GB2530915A

GB2530915A - Air conditioner

Info

Publication number: GB2530915A
Application number: GB1518446.8A
Authority: GB
Inventors: Yuki Ugajin; Hideaki Maeyama; Takashi Okazazaki; Daisuke Ito; Yohei Kato
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2013-06-19
Filing date: 2013-06-19
Publication date: 2016-04-06
Anticipated expiration: 2033-06-19
Also published as: GB2530915B; GB201518446D0; WO2014203353A1; JPWO2014203353A1; JP6141429B2; GB2530915C

Abstract

Provided is an air conditioner that is very safe and has improved operating pressure but does not have a complicated configuration. This air conditioner (1) has a refrigerant circuit (1a) that circulates a refrigerant and is formed by connecting, by means of pipes, a compressor (3), a first heat exchanger (6), an expansion means (7), and a second heat exchanger (9). The refrigerant is an ethylene-type fluorohydrocarbon in which a flame-resistant refrigerant has been mixed.

Description

DESCRIPTION

Title of Invention

AIR-CONDITIONING APPARATUS

Technical Field

[0001] The present invention relates to an air-conditioning apparatus including a refrigerant circuit.

BackgroundArt

[0002] Currently, HEC refrigerant, such as R41OA, which is a refrigerant mixture of an R32 refrigerant and an Ri 25 refrigerant, and Ri 34a, are used as refrigerant for use in refrigerating and air-conditioning. The HEC refrigerant has a relatively high global warming potential (GWP). Accordingly, as one of the efforts to prevent global warming, an effort is in progress to replace refrigerant (working fluid) to be used in an apparatus in which a refrigeration cycle is formed, such as a refrigerator-freezer, an air-conditioning apparatus, or a water heating apparatus, with refrigerant whose GWP is significantly lower than that of the HFC refrigerant.

[0003] As one of such alternative refrigerant, there has been proposed a halogenated hydrocarbon having a carbon-carbon double bond in its composition. As the halogenated hydrocarbon, there is known, for example, propylene fluorohydrocarbon: HFO-1234yf (CF3CF=CH2), which is a hydrocarbon having one carbon-carbon double bond in its molecule. This HFO-1234yf refrigerant has a GWP of 4, which is extremely lower than that of R41 OA, which is 2,088, and that of Ri 34a, which is 1,430.

Accordingly, HFO-1234yf is expected to contribute to prevention of global warming, and an investigation of a technique for applying HFO-i234yf to an air-conditioning apparatus is being conducted.

[0004] However, HFO-1234y1 has a higher standard boiling point and a lower working pressure as compared with R41OA. Accordingly, when R41OA, which has been used mainly up to now, is replaced with HFO-1 234yf as the refrigerant for a home-use or business-use air-conditioning apparatus, in order to maintain the same capacity that is exhibited using R41OA, it is necessary to increase frequency of the compressor or increase a volume flow rate (amount of circulating refrigerant) by increasing the amount of filled refrigerant. In a circuit of the refrigeration cycle in which the volume flow rate of the refrigerant is increased in this manner, a flow velocity of the refrigerant flowing through the circuit is higher than when the volume flow rate of the refrigerant is not increased in the same circuit. Accordingly, the pressure loss caused by the refrigerant in the refrigeration cycle increases. In addition, when the volume flow rate of the refrigerant increases, an amount of the refrigerant sucked into the compressor also increases, and hence operation efficiency of the refrigeration cycle deteriorates. In view of this, Patent Literature 1 is disclosed as a technique for reducing the pressure loss.

[0005] In Patent Literature 1, there is disclosed a refrigeration cycle apparatus in which a hydrofluoroolefin such as HFO-1234yf is used as the refrigerant. In Patent Literature 1, an opening degree of an expansion valve is adjusted based on a temperature of a condenser, a temperature of an internal heat exchanger on a low-pressure side, and a temperature of a compressor on a discharge side. In this way, this related art aims to enhance, even when the refrigerant causing a high pressure loss, such as HFO-1234yf, is used, the operation efficiency by reducing the high pressure loss.

[0006] Further, in Patent Literature 2, there is disclosed a technique in which a polymerization inhibitor is added to tetrafluoroethylene (C2F4). The tetrafluoroethylene is an ethylene derivative having a molecular structure similar to that of ethylene fluorohydrocarbon. In addition, the tetrafluoroethylene is useful as a monomer for manufacture of a fluororesin or a fluorine-containing elastomer having, for example, a heat-resistant property and a chemical-resistant property, whereas the tetrafluoroethylene has a disadvantage of being extremely liable to be polymerized.

Patent Literature 2 aims to suppress the polymerization of the tetrafluoroethylene by adding the polymerization inhibitor to the tetrafluoroethylene.

Citation List Patent Literature [0007] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2012-1 32578 (Claim 1, Page 5 to Page 9) Patent Literature 2: Japanese Unexamined Patent Application Publication No. Hei 11-246447 (Claim 1, Page 2)

Summary of Invention

Technical Problem [0005] However, in Patent Literature 1, a temperature sensor and others are provided in order to reduce the pressure loss caused when HFO-1234y1 is used as the refrigerant, and hence a configuration of the apparatus is complicated. Moreover, HFO-1234yf is a combustible refrigerant, and hence there is a problem in safety at the time of operation.

[0009] In contrast, ethylene fluorohydrocarbon, which has a molecular structure similar to that of the tetrafluoroethylene disclosed in Patent Literature 2, causes a lower pressure loss than HFO-1234yf. However, the ethylene fluorohydrocarbon is also liable to be polymerized similarly to the tetrafluoroethylene. Accordingly, when the ethylene fluorohydrocarbon is used as the refrigerant, it is necessary to suppress the polymerization of the ethylene fluorohydrocarbon by adding the polymerization inhibitor in the same manner as in the related art disclosed in Patent Literature 2.

[0010] However, the refrigerant circulates through the refrigeration cycle while changing its phase to liquid, gas, or other phases, and in portions where a temperature increases to a high level and polymerization is liable to occur, such as a sliding portion of the compressor and a winding portion of a motor, the refrigerant vaporizes together with the polymerization inhibitor When the polymerization inhibitor vaporizes together with the refrigerant in this way from, for example, the sliding portion of the compressor and the winding portion of the motor, the polymerization inhibitor does not sufficiently reach the high-temperature portions of the refrigeration cycle. This lessens the effect of suppressing the polymerization of the refrigerant. In particular, when opposing surfaces of the sliding portion of the compressor are made of metal, the temperature of the sliding surfaces increases to a high level due to a sliding operation, and the metal is activated. The activated metal acts as a catalyst to promote the decomposition of the ethylene fluorohydrocarbon, and hence when the polymerization inhibitor is not sufficiently reached, the polymerization of the decomposed ethylene fluorohydrocarbon is also promoted.

[0011] As described above, even when the ethylene fluorohydrocarbon is intended to be used as the refrigerant, it is difficult to apply the ethylene fluorohydrocarbon to the refrigeration cycle because a physical property of the refrigerant is unstable under a high temperature.

[0012] The present invention has been made in view of the problems described above, and provides an air-conditioning apparatus without a complicated configuration, which is capable of enhancing a working pressure and is high in safety.

Solution to Problem [0013] According to one embodiment of the present invention, there is provided an air-conditioning apparatus, including a refrigerant circuit for allowing refrigerant to circulate therethrough, the refrigerant circuit including a compressor, a first heat exchanger, an expansion unit, and a second heat exchanger that are connected by pipes, in which the refrigerant is ethylene fluorohydrocarbon having a flame-retardant refrigerant mixed therein.

Advantageous Effects of Invention [0014] According to the one embodiment of the present invention, the ethylene fluorohydrocarbon having a high standard boiling point is used as the refrigerant, and hence the cooling and heating capacities of the air-conditioning apparatus may be enhanced. In addition, the refrigerant is the ethylene fluorohydrocarbon having the flame-retardant refrigerant mixed therein, and hence the safety of the air-conditioning apparatus is high.

Brief Description of Drawings

[0015] [Fig. 1] Fig. 1 is a circuit diagram illustrating an air-conditioning apparatus 1 according to Embodiment 1 of the present invention.

[Fig. 2] Fig. 2 is a table showing chemical formulae of refrigerant according to Embodiment 1.

[Fig. 3] Fig. 3 is a graph showing a relationship between a GWP and a combustible concentration according to Embodiment 1.

[Fig. 4] Fig. 4 is a circuit diagram illustrating an air-conditioning apparatus 1 according to Embodiment 3 of the present invention.

[Fig. 5] Fig. 5 is a gas-liquid equilibrium diagram showing characteristics of a zeotropic refrigerant mixture.

[Fig. 6] Fig. 6 is a gas-liquid equilibrium diagram showing a relationship between a circulation composition and a temperature according to Embodiment 3.

[Fig. 7] Fig. 7 is a graph to be used for calculation of the circulation composition that is based on a quality.

[Fig. 8] Fig. 8 is a front view illustrating a first heat exchanger 6 according to Embodiment 4 of the present invention.

[Fig. 9] Fig. 9 is a front view illustrating a first heat exchanger 6 according to Embodiment 5 of the present invention.

[Fig. 10] Fig. 10 is a front view illustrating a first heat exchanger 6 according to Embodiment 6 of the present invention.

Description of Embodiments

[0016] Now, an air-conditioning apparatus according to each of embodiments of the present invention is described with reference to the drawings. Note that, the present invention is not limited to the embodiments described below. Moreover, in the drawings including Fig. 1 and referred to below, the size relationship between components may be different from the reality in some cases.

[0017] Embodiment 1 Fig. 1 is a circuit diagram illustrating an air-conditioning apparatus 1 according to Embodiment 1 of the present invention. Referring to Fig. 1, the air-conditioning apparatus 1 is described. As illustrated in Fig. 1, the air-conditioning apparatus 1 includes an outdoor unit 2 and an indoor unit 3. The outdoor unit 2 includes a compressor 4, a four-way valve 5, a first heat exchanger 6, and an electronic expansion valve 7 serving as an expansion unit. The compressor 4 is configured to compress sucked refrigerant, and a positive-displacement compressor is used in Embodiment 1. Examples of the positive-displacement compressor include a rotary compressor, a scroll compressor, a screw compressor, and a reciprocating compressor. Further, the compressor 4 in Embodiment 1 is a capacity-controllable compressor whose rotation speed is controlled by an inverter circuit (not shown).

Further, the four-way valve 5 is configured to switch a passage of the refrigerant.

Further, the first heat exchanger 6 includes an outdoor fan 6a, and in the first heat exchanger 6, the refrigerant exchanges heat with ambient air of the outdoor unit 2 conveyed by the outdoor fan 6a. The electronic expansion valve 7 is configured to adjust a valve opening degree to control a flow rate of the refrigerant, and is an example of a pressure reduction mechanism.

[0018] The indoor unit 3 includes a second heat exchanger 9, and the second heat exchanger 9 includes an indoor fan 9a. In the second heat exchanger 9, the refrigerant exchanges heat with ambient air of the indoor unit 3 conveyed by the indoor fan 9a. The indoor unit 3 and the outdoor unit 2 are connected to each other by a liquid pipe 8 and a gas pipe 10 forming a refrigerant passage, and this connection forms a refrigeration cycle including a refrigerant circuit 1 a. Note that, in Embodiment 1, if necessary, a reheat valve, an accumulator, a gas-liquid separator or other such components may be added to the above-mentioned basic refrigerant circuit 1 a as another component. Further, a plurality of the indoor units 3 may be connected to one outdoor unit 2.

[0019] In the refrigerant circuit 1 a, the four-way valve 5 switches a mode of the refrigerant circuit 1 a between a cooling energy supply mode (cooling operation) in which cooling energy is supplied to an inside of a room from the second heat exchanger 9 and a heating energy supply mode (heating operation) in which heating energy is supplied to the inside of the room from the second heat exchanger 9. Of those modes, in the cooling energy supply mode, the refrigerant discharged from the compressor 4 passes through the solid-line passage in the four-way valve 5 of Fig. 1 to circulate through the refrigerant circuit la. Specifically, the refrigerant passes in a circular manner in the following order: the compressor 4, the four-way valve 5, the first heat exchanger 6, the electronic expansion valve 7, the liquid pipe 8, the second heat exchanger 9, and the gas pipe 10. The refrigerant then returns to the compressor 4 after passing through the four-way valve 5. In this case, the first heat exchanger 6 functions as a condenser, and the second heat exchanger 9 functions as an evaporator. Then, the low-temperature refrigerant passing through the second heat exchanger 9 is subjected to heat exchange with the ambient air of the indoor unit 3 by the second heat exchanger 9. In this manner, the cooling operation for cooling an indoor space is performed.

[0020] On the other hand, in the heating energy supply mode, the refrigerant discharged from the compressor 4 passes through the dotted-line passage in the four-way valve 5 of Fig. ito circulate through the refrigerant circuit la. Specifically, the refrigerant passes in a circular manner in the following order: the compressor 4, the four-way valve 5, the gas pipe 10, the second heat exchanger 9, the liquid pipe a, the electronic expansion valve 7, and the first heat exchanger 6. The refrigerant then returns to the compressor 4 after passing through the four-way valve 5. In this case, the second heat exchanger 9 functions as a condenser, and the first heat exchanger 6 functions as an evaporator The high-temperature refrigerant passing through the second heat exchanger 9 is subjected to heat exchange with the ambient air of the indoor unit 3 by the second heat exchanger 9. In this manner, the heating operation for heating the indoor space is performed.

[0021] Next, the refrigerant circulating through the refrigerant circuit la is described.

In Embodiment 1, as the refrigerant, ethylene fluorohydrocarbon having a flame-retardant refrigerant mixed therein is used. First, the ethylene fluorohydrocarbon refrigerant is described. As the refrigerant of the air-conditioning apparatus 1, propylene fluorohydrocarbon, which is a low-GWP refrigerant, such as HFO-1234yf (CF3CF=GH2), is attracting attention in the field of automobile air-conditioning.

However, HFO-1234yf has a high standard boiling point and a low working pressure as compared with R41OA, which is mainly used in a home-use or business-use and stationary air-conditioning apparatus. Accordingly, a pressure loss in a refrigerant pipe increases, and hence the performance of the refrigeration cycle, in particular, the performance of the evaporator, is liable to deteriorate. Therefore, in order to apply a low-GWP refrigerant to the air-conditioning apparatus, it is appropriate that a low-GWP refrigerant having a low standard boiling point be used. In this case, in general, the refrigerant tends to have a lower standard boiling point when its composition has a smaller carbon number. In view of this, a standard boiling point of the ethylene fluorohydrocarbon having a carbon number of 2, such as R1132(E), is considered to be higher than the propylene fluorohydrocarbon having a carbon number of 3.

Therefore, the use of the refrigerant as Ri 132(E) enables the operation to be performed at a low GWP and at the same working pressure as in R4iOA.

[0022] Fig. 2 is a table showing chemical formulae of refrigerant according to Embodiment 1. For example, the refrigerant used in Embodiment 1 may include, as shown in Fig. 2, Ri132(Z): cis-1,2-difluoroethylene or Rii32a: i,i-difluoroethylene, in addition to Rii32(E): trans-i,2-difluoroethylene. Further, in addition to those i 0 refrigerant, when refrigerant containing, for example, Ri i 4i: fluoroethylene or Ri 123: 1,i,2-trifluoroethylene is used, the operation can also be performed at a low GWP and at the same working pressure as in R41 OA in the same manner as in Ri i 32(E).

Note that, among those refrigerant, the refrigerant except Ril4i contain a plurality of fluorine elements, which are halogen elements, but one of the plurality of fluorine iS elements may be substituted with a halogen element other than fluorine, such as chlorine, bromine, or iodine. With this, such an effect that the stability of a compound is enhanced is achieved.

[0023] Next, the flame-retardant refrigerant to be added to the ethylene fluorohydrocarbon is described. Fig. 3 is a graph showing a relationship between the GWP and a combustible concentration according to Embodiment i. The Rii32(E) refrigerant, which is the ethylene fluorohydrocarbon, is a combustible refrigerant. The combustible concentration of the Rii32(E) refrigerant before being mixed with the flame-retardant refrigerant is indicated by the solid line connecting the marks "0" of Fig. 3. In Fig. 3, the horizontal axis represents the GWP, and the vertical axis represents the combustible concentration. As a combustible concentration to be compared with the combustible concentration of R1i32(E), a combustible concentration of R32 is shown (solid line connecting the marks "A" of Fig. 3). As shown in Fig. 3, the GWP of Rii32(E) is extremely lower than that of R32, and a range between upper and lower limits of the combustible concentration of R1132(E) is slightly smaller than that of R32. Further, the combustible concentration of the refrigerant obtained by mixing the flame-retardant refrigerant into R1132(E) is indicated by the solid line connecting the marks "*" of Fig. 3.

[0024] As described above, when the flame-retardant refrigerant is mixed into R1132(E), a minimum combustible concentration increases while a maximum combustible concentration does not change significantly In other words, the range between the upper and lower limits of the combustible concentration of the refrigerant obtained by mixing the flame-retardant refrigerant into R1132(E) is narrower than that of the refrigerant of only Ri 132(E) (dotted line of Fig. 3). Therefore, this refrigerant mixture is flame-retardant. Note that, it is preferred that a mixing proportion of the flame-retardant refrigerant to the ethylene fluorohydrocarbon be 50% or less. With this, a flame-retardant refrigerant can be achieved while suppressing an increase in GWP.

[0025] Next, an action of the air-conditioning apparatus i according to Embodiment i is described. As described above, the refrigerant of the air-conditioning apparatus 1 is the ethylene fluorohydrocarbon having the flame-retardant refrigerant mixed therein.

The ethylene fluorohydrocarbon is considered to have the same standard boiling point as that of R41OA, and hence the cooling and heating operations can be performed at the same working pressure as that of R41OA. Moreover, the GWP of the ethylene fluorohydrocarbon is lower than that of R41 OA, and hence the use of the ethylene fluorohydrocarbon contributes to suppression of global warming. As described above, the air-conditioning apparatus 1 is capable of achieving a low GWP while exhibiting the same performance of the refrigeration cycle as that of R41A.

Further, although the ethylene fluorohydrocarbon is relatively combustible as with HFO-i234yf, in Embodiment 1, the flame-retardant refrigerant is mixed into the ethylene fluorohydrocarbon, and hence the refrigerant is flame-retardant. Therefore, the safety of the air-conditioning apparatus 1 can be enhanced as compared with the air-conditioning apparatus using HFO-1234yf.

[0026] Further, when the refrigeration cycle according to Embodiment 1 is filled with refrigerating machine oil, it is necessary to allow this refrigerating machine oil to circulate through the refrigeration cycle smoothly. In order to allow the refrigerating machine oil to circulate through the refrigeration cycle smoothly, when the refrigeration capacity is 1 horsepower or less, the diameter of the pipe on the discharge side of the compressor 4 is designed to be 9.52 mm or less. With this, a zero penetration velocity or more can be secured as a flow velocity of the refrigerant, and therefore, a backward flow of the refrigerating machine oil into the compressor 4 can be suppressed while reducing an amount of refrigerant.

[0027] Embodiment 2 Next, an air-conditioning apparatus 1 according to Embodiment 2 of the present invention is described. In Embodiment 2, R134a or R125 is used as the flame-retardant refrigerant. In Embodiment 2, by adding the refrigerant that is particularly flame-retardant, such as Ri 34a or Ri 25, to the ethylene fluorohydrocarbon, the air-conditioning apparatus 1 with high performance and enhanced safety can be obtained while achieving a low GWP.

[0028] Embodiment 3 Next, an air-conditioning apparatus i according to Embodiment 3 of the present invention is described. Fig. 4 is a circuit diagram illustrating the air-conditioning apparatus 1 according to Embodiment 3. Embodiment 3 differs from Embodiment 1 in that R134a is used as the flame-retardant refrigerant and that a configuration for detecting a circulation composition of the refrigerant circulating through the refrigerant circuit 1 a is added. In Embodiment 3, the same components as in Embodiment 1 are denoted with the same reference numerals to omit descriptions thereof, and the differences from Embodiment 1 are mainly described.

[0029] As illustrated in Fig. 4, the air-conditioning apparatus 1 includes the outdoor ii unit 2 and the indoor unit 3. The outdoor unit 2 includes the compressor 4, the four-way valve 5, the first heat exchanger 6, and the electronic expansion valve 7 serving as the expansion unit, and those components are the same as in Embodiment 1. In Embodiment 3, an accumulator 13 is provided on a suction side of the compressor 4, and further, a bypass lb is provided so as to bypass the compressor 4 from a branch point 17 located in the middle of a discharge pipe connecting the discharge side of the compressor 4 and the four-way valve 5 to a junction point 18 located in the middle of a suction pipe connecting the suction side of the compressor 4 and the accumulator 13. Further, an intermediate heat exchanger 11 and a capillary tube 12 serving as a pressure reducer are provided to the bypass lb. Still further, in the outdoor unit 2, a controller 19 for adjusting the opening degree of the electronic expansion valve 7 is provided.

[0030] The intermediate heat exchanger 11 is configured to condense the refrigerant discharged from the compressor 4 and evaporate the refrigerant flowing from the capillary tube 12. Further, the capillary tube 12 is configured to reduce the pressure of the refrigerant flowing from the intermediate heat exchanger 11. Further, on inlet and outlet sides of the capillary tube 12, thermistors 14 serving as a temperature detection unit are installed, and the thermistors 14 are configured to detect a temperature inside the bypass lb. Further, on the outlet side of the capillary tube 12, a pressure sensor 15 serving as a pressure detection unit is installed, and the pressure sensor 15 is configured to detect a pressure inside the bypass lb. Further, a composition calculator 16 serving as a composition calculation unit is provided to the bypass ib, and the composition calculator 16 is connected to the thermistors 14 and the pressure sensor 15. The composition calculator 16 is configured to calculate a composition ratio of the refrigerant based on the temperature detected by the thermistor 14 and the pressure detected by the pressure sensor 15.

[0031] Note that, the compressor 4 is configured to compress sucked refrigerant, and a positive-displacement compressor is used in Embodiment 3. Examples of the positive-displacement compressor include a rotary compressor, a scroll compressor, a screw compressor, and a reciprocating compressor. Further, the compressor 4 in Embodiment 1 is a capacity-controllable compressor whose rotation speed is controlled by an inverter circuit (not shown). Further, the four-way valve 5 is configured to switch a passage of the refrigerant. Further, the first heat exchanger 6 includes the outdoor fan 6a, and in the first heat exchanger 6, the refrigerant exchanges heat with ambient air of the outdoor unit 2 conveyed by the outdoor fan Ga.

The electronic expansion valve 7 is configured to adjust the valve opening degree to control a flow rate of the refrigerant, and is an example of the pressure reduction mechanism.

[0032] The indoor unit 3 includes the second heat exchanger 9, and the second heat exchanger 9 includes the indoor fan 9a. In the second heat exchanger 9, the refrigerant exchanges heat with ambient air of the indoor unit 3 conveyed by the indoor fan 9a. The indoor unit 3 and the outdoor unit 2 are connected to each other by the liquid pipe Sand the gas pipe 10 forming the refrigerant passage, and this connection forms the refrigeration cycle including the refrigerant circuit 1 a.

[0033] In the refrigerant circuit 1 a, the four-way valve 5 switches the mode of the refrigerant circuit 1 a between the cooling energy supply mode (cooling operation) in which cooling energy is supplied to an inside of a room from the second heat exchanger 9 and the heating energy supply mode (heating operation) in which heating energy is supplied to the inside of the room from the second heat exchanger 9. Of those modes, in the cooling energy supply mode, the refrigerant discharged from the compressor 4 passes through the solid-line passage in the four-way valve 5 of Fig. ito circulate through the refrigerant circuit la. Specifically, the refrigerant passes in a circular manner in the following order: the compressor 4, the four-way valve 5, the first heat exchanger 6, the electronic expansion valve 7, the liquid pipe 8, the second heat exchanger 9, and the gas pipe 10. The refrigerant then returns to the compressor 4 after passing through the four-way valve 5. In this case, the first heat exchanger 6 functions as a condenser, and the second heat exchanger 9 functions as an evaporator. Then, the low-temperature refrigerant passing through the second heat exchanger 9 is subjected to heat exchange with the ambient air of the indoor unit 3 by the second heat exchanger 9. In this manner, the cooling operation for cooling an indoor space is performed.

[0034] On the other hand, in the heating energy supply mode, the refrigerant discharged from the compressor 4 passes through the dotted-line passage in the four-way valve 5 of Fig. ito circulate through the refrigerant circuit la. Specifically, the refrigerant passes in a circular manner in the following order: the compressor 4, the four-way valve 5, the gas pipe 10, the second heat exchanger 9, the liquid pipe 8, the electronic expansion valve 7, and the first heat exchanger 6. The refrigerant then returns to the compressor 4 after passing through the four-way valve 5. In this case, the second heat exchanger 9 functions as a condenser, and the first heat exchanger 6 functions as an evaporator. The high-temperature refrigerant passing through the second heat exchangerS is subjected to heat exchange with the ambient air of the indoor unit 3 by the second heat exchangerS. In this manner, the heating operation for heating the indoor space is performed.

[0035] Next, a refrigerant composition of a zeotropic refrigerant mixture, which is a mixture of refrigerant having different standard boiling points, is described. Fig. 5 is a gas-liquid equilibrium diagram showing characteristics of the zeotropic refrigerant mixture. In Fig. 5, the horizontal axis represents the circulation composition, and the vertical axis represents a temperature. The circulation composition refers to the composition ratio (proportion) of a low-boiling point component in the refrigerant mixture circulating through the refrigerant circuit la. When the circulation composition is small, an amount of the low-boiling point component is small, and when the circulation composition is large, an amount of the low-boiling point component is large. Note that, a refrigerant composition of the refrigerant immediately after the refrigerant is filled into the refrigeration cycle is referred to as "filling composition". As shown in Fig. 5, the relationship between the circulation composition and the temperature changes when, for example, the pressure changes from PL to PH. Further, in a state of the refrigerant, a boundary between a two-phase gas-liquid state and a superheated vapor state is a saturated vapor line, and the refrigerant is in the superheated vapor state on a high-temperature side of the saturated vapor line. Further, in the state of the refrigerant, a boundary between the two-phase gas-liquid state and a subcooling state is a saturated liquid line, and the refrigerant is in the subcooling state on a low-temperature side of the saturated liquid line. Note that, a region enclosed by the saturated vapor line and the saturated liquid line represents the two-phase gas-liquid state.

[0036] The alternate long and short dash line of Fig. 5 (circulation composition 7) indicates the circulation composition immediately after the refrigerant mixture is filled into the refrigeration cycle. Further, "a" on the alternate long and short dash line (high-temperature and high-pressure state) indicates a state of the refrigerant on an inlet side of the intermediate heat exchanger 11, and "b' on the alternate long and short dash line (low-temperature and high-pressure state) indicates a state of the refrigerant on an outlet side of the intermediate heat exchanger 11, that is, on the inlet side of the capillary tube 12. Further, "c" on the alternate long and short dash line (low-temperature and low-pressure state) indicates a state of the refrigerant on the outlet side of the capillary tube 12, and "d" on the alternate long and short dash line (high-temperature and low-pressure state) indicates a state of the refrigerant on the suction side of the compressor 4.

[0037] In general, in the refrigeration cycle using the zeotropic refrigerant mixture, the filling composition of the refrigerant immediately after the refrigerant is filled into the refrigeration cycle is not necessarily the same as the circulation composition of the refrigerant circulating through the refrigeration cycle. At the point A (portion of the two-phase gas-liquid state in the refrigeration cycle) of Fig. 5, the circulation composition of a liquid refrigerant is X smaller than the filling composition Z, and the circulation composition of a vapor refrigerant is Y larger than the filling composition Z. In such a refrigeration cycle as in Embodiment 3 in which the accumulator 13 is provided on the pipe on the suction side of the compressor 4, the liquid refrigerant accumulates in the accumulator 13. The circulation composition of the liquid refrigerant is smaller than the filling composition as described above, that is, the amount of the low-boiling point component is small (the amount of a high-boiling point component is large). Accordingly, when the liquid refrigerant accumulates in the accumulator 13, in the circulation composition of the refrigerant circulating through the refrigeration cycle, the amount of the low-boiling point component tends to become larger than that of the filling composition.

[0038] Further, a case where the circulation composition changes is not limited to this case, and also when the refrigerant in the refrigeration cycle leaks to the outside of the refrigerant circuit la, the circulation composition of the refrigerant in the refrigeration cycle changes. For example, at the point A (portion of the two-phase gas-liquid state in the refrigeration cycle) of Fig. 5, when the leakage of the liquid refrigerant occurs, because the circulation composition of the liquid refrigerant is X smaller than the filling composition 7, the amount of the low-boiling point component of the circulation composition of the refrigerant circulating through the refrigeration cycle tends to become larger than that of the filling composition. On the other hand, at the point A (portion of the two-phase gas-liquid state in the refrigeration cycle) of Fig. 5, when the leakage of the vapor refrigerant occurs, because the circulation composition of the vapor refrigerant is Y larger than the filling composition 7, the amount of the low-boiling point component of the circulation composition of the refrigerant circulating through the refrigeration cycle tends to become smaller than that of the filling composition. As described above, in the refrigeration cycle using the zeotropic refrigerant mixture, the composition of the refrigerant circulating through the refrigeration cycle significantly changes depending on, for example, the operation state of the refrigeration cycle or the leakage of the refrigerant.

[0039] Next, an action of the air-conditioning apparatus 1 according to Embodiment 3 is described. Fig. 6 is a gas-liquid equilibrium diagram showing a relationship between the circulation composition and the temperature according to Embodiment 3.

A high-temperature, high-pressure, and gaseous refrigerant compressed by the compressor 4 branches at the branch point 17 into refrigerant that is to flow through the normal path, that is, to flow through the refrigerant circuit 1 a to flow into the four-way valve 5 and refrigerant that is to flow through the bypass lb to flow into the intermediate heat exchanger 11. Of those, the refrigerant to flow through the bypass lb flows into the intermediate heat exchanger 11 from the inlet of the intermediate heat exchanger 11, condensed and liquefied, and discharged from the outlet of the intermediate heat exchanger 11. Then, the refrigerant discharged from the intermediate heat exchanger 11 becomes a two-phase gas-liquid refrigerant after passing through the capillary tube 12. After that, the refrigerant flows again into the intermediate heat exchanger 11 and is evaporated, reaches the junction point 18, and then returns again to the compressor 4.

[0040] Further, when the refrigerant flows through the normal path, that is, the refrigerant circuit la and the bypass lb, the pressure sensor 15 installed on the bypass lb detects the pressure inside the bypass lb. The refrigerant flowing through this refrigeration cycle is the ethylene fluorohydrocarbon having the flame-retardant refrigerant added thereto, and when, for example, the refrigerant is the zeotropic refrigerant mixture of two types of refrigerant, the composition calculator 16 calculates a gas-liquid equilibrium diagram (Fig. 6) based on the pressure PH detected by the pressure sensor 15 and the type of refrigerant mixture filled into the refrigeration cycle. Further, in the bypass 1 b, not only the pressure but also the temperature inside the bypass lb is detected, and the temperature is detected by the thermistor 14 installed on the bypass lb. Further, assuming that the state of the refrigerant after passing through the capillary tube 12 is saturated liquid, the composition calculator 16 calculates the circulation composition Z in the refrigeration cycle based on the saturated liquid line of Fig. 6 and a temperature TH detected by the thermistor 14. Further, based on the circulation composition Z of the refrigerant calculated by the composition calculator 16, the controller 19 adjusts the opening degree of the electronic expansion valve 7.

[0041] As described above, when the circulation composition in the refrigeration cycle changes, the relationship between the pressure and the saturation temperature of the refrigerant changes, and the cooling capacity significantly changes as well. In Embodiment 3, through the provision of the bypass ib, the composition calculator 16 calculates the circulation composition in the refrigeration cycle based on the temperature and pressure inside the bypass lb. Then, based on the calculated circulation composition, the opening degree of the electronic expansion valve 7 is adjusted. With this, in the refrigeration cycle, the degree of subcooling or the degree of superheat can be controlled to a desired degree of subcooling or a desired degree of superheat. Therefore, the high-performance air-conditioning apparatus 1 capable of enabling the refrigeration cycle to operate stably and exhibit desired performance can be obtained. Note that, in order to enable the refrigeration cycle to operate optimally, not only the opening degree of the electronic expansion valve 7 but also the rotation speed of the compressor 4 may be controlled based on the circulation composition.

[0042] Through further development of the above-mentioned unit for detecting the circulation composition, the circulation composition of the zeotropic refrigerant mixture of two types of refrigerant can be calculated based also on a quality of the refrigerant.

Fig. 7 is a graph to be used for calculation of the circulation composition that is based on the quality. A quality X of the refrigerant is a value obtained by dividing a mass flow rate of the entire refrigerant by a mass flow rate of refrigerant vapor (X=(mass flow rate of refrigerant vapor)/(mass flow rate of entire refrigerant)). Further, the temperature and pressure of the refrigerant having the quality X are detected by the thermistor 14 and the pressure sensor 15. When the detected pressure is a constant value P, the gas-liquid equilibrium diagram is as shown in Fig. 7. As shown in Fig. 7, on the saturated vapor line, the quality X is 1 because the entire refrigerant is gas, and on the saturated liquid line, the quality X is 0 because the entire refrigerant is liquid. In addition, a relationship between the temperature of the refrigerant and the circulation composition of the refrigerant obtained when the quality X is a predetermined value is indicated by the alternate long and short dash line of Fig. 7. With this, when the temperature of the refrigerant having the quality X at the pressure P is known, the circulation composition of the refrigerant can be calculated.

As described above, by obtaining the pressure, temperature, and quality of the two-phase gas-liquid refrigerant, the circulation composition of the refrigerant in the refrigeration cycle as well as information on whether the refrigerant is saturated vapor or saturated liquid can be obtained.

[0043] Moreover, in Embodiment 3, an opening degree detection unit for detecting the opening degree of the electronic expansion valve 7 can be provided, and a subcooling degree detection unit can be provided on the outlet side of one of the first heat exchanger 6 and the second heat exchanger 9 that functions as the evaporator.

As compared with the propylene fluorohydrocarbon such as HFO-1234yf, the ethylene fluorohydrocarbon is highly reactive and is unstable thermally and chemically, and thus polymerization or decomposition is liable to occur. When the ethylene fluorohydrocarbon causes a polymerization reaction, sludge is produced, and the amount of refrigerant decreases. Further, the sludge produced due to the polymerization adheres to the electronic expansion valve 7, which may be a cause of clogging of the electronic expansion valve 7. In Embodiment 3, through the provision of the opening degree detection unit, a level of clogging of the electronic expansion valve 7 is detected. However, only by detecting whether or not the electronic expansion valve 7 is clogged, it cannot be determined whether the clogging is caused by the sludge produced due to the polymerization of the refrigerant or caused by sludge produced due to a cause other than the polymerization of the refrigerant.

[0044] In this case, when the sludge is produced due to the polymerization of the refrigerant, the amount of refrigerant decreases as described above. In view of this, in Embodiment 3, by providing the subcooling degree detection unit to detect the amount of refrigerant, it is determined whether the clogging of the electronic expansion valve 7 is caused by the sludge produced due to the polymerization of the refrigerant or caused by the sludge produced due to a cause other than the polymerization of the refrigerant. When the amount of refrigerant decreases, the amount of refrigerant subcooled by the condenser decreases, and the degree of subcooling on an outlet side of the condenser lowers. Therefore, by the subcooling degree detection unit detecting the degree of subcooling on the outlet side of the condenser, it can be detected whether or not the amount of refrigerant has decreased.

As described above, by the opening degree detection unit detecting the clogging of the electronic expansion valve 7 and the subcooling degree detection unit detecting the amount of refrigerant, it can be determined whether or not the refrigerant has been polymerized. Further, Embodiment 3 has the configuration for detecting the circulation composition of the refrigerant, and hence even when the refrigerant is polymerized and the circulation composition is changed, the changed circulation composition can be detected.

[0045] Note that, in place of the above-mentioned subcooling degree detection unit, a superheat degree detection unit may be provided on the outlet side of the evaporator.

As described above, when the amount of refrigerant decreases, the amount of refrigerant subcooled by the condenser decreases, and the degree of subcooling on the outlet side of the condenser lowers. When the electronic expansion valve 7 is controlled so that the degree of subcooling of the refrigerant flowing through the evaporator is constant, the opening degree of the electronic expansion valve 7 is controlled to decrease, and the amount of refrigerant to flow into the evaporator decreases. When the amount of refrigerant to flow into the evaporator decreases in this manner, the degree of superheat on the outlet side of the evaporator increases by a corresponding amount. Therefore, by the superheat degree detection unit detecting the degree of superheat on the outlet side of the evaporator, it can be detected whether or not the amount of refrigerant has decreased. Further, a discharge temperature detection unit for detecting a temperature on the discharge side of the compressor 4 may be provided. When the degree of superheat on the outlet side of the evaporator increases, the compressor 4 is controlled to increase its frequency in order to maintain the cooling/heating capacity. With this, the pressure loss in the refrigeration cycle increases, and a suction pressure into the compressor 4 is liable to decrease. As a result, the temperature of the refrigerant discharged from the compressor 4 increases. Therefore, by the discharge temperature detection unit detecting the temperature on the discharge side of the compressor 4, it can be detected whether or not the amount of refrigerant has decreased.

[0046] Embodiment 4 Next, an air-conditioning apparatus 1 according to Embodiment 4 of the present invention is described. Fig. 8 is a front view illustrating a first heat exchanger 6 according to Embodiment 4. Embodiment 4 differs from Embodiment 1 in that a tube diameter of the first heat exchanger 6 is specified. In Embodiment 4, the same components as in Embodiment 1 are denoted with the same reference numerals to omit descriptions thereof, and the difference from Embodiment 1 is mainly described.

[0047] In Embodiment 4, as illustrated in Fig. 8, the first heat exchanger 6 is a cylindrical heat transfer tube, and a tube diameter ri of the first heat exchanger 6 is designed to be 7.0 mm or less. A tube diameter of a heat exchanger to be used in a home-use air-conditioning apparatus using R41 OA as its refrigerant is set to, for example, 7.0 mm. In the air-conditioning apparatus, when HFO-1234yf is used as the refrigerant, because HFO-1234yf has a high standard boiling point and a low working pressure, the pressure loss in the refrigerant pipe increases. Accordingly, in order to maintain the same performance that is exhibited using R41 OA, the pressure loss in the refrigerant pipe needs to be reduced by increasing the tube diameter of the refrigerant circuit 1 a or the tube diameter of the heat exchanger.

[0048] In contrast, in Embodiment 4, R1132(E), which is the ethylene fluorohydrocarbon, is used as the refrigerant, and R1132(E) has the lower standard boiling point and the higher working pressure than HFO-1 234yf. Accordingly, in Embodiment 4, the pressure loss in the refrigerant pipe can be made smaller than when HFO-1234yf is used. Therefore, the following effect is achieved. Specifically, the high-performance air-conditioning apparatus 1 can be obtained, which is less liable to be affected by the pressure loss in the refrigerant pipe and is capable of reducing the amount of refrigerant even when the tube diameter ri of the first heat exchanger 6 is 7.0 mm or less. Note that, instead of the tube diameter of the first heat exchanger 6, the tube diameter of the second heat exchanger 9 may be set to 7.0 mm or less, or both of the tube diameters may be set to 7.0 mm or more.

[0049] Note that, in Embodiment 4, the tube diameter of the heat exchanger is specified, but a relationship between the tube diameter of the first heat exchanger 6 and the tube diameter of the second heat exchanger 9 may be specified. For example, when the first heat exchanger 6 is caused to function as the condenser and the second heat exchanger 9 is caused to function as the evaporator, that is, in the cooling energy supply mode (cooling operation), the tube diameter of the second heat exchanger 9 is made smaller than the tube diameter of the first heat exchanger 6.

Through the second heat exchanger 9 functioning as the evaporator, the liquid refrigerant mainly flows, and through the first heat exchanger 6 functioning as the condenser, the gaseous refrigerant mainly flows. Further, a density of the liquid refrigerant is higher than that of the gaseous refrigerant. Accordingly, by setting the tube diameter of the second heat exchanger 9 (evaporator) through which the liquid refrigerant mainly flows to a value smaller than the tube diameter of the first heat exchanger 6 (condenser) through which the gaseous refrigerant mainly flows, the balance between the amount of liquid refrigerant and the amount of gaseous refrigerant can be maintained.

[0050] Further, in Embodiment 4, when the first heat exchanger 6 is caused to function as the evaporator and the second heat exchanger 9 is caused to function as the condenser, that is, in the heating energy supply mode (heating operation), an inside of the first heat exchanger 6 may be structured such that one flow path of the refrigerant branches into two flow paths of the refrigerant from an inlet side to an outlet side of the first heat exchanger 6. Through the first heat exchanger 6 functioning as the evaporator, the liquid refrigerant mainly flows, and the liquid refrigerant passes through the first heat exchanger 6 to change into the gaseous refrigerant. Further, the density of the liquid refrigerant is higher than that of the gaseous refrigerant. At this time, when the inside of the first heat exchanger 6 has a "1-2 path structure" in which one flow path branches into two flow paths, even when the density of the refrigerant decreases and the refrigerant expands after the state of the refrigerant changes from liquid to gas while passing through the first heat exchanger 6, the passage is enlarged by a corresponding amount. Therefore, the pressure loss of the refrigerant in the first heat exchanger 6 can be reduced. Note that, when the second heat exchanger 9 is caused to function as the evaporator, an inside of the second heat exchanger 9 may also be structured such that one flow path of the refrigerant branches into two flow paths of the refrigerant from an inlet side to an outlet side of the second heat exchanger 9.

[0051] Further, a groove may be formed in an inner surface of the heat transfer tube of at least one of the first heat exchanger 6 and the second heat exchanger 9 so as to produce an internally-grooved heat transfer tube. In this case, an inner surface area of the heat transfer tube is increased, and at the same time, an effect of causing a flow of the refrigerant to be a turbulent flow is promoted, and hence heat transfer performance of the heat transfer tube can be enhanced.

[0052] EmbodimentS Next, an air-conditioning apparatus 1 according to Embodiment 5 of the present invention is described. Fig. 9 is a front view illustrating a first heat exchanger 6 according to Embodiment 5. Embodiment 5 differs from Embodiment 1 in that a structure of the first heat exchanger 6 is specified. In EmbodimentS, the same components as in Embodiment 1 are denoted with the same reference numerals to omit descriptions thereof, and the difference from Embodiment 1 is mainly described.

[0053] In Embodiment 5, as illustrated in Fig. 9, the first heat exchanger 6 serving as the heat transfer tube is not a cylindrical tube but a flattened tube whose volume is smaller than that of the cylindrical tube. In this manner, by flattening the first heat exchanger 6 to reduce the tube volume, the amount of refrigerant can be reduced.

Therefore, the high-performance air-conditioning apparatus 1 can be obtained. Note that, instead of the shape of the first heat exchanger 6, the shape of the second heat exchanger 9 may be flattened, or both of the shapes of the first heat exchanger 6 and the second heat exchanger 9 may be flattened.

[0054] Embodiment 6 Next, an air-conditioning apparatus 1 according to Embodiment 6 of the present invention is described. Fig. 10 is a front view illustrating a first heat exchanger 6 according to Embodiment 6. Embodiment 6 differs from EmbodimentS in that a diameter of the first heat exchanger 6 on a short-axis side thereof (short-axis diameter) is specified. In Embodiment 6, the same components as in Embodiment 5 are denoted with the same reference numerals to omit descriptions thereof, and the difference from Embodiment 5 is mainly described.

[0055] In Embodiment 6, as illustrated in Fig. 10, a short-axis diameter r2 of the first heat exchanger 6 having a flattened shape is designed to be 2.0 mm or less. This short-axis diameter r2 is appropriately determined from the viewpoints of, for example, the "1-2 path structure" of the heat transfer tube and the pressure loss in the refrigerant pipe, which are described in Embodiment 4. With this, in Embodiment 6, the amount of refrigerant can be reduced, and as a result, the performance of the air-conditioning apparatus 1 can be enhanced. Note that, instead of the shape of the first heat exchanger 6, the shape of the second heat exchanger 9 may be flattened and a short-axis diameter r2 of the second heat exchanger 9 may be set to 2.0 mm or less, or both of the shapes of the first heat exchanger 6 and the second heat exchanger 9 may be flattened and both of the short-axis diameters r2 of the first heat exchanger 6 and the second heat exchanger 9 may be set to 2.0 mm or less.

Reference Signs List [0056] 1 air-conditioning apparatus 1 a refrigerant circuit lb bypass 2 outdoor unit 3 indoor unit 4 compressor 5 four-way valve 6 first heat exchanger 6a outdoor fan 7 electronic expansion valve (expansion unit) 8 liquid pipe 9 second heat exchanger 9a indoor fan 10 gas pipe 11 intermediate heat exchanger 12 capillary tube 13 accumulator 14 thermistor pressure sensor 16 composition calculator 17 branch point 18 junction point 19 controller