US3577742A

US3577742A - Refrigeration system having a screw compressor with an auxiliary high pressure suction inlet

Info

Publication number: US3577742A
Application number: US832979A
Authority: US
Inventors: Erich J Kocher
Original assignee: Vilter Manufacturing LLC
Current assignee: Copeland Industrial LP
Priority date: 1969-06-13
Filing date: 1969-06-13
Publication date: 1971-05-04
Anticipated expiration: 1988-05-04
Also published as: GB1271476A; DE2028842A1

Abstract

A refrigeration system having a screw compressor for compressing low pressure suction gas that is received from an evaporator and compressing it and discharging it into a condenser; including an auxiliary high-pressure suction inlet to the compressor for conducting high-pressure suction vapor from a pressure-reducing means and to the compressor for being compressed along with lowpressure suction vapor. The invention is used with a refrigeration system having either two operating suction pressure levels, or having a single suction level. The high-pressure suction vapor is introduced into the compressor at a point after the low-pressure suction is cut off, and therefore no reduction in the low-pressure suction capacity results. Increased compressor capacity is thus accomplished by the addition of this high pressure vapor.

Description

United States Patent Inventor Appl. No.

Filed Patented Assignee REFRIGERATION SYSTEM HAVING A SCREW Erich J- Kocher Milwaukee, Wis.

June 13, l 969 May 4, 197 1 Vilter Manufacturing Corporation Milwaukee, Wis.

COMPRESSOR WITH AN AUXILIARY HIGH Primary, Examiner-Meyer Perlin Attorney-James E. Nilles ABSTRACT: A refrigeration system having a screw compressor for compressing low pressure suction gas that is received from an evaporator and compressing it and discharging it into a condenser; including an auxiliary high-pressure suction inlet to the compressor for conducting high-pressure suction vapor from a pressure-reducing means and to the compressor for being compressed along with low-pressure suction vapor. The invention is used with a refrigeration system having either two operating suction pressure levels, or having a single suction level. The high-pressure suction vapor is introduced into the compressor at a point after the low-pressure suction is cut off, and therefore no reduction in the low-pressure suction capaci- 2,277,647 3/1942 Jones 62/510X ty results. Increased compressor capacity is thus accomplished 2,481,605 9/ 1949 MacLeod 62/510 by the addition of this high pressure vapor.

2 1 & 6 1 :20 1

COMPRE$$OR vAZ C'c NDEN SEE go 5 2 l RECEIVER REFRIGERATION SYSTEM HAVING A SCREW COMPRESSOR WITH AN AUXILIARY HIGH PRESSURE SUCTION INLET BACKGROUND OF THE INVENTION In the prior art refrigeration systems, two operating suction pressure levels are required to accommodate certain load conditions. In these devices, it is conventional to use two compressors, one for each pressure level. While this arrangement is satisfactory from a refrigeration stand-point, it is expensive since duplicate components such as motors, starters, and sets of controls must be provided.

It is also known to have a single compressor which may be used to handle the double level loads by operating at a lowpressure suction level, and then having the high-pressure suction vapor feed into the low pressure suction line through a back pressure regulator. This prior art type of system is inefficient in that it requires a larger compressor because the higher pressure suction vapor expands when being reduced to the low pressure level through the back pressure regulator. In addition, compressing all of the vapors from the low suction pressure to the condensing pressure requires additional horsepower.

SUMMARY OF THE INVENTION The present invention provides a refrigeration circuit including a screw compressor having a low-pressure suction inlet at one end and a discharge port for discharging high-pressure vapor which has been compressed by the rotors of the compressor into the high-pressure condenser; the condenser discharges into a receiver and then the liquid from the receiver is conducted through a pressure-reducing means which controls the flow of refrigerant to a flash chamber or evaporator. The evaporators can take the formof either a flash chamber in which some liquid is evaporated to cool itself as in a single level system or takes the form of evaporators to produce refrigeration in a two level system. The invention contemplates taking high-pressure suction vapors from the pressure-reducing means and introducing it into the screw compressor for being compressed along with the low-pressure suction vapor, thereby increasing compressor capacity. A more specific aspect of the invention provides that the highpressure suction vapor is introduced into the compressor at a point before compression commences.

These and other objects and advantages of the present invention will appear hereinafter as this disclosure progresses, reference being had to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a refrigerating system of the two suction pressure level type, which embodies the present invention;

FIG. 2 is a schematic diagram of a refrigeration system of the single suction pressure level type and which embodies a flash chamber;

FIG. 3 is an enlarged plan view, partially in section of the compressor shown in FIGS. 1 and 2;

' FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 3; and

FIG. 5 is an enlarged plan view of the compressor, with parts being shown as cut away and removed for clarity.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 shows the invention as applied to a refrigeration circuit having two evaporators E and E1 so as to provide two operating suction pressure levels. These evaporators themselves are conventional and may be of the shell and tube bri'ne cooler type in which brine is introduced into and taken out of the evaporator by conduits 1 and 2. Evaporator E1 is at a .higher temperature than in evaporator E so as to produce refrigeration at a different temperature level, as in a separate room. A float valve 3 is provided for each of the evaporators to control the flow of refrigerant to these evaporators from the high-pressure receiver 4. TI-Ie float valves function in the known manner to reduce the pressure of the liquid from the receiver pressure to the evaporator pressure.

The evaporators vaporize the remaining liquid fed by the float valves, to produce refrigeration. The vapor is pumped away by the compressor through the suction conduits.

The circuit also includes a screw compressor C of the type having a pair of oppositely rotating and constant mesh

helical lobe rotors

6 and 7 which cooperate to provide a pumping and compressing action. The rotors define interlobe cavities which close off a low-pressure suction inlet 8, and these cavities become progressively smaller to thereby compress the vapor therebetween. Low-pressure suction vapor is introduced via conduit 10 from the evaporator E and to the low-pressure suction inlet 8 of the compressor.

TI-Ie compressor then has a discharge port 12 for discharging high pressure vapor which has been compressed by the rotors, and this vapor is discharged by conduit 13 to a condenser 14. The condenser 14 is of conventional character and it functions to receive high-pressure vapor from the compressor discharge, and then the condenser discharges the condensed refrigerant to the high-pressure receiver 4.

Referring again to the screw compressor C, it is driven in a conventional manner by an electric motor 16. The compressor also has a high-pressure suction port 20 which is in communication with the above-mentioned interlobe cavities, and this communication is at a location immediately past the point where the low pressure suction inlet is cut off by the action on the intermeshing rotors. The location of the introduction of this high-pressure suction vapor is also preferably at the beginning of the compression of the vapor due to the rotation of the rotors, but under some conditions, can be introduced at a later point after some compression has taken place. Stated otherwise, high pressure suction vapor is conducted by a line 22 from the evaporator E1, which vaporize refrigerant to produce refrigeration. This high-pressure suction vapor is introduced between the rotors at a point after the low-pressure suction vapor has been cut off and preferably prior to the point where any appreciable compression has taken place in the compressor.

With the above-described circuit and apparatus, a highpressure suction line is provided for conducting some highpressure suction vapor from the pressure-reducing means and to the high-pressure suction port of the screw compressor. Consequently, the high-pressure suction vapor is compressed along with the low-pressure suction vapor thereby increasing the compressor capacity, and two pressure levels may be handled by a multiple effect screw compressor without the disadvantage of the prior art previously referred to.

FIGURE 2 The circuit shown in FIG. 2 has a number of parts that are identical to those shown in FIG. 1 and have been correspondingly identified. It will be noted however, that only one evaporator E is used and a flash chamber '40 is interposed between the high-pressure receiver and the evaporator E.

This flash chamber serves to reduce the pressure of the liquid received from the receiver and thus the flash chamber also constitutes a pressure-reducing means for receiving liquid from the receiver for reducing the pressure of the liquid, and consequently forming some refrigerant vapor. The flash chamber thus reduces the pressure of the liquid and thereby provides cooler liquid to the evaporator E so the latter is able to do more work.

In this embodiment of the invention, the high-pressure suction line 22 is connected between the upper portion of the flash chamber 40, where the vapors are located, and the line 22 serves to conduct this high-pressure suction vapor to the screw compressor C, as previously described.

With the single level system as shown in FIG. 2, the screw compressor C has a greater refrigerating capacity than the ordinary screw compressor of equal displacement on such a single suction level system. This increased capacity is accomplished by interposing the flash chamber in the main liquid line from the receiver to the evaporator and bleeding off the flash gas into the auxiliary high-pressure suction inlet connection to the compressor. More refrigerating effect can be obtained from a given amount of cold liquid leaving the flash chamber than from the same amount of warm liquid leaving the receiver. Since the bleed vapor from the flash tank that enters the compressor does not reduce the amount of low-pressure vapor entering the main suction to the compressor, and since cold vaporized liquid has a greater refrigerating effect than vaporized warm liquid, the compressor capacity is increased.

RESUME The present invention provides a refrigerating circuit including a screw compressor having two close clearance helical lobe rotors turning in synchronous mesh. The low suction pressure vapor enters the compressor through the inlet port into enlarging interlobe cavities. When the cavities pass the inlet port, they are cut off from the low-pressure suction chamber. The cavities then become progressively smaller as rotation of the rotors continues, thereby compressing the vapor until full compression is reached at the discharge port. The high-pressure suction line is introduced into the compressor housing so as to communicate with the cavities at a point immediately after the low pressure suction cut off and preferably at the beginning of the compression before the pressure builds up in the compressor. The high-pressure suction vapor flows into the exposed cavities because the pressure in the high-pressure suction line is higher than the pressure in the cavities which are filled with low pressure vapor. Consequently, some high-pressure suction vapor is trapped along with the low pressure vapor. Because the high-pressure vapor is introduced after the low-pressure cutoff, no reduction in the low-pressure suction capacity results, and the addition of highpressure vapor results in obtaining more work and thereby increases the compressor capacity.

Iclaim:

1. A refrigeration system comprising; a screw compressor including a pair of oppositely rotating and constant mesh helical lobe rotors which cooperate to provide a pumping and compressing action; said compressor having a low-pressure suction inlet at one end for receiving low suction pressure vapor, a high-pressure suction port past said low pressure suction inlet, and a discharge port for discharging high-pressure vapor which has been compressed by said rotors; a high-pressure condenser in communication with said compressor discharge port for receiving high-pressure vapor therefrom, a receiver for receiving condensed refrigerant from the condenser, pressure-reducing means for receiving liquid from said receiver and for reducing the pressure of said liquid and consequently forming some refrigerant vapor, a low-pressure suction line connected between said pressure-reducing means and said low-pressure suction inlet of said compressor, and a high-pressure suction line for conducting some high-pressure suction vapor from said pressure-reducing means to said highpressure suction port of said compressor for being compressed along with low pressure suction vapor, thereby increasing compressor capacity.

2. A system as defined in claim 1 further characterized in that said pressure-reducing means includes a flash chamber for reducing pressure of liquid received from said receiver, and said high-pressure suction line places said flash chamber in communication with said high-pressure suction port of said compressor.

3. A system as defined in claim 2 wherein the system is a two pressure level system in which said pressure-reducing means includes a tgair of evaporators, one at a higher temperature than the 0 er; said high-pressure suction line placlng one of said evaporators in communication with said high-pressure suction port of said compressor.

4. The system set forth in claim 3 further characterized in that said high-pressure suction line is in communication with that evaporator of higher temperature.

5. A refrigeration system comprising; a screw compressor including a pair of oppositely rotating and constant mesh helical lobe rotors which cooperate to provide a pumping and compressing action, said compressor having a low-pressure suction inlet at one end for receiving low-suction pressure vapor, said compressor defining interlobe cavities which close off said low-pressure suction inlet and then become progressively smaller to thereby compress the vapor therebetween, said compressor having a high-pressure suction port in communication with said cavities at a location immediately past said low-pressure suction inlet and at the beginning of compression of the vapor by rotation of said rotors, said compressor also having a discharge port for discharging high-pressure vapor which has been compressed by said rotors; a high pressure condenser in communication with said compressor discharge port for receiving high-pressure vapor therefrom, a receiver for receiving condensed refrigerant from the condenser, pressure-reducing means for receiving liquid from said receiver and for reducing the pressure of said liquid and consequently forming some refrigerant vapor, a low-pressure suction line connected between said pressure-reducing means and said low-pressure suction inlet of said compressor, and a high-pressure suction line for conducting some high-pressure suction vapor from said pressure-reducing means to said highpressure suction port of said compressor for being compressed along with low-pressure suction vapor, thereby increasing compressor capacity.

6. A system as defined in claim 5 further characterized in that said pressure-reducing means includes a flash chamber for reducing pressure of liquid received from said receiver, and said high-pressure suction line places said flash chamber in communication with said high-pressure suction port of said compressor.

7. A system as defined in claim 6 wherein the system is a two pressure level system in which said pressure-reducing means includes a pair of evaporators, one at a higher temperature than the other; said high-pressure suction line placing one of said evaporators in communication with said high-pressure suction port of said compressor.

8. The system set forth in claim 7 further characterized in that said high-pressure suction line is in communication with that evaporator of higher temperature.

Claims

1. A refrigeration system comprising; a screw compressor including a pair of oppositely rotating and constant mesh helical lobe rotors which cooperate to provide a pumping and compressing action; said compressor having a low-pressure suction inlet at one end for receiving low suction pressure vapor, a high-pressure suction port past said low pressure suction inlet, and a discharge port for discharging high-pressure vapor which has been compressed by said rotors; a high-pressure condenser in communication with said compressor discharge port for receiving high-pressure vapor therefrom, a receiver for receiving condensed refrigerant from the condenser, pressure-reducing means for receiving liquid from said receiver and for Reducing the pressure of said liquid and consequently forming some refrigerant vapor, a low-pressure suction line connected between said pressurereducing means and said low-pressure suction inlet of said compressor, and a high-pressure suction line for conducting some high-pressure suction vapor from said pressure-reducing means to said high-pressure suction port of said compressor for being compressed along with low pressure suction vapor, thereby increasing compressor capacity.

3. A system as defined in claim 2 wherein the system is a two pressure level system in which said pressure-reducing means includes a pair of evaporators, one at a higher temperature than the other; said high-pressure suction line placing one of said evaporators in communication with said high-pressure suction port of said compressor.

5. A refrigeration system comprising; a screw compressor including a pair of oppositely rotating and constant mesh helical lobe rotors which cooperate to provide a pumping and compressing action, said compressor having a low-pressure suction inlet at one end for receiving low-suction pressure vapor, said compressor defining interlobe cavities which close off said low-pressure suction inlet and then become progressively smaller to thereby compress the vapor therebetween, said compressor having a high-pressure suction port in communication with said cavities at a location immediately past said low-pressure suction inlet and at the beginning of compression of the vapor by rotation of said rotors, said compressor also having a discharge port for discharging high-pressure vapor which has been compressed by said rotors; a high pressure condenser in communication with said compressor discharge port for receiving high-pressure vapor therefrom, a receiver for receiving condensed refrigerant from the condenser, pressure-reducing means for receiving liquid from said receiver and for reducing the pressure of said liquid and consequently forming some refrigerant vapor, a low-pressure suction line connected between said pressure-reducing means and said low-pressure suction inlet of said compressor, and a high-pressure suction line for conducting some high-pressure suction vapor from said pressure-reducing means to said high-pressure suction port of said compressor for being compressed along with low-pressure suction vapor, thereby increasing compressor capacity.