U.S. patent application number 13/498680 was filed with the patent office on 2012-09-13 for parameter control in transport refrigeration system and methods for same.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Suresh Duraisamy, Gilbert B. Hofsdal, Hans-Joachim Huff, Lucy Yi Liu.
Application Number | 20120227427 13/498680 |
Document ID | / |
Family ID | 43431805 |
Filed Date | 2012-09-13 |
United States Patent
Application |
20120227427 |
Kind Code |
A1 |
Liu; Lucy Yi ; et
al. |
September 13, 2012 |
PARAMETER CONTROL IN TRANSPORT REFRIGERATION SYSTEM AND METHODS FOR
SAME
Abstract
Embodiments of transport refrigeration systems, apparatus,
and/or methods for the same can provide exemplary verification for
operating characteristics thereof. In one embodiment, a calculated
compressor mid stage pressure can be verified using a prescribed
relationship to other transport refrigeration system
characteristics.
Inventors: |
Liu; Lucy Yi; (Fayetteville,
NY) ; Duraisamy; Suresh; (Liverpool, NY) ;
Hofsdal; Gilbert B.; (Chittenango, NY) ; Huff;
Hans-Joachim; (Mainz, DE) |
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
43431805 |
Appl. No.: |
13/498680 |
Filed: |
October 12, 2010 |
PCT Filed: |
October 12, 2010 |
PCT NO: |
PCT/US10/52267 |
371 Date: |
March 28, 2012 |
Current U.S.
Class: |
62/115 ;
62/190 |
Current CPC
Class: |
F25B 2309/061 20130101;
F25B 2500/19 20130101; F25B 2700/21152 20130101; F25B 2600/0261
20130101; F25B 2700/21163 20130101; F25B 49/005 20130101; F25B
2700/21172 20130101; F25B 2400/13 20130101; F25B 2600/2509
20130101; F25B 2700/2102 20130101; F25B 2700/21151 20130101; F25B
41/043 20130101; F25B 2341/0662 20130101; F25B 31/008 20130101;
F25B 1/10 20130101; F25B 2700/1933 20130101; F25B 2700/21173
20130101; F25B 2600/2513 20130101; F25B 9/008 20130101; F25B 49/02
20130101; F25B 2700/1931 20130101; F25B 2400/23 20130101 |
Class at
Publication: |
62/115 ;
62/190 |
International
Class: |
F25B 49/02 20060101
F25B049/02; F25B 1/00 20060101 F25B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2009 |
US |
61254280 |
Claims
1. A refrigerant vapor compression system comprising: a refrigerant
compression device to include a first compression stage and a
second compression stage; 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; a first expansion device disposed
downstream of said refrigerant heat rejection heat exchanger and
upstream of said refrigerant heat absorption heat exchanger; a
sensor coupled to an output of the heat rejection heat exchanger,
the sensor to measure a refrigerant temperature; and a controller
to control operations of the refrigeration vapor compression
system, said controller operative to indirectly verify the measured
refrigerant temperature.
2. The refrigerant vapor compression system of claim 1, where the
refrigerant temperatures at the output of the heat rejection heat
exchanger is first determined by measurement using the sensor,
wherein the refrigerant temperature is second determined by
calculation using ambient temperature and vapor pressure system
capacity.
3. The refrigerant vapor compression system of claim 2, where a
vapor compression system capacity has a prescribed relationship
with an operating mode or difference between supply air temperature
and return air temperature; and wherein an offset is added to the
ambient temperature responsive to the vapor compression system
capacity.
4. The refrigerant vapor compression system of claim 3, the
controller to operate the vapor compression system with the
calculated value for the refrigerant temperature when the measured
refrigerant temperature is different from the calculated
temperature value.
5. The vapor compression system of claim 1, where said sensor is a
pressure sensor or a temperature sensor.
6. The refrigerant vapor compression system of claim 1, comprising
a second sensor to measure a compressor mid stage pressure, said
controller to indirectly verify said measured compressor mid stage
pressure.
7. The refrigerant vapor compression system of claim 6, where the
compressor mid stage pressure is calculated using a discharge
pressure and an inlet pressure of the compressor.
8. The refrigerant vapor compression system of claim 7, wherein the
controller to operate the vapor compression system using the
verified value of the compressor mid stage pressure where the
measured compressor mid stage pressure does not match the
indirectly verified value.
9. The refrigerant vapor compression system of claim 8, comprising:
a second valve disposed downstream of the heat rejection heat
exchanger; and an economizer circuit disposed downstream of the
second valve and upstream of the first expansion device, the
economizer circuit including a refrigerant injection line to open
to an intermediate pressure stage of the compression device and a
flow control valve disposed in the refrigerant injection line.
10. The refrigerant vapor compression system of claim 9, said
controller to close the flow control valve when the compressor
mid-stage pressure is operative to cause refrigerant flow toward
the economizer circuit.
11. The refrigerant vapor compression system of claim 1,
comprising: a flash tank economizer disposed in serial flow
relationship between the heat rejection heat exchanger and the
first expansion device, said flash tank economizer including: a
flash tank; a first flow control device disposed between the heat
rejection heat exchanger and said flash tank; an economizer vapor
line to fluidly interconnect said flash tank to a mid-stage of the
compressor; and a second flow control device disposed in said
economizer vapor line.
12. A method for determining a characteristic of a refrigerant
vapor compression system having a 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, a sensor to sense a characteristic used
to determine a system capacity of the refrigerant vapor compression
system during operation, and interconnecting refrigerant lines as
active components, the method comprising: operating the refrigerant
vapor compression system in a mode where the refrigerant is
circulating within the active components of the refrigerant
circuit; indirectly determining said characteristic used to
determine the system capacity; comparing the sensed value of said
characteristic used to determine the system capacity against said
indirectly determined value of said characteristic; and determining
an error condition of a corresponding sensor when a result of the
comparison does not match.
13. The method of claim 12, comprising subsequently using the
indirectly determined value in operating the vapor compression
system.
14. The method of claim 13, wherein said characteristic to
determine system capacity is a refrigerant temperature at an output
of the heat rejection heat exchanger.
15. A computer program product comprising a computer usable storage
medium to store a computer readable program that, when executed on
a computer, causes the computer to perform operations to operate a
transport refrigeration unit, the operations comprising: operating
the transport refrigeration unit in a mode where a refrigerant is
circulating within a refrigerant circuit; sensing a characteristic
used to determine a system capacity of the transport refrigeration
unit during operation; indirectly determining said characteristic
used to determine the system capacity; comparing the sensed value
of the said characteristic used to determine the system capacity
against said indirectly determined value; and determining an error
condition of a corresponding sensor when a result of the comparison
does not match.
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.
61/254,280, filed Oct. 23, 2009, and entitled PARAMETER CONTROL IN
TRANSPORT REFRIGERATION SYSTEM AND METHODS FOR SAME, which
application is incorporated herein in its entirety by
reference.
TECHNICAL FIELD
[0002] This invention relates generally to transport refrigeration
systems and methods for same and, more particularly, to methods and
apparatus for controlling vapor compression systems.
BACKGROUND OF THE INVENTION
[0003] A particular difficulty of transporting perishable items is
that such items must be maintained within a temperature range to
reduce or prevent, depending on the items, spoilage or conversely
damage from freezing. A transport refrigeration unit is used to
maintain proper temperatures within a transport cargo space. The
transport refrigeration unit can be under the direction of a
controller. The controller ensures that the transport refrigeration
unit maintains a certain environment (e.g. thermal environment)
within the transport cargo space. The controller can operate a
transport refrigeration system and/or components thereof responsive
to sensors disposed in the system.
[0004] A vapor compression system can include a compressor, a heat
rejection heat exchanger (e.g., condenser or gas cooler), an
expansion device, and an evaporator. Economizer cycles are
sometimes employed to increase the efficiency and/or capacity of
the system. Economizer cycles operate by expanding the refrigerant
leaving the heat rejecting heat exchanger to an intermediate
pressure and separating the refrigerant flow into two streams. One
stream is sent to the heat absorbing heat exchanger, and the other
is sent to cool the flow between two compression stages. In one
form of an economizer cycle, a flash tank is used to perform the
separation. In an economizer cycle with flash tank, a refrigerant
discharged from the gas cooler passes through a first expansion
device, and its pressure is reduced. Refrigerant collects in the
flash tank as part liquid and part vapor. The vapor refrigerant is
used to cool refrigerant exhaust as it exits a first compression
device, and the liquid refrigerant is further expanded by a second
expansion device before entering the evaporator. Such a flash tank
economizer is particularly useful when operating in transcritical
conditions, such as are required when carbon dioxide is used as the
working fluid.
[0005] Due to the thermophysical properties of CO.sub.2, the
refrigeration system can operate in both the subcritical and
transcritical modes. The subcritical mode is similar to the
operation of systems with conventional refrigerants. In the
transcritical mode the refrigerant pressure in the heat rejection
heat exchanger, and possibly in the flash tank, is above the
critical pressure, while the evaporator operates as in the
subcritical mode.
DISCLOSURE OF THE INVENTION
[0006] In view of the background, it is an aspect of the
application to provide a transport refrigeration system, transport
refrigeration unit, and methods of operating the same that can
maintain cargo quality by selectively controlling transport
refrigeration system components.
[0007] One embodiment according to the application can include a
control module for a transport refrigeration system. The control
module includes a controller for controlling the transport
refrigeration system to selectively verify operations of components
thereof.
[0008] In accordance with one aspect of the invention, operations
of components of a transport refrigeration system can be directly
measured (e.g., sensors) and/or indirectly verified (e.g., without
sensors).
[0009] In accordance with one aspect of the invention, an
economizer includes a control for controlling operations of the
economizer responsive to pressure in a compressor.
[0010] In accordance with an aspect of the application, there is
provided a refrigerant vapor compression system that can include a
refrigerant compression device to include a first compression stage
and a second compression stage, 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, a first expansion device disposed
downstream of the refrigerant heat rejection heat exchanger and
upstream of the refrigerant heat absorption heat exchanger, a
sensor coupled to an output of the heat rejection heat exchanger,
the sensor to measure a refrigerant temperature, and a controller
to control operation of the refrigeration vapor compression system,
the controller operative to indirectly verify the measured
refrigerant temperature.
[0011] In accordance with an aspect of the application, there is
provided a computer program product comprising a computer usable
storage medium to store a computer readable program that, when
executed on a computer, causes the computer to perform operations
to operate a transport refrigeration unit, the operations that can
include operating the transport refrigeration unit in a mode where
a refrigerant is circulating within a refrigerant circuit, sensing
a characteristic used to determine a system capacity of the
transport refrigeration unit during operation, indirectly
determining the characteristic used to determine the system
capacity, comparing the sensed value of the characteristic used to
determine the system capacity against the indirectly determined
value, and determining an error condition of a corresponding sensor
when a result of the comparison does not match.
[0012] In accordance with an aspect of the application, there is
provided a method for determining a characteristic of a refrigerant
vapor compression system having a 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, a sensor to sense a characteristic used
to determine a system capacity of the refrigerant vapor compression
system and interconnecting refrigerant lines as active components,
the method that can include operating the refrigerant vapor
compression system in a mode where the refrigerant is circulating
within the active components of the refrigerant circuit, indirectly
determining the characteristic used to determine the system
capacity, comparing the sensed value of the characteristic used to
determine the system capacity against the indirectly determined
value of the characteristic, and determining an error condition of
a corresponding sensor when a result of the comparison does not
match.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a diagram that shows an embodiment of a transport
refrigeration system according to the application;
[0014] FIG. 2 is a diagram that shows another embodiment of a
transport refrigeration system according to the application;
[0015] FIG. 3 is a schematic illustration of an embodiment of a
vapor compression system according to the application;
[0016] FIG. 4 is a diagram graphically showing exemplary
refrigerant temperature exiting a heat rejection heat exchanger as
a function of system capacity;
[0017] FIG. 5 is a diagram graphically showing exemplary compressor
mid-stage pressure as a function of compressor discharge pressure
for various compressor suction pressures according to embodiments
of the application; and
[0018] FIG. 6 is a flow diagram showing an embodiment of a method
for operating a transport refrigeration system according to the
application.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0019] Reference will now be made in detail to exemplary
embodiments of the application, examples of which are illustrated
in the accompanying drawings. Whenever possible, the same reference
numerals will be used throughout the drawings to refer to the same
or like parts.
[0020] FIG. 1 is a diagram that shows an embodiment of a transport
refrigeration system. As shown in FIG. 1, transport refrigeration
system 100 can include a transport refrigeration unit 10 coupled to
an enclosed space within a container 12. The transport
refrigeration system 100 may be of the type commonly employed on
refrigerated trailers. As shown in FIG. 1, the transport
refrigeration unit 10 is configured to maintain a prescribed
thermal environment within the container 12 (e.g., cargo in an
enclosed volume).
[0021] In FIG. 1, the transport refrigeration unit 10 is connected
at one end of the container 12. Alternatively, the transport
refrigeration unit 10 can be coupled to a prescribed position on a
side or more than one side of the container 12. In one embodiment,
a plurality of transport refrigeration units can be coupled to a
single container 12. Alternatively, a single transport
refrigeration unit 10 can be coupled to a plurality of containers
12 or multiple enclosed spaces within a single container. The
transport refrigeration unit 10 can operate to induct air at a
first temperature and to exhaust air at a second temperature. In
one embodiment, the exhaust air from the transport refrigeration
unit 10 will be warmer than the inducted air such that the
transport refrigeration unit 10 is employed to warm the air in the
container 12. In one embodiment, the exhaust air from the transport
refrigeration unit 10 will be cooler than the inducted air such
that the transport refrigeration unit 10 is employed to cool the
air in the container 12. The transport refrigeration unit 10 can
induct air from the container 12 having a return temperature Tr
(e.g., first temperature) and exhaust air to the container 12
having a supply temperature Ts (e.g., second temperature).
[0022] In one embodiment, the transport refrigeration unit 10 can
include one or more temperature sensors to continuously or
repeatedly monitor the return temperature Tr and/or the supply
temperature Ts. As shown in FIG. 1, a first temperature sensor 24
of the transport refrigeration unit 10 can provide the supply
temperature Ts and a second temperature sensor 22 of the transport
refrigeration unit 10 can provide the return temperature Tr to the
transport refrigeration unit 10, respectively. Alternatively, the
supply temperature Ts and the return temperature Tr can be
determined using remote sensors.
[0023] A transport refrigeration system 100 can provide air with
controlled temperature, humidity or/and species concentration into
an enclosed chamber where cargo is stored such as in container 12.
As known to one skilled in the art, the transport refrigeration
system 100 (e.g., controller 250) is capable of controlling a
plurality of the environmental parameters or all the environmental
parameters within corresponding ranges with a great deal of variety
of cargos and under all types of ambient conditions.
[0024] FIG. 2 is a diagram that shows an embodiment of a transport
refrigeration system. As shown in FIG. 2, a transport refrigeration
system 200 can include a transport refrigeration unit 210 coupled
to a container 212, which can be used with a trailer, an intermodal
container, a train railcar, a ship or the like, used for the
transportation or storage of goods requiring a temperature
controlled environment, such as, for example foodstuffs and
medicines (e.g., perishable or frozen). The container 212 can
include an enclosed volume 214 for the transport/storage of such
goods. The enclosed volume 214 may be an enclosed space having an
interior atmosphere isolated from the outside (e.g., ambient
atmosphere or conditions) of the container 212.
[0025] The transport refrigeration unit 210 is located so as to
maintain the temperature of the enclosed volume 214 of the
container 212 within a predefined temperature range. In one
embodiment, the transport refrigeration unit 210 can include a
compressor 218, a condenser heat exchanger unit 222, a condenser
fan 224, an evaporation heat exchanger unit 226, an evaporation fan
228, and a controller 250. Alternatively, the condenser 222 can be
implemented as a gas cooler.
[0026] The compressor 218 can be powered by single phase electric
power, three phase electrical power, and/or a diesel engine and
can, for example, operate at a constant speed. The compressor 218
may be a scroll compressor, a rotary compressor, a reciprocal
compressor, or the like. The transport refrigeration system 200
requires electrical power from, and can be connected to a power
supply unit (not shown) such as a standard commercial power
service, an external power generation system (e.g., shipboard), a
generator (e.g., diesel generator), or the like.
[0027] The condenser heat exchanger unit 222 can be operatively
coupled to a discharge port of the compressor 218. The evaporator
heat exchanger unit 226 can be operatively coupled to an input port
of the compressor 218. An expansion valve 230 can be connected
between an output of the condenser heat exchanger unit 222 and an
input of the evaporator heat exchanger unit 226.
[0028] The condenser fan 224 can be positioned to direct an air
stream onto the condenser heat exchanger unit 222. The air stream
from the condenser fan 224 can allow heat to be removed from the
coolant circulating within the condenser heat exchanger unit
222.
[0029] The evaporator fan 228 can be positioned to direct an air
stream onto the evaporation heat exchanger unit 226. The evaporator
fan 228 can be located and ducted so as to circulate the air
contained within the enclosed volume 214 of the container 212. In
one embodiment, the evaporator fan 230 can direct the stream of air
across the surface of the evaporator heat exchanger unit 226. Heat
can thereby be removed from the air, and the reduced temperature
air can be circulated within the enclosed volume 214 of the
container 212 to lower the temperature of the enclosed volume
214.
[0030] The controller 250 such as, for example, a MicroLink.TM. 2i
or Advanced controller, can be electrically connected to the
compressor 218, the condenser fan 224, and/or the evaporator fan
228. The controller 250 can be configured to operate the transport
refrigeration unit 210 to maintain a predetermined environment
(e.g., thermal environment) within the enclosed volume 214 of the
container 212. The controller 250 can maintain the predetermined
environment by selectively controlling operations of the condenser
fan 224, and/or the evaporator fan 228 to operate at a low speed or
a high speed. For example, if increased cooling of the enclosed
volume 214 is required, the controller 250 can increase electrical
power to the compressor 218, the condenser fan 224, and the
evaporator fan 228. In one embodiment, an economy mode of operation
of the transport refrigeration unit 210 can be controlled by the
controller 250. In another embodiment, variable speeds of
components of the transport refrigeration unit 210 can be adjusted
by the controller 250. In another embodiment, a full cooling mode
for components of the transport refrigeration unit 210 can be
controlled by the controller 250. In one embodiment, the electronic
controller 250 can adjust a flow of coolant supplied to the
compressor 218.
[0031] FIG. 3 is a diagram that shows an embodiment of a vapor
compression system according to the application. As shown in FIG.
3, an exemplary embodiment of a refrigerant vapor compression
system 300 designed for operation in a transcritical cycle with a
low critical point refrigerant, such as for example, but not
limited to, carbon dioxide and refrigerant mixtures containing
carbon dioxide. However, it is to be understood that the
refrigerant vapor compression system 300 may also be operated in a
subcritical cycle with a higher critical point refrigerant such as
conventional hydrochlorofluorocarbon and hydrofluorocarbon
refrigerants.
[0032] The refrigerant vapor compression system 300 is particularly
suitable for use in a transport refrigeration system for
refrigerating the air or other gaseous atmosphere within the
temperature controlled enclosed volume 214 such as a cargo space of
a truck, trailer, container, or the like for transporting
perishable/frozen goods. The refrigerant vapor compression system
300 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.
[0033] The refrigerant vapor compression system 300 includes a
multi-stage compression device 320, a refrigerant heat rejection
heat exchanger 330, a refrigerant heat absorption heat exchanger
350, also referred to herein as an evaporator, and a primary
expansion valve 355, such as for example an electronic expansion
valve as depicted in FIG. 3, operatively associated with the
evaporators 350, with refrigerant lines 302, 304, and 306
connecting the aforementioned components in a primary refrigerant
circuit. As depicted in FIG. 3, the refrigerant vapor compression
system 300 may also include an unload bypass line 316 that
establishes refrigerant flow communication between an intermediate
pressure stage of the multi-stage compression device 320 and the
suction pressure portion of the refrigerant circuit, which
constitutes refrigerant line 306 extending from the outlet of the
evaporator 350 to the inlet of the compression device 320.
[0034] Additionally, the refrigerant vapor compression system 300
can include an economizer circuit having an economizer device 340,
a secondary expansion valve 345 and a refrigerant vapor injection
line 314. As shown in FIG. 3, the economizer circuit includes a
flash tank economizer 340 interdisposed in refrigerant line 304 of
the primary refrigerant circuit downstream with respect to
refrigerant flow of the refrigerant heat rejection heat exchanger
330 and upstream with respect to refrigerant flow of the
refrigerant heat absorption heat exchanger 350. The secondary
expansion device 345 is interdisposed in refrigerant line 304 in
operative association with and upstream of the economizer The
secondary expansion device 345 may be an expansion valve, such as a
high pressure electronic expansion valve as depicted in FIG. 3.
Refrigerant traversing the secondary expansion device 345 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 340 includes a separation chamber 342 wherein
refrigerant in the liquid state collects in a lower portion of the
separation chamber 342 and refrigerant in the vapor state collects
in the portion of the separation chamber 342 above the liquid
refrigerant.
[0035] The refrigerant vapor injection line 314 establishes
refrigerant flow communication between an upper portion of the
separation chamber 342 of the flash tank economizer 340 and an
intermediate stage of the compression process. A vapor injection
flow control device 343 is interdisposed in vapor injection line
314. The vapor injection flow control device 343 may comprise a
flow control valve selectively positionable between an open
position where refrigerant vapor flow may pass through the
refrigerant vapor injection line 314 and a closed position where
refrigerant vapor flow through the refrigerant vapor injection line
314 is reduced or blocked. In one embodiment, the vapor injection
flow control valve 343 comprises a two-position solenoid valve of
the type selectively positionable between a first open position and
a second closed position.
[0036] The refrigeration vapor compression system 300 can also
include an optional variable flow device (VFD) or a suction
modulation valve (SMV) 323 interdisposed in refrigerant line 306 at
a location between the outlet of the refrigeration heat absorption
heat exchanger 350 and an inlet to the compression device 320. In
the exemplary embodiment depicted in FIG. 3, the suction modulation
valve 323 is positioned in refrigerant line 306 between the outlet
of the evaporator 350 and the point at which the compressor unload
bypass line 316 intersects refrigerant line 306. In one embodiment,
the suction modulation valve 323 may comprise a pulse width
modulated solenoid valve.
[0037] In a refrigerant vapor compression system operating in a
transcritical cycle, the refrigerant heat rejection heat exchanger
330 constitutes a gas (refrigerant vapor) cooler through which
supercritical refrigerant passes in heat exchange relationship with
a cooling medium, such as for example, but not limited to ambient
gas or liquid (e.g., air or water), and may be also referred to
herein as a gas cooler. In a refrigerant vapor compression system
operating in a subcritical cycle, the refrigerant heat rejection
heat exchanger 330 can constitute a refrigerant condensing heat
exchanger through which hot, high pressure refrigerant vapor passes
in heat exchange relationship with the cooling medium and is
condensed to a liquid. As shown in FIG. 3, the refrigerant heat
rejection heat exchanger 330 includes a finned tube heat exchanger
332, 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
being drawn through the finned tube heat exchanger 332 by the
fan(s) 334 associated with an exemplary gas cooler 330.
[0038] Whether the refrigerant vapor compression system 300 is
operating in a transcritical cycle or a subcritical cycle, the
refrigerant heat absorption heat exchanger 350 serves an evaporator
wherein refrigerant liquid or a mixture of refrigerant liquid and
vapor 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, such as a 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. As shown in FIG. 3 the refrigerant heat absorption heat
exchanger 350 comprises a finned tube heat exchanger 352 through
which refrigerant passes in heat exchange relationship with air
drawn from and returned to the refrigerated container 212 by the
evaporator fan(s) 354 associated with the evaporator 350. The
finned tube heat exchanger 352 may comprise, for example, a fin and
round tube heat exchange coil or a fin and mini-channel flat tube
heat exchanger.
[0039] The compression device 320 functions to compress the
refrigerant and to circulate refrigerant through the primary
refrigerant circuit as described in detail herein. In the
embodiment depicted in FIG. 3, the compression device 320 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 320a and a second compression stage 320b. The
first and second compression stages are disposed in series
refrigerant flow relationship with the refrigerant leaving the
first compression stage 320a passing directly to the second
compression stage 320b for further compression. Alternatively, the
compression device 320 may comprise a pair of independent
compressors 320a and 320b, connected in series refrigerant flow
relationship in the primary refrigerant circuit via a refrigerant
line connecting the discharge outlet port of the first compressor
320a in refrigerant flow communication with an inlet port (e.g. the
suction inlet port) of the second compressor 320b. In the
independent compressor embodiment, the compressors 320a and 320b
may be scroll compressors, screw compressors, reciprocating
compressors, rotary compressors or any other type of compressor or
a combination of any such compressors. In the embodiment depicted
in FIG. 3, the refrigerant vapor compression system 300 includes a
refrigerant bypass line 316 providing a refrigerant flow passage
from an intermediate pressure stage of the compression device 320
back to the suction side of the compression device 320. An unload
valve 327 is interdisposed in the bypass line 316. The unload valve
327 may be selectively positioned in an open position in which
refrigerant flow passes through the bypass line 316 and a closed
position in which refrigerant flow through the bypass line 316 is
reduced or blocked.
[0040] In the embodiment depicted in FIG. 3, the refrigerant vapor
compression system 300 further includes a refrigerant liquid
injection line 318. The refrigerant liquid injection line 318 can
tap into refrigerant line 304 at location downstream of the flash
tank economizer 340 and upstream of the primary expansion valve 355
and open into an intermediate stage of the compression process.
Thus, the refrigerant liquid injection line 318 can establish
refrigerant flow communication between a lower portion of the
separation chamber 342 of the flash tank economizer 340 and an
intermediate pressure stage of the compression device 320. In one
embodiment, the refrigerant liquid injection line 318 can establish
refrigerant flow communication between a lower portion of the
separation chamber 342 of the flash tank economizer 340 and a
compressor suction line (e.g., an inlet to the compression device).
A liquid injection flow control device 353 can be interdisposed in
refrigerant liquid injection line 318. The liquid injection flow
control device 353 may comprise a flow control valve selectively
positionable between an open position wherein refrigerant liquid
flow may pass through the liquid injection line 318 and a closed
position wherein refrigerant liquid flow through the refrigerant
liquid injection line 318 is reduced or blocked. In an embodiment,
the liquid injection flow control device 353 comprises a
two-position solenoid valve of the type selectively positionable
between a first open position and a second closed position.
[0041] In the exemplary embodiment of the refrigerant vapor
compression system 300 depicted in FIG. 3, 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 320a into the second
compression stage 320b of the compression device 320.
[0042] Liquid refrigerant collecting in the lower portion of the
flash tank economizer 340 can pass therefrom through refrigerant
line 304 and traverse the primary refrigerant circuit expansion
valve 355 interdisposed in refrigerant line 304 upstream with
respect to refrigerant flow of the evaporator 350. As this liquid
refrigerant traverses the first expansion device 355, it expands to
a lower pressure and temperature before entering the evaporator
350. The evaporator 350 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 355 meters the
refrigerant flow through the refrigerant line 304 to maintain a
desired level of superheat in the refrigerant vapor leaving the
evaporator 350 to ensure that no liquid is present in the
refrigerant leaving the evaporator. The low pressure refrigerant
vapor leaving the evaporator 350 returns through refrigerant line
306 to the input port of the first compression stage or first
compressor 320a of the compression device 320 in the embodiment
depicted in FIG. 3.
[0043] The refrigerant vapor compression system 300 also includes a
control system operatively associated therewith for controlling
operation of the refrigerant vapor compression system 300. The
control system can include a controller 390 that can determine the
desired mode of operation in which to operate the refrigerant vapor
compression system 300 based upon consideration of refrigeration
load requirements, ambient conditions and various sensed system
operating parameters. As shown in FIG. 3, the controller 390 also
includes various sensors operatively associated with the controller
390 and disposed at selected locations throughout the system for
monitoring various operating parameters by use of various sensors
operatively associated with the controller. The control system may
include, by way of example but not limitation, a pressure sensor
392 disposed in operative association with the flash tank
economizer 340 to sense the pressure within the separation chamber
342, a temperature sensor 393 and a pressure sensor 394 for sensing
the refrigerant inlet or suction temperature and pressure,
respectively, and a temperature sensor 395 and a pressure sensor
396 for sensing refrigerant discharge temperature and pressure,
respectively. In transport refrigeration applications, the
refrigeration vapor compression system may also include a
temperature sensor 397a for sensing the temperature of the air
returning to the evaporator from the container 212 and a
temperature sensor 397b for sensing a temperature of the air being
supplied to the container 212. Sensors (not shown) may also be
provided for monitoring ambient outdoor conditions, such as or
example ambient outdoor air temperature and humidity. By way of
example but not limitation; the pressure sensors 392, 394, 396 may
be conventional pressure sensors, such as for example, pressure
transducers, and the temperature sensors 393, 395 may be
conventional temperature sensors, such as for example,
thermocouples or thermistors.
[0044] The controller 390 processes the data received from the
various sensors and controls operation of the compression device
320, operation of the fan(s) 334 associated with the refrigerant
heat rejection heat exchanger 330, operation of the fan(s) 354
associated with the evaporator 350, operation of the primary
expansion device 355, operation of the secondary expansion device
345, and operation of the suction modulation valve 323. The
controller 390 also controls the positioning of the vapor injection
valve 343 and liquid injection valve 353. The controller 390
positions the vapor injection valve 343 in an open position for
selectively permitting refrigerant vapor to pass from the flash
tank economizer 340 through refrigerant vapor injection line 314
for injection into an intermediate stage of the compression
process. Similarly, the controller 390 positions the liquid
injection valve 353 in an open position for selectively permitting
refrigerant liquid to pass from the flash tank economizer 340
through refrigerant liquid injection line 318 for injection into an
intermediate pressure stage of the compression process. In the FIG.
3 embodiment, the controller 390 can also control the positioning
of the unload valve 327 to selectively open the unload valve 327 to
bypass refrigerant from an intermediate pressure stage of the
compression device 320 through bypass line 316 back to the suction
side of the compression device 320 when it is desired to unload the
first stage of the compression device 320.
[0045] According to embodiments of the application, there are
selected operation characteristics in a transport refrigeration
system that can affect performance or overall system performance.
During transport refrigeration system operations, it is desirable
to check such characteristics to determine proper component or
system functions and/or operations. In one embodiment, a measured
value and a calculated value for a component/system performance
characteristic can be determined and compared, and then a judgment
can be made responsive to or based on the comparison.
[0046] For example, a compressor mid-stage pressure and gas cooler
exit temperature can be used to control or optimize CO.sub.2
economized refrigeration system operations for capacity and/or
efficiency. In one embodiment, gas cooler exit temperature is used
to determine a prescribed compressor discharge pressure. In an
embodiment, compressor mid-stage pressure is used to determine
whether economized mode can/is entered by a vapor compression
system.
[0047] In a refrigeration system, the refrigerant temperature
exiting the heat rejection heat exchanger reflects the heat
exchanger coil and fan performance. When the transport
refrigeration system operates in a transcritical application, then
the refrigerant temperature exiting the heat rejection heat
exchanger is in the function that can determine or optimize
compressor discharge pressure in the refrigeration system for
either higher cooling capacity or higher energy efficiency. For at
least this reason, embodiments of the application can determine or
verify that this performance characteristic (e.g., refrigerant
temperature exiting the gas cooler) is within a prescribed range or
a system design range. In one embodiment, the heat rejection heat
exchanger is sized for the highest capacity conditions of the
system 300 (e.g., under which the system can be intended to
operate). Therefore, for a majority or almost all of designed
operating conditions, the heat rejection heat exchanger is
oversized. As determined by the inventors, the refrigerant
temperature exiting heat rejection heat exchanger (e.g., shown as
GCXT in the graph in FIG. 4) was determined (e.g., tested) to be
only slightly higher than ambient temperature. Thus, in one
embodiment, the exiting temperature of refrigerant for the heat
rejection heat exchanger can be calculated or verified using
ambient temperature plus a variable offset. The variable offset can
be determined to have a prescribed relationship to the cooling
capacity of the system 300. In one embodiment, the highest offset
can occur at highest cooling capacity conditions. As shown in FIG.
4, an offset is shown on the Y axis and can be defined as
(Tamb-GCXT). The temperature difference between evaporator return
air temperature (RTS) and supply air temperature (STS) is shown on
X axis. The temperature difference (RTS-STS) is one exemplary
measurement of system 300 cooling capacity. In one embodiment, the
temperature difference (RTS-STS) is directly related (e.g., a
prescribed relationship) to the transport refrigeration system
cooling capacity.
[0048] In one embodiment, the transport refrigeration system
capacity can be determined responsive to an operating mode of the
transport refrigeration system.
[0049] A sensor 382 can be provided in the system 300 shown in FIG.
3 to measure the refrigerant temperature exiting heat rejection
heat exchanger 330. The sensor 382 can be a temperature sensor.
Alternatively, the sensor 382 can be a pressure sensor where the
temperature can be determined using the pressure. In one
embodiment, a calculated temperature can be compared to the
temperature provided using the sensor 382. When corresponding
values do not match, an error condition in the sensor 382 can be
identified by the controller 390 provided to an operator or the
like.
[0050] In an economized refrigeration system, compressor mid stage
pressure is an operation characteristic that can be monitored
because the compressor mid stage pressure affects whether the
system can transition into economized mode for higher capacity and
higher energy efficiency. For at least this reason, the controller
390 can operate to verify proper compressor functions determined
through a compressor mid stage pressure performance check during
system 300 operations which can be executed according to
embodiments of the application by a comparison of a measured value
and a calculated (e.g., indirect) value for the compressor
mid-stage pressure.
[0051] An exemplary indirect determination for the compressor
mid-stage pressure will now be described. FIG. 5 shows the
compressor mid-stage pressure as a function of the compressor
discharge pressure for various compressor suction pressures. As
shown in FIG. 5, the compressor mid-stage pressure can be
determined when the suction and discharge pressure of the
compressor 320 are known. The same information can be written in
the form of an exemplary two-dimensional lookup table below.
TABLE-US-00001 P Suction 1 P Suction 2 P Suction 3 P Suction 4 P
Discharge 1 P Mid-Stage 1, 1 P Mid-Stage 1, 2 P Mid-Stage 1, 3 P
Mid-Stage 1, 4 P Discharge 2 P Mid-Stage 2, 1 P Mid-Stage 2, 2 P
Mid-Stage 2, 3 P Mid-Stage 2, 4 P Discharge 3 P Mid-Stage 3, 1 P
Mid-Stage 3, 2 P Mid-Stage 3, 3 P Mid-Stage 3, 4 P Discharge 4 P
Mid-Stage 4, 1 P Mid-Stage 4, 2 P Mid-Stage 4, 3 P Mid-Stage 4,
4
[0052] It should be understood that the values of the suction,
discharge, and mid-stage pressures are specific to the compressor
design and operating conditions (e.g., compressor 320). When the
operating conditions for a given compressor machine change, for
instance if the suction superheat changes, the values of the
mid-stage pressure for a particular combination of suction and
discharge pressure may change. This can be more pronounced if the
compressor design allows to independently control the speed of the
two compressor stages, for instance if the two stages are driven by
different motors, for which the speed can be adjusted independently
from each other. In this case, an additional dimension can be added
to the graph or lookup table. For example, an additional dimension
can be accomplished by providing additional graphs or tables, each
for a constant value of the additional variable.
[0053] A sensor 384 can be provided in the system 300 shown in FIG.
3 to measure the compressor mid-stage pressure. The sensor 384 can
be a pressure sensor. In one embodiment, a calculated compressor
mid-stage pressure can be compared to the compressor mid-stage
pressure provided using the sensor 384. When corresponding values
do not match, an error condition in the sensor 384 can be
determined by the controller 390 provided to an operator or the
like.
[0054] An embodiment of a method of operating a transport
refrigeration unit according to the application will now be
described. The method embodiment shown in FIG. 6, can be
implemented in and will be described using a refrigerant vapor
compression system embodiment shown in FIG. 3, however, the method
embodiment is not intended to be limited thereby.
[0055] Referring now to FIG. 6, a process as performed by the
controller 390 can be shown in block diagram form. After a process
starts during system operations, an operating characteristic of the
system can be measured (e.g., Cm) (operation block 610). Then, the
operating characteristic of the system can be indirectly determined
or calculated (e.g., Cc) from other system components and/or
characteristics according to a prescribed relationship (operation
block 620). It can be determined whether Cm and Cc match (operation
block 630). When the determination in operation block 630 is
negative, an error condition can be processed (operation block
640). When the determination in operation block 630 is affirmative
or from operation block 640, a delay period (operations block 650)
can be processed before control returns to operation block 610.
[0056] In one embodiment, a calculated measurement for a system
characteristic can be more accurate than a measured value. Thus,
the error condition can be processed in operation block 640 by
having the controller 390 stop using the measure value Cm and begin
using the calculated value Cc.
[0057] In one embodiment, a calculated or indirect measurement of
selected characteristics (e.g., compressor unit stage pressure
and/or gas cooler refrigerant exit temperature) of transport
refrigeration systems including refrigerant vapor compression
systems can be determined with sufficient accuracy that sensors can
be reduced or eliminated from the system, which may increase
reliability and decrease size and cost. In one embodiment, the
controller 390 can be responsive to a pressure difference between
the flash tank and a mid-stage of the compressor to protect or
prevent operation of the economizer during periods in which the
pressure at the mid-stage is greater than the pressure in the flash
tank or control operations of a flow control device (e.g., flow
control device 343, 353) coupled thereto.
[0058] Embodiments according to the application can use remote
sensors to respectively measure an environment within the container
12 such as the return air temperature RTS and the supply air
temperature STS. Remote sensors, as known to one skilled in the
art, can communicate with a controller (e.g., transport
refrigeration unit 10) through wire or wireless communications. For
example, wireless communications can include one or more radio
transceivers such as one or more of 802.11 radio transceiver,
Bluetooth radio transceiver, GSM/GPS radio transceiver or WIMAX
(802.16) radio transceiver. Information collected by remote
sensor(s) can be used as input parameters for a controller to
control various components in transport refrigeration systems. In
one embodiment, remote sensors may monitor additional criteria such
as humidity, species concentration or the like.
[0059] It should be recognized that selected procedures described
herein may result in some liquid refrigerant entering the
compressor inlet. Although this is generally undesirable, it may
occur for short periods of time without any significant damage to
the compressor.
[0060] While the present invention has been described with
reference to a number of specific embodiments, it will be
understood that the true spirit and scope of the invention should
be determined only with respect to claims that can be supported by
the present specification. Further, while in numerous cases herein
wherein systems and apparatuses and methods are described as having
a certain number of elements it will be understood that such
systems, apparatuses and methods can be practiced with fewer than
the mentioned certain number of elements. Also, while a number of
particular embodiments have been set forth, it will be understood
that features and aspects that have been described with reference
to each particular embodiment can be used with each remaining
particularly set forth embodiment. For example, features or aspects
described with respect to FIG. 3 can be used, combined with or
replace features described using FIGS. 4-6.
* * * * *