Abstract:
The present invention provides a process for utilizing waste heat released by condensers of conventional air conditioning systems and more particularly using this low grade heat or other low grade sources that are slightly above ambient air temperatures to alter concentration of a liquid desiccant that contacts an ambient air stream thereby reducing its relative humidity while its temperature is controlled and generally reduced by heat exchange with another air stream that is saturated with water.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/204,705, filed Jan. 9, 2009. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a process for utilizing waste heat released by condensers of conventional air conditioning systems and more particularly using this low grade heat or other low grade sources that are slightly above ambient air temperatures to alter concentration of a liquid desiccant that contacts an ambient air stream thereby reducing its relative humidity while its temperature is controlled and generally reduced by heat exchange with another air stream that is saturated with water. 
       BACKGROUND OF THE INVENTION 
       [0003]    Concerns related to expanding utilization of electrical energy along with related cost issues have caused increased interest in energy efficiency. A related concern is limiting emissions from electrical generating plants owing to greenhouse gas issues. A further concern is an economical means to dehumidify and cool outside air before its injection into interior spaces. Historically, needs to meet additional air conditioning requirements have been met by increasing application of standard compressor based systems, a technology that is nearly 80 years old. Other compressor-based methods have been contemplated. U.S. Pat. No. 7,340,912 by Yoho et al teach placing a dedicated compressor with the evaporator in one air stream and the condenser in another. Combination of a separate compressor-based heat pump with a revolving solid desiccant impregnated wheel is taught by Maeda et al in U.S. Pat. No. 6,205,797 Rejected heat from the heat pump is used to partially evaporate water absorbed by the wheel. Operation of these wheels is adiabatic meaning that the energy of the air remains constant thus moisture removal is accompanied by an increase in heat. A separate heated stream of air is employed to remove absorbed moisture from the wheel. Use of revolving desiccant wheels desiccant is taught most recently in U.S. Pat. No. 7,338,548 to Boutall which adds that the air streams are in heat exchange with each other. Also using two air streams, Forkush et al in U.S. Pat. No 6,976,365 describes a dedicated compressor where the condenser and evaporator have separate air streams to either absorb or reject moisture from a liquid desiccant. Another form of cooling and dehumidification is the absorption chiller operating on pressures and vacuums that requires regeneration at high temperature, approximately 180 degrees F. with the heat generally supplied by fossil fuel. The major disadvantage of the existing technologies is that all of them require a dedicated thermal input in order to be functional. A practice that would reduce energy utilization of these devices would be to possibly bring operating temperatures of the devices into closer proximity. For instance, a general heat and mass transfer device that allows for improved temperature approaches of gas streams is taught by Albers et al in U.S. Pat. No. 4,832,115. Another device operating at closer temperature approximations is taught by Maisotsenko et al in U.S. Pat. No. 4,350,570. The apparatus employs an air stream of generally low humidity and is divided into primary and secondary flows with one serving to cool a separate condensation element. 
       SUMMARY OF THE INVENTION 
       [0004]    In view of the foregoing energy utilization disadvantages inherent in the known methods to provide dehumidification and air temperature reduction, the present invention offers closer proximities of heat and mass transfer throughout all of its steps allowing employment of low grade waste energy as is available from existent air conditioner condensers that have not been specially dedicated to the process or, as an example, from low grade solar means such as air heating devices. 
         [0005]    The novel features as disclosed in the present invention, which will be described subsequently in greater detail, can be best established by first employing a limited discussion of air properties represented herein. Reviewing temperatures exiting conventional compressor-based air conditioners it is found that while there is variance in these exhaust temperatures, many industry sources place the rise at only 15° F. While seemingly small this change can have a substantial effect on the relative humidity of air. For instance, at an American test condition (ARI-A) temperatures are established at 95° F. dry bulb and 75° F. wet bulb resulting in a relative humidity of 40%. By increasing the dry bulb temperature to 110° F., when using heat generated by an air cooled compressor, allows reduction of relative humidity to 25 percent, a reduction of slightly less than 40 percent. Also of importance in the process of the present invention is the water saturated wet bulb temperature of the air which in this case is 75° F. In this environment, possible operational parameters would be conditions where the maximum relative humidity reduction to an ambient air stream would not fall below 25 percent and the maximum temperature reduction would be limited to 75° F. An air stream also contains mass component that is expressed as moisture contained within the air. This can be articulated as pounds of water per pound of air or a volume of a cube measuring approximately 2.5 feet per side. At the maximum conditions expressed above, air would contain 0.014 pounds of water per pound of air. At the minimum conditions the air holds 0.0046 pounds of water per pound of air. Were this air then saturated with water its temperature would be 55° F. The heat (temperature) and the moisture content (mass) make up in general terms the energy contained in the air. In the imperial system this is expressed as British Thermal Units or Btu. At the maximum conditions this is 38.4 Btu per pound of air while the delivery condition would be 23 Btu per pound of air. Given the significantly reduced humidity of the supply air, this air may be injected into the interior building space to assist dehumidification of this space or could be nearly saturated at delivery in order to be in correspondence with the normal delivery conditions of compressor-based air conditioners. On a theoretical basis the delivery conditions obtained by the present invention at the ARI-A test conditions would equal the delivery conditions achieved by conventional compressor-based air conditioners. 
         [0006]    The present invention combines dehumidification by employing a liquid desiccant and cooling by means of heat exchange with a saturated air stream in a staged manner that allows for close temperature approaches. The invention is generally carried out through utilization of three air streams. The first ambient air flow is augmented in temperature by a low temperature waste heat source. In many cases this air exits from an air conditioner condenser if the condenser is air cooled or air in heat exchange between the liquid desiccant and the hot water source by means of liquid-to-liquid heat exchangers if the condenser is cooled with water. The amount of heat rejected to the condenser is equal to the cooling capacity of the air conditioner plus the heat generated by the inefficiency of the compressor system, an amount equal to at least 10 percent of the cooling capacity. This heated air can evaporate water from a liquid desiccant owing to its reduced relative humidity. This regeneration air stream is exhausted to the environment at the same energy content as at its entrance but with at a lower temperature and with a higher moisture level. The liquid desiccant then contacts a separate ambient air stream, known as the supply air stream, and after removing moisture from this air stream is returned for regeneration. As the desiccant removes moisture from this supply air stream the energy of this air stream remains constant with the energy removed by moisture deleted balanced by energy related to its rise in temperature. The effect of this temperature increase of this supply air is mitigated by utilization of a third air stream that is maintained in a near saturated condition, in this case substituting moisture for heat. This air stream passes counter-currently in a staged manner and the cooled water, coming into balance with the reduced temperature caused by water evaporation into the air stream, is in liquid-to-liquid heat exchange with the liquid desiccant. Heat is then exchanged between the liquid desiccant and the supply air flow owing to direct contact. Heat of dehydration of the supply air is mostly transferred to this saturated air stream and depending on its wet bulb temperature most likely will reduce temperature of the supply air to less than ambient air conditions. This temperature reduction causes the relative humidity of the air to increase thereby increasing the effectiveness of moisture removal by the liquid desiccant. 
         [0007]    The heat and mass of each air stream should not be mixed during passage through the device of the current invention as when in heat exchange with another air stream the driving force or temperature differential between air streams would be significantly reduced. As an example, an air stream with entering temperatures of 90 degrees F. and transferring heat providing an exit air temperatures of 70 degrees F. would have an a average temperature of 80 degrees F. Were two stages employed, the average of the uppermost stage would be approximately 85 degrees F. and the lower stage 75 degrees F. thus providing both higher and lower temperature heat exchange possibilities. Without staging, the moisture content of an air stream would be blended thus averaging relative humidity of an air stream as well as its temperature. This mixing is largely prevented in the process of this invention and is provided by the development of stages, each with unique properties of heat and mass. Each stage contains a basin that is connected to a separate pump. The pumped basin liquid from a supply air stage is directed through a liquid-to-liquid heat exchanger that exchanges heat with a correspondent liquid from a saturated air stage. After passage through the liquid-to-liquid heat exchanger caused by a dedicated pump, liquids are distributed upon media such as that found in evaporative coolers or in small cooling towers where the liquids are in contact with the air flow before falling into the basin thereby providing contact between the liquid and the air stream. A small stream of desiccant is allowed to flow between stages of the supply air stream before its return to contact the regenerative air stream. This heated regenerative air stream is likewise segregated into stages in order that each stage can maintain its own temperature and relative humidity composition. In the same manner as in the supply air stream, a small flow of desiccant is allowed to course counter-currently to the air stream with the air stream being first in contact with the coolest and highest relative humidity air progressively flowing to contact the highest temperature of the air stream that has the lower relative humidity. 
         [0008]    It is to be understood that the invention is not limited in its application to the details of construction for operation at atmospheric pressure as presented or at other pressures or vacuums, and to the arrangements of the components, set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments, especially as related to utilization of other heat sources generally described as “waste heat” or use of other forms of heating such as provided by solar air heaters along with the ability to store concentrated desiccant for evening uses as would be especially useful in most solar applications, all of which might be carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Referring to the drawings: 
           [0010]      FIG. 1  is a plan view with a portion of its cover removed of a device according to the present invention showing major components with certain of these shown schematically; and 
           [0011]      FIG. 2  is a cross-sectional view taken along lines  2 - 2  of  FIG. 1  with portions including connecting pasts thereto shown schematically. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The apparatus for implementing the invention consists of a staged regenerator for removing moisture from a liquid desiccant, a staged air dehumidifier and cooler removing moisture from an air stream, and a staged saturator that maintains an air stream in a near saturated condition while exchanging heat with the dehumidifier and cooler. These three modules are generally placed in a horizontal position and they may be stacked one on the other or they may be physically separated from each other as long as they are thermally connected thermally or by means of a flow of desiccant. Each module consists of a number of stages with each stage consisting of wetting media, dedicated basin, pump and access to a liquid flow. The stages in two of the modules are thermally connected by liquid-to-liquid heat exchangers and two modules are connected by desiccant flow. Each module contains an air movement means that allows a supply of air that is separate from the other modules wherein the flow through each module may be different in each module. 
         [0013]    Referring descriptively to the drawings for mechanical function, in which similar reference characters denote similar elements throughout the several views, a device of the present invention is generally indicated as device  11  in  FIG. 1  and  FIG. 2 . The plan view of device  11  as shown in  FIG.1  depicts the configuration of each of the three modules designated as modules  60 ,  70  and  80  in  FIG. 2 . Configuration is generally the same for each module allowing for common designations. Device  11  is schematically shown as rectangular with each of modules  60 ,  70 , and  80  having side walls  21  and  22 , end walls  23  and  24 , top wall  25  (partially removed in  FIG. 1 ) and bottom wall  26 . If desirable, the walls in thermal contact with ambient conditions may be thermally protected with insulation  27  that may be any efficient and highly vapor and liquid resistant material. Chamber length, height, and width dimensions are generally consistent throughout the modules of device  11  although the modules could be of different dimensions and each may vary along their length. Materials may be of metal such as steel sheet or aluminum, or made in part from a rigid plastic. It is apparent from the above description that the modules may be stacked or positioned at some distance from each other and positioned directionally independently of each other as long as, where appropriate, thermal correspondence between stages and liquid desiccant flow between modules is maintained. 
         [0014]    Basins  30  are utilized for liquids present in modules  60 ,  70 , and  80 . These basins are each segmented into at least two stages, with four being shown in  FIG. 1  as stages  31 ,  32 ,  33 , and  34  of basin  30 . The effective separation of temperatures and relative humidity concentrations is generally increased by augmenting the number of stages. Pipe  35  is located at the terminus of stage  31  while pipe  36  is located at the terminus of stage  34 . Liquids associated with the stages are largely contained within stages; for instance within stage  31  by wall  37  having an opening provision  38  for staged-flow between stages as located between stages  31  and  32 ,  32  and  33 , and  33  and  34  of basin  30 . The opening provision may be a slit in wall  38  or maybe a tube inserted in wall  38 . Basins  30  are normally molded from a high temperature withstanding plastic or FRP to avoid seams but could be of a stronger material depending upon structural requirements. The profile of these basins generally includes surface area  40  to collect liquids, a sump  41 , A pump  42  is dedicated to each stage and is generally placed external to sump  41  and connected by pipe  43  to sump  41  or may be located within sump  41 . The pumped liquid first passes from pump  42  via pipe  44  of module  60  to heat exchanger  45 . The liquid-to-liquid heat exchangers may be of standard configuration such as shell and tube, or plate and frame. Flow from liquid-to-liquid heat exchanger  45  is directed by pipe  46  to liquid discharge assembly  47  of module  60  that distributes basin liquid onto media  48  that is supported by open grid  49 . Liquid thus distributed falls through media  48  by gravity into basins  30 . Materials with augmented surface suitable for media  48  include that typically found in evaporator cooler products, small saddles or rings found in smaller cooling towers, or other suitable material. View of one type of liquid discharge assembly  47  found adequate for distribution is presented in each stage of device  11  of  FIG. 1  and has been designed so that liquid flow is nearly evenly distributed over the media surface with any bias counter to the air flow. Assembly  47  which is generally the same in modules  60 ,  70 , and  80  may incorporate additional distribution tubes or other means to improve disposition of the liquid. The pipes may be of suitable plastic material with spaced openings  50  cut into the liquid discharge assembly  47  along its top surface in a “v” shaped pattern or these spaced openings could contain low pressure nozzles inserted into assembly  47 . Liquid desiccant enters and exits basins  30  via pipes  35  and  36  of module  60  moving counter-currently to an air stream flowing through module  60  directionally moving from basin  34  to basin  30  with air flow shown by arrow  61 . 
         [0015]    Thermal connection between the correspondent stages of modules  60  and  70  is via liquid-to-liquid heat exchanger  45 . Liquid from basin  30  of module  70  flows through pipe  53  to pump  42  of module  70  and from pump  42  to liquid-to-liquid heat exchanger  45  by means of pipe  55  where the liquid flows counter-currently to liquid passing from pipe  43  to pipe  46 . The liquid exits liquid-to-liquid heat exchanger  45  through pipe  56  then discharged into liquid discharge assembly  47  of module  70 . Correspondence between stages  31 ′ through  34  of module  60  and  31  through  34  of module  70  are maintained with like stages of module  70  by means of counter-current liquid flows through the corresponding liquid-to-liquid heat exchanger  45 . Water generally enters and exits basins  30  via pipes  35  and  36  of module  70 . The directional flow of the water relative to an air stream flowing through module  70  is significant only in that temperature differential between the water and the air stream is generally minimized if the water and air flow designated by arrow  71  is counter-current. In other configurations water could be directly injected into each stage however flow through all stages is preferred as an overflow at the exit prevents mineral accumulations. The direction of air flow  71  of module  70  is counter-current to air flow  61  of module  60 . 
         [0016]    Dilute liquid desiccant flows from pipe  36  of module  60  to module  80 , the desiccant regenerator, by means of pipe  36  located thereto to stage  34 . An air stream, shown by arrow  81 , flows counter-currently to the liquid desiccant flow which exits stage  31  via pipe  35  of module  80  that connects by means of pump  82  with pipe  35  of module  60 . The construction and features of the stages of module follows that earlier described including pathway  38  allowing liquid connection throughout the length of module  80 . In preferred embodiment of the present invention air stream  81  passing through module  80  is generated and heated by an air cooled condenser of an air conditioning system. Heated air from other sources, such as solar or waste heat air heaters could likewise be employed. Alternatively, a heated water stream, such as found in larger commercial air conditioners or from other sources or other heated liquids could be utilized. In this mode of operation a series of liquid-to-liquid heat exchangers, again illustrated by the numeral  45 , could be employed with the highest temperature water entering the liquid-to-liquid heat exchanger associated with stage  31 . The liquid desiccant flow pattern is the same as presented for module  60 . Heat exchange is by means of pipes  55  and  56  flowing liquid counter-currently to the liquid desiccant flow through liquid-to-liquid heat exchanger  45 . Pipe  56  exiting liquid-to-liquid heat exchanger  45  of a stage connects with pipe  55  in the next stage allowing for the stream of hot liquid to be counter-flow to the stream of air throughout the stages of device  80 . With the modules placed as displayed in  FIG. 2 , the flow of liquid desiccant may be by gravity from module  60  to module  80  with concentrated liquid desiccant returned from module  80  to module  60  by means of pump  82  or the function of pump  80  may be assumed by a pump already existent in module  80 . Other arrangements of the modules in relationship to each other may require alternate placement of gravity discharge and liquid desiccant pumping activities. 
         [0017]    The advantage of employing stages in order to obtain close proximity of air temperatures and improved management of air relative humidity can be shown by presenting a calculated example, employing ambient conditions previously presented. Accepting an air cooled condenser and a rise above ambient temperature of 15° F., air conditions would be 110° F. dry bulb, 79° F. wet bulb with a moisture loading of 0.0141 pounds of moisture per pound of air, energy of 42 Btu per pound of air, and a relative humidity of 25%. Assuming a compressor-based air conditioner of one ton (12,000 Btu) output, heat available to the regenerator would be 13,200 Btu. Given the 15° F. temperature rise, air needed to remove heat from the condenser would 3,670 pounds as the air stream moisture content change, as determined from psychrometric tables, would be 3.6 Btu per pound of air. Assuming air leaving the regenerator at 50% relative humidity in the fourth stage, water removed by evaporation per pound of air would be 0.0035 pounds with air exiting the regenerator at 94° F. At 3,670 pounds air per hour water removal would be 12.8 pounds with the equilibrium value of the liquid desiccant exiting the regenerator equal to an air stream of 30% relative humidity. Looking to the air dehumidification and air cooing module, Air delivery temperature of 85° F. would be obtainable given the ambient wet bulb being 75° F. in heat exchange with the saturated air stream of module  70 . Relative humidity could be reduced to 35% resulting in a moisture reduction from 0.0141 to 0.009 or a reduction of 0.0051 pounds of moisture per pound of air. Regenerator removal of 12.8 pounds divided by 0.0051 develops an air flow of 2,500 pounds of air per hour. Energy reduction would be 38.4 less 30.4 or 8 Btu per pound of air that when multiplied by 2,500 pounds of air per hour yields a computed value of 18,300 Btu of energy reduction, an amount adding 150% to the original compressor-driven cooling capacity of 12,000 Btu per hour. 
         [0018]    Elimination of the staged approach results in average temperatures obtained in each module Instead of 16° F. temperature differential in module  80 , the average of 8° F. might be obtained yielding an air stream with a relative humidity of 32% compared with 25%. The saturated air stream of module  70  would have average temperatures of 79° F. compared with 75° F. when staging. Given the same driving force differentials, air delivery conditions would be 89° F. and 42% relative humidity. Moisture removal would be reduced to one-third of former values (from 0.0056 per pound of air to 0.0018) while energy reduction reduces by 60% from 8 to 3.5 Btu per pound of air; the changes rendering this non-staged approach to low temperature waste resource utilization to lose economic appeal. 
         [0019]    As to further discussion of the manner, usage, and operation of the present invention, the same should be apparent from the above description. Accordingly, no further discussion relating to the manner of usage and operation will be provided. With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function, and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described.