Patent Publication Number: US-2023160610-A1

Title: Heat Pump with Ejector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Benefit is claimed of U.S. Pat. Application No. 63/396,768, filed Aug. 10, 2022, and entitled “Heat Pump with Ejector”, and this is a continuation in part of U.S. Pat. Application No. 16/989,603, filed Aug. 10, 2020, and entitled “Heat Pump with Ejector, which is a continuation of U.S. Pat. Application No. 15/776,561, filed May 16, 2018, now U.S Pat. No. 10,739,052 and entitled “Heat Pump with Ejector”, which is a 371 U.S national stage application of PCT/US2016/062759, filed Nov. 18, 2016, which claims benefit of U.S. Pat. Application No. 62/258,345, filed Nov. 20, 2015, and entitled “Heat Pump with Ejector”, the disclosures of all of which applications are incorporated by reference herein in their entireties as if set forth at length. 
    
    
     BACKGROUND 
     The disclosure relates to heat pumps. More particularly, the disclosure relates to heat pumps featuring an ejector. 
     Vapor compression systems have long been used for air conditioning. An exemplary vapor compression air conditioner comprises a refrigerant compressor, an outdoor heat exchanger downstream of the compressor along a refrigerant flowpath, an expansion device downstream of the outdoor heat exchanger, and an indoor heat exchanger downstream of the expansion device prior to the refrigerant flowpath returning to the compressor. Refrigerant is compressed in the compressor. Refrigerant then rejects heat in the outdoor heat exchanger and loses temperature. An exemplary outdoor heat exchanger is a refrigerant-air heat exchanger wherein fan-forced outdoor air acquires heat from refrigerant. By rejecting heat, the refrigerant may condense from vapor to liquid in the heat rejection heat exchanger. Accordingly, such exchangers are often referred to as condensers. In other systems, the refrigerant remains vapor and such are referred to as gas coolers. 
     The refrigerant expands in the expansion device and decreases in temperature. The reduced temperature of the refrigerant thus absorbs heat in the heat absorption heat exchanger (e.g., evaporator). Again, the evaporator may be a refrigerant-air heat exchanger across which a fan-forced interior/indoor airflow is driven with the interior/indoor airflow rejecting heat to the refrigerant. 
     Such vapor compression systems may also be used to heat interior spaces. In such cases, the refrigerant flow direction is altered to pass first from the compressor to the indoor heat exchanger and return from the outdoor heat exchanger to the compressor. Such arrangements are referred to as heat pumps. 
     In addition to simple expansion devices such as orifices and valves, ejectors have been used as expansion devices. Ejectors are particularly efficient where there is a large temperature difference between the indoor and outdoor environments. 
     An exemplary ejector is formed as the combination of a motive (primary) nozzle nested within an outer member or body. The ejector has a motive flow inlet (primary inlet) which may form the inlet to the motive nozzle. The ejector outlet may be the outlet of the outer member. A motive/primary refrigerant flow enters the inlet and then passes into a convergent section of the motive nozzle. It then passes through a throat section and an expansion (divergent) section and through an outlet of the motive nozzle. The motive nozzle accelerates the flow and decreases the pressure of the flow. The ejector has a secondary inlet forming an inlet of the outer member. The pressure reduction caused to the primary flow by the motive nozzle helps draw a suction flow or secondary flow into the outer member through the suction port. The outer member may include a mixer having a convergent section and an elongate throat or mixing section. The outer member also has a divergent section or diffuser downstream of the elongate throat or mixing section. The motive nozzle outlet may be positioned within the convergent section. As the motive flow exits the motive nozzle outlet, it begins to mix with the suction flow with further mixing occurring through the mixing section which provides a mixing zone. 
     Ejectors may be used with a conventional refrigerant or a CO 2 -based refrigerant. In an exemplary operation with CO 2 , the motive flow may typically be supercritical upon entering the ejector and subcritical upon exiting the motive nozzle. The secondary flow is gaseous (or a mixture of gas with a smaller amount of liquid) upon entering the secondary inlet. The resulting combined flow is a liquid/vapor mixture and decelerates and recovers pressure in the diffuser while remaining a mixture. 
     U.S Pat. 6550265 of Takeuchi et al., issued Apr. 22, 2003, and entitled “Ejector Cycle System” discloses switching arrangements for use of an ejector in a cooling mode and a heating mode. U.S Pat. Application Publication 2012/0180510A1 of Okazaki et al., published Jul. 19, 2012, and entitled “Heat Pump Apparatus” discloses a configuration with ejector and non-ejector heating modes and a non-ejector defrost mode. Additionally, PCT/US2015/030709 of Feng et al., filed May 14, 2015, and entitled “Heat Pump with Ejector” discloses a configuration with alternative ejector and non-ejector heating modes and a non-ejector cooling mode. 
     SUMMARY 
     One aspect of the disclosure involves a system comprising: a compressor having a suction port and a discharge port; an ejector having a motive flow inlet, a suction flow inlet, and an outlet; a separator having an inlet, a vapor outlet, and a liquid outlet; a first heat exchanger; at least one expansion device; a second heat exchanger; and a plurality of conduits and a plurality of valves. The ejector is a controllable ejector having a needle shiftable between a closed position and a plurality of open positions. The conduits and valves are positioned to provide alternative operation in: a cooling mode; a first heating mode; and a second heating mode. 
     In one or more embodiments, in the cooling mode, a flowpath segment passes from the first heat exchanger through a first expansion device of the at least one expansion device to the second heat exchanger and the needle is in the closed position to block flow from the motive flow inlet. In the first heating mode, a flowpath segment passes from the second heat exchanger through the motive flow inlet, the separator inlet and liquid outlet, and the first expansion device and to the first heat exchanger. In the second heating mode, a flowpath segment passes from the second heat exchanger through the first expansion device to the first heat exchanger and the ejector has a suction flow and the needle is in the closed position to block flow from the motive flow inlet. 
     In one or more embodiments, in the cooling mode wherein the needle is in the closed position to block flow from the motive flow inlet. In the first heating mode wherein a flowpath segment passes from the second heat exchanger through the motive flow inlet, the separator inlet and liquid outlet, and the expansion device and to the first heat exchanger. In the second heating mode wherein the needle is in the closed position to block flow from the motive flow inlet. 
     In one or more embodiments of any of the foregoing embodiments, in the cooling mode, the ejector has a secondary flow. 
     In one or more embodiments of any of the foregoing embodiments, the system has only a single said ejector. 
     In one or more embodiments of any of the foregoing embodiments, the system has only a single said expansion device. 
     In one or more embodiments of any of the foregoing embodiments, the system has only a single four-port switching valve and no three-port switching valves. 
     In one or more embodiments of any of the foregoing embodiments, the plurality of conduits comprises a first conduit between the first heat exchanger and the second heat exchanger; the at least one expansion device comprises an expansion device along the first conduit; the plurality of conduits comprises a second conduit between the separator liquid outlet and the first conduit; and the plurality of valves comprises a check valve the second conduit. 
     In one or more embodiments of any of the foregoing embodiments, the first conduit comprises: a trunk between the first heat exchanger and the expansion device; a first branch to a first port on the second heat exchanger; and a second branch extending to a second port on the second heat exchanger. 
     In one or more embodiments of any of the foregoing embodiments, the plurality of valves comprises a check valve along the first branch and a two way valve along the second branch. 
     In one or more embodiments of any of the foregoing embodiments, the plurality of conduits comprises a conduit extending from the second branch to the motive flow inlet. 
     In one or more embodiments of any of the foregoing embodiments, a controller is configured to switch the system between: running in the cooling mode; running in the first heating mode; and running in the second heating mode. 
     In one or more embodiments of any of the foregoing embodiments, the controller is configured to switch the system between said first heating mode and said second heating mode based on a sensed outdoor temperature. 
     In one or more embodiments of any of the foregoing embodiments, a method for using the system comprises: running in the cooling mode; running in the first heating mode; and running in the second heating mode. 
     In one or more embodiments of any of the foregoing embodiments, the method further comprises selecting which of the first heating mode and second heating mode in which to run based at least partially on a sensed outdoor temperature. 
     In one or more embodiments of any of the foregoing embodiments, a switching between at least two of the modes comprises actuating a single 4-way switching valve and no 3-way switching valve. 
     In one or more embodiments of any of the foregoing embodiments, the switching between at least two of the modes comprises a switching between at least two of the modes comprises actuating a single 4-way switching valve, no 3-way switching valves, and one or more of 2-way valves. 
     In one or more embodiments of any of the foregoing embodiments: in the cooling mode, a first portion of refrigerant exiting tubes of the second heat exchanger passes through a check valve of the plurality of valves to merge with a second portion and, in turn, pass from a port of the second heat exchanger; and in the first heating mode and second heating mode, refrigerant enters the port of the second heat exchanger into the tubes and from the tubes out a second port. 
     Another aspect of the disclosure involves a system comprising: a compressor having a suction port and a discharge port; an ejector having a motive flow inlet, a suction flow inlet, and an outlet, the ejector being a controllable ejector having a needle shiftable between a closed position and a plurality of open positions; a separator having an inlet, a vapor outlet, and a liquid outlet; a first heat exchanger; an expansion device; a second heat exchanger having a first section and a second section; and a plurality of conduits and a plurality of valves. The conduits and valves are positioned to provide alternative operation in: a cooling mode wherein the needle is in the closed position to block flow from the motive flow inlet; and a heating mode wherein a flowpath segment passes from the second heat exchanger through the motive flow inlet, the separator inlet and liquid outlet, and the expansion device and to the first heat exchanger. The plurality of valves are positioned so that: in the heating mode refrigerant passes sequentially from the first section to the second section; and in the cooling mode refrigerant passes in parallel through the first section and the second section. 
     In one or more embodiments of any of the foregoing embodiments, the first heat exchanger comprises: a first manifold; a second manifold; and a third manifold. In the cooling mode refrigerant passes through a first section of the first heat exchanger and a second section of the first heat exchanger in series. In the heating mode refrigerant passes through the first section of the first heat exchanger and the second section of the first heat exchanger in parallel. 
     In one or more embodiments of any of the foregoing embodiments: the first heat exchanger first section is larger than the first heat exchanger second section; and the second heat exchanger first section is larger than the second heat exchanger second section. 
     In one or more embodiments of any of the foregoing embodiments, a size ratio of the first heat exchanger first section to the first heat exchanger second section is smaller than a size ratio of the second heat exchanger first section to the second heat exchanger second section. 
     In one or more embodiments of any of the foregoing embodiments, the system has only a single ejector. 
     In one or more embodiments of any of the foregoing embodiments: the heating mode is a first heating mode; the plurality of conduits and the plurality of valves are further positioned to provide alternative operation in a second heating mode wherein the needle is in the closed position to block flow from the motive flow inlet; and the plurality of valves are positioned so that in the second heating mode refrigerant passes sequentially from the first section to the second section. 
     In one or more embodiments of any of the foregoing embodiments, the system further comprises a controller configured to switch the system between: running in the cooling mode; running in the first heating mode; and running in the second heating mode. 
     In one or more embodiments of any of the foregoing embodiments, the controller is configured to switch the system between said first heating and said second heating mode based on a sensed outdoor temperature. 
     In one or more embodiments of any of the foregoing embodiments, the first heat exchanger comprises: a first port; a second port; a first check valve of said plurality of valves positioned to block flow from the first manifold to the second manifold; a second check valve of said plurality of valves positioned to block flow from the second port to the second manifold; and a third check valve of said plurality of valves positioned to block flow from the third manifold to the second port. 
     Another aspect of the disclosure involves a system comprising: a compressor having a suction port and a discharge port; an ejector having a motive flow inlet, a suction flow inlet, and an outlet, the ejector being a controllable ejector having a needle shiftable between a closed position and a plurality of open positions; a separator having an inlet, a vapor outlet, and a liquid outlet; a first heat exchanger; at least one expansion device; a second heat exchanger; and a plurality of conduits and a plurality of valves. The conduits and valves are positioned to provide alternative operation in: a cooling mode wherein a flowpath segment passes from the first heat exchanger through a first expansion device of the at least one expansion device to the second heat exchanger and the needle is in the closed position to block flow from the motive flow inlet; a first heating mode wherein a flowpath segment passes from the second heat exchanger through the motive flow inlet, the separator inlet and liquid outlet, and the first expansion device and to the first heat exchanger; and a second heating mode wherein a flowpath segment passes from the second heat exchanger through the first expansion device to the first heat exchanger, the ejector has a suction flow and the needle is in the closed position to block flow from the motive flow inlet. The first heat exchanger comprises: a first manifold; a second manifold; a third manifold. In the cooling mode refrigerant passes through a first section of the first heat exchanger and a second section of the first heat exchanger in series. In the first heating mode refrigerant passes through the first section of the first heat exchanger and the second section of the first heat exchanger in parallel. 
     In one or more embodiments of any of the foregoing embodiments, the first heat exchanger comprises: a first port; a second port; a first check valve of said plurality of valves positioned to block flow from the first manifold to the second manifold; a second check valve of said plurality of valves positioned to block flow from the second port to the second manifold; and a third check valve of said plurality of valves positioned to block flow from the third manifold to the second port. 
     Another aspect of the disclosure involves a system comprising: a compressor having a suction port and a discharge port; an ejector having a motive flow inlet, a suction flow inlet, and an outlet, the ejector being a controllable ejector having a needle shiftable between a closed position and a plurality of open positions; a separator having an inlet, a vapor outlet, and a liquid outlet; a first heat exchanger; at least one expansion device other than the ejector; a second heat exchanger; and a plurality of conduits and a plurality of valves. The conduits and valves are positioned to provide alternative operation in: a cooling mode wherein a flowpath segment passes from the first heat exchanger through a first expansion device of the at least one expansion device to the second heat exchanger and the needle is in the closed position to block flow from the motive flow inlet; and a first heating mode wherein a flowpath segment passes from the second heat exchanger through the motive flow inlet, the separator inlet and liquid outlet, and the first expansion device and to the first heat exchanger. The first heat exchanger comprises: a first manifold; a second manifold; a third manifold. In the cooling mode refrigerant passes through a first section of the first heat exchanger and a second section of the first heat exchanger in series. In the first heating mode refrigerant passes through the first section of the first heat exchanger and the second section of the first heat exchanger in parallel. 
     In one or more embodiments of any of the foregoing embodiments, the first heat exchanger comprises: a first port; a second port; a first check valve of said plurality of valves positioned to block flow from the first manifold to the second manifold; a second check valve of said plurality of valves positioned to block flow from the second port to the second manifold; and a third check valve of said plurality of valves positioned to block flow from the third manifold to the second port. 
     In one or more embodiments of any of the foregoing embodiments, the second heat exchanger has a first section and a second section; and the plurality of valves are positioned so that: in the first heating mode refrigerant passes sequentially from the second heat exchanger first section to the second heat exchanger second section; and in the cooling mode refrigerant passes in parallel through the second heat exchanger first section and the second heat exchanger second section. 
     In one or more embodiments of any of the foregoing embodiments, the plurality of conduits and the plurality of valves are positioned to further provide operation in: a second heating mode wherein: a flowpath segment passes from the second heat exchanger through the first expansion device to the first heat exchanger; and the ejector has a suction flow and the needle is in the closed position to block flow from the motive flow inlet. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of a vapor compression system showing refrigerant flow directions associated with a cooling mode. 
         FIG.  1 A  is a schematic view of an ejector of the system of  FIG.  1   . 
         FIG.  2    is a schematic view of the system of  FIG.  1    showing refrigerant flow directions associated with a first heating mode. 
         FIG.  2 A  is a schematic view of the ejector in the first heating mode. 
         FIG.  3    is a schematic view of the system of  FIG.  1    showing refrigerant flow directions associated with a second heating mode. 
         FIG.  4    is a schematic view of a second vapor compression system showing refrigerant flow directions associated with a cooling mode. 
         FIG.  4 A  is a schematic view of an indoor heat exchanger of the system of  FIG.  4   . 
         FIG.  5    is a schematic view of the system of  FIG.  4    showing refrigerant flow directions associated with a first heating mode. 
         FIG.  5 A  is a schematic view of the indoor heat exchanger of the system of  FIG.  5   . 
         FIG.  6    is a schematic view of the system of  FIG.  4    showing refrigerant flow directions associated with a second heating mode. 
         FIG.  7    is a schematic view of a third vapor compression system showing refrigerant flow directions associated with a cooling mode. 
         FIG.  7 A  is a schematic view of an outdoor heat exchanger of the system of  FIG.  7   . 
         FIG.  8    is a schematic view of the system of  FIG.  7    showing refrigerant directions associated with a first heating mode. 
         FIG.  8 A  is a schematic view of the outdoor heat exchanger of the system of  FIG.  8   . 
         FIG.  9    is a schematic view of the system of  FIG.  7    showing refrigerant flow directions associated with a second heating mode. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG.  1    shows a vapor compression system  20  comprising one or more compressors  22  ( 22 A and  22 B shown in parallel) for driving a flow of refrigerant along a recirculating flowpath. The system further includes at least one first heat exchanger  24  and at least one second heat exchanger  26 . In an example, the system can operate as a heat pump or air conditioner, in this case the first heat exchanger is an outdoor heat exchanger (coil) and the second heat exchanger is an indoor heat exchanger (coil). 
     In the  FIG.  1    cooling or air conditioning mode, the first heat exchanger  24  is a heat rejection heat exchanger and the second heat exchanger  26  is a heat absorption heat exchanger. In certain air temperature control examples, both heat exchangers may be refrigerant-air heat exchangers. In other examples, such as chillers, one or both heat exchangers may be a refrigerant-water heat exchanger, a refrigerant-brine heat exchanger, or the like. 
     In the  FIG.  2    and  FIG.  3    heat pump (heating) modes, the thermal functions of the two heat exchangers are essentially reversed relative to the  FIG.  1    cooling mode. The heat exchanger  24  is a heat absorption heat exchanger and the heat exchanger  26  is a heat rejection heat exchanger. 
     The system can include one or more expansion devices  28  (e.g., an electronic expansion valve (EEV or EXV), not an ejector). As is discussed further below, the system also includes an ejector  32  and a separator  34 . The  FIG.  2    and  FIG.  3    modes differ from each other in at least the roles of the expansion device, ejector, and separator. The  FIG.  2    mode makes full use of the ejector as an expansion device and may be used in a relatively low ambient temperature range. The  FIG.  3    mode effectively disables the ejector (e.g., no motive flow or essentially no motive flow as would be associated with internal leakage levels of flow which are insufficient for driving the associated flows through the suction port) and relies on one or more of the other expansion devices (e.g., the expansion device  28 ). The  FIG.  3    mode may be used in a relatively high ambient temperature range. The exemplary  FIG.  1    mode also disables the ejector. For example, the boundary between low and high may be selected for efficient operation. The ejector loses efficiency at lower temperature differences. For heat pump operation, lower temperature differences are associated with higher ambient temperatures. Control may be responsive to measured temperature difference or responsive to sensed ambient temperature (it being assumed that the target indoor temperature will always be about a typical value).Particular desirable boundaries will depend on the particular refrigerant and construction details of the system. For many systems an appropriate boundary is likely to be associated with an ambient (outdoor) temperature in the range of 30 F (-1.1° C.) to 47° F. (8.3° C.). An alternative upper limit is 60° F. (15.6° C.). Typical temperature (indoor vs. outdoor) differences if controlled based on the difference would be in the range of at least 10° F. (5.6° C.) or at least 23° F. (12.8° C.). 
     The compressor  22  has a suction port (inlet)  40  and a discharge port (outlet)  42 . The ejector comprises a motive flow inlet (primary inlet)  50 , a suction flow inlet (secondary flow inlet)  52 , and an outlet  54 . The exemplary ejector comprises a motive flow nozzle (motive nozzle)  56  positioned to receive a motive flow (e.g., in the  FIG.  2    mode) through the motive flow inlet  50  upstream of a mixing location for flow delivered through the suction flow inlet  52 . 
     The exemplary motive nozzle  56  ( FIG.  1 A ) is a convergent-divergent nozzle having an exit  57  within a convergent portion of a mixer  58  upstream of a straight mixing portion. A divergent diffuser  59  extends downstream from the mixer. The exemplary ejector is a controllable ejector having a control needle  60  ( FIG.  1 A ) and an actuator  61 . The actuator  61  shifts a tip portion  62  of the needle into and out of the throat section  63  of the motive nozzle  56  to modulate flow through the motive nozzle and, in turn, the ejector overall. The actuator  61  can be electrically driven (e.g., solenoid, stepper motor, or the like), mechanically driven, or driven by any suitable means known in the art. The actuator may be coupled to and controlled by a controller  400  ( FIG.  1   ; discussed below). Exemplary controllable ejectors are found in U.S Pat. 7178360 and International Publication WO2015/116480A1 . The exemplary needle has a fully extended fully closed/sealed/seated position/condition ( FIG.  1 A ) and a stepwise or continuous plurality of open positions/conditions (one shown in  FIG.  2 A ) retracted relative thereto. 
     In the operational modes depicted in  FIG.  1    and  FIG.  3   , the needle  60  is in its closed position to block/prevent ejector motive flow as depicted in  FIG.  1 A . In the operational mode depicted in  FIG.  2   , the needle is in an open position permitting a motive flow as depicted in  FIG.  2 A . 
     The separator  34  comprises a vessel  70  having an inlet port  72 , a vapor outlet  74 , and a liquid outlet  76 . A liquid phase may accumulate in a lower portion of the vessel and a vapor phase in its headspace. A compressor suction line  80  extends between vapor outlet  74  and the compressor suction port  40 . 
     Interconnecting the various components are a plurality of conduits (lines) and a plurality of additional components including valves, filters, strainers, and the like. As is discussed further below, the valves include a four-way switching valve  100  having a first port  102 . The first port serves as an inlet connected to the discharge port  42  of the compressor via an associated discharge line  110  to receive a flow  600  of compressed refrigerant. The switching valve  100  further comprises a second port  104 , a third port  106 , and a fourth port  108 . The exemplary switching valve is configured with a rotary valve element  112  (in housing  114 ) having passageways for establishing two conditions of operation: selectively placing the first port  102  in communication with one of the third port and fourth port while placing the second port  104  in communication with the other. Actuation of the valve element  112  between these two conditions, along with other valve actuations discussed below, facilitates transition between the respective three modes of operation of  FIGS.  1 - 3   . The switching valve may include an actuator (not shown) to effectuate switching the four-way switching valve  100  between the two conditions, such as a rotary actuator to drive rotation of the valve element  112  between the two conditions. 
       FIG.  1    further shows a controllable valve  120  (e.g., an on-off solenoid valve or, among examples, a motorized, pneumatic, hydraulic valve as may be the other bistatic on-off valves discussed) having ports  122  and  124  and a check valve (one-way valve)  130  having ports  132  and  134 . In an embodiment, the expansion device  28  and valve  120  are in a line  140  (one of the aforementioned conduits) between the two heat exchangers (an inter-heat exchanger line). The check valve  130  is in a branch line  144  extending from the separator liquid outlet  76  to the inter-heat exchanger line  140 . The line  144  and associated flowpath segment joins the inter-heat exchanger line  140  at a junction  146  between the expansion device  28  and controllable valve  120 . 
     A motive flow line  148  and associated flowpath segment extends from a junction  150  with the inter-heat exchanger line  140  to the ejector motive flow inlet  50 . Additionally, in an embodiment, additional lines and their associated flowpaths include: a line  152  from the port  104  to the ejector secondary inlet  52 ; a line  154  from the port  106  to the first heat exchanger first port (cooling mode inlet)  162 ; and a line  156  from the second heat exchanger second port (cooling mode outlet)  168  to the port  108 . 
     The  FIG.  1    cooling mode effectively disables the ejector (e.g., no motive flow) and relies on one or more of the other expansion devices. In this specific example, the expansion device  28  is utilized. Refrigerant compressed by the compressor  22  passes through the switching valve  100  to the heat exchanger  24 . The two exemplary heat exchangers each have two general places for flow inlet or outlet. In the heat exchanger  24 , these two places include a first port  162  coupled to receive refrigerant from the compressor, and a second port  164  positioned to pass refrigerant to the heat exchanger  26  (via the expansion device(s)  28 ). 
     In the  FIG.  1    cooling mode, the valve  120  is open allowing refrigerant to pass through the inter-heat exchanger line  140  from the second port  164  of the heat exchanger  24  through the expansion device  28  and to the port  166  of the heat exchanger  26 . With the ejector needle closed, no flow would pass along the motive flow line  148  to the ejector motive flow inlet  50 . This line  148  branches off from the inter-heat exchanger line  140  or flowpath between the valve  120  and the heat exchanger  26  so as to allow the diversion discussed below relative to the  FIG.  2    heating mode. 
     In the  FIG.  1    cooling mode, refrigerant exiting the second port  168  of the second heat exchanger  26  proceeds along line  156  and its associated flowpath segment to port  108  of the four-way valve  100  and, therefrom, through port  104  and line  152  to the ejector suction port  52 . This flow then continues through the ejector to the separator inlet  72 . However, the second heat exchanger  26  imposes a pressure drop. Thus, the pressure at the separator will be less than the pressure upstream of the second heat exchanger  26 . This pressure difference is essentially imposed across the check valve  130  in the opposite of its preferred flow direction. Accordingly, there will be no flow through the check valve  130  and the separator  34  will instead behave as an accumulator. 
     A defrost mode (not shown) for defrosting the heat exchanger  24  may be similar to the  FIG.  1    cooling mode. For example, an electric fan  169  that would normally drive an air flow across the heat exchanger  24  may be shut down to limit heat rejection in the heat exchanger  24 . This will raise the temperature of refrigerant delivered to the heat exchanger  24  to cause the heat exchanger  24  to reject heat to melt any ice buildup. An electric heater (not shown) downstream of the heat exchanger  26  along an air flowpath driven by an indoor fan  171  may heat the indoor air to avoid undesirable cooling of indoor air by the heat exchanger  26 . 
     The  FIG.  2    heating mode utilizes the ejector  32  as an ejector/expansion device. To switch into this mode (or the  FIG.  3    heating mode discussed below) the switching valve  100  is actuated from its  FIG.  1    condition to its  FIG.  2   /3 condition. In this condition, flow communication is established between the ports  102  and  108  and separate flow communication is established between the ports  104  and  106 . The result is that the flow  600  of compressed refrigerant is delivered from the compressor to the second heat exchanger  26  (via port  168 ) and refrigerant passing from the first heat exchanger  24  is passed to the ejector suction port  52 . In this implementation, the  FIG.  2    refrigerant flow through the heat exchanger  26  is in the opposite direction of that of  FIG.  1   . Similarly, the flow through the expansion device  28  and first heat exchanger  24  is in the opposite direction of that of  FIG.  1   . 
     In the  FIG.  2    heating mode, there is a motive flow through the ejector to entrain/drive the ejector suction flow. To provide such motive flow, the valve  120  is closed by the controller  400 . In the  FIG.  1    and  FIG.  3    modes, the valve  120  is open. In the  FIG.  2    mode, refrigerant passes along the discharge line  110  from the compressor discharge port to the port  102  of the valve  100  and then passes through port  108  to the line  156  extending to the heat exchanger  26 . 
     The  FIG.  2    mode may be used in situations where ejector heat pumps are efficient. For example, as noted above, this may be relevant where there is a relatively high temperature difference between indoor and outdoor conditions. 
     The  FIG.  3    heating mode effectively disables the ejector (e.g., no motive flow) and relies on the expansion device  28 . As noted above, his mode may be used when an ejector is less efficient such as when there is a low temperature difference between indoor and outdoor conditions. Relative to the  FIG.  2    mode, the valve  120  is open and the direction of pressure difference across the check valve  130  (higher pressure at port  132  than at port  134 ) means there is no flow through the separator liquid outlet (so that the separator serves as an accumulator). Accordingly, fluid passes directly from the heat rejection heat exchanger(s)  26  to the expansion device(s)  28  via the line  140 . 
       FIG.  1    further shows a controller  400 . The controller may receive user inputs from an input device (e.g., switches, keyboard, or the like) and sensors (not shown, e.g., pressure sensors and temperature sensors at various system locations). The controller may be coupled to the sensors and controllable system components (e.g., valves, the bearings, the compressor motor, vane actuators, and the like) via control lines (e.g., hardwired or wireless communication paths). The controller may include one or more: processors; memory (e.g., for storing program information for execution by the processor to perform the operational methods and for storing data used or generated by the program(s)); and hardware interface devices (e.g., ports) for interfacing with input/output devices and controllable system components. 
       FIGS.  4 - 6    show a second system  300  that may be otherwise similar to the system  20  in structure, manufacture, and operation.  FIG.  4   ,  FIG.  5   , and  FIG.  6    show modes similar to the respective  FIG.  1   ,  FIG.  2   , and  FIG.  3    modes. Actuation of the ejector needle to switch between the respective modes may be the same as that for the system  20 . Differences include the indoor heat exchanger  302  contrasting with the indoor heat exchanger  26 , the addition of a check valve  310  (discussed below) and the use of an on-off valve  320  in place of the valve  120 . The valve  320  (having ports  322  and  324 ) may be of similar structure to the valve  120  but is actuated in different circumstances. The indoor heat exchanger  302  has three ports  304 ,  306 , and  308 . 
     The inter-heat exchanger line  140  splits, having a trunk  140 - 1  extending from the outdoor heat exchanger  24  to the expansion device  28 . The inter-heat exchanger line  140  has a pair of branches  140 - 2  and  140 - 3 . The first branch  140 - 2  extends between a junction  141  with the second branch  140 - 3  and the port  304 . The check valve  310  is along this branch and associated flowpath leg. The check valve  310  is oriented to permit flow into the port  304  but not out from the port  304 . The second branch  140 - 3  and associated flowpath leg extends to the port  308 . The valve  320  is located along this branch and flowpath leg. Similarly, the junction  150  is along this branch and flowpath leg. 
     The heat exchanger  302  comprises an array or bundle of tubes (tube lengths/legs)  330  ( FIG.  4 A ). The tube array comprises tube lengths extending between a first side and a second side with respective connectors  332  and  334  joining tube legs at the first side and second side. The array of tubes has a first face  340  and a second face  342 . In the exemplary implementation, the face  340  is upstream in the direction of an airflow  344  (e.g., fan-forced) and the face  342  is downstream. The tubes are connected to several manifolds for inlet and/or outlet of refrigerant. A first manifold is formed by a distributor  350  whose inlet is formed by the port  304  and which becomes operational in the  FIG.  4    cooling mode. The distributor has individual branches  352  extending to associated tube legs. A second manifold  360  is a header in parallel with the distributor  350  and is relevant in heating modes ( FIGS.  5  and  6   ) wherein there is no flow through the inlet  304 . The exemplary header  360  has branches  362  connecting with the associated respective legs. In an embodiment, the header  360  is an existing header of a baseline heat exchanger and the distributor and its branches are added with the branches  352  patching into respective associated branches  362 . 
     In an embodiment, the tube array is divided into two respective sections  336  and  338 . In the heating modes, the header  360  serves to pass refrigerant sequentially from the section  336  to the section  338 . The sequential arrangement increases the refrigerant flowpath length of a pass through the indoor heat exchanger relative to the cooling mode. This increased length enables increased pressure drop corresponding to increased heat transfer duty for a given heat exchanger size and general construction. 
     The sequential flow is not needed in the cooling mode. In the cooling mode, the heat exchanger  302  is an evaporator where extra length would provide superheat instead of subcooling. But this would require a high penalty in heat exchanger size and pressure drop to the decreased density of the superheated refrigerant. In contrast heating mode subcooling does not involve such a penalty due to the high density of the subcooled refrigerant. 
     To allow such sequential passage, a third manifold  370  is formed as a second header including the ports  306  and  308 . The manifold  370  has associated branches  372  in communication with the adjacent legs of the heat exchanger. To facilitate the heating mode operation, the manifold  370  is divided by a check valve  380  into a first portion  374  and a second portion  376  (alternatively, these may be viewed as separate manifolds). 
     The check valve  380  is positioned to allow flow from the section  376  to the section  374  but not flow in the opposite direction. Accordingly, in the  FIG.  4    cooling mode, refrigerant passes from the compressor through the expansion device  28  as in the  FIG.  1    mode. As noted above, unlike the  FIG.  1    mode, the valve  320  is closed so that flow passes along the branch  140 - 2  through the check valve  310  to the inlet  304  and distributor  350 . With the closure of the ejector needle and the closure of the valve  320 , there is no flow to pass through the port  308  along the branch  140 - 3 . Accordingly, refrigerant passes through the distributor, through the lines  352 , and through both sections  336  and  338  of the tube bundle in parallel to the manifold  370 . The portion of the flow reaching the manifold section  376  will pass through the check valve  380  and then to the manifold section  374  and therefrom out the port  306  to ultimately pass to the ejector secondary port  52 . 
     In the heating modes ( FIGS.  5  and  6   ), flow enters the port  306 , passes through the section  374  ( FIG.  5 A ) of the manifold  370  to the section  336  of the tube bundle and, therefrom, into the manifold  360 . From the manifold  360 , the refrigerant passes back into the section  338  of the tube bundle and, therefrom, into the section  376  of the manifold  370  to then exit the port  308  to pass through the valve  320  to the expansion device  28 . The check valve  310  blocks (prevents) flow out of the port  304  and thus effectively blocks flow from the tube bundle into the distributor. 
     The positioning of the check valve  380  ( FIG.  5 A ) determines the relative sizes of the two sections  336  and  338  of the tube bundle. The illustrated example places five circuits in the bundle  336  and three in the bundle  338 . The size balance between the two sections will depend on the properties of the refrigerant, heat exchanger geometry, and the target operating temperature. The condensing of the refrigerant will be expected to be associated with a smaller number of circuits in the bundle section  338  which receives at least partially condensed refrigerant from the bundle section  336 . Thus, the separation into two sections and the alternate parallel and series flows provides additional refrigerant flowpath length when rejecting heat vs. absorbing heat. The extra length imposes extra pressure difference. When rejecting heat, the pressure drop impacts performance less than when absorbing heat. 
     A control routine may be programmed or otherwise configured into the controller  400 . The routine provides automatic selection of which of the two heating modes to use based on sensed conditions. In a reengineering of a baseline heat pump system, this selection may be superimposed upon the controller’s normal programming/routines (e.g., providing the basic operation of baseline system to which the foregoing mode control is added). In one example, the switching of the two heating modes can be controlled responsive only to the outdoor ambient temperature sensor  402  and/or pressure sensors (transducers)  404  (positioned to sense pressure at the ejector outlet  54 ) and  408  (positioned to sense pressure at the secondary inlet  52 ), and/or the compressor speed signal (from a sensor  406  or logic internal to the controller). The controller may determine a pressure difference between the pressure sensors  404  and  408 . In an exemplary control routine, the ejector can be enabled during the heating mode once the temperature sensor  402  reading is below a threshold (e.g., 32° F. (0° C.)), and/or once the pressure difference is less than a certain target number (e.g., 2 psid (14 kPa)), and/or once the compressor reaches its minimum speed. Although a single compressor may be used, two are shown and may be used according to known methods for optimizing load handling. 
     In the  FIG.  2    or  FIG.  4    ejector modes, the ejector needle  60  may be positioned by the controller controlling the actuator  61  responsive to a control algorithm based on operating pressure sensed by a sensor  410  (e.g., positioned to measure pressure between motive inlet and the indoor heat exchanger  26 ). To optimize ejector efficiency, the pressure at that location can be regulated by adjusting the ejector needle with the objective of providing the optimum degree of refrigerant subcooling leaving the heat exchanger  26 , through port  166 . This may be done according to known needle control procedures for ejector refrigeration systems. 
       FIGS.  7 - 9    show a third system  600  that may be otherwise similar to the systems  20  and  300  in structure, manufacture, and operation.  FIGS.  7 ,  8 , and  9    show modes similar to the respective  FIG.  1   /4, ⅖, and 3/6 modes. Actuation of the ejector needle to switch between the respective modes may be the same as that for the systems  20  and  300 . Differences include the outdoor heat exchanger  602  contrasting with the outdoor heat exchanger  26  in similar fashion to the contrasting of the indoor heat exchanger  302  with the indoor heat exchanger  26 . 
     Specifically, the example outdoor heat exchanger  602  has manifolds  620  and  622  forming headers for an array or bundle of tubes  630  ( FIG.  7 A ). The tubes have similar connectors  632 ,  634  to the  FIG.  4 A  heat exchanger  320 . Other similarities are not discussed. In similar fashion to the manifold/header  370 , the manifold/header  620  is divided by a check valve  680  into a first portion or section  674  and a second portion or section  676  (alternatively, these may be viewed as separate manifolds). The check valve  680  is positioned to allow flow from the second portion  676  to the first portion  674  but not flow in an opposite direction. The end of the first portion  674  opposite the check valve  380  forms the port  162  or is otherwise open thereto. The end of the second portion  676  opposite the check valve  680  is in communication with an oppositely-oriented second check valve  682 . Thus, the check valves  680  and  682  are positioned to permit outlet flow from their respective ends of the second portion  676  but not inlet flow. Inlet flow to the second portion  676  is limited to flow from the array or bundle of tubes  630 . 
     In example implementations, the outdoor heat exchanger  602  is configured as an updraft draw-through heat exchanger where the fan is at the top and the bundle  630  extends around a lateral periphery with the manifolds  620 ,  622  vertically oriented to form a pair of headers. The headers  620 ,  622  extend vertically close to each other (e.g., near one corner of a rounded square footprint outdoor heat exchanger) with the tube bundle either being generally the major arc of a circle or a rounded corner square (with inter-header gap at one corner). The headers  620 ,  622  may be formed of pipestock/tubestock. For example, the check valve  680  may be a conventional check valve fitting inline between respective pieces (e.g., straight pieces) of pipestock/tubestock forming the manifolds  674  and  676 . The valves  682  and  684  may be at ends of the pieces forming manifolds  676  and  622  or at ends of elbows between those and the junction (e.g., Y fitting or T fitting ) forming or leading to the port  164 . 
     The manifold  622  has a closed end and an opposite end in communication with a check valve  684  positioned to permit inflow to the header  622  but not outflow from the header. The opposite ends of the check valves  682  and  684  are connected in parallel to the port  164 . The groups of tubes forming the section  638  connect to the manifold  676 ; whereas, groups of tubes forming the section  636  connect to the manifold  674 . 
     Thus, in the  FIG.  7    cooling mode, the inlet flow passes through the port  162  into the manifold  674  and then through the associated tubes of the section  636  into the manifold  622 . Outflow from the manifold  622  to the port  164  is blocked by the check valve  684 . Accordingly, the flow then passes through the tubes of the section  638  to the manifold  676  and exits to the outlet  164  via the check valve  682 . 
     In contrast, in the  FIG.  8   /8A heating mode (otherwise similar to the  FIG.  5    heating mode), flow enters the port  164 . The check valve  682  blocks inflow to the manifold  676 ; whereas, the check valve  684  allows inflow to the manifold  622 . Flow can exit the manifold  622  through both tube bank sections  636  and  638 . Flow passing through the section  636  passes directly to the manifold  674  and out the outlet  162 . Flow passing through the section  638  passes to the manifold  676 , and therefrom through the check valve  680  into the manifold  674  to exit the port  672 . 
     Thus, in the  FIG.  7    cooling mode, the flow through the outdoor heat exchanger  602  is sequential from the inlet  162 , through the manifold  674 , the tubes forming the section  636 , the manifold  622 , through the tubes forming the section  638 , the manifold  676  and then the check valve  682  to the outlet  674 . The series flow increases the length of flowpath within the heat exchanger  602  experienced by the refrigerant and thus increases subcooling. Similarly, the flow restriction (of first using the majority section  636  but then using a smaller section  638 ) increases pressure drop (to further increase subcooling) vs using both groups in parallel. In contrast, the  FIG.  8    heating mode has flow through both groups in parallel with the flow through the section  636  being in opposite direction to the cooling mode and the flow through the section  638  being in the same direction as in the cooling mode. 
     The positioning of the check valve  680  ( FIG.  7 A ) determines the relative sizes of the two sections  636  and  638  of the tube bundle. In the  FIGS.  7 - 9    embodiment, the size of the section  636  is greater than that of the section  638 . Specifically, each section is composed of series groups of tubes between the associated manifolds. The section  636  has a larger number of groups (nine in the illustration) than does the section  638  (two in the illustration). The size balance between the two sections will depend on the properties of the refrigerant, heat exchanger geometry, and the target operating temperature. The condensing of the refrigerant will be expected to be associated with a smaller number of circuits in the bundle section  638  which receives partially condensed refrigerant from the bundle section  636  in the cooling mode. 
     As noted above, a similar situation attends the indoor heat exchanger  302 . The indoor heat exchanger  302  has flow in parallel through the sections  336  and  338  in the  FIG.  4    cooling mode and series flow from the section  336  to the section  338  in the heating mode ( FIG.  5 A ). The example indoor heat exchanger  302  has a more even balance of groups (lower size ratio of the groups) in the two sections with five groups in the example section  336  and three groups in the example section  338 . This is due to significant geometric considerations when comparing indoor heat exchanger  302  and outdoor heat exchanger  602 . This includes considerations of size and airflow. The outdoor heat exchanger can be larger. Particularly, when fixed speed fans are used, the outdoor heat exchanger can have greater airflow. 
     Additionally, the example outdoor heat exchanger  602  lacks the distributor  350  of the indoor heat exchanger  302 . This is because in the cooling mode the flow downstream of the expansion device  28  is two-phase so the distributor distributes uniformly to the indoor heat exchanger. In the ejector heating mode, the expansion device does not expand refrigerant so that relatively “low quality” (mostly liquid) or all liquid refrigerant enters the outdoor heat exchanger  602 . 
     In the ejector heating mode of  FIG.  8   , the liquid refrigerant leaves the separator  70  through port  76  and said liquid refrigerant is evenly distributed into the outdoor heat exchanger (acting as an evaporator)  602  via port  164 . In the outdoor heat exchanger it is fully vaporized before leaving via port  162 . 
     In  FIG.  9   , higher quality two-phase flow enters at port  164  instead of the  FIG.  8    lower quality (e.g., single phase liquid). Inefficiency due to maldistribution of the two-phase flow entering the heat exchanger is minor given lower expected use of the  FIG.  9    mode relative to the  FIG.  8    mode. In some implementations, the control may be configured to never use the  FIG.  9    mode. 
     The use of “first”, “second”, and the like in the description and following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as “first” (or the like) does not preclude such “first” element from identifying an element that is referred to as “second” (or the like) in another claim or in the description. 
     Where a measure is given in English units followed by a parenthetical containing SI or other units, the parenthetical’s units are a conversion and should not imply a degree of precision not found in the English units. 
     One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing basic system, details of such configuration or its associated use may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims.