U.S. patent application number 12/672709 was filed with the patent office on 2011-04-28 for multi-stage refrigerant system with different compressor types.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20110094259 12/672709 |
Document ID | / |
Family ID | 40549441 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110094259 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
April 28, 2011 |
MULTI-STAGE REFRIGERANT SYSTEM WITH DIFFERENT COMPRESSOR TYPES
Abstract
Multi-stage refrigerant systems operate with a lower stage
compressor of a first type and a higher stage compressor of a
second type. In one embodiment, the lower stage compressor type is
selected to have the most beneficial characteristics at lower
pressure operation, while the higher pressure stage compressor type
is selected to have the most beneficial characteristics at higher
pressure operation.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Family ID: |
40549441 |
Appl. No.: |
12/672709 |
Filed: |
October 10, 2007 |
PCT Filed: |
October 10, 2007 |
PCT NO: |
PCT/US07/80870 |
371 Date: |
February 9, 2010 |
Current U.S.
Class: |
62/510 |
Current CPC
Class: |
F25B 2309/06 20130101;
F25B 9/008 20130101; F25B 2309/061 20130101; F25B 7/00 20130101;
F25B 2400/13 20130101; F25B 1/10 20130101 |
Class at
Publication: |
62/510 |
International
Class: |
F25B 1/10 20060101
F25B001/10 |
Claims
1. A multi-stage refrigerant system comprising: at least two
compressors, with a lower stage compressor and a higher stage
compressor; a heat rejection heat exchanger for receiving
refrigerant from said higher stage compressor, and a heat accepting
heat exchanger for delivering refrigerant to a lower stage
compressor; and said higher and lower stage compressors being
different compressor types.
2. The refrigerant system as set forth in claim 1, wherein said
lower stage compressor and said higher stage compressor are
positioned to compress refrigerant in a serial fashion.
3. The refrigerant system as set forth in claim 2, wherein an
intercooler is positioned between said lower stage compressor and
said higher stage compressor.
4. The refrigerant system as set forth in claim 2, wherein an
economizer circuit is provided within the refrigerant system and
returns a tapped refrigerant to an intermediate compression point
between said lower stage compressor and said higher stage
compressor.
5. The refrigerant system as set forth in claim 1, wherein the
multi-stage refrigerant system includes two to four stages.
6. The refrigerant system as set forth in claim 1, wherein the
multi-stage refrigerant system operates in a transcritical cycle
for at least a portion of the time.
7. The refrigerant system as set forth in claim 1, wherein at least
one of the multiple stages operates with the CO.sub.2
refrigerant.
8. The refrigerant system as set forth in claim 1, wherein said
higher stage compressor and said lower stage compressor are each
part of their own closed-loop refrigerant circuit, and wherein
refrigerant compressed by said lower stage compressor is delivered
into a refrigerant-to-refrigerant heat exchanger, and refrigerant
received by said higher stage compressor is delivered from the same
refrigerant-to-refrigerant heat exchanger.
9. The refrigerant system as set forth in claim 1, wherein said
lower stage compressor is a scroll compressor.
10. The refrigerant system as set forth in claim 9, wherein said
higher stage compressor is not a scroll compressor.
11. The refrigerant system as set forth in claim 1, wherein said
higher stage compressor is a reciprocating compressor.
12. The refrigerant system as set forth in claim 11, wherein said
lower stage compressor is not a reciprocating compressor.
13. The refrigerant system as set forth in claim 1, wherein said
different compressor types are selected based on at least one of
suction pressure, discharge pressure, equilibrium pressure,
pressure ratio, pressure difference, discharge temperature, suction
temperature.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to a multi-stage refrigerant
system, wherein a lower compression stage and a higher compression
stage are provided with different compressor types.
[0002] In known refrigerant systems, a refrigerant is circulated
from a compressor, to a heat rejection heat exchanger, known as a
condenser for subcritical systems and as gas cooler for
transcritical systems, then through an expansion device, and to a
heat accepting heat exchanger, known as an evaporator. Many
enhancement options and design features can be provided to improve
operation of these basic refrigerant systems.
[0003] One enhancement that is known in the art of air conditioning
and refrigeration is the use of multi-stage refrigerant system
design concepts. In a multi-stage refrigerant system, a lower stage
operates at a lower pressure and a higher stage operates at a
higher pressure. Recently, R774 refrigerant, commonly known as
CO.sub.2, has been identified as a promising natural refrigerant
that has zero ozone depletion potential, and extremely low global
warming potential. Thus, CO.sub.2 is becoming more widely utilized
as a refrigerant of choice to replace conventional refrigerants.
However, refrigerant systems utilizing CO.sub.2 as a refrigerant
must operate at a higher pressure, and quite often at a higher
discharge temperature. Also, the CO.sub.2 refrigerant systems are
often not as efficient as refrigerant systems employing
conventional refrigerants. To alleviate these problems, multi-stage
refrigerant system schematics, rather than single stage refrigerant
system schematics, are more likely to be implemented for
applications utilizing an environmentally friendly natural CO.sub.2
refrigerant.
[0004] A multi-stage refrigerant system can be provided by having
two compressors operating in series. A lower stage compressor
compresses the refrigerant to an intermediate pressure, and that
refrigerant then passes to a higher stage compressor.
[0005] In another type of multi-stage refrigerant system, or
so-called cascade refrigerant systems, the lower and higher stages
are associated with entirely separate circuits. In a lower pressure
closed-loop circuit, the lower stage compressor discharges
refrigerant into a refrigerant-to-refrigerant heat exchanger, which
plays a role of a heat rejection heat exchanger for this circuit,
passes that refrigerant through an expansion device and heat
accepting heat exchanger connected in series and then returns the
refrigerant to the lower stage compressor. In a higher pressure
closed-loop circuit, the higher stage compressor receives
refrigerant from the same refrigerant-to-refrigerant heat
exchanger, which is a heat accepting heat exchanger for this
circuit, discharges that refrigerant to a heat rejection heat
exchanger (either a condenser or a gas cooler) and then passes the
refrigerant through an expansion device, downstream of which the
refrigerant is returned to the refrigerant-to-refrigerant heat
exchanger. Thus, in cascade refrigerant systems, the heat is
transferred from the lower stage to the higher stage in the
refrigerant-to-refrigerant heat exchanger, which is typically
configured as a counterflow heat exchanger.
[0006] Some compressor types, which are suitable for low pressure
operation, cannot reliably operate at a high pressure. One such
compressor is a scroll compressor. A conventional scroll compressor
may not operate reliably and/or efficiently above about 700 psia.
The use of CO.sub.2 refrigerant would normally call for operation
at discharge pressures about 2000 psia. Thus, this makes
conventional scroll compressor designs not applicable for many
CO.sub.2 applications. Further, different compressor types may be
suitable for different pressure ratios or pressure difference
ranges, depending on a particular compressor type design.
[0007] To date, refrigerant systems which utilize two stages have
employed the same type compressors for both stages. In the past,
this was acceptable for many compressor types, such as scroll
compressors, screw compressors, rotary compressors, reciprocating
compressors and the like, while also using conventional relatively
low pressure refrigerants such as R134a, R22, R410A, R404A and the
like. However, the high pressure refrigerants, such as CO.sub.2,
precluded the use of many compressor types, which, at least to
date, have experienced difficulty in operating as a higher pressure
stage compressor.
SUMMARY OF THE INVENTION
[0008] In the disclosed embodiment of this invention, a refrigerant
system is provided with multiple sequential stages (and at least
two sequential stages). At least one compressor associated with one
of the multiple stages, is a distinct compressor type as compared
to the other stages. In this way, a compressor which is best suited
for the lower pressure stage can be used for the lower pressure
stage, while a compressor that is best suited for a higher pressure
stage can be utilized for the higher pressure stage. The
multi-stage refrigerant system can utilize multiple compressors
compressing the refrigerant in series, or can utilize cascaded
refrigerant circuits.
[0009] 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
[0010] FIG. 1 shows a first schematic of this invention.
[0011] FIG. 2 shows the second schematic of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] FIG. 1 shows a refrigerant system 20 incorporating a lower
stage compressor 22 which delivers a compressed refrigerant to an
optional intercooler 24. From the intercooler 24 the refrigerant
moves to a higher stage compressor 26, and then to a heat rejection
heat exchanger 28. The refrigerant system 20 may also be equipped
with an optional, to this invention, economizer cycle. In this
case, a portion of refrigerant may be tapped to a tap refrigerant
line 30 downstream of the heat rejection heat exchanger 28, and
passed through an economizer expansion device 32. The tapped
partially expanded refrigerant passes through an economizer heat
exchanger 34 at which it further cools the main refrigerant flow in
a liquid refrigerant line 31. The tapped partially expanded
refrigerant is returned through a return refrigerant line 36 to an
intermediate compression point between the two compression stages
22 and 26. It has to be noted that the return point of the
refrigerant line 36 is preferably located downstream of the
intercooler 24. The refrigerant circuit elements (or components)
30, 32, 34, and 36 is known as an economizer circuit. While the
tapped refrigerant flow is shown passing in the same direction
through the economizer heat exchanger 34 as the main refrigerant
flow, in practice, it is often preferable to pass the two
refrigerant flows in a counterflow configuration. However, for
illustration simplicity the refrigerant streams are shown flowing
in the same direction. Also, it should be understood that, in the
context of this invention, a flash tank can be considered as a
subset of an economizer heat exchanger. Further, various economizer
cycle configurations are feasible and within the scope of the
invention.
[0013] Downstream of the economizer heat exchanger 34 the
refrigerant passes through a main expansion device 38, and then a
heat accepting heat exchanger 40.
[0014] In a disclosed feature of this application, the lower stage
compressor 22 is a distinct compressor type from the higher stage
compressor type 26. In one embodiment, the lower stage compressor
22 may be a scroll compressor, which has beneficial characteristics
at lower pressure operation. The higher stage compressor 26 may be
selected to have beneficial characteristics at higher pressure
operation. As an example, the higher stage compressor 26 may be a
reciprocating compressor. Further, the distinct compressor types
may be selected based on a pressure ratio, pressure difference,
discharge temperature, suction temperature or a combination of
these parameters.
[0015] By employing this arrangement, existing scroll compressors,
for instance, can be utilized in applications to which they are
best suited, while not being utilized, for instance, in the higher
pressure stages where they are perhaps provide less reliable or/and
efficient operation.
[0016] While only two compressor types are disclosed, the two
distinct compressor types 22 and 26 can be of any other compressor
types such as screw compressors, rotary compressors, etc. Further,
more than two sequential compression stages may be provided with
the refrigerant system 20, if desired.
[0017] FIG. 2 shows a refrigerant system 120 incorporating two
cascaded closed-loop refrigerant circuits 121 and 123. A lower
stage refrigerant circuit 123 includes a lower stage compressor 122
delivering a compressed refrigerant into a
refrigerant-to-refrigerant heat exchanger 124 that is a heat
rejection heat exchanger for the refrigerant circuit 123. The
refrigerant-to-refrigerant heat exchanger 124 is preferably
positioned outside of an environment 132 to be conditioned.
Refrigerant passes from the heat exchanger 124 through an expansion
device 126, and to a heat accepting heat exchanger or evaporator
128. As known, a fan 130 may be associated with and blow air over
external surfaces of the heat accepting heat exchanger 128 to
deliver that conditioned air into the climate-controlled
environment 132. The lower stage refrigerant circuit 123 would
normally be charged with a refrigerant that would operate in a
subcritical region. One such environmentally friendly natural
refrigerant that can be used for the circuit 123 would be the
CO.sub.2 refrigerant that, while in the lower cascaded circuit,
would still be operating in the subcritical region. If the CO.sub.2
refrigerant is used in the upper cascaded circuit, it is likely to
operate in a transcritical region. In the upper stage refrigerant
circuit 121, an upper stage compressor 134 compresses a refrigerant
and delivers it to a heat rejection heat exchanger 136. A fan 138
may be associated with and blow air over the external surfaces of
the heat rejection heat exchanger 136. Refrigerant passes from the
heat rejection heat exchanger 136 downstream to an expansion device
140, and then back through the refrigerant-to-refrigerant heat
exchanger 124, which is a heat accepting heat exchanger for the
upper refrigerant circuit 121, to the upper stage compressor 134.
It has to be noted that if the upper refrigerant circuit 121 is
operating in a transcritical cycle, the heat rejection heat
exchanger 136 is a gas cooler. On the other hand, if the upper
refrigerant circuit 121 is operating in a subcritical cycle, the
heat rejection heat exchanger 136 is a condenser. In some
applications, the upper refrigerant circuit 121 may be operating
for part of the time in a transcritical cycle and for part of the
time in a subcritical cycle.
[0018] Again, the compressors 122 and 134 are selected to be of
distinct types. In one disclosed embodiment, the lower stage
compressor 122 is a scroll compressor while the higher stage
compressor 134 may be a reciprocating compressor. Once again, as
has been explained above, the distinct compressor types may be
selected based on the suction pressure, discharge pressure,
equilibrium pressure, pressure ratio, pressure difference,
discharge temperature, suction temperature or a combination of
these parameters.
[0019] It also should be understood that the number of the
closed-loop cascaded refrigerant circuits may be more than two and
the number of distinct compressor types may be more than two as
desired.
[0020] The embodiments of FIGS. 1 and 2 are particularly well
suited for refrigerant systems utilizing CO.sub.2 as a refrigerant.
It should be understood that other means of heat exchange between
the refrigerant and conditioned environment as well as the
refrigerant and heat rejection environment may be employed,
including, for example, a delivery of water or brine by pumps.
Also, as mentioned above, it should be understood that while the
FIGS. 1 and 2 show the two-stage refrigerant systems, more than two
stages can be employed, with at least one compressor type being
different form the rest.
[0021] It should be pointed out that many different compressor
types could be used in this invention. For example, scroll, screw,
rotary, or reciprocating compressors can be employed.
[0022] The refrigerant systems that utilize this invention can be
used in many different applications, including, but not limited to,
air conditioning systems, heat pump systems, marine container
units, refrigeration truck-trailer units, and supermarket
refrigeration systems.
[0023] While embodiments of this invention have 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.
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