| WO/2009/107617 | REFRIGERATION DEVICE |
| JP05203270 | TWO-STAGE COMPRESSI0N TYPE REFRIGERATING CYCLE APPARATUS |
| JP2005083334 | HERMETIC TWO-STAGE COMPRESSION TYPE COMPRESSOR |
MAHNERT, Manfred (Ruedigerstr. 65, Cologne, 51109, DE)
| Claims 1 . Refrigeration system, comprising: a first compressor unit (4), a condenser/gas cooler (6), and a refrigerant collecting container (10); a normal refrigeration branch coupled between the refrigerant collecting container (10) and a suction side of the first compressor unit (4), the normal refrigeration branch comprising a first expansion device and a first evaporator; a freezing branch coupled between the refrigerant collecting container (10) and the suction side of the first compressor unit (4), the freezing branch comprising a second expansion device, a second evaporator, and a second compressor unit (22); refrigerant conduits for connecting said elements and for circulating a refrigerant therethrough; an oil balance line (34) connecting at least two compressors of the first compressor unit (4); an oil collecting container (26) being connected or connectible to at least one compressor of the second compressor unit (22); an oil refeeding line (36) extending between the oil collecting container (26) and the oil balance line (34); and a pressure line (40) attaching to the oil collecting container (26) that can opened and closed; wherein, if the oil level in the oil collecting container (26) exceeds a predetermined height, the pressure line (40) is opened thereby effecting oil flow from the oil collecting container (26) to the oil balance line (34). 2. Refrigeration system of claim 1 , wherein the pressure line is formed as an intermediate pressure line (40) attaching with its other end to a point in the intermediate pressure portion of the refrigeration circuit (2). 3. Refrigeration system of claim 2, wherein the intermediate pressure line (40) attaches with its other end to the refrigerant collecting container (10), in particular to the gas space of the refrigerant collecting container (10). 4. Refrigeration system of any of the preceding claims, wherein the oil refeeding line (36) attaches to a lower portion in the oil collecting container (26). 5. Refrigeration system of any of the preceding claims, wherein the intermediate pressure line/pressure line (40) can be switched open or closed by means of a solenoid valve (42) arranged therein. 6. Refrigeration system of any of the preceding claims, wherein the oil refeeding line (36) can be switched open or closed by means of a solenoid valve (38) arranged therein. 7. Refrigeration system of any of the preceding claims, wherein a solenoid valve (32) is arranged in the oil line (30) from the at least one compressor of the second compressor unit (22) to the oil collecting container (26). 8. Refrigeration system of any of the preceding claims, wherein a liquid level switch (28) is provided in or at the oil collecting container (26) for determining if the oil level in the oil collecting container (26) exceeds a predetermined height or falls below a predetermined height. 9. Refrigeration system of any of the preceding claims, wherein, if the oil level in the oil collecting container (26) falls below a predetermined height, the intermediate pressure line/pressure line (40) is closed thereby ending the oil refeeding from the oil collecting container (26) to the oil balance line (34). 10. Method for balancing the oil levels between compressors (4, 22) of a refrigeration system (2), comprising a first compressor unit (4), a condenser/gas cooler (6), and a refrigerant collecting container (10); a normal refrigeration branch coupled between the refrigerant collecting container (10) and a suction side of the first compressor unit (4), the normal refrigeration branch comprising a first expansion device and a first evaporator; a freezing branch coupled between the refrigerant collecting container (10) and the suction side of the first compressor unit (4), the freezing branch comprising a second expansion device, a second evaporator, and a second compressor unit (22); refrigerant conduits for connecting said elements and for circulating a refrigerant therethrough; an oil balance line (34) connecting at least two compressors of the first compressor unit (4); an oil collecting container (26) being connected or connectible to at least one compressor of the second compressor unit (22); an oil refeeding line (36) extending between the oil collecting container (26) and the oil balance line (34); a pressure line (40) attaching to the oil collecting container (26) that can be opened and closed; the method comprising the step of: if the oil level in the oil collecting container (26) exceeds a predetermined height, opening the pressure line (40) thereby effecting oil flow from the oil collecting container (26) to the oil balance line (34). 1 1. Method of claim 10, wherein, if the oil level in the oil collecting container (26) falls below a predetermined height, the pressure line (40) is closed, thereby stopping the oil flow from the oil collecting container (26) to the oil balance line (34). 12. Method of claim 10 or 1 1 , wherein when opening the pressure line (40), the oil collecting container (26) is connected to a point in the intermediate pressure portion of the refrigeration system (2). 13. Method of any of claims 9 to 12, wherein, if the oil level in the oil collecting container (26) exceeds a predetermined value the oil line (30) from the second compressor unit (22) is closed thereby interrupting oil flow from the second compressor unit (22) to the oil collecting container (26). |
The invention is related to a refrigeration system and a method for balancing the oil levels between compressors of a refrigeration system.
From the WO/2006/015741 a refrigeration system is known that employs both a medium temperature compressor set and a low temperature compressor set and allows normal temperature refrigeration of normal cold consumers and freezing temperature refrigeration of freezing cold consumers. Such refrigeration system is also referred to as booster refrigeration system.
In practical installations of such refrigeration systems it has been discovered that the medium temperature compressors and the low temperature compressors are prone to defects due to too high or too low oil levels.
If a too high or too low oil level is detected early enough in the medium temperature compressors or the low temperature compressors, then the refrigeration system can be switched off in order to avoid defects of the compressors, however this negatively effects the performance of such booster refrigeration systems.
Accordingly, it would be beneficial to provide a refrigeration system having both medium temperature and low temperature compressors and a method for operating the same that ensures a better oil distribution and reliably avoids defects of the compressors.
According to exemplary embodiments of the invention, a refrigeration system comprises a first compressor unit, a condenser/gas cooler, and a refrigerant collecting container; a normal refrigeration branch coupled between the refrigerant collecting container and a suction side of the first compressor unit, the normal refrigeration branch comprising a first expansion device and a first evaporator; a freezing branch coupled between the refrigerant collecting container and the suction side of the first compressor unit, the freezing branch comprising a second expansion device, a second evaporator, and a second compressor unit; refrigerant conduits for connecting said elements and for circulating a refrigerant therethrough; an oil balance line connecting at least two compressors of the first compressor unit; an oil collecting container being connected or connectible to at least one compressor of the second compressor unit; an oil refeeding line extending between the oil collecting container and the oil balance line; a pressure line attaching to the oil collecting container that can opened and closed; wherein, if the oil level in the oil collecting container exceeds a predetermined height, the pressure line is opened thereby effecting oil flow from the oil collecting container to the oil balance line.
According to further exemplary embodiments of the invention, a method for balancing the oil levels between compressors of a refrigeration system comprises a first compressor unit, a condenser/gas cooler, and a refrigerant collecting container; a normal refrigeration branch coupled between the refrigerant collecting container and a suction side of the first compressor unit, the normal refrigeration branch comprising a first expansion device and a first evaporator; a freezing branch coupled between the refrigerant collecting container and the suction side of the first compressor unit, the freezing branch comprising a second expansion device, a second evaporator, and a second compressor unit; refrigerant conduits for connecting said elements and for circulating a refrigerant therethrough; an oil balance line connecting at least two compressors of the first compressor unit; an oil collecting container being connected or connectible to at least one compressor of the second compressor unit; an oil refeeding line extending between the oil collecting container and the oil balance line; and a pressure line attaching to the oil collecting container that can be opened and closed; the method comprising the step of, if the oil level in the oil collecting container exceeds a predetermined height, opening the pressure line thereby effecting oil flow from the oil collecting container to the oil balance line.
Exemplary embodiments of the invention will be described in greater detail below taking reference to the accompanying drawings.
Fig. 1 shows a schematic view of a C0 2 booster refrigeration system according to an exemplary embodiment of the invention; and
Fig. 2 shows a detail of the C0 2 booster refrigeration system of Fig. 1.
The C0 2 booster refrigeration system 2 comprises an oil refeeding and balancing concept that is described in further detail below.
The C0 2 booster refrigeration system 2 comprises, in flow direction of the refrigerant, a medium temperature compressor set 4 comprising two medium temperature compressors 4 connected in parallel, a condenser/gas cooler 6, an intermediate pressure expansion device 8, an intermediate pressure refrigerant collecting container 10 having a lower liquid space portion in which liquid refrigerant collects and an upper gaseous refrigerant portion in which gaseous refrigerant collects, and a common liquid line to both medium temperature (normal) cold consumers and low temperature (freezing) cold consumers. The medium temperature cold consumers and the low temperature cold consumers as well as the respective expansion devices arranged before them are not depicted in Fig. 1. The medium and low temperature cold consumers can be formed as refrigerating furnitures, like refrigerating cabinets, refrigerating chests or refrigerating islands, or as refrigerating rooms, that provide the goods arranged therein with refrigeration at normal or freezing temperatures.
In the condenser/gas cooler 6, the refrigerant is cooled down against a secondary medium. In the exemplary embodiment of Fig. 1 , the secondary medium is air. However, other secondary media, such as water or air enriched with water particles, may also be used. In the case of C0 2 being the refrigerant, the condenser/gas cooler is referred to as a gas cooler, as the refrigerant leaves the gas cooler 6 in a gaseous phase. For other refrigerants, a condensation may take place in the condenser/gas cooler 6, such that this refrigerant circuit element is referred to as a condenser.
The C0 2 booster refrigeration system 2 further comprises a suction line 14 from the medium temperature cold consumers (not shown) and leading to the medium temperature compressor set 4.
The C0 2 booster refrigeration system 2 further comprises a suction line 20 returning gaseous refrigerants from the low temperature cold consumers (not shown) and leading to a low temperature compressor set 22 comprising two low temperature compressors 22 connected in parallel.
As can be seen in Fig. 1 , the refrigerant line coming from the intermediate pressure expansion device 8 connects to an upper portion of the intermediate pressure refrigerant collecting container 10, and the liquid line 12 to the medium and low temperature cold consumers 12 connects to a lower portion of the refrigerant collecting container 10.
Attaching to the upper gas space portion of the intermediate pressure refrigerant collecting container 10 and leading to the suction side of the medium temperature compressor set 4, there is provided a flash gas line 16 having a control valve 18 arranged therein. By means of this flash gas line 16 excess flash gas from the intermediate pressure refrigerant collecting container 10, in particular from its upper gas space portion can be sucked off from the medium temperature compressor set 4 in case the control valve 18 is opened. The common pressure line 24 coming from the low temperature compressor set 22 attaches to the portion of the flash gas line 16 positioned after the control valve 18 such that in normal operation of the C0 2 booster refrigeration system 2 the refrigerant that is compressed by the low temperature compressor set 22 to the input pressure of the medium temperature compressor set 4 is led to the medium temperature compressor set 4 and compressed therein, together with the gaseous refrigerant returning from the medium temperature cold consumers over the suction line 14 to high pressure.
Between the oil sumps of the medium temperature compressors 4 there is provided an oil balance line 34 of the medium temperature compressors 4. By means of this oil balance line 34 the oil levels within the oil sumps of the medium temperature compressors 4 is balanced automatically.
At the side of the low temperature compressors 22 there is provided an oil collecting container 26 that is connected, by means of an oil line 30, to the oil sumps of the low temperature compressors 22.
In the embodiment of Fig. 1 , this oil line 30 has a first common part and then branches into a first line portion leading to the oil sump of the first low temperature compressor 22 and into a second line portion leading to the oil sump of the second low temperature compressor 22. In this oil line 30 there is provided an appropriate means for opening and closing the same. In the embodiment of Fig. 1 , this means is formed by a solenoid valve 32 that is arranged in the first common part of the oil line 30. If this solenoid valve 32 is in its open position, excess oil from the oil sumps of the low temperature compressors 22 flows into the oil collecting container 26 and collects therein.
There is further provided an oil refeeding line 36 that attaches with its first end to a lower portion at or within the oil collecting container 26 and attaches with its second end to the oil balance line 34 of the medium temperature compressors 4. In this oil refeeding line 26 there can be arranged a further valve 38. In the embodiment of Fig. 1 , this valve is formed by a solenoid valve 38, that is configured for opening and closing the oil refeeding line 36.
The intermediate pressure expansion device 8 expands the high pressure refrigerant that has been cooled by the condenser/gas cooler 6 to an intermediate pressure.
Typical pressure levels are 10 to 120 bar at the high pressure side between the medium temperature compressors 4 and the intermediate pressure expansion device 8 and 5 to 40 bar at the intermediate pressure side between the intermediate pressure expansion device 8 and the expansion devices arranged before the cold consumers (not shown in Fig. 1 ). In the exemplary embodiment of Fig. 1 , the intermediate pressure level is approx. 34 bar (corresponding to a temperature of -1 °C). The low temperature evaporation pressure within the oil collecting container 26 can be approximately 10 bar (corresponding to a temperature of -40°C). The medium temperature evaporation pressure within the oil refeeding line after the solenoid valve 38 can be at approximately 29 bar (corresponding to a temperature of -10°C).
The C0 2 booster refrigeration system 2 further comprises an intermediate pressure line 40 extending between the gas space portion of the refrigerant collecting container 10 and an upper portion of the oil collecting container 26. In this intermediate pressure line 40 there is arranged a solenoid valve 42 being configured to open and close this intermediate pressure line 40 as needed.
In the particular embodiment of Fig. 1 both the flash gas line 16 and the intermediate pressure line 40 join at a connection point that is positioned above the refrigerant collecting container 10 and both have a common portion leading from the upper gaseous space portion of the refrigerant collecting container 10 upwardly to this connection point. In or at the oil collecting container 26 there is provided a liquid level switch 28 that detects if the oil level within the oil collecting container 26 exceeds a predetermined height or falls below this predetermined height again and generates a switching signal by means of which the valve 32 can be closed and opened and the valves 42 and 38 can be opened and closed.
Fig. 2 shows a detail of the C0 2 booster refrigeration system 2.
In Fig. 2 only the right low temperature compressor 22 of the two low temperature compressors 22 is shown for simplicity. There is depicted an oil sight glass 44 being connected to the oil sump of the low temperature compressor 22. This oil sight glass 44 is connected to the oil line 30 leading to the oil collecting container 26.
As can be seen in Fig. 2, the intermediate pressure line 40 connects to the uppermost portion of the oil collecting container 26, whereas the oil refeeding line 36 connects to a quite low point within the oil collecting container 26. This connection point is depicted as an oil tapping point 46 arranged close to the bottom of the oil collecting container 26.
During normal operation of the C0 2 booster refrigeration system 2, the excess oil from the oil sumps of the low temperature compressors 22 is fed via the oil sight glass 44 and the oil line 30 into the oil collecting container 26. If the liquid level switch 28 detects that the oil level within the oil collecting container 26 exceeds a predetermined height then the C0 2 booster refrigeration system 2 is switched into the oil balancing and refeeding operation that can be carried out simultaneously to the normal refrigeration operation.
For the oil balancing and refeeding operation, the solenoid valve 32 in the oil line 30 is closed preventing further oil flow from the oil sumps of the low temperature compressors 22 into the oil collecting container 26. Furthermore, the solenoid valve 42 within the intermediate pressure line 40 and the valve 38 within the oil refeeding line 36 are opened such that intermediate pressure gaseous refrigerant is pressed into the oil collecting container 26 and presses oil from the oil collecting container 26 through the oil refeeding line 36 to the oil balance line 34 of the medium temperature compressors 4.
If the oil level in the oil collecting container 26 is lower than a predetermined height, the excess oil from the low temperature compressor 22 flows automatically into the oil container 26. By opening the intermediate pressure line 40 to the oil collecting container 26, pressurized gaseous refrigerant is led into the oil collecting container 26 thereby effecting oil flow from the oil collecting container 26 to the oil balance line 34.
Since the oil refeeding line 36 attaches at a lower portion of the oil collecting container 26 it is guaranteed that the liquid level switch 28 detects that the oil level within the oil collecting container 26 falls under the predetermined height again and closes the solenoid valve 42 before gaseous refrigerant can enter into the oil refeeding line 36. If the liquid level switch 28 detects that the oil level within the oil collecting container 26 has fallen under the predetermined height again, then also the valve 38 is closed again and the solenoid valve 32 is opened again.
The solenoid valve 38 can also be formed as a simple non-return valve allowing oil flow in one direction if the pressure within the oil refeeding line 36 exceeds the predetermined value and always preventing oil back-flow in the other direction.
The gaseous refrigerant that has entered the upper portion of the oil collecting container 26 can be sucked off by the normal temperature compressors 22 in normal operation.
In another embodiment a control unit can be present that receives the switching signal from the liquid level switch 28 and opens and closes the valves 30, 38 and 42 based on this switching signal. This control unit can also effect the normal control of the C0 2 booster refrigeration system 2 and its elements shown in Fig. 1 and, additionally, the cold consumers and the respective expansion devices.
In order to realize the electrical switching between the liquid level switch 28 and the valves 32, 42 and, if applicable, valve 38 can be realized by a relay having two alternating contacts.
While it has been described, as an exemplary embodiment with reference to the figures, that the oil collecting container 26 is connected via the intermediate pressure line 40 to the refrigerant collecting container 10, according to alternative embodiments, the pressure line attaching to the oil collecting container 26 can supply pressurized refrigerant that presses the excess oil from the oil collecting container 26 through the oil refeeding line 36 to the oil balance line 34 from anywhere, either from at least one point in the C0 2 booster refrigeration system 2 or from an external source. In particular, the oil collecting container 26 can be connected to any point within the intermediate pressure portion of the refrigeration system.
While the refrigerating circuit and the corresponding method according to exemplary embodiments, as described above, is generally suitable for a wide variety of refrigerants, carbondioxide (C0 2 ) is particularly well suited. Within the context of this application, both C0 2 and C0 2 blends are to be understood as C0 2 refrigerant.
By exemplary embodiments of the invention, as described above, the oil levels of the medium temperature compressors and the low temperature compressors are balanced automatically. The excess amount of oil that regularly collects at the low temperature compressor side, in particular in the oil collecting container, is automatically fed back to the medium temperature compressor side, in particular to the oil balance line of the medium temperature compressors. Thereby too low oil levels at the medium temperature compressor side and too high oil levels at the low temperature compressor side are reliably avoided and therefore defects of those compressors being caused by insufficient lubrication or by oil hits can be considerably reduced.
The automatic oil balancing and oil refeeding provided by the particular embodiments, as described above, can be realized easily and cost-efficiently for all booster systems no matter what performance.
All the advantages and the embodiments that have been described with respect to the refrigerating circuit also hold true for the corresponding method for balancing the oil levels between compressors of a refrigeration system. These advantages and embodiments are herewith explicitly disclosed also in terms of corresponding method steps, however without repeating them again.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt the particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
List of reference numerals
2 C0 2 booster system
4 medium temperature compressors
6 condenser/gas cooler
8 intermediate pressure expansion device
10 refrigerant collecting container
12 liquid line to medium temperature and low temperature cold
14 suction line from medium temperature cold consumers
16 flash gas line
18 control valve
20 suction line from low temperature cold consumers
22 low temperature compressors
24 pressure line of low temperature compressors
26 oil collecting container
28 liquid level switch
30 oil line from low temperature compressors
32 solenoid valve
34 oil balance line of medium temperature compressors
36 oil refeeding line
38 solenoid valve
40 intermediate pressure line to oil collecting container
42 solenoid valve
44 oil sight glass
46 oil tapping point
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