Patent Publication Number: US-9903663-B2

Title: Brazed heat exchanger with fluid flow to serially exchange heat with different refrigerant circuits

Description:
FIELD 
     The disclosure herein relates to a heat exchanger, such as for example a brazed heat exchanger, which may be a brazed plate heat exchanger, and which may be used for example in a heating, ventilation, and air conditioning system (HVAC) system and/or unit thereof. The heat exchanger includes a flow structure to allow a fluid stream, for example a chilled fluid stream to exchange heat serially with more than one refrigerant circuit where each refrigerant circuit is a distinct and independent refrigerant circuit. 
     BACKGROUND 
     Heat exchangers that may be used for example in HVAC systems can include various types of heat exchangers, for example brazed heat exchangers. 
     SUMMARY 
     Brazed heat exchangers are described, and which may be brazed plate heat exchangers, and used for example in a heating, ventilation, and air conditioning system (HVAC) system and/or unit thereof. 
     Generally, the heat exchanger includes a flow structure to allow a fluid stream, for example a chilled fluid stream to exchange heat serially with more than one refrigerant circuit where each refrigerant circuit is a distinct and independent refrigerant circuit. 
     In one embodiment, an apparatus to exchange heat serially with more than one heat exchange fluid circuit includes an internal flow path that allows a working fluid to flow through a first brazed heat exchanger, through one or more internal routing channels, and through a second brazed heat exchanger. 
     In one embodiment, the first brazed heat exchanger has a working fluid inlet in fluid communication with a working fluid circuit, and a first heat exchanger fluid inlet and outlet in fluid communication with a first heat exchange fluid circuit. The first heat exchanger fluid inlet and outlet are configured to allow fluid flow of a first heat exchange fluid into and out of the first brazed heat exchanger. The first brazed heat exchanger includes working fluid flow channels in fluid communication with the working fluid inlet, and includes first heat exchanger fluid flow channels in fluid communication with the first heat exchanger fluid inlet and outlet. The working fluid flow channels are configured relative to the first heat exchanger fluid flow channels so that the working fluid flowing through the working fluid flow channels exchanges heat with the first heat exchange fluid flowing through the first heat exchanger fluid channels. The internal flow path includes the working fluid flow channels of the first brazed heat exchanger and the one or more internal routing channels. 
     In one embodiment, the second brazed heat exchanger has working fluid flow channels in fluid communication with the one or more internal routing channels. The second brazed heat exchanger includes a second heat exchanger fluid inlet and outlet in fluid communication with a second heat exchange fluid circuit that is separate from the first heat exchange fluid circuit. The second heat exchanger fluid inlet and outlet are configured to allow fluid flow of a second heat exchange fluid into and out of the second brazed heat exchanger. The second brazed heat exchanger includes second heat exchanger fluid flow channels in fluid communication with the second heat exchanger fluid inlet and outlet. The working fluid channels of the second brazed heat exchanger are configured relative to the second heat exchanger fluid flow channels so that the working fluid flowing through the working fluid flow channels exchanges heat with the second heat exchange fluid flowing through the second heat exchanger fluid channels. The second brazed heat exchanger includes an outlet in fluid communication with the working fluid flow channels of the second brazed heat exchanger. The internal flow path includes the working fluid flow channels of the second brazed heat exchanger. 
     The internal flow path thus comprises the working fluid flow channels of the first brazed heat exchanger, the one or more internal routing channels, and the working fluid flow channels of the second brazed heat exchanger. The one or more internal routing channels are in fluid communication with the working fluid flow channels, such that the working fluid exits the first brazed heat exchanger and enters the second brazed heat exchanger internally of the apparatus, and so that working fluid does not route from an external exit of the first brazed heat exchanger and does not route to an external entrance of the second brazed heat exchanger. 
     By “internal” flow path, it is meant that that fluid flow from the first heat exchanger to the second heat exchanger is not from an external outlet of the first heat exchanger to an external inlet of the second heat exchanger. 
     In one embodiment, the first and/or the second brazed heat exchangers are brazed plate heat exchangers. 
     In one embodiment, the internal routing channel(s) can be disposed between the first and second brazed heat exchangers. 
     In one embodiment, a divider is disposed between the first and second brazed heat exchangers. 
     In one embodiment, the one or more routing channels make up the divider between the first and second heat exchangers. 
     In one embodiment, the first brazed heat exchanger, the one or more routing channels, and the second brazed heat exchanger are constructed and arranged as a single unit, without external piping for the internal flow path. In one embodiment, the apparatus is a single entity, constructed and arranged as a single component. 
     In one embodiment, the configuration of the working fluid flow channels relative to the heat exchanger fluid flow channels, in the first and/or second brazed heat exchanger, can be constructed and arranged in various ways that include but are not limited to counter flow, parallel flow, cross flow, or the like. 
     In one embodiment, the apparatus and heat exchangers used therein can be implemented in a cascade effect using multiple heat exchange fluid circuits, which may run through a single apparatus or employ multiple apparatuses herein to account for the number of heat exchange fluid circuits leveraged. 
     In one embodiment, a method to exchange heat from a working fluid serially with more than one heat exchange fluid circuit includes directing a working fluid through an internal flow path that directs the working fluid to flow through a first brazed heat exchanger, through one or more internal routing channels, and through a second brazed heat exchanger. 
     In one embodiment, the method includes directing the working fluid into an inlet of the first brazed heat exchanger, and directing a first heat exchange fluid into another inlet of the first heat exchanger. The working fluid is directed through working fluid channels of the first brazed heat exchanger, and the first heat exchange fluid is directed through first heat exchanger fluid channels. The working fluid flowing through the working fluid channels of the first brazed heat exchanger exchanges heat with the first heat exchange fluid flowing through the first heat exchanger fluid channels. The working fluid is directed to one or more internal routing channels, and is internally routed to the second brazed heat exchanger, and through working fluid channels of the second heat exchanger. A second heat exchange fluid is directed into an inlet of the second brazed heat exchanger and through second heat exchanger fluid channels. The working fluid flowing through the working fluid flow channels of the second brazed heat exchanger exchanges heat with the second heat exchange fluid flowing through the second heat exchanger fluid channels. The working fluid is directed to an outlet in fluid communication with the working fluid flow channels of the second brazed heat exchanger. 
     The apparatuses and methods herein and the brazed heat exchangers described herein may be used for example in a heating, ventilation, and air conditioning system (HVAC) system and/or unit thereof. For example, the apparatuses and methods herein can be used with various types of water chillers, that may use various types of compressors including but not limited to scroll, screw, reciprocating compressors, and that may have varying capacities including but not limited to about 10 ton to about 100 ton cooling capacity, which may make use of the compact and low inventory requirements of brazed heat exchangers. It will be appreciated, however, that as certain designs become larger, such as for example, at about 120 tons to higher at about 150 tons to about 250 tons, where flow rates and distributions may be adequately addressed to avail use of brazed heat exchangers. 
     In one embodiment, the HVAC systems and/or units in which the apparatuses and methods herein may be suitable can include scroll compressor water chillers at about 10 ton to about 100 ton cooling capacity. 
     Other features and aspects of the embodiments will become apparent by consideration of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the drawings in which like reference numbers represent corresponding parts throughout. 
         FIG. 1  is perspective view of an example brazed plate heat exchanger. 
         FIG. 2  is a schematic plan view of an embodiment of an apparatus to exchange heat serially with more than one heat exchange fluid circuit. 
         FIG. 3  is a schematic plan view of an embodiment of an apparatus to exchange heat serially with more than one heat exchange fluid circuit. 
         FIGS. 4A and 4B  show a schematic plan view of another embodiment of an apparatus to exchange heat serially with more than one heat exchange fluid circuit.  FIG. 4A  shows a side sectional view.  FIG. 4B  shows a front view. 
         FIGS. 5A and 5B  show a schematic plan view of another embodiment of an apparatus to exchange heat serially with more than one heat exchange fluid circuit.  FIG. 5A  shows a front view.  FIG. 5B  shows a side sectional view. 
         FIG. 6  shows a fluid flow scheme consistent with the apparatus shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Apparatuses and methods that employ brazed heat exchangers are described, and which the brazed heat exchangers may be brazed plate heat exchangers, and can used for example in a heating, ventilation, and air conditioning system (HVAC) system and/or unit thereof. The heat exchanger includes a flow structure to allow a fluid stream, for example a chilled fluid stream to exchange heat serially with more than one refrigerant circuit where each refrigerant circuit is a distinct and independent refrigerant circuit. Generally, an apparatus to exchange heat serially with more than one heat exchange fluid circuit includes an internal flow path that allows a working fluid to flow through a first brazed heat exchanger, through one or more internal routing channels, and through a second brazed heat exchanger. 
     With some reference first to brazed heat exchangers, flow management for example in a single, brazed heat exchanger can allow chilled fluid to exchange heat from one refrigerant circuit to one or more other circuits in a series fashion. A series arrangement can leverage the temperature cascade effect from the multiple refrigerant circuits to enhance the thermodynamic cycle efficiency, for example in a refrigeration process. 
     In the example of a refrigeration or chiller system comprised of multiple (more than one) refrigerant circuits, the arrangement of the source and sink streams relative to the individual refrigerant circuits can be leveraged to improve the overall efficiency, e.g. coefficient of performance (COP), of the refrigeration system. As one example, for a system composed of two independent refrigerant circuits, if the source (chilled fluid) stream exchanges heat with one circuit followed by the other in series, the average temperature of the saturated refrigerant leaving one circuit is higher than when the source stream interacts with both circuits simultaneously or in parallel. 
     A brazed heat exchanger, for example a brazed plate heat exchanger (BPHE) is composed of corrugated metallic sheets which are in turn brazed together. Such a construction can offer some advantages and may be deployed in chiller or refrigeration systems such as for example in evaporators, condensers, subcoolers, economizers, oil coolers as some examples. Generally, a BPHE can include very compact profile and footprints, can have low internal (fluid) volume, and a unified and rigid structure. The components of the BPHE are brazed together during its construction and the result is a single, unified heat exchanger which can be attached into a larger system. 
       FIG. 1  shows one example of a brazed plate heat exchanger (BPHE)  10 . The BPHE  10  can be composed of corrugated metallic sheets, see e.g.  12  and  14 , which are brazed together. As shown, plate  14  allows one fluid stream for example a source stream, such as a chilled fluid which may be water, to flow on one side, while plate  12  allows another fluid stream, for example a refrigerant stream to flow on the other side. The fluids exchange heat for example such that the fluid stream flowing through plate  12  cools the fluid stream (e.g. water) flowing through plate  14 . A cover  28  can have openings  16 ,  18 ,  20 , and  22  that are respective inlets and outlets for each of the fluid streams. Plate  14  can have openings  24  in fluid communication with the openings  16 ,  18 ,  20 , and  22  to allow flow into and out of each of plates  12 ,  14 . A cover  26  can close the other side of the BPHE  10 . 
     A BPHE, such as BPHE  10 , can be capable of handling a variety of flow situations. One flow situation is a fluid stream exchanging energy with one other fluid stream. In other flow situations, such as described in the apparatuses and methods herein, multiple fluid streams can interact within one unified brazed heat exchanger. For instance, two refrigerant circuits can exchange heat with a common working fluid circuit, such as but not limited to for example a water circuit or a glycol circuit. It is possible to braze more than one BPHE together to form a side-by-side, back-to-back, or adjacent arrangements of heat exchangers. 
       FIG. 2  is a schematic plan view of one embodiment of an apparatus  100  to exchange heat serially with more than one heat exchange fluid circuit, e.g.  102 ,  104  which can act as separate heat exchangers. In one embodiment, the apparatus  100  can be a series integrated brazed exchanger that brings together the thermodynamic benefit of series water pass through multiple circuit refrigeration equipment, e.g. performing serial heat exchanges, but where the apparatus  100  is constructed and arranged as a single component and unified brazed plate heat exchanger structure. In some examples a chilled fluid, such as water or glycol, enters the apparatus  100  at inlet  106 . It is then routed internally to exchange heat with the first refrigerant circuit, e.g. heat exchanger  102 . Depending on the particular application, the fluid flow of chilled fluid through the internal channels of the first heat exchanger  102  can be arranged for example but not limited to counter flow, parallel flow, or cross flow. After interaction with the first refrigerant circuit (e.g. first exchanger  102 ) is complete, the chilled fluid is routed internally to interact with the second refrigerant circuit, e.g. second heat exchanger  104 . In such a configuration, the chilled fluid routing during the entire process takes place internally. It will be appreciated that the flow passages to route the flow of chilled fluid through the first and second circuits, e.g. first and second heat exchangers  102 ,  104  can be specifically designed, configured, and oriented so as to provide adequate and/or optimum flow with respect to the first circuit and second circuit. It will also be appreciated that additional circuits may be employed in a cascading configuration. For example, the chilled fluid outlet  108  shown in  FIG. 2  may be structured as another one or more internal routing channels to add on another circuit, which may be similar to  102 ,  104 . 
     In the configuration shown in  FIG. 2 , the apparatus  100  can be constructed and arranged as a single entity, which can eliminate the need for external piping, the number of piping joints can be reduced, and handling and servicing of one entity can be suitable to handling and applying two or more units. 
     With further reference to  FIG. 2 , the fluid flow may be as follows. For convenience of description, water can be the chilled fluid for the embodiment shown and the apparatus  100  is one in which its heat exchangers act as evaporators. Relatively warm water enters the chilled fluid inlet  106 . Then, in this example, the water flows downward through the channel matrix or working fluid channels  116 . In the embodiment shown, the water flow is a counter flow relative to the first heat exchange fluid, e.g. refrigerant, circulating in the first circuit, e.g. heat exchanger  102 . The refrigerant absorbs energy from the water and boils, and can leave in gaseous form for example through an outlet (not shown) toward the top of the heat exchanger  102 . In some embodiments, if the amount of heat exchange is sufficient, then the refrigerant may be boiled to a superheated condition which may be useful for other purposes in the first circuit. In turn, the water is cooled in this process of heat exchange with the first heat exchanger  102 . After passing through the working fluid channels associated with the first heat exchanger  102 , the water may be routed from the bottom of the first heat exchanger  102  to the second heat exchanger  104 . In some embodiments, the water is routed back to the top of the apparatus  100  to begin the process of heat exchange with the second refrigerant circuit, e.g. second heat exchanger  104 . The routing is accomplished through one or more internal routing channels  120 . In some embodiments, the internal routing channels  120  do not allow heat to be exchanged, or at least allow only a very little heat transfer with either refrigerant circuit, e.g. heat exchangers  102 ,  104 , such that the benefits of the cascade effect may still be realized. Generally, the internal routing channels  120  are configured to position the water for introduction into a heat exchange relationship with the second circuit, e.g. into second heat exchanger  104 . The water can then flow through the brazed channel matrix, e.g. the working fluid channels  116 , of the second heat exchanger  104 . It will be appreciated that in some embodiments, other flow chambers, channels, headers, or other flow path structures, as depicted by  118  in  FIG. 2 , may also be employed to route the chilled fluid. 
     Similar to the process occurring in the first circuit, the refrigerant is boiled off and leaves the second heat exchanger  104  through the second heat exchange fluid channels  112 , while the water cools off. Finally, the water is routed to the outlet  108  and may then leave the heat exchanger  104  and/or the apparatus  100 . 
     It will be appreciated that the apparatus  100  can include additional circuits, for example sequentially added in a similar arrangement as the second circuit, e.g. second heat exchanger  104 , is added to the first circuit, e.g. first heat exchanger  102 . 
     In such a configuration, the outlet  108  can be replaced with additional internal routing channel(s) and be disposed further downstream until after the last circuit has been incorporated. The resulting chilled fluid, e.g. water, can then be circulated such as by using conventional implementations, to cool an industrial process, provide air conditioning, cool food or provide some useful benefit to society. 
     Thus, as shown in  FIG. 2 , the first brazed heat exchanger  102  can have a working fluid inlet  106  in fluid communication with a working fluid circuit, and a first heat exchanger fluid inlet and outlet (see e.g.  214   a ,  214   b  in  FIG. 3 ) in fluid communication with a first heat exchange fluid circuit. The first heat exchanger fluid inlet and outlet are configured to allow fluid flow of a first heat exchange fluid into and out of the first brazed heat exchanger  102 . The first brazed heat exchanger  102  includes working fluid flow channels  116  in fluid communication with the working fluid inlet  106 , and includes first heat exchanger fluid flow channels  110  in fluid communication with the first heat exchanger fluid inlet and outlet. The working fluid channels  116  are configured relative to the first heat exchanger fluid flow channels  110  so that the working fluid flowing through the working fluid flow channels  116  exchanges heat with the first heat exchange fluid flowing through the first heat exchanger fluid channels  110 . The internal flow path includes the working fluid flow channels  110  of the first brazed heat exchanger  102  and the one or more internal routing channels  120 . 
     In one embodiment, the second brazed heat exchanger  104  has working fluid flow channels  116  in fluid communication with the one or more internal routing channels  120 . The second brazed heat exchanger  104  includes a second heat exchanger fluid inlet and outlet (see e.g.  214   c ,  214   d  in  FIG. 3 ) in fluid communication with a second heat exchange fluid circuit that is separate from the first heat exchange fluid circuit. The second heat exchanger fluid inlet and outlet are configured to allow fluid flow of a second heat exchange fluid into and out of the second brazed heat exchanger  104 . The second brazed heat exchanger  104  includes second heat exchanger fluid flow channels  112  in fluid communication with the second heat exchanger fluid inlet and outlet. The working fluid channels  116  of the second brazed heat exchanger  104  are configured relative to the second heat exchanger fluid flow channels  112  so that the working fluid flowing through the working fluid flow channels  116  exchanges heat with the second heat exchange fluid flowing through the second heat exchanger fluid channels  112 . The second brazed heat exchanger  104  includes an outlet  108  in fluid communication with the working fluid flow channels  116  of the second brazed heat exchanger  104 . The internal flow path includes the working fluid flow channels  116  of the second brazed heat exchanger  104 . 
     The internal flow path thus comprises the working fluid flow channels  116  of first brazed heat exchanger  102 , the one or more internal routing channels  120 , and the working fluid flow channels  116  of the second brazed heat exchanger  104 . The one or more internal routing channels  120  are in fluid communication with the working fluid flow channels  116 , such that the working fluid exits the first brazed heat exchanger  102  and enters the second brazed heat exchanger  104  internally of the apparatus  100 , and so that working fluid does not route from an external exit of the first brazed heat exchanger  102  does not route to an external entrance of the second brazed heat exchanger  104 . 
     By “internal” flow path, it is meant that that fluid flow from the first heat exchanger  102  to the second heat exchanger  104  is not from an external outlet of the first heat exchanger to an external inlet of the second heat exchanger. 
     In one embodiment, the first and/or the second brazed heat exchangers  102 ,  104  are brazed plate heat exchangers. 
     In one embodiment, the internal routing channel(s)  120  can be disposed between the first and second brazed heat exchangers  102 ,  104 . 
     In one embodiment, a divider is disposed between the first and second brazed heat exchangers  102 ,  104 . 
     In one embodiment, the one or more routing channels  120  make up the divider between the first and second heat exchangers  102 ,  104 . 
     In one embodiment, the first brazed heat exchanger  102 , the one or more routing channels  120 , and the second brazed heat exchanger  104  are constructed and arranged as a single unit, such as shown, without external piping for the internal flow path. In one embodiment, the apparatus  100  is a single entity, constructed and arranged as a single component. 
     In one embodiment, the configuration of the working fluid flow channels  116  relative to the heat exchanger fluid flow channels  110 ,  112 , in the first and/or second brazed heat exchanger  102 ,  104 , can be constructed and arranged in various ways that include but are not limited to counter flow, parallel flow, cross flow, or the like. 
     In one embodiment, the apparatus  100  and heat exchangers  102 ,  104  used herein can be implemented in a cascade effect using multiple heat exchange fluid circuits, which may run through a single apparatus or employ multiple apparatuses herein to account for the number of heat exchange fluid circuits leveraged. 
     It will be appreciated that specific flow configurations through the heat exchangers  102 ,  104 , placement and configuration of the internal routing channel(s) as shown in  FIG. 2  are merely exemplary and are not meant to be limiting. Other configurations may also be suitable that arrange the respective elements in manner that is different from what is shown in  FIG. 2 . 
       FIG. 3  is a schematic plan view of another embodiment of an apparatus  200  to exchange heat serially with more than one heat exchange fluid circuit.  FIG. 3  shows a different flow orientation, which could be designed within a plate stack and which could achieve the same effect as in  FIG. 2 . In  FIG. 3 , the first and second circuits may be split, for example in a side to side configuration, and where the split includes one or more routing channels oriented generally vertically. Similar reference numbers correspond to those used in  FIG. 2 . The apparatus  200  includes a first heat exchanger  202 , a second heat exchanger  204 , and one or more internal routing channels  220 . The first heat exchanger  202  has an inlet  206 , and the second heat exchanger  204  can have an outlet  208 . Working fluid channels  216  are schematically shown (and suitable other flow chambers, channels, headers, or other flow path structures may be used, as depicted by  218 ). First and second heat exchange fluid channels  210 ,  212  are also shown. Also, shown are the inlets, outlets  214   a ,  214   b ,  214   c , and  214   d  which are respectively in fluid communication with the first and second heat exchange fluid channels  210 ,  212 . 
     It will be appreciated that the orientation of the flow through the first and second heat exchangers and the routing channel(s) is not meant to be limiting. In other examples, a diagonal split may be useful, depending on BPHE manufacturing and depending on the flow designs. 
     It will be appreciated that the one or more internal routing channels may be sized with an appropriate width, wall thickness, and surface characteristics to achieve a desired fluid flow through the internal routing chambers. Likewise, the routing channels may be constructed in a manner and of a material that can achieve a desired thermoconductivity and/or insulation, for example relative to other parts of the apparatus including but not limited to the first and second heat exchangers. 
     It will also be appreciated that existing system pressures, e.g. from an external pump which may be present in the system and/or unit for example a pump of a chiller, may be employed to provide the fluid pressure to drive the fluid through the apparatus. 
     It will be appreciated that the apparatuses of  FIGS. 2 and 3  may be incorporated in systems and/or units that include for example multiple circuited chillers. 
     Two other approaches that differ from  FIGS. 2 and 3  may also be incorporated in multiple circuited chillers, and which are described below with respect to  FIGS. 4 to 6 . 
       FIGS. 4A and 4B  show a series arranged BPHE with a configuration of back-to-back circuits and external piping  420 .  FIGS. 4A and 4B  show multiple separate heat exchangers, e.g. two heat exchangers, which are divided by a divider plate  422 .  FIGS. 4A and 4B  thus show a single exchanger comprised of two independent exchangers  402 ,  404  brazed together back-to-back. Here, the chilled fluid is routed completely through one heat exchanger (on the left) through  406 ,  408  and exchange heat with fluid flowing through inlet  214   a  to outlet  214   b , leaves the first heat exchanger at  408 , is routed to the second heat exchanger through  406   a ,  408   a , and then through the other (on the right) in a series fashion, but using the external piping. With this arrangement, an improvement in the chiller system COP may be realized relative to an interlaced concept (described below with respect to  FIGS. 5 and 6 ). Some potential drawbacks of the external piping configuration is the additional external piping which must be provided to route the chilled fluid stream from one exchanger (or one half for back-to-back) to the other side. The external piping can increase the footprint of the overall apparatus. Further, pressure losses may penalize efficiencies gained due to the number of bends (see e.g. four bends in the external piping) that may be present in the routing of the external tubing. Further, due to the use of external tubing there may be some heat transfer losses to the environment. 
       FIGS. 5A, 5B, and 6  show an interlaced construction method of a heat exchanger apparatus  500 , but where the heat exchange is not serial and so improvements in COP may not be realized.  FIG. 5  shows a front view (left) and a side view (right). In this arrangement, the internal passages of the BPHE direct flow through alternating channels. See e.g.  FIG. 6 . The chilled fluid (W) flows through the first channel, then refrigerant from circuit  1  (R 1 ) flows through the next channel. This is followed by another water channel (W) which is followed by refrigerant flowing through circuit  2  (R 2 ) then the pattern repeats. In this case, the two refrigerant circuits exchange heat with the same chilled fluid stream. Thus the heat exchange rate and ultimately the same exit temperature will be developed for both refrigerant circuits, resulting in identical refrigerant conditions leaving the heat exchanger. Thus the COP developed in each of the circuits will generally be the same. 
       FIG. 5  shows an example of interlaced, dual circuit brazed plate heat exchanger  500 . Openings on the left  514   a ,  514   b  represent entry and exit of refrigerant from circuit  1 . Openings on the right  514   c ,  514   d  represent entry and exit of refrigerant from circuit  2 . Openings in the middle  506 ,  508  represent entry and exit of chilled fluid.  FIG. 6  shows the flow streams inside an interlaced, dual circuit brazed plate heat exchanger, such as shown in  FIG. 5 . 
     Aspects 
     It will be appreciated that any one of the aspects below may be combined with any one or more of the other aspects below. 
     Aspect. Brazed heat exchangers are described, and which may be brazed plate heat exchangers, and used for example in a heating, ventilation, and air conditioning system (HVAC) system and/or unit thereof. 
     Aspect. Generally, the heat exchanger includes a flow structure to allow a fluid stream, for example a chilled fluid stream to exchange heat serially with more than one refrigerant circuit where each refrigerant circuit is a distinct and independent refrigerant circuit. 
     Aspect. In one embodiment, an apparatus to exchange heat serially with more than one heat exchange fluid circuit includes an internal flow path that allows a working fluid to flow through a first brazed heat exchanger, through one or more internal routing channels, and through a second brazed heat exchanger. 
     Aspect. In one embodiment, the first brazed heat exchanger has a working fluid inlet in fluid communication with a working fluid circuit, and a first heat exchanger fluid inlet and outlet in fluid communication with a first heat exchange fluid circuit. The first heat exchanger fluid inlet and outlet are configured to allow fluid flow of a first heat exchange fluid into and out of the first brazed heat exchanger. The first brazed heat exchanger includes working fluid flow channels in fluid communication with the working fluid inlet, and includes first heat exchanger fluid flow channels in fluid communication with the first heat exchanger fluid inlet and outlet. The working fluid channels are configured relative to the first heat exchanger fluid flow channels so that the working fluid flowing through the working fluid flow channels exchanges heat with the first heat exchange fluid flowing through the first heat exchanger fluid channels. 
     Aspect. The internal flow path includes the working fluid flow channels of the first brazed heat exchanger and the one or more internal routing channels. 
     Aspect. In one embodiment, the second brazed heat exchanger has working fluid flow channels in fluid communication with the one or more internal routing channels. The second brazed heat exchanger includes a second heat exchanger fluid inlet and outlet in fluid communication with a second heat exchange fluid circuit that is separate from the first heat exchange fluid circuit. The second heat exchanger fluid inlet and outlet are configured to allow fluid flow of a second heat exchange fluid into and out of the second brazed heat exchanger. The second brazed heat exchanger includes second heat exchanger fluid flow channels in fluid communication with the second heat exchanger fluid inlet and outlet. The working fluid channels of the second brazed heat exchanger are configured relative to the second heat exchanger fluid flow channels so that the working fluid flowing through the working fluid flow channels exchanges heat with the second heat exchange fluid flowing through the second heat exchanger fluid channels. The second brazed heat exchanger includes an outlet in fluid communication with the working fluid flow channels of the second brazed heat exchanger. 
     Aspect. The internal flow path includes the working fluid flow channels of the second brazed heat exchanger. 
     Aspect. The internal flow path thus comprises the working fluid flow channels of first brazed heat exchanger, the one or more internal routing channels, and the working fluid flow channels of the second brazed heat exchanger. 
     Aspect. The one or more internal routing channels are in fluid communication with the working fluid flow channels, such that the working fluid exits the first brazed heat exchanger and enters the second brazed heat exchanger internally of the apparatus, and so that working fluid does not route from an external exit of the first brazed heat exchanger does not route to an external entrance of the second brazed heat exchanger. 
     Aspect. By “internal” flow path, it is meant that that fluid flow from the first heat exchanger to the second heat exchanger is not from an external outlet of the first heat exchanger to an external inlet of the second heat exchanger. 
     Aspect. In one embodiment, the first and/or the second brazed heat exchangers are brazed plate heat exchangers. 
     Aspect. In one embodiment, the internal routing channel(s) can be disposed between the first and second brazed heat exchangers. 
     Aspect. In one embodiment, a divider is disposed between the first and second brazed heat exchangers. 
     Aspect. In one embodiment, the one or more routing channels make up the divider between the first and second heat exchangers. 
     Aspect. In one embodiment, the first brazed heat exchanger, the one or more routing channels, and the second brazed heat exchanger are constructed and arranged as a single unit, without external piping for the internal flow path. In one embodiment, the apparatus is a single entity, constructed and arranged as a single component. 
     Aspect. In one embodiment, the configuration of the working fluid flow channels relative to the heat exchanger fluid flow channels, in the first and/or second brazed heat exchanger, can be constructed and arranged in various ways that include but are not limited to counter flow, parallel flow, cross flow, or the like. 
     Aspect. In one embodiment, the apparatus and heat exchangers used therein can be implemented in a cascade effect using multiple heat exchange fluid circuits, which may run through a single apparatus or employ multiple apparatuses herein to account for the number of heat exchange fluid circuits leveraged. 
     Aspect. In one embodiment, a method to exchange heat from a working fluid serially with more than one heat exchange fluid circuit includes directing a working fluid through an internal flow path that directs the working fluid to flow through a first brazed heat exchanger, through one or more internal routing channels, and through a second brazed heat exchanger. 
     Aspect. In one embodiment, the method includes directing the working fluid into an inlet of the first brazed heat exchanger, and directing a first heat exchange fluid into another inlet of the first heat exchanger. The working fluid is directed through working fluid channels of the first brazed heat exchanger, and the first heat exchange fluid is directed through first heat exchanger fluid channels. The working fluid flowing through the working fluid channels of the first brazed heat exchanger exchanges heat with the first heat exchange fluid flowing through the first heat exchanger fluid channels. The working fluid is directed to one or more internal routing channels, and is internally routed to the second brazed heat exchanger, and through working fluid channels of the second heat exchanger. A second heat exchange fluid is directed into an inlet of the second brazed heat exchanger and through second heat exchanger fluid channels. The working fluid flowing through the working fluid flow channels of the second brazed heat exchanger exchanges heat with the second heat exchange fluid flowing through the second heat exchanger fluid channels. The working fluid is directed to an outlet in fluid communication with the working fluid flow channels of the second brazed heat exchanger. 
     Aspect. The apparatuses and methods herein and the brazed heat exchangers described herein may be used for example in a heating, ventilation, and air conditioning system (HVAC) system and/or unit thereof. 
     Aspect. For example, the apparatuses and methods herein can be used with various types of water chillers, that may use various types of compressors including but not limited to scroll, screw, reciprocating compressors, and that may have varying capacities including but not limited to about 10 ton to about 100 ton cooling capacity, which may make use of the compact and low inventory requirements of brazed heat exchangers. 
     Aspect. In some embodiments, the refrigerant which may be used may include but are not limited to relatively high pressure refrigerants that are relatively dense. It will be appreciated that depending on the BPHE manufacture and flow designs other refrigerants may be suitable for use with the apparatuses and methods herein. 
     Aspect. It will be appreciated, however, that as certain designs become larger, such as for example, at about 120 tons to higher at about 150 tons to about 250 tons, where flow rates and distributions may be adequately addressed to avail use of brazed heat exchangers. 
     Aspect. In one embodiment, the HVAC systems and/or units in which the apparatuses and methods herein may be suitable can include scroll compressor water chillers at about 10 ton to about 100 ton cooling capacity. 
     With regard to the foregoing description, it is to be understood that changes may be made in detail, without departing from the scope of the present invention. It is intended that the specification and depicted embodiments are to be considered exemplary only, with a true scope and spirit of the invention being indicated by the broad meaning of the claims.