REFRIGERANT SUPERCOOLING CIRCUIT

Abstract

 A refrigerant supercooling circuit comprising a receiver (5) for retention of a liquid-phase refrigerant installed in a refrigerant line (23) connecting a first expansion valve (45) and a plurality of second expansion valves (71), an extraction line (61) for taking out the liquid-phase refrigerant in the receiver (5), a third expansion valve (62) in the extraction line, the portion of the extraction line (61) downstream of the third expansion valve (62) being passed through the receiver (5) or through a supercooling tank (63), the arrangement being such that the degree of opening of the first expansion valve (45) is controlled either according to the refrigerant pressure (P1) on a refrigerant line (21) connecting the delivery side of a compressor (2) and a four-way valve (3), or according to the degree of supercooling (SC) in the outlet of an outdoor heat exchanger (4), or according to the pressure difference across the first expansion valve (45).

Description

Technical Field

[0001] The present invention relates to a refrigerant supercooling circuit for an air-conditioning system with the object of improving its refrigerant cycle efficiency during an air-cooling operation, particularly, for an air-conditioning system which is provided with plural indoor units comprising indoor heat exchangers connected in multiple to one outdoor unit comprising a compressor, a compressor motor, and an outdoor heat exchanger.

Background Art

[0002] Conventionally, in a refrigerant circuit of an air-conditioning system during its air-cooling operation, a compressor delivers a warm and high-pressured gas-phase refrigerant to an outdoor heat exchanger. In the outdoor heat exchanger, the gas-phase refrigerant is cooled so as to turn into a high-pressured liquid-phase refrigerant. Then, the liquid-phase refrigerant is sent to an indoor unit. In the indoor unit, the liquid-phase refrigerant is expanded and absorbs evaporation heat from the indoor air so as to turn into a low-pressured gas-phase refrigerant. The low-pressured gas-phase refrigerant is recovered into the compressor.

[0003] The conventional air-conditioning system is requested that its operational efficiency should be further improved while its compressor and its outdoor heat exchanger are to be minimized. A supercooling cycle serves as one of available means for improving the operational efficiency of the air-conditioning system during its air-cooling operation. This is a heat-exchanging cycle between a high-pressured liquid-phase refrigerant and a low-pressured gas-phase refrigerant, and is provided to the above-mentioned refrigerant circuit so as to supercool the high-pressured liquid-phase refrigerant.

[0004] As disclosed in U.S. Patent Nos. 5,228,301 and 5,465,587, one of conventional supercooling cycles comprises a pair of refrigerant extraction pipes. One refrigerant extraction pipe which branches from a high-pressured liquid-phase refrigerant pipe downstream of an outdoor heat exchanger is provided to expand the high-pressured liquid-phase refrigerant flowing therein so as to turn it into a low-pressured gas-phase refrigerant. The other refrigerant extraction pipe branches from a low-pressured gas-phase refrigerant pipe downstream of an indoor heat exchanger. The low-pressured air-phase refrigerant from both the refrigerant extraction pipes is made to surround the high-pressured liquid-phase refrigerant pipe downstream of the outdoor heat exchanger, thereby supercooling the high-pressured liquid-phase refrigerant flowing in the high-pressured liquid-phase refrigerant pipe.

[0005] However, in this cycle, the refrigerant flowing in the refrigerant extraction pipes is not particularly stored but is used for supercooling as much as it is taken out. Especially in an air-conditioning system having plural indoor heat exchangers connected in multiple to a single outdoor exchanger, the number of operated indoor heat exchangers varies so as to change the quantity of refrigerant circulated in the refrigerant circuit. Therefore, the quantity of refrigerant taken out for supercooling is not constant and the effect of supercooling is not stable.

[0006] Furthermore, the low-pressured gas-phase refrigerant flowing in the refrigerant extraction pipe from the downstream side of the indoor heat exchanger has been heated in the indoor unit. This heated refrigerant is mixed with the expanded cold low-pressured gas-phase refrigerant which is taken out from the high-pressured liquid-phase refrigerant pipe. Therefore, the temperature difference between the resultant extracted refrigerant and the high-pressured liquid-phase refrigerant in the high-pressured liquid-phase refrigerant pipe is reduced, thereby causing insufficient effect of supercooling.

[0007] Besides, U.S. Patent No. 5,174,123 discloses such a structure that a refrigerant pipe upstream of an expansion valve, in which a high-pressured liquid-phase refrigerant flows, is located adjacent to a refrigerant pipe downstream of the expansion valve, in which a low-pressure gas-and-liquid-phase refrigerant flows. However, in this structure, the low-pressured gas-and-liquid-phase refrigerant absorbs the heat of the high-pressured liquid-phase refrigerant so as to be heated, thereby reducing the air-cooling effect of the indoor unit.

[0008] Furthermore, there is a general problem that, when the air temperature is high, the low-pressured gas-phase refrigerant absorbs heat from the air, thereby reducing its absorption of heat from the high-pressured liquid-phase refrigerant. Thus, the high-pressured liquid-phase refrigerant is insufficiently supercooled.

[0009] Then, it comes to be considered that an expansion valve of an outdoor unit, which is usually fully opened during an air-cooling operation so as to allow a gas-and-liquid-phase refrigerant from the outdoor heat exchanger to flow therethrough (and which serves as a proper expansion valve during the air-heating operation), is throttled so as to make the gas-and-liquid-phase refrigerant stagnate for the promotion of supercooling. However, such a throttle valve, if its throttle is considerably great (or if the opening degree thereof is too small), may cause the increase of delivery pressure of a compressor and the reduction of operational efficiency.

Disclosure of the Invention

[0010] The present invention is a refrigerant supercooling circuit which is constructed in a refrigerant circuit of an air-conditioning system for its air-cooling operation, wherein a receiver for retention of a liquid-phase refrigerant is installed in a refrigerant line connecting a first expansion valve downstream of an outdoor heat exchanger to a plurality of second expansion valves upstream of respective indoor heat exchangers, and wherein a third expansion valve is installed in an extraction line for taking out a part of a liquid-phase refrigerant from any portion of the refrigerant circuit of the air-conditioning system so as to make a portion of the extraction line downstream of the third expansion valve supercool the liquid-phase refrigerant which is retained in the receiver or is taken out from the receiver after being retained therein. The opening degree of the first expansion valve, through which a gas-and-liquid-phase refrigerant flows from the outdoor heat exchanger, is controlled so that an adequate effect of supercooling is obtained and load applied on a compressor and a compressor motor is restricted so as to improve the operational efficiency of the air-conditioning system, while the air-conditioning system having a plurality of indoor heat exchangers connected in multiple to the single outdoor heat exchanger is attended with variation of the number of the operated indoor heat exchangers.

[0011] The first expansion valve is controlled according to the refrigerant pressure in the refrigerant line connecting a delivery port of the compressor to a directional control valve. Therefore, the throttle of the first expansion valve, which is throttled for enhancing the effect of supercooling, is controlled according to detection of the delivery pressure of the compressor, thereby avoiding excessive load on the compressor and the compressor motor.

[0012] Alternatively, the first expansion valve may be controlled according to a supercooling degree at an outlet of the outdoor heat exchanger. When an excessive effect of supercooling is obtained, the throttling of the first expansion valve is stopped so as to avoid excessive load on the compressor and the compressor motor and reduction of operational efficiency.

[0013] Alternatively, the first expansion valve may be controlled according to a pressure difference across the first expansion valve. During the throttling control of the first expansion valve for obtaining supercooling effect, if the detected pressure difference reaches a certain value, the throttling thereof is stopped so as to avoid excessive load on the compressor and the compressor motor.

[0014] As a first attempt for supercooling the liquid-phase refrigerant which is retained in the receiver or flows out from the receiver after being retained, a portion of the extraction line downstream of the extraction line is passed through in the receiver so as to supercool the liquid-phase refrigerant retained in the receiver. Therefore, another means for taking out a liquid-phase refrigerant for supercooling is unnecessary, thereby effecting economy.

[0015] In this construction, the extraction line is constructed so as to take out a liquid-phase refrigerant from either the receiver or the outdoor heat exchanger. Therefore, the high-pressured liquid-phase refrigerant which is going to be evaporated for supercooling can be stably extracted into the extraction line.

[0016] As a second attempt for the same purpose, a supercooling tank for retention of a liquid-phase refrigerant in tandem with the receiver may be disposed whether upstream or downstream of the receiver. In this case, the extraction line is also constructed so as to take out a liquid-phase refrigerant from either the receiver or the outdoor heat exchanger, thereby stabling the extraction of the liquid-phase refrigerant. The portion of the extraction line downstream of the third expansion valve is passed through in the supercooling tank. Since the tank serving as a supercooler is separated from the receiver, the voluminal variation of the supercooling tank is allowed to be free from the voluminal capacity of the receiver.

[0017] The extraction line passed through in either the receiver or the supercooling tank as the above-mentioned first and second attempts may be constituted by a coiled refrigerant tube in either the receiver or the supercooling tank. This coiled refrigerant tube may be supported by a plurality of rod-like members along an inner wall of the receiver or the supercooling tank. In this way, between the outer peripheral edge of the refrigerant tube and the inner wall of the receiver or the supercooling tank is secured a gap having a distance as large as a diameter of the rod-like member so that the extraction line is prevented from directly contacting with the inner wall of the receiver or the supercooling tank. Accordingly, the condition of the refrigerant in the extraction line resists being changed by outside air, thereby stabilizing the supercooling effect. The refrigerant tube fixedly supported by the rod-like members is unified with the receiver or the supercooling tank so as to facilitate assembling the supercooling circuit.

[0018] Furthermore, every adjoining loops of the coil of the refrigerant tube in the receiver or the supercooling tank may be fixedly jointed to each other, thereby unifying the extraction line with the receiver or the supercooling tank more stably and more strongly.

[0019] As a third attempt for the same purpose, the refrigerant line connecting the receiver to the plurality of second expansion valves in multiple may be passed through in a supercooling tube having an expanded space. The extraction line takes out the liquid-phase refrigerant from the receiver and the portion of the extraction line downstream of the third expansion valve is passed through the supercooling tube. Therefore, the extraction line can be supplied with stable extraction of liquid-phase refrigerant from the receiver. Also, the variation of the supercooling tube in construction for determining the quantity of heat exchanged between the refrigerant in the extraction line and the liquid-phase refrigerant in the refrigerant line to the second expansion valves is free from the retentive capacity of the receiver.

[0020] In each of the first to third attempts of a supercooling circuit, while the high-pressured liquid-phase refrigerant is extracted from any of the outdoor heat exchanger, the receiver and the supercooling tank into the portion of the extraction line upstream of the third expansion valve, the portion of the extraction line downstream of the third expansion valve joins a refrigerant line between the multiple indoor heat exchanger and the directional control valve after supercooling the liquid-phase refrigerant sent to the indoor units so as to allow the liquid-phase refrigerant supercooled downstream of the third expansion to be joined with the low-pressured gas-phase refrigerant in this refrigerant line, thereby increasing the pressure difference across the third expansion valve so as to enhance the supercooling effect.

[0021] Alternatively, after supercooling the liquid-phase refrigerant, the extraction line may be connected to a refrigerant line connecting the directional control valve to an auxiliary refrigerant evaporator which leads cooling water for cooling the compressor motor. In this case, in addition to the above-mentioned effect, load on the compressor can be lightened because the pressure of refrigerant absorbed into the compressor is allowed to be increased by use of the extraction line and the waste heat of the compressor motor even if the pressure of wet steam refrigerant led into the auxiliary refrigerant evaporator is low. Furthermore, in the auxiliary refrigerant evaporateur the waste heat of the compressor motor is also used as energy for evaporating the liquid-phase refrigerant in the extraction line so as to restrict the increase of temperature of the refrigerant absorbed into the compressor.

[0022] The refrigerant line between the first expansion valve and the receiver is formed into two ways. One way is connected to the upper portion of the receiver, wherein a check valve is installed so as to intercept a refrigerant flow from the receiver. The other way is connected to the lower portion of the receiver, wherein a check valve is installed so as to intercept a refrigerant flow from the first expansion valve. Thus, the switching of this two-way refrigerant line can be easily performed only by operation of two check valves.

[0023] These, other and further objects, features and advantages of the invention will appear more fully from the following detailed description taken in connection with the accompanying drawings.

Brief Description of the Drawings

[0024] 

Fig. 1 is a diagram of an entire air-conditioning system including a refrigerant supercooling circuit according to the present invention while the air-conditioning system is operated for air-cooling;

Fig. 2 is a diagram of the same system modified so as to include a pressure sensor, a temperature sensor and the like for controlling a first expansion valve;

Fig. 3 illustrates a relationship of a cooling effect with the opening degree of a third expansion valve;

Fig. 4 illustrates a relationship of a delivery pressure of a compressor with the third expansion valve;

Fig. 5 illustrates a relationship of a cooling effect with the opening degree of a first expansion valve;

Fig. 6 illustrates a relationship of an air-conditioning performance with the delivery pressure;

Fig. 7 illustrates a supercooling effect with a pressure difference across the first expansion valve;

Fig. 8 is a flowchart of a first controlling manner of the first expansion valve according to the present invention;

Fig. 9 is a flowchart of a second controlling manner of the first expansion valve according to the present invention;

Fig. 10 is a flowchart of a third controlling manner of the first expansion valve according to the present invention;

Fig. 11 is a diagram of a refrigerant circuit comprising an extraction line branching from an outdoor heat exchanger;

Fig. 12 is a diagram of an embodiment wherein a receiver and a supercooling tank are separated from each other;

Fig. 13 is a diagram of an embodiment wherein the receiver and the supercooling tank are separated from each other and an extraction line for supercooling is extended from a lower portion of the receiver;

Fig. 14 is a diagram of another embodiment wherein the receiver and the supercooling tank are separated from each other;

Fig. 15 is a diagram of another embodiment wherein the receiver and the supercooling tank are separated from each other and the extraction line for supercooling is extended from a lower portion of the receiver;

Fig. 16 is a diagram of an embodiment wherein a supercooler is constituted by a double-tube heat exchanger;

Fig. 17 is a side view partly in section of the supercooler;

Fig. 18 is a plan view of the supercooler; and

Fig. 19 is a Mollier diagram of specific enthalpy in relative to a refrigerant pressure.

Best Mode for Carrying out the Invention

[0025] Description will be given of a refrigerant circuit of an air-conditioning system (for air-cooling and air-heating) shown in Figs. 1 and 2. The refrigerant circuit comprises a compressor (in this embodiment, a multi-compressor) 2, a four-way valve 3 serving as a directional control valve, an outdoor heat exchanger 4 (in this embodiment, two outdoor heat exchangers 4), a (multiple) first expansion valve 45, a plurality of second expansion valves 71, a plurality of indoor heat exchangers 70 corresponding to respective second expansion valves 71, and so on. There are provided refrigerant lines, that is, a refrigerant line 20 connecting a delivery port of the compressor 2 to the four-way valve 3, a refrigerant line 26 connecting a suction port of the compressor 2 to the four-way valve 3, a refrigerant line 21 connecting the four-way valve 3 to the outdoor heat exchangers 4, refrigerant lines 22 connecting the outdoor heat exchangers 4 to the respective first expansion valves 45 downstream thereof, a refrigerant line 23 wherein lines from the respective first expansion valves 45 join into one and then the joint line spreads into branches to all the second expansion valves 71, refrigerant lines 24 connecting the second expansion valves 71 to the respective indoor heat exchangers 70, and a refrigerant line 25 connecting all the indoor heat exchangers 70 to the four-way valve 3.

[0026] A receiver 5 serving as a tank for retention of a liquid-phase refrigerant is installed in the joint line portion of the refrigerant line 23. An extraction line 61 for taking out the liquid-phase refrigerant is disposed in a tank of the receiver 5. A third expansion valve 62 is installed in the extraction line 61. A portion of the extraction line 61 downstream of the second expansion valve 62 is passed through in the receiver 5 again. Then, the extraction line 61 is connected to either the refrigerant line 26, as shown in Fig. 1, or the refrigerant line 25, as shown in Fig. 2. In the receiver 5, the extraction line 61 is formed into a supercooler 6. For example, the supercooler 6 may be a coiled refrigerant tube serving as a heating tube 60. The supercooler 6, which is disposed in the receiver 5 in the embodiments of Figs. 1 and 2, may be a unit separated from the receiver 5, as discussed later.

[0027] Incidentally, in the refrigerant line 23, the joint line of the lines from the respective first expansion valves 45 is bifurcated into two branches. One branch is constituted by a receiver inflow pipe 51 connected to an upper portion of the receiver 5. The other branch is constituted by a return pipe 55 for air-heating connected to a lower portion of the receiver 5. A check valve 46 is installed in the receiver inflow pipe 51 so as to intercept a refrigerant flow from the receiver 5 to the first expansion valves 45. A check valve 47 is installed in the return pipe 55 for air-heating so as to intercept a refrigerant flow from the first expansion valves 45 to the receiver 5.

[0028] During an air-cooling cycle operation, the refrigerant passed through the first expansion valves 45 is passed through the check valve 46 to flow into the tank of the receiver 5 via the upper portion thereof. During an air-heating cycle operation, the refrigerant flows out from the lower portion of the tank of the receiver 5 and is passed through the check valve 46 to flow to the first expansion valves 45. The refrigerant flow for air-cooling and for air-heating can be controlled by such a simple construction using two check valves 46 and 47, thereby saving costs.

[0029] In each of the indoor units 7 is disposed the indoor heat exchanger 70, a cooler fan 72 and so on. All parts other than those of the indoor units 7, i.e., the compressor 2, the fourway valve 3, an auxiliary heat absorber (an auxiliary refrigerant evaporator) 8, an accumulator 9, the outdoor heat exchangers 4, the receiver 5 and so on, are unified as an outdoor unit.

[0030] During the air-heating operation, by the four-way valve 3, the refrigerant line 20 from the delivery port of the compressor 2 is connected to the refrigerant line 25 to the indoor units 7, and the refrigerant line 26 to the suction port of the compressor 2 is connected to the refrigerant line 21 from the outdoor heat exchangers 4, so that the refrigerant delivered from the compressor 2 flows from the indoor units 7 to the outdoor unit. During the air-cooling operation, as shown in Figs. 1 and 2, by the four-way valve 3, the refrigerant line 20 from the delivery port of the compressor 2 is connected to the refrigerant line 21 to the outdoor heat exchangers 4, and the refrigerant line 26 to the suction port of the compressor 2 is connected to the refrigerant line 25 from the indoor units 7, so that the refrigerant delivered from the compressor 2 flows from the outdoor unit to the indoor units 7.

[0031] During the air-heating operation, the first expansion valves 45 expand a refrigerant from the indoor units 7 and send it to the outdoor heat exchangers 4 functioning as evaporators. During the air-cooling operation, the second expansion valves 71 expand a high-pressured cold liquid-phase refrigerant from the outdoor heat exchangers 4 and the receiver 5 so as to reduce the pressure thereof and send it to the indoor heat exchangers 70.

[0032] An engine 1 is provided as a compressor motor, i.e., a prime mover for driving the compressor 2. There is constructed a cooling water circuit 10 in which cooling water heated by absorbing heat of the engine 1 is guided into a radiator 11 so as to be radiated and then returned to the engine 1 for its cooling. An auxiliary circuit 12 reaching a later-discussed auxiliary heat absorber 8 is paralleled to the cooling water circuit 10.

[0033] Description will now be given of a refrigerant circulation cycle during the air-cooling operation in the above-mentioned air-conditioning system.

[0034] A refrigerant is compressed by the compressor (in this embodiment, multi-compressor) 2 so as to become a high-pressured and supersaturated warm vapor which is then pressure-charged to the outdoor heat exchanger(s) 4 through the refrigerant line 20, the four-way valve 3 and the refrigerant line 21. In (each) outdoor heat exchanger 4, the refrigerant, during passing through the cooling fins thereof, is cooled by the cooling wind generated from a cooling fan 41 so as to turn into a high-pressured gas-and-liquid-phase refrigerant. Then, the refrigerant is passed through the refrigerant line(s) 22, the first expansion valve(s) 45 and the refrigerant line 23. On the way of being passed through refrigerant line 23, the refrigerant is retained in the receiver 5 while being supercooled by the supercooler 6. Only the supercooled high-pressured liquid-phase refrigerant is taken out from the receiver 5 so as to be expanded in the second expansion valves 71 and sent to the indoor heat exchangers 70.

[0035] From the refrigerant line 23 to the indoor heat exchangers 70, the refrigerant is passed through an indoor pipe 75. Then, the refrigerant is passed through a return pipe 76 from the indoor heat exchangers 70. However, the generation of bubbles in the refrigerant is restricted during its passing through the indoor pipe 75 because the refrigerant is supercooled. Accordingly, pipes which are diametrically smaller than conventional ones can be used as the indoor pipe 75 and the return pipe 76. Such diametrically small pipes facilitate their bending and enhance the variation of their arrangement.

[0036] The refrigerant passed through the refrigerant line 23, each second expansion valve 71 and the refrigerant line 24 absorbs heat from the indoor air in each indoor heat exchanger 70 so as to be evaporated, thereby cooling the indoor air. Furthermore, each cooler fan 72 generates the wind so as to exert the cooling effect to an indoor space. The refrigerant evaporated in each indoor heat exchanger 70 is passed through the refrigerant line 25 and the four-way valve 3, and then returned to the compressor 2 through the auxiliary heat absorber 8, the accumulator 9 and so on.

[0037] Detailed description will now be given of the supercooler 6 which is disposed in the receiver 5 as shown in Figs. 1 and 2. The extraction line 61 for supercooling extended from the bottom of the receiver 5 is passed through the third expansion valve 62. Then, the extraction line 61 is led into the receiver 5 from the lower portion of the receiver 5 and upwardly extended as a coiled heating tube 60 in the receiver 5 so as to be extended outward from the upper portion of the receiver 5. Then, the extraction line 61 is connected to either a portion of the refrigerant line 26 between the four-way valve 3 and the auxiliary heat absorber 8, as shown in Fig. 1, or the refrigerant line 25 between the four-way valve 3 and the indoor units 7, as shown in Fig. 2. Thus, a part of the liquid-phase refrigerant taken out from the receiver 5 to the extraction line 61 is expanded and cooled by the third expansion valve 62, and then flows through the supercooler 60 so as to supercool the liquid-phase refrigerant in the receiver 5.

[0038] An outlet end of the receiver inflow pipe 51 extended from the first expansion valve 45 is connected to the upper portion of the receiver 5. In the receiver 5, a receiver outflow pipe 52 is extended upward while its bottom inlet end is disposed adjacent to the bottom of the receiver 5.

[0039] In this structure, the high-pressured liquid-phase refrigerant led into the receiver 5 through the receiver inflow pipe 51 flows into the inlet end of the receiver outflow pipe 52 disposed adjacent to the bottom of the receiver 5. This flow is opposite to the upward flow of the refrigerant in the heating tube 60, thereby increasing the supercooling effect thereof with the refrigerant flowing in the heating tube 60.

[0040] Alternatively, the heating tube 60 may be disposed along the inner peripheral surface of the receiver 5 so as to surround the outlet end of the receiver inflow pipe 51 and the receiver outflow pipe 52. Therefore, a radius of the coil of the heating tube 60 is extended to a whole inner radius of the receiver 5 so as to expand its heat-exchanging area with the liquid-phase refrigerant, thereby increasing the supercooling effect.

[0041] Description will now be given of a structure for supporting the heating tube 60 of the supercooler 6 in accordance with Figs. 17 and 18.

[0042] A housing of the supercooler 6, which is the receiver 5 in the embodiments of Figs. 1 and 2, is a supercooling tank 63 in later-discussed embodiments of Figs. 12 to 15. In this way, the supercooler 6 may be constructed in a unit which is separate from the receiver 5. A reference numeral 6 in Figs. 17 and 18 is adaptable to any states where the supercooler 6 is a unit which is different from the receiver 5.

[0043] Along an inside surface of a side wall 5a of the receiver 5 (which may be hereinafter replaced with a side wall 6a of the supercooler 6) is fixedly disposed a plurality of (in this embodiment, three) fixed pipes 5b (6b) in parallel to an axis of the receiver 5 (supercooler 6). The heating tube 60 is coiled at the inward space encircled by the fixed pipes 5b (6b) in the receiver 5 (supercooler 6). Each loop 60a of the coil of the heating tube 60 is fixed to the fixed pipes 5b (6b) by welding or through another member every when it contacts with each fixed pipe 5b (6b). Consequently, each loop 60a is fixed at a plurality positions (in this embodiment, three positions) on its circular shape when viewed in plan.

[0044] Furthermore, every pair of upper and lower adjoining loops 60a are fixed to each other by welding or through another member at each position 60b between the adjoining fixed pipes 5b (6b).

[0045] Due to such a construction, the outer peripheral edge of the heating tube 60 is surely spaced from the side wall 5a of the receiver 5, thereby maintaining the supercooling effect. The assembly of the receiver 5 with the heating tube 60 is increased in its strength so as to have an excellent durability. Also, the strength of the heating tube 60 itself is maintained to be high so that the heating tube 60, even if used for a long time, is prevented from being damaged so as to maintain its excellent supercooling effect.

[0046] Alternatively, rods may replace the fixed tubes 5b (6b) for supporting the coiled heating tube 60.

[0047] Various embodiments wherein the supercooler 6 is a unit that is different from the receiver 5 will be described. As shown in Figs. 12 to 15, in the joint line in the refrigerant line 23 connecting the first expansion valve(s) 45 to the second expansion valves 71 are installed a tandem twin tanks. One tank is the receiver 5. The other is a supercooling tank 63 containing the supercooler 6.

[0048] In Fig. 12. of the twin tanks, one disposed nearer to the first expansion valve(s) 45 is the receiver 5, and the other disposed nearer to the second expansion valves 71 is the supercooling tank 63.

[0049] In this structure, the high-pressured liquid-phase or gas-and-liquid-phase refrigerant sent through the first expansion valve(s) 45 from the outdoor heat exchanger(s) 4 flows into the receiver 5 through the receiver inflow pipe 51 so as to be retained as a liquid-phase refrigerant. Then, the refrigerant flows from the receiver outflow pipe 52 into the supercooling tank 63 through a tank outflow pipe 64 and the upper portion of the supercooler 6. Then, the liquid-phase refrigerant is sent to the indoor units 7 through the refrigerant line 23 from a tank outflow pipe 65, which is extended so as to arrange its lower end in the lower portion of the supercooling tank 63.

[0050] The extraction line 61 for supercooling is extended from the lower portion of the supercooling tank 63. The extraction line 61 is passed through the third expansion valve 63, and then passed through the supercooling tank 63 again so as to be formed therein into the heating tube 60 as mentioned above. Then, as shown in Fig. 2, the extraction line 61 is connected to the refrigerant line 25 connecting the indoor heat exchangers 70 to the four-way valve 3. Alternatively, the extraction line 61 may be connected to the refrigerant line 26, as shown in Fig. 1. The same is true in various embodiments described later.

[0051] In the supercooling tank 63, the flow of refrigerant from the tank inflow pipe 64 to the tank outflow pipe 65 is opposite to that in the heating tube 60, thereby having the excellent supercooling effect. Furthermore, according to the present invention, the extraction line 61 is not branched from an intermediate portion of a circuit but is extended from the lower portion of the supercooling tank 63 so as to stabilize the quantity of the flow of refrigerant and improve the heat exchanging efficiency between the refrigerants, thereby also enhancing the supercooling effect. This structure is especially advantageous for the refrigerant circle regarding the invention,
wherein the ratio of the indoor heat exchangers 70 to the outdoor heat exchanger(s) 4 in number is multiple, because a constantly extracted refrigerant can be supplied to the operated indoor heat exchangers 70 so as to surely maintain a sufficient supercooling effect however the number of the operated indoor heating exchangers 70 may vary.

[0052] In an embodiment of Fig. 13, a twin tanks consisting of the receiver 5 disposed nearer to the first expansion valve(s) 45 and the supercooling tank 63 disposed nearer to the second expansion valves 71 are installed in the joint line of the refrigerant line 23, similarly with Fig. 12. However, the extraction line 61 is extended from the lower portion of the tank of the receiver 5. The extraction line 61 is passed through the third expansion valve 62 and the supercooling tank 63. In the supercooling tank 63, the extraction line 62 is formed into the heating tube 60. Then, the extraction line 61 is connected to the refrigerant line 25 connecting the indoor heat exchangers 70 to the four-way valve 3. In the supercooling tank 63, the flow of refrigerant from the tank inflow pipe 64 to the tank outflow pipe 65 is also opposed to that in the heating tube 60, and the extraction line 61 is extended from the lower portion of the tank of the receiver 5, thereby having an excellent supercooling effect.

[0053] Referring to Figs. 14 and 15, the supercooling tank 63 is disposed nearer to the first expansion valve(s) 45, and the receiver 5 is disposed nearer to the second expansion valves 71. The liquid-phase refrigerant is passed through the first expansion valve(s) 45 from the outdoor heat exchangers 4 and flows into the supercooling tank 63 through the tank inflow pipe 64. Then, the liquid-phase refrigerant is guided into the receiver 5 through the tank outflow pipe 65 and the receiver inflow pipe 51. The liquid-phase refrigerant which has been separated and retained in the receiver 5 flows out from the receiver outflow pipe 52 so as to be sent to the indoor units 7.

[0054] The extraction line 61 for supercooling, which is extended from either the lower portion of the supercooling tank 63 serving as a first tank, as shown in Fig. 14, or the lower portion of the tank of the receiver 5, as shown in Fig. 15, is passed through the third expansion valve 62, and then passed through the supercooling tank 63. In the supercooling tank 63, the extraction line 61 is formed into the heating tube 60. Then, the extraction line 61 is connected to the refrigerant line 25 (26) connecting the indoor heat exchangers 70 to the four-way valve 3. Both the embodiments has a common advantage in stabilization of the quantity of refrigerant flow for improving the heat exchanging between the refrigerants because the flow of liquid-phase refrigerant in the supercooling tank 62 is opposite to that in the heating tube 60 and the extraction line 61 is extended from the lower portion of a tank, thereby having the excellent supercooling effect.

[0055] Furthermore, in the embodiments of Figs. 12 to 15, the permissible voluminal variation in each of the receiver 5 serving as a refrigerant retention tank and the supercooling tank 63 serving as the supercooler 6 is enhanced because they are separated from each other.

[0056] Next, an embodiment of the supercooler 6 using a double-tube heat exchanger will be described in accordance with Fig. 16. In this embodiment, in the joint line of the refrigerant line 23, the receiver 5 for retaining a liquid-phase refrigerant is installed nearer to the first expansion valve(s) 45, and a supercooling tube 67 which has an expanded space is installed nearer to the second expansion valves 71. In this structure, the refrigerant flows into the receiver 5 through the first expansion valve(s) 45 from the outdoor heat exchanger(s) 4 and is separated therein into a liquid-phase refrigerant and a gas-phase refrigerant. The liquid-phase refrigerant is passed through the receiver outflow pipe 52 and flows into a main refrigerant tube 66 which penetrates the supercooling tube 67. Then, the liquid-phase refrigerant is sent to the indoor units 7. The extraction line 61 is extended from a lower portion of the tank of the receiver 5. The extraction line 61 is passed through the third expansion valve 62, and passed through in the supercooling tube 67. In the supercooling tube 67, the extraction line 61 is formed into the heating tube 60. Then, the extraction line 61 is connected to the refrigerant line 25 connecting the indoor heat exchangers 70 to the four-way valve 3. That is, the supercooling tube 67, the main refrigerant tube 66 and the heating tube 60 constitute a double-tube heat exchanger, wherein the flow of refrigerant in the main refrigerant tube 66 is opposite to that in the heating tube 60, thereby having a supercooling effect. Alternatively, the supercooler 6 may be a multi-plate heat exchanger.

[0057] Similarly with the embodiments of Figs. 1 and 2, in the embodiments of Figs. 12 to 16, wherein supercooler 6 is a unit separated from receiver 5, return pipe 55 for air-heating having check valve 47 is interposed between the bottom portion of receiver 5 and the first expansion valve(s) 45. Incidentally, in the embodiments of Figs. 12 and 13, between the tank outflow pipe 65 and the receiver outflow pipe 52 is interposed a return pipe 56 for air-heating, which has a check valve allowing only a flow from the tank outflow pipe 65 to the receiver outflow pipe 52. During the air-heating operation, the refrigerant from the indoor units 7 is passed through the return pipe 56 beyond the supercooling tank 63 so as to be led into the receiver 5. Then, the refrigerant is introduced into the first expansion valve(s) 45 through the return pipe 55.

[0058] In the foregoing structures, the extraction line 61 for supercooling is extended from either the receiver 5 or the supercooling tank 63 in the refrigerant line 23. Alternatively, the liquid-phase refrigerant may be taken out from the outdoor heat exchanger(s) 4, as shown in Fig. 11.

[0059] Referring to Fig. 11, a gas/liquid separator 35 is disposed on the way of each outdoor heat exchanger 4. The gas/liquid separator 35 is connected to the heating tube 60 through the extraction line 61 having an open/close valve 36 and the third expansion valve 62. A portion of the extraction line 61 downstream of the heating tube 60 is connected to the refrigerant line 26 which reaches the accumulator 9.

[0060] In this structure, from the gas/liquid separator 35 is extracted a (e.g., 10 %) refrigerant which has been liquefied already. This separated high-pressured liquid (R134a Rich) is passed through the open/close valve 36 so as to be expanded in the third expansion valve 62, and then passed through the heating tube 60 while supercooling the refrigerant liquid between the receiver inflow pipe 51 and the receiver outflow pipe 52. Thus, it turns into a low-pressured gas-phase refrigerant and then flows into the portion of the extraction line 61 downstream of the heating tube 60 so as to be joined with the low-pressured gas-phase refrigerant in the refrigerant line 26.

[0061] In the embodiment of Fig. 11, temperature sensors 31 and 32 are disposed at an inlet side and an outlet side (during the air-cooling operation) of each indoor heat exchanger 70, respectively, and electrically connected to the second expansion valve 71.

[0062] In this structure, when signals indicating the same temperature are produced by both temperature sensors 31 and 32, it means that a liquid-phase refrigerant passes through the outlet of the indoor heat exchanger 70, that is, the refrigerant insufficiently absorb heat to be vaporized (for air-cooling of the indoor space) from the indoor space. At this time, the second expansion valve 71 is controlled to be further throttled. If the temperature indicated by the signal from the temperature sensor 32 is higher than that from the temperature sensor 31, it means that the refrigerant absorbs sufficient heat from the indoor space in the indoor heat exchanger 70 so as to be vaporized. If the temperature difference exceeds a predetermined value, the opening degree of the second expansion valve 71 is increased so as to increase the quantity of refrigerant which flows therethrough, thereby enhancing the air-cooling effect. By this control, which is a conventional heating-degree controlling manner, low-pressured gas is constantly passed through the refrigerant line 25. The second expansion valves 71 are valves of a conventional type which functions as a throttle only during the air-cooling operation as described and is fully opened during the air-heating operation (during the reverse flowing).

[0063] Furthermore, temperature sensors 33 and 34 for measuring a temperature difference across the third expansion valve 62 are electrically connected to the third expansion valve 62. During the air-cooling operation, the opening degree of the third expansion valve 62 is controlled similarly with each second expansion valve 71 so that a gas-phase refrigerant is constantly passed through a portion of the extraction line 61 downstream of the third expansion valve 62.

[0064] According to the present invention, in the above-mentioned various embodiments of the supercooler 6 and a refrigerant circuit, the opening degree(s) of the first expansion valve(s) 45 is (are) controlled as discussed later.

[0065] The object of supercooling in the air-cooling operation and the problem caused by the supercooling will now be explained in accordance with Fig. 19 and so on. In the Mollier diagram of specific enthalpy in relative to a refrigerant pressure, shown in Fig. 19, a range thereof referred to as "Q1 → Q2" means a pressure increased by the work of the compressor 2. The high-pressured gas-phase refrigerant Q2 delivered by the compressor 2 is cooled in the outdoor heat exchanger 4 serving as a condenser so as to be brought into a gas-liquid equilibrium condition. Extremely, it is cooled to a border between the gas-liquid equilibrium and a liquid-phase (its specific enthalpy is lowered). Then, it is more cooled at a temperature of supercooling degree L1, thereby turning into a perfect liquid-phase refrigerant Q3. The high-pressured liquid-phase refrigerant Q3 is depressed by the second expansion valve 71, thereby turning into a gas-and-liquid-phase refrigerant Q4. Then, the gas-and-liquid-phase refrigerant Q4 absorbs evaporation heat in the indoor heat exchanger 70 so as to be heated, whereby its specific enthalpy is increased as much as the heat so that the refrigerant turns into the low-pressured gas-phase refrigerant Q1 to be absorbed into the compressor 2.

[0066] The increase of specific enthalpy of refrigerant in the gas-liquid equilibrium range referred to as "Q4 → Q1", that is, the amount of heat exchanged in evaporators (the indoor heat exchangers 70) is reflected in the air-cooling capacity. If the supercooling effect with the supercooler 6 is not obtained, the position of Q3 shifts to the border between the gas-liquid equilibrium range and the liquid-phase range rightward from the position thereof illustrated in Fig. 19, thereby shifting the position Q4 rightward as much as the shift of Q3. The increase amount of specific enthalpy of refrigerant in the gas-liquid equilibrium range is reduced as much as the shift of Q4, thereby reducing the air-cooling effect. Conversely speaking, by supercooling (SC), the increasing degree of specific enthalpy of gas-and-liquid-phase refrigerant in the indoor heat exchangers 70, i.e., the amount of heat exchanged in the indoor heat exchangers 70 is increased as much as the supercooling degree L1, thereby enabling the air-cooling effect to be improved.

[0067] However, the increase degree of specific enthalpy of "Q4 → Q1" is constant. Therefore, in comparison with the case without supercooling, the position of Q1 also shifts leftward (more leftward than Q2) as much as the leftward shift of Q4 corresponding to the supercooling degree L1. Thus, in the range "Q1 → Q2", the compressor 2 is necessarily operated to increase the specific enthalpy of Q1 to the predetermined degree of Q2 in addition to its work for increasing the refrigerant pressure. That is, due to this operation, the delivery pressure of the compressor 2 must increase to be lager than that corresponding to the original increase of refrigerant pressure. In this manner, supercooling which improves an air-cooling effect has such a defect that the work of the compressor 2 must be increased so as to increase load on the compressor 2 and the engine 1.

[0068] Furthermore, in the air-conditioning system having the multiple indoor unit 7 as the present embodiments, the degree of supercooling varies according to the number and condition of the operated indoor units 7. Therefore, the operational condition of the compressor 2 must be changed in correspondence to the variation of the supercooling degree. On the other hand, considering the maximum supercooling degree L1 in the condition where the indoor units 7 are operated at their maximum degree, the capacity of the compressor 2 must be set to be very large.

[0069] Therefore, a solution of the problem exists in how to increase the excellent supercooling effect (air-cooling effect) while the work (that is, the delivery pressure) of the compressor 2 is restricted but is secured in its efficiency. Referring to Fig. 19, the delivery pressure of the compressor 2 can be reduced by reducing the pressure difference in the range "Q3 → Q4". This pressure difference may be reduced by enlarging the opening of a valve serving as a throttle valve in the refrigerant circuit to some degree. However, importantly,. the opening thereof must be adjusted while preventing detraction of the supercooling effect. Also, it is required that an air-cooling cycle efficiency "COP", i.e., an operational efficiency is not reduced.

[0070] Considering the representation in Fig. 3, the supercooling degree SC at the inlets of the second expansion valves 71 and the cooling effect (the air-cooling effect) caused by the indoor heat exchange are improved by reducing the opening degree of the third expansion valve 62 (throttling the third expansion valve 62). The supercooling degree SC with the outdoor heat exchanger(s) 4 is increased according to increase of the pressure difference across the third expansion valve 62. Therefore, in order to increase the supercooling degree SC for enhancing the supercooling effect, the third expansion valve 62 is throttled and then a starting end and a last end of the extraction line 61 are desirably connected to the refrigerant line so as to increase the pressure difference across the third expansion valve 62. From this view point, in the above-mentioned supercooling circuit, the starting end of the extraction line 61 is connected to any of the receiver 5, the supercooling tank 63, the gas/liquid separator 35 in the outdoor heat exchanger 4 and the like so as to take out a high-pressured liquid-phase refrigerant. Also, the last end of the extraction line 61 is connected to a refrigerant line through which a low-pressured gas-phase refrigerant is passed, e.g., the refrigerant line 26 as shown in Figs. 1 and 11, or the refrigerant line 25 as shown in Fig. 2, so as to secure a large pressure difference across the third expansion valve 62.

[0071] However, if the pressure difference across the third expansion valve 62 is excessively large in such a condition where the layout of the extraction line 61 and the opening degree of the third expansion valve 62 are determined so as to secure a sufficient supercooling effect, as shown in Fig. 4, the delivery pressure of the compressor 2 becomes large so as to increase load on the engine 1.

[0072] Thus, according to the present invention, the first expansion valve 45, which is essentially used as an expansion valve for air-heating, is utilized for promotion of supercooling and reduction of load on the compressor. That is, in the above-mentioned air-cooling cycle, the first expansion valve 45 interposed between the outdoor heat exchanger 4 and the receiver 5 withstands a free flow of refrigerant from the outdoor heat exchanger 4 to the receiver 5, thereby enabling a high-pressured liquid-phase refrigerant to be adequately stored in the outdoor heat exchanger 4. Thus, the cooling effect of the outdoor heat exchanger 4 can be sufficiently spread to the whole of the refrigerant circuit so as to improve the cooling effect by heat exchange between refrigerants in the supercooler 6 in comparison with a case without the first expansion valve 45.

[0073] By the function of the first expansion valve 45 as a throttle valve, the refrigerant line 22 is throttled during the air-cooling operation so as to completely liquefy the refrigerant at the outlet of the outdoor heat exchanger 4, thereby promoting the cooling, that is, supercooling of the liquid-phase refrigerant in the receiver 5. Of course, the first expansion valve 45 is a two way type valve which also functions as an expansion valve during the air-heating operation.

[0074] When the first expansion valve 45 functions as a throttle valve, the supercooling effect is improved (this effect is shown in Fig. 5). However, a large load is applied on the compressor 2 so as to reduce the operational efficiency because the corresponding refrigerant line is throttled. This relationship is shown in Fig. 6. When the opening degree of the first expansion valve 45 is adjusted so as to be smaller than a standard value, the above-mentioned cooling effect is enhanced so as to increase the air-cooling capacity, thereby increasing the operational efficiency. However, if the opening degree thereof is excessively reduced so as to be smaller than a certain value, the cooling capacity is continuously increased but the operational efficiency COP is reduced.

[0075] Thus, according to the present invention, the opening degree of the first expansion valve 45 is optimally controlled in following manners so as to agree with the two antinomic requirements, of which one is to obtain the supercooling effect and the other is to secure the operational efficiency COP and to reduce load on the compressor 2.

[0076] A first controlling manner will now be described. In this manner, an optimal value of the delivery pressure of the compressor is predetermined so as to avoid a reduction of the operational efficiency while each of supercooling degrees, which are predetermined correspondingly to various operational conditions of the indoor units, is secured. The opening degree of the first expansion valve 45 is controlled while an actual delivery pressure of the compressor is detected at appropriate times so as to compute a difference thereof from the optimal value.

[0077] As shown in Fig. 2, a pressure sensor P1 is installed in the refrigerant line 20 between the compressor 2 and the four-way line 3 so as to detect the actual delivery pressure of the compressor 2. This detected pressure value is input to the controller 16, thereby controlling the first expansion valve 45.

[0078] This controlling manner will be described in accordance with a flowchart of Fig. 8. First of all, the opening degree of the first expansion valve 45 is adjusted to an original degree EV0 set by the controller 16. In this original setting condition, an air-cooling cycle is operated (at a step S11). Next, an actual compressor delivery pressure Pd detected by the pressure sensor P1 is input into the controller 16 (at a step S12). A difference ε of the actual pressure value Pd from a target value of compressor delivery pressure Pd' is calculated (at a step S13). The difference ε is substituted for a variable of a function f for computing a shift value of valve opening degree, thereby determining a shift value of valve opening degree Δ My (at a step S14). The opening of the first expansion valve 45 is controlled according to the determined shift value of the valve opening degree Δ Mv (at a step S15). Then, it is determined whether the supercooling cycle should be continued or not (at a step S16). This control routine is repeated until the actual compressor delivery pressure agrees with the target value.

[0079] According to this controlling manner, the first expansion valve 45 is throttled in the operational efficiency increasing range shown in Fig. 6 so as to enhance the supercooling effect and increase the air-cooling capacity. Then, if the opening degree of the first expansion valve 45 is more reduced so as to increase the compressor delivery pressure, the operational efficiency (COP) is directed to be reduced. Thus, at this time, the controller 16 adjusts the opening degree of the first expansion valve 45 to the optimal value for increasing both the air-cooling capacity and the operational efficiency. When the actual compressor discharging pressure reaches the target value, the reduction of the valve opening degree is stopped so as to prevent a further reduction of the operational efficiency.

[0080] A second controlling manner will be described. The first controlling manner is performed on the basis of the delivery pressure of the compressor concerning the operational efficiency. However, the second controlling manner is performed on the basis of the supercooling degree concerning the air-cooling effect.

[0081] As shown in Fig. 2, a pressure sensor P2 and a temperature sensor T1 are installed in the refrigerant line 22 between the outdoor heat exchanger 4 and the first expansion valve 45. The pressure sensor P2 detects a pressure (a condensation pressure) of the refrigerant flowing out from the outdoor heat exchanger 4. The temperature sensor T1 detects a temperature of the refrigerant flowing out from the outdoor heat exchanger 4. The values detected by the respective sensors P1 and T1 are input into the controller 16. This controlling manner will be described in accordance with a flowchart of Fig. 9. First of all, the opening degree of the first expansion valve 45 is adjusted to an original degree EVO set by the controller 16 (at a step S21). Next, an actual condensation pressure Pc detected by the pressure sensor P2 and an actual outlet temperature Tout detected by the temperature sensor T1 at the outlet of the first expansion valve 45 are input into the controller 16 (at a step S22). Then, the controller 16 computes a supercooling degree SC (at a step S23). The supercooling degree SC is computed as a difference of the outlet temperature Tout from a saturation temperature Tc. Thus, a difference ε of the actual supercooling degree SC from a target value of supercooling degree SC' is calculated (at a step S24). The difference ε is substituted for a variable of a function f for computing a shift value of valve opening, thereby determining a shift value of valve opening degree Δ Mv (at a step S25). The opening degree of the first expansion valve 45 is controlled according to the determined shift value of the valve opening degree Δ Mv (at a step S26). Then, it is determined whether the supercooling cycle should be continued or not (at a step S27). This control routine is repeated until the actual supercooling degree SC at the outlet of the outdoor heat exchanger 4 agrees with the target value.

[0082] Alternatively, the supercooling degree SC at the outdoor heat exchanger 4 may be computed by substitution of a temperature difference across the outdoor heat exchanger 4. That is, as shown in Fig. 2, a temperature sensor T2 is installed in the refrigerant line 21 upstream of the outdoor heat exchanger 4 so as to calculate the temperature difference across the outdoor heat exchanger 4 from the values detected by the temperature sensors T1 and T2, thereby calculating the supercooling degree SC.

[0083] Due to this control, the opening degree of the first expansion valve 45 reduced for increasing the supercooling effect and the air-cooling capacity is adjusted so as to be prevented from being less than a certain value, thereby avoiding the reduction of the operational efficiency. Thus, the opening degree is adjusted so as to establish the optimal supercooling degree allowing both the air-cooling capacity and the operational efficiency to be increased.

[0084] A third controlling manner will be described. In this manner, a border of the pressure difference across the first expansion valve 45 is predetermined. The opening degree of the first expansion valve 45 is adjusted so as to prevent the delivery pressure of the compressor from exceeding a certain value thereof while the supercooling effect being secured.

[0085] Referring to Fig. 7, the air-cooling capacity and the operational efficiency COP are increased according to increase of the pressure difference across the first expansion valve 45. For increasing the pressure difference across the first expansion valve 45, if the pressure at the outlet side of the first expansion valve 45 is reduced, the operational efficiency COP is reduced. Thus, the pressure at the inlet side of the first expansion valve 45 must be increased. For increasing this pressure, the delivery pressure of the compressor 2 must be increased, thereby resulting similarly with that of Fig. 3 concerning the third expansion valve 62. Therefore, the pressure difference across the first expansion valve 45 is not allowed to increase without limitation.

[0086] Then, in addition to the pressure sensor P2, the pressure sensor P3 is installed in the refrigerant line 23 between the first expansion valve 45 and the receiver 5, as shown in Fig. 2. The pressure sensor P3 detects the pressure of the refrigerant which has been passed through the outdoor heat exchanger 4 and the first expansion valve 45. This detection value is input to the controller 16. Briefly, the controller 16 is allowed to calculate the pressure difference across the first expansion valve 45 on the basis of the values detected by the pressure sensors P2 and P3.

[0087] This controlling manner will be described in accordance with a flowchart of Fig. 10. First of all, the opening degree of the first expansion valve 45 is adjusted to an original value EVO set by the controller 16 (at a step S31). Next, the controller 16 calculates an actual pressure difference dPEV across the first expansion valve 45 on the basis of the detection by the pressure sensors P2 and P3 (at a step S32), and calculates a difference ε of the actual pressure difference dPEV from a target discharging pressure difference dPEV' (at a step S33). Accordingly, the controller 16 determines a shift value of valve opening degree Δ My (at a step S34) and controls the opening degree-of the first expansion valve 45 according to the determined shift value of the valve opening degree Δ Mv (at a step S35). Then, it is determined whether the supercooling cycle should be continued or not (at a step S36). This control routine is repeated until the actual pressure difference across the first expansion valve 45 agrees with the target value.

[0088] In this way, the opening degree of the first expansion valve 45 is optimally controlled so as to secure the air-cooling capacity and restrict load on the compressor 2 to be less than a certain degree.

[0089] According to the present invention, the first expansion valve 45 may be controlled by using the first, second and third controlling manners at the same time. For example, both the supercooling degree at the outlet of the outdoor heat exchanger 4 and the pressure difference across the first expansion valve 45 may be detected by the controller 16 so as to adjust the opening degree of the first expansion valve 45 to the optimal value corresponding to both the supercooling degree and the pressure difference.

[0090] As mentioned above, these controlling manners are adaptable to various air-conditioning systems including the respective embodiments of Figs. 1, 2 and 11 to 16 and other supercooling circuits.

[0091] In conclusion, description will be given of the meaning that the extraction line 61 passing through the receiver 5 downstream of the third expansion valve 62 is connected to a portion of the refrigerant line 26 between the four-way valve 3 and the auxiliary heat absorber 8 in the embodiment shown in Fig. 1.

[0092] As mentioned above, the auxiliary circuit 12 is paralleled to the cooling water circuit 10 for the engine 1 so that the cooling water heated by its cooling of the engine 1 is sent to the auxiliary heat absorber 8 through a motor valve 13 so as to exchange its heat with the waste heat of the engine 1, and then returned to the cooling water circuit 10.

[0093] The refrigerant, which is vaporized in the indoor heat exchanger 70 by cooling the indoor air, is returned to the accumulator 9 through the refrigerant line 25, the four-way valve 3 and the refrigerant line 26. However, the refrigerant from the indoor heat exchangers 70 may have a considerably large wetness. At this time, the refrigerant is more vaporized by the waste heat of the engine 1 which is absorbed by the auxiliary heat absorber 8. In combination with the gas/liquid separation with the accumulator 9, this vaporization with the auxiliary heat absorber 8 can surely remove liquid drops from the refrigerant absorbed into the compressor 2.

[0094] However, the wet steam refrigerant sent from the indoor heat exchangers 70 to the auxiliary heat absorber 8, if the pressure thereof is considerably high, is necessarily intercepted by the auxiliary heat absorber 8 so as to reduce the quantity of the refrigerant returned from the indoor units 7. Consequently, the quantity of circulated refrigerant becomes insufficient. Thus, in the embodiment of Fig. 1, there is provided a bypass circuit 80 which bypasses the auxiliary heat absorber 8 and reaches the accumulator 9. A pressure sensor 82 is disposed at the inlet side of the auxiliary heat absorber 8. An electromagnetic valve 81 is installed in the bypass circuit 80. Due to this structure, if the pressure of the wet steam refrigerant led into the auxiliary heat absorber 8 exceeds a predetermined value, the electromagnetic valve 81 is opened so as to allow the wet steam refrigerant to bypass the auxiliary heat absorber 8.

[0095] In this way, during the supercooling cycle in the normal air-cooling operation, the pressure of the refrigerant passing through the heating tube 60 downstream of the third expansion valve 62 is reduced by reduction of the opening degree of the third expansion valve 62, thereby being ready for evaporation. In the supercooler 6, this refrigerant passed through the heating tube 60 supercools the refrigerant from the receiver inflow pipe 51 to the receiver outflow pipe 52, thereby absorbing heat so as to be evaporated and led into the auxiliary heat absorber 8.

[0096] By increasing the opening degree of the third expansion valve 62, this refrigerant is allowed to be liquefied and returned to the extraction line 61 downstream of the heating tube 60. This function causes two effects as follows:

[0097] A first effect will be described. As mentioned above, the wet steam refrigerant flowing from the indoor heat exchangers 70 to the accumulator 9 is further evaporated and expanded in the auxiliary heat absorber 8 by use of the waste heat of the engine 1. However, if the pressure of the wet steam refrigerant led into the auxiliary heat absorber 8 is excessively low, the refrigerant pressure absorbed into the compressor 2 runs short for all effects of the auxiliary heat absorber 8, thereby increasing load on the compressor 2. Then, if the pressure value detected by the pressure sensor 82 becomes less than a predetermined value, the third expansion valve 62 installed in the extraction line 61 of the supercooler 6 is opened. Therefore, a liquid-phase refrigerant is led from the receiver 5 into the refrigerant line 26 through the extraction line 61, thereby flowing into the auxiliary heat absorber 8. This liquid-phase refrigerant is joined with the wet steam refrigerant from the indoor heat exchangers 70 and evaporated in the auxiliary heat absorber 8 so as to be high-pressured, and then, the resultant refrigerant is absorbed into the compressor 2.

[0098] Briefly, even if the pressure of the wet steam refrigerant led into the auxiliary heat absorber 8 is low, the load on the compressor 2 can be lightened by increasing the pressure of refrigerant absorbed into the compressor 2 with utilization of the extraction line 61 and the waste heat of the engine 1.

[0099] Next, a second effect will be described. As mentioned above, during the air-cooling operation, the compressor 2 absorbs a gas-phase refrigerant returned from the indoor heat exchangers 70 and compresses it so as to deliver a high-pressured warm refrigerant to the outdoor heat exchanger(s) 4. However, if the temperature of the high-pressured warm refrigerant is too high, load applied on the outdoor heat exchanger(s) 4 is increased, thereby making its condensation effect insufficient. Furthermore, if the wet steam refrigerant returned from the indoor heat exchangers 70, which will be more vaporized in the auxiliary heat absorber 8 with the waste heat of the engine 1, has few wetness, the gasified refrigerant in the wet steam refrigerant is more heated by absorbing the waste heat of the engine 1, thereby increasing the temperature of the gas-phase refrigerant absorbed into the compressor 2.

[0100] Thus, the temperature of the refrigerant delivered from the compressor 2 is detected by a temperature sensor T3. If the detected temperature is higher than a predetermined value, the third expansion valve 62 is opened so that the liquid-phase refrigerant in the receiver 5 is led into the auxiliary heat absorber 8 through the extraction line 61 and the refrigerant line 26. Consequently, in the auxiliary heat absorber 8, the waste heat of the engine 1 is used for vaporization of this liquid-phase refrigerant from the receiver 5, thereby preventing the temperature of the refrigerant absorbed into the compressor 2 from excessively increasing.

Industrial Possibility of the Invention

[0101] The refrigerant supercooling circuit for a heat pump according to the present invention is adaptable to various types of air-conditioners. Particularly, it is greatly advantageous to air-conditioners used in a building, a factory and the like, wherein a multiple indoor heat exchanger is connected to every one outdoor heat exchanger.

Claims

1. A refrigerant supercooling circuit constructed in a refrigerant circuit of an air-conditioning system used during an air-cooling operation, comprising:

a refrigerant line connecting a first expansion valve downstream of an outdoor heat exchanger to a plurality of second expansion valves upstream of respective indoor heat exchangers;

a receiver for retention of a liquid-phase refrigerant installed in said refrigerant line;

an extraction line for taking out a part of a liquid-phase refrigerant extended from any portion of said refrigerant circuit of an air-conditioning system; and

a third expansion valve installed in said extraction line,

wherein a portion of said extraction line downstream of said third expansion valve is constructed so as to supercool a liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein,

characterized in that an opening degree of said first expansion valve is controlled according to a refrigerant pressure in a refrigerant line connecting a delivery port of a compressor to a directional control valve.

2. The refrigerant supercooling circuit as set forth in claim 1, wherein a portion of said extraction line downstream of said third expansion valve is passed through in said receiver.

3. The refrigerant supercooling circuit as set forth in claim 2, wherein said extraction line takes out said liquid-phase refrigerant from said outdoor heat exchanger.

4. The refrigerant supercooling circuit as set forth in claim 2, wherein said extraction line takes out said liquid-phase refrigerant from said receiver.

5. The refrigerant supercooling circuit as set forth in claim 2, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein said coiled refrigerant tube is supported by a plurality of pipes fixed to an inner wall of said tank.

6. The refrigerant supercooling circuit as set forth in claim 2, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein every adjoining loops of the coil of said refrigerant tube are fixedly jointed to each other.

7. The refrigerant supercooling circuit as set forth in claim 1, further comprising:

a supercooling tank for retaining a liquid-phase refrigerant disposed in tandem with said receiver whether

upstream or downstream of said receiver,

wherein said extraction line takes out said liquid-phase refrigerant from either said receiver or said supercooling tank, and

wherein a portion of said extraction line downstream of said third expansion valve is passed through in said supercooling tank.

8. The refrigerant supercooling circuit as set forth in claim 7, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein said coiled refrigerant tube is supported by a plurality of pipes disposed along an inner wall of said tank.

9. The refrigerant supercooling circuit as set forth in claim 7, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein every adjoining loops of the coil of said refrigerant tube are fixedly jointed to each other.

10. The refrigerant supercooling circuit as set forth in claim 1, further comprising:

a supercooling tube having an expanded space,

wherein a refrigerant line connecting said receiver to said plurality of second expansion valves is passed through in said supercooling tube,

wherein said extraction line takes out a liquid-phase refrigerant from said receiver, and

wherein a portion of said extraction line downstream of said third expansion valve is passed through in said supercooling tube.

11. The refrigerant supercooling circuit as set forth in claim 1, wherein a refrigerant line interposed between said first expansion valve and said receiver is formed into two ways which are connected to upper and lower portions of said receiver, respectively, further comprising:

a check valve installed in one of said two ways connected to said upper portion of said receiver so as to intercept a refrigerant flow from said receiver; and

a check valve installed in the other of said two ways connected to said lower portion of said receiver so as to intercept a refrigerant flow from said first expansion valve.

12. The refrigerant supercooling circuit as set forth in claim 1, wherein said extraction line downstream of said third expansion valve joins to a refrigerant line connecting said plurality of indoor heat exchangers to said directional control valve after supercooling said liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein.

13. The refrigerant supercooling circuit as set forth in claim 1, wherein an auxiliary refrigerant evaporator is installed in said refrigerant line between said delivery port of said compressor and said directional control valve so as to lead cooling water for cooling a prime mover for driving said compressor, and
   wherein said extraction line downstream of said third expansion valve joins to a refrigerant line connecting said directional control valve to said auxiliary refrigerant evaporator after supercooling said liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein.

14. A refrigerant supercooling circuit constructed in a refrigerant circuit of an air-conditioning system used during an air-cooling operation, comprising:

a refrigerant line connecting a first expansion valve downstream of an outdoor heat exchanger to a plurality of second expansion valves upstream of respective indoor heat exchangers;

a receiver for retention of a liquid-phase refrigerant installed in said refrigerant line;

an extraction line for taking out a part of a liquid-phase refrigerant extended from any portion of said refrigerant circuit of an air-conditioning system; and

a third expansion valve installed in said extraction line,

wherein a portion of said extraction line downstream of said third expansion valve is constructed so as to supercool a liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein,

characterized in that an opening degree of said first expansion valve is controlled according to a degree of supercooling at an outlet of said outdoor heat exchanger.

15. The refrigerant supercooling circuit as set forth in claim 14, wherein a portion of said extraction line downstream of said third expansion valve is passed through in said receiver.

16. The refrigerant supercooling circuit as set forth in claim 15, wherein said extraction line takes out said liquid-phase refrigerant from said outdoor heat exchanger.

17. The refrigerant supercooling circuit as set forth in claim 15, wherein said extraction line takes out said liquid-phase refrigerant from said receiver.

18. The refrigerant supercooling circuit as set forth in claim 15, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein said coiled refrigerant tube is supported by a plurality of pipes fixed to an inner wall of said tank.

19. The refrigerant supercooling circuit as set forth in claim 15, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein every adjoining loops of the coil of said refrigerant tube are fixedly jointed to each other.

20. The refrigerant supercooling circuit as set forth in claim 14, further comprising:

a supercooling tank for retaining a liquid-phase refrigerant,said supercooling tank being disposed either upstream or downstream of said receiver so as to be in tandem with said receiver,

wherein said extraction line takes out said liquid-phase refrigerant from either said receiver or said supercooling tank, and

wherein a portion of said extraction line downstream of said third expansion valve is passed through in said supercooling tank.

21. The refrigerant supercooling circuit as set forth in claim 20, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein said coiled refrigerant tube is supported by a plurality of pipes disposed along an inner wall of said tank.

22. The refrigerant supercooling circuit as set forth in claim 20, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein every adjoining loops of the coil of said refrigerant tube are fixedly jointed to each other.

23. The refrigerant supercooling circuit as set forth in claim 14, further comprising:

a supercooling tube having an expanded space,

wherein a refrigerant line connecting said receiver to said plurality of second expansion valves is passed through in said supercooling tube,

wherein said extraction line takes out a liquid-phase refrigerant from said receiver, and

wherein a portion of said extraction line downstream of said third expansion valve is passed through in said supercooling tube.

24. The refrigerant supercooling circuit as set forth in claim 14, wherein a refrigerant line interposed between said first expansion valve and said receiver is formed into two ways which are connected to upper and lower portions of said receiver, respectively, further comprising:

a check valve installed in one of said two ways connected to said upper portion of said receiver so as to intercept a refrigerant flow from said receiver; and

a check valve installed in the other of said two ways connected to said lower portion of said receiver so as to intercept a refrigerant flow from said first expansion valve.

25. The refrigerant supercooling circuit as set forth in claim 14, wherein said extraction line downstream of said third expansion valve joins to a refrigerant line connecting said plurality of indoor heat exchangers to said directional control valve after supercooling said liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein.

26. The refrigerant supercooling circuit as set forth in claim 14, wherein an auxiliary refrigerant evaporator is installed in said refrigerant line between said discharge port of said compressor and said directional control valve so as to lead cooling water for cooling a prime mover for driving said compressor, and
   wherein said extraction line downstream of said third expansion valve joins to a refrigerant line connecting said directional control valve to said auxiliary refrigerant evaporator after supercooling said liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein.

27. A refrigerant supercooling circuit constructed in a refrigerant circuit of an air-conditioning system used during an air-cooling operation, comprising:

a refrigerant line connecting a first expansion valve downstream of an outdoor heat exchanger to a plurality of second expansion valves upstream of respective indoor heat exchangers;

a receiver for retention of a liquid-phase refrigerant, said receiver being installed in said refrigerant line;

an extraction line for taking out a part of a liquid-phase refrigerant, said extraction line being extended from any portion of said refrigerant circuit of an air-conditioning system; and

a third expansion valve installed in said extraction line,

wherein a portion of said extraction line downstream of said third expansion valve is constructed so as to supercool a liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein,

characterized in that an opening degree of said first expansion valve is controlled according to a pressure difference across said first expansion valve.

28. The refrigerant supercooling circuit as set forth in claim 27, wherein a portion of said extraction line downstream of said third expansion valve is passed through in said receiver.

29. The refrigerant supercooling circuit as set forth in claim 28, wherein said extraction line takes out said liquid-phase refrigerant from said outdoor heat exchanger.

30. The refrigerant supercooling circuit as set forth in claim 28, wherein said extraction line takes out said liquid-phase refrigerant from said receiver.

31. The refrigerant supercooling circuit as set forth in claim 28, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein said coiled refrigerant tube is supported by a plurality of pipes fixed to an inner wall of said tank.

32. The refrigerant supercooling circuit as set forth in claim 28, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein every adjoining loops of the coil of said refrigerant tube are fixedly jointed to each other.

33. The refrigerant supercooling circuit as set forth in claim 27, further comprising:

a supercooling tank for retaining a liquid-phase refrigerant,said supercooling tank being disposed either upstream or downstream of said receiver so as to be in tandem with said receiver,

wherein said extraction line takes out said liquid-phase refrigerant from either said receiver or said supercooling tank, and

wherein a portion of said extraction line downstream of said third expansion valve is passed through in said supercooling tank.

34. The refrigerant supercooling circuit as set forth in claim 33, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein said coiled refrigerant tube is supported by a plurality of pipes disposed along an inner wall of said tank.

35. The refrigerant supercooling circuit as set forth in claim 33, wherein a portion of said extraction line in said receiver is constituted by a coiled refrigerant tube, and
   wherein every adjoining loops of the coil of said refrigerant tube are fixedly jointed to each other.

36. The refrigerant supercooling circuit as set forth in claim 27, further comprising:

a supercooling tube having an expanded space,

wherein a refrigerant line connecting said receiver to said plurality of second expansion valves is passed through in said supercooling tube,

wherein said extraction line takes out a liquid-phase refrigerant from said receiver, and

wherein a portion of said extraction line downstream of said third expansion valve is passed through in said supercooling tube.

37. The refrigerant supercooling circuit as set forth in claim 27, wherein a refrigerant line interposed between said first expansion valve and said receiver is formed into two ways which are connected to upper and lower portions of said receiver, respectively, further comprising:

a check valve installed in one of said two ways connected to said upper portion of said receiver so as to intercept a refrigerant flow from said receiver; and

a check valve installed in the other of said two ways connected to said lower portion of said receiver so as to intercept a refrigerant flow from said first expansion valve.

38. The refrigerant supercooling circuit as set forth in claim 27, wherein said extraction line downstream of said third expansion valve joins to a refrigerant line connecting said plurality of indoor heat exchangers to said directional control valve after supercooling said liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein.

39. The refrigerant supercooling circuit as set forth in claim 27, wherein an auxiliary refrigerant evaporator is installed in said refrigerant line between said discharge port of said compressor and said directional control valve so as to lead cooling water for cooling a prime mover for driving said compressor, and
   wherein said extraction line downstream of said third expansion valve joins to a refrigerant line connecting said directional control valve to said auxiliary refrigerant evaporator after supercooling said liquid-phase refrigerant, which is retained in said receiver or flows out from said receiver after being retained therein.

Drawing