EP3875872A1

EP3875872A1 - Refrigeration cycle apparatus

Info

Publication number: EP3875872A1
Application number: EP18938547.9A
Authority: EP
Inventors: Hiroki Ishiyama
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2018-10-31
Filing date: 2018-10-31
Publication date: 2021-09-08
Also published as: JP7150046B2; CN112888906B; EP3875872A4; WO2020090040A1; JPWO2020090040A1; CN112888906A

Abstract

A refrigerant and a lubricant circulate in the order of a compressor (1), a first heat exchanger (2), a third heat exchanger (7), a first decompressor (3), and a second heat exchanger (4), and also circulates in the order of the compressor (1), the first heat exchanger (2), a second decompressor (5), the third heat exchanger (7), and a bypass unit (8). The bypass unit (8) includes a reservoir (81) extending in the direction of gravity. The refrigerant and the lubricant flow through the reservoir (81) against the direction of gravity. If the quantity of refrigerant that flows through the bypass unit (8) per unit time is a reference flow rate, the reservoir (81) has a diameter satisfying a relationship that the velocity of the refrigerant flowing through the reservoir (81) is slower than a critical velocity. When the relationship is satisfied, the quantity of lubricant flowing into the reservoir (81) is more than the quantity of lubricant flowing out of the reservoir (81). The critical velocity is determined from the gravitational acceleration, the diameter of the reservoir (81), the density of the lubricant, and the density of a gas of the refrigerant.

Description

TECHNICAL FIELD

The present invention relates to a refrigeration cycle apparatus through which a lubricant for a compressor and a refrigerant circulate.

BACKGROUND ART

Conventionally, refrigeration cycle apparatuses are known through which a lubricant for a compressor and a refrigerant circulate. For example, WO 2013/099047 (PTL 1) discloses an air-conditioner which includes: an oil separator for separating a refrigeration oil from a refrigerant discharged from a compressor; and an oil reservoir storing the refrigeration oil separated by the oil separator. With the air-conditioner, by storing an excess refrigeration oil in the oil reservoir, a required quantity of refrigeration oil can be returned from the oil reservoir to the compressor.

CITATION LIST

PATENT LITERATURE

PTL 1: WO 2013/099047

SUMMARY OF INVENTION

TECHNICAL PROBLEM

The air-conditioner disclosed in PTL 1 includes an oil separator connected between the outdoor heat exchanger and the compressor. The oil separator can increase the pressure loss of a flow path circulating in the order of the compressor, the outdoor heat exchanger, the expansion valve, and the indoor heat exchanger. As a result, performance of the air-conditioner can deteriorate.
The present invention is made to solve problems as described above, and an object of the present invention is to provide a refrigeration cycle apparatus the deterioration of performance which can be suppressed.

SOLUTION TO PROBLEM

In a refrigeration cycle apparatus according to the present invention, a refrigerant circulates. The refrigeration cycle apparatus includes a compressor, a first heat exchanger, a first decompressor, a second heat exchanger, a second decompressor, a third heat exchanger, and a bypass unit. The compressor stores a lubricant. The refrigerant and the lubricant circulates through the refrigeration cycle apparatus in the order of the compressor, the first heat exchanger, the third heat exchanger, the first decompressor, and the second heat exchanger, and also circulate in the order of the compressor, the first heat exchanger, the second decompressor, the third heat exchanger, and the bypass unit. The bypass unit includes a reservoir extending in the direction of gravity. The refrigerant and the lubricant flow through the reservoir against the direction of gravity. If the quantity of refrigerant that flows through the bypass unit per unit time is a reference flow rate, the diameter of the reservoir satisfies a relationship that the velocity of the refrigerant flow through the reservoir is slower than a critical velocity. If the relationship is satisfied, a quantity of lubricant flow into the reservoir is more than a quantity of lubricant flow out of the reservoir. The critical velocity is determined by gravitational acceleration, the diameter of the reservoir, the density of the lubricant, and a density of a gas of the refrigerant.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the diameter of the reservoir satisfying the relationship that the velocity of the refrigerant flow through the reservoir is slower than the critical velocity can suppress deterioration in performance of the refrigeration cycle apparatus.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a functional block diagram showing a configuration of a refrigeration cycle apparatus according to Embodiment 1.
Fig. 2 is a pressure-enthalpy diagram showing state changes of a refrigerant circulating through the refrigeration cycle apparatus of Fig. 1.
Fig. 3 is a diagram illustrating one example of the refrigerant and a lubricant flowing into a bypass unit when the refrigeration cycle apparatus of Fig. 1 is in a steady state.
Fig. 4 is a diagram illustrating another example of the refrigerant and the lubricant flowing into the bypass unit when the refrigeration cycle apparatus of Fig. 1 is in the steady state.
Fig. 5 is a diagram showing the refrigerant and the lubricant flowing into an oil receiver when the refrigeration cycle apparatus of Fig. 1 is in a transient state.
Fig. 6 is a diagram showing relationships between the quantity of lubricant within a compressor and the operation times of the refrigeration cycle apparatuses according to Comparative Example 1, Comparative Example 2, and Embodiment 1.
Fig. 7 is a diagram illustrating one example aspect of connection between an oil separator and pipes in the bypass unit included in the refrigeration cycle apparatus according to Embodiment 1.
Fig. 8 is a diagram showing an example case where the reservoir and the pipes are integrally formed in the bypass unit included in the refrigeration cycle apparatus according to Embodiment 1.
Fig. 9 is a functional block diagram showing a configuration of the refrigeration cycle apparatus according to a variation of Embodiment 1.
Fig. 10 is a pressure-enthalpy diagram showing state changes of the refrigerant circulating through the refrigeration cycle apparatus of Fig. 9.
Fig. 11 is a functional block diagram showing a configuration of a refrigeration cycle apparatus according to Embodiment 2.
Fig. 12 is a flowchart showing a flow of a process, performed by a controller of Fig. 11, of adjusting the quantity of lubricant that returns from an oil receiver to the compressor.
Fig. 13 is a flowchart involving a specific condition that the variation in driving frequency of the compressor per unit time is less than a reference variation, in the process of adjusting the quantity of lubricant that returns from the oil receiver to the compressor.
Fig. 14 is a flowchart involving a specific condition that the height of the liquid level in the compressor is greater than a reference height in the process of adjusting the mount of lubricant that returns from the oil receiver to the compressor.
Fig. 15 is a flowchart involving a specific condition that the concentration of the lubricant in a liquid within the compressor is greater than a reference concentration in the process of adjusting the quantity of lubricant that returns from the oil receiver to the compressor.
Fig. 16 is a functional block diagram showing a configuration of the refrigeration cycle apparatus according to a variation of Embodiment 2.
Fig. 17 is a functional block diagram showing a configuration of a refrigeration cycle apparatus according to Embodiment 3.
Fig. 18 is a flowchart showing a flow of a process, performed by a controller of Fig. 17, of adjusting the quantity of lubricant that returns from the oil receiver to the compressor.
Fig. 19 is a functional block diagram showing a configuration of the refrigeration cycle apparatus according to a variation of Embodiment 3.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments according to the present invention will be described, with reference to the accompanying drawings. Note that the same reference signs are used to refer to the same or like parts, and the description thereof will in principle not be repeated.

Embodiment 1

Fig. 1 is a functional block diagram showing a configuration of a refrigeration cycle apparatus 100 according to Embodiment 1. As shown in Fig. 1, refrigeration cycle apparatus 100 includes: a compressor 1 storing a lubricant; a condenser (a first heat exchanger); an expansion valve 3 (a first decompressor); an evaporator 4 (a second heat exchanger); an expansion valve 5 (a second decompressor); an internal heat exchanger 7 (a third heat exchanger); a bypass unit 8 which includes an oil receiver 81; and a controller 10. Controller 10 controls a driving frequency fc of compressor 1, thereby controlling a quantity of refrigerant that is discharged by compressor 1 per unit time.
In refrigeration cycle apparatus 100, the refrigerant circulates in the order of compressor 1, a condenser 2, internal heat exchanger 7, and evaporator 4. Hereinafter, a flow path that leads the refrigerant to compressor 1, condenser 2, internal heat exchanger 7, and evaporator 4 in the listed order will be referred to as a primary flow path. The refrigerant also circulates in the order of compressor 1, condenser 2, expansion valve 5, internal heat exchanger 7, and bypass unit 8. Hereinafter, a flow path that branches off from the flow path between condenser 2 and internal heat exchanger 7 and merges with the flow path between evaporator 4 and compressor 1 will be referred to as a bypass flow path.
The refrigerant came from evaporator 4 merges at a node N6 with the refrigerant from oil receiver 81, and is drawn into compressor 1. Internal heat exchanger 7 exchanges heat between the refrigerant came from condenser 2 and the refrigerant came from expansion valve 5. Specifically, the refrigerant came from condenser 2 is cooled by the refrigerant from expansion valve 5.
The refrigerant that flows between compressor 1 and condenser 2 passes through a node N1. The refrigerant flew out of condenser 2 passes through a node N2. The refrigerant that flows between internal heat exchanger 7 and expansion valve 3 passes through a node N3. The refrigerant that flows between internal heat exchanger 7 and evaporator 4 passes through a node N4. The refrigerant that flows between evaporator 4 and node N6 passes through a node N5. The refrigerant that flows between expansion valve 5 and internal heat exchanger 7 passes through a node N7. The refrigerant that flows between internal heat exchanger 7 and bypass unit 8 passes through a node N8. The refrigerant that flows between oil receiver 81 and node N6 passes through a node N9.
Fig. 2 is a pressure-enthalpy diagram showing state changes of a refrigerant circulating through refrigeration cycle apparatus 100 of Fig. 1. The states of the refrigerant shown in Fig. 2 correspond to the respective states of the refrigerant at nodes N1 through N9 of Fig. 9. In Fig. 4, curves LCI, GC1 show a saturated liquid line and a saturated vapor line, respectively. Saturated liquid line LC1 and saturated vapor line GC1 are connected to each other at a critical point CP1. The same is true for Fig. 10 described below.
Referring to both Figs. 1 and 2, the process from the state of the refrigerant at node N6 to the state of the refrigerant at node N1 shows an adiabatic compression process by compressor 1. The process from the state of the refrigerant at node N1 to the state of the refrigerant at node N2 shows a condensation process by condenser 2. The process from the state of the refrigerant at node N2 to the state of the refrigerant at node N3 shows a heat exchanging process by internal heat exchanger 7. The process from the state of the refrigerant at node N3 to the state of the refrigerant at node N4 shows a decompression process by expansion valve 3. The process from the state of the refrigerant at node N4 to the state of the refrigerant at node N5 shows an evaporation process by evaporator 4.
The process from the state of the refrigerant at node N2 to the state of the refrigerant at node N7 shows a decompression process by expansion valve 5. The process from the state of the refrigerant at node N7 to the state of the refrigerant at node N8 is a heat exchanging process by internal heat exchanger 7. The state of the refrigerant at node N8 (the state of the refrigerant flowing into oil receiver 81) and the state of the refrigerant at node N9 (the state of the refrigerant flowing out of the oil receiver 81) are substantially the same. The refrigerant came from evaporator 4 and the refrigerant came from oil receiver 81 merge with each other at node N6 and are drawn into compressor 1.
Such as in the refrigeration cycle apparatus 100, a lubricant may be stored in the compressor in order to lubricate the compression mechanism of the compressor. If a lubricant is stored in the compressor, the lubricant is discharged from the compressor, together with the refrigerant. It is known that as the lubricant flows into the pipes and the heat exchanger, the pressure loss increases and the heat exchange efficiency of the heat exchanger deteriorates. For this reason, an oil separator may be installed in the refrigeration cycle apparatus so as to receive the refrigerant discharged from the compressor. The oil separator separates the refrigerant and the lubricant that are discharged from the compressor and stores the lubricant. The refrigerant stored in the oil separator is returned to the compressor via a pipe connecting the compressor and the oil separator.
If the oil separator is installed so as to receive the refrigerant discharged from the compressor, the pressure loss is increased by the oil separator flow path resistance. When the lubricant is returned from the oil separator to the compressor, the refrigerant is also returned thereto together with the lubricant. Thus, the quantity of refrigerant (the quantity of circulating refrigerant) circulating in the refrigeration cycle apparatus decreases, which deteriorates the performance of the refrigeration cycle apparatus.
Furthermore, upon the start-up of the refrigeration cycle apparatus, for example, in a transient state in which the variation in driving frequency of the compressor per unit time is temporarily greater than or equal to a reference variation, the lubricant in the compressor decreases abruptly. If the lubricant is pre-stored in the oil separator while refrigeration cycle apparatus 100 is in the transient state to prevent the lubricant in the compressor from being depleted before the operation of the refrigeration cycle apparatus is brought into a steady state (an operational status where the variation in driving frequency of the compressor is less than the reference variation), the lubricant is returned from the oil separator to the compressor when refrigeration cycle apparatus 100 is in the transient state. This can prevent depletion of the lubricant for the compressor. However, the supply of the lubricant from the oil separator to the compressor still continues even after the operational status of the refrigeration cycle apparatus is brought into the steady state, resulting in an excessive quantity of lubricant in the compressor. Thus, performance of the compressor can deteriorate.
Thus, refrigeration cycle apparatus 100 includes oil receiver 81 disposed on the bypass flow path, between internal heat exchanger 7 and compressor 1. Since oil receiver 81 is disposed on the bypass flow path, no pressure loss is caused on the primary flow path of refrigeration cycle apparatus 100.
In addition, in refrigeration cycle apparatus 100, oil receiver 81 is disposed so that the refrigerant and the lubricant are allowed to flow through oil receiver 81 against the direction of gravity and oil receiver 81 has a diameter satisfying Equation (3) described below. The lubricant is stored in oil receiver 81 when refrigeration cycle apparatus 100 is in the steady state, and the lubricant is returned from oil receiver 81 to compressor 1 when the operational status of refrigeration cycle apparatus 100 is in a transient state. With refrigeration cycle apparatus 100, the reduction of the quantity of circulating refrigerant in the steady state can be prevented; an excess of the lubricant in the compressor when refrigeration cycle apparatus 100 is in the steady state can be prevented; and the lubricant in the compressor can be prevented from being depleted when refrigeration cycle apparatus 100 is in the transient state. As a result, deterioration in performance of refrigeration cycle apparatus 100 can be prevented.
Figs. 3 and 4 are diagrams each showing the refrigerant and the lubricant flowing into bypass unit 8 when refrigeration cycle apparatus 100 of Fig. 1 is in the steady state. In the following, a liquid refrigerant and the lubricant, which are liquids that flow into oil receiver 81, will be referred to as a mixed solution Ro. A degree of dryness of the refrigerant expected to flow into oil receiver 81 when refrigeration cycle apparatus 100 is in the steady state, is substantially 1. The direction of gravity in Figs. 3 and 4 is Z-axis direction. The same is true for Figs. 5 and 6.
As shown in Fig. 3, oil receiver 81 is connected between pipes 811 and 812. Oil receiver 81 extends in Z-axis direction. Oil receiver 81 has a cylindrical shape having a diameter D1. The refrigerant and the lubricant flow from pipe 811 into oil receiver 81, and flows out of oil receiver 81 through pipe 812. Velocity Vg of a gas refrigerant Rg that flows through oil receiver 81 is represent by Equation (1):
[MATH 1] $V_{g} = \frac{Gr}{ρ_{g} \cdot \frac{{D_{1}}^{2}}{4} \cdot π}$
where Gr denotes a quantity of refrigerant that passes through oil receiver 81 per unit time when refrigeration cycle apparatus 100 is in the steady state. ρg denotes the density of a gas of refrigerant (gas refrigerant) Rg.
If the velocity of gas refrigerant Rg is less than or equal to a critical velocity Vgc represented by Equation (2) below, most of mixed solution Ro does not flow out of oil receiver 81 and stored in oil receiver 81, due to the gravity.
[MATH 2] $V_{gc} = \sqrt{\frac{G_{a} \cdot D_{1} \cdot (ρ_{b} - ρ_{g})}{ρ_{g}}}$
where, Ga denotes the gravitational acceleration, and pb denotes the density of the lubricant.
Due to the relationship Vg≤Vgc, the range of diameter D1 is derived as follows:
[MATH 3] $D_{1} \geq \sqrt[5]{\frac{16 \cdot {Gr}^{2}}{G_{a} \cdot (ρ_{b} - ρ_{g}) \cdot π^{2}}}$
Diameter D1 satisfying Equation (3) allows mixed solution Ro, including the lubricant, to be stored in oil receiver 81 when refrigeration cycle apparatus 100 is in the steady state, as shown in Figs. 3 and 4.
Fig. 5 is a diagram showing the refrigerant and the lubricant flowing into oil receiver 81 when refrigeration cycle apparatus 100 of Fig. 1 is in a transient state. In the transient state, a more liquid refrigerant Rq flows into the oil receiver than when refrigeration cycle apparatus 100 is in the steady state. As a result, an area in which gas refrigerant Rg can pass through when refrigeration cycle apparatus 100 is in the transient state, is narrower than an area in which gas refrigerant Rg can pass through when refrigeration cycle apparatus 100 is in the steady state. As a result, the velocity of gas refrigerant Rg increases faster than critical velocity Vgc, causing mixed solution Ro to flow out of oil receiver 81.
Fig. 6 is a diagram showing relationships C11, C12, C1 between the quantity of lubricant in the compressor and the operation times of the refrigeration cycle apparatus according to Comparative Example 1, the refrigeration cycle apparatus according to Comparative Example 2, and refrigeration cycle apparatus 100 according to Embodiment 1. Note that the refrigeration cycle apparatus according to Comparative Example 1 includes no oil separator. The refrigeration cycle apparatus according to Comparative Example 2 includes an oil separator installed so as to receive a refrigerant discharged from a compressor.
Referring to Fig. 6, in order to secure the reliability of the compressor by lubricating the compression mechanism of the compressor, the quantity of lubricant in the compressor is, desirably, greater than or equal to q1. In order to secure the performance of the compressor, the quantity of lubricant in the compressor is desirably less than or equal to q2 so that an excess quantity of lubricant can be prevented. In other words, the correct range of the quantity of lubricant in the compressor is greater than or equal to q1 and less than or equal to q2. In any of Comparative Example 1, Comparative Example 2, and Embodiment 1, the operation times 0 through t1 are where refrigeration cycle apparatus 100 is in a transient state, and refrigeration cycle apparatus 100 is in the steady state after operation time t1. Quantities of lubricants q1, q2 can be determined, as appropriate, by experiment using actual apparatus or simulation.
As shown in Fig. 6, regarding the curve C11 corresponding to the refrigeration cycle apparatus according to Comparative Example 1, a time period is present in which the lubricant is depleted when the refrigeration cycle apparatus is in a transient state, and the quantity of lubricant continues on an excess scale when the refrigeration cycle apparatus is in the steady state. Regarding the curve C12 corresponding to the refrigeration cycle apparatus according to Comparative Example 2, the quantity of lubricant is not depleted when the refrigeration cycle apparatus is in a transient state. However, as compared to Comparative Example 1, the lubricant continues on a further excess scale when the refrigeration cycle apparatus according to Comparative Example 2 is in the steady state. In contrast, the lubricant is not depleted when refrigeration cycle apparatus 100 is in a transient state, and, the quantity of lubricant continues within the correct range a period of time after operation time t1. According to the refrigeration cycle apparatus of Embodiment 1, the depletion of the lubricant in a transient state and an excess of the lubricant in the steady state can be prevented.
Embodiment 1 has been described with reference to two pipes being connected to both ends of the oil receiver in the direction of gravity. The pipes connected to the oil receiver may be connected anywhere, insofar as the connection allows the refrigerant and the lubricant to flow through the oil receiver against the direction of gravity. For example, such as in bypass unit 8A shown in Fig. 7, a pipe 811A may be connected to the lower portion of a side surface of oil receiver 81A, and a pipe 812A may be connected to the upper portion of a side surface of oil receiver 81A. With bypass unit 8A, the refrigerant and the lubricant flow into oil receiver 81A through pipe 811A and flow out of oil receiver 81A through pipe 812A.
Embodiment 1 has been described with reference to the reservoir being an oil receiver separate from the pipes. The reservoir may be integrally formed with the pipes. For example, a reservoir 81B and pipes 811B, 812B may be integrally formed, such as bypass unit 8B shown in Fig. 8. In other words, reservoir 81B is a thicker portion of the pipe included in bypass unit 8B than the portion other than reservoir 81B.

Variation of Embodiment 1

The refrigeration cycle apparatus according to a variation of Embodiment 1 is now described, with reference to a refrigeration cycle apparatus including an internal heat exchanger having a different aspect than Embodiment 1.
Fig. 9 is a functional block diagram showing a configuration of refrigeration cycle apparatus 100A according to a variation of Embodiment 1. Refrigeration cycle apparatus 100A has the same configuration as refrigeration cycle apparatus 100 of Fig. 1, except for further including an expansion valve 3A (a third decompressor) and a refrigerant container 11, and including an internal heat exchanger 7A replacing the internal heat exchanger 7 of Fig. 1. Thus, the description will not be repeated.
As shown in Fig. 9, refrigerant container 11 is in communication with expansion valve 5. Expansion valve 3A is connected between refrigerant container 11 and condenser 2. Internal heat exchanger 7A is disposed within refrigerant container 11.
Nodes N1, N2, N4 through N6, N8, N9 are the same as those according to Embodiment 1, and thus the description thereof will not be repeated. The refrigerant that flows between expansion valve 3A and refrigerant container 11 passes through node N10. The refrigerant that flows between refrigerant container 11 and expansion valve 3 passes through node N11. The refrigerant that flows between refrigerant container 11 and expansion valve 5 passes through node N12. The refrigerant that flows between expansion valve 5 and internal heat exchanger 7A passes through node N13.
Fig. 10 is a pressure-enthalpy diagram showing state changes of the refrigerant circulating through refrigeration cycle apparatus 100A of Fig. 9. The states of the refrigerant shown in Fig. 9 correspond to the respective states of the refrigerant at nodes N1, N2, N4 through N6, N8 through N13 of Fig. 9.
Referring to both Figs. 9 and 10, the process from the state of the refrigerant at node N6 to the state of the refrigerant at node N2 via the state of the refrigerant at node N1 is the same as Embodiment 1. The process from the state of the refrigerant at node N2 to the state of the refrigerant at node N10 represents a decompression process performed by expansion valve 3A. Each state at nodes N11, N12 is a state of a saturated liquid flowing out of refrigerant container 11, and indicated on saturated liquid line LC1 of Fig. 10. The process from the state of the refrigerant at node N11 to the state of the refrigerant at node N4 represents a decompression process performed by expansion valve 3. The process from the state of the refrigerant at node N4 to the state of the refrigerant at node N1 via the states of the refrigerant at nodes N5, N6 is the same as Embodiment 1.
The process from the state of the refrigerant at node N12 to the state of the refrigerant at node N13 represents a decompression process performed by expansion valve 5. The process from the state of the refrigerant at node N13 to the state of the refrigerant at node N8 is a heat exchanging process performed by internal heat exchanger 7.
As described above, according to the refrigeration cycle apparatus of Embodiment 1 and the variation thereof, deterioration in performance of the refrigeration cycle apparatus can be prevented.

Embodiment 2

In Embodiment 2, a configuration will be described in which a degree of opening of a second decompressor is adjusted by determining a specific condition indicating that the quantity of lubricant within a compressor is more than a reference quantity (the lubricant is not depleted), thereby adjusting the quantity of lubricant that returns from an oil receiver to the compressor.
Fig. 11 is a functional block diagram showing a configuration of a refrigeration cycle apparatus 200 according to Embodiment 2. Refrigeration cycle apparatus 200 has the same configuration as refrigeration cycle apparatus 100 of Fig. 1, except for further including a sensor unit 21, and including a controller 20 replacing the controller 10 of Fig. 1. Thus, the description will not be repeated.
As shown in Fig. 11 controller 20 controls a driving frequency fc of compressor 1 to control the quantity of refrigerant that is discharged from compressor 1 per unit time. Controller 20 obtains, from sensor unit 21, information necessary for the determination of the specific condition indicating that the lubricant in compressor 1 is not depleted (e.g., a degree of superheat of the refrigerant passing through compressor 1, the height of the liquid level in compressor 1, or the density of the lubricant). Using the information obtained from sensor unit 21, controller 20 controls a degree of opening of expansion valve 5 to adjust the quantity of lubricant that returns from oil receiver 81 to compressor 1.
Fig. 12 is a flowchart showing a flow of a process, performed by controller 20 of Fig. 11, of adjusting the quantity of lubricant that returns from the oil receiver to the compressor. The process illustrated in Fig. 12 is invoked by the main routine (not shown) that performs an integrated control of refrigeration cycle apparatus 200. In the following description, the steps will be simply described as "S".
As shown in Fig. 12, in S101, controller 20 determines whether a condition (the specific condition) is satisfied that a degree of superheat of the refrigerant passing through compressor 1 is greater than a reference value. If a degree of superheat of the refrigerant passing through compressor 1 is greater than the reference value, the operational status of refrigeration cycle apparatus 200 is in the steady state, hardly causing abrupt reduction in the quantity of lubricant in compressor 1 as is caused when refrigeration cycle apparatus 200 is in a transient state. For this reason, if a degree of superheat of the refrigerant passing through compressor 1 is greater than the reference value, controller 20 determines that the lubricant in compressor 1 is not depleted. Note that the refrigerant passing through compressor 1 includes at least one of the refrigerant drawn into compressor 1 and the refrigerant discharged from compressor 1. The reference value can be calculated, as appropriate, by simulation, or experiment using actual apparatus.
If the degree of superheat of the refrigerant passing through compressor 1 is greater than the reference value (YES in S101), controller 20, in S102, reduces the degree of opening of expansion valve 5, and returns the process back to the main routine. If the degree of superheat of the refrigerant passing through the compressor is less than or equal to the reference value (NO in S101), controller 20, in S103, increases the degree of opening of expansion valve 5, and returns the process back to the main routine. In S103, controller 20 may fully open the degree of opening of expansion valve 5.
If the lubricant in compressor 1 is not depleted (the specific condition is satisfied), refrigeration cycle apparatus 200 reduces the quantity of refrigerant that flows into oil receiver 81 per unit time. As a result, velocity Vg of the refrigerant passing through oil receiver 81 (see Equation (1)) decreases less than or equal to the critical velocity Vgc (see Equation (2)), resulting in the lubricant being stored into oil receiver 81. In contrast, if the lubricant in compressor 1 is depleted (the specific condition is not satisfied), refrigeration cycle apparatus 200 increases the quantity of refrigerant that flows into oil receiver 81 per unit time to increase the quantity of lubricant that returns from oil receiver 81 to compressor 1. According to refrigeration cycle apparatus 200, the lubricant can be returned from oil receiver 81 to compressor 1 in a timely manner, as compared to Embodiment 1, thereby allowing further improvement in reliability and performance of the refrigeration cycle apparatus.
Embodiment 2 has been described with reference to using the condition that a degree of superheat of the refrigerant passing through the compressor is greater than the reference value, as the specific condition indicating that the quantity of lubricant in the compressor is more than the reference quantity. The specific condition may be any insofar as it indicates that the quantity of lubricant in the compressor is more than the reference quantity. For example, the condition that the variation in driving frequency of the compressor per unit time is less than a reference variation (S111 of Fig. 13), the condition that the height of the liquid level in the compressor is greater than a reference height (S121 of Fig. 14), or the condition that the concentration of the lubricant in the liquid stored in the compressor is greater than a reference concentration (S131 of Fig. 15) may be employed as the specific condition. The reference quantity, the reference variation, the reference height, and the reference concentration can be calculated, as appropriate, by simulation, or experiment using actual apparatus.
The aspect of the internal heat exchanger included in the refrigeration cycle apparatus according to Embodiment 2 may be similar to the variation of Embodiment 1 shown in Fig. 9, such as the refrigeration cycle apparatus 200A according to the variation of Embodiment 2 shown in Fig. 16.
As describe above, according to the refrigeration cycle apparatus of Embodiment 2 and the variation thereof, deterioration in performance of the refrigeration cycle apparatus can be prevented.

Embodiment 3

Fig. 17 is a functional block diagram showing a configuration of a refrigeration cycle apparatus 300 according to Embodiment 3. Refrigeration cycle apparatus 300 has the same configuration as refrigeration cycle apparatus 200 of Fig. 11, except for further including a bypass valve 82 in bypass unit 8, and including a controller 30 replacing the controller 20. Thus, the description will not be repeated. As shown in Fig. 17, bypass valve 82 is connected between the lower portion of oil receiver 81 and the inlet of compressor 1.
Fig. 18 is a flowchart showing a flow of a process, performed by controller 30 of Fig. 17, of adjusting a quantity of lubricant that returns from an oil receiver 81 to a compressor 1. The process illustrated in Fig. 18 is invoked by the main routine (not shown) that performs an integrated control of refrigeration cycle apparatus 300.
As shown in Fig. 18, in S201, controller 30 determines whether a specific condition is satisfied. The conditions that are shown in S101 of Fig. 12, S111 of Fig. 13, S121 of Fig. 14, or S131 of Fig. 15 can be employed as the specific condition.
If the specific condition is satisfied (YES in S201), controller 30, in S202, reduces the degree of opening of bypass valve 82, and returns the process back to the main routine. If the specific condition is not satisfied (NO in S201), controller 30, in S303, increases the degree of opening of bypass valve 82, and returns the process back to the main routine. Controller 30 may close bypass valve 82 in S302, or fully open the bypass valve in S303.
With refrigeration cycle apparatus 300, if the specific condition is not satisfied (if the lubricant in compressor 1 is depleted), the lubricant is returned to compressor 1 from oil receiver 81 also through the lower portion. According to refrigeration cycle apparatus 300, when the lubricant in compressor 1 is depleted, a required quantity of lubricant can be returned from oil receiver 81 to compressor 1 in a shorter time than Embodiment 2, thereby further improving the reliability of the refrigeration cycle apparatus.
The aspect of the internal heat exchanger included in the refrigeration cycle apparatus according to Embodiment 3 may be similar to the variation of Embodiment 1 shown in Fig. 9, such as the refrigeration cycle apparatus 300A according to the variation of Embodiment 3 shown in Fig. 19.
As describe above, according to the refrigeration cycle apparatus of Embodiment 3 and the variation thereof, deterioration in performance of the refrigeration cycle apparatus can be prevented.
The presently disclosed embodiments are also expected to be combined and implemented as appropriate within a consistent range. The presently disclosed embodiments should be considered in all aspects as illustrative and not restrictive.
The scope of the present invention is defined by the appended claims, rather than by the description above. All changes which come within the meaning and range of equivalency of the appended claims are to be embraced within their scope.

REFERENCE SIGNS LIST

1 compressor; 2 condenser; 3, 3A, 5 expansion valve; 4 evaporator; 7, 7A internal heat exchanger; 8, 8A, 8B bypass unit; 10, 20, 30 controller; 11 refrigerant container; 21 sensor unit; 81, 81A oil receiver; 81B reservoir; 82 bypass valve; 100, 100A, 200, 200A, 300, 300A refrigeration cycle apparatus; 811, 811A, 811B, 812, 812A, and 812B pipe.

Claims

A refrigeration cycle apparatus through which a refrigerant circulates, the refrigeration cycle apparatus comprising:
a compressor in which a lubricant is stored;

a first heat exchanger;

a first decompressor;

a second heat exchanger;

a second decompressor;

a third heat exchanger; and

a bypass unit, wherein

the refrigerant and the lubricant circulate in order of the compressor, the first heat exchanger, the third heat exchanger, the first decompressor, and the second heat exchanger, and circulate in order of the compressor, the first heat exchanger, the second decompressor, the third heat exchanger, and the bypass unit,

the bypass unit includes a reservoir extending in a direction of gravity,

the refrigerant and the lubricant flow through the reservoir against the direction of gravity,

if a quantity of the refrigerant that flows through the bypass unit per unit time is a reference flow rate, the reservoir has a diameter satisfying a relationship that the velocity of the refrigerant flowing through the reservoir is slower than a critical velocity,

when the relationship is satisfied, a quantity of the lubricant that flows into the reservoir is more than a quantity of the lubricant that flows out of the reservoir, and

the critical velocity is determined from gravitational acceleration, the diameter, a density of the lubricant, and a density of a gas of the refrigerant.
The refrigeration cycle apparatus according to claim 1, further comprising:
a refrigerant container in communication with the second decompressor; and

a third decompressor connected between the refrigerant container and the first heat exchanger, wherein

the third heat exchanger is disposed within the refrigerant container.
The refrigeration cycle apparatus according to claim 1 or 2, wherein
a degree of opening of the second decompressor when a specific condition is satisfied is smaller than a degree of opening of the second decompressor when the specific condition is not satisfied, and

the specific condition indicates that a quantity of the lubricant in the compressor is more than a reference quantity.
The refrigeration cycle apparatus according to claim 1 or 2, wherein
the bypass unit further includes a bypass valve connected between a lower portion of the reservoir and an inlet of the compressor.
The refrigeration cycle apparatus according to claim 4, wherein
a degree of opening of the bypass valve when the specific condition is satisfied is smaller than a degree of opening of the bypass valve when the specific condition is not satisfied, and

the specific condition indicates that a quantity of the lubricant in the compressor is more than a reference quantity.
The refrigeration cycle apparatus according to claim 3 or 5, wherein
the specific condition is that a degree of superheat of the refrigerant passing through the compressor is greater than a reference value.
The refrigeration cycle apparatus according to claim 3 or 5, wherein
the specific condition is that a variation in driving frequency of the compressor per unit time is less than a reference variation.
The refrigeration cycle apparatus according to claim 3 or 5, wherein
the specific condition is that a height of a liquid level in the compressor is greater than a reference height.
The refrigeration cycle apparatus according to claim 3 or 5, wherein
the specific condition is that a concentration of the lubricant in a liquid stored in the compressor is greater than a reference concentration.
The refrigeration cycle apparatus according to any one of claims 1 to 9, wherein
the reservoir is integrally formed with a pipe included in the bypass unit.