of a refrigeration cycle apparatus, the outdoor unit being connectable to a load device including a first expansion valve and an evaporator. The outdoor unit includes: a compressor having a suction port, a discharge port, and an intermediate pressure port; a condenser; a heat exchanger having a first passage and a second passage and configured to exchange heat between refrigerant flowing in the first passage and the refrigerant flowing in the second passage; and a second expansion valve. A flow path from the compressor to the second expansion valve via the condenser and the first passage of the heat exchanger forms, together with the load device, a circulation flow path through which the refrigerant circulates. The outdoor unit further includes an injection flow path configured to cause the refrigerant to flow from a branching portion to the compressor, the branching portion being between an outlet of the condenser and an inlet of the first passage in the circulation flow path. The injection flow path is provided with: a first refrigerant flow path configured to cause the refrigerant to flow from the branching portion to an inlet of the second passage; a second refrigerant flow path configured to cause the refrigerant to flow from an outlet of the second passage to the suction port or the intermediate pressure port of the compressor; a receiver disposed on the first refrigerant flow path; a third expansion valve disposed at a portion between the branching portion and an inlet of the receiver in the first refrigerant flow path; and a flow rate control valve disposed at a portion between an outlet of the receiver and the inlet of the second passage in the first refrigerant flow path. The outdoor unit further includes: a controller configured to control the compressor, the second expansion valve, the third expansion valve, and the flow rate control valve; and a notification device configured to notify a user of information from the controller. When a supercritical state is reached where a discharge pressure of the compressor exceeds a critical pressure of the refrigerant, the controller determines whether or not the refrigerant included in the circulation flow path and the injection flow path is insufficient, based on a degree of opening of the flow rate control valve.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, it is possible to determine, in a refrigeration cycle apparatus using refrigerant that can reach a supercritical state, whether or not the refrigerant in a refrigerant circuit is insufficient, even under an operation condition in the supercritical state.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is an overall configuration diagram of a refrigeration cycle apparatus.
Fig. 2 is a diagram showing various sensors and a controller disposed in a refrigeration cycle apparatus 1.
Fig. 3 is a Mollier diagram schematically showing an aspect of change in refrigerant in a normal state.
Fig. 4 is a Mollier diagram schematically showing an aspect of change in the refrigerant in a supercritical state.
Fig. 5 is a flowchart showing an example of a processing procedure when the controller performs refrigerant amount adjustment and refrigerant shortage detection.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Although a plurality of embodiments will be described below, it is originally intended from the time of filing the present application to combine features described in the embodiments as appropriate. It should be noted that identical or corresponding parts in the drawings will be designated by the same reference characters, and the description thereof will not be repeated.

(Configuration of Refrigeration Cycle Apparatus)

Fig. 1 is an overall configuration diagram of a refrigeration cycle apparatus according to an embodiment. It should be noted that Fig. 1 functionally shows the connection relation and the arrangement configuration of devices in the refrigeration cycle apparatus, and does not necessarily show an arrangement in a physical space.
Referring to Fig. 1, a refrigeration cycle apparatus 1 includes an outdoor unit 2, a load device 3, and extension pipes 84 and 88.
Outdoor unit 2 is an outdoor unit of refrigeration cycle apparatus 1, the outdoor unit being connectable to load device 3. Outdoor unit 2 includes a compressor 10 having a suction port G1, a discharge port G2, and an intermediate pressure port G3, a condenser 20, a fan 22, a heat exchanger (economizer) 30, a second expansion valve 40, and pipes 80 to 83 and 89. Heat exchanger 30 has a first passage H1 and a second passage H2, and is configured to exchange heat between refrigerant flowing in first passage H1 and the refrigerant flowing in second passage H2.
Load device 3 includes a first expansion valve 50, an evaporator 60, and pipes 85, 86, and 87. Evaporator 60 exchanges heat between air and the refrigerant. In refrigeration cycle apparatus 1, evaporator 60 evaporates the refrigerant by absorbing heat from the air in a space to be cooled. First expansion valve 50 is an electronic expansion valve which can decompress the refrigerant. It should be noted that first expansion valve 50 may be, for example, a temperature expansion valve controlled independently of outdoor unit 2.
Compressor 10 compresses the refrigerant suctioned from pipe 89 and pipe 96, and discharges the compressed refrigerant to pipe 80. Compressor 10 can arbitrarily change a drive frequency by inverter control. Further, compressor 10 is provided with intermediate pressure port G3, and allows the refrigerant from intermediate pressure port G3 to flow into an intermediate portion of a compression process. Compressor 10 is configured to adjust a rotation speed according to a control signal from a controller 100 (see Fig. 2). By adjusting the rotation speed of compressor 10, a circulation amount of the refrigerant is adjusted, and the capability of refrigeration cycle apparatus 1 can be adjusted. As compressor 10, various types of compressors can be adopted, and for example, a compressor of scroll type, rotary type, screw type, or the like can be adopted.
Condenser 20 is configured such that the high-temperature, high-pressure gas refrigerant discharged from compressor 10 performs heat exchange with outside air (heat dissipation). By this heat exchange, the refrigerant is condensed and transforms into a liquid phase. The refrigerant discharged from compressor 10 to pipe 80 is condensed and liquefied in condenser 20, and flows into pipe 81. Fan 22 for blowing the outside air is attached to condenser 20 in order to increase the efficiency of heat exchange. Fan 22 supplies condenser 20 with the outside air with which the refrigerant performs heat exchange in condenser 20. By adjusting a rotation speed of fan 22, a refrigerant pressure on a discharge side of compressor 10 (a high pressure-side pressure) can be adjusted. Second expansion valve 40 is an electronic expansion valve which can decompress the refrigerant flowing out from condenser 20.
A flow path from compressor 10 to second expansion valve 40 via condenser 20 and first passage H1 of heat exchanger 30 forms, together with a flow path on which first expansion valve 50 and evaporator 60 of load device 3 are disposed, a circulation flow path through which the refrigerant circulates. Hereinafter, this circulation flow path will also be referred to as a "main refrigerant circuit" of a refrigeration cycle.
Outdoor unit 2 further includes an "injection flow path 101" which branches from the main refrigerant circuit and delivers the refrigerant to compressor 10 via second passage H2. Injection flow path 101 includes a "first refrigerant flow path" (pipes 91 to 94) configured to cause the refrigerant to flow from pipe 81, which is a high pressure portion of the main refrigerant circuit, to an inlet of second passage H2, and a "second refrigerant flow path" (pipe 96) configured to cause the refrigerant to flow from an outlet of second passage H2 to intermediate pressure port G3 of compressor 10.
An on-off valve 75 is disposed on the second refrigerant flow path (pipe 96) of injection flow path 101. On-off valve 75 can adjust whether or not to supply the refrigerant to intermediate pressure port G3 of compressor 10. It should be noted that, although not shown in Fig. 1, there may be further provided a flow path switching device disposed on the second refrigerant flow path (pipe 96) and configured to select one of suction port G1 and intermediate pressure port G3 as a destination of the refrigerant flowing out from the outlet of second passage H2.
A receiver 73 configured to store the refrigerant and a third expansion valve 71 are disposed on the first refrigerant flow path of injection flow path 101. An inlet of receiver 73 is connected to pipe 81 (that is, a portion between an outlet of condenser 20 and an inlet of first passage H1 in the circulation flow path) using pipes 91 and 92. Third expansion valve 71 is disposed at an intermediate portion between pipes 91 and 92.
A flow rate control valve 72 and a degassing passage 95 are further disposed on the first refrigerant flow path of injection flow path 101. Flow rate control valve 72 is an expansion valve disposed between pipe 93 at an outlet of receiver 73 and pipe 94 leading to second passage H2. Degassing passage 95 connects a gas exhaust outlet of receiver 73 to second passage H2 and exhausts refrigerant gas within receiver 73.
Pipe 91 is a pipe which branches from pipe 81 as the high pressure portion of the main refrigerant circuit and causes the refrigerant to flow into receiver 73. Third expansion valve 71 is an electronic expansion valve which can decrease the pressure of the refrigerant in pipe 81 as the high pressure portion of the main refrigerant circuit to an intermediate pressure. Receiver 73 is a container in which the refrigerant decompressed and having two phases is separated into gas and liquid, and which can store the refrigerant and adjust the amount of the refrigerant in the main refrigerant circuit. Degassing passage 95 connected to an upper portion of receiver 73 and pipe 93 connected to a lower portion of receiver 73 are pipes for taking out the refrigerant separated into gas refrigerant and liquid refrigerant within receiver 73, in a separated state. Flow rate control valve 72 adjusts a circulation amount of the liquid refrigerant to be exhausted from pipe 93, and thereby can adjust the amount of the refrigerant in receiver 73.
By providing receiver 73 on injection flow path 101 as described above, it becomes easy to ensure a subcool in pipes 82 and 83, which are liquid pipes of the main refrigerant circuit. This is because, since receiver 73 generally includes the gas refrigerant therein and a refrigerant temperature within receiver 73 reaches a saturation temperature, if receiver 73 is disposed on pipe 82 as the liquid pipe of the main refrigerant circuit, a refrigerant temperature within pipe 82 is less likely to become lower than the saturation temperature, and thus it is not possible to ensure a subcool.
Heat exchanger 30 exchanges heat between the refrigerant flowing in first passage H1 as a portion of the main refrigerant circuit and the refrigerant flowing in second passage H2 as a portion of injection flow path 101.
If receiver 73 is provided on pipe 81, 91 as the high pressure portion of the main refrigerant circuit, when the pressure in pipe 81, 91 is high and the refrigerant within pipe 81, 91 is in a supercritical state, it is not possible to store the liquid refrigerant in receiver 73, and receiver 73 loses the function of buffering an excessive amount of the refrigerant. In contrast, in the present embodiment, since receiver 73 is provided on pipe 92 as an intermediate pressure portion with a pressure decreased by third expansion valve 71 to the intermediate pressure, the amount of the refrigerant can be adjusted even in operation in the supercritical state.
Fig. 2 is a diagram showing various sensors and controller 100 disposed in refrigeration cycle apparatus 1 shown in Fig. 1. Referring to Fig. 2, outdoor unit 2 further includes pressure sensors 110 to 113, temperature sensors 120 to 125, a notification device 150, and controller 100.
Pressure sensor 110 detects a pressure PL at the suction port portion of compressor 10, and outputs a detection value thereof to controller 100. Pressure sensor 111 detects a discharge pressure PH of compressor 10, and outputs a detection value thereof to controller 100. Pressure sensor 112 detects a pressure P1 in pipe 83 at an outlet of second expansion valve 40, and outputs a detection value thereof to controller 100. Further, pressure sensor 113 detects an intermediate pressure PM in pipe 92 behind third expansion valve 71, and outputs a detection value thereof to controller 100.
By providing second expansion valve 40 to the liquid pipe, outdoor unit 2 can decompress the refrigerant pressure to be lower than or equal to a design pressure of load device 3 (for example, 4 MPa), and then deliver the refrigerant to load device 3. Thereby, even if refrigerant utilizing supercriticality such as CO₂ is used, a general-purpose product having the same design pressure as that of a conventional load device can be used as load device 3.
Temperature sensor 120 detects a discharge temperature TH of compressor 10, and outputs a detection value thereof to controller 100. Temperature sensor 121 detects a refrigerant temperature T1 in pipe 81 at the outlet of condenser 20, and outputs a detection value thereof to controller 100. Temperature sensor 122 detects a refrigerant temperature at an outlet of first passage H1 on a cooled side of heat exchanger 30, as an outlet temperature T2 of heat exchanger 30, and outputs a detection value thereof to controller 100.
Temperature sensor 123 detects an ambient temperature of outdoor unit 2 as an outside air temperature TA, and outputs a detection value thereof to controller 100. Temperature sensor 125 detects a temperature at the outlet of second passage H2 of heat exchanger 30, and outputs a detection value thereof to controller 100. Temperature sensor 124 detects a temperature TL in a suction pipe of compressor 10, and outputs a detection value thereof to controller 100.
Notification device 150 is configured to notify a user of various information upon request from controller 100. Notification device 150 may include at least one of a display device (for example, a touch panel display), a speaker (for example, a smart speaker), and an alarm lamp.
Controller 100 includes a CPU (Central Processing Unit) 102, a memory 104 (a ROM (Read Only Memory) and a RAM (Random Access Memory)), input/output buffers (not shown) for inputting/outputting various signals, and the like. CPU 102 expands programs stored in the ROM onto the RAM or the like and executes the programs. The programs stored in the ROM are programs describing processing procedures of controller 100. According to these programs, controller 100 performs control of the devices in outdoor unit 2. This control can be processed not only by software but also by dedicated hardware (electronic circuitry).
In the present embodiment, CO₂ is used as refrigerant used for a refrigerant circuit of refrigeration cycle apparatus 1. When CO₂ is used as the refrigerant, a state where the pressure of the refrigerant is less than a critical pressure (hereinafter also referred to as a "normal state"), or a state where the pressure of the refrigerant exceeds the critical pressure (hereinafter also referred to as a "supercritical state") may be reached, depending on the operation condition.
Fig. 3 is a Mollier diagram schematically showing an aspect of change in the refrigerant in the normal state. Fig. 4 is a Mollier diagram schematically showing an aspect of change in the refrigerant in the supercritical state. In Figs. 3 and 4, the axis of abscissas represents enthalpy (heat quantity of the refrigerant), and the axis of ordinates represents the pressure of the refrigerant. A curve L1 represents a saturated liquid line, and a curve L2 represents a saturated vapor line.
As shown in Fig. 3, in the normal state, since the pressure of the refrigerant is less than the critical pressure, the state of the refrigerant straddles saturated liquid line L1 when the enthalpy is decreased in condenser 20. Thus, subcooling can be defined.
In contrast, as shown in Fig. 4, in the supercritical state, since the pressure of the refrigerant exceeds the critical pressure, the state of the refrigerant does not straddle saturated liquid line L1 when the enthalpy is decreased in condenser 20. In this case, subcooling cannot be defined. It should be noted that, in the present specification, for ease of description, an amount of decrease from a reference temperature of the refrigerant temperature in the supercritical state will also be referred to as a subcool.

[Control of Pressure within Load Device 3]

As described above, when CO₂ is used as the refrigerant, a supercritical region of the refrigerant may be used, depending on the operation condition. Even when the supercritical region of the refrigerant is used, controller 100 performs control of compressor 10 and second expansion valve 40 such that the pressure of the refrigerant within load device 3 does not exceed the design pressure of load device 3. On this occasion, in order to allow load device 3 to be used in common with a device used with an ordinary refrigerant, controller 100 performs decompression by second expansion valve 40. Specifically, controller 100 controls second expansion valve 40 as described below.
Controller 100 feedback-controls second expansion valve 40 such that pressure P1 in pipe 83 at the outlet of second expansion valve 40 matches a target pressure. Specifically, when pressure P1 is higher than the target pressure, controller 100 decreases the degree of opening of second expansion valve 40. Thereby, the amount of decompression by second expansion valve 40 increases, and thus pressure P1 decreases. On the other hand, when pressure P1 is lower than the target pressure, controller 100 increases the degree of opening of second expansion valve 40.
Thereby, the amount of decompression by second expansion valve 40 decreases, and thus pressure P1 increases. When pressure P1 is equal to the target pressure, controller 100 maintains the degree of opening of second expansion valve 40 in the present state.
Since pressure P1 is controlled as described above, the pressure of the refrigerant within load device 3 can be set to be lower than or equal to a design pressure of a conventional refrigeration apparatus which uses an ordinary refrigerant whose supercritical region is not used (for example, R410A or the like), and load device 3 can be used in common with a conventional load device which uses an ordinary refrigerant.

[Control of Third Expansion Valve 71 and Flow Rate Control Valve 72]

In refrigeration cycle apparatus 1 according to the present embodiment, discharge temperature TH of compressor 10 in the main refrigerant circuit can be controlled, subcooling in the main refrigerant circuit can be ensured, and the amount of the refrigerant in the main refrigerant circuit can be adjusted by providing injection flow path 101 branching from the main refrigerant circuit. That is, injection flow path 101 can control discharge temperature TH of compressor 10 by causing the refrigerant in pipe 81 decompressed and having two phases to flow into compressor 10. Further, subcooling of the refrigerant in the main refrigerant circuit can be ensured by using second passage H2 of heat exchanger 30 as a portion of injection flow path 101. Further, the amount of the refrigerant in the main refrigerant circuit can be adjusted by receiver 73 placed on injection flow path 101.
Controller 100 according to the present embodiment controls third expansion valve 71 and flow rate control valve 72 to allow injection flow path 101 to exhibit the functions of controlling discharge temperature TH in the main refrigerant circuit, ensuring subcooling in the main refrigerant circuit, and adjusting the amount of the refrigerant in the main refrigerant circuit, under each operation condition.

(Control of Discharge Temperature TH)

Controller 100 feedback-controls the degree of opening of third expansion valve 71 such that discharge temperature TH of compressor 10 matches a target temperature. Specifically, when discharge temperature TH of compressor 10 is higher than the target temperature, controller 100 increases the degree of opening of third expansion valve 71. Thereby, the refrigerant flowing into intermediate pressure port G3 via receiver 73 increases, and thus discharge temperature TH decreases.
On the other hand, when discharge temperature TH of compressor 10 is lower than the target temperature, controller 100 decreases the degree of opening of third expansion valve 71. Thereby, the refrigerant flowing into intermediate pressure port G3 via receiver 73 decreases, and thus discharge temperature TH increases.
When discharge temperature TH is equal to the target temperature, controller 100 maintains the degree of opening of third expansion valve 71 in the present state.
Thus, controller 100 controls the degree of opening of third expansion valve 71 such that discharge temperature TH of compressor 10 approaches the target temperature.

(Refrigerant Amount Adjustment and Refrigerant Shortage Detection in Normal State)

Under an operation condition in the normal state, controller 100 controls flow rate control valve 72 according to a temperature efficiency ε of heat exchanger 30 in order to ensure subcooling. In the present embodiment, temperature efficiency ε of heat exchanger 30 represents the ratio of a temperature difference (= T1-T2) between the inlet and the outlet of first passage H1 of heat exchanger 30 to a degree of superheat of second passage H2 of heat exchanger 30.
Specifically, controller 100 calculates temperature efficiency ε of heat exchanger 30 from a difference between refrigerant temperature T1 at the outlet of condenser 20 and outlet temperature T2 of heat exchanger 30. Then, when calculated temperature efficiency ε is larger than a target value, it is considered that the amount of the refrigerant in the main refrigerant circuit is excessive, and thus controller 100 decreases the degree of opening of flow rate control valve 72. Thereby, the amount of the liquid refrigerant passing through receiver 73 decreases and the amount of the liquid refrigerant within receiver 73 increases, and thus the amount of the refrigerant circulating through the main refrigerant circuit decreases. On the other hand, when calculated temperature efficiency ε is smaller than the target value, it is considered that the refrigerant is excessively stored in receiver 73 and the amount of the refrigerant in the main refrigerant circuit is insufficient, and thus controller 100 increases the degree of opening of flow rate control valve 72. Thereby, the amount of the liquid refrigerant in receiver 73 decreases, and thus the amount of the refrigerant circulating through the main refrigerant circuit increases. When temperature efficiency ε is equal to the target value, controller 100 maintains the degree of opening of flow rate control valve 72 in the present state.
Thus, under the operation condition in the normal state, controller 100 feedback-controls the degree of opening of flow rate control valve 72 such that temperature efficiency ε of heat exchanger 30 is equal to the target value. Thereby, temperature efficiency ε of heat exchanger 30 is maintained at the target value, and cooling of the refrigerant by heat exchanger 30 is performed efficiently. Thereby, subcooling is ensured.
It should be noted that, instead of feedback-controlling flow rate control valve 72 such that temperature efficiency ε of heat exchanger 30 is equal to the target value, flow rate control valve 72 may be feedback-controlled such that refrigerant temperature T1 at the outlet of condenser 20 is equal to a target temperature. In this case, it is only necessary to set the target temperature of refrigerant temperature T1 to a temperature of refrigerant temperature T1 when temperature efficiency ε of heat exchanger 30 is equal to the target value.
As described above, under the operation condition in the normal state, when temperature efficiency ε of heat exchanger 30 is smaller than the target value, controller 100 increases the degree of opening of flow rate control valve 72 to increase the amount of the refrigerant flowing from receiver 73 to the main refrigerant circuit, and thereby temperature efficiency ε approaches the target value.
However, when the amount of the refrigerant in the entire refrigerant circuit including the main refrigerant circuit and injection flow path 101 is originally insufficient, a sufficient amount of the refrigerant does not circulate through the main refrigerant circuit even if the degree of opening of flow rate control valve 72 is increased. Thus, it is conceivable that temperature efficiency ε may fail to approach the target value and have a value less than the target value.
In view of this point, when temperature efficiency ε of heat exchanger 30 is less than a lower limit value that is lower than the target value, controller 100 determines that the refrigerant in the entire refrigerant circuit is insufficient, and controls notification device 150 to notify the user of a determined result.

(Refrigerant Amount Adjustment and Refrigerant Shortage Detection in Supercritical State)

The refrigerant amount adjustment and refrigerant shortage determination using temperature efficiency ε as performed in the normal state have a high determination accuracy, and also have a good following property. However, under an operation condition in the supercritical state, it is not possible to define the saturation temperature and to confirm whether subcooling is ensured. Thus, it is difficult to perform refrigerant amount adjustment and refrigerant shortage determination using the same method as that for the normal state (that is, the method that uses temperature efficiency ε).
In view of this point, under the operation condition in the supercritical state, controller 100 performs refrigerant amount adjustment and refrigerant shortage determination using a method different from that for the normal state, that is, a method that does not use temperature efficiency ε. Specifically, under the operation condition in the supercritical state, controller 100 controls the degree of opening of flow rate control valve 72 using a temperature difference ΔT1 between outside air temperature TA detected by temperature sensor 123 and refrigerant temperature T1 at the outlet of condenser 20 detected by temperature sensor 121. By using temperature difference ΔT1 and thereby utilizing that there is a change in density due to a change in the temperature of the refrigerant, the amount of the refrigerant can be adjusted with respect to a limit temperature of heat exchange by condenser 20 (an air heat exchanger). For example, when temperature difference ΔT1 is large, it is considered that the refrigerant is excessively stored in receiver 73 and the amount of the refrigerant in the main refrigerant circuit is insufficient. Thus, controller 100 increases the degree of opening of flow rate control valve 72 according to the magnitude of temperature difference ΔT1. Thereby, the amount of the liquid refrigerant flowing from receiver 73 to the main refrigerant circuit is increased.
Further, under the operation condition in the supercritical state, controller 100 determines whether or not the refrigerant is insufficient, based on the "degree of opening of flow rate control valve 72" which is feedback-controlled according to temperature difference ΔT1 as described above.
For example, when temperature difference ΔT1 is large, the degree of opening of flow rate control valve 72 is increased according to the magnitude of temperature difference ΔT1 by the feedback control for refrigerant amount adjustment described above. Thereby, the amount of the liquid refrigerant flowing from receiver 73 to the main refrigerant circuit is increased.
However, when the amount of the refrigerant in the entire refrigerant circuit including the main refrigerant circuit and injection flow path 101 is originally insufficient, a sufficient amount of the refrigerant does not circulate through the main refrigerant circuit even if the degree of opening of flow rate control valve 72 is increased to an upper limit degree of opening. Thus, it is conceivable that temperature difference ΔT1 does not change (does not decrease).
In view of this point, when there is no change in temperature difference AT1 even if a state where the degree of opening of flow rate control valve 72 is the upper limit degree of opening continues for a predetermined period of time, controller 100 determines that the amount of the refrigerant in the entire refrigerant circuit including the main refrigerant circuit and the injection flow path is insufficient, and controls notification device 150 to notify the user of a determined result.
Although the method of determining whether the refrigerant is insufficient based on the "degree of opening of flow rate control valve 72" which is feedback-controlled according to temperature difference ΔT1 may have a poor following property when compared with the method that uses temperature efficiency ε, switching between the determination methods as described above allows determination of whether or not the refrigerant is insufficient in the entire operation range including the normal state and the supercritical state.

(Adjustment of Amount of Sealed Refrigerant)

Adjustment of the amount of the sealed refrigerant when the refrigerant is sealed in the refrigerant circuit will be described below. At initial sealing that seals the refrigerant for the first time in the refrigerant circuit which is not filled with the refrigerant, conventionally, adjustment is performed, for example, by providing a sight glass on pipe 83 to check if flash gas exists in the refrigerant in pipe 83.
However, in the refrigerant circuit according to the present embodiment, expansion by second expansion valve 40 within outdoor unit 2 is performed in addition to expansion by first expansion valve 50 within load device 3, to decrease the pressure within load device 3. When expansion by second expansion valve 40 is performed, the relation between the amount of the refrigerant and subcooling in pipe 83 is not satisfied. Accordingly, the sealed amount is adjusted using the above determined result that the amount of the refrigerant is insufficient. Specifically, while it is determined that the refrigerant is insufficient, sealing of the refrigerant is continued, and when it is not determined that the refrigerant is insufficient, it is determined that the refrigerant in an appropriate amount is filled, and sealing of the refrigerant is stopped.
It should be noted that sealing of the refrigerant may be performed manually by the user of outdoor unit 2 (including an operator who installs outdoor unit 2), or may be performed automatically by controller 100. An example where controller 100 automatically performs initial sealing will be described below.
At initial sealing, first, with compressor 10 being stopped, controller 100 seals the refrigerant in the refrigerant circuit until discharge pressure PH of compressor 10 detected by pressure sensor 111 reaches a threshold value. Then, controller 100 activates compressor 10 and continues sealing of the refrigerant. Since discharge pressure PH of compressor 10 is not supercritical on this occasion, refrigerant shortage detection using temperature efficiency ε (refrigerant shortage detection in the normal state) is performed. While it is determined by the refrigerant shortage detection using temperature efficiency ε (refrigerant shortage detection in the normal state) that the refrigerant is insufficient, controller 100 continues sealing of the refrigerant.
Then, when the rotation speed of compressor 10 increases and discharge pressure PH of compressor 10 exceeds the critical pressure, refrigerant shortage detection using the "degree of opening of flow rate control valve 72" which is feedback-controlled according to temperature difference ΔT1 (refrigerant shortage detection in the supercritical state) is performed. Unless the degree of opening of flow rate control valve 72 is the upper limit degree of opening after discharge pressure PH of compressor 10 exceeds the critical pressure, it is not determined that refrigerant shortage is detected. Accordingly, when it is not determined that refrigerant shortage is detected after discharge pressure PH of compressor 10 becomes supercritical, controller 100 determines that the refrigerant in an appropriate amount is filled, and stops sealing of the refrigerant. Thereby, the accuracy of sealing the refrigerant and the following property can be ensured even at initial sealing in which the amount of the refrigerant changes significantly.

(Determination of Overflow)

A case where the refrigerant is excessively filled in the refrigerant circuit will be described. In this case, discharge pressure PH of compressor 10 detected by pressure sensor 111 increases and reaches the supercritical state where discharge pressure PH exceeds the critical pressure. On this occasion, the degree of opening of flow rate control valve 72 is decreased to a lower limit degree of opening by the feedback control for refrigerant amount adjustment described above. When discharge pressure PH of compressor 10 does not change (does not decrease) even if a predetermined period of time has passed in a state where the degree of opening of flow rate control valve 72 is the lower limit degree of opening, controller 100 determines that the refrigerant circuit is in an overfilled state, and controls notification device 150 to notify the user of a determined result.
After controller 100 determines that the refrigerant circuit is in the overfilled state, controller 100 determines whether or not the magnitude of a decreasing speed of discharge temperature TH of compressor 10 detected by temperature sensor 120 is greater than a reference value. Then, when the magnitude of the decreasing speed of discharge temperature TH is greater than the reference value, that is, when discharge temperature TH is decreasing rapidly, controller 100 determines that receiver 73 is in an overflow state where receiver 73 is filled with the liquid refrigerant, and controls notification device 150 to notify the user of a determined result.
After controller 100 determines that receiver 73 is in the overflow state, controller 100 determines whether or not a discharge degree of superheat, which is a difference between discharge temperature TH of compressor 10 and the saturation temperature at discharge pressure PH, falls within a specification range of compressor 10. When the discharge degree of superheat does not fall within the specification range of compressor 10, controller 100 stops compressor 10.

(Flow of Control of Refrigerant Amount Adjustment and Refrigerant Shortage Detection)

Fig. 5 is a flowchart showing an example of a processing procedure when controller 100 performs refrigerant amount adjustment and refrigerant shortage detection.
Controller 100 determines whether or not discharge pressure PH of compressor 10 exceeds the critical pressure (step S10). When the supercritical state is reached where discharge pressure PH of compressor 10 exceeds the critical pressure (YES in step S10), controller 100 controls the degree of opening of flow rate control valve 72 using temperature difference ΔT1 between outside air temperature TA and refrigerant temperature T1 at the outlet of condenser 20 (step S11), as described above. For example, when temperature difference ΔT1 is large, controller 100 increases the degree of opening of flow rate control valve 72 according to the magnitude of temperature difference ΔT1.
Subsequently, controller 100 determines whether or not the degree of opening of flow rate control valve 72 is the upper limit degree of opening (step S12). When the degree of opening of flow rate control valve 72 is not the upper limit degree of opening (NO in step S12), controller 100 advances the processing to step S22.
On the other hand, when the degree of opening of flow rate control valve 72 is the upper limit degree of opening (YES in step S12), controller 100 determines whether or not the state where the degree of opening of flow rate control valve 72 is the upper limit degree of opening continues for a predetermined period of time (step S14). When the state where the degree of opening of flow rate control valve 72 is the upper limit degree of opening does not continue for the predetermined period of time (NO in step S14), controller 100 skips the subsequent processing and advances the processing to RETURN.
When the state where the degree of opening of flow rate control valve 72 is the upper limit degree of opening continues for the predetermined period of time (YES in step S14), controller 100 determines that the refrigerant in the entire refrigerant circuit is insufficient, and controls notification device 150 to notify the user of a determined result (step S16).
On the other hand, when the normal state is reached where discharge pressure PH of compressor 10 does not exceed the critical pressure (NO in step S10), controller 100 calculates temperature efficiency ε of heat exchanger 30 from the difference between refrigerant temperature T1 at the outlet of condenser 20 and outlet temperature T2 of heat exchanger 30, and controls flow rate control valve 72 according to calculated temperature efficiency ε (step S20), as described above.
Subsequently, controller 100 determines whether or not calculated temperature efficiency ε is less than the lower limit value (step S21). When temperature efficiency ε is less than the lower limit value (YES in step S21), controller 100 determines that the refrigerant in the entire refrigerant circuit is insufficient, and controls notification device 150 to notify the user of a determined result (step S40).
On the other hand, when temperature efficiency ε is not less than the lower limit value (NO in step S21), controller 100 advances the processing to step S22.
In step S22, controller 100 determines whether or not the degree of opening of flow rate control valve 72 is the lower limit degree of opening. When the degree of opening of flow rate control valve 72 is not the lower limit degree of opening (NO in step S22), controller 100 skips the subsequent processing and advances the processing to RETURN.
When the degree of opening of flow rate control valve 72 is the lower limit degree of opening (YES in step S22), controller 100 determines whether or not discharge pressure PH of compressor 10 is greater than a threshold value, even after the state where the degree of opening of flow rate control valve 72 is the lower limit degree of opening continues for a predetermined period of time (step S24). It should be noted that the "threshold value" used in step S24 is set, for example, to a value lower than the critical pressure. When the state where the degree of opening of flow rate control valve 72 is the lower limit degree of opening does not continue for the predetermined period of time, or when discharge pressure PH of compressor 10 is less than the threshold value (NO in step S24), controller 100 skips the subsequent processing and advances the processing to RETURN.
When discharge pressure PH of compressor 10 is greater than the threshold value even after the state where the degree of opening of flow rate control valve 72 is the lower limit degree of opening continues for the predetermined period of time (YES in step S24), controller 100 determines that the refrigerant circuit is in the overfilled state, and controls notification device 150 to notify the user of a determined result (step S26).
After controller 100 determines that the refrigerant circuit is in the overfilled state, controller 100 determines whether or not discharge temperature TH of compressor 10 is decreasing rapidly, specifically, whether or not the magnitude of the decreasing speed of discharge temperature TH of compressor 10 is greater than the reference value (step S28). Then, when the magnitude of the decreasing speed of discharge temperature TH is greater than the reference value, that is, when discharge temperature TH is decreasing rapidly, controller 100 determines that receiver 73 is in the overflow state where receiver 73 is filled with the liquid refrigerant, and controls notification device 150 to notify the user of a determined result (step S30).
After controller 100 determines that receiver 73 is in the overflow state, controller 100 determines whether or not the discharge degree of superheat, which is the difference between discharge temperature TH of compressor 10 and the saturation temperature at discharge pressure PH of compressor 10, falls within the specification range of compressor 10 (step S32). When the discharge degree of superheat falls within the specification range of compressor 10 (NO in step S32), controller 100 skips the subsequent processing and advances the processing to RETURN. On the other hand, when the discharge degree of superheat does not fall within the specification range of compressor 10 (YES in step S32), controller 100 stops compressor 10 (step S34).
As described above, under the operation condition in the normal state, controller 100 according to the present embodiment determines whether or not the refrigerant is insufficient, using temperature efficiency ε of heat exchanger 30. On the other hand, under the operation condition in the supercritical state, controller 100 determines whether or not the refrigerant is insufficient, using the "degree of opening of flow rate control valve 72" which is feedback-controlled according to temperature difference ΔT1 between outside air temperature TA and refrigerant temperature T1 at the outlet of condenser 20, instead of using temperature efficiency ε of heat exchanger 30. Switching between the methods for determining whether the refrigerant is insufficient as described above allows appropriate determination of whether or not the refrigerant is insufficient in the refrigerant circuit, even under the operation condition in the supercritical state. As a result, in refrigeration cycle apparatus 1 using the refrigerant that can reach the supercritical state, it is possible to determine whether or not the refrigerant is insufficient in the entire operation range including the normal state and the supercritical state.
It should be noted that, although the above embodiment has been described by illustrating a refrigerating machine including refrigeration cycle apparatus 1, refrigeration cycle apparatus 1 may be utilized in an air conditioner or the like.
It should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the scope of the claims, rather than the description described above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

REFERENCE SIGNS LIST

1: refrigeration cycle apparatus; 2: outdoor unit; 3: load device; 10: compressor; 20: condenser; 22: fan; 30: heat exchanger; 40: second expansion valve; 50: first expansion valve; 60: evaporator; 71: third expansion valve; 72: flow rate control valve; 73: receiver; 75: on-off valve; 80, 81 to 83, 85, 89, 91 to 94, 96: pipe; 84, 88: extension pipe; 95: degassing passage; 100: controller; 101: injection flow path; 102: CPU; 104: memory; 110 to 113: pressure sensor; 120 to 125: temperature sensor; 150: notification device; G1: suction port; G2: discharge port; G3: intermediate pressure port; H1: first passage.

Claims

An outdoor unit of a refrigeration cycle apparatus, the outdoor unit being connectable to a load device including a first expansion valve and an evaporator, the outdoor unit comprising:
a compressor having a suction port, a discharge port, and an intermediate pressure port;

a condenser;

a heat exchanger having a first passage and a second passage and configured to exchange heat between refrigerant flowing in the first passage and the refrigerant flowing in the second passage;

a second expansion valve, wherein

a flow path from the compressor to the second expansion valve via the condenser and the first passage of the heat exchanger forms, together with the load device, a circulation flow path through which the refrigerant circulates;

an injection flow path configured to cause the refrigerant to flow from a branching portion to the compressor, the branching portion being between an outlet of the condenser and an inlet of the first passage in the circulation flow path, wherein

the injection flow path is provided with:
a first refrigerant flow path configured to cause the refrigerant to flow from the branching portion to an inlet of the second passage;

a second refrigerant flow path configured to cause the refrigerant to flow from an outlet of the second passage to the suction port or the intermediate pressure port of the compressor;

a receiver disposed on the first refrigerant flow path;

a third expansion valve disposed at a portion between the branching portion and an inlet of the receiver in the first refrigerant flow path; and

a flow rate control valve disposed at a portion between an outlet of the receiver and the inlet of the second passage in the first refrigerant flow path;

a controller configured to control the compressor, the second expansion valve, the third expansion valve, and the flow rate control valve; and

a notification device configured to notify a user of information from the controller, wherein

when a supercritical state is reached where a discharge pressure of the compressor exceeds a critical pressure of the refrigerant, the controller determines whether or not the refrigerant included in the circulation flow path and the injection flow path is insufficient, based on a degree of opening of the flow rate control valve.
The outdoor unit according to claim 1, wherein
when the supercritical state is reached, the controller increases an amount of the refrigerant flowing from the receiver to the circulation flow path by increasing the degree of opening of the flow rate control valve as a difference between a discharge temperature of the compressor and an outside air temperature is greater, and

when the supercritical state is reached and when a state where the degree of opening of the flow rate control valve is an upper limit degree of opening continues for a predetermined period of time, the controller determines that the refrigerant included in the circulation flow path and the injection flow path is insufficient.
The outdoor unit according to claim 2, wherein, when the supercritical state is not reached and when temperature efficiency of the heat exchanger is less than a lower limit value, the controller determines that the refrigerant included in the circulation flow path and the injection flow path is insufficient.
The outdoor unit according to claim 2 or 3, wherein
when the supercritical state is not reached, the controller decreases the amount of the refrigerant flowing from the receiver to the circulation flow path by decreasing the degree of opening of the flow rate control valve as temperature efficiency of the heat exchanger is greater, and

when the supercritical state is not reached and when a state where the degree of opening of the flow rate control valve is a lower limit degree of opening continues for a predetermined period of time, the controller determines that the refrigerant included in the circulation flow path and the injection flow path is excessive.
The outdoor unit according to claim 3 or 4, wherein the controller calculates the temperature efficiency of the heat exchanger from a difference between an inlet temperature and an outlet temperature of the heat exchanger.
The outdoor unit according to any one of claims 1 to 5, wherein, when a magnitude of a decreasing speed of a discharge temperature of the compressor is greater than a reference value, the controller determines that the receiver is in a state filled with liquid refrigerant, and stops the compressor.
The outdoor unit according to any one of claims 1 to 6, wherein the controller adjusts a degree of opening of the second expansion valve such that an outlet pressure of the second expansion valve in the circulation flow path does not exceed a design pressure of the load device.
A refrigeration cycle apparatus comprising:
the outdoor unit according to any one of claims 1 to 7; and

the load device.