U.S. patent application number 13/258180 was filed with the patent office on 2012-01-19 for refrigerant vapor compression system with hot gas bypass.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Yu H. Chen, Suresh Duraisamy, Daqing Li, Alexander Lifson, Lucy Yi Liu, Biswajit Mitra, Jason Scarcella.
Application Number | 20120011866 13/258180 |
Document ID | / |
Family ID | 42936838 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120011866 |
Kind Code |
A1 |
Scarcella; Jason ; et
al. |
January 19, 2012 |
REFRIGERANT VAPOR COMPRESSION SYSTEM WITH HOT GAS BYPASS
Abstract
A refrigerant vapor compression system includes a hot gas bypass
line establishing refrigerant vapor flow communication between the
compression device and the refrigerant heat absorption heat
exchanger, and bypassing the refrigerant heat rejection heat
exchanger and the primary expansion device. A refrigerant vapor
flow control device is interdisposed in the hot gas bypass line.
The flow control device has at least a first open position in which
refrigerant vapor flow may pass through the hot gas bypass line and
a closed position in which refrigerant vapor flow may not pass
through the hot gas bypass line.
Inventors: |
Scarcella; Jason; (Cicero,
NY) ; Lifson; Alexander; (Manlius, NY) ; Li;
Daqing; (Manlius, NY) ; Mitra; Biswajit;
(Huntersville, NC) ; Liu; Lucy Yi; (Fayetteville,
NY) ; Duraisamy; Suresh; (Liverpool, NY) ;
Chen; Yu H.; (Manlius, NY) |
Assignee: |
Carrier Corporation
Farmington
CT
|
Family ID: |
42936838 |
Appl. No.: |
13/258180 |
Filed: |
April 6, 2010 |
PCT Filed: |
April 6, 2010 |
PCT NO: |
PCT/US10/30025 |
371 Date: |
September 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61167972 |
Apr 9, 2009 |
|
|
|
Current U.S.
Class: |
62/79 ; 62/498;
62/80 |
Current CPC
Class: |
F25B 41/39 20210101;
B60H 1/3228 20190501; F25B 41/00 20130101; F25B 2600/2501 20130101;
F25B 2700/1933 20130101; F25B 41/22 20210101; F25B 2600/2509
20130101; F25B 2400/23 20130101; F25B 2700/1931 20130101; F25B
31/008 20130101; F25B 2400/0411 20130101; F25B 2700/21151 20130101;
F25B 2400/0403 20130101; F25B 2700/21152 20130101; F25B 2400/13
20130101; F25B 1/10 20130101 |
Class at
Publication: |
62/79 ; 62/498;
62/80 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F25D 21/00 20060101 F25D021/00; F25B 29/00 20060101
F25B029/00 |
Claims
1. A refrigerant vapor compression system comprising: a primary
refrigerant circuit including a refrigerant compression device, a
refrigerant heat rejection heat exchanger downstream of said
compression device, a refrigerant heat absorption heat exchanger
downstream of said refrigerant heat rejection heat exchanger, and a
primary expansion device disposed in the refrigerant circuit
downstream of said refrigerant heat rejection heat exchanger and
upstream of said refrigerant heat absorption heat exchanger; a hot
gas bypass line establishing refrigerant vapor flow communication
between a location upstream with respect to refrigerant vapor flow
of said refrigerant heat rejection heat exchanger and a location
upstream with respect to refrigerant flow of said refrigeration
heat absorption heat exchanger and downstream of said primary
expansion device, said hot gas bypass line bypassing said
refrigerant heat rejection heat exchanger and said primary
expansion device; and a refrigerant vapor flow control device
interdisposed in said hot gas bypass line, said refrigerant flow
control device having at least a first open position in which
refrigerant vapor flow may pass through said hot gas bypass line
and a closed position in which refrigerant vapor flow may not pass
through said hot gas bypass line.
2. The refrigerant vapor compression system as recited in claim 1
wherein the hot gas bypass line opens into a mid-stage of the
compression device to receive refrigerant vapor from the
compression device at an intermediate pressure between a
compression device suction pressure and a compression device
discharge pressure.
3. The refrigerant vapor compression system as recited in claim 1
wherein the hot gas bypass line opens into the primary refrigerant
circuit at a location between an inlet to the refrigerant heat
rejection heat exchanger and a refrigerant vapor discharge outlet
of the compression device to receive refrigerant vapor at a
compression discharge pressure.
4. The refrigerant vapor compression system as recited in claim 1
wherein said refrigerant flow control device comprises a solenoid
valve.
5. The refrigerant vapor compression system as recited in claim 1
wherein said refrigerant flow control device comprises an expansion
valve.
6. The refrigerant vapor compression system as recited in claim 1
further comprising a suction modulation valve interdisposed in said
refrigerant circuit downstream of said refrigerant heat absorption
heat exchanger and upstream of the compression device.
7. The refrigerant vapor compression system as recited in claim 1
wherein said system operates in a transcritical cycle.
8. The refrigerant vapor compression system as recited in claim 1
wherein the refrigerant comprises carbon dioxide.
9. The refrigerant vapor compression system as recited in claim 1
wherein the hot gas bypass line opens into a mid-stage located
between a first independent compression stage and a second
independent compression stage.
10. The refrigerant vapor compression system as recited in claim 1
further comprising a controller for modulating said refrigerant
vapor flow control device to selectively vary the opening of a flow
passage through said refrigeration vapor flow control device when
operating said refrigerant vapor compression system in one of a
heating mode or a defrost mode.
11. The refrigerant vapor compression system as recited in claim 10
wherein said controller modulates said refrigerant vapor flow
control device to selectively vary the opening of a flow passage
through said refrigeration vapor flow control device in response to
a sensed compressor discharge refrigerant temperature.
12. A method for controlling the capacity of a refrigerant vapor
compression system operating in one of a heating mode and a defrost
mode, the refrigerant vapor compression system including a
refrigerant circuit having a compression device, a refrigerant heat
rejection heat exchanger, and a refrigerant heat absorption heat
exchanger disposed in serial refrigerant flow relationship, said
method comprising the steps of: bypassing refrigerant vapor through
a bypass line from a location upstream of the refrigerant heat
rejection heat exchanger directly to the refrigerant heat
absorption heat exchanger; disposing a refrigerant vapor flow
control device in the bypass line; disposing a suction modulation
valve in a refrigerant line connecting a refrigerant outlet of the
refrigerant heat absorption heat exchanger in refrigerant flow
communication with a suction inlet of the compression device;
selectively modulating the flow of refrigerant vapor through the
refrigerant flow control device; and selectively modulating the
flow of refrigerant through the suction modulation valve.
13. The method as recited in claim 12 further comprising the steps
of: sensing a compressor discharge refrigerant pressure;
selectively modulating the flow of refrigerant vapor through the
refrigerant flow control device in response to the sensed
compressor discharged refrigerant pressure; and selectively
modulating the flow of refrigerant through the suction modulation
valve to control refrigerant mass flow.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Reference is made to and this application claims priority
from and the benefit of U.S. Provisional Application Ser. No.
61/167,972, filed Apr. 9, 2009, entitled "REFRIGERANT VAPOR
COMPRESSION SYSTEM WITH HOT GAS BYPASS", which application is
incorporated herein in its entirety by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to refrigerant vapor
compression systems and, more particularly, to bypassing hot
refrigerant gas around the gas cooler in a refrigerant vapor
compression system operating in a transcritical cycle.
BACKGROUND OF THE INVENTION
[0003] Refrigerant vapor compression systems are well known in the
art and commonly used for conditioning air to be supplied to a
climate controlled comfort zone within a residence, office
building, hospital, school, restaurant or other facility.
Refrigerant vapor compression system are also commonly used in
refrigerating air supplied to display cases, merchandisers, freezer
cabinets, cold rooms or other perishable/frozen product storage
areas in commercial establishments.
[0004] Refrigerant vapor compression systems are also commonly used
in transport refrigeration systems for refrigerating air supplied
to a temperature controlled cargo space of a truck, trailer,
container or the like for transporting perishable/frozen items by
truck, rail, ship or intermodal. Refrigerant vapor compression
systems used in connection with transport refrigeration systems are
generally subject to more stringent operating conditions due to the
wide range of operating load conditions and the wide range of
outdoor ambient conditions over which the refrigerant vapor
compression system must operate to maintain product within the
cargo space at a desired temperature. The desired temperature at
which the cargo needs to be controlled can also vary over a wide
range depending on the nature of cargo to be preserved. The
refrigerant vapor compression system must not only have sufficient
capacity to rapidly pull down the temperature of product loaded
into the cargo space at ambient temperature, but also operate
efficiently at low load when maintaining a stable product
temperature during transport.
[0005] Traditionally, conventional refrigerant vapor compression
systems commonly operate at subcritical refrigerant pressures and
typically include a compressor, a condenser, and an evaporator, and
expansion device, commonly an expansion valve, disposed upstream,
with respect to refrigerant flow, of the evaporator and downstream
of the condenser. These basic refrigerant system components are
interconnected by refrigerant lines in a closed refrigerant
circuit, arranged in accord with known refrigerant vapor
compression cycles, and operated in the subcritical pressure range
for the particular refrigerant in use. Refrigerant vapor
compression systems operating in the subcritical range are commonly
charged with fluorocarbon refrigerants such as, but not limited to,
hydrochlorofluorocarbons (HCFCs), such as R22, and more commonly
hydrofluorocarbons (HFCs), such as R134a, R410A, R404A and
R407C.
[0006] In today's market, greater interest is being shown in
"natural" refrigerants, such as carbon dioxide, for use in air
conditioning and transport refrigeration systems instead of HFC
refrigerants. However, because carbon dioxide has a low critical
temperature, most refrigerant vapor compression systems charged
with carbon dioxide as the refrigerant are designed for operation
in the transcritical pressure regime. In refrigerant vapor
compression systems operating in a subcritical cycle, both the
condenser and the evaporator heat exchangers operate at refrigerant
temperatures and pressures below the refrigerant's critical point.
However, in refrigerant vapor compression systems operating in a
transcritical cycle, the heat rejection heat exchanger, which is a
gas cooler rather than a condenser, operates at a refrigerant
temperature and pressure in excess of the refrigerant's critical
point, while the evaporator operates at a refrigerant temperature
and pressure in the subcritical range. Thus, for a refrigerant
vapor compression system operating in a transcritical cycle, the
difference between the refrigerant pressure within the gas cooler
and refrigerant pressure within the evaporator is
characteristically substantially greater than the difference
between the refrigerant pressure within the condenser and the
refrigerant pressure within the evaporator for a refrigerant vapor
compression system operating in a subcritical cycle.
[0007] It is also common practice to incorporate an economizer into
the refrigerant circuit for increasing the capacity of the
refrigerant vapor compression system. In some transcritical cycle
systems, a flash tank economizer is incorporated into the
refrigerant circuit between the condenser and the evaporator. In
such case, the refrigerant leaving the condenser is expanded
through an expansion device, such as a thermostatic expansion valve
or an electronic expansion valve, prior to entering the flash tank
wherein the expanded refrigerant separates into a liquid
refrigerant component and a vapor refrigerant component. The vapor
component of the refrigerant is thence directed from the flash tank
into an intermediate pressure stage of the compression process. The
liquid component of the refrigerant is directed from the flash tank
through the system's main expansion valve prior to entering the
evaporator. U.S. Pat. No. 6,385,980 discloses a transcritical
refrigerant vapor compression system incorporating a flash tank
economizer in the refrigerant circuit between the gas cooler and
the evaporator.
[0008] The refrigerant coils of the evaporator in a transcritical
cycle transport refrigeration, as in any subcritical cycle
transport refrigeration system are subject, depending upon
operating conditions, to frost formation and frost build-up from
moisture in the air circulating from the cargo box and passing over
the refrigerant coils. Thus, it is common practice to provide
electric resistance heaters in operative association with the
refrigerant coils that are periodically operated to melt frost from
the refrigerant coils. The electric resistance heaters can also be
employed to heat the circulating air when it is desired to raise
the air temperature within the cargo box to prevent over cooling of
the cargo. However, electric resistance heaters increase the
consumption of power, the availability of which is often limited.
Electric resistance heaters and related components are also
expensive and raise the initial cost and operating cost of the
refrigeration unit.
[0009] U.S. Pat. No. 7,028,494 discloses a heat pump water heating
system operating in a transcritical cycle wherein to defrost the
evaporator, refrigerant from the discharge of the compressor
bypasses the gas cooler, passes through the evaporator expansion
device, and thence through the evaporator to melt frost off the
external surface of the evaporator.
SUMMARY OF THE INVENTION
[0010] In an aspect of the invention, a refrigerant vapor
compression system includes: a primary refrigerant circuit
including a refrigerant compression device, a refrigerant heat
rejection heat exchanger downstream of the compression device, a
refrigerant heat absorption heat exchanger downstream of the
refrigerant heat rejection heat exchanger, and a primary expansion
device. The primary expansion device is interdisposed in the
refrigerant circuit downstream of said refrigerant heat rejection
heat exchanger and upstream of the refrigerant heat absorption heat
exchanger. A hot gas bypass line establishes refrigerant vapor flow
communication between the compression device and the refrigerant
heat absorption heat exchanger. The hot gas bypass line bypasses
the refrigerant heat rejection heat exchanger and the primary
expansion device. A refrigerant vapor flow control device is
interdisposed in the hot gas bypass line. The refrigerant flow
control device has at least a first open position in which
refrigerant vapor flow may pass through the hot gas bypass line and
a closed position in which refrigerant vapor flow may not pass
through the hot gas bypass line. A suction modulation valve may be
interdisposed in the primary refrigerant circuit downstream of said
refrigerant heat absorption heat exchanger and upstream of the
compression device.
[0011] In an embodiment, the refrigerant flow control device
comprises a solenoid valve. In an embodiment, the hot gas bypass
line opens from the mid-stage of the compression device to receive
refrigerant vapor from the compression device at an intermediate
pressure between a compression device suction pressure and a
compression device discharge pressure. In an embodiment, the hot
gas bypass line opens from the primary refrigerant circuit at a
location between an inlet to the refrigerant heat rejection heat
exchanger and a refrigerant vapor discharge outlet of the
compression device to receive refrigerant vapor at a compression
discharge pressure.
[0012] In an aspect of the invention, a method is provided for
controlling the capacity of a refrigerant vapor compression system
operating in one of a heating mode and a defrost mode, the
refrigerant vapor compression system including a refrigerant
circuit having a compression device, a refrigerant heat rejection
heat exchanger, and a refrigerant heat absorption heat exchanger
disposed in serial refrigerant flow relationship. The method
includes the steps of: bypassing refrigerant vapor through a bypass
line from a location upstream of the refrigerant heat rejection
heat exchanger directly to the refrigerant heat absorption heat
exchanger; disposing a refrigerant vapor flow control device in the
bypass line; disposing a suction modulation valve in a refrigerant
line connecting a refrigerant outlet of the refrigerant heat
absorption heat exchanger in refrigerant flow communication with a
suction inlet of the compression device; selectively modulating the
flow of refrigerant vapor through the refrigerant flow control
device; and selectively modulating the flow of refrigerant through
the suction modulation valve. The method may also include the steps
of: sensing a compressor discharge refrigerant pressure;
selectively modulating the flow of refrigerant vapor through the
refrigerant flow control device in response to the sensed
compressor discharged refrigerant pressure; and selectively
modulating the flow of refrigerant through the suction modulation
valve to control refrigerant mass flow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a further understanding of the disclosure, reference
will be made to the following detailed description which is to be
read in connection with the accompanying drawing, where:
[0014] FIG. 1 is a schematic diagram illustrating an exemplary
embodiment of a refrigerant vapor compression system in accord with
the invention; and
[0015] FIG. 2 is a graph illustrating the variation of refrigerant
pressure with enthalpy over the compression cycle.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Referring now to FIG. 1, there are depicted therein
exemplary embodiments of a refrigerant vapor compression system 10
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 10 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 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.
[0017] The refrigerant vapor compression system 10 is particularly
adapted for operation in a transcritical cycle with a low critical
temperature refrigerant, such as for example, but not limited to,
carbon dioxide. However, it is to be understood that the
refrigerant vapor compression system 10 may also be operated in a
subcritical cycle with a higher critical temperature refrigerant
such as conventional hydrochlorofluorocarbon and hydrofluorocarbon
refrigerants. The refrigerant vapor compression system 10 includes
a multi-step compression device 20, a refrigerant heat rejecting
heat exchanger 40, a refrigerant heat absorbing heat exchanger 50,
also referred to herein as an evaporator, and a primary expansion
valve 55, such as for example an electronic expansion valve or a
thermostatic expansion valve, operatively associated with the
evaporator 50, with refrigerant lines 2, 4 and 6 connecting the
aforementioned components in a primary refrigerant circuit as
illustrated in FIG. 1. A suction modulation valve (SMV) 23 may be
interdisposed in refrigerant line 6 intermediate the outlet of the
evaporator 50 and the suction inlet to the compression device 20.
In the exemplary embodiments depicted in drawings, the suction
modulation valve 23 is positioned in refrigerant line 6 between the
outlet of the evaporator 50 and the point at which the compressor
unload bypass line 16 intersects refrigerant line 6.
[0018] In a refrigerant vapor compression system operating in a
transcritical cycle, the refrigerant heat rejecting heat exchanger
40 constitutes a gas cooler through which supercritical refrigerant
passes in heat exchange relationship with a cooling medium, such as
for example, but not limited to ambient air or water, and may be
also be referred to herein as a gas cooler. In the depicted
embodiments, the refrigerant heat rejecting heat exchanger 40
includes a finned tube heat exchanger 42, such as for example a fin
and round tube heat exchange coil or a fin and mini-channel flat
tube heat exchanger, through which the refrigerant passes in heat
exchange relationship with ambient air or other cooling media being
drawn through the finned tube heat exchanger 42 by the fan(s) 44
associated with the gas cooler 40. The transcritical cycle
refrigerant vapor compression system may optionally include a water
cooled condenser 46 disposed in refrigerant line 4 downstream with
respect to refrigerant flow of the gas cooler 40, such as depicted
in FIG. 1. In such case, the high pressure refrigerant gas having
traversed the gas cooler 40 passes through the water cooled
condenser 46, wherein the refrigerant gas is further cooled as it
passes in heat exchange relationship with cooling water 48 to
further cool the refrigerant gas and, depending upon operating
conditions, a portion of the refrigerant gas to a refrigerant
liquid may be condensed.
[0019] The refrigerant heat absorption heat exchanger 50 serves an
evaporator wherein refrigerant liquid is passed in heat exchange
relationship with a fluid to be cooled, most commonly air, drawn
from and to be returned to a temperature controlled environment
200, such as the cargo box of a refrigerated transport truck,
trailer or container, or a display case, merchandiser, freezer
cabinet, cold room or other perishable/frozen product storage area
in a commercial establishment, or to a climate controlled comfort
zone within a residence, office building, hospital, school,
restaurant or other facility. In the depicted embodiments, the
refrigerant heat absorbing heat exchanger 50 comprises a finned
tube heat exchanger 52 through which refrigerant passes in heat
exchange relationship with air drawn from and returned to the
refrigerated cargo box 200 by the evaporator fan(s) 54 associated
with the evaporator 50. The finned tube heat exchanger 52 may
comprise, for example, a fin and round tube heat exchange coil or a
fin and mini-channel flat tube heat exchanger.
[0020] The compression device 20 functions to compress the
refrigerant and to circulate refrigerant through the primary
refrigerant circuit as will be discussed in further detail
hereinafter. The compression device 20 may comprise a single
multiple stage refrigerant compressor, such as for example a screw
compressor or a reciprocating compressor, disposed in the primary
refrigerant circuit and having a first compression stage 20a and a
second compression stage 20b. The first and second compression
stages are disposed in series refrigerant flow relationship with
the refrigerant leaving the first compression stage passing
directly to the second compression stage for further compression.
Also, the compression device 20 may comprise a single compression
device, such as a scroll compressor, having a compression chamber
having one or more ports opening directly into the compression
chamber at an intermediate pressure stage of the compression
chamber through which refrigerant may be injected into or withdrawn
from the compression chamber. Alternatively, the compression device
20 may comprise a pair of independent compressors 20a and 20b,
connected in series refrigerant flow relationship in the primary
refrigerant circuit via a refrigerant line connecting the discharge
outlet port of the first compressor 20a in refrigerant flow
communication with the suction inlet port of the second compressor
20b. In the independent compressor embodiment, the compressors 20a
and 20b may be scroll compressors, screw compressors, reciprocating
compressors, rotary compressors or any other type of compressor or
a combination of any such compressors.
[0021] Additionally, the transcritical cycle refrigerant vapor
compression system 10 includes a flash tank economizer 70
interdisposed in refrigerant line 4 of the primary refrigerant
circuit upstream with respect to refrigerant flow of the evaporator
50 and downstream with respect to refrigerant flow of the gas
cooler 40 and, if present, downstream of the condenser 46. A
secondary expansion device 65 is interdisposed in refrigerant line
4 in operative association with and upstream of the flash tank
economizer 70. The secondary expansion device 65 may be an
electronic expansion valve, such as depicted in FIG. 1, or a fixed
orifice expansion device. Refrigerant traversing the secondary
expansion device 65 is expanded to a lower pressure sufficient to
establish a mixture of refrigerant in a vapor state and refrigerant
in a liquid state. The flash tank economizer 70 defines a
separation chamber 72 wherein refrigerant in the liquid state
collects in a lower portion of the separation chamber and
refrigerant in the vapor state collects in the portion of the
separation chamber 72 above the liquid refrigerant. The flash tank
economizer 70 also functions as a refrigerant charge tank with the
separation chamber providing a reservoir for collecting excess
refrigerant.
[0022] Liquid refrigerant collecting in the lower portion of the
flash tank economizer 70 passes therefrom through refrigerant line
4 and traverses the primary expansion valve 55, which is
interdisposed in refrigerant line 4 upstream with respect to
refrigerant flow of the evaporator 50. As this liquid refrigerant
traverses the primary expansion device 55, it expands to a lower
pressure and temperature before entering enters the evaporator 50.
The evaporator 50 constitutes a refrigerant evaporating heat
exchanger through which expanded refrigerant passes in heat
exchange relationship with the air to be cooled, whereby the
refrigerant is vaporized and typically superheated. As in
conventional practice, the primary expansion valve 55 meters the
refrigerant flow through the refrigerant line 4 to maintain a
desired level of superheat in the refrigerant vapor leaving the
evaporator 50 to ensure that no liquid is present in the
refrigerant leaving the evaporator. The low pressure refrigerant
vapor leaving the evaporator 50 returns through refrigerant line 6
to the suction port of the first compression stage or first
compressor 20a of the compression device 20.
[0023] The refrigerant vapor compression system 10 may also include
a refrigerant vapor injection line 14 and a refrigerant liquid
injection line 18. The refrigerant vapor injection line 14
establishes refrigerant flow communication between an upper portion
of the separation chamber 72 of the flash tank economizer 70 and an
intermediate stage of the compression process through branch 14a
and a suction pressure portion of the refrigerant circuit through
branch 14b. The refrigerant liquid injection line 18 establishes
refrigerant flow communication between a lower portion of the
separation chamber 72 of the flash tank 70, typically by tapping
refrigerant line 4 downstream of the flash tank 70 and upstream of
the primary expansion valve 55, and discharging into an
intermediate stage of the compression process through a portion of
branch 14 b of refrigerant vapor injection line 14 and thence
branch 14a of refrigerant vapor injection line 14. In an alternate
embodiment, the refrigerant liquid injection line 18 may open
directly into and discharge into refrigerant line 6 of the primary
refrigerant circuit at a location downstream with respect to
refrigerant flow of the suction modulation valve 23 and upstream
with respect to refrigerant flow of the suction inlet to the first
compressor 20a.
[0024] In the depicted exemplary embodiments of the transcritical
cycle refrigerant vapor compression system 10, injection of
refrigerant vapor or refrigeration liquid into the intermediate
pressure stage of the compression process would be accomplished by
injection of the refrigerant vapor or refrigerant liquid into the
refrigerant passing from the first compression stage 20a into the
second compression stage 20b of a single compressor or passing from
the discharge outlet of the first compressor 20a to the suction
inlet of the second compressor 20b. If the compression device 20 of
the refrigerant vapor compression system 10 were a single scroll
compressor, injection of refrigerant vapor or refrigerant liquid
into the intermediate pressure stage of the compression process
would be accomplished by injection of the refrigerant vapor or the
refrigerant liquid through a port opening into the intermediate
pressure port of the compression chamber of the scroll
compressor.
[0025] The refrigerant vapor compression system 10 may also include
a compressor unload bypass line, which in the depicted embodiment
is made up of refrigerant branch lines 14a and 14b, that
establishes refrigerant flow communication via flow control device
83, between an intermediate pressure stage of the compression
device 20 and the suction pressure portion of the refrigerant
circuit, which as noted previously constitutes refrigerant line 6
extending between the outlet of the evaporator 50 and the suction
inlet of the compression device 20. The refrigerant vapor
compression system 10 may also include an economizer vapor
injection bypass line 14b that establishes refrigerant flow
communication between the refrigerant vapor injection line 14, from
a location downstream with respect to refrigerant flow of the flash
tank 70 and upstream with respect to refrigerant flow of the
injection site to intermediate pressure stage of the compression
device 20, and the suction pressure portion of refrigerant line 6
of the refrigerant circuit.
[0026] The refrigerant vapor compression system 10 may, as depicted
in FIG. 1, include a control system operatively associated with the
compression device and other components of the system, including
but not limited to the fans 44 and 54. In an embodiment of the
refrigerant vapor compression system 10, the control system
includes a controller 100 and a plurality of flow control devices
operatively associated with the various refrigerant lines. In
operation, the controller 100 selectively controls the positioning
of each of the plurality of flow control devices between its
respective open and closed positions to selectively direct
refrigerant flow through the various refrigerant lines.
[0027] The flow control devices, in addition to the suction
modulation valve 23, may include, without limitation, a first flow
control device 73 interdisposed in a downstream portion of
refrigerant vapor injection line 14, a second flow control device
53 interdisposed in an upstream portion of refrigerant liquid
injection line 18, and a third flow control device 83 interdisposed
in refrigerant branch line 14b. Each of the aforementioned flow
control devices 53, 73, 83 may comprise a flow control valve
selectively positionable between an open position wherein
refrigerant flow may pass through the refrigerant line in which the
flow control valve is interdisposed and a closed position wherein
refrigerant flow is blocked through the refrigerant line in which
the flow control valve is interdisposed. In an embodiment, each of
the flow control valves 53, 73, 83 comprises a two-position
solenoid valve of the type positionable selectively positionable
under the control of the controller 100 between a first open
position and a second closed position. In an embodiment, the
suction modulation flow control valve 23 comprises a flow control
valve having at least one partially open position between a fully
closed position and a fully open position, such as for example an
electronic stepper valve or a pulse width modulated solenoid
valve.
[0028] The controller 100 not only controls operation of the
various flow control valves 23, 53, 73, 83 to selectively direct
refrigerant flow through the respective refrigerant lines in which
the valves are interdisposed, but also may control operation of the
electronic expansion valves 55 and 65, the compression device 20,
and the fans 44 and 54. As in conventional practice, in addition to
monitoring ambient conditions, the controller 100 may also monitor
various operating parameters by means of various sensors
operatively associated with the controller 100 and disposed at
selected locations throughout the system. For example, in the
exemplary embodiments depicted in FIG. 1, a pressure sensor 102 is
disposed in operative association with the flash tank 70 to sense
the pressure within the flash tank 70, a temperature sensor 103 and
a pressure sensor 104 are provided to sense the refrigerant suction
temperature and pressure, respectively, and a temperature sensor
105 and a pressure sensor 106 are provided to sense refrigerant
discharge temperature and pressure, respectively. The pressure
sensors 102, 104, 106 may be conventional pressure sensors, such as
for example, pressure transducers, and the temperature sensors 103
and 105 may be conventional temperature sensors, such as for
example, thermocouples or thermistors.
[0029] The refrigerant vapor compression system 10 may include
either a mid-stage hot gas bypass line 24 or a discharge hot gas
bypass line 26 or both. The mid-stage hot gas byline 24 establishes
refrigerant flow communication between an intermediate pressure
compression stage of the compression device 20 and refrigerant line
4 of the primary refrigerant circuit downstream of the flash tank
70. In the exemplary embodiment depicted in FIG. 1, the mid-stage
hot gas bypass line 24 opens into the compression device 20 at a
point between the refrigerant outlet of the first compression stage
20a and the refrigerant inlet to the second compression stage 20b
to receive intermediate pressure, hot refrigerant vapor and opens
into refrigerant line 4 of the primary refrigerant circuit at a
location upstream of the evaporator 50 and downstream with respect
to refrigerant flow through refrigerant line 4 of the primary
expansion device 55 to discharge the intermediate pressure, hot gas
into refrigerant line 4 upstream of the refrigerant coil 52 of the
evaporator.
[0030] Additionally, a flow control device 87 is interdisposed into
the mid-stage hot gas bypass line 24. The flow control device 87 is
operated by the controller 100 to selectively open the mid-stage
hot gas bypass line 24 to refrigerant vapor flow therethrough when
it is desired to operate the refrigerant vapor compression system
10 in a defrost mode and close the mid-stage hot gas bypass line 24
to refrigerant vapor flow therethrough whenever the refrigerant
vapor compression system 10 is not operating in a defrost mode. In
an embodiment, the flow control device 87 may comprise a solenoid
valve that is selectively positionable in either a fully open
position or a fully closed position or, in addition thereto, at
least one partially open position between a fully closed position
and a fully open position, such as for example an electronic
stepper valve or a pulse width modulated solenoid valve. When the
flow control device 87 is positioned in the open position,
refrigerant vapor will flow from the compression device 20 through
the mid-stage hot gas bypass line 24 directly to and through the
evaporator coil 52 to melt any frost deposited on the external
surface of the refrigeration coil 52. In the defrost mode, the
controller 100 will turn the power to the evaporator fan(s) 54 off
to stop the circulation of air from the cargo box 200 through the
evaporator 50 to eliminate an unintended rise in air temperature
within the cargo box 200.
[0031] The hot gas bypass line 26 establishes refrigerant flow
communication between a discharge outlet of the second compression
stage 20b of the compression device 20 and refrigerant line 4 of
the primary refrigerant circuit downstream of the flash tank 70. In
the exemplary embodiment depicted in FIG. 1, the hot gas bypass
line 26 opens into the refrigerant line 2 of the primary
refrigerant circuit at a point between the refrigerant inlet to the
gas cooler 40 and the refrigerant vapor discharge outlet of the
second compression stage 20b to receive high pressure, hot
refrigerant vapor and opens into refrigerant line 4 of the primary
refrigerant circuit at a location upstream of the evaporator 50 and
downstream with respect to refrigerant flow through refrigerant
line 4 of the primary expansion device 55 to discharge the hot gas
into refrigerant line 4 upstream of the refrigerant coil 52 of the
evaporator.
[0032] Additionally, a flow control device 85 is interdisposed into
the hot gas bypass line 26. In the embodiment depicted in FIG. 1,
the flow control device 85 is a open/closed flow control device
operated by the controller 100 to selectively open the hot gas
bypass line 26 to refrigerant vapor flow therethrough when it is
desired to operate the refrigerant vapor compression system 10 in a
defrost mode and close the hot gas bypass line 26 to refrigerant
vapor flow therethrough whenever the refrigerant vapor compression
system 10 is not operating in a defrost mode. In this embodiment,
the flow control device 85 may comprise a solenoid valve that is
selectively positionable in either a fully open position or a fully
closed position or, in addition thereto, at least one partially
open position between a fully closed position and a fully open
position, such as for example an electronic stepper valve or a
pulse width modulated solenoid valve. When the flow control device
85 is positioned in the open position, refrigerant vapor will flow
from the compression device 20 through the hot gas bypass line 26
directly to and through the evaporator coil 52 to melt any frost
deposited on the external surface of the refrigeration coil 52. In
the defrost mode, the controller 100 will turn the power to the
evaporator fan(s) 54 off to stop the circulation of air from the
cargo box 200 through the evaporator 50 to eliminate an unintended
rise in air temperature within the cargo box 200.
[0033] Whenever it is necessary to defrost the evaporator heat
exchange surface, the controller 100 will close each of the valves
53, 73, 83 as well as the electronic expansion valves 55 and 65,
and either open the flow control valve 87 to permit the flow of
high pressure, hot refrigerant vapor from the discharge outlet of
the compression device 20 to flow through the hot gas bypass line
24 into and through the evaporator coil 52, or open the mid-stage
flow control valve 85 to permit the flow of intermediate pressure,
intermediate temperature hot refrigerant vapor from an intermediate
pressure stage of the compression device 20 to flow through the
mid-stage hot gas bypass line 26 into and through the evaporator
coil 52. As the refrigerant vapor passes through the refrigerant
passages of the evaporator 50, the frost formed on the evaporator
heat exchange surface is melted. In the defrost mode, the
controller 100 will also turn the power to the evaporator fan(s) 54
off to stop the circulation of air from the cargo box 200 through
the evaporator 50 to eliminate an unintended rise in air
temperature within the cargo box 200.
[0034] Additionally, whenever it is desired to heat the air
returning from the cargo box 200, for example in the event of an
ambient outdoor temperature that is lower than the desired cargo
box air temperature to be maintained, the controller 100 will close
each of the valves 53, 73, 83 as well as the electronic expansion
valves 55 and 65, and either open the flow control valve 87 to
permit the flow of high pressure, hot refrigerant vapor from the
discharge outlet of the compression device 20 to flow through the
hot gas bypass line 24 into and through the evaporator coil 52, or
open the mid-stage flow control valve 85 to permit the flow of
intermediate pressure, intermediate temperature hot refrigerant
vapor from an intermediate pressure stage of the compression device
20 to flow through the mid-stage hot gas bypass line 26 into and
through the evaporator coil 52. In the heating mode, however, the
evaporator fan(s) 54 remain in operation to circulate air from the
cargo box 200 through the evaporator 50 in heat exchange
relationship with the hot refrigerant vapor passing through the
evaporator coil 52. Thus, as the hot refrigerant vapor passes
through the refrigerant passages of the evaporator 50, the air
returning from the cargo space 200 is heated and supplied by the
evaporator fan 54 back to the cargo space 200.
[0035] In an embodiment, one or both of the refrigerant flow
control devices 85 disposed in the hot gas bypass line 26 and the
refrigerant flow control device 87 disposed in the mid-stage hot
gas bypass line 24 may be an electronic expansion valve. In this
embodiment, the heating capacity of a refrigeration system during
operation in a heating or defrosting mode may be relatively
precisely controlled by regulating the hot gas bypass valve
downstream of the compressor along with modulating the suction
modulation valve upstream of the compressor. In this embodiment,
during the heating mode and also during the defrost mode, the
controller 100 will close each of the valves 53, 73, 83 as well as
the electronic expansion valves 55 and 65, and then modulate the
opening of the expansion valve 85, 87 and also modulate the opening
of the of the suction modulation valve 23, to control the heating
capacity of the refrigerant vapor compression system 10. As noted
previously, the pressure and temperature of the hot refrigerant
vapor decrease as it traverses the expansion valve 85, 87. The
pressure of the refrigerant vapor leaving the evaporator coil 52 is
further reduced to a desired suction pressure as the refrigerant
flow is throttled in traversing the suction modulation valve 23
disposed in refrigerant line 6. The magnitude of each pressure drop
may be independently controlled by modulating the opening of the
respective one of the expansion valve 85 or the suction modulation
valve 23. In a method of practice, the degree of opening of the
expansion valve 85, 87 is modulated in response to the sensed
compressor discharged refrigerant pressure to control the
compressor discharge refrigerant pressure and the degree of opening
of the SMV 23 is modulated to control refrigerant mass flow.
[0036] If heating or defrosting capacity needs to be increased, the
controller 100 will increase the opening of the expansion valve 85,
87 to raise the pressure and temperature of the refrigerant vapor
passing through the evaporator coil 52 and also further reduce the
opening of the suction modulation valve 23 to provide greater
throttling, as necessary, to keep the pressure of the refrigerant
vapor entering the compression device 20 from the refrigerant line
6 at the desired suction pressure. Conversely, if heating or
defrosting capacity needs to be decreased, the controller 100 will
decrease the opening of the expansion valve 85, 87 to lower the
pressure and temperature of the refrigerant vapor passing through
the evaporator coil 52 and also further increase the opening of the
suction modulation valve 23 to provide lesser throttling, as
necessary, to keep the pressure of the refrigerant vapor entering
the compression device 20 from the refrigerant line 6 at the
desired suction pressure.
[0037] With the valves 53, 73, 83, as well as the electronic
expansion valves 55 and 65, being closed, the compressor discharge
pressure is determined by the amount of charge in the active part
of the system 10, that is the amount of refrigerant passing through
the evaporator 50 during the heating mode or the defrost mode.
Referring now to FIG. 2, a pressure-to-enthalpy diagram is depicted
for a transport refrigeration system operating in a transcritical
cycle with carbon dioxide as the refrigerant. The refrigerant vapor
enters the compression device 20 at point a, and discharges from
the compression device as a hot, high pressure vapor at point b.
After traversing the hot gas expansion valve 85, refrigeration
vapor pressure lowers to point c and the refrigerant vapor enters
evaporator 50. At the exit of evaporator 50, refrigerant state is
at point d before throttling down to point a by SMV. If heating or
defrosting capacity need to be increased, the controller 100 will
open up the expansion valve 85 to raise evaporating pressure from
cd to c'd'. Thus, since refrigerant temperature increases with
higher pressure, this results in a higher temperature difference
between refrigerant and air. Therefore, higher heating capacity can
be expected. If heating or defrosting capacity need to be
decreased, the controller 100 will reduce the opening through the
expansion valve to decrease evaporating pressure from cd to c''d''.
Thus, since refrigerant temperature is decreased with lower
pressure, this results in a lower temperature difference between
refrigerant and air. Therefore, lower heating or defrosting
capacity can be expected. The heating or defrosting capacity can
hence be modified such that the point d (d' or d'') is at the
optimal point away from the dome (i.e., in the vapor region, with a
desired superheat range).
[0038] In the exemplary embodiment of the refrigerant vapor
compression system 10 described and depicted herein, the system
includes both a mid-stage pressure hot gas bypass line 24 and a
discharge pressure hot gas bypass line 26. It is to be understood,
that the system may be operated in the heating mode or defrost mode
selectively with only the mid-stage pressure hot gas bypass line 24
open, or with only the discharge pressure hot gas bypass line 26
open, or with both hot gas bypass lines 24 and 26 open
simultaneously, as desired. Further, it is to be understood that in
other embodiments, the refrigerant vapor compression system 10 may
include only one of the hot gas bypass lines 24 and 26, as desired,
rather than both hot gas bypass lines.
[0039] As noted previously, when operating in the heating mode or
the defrost mode, typically, each of the flow control valves 53,
73, 83 and the expansion valves 55 and 65 is closed and system
capacity is controlled by modulating whichever of valves 85 and 87
that is then active. However, it is to be understood that in some
instances it may be desirable to adjust the refrigerant charge
circulating through the active part of the system by selectively
opening one of the flow control valve 53 or the expansion valve 65.
For example, during operation in the heating or defrost mode, if
the refrigerant temperature at the discharge outlet of the
compression device 20, i.e. the compressor discharge temperature,
exceeds a preselected upper limit temperature, then the controller
100 may open the flow control valve 53 in the refrigerant liquid
injection line 18 to allow refrigerant liquid to drain from the
reservoir 72 of the flash tank 70 back into the primary refrigerant
circuit, thereby increasing the amount of refrigerant charge in the
active portion of the primary refrigerant circuit. As another
example, during operation in the heating or defrost mode, if the
refrigerant pressure at the discharge outlet of the compression
device 20, i.e. the compressor discharge pressure, is still too
high in spite of the opening of the controller 100 whichever of
valves 85 and 87 that is then active, then the controller 100 may
open the expansion valve 65 to allow refrigerant to pass from
refrigerant line 4 of the primary refrigerant circuit into the
flash tank 70 to collect in the reservoir 72, thereby reducing the
amount of refrigerant charge in the active portion of the primary
refrigerant circuit.
[0040] Those skilled in the art will recognize that many variations
may be made to the particular exemplary embodiments described
herein. For example, the refrigerant vapor compression system may
also be operated in a subcritical cycle, rather than in a
transcritical cycle as described hereinbefore. 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.
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