TURBOEXPANSION REVERSIBLE HEAT PUMP CYCLE

TECHNICAL FIELD

[0001]This disclosure relates to heat pump cycles.

BACKGROUND

[0002]Heat spontaneously flows from a region of higher temperature to a region of lower temperature. Heat does not spontaneously flow from lower temperature to higher, but heat can be made to flow in this direction if work is performed. A heat pump is a device that uses work to transfer heat from a cool space to a warm space by transferring thermal energy using a refrigeration cycle, which cools the cool space and warms the warm space. For example, in cold weather, a heat pump can transfer heat from the cool outdoors to warm the inside of a house, building or enclosure (e.g., an electronics enclosure, server room or other type of enclosure). As another example, in warm weather, a heat pump can transfer heat from the inside of a house, building or enclosure to the warmer outdoors. Heat pumps are also used in industrial heating/cooling and energy transfer applications, such as steam flash recovery, absorption, solvent recovery, product drying, and others.

SUMMARY

[0003]This disclosure describes technologies relating to heat pump cycles. Certain aspects of the subject matter described can be implemented as a heat pump system. The heat pump system includes a first heat exchanger, a compressor, a second heat exchanger, a first flowline, a throttle valve, a second flowline, and a flow-through electric generator. The first heat exchanger is configured to exchange heat between a working fluid and a first environment in which the first heat exchanger is disposed. The compressor is in fluid communication with the first heat exchanger. The compressor is configured to pressurize the working fluid. The second heat exchanger is in fluid communication with the compressor. The second heat exchanger is configured to exchange heat between the working fluid and a second environment in which the second heat exchanger is disposed. The second environment is different from the first environment. The first flowline connects the first heat exchanger and the second heat exchanger. The first flowline is configured to flow the working fluid. The throttle valve is installed on the first flowline. The throttle valve defines an adjustable flow restriction configured to reduce a pressure of a first portion of the working fluid as the first portion of the working fluid flows through the throttle valve. The second flowline connects the first heat exchanger and the second heat exchanger around the throttle valve. The second flowline provides an alternative flow path for a second portion of the working fluid to bypass the throttle valve. The flow-through electric generator is installed on the second flowline. The flow-through electric generator includes a turbine wheel, a rotor, and a stator. The turbine wheel is configured to receive the second portion of the working fluid and rotate in response to expansion of the second portion of the working fluid flowing into an inlet of the turbine wheel and out of an outlet of the turbine wheel. The rotor is coupled to the turbine wheel and configured to rotate with the turbine wheel. The flow-through electric generator is configured to generate electrical power upon rotation of the rotor within the stator.

[0004]This, and other aspects, can include one or more of the following features. In some implementations, the second flowline branches from and reconnects to the first flowline around the throttle valve. In some implementations, the system includes a first reversible valve switchable between a first position and a second position. In some implementations, the first reversible valve is in fluid communication with the first heat exchanger, the second heat exchanger, and the compressor. In some implementations, the system includes a second reversible valve. In some implementations, the second reversible valve is installed on the second flowline. In some implementations, the second reversible valve is switchable between a third position and a fourth position. In some implementations, the second reversible valve is in fluid communication with the first heat exchanger, the second heat exchanger, and the flow-through electric generator. In some implementations, when the first reversible valve is in the first position and the second reversible valve is in the third position, flow of the working fluid is directed through the first heat exchanger, the second heat exchanger, and the throttle valve in a first direction. In some implementations, when the first reversible valve is in the second position and the second reversible valve is in the fourth position, flow of the working fluid is directed through the first heat exchanger, the second heat exchanger, and the throttle valve in a second direction opposite the first direction. In some implementations, the rotor of the flow-through electric generator is coupled to an impeller of the compressor. In some implementations, the impeller of the compressor coupled to the rotor of the flow-through electric generator is configured to rotate with the rotor of the flow-through electric generator for pressurizing the working fluid. In some implementations, the flow-through electric generator is electrically connected to the compressor and is configured to provide at least a portion of the generated electrical power to the compressor for pressurizing the working fluid. In some implementations, the system includes a power electronics system electrically connected to an electrical output of the flow-through electric generator and electrically connected to the compressor. In some implementations, the power electronics system is configured to receive the generated electrical power from the flow-through electric generator and convert the received electrical power to specified power characteristics for delivery to the compressor for pressurizing the working fluid. In some implementations, a first outlet temperature of the first portion of the working fluid exiting the throttle valve is greater than a second outlet temperature of the second portion of the working fluid exiting the flow-through electric generator. In some implementations, the flow-through electric generator includes a hermetically sealed housing enclosing the turbine wheel. In some implementations, the rotor and the stator are hermetically sealed inline in the second flowline flowing the second portion of the working fluid, such that the second portion of the working fluid flows across the turbine wheel and the stator. In some implementations, the rotor includes a permanent magnet rotor.

[0005]Certain aspects of the subject matter described can be implemented as a method of operating a heat pump cycle. The method includes circulating a working fluid through the heat pump cycle in a first direction. Circulating the working fluid through the heat pump cycle in the first direction includes transferring heat, by a first heat exchanger, from a first environment in which the first heat exchanger is disposed to the working fluid, thereby causing at least a portion of the working fluid to vaporize. Circulating the working fluid through the heat pump cycle in the first direction includes pressurizing, by a compressor, the working fluid received from the first heat exchanger. Circulating the working fluid through the heat pump cycle in the first direction includes transferring heat, by a second heat exchanger, from the working fluid to a second, different environment in which the second heat exchanger is disposed, thereby causing at least a portion of the working fluid to condense. Circulating the working fluid through the heat pump cycle in the first direction includes flowing a first portion of the working fluid from the second heat exchanger through a throttle valve, thereby reducing a pressure of the first portion of the working fluid. Circulating the working fluid through the heat pump cycle in the first direction includes flowing a second portion of the working fluid from the second heat exchanger to a turbine wheel of a flow-through electric generator. Circulating the working fluid through the heat pump cycle in the first direction includes generating electrical power, by the flow-through electric generator, in response to the second portion of the working fluid flowing across the turbine wheel. Circulating the working fluid through the heat pump cycle in the first direction includes flowing the first portion of the working fluid from the throttle valve to the first heat exchanger and flowing the second portion of the working fluid from the flow-through electric generator to the first heat exchanger.

[0006]This, and other aspects, can include one or more of the following features. In some implementations, a rotor of the flow-through electric generator is coupled to an impeller of the compressor. In some implementations, flowing the second portion of the working fluid to the turbine wheel causes rotation of the rotor of the flow-through electric generator and co-rotation of the impeller of the compressor that is coupled to the rotor of the flow-through electric generator, thereby imparting at least a portion of work to the compressor for pressurizing the working fluid. In some implementations, the flow-through electric generator is electrically connected to the compressor. In some implementations, the method includes providing at least a portion of the generated electrical power to the compressor for pressurizing the working fluid. In some implementations, a first outlet temperature of the first portion of the working fluid exiting the throttle valve is greater than a second outlet temperature of the second portion of the working fluid exiting the flow-through electric generator. In some implementations, the heat pump cycle includes a first reversible valve. In some implementations, the first reversible valve is switchable between a first position and a second position. In some implementations, the first reversible valve is in fluid communication with the first heat exchanger, the second heat exchanger, and the compressor. In some implementations, the heat pump cycle includes a second reversible valve. In some implementations, the second reversible valve is switchable between a third position and a fourth position. In some implementations, the second reversible valve is in fluid communication with the first heat exchanger, the second heat exchanger, and the flow-through electric generator. In some implementations, the working fluid is circulated through the heat pump cycle in the first direction while the first reversible valve is in the first position and the second reversible valve is in the third position. In some implementations, the method includes switching the first reversible valve to the second position and switching the second reversible valve to the fourth position, thereby circulating the working fluid through the heat pump cycle in a second direction, different from the first direction. In some implementations, circulating the working fluid through the heat pump cycle in the second direction includes transferring heat, by the second heat exchanger, from the second environment to the working fluid, thereby causing at least a portion of the working fluid to vaporize. In some implementations, circulating the working fluid through the heat pump cycle in the second direction includes pressurizing, by the compressor, the working fluid received from the second heat exchanger. In some implementations, circulating the working fluid through the heat pump cycle in the second direction includes transferring heat, by the first heat exchanger, from the working fluid to the first environment, thereby causing at least a portion of the working fluid to condense. In some implementations, circulating the working fluid through the heat pump cycle in the second direction includes flowing the first portion of the working fluid from the first heat exchanger through the throttle valve, thereby reducing the pressure of the first portion of the working fluid. In some implementations, circulating the working fluid through the heat pump cycle in the second direction includes flowing the second portion of the working fluid from the first heat exchanger to the turbine wheel of the flow-through electric generator. In some implementations, circulating the working fluid through the heat pump cycle in the second direction includes continuing to generate electrical power, by the flow-through electric generator, in response to the second portion of the working fluid flowing across the turbine wheel. In some implementations, circulating the working fluid through the heat pump cycle in the second direction includes flowing the first portion of the working fluid from the throttle valve to the second heat exchanger and flowing the second portion of the working fluid from the flow-through electric generator to the second heat exchanger. In some implementations, the method includes switching the first reversible valve from the second position to the first position and switching the second reversible valve from the fourth position to the third position to switch from circulating the working fluid through the heat pump cycle in the second direction to circulating the working fluid through the heat pump cycle in the first direction. In some implementations, the compressor rotates in the same direction regardless of whether the first reversible valve is energized or de-energized, wherein the turbine wheel of the flow-through electric generator rotates in the same direction regardless of whether the second reversible valve is energized or de-energized. In some implementations, the flow-through electric generator further includes a stator and a hermetically sealed housing enclosing the turbine wheel. In some implementations, the stator and the rotor are hermetically sealed inline in a flowline flowing the second portion of the working fluid, such that the second portion of the working fluid flows across the turbine wheel and the stator. In some implementations, the rotor includes a permanent magnet rotor.

[0007]Certain aspects of the subject matter described can be implemented as a heat pump system. The heat pump system includes a first heat exchanger, a compressor, a second heat exchanger, a throttle valve, and a flow-through turboexpander generator. The first heat exchanger is configured to exchange heat between a working fluid and a first environment in which the first heat exchanger is disposed. The compressor is configured to pressurize the working fluid. The second heat exchanger is configured to exchange heat between the working fluid and a second environment in which the second heat exchanger is disposed. The second environment is different from the first environment. The throttle valve is configured to reduce a pressure of a first portion of the working fluid as the first portion of the working fluid flows through the throttle valve. The flow-through turboexpander generator is configured to receive a second portion of the working fluid and generate electrical power in response to expansion of the second portion of the working fluid flowing through the flow-through turboexpander generator. The flow-through turboexpander generator includes a stator, a turbine wheel, a rotor coupled to the turbine wheel, and a hermetically sealed housing enclosing a turbine wheel. The stator and the rotor are hermetically sealed inline in a flowline flowing the second portion of the working fluid, such that the second portion of the working fluid flows across the turbine wheel and the stator. The rotor includes a permanent magnet rotor.

[0008]This, and other aspects, can include one or more of the following features. In some implementations, the system includes a first reversible valve. In some implementations, the first reversible valve is switchable between a first position and a second position. In some implementations, the first reversible valve is in fluid communication with the first heat exchanger, the second heat exchanger, and the compressor. In some implementations, the system includes a second reversible valve. In some implementations, the second reversible valve is installed on the second flowline. In some implementations, the second reversible valve is switchable between a third position and a fourth position. In some implementations, the second reversible valve is in fluid communication with the first heat exchanger, the second heat exchanger, and the flow-through electric generator. In some implementations, when the first reversible valve is in the first position and the second reversible valve is in the third position, flow of the working fluid is directed through the first heat exchanger, the second heat exchanger, and the throttle valve in a first direction. In some implementations, when the first reversible valve is in the second position and the second reversible valve is in the fourth position, flow of the working fluid is directed through the first heat exchanger, the second heat exchanger, and the throttle valve in a second direction opposite the first direction. In some implementations, the flow-through turboexpander generator is electrically connected to the compressor. In some implementations, the flow-through turboexpander generator is configured to provide at least a portion of the generated electrical power to the compressor for pressurizing the working fluid.

[0009]The details of one or more implementations of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

DESCRIPTION OF DRAWINGS

[0010]FIG. 1 is a schematic diagram of an electrical power generation system including a turboexpander.

[0011]FIG. 2A is a schematic diagram of a reversible heat pump cycle including a turboexpander, in a cooling mode.

[0012]FIG. 2B is a schematic diagram of the reversible heat pump cycle of FIG. 2A in a heating mode.

[0013]FIG. 2C is a schematic diagram of a reversible heat pump cycle including a turboexpander, in a cooling mode.

[0014]FIG. 2D is a schematic diagram of the reversible heat pump cycle of FIG. 2C in a heating mode.

[0015]FIGS. 2E and 2F are schematic diagrams of a valve configuration that can replace a first reversible valve in any of the heat pump cycles of FIGS. 2A, 2B, 2C, or 2D.

[0016]FIGS. 2G and 2H are schematic diagrams of a valve configuration that can replace a second reversible valve in any of the heat pump cycles of FIGS. 2A, 2B, 2C, or 2D.

[0017]FIG. 3A is a flow chart of an example method for operating a reversible heat pump cycle including a turboexpander.

[0018]FIG. 3B is a flow chart of an example method for operating a reversible heat pump cycle including a turboexpander.

[0019]FIG. 3C is a flow chart of an example method for operating a reversible heat pump cycle including a turboexpander.

DETAILED DESCRIPTION

[0020]A heat pump cycle uses a refrigeration cycle to transfer heat from a cooler region to a warmer region. In some cases, a heat pump cycle is configured to switch between a cooling mode and a heating mode. Such heat pump cycles can be particularly useful in cases in which the two regions can switch from being cooler and warmer in relation to each other at different times. For example, such heat pump cycles are particularly useful when one of the regions is an outdoor environment and the other region is an indoor environment. In the winter, the outdoor environment can be cooler than the indoor environment, and in the summer, the outdoor environment can be warmer than the indoor environment. Typically, an expansion valve (such as a Joule-Thomson valve) is used in the refrigeration cycle to quickly cool and depressurize (expand) the working fluid for circulation in the refrigeration cycle. As described herein, a turboexpander can be installed in parallel to the expansion valve to recover expansion work to generate useful electrical power. By recovering lost energy from pressure letdown applications in heat pump cycles, the turboexpander can generate electricity while also reducing CO₂ emissions, increasing overall energy efficiency, and offsetting electrical costs.

[0021]The subject matter described in this disclosure can be implemented in particular implementations, so as to realize one or more of the following advantages. By including a turboexpander in parallel to a pressure letdown valve, useful electrical power can be generated from the gas expansion work involved in typical refrigeration cycles. The turboexpander can further decrease an operating temperature of the working fluid flowing through the turboexpander in comparison to a pressure letdown valve, which allows for more efficient refrigeration in the heat pump cycle. The reduced operating temperature of the working fluid can allow for decreased equipment sizing (for example, decreased heat exchanger sizing), thereby reducing capital costs. In some cases, the electrical power generated by the turboexpander can be used to power the compressor in the refrigeration cycle for pressurizing the working fluid. In some cases, the rotor of the turboexpander can be coupled to an impeller of the compressor to transfer work to the compressor for pressurizing the working fluid, thereby reducing power requirements of the compressor. Thus, inclusion of the turboexpander in heat pump cycles can reduce operating costs.

[0022]FIG. 1 is a schematic diagram of an electrical power generation system 100. The electrical power generation system 100 can be added into a heat pump cycle to capture energy from gas expansion. The electrical power generation system 100 includes a turboexpander 102 in parallel with a pressure control valve 130. The turboexpander 102 is arranged axially so that the turboexpander 102 can be mounted in-line with a pipe. The turboexpander 102 acts as an electric generator by generating electrical energy from rotational kinetic energy derived from expansion of a process gas 120 (e.g., refrigerant flowing from a compressor) through a turbine wheel 104. For example, rotation of the turbine wheel 104 can be used to rotate a rotor 108 within a stator 110, which then generates electrical power.

[0023]The turboexpander 102 includes a high-performance, high-speed permanent magnet generator with an integrated radial in-flow expansion turbine wheel 104 and low loss active magnetic bearings (AMBs) 116a,b. The rotor assembly consists of the permanent magnet section with the turbine wheel 104 mounted directly to the rotor hub. The rotor 108 is levitated by the magnetic bearing system creating a frictionless (or near frictionless) interface between dynamic and static components. The AMBs 116a,b facilitate a lossless (or near lossless) rotation of the rotor 108.

[0024]The turboexpander 102 is designed to have the process gas 120 flow through the system 100, which cools the generator and eliminates the need for auxiliary cooling equipment. The power electronics 118 for the turboexpander 102 combines a power converter 206 and Magnetic Bearing Controller (MBC) 209 into one cabinet, in some implementations. The power converter 206 allows for consistent delivery of generated power from the turboexpander 102. For example, the power converter 206 regulates the frequency and voltage of the generated current to match a local power grid. As another example, the power converter 206 regulates the frequency and voltage of the generated current to be compatible for use by a power user, such as an electrolysis unit. After expansion, the process gas 120 exits the turboexpander 102 along the same axial path for downstream processes.

[0025]The turboexpander 102 includes a flow-through configuration. The flow-through configuration permits the process gas 120 to flow from an inlet side of the turboexpander 102 to an outlet side of the turboexpander 102. The process gas 120 flows into a radial gas inlet 154 to the turbine wheel 104 and out of the turbine wheel 104 from an axial gas outlet 156. The process gas 120 then flow through the generator and out of the outlet 154, where the process gas 120 rejoins the gas pipeline 170. Generally, high pressure process gas 120 is directed to flow into the turboexpander 102 through a flow control system 126. The flow control system 126 includes a flow or mass control valve and an emergency shut off valve. Flow control system 126 can be controlled by power electronics 118 or other electrical, mechanical, or electromagnetic signal. For example, a fault condition can signal the flow control system 126 to close or partially close, thereby removing or restricting gas supply to the turboexpander 102. When the rotor 108 is operating at a constant speed, restricting or removing gas flow to the turboexpander 102 reduces the torque applied to the rotor 108 and, consequently, reduces the amount of current generated by the power converter 206. In the example shown in FIG. 1, a signal channel 164 from the power electronics 118 can be used to open and/or close the flow control system 126. In some implementations, the turboexpander housing 112 is hermetically sealed.

[0026]The process gas 120 is expanded by flowing across the turbine wheel 104, resulting in a pressure letdown of the process gas 120. The process gas 120 exits the turboexpander 102 at a decreased pressure. The expansion of the process gas 120 across the turbine wheel 104 causes the turbine wheel 104 to rotate, which causes the rotor 108 to rotate. The rotation of the rotor 108 within the stator 110 generates electrical power. The turboexpander 102 achieves the desired pressure letdown and captures the energy from the pressure letdown to generate electrical power. A pressure control valve 130, such as a conventional pressure regulator, can be installed in parallel to the turboexpander 102. Any excess high pressure process gas 120 that is not directed into the turboexpander 102 can be directed through the pressure control valve 130. For example, the pressure control valve 130 is configured to provide a constriction of an adjustable size for the portion of the process gas 120 flowing through the pressure control valve 130 to expand adiabatically across the pressure control valve 130. The pressure of the portion of the process gas 120 exiting the pressure control valve 130 equalizes with the pressure of the portion of the process gas 120 exiting the turboexpander 102. As such, the pressure control valve 130 and the flow control system 126 can work together to control the pressure of the process gas 120 that flows through the turboexpander and, in turn, control the amount of current generated by the power converter 206.

[0027]The turboexpander 102 includes a turbine wheel 104. The turbine wheel 104 is shown as a radial inflow turbine wheel, though other configurations are within the scope of this disclosure, such as axial flow turbine wheels. In this example, the process gas 120 is received from an inlet conduit 150 of the housing 112 enters a radially oriented inlet 154 of the turbine wheel 104. In some implementations, the process gas 120 flows through an inlet conduit 150 and is diverted by a flow diverter to a radial inlet 154 that directs the fluid into the radial inflow of the turbine wheel 104. After expanding, the process gas 120 exits the turbine wheel 104 from an axially oriented outlet 156 to outlet conduit 152 of the housing 112.

[0028]The turbine wheel 104 can be directly affixed to the rotor 108, or to an intermediate common shaft, for example, by fasteners, rigid drive shaft, welding, or other manner. For example, the turbine wheel 104 may be received at an end of the rotor 108, and held to the rotor 108 with a shaft. The shaft threads into the rotor 108 at one end, and at the other, captures the turbine wheel 104 between the end of rotor 108 and a nut threadingly received on the shaft. The turbine wheel 104 and rotor 108 can be coupled without a gearbox and rotate at the same speed. In other instances, the turbine wheel 104 can be indirectly coupled to the rotor 108, for example, by a gear train, clutch mechanism, or other manner.

[0029]The turbine wheel 104 includes a plurality of turbine wheel blades 106 extending outwardly from a hub and that interact with the expanding process gas 120 to cause the turbine wheel 104 to rotate. FIG. 1 shows an unshrouded turbine wheel 104, in which each of the turbine blades 106 has an exposed, generally radially oriented blade tip extending between the radial inlet 154 and axial outlet 156. As discussed in more detail below, the blade tips seal against a shroud 114 on the interior of the housing 112. In certain instances, the turbine wheel 104 is a shrouded turbine wheel.

[0030]In configurations with an un-shrouded turbine wheel 104, the housing 112 includes an inwardly oriented shroud 114 that resides closely adjacent to, and at most times during operation, out of contact with the turbine wheel blades 106. The close proximity of the turbine wheel blades 106 and shroud 114 seals against passage of process gas 120 therebetween, as the process gas 120 flows through the turbine wheel 104. Although some amount of the process gas 120 may leak or pass between the turbine wheel blades 106 and the shroud 114, the leakage is insubstantial in the operation of the turbine wheel 104. In certain instances, the leakage can be commensurate with other similar unshrouded-turbine/shroud-surface interfaces, using conventional tolerances between the turbine wheel blades 106 and the shroud 114. The amount of leakage that is considered acceptable leakage may be predetermined. The operational parameters of the turbine generator may be optimized to reduce the leakage. In some implementations, the housing 112 is hermetically sealed to prevent process gas 120 from escaping the radial inlet 154 of the turbine wheel 104.

[0031]The shroud 114 may reside at a specified distance away from the turbine wheel blades 106, and is maintained at a distance away from the turbine wheel blades 106 during operation of the turboexpander 102 by using magnetic positioning devices, including active magnetic bearings and position sensors.

[0032]Bearings 116a and 116b are arranged to rotatably support the rotor 108 and turbine wheel 104 relative to the stator 110 and the shroud 114. The turbine wheel 104 is supported in a cantilevered manner by the bearings 116a and 116b. In some implementations, the turbine wheel 104 may be supported in a non-cantilevered manner and bearings 116a and 116b may be located on the outlet side of turbine wheel 104. In certain instances, one or more of the bearings 116a or 116b can include ball bearings, needle bearings, magnetic bearings, foil bearings, journal bearings, or others.

[0033]Bearings 116a and 116b may be a combination radial and thrust bearing, supporting the rotor 108 in radial and axial directions. Other configurations could be utilized. The bearings 116a and 116b need not be the same types of bearings.

[0034]In implementations in which the bearings 116a and 116b are magnetic bearings, a magnetic bearing controller (MBC) 209 is used to control the magnetic bearings 116a and 116b. Position sensors 117a, 117b can be used to detect the position or changes in the position of the turbine wheel 104 and/or rotor 108 relative to the housing 112 or other reference point (such as a predetermined value). Position sensors 117a, 117b can detect axial and/or radial displacement. The magnetic bearing 116a and/or 116b can respond to the information from the position sensors 117a, 117b and adjust for the detected displacement, if necessary. The MBC 209 may receive information from the position sensor(s) 117a, 117b and process that information to provide control signals to the magnetic bearings 116a, 116b. MBC 209 can communicate with the various components of the turboexpander 102 across a communications channel 162.

[0035]The use of magnetic bearings 116a, 116b and position sensors 117a, 117b to maintain and/or adjust the position of the turbine wheel blades 106 such that the turbine wheel blades 106 stay in close proximity to the shroud 114 permits the turboexpander 102 to operate without the need for seals (e.g., without the need for dynamic seals). The use of the active magnetic bearings 116a,b in the turboexpander 102 eliminates physical contact between rotating and stationary components, as well as eliminate lubrication, lubrication systems, and seals.

[0036]The turboexpander 102 may include one or more backup bearings. For example, at start-up and shut-down or in the event of a power outage that affects the operation of the magnetic bearings 116a and 116b, bearings may be used to rotatably support the turbine wheel 104 during that period of time. The backup bearings and may include ball bearings, needle bearings, journal bearings, or the like.

[0037]As mentioned previously, the turboexpander 102 is configured to generate electrical power in response to the rotation of the rotor 108. In certain instances, the rotor 108 can include one or more permanent magnets. The stator 110 includes a plurality of conductive coils. Electrical power is generated by the rotation of the magnet within the coils of the stator 110. The rotor 108 and stator 110 can be configured as a synchronous, permanent magnet, multiphase alternating current (AC) generator. The electrical output 160 can be a three-phase output, for example. In certain instances, stator 110 may include a plurality of coils (e.g., three or six coils for a three-phase AC output). When the rotor 108 is rotated, a voltage is induced in the stator 110. At any instant, the magnitude of the voltage induced in stator coils is proportional to the rate at which the magnetic field encircled by the coil is changing with time (i.e., the rate at which the magnetic field is passing the two sides of the coil). In instances where the rotor 108 is coupled to rotate at the same speed as the turbine wheel 104, the turboexpander 102 is configured to generate electrical power at that speed. Such a turboexpander 102 is what is referred to as a “high speed” turbine generator. For example, the turboexpander 102 can produce up to 280 kW at a continuous speed of 30,000 rpm. In some implementations, the turboexpander produces on the order of 350 kW at higher rotational speeds (e.g., on the order of 35,000 rpm).

[0038]In some implementations, the design of the turbine wheel 104, rotor 108, and/or stator 110 can be based on a desired parameter of the output gas from the turboexpander 102. For example, the design of the rotor and stator can be based on a desired temperature of the process gas 120 exiting the turboexpander 102.

[0039]The turboexpander 102 can be coupled to a power electronics 118. Power electronics 118 can include a power converter 206 and the magnetic bearing controller (MBC) 209 (discussed above). The power converter 206 can be, for example, a variable speed drive (VSD) or a variable frequency drive.

[0040]The electrical output 160 of the turboexpander 102 is connected to the power converter 206, which can be programmed to specific power requirements. The power converter 206 can include an insulated-gate bipolar transistor (IGBT) rectifier 207 to convert the variable frequency, high voltage output from the turboexpander 102 to a direct current (DC). The rectifier 207 can be a three-phase rectifier for three-phase AC input current. An inverter 208 then converts the DC from the rectifier 207 to AC for supplying to the power grid 140. The inverter 208 can convert the DC to 380 VAC-480 VAC at 50 to 60 Hz for delivery to the power grid 140. The specific output of the power converter 206 depends on the power grid 140 and application. Other conversion values are within the scope of this disclosure. The power converter 206 matches its output to the power grid 140 by sampling the grid voltage and frequency, and then changing the output voltage and frequency of the inverter 208 to match the sampled power grid voltage and frequency.

[0041]In some implementations, the power converter 206 is a bidirectional power converter. In such implementations, the rectifier 207 can receive an alternating current from the power grid 140 and convert the alternating current into a direct current. The inverter 208 can then convert DC from the rectifier 207 to AC for supplying to the generator. In such implementations, power can be delivered from the power grid 140 to the generator to drive rotation of the rotor 108, and in turn, the turbine wheel 104 to induce flow of a process gas. In sum, in implementations in which the power converter 206 is a bidirectional power converter, the flow of power can be reversed and used by the generator to induce flow of a process gas (as opposed to the process gas contributing expansion work to generate power).

[0042]The turboexpander 102 is also connected to the MBC 209 in the power electronics 118. The MBC 209 constantly monitors position, current, temperature, and other parameters to ensure that the turboexpander 102 and the active magnetic bearings 116a and 116b are operating as desired. For example, the MBC 209 is coupled to position sensors 117a, 117b to monitor radial and axial position of the turbine wheel 104 and the rotor 108. The MBC 209 can control the magnetic bearings 116a, 116b to selectively change the stiffness and damping characteristics of the magnetic bearings 116a, 116b as a function of spin speed. The MBC 209 can also control synchronous cancellation, including automatic balancing control, adaptive vibration control, adaptive vibration rejection, and unbalance force rejection control.

[0043]FIG. 2A is a schematic diagram of an example heat pump system 200. The system 200 includes a first heat exchanger 210, a compressor 220, a second heat exchanger 230, a throttle valve 240, the turboexpander 102 (flow-through electric generator), a first reversible valve 250a, and a second reversible valve 250b. The first heat exchanger 210 is configured to exchange heat between a working fluid 202 and a first environment 212 in which the first heat exchanger 210 is disposed. The compressor 220 is in fluid communication with the first heat exchanger 210. The compressor 220 is configured to pressurize the working fluid 202. The second heat exchanger 230 is in fluid communication with the compressor 220. The second heat exchanger 230 is configured to exchange heat between the working fluid 202 and a second environment 232 in which the second heat exchanger 230 is disposed. The first environment 212 is different from the second environment 232. As an example, the first environment 212 is an interior of an enclosure or building (such as a house), and the second environment 212 is an area external to the enclosure or building.

[0044]A first flowline 260 connects the first heat exchanger 210 and the second heat exchanger 230. The throttle valve 240 is installed on the first flowline 260. A second flowline 262 parallels the first flowline 260. The second flowline 262 is shown branching from the first flowline 260 and reconnecting to the first flowline 260 around the throttle valve 240, but the flowlines 260, 262 could be configured different (e.g., branching from a common wye). The second flowline 262 provides an alternative flow path for a portion of the working fluid 202 to bypass the throttle valve 240. The turboexpander 102 is installed on the second flowline 262. A first portion 202a of the working fluid 202 can flow through the first flowline 260 and through the throttle valve 240. The throttle valve 240 defines an adjustable flow restriction configured to reduce a pressure of the first portion 202a of the working fluid 202 as the first portion 202a of the working fluid 202 flows through the throttle valve 240. A second portion 202b of the working fluid 202 can flow through the second flowline 262 and through the turboexpander 102. The housing (112) of the turboexpander 102 is hermetically sealed to the second flowline 262, such that the second portion 202b of the working fluid 202 flows through the turboexpander 102 and is prevented from escaping the radial inlet of the turbine wheel (104) of the turboexpander 102. The size of the adjustable flow restriction defined by the throttle valve 240 can be adjusted to control the split between the first portion 202a of the working fluid 202 flowing through the throttle valve 240 versus the second portion 202b of the working fluid 202 flowing through the turboexpander 102. For example, reducing the size of the adjustable flow restriction defined by the throttle valve 240 can cause a larger portion (second portion 202b) of the working fluid 202 to flow through the turboexpander 102 in comparison to the throttle valve 240. Thus, the throttle valve 240 can be used to regulate flow of the second portion 202b of the working fluid 202 through the turboexpander 102 to maintain operation of the turboexpander 102 in its efficiency islands over various operating conditions of the heat pump system 200.

[0045]The first reversible valve 250a is switchable between a first position and a second position. The first reversible valve 250a is in fluid communication with the first heat exchanger 210, the second heat exchanger 230, and the compressor 220. The first reversible valve 250a defines four ports: two inlet ports and two outlet ports. A first flow path through the first reversible valve 250a connects the first inlet port and the first outlet port of the first reversible valve 250a. A second flow path through the first reversible valve 250a connects the second inlet port and the second outlet port of the first reversible valve 250a. Regardless of whether the first reversible valve 250a is in the first position or the second position, the first outlet port is in fluid communication with the suction of the compressor 220, and the second inlet port is in fluid communication with the discharge of the compressor 220, such that flow of the working fluid 202 is directed from the first inlet port to the first outlet port and then from the second inlet port to the second outlet port through the first reversible valve 250a. While in the first position, the first inlet port is in fluid communication with the first heat exchanger 210 and the second outlet port is in fluid communication with the second heat exchanger 230, such that the first reversible valve 250a directs flow of the working fluid 202 from the first heat exchanger 210 through the compressor 220 to the second heat exchanger 230. While in the second position, the first inlet port is in fluid communication with the second heat exchanger 230 and the second outlet port is in fluid communication with the first heat exchanger 210, such that the first reversible valve 250a directs flow of the working fluid 202 from the second heat exchanger 230 through the compressor 220 to the first heat exchanger 210.

[0046]The second reversible valve 250b is switchable between a third position and a fourth position. The second reversible valve 250b is installed on the second flowline 262. The second reversible valve 250b is in fluid communication with the first heat exchanger 210, the second heat exchanger 230, and the turboexpander 102. The second reversible valve 250b defines four ports: two inlet ports and two outlet ports. A first flow path through the second reversible valve 250b connects the first inlet port and the first outlet port of the second reversible valve 250b. A second flow path through the second reversible valve 250b connects the second inlet port and the second outlet port of the second reversible valve 250b. Regardless of whether the second reversible valve 250b is in the third position or the fourth position, the first outlet port is in fluid communication with the suction of the turboexpander 102, and the second inlet port is in fluid communication with the discharge of the turboexpander 102, such that flow of the second portion 202b of the working fluid 202 is directed from the first inlet port to the first outlet port and then from the second inlet port to the second outlet port through the second reversible valve 250b. While in the third position, the first inlet port is in fluid communication with the second heat exchanger 230 and the second outlet port is in fluid communication with the first heat exchanger 210, such that the second reversible valve 250b directs flow of the second portion 202b of the working fluid 202 from the second heat exchanger 230 through the turboexpander 102 to the first heat exchanger 210. While in the fourth position, the first inlet port is in fluid communication with the first heat exchanger 210 and the second outlet port is in fluid communication with the second heat exchanger 230, such that the second reversible valve 250b directs flow of the second portion 202b of the working fluid 202 from the first heat exchanger 210 through the turboexpander 102 to the second heat exchanger 230.

[0047]While the first reversible valve 250a is in the first position and the second reversible valve 250b is in the third position, the reversible valves 250a, 250b are cooperatively configured to direct flow of the working fluid 202 through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in a first direction. While the first reversible valve 250a is in the second position and the second reversible valve 250b is in the fourth position, the reversible valves 250a, 250b are cooperatively configured to direct flow of the working fluid 202 through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in a second direction opposite the first direction. When the first reversible valve 250a is in the first position, the second reversible valve 250b is in the third position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the first direction, the system 200 is in a cooling mode in which heat is generally transferred from the first environment 212 to the second environment 232. When the first reversible valve 250a is in the second position, the second reversible valve 250b is in the fourth position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the second direction, the system 200 is in a heating mode in which heat is generally transferred from the second environment 232 to the first environment 212.

[0048]It is important to note, that regardless of whether the first reversible valve 250a is in the first position or the second position, the working fluid 202 flows through the compressor 220 in the same direction, such that the impellers of the compressor 220 rotate in the same direction whether the system 200 is in the cooling mode (first reversible valve 250a in the first position) or the heating mode (first reversible valve 250a in the second position). Similarly, regardless of whether the second reversible valve 250b is in the third position or in the fourth position, the second portion 202b of the working fluid 202 flows through the turboexpander 102 in the same direction, such that the impellers of the turboexpander 102 rotate in the same direction whether the system 200 is in the cooling mode (second reversible valve 250b in the third position) or the heating mode (second reversible valve 250b in the fourth position). In some implementations, the first reversible valve 250a includes a solenoid valve that can be electrically energized/de-energized for switching between the first and second positions. In some implementations, the second reversible valve 250b includes a solenoid valve that can be electrically energized/de-energized for switching between the third and fourth positions.

[0049]In the system 200 shown in FIG. 2A, the first reversible valve 250a is in the first position, the second reversible valve 250b is in the third position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the first direction, so the system 200 is in the cooling mode. In the cooling mode, the working fluid 202 flows through the first heat exchanger 210. In the first heat exchanger 210, heat is transferred from the first environment 212 to the working fluid 202. In response to receiving heat from the first environment 212 via the first heat exchanger 210, the working fluid 202 at least partially vaporizes. In some cases, the working fluid 202 completely vaporizes in response to receiving heat from the first environment 212 via the first heat exchanger 210.

[0050]The working fluid 202 exiting the first heat exchanger 210 flows to the compressor 220 via the first reversible valve 250a in the first position. The compressor 220 pressurizes the working fluid 202 as the working fluid 202 flows through the compressor 220. A discharge pressure of the working fluid 202 exiting the compressor 220 is greater than a suction pressure of the working fluid 202 entering the compressor 220.

[0051]The working fluid 202 exiting the compressor 220 flows to the second heat exchanger 230 via the first reversible valve 250a in the first position. In the second heat exchanger 230, heat is transferred from the working fluid 202 to the second environment 232. In response to losing heat to the second environment 232 via the second heat exchanger 230, the working fluid 202 at least partially condenses. In some cases, the working fluid 202 completely condenses in response to losing heat to the second environment 232 via the second heat exchanger 230.

[0052]The working fluid 202 exiting the second heat exchanger 230 flows to the first flowline 260. The working fluid 202 splits into the first portion 202a and the second portion 202b. The first portion 202a continues to flow through the first flowline 260 and to the throttle valve 240. The throttle valve 240 can be a Joule-Thomson valve that causes a pressure drop to effect a temperature drop (rapid cooling) during expansion of the first portion 202a as the first portion 202a flows through the throttle valve 240. The second portion 202b flows from the first flowline 260 through the second flowline 262 to the turboexpander 102 via the second reversible valve 250b in the third position. The system 200 can be configured to flow all of the working fluid 202 through only the throttle valve 240 in the first direction or only the turboexpander 102 during some operating conditions. The throttle valve 240 can be designed to handle the full flow of the working fluid 202 flowing through the throttle valve 240 in the first direction. The turboexpander 102 can be designed to handle the full flow of the working fluid 202 flowing through the turboexpander 102. For example, the aerodynamic aspects of the turboexpander 102 (such as the turbine wheel 104 and aero surfaces adjacent the turbine wheel 104) are designed to handle the full flow of the working fluid 202 flowing through the turboexpander 102. As such, the system 200 is capable of handling the full range across flowing all of the working fluid 202 through the throttle valve 240 in the first direction (with no flow through the turboexpander 102) and flowing all of the working fluid 202 through the turboexpander 102 (with no flow through the throttle valve 240), including all split ratios of the working fluid 202 between the throttle valve 240 and the turboexpander 102. The split of the working fluid 202 into the first portion 202a and the second portion 202b can be adjusted based on the operating conditions of the heat pump cycle, the first environment 212, the second environment 232, or any combinations of these. In some implementations, a pressure control valve is installed on the second flowline 262 upstream of the turboexpander 102. The pressure control valve can reduce a pressure of the second portion 202b to ensure the second portion 202b entering the turboexpander 102 is in a vapor state. The second portion 202b expands through the turbine the turboexpander 102, dropping the pressure and temperature of the second portion 202b and rotating the turbine and rotor of the turboexpander 102, causing the turboexpander 102 to generate electrical power. The second portion 202b exiting the turboexpander 102 continues to flow through the second flowline 262 and rejoins the first portion 202a (via the second reversible valve 250b in the third position) exiting the throttle valve 240 in the first flowline 260 to reform the working fluid 202. In some implementations, the second portion 202b exiting the turboexpander 102 has an operating temperature that is less (cooler) than an operating temperature of the first portion 202a exiting the throttle valve 240. Thus, inclusion of the turboexpander 102 can generate a cooler operating temperature for the working fluid 202 to more efficiently cool the first environment 212 in comparison to a heat pump cycle that does not include the turboexpander 102. The working fluid 202 then flows to the first heat exchanger 210 to continue the heat pump cycle in the system 200. In the cooling mode, the system 200 effectively transfers heat from the first environment 212 to the second environment 232 even though the first environment 212 is cooler in temperature in comparison to the second environment 232. The cooling mode is applicable, for example, during warm weather in which the first environment 212 is an indoor environment that is cooler than the second environment 232, which is an outdoor environment.

[0053]In certain instances, the turboexpander 102 is electrically connected to the compressor 220. In some implementations, the system 200 includes the power electronics 118 of system 100 (described previously and shown in FIG. 1), including a VSD 206. The electrical output of the generator of the turboexpander 102 is coupled to the power electronics 118. The output of the VSD 206 can be electrically coupled to a load, such as a power grid to supply power to the grid, as described above, a microgrid for supplying power to equipment, and/or directly to one or more pieces of equipment, such as the compressor 220. For example, the electrical power generated by the turboexpander 102 (in response to expansion of the second portion 202b) can be supplied to the compressor 220 via the power electronics 118 for use in driving the compressor 220 (e.g., powering an electric motor that drives the compressor impeller) to pressurize the working fluid 202 received from the first heat exchanger 210.

[0054]In the system 200 shown in FIG. 2B, the first reversible valve 250a is in the second position, the second reversible valve 250b is in the fourth position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the second direction, so the system 200 is in the heating mode. In the heating mode, the working fluid 202 flows through the second heat exchanger 230. In the second heat exchanger 230, heat is transferred from the second environment 232 to the working fluid 202. In response to receiving heat from the second environment 232 via the second heat exchanger 230, the working fluid 202 at least partially vaporizes. In some cases, the working fluid 202 completely vaporizes in response to receiving heat from the second environment 232 via the second heat exchanger 230.

[0055]The working fluid 202 exiting the second heat exchanger 230 flows to the compressor 220 via the first reversible valve 250a in the second position. The compressor 220 pressurizes the working fluid 202 as the working fluid 202 flows through the compressor 220. A discharge pressure of the working fluid 202 exiting the compressor 220 is greater than a suction pressure of the working fluid 202 entering the compressor 220.

[0056]The working fluid 202 exiting the compressor 220 flows to the first heat exchanger 210 via the first reversible valve 250a in the second position. In the first heat exchanger 210, heat is transferred from the working fluid 202 to the first environment 212. In response to losing heat to the first environment 212 via the first heat exchanger 210, the working fluid 202 at least partially condenses. In some cases, the working fluid 202 completely condenses in response to losing heat to the first environment 212 via the first heat exchanger 210.

[0057]The working fluid 202 exiting the first heat exchanger 210 flows to the first flowline 260. The working fluid 202 splits into the first portion 202a and the second portion 202b. The first portion 202a continues to flow through the first flowline 260 and to the throttle valve 240. The second portion 202b flows from the first flowline 260 through the second flowline 262 to the turboexpander 102 via the second reversible valve 250b in the fourth position. The system 200 can be configured to flow all of the working fluid 202 through only the throttle valve 240 in the second direction or only the turboexpander 102 during some operating conditions. The throttle valve 240 can be designed to handle the full flow of the working fluid 202 flowing through the throttle valve 240 in the second direction. The turboexpander 102 can be designed to handle the full flow of the working fluid 202 flowing through the turboexpander 102. For example, the aerodynamic aspects of the turboexpander 102 (such as the turbine wheel 104 and aero surfaces adjacent the turbine wheel 104) are designed to handle the full flow of the working fluid 202 flowing through the turboexpander 102. As such, the system 200 is capable of handling the full range across flowing all of the working fluid 202 through the throttle valve 240 in the second direction (with no flow through the turboexpander 102) and flowing all of the working fluid 202 through the turboexpander 102 (with no flow through the throttle valve 240), including all split ratios of the working fluid 202 between the throttle valve 240 and the turboexpander 102. The split of the working fluid 202 into the first portion 202a and the second portion 202b can be adjusted based on the operating conditions of the heat pump cycle, the first environment 212, the second environment 232, or any combinations of these. The turboexpander 102 generates electrical power as the second portion 202b expands through the turboexpander 102. The second portion 202b exiting the turboexpander 102 continues to flow through the second flowline 262 and rejoins the first portion 202a (via the second reversible valve 250b in the fourth position) exiting the throttle valve 240 in the first flowline 260 to reform the working fluid 202. In some implementations, the second portion 202b exiting the turboexpander 102 has an operating temperature that is less (cooler) than an operating temperature of the first portion 202a exiting the throttle valve 240. Thus, inclusion of the turboexpander 102 can generate a cooler operating temperature for the working fluid 202 to more efficiently receive heat from the second environment 232 in comparison to a heat pump cycle that does not include the turboexpander 102. The working fluid 202 then flows to the second heat exchanger 230 to continue the heat pump cycle in the system 200. In the heating mode, the system 200 effectively transfers heat from the second environment 232 to the first environment 212 even though the second environment 232 is cooler in temperature in comparison to the first environment 212. The heating mode is applicable, for example, during cool weather in which the first environment 212 is an indoor environment that is warmer than the second environment 232, which is an outdoor environment. In the heating mode, the electrical power generated by the turboexpander 102 (in response to expansion of the second portion 202b) can be supplied to the compressor 220 via the power electronics 118 for the compressor 220 to pressurize the working fluid 202 received from the second heat exchanger 230.

[0058]FIGS. 2C and 2D illustrate an implementation of the system 200 in which the turboexpander 102 is mechanically coupled to the compressor 220. The rotor 108 of the turboexpander 102 is coupled to an impeller 221 of the compressor 220 so that they rotate together. For example, the impeller 221 of the compressor 220 can be coupled to a shaft of the compressor 220, and the shaft of the compressor 220 can be coupled to the rotor 108 of the turboexpander 102. Because the rotor 108 of the turboexpander 102 is coupled to the impeller 221 of the compressor 220, the impeller 221 rotates with the rotor 108 of the turboexpander 102. In some implementations, as shown in FIGS. 2C and 2D, the rotor 108 of the turboexpander 102 is coupled to the impeller 221 of the compressor 220 by a drive shaft 225. In some implementations, the drive shaft 225 directly couples the rotor 108 to the impeller 221, such that the turboexpander 102 and the compressor 220 rotate at the same rotational speed. In some implementations, the rotor 108 of the turboexpander 102 is coupled to the impeller 221 of the compressor 220 by a gear train with multiple drive shafts for indirectly coupling the rotor 108 to the impeller 221, such that the turboexpander 102 and the compressor 220 rotate at different rotational speeds. Because of this coupling, the expansion work from the expansion of the second portion 202b of the working fluid 202 can be transferred to the compressor 220 for pressurizing the working fluid 202 flowing through the compressor 220. By transferring the expansion work from the turboexpander 102 to the compressor 220, the electrical power necessary for the compressor 220 to pressurize the working fluid 202 can be reduced.

[0059]In the system 200 shown in FIG. 2C, the first reversible valve 250a is in the first position, the second reversible valve 250b is in the third position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the first direction, so the system 200 is in the cooling mode. In the system 200 shown in FIG. 2D, the first reversible valve 250a is in the second position, the second reversible valve 250b is in the fourth position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the first direction, so the system 200 is in the heating mode.

[0060]FIGS. 2E and 2F depict a valve configuration 200E that can be implemented in any of the heat pump cycles of FIGS. 2A, 2B, 2C, or 2D. The valve configuration 200E includes a first three-way valve 251a and a second three-way valve 251b, which can replace the first reversible valve 250a (shown in FIGS. 2A, 2B, 2C, and 2D). The first three-way valve 251a is switchable between a fifth position and a sixth position. The first three-way valve 251a is installed on the first flowline 260 (instead of the first reversible valve 250a shown in FIGS. 2A, 2B, 2C, and 2D). The first three-way valve 251a defines two ports: an inlet port and an outlet port. A flow path through the first three-way valve 251a connects the inlet port and the outlet port of the first three-way valve 251a. When in the fifth position, the inlet port of the first three-way valve 251a is in fluid communication with the first heat exchanger 210, and the outlet port of the first three-way valve 251a is in fluid communication with the suction of the compressor 220, such that the first three-way valve 251a directs flow of the working fluid 202 from the first heat exchanger 210 to the compressor 220.

[0061]A third flowline 264 parallels the first flowline 260. The third flowline 264 is shown branching from the first flowline 260 and reconnecting to the first flowline 260 around the first three-way valve 251a. The second three-way valve 251b is switchable between a seventh position and an eighth position. The second three-way valve 251b is installed on the third flowline 264. The second three-way valve 251b defines two ports: an inlet port and an outlet port. A flow path through the second three-way valve 251b connects the inlet port and the outlet port of the second three-way valve 251b. When in the seventh position, the inlet port of the second three-way valve 251b is in fluid communication with the discharge of the compressor 220, and the outlet port of the second three-way valve 251b is in fluid communication with the second heat exchanger 230, such that the second three-way valve 251b directs flow of the working fluid 202 from the compressor 220 to the second heat exchanger 230.

[0062]FIG. 2E depicts the valve configuration 200E with the first three-way valve 251a in the fifth position and the second three-way valve 251b in the seventh position. When the first three-way valve 251a is in the fifth position, the second three-way valve 251b is in the seventh position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the first direction, the system 200 is in the cooling mode in which heat is generally transferred from the first environment 212 to the second environment 232.

[0063]FIG. 2F depicts the valve configuration 200E with the first three-way valve 251a in the sixth position and the second three-way valve 251b in the eighth position. When in the sixth position, the inlet port of the first three-way valve 251a is in fluid communication with the second heat exchanger 230 and the outlet port of the first three-way valve 251a is in fluid communication with the suction of the compressor 220, such that the first three-way valve 251a directs flow of the working fluid 202 from the second heat exchanger 230 to the compressor 220. When in the eighth position, the inlet port of the second three-way valve 251b is in fluid communication with the discharge of the compressor 220, and the outlet port of the second three-way valve 251b is in fluid communication with the first heat exchanger 210, such that the second three-way valve 251b directs flow of the working fluid 202 from the compressor 220 to the first heat exchanger 210. When the first three-way valve 251a is in the sixth position, the second three-way valve 251b is in the eighth position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the second direction, the system 200 is in the heating mode in which heat is generally transferred from the second environment 232 to the first environment 212.

[0064]When the first three-way valve 251a is in the fifth position, the second three-way valve 251b is in the seventh position (example shown in FIG. 2E). When the first three-way valve 251a is in the sixth position, the second three-way valve 251b is in the eighth position (example shown in FIG. 2F). Because of this configuration, the working fluid 202 flows through the compressor 220 in the same direction, such that the impellers of the compressor 220 rotate in the same direction whether the system 200 is in the cooling mode (first three-way valve 251a in fifth position and second three-way valve 251b in seventh position) or the heating mode (first three-way valve 251a in sixth position and second three-way valve 251b in eighth position). The first three-way valve 251a can be configured to switch from the fifth position to the sixth position as the second three-way valve 251b switches from the seventh position to the eighth position. The first three-way valve 251a can be configured to switch from the sixth position to the fifth position as the second three-way valve 251b switches from the eighth position to the seventh position. The second three-way valve 251b can be configured to switch from the seventh position to the eighth position as the first three-way valve 251a switches from the fifth position to the sixth position. The second three-way valve 251b can be configured to switch from the eighth position to the seventh position as the first three-way valve 251a switches from the sixth position to the fifth position.

[0065]FIGS. 2G and 2H depict a valve configuration 200G that can be implemented in any of the heat pump cycles of FIGS. 2A, 2B, 2C, or 2D. The valve configuration 200G includes a third three-way valve 251c and a fourth three-way valve 251d, which can replace the second reversible valve 250b (shown in FIGS. 2A, 2B, 2C, and 2D). The third three-way valve 251c is switchable between a ninth position and a tenth position. The third three-way valve 251c is installed on the second flowline 262 (instead of the second reversible valve 250b shown in FIGS. 2A, 2B, 2C, and 2D). The third three-way valve 251c defines two ports: an inlet port and an outlet port. A flow path through the third three-way valve 251c connects the inlet port and the outlet port of the third three-way valve 251c. When in the ninth position, the inlet port of the third three-way valve 251c is in fluid communication with the second heat exchanger 230, and the outlet port of the third three-way valve 251c is in fluid communication with the suction of the turboexpander 102, such that the third three-way valve 251c directs flow of the second portion 202b of the working fluid 202 from the second heat exchanger 230 to the turboexpander 102.

[0066]A fourth flowline 266 parallels the second flowline 262. The fourth flowline 266 is shown branching from the first flowline 260 and reconnecting to the first flowline 260 around the second flowline 262 and the throttle valve 240. In the valve configuration 200G, the second flowline 262 and the fourth flowline 266 cooperatively provide an alternative flow path for the second portion 202b of the working fluid 202 to bypass the throttle valve 240. The fourth three-way valve 251d is switchable between an eleventh position and a twelfth position. The fourth three-way valve 251d is installed on the fourth flowline 262. The fourth three-way valve 251d defines two ports: an inlet port and an outlet port. A flow path through the fourth three-way valve 251d connects the inlet port and the outlet port of the fourth three-way valve 251d. When in the eleventh position, the inlet port of the fourth three-way valve 251d is in fluid communication with the discharge of the turboexpander 102, and the outlet port of the fourth three-way valve 251d is in fluid communication with the first heat exchanger 210, such that the fourth three-way valve 251d directs flow of the second portion 202b of the working fluid 202 from the turboexpander 102 to the first heat exchanger 210.

[0067]FIG. 2G depicts the valve configuration 200G with the third three-way valve 251c in the ninth position and the fourth three-way valve 251d in the eleventh position. When the third three-way valve 251c is in the ninth position, the fourth three-way valve 251d is in the eleventh position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the first direction, the system 200 is in the cooling mode in which heat is generally transferred from the first environment 212 to the second environment 232.

[0068]FIG. 2H depicts the valve configuration 200G with the third three-way valve 251c in the tenth position and the fourth three-way valve 251d in the twelfth position. When in the tenth position, the inlet port of the third three-way valve 251c is in fluid communication with the first heat exchanger 210, and the outlet port of the third three-way valve 251c is in fluid communication with the suction of the turboexpander 102, such that the third three-way valve 251c directs flow of the second portion 202b of the working fluid 202 from the first heat exchanger 210 to the turboexpander 102. When in the twelfth position, the inlet port of the fourth three-way valve 251d is in fluid communication with the discharge of the turboexpander 102, and the outlet port of the fourth three-way valve 251d is in fluid communication with the second heat exchanger 230, such that the fourth three-way valve 251d directs flow of the second portion 202b of the working fluid 202 from the turboexpander 102 to the second heat exchanger 230. When the third three-way valve 251c is in the tenth position, the fourth three-way valve 251d is in the twelfth position, and the working fluid 202 is flowing through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 in the second direction, the system 200 is in the heating mode in which heat is generally transferred from the second environment 232 to the first environment 212.

[0069]When the third three-way valve 251d is in the ninth position, the fourth three-way valve 251d is in the eleventh position (example shown in FIG. 2G). When the third three-way valve 251c is in the tenth position, the fourth three-way valve 251d is in the twelfth position (example shown in FIG. 2H). Because of this configuration, the second portion 202b of the working fluid 202 flows through the turboexpander 102 in the same direction, such that the impellers of the turboexpander 102 rotate in the same direction whether the system 200 is in the cooling mode (third three-way valve 251c in ninth position and fourth three-way valve 251d in eleventh position) or the heating mode (third three-way valve 251c in tenth position and fourth three-way valve 251d in twelfth position). The third three-way valve 251c can be configured to switch from the ninth position to the tenth position as the fourth three-way valve 251d switches from the eleventh position to the twelfth position. The third three-way valve 251c can be configured to switch from the tenth position to the ninth position as the fourth three-way valve 251d switches from the twelfth position to the eleventh position. The fourth three-way valve 251d can be configured to switch from the eleventh position to the twelfth position as the third three-way valve 251c switches from the ninth position to the tenth position. The fourth three-way valve 251d can be configured to switch from the twelfth position to the eleventh position as the third three-way valve 251c switches from the tenth position to the ninth position.

[0070]FIG. 3A is a block flow diagram of a method 300A for operating a reversible heat pump cycle (such as the system 200) including a turboexpander (such as the turboexpander 102). At block 302, a working fluid (such as the working fluid 202) is circulated through the heat pump cycle (system 200) in a first direction. Circulating the working fluid 202 through the heat pump cycle (system 200) in the first direction at block 302 includes blocks 304, 306, 308, 310, 312, 314, and 316. At block 304, a first heat exchanger (such as the first heat exchanger 210) transfers heat from a first environment (such as the first environment 212) to the working fluid 202. As described previously, the first heat exchanger 210 is disposed in the first environment 212. Transferring heat from the first environment 212 to the working fluid 202 via the first heat exchanger 210 at block 304 causes at least a portion of the working fluid 202 to vaporize. In some cases, transferring heat from the first environment 212 to the working fluid 202 via the first heat exchanger 210 at block 304 causes the working fluid 202 to fully vaporize. At block 306, a compressor (such as the compressor 220) pressurizes the working fluid 202 received from the first heat exchanger 210. At block 308, a second heat exchanger (such as the second heat exchanger 230) transfers heat from the working fluid 202 to a second, different environment (such as the second environment 232). As described previously, the second heat exchanger 230 is disposed in the second environment 232. Transferring heat from the working fluid 202 to the second environment 232 via the second heat exchanger 230 at block 308 causes at least a portion of the working fluid 202 to condense. In some cases, transferring heat from the working fluid 202 to the second environment 232 via the second heat exchanger 230 at block 308 causes the working fluid 202 to fully condense. At block 310, a first portion (such as the first portion 202a) of the working fluid 202 is flowed from the second heat exchanger 230 through a throttle valve (such as the throttle valve 240). Flowing the first portion 202a of the working fluid 202 through the throttle valve 240 at block 310 reduces a pressure of the first portion 202a of the working fluid 202. At block 312, a second portion (such as the second portion 202b) of the working fluid 202 is flowed to a turbine wheel (such as the turbine wheel 104) of a flow-through electric generator (such as the turboexpander 102). At block 314, the flow-through electric generator (turboexpander 102) generates electrical power in response to the second portion 202b of the working fluid 202 flowing across the turbine wheel 104, as a result of block 312. At block 316, the first portion 202a of the working fluid 202 is flowed from the throttle valve 240 to the first heat exchanger 210, and the second portion 202b of the working fluid 202 is flowed from the flow-through electric generator (turboexpander 102) to the first heat exchanger 210. In some implementations, the first portion 202a of the working fluid 202 exiting the throttle valve 240 and the second portion 202b of the working fluid 202 exiting the flow-through electric generator (turboexpander 102) are combined to reform the working fluid 202, and the working fluid 202 is flowed to the first heat exchanger 210 at block 316. The circulation of the working fluid 202 through the heat pump cycle (system 200) in the first direction can continue back at block 304 to repeat the cycle.

[0071]FIG. 3B is a block flow diagram of a method 300B for operating a reversible heat pump cycle (such as the system 200) including a turboexpander (such as the turboexpander 102). At block 302′, a working fluid (such as the working fluid 202) is circulated through the heat pump cycle (system 200) in a second direction (different from the first direction at block 302 of method 300A). Circulating the working fluid 202 through the heat pump cycle (system 200) in the second direction at block 302′ includes blocks 304′, 306′, 308′, 310′, 312′, 314′, and 316′. At block 304′, a second heat exchanger (such as the second heat exchanger 230) transfers heat from a second environment (such as the second environment 232) to the working fluid 202. Transferring heat from the second environment 232 to the working fluid 202 via the second heat exchanger 230 at block 304′ causes at least a portion of the working fluid 202 to vaporize. In some cases, transferring heat from the second environment 232 to the working fluid 202 via the second heat exchanger 230 at block 304′ causes the working fluid 202 to fully vaporize. At block 306′, a compressor (such as the compressor 220) pressurizes the working fluid 202 received from the second heat exchanger 210′. At block 308′, a first heat exchanger (such as the first heat exchanger 210) transfers heat from the working fluid 202 to a first environment (such as the first environment 212). Transferring heat from the working fluid 202 to the first environment 212 via the first heat exchanger 210 at block 308′ causes at least a portion of the working fluid 202 to condense. In some cases, transferring heat from the working fluid 202 to the first environment 212 via the first heat exchanger 210 at block 308′ causes the working fluid 202 to fully condense. At block 310′, a first portion (such as the first portion 202a) of the working fluid 202 is flowed from the first heat exchanger 210 through a throttle valve (such as the throttle valve 240). Flowing the first portion 202a of the working fluid 202 through the throttle valve 240 at block 310′ reduces a pressure of the first portion 202a of the working fluid 202. At block 312′, a second portion (such as the second portion 202b) of the working fluid 202 is flowed to a turbine wheel (such as the turbine wheel 104) of a flow-through electric generator (such as the turboexpander 102). At block 314′, the flow-through electric generator (turboexpander 102) generates electrical power in response to the second portion 202b of the working fluid 202 flowing across the turbine wheel 104, as a result of block 312′. At block 316′, the first portion 202a of the working fluid 202 is flowed from the throttle valve 240 to the second heat exchanger 230, and the second portion 202b of the working fluid 202 is flowed from the flow-through electric generator (turboexpander 102) to the second heat exchanger 230. In some implementations, the first portion 202a of the working fluid 202 exiting the throttle valve 240 and the second portion 202b of the working fluid 202 exiting the flow-through electric generator (turboexpander 102) are combined to reform the working fluid 202, and the working fluid 202 is flowed to the second heat exchanger 210 at block 316′. The circulation of the working fluid 202 through the heat pump cycle (system 200) in the second direction can continue back at block 304′ to repeat the cycle.

[0072]FIG. 3C is a block flow diagram of a method 300C for operating a reversible heat pump cycle (such as the system 200) including a turboexpander (such as the turboexpander 102). The method 300C includes alternating between block 302 of method 300A and block 302′ of method 300B. Proceeding from block 302 to block 302′ can involve switching a first reversible valve (such as the first reversible valve 250a) from the first position to the second position and switching a second reversible valve (such as the second reversible valve 250b) from the third position to the fourth position. Progressing from block 302′ to block 302 can involve switching the first reversible valve 250a from the second position to the first position and switching the second reversible valve 250b from the fourth position to the third position.

[0073]As mentioned previously, the working fluid 202 flows through the compressor 220 in the same direction regardless of the positions of the reversible valves 250a, 250b. Similarly, the second portion 202b of the working fluid 202 flows through the turboexpander 102 in the same direction regardless of the positions of the reversible valves 250a, 250b. The switching of positions of the reversible valves 250a, 250b changes the direction of flow of the working fluid 202 through the first heat exchanger 210, the second heat exchanger 230, and the throttle valve 240 but does not affect the direction of flow of the working fluid 202 through the compressor 220 and flow of second portion 202b through the turboexpander 102.

[0074]While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular implementations. Certain features that are described in this specification in the context of separate implementations can also be implemented, in combination, in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations, separately, or in any sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0075]As used in this disclosure, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[0076]Particular implementations of the subject matter have been described. Other implementations, alterations, and permutations of the described implementations are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results. In certain circumstances, multitasking or parallel processing (or a combination of multitasking and parallel processing) may be advantageous and performed as deemed appropriate.

[0077]Moreover, the separation or integration of various system modules and components in the previously described implementations should not be understood as requiring such separation or integration in all implementations, and it should be understood that the described components and systems can generally be integrated together or packaged into multiple products.

[0078]Accordingly, the previously described example implementations do not define or constrain the present disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of the present disclosure.