US3386262A

US3386262A - Refrigeration apparatus with compressors in parallel

Info

Publication number: US3386262A
Application number: US590744A
Authority: US
Inventors: Reuben J Hackbart; Duane F Sanborn
Original assignee: Trane Co
Current assignee: Trane US Inc
Priority date: 1966-10-31
Filing date: 1966-10-31
Publication date: 1968-06-04
Anticipated expiration: 1985-06-04

Description

- June 4, 19

68 R. J. HACKBART' 'ETAL 3,386,262

REFRIGERATION APPARATUS WITH COMPRESSORS IN PARALLEL Filed Oct. 31, 1966 INVENTOR REUBEN J. HACKBART BY DUANE F. SANBORN ATTORN'EY United States Patent 3,386,262 REFRIGERATION APPARATUS WITH COMPRESSORS IN PARALLEL Reuben J. Hackbart and Duane F. Sanborn, La Crosse, Wis., assignors to The Trane Company, La Crosse, Wis., a corporation of Wisconsin Filed Oct. 31, 1966, Ser. No. 590,744 9 Claims. (Cl. 62-469) ABSTRACT OF THE DISCLOSURE A refrigeration system having parallel circuited compressors in which means is provided for maintaining the oil Sump of one compressor at a higher pressure than the oil sump of the other compressor so that excess oil in the one compressor may fiow through an oil equalizer conduit to the other compressor; and means for directing a greater portion of the oil returned from the evaporator to the higher pressure oil sump.

This invention relates to refrigeration apparatus of the compression cycle type using a plurality of compressors arranged in parallel in a closed refrigerant circuit. More particularly this invention relates to the problem of maintaining sufiicient oil in each of the compressors.

In a refrigeration system using a compressor, it is well known that a small portion of the lubricating oil for the compression mechanism becomes entrained with the refrigerant gas discharged from he compressor. If the amount of such oil entrained in the gas is relatively small so as not to materially reduce the heat transfer at the condenser and evaporator, no specific problem is created if a single compressor is used as the oil will pass through the evaporator and be returned to the compressor via the suction line. However, if two or more compressors are used and arranged in parallel in the refrigerant circuit, the oil leaving the evaporator outlet may be returned unequally to the compressors thus starving one or more of the compressors of the necessary lubrication required for long life. Many attempts have been made to solve this oil equalization problem, most of which rely upon such schemes as pumping oil from one compressor to the other or equalizing the crankcase or oil sump pressures. It is difficult to uniformly obtain equal pressures in the crankcases or oil sumps from one installation to another and the use of an oil pump even of the ejector type may be very costly.

Such systems are inherently complicated and/or difcult to control resulting in a more expensive device, the cost of which must be passed on to the customer public.

It is thus an object of the instant invention to provide a refrigeration system using parallel compressors which is low in cost, reliable and uniformly controlled for maintaining adequate lubricating oil in each compressor enhancing the life of the compressors.

A further object of the instant invention is to provide a refrigeration circuit for parallel compressors which does not depend upon the equalization of crankcase or oil sump pressures.

Another object is to provide a refrigeration circuit for parallel compressors which requires no special oil pumping means for maintaining adequate lubricating oil in each of the compressors.

Still another object of this invention is to provide a refrigeration circuit apparatus for parallel compressors which requires no special check valves to obtain adequate lubrication in each of the compressors.

The instant invention specifically involves refrigeration apparatus comprising a refrigerant condenser means; a refrigerant evaporator means; first conduit means connecting the outlet of said refrigerant condenser means to the inlet of said refrigerant evaporator means; first and second refrigerant compressors; a first oil sump for said first refrigerant compressor; a second oil sump for said second refrigerant compressor; a first suction conduit connected to the inlet of said first refrigerant compressor and disposed in fluid communication with the outlet of said refrigerant evaporator means for conducting refrigerant from said refrigerant evaporator means to said first refrigerant compressor; a second suction conduit connected to the inlet of said second refrigerant compressor and disposed in fluid communication with the outlet of said refrigerant evaporator means for conducting refrigerant from said refrigerant evaporator means to said second refrigerant compressor; a discharge conduit means connecting the outlets of said first and second refrigerant compressors to the inlet of said refrigerant condenser means for conducting refrigerant from said first and second refrigerant compressors to said refrigerant condenser means; an oil equalizer conduit connecting said first oil sump to said second oil sump; means for operating said first and second refrigerant compressors simultaneously; means for maintaining the pressure in said first oil sump higher than the pressure in said second oil sump during simultaneous operation of said first and second compressors whereby excess oil in said first oil sump will flow through said oil equalizer conduit to said second oil sump; and means for returning a major portion of any oil entrained in the refrigerant leaving said evaporator means to said first oil sump.

Other objects and advantages will become apparent as the specification proceeds to describe this invention with reference to the accompanying drawing schematically showing a refrigeration system employing two hermetically sealed reciprocating refrigerant compressors arranged in parallel relation.

Now referring to the sole drawing, a refrigeration system It) for cooling a conditioned space 12 is shown having a refrigerant condenser 14, a refrigerant receiver 16, a refrigerant throttling means such as thermal responsive expansion valve 18, a refrigerant evaporator 20 disposed in heat exchange relation with conditioned space 12, and a refrigerant compression mechanism 22 serially arranged in a closed refrigerant circuit.

Compression mechanism 22 includes a first compressor 24 and a second compressor 26.

Compressors

24 and 26 may be identical and a description of one will suflice for both. Compressor 24 has a hermetic casing 28. Disposed within casing 28 is a motor-compressor unit 30 which includes a motor portion 32 for driving a compress-or portion 34. Motor-compressor unit 30 is resiliently mounted within casing 28 via a centrally located upper spring 36 and a plurality of circumferentially spaced lower springs 38. The lower portion of casin 28 is filled with lubricating oil thereby defining an oil sump 40. Compressor portion 34 may include an oil pumping mechanism 42 which extends into the oil sump 40 for withdrawing oil therefrom and lubricating the mechanism of the compressor portion. It will be understood that substantially all such compressing mechanism inherently entrain small amounts of lubricating oil with the refrigerant gas being compressed. Compressor 24 further includes a suction inlet opening 44 in casing 28. Refrigerant gas within casing 28 is drawn into the motor-compressor unit through an opening 46 which is preferably at the motor portion end. Compressed gas is discharged from the motor-compressor unit at 48 from whence it passes through a resilient discharge tube 50 which extends through casing 28 as the compressor discharge outlet 52.

An oil level equalizer conduit 54 communicates and connects the casings 28 of

compressors

24 and 26 at the desired gas-oil interface in oil sumps 40. Since this invention contemplates a difference between the suction pressures in the casings 28 of

compressors

24 and 26, it will be appreciated that oil equalizer conduit 54 will also conduct a flow of refrigerant gas. Adjacent the inlet to conduit 54 the gas velocity may be sufficiently high so as to carry along oil at the gas-oil interface. To abate this type of oil transfer, a baffle plate 56 may be placed in each casing 28 in spaced alignment with the ends of conduit 54.

Compressors

24 and 26 are connected in parallel in the refrigerant circuit in the following manner. Each of the compressor discharge outlets is connected to a discharge conduit 58 and each of conduits 58 communicates with the inlet of condenser 14. On the suction side of compressor mechanism 22 is a T- or Y-shaped conduit connector 60 having an inlet 62 connected to the outlet of evaporator 20, a first outlet 64 disposed in substantial flow alignment with inlet 62 and connected to a first suction conduit 66 which connects to the suction inlet 44 of first compressor 24. Connector 60 has a second outlet 68 which is substantially out of flow alignment with inlet 62. Outlet 68 is connected to a second suction conduit 70 which connects to the suction inlet of a second compressor 26. Conduit 70 is crimped at 72 to provide within the conduit a desired flow resistance for reasons hereinafter described. Connector 60 may be similar in configuration to the branch coupling shown in US. Patent 24,179.

It will be observed that outlet 68 makes an acute angle with inlet 62 while outlet 64 makes an obtuse angle with outlet 68. Stated another way, outlet 64 makes a larger angle with inlet 62 than the angle between outlet 68 and inlet 62. It will be evident from this structure that the inertia of oil entrained within suction gas leaving evaporator 20 will cause a major portion of the oil to pass through the outlet 64 of connector 60 through suction conduit '66 into the casing 28 of compressor 24 where it may settle into the oil sump 40 of compressor 24. For the same reasons a slightly greater amount of refrigerant gas should pass from outlet 64 than from outlet 68 thereby maintaining a higher suction pressure in compressor 24 than compressor 26. To adjust or increase this pressure differential suction conduit 70 is crimped at 72 a desired amount as aforementioned.

The motor portions 32 of

compressors

24 and 26 may be connected in parallel to a source 74 of electric power through a thermostat 76 disposed to respond to the tem perature of the conditioned space 12 for simultaneous operation of the compressors. Should it be desired to use a two-stage thermostat to sequentially operate first one and then both compressors, compressors 24 having the normally higher suction pressure should be selected as the compresor which is operated alone for low capacity cooling.

Operation As the temperature in the conditioned space 12 rises to a predetermined level, thermostat 76 closes the circuit for conducting electric current from power source 74 to each of the motors of

compressors

24 and 26 for operation thereof. During operation of

compressors

24 and 26 compressed refrigerant gas having small amounts of entrained oil discharges from each of outlets 52 and is conducted via discharge conduits 58 to the inlet of condenser 14 wherein the refrigerant is cooled and condensed. The refrigerant condensate containing small amounts of Inbricating oil passes from the condenser outlet into receiver 16 from whence it flows to expansion valve 18. Expansion valve 18 throttles the oil containing refrigerant liquid to a substantially lower pressure into the inlet of evaporator 20. In evaporator 20' heat absorbed from the conditioned space causes the liquid refrigerant to vaporize. The fiow of vaporized refrigerant sweeping through the evaporator carries the entrained lubrication oil through the evaporator outlet into the inlet 62 of connector 60. A major portion of the entrained oil in the refrigerant entering inlet 62 passes on through outlet 64 of connector 60 for return to compressor 24 via suction conduit 66. The fact that a major portion of the oil entering inlet 62 passes out through outlet 64 may be attributed to the flow alignment of the inlet 62 and outlet 64. Suction gas entering inlet 62 of connector 60 passes to

compressors

24 and 26 via suction conduits 66 and 76 respectively. The construction of connector 60 also facilitates the maintenance of a higher suction pressure in compressor 24 than in compressor 26. Since a major portion of the oil is returned to compressor 24, the oil level in sump 46 of compressor 24 will begin to exceed the level permitted by the oil equalizer conduit 54. As the oil level rises to the inlet of equalizer conduit 54 in compresor 24, oil will be carried through the equalizer conduit 54 from compressor 24 to compressor 26 owing to the higher pressure in compressor 24. Bafile 56 prevents the refrigerant gas flowin into conduit 54 from carrying an excessive amount of oil to compressor 26. Should the suction pressure differential between

compressors

24 and 26 be insufiicient to cause the desired oil flow from the compressor receiving the major portion of the oil, it may be desirable to slightly crimp or otherwise restrict the suction conduit of the other compressor as is shown at 72.

Thus it will be seen that the oil return system described herein does not require the use of check valves and pumps and does not attempt the difiicult task of maintaining equal suction pressure on the compressors. The oil return scheme is simple, inherently reliable, and low in cost. This invention has been found to materially increase the reliability of compressors arranged in parallel relationship.

Having thus described in detail the preferred embodiment of our invention, we contemplate that many changes may be made without departing from the scope or spirit of our invention and we desire to be limited only by the claims.

We claim:

1. A refrigeration apparatus comprising: a refrigerant condenser means; a refrigerant evaporator means; first conduit means connecting the outlet of said refrigerant condenser means to the inlet of said refrigerant evaporator means; first and second refrigerant compressors; a first oil sump for said first refrigerant compressor; a second oil sump for said second refrigerant compressor; a first suction conduit connected to the inlet of said first refrigerant compressor and disposed in fluid communication with the outlet of said refrigerant evaporator means for conducting refrigerant from said refrigerant evaporator means to said first refrigerant compressor; a second suction conduit connected to the inlet of said second refrigerant compressor and disposed in fluid communication with the outlet of said refrigerant evaporator means for conducting refrigerant from said refrigerant evaporator means to said second refrigerant compressor; a discharge conduit means connecting the outlets of said first and sec ond refrigerant compressors to the inlet of said refrigerant condenser means for conducting refrigerant from said first and second refrigerant compressors to said refrigerant condenser means; means for operating said first and second refrigerant compressors simultaneously; means for maintaining the pressure in said first oil sump higher than the pressure in said second oil sump during simultaneous operation of said first and second refrigerant compressors; means for returning a greater portion of any oil entrained in the refrigerant leaving said evaporator means to said first oil sump than said second oil sump; and an oil equalizer conduit means separate from said second suction conduit connecting said first oil sump to said second oil sump for conducting excess oil from said first oil sump to said second oil sump via the pressure differential between said first and second oil sumps.

2. The apparatus as defined by claim 1 wherein said means for returning a greater portion of the oil entrained in the refrigerant leaving said evaporator means to said first compressor includes a three-way connection having an inlet connected to the outlet of said refrigerant evaporator means, a first outlet disposed substantially in fluid fiow alignment with said last mentioned inlet and connected to said first suction conduit, and a second outlet disposed substantially out of fluid flow alignment with said last mentioned inlet and connected to said second suction conduit whereby oil entrained in refrigerant gas entering said last mentioned inlet tends to be discharged from said three-way connection through said first outlet.

3. The apparatus as defined by claim 2 wherein said three-way connection is generally T-shaped wherein the angle between the inlet thereof and said second outlet is acute and the angle between said first and second outlets is obtuse.

4. The apparatus as defined by claim 1 wherein said means for maintaining the pressure in said first oil sump higher than the pressure in said second oil sump includes means for rendering said second suction conduit of greater resistance to fluid flow than said first suction conduit.

5. The apparatus as defined by claim 4 wherein said means for rendering said second suction conduit of greater resistance to fluid flow that said first suction conduit is a discrete flow restrictor disposed within said second suction conduit.

6. The apparatus as defined by claim 5 wherein said discrete flow restrictor comprises a crimp in the walls of said second suction conduit.

7. The apparatus as defined by claim 1 wherein said means for returning a greater portion of any oil entrained in the refrigerant leaving said evaporator means to said first oil sump returns said greater portion of said oil via said first suction conduit.

8. A refrigeration apparatus comprising: a refrigerant condenser means; a refrigerant evaporator means; first conduit means connecting the outlet of said refrigerant condenser means to the inlet of said refrigerant evaporator means; a first hermetically sealed casing; a first motorcompressor unit resiliently mounted within said first casing; a. second hermetically sealed casing; a second motorcompressor unit resiliently mounted within said second casing; said first motor-compressor unit having a suction inlet in fluid communication with the interior of said first casing and said second motor-compressor unit having a suction inlet in fluid communication with the interior of said second casing; discharge conduit means extending through each of said casings connecting the discharge outlet of each of said first and second motor-compressor units to the inlet of said con-denser means; each of said casings defining in the lower portion thereof an oil sump for the motor-compressor unit disposed therein; a first suction conduit connected to the interior of said first casing and disposed in fluid communication with the outlet of said refrigerant evaporator means for conducting refrigerant from said refrigerant evaporator means to said first casing; a second suction conduit connected to the interior of said second casing and disposed in fluid communication with the outlet of said refrigerant evaporator means for conducting refrigerant from said refrigerant evaporator means to said second casing; means for operating said first and second motor-compressor units simultaneously; means for maintaining the pressure in said first casing higher than the pressure in said second casing during simultaneous operation of said first and second motorcompressor units; means for returning a greater portion of any oil entrained in the refrigerant leaving said evaporator means to said first casing via said first suction conduit than to said second casing via said second suction conduit; and an oil equalizer conduit means separate from said second suction conduit for conducting excess oil in said first oil sump to said second oil sump via the pressure differential between said first and second casings.

9. The apparatus as defined by claim 8 wherein a baffie is disposed in said first casing adjacent the connection of said oil equalizer conduit to retard the entrainment of oil in the gas passing through said oil equalizer conduit from said first casing to said second casing.

References Cited UNITED STATES PATENTS 2 076,332 4/1937 Zercher 62-468 X 2,294,552 9/ 1942 Gygax 625 10 X 2,663,164 12/1953 Kurtz 62-468 ROBERT A. OLEARY, Primary Examiner.

W. E. WAYNER, Assistant Examiner.