US20100083679A1

US20100083679A1 - Temperature control system with a directly-controlled purge cycle

Info

Publication number: US20100083679A1
Application number: US12/245,974
Authority: US
Inventors: Kim Carl Kolstad; Panayu Robert Srichai; William Francis Mohs; YoungChan Ma; Robert Lattin
Original assignee: Thermo King Corp
Current assignee: Thermo King Corp
Priority date: 2008-10-06
Filing date: 2008-10-06
Publication date: 2010-04-08
Also published as: EP2172720A1; JP2010091264A; ATE540275T1; EP2172720B1

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.

Description

BACKGROUND

The present invention relates to temperature control systems. More particularly, the present invention relates to a temperature control system for a transport vehicle.
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.
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

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.
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.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a temperature control system according to one embodiment of the present invention, illustrating a cooling mode.

FIG. 2 is a schematic of the temperature control system of FIG. 1, illustrating a condenser evacuation mode.

FIG. 3 is a schematic of the temperature control system of FIG. 1, illustrating a heating/defrost mode.

DETAILED DESCRIPTION

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

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.