U.S. patent application number 13/057959 was filed with the patent office on 2011-06-16 for improved operation of a refrigerant system.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20110138827 13/057959 |
Document ID | / |
Family ID | 41664200 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110138827 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
June 16, 2011 |
IMPROVED OPERATION OF A REFRIGERANT SYSTEM
Abstract
A method and system for operating a refrigerant system having a
reciprocating compressor with a main cylinder module and an
economizer cylinder module includes regulating a flow of
refrigerant into the main cylinder module and regulating a flow of
refrigerant into the economizer cylinder module. The main cylinder
module and the economizer cylinder module have separate inlet and
outlet discharge streams. The flow through each module is regulated
as a function of an operating mode of the refrigerant system, which
includes various modes of loading and unloading based, in part, on
a cooling demand. In some embodiments, the refrigerant system may
include a connector refrigerant line configured to redirect
refrigerant from the economizer cylinder module to the main
cylinder module or from the main cylinder module to the economizer
cylinder module.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
41664200 |
Appl. No.: |
13/057959 |
Filed: |
August 6, 2009 |
PCT Filed: |
August 6, 2009 |
PCT NO: |
PCT/US2009/052995 |
371 Date: |
February 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61087008 |
Aug 7, 2008 |
|
|
|
Current U.S.
Class: |
62/117 ; 62/115;
62/190; 62/196.1 |
Current CPC
Class: |
F25B 2400/13 20130101;
F25B 2700/1931 20130101; F25B 2700/2106 20130101; F25B 1/10
20130101; F04B 39/00 20130101; F25B 2600/2509 20130101; F25B 41/22
20210101 |
Class at
Publication: |
62/117 ; 62/190;
62/196.1; 62/115 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F25D 17/02 20060101 F25D017/02; F25B 41/04 20060101
F25B041/04 |
Claims
1. A refrigerant system comprising: a high pressure heat exchanger
configured to absorb heat from refrigerant as the refrigerant
passes through the high pressure heat exchanger; an economizer
module configured to receive a first refrigerant stream and a
second refrigerant stream derived from the refrigerant exiting the
high pressure heat exchanger; an evaporator configured to evaporate
the first refrigerant stream; a first refrigerant line extending
from the evaporator and configured to receive the first refrigerant
stream; a second refrigerant line extending from the economizer
module and configured to receive the second refrigerant stream; a
reciprocating compressor comprising: a main cylinder module having
a first inlet connected to the first refrigerant line and
configured to receive the first refrigerant stream and direct the
first refrigerant stream through the main cylinder module; and an
economizer cylinder module having a second inlet connected to the
second refrigerant line and configured to receive the second
refrigerant stream and direct the second refrigerant stream through
the economizer cylinder module; and a controller for controlling
flow of at least one of the first refrigerant stream and the second
refrigerant stream.
2. The refrigerant system of claim 1 further comprising at least
one of a first valve in the first refrigerant line to control flow
of the first refrigerant stream into the reciprocating compressor
and a second valve in the second refrigerant line to control flow
of the second refrigerant stream into the reciprocating
compressor.
3. The refrigerant system of claim 2 further comprising: a
connector refrigerant line between the first refrigerant line and
the second refrigerant line and configured to perform at least one
of bypassing at least a portion of the first refrigerant stream
into the economizer cylinder module and bypassing the second
refrigerant stream into the main cylinder module; and a valve in
the connector refrigerant line to control at least one of the
bypass of the first refrigerant stream into the economizer cylinder
module and the bypass of the second refrigerant stream into the
main cylinder module.
4. The refrigerant system of claim 3 wherein the valve in the
connector refrigerant line is located downstream of a valve in the
second refrigerant line and upstream of a valve in the first
refrigerant line.
5. The refrigerant system of claim 4 wherein the controller is
configured to at least partially close the valve in the second
refrigerant line and at least partially open the valve in the
connector refrigerant line such that at least a portion of the
first refrigerant stream flows through the second refrigerant line
and through the economizer cylinder module.
6. The refrigerant system of claim 4 wherein the controller is
configured to at least partially close the valve in the first
refrigerant line such that the first refrigerant stream flows
through the second refrigerant line and through the economizer
cylinder module.
7. The refrigerant system of claim 4 wherein the controller is
configured to at least partially open the valves in the first and
second refrigerant lines and at least partially open the valve in
the connector refrigerant line such that a portion of the second
refrigerant stream flows through the first refrigerant line and
through the main cylinder module.
8. A method of operating a refrigerant system configured to provide
cooling using a refrigerant and including a high pressure heat
exchanger, an economizer module, an evaporator, and a reciprocating
compressor having a main cylinder module with a first inlet and a
first outlet and an economizer cylinder module with a second inlet
and a second outlet, the method comprising: flowing the refrigerant
through the high pressure heat exchanger, the economizer module,
the evaporator, and at least one of the main cylinder module and
the economizer cylinder module, wherein the refrigerant exiting the
economizer module is in a main refrigerant stream and an economizer
refrigerant stream, and the main refrigerant stream flows through
the evaporator; controlling a flow of the refrigerant into the main
cylinder module of the reciprocating compressor at least in part as
a function of an operating mode of the refrigerant system; and
controlling a flow of refrigerant into the economizer cylinder
module of the reciprocating compressor at least in part as a
function of the operating mode.
9. The method of claim 8 wherein the operating mode is a function
of at least one of an ambient air temperature, a set point air
temperature, a pressure at an inlet of the reciprocating
compressor, and a pressure at an outlet of the reciprocating
compressor.
10. The method of claim 8 wherein controlling a flow of the
refrigerant into the main cylinder module includes preventing the
main refrigerant stream exiting the evaporator from entering the
main cylinder module.
11. The method of claim 10 further comprising: directing the main
refrigerant stream exiting the evaporator through the economizer
cylinder module.
12. The method of claim 8 wherein controlling a flow of the
refrigerant into the economizer cylinder module includes preventing
the economizer refrigerant stream exiting the economizer module
from entering the economizer cylinder module.
13. The method of claim 12 further comprising: directing at least a
portion of the main refrigerant stream exiting the evaporator
through the economizer cylinder module.
14. The method of claim 12 further comprising: directing the
economizer refrigerant stream exiting the economizer module through
the main cylinder module.
15. The method of claim 8 wherein the refrigerant system comprises:
a first refrigerant line connecting the evaporator to the first
inlet of the main cylinder module of the reciprocating compressor;
and a second refrigerant line connecting the economizer module to
the second inlet of the economizer cylinder module.
16. The method of claim 15 wherein the refrigerant system further
comprises: a connector refrigerant line between the first
refrigerant line and the second refrigerant line; and a valve in
the connector refrigerant line.
17. The method of claim 16 wherein the refrigerant system further
comprises: a first valve in the first refrigerant line; and a
second valve in the second refrigerant line, wherein the valve in
the connector refrigerant line is located downstream of the second
valve and upstream of the first valve.
18. A method of controlling a refrigerant system configured to
circulate a refrigerant and including a high pressure heat
exchanger, an economizer module, an evaporator, a reciprocating
compressor having a first inlet and a second inlet and configured
to receive two separate refrigerant streams, a first refrigerant
line between the evaporator and the first inlet of the
reciprocating compressor, and a second refrigerant line between the
economizer module and the second inlet of the reciprocating
compressor, the method comprising: monitoring at least one of an
ambient air temperature, a set point air temperature, a pressure at
an inlet of the reciprocating compressor, and a pressure at an
outlet of the reciprocating compressor to determine an operating
mode of the refrigerant system; regulating flow of the refrigerant
through the first refrigerant line and into the main cylinder
module at least in part as a function of the operating mode; and
regulating flow of the refrigerant through the second refrigerant
line and into the economizer cylinder module at least in part as a
function of the operating mode.
19. The method of claim 18 further comprising: regulating flow of
the refrigerant between the first refrigerant line and the second
refrigerant line.
20. The method of claim 19 wherein regulating flow of the
refrigerant through the second refrigerant line includes directing
at least a portion of the refrigerant from the evaporator into the
economizer cylinder module.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a refrigerant system having
an economizer module and a reciprocating compressor. More
particularly, the present invention relates to a method and system
for operating the refrigerant system in various modes of loading
and unloading.
BACKGROUND
[0002] Refrigerant systems are used to condition air in an
environment by controlling the temperature and/or the humidity of
the air. In a typical air conditioning or refrigeration system, a
compressor delivers a compressed refrigerant to an outdoor high
pressure heat exchanger, known as a condenser or a gas cooler. If
the refrigerant in the outdoor heat exchanger, when cooled,
condenses into a liquid this heat exchanger is commonly referred to
as a condenser. If the refrigerant exiting the compressor is at a
thermodynamic state above critical point, then the refrigerant upon
cooling in the heat exchanger may not condense into a liquid but
would simply be cooled to a lower temperature. In this case, this
heat exchanger is commonly referred to as a gas cooler. From the
high pressure heat exchanger, the refrigerant passes through an
expansion device, and then to an indoor heat exchanger, known as an
evaporator. In the evaporator, the air is blown over the evaporator
external surfaces to lower a temperature of the air, and moisture
may also be removed from the air to lower its humidity. From the
evaporator, the refrigerant is returned back to the compressor.
[0003] An economizer cycle may be used in a refrigerant system to
increase the capacity and efficiency of the system. When the
economizer cycle is actuated, a portion of the refrigerant is
tapped from a main refrigerant circuit at a position downstream of
the high pressure heat exchanger. The tapped refrigerant is
expanded to a lower intermediate pressure and temperature, at which
point it passes through an economizer module, which is commonly
called an economizer heat exchanger, to further cool high pressure
refrigerant in the main refrigerant circuit. The tapped refrigerant
is returned back to the compressor, typically at an intermediate
pressure. The main refrigerant travels to the evaporator where it
has a greater thermodynamic cooling potential (cooling capacity),
due to the fact that it has been additionally cooled in the
economizer heat exchanger. An economizer cycle can also be achieved
through the use of a flash tank, instead of the economizer heat
exchanger, as known in the art.
[0004] In one design, the refrigerant system may use a
reciprocating compressor having two separate sets of cylinder
modules, which are configured to receive and compress two separate
refrigerant streams. An economizer cylinder module may be used to
compress the tapped refrigerant from the economizer module, whereas
a main cylinder module may be configured for compressing the main
refrigerant from the evaporator. Downstream of the compressor, the
two refrigerant streams may be combined before flowing back to the
high pressure heat exchanger.
[0005] During operation of the refrigerant system, there may be
conditions in which it is ineffective to use the economizer cycle,
even though the refrigerant system is operating at or near full
load. For example, if the ambient air temperature is high and the
suction pressure entering the compressor is also high then the
economizer cycle engagement may not add any additional cooling and
thus the economizer cycle may be disengaged, even if there is a
high cooling demand (i.e. full load). At other times, it may be
beneficial to operate a refrigerant system in a mode that limits
the cooling capacity by limiting a flow of refrigerant through the
system, which may be referred to as unloading. The unloading can be
achieved by disengaging the economizer circuit or providing by-pass
operation. There is a need for improved flexibility to vary a
cooling capacity for a refrigerant system having an economizer
cycle and a reciprocating compressor with a dedicated economizer
cylinder module.
SUMMARY
[0006] A method and system is described herein for operating a
refrigerant system having a reciprocating compressor with a main
cylinder module and an economizer cylinder module. In the context
of this application a single cylinder module may be substituted by
bank of cylinders modules. The refrigerant system provides cooling
by circulating a refrigerant through a high pressure heat
exchanger, an economizer module, an evaporator, and at least one of
the main cylinder modules and at least one of the economizer
cylinder modules. The main cylinder module and the economizer
cylinder module have separate inlet and outlet streams. The flow of
refrigerant into the main cylinder module may be controlled as a
function of an operating mode of the refrigerant system, which
includes various modes of loading and unloading based, in part, on
a cooling demand. The flow of refrigerant into the economizer
cylinder module may separately be controlled as a function of the
operating mode. In some embodiments, the refrigerant system may
include a connector line configured to redirect refrigerant from
the economizer cylinder module to the main cylinder module or from
the main cylinder module to the economizer cylinder module.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic of a refrigerant system including an
economizer module, a reciprocating compressor having a first inlet
connected to a main refrigerant line and a second inlet connected
to an economizer refrigerant line, a first valve in the main
refrigerant line, and a second valve in the economizer refrigerant
line.
[0008] FIG. 2 is a schematic of an alternative embodiment of the
refrigerant system from FIG. 1, and includes a connector line and
corresponding valve between the main refrigerant line and the
economizer refrigerant line.
[0009] FIG. 3 is a schematic of a flash tank that may be used in
the economizer module as an alternative to an economizer heat
exchanger.
DETAILED DESCRIPTION
[0010] FIG. 1 is a schematic of refrigerant system 10 including
compressor 12, high pressure heat exchanger 14, first expansion
device 16, economizer module 18, second expansion device 20,
evaporator 22, first valve 24, second valve 26 and controller 28.
Refrigerant system 10 is configured to circulate a refrigerant
through system 10 to provide cooling and condition an air stream
(not shown) passing through evaporator 22.
[0011] Compressor 12 is a reciprocating compressor and includes
main cylinder module 30 and economizer cylinder module 32. It is
recognized that one or both of main cylinder module 30 and
economizer cylinder module 32 may include more than one cylinder
and more than one cylinder module. In an exemplary embodiment, main
cylinder module 30 has higher displacement than economizer cylinder
module 32. Compressor 12 includes first suction inlet 34, which is
connected to main cylinder module 30, and second suction inlet 36,
which is connected to economizer cylinder module 32. Similarly,
compressor 12 also includes first discharge outlet 38 extending
from main cylinder module 30 and second discharge outlet 40
extending from economizer cylinder module 32. System 10 is designed
such that main cylinder module 30 and economizer cylinder module 32
each receive a distinct refrigerant stream for compression. As
shown in FIG. 1, main cylinder module 30 is configured to receive
refrigerant from evaporator 22 and economizer cylinder module 32 is
configured to receive refrigerant from economizer module 18.
[0012] Two refrigerant streams exit compressor 12 via first outlet
38 and second outlet 40 respectively. Before entering high pressure
heat exchanger 14, the refrigerant streams are recombined such that
high pressure heat exchanger 14 receives one refrigerant stream. In
high pressure heat exchanger 14 operating as a condenser, the vapor
refrigerant condenses to form liquid refrigerant. In an alternative
embodiment of refrigerant system 10, high pressure heat exchanger
14 may be substituted with a gas cooler, where refrigerant stays in
a single phase thermodynamic state.
[0013] Once the refrigerant exits high pressure heat exchanger 14,
the refrigerant may again be split into two refrigerant streams. A
main refrigerant stream flows through main refrigerant line 42a; an
economizer refrigerant stream flows through tap line 44a, also
referred to as economizer refrigerant line 44a. The refrigerant in
tap refrigerant line 44a passes through first expansion device 16
in order to lower its temperature and pressure before passing
through economizer module 18. Expansion device 16, as well as
second expansion device 20, may include a capillary tube, an
orifice, a thermostatic expansion device, or an electronic
expansion device.
[0014] Inside economizer module 18, the refrigerant flowing through
tap line 44a further decreases a temperature of the main
refrigerant stream passing through main refrigerant line 42a.
Economizer module 18 is used to provide additional cooling capacity
to the main refrigerant stream. In an exemplary embodiment,
economizer module 18 is a heat exchanger. An alternative embodiment
of module 18 is described in further detail below. Also, as known,
the economizer refrigerant flow may be tapped downstream (instead
of upstream) of economizer module 18. Such system configurations
are within the scope and can equally benefit from the
invention.
[0015] After exiting economizer module 18, the main refrigerant
stream passes through second expansion device 20, and then to
evaporator 22 through main refrigerant line 42b. The main
refrigerant is evaporated inside evaporator 22 by removing heat
from air passing over external surfaces of evaporator 22. Main
refrigerant line 42c connects evaporator 22 to inlet 34 of main
cylinder module 30, and the refrigerant flows through main
refrigerant line 42c to undergo compression in a separate
compression path in the main cylinder module 30. First valve 24 is
located in main refrigerant line 42c and regulates a flow of the
main refrigerant between evaporator 22 and compressor 12. The
economizer refrigerant stream flows directly from economizer module
18 to compressor 12 through economizer refrigerant line 44b. Second
valve 26 is located in economizer line 44b and regulates a flow of
the economizer refrigerant between economizer module 18 and
compressor 12. More specifically, economizer refrigerant line 44b
connects to second inlet 36 of compressor 12.
[0016] The present invention includes the use of valves 24 and 26
to control a flow of refrigerant into compressor 12, and more
specifically to control a flow of refrigerant through main cylinder
module 30 and economizer cylinder module 32. An amount of cooling
provided by refrigerant system 10 may be controlled by controlling
a circulation of the refrigerant through main cylinder module 30
and economizer cylinder module 32, as described further below. A
cooling capacity of refrigerant system 10 may be varied by
operating the system in loading or unloading modes. These
operational modes are also described in further detail below.
[0017] Valve 24 is used to control the flow of refrigerant into
main cylinder module 30, which directly impacts an amount of
cooling provided by evaporator 22. As more refrigerant is pumped
through cylinder module 30, more refrigerant is circulated through
evaporator 22, which results in increased amount of cooling of air
passing over the evaporator 22. Similarly, valve 26 controls flow
of refrigerant through economizer cylinder module 32. As more
refrigerant is pumped through cylinder module 32, more refrigerant
is circulated through economizer module 18, which provides
additional cooling to the refrigerant in main refrigerant line. As
described below, valves 24 and 26 are controlled in order to
regulate an amount of cooling provided in evaporator 22.
[0018] For a refrigerant system similar to system 10, but not
including valves 24 and 26, unloading may not be possible, or be
very limited, without essentially shutting down system 10, which
may be undesirable for several reasons. In refrigerant system 10 of
FIG. 1, three levels of unloading are made feasible by valves 24
and 26. Refrigerant system 10 is able to operate in four different
operating modes shown in Table 1 below, depending on a position of
valves 24 and 26.
TABLE-US-00001 TABLE 1 Operating First Second Mode Valve 24 Valve
26 Comments Full loading Open Open Typical for high pressure ratio.
with Would be identical if valves 24 economizer and 26 are not
present in system Mid-level Open Closed Economizer cycle blocked
unloading Full Closed Open Unloading with discharge flow unloading
A cooling Full Closed Closed Unloading without discharge unloading
B flow cooling
[0019] In the scenario in which both valves 24 and 26 are open
(i.e. full loading with economizer), refrigerant system 10 operates
the same as a refrigerant system not having valves 24 and 26 for
controlling refrigerant flow into the reciprocating compressor 12.
In the full loading mode of Table 1, the economizer cycle is being
utilized since valve 26 is open. In the economizer mode, economizer
module 18 uses refrigerant in the tapped refrigerant line 44a to
further cool refrigerant in the main refrigerant line 42a such that
the main refrigerant provides additional cooling to the air in
evaporator 22. This operating mode is referred to as "Full loading
with economizer" since valve 26 in economizer line 44b is open and
both cylinder modules 30 and 32 are operating at full capacity.
[0020] The economizer cycle is generally used when a ratio of
discharge pressure to suction pressure in compressor 12 is high
(typically when the system operates at pressure ratio above 3). As
such, the pressure at the suction or inlet of compressor 12 is
typically low, which is a function of low pressure inside
evaporator 22. A low evaporator pressure typically correlates to a
low ambient air temperature. In that case, refrigerant system 10
may operate in the economizer mode (i.e. valve 26 open) to further
decrease the air temperature.
[0021] In the second mode shown in Table 1 and designated as
"Mid-level unloading", the economizer cycle is blocked by closing
valve 26, which prevents refrigerant from circulating through
economizer module 18. As such, refrigerant in the tapped
refrigerant line essentially stops providing cooling to refrigerant
in the main refrigerant line in economizer module 18. This
mid-level unloading mode may commonly be used at low to moderate
pressure ratio applications (typically in pressure ratio range from
1 to 3). When the air requiring cooling is at a high temperature,
refrigerant system 10 provides higher cooling capacity when the
economizer cycle is not active. A higher ambient air temperature
commonly results in a high pressure in the evaporator. As such, a
high ambient air temperature usually correlates to a low pressure
ratio (discharge to suction). The pressure ratio may commonly be
monitored or calculated to determine whether to engage or disengage
the economizer cycle.
[0022] In the third mode of Table 1, labeled as "Full unloading A",
valve 24 is blocked such that the only refrigerant flowing through
compressor 12 is the tapped refrigerant from economizer module 18.
Because valve 26 is closed, refrigerant stops circulating through
evaporator 22 and ceases to provide cooling to air passing through
evaporator 22. This high level of unloading may be used when there
is little to no cooling load required, yet it is desirable to
continue operating refrigerant system 10, instead of completely
shutting it down. By flowing the tapped refrigerant line from
economizer module 18 through compressor 12, discharge cooling may
be provided to compressor 12.
[0023] Finally, the last fourth mode shown in Table 1 and is
designated as "Full unloading B" is a mode in which both valves 24
and 26 are closed. As such, the refrigerant stops circulating
through refrigerant system 10 and is no longer able to provide
cooling to air passing through evaporator 22. Similar to the "Full
unloading A" mode above, refrigerant system 10 may operate in this
mode when there is minimal, if any, cooling load present. It is
recognized that this last mode is an unusual operating condition
and additional steps may need to be taken to ensure that compressor
12, as well as other equipment in refrigerant system 10, does not
overheat.
[0024] Valves 24 and 26 may be ON/OFF valves that have two
positions--fully open and fully closed. This type of valve is
typically a solenoid valve. Alternatively, either or both of valves
24 and 26 may be a variable opening valve or "stepper motor drive"
valve. The stepper motor may position valves 24 and 26 at a fully
open position, a fully closed position, and anywhere in between. In
preferred embodiments, valves 24 and 26 have a variable opening,
since this provides greater flexibility and additional stages of
loading and unloading. It is recognized that variations of the four
modes shown in Table 1 are possible by adjusting one or both of
valves 24 and 26 at an intermediate position between open and
closed. If the stepper motor valves are utilized then, for example,
for modes three and four, valve 24 may not be fully closed and, in
this case, refrigerant system 10 will not have a full unloading
operation.
[0025] Operation of valves 24 and 26 may be controlled by
controller 28, which determines a most effective mode of operation
based on particular parameters inside refrigerant system 10.
Depending on sensed parameters, controller 28 adjusts valves 24 and
26. In the case of solenoid valves, the adjustments may be either
an ON or OFF position. For variable opening valves, controller 28
may adjust the valves from fully open, fully closed or an
intermediate position. To determine an operating mode and hence a
position of valves 24 and 26, parameters sensed and relayed to
controller 28 may include, but are not limited to, a temperature
inside evaporator 22, a set point temperature of the air to be
conditioned, a pressure at an inlet of compressor 12 (i.e. suction
pressure), and a pressure at an outlet of compressor 12 (i.e.
discharge pressure).
[0026] System 10 includes various sensors that communicate with
controller 28. As shown in FIG. 1, temperature sensor 50 may be
associated with evaporator 22 for sensing a temperature (T1) in
evaporator 22. It is recognized that sensor 50 may include more
than one temperature sensor positioned at various locations at
evaporator 22. Several pressure sensors are also included in
refrigerant system 10. As described above, the ratio of discharge
pressure to suction pressure for compressor 12 may be used to
determine an operating mode of refrigerant system 10. The suction
pressure usually correlates to the pressure of the refrigerant
exiting evaporator 22 and may commonly be measured at suction inlet
34 of main refrigerant line 42c. However, if valve 24 is closed,
refrigerant is not able to flow through suction inlet 34.
Therefore, first pressure sensor 52 may be included in main
refrigerant line 42c at a position upstream of first valve 24 to
measure suction pressure (P1) of the main refrigerant. Second
pressure sensor 54 may be located near first discharge outlet 38 of
main cylinder module 30 to sense a discharge pressure (P2) of the
main refrigerant exiting compressor 12. Pressure sensor 56 may also
be located in economizer line 44b to measure a pressure (P3) in
economizer line 44b; and pressure sensor 58 may be located near
second discharge outlet 40 of economizer cylinder module 32 to
measure a discharge pressure (P4) at the exit from economizer
cylinder module 32. In some embodiments, suction pressure (P3) and
discharge pressure (P4) of economizer cylinder module 32 may not be
included in refrigerant system 10. Pressures (P3) and (P4) may be
less significant than suction pressure (P1) and discharge pressure
(P2) of main cylinder module 30, which are used to analyze
conditions at evaporator 22.
[0027] Data from sensors 50, 52, 54, 56 and 58 include temperature
(T1) and pressures (P1) through (P4), which are inputs to
controller 28, as shown in FIG. 1. In addition, temperature sensor
60 may be used to measure an ambient air temperature (AT), which is
also an input to controller 28. User input 62 may include a set
point temperature (SPT) for the air to be cooled in evaporator 22.
It is recognized that additional sensors and additional inputs to
controller 28 not shown in FIG. 1, may be included in refrigerant
system 10. Based on the various inputs to controller 28, controller
28 regulates a position of valves 24 and 26 such that refrigerant
system 10 operates efficiently and avoids nuisance shutdowns.
[0028] In the exemplary embodiment shown in FIG. 1, refrigerant
system 10 includes first valve 24 in main refrigerant line 42c
between evaporator 22 and compressor 12, and second valve 26 in
economizer refrigerant line 44b between economizer module 18 and
compressor 12. In an alternative embodiment, a refrigerant system
may include only one of valves 24 and 26, and in that case, the
refrigerant system is configured to operate in two of the four
operating modes shown in Table 1.
[0029] FIG. 2 is a schematic of refrigerant system 110, which is an
alternative embodiment of refrigerant system 10 of FIG. 1. Similar
to refrigerant system 10, refrigerant system 110 includes
compressor 112, high pressure heat exchanger 114, first expansion
device 116, economizer module 118, second expansion device 120,
evaporator 122, first valve 124, second valve 126, controller 128,
and variable frequency drive (VFD) 129. Refrigerant system 110
operates in a similar manner to refrigerant system 10 described
above. Compressor 112 includes main cylinder module 130 and
economizer cylinder module 132. Each cylinder module 130 and 132
has its own inlet leading to the module and outlet exiting the
module, and one or both of cylinder modules 130 and 132 may include
more than one cylinder and more than one cylinder module. As shown
in FIG. 2, first valve 124 is installed in main refrigerant line
142c between evaporator 122 and inlet 134 to main cylinder module
130; second valve 126 is installed in economizer refrigerant line
144b between economizer module 18 and inlet 136 of economizer
cylinder module 132. Unlike refrigerant system 10, refrigerant
system 110 includes connector refrigerant line 170 located between
main refrigerant line 142c and economizer refrigerant line 144b,
and third valve 172 installed in connector refrigerant line 170. In
preferred embodiments, valves 124, 126 and 172 have variable
openings such that refrigerant system 110 has additional
flexibility to position valves 124, 126 and 172 at an intermediate
position between fully open and fully closed.
[0030] In refrigerant system 10 shown in FIG. 1, valves 24 and 26
provide flexibility in terms of controlling flow from evaporator 22
to main cylinder module 30 and from economizer module 18 to
economizer cylinder module 32. However, it is not possible in
refrigerant system 10 to redirect refrigerant from main refrigerant
line 42c to economizer refrigerant line 44b, and vice versa. As
such, refrigerant system 10 prevents the main refrigerant stream
from flowing through economizer cylinder module 32 and the
economizer stream from flowing through main cylinder module 30.
Refrigerant system 110 overcomes these limitations by installing
connector line 170 between main refrigerant line 142c and
economizer refrigerant line 144b. Valve 172 in connector
refrigerant line 170 is preferably a bi-directional valve such that
refrigerant can flow in either direction between main refrigerant
line 142c and economizer refrigerant line 144b. Therefore
refrigerant system 110 offers additional flexibility and control in
terms of loading and unloading.
[0031] Refrigerant system 110 is able to operate in eight different
operating modes, based on a position of valves 124, 126 and 172.
The operating modes are generally ordered from highest to lowest
cooling capacity. For purposes of the description below, a higher
level of unloading corresponds to a lower cooling capacity. Four of
the eight operating modes shown in Table 2 for refrigerant system
110 are feasible in refrigerant system 10 of FIG. 1. As described
further below, system 110 provides even greater flexibility and
control for unloading, as compared to refrigerant system 10 of FIG.
1. Moreover, system 110 also provides for greater cooling capacity
than system 10 when the economizer cycle is not being used.
TABLE-US-00002 TABLE 2 Operating First Second Third Mode Valve 124
Valve 126 Valve 172 Comments 1. Full loading with Open Open Closed
High pressure ratio. This mode economizer also feasible in system
10 (see Table 1). Same as if there are no valves 2. Full loading
Open Closed Open Low pressure ratio without economizer 3. Low to
mid-level Open Open Open Flow from both economizer and unloading
line through main line 4. Mid-level Open Closed Closed This mode
also feasible for unloading refrigerant system 10 (see Table 1). 5.
Mid-level Closed Closed Open Evaporator flow only unloading
economized cylinder module 6. Mid to high level Closed Open Open
Flow from both main and unloading economizer line through
economized cylinder module 7. Full unloading Closed Open Closed
Discharge flow cooling. This mode is also feasible for refrigerant
system 10 (see Table 1). 8. Full unloading Closed Closed Closed
This mode is also feasible for refrigerant system 10 (see Table
1).
[0032] Two "Full loading" operating modes are shown above in Table
2. First, the "Full loading with economizer" mode was described
above in reference to refrigerant system 10. Since both valves 124
and 126 are open, and valve 172 is closed, this mode is the same as
a system having no valves in lines 142 and 144. The second "Full
loading" operating mode, referred to in Table 2 as "Full loading
without economizer", is not feasible for refrigerant system 10 and
allows for increased loading (i.e. increased cooling capacity) when
the economizer cycle is not being used for low pressure ratio
operation.
[0033] As described above in reference to FIG. 1 and Table 1, it
may not be efficient to use the economizer cycle under some
conditions, such as at low pressure ratio operation. In this case,
refrigerant system 110 achieves a greater cooling capacity than
refrigerant system 10 when the economizer cycle is blocked. In the
second mode referred to as "Full loading without economizer", valve
126 is closed, and valves 124 and 172 are open. As such, a portion
of refrigerant from evaporator 122 flows from main refrigerant line
142c through connector refrigerant line 170 and into economizer
cylinder module 132. The remaining refrigerant from evaporator 122
flows through main cylinder module 130. As such, main cylinder
module 130 and economizer cylinder module 132 operate in parallel
to compress the main refrigerant from evaporator 122. By using all
of the cylinder modules in compressor 112, instead of only main
cylinder module 130, refrigerant system 110 is able to circulate a
greater amount of refrigerant through evaporator 122. This allows
evaporator 122 to generate more cooling during those times when the
economizer cycle is not being used, but a high cooling capacity is
desired.
[0034] It is recognized that the level of unloading may be adjusted
for any given mode based on a position of valves 124, 126 and 172,
in those embodiments in which the valves have variable
openings.
[0035] In operating mode three, designated as low to mid-level
unloading, all three valves 124, 126 and 172 are open. As such, at
least a portion of flow from economizer refrigerant line 144b flows
through connector refrigerant line 170 and is combined with main
refrigerant in main refrigerant line 142c. In this mode, a greater
portion, if not all of the refrigerant, flows through main cylinder
module 130, and economizer cylinder module 132 compresses a minimal
amount of refrigerant. Due to a limited capacity of main cylinder
module 130, less cooling is provided in evaporator 122 in this
mode, as compared to a mode in which all refrigerant from
economizer refrigerant line 144b were flowing through economizer
cylinder module 130.
[0036] For operating mode four, first valve 124 is open, and second
valve 126 and third valve 172 are closed. This operating mode was
also feasible in refrigerant system 10 and was described above as
mid-level unloading in Table 1. The economizer cycle is blocked in
operating mode four. Because valve 172 is closed and economizer
cylinder module 132 is thus not used, operating mode four provides
less cooling as compared to operating mode two (i.e. full loading
without economizer), and is therefore designated as an unloading
mode. Additional unloading may be accomplished by partially closing
first valve 124.
[0037] In operating mode five valves 124 and 126 are closed, while
third valve 172 in connector refrigerant line 170 is open. Since
valve 126 is closed, the economizer cycle is blocked, similar to
operating mode four. However, in operating mode five, because valve
124 is also closed, all refrigerant flowing through line 142c from
evaporator 122 is directed through connector refrigerant line 170
and into economizer cylinder module 132.
[0038] Similar to the mode above, in operating mode six, first
valve 124 is closed and third valve 172 is open. However, in
contrast to above, the economizer cycle is activated by opening
second valve 126. Since valve 124 is closed, the main refrigerant
from evaporator 122 is directed through economizer cylinder module
132 in addition to the economizer refrigerant flowing through
economizer refrigerant line 144b. In the final two operating modes
seven and eight of Table 2, designated as full unloading, third
valve 172 in connector refrigerant line 170 is closed. Therefore,
these two operating modes are feasible in a refrigerant system
without a connector line, like refrigerant system 10 of FIG. 1, and
were described above. Operating modes seven and eight are not
common; if refrigerant system 110 operates in either of these
modes, typically it is temporary operating mode and is used to
avoid shutting down refrigerant system 110. Either of modes seven
and eight may be adjusted to mid-level unloading or even a low
level unloading by only partially closing one of the valves
designated as being closed in Table 2. For example, if valve 124 is
partially closed in either operating mode seven or eight, system
110 may operate between a low and mid-level unloading, depending on
a specific position of valve 124.
[0039] Controller 128 regulates a position of valves 124, 126 and
172 in order to operate refrigerant system 110 in an operating mode
that aligns with the cooling load demands, while still operating
efficiently and avoiding nuisance shutdowns. As described above in
reference to controller 28 of refrigerant system 10, controller 128
controls a position of valves 124, 126 and 172 based on sensed
parameters in refrigerant system 110. Similar to refrigerant system
10, refrigerant system 110 may include temperature sensors 150 and
160 for measuring, respectively, a temperature (T1) inside
evaporator 122 and an ambient air temperature (AT). Refrigerant
system 110 also includes pressure sensors 152, 154 and 156 and 158,
which are located in similar locations to those shown in FIG. 1.
Due to a presence of connector refrigerant line 170, refrigerant
system 110 may also include pressure sensor 159 located closer to
suction inlet 134 for measuring pressure (P5). Pressure sensors 156
and 159 may be helpful during those modes when valve 172 is open in
order to monitor a flow of refrigerant being redirected either from
economizer refrigerant line 144b to main refrigerant line 142c or
vice versa. The inputs to controller 128, as shown in FIG. 2, may
include evaporator temperature (T1) and the ambient temperature
(AT), as well as pressures (P1) through (P5). It is recognized that
additional sensors and inputs not shown in FIG. 2 may be included
in refrigerant system 110.
[0040] In the exemplary embodiment shown in FIG. 2, refrigerant
system 110 also includes variable frequency drive 129 (VFD), which
is used to drive an electric motor of compressor 112 and vary the
speed of the motor. Variable frequency drive 129 is controlled by
controller 128. Although VFD 129 is not required in refrigerant
system 110, it may be used for additional capacity control since
the speed of the motor impacts the capacity of compressor 112.
Other types of adjustable speed drives may also be used. A variable
frequency drive may also be used in refrigerant system 10 of FIG.
1.
[0041] Through the use of valves 124, 126, 172 and connector
refrigerant line 170, refrigerant system 110 provides superior
flexibility during unloading, as well as the feasibility to achieve
a greater cooling capacity when the economizer module is not being
used. In the exemplary embodiment shown in FIG. 2, refrigerant
system 110 includes both valves 124 and 126 in combination with
connector refrigerant line 170 and valve 172. In alternative
embodiments, valve 124 or valve 126 may be eliminated.
[0042] In the embodiments shown in FIGS. 1 and 2, economizer module
18 is a heat exchanger. FIG. 3 is an alternative embodiment in
which economizer module 218 is a flash tank. In refrigerant systems
10 and 110 the refrigerant exiting the high pressure heat exchanger
is split into two refrigerant streams prior to entering the
economizer heat exchanger. In contrast, in economizer module 218 of
FIG. 3, the single refrigerant stream from the high pressure heat
exchanger passes through expansion device 219, where it is
partially expanded to an intermediate pressure and temperature. As
such, the refrigerant entering flash tank 218 is usually in a
two-phase thermodynamic state. Inside flash tank 218, phase
separation occurs and refrigerant vapor exits flash tank 218
through economizer refrigerant line 242, at which point it travels
to the economizer cylinder module (not shown). Liquid refrigerant
exits flash tank 218 through refrigerant line 244 and passes
through expansion or float flow control device 221 before traveling
to the evaporator (not shown). In those embodiments using a float
flow control device, float flow control device 221 is configured to
open when a liquid level in the flash tank reaches a predetermined
level or provide a certain restriction to a refrigerant flow to
maintain a desired refrigerant level. The refrigerant exiting flash
tank 218 through refrigerant line 244 has low vapor and high liquid
content, which enhances cooling capacity in the evaporator.
[0043] The refrigerant system and operating method described herein
may easily be implemented into existing refrigerant systems. The
refrigerant systems may include supermarket refrigerant systems,
container refrigerant systems, truck/trailer refrigerant systems,
rooftop air conditioning and heat pump refrigerant systems, and
residential air conditioning refrigerant systems. The valves may be
installed in existing refrigerant lines, and in some cases, a
connector refrigerant line may also be added between the economizer
refrigerant line and the main refrigerant line. The valves and
connector refrigerant line described herein may also be
incorporated into the design of new refrigerant systems.
[0044] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
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