Abstract:
Heat exchangers containing various tube configurations and a heating, ventilation, air conditioning and refrigeration (HVAC&amp;R) system employing these heat exchangers are provided which allow flexibility in directing fluids through a heat exchanger. Groups of tubes may be placed at different locations within a heat exchanger slab in order to tailor the heat transfer properties of each tube group to their location on the heat exchanger slab. Groups of tubes may be connected using manifolds to create coil circuits.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 60/867,043, entitled MICROCHANNEL HEAT EXCHANGER APPLICATIONS, filed Nov. 22, 2006, and U.S. Provisional Application Ser. No. 60/882,033, entitled MICROCHANNEL HEAT EXCHANGER APPLICATIONS, filed Dec. 27, 2006, which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates generally to multi-block circuit multichannel heat exchangers. 
         [0003]    Heat exchangers are used in heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) systems. Multichannel heat exchangers generally include multichannel tubes for flowing refrigerant through the heat exchanger. Each multichannel tube may contain several individual flow channels. Fins may be positioned between the tubes to facilitate heat transfer between refrigerant contained within the tube flow channels and external air passing over the tubes. Multichannel heat exchangers may be used in small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems. 
         [0004]    In general, heat exchangers transfer heat by circulating a refrigerant through a cycle of evaporation and condensation. In some systems, one heat exchanger may contain multiple coil circuits for circulating two or more fluids in order to provide cooling or heating to different parts of a system. In other systems, one heat exchanger may contain multiple coil circuits for circulating the same fluid through the heat exchanger more than once in order to provide increased heating or cooling. 
         [0005]    The location of a coil circuit within the heat exchanger may impact the rate of heat transfer because environmental conditions may vary depending on a tube&#39;s position within the heat exchanger. For example, in a heat exchanger containing horizontal tubes, the bottom tubes may receive less airflow than the top tubes, resulting in a lower rate of heat transfer between the bottom tubes and the environment. In a heat exchanger containing vertical tubes, the outer tubes may receive less airflow based on proximity to other equipment or an outer wall. In a multiple heat exchanger configuration, the outer heat exchanger coils may receive more airflow, resulting in a higher rate of heat transfer between these tubes and the environment. 
         [0006]    Furthermore, the type of fluid within a coil circuit may be used to configure the location of the circuit within the heat exchanger slab. For example, it may be desirable to locate a condenser circuit containing a lower temperature fluid within a section of the heat exchanger that receives less airflow because less heat transfer is generally needed between the lower temperature fluid and the environment. In some applications, the lower temperature fluid may be a refrigerant requiring subcooling or an electrical coolant used to cool an electrical power circuit. Conversely, it may be desirable to locate a fluid undergoing a phase change in a section of the heat exchanger that receives more airflow. 
       SUMMARY 
       [0007]    In accordance with aspects of the invention, a heat exchanger is presented that includes four groups of multichannel tubes disposed adjacent to one another. Group A is configured to receive a flow of a first fluid to be cooled or heated. Group B is configured to receive the flow of the first fluid from group A. Group C is configured to receive a flow of a second fluid to be cooled or heated. Group D is configured to receive the flow of the second fluid from group C. 
         [0008]    In accordance with further aspects of the invention, a heat exchanger and a system including a heat exchanger are presented. The heat exchanger includes a first manifold, a second manifold, a first multi-pass circulating block in fluid communication with the manifolds, and a second multi-pass circulating block in fluid communication with the manifolds. The first block includes two groups, group A and group B, of multichannel tubes disposed adjacent to one another. Group A is configured to receive a flow of a first fluid to be cooled or heated, and group B is configured to receive the flow of the first fluid from group A. The second block includes two other groups, group C and group D, of multichannel tubes disposed adjacent to one another. Group C is configured to receive a flow of a second fluid to be cooled or heated, and group D is configured to receive the flow of the second fluid from group C. 
     
    
     
       DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an exemplary residential air conditioning or heat pump system of the type that might employ a heat exchanger 
           [0010]      FIG. 2  is a partially exploded view of the outside unit of the system of  FIG. 1 , with an upper assembly lifted to expose certain of the system components, including a heat exchanger. 
           [0011]      FIG. 3  is a perspective view an illustration of an exemplary commercial or industrial HVAC&amp;R system that employs a chiller and air handlers to cool a building and that may also employ heat exchangers. 
           [0012]      FIG. 4  is a diagrammatical overview of an exemplary air conditioning system which may employ one or more heat exchangers containing coil circuits. 
           [0013]      FIG. 5  is a diagrammatical overview of an exemplary heat pump system which may employ one or more heat exchangers containing coil circuits. 
           [0014]      FIG. 6  is a perspective view of an exemplary heat exchanger illustrating coil circuiting positions. 
           [0015]      FIG. 7  is a detail perspective view of the heat exchanger of  FIG. 6  sectioned through the multichannel tubes. 
           [0016]      FIG. 8  is a perspective view of exemplary heat exchanger illustrating an alternate coil circuiting positions. 
           [0017]      FIG. 9  is a perspective view of exemplary heat exchanger illustrating another alternate coil circuiting position. 
           [0018]      FIG. 10  is a detail perspective of the manifold employed in the coil circuiting position illustrated in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIGS. 1-3  depict exemplary applications for heat exchangers. Such systems, in general, may be applied in a range of settings, both within the HVAC&amp;R field and outside of that field. In presently contemplated applications, however, heat exchanges may be used in residential, commercial, light industrial, industrial and in any other application for heating or cooling a volume or enclosure, such as a residence, building, structure, and so forth. Moreover, the heat exchanges may be used in industrial applications, where appropriate, for basic refrigeration and heating of various fluids.  FIG. 1  illustrates a residential heating and cooling system. In general, a residence, designated by the letter R, will be equipped with an outdoor unit OU that is operatively coupled to an indoor unit IU. The outdoor unit is typically situated adjacent to a side of the residence and is covered by a shroud to protect the system components and to prevent leaves and other contaminants from entering the unit. The indoor unit may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit is coupled to the indoor unit by refrigerant conduits RC that transfer primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction. 
         [0020]    When the system shown in  FIG. 1  is operating as an air conditioner, a coil in the outdoor unit serves as a condenser for recondensing vaporized refrigerant flowing from indoor unit IU to outdoor unit OU via one of the refrigerant conduits. In these applications, a coil of the indoor unit, designated by the reference characters IC, serves as an evaporator coil. The evaporator coil receives liquid refrigerant (which may be expanded by an expansion device described below) and evaporates the refrigerant before returning it to the outdoor unit. 
         [0021]    The outdoor unit draws in environmental air through sides as indicated by the arrows directed to the sides of unit OU, forces the air through the outer unit coil by a means of a fan (not shown) and expels the air as indicated by the arrows above the outdoor unit. When operating as an air conditioner, the air is heated by the condenser coil within the outdoor unit and exits the top of the unit at a temperature higher than it entered the sides. Air is blown over indoor coil IC, and is then circulated through the residence by means of ductwork D, as indicated by the arrows in  FIG. 1 . The overall system operates to maintain a desired temperature as set by a thermostat T. When the temperature sensed inside the residence is higher than the set point on the thermostat (plus a small amount), the air conditioner will become operative to refrigerate additional air for circulation through the residence. When the temperature reaches the set point (minus a small amount), the unit will stop the refrigeration cycle temporarily. 
         [0022]    When the unit in  FIG. 1  operates as a heat pump, the roles of the coils are simply reversed. That is, the coil of the outdoor unit will serve as an evaporator to evaporate refrigerant and thereby cool air entering the outdoor unit as the air passes over the outdoor unit coil. Indoor coil IC will receive a stream of air blown over it and will heat the air by condensing a refrigerant. 
         [0023]      FIG. 2  illustrates a partially exploded view of one of the units shown in  FIG. 1 , in this case outdoor unit OU. In general, the unit may be thought of as including an upper assembly UA made up of a shroud, a fan assembly, a fan drive motor, and so forth. In the illustration of  FIG. 2 , the fan and fan drive motor are not visible because they are hidden by the surrounding shroud. An outdoor coil OC is housed within this shroud and is generally deposed to surround or at least partially surround other system components, such as a compressor, an expansion device, a control circuit. 
         [0024]      FIG. 3  illustrates another exemplary application, in this case an HVAC&amp;R system for building environmental management. A building BL is cooled by a system that includes a chiller CH, which is typically disposed on or near the building, or in an equipment room or basement. Chiller CH is an air-cooled device that implements a refrigeration cycle to cool water. The water is circulated to a building through water conduits WC. The water conduits are routed to air handlers AH at individual floors or sections of the building. The air handlers are also coupled to ductwork DU that is adapted to blow air from an outside intake OI. 
         [0025]    Chiller CH, which includes heat exchangers for both evaporating and condensing a refrigerant as described above, cools water that is circulated to the air handlers. Air blown over additional coils that receive the water in the air handlers causes the water to increase in temperature and the circulated air to decrease in temperature. The cooled air is then routed to various locations in the building via additional ductwork. Ultimately, distribution of the air is routed to diffusers that deliver the cooled air to offices, apartments, hallways, and any other interior spaces within the building. In many applications, thermostats or other command devices (not shown in  FIG. 3 ) will serve to control the flow of air through and from the individual air handlers and ductwork to maintain desired temperatures at various locations in the structure. 
         [0026]      FIG. 4  illustrates an air conditioning system  10 , which uses heat exchangers containing multichannel tubes. Refrigerant flows through the system within closed refrigeration loop  12 . The refrigerant may be any fluid that absorbs and extracts heat. For example, the refrigerant may be hydrofluorocarbon (HFC) based R-410A, R-407, or R-134a, or it may be carbon dioxide (R-744a) or ammonia (R-717). Air conditioning system  10  includes control devices  14  that enable system  10  to cool an environment to a prescribed temperature. 
         [0027]    System  10  cools an environment by cycling refrigerant within closed refrigeration loop  12  through condenser  16 , compressor  18 , expansion device  20 , and evaporator  22 . The refrigerant enters condenser  16  as a high pressure and temperature vapor and flows through the multichannel tubes of condenser  16 . A fan  24 , which is driven by a motor  26 , draws air across the multichannel tubes. Fan  24  may push or pull air across the tubes. Heat transfers from the refrigerant vapor to the air producing heated air  28  and causing the refrigerant vapor to condense into a liquid. The liquid refrigerant then flows into an expansion device  20  where the refrigerant expands to become a low pressure and temperature liquid. Typically, expansion device  20  will be a thermal expansion valve (TXV); however, in other embodiments, the expansion device may be an orifice or a capillary tube. After the refrigerant exits the expansion device, some vapor refrigerant may be present in addition to the liquid refrigerant. 
         [0028]    From expansion device  20 , the refrigerant enters evaporator  22  and flows through the evaporator multichannel tubes. A fan  30 , which is driven by a motor  32 , draws air across the multichannel tubes. Heat transfers from the air to the refrigerant liquid producing cooled air  34  and causing the refrigerant liquid to boil into a vapor. In some embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes. 
         [0029]    The refrigerant then flows to compressor  18  as a low pressure and temperature vapor. Compressor  18  reduces the volume available for the refrigerant vapor, consequently, increasing the pressure and temperature of the vapor refrigerant. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor. Compressor  18  is driven by a motor  36  that receives power from a variable speed drive (VSD) or a direct AC or DC power source. In one embodiment, motor  36  receives fixed line voltage and frequency from an AC power source although in some applications the motor may be driven by a variable voltage or frequency drive. The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type. The refrigerant exits compressor  18  as a high temperature and pressure vapor that is ready to enter the condenser and begin the refrigeration cycle again. 
         [0030]    The operation of the refrigeration cycle is governed by control devices  14  that include control circuitry  38 , an input device  40 , and a temperature sensor  42 . Control circuitry  38  is coupled to motors  26 ,  32 , and  36  that drive condenser fan  24 , evaporator fan  30 , and compressor  18 , respectively. The control circuitry uses information received from input device  40  and sensor  42  to determine when to operate motors  26 ,  32 , and  36  that drive the air conditioning system. In some applications, the input device may be a conventional thermostat. However, the input device is not limited to thermostats, and more generally, any source of a fixed or changing set point may be employed. These may include local or remote command devices, computer systems and processors, and mechanical, electrical, and electromechanical devices that manually or automatically set a temperature-related signal that the system receives. For example, in a residential air conditioning system, the input device may be a programmable 24-volt thermostat that provides a temperature set point to the control circuitry. Sensor  42  determines the ambient air temperature and provides the temperature to control circuitry  38 . Control circuitry  38  then compares the temperature received from the sensor to the temperature set point received from the input device. If the temperature is higher than the set point, control circuitry  38  may turn on motors  26 ,  32 , and  36  to run air conditioning system  10 . The control circuitry may execute hardware or software control algorithms to regulate the air conditioning system. In some embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. Other devices may, of course, be included in the system, such as additional pressure and/or temperature transducers or switches that sense temperatures and pressures of the refrigerant, the heat exchangers, the inlet and outlet air, and so forth. 
         [0031]      FIG. 5  illustrates a heat pump system  44  that uses multichannel tubes. Because the heat pump may be used for both heating and cooling, refrigerant flows through a reversible refrigeration/heating loop  46 . The refrigerant may be any fluid that absorbs and extracts heat. The heating and cooling operations are regulated by control devices  48 . 
         [0032]    Heat pump system  44  includes an outside coil  50  and an inside coil  52  that both operate as heat exchangers. The coils may function either as an evaporator or as a condenser depending on the heat pump operation mode. For example, when heat pump system  44  is operating in cooling (or “AC”) mode, outside coil  50  functions as a condenser, releasing heat to the outside air, while inside coil  52  functions as an evaporator, absorbing heat from the inside air. When heat pump system  44  is operating in heating mode, outside coil  50  functions as an evaporator, absorbing heat from the outside air, while inside coil  52  functions as a condenser, releasing heat to the inside air. A reversing valve  54  is positioned on reversible loop  46  between the coils to control the direction of refrigerant flow and thereby to switch the heat pump between heating mode and cooling mode. 
         [0033]    Heat pump system  44  also includes two metering devices  56  and  58  for decreasing the pressure and temperature of the refrigerant before it enters the evaporator. The metering device also acts to regulate refrigerant flow into the evaporator so that the amount of refrigerant entering the evaporator equals the amount of refrigerant exiting the evaporator. The metering device used depends on the heat pump operation mode. For example, when heat pump system  44  is operating in cooling mode, refrigerant bypasses metering device  56  and flows through metering device  58  before entering the inside coil  52 , which acts as an evaporator. In another example, when heat pump system  44  is operating in heating mode, refrigerant bypasses metering device  58  and flows through metering device  56  before entering outside coil  50 , which acts as an evaporator. In other embodiments, a single metering device may be used for both heating mode and cooling mode. The metering devices typically are thermal expansion valves (TXV), but also may be orifices or capillary tubes. 
         [0034]    The refrigerant enters the evaporator, which is outside coil  50  in heating mode and inside coil  52  in cooling mode, as a low temperature and pressure liquid. Some vapor refrigerant also may be present as a result of the expansion process that occurs in metering device  56  or  58 . The refrigerant flows through multichannel tubes in the evaporator and absorbs heat from the air changing the refrigerant into a vapor. In cooling mode, the indoor air passing over the multichannel tubes also may be dehumidified. The moisture from the air may condense on the outer surface of the multichannel tubes and consequently be removed from the air. 
         [0035]    After exiting the evaporator, the refrigerant passes through reversing valve  54  and into compressor  60 . Compressor  60  decreases the volume of the refrigerant vapor, thereby, increasing the temperature and pressure of the vapor. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor. 
         [0036]    From the compressor, the increased temperature and pressure vapor refrigerant flows into a condenser, the location of which is determined by the heat pump mode. In cooling mode, the refrigerant flows into outside coil  50  (acting as a condenser). A fan  62 , which is powered by a motor  64 , draws air over the multichannel tubes containing refrigerant vapor. In some embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes. The heat from the refrigerant is transferred to the outside air causing the refrigerant to condense into a liquid. In heating mode, the refrigerant flows into inside coil  52  (acting as a condenser). A fan  66 , which is powered by a motor  68 , draws air over the multichannel tubes containing refrigerant vapor. The heat from the refrigerant is transferred to the inside air causing the refrigerant to condense into a liquid. 
         [0037]    After exiting the condenser, the refrigerant flows through the metering device ( 56  in heating mode and  58  in cooling mode) and returns to the evaporator (outside coil  50  in heating mode and inside coil  52  in cooling mode) where the process begins again. 
         [0038]    In both heating and cooling modes, a motor  70  drives compressor  60  and circulates refrigerant through reversible refrigeration/heating loop  46 . The motor may receive power either directly from an AC or DC power source or from a variable speed drive (VSD). The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type. 
         [0039]    The operation of motor  70  is controlled by control circuitry  72 . Control circuitry  72  receives information from an input device  74  and sensors  76 ,  78 , and  80  and uses the information to control the operation of heat pump system  44  in both cooling mode and heating mode. For example, in cooling mode, input device  74  provides a temperature set point to control circuitry  72 . Sensor  80  measures the ambient indoor air temperature and provides it to control circuitry  72 . Control circuitry  72  then compares the air temperature to the temperature set point and engages compressor motor  70  and fan motors  64  and  68  to run the cooling system if the air temperature is above the temperature set point. In heating mode, control circuitry  72  compares the air temperature from sensor  80  to the temperature set point from input device  74  and engages motors  64 ,  68 , and  70  to run the heating system if the air temperature is below the temperature set point. 
         [0040]    Control circuitry  72  also uses information received from input device  74  to switch heat pump system  44  between heating mode and cooling mode. For example, if input device  74  is set to cooling mode, control circuitry  72  will send a signal to a solenoid  82  to place reversing valve  54  in air conditioning position  84 . Consequently, the refrigerant will flow through reversible loop  46  as follows: the refrigerant exits compressor  60 , is condensed in outside coil  50 , is expanded by metering device  58 , and is evaporated by inside coil  52 . If the input device is set to heating mode, control circuitry  72  will send a signal to solenoid  82  to place reversing valve  54  in heat pump position  86 . Consequently, the refrigerant will flow through the reversible loop  46  as follows: the refrigerant exits compressor  60 , is condensed in inside coil  52 , is expanded by metering device  56 , and is evaporated by outside coil  50 . 
         [0041]    The control circuitry may execute hardware or software control algorithms to regulate the heat pump system  44 . In some embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. 
         [0042]    The control circuitry also may initiate a defrost cycle when the system is operating in heating mode. When the outdoor temperature approaches freezing, moisture in the outside air that is directed over outside coil  50  may condense and freeze on the coil. Sensor  76  measures the outside air temperature, and sensor  78  measures the temperature of outside coil  50 . These sensors provide the temperature information to the control circuitry which determines when to initiate a defrost cycle. For example, if either of sensors  76  or  78  provides a temperature below freezing to the control circuitry, system  44  may be placed in defrost mode. In defrost mode, solenoid  82  is actuated to place reversing valve  54  in air conditioning position  84 , and motor  64  is shut off to discontinue air flow over the multichannels. System  44  then operates in cooling mode until the increased temperature and pressure refrigerant flowing through outside coil  50  defrosts the coil. Once sensor  78  detects that coil  50  is defrosted, control circuitry  72  returns the reversing valve  54  to heat pump position  86 . As will be appreciated by those skilled in the art, the defrost cycle can be set to occur at many different time and temperature combinations. 
         [0043]      FIG. 6  is a perspective view of an exemplary heat exchanger  88  that may be used in air conditioning system  10  or heat pump system  44 . The exemplary heat exchanger may be a condenser  16 , an evaporator  22 , an outside coil  50 , or an inside coil  52 , as shown in  FIGS. 4 and 5 . It should also be noted that in similar or other systems, the heat exchanger may be used as part of a chiller or in any other heat exchanging application. Heat exchanger  88  includes a top manifold  90  and a bottom manifold  92 , which are connected by multichannel tubes  94 . Although sixty tubes are shown in FIG.  6 , the number of tubes may vary. The manifolds and tubes may be constructed of aluminum or any other material that promotes good heat transfer. Refrigerant flows vertically within multichannel tubes  94  between manifolds  90  and  92 . In some embodiments, the heat exchanger may be rotated approximately 90 degrees so the multichannel tubes run horizontally between a left manifold and a right manifold. The heat exchanger may be inclined at an angle relative to the vertical axis. Furthermore, although the multichannel tubes are depicted as having an oblong shape, the tubes may be any shape, such as tubes with a cross-section in the form of a rectangle, square, circle, oval, ellipse, triangle, trapezoid, or parallelogram. In some embodiments, the tubes may have a diameter ranging from 0.5 mm to 3 mm. It should also be noted that the heat exchanger may be provided in a single plane or slab, or may include bends, corners, contours, and so forth. 
         [0044]    Fins  96  are located between the multichannel tubes  94  to promote the transfer of heat between the tubes  94  and the environment. In one embodiment, the fins are constructed of aluminum, brazed or otherwise joined to the tubes, and disposed generally perpendicular to the flow of refrigerant. However, in other embodiments the fins may be made of other materials that facilitate heat transfer and may extend parallel or at varying angles with respect to the flow of the refrigerant. The fins may be louvered fins, corrugated fins, or any other suitable type of fin. 
         [0045]    Baffles  98 ,  100 ,  102 , and  104  separate the multichannel tubes  94  into two coil circuits containing four groups of tubes. The four groups of tubes are disposed adjacent to one another to form a single slab heat exchanger  88 . Each individual group of tubes contains several tubes disposed adjacent to one another. The baffles direct the flow of refrigerant between manifolds  90  and  92 . Baffles  98 ,  100 , and  102  divide top manifold  90  into four separate sections corresponding to the four groups of tubes, while baffle  104  divides bottom manifold  92  into two separate sections corresponding to two coil circuits. The baffles may be composed of any material which acts as a barrier to the flow of refrigerant. For example, in some embodiments, the baffles may be made from aluminum. In other embodiments, the baffles may be made from material having a low thermal conductivity in order to provide insulation between the groups of the tubes and the coil circuits. 
         [0046]    Baffles  98  and  100  divide top manifold  90  into a tube group A  106  and a tube group B  108 . Baffle  100  directs the flow of refrigerant from top manifold  90  down to bottom manifold  92  through the multichannel tubes of group A  106 . The fluid then returns to the top manifold  90  through the multichannel tubes of group B  108 . Baffle  98  prevents the fluid that has returned to top manifold  90  from entering the tubes of tube group C  110 . 
         [0047]    Baffles  98  and  102  divide top manifold  90  into a tube group C  110  and a tube group D  112 . Baffle  102  directs the flow of refrigerant from top manifold  90  down to bottom manifold  92  through the multichannel tubes of group C  110 . The refrigerant then returns to top manifold  90  through the multichannel tubes of group D  112 . 
         [0048]    Baffles  98  and  104  divide the heat exchanger into two independent coil circuits. Baffle  98  divides top manifold  90  in order to prevent the fluid flowing within tube group B  108  from contacting the fluid flowing within tube group C  110 . Baffle  104  divides bottom manifold  92  to prevent the fluid flowing within tube group B  108  from contacting the fluid flowing within tube group C  110 . Consequently, the refrigerant that flows within the tubes of group A and group B does not contact the refrigerant that flows within the tubes of group C and group D. 
         [0049]    Each independent coil circuit has its own inlet and outlet. The first coil circuit containing multichannel tubes of group A  106  and group B  108  includes inlet  114  and outlet  116 . Consequently, the refrigerant flows through the first coil circuit as follows: the refrigerant enters top manifold  90  through inlet  114 , flows through the group A  106  multichannel tubes to bottom manifold  92 , returns to top manifold  90  through the group B  108  multichannel tubes, and exits the heat exchanger through outlet  116 . Baffle  100  directs the flow of refrigerant from top manifold  90  to bottom manifold  92  while baffles  98  and  104  separate the first coil circuit from the second coil circuit. 
         [0050]    The second coil circuit containing multichannel tubes of group C  110  and group D  112  has an inlet  118  and an outlet  120 . Consequently, the refrigerant flows through the second coil circuit as follows: the refrigerant enters the top manifold  90  through inlet  118 , flows through the group C  110  multichannel tubes to bottom manifold  92 , returns to top manifold  90  through the group D  112  multichannel tubes, and exits the heat exchanger through outlet  120 . Baffle  102  directs the flow of refrigerant from top manifold  90  to bottom manifold  92  while baffles  98  and  104  separate the second coil circuit from the first coil circuit. 
         [0051]    The fluid that flows through the first coil circuit containing group A and B tubes may be the same type of fluid or different type of fluid than the fluid that flows through the second coil circuit containing group C and D tubes. In some embodiments, the fluid flowing through the first coil circuit may be the same fluid that flows through the second coil circuit, only at different stages in the heating and cooling process. For example, the second coil circuit may be used to provide a second pass for heating and cooling of the refrigerant. In other embodiments, the fluid flowing through the second coil circuit may be an independent fluid used to cool a separate part of the system such as a compressor or an electronic power circuit. 
         [0052]    The number of tubes within each group may vary. For example, tube group A and tube group B may contain twenty tubes each while tube group C and tube group D contain thirty tubes each. In another example, tube group A may contain twenty tubes while tube group B contains fifteen tubes. Variations in the number of tubes may be used to improve heat transfer in each tube group by accounting for factors such as the phase of the refrigerant and the tube group location within the heat exchanger. 
         [0053]    In other embodiments, the heat exchanger may be inclined at an angle or rotated 90 degrees so the fluid flows horizontally through the multichannel tubes instead of vertically. In the rotated embodiment, the manifolds may be positioned vertically on the sides of the heat exchanger. The coil circuiting concepts shown in  FIG. 6 , as well as those shown in  FIGS. 8 and 9 , may be used in other coil geometries, such as coils having an S-shape or an angled configuration. Furthermore, the coil circuiting concepts shown in  FIGS. 6-9  may be repeated within a condenser slab to form a heat exchanger with more than four tube groups. 
         [0054]      FIG. 7  depicts the heat exchanger of  FIG. 6  sectioned through the multichannel tubes  94  to illustrate the internal configuration of the tubes. Refrigerant flows through flow channels  122  contained within tubes  94 . The direction of fluid flow  124  is from manifold  92 , shown in  FIG. 6 , to manifold  90 . For example, as shown in  FIG. 6 , tubes  94  of  FIG. 7  may correspond to tubes from either group B or group D. The fluid flows through adjacent flow channels  122  in a relatively parallel flow between the manifolds. Flow channels  122  have a round cross-section with a small diameter relative to the size of the tubes  94 . In other embodiments, the flow channels may have a different cross-section such as that of a rectangular or oval shape. The cross-section and size of the flow channels may vary between the different tube groups. 
         [0055]      FIG. 8  depicts an alternate coil circuiting configuration for the heat exchanger  88 . Note that the multichannel tubes and fins have been omitted for clarity. In this embodiment, tube group C  110  and tube group D  112  are located in between tube group A  106  and tube group B  108 . Fluid enters the multichannel tubes of group A  106  through inlet  114  and flows to bottom manifold  92 . The fluid flows across bottom manifold  92  to the multichannel tubes of group B  108  where it returns to the top manifold  90  and exits outlet  120 . Baffles  125  divide top manifold  90  into the four tube groups. Bottom manifold  92 , on the other hand, has a bypass  126  instead of a baffle. A second fluid enters the inlet  118  and flows through the tubes of group C  110  to the bypass  126  located within bottom manifold  92 . The bypass  126  may be constructed of any material sufficient for separating the fluids. The fluid flows through the bypass to the tubes of group D  112  which return it to the top manifold  90  where it exits through outlet  116 . 
         [0056]      FIG. 9  depicts another alternate coil circuiting configuration for the heat exchanger  88 . Note that the multichannel tubes and fins have been omitted for clarity. In this embodiment, the tube groups A  106  and B  108  of the first coil circuit are alternated between the tube groups C  110  and D  112  of the second coil circuit. The top manifold  90  contains baffles  125  that divide it into the four tube groups, while the bottom manifold  92  contains a bypass  128 . Fluid enters the multichannel tubes of group A  106  through inlet  114  and flows to bottom manifold  92  where it enters a bypass  128 . Bypass  128  may be constructed of any material sufficient for separating fluids, such as aluminum. The fluid flows through the bypass to the multichannel tubes of group B  108  where it returns to top manifold  90  and exits through outlet  120 . A second refrigerant enters inlet  118  and flows through the tubes of group C  110  to bottom manifold  92 . The fluid flows through bottom manifold  92  to the tubes of group D  112  which return it to top manifold  90  where it exits through outlet  116 . 
         [0057]      FIG. 10  shows manifold  90  configured for the coil circuiting shown in  FIG. 9 . The cross-sectional view illustrates bypass  128  contained within manifold  90 . Bypass  128  divides the manifold into two flow sections, an outer flow section  130  and an inner flow section  132 . Fluid from group A, shown in  FIG. 9 , flows through bypass  128  within inner flow section  132  to group B, shown in  FIG. 9 . Fluid from group C, shown in  FIG. 9 , flows through outer section  130  of the manifold to group D, shown in  FIG. 9 . The outer flow exits the manifold to enter group D through an opening  134 . A similar inlet (not shown) directs the inner flow from the bypass into group B. 
         [0058]    The coil circuiting configurations described herein may find application in a variety of heat exchangers and HVAC&amp;R systems containing heat exchangers. However, the configurations are particularly well-suited to heat exchangers functioning as evaporators and condensers within chillers, air conditioners, and heat pumps. The coil circuiting configurations are intended to improve the overall efficiency of a heat exchanger by allowing tube groups to be positioned in a location of a heat exchanger that is tailored to the heat transfer properties of the tube group. 
         [0059]    It should be noted that the present discussion makes use of the term “multichannel” tubes or “multichannel heat exchanger” to refer to arrangements in which heat transfer tubes include a plurality of flow paths between manifolds that distribute flow to and collect flow from the tubes. A number of other terms may be used in the art for similar arrangements. Such alternative terms might include “microchannel” and “microport.” The term “microchannel” sometimes carries the connotation of tubes having fluid passages on the order of a micrometer and less. However, in the present context such terms are not intended to have any particular higher or lower dimensional threshold. Rather, the term “multichannel” used to describe and claim embodiments herein is intended to cover all such sizes. Other terms sometimes used in the art include “parallel flow” and “brazed aluminum.” However, all such arrangements and structures are intended to be included within the scope of the term “multichannel.” In general, such “multichannel” tubes will include flow paths disposed along the width or in a plane of a generally flat, planar tube, although, again, the invention is not intended to be limited to any particular geometry unless otherwise specified in the appended claims. 
         [0060]    While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. 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. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions must 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.