Patent Description:
There has conventionally been known an air conditioner as a type of a refrigeration cycle apparatus disclosed in Patent Literature <NUM> (<CIT>). The air conditioner according to Patent Literature <NUM> has a small load during low-outdoor temperature cooling operation of executing cooling operation when outdoor air temperature is not quite high. As described in Patent Literature <NUM>, executed during low-outdoor temperature cooling operation is small load operation with a smaller number of revolutions of a compressor in comparison to rated operation, in order to be adapted to the small load.

<CIT> discloses a refrigeration cycle apparatus having the features according to the preamble of claim <NUM>. <CIT> and <CIT> are further prior art.

Small load operation executed during low-outdoor temperature cooling operation described in Patent Literature <NUM> leads to decrease in number of revolutions of the compressor, to decrease speed of a refrigerant flowing in the outdoor heat exchanger. In such a state, a liquid refrigerant is accumulated in the outdoor heat exchanger and the refrigerant is likely to be insufficient in comparison to appropriate refrigerant volume of the refrigeration cycle apparatus. Such insufficient refrigerant volume will cause efficiency deterioration during small load operation.

The refrigeration cycle apparatus has a problem that a liquid refrigerant is likely to be accumulated in the outdoor heat exchanger functioning as a condenser during small load operation at low outdoor temperature.

A refrigeration cycle apparatus according to a first aspect includes a refrigerant circuit provided with an outdoor heat exchanger configured to cause heat exchange between outdoor air and a refrigerant and a compressor configured to discharge a compressed refrigerant, and the refrigerant circuit configured to achieve a vapor compression refrigeration cycle while the outdoor heat exchanger functions as a condenser. The outdoor heat exchanger includes an inlet port, an outlet port, a plurality of heat exchange paths, a junction flow passage, and a branching passage. At the inlet port a refrigerant flows into the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser. At the outlet port a refrigerant flows out of the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser. The plurality of heat exchange paths include a plurality of heat transfer tubes configured to cause the refrigerant flowing in through the inlet port upon heat exchange to be distributed to flow in parallel. The junction flow passage is disposed between the plurality of heat exchange paths and the outlet port, and causes refrigerants flowing from the plurality of heat exchange paths to the outlet port to join and then flow therein. The plurality of heat exchange paths include a first path disposed in a lower portion of the outdoor heat exchanger and a second path disposed above the first path. The junction flow passage causes refrigerants having passed at least the first path and the second path to join and then flow therein. The branching passage has a first end connected to the first path, and a second end connected to the junction flow passage. The outdoor heat exchanger is configured to increase, upon decrease in load, a flow rate ratio of the refrigerant flowing to the branching passage to volume of the refrigerant flowing to the first path.

The refrigeration cycle apparatus according to the first aspect can decrease volume of the refrigerant flowing to the branching passage to inhibit deterioration in performance when the refrigeration cycle apparatus has a large load, and can cause large volume of the refrigerant to flow to the branching passage to inhibit accumulation of a liquid refrigerant in the first path during small load operation with a small load.

A refrigeration cycle apparatus according to the invention has the branching passage including a capillary tube.

The refrigeration cycle apparatus according to the invention is configured to increase, upon decrease in load, the flow rate ratio of the refrigerant flowing to the branching passage to volume of the refrigerant flowing to the first path, with use of the capillary tube without complicated control, for cost reduction for the apparatus.

A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the first or second aspect, in which the flow rate ratio of the refrigerant flowing to the branching passage to volume of the refrigerant flowing from the first path to the junction flow passage without passing the branching passage during predetermined small load operation is five times or more the flow rate ratio during rated operation.

In the refrigeration cycle apparatus according to the third aspect, the flow rate ratio of the refrigerant flowing to the branching passage to volume of the refrigerant flowing from the first path to the junction flow passage without passing the branching passage during predetermined small load operation is five times or more the flow rate ratio during rated operation, to achieve a sufficient flow of a liquid refrigerant during predetermined small load operation.

During predetermined small load operation, the compressor has the lowest operating frequency in this case.

A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to any one of the first to third aspects, in which the refrigerant flowing to the refrigerant circuit is an R32 refrigerant. A ratio of pressure loss from the first end to the second end of the branching passage to pressure loss from the first path to the second end via the junction flow passage is less than one during predetermined small load operation.

In the refrigeration cycle apparatus according to the fourth aspect, the ratio of pressure loss from the first end to the second end of the branching passage to pressure loss from the first path to the second end via the junction flow passage is set to be less than one during predetermined small load operation, to achieve a sufficient flow of a liquid refrigerant during load operation.

A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to the first aspect, in which the branching passage includes a motor valve that may change a opening degree, and the refrigeration cycle apparatus includes a control unit configured to control the opening degree of the motor valve in accordance with a load.

The refrigeration cycle apparatus according to the fifth aspect is configured to increase, upon decrease in load, the flow rate ratio of the refrigerant flowing to the branching passage to volume of the refrigerant flowing to the first path, easily with use of the control unit and the motor valve.

A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to the fifth aspect, in which the control unit controls the motor valve so as to maximize the opening degree at a predetermined small load and decrease the opening degree as the load increases when the outdoor heat exchanger functions as a condenser, and controls the motor valve to minimize the opening degree when the outdoor heat exchanger functions as an evaporator.

In the refrigeration cycle apparatus according to the sixth aspect, the motor valve is controlled to be decreased in opening degree as the load increases when the outdoor heat exchanger functions as a condenser, for improvement in performance of the refrigeration cycle apparatus. Furthermore, the motor valve is controlled to have the minimum opening degree when the outdoor heat exchanger functions as an evaporator, for inhibition of deterioration in performance of the refrigeration cycle apparatus due to provision of the branching passage.

The description is made to an air conditioner <NUM> depicted in <FIG>, which exemplifies a refrigeration cycle apparatus.

The air conditioner <NUM> includes a refrigerant circuit <NUM>. The refrigerant circuit <NUM> includes a compressor <NUM>, an outdoor heat exchanger <NUM>, an electric expansion valve <NUM>, and an indoor heat exchanger <NUM>. The refrigerant circuit <NUM> is filled with a refrigerant. Examples of the refrigerant include an R32 refrigerant. The refrigerant in the refrigerant circuit <NUM> circulates to achieve a vapor compression refrigeration cycle.

The refrigerant circuit <NUM> in the air conditioner <NUM> includes a four-way valve <NUM>. The four-way valve <NUM> switches a circulation direction of the refrigerant circuit <NUM> to allow the air conditioner <NUM> to achieve two types of the vapor compression refrigeration cycle. The four-way valve <NUM> is switched between a first state and a second state to switch the circulation direction of the refrigerant flowing in the refrigerant circuit. In other words, the four-way valve <NUM> is a flow path switching mechanism configured to switch a flow path in the refrigerant circuit <NUM> to switch a refrigerant flow direction.

When the four-way valve <NUM> comes into the first state, the refrigerant discharged from the compressor <NUM> in the refrigerant circuit <NUM> flows in the outdoor heat exchanger <NUM>, the electric expansion valve <NUM>, the indoor heat exchanger <NUM>, and the compressor <NUM> in the mentioned order. When the four-way valve <NUM> is in the first state, the refrigerant is compressed by the compressor <NUM>, the refrigerant is condensed by the outdoor heat exchanger <NUM>, the refrigerant is decompressed by the electric expansion valve <NUM>, and the refrigerant is evaporated by the indoor heat exchanger <NUM>. In this case, the outdoor heat exchanger <NUM> functions as a condenser and the indoor heat exchanger <NUM> functions as an evaporator. In the outdoor heat exchanger <NUM> functioning as a condenser, the refrigerant is condensed through heat exchange between outdoor air and the refrigerant. In this case, the refrigerant being condensed emits heat to the outdoor air in the outdoor heat exchanger <NUM>. In the indoor heat exchanger <NUM> functioning as an evaporator, the refrigerant is evaporated through heat exchange between indoor air and the refrigerant. In this case, the refrigerant being evaporated removes heat from the indoor air in the indoor heat exchanger <NUM>. During cooling operation, the four-way valve <NUM> is switched into the first state and the refrigerant being evaporated removes heat from indoor air to cool the indoor air in the indoor heat exchanger <NUM>.

When the four-way valve <NUM> comes into the second state, the refrigerant discharged from the compressor <NUM> in the refrigerant circuit <NUM> flows in the indoor heat exchanger <NUM>, the electric expansion valve <NUM>, the outdoor heat exchanger <NUM>, and the compressor <NUM> in the mentioned order. When the four-way valve <NUM> is in the second state, the refrigerant is compressed by the compressor <NUM>, the refrigerant is condensed by the indoor heat exchanger <NUM>, the refrigerant is decompressed by the electric expansion valve <NUM>, and the refrigerant is evaporated by the outdoor heat exchanger <NUM>. In this case, the outdoor heat exchanger <NUM> functions as an evaporator and the indoor heat exchanger <NUM> functions as a condenser. In the outdoor heat exchanger <NUM> functioning as an evaporator, the refrigerant is evaporated through heat exchange between outdoor air and the refrigerant. In this case, the refrigerant being evaporated removes heat from the outdoor air in the outdoor heat exchanger <NUM>. In the indoor heat exchanger <NUM> functioning as a condenser, the refrigerant is condensed through heat exchange between indoor air and the refrigerant. In this case, the refrigerant being condensed emits heat to the indoor air in the indoor heat exchanger <NUM>. During heating operation, the four-way valve <NUM> is switched into the second state, and the refrigerant being condensed in the indoor heat exchanger <NUM> emits heat to the indoor air to warm the indoor air.

The air conditioner <NUM> includes an outdoor fan <NUM> configured to generate a flow of outdoor air passing the outdoor heat exchanger <NUM>, and an indoor fan <NUM> configured to generate a flow of indoor air passing the indoor heat exchanger <NUM>. <FIG> includes arrows of two-dot chain lines indicating airflows generated by the outdoor fan <NUM> and the indoor fan <NUM>. Each of the outdoor fan <NUM> and the indoor fan <NUM> has a variable number of revolutions of its fan. The outdoor fan <NUM> and the indoor fan <NUM> each have a varied number of revolutions to vary airflow volume of outdoor air passing the outdoor heat exchanger <NUM> and airflow volume of indoor air passing the indoor heat exchanger <NUM>.

The refrigeration cycle of the refrigerant circuit <NUM> described above is controlled by a control unit <NUM>. The control unit <NUM> accordingly controls an operating frequency of the compressor <NUM> in accordance with a load. The control unit <NUM> controls an opening degree of the electric expansion valve <NUM>. The control unit <NUM> controls the number of revolutions of each of the outdoor fan <NUM> and the indoor fan <NUM>. The control unit <NUM> is connected to various sensors provided in the air conditioner <NUM> to monitor a state of the refrigerant circuit <NUM>. As depicted in <FIG>, the control unit <NUM> includes an outdoor unit control unit <NUM> and an indoor unit control unit <NUM> connected by means of a transmission line <NUM>.

An outdoor unit <NUM> is disposed in a space in which outdoor air outside an air conditioning target space flows. The outdoor unit <NUM> is disposed on a roof or a balcony of a building equipped with the air conditioner <NUM>, a site adjacent to the building, or the like.

The outdoor unit <NUM> accommodates the compressor <NUM>, the four-way valve <NUM>, the outdoor heat exchanger <NUM>, the electric expansion valve <NUM>, an accumulator <NUM>, the outdoor fan <NUM>, and the outdoor unit control unit <NUM> (see <FIG>). The outdoor unit <NUM> accommodates various sensors such as an outdoor heat exchanger temperature sensor <NUM>.

The four-way valve <NUM> accommodated in the outdoor unit <NUM> includes a first port 22a, a second port 22b, a third port 22c, and a fourth port 22d. In the four-way valve <NUM> in the first state, the first port 22a and the second port 22b communicate with each other, and the third port 22c and the fourth port 22d communicate with each other. In the four-way valve <NUM> in the second state, the first port 22a and the fourth port 22d communicate with each other, and the second port 22b and the third port 22c communicate with each other.

The first port 22a of the four-way valve <NUM> communicates with a discharge port of the compressor <NUM>. The second port 22b of the four-way valve communicates with a gas side inlet-outlet port 23a of the outdoor heat exchanger <NUM>, and a liquid side inlet-outlet port 23b of the outdoor heat exchanger <NUM> communicates with a first end of the electric expansion valve <NUM>. The third port 22c of the four-way valve <NUM> communicates with a suction port of the compressor <NUM> via the accumulator <NUM>.

The compressor <NUM> is configured to suck a low-pressure refrigerant through the suction port, compress the refrigerant in the compressor, and discharge a high-pressure refrigerant obtained by compression through the discharge port. The air conditioner <NUM> includes the single compressor <NUM> accommodated in the outdoor unit <NUM>. The compressor <NUM> included in the air conditioner <NUM> is not limited to one, and the air conditioner <NUM> may alternatively include a plurality of compressors. The compressor <NUM> is a positive displacement compressor and is driven by a motor 21a. The motor 21a has an operating frequency that can be controlled by an inverter or the like. Control of the operating frequency of the motor 21a leads to control of capacity of the compressor <NUM>. Accordingly, increase in operating frequency of the motor 21a leads to increase in flow rate of the refrigerant flowing in the refrigerant circuit <NUM>.

The electric expansion valve <NUM> is configured to be change in opening degree to regulate pressure and the flow rate of the refrigerant flowing in the refrigerant circuit <NUM>. Increase in opening degree of the electric expansion valve <NUM> leads to increase in difference between pressure of the refrigerant flowing into the electric expansion valve <NUM> and pressure of the refrigerant flowing out, and decrease in flow rate of the refrigerant flowing in the refrigerant circuit <NUM>.

The accumulator <NUM> is connected to the suction port of the compressor <NUM> (see <FIG>). The accumulator <NUM> is a vessel having a function of storing an excessive refrigerant generated due to operation load variation of an indoor unit <NUM> or the like. The accumulator <NUM> has a gas-liquid separation function of separating an incoming refrigerant into a gas refrigerant and a liquid refrigerant. The refrigerant flowing into the accumulator <NUM> is separated into a gas refrigerant and a liquid refrigerant, and the gas refrigerant collecting in an upper space flows out to the compressor <NUM>. The refrigerant circuit <NUM> may alternatively include a receiver having a function of storing an excessive refrigerant, in place of or along with the accumulator <NUM>.

The outdoor fan <NUM> is configured to supply the outdoor heat exchanger <NUM> with outdoor air. Specifically, the outdoor fan <NUM> is configured to suck outdoor air into a casing (not depicted) of the outdoor unit <NUM>, cause the outdoor air to pass the outdoor heat exchanger <NUM>, and exhaust air having exchanged heat with the refrigerant in the outdoor heat exchanger <NUM> to outside the casing of the outdoor unit <NUM>. The outdoor fan <NUM> is driven by a motor 28a having a variable number of revolutions. Accordingly, increase in number of revolutions of the motor 28a of the outdoor fan <NUM> leads to increase in volume of airflow passing the outdoor heat exchanger <NUM>.

The outdoor unit <NUM> includes various sensors. The sensors provided in the outdoor unit <NUM> include a discharge temperature sensor <NUM>, the outdoor heat exchanger temperature sensor <NUM>, and an outdoor temperature sensor <NUM> (see <FIG>). The discharge temperature sensor <NUM> measures discharge temperature Td as temperature of the refrigerant discharged from the compressor <NUM>.

The outdoor heat exchanger temperature sensor <NUM> is provided at the outdoor heat exchanger <NUM> (see <FIG>). The outdoor heat exchanger temperature sensor <NUM> measures temperature of the refrigerant flowing in the outdoor heat exchanger <NUM>. The outdoor heat exchanger temperature sensor <NUM> measures refrigerant temperature corresponding to condensation temperature Tc when the outdoor heat exchanger <NUM> functions as a condenser, and measures refrigerant temperature corresponding to evaporation temperature Te when the outdoor heat exchanger <NUM> functions as an evaporator. The outdoor temperature sensor <NUM> measures outdoor air temperature To. The outdoor temperature sensor <NUM> exemplarily measures temperature of outdoor air sucked into the outdoor unit <NUM> by the outdoor fan <NUM> and not yet having exchanged heat in the outdoor heat exchanger <NUM>.

The outdoor unit control unit <NUM> is embodied by a computer or the like. The outdoor unit control unit <NUM> exemplarily includes a control arithmetic device and a storage device. Examples of the control arithmetic device can include a processor such as a CPU. The control arithmetic device executes arithmetic processing of reading a program stored in the storage device. The control arithmetic device is further configured to write an arithmetic result to the storage device, and read information stored in the storage device, in accordance with the program.

The outdoor unit control unit <NUM> is electrically connected to the compressor <NUM>, the four-way valve <NUM>, the electric expansion valve <NUM>, the outdoor fan <NUM>, the discharge temperature sensor <NUM>, the outdoor heat exchanger temperature sensor <NUM>, and the outdoor temperature sensor <NUM> so as to transmit and receive control signals and information (see <FIG>).

The outdoor unit control unit <NUM> is connected to the indoor unit control unit <NUM> of the indoor unit <NUM> by means of the transmission line <NUM> so as to transmit and receive control signals and the like. The outdoor unit control unit <NUM> and the indoor unit control unit <NUM> cooperate with each other to function as the control unit <NUM> configured to control behavior of the entire air conditioner <NUM>. The outdoor unit control unit <NUM> and the indoor unit control unit <NUM> may not be connected to each other by means of the physical transmission line <NUM>, and may alternatively be wirelessly connected to be communicable each other.

<FIG> schematically depicts a configuration of the outdoor heat exchanger <NUM>. <FIG> is a side view of the outdoor heat exchanger <NUM>. The outdoor heat exchanger <NUM> includes a body <NUM>, an auxiliary heat exchange unit <NUM>, a header <NUM>, and seven flow dividers <NUM>. The seven flow dividers <NUM> include a first flow divider <NUM>, a second flow divider <NUM>, a third flow divider <NUM>, a fourth flow divider <NUM>, a fifth flow divider <NUM>, a sixth flow divider <NUM>, and a seventh flow divider <NUM>.

The body <NUM> and the auxiliary heat exchange unit <NUM> include a heat transfer tube <NUM> and a heat transfer fin (not depicted). The heat transfer tube <NUM> includes straight tubes <NUM> extending to penetrate the heat transfer fin and a U tube <NUM> connecting two straight tubes <NUM> of the heat transfer tube <NUM>. <FIG> depicts the straight tubes <NUM> indicated by circles, and the U tube <NUM> indicated by a straight solid line or a straight broken line.

The heat transfer tube <NUM> shapes a plurality of paths P1, P2, P3, P4, P5, P6, P7, and P8 in the body <NUM>. The paths P1 to P8 each have heat exchange executed between outdoor air and the refrigerant. A path has connection between a straight tube <NUM> and a U tube <NUM> in the body <NUM>. In other words, a path is a continuous flow path between the header <NUM> and a flow divider <NUM>, and is constituted by the heat transfer tube <NUM> disposed in the body <NUM>. As depicted in <FIG>, the path P8 is disposed at an uppermost portion of the body <NUM> in the outdoor heat exchanger <NUM>. The path P7 is disposed below and adjacent to the path P8. The paths P7 and P8 each communicate with the fourth flow divider <NUM>. When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerants flowing in the paths P7 and P8 join at the fourth flow divider <NUM> and flow to the sixth flow divider <NUM>. The refrigerant flowing out of the fourth flow divider <NUM> passes the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> and flows to the sixth flow divider <NUM>.

The path P6 is disposed below and adjacent to the path P7. The path P5 is disposed below and adjacent to the path P6. The paths P5 and P6 each communicate with the third flow divider <NUM>. When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerants flowing in the paths P5 and P6 join at the third flow divider <NUM> and flow to the sixth flow divider <NUM>. The refrigerant flowing out of the third flow divider <NUM> passes the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> and flows to the sixth flow divider <NUM>.

As depicted in <FIG>, the paths P5 to P8 are positioned above a vertical center of the body <NUM>. When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerants flowing in the paths P5 to P8 join at the third flow divider <NUM> and the fourth flow divider <NUM>, then further join at the sixth flow divider <NUM>, and flow to the seventh flow divider <NUM>. The refrigerant flowing out of the sixth flow divider <NUM> passes the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> and flows to the seventh flow divider <NUM>.

As depicted in <FIG>, the path P4 is disposed below and adjacent to the path P5. The path P3 is disposed below and adjacent to the path P4. The paths P3 and P4 each communicate with the second flow divider <NUM>. When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerants flowing in the paths P3 and P4 join at the second flow divider <NUM> and flow to the fifth flow divider <NUM>. The refrigerant flowing out of the second flow divider <NUM> passes the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> and flows to the fifth flow divider <NUM>.

The path P2 is disposed below and adjacent to the path P3. The path P1 is disposed below and adjacent to the path P2. The paths P1 and P2 each communicate with the first flow divider <NUM>. When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerants flowing in the paths P1 and P2 join at the first flow divider <NUM> and flow to the fifth flow divider <NUM>. The refrigerant flowing out of the first flow divider <NUM> passes the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> and flows to the fifth flow divider <NUM>. A liquid refrigerant is particularly hard to flow where the refrigerant needs to flow upward from the path P1 disposed at a lower portion of the outdoor heat exchanger <NUM> in the first flow divider <NUM>.

As depicted in <FIG>, the paths P1 to P4 are positioned below the vertical center of the body <NUM>. When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerants flowing in the paths P1 to P4 join at the first flow divider <NUM> and the second flow divider <NUM>, then further join at the fifth flow divider <NUM>, and flow to the seventh flow divider <NUM>. The refrigerant flowing out of the fifth flow divider <NUM> passes the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> and flows to the seventh flow divider <NUM>.

When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerants flowing in the paths P1 to P8 eventually join at the seventh flow divider <NUM> and pass the liquid side inlet-outlet port 23b to flow out of the outdoor heat exchanger <NUM>.

When the outdoor heat exchanger <NUM> functions as a condenser, the refrigerant flowing into the header <NUM> through one flow in-out port communicating with the gas side inlet-outlet port 23a is divided into eight flows to flow out toward the eight paths P1 to P8 of the body <NUM>.

The outdoor heat exchanger <NUM> includes a branching passage <NUM>. The branching passage <NUM> includes a capillary tube <NUM>. The branching passage <NUM> has a first end <NUM> connected to the path P1 as a first path, and a second end <NUM> connected to a junction flow passage <NUM>.

The junction flow passage <NUM> is a flow path included in a junction part <NUM>. The junction part <NUM>, the junction flow passage <NUM> in more detail, is disposed between the paths P1 to P4 as a plurality of heat exchange paths of the outdoor heat exchanger and the liquid side inlet-outlet port 23b serving as an outlet port. The junction flow passage <NUM> causes the refrigerants flowing from the paths P1 to P4 to the liquid side inlet-outlet port 23b to join and then flow therein. The junction part <NUM> is constituted by the first flow divider <NUM>, the second flow divider <NUM>, the fifth flow divider <NUM>, the heat transfer tube <NUM> connected thereto, and a pipe of the junction flow passage <NUM>.

When the outdoor heat exchanger <NUM> functions as an evaporator, the refrigerant flows in through the liquid side inlet-outlet port 23b. The refrigerant flowing in through the liquid side inlet-outlet port 23b is divided by the seventh flow divider <NUM> into two flow paths, which are divided by the fifth flow divider <NUM> and the sixth flow divider <NUM> into four flow paths, which are further divided by the first to fourth flow dividers <NUM> to <NUM> into eight flow paths. The eight flow paths thus divided by the first to fourth flow dividers <NUM> to <NUM> are connected with the paths P1 to P8. When the outdoor heat exchanger <NUM> functions as an evaporator, the refrigerants having passed the paths P1 to P8 flow into the header <NUM> to join, flow from the header <NUM> to pass the gas side inlet-outlet port 23a, and flow out of the outdoor heat exchanger <NUM>.

The outdoor heat exchanger temperature sensor <NUM> is attached to the U tube <NUM> disposed halfway on the path P3 or the like. The outdoor heat exchanger temperature sensor <NUM> is used to detect defrosting completion timing upon defrosting operation of removing frost adhering during heating operation. Frost melts gradually from the top of the outdoor heat exchanger <NUM> during defrosting operation. The outdoor heat exchanger temperature sensor <NUM> is thus preferably attached below the outdoor heat exchanger <NUM>. In order for detection of defrosting completion timing, the outdoor heat exchanger temperature sensor <NUM> is preferably attached to a path disposed at a lower portion of the body <NUM>, such as the path P1, P2, or P3. Particularly in a case where the refrigerant is divided at the header <NUM> into flows equal in number to the paths, the outdoor heat exchanger temperature sensor <NUM> may be attached to the lowermost path P1 of the outdoor heat exchanger <NUM> in view of detection of defrosting completion timing.

The indoor unit <NUM> is disposed for the air conditioning target space. Examples of the air conditioning target space include the interior of a room. The indoor unit <NUM> is of a wall hung type to be attached to a wall in the room, of a ceiling embedded type to be embedded in a ceiling in the room, of a floor-standing type to be placed on a floor in the room, or the like. The indoor unit <NUM> may be disposed inside or outside the air conditioning target space. The indoor unit <NUM> may be disposed outside the air conditioning target space, exemplarily in an attic space, a machine chamber, or a garage. When the indoor unit <NUM> is disposed outside the air conditioning target space, there is disposed an air passage for supply, from the indoor unit <NUM> to the air conditioning target space, of air having exchanged heat with the refrigerant in the indoor heat exchanger <NUM>. Examples of the air passage include a duct.

The indoor unit <NUM> accommodates the indoor heat exchanger <NUM>, the indoor fan <NUM>, the indoor unit control unit <NUM>, and various sensors (see <FIG>). The sensors provided in the indoor unit <NUM> include an indoor heat exchanger temperature sensor <NUM> and an indoor temperature sensor <NUM> (see <FIG>). The indoor temperature sensor <NUM> measures indoor air temperature Tr. The indoor temperature sensor <NUM> exemplarily measures temperature of indoor air sucked into the indoor unit <NUM> by the indoor fan <NUM> and not yet having exchanged heat in the indoor heat exchanger <NUM>. The indoor heat exchanger temperature sensor <NUM> measures temperature of the refrigerant flowing in the indoor heat exchanger <NUM>. The indoor heat exchanger temperature sensor <NUM> measures refrigerant temperature corresponding to the condensation temperature Tc when the indoor heat exchanger <NUM> functions as a condenser, and measures refrigerant temperature corresponding to the evaporation temperature Te when the indoor heat exchanger <NUM> functions as an evaporator.

The indoor heat exchanger <NUM> causes heat exchange between the refrigerant flowing in the indoor heat exchanger <NUM> and air in the air conditioning target space (indoor air). The indoor heat exchanger <NUM> is exemplarily a fin-and-tube heat exchanger including a plurality of heat transfer tubes and a plurality of fins (not depicted). The indoor heat exchanger <NUM> has a liquid side inlet-outlet port communicating with a second end of the electric expansion valve <NUM>. The indoor heat exchanger <NUM> has a gas side inlet-outlet port communicating with the fourth port 22d of the four-way valve <NUM>.

The indoor fan <NUM> is configured to supply the indoor heat exchanger <NUM> with indoor air (air in the air conditioning target space). The indoor fan <NUM> is driven by a motor 53a having a variable number of revolutions. Increase in number of revolutions of the motor 53a of the indoor fan <NUM> leads to increase in volume of airflow passing the indoor heat exchanger <NUM>.

The indoor temperature sensor <NUM> is provided on an air suction side of a casing (not depicted) of the indoor unit <NUM>. The indoor temperature sensor <NUM> detects temperature (the indoor air temperature Tr) of air in the air conditioning target space flowing into the casing of the indoor unit <NUM>.

The indoor unit control unit <NUM> controls behavior of respective parts of the indoor unit <NUM>. The indoor unit control unit <NUM> is embodied by a computer or the like. The indoor unit control unit <NUM> exemplarily includes a control arithmetic device and a storage device. Examples of the control arithmetic device can include a processor such as a CPU. The control arithmetic device executes arithmetic processing of reading a program stored in the storage device. The control arithmetic device is further configured to write an arithmetic result to the storage device, and read information stored in the storage device, in accordance with the program.

The indoor unit control unit <NUM> is electrically connected between the indoor fan <NUM> and the indoor temperature sensor <NUM> so as to transmit and receive control signals and information (see <FIG>).

The indoor unit control unit <NUM> is configured to receive various signals transmitted from a remote controller (not depicted) provided to operate the indoor unit <NUM>. Examples of the various signals transmitted from the remote controller include a command signal to operate or stop the indoor unit <NUM>, an operating mode switch signal, and a signal relevant to set temperature Trs of indoor air for cooling operation or heating operation.

When the air conditioner <NUM> is commanded to execute cooling operation by means of the remote controller or the like, the control unit <NUM> sets the operating mode of the air conditioner <NUM> to a cooling operation mode. In the cooling operation mode, the control unit <NUM> switches the four-way valve <NUM> on the refrigerant circuit <NUM> into the first state, and then drives the compressor <NUM>, the outdoor fan <NUM>, and the indoor fan <NUM>.

During cooling operation, the control unit <NUM> controls the number of revolutions of the motor 53a of the indoor fan <NUM> in accordance with a command inputted to the remote controller, such as a command on airflow volume, or the like. The control unit <NUM> controls the opening degree of the electric expansion valve <NUM> in order to suppress, to or less than a predetermined value, a rate of a liquid refrigerant in the refrigerant sucked into the compressor <NUM>. The control unit <NUM> thus controls such that a difference (Td - Tc) between the discharge temperature Td and the condensation temperature Tc is equal to or more than first predetermined temperature. In other words, the control unit <NUM> controls the opening degree of the electric expansion valve <NUM> in accordance with a discharge superheating degree. The outdoor heat exchanger temperature sensor <NUM> can normally measure temperature (saturation temperature) of a refrigerant in a gas-liquid two-phase state, and the control unit <NUM> thus adopts a measurement value of the outdoor heat exchanger temperature sensor <NUM> as the condensation temperature Tc.

The control unit <NUM> controls the operating frequency of the compressor <NUM> in accordance with a load. The control unit <NUM> decreases the operating frequency of the compressor <NUM> when the air conditioner <NUM> has a small load. In an exemplary case where a difference (To - Tr) between the outdoor air temperature To and the indoor air temperature Tr and a difference (Tr - Trs) between the indoor air temperature Tr and the set temperature Trs are both small during cooling operation, the air conditioner <NUM> has a small load and the control unit <NUM> accordingly decreases the operating frequency of the compressor <NUM>. During normal operation other than small load operation or the like, the operating frequency of the compressor <NUM> is exemplarily from several tens of Hz to one hundred and several tens of Hz. During small load operation smaller in load than normal operation, the control unit <NUM> controls the operating frequency of the compressor <NUM> so as to be less than <NUM> or the like. The compressor <NUM> has the lowest operating frequency particularly during predetermined small load operation. The control unit <NUM> further controls the number of revolutions of the motor 28a of the outdoor fan <NUM> in accordance with the outdoor air temperature To.

During small load operation, the operating frequency of the compressor <NUM> is small and the refrigerant is thus likely to be accumulated in the outdoor heat exchanger <NUM>. Particularly upon small load operation at low outdoor air temperature during cooling operation, a liquid refrigerant may be accumulated in the heat transfer tube <NUM> in a lower region of the outdoor heat exchanger <NUM>. If the outdoor heat exchanger temperature sensor <NUM> is attached to the heat transfer tube <NUM> in the lower region, the outdoor heat exchanger temperature sensor <NUM> measures temperature of a refrigerant in a liquid state, failing to measure temperature (saturation temperature) of the refrigerant in the gas-liquid two-phase state. In such a case, the control unit <NUM> cannot adopt, as the condensation temperature Tc, the measurement value of the outdoor heat exchanger temperature sensor <NUM>, upon control of the refrigeration cycle of the refrigerant circuit <NUM>.

If the outdoor heat exchanger <NUM> has large volume of a liquid refrigerant accumulated during small load operation, the refrigerant circuit <NUM> has circulation of an insufficient refrigerant.

In order to prevent defects mentioned above, the outdoor heat exchanger <NUM> is provided with the branching passage <NUM> such that a liquid refrigerant is unlikely to be accumulated in the outdoor heat exchanger <NUM>. The outdoor heat exchanger <NUM> is configured to increase, upon decrease in load, a flow rate ratio of the refrigerant flowing to the branching passage <NUM> to volume of the refrigerant flowing to the lowermost path P1 (first path) of the body <NUM>.

During rated operation (during large load operation), the ratio of volume of the refrigerant flowing in the branching passage to volume of the refrigerant flowing from the path P1 (first path) to the junction flow passage <NUM> without passing the branching passage <NUM> is <NUM>/<NUM> or the like. In contrast, during small load operation, the ratio of volume of the refrigerant flowing in the branching passage to volume of the refrigerant flowing from the path P1 (first path) to the junction flow passage <NUM> without passing the branching passage <NUM> is less than <NUM>/<NUM> or the like. In this manner, the flow rate ratio of the refrigerant flowing to the branching passage <NUM> to volume of the refrigerant flowing from the path P1 (first path) to the junction flow passage <NUM> without passing the branching passage <NUM> during predetermined small load operation is preferably five times or more the flow rate ratio during rated operation. During predetermined small load operation, the compressor in the air conditioner <NUM> has the lowest operating frequency. The operating frequency of the compressor is <NUM> or the like during predetermined small load operation.

When the refrigerant flowing to the refrigerant circuit <NUM> is an R32 refrigerant, a ratio (PL2/PL1) of pressure loss PL2 from the first end <NUM> to the second end <NUM> of the branching passage <NUM> to pressure loss PL1 from the path P1 (first path) to the second end <NUM> of the branching passage <NUM> via the junction part <NUM> is preferably less than one during predetermined small load operation.

When the air conditioner <NUM> is commanded to execute heating operation by means of the remote controller or the like, the control unit <NUM> sets the operating mode of the air conditioner <NUM> to a heating operation mode. In the heating operation mode, the control unit <NUM> switches the four-way valve <NUM> on the refrigerant circuit <NUM> into the second state, and then drives the compressor <NUM>, the outdoor fan <NUM>, and the indoor fan <NUM>.

During heating operation, the control unit <NUM> controls the number of revolutions of the motor 53a of the indoor fan <NUM> in accordance with a command inputted to the remote controller, such as a command on airflow volume, or the like. The control unit <NUM> controls the refrigeration cycle assuming that refrigerant temperature measured by the indoor heat exchanger temperature sensor <NUM> is the condensation temperature Tc. The control unit <NUM> controls the opening degree of the electric expansion valve <NUM> in order to suppress the rate of a liquid refrigerant in the refrigerant sucked into the compressor <NUM>. The control unit <NUM> thus controls such that the difference (Td - Tc) between the discharge temperature Td and the condensation temperature Tc is equal to or more than the first predetermined temperature.

The control unit <NUM> controls the operating frequency of the compressor <NUM> in accordance with a load. The control unit <NUM> decreases the operating frequency of the compressor <NUM> when the air conditioner <NUM> has a small load. In an exemplary case where the difference (To - Tr) between the outdoor air temperature To and the indoor air temperature Tr and a difference (To - Trs) between the outdoor air temperature To and the set temperature Trs are both small during cooling operation, the air conditioner <NUM> has a small load and the control unit <NUM> accordingly decreases the operating frequency of the compressor <NUM>. The control unit <NUM> further controls the number of revolutions of the motor 28a of the outdoor fan <NUM> in accordance with the outdoor air temperature To.

The control unit <NUM> executes defrosting operation in order to remove frost adhering to the outdoor heat exchanger <NUM> during heating operation. Defrosting is achieved when the outdoor heat exchanger <NUM> functions as a condenser as in cooling operation, through operation (called reverse cycle defrosting operation) of melting frost with use of a high-temperature refrigerant supplied to the outdoor heat exchanger <NUM>. A defrosting method is not limited to the reverse cycle defrosting operation, and defrosting may alternatively be executed in accordance with a different method.

The embodiment described above refers to the case where the refrigeration cycle apparatus is the air conditioner <NUM>. However, the refrigeration cycle apparatus should not be limited to the air conditioner <NUM>. Examples of the refrigeration cycle apparatus include a refrigerator, a freezer, a hot water supplier, and a floor heater.

The junction part <NUM> according to the above embodiment includes the junction flow passage <NUM> configured to cause the refrigerants flowing from the paths P1 to P4 to the liquid side inlet-outlet port 23b to join and flow therein, and is constituted by the first flow divider <NUM>, the second flow divider <NUM>, and the fifth flow divider <NUM>, the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> connected thereto, and the pipe of the junction flow passage <NUM>. However, the junction part <NUM> is not limited to the above in terms of its configuration. For example, the second end <NUM> of the branching passage <NUM> may be connected to a point E1 indicated in <FIG>. In this case, the junction part incudes a junction flow passage (a flow path at the point E1) configured to cause the refrigerants flowing from the paths P1 and P2 to the liquid side inlet-outlet port 23b to join and flow therein. The junction part in this case is constituted by the first flow divider <NUM>, the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> connected thereto, and the pipe of the junction flow passage.

Furthermore, the second end <NUM> of the branching passage <NUM> may be connected to a point E2 indicated in <FIG>. In this case, the junction part incudes a junction flow passage (a flow path at the point E2) configured to cause the refrigerants flowing from the paths P1 to P8 to the liquid side inlet-outlet port 23b to join and flow therein. The junction part in this case is constituted by the first to seventh flow dividers <NUM> to <NUM>, the heat transfer tube <NUM> of the auxiliary heat exchange unit <NUM> connected thereto, and the pipe of the junction flow passage.

The above embodiment refers to the outdoor heat exchanger <NUM> divided into the body <NUM> and the auxiliary heat exchange unit <NUM>. The outdoor heat exchanger <NUM> may alternatively be constituted only by the body <NUM> without including the auxiliary heat exchange unit <NUM>. Furthermore, in the body <NUM> according to the above embodiment includes the heat transfer tubes <NUM> (straight tubes <NUM>) arranged in two rows in an outdoor air passing direction. The heat transfer tubes in the body are not limitedly arranged in the two rows, and may alternatively be arranged in a single row, or three or more rows. The above embodiment refers to the case where the body <NUM> is provided with the eight paths P1 to P8. The outdoor heat exchanger <NUM> should not be limited to eight in terms of its number of the paths.

The above embodiment refers to the case where the branching passage <NUM> is provided only with the capillary tube <NUM>. As depicted in <FIG>, the branching passage <NUM> may alternatively be provided with a check valve <NUM> in addition to the capillary tube <NUM>. The check valve <NUM> provided at the branching passage <NUM> is attached so as to allow a flow of a refrigerant from the path P1 toward the liquid side inlet-outlet port 23b and prevent a reverse flow of a refrigerant from the liquid side inlet-outlet port 23b toward the path P1. In this case, the capillary tube <NUM> and the check valve <NUM> are connected in series between the first end <NUM> and the second end <NUM> of the branching passage <NUM>. Due to the check valve <NUM>, the refrigerant is unlikely to flow to the branching passage <NUM> when the outdoor heat exchanger <NUM> functions as an evaporator, to inhibit deterioration in heat exchange efficiency because the auxiliary heat exchange unit <NUM> has no refrigerant flow.

The above embodiment refers to the case where the branching passage <NUM> includes the capillary tube <NUM>. As depicted in <FIG>, the branching passage <NUM> may alternatively include a motor valve <NUM> having a variable opening degree, in place of the capillary tube <NUM>. In the case where the branching passage <NUM> includes the motor valve <NUM>, the outdoor unit control unit <NUM> in the control unit <NUM> controls the opening degree of the motor valve <NUM>. When the outdoor heat exchanger <NUM> functions as a condenser, the outdoor unit control unit <NUM> in the control unit <NUM> controls to increase the opening degree of the motor valve <NUM> as the load decreases. The control unit <NUM> maximizes the opening degree of the motor valve <NUM> during predetermined small load operation, in other words, when the load is minimized. When the opening degree of the motor valve <NUM> is controlled to increase as the load decreases, a liquid refrigerant is likely to flow through the branching passage <NUM> as the load decreases. This can inhibit accumulation of a liquid refrigerant in the outdoor heat exchanger <NUM> during small load operation. The control unit <NUM> controls the motor valve <NUM> to have the minimum opening degree when the outdoor heat exchanger <NUM> functions as an evaporator. Accordingly, the refrigerant is unlikely to flow to the branching passage <NUM> when the outdoor heat exchanger <NUM> functions as an evaporator, to inhibit deterioration in heat exchange efficiency because of no refrigerant flow in the auxiliary heat exchange unit <NUM> when the outdoor heat exchanger <NUM> functions as an evaporator.

The above embodiment refers to the air conditioner <NUM> configured to cool (inclusive of dehumidifying) and heat the air conditioning target space. The air conditioner may alternatively be configured to execute only cooling operation.

When the outdoor heat exchanger <NUM> functions as a condenser, the air conditioner <NUM> described above can decrease volume of the refrigerant flowing to the branching passage <NUM> to inhibit deterioration in performance when the air conditioner <NUM> has a large load, and can cause large volume of the refrigerant to flow to the branching passage <NUM> to inhibit accumulation of a liquid refrigerant in the path P1 during small load operation with a small load. In the above embodiment, the path P1 corresponds to the first path and the path P2 corresponds to the second path. The junction flow passage <NUM> causes the refrigerants having passed at least the path P1 (first path) and the path P2 (second path) to join and then flow therein. The outdoor heat exchanger <NUM> can inhibit accumulation of a liquid refrigerant therein during small load operation where the outdoor heat exchanger <NUM> functions as a condenser, to inhibit shortage of the refrigerant for achievement of an appropriate refrigeration cycle. It is also possible to prevent failing in measuring the condensation temperature Tc because the portion of the heat transfer tube <NUM> provided with the outdoor heat exchanger temperature sensor <NUM> is immersed in a liquid refrigerant. When the outdoor heat exchanger <NUM> functions as a condenser, the gas side inlet-outlet port 23a serves as a refrigerant inlet port, and the liquid side inlet-outlet port 23b serves as a refrigerant outlet port.

The air conditioner <NUM> described above is configured to increase, upon decrease in load, the flow rate ratio of the refrigerant flowing to the branching passage <NUM> to volume of the refrigerant flowing to the path P1 (first path), with use of the capillary tube <NUM> without complicated control. The air conditioner <NUM> can thus inhibit accumulation of a liquid refrigerant in the outdoor heat exchanger <NUM> at low cost.

In the air conditioner <NUM>, the flow rate ratio of the refrigerant flowing to the branching passage <NUM> to volume of the refrigerant flowing from the path P1 (first path) to the junction flow passage <NUM> without passing the branching passage <NUM> during predetermined small load operation is five times or more the flow rate ratio during rated operation, to achieve a sufficient flow of a liquid refrigerant during predetermined small load operation. During predetermined small load operation, the compressor <NUM> has the lowest operating frequency in this case.

In the air conditioner <NUM>, the ratio of pressure loss from the first end <NUM> to the second end <NUM> of the branching passage to pressure loss from the path P1 (first path) to the second end via the junction part <NUM>, the junction flow passage <NUM> in more detail, is set to be less than one during predetermined small load operation, to achieve a sufficient flow of a liquid refrigerant during load operation.

The air conditioner <NUM> according to the modification example E is configured to increase, upon decrease in load, the flow rate ratio of the refrigerant flowing to the branching passage <NUM> to volume of the refrigerant flowing to the path P1 (first path), easily with use of the control unit <NUM> and the motor valve <NUM>. For example, the control unit <NUM> finds increase and decrease in load and commands the operating frequency of the compressor <NUM>, and thus increases or decreases volume of the refrigerant flowing to the branching passage <NUM> in accordance with the load with reference to information kept by the control unit <NUM> itself.

In the air conditioner <NUM> according to the modification example E, the motor valve <NUM> is controlled to be decreased in opening degree as a load increases when the outdoor heat exchanger <NUM> functions as a condenser, for improvement in performance of the air conditioner <NUM>. Furthermore, the motor valve <NUM> is controlled to have the minimum opening degree when the outdoor heat exchanger <NUM> functions as an evaporator, for inhibition of deterioration in performance of the refrigeration cycle apparatus due to provision of the branching passage <NUM>.

The embodiments of the present invention have been described above.

Claim 1:
A refrigeration cycle apparatus (<NUM>) comprising a refrigerant circuit (<NUM>) including an outdoor heat exchanger (<NUM>) configured to cause heat exchange between outdoor air and a refrigerant and a compressor (<NUM>) configured to discharge a compressed refrigerant, the refrigerant circuit configured to achieve a vapor compression refrigeration cycle while the outdoor heat exchanger functions as a condenser, wherein
the outdoor heat exchanger includes
an inlet port (23a) where a refrigerant flow into the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser,
an outlet port (23b) where a refrigerant flow out the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser,
a plurality of heat exchange paths (P1 to P8) including a plurality of heat transfer tubes (<NUM>) configured to cause the refrigerant flowing in through the inlet port upon the heat exchange to be distributed and flow in parallel,
a junction flow passage (<NUM>) disposed between the plurality of heat exchange paths and the outlet port and configured to cause refrigerants flowing from the plurality of heat exchange paths to the outlet port to join and then flow therein, and
a branching passage (<NUM>),
the plurality of heat exchange paths include a first path (P1) disposed in a lower portion of the outdoor heat exchanger, and a second path (P2) disposed above the first path,
the junction flow passage is configured to cause refrigerants having passed at least the first path and the second path to join and then flow therein,
the branching passage has a first end (<NUM>) connected to the first path and a second end (<NUM>) connected to the junction flow passage, characterized in that
the branching passage (<NUM>) includes a capillary tube (<NUM>), and
the outdoor heat exchanger (<NUM>) is, with use of the capillary tube (<NUM>), configured to be increased in flow rate ratio of the refrigerant flowing to the branching passage (<NUM>) to the flow rate of the refrigerant flowing to the first path (P1) upon decrease in load.