Abstract:
A water harvesting apparatus includes a condenser system and an absorption refrigerator connected to the condenser system. The condenser system has a condenser for condensing water from ambient air. The absorption refrigerator cools the condenser, and derives its heat from waste heat. A method of harvesting water from the air includes the steps of introducing ambient air to a condenser system which has a condenser for condensing water from air, supplying waste heat to an absorption refrigerator to cool a refrigerant, transferring the cooled refrigerant to the condenser to the cool the condenser, and condensing water from ambient air.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to water production, and more particularly to producing potable water. 
     Although vast improvements have been made in modern times in obtaining suitable quantities of potable water, problems still exist for people temporarily located in places remote from settled communities. This is particularly true for researchers working in the field as well as military encampments. Currently, the methods of providing potable water in the field typically include shipping in bottled water, using existing water treatment infrastructure or constructing a small conventional water treatment plant, using a reverse osmosis treatment, or using a chemical treatment method and/or apparatus. Each of these treatment methods presents a variety of problems. For example, the source of bottled water may call into question the quality of the water. Transporting large volumes of water is logistically undesirable, requiring additional vehicles, fuel and manpower, and may put soldiers at risk when transporting water through unfriendly areas. 
     Depending upon location, in some instances it may be feasible to use a local water treatment plant. However, such use may be limited by the quality of the water that can be produced by the plant and whether the facilities are susceptible to sabotage and intentional contamination. 
     High quality water can be produced in both small and large scale procedures using a reverse osmosis system. Such water treatment procedures, however, require that the system be situated near a water source. In addition, such systems are energy intensive and the membranes, which have finite lifetimes, are expensive to replace. 
     Numerous point of use devices (such as a canteen, a hydration pack or a portable water purifier) are currently available that can supply a sufficient amount of water for one or several people. These devices have limitations such as requiring a source of water and in many cases a chemical treatment agent, such as a halogen treatment agent, typically an iodine tablet. Most of these devices are capable of providing limited amounts of potable water batch wise. In addition, these commonly used devices are not effective against all possible contaminants. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to supply potable drinking water. 
     This and other objects of the invention are achieved in one aspect by a water harvesting apparatus having a condenser system including a condenser for condensing water from ambient air, and an absorption refrigerator connected to the condenser system for cooling the condenser, the absorption refrigerator deriving its heat from waste heat. 
     Another aspect of the invention involves a method of harvesting water from the air that includes introducing ambient air to a condenser system having a condenser for condensing water from air, providing waste heat to an absorption refrigerator to cool a refrigerant, transferring the cooled refrigerant to the condenser to the cool the condenser, and condensing water from ambient air. 
     Only in the realm of theoretical physics where isolated systems in equilibrium are considered can the total inter-conversion of one form of energy to another single form of energy take place with an efficiency approaching 100%. Heat is often a byproduct form of energy when most mechanical devices are used, and this is particularly true of internal combustion engines. Typically the byproduct heat produced in the operation of many of these devices is unwanted and in many situations the heat produced may be detrimental to the device itself or to the environment. This unwanted heat, referred to herein as “waste heat” and sometimes identified in the Second Law of Thermodynamics by the same term, is produced as the byproduct of mechanical, electrical or electromechanical processes Such waste heat is scavenged in the invention which is capable of producing potable drinking water at almost any inhabitable location on Earth. The invention uses an absorption-refrigeration cycle and associated apparatus in combination with a condenser system to remove water from air. The majority of energy required to power the absorption-refrigeration cycle is derived from waste-heat and all of the thermal energy required to vaporize refrigerant in the absorption-refrigeration cycle may be supplied by waste heat. Any piece of equipment that produces waste-heat can be coupled with the water production device. As an example, when the invention is coupled with a generator-set, water and electricity can be produced with one unit. It is estimated that this invention can produce 7,000 Gal/day of potable water (basic water needs for 550 troops) with the waste-heat produced from one 840 kW generator-set (a generator-set used by the US Army in the field). 
     Additional advantages and features will become apparent as the subject invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The sole FIGURE shows the water harvesting apparatus in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the FIGURE, the water harvesting apparatus includes a condenser system  11  having a condenser  13  for condensing water from ambient air, and an absorption refrigerator  15  connected to the condenser system for cooling the condenser. 
     The condenser system  11  includes an air inlet  17  and an air outlet  19 . A fan  21  is disposed at the air inlet  17  to draw ambient air into the condenser  13 . The air may also be introduced into the condenser  13  by density driven flow (without fan). Although the fan  21  is shown placed at the entrance to the condenser system  11 , arranged to blow ambient air into the system, the fan may be placed at the air outlet  19  at the downstream end of the condenser system  11  so that it draws air through the system. Ambient air entering the system  11  is thereafter preferably pretreated with a means for particulate removal  23 , such as a particulate filter or particulate absorber, but may alternatively include a bag-house, or cyclone. The filtered air may then be conducted past a UV radiation source  25 , optionally provided to be used as a disinfecting means in situations where there is concern that there may be an unusually high concentration of airborne pathogens in the area. The air is then conducted to a contracted portion of a housing  27  that forms the condenser&#39;s throat and contains the condenser&#39;s cooling coils  29  wherein the air passes over the coils. As the air is cooled by the condenser  13 , water condenses on the coils  29 . The cooling coils may be coated with a hydrophilic, high thermal conductivity polymer composite to increase the efficiency of the phase change process. The condensate is collected in a wet well  31 . Condensate in the condenser  13  throat and the wet well  31  may optionally be disinfected with the UV radiation source  25  that may be used if the apparatus has not been adequately disinfected between uses. The polymer, if one is used to coat the condenser coils  29 , can also be impregnated with a disinfectant (e.g. silver) to enhance inactivation of microbes. Condensate is optionally transferred by a pump  33  from the wet well  31 , to a tap  35  through some means to remove any remaining nuclear, biological, or chemical contaminants, such as a nuclear, biological, and chemical (NBC) filter and/or ultrafiltration membrane  37 . This water can then be further disinfected (with one or a combination of disinfectant(s) e.g. salt electrolysis, iodine, silver, ozone, chlorine, UV radiation, gamma radiation, chlorine dioxide, etc.). 
     Although all of the disinfection means and agents mentioned above are optional, it is preferred that at least one means or agent be used. Where it is desirable to use a UV source in more than one location, and where it is possible to do so, the elements of the condenser system  11  may be so arranged that a single UV source may used to provide radiation to several sites. 
     Turning now to the absorption refrigerator, the absorption-refrigeration cycle (identified in the FIGURE by dotted lines) can work with any evaporating refrigerant. Preferred is a water-lithium bromide (H 2 O—LiBr) system because it will operate with waste-heat fluids at temperatures less than 100° C., which corresponds to internal combustion engine coolant temperatures. Another advantage to using a salt absorber (eg. LiBr) over a liquid absorber (e.g. H 2 O) is that the solid absorber will not evaporate in the gas generator, which results in a higher efficiency. The refrigerant (e.g. water) is first dissolved in the absorbent (e.g. LiBr) in an absorber chamber  39 . Cooling water used to prepare the refrigerant and to remove the latent heat of vaporization may be supplied to the absorber chamber  39  from the condenser coils  29  or a refrigerant condenser chamber  41  (discussed below). Stored potable water may also be sufficient for this application. The solution is then transferred with a pump  43  to a gas generator  45  where the refrigerant is vaporized at higher pressure and elevated temperature since, by design, bulk boiling of absorbent does not occur under these thermodynamic conditions. A valve  46  is provided to control the flow of absorbent that is returned to the absorber chamber  39 . 
     The majority of energy needed to vaporize the refrigerant is derived from waste-heat provided to the gas generator  45 . This is a significant advantage over conventional refrigeration systems that use compressors, which have a relatively large mechanical energy demand. The purified high pressure refrigerant vapor is then transferred to the refrigerant condenser chamber  41  and then passed through an expansion valve  47  that converts the refrigerant from a high pressure liquid to a low pressure, low temperature liquid-vapor mixture. A heat sink, such as ambient air or cooling water, is required for the refrigerant condenser chamber  41 . The liquid-vapor mixture is used to absorb heat in the condenser coils  29  of the condenser system and condense water vapor from the surrounding air. A control system can be used to adjust the air flow rate to prevent the removal of excess sensible heat (i.e., the heat necessary to increase or decrease temperature) from the water thereby maximizing process efficiency and setting potable water temperature. 
     A variety of sources as well as various methods may be used to conduct waste heat from a source to the gas generator  45 . Basically any source of waste heat may be used to supply sufficient heat to vaporize the refrigerant in the gas generator. Preferred, however, is any machinery that normally would be used at the same location as the water harvesting apparatus. Since an electrical generator may typically be present, such a device is preferred. The waste heat may be transferred from the source of the waste heat to the gas generator  45  by any suitable means. This might include something as simple as insulated shrouds around the source of the waste heat and the gas generator and a conduit possibly containing a fan communicating between the shrouds. However, where possible, it is preferable to pass a fluid heated by the waste heat source through a conduit, such as a coil, that is inserted into the refrigerant contained in the gas generator  45 . With apparatus such as diesel powered, liquid cooled generators, this would be easy to accomplish. This may be done by transferring the coolant fluid using a coolant pump on a diesel generator or by natural circulation. 
     It is obvious that many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as described.