Abstract:
A refrigeration system that utilizes both an air-cooled heat exchanger and a cooling tower to cool refrigerant prior to the refrigerant being provided to the evaporator. This multi-stage cooling permits the refrigeration system to operate with improved efficiency, while reducing the amount of water lost to evaporative cooling in the cooling tower, since the thermal load handled by the cooling tower is reduced by the air-cooled heat exchanger. This in turn means less water is required to replace water lost to evaporative cooling. In arid regions or regions of low water quality, both efficiency increase and reduction of water lost to evaporative cooling are important improvements.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed at a hybrid refrigeration system, and specifically, a refrigeration system that cools refrigerant with both an air radiation system and with a cooling tower system to minimize water loss to evaporation, thereby achieving supercooling of the refrigerant while reducing water loss through the cooling tower system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Refrigeration systems can accomplish heat rejection by heat transfer using either condenser-cooling tower systems or through water-cooled condensers wherein water extracts heat from the refrigerant. The water is subsequently cooled by air through a radiation system. 
         [0003]    Cooling towers are extremely efficient in removing heat from condensers, and are used extensively in areas where water is abundant. Cooling towers and not closed systems, however, and require a substantial amount of make-up water, as cooling towers take advantage of the principles of evaporative cooling in removing heat from the system. Cooling towers also require a make-up source of water that is substantially pure, as lesser quality water or contaminated water can lead to degradation of performance of the heat exchanger components and other components that contact the water. Performance is lost as the components accumulate dirt and contaminants. Restoring the components to optimum performance conditions requires cleaning. Cleaning is expensive and can result in equipment downtime and replacement of corroded equipment. Furthermore, when less than pure water is used, components can be fabricated from expensive corrosion-resistant materials. This can reduce down-time required to replace corroded equipment, although cleaning may still be required periodically. Thus, systems using cooling towers are not practical in arid areas where water is scarce or in areas where water cannot readily be provided in a purified mode. In fact, in many regions of the world, good quality water is or is becoming a scarce and expensive commodity. Cooling towers require a continuous supply of water for make-up, thereby limiting their geographic applications. 
         [0004]    Water-cooled condensers having water cooled by an air radiation system have higher heat rejection temperatures and require larger heat exchanger surface areas, which adds to their cost. The efficiency of such systems is reduced compared to systems utilizing cooling towers. 
         [0005]    What is needed is a system that provides efficient cooling while minimizing the use of precious water. 
       SUMMARY OF THE INVENTION 
       [0006]    A refrigeration system utilizes both an air-cooled heat exchanger and a cooling tower to cool refrigerant prior to the refrigerant being provided to the evaporator. The refrigeration system utilizes an air-cooled heat exchanger to cool and change the state of refrigerant provided by a compressor to a condenser from a gas to a liquid and cool the refrigerant in the condenser to a first temperature, T 1 . The air-cooled heat exchanger is a closed water loop system having a first heat exchanger in heat exchange communication with the condenser wherein water extracts heat from the refrigerant, and a second heat exchanger in heat exchange communication with air to cool the heated water. To improve the efficiency of the system, the refrigerant is then cooled to a second temperature, T 2 . This is accomplished by utilizing a cooling tower. Water in an open loop circulates between a subcooler and the cooling tower. Water from the cooling tower removes heat from the refrigerant in the subcooler (or a different portion of the condenser) to cool the refrigerant to the second temperature T 2 . The water in the open loop is then circulated to the cooling tower where its temperature is cooled by both convection and evaporative cooling. Water lost by evaporation must be replaced. Because the refrigeration system utilizes an air-cooled heat exchanger to cool the refrigerant to a first temperature T 1 , the thermal load on the water in the cooling tower loop, which is used to cool the refrigerant to the second temperature T 2 , prior to being cycled to an evaporator, is reduced. This reduced thermal load means that the cooling tower can be smaller and the amount of water lost to evaporation by evaporative cooling in the cooling tower is reduced. 
         [0007]    An advantage of this system is that the expense required to build a cooling tower is reduced, since the cooling tower may be of a reduced size. 
         [0008]    Another advantage of this system is that the amount of water required to replace the water lost by the cooling tower due to evaporative cooling is reduced. In arid or dry climates where water is a precious commodity and in short supply, this is a significant improvement, since no longer is the property owner faced with a choice between reduced efficiency from solely using an air-cooled heat exchanger or using a system that relies on a cooling tower requiring large amounts of water for water replacement due to evaporative cooling. 
         [0009]    This system also has an advantage in areas in which water quality is poor. Since less water is required for water replacement due to evaporative cooling, there will be less corrosion or dirt build up as water circulates over the equipment. If the water is treated before being added to the open water loop associated with the cooling tower, there will be less water required which will lower the water treatment costs. 
         [0010]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]      FIG. 1  is a cut-away view of a building having a refrigeration system having an air-cooled heat exchanger outside the building and a cooling tower on the roof of the building. 
           [0012]      FIG. 2  is a cut-away view of a building having a refrigeration system having an air-cooled heat exchanger outside the building and a cooling tower remote from the building but adjacent to a body of water. 
           [0013]      FIG. 3  is a view of a prepackaged hybrid condenser/subcooler unit, having internal connections between the condenser and subcooler and which requires external connections to the compressor, the evaporator, the air heat exchanger and the cooling tower. 
           [0014]      FIG. 4  is a view a condenser and subcooler which require a separate connection of the condenser to the subcooler. 
           [0015]      FIG. 5  is a view of a prepackaged refrigeration system having a compressor, an evaporator, and a condenser/subcooler, requiring external connections to a cooling tower, to an air-cooled heat exchanger and to the building air handler units. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  depicts a refrigeration system installed in a building  12 . The refrigeration system includes a cooling tower  14  positioned on the roof of building  12 . In other exemplary embodiments, cooling tower  14  may be located elsewhere, such as on the ground near building  12 , adjacent a body of water or any other suitable location. Cooling tower  14  frequently is located away from the building and adjacent to a river, pond, lake or other body of water, such as cooling tower  140  depicted in  FIG. 2 . Cooling tower  14 ,  FIG. 1 , and cooling tower  140 ,  FIG. 2 , are not closed loop systems. Water lost to the atmosphere through evaporation by evaporative cooling must be replenished. A body of water can provide the make-up water required for efficient cooling tower operation, although water may come from an available public system piped into the building, such as is shown in  FIG. 1 . 
         [0017]    In an exemplary embodiment, cooling tower supply water  38  is supplied to cooling tower  14  from condenser/subcooler  36 , and cooling tower return water is returned to condenser/subcooler  36  by cooling tower return line  40 . In  FIG. 1 , a cooling tower return water replenishment line  61  is connected to cooling tower return line  40  to replenish water lost by evaporation in cooling tower  14 . In  FIG. 2 , water lost by evaporation in cooling tower  140  may be replenished from a naturally occurring water source, which may be a lake, river or pond, through water replenishment line  610 . Condenser/subcooler  36  is also connected to air-cooled heat exchanger  30  located outside of building  12  adjacent the ground floor in  FIGS. 1 and 2 , and to an evaporator  46 . Air-cooled heat exchanger  30  may be located in any suitable area, and is connected to the condenser/subcooler  36  by closed loop return line  32  and closed loop supply line  34 . Water or other suitable fluid(s) circulates in a closed system through lines  32 ,  34  between heat exchanger  30  and condenser/subcooler  36 . Refrigerant circulates as a gas from compressor  54 , driven by motor  56  through refrigerant line  58  to condenser/subcooler  36  where it undergoes a change of state and is condensed to a liquid. Although compressor  54  is depicted as a single compressor, the refrigerant system may include a plurality of compressors  54  operating in series, in which refrigerant gas flows from a first compressor to a second compressor and so forth prior to circulation to condenser/subcooler  36 , or in parallel, in which the refrigerant gas is split between multiple compressors  54  prior to being circulated to condenser/subcooler  36 . Heat is removed from the refrigerant gas in condenser  36 , cooling the refrigerant to a first temperature T 1  by heat exchange with water from the closed loop system connected to heat exchanger  30 . The water in the closed-loop system then circulates to heat exchanger  30 , where heat is removed convectively from the water by air. 
         [0018]    Refrigerant at temperature T 1  is further cooled in condenser/subcooler  36  after cooling to temperature T 2  by water from cooling tower  14 , provided by cooling water return line, which may be supplemented by water from cooling tower return water replenishment line  61 . Condenser/subcooler  36  is a hybrid unit that includes two separate heat exchange units, a condenser  60  and a subcooler  62 . This hybrid condenser/subcooler may be packaged together for installation as a single unit or as part of a package, as depicted in  FIGS. 3 and 5 , or the condenser  60  and subcooler  62  may be provided as separate apparatus for installation as depicted in  FIG. 4 . 
         [0019]    Heat removed from the refrigerant by the “cooling tower” water further reduces the refrigerant temperature from a temperature T 1  to a temperature T 2  in subcooler  62  while the water temperature is increased. This water is returned to cooling tower  14  through cooling tower supply line  38 , where the heated water is cooled. In the cooling tower  14 , water flows over fill, for example a plastic or a wood material used to maximize the surface area that the water contacts, to improve its heat exchange ability. Cooling tower  14  may additionally include fans to further improve heat removal from the water by providing additional air flow over the water. Some of the water evaporates, and the change in state of the water from a liquid to a gas absorbs energy from the water, further cooling the remaining liquid. The cooled liquid is then returned via cooling water return line  40  to the subcooler. 
         [0020]    Subcooled refrigerant is then circulated from condenser/subcooler  36  to an evaporator  46  through refrigerant line  42 , and optionally through an expansion valve. The cooled refrigerant in evaporator  46  absorbs heat from water circulated in evaporator  46  to provide chilled water to be circulated through chiller water supply line  48  to air handler system  22 . The cooled refrigerant also undergoes a phase change as it absorbs heat in evaporator  46 . As shown in  FIG. 1 , the chilled water is circulated through chiller water supply line  48  to air handler  22 . Building  12  may include a plurality of air handlers  22  connected to chiller water supply line  48 . However, the chilled water can be routed for other purposes in addition for use with air handler(s)  22 . As shown in  FIG. 1 , each floor of building  12  includes an air handler  22 , but building  12  may have as few as one air handler  22  or may have a plurality of air handlers  22  for each floor, as shown. Air handlers  22  cool air from return ducts  18  through a heat exchange relationship with the chilled water. For example, fans may blow air across a heat exchanger utilizing the chilled water, thereby cooling the air. The cooled air then is circulated to the building areas through supply ducts  20 . Water, heated by the heat exchange relationship with the return air, is returned to evaporator  46  by chiller water return line  50  for recirculation through the system. The refrigerant, converted to a refrigerant gas in evaporator  46 , is returned to compressor  54 , to be again compressed as a gas to a high pressure and an elevated temperature before being recirculated to condenser  60 . 
         [0021]      FIG. 3  depicts condenser/subcooler  36  of  FIGS. 1 and 2  as a single unit. Condenser/subcooler  36  includes a first heat exchanger, condenser  60 , in series with a second heat exchanger, subcooler  62 . These units may be oriented horizontally or vertically with respect to one another. Condenser  60  is plumbed so that refrigerant gas at an elevated temperature and pressure from compressor  54  enters condenser/subcooler  36 , runs through condenser  60 , where it is condensed to a liquid at a first temperature T 1 , passes through subcooler  62 , and then exits condenser/subcooler  36  at a second temperature T 2  to evaporator  46  via refrigerant line  42 . Refrigerant gas entering condenser  60  from compressor  54  in refrigerant loop at an elevated temperature and pressure enters into a heat exchange relationship with water in water loop in a closed loop system entering condenser  60  through line  34  from air heat exchanger  30 . The water from line  34  absorbs heat from the refrigerant in the heat exchanger and changes the state of the refrigerant from a gas to a liquid, lowering the refrigerant temperature to temperature T 1 . Water from condensor  60  returns via line  32  in the water loop at an elevated temperature to air heat exchanger  30  where heat is removed as air is passed over the water loop, cooling the water. 
         [0022]    Refrigerant at a temperature T 1  from condenser  60  enters subcooler  62  in the refrigerant loop where water in a water loop from cooling tower  14  or  140  enters through line  40  and is placed in heat exchange relationship with the refrigerant in subcooler  62 , further lowering the refrigerant temperature to temperature T 2 . The water from line  40 , having absorbed heat from the refrigerant, is returned to the cooling tower through cooling water return line  38 . Chilled refrigerant at temperature T 2  is delivered to evaporator  46  via refrigerant line  42 . When condenser/subcooler  36  is supplied as a single unit as shown in  FIG. 3 , it can be installed on-site by connecting refrigerant lines  58  and  42  to the compressor and the evaporator respectively, and by connecting lines  32 ,  34  extending from condenser/subcooler  36  to air heat exchanger  30 , and by connecting lines  38 ,  40  extending from condenser/subcooler  36  to cooling tower. 
         [0023]      FIG. 4  depicts condenser/subcooler  36  in a system where condenser  60  and subcooler  62  are separate items and connected on-site. While condenser/subcooler  36  of  FIG. 4  operates exactly as condenser/subcooler  36  described in  FIG. 3 , above, assembly of condenser/subcooler  36  of  FIG. 3  is slightly different. A refrigerant connection is made between condenser  60  and subcooler  62 , since these components may be shipped and provided to the site unconnected to one another. Refrigerant line  58  from compressor  54  is connected to condenser  60  and refrigerant line  42  from subcooler  62  is connected to evaporator  46 . Lines  32 ,  34  from closed loop heat exchanger are connected to condenser  60  and lines  38 ,  40  from cooling tower  14  are connected to subcooler  62 . In this embodiment, plumbing connections between condenser  60  and subcooler  62  are joined on-site. The flow of refrigerant and cooling water is identical to the flow set forth in the description of  FIG. 3  above. 
         [0024]      FIG. 5  depicts the refrigeration system  10  including condenser/subcooler  36  as a single, packaged unit. The system functions as described in  FIG. 1 . Some of the plumbing connections are not made on-site, as the single, packaged unit can be preassembled. The system can be installed by connecting piping extending from the refrigeration system to piping systems in building  12 . Once refrigeration system  10  is positioned on-site, connections are made through lines  38 ,  40  to cooling tower  14  and through lines  32 ,  34  to air-cooled heat exchanger  30 . Cooling tower return water replenishment line  61 ,  FIG. 1 , or line  610 ,  FIG. 2 , may be connected to line  40  outside of refrigeration system  10 . The chilled water system that supply chilled water from the evaporator to the air handler(s)  22  is also connected to the refrigeration system through lines  48 ,  50 . 
         [0025]    Condenser/subcooler  36  provides improved efficiency over a water-cooled condenser system using water cooled by an air radiation system. This system provides efficiency slightly reduced from that of a system solely utilizing a cooling tower, but uses less water than such a system. A smaller cooling tower can be utilized with condenser/subcooler  36  because of a smaller thermal load in the cooling tower water loop as a result of the refrigerant temperature first being lowered to temperature T 1  by the closed-loop, water-cooled air-cooled heat exchanger. The smaller cooling tower requires less heat transfer surface and loses less water to evaporation, requiring less water replenishment. The condenser/subcooler  36  provides heat transfer properties that are comparable to that of a water tower system, and provides a cost advantage in that a smaller cooling tower can be utilized, and expensive replenishment water supplies are reduced. Importantly, condenser/subcooler  36  provides a lower exiting refrigerant temperature T 2  than an air radiation system. The temperature of refrigerant exiting condenser/subcooler  36  approaches that of a cooling tower-only system. A smaller cooling tower also provides an advantage of not only reduced cost, but also of reduced space when space is a consideration, such as in a crowded or congested area. 
         [0026]    While only certain features and embodiments of the invention have been shown and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.