U.S. patent application number 12/245974 was filed with the patent office on 2010-04-08 for temperature control system with a directly-controlled purge cycle.
This patent application is currently assigned to THERMO KING CORPORATION. Invention is credited to Kim Carl Kolstad, Robert Lattin, YoungChan Ma, William Francis Mohs, Panayu Robert Srichai.
Application Number | 20100083679 12/245974 |
Document ID | / |
Family ID | 41401700 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100083679 |
Kind Code |
A1 |
Kolstad; Kim Carl ; et
al. |
April 8, 2010 |
TEMPERATURE CONTROL SYSTEM WITH A DIRECTLY-CONTROLLED PURGE
CYCLE
Abstract
A temperature control system includes a compressor, a condenser,
an evaporator, and an accumulator. A liquid level sensor is
associated with the accumulator tank generates a signal indicative
of the level of the liquid heat transfer fluid inside the
accumulator. A valve is in fluid communication with the condenser,
the compressor, and the evaporator and is operable in a first
position and a second position. The first position directs the heat
transfer fluid from the compressor to the condenser, and the second
position directs the heat transfer fluid from the compressor to the
evaporator without passing through the first heat exchanger. A
controller is in electrical communication with the liquid level
sensor and the valve and is operable to receive the signal and move
the valve from the first position to the second position based on
the signal.
Inventors: |
Kolstad; Kim Carl;
(Lonsdale, MN) ; Srichai; Panayu Robert;
(Minneapolis, MN) ; Mohs; William Francis;
(Minneapolis, MN) ; Ma; YoungChan; (Bloomington,
MN) ; Lattin; Robert; (Minneapolis, MN) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Assignee: |
THERMO KING CORPORATION
Minneapolis
MN
|
Family ID: |
41401700 |
Appl. No.: |
12/245974 |
Filed: |
October 6, 2008 |
Current U.S.
Class: |
62/117 ; 62/129;
62/197; 62/515 |
Current CPC
Class: |
F25B 2400/0403 20130101;
F25B 13/00 20130101; F25B 2700/04 20130101; F25B 2600/2501
20130101; F25B 43/006 20130101; F25B 47/025 20130101; F25B
2400/0409 20130101; F25B 2400/0411 20130101; F25B 2313/02731
20130101; F25B 2313/0292 20130101; F25B 2313/007 20130101 |
Class at
Publication: |
62/117 ; 62/515;
62/197; 62/129 |
International
Class: |
F25B 5/00 20060101
F25B005/00; F25B 39/02 20060101 F25B039/02; F25B 41/04 20060101
F25B041/04; F25B 49/00 20060101 F25B049/00 |
Claims
1. A temperature control system comprising: a compressor configured
to compress a heat transfer fluid; a first heat exchanger in fluid
communication with the compressor and configured to receive the
heat transfer fluid from the compressor and to cool and condense
the heat transfer fluid; a second heat exchanger in fluid
communication with the first heat exchanger and the compressor and
configured to exchange heat with a temperature-controlled space; an
accumulator in fluid communication with the second heat exchanger
and the compressor and configured to receive a mixture of liquid
and vapor heat transfer fluid from the second heat exchanger and
direct a vapor portion of the heat transfer fluid to the
compressor; a liquid level sensor associated with the accumulator
tank and operable to generate a signal indicative of the level of
the liquid heat transfer fluid inside the accumulator; a valve in
fluid communication with the first heat exchanger, the compressor,
and the second heat exchanger, the valve operable in a first
position and a second position, wherein the first position is
operable to direct the heat transfer fluid from the compressor to
the first heat exchanger and the second position is operable to
direct the heat transfer fluid from the compressor to the second
heat exchanger without passing through the first heat exchanger;
and a controller in electrical communication with the liquid level
sensor and the valve, the controller operable to receive the signal
and move the valve from the first position to the second position
based on the signal.
2. The temperature control system of claim 1, wherein the first
position corresponds to a cooling mode of the temperature control
system and the second position corresponds to a heating mode of the
temperature control system.
3. The temperature control system of claim 2, wherein the cooling
mode defines a cooling circuit for cooling the
temperature-controlled space, wherein the cooling circuit includes
the compressor, the first heat exchanger, the second heat
exchanger, and the accumulator fluidly connected in series.
4. The temperature control system of claim 3, wherein the heating
mode defines a heating circuit for at least one of defrosting the
second heat exchanger and heating and the temperature-controlled
space, wherein the heating circuit bypasses the first heat
exchanger and includes the compressor, the second heat exchanger,
and accumulator fluidly connected in series.
5. The temperature control system of claim 4, wherein the liquid
level sensor is operable to generate a signal indicative of an
optimal level of liquid heat transfer fluid inside the accumulator,
and wherein the controller is operable to receive the signal
indicative of the optimal level and to move the valve to the second
position.
6. The temperature control system of claim 5, wherein the optimum
level includes a level of refrigerant that provides heating
capacity during the heating mode, and wherein liquid heat transfer
fluid at or below the optimum level does not enter the
compressor.
7. The temperature control system of claim 4, further comprising a
second valve in fluid communication with the first heat exchanger
and the accumulator, the valve operable in an open position and a
closed position, wherein the open position is operable to direct at
least a portion of the condensed heat transfer fluid from the first
heat exchanger to the accumulator without passing through the
second heat exchanger, and wherein the controller is in electrical
communication with the second valve and operable to move the valve
between open and closed positions.
8. The temperature control system of claim 7, wherein the open
position corresponding to a condenser evacuation mode of the
temperature control system.
9. The temperature control system of claim 8, wherein the condenser
evacuation mode defines an evacuation circuit configured to allow
at least a portion of the condensed heat transfer fluid to enter
the accumulator from the first heat exchanger, bypassing the second
heat exchanger, wherein the evacuation circuit includes the
compressor, the condenser, and the accumulator fluidly connected in
series.
10. The temperature control system of claim 9, wherein the
temperature control system enters the condenser evacuation mode
after the temperature control system exits the cooling mode and
before the temperature control system enters the heating mode.
11. A method of operating a temperature control system, the method
comprising: compressing a heat transfer fluid with a compressor;
directing the heat transfer fluid from the compressor to a first
heat exchanger with a valve in a first position; cooling and
condensing the heat transfer fluid from the compressor in a first
heat exchanger; exchanging heat with a temperature-controlled space
with the second heat exchanger; receiving a mixture of liquid and
vapor heat transfer fluid from the second heat exchanger into an
accumulator; directing a vapor portion of the heat transfer fluid
in the accumulator to the compressor; generating with a liquid
level sensor associated with the accumulator a signal indicative of
the level of the liquid heat transfer fluid inside the accumulator;
receiving the signal with a controller; moving the valve with the
controller from the first position to a second position based on
the signal; and directing the heat transfer fluid from the
compressor to the second heat exchanger without passing through the
first heat exchanger with the valve in the second position.
12. The method of claim 11, further comprising: operating the
temperature control system in a cooling mode when the valve is in
the first position; and operating the temperature control system in
a heating mode when the valve is in the second position.
13. The method of claim 12, further comprising: fluidly connecting
in series a cooling circuit including the compressor, the first
heat exchanger, the second heat exchanger, and the accumulator when
operating in the cooling mode; and cooling the
temperature-controlled space when operating in the cooling
mode.
14. The method of claim 13, further comprising: fluidly connecting
in series a heating circuit including the compressor, the second
heat exchanger, and accumulator when operating in the heating mode;
bypassing the first heat exchanger when operating in the heating
mode; and at least one of defrosting the second heat exchanger and
heating and the temperature-controlled space when operating in the
heating mode.
15. The method of claim 14, further comprising generating a signal
indicative of an optimal level of liquid heat transfer fluid inside
the accumulator, receiving the signal indicative of the optimal
level with the controller; moving the valve from the first position
to the second position with the controller based on the signal
indicative of the optimal level.
16. The method of claim 15, further comprising: initiating the
heating mode; providing heating capacity in the heating mode when
the heating mode is initiated with the optimum level of refrigerant
in the accumulator; and inhibiting liquid heat transfer fluid from
entering the compressor in the heating mode when the heating mode
is initiated with the optimal level of refrigerant.
17. The method of claim 14, further comprising directing at least a
portion of the condensed heat transfer fluid from the first heat
exchanger to the accumulator without passing through the second
heat exchanger with a second valve in an open position.
18. The method of claim 17, further comprising operating the
temperature control system in a condenser evacuation mode when the
second valve is in the open position.
19. The method of claim 18, further comprising moving the second
valve with the controller from the closed position to the open
position; fluidly connecting in series an evacuation circuit
including the compressor, the first heat exchanger, and the
accumulator when operating in the condenser evacuation mode;
allowing at least a portion of the condensed heat transfer fluid to
enter the accumulator from the first heat exchanger when operating
in the condenser evacuation mode; and bypassing the second heat
exchanger when operating in the condenser evacuation mode.
20. The method of claim 19, further comprising entering the
condenser evacuation mode after the temperature control system
exits the cooling mode and before the temperature control system
enters the heating mode.
Description
BACKGROUND
[0001] The present invention relates to temperature control
systems. More particularly, the present invention relates to a
temperature control system for a transport vehicle.
[0002] Generally, transport vehicles (e.g., straight trucks and
tractor-trailer combinations) are used to transport temperature
sensitive cargo that is maintained at predetermined conditions
using a temperature control system during transportation to
preserve the quality of the cargo. The cargo is transported,
stored, or otherwise supported within a cargo space of the
transport vehicle.
[0003] In some transport units, the temperature control system must
be capable of cooling and heating the cargo space to maintain a
desired temperature (i.e., a setpoint temperature). A controller
switches the temperature control unit between heating and cooling
modes based on the relative difference between a sensed temperature
and the setpoint temperature to regulate the condition of the cargo
space. Typically, the temperature control system is capable of
operating a conventional refrigeration cycle utilizing a
phase-change refrigerant to cool the cargo space. Refrigerant is
compressed by a compressor, condensed, and evaporated in a heat
exchanger in thermal communication with the cargo space to cool the
cargo space. Heating is typically accomplished by bypassing the
condenser and directing hot compressed refrigerant directly to the
heat exchanger in thermal communication with the cargo space to
heat the cargo space.
SUMMARY
[0004] In one embodiment, the invention provides a temperature
control system including a compressor configured to compress a heat
transfer fluid, a first heat exchanger in fluid communication with
the compressor and configured to receive the heat transfer fluid
from the compressor and to cool and condense the heat transfer
fluid, a second heat exchanger in fluid communication with the
first heat exchanger and the compressor and configured to exchange
heat with a temperature-controlled space, and an accumulator in
fluid communication with the second heat exchanger and the
compressor and configured to receive a mixture of liquid and vapor
heat transfer fluid from the second heat exchanger and direct a
vapor portion of the heat transfer fluid to the compressor. A
liquid level sensor is associated with the accumulator tank and
operable to generate a signal indicative of the level of the liquid
heat transfer fluid inside the accumulator. A valve is in fluid
communication with the first heat exchanger, the compressor, and
the second heat exchanger. The valve is operable in a first
position and a second position. The first position is operable to
direct the heat transfer fluid from the compressor to the first
heat exchanger and the second position is operable to direct the
heat transfer fluid from the compressor to the second heat
exchanger without passing through the first heat exchanger. A
controller is in electrical communication with the liquid level
sensor and the valve. The controller is operable to receive the
signal and move the valve from the first position to the second
position based on the signal.
[0005] In another embodiment the invention provides a method of
operating a temperature control system. The method comprises
compressing a heat transfer fluid with a compressor, directing the
heat transfer fluid from the compressor to a first heat exchanger
with a valve in a first position, cooling and condensing the heat
transfer fluid from the compressor in a first heat exchanger,
exchanging heat with a temperature-controlled space with the second
heat exchanger, receiving a mixture of liquid and vapor heat
transfer fluid from the second heat exchanger into an accumulator,
directing a vapor portion of the heat transfer fluid in the
accumulator to the compressor, generating with a liquid level
sensor associated with the accumulator a signal indicative of the
level of the liquid heat transfer fluid inside the accumulator,
receiving the signal with a controller, moving the valve with the
controller from the first position to a second position based on
the signal, and directing the heat transfer fluid from the
compressor to the second heat exchanger without passing through the
first heat exchanger with the valve in the second position.
[0006] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic of a temperature control system
according to one embodiment of the present invention, illustrating
a cooling mode.
[0008] FIG. 2 is a schematic of the temperature control system of
FIG. 1, illustrating a condenser evacuation mode.
[0009] FIG. 3 is a schematic of the temperature control system of
FIG. 1, illustrating a heating/defrost mode.
DETAILED DESCRIPTION
[0010] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. Also, it is to be understood that the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including,"
"comprising," or "having" and variations thereof herein is meant to
encompass the items listed thereafter and equivalents thereof as
well as additional items. Unless specified or limited otherwise,
the terms "mounted," "connected," "supported," and "coupled" and
variations thereof are used broadly and encompass both direct and
indirect mountings, connections, supports, and couplings. Further,
"connected" and "coupled" are not restricted to physical or
mechanical connections or couplings.
[0011] FIGS. 1-3 illustrate a temperature control system 10 for a
transport vehicle. The temperature control system 10 is capable of
cooling and heating a cargo space of the transport vehicle to
maintain a desired temperature (i.e., a setpoint temperature). The
temperature control system 10 includes a controller 12 that
switches the temperature control system 10 between heating and
cooling modes based on the relative difference between a sensed
temperature and the setpoint temperature to regulate the condition
of the cargo space. It is to be understood that the refrigeration
system 10 may be utilized for other refrigeration applications and
is not limited to transport refrigeration applications.
[0012] The temperature control system 10 includes a compressor 14,
a first heat exchanger 16, a receiver 18, an expansion valve 20, a
second heat exchanger 22 and an accumulator 24 connected in series
by fluid conduits. The first heat exchanger 16 is in thermal
communication with air outside of the transport vehicle. The second
heat exchanger 22 is in thermal communication with air inside the
cargo space of the transport vehicle. In other constructions, there
may be more than one heat exchanger in thermal communication with
air inside the cargo space. A distributor 40 may be employed, as is
well known in the art, to distribute refrigerant to a plurality of
second heat exchangers (not shown). A first portion 44 of the
temperature control system 10, including the second heat exchanger
22, is preferably positioned within the cargo space. A second
portion 46 of the temperature control system 10, including the
first heat exchanger 16, is preferably positioned outside of the
cargo space.
[0013] In the cooling mode, the receiver 18 receives a heat
transfer fluid (e.g., refrigerant) from the first heat exchanger 16
and directs refrigerant to the second heat exchanger 22. The
expansion valve 20 reduces the pressure of the refrigerant just
upstream of the second heat exchanger 22. The accumulator 24
receives a liquid and gaseous mixture of refrigerant from the
second heat exchanger and includes a liquid level sensor 32 for
detecting a level of liquid in the accumulator 24. Liquid
refrigerant accumulates at the bottom of the accumulator 24 and
gaseous refrigerant is displaced to the top. The accumulator 24
includes a U-tube 42 (i.e., a U-shaped tube) for drawing gaseous
refrigerant from the top of the accumulator 24 into the compressor
suction line, as is well known in the art. The liquid level must
remain below the inlet of the U-tube 42 in order to prevent the
liquid from entering the compressor suction line. The liquid level
sensor 32 is positioned at an optimum height within the accumulator
tank. The optimum height is chosen such that a liquid level at or
below the optimum height is unlikely to result in liquid entering
the compressor 14 during movement of the transport vehicle and
operation of the temperature control system 10. In other
constructions, such as non-transport applications, the optimum
height may be closer to the top of the U-tube 42 since movement of
the liquid is not expected. Furthermore, the optimum height ensures
that an adequate amount of refrigerant is available during a
heating/defrost mode of operation, which will be explained in
further detail below.
[0014] The liquid level sensor 32 generates a first signal
indicative of a refrigerant level below the optimal level and a
second signal indicative of a refrigerant level at or above the
optimal level. In other embodiments, the sensor 32 may generate an
output when the level is below the optimal level (i.e., generate a
voltage output value) and not generate any output (i.e., voltage)
when the level is at or above the optimal level. In such
embodiments, the lack of an output, which can be recognized by the
controller 12 as indicative of a liquid level at or above the
optimal level, should be considered to be the generation of a
signal indicative of the refrigerant level. The liquid level sensor
can be a float device, a hydrostatic device, a load cell, a
magnetic level gauge, a capacitance transmitter, a magnetostrictive
level transmitter, an ultrasonic level transmitter, a laser level
transmitter, a radar level transmitter, or the like.
[0015] The temperature control system 10 also includes a suction
line heat exchanger 26 and a purge valve 28. The suction line heat
exchanger 26 is a shell and tube heat exchanger that transfers heat
between the warm liquid refrigerant entering the second heat
exchanger 22 and cold vapor refrigerant leaving the second heat
exchanger 22. It is to be understood that other types of heat
exchangers may be used to accomplish the same results. The purge
valve 28 is a solenoid valve in communication with a fluid conduit
34 that fluidly connects the first heat exchanger 16 to the
accumulator 24, bypassing the suction line heat exchanger 26, the
expansion valve 20 and the second heat exchanger 22.
[0016] A three-way valve 30 is operable in a first position (FIGS.
1 and 2) in which refrigerant is directed from the compressor 14 to
the first heat exchanger 16 and a second position (FIG. 3) in which
refrigerant is directed from the compressor 14 to the second heat
exchanger 22. In the first position, a refrigeration or cooling
circuit is formed. In the second position, a heating/defrost
circuit is formed. The controller 12 controls the position of the
three-way valve 30 by opening and closing a pilot solenoid valve 36
in a manner well understood in the art. The three-way valve 30 is
kept in the first position by maintaining the pilot solenoid valve
36 closed, which builds pressure to hold the valve 30 in the first
position. When the controller 12 opens the pilot solenoid valve 36,
the pressure is released and the three-way valve 30 moves from the
first position to the second position. When the controller 12
closes the pilot solenoid valve 36, the pressure builds and the
three-way valve 30 moves from the second position to the first
position. In other constructions, other types of switching
mechanisms may be employed to switch the system between a
refrigeration circuit and a heating/defrost circuit.
[0017] The temperature control system 10 is operable in a cooling
mode, a condenser evacuation mode, and a heating/defrost mode. The
controller 12 communicates with the pilot solenoid valve 36 to
place the three-way valve 30 in the first position during the
cooling mode and the condenser evacuation mode, and in the second
position during the heating/defrost mode.
[0018] During the cooling mode, illustrated in FIG. 1, the
three-way valve is in the first position to direct high pressure
gas refrigerant from the compressor to the first heat exchanger 16.
The high pressure gas refrigerant is condensed in the first heat
exchanger 16 to a high pressure liquid refrigerant, which is
directed to the receiver 18. The receiver 18 ensures that only
liquid refrigerant is directed toward the second heat exchanger 22.
Prior to the high pressure liquid refrigerant entering the second
heat exchanger 22, the high pressure liquid refrigerant enters the
suction line heat exchanger 26 to be pre-cooled by low pressure
refrigerant exiting the second heat exchanger 22. Then, the high
pressure liquid refrigerant is passed through an expansion valve 20
to lower the pressure of the refrigerant. At least a portion of the
refrigerant evaporates in the second heat exchanger 22 to create a
mixture of low pressure liquid and low pressure gas. The mixture
passes through the second heat exchanger 22 and absorbs heat from
air being directed into the cargo space to thereby cool the cargo
space. The mixture then passes through the suction line heat
exchanger 26 and exchanges heat with the high pressure liquid
refrigerant approaching the second heat exchanger 22. Then, the
mixture is separated in the accumulator 24 in which low pressure
liquid refrigerant is collected at the bottom and low pressure gas
refrigerant is drawn from the top into the compressor suction line
via the U-tube 42. During the cooling mode, the controller 12
ensures that the purge valve 28 is closed to prevent the movement
of high pressure liquid refrigerant into the accumulator 24. The
temperature control system 10 remains in the cooling mode until a
heating or defrost operation is needed. When a heating or defrost
operation is needed, the controller switches to the condenser
evacuation mode.
[0019] The condenser evacuation mode, illustrated in FIG. 2, is
operated between the cooling and heating/defrost modes to move an
optimal amount of refrigerant from the high pressure side to the
low pressure side for use during the heating/defrost mode. During
the condenser evacuation mode, the three-way valve 30 is in the
first position. Upon entering the condenser evacuation mode, the
controller 12 opens the purge valve 28 to allow the passage of high
pressure liquid refrigerant from the receiver 18 and the first heat
exchanger 16 into the accumulator 24. Refrigerant introduced to the
accumulator 24 becomes available for use during the heating/defrost
cycle. The amount of refrigerant moved into the accumulator 24 must
be large enough to provide adequate capacity for heating but not so
much that the liquid refrigerant enters the compressor suction
line, which can damage the compressor. The liquid level sensor 32
detects the presence of liquid at a predetermined optimal height.
When the optimal height is detected, the liquid level sensor 32
sends a signal to the controller 12, which switches the three-way
valve 30 to the second position in response to the signal by
opening a pilot solenoid valve 36, as is well understood in the
art, and initiates the heating/defrost mode. When the three-way
valve 30 is switched to the second position, high pressure liquid
refrigerant no longer enters the accumulator 24 by way of fluid
conduit 34 and purge valve 28. The purge valve 28 may be closed to
ensure that high pressure liquid refrigerant does not enter the
accumulator 24; however, it is possible that the purge valve 28 may
be open and still high pressure refrigerant will not enter the
accumulator 24 because of the pressure increase in the accumulator
24 when the system is switched to the heating/defrost mode.
[0020] During the heating/defrost mode, illustrated in FIG. 3, the
three-way valve 30 is in the second position. In the second
position, refrigerant bypasses the first heat exchanger 16 and hot
gas refrigerant is directed from the compressor 14 to the second
heat exchanger 22 to heat the cargo space or to defrost the second
heat exchanger coil. A pressure regulating device 38 (e.g., a
differential pressure regulating (DPR) valve) is positioned between
the compressor 14 and the second heat exchanger 22. Refrigerant is
directed from the compressor 14 to the pressure regulating device
38 to the second heat exchanger 22, bypassing the expansion valve
20. The refrigerant goes through the second heat exchanger coil 22
where it is cooled and/or partially condensed. As the refrigerant
passes through the second heat exchanger 22, the refrigerant
releases heat either to ice formed on the external surfaces of the
second heat exchanger 22 to thereby defrost the second heat
exchanger 22, to air being directed into the cargo space to thereby
heat the cargo space, or to both. The refrigerant enters the
accumulator 24 where condensed liquid refrigerant is separated from
vapor refrigerant. The vapor refrigerant returns to the compressor
by way of U-tube 42 and is compressed to a high pressure and high
temperature gas, and the cycle repeats. If cooling is demanded, the
controller 12 switches to the refrigeration mode by switching the
three-way valve 30 to the first position and closing the purge
valve 28.
[0021] Thus, the invention provides, among other things, a
temperature control system 10 having a controller 12 operable to
switch the system from a cooling circuit to a heating/defrost
circuit in response to a signal from a liquid level sensor 32
indicating that an optimal level of liquid refrigerant has
accumulated in the accumulator 24. Various features and advantages
of the invention are set forth in the following claims.
* * * * *