U.S. patent application number 12/599888 was filed with the patent office on 2010-10-07 for economized refrigerant system with flow control.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20100251750 12/599888 |
Document ID | / |
Family ID | 40032179 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100251750 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
October 7, 2010 |
ECONOMIZED REFRIGERANT SYSTEM WITH FLOW CONTROL
Abstract
A refrigerant vapor compression system has a primary refrigerant
circuit including a compression device, a refrigerant heat
rejection heat exchanger and a refrigerant heat absorption heat
exchanger, and an economizer circuit including an economizer
refrigerant line. A bypass flow control device controls refrigerant
vapor flow through a bypass line extending between the economizer
refrigerant line and a suction pressure portion of the primary
refrigerant circuit. A flow control apparatus operatively
associated with the economizer refrigerant line provides different
flow resistance to refrigerant flow through the economizer
refrigerant line in a first direction from an intermediate stage of
the compression device to the suction portion of the primary
refrigerant circuit and in a second direction from the economizer
into an intermediate pressure stage of the compression device.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
Carrier Corporation
Farmington
CT
|
Family ID: |
40032179 |
Appl. No.: |
12/599888 |
Filed: |
May 17, 2007 |
PCT Filed: |
May 17, 2007 |
PCT NO: |
PCT/US07/11797 |
371 Date: |
November 12, 2009 |
Current U.S.
Class: |
62/434 ; 62/510;
62/513 |
Current CPC
Class: |
F25B 2400/13 20130101;
F25B 2600/2509 20130101; F25B 1/10 20130101; F25B 2600/2513
20130101 |
Class at
Publication: |
62/434 ; 62/510;
62/513 |
International
Class: |
F25D 17/02 20060101
F25D017/02; F25B 1/10 20060101 F25B001/10; F25B 41/00 20060101
F25B041/00 |
Claims
1. A refrigerant vapor compression system comprising: a primary
refrigerant circuit including a refrigerant compression device, a
refrigerant heat rejection heat exchanger, a refrigerant heat
absorption heat exchanger, and a primary expansion device
interdisposed in the primary refrigerant circuit downstream of said
refrigerant heat rejection heat exchanger and upstream of said
refrigerant heat absorption heat exchanger; an economizer circuit
including an economizer and an economizer refrigerant line in
refrigerant vapor flow communication between said economizer and an
intermediate pressure stage of said compression device; a bypass
line in refrigerant flow communication between said economizer
refrigerant line at a location intermediate said economizer and an
intermediate stage of said compression device and said primary
refrigerant circuit at a location downstream with respect to
refrigerant flow of said refrigerant heat absorption heat
exchanger; a bypass flow control device disposed in said bypass
line, said bypass flow control device having a first open position
whereat refrigerant may flow through said bypass line and a second
closed position whereat refrigerant is blocked from flowing through
said bypass line; and a flow control apparatus disposed in said
economizer refrigerant line providing a first flow path through
said economizer refrigerant line in a first direction from the
intermediate pressure stage of said compression device to said
bypass line and a second flow path through said economizer
refrigerant line in a second direction from said economizer into
the intermediate pressure stage of said compression device, said
first flow path having a first hydraulic resistance to refrigerant
flow through said first flow path and said second flow path having
a second hydraulic resistance to refrigerant flow through said
second flow path, the first and second hydraulic resistances being
different.
2. A refrigerant vapor compression system as recited in claim 1
wherein said bypass flow control device comprises a solenoid valve
having a first open position and a second closed position.
3. A refrigerant vapor compression system as recited in claim 1
wherein said flow control apparatus comprises a fluid diode device
interdisposed in said economizer refrigerant fine at a location
intermediate said bypass line and the intermediate pressure stage
of said compression device, said fluid diode device providing a
first flow path through said economizer refrigerant line in the
first direction from the intermediate pressure stage of said
compression device to said bypass line having a first relatively
lower hydraulic resistance to refrigerant flow therethrough, and a
second flow path through said economizer refrigerant line in a
second direction from said economizer into the intermediate
pressure stage of said compression device having a second
relatively higher hydraulic resistance to refrigerant flow
therethrough.
4. A refrigerant vapor compression system as recited in claim 3
wherein said fluid diode device comprises a check valve
interdisposed in said economizer refrigerant line at a location
intermediate the intermediate pressure stage of said compression
device and said bypass line, said check valve having a first
position wherein refrigerant may flow therethrough in the first
direction through said first flow path from the intermediate
pressure stage of said compression device to said bypass line and
the second position wherein refrigerant may flow therethrough in a
second direction through said economizer refrigerant line in a
second direction from said economizer into the intermediate
pressure stage of said compression device.
5. A refrigerant vapor compression system as recited in claim 1
wherein said flow control apparatus comprises a first branch
refrigerant line in refrigerant flow communication with said first
flow path through said economizer refrigerant line, a second branch
refrigerant line in refrigerant flow communication with said second
flow path through said economizer refrigerant line and disposed in
parallel with said first branch refrigerant line, and a check valve
disposed in the first branch refrigerant line, said check valve
having a first position wherein refrigerant may flow through said
first branch refrigerant line and said first flow path and a second
position wherein refrigerant flow through said first branch
refrigerant line and said first flow path is blocked.
6. A refrigerant vapor compression system as recited in claim 5
wherein said first branch refrigerant line has a relatively lower
hydraulic resistance to refrigerant flow therethrough and said
second branch refrigerant line has a relatively higher hydraulic
resistance to refrigerant flow therethrough.
7. A refrigerant vapor compression system as recited in claim 5
further comprising a fixed restriction flow control device disposed
in said second branch refrigerant line.
8. A refrigerant vapor compression system as recited in claim 7
wherein said cheek valve in its first position provides a
relatively lower hydraulic resistance to refrigerant flow through
said first branch refrigerant line and said fixed restriction flow
control device provides a relatively higher hydraulic resistance to
refrigerant flow through said second branch refrigerant line.
9. A refrigerant vapor compression system as recited in claim 1
wherein said flow control apparatus comprises a first branch
refrigerant line in refrigerant flow communication with said first
flow path through said economizer refrigerant line, a second branch
refrigerant line in refrigerant flow communication with said second
flow path through said economizer refrigerant line and disposed in
parallel with said first branch refrigerant line, and a solenoid
valve disposed in said first branch refrigerant line, said solenoid
valve having a first position wherein refrigerant may flow through
said first branch refrigerant line and a second position wherein
refrigerant flow through said first branch refrigerant line is
blocked and refrigerant may flow only through said second branch
refrigerant line.
10. A refrigerant vapor compression system as recited in claim 9
further comprising a fixed restriction flow control device disposed
in said second branch refrigerant line.
11. A refrigerant, vapor compression system as recited in claim 1
wherein said economizer comprises a refrigerant-to-refrigerant heat
exchanger.
12. A refrigerant vapor compression system as recited in claim 1
wherein said refrigerant-to-refrigerant heat exchanger includes a
first refrigerant pass and a second refrigerant pass disposed in
heat exchange relationship with said first refrigerant pass, said
first refrigerant pass interdisposed in said primary refrigerant
circuit and said second refrigerant pass interdisposed in said
economizer refrigerant line, said economizer refrigerant line
extending in fluid communication from said primary refrigerant
circuit through said second refrigerant pass to an intermediate
pressure stage of said compression device.
13. A refrigerant vapor compression system as recited in claim 12
further comprising an economizer expansion device interdisposed in
said economizer refrigerant line upstream with respect to
refrigerant flow of the second refrigerant pass of said
refrigerant-to-refrigerant heat exchanger.
14. A refrigerant vapor compression system as recited in claim 13
wherein said economizer expansion device comprises an expansion
device selected from the group comprising electronic expansion
valves, thermostatic expansion valves and fixed orifice flow
restriction devices.
15. A refrigerant vapor compression system as recited in claim 1
wherein said economizer heat exchanger is a flash tank
interdisposed in said primary refrigerant circuit downstream with
respect to refrigerant flow of said refrigerant heat rejection heat
exchanger and upstream with respect to refrigerant flow of said
primary expansion device.
16. A refrigerant vapor compression system as recited in claim 15
further comprising an economizer expansion device interdisposed in
said primary refrigerant circuit upstream with respect to
refrigerant flow of said flash tank.
17. A refrigerant vapor compression system as recited in claim 16
wherein said economizer expansion device comprises an expansion
device selected from the group comprising electronic expansion
valves, thermostatic expansion valves and fixed orifice flow
restriction devices.
18. A refrigerant vapor compression system as recited in claim 1
wherein said primary expansion device comprises an expansion device
selected from the group comprising electronic expansion valves,
thermostatic expansion valves and fixed orifice flow restriction
devices.
19. A refrigerant vapor compression system as recited in claim 1
wherein said compression device comprises a single compressor
having at least two compression stages.
20. A refrigerant vapor compression system as recited in claim 1
wherein said compression device comprises at least two compressors
disposed in said primary refrigerant circuit in a series
relationship with respect to refrigerant flow.
21. A refrigerant vapor compression system as recited in claim 1
wherein said compression device comprises at least one compressor
selected from the group of compressors comprising scroll
compressors, reciprocating compressors, screw compressors,
centrifugal compressors and rotary compressors.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to refrigerant vapor
compression systems and, more particularly, to refrigerant vapor
compression systems equipped with an economizer cycle.
BACKGROUND OF THE INVENTION
[0002] Refrigerant vapor compression systems are well known in the
art and commonly used for conditioning air (or other secondary
media) to be supplied to a climate-controlled comfort zone within a
residence, office building, hospital, school, restaurant or other
facility. Refrigerant vapor compression systems are also commonly
used in transport refrigeration for refrigerating air supplied to a
temperature-controlled cargo space of a truck, trailer, container
or the like for transporting perishable items, and in commercial
refrigeration for cooling air supplied to a temperature-controlled
space in a cold room, a beverage cooler, a diary case or a
refrigerated merchandiser for displaying perishable foods item in a
chilled or frozen state, as appropriate. Typically, these
refrigerant vapor compression systems include: a compressor, a
condenser, an evaporator; and an expansion device. Commonly, the
expansion device, typically a fixed orifice, a capillary tube, a
thermostatic expansion valve (TXV) or an electronic expansion valve
(EXV), is disposed in the refrigerant line upstream, with respect
to refrigerant flow, of the evaporator and downstream of the
condenser. These basic refrigerant vapor compression system
components are serially interconnected by refrigerant lines in a
closed-loop refrigerant circuit, arranged in accord with known
refrigerant vapor compression cycles.
[0003] To improve performance of the refrigerant vapor compression
system and to control the temperature of the refrigerant vapor
discharged from the final stage of the compressor over a wide range
of operating conditions, it is known to equip such systems with an
economizer cycle incorporating a refrigerant-to-refrigerant
economizer heat exchanger. The economizer heat exchanger is
generally disposed hi the refrigerant circuit intermediate the
condenser and the evaporator. In operation, a portion of the
refrigerant leaving the condenser is diverted from the primary
refrigerant circuit, expanded to an intermediate pressure and then
passed through the economizer heat exchanger in heat exchange
relationship with the main portion of the refrigerant leaving the
condenser. In this manner, any liquid in the economized expanded
refrigerant flow is evaporated, and then the evaporated refrigerant
is typically superheated, while the refrigerant passing through the
primary refrigerant circuit from the condenser to the evaporator is
further cooled. Typically, the expanded refrigerant vapor is
injected into an intermediate stage in the compression process,
either through an injection port or ports opening into an
intermediate pressure stage of the compression chamber (or
chambers) of a single compressor or, in the case of a multiple
compressor system, into a refrigerant line extending between the
discharge outlet of the upstream compressor and the suction inlet
of the downstream compressor.
[0004] For example, U.S. Pat. No. 6,571,576 discloses a refrigerant
vapor compression system operating in a subcritical cycle and
equipped with an economizer heat exchanger, wherein vapor
refrigerant and liquid refrigerant are returned to, an intermediate
stage of the compression process through one or more economizer
injection ports opening into the compression chambers of a scroll
compressor. To provide the refrigerant vapor for injection into the
compressor, a portion of liquid refrigerant is taken from the
primary refrigerant circuit at a location downstream of the
condenser, expanded to an intermediate pressure and lower
temperature by means of an expansion device, such as a valve, to
form a refrigerant liquid/vapor mixture which is thereafter passed
through the economizer heat exchanger in heat exchange relationship
with the main flow of refrigerant liquid. In traversing the
economizer heat exchanger, this refrigerant liquid/vapor mixture
extracts heat from the main flow of refrigerant liquid, further
cooling this liquid, thereby evaporating any remaining liquid
component in the two-phase mixture and typically further heating
the vapor. The refrigerant vapor leaving the economizer heat
exchanger is then injected into the compressor through the
economizer injection ports at the intermediate (between suction and
discharge) pressure. Additionally, liquid refrigerant is
selectively taken from the refrigerant circuit at a location
downstream of the condenser and mixed into the refrigerant vapor
being passed from the economizer to the compressor and injected
into an intermediate pressure stage of the compression chambers of
the scroll compressor together with the refrigerant vapor through
the same economizer injection ports.
[0005] U.S. Pat. No. 7,114,349 discloses a refrigerant vapor
compression system with a refrigerant-to-refrigerant heat exchanger
interdisposed in the refrigerant circuit downstream of the
condenser, with respect to refrigerant flow, and upstream of the
evaporator, with respect to refrigerant flow. Through various
bypass lines and manipulation of various open/closed solenoid
valves associated with the bypass lines, the common heat exchanger
may be operated either as an economizer heat exchanger or as a
liquid-suction heat exchanger. When the system is operating with
the refrigerant-to-refrigerant heat exchanger functioning as an
economizer, refrigerant is passed from the primary refrigerant
circuit through an economizer expansion device and thence through
the refrigerant-to-refrigerant heat exchanger in heat exchange
relationship with the remainder of the refrigerant passing through
the primary refrigerant circuit from the condenser to the
evaporator. After traversing the refrigerant-to-refrigerant heat
exchanger, the expanded refrigerant is injected into an
intermediate pressure stage of the compressor or returned to the
primary refrigerant circuit at a point downstream, with respect to
refrigerant flow, of the evaporator and upstream of the suction
inlet of the compressor.
[0006] U.S. Pat. No. 6,058,729 discloses a subcritical refrigerant
vapor compression system for a transport refrigeration unit
incorporating a refrigerant-to-refrigerant heat exchanger into the
refrigerant circuit as an economizer. The disclosed system also
includes a suction modulation valve (SMV) for throttling
refrigerant flow to the suction inlet of the compressor and an
intermediate pressure-to-suction pressure unload circuit for
compressor capacity control.
SUMMARY OF THE INVENTION
[0007] The refrigerant vapor compression system of the invention
includes a primary refrigerant circuit, an economizer circuit, a
bypass line, a bypass flow control device, and an
economizer/compressor unload flow control apparatus. The primary
refrigerant circuit includes a refrigerant compression device, a
refrigerant heat rejection heat exchanger, a refrigerant heat
absorption heat exchanger, and a primary expansion device
interdisposed in the primary refrigerant circuit downstream of the
refrigerant heat rejection heat exchanger and upstream of the
refrigerant heat absorption heat exchanger. The economizer circuit
includes an economizer refrigerant line extending in refrigerant
flow communication between the economizer and an intermediate
pressure stage of the compression device.
[0008] A bypass line extends in refrigerant flow communication from
the economizer refrigerant line to the primary refrigerant circuit
at a location downstream, with respect to refrigerant flow, of the
refrigerant heat absorption heat exchanger. A bypass flow control
device is disposed in the bypass line. The bypass flow control
device has a first open position whereat refrigerant may flow
through the bypass line and a second closed position whereat
refrigerant is blocked from flowing through the bypass line. In an
embodiment, the bypass flow control device may comprise a solenoid
valve having a first open position and a second closed
position.
[0009] Additionally, a flow control apparatus disposed in the
economizer refrigerant line provides a first flow path through the
economizer refrigerant line in a first direction from the
intermediate pressure stage of the compression device to the bypass
line and a second flow path through the economizer refrigerant line
in a second direction from the economizer into the intermediate
pressure stage of the compression device. The first flow path has a
first hydraulic resistance to refrigerant flow through the first
flow path and the second flow path has a second hydraulic
resistance to refrigerant flow through the second flow path, the
first hydraulic resistance being different from the second
hydraulic resistance. In an embodiment, the first hydraulic
resistance is relatively lower and the second hydraulic resistance
is relatively higher.
[0010] In an embodiment, flow control apparatus comprises a "fluid
diode" device interdisposed in the economizer refrigerant line at a
location intermediate the intermediate pressure stage of the
compression device and the bypass line. The "fluid diode" device
has different flow resistance depending on the direction of the
flow through the "fluid diode". A check valve with two position
openings is one embodiment of such a "fluid diode" device. The
check valve is used to illustrate this embodiment; however, other
types of "fluid diodes" known in the art would fall within the
scope of this invention. The check valve has a first position
wherein refrigerant may flow therethrough in a first direction from
the intermediate pressure stage of the compression device to the
bypass line and a second flow path through the economizer
refrigerant line in a second direction from the second refrigerant
pass of the refrigerant-to-refrigerant heat exchanger into the
intermediate pressure stage of the compression device.
[0011] In an embodiment, the flow control apparatus comprises a
first branch refrigerant line in refrigerant flow communication
with the economizer refrigerant line, a second branch refrigerant
line in refrigerant flow communication with the economizer
refrigerant line and disposed in parallel with the first branch
refrigerant line, and a check valve disposed in the first branch
refrigerant line and having a first position wherein refrigerant
may flow through the first branch refrigerant line and a second
position wherein refrigerant flow through the first branch
refrigerant line is blocked and refrigerant may flow through the
second branch refrigerant line.
[0012] The economizer may be a heat exchanger economizer or a flash
tank economizer. In an embodiment, the economizer comprises a
refrigerant-to-refrigerant heat exchanger including a first
refrigerant pass and a second refrigerant pass disposed in heat
exchange relationship with said first refrigerant pass. The first
refrigerant pass interdisposed in the primary refrigerant circuit
and the second refrigerant pass interdisposed in the economizer
refrigerant line. The economizer refrigerant line extends in fluid
communication from the primary refrigerant circuit through the
second refrigerant pass to an intermediate pressure stage of the
compression device. In this embodiment, an economizer expansion
device is interdisposed in the economizer refrigerant line upstream
with respect to refrigerant flow of the second refrigerant pass of
the refrigerant-to-refrigerant heat exchanger.
[0013] The invention may be equally applied to flash tank type
economized systems. In such systems, the control of the bypass flow
and economizer vapor flow is accomplished in a similar fashion by
controlling flow through the refrigerant economizer line. In such
an embodiment, the flash tank economizer is interdisposed in the
primary refrigerant circuit downstream, with respect to refrigerant
flow, of the refrigerant heat rejection heat exchanger and
upstream, with respect to refrigerant flow, of the primary
expansion device. The economizer refrigerant line extends in
refrigerant vapor flow communication from the flash tank economizer
to an intermediate pressure stage of the compression device and an
economizer expansion device is interdisposed in the primary
refrigerant circuit upstream with respect to refrigerant flow of
the flash tank economizer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a further understanding of the invention, reference will
be made to the following detailed description of the invention
which is to be read in connection with the accompanying drawing,
where:
[0015] FIG. 1 is a schematic diagram illustrating an exemplary
embodiment of a refrigerant vapor compression system in accord with
the invention; and
[0016] FIG. 2 is a schematic diagram illustrating another exemplary
embodiment of a refrigerant vapor compression system in accord with
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention will be described further herein with respect
to the exemplary embodiments of the refrigerant vapor compression
system 20 depicted in FIGS. 1-2. As in conventional systems, the
refrigerant vapor compression system 20 includes a compression
device 22, a heat rejection heat exchanger 24, an evaporator
expansion device 26, and an evaporator 28, interconnected by
various refrigerant lines 3, 5 and 7 in serial refrigerant flow
communication in a conventional refrigeration cycle in a primary
refrigerant circuit. The refrigerant vapor compression system 20 is
suitable for use in a transport refrigeration system for
refrigerating the air or other gaseous atmosphere within the
temperature-controlled cargo space of a truck, trailer, container
or the like for transporting perishable/frozen goods. The
refrigerant vapor compression system 20 is also suitable for use in
conditioning air to be supplied to a climate-controlled comfort
zone within a residence, office building, hospital, school,
restaurant or other facility. The refrigerant vapor compression
system 20 could also be employed in refrigerating air supplied to
display cases, merchandisers, freezer cabinets, cold rooms or other
perishable/frozen product storage areas in commercial
establishments.
[0018] The compression device 22 may comprise a single refrigerant
compressor having at least a first compression stage and a second
compression stage, such as, for example, a scroll compressor, such
as illustrated in FIG. 1, or a screw compressor having staged
compression pockets, or a reciprocating compressor having at least
a first bank and a second bank of cylinders, or a pair of
compressors 22A and 228 connected in series refrigerant flow
relationship as illustrated in FIG. 2, such as, for example, a pair
of scroll compressors, screw compressors, centrifugal compressors,
reciprocating compressors (or separate cylinders of a single
reciprocating compressor) or rotary compressors, with the discharge
outlet port of the upstream compressor connected in serial
refrigerant flow communication with the suction inlet port of the
downstream compressor.
[0019] In the compression device 22, refrigerant vapor is
compressed from a suction pressure at which the refrigerant vapor
enters the suction inlet port of the compression device 22 to a
discharge pressure, substantially higher than the suction pressure.
The hot, high pressure refrigerant vapor passes from the discharge
outlet port of the compression device 22 through refrigerant fine 3
of the primary refrigerant circuit to and through the heat
rejection heat exchanger 24. In the heat rejection heat exchanger
24, the hot, high pressure refrigerant passes in heat exchange
relationship with a cooling medium to cool and, in a subcritical
cycle, condense the refrigerant vapor. The heat rejection heat
exchanger 24 may comprise, for example, a finned tube heat
exchanger, such as for example a plate fin and round tube heat
exchanger or a fin and minichannel flat tube heat exchanger,
wherein the refrigerant passes through the heat exchanger tubes in
heat exchange relationship with ambient (typically outdoor) air
being drawn through the finned tube heat exchanger by an air mover,
such as one or more fans (not shown) operatively associated with
the heat rejection heat exchanger 24.
[0020] The refrigerant leaving the heat rejection heat exchanger 24
passes through refrigerant line 5 of the primary refrigerant
circuit to the evaporator 28. In doing so, the refrigerant
traverses the evaporator expansion device 26 interdisposed in
refrigerant line 5 and expands to a lower temperature, lower
pressure liquid refrigerant or more commonly a liquid/vapor
refrigerant mixture, before entering the evaporator 28. The
evaporator expansion device 26 may be a restriction type expansion
device, such as a capillary tube or a fixed plate orifice, a
thermostatic expansion valve or an electronic expansion valve. The
evaporator 28 constitutes a refrigerant heat absorbing heat
exchanger through which the liquid or liquid/vapor refrigerant
mixture passes in heat exchange relationship with a secondary fluid
to be cooled, and typically dehumidified, and delivered to a
conditioned environment. The refrigerant is heated thereby
evaporating the liquid component and typically superheating the
resultant vapor. The secondary fluid, typically air to be supplied
to a climate-controlled environment, in the conditioned, cooled and
typically dehumidified, state. In an embodiment, the evaporator 28
may comprise a finned tube heat exchanger through which refrigerant
passes in heat exchange relationship with air that may be drawn
from and returned to a climate-controlled environment by the one or
more fans (not shown) operatively associated with the evaporator
28. The finned tube heat exchanger may comprise, for example, a
plate fin and round tube heat exchanger or a fin and minichannel
flat tube heat exchanger. The refrigerant vapor leaving the
evaporator 28 passes through the refrigerant line 7 of the primary
refrigerant circuit to reenter the compression device 22 through
the suction inlet port of the compression device.
[0021] The refrigerant vapor compression system 20 further includes
an economizer circuit comprising an economizer refrigerant line 9,
an economizer heat exchanger 30 and an associated economizer
expansion device 32 interdisposed in the economizer refrigerant
line 9. The economizer heat exchanger 30 comprises a
refrigerant-to-refrigerant heat exchanger having a first
refrigerant pass 31 and a second refrigerant pass 33 disposed in
heat exchange relationship. The first refrigerant pass 31 is
interdisposed in refrigerant line 5 of the primary refrigerant
circuit downstream, with respect to refrigerant flow, of the heat
rejection heat exchanger 24 and upstream, with respect to
refrigerant flow, of the evaporator expansion device 26. The second
refrigerant pass 33 is interdisposed in the economizer refrigerant
line 9 downstream, with respect to refrigerant flow, of the
economizer expansion device 32. Refrigerant passing through the
refrigerant line 5 of the primary refrigerant circuit passes
through the first refrigerant pass 31 of the economizer heat
exchanger 30 in heat exchange relationship with a flow of
refrigerant tapped off the refrigerant line 5 into the economizer
refrigerant line 9 to pass through the second refrigerant pass 33
of the economizer heat exchanger 30.
[0022] The economizer refrigerant line 9 establishes refrigerant
flow communication between the refrigerant line 5 of the primary
refrigerant circuit and an intermediate pressure stage of the
compression process. The economizer refrigerant line 9 may tap a
portion of refrigerant from the refrigerant line 5 at a location
upstream with respect to refrigerant flow of the first refrigerant
pass 31 of the economizer heat exchanger 30, as depicted in FIG. 1,
or at a location downstream with respect to refrigerant flow of the
first refrigerant pass 31 of the economizer heat exchanger 30, as
depicted in FIG. 2. If the compression device 22 of the refrigerant
vapor compression system 20 is a single compressor, such as a
scroll compressor as illustrated in FIG. 1, the economizer
refrigerant line 9 communicates in refrigerant flow communication
via an injection port 25 that opens into an intermediate pressure
stage of the compression chambers of the compressor 22. If the
compression device 22 of the refrigerant vapor compression system
20 is a pair of compressors 22A and 22B, the economizer refrigerant
line 9 communicates in refrigerant flow communication with a
refrigerant line 11 connecting the outlet of the first compressor
22A with the inlet to the second compressor 22B as illustrated in
FIG. 2.
[0023] The refrigerant vapor compression system 20 also includes a
compressor unloading circuit comprising a bypass line 17, which
establishes refrigerant flow communication between the economizer
refrigerant, line 9 and the suction refrigerant line 7 of the
primary refrigerant circuit, and a flow control device such as
valve 50 interdisposed in the bypass line 17. The flow control
device 50 has at least a first open position and a second closed
position. In an embodiment, the flow control device may comprise a
two-position solenoid valve having a first open position and a
second closed position. At its inlet, the bypass line 17 taps into
the economizer refrigerant line 9 at a location downstream, with
respect to refrigerant flow, of the second refrigerant pass 33 of
the economizer heat exchanger 30 and upstream, with respect to
refrigerant flow, of the terminus of the economizer refrigerant
line 9 at an intermediate compression stage of the compression
device 22. At its outlet end, the refrigerant bypass line 17 taps
into the refrigerant suction line 7 of the primary refrigerant
circuit at a location downstream, with respect to refrigerant flow,
of the outlet of the evaporator 28 and upstream, with respect to
refrigerant flow, of the suction inlet port of the compression
device 22. In this manner, the bypass line 17 provides a
refrigerant flow path through which intermediate pressure
refrigerant may pass from an intermediate pressure stage in the
compression process into the primary refrigerant circuit, in a
region thereof where the refrigerant is at suction pressure, in
order to unload the compressor. As used in herein, the term
"downstream portion" with reference to the economizer refrigerant
line 9 refers to that part of the economizer refrigerant line 9
extending between the junction of the bypass line 17 with the
economizer refrigerant line 9 and the terminus of the economizer
refrigerant line 9 at an intermediate stage of the compression
device 22, and the term "upstream portion" with reference to the
economizer refrigerant line 9 refers to that part of the economizer
refrigerant line 9 extending between refrigerant line 5 of the
primary refrigerant circuit and the junction of the bypass line 17
with the economizer refrigerant line 9.
[0024] The refrigerant vapor compression system 20 further includes
a check valve 40 interdisposed in a downstream portion of the
economizer refrigerant line 9. The check, valve 40 has a first
position wherein the check valve opens to refrigerant vapor flow
through the downstream portion of the economizer refrigerant line 9
in a direction from an intermediate stage of the compression
process with the compression device 22, and a second position
wherein the check valve 40 restricts refrigerant flow through the
downstream portion of the economizer refrigerant line 9 in a
direction from the upstream portion of the economizer refrigerant
line 9 into an intermediate stage of the compression process within
the compression device 22.
[0025] Referring now to FIG. 1, in the exemplary embodiment of the
refrigerant vapor compression system 20 depicted therein, a flow
metering device 42 is disposed in parallel flow arrangement with
the check valve 40. For example, the flow metering device 42 and
the check valve 40 may be interdisposed respectively in parallel
branches 9a and 9b of the downstream portion of the economizer
refrigerant line 9 such as depicted in FIG. 1. In this embodiment,
when the refrigerant vapor compression system 20 is operating in an
economized mode without compressor unloading, the flow control
device 50 in the bypass line 17 is closed and the flow of
refrigerant from the upstream portion of the economizer refrigerant
line 9 into the downstream portion of the economizer refrigerant
line 9 sets the check valve 40 in branch line 9b in its second
position, which, in this embodiment, completely closes the check
valve. With the check valve 40 fully closed, refrigerant from the
economizer passes from the upstream portion of the refrigerant line
9 through the flow metering device 42 in the branch 9b of the
downstream portion of the economizer refrigerant line 9 to enter
into an intermediate pressure stage of the compression process of
the compression device 22. The flow metering device 42 may
comprise, but is not limited to, a fixed flow area orifice. For
example, in an embodiment, the flow metering function desired in
the economized mode of operation may be provided by an appropriate
sizing of the branch line 9a, whereby the branch line 9a itself
provides the desired flow restriction thereby eliminating the need
for a fixed area orifice or other form of flow metering device 42
in the branch line 9a.
[0026] However, when the refrigerant vapor compression system 20 is
operating with compressor unloading, the bypass flow control valve
50 in the bypass line 17 is open, whereby refrigerant vapor flows
from an intermediate stage of the compression process of the
compression device 22 through the branch 9a of the downstream
portion of the economizer refrigerant line 9, setting the check
valve 40 in its open position, and flowing into and through the
bypass line 17 and thence the refrigerant line 7 of the primary
refrigerant circuit to reenter the compression device 22 through
the suction inlet port thereof. If the refrigerant vapor
compression system 20 is operating in the economized mode when the
compressor is unloaded, the refrigerant passing through the
upstream portion of the economizer refrigerant line 9 passes into
the bypass 17 and also passes therethrough into refrigerant line 7
of the primary refrigerant circuit to reenter the compression
device 22 through the suction inlet port thereof.
[0027] Referring now to FIG. 2, in the exemplary embodiment of the
refrigerant vapor compression system 20 depicted therein, the check
valve 40 interdisposed in the downstream portion of the economizer
refrigerant line 9 has a first full open position and a second
partially open position. In this embodiment, when the refrigerant
vapor compression system 20 is operating in a economized mode
without compressor unloading, the flow control device 50 in the
bypass line 17 is closed and the flow of refrigerant from the
upstream portion of the economizer refrigerant line 9 into the
downstream portion of the economizer refrigerant line 9 sets the
check valve 40 in its second partially open position, which in this
embodiment meters the refrigerant flow passing therethrough into an
intermediate pressure stage of the compression process of the
compression device 22. However, in this embodiment, when the
refrigerant vapor compression system 20 is operating with
compressor unloading, the bypass flow control device 50 in the
bypass line 17 is open, whereby refrigerant vapor flows from an
intermediate stage of the compression process of the compression
device 22 through the downstream portion of the economizer
refrigerant line 9, setting the cheek valve 40 in its first fully
open position, and flowing into and through the bypass line 17 and
thence the refrigerant line 7 of the primary refrigerant circuit to
reenter the compression device 22 through the suction inlet port
thereof. Again, if the refrigerant vapor compression system 20 is
operating in the economized mode when the compressor is unloaded,
the refrigerant passing through the upstream portion of the
economizer refrigerant line 9 passes into the bypass line 17 and
also passes therethrough into the refrigerant line 7 of the primary
refrigerant circuit to reenter the compression device 22 through
the suction inlet port thereof.
[0028] In either embodiment of the invention, in the economized
mode of operation without bypass, the portion of the refrigerant
having traversed the second refrigerant pass 33 of the economizer
heat exchanger 30 flows through the economizer refrigerant line 9
to return to the compression device 22 at an intermediate pressure
state in the compression process. If the compression device is a
single refrigerant compressor 22, such as for example a scroll
compressor as illustrated in FIG. 1, or a screw compressor or a
multi-bank reciprocating compressor, the refrigerant from the
second refrigerant pass 33 of the economizer heat exchanger 30
enters the compressor 22 through at least one injection port
opening at an intermediate pressure state of compression process
within the compressor 22. If, as depicted in FIG. 2, the
compression device is a pair of compressors 20A and 20B connected
in series relationship, with respect to refrigerant flow, the
refrigerant having traversed the second refrigerant pass 33 of the
economizer heat exchanger 30 is injected into the refrigerant line
ii interconnecting the discharge outlet of the first stage
compressor 20A in refrigerant flow communication with the suction
inlet of the second stage compressor 20B.
[0029] The positioning of the bypass flow control device 50 may be
controlled by a controller 80 operatively associated with the
refrigerant vapor compression system 20. In an embodiment, the
controller 80 may constitute the main system controller and may
receive operating data regarding various system operating
parameters as in conventional practice, such as for purposes of
illustration but not limitation, the refrigerant temperature and/or
pressure at the compressor discharge, at the compressor suction
inlet, at the evaporator outlet, and other locations, as desired,
provided by appropriately disposed sensors (not shown). If the
primary expansion device 26 is an electronic expansion valve, the
controller 80 may also control the operation of the primary
expansion device in response to selected operating parameters.
Similarly, if the economizer expansion device 32 is an electronic
expansion valve, the controller 80 may also control the operation
of the economizer expansion device in response to selected
operating parameters.
[0030] In prior art refrigerant vapor compression systems using a
common portion of the economizer refrigerant line through which
refrigerant passes in a first direction into, an intermediate
pressure stage of the compression device from the economizer heat
exchanger, during an economized mode operation, but in a second
direction from an intermediate pressure stage of the compression
device to return to the suction inlet of the compression device,
during an unload mode of operation, the refrigerant line can not be
optimally sized for each of the flow control conditions. Typically,
the optimal flow area of a refrigerant line for unloading the
compression device is significantly larger, for example, by as much
an order of magnitude, than the optimal flow area of a refrigerant
line for injecting, refrigerant into an intermediate pressure stage
of the compression device.
[0031] However, in the refrigerant vapor compression system 20 of
the invention, a flow control apparatus is provided having a first
flow path through the economizer refrigerant line in a first
direction from the intermediate pressure stage of the compression
device to the bypass line and a second flow path through the
economizer refrigerant line in a second direction from the second
refrigerant pass of the refrigerant-to-refrigerant economizer heat
exchanger into the intermediate pressure stage of the compression
device. The first flow path has a first hydraulic resistance to
refrigerant flow through the first flow path and the second flow
path has a second hydraulic resistance to refrigerant flow through
the second flow path, with the first hydraulic resistance being
different from the second hydraulic resistance. In an embodiment,
the first hydraulic resistance is relatively lower and the second
hydraulic resistance is relatively higher. Therefore, the flow area
of each of these flow paths may be optimally sized for the
respective refrigerant vapor flows therethrough, which may improve
compressor efficiency by as much as 10%.
[0032] In the exemplary embodiment depicted in FIG. 1, in its open
position, the check valve 40 provides a relatively lower hydraulic
resistance to refrigerant flow through the branch refrigerant line
9b, while the flow restrictor 42 provides a relatively higher
hydraulic resistance to refrigerant flow through the branch
refrigerant line 9a. In the exemplary embodiment depicted in FIG.
2, The check valve 40 provides a relatively lower hydraulic
resistance to refrigerant flow through the economizer refrigerant
line 9 in the direction of flow from the intermediate pressure
stage of the compression device 22 to the bypass line 17 and
provides a relatively higher hydraulic resistance to refrigerant
flow through the economizer refrigerant line 9 in the direction of
flow from the economizer 30 into the port 25 opening into the
intermediate stage of the compression device 22.
[0033] The invention may be equally applied to flash tank type
economized systems. In such systems, the control of the bypass flow
and economizer vapor flow is accomplished in a similar fashion by
controlling flow through the refrigerant economizer line. In such
an embodiment, the flash tank economizer is interdisposed in the
primary refrigerant circuit downstream, with respect to refrigerant
flow, of the refrigerant, heat rejection heat exchanger and
upstream, with respect to refrigerant flow, of the primary
expansion device. The economizer refrigerant line extends in
refrigerant vapor flow communication from the flash tank economizer
to an intermediate pressure stage of the compression device and an
economizer expansion device is interdisposed in the primary
refrigerant circuit upstream, with respect to refrigerant flow, of
the flash tank economizer.
[0034] While the present invention has been particularly, shown and
described with reference to the exemplary embodiments as
illustrated in the drawings, it will be understood by one skilled
in the art that various changes in detail may be effected therein
without departing from the spirit and scope of the invention as
defined by the claims. For example, the check valve 40 of the FIG.
2 embodiment may be positioned externally or internally, in
relation to the shell of the compression device 22. Also, the check
valve 40 may be substituted by a solenoid valve that would be
controlled by the controller 80.
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