US20130177404A1

US20130177404A1 - Compression device, and a thermodynamic system comprising such a compression device

Info

Publication number: US20130177404A1
Application number: US13/732,847
Authority: US
Inventors: Jean Bernardi; Patrice Bonnefoi; Xavier DURAND; Fabien GALL; Jean-Francois LE COAT
Original assignee: Danfoss Commercial Compressors SA
Current assignee: Danfoss Commercial Compressors SA
Priority date: 2012-01-11
Filing date: 2013-01-02
Publication date: 2013-07-11
Also published as: CN103206359A; FR2985552A1; DE102013000189A1

Abstract

This compression device comprises first and second compressors mounted in parallel, a suction line intended to be connected to an outlet of an evaporator, first and second suction conduits arranged for putting the suction line respectively in communication with the admission orifices of the first and second compressors, and an oil level equalization conduit connecting the oil pans of the first and second compressors. The compression device further comprises an oil separator mounted on the suction line or on the second suction conduit, and an oil return conduit arranged for connecting an oil outflow orifice of the oil separator to the oil pan of the first compressor.

Description

The present invention relates to a compression device, and to a thermodynamic system comprising such a compression device.
Document FR 2 605 393 describes a thermodynamic system, and more particularly a cooling system, comprising:

- a circuit for circulating a coolant fluid successively including a condenser, an expansion valve, an evaporator and a compression device connected in series, the compression device comprising at least a first compressor with a fixed capacity and a second compressor with a fixed capacity mounted in parallel, each compressor comprising an enclosure including a low pressure portion containing a motor and an oil pan positioned in the bottom of the enclosure on the one hand, and an orifice for admitting a coolant fluid, opening into the low pressure portion on the other hand,
- a suction line connected to the evaporator,
- a first suction conduit putting the suction line in communication with the admission orifice of the first compressor,
- a second suction conduit putting the suction line in communication with the admission orifice of the second compressor,
- a restriction member positioned in the second suction conduit and arranged for maintaining a pressure in the low pressure portion of the first compressor, greater than the pressure in the low pressure portion of the second compressor when the first and second compressors are operating simultaneously,
- a flow separation device positioned between the suction line and the first and second suction conduits, the flow separation device being arranged in order to carry away the major portion of the coolant fluid from the evaporator towards the first compressor, and
- an oil level equalization conduit promoting transfer of oil between both compressors.

Such a thermodynamic system ensures return of the major portion of the oil carried away by the coolant fluid towards the first compressor. Because of the high pressure prevailing in the low pressure portion of the first compressor (due to the presence of the restriction member in the second suction line), the oil present in the oil pan of the first compressor is driven towards the oil pan of the second compressor, via the oil level equalization conduit, so as to balance the oil levels in the first and second compressors.
Such a solution, although satisfactory for a thermodynamic system including two fixed-capacity compressors having close capacities, is absolutely not satisfactory for a thermodynamic system including at least one compressor with variable capacity and more particularly with variable speed, or two fixed-capacity compressors having very different capacities.
Indeed, when the compressor with variable speed operates at a low speed, for example less than or of the order of 30 Hz, for a certain period and that the second compressor operates, a pressure unbalance is established between the oil pans of both compressors, causing a transfer of the majority of the oil from the evaporator towards the second compressor, and therefore a significant increase of the oil level in the oil pan of the second compressor and depletion of oil in the oil pan of the first compressor which may lead to significant damage of the latter.
The same applies when the two compressors are with a fixed capacity and that the second compressor has a capacity much greater than that of the first compressor.
Therefore, the solution mentioned earlier does not give the possibility of obtaining satisfactory balance between the oil levels regardless of the type of compressors used, and regardless of the operating conditions of the latter.
The present invention aims at finding a remedy to these drawbacks.
The technical problem at the basis of the invention therefore consists of providing a compression device which is of a simple and economical structure, with which balancing of the oil levels may be obtained in each compressor regardless of the operating conditions of the compression device, and regardless of the type of compressors used.
For this purpose, the present invention relates to a compression device comprising:

- at least one first compressor and one second compressor mounted in parallel, each compressor comprising a leakproof enclosure including a low pressure portion containing an engine and an oil pan on the one hand, and an admission orifice opening into the low pressure portion on the other hand,
- a suction line intended to be connected to an outlet of an evaporator,
- a first suction conduit arranged for putting the suction line in communication with the admission orifice of the first compressor,
- a second suction conduit arranged for putting the suction line in communication with the admission orifice of the second compressor, and
- an oil level equalization conduit arranged for putting the oil pans of the first and second compressors in communication,

wherein the compression device further comprises:

- at least one oil separator mounted on the suction line or on the second suction conduit, the oil separator comprising an oil outlet orifice, and
- an oil return conduit arranged for connecting the oil outflow orifice of the oil separator to the oil pan of the first compressor.

The presence of an oil separator on the suction line or on the second suction conduit gives the possibility of ensuring, regardless of the operating conditions of the compression device, and regardless of the type of compressors used, a return of the major portion of the oil driven by the coolant fluid towards the first compressor via the oil return conduit. The oil present in the oil pan of the first compressor is then driven towards the oil pan of the second compressor, via the oil level equalization conduit, so as to balance the oil levels in the first and second compressors.
The compression device according to the invention therefore ensures balancing of the oil levels in each compressor regardless of the operating conditions of the compression device, and regardless of the type of compressors used, the whole only by means of a low cost oil separator. Further, the compression device according to the invention ensures the presence of a minimum amount of oil in the oil pan of the first compressor.
Advantageously, the oil separator further comprises an inlet orifice intended to be connected to the outlet of the evaporator so as to allow an oil-coolant fluid mixture to be introduced into the oil separator, and a coolant fluid discharge orifice connected to at least the admission orifice of the second compressor.
Preferably, the oil separator comprises a separation chamber, the inlet orifice and the coolant fluid discharge orifice of the oil separator being respectively in communication with the separation chamber. The inlet orifice of the oil separator is thus intended to be connected to the outlet of the evaporator so as to allow an oil-coolant fluid mixture to be introduced in the separation chamber.
According to a first embodiment of the invention, the suction line comprises a first connection conduit connected to the inlet orifice of the oil separator and intended to be connected to the outlet of the evaporator, and a second connection conduit arranged for putting the coolant fluid discharge orifice of the oil separator in communication with the first and second suction conduits. The first and second connection conduits for example have substantially identical diameters.
Preferably, the first connection conduit is arranged so as to extend from the outlet of the evaporator as far as the inlet orifice of the oil separation device.
According to an embodiment of the invention, the second connection conduit extends from the coolant fluid discharge orifice of the oil separator as far as a diversion point, the first suction conduit extends from the diversion point as far as the admission orifice of the first compressor, and the second suction conduit extends from the diversion point as far as the admission orifice of the second compressor.
According to an embodiment of the invention, the second connecting conduit protrudes inside the separation chamber.
According to a second embodiment of the invention, the second suction conduit comprises an upstream conduit portion arranged for putting the inlet orifice of the oil separator in communication with the suction line, and a downstream conduit portion arranged for putting the coolant fluid discharge orifice of this oil separator in communication with the admission orifice of the second compressor.
According to an embodiment of the invention, the downstream conduit portion protrudes inside the separation chamber.
Preferably, the suction line is arranged so as to extend from the outlet of the evaporator as far as a diversion point, the first suction conduit extends from the diversion point as far as the admission orifice of the first compressor, the upstream conduit portion extends from the diversion point as far as the inlet orifice of the oil separator, and the downstream conduit portion extends from the coolant fluid discharge orifice of the oil separator as far as the admission orifice of the second compressor.
According to an embodiment of the invention, the oil return conduit is arranged for opening into the first suction conduit. According to another embodiment of the invention, the oil return conduit is arranged for opening into the oil pan of the first compressor.
Advantageously, the second suction conduit comprises restriction means arranged for reducing the flow section of the coolant fluid in the second suction conduit. The restriction means are preferentially arranged for maintaining pressure in the low pressure portion of the first compressor, greater than the pressure in the low pressure portion of the second compressor when the first and second compressors are operating simultaneously.
Advantageously, the restriction means are arranged so that the flow section of the coolant fluid at the restriction means is less than the flow section of the coolant fluid at the admission orifice of the second compressor.
The restriction means for example include a restriction member positioned in the second suction conduit.
According to an embodiment of the invention, the first compressor is a variable-capacity compressor and the second compressor is a fixed-capacity compressor.
Thus, by positioning the oil separator on the suction line or the second suction conduit and by connecting the oil outlet orifice of the oil separator to the oil pan of the first compressor, it is possible to protect the most expensive compressor of the compression device and most subject to pressure variations in its oil pan.
By compressor with variable capacity is meant any compressor which may have a variable output (or several outputs) with regard to the suction of the compressor for a same operating point (an operating point corresponding to a suction pressure, a suction temperature and a discharge pressure which are given). Among the known technical solutions for making a compressor with variable capacity, mention will be made for example of:

- a compressor driven by a variable-speed motor,
- a compressor driven by a motor with two speeds (a two/four pole motor type),
- a compressor driven by a fixed-speed motor plus a gear box,
- a compressor driven by a fixed-speed motor plus an epicycloidal gear (planetary gear),
- a compressor with discharge valves either opening or closing an internal bypass to the compressor,
- a compressor with multiple compression units, some of which may be uncoupled,
- a compressor with an internal mechanism for generating intermittent compression.

According to an alternative embodiment of the invention, the first and second compressors may be fixed-capacity compressors. The first and second fixed-capacity compressors may for example have different capacities.
Advantageously, the oil separator is a cyclone oil separator.
Preferably, the oil level equalization conduit includes at least one first end portion protruding inside the enclosure of one of the first and second compressors, the first end portion including an end wall extending transversely to the longitudinal direction of said first end portion and an aperture made above said end wall so that, when the oil level in the oil pan of the compressor into which the first end portion protrudes, extends above the upper level of said end wall, oil flows through said aperture towards the other compressor. Preferably, the first end portion protrudes inside the enclosure of the second compressor.
The oil level equalization conduit advantageously includes a second end portion protruding inside the enclosure of the other one of the first and second compressors, the second end portion including an end wall extending transversely to the longitudinal direction of said second end portion and an aperture made above the end wall of said second end portion so that, when the oil level in the oil pan of the compressor, into which protrudes the second end portion, extends above the upper level of the end wall of the second end portion, oil flows through the aperture of the second end portion towards the other compressor.
According to an embodiment of the invention, at least one of the first and second end portions includes an oil return orifice located below the upper level of the end wall of said end portion.
Each of the first and second compressors is for example a compressor with scrolls.

Anyhow, the invention will be well understood by means of the description which follows, with reference to the appended schematic drawing illustrating as non-limiting examples, two embodiments of this compression device.

FIG. 1 is a schematic view of a thermodynamic system according to a first embodiment of the invention.

FIG. 2 is a schematic sectional view of a compression device of the thermodynamic system of FIG. 1.

FIGS. 3 a and 3 b are perspective and top views respectively of an end portion of an oil level equalization conduit of the compression device of FIG. 2.

FIG. 4 is a schematic view of a thermodynamic system according to a second embodiment of the invention.

FIG. 5 schematically illustrates the main components of a thermodynamic system 1. The thermodynamic system 1 may be a cooling system.

The thermodynamic system 1 comprises a circuit 2 for circulating a coolant fluid successively including a condenser 3, an expansion valve 4, an evaporator 5 and a compression device 6 connected in series.
The compression device 6 comprises a first compressor 7 with variable capacity, and more particularly with variable speed, and a second compressor 8 with fixed capacity, and more particularly with a fixed speed, mounted in parallel. Each compressor 7, 8 is for example a compressor with scrolls. Each compressor 7, 8 comprises a body 9 including a low pressure portion 11 containing a motor 12 and an oil pan 13 positioned in the bottom of the body 9, and a high pressure portion 14, positioned above the low pressure portion 11, containing a compression stage.
The body 9 of each compressor 7, 8 further includes an orifice 15 for admitting coolant fluid, opening into an upper portion of the low pressure portion 11, an equalization orifice 16 opening into the oil pan 13, and a discharge orifice 17 opening into the high pressure portion 14.
The compression device 6 also comprises a suction line 19 connected to the evaporator 5, a first suction conduit 21 putting the suction line 19 in communication with the admission orifice 15 of the first compressor 7, and a second suction conduit 22 putting the suction line 19 in communication with the admission orifice 15 of the second compressor 8. Each suction conduit 21, 22 comprises a suction tube 21 a, 22 a, connected to the suction line 19 and a connecting sleeve 21 b, 22 b connected to the corresponding admission orifice 15, respectively.
As shown in FIG. 2, the second suction conduit 22 comprises restriction means arranged for reducing the flow section of the coolant fluid in said suction conduit. The restriction means are arranged so that the flow section of the coolant fluid at the restriction means is less than the flow section of the coolant fluid at the admission orifice 15 of the second compressor 8. The restriction means are advantageously positioned in proximity to the admission orifice 15 of the second compressor 8.
The restriction means preferably comprise an annular ring 23 attached in the second suction conduit 22, for example by brazing or crimping. The annular ring 23 includes a longitudinal through-orifice centered with respect to the wall of the second suction conduit 22. It should be noted that the outer diameter of the annular ring 23 substantially corresponds to the inner diameter of the diversion tube 22 a of the second suction conduit 22.
According to an alternative embodiment not shown in the figures, the annular ring 23 may be attached in the connecting sleeve 22 b of the second suction conduit 22.
The compression device 6 further comprises an oil level equalization conduit 24 connecting the first equalization orifices 16 of the first and second compressors 7, 8 and in fact putting the oil pans 13 of the first and second compressors in communication.
The compression device 6 also comprises a discharge line 26 connected to the condenser 3, a first discharge conduit 27 putting the discharge line 26 in communication with the discharge orifice 17 of the first compressor 7, and a second discharge conduit 28 putting the discharge line 26 in communication with the discharge orifice 17 of the second compressor 8.
The compression device 6 further comprises control means 29 arranged for selectively controlling the respective switching of the first and second compressors 7, 8 between an operating mode and a standstill mode, on the one hand, and for modulating the speed of the motor 12 of the first compressor 7 between a minimum speed and a maximum speed on the other hand.
The compression device 6 also comprises an oil separator 31 mounted on the suction line 19. The oil separator 31 includes a body 32 delimiting a separation chamber 34. The separation chamber 34 includes a cylindrical upper portion extended with a converging frusto-conical lower portion opposite to the upper portion. The oil separator 31 thus forms a cyclone oil separator.
The oil separator 31 also comprises an inlet orifice 35 for example opening radially or tangentially into the separation chamber 34, an oil outflow orifice 36 opening into the lower end of the separation chamber 34, and an orifice for discharging coolant fluid 37, opening axially into the upper end of the separation chamber 34.
The suction line 19 more particularly comprises a first connecting conduit 19 a connected to the outlet of the evaporator 5 on the one hand and to the inlet orifice 35 of the oil separator 31 on the other hand so as to allow an oil-coolant fluid mixture to be introduced into the separation chamber 34, and a second connecting conduit 19 b connected to the discharge orifice 37 of the oil separator 31 on the one hand and to the first and second suction conduits 21, 22 on the other hand. The first and second connecting conduits 19 a, 19 b for example have substantially identical diameters. Advantageously, the second connecting conduit 19 b protrudes inside the separation chamber 34.
The second connecting conduit 19 b preferably extends from the discharge orifice 37 of the oil separator 31 as far as a diversion point 38, and the first and second suction conduits 21, 22 respectively extend from the diversion point 38 as far as the admission orifice 15 of the respective compressor.
The compression device 6 finally comprises an oil return conduit 39 arranged for connecting the oil outflow orifice 36 of the oil separator 31 to the oil pan 13 of the first compressor 7. The oil return conduit 39 is more particularly arranged for opening into the first suction conduit 21.
The operation of the thermodynamic system 1 will now be described.
When the first and second compressors 7, 8 are operating, the oil-coolant fluid mixture from the evaporator 5 penetrates into the separation chamber 34 of the oil separator 31 via the first connecting conduit 19 a and the inlet orifice 35. Subsequently, because of the configuration of the separation chamber 34, the oil-coolant fluid mixture begins to turn along the internal wall of the separation chamber 34, which causes centrifugation of the oil-coolant fluid mixture. The result of this is the coalescence of the oil drops on the internal wall of the separation chamber 34, and then the fall of the oil by gravity towards the lower end of the separation chamber 34, i.e. towards the oil outflow orifice 36, and the flow of coolant fluid through the discharge orifice 37 towards the inlet orifices 15 of the first and second compressors 7, 8. The coolant fluid flow penetrating into the second compressor 8 is then not very loaded with oil.
The oil separated in the separation chamber 34 then flows in the oil return conduit 39 towards the oil pan 13 of the first compressor 7 via the first suction conduit 21. The coolant fluid flow penetrating into the first compressor 7 is then highly loaded with oil. Because of the high pressure prevailing in the low pressure portion 11 of the first compressor 7 (due to the presence of the restriction member 23 in the second suction conduit 22), the oil present in the oil pan 13 of the first compressor 7 is driven towards the oil pan 13 of the second compressor 8, via the oil level equalization conduit 24, so as to balance the oil levels in the first and second compressors 7, 8.
According to an alternative embodiment of the compression device 6 illustrated in FIGS. 3 a and 3 b, the oil level equalization conduit 24 includes at least one first end portion 41 protruding inside one of the first and second compressors 7, 8.
The first end portion 41 includes an end wall 42 extending transversely to the longitudinal direction of the first end portion 41 and an aperture 43 made above the end wall 42 so that, when the oil level in the oil pan 13 of the compressor into which protrudes the first end portion 41, extends above the upper level of the end wall 42, oil flows through the aperture 43 towards the other compressor. Preferably, each aperture 43 extends over a portion of the side wall 44 of the corresponding end portion 41.
The first end portion 41 further includes an oil return orifice 45 located below the upper level of the end wall 42 of the first end portion 41. This position of the oil return orifice 45 gives the possibility of avoiding storage of oil beyond a predetermined level inside the enclosure of the compressor into which protrudes the first end portion 41.
According to an alternative embodiment of the compression device 6, the oil level equalization conduit 24 includes a second end portion 41 substantially identical with the first end portion, the first end portion 41 protruding inside one of the first compressors 7, 8, while the second end portion 41 protrudes inside the other one of the first and second compressors 7, 8.
FIGS. 4 and 5 illustrate a thermodynamic system 1 according to a second embodiment of the invention which differs from the one illustrated in FIGS. 1 and 2 essentially in that the oil separator 31 is mounted on the second suction conduit 22, in that the second suction conduit 22 comprises an upstream conduit portion 46 a arranged for putting the inlet orifice 35 of the oil separator 31 in communication with the suction line 19, and a downstream conduit portion 46 b arranged for putting the discharge orifice 37 of the oil separator 31 in communication with the admission orifice 15 of the second compressor 8, and in that the oil return conduit 39 directly opens into the oil pan 13 of the first compressor 7.
According to a second embodiment of the invention, the suction line 19 extends from the outlet of the evaporator 5 as far as the diversion point 38, the first suction conduit 21 extends from the diversion point 38 as far as the admission orifice 15 of the first compressor 7, the upstream conduit portion 46 a extends from the diversion point 38 as far as the inlet orifice 35 of the oil separator 31, and the downstream conduit portion 46 b extends from the discharge orifice 37 of the oil separator 31 as far as the admission orifice 15 of the second compressor 8. Advantageously, the downstream conduit portion 46 b protrudes inside the separation chamber 34.
According to this second embodiment of the invention, the downstream conduit portion 46 b comprises restriction means, and more particularly the annular ring 23.
According to an alternative embodiment of the second embodiment of the invention, the second suction conduit 22 may be without any restriction means in order to limit the manufacturing costs of the compression device. The oil separator according to this alternative embodiment is arranged for maintaining pressure in the low pressure portion of the first compressor, greater than the pressure in the low pressure portion of the second compressor when the first and second compressors are operating simultaneously.
As this is obvious, the invention is not limited to the sole embodiments of this compression device, described above as an example, on the contrary, it encompasses all the alternative embodiments thereof.

Claims

1. A compression device comprising:

at least one first compressor and one second compressor mounted in parallel, each compressor comprising a leakproof enclosure including a low pressure portion containing a motor and an oil pan on the one hand, and an admission orifice opening into the low pressure portion on the other hand,

a suction line intended to be connected to an outlet of an evaporator,

a first suction conduit arranged for putting the suction line in communication with the admission orifice of the first compressor,

a second suction conduit arranged for putting the suction line in communication with the admission orifice of the second compressor, and

an oil level equalization conduit arranged for putting the oil pans of the first and second compressors in communication,

wherein the compression device further comprises:

at least one oil separator mounted on the suction line or on the second suction conduit, the oil separator comprising an oil outflow orifice, and

an oil return conduit arranged for connecting the oil outflow orifice of the oil separator to the oil pan of the first compressor.

2. The compression device according to claim 1, wherein the oil separator further comprises an inlet orifice intended to be connected to the outlet of the evaporator so as to allow the introduction of an oil-coolant fluid mixture into the oil separator, and a coolant fluid discharge orifice connected to at least the admission orifice of the second compressor.

3. The compression device according to claim 2, wherein the oil separator comprises a separation chamber, the inlet orifice and the coolant fluid discharge orifice of the oil separator respectively being in communication with the separation chamber.

4. The compression device according to claim 2, wherein the suction line comprises a first connecting conduit connected to the inlet orifice of the oil separator and intended to be connected to the outlet of the evaporator, and a second connecting conduit arranged for putting the coolant fluid discharge orifice of the oil separator in communication with the first and second suction conduits.

5. The compression device according to claim 2, wherein the second suction conduit comprises an upstream conduit portion arranged for putting the inlet orifice of the oil separator in communication with the suction line, and a downstream conduit portion arranged for putting the coolant fluid discharge orifice of the oil separator in communication with the admission orifice of the second compressor.

6. The compression device according to claim 1, wherein the oil return conduit is arranged for opening into the first suction conduit.

7. The compression device according to claim 1, wherein the oil return conduit is arranged for opening into the oil pan of the first compressor.

8. The compression device according to claim 1, wherein the second suction conduit comprises restriction means arranged so as to reduce the flow section of the coolant fluid in the second suction conduit.

9. The compression device according to claim 1, wherein the restriction means are arranged for maintaining pressure in the low pressure portion of the first compressor greater than the pressure in the low pressure portion of the second compressor when the first and second compressors are operating simultaneously.

10. The compression device according to claim 1, wherein the first compressor is a variable-capacity compressor.

11. The compression device according to claim 1, wherein the second compressor is a fixed-capacity compressor.

12. The compression device according to claim 1, wherein the oil separator is a cyclone oil separator.

13. A thermodynamic system comprising a condenser, an expansion valve, an evaporator and a compression device according to claim 1, connected in series.