U.S. patent application number 12/937501 was filed with the patent office on 2011-04-07 for compressor for a refrigeration cycle, refrigeration cycle and method for operating the same.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Markus Hafkemeyer, Tobias H. Sienel.
Application Number | 20110081254 12/937501 |
Document ID | / |
Family ID | 40350024 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110081254 |
Kind Code |
A1 |
Hafkemeyer; Markus ; et
al. |
April 7, 2011 |
COMPRESSOR FOR A REFRIGERATION CYCLE, REFRIGERATION CYCLE AND
METHOD FOR OPERATING THE SAME
Abstract
A compressor (2) for a refrigeration cycle according to the
invention comprises an inlet port (6), a compression element (10),
an outlet port (18), wherein in operation a refrigerant flow (20)
of a gaseous refrigerant carrying an amount of oil circulates
through the inlet port (6), the compression element (10) and the
outlet port (18), and an oil sump (8) in which part of the oil
carried by the gaseous refrigerant collects. An oil circulation
rate enhancement feature (16) is provided being configured so as to
direct oil from the oil sump (8) to the refrigerant flow (20), when
the oil in the oil sump (8) exceeds a predetermined oil sump level
(24).
Inventors: |
Hafkemeyer; Markus; (Bonn,
DE) ; Sienel; Tobias H.; (Easthampton, MA) |
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
40350024 |
Appl. No.: |
12/937501 |
Filed: |
June 12, 2008 |
PCT Filed: |
June 12, 2008 |
PCT NO: |
PCT/EP2008/004734 |
371 Date: |
October 15, 2010 |
Current U.S.
Class: |
417/13 ;
417/228 |
Current CPC
Class: |
F04B 39/0269 20130101;
F04B 39/023 20130101; F25B 31/002 20130101; F04B 39/0207
20130101 |
Class at
Publication: |
417/13 ;
417/228 |
International
Class: |
F04B 49/00 20060101
F04B049/00 |
Claims
1. A compressor for a refrigeration cycle comprising: an inlet
port; a compression element; an outlet port; wherein in operation a
refrigerant flow of a gaseous refrigerant carrying an amount of oil
circulates through the inlet port, the compression element and the
outlet port; and an oil sump in which part of the oil carried by
the gaseous refrigerant collects, characterized by an oil
circulation rate enhancement feature configured so as to direct oil
from the oil sump to the refrigerant flow, when the oil in the oil
sump exceeds a predetermined oil sump level.
2. The compressor of claim 1, wherein characterized in that the oil
circulation rate enhancement feature is formed by the crankshaft
rotatably driven by a motor, said crankshaft being configured so as
to dip into the oil sump and to disperse an amount of oil to form
an oil mist to be entrained by the refrigerant flow, when the oil
in the oil sump reaches the predetermined oil sump level.
3. The compressor of claim 1, wherein the oil circulation rate
enhancement feature is formed by an oil dispersing element,
especially a blade or a disk, fixed to the crankshaft and rotatably
driven by a motor, said oil dispersing element being configured so
as to dip into the oil sump and to disperse an amount of oil to
form an oil mist to be entrained by the refrigerant flow, when the
oil in the oil sump reaches the predetermined oil sump level.
4. The compressor of claim 1, wherein the oil circulation rate
enhancement feature is formed by a bypass line extending between
the oil sump substantially at a height of the predetermined oil
sump level and the refrigerant flow at a position before the
compression element internal or external to the compressor
housing.
5. The compressor of claim 4, wherein an ejector is provided for
transporting oil from the oil sump to the refrigerant flow.
6. The compressor of claim 4, wherein oil is transported from the
oil sump to the refrigerant flow by static pressure
entrainment.
7. The compressor of claim 4, wherein the bypass line extends
between the oil sump at the height of the predetermined oil sump
level and the inlet port.
8. The compressor of claim, wherein the bypass line extends between
the oil sump at the height of the predetermined oil sump level and
a suction line connecting to the inlet port (external).
9. The compressor of any claim, wherein the bypass line extends
between the oil sump at the height of the predetermined oil sump
level and a compression element suction line or a compression
element suction portion.
10. (canceled)
11. A refrigeration cycle, comprising: at least one lower suction
pressure compressor, at least one higher suction pressure
compressor, a heat-rejection heat exchanger, preferably a
collecting container, at least one lower suction pressure
evaporator having an expansion device connected upstream thereof,
at least one higher suction pressure evaporator having an expansion
device connected upstream thereof and conduits circulating a
refrigerant therethrough; wherein the at least one lower suction
pressure compressor includes an inlet port, a compression element,
an outlet port, and an oil sump, wherein in operation a refrigerant
flow of a gaseous refrigerant carrying an amount of oil circulates
through the inlet port, the compression element and the outlet
port, wherein a part of the oil carried by the gaseous refrigerant
collects within the oil sump, which lower suction pressure
compressor is characterized by an oil circulation rate enhancement
feature configured so as to direct oil from the oil sump to the
refrigerant flow, when the oil in the oil sump exceeds a
predetermined oil sump level.
12. The refrigeration cycle of claim 11, further comprising
compressors having different sizes.
13. The refrigeration cycle of claim 11, wherein the at least one
lower suction pressure compressor and the at least one higher
suction pressure compressor are connected in parallel.
14. The refrigeration cycle of claim 11, wherein the at least one
lower suction pressure compressor and the at least one higher
suction pressure compressor are connected in series.
15. The refrigeration cycle of claim 13, wherein the lower suction
pressure compressor and the higher suction pressure compressor are
configured such that when the oil sump level of the lower suction
pressure compressor is less than its predetermined oil sump level,
its oil circulation rate is always lower than the oil circulation
rate of the higher suction pressure compressor.
16. The refrigeration cycle of claim 15, wherein the lower suction
pressure compressor and the higher suction pressure compressor are
configured such that when the oil sump level of the lower suction
pressure compressor exceeds its predetermined oil sump level, its
oil circulation rate is always higher than the oil circulation rate
of the higher suction pressure compressor.
17. The refrigeration cycle of claim 11, wherein the lower suction
pressure compressor is configured such that when the oil sump level
of the lower suction pressure compressor is less than its
predetermined oil sump level its oil circulation rate is always
lower than the oil circulation rate entering the lower suction
pressure compressor.
18. The refrigeration cycle of claim 11, wherein the lower suction
pressure compressor is configured such that when the oil sump level
of the lower suction pressure compressor exceeds its predetermined
oil sump level its oil circulation rate is always higher than the
oil circulation rate entering the lower suction pressure
compressor.
19. A method for operating a compressor of a refrigeration cycle,
comprising: operating the compression element such that a
refrigerant flow of a gaseous refrigerant carrying an amount of oil
circulates through the inlet port, the compression element and the
outlet port, and that part of the oil carried by the gaseous
refrigerant collects in the oil sump, characterized by the step of
directing oil from the oil sump to the refrigerant flow, when the
oil in the oil sump exceeds a predetermined oil sump level.
20. A method for operating a refrigeration cycle, comprising:
providing at least one lower suction pressure compressor and at
least one higher suction pressure compressor connected in series
and being configured such that when the oil sump level of the lower
suction pressure compressor is less than its predetermined oil sump
level, its oil circulation rate is always lower than the oil
circulation rate of the higher suction pressure compressor and that
when the oil sump level of the lower suction pressure compressor
exceeds its predetermined oil sump level, its oil circulation rate
is always higher than the oil circulation rate of the higher
suction pressure compressor: operating the compression elements
such that a refrigerant flow of a gaseous refrigerant carrying an
amount of oil circulates through the inlet port, the compression
element and the outlet port, and that part of the oil carried by
the gaseous refrigerant collects in the oil sump; directing, in the
lower suction pressure compressors, oil from the oil sump to the
refrigerant flow and thus to the higher suction pressure
compressors connected downstream, when the oil in the oil sump
exceeds a predetermined oil sump level and thereby achieving a
self-regulating balance of oil between the lower suction pressure
compressors and the higher suction pressure compressors.
Description
[0001] This application is entitled to the benefit of, and
incorporates by reference essential subject matter disclosed in PCT
Application No. PCT/EP2008/004734 filed on Jun. 12, 2008.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The invention relates to a compressor for a refrigeration
cycle, a refrigeration cycle and to methods for operating the
same.
[0004] 2. Background Information
[0005] In current refrigeration cycles multiple compressors forming
one or more sets of compressors are used. In order to reduce the
wear of moved parts of the compressors, like the piston in case of
reciprocating compressors or the scroll in case of scroll
compressors, the refrigerant circulated through such compressors
carries an amount of lubricant, especially machine oil. Normally
part of the amount of oil carried by the refrigerant collects in
the oil sump of the compressors.
[0006] Each compressor has a certain oil discharge rate or oil
circulation rate depending on its design and operating conditions.
The oil circulation rate of a compressor defines the amount of oil
that can be transported through the compressor and discharged from
the compressor per time unit. When multiple compressors are working
within a refrigeration cycle, especially when compressors of
different sizes having different oil circulation rates are used, it
happens that compressors are damaged due to a lack of lubrication
when they receive too little oil or due to oil strokes when they
receive too much oil. This happens in particular when compressors
in such a refrigeration system having a low oil circulation rate
receive more oil than they can discharge and when compressors in
such a refrigeration system having a high oil circulation rate
receive less oil than they need for lubrication thereof. This
situation is made even worse if one or more of these compressors is
running at variable speed and having different oil circulation
rates and displacements than the others.
[0007] It is conceivable to use active oil distribution systems in
order to balance the oil distribution for the multiple compressors
used therein. However such active oil distribution systems are
expensive and add the risk of failure and malfunction to the
refrigeration system.
[0008] Accordingly, it would be beneficial to provide a more
reliable and failure-free compressor for use in refrigeration
systems. Moreover, it would be beneficial to provide a reliable and
failure-free operation of refrigeration systems where compressors
of different sizes and variable speeds are running
SUMMARY OF THE INVENTION
[0009] Exemplary embodiment of the invention include a compressor
for a refrigeration cycle, comprising an inlet port, a compression
element, an outlet port, wherein in operation a refrigerant flow of
a gaseous refrigerant carrying an amount of oil circulates through
the inlet port, the compression element and the outlet port, and an
oil sump in which part of the oil carried by the gaseous
refrigerant collects, and further comprising an oil circulation
rate enhancement feature configured so as to direct oil from the
oil sump to the refrigerant flow, when the oil in the oil sump
exceeds a predetermined oil sump level.
[0010] Exemplary embodiment of the invention further include a
refrigeration cycle, comprising, in flow direction, at least one
compressor, a heat-rejection heat exchanger, preferably a
collecting container, at least one evaporator having an expansion
device connected upstream thereof and conduits circulating a
refrigerant therethrough.
[0011] Exemplary embodiment of the invention further include a
refrigeration cycle, comprising at least one lower suction pressure
compressor, at least one higher suction pressure compressor, a
heat-rejection heat exchanger, preferably a collecting container,
at least one lower suction pressure evaporator having an expansion
device connected upstream thereof, at least one higher suction
pressure evaporator having an expansion device connected upstream
thereof and conduits circulating a refrigerant therethrough,
wherein the at least one lower suction pressure compressor is
configured according to any of the preceding claims.
[0012] Exemplary embodiment of the invention further include a
method for operating a compressor of a refrigeration cycle,
comprising operating the compression element such that a
refrigerant flow of a gaseous refrigerant carrying an amount of oil
circulates through the inlet port, the compression element and the
outlet port, and that part of the oil carried by the gaseous
refrigerant collects in the oil sump, further comprising the step
of directing oil from the oil sump to the refrigerant flow, when
the oil in the oil sump exceeds a predetermined oil sump level.
[0013] Exemplary embodiment of the invention further include a
method for operating a refrigeration cycle, comprising providing at
least one lower suction pressure compressor and at least one higher
suction pressure compressor connected in series and being
configured such that when the oil sump level of the lower suction
pressure compressor is less than its predetermined oil sump level,
its oil circulation rate is always lower than the oil circulation
rate of the higher suction pressure compressor and that when the
oil sump level of the lower suction pressure compressor exceeds its
predetermined oil sump level, its oil circulation rate is always
higher than the oil circulation rate of the higher suction pressure
compressor, operating the compression elements such that a
refrigerant flow of a gaseous refrigerant carrying an amount of oil
circulates through the inlet port, the compression element and the
outlet port, and that part of the oil carried by the gaseous
refrigerant collects in the oil sump, directing, in the lower
suction pressure compressors, oil from the oil sump to the
refrigerant flow and thus to the higher suction pressure
compressors connected downstream, when the oil in the oil sump
exceeds a predetermined oil sump level and thereby achieving a
self-regulating balance of oil between the lower suction pressure
compressors and the higher suction pressure compressors.
DESCRIPTION OF THE DRAWINGS
[0014] Embodiments of the invention are described in greater detail
below with reference to the figures, wherein:
[0015] FIG. 1 shows a schematic view of a compressor of arbitrary
type according to an embodiment of the invention;
[0016] FIG. 2 shows a schematic view of a reciprocating compressor
according to an embodiment of the invention;
[0017] FIG. 3 shows a schematic view of a scroll compressor
according to an embodiment of the invention;
[0018] FIG. 4 shows a schematic side view of a reciprocating
compressor according to an embodiment of the invention;
[0019] FIG. 5 shows a first oil circulation rate balancing
diagram;
[0020] FIG. 6 shows a schematic view of a first multiple compressor
refrigeration system according to an embodiment of the
invention;
[0021] FIG. 7 shows a schematic view of a second multiple
compressor refrigeration system according to an embodiment of the
invention;
[0022] FIG. 8 shows a schematic view of a third multiple compressor
refrigeration system according to an embodiment of the invention;
and
[0023] FIG. 9 shows a second oil circulation rate balancing
diagram.
DETAILED DESCRIPTION OF THE INVENTION
[0024] FIG. 1 shows a compressor 2 of arbitrary type for use in a
refrigeration cycle.
[0025] The compressor 2 comprises a housing 4 including a crank
case, an inlet port 6, an oil sump 8, a compression element 10,
which can be the compression element of a reciprocating compressor
including a piston, a piston rod and the like or the compression
element of a scroll compressor including scrolls and the like or
the compression element of any other type of compressor, a crank
shaft 12 for driving the compression element 10, a motor 14
rotating the crank shaft 12 and an outlet port 18. The inlet port 6
is connected a suction conduit, especially a piping, to one or more
evaporators connected upstream thereof. The outlet port 18 is
connected to a discharge or pressure conduit, especially a piping,
to a heat-rejection heat exchanger connected downstream thereof.
The inlet port 6 of the compressor attaches to its right-hand side
wall and the outlet port 18 is attached to the upper side of the
compressor 2.
[0026] When the compression element 10 is operated, a refrigerant
flow 20 of a gaseous refrigerant carrying an amount of oil, which
is depicted by arrows in FIG. 1, forms through the inlet port 6,
the compression element 10 and the outlet port 18. Part of the oil
carried by the gaseous refrigerant is separated on its way to the
compression element 10 and falls into the oil sump 8, where it
collects. The gaseous refrigerant together with the remaining oil
is sucked into the compression element 10, compressed therein and
leaves the compressor 2 at the outlet port 18. The oil from the oil
sump 8 is taken to lubricate the bearings, pistons and the like and
is finally also leaving the compressor 2 to the heat-rejection heat
exchanger connected downstream thereof. If more oil is separated
than disgorged, the oil level in the oil sump 8 rises.
[0027] At normal oil level, the oil circulation rate of the
compressor 2 is nominal. At a certain predetermined oil sump level
the oil circulation rate enhancement feature 16 gets into operation
and rises the oil circulation rate of the compressor 2. This oil
circulation rate enhancement feature 16 forces oil transport and
directs oil from the oil sump 8 to the refrigerant flow 20, when
the oil in the oil sump 8 exceeds the predetermined oil sump level
24.
[0028] FIG. 2 shows a reciprocating compressor 26 for use in a
refrigeration cycle.
[0029] The oil sump 8 of the reciprocating compressor 26 is formed
in the lower left-hand portion of the housing 4. The inlet port 6
attaches on the upper side in the right-hand portion. Directly
adjacent to the outlet port 18 a compression element suction line
40 is arranged through which at least part of the refrigerant flow
20 and the oil mist flow 42 runs. The compression element of the
reciprocating compressor 26 is formed by the horizontally extending
crank shaft 12 rotatably driven by the motor 14 and driving the
piston rod 30 which in turn drives the piston 32 and compresses the
refrigerant carrying the oil in a compression chamber. Spaced apart
to the left-hand side of the bent portion of the crank shaft 12 an
oil dispersing blade 28 is fixed to the crank shaft 12 to be
rotatably driven by the motor 14. The oil dispersing blade 28 has
the function of a slinger. It dips into the oil sump 8 and
disperses an amount of oil to form an oil mist in the crank case to
be entrained by the refrigerant flow 20, when the oil in the oil
sump 8 reaches the predetermined oil sump level 24. This oil mist
entrained into the refrigerant gas flow 20 is sucked to the
compression chamber and as a result more oil is transported out of
the compressor 26 and the oil circulation rate will be
increased.
[0030] The crank shaft rotation is indicated by reference numeral
36, the piston rod movement is indicated by reference numeral 38
and the dispersing movement of the oil mist is indicated by
reference numeral 34.
[0031] The design of the oil dispersing blade 28 will influence the
characteristics of the oil circulation rate. The outer radius and
the diameter of the oil dispersing blade 28 measured from the crank
shaft axis will control the level of the increase of the oil
circulation rate. Its shape will give a function of oil circulation
rate as a parameter of the oil level. Alternatively, an oil
dispersing disc or another feature which is fixed with the crank
shaft and rotates with it can be employed.
[0032] The same dispersing effect can be achieved by using the
crank shaft 12 itself as a tool which increases the oil circulation
rate. When the oil in the oil sump 8 reaches the predetermined oil
sump level 24, the crank shaft itself will dip into the oil sump 8
and disperse an amount of oil to form an oil mist to be entrained
by the refrigerant flow 20 thereby increasing the oil circulation
rate.
[0033] Additional features can be placed on the crankshaft to
further amplify the oil dispersion if needed.
[0034] In these embodiments, the flow of oil mist within the crank
case must be sufficiently high to transport the oil into the
suction of the compression element 10. This can be done by
appropriately sizing the crankcase as well as the passages which
lead from the crankcase to the compression element 10.
[0035] In FIG. 2 the oil circulation rate balancing is carried out
by means of an oil dispersing plate 28.
[0036] FIG. 3 shows a scroll compressor 44 for use in a
refrigeration cycle.
[0037] In FIG. 3, the crank shaft 12 extends substantially in a
vertical direction, the inlet port 6 attaches to the left-hand side
wall and the outlet port 18 attaches to the upper side of the
housing 4. A by-pass line 46 extends between an entrainment point
48 positioned at the left-hand side wall of the crank case 4
substantially at the height of the predetermined oil sump level 24
and the inlet port 6 connected with the suction line leading to the
compression element 10. The by-pass line 46 can be fowled as a
bore, as a canal or a pump line and can be internal to the
compressor housing or external as shown.
[0038] When the level oil in the oil sump 8 exceeds the
predetermined oil sump level 24 which equals the nominal oil level,
there will be a net flow of oil leaving the oil sump 8 and being
entrained into the suction flow to the compression element 10 which
will increase the oil circulation rate of the compressor 44. This
effect can be achieved by static pressure entrainment which will
work best when the entrainment point 48 is as close as possible to
the suction line of the compression element 10, where the static
pressure is the lowest. This effect can also be achieved by dynamic
pressure entrainment, for example by providing an ejector.
[0039] Since the by-pass line 46 connects the entrainment point 48
to a point internal to the inlet port 6 or the suction line
external to the inlet port 6 the static pressure difference will
cause a considerable amount of oil from the oil sump 8 to directed
to the refrigerant flow 20.
[0040] The oil feeding flow within the by-pass line 46 is depicted
by the arrows 50. When additionally providing a pump or an ejector
the oil feeding flow from the oil sump 8 to the suction line of the
compression element 10 can be further increased.
[0041] FIG. 4 shows a reciprocating compressor 52 for use in a
refrigeration cycle.
[0042] In the side view of FIG. 4, the basic configuration of the
reciprocating compressor 52 comprising the rotating crankshaft 12,
the piston rod 30 and the piston 32 can be seen. Different from the
by-pass line 46, the by-pass line 54 of the reciprocating
compressor 52 extends between the entrainment point 56 at the
predetermined oil sump level 24 and the compression element suction
line 58 through which the refrigerant flow 20 comprising the oil
flow 62 runs. The oil feeding flow within the by-pass line 54 is
depicted by arrows 60.
[0043] In FIGS. 3 and 4 the oil circulation rate balancing is
carried out by means of suction gas entrainment.
[0044] According to the embodiments of the invention, as described
above, the oil circulation rate of the compressor is artificially
increased when the oil sump level in the compressor is higher than
a nominal value. When the oil sump level in the oil sump is high,
the oil circulation rate is increased, and the amount of oil
leaving the compressor exceeds the net flow of oil entering the
compressor. In this way, the oil sump level in the oil sump will
decrease until the predetermined oil sump level and, respectively,
the nominal level again. At this point, the oil circulation rate
will decrease and the amount of oil leaving the compressor will be
less than the amount of oil entering the compressor.
[0045] According to embodiments of the invention, as described
herein, a self-regulating mechanism for controlling the amount of
oil in the compressors employed is achieved, and the balancing of
oil between compressors in a multiple compressor system is allowed
in a passive or semi-passive way. Thereby the applied costs can be
decreased while the reliability of the systems is increased.
[0046] FIG. 5 shows a first oil circulation rate balancing diagram
64.
[0047] This diagram 64 depicts the variation of the oil circulation
rate depending on an increasing oil sump level by means of two
exemplary functions, namely a gradual change function f1 and a step
function f2.
[0048] When the oil in the oil sump 8 exceeds the predetermined oil
sump level 24 the oil circulation rate is increased by means of the
oil circulation rate enhancement features 16, 28, 46, 54 or any
other oil circulation rate enhancement feature such that more oil
is transported out of the compressor than fresh oil enters the
compressor.
[0049] By adjusting the intensity of the operation of the oil
circulation rate enhancement feature a more gradual adjustment of
the oil circulation rate like depicted by f1 or a more abrupt
adjustment as depicted by the step function f2 can be achieved.
[0050] FIG. 6 shows a first multiple compressor refrigeration
system 66.
[0051] The first multiple compressor refrigeration system 66
comprises in flow direction a set of three compressors 68, a
heat-rejecting heat exchanger 70, a collecting container 72 and
three parallel evaporators 74 having corresponding expansion valves
76 connected upstream thereof
[0052] The suction line from the set of evaporators 74 divides into
three separate suction lines for each compressor of the set of
compressors 68, and the pressure lines from the three compressors
of the set of compressors 68 join to form a single pressure line
before the heat-rejecting heat exchanger 70. Likewise, the line
from the collecting container 72 to the set of evaporators 74
divides into three separate lines, and the suction lines from the
evaporators 74 join to form a single suction line for the set of
compressors 68.
[0053] By providing the compressors 68 with an oil circulation rate
enhancement feature, as described above, the oil circulation rate
thereof will be individually adjusted and increased in case too
much oil collects in the oil sump of one or more compressors 68.
Moreover a reliable balancing of the oil in the compressors 68 can
be attained in a simple and cost-effective manner. By avoiding that
too much oil collects in one compressor, it is guaranteed that the
amount of oil returning to the other compressors is sufficient and
that they do not receive too little oil.
[0054] FIG. 7 shows a second multiple compressor refrigeration
system 68.
[0055] The second multiple compressor refrigeration system 78
comprises two sets of compressors connected in series, namely a set
of three lower suction pressure compressors 80 and a set of three
medium suction pressure compressors 82, a heat-rejection heat
exchanger 70, a collecting container 72 and two sets of evaporators
connected in parallel, namely a first set of three medium suction
pressure evaporators 88 having respective expansion valves 90
collected upstream thereof and a second set of lower suction
pressure evaporators 84 having respective expansion valves 86
collected upstream thereof.
[0056] The discharge lines of the lower suction pressure
evaporators 84 combine into a common suction line which then
divides into three separate suction lines for each of the lower
suction pressure compressors 80. The pressure lines of the lower
suction pressure compressors 80 combine into a common suction line
that divides into three separated suction lines for the medium
suction pressure compressors 82. The pressure lines of the medium
suction pressure compressors 82 combine into a common pressure line
leading to the heat-rejection heat exchanger 70. The discharge
lines of the medium suction pressure evaporators 88 combine into a
common suction line discharging into the suction line leading to
the medium suction pressure compressors 82.
[0057] For refrigeration systems with compressors in series, like
the embodiment of FIG. 7, careful consideration must be made
between the oil circulation rates of the lower suction pressure
compressors and the higher suction pressure compressors.
[0058] According to a particular embodiment of this invention, the
higher suction pressure compressors 82 are selected to have a
nominal oil circulation rate wherein the lower suction pressure
compressors 80 comprise an oil circulation rate enhancement
feature, as described above, in order to provide a self-regulating
circulation rate.
[0059] It is desirable to choose the variability of the oil
circulation rate between the compressors and the operating
conditions of the higher suction pressure compressors and the lower
suction pressure compressors such that when the oil sump levels of
the lower suction pressure compressors are less than nominal, their
oil circulation rate is always lower than the one of the higher
suction pressure compressors, and that when the oil sump levels of
the lower suction pressure compressors are higher than nominal,
their oil circulation rate is always higher than the one of the
higher suction pressure compressors. In such way, a self-regulating
balance of oil between the higher suction pressure compressors and
the lower suction pressure compressors can be achieved.
[0060] If additional lines between the discharge of the higher
suction pressure compressors 82 and the suction of the lower
suction pressure compressors 80 exist, which change the oil
circulation rate entering the lower suction pressure compressors
80, the oil circulation rate of the lower suction pressure
compressors 80 must be higher than the highest possible oil
circulation rate entering the lower suction pressure compressors
80, when the oil sump level of the lower suction pressure
compressors 80 is above the predetermined level 24. When the oil
sump level is below the predetermined level 24 then the oil
discharge rate should be lower than the lowest possible oil
circulation rate entering the compressor.
[0061] FIG. 8 shows a third multiple compressor refrigeration
system 92.
[0062] The third multiple compressor refrigeration system 92
corresponds to the second multiple compressor refrigeration system
78 with the exception that the two sets of compressors, namely the
set of the three lower suction pressure compressors 94 and the set
of the three higher suction pressure compressors 96 are not
connected in series, but rather in parallel.
[0063] For that purpose the discharge lines of the lower suction
pressure evaporators 84 combine into a common suction line for the
set of lower suction pressure compressors 94 which then divides up
into three separate suction lines for each of the lower suction
pressure compressors 94. Likewise, the discharge lines of the
medium suction pressure evaporators 88 combine into a common
suction line for the set of higher suction pressure compressors 96
which then divides into three separate suction lines for each of
the higher suction pressure compressors 96. The pressure lines of
the lower suction pressure compressors 94 combine into a common
pressure line and the pressure lines of the higher suction pressure
compressors 96 combine into a common pressure line, both pressure
lines joining before the heat-rejection heat exchanger 70.
[0064] In both multiple compressor refrigeration system 78 and 92
one or more of the compressors can be configured according to this
invention to contain an oil circulation rate enhancement feature,
as described above, that directs oil from the respective oil sump
to the refrigerant flow, when the oil in the oil sump exceeds a
predetermined oil sump level.
[0065] The heat-rejection heat exchanger 70 of all multiple
compressor refrigeration systems 68, 78, 92 can be both a gas
cooler when operated in a transcritical mode or a condenser when
operated in a subcritical mode.
[0066] According to a further embodiment of the invention a
combination of series and parallel compressor sets are also
possible.
[0067] All of the aforementioned embodiments require a balance to
exist in oil transport to allow the oil levels in all compressor
sets to be stable and within a certain range, namely not too low or
too high. This balancing is achieved by providing one or more
compressors with the oil circulation rate enhancement feature
according to embodiments of the invention, as described herein.
[0068] FIG. 9 shows a second oil circulation rate balancing diagram
98 derived from test data for a specific compressor, as an example
of the desired effect.
[0069] This diagram 98 shows the oil circulation rate for both the
lower suction pressure compressors 94 and the higher suction
pressure compressors 96 as a function of increasing oil flow in
liters wherein the lower suction pressure compressors 94 are
provided with oil circulation rate enhancement features according
to the invention therefor allowing for a oil circulation rate
adjustment, wherein the higher suction pressure compressors 96 have
a nominal oil circulation rate in the range of 0.8 to 1.6% as
depicted in the second oil circulation rate balancing diagram
98.
[0070] As can be seen by the curve for the lower suction pressure
compressors 94 the oil circulation rate thereof changes flexibly
with increasing oil fill so to allow for reliable operation of the
refrigeration circuit.
[0071] In FIG. 9 test data for a lower suction pressure
reciprocating compressor is shown as a function of the oil sump
level. The self-regulating concept of the invention can clearly be
seen in this Figure.
[0072] According to a further embodiment of the invention, by
ensuring that the nominal oil circulation rate of the higher
suction pressure compressors is high relative to the nominal oil
circulation rate of the lower suction pressure compressors, various
lower suction pressure compressor sizes can be used without danger
of oil balancing issues between the lower suction pressure
compressors. Each lower suction pressure compressor will be able to
self-regulate the amount of oil in its sump to achieve a safe
level. With a variety of lower suction pressure compressors sizes
in parallel, a closer balance between the required capacity and the
delivered capacity can be achieved, which will result in less
on/off cycling and lower variations between the desired and actual
suction pressure, which will serve to increase the reliability and
decrease of energy consumption of the refrigeration system.
[0073] According to exemplary embodiments of the invention, as
described above, the oil circulation rate of the compressors rather
than the amount of ingoing oil is adjusted. No further parts are
needed for active oil supply management, the modifications needed
to achieve the desired effects are very inexpensive, the
reliability of the system will be improved, and overfilling of the
oil sump is reliably avoided. The oil circulation rate enhancement
feature works even in complex systems, such as CO2 booster systems,
where the rate of higher suction pressure compressors can be
approximately ten times higher than the one of the lower suction
pressure compressors, and in cases where the operating conditions
of the refrigeration system are changing. Both overfilling with oil
and running out of oil can be safely avoided by the exemplary
embodiments of the invention.
[0074] According to an exemplary embodiment of the invention, the
compressors are provided with a mechanism for self-regulation,
which is particularly effective when a big amount of oil circulates
within the refrigeration cycle.
[0075] It a particular embodiment of the invention, compressors of
various sizes are used in a common suction line to better match the
required capacity of the system on a dynamic basis.
[0076] All the embodiments and advantages as described herein with
regards to the compressors or the refrigeration systems also apply
mutatis mutandis for the method for operating a compressor and a
method for operating a refrigeration system. Such embodiments and
advantages are therefore not repeated with regard to such methods
in order to avoid redundancy.
[0077] 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 elements may be
substituted for equivalents thereof without departing from the
scope the invention. In addition, many modifications may be made to
adapt a 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 invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *