Abstract:
A composite desiccant material is formed by a porous, absorbent substrate of PVA foam or non-woven fibrous sheet is soaked in a solution of a hygroscopic desiccant such as CaCl. The desiccant is held in pores or fibrous entraining areas sized ranging from 50 microns to 1000 microns. Thin sheets are arranged in a stack in a multi-chamber system, while in an absorption state, uses this stack in a main chamber to absorb H 2 O from atmospheric gas flowing through that chamber. In a regeneration state atmospheric flow is stopped and low-grade energy releases the H 2 O from the desiccant into that chamber. Fans circulate moist air through the main chamber and into an adjacent chamber for H 2 O transfer through or past a partially permeable barrier into a cooling/condensing area. Both H 2 O and dry gas may be produced.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional application 61/318,093, now pending, filed Mar. 26, 2010, which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The subject relates to materials, methods, and apparatus for extracting water vapor from a gas. Particularly it includes methods and devices related to extracting water from atmospheric air via a hygroscopic material dispersed within an absorbent sheet material of effective form factor for sorption and for regeneration. 
       BACKGROUND 
       [0003]    There are many materials identified as desiccants and many known configurations and systems employing desiccants to dry a gas. Systems include those using a solid desiccant and those using a liquid desiccant. In the case of systems based upon liquid desiccants, many existing concepts increase the exposed surface area of desiccant by spraying the desiccant in a mist. Besides the mechanism and energy required for such schemes the resulting chemical mist might, undesirably, be present in the output gas and output water. Solid forms of desiccant avoid these problems but generally do so at the cost of a relatively small exposed surface area per unit of mass leading to inefficiencies. Solid desiccants can also have relatively long regeneration times. 
         [0004]    There is a need for a form of desiccant that provides a high ratio of surface area to mass in a convenient to deploy form factor. Also needed are systems employing such a material to dry a gas, preferably using low-grade energy in an efficient manner. 
       SUMMARY 
       [0005]    Deficiencies in previous desiccant and air-to-water systems can be solved by a desiccant subsystem that can include a stack of spaced-apart thin sorbent sheets of a composite desiccant. The composite desiccant can be a sheet of a porous material with small pores for retaining moisture and larger pores allowing the flow of moist gas within its structure. The composite desiccant material is made up of a substrate of the sorbent sheet that contains dispersed particles of a hygroscopic chemical. 
         [0006]    To enhance water retention capacity, the stack can be mounted perpendicular to the direction of gravity or acceleration. This can engender a more even distribution of held water with no low spot for water to collect and drip from. 
         [0007]    A system of efficiently extracting water from air can be constructed with the desiccant stack attracting and retaining moisture in air fed to it and through it by fans. A control system can chose to operate the fans when conditions of humidity and the remaining capacity of the desiccant stack are conducive to efficient charging operation. A control system can further initiate a regeneration cycle when the availability of low-grade heat energy and the fullness of the desiccant stack are conducive to efficient regeneration operation. Further, a control system can initiate a condensing mode when the degree of moisture in a regeneration chamber is high enough relative to the temperature of an available cold source for efficient condensing operation. The condensing operation can involve a filter or membrane to differentially engender the passage of water molecules to be condensed versus other warm gases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1A  shows a photomicrograph at a magnification of 400× of a PVA foam dry; 
           [0009]      FIG. 1B  shows a photomicrograph at a magnification of 400× of the PVA foam of  FIG. 1A  damp; 
           [0010]      FIG. 1C  shows a photomicrograph at a magnification of 400× of the PVA foam of  FIG. 1A  saturated with water; 
           [0011]      FIG. 2  shows a photomicrograph at a magnification of 400× of a human hair; 
           [0012]      FIG. 3A  shows a photomicrograph at a magnification of 400× of a PVA foam with CaCl dispersed within its pores, dry; 
           [0013]      FIG. 3B  shows a photomicrograph at a magnification of 400× of the PVA foam with CaCl of  FIG. 3A , damp; 
           [0014]      FIG. 3C  shows a photomicrograph at a magnification of 400× of a non-woven rayon fabric, dry; 
           [0015]      FIG. 4  schematically illustrates a sheet of a composite desiccant formed from a PVA foam with disbursed CaCl; 
           [0016]      FIG. 5  schematically shows a stack of desiccant sheets in perspective and an airflow direction; 
           [0017]      FIG. 6  illustrates, in elevation, a stack of desiccant sheets mounted together by spacers with openings; the stack viewed from the front, air input side; 
           [0018]      FIG. 7  shows a side view of the desiccant stack of  FIG. 6 ; 
           [0019]      FIG. 8  illustrates an alternative stack of desiccant sheets mounted together by solid spacers that extend partially over the width of the stack viewed from the front, which is the air input side; 
           [0020]      FIG. 9  is a plan view of the stack of  FIG. 8  seen with the uppermost sheet removed; 
           [0021]      FIG. 10  is a schematic diagram of a system for extracting water from air showing the air circulation patterns in three distinct modes; 
           [0022]      FIG. 11  is a block diagram view of a control system for an air-to-water system; 
           [0023]      FIG. 12  is a schematic diagram of a condenser portion of the system of  FIG. 10  with a filter; 
           [0024]      FIG. 13  is a schematic diagram of an alternate condenser portion of the system of  FIG. 10  with a membrane; 
           [0025]      FIG. 14  is a state diagram of the states of the control system of  FIG. 11 ; 
           [0026]      FIG. 15  is a table showing criteria for transitioning states; 
           [0027]      FIG. 16  is a flow chart of the actions of the system of  FIG. 10  and  FIG. 11  in the charging mode; 
           [0028]      FIG. 17  is a flow chart of the actions of the system of  FIG. 10  and  FIG. 11  in the regeneration mode; 
           [0029]      FIG. 18  is a flow chart of the actions of the system of  FIG. 10  and  FIG. 11  in the condensing mode; 
           [0030]      FIG. 19  is a flow chart of the actions of the system of  FIG. 10  and  FIG. 11  in the quiescent mode; 
           [0031]      FIG. 20  illustrates an embodiment of a split system air-to-water system; 
           [0032]      FIGS. 21-23  illustrate a compact embodiment of an air-to-water system with a membrane. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    In conjunction with the included drawings, this detailed description is intended to impart an understanding of the teachings herein and not to define their metes and bounds. 
       Introduction 
       [0034]    One aspect of the present invention is a composite desiccant material in an effective form factor. Another aspect is a desiccant subsystem based upon that composite desiccant material, and a third aspect includes systems and methods of extracting water from air employing the subsystem. 
       Structure 
     Desiccant Material and Subsystem 
       [0035]    The desiccant composition includes a porous support material and a hydroscopic absorbent dispersed within the porous support material. The porous support material has pores or pore-like small random gaps of a wide range of sizes. Small pores include pores of about 70 microns to large pores of about 1000 micrometers. This porous support material can include a material such as PVA foam or a non-woven fabric such as rayon. The desiccant composition disbursed with the support material includes a hygroscopic absorbent such as CaCl. 
         [0036]    Another aspect of these teachings is directed to a method for producing a desiccant composition comprising the steps of: (a) providing a porous support material having a range of pores from 70 micros to 1000 microns; (b) contacting the porous support material with a flowable medium comprising a hygroscopic absorbent, for a time sufficient to substantially fill porosity in the porous support material and then drying the porous support material to remove liquid from the flowable medium and form a desiccant composition comprising the absorbent dispersed on the porous support. A supporting PVA sheet  10 , seen in photomicrographs in  FIGS. 1A ,  1 B, and  1 C, is a preferred support material. That material then has embedded, but not positionally captivated, particles of a chemically active desiccant. 
         [0037]    Appropriate soaking of the porous support material in a liquid solution of a chemical such as CaCl, Ethyl Glycol, and Lithium Bromide followed by drying the material can be an effective manner of producing such a composite. This is generally taught in Type “Salt-in-a-Porous-Matrix” Sorbents in Hydrocarbon Processing, by E. A. Buluchevskii. This article is found in the Russian Journal of General Chemistry 2007, Vol. 77, pp. 2284-2291. Pleiades Publishing, Ltd., 2007. Other related teachings are seen in U.S. Pat. No. 6,559,096, May 6, 2003, of Smith et. al. In contrast with these and other “salt in a porous matrix” materials, herein is taught a non-captive entrainment of the adsorbent salt in the absorbent material. The desiccant salt particles and brine can migrate within the absorbent substrate due to the larger pores and can be mechanically removed from the substrate. 
         [0038]      FIG. 1A  is a 400× microphotograph of PVA foam in a dry state. The PVA foam used in this example was purchased from Ninbo Goldtime Household Necessaries CO LTD, item SP703-1 called PVA towel 66*43*0.2 cm, dark gray. The pore structure is seen to include both relatively small pores  5  and relatively larger pores  6 . In  FIG. 1B  the same material is shown damp, but not saturated. Generally smaller pores are filled with water, held by surface tension while relatively larger pores are open, allowing the passage of moist air from the environment. The same material is seen in  FIG. 1C  in a saturated state. Substantially all pores contain brine. For size comparison purposes,  FIG. 2  shows a human hair. 
         [0039]    The same PVA foam, after the disbursement of CaCl by soaking in a solution and then drying, is seen in a dry state in  FIG. 3A , and a damp state in  FIG. 3B . 
         [0040]      FIG. 3C  shows a non-woven rayon fabric in a dry state. It has air gaps that effectively act as pores. It has a range of gap sizes formed by the random pattern of threads  8 . The particular material tested and shown in  FIG. 3C  was purchased from Hefei Telijie Sanitary Material Co., Ltd. Their designation is: Nonwoven Cleaning Cloth. Material: Dipping nonwoven fabric; Size: 110 cm width; Length: 50M; Thickness: Around 3.4 mm; Packing: 50M/Roll; G.W.: 69 KGs. Not pictured is another material tested which is: TSV-5, purchased from ShopMicrofiber.com. 
         [0041]    The amount of fluid retained in the absorbent material increases as the desiccant absorbs water. It is possible for the amount of fluid to exceed the holding capacity of the absorbent material that can result in dripping of the brine out of the absorbent. The amount of fluid can be maximized if the absorbent is composed in a sheet  12  form as depicted in  FIG. 4  and, in use, is oriented with its major plane perpendicular to the vector of gravity. The sheets are generally flexible and should be held in a frame to minimize sagging or the fluid will drip out of the low points. For this composite material to provide a high ratio of H 2 O holding capacity to mass, the support material should have particular properties including a rapid rate of absorbing H20, a high capacity for absorbing H20, a rapid wicking of H20, and a rapid drying of absorbed H20. Some materials that have been tested include a PVA foam, a loose weave Rayon fabric, a microfiber fabric, an unwoven fabric, cellulose foams, and various other foams including M11. 
         [0042]    Some of these substrate materials as tested by the inventor, have been seen to have the following properties: Total absorption of liquid water into dry media held in horizontal plane ranges from 400% to 1,000% of the weight of the dry  170  media&#39;s weight. The media can hold more water when oriented in thin sheets held on a horizontal plane that ranges from 200% to 700% of the amount of water retained when the absorbent sheet is held on the vertical plane. 
         [0043]    Thinner sheets with wider gaps present more effective airflow, but yield lower total absorption capacity at higher labor assembly costs. The effective  175  thickness will range from 0.4 mm through 12 mm. Testing has shown that thickness over 12 mm will not regenerate in effective times and also experience an increased incidence of the desiccant collecting in the lower portion of the sheet and dripping out even when the sheet is maintained in the horizontal plane. 
         [0044]    Because the absorbent media is not rigid when desiccant is in the fluid state, the airflow rate should be low enough to prevent flapping which would fatigue and eventually destroy the media. Higher airflows can be tolerated by using thicker media and by adding more supports. In general, the maximum airflow effective in embodiments will not exceed 30 MPH gas flow across the media surface. 
         [0045]    Chemical Hygroscopic Desiccant 
         [0046]    Most testing has been done with CaCl as the prime hygroscopic desiccant. Other compounds with hygroscopic properties such as glycol might be used with success. A combination of CaCl and glycol has been seen to be advantageous. Lithium bromide, magnesium chloride, and lithium chloride have also been demonstrated as effective desiccants. 
         [0047]    Composite Desiccant Element 
         [0048]    Soaking the support material in a solution of CaCl and then drying the support material can disburse the chemical in the pores and structure of the support material. Other methods to produce the composite are possible. Since a goal of the composite is to maximally expose the surface area of the hygroscopic desiccant to any gaseous H 2 O in its environment, the sheets shown are relatively thin. One manner to produce a composite can be to soak a mounted sheet or sheets of a suitable support material in a ridged framework in a solution of CaCl and water with an equal weight of water to CaCl. The maximum CaCl that can be absorbed by water is dependent on the temperature of the solution. One way to obtain an effective mixture is to create a solution wherein some CaCl settles to the bottom at 65 degrees-F., but at 75 degrees-F. has all the CaCl in solution. In addition, it can be desirable to achieve a ratio in a composite of between 5%-300% CaCl to the total of CaCl plus substrate by weight. The total amount of CaCl that is recommended varies upon the conditions of operation. In general, environments that are more humid will require less CaCl to reach the point where they have absorbed all of the water possible without excessive dripping. 
         [0049]    In dry locations, more CaCl can increase absorption. As known to those skilled in the art, and according to Dow Chemical, a supplier of industrial CaCl, the trend is that at lower humidity CaCl will absorb less than it will at higher humidity. Temperature also has an effect on the maximum absorption of CaCl. As a result, the CaCl loading density can be adjusted for local conditions to improve operations. In less humid locations the CaCl loading density might be higher and in sufficiently dry locations CaCl may remain in its solid form even though it is absorbing water and the process continues to work. 
         [0050]    Desiccant Sub-System 
         [0051]    As seen in  FIG. 5  in a schematic manner, one way to deploy the composite material is as parallel sheets  12  with each sheet parallel to the flow direction  16  of a gas. This configuration exposes both sides of each sheet to the gas. The spacing and other details provided by a supporting structure can be such as to have a higher or lower air resistance to the flow. Thinner gaps between the sheets can increase total absorption per unit volume but may do so at the expense of increased airflow resistance. The gap between sheets might range from 2 mm to 40 mm in some embodiments. The configuration may also be such that a particular degree of turbulence is achieved, affecting the interaction of gaseous H 2 O and the desiccant composite sheet.  FIGS. 6 and 7  depict an example structure for mounting stacked sheets. In  FIG. 6 , an end spacer  20 , with significant area occupied by openings  21 , is used to separate and support the multiple sheets. This might be constructed from a corrugated plastic. The back of this stack is identical to the front. While holes shown in the spacer are circular, they may be any shape. While the spacers are shown on the ends there may in fact be multiple spacers placed periodically along the length of the sheet to prevent sagging of the supported media. There are also one or more similar corrugated strips within the stack to provide intermediate supports. The side supporting spacers  23  are solid on each of the sides of the stack as seen in the side view of  FIG. 7 . An alternate way to construct the stack is by sandwiching a single spacer sheet with teeth extruded on both sides between each desiccant sheet. 
         [0052]    In some versions, as seen in the front view of  FIG. 8  and the plan view of  FIG. 9  (the top sheet is removed), one or more baffles  24  can be used to create a turbulence-enhancing air path between the sheets. Those skilled in the art will recognize many alternate structures for supporting the parallel sheets and engendering a desired trade-off between pressure drop and a desired turbulent interaction. Material thickness of the desiccant substrate is predominantly limited by the material&#39;s moisture holding characteristics when oriented in a horizontal plane. Another factor for thickness determination is the rate of absorption. 
         [0053]    A thicker sheet might be appropriate for a material with faster wicking and absorption. If the material is too thick it may then accumulate a saturating degree of fluid in its lower portions leaving the upper portions drier and can result in dripping. Overly thick sheets would also make inefficient use of the desiccant by weight and by volume. In general, the thickness of the material is chosen to allow the maximum absorption in a given environment consistent with the average 250 charging time. For an overnight charging system, a thickness from 2 mm through 10 mm can be effective. For a system delivering multiple batches per day, a material thickness as thin as 0.5 mm may be more effective. In systems for continuous drying of a gas, a sheet thickness of 0.1 mm to 0.5 mm and a spacing of between ½ and 1 times the thickness may be advantageous. Sheet spacing in embodiments with longer airflow channels may generally have wider gaps to maintain a particular flow at a desired low degree of pressure. Shorter channel systems can have lower gaps and maintain a comparable pressure drop. In practice, a spacing of between 1/64″ and 2″ would cover many applications. A narrower practical range, taking material sag and volume constraints into consideration, can be 1/16″ to ½″. A smaller gap can be advantageous in allowing more sheets and therefore more desiccant mass in a given volume. 
         [0054]    Those skilled in the art will understand that various mountings and stiffening schemes are available with different tradeoffs. Sheets used in a subsystem may be pre-dried and tested for dripping to a desired specification. A system could take advantage of that to cease operating in an absorption mode with a desired margin before dripping was likely to occur. In some cases, it may be advantageous to construct a stack of the substrate material and then soak the subsystem. In other cases the composite sheets might be created and then assembled into a stack. Systems can be manufactured over-saturated with desiccant that is then removed by operation on-site to allow for environmental differences at various sites. One implementation approach is to assemble the subsystem with untreated absorbent media and then soak the subsystem in the desiccant solution. The desiccant charge would then likely be substantially over-charged. The subsystem can then be conditioned in an environment that approximated the humidity and temperature  275  expected to occur in a target deployment location. This conditioning step allows the desiccant charge to absorb the maximum water it is likely to absorb in the field and allows excess solution to drip out to be re-used. The unit is then dried. 
       Operation 
     Desiccant Subsystem 
       [0055]    The H 2 O holding capacity of the subsystem is affected by various factors  280  including the support material, the chemical desiccant, the sheet thickness, and the number of sheets. In addition, as the amount of H 2 O nears the capacity of the material, the liquid will appear at the surface and may drip. By keeping the sheet-stack parallel to the ground, the capacity before dripping that occurs is increased. Some mounting arrangements may provide a leveling indication and some may provide a leveling adjustment for the subsystem while others may provide a leveling indication and adjustment at the system level. In alternate inertial environments, the mounting orientation could be dynamically altered in order to maintain a perpendicular relationship with the vector of gravity/acceleration. 
       Structure 
     Air-to-Water System 
       [0056]    A schematic view of an example air-to-water system is shown in  FIG. 10 . Its structure includes a main chamber  100  containing a desiccant subsystem  101 . It also includes a heat exchanger  102  to provide energy in the regeneration phase and a condensing chamber  103  to harvest water freed during regeneration. There are three primary airflow paths (1) ambient in, dried air out  117  (2) recirculation hot air for regeneration  115 , and (3) recirculation of moist air through a condenser  116 . Fans engender the flows. Flaps (not shown in  FIG. 10 ) associated with each of the three airflow patterns, respectively, prevent undesired flow. The system shown includes both temperature and moisture sensors in various locations. 
         [0057]    An intake fan  105  can direct ambient air into the desiccant chamber and an exhaust fan  106  removes the dried air. Temperature T 1  T 2  and moisture M 1  M 2  sensors allow for measurement of the intake and exhaust air respective properties. 
         [0058]    A source of heat  107  that might be hot water from a solar panel, or might be from a low-grade waste heat source is connected to the heat exchanger  102  to allow heating of recirculating airflow  105  through the desiccant subsystem  101  in the main chamber  100 . In applications that produce drinking water, the metallic components of the heat exchanger  102  can be constructed from stainless steel. A pump  108  is shown in the hot water path. A regeneration flow fan  109  is in the recirculation airflow path that goes through the heat exchanger and the desiccant chamber. 
         [0059]    Condensing occurs in a condensing chamber  103  that is coupled to the main chamber via two fans in the system of  FIG. 10 . One fan  111  is pulling air from the desiccant chamber while the second, exit fan  112 , is pulling air through the condensing chamber and back into the main chamber and through the desiccant subsystem  101 . A source of cooling  113  is provided to the condensing chamber coupled by a heat exchanger  126  and water is produced at a drain outlet  121 . 
         [0060]    A control system  200  is shown schematically in  FIG. 11 . The temperature and moisture sensors seen in  FIG. 10  provide inputs to the control system. Another input is the state of charge  114  of the battery  201 . The control system&#39;s various outputs signal the various phases of operation, enabling fans and pumps. 
       Operation 
     Air-to-Water System 
       [0061]    A goal of many embodiments of these teachings is to produce drinking water from ambient air under a variety of conditions with a minimal expenditure of energy. In a typical operation cycle, photovoltaic panels  202  charge a bank of batteries  201  during the day. 
         [0062]    At night, the system might start out in a quiescent state, neither charging, regenerating, nor condensing. From past operation, the control system has a stored value representative of the extent of H 2 O held in the desiccant subsystem. The stored electrical energy in the battery is used conservatively. The control system makes decisions based upon the degree of moisture in the ambient air measured by sensor M 1 , the temperature of the ambient air measured by sensor T 1 , the extent of H20 presently held in the desiccant subsystem  101 , and the state-of-charge  114  of the batteries. The intake  105  and exhaust fans  106  are energized to further charge the desiccant only when “it is worth it”. That is, if a modeling of the system by the control logic indicates that there will be an adequate addition to the held H20 by taking in ambient air, the CHARGE signal will be activated. This will engage both the intake fan  105  and the exhaust fan  106 . This mode will stay in operation so long as the control systems models, according to predetermined rules, that further operation meets a criterion of efficiency. The other flow patterns are inactive and blocked by closed flaps. 
         [0063]    When the held H 2 O in the desiccant subsystem  101  is at the maximum or if the ambient conditions are such that no charging or an ineffective degree of charging would take place, the charge mode ceases. In a system using solar water heating as its regeneration energy source, the temperature of the hot water source as measured by the sensor T 5  will increase as the day goes on and the sun rises. To conserve battery power, the control system will not initiate regeneration mode until the hot water has achieved a temperature level that can efficiently cause regeneration of the desiccant. This computation is based on the present state of the desiccant chamber. When the criteria are met, the control system will energize the REGEN signal. 
         [0064]    In regeneration mode the hot water source pump  108  is engaged as well as the fan that engenders the regenerating flow pattern  115 . That pattern is through the heat exchanger  102  and through the desiccant subsystem  101  in a closed-circuit manner. In this mode the other patterns of flow are inactive and blocked by flaps. The regeneration mode&#39;s function is to release held H 2 O out of the desiccant and into the atmosphere of the main chamber. This mode is continued as long as the heat provided through the heat exchanger is continuing to effectively release additional H 2 O. One parameter involved with this calculation is the humidity or moisture content of the atmosphere within the main chamber  100 . While this may be measured directly, the harsh conditions in this system have proven to be destructive to the useful life of many conventional sensors. In the system of  FIG. 10  and  FIG. 11 , only a temperature sensor T 4  is located in the main chamber. In that example system, the moisture level within the closed chamber is determined by modeling the system, starting with the known state of the amount of H 2 O held in the desiccant and taking into account the input ambient air, output air and the degree of heat energy injected via the regenerative flow and amount of moisture condensed. 
         [0065]    The condensing mode is entered when the atmosphere within the main chamber  100  is sufficiently saturated as to be effectively condensable given the temperature delta between that of the main chamber and that of the cold source  113  whose temperature is measured by a temperate sensor T 6 . When the criteria are met, the control system will activate the CONDENSE signal. If a criteria set according to predetermined rules is met, the control system will enter the condensing mode. In this mode, energizing the condensing flow fans  111   112  will engender the condensing air pattern. Closed flaps prevent the other airflow patterns. 
         [0066]    This condensing airflow pattern  116  is a recirculation flow through the desiccant subsystem  101  and the condensing chamber  103 . Due to the temperature drop provided by the cold source, water condenses and is available to exit the chamber at a drain point  121 . This mode is continued as long as the moisture level on the main chamber and the temperature difference between the main chamber and the cold source  113  provide for effective continued production of water. 
         [0067]      FIG. 12  shows a more detailed schematic of the condensing chamber  103  and its entrance and exhaust fans of this first example system. Air is pulled from one end of the main chamber by an entrance fan  111  and pushed back into the other end of the desiccant chamber by the exit fan  112 . Within the condensing chamber  103  the hot moist air first enters a separation area  138  and then a portion of the moist air passes through a filter  124 . In this example system it is a HEPA filter. One purpose of the filter  124  is to prevent particulate contamination of the water being produced. The H 2 O is condensed in the condensing region  132  from the air via a heat exchanger  126  connected to a cold source. This might be a fluid pumped through a ground loop, ambient air, or other source of relative coldness. The condensed water is available at a drain point  121 . 
       Alternative System Embodiments 
       [0068]    Alternative Condensing Chamber—With Membrane 
         [0069]      FIG. 13  shows a schematic view of an alternative condensing chamber  103 ′. In this version a membrane  130  separates an initial separation region  138  from the actual cold condensing region  132 ′. Rather than direct the recirculating air pattern through the condensing region itself, the recirculation is done in the separation sub-chamber with the path having a sidewall  141  comprising an H 2 O permeable membrane  130 . The recirculation flow  116 ′ is parallel with the length of the membrane rather than being directed to the membrane. 
         [0070]    On the opposite side of the membrane  130  is a sweep region  133 . On the side of the membrane opposite to that abutting recirculating flow, two sweep fans  134   135  direct airflow  140  in parallel to the membrane. The sweep region is a plenum defined by the membrane and a plenum wall  142 . H 2 O molecules will permeate the membrane assisted by the turbulent flows on both sides. However, the other components of the hot moist air will not substantially permeate the membrane. This provides multiple benefits. One is that there is a minimum of mass heat transfer from the hot side of the membrane to the condensing side of the membrane. While it is necessary to cool the H 2 O water vapor to condense it to liquid water, it is desirable that the bulk of the recirculating flow  116 ′ not be cooled since it is being fed back into the main chamber  100 . The main chamber must be kept hot in order to keep the H 2 O in its atmosphere rather than in the desiccant. 
         [0071]    A second benefit of the membrane version is that a partial vacuum is created as the H 2 O expands on the sweep region  133  side of the membrane. This pressure differential further enhances the flow of H 2 O molecules through the membrane. Several materials can be used in the composition of a suitable membrane. One is Nafion. An alternate material that has been successfully tested is a monolithic urethane material, part number PT1700S by Deerfield Urethane. The sweep flow circulates through the sweep region  133  and back through the actual condensing region  132 . There the flow is in communication with the cold source via the heat exchanger  126 ′. 
       Method of Operation 
       [0072]      FIGS. 14-19  show states, criteria, and steps involved in the operation of the system of  FIGS. 10-13 . In  FIG. 14  a state diagram illustrates the four major states of the system: Quiescent  260 , Charging  261 , Regenerating  263  and Condensing  262 . 
         [0073]    While in the Quiescent  260  state:
       (a) Detection of high moisture content in the ambient air with a remaining water holding capacity of the desiccant subsystem  101  is a condition that will cause a transition  250  to the Charge state  261 .   (b) Detection of significant held water in the desiccant subsystem in conjunction with a sufficient source of low-grade heat is a condition that will cause a transition  255  to the Regen state  263 .       
 
         [0076]    When in the Charge state  261 :
       (a) Detection of low moisture content in the ambient air OR a low remaining water holding capacity of the desiccant subsystem is a condition that will cause a transition  251  to the Quiescent state  260 .       
 
         [0078]    When in Regen state  263 :
       (a) Detection of insufficient low-grade energy to efficiently release moisture from the desiccant subsystem will cause a transition  254  to the Quiescent state  260 .   (b) Detection of significant held water in the desiccant subsystem in conjunction with a sufficient source of low-grade heat is a condition that will cause a transition  252  to the Condense state  262 .       
 
         [0081]    When in Condense state  262 :
       (a) Detection of insufficient moisture in the main chamber  100  will cause a transition  253  to the Regen state  263 .       
 
         [0083]    State Transition 
         [0084]    Various conditions detected by logic and system state modeling in the control system  200  cause state transitions. The state transition logic is shown in the state table  FIG. 15 . 
         [0085]    The box for the criteria for moving from regeneration to condensing mode  299  requires additional explanation. When using waste heat or split collectors then rather than measuring light sensor for heating conditions this simply measures input of heating fluid. 
         [0086]    Calculated dew point of humidity in the chamber, Z, is based on the calculated dew point, humidity, and temperature of the highest 2-hour average humidity as measured in input air during prior charge period. This is used to calculate a minimum temperature delta between the ambient temperature and the condensing dew point. This is used as the minimum condensing delta. Minimum condensing Delta is increased by a set constant such as 10-degrees F. for each hour regeneration is run, to allow for reduced humidity available in desiccant because of water reclaimed. The adjustment per hour is tuned for local conditions and known over-sizing of desiccant stack. Larger oversized desiccant stack will allow a lower increase per hour while smaller desiccant stacks will require a higher increase per hour. 
         [0087]    Charge Mode 
         [0088]    In  FIG. 16  the steps of Charge mode are seen. First, the main intake and exhaust airflow fans or blowers are energized and engaged S 100  S 101 . Then a loop is entered where the temperature sensors and moisture sensors are monitored and the information used to continually update a model of the state of the desiccant subsystem and the relative humidity of the chambers S 102 . Within this loop, the criteria described above regarding causes of state transitions is reevaluated S 103 . If the conditions are such as to cause a transition to the Quiescent state, the main intake and exhaust fans are dis-engaged and the Quiescent state is entered S 104 . If no transition is called for by the conditions, the loop continues. 
         [0089]    Condense Mode 
         [0090]    In  FIG. 17  the steps of Condense mode are seen. First the condensing entrance  111  and exit fans  112  are engaged S 120 , and the coolant flow pump  135  to cause cold water to flow through the heat exchanger  126  is engaged S 121 . Then a loop is entered where the temperature sensors and moisture sensors are monitored and the information used to continually update a model of the state of the desiccant subsystem and the relative humidity of the chambers S 122 . Within this loop, the criteria described above regarding causes of state transitions is reevaluated S 123 . If conditions dictate a transition to the Regen state, condensing entrance and exit fans and coolant flow pump are dis-engaged, and the Regen state is entered S 125 . If no transition is called for by the conditions, the loop continues. 
         [0091]    Quiescent Mode 
         [0092]    In  FIG. 18  the steps of Quiescent mode are seen. First the all pumps and fans are disengaged S 130 . Any flaps are closed. Then a loop is entered where the temperature sensors and moisture sensors are monitored and the information used to continually update a model of the state of the desiccant subsystem and the relative humidity of the chambers S 131 . Within this loop the criteria described above regarding causes of state transitions is reevaluated S 132 . If the conditions are such as to cause a transition to the Charge state, that state is entered S 133 . If conditions dictate a transition to the Regen state, that state is entered S 134 . If no transition is called for by the conditions, the loop continues. 
         [0093]    Regen Mode 
         [0094]    In  FIG. 19  the steps of Regen mode are seen. First, the regeneration, recirculation fan  109  is energized and engaged S 110 . In this same step, the pump  108  is engaged. Then a loop is entered where the temperature sensors and moisture sensors are monitored and the information used to continually update a model of the state of the desiccant subsystem and the relative humidity of the chambers S 112 . Within this loop the criteria described above regarding causes of state transitions is reevaluated S 113 . If the conditions are such as to cause a transition to the Quiescent state, the regeneration fan and hot water pump are dis-engaged and the Quiescent state is entered S 114 . However if conditions dictate a transition to the Condense state, the regeneration fan and hot water pump are dis-engaged and the Condense state is entered S 116 . If no transition is called for by the conditions, the loop continues S 115 . 
       Further, More Detailed Embodiments 
       [0095]    Although those skilled in the art will understand the materials and techniques used in the design and construction of systems according to these teachings, two specific implementations are described below. 
         [0096]    Split System 
         [0097]    The version diagramed in  FIG. 20  is a “split system” in that the subcomponents of the system may be located other than immediately adjacent to each other. Because of this flexibility a wide range of physical embodiments are possible by one skilled in the field. This specific version gets much of its energy input from solar and wind power. 
         [0098]    Solar collectors  275 , possibly located on a roof, are used to create a heated fluid  276  which a circulating pump  277  can bring to a heat exchanger  278  in a chamber with the desiccant stack  279  in a charging mode. Air is pushed in a charging flow  291  by the charge blower  290  from an inlet charge port  280 , through the heat exchanger  278 , and then through the stack out to a roof-mounted passive exhaust fan  281 . A controlled damper  282  opens this path in a charge mode. 
         [0099]    For regeneration, a fan  283  forces airflow  292  through the desiccant stack  279  in a continued loop. As detailed above, regeneration continues until a desired set of conditions causes a mode transition to a condensing mode. In the condensing mode, the regeneration flow path is diverted through a filter  294  into a condensing airflow path  284 . This condensing airflow is caused by the condensing fan  293 . The condensed water goes to a drain  285  and out an outlet  286 . The condensation is promoted by a primary condenser  287  being cooled by a fan  288 . That primary condenser provides a flow of a cold fluid to the heat reclaiming condenser  289 . 
         [0100]    Small Unit with Membrane 
         [0101]    One compact embodiment using a thermoelectric semiconductor  310  is shown in simplified two-dimensional form in  FIGS. 21 ,  22 , and  23 . Referencing  FIG. 21  its structure includes an outer enclosure  314  with several sub-chambers and air conduits  320 . The major sub component with the enclosure include a desiccant stack  309  and a membrane  308  that allows water vapor but not other molecules of the air to pass. In this example, the heating for regeneration and the cooling for condensing are both caused, literally, by two-sides of the same semiconductor. When an electric current flows through the thermoelectric device  310  the by the Peltier effect, one side becomes hot  313  while the opposite side becomes cold  312 . To achieve the compact design an air conduit  320  provides a path from one side of the desiccant stack  309  to the other side of the stack for the regeneration recirculating flow  318 . In these two-dimensional views the conduit appears to bifurcate the stack into two regions. This is not the case. The conduit does not extend across the whole width in the third dimension. Therefore, it does not bifurcate the desiccant stack nor does it block the condensing pathway  315 . The three fans shown include one fan for charging airflow  304  at the exhaust port  322 , a second regeneration-recirculating fan  302  and a condensing mixing fan  303 . A tray  307  at the base of the condensing area  315  provides for the collection of condensed water that can exit the unit out of the water outlet  306 . 
         [0102]    Small Unit Operation 
         [0103]    The charging state is seen in  FIG. 21 . The charging exhaust fan  304  is energized. That pulls external air into the inlet, pushing open both the inlet flap  300  and the outlet flap  301 . The charging flow  317  is shown coming in the inlet, flowing through the desiccant stack  309 , around the side of the membrane  308  and past the condensing area. Finally, the charging air flow exits via the exhaust port. Charging leaves the desiccant stack in a water-holding state. The heat pipe does not block the exit flow since it does not extend to fill the space in the third dimension. 
         [0104]    In  FIG. 22 , the regeneration flow is diagramed. In this recirculation flow  318  the inlet and outlet flaps  300   301  are closed since the exhaust fan  304  is not energized. However, the recirculating fan  302  is energized. The recirculating flow goes through the desiccant stack  309 , around the membrane and back up a recirculation channel to the air conduit  320 . During this mode the thermoelectric device  310  is energized to heat the recirculating air to pull the stored moisture out of the desiccant stack. 
         [0105]    In  FIG. 23 , the condensing flow  319  is shown. In this mode the only energized fan is the condensing mixing fan  303 . Hot, moist air is drawn from the area of the desiccant stack  309  towards one face of the membrane  308  by a partial vacuum initiated by the pump  305 . The water vapor penetrates the membrane but the bulk of the air (and heat) does not. This allows the hot air to remain hot to continue regeneration, while the water proceeds to the condensing area. As the water vapor emerges from the opposite side of the membrane, the partial vacuum is reinforced, further enhancing the “pull” of moisture through the membrane and reducing the work required by the pump. The hot water vapor first passes through an area that provides initial cooling in a passive manner via a heat pipe  311 . The heat pipe extends to the outside of the enclosure  314 . Then the partially cooled water vapor is actively cooled by the cold side  312  of the thermoelectric device  310 . As mentioned above, a shelf  307  holds the condensed water until it is brought out of the unit by action of the pump  305 . 
         [0106]    Those skilled in the art will be aware of materials, techniques and equipment suitable to produce the example embodiments presented as well as variations on the those examples. Alternate materials that can be used for the sheet substrate include: microfiber, woven or nonwoven bamboo, or cotton, or hemp, woven or nonwoven stainless, woven or nonwoven propylene. This teaching is presented for purposes of illustration and description but is not intended to be exhaustive or limiting to the forms disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments and versions help to explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand it. Various embodiments with various modifications as are suited to the particular application contemplated are expected. 
         [0107]    In the following claims, the words “a” and “an” should be taken to mean “at least one” in all cases, even if the wording “at least one” appears in one or more claims explicitly. The scope of the invention is set out in the claims below.