WO2010116388A1

WO2010116388A1 - Screw compressor specially suitable to be connected in parallel in compression units

Info

Publication number: WO2010116388A1
Application number: PCT/IT2009/000145
Authority: WO
Inventors: Stefano Bazzato
Original assignee: Refcomp Spa
Priority date: 2009-04-06
Filing date: 2009-04-06
Publication date: 2010-10-14
Also published as: EP2417357A1; CN102428276A

Abstract

Compressor comprising a body (2) in which it is possible to identify: an intake (3) for a fluid made up of a mixture of gas (G) and auxiliary fluid (L); compression means (5) located downstream of the intake (3); a separation chamber (6) downstream of the compression means (5) to separate the gas (G) from the auxiliary fluid (L); a duct (7) placing the area (54) downstream of the compression means (5) in communication with the separation chamber (6); an auxiliary circuit (8) comprising a pipe (81) connected between the separation chamber (6) and the area (53) upstream of the compression means (5) that makes the auxiliary fluid (L) return into the compression means (5); a delivery outlet (4) connected to an outlet duct (102) of the compressed gas (G). A check valve (10) is inserted in the duct (7) that places the compression means (5) in communication with the separation chamber (6) and a solenoid valve (11) is inserted in the pipe (81) of the auxiliary circuit (8).

Description

SCREW COMPRESSOR SPECIALLY SUITABLE TO BE CONNECTED IN PARALLEL IN COMPRESSION UNITS

The invention concerns an improved volumetric compressor particularly suited to be included in an air conditioning or refrigeration system for adjusting and lowering the temperature inside closed spaces.

The invention also concerns a compression unit obtained by connecting two or more of the above mentioned compressors in parallel.

Finally, the invention concerns the air conditioning or refrigeration system comprising said compression unit.

It is known that in many situations, for example, there is the need to use refrigeration systems for adjusting and lowering the temperature inside closed spaces.

In particular, in the case of cold rooms or IT rooms it is necessary to keep the temperature at a certain level in order to be able to preserve degradable products as long as possible, in the first instance, and to prevent the overheating of the electronic devices, so as to guarantee their maximum functionality, in the second instance.

The above mentioned refrigeration systems substantially comprise one or more compression devices, which in technical jargon are called compressors, which pressurize a refrigerant fluid and allow it to circulate through a plurality of pipes belonging to the system itself and arranged in the closed places to be cooled.

It is also known that in many cases, in order to carry out a refrigeration system characterized by a simple and linear configuration, a single compression device is provided, which is adjusted by means of a control device that in technical jargon is called "inverter".

In other types of compressors, instead of the inverter device slide valves are employed, which are arranged inside the compressor itself and make it possible to adjust the flow rate of the fluid to be compressed in a mechanical manner.

This alternative, however, poses a major drawback represented by the fact that the adjustment of the flow rate of the fluid exiting the compressor does not allow a precision level to be obtained that can be compared to that guaranteed by the use of the inverter. A further method for adjusting the flow rate of the fluid exiting the compressor consists in the use of the so-called "bypass'-system.

This system allows part of the compressed fluid to be returned into the compressor, in such a way as to limit the quantity of the above mentioned fluid introduced in the refrigeration circuit.

Also in this case the adjustment is not so precise as the adjustment carried out through inverter and in addition there is a loss in performance due to the fact that a portion of fluid is compressed which successively is not used by the conditioning or refrigeration cycle, As far as the inverter device is concerned, in particular, it makes it possible to modulate the amplitude and frequency of the electric signal suited to control the compressor device, in such a way as to vary its operating speed and thus permit differentiation of the flow rate of the refrigerant fluid that passes through the already mentioned pipes. The above mentioned variation of the flow rate of the refrigerant fluid makes it possible, in fact, to modify the level of the temperature set inside a closed place, and thus to make the entire refrigeration system easy to control and adjust with greater precision.

This need occurs, for example, in IT rooms, due to the fact that the entire range of the processing devices is inserted and arranged inside them within a time interval that in most cases isn't less than one year.

In this situation, in fact, during the starting period there is no need to operate the refrigeration system at its maximum rated power.

In particular, at the beginning the refrigeration system is started at a predefined base temperature and then the temperature is changed gradually until reaching the rated operating conditions, when all the electronic devices have been arranged as planned.

The configuration described above and said operating mode of the refrigeration system, and in particular of the compressor, however, pose some serious drawbacks that are described here below.

A first drawback is related to the high cost of the inverter device used for adjusting the high power compressors used in these particular refrigeration systems.

In general, in fact, the commercial cost of an inverter device increases almost exponentially with the increase of the maximum power of the compressor. A second important drawback lies in that energy consumption and heat dissipation in a compressor are higher when the latter works at a lower rate compared to the rated operating conditions. Therefore, the continuous presence of the said drawbacks has led most manufacturers of said refrigeration systems to replace the single compressor, which has a given maximum power, with two compressors connected in parallel, each one of which has half the power than the compressor described in the previous example. This system is configured by connecting with each other, respectively, the intakes and the delivery outlets of the two compressors, in such a way as to obtain a compression power substantially identical to that of the configuration described above, with the advantage of overcoming the mentioned drawbacks. In particular, it is possible to overcome the problem represented by the high cost of the inverter used for controlling the two compressors, since each of them has a maximum rated power that is half the power of the single compressor.

Furthermore, the above mentioned refrigeration systems are used for most of the time at maximum power and therefore with both compressors working at full rate, or with half power, which means with one compressor working at the maximum rated value and the other completely at rest.

Furthermore, there are transition operating periods, like for example during the start of an IT room, during which there is the need to modulate and adjust the power of the above mentioned system between the minimum value and 50% of the maximum rated value. Therefore, it is clear that with this configuration it is sufficient to include a single inverter device applied to one of the two compressors, thus ensuring further savings thanks to the absence of the other inverter.

Furthermore, the fact that the system operates for most of the time at full power with both compressors on or, alternatively, at half power, which means with only one compressor working at the maximum rated power, ensures considerable savings in terms of energy consumption and heat dissipation, compared to the intermediate operating conditions that occur with the configuration with one compressor only, as previously described. It is also known that in order to be able to connect two compression devices in parallel it is necessary to take some measures in order to avoid any general malfunctioning of the whole refrigeration system.

In particular, in the case where the compression devices are volumetric screw compressors, it is necessary to configure the above mentioned system, called "tandem" system, adopting the measures that are described in greater detail below.

First of all, in order to be able to understand the techniques for connecting two screw compressors in parallel, it is important to describe the structure of a single volumetric screw compressor. The above mentioned compressor substantially comprises a body made of a metallic material, on which it is possible to identify an intake and a delivery outlet connected at the inlet and at the outlet to the rest of the refrigeration system.

Furthermore, the metallic body comprises, in its internal part, compression means that, as already mentioned, in the form considered herein are constituted by one or more screws.

The above mentioned one or more screw/s presents/present, at the level of its/their ends, which are hinged to the metallic body of the compressor, bearing-shaped means that allow the screws themselves to rotate around their longitudinal axis. In particular, said compression means may comprise a single compression rotor, which in technical jargon is called "single screw", or can be carried out with two screws meshing with each other.

It cannot be excluded that in different embodiments said compression means may be provided with more than two screws. The function of the above mentioned compression means is to receive, at the inlet, a low pressure fluid and compress it so that at the outlet its pressure is much higher.

Said outlet of the compression means is connected, through a duct, with a separation chamber in which the substances that make up the above mentioned high-pressure fluid are separated.

In fact, the fluid that reaches the inlet of the compression means is constituted by the refrigerant gas that successively flows through the refrigeration system and by an auxiliary fluid that is necessary to lubricate, among the other things, the above mentioned bearings, so as to reduce frictio, and cool them, since they heat up during rotation, and finally to guarantee the tightness of the meshing screws.

In particular, in the construction form considered herein, said auxiliary fluid is oil.

This separation process, therefore, is extremely important, due to the fact that, as already explained above, the refrigerant gas flows out through the delivery outlet of the compressor positioned downstream of the separation chamber and is introduced in the refrigeration system, while the auxiliary fluid is conveyed in such a way as to make it return to the beginning of the compression cycle through an auxiliary circuit that connects the above mentioned separation chamber with the inlet of the compression means.

The displacement of both the refrigerant gas from the compressor to the pipes of the system and the auxiliary fluid from the separation chamber to the inlet of the compression means takes place due to the pressure difference that is created between the various rooms. In practice, the auxiliary fluid is conveyed from the high pressure area, constituted by the separation chamber, to the low pressure area, which coincides with the inlet of the compression means.

The auxiliary circuit is provided with at least one tank suited to store the auxiliary fluid present inside the compressor. The characteristics of a volumetric screw compressor having been defined, it is now possible to describe the necessary measures that must be adopted in order to be able to connect two or more of the above mentioned compression devices with each other.

A first problem that occurs following the above mentioned parallel connection is the return of the refrigerant gas flowing out of the delivery outlet of a compressor towards the delivery outlet of a second compressor in the direction opposite the normal operating direction.

This situation may occur at the moment when one of the two compressors connected in parallel is in operation and the other one is off. In particular, the area corresponding to the outlet of the functioning compressor is under high pressure while the area of the delivery outlet of the compressor that is not in operation is under low pressure and therefore, as we have already seen, the gas tends to flow from the first to the second.

This may cause the introduction of the above mentioned refrigerant gas inside the compressor that is off, also causing the rotation of the compression means in the direction opposite the normal operating direction.

This situation may cause the above mentioned compression means to seize, making it necessary to replace the pieces.

In order to avoid this inconvenience, downstream of the delivery outlet of each compressor there is a check valve that allows only the compressed gas to flow out and prevents any flow in the opposite direction.

A second problem that may occur with this type of compressors connected in parallel derives from the fact that the separation of the auxiliary fluid from the refrigerant gas inside the separation chamber doesn't take place in a perfect manner.

This means that inside the refrigerant gas that flows into the system pipes there may be a small quantity of auxiliary fluid that successively, at the end of the cooling cycle, returns again inside the compressor.

In the case where both compressors are on, it may happen that due to slight differences in their operation, and therefore slight differences in the pressure values, said small quantity of auxiliary fluid returns into one compressor only.

In the long term, the continued and repeated occurrence of this situation may cause a diversification in the level of the auxiliary fluid present in the compressors, running the risk of making one of them seize. In order to solve said problem, it is therefore necessary to connect the sumps of the compressors with each other through a pipe, in such a way as to exploit the principle of the communicating vessels and therefore avoid any difference between the two levels.

The execution of the said operation allows the problem represented by the levels of the auxiliary fluid to be solved, but on the other hand poses another drawback that takes place when one of the two compressors is at rest.

In fact, inside the compressor in operation the auxiliary fluid separated from the gas, as already mentioned, tends to flow towards the low pressure area.

In this case, since the two sumps are connected with each other, the auxiliary fluid, in addition to returning upstream of the compression means through the auxiliary circuit, tends to flow into the sump of the compressor that is at rest through the above mentioned connection pipe.

If this situation persists, there is a higher risk that the auxiliary fluid runs out at the level of the compressor in operation, which would make the latter seize. Furthermore, a second negative effect lies in that the excess auxiliary fluid accumulated in the sump of the compressor at rest tends to flow upstream of the compression means through the auxiliary circuit, due to the already mentioned pressure difference.

The above mentioned excess auxiliary fluid may cause permanent damage to the mechanical elements at the moment when the compressor, previously at rest, is re-started with the rotation of the compression means. In order to overcome these drawbacks, according to a known construction form, a stop valve is arranged at the level of the above mentioned pipe connecting the two sumps, and said stop valve is activated when one of the two compressors is off, in such a way as to prevent the passage of the auxiliary fluid.

In particular, in this situation, due both to the considerable size of the diameter of the connection pipe, and to the fact that there is no pressure difference between the two sumps at the moment when both compressors are in operation, the valve cannot be of the solenoid type.

In this case, in fact, it is necessary to use a more complex and consequently more expensive valve, like for example powered and/or servo assisted valves. Therefore, the high cost of the above mentioned type of valves, necessary for the correct operation of a system with more than one compressor, represents a major drawback of the known art.

Furthermore, should said valve not work properly, there would be no other safety device suited to prevent the passage of auxiliary fluid from one compressor to the other. A further drawback of the construction form just described is constituted by the rather complicated and articulated system used for connecting two compressors.

The present invention aims to overcome the drawbacks listed above. In particular, it is a first object of the invention to develop a volumetric compressor that can be connected in parallel to other compression devices of the same type with no need to introduce external elements to guarantee a correct overall operation.

Consequently, a further object of the invention is to carry out a volumetric compressor that makes it possible to decrease and/or avoid additional costs for carrying out its connection to other compressors of the same type. Another object of the invention is to produce a volumetric compressor that is safer and less liable to be damaged than the compressors carried out according to the known art.

For this reason, a further object of the present invention is to carry out a volumetric compressor that in its internal part prevents the return of the auxiliary fluid and of the compressed gas in the direction opposite the correct operating direction.

A further, yet not the least object of the invention is to carry out a compressor whose structure is such as to allow the level of the auxiliary fluid inside it to be maintained substantially constant when it is connected in parallel to other compression devices of the same type.

The objects described above are achieved by a volumetric compressor carried out according to the main claim.

Further details of the compressor are described in the dependent claims.

The successive claims contain further characteristics of the compressor as well as of the compression system consisting of two or more of the above mentioned compressors connected in parallel, and finally of the conditioning or refrigeration system comprising said compression system, such as to achieve the set objects.

Advantageously, the compressor that is the subject of the invention makes it possible to obtain a more flexible and economic system.

The objects and advantages described above will be highlighted in greater detail in the description of a preferred embodiment of the invention that is supplied as an indicative, non-limiting example, with reference to the enclosed drawings, wherein: - Figure 1 shows an axonometric view of the improved compressor that is the subject of the invention;

- Figure 2 shows a schematic view of the improved compressor that is the subject of the invention;

- Figure 3 shows an axonometric view of a first section plane of the compressor that is the subject of the invention;

- Figure 4 shows an axonometric view of a second section plane of the compressor that is the subject of the invention;

- Figure 5 shows an axonometric view of the compressor unit that is the subject of the invention, consisting of two improved compressors connected in parallel; - Figure 6 is a schematic view of the compression unit that is the subject of the invention;

- Figure 7 shows a schematic view of the refrigeration system of the invention comprising a compression unit also belonging to the invention. The improved compressor that is the subject of the invention is shown in its whole in Figures 1 and 2, where it is indicated by 1.

It can be observed, always in Figure 2, that in the construction form described and represented herein the compressor 1, which is the subject of the invention and causes the compression of the refrigerant fluid and its introduction in a refrigeration system, is of the type with screw.

In other construction forms, not described herein, the compressor 1 may be used to compress the fluid and introduce it in a type of system different from a refrigeration system. Furthermore, in alternative construction forms, the compressor 1 that is the subject of the invention may not be of the type with screw, but be provided with different compression means, on condition that it maintains the main characteristics described in the main claim, as already stated above. Another important characteristic of the compressor 1 described herein lies in that it is of the "compact" screw type, as is illustrated in greater detail below. In Figure 1 it is possible to note that the compressor 1 of the invention consists of an external body 2 made of a metallic material, on which it is possible to identify an intake 3 connected, during installation of a generic system 200, shown in Figure 7, with an inlet duct 201 of the low pressure fluid Fb, indicated by the arrow, and a delivery outlet 4 that is placed in communication with an outlet duct 202 belonging to the same system 200 in which high pressure fluid Fa is introduced.

In the construction form described herein the fluid in question substantially comprises a refrigerant gas G that initially is brought to a condition of high pressure by the compressor 1 and then passes to the successive steps of the refrigeration cycle and, finally, returns to the compressor itself via the above mentioned inlet duct 201.

Furthermore, the fluid comprises an auxiliary fluid L, mixed with the above mentioned refrigerant gas G, which is necessary to reduce friction between the mechanical elements that make up the compressor 1. In the construction form described herein and in most cases the auxiliary fluid L is oil, but it cannot be excluded that in different embodiments said fluid may be of a different type.

As far as the internal part of the compressor 1 is concerned, as shown in

Figure 2, it comprises compression means 5 arranged downstream and communicating with the above mentioned intake 3.

As already explained, said compression means 5 have the function of compressing the low pressure fluid Fb present at their inlet 53, so as to produce a condition of high pressure at the outlet.

In the construction form presented herein the compression means 5 just described are of the type with screw, from which the name of the compressor derives, as already explained.

The compression means 5 preferably but not necessarily comprise two screws arranged on two parallel axes and meshing in such a way as to compress said fluid to be compressed and make it advance inside the air conditioning or refrigeration system 200.

In different construction forms, the screw compression means 5 may comprise a single screw or they may comprise more than two screws, provided that they are carried out according to the known art.

As already explained, in other construction forms, not described and not represented herein, the compression means 5 may not be of the type with screw, provided that they belong to the known art and that the entire compressor made up as described has the same characteristics and the same behaviour as the compressor 1 of the current embodiment.

Furthermore, inside the above mentioned metallic body 2 there is a separation chamber 6 arranged downstream of the compression means 5.

Said separation chamber serves to separate the two substances, the refrigerant gas G and the auxiliary fluid L, which mixed together make up the fluid F circulating inside the system 200.

As already explained, the above mentioned compressor 1 is called of the compact type due to the fact that it includes the separation chamber 6, differently from other types of compressor where said separation chamber is outside the metallic body 2.

In particular, the separation is obtained by thrusting the just compressed fluid F at high speed against the inner wall 61 of the above mentioned separation chamber 6. In this way the two substances are separated and consequently the auxiliary fluid L flows downward and the compressed gas G moves upwards.

As shown in Figures 3 and 4, inside the body 2 of the above mentioned compressor 1 there is also a communication duct 7 interposed between the separation chamber 6 and the outlet 54 of the compression means 5, in such a way as to guarantee the passage of the high pressure fluid Fa.

Said duct 7, as specified below, is a very important element for the implementation of the present invention.

Finally, the compressor 1 of the invention comprises an auxiliary circuit 8 consisting of one or more pipes 81 that make it possible to place said separation chamber 6 in communication with the area 53 at the inlet of the compression means 5.

In particular, in the embodiment shown in Figure 2, there is a single pipe 81, but it cannot be excluded that in different embodiments the auxiliary circuit may comprise more than one pipe.

In any case, the pipe or pipes 81 has/have the function of making the auxiliary fluid L return from the separation chamber 6, in which it was separated from the gas G, to the inlet area 53 of the compression means 5.

This path of the auxiliary fluid L is made possible by the difference in pressure between the two distinct areas.

In fact, as already mentioned, the separation chamber 6 is under high pressure, while at the inlet 53 of the compression means 5 there is a condition of low pressure.

In the construction form described and represented herein, the auxiliary circuit 8 is provided with an accumulation tank 82, which makes it possible to store the auxiliary fluid L present inside the compressor 1 during its various activity and inactivity stages.

In different embodiments of the invention not represented or described herein, the accumulation tanks 82 can be more than one, depending on the design needs.

In further construction forms the auxiliary circuit 8 may not be provided with the above mentioned accumulation tank 82.

As shown in Figure 3, the present embodiment comprises also filtering means 9 interposed between the separation chamber 6 and the delivery outlet 5. Said filtering means 9 make it possible to further "clean" the compressed refrigerant gas G removing any impurities due to the presence of very small quantities of auxiliary fluid L.

In different construction forms said filtering means 9 may not be provided, which however means compromising on the purity of the above mentioned refrigerant gas G placed in circulation in the pipes of the system 200.

According to the invention, the compressor 1 is provided with a check valve 10 inserted in said communication duct 7 that connects the compression means 5 to the separation chamber 6, in such a way as to prevent the high pressure fluid Fa from returning inside the compression means 5 flowing in the direction opposite the normal operating direction, as will be described in greater detail during the description of the installation of said compressor in a conditioning or refrigeration system 200.

Furthermore, the compressor 1 of the invention includes a solenoid valve 11 at the level of the pipe 81 belonging to the above mentioned auxiliary circuit 8 that connects the separation chamber 6 and the compression means 5.

Said solenoid valve 11 is closed and serves to prevent the passage of the auxiliary fluid L when the compressor 1 is not in operation.

The particular functions of the two valves 10 and 11 just introduced are illustrated in greater detail below, during the description of the compression unit 100 that is shown in Figures 5 and 6 and consists of more than one compressor 1 of the invention connected in parallel and of the conditioning or refrigeration system 200 of Figure 7 comprising the compression unit 100 just introduced, both claimed as the subject of the present patent. As shown in Figure 5, in the main embodiment represented herein the compression unit 100 comprises two compressors 1 of the invention connected in parallel.

It cannot be excluded that in other construction variants the compression unit 100 may consist of more than two compressors 1 of the invention connected in parallel.

In particular, the above mentioned compression unit 100 is provided with an inlet duct 101 suited to connect the intakes 3 of each compressor 1 present in the compression unit.

Furthermore, the compression unit 100 is provided with an outlet duct 102 suited to connect the delivery outlets 4 of the above mentioned compressors 1. Obviously, both the inlet duct 101 and the outlet duct 102 are provided with further openings 103 and 104, respectively for the inlet of the low pressure refrigerant gas G coming from the air conditioning or refrigeration system 200 and for the conveyance of the same compressed gas from the above mentioned compressors 1 to the system itself.

Finally, the compression unit 100, as shown in Figure 6, comprises a pipe 105 that makes it possible to connect the accumulation tanks 82 of each compressor 1 of the invention belonging to the above mentioned unit 100. According to the embodiment described and represented herein, the compression unit 100 preferably but not necessarily includes, downstream of each delivery outlet 4 of the compressors 1 , a check valve 106 that is connected thereto in order to increase the safety of the whole system 200. In particular, as shown in Figure 6, each one of the above mentioned check valves 106 prevents the return of the high pressure refrigerant gas G inside the compressor 1 , causing the reverse rotation of the compression means 5 with respect to the correct operating direction and consequently damaging them. In the preferred embodiment of the invention described herein, the compression unit 100 of the invention is also provided with an inverter device 107 connected to one of the two compressors 1 of the invention and having the function of modulating and adjusting the flow rate of the refrigerant gas G that flows out of the same device, as described in detail in the presentation of the known art.

In other construction variants not illustrated herein, an inverter device 107 may be coupled with each compressor 1 belonging to the compression unit 100, in such a way as to make the system easier to adjust.

Again, according to further construction variants, the compression unit 100 and in particular each compressor 1 may not be provided with inverter devices 107. In further embodiments of the invention not represented or described herein the compressors 1 of the invention that make up the compression unit 100 may be provided with adjusting means different from the inverter 107.

In particular, each single compressor 1 may be provided with a slide valve or bypass system, as described during the presentation of the known art. As already mentioned above and as can be seen in Figure 7, the invention comprises also the air conditioning or refrigeration system 200 comprising the compression unit 100 whose characteristics have just been described. Said system 200 also comprises, as shown in Figure 7, a plurality of pipes 203 that distribute the refrigerant gas G in the various closed rooms to be cooled and are connected to the above mentioned compression unit 100 through the inlet and outlet ducts 201 and 202. In particular, in the construction form described herein the system 200 comprises two heat exchangers 204 arranged along the above mentioned pipes 203.

As already mentioned, the system 200 may serve as a heat pump, with a first heat exchanger 204 connected to one or more users U. Otherwise, the same system may be used as a refrigeration system, by connecting the second heat exchanger 204 to one or more users U.

Operatively, a refrigeration system 200 comprising a compression unit 100 of the invention, as already mentioned, after installation is not operated immediately at full rate, but is operated progressively. In particular, this means that at the beginning the system 200 is started with only one compressor 110, represented in Figure 7, functioning, said compressor being controlled and adjusted by the relevant inverter device 107, while the second compressor 111 remains inactive.

In this operating stage, the above mentioned solenoid valve 11 present in the compressor that is off is operated in such a way as to prevent the passage of the auxiliary fluid L from the separation chamber 6 to the inlet area 53 of the compression means 5.

Said closure is necessary, as already seen above, since the two compressors

110 and 111 have the respective accumulation tanks 82 in communication through the above mentioned pipe 105 and therefore the auxiliary fluid L may pass first from the operating compressor 110 to the non operating compressor

111 and successively from the tank 82 of the latter to the area 53 upstream of the compression means 5, causing said auxiliary fluid L to accumulate just in that part. Consequently, as already seen, said excess auxiliary fluid L at the level of the compression means 5 in the starting stage may cause serious damage to the compressor 111.

Closing said valve 11 prevents the flow of the auxiliary fluid L from one area to the other and consequently increases the safety level of the compressor 1 , thus reaching one of the objects of the invention. Furthermore, always from the point of view of the inactive compressor 111, the check valve 10, which is present in the communication duct 7 and connects the compression means 5 to the separation chamber 6, prevents the compressed gas G flowing out of the operating compressor 110 from flowing back inside it, thus avoiding the rotation of the compression means 5 in the direction opposite the correct operating direction and protecting them from any damage. It is evident that, if the compression unit 100 includes a check valve 106 also downstream of the delivery outlet 4, as in the case described herein, it is doubly guaranteed that the gas G cannot return in the wrong direction. Also in this case, therefore, the objects of the present invention are achieved. When the refrigeration system 200 progressively reaches 50% of its maximum rated power, also the second compressor 111 is activated which, in the construction form described herein, is not coupled with a control inverter 107 and therefore is immediately started at maximum power. In different embodiments of the invention, as already mentioned, also the second compressor 111 is adjusted by an inverter 107 and therefore its operating power can be progressively increased until reaching its rated value. In the moment when said second compressor 111 is activated, the solenoid valve 11 provided along the pipe 81 of the auxiliary circuit 8 is deactivated and for this reason the auxiliary fluid L is free to flow from the separation chamber 6 to the inlet 53 of the compression means 5.

In this configuration the two compressors 110 and 111 that make up the compression unit 100 work in parallel without posing the drawbacks described above and belonging to the known art. On the other hand, it is important to consider that the compressor 1 of the invention can be used even individually, as it doesn't pose any drawback compared to the compressors of the known art, and with no need to connect it in parallel to other devices of the same type. On the basis of the above, it is clear that the compressor that is the subject of the invention achieves all the set objects.

In particular, the invention achieves the object to develop a volumetric compressor that can be connected in parallel to other compression devices of the same type, with no need to introduce external elements to guarantee a correct overall operation. Consequently, the invention also achieves the object to carry out a volumetric compressor that makes it possible to decrease and/or avoid additional costs for carrying out its connection with other compressors of the same type. Another object achieved by the invention is to produce a volumetric compressor that is safer and less liable to be damaged than the compressors of the known art.

For this reason, the invention also achieves the object to carry out a volumetric compressor that in its internal part prevents the return of the auxiliary fluid and of the compressed gas in the direction opposite the correct operating direction. Lastly, the invention also achieves the object to carry out a compressor whose structure is such as to allow the level of the auxiliary fluid inside it to be maintained substantially constant when it is connected in parallel to other compression devices of the same type.

On implementation, the compressor, the compression unit and the refrigeration system that are the subjects of the invention may undergo changes that, though not illustrated or described herein, shall nonetheless be covered by the present patent, provided that they come within the scope of the claims that follow.

In the cases where the technical characteristics illustrated in the claims are followed by references, these have been added only with the aim to facilitate the comprehension of the claims themselves and therefore said references do not have any limiting effect on the degree of protection to be granted to each element they identify only by way of example.

Claims

1) Improved compressor (1) of the type comprising a compressor body (2) inside which it is possible to identify:

- an intake (3) connected to an inlet duct (101) of a fluid (F) to be compressed consisting of a mixture of gas (G) and auxiliary fluid (L);

- compression means (5) positioned downstream of said intake (3) for compressing said outflowing fluid (F);

- a separation chamber (6) located downstream of said compression means (5) and suited to separate said compressed gas (G) from said auxiliary fluid (L);

- a communication duct (7) suited to place the area (54) downstream of said compression means (5) in communication with said separation chamber

(6);

- an auxiliary circuit (8) comprising at least one pipe (81) connected between said separation chamber (6) and the area (53) upstream of said compression means (5) and suited to make said auxiliary fluid (L) return into said compression means (5);

- a delivery outlet (4) arranged downstream of and communicating with said separation chamber (6), said delivery outlet (4) being connected with an outlet duct (102) of said compressed gas (G), characterized in that it comprises a check valve (10) inserted in said communication duct (7) that connects said compression means (5) to said separation chamber (6) and a solenoid valve (11) arranged in said pipe (81) belonging to said auxiliary circuit (8) and connecting said separation chamber (6) to the area (53) upstream of said compression means (5).

2) Compressor (1) according to claim 1), characterized in that said auxiliary circuit (8) comprises an accumulation tank (82) of said auxiliary fluid (L) coming from said separation chamber (6).

3) Compressor (1) according to any one of the preceding claims, characterized in that said compression means (5) are compression means of the type with one screw.

4) Compressor (1) according to any one of the claims from 1) to 3), characterized in that said compression means (5) are compression means of the type with double screw. 5) Compressor (1) according to any one of the claims from 1) to 3), characterized in that said compression means (5) are compression means of the type with more than two screws.

6) Compressor (1) according to any one of the preceding claims, characterized in that it comprises filtering means (9) interposed between said separation chamber (6) and said delivery outlet (4) and suited to separate in a capillary way said gas (G) from said auxiliary fluid (L).

7) Compressor (1) according to any one of the preceding claims, characterized in that it also comprises a slide valve suited to control and adjust the flow rate of said fluid (F) flowing out of said delivery outlet (4). 8) Compressor (1) according to any one of the claims from 1) to 6), characterized in that it also comprises a bypass circuit suited to control and adjust the flow rate of said fluid (F) flowing out of said delivery outlet (4).

9) Compressor (1) according to any one of the claims from 1) to 6), characterized in that it also comprises an inverter device (107) suited to control and adjust the flow rate of said fluid (F) flowing out of said delivery outlet (4).

10) Compression unit (100) comprising two or more compressors (1) according to claim 1) connected to each other in parallel.

11) Compression unit (100) according to claim 10), characterized in that said two or more compressors (1) share an inlet duct (101) for connecting said intakes (3) in parallel, an outlet duct (102) for connecting said delivery outlets (4) in parallel and one pipe (105) for connecting said accumulation tanks (81) in parallel.

12) Compression unit (100) according to claim 11), characterized in that a check valve (106) is connected downstream of the delivery outlet (4) of each one of said compressors (1).

13) Refrigeration system (200), characterized in that it comprises a compression unit (100) carried out according to any one of the claims from 7) to 10).