Patent Publication Number: US-2017362800-A1

Title: Water conservation using floating optically-reflective devices

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application Ser. No. 62/081,544, entitled “Water conservation using floating reflectors”, filed on Nov. 18, 2014, which is hereby incorporated by reference as if set forth in full in this application for all purposes. 
    
    
     BACKGROUND 
     Conservation of water is a matter of great concern and interest, especially at times of ongoing or anticipated drought. Issues of potential environmental damage, human displacement, and overall costs are serious disincentives to infrastructural approaches such as constructing or expanding reservoirs or building dams. Evaporation due to absorption of incident sunlight by the water in existing reservoirs makes up a significant fraction of potentially avoidable water loss. Simple surface covers, as currently used to prevent water loss in small ponds or swimming pools by physically blocking evaporation, can reduce gas exchange, block incident light and increase underlying water temperature, so even if such covers could be scaled up to reservoir-size, they would have very negative consequences to the ecosystem of the reservoir. 
     Covering the water surface using surface films of oils and hydrocarbon-based materials has also been proposed. This has the additional disadvantage of adding a non-aqueous liquid, and potential pollutant, to the reservoirs. 
     It is therefore desirable to provide a scalable method of reducing absorption of incident sunlight that allows adequate atmospheric gas exchange. The ability to keep underlying water temperature within a predetermined range, and to avoid permanently shading any particular region without introducing potential pollutants would be additional desirable features. 
     SUMMARY 
     The present invention includes a method for conserving water in a reservoir. In one embodiment, the method comprises deploying onto the upper surface of water in a reservoir a floatable device with a wettable lower surface, wherein the device comprises a first element and a second element, the first element providing the device with a high albedo upper surface. In one embodiment, the first element comprises a plurality of highly reflective particles and the second element comprises a binder configured to hold the reflective particles together. In one embodiment the reflective particles comprise hollow glass spheres and the binder comprises a biodegradable bioplastic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section view illustrating a floatable high albedo device with a wettable lower surface according to one embodiment. 
         FIG. 2  is a top-down view illustrating a floatable high albedo wettable device according to another embodiment. 
         FIG. 3  is a flowchart illustrating the steps of a method for using a floatable high albedo device with a wettable lower surface to conserve water according to one embodiment. 
         FIG. 4  is a flowchart illustrating the steps of a method for forming a floatable high albedo device with a wettable lower surface according to one embodiment. 
         FIG. 5  is a flowchart illustrating the steps of a method for using a floatable high albedo device with a wettable lower surface to cool a body containing water trapped in the form of ice, snow, or permafrost, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The manner in which the present invention provides its advantages can be more easily understood with reference to  FIGS. 1 and 2 . 
       FIG. 1  shows a device with a high albedo upper surface  106 . The device comprises a first element  102 , which in the shown embodiment takes the form of a plurality of highly reflective particles, which provide the high albedo upper surface. In some embodiments the particles may be hollow glass particles, which may be spherical. In other embodiments, the particles may be porous and/or non-spherical. The lower surface of the device is wettable, such that when the device is positioned on the upper surface of a body of water, the water makes good contact with the device&#39;s lower surface, wetting it. The device further comprises a second element  104 , which acts as a binder to hold the particles of the first element together. In some embodiments the second element may also be responsible for providing the device with a highly wettable lower surface  108 . In these cases, the second element may be chosen in part for its ability to bind the particles together by making strong bonds to the particles&#39; surfaces, and in part for characteristics enabling the resulting composite of particles and binder to exhibit high wettability. In other embodiments, the first element may be responsible for providing the device with a highly wettable lower surface. 
     In some embodiments, the wettability may be provided by a third element, not shown in  FIG. 1 , rather than by the second element. 
     Wettability offers several advantages to the device. One is that it helps the device “cling” to the water surface, so that it will be less likely to be lifted off or blown away in windy or stormy conditions. Another is that the underlying water can be drawn into the thickness of the device, penetrating to the upper surface, where gas exchange may occur with the overlying atmosphere. In some embodiments the device may comprise an element having high porosity, facilitating the water penetration and gas exchange. In some embodiments the high porosity element may be the same element as the second element 
     In some embodiments, the entire lower surface of the device may be wettable. In some cases, adequate cling and gas exchange may be achieved with a fraction of the lower surface significantly less than 100% being wettable. 
     In some embodiments, the binding material may be dispensed with altogether, and the particles of the first element may be enclosed within a container such as a mesh bag. The shape and relative volume of the container with respect to the volume of the contained particles may be chosen such that when the device is allowed to float on a water surface, there are sufficient spaces between the particles to allow gas exchange to occur. Wettability may not be a relevant parameter in these embodiments. 
     In some embodiments, whether or not a binder is used, a container used to restrict the area over which the reflective particles spread may be a boom, such as those used to contain oil spills, rather than a more completely enclosing structure such as a mesh bag. 
       FIG. 2  is a top-down view illustrating one embodiment  200  including floating reflective particles  202  whose spread over the surface of a body of water, indicated by dashed lines, is confined to a limited area by a floating boom  210 . 
     It should be noted that the density and dimensions of the particles relative to the surfaces and dimensions of device  100  are not shown to scale in  FIGS. 1 and 2 . 
       FIG. 3  is a flowchart of the steps of a method  300  for using a device of the type shown in  FIG. 1  to conserve water in a reservoir. In step  302 , a floatable device comprising a first element and a second element is obtained, the device having a wettable lower surface and a high albedo upper surface, the high albedo upper surface being provided by the first element. In step  304 , the device is deployed onto the top surface of water in the reservoir. 
       FIG. 4  is a flowchart of the steps of a method  400  for making a device of the type shown in  FIG. 1 . At step  402 , a first element with high reflectivity is obtained. At step  404 , a second binding element is obtained. At step  406 , the first and second elements are mixed together, and shaped as desired. At step  408 , the shaped mixture is exposed to an elevated temperature for a time sufficient to allow good binding to occur. At step  410 , the resulting heated mixture is allowed to cool to room temperature, forming the desired device. In some embodiments, a temperature of 325 degrees Fahrenheit for 10 minutes has been found to be suitable for an experimental mixture involving hollow glass spheres and PLA—Polylactic acid or polylactide, a compostable thermoplastic aliphatic polyester derived from corn. In this particular mixture, the glass spheres provide high reflectivity and wettability, while the PLA is attractive for its excellent binding properties, its non-toxicity, its biological derivation and compostability, and its brightness. Glass is also a very good choice for its innocuousness in the natural environment. 
     Examples of glass-based commercially available products that may be considered for the particles of the first element include perlite, an amorphous volcanic glass, 3M™ Glass Bubbles K1, and Poraver® beads formed from post-consumer recycled glass. 
     In the water conservation applications of most interest to the present invention, it is envisaged that a plurality of devices such as the one shown in  FIG. 1  may be deployed to float on the upper surface of the body of water of interest. It may be desirable to limit the fraction of the water surface area covered by these devices to well under 100%, in order to maintain adequate levels of gas exchange between the water and the overlying atmosphere. In one embodiment, the number of devices deployed may be chosen such that no more than 30% of the total water surface would be covered. 
     In some embodiments, each device may be formed to include one or more through holes that extend through the thickness to facilitate gas exchange between the underlying water and the overlying atmosphere. 
     It some embodiments, each deployed device may be allowed to float freely over the water surface. However, there may be advantages to constraining the motion of the device to some extent. Prevailing wind and currents may act to drive all the devices towards one end of the reservoir, maybe even piling them up against the banks, so reducing coverage to below the desired levels. Even if the devices remain separate, so that the total covered volume remains constant, there may be negative consequences to aquatic life if one portion of the water surface is continuously kept shaded. Another problem is the practical consideration of how difficult it may be to gather up a large number of freely floating devices when desired, for example, prior to removing and/or replacing them. 
     These problems may be addressed by designing the floatable device to include a central member that can be attached to a restraining or anchoring device that in turn is attached either to the bed of the reservoir, or the shore, or a dock. The attachment may be fully rigid, hinged or pivoting, or even flexible, for example with some sort of rubbery connecting member. Portions of the floatable device other than the central member may themselves be attached to the central member by rigid, hinged, pivoting, or flexible means. In all these cases, the resulting constrained area of movement will enable the devices to be relatively easily accessed for removal or replacement, and will avoid the potential weather-driven concentration of devices at one portion of the reservoir. In some embodiments where non-rigid attachments as discussed above are used, there will be the additional advantage that small movements of the high albedo surface responsive to wind and currents can occur and will typically “average out” the shading of the underlying water. 
     The methods and apparatus described herein may also be advantageous in applications other than the water conservation of immediate interest as described. One example is to help stabilize permafrost, with a possible side benefit of preventing release of methane (a powerful greenhouse gas). Other possibilities include snow stabilization, avalanche prevention, maintaining lower temperatures in glacial melt ponds, and in flood control. The materials used must be carefully selected for appropriate levels of safety, to humans and the environment as a whole, in any and all such deployment locations. 
       FIG. 5  is a flowchart of the steps of a method  500  for using a device of the type shown in  FIG. 1  to cool a body containing water trapped in the form of ice, snow, or permafrost. In step  502 , a floatable device comprising a first element and a second element is obtained, the device having a wettable lower surface and a high albedo upper surface, the high albedo upper surface being provided by the first element. In step  304 , the device is deployed onto the top surface of the body. 
     The term “reservoir” is used in this application to refer to any body of water with an upper surface exposed to incident sunlight. As such, it includes man-made reservoirs and naturally occurring lakes and other similar bodies that could be considered to be water sources for human use. 
     The term “wettable” as a characteristic of a material surface is used in this application to mean hydrophilic or able to be easily and thoroughly wetted by water. The contact angle between water and a wettable surface is less than 90 degrees, possibly even 0 degrees. 
     The terms “highly reflective” and “high albedo” are used in this application to mean having a reflectivity over the visible spectrum greater than 15% (which is higher than the average reflectivity of an exposed water surface to incident sunlight) and preferably greater than 90%. Values in these reflectivity ranges are significantly greater than the average reflectivity of water to incident sunlight. 
     Embodiments of the present invention thus enable the environmentally benign generation and deployment of high albedo devices to areas in which the resulting cooling of the surface (e.g. water, permafrost, snow, ice etc) in the vicinity of the deployment may be highly beneficial. 
     The above-described embodiments should be considered as examples of the present invention, rather than as limiting the scope of the invention. Various modifications of the above-described embodiments of the present invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, the present invention is to be limited solely by the scope of the following claims.