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Title:
COMMON UNIT FOR REFRIGERANT GAS HANDLING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2021/037970
Kind Code:
A1
Abstract:
A common unit (10) for a refrigerant gas handling system (1) is described, the common unit (10) comprising an accumulator (4), a check valve (11), and a reversing valve (3). The check valve (11) and the reversing valve (3) are arranged together in a first area and the accumulator (4) is arranged in a second area. Such a system should achieve a good efficiency and a high reliability. To this end, the reversing valve (3) is connected to an actuator, wherein the actuator is arranged in the second area as well.

Inventors:
VAN BEEK JOHAN (DK)
BUSBY BRUCE (DK)
BIRKELUND MICHAEL (DK)
Application Number:
PCT/EP2020/073956
Publication Date:
March 04, 2021
Filing Date:
August 27, 2020
Export Citation:
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Assignee:
DANFOSS AS (DK)
International Classes:
F25B13/00; F25B43/00; F25B43/02
Foreign References:
US20060230770A12006-10-19
EP2290273A22011-03-02
CN206644963U2017-11-17
Attorney, Agent or Firm:
KEIL & SCHAAFHAUSEN PATENTANWÄLTE PARTGMBB (DE)
Download PDF:
Claims:
Claims:

1. Common unit (10) for a refrigerant gas handling system (1), the common unit (10) comprising an accumulator (4), a check valve (11), and a reversing valve (3), wherein the check valve (11 ) and the reversing valve (3) are arranged together in a first area and the accumulator (4) is arranged in a second area, characterized in that the reversing valve (3) is connected to an actuator, wherein the actuator is arranged in the second area.

2. Common unit (10) according to claim 1, characterized in that the first area and the second area are thermically decoupled.

3. Common unit (10) according to claim 1 or 2, characterized in that the actu- ator is a motor (16).

4. Common unit (10) according to any claims 1 to 3, characterized in that the first area is arranged above the second area in the direction of gravity. 5. Common unit (10) according to any of claims 1 to 4, characterized in that the first area and the second area are connected by a tube (13), the tube (13) forming a gas passage, wherein a driving shaft (18) of the actuator extends through the gas passage. 6. Common unit (10) according to any of claims 1 to 5, characterized in that the accumulator (4) forms a main component of the second area.

7. Common unit (10) according to any of claims 1 to 6, characterized in that the actuator is a rotary actuator and that the reversing valve (3) is a rotary valve having an axis of rotation (12), wherein reversing valve (3) can be directly driven by the actuator.

8. Common unit (10) according to claim 7, characterized in that the reversing valve (3) is a 4 way valve or a 5 way valve.

9. Common unit (10) according to claim 7 or 8, characterized in that the check valve (11) comprises a valve element (33) which is movable radially with respect to the axis of rotation (12).

10. Common unit (10) according to any of claims 7 to 9, characterized in that the check valve (11 ) and the reversing valve (13) are together mounted in a hous ing (14), wherein the housing (14) comprises cylindrical wall (15) surrounding the check valve (11 ) and the reversing valve (3).

11. Common unit (10) according to any of claims 7 to 10, characterized in that a plurality of check valves (11) are provided which are distributed in circumferen tial direction around the axis of rotation (12).

12. Common unit (10) according to any of claims 1 to 11 , characterized in that an oil separator (5) is arranged in the first area.

13. Common unit (10) according to claim12, characterized in that the oil sepa rator (5) is arranged around the reversing valve (3).

14. Common unit (10) according to claim 12 or 13, characterized in that the oil separator (5) is arranged above the accumulator (4) in the direction of gravity. 15. Common unit (10) according to any of claims 12 to 14, characterized in that the check valve (11) is arranged between the oil separator (5) and the reversing valve (3). 16. Refrigerant gas handling system (1), characterized in that the refrigerant gas handling system (1) comprises a common unit (10) according to any one of the preceding claims.

Description:
COMMON UNIT FOR REFRIGERANT GAS HANDLING SYSTEM

The present invention relates to a refrigerant gas handling system comprising an accumulator, a check valve and a reversing valve.

Such a refrigerant gas handling system is used, for example, in a variable refrig erant flow system (VRF) or variable refrigerant volume system (VRV), which are sub-groups of air conditioning systems.

In most cases the above-mentioned components are supplied by different sup pliers and are assembled in the place of installation which requires some skill for the installer. Even if they are assembled in a factory, this requires additional work for the manufacturer and added cost.

The object underlying the invention is to achieve a good efficiency and high reli ability of a VRF or VRV system.

This object is solved by common unit for a refrigerant gas handling system with the features according to claim 1.

In the common unit, the check valve and the reversing valve are arranged to gether in a first area and the accumulator is arranged in a second area.

Preferably, the first area and the second area are thermically decoupled.

More preferably, the term "thermically decoupled" means the following: If a tem perature in the first area is 60 °C and a temperature in the second area is 10 °C during operation, a heat transfer from the first area to the second area is less than 1000 W, more preferably less than 600 W, and most preferably less than 450 W. When the check valve and the reversing valve are arranged together in a first area, they can be preassembled thus requiring fewer parts. Joints and assembly time can be saved. The thermically decoupling of the first area and the second area makes the common unit energy efficient, since there is less heat transfer from the first area to the second area.

Furthermore, the reversing valve is connected to an actuator, wherein the actua tor is arranged in the second area. The actuator can be in form of a motor, for example an electric motor. Especially if the first area and the second area are thermically decoupled from each other, the actuator can be arranged in the sec ond area. The first area is adapted to receive refrigerant gas from a compressor at an elevated temperature, since the compression of the gas raises the temper ature of the gas. The second area is adapted to be connected to the suction side of the compressor. At the suction side of the compressor, the refrigerant gas has a somewhat lower temperature. When the actuator is arranged in an area having a lower temperature, this is positive for the lifetime of the actuator and avoids requirements to cope with high temperatures. In other words, the re liability of the system is increased.

The term "hot area" may be used for the first area and the term "cold area" may be used for the second area in order to outline a difference in temperature be tween the two areas during operation.

The first area and the second area are combined in the common unit. The com mon unit is accommodated in a common shell or housing, so that all parts are kept together. Preferably, the shell can withstand several times atmospheric pressure, for example at least twice atmospheric pressure. The shell can com prise a part housing the check valve and the reversing valve, an accumulator shell and a tube connecting the housing and the accumulator shell. The housing part may be designed to be able to withstand a pressure higher than the accu mulator shell. By integrating the components or elements into one unit the indi vidual pressure bearing shells of the various components can be avoided. Such a common unit is produced and supplied by a single supplier, so that the num bers of suppliers can be reduced. The responsibility for such a common unit is at one supplier. Joints and assembly time can be saved. The assembly process is improved. Furthermore, leakage risks are reduced. The less leakages the more energy efficient is the common unit.

Preferably, in operation, the whole common unit is pressurized by the refriger ant. The shell constitutes a common outer pressure shell for the whole common unit. This results in several advantages. The integrated, common unit can be very small compared to usual systems, in which each of the elements has its own pressure shell. Hence, the common unit according to the present invention is considerably less bulky. Furthermore, as only one common pressure shell is necessary, material is saved. The common unit is cheaper to produce and saves resources. Further, it is comparatively light. The common unit according to the present invention facilitates transportation, installation, maintenance, deinstalla tion, and scrapping. Furthermore, as there is only one common pressure shell, the risk of leakages is reduced.

More preferably, a whole interior of the common unit (a whole interior of the common outer pressure shell) is pressurized by the refrigerant during operation. Of course, although there is only one common pressure shell, the interior of said common outer pressure shell can be divided into different areas having different pressures during operation. Especially, the first area can be adapted to be pres surized by a discharge pressure of the compressor, wherein the second area can be adapted to be pressurized by a suction pressure of the compressor. Nat urally, the suction pressure may be considerably less than the discharge pres- sure. The part (of the shell) housing the check valve and the reversing valve may also be denoted as upper shell part.

In an embodiment of the invention, the upper shell part and the tube may be de tachably fixed to each other. This facilitates maintenance. For example, the up per shell part may be detachably fixed with the tube by means of a threaded connection. Especially, the tube may comprise a fixing flange, wherein an outer thread is provided at an outer circumference of the fixing flange. The tube may be at least partially inserted into an insertion space on the upper shell part. The insertion space may be of an at least substantially cylindrical shape. A corre sponding inner thread may be provided at an outer circumference of the inser tion space, for example at a lower axial end of the insertion space. Said lower axial end is the end in an axial direction of the insertion space, which corre sponds to an axial direction of the tube,

Additionally or alternatively, the tube may be detachably fixed to the accumula tor shell. For example, a flange (or a block) may be provided at an upper and of the accumulator shell and a corresponding flange may be provided at a lower end of the tube facing the accumulator shell. The upper end of the accumulator shell is the end facing the tube. The lower end of the tube is the end of the axial direction of the tube facing away from the upper shell part and facing towards the accumulator shell. The flange of the tube may be connected to the flange (or the block) of the accumulator shell by means of a plurality of threaded screws. For example, the threaded screws engage with corresponding threaded holes in the flange (or the block) of the accumulator shell. If the block is provided, the block may be of an at least substantially hollow-cylindrical shape, wherein an upper end face of the block constitutes a flange-like end face. The block may be regarded as a part of the accumulator shell. In a more preferred embodiment, the common unit is configured such that the actuator can be taken out of the accumulator shell when the tube is detached from the accumulator shell. Although the actuator may be located (at least partly) in the accumulator shell when the tube and the upper shell part are fixed to the accumulator shell, the actuator might be fixed to the tube and/or to the up per shell part. Hence, the actuator can be easily removed from the accumulator shell if the tube is detached from accumulator shell. This facilitates the mainte nance and the replacement of the actuator.

In an embodiment of the invention, the first area is arranged above the second area in the direction of gravity. Thus, the first area does not adversely affect the second area by convection. A heat transfer from the first area to the second area can be avoided or be kept at least rather small. This is positive for the en ergy efficiency of the system.

In an embodiment of the invention, the first area and the second area are con nected by a tube, the tube forming a gas passage, wherein a driving shaft of the actuator extends through the gas passage. The tube is used to guide the refrig erant gas from the reversing valve to the second area and at the same time ac commodates the driving shaft. Thus, the actuator can be placed in the second area which influences positively the lifetime of the actuator. By placing the actu ator in the cold area and not outside the shell or the housing, the use of dynamic seals can be avoided.

In an embodiment of the invention, the accumulator forms a main component of the second area. The accumulator can be basically the second area. As men tioned above, the actuator as well as some sensors can be part of the second area. In an embodiment of the invention, the reversing valve is a rotary valve having an axis of rotation. The rotary valve can directly be driven by a rotary actuator. A rotary valve comprises a valve element which can be rotated in relation to a valve housing. Thus, the rotary valve maintains the outer dimension inde pendently of the switching state of the valve.

In an embodiment of the invention, the reversing valve is a 4 or 5 way valve. A 4 way valve has four ports. A 5 way valve has five ports. One port can be con nected to the discharge side of a compressor. One port can be connected to the suction side of the compressor. The remaining two ports can be connected to an indoor heat exchanger and an outdoor heat exchanger. If a 5 way valve is used, the remaining port can be connected to an energy storage system, for example a PCM energy storage system (phase change material energy storage system), an indoor heat exchanger and an outdoor heat exchanger. In such a way it is possible to use the system for heating even in case the outdoor heat exchanger is defrosted. During heating in the common building, the outdoor heat exchanger serves as an evaporator. When it is defrosted neither the indoor heat exchanger nor the outdoor heat exchanger produces suction gas. This task is then handled by sending the condensed refrigerant from both the indoor and the outdoor heat exchanger through the PCM storage system where it absorbs heat.

In an embodiment of the invention, the check valve comprises a valve element which is movable radially with respect to the axis of rotation. Thus, the move ment of the check valve does not require additional space. It is possible to direct the flow of the refrigerant gas radially into the reversing valve.

In an embodiment of the invention, the check valve and the reversing valve are together mounted in a housing, wherein the housing comprises a cylindrical wall surrounding the check valve and the reversing valve. Thus, the housing can have a rather large pressure resistance, however, with a simple construction. In an embodiment of the invention, a plurality of check valves is provided which are distributed in circumferential direction around the axis of rotation. In this way it is possible to minimize the flow resistance of the check valves.

In an embodiment of the invention, an oil separator is provided. This is in partic ular useful in a system needing oil for lubricating, for example, the compressor. The oil separator is used to remove oil droplets or other oil particles out of the flow of refrigerant gas.

In an embodiment of the invention, the oil separator is arranged in the first area. Thus, it can be arranged in the housing surrounding the reversing valve and the check valve. Oil is removed before the refrigerant gas flow enters the reversing valve.

In an embodiment of the invention, the oil separator is arranged around the re versing valve. This makes such a construction compact. There is basically no possibility for the refrigerant gas to bypass the oil separator.

In an embodiment of the invention, the accumulator comprises a U-shaped tube in an interior of the accumulator adapted for sucking refrigerant out of the inte rior of the accumulator. The U-shaped tube can be fluidly connected to an outlet of the accumulator. Said outlet can be adapted to be fluidly connected to the in let of the compressor.

Additionally or alternatively, the accumulator preferably comprises an integrated heat exchange duct extending through the interior of the accumulator. The heat integrated heat exchange duct may comprise an own first fluid port and an own second fluid port. In between the first fluid port of the integrated heat exchange duct and the second fluid port of the integrated heat exchange duct, the inte grated heat exchange tube extends through the interior of the accumulator. The integrated heat exchange duct is adapted to provide heat exchange between a fluid (for example refrigerant) flowing through the integrated heat exchange duct and refrigerant in the interior of the accumulator and/or refrigerant flowing in the U-shaped tube. The fluid flowing through the integrated heat exchange duct may flow from the first fluid port to the second fluid port or vice versa.

As the integrated heat exchange duct extends in the interior of the accumulator, no additional heat exchanger unit must be provided. The accumulator shell is at the same time used as pressure shell for the heat exchange capability. This saves material and weight and reduces the packaging size. It also results in lower costs for production.

Furthermore, a separate heat exchanger would be a further pressure system de vice. The conformity of separate heat exchanger with rules, standards and/or laws, especially regarding pressure resistance, would have to be proven addi tionally. With the mentioned embodiment, this is not necessary. The accumula tor with its accumulator shell must be proven anyhow.

More preferably, the integrated heat exchange duct at least party encompasses the U-shaped tube. This ensures the capability for extensive heat exchange be tween fluid flowing through the integrated heat exchange duct and the refriger ant flowing through the U-shape tub. In addition, this ensures the capability for extensive heat exchange between fluid flowing through the integrated heat ex change duct and the refrigerant, which is in the in the interior of the accumulator but outside the U-shaped tube.

In an embodiment of the invention, the oil separator is arranged above the accu mulator in the direction of gravity. The oil separated from the refrigerant gas flow is driven by a pressure difference between the hot area and the cold area and can flow into the outlet of the U-shaped tube in the accumulator or alternatively into the compressor suction line whereby it is transferred back to the compres sor.

In an embodiment of the invention, the check valve is arranged between the oil separator and the reversing valve. Thus, the oil separator removes oil from the refrigerant gas flow before the gas flow enters the check valve. In summary, this gives a rather compact construction.

A preferred embodiment of the invention will now be described in more detail with reference to the drawing, wherein:

Fig. 1 shows a refrigerant gas handling system,

Fig. 2 shows a common unit of the refrigerant gas handling system,

Fig. 3 shows some elements of the common unit in a larger scale,

Fig. 4 shows a second embodiment of a refrigerant gas handling system,

Fig. 5 shows a common unit of the second embodiment of the refrigerant gas handling system,

Fig. 6 shows some elements of the second embodiment of the common unit in a larger scale,

Fig. 7: shows a third embodiment of a refrigerant gas handling system in heating mode, Fig. 8: is a sectional view through another embodiment of a common unit,

Fig. 9: shows the third embodiment of the refrigerant gas handling system of Fig. 7 in cooling mode,

Fig. 10: is a sectional view through a modification of the embodiment of the common unit shown in Fig. 8, and

Fig. 11 is an enlarged part of Fig. 8 and Fig. 10.

Fig. 1 shows schematically a circuit diagram of a refrigerant gas handling sys tem 1. The system comprises a compressor 2, a reversing valve 3, and an accu mulator 4. Furthermore, an oil separator 5 can be provided. The oil separator 5 can be omitted when an oil-free system is used.

The system furthermore comprises a number of indoor heat exchangers 6 which can, for example, be arranged in a common building 7, and an outdoor heat ex changer 8. Furthermore, a phase change material energy storage 9 can be pro vided.

Fig. 1 shows a condition of the system 1 relating to cooling. Refrigerant gas which is compressed by the compressor 2 is guided to the outdoor heat ex changer 8 in which heat is removed from the compressed refrigerant gas and the refrigerant gas is converted into a refrigerant liquid. The refrigerant is guided to the indoor heat exchangers 6 in which it receives heat from the room to be cooled and then fed back to the accumulator.

When heating is required, the reversing valve 3 is actuated to connect the out put of the compressor 2 to supply hot refrigerant gas to the indoor heat ex changers 6. This hot refrigerant gas transfers heat to the room to be heated and is then guided back to the accumulator 4 via the outdoor heat exchanger 8. At the same time, it is possible to direct some of the hot refrigerant gas flow to the energy storage 9 so that heat energy is available during a period in which the outdoor heat exchanger 8 is defrosted. This improves user comfort in the build ing 7.

When the reversing valve 3 is actuated to be moved in the third position, the output of the compressor 2 is connected to the indoor heat exchanger 6 and at the same time to the outdoor heat exchanger 8 to defrost the outdoor heat ex changer 8. The energy in the phase change material is used to be absorbed by the liquid refrigerant entering the energy storage 9, so that suction gas is pro duced.

Fig. 2 shows a common unit 10 with which some of the functions mentioned above can be realized.

The common unit 10 comprises the accumulator 4, the oil separator 5, the re versing valve 3 and a check valve 11 opening a direction towards the reversing valve 3. As can be seen in fig. 2 and 3, a plurality of check valves 11 can be pro vided instead of a single check valve. The check valves 11 are distributed in cir cumferential direction around the reversing valve 3.

The reversing valve 3 is a rotary valve which can be rotated around an axis of rotation 12. It is a 5 way valve, as explained above. An embodiment having a 4 way valve is shown in Fig. 7 and explained below.

The accumulator 4 is connected to a tube 13 which extends into a housing 14. The check valve 11 and the reversing valve 3 are together mounted in this hous ing 14, wherein the housing 14 comprises a cylindrical wall 15 surrounding the check valve 11 and the reversing valve 3. The reversing valve 3 is actuated by means of an actuator, for example in form of an electric motor 16, in particular in form of a stepper motor. The motor 16 can be connected to the reversing valve 3 via a gearbox 17 having a transmis sion ratio of, for example, 1:100. A driving shaft 18 of the motor-gearbox-unit 16, 17 is guided through the tube 13 to the reversing valve 3. The tube 13 at the same time forms a gas passage from the reversing valve 3 to the accumulator 4.

The housing 14 comprises a first port 19 which is connected to the discharge side of the compressor 2. Furthermore, the housing comprises two more ports 20, 21 which can be connected to the indoor heat exchanger 6 and the outdoor heat exchanger 8. A further port is provided (not visible) to connect the reversing valve 3 to the energy storage 9.

The oil separator 5 is arranged around the reversing valve 3. The check valve 11 (or the check valves 11 ) is arranged between the oil separator 5 and the reversing valve 3.

The housing 14 furthermore comprises a high-pressure transmitter 22. A low- pressure transmitter 23 can be provided at the accumulator.

The accumulator 4 is provided with a port 24 which is connected to the suction side of the compressor 2. The port 24 is formed by an end of a tube 25 which is U-shaped. The housing 14 forms a first area which can be termed "hot area", since it receives hot discharge gas from the compressor 2. The accumulator 4 forms a second area which can be termed "cold area", since it receives a refrig erant gas from the indoor heat exchanger 6 or from the outdoor heat ex changer 8 having a somewhat lower temperature. The first area including housing 14 is arranged above the second area including accumulator 4 in the direction of gravity. Thus, heat transferred from the hous ing 4 to the ambient air cannot be transferred to the accumulator 4 by direct con vection. In addition, due to the distance between the housing 14 and the accu mulator 4, the heat transfer by radiation is rather small. Furthermore, this en sures that particles, oil and liquid refrigerant drops can automatically move into the accumulator 4.

When an oil separator 5 is provided, the housing 14 comprises an oil sump 26 which is connected via a capillary tube 27 to the U-shaped tube 25 in the accu mulator 4.

A line 28 shows the path of a flow of hot refrigerant gas from the compressor 2 through the first area. The flow passes the oil separator 5 which surrounds the reversing valve 3 and the check valve 11. Thereafter, the gas flows to the desti nation defined by the reversing valve 3. A line 29 shows the path of the flow coming back from the indoor heat exchanger 6. Gas flows through the tube 13 into the accumulator 4. This gas flow is basically oil-free. It enters the end of the U-shaped tube 25 in the accumulator 4 opposite to the port 24. This end is lo cated near the first area, i.e. near housing 14. An oil return opening 46 is lo cated in a lower part of the U-shaped tube 25.

Thus, the accumulator 4, the check valve 11 and the reversing valve 3 are inte grated in the common unit 10. This common unit 10 can be produced by a single supplier and it is not necessary to produce joints or connections between com ponents in the place where the components are needed. These joints and con nections can be produced in a factory, can be checked before delivery and have a higher degree of reliability. The oil separator 5 can work in different modes, for example with centrifugal force, with flow speed reaction and gravity, with impact in sponge and fine mesh, or with a splash plate. Of course, these possibilities can be combined and the list of possibilities is not exhausting. Further possibilities can be used.

An air gap 30 is provided between the tube 13 and the housing 14. This air gap 30 forms a further thermal barrier between the first or hot area and the sec ond or cold area.

The motor 16 together with the gear 17 is accommodated in a motor housing 31. The motor housing 31 is surrounded by a spring 32 in a direction towards the re versing valve 3. Thus, the driving shaft 18 produces a force pressing a rotary valve element 33 of the reversing valve 3 against a seal 34 provided at a front face of the rotary valve element 33. The spring 32 is supported by a carrier 35 fixed to the U-shaped tube 25 in the accumulator.

The valve 33 element is preferably made of plastic material. This improves ther mal insulation between cold and hot gas flow.

The tube 13 comprises a number of openings 36 so that the interior of the tube 13 is connected to the interior of the accumulator 4. Gas can flow out of the tube 13 into the accumulator 4.

Fig. 4 to 6 show a second embodiment of a refrigerant gas handling system. Same elements are denoted with the same reference numerals as in fig. 1 to 3.

The second embodiment is an oil free system, i.e. the compressor 2 supplies the refrigerant gas directly to the reversing valve 3. Thus, as shown in fig. 5, the gas flow entering the housing 14 via the first port 19 flows directly into the reversing valve 3. Other means related to the oil separation, like the oil sump 26 and the capillary tube 27, can be omitted as well.

Fig. 7 shows a third embodiment of a gas handling system which is similar to the system shown in fig. 1. The same elements are denoted with the same refer ence numerals.

The first difference to the embodiment shown in fig. 1 is that the reversing valve 3 is a 4 way valve having four ports. Two of the ports are connected to the accu mulator 4 and to the oil separator 5. The other two ports are connected to a group of indoor heat exchangers 6 and to an outdoor heat exchanger 8. In this embodiment there is no energy storage 9.

The accumulator 4 is provided with a heat exchanger arrangement 37 which is explained in more detail with reference to fig. 8.

Fig. 7 shows the flow during heating mode. The heat exchange in the accumula tor 4 ensures that the refrigerant is subcooled and thereby enters the outdoor heat exchangers 8 as subcooled refrigerant before it is expanded into the out door heat exchanger 8. From the outdoor heat exchanger 8 it will flow into the accumulator 4 and from there it flows to the compressor 2. When it is very cold outdoor an injection valve 38 next to a liquid burst valve 39 will become active and part of the refrigerant from the indoor heat exchangers 6 will be expanded into the accumulator 4 and mix with refrigerant from the outdoor heat exchanger 8. This provides additional cooling of the suction gas whereby overheating of the compressor 2 can be avoided. The problem of overheating of the compressor 2 can occur during very cold weather (-20 degrees C). Only 5 to 10 % of the flow from the indoor heat exchangers 6 goes through the injection valve 38. The liq- uid burst valve 39 is a safety valve that opens if the pressure in the piping be comes too high. This can happen when the valves before the indoor heat ex changers 6 and the outdoor heat exchanger 8 are closed, whereby liquids in the piping becomes trapped.

A possible way to realize such a heat exchanger arrangement 37 is shown in fig. 8.

The tube 13 between the accumulator 4 and the housing 14 has been reinforced by means of block 40 which can accommodate the injection valve 38 and the liq uid burst valve 39 and can accommodate the actuator 16 as well. The U-shaped tube 25 is provided with sleeves 41, 42 on the vertical legs so that a ring-shaped channel 43, 44 is formed around each leg. Refrigerant can be fed into the chan nels 43, 44 and flows vertically along the vertical legs of the U-shaped tube 25.

The channels 43, 44 can be connected at the lower ends by means of a con necting tube 45. The connecting tube 45 allows additional heat exchange be tween the refrigerant flowing through its inside and the refrigerant in the interior of the accumulator 4 that encompasses the connecting tube 25.

The fluid channel for heat exchange within the accumulator 4, which extends through the interior of the accumulator 4 and at least partially encompasses the U-shaped tube 25, may be called "integrated heat exchange duct". In this case, the integrated heat exchange duct is constituted by the vertical channels 43, 44 and the connecting tube 45.

The large area of the surfaces of the integrated heat exchange duct ensures that a large amount of heat can be exchanged within the accumulator 4. Fig. 10 shows a modification of the heat exchanger arrangement 37 shown in fig. 8. The only difference is that the fluid ports 43a, 44a for the channels 43, 44 are within the section plane and hence can be seen in fig. 10. For example, the refrigerant can enter through a first fluid port 43a, flow downwardly in the chan- nel 43, further flow from the channel 43 through the connecting tube 45 into the channel 44, flow upwardly in the channel 44, and then flow out through a second fluid port 44a. By switching between the heating mode and the cooling mode, a direction of flow through the integrated heat exchange duct is reversed. Fig. 9 shows the flow in the refrigerant gas handling system of Fig. 7 during cooling mode. Switching the 4 way valve 3 from a first state shown in Fig. 7 to a second state shown in Fig. 9 causes switching from the heating mode to the cooling mode and vice versa. In the cooling mode, the refrigerant flowing out from the outdoor heat exchanger 8 flows through the integrated heat exchange duct. Thereby, the liquid refrigerant from the outdoor heat exchanger 8 ex changes heat with the refrigerant within the accumulator 8.

The temperature of the refrigerant entering the compressor 2 should be suffi ciently above a saturation temperature of the refrigerant in order to avoid that liquid refrigerant reaches the compressor 2 or condenses within the compres sor 2. Otherwise, the compressor 2 could be damaged. If the temperature of the refrigerant flowing through the U-shaped pipe 25 towards the compressor is low, this increases the risk that liquid refrigerant reaches the compressor 2 and/or condenses in the compressor 2. Flowever, when the refrigerant gathering in the interior of the accumulator 4 and flowing through the U-shaped tube 25 is cold, it is heated by the refrigerant from the outdoor heat exchanger 8 that flows through the heat exchange duct (inside the channels 43, 44 and the connector 45). Thus, the integrated heat exchange duct helps to ensure that the tempera ture of the refrigerant entering the compressor 2 has a temperature above the saturation temperature of the refrigerant and that no liquid refrigerant can dam age the compressor 2. On the other hand, the heat exchange within the accu mulator 4 enhances subcooling of the refrigerant flowing to the indoor heat ex changers 6.

In the heating mode shown in Fig. 7, under normal conditions, the temperature of the gaseous refrigerant from the outdoor heat exchanger 8 arriving at the ac cumulator 4 is lower than the temperature of the liquid refrigerant from the in door heat exchangers 6 flowing through the integrated heat exchange duct within the accumulator 4. Hence, also in this case, the refrigerant gathering in the interior of the accumulator 4 and flowing through the U-shaped tube 25 is heated by the heat exchange within the accumulator 4. Again, the integrated heat exchange duct helps to ensure that the temperature of the refrigerant en tering the compressor 2 has a temperature above the saturation temperature of the refrigerant and that no liquid refrigerant can damage the compressor 2. On the other hand, the heat exchange within the accumulator 4 enhances subcool ing of the refrigerant flowing to the outdoor heat exchanger 8.

In the embodiment shown in Fig. 8 and its modification in Fig. 10, the tube 13 is detachably fixed to the accumulator 4. This is explained with regard to Fig. 11. Fig. 11 shows an enlarged part of Fig. 8 and Fig. 10 including the tube 13.

The tube 13 extends along an axial direction. At a lower end in the axial direc tion, the tube 13 comprises a terminal flange 61 for fixing the tube 13 to the ac cumulator 4. At its upper end in the axial direction, the accumulator 4 comprises the block 40 which is firmly and sealingly fixed to a shell of the accumulator 4. The block 40 is of basically hollow-cylindrical shape. The terminal flange 61 of the tube 13 abuts on an upper end face of the block 40. Several threaded screws (not shown) are inserted from above through the terminal flange 61 of the tube 13 and engage threaded holes (not shown) provided in the block 40. By this, the terminal flange 61 is detachably fixed to the block 40 and hence to the accumulator 4. A sealing 62 may be provided to seal between the block 40 and the tube 13 when the tube 13 is fixed to the block 40.

Further, the tube 13 is detachably fixed to the housing 14, which houses the 4- way valve 3 and the check valves 11. In more detail, an insertion space 50 re ceiving an upper part of the tube 13 is provided in the housing 14. The insertion space 50 is of basically cylindrical shape. It is surrounded by a sleeve-like inner wall 51 , which is part of the housing 14. The inner wall 51 constitutes an inner wall of the housing 14. At a lower end 52 of the insertion space 50 (and hence on a lower end of the inner wall 51 ) in the axial direction, an inner thread is pro vided. A fixing flange 63 for detachably fixing the tube 13 to the housing 14 is provided at an outer circumferential surface of the tube 13. A corresponding outer thread is provided at an outer circumferential surface of the fixing flange 63. Hence, the outer thread of the fixing flange 63 and the inner thread at the lower end 52 of the insertion space 50 engage and hence form a threaded con nection 60. The tube 13 is detachably fixed to the housing 14 by this threaded connection 60.

At (or at least near to) an upper end of the tube 13 in the axial direction, an abutment flange 64 is provided on the tube 13. If the tube 13 is fixed to the housing 14, the abutment flange 64 abuts an annular shoulder 53 formed at the wall of the insertion space 50 (i.e. a radially inner surface of the inner wall 51 ). A sealing 65 for sealing between the wall of the insertion space 50 and the tube 13 is provided at an outer circumferential surface of the abutment flange.

It can be seen in Fig. 11 that the driving shaft 18 extends along the axial direc tion in an interior of the tube 13. The motor-gearbox-unit 16, 17 is connected to the driving shaft 18. The motor-gearbox-unit 16, 17 is positioned in the accumu lator 4. In particular, an upper part of the motor-gearbox unit 16, 17 is located within an interior of the block 40, wherein a lower part of the motor-gearbox unit 16, 17 with the motor 16 extends further into the interior of the accumula tor 4. The motor-gearbox unit 16, 17 is not directly fixed to the accumulator 4. In fact, the motor-gearbox-unit 16, 17 is fixed to the tube 13. In more detail, it is fixed to the lower end of the tube 13 by means of several threaded screws 66 engaging corresponding threaded holes provided in the lower end of the tube 13. If the tube 13 is detached from the accumulator 14, the motor-gearbox-unit 16, 17 is removed from the accumulator 4 as well. This facilitates maintaining the motor-gearbox-unit 16, 17 and replacing it, if necessary.

If the tube 13 is fixed to the housing 14 and if the tube 13 is fixed to the accumu lator 4, the housing 14, the tube 13 and the shell of the accumulator 4 form a common shell for the whole common unit. In operation, the whole interior of the common shell is pressurized by the refrigerant. The interior of the accumulator 4 is fluidly connected to the inlet of the compressor 2. In operation, the pressure in the interior of the accumulator 4 becomes an inlet pressure (suction pressure) of the compressor 2. The first area (hot area), which is enclosed within the hous ing 14, is fluidly connected to the discharge outlet of the compressor 2. In opera tion, the pressure in the first area becomes a discharge pressure of the com- pressor 2. Naturally, the discharge pressure is considerably higher than the suc tion pressure. In operation, the interior of the tube 13 is pressurized as well as it is in fluid connection with the interior of the accumulator 4.