U.S. patent number RE29,621 [Application Number 05/732,697] was granted by the patent office on 1978-05-02 for variable capacity multiple compressor refrigeration system.
This patent grant is currently assigned to Westinghouse Electric Corp.. Invention is credited to Thomas F. Conley, Ernest F. Gylland, Jr..
United States Patent |
RE29,621 |
Conley , et al. |
May 2, 1978 |
Variable capacity multiple compressor refrigeration system
Abstract
A variable capacity multiple compressor refrigeration system
having first and second compressors with the first compressor to be
always running when the system is operating and the second
compressor to be cycled off or to vary the capacity of the system
on while the first compressor continues to run. The discharge lines
of both compressors are connected together in parallel to the
system and a check valve is provided in the discharge line
connection between the compressors to prevent discharge pressure
from the operating compressor from entering the discharge port of
the nonrunning compressor. A by-pass line connects the suction of
the system at the inlet of the second compressor to its discharge
line between the check valve and its discharge port and a solenoid
valve in the by-pass line is arranged to be closed when the second
compressor is running and open when it is cycled off. In one form
of the invention, both compressors are multiple cylinder hermetic
shell compressors and the inlet of the second compressor is
connected to the system through the shell of the first compressor.
Also, the first compressor is provided with unloading mechanism to
unload some of its cylinders for part unloaded operation, so that
four steps of different capacity may be obtained by running the
first compressor either loaded or partly unloaded while the second
compressor is cycled off or on and therefore, with the
aforementioned inlet arrangement, effectively high saturated gas
discharge temperatures may be obtained without over heating either
compressor for any of the capacity steps of operation.
Inventors: |
Conley; Thomas F. (Staunton,
VA), Gylland, Jr.; Ernest F. (Seattle, WA) |
Assignee: |
Westinghouse Electric Corp.
(Pittsburgh, PA)
|
Family
ID: |
23040923 |
Appl.
No.: |
05/732,697 |
Filed: |
October 14, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
272704 |
Jul 17, 1972 |
03775995 |
Dec 4, 1973 |
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Current U.S.
Class: |
62/196.2; 62/227;
62/228.1; 62/510 |
Current CPC
Class: |
F04B
39/12 (20130101); F04B 49/007 (20130101); F25B
31/00 (20130101); F25B 49/022 (20130101); F25B
2600/0251 (20130101); F25B 2400/075 (20130101); F25B
2400/0751 (20130101) |
Current International
Class: |
F04B
39/12 (20060101); F04B 49/00 (20060101); F25B
31/00 (20060101); F25B 49/02 (20060101); F25B
041/00 () |
Field of
Search: |
;62/196A,510,227,228,175,176B ;236/1E |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wayner; William E.
Attorney, Agent or Firm: Arenz; E. C.
Claims
What we claim is:
1. A variable capacity multiple compressor refrigeration system
comprising first and second .Iadd.hermetic shell
.Iaddend.refrigerant compressors, each compressor having suction
inlet and discharge ports, .Iadd.the first compressor having its
suction inlet port .Iaddend.adapted to be connected to the suction
line of the system, .Iadd.and the second compressor having its
suction inlet port connected to the interior of the shell of the
first compressor so that gas received by said second compressor is
received only through the shell of said first compressor,
.Iaddend.means to connect the discharge ports in parallel to the
refrigeration system, means to cycle-off said second compressor
while the first compressor continues to run for reduced capacity of
the system, a check valve in said means to connect to prevent
discharge gas from said first compressor from entering the
discharge port of the second cycled-off compressor, a bypass line
connected to the suction of the system and to said means to connect
at a point between the check valve and the discharge port of the
second compressor, a valve in said bypass line, and valve control
means to control said valve to be closed when both compressors are
running and to be open when said second compressor is
cycled-off.Iadd., said first compressor is a multiple cylinder
compressor having means to controllably unload some of its
cylinders for running part unloaded to reduce the capacity of the
system and said first compressor is always running when the system
is operating. .Iaddend. .[.
2. The invention of claim 1 in which said compressors are hermetic
shell compressors..]. .[.3. The invention of claim 1 in which said
first compressor is a multiple cylinder compressor having means to
controllably unload some of its cylinders for running part unloaded
to reduce the
capacity of the system..]. .[.4. The invention of claim 3 in which
said
compressors are hermetic shell compressors..]. 5. The invention of
claim .[.4.]. .Iadd.1 .Iaddend.in which multiple steps of variable
capacity are provided .[.with the inlet of said second compressor
being connected to the system through the shell of said first
compressor.]., and a multi-step capacity control comprising logic
switch cycle control means responsive to refrigeration demand to
cycle both compressors on for one capacity step corresponding to
maximum capacity, to operate said first compressor unloading means
to unload some of its cylinders while both compressors are
cycled-on for a second capacity step of reduced capacity, to
cycle-off said second compressor while at the same time operating
said first compressor unloading means to not unload any of its
cylinders and thereby cause only said first compressor to run at
full capacity for a third capacity step of reduced capacity, and to
cycle-off said second compressor and at the same time operate said
first compressor unloading means to unload some of the cylinders of
the first compressor while only the first compressor is running for
a fourth capacity step of reduced capacity of
the system. 6. The invention of claim .[.4.]. .Iadd.1 .Iaddend.in
which multiple steps of variable capacity are provided .[.with the
inlet of said second compressor being connected to the system
through the shell of said first compressor.]., and a multi-step
capacity control comprising logic switch cycle control means
responsive to refrigeration demand to cycle both compressors on for
one capacity step corresponding to maximum capacity, to operate
said first compressor unloading means to unload some of its
cylinders while both compressors are cycled-on for a second
capacity step of reduced capacity, to cycle-off said second
compressor and operate said valve control means to control said
valve to be open while at the same time operating said first
compressor unloading means to not unload any of its cylinders and
thereby cause only said first compressor to run at full capacity
for a third capacity step of reduced capacity, and to cycle-off
said second compressor and operate said valve control means to
control said valve to be open and at the same time operate said
first compressor unloading means to unload some of the cylinders of
the first compressor while only the one compressor is running for a
fourth capacity step of reduced capacity of the system.
Description
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
A dual compressor refrigeration system is disclosed and claimed in
the co-pending patent application Ser. No. 264,101, assigned to the
same assignee as the subject patent application.
BACKGROUND OF THE INVENTION
It is known to provide two or more compressors to be connected in
parallel to a single refrigeration system and to cycle off or on a
compressor while another compressor continues to run to provide
variable capacity for the system. However, such systems have
problems involved when a cycled-off compressor is turned on to
start running while another compressor is at that time running in
the system to create a system pressure against which the starting
compressor must start. Also, if any of the multiple compressors are
of the part unloading multiple cylinder hermetic shell type, the
maximum saturated discharge temperature for safe operation of the
part unloaded running compressor will be lower than when the
compressor is running fully loaded because of the work done on and
the heating of the recirculating refrigerant gas in the shell of
the part unloaded compressor. In a multiple compressor system, this
means that the upper limit of saturated gas discharge temperature
will be lower than would be possible if no part unloading
compressors were to be in operation. It is believed desirable to
have the safe upper limit of saturated gas discharge temperature to
be as high as possible for any given step capacity condition of
operation of the system. According to this invention, a first one
of the hermetic shell compressors is a multicylinder part unloading
compressor to be always running either fully loaded or part
unloaded when the system operates and the second hermetic shell
compressor which is to be cycled off or on is connected to the
system with its inlet suction line connected through the shell of
the first compressor so that when the first compressor is running
in part unloaded condition, the recirculating gas in its shell will
be mixed with and drawn into the shell of the second compressor,
when running, enabling the safe saturated gas upper temperature
limit for the discharge gas from either compressor to be higher
than could be possible if the suction inlet for the second
compressor was not connected to the system through the shell of the
first compressor.
PRIOR ART
Applicants are not aware of any prior art patents disclosing
refrigeration systems with multiple hermetic compressors connected
in the arrangement of the invention for providing improved starting
and running characteristics for the system and the compressors in
the system.
SUMMARY
A variable capacity multiple compressor refrigeration system is
provided with first and second having their discharge ports
connected together in parallel by suitable discharge lines to the
system. The first compressor is intended to be always running when
the system operates while at the same time the second compressor
may be cycled off or on to vary the capacity of the system. A check
valve is provided in the parallel connection of the discharge lines
to prevent discharge pressure of the first compressor from entering
the discharge port of the second compressor when the second
compressor is not running. In order to prevent the buildup of
discharge in the port of the second compressor as may be caused by
leakage of the check valve, a by-pass line is provided from the
discharge port of the second compressor to its suction and a valve
is positioned in the by-pass line and controlled to be open when
the second compressor is not running and closed when such
compressor is running. Thus, the second compressor may be started
without being loaded by pressure in the system while the first
compressor is running and without danger of liquid slugging.
In a preferred form of the invention, the first and second
compressors are hermetic shell compressors and in addition the
first compressor is a multi-cylinder compressor having means to
controllably unload some of its cylinders so that it may be
operated part unloaded for reduced capacity. It is known that a
part unloaded compressor will have a lower safe upper operating
limit of saturated discharge gas temperature due to the work done
on and heating of the recirculating gas in the hermetic compressor
shell by the unloaded cylinders and apparatus. In accordance with
this invention, the inlet for the second compressor is connected to
the system through the shell of the first compressor so that some
of the recirculating gas in the first compressor, while operating
partly unloaded, is distributed to the second compressor when the
second compressor is operating. Thus, a higher safe operating limit
of saturated gas discharge temperature for the system may be be
obtained without damage to the first compressor when operating part
unloaded under such conditions. Logic switch cycle control means
responsive to refrigeration demand is provided to enable four steps
of different capacity for the system to be obtained as follows.
When the switch is in a first position corresponding to maximum
demand, both compressors are controlled to be operating fully
loaded with the valve in the bypass line controlled to be closed. A
second position of the logic switch will partly unload the first
compressor while the second compressor continues to run, also with
the bypass valve closed. The third position of the logic switch
will control the first compressor to run fully loaded and cycle off
the second compressor while at the same time controlling the valve
in the bypass line to be open. A fourth position of the logic
switch will partly unload the first compressor while cycling off
the second compressor and keeping the bypass valve open.
Further features and advantages of the invention will be apparent
with reference to the following detailed specification and the
drawing.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary diagrammatic layout of a refrigeration
system with refrigerant compressors connected in the manner of the
invention;
FIG. 2 is a logic operational diagram of a control switch and the
interconnections to the system elements shown in FIG. 1; and
FIG. 3 is a chart of typical conditions of operation for four
different capacity steps as enabled by the system of the invention
shown in FIGS. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 of the drawing, a first compressor 10 and a
second compressor 20 which are preferably of the hermetic shell
type well known in the art are adapted to be connected to the
refrigeration system (not shown) in the manner of the invention to
be described. The suction port 11 communicating with the interior
of the shell of the first compressor 10 is to be connected to the
refrigeration system at the conventional point (not shown). The
suction port of the second compressor 20 is connected at 21 into
the shell of the hermetic compressor 10 and therethrough to the
suction port connection 11 and to the refrigeration system. The
first hermetic compressor 10 which may be a multi-cylinder part
unloading type well known in the art can be provided with a
discharge port 12 connected to the cylinders that cannot be
unloaded and a discharge port 13 connected to the cylinders that
can be unloaded and it should be understood that there is a check
valve (not shown) in the port 13 to the unloading cylinders as is
well known in the art to enable the loaded cylinder discharge from
port 12 to establish a pressure in the refrigeration system when
the unloading cylinders are in the unloaded condition. Compressor
20 is provided with a single discharge port 22 and all of the
discharge ports 12, 13 and 22 are adapted to be connected in
parallel by the discharge line 30 to the high pressure side of the
refrigeration system.
In accordance with the invention, a check valve 31 is interposed
between the discharge line 30 and the discharge port 22 to prevent
the high gas pressure in the line 30, when only compressor 10 is
running, from feeding back to the discharge port 22 of the not
running compressor 20 when such condition of operation for the
compressors is required as will be later described. In the system
being described, it is intended that compressor 10 will be always
running and compressor 20 will be at times cycled off to be not
running for a lower capacity of the system. When compressor 20 is
to be restarted while compressor 10 is already running with
pressure in the system, the provision of the check valve 31
facilitates the restarting of compressor 20 without necessarily
having to overcome the existing high pressure of the system,
assuming the pressure in the discharge port of compressor 20 to
have been equalized.
Since it is possible that the check valve 31 might leak slightly to
gradually build up a pressure in the discharge port 22, which could
cause slugging of the compressor 20 when it is started, the
invention provides a by-pass line 33 connected between the
discharge port 22 and the suction port 21 of the compressor 20. A
solenoid valve 34 is positioned in the by-pass line 33 to be
controlled to be closed when compressor 20 is running and open when
it is not running so that any leakage past the check valve 31 will
be returned to the suction port 21 and the shells of the
compressors 10 and 20 without building up a pressure in the
discharge port 22 when compressor 20 is not running. Also, when the
valve 34 is open, any pre-existing pressure in the discharge port
22 will be by-passed and equalized. Of course, when compressor 20
is to be started to run, the solenoid valve 34 is operated to be
closed so that discharge pressure in the port 22 will not be
by-passed back to suction.
Referring to FIG. 2 of the drawing, a capacity control logic switch
40 is shown by a logic diagram to have four switch position of
operation which may be determined by a refrigerant load sensor 41
of any suitable type known to those skilled in the art. The first
switch position shown at 40a corresponds to the position assumed
when 100 percent of the system capacity is required by the load
sensor. When the switch 41 is in position 40a, the unloading
solenoid 42, which when in the on position will unload the
cylinders connected to discharge port 13, will not be energized and
will be in the off position and both compressors 10 and 20 will be
started and running to give full or 100 percent capacity to the
system. When the capacity control switch 40 is moved by the load
sensor 41 to switch position 40b corresponding to a demand of 75
percent of system capacity, the unloading solenoid 42 will be in
the on position to unload the cylinders connected to the discharge
port 13. For purposes of this description, it is assumed that half
of the cylinders of compressor 10 are unloaded cylinders connected
to port 13 and that the capacities of both compressors 10 and 20
are equal. Thus, when both compressors 10 and 20 are running, with
switch 41 at position 40b and half of the cylinders of compressor
10 unloaded, a capacity equal to 75 percent of the system capacity
is produced. When the capacity switch control 40 is in position
40c, the starter switch and circuit 43 for compressor 20 will be
conditioned off to stop compressor 20 from running while compressor
10 continues to run. However, at this time, the unload solenoid 42
will not be in the on position and compressor 10 will be running at
its fully loaded condition so that 50 percent capacity of the
system is obtained. At the same time, the anti-slug solenoid 44 for
the solenoid valve 34 will be in the on or valve open condition so
as to bypass any leakage of gas passing check valve 31 as
previously described and preventing slugging of compressor 20 when
it is subsequently restarted. At position 41d of the capacity
control switch 40, the unload solenoid 42 will be in the on
position, compressor starter 43 for compressor 20 will be off and
the anti-slug solenoid 44 will be on to open valve 34 thus
producing 25 percent of the total capacity of the system by only
operating compressor 10 in half unloaded condition.
Referring to the chart of FIG. 3, comparative values are given to
show the performance of the system described above. Assuming a
saturated gas suction temperature of 40.degree. F with both
compressors 10 and 20 running fully loaded, an upper limit of
saturated discharge temperature of 145.degree. F is obtainable
without damage to the compressors for a given system and
compressors. At 75 percent capacity with compressor 10 running half
unloaded, the upper safe limit of saturated discharge temperature
is 135.degree. F for the same system which is only 10.degree. F
less than for 100 percent capacity operation. At 50 percent of
system capacity, with only compressor 10 running fully loaded, the
upper saturated discharge gas temperatue is again 145.degree. F for
the same system. At 25 percent of system capacity with only
compressor 10 running half unloaded, the upper safe limit of
saturated discharge gas temperature is 125.degree. F which is the
lowest safe limit mentioned for the same system because there is no
distribution of recirculating gas from the shell of compressor 10
into the shell of compressor 20 when compressor 20 is not
running.
In order to simplify the description, no electrical circuit details
for implementing the logic diagram of FIG. 2 have been given, it
being obvious to one skilled in the art that various circuits,
solenoid valves, and compressor unloading solenoid arrangements
that are well known could be used. Also, although four
combinational arrangements of two compressors of equal capacity in
which only one compressor is capable of being unloaded to 50
percent of its capacity have been specifically described, the
teachings of this invention are applicable with the advantages as
described to other combinations of compressors of different
capacities that may be part unloaded or not so long as the suction
gas for the compressor that may at times be not running is drawn
through the shell of the always running compressor of the system.
Various other modifications will occur to those skilled in the
art.
* * * * *