Patent Description:
A known refrigeration cycle apparatus includes a subcooling circuit, and a gas-liquid separator provided on the upstream side of the subcooling circuit.

The conventional refrigeration cycle apparatus separates a refrigerant in gas-liquid two-phase state into a gas refrigerant and a liquid refrigerant by the gas-liquid separator, causes only the separated liquid refrigerant to flow into the subcooling circuit, and bypasses the separated gas refrigerant to a compressor.

<CIT> discloses a refrigeration cycle apparatus including: a compressor; a condenser; an indoor expansion valve; a subcooling circuit that is disposed between the condenser and the indoor expansion valve; an evaporator; and a refrigerant pipe that connects the compressor, the condenser, the subcooling circuit, the indoor expansion valve, and the evaporator, and circulates a refrigerant. The refrigerant pipe includes: a main circuit pipe that circulates the refrigerant through the compressor, the condenser, the subcooling circuit, the indoor expansion valve, and the evaporator; a bypass circuit pipe that branches from the middle of the main circuit pipe connecting the subcooling circuit to the indoor expansion valve and bypasses the refrigerant to the compressor; and a branch portion that connects the main circuit pipe and the bypass circuit pipe. The branch portion includes an upstream pipe portion, a main-circuit branch pipe portion and a bypass-circuit branch pipe portion.

<CIT> relates to a gas-liquid separator constituted of a flow rectifying part having such a shape that it converges almost from the center toward both ends, a gas collecting tool one end of which is communicated with one end of the flow rectifying part coaxially and which has a hollow part for collecting gas, a liquid collecting tool one end of which is communicated with the other end of the flow rectifying part coaxially and which has a hollow part for collecting the liquid, a mixed fluid injecting hole opened on a flow rectifying tool in the tangential direction, a gas sending hole opened to the gas collecting tool on the axial line of the hollow part for collecting the gas and a liquid sending hole opened to the liquid collecting tool.

<CIT> discloses a compression refrigeration system in which at least on refrigerant circulates in a hermetic circuit and in which the lubricating oil of the compressor is stirred and circulates with said refrigerant, a separation process; the oil characterized in that a separating fluid is provided with a boiling point higher than the refrigerant and more soluble in the lubricating oil than the refrigerant, the separating fluid is mixed with the vapors of the refrigerant, the mixture is compressed and the compressed mixture is partially condensed in order to dissolve the lubricating oil in the liquefied separating fluid. The oil-loaded separating fluid is separated from the vapors of the refrigerant, the separated oil-loaded separating fluid is expanded to a lower pressure, and the oil-loaded separating fluid is recycled into the mixing phase.

The conventional refrigeration cycle apparatus requires the gas-liquid separator and piping that bypasses the separated gas refrigerant to the compressor. These gas-liquid separator and bypass-piping increase the cost of the refrigeration cycle apparatus and complicate the piping system.

For this reason, the present invention proposes a refrigeration cycle apparatus that can sufficiently exhibit performance of a subcooling circuit with a simple configuration.

To achieve the above object, the present invention provides a refrigeration cycle apparatus including: a compressor; a condenser; an indoor expansion valve; a subcooling circuit that is disposed between the condenser and the indoor expansion valve; an evaporator; and a refrigerant pipe that connects the compressor, the condenser, the subcooling circuit, the indoor expansion valve, and the evaporator, and circulates a refrigerant. The refrigerant pipe includes: a main circuit pipe that circulates the refrigerant through the compressor, the condenser, the subcooling circuit, the indoor expansion valve, and the evaporator; a bypass circuit pipe that branches from the middle of the main circuit pipe connecting the subcooling circuit to the indoor expansion valve and bypasses the refrigerant to the compressor; and a branch portion that connects the main circuit pipe and the bypass circuit pipe. The branch portion includes an upstream pipe portion, a main-circuit branch pipe portion and a bypass-circuit branch pipe portion. The main-circuit branch pipe portion branches upward from the upstream pipe portion toward the indoor expansion valve; and the bypass-circuit branch pipe portion branches downward from the upstream pipe portion and extends toward the subcooling circuit. The main-circuit branch pipe portion and the bypass-circuit branch pipe portion constitute a continuous straight pipe; and the upstream pipe portion is connected to the straight pipe in a tee-shape. A flow-path cross-sectional area of the straight pipe is twice a flow-path cross-sectional area of the upstream pipe portion or more.

It may be desired that the upstream pipe portion extends substantially in a horizontal direction; and the main-circuit branch pipe portion and the bypass-circuit branch pipe portion extend substantially in a vertical direction.

It may be desired that an extended line of a centerline of the upstream pipe portion intersects neither a centerline of the main-circuit branch pipe portion nor a centerline of the bypass-circuit branch pipe portion.

Embodiments of a refrigeration cycle apparatus according to the present invention will now be described by referring to <FIG>. The same reference signs are given to identical or equivalent components in each figure.

<FIG> is a schematic diagram illustrating a refrigeration cycle apparatus according to one embodiment of the present invention.

As shown in <FIG>, the refrigeration cycle apparatus <NUM> according to the present embodiment is, for example, an air conditioner. The refrigeration cycle apparatus <NUM> includes: a compressor <NUM>; an outdoor heat exchanger <NUM>; an outdoor expansion valve <NUM>; a subcooling circuit <NUM>; an indoor expansion valve <NUM>; an indoor heat exchanger <NUM>; and a refrigerant pipe <NUM> that connects the compressor <NUM>, the outdoor heat exchanger <NUM>, the subcooling circuit <NUM>, the indoor expansion valve <NUM>, and the indoor heat exchanger <NUM> so as to circulate a refrigerant.

The refrigeration cycle apparatus <NUM> further includes: a four-way valve <NUM> that sends the refrigerant to be discharged from the compressor <NUM> to one of the outdoor heat exchanger <NUM> and the indoor heat exchanger <NUM>, and causes the compressor <NUM> to suck in the refrigerant having passed through the other of the outdoor heat exchanger <NUM> and the indoor heat exchanger <NUM> again; and an accumulator <NUM> that is provided on the refrigerant pipe <NUM> between the four-way valve <NUM> and the compressor <NUM>.

The refrigeration cycle apparatus <NUM> further includes: an outdoor unit <NUM> to be installed outside a building such as a house; and at least one indoor unit <NUM> to be installed inside the building. The refrigeration cycle apparatus <NUM> according to the present embodiment includes, for example, one outdoor unit <NUM> and a plurality of indoor units <NUM> to be connected in parallel to the outdoor unit <NUM>.

The outdoor unit <NUM> houses the compressor <NUM>, the outdoor heat exchanger <NUM>, the outdoor expansion valve <NUM>, the subcooling circuit <NUM>, the four-way valve <NUM>, and the accumulator <NUM>. The outdoor unit <NUM> is provided with an outdoor blower <NUM> that sucks in air from the outside of the outdoor unit <NUM> and blows out the air having exchanged heat with the outdoor heat exchanger <NUM> to the outside of the outdoor unit <NUM>. The outdoor blower <NUM> includes: a propeller fan <NUM> that faces the outdoor heat exchanger <NUM>; and an electric motor <NUM> that rotationally drives the propeller fan <NUM>.

The indoor unit <NUM> houses the expansion valve <NUM> and the indoor heat exchanger <NUM>. The indoor unit <NUM> is provided with an indoor blower <NUM> that sucks in air from the outside of the indoor unit <NUM> and blows out the air having exchanged heat with the indoor heat exchanger <NUM> to the outside of the indoor unit <NUM>. The indoor blower <NUM> includes: a propeller fan <NUM> that faces the indoor heat exchanger <NUM>; and an electric motor <NUM> that rotationally drives the propeller fan <NUM>.

Each of the outdoor heat exchanger <NUM> and the indoor heat exchanger <NUM> is, for example, a fin-and-tube type.

The outdoor heat exchanger <NUM> functions as a condenser when the refrigeration cycle apparatus <NUM> is operated for cooling, and functions as an evaporator when the refrigeration cycle apparatus <NUM> is operated for heating.

The indoor heat exchanger <NUM> functions as an evaporator when the refrigeration cycle apparatus <NUM> is operated for cooling, and functions as a condenser when the refrigeration cycle apparatus <NUM> is operated for heating.

The compressor <NUM> compresses the refrigerant, then boosts the refrigerant, and then discharges the refrigerant. The compressor <NUM> may be, for example, a compressor that can change its operating frequency by known inverter control or a compressor that cannot change its operating frequency.

Each of the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> is, for example, a Pulse Motor Valve (PMV). Each of the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> can adjust its valve opening. The indoor expansion valve <NUM> functions as an expansion valve mainly during cooling operation, and functions as a subcooling-degree adjusting valve for the indoor heat exchanger <NUM> mainly during heating operation. The outdoor expansion valve <NUM> functions as an expansion valve mainly during heating operation, and functions as a subcooling-degree adjusting valve for the outdoor heat exchanger <NUM> mainly during cooling operation. Although it is not illustrated, each of the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> includes: a valve body having a through hole; a needle capable of advancing and retreating with respect to the through hole; and a power source for advancing and retreating the needle, for example. When the through hole is closed with the needle, the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> stop (block) the flow of the refrigerant in the refrigeration cycle apparatus <NUM>. At this time, the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> are in the closed state, and the opening degree of each of the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> is the smallest. When the needle is situated farthest from the through hole, the amount of the refrigerant flow in the refrigeration cycle apparatus <NUM> is maximized and the opening degree of each of the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> is the largest at this time.

The power source is, for example, a stepping motor. When the number of pulses to be inputted to the stepping motor is zero, the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> are closed. When the number of pulses to be inputted to the stepping motor is the maximum pulse, the indoor expansion valve <NUM> and the outdoor expansion valve <NUM> reach the maximum opening degree. The maximum number of pulses is, for example, several hundred pulses such as <NUM> pulses.

The refrigerant pipe <NUM> connects the compressor <NUM>, the accelerator <NUM>, the four-way valve <NUM>, the outdoor heat exchanger <NUM>, the outdoor expansion valve <NUM>, the subcooling circuit <NUM>, the indoor expansion valve <NUM>, and the indoor heat exchanger <NUM>. The refrigerant pipe <NUM> includes: a main circuit pipe <NUM> that circulates the refrigerant through the compressor <NUM>, the accelerator <NUM>, the four-way valve <NUM>, the outdoor heat exchanger <NUM>, the outdoor expansion valve <NUM>, the subcooling circuit <NUM>, the indoor expansion valve <NUM>, and the indoor heat exchanger <NUM>; a bypass circuit pipe <NUM> that branches from the middle of the main circuit pipe <NUM> interconnecting the subcooling circuit <NUM> and the indoor expansion valve <NUM> so as to bypass the refrigerant to the compressor <NUM>; and a branch portion <NUM> that branches the bypass circuit pipe <NUM> from the main circuit pipe <NUM>.

The main circuit pipe <NUM> includes: a first main refrigerant pipe 31a that connects the discharge side of the compressor <NUM> and the four-way valve <NUM>; a second main refrigerant pipe 31b that connects the suction side of the compressor <NUM> and the four-way valve <NUM>; a third main refrigerant pipe 31c that connects the four-way valve <NUM> and the outdoor heat exchanger <NUM>; a fourth main refrigerant pipe 31d that connects the outdoor heat exchanger <NUM> and the indoor heat exchanger <NUM>; and a fifth main refrigerant pipe 31e that connects the indoor heat exchanger <NUM> and the four-way valve <NUM>.

The fourth main refrigerant pipe 31d connects the outdoor heat exchanger <NUM> and the indoor heat exchanger <NUM> via a first pipe-connection-portion 31f of the outdoor unit <NUM> and a second pipe-connection-portion <NUM> of the indoor unit <NUM>.

The fifth main refrigerant pipe 31e connects the indoor heat exchanger <NUM> and the four-way valve <NUM> via a third pipe-connection-portion <NUM> of the indoor unit <NUM> and a fourth pipe-connection-portion 31i of the outdoor unit <NUM>.

The branch portion <NUM> is disposed in the middle of the fourth main refrigerant pipe 31d that connects the outdoor heat exchanger <NUM> and the first pipe-connection-portion 31f of the outdoor unit <NUM>.

The accumulator <NUM> is provided in the middle of the second main refrigerant pipe 31b.

The outdoor expansion valve <NUM>, the subcooling circuit <NUM>, and the indoor expansion valve <NUM> are provided in the middle of the fourth main refrigerant pipe 31d. The subcooling circuit <NUM> is closer to the outdoor heat exchanger <NUM> than the indoor expansion valve <NUM>. The outdoor expansion valve <NUM> is closer to the outdoor heat exchanger <NUM> than the subcooling circuit <NUM>. The indoor expansion valve <NUM> is closer to the indoor heat exchanger <NUM> than the subcooling circuit <NUM>. In other words, the outdoor expansion valve <NUM> is disposed between the outdoor heat exchanger <NUM> and the subcooling circuit <NUM>. The subcooling circuit <NUM> is disposed between the outdoor heat exchanger <NUM> and the indoor expansion valve <NUM>. The subcooling circuit <NUM> is disposed between the outdoor expansion valve <NUM> and the indoor expansion valve <NUM>. In addition, the outdoor expansion valve <NUM> is disposed in the middle of the fourth main refrigerant pipe 31d that connects the outdoor heat exchanger <NUM> and the first pipe-connection-portion 31f of the outdoor unit <NUM>. The subcooling circuit <NUM> is disposed in the middle of the fourth main refrigerant pipe 31d that connects the outdoor heat exchanger <NUM> and the first pipe-connection-portion 31f of the outdoor unit <NUM>. The indoor expansion valve <NUM> is disposed in the middle of the fourth main refrigerant pipe 31d that connects the second pipe-connection-portion <NUM> of the indoor unit <NUM> and the indoor heat exchanger <NUM>.

The four-way valve <NUM> switches the direction of the refrigerant flow in the refrigerant pipe <NUM>. When the refrigeration cycle apparatus <NUM> is operated for cooling (with the flow of the refrigerant shown by the solid line in <FIG>) to lower the room temperature in the building, the four-way valve <NUM> circulates the refrigerant from the first main refrigerant pipe 31a to the third main refrigerant pipe 31c and circulates the refrigerant from the fifth main refrigerant pipe 31e to the second main refrigerant pipe 31b. When the refrigeration cycle apparatus <NUM> is operated for heating (with the flow of the refrigerant shown by the broken line in <FIG>) to raise the room temperature in the building, the four-way valve <NUM> circulates the refrigerant from the first main refrigerant pipe 31a to the fifth main refrigerant pipe 31e and circulates the refrigerant from the third main refrigerant pipe 31c to the second main refrigerant pipe 31b.

<FIG> is a schematic diagram illustrating the subcooling circuit of the refrigeration cycle apparatus according to the embodiment of the present invention.

As shown in <FIG> and <FIG>, the subcooling circuit <NUM> of the refrigeration cycle apparatus <NUM> according to the present embodiment includes: the bypass circuit pipe <NUM>; a subcooling expansion valve <NUM>; and a subcooling heat exchanger <NUM>.

The bypass circuit pipe <NUM> branches the refrigerant flowing from the outdoor heat exchanger <NUM> to the indoor heat exchanger <NUM> in the main circuit pipe <NUM> during the cooling operation, and bypasses the refrigerant to the accelerator <NUM> without passing through the indoor expansion valve <NUM> and the indoor heat exchanger <NUM>. The bypass circuit pipe <NUM> branches from the branch portion <NUM>, i.e., the middle of the fourth main refrigerant pipe 31d that connects the outdoor heat exchanger <NUM> and the first pipe-connection-portion 31f of the outdoor unit <NUM>. The bypass circuit pipe <NUM> joins the second main refrigerant pipe 31b of the main circuit pipe <NUM> in the middle of the second main refrigerant pipe 31b that connects the accumulator <NUM> and the four-way valve <NUM>.

The subcooling expansion valve <NUM> decompresses the refrigerant that has flowed from the branch portion <NUM> into the bypass circuit pipe <NUM>.

The subcooling heat exchanger <NUM> exchanges heat between the refrigerant decompressed by the subcooling expansion valve <NUM> and the refrigerant flowing through the main circuit pipe <NUM> (specifically, the portion upstream of the branch portion <NUM> in the fourth main refrigerant pipe 31d) so as to subcool the refrigerant flowing through the main circuit pipe <NUM>.

The bypass circuit pipe <NUM> includes: a first bypass refrigerant pipe 32a that connects the branch portion <NUM> and the subcooling expansion valve <NUM>; a second bypass refrigerant pipe 32b that connects the subcooling expansion valve <NUM> and the subcooling heat exchanger <NUM>; and a third bypass refrigerant pipe 32c that connects the subcooling heat exchanger <NUM> and the second main refrigerant pipe 31b of the main circuit pipe <NUM>.

In addition, the refrigeration cycle apparatus <NUM> includes a controller <NUM> that is electrically connected to the four-way valve <NUM> via a signal line (not shown). The controller <NUM> may be connected to the compressor <NUM> that can change its operating frequency.

The controller <NUM> includes: a central processing unit (not shown) and a storage device (not shown) that stores various arithmetic programs and parameters to be executed by the central processing unit. The controller <NUM> reads various control programs from an auxiliary storage device into a main storage device, and causes the central processing unit to execute the various control programs having been read into the main storage device.

The controller <NUM> switches between the cooling operation and the heating operation of the refrigeration cycle apparatus <NUM> by switching the state of the four-way valve <NUM> on the basis of a request to be inputted into an input device such as a remote controller.

The controller <NUM> controls the opening degree of the subcooling expansion valve <NUM> on the basis of: a first temperature sensor <NUM> that measures temperature of the refrigerant flowing through the fourth main refrigerant pipe 31d between the outdoor heat exchanger <NUM> and the subcooling circuit <NUM>; a second temperature sensor <NUM> that measures temperature of the refrigerant flowing through the fourth main refrigerant pipe 31d between the subcooling circuit <NUM> and the first pipe-connection-portion 31f; a third temperature sensor <NUM> that measures temperature of the refrigerant flowing through the third bypass refrigerant pipe 32c; and saturated suction temperature.

The saturated suction temperature is calculated by converting the value of a suction pressure sensor <NUM> that measures the pressure of the refrigerant flowing through the fourth main refrigerant pipe 31d.

During the cooling operation, the refrigeration cycle apparatus <NUM> discharges the compressed high-temperature and high-pressure refrigerant from the compressor <NUM>, and then sends this refrigerant to the outdoor heat exchanger <NUM> via the four-way valve <NUM>. The outdoor heat exchanger <NUM> exchanges heat between the air outside the building and the refrigerant passing through the tube, and cools the refrigerant in order to liquefy the refrigerant into a high-pressure liquefied refrigerant. That is, during the cooling operation, the outdoor heat exchanger <NUM> functions as a condenser. The refrigerant having passed through the outdoor heat exchanger <NUM> passes through the indoor expansion valve <NUM> so as to be depressurized and brought into a low-pressure gas-liquid two-phase refrigerant, and then reaches the indoor heat exchanger <NUM>. The indoor heat exchanger <NUM> cools the air inside the building by exchanging heat between the air inside the building and the refrigerant passing through the tube. At this time, the indoor heat exchanger <NUM> functions as an evaporator that evaporates the refrigerant into a gaseous state. The refrigerant having passed through the indoor heat exchanger <NUM> is sucked back into the compressor <NUM>.

During the heating operation, the refrigeration cycle apparatus <NUM> inverts the four-way valve <NUM> to generate a flow of refrigerant that is opposite to the flow of the refrigerant during the cooling operation in the refrigeration cycle, causes the indoor heat exchanger <NUM> to function as a condenser, and causes the outdoor heat exchanger <NUM> to function as an evaporator.

The refrigeration cycle apparatus <NUM> may be dedicated to cooling without the four-way valve <NUM>. In this case, the discharge side of the compressor <NUM> is connected to the outdoor heat exchanger <NUM> through the refrigerant pipe <NUM>, and the suction side of the compressor <NUM> is connected to the indoor heat exchanger <NUM> through the refrigerant pipe <NUM>.

The subcooling circuit <NUM> is used for reducing the dryness of the refrigerant flowing from the outdoor heat exchanger <NUM> to the indoor expansion valve <NUM> and for reducing the amount of the refrigerant circulating in the indoor unit <NUM>.

The subcooling circuit <NUM> is generally used in the cooling operation. In the subcooling circuit <NUM>, a part of the liquid refrigerant condensed by the outdoor heat exchanger <NUM> is branched at the branch portion <NUM> and expanded at a low pressure by the subcooling expansion valve <NUM>. The subcooling heat exchanger <NUM> exchanges heat between the two-phase refrigerant expanded at a low pressure by the subcooling expansion valve <NUM> and the refrigerant flowing through the main circuit pipe <NUM> (specifically, the portion upstream of the branch portion <NUM> in the fourth main refrigerant pipe 31d) so as to cool the refrigerant flowing through the main circuit pipe <NUM>.

When a part of the refrigerant is not condensed in the outdoor heat exchanger <NUM> and flows out to the fourth main refrigerant pipe 31d in the state of gas refrigerant, there is a possibility that the two-phase refrigerant flows into the subcooling circuit <NUM>. Generally, the subcooling expansion valve <NUM> has an insufficient pipe diameter for circulating the two-phase refrigerant. Accordingly, the amount of refrigerant flowing through the subcooling circuit <NUM> is insufficient, and thus, the heat exchange amount of the subcooling circuit <NUM> decreases. When the heat exchange amount of the subcooling circuit <NUM> decreases, the gas refrigerant is mixed into the fourth main refrigerant pipe 31d of the main circuit pipe <NUM> and the gas refrigerant is sent to the indoor unit <NUM>.

For this reason, the branch portion <NUM> of the refrigeration cycle apparatus <NUM> according to the present embodiment includes: an upstream pipe portion <NUM>; a main-circuit branch pipe portion <NUM> that branches upward (solid arrow U in <FIG>) from the upstream pipe portion <NUM> and extends toward the indoor expansion valve <NUM>; and a bypass-circuit branch pipe portion <NUM> that branches downward (solid arrow D in <FIG>) from the upstream pipe portion <NUM> and extends towards the subcooling circuit <NUM>. The upstream pipe portion <NUM> and the main-circuit branch pipe portion <NUM> correspond to a part of the fourth main refrigerant pipe 31d of the main circuit pipe <NUM>, and the bypass-circuit branch pipe portion <NUM> corresponds to a part of the first bypass refrigerant pipe 32a of the bypass circuit pipe <NUM>.

The main-circuit branch pipe portion <NUM> and the bypass-circuit branch pipe portion <NUM> constitute a continuous straight pipe <NUM>. In other words, the main-circuit branch pipe portion <NUM> configured as a part of the straight pipe <NUM> corresponds to a part of the fourth main refrigerant pipe 31d of the main circuit pipe <NUM>, and the bypass-circuit branch pipe portion <NUM> configured as the rest of the straight pipe <NUM> corresponds to a part of the first bypass refrigerant pipe 32a of the bypass circuit pipe <NUM>. The straight pipe <NUM> has a substantially uniform flow-path cross-sectional area from the portion corresponding to the main-circuit branch pipe portion <NUM> to the portion corresponding to the bypass-circuit branch pipe portion <NUM>. The boundary between the fourth main refrigerant pipe 31d of the main circuit pipe <NUM> and the first bypass refrigerant pipe 32a of the bypass circuit pipe <NUM> is the confluence of the straight pipe <NUM> and the upstream pipe portion <NUM>.

The fourth main refrigerant pipe 31d may be bent except the portion that corresponds to a part of the straight pipe <NUM>. Additionally, the first bypass refrigerant pipe 32a may be bent except the portion that corresponds to the rest of the straight pipe <NUM>.

The main-circuit branch pipe portion <NUM> and the bypass-circuit branch pipe portion <NUM> extend substantially in the vertical direction. The main-circuit branch pipe portion <NUM> and the bypass-circuit branch pipe portion <NUM> may be tilted in the range of <NUM> degrees (± <NUM> degrees) with respect to the vertical line VL.

The upstream pipe portion <NUM> is connected to the straight pipe <NUM> in a tee-shape. In other words, the upstream pipe portion <NUM> abuts on the straight pipe <NUM> from the radial direction of the straight pipe <NUM>. The upstream pipe portion <NUM> extends substantially in the horizontal direction. The upstream pipe portion <NUM> may be tilted within a range of <NUM> degrees (± <NUM> degrees) with respect to the horizontal plane HP. The angle θ formed by the upstream pipe portion <NUM> and the straight pipe <NUM> is preferably <NUM> degrees or more.

For example, when the upstream pipe portion <NUM> abuts on the straight pipe <NUM> from the radial direction of the straight pipe <NUM>, the angle θ formed by the upstream pipe portion <NUM> and the straight pipe <NUM> is <NUM> degrees. In this case, the upstream pipe portion <NUM> and the straight pipe <NUM> form a tee-shape rotated by <NUM> degrees.

The flow-path cross-sectional area PA1 of the straight pipe <NUM> is twice the flow-path cross-sectional area PA2 of the upstream pipe portion <NUM> or more.

The branch portion <NUM> of the refrigeration cycle apparatus <NUM> according to the present embodiment causes the mainstream (i.e., flow of the refrigerant flowing through the main circuit pipe <NUM>) in the direction of the solid arrow A in <FIG>, and causes a bypass flow (i.e., flow of the refrigerant flowing through the subcooling circuit <NUM>) in the direction of the solid arrow B in <FIG>. The amount of the refrigerant to be bypassed toward the subcooling circuit <NUM> is determined by the inner diameter of the bypass circuit pipe <NUM> and the valve opening degree of the subcooling expansion valve <NUM>. The amount of the refrigerant to be bypassed toward the subcooling circuit <NUM> is, for example, from <NUM>% (when the subcooling expansion valve <NUM> is fully closed) to <NUM>% (when the subcooling expansion valve <NUM> is fully open) of the mainstream. Thus, in the first bypass refrigerant pipe 32a, the gas refrigerant is separated upward and the liquid refrigerant is separated downward due to the influence of buoyancy and gravity. Accordingly, the proportion of the liquid refrigerant flowing into the subcooling circuit <NUM> increases, and the proportion of the gas refrigerant flowing into the subcooling circuit <NUM> decreases.

Once the flow rate of the liquid refrigerant flowing to the subcooling circuit <NUM> is secured, even if the gas-liquid two-phase refrigerant flows out from the outdoor heat exchanger <NUM>, the gas-liquid two-phase refrigerant can be condensed into the liquid refrigerant by the subcooling circuit <NUM>. That is, the outflow of the gas refrigerant to the side of the indoor unit <NUM> is eliminated or reduced.

When the flow-path cross-sectional area of the straight pipe <NUM> is twice the flow-path cross-sectional area of the upstream pipe portion <NUM> or more, the flow velocity of the refrigerant in the straight pipe <NUM> is reduced. This reduction effect reduces the flow velocity of the refrigerant in the first bypass refrigerant pipe 32a (i.e., flow velocity of the bypass flow) to, for example, about <NUM>% of the flow velocity of the refrigerant in the fourth main refrigerant pipe 31d (i.e., flow velocity of the mainstream). This reduction of the flow velocity of the refrigerant makes the buoyancy of the gas refrigerant larger than the force to be received from the flow of the liquid refrigerant. Thus, the effect of gas-liquid separation appears more prominently.

<FIG> is a diagram showing a comparison of heat exchange amount between the subcooling circuit of the refrigeration cycle apparatus according to the embodiment of the present invention and a subcooling circuit of a comparative example.

The solid line α in <FIG> indicates the relationship between the dryness and the heat exchange amount in the subcooling circuit <NUM> of the refrigeration cycle apparatus <NUM> according to the present embodiment. The broken line β in <FIG> indicates the relationship between the dryness and the heat exchange amount in the subcooling circuit of the refrigeration cycle apparatus of the comparative example.

First, the branch portion of the refrigeration cycle apparatus in the comparative example is assumed to include: a main circuit pipe (corresponding to the fourth main refrigerant pipe 31d) that extends in the horizontal direction and connects the outdoor heat exchanger <NUM> to the indoor heat exchanger <NUM>; and a bypass-circuit pipe (corresponding to the first bypass refrigerant pipe 32a) that hangs down from the lower face of the main circuit pipe and branches so as to be connected to the subcooling expansion valve <NUM>. In other words, the refrigeration cycle apparatus of the comparative example includes: the main circuit pipe; and a tee-shaped branch portion of the bypass-circuit pipe hanging down from a straight-pipe portion of the main circuit pipe.

As shown in <FIG>, in the refrigeration cycle apparatus of the comparative example, the flow rate in the subcooling expansion valve is insufficient unless the dryness is zero or less. Thus, in the subcooling circuit of the comparative example, the heat exchange amount becomes insufficient when the dryness exceeds the zero value.

Even in the gas-liquid two-phase region where the dryness is larger than zero, the refrigeration cycle apparatus <NUM> according to the present embodiment can flow the liquid refrigerant through the subcooling expansion valve <NUM> by the gas-liquid separation effect of the branch portion <NUM>. Thus, the subcooling circuit <NUM> according to the present embodiment can increase the heat exchange amount even if the dryness is larger than the zero value.

<FIG> and <FIG> are cross-sectional views illustrating another aspect of the branch portion of the refrigeration cycle apparatus according to the embodiment of the present invention. <FIG> is a cross-sectional view of passing through the center of the upstream pipe portion <NUM> of the branch portion <NUM> and orthogonal to the respective centers of the bypass-circuit branch pipe portion <NUM> and the main-circuit branch pipe portion <NUM>. <FIG> is a cross-sectional view of passing through the respective centers of the bypass-circuit branch pipe portion <NUM> and the main-circuit branch pipe portion <NUM>.

As shown in <FIG> and <FIG>, the refrigeration cycle apparatus <NUM> according to the present embodiment includes a branch portion 33A. The extended line of the centerline Ca of the upstream pipe portion <NUM> of the branch portion 33A intersects neither the centerline Cb of the main-circuit branch pipe portion <NUM> nor the centerline Cc of the bypass-circuit branch pipe portion <NUM>. In other words, the extended line of the centerline Ca of the upstream pipe portion <NUM> is biased outward in the radial direction of the main-circuit branch pipe portion <NUM> and the bypass-circuit branch pipe portion <NUM> with respect to the centerline Cb of the main-circuit branch pipe portion <NUM> and the centerline Cc of the bypass-circuit branch pipe portion <NUM>.

It is preferred that the upstream pipe portion <NUM> is connected along the tangent TL of the bypass-circuit branch pipe portion <NUM> and the main-circuit branch pipe portion <NUM> in the cross-section of <FIG>.

Further, it is preferred that the pipe diameter of the upstream pipe portion <NUM> is equal to or smaller than half the pipe diameter of the bypass-circuit branch pipe portion <NUM> and the main-circuit branch pipe portion <NUM>.

In the branch portion 33A, the refrigerant flowing from the upstream pipe portion <NUM> into the straight pipe <NUM> (i.e., the main-circuit branch pipe portion <NUM> and the bypass-circuit branch pipe portion <NUM>) causes a circumferential flow (solid arrow R) in the straight pipe <NUM>. This swirling flow R causes a separation effect between the gas refrigerant g and the liquid refrigerant I due to centrifugal force at the branch portion between the upstream pipe portion <NUM> and the straight pipe <NUM>. Further, the swirling flow R reduces the flow velocity of the refrigerant in the longitudinal direction in the straight pipe <NUM>. This reduction of the flow velocity makes it easier for the gas refrigerant to float upward and the liquid refrigerant to fall downward. That is, the supply ratio of the liquid refrigerant to the subcooling circuit <NUM> is improved.

The refrigeration cycle apparatus <NUM> according to the present embodiment has the branch portion <NUM> or 33A, and this branch portion <NUM> or 33A includes: the main-circuit branch pipe portion <NUM> that branches upward from the upstream pipe portion <NUM> and extends toward the indoor expansion valve <NUM>; and a bypass-circuit branch pipe portion <NUM> that branches downward from the upstream pipe portion <NUM> and extends toward subcooling circuit <NUM>. Consequently, even if the refrigerant in the state of gas-liquid two-phase flows out of the outdoor heat exchanger <NUM>, the refrigeration cycle apparatus <NUM> increases the proportion of the liquid refrigerant flowing into the subcooling circuit <NUM> and decreases the proportion of the gas refrigerant flowing into the subcooling circuit <NUM>. Once the flow rate of the liquid refrigerant flowing to the subcooling circuit <NUM> is satisfied, even if the refrigerant in the state of gas-liquid two-phase flows out of the outdoor heat exchanger <NUM>, the refrigerant in the state of gas-liquid two-phase can be condensed into the liquid refrigerant by the subcooling circuit <NUM>. That is, the refrigeration cycle apparatus <NUM> can eliminate or reduce the outflow of the gas refrigerant to the side of the indoor unit <NUM> by the branch portion <NUM> or 33A having a simple structure.

Additionally, the refrigeration cycle apparatus <NUM> according to the present embodiment includes: the straight pipe <NUM> configured with the main-circuit branch pipe portion <NUM> and the bypass-circuit branch pipe portion <NUM> continuously; and the upstream pipe portion <NUM> that is connected to the straight pipe <NUM> in the tee-shape. Consequently, the refrigeration cycle apparatus <NUM> can reduce the outflow of the gas refrigerant to the side of the indoor unit <NUM> by the branch portion <NUM> or 33A having an extremely simple structure.

Further, the refrigeration cycle apparatus <NUM> according to the present embodiment includes the straight pipe <NUM> having a flow-path cross-sectional area that is twice or more than twice the flow-path cross-sectional area of the upstream pipe portion <NUM>. Consequently, the refrigeration cycle apparatus <NUM> can reduce the flow velocity of the refrigerant in the straight pipe <NUM>. This reduction effect significantly reduces the flow velocity of the refrigerant in the first bypass refrigerant pipe 32a than the flow velocity of the refrigerant in the fourth main refrigerant pipe 31d. This reduction in the flow velocity of the refrigerant makes the buoyancy of the gas refrigerant larger than the force to be received from the flow of the liquid refrigerant. That is, the refrigeration cycle apparatus <NUM> can exert the effect of gas-liquid separation more remarkably.

Moreover, the refrigeration cycle apparatus <NUM> according to the present embodiment includes: the upstream pipe portion <NUM> extending substantially horizontally; and the main-circuit branch pipe portion <NUM> and the bypass-circuit branch pipe portion <NUM>, both of which extend substantially vertically. Consequently, the refrigeration cycle apparatus <NUM> can more reliably separate the refrigerant in the state of gas-liquid two-phase into the gas refrigerant and the liquid refrigerant, and introduce the separated liquid refrigerant into the subcooling circuit <NUM>.

Furthermore, the refrigeration cycle apparatus <NUM> according to the present embodiment includes the upstream pipe portion <NUM>, extended line of the centerline of which intersects neither the centerline of the main-circuit branch pipe portion <NUM> nor the centerline of the bypass-circuit branch pipe portion <NUM>. Consequently, the refrigeration cycle apparatus <NUM> can generate a swirling flow in the branch portion 33A, and create a synergistic effect by the separation effect between the gas refrigerant and the liquid refrigerant using centrifugal force in addition to the separation effect between the gas refrigerant and the liquid refrigerant using gravity.

Claim 1:
A refrigeration cycle apparatus (<NUM>) comprising:
a compressor (<NUM>);
a condenser (<NUM>);
an indoor expansion valve (<NUM>);
a subcooling circuit (<NUM>) that is disposed between the condenser (<NUM>) and the indoor expansion valve (<NUM>);
an evaporator (<NUM>); and
a refrigerant pipe (<NUM>) that connects the compressor (<NUM>), the condenser (<NUM>), the subcooling circuit (<NUM>), the indoor expansion valve (<NUM>), and the evaporator (<NUM>), and circulates a refrigerant,
wherein the refrigerant pipe (<NUM>) includes: a main circuit pipe (<NUM>) that circulates the refrigerant through the compressor (<NUM>), the condenser (<NUM>), the subcooling circuit (<NUM>), the indoor expansion valve (<NUM>), and the evaporator (<NUM>); a bypass circuit pipe (<NUM>) that branches from the middle of the main circuit pipe (<NUM>) connecting the subcooling circuit (<NUM>) to the indoor expansion valve (<NUM>) and bypasses the refrigerant to the compressor (<NUM>); and a branch portion (<NUM>, 33A) that connects the main circuit pipe (<NUM>) and the bypass circuit pipe (<NUM>), and
wherein the branch portion(<NUM>, 33A) includes an upstream pipe portion (<NUM>), a main-circuit branch pipe portion (<NUM>) and a bypass-circuit branch pipe portion (<NUM>),
characterized in that the main-circuit branch pipe portion (<NUM>) branches upward from the upstream pipe portion (<NUM>) toward the indoor expansion valve (<NUM>); and the bypass-circuit branch pipe portion (<NUM>) branches downward from the upstream pipe portion (<NUM>) and extends toward the subcooling circuit (<NUM>);
the main-circuit branch pipe portion (<NUM>) and the bypass-circuit branch pipe portion (<NUM>) constitute a continuous straight pipe (<NUM>);
the upstream pipe portion (<NUM>) is connected to the straight pipe (<NUM>) in a tee-shape; and
a flow-path cross-sectional area of the straight pipe (<NUM>) is twice a flow-path cross-sectional area of the upstream pipe portion (<NUM>) or more.