EP0631095B1

EP0631095B1 - Method of sealing in a non-azeotrope refrigerant and controlling the composition of the refrigerant in a refrigeration cycle

Info

Publication number: EP0631095B1
Application number: EP19940109583
Authority: EP
Inventors: Kensaku Oguni; Kazumoto Urata; Masatoshi Muramatsu; Takeshi Endo; Hiroaki Matsushima
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1993-06-24
Filing date: 1994-06-21
Publication date: 2000-01-12
Anticipated expiration: 2014-06-21
Also published as: EP0838643B1; EP0838643A3; DE69422551D1; EP0631095A2; DE69422551T2; DE69432489T2; EP0838643A2; JPH0712411A; EP0631095A3; DE69432489D1

Description

The invention relates to a method of controlling the composition of a refrigerant in a refrigeration cycle.
First, a case in which a non-azeotrope refrigerant is used as a working medium will be explained. The non-azeotrope refrigerant is a refrigerant in which two or more types of refrigerants having different boiling points are mixed, and has characteristics shown in Fig. 3. Fig. 3 is a vapor-liquid equilibrium diagram illustrating characteristics of a non-azeotrope refrigerant in which two types of refrigerants are mixed. The horizontal axis indicates the composition ratio X of a refrigerant having a low boiling point, and the vertical axis indicates temperature. With pressure as a parameter, a saturation vapor line and a saturation liquid line exist in a high temperature region indicated by pressure P_H when, for example, pressure is high and when,conversely, pressure is low, these lines exist in a low temperature region indicated by pressure P_L. The composition ratio X = 0 indicates that the refrigerant is formed of only a high-boiling-point refrigerant, and the composition ratio X = 1.0 indicates that the refrigerant is formed of only a low-boiling-point refrigerant. In a mixture refrigerant, as shown in Fig. 3, a saturation liquid line and a saturation vapor line are determined by the composition thereof. The area below the saturation liquid line indicates the supercooled state, and the area above the saturation vapor line indicates the superheated state. The portion surrounded by the saturation liquid line and the saturation vapor line is a two-phase state of liquid and vapor. In Fig. 3, X₀ denotes the composition ratio of a refrigerant sealed in a refrigeration cycle. Points P1 to P4 indicate the typical points of the refrigeration cycle, and point P1 indicates a compressor outlet portion; point P2 indicates a condenser outlet portion; point P3 indicates an evaporator inlet portion; and point P4 indicates a compressor inlet portion.
An explanation will be given below of problems relating to leakage out of the refrigeration cycle, to variations in the composition of a circulating refrigerant within the refrigeration cycle in a non-steady state such as at the start-up time of the refrigeration cycle, and to refrigeration cycle operation control.
The leakage of a refrigerant out of the refrigeration cycle is not none even in a hermetically sealed type air-conditioner or refrigerator. In Fig. 3, point A indicates the two-phase portion in the refrigeration cycle, in which the liquid of composition X_a1 and the vapor of composition X_a2 exist. If the mixture refrigerant should leak out of a heat-transfer tube of a heat exchanger or from a connection tube of a component, it would be a refrigerant of composition ratio X_a1 in the case of liquid leakage, and a refrigerant of composition ratio X_a2 in the case of vapor leakage. Therefore, the composition ratio of the refrigerant remaining within the refrigeration cycle differs depending upon whether liquid or vapor leaks.
Fig. 4 is an illustration of a problem caused by the leakage of a refrigerant to the outside. If liquid leaks, the remaining mixture refrigerant enters the state of X₁ in which the ratio of a low boiling-point refrigerant is large; if vapor leaks, the remaining mixture refrigerant enters the state of X₂ in which the ratio of a high boiling-point refrigerant is large. In Fig. 2, X₀ indicates the composition ratio of a refrigerant which is sealed in initially. If a state in which the composition is X₀ is compared with a state in which the composition is X₁ at the same pressure, the temperature when the composition is X₁ is lower. If, however, a state in which the composition is X₀ is compared with a state in which the composition is X₂ at the same pressure, the temperature when the composition is X₂ is higher.
Fig. 5 shows general characteristics of a refrigeration cycle with respect to the composition ratio of the low boiling-point refrigerant. When the composition ratio X becomes larger, and therefore heating and cooling performance improves.
If the refrigerant leaks out of the refrigeration cycle in which a non-azeotrope refrigerant is used as a working medium, as described above, the composition ratio of the refrigerant remaining within the refrigeration cycle changes from the initial composition ratio, i.e., from the designed composition ratio for the apparatus depending upon leaked portions. Even if there is no leakage to the outside, there is a possibility that the composition ratio of the refrigerant circulating within the refrigeration cycle may vary in the non-steady state of the refrigeration cycle.
Changes in the composition ratio of the refrigerant within the refrigeration cycle cause problems; for example, heating and cooling capacity is varied, or pressure or temperature becomes abnormal. Therefore, the refrigeration cycle must be controlled properly.
Since a chlorofluorocarbon refrigerant containing chlorine is considered to damage an ozone layer, a non-azeotropic mixture of a chlorofluorocalcium refrigerant containing no chlorine has been proposed as an alternative refrigerant. A consideration must be given to the mixture refrigerant in order to safeguard the earth environment.
The control of a refrigeration cycle in which a non-azeotropic mixture is used as a working medium is disclosed in, for example, Japanese Patent Unexamined Publication Nos. 59-129366, 61-213554, and 64-58964.
Japanese Patent Unexamined Publication No. 59-129366 discloses that an electrostatic capacitance sensor is used as a means for detecting the composition of a refrigerant circulating within the refrigeration cycle. Further, it is disclosed that the refrigeration cycle comprises a first liquid receiver and a second liquid receiver, an electric heater being disposed in the second liquid receiver. When the outdoor air temperature is low during a heating operation, the electric heater of the second liquid receiver is operated and controlled so that a set refrigerant concentration is reached.
Disclosed in Japanese Patent Unexamined Publication No. 61-213554 is an apparatus comprising a separator for separating a low-boiling-point refrigerant, a liquid receiver for storing a low-boiling-point refrigerant, and a control valve for returning the refrigerant from the liquid receiver, which apparatus controls the composition of the refrigerant on the basis of the temperature of an element to be cooled.
Disclosed in Japanese Patent Unexamined Publication No. 64-58964 is a mixture refrigerant composition variable refrigeration cycle in which the upper portion of the liquid receiver is connected to a refrigerant tank and the lower portion of the liquid receiver is connected to the refrigerant tank, which refrigeration cycle comprises a refrigerant tank capable of exchanging heat with a gas pipe through which a heat-source-side heat exchanger is connected to a use-side heat exchanger, a liquid receiver and the like.
As described above, in the refrigeration cycle in which a non-azeotrope refrigerant is sealed in, the composition ratio of the refrigerant within the refrigeration cycle may vary when the refrigerant leaks out of the refrigeration cycle or during the non-steady operation of the refrigeration cycle. The capacity of the refrigeration cycle can be varied by making the composition variable. Therefore, to obtain a high-capacity refrigeration cycle, it is important to control the refrigerant composition ratio within the refrigeration cycle so as to realize a stable operation. There has been a demand for a method of varying this composition ratio inexpensively. Further, it is necessary to use a refrigerant which does not contain chlorine and does not damage the ozone layer, in which a consideration is given to safeguard the earth environment.
US-A-5 186 012 discloses a heat pump system using a non-azeotropic refrigerant mixture comprising a main refrigeration circuit, an engine coolant circuit, and a refrigerant rectifier circuit interfacing with main refrigeration circuit, and the engine coolant circuit. The refrigerant rectifier circuit comprises in order of decreasing relative elevation a condenser, a storage vessel in communication with a condenser, a rectifier in communication with a storage tank and a condenser, a receiver vessel in communication with a rectifier, and a boiler in communication with the rectifier and the receiver vessel. The refrigerant rectifier circuit is used to adjust the relative concentrations of lower boiling point refrigerant, and higher boiling point refrigerant in the non-azeotropic refrigerant mixture thereby changing the cooling or heating capacity of the heat pump system.
For various problems of such refrigeration cycles using a non-azeotrope refrigerant, only the concentration of one of the non-azeotrope refrigerants is adjusted actively in the above-described prior art. Therefore, the prior art has the problem that the width of the adjustment of the concentration is narrow.
It is an object of the invention to provide a method of controlling the composition of a refrigerant in a refrigeration cycle, which method ensures a wide range of adjustment as well as high accuracy.
This object is achieved by a method according to claim 1.
According to the present invention, it is possible to vary the composition ratio of the refrigerant within the refrigeration cycle in which a non-azeotrope refrigerant is sealed in by using an inexpensive apparatus and to stabilize the composition ratio of the non-azeotrope refrigerant.
An advantageous and preferred development of the method according to the invention is subject matter of claim 2.
Preferred embodiments of the invention will now be described with respect to the accompanying drawings in which
Fig. 1 is a schematic view of a refrigeration cycle having a control apparatus for controlling the composition of a non-azeotrope refrigerant;
Fig. 2 is a longitudinal sectional view of a refrigerant circuit for controlling the composition of the refrigerant;
Fig. 3 is a diagram illustrating the characteristics of a non-azeotrope refrigerant;
Fig. 4 is a diagram illustrating the relationship between the composition of the non-azeotrope refrigerant and temperature;
Fig. 5 is a diagram illustrating the characteristics of a refrigeration cycle in which a non-azeotrope refrigerant is used;
Fig. 6 is a diagram illustrating the characteristics of a non-azeotrope refrigerant;
Fig. 7 shows an example of the composition of three-type mixture refrigerant;
Fig. 8 is a sectional view of an electrostatic capacitance type composition ratio detecting sensor;
Fig. 9 is a diagram illustrating the relationship between the composition of the non-azeotrope refrigerant and the electrostatic capacitance value;
Fig. 10 is a flowchart illustrating the control of the composition of the non-azeotrope refrigerant;
Fig. 11 is a schematic view of a refrigeration cycle having a sensor for detecting the composition ratio of the non-azeotrope refrigerant and a sensor for detecting the amount of the refrigerant;
Fig. 12 is a schematic view of a refrigeration cycle having a sensor for detecting the composition ratio of the non-azeotrope refrigerant and a sensor for detecting the amount of the refrigerant;
Fig. 13 is a schematic view of a refrigeration cycle having a composition ratio detecting sensor and a refrigerant amount sensor;
Fig. 14 is a diagram illustrating the composition within a refrigerant bomb; and
Fig. 15 is a schematic view of a refrigeration cycle having a composition ratio detecting apparatus.
Fig. 1 illustrates a refrigeration cycle in which a plurality of indoor machines are connected to one outdoor machine in accordance with a first embodiment of the present invention. Referring to Fig. 1, reference numeral 1 denotes a compressor; reference numeral 2 denotes an outdoor heat exchanger; reference numeral 3 denotes an outdoor air blower; reference numeral 4 denotes a four-way valve; reference numeral 5 denotes an accumulator; reference numeral 6 denotes a receiver; and reference numeral 7 denotes an outdoor refrigerant control valve which acts as a pressure reducing mechanism during a heating operation. Reference numeral 8 denotes a sensor for detecting the composition of a non-azeotrope refrigerant; reference numeral 10 denotes a refrigerant tank; reference numeral 11 denotes a cooling unit; reference numerals 12, 13 and 14 denote open/close valves; reference numerals 15, 16 and 17 denote pipes; reference numerals 91, 92, 93 and 94 denote check valves which constitute an outdoor machine. Reference numerals 20a and 20b denote indoor heat exchangers; reference numerals 21a and 21b denote indoor refrigerant control valves which act as a pressure reducing mechanism during a cooling operation; reference numerals 22 and 23 denote refrigerant distribution units; and reference numerals 24 and 25 denote pipes for connecting indoor machines to outdoor machines. The illustration of the indoor air blower is omitted.
Next, a detecting apparatus in which an electrostatic capacitance sensor 8 for detecting the composition of a non-azeotrope refrigerant is used, and a control apparatus for controlling the open/ close valves 12, 13 and 14 are disposed on the outdoor side. In Fig. 1, the illustration of the control system of the refrigeration cycle is omitted. A refrigerant which does not contain chlorine and does not damage the ozone layer is used as the refrigerant. In this embodiment, an example in which HFC32 and HFC134a are used as the non-azeotrope refrigerant will be explained.
Next, the flow of the refrigerant will be explained. During a cooling operation, the refrigerant discharged from the compressor flows in the following order: the four-way valve 4 → the outdoor heat exchanger 2 → the check valve 93 → the composition sensor 8 → the outdoor refrigerant control valve 7 → the check valve 92 → the receiver 6. The refrigerant is distributed by a refrigerant distribution unit 23; part of the refrigerant flows in the order: the indoor heat exchanger 20a → the indoor refrigerant control valve 21a, and the other flow in the order: the indoor heat exchanger 20b → the indoor refrigerant control valve 21b. They merge in a distribution unit 22 and flow in the order: the pipe 24 → the four-way valve 4 → the accumulator 5, and return to the compressor. At this time, the indoor heat exchangers 20a and 20b act as evaporators and a cooling operation is performed.
On the other hand, during a heating operation, the refrigerant discharged from the compressor flows in the following order: the four-way valve 4 → the pipe 24 → the distribution unit 22. A part of the refrigerant flows in the order: the indoor refrigerant control valve 21a → the indoor heat exchanger 20a, and the other flow in the order: the indoor refrigerant control valve 21b → the indoor heat exchanger 20b. They merge in a distribution unit 23 and flow in the order: the pipe 25 → the receiver 6 → the check valve 94 → the composition sensor 8 → the outdoor control valve 7 → the check valve 91 → the outdoor heat exchanger 2 → the four-way valve 4 → the accumulator 5, and return to the compressor. At this time, the indoor heat exchangers 20a and 20b act as condensers and a heating operation is performed.
The details of the low-boiling-point refrigerant separation circuit of Fig. 1 are shown in Fig. 2. In Fig. 2, a cooling unit 11 is a double-pipe heat exchanger. When a liquid refrigerant is stored in a refrigerant storage tank 10, the open/ close valves 12 and 13 are opened. In this case, the liquid in the bottom of the receiver 6 flows out through the open/close valve 12, and the liquid is formed into a low-temperature refrigerant by the pressure reducing effect of the open/ close valve 12 and guided into the inner pipe of the cooling unit 11. On the other hand, gas inside the receiver 6 flows out through the open/close valve 13 and is guided into the outer pipe of the cooling unit 11. The low-temperature refrigerant gas of the inner pipe exchanges heat with the gas of the outer pipe, and the low-temperature refrigerant is gasified and guided into the accumulator 5 through the pipe 15. The condensed liquefied refrigerant of the outer pipe is guided into the refrigerant storage tank 10. When a predetermined amount of liquid refrigerant is stored in the refrigerant storage tank 10, the open/ close valves 12 and 13 are closed. The above operation and effect make it possible to store the liquid refrigerant in the refrigerant storage tank 10. To discharge the liquid refrigerant from the refrigerant storage tank 10, the open/close valve 14 is opened so that the liquid refrigerant can be discharged to the accumulator 5 through the pipe 15.
The composition varying effect will be explained below.
The state of the refrigerant inside the receiver, which is made clear by the experiment conducted by the inventors of the present invention, will now be explained using a cooling operation as an example. Gas and liquid flow into the receiver 6 from the pipe 17, and the gas rises in the liquid layer inside the receiver 6, forming a gas layer. Then, the gas is condensed by the inner wall of the receiver 6 and liquefied. Thereafter, the gas is formed into only liquid in an outlet pipe 16 and flows out. The experimental results show that when the refrigerant dryness of the inlet is great, the liquid disappears inside the receiver 6, and when the refrigerant dryness is small, the receiver 6 is filled with the liquid. The experiment also revealed that the variation of the dryness with respect to the variation in the amount of liquid is 0.01 or less. That is, the dryness of the refrigerant which flows into the receiver is very small.
Fig. 6 illustrates changes of the state of the refrigerant in a refrigerant passage from the condenser to the receiver when a non-azeotrope refrigerant is used as a thermal medium. The horizontal axis indicates the composition ratio X of the low-boiling-point refrigerant, i.e., HFC32, and the vertical axis indicates temperature, with pressure being constant. The state X = 0 indicates a state in which only HFC134a is contained in the refrigerant, and the state X = 1 indicates a state in which the refrigerant is formed of only HFC32. In the non-azeotrope refrigerant, as shown in the figure, the temperature of the saturation vapor differs from that of the saturation liquid at the same pressure. The composition ratio X₀ indicates the composition ratio of the refrigerant sealed in the refrigeration cycle. Point A indicates the state of the inlet of the condenser; point B indicates the condensation start point; point C indicates the state of the inside of the receiver; and point D indicates the state of the outlet of the cooling unit. Point C, as described above, indicates that the flow rate of the liquid is very small. Point E indicates the liquid state inside the receiver, and the composition ratio of HFC32 is X₁. Point F indicates the gas state, and the composition ratio of HFC32 is X_g. It can be seen that the composition ratio of gas at point F is greater than the composition ratio X₀ of the refrigerant sealed in the refrigeration cycle, and the composition ratio in the refrigeration cycle can be varied by taking out gas.
In Figs. 1 and 2, a gas refrigerant having a large composition ratio of HFC32 taken out from the upper portion of the receiver 6 is liquefied in the cooling unit 11 and stored in the tank 10. As a result, the composition ratio of the refrigerant within the refrigeration cycle becomes smaller than X₀. When the composition ratio of the refrigerant within the refrigeration cycle is smaller than X₀, it is possible to return the refrigerant having a large composition ratio of HFC32 to the refrigeration cycle by opening the open/ close valve 14.
As described above, the refrigerant composition ratio in the main refrigeration cycle can be varied by taking out or returning the gas refrigerant inside the receiver.
Although the above-described embodiment describes a case in which a mixture refrigerant of two types of refrigerants, i.e., HFC32 and HFC134a, are used as a refrigerant, the present invention may be applied to a mixture refrigerant of more than two types. For example, the present invention may be applied to a three-type mixture refrigerant of HFC32, HFC125 and HFC134a shown in Fig. 7. The numeric values shown in Fig. 7 indicates weight percentage(%) of HFC32, HFC125 and HFC134a, and a mixture refrigerant of various weight percentages may be considered. Of HFC32, HFC125 and HFC134a, the boiling points of HFC32 and HFC125 are higher than that of HFC134a, and therefore the present invention utilizing the difference between the boiling points of mixed refrigerants may be applied. HFC32 and HFC125 exhibit azeotropic characteristics which can be regarded as a single refrigerant, and the above-described mixture refrigerant can be assumed as a mixture refrigerant of the azeotrope refrigerant of HFC32 and HFC125, and HFC134a. The composition varying function of the present invention may be exhibited for a mixture refrigerant of HFC32, HFC125 and HFC134a. In Figs. 1 and 2, gas in the upper portion of the receiver 6 is a low-boiling-point refrigerant having a large refrigerant composition ratio, whose compositions of HFC32 and HFC125 from among the three types of refrigerants are large. The gas having large compositions of HFC32 and HFC125, taken out from the upper portion of the receiver 6, is liquefied by the cooling unit 11 and stored in the tank 10. As a result, regarding the composition ratio of the refrigerant within the refrigeration cycle, the composition ratios of low-boiling-point refrigerants, i.e., HFC32 and HFC125, are small, and the composition ratio of the high-boiling-point refrigerant, i.e., HFC134a, is large. Regarding the composition ratio within the refrigeration cycle, it is possible to return the composition ratio of the HFC32 and HFC125 to the original state by opening the open/close valve 14. As stated above, it is possible to vary the composition of the refrigerant in the case of a three-type mixture refrigerant.
Next, an explanation will be given of an embodiment of the electrostatic capacitance type sensor 8 for detecting the composition of a mixture refrigerant. Fig. 8 is a sectional view of the electrostatic capacitance type composition detecting sensor 8 shown in Fig. 1. In Fig. 8, reference numeral 53 denotes an outer tube electrode, and reference numeral 54 denotes an inner tube electrode, both of which are hollow tubes. The inner tube electrode 54 is fixed at its both ends by stoppers 55a and 55b in which a circular groove is provided in the central portion of the outer tube electrode 53. The outer diameter of the stoppers 55a and 55b is nearly the same as the inner diameter of the outer tube electrode 53, and the side opposite to the inner tube electrode holding side is fixed by the refrigerant introduction pipe 59 having an outer diameter nearly the same as the inner diameter of the outer tube electrode 53. In addition, the refrigerant introduction pipe 59 is fixed to the outer tube electrode 53.
As a result, the inner tube electrode 54 is fixed to the central portion of the outer tube electrode 53. An outer-tube electrode signal line 56 and an inner-tube electrode signal line 57 are connected to the outer tube electrode 53 and the inner tube electrode 54 in order to detect an electrostatic capacitance value. A signal line guide tube 58 (e.g., a hermetic terminal) for guiding the inner-tube electrode signal line 57 to the outside of the outer tube electrode 53 and for preventing the refrigerant inside from escaping to the outside, are disposed outside the inner-tube electrode signal line 57. In the stoppers 55a and 55b, at least one through passage having a size smaller than the inner diameter of the inner tube electrode 54 is disposed in the central portion thereof, and at least one passage for the refrigerant is disposed at a place between the inner tube electrode 54 and the outer tube electrode 53, so that the flow of the mixture refrigerant flowing through the inside is not obstructed.
Next, an explanation will be given of a method of detecting the composition of a mixture refrigerant by using the electrostatic capacitance type composition ratio detecting sensor 8. Fig. 9 illustrates the relationship between the composition ratio of the refrigerant and the electrostatic capacitance value when the electrostatic capacitance sensor is used. Fig. 9 illustrates measured values obtained when HFC134a is used as a high boiling-point refrigerant and HFC32 is used as a low boiling-point refrigerant from among the mixture refrigerant and they are sealed in the composition ratio detecting sensor shown in Fig. 8 as gas and liquid, respectively. The horizontal axis indicates the composition ratio of the HFC32, and the vertical axis indicates the electrostatic capacitance value which is an output from the composition ratio detecting sensor 8.
In Fig. 9, a comparison of the electrostatic capacitance value of gas of each refrigerant with that of liquid of each refrigerant shows that the liquid refrigerant has a larger value, and the difference between the electrostatic capacitance value of gas and that of liquid is large, in particular, in the HFC134a. This indicates that the electrostatic capacitance value varies when the dryness of the refrigerant varies. In contrast, a comparison between the electrostatic capacitance values of HFC134a and HFC32 shows that HFC32 has a larger electrostatic capacitance value for both liquid and gas. This indicates that only a gas or liquid refrigerant exists in the composition ratio detecting sensor 8, and when the composition of the refrigerant varies, the electrostatic capacitance value varies.
However, since the inside of the composition ratio detecting sensor 8 enters a two-phase state of gas and liquid, the electrostatic capacitance value varies due to the dryness of the refrigerant in addition to the composition ratio of the mixture refrigerant, it becomes impossible to detect the composition ratio. Therefore, when the composition ratio of the mixture refrigerant is detected by using the composition ratio detecting sensor 8, it is necessary to dispose the composition ratio detecting sensor 8 in a portion where the refrigerant is always gas or liquid in the refrigeration cycle. In this embodiment, since the check valves 91 to 94 are arranged, the refrigerant passing through the composition ratio detecting sensor 8 is in a liquid state. Means other than the electrostatic capacitance type may be used for the composition ratio detecting means.
Next, Fig. 10 is a flowchart illustrating a method of controlling the refrigeration cycle shown in Fig. 1. When a predetermined condition is satisfied after the refrigeration cycle is started, the composition ratio is determined on the basis of a signal from the composition ratio detecting sensor 8. A check is made to determine whether the detected composition ratio X is greater than the composition ratio X₀ of the refrigerant sealed in the refrigeration cycle. When X > (X₀ + α), the open/ close valves 12 and 13 are opened. When the condition (X₀ - α) ≤ X ≤ (X₀ + α) is satisfied, the open/ close valves 12 and 13 are closed. When the detected composition ratio X < (X₀ - α), the open/close valve 14 is opened, and when (X₀ - α) ≤ X ≤ (X₀ + α) is satisfied, the open/close valve 14 is closed. a is the tolerance.
Therefore, it is possible to control the composition of the refrigerant within the refrigeration cycle to X₀ or thereabouts, making it possible to prevent the pressure on the high pressure side from abnormally increasing and making a stable operation possible. Since the composition ratio of the non-azeotrope refrigerant can be varied, it becomes possible to vary the heating and cooling capacity as shown in Fig. 3.
In Fig. 11, reference numeral 1 denotes a compressor; reference numeral 2 denotes an outdoor heat exchanger; reference numeral 3 denotes an outdoor air blower; reference numeral 4 denotes a four-way valve; reference numeral 5 denotes an accumulator; reference numeral 6 denotes a receiver; reference numeral 7 denotes an outdoor refrigerant control valve; reference numeral 8 denotes a sensor for detecting the composition ratio of a non-azeotrope refrigerant; reference numerals 91, 92, 93 and 94 denote check valves which are disposed in outdoor machines. Reference numerals 20a and 20b denote indoor heat exchangers; reference numerals 21a and 21b denote indoor refrigerant control valves; reference numerals 22 and 23 denote refrigerant distribution units; and reference numerals 24 and 25 denote pipes through which the indoor side is connected to the outdoor side. An electrostatic capacitance type liquid level sensor 60 for detecting the liquid level of the refrigerant inside the receiver 6 is disposed inside the receiver 6. In addition, disposed are the electrostatic capacitance sensor 8 for detecting the composition ratio of the non-azeotrope refrigerant, the electrostatic capacitance type liquid level sensor 60 for detecting the liquid level of the refrigerant, a liquid-level detection apparatus, a computation apparatus for computing the composition of a refrigerant, a computation apparatus for computing the amount of the refrigerant, and a display apparatus.
In this embodiment, a refrigerant which does not contain chlorine and does not damage the ozone layer is used as a working medium. Examples of such refrigerants include a mixture refrigerant of HFC32 and HFC134a, which is a non-azeotrope refrigerant. An example in which this refrigerant is used will be explained below.
The flow of the refrigerant of this embodiment will be explained. During a cooling operation, the refrigerant discharged from the compressor flows in the following order: the four-way valve 4 → the outdoor heat exchanger 2 → the check valve 93 → the composition ratio detecting sensor 8 → the outdoor refrigerant control valve 7 → the check valve 92 → the receiver 6. The refrigerant is distributed by the distribution unit 23. A part of the refrigerant flows in the order: the indoor heat exchanger 20a → the indoor refrigerant control valve 21a, and the other flows in the order: the indoor heat exchanger 20b → the indoor refrigerant control valve 21b. They merge in the distribution unit 22, flow in the order: the pipe 24 → the four-way valve 4 → the accumulator 5, and return to the compressor. The indoor heat exchangers 20a and 20b act as evaporators, and a cooling operation is performed. During a heating operation, on the other hand, the refrigerant discharged from the compressor flows in the order: the four-way valve 4 → the pipe 24 → the distribution unit 22. A part of the refrigerant flows in the order: the indoor refrigerant control valve 21a → the indoor heat exchanger 20a, and the other flows in the order: the indoor refrigerant control valve 21b → the indoor heat exchanger 20b. They merge in the distribution unit 23, and flow in the following order: the pipe 25 → the receiver 6 → the check valve 94 → the composition ratio detecting sensor 8 → the outdoor refrigerant control valve 7 → the check valve 91 → the outdoor heat exchanger 2 → the four-way valve 4 → the accumulator 5, and return to the compressor. In this case, the indoor heat exchangers 20a and 20b act as condensers, and a heating operation is performed.
When the refrigerant sealed in the refrigeration cycle leaks outside and the composition ratio of the non-azeotrope refrigerant varies, the composition of the refrigerant within the refrigeration cycle can be detected by the composition ratio detecting sensor 8 as stated before. Since there is a correlation between the the liquid level of the receiver 6 and the amount of the refrigerant within the refrigeration cycle, it is possible to detect the amount of refrigerant within the refrigeration cycle by the liquid level sensor disposed inside the receiver 6 as shown in Fig. 11. In this embodiment, since an electrostatic capacitance type sensor is used as a liquid level sensor, the signal from the liquid level sensor 60 varies even when the composition ratio of the refrigerant varies. However, it is possible to correct the signal from the liquid level sensor 60 on the basis of the composition ratio detected by the composition ratio detecting sensor 8.
With the refrigeration cycle constructed as described above, it is possible to easily maintain the refrigeration cycle even when the refrigerant sealed in the refrigeration cycle leaks outside and the composition ratio of the non-azeotrope refrigerant varies. More specifically, it is possible to selectively display the amount of refrigerant within the refrigeration cycle, the composition ratio of the refrigerant, a display of whether the type and amount of the refrigerant are normal or not, the type of the refrigerant to be added, and the amount of the refrigerant to be added, facilitating a maintenance operation to a greater extent.
An embodiment of the present invention will be explained below. Fig. 12 shows an example in which a valve 61 for sealing in a refrigerant is added to the refrigeration cycle shown in Fig. 11. The valve 61 is disposed on the inlet side of the accumulator 5 of the refrigeration cycle. Reference numeral 62 denotes a bomb for a low-boiling-point refrigerant; and reference numeral 63 denotes a bomb for a high-boiling-point refrigerant. When the refrigerant within the refrigeration cycle becomes deficient, the low-boiling-point refrigerant bomb 62 is connected to the refrigerant sealing-in valve 61 and the refrigerant is sealed in when the refrigerant to be added is a low-boiling-point refrigerant. When, however, the refrigerant to be added is a high-boiling-point refrigerant, there is a case in which the pressure in the refrigerant bomb is lower than that inside the refrigeration cycle. In such a case, the refrigeration cycle is operated, and the opening of the indoor refrigerant control valve 21a or 21b is decreased during a cooling operation so that the pressure on the low pressure side of the refrigeration cycle is decreased less than the pressure of the refrigerant bomb 63. As a result, it becomes possible to seal in a refrigerant. In the case of a heating operation, the opening of the outdoor refrigerant control valve may be decreased.
Next, a description will be given of the operation when the above-described refrigeration cycle is used. Fig. 13 shows an example in which the refrigerant sealing-in valve 61 is added to the refrigeration cycle of Fig. 11. The refrigerant sealing-in valve 61 is disposed on the inlet side of the accumulator 5 of the refrigeration cycle. In Fig. 13, reference numeral 64 denotes a refrigerant bomb in which a non-azeotrope refrigerant is sealed in. The refrigerant bomb 64 is provided with a valve 65 for taking out the refrigerant from the upper portion of the bomb and a valve 67 for taking out the refrigerant from the lower portion of the bomb.
Fig. 14 illustrates the internal state of the refrigerant bomb 64. Gas having the composition at point K and liquid having the composition at point L in the figure coexist inside the refrigerant bomb 64. Therefore, it is possible to take out a refrigerant having a large composition ratio of a low-boiling-point refrigerant by taking out gas, and by taking out liquid, it is possible to take out a refrigerant having a large composition ratio of a high-boiling-point refrigerant. In a case in which the refrigerant is sealed in the refrigeration cycle, by using the above-described characteristics, the refrigerant is taken out from the valve 65 in Fig. 13 when a low-boiling-point refrigerant is sealed in, and a refrigerant is taken out from the valve 67 in Fig. 13 when a high-boiling-point refrigerant is sealed in.
Next, another embodiment of the present invention will be explained with reference to Fig. 15.
Referring to Fig. 15, reference numeral 1 denotes a compressor; reference numeral 2 denotes an outdoor heat exchanger; reference numeral 3 denotes an outdoor air blower; reference numeral 4 denotes a four-way valve; reference numeral 5 denotes an accumulator; reference numeral 6 denotes a receiver; reference numeral 7 denotes an outdoor refrigerant control valve; reference numeral 8 denotes a sensor for detecting the composition of a non-azeotrope refrigerant; reference numerals 91, 92, 93 and 94 denote check valves which are disposed in an outdoor machine; reference numerals 20a and 20b denote indoor heat exchangers; reference numerals 21a and 21b denote indoor refrigerant control valves; reference numerals 22 and 23 denote refrigerant distribution units; reference numerals 24 and 25 denote pipes through which the indoor side is connected to the outdoor side; reference numerals 81 and 82 denote pipes; reference numerals 83 and 84 denote open/close valves; reference numeral 80 denotes a detection display apparatus for detecting and displaying the composition ratio of a non-azeotrope refrigerant; and reference numeral 85 denotes an electrostatic capacitance sensor. The detection display apparatus 80 is provided, in addition to the electrostatic capacitance sensor 85, with a computation apparatus for computing the composition of a refrigerant and a display apparatus for displaying the composition thereof. In this embodiment, HFC32 and HFC134a are used as the non-azeotrope refrigerant.
Next, the flow of the refrigerant will be explained. During a cooling operation, the refrigerant discharged from the compressor flows in the following order: the four-way valve 4 → the outdoor heat exchanger 2 → the check valve 93 → the outdoor refrigerant control valve 7 → the check valve 92 → the receiver 6. The refrigerant is distributed by the distribution unit 23. A part of the refrigerant flows in the order: the indoor heat exchanger 20a → the indoor refrigerant control valve 21a, and the other flows in the order: the indoor heat exchanger 20b → the indoor refrigerant control valve 21b. They merge in the distribution unit 22, flow in the order: the pipe 24 → the four-way valve 4 → the accumulator 5, and return to the compressor. In this case, the indoor heat exchangers 20a and 20b act as evaporators, and a cooling operation is performed. During a heating operation, on the other hand, the refrigerant discharged from the compressor flows in the following order: the four-way valve 4 → the pipe 24 → the distribution unit 22. A part of the refrigerant flows in the order: the indoor refrigerant control valve 21a → the indoor heat exchanger 20a, and the other flows in the order: the indoor refrigerant control valve 21b → the indoor heat exchanger 20b. They merge in the distribution unit 23, flow in the following order: the pipe 25 → the receiver 6 → the check valve 94 → the outdoor refrigerant control valve 7 → the check valve 91 → the outdoor heat exchanger 2 → the four-way valve 4 → the accumulator 5, and return to the compressor. In this case, the indoor heat exchangers 20a and 20b act as condensers, and a heating operation is performed.
When the composition of the refrigerant is to be detected, the sensor 85 of the detection display apparatus 80 is connected between the open/ close valves 83 and 84, and the refrigerant is made to flow through the sensor 85 while a cooling or heating operation is being performed. As described above, a refrigerant take-out section for detecting the composition of the refrigerant is disposed in the refrigeration cycle, and the composition ratio can be detected by the detection display apparatus 80 which is disposed separately from the refrigeration cycle system. As a result, there is no need to dispose a composition ratio sensor in the refrigeration cycle, and therefore the refrigeration cycle can be constructed at a low cost.
If no refrigerant has been sealed in the refrigeration cycle, first the cycle is evacuated to a vacuum by a vacuum pump, and then refrigerants may be sealed in according to the descending order of their boiling points, each by a predetermined amount. When such operation has been completed, it is possible to bring the composition ratio of the non-azeotrope refrigerant within the refrigeration cycle close to a set value.

Claims

A method of sealing in a non-azeotrope refrigerant and controlling the composition of the refrigerant in a refrigeration cycle comprising a compressor (1); a heat-source-side heat exchanger (2); a use-side heat exchanger (20a, 20b); and a refrigerant pressure reducing apparatus (7), said method comprising the steps of:

evacuating the refrigeration cycle to a vacuum by a vacuum pump before a non-azeotrope refrigerant is sealed in, and

sealing in refrigerants which form said non-azeotrope refrigerant according to the descending order of their boiling points, each by a predetermined amount.
A method according to claim 1 comprising the step of decreasing the pressure on a low pressure side of the refrigeration cycle less than the saturation pressure of a high-boiling-point refrigerant and sealing in a high-boiling-point refrigerant when a refrigerant is added to the refrigeration cycle on the basis of the type and amount of the refrigerant to be added, displayed on a display apparatus for displaying the type and amount of the refrigerant.