Refrigeration circuit and refrigerator, air conditioner, or water heater equipped with this refrigeration circuit

Abstract

To provide a refrigeration circuit that uses a non-azeotropic mixed refrigerant that can reduce the compression power of the compressor. [Solution] The refrigeration circuit (1) circulates a refrigerant by connecting a compression unit (10), a condenser (20), an expansion unit (30), and an evaporator (40) with piping (2). The refrigerant is a non-azeotropic mixed refrigerant. The compression unit has a first compression chamber (11) and a second compression chamber (12). The expansion unit has an upstream expansion unit (31) and a downstream expansion unit (32) connected in series via a gas-liquid separator (33). The gas-liquid separator receives the intermediate pressure refrigerant from the upstream expansion unit. The system is configured to supply a first refrigerant gas, obtained by separating the gas and liquid components, to the first compression chamber, and to supply the refrigerant liquid to the downstream expansion means. The evaporator evaporates the low-pressure refrigerant liquid from the downstream expansion means and supplies a second refrigerant gas to the second compression chamber. The condenser is configured to exchange heat between the first and second refrigerant gases compressed in the first and second compression chambers in the corresponding first and second condensers, then mix them and exchange heat again in the third condenser to condense the high-pressure refrigerant and supply it to the upstream expansion means.

Description

Technical Field

[0001] The present invention relates to a refrigeration circuit using a zeotropic refrigerant mixture as a refrigerant, and a refrigerator, an air conditioner, or a water heater using this refrigeration circuit.

Background Art

[0002] Conventionally, a refrigeration circuit configured such that a refrigerant compressed by a compressor dissipates heat by heat exchange in a condenser, then expands through an expansion valve, and absorbs heat by heat exchange in an evaporator and returns to the compressor has been widely used. For example, in a refrigerator, a low-temperature refrigerant in an evaporator absorbs heat from a heat source (cooling target) to cool the cooling target, compresses the refrigerant evaporated by heat absorption to a high temperature, then dissipates heat to the outside in a condenser, and expands the refrigerant whose temperature has decreased to an even lower temperature and supplies it to the evaporator.

[0003] On the other hand, for example, a refrigeration circuit used as a heat pump of a water heater is configured such that a compressed high-temperature refrigerant heats the hot water of a heating target by heat exchange in a condenser, and expands the refrigerant whose temperature has decreased by this heat exchange to an even lower temperature. Then, the refrigerant is evaporated by heat absorption from a heat source (external air) in an evaporator, the evaporated refrigerant is compressed to a high temperature, and supplied to the condenser. This refrigeration circuit is also used in an air conditioner that heats indoor air as a heating target.

[0004] In an environment where the temperature is low, a low-temperature and low-pressure refrigerant is supplied from an evaporator to a compressor, and in order to compress this refrigerant so that it reaches a predetermined pressure in the compressor, the compression power increases, and the coefficient of performance (COP), which is an index of the operating efficiency of the heat pump, decreases. Therefore, a Lorentz cycle using a zeotropic refrigerant mixture obtained by mixing a low-boiling refrigerant and a high-boiling refrigerant as a refrigerant has been proposed.

[0005] In a typical refrigeration cycle using a single-component refrigerant, the refrigerant temperature remains constant during the condensation and evaporation processes. However, the Lorentz cycle, as shown in the Th diagram in Figure 4 (where the vertical axis is temperature T and the horizontal axis is specific enthalpy h), exhibits a temperature glide (temperature change dT) where the refrigerant temperature decreases during the condensation process and increases during the evaporation process. The curves represent the saturated liquid and saturated vapor lines of the refrigerant.

[0006] For example, when heating water, by flowing the water opposite the refrigerant and utilizing the temperature glide during the condensation process, the heat exchange efficiency can be increased by ensuring a temperature difference between the refrigerant, whose temperature is decreasing, and the water, whose temperature is increasing as shown by the dashed line. A high-pressure refrigerant, compressed to become superheated steam, loses heat during the condensation process, and its temperature decreases. When it reaches the intersection with the saturated vapor line (dew point), it continues to condense, its temperature decreasing until it reaches the intersection with the saturated liquid line (boiling point), and its temperature decreases further. Then, due to expansion, the pressure and temperature of this refrigerant decrease. This low-temperature, low-pressure refrigerant completely evaporates during the evaporation process, for example by absorbing heat from the air, and is introduced into a compressor where it is compressed.

[0007] Patent Document 1 discloses a refrigeration circuit using a non-azeotropic mixed refrigerant, which is a mixture of the high-boiling-point refrigerant R21 and the low-boiling-point refrigerant R23. The refrigerant compressed by the compressor is partially condensed in the pre-cooler (condenser), and separated in the gas-liquid separator into a refrigerant gas containing a relatively large amount of low-boiling-point components and a refrigerant liquid containing a relatively large amount of high-boiling-point components. After heat exchange in the first and second heat exchangers, the refrigerant gas expands in the first expansion valve and evaporates in the evaporator. The refrigerant liquid expands in the second expansion valve and its temperature decreases. The refrigerant evaporated in the evaporator exchanges heat with the refrigerant gas before expansion in the second heat exchanger, is mixed with the vaporized refrigerant in the second expansion valve, and then exchanges heat with the refrigerant gas that has passed through the gas-liquid separator in the first heat exchanger before being supplied to the compressor.

[0008] Patent Document 2 discloses a refrigeration circuit using a non-azeotropic mixed refrigerant as the refrigerant. The refrigerant compressed by the compressor is partially condensed in the condenser and separated into refrigerant gas and refrigerant liquid in the gas-liquid separator. The separated refrigerant gas undergoes heat exchange in the first heat exchanger, then expands in the second expansion valve and evaporates in the evaporator. The refrigerant liquid undergoes heat exchange in the second heat exchanger, then expands in the first expansion valve, is heated in the first heat exchanger by heat exchange with the refrigerant gas before expansion, and is further heated in the second heat exchanger by heat exchange with the refrigerant liquid before expansion. The refrigerant gas that has passed through the evaporator and the refrigerant that has evaporated due to the expansion and heating of the refrigerant liquid are then mixed and supplied to the compressor.

[0009] Patent Document 3 discloses a refrigeration circuit using a non-azeotropic mixed refrigerant as the refrigerant. The refrigerant, which is compressed and mixed in the first and second compressors respectively, is partially condensed in the condenser and separated into refrigerant gas and refrigerant liquid in the gas-liquid separator. The separated refrigerant gas is cooled by heat exchange in the heat exchanger, expands by the second expansion means, evaporates in the evaporator, and is supplied to the first compressor. The separated refrigerant liquid evaporates by expansion in the first expansion valve and heat exchange with the refrigerant gas in the heat exchanger, and is supplied to the second compressor. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 3174081 [Patent Document 2] Japanese Patent Application Publication No. 4-324072 [Patent Document 3] Japanese Utility Model Publication No. 5-42964 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] When a refrigerant with a high proportion of low-boiling-point components and a refrigerant with a high proportion of high-boiling-point components are compressed so that the discharge pressure of the compressor is the same, the temperature of the compressed refrigerant with a high proportion of low-boiling-point components will be lower than the temperature of the compressed refrigerant with a high proportion of high-boiling-point components. Therefore, when a refrigerant with a high proportion of low-boiling-point components and a refrigerant with a high proportion of high-boiling-point components are mixed and compressed to a predetermined temperature, the discharge pressure of the compressor will be higher than when only the refrigerant with a high proportion of high-boiling-point components is compressed to the predetermined temperature. In Patent Documents 1 and 2, the refrigerant gas with a high proportion of low-boiling-point components and the refrigerant liquid with a high proportion of high-boiling-point components are each expanded after being separated into gas and liquid form, then mixed and compressed by a compressor. As a result, the discharge pressure of the compressor required to reach the predetermined temperature is higher, and the compression power of the compressor increases.

[0012] In Patent Document 3, a refrigerant gas with a high proportion of low-boiling-point components separated into gas and liquid is expanded and compressed in a first compressor, while a refrigerant liquid with a high proportion of high-boiling-point components separated into gas and liquid is expanded and compressed in a second compressor. These are then mixed and supplied to a condenser. If the pressures at the outlets of the first and second compressors are equal, the temperatures of the discharged refrigerants will differ, and the temperature of the refrigerant supplied to the condenser after mixing will be lower than the temperature at the outlet of the second compressor of the refrigerant with a high proportion of high-boiling-point components. To bring the refrigerant to a predetermined temperature while taking this temperature drop into account, the discharge pressures of the first and second compressors must be increased, which increases the compression power of the compressors.

[0013] Therefore, the present invention aims to provide a refrigeration circuit that uses a non-azeotropic mixed refrigerant that can reduce the compression power of the compressor. [Means for solving the problem]

[0014] The refrigeration circuit of claim 1 is a refrigeration circuit in which a compressor, a condenser, an expansion means, and an evaporator are connected by piping, and a refrigerant sealed in the piping is circulated, wherein the refrigerant is a non-azeotropic mixed refrigerant, the compressor has a first compression chamber and a second compression chamber arranged in parallel for compressing the refrigerant, the expansion means has an upstream expansion means, a downstream expansion means, and a gas-liquid separator, the upstream expansion means and the downstream expansion means are connected in series via the gas-liquid separator, the gas-liquid separator separates the refrigerant at intermediate pressure expanded by the upstream expansion means into a first refrigerant gas and a refrigerant liquid, and supplies the first refrigerant gas to the first compression chamber and the The refrigerant liquid is supplied to the downstream expansion means, the evaporator evaporates the refrigerant liquid whose pressure has been reduced by the downstream expansion means, and supplies this evaporated low-pressure second refrigerant gas to the second compression chamber, and the condenser has a first condenser to which the first refrigerant gas compressed in the first compression chamber is supplied, a second condenser to which the second refrigerant gas compressed in the second compression chamber is supplied, and a third condenser to which the first refrigerant gas that has passed through the first condenser and the second refrigerant gas that has passed through the second condenser are mixed and supplied, and is characterized in that it is configured to condense the high-pressure refrigerant supplied from the compression section and supply it to the upstream expansion means.

[0015] According to the above configuration, in the condenser, the high-pressure first refrigerant gas is heat-exchanged in the first condenser, and the high-pressure second refrigerant gas is heat-exchanged in the second condenser, thereby lowering the temperature to, for example, near the dew point of the first refrigerant gas. Then, the high-pressure refrigerant, which is a mixture of these first and second refrigerant gases, is further heat-exchanged in the third condenser to lower its temperature even further. Since the compressed first refrigerant gas and the compressed second refrigerant gas are heat-exchanged separately, heat exchange with a predetermined high-temperature second refrigerant gas can be performed without increasing the compression power. At this time, the efficiency of heat exchange can be improved by configuring the first to third condensers, which are supplied with refrigerants of the same pressure but different temperatures, in a counterflow configuration so that the temperature glide of the refrigerant in each condenser matches the temperature change of the hot water. The high-pressure refrigerant condensed in the condensers is supplied to the upstream expansion means, and the intermediate-pressure refrigerant, whose pressure has decreased due to expansion, is supplied to the gas-liquid separator. The gas-liquid separation device separates the refrigerant at this intermediate pressure into gas and liquid, supplying the first refrigerant gas at intermediate pressure to the first compression chamber and the refrigerant liquid at intermediate pressure to the downstream expansion means. The downstream expansion means expands this refrigerant liquid at intermediate pressure and supplies it to the evaporator. The evaporator evaporates the expanded refrigerant to produce a low-pressure second refrigerant gas, and supplies this low-pressure second refrigerant gas to the second compression chamber. The first refrigerant gas has a higher proportion of low-boiling-point components that are relatively difficult to condense in the non-azeotropic refrigerant mixture, while the second refrigerant gas, obtained by evaporating the refrigerant liquid, has a higher proportion of high-boiling-point components that are relatively easy to condense in the non-azeotropic refrigerant mixture. Since the first and second refrigerant gases are compressed separately, the compression power of the compressor can be reduced while the second refrigerant gas, which has a higher proportion of high-boiling-point components, can be brought to a predetermined high temperature. In addition, since the first refrigerant gas, which has a higher proportion of low-boiling-point components, is compressed from an intermediate pressure, the compression power can be reduced.

[0016] The refrigeration circuit of claim 2 is characterized in that, in the invention of claim 1, it has an internal heat exchanger between the condenser and the upstream expansion means for exchanging heat between the high-pressure refrigerant supplied from the condenser and the low-pressure second refrigerant gas supplied to the second compression chamber. With the above configuration, the internal heat exchanger can transfer heat from the high-pressure refrigerant to the low-pressure second refrigerant gas, thus lowering the temperature of the refrigerant liquid and raising the temperature of the second refrigerant gas supplied to the second compression chamber. As the temperature of the refrigerant liquid decreases, it expands and its temperature drops when supplied to the evaporator, increasing the temperature difference with the air in the evaporator and improving the heat exchange efficiency in the evaporator. Furthermore, the enthalpy of the evaporated second refrigerant gas can be increased even further, allowing the suction pressure of the compressor to be increased compared to when there is no internal heat exchanger, and thus reducing the compression power.

[0017] The refrigeration circuit of claim 3 is characterized in that, in the invention of claim 1, the first compression chamber and the second compression chamber are two compression chambers in a twin rotary compressor. According to the above configuration, by using the two compression chambers of the twin rotary compressor as the first compression chamber 11 and the second compression chamber 12, the refrigerant can be compressed in the first compression chamber 11 and the second compression chamber 12 respectively by a single compression power source, and the compression unit 10 can be made smaller and quieter.

[0018] The refrigeration circuit of claim 4 is characterized in that, in the invention of claim 1, the evaporator is configured with a blower for circulating air and three or more heat exchangers arranged in line with the direction of air flow. According to the above configuration, three or more heat exchangers arranged along the direction of airflow can circulate the refrigerant in a pseudo-counterflow manner relative to the air. This allows for a reduction in airflow rate for the same amount of heat exchange. Consequently, the blower and each heat exchanger can be miniaturized.

[0019] The refrigerator, air conditioner, or water heater of the invention of claim 5 is characterized by comprising a refrigeration circuit as described in any one of claims 1 to 4. According to the above configuration, the refrigeration circuit, which can reduce the compression power of the compressor, can improve the efficiency of refrigerators, air conditioners, or water heaters. [Effects of the Invention]

[0020] According to the refrigeration circuit of the present invention, while using azeotropic refrigerant mixtures, it is possible to reduce the compression power of the compressor.

Brief Description of the Drawings

[0021] [Figure 1] It is a configuration diagram of a refrigeration circuit according to an embodiment of the present invention. [Figure 2] It is a T-h diagram of a refrigeration cycle according to an embodiment of the present invention. [Figure 3] It is a chart showing the relationship between the temperature glide, COP, and pressure with respect to the refrigerant composition in the Lorentz cycle. [Figure 4] It is a T-h diagram showing an example of the Lorentz cycle.

Modes for Carrying Out the Invention

[0022] Hereinafter, embodiments for carrying out the present invention will be described based on examples.

Examples

[0023] As shown in FIG. 1, the refrigeration circuit 1 is configured to connect a compression unit 10, a condenser 20, an expansion means 30, and an evaporator 40 in a closed loop by piping 2 and circulate a refrigerant enclosed in the piping 2. As the refrigerant, an azeotropic refrigerant mixture in which refrigerants having different boiling points (low-boiling refrigerant and high-boiling refrigerant) are mixed at a predetermined ratio is used. Hereinafter, this azeotropic refrigerant mixture may be referred to as a refrigerant, and the low-boiling refrigerant and high-boiling refrigerant contained in the refrigerant may be referred to as a low-boiling component and a high-boiling component, respectively. The low-boiling refrigerant is, for example, carbon dioxide, and the high-boiling refrigerant is, for example, propane, propylene, butane, etc., but is not limited thereto. In addition, the arrow along the piping 2 indicates the flow direction of the refrigerant.

[0024] The compression unit 10 has a first compression chamber 11 and a second compression chamber 12, which are arranged in parallel. The first compression chamber 11 functions as a low-boiling-point compression chamber for compressing a first refrigerant gas in which the proportion of low-boiling-point components is higher than a predetermined proportion, and supplies the compressed, high-pressure first refrigerant gas (superheated steam), whose temperature has risen, to the condenser 20. The second compression chamber 12 functions as a high-boiling-point compression chamber for compressing a second refrigerant gas in which the proportion of high-boiling-point components is higher than a predetermined proportion, and supplies the compressed, high-pressure second refrigerant gas (superheated steam), whose temperature has risen, to the condenser 20. The pressures of the first and second refrigerant gases supplied to the condenser 20 are the same.

[0025] The condenser 20 includes a first condenser 21 and a second condenser 22 arranged in parallel, and a third condenser 23 arranged in series with respect to the first condenser 21 and the second condenser 22. The first condenser 21 is supplied with high-pressure first refrigerant gas compressed in the first compression chamber 11. The second condenser 22 is supplied with high-pressure second refrigerant gas compressed in the second compression chamber 12. The third condenser 23 is supplied with a mixture of the first refrigerant gas that has passed through the first condenser 21 and the second refrigerant gas that has passed through the second condenser 22.

[0026] In this condenser 20, as indicated by arrow F, the fluid supplied from the outside is heated by heat exchange with the high-pressure refrigerant, which has been compressed and heated in the compression section 10. The fluid flows countercurrently opposite to the refrigerant flowing through the condenser 20, and after heat exchange in the third condenser 23, it exchanges heat again in the first and second condensers 21 and 22. The fluid can be, for example, hot water for hot water supply, or air or hot water for heating.

[0027] The high-pressure refrigerant, whose temperature has decreased due to heat exchange with the fluid, condenses and liquefies, and is supplied to the expansion means 30. At this time, the low-boiling point components of the refrigerant are less likely to condense (more likely to vaporize) than the high-boiling point components, so the condensation of the high-boiling point components progresses relatively, and the proportion of the low-boiling point components in the gas phase increases. To utilize the temperature glide, which is the decrease in the temperature of the mixed refrigerant due to the change in the composition of the gas and liquid phases during this phase change, the fluid flow path in the condenser 23 is configured to start heat exchange at the refrigerant outlet side of the third condenser 23, start heat exchange in the first and second condensers 21 and 22 after the heat exchange in the third condenser 23 is completed, and end heat exchange at the refrigerant inlet side of the first and second condensers 21 and 22. An appropriate temperature difference between the fluid and the refrigerant can be ensured from the fluid inlet to the outlet of the condenser 20, and the fluid can be heated.

[0028] The expansion means 30 includes an upstream expansion means 31, a downstream expansion means 32, and a gas-liquid separator 33. The upstream expansion means 31 and the downstream expansion means 32 are connected in series via the gas-liquid separator 33 located between them, and are configured to expand the high-pressure refrigerant that has passed through the condenser 20 in two stages, thereby reducing the temperature and pressure of the refrigerant in two stages. The upstream expansion means 31 and the downstream expansion means 32 are each expansion valves or throttles.

[0029] The upstream expansion means 31 expands the high-pressure refrigerant supplied from the condenser 20, and supplies the refrigerant, whose temperature and pressure have decreased to an intermediate pressure, to the gas-liquid separator 33. At this time, the low-boiling point components, which vaporize more easily than the high-boiling point components, vaporize due to the expansion, and the gaseous portion becomes a first refrigerant gas rich in low-boiling point components, with an increased proportion of low-boiling point components. The liquid portion then becomes a refrigerant liquid rich in high-boiling point components, with an increased proportion of high-boiling point components.

[0030] The gas-liquid separator 33 separates the first refrigerant gas, which is the gaseous portion of the refrigerant at an intermediate pressure, and supplies it to the first compression chamber of the compression unit 10, while also supplying the refrigerant liquid, which is the liquid portion, to the downstream expansion means 32. The gas-liquid separator 33 can be of any type, such as one that utilizes centrifugal force or one that utilizes the surface tension of the refrigerant, and the separation method is not particularly limited.

[0031] The downstream expansion means 32 expands the refrigerant liquid that has passed through the gas-liquid separator 33, and supplies the low-pressure refrigerant, whose temperature and pressure have decreased and which has partially vaporized, to the evaporator 40. The evaporator 40 heats the low-pressure refrigerant, for example by heat exchange with air, and supplies the low-pressure second refrigerant gas, which has been evaporated, to the second compression chamber 12 of the compression unit 10. At this time, in the evaporator 40, as the low-pressure refrigerant evaporates, the proportion of high-boiling-point components in the gaseous portion increases, and the temperature of the low-pressure refrigerant rises along with this compositional change during the phase change.

[0032] The evaporator 40 is composed of a blower 41 that circulates air, which is the heat source, and a plurality (for example, three) of heat exchangers 42a to 42c arranged from upstream to downstream along the direction of air flow by the blower 41, indicated by arrow A. The low-pressure refrigerant flows in a pseudo-counterflow manner in the order of the downstream heat exchanger 42c, the middle heat exchanger 42b, and the upstream heat exchanger 42a, opposite to the direction of air flow. Due to the temperature glide of the low-pressure refrigerant in the evaporator 40, the temperature of the low-pressure refrigerant flowing in the order of heat exchanger 42c, heat exchanger 42b, and heat exchanger 42a rises.

[0033] The temperature of the air exchanging heat with the refrigerant decreases due to the heat exchange, reducing the temperature difference between the downstream air and the refrigerant, and thus decreasing the heat exchange efficiency. Therefore, the cross-sectional area of ​​the airflow path and the airflow rate are usually increased to suppress the decrease in heat exchange efficiency, but this requires increasing the size of the heat exchanger and blower.

[0034] The temperature of the air flowing through the evaporator 40 also decreases downstream due to heat exchange. However, by utilizing the temperature glide of the low-pressure refrigerant flowing through multiple heat exchangers 42a to 42c arranged along the direction of air flow, an appropriate temperature difference between the low-pressure refrigerant and the air can be maintained from the inlet to the outlet of the evaporator 40. Therefore, the amount of heat exchanged from a given amount of air can be increased. In other words, for the same amount of heat exchanged, the air flow rate and velocity can be reduced. Consequently, the blower 41 and heat exchangers 42a to 42c can be miniaturized, and the evaporator 40 can be miniaturized as well. Note that the number of heat exchangers in the evaporator 40 is not limited to three; there may be four or more.

[0035] Here, an internal heat exchanger 50 is provided between the condenser 20 and the expansion means 30 (between the side including the compression section 10 and the condenser 20 and the side including the expansion means 30 and the evaporator 40). The internal heat exchanger 50 transfers the heat from the high-pressure refrigerant supplied from the condenser 20 to the expansion means 30 to the low-pressure second refrigerant gas supplied from the evaporator 40 to the second compression chamber 12, thereby heating the low-pressure second refrigerant gas.

[0036] The internal heat exchanger 50 lowers the temperature of the high-pressure refrigerant, which in turn lowers the temperature of the low-pressure refrigerant supplied to the evaporator 40, thereby promoting heat exchange in the evaporator 40. Furthermore, the internal heat exchanger 50 eliminates the need to heat the low-pressure second refrigerant gas supplied to the second compression chamber 12 with a heat source. This allows the suction pressure of the compressor 10 to be increased compared to when the internal heat exchanger 50 is not present, enabling the acquisition of a predetermined high temperature while reducing compression power. Even if some refrigerant liquid remains in the evaporator 40 because it has not completely evaporated, the internal heat exchanger 50 can promote evaporation.

[0037] The compression unit 10 compresses the first refrigerant gas at an intermediate pressure in the first compression chamber 11, and supplies the high-pressure first refrigerant gas, whose temperature has risen, to the first condenser 21. At the same time, it compresses the second refrigerant gas at a low pressure in the second compression chamber 12, and supplies the high-pressure second refrigerant gas, which has reached a predetermined high temperature, to the second condenser 22. A twin rotary compressor having one drive source and two compression chambers is suitable for a compression unit 10 having a first compression chamber 11 and a second compression chamber 12, and the compression unit 10 can be made, for example, smaller and quieter.

[0038] Next, we will describe the refrigeration cycle in refrigeration circuit 1. The refrigeration circuit 1 uses a non-azeotropic mixed refrigerant, for example, a mixture of propane and carbon dioxide in a predetermined ratio, and operates in the refrigeration cycle (Lorentz cycle) shown in the Th diagram of Figure 2. The curves are the saturated liquid line and saturated vapor line of the non-azeotropic mixed refrigerant. In the compression section 10, a first refrigerant gas rich in low-boiling-point components and at an intermediate pressure is compressed in the first compression chamber 11, and a second refrigerant gas rich in high-boiling-point components and at a low pressure is compressed in the second compression chamber 12. Then, a first refrigerant gas at a high temperature and high pressure, for example around 80°C, and a second refrigerant gas at a predetermined high temperature and high pressure, for example around 90°C, are discharged, respectively.

[0039] In the condenser 20, the high-temperature, high-pressure first and second refrigerant gases heat the fluid supplied from the outside through heat exchange. In the first condenser 21, the temperature of the high-temperature, high-pressure first refrigerant gas decreases due to heat exchange with the fluid, and in the second condenser 22, the temperature of the high-temperature, high-pressure second refrigerant gas decreases to the dew point through heat exchange with the fluid, before gradually condensing and liquefying. The high-pressure first refrigerant gas that has passed through the first condenser 21 and the high-pressure second refrigerant gas that has passed through the second condenser 22 are then mixed and supplied to the third condenser 23. In the third condenser 23, the high-pressure refrigerant condenses through heat exchange with the fluid, causing its temperature to decrease, and it is then supplied to the internal heat exchanger 50.

[0040] In the internal heat exchanger 50, the high-pressure refrigerant is cooled to approximately 5°C through heat exchange with the low-pressure second refrigerant gas that has passed through the evaporator 40, and is supplied to the upstream expansion means 31. The intermediate-pressure refrigerant, which has expanded in the upstream expansion means 31 and whose pressure has decreased, is cooled to approximately 0°C and is supplied to the gas-liquid separator 33. In the gas-liquid separator 33, this intermediate-pressure refrigerant is separated into an intermediate-pressure first refrigerant gas rich in low-boiling-point components and an intermediate-pressure refrigerant liquid rich in high-boiling-point components.

[0041] The first refrigerant gas, rich in low-boiling-point components and at an intermediate pressure, is supplied to the first compression chamber 11 and compressed again. Meanwhile, the refrigerant liquid, rich in high-boiling-point components and at an intermediate pressure, is supplied to the downstream expansion means 32, where it expands, its pressure decreases, and its temperature drops to, for example, about -15°C, before being supplied to the evaporator 40.

[0042] In the evaporator 40, the low-pressure refrigerant vaporizes through heat exchange with the air, its temperature rises, and it completely evaporates. Since the evaporator 40 utilizes this refrigerant temperature glide, even in environments where the ambient temperature is relatively low, the low-pressure refrigerant can absorb sufficient heat from the air through the multiple heat exchangers 42a to 42c. The second refrigerant gas supplied from the evaporator 40 to the internal heat exchanger 50 is heated in the internal heat exchanger 50 through heat exchange with the high-pressure refrigerant and supplied to the second compression chamber 12, where it is compressed again.

[0043] To effectively utilize thermal glide, it is preferable that the temperature change in each of the condensation and evaporation processes be 10°C or more. For example, as shown in Figure 3, in a non-azeotropic mixed refrigerant obtained by mixing propane with carbon dioxide (CO2), if the proportion (mole fraction) of carbon dioxide exceeds 0.1, the thermal glide (temperature change) dT in condensation and evaporation will each exceed 10°C. However, as the proportion of carbon dioxide increases, the discharge pressure of the compression section 10 tends to increase. Therefore, it is preferable that the proportion (mole fraction) of carbon dioxide in the non-azeotropic mixed refrigerant used in this refrigeration circuit 1 be in the range of, for example, 0.1 to 0.2.

[0044] The operation and effects of the above-described refrigeration circuit 1 will be explained. The compression unit 10 compresses the first refrigerant gas, which is rich in low-boiling-point components, and the second refrigerant gas, which is rich in high-boiling-point components, respectively, which are separated from the non-azeotropic mixed refrigerant by the gas-liquid separation device 33. Compared to the case where the refrigerants are mixed and compressed, a predetermined high temperature can be obtained at a relatively low pressure, and the compression power can be reduced. Furthermore, since the first refrigerant gas, which is rich in low-boiling-point components, is compressed from an intermediate pressure, the compression power can be reduced.

[0045] The internal heat exchanger 50 increases the temperature of the second refrigerant gas evaporated in the evaporator 40, thereby increasing its enthalpy. This allows the suction pressure of the compressor 10 to be increased compared to when the internal heat exchanger 50 is not present, and reduces the compression power required to reach a predetermined temperature. Furthermore, the internal heat exchanger 50 lowers the temperature of the low-pressure refrigerant supplied to the evaporator 40, increasing the temperature difference between the low-pressure refrigerant and the air in the evaporator 40, thereby improving the heat exchange efficiency in the evaporator 40.

[0046] In the condenser 20, the first condenser 21 and the second condenser 22 separately exchange heat between the compressed first refrigerant gas and the compressed second refrigerant gas, allowing heat exchange with the second refrigerant gas at a predetermined high temperature without increasing the compression power. The first and second refrigerant gases that have exchanged heat in the first and second condensers 21 and 22 are mixed and supplied to the third condenser, so the temperature glide of this refrigerant can be used to heat the fluid to be heated in a countercurrent.

[0047] By using the two compression chambers of the twin rotary compressor as the first and second compression chambers 11 and 12, compression can be performed in both the first and second compression chambers 11 and 12 using a single power source, allowing for a smaller and quieter compression unit 10. Furthermore, in the evaporator 40, the heat exchange efficiency is increased by the heat exchangers 42a to 42c, increasing the amount of heat exchanged from a given amount of air. Therefore, for the same amount of heat exchanged, the amount of air supplied to the evaporator 40 can be reduced. Consequently, the blower 41 and each of the heat exchangers 42a to 42c can be miniaturized, and the evaporator 40 can be miniaturized as well.

[0048] The description explains how to heat water using the refrigeration circuit 1, but air can also be heated, and the refrigeration circuit 1 can also be used to cool the object to be cooled. When the refrigeration circuit 1 is applied to a refrigerator, air conditioner, or water heater, efficiency can be increased by reducing the compression power of the refrigeration circuit 1 and improving the heat exchange efficiency. In addition, the refrigerator, air conditioner, or water heater can be made smaller by miniaturizing the compression unit 10 and the evaporator 40.

[0049] Furthermore, those skilled in the art can implement the present invention in various forms with modifications to the above embodiments without departing from the spirit of the invention, and the present invention encompasses such modifications. [Explanation of symbols]

[0050] 1: Refrigeration circuit 2: Piping 10: Compression section 11: First Compression Chamber 12: Second Compression Chamber 20: Condenser 21: First condenser 22: Second condenser 23: Third condenser 30: Expansion method 31: Upstream expansion means 32: Downstream expansion means 33: Gas-liquid separation device 40: Evaporator 41: Blower 42: Countercurrent heat exchanger 42a~42c: Heat exchanger 50: Internal heat exchanger

Claims

1. A refrigeration circuit in which a compressor, a condenser, an expansion means, and an evaporator are connected by piping, and a refrigerant sealed in this piping is circulated, wherein the refrigerant is a non-azeotropic mixed refrigerant, The compression unit has a first compression chamber and a second compression chamber arranged in parallel for compressing the refrigerant. The expansion means comprises an upstream expansion means, a downstream expansion means, and a gas-liquid separator, and the upstream expansion means and the downstream expansion means are connected in series via the gas-liquid separator. The gas-liquid separation device separates the refrigerant at intermediate pressure, expanded by the upstream expansion means, into a first refrigerant gas and a refrigerant liquid, supplies the first refrigerant gas to the first compression chamber, and supplies the refrigerant liquid to the downstream expansion means. The evaporator evaporates the refrigerant liquid whose pressure has been reduced by the downstream expansion means, and supplies this evaporated low-pressure second refrigerant gas to the second compression chamber. The refrigeration circuit is characterized in that the condenser comprises a first condenser to which the first refrigerant gas compressed in the first compression chamber is supplied, a second condenser to which the second refrigerant gas compressed in the second compression chamber is supplied, and a third condenser to which the first refrigerant gas that has passed through the first condenser and the second refrigerant gas that has passed through the second condenser are mixed and supplied, and is configured to condense the high-pressure refrigerant supplied from the compression unit and supply it to the upstream expansion means.

2. The refrigeration circuit according to claim 1, further comprising an internal heat exchanger between the condenser and the upstream expansion means, which exchanges heat between the high-pressure refrigerant supplied from the condenser and the low-pressure second refrigerant gas supplied to the second compression chamber.

3. The refrigeration circuit according to claim 1, characterized in that the first compression chamber and the second compression chamber are two compression chambers in a twin rotary compressor.

4. The refrigeration circuit according to claim 1, characterized in that the evaporator is configured with a blower for circulating air and three or more heat exchangers arranged in line with the direction of air flow.

5. A refrigerator, air conditioner, or water heater characterized by being equipped with a refrigeration circuit as described in any one of claims 1 to 4.

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