Turboexpansion Reversible Heat Pump Cycle

This disclosure relates to heat pump cycles.

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.

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.

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.

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.

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.

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.

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.

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.

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 COemissions, increasing overall energy efficiency, and offsetting electrical costs.

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.

is a schematic diagram of an electrical power generation system. The electrical power generation systemcan be added into a heat pump cycle to capture energy from gas expansion. The electrical power generation systemincludes a turboexpanderin parallel with a pressure control valve. The turboexpanderis arranged axially so that the turboexpandercan be mounted in-line with a pipe. The turboexpanderacts as an electric generator by generating electrical energy from rotational kinetic energy derived from expansion of a process gas(e.g., refrigerant flowing from a compressor) through a turbine wheel. For example, rotation of the turbine wheelcan be used to rotate a rotorwithin a stator, which then generates electrical power.

The turboexpanderincludes a high-performance, high-speed permanent magnet generator with an integrated radial in-flow expansion turbine wheeland low loss active magnetic bearings (AMBs)The rotor assembly consists of the permanent magnet section with the turbine wheelmounted directly to the rotor hub. The rotoris levitated by the magnetic bearing system creating a frictionless (or near frictionless) interface between dynamic and static components. The AMBsfacilitate a lossless (or near lossless) rotation of the rotor.

The turboexpanderis designed to have the process gasflow through the system, which cools the generator and eliminates the need for auxiliary cooling equipment. The power electronicsfor the turboexpandercombines a power converterand Magnetic Bearing Controller (MBC)into one cabinet, in some implementations. The power converterallows for consistent delivery of generated power from the turboexpander. For example, the power converterregulates the frequency and voltage of the generated current to match a local power grid. As another example, the power converterregulates 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 gasexits the turboexpanderalong the same axial path for downstream processes.

The turboexpanderincludes a flow-through configuration. The flow-through configuration permits the process gasto flow from an inlet side of the turboexpanderto an outlet side of the turboexpander. The process gasflows into a radial gas inletto the turbine wheeland out of the turbine wheelfrom an axial gas outlet. The process gasthen flow through the generator and out of the outlet, where the process gasrejoins the gas pipeline. Generally, high pressure process gasis directed to flow into the turboexpanderthrough a flow control system. The flow control systemincludes a flow or mass control valve and an emergency shut off valve. Flow control systemcan be controlled by power electronicsor other electrical, mechanical, or electromagnetic signal. For example, a fault condition can signal the flow control systemto close or partially close, thereby removing or restricting gas supply to the turboexpander. When the rotoris operating at a constant speed, restricting or removing gas flow to the turboexpanderreduces the torque applied to the rotorand, consequently, reduces the amount of current generated by the power converter. In the example shown in, a signal channelfrom the power electronicscan be used to open and/or close the flow control system. In some implementations, the turboexpander housingis hermetically sealed.

The process gasis expanded by flowing across the turbine wheel, resulting in a pressure letdown of the process gas. The process gasexits the turboexpanderat a decreased pressure. The expansion of the process gasacross the turbine wheelcauses the turbine wheelto rotate, which causes the rotorto rotate. The rotation of the rotorwithin the statorgenerates electrical power. The turboexpanderachieves the desired pressure letdown and captures the energy from the pressure letdown to generate electrical power. A pressure control valve, such as a conventional pressure regulator, can be installed in parallel to the turboexpander. Any excess high pressure process gasthat is not directed into the turboexpandercan be directed through the pressure control valve. For example, the pressure control valveis configured to provide a constriction of an adjustable size for the portion of the process gasflowing through the pressure control valveto expand adiabatically across the pressure control valve. The pressure of the portion of the process gasexiting the pressure control valveequalizes with the pressure of the portion of the process gasexiting the turboexpander. As such, the pressure control valveand the flow control systemcan work together to control the pressure of the process gasthat flows through the turboexpander and, in turn, control the amount of current generated by the power converter.

The turboexpanderincludes a turbine wheel. The turbine wheelis 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 gasis received from an inlet conduitof the housingenters a radially oriented inletof the turbine wheel. In some implementations, the process gasflows through an inlet conduitand is diverted by a flow diverter to a radial inletthat directs the fluid into the radial inflow of the turbine wheel. After expanding, the process gasexits the turbine wheelfrom an axially oriented outletto outlet conduitof the housing.

The turbine wheelcan be directly affixed to the rotor, or to an intermediate common shaft, for example, by fasteners, rigid drive shaft, welding, or other manner. For example, the turbine wheelmay be received at an end of the rotor, and held to the rotorwith a shaft. The shaft threads into the rotorat one end, and at the other, captures the turbine wheelbetween the end of rotorand a nut threadingly received on the shaft. The turbine wheeland rotorcan be coupled without a gearbox and rotate at the same speed. In other instances, the turbine wheelcan be indirectly coupled to the rotor, for example, by a gear train, clutch mechanism, or other manner.

The turbine wheelincludes a plurality of turbine wheel bladesextending outwardly from a hub and that interact with the expanding process gasto cause the turbine wheelto rotate.shows an unshrouded turbine wheel, in which each of the turbine bladeshas an exposed, generally radially oriented blade tip extending between the radial inletand axial outlet. As discussed in more detail below, the blade tips seal against a shroudon the interior of the housing. In certain instances, the turbine wheelis a shrouded turbine wheel.

In configurations with an un-shrouded turbine wheel, the housingincludes an inwardly oriented shroudthat resides closely adjacent to, and at most times during operation, out of contact with the turbine wheel blades. The close proximity of the turbine wheel bladesand shroudseals against passage of process gastherebetween, as the process gasflows through the turbine wheel. Although some amount of the process gasmay leak or pass between the turbine wheel bladesand the shroud, the leakage is insubstantial in the operation of the turbine wheel. In certain instances, the leakage can be commensurate with other similar unshrouded-turbine/shroud-surface interfaces, using conventional tolerances between the turbine wheel bladesand the shroud. 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 housingis hermetically sealed to prevent process gasfrom escaping the radial inletof the turbine wheel.

The shroudmay reside at a specified distance away from the turbine wheel blades, and is maintained at a distance away from the turbine wheel bladesduring operation of the turboexpanderby using magnetic positioning devices, including active magnetic bearings and position sensors.

Bearingsandare arranged to rotatably support the rotorand turbine wheelrelative to the statorand the shroud. The turbine wheelis supported in a cantilevered manner by the bearingsandIn some implementations, the turbine wheelmay be supported in a non-cantilevered manner and bearingsandmay be located on the outlet side of turbine wheel. In certain instances, one or more of the bearingsorcan include ball bearings, needle bearings, magnetic bearings, foil bearings, journal bearings, or others.

Bearingsandmay be a combination radial and thrust bearing, supporting the rotorin radial and axial directions. Other configurations could be utilized. The bearingsandneed not be the same types of bearings.

In implementations in which the bearingsandare magnetic bearings, a magnetic bearing controller (MBC)is used to control the magnetic bearingsandPosition sensorscan be used to detect the position or changes in the position of the turbine wheeland/or rotorrelative to the housingor other reference point (such as a predetermined value). Position sensorscan detect axial and/or radial displacement. The magnetic bearingand/orcan respond to the information from the position sensorsand adjust for the detected displacement, if necessary. The MBCmay receive information from the position sensor(s)and process that information to provide control signals to the magnetic bearingsMBCcan communicate with the various components of the turboexpanderacross a communications channel.

The use of magnetic bearingsand position sensorsto maintain and/or adjust the position of the turbine wheel bladessuch that the turbine wheel bladesstay in close proximity to the shroudpermits the turboexpanderto operate without the need for seals (e.g., without the need for dynamic seals). The use of the active magnetic bearingsin the turboexpandereliminates physical contact between rotating and stationary components, as well as eliminate lubrication, lubrication systems, and seals.

The turboexpandermay 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 bearingsandbearings may be used to rotatably support the turbine wheelduring that period of time. The backup bearings and may include ball bearings, needle bearings, journal bearings, or the like.

As mentioned previously, the turboexpanderis configured to generate electrical power in response to the rotation of the rotor. In certain instances, the rotorcan include one or more permanent magnets. The statorincludes a plurality of conductive coils. Electrical power is generated by the rotation of the magnet within the coils of the stator. The rotorand statorcan be configured as a synchronous, permanent magnet, multiphase alternating current (AC) generator. The electrical outputcan be a three-phase output, for example. In certain instances, statormay include a plurality of coils (e.g., three or six coils for a three-phase AC output). When the rotoris rotated, a voltage is induced in the stator. 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 rotoris coupled to rotate at the same speed as the turbine wheel, the turboexpanderis configured to generate electrical power at that speed. Such a turboexpanderis what is referred to as a “high speed” turbine generator. For example, the turboexpandercan 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).

In some implementations, the design of the turbine wheel, rotor, and/or statorcan be based on a desired parameter of the output gas from the turboexpander. For example, the design of the rotor and stator can be based on a desired temperature of the process gasexiting the turboexpander.

The turboexpandercan be coupled to a power electronics. Power electronicscan include a power converterand the magnetic bearing controller (MBC)(discussed above). The power convertercan be, for example, a variable speed drive (VSD) or a variable frequency drive.

The electrical outputof the turboexpanderis connected to the power converter, which can be programmed to specific power requirements. The power convertercan include an insulated-gate bipolar transistor (IGBT) rectifierto convert the variable frequency, high voltage output from the turboexpanderto a direct current (DC). The rectifiercan be a three-phase rectifier for three-phase AC input current. An inverterthen converts the DC from the rectifierto AC for supplying to the power grid. The invertercan convert the DC to 380 VAC-480 VAC at 50 to 60 Hz for delivery to the power grid. The specific output of the power converterdepends on the power gridand application. Other conversion values are within the scope of this disclosure. The power convertermatches its output to the power gridby sampling the grid voltage and frequency, and then changing the output voltage and frequency of the inverterto match the sampled power grid voltage and frequency.

In some implementations, the power converteris a bidirectional power converter. In such implementations, the rectifiercan receive an alternating current from the power gridand convert the alternating current into a direct current. The invertercan then convert DC from the rectifierto AC for supplying to the generator. In such implementations, power can be delivered from the power gridto the generator to drive rotation of the rotor, and in turn, the turbine wheelto induce flow of a process gas. In sum, in implementations in which the power converteris 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).

The turboexpanderis also connected to the MBCin the power electronics. The MBCconstantly monitors position, current, temperature, and other parameters to ensure that the turboexpanderand the active magnetic bearingsandare operating as desired. For example, the MBCis coupled to position sensorsto monitor radial and axial position of the turbine wheeland the rotor. The MBCcan control the magnetic bearingsto selectively change the stiffness and damping characteristics of the magnetic bearingsas a function of spin speed. The MBCcan also control synchronous cancellation, including automatic balancing control, adaptive vibration control, adaptive vibration rejection, and unbalance force rejection control.

is a schematic diagram of an example heat pump system. The systemincludes a first heat exchanger, a compressor, a second heat exchanger, a throttle valve, the turboexpander(flow-through electric generator), a first reversible valveand a second reversible valveThe first heat exchangeris configured to exchange heat between a working fluidand a first environmentin which the first heat exchangeris disposed. The compressoris in fluid communication with the first heat exchanger. The compressoris configured to pressurize the working fluid. The second heat exchangeris in fluid communication with the compressor. The second heat exchangeris configured to exchange heat between the working fluidand a second environmentin which the second heat exchangeris disposed. The first environmentis different from the second environment. As an example, the first environmentis an interior of an enclosure or building (such as a house), and the second environmentis an area external to the enclosure or building.

A first flowlineconnects the first heat exchangerand the second heat exchanger. The throttle valveis installed on the first flowline. A second flowlineparallels the first flowline. The second flowlineis shown branching from the first flowlineand reconnecting to the first flowlinearound the throttle valve, but the flowlines,could be configured different (e.g., branching from a common wye). The second flowlineprovides an alternative flow path for a portion of the working fluidto bypass the throttle valve. The turboexpanderis installed on the second flowline. A first portionof the working fluidcan flow through the first flowlineand through the throttle valve. The throttle valvedefines an adjustable flow restriction configured to reduce a pressure of the first portionof the working fluidas the first portionof the working fluidflows through the throttle valve. A second portionof the working fluidcan flow through the second flowlineand through the turboexpander. The housing () of the turboexpanderis hermetically sealed to the second flowline, such that the second portionof the working fluidflows through the turboexpanderand is prevented from escaping the radial inlet of the turbine wheel () of the turboexpander. The size of the adjustable flow restriction defined by the throttle valvecan be adjusted to control the split between the first portionof the working fluidflowing through the throttle valveversus the second portionof the working fluidflowing through the turboexpander. For example, reducing the size of the adjustable flow restriction defined by the throttle valvecan cause a larger portion (second portion) of the working fluidto flow through the turboexpanderin comparison to the throttle valve. Thus, the throttle valvecan be used to regulate flow of the second portionof the working fluidthrough the turboexpanderto maintain operation of the turboexpanderin its efficiency islands over various operating conditions of the heat pump system.

The first reversible valveis switchable between a first position and a second position. The first reversible valveis in fluid communication with the first heat exchanger, the second heat exchanger, and the compressor. The first reversible valvedefines four ports: two inlet ports and two outlet ports. A first flow path through the first reversible valveconnects the first inlet port and the first outlet port of the first reversible valveA second flow path through the first reversible valveconnects the second inlet port and the second outlet port of the first reversible valveRegardless of whether the first reversible valveis in the first position or the second position, the first outlet port is in fluid communication with the suction of the compressor, and the second inlet port is in fluid communication with the discharge of the compressor, such that flow of the working fluidis 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 valveWhile in the first position, the first inlet port is in fluid communication with the first heat exchangerand the second outlet port is in fluid communication with the second heat exchanger, such that the first reversible valvedirects flow of the working fluidfrom the first heat exchangerthrough the compressorto the second heat exchanger. While in the second position, the first inlet port is in fluid communication with the second heat exchangerand the second outlet port is in fluid communication with the first heat exchanger, such that the first reversible valvedirects flow of the working fluidfrom the second heat exchangerthrough the compressorto the first heat exchanger.

The second reversible valveis switchable between a third position and a fourth position. The second reversible valveis installed on the second flowline. The second reversible valveis in fluid communication with the first heat exchanger, the second heat exchanger, and the turboexpander. The second reversible valvedefines four ports: two inlet ports and two outlet ports. A first flow path through the second reversible valveconnects the first inlet port and the first outlet port of the second reversible valveA second flow path through the second reversible valveconnects the second inlet port and the second outlet port of the second reversible valveRegardless of whether the second reversible valveis in the third position or the fourth position, the first outlet port is in fluid communication with the suction of the turboexpander, and the second inlet port is in fluid communication with the discharge of the turboexpander, such that flow of the second portionof the working fluidis 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 valveWhile in the third position, the first inlet port is in fluid communication with the second heat exchangerand the second outlet port is in fluid communication with the first heat exchanger, such that the second reversible valvedirects flow of the second portionof the working fluidfrom the second heat exchangerthrough the turboexpanderto the first heat exchanger. While in the fourth position, the first inlet port is in fluid communication with the first heat exchangerand the second outlet port is in fluid communication with the second heat exchanger, such that the second reversible valvedirects flow of the second portionof the working fluidfrom the first heat exchangerthrough the turboexpanderto the second heat exchanger.

While the first reversible valveis in the first position and the second reversible valveis in the third position, the reversible valvesare cooperatively configured to direct flow of the working fluidthrough the first heat exchanger, the second heat exchanger, and the throttle valvein a first direction. While the first reversible valveis in the second position and the second reversible valveis in the fourth position, the reversible valvesare cooperatively configured to direct flow of the working fluidthrough the first heat exchanger, the second heat exchanger, and the throttle valvein a second direction opposite the first direction. When the first reversible valveis in the first position, the second reversible valveis in the third position, and the working fluidis flowing through the first heat exchanger, the second heat exchanger, and the throttle valvein the first direction, the systemis in a cooling mode in which heat is generally transferred from the first environmentto the second environment. When the first reversible valveis in the second position, the second reversible valveis in the fourth position, and the working fluidis flowing through the first heat exchanger, the second heat exchanger, and the throttle valvein the second direction, the systemis in a heating mode in which heat is generally transferred from the second environmentto the first environment.

It is important to note, that regardless of whether the first reversible valveis in the first position or the second position, the working fluidflows through the compressorin the same direction, such that the impellers of the compressorrotate in the same direction whether the systemis in the cooling mode (first reversible valvein the first position) or the heating mode (first reversible valvein the second position). Similarly, regardless of whether the second reversible valveis in the third position or in the fourth position, the second portionof the working fluidflows through the turboexpanderin the same direction, such that the impellers of the turboexpanderrotate in the same direction whether the systemis in the cooling mode (second reversible valvein the third position) or the heating mode (second reversible valvein the fourth position). In some implementations, the first reversible valveincludes a solenoid valve that can be electrically energized/de-energized for switching between the first and second positions. In some implementations, the second reversible valveincludes a solenoid valve that can be electrically energized/de-energized for switching between the third and fourth positions.

In the systemshown in, the first reversible valveis in the first position, the second reversible valveis in the third position, and the working fluidis flowing through the first heat exchanger, the second heat exchanger, and the throttle valvein the first direction, so the systemis in the cooling mode. In the cooling mode, the working fluidflows through the first heat exchanger. In the first heat exchanger, heat is transferred from the first environmentto the working fluid. In response to receiving heat from the first environmentvia the first heat exchanger, the working fluidat least partially vaporizes. In some cases, the working fluidcompletely vaporizes in response to receiving heat from the first environmentvia the first heat exchanger.

The working fluidexiting the first heat exchangerflows to the compressorvia the first reversible valvein the first position. The compressorpressurizes the working fluidas the working fluidflows through the compressor. A discharge pressure of the working fluidexiting the compressoris greater than a suction pressure of the working fluidentering the compressor.

The working fluidexiting the compressorflows to the second heat exchangervia the first reversible valvein the first position. In the second heat exchanger, heat is transferred from the working fluidto the second environment. In response to losing heat to the second environmentvia the second heat exchanger, the working fluidat least partially condenses. In some cases, the working fluidcompletely condenses in response to losing heat to the second environmentvia the second heat exchanger.

The working fluidexiting the second heat exchangerflows to the first flowline. The working fluidsplits into the first portionand the second portionThe first portioncontinues to flow through the first flowlineand to the throttle valve. The throttle valvecan be a Joule-Thomson valve that causes a pressure drop to effect a temperature drop (rapid cooling) during expansion of the first portionas the first portionflows through the throttle valve. The second portionflows from the first flowlinethrough the second flowlineto the turboexpandervia the second reversible valvein the third position. The systemcan be configured to flow all of the working fluidthrough only the throttle valvein the first direction or only the turboexpanderduring some operating conditions. The throttle valvecan be designed to handle the full flow of the working fluidflowing through the throttle valvein the first direction. The turboexpandercan be designed to handle the full flow of the working fluidflowing through the turboexpander. For example, the aerodynamic aspects of the turboexpander(such as the turbine wheeland aero surfaces adjacent the turbine wheel) are designed to handle the full flow of the working fluidflowing through the turboexpander. As such, the systemis capable of handling the full range across flowing all of the working fluidthrough the throttle valvein the first direction (with no flow through the turboexpander) and flowing all of the working fluidthrough the turboexpander(with no flow through the throttle valve), including all split ratios of the working fluidbetween the throttle valveand the turboexpander. The split of the working fluidinto the first portionand the second portioncan be adjusted based on the operating conditions of the heat pump cycle, the first environment, the second environment, or any combinations of these. In some implementations, a pressure control valve is installed on the second flowlineupstream of the turboexpander. The pressure control valve can reduce a pressure of the second portionto ensure the second portionentering the turboexpanderis in a vapor state. The second portionexpands through the turbine the turboexpander, dropping the pressure and temperature of the second portionand rotating the turbine and rotor of the turboexpander, causing the turboexpanderto generate electrical power. The second portionexiting the turboexpandercontinues to flow through the second flowlineand rejoins the first portion(via the second reversible valvein the third position) exiting the throttle valvein the first flowlineto reform the working fluid. In some implementations, the second portionexiting the turboexpanderhas an operating temperature that is less (cooler) than an operating temperature of the first portionexiting the throttle valve. Thus, inclusion of the turboexpandercan generate a cooler operating temperature for the working fluidto more efficiently cool the first environmentin comparison to a heat pump cycle that does not include the turboexpander. The working fluidthen flows to the first heat exchangerto continue the heat pump cycle in the system. In the cooling mode, the systemeffectively transfers heat from the first environmentto the second environmenteven though the first environmentis cooler in temperature in comparison to the second environment. The cooling mode is applicable, for example, during warm weather in which the first environmentis an indoor environment that is cooler than the second environment, which is an outdoor environment.

In certain instances, the turboexpanderis electrically connected to the compressor. In some implementations, the systemincludes the power electronicsof system(described previously and shown in), including a VSD. The electrical output of the generator of the turboexpanderis coupled to the power electronics. The output of the VSDcan 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. For example, the electrical power generated by the turboexpander(in response to expansion of the second portion) can be supplied to the compressorvia the power electronicsfor use in driving the compressor(e.g., powering an electric motor that drives the compressor impeller) to pressurize the working fluidreceived from the first heat exchanger.

In the systemshown in, the first reversible valveis in the second position, the second reversible valveis in the fourth position, and the working fluidis flowing through the first heat exchanger, the second heat exchanger, and the throttle valvein the second direction, so the systemis in the heating mode. In the heating mode, the working fluidflows through the second heat exchanger. In the second heat exchanger, heat is transferred from the second environmentto the working fluid. In response to receiving heat from the second environmentvia the second heat exchanger, the working fluidat least partially vaporizes. In some cases, the working fluidcompletely vaporizes in response to receiving heat from the second environmentvia the second heat exchanger.

The working fluidexiting the second heat exchangerflows to the compressorvia the first reversible valvein the second position. The compressorpressurizes the working fluidas the working fluidflows through the compressor. A discharge pressure of the working fluidexiting the compressoris greater than a suction pressure of the working fluidentering the compressor.

The working fluidexiting the compressorflows to the first heat exchangervia the first reversible valvein the second position. In the first heat exchanger, heat is transferred from the working fluidto the first environment. In response to losing heat to the first environmentvia the first heat exchanger, the working fluidat least partially condenses. In some cases, the working fluidcompletely condenses in response to losing heat to the first environmentvia the first heat exchanger.

The working fluidexiting the first heat exchangerflows to the first flowline. The working fluidsplits into the first portionand the second portionThe first portioncontinues to flow through the first flowlineand to the throttle valve. The second portionflows from the first flowlinethrough the second flowlineto the turboexpandervia the second reversible valvein the fourth position. The systemcan be configured to flow all of the working fluidthrough only the throttle valvein the second direction or only the turboexpanderduring some operating conditions. The throttle valvecan be designed to handle the full flow of the working fluidflowing through the throttle valvein the second direction. The turboexpandercan be designed to handle the full flow of the working fluidflowing through the turboexpander. For example, the aerodynamic aspects of the turboexpander(such as the turbine wheeland aero surfaces adjacent the turbine wheel) are designed to handle the full flow of the working fluidflowing through the turboexpander. As such, the systemis capable of handling the full range across flowing all of the working fluidthrough the throttle valvein the second direction (with no flow through the turboexpander) and flowing all of the working fluidthrough the turboexpander(with no flow through the throttle valve), including all split ratios of the working fluidbetween the throttle valveand the turboexpander. The split of the working fluidinto the first portionand the second portioncan be adjusted based on the operating conditions of the heat pump cycle, the first environment, the second environment, or any combinations of these. The turboexpandergenerates electrical power as the second portionexpands through the turboexpander. The second portionexiting the turboexpandercontinues to flow through the second flowlineand rejoins the first portion(via the second reversible valvein the fourth position) exiting the throttle valvein the first flowlineto reform the working fluid. In some implementations, the second portionexiting the turboexpanderhas an operating temperature that is less (cooler) than an operating temperature of the first portionexiting the throttle valve. Thus, inclusion of the turboexpandercan generate a cooler operating temperature for the working fluidto more efficiently receive heat from the second environmentin comparison to a heat pump cycle that does not include the turboexpander. The working fluidthen flows to the second heat exchangerto continue the heat pump cycle in the system. In the heating mode, the systemeffectively transfers heat from the second environmentto the first environmenteven though the second environmentis cooler in temperature in comparison to the first environment. The heating mode is applicable, for example, during cool weather in which the first environmentis an indoor environment that is warmer than the second environment, which is an outdoor environment. In the heating mode, the electrical power generated by the turboexpander(in response to expansion of the second portion) can be supplied to the compressorvia the power electronicsfor the compressorto pressurize the working fluidreceived from the second heat exchanger.

illustrate an implementation of the systemin which the turboexpanderis mechanically coupled to the compressor. The rotorof the turboexpanderis coupled to an impellerof the compressorso that they rotate together. For example, the impellerof the compressorcan be coupled to a shaft of the compressor, and the shaft of the compressorcan be coupled to the rotorof the turboexpander. Because the rotorof the turboexpanderis coupled to the impellerof the compressor, the impellerrotates with the rotorof the turboexpander. In some implementations, as shown in, the rotorof the turboexpanderis coupled to the impellerof the compressorby a drive shaft. In some implementations, the drive shaftdirectly couples the rotorto the impeller, such that the turboexpanderand the compressorrotate at the same rotational speed. In some implementations, the rotorof the turboexpanderis coupled to the impellerof the compressorby a gear train with multiple drive shafts for indirectly coupling the rotorto the impeller, such that the turboexpanderand the compressorrotate at different rotational speeds. Because of this coupling, the expansion work from the expansion of the second portionof the working fluidcan be transferred to the compressorfor pressurizing the working fluidflowing through the compressor. By transferring the expansion work from the turboexpanderto the compressor, the electrical power necessary for the compressorto pressurize the working fluidcan be reduced.

In the systemshown in, the first reversible valveis in the first position, the second reversible valveis in the third position, and the working fluidis flowing through the first heat exchanger, the second heat exchanger, and the throttle valvein the first direction, so the systemis in the cooling mode. In the systemshown in, the first reversible valveis in the second position, the second reversible valveis in the fourth position, and the working fluidis flowing through the first heat exchanger, the second heat exchanger, and the throttle valvein the first direction, so the systemis in the heating mode.

depict a valve configurationE that can be implemented in any of the heat pump cycles of, orD. The valve configurationE includes a first three-way valveand a second three-way valvewhich can replace the first reversible valve(shown in). The first three-way valveis switchable between a fifth position and a sixth position. The first three-way valveis installed on the first flowline(instead of the first reversible valveshown in, andD). The first three-way valvedefines two ports: an inlet port and an outlet port. A flow path through the first three-way valveconnects the inlet port and the outlet port of the first three-way valveWhen in the fifth position, the inlet port of the first three-way valveis in fluid communication with the first heat exchanger, and the outlet port of the first three-way valveis in fluid communication with the suction of the compressor, such that the first three-way valvedirects flow of the working fluidfrom the first heat exchangerto the compressor.