Patent Application
20100083679
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.
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.
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.
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 (
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
The condenser evacuation mode, illustrated in
During the heating/defrost mode, illustrated in
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.
