Abstract:
A system for providing cooling to a building includes a cooling tower for transferring waste heat from the building to the atmosphere and a liquid desiccant system for dehumidifying an air stream entering the cooling tower to increase cooling efficiency of the cooling tower. The liquid desiccant system includes a conditioner and a regenerator. The conditioner utilizes a liquid desiccant for dehumidifying the air stream entering the cooling tower. The regenerator is connected to the conditioner for receiving dilute liquid desiccant from the conditioner, concentrating the dilute liquid desiccant using waste heat from the building, and returning concentrated liquid desiccant to the conditioner.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 61/733,209 filed on Dec. 4, 2012 entitled DESICCANT SYSTEMS and U.S. Provisional Patent Application No. 61/787,948 filed on Mar. 15, 2013 entitled METHODS AND SYSTEMS FOR COOLING BUILDINGS WITH LARGE HEAT LOADS USING DESICCANT CHILLERS, which are both hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present application relates generally to the use of liquid desiccants to dehumidify an air stream entering a cooling tower. More specifically, the application relates to a cooling system construction that operates using a 2- or 3-way liquid desiccant mass and heat exchanger that can dehumidify an air stream entering a cooling tower, wherein the desiccant is absorbing moisture from the air stream in such a way that the cooling tower experiences a much higher temperature drop than is normally the case, and wherein the desiccant is subsequently regenerated using a waste heat source, which—if available—can be waste heat from the building itself, to which cooling is provided. 
     Datacenters are an example of buildings that contain a large amount of equipment that generates a large amount of sensible heat. Other examples include semiconductor manufacturing facilities, plastics processing facilities, industrial facilities, and other buildings where large internal sensible heat loads need to be dissipated. Datacenters typically do not have a large number of people in their space, so there is typically no need to bring in a lot of outside air, and therefore the outside air (which in other buildings can be as much as 60% of the overall heat- and moisture-load of a building) does generally not constitute a large load for a datacenter and neither is there a large humidity (latent) heat-load in the datacenter itself. Oftentimes the sensible heat that is generated in these buildings by computers and the like is rejected to a chilled water or cooling water loop that is connected to a central chiller facility, which in turn rejects its heat to a cooling tower. The problem with cooling towers is that in hot, humid climates, the cooling tower is unable to evaporate a lot of water and thus the temperature drop in the cooling water is not very large. This means that either the cooling tower has to be oversized or other means of heat rejection have to be employed. Most of the heat in a datacenter is rejected to a chilled water loop and some is rejected to the air in the datacenter which is replenished with outside air. Datacenters in effect use a lot of electricity and reject the heat that the electrical consumption generates to a chiller plant and eventually to a cooling tower. It could be very desirable if the datacenter&#39;s waste heat could be used for other purposes, in particular if the heat could be used for more efficient cooling of the datacenter itself. 
     Liquid desiccants have been used parallel to conventional vapor compression HVAC equipment to help reduce humidity in spaces, particularly in spaces that require large amounts of outdoor air or that have large humidity loads inside the building space itself. Humid climates, such as for example Miami, Fla. require a lot of energy to properly treat (dehumidify and cool) the fresh air that is required for a space&#39;s occupant comfort. Liquid desiccant systems are however not very common on datacenters and the like, simply because datacenters have large sensible loads internally and not large latent loads, nor do datacenter use large amounts of outside air. However, the cooling towers that support a datacenter do have large latent loads since they take in outside air. It would therefore be desirable to supply these cooling towers with dry air to improve their efficiency. 
     Liquid desiccant systems have been used for many years and are generally quite efficient at removing moisture from an air stream. However, liquid desiccant systems generally use concentrated salt solutions such as ionic solutions of LiCl, LiBr, or CaCl 2  and water. Such brines are strongly corrosive, even in small quantities, so numerous attempts have been made over the years to prevent desiccant carry-over to the air stream that is to be treated. In recent years efforts have begun to eliminate the risk of desiccant carry-over by employing micro-porous membranes to contain the desiccant. An example of such as membrane is the EZ2090 poly-propylene, microporous membrane manufactured by Celgard, LLC, 13800 South Lakes Drive Charlotte, N.C. 28273. The membrane is approximately 65% open area and has a typical thickness of about 20 μm. This type of membrane is structurally very uniform in pore size (100 nm) and is thin enough to not create a significant thermal barrier. It has been shown that these membranes are effective in inhibiting desiccant carry-over. 
     Liquid desiccant systems generally have two separate components. The conditioning side of the system provides conditioning of air to the required conditions, which are typically set using thermostats or humidistats. The regeneration side of the system provides a reconditioning function of the liquid desiccant most often using heat, so that it can be re-used on the conditioning side. Liquid desiccant is typically pumped between the two sides through a heat exchanger so as to prevent a large heat load from the regenerator on the conditioner. 
     There thus remains a need to provide a cooling system for datacenters and other buildings with high heat loads, wherein the datacenter&#39;s internally generated heat could be used for a more efficient cooling of the datacenter itself. 
     BRIEF SUMMARY 
     In accordance with one or more embodiments, a system is provided for providing cooling to a building. The system includes a cooling tower for transferring waste heat from the building to the atmosphere and a liquid desiccant system for dehumidifying an air stream entering the cooling tower to increase cooling efficiency of the cooling tower. The liquid desiccant system includes a conditioner and a regenerator. The conditioner utilizes a liquid desiccant for dehumidifying the air stream entering the cooling tower. The regenerator is connected to the conditioner for receiving dilute liquid desiccant from the conditioner, concentrating the dilute liquid desiccant using waste heat from the building, and returning concentrated liquid desiccant to the conditioner. 
     Provided herein are methods and systems used for the efficient dehumidification of an air stream using a liquid desiccant. In accordance with one or more embodiments, the liquid desiccant is running down the face of a support plate as a falling film. In accordance with one or more embodiments, the desiccant is contained by a microporous membrane and the air stream is directed in a primarily vertical orientation over the surface of the membrane and whereby both latent and sensible heat are absorbed from the air stream into the liquid desiccant. In accordance with one or more embodiments, the support plate is filled with a heat transfer fluid that ideally is flowing in a direction counter to the air stream. In accordance with one or more embodiments, the system comprises a conditioner that removes latent and sensible heat through the liquid desiccant and a regenerator that removes the latent and sensible heat from the system. In accordance with one or more embodiments, the heat transfer fluid in the conditioner is cooled by an external source of cold heat transfer fluid. In accordance with one or more embodiments, the regenerator is heated an external source of hot heat transfer fluid. 
     In accordance with one or more embodiments, the liquid desiccant conditioner is providing treated air to a cooling tower thereby making the cooling tower a more efficient device. In one or more embodiments, the treated air is cooler than the air would have been without a liquid desiccant dehumidifier. In one or more embodiments, the treated air is drier than the air would have been without a liquid desiccant dehumidifier. In one or more embodiments, the conditioner contains membranes to contain the liquid desiccant. In accordance with one or more embodiments the liquid desiccant conditioner is receiving cold water from the same cooling tower. In one or more embodiments, the cold water is delivered by a chiller system. 
     In accordance with one or more embodiments, the liquid desiccant regenerator is provided a warm air stream by directing a warm air stream from a building with high internal heat loads to the regenerator. In one or more embodiments, the regenerator receives hot waste water from the building. In one or more embodiments, the hot waste water and/or hot waste air is used to concentrate a desiccant. 
     In accordance with one or more embodiments, the external sources of cold and hot heat transfer fluid are idled while heat is transferred from the building with high heat load to the liquid desiccant side of the system. In one or more embodiments, the regenerator functions as a replacement for a cooling tower. In one or more embodiments, the conditioner and regenerator are both acting like a cooling tower. In one or more embodiments, the cooling tower and chiller are bypassed and the liquid desiccant system is actively cooling the datacenter. In one or more embodiments, the compressor of the chiller system is bypassed and liquid refrigerant is pumped without the use of a compressor. 
     In no way is the description of the applications intended to limit the disclosure to these applications. Many construction variations can be envisioned to combine the various elements mentioned above each with its own advantages and disadvantages. The present disclosure in no way is limited to a particular set or combination of such elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a 3-way liquid desiccant air conditioning system using a chiller or external heating or cooling sources. 
         FIG. 2  shows a flexibly configurable membrane module that incorporates 3-way liquid desiccant plates. 
         FIG. 3  illustrates an example of a single membrane plate in the liquid desiccant membrane module of  FIG. 2 . 
         FIG. 4  shows a typical datacenter cooling system setup. 
         FIG. 5  shows the integration between a liquid desiccant system and the datacenter cooling system from  FIG. 4  in accordance with one or more embodiments. 
         FIG. 6  illustrates the psychrometric processes of  FIGS. 4 and 5  in accordance with one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a new type of liquid desiccant system as described in further detail in U.S. patent application Ser. No. 13/115,736, filed on May 25, 2011, which is incorporated by reference herein. A conditioner  501  comprises a set of plate structures that are internally hollow. A cold heat transfer fluid is generated in cold source  507  and entered into the plates. Liquid desiccant solution at  514  is brought onto the outer surface of the plates and runs down the outer surface of each of the plates. The liquid desiccant runs behind a thin membrane that is located between the air flow and the surface of the plates. Outside air  503  is now blown through the set of wavy plates. The liquid desiccant on the surface of the plates attracts the water vapor in the air flow and the cooling water inside the plates helps to inhibit the air temperature from rising. The treated air  504  is put into a building space. 
     The liquid desiccant is collected at the bottom of the wavy plates at  511  and is transported through a heat exchanger  513  to the top of the regenerator  502  to point  515  where the liquid desiccant is distributed across the wavy plates of the regenerator. Return air or optionally outside air  505  is blown across the regenerator plate, and water vapor is transported from the liquid desiccant into the leaving air stream  506 . An optional heat source  508  provides the driving force for the regeneration. The hot transfer fluid  510  from the heat source can be put inside the wavy plates of the regenerator similar to the cold heat transfer fluid on the conditioner. Again, the liquid desiccant is collected at the bottom of the wavy plates  502  without the need for either a collection pan or bath so that also on the regenerator the air can be vertical. An optional heat pump  516  can be used to provide cooling and heating of the liquid desiccant. It is also possible to connect a heat pump between the cold source  507  and the hot source  508 , which is thus pumping heat from the cooling fluids rather than the desiccant. 
       FIG. 2  describes a 3-way heat exchanger as described in further detail in U.S. patent application Ser. Nos. 13/915,199 filed on Jun. 11, 2013, 13/915,222 filed on Jun. 11, 2013, and No. 13/915,262 filed on Jun. 11, 2013, which are all incorporated by reference herein. A liquid desiccant enters the structure through ports  304  and is directed behind a series of membranes as described in  FIG. 1 . The liquid desiccant is collected and removed through ports  305 . A cooling or heating fluid is provided through ports  306  and runs counter to the air stream  301  inside the hollow plate structures, again as described in  FIG. 1  and in more detail in  FIG. 3 . The cooling or heating fluids exit through ports  307 . The treated air  302  is directed to a space in a building or is exhausted as the case may be. 
       FIG. 3  describes a 3-way heat exchanger as described in more detail in U.S. Provisional Patent Application Ser. No. 61/771,340 filed on Mar. 1, 2013, which is incorporated by reference herein. The air stream  251  flows counter to a cooling fluid stream  254 . Membranes  252  contain a liquid desiccant  253  that is falling along the wall  255  that contain a heat transfer fluid  254 . Water vapor  256  entrained in the air stream is able to transition the membrane  252  and is absorbed into the liquid desiccant  253 . The heat of condensation of water  258  that is released during the absorption is conducted through the wall  255  into the heat transfer fluid  254 . Sensible heat  257  from the air stream is also conducted through the membrane  252 , liquid desiccant  253  and wall  255  into the heat transfer fluid  254 . 
       FIG. 4  shows a high level schematic of a typical datacenter cooling system setup. The datacenter itself  401  comprises a large number of computer racks  404  that are cooled by fans  406  that blow building air (“BA”)  405  through the computer racks  404  or the computer racks  404  are cooled by heat transfer fluid (oftentimes cooling water)  419 . Some of the air recirculates  418  in the space itself; however some of the air  407  (“RA”) is exhausted. The exhausted air  407  is made up by an external outside air intake  425  (“OA”). The computer racks  404  are powered by electricity feeds  417  and the heat that is generated by the electrical consumption is rejected to the cooling water  420 , the exhaust air  407  and the recirculating air  418 . The chiller system  402  receives the cooling water  420  which is pumped through an evaporator heat exchanger  409  that is the evaporator of the chiller system  402  with compressor  408  compressing a refrigerant  421 . The heat of compression is rejected to condenser heat exchanger  410 . The heat exchanger  410  is then coupled to a cooling tower  403  that includes a fan  413  that blows outside air (“OA”)  412  through a filter media  411  which is then exhausted at near fully saturated conditions  414  (“EA 1 ”). Cooling water  423  is sprayed on top of the filter media  411  where a portion of the cooling water evaporates. This causes a cooling effect in the water and the cooled water  422  is pumped back to the heat exchanger  410 . Make-up water  424  is provided to the cooling tower to replace the water that is lost through evaporation. It is possible to not compress the refrigerant using compressor  408 , but instead to use a refrigerant pump  426  to create a refrigerant bypass loop  427  that can be used in part-load conditions, which can lead to substantial energy savings. It is also possible to use a cooling fluid bypass loop  428  and return cooling fluid loop  429  that bypasses the chiller section entirely. The electrical consumption of the complete system comprises primarily of electrical power  417  provided to the datacenter  401 , which largely turns into sensible heating of the building air  405  and cooling water  419 . Other electrical consumption comprises electrical power  416  for the chiller plant  402  and primarily the compressors  408  inside that plant and electrical power  415  for the cooling tower  403 , which is relatively small compared to the datacenter electrical power  417  and chiller plant electrical power  416 . 
       FIG. 5  illustrates the integration of the datacenter cooling system of  FIG. 4  with a liquid desiccant cooling system. The liquid desiccant system  601  comprises a 3-way conditioner  607  (shown in  FIG. 1  as  501 ) and a 3-way regenerator  610  (shown in  FIG. 1  as  502 ). The conditioner  607  receives cold water  605  from the cooling tower. Concentrated liquid desiccant  611  is supplied to the 3-way conditioner  607 . Outside air  603  (“OA”) is supplied to the conditioner  607  as well, which results in a much cooler and drier air stream  604  (“SA”) supplied to the cooling tower  403 . The liquid desiccant  611  absorbs moisture in the air stream  603  while simultaneously cooling the air stream. The supply air  604  (“SA”) to the cooling tower is thus drier and cooler then the outside air was. The warmer cooling water  606  is returned to the cooling tower. Diluted desiccant  609  is pumped through a heat exchanger  608  to the 3-way regenerator  610 . The regenerator  610  receives hot water  612  from the chiller&#39;s condenser heat exchanger  410  which is used as a heat source for desiccant regeneration. The somewhat cooler water  613  coming from the regenerator  610  is subsequently directed to the cooling tower  403  or back towards the condenser heat exchanger  410 . Warm return air  407  (“RA”) from the data center  401  is directed to the regenerator  610 . An outside air stream  614  can optionally be mixed in with the return air to create a mixed air condition  602 . The dilute desiccant  609  is directed over the regenerator plates and is thus re-concentrated by the heat from the datacenter. The regenerator exhausts a much higher temperature and humidity air stream  615  (“EA 3 ”), which contains the water vapor that was removed at the conditioner  607 . Like the system of  FIG. 4 , it is possible to not compress the refrigerant using compressor  408 , but instead to use a refrigerant pump  426  to create a refrigerant bypass loop  427  that can be used in part-load conditions, which can lead to substantial energy savings. It is also possible to use a cooling fluid bypass loop  428  and return cooling fluid loop  429  that bypasses the chiller section entirely. The refrigerant bypass loop and cooling fluid bypass loops have been omitted from the figure for clarity. 
       FIG. 6  illustrates the psychometric processes in the system of  FIGS. 4 and 5 . In a conventional cooling tower (as illustrated in  FIG. 4 ) the outside air (labeled “OA”) is subjected to an adiabatic humidification process (line segment OA to EA 1 ) and the air leaves the cooling tower at a slightly lower temperature but more humid (point EA 1 ). However, with a desiccant conditioner the outside air (“OA”) is cooled and dehumidified (line segment OA to SA) and the cooler and drier air SA is supplied to the cooling tower, wherein the air undergoes an adiabatic humidification process (line segment SA to EA 2 ). This results in a much more efficient cooling process since the temperature of EA 2  is significantly below the temperature of EA 1 . In essence the waste heat air  407  of the datacenter has been used to create a concentrated desiccant, which otherwise would have been rejected without getting used. The regenerator process is shown as well: the building air  405  (“BA”) is heated by the equipment  404  in the space to a higher sensible temperature but without adding any significant water vapor. The resulting waste heat air  407  (“RA”) is then directed through the regenerator plates where both heat and moisture are added resulting in an exhaust air stream 
     Having thus described several illustrative embodiments, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to form a part of this disclosure, and are intended to be within the spirit and scope of this disclosure. While some examples presented herein involve specific combinations of functions or structural elements, it should be understood that those functions and elements may be combined in other ways according to the present disclosure to accomplish the same or different objectives. In particular, acts, elements, and features discussed in connection with one embodiment are not intended to be excluded from similar or other roles in other embodiments. Additionally, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions. Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting.