Abstract:
A novel system for using a high water content polymer and its various implementations to provide a means of evaporative cooling and temperature regulation for buildings and structures. This invention will provide benefits at much lower initial and ongoing costs than competing solutions and will bring other benefits and extensions inherent in its design and implementation.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 61/749,969, entitled “Evaporative Cooling System,” filed Jan. 8, 2013, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    Conserving energy is important for many economic and environmental reasons. New technologies and approaches are being developed to help reduce energy needs and improve efficiencies. These technologies range from relatively simple to very complex, with a mix of cost-benefit ratios. Because of the claimed value of some of these technologies, cost-benefit ratios can be skewed to greater favorability by various incentives like specific tax breaks, funding grants and others. 
         [0003]    Often a real breakthrough comes from an unexpected source, including a different industry or material application. Such is the case of the invention disclosed herein: a novel polymer compound invented for other purposes finds substantial suitability to the application of energy conservation. It will be shown in this document that this polymeric compound allows for a means of biological mimicry for energy conservation. When combined with various enhancements, some of which are also disclosed herein, the benefits can be dramatic. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention described in this disclosure provides a novel system for using a high water content polymer and its various implementations to provide a means of evaporative cooling and temperature regulation. This invention will provide benefits at much lower initial and ongoing costs than competing solutions and will bring other benefits and extensions inherent in its design and implementation. 
         [0005]    In the preferred embodiment, a polymer is used to retain water on a building roof in order to enable phase change of the water, thereby removing substantial amounts of heat from the roof surface. This heat removal will reduce heat load to the building and reduce energy required to mitigate the heating and cooling of the building. 
         [0006]    Several application implementations are described. These various application implementations enable application of the invention to different types of surfaces, including flat and pitched roofs and sidewalls. Moreover, the invention includes various enhancements that increase usability, longevity and maintenance. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0007]    The field of energy research has grown tremendously in recent decades. From the most basic, including simple means of conservation, to fairly complex generation systems, like fusion, the quest to extend energy availability is at the forefront of much interest. Sometimes breakthroughs come from approaches different from existing solutions and appear on the surface to be quite logical or natural. It is, however, recent developments of technology that allow for such seemingly natural approaches to become viable. This invention is such a case. 
         [0008]    Polymer compounds have been synthesized for decades and have a wide range of applications. Each developed for specific characteristics necessary for a primary application, polymers are unique combinations of chemicals (monomers) in specific formulations and conditions to enable creation of the polymer. Often, however, the application of a particular polymer to something other than its primary application can yield very interesting results. 
         [0009]    The Polymeric Evaporative Cooling (PEC) is just such an application. Of particular interest for PEC is the removal of heat from structures like buildings and houses. Effective heat removal can have demonstrable effects on energy requirements for cooling, and thereby reducing costs. Widespread reduction in energy requirements as a result of heat removal from buildings can have significant impact in the production of energy and a commensurate benefit to the environment. 
         [0010]    In some respects the PEC mimics various biological systems in that it enables a phase change (i.e., evaporation) to remove heat from a surface much like perspiration cools a human body. The key attributes and novel aspects of PEC are found in the materials used and the applications of those materials. 
         [0011]    For the purposes of this description, a high water content polymer is considered. Such a polymer may be found in U.S. Pat. No. 6,201,089 (“Example Polymer”) and myriad other formulations. This example patent describes hydrophilic polymers with 95-99.9% water content. While developed for other applications, the characteristics of the polymers described are very suitable to the application of the PEC. Among these, the small pore size (nominally 90-100 Å) allows for ready flow of water while blocking the flow (or intrusion) of unwanted materials. Additionally, as will be described later, the formulation of the polymer provides features that enhance the benefits beyond simple evaporative cooling. 
         [0012]    The PEC is best considered in terms of a layer of polymer on the roof of a building or house as shown in  FIG. 1 . This layer  102 , which can be varied in thickness, will conform to the roofing surface  101  in order to maximize the heat transfer from the structure. Properly hydrated, the PEC will be predominately water that, as the temperature rises, will change phase from a liquid to a gas. That is, it will evaporate. It will be obvious that, while water is suitable for PEC and used throughout this document, other fluids or fluid mixes may be used as well. 
         [0013]    Those versed in basic physics will understand that phase change—from one state of matter to another—involves far greater energy exchange than simple temperature change. For example, when water temperature rises a single degree it requires ˜4180 J/kg (1 BTU/lb), but changing from liquid to gas (with no temperature rise necessary) requires approximately ˜2260 kJ/kg (˜972 BTU/lb). Similarly, the same amount of energy is given off when reversing that phase change. 
         [0014]    With the evaporation of the water in the PEC, significant heat removal is possible. Many variables can be manipulated to gain maximum advantage for the location or specific use. Some of these variables may include thickness of the layer, format of the layer, and enhancements. 
         [0015]    In the preferred embodiment, the PEC polymer is applied to an existing roof structure. Sprayed on to the roof surface, as one would consider a standard coating like paint or roofing sealant, the PEC polymer can be applied either dry or pre-hydrated. 
         [0016]    In the preferred embodiment, in a spray-on application, the hydrated polymer will be part of a liquid mix that includes an adhesive component. The adhesive component provides for a mean to keep the polymer layer attached to the roof surface in addition to any natural adhesion found in the polymer itself The correct mixture of polymer to adhesive can be varied depending on the target surface type, expected thickness of the polymer layer, environment and other variables. 
         [0017]    Alternatively, a layer of adhesive may be applied prior to the spray-on of the polymer as shown in  FIG. 2 . In this case, polymer layer  102  is affixed to structure  101  with adhesive layer  203 . 
         [0018]    An additional alternative is the inclusion of an adhesive monomer in the polymer formulation. Such may be selected for application to specific roof coating materials in order to maximize adhesion, longevity or other characteristics. 
         [0019]    Some applications may not be amenable to a spray-on treatment. In such cases, the ability to spread the polymer material with a brush, mop or other device becomes preferable. It may also be forced into existing flexible roof surfaces like tar or membranes. Further, it may be allowed to settle into porous surfaces, like stone or gravel coatings. This is particularly useful in some flat roof applications like those common in industrial structures. 
         [0020]    The advantage of the spray-on application is that specific roof design does not matter. For example, pitched-roof houses can be comprised of asphalt or wood shingles, tile and gravel, all of which are compatible with a spray-on coating. In fact, in some cases, the spray-on polymer layer may enhance the overall appearance and viability of the roof surface. This may be the case, for instance in the case of wood shingles that have become aged and brittle over time but that are effectively sealed with the polymer mix. 
         [0021]    Alternative means of application of the polymer are also considered in this invention. In one alternative, the polymer may be cast in a form very similar to tiles such that each are individually applied to the surface. Such may be more suitable in cases that require more precise polymer thickness or other special considerations. In the case of such a tiling arrangement, adhesive may be applied prior to application or may already be integrated into one or more surfaces of the polymer tile. Here again, the specific implementation may guide the choice. 
         [0022]    Yet another alternative is to integrate the polymer into existing structural elements. For example, the polymer may be applied to the surface of or integrated into the composition of various roof treatments like tiles. The advantage of such an implementation is that it becomes a standard part of a workflow during construction or refurbishment. A further advantage of such an implementation is that it allows for a sporadic or patterned distribution to allow for access to portions of the structure without potential damage from stepping on the polymer itself. 
         [0023]    For applications to surfaces like roofs that require repeated access, an enhancement to this invention is the incorporation of channels, gaps or superstructures interspersed in the polymer coating layer. These will allow for access ways without risking damage to the layer itself. It is important to note that direct exposure to the sun is not necessary for performance, which allows for application below existing structures like catwalks and access paths. 
         [0024]    Still another implementation of the PEC is the formation of the polymer into a rollable form that is similar to other roofing materials. As such, the polymer may be fully or partially hydrated or unhydrated at any time prior to installation and rolled onto the surface. As with other implementations, an adhesive may be integrated or may be added at the time of PEC installation. 
         [0025]    It is important to consider that a hydrated polymer may be quite fragile. Polymer fragility may be mitigated somewhat with increased thickness but may also incorporate additional means to provide structural stability. A simple example to be considered, as shown in  FIG. 3 , is a mesh  301  around which the polymer  102  is cast. Such casting may an active part of the polymerization process or it may be post-polymerization stages and include adhesive to provide connection to the mesh. The mesh may be flexible or rigid. 
         [0026]    An alternative to the mesh integration is the application approach similar to that used when applying stucco to buildings. In this case, a mesh is installed and the material is applied to the mesh either by spraying, trowelling, some other method or a combination of these. The key to the application is to rely on the mesh as a structure with the polymer engulfing the mesh. 
         [0027]    Whether formed directly around a mesh or applied on a mesh, the structure provides additional benefit during periods of dehydration. One would reasonable expect a drying polymer to separate during shrinkage. With a properly designed and sized mesh, the shrinkage will take place in the mesh gaps while allowing the polymer to remain attached to the mesh. An example of this is shown in  FIG. 4 , in which polymer  102  is affixed to mesh  401  such that any shrinkage occurs in the gaps of the mesh  401 , thereby maintaining the integrity of the polymer layer upon rehydration. 
         [0028]    Additionally, the polymer may be encapsulated in some porous layer as shown in  FIG. 5 . The porous layer  501  will allow for water to enter and escape the polymer  102  but will also provide for some protection of the polymer itself. The porous layer  501  may be that of a fabric material or rigid and may be on a single side or both top and bottom. An advantage of this implementation is the ability for the polymer layer to be installed temporarily or moved and adjusted to fit the specific and/or changing needs. 
         [0029]    Another advantage of the PEC being encapsulated in a porous layer  501  is that it can help contain the polymer if it becomes completely dehydrated. In a case of complete dehydration, a nominally 95% water content polymer can shrink, become brittle and fracture into small pieces. 
         [0030]    It is with possible shrinkage in mind that the selection of a flexible adhesive may be beneficial. With sufficient elasticity in the adhesive component, during dehydration the PEC remains in place and will upon rehydration return to its desired form. This capability can be enhanced by applying in a very specific manner such that the polymer is applied in the dry state and in a pattern that allows for rapid expansion upon rehydration. 
         [0031]    Another approach to mitigate issues resulting from dehydration is the ability to process in the polymer in a means that allows for expansion upon hydration in only the vertical direction. Such an enhancement will mitigate concerns of expansion and contraction during wet and dry periods, respectively, and any resulting mechanical separation. 
         [0032]    Yet another alternative implementation of the invention is the ability to actually polymerize the polymer upon application to a UV-exposed source. For example, the incorporation of a UV initiator for polymerization may be sufficient to enable the UV delivered by the sun to actually cause polymerization after the polymer&#39;s monomer mix has be applied to a surface. 
         [0033]    It will be well understood that this PEC may also be applied to other than roof structures and that application format may vary. Such an alternative application may be for the sidewalls of buildings and structures or integrated into other heat exchanger systems that can take advantage of the phase change cooling system. 
         [0034]    In the preferred embodiment, the polymer used will have sufficient hydrophilicity that rehydration will be easily accomplished. In some high humidity areas, such rehydration may occur naturally during low-heat periods like at night. An alternative is to provide water to rehydrate the polymer. As shown in  FIG. 6 , providing water  601  may be accomplished in a manner similar to that provided to lawns and landscaping plants with sprinklers, misters or trickle water systems  602 . Fortunately, such a system can be tied directly into a landscape system such that it operates during non-peak heat times. The use of non-potable water, used in many locations specifically for irrigation, is readily compatible with this embodiment of PEC. 
         [0035]    It is important to note that proper polymer selection for PEC may have additional benefits. The incorporation of specific elements into the polymer may help provide cold-weather performance benefits. For example, the Example Polymer requires initial hydration using a particular buffered solution. This buffered solution interacts with the organic acids in the polymer composition and provides a sodium (Na) atom to become part of the polymer. This sodium atom provides some amount of freeze point depression, which can be advantageously used to mitigate ice build-up from roofs and other structures. An additional benefit to this implementation is that the phase change from liquid to solid (i.e., water to ice) releases energy that can be absorbed by the structure. It will be easily understood that other fluids, like glycol solutions, may be used to enhance cold weather performance. 
         [0036]    An advantage of using water as the working fluid for PEC is that it also provides a high degree of reflectivity at higher angles and transmissivity at smaller angles, allowing for additional reflectivity from underlying surfaces. This is beneficial in that it further helps reduce heat energy that may be absorbed by a structure. Such transmissivity and reflectivity may be enhanced with the addition to the polymer of specific elements or pigments or the selection of one or more adhesive components. 
         [0037]    As with the anti-icing attributes of PEC, various means may be incorporated to enhance cold weather performance. For example, absorbing elements or pigments may be added to the polymer specifically to provide additional heat absorption during cold weather periods. Any adhesive element may also contribute to this quality. 
         [0038]    Ideally a temperature-responsive element may be incorporated in PEC such that during warm periods reflectivity is enhanced, perhaps by appearing white in color, and during cold periods absorbance is increased, perhaps by appearing darker in color. 
         [0039]    An alternative to providing such opposing functions for PEC is to implement it in some mechanical fashion that takes advantage of the sun&#39;s angle of incidence during different parts of the year. The ability to effectively change exposed colors to enhance reflectivity and absorbance is conceptually straightforward and is shown schematically in  FIG. 7  with mechanical element  701  installed. Such mechanical element can take many forms but would nominally have a surface optimized for absorbing heat energy when the source, like the sun  702 , is at a seasonally low position but does not obscure heat energy when the source, like sun  703 , is seasonally at a high angle. Such optimization may include coloring or mechanical features. It is understood that mechanical element  701  may also include additional reflective surface to enhance performance when the source is at a high angle as in  703 . The combination of this approach with a hydrophilic polymer that also incorporates enhanced anti-icing qualities is beneficial to many. 
         [0040]    Yet another alternative for enhancing heat reflectivity or absorbance is the incorporation of electro-active chromophoric elements into the polymer material. Similar to those found in liquid crystal displays (LCDs) or organic light emitting diodes (OLEDs) these electro-active elements may provide for an active color change element upon the application of a small electrical charge. 
         [0041]    One can easily envision, for example, the incorporation of an element that become bright upon charging. Not only does the reflectivity increase because of the brightness, but heat issues are greatly minimized if not eliminated altogether from the glowing elements because of the water content of the material. In the same manner, an element that turns dark in the winter may greatly enhance the retention of heat energy absorption. The electrical source may be a small solar panel, house current, battery or other source. 
         [0042]    It will be easily understood that while a suitable polymer may have sufficiently small pore size to prevent plant and other intrusions into the polymer matrix, the water content may invite surface or under-layer growth. An enhancement to this invention is the inclusion of elements or compounds into the mix to further enhance the inability for plant, fungi and bacterial matter to grow. 
         [0043]    Similarly, another enhancement is to address the possibility that exposure to the sun&#39;s UV rays may degrade the polymer over time. To mitigate this, at least partially if not completely, UV inhibitor means and compounds may be incorporated into the polymer formulation or the polymer mix. 
       EXAMPLE 
       [0044]    Existing high water content polymers like that disclosed in U.S. Pat. No. 6,201,089 provides a straightforward basis for an example implementation of this invention. 
         [0045]    A hydrated polymer, combined with a liquid adhesive component is mixed with a working fluid to provide the proper application viscosity. Viscosity requirements may be based on several factors, but at a minimum will have to allow compatibility with application means. For the sake of this example, the application means is a spray system commonly used in the construction trade for applying paints or expandable foam insulation and other surface coatings. 
         [0046]    After clearing an existing roof from debris and easily removed dirt and residue, an operator uses the spray system to apply a layer of the polymer mix. Environmental factors like temperature and humidity may impact the speed at which the operator can apply the material. As is often the case in applying paint, multiple applications may be necessary to provide the desired thickness. While the desired thickness is likely determined well before application, it is understood that it may be increased at a later time. After the desired area is coated to the desired thickness of the polymer mix, the operator simply lets it set and the adhesive cure in place. 
         [0047]    For this example, one may assume that during peak summer seasons the polymer will likely face periods of extended dryness. To maintain the polymers beneficial actions, during the relatively cooler nighttime a sprinkler system tied to the non-potable landscape water source sprays water on the polymer-covered roof. This will ensure optimal performance during the next days heat cycle. Such a sprinkler cycle will not be necessary if there is rain or sufficient moisture available in the atmosphere. 
         [0048]    In an area of high humidity there is always a concern about the growth of mold, mildew, algae and other unwanted plant life. For the example polymer mix, this is easy dealt with by periodic application of a simple sodium bicarbonate and water or similar mixture. Not only does this provide moisture to the polymer but the nature of the mixture will kill any surface growth. Such an application may be ideally performed at least once per year. Should additional action be required against molds, mildews, algae or other unwanted growth—commercially available biocides, algicides or other treatments can be applied, including as part of the water rejuvenation feed through the sprinkler system. 
         [0049]    Should there be any work done on the roof system, ventilation system maintenance for example, any damage to the polymer layer is easily fixed with a simple spray of more polymer mix. There is not issue of compatibility with the existing polymer layer. 
         [0050]    While specific polymer types and embodiments are cited in this description, it will be well understood by those schooled in the art that variations are possible. Nothing in this description is to be read as limiting with respect to such potential variations. Moreover, while synthetic polymers are used for example purposes, the invention disclosed herein may be applicable to the use of naturally derived or hybrid natural/synthetic formulations.