CROSS-REFERENCE TO RELATED APPLICATION

[0001] Benefit is claimed of U.S. Patent Application No. 62/253,081, filed November 9, 2015, and entitled "Series Loop Intermodal Container", the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.

BACKGROUND

[0002] The disclosure relates to refrigerated transport systems such as intermodal containers. More particularly, the disclosure relates to refrigerant safety in such refrigerated transport systems.

[0003] An exemplary refrigerated intermodal container (also known as a shipping container or intermodal shipping container) has an equipment module at one end of the container. The equipment module contains a vapor compression system having a compressor, a heat rejection heat exchanger downstream of the compressor along a refrigerant flow path, an expansion device, and a heat absorption heat exchanger. One or more first fans may drive an external air flow across the heat rejection heat exchanger. One or more second fans may drive an internal air flow across the heat absorption heat exchanger. In various implementations, for powering the container, there may be a power cord for connecting to an external power source. For ease of manufacture or service, the equipment module may be pre-formed as a module mateable to a remainder of the container body (e.g., insertable into an open front end of the body). One example of such a container refrigeration system is sold by Carrier Corporation of Farmington, Connecticut under the trademark ThinLINE. An example of such a system is seen in US Patent Application 62/098144, of Rau, filed December 30, 2014 and entitled "Access Panel", the disclosure of which is incorporated in its entirety herein as if set forth at length. Additionally, refrigerated truck boxes, refrigerated railcars, and the like may have refrigeration systems with different forms or degrees of modularity. [0004] There has been a general move to seek low global warming potential (GWP) refrigerants to replace conventional refrigerants such as R-134a. A number of proposed and possible future replacement refrigerants having low GWP also may have higher flammability and/or toxicity levels than prior refrigerants. These include various hydro fluorocarbon (HFC) and hydrocarbon (HC) refrigerants. Background flame arrestor technology for use with flammable refrigerants is found International Publication No. WO2015/009721A1, published January 22, 2015, the disclosure of which is incorporated herein in its entirety by reference as if set forth at length.

[0005] Separately, series loop refrigeration systems have been proposed. An example of such a system is seen in US Patent Application Publication 2014/0260404 Al, of Verma et al., published September 18, 2014, and entitled "High Efficiency Refrigeration System", the disclosure of which is incorporated in its entirety herein as if set forth at length. Further examples are seen in International Publication Number WO 2015/057299 Al, of Feng et al., published April 23, 2015, and entitled "Two-Phase Refrigeration System" and International Publication Number WO 2015/057297 Al, of Feng et al., published April 23, 2015, and entitled "Operation of a Cascade Air Conditioning System with Two-Phase Loop", the disclosures of which are incorporated in their entireties herein as if set forth at length.

SUMMARY

[0006] One aspect of the disclosure involves a refrigerated transport system comprising a body enclosing a refrigerated compartment. A refrigeration system comprises: a vapor compression loop having a first heat exchanger positioned to reject heat to an external environment in a cooling mode. A heat transfer loop has a second heat exchanger positioned to absorb heat from the refrigerated compartment in the cooling mode. An inter-loop heat exchanger has a first leg along the vapor compression loop and a second leg along the heat transfer loop in heat exchange relation with the first leg.

[0007] In one or more embodiments of any of the foregoing embodiments, the vapor compression loop sequentially comprises: a compressor; said first heat exchanger; an expansion device; and said first leg. The heat transfer loop sequentially comprises: a pump; said second heat exchanger; and said second leg.

[0008] In one or more embodiments of any of the foregoing embodiments, an electric fan is positioned to drive a recirculating air flow from the refrigerated compartment across the second heat exchanger. [0009] In one or more embodiments of any of the foregoing embodiments, the first heat exchanger is a refrigerant- air heat exchanger.

[0010] In one or more embodiments of any of the foregoing embodiments, the inter-loop heat exchanger is a brazed plate heat exchanger.

[0011] In one or more embodiments of any of the foregoing embodiments, a carbon dioxide detector may be coupled to control a ventilation fan.

[0012] In one or more embodiments of any of the foregoing embodiments, a refrigerant charge of the vapor compression loop comprises at least 50% or at least 90% by weight propane.

[0013] In one or more embodiments of any of the foregoing embodiments, a heat transfer fluid of the heat transfer loop comprises at least 50% carbon dioxide, by weight.

[0014] In one or more embodiments of any of the foregoing embodiments, the system is an intermodal shipping container. The one or more doors are at a first end and the refrigeration system is mounted in an equipment module at a second end of the body opposite the first end.

[0015] In one or more embodiments of any of the foregoing embodiments: a wall of the equipment module divides the external environment from the refrigerated compartment; the inter loop heat exchanger is on the external environment side of the wall; and the second heat exchanger is on the refrigerated compartment side of the wall.

[0016] In one or more embodiments of any of the foregoing embodiments, the pump is on the refrigerated compartment side of the wall.

[0017] In one or more embodiments of any of the foregoing embodiments, one or more flame arrestors are across one or more openings of the equipment module.

[0018] In one or more embodiments of any of the foregoing embodiments, the one or more openings are along the front of the equipment module.

[0019] In one or more embodiments of any of the foregoing embodiments, the one or more flame arrestors comprise metallic wire mesh or perforated mesh.

[0020] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a cutaway view of a refrigerated cargo container. [0022] FIG. 2 is a rear view of the refrigerated cargo container.

[0023] FIG. 3 is a schematic view of a refrigeration system of the refrigerated cargo container.

[0024] FIG. 4 is a front view of a refrigeration unit of the container of FIG. 1.

[0025] FIG. 5 is a schematic side cutaway view of the refrigerated cargo container.

[0026] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0027] FIG. 1 shows an intermodal container 20 that may be shipped, trucked, trained or the like. The container has a body 22 enclosing an interior 24. The body and interior are formed essentially as right parallelepipeds. The body has a top 22A, a bottom 22B, a first side 22C, a second side 22D, a first end 22E and a second end 22F. The top, bottom, and sides may be an integral rigid metallic structural system. The first end may be formed, in part, by an equipment module 26 ("equipment box"). The second end may essentially be formed by a pair of oppositely hinged doors 28A, 28B (FIG. 2).

[0028] The equipment module contains a refrigeration system 30 (FIG. 3) comprising a vapor compression loop 31 in tandem or series with a heat transfer loop 32. The heat transfer loop utilizes a relatively nonflammable and/or nontoxic working fluid compared with the refrigerant of the vapor compression loop. As is discussed below, the heat transfer loop may be a pumped loop (rather than a compression loop) and may have phase change. This avoids issues of flammable and/or toxic vapor accumulating in the refrigerated compartment and potentially causing explosion/fire, poisoning, or other safety issues. As is discussed below, various means may be taken to isolate the compartment interior from exposure to the refrigerant of the vapor compression loop. Additionally, various safety measures may be taken for the vapor compression loop (e.g., use of explosion proof components and other safety measures) but not necessarily at the same level as would be required for situations where the refrigerant could accidentally be introduced into the closed space of the refrigerated compartment.

[0029] Constructional and operational details of the refrigeration system may include some to all of those from the aforementioned US Patent Application Publication 2014/0260404 Al, International Publication Number WO 2015/057299 Al, and International Publication Number WO 2015/057297 Al.

[0030] The illustrated vapor compression loop comprises sequentially along a refrigerant flowpath 34, a compressor 36, a heat rejection heat exchanger 38, an expansion device 40 (e.g., electronic expansion valve, thermal expansion valve, orifice, or the like), and a leg 42 of an inter- loop heat exchanger 44.

[0031] One or more first fans 50 may drive an external air flow 520 across the heat rejection heat exchanger. [0032] The heat transfer loop comprises, sequentially along a flowpath 54, a pump 56, a heat absorption heat exchanger 58 and a leg 43 of the inter-loop heat exchanger 44 in heat exchange relation with the leg 42. An optional receiver 59 is between the leg 43 and pump 56.

[0033] One or more second fans 60A, 60B (FIGS. 3 and 5) may drive an internal air flow 522A, 522B along respective flowpaths 510A, 510B across the heat absorption heat exchanger. In normal cooling operation, the pump may pump liquid refrigerant of the heat transfer loop to the heat absorption heat exchanger where the refrigerant receives heat from the air flows 522A, 522B. The heat absorption may cause a phase change to vapor. The refrigerant then passes to the leg 43 where it rejects heat to refrigerant in the leg 42. This will re-condense refrigerant to then pass as liquid back to the pump.

[0034] In various implementations, for powering the container, there may be a power cord (not shown) for connecting to an external power source. Additionally, the container may be associated with a generator 62 (FIG. 3, e.g., having an internal combustion engine). For intermodal containers, the generator may be a part of an accessory "genset" that may separately mount to a vehicle (trailer or rail car) carrying the container. Other transport refrigeration systems such as dedicated trailers may integrate the generator into an equipment body mounted to the front of the trailer box. The refrigeration system may include a main controller 64 (e.g., having a processor, memory and storage for running a program to perform the required functions) powered by a main battery 66. The battery is typically a rechargeable battery that charges when the container is plugged into external power or a running genset.

[0035] FIG 3 generically shows a boundary 67 (formed by walls of the equipment module) between the exterior 68 which is open to the external environment and a climate controlled section 69 of the body interior. For safety, the vapor compression loop is kept completely on the exterior side of the boundary with the heat transfer loop line/conduit making two penetrations of that boundary.

[0036] For ease of manufacture or service, the equipment module (box) may be pre-formed as a module mateable to a remainder of the container body (e.g., insertable into an open front end of the body).

[0037] The module 26 comprises a front panel 70 (FIG. 2). The panel 70 may have a plurality of openings of which some may be closed by various means. Two of the openings 72A, 72B (FIGS. 3 A and 5 A) are along the respective air flowpaths 510A, 510B of the two evaporator fans. These flowpaths may be isolated from each other or may merely be adjacent halves of a single flowpath (or may be a combination, separating and merging). In this example, the opening spans the fan, so that a portion of the opening is upstream of the fan and a portion of the opening is downstream. The openings 72A, 72B are closed by respective access panels 80A, 80B (FIG. 2). The exemplary panel 80A includes a rotary gate valve for venting. It may also have a small blower fan 81A to withdraw air from the flowpath 510A (or may rely on leakage across the adjacent evaporator fan). Other valve/gate structures may be provided. Other valve/gate structures may be provided. The exemplary panel 80B lacks any vent/valve.

[0038] A beneficial combination of working fluid for the two loops is propane for the vapor compression loop and carbon dioxide for the heat transfer loop. Both are low cost and non-toxic and propane is a highly efficient refrigerant. Under ANSI/ASHRAE Standard 34-2007, R-290 (propane) is rated A3 (non-toxic, highly flammable) and R744 is rated as Al (non-toxic, non-flammable).

[0039] In the two respective loops, the total refrigerant charge may consist essentially of said propane and said carbon dioxide, respectively, (e.g., allowing for industry standard levels of contaminants and additives such as corrosion inhibitors) or at least be 50% or at least 90% by weight said propane and said carbon dioxide.

[0040] Various mitigation measures may be taken regarding the two loops. As noted above, propane-carrying components are isolated from the refrigerated compartment and seals around and in the equipment module prevent propane leakage into the refrigerated compartment. Thus, additional safety measures relating to actions once propane has entered the refrigerated compartment may be avoided (e.g., as distinguished from situations where a propane-containing evaporator is exposed to the refrigerated compartment). Mitigation measures may then be limited to external propane leakage and internal carbon dioxide leakage if at all.

[0041] Exemplary propane leakage mitigation is passive and is discussed below.

[0042] Exemplary carbon dioxide mitigation is active responsive to detecting of a refrigerant leak by a detector 232 (FIG. 5). Carbon dioxide detectors are used to maximize produce freshness by controlling carbon dioxide build up in refrigerated containers generally (e.g., including those using refrigerants other than carbon dioxide). That same detector or an added detector may be used to mitigate leaks of carbon dioxide into the refrigerated compartment. A number of possible locations exist for such a detector including locations within the equipment box (e.g., adjacent the evaporator in a duct along one of the flowpaths 510A or 510B either inside or outside the equipment module communicating with the rest of the refrigerated compartment or space) or more remote (e.g., even as far away as on or adjacent the doors). Exemplary detectors comprise infrared sensors along with signal processing and output electronics as may be appropriate. Exemplary infrared sensors are non-dispersive infrared (NDIR) sensors. Exemplary NDIR sensors have target sensing ranges associated with carbon dioxide.

[0043] Although there may be various hardwired/hardcoded or analog implementations with little control logic, an exemplary implementation involves the detector 232 communicating with a programmed controller which in turn communicates with the active mitigation components. The controller may be the main controller 64 of the refrigeration system or may be a separate unit 234 (FIG. 5, e.g., having a processor, memory and storage for running a program to perform the required functions and, optionally, its own battery 258 (e.g., an alkaline battery)).

[0044] For carbon dioxide mitigation, the detector and controller may be coupled to a ventilation system for venting the interior of the container in response to leak detection. Some implementations may use baseline fresh air exchange vents (e.g., 80A shown above and, its associated blower fan, if any, and/or evaporator fan) to do the venting. For example,

implementation might involve the opening of the gate valve 80A and the running of the fan 81A and/or 60A. This may be done regardless of whether the refrigeration system is running. For example, carbon dioxide leaks may occur even when the system is off but. In some

implementations, the detection may cause a shutting down of the refrigeration system (e.g., the compressor and pump).

[0045] As an alternative to the use of the gate valve 80A or other means associated with a baseline system, venting may be done by a dedicated additional venting fan (e.g., along with controllable shutter or other valving). In such a situation, the fan unit could include its own battery and electronics optionally integrated with one of the other components such as the controller 234 and/or the detector 232.

[0046] Propane mitigation may include use of components to prevent or block sparking or arcing, including use of known forms of explosion-proof motors. Relevant motors for scrutiny include: the compressor motor; fan motors (particularly for the heat rejection heat exchanger); and actuator motors. This may include replacing or modifying baseline motors and adding motors associated with features such as supplemental vents, supplemental fans, and the like.

[0047] Arcing would be undesirable in motor commutation. Induction motors would be good choices. Such a motor may have a totally enclosed frame and be sealed from any vapor penetration, this would include seals to shafts that would drive the fan. All connections to such motors may be sealed from any vapor penetration. This sealing would include the conduit via which wire enters the motor connection box

[0048] Totally hermetic heaters would be used along the recirculating flowpaths (used for evaporator defrost and heating when external temperatures are so low that the compartment must be heated rather than cooled). Thus, any failure mode would not result in an electrical arc.

[0049] Some-to-all electrical interconnections (wire, cable) potentially exposed to propane leaks may be sealed in exposition proof conduit. Penetrations between the exterior side and the evaporator side of the equipment module would be explosion proof (no vapor penetration). Some-to-all sensors along the exterior side may be sealed from vapor penetration so that any failure mode would not result in an electrical arc in a location of possible refrigerant exposure.

[0050] As noted above, such propane mitigation may be avoided for electrical components and connections on the evaporator side such as: the evaporator fan motors; evaporator side heaters; and the DTS (defrost termination sensor) on the evaporator coil, HTT (high temperature termination sensor) on the evaporator coil, and temperature measurement sensor located slightly downstream of the evaporator.

[0051] Additional propane mitigation involves the placement of flame arrestors in a number of exterior locations. Background flame arrestor technology which may be utilized is found International Publication No. WO2015/009721A1, published January 22, 2015, the disclosure of which is incorporated herein in its entirety by reference as if set forth at length. One exemplary flame arrestor is one or more woven wire or perforated mesh (e.g., expanded metal mesh) panels 400 (FIG. 4) across openings along the front of the equipment box. This may cover openings to the compressor, heat exchangers, and any piping or other refrigerant carrying components of the vapor compression loop 31. Mesh opening size will depend on the inherent flammability and expected operating conditions of the particular refrigerant. However, locations along the flowpaths 510A and 510B may be avoided.

[0052] The system may be made using otherwise conventional or yet-developed materials and techniques.

[0053] The use of "first", "second", and the like in the description and following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as "first" (or the like) does not preclude such "first" element from identifying an element that is referred to as "second" (or the like) in another claim or in the description.

[0054] Where a measure is given in English units followed by a parenthetical containing SI or other units, the parenthetical' s units are a conversion and should not imply a degree of precision not found in the English units.

[0055] One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing basic refrigeration system and/or container construction and associated use methods, details of such existing configuration or its associated use may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims.