US3885938A

US3885938A - Refrigeration system with capacity control

Info

Publication number: US3885938A
Application number: US434756A
Authority: US
Inventors: Carlos R Ordonez
Original assignee: Westinghouse Electric Corp
Current assignee: Daikin Applied Americas Inc
Priority date: 1974-01-18
Filing date: 1974-01-18
Publication date: 1975-05-27
Anticipated expiration: 1992-05-27
Also published as: CA1013160A; GB1486101A; AU7709175A; JPS50107546A; JPS5426017B2

Abstract

A refrigeration system having at least one unloadable compressing apparatus and at least one always loaded compressing apparatus is provided with separate gas discharge lines connected to respectively separate condenser coil surfaces, and a valve arrangement is provided in those discharge lines connected to the unloadable compressing apparatus for closing those lines in response to an unloaded condition of the particular compressing apparatus serving the lines. The system has condenser coil surfaces matched to the unloading steps of the compressing apparatus. In one embodiment the valves in the discharge lines subject to being loaded or shut down are of the pilot type in which the pilot control is derived from the always loaded discharge line.

Description

United States Patent [1 1 Ordonez [451 May 27, 1975 REFRIGERATION SYSTEM WITH CAPACITY CONTROL [75] Inventor:

173] Assignee: Westinghouse Electric Corp.,

Pittsburgh, Pa.

22 Filed: Jan. 18,1974

2| Appl.No.:434,756

Carlos R. Ordonez, Staunton, Va.

[52] US. Cl. 62/196; 62/228; 62/510 [51] Int. Cl. F25b 41/00 [58] Field of Search 62/196, 510, 228

[56] References Cited UNITED STATES PATENTS 2,755,634 7/1956 Simmons 62/510 3,280,582 10/1966 62/510 3,386,262 6/1968 Haekbert 1 1 4 i v 1 62/510 3,503,223 3/1970 Parker 1 62/510 3,775,995 12/1973 Conley 62/196 Primary Examiner-Meyer Perlin Attorney, Agent, or Firm-E. C. Arenz [57] ABSTRACT A refrigeration system having at least one unloadable compressing apparatus and at least one always loaded compressing apparatus is provided with separate gas discharge lines connected to respectively separate condenser coil surfaces, and a valve arrangement is provided in those discharge lines connected to the unloadable compressing apparatus for closing those lines in response to an unloaded condition of the particular compressing apparatus serving the lines. The system has condenser coil surfaces matched to the unloading steps of the compressing apparatus. In one embodiment the valves in the discharge lines subject to being loaded or shut down are of the pilot type in which the pilot control is derived from the always loaded discharge line.

9 Claims, 5 Drawing Figures 2 4 2o so CONDENSER r(;---

couosusze 44 couoeusse r{r LOAD FATENTEDMAY 27 ms SHEET LOAD g 20 3o CONDENSER CONDENSER CONDENSER FIG. I.

SHEET CTION RESPONSIVE CONTROLLER SSURE FIG. 5.

J/ -E I L 1 L k E L...[

94 FIG. 3.

J60 COMP OAD LINE VA CL 0 RELIEF VALVE 5 4 J62 OPENED com? 3 OFF 1' 8 LINE VALVE 1g CLOSED REFRIGERATION SYSTEM WITH CAPACITY CONTROL BACKGROUND OF THE INVENTION The invention pertains to the art of refrigeration systems having at least one unloadable compressor and the refrigerant piping and control arrangement for the system.

DESCRIPTION OF THE PRIOR ART Conley et al., U.S. Pat. No. 3,775,995 is the closest prior art of which applicants are aware in that it discloses and claims a capacity control arrangement for dual compressors, one of which is unloadable.

Examples of other U.S. patents which disclose refrigeration systems including either unloadable compressors or multiple compressors feeding separate condenser coil surfaces in one way or another are U.S. Pat. Nos. 3,013,403, 2,760,348, 2,677,944, 2,274,774, 2,274,336, 2,168,157, 2,079,687 and 2,008,407. However, they do not deal with the hermetically sealed shell type of compressors in which the interiors of the shells are in communication with each other and which occasions the passage of a refrigerant from a warmer environment to a colder non-operating environment. Accordingly, the exemplary patents are not considered particularly pertinent to the invention.

Some of the commercial background of the apparatus involved may lend a better understanding of the invention. The invention is particularly applicable to aircooled condensing units of the 25 to 40 ton sizes, for example. In such units a dual compressor assembly is provided having two hermetically sealed, multicylinder compressors mounted on a single base with the compressors being in tandem with respect to receiving suction gas. This permits a single suction connection to be made to the two compressors. The lead compressor is 50 percent unloading and accordingly has a nonunloading discharge line and an unloadable discharge line. The lag compressor is non-unloading and operates either fully loaded or not at all. Thus it has its two discharge lines joined together into a common discharge line.

In carrying out the invention, to obtain a matching of the condenser coil surfaces to the operation of the system in the various unloading steps, the condenser serving the lead shell is the same size as that serving'the lag shell but is split so that each of the condenser parts serves one of the two discharges from the lead compressor. Under certain conditions of partly unloaded operation, there is a tendency for passage or leakage of refrigerant from a warm environment to a colder environment. Thus, for example, when the system is operating under low ambient conditions with the lag compressor off there may be passage of suction gas refrigerant from the hot operating lead compressor through the suction gas connection to the lag compressor, which may still have a higher interior temperature than its condenser coil because of the low ambient temperature. This suction gas received by the cold condenser coil through the lag compressor may condense and accumulate in liquid form and accordingly decrease the refrigerant charge in the system as a whole. This may possibly cause the system to shut down because of low suction pressure. Under a condition of high ambient temperatures with only the lead compressor operating refrigerant can pass from the warm lag compressor coil to the relatively colder lag compressor. If condensation of this refrigerant occurs, liquid can accumulate on top of the compressor and possibly cause damage to the compressor upon a subsequent start-up. Problems of this general character are also discussed in the noted Conley et al. patent.

The aim of the invention is to provide a refrigeration system in which condensing surfaces are matched to the compressing capacity and in which the system avoids the noted problems experienced with migrating refrigerant.

SUMMARY OF THE INVENTION In accordance with the invention a refrigeration system is provided in which separate discharges for the loaded and unloaded parts of an unloading compressor are provided, the condensing coil capacity is matched to the loaded condition of the system and means are provided to effect isolation from the remainder of the refrigeration system of the inlets and outlets of the condensers which are not being fed due to the unloaded condition of the system. Additionally, the invention contemplates the provision of a pilot type valve for effecting the isolation of the unused condenser portion during a partly unloaded operation.

DRAWING DESCRIPTION FIG. I is a schematic view of a refrigeration system according to one embodiment of the invention;

FIG. 2 is a schematic view of another embodiment of the refrigeration system according to the invention;

FIG. 3 is a sectional view of one example of a pilot valve usable in carrying out the invention;

FIG. 4 is a view of a fragmentary portion of the end of the pilot valve having a pair of inlet connections and a relief connection; and

FIG. 5 is an operational diagram of a control arrangement for use in connection with the FIG. 1 embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a 50% unloadable, multicylinder compressor 10 of the hermetically sealed shell type has an always loaded discharge port 12 and an unloadable discharge port 14 which are connected to hot

gas discharge lines

16 and 18 respectively. Each compressor may be of the general type disclosed in U.S. Pat. Nos. 3,171,588 and 3,259,307, for example. The non-unloading port and line may also be referred to as the always loaded port and line, meaning, of course, always loaded while the system is in operation. The unloadable compressor 10 is also commonly referred to as the lead compressor in the art. The lines 16 and [8 are connected to a split condenser coil 20, one-half 22 of which is served by the always loaded line 16 and the other half 24 of which is served by the unloadable line 18. The tubes of the coil 20 are not interlaced, so each half effectively functions as a separate coil.

The line 18 has a check valve 26 and a solenoid valve 28 therein, and the outlet of condenser half 24 has a check valve 30 therein.

The lag compressor 32 is a non-unloadable, multicylinder compressor of the hermetically sealed shell type and has its interior connected to the interior of the lead compressor shell by a suction gas connection 34 so that the connection of the compressors with respect to the receipt of suction gas in the system is characterized as a tandem arrangement. The two hot gas discharge ports of the lag compressor 32 have lines connected thereto which join to form a common line 36 which leads to the condenser 38 for the lag compressor. The common line 36 has a check valve 40 and a solenoid valve 42 therein, and a check valve 44 is provided in the outlet line from the condenser 38. The outlet lines from the split condenser 20 and from the condenser 38 join on the downstream side of the

check valves

30 and 44 to form a common line 46 which leads to the evaporator or load 48 which is connected by suction gas line 50 back to the inlet of the lead compressor 10. A relief line 52 having a solenoid valve 54 therein connects between the common line 36 on the upstream side of the solenoid valve 42 with the common Suction 50.

A controller 56 responsive to the suction pressure in the common suction line 50 functions to provide capacity control through switch means 58 (FIG. for controlling the energization of the compressors l0 and 32 as well as the various solenoid valves in the lines. The capacity control steps are accomplished as follows. As noted before the lead compressor is 50% unloading while the lag compressor 32 is always fully loaded or off and is of the non-unloading type. Four equal steps of capacity control are accomplished through a combination of unloading the lead compressor and shutting down the lag compressor. For full capacity, the lead compressor 10 is operated fully loaded and the lag compressor 32 is also operated. For three-fourths capacity, the compressor 10 is operated 50% unloaded with the lag compressor operating at full load. For half capacity of the system, the lead compressor is operated fully loaded while the lag compressor is off. For onefourth capacity, the lead compressor is operated 50% unloaded while the lag compressor is off. As may be seen from the operating condition legends in the

boxes

60, 62 and 64 in FIG. 5, the solenoid valve 28 in the unloadable discharge line 18 is closed whenever the lead compressor 10 is half unloaded. As shown in box 64, the same condition exists for the solenoid valve 42 in the discharge line 36 when the lag compressor is off. Likewise, the relief valve 54 is operated to an open po sition whenever the compressor 32 is shut down.

The manner in which the described system functions to obtain the advantages of the invention under various operating conditions will now be described. Under a low ambient temperature condition with only the lead compressor 10 operating, the temperature of condenser 38 normally served by the lag compressor 32 may be lower than the suction gas temperature which is permitted to pass into the lag compressor shell through the suction crossover line 34. Thus the lag compressor interior, which is not operating, may well be warmer than the condenser 38 and the tendency of the refrigerant is to pass to the colder environment. The check valve 40 does not prevent flow in the direction from the lag compressor 32 to the condenser 38. However, the closed solenoid valve 42 does prevent this flow. If the refrigerant were permitted to pass into the cold condenser coil, it could condense and tend to fill it with liquid which would decrease the charge in the system as a whole, possibly causing the system to shut down because of low suction pressure. In that connection it is noted that the usual protective devices such as high pressure and temperature cutouts, low

pressure cutouts, etc., are not shown in the system, but it will be understood they are used in accordance with conventional practice.

Under a high ambient temperature condition in which only the lead compressor 10 is operating, the passage of refrigerant can be from the hot condenser coil 38 to the cold compressor 32, which has a temperature corresponding generally to the suction gas temperature in the lead compressor shell. The solenoid valve normally prevents the flow in reverse direction. However, since it is possible that the relatively high pressure associated with the high temperature of the condenser could cause the solenoid valve to be popped open, the check valve serves as a back-up to insure that reverse flow cannot occur. The passage of refrigerant back into the lag compressor when it is not operating can cause the accumulation of liquid refrigerant at the top of the compressor and cause damage to the compressor upon a subsequent start-up.

The purpose of the reliefline 52 with the solenoid 54 therein is to bleed gas back to the lead compressor under a condition when the lag compressor is off. The relief valve 54 is closed when both compressors are operating. When the relief line 52 is open it prevents high pressure gas or liquid due to condensation from accumulating on the discharge side of the lag shell and also provides the advantage of an unloaded start of the lag compressor. The relief line is not required for the unloadable line 18 of the lead compressor since the lead compressor is always operating under all steps of capacity control.

The corresponding arrangement for the unloadable discharge line 18 of the lead compressor circuit, that is, the check valve 26, solenoid valve 28 and check valve 30, functions in the same way when the lead compressor is half unloaded, with the exception that there is no necessity for the relief line since the part of the line 18 upstream from the solenoid valve is in close communication with the operating compressor 10.

From the foregoing description in connection with FIGS. 1 and 5 it will be appreciated that the invention provides a separate discharge for the loaded and unloaded parts of the compressing apparatus, it matches the number of compressor unloading steps to the capacity or surface area of the condensers, and it provides for the isolation of those condensers not being fed with refrigerant gas during partly unloaded operation of the system.

The system shown in FIG. 2 has identical numerals applied to those parts corresponding to parts in FIG. 1. The system functions to accomplish the same general purpose as that shown in FIG. 1, the basic difference being that the check valve and solenoid valve in each of the unloadable lines is replaced by a pilot type valve designated in

line

18 and 72 in line 36. Before describing the operation of these valves in the system as a whole, the basic valve structure illustrated in FIG. 3 will be described.

The valve 72 includes a body 74 having a diametrically stepped chamber therein in which a correspondingly diametrically stepped piston 76 is movably fitted. The chamber at the smaller end of the piston is called the pilot chamber 78 while the chamber at the larger end is called the inlet chamber 80. The portion of the chamber intermediate the ends is designated 82. The valving operation occurs between the valve port 84 and the valve seat 86 at the diametrically larger end of the piston 76, these parts being located between the inlet chamber 80 and an outlet chamber 88. The piping inlet connections for the two lines from the lag compressor are identified as 90 and 92, while the relief connection, which is also in communication with the inlet chamber 80, is identified as 94 (FIGS. 3 and 4).

A discharge pressure connection 96 is adapted to place the pilot chamber 78 in communication with the discharge line 16 connected to the always loaded port of the lead compressor. A pressure vent connection 99 (suggested by another as possibly being desirable if significant leakage occurs past either O-ring seals 97 or 98) would, if used, be in communication with the intermediate chamber 82 and connected to the relief line 52 (FIG. 2) to obviate the possibility of the intermediate chamber filling up with gas or liquid due to such leakage.

The pilot type valve 70 serving the unloadable line 18 (FIG. 2) of the lead compressor needs only a single inlet connection, and does not require the relief connection, for the same reason that the line 18 of the sys tem of FIG. I does not require a relief connection.

The manner in which the pilot type valves operate is as follows. The pilot chamber 78 in each is subject to the discharge gas pressure of the always loaded line 16 of the lead compressor. If the loading of the system is such that the inlet chamber 80 is being supplied with refrigerant gas, the differential in area between the valve seat part of the piston 76 and the pilot chamber end of the piston will cause the valve to move to a fully open position so that the valve will permit the flow to the respective condenser it serves. However, if the compressing apparatus feeding the inlet chamber is inoperative while the always loaded part of the lead compressor is operating, then the force exerted upon the small end of the piston will cause the pilot valve to move to a closed position. In this case, the relief from the upstream side of the pilot type valve can still occur since the relief connection is in communication with the inlet chamber 80.

From the foregoing it will be appreciated that in the FIG. 2 embodiment the pilot type valves take the place of and function in the same manner as the solenoid valves and check valves of the FIG. 1 embodiment. However, they operate from compressor pressures so that no electrical connections are needed, incorporate the relief valve connection in the valve itself so that no separate connection need be made to the line, and are believed to provide a somewhat less expensive arrangement than the arrangement of FIG. 1.

It will also be noted that the concept of the invention is applicable to a single compressor which is unloadable in part, such as 10.

I claim:

1. The combination of a refrigeration system including an unloadable, hermetic shell, multi-cylinder compressor having an always loaded discharge port and an unloadable discharge port, and a non-unloading, hermetic shell, multi-cylinder compressor, said shells of said compressors being connected to receive suction gas returned from said system and being in open communication with each other, a condenser arrangement including a split condenser coil having one part connected by a first line to said always loaded discharge port, and another part connected by a second line to said unloadable discharge port, and another condenser connected by third line means to the discharge of said non-unloading compressor, and means to effect isolation from the remainder of said refrigeration system, of the inlet and outlet of said another part of said split condenser during operation of said unloadable compressor in an unloaded mode, and of the inlet and outlet of said another condenser during periods of nonoperation of said non-unloading compressor.

2. The combination of claim I wherein:

said shells are connected in tandem to receive said suction gas from said system first to said unloadable compressor and then said non-unloading compressor.

3. The combination of claim I including:

control means to effect capacity control in steps for successively reduced capacity by operating both said compressors fully loaded for maximum capacity, operating said unloadable compressor half loaded and said non-loading compressor fully loaded for three-fourths capacity, operating said unloadable compressor fully loaded with said nonunloading compressor shut down for half capacity, and operating said unloadable compressor half loaded with said non-unloading compressor shut down for one-fourth capacity.

4. The combination of claim I wherein:

said means to effect isolation includes a check valve and a solenoid valve in both said second line and said third line means;

means for operating each of said solenoid valves in accordance with the discharge of said second line and to said third line means.

5. The combination of claim 4 including:

a relief line connecting said third line means upstream of said solenoid valve to the suction side of the refrigeration system, said line including valve means therein having a closed position when said non-unloading compressor is operating, and an open position when said non-unloading compressor is shut down.

6. In a refrigeration system including an unloadable, hermetic shell, multi-cylinder compressor having an always loaded discharge port and an unloadable discharge port, and a non-unloading, hermetic shell, multi-cylinder compressor, said shells of said compressors being connected to receive suction gas returned from said system and being in communication with each other, a condenser arrangement including a split condenser coil having one part connected by a first line to said always loaded discharge port, and another part connected by a second line to said unloadable discharge port, and another condenser connected by third line means to the discharge of said non-unloading compressor, and valve means in both said second line and said third line means to close off said lines in response to the absence of discharge gas flow in said second line and said third line means respectively, each of said valves having a pilot chamber connected to said always loaded discharge part for creating a force in a closing direction corresponding to the discharge pressure in said first line.

7. In a refrigeration system according to claim 6 wherein:

each of said valves includes an inlet chamber connected to receive discharge gas from its respective line and line means;

a stepped piston interposed between said pilot chamber and said inlet chamber, the end of said piston presented to said pilot chamber having a reduced cross sectional area relative to the end of said piston presented to said inlet chamber so that said piston is movable in the direction of said pilot chamher to open in response to discharge gas pressure imposed in both said pilot chamber and said inlet chamber.

8. In a refrigeration system having at least one unloadable compressing apparatus and at least one always loaded compressing apparatus, and separate discharge lines for said compressing apparatuses connected to respectively separate condenser coil surfaces, valve means in the discharge lines connected to said unloadable compressing apparatus for closing said lines in response to an unloaded condition of the particular compressing apparatus serving said lines.

9. [n a system according to claim 8 wherein: said valve means comprises a pilot type valve having

Claims

2. The combination of claim 1 wherein: said shells are connected in tandem to receive said suction gas from said system first to said unloadable compressor and then said non-unloading compressor.

3. The combination of claim 1 including: control means to effect capacity control in steps for successively reduced capacity by operating both said compressors fully loaded for maximum capacity, operating said unloadable compressor half loaded and said non-loading compressor fully loaded for three-fourths capacity, operating said unloadable compressor fully loaded with said non-unloading compressor shut down for half capacity, and operating said unloadable compressor half loaded with said non-unloading compressor shut down for one-fourth capacity.

4. The combination of claim 1 wherein: said means to effect isolation includes a check valve and a solenoid valve in both said second line and said third line means; means for operating each of said solenoid valves in accordance with the discharge of said second line and to said third line means.

5. The combination of claim 4 including: a relief line connecting said third line means upstream of said solenoid valve to the suction side of the refrigeration system, said line including valve means therein having a closed position when said non-unloading compressor is operating, and an open position when said non-unloading compressor is shut down.

7. In a refrigeration system according to claim 6 wherein: each of said valves includes an inlet chamber connected to receive discharge gas from its respective line and line means; a stepped piston interposed between said pilot chamber and said inlet chamber, the end of said piston presented to said pilot chamber having a reduced cross sectional area relative to the end of said piston presented to said inlet chamber so that said piston is movable in the direction of said pilot chamber to open in response to discharge gas pressure imposed in both said pilot chamber and said inlet chamber.

9. In a system according to claim 8 wherein: said valve means comprises a pilot type valve having a movable, stepped-diameter piston in a correspondingly stepped-diameter chamber, the cross sectionally smaller end of said piston being subject to pressure from always loaded compressing apparatus, and the opposite, cross-sectionally larger end being subject to pressure from said unloadable compressing apparatus, so that when both said compressing apparatuses operate said piston moves in the direction of said smaller end to effect opening of said valve, and when only said always loaded compressing apparatus is operating said piston moves in the opposite direction to close said valve.