U.S. patent application number 12/515471 was filed with the patent office on 2010-03-25 for co2 refrigerant system with tandem compressors, expander and economizer.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20100071391 12/515471 |
Document ID | / |
Family ID | 39562801 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100071391 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
March 25, 2010 |
CO2 REFRIGERANT SYSTEM WITH TANDEM COMPRESSORS, EXPANDER AND
ECONOMIZER
Abstract
A refrigerant system utilizes an expander that provides a more
efficient expansion process and recovers at least a portion of
energy from this expansion process. At least a portion of
refrigerant that has been at least partially expanded in the
expander is tapped and passed through an economizer heat exchanger.
In the economizer heat exchanger, the tapped refrigerant cools a
main circuit refrigerant increasing its thermodynamic potential.
Further, a compression section is provided with at least two
compressors operating in tandem and allowing for multiple stages of
unloading. By selectively utilizing one or more of the tandem
compressors, the economizer cycle, and the expander, the
refrigerant system can achieve very efficient operation and provide
enhanced control flexibility, in particular, for the CO.sub.2
refrigerant system operating in the transcritical cycle.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
39562801 |
Appl. No.: |
12/515471 |
Filed: |
December 26, 2006 |
PCT Filed: |
December 26, 2006 |
PCT NO: |
PCT/US2006/049286 |
371 Date: |
May 19, 2009 |
Current U.S.
Class: |
62/115 ; 62/510;
62/513 |
Current CPC
Class: |
F25B 2400/075 20130101;
F25B 9/06 20130101; F25B 2400/02 20130101; F25B 2309/06 20130101;
F25B 2400/0751 20130101; F25B 2400/13 20130101; F25B 9/008
20130101; F25B 2600/2509 20130101; F25B 2309/061 20130101; F25B
1/10 20130101 |
Class at
Publication: |
62/115 ; 62/510;
62/513 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F25B 1/10 20060101 F25B001/10; F25B 41/00 20060101
F25B041/00 |
Claims
1-30. (canceled)
31. A refrigerant system comprising: at least two compressors
operating in tandem, said compressors compressing refrigerant and
delivering it downstream to a first heat exchanger, refrigerant
passing from said first heat exchanger through a first pass of an
economizer heat exchanger, and then to an expander, refrigerant
expanding in said expander, and said expander recovering at least a
portion of energy from the expansion process of said refrigerant,
and said recovered energy utilized to assist in driving of at least
one of the refrigerant system components; a second heat exchanger
positioned downstream of said expander, and refrigerant passing
from said expander through said second heat exchanger, and then
back to said at least two compressors; and a portion of refrigerant
being tapped at a location where it has been at least partially
expanded in said expander, and passed through a second pass of said
economizer heat exchanger to cool refrigerant in a main refrigerant
circuit, said tapped portion of refrigerant then being returned to
at least one of said at least two compressors.
32. The refrigerant system as set forth in claim 31, wherein said
tapped portion of refrigerant is returned to both of at least two
compressors.
33. The refrigerant system as set forth in claim 31, wherein said
at least two compressors have at least one common manifold.
34. The refrigerant system as set forth in claim 31, wherein said
at least two compressors are of different sizes.
35. The refrigerant system as set forth in claim 31, wherein at
least one of said at least two compressors consists of at least two
separate stages.
36. The refrigerant system as set forth in claim 31, wherein said
expander has separate expansion stages for the main and tapped
refrigerant flows.
37. The refrigerant system as set forth in claim 31, wherein there
are at least three of said compressors operating in tandem.
38. The refrigerant system as set forth in claim 31, wherein said
tapped portion of refrigerant being returned to at least one of
said at least two compressors.
39. The refrigerant system as set forth in claim 31, wherein said
refrigerant is CO2.
40. The refrigerant system as set forth in claim 31, wherein said
refrigerant system operates in a transcritical cycle for at least a
portion of the time.
41. The refrigerant system as set forth in claim 31, wherein said
refrigerant system operates in a subcritical cycle for at least a
portion of the time.
42. The refrigerant system as set forth in claim 31, wherein said
at least two compressors can be controlled individually or in
combination with each other.
43. The refrigerant system as set forth in claim 31, wherein the
economizer circuit can be selectively actuated.
44. The refrigerant system as set forth in claim 31, wherein more
than two sequential compression stages and more than two economizer
circuits are utilized.
45. The refrigerant system as set forth in claim 31, wherein said
recovered energy is utilized to at least partially drive at least
one of said at least two compressors.
46. The refrigerant system as set forth in claim 31, wherein said
recovered energy is utilized to assist in driving at least one of
said at least two compressors.
47. The refrigerant system as set forth in claim 31, wherein said
recovered energy is utilized to assist in driving a shaft for said
at least one of the refrigerant system components, or to generate
electricity to assist in driving said at least one of the
refrigerant system components.
48. A method of operating a refrigerant system comprising the steps
of: (1) providing at least two compressors operating in tandem,
said compressors compressing refrigerant and delivering it
downstream to a first heat exchanger, refrigerant passing from said
first heat exchanger through a first pass of an economizer heat
exchanger, and then to an expander, refrigerant expanding in said
expander, and said expander recovering at least a portion of energy
from the expansion process of said refrigerant, and said recovered
energy utilized to assist in driving of at least one of the
refrigerant system components; (2) providing a second heat
exchanger positioned downstream of said expander, and refrigerant
passing from said expander through said second heat exchanger, and
then back to said at least two compressors; and (3) tapping a
portion of refrigerant from a location where it has been at least
partially expanded in said expander, and passing it through a
second pass of said economizer heat exchanger to cool refrigerant
in a main refrigerant circuit, said tapped portion of refrigerant
then being returned to at least one of said at least two
compressors.
49. The method as set forth in claim 48, wherein said tapped
portion of refrigerant is returned to both of at least two
compressors.
50. The method as set forth in claim 48, wherein said at least two
compressors have at least one common manifold.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to a refrigerant system wherein an
expander is utilized to provide a more efficient expansion process,
by recapturing energy from this expansion process and utilizing
that energy to power at least one system component. A portion of
refrigerant is tapped from a location in the expander at which it
has been at least partially expanded, and the tapped refrigerant is
then utilized to subcool a main refrigerant flow in an economizer
heat exchanger. In this manner, a single expander can provide both
main and economizer expansion device functions for the refrigerant
system, and enhance these main and economizer expansion device
functions. Further, the refrigerant system includes tandem
compressors only some of which may be economized. Lastly, the
refrigerant system may be charged with CO.sub.2 refrigerant that,
at least for a portion of the time, may operate in a transcritical
cycle.
[0002] Refrigerant compressors circulate a refrigerant through a
refrigerant system to condition a secondary fluid. Typically, a
compressor compresses a refrigerant and delivers it to a first heat
exchanger. Refrigerant from the first heat exchanger passes through
an expansion device, in which its pressure and temperature are
reduced. Downstream of the expansion device, a refrigerant passes
through a second heat exchanger, and then back to the
compressor.
[0003] One option in a refrigerant system design is the use of an
economizer, or so-called vapor injection function. In an economizer
function, a portion of refrigerant is tapped from a main
refrigerant stream downstream of the first heat exchanger. This
tapped refrigerant is passed through an expansion device, to be
expanded to an intermediate pressure and temperature, and then this
partially expanded tapped refrigerant passes in heat exchange
relationship with a main refrigerant flow in an economizer heat
exchanger. In this manner, the main refrigerant is subcooled such
that it will have a greater thermodynamic potential when it reaches
the second heat exchanger. The tapped refrigerant, typically in a
superheated thermodynamic state, is returned to an intermediate
compression point in the compressor downstream of the economizer
heat exchanger.
[0004] It is also known to provide at least two compressors
operating in parallel and known as "tandem" compressors. Tandem
compressor configurations allow the control of the overall capacity
provided by the refrigerant system by selectively engaging the
tandem compressors. Further, all or only some of the tandem
compressors may be economized, and the economizer function may be
activated or deactivated to precisely match capacity delivered by a
refrigerant system to thermal load demands in the conditioned
space.
[0005] Another feature utilized in refrigerant systems is the use
of an expander to provide a more efficient so-called active
expansion process (this process can closely follow an isentropic
line rather than isenthalpic line for so-called passive expansion
devices such as expansion valves and fixed restriction devices).
The expanders could be of various designs such as centrifugal,
scroll, rotary, screw, shaft-connected piston, free-piston or any
other type.
[0006] The refrigerants that are being utilized in refrigerant
systems are different nowadays, with continuously increasing number
of installations charged with natural refrigerants. CO.sub.2 (also
known as carbon dioxide or R744) is one such refrigerants that is
becoming more widely used in various applications such as
supermarket refrigeration, display cases, bottle coolers, transport
refrigeration, environmental control units, etc. In particular,
CO.sub.2 refrigerant can benefit greatly from any of the
above-mentioned system enhancement options, especially in
transcritical applications. However, no refrigerant system to date
has included an expander, tandem compressors and an economizer
cycle combined together to provide a powerful combination of
operational options and enhancement features.
SUMMARY OF THE INVENTION
[0007] In a disclosed embodiment of this invention, an expander is
utilized to provide a more efficient active expansion process to
potentially recapture energy from this expansion process, and
utilize that energy to power at least one refrigerant system
component. The expander increases capacity and enhances efficiency
of a refrigerant system through a more efficient expansion process
(reduced irreversible losses) and recovering, at least partially,
the expansion process energy. Further, a portion of refrigerant
that has been at least partially expanded in the expander (or
through the first stage of the expander) is tapped and passed
through an economizer heat exchanger in heat exchange relationship
with a main refrigerant flow. This tapped refrigerant is injected
back into the compressor (a single compressor or a multi-stage
compressor system consisting of compressors connected in series) at
some intermediate pressure. All or only some of the compressors may
be economized. Exiting the economizer heat exchanger, the main
refrigerant has a higher thermodynamic potential that allows for
enhanced refrigerant system performance. In addition, the
refrigerant system includes at least two tandem compressors that,
along with the economizer function, allow for efficient system
unloading and precise matching of delivered system capacity to
thermal load demands in the conditioned space. The expander may
transfer the recovered energy from the expansion process, directly
or indirectly through an energy conversion device, to at least
partially power one of the tandem compressors. The refrigerant
system, as disclosed, may use a natural refrigerant such as
CO.sub.2. The proposed refrigerant system enhancements are
particularly beneficial for the CO.sub.2 refrigerant system
operating in a transcritical cycle.
[0008] The provision of the combination of the economizer cycle,
expander, and tandem compressors provides the ability to closely
tailor the provided capacity of the refrigerant system to thermal
load demands in the conditioned space and to enhance performance of
the refrigerant system through a more efficient expansion process,
economizer cycle and energy recovery, especially for a CO.sub.2
refrigerant system operating in a transcritical cycle.
[0009] In one embodiment, a portion of refrigerant is tapped form a
single intermediate tap in the expander to flow through the
economizer heat exchanger in the economizer cycle. In another
embodiment, there are two such taps at two distinct intermediate
pressure levels associated with two economizer heat exchangers. Of
course, a worker of ordinary skill in the art would recognize that
more taps and economizer circuits are within the scope and can
equally benefit from the present invention.
[0010] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a schematic of a first inventive refrigerant
system.
[0012] FIG. 2 shows a second schematic.
[0013] FIG. 3A shows a third schematic.
[0014] FIG. 3B shows an alternate tandem compressor configuration
for the refrigerant system depicted in FIG. 3A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] A refrigerant system 20 is illustrated in FIG. 1. As shown,
two compressors 22 and 24 operate in tandem to provide compressed
refrigerant and deliver it throughout the refrigerant system 20.
Obviously, more than two compressors can be connected in parallel
arrangement and operated simultaneously or individually, based on
thermal load demands in the conditioned space. Although in a
conventional configuration shown in FIG. 1, the tandem compressors
have common suction and common discharge manifolds, as known to a
person ordinarily skilled in the art, the tandem compressors may
have a common suction manifold and separate discharge lines as well
as separate suction lines and a common discharge manifold.
Additionally, tandem compressors 22 and 24 may have oil and vapor
equalization lines (not shown), as known in the art.
[0016] A compressed refrigerant passes through a heat exchanger 26,
and downstream to an expander 28. As known to a person skilled in
the art, the heat exchanger 26 becomes a condenser, in the
subcritical applications, and a single-phase heat exchanger, or a
gas cooler, in the transcritical applications. As mentioned above,
it is known to use an active expander instead of a passive
expansion device, such as an expansion valve or a fixed restriction
expansion device, in which energy from a more efficient isentropic
expansion process is recaptured and utilized to power or drive (at
least partially) at least one refrigerant system component, such as
one of the compressors 22 and 24 (as shown schematically at 29).
This energy recovery and transfer can be done directly or
indirectly. For instance, for a direct energy recovery, the
expander 28 and the compressor 22 can be located on the same shaft
or connected through a mechanical transmission device. On the other
hand, for an indirect energy recovery, the energy from the
expansion process may be converted to an electric energy that in
turn may assist in driving the compressor 22. Downstream of the
expander 28, the refrigerant passes through an evaporator 30, and
then back to the compressors 22 and 24. An economizer heat
exchanger 32 is incorporated into the circuitry of the refrigerant
system 20. As known, an economizer function allows for additional
stages of unloading as well as performance (capacity and
efficiency) enhancement.
[0017] A portion of refrigerant is tapped from a tap line 51
connected to an intermediate expansion port in the expander 28 and
passed through the economizer heat exchanger 48. The tap line 51 is
communicated to a point in the expansion process at which the
refrigerant has been at least partially expanded to a pressure
intermediate of suction and discharge pressures. The refrigerant
flowing in the tap line 51 is at lower pressure and temperature
than the refrigerant in the main refrigerant circuit leaving the
heat exchanger 26 and cools this refrigerant passing through the
economizer heat exchanger 48, preferably in a counterflow heat
transfer relationship. The tapped refrigerant is returned through a
vapor injection line 53 to the compressors 22 and 24, typically in
a superheated state. As is known, the vapor injection line 53
manifolds refrigerant to the compressors 22 and 24 and delivers it
into the compression chambers within the compressor at an
intermediate point in the compression process. As known, each of
individual compressors 22 and 24 can be replaced with two
compressor stages connected in series.
[0018] This embodiment achieves the inclusion of the economizer
circuit without the need for a separate economizer expansion
device, since the expander 28 utilizes an intermediate expansion
port for delivering of the economizer branch refrigerant. In this
manner, a single expander can provide both main and economizer
expansion device functions at higher efficiency levels than in
conventional refrigerant systems equipped with passive expansion
devices. Obviously, two separate expansion stages for the main and
economized refrigerant flow can be used instead, and in this case,
the economizer branch refrigerant and the tap line 51 can be
positioned downstream as well as upstream of the economizer heat
exchanger 32.
[0019] The use of the tandem compressors 22 and 24 allows for a
more flexible system control by selectively actuating one or both
of the compressors to provide a necessary capacity to adequately
satisfy thermal load requirements in the conditioned space.
Compressors 22 and 24 may have different sizes to allow for more
stages of capacity adjustment. In addition, the economizer function
can be enabled or disabled, for each compressor individually or
simultaneously for both compressors, to provide additional capacity
stages when necessary. As shown in FIG. 1, valves 62 and 64 allow
for selective engagement and disengagement of the economizer
function for the compressors 22 and 24 respectively.
[0020] The refrigerant system 20 may utilize CO.sub.2 as the
refrigerant. In this case, the refrigerant system 20 may operate in
the transcritical cycle, at least for a portion of the time. As
known, the transcritical cycle is normally less efficient than the
subcritical cycle, so the abovementioned enhancement features and
control options of the present invention (the tandem compressors in
combination with the expander and the economizer cycle) will be the
most beneficial for the transcritical cycle.
[0021] FIG. 2 shows another embodiment 70, which is similar to the
embodiment 20, however, three tandem compressors 72, 74 and 76,
with only one compressor 72 being economized, are illustrated.
Again, the refrigerant system 70 would provide additional benefits
in operation control and performance enhancement. The combination
of the expander 28, the economizer circuit and economizer heat
exchanger 32, along with the tandem compressor allows close
tailoring of the refrigerant system capacity to achieve desired
conditions in the climate controlled environment in the most
efficient manner. The control (not shown) for the refrigerant
system 70 may be configured to operate the individual compressors
72, 74 and 76 (which, once again, may be of different sizes) or any
combinations of them to provide a desired number of unloading
staged.
[0022] As mentioned above and shown in FIG. 2, the economized
refrigerant is returned to only one compressor 72. A worker skilled
in this art would recognize the various features and benefits, such
as performance, control flexibility, control complexity and cost,
that would be provided by returning the refrigerant to one or more
than one of the compressors, and can select an appropriate design
accordingly.
[0023] As can be recognized by a person ordinarily skilled in the
art, more than two sequential compression-expansion stages and more
than one economizer circuit may be integrated into the refrigerant
systems 20 and 70. The number of stages is primarily defined by a
cost-performance benefit tradeoff. These sequential stages may be
represented by stand-alone devices or integrated into a single
device. One of such refrigerant systems having two economizer
circuits and three compression-expansion stages is shown in FIG.
3A. In the refrigerant system 170 depicted in FIG. 3A, an expander
128 has two intermediate pressure ports associated with two
economizer circuits. A higher pressure port 136 communicates with
an economizer heat exchanger 134 operating at a higher pressure and
temperature, and a lower pressure port 138 communicates with an
economizer heat exchanger 132 operating at a lower pressure and
temperature. It has to be noted that both higher and lower
intermediate pressures mentioned above are positioned between the
suction and discharge operating pressures for the refrigerant
system 170. Further, there are three compression stages
incorporated into the refrigerant system 170, and a vapor injection
line 157 for the higher pressure economizer circuit is positioned
between the second and third compression stages, while a vapor
injection line 153 for the lower pressure economizer circuit is
positioned between the first and second compression stages.
Refrigerant flow control devices such as a valve 166 and valves 162
and 164 selectively activate the higher and lower pressure
economizer circuits respectively. The valve 164 deactivates the
economizer function for both lower pressure compressors 172 and
174, while the valve 162 deactivates the economizer function just
for the compressor 172. Once again, only two (out of three) lower
pressure tandem compressors 172, 174 and 176 are equipped with the
economizer ports, the compressors 172 and 174 in particular. The
first and second compression stage of the economized tandem
compressors 172 and 174 represent the first and second compression
stages of the refrigerant system 170, while the non-economized
tandem compressor 176 operates between the same manifold pressures
as the two sequential stages of the economized compressors 172 and
174. Two higher pressure non-economized tandem compressors 182 and
184 represent the third compression stage of the refrigerant system
170. Furthermore, the recovered portion of the expansion process
energy in the expander 128 is transmitted to at least partially
power the non-economized lower pressure compressor 176. Obviously,
any other compressor of the refrigerant system 170 can be connected
to the power source provided by the expender 128, in a similar
manner. In all other aspects, the embodiment 170 of FIG. 3A is
similar to the FIG. 1 and FIG. 2 embodiments 20 and 70
respectively.
[0024] FIG. 3B embodiment shows an alternate tandem compressor
configuration for the refrigerant system depicted in FIG. 3A. In
this embodiment, the compressor 182 of the third compression stage
directly communicates with the downstream compressors 172 and 174,
while the compressor 184 of the same third compression stage
directly communicates with the downstream compressor 176. Two
refrigerant flow control valves 192 and 194 in FIG. 3B replace a
single refrigerant flow control valve 166 of FIG. 3A, to
selectively engage and disengage the economizer function for each
of the compressors 182 and 184 respectively. Lastly, the compressor
184 now takes advantage of the energy recovery from the refrigerant
system expander, as shown at 29 in FIG. 3B. It is understood that a
person skilled in the art would recognize that many other
variations of tandem compressor and economizer circuit
configurations, as well as energy recovery arrangements, are
feasible and can equally benefit from the invention.
[0025] The tandem compressors described in this application can be
separate compressor units, or the compression elements of each of
those compressors can be combined within a single compressor shell
(as, for example, the compression elements positioned on the
opposite ends of the rotating shaft or separate compression
elements and associated motors simply enclosed within a single
shell).
[0026] It should be noted that this invention is not limited to the
system shown in the FIG. 1, as the actual refrigerant system may
include additional components, such as, for example, a
liquid-suction heat exchanger, a reheat coil, an intercooler,
additional economizer heat exchangers or flash tanks. The
individual tandem compressors can be of variable capacity type,
including variable speed and multi-speed configurations. Further,
the compressors may have various unloading options, including
intermediate pressure to suction pressure bypass arrangements. The
compressors may be unloaded internally, as for example, by
separating fixed and orbiting scrolls from each on an intermittent
basis. These system configurations are also not limited to a
particular compressor type and may include scroll compressors,
screw compressors (single or multi-rotor configurations),
reciprocating compressors (where, for example, some of the
cylinders are used as a low compression stage and the other
cylinders are used as a high compression stage) and rotary
compressors. The refrigerant system may also consist of multiple
separate circuits. The present invention would also apply to a
broad range of systems, for example, including mobile container,
truck-trailer and automotive systems, packaged commercial rooftop
units, supermarket installations, residential units, environmental
control units, etc.
[0027] Although a preferred embodiment of this invention has been
disclosed, a worker of ordinary skill in this art would recognize
that certain modifications would come within the scope of this
invention. For that reason, the following claims should be studied
to determine the true scope and content of this invention.
* * * * *