U.S. patent application number 12/813079 was filed with the patent office on 2010-12-16 for high efficiency r744 refrigeration system and cycle.
Invention is credited to Giridhari L. Agrawal, Charles William Buckley, JongSik Oh.
Application Number | 20100313582 12/813079 |
Document ID | / |
Family ID | 43305186 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100313582 |
Kind Code |
A1 |
Oh; JongSik ; et
al. |
December 16, 2010 |
HIGH EFFICIENCY R744 REFRIGERATION SYSTEM AND CYCLE
Abstract
A high efficiency R744 air conditioning and refrigeration system
and cycle comprises a vapor compressor and two independent ejectors
operatively connected to high and low-pressure sides of the
compressor, respectively. The two ejectors reduce the overall
pressure ratio of the mechanical vapor compressor resulting in
dramatically increased thermodynamic cycle efficiency. As one
example of its potential applications for residential, commercial
or industrial uses, a 150 ton capacity of a water-cooled chiller
designed in accordance with the present invention is predicted to
provide the power consumption as low as 0.47 kW/ton, when operated
in accordance with the cooling methods of the present invention,
which corresponds to 7.47 of Coefficient of Performance (COP).
Inventors: |
Oh; JongSik; (Simsbury,
CT) ; Agrawal; Giridhari L.; (Simsbury, CT) ;
Buckley; Charles William; (West Hartford, CT) |
Correspondence
Address: |
MCCORMICK, PAULDING & HUBER LLP
CITY PLACE II, 185 ASYLUM STREET
HARTFORD
CT
06103
US
|
Family ID: |
43305186 |
Appl. No.: |
12/813079 |
Filed: |
June 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61185834 |
Jun 10, 2009 |
|
|
|
Current U.S.
Class: |
62/115 ; 62/500;
62/510; 62/512 |
Current CPC
Class: |
F25B 41/00 20130101;
F25B 40/00 20130101; F25B 9/008 20130101; F25B 2341/0015 20130101;
F25B 2309/061 20130101; F25B 2341/0012 20130101 |
Class at
Publication: |
62/115 ; 62/500;
62/512; 62/510 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F25B 1/06 20060101 F25B001/06; F25B 43/00 20060101
F25B043/00; F25B 1/10 20060101 F25B001/10 |
Claims
1. A refrigeration system using a refrigerant cycled therethrough,
said refrigeration system comprising: a vapor compressor comprising
a low-pressure side and a high-pressure side; a first ejector in
operative communication with the high-pressure side of the vapor
compressor, wherein the first ejector boosts the pressure of
vapor-phase refrigerant received from the vapor compressor using a
pressurized sub-cooled liquid mixed with said vapor-phase
refrigerant, and further wherein said first ejector discharges a
vapor stream having an elevated pressure that is greater than the
pressure of either the input vapor-phase refrigerant received from
the vapor compressor or the pressurized sub-cooled liquid; a
condenser for converting the vapor stream discharged from the first
ejector into a liquid-phase refrigerant; a heat exchanger for
converting the liquid-phase refrigerant into a sub-cooled
liquid-phase refrigerant; a second ejector in operative
communication with the low-pressure side of the vapor compressor,
wherein the second ejector boosts the pressure of vapor-phase
refrigerant using at least a portion of the sub-cooled liquid-phase
refrigerant discharged from the heat exchanger mixed with said
vapor-phase refrigerant, and further wherein the boosted
vapor-phase refrigerant is provided to the low-pressure side of the
vapor compressor.
2. The refrigeration system as claimed in claim 1, further
comprising: a liquid-vapor separator in operative communication
with a discharge outlet of the second ejector for separating the
refrigerant discharged from the second ejector into a vapor-phase
and a liquid-phase; and an evaporator that evaporates the
liquid-phase refrigerant separated by the liquid-vapor separator
into a vapor-phase refrigerant that is provided to an input of the
second ejector for mixing with said at least a portion of the
sub-cooled liquid refrigerant therein; wherein the vapor-phase
refrigerant separated by the liquid-vapor separator is the boosted
refrigerant vapor provided to the low-pressure side of the vapor
compressor.
3. The refrigeration system as claimed in claim 2, further
comprising an expansion valve operatively positioning between the
liquid-vapor separator and the evaporator for expanding the
liquid-phase refrigerant provided to the evaporator.
4. The refrigeration system as claimed in claim 2, wherein the
vapor-phase refrigerant separated by the liquid-vapor separator is
superheated through the heat exchanger before being provided to the
low-pressure side of the vapor compressor.
5. The refrigeration system as claimed in claim 1, further
comprising a centrifugal pump for pressurizing at least a portion
of the sub-cooled liquid-phase refrigerant discharged from the heat
exchanger, wherein said pressurized sub-cooled liquid is provided
to the first ejector for mixing with vapor-phase refrigerant
therein.
6. The refrigeration system as claimed in claim 1, wherein the
vapor compressor is a single-stage compressor.
7. The refrigeration system as claimed in claim 1, wherein the
vapor compressor is a two-stage compressor with a first compression
stage and a second compression stage, said second compression stage
operating at a higher pressure than the first compression
stage.
8. The refrigeration system as claimed in claim 7, wherein each
stage of the vapor compressor is driven by a motor.
9. The refrigeration system as claimed in claim 8, wherein each
stage of the vapor compressor includes an impeller operatively
connected to the motor for rotation.
10. The refrigeration system as claimed in claim 1, wherein the
loads of the first and second ejectors are cooled by at least one
of air or water.
11. The refrigeration system as claimed in claim 1, wherein the
vapor compressor is a positive displacement compressor.
12. The refrigeration system as claimed in claim 1, wherein the
vapor compressor is a centrifugal turbocompressor.
13. A refrigeration system using a refrigerant cycled therethrough,
said refrigeration system comprising: a two-stage vapor compressor
comprising a first compression stage and a second compression
stage, said second compression stage operating at a higher pressure
than the first compression stage; a first high-pressure ejector in
operative communication with the second compression stage of the
vapor compressor, wherein the first ejector boosts the pressure of
vapor-phase refrigerant received from the vapor compressor using a
pressurized sub-cooled liquid mixed with said vapor-phase
refrigerant, and further wherein said first ejector discharges a
vapor stream having an elevated pressure that is greater than the
pressure of either the input vapor-phase refrigerant received from
the vapor compressor or the pressurized sub-cooled liquid; a
condenser for converting the vapor stream discharged from the first
ejector into a liquid-phase refrigerant; a heat exchanger for
converting the liquid-phase refrigerant into a sub-cooled
liquid-phase refrigerant; a centrifugal pump for pressurizing a
first portion of the sub-cooled liquid-phase refrigerant discharged
from the heat exchanger, wherein said pressurized sub-cooled liquid
is provided to the first ejector for mixing with vapor-phase
refrigerant therein; a second low-pressure ejector in operative
communication with the first compression stage of the vapor
compressor, wherein the second ejector boosts the pressure of
vapor-phase refrigerant using a second portion of the sub-cooled
liquid-phase refrigerant discharged from the heat exchanger mixed
with said vapor-phase refrigerant, and further wherein the second
ejector discharges a mixed refrigerant; a liquid-vapor separator in
operative communication with a discharge outlet of the second
ejector for separating the mixed refrigerant discharged from the
second ejector into a vapor-phase and a liquid-phase; and an
evaporator that evaporates the liquid-phase refrigerant separated
by the liquid-vapor separator into a vapor-phase refrigerant that
is provided to an input of the second ejector for mixing with said
second portion of the sub-cooled liquid-phase refrigerant therein;
wherein the vapor-phase refrigerant separated by the liquid-vapor
separator is provided to the first compression stage of the vapor
compressor.
14. The refrigeration system as claimed in claim 13, further
comprising an expansion valve operatively positioning between the
liquid-vapor separator and the evaporator for expanding the
liquid-phase refrigerant provided to the evaporator.
15. The refrigeration system as claimed in claim 14, wherein the
vapor-phase refrigerant separated by the liquid-vapor separator is
superheated through the heat exchanger before being provided to the
low-pressure side of the vapor compressor.
16. The refrigeration system as claimed in claim 14, wherein the
loads of the first and second ejectors are cooled by at least one
of air or water.
17. A refrigeration cycling method comprising: providing a
mechanical vapor compressor having a low-pressure side and a
high-pressure side; providing a first ejector in operative
communication with the high-pressure side of the vapor compressor;
mixing vapor-phase refrigerant discharged from the vapor compressor
with a pressurized sub-cooled liquid in the first ejector so as to
boost the pressure of the vapor-phase refrigerant to an elevated
pressure that is greater than the pressure of either the input
vapor-phase refrigerant received from the vapor compressor or the
pressurized sub-cooled liquid; converting the vapor stream
discharged from the first ejector into a sub-cooled liquid-phase
refrigerant; providing a second ejector in operative communication
with the low-pressure side of the vapor compressor; mixing
vapor-phase refrigerant with the sub-cooled liquid-phase
refrigerant in the second ejector so as to boost the pressure of
the vapor-phase refrigerant to an elevated pressure; separating the
mixed refrigerant discharged from the second ejector into a
vapor-phase and a liquid-phase; evaporating the separated
liquid-phase refrigerant into a vapor-phase refrigerant that is
provided to an input of the second ejector for mixing with the
sub-cooled liquid-phase refrigerant therein; superheating the
separated vapor-phase refrigerant; and providing the superheated
vapor-phase refrigerant to the low-pressure side of the vapor
compressor.
18. The refrigeration cycling method as claimed in claim 17,
wherein the vapor compressor is a two-stage compressor with a first
compression stage and a second compression stage, said second
compression stage operating at a higher pressure than the first
compression stage.
19. The refrigeration cycling method as claimed in claim 17,
wherein each of the first and second ejectors comprises a two-phase
ejector.
20. The refrigeration cycling method as claimed in claim 17,
further comprising the step of cooling the loads of the first and
second ejectors by at least one of air or water.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/185,834, filed Jun. 10, 2009, which is
incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to refrigeration units and
operation cycles, and more particularly to an R744 (carbon dioxide)
vapor compression refrigeration system usable in numerous
applications with improved cycle efficiency without any detrimental
environmental effect.
BACKGROUND OF THE INVENTION
[0003] From residential or automobile air conditioning units to
large packaged water chillers for air conditioning and
refrigeration in commercial and industrial facilities, all
mechanical vapor compression cycles now generally use
environmentally harmful chemical refrigerants of
hydrochlorofluorocarbon (HCFC) or hydrofluorocarbon (HFC) fluids.
Emissions of halogenated synthetic refrigerants represent a major
challenge for the environment due to their green house warming
potential, as well as their contribution to ozone depletion. These
harmful refrigerants are scheduled to be phased out, especially,
HCFC-123, an ozone-depleting chemical, that has been designated by
the Montreal Protocol and the U.S. Clean Air Act as a transitional
refrigerant to be phased out soon. Similarly, the European
Commission issued a directive in 2006 mandating the phase out of
HFC-134a in mobile air conditioning units to help meet the European
Union's Kyoto Protocol. Despite negligible ozone-depleting
potential, HFC-134a has a very high Global Warming Potential (GWP)
of 1,300 relative to 1 for natural refrigerants such as ammonia or
carbon dioxide. Accordingly, the European Commission has instituted
a requirement that mobile air conditioning units utilize
refrigerants with a GWP no higher than 150.
[0004] A new synthetic refrigerant, HFO-1234yf, has been recently
developed by DuPont and Honeywell for use in various air
conditioning and refrigeration units. HFO-1234yf has a low GWP of
about 4 to 6, and offers comparable performance to HFC-134a.
However, there is still uncertainty about toxicity and
flammability, which are critical to human life and safety.
Suppliers say that HFO-1234yf has low acute and chronic toxicity,
and manageable mild flammability; it still has a potential for A2
class of ISO 817 refrigerant classification, which means low
toxicity and low flammability. However, in a press release issued
on Oct. 31, 2008, Toyota Germany decided to move away from
HFO-1234yf for car air conditioners after several independent tests
raised issues about its flammability. The tests revealed that
HFO-1234yf is flammable, releasing the decomposition product
hydrogen fluoride that develops into the highly toxic gas
hydrofluoric acid when in contact with water.
[0005] An alternative refrigerant option for air conditioning and
refrigeration units has been to use R744 (carbon dioxide). R744 is
a natural refrigerant that is free from ozone-depletion and has a
negligible global warming potential. R744 has been used as a
refrigerant for well over a century like other natural
refrigerants, including R717 (ammonia), some of which have been
excluded from use because of safety implications both in terms of
toxicity and moderate flammability. R744 is neither flammable nor
toxic, provided it is used in reasonable volumes, and thus provides
desirable safety without having a detrimental environmental impact.
However, in ordinary use, the low critical temperature of R744
(approximately 31.degree. C.) forces the air conditioning system to
work in the transcritical cycle at significantly higher pressures
than desired. Accordingly, such prior art systems using R744 tend
to utilize increased amounts of energy and thus, have not operated
efficiently. For example, even though the increased performance
density of R744 leads to smaller and lighter components, the basic
transcritical cycle is potentially less efficient than a
conventional vapor compression cycle because it suffers from larger
thermodynamic losses at such a low critical temperature. Higher
heat rejection temperatures with increased loss of energy result in
greater throttling losses. As a result, the theoretical cycle work
increases and refrigerant capacity is reduced. A direct application
of R744 to the conventional air conditioning and refrigeration
cycle therefore requires high power consumption, which is not
desirable.
[0006] A simple prior art refrigeration cycle is generally
illustrated in FIG. 1. As shown, the refrigeration cycle 10
includes a refrigerant loop through which a refrigerant is cycled,
in order, through a compressor 12, a condenser 14, an expansion
valve 16 and an evaporator 18. More particularly, a refrigerant
enters the evaporator 18 as a mixture of liquid and vapor by being
metered through the expansion valve 16, which lowers the pressure
of the refrigerant, and therefore its temperature as well. Since
the temperature of the refrigerant is colder than chilled water
cycled through the evaporator 18, the refrigerant absorbs heat to
boil into a saturated vapor. In order to dump out the absorbed
heat, the refrigerant's temperature is raised by increasing its
pressure using the compressor 12. In the condenser 14, the
superheated vapor at the exit of the compressor 12 is condensed
into liquid by losing heat into cooling water cycled through the
condenser 14. The saturated liquid enters the expansion valve 16 to
complete the cycle. The basic refrigeration cycle illustrated in
FIG. 1 is currently utilized in most commercial air conditioning
refrigeration units used today. Depending on the cooling loop
fluid, the cycle may utilize either an air-cooled or a water-cooled
condenser.
[0007] An alternate prior art refrigeration cycle is generally
illustrated in FIG. 2. This refrigeration cycle has been recently
developed for air conditioning units in passenger cars, and
utilizes R744 refrigerant. As shown, the refrigeration cycle 110
includes an ejector 112, a separator 114, an internal heat
exchanger 116, a compressor 118, a gas cooler 120, a metering valve
122, and an evaporator 124. In such a transcritical R744 cycle, a
primary liquid flow with high pressure is supplied to the ejector
112 from the internal heat exchanger 116, and a secondary vapor
flow with low pressure is supplied from the evaporator 124. The
high-pressure and low-pressure flows are mixed in the ejector 112
and discharged at an intermediate pressure that is typically higher
than the secondary vapor pressure. The mixed refrigerant is
separated into a liquid flow and a vapor flow by the separator 114.
The liquid flow separated by the separator 114 is throttled through
the metering valve 122 and to the evaporator 124 to absorb heat.
The vapor flow separated by the separator 114 is directed to the
internal heat exchanger 116 to contribute to sub-cooling the
ejector primary flow before entering the compressor 118. The gas
cooler 120 is used to condense the compressed vapor flow into a
liquid flow. A gas cooler is typically used in lieu of a condenser
because of the use of supercritical R744 refrigerant. As noted
above, the low critical temperature of R744 (approximately
31.degree. C.) forces refrigeration cycle 110 to work in the
transcritical cycle at significantly higher pressures than desired.
Thus, the refrigeration cycle 110 requires high power consumption,
which is not desirable or efficient.
[0008] In view of the foregoing, there is a need for a
refrigeration unit and cycle that operates with high thermodynamic
cycle efficiency with minimal harm to human safety and with minimal
detrimental effect on the environment. Moreover, such a
refrigeration unit and cycle should not be restricted to particular
refrigerants in order to operate as desired. Indeed, a desirable
system will operate efficiently regardless of the refrigerant
used.
[0009] Additionally, there is a need for significant research
efforts on the components and means used for refrigeration units
and systems so as to improve cycle efficiency, including
development and improvement of expanders (instead of expansion
valves), ejectors and internal heat exchangers, so that losses
incurred during a refrigeration cycle and operation of the system
can be recovered.
[0010] Accordingly, it is a general object of the present invention
to provide a refrigeration unit that overcomes the problems and
drawbacks associated with existing refrigeration units and cycles
and with use of various refrigerants.
SUMMARY OF THE INVENTION
[0011] The present invention is directed to an innovative air
conditioning and refrigeration system. In a first aspect of the
present invention, a refrigeration system using a refrigerant
cycled therethrough, comprises a vapor compressor having a
low-pressure side and a high-pressure side, a first ejector in
operative communication with the high-pressure side of the vapor
compressor, and a second ejector in operative communication with
the low-pressure side of the vapor compressor. The first ejector
boosts the pressure of vapor-phase refrigerant received from the
vapor compressor using a pressurized sub-cooled liquid mixed with
the vapor-phase refrigerant. The first ejector discharges a vapor
stream having an elevated pressure that is greater than the
pressure of either the input vapor-phase refrigerant received from
the vapor compressor or the pressurized sub-cooled liquid. The
second ejector boosts the pressure of vapor-phase refrigerant using
sub-cooled liquid-phase refrigerant mixed with the vapor-phase
refrigerant. Boosted vapor-phase refrigerant discharged from the
second ejector is provided to the low-pressure side of the vapor
compressor. The refrigeration system further comprises a condenser
for converting the vapor stream discharged from the first ejector
into a liquid-phase refrigerant, and a heat exchanger for
converting the liquid-phase refrigerant into a sub-cooled
liquid-phase refrigerant that is supplied to the first ejector, the
second ejector, and preferably both ejectors.
[0012] The refrigeration system of the present invention may
further include a liquid-vapor separator in operative communication
with a discharge outlet of the second ejector for separating the
refrigerant discharged from the second ejector into a vapor-phase
and a liquid-phase, and an evaporator that evaporates the
liquid-phase refrigerant separated by the liquid-vapor separator
into a vapor-phase refrigerant that is provided to an input of the
second ejector for mixing with said at least a portion of the
sub-cooled liquid-phase refrigerant therein. The vapor-phase
refrigerant separated by the liquid-vapor separator is provided to
the low-pressure side of the vapor compressor, and preferably is
superheated through the heat exchanger before being provided to the
low-pressure side of the vapor compressor.
[0013] The refrigeration system of the present invention may
further comprise a centrifugal pump for pressurizing at least a
portion of the sub-cooled liquid-phase refrigerant discharged from
the heat exchanger, wherein said pressurized sub-cooled liquid is
provided to the first ejector for mixing with vapor-phase
refrigerant therein.
[0014] In a second aspect of the present invention, a refrigeration
system comprises a two-stage vapor compressor having a first
compression stage and a second compression stage, the second
compression stage operating at a higher pressure than the first
compression stage. A first high-pressure ejector is in operative
communication with the second compression stage of the vapor
compressor, wherein the ejector boosts the pressure of vapor-phase
refrigerant received from the vapor compressor using a pressurized
sub-cooled liquid mixed with the vapor-phase refrigerant. The first
ejector discharges a vapor stream having an elevated pressure that
is greater than the pressure of either the input vapor-phase
refrigerant received from the vapor compressor or the pressurized
sub-cooled liquid. A condenser converts the vapor stream discharged
from the first ejector into a liquid-phase refrigerant, and a heat
exchanger converts the liquid-phase refrigerant into a sub-cooled
liquid-phase refrigerant. A centrifugal pump pressurizes a first
portion of the sub-cooled liquid-phase refrigerant discharged from
the heat exchanger, and the pressurized sub-cooled liquid is
provided to the first ejector for mixing with vapor-phase
refrigerant therein.
[0015] The refrigeration system also includes a second low-pressure
ejector in operative communication with the first compression stage
of the vapor compressor. The second ejector boosts the pressure of
vapor-phase refrigerant using a second portion of the sub-cooled
liquid-phase refrigerant discharged from the heat exchanger that is
mixed with the vapor-phase refrigerant in the second ejector. The
second ejector discharges a mixed refrigerant that is separated by
a liquid-vapor separator in operative communication with a
discharge outlet of the second ejector into a vapor-phase and a
liquid-phase. An evaporator evaporates the liquid-phase refrigerant
into a vapor-phase refrigerant that is provided to an input of the
second ejector for mixing with the sub-cooled liquid-phase
refrigerant therein. The vapor-phase refrigerant separated by the
liquid-vapor separator is provided to the first compression stage
of the vapor compressor.
[0016] In accordance with an advantage of the present invention,
two independent ejectors are utilized to reduce total compression
of the refrigeration cycle, and, as a result, reduce the electric
power consumption of the vapor compressor. As a further result, the
refrigeration system operates with higher cycle efficiency than for
prior art systems.
[0017] In accordance with another advantage of the present
invention, the system can be operated with negligible global
warming potential and zero ozone depletion potential.
[0018] In accordance with yet another advantage of the present
invention, the system is not limited to being used with any one
refrigerant, which means that any refrigerants, including the
preferred R744 refrigerant, may be used without departing from the
spirit and principles of the invention.
[0019] In another aspect of the present invention a refrigeration
cycling method comprises providing a mechanical vapor compressor
having a low-pressure side and a high-pressure side, a first
ejector in operative communication with the high-pressure side of
the vapor compressor, and a second ejector in operative
communication with the low-pressure side of the vapor compressor.
Pursuant to the method, vapor-phase refrigerant discharged from the
vapor compressor is mixed with a pressurized sub-cooled liquid in
the first ejector so as to boost the pressure of the vapor-phase
refrigerant to an elevated pressure that is greater than the
pressure of either the input vapor-phase refrigerant received from
the vapor compressor or the pressurized sub-cooled liquid. The
vapor stream discharged from the first ejector is converted into a
sub-cooled liquid-phase refrigerant. Within the second ejector, the
vapor-phase refrigerant is mixed with the sub-cooled liquid-phase
refrigerant so as to boost the pressure of the vapor-phase
refrigerant to an elevated pressure. The mixed refrigerant
discharged from the second ejector is then separated into a
vapor-phase and a liquid-phase, with the separated liquid-phase
refrigerant being evaporated into a vapor-phase refrigerant that is
provided to an input of the second ejector for mixing with the
sub-cooled liquid-phase refrigerant therein, and the separated
vapor-phase refrigerant being superheated and provided to the
low-pressure side of the vapor compressor.
[0020] As one example of potential applications for the present
invention, a 150-ton capacity, water-cooled chiller cycle is
considered. The water-cooled chiller cycle is predicted through a
preliminary cycle analysis for standard rating conditions
controlled by ARI 550/590 to provide power consumption as low as
0.47 kW/ton, which corresponds to about 7.47 of Coefficient of
Performance (COP).
[0021] The present invention cycle can be applied to air
conditioning and refrigeration units and systems for various
applications, including residential, automobile, industrial and
commercial applications. The present invention is adaptable to
various types of mechanical vapor compressors to accommodate
various such applications. The liquid centrifugal pump of the
disclosed embodiments can be either positive displacement machines
or high-speed turbomachines. Heat exchanging methods used in the
refrigeration cycle of the units or systems can be air-cooled,
water-cooled or both.
[0022] These and other feature of the present invention are
described with reference to the drawings of preferred embodiments
of a refrigeration system. The illustrated embodiments of the
system in accordance with the present invention are intended to
illustrate, but not limit, the invention.
BRIEF DESCRIPTION DRAWINGS
[0023] FIG. 1 is a schematic diagram of a prior art refrigeration
system and cycle.
[0024] FIG. 2 is a schematic diagram of another prior art
refrigeration system and cycle.
[0025] FIG. 3 is a schematic diagram of a refrigeration system and
cycle in accordance with the present invention.
[0026] FIG. 4 is an exemplary pressure-enthalpy thermodynamic
diagram for a refrigeration cycle in accordance with the present
invention used for air conditioning applications.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
THEREOF
[0027] FIGS. 3 and 4 represent an R744 vapor compression
refrigeration system and cycle in accordance with the present
invention. More specifically, FIG. 3 illustrates the present
invention in the form of a water-cooled chiller, generally
designated by reference numeral 210, which is one of several
applications for the innovative refrigeration cycle of the present
invention. FIG. 4 provides an exemplary pressure-enthalpy
thermodynamic diagram for the water-cooled chiller of FIG. 3. Both
FIGS. 3 and 4 identify and correspond to various steps in the
refrigeration cycle by reference to encircled reference
numerals.
[0028] The illustrated water-cooled chiller generally has a 150-ton
capacity and comprises a mechanical vapor compressor 212 driven by
a high-speed electric motor 214. The vapor compressor 212 may be
either a single stage or multi-staged compressor and of either a
positive displacement-type or a centrifugal turbo-type. As
illustrated in FIG. 3, the compressor 212 is a centrifugal,
two-staged design, with a first compression stage 216 [Step B] and
a second compression stage 218 [Step C]. In a design of the present
invention utilizing a single-stage compressor, the compressor still
comprises a high-pressure side and a low-pressure side. In
preferred designs of the compression stages 216 and 218, each stage
comprises an independent rotating impeller driven by the motor 214.
In accordance with operation of the vapor compressor, as described
below, the second compression stage 218 operates at a higher
pressure than the first compression stage 216.
[0029] A high-pressure ejector 220 and a low-pressure ejector 230
are operatively connected to a high-pressure side and a
low-pressure side of the vapor compressor 212, respectively. The
high-pressure ejector 220 is preferably a two-phase jet device in
which a sub-cooled liquid refrigerant, preferably R744 refrigerant,
pressurized by a centrifugal pump 226 driven by a high-speed
electric motor 228, is mixed with vapor refrigerant, compressed by
the centrifugal vapor compressor 212. The centrifugal pump 226 can
be either a positive displacement machine or a high-speed
turbomachine.
[0030] As shown in FIG. 3, the compressed vapor refrigerant is
discharged from the second compression stage 212 and delivered to a
first input of the high-pressure ejector 220. The pressurized
sub-cooled liquid refrigerant from the centrifugal pump 226 is
delivered to a second input of the high-pressure ejector 220. The
sub-cooled pressurized liquid refrigerant is used as a driving
fluid to boost the vapor pressure of the vapor refrigerant received
from the mechanical vapor compressor 212.
[0031] In operation, the high-pressure ejector 220 produces a final
gas stream [Step F] with an elevated pressure that is higher than
the pressure of either of the two inlet streams [Steps D and Q].
The high-pressure ejector 220 comprises a convergent section 220a,
a constant section 220b and a diffuser section 220c. The mixing of
the pressurized sub-cooled liquid refrigerant with the vapor
refrigerant takes place first in the convergent section 220a of the
ejector 220, and then in the constant section 220b [Step R]. The
two-phase mixed flow is converted into a gas stream across the R744
critical point in the diffuser section 220c [Step E], as shown in
FIG. 4. The high-pressure ejector 220 reduces total compression of
the refrigeration cycle 210, and, as a result, the electric power
consumption of the vapor compressor 212 is reduced. Such
consumption levels are reduced, in part, by using the high-pressure
ejector 220 in the manner described above to expand a portion of
sub-cooled liquid refrigerant that is pressurized in advance by the
centrifugal pump 226.
[0032] The gas stream ejected from an outlet of the high-pressure
ejector 220 [Step F] is converted into a liquid refrigerant by a
water-cooled condenser 220. As illustrated, the condenser 220
elevates the input water from about 85.degree. F. to an output
temperature of about 95.degree. F. The liquid refrigerant is then
fed to a secondary internal heat exchanger 224 [Step G], which
converts the refrigerant into a sub-cooled liquid refrigerant. More
particularly, the heat exchanger 224 allows the superheating
process to take heat from the liquid refrigerant. Heat exchanging
methods used in the refrigeration cycle of the present invention
can be air-cooled, water-cooled or both. A portion of the
sub-cooled liquid refrigerant, split at a flow branch 225 [Step H],
is then depressurized and expanded through a nozzle arrangement at
a first input of the low-pressure ejector 230. Another portion of
the sub-cooled liquid from the secondary heat exchanger 224 is
pressurized by the centrifugal pump 226. As noted above, the
pressurized liquid from the pump 226 is utilized as a driving fluid
in the high-pressure ejector 220 [Step Q] to boost vapor pressure
from the mechanical vapor compressor 212.
[0033] The low-pressure ejector 230 is preferably a two-phase jet
device comprising a convergent section 230a, a constant section
230b and a diffuser section 230c. High-pressure refrigerant
discharged from the low-pressure ejector 230 [Step K] exerts a
drawing force to draw in a vapor-phase refrigerant [Step N], which
is evaporated in an evaporator 236, through a second input of the
low-pressure ejector 230. The evaporator 236 decreases the
temperature of an input processing water from about 54.degree. F.
to an output temperature of about 44.degree. F. The expansion
energy of the refrigerant from the inlet of the low-pressure
ejector 230 through the convergent section 230a of the ejector
(e.g., from Step H to Step I) is utilized to contribute to the
increase of the intake pressure of the first compression stage 216
of the vapor compressor 212. The low-pressure ejector 230 reduces
total compression of the refrigeration cycle 210 and therefore the
electric power consumption of the vapor compressor 212 is reduced
by recovering energy from the main expansion process for a portion
of sub-cooled liquid refrigerant supplied to the ejector 230.
Within the low-pressure ejector 230, the sub-cooled pressurized
liquid refrigerant boosts the vapor pressure of the vapor-phase
refrigerant received from the evaporator 236.
[0034] Liquid-phase refrigerant, which is separated by a
liquid-vapor separator 232 downstream of the low-pressure ejector
230, is supplied to the evaporator 236 through an expansion valve
234 [Steps L and M]. The remaining vapor-phase refrigerant is
supplied to the vapor compressor 212 through the secondary internal
heat exchanger 224 to complete the vapor compression cycle [Steps P
and A]. Specifically, the saturated vapor separated from the
liquid-vapor separator 232 is superheated through the secondary
internal heat exchanger 224 by the sub-cooling process downstream
of the condenser 222, as discussed above [Step G].
[0035] In the refrigeration cycle 210 of the present invention, the
centrifugal vapor compressor 212 has a two-stage compression 216
and 218, and intercooling is accomplished in the water-cooled
condenser 222. The R744 refrigerant cycled through the system is
utilized as a coolant for the electric motors 214 and 228. The
loads of the high-pressure ejector 220 and the low-pressure ejector
230 may be cooled by air, water or both.
[0036] Thermodynamic processes of the present cycle are illustrated
in FIG. 4 where all the encircled point designations match with the
cycle step designations in FIG. 3. For example, at Step A, vapor
phase refrigerant is supplied to the low-pressure side 216 of the
vapor compressor 212. The refrigerant is compressed through the
first compression stage and passed through the water-cooled
condenser at Step B. The refrigerant is then compressed through the
second compression stage on the high-pressure side 218 of the vapor
compressor at Step C. At Step D, a compressed vapor refrigerant is
output from the second compression stage 212 and delivered to a
first input of the high-pressure ejector 220. The high-pressure
ejector 220 also receives a sub-cooled pressurized liquid from the
centrifugal pump 226 at Step Q.
[0037] The high-pressure ejector 220 utilizes the pressurized
liquid from the pump 226 as a driving fluid to boost the vapor
pressure of the refrigerant received from the mechanical vapor
compressor 212. Within the high-pressure ejector 220, at Step R,
the pressurized sub-cooled liquid refrigerant is mixed with the
vapor refrigerant, first in the convergent section 220a of the
ejector 220, and then in the constant section 220b. Then, at Step
E, the two-phase mixed flow is converted into a gas stream in the
diffuser section 220c of the ejector 220. At Step F, the
high-pressure ejector 220 outputs a final gas stream with an
elevated pressure that is directed to the condenser 222, which
elevates the temperature of processing water while cooling the gas
stream.
[0038] At Step G, the condenser sends the liquid refrigerant to the
heat exchanger 224, which converts the refrigerant into a
sub-cooled liquid refrigerant by allowing the superheating process
to draw heat from the liquid refrigerant. At Step H, the sub-cooled
refrigerant is split, with one part being directed to the
centrifugal pump 226 for pressurization and delivery to the input
of the high-pressure ejector 220, and the other part being directed
to the low-pressure ejector 230.
[0039] The sub-cooled liquid refrigerant is mixed with vapor-phase
refrigerant within the low-pressure ejector 230, more particularly
in the convergent section 230a and the constant section 220b, at
Step I. At Step J, the two-phase mixed flow is a high-pressure
refrigerant in the divergent section 230c of the ejector 230, which
is then discharged from the ejector 230 and directed to the
liquid-vapor separator 232 at Step K. The high-pressure refrigerant
in the divergent section 230c exerts a drawing force to draw in the
vapor-phase refrigerant from the evaporator 236 at Step N for
mixing within the low-pressure ejector 230.
[0040] At Steps L and P, liquid-vapor separator 232 separates the
two-phase refrigerant flow into liquid-phase refrigerant and a
saturated vapor-phase refrigerant. The liquid-phase refrigerant is
directed through an expansion valve 234 and to the evaporator 236
at Step M, where the refrigerant is evaporated. The saturated
vapor-phase refrigerant is superheated through the heat exchanger
224 at Step P, and then directed back to the vapor compressor at
Step A.
[0041] Both the high-pressure ejector 220 and the low-pressure
ejector 230 of the present invention reduce total compression of
the refrigeration cycle and the power consumption of the vapor
compressor. With regard to the high-pressure ejector 220,
consumption levels are reduced, in part, by using the high-pressure
ejector 220 to expand a portion of sub-cooled liquid refrigerant
that is pressurized by the centrifugal pump 226 in advance of
feeding the liquid refrigerant to the ejector 220. With regard to
the low-pressure ejector 230, consumption levels are reduced by
recovering energy from the main expansion process for a portion of
sub-cooled liquid refrigerant.
[0042] The refrigeration system and cycle in accordance with the
present invention provides higher cycle efficiency without
increases electric power consumption to undesirable levels. In
particular, the design of the system reduces the overall pressure
ratio of the vapor compressor, resulting in dramatically increased
thermodynamic cycle efficiency. Additionally, the present invention
permits the refrigeration system and cycle to operate with
negligible global warming potential and zero ozone depletion
potential. Moreover, the present invention is not limited to use
with particular refrigerant, which means that any refrigerant may
be utilized without compromising the efficiency of the system. R744
is discussed as a preferred refrigerant because of its known
negligible global warming potential and zero ozone depletion
potential. However, other refrigerants may be utilized in the
refrigeration system and cycle described herein without departing
from the spirit and principles of the invention.
[0043] Based on standard rating conditions of packaged water
chillers controlled by ARI 550/590, a preliminary evaluation of the
innovative R744 refrigeration cycle of the present invention for
150-ton capacity shows 0.47 kW/ton of power consumption and 7.47 of
COP when both ejectors 220 and 230 have a pressure ratio of about
1.2, and 81% and 80% of isentropic efficiencies are assumed for the
first and second stages 216 and 218 of the centrifugal vapor
compressor 212. A 50% split of mass flow rate is also assumed at
the flow branch 225. In the case of 150 tons of cooling capacity,
the centrifugal vapor compressor 212 consumes about 68 kW of input
power, and the centrifugal pump 226 requires only about 2.5 kW.
Considering the averaged COP level of current state-of-the-art
water chillers using HFC-134a is around 5.5, the present innovative
R744 cycle 210 provides a great improvement in energy savings.
[0044] The foregoing description of the present invention has been
presented for the purpose of illustration and description. It is
not intended to be exhaustive as to limit the invention to the form
disclosed. Obvious modifications and variations are possible in
light of the above disclosure. The embodiments described were
chosen to best illustrate the principles of the invention and
practical applications thereof to enable one of ordinary skill in
the art to utilize the invention in various embodiments and with
various modifications as suited to the particular uses
contemplated.
[0045] The present invention cycle can be applied to air
conditioning and refrigeration units and systems for a variety of
applications, including residential, automobile, industrial and
commercial applications. The present invention is adaptable to
various types of mechanical vapor compressors to accommodate
various such applications. The liquid pump of the disclosed
embodiments can be either positive displacement machines or
high-speed turbomachines. Heat exchanging methods used in the
refrigeration cycle of the units or systems can be air-cooled,
water-cooled or both. FIG. 1 shows one of potential
applications.
[0046] It is intended that the scope of the present invention be
defined by the claims appended hereto.
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