Ejector Heat Pump Operation

Abstract

A method for operating a heat pump (20; 300) includes operating in a cooling mode wherein heat is absorbed by refrigerant in the indoor heat exchanger (26) and rejected by refrigerant in the outdoor heat exchanger (24). The heat pump switches to operation in a heating mode wherein heat is rejected by refrigerant in the indoor heat exchanger, heat is absorbed by refrigerant in the outdoor heat exchanger, and there is an ejector (60) motive flow and ejector secondary flow. In the heating mode a refrigerant pressure (PH) or temperature (TL) is measured and, responsive to the measured refrigerant pressure or temperature, at least one of a fan speed is changed and a needle (132) of the ejector is actuated.

Claims

1. A method for operating a heat pump (20; 300), the heat pump comprising: a compressor (22); an indoor heat exchanger (26); an outdoor heat exchanger (24); and an ejector (60), the method comprising: operating in a cooling mode wherein heat is absorbed by refrigerant in the indoor heat exchanger and rejected by refrigerant in the outdoor heat exchanger; switching to operation in a heating mode wherein heat is rejected by refrigerant in the indoor heat exchanger, heat is absorbed by refrigerant in the outdoor heat exchanger, and there is an ejector motive flow and ejector secondary flow; and in the heating mode: measuring a refrigerant pressure or temperature; and responsive to the measured refrigerant pressure or temperature: changing a fan speed speed; and optionally actuating a needle, if any, of the ejector.

2. The method of claim 1 wherein: the ejector is a non-controllable ejector.

3. The method of claim 1 wherein: in the cooling mode there is no motive flow to the ejector.

4. The method of claim 1 wherein: in the heating mode, refrigerant passes from the indoor heat exchanger as the ejector motive flow.

5. The method of claim 1 wherein: in the cooling mode, flow passes through an expansion device (98) to the indoor heat exchanger; and in the heating mode, there is no flow through the expansion device.

6. The method of claim 1 wherein: in the cooling mode, flow passes through an expansion device (98) to the indoor heat exchanger; and in the heating mode, flow passes through the expansion device to the outdoor heat exchanger.

7. The method of claim 1 wherein in the heating mode: the measuring of a refrigerant pressure is a measuring of a discharge pressure of the compressor.

8. The method of claim 7 wherein in the heating mode: the changing the fan speed occurs and comprises increasing fan speed when the measured pressure exceeds a first threshold pressure (P.sub.high) and decreasing fan speed when the measured pressure falls below a second threshold pressure (P.sub.low).

9. The method of claim 7 wherein in the heating mode: the actuating the needle of the ejector occurs and comprises retracting the needle when the measured pressure exceeds a first threshold pressure (P.sub.high) and extending the needle when the measured pressure falls below a second threshold pressure (P.sub.low).

10. A heat pump (20; 300) having a controller (200) configured to perform the method of claim 1.

11. The heat pump (20) of claim 10 wherein the controller is configured so that: in the cooling mode, flow passes through an expansion device (98) to the indoor heat exchanger; and in the heating mode, there is no flow through the expansion device.

12. The heat pump (300) of claim 10 wherein the controller is configured so that: in the cooling mode, flow passes through an expansion device (98) to the indoor heat exchanger; and in the heating mode, flow passes to the outdoor heat exchanger without the need of an expansion device.

13. The heat pump (20; 300) of claim 10 wherein the controller is configured so that: the changing the fan speed comprises increasing fan speed when the measured pressure exceeds a first threshold pressure (P.sub.high) and decreasing fan speed when the measured pressure falls below a second threshold pressure (P.sub.low).

14. The heat pump (20; 300) of claim 10 wherein the controller is configured so that: the actuating the needle of the ejector comprises retracting the needle when the measured pressure exceeds a first threshold pressure (P.sub.high) and extending the needle when the measured pressure falls below a second threshold pressure (P.sub.low).

15. The heat pump (20; 300) of claim 10 wherein there is no expansion device in parallel with the ejector.

16. A heat pump (20; 300), the heat pump comprising: a compressor (22); an indoor heat exchanger (26); a fan (38) positioned to drive an air flow (34) across the indoor heat exchanger; an outdoor heat exchanger (24); an ejector (60); a controller (200), at least one of the ejector being a controllable ejector and the fan being a variable speed fan controlled by the controller; and means for switching between: a cooling mode wherein heat is absorbed by refrigerant in the indoor heat exchanger and rejected by refrigerant in the outdoor heat exchanger; and a heating mode wherein heat is rejected by refrigerant in the indoor heat exchanger, heat is absorbed by refrigerant in the outdoor heat exchanger, and there is an ejector motive flow and ejector secondary flow, wherein the controller (200) is configured to in the heating mode: measure a refrigerant pressure or temperature; and responsive to the measured refrigerant pressure or temperature, change the fan speed and, optionally, actuate a needle, if any, of the ejector.

17. The heat pump (20) of claim 16 wherein the controller is configured so that: in the cooling mode, flow passes through an expansion device (98) to the indoor heat exchanger; and in the heating mode, there is no flow through the expansion device.

18. The heat pump (300) of claim 16 wherein the controller is configured so that: in the cooling mode, flow passes through an expansion device (98) to the indoor heat exchanger; and in the heating mode, flow passes to the outdoor heat exchanger without the need of an expansion device.

19. The heat pump (20; 300) of claim 16 wherein the controller is configured so that: the changing the fan speed comprises increasing fan speed when the measured pressure exceeds a first threshold pressure (P.sub.high) and decreasing fan speed when the measured pressure falls below a second threshold pressure (P.sub.low).

20. The heat pump (20; 300) of claim 16 wherein the controller is configured so that: the actuating the needle of the ejector comprises retracting the needle when the measured pressure exceeds a first threshold pressure (P.sub.high) and extending the needle when the measured pressure falls below a second threshold pressure (P.sub.low).

21. The heat pump (20; 300) of claim 16 wherein at least one of: there is no expansion device in parallel with the ejector; and the ejector is a non-controllable ejector.

22. A method for operating a heat pump (20; 300), the heat pump comprising: a compressor (22); an indoor heat exchanger (26); an outdoor heat exchanger (24); and an ejector (60), method comprising: operating in a cooling mode wherein heat is absorbed by refrigerant in the indoor heat exchanger and rejected by refrigerant in the outdoor heat exchanger and there is no motive flow to the ejector; switching to operation in a heating mode wherein heat is rejected by refrigerant in the indoor heat exchanger, heat is absorbed by refrigerant in the outdoor heat exchanger, and there is an ejector motive flow and ejector secondary flow; and in the heating mode: measuring a refrigerant pressure or temperature; and responsive to the measured refrigerant pressure or temperature, at least one of changing a fan speed and actuating a needle, if any, of the ejector.

23. The method of claim 22 wherein: the ejector is a non-controllable ejector.

24. A method for operating a heat pump (20; 300), the heat pump comprising: a compressor (22); an indoor heat exchanger (26); an outdoor heat exchanger (24); and an ejector (60), the method comprising: operating in a cooling mode wherein heat is absorbed by refrigerant in the indoor heat exchanger and rejected by refrigerant in the outdoor heat exchanger and flow passes through an expansion device (98) to the indoor heat exchanger; switching to operation in a heating mode wherein heat is rejected by refrigerant in the indoor heat exchanger, heat is absorbed by refrigerant in the outdoor heat exchanger, and there is an ejector motive flow and ejector secondary flow and there is no flow through the expansion device; and in the heating mode: measuring a refrigerant pressure or temperature; and responsive to the measured refrigerant pressure or temperature, at least one of changing a fan speed and actuating a needle, if any, of the ejector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a schematic view of a first heat pump system in a heating mode.

[0033] FIG. 1A is a view of a fixed ejector in the first heat pump system.

[0034] FIG. 1B is a view of an alternative controllable ejector in the first heat pump system.

[0035] FIG. 2 is a schematic view of the first heat pump system in a cooling mode.

[0036] FIG. 3 is a control flowchart for switching between the heating mode, the cooling mode, and a defrost mode.

[0037] FIG. 4 is a control flowchart for operation within the heating mode.

[0038] FIG. 5 is a schematic view of a second heat pump system in a heating mode.

[0039] FIG. 6 is a schematic view of the second heat pump system in a cooling mode.

[0040] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a vapor compressor system 20 which, in one group of examples, is a commercial type heat pump unit. The system 20, along a vapor compression flowpath, has: a compressor 22; an outdoor heat exchanger 24; and an indoor heat exchanger 26. The exemplary heat exchangers 24 and 26 are refrigerant-air heat exchangers each having a respective associated fan 28, 30 for driving a respective airflow 32, 34 across the heat exchanger to exchange heat with refrigerant passing along a leg of the refrigerant flowpath through the heat exchanger. Exemplary refrigerant is an HFC such as R410A, R134a, and the like.

[0042] Exemplary fans are electrically-powered fans having respective electric motors 36, 38.

[0043] The compressor 22 has a suction or inlet port 40 and a discharge or outlet port 42. The compressor also includes an electric motor (not shown) for driving working elements of the compressor to compress low pressure refrigerant received through the suction port and discharge high pressure refrigerant from the discharge port. FIG. 1 also shows a control system or controller 200 coupled to control operation of the fan motors and compressor motor and other controllable system components to allow operation in a heating mode and a cooling mode.

[0044] In the heating mode, heat is rejected by refrigerant in the indoor heat exchanger 26 and absorbed by refrigerant in the outdoor heat exchanger 24. In the cooling mode, heat is rejected by refrigerant in the outdoor heat exchanger 24 and absorbed by refrigerant in the indoor heat exchanger 26.

[0045] The controllable components for mode switching include one or more valves. The one or more valves include an exemplary four-way valve 50 used to switch between the modes.

[0046] In an exemplary configuration as a residential heat pump, the outdoor heat exchanger and compressor are in an outdoor unit and the indoor heat exchanger is in an indoor unit. In another exemplary configuration as a commercial heat pump, both the outdoor and indoor heat exchangers and compressor are in one outdoor unit. Components of the control system may be distributed throughout as is known in the art (e.g., a thermostat 230 indoors while main control portions are outdoors in the outdoor unit). As so far described, the system is representative of several of many baseline systems to which the further teachings below may be applied.

[0047] The FIG. 1 system includes an ejector 60. The exemplary ejector 60 (FIG. 1A) is formed as the combination of a motive (primary) nozzle 62 nested within an outer member 64. The motive (primary) flow inlet 66 is the inlet to the motive nozzle. The outlet 68 is the outlet of the outer member 64. The motive refrigerant flow enters the inlet 66 and then passes into a convergent section 114 of the motive nozzle. It then passes through a throat section 116 and an expansion (divergent) section 118 through an outlet (exit) 120 of the motive nozzle. The motive nozzle accelerates the flow and decreases the pressure of the flow.

[0048] The secondary flow inlet 70 forms an inlet of the outer member 64. The pressure reduction caused to the motive flow by the motive nozzle helps draw the secondary flow into the outer member. The outer member includes a mixer having a convergent section 124 and an elongate throat or mixing section 126. The outer member also has a divergent section or diffuser 128 downstream of the elongate throat or mixing section 126. The motive nozzle outlet 120 is positioned within the convergent section 124. As the motive flow exits the outlet 120, it begins to mix with the secondary flow with further mixing occurring through the mixing section 126 which provides a mixing zone. Thus, respective motive and secondary flowpaths extend from the motive flow inlet and secondary flow inlet to the outlet, merging at the exit.

[0049] The exemplary ejector 60 is a fixed or uncontrolled ejector lacking a needle or similar means for throttling the motive nozzle. Alternative embodiments comprising a controlled ejector are discussed below. The ejector secondary inlet 70 is coupled to receive refrigerant from the outdoor heat exchanger in the FIG. 1 heating mode. In the example shown, the four-way valve 50 has an inlet 51 positioned to receive compressed refrigerant from a flowpath leg or segment 520 from the compressor discharge port 42. Of the three remaining ports, a port 52 is coupled to the outdoor heat exchanger via flowpath leg 532, a port 53 is coupled to the ejector secondary port 70 via flowpath leg 534, and a port 54 is coupled to the indoor heat exchanger via flowpath leg 522. In the FIG. 1 heating mode, the valve element of the four-way valve provides communication between the ports 52 and 53 on the one hand and 51 and 54 on the other hand. Thus, compressed refrigerant is passed to a port 56 of the indoor heat exchanger and refrigerant from a port 55 on the outdoor heat exchanger is passed to the ejector secondary inlet 70.

[0050] The refrigerant compressed by the compressor and received by the indoor heat exchanger is condensed in the indoor heat exchanger. The condensed refrigerant passes from a port 57 on the indoor heat exchanger along a flowpath leg 524 to the motive inlet 66. The flowpath leg 524 is a controlled flowpath leg controlled by the controller 200 using a valve 72 (e.g., a solenoid valve). The exemplary bistatic solenoid valve provides simple on-off control. The combined flow discharged from the ejector outlet 68 passes along a flowpath leg 526 to a vessel 80 which, in this mode, functions as a separator. The vessel 80 has an inlet port 81 receiving the combined flow, a first outlet 82 returning vapor via a flowpath leg 528 to the compressor suction port 40 and a second outlet port 83 passing refrigerant via a flowpath leg 530 (having sublegs or segments 530-1 or 530-2) to a port 58 on the evaporator through a flowpath segment. The flowpath leg 530 includes a check valve 88 to ensure that flow can only exit the port 83. An additional flowpath leg 536 is inoperative in this mode. The additional flowpath leg or branch 536 extends from a tee 94 along the leg 530 (at the junction of legs 530-1 and 530-2) to a port 59 (inlet port) on the indoor heat exchanger. This port is specially configured for two phase flow and may comprise a bundle of capillary tubes.

[0051] Notably, the leg 536 includes a check valve 96 ensuring only flow to the indoor heat exchanger. Thus, in an operating condition wherein there is higher pressure at the port 59 than at the tee 94, there will be no flow along this leg 536. The leg 536 further includes an expansion device 98 (e.g., an electronic expansion valve) downstream of the check valve 96 and a distributor 100 downstream of the expansion device. Downstream of the expansion valve 98, two phase refrigerant is distributed through the distributor 100 to many small tubes (not shown) and fed to each coil circuit of the indoor heat exchanger; whereas port 57 is a manifold outlet for single phase refrigerant. A filter 102 may also be located in the leg 536 (e.g., upstream of the check valve to most efficiently filter liquid refrigerant). Operation of this leg 536 in the cooling mode is discussed further below.

[0052] Operation may be responsive to multiple sensors coupled to the controller 200. The controller may receive user inputs from input devices (e.g., switches, keyboard, or the like such as end user-controllable thermostat switches and manufacturer/installer controllable switches-(not shown)) and sensors (both shown and 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 fan motors, 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. The controller hardware may represent existing baseline hardware. The controller programming may represent a baseline modified to provide the operation discussed below. FIGS. 3 and 4 show portions of a control routine which may be programmed or otherwise configured into the controller.

[0053] FIG. 1 shows a low side pressure sensor 220 and a high side pressure sensor 222 (e.g., both piezoelectric-type). A refrigerant temperature sensor 224 (e.g., thermistor-type) measures the temperature of refrigerant discharged from the indoor heat exchanger to the ejector motive inlet. Additional exemplary temperature sensors (e.g., thermistor-type) include an outdoor coil temperature sensor 226 that measures surface temperature of the condenser coil (Tem) and an indoor temperature sensor 228 to measure indoor temperature (T.sub.zone) in the zone being climate controlled (e.g., integrated with a thermostat/user interface unit 230). Additional temperature and pressure sensors may be located throughout as is known in the art for controlling basic system function. Most notably, an indoor air inlet temperature sensor.

[0054] FIG. 2 shows the cooling mode of the system 20 wherein the four-way valve 50 has been switched to place ports 51 and 52 in communication and thereby direct high pressure compressor discharge to the port 55 of the outdoor heat exchanger. Thus, flow through the legs 532 and 530-2 is in the opposite direction of the FIG. 1 heating mode. The check valve 88, however, blocks reverse flow along the leg 530-1. Accordingly, flow may proceed along the leg 536 through the filter 102, check valve 96, expansion device 98, and distributor 100 to the port 59. Flow exits the indoor heat exchanger by the port 56 and passes along the leg 522 in the opposite direction to the FIG. 1 heating mode. The four-way valve 50 places the ports 53 and 54 in communication so that the flow proceeds through the leg 534.

[0055] However, the flow through the leg 534 does not mix with any flow through the leg 524. The controller has shut the valve 72 to block flow along the leg 524. Thus, flow on the leg 534 proceeds through the ejector along the leg 526 as in the first mode.

[0056] An additional mode (not illustrated) is a defrost mode wherein, as in the cooling mode, compressed refrigerant is fed directly to the outdoor heat exchanger to defrost. One potential difference relative to the cooling mode is that the outdoor fan may be shut off. For example, the outdoor fan 36 may be shut off to reduce heat extraction by cold outdoor air from the system and thus accelerate the defrosting process (e.g. hot gas delivered to the outdoor heat exchanger).

[0057] Switching between the heating, cooling, and defrost modes may reflect a prior art or modified logic. In an exemplary FIG. 3 logic 400, four set temperatures are involved. The logic comprises operating the system to keep indoor air temperature (T.sub.zone) between a high temperature (the cooling control point T.sub.set1) and a low temperature (the heating control point T.sub.set2). These temperatures may be entered by a user such as on a thermostat which may also include a temperature sensor for measuring T.sub.zone. Alternative temperature for measuring T.sub.zone may be along a flowpath for the airflow 34 upstream of the indoor heat exchanger 26. In one example, T.sub.set1 may be set to 77° F. (25° C.) while T.sub.seil2 may be set to 68° F. (20° C.).

[0058] The third set temperature (T.sub.set3) is used to determine whether to go into defrost mode. Exemplary T.sub.set3 is set at the factory or by an installation technician. An exemplary T.sub.set3 is 28F. The fourth set temperature (T.sub.set4) is used to determine whether to end defrosting and back to the heating mode. An exemplary T.sub.set4 is 68° F. (20° C.). Exemplary T.sub.set4 is also set at the factory or by an installation technician. When the system enters the defrosting mode, the controller continuously compares condenser surface temperature (T.sub.con) to T.sub.set4 to determine whether to continue or end the defrosting mode.

[0059] The exemplary FIG. 3 decision matrix or logic 400 involves, after a start 402 determining 404 whether T.sub.zone is within the target range. If no, the logic recursively determines 406, 410 whether T.sub.zone is greater than T.sub.set1 and if yes running 408 in the cooling mode. If no, then the controller determines 412, 416 whether T.sub.zone is less than T.sub.set2 and if yes running 414 in the heating mode. If T.sub.zone is between those two set temperatures, then the logic loops back repeating until the controller determines T.sub.zone is out of that target range (then respectively stopping 418, 420 the cooling mode or heating mode and looping back to the determination 404. If T.sub.zone is out of the range, the controller runs the system in either heating mode or cooling mode. In the heating mode, the control has steps for determining whether to start defrosting and whether to end defrosting.

[0060] The controller places 432 the system in the defrost mode when the controller determines 430 that the temperature T.sub.con measured by the outdoor coil temperature sensor 226 falls below T.sub.set3. The controller ends 436 the defrost mode and returns the system returns to heating mode when it determines 434 that the temperature rises above T.sub.set4. As is discussed below, parameters of operation while in the heating mode may be controlled by the controller controlling fan speed of one or both fans. This is particularly the case for fixed ejectors such as FIG. 1A. If a controllable ejector is used, throttling of the ejector (e.g., via control of its needle) may alternatively or additionally be used with the same basic logic. FIG. 1B shows controllability provided by a needle valve 130 having a needle 132 and an actuator 134. The actuator 134 shifts a tip portion 136 of the needle into and out of the throat section 116 of the motive nozzle 100 to modulate flow through the motive nozzle and, in turn, the ejector overall. Exemplary actuators 134 are electric (e.g., solenoid or the like). The actuator 134 may be coupled to and controlled by the controller 200.

[0061] In the exemplary heating mode, the fan and/or ejector control is based upon the input received from the pressure sensors 220 and/or 222. In the illustrated FIG. 4 example, only the sensor 222 is used. This is repeatedly compared to two preset reference temperatures P.sub.high and P.sub.low. These two reference pressures represent limits selected based on experimentation or modeling to correspond to a range where the ejector offers improved performance. P.sub.h is constantly compared to P.sub.high and, if greater, the airflow is increased and/or the ejector needle retracted to open up the ejector. In one example, only the indoor airflow is increased (and not the outdoor airflow). In another example, both airflows are increased. Increasing only the indoor airflow is particularly relevant in legacy systems that have only a single speed outdoor fan. Whereas, increasing both airflows offers ability to tailor while maintaining desired minimum indoor airflows for purposes such as temperature maintenance or air quality. The increase in airflow may be achieved by the controller positively incrementing fan speed by a given amount.

[0062] FIG. 4 shows an exemplary logic 450 of heating mode operation utilizing fan and/or ejector control as discussed above. High side refrigerant pressure P.sub.h is impacted by indoor return air temperature, outdoor air temperature, the indoor air flow, and outdoor air flow (outdoor fan speed and air flow having a lesser effect than indoor). With only fan control, high side pressure is maintained in the optimal range unless the fan speed reaches its minimum or maximum. High side pressure may be similarly controlled by the ejector needle control. High side refrigerant pressure P.sub.H may be measured at the compressor discharge (sensor 222), condenser outlet, or ejector motive inlet or anywhere therebetween. Fan and or ejector control is by checking 454 and ensuring the compressor is on. If the controller determines 456, 460 P.sub.H is higher than the set upper limit (P.sub.high), the controller increases 458 indoor or outdoor air flow or ejector motive flow by increasing the indoor fan speed or retracting the control needle. The simplest embodiment has a non-controllable ejector and the indoor fan is the sole control method for high-side pressure (e.g., outdoor fan may be a fixed speed fan). If the controller determines 462, 466 P.sub.H is lower than the set low limit (P.sub.low), the controller reduces 464 air flow or ejector motive flow by decreasing indoor fan speed or inserting the needle.

[0063] Once the high-side pressure P.sub.H is within the optimal pressure range (i.e., between P.sub.low and P.sub.high) the fan speed and/or the needle position is maintained without changing.

[0064] FIG. 5 shows an alternate system 300 which differs from the system 20 in enabling ejector 60 to be utilized in the cooling mode with a similar control of fan(s) and/or the ejector to that of the heating mode. The bypass leg 536 of FIG. 1 and flowpath legs 524 and 530 are modified. The leg 530 is replaced by leg 550 in the FIG. 5 mode having segments or legs 550-1, 550-2, 550-3. The filter 102 and EXV 98 are shifted to the leg 550-1 from the FIG. 1 bypass leg 536. The FIG. 1 bypass leg 536 is replaced with a bypass leg 556 still including the distributor 100 and extending from an exemplary three-way valve 150 at the junction of the legs 550-1 and 550-2.

[0065] In the FIG. 5 heating mode, the controller 200 maintains the three-way valve providing communication from the leg 550-1 to the leg 550-2 and preventing flow through the leg 556. The bistatic two-way valve 72 of FIG. 1 is also replaced by a second three-way valve 160. Flowpath legs 560-1 and 560-2 respectively meet at the three-way valve 160 and combine to replace the FIG. 1 flowpath leg 524. However, again a further bypass leg 562 is also provided from a tee or junction 160 at the junction of legs 550-2 and 550-3. Again in the FIG. 5 mode, the controller maintains no flow along the leg 562.

[0066] In the FIG. 6 cooling mode, however, the controller has switched the states of the two valves 150 and 160 to block flow along the leg 550-2 and, thus: (a) pass flow from the leg 550-1 through the bypass leg 556; and (b) pass flow from the outdoor heat exchanger port 58 along the leg 550-3 to the leg 562 and therefrom 560-2 to the ejector motive inlet 66. Similarly, the same high side pressure control logic may apply to the cooling mode where the ejector is not bypassed. For example, in the FIG. 6 system there may be different threshold pressures than are used in heating.

[0067] Further variations may include multiple staged compressors.

[0068] Thus, in the heating mode, the method proposed (e.g. adjusting condenser flow rate, ejector needle control) may provide low cost means of operation to solve the loss of ejector motive pumping potential (i.e., performance) when low or very low potential of work recovery operation is experienced (e.g., heating at ambient temperatures >30° F. (>−1.1° C.)). Under these cases and in prior art a parallel expansion device (e.g., orifice, TXV, EXV) usually is utilized to bypass the ejector. This may eliminate the need for a ejector bypass with an expansion device.

[0069] As an alternative, a temperature may be used as a proxy. For example the temperature T.sub.L may serve as a rough proxy for P.sub.H. One can also control based on T.sub.sat which is the saturation temperature and provides a more direct proxy for P.sub.H. This may be measured by a temperature sensor (not shown) at an intermediate location along the condenser 30 where there is expected to be two-phase refrigerant. In the flowchart calculations, corresponding reference temperatures may replace P.sub.high and P.sub.low.

[0070] The system may be made using otherwise conventional or yet-developed materials and techniques. Exemplary temperature sensors are thermocouples, thermistor-type sensors, and resistance temperature detectors. Exemplary pressure sensors are diaphragm-type or bellows-type. This may include retrofitting existing systems or reengineering existing system configurations.

[0071] 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.

[0072] 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.

[0073] 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.