Patent Publication Number: US-2015075747-A1

Title: Flexible heat and moisture transfer system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/964,924, filed Aug. 12, 2013, which claims priority to U.S. Provisional Patent Application Ser. No. 61/682,232, filed Aug. 11, 2012, each of which is hereby incorporated by reference in their entirety. 
    
    
     INTRODUCTION 
     Mechanically heated or cooled and ventilated buildings and other structures require that some portion of fresh make-up air be added continuously to the total volume of circulated air to keep the space fresh, comfortable, and healthy. A corresponding portion of the air which has already been heated or cooled to the desired supply conditions must be exhausted, resulting in a loss of heat energy and a corresponding reduction in the heating or cooling efficiency of the system conditioning the air in the spaces. Heat exchangers are sometimes used in the exhaust air and makeup airflow paths of these systems such that heat is transferred between the two airstreams according to the temperature differential, leaving less cooling or heating to be performed by the mechanical system to bring the supply airstream to its desired conditions. So-called “total heat exchangers” or “energy recovery ventilators” exchange moisture as well as heat between the two airstreams, affecting the amount of humidification or dehumidification as well as the amount of heating or cooling required of the mechanical system. 
     Materials used for heat exchangers commonly include metal foils and sheets, plastic films, paper sheets, and the like. Good heat exchange is generally possible with these materials, but moisture exchange cannot easily be performed. Desiccants, or moisture adsorbing materials, are occasionally employed to transfer moisture. With this method, the desiccant merely holds the moisture. To effect transfer moisture between gas streams, the desiccant must be relocated from the gas stream of higher moisture content to the gas stream of lower moisture content, requiring an additional input of mechanical energy. With many desiccant materials, satisfactory performance can be achieved only with the input of additional thermal energy to induce the desiccant to desorb the accumulated moisture. 
     Heat and moisture exchange are both possible with an exchange-film made of paper. However, water absorbed by the paper from condensation, rain, or moisture present in the air can lead to corrosion, deformation, and mildew growth, and, hence, deterioration of the paper exchange film. The various types of heat and moisture exchangers in common usage are generally contained within an opaque metal housing and located at or near the building air handling units in the mechanical room, basement, or rooftop of the building. In the case of temporary or portable structures, the exchangers may be integrated into or located adjacent the stand alone equipment or “environmental control units” used to supply the ventilation air. The nature of moisture exchange requires a very large surface area in contact with the gas stream, and, consequently, total heat exchangers are often very large in size when compared to heat-only exchangers. A larger exchanger in the conventional location requires additional mechanical room space and/or additional load-bearing capacity of the roof in the case of a roof-top unit. 
     Porous polymeric or ceramic films are capable of transferring both heat and moisture when interposed between air streams of differing energy and moisture states. A system for heat and moisture exchange employing a porous membrane is described in Japanese Laid-Open Patent Application No. 54-145048. A study of heat and moisture transfer through a porous membrane is given in Asaeda, M., L. D. Du, and K. Ikeda. “Experimental Studies of Dehumidification of Air by an Improved Ceramic Membrane,” Journal of Chemical Engineering of Japan, 1986, Vol. 19, No. 3. A disadvantage of such porous composite film is that it also permits the exchange of substantial amounts of air between the gas streams, as well as particles, cigarette smoke, cooking odors, harmful fumes, and the like. From the point of view of building indoor air quality, this is undesirable. In order to prevent this contamination of make-up air, the pore volume of a porous film is preferably no more than about 15%, which is difficult and expensive to achieve uniformly. Furthermore, a porous film made to a thickness of 5 to 40 micrometers in order to improve heat exchange efficiency tears easily and is difficult to handle. 
     SUMMARY 
     In a first example, an environmental control system may include an environmental control device having a supply air inlet and a conditioned air outlet in fluid communication with an enclosed space; and a flexible heat and moisture exchanger including a flexible shell enclosing an interior channel, and a flexible, water vapor-permeable barrier disposed within the interior channel, the barrier partitioning the interior channel into a plurality of separate subchannels such that a first subchannel is in fluid communication with an atmosphere external to the enclosed space and with the supply air inlet, and a second, adjacent subchannel is in fluid communication with the external atmosphere and with the enclosed space; wherein the exchanger is configured to receive a supply air stream flowing in a first direction through the first subchannel, and to receive an exhaust air stream flowing simultaneously in a second direction through the second subchannel. 
     In a second example, an apparatus for enabling heat and moisture exchange may include a flexible shell enclosing an interior channel, and a flexible, water vapor-permeable barrier within the interior channel, the barrier partitioning the interior channel into a plurality of separate subchannels; wherein the apparatus is configured to receive a first gas stream flowing in a first direction through a first one of the subchannels and a second gas stream flowing simultaneously in a second direction through an adjacent second one of the subchannels. 
     In a third example, a heat and moisture transfer apparatus may include a flexible heat and moisture exchanger having a flexible outer shell enclosing a plurality of subchannels formed by at least one flexible, water vapor-permeable barrier; wherein the exchanger is convertible without disassembling the exchanger between an operational mode in which a first air stream is received flowing in a first direction through a first subchannel and a second air stream is simultaneously received flowing in a second direction through an adjacent second subchannel, and a collapsed mode in which the exchanger is disconnected from the first and second air streams and arranged into a portable configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative flexible heat and moisture transfer system. 
         FIG. 2  is a schematic diagram of another illustrative flexible heat and moisture transfer system. 
         FIG. 3  is an isometric view of an illustrative flexible heat and moisture exchanger showing cross-flow through a plurality of subchannels, with a cutaway view of an upper subchannel. 
         FIG. 4  is an isometric view of another illustrative flexible heat and moisture exchanger showing optional integration with an enclosure surface, as well as a different outer shell configuration and number of subchannels. 
         FIG. 5  is an isometric view of an end portion of an illustrative flexible heat and moisture exchanger, showing a transition from the exchanger to an illustrative header and manifold. 
         FIG. 6  is an isometric view of an end portion of another illustrative flexible heat and moisture exchanger, showing a transition from the exchanger to another illustrative header and manifold. 
         FIG. 7  shows an example of a flexible heat and moisture transfer system installed in operational configuration on a portable shelter. 
         FIG. 8  is a sectional view of the system of  FIG. 7  taken at line  8 - 8  as indicated in  FIG. 7 . 
         FIGS. 9 and 10  are schematic side views of illustrative portable configurations of the flexible heat and moisture exchanger of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     An efficient heat and moisture exchange apparatus is described herein which will not contaminate make-up air, and which has excellent heat exchange efficiency, high moisture exchange capability, and serves as a barrier to air flow between exhaust and makeup air streams. Furthermore, the exchanger described in the present disclosure is suitable for use with lightweight temporary, portable, and permanent structures in which the mechanical conditioning and ventilation equipment may not be located within or atop the structure but may instead stand on the ground adjacent the structure. In many of these cases, the structures may be pliable and flexible to enable packing and transport, such as tents, that are not amenable to large-scale rigid elements. Accordingly, a flexible heat and moisture exchanger is described that can be used in the operation of these flexible, mobile structures but can also be packed and transported easily with them. 
     Illustrative flexible heat and moisture transfer systems are shown schematically in  FIGS. 1 and 2  and throughout the drawings. Unless explicitly stated otherwise, the systems and apparatuses shown in the drawings may include one or more components, structures, variations, and/or functions of one or more other systems and apparatuses described in the present disclosure. Furthermore, the structures, components, functionalities, and/or variations described, illustrated, and/or incorporated herein in connection with flexible heat and moisture transfer systems may, but are not required to, be included in other heat and moisture transfer, heating, and/or cooling systems. 
     In general, a flexible heat and moisture transfer system may include a lightweight, flexible, compressible, resilient, counter-flow air-to-air heat and moisture exchanger in fluid communication with an enclosed space and an environment control unit (ECU) such as an air conditioner, where the ECU is used to condition the air of the enclosed space and the exchanger is used to precondition a supply stream for the ECU by extracting useful energy from an exhaust stream exiting the enclosed space. The term “environmental control device” may be used interchangeably herein with the term “ECU.” 
     The lightweight and flexible nature of the exchanger facilitates new capabilities such as installing one or more exchangers in an operational mode on top of an enclosed space, which may be in the form of a portable shelter such as a tent. One or more exchangers may also be integrated into the enclosing surfaces of a portable structure. A flexible and resilient exchanger may also be collapsed for transport or storage. For example, an exchanger according to the present disclosure may simply be rolled or folded without affecting the integrity of the apparatus. 
     Turning to  FIG. 1 , an illustrative flexible heat and moisture transfer system  10  includes an ECU  12 , an enclosed space  14 , and a flexible heat and moisture exchanger  16 . ECU  12  is in fluid communication with the enclosed space and is configured to supply enclosed space  14  with conditioned air. ECU  12  may include any suitable environment control device configured to alter one or more characteristics of the air within the enclosed space, such as temperature and/or humidity. For example, ECU  12  may include an air conditioner, a dehumidifier, a humidifier, a cooler, a heater, a furnace, a heat pump, and/or any other typical HVAC device or system. ECU  12  may include a completely portable device or system. In some examples, ECU  12  may include one or more permanently installed or non-portable components. 
     Enclosed space  14  may include any substantially enclosed space having an internal atmosphere capable of being controlled or conditioned using ECU  12 . Enclosed space  14  may include a human-occupied enclosure, and may include openings such as one or more doors, windows, ports, curtained access points, chimneys, and the like. In some examples, enclosed space  14  is configured to house equipment or vehicles, such as an enclosure for protecting electronic equipment in a cooled environment. In some examples, enclosed space  14  includes a temporary enclosure such as a tent or shed. In some examples, enclosed space  14  is itself collapsible and portable. In some examples, enclosed space  14  is a non-portable enclosure such as a house or cabin. 
     Streams of air are communicated through system  10 . As shown in  FIG. 1 , a supply stream S passes into enclosed space  14 , and an exhaust stream E passes out of enclosed space  14 . Supply stream S may generally be driven by a motive force imparted by ECU  12  and/or an associated fan or blower. Exhaust stream E may be driven out of enclosed space  14  by a pressure differential caused by the incoming stream S, or may itself be motivated by a fan or blower. The term “make-up” may be used interchangeably herein with the term “supply.” The term “return” may be used interchangeably herein with the term “exhaust.” 
     Exchanger  16  is a flexible heat and moisture exchanger and may include a flexible outer shell enclosing a channel divided into at least two subchannels  18  and  20  by a membrane  22 . Membrane  22  is a flexible membrane that is substantially impermeable to the constituent gases found in air, but is water vapor-permeable and capable of facilitating heat exchange. Examples of membrane  22  are described in further detail below. In some examples, membrane  22  may be separated from the outer shell and from any additional membranes included in the exchanger by including a resilient medium in each subchannel. In these examples, the resilient medium is sufficiently air-permeable to allow adequate flows of air through the subchannels during operation. For example, the resilient medium may be porous or may include apertures or channels through the medium to bias the subchannel against collapse while still allowing air flow. 
     Supply and exhaust streams pass through exchanger  16 , and exchange both heat and moisture via membrane  22 . In an example including an air conditioner (AC unit), the AC unit functions to cool and dehumidify the air in the enclosed space, and the exchanger functions to cool and dehumidify incoming air being supplied to the AC unit. Generally speaking, exhaust air from the enclosed space will be cooler and dryer than air being supplied from an atmosphere external to the space. Accordingly, heat and moisture from the supply air will be passed to the exhaust stream due to the temperature and humidity differential across membrane  22 . In an example including a heating unit, the heat exchange is reversed as incoming air is cooler than the exhaust. 
     In this example, exchanger  16  has a cross-flow or counter-flow configuration, and supply stream S passes through subchannel  18  in one direction at the same time exhaust stream E passes through subchannel  20  in another direction. These directions may be substantially opposite to each other, or may be transverse, such as when the flows are orthogonal to each other. In some examples, a combination of opposite and transverse flow pathways may be included in the exchanger. It should be understood that in a multi-direction arrangement, the streams may at times be parallel (i.e., flowing in the same direction) without altering the substantially cross-flow nature of the exchanger. In some examples, an exchanger according to the present disclosure may be substantially completely parallel. These examples are less efficient in terms of heat and moisture exchange, but do simplify associated header configurations, and may be suitable to certain applications. The examples described herein will be cross-flow in configuration. 
     In some examples, more than one membrane  22  may be included, or membrane  22  may be arranged in such a way, as to create more than two subchannels. For example, multiple parallel membranes may create stacked or layered subchannels. In other examples, subchannels may be created that are side-by-side, honey-combed, or labyrinthine. In these examples, as in the one shown in  FIG. 1 , adjacent subchannels will be configured to pass either supply stream S or exhaust stream E (or substreams thereof) in order to effect heat and moisture exchange across the interposed membrane. 
     In addition to the exchanger, ECU, and enclosed space, various conduits may be used to direct the flow of supply stream S and exhaust stream E. For example, a header  24 ,  26  may be included at either or both ends of exchanger  16 . Each header  24 ,  26  may include any suitable conduit structure configured to direct the flow of a stream into or out of its associated subchannels. For example, at a first end indicated at A in  FIG. 1 , header  24  may interface with the end of exchanger  16  such that incoming air is directed selectively into subchannel  18 , while air from exhaust stream E is directed out of subchannel  20  and away from the source of incoming air to prevent exhaust from recirculating immediately into the supply system. At a second end indicated at B in  FIG. 1 , header  26  may interface with end B such that supply stream S is directed out of subchannel  18  and toward an inlet of ECU  12 , while exhaust stream E from enclosed space  14  may be directed into subchannel  20 . Specific examples of headers such as headers  24  and  26  are described below. 
     Additional conduits may be included at either or both ends of exchanger  16 . For example, manifold  28  may be connected to header  24  and manifolds  30  and  32  may be connected to header  26  to act as conduits for supply stream S and exhaust stream E, respectively. Each manifold may include any suitable conduit structure configured to interface with one or more headers to direct either supply or exhaust air between the header and a second location. While only a supply type of manifold is shown connected to header  24 , an exhaust manifold may also (or instead) be provided, to direct exhaust air away from header  24 . On the other hand, header  24  may be configured such that neither type of manifold is required. These conduits are referred to as manifolds because they may be used for connecting multiple headers from multiple exchangers, to handle cumulative exhaust and/or supply streams. 
     Accordingly an illustrative pathway for incoming supply air (supply stream S) may be described as flowing into manifold  28  from the external atmosphere, passing through header  24  and into subchannel  18 . Flowing through subchannel  18 , supply stream S exchanges heat and/or moisture with a counter-flowing exhaust stream E via membrane  22 . A pre-conditioned supply stream S then exits the exchanger and passes through header  26  where it is directed into manifold  30 . From manifold  30 , the stream passes into ECU  12 , where it is fully conditioned (e.g., cooled, dehumidified, heated, etc.) and forced into enclosed space  14 . At the same time, an illustrative pathway for outgoing exhaust air (exhaust stream E) may be described as flowing into exhaust manifold from within enclosed space  14 , and passing through header  26  into subchannel  20 . As exhaust stream E flows through subchannel  20 , heat and/or moisture are exchanged with counter-flowing supply stream S. The exhaust then passes out of the exchanger and is directed by header  26  away from any intake ports or manifolds, possibly through an exhaust manifold before being exhausted into the external atmosphere. 
     Exchanger  16  may be disposed at least partly on or forming a part of an outer surface of enclosed space  14 . Exchanger  16  may act as an insulating device positioned between the space and an external environment. Because exhaust stream E will typically be closer in temperature to the interior of space  14  than supply stream S, exchanger  16  may be disposed such that subchannel  20  is adjacent to the space to maximize insulating effect. The physical flexibility of exchanger  16  may allow the exchanger to conform to many irregular or shaped surfaces such as those found on portable structures, tents, and the like. 
       FIG. 2  is a schematic diagram showing another example of a flexible heat and moisture transfer system  40  similar to system  10 . System  40  includes an ECU  42 , an enclosed space  44 , and a plurality of flexible heat and moisture exchangers  46 ,  48 , and  50 . ECU  42  is substantially identical to ECU  12 , enclosed space  44  is substantially identical to enclosed space  14 , and each exchanger ( 46 ,  48 ,  50 ) is substantially identical to exchanger  16 . System  40  shows an example of multiple exchangers serving a single space, with a corresponding illustrative arrangement of headers and manifolds to accommodate the added exchangers. 
     As shown in  FIG. 2 , each exchanger includes a header at each end, and manifolds connect and accumulate the various respective supply and exhaust streams. Exchanger  46  includes a header  52  at a first end A′, and a header  54  at the opposite second end B′. Exchanger  48  includes a header  56  at A′ and a header  58  at B′. Exchanger  50  includes a header  60  at A′ and a header  62  at B′. Manifold  64  connects the supply subchannels of headers  52 ,  56 , and  60 , and directs supply stream S′ to each exchanger. Manifold  66  connects the supply stream subchannels at the other end, at headers  54 ,  58 , and  62 , and directs the cumulative supply stream S′ to ECU  42 . Likewise, manifold  68  connects the exhaust stream subchannels at headers  54 ,  58 , and  62  and directs exhaust stream E′ to each exchanger. 
       FIGS. 3 and 4  show two illustrative configurations of layered subchannels within a flexible heat and moisture exchanger similar to exchangers  16 ,  46 ,  48 , and  50 .  FIG. 3  shows a six-subchannel flexible heat and moisture exchanger  70  in an isometric, sectional, partially cutaway view. Exchanger  70  includes a flexible outer shell  72  and five parallel membranes  74 ,  76 ,  78 ,  80 , and  82 , each an example of membrane  22 , separating the channel formed by shell  72  into six subchannels  86 A,  86 B,  86 C,  88 A,  88 B, and  88 C. Situated within each subchannel is a biasing material  90 . 
     Flexible outer shell  72  may include any suitable fabric or fabric-like material that is flexible, capable of withstanding environmental conditions such as adverse weather and solar radiation, and capable of being formed into a substantially airtight, substantially waterproof, lateral enclosure or housing for conducting one or more streams of air. Flexible outer shell  72  may include a flexible material that may be a cast, woven, or molded sheet. For example, outer shell  72  may include nylon, rubber, PTFE fabric, canvas, and/or other materials. In some examples, outer shell  72  may include on an outward and/or inward-facing surface, a layer that is reflective or has a low emissivity in the solar spectrum, or the material of outer shell  72  may itself have this property. For example, an emissive layer may have an emissivity in the solar spectrum of about 0.05 to about 0.15, and may have an emissivity of approximately 0.08. Such properties may be achieved by a layer of highly reflective material such as aluminum or metallized film that is coated onto, laminated together with, adhered to, impregnated into or otherwise combined with the outer shell. 
     Each flexible membrane  74 ,  76 ,  78 ,  80 , and  82  is moisture- or water vapor-permeable and also capable of facilitating heat transfer between gases on either side of the membrane. The term “barrier” may be used interchangeably with the term “membrane.” In some examples, each water vapor-permeable barrier may include an anisotropic composite film made of porous polymeric substrate having applied thereto a water vapor-permeable polymeric material so as to form a nonporous barrier with respect to air and other gases. In some examples, the porous polymeric substrate may include a porous PTFE membrane. In some examples, the non-porous water vapor-permeable polymeric material may include a hydrophilic polyurethane polymer. 
     As generally described above, each membrane  74 ,  76 ,  78 ,  80 ,  82  may be interposed between a gas stream having a first, higher water content, and a gas stream having a second, lower water content stream. Moisture from the gas stream having the higher water content permeates through the composite film to the side adjacent the gas stream having the lower water content where the moisture is taken up by the gas stream having the lower water content. Heat from the higher temperature gas stream is conducted through the composite film and taken up by the lower temperature gas stream, thereby effecting heat and moisture exchange between the gas streams adjacent each side of the barrier. 
     Accordingly, supply and exhaust streams will be passed through alternating subchannels to enable the heat and moisture exchange discussed above, as shown in  FIG. 3 . Specifically, exhaust streams will be passed through subchannels  86 A,  86 B, and  86 C, while supply streams are simultaneously passed through subchannels  88 A,  88 B, and  88 C. 
     Biasing material  90  may be included in each subchannel to bias the respective subchannel against collapse. Because the various components of exchanger  70  are flexible, a continuous opening along the length of any given subchannel may not be guaranteed. Accordingly, some sort of biasing material or structure may be included within a subchannel to maintain a continuous path for an air stream. Biasing material  90  may include any suitable lightweight, flexible structure and/or material that is porous or permeable with respect to the constituent gases of air, while being resilient and sufficiently structural to prevent collapse of the subchannel during normal operation. In some examples, biasing material  90  may include a resilient corrugated structure forming longitudinal channels within the subchannel while separating adjacent membranes. In some examples, biasing material  90  may include a thick, porous, air-permeable sheet formed of a heat-set polyamide mesh. The term “spacer” may be used interchangeably with “biasing material.” 
     Biasing material  90  may also facilitate the portable or storage configuration of an exchanger, because the resilience of biasing material  90  allows the exchanger to be partly or completely collapsed and subsequently placed back into operation without losing structural integrity. In other words, the exchanger itself does not need to be disassembled in order to collapse it for transport or storage. Additionally, in some examples, the spacer material may be unattached or substantially physically independent of the membranes and outer shell, which may further facilitate collapse by preventing binding during folding or rolling of the exchanger. In some examples, the spacer material is removable for replacement or disassembly. 
     Spacer or biasing material  90  may function to create a more tortuous path for air flow through an otherwise continuous subchannel, thereby increasing potential heat and moisture exchange. However, biasing material  90  should not cause a large drop in pressure across the exchanger, in order to remain adequately functional as a conduit for air flow. In some examples, a permeability of the biasing material may be preferably no less than approximately 254.0 cm 3 /s-cm 2  (i.e., 500 ft 2 /min/ft 2 ) when tested per ASTM Standard D737-04 (2012) at testing conditions of 21±1 degree C., 65±1% relative humidity, and 125 Pa. 
       FIG. 4  shows another example of a flexible heat and moisture exchanger  90  in an isometric sectional view. Exchanger  90  is substantially similar to exchanger  70 . However, exchanger  90  includes an outer shell  92  that is sewn or welded together at a flange  94 , and includes three membranes  96 ,  98 , and  100  separating four subchannels  102 A,  102 B,  104 A, and  104 B, each biased against collapse by a fill material  106 . In this example, exhaust air may flow through subchannels  102 A and  102 B, while supply air flows through subchannels  104 A and  104 B. In some examples, exchanger  90  may be joined to or integrated into portions of a wall or other surface  107  of the enclosed space, such as at flange  94 . In these examples, the exchanger itself comprises a portion of the enclosure. 
       FIGS. 5 and 6  show two different examples of terminal ends of exchangers such as exchanger  70  and  90 , with different header and manifold configurations.  FIG. 5  is a partially-exploded, isometric view of a four-subchannel flexible heat and moisture exchanger  110  that is substantially similar to the exchangers described above. In this example, exchanger  110  includes four subchannels  112 A,  1128 ,  114 A, and  1148 , and terminates in a triangular configuration  116 , forming two faces  118  and  120 . Each face exposes open ends of the subchannels. In this example, subchannels  112 A and  1128  are used for an exhaust stream, while alternating subchannels  114 A and  1148  are used for a supply stream. On face  118 , corresponding subchannels  114 A and  114 B are blocked, while on face  120 , corresponding subchannels  112 A and  112 B are blocked. Accordingly, face  118  allows the exhaust stream to pass through while blocking the supply stream, and face  120  allows the supply stream to pass through while blocking the exhaust stream. 
     A header  122  is configured to attach to the end of exchanger  110  as shown in  FIG. 5 , by sliding over the end or otherwise attaching such that faces  118  and  120  are enclosed within the header. An apex  124  where faces  118  and  120  meet is configured to contact an inner wall of the header, and the header is friction fit to the top and bottom of the exchanger, thereby isolating face  118  from  120 . Header  122  includes two legs  126  and  128 , each leg forming a duct or conduit extending from a respective face of exchanger  110 . In this example, leg  126  extends from face  118 , and leg  128  extends from face  120 . A distal end of each leg is configured to be operatively connected to a manifold, such as to manifolds  130  and  132  depicted in  FIG. 5 . 
     Multiple exchangers may be disposed side by side. Accordingly, legs  126  and  128  may be shaped or positionable to avoid interfering with adjacent headers or manifolds. For example, as depicted in  FIG. 5 , leg  128  may have an S-shaped profile to place a distal end of the leg in a different plane than a distal end of leg  126 . This arrangement would allow, for example, the overlapping configuration of manifolds shown in  FIG. 2 . Other configurations are possible. 
     Turning to  FIG. 6 , another example of an exchanger/header/manifold is depicted in an isometric, partially exploded view. In this example, a flexible four-subchannel heat and moisture exchanger  140  that is substantially similar to the exchangers described above. In this example, exchanger  140  includes four subchannels  142 A,  142 B,  144 A, and  144 B, and terminates in a rectangular configuration  146 , forming two faces  148  and  150 . Each face exposes open ends of the subchannels. In this example, similar to the example of  FIG. 5 , subchannels  142 A and  142 B are used for an exhaust stream, while alternating subchannels  144 A and  144 B are used for a supply stream. On face  148 , corresponding subchannels  144 A and  144 B are blocked, while on face  150 , corresponding subchannels  142 A and  142 B are blocked. Accordingly, face  148  allows the exhaust stream to pass through while blocking the supply stream, and face  150  allows the supply stream to pass through while blocking the exhaust stream. 
     As with the previous example, a header  152  is configured to attach to the end of exchanger  140  as shown in  FIG. 6 , by sliding over the end or otherwise attaching such that faces  148  and  150  are enclosed within the header. Here, however, the header is shaped to friction fit to all four sides of the exchanger, isolating face  148  from face  150  by providing spaced apart legs  156  and  158  that each only opens to one face of the exchanger. Each leg forms a duct or conduit extending from a respective face of exchanger  140 , and includes a distal end configured to be operatively connected to a manifold, such as to manifolds  160  and  162  depicted in  FIG. 6 . 
     As in the previous example, the legs of header  152  may be shaped or positionable to avoid interference when multiple exchangers are disposed side by side. In this example, legs  156  and  158  extend in orthogonal directions to place a terminal end of leg  156  to a different plane and a different orientation than a terminal end of leg  158 . This arrangement would allow, for example, the parallel manifold configuration shown in  FIG. 6 . Other configurations are possible. 
       FIGS. 7 and 8  respectively show an isometric view and a sectional view of an illustrative heat and moisture transfer system  170  installed in an operational configuration  172 . System  170  includes an ECU in the form of an AC unit  174 , an enclosed space in the form of a tent  176 , multiple flexible heat and moisture exchangers  178 ,  180 , and  182 , and a combination header and manifold  184 . 
     The components shown in  FIGS. 7 and 8  are substantially similar to the corresponding components described above for systems  10  and  40 . Exchangers  178 ,  180 , and  182  are configured as panel-like, flexible devices that are laid side-by-side over the top of tent  176 . In this example, tent  176  has a rounded roof. It should be understood that exchangers constructed according to the present disclosure could be laid over a tent or other structure having a peaked roof or any other practical profile. For ease of explanation, exchangers  178 ,  180 , and  182  are depicted as two-subchannel exchangers. However, each exchanger may have any number of subchannels, as described above. 
     The three exchangers in this example are connected at one end to a single divided manifold  184  that also functions as a header similar to those described regarding  FIGS. 5 and 6 . Manifold  184  may be constructed of a fabric or other material similar to the outer shell of an exchanger, or may be constructed of a rigid material such as sheet metal or standard ducting. Manifold  184  may be temporarily or permanently connected to the exchangers, and may be collapsible along with the exchangers when converting them to transport or storage configuration. 
     Operation of the system depicted in  FIGS. 7 and 8  will now be described, in order to explain further the various structures and devices involved. Beginning at the distal ends of the exchangers, supply air is drawn into a supply subchannel  186  by a motive force provided by AC unit  174  or by a fan or blower (not shown). Passing through the exchangers, supply air is cooled and dehumidified by exchanging heat and moisture with cooler, dryer exhaust air in an adjacent exhaust subchannel  188  via a membrane  190 . The supply air then exits the exchangers and passes into a supply side  192  of manifold  184 , where it accumulates and passes through a duct  194  leading from the manifold to the AC unit. The AC unit then conditions the air by cooling and dehumidifying, and pumps the conditioned air through a port in the tent via another duct or conduit  196 . 
     The conditioned air then becomes a part of the general atmosphere internal to the tent. The air circulates throughout the space, and generally is heated and becomes more humid as it encounters occupants, outside air entering through a door or window, general heat transfer through the walls of the tent, and other phenomena. Due to a pressure differential or a motive force such as a fan or blower (not shown), air inside the tent is expelled through one or more exhaust ports  198  and into an exhaust side  200  of manifold  184 . From there, the exhaust stream enters exhaust subchannel  188  of each exchanger, and travels through the exchangers. Because the exhaust stream is typically still cooler and dryer than outside air in the supply stream, heat and moisture are transferred to the exhaust stream from the supply stream via membrane  190 . The exhaust stream then exits the exchangers, and may pass through a manifold or other conduit (not shown) before entering the general outdoor atmosphere. 
       FIGS. 9 and 10  are schematic side views of two different portable configurations or modes of an exchanger such as the exchangers described in the previous example. 
       FIG. 9  shows a portable configuration or mode  202  in which an exchanger  204  is rolled.  FIG. 10  shows a portable configuration or mode  206  in which an exchanger  208  is folded. One having skill in the art will appreciate that many possible configurations are possible for placing a lightweight flexible heat and moisture exchanger into a collapsed mode allowing it to be easily stored or transported. It will also be understood that, although portions of the exchanger may be collapsed, crushed, or pinched, the resilient and flexible characteristics provided by the components of an exchanger constructed according to the present disclosure will facilitate placing the exchanger back into operation without a loss of functionality. 
     EXAMPLES AND ADDITIONAL DETAILS 
     Some embodiments of the present disclosure may be described as an apparatus for enhanced heat and moisture exchange between make-up and exhaust air streams including a flexible housing having an exterior wall defining an interior channel through which air streams may pass and a water vapor permeable barrier disposed within the interior channel so as to partition the interior channel into a plurality of subchannels. The flexible housing may comprise a flexible material that may be created as a cast, woven, molded sheet or other format. The layers of water vapor permeable membrane, which are also flexible, may be separated into a plurality of subchannels by the insertion of a flexible, porous sheet medium between membrane layers. The porous medium may be created from woven or non woven nylon, cast or molded plastic, or other organic and inorganic materials. 
     Some embodiments of the present disclosure may be described as an apparatus for enabling heat and moisture exchange including an exchanger housing comprising a flexible exterior wall defining an interior channel through which a gas stream may pass. A water vapor permeable barrier is disposed within the interior channel and partitions the interior channel into a plurality of subchannels. The subchannels defined within the apparatus are connectable to makeup and exhaust air streams or sources thereof. 
     Some embodiments of the present disclosure may be described as a heat exchanger enclosed in a flexible housing comprising a flexible material that may be created as a cast, woven, molded sheet or other format. 
     Some embodiments of the present disclosure may be described as having layers of water vapor permeable, flexible membrane that may be separated into a plurality of subchannels by the insertion of a flexible, porous sheet medium between membrane layers. The porous medium may be created from woven or non-woven nylon, cast or molded plastic, or other organic and inorganic materials. 
     Some embodiments of the present disclosure may be described as having the pressure of the gas streams controlled so that the makeup and exhaust streams flow through the subchannels of the exchanger apparatus in different directions. 
     Some embodiments of the present disclosure may be described as having the radiant exchange between surfaces of the apparatus controlled or affected through the inclusion of one or more material layers with particular reflective or transmissive properties within the radiation spectrum of interest. The radiant barrier layer or layers may comprise a layer forming the exchanger housing, an interior subchannel layer, or it may be formed by coating a substance with the desired radiant properties onto a surface of one of the existing material layers within the apparatus. 
     Some embodiments of the present disclosure may be described as a flexible heat and moisture exchanger mounted onto or incorporated within the exterior surface of the structure where, by virtue of the heat and moisture exchange between the airstreams flowing within it, the exchanger alters the overall transfer of heat between the interior and exterior of the structure. 
     Some embodiments of the present disclosure may be described as having an entire exchanger apparatus constructed from flexible materials as described above in order to enable it to conform to the surface of a structure with complex geometry. The exchanger apparatus may also be constructed from flexible materials to enable it to be packable and lightweight for easier transport. 
     Some embodiments of the present disclosure may be described as a flexible exchanger laid over the exterior surface or connected to the interior surface of a lightweight or temporary structure, such as a tent. In this embodiment, the subchannels of the exchanger are connected to the supply and return airstreams of the mechanical ventilation and conditioning unit serving the structure. 
     Some embodiments of the present disclosure may be described as a flexible exchanger integrated into the surface of a lightweight or portable structure. In the case of a tent or fabric structure, the exchanger apparatus may be sewn or welded into the tent surface. The exchanger may be connected to the supply and return airstreams as described in the previous embodiment. 
     Some embodiments of the present disclosure may be described as a method for exchanging heat and moisture between a first gas stream having a higher water content and a second gas stream having a lower water content comprises the steps of separating the first gas stream and the second gas stream with a flexible water vapor permeable barrier, and controlling the pressure of the first gas stream and second gas stream to enable exchange of heat and moisture between the streams. 
     Some embodiments of the present disclosure may be described as having a membrane dividing the two channels through which the gas streams flow, configured to maximize surface contact with the gas streams and tortuousity of the gas stream flow. Both configuring the geometry to maximize gas stream surface contact and gas stream turbulence and tortuousity serve to enhance the transfer of heat and permeation of water vapor from one gas stream to the other. 
     Some embodiments of the present disclosure may be described as including a membrane impregnated with a substance to enhance the permeation of water vapor from one gas stream to the other. Such substance may be highly hygroscopic. Further, the substance may be a hygroscopic electrolyte that would enhance the flux factor by two to five without any adverse effects on the selectivity. Preferably, the electrolyte is a salt of an alkali metal, an alkaline-earth metal or a transition metal. In particular, the metals lithium, sodium, potassium, magnesium and calcium are available, but also other metals from the groups named. The salt is preferably a chloride, bromide, fluoride, sulphate or nitrate. Preferably, the choice is for a salt whose saturated solution in water has a vapor tension which is lower than the partial water vapor tension of the mixture to be dehydrated. Salts such as LiBr, KCl, MgCl 2 , CaCl 2 , SrSO 4 , and NaNO 3  are found to give an excellent result. Salts which are readily soluble in water and have hygroscopic properties may be capable of producing satisfactory results. 
     Based on the above description and the associated drawings, the following numbered paragraphs describe examples of various embodiments of systems and apparatuses of the disclosure. 
     A0. An environmental control system comprising: an environmental control device having a supply air inlet and a conditioned air outlet in fluid communication with an enclosed space; and a flexible heat and moisture exchanger including: a flexible shell enclosing an interior channel; and a flexible, water vapor-permeable barrier disposed within the interior channel, the barrier partitioning the interior channel into a plurality of separate subchannels such that a first subchannel is in fluid communication with an atmosphere external to the enclosed space and with the supply air inlet, and a second, adjacent subchannel is in fluid communication with the external atmosphere and with the enclosed space; wherein the exchanger is configured to receive a supply air stream flowing in a first direction through the first subchannel, and to receive an exhaust air stream flowing simultaneously in a second direction through the second subchannel. 
     A1. The system of paragraph A0, further including a resilient, air-permeable spacer disposed within each subchannel configured to bias the respective subchannel against collapse. 
     A2. The system of paragraph A0, wherein the heat and moisture exchanger is convertible, without disassembly of the heat and moisture exchanger, between an operational configuration in which the heat and moisture exchanger conforms at least in part to a surface of the enclosed space, and a portable configuration in which the heat and moisture exchanger is collapsed. 
     A3. The system of paragraph A0, wherein the water vapor-permeable barrier comprises a membrane that is substantially impermeable to constituent gases of air. 
     A4. The system of paragraph A0, further including a conduit portion configured to conduct the supply air stream from an end portion of the heat and moisture exchanger to the supply air inlet of the air conditioning device. 
     A5. The system of paragraph A4, further including a header portion configured to directionally separate the supply air stream from the exhaust air stream at the end portion of the heat and moisture exchanger. 
     A6. The system of paragraph A0, wherein the heat and moisture exchanger is a first heat and moisture exchanger, the system further including a substantially identical second heat and moisture exchanger and a flexible manifold configured to place the respective end portions of the first and second heat and moisture exchangers into fluid communication with each other. 
     A7. The system of paragraph A0, wherein the flexible heat and moisture exchanger is further configured to be disposed at least partially on a surface of the enclosed space. 
     A8. The system of paragraph A7, wherein flexible heat and moisture exchanger is further configured to be disposed with the second subchannel disposed closer to the surface of the enclosed space than the first subchannel. 
     A9. The system of paragraph A0 wherein the flexible heat and moisture exchanger is integrated into a surface of the enclosed space. 
     B0. An apparatus for enabling heat and moisture exchange, the apparatus comprising:
         a flexible shell enclosing an interior channel; and   a flexible, water vapor-permeable barrier within the interior channel, the barrier partitioning the interior channel into a plurality of separate subchannels;   wherein the apparatus is configured to receive a first gas stream flowing in a first direction through a first one of the subchannels and a second gas stream flowing simultaneously in a second direction through an adjacent second one of the subchannels.       

     B1. The apparatus of paragraph B0, further including a resilient, air-permeable material disposed within each subchannel for biasing the respective subchannel against collapse. 
     B2. The apparatus of paragraph B0, wherein the water vapor-permeable barrier comprises a membrane that is substantially impermeable to constituent gases of air. 
     B3. The apparatus of paragraph B0, wherein the flexible shell further comprises a layer having an emissivity of about 0.05 to about 0.15 in the solar spectrum. 
     B4. The apparatus of paragraph B0, wherein the apparatus is configured to be in fluid communication with an enclosed space. 
     B5. The apparatus of paragraph B4, wherein the apparatus is configured to conform at least in part to a surface of the enclosed space. 
     B6. The apparatus of paragraph B5, wherein the enclosed space comprises a tent, and the apparatus is configured to conform at least in part to a roof portion of the tent. 
     B7. The apparatus of paragraph B4, wherein the apparatus is configured to form at least a portion of an outer surface of the portable enclosed space. 
     C0. A heat and moisture transfer apparatus comprising: a flexible heat and moisture exchanger having a flexible outer shell enclosing a plurality of subchannels formed by at least one flexible, water vapor-permeable barrier; 
     wherein the exchanger is convertible without disassembling the exchanger between an operational mode in which a first air stream is received flowing in a first 
     direction through a first subchannel and a second air stream is simultaneously received flowing in a second direction through an adjacent second subchannel, and a collapsed mode in which the exchanger is disconnected from the first and second air streams and arranged into a portable configuration. 
     C1. The system of paragraph C0, wherein the exchanger is configured to be arranged into the portable configuration by folding. 
     C2. The system of paragraph C0, the first subchannel of the exchanger further including a resilient, porous spacer configured to bias the first subchannel against collapse. 
     CONCLUSION 
     The disclosure set forth above may encompass multiple distinct inventions with independent utility. Although each of these inventions has been disclosed in its preferred form(s), the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense, because numerous variations are possible. 
     The subject matter of the inventions includes all novel and nonobvious combinations and subcombinations of the various elements, features, functions, and/or properties disclosed herein. The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. Inventions embodied in other combinations and subcombinations of features, functions, elements, and/or properties may be claimed in applications claiming priority from this or a related application. Such claims, whether directed to a different invention or to the same invention, and whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the inventions of the present disclosure.