Abstract:
An evaporative cooler air conditioning system comprising an air-to-air counter-flow heat exchanger having separate dry cooling and wet evaporating chambers, air saturating elements, and air movement devices. Ambient supply air or other fluid is forced through the dry cooling chamber of the heat exchanger and exits, after transferring through the heat exchanger, into the cooled spaced or room to be cooled. The air in the cooled space absorbs heat from the heat load and reaches an equilibrium at a warmer temperature, and is then forced directly through the wet evaporative chamber of the heat exchanger where it is heavily saturated with water or other liquid. As the air or other fluid passes through the wet evaporating enclosure a reverse temperature profile results and heat is drawn from the supply air fluid on the dry side through the heat exchanger to evaporate the water or other liquid; it results in the cooling of the supply air or other fluid exiting the dry side of the heat exchanger to a temperature that can be significantly below its wet-bulb temperature and approaching to its dew point temperature.

Description:
This Application Ser. No. 778,412, filed Sept. 20, 1985 by Christopher E. Wainwright for an IMPROVED EVAPORATIVE COOLER INCLUDING AN AIR-TO-AIR COUNTER-FLOW HEAT EXCHANGER HAVING A REVERSE TEMPERATURE PROFILE is a Continuation-In-Part of Application Ser. No. 550,711, filed 11-9-83, now abandoned, by Christopher E. Wainwright for an IMPROVED EVAPORATIVE COOLER, which in turn, is a Continuation of Application Ser. No. 305,397, filed 9-25-81, by Christopher E. Wainwright for an IMPROVED EVAPORATIVE COOLER, now abandoned, and is entitled to the filing date thereof. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to evaporative coolers and more specifically to an evaporative cooler air conditioning system; wherein an ambient airstream is cooled, sensibly, by means of a counter-flow heat exchanger such that evaporation continues within the heat exchanger in an exhausting airstream during the heat exchange process so that the temperature of the cooled air can be well below the wet-bulb temperature and even to a temperature close to the dew point temperature of the ambient air. 
     2. Description of the Prior Art 
     The concept of using evaporative cooler systems to provide an efficient method of cooling air for the purpose of cooling homes, apartments, industrial buildings, commercial buildings, house trailers and other enclosures, is old and well-established in the art. 
     In the past, there have been disclosed in the prior art many different apparatus and methods of using the cooling effect of the evaporation of water to lower the temperature of an airstream. Conventional evaporative coolers, cool air at a constant enthalpy; that is, the air is cooled by the evaporation of water without the addition or subtraction of heat. As a result, the minimum theoretical temperature which could be reached or to which a conventional evaporative cooler can cool the incoming air, is the wet-bulb temperature of its initial state. 
     In U.S. Pat. No. 1,985,529, to Ray; a process was disclosed whereby the temperature of the air circulated in an evaporate cooler air conditioning system was reduced below the wet-bulb temperature of the air entering the apparatus. In accordance with Ray&#39;s invention, raw or atmospheric air was introduced into a heat exchanger. The air emerged from the heat exchanger and entered a first vestibule, at which point, part of the air, having a lower dry and wet-bulb temperature than it did upon entering the heat exchanger, can be drawn off or bled for cooling purposes. The remaining air leaving the first vestibule entered a washer or humidifier where the air had a tendency to further cool the water. Since the air was not saturated, the air could absorb water, and continue to abstract heat from the air by conventional water vaporization. 
     The air left the washer and entered a second vestibule where part of it could be bled off for use, if desired. The air in the second vestibule was more saturated and lower in temperature than the air in the first vestibule. If the air in the second vestibule was bled off, it was required to place eliminators between the washer and point of bleeding to remove the entrained moisture. The saturated and cold air leaving the vestibule, and not bled off for use, was again washed with a spray of water to insure a high degree of saturation. It was then forced through the heat exchanger where the heat for the evaporation process could be drawn from the entering warm air. 
     Whereas this invention was capable of cooling air to below the wet-bulb temperature of the raw air or atmospheric air entering the heat exchanger, it was quite complicated, complex, required extensive spraying apparatus and ductwork and was quite expensive and relatively inefficient. Also, the cooled air was usually very high in humidity since it was exposed directly to the water in the wash compartment. The thermal efficiency of this system was, therefore, not nearly as high as it should have been or could have been. 
     U.S. Pat. No. 2,174,060, to Niehart, discloses an improved air conditioning apparatus that provided a means and operated by a method which comprised reducing the temperature of incoming air towards its dew point temperature by employing a heat transfer through a partition which was dry on one side and wet on the other. The total initial volume of the incoming air was first passed over the dry surface, and then was divided into a stream which flowed into the room to be cooled. A second stream which was then passed into contact with the wet side of the partition so that the air that contacted the wet side of the partition had already been reduced in temperature by its movement from the dry side. When the air first came into contact with the wet surface, this surface was at or near the new wet-bulb temperature and by the action of the heat transmitted through the partition from the dry side and taken up by water and air current, the wet-bulb temperature of the air flowing over the wet side increased until it had absorbed the heat being transmitted through the partition. Accordingly, more heat was absorbed through the process of increasing the wet-bulb temperature on the wet side of the partition and little heat was lost by increasing the temperature of the water therein. 
     The apparatus disclosed by Niehart incorporated the return of cold air into the hot end of the heat exchanger thereby resulting in the injection of cold air into a hot ambient airstream. This caused a lowering of the temperature at the hot end of the heat exchanger and a consequential lowering of the temperature of the humid exhaust air. Unnecessary heat was gained by the system due to a cooler exhaust air than need be. In addition, the cooling capacity of this system was greatly reduced to a lower amount of water per unit of mass flow of air that could be absorbed by the cold air entering the atmosphere of the wet evaporating chamber. 
     U.S. Pat. No. 4,023,949, issued on May 17, 1977 to Leslie A. Schlom et al for an EVAPORATIVE REFRIGERATION SYSTEM. This patent disclosed a system wherein air is evaporatively cooled by water in which the evaporating water is kept separate from the useful air of the cooled airstream by means of a heat exchanger so that cooling is performed without the addition of water vapor to the useful air and in which the working air absorbing the water vapor is drawn from the load. A heat exchanger is disclosed which operates by movement of the working air internally through tubular conduits concurrently to water flowing downward on the inner surfaces thereof while the air to be cooled passes externally across the conduits. 
     Therefore, the incoming fresh air is in an air-to-air cross-flow heat exchanger configuration to the return air and the return air is in an air-to-water counter-flow heat exchange configuration in which the water flows in the opposite direction. The Schlom et al application teaches a heat exchanger with separate dry sides and wet sides with the evaporating water being kept separate from the useful air so that cooling is performed without the addition of water vapor to the useful air; and all of the working air is drawn from the load and recirculated from the enclosure to be cooled to the wet side of the heat exchanger. Schlom et al specifically states that the wet side of the heat exchanger operates by movement of the working air internally through conduits counter-currently or in a counter flow with the water flowing downwardly along the conduit tubes inner surfaces while the useful air passes through the dry side in cross-flow to the return air in the conduit. This patent specifically teaches that the obtained increases in efficiency are due to flowing the moisture-laden return air exhausted from the wet side of the heat exchanger in a cross-flow heat exchanger which includes a separated relationship between the fresh air flow upstream from the dry side of the heat exchanger. Since the evaporating water is kept totally separate from the cooling airstream by means of the heat exchanger so the cooling is performed without the addition of water vapor, sensible cooling is achieved. While this patent represents an increase in efficiency, it nonetheless discloses a relatively complex and complicated system requiring costly equipment which still does not maximize the efficiency possible or solve many of the basic problems in evaporative cooler systems. 
     U.S. Pat. No. 4,188,994, issued to Louis W. Hinshaw on Feb. 19, 1980 for a COOLING AND HEATING APPARATUS. The patent teaches a cooling apparatus having an evaporative cooler interfaced with insulated air chamber and detachable therefrom to be replaced with a solar heater collecting panel. The insulated air chamber is connected to a home or other structure by a passage means; and the evaporative cooler is operable by other than the conventional electrical energy source as well as the usual electrical energy source so that the assembly can be used for cooling and heating of houses and other structures. 
     Hinshaw claims to be the first to use a dry air interface to directly cool air in an evaporative cooler system. The system involves exhausting the evaporated moisture into the atmosphere rather than into the building to be cooled. A metal plate is disposed on one face of the evaporative cooler to serve as an interface between the evaporative cooler and the body of the insulative box and the solar panel portion has been detached. As the warm air flows into the system and its temperature drops, moisture will condense and run off of the baffles and back on the interface into the bottom of the chamber. This will cause the cooling system to de-humidify the air as well as to cool it. 
     The heat exchange method of this patent is relatively expensive an ineffective and the efficiency of this system is far from that of the present evaporative system. 
     Therefore, a long-felt need has existed and continues to exist for an improved evaporative cooler system capable of efficiently cooling air below the wet-bulb temperature of the supply air while remaining relatively simple in design, structure, fabrication techniques required, and energy used. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to economically cool the interior of an enclosure, such as a room. 
     It is another object of the present invention to provide a simple and efficient method of ventilating an enclosure. 
     It is still another object of the present invention to conserve heat and cooling energy during the ventilation of an enclosure. 
     It is yet another object of the present invention to provide an apparatus and method for heating the interior of an enclosure. 
     It is another object of the present invention to provide an intake air-to-return air counter-flow heat exchanger with the return air being cooled by water evaporation to become the heat sink which cools the intake air. 
     It is still a further object of the present invention to provide an evaporative cooling system wherein the evaporation process continues within the heat exchanger during the heat exchange operation. 
     It is yet a further object of the present invention to provide an improved evaporative cooler system. 
     It is still another object of the present invention to provide an improved evaporative cooler wherein the absorption of water is not at a constant &#34;enthalpy&#34; but at a constant relative &#34;humidity&#34;. 
     It is yet a further object of the present invention to provide an improved evaporative cooler system which can absorb more water per pound of air and can achieve significantly better performance than conventional evaporative coolers. 
     It is yet another object of the present invention to provide an improved evaporative cooler wherein the evaporation process occurs with the addition of heat in a &#34;reverse temperature profile&#34; to that of conventional evaporative coolers with the addition of heat being provided by an air-to-air counter-flow heat exchange from the heat gained in cooling the air. 
     It is still another object of the present invention to provide a cooling system which results in the absorption of many times the water per unit of mass air than that of simple evaporative coolers, and wherein the exhausted air requires significantly more heat energy to evaporate the added water than can possibly be extracted in the same mass of intake air in conventional evaporative coolers. 
     It is yet a further object of the present invention to provide a cooling system which produces a significantly lower temperature of cold air than that possible from conventional evaporative coolers. 
     It is yet another object of this invention to provide an evaporative cooler system which operates with an air-to-air counter-flow heat exchanger to produce a &#34;reverse temperature profile&#34; in which unlike conventional air-to-water or water-to-air evaporation means where the air temperature decreases, rather than increases, with distance in the direction of the evaporating air flow. 
     It is still another object of the present invention to provide an improved and more efficient evaporative cooling system than was heretofor possible in the prior art while also avoiding substantially all of the problems of the prior art. 
     Accordingly, the present invention provides an improved evaporative cooling system wherein the inlet air flows through a supply chamber and into an enclosure while the return air flows from the enclosure through a return chamber into the atmosphere. Heat is transferred from the supply chamber to the return chamber and vise versa such that evaporative cooling in accordance with the present invention is usable to economically cool a room significantly below the wet-bulb temperature of the inlet air. 
     As a result, the improved evaporative cooler air conditioning system of the present invention is capable of cooling air to temperatures well-below the wet-bulb temperature of the ambient air and even to temperatures approaching the dew point temperature and with significantly less relative humidity within the temperature controlled space or enclosure than with any other known evaporative cooler. 
     The foregoing and other objects, features and advantages of the present invention will be more fully apparent from the following detailed description of the preferred embodiment of the invention, the claims, and the accompanying drawings which are briefly described hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of the evaporative cooler air conditioning system of the present invention illustrating a counter-flow air-to-air heat exchanger; 
     FIG. 2 is a schematic illustration of a cross-flow air-to-air heat exchanger of the prior art; 
     FIG. 3 is a sectional side view of the conventional cross-flow heat exchanger of FIG. 2; 
     FIG. 4 is a schematic illustration of the counter-flow heat exchanger of the present invention; 
     FIG. 5 is a sectional side view of the air-to-air counter-flow heat exchanger of FIG. 4; 
     FIG. 6 illustrates a conventional evaporative cooling apparatus. 
     FIG. 7 illustrates, graphically, the normal temperature profile of conventional evaporative cooling apparatuses; 
     FIG. 8 illustrates Applicant&#39;s air-to-air, counter-flow, heat exchanger. 
     FIG. 9 illustrates, graphically, the reverse temperature profile of the innovative air-to-air, counter-flow, heat exchanger of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a cross-sectional diagram showing the preferred embodiment of the improved evaporative cooler system 10 of the present invention. The evaporative cooler system 10 includes a heat-exchanger portion 14 which has a supply chamber 52 physically separated from a return chamber 50 by a thermally conductive membrane 30. An air inlet port 26 of supply chamber 52 is connected to an air blower 12 through an entry duct 24. 
     The blower 12 includes a fan 20 that forces a flow of inlet supply air from the atmosphere 22 through supply chamber 52. An outlet port 32 of the chamber 52 is connected to a supply duct 34. As explained hereinafter, the supply air is cooled in supply chamber 52 by heat transfer through the membrane 30 and the cooled supply air flows into the supply duct 34 from supply chamber 52. The supply duct 34 is connected to an enclosure or room 18 through a supply register 36. The cooled supply air passes through the register 36 and into the room or enclosure 18 thereby cooling the airspace within the room 18. 
     The room 18 is then connected to a return duct 40 through a return register 38. Preferably, the registers 36 and 38 have as large a spatial separation as physically practical within the particular room or enclosure 18 in which they are used. 
     Returned air from the room 18 flows into the return duct 40. Because of the spatial separation of the registers 36 and 38, and because of the heat load of the room 18, the temperature of the returned air is significantly higher than the temperature of the cooled air supply. From the explanation given hereinbefore, the first embodiment of the present invention relates to a system that is closed between the chamber 50 and 52. 
     The return duct 40 is connected to a return port 42 of return chamber 50. An exhaust port 54 at the opposite end of return chamber 50 is connected to the atmosphere 22 by an exhaust duct 56. Accordingly, the returned air that flows into return duct 40 also flows through the wet return chamber 50 and into the atmosphere 22. As explained hereinafter, the temperature of the returned air flowing past the membrane 30 is below the temperature of the supply air, thereby causing a transfer of heat from the air within chamber 52 to the air within chamber 50 via the membrane 30. This heat transfer causes a heating of the returned air and a cooling of the supply air. 
     A water evaporator 46 is disposed in any suitable manner within return chamber 50 near the port 42. The evaporator 46 is connected to a source of water, not shown, but known in the art, through a conventional pipe 16. The evaporator 46 may be a spray nozzle or any other device that causes that evaporation of water. 
     Water is forced through the water evaporator 46 into return chamber 50 as spray 44 wherein it is evaporated. The evaporation process substantially saturates the returned air with water vapor. Because of the evaporation, the temperature of the vapor-saturated returned air is significantly below the temperature of the inlet air on the opposite sides of the membrane 30. 
     From the explanation given hereinbefore, the supply air is cooled without being saturated with water vapor. Moreover, evaporation takes place as the heat transfer causes a heating of the returned air. The heating of the returned air increases the amount of water which can vaporize, thereby providing an increased heat absorption and cooling effect of the evaporation. This effect is greatly enhanced because the heat exchange occurs when supply air and return air move in opposite directions as in the air-to-air counter-flow heat exchanger of the present invention. Because of the increased heat absorption in the returned air, the cooled supply air may have a temperature significantly below the wet-bulb temperature of the inlet air. 
     In should be understood that the present invention utilizes evaporative cooling. Because of the evaporative cooling process, the apparatus in accordance with the present invention is inherently more simple, efficient, and more economical to operate than a cooling system which utilizes refrigeration. However, because supply air is cooled without the addition of water, the apparatus provides cooling comparable to that provided by a true refrigeration system. 
     In an alternate embodiment of the present invention, the blower 12 may alternately be disposed in either the duct 34, the duct 40, or the duct 56. Furthermore, as shown in the preferred embodiment, a valve 17 may be disposed within the pipe 16 so when cooling is not desired, the valve 17 can be operable to occlude pipe 16 and prevent evaporation. The returned air thereby warms or cools the supply air to conserve or preserve a desired temperature via the membrane 30. The supply air thereby ventilates the room 18. 
     Accordingly, the apparatus of the present invention is useful in ventilating an enclosure 18 and maintaining a desired temperature therein by recuperation of the heat in the returned air. A leakage of air from the room 18 is represented by an arrow 58 and the leakage of air into the room 18 is represented by an arrow 60. Either of the leakages reduces the cooling efficiency and the recuperation efficiencies of the apparatuses described hereinabove. A blower may be connected to the duct 56 or in duct 40 to force air therefrom and thereby equalize air pressure between the room 18 and the atmosphere 22 to substantially eliminate such leakage. 
     FIG. 2 illustrates a conventional air-to-air cross-flow heat exchanger as indicated by reference numeral 71. A first fluid, such as the supply air, flows in the direction as indicated by the arrow 72, while a second fluid, such as the return air, is represented by the arrow 73. FIG. 3 is a cross-sectional end view of the air-to-air cross-flow heat exchange system 71 of FIG. 2 with the arrow 73 showing the direction of flow of the second fluid and the dots representing the arrows 72 to indicate the direction of flow of the first fluid. It will be noted that in both FIGS. 2 and 3, the air-to-air cross-flow configuration has the two airstreams flowing generally orthogonally or perpendicular to one another. It will of course, be recognized that individual heat exchange plates 74 of FIG. 3 may alternately be tubes or any conventional heat exchange material. 
     FIGS. 4 and 5 illustrate the air-to-air counter-flow heat exchanger technique of the present invention. FIG. 4 shows the direction of the first fluid, such as the supply air, as indicated by the arrow 76 and the direction of flow of the second fluid, such as the return air, indicated by the dashed arrow 77. It will be noted that rather than passing in orthogonal relationship to one another, the streams of air flow are parallel to one another and in opposite directions. 
     FIG. 5 shows a cross-sectional end view of the air-to-air counter-flow system 75 of FIG. 4 and shows that the first fluid such as the supply air is flowing in the direction of the arrow 76 while the return air is flowing in the opposite direction as indicated by reference arrow 77. The individual plates 74 of the heat exchanger of FIG. 5 could also be tubes or any conventional heat exchanger media known in the prior art. It will be observed that the counter-fluid technique of FIGS. 4 and 5 is quite different from the cross-flow technique of FIGS. 2 and 3. Each has a well-known established technical meaning within the heat exchange art and they are in no way equivalent, and they do not function in the same manner. 
     FIG. 6 illustrates a conventional evaporative cooling system 81; wherein, the inlet air is designated by the arrow 83; wherein, said inlet air passes through an evaporating medium 85; wherein, said evaporating medium 85 can be an aspen fiber pad or its equivalent; wherein, said inlet air 83 becomes cooled air that is represented by the arrows labeled by reference numeral 87 that exit the evaporation medium 85; and wherein, said cooled air 87 is much cooler than the inlet air 83. 
     FIG. 7 illustrates the temperature profile of the inlet air 83 as it becomes cooled air 87 within the evaporating medium 85 and shows that the inlet air temperature drops with distance as it moves through the evaporating medium 85. This is the &#34;normal temperature profile&#34; as generally taught in the prior art. 
     FIG. 8 illustrates the air-to-air counter-flow heat exchanger 91 of Applicant&#39;s invention. In FIG. 8, the atmospheric air represented by the arrow 92 enters entry duct 24 and passes through the heat exchange path in supply chamber 52 to exit through supply duct 34 into the room or enclosure 18 to be cooled as the inlet air represented by the arrow designated by reference numeral 93. Simultaneously, the return air indicated by the dashed arrow 94 enters through the outlet vent from the room through return duct 40 and into the second heat exchange path in return chamber 50 to exit to atmosphere via exhaust duct 56 as the exhaust represented by the dashed arrow 95. Supply chamber 52 and return chamber 50 are separated by a heat exchange membrane 30. Supply chamber 50 serves as the evaporation chamber and water is sprayed from a water inlet system 46 into that chamber as a fine mist or spray 44. As return air 94 from the enclosed space 18 is passed passes through the water evaporating return chamber 50 of the heat exchanger 91, it enters the water or mist 44 and becomes heavily saturated with that water sensible heat is absorbed by the latent heat of evaporation as this water saturated air is forced through return chamber 50, heat is drawn from the air being forced through supply chamber 52; where supply chamber 52 is on the opposite side of the membrane 30 and functions as a dry cooling chamber. In this manner, the air within return chamber 50 is heated and water is evaporated which results in the sensible cooling of the air forced through supply chamber 52 so that the air exiting the exhaust duct 56 is hot and very humid and the air exiting supply duct 34 is cool and dry. 
     The reverse temperature profile characteristic of Applicant&#39;s application, is illustrated in the graph of FIG. 9 which plots the air temperature against the distance in the direction of evaporative flow and shows a &#34;reverse temperature profile&#34; in which the air temperature increases with distance which is exactly opposite to the &#34;normal temperature profile&#34; of FIG. 5. Therefore, Applicant actually produces and uses the &#34;reverse temperature profile&#34; which is important to his invention; and this is totally contrary to the teachings of the normal temperature profiles associated with all known air-to-air heat exchangers using cross-flow techniques or conventional systems such as the evaporative cooling system 51 of FIG. 4 in which air temperatures drop or decrease with distance. 
     For a full understanding of the present invention, the distinctions illustrated with respect to FIGS. 2, 3, 4, and 5 must be understood since there is a basic thermo-dynamic difference between a cross-flow heat exchanger and counter-flow heat exchanger. The difference between these two types of heat exchangers is much more than the superficial fact of flow direction. 
     The heat transfer process in a cross-flow heat exchanger is highly non-linear. Temperature gradients across the heat exchange member are complex, and fluid temperature distributions are not simple. In a well-designed, counter-flow heat exchanger, the the equal mass flow rates, temperature gradient is relatively constant with distance, and fluid temperatures vary linearly. Because of these basic temperature characteristics and for a given amount of exchange membrane, cross-flow heat exchangers are no way near as effective as counter-flow heat exchangers. The potential linearity of counter-flow heat exchangers provides for the optimal use of the heat exchange materials. 
     However, in the case of the present invention, the most significant difference between the two archtypes of heat exchangers is not only the efficient of use of heat exchange materials, but it is in the differences in the basic thermodynamic processes themselves which occur within the exchanger. 
     Because of its geometry, a cross-flow heat exchanger has areas of very large temperature gradients across the heat exchange membrane and yet other areas a very small temperature gradients. When such an exchanger is used in conjunction with simultaneous evaporation, processes within certain areas are predominantly that of heat transfer, and yet other areas are predominantly that of evaporation. For significant portions of the cross-flow heat exchanger, evaporation and heat exchange are effectively separated. Evaporation within a cross-flow heat exchanger is little more effective than that of a separate evaporator with heat exchanger. Additionally, the high transfer rates of some areas necessitate liberal irrigation of the evaporative surfaces and this liberal irrigation mitigates against the very process which lies at the base of Applicant&#39;s invention. 
     The present invention teaches the use of a heat exchanger as a means of maximizing the cooling effect of water evaporation in the air by extending the evaporative process in the air flow as that air flow is caused to rise in temperature in the wet heat exchanger chamber to within a few degrees of ambient dry-bulb temperature. The present invention teaches that the evaporating air temperature rises during evaporation rather than the temperature falling during evaporation as occurs with all known prior art devices, since hot air absorbs more moisture and sensible heat than cold air. Therefore, the present application teaches a reverse temperature profile along the entire path of evaporation and such a reverse temperature profile can only be effectively achieved in a counter-flow heat exchanger. 
     As seen in FIGS. 2-4, the rise in temperature in return air is used to enhance the evaporation process and, via the heat exchanger, the cooling effect of evaporation of the supply air. The difference in temperature profiles is clearly illustrated in FIGS. 7 and 9. 
     Although it is theoretically possible that the process taught by the prior art can minutely occur in certain minuscule regions of a cross-flow heat exchanger, other areas of the exchanger will have quite the opposite effect. Over all, therefore, a cross-flow heat exchanger is quite ineffective and non-linear, and any reverse temperature profile is purely incidental and not deliberate and none has been recognized by any specific teaching in the prior art known to the present inventor. 
     Broadly, therefore, Applicant teaches the first known use of an air-to-air counter-flow heat exchanger in conjunction with the simultaneous evaporation of water to achieve a reverse temperature profile to that normally experienced in evaporation systems so as to maximize the cooling potential of water evaporation in air. 
     With this detailed description of the specific apparatus and method used to illustrate the present invention and the operation thereof, it will obvious to those skilled in the art that various modifications can be made in the construction, design and materials thereof and in the method contemplated thereby without departing from the spirit and scope of the present invention which is limited only by the appended claims.