Cascading heat pump systems with self-drain and heat-output control functionalities

Abstract

Provided herein are systems and methods for generating steam and other heat-generating applications, cascading heat pump systems that are capable of operating efficiently across a wide range of heat source conditions (e.g., ambient temperatures) and sink conditions (e.g., heat output demands, such as temperature, flow rates). A first working fluid circulates through a bottom heat pump cycle, transferring heat to a second working fluid in a top heat pump cycle via a cascading heat exchanger. The heat is output (e.g., steam produced) at the heat-sink heat exchanger of the top cycle and may be further boosted using one or more downstream compressors. The system includes passively positioned receivers at lower elevations relative to heat exchanges and compressors to facilitate gravity-driven liquid-charge management, enabling heated working fluids (e.g., refrigerants) to relocate during inactive states. Furthermore, a compressor set may utilize valves with different crack pressures to bypass one or more compressors.

Description

PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 1 of 59PCT ApplicationCascading Heat Pump Systems with Self-Drain and Heat-Output Control FunctionalitiesCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119(e) of US Provisional Patent Application 63 / 680,000, filed on 2024-08-06, which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] Industrial steam generation is one of the most carbon-intensive and technically challenging processes to decarbonize. In the United States, the industrial sector contributes approximately 1.5 gigatons of carbon dioxide (CO2) equivalent emissions annually, with steam production alone accounting for over 200 million metric tons of CO2and consuming nearly 4 quads of primary energy each year. The vast majority of this steam is produced by combustionbased systems— such as fossil-fueled boilers and cogeneration units— that are inflexible, inefficient under partial loads, and inherently incompatible with full electrification goals. While electric boilers offer a direct electrification path, they suffer from poor efficiency and high electricity costs. Waste heat-driven heat pumps have also been explored, but their reliance on site-specific heat sources severely limits deployment potential due to inconsistent waste heat availability and high integration complexity. These technical and logistical constraints have left industrial users with few viable options for flexible, high-temperature, zero-emission steam generation.SUMMARY

[0003] Provided herein are cascading heat pump systems and methods operating such systems (e.g., for generating steam and other heat-generating applications). Such systems are capable of operating efficiently across a wide range of heat source conditions (e.g., ambient temperatures) and sink conditions (e.g., heat output demands, such as temperature, flow rates). A first working fluid circulates through a bottom heat pump cycle, transferring heat to a second working fluid in a top heat pump cycle via a cascading heat exchanger. The heat is output (e.g., steam produced) at the heat-sink heat exchanger of the top cycle and may be further boostedPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 2 of 59PCT Application using one or more downstream compressors. The system includes passively positioned receivers at lower elevations relative to heat exchangers and compressors to facilitate gravity- driven liquid-charge management, enabling heated working fluids (e.g., refrigerants) to relocate during inactive states. Furthermore, a compressor set may utilize valves with different crack pressures to bypass one or more compressors.

[0004] Clause 1. A cascading heat pump system 100 for receiving heat from a heat source and providing heat to an input stream 171, the cascading heat pump system 100 comprising: a bottom heat pump cycle 120 comprising a bottom-cycle compressor set 130, a bottom-cycle receiver 121, a bottom-cycle expansion valve 129, and a bottom-cycle heat exchanger 122, utilizing a bottom-cycle working fluid 189 and configured to receive the heat from the heat source; a top heat pump cycle 140 comprising a top-cycle compressor set 150, a top-cycle expansion valve 149, and a heat-sink heat exchanger 162, utilizing a top-cycle working fluid 199 and configured to receive the input stream 171 and to transfer heat from the top-cycle working fluid 199 to the input stream 171, thereby generating an output stream 172; and a cascading heat exchanger 142 thermally coupling the bottom heat pump cycle 120 and the top heat pump cycle 140 and configured to transfer heat from the bottom-cycle working fluid 189, discharged from the bottom-cycle compressor set 130, to the top-cycle working fluid 199 received from the top-cycle expansion valve 149 and directed to the top-cycle compressor set 150, wherein: the bottom-cycle receiver 121 is positioned downstream from the cascading heat exchanger 142 and configured to hold the bottom-cycle working fluid 189 received from the cascading heat exchanger 142, and the bottom-cycle receiver 121 is positioned at a lower elevation relative to the cascading heat exchanger 142, such that the bottom-cycle working fluid 189 drains from the cascading heat exchanger 142 into the bottom-cycle receiver 121 when the bottom-cycle compressor set 130 is not operational.

[0005] Clause 2. The cascading heat pump system 100 of clause 1, wherein the cascading heat exchanger 142 is positioned at a lower elevation relative to the bottom-cycle compressor set 130 such that the bottom-cycle working fluid 189 drains from the bottom-cycle compressor set 130 and through the cascading heat exchanger 142 into the bottom-cycle receiver 121 when the bottom-cycle compressor set 130 is not operational.

[0006] Clause 3. The cascading heat pump system 100 of clause 1, wherein the top heat pump cycle 140 further comprises a top-cycle receiver 141, wherein: the top-cycle receiver 141 isPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 3 of 59PCT Application positioned downstream from the heat-sink heat exchanger 162 and configured to hold the topcycle working fluid 199 received from the heat-sink heat exchanger 162, and the top-cycle receiver 141 is positioned at a lower elevation relative to the heat-sink heat exchanger 162, such that the top-cycle working fluid 199 drains from the heat-sink heat exchanger 162 into the top-cycle receiver 141 when the top-cycle compressor set 150 is not operational.

[0007] Clause 4. The cascading heat pump system 100 of clause 3, wherein the top-cycle compressor set 150 is positioned at a higher elevation than the heat-sink heat exchanger 162 such that the top-cycle working fluid drains from the top-cycle compressor set 150 through the heat-sink heat exchanger 162 and into the top-cycle receiver 141 when the top-cycle compressor set 150 is not operational.

[0008] Clause 5. The cascading heat pump system 100 of clause 1, wherein the bottom-cycle receiver 121 is operable as a bottom-cycle economizer 128 and comprises a bottom-cycle- economizer expansion valve 126.

[0009] Clause 6. The cascading heat pump system 100 of clause 1, wherein the bottom-cycle receiver 121 has a volume of at least 125% of the cascading heat exchanger 142.

[0010] Clause 7. The cascading heat pump system 100 of clause 1, wherein the bottom-cycle receiver 121 has a volume of at least 30% of the bottom heat pump cycle 120.

[0011] Clause 8. The cascading heat pump system 100 of clause 1, wherein the bottom-cycle receiver 121 comprises a drain plug for removing the bottom-cycle working fluid 189 from the bottom heat pump cycle 120.

[0012] Clause 9. The cascading heat pump system 100 of clause 1, wherein the bottom-cycle receiver 121 is fluidically coupled to the bottom-cycle compressor set 130 for pumping the bottom-cycle working fluid 189 in a liquid form into the bottom-cycle compressor set 130 for lubricating the bottom-cycle compressor set 130 when the cascading heat pump system 100 is starting up.

[0013] Clause 10. The cascading heat pump system 100 of clause 1, wherein the heat-sink heat exchanger 162 and the top-cycle receiver 141 are fluidically connected by a heat-sink heat exchanger exit line 194 that is sloped toward the top-cycle receiver 141.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 4 of 59PCT Application

[0014] Clause 11. The cascading heat pump system 100 of clause 1, wherein the top-cycle compressor set 150 and the heat-sink heat exchanger 162 are fluidical ly connected by a topcycle discharge line 193 that is sloped toward the heat-sink heat exchanger 162.

[0015] Clause 12. The cascading heat pump system 100 of clause 1, wherein the bottom-cycle receiver 121 is positioned between the cascading heat exchanger 142 and the bottom-cycle expansion valve 129 and is configured to shut down when the bottom-cycle compressor set 130 is not operational, thereby maintaining the bottom-cycle working fluid 189 in the bottom-cycle receiver 121.

[0016] Clause 13. The cascading heat pump system 100 of clause 1, wherein the bottom-cycle receiver 121 is connected with the bottom-cycle expansion valve 129 by a bottom-cycle return line 186, forming a trap, thereby maintaining the bottom-cycle working fluid 189 in the bottomcycle receiver 121.

[0017] Clause 14. The cascading heat pump system 100 of clause 1, wherein each of the bottom-cycle working fluid 189 and the top-cycle working fluid 199 is selected from the group consisting of water, steam, glycol, air, a fluorocarbon, a hydrofluoroolefin, a hydrofluoroether, a hydrochlorofluoroolefins, a hydrocarbon, ammonia (NH3), water (H2O), carbon dioxide (CO2), pentane (C5H12), butane (C4H10), isobutane (HC(CH3)3), propane (C3H8), and propene (C3H6), or a combination thereof.

[0018] Clause 15. The cascading heat pump system 100 of clause 1, wherein each of the bottom-cycle compressor set 130 and the top-cycle compressor set 150 comprises a centrifugal compressor.

[0019] Clause 16. The cascading heat pump system 100 of clause 1, wherein each of the bottom-cycle compressor set 130 and the top-cycle compressor set 150 comprises a set of four compressors connected in series.

[0020] Clause 17. The cascading heat pump system 100 of clause 1, wherein at least the bottom heat pump cycle 120 comprises a bottom-cycle suction line 180 and an additional bottom-cycle suction line 181 extending from the bottom-cycle heat exchanger 122 to different compressors in the bottom-cycle compressor set 130.

[0021] Clause 18. The cascading heat pump system 100 of clause 17, wherein at least one of the bottom-cycle suction line 180 and the additional bottom-cycle suction line 181 comprises aPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 5 of 59PCT Application control valve for controlling distribution of the bottom-cycle working fluid 189 between the bottom-cycle suction line 180 and the additional bottom-cycle suction line 181.

[0022] Clause 19. The cascading heat pump system 100 of clause 1, further comprising a heatsource cycle 110 comprising a heat-source heat exchanger 112, configured to transfer heat from ambient air into a heat-source working fluid, and a pump 114, configured to pump the heatsource working fluid to the bottom-cycle heat exchanger 122.

[0023] Clause 20. The cascading heat pump system 100 of clause 1, further comprising a downstream cycle 170 comprising a compressor 174 such that the input stream 171 passes through the heat-sink heat exchanger 162 and forms an output stream 172, which is directed to the compressor 174 to form an elevated output stream 175.

[0024] Clause 21. A cascading heat pump system 100 comprising: a bottom heat pump cycle 120; a top heat pump cycle 140 thermally coupled to the bottom heat pump cycle 120 via a cascading heat exchanger 142; a heat-sink heat exchanger 162 configured to receive compressed top-cycle working fluid 199 from the top heat pump cycle 140 and generate an output stream 172; a downstream cycle 170 comprising a downstream controller 179 and a downstream compressor 174 configured to receive the output stream 172 and generate an elevated output stream 175, wherein the downstream controller 179 is configured to regulate thermal output of the cascading heat pump system 100 by modifying at least an output of the compressor 174.

[0025] Clause 22. The cascading heat pump system 100 of clause 21, wherein: the downstream cycle 170 further comprises a downstream heat exchanger 177 configured to receive the elevated output stream 175 and form a controlled output stream 176, the downstream heat exchanger 177 is further configured to receive an input fluid 178 and form a heated fluid 178a by transferring heat from the elevated output stream 175 to the input fluid 178.

[0026] Clause 23. The cascading heat pump system 100 of clause 22, wherein the downstream controller 179 is configured to control a flow rate of the input fluid 178 through the downstream heat exchanger 177.

[0027] Clause 24. The cascading heat pump system 100 of clause 22, wherein the input fluid178 received by the downstream heat exchanger 177 is selected from the group consisting ofPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 6 of 59PCT Application water, a bottom-cycle working fluid 189 used in the bottom heat pump cycle 120, a top-cycle working fluid 199 used in the top heat pump cycle 140, or ambient air.

[0028] Clause 25. The cascading heat pump system 100 of clause 21, further comprising a water injector 165 configured to introduce an additional fluid 173 into one or more of the output stream 172 and the elevated output stream 175.

[0029] Clause 26. The cascading heat pump system 100 of clause 25, wherein: the output stream 172 is steam; and the additional fluid 173 is water injected to control a superheating level in the elevated output stream 175.

[0030] Clause 27. The cascading heat pump system 100 of clause 21, wherein the downstream controller 179 is configured to maintain the output stream 172 within a target pressure and temperature band by modulating speed or flow rate through the downstream compressor 174.

[0031] Clause 28. The cascading heat pump system 100 of clause 21, wherein the downstream cycle 170 further comprises an additional compressor 174a connected in series with the downstream compressors 174.

[0032] Clause 29. The cascading heat pump system 100 of clause 28, wherein the additional compressor 174a is controlled independently of the downstream compressor 174 to provide a staged pressure increase across the downstream cycle 170.

[0033] Clause 30. The cascading heat pump system 100 of clause 28, wherein the downstream compressor 174 and the additional compressor 174a are mounted on a shared shaft and operate at coordinated rotational speeds.

[0034] Clause 31. The cascading heat pump system 100 of clause 28, wherein the additional compressor 174a is configured to activate only when the elevated output stream 175 requires a pressure greater than a defined threshold.

[0035] Clause 32. The cascading heat pump system 100 of clause 21, wherein the downstream cycle 170 further comprises an additional compressor 174a connected in parallel with the downstream compressor 174.

[0036] Clause 33. The cascading heat pump system 100 of clause 32, wherein each of the downstream compressor 174 and the additional compressor 174a is configured to receive a portion of the output stream 172 simultaneously.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 7 of 59PCT Application

[0037] Clause 34. The cascading heat pump system 100 of clause 32, wherein the output of the downstream compressor 174 and the additional compressor 174a is merged into a common elevated output stream 175.

[0038] Clause 35. The cascading heat pump system 100 of clause 32, wherein the downstream controller 179 is configured to selectively enable or disable the additional compressor 174a based on one or more of steam demand and temperature of a heat-source cycle 110.

[0039] Clause 36. The cascading heat pump system 100 of clause 21, wherein the downstream compressor 174 is a steam compressor selected from the group consisting of a centrifugal compressor, a positive-displacement compressor, and a rotary compressor.

[0040] Clause 37. The cascading heat pump system 100 of clause 21, wherein the downstream compressor 174 is a high-speed centrifugal compressor configured to operate at speeds greater than 30,000 rpm.

[0041] Clause 38. The cascading heat pump system 100 of clause 21, wherein the bottom heat pump cycle 120 comprises a bottom-cycle compressor set 130 having at least two compressors configured to operate in series.

[0042] Clause 39. The cascading heat pump system 100 of clause 21, further comprising a topcycle compressor set 150 comprising two or more compressors arranged in series.

[0043] Clause 40. The cascading heat pump system 100 of clause 21, wherein the top heat pump cycle 140 is configured to maintain a discharge temperature between approximately +120°C and +185°C.

[0044] Clause 41. A cascading heat pump system 100 comprising: a bottom heat pump cycle 120 comprising a bottom-cycle compressor set 130, wherein the bottom-cycle compressor set 130 comprises a first bottom-cycle compressor 131 and a second bottom-cycle compressor 132 defining a bottom low-pressure group 135a, and a third bottom-cycle compressor 133 and a fourth bottom-cycle compressor 134 defining a bottom high-pressure group 135b, wherein the cascading heat pump system 100 is configured such that: (i) during a first operating condition, a bottom-cycle working fluid 189 flows through the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132 prior to entering the third bottom-cycle compressor 133 and the fourth bottom-cycle compressor 134, and (ii) during a second operating condition, the bottom-cycle working fluid 189 bypasses the first bottom-cycle compressor 131 and the secondPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 8 of 59PCT Application bottom-cycle compressor 132 and flows directly to the third bottom-cycle compressor 133 and the fourth bottom-cycle compressor 134.

[0045] Clause 42. The cascading heat pump system 100 of clause 41, further comprising a bypass valve 123 positioned between a bottom-cycle heat exchanger 122 and the bottom-cycle compressor set 130, wherein the bypass valve 123 selectively directs the bottom-cycle working fluid 189 through a bottom-cycle suction line 180 or an additional bottom-cycle suction line 181.

[0046] Clause 43. The cascading heat pump system 100 of clause 41, wherein the bottomcycle compressor set 130 comprises an add-on compressor 139 disposed upstream of the first bottom-cycle compressor 131.

[0047] Clause 44. The cascading heat pump system 100 of clause 43, wherein the add-on compressor 139 is configured to increase suction pressure to the bottom low-pressure group 135a.

[0048] Clause 45. The cascading heat pump system 100 of clause 43, further comprising a first add-on valve 137a and a second add-on valve 137b configured to isolate or engage the add-on compressor 139.

[0049] Clause 46. The cascading heat pump system 100 of clause 41, wherein the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132 are staged in series.

[0050] Clause 47. The cascading heat pump system 100 of clause 46, further comprising a first check valve 138a positioned in a bypass line configured to bypass the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132.

[0051] Clause 48. The cascading heat pump system 100 of clause 47, further comprising a second check valve 138b disposed at a discharge of the second bottom-cycle compressor 132.

[0052] Clause 49. The cascading heat pump system 100 of clause 48, wherein the second check valve 138b has a higher crack pressure than the first check valve 138a.

[0053] Clause 50. The cascading heat pump system 100 of clause 48, wherein the first check valve 138a is configured to open and permit fluid flow when the low-pressure compressor stage135a is inactive.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 9 of 59PCT Application

[0054] Clause 51. The cascading heat pump system 100 of clause 48, wherein the second check valve 138b is configured to open and the first check valve 138a is configured to close when the low-pressure compressor stage 135a becomes active.

[0055] Clause 52. The cascading heat pump system 100 of clause 41, further comprising a bottom-cycle suction line 180, connected to the low-pressure compressor stage 135a, and an additional bottom-cycle suction line 181, bypassing the low-pressure compressor stage 135a and connected to the bottom high-pressure group 135b.

[0056] Clause 53. The cascading heat pump system 100 of clause 52, further comprising a bottom-cycle heat exchanger 122 comprising multiple outlet ports, each coupled to a separate suction line, comprising the bottom-cycle suction line 180 and the additional bottom-cycle suction line 181.

[0057] Clause 54. The cascading heat pump system 100 of clause 53, wherein the bottomcycle heat exchanger 122 is a shell-and-tube heat exchanger.

[0058] Clause 55. The cascading heat pump system 100 of clause 41, wherein each of the first bottom-cycle compressor 131, the second bottom-cycle compressor 132, the third bottom-cycle compressor 133, and the fourth bottom-cycle compressor 134 is a centrifugal compressor.

[0059] Clause 56. The cascading heat pump system 100 of clause 41, wherein the third bottom-cycle compressor 133 and the fourth bottom-cycle compressor 134 are configured to operate independently of the low-pressure group 135a.

[0060] Clause 57. The cascading heat pump system 100 of clause 41, wherein operation switches from a four-stage configuration to a two-stage configuration based on heat source temperature.

[0061] Clause 58. The cascading heat pump system 100 of clause 57, wherein the switch occurs when the heat source temperature exceeds a heating set temperature.

[0062] Clause 59. The cascading heat pump system 100 of clause 57, wherein the system reverts to the four-stage configuration when the heat source temperature falls below a cooling set.

[0063] Clause 60. The cascading heat pump system 100 of clause 59, wherein a difference between the heating and cooling set temperatures is at least 5°C.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 10 of 59PCT Application

[0064] These and other examples are described further below with reference to the figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The included drawings are for illustrative purposes and serve only to provide examples of possible structures and operations for the disclosed inventive systems, apparatus, and methods. These drawings in no way limit any changes in form and detail that may be made by one skilled in the art without departing from the spirit and scope of the disclosed implementations.

[0066] FIG. 1 illustrates a cascading heat pump system comprising a heat-source fluid cycle, a bottom heat pump cycle, a top heat pump cycle, and a downstream compressor, in accordance with some examples.

[0067] FIG. 2 illustrates a cascading heat pump system with gravity-driven self-drain features enabled by lower-elevation receivers that promote the redistribution / self-drain of the working fluid during idle periods of the system, in accordance with some examples.

[0068] FIGS. 3A and 3B illustrate examples of controlling the downstream process conditions using a downstream heat exchanger and / or a fluid injector.

[0069] FIGS. 4A and 4B illustrate examples of controlling the downstream process conditions using two downstream compressors.

[0070] FIG. 4C is an example of connecting a downstream compressor to two cascading heat pump systems.

[0071] FIG. 5A is an example of using a bypass valve to bypass one or more compressors in a compressor set.

[0072] FIG. 5B are plots of different parameters as a function of heat source temperature corresponding to the operation of a compressor set in FIG. 5A.

[0073] FIG. 5C is an example of a bypassable add-on compressor valve in a compressor set.

[0074] FIGS. 5D and 5E illustrate examples of using check valves with different crack pressures to bypass compressors in a compressor set.

[0075] FIG. 6 is a process flowchart corresponding to a method of operating a cascading heat pump system, in accordance with some examples.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 11 of 59PCT ApplicationDETAILED DESCRIPTION

[0076] While various examples have been shown and described herein, it will be obvious to those skilled in the art that such examples are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the disclosure. It should be understood that various alternatives to the examples described herein may be employed.Introduction

[0077] Industrial heat supply (e.g., steam generation) remains a critical challenge in the global effort to decarbonize high-emission sectors. The vast majority of industrial heat / steam is produced using fossil-fueled boilers, which are inherently inflexible, highly carbon-intensive, and poorly suited to electrification. While conventional electric boilers offer a partial solution, they suffer from low efficiency and high operating costs. Heat pumps represent a more promising pathway, but existing designs typically operate within narrow temperature ranges and are often reliant on site-specific waste heat sources, which severely limits their applicability across diverse industrial settings.

[0078] This disclosure presents systems and methods for generating steam and other heatgenerating applications and cascading heat pump systems that are capable of operating efficiently across a wide range of heat source conditions (e.g., ambient temperatures) and sink conditions (e.g., heat output demands, such as temperature, flow rates). For example, these cascading heat pump systems can operate over a wide range of ambient or process heat source conditions (e.g., from -20°C to +40°C) and heat sink targets (e.g., +80°C to +200°C steam). A first working fluid circulates through a bottom heat pump cycle, transferring heat to a second working fluid in a top heat pump cycle via a cascading heat exchanger. Furthermore, a compressor set (in one of the heat pump cycles) may utilize valves with different crack pressures to bypass one or more compressors.

[0079] The heat is output (e.g., steam produced) at the heat-sink heat exchanger of the top cycle and may be further boosted by using one or more downstream compressors. When multiple downstream compressors are used, these compressors may be connected in series orPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 12 of 59PCT Application parallel and / or may be controlled independently. Furthermore, in other examples, a single downstream compressor may be connected to two cascading heat pump systems. The output stream (e.g., directed to one or more downstream compressors) may have various injection points that allow additional control of the temperature of the output stream. These injections may be before the downstream compressors, into the downstream compressors, and / or after the downstream compressors.

[0080] The system may include passively positioned receivers at lower elevations relative to heat exchanges and compressors to facilitate gravity-driven liquid-charge management, enabling heated working fluids (e.g., refrigerants) to relocate during inactive states. Specifically, by locating one or more receivers below key heat exchangers and compressors in each cycle, working fluid is drained by gravity during shutdown conditions, preventing residual hot working fluids from remaining in components like steam generators or motor cavities. This simplifies startup (by having the liquid working fluid available for pumping for lubrication of the compressors), improves energy efficiency, and reduces the risk of overheating or refrigerant boil-off during idle periods. Importantly, the gravity-fed arrangement eliminates the need for expensive, high-temperature-rated refrigerant pumps and associated control logic.Definitions

[0081] The term "heat exchanger," as used herein, generally refers to a mechanism configured to transfer heat from a first one or more fluids to a second one or more fluids. These fluids may be gases and / or liquids. In an instance, a heat exchanger may be a single heat exchanger and / or a multiple heat exchanger arrangement. A multiple heat-exchanger arrangement may comprise two or more heat exchangers (in parallel and / or series). A heat exchanger may refer to a steam generator, a hot water generator, an evaporator, a condenser, a two-phase heat exchanger, a three-fluid heat exchanger, a heat recovery heat exchanger, a waste heat exchanger, a suction-line heat exchanger, a subcooler, a de-superheater, and / or a combination thereof. A heat exchanger may be an air-source heat exchanger. A heat exchanger may change the temperature, pressure, composition, phase, or a combination thereof of one or more fluids put through the heat exchanger. A heat exchanger described herein may refer to, or be, a shell and tube heat exchanger, a brazed plate, a welded plate, a gasketed plate, a plate- fin, plate and shell, or a microtube. For example, a heat exchanger may have a fin tube on a sidePCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 13 of 59PCT Application in thermal contact with an ambient air stream, may comprise a microtube, may be additively manufactured, and / or may comprise a tube-in-tube heat exchanger. A heat exchanger may have multiple inlet or outlet ports to perform multiple functions of the heat pump. Additional elements and configurations may be selected to increase the heat exchanger efficiency, such as one or more heat transfer enhancers selected from the group consisting of an extended surface, a fin, turbulators (e.g., twisted tape) to increase turbulence of a fluid passing through the heat exchanger, and / or surface treatments (e.g., porous media).

[0082] The term "working fluid," as used herein, generally refers to a substance (e.g., a liquid, vapor, gas, or a combination thereof) that interacts with at least one element of a system. A working fluid refers to a heat transfer fluid and / or a feed fluid (e.g., feed stream). A working fluid may refer to a fluid at a stage of a fluid circulating through a system and / or cycle. A working fluid may reject or absorb heat, change composition, and / or phase while circulating through a cycle. A working fluid may be a coolant, a refrigerant, and / or a lubricant. Some examples of a working fluid, include but are not limited to, water, steam, glycol, air, a fluorocarbon, a hydrofluoroolefin, a hydrofluoroether, a hydrochlorofluoroolefins, a hydrocarbon, ammonia (NH3), water (H2O), carbon dioxide (CO2), pentane (C5H12), butane (C4H10), isobutane (HCfCHsh), propane (CsHs), and propene (CsHe), or a combination thereof.

[0083] The term "compressor," as used herein, generally refers to a mechanism for increasing the pressure of a substance (e.g., a working fluid). In some examples, a compressor may be a single compressor or a multiple-stage compressor arrangement (e.g., two or more compressors connected in parallel, series, or a combination thereof). Some examples of a compressor include,, but are not limited to, a double ended compressor, a centrifugal compressor, a lubricated compressor, an oil free compressor, an axial compressor, a steam compressor, a single shaft compressor, a magnetically coupled compressor, a multiple shaft compressor, and / or a positive displacement compressor (e.g., a screw compressor, a scroll compressor, a reciprocating compressor, etc.). A double-ended compressor may be a double-ended centrifugal compressor. In some examples, a centrifugal compressor may be an oil-free centrifugal compressor (e.g., configured to provide a refrigerant to a shaft and or rotor of the compressor with the refrigerant at least partially evaporating in a motor cavity of the compressor).

[0084] The term "hot water" or "high temperature water" may refer to a water stream that has a temperature of +30°C to +100°C or, more specifically, +40°C to +80°C. The temperature ofPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 14 of 59PCT Application hot water may be greater than +40°C, +45°C, +50°C, +55°C, +60°C, +65°C, +70°C, +75°C, +80°C, +85°C, +90°C, or even 9+5°C. The term "pressurized hot water" or "pressurized high temperature water" may refer to a water stream that has a temperature of +100°C to +200°C. The temperature of pressurized hot water may be greater than +100°C, +110°C, +120°C, +130°C, +140°C, +150°C, +160°C, +170°C, +180°C, and even +190°C. The term "warm water" or "low-temperature water" may refer to water stream that has a temperature +10°C to +50°C or, more specifically, +15°C to +40°C, such as less +50°C, +45°C, +40°C, +35°C, +30°C, +25°C, +20°C, 1+5°C, +10°C, or even +5°C.

[0085] Whenever the term "at least," "greater than," or "greater than or equal to" precedes the first numerical value in a series of two or more numerical values, the term "at least" or "greater than" applies to each one of the numerical values in that series of numerical values. Whenever the term "no more than," "less than," or "less than or equal to" precedes the first numerical value in a series of two or more numerical values, the term "no more than" or "less than" applies to each one of the numerical values in that series of numerical values. The term "about" or "nearly" as used herein generally refers to within (plus or minus) 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of a designated value. As used herein, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise.

[0086] The term "heat-source cycle" may be used interchangeably with "transfer fluid pump cycle" and "heat transfer fluid cycle."General Features

[0087] In some examples, a temperature of a feed stream (e.g., a feed stream comprising water) to a heat exchanger (e.g., a steam generator) of a system described herein may be less than or equal to about 150°C, 140°C, 130°C, 120°C, 110°C, 100°C, 95°C, 90°C, 85°C, 80°C, 75°C, 70°C, 65°C, 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C, 5°C or lower. The temperature of the feed stream (e.g., a feed stream comprising water) to a heat exchanger (e.g., a steam generator) of a system described herein may be greater than or equal to about, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or greater. The temperature of the feed stream (e.g., a feed stream comprising water) to a heat exchanger (e.g., a steamPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 15 of 59PCT Application generator) of a system described herein may be between the two temperatures described above, for example, between 15-95°C.

[0088] In some cases, the first heat pump cycle (e.g., a bottom cycle) may receive an ambient air stream with an air temperature that is less than or equal to about 150°C, 140°C, 130°C, 120°C, 110°C, 100°C, 95°C, 90°C, 85°C, 80°C, 75°C, 70°C, 65°C, 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C, 5°C or lower, and may output a working fluid at a temperature that is greater than or equal to about 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or greater.

[0089] In some examples, a second heat pump cycle (e.g., a top cycle) may receive a working fluid with a temperature that is less than or equal to about 150°C, 140°C, 130°C, 120°C, 110°C, 100°C, 95°C, 90°C, 85°C, 80°C, 75°C, 70°C, 65°C, 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C, 5°C or lower, and may output a working fluid at a temperature that is greater than or equal 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or greater. For example, the first heat pump (e.g., bottom cycle) may receive an ambient air stream with an air temperature of 15°C and deliver heat (e.g., output a working fluid) at a temperature of 65°C, and the second heat pump (e.g., top cycle) may receive the 65°C working fluid through a heat exchanger coupled to the first heat pump and second heat pump cycles and the second heat pump cycle may generate steam at a temperature of 150°C.

[0090] In some examples, the coefficient of performance of the system may be greater than or equal to about 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.5, 4.0, 4.5, 5, or greater. The coefficient of performance of the system may be between any two values described herein.

[0091] In some examples, the system may comprise a compressor. The isentropic efficiency of the compressor may be greater than or equal to about 60%, 70%, 80%, 90% or greater. The isentropic efficiency of the compressor may be between any two values described herein. The compressor may have a motor that is greater than or equal to about 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% efficient. The efficiency of the motor may be between any two values described herein. The compressor may be designed (e.g., through double-ended, preloaded springs and / or magnetic coils) to have a thrust of less than about 400 lbs, 300 lbs, 250 lbs, 200PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 16 of 59PCT Application lbs, 175 lbs, 150 lbs, 125 lbs, or 100 lbs. The thrust of the compressor may be between any two values described herein.

[0092] In some examples, the system may have a steam flow rate greater than or equal to about 0.5 t / hr, 1 t / hr, 2 t / hr, 4 t / hr, 6 t / hr, 8 t / hr, 10 t / hr, 12 t / hr, 15 t / hr, or 20 t / hr. In some examples, the system may have a steam flow rate less than or equal to about 0.5 t / hr, 1 t / hr, 2 t / hr, 4 t / hr, 6 t / hr, 8 t / hr, 10 t / hr, 12 t / hr, 15 t / hr, or 20 t / hr. The steam flow rate may be between any two values described herein.

[0093] In some examples, the system may comprise an air-source heat exchanger. The capacity of the air-source heat exchanger may be greater than or equal to about 100 kW, 200 kW, 300 kW, 400 kW, 500 kW, 600 kW, 800 kW, 1 MW, 2 MW, 4 MW, 6 MW, 8 MW, or 10 MW. The capacity of the air-source heat exchanger may be less than or equal to about 100 kW, 200 kW, 300 kW, 400 kW, 500 kW, 600 kW, 800 kW, 1 MW, 2 MW, 4 MW, 6 MW, 8 MW, or 10 MW. The capacity of the air-source heat exchanger may be between any two values described herein.

[0094] In some examples, the system may comprise a glycol loop and an evaporator. The pinch point between the glycol loop and the evaporator saturation temperature may be greater than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, or 10°C. The pinch point between the glycol loop and the evaporator saturation temperature may be less than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, or 10°C. The pinch point between the glycol loop and the evaporator saturation temperature may be between any two values described herein.

[0095] In some examples, the system may comprise a steam generator and steam. The pinch point between the top cycle refrigerant saturation temperature in the steam generator and the steam may be greater than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, or 10°C. The pinch point between the top cycle refrigerant saturation temperature in the steam generator and the steam may be less than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, or 10°C. The pinch point between the top cycle refrigerant saturation temperature in the steam generator and the steam may be between any two values described herein.

[0096] In some examples, the system may comprise a condenser and pressurized hot water.The pinch point between the top cycle refrigerant temperature in the condenser and thePCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 17 of 59PCT Application pressurized hot water may be greater than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, 10°C, 15°C, or 20°C. The pinch point between the top cycle refrigerant temperature in the condenser and the pressurized hot water may be less than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, 10°C, 15°C, or 20°C. The pinch point between the top cycle refrigerant temperature in the condenser and the pressurized hot water may be between any two values described herein.

[0097] In some examples, the system may comprise a top cycle evaporator and a bottom cycle condenser. The pinch point between the top cycle evaporator saturation temperature and the bottom cycle condenser saturation temperature may be greater than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, or 10°C. The pinch point between the top cycle evaporator saturation temperature and the bottom cycle condenser saturation temperature may be less than or equal to about 0.1°C, 0.2°C, 0.4°C, 0.6°C, 0.8°C, 1°C, 2°C, 4°C, 6°C, 8°C, or 10°C. The pinch point between the top cycle evaporator saturation temperature and the bottom cycle condenser saturation temperature may be between any two values described herein.

[0098] In some examples, the system may comprise an economizer. The temperature of the superheat in the economizer may be greater than or equal to about 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 40°C, or 50°C. The temperature of the superheat in the economizer may be less than or equal to about 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 40°C, or 50°C. The temperature of the superheat in the economizer may be between any two values described herein. The flow of the economizer may be greater than or equal to about 0%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, or 50% of the main refrigerant flow. The flow of the economizer may be less than or equal to about 0%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, or 50% of the main refrigerant flow. The flow of the economizer may be between any two values described herein.

[0099] In some examples, the system may comprise a suction line heat exchanger. The suction line heat exchanger may have an effectiveness of greater than or equal to about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1. The effectiveness of the suction line heat exchanger may be between any two values described herein.

[0100] In some examples, the system may comprise motor coolant. The motor coolant flow may be greater than or equal to about 0%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, or 20% of the main refrigerant flow. The motor coolant flow may be less than or equal to about 0%, 1%,PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 18 of 59PCT Application2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, or 20% of the main refrigerant flow. The motor coolant flow may be between any two values described herein.FIG. 1: Cascading Heat Pump Systems

[0101] FIG. 1 is a block diagram of a cascading heat pump system 100, in accordance with some examples. As shown, the cascading heat pump system 100 may comprise a heat-source cycle 110, a bottom heat pump cycle 120, a top heat pump cycle 140, and a downstream cycle 170. In some examples, the cascading heat pump system 100 may not include one or both of the heat-source cycle 110 and the downstream cycle 170, e.g., heat may be supplied (into the cascading heat pump system 100) directly into the heat-source cycle 110. Similarly, heat may be removed directly from the top heat pump cycle 140. Furthermore, the cascading heat pump system 100 may include one or more additional heat pump cycles, which are connected in series and / or parallel with the bottom heat pump cycle 120 and / or the top heat pump cycle 140.

[0102] These cycles are thermally coupled / interconnected by various heat exchangers. For example, the cascading heat pump system 100 may comprise a bottom-cycle heat exchanger 122 that thermally couples and is a part of both the heat-source cycle 110 and the bottom heat pump cycle 120. The cascading heat pump system 100 may also comprise a cascading heat exchanger 142 that thermally couples and is a part of both the bottom heat pump cycle 120 and the top heat pump cycle 140. Finally, the cascading heat pump system 100 may also comprise a heat-sink heat exchanger 162 that thermally couples and is a part of both the top heat pump cycle 140 and the downstream cycle 170.Heat-source cycle examples

[0103] The heat-source cycle 110 comprises a heat-source heat exchanger 112 used to heat a working fluid (e.g., glycol) and pumped into a bottom-cycle heat exchanger 122, where this working fluid is used to heat a bottom-cycle working fluid. In some examples, the heat-source cycle 110 also comprises a pump 114 for pumping the working fluid. In some examples, the heat-source heat exchanger 112 is an "air-sourced heat exchanger", which may also be referredPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 19 of 59PCT Application to as "air-source heat exchanger." In these examples, the ambient air may be used as a heat source, e.g., by flowing / forcing the ambient air through the heat-source heat exchanger 112.

[0104] As noted above, the heat-source cycle 110 may be a separate fluid loop, thermally coupled to the bottom heat pump cycle 120 by a bottom-cycle heat exchanger 122. This separation may provide various benefits, e.g., increased efficiency, ability to decouple an air source heat exchanger from the main components of the heat pump system (e.g., locating the air source heat exchanger outside and the heat pump inside or close to the steam end-user, defined by the downstream cycle 170), avoids long piping routes of pressurized refrigerant, simplicity in controls (e.g., easier methods of defrosting during cold weather by heating a glycol loop), and / or easier integration with other processes (e.g., waste heat sources or refrigeration system integration). The benefits of locating the heat pump closer to the steam end-user may include generation of lower pressure steam and / or increased efficiency of the heat pump. The benefits of shorter piping routes may include decreased risk of leakage and / or lower pressure drops, which may increase the efficiency of the heat pump.

[0105] In some examples, the temperature of an ambient air stream that passes through the heat-source heat exchanger 112 is -30°C to +50°C or, more specifically, -20°C to +40°C or even 0°C to +25°C.Bottom heat pump cycle examples

[0106] The bottom heat pump cycle 120 comprises at least a bottom-cycle compressor set 130 and a bottom-cycle expansion valve 129, forming a fluidic loop together with the cascading heat exchanger 142 and configured to circulate a bottom-cycle working fluid 189. Depending on the location in the bottom heat pump cycle 120, the bottom-cycle working fluid 189 has different temperatures, thereby enabling the heat received from the heat-source cycle 110 and the heat release to the top heat pump cycle 140.

[0107] In some examples, the bottom heat pump cycle 120 also comprises a bottom-cycle economizer 128 and a bottom-cycle-economizer expansion valve 126. For example, the bottomcycle economizer 128 may be positioned downstream from the cascading heat exchanger 142 and used to recover some additional heat before sending a portion of the bottom-cycle working fluid 189 to the bottom-cycle expansion valve 129. Another portion of the bottom-cycle workingPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 20 of 59PCT Application fluid 189 is sent to the bottom-cycle compressor set 130. In some examples, the bottom heat pump cycle 120 also comprises a bottom-cycle suction line heat exchanger, which provides a heat transfer from the stream directed to the bottom-cycle expansion valve 129 to the stream leaving the bottom-cycle heat exchanger 122 and directed to the bottom-cycle compressor set 130, in a manner similar to a top-cycle suction line heat exchanger described below.

[0108] The bottom-cycle compressor set 130 receives the bottom-cycle working fluid 189 from the bottom-cycle heat exchanger 122 via a bottom-cycle suction line 180. The bottomcycle compressor set 130 then compresses the bottom-cycle working fluid 189, thereby increasing its pressure and temperature. For example, the bottom-cycle compressor set 130 may increase the pressure by a factor greater than or equal to about 1.1, 1.2, 1.5, 2, 5, 10, 20, or 30. The bottom-cycle compressor set 130 may increase the pressure by a factor between any two values described here. The bottom-cycle compressor set 130 may increase the temperature by at least 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 80°C, 100°C, 120°C, or even 150°C. The temperature increase by the compressor may be between any two values described herein. For example, the temperature of the bottom-cycle working fluid 189 in the bottom-cycle suction line 180 may be -30°C to +60°C or, more specifically, -20°C to +40°C. This temperature may be referred to as a saturation temperature. In the same or other examples, the temperature of the bottom-cycle working fluid 189 in a bottom-cycle discharge line 183 (connected to the outlet of the bottom-cycle compressor set 130) may be 30-120°C or, more specifically, 60-85°C. This temperature may be referred to as the saturation temperature and may depend on the suction temperature presented above.

[0109] The bottom-cycle working fluid 189 is sent from the bottom-cycle compressor set 130 via the bottom-cycle discharge line 183 to the cascading heat exchanger 142. The bottom-cycle working fluid cools in the cascading heat exchanger 142 (by releasing the heat to the top-cycle working fluid 199) and is then directed to a bottom-cycle cascading heat exchanger exit line 184, e.g., at a temperature of +30°C to +90°C or, more specifically, +55°C to +75°C. The bottomcycle cascading heat exchanger exit line 184 may be connected to a bottom-cycle economizer 128 (when one is present) or directly to the bottom-cycle expansion valve 129 (when the bottom-cycle economizer 128 is not present, in which case the bottom-cycle cascading heat exchanger exit line 184 also functions as a bottom-cycle return line 186).PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 21 of 59PCT Application

[0110] When the bottom-cycle economizer 128 is present, the bottom-cycle cascading heat exchanger exit line 184 is split such that a portion of the bottom-cycle working fluid 189 is split into a first stream and a second stream. In some examples, the bottom heat pump cycle 120 comprises a flash tank type economizer, in which the fluid in the cascading heat exchanger line enters a first expansion valve, lowering the pressure and temperature before entering an economizer tank. The economizer tank separates vapor, which is routed to the compressor set, and liquid, which is routed to a second expansion valve.

[0111] The first stream passes through the bottom-cycle-economizer valve 126, which causes the first stream to drop in pressure and temperature, e.g., to a temperature of -20°C to +80°C or, more specifically, +20°C to +40°C. As both streams pass through the bottom-cycle economizer 128, the second stream (which is still at a higher pressure) releases heat to the first stream. The first stream may then be sent directly to the bottom-cycle compressor set 130, e.g., using a bottom-cycle economizer return line 185. The second stream is directed to the bottomcycle expansion valve 129 using a bottom-cycle return line 186. As the bottom-cycle working fluid 189 passes through the bottom-cycle expansion valve 129, the temperature of the bottomcycle working fluid 189 is reduced to -30°C to +60°C or, more specifically, -20°C to +40°C. From the bottom-cycle heat exchanger 122, the bottom-cycle working fluid 189 is directed into the bottom-cycle heat exchanger 122 and, thereafter, into the bottom-cycle suction line 180, at which point the cycle repeats.

[0112] In some examples, a portion of the bottom-cycle working fluid 189 exiting the bottomcycle heat exchanger 122 is split into an additional bottom-cycle suction line 181, which is directed to an intermediate stage of the bottom-cycle compressor set 130. For example, FIG. 1 illustrates that the additional bottom-cycle suction line 181 is connected to a line interconnecting the second bottom-cycle compressor 132 and the third bottom-cycle compressor 133. However, the additional bottom-cycle suction line 181 may be connected to any other compressor interconnecting lines. Similarly, the bottom-cycle economizer return line 185 is shown connected to a line interconnecting the third bottom-cycle compressor 133 and the fourth bottom-cycle compressor 134. However, the bottom-cycle economizer return line 185 may be connected to any other compressor interconnecting lines.

[0113] The bottom-cycle compressor set 130 may include any number of compressors (e.g., one, two, or more). For example, FIG. 1 illustrates an example with four compressors, e.g., aPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 22 of 59PCT Application first bottom-cycle compressor 131, a second bottom-cycle compressor 132, a third bottomcycle compressor 133, and a fourth bottom-cycle compressor 134. These compressors work in stages, e.g., the output of the first bottom-cycle compressor 131 is fed into the second bottomcycle compressor 132, and so on. In some examples, a pair of compressors may be driven by the same motor, e.g., a first bottom-cycle compressor 131 and a second bottom-cycle compressor 132 (or separately, a third bottom-cycle compressor 133 and a fourth bottom-cycle compressor 134), which means that these compressors operate at the same speed. In further examples, different motors may be used to drive different compressors (e.g., FIG. 1 illustrates a pair of the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132 may be driven by one motor, while a pair of the third bottom-cycle compressor 133 and the fourth bottomcycle compressor 134 is driven by another motor). Different motors enable the use of different speeds for different compressor stages. Furthermore, different compressors connected to the same motors may have different gearings that provide different speeds (e.g., specifically selected for each compressor). The initial stage of the bottom-cycle compressor set 130 may be operated at a speed of 3,000-60,000 rpm, 10,000-40,000 rpm, or, more specifically, 14, DOO- 36, 000 rpm, while a later stage in the bottom-cycle compressor set 130 may be operated at a speed of 3,000-60,000 rpm, 14,000-36,000 rpm, or, more specifically, 14,000-36,000 rpm.Top heat pump cycle examples

[0114] The top heat pump cycle 140 may be configured in a manner similar to the bottom heat pump cycle 120, e.g., the top heat pump cycle 140 may comprise a top-cycle compressor set 150 and a top-cycle expansion valve 149. In some examples, the top heat pump cycle 140 may comprise a top-cycle economizer 148 and a top-cycle-economizer valve 146, e.g., as shown in FIG. 1. FIG. 1 also illustrates the top heat pump cycle 140 comprising a top-line suction line heat exchanger 144.

[0115] The top-cycle working fluid 199 from the cascading heat exchanger 142 is directed via a top-cycle suction line 190 into a top-cycle compressor set 150. When a top-line suction line heat exchanger 144 is present, the top-cycle suction line 190 may pass through the top-line suction line heat exchanger 144 first. In some examples, the temperature of the top-cycle working fluid 199 in the top-cycle suction line 190 as it leaves the cascading heat exchanger 142 may be +30°C to +90 °C or, more specifically, +50°C to +70 °C, and when it leaves the top-linePCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 23 of 59PCT Application suction line heat exchanger 144, it may be +40°C to +150°C or, more specifically, +100°C to +140°C. The top-cycle compressor set 150 compresses the top-cycle working fluid 199, thereby increasing its pressure and temperature and sending the top-cycle working fluid 199 via a topcycle discharge line 193 into the heat-sink heat exchanger 162. The temperature of the topcycle working fluid 199 in the top-cycle working fluid 199 may be 100-230°C. This temperature depends on the heat-sink temperature and whether the economizer or the suction heat exchanger is used.

[0116] The top-cycle working fluid 199 cools in the heat-sink heat exchanger 162 (by releasing the heat to an input stream 171, which is also fed into the heat-sink heat exchanger 162 as a part of the downstream cycle 170). As the top-cycle working fluid 199 leaves the heat-sink heat exchanger 162 via a heat-sink heat exchanger exit line 194, the temperature of the top-cycle working fluid 199 may be +100°C to +160°C. When the top-cycle economizer 148 and the top- line suction line heat exchanger 144 are not present, the heat-sink heat exchanger exit line 194 may lead directly into the top-cycle expansion valve 149. When the top-cycle economizer 148, but not the top-line suction line heat exchanger 144, is present, the routing may be the same as in the bottom heat pump cycle 120 illustrated in FIG. 1. In some examples, when both the topcycle economizer 148 and the top-line suction line heat exchanger 144 are present, the topcycle working fluid 199 passes through the top-cycle economizer 148 and heats a portion of the working fluid returned from the top-line suction line heat exchanger 144 and passed through the top-cycle-economizer valve 146. Alternatively, the top-line suction line heat exchanger 144 and the top-cycle economizer 148 are connected such the economizer's secondary fluid line splits off downstream of the heat-sink heat exchanger 162, like the bottom heat pump cycle 120.

[0117] This heated portion of the working fluid may then be returned to the top-cycle compressor set 150, e.g., connected to a line interconnecting the second top-cycle compressor 152 and the third top-cycle compressor 153. The top-cycle working fluid 199 from the top-cycle economizer 148 is directed via a top-cycle economizer exit line 195 into the top-line suction line heat exchanger 144, where this top-cycle working fluid 199 heats the top-cycle working fluid 199 received from the cascading heat exchanger 142 via a top-cycle suction line 190. The top- line suction line heat exchanger 144 is connected to both the top-cycle-economizer valve 146 and the top-cycle expansion valve 149 via a top-cycle return line 196. Once the top-cycle working fluid 199 passes through the top-cycle expansion valve 149, the top-cycle working fluidPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 24 of 59PCT Application199 drops its pressure / temperature to a ranger of +30°C to +90°C or, more specifically, +50°C to +70°C and is directed to a cascading heat exchanger 142, at which point the cycle repeats.

[0118] As noted above, a suction-line heat exchanger may be used in one or both of the bottom heat pump cycle 120 and top heat pump cycle 140 (e.g., as a top-line suction line heat exchanger 144 shown in FIG. 1). The suction-line heat exchanger may be positioned upstream from a compressor set, e.g., between a heat exchanger and a corresponding compressor set. Alternatively, the suction-line heat exchanger may be located between a heat exchanger and a corresponding expansion valve. The benefits of the suction-line heat exchanger may include precooling a working fluid before entry into a heat exchanger, preheating a working fluid before entry into a compressor, and / or decreasing the density of a fluid before entry into a compressor. The benefits of preheating a working fluid before entry into a compressor may include preventing liquid droplet formation, thereby reducing the risk of damage to the compressor. The benefits of decreasing the density of a fluid before entry into a compressor may include increasing volumetric flow rate, which may help to balance speeds between the compressor stages for larger lift situations.

[0119] Similar to the bottom-cycle compressor set 130, a top-cycle compressor set 150 may include any number of compressors (e.g., one, two, or more). For example, FIG. 1 illustrates an example with four compressors, e.g., a first top-cycle compressor 151, a second top-cycle compressor 152, a third top-cycle compressor 153, and a fourth top-cycle compressor 154. These compressors work, e.g., the output of the first top-cycle compressor 151 is fed into the second top-cycle compressor 152, and so on. As such, an example of the top-cycle compressor set 150 in FIG. 1 may also be referred to as a four-stage compressor system or simply a four- stage compressor. The top-cycle compressor set 150 may increase the pressure by a factor greater than or equal to about 1.1, 1.2, 1.5, 2, 5, 10, 20, or 30. The top-cycle compressor set 150 may increase the pressure by a factor between any two values described here. The bottomcycle compressor set 130 may increase the temperature by at least 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 80°C, 100°C, 120°C, or even 150°C. The temperature increase by the compressor may be between any two values described herein. For example, the temperature of the topcycle working fluid 199 in the top-cycle suction line 190 may be +30 to +90°C or, more specifically, +50°C to +70 °C.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 25 of 59PCT ApplicationDownstream cycle examples

[0120] The downstream cycle 170 involves various uses of the heat provided by the heat-sink heat exchanger 162. For example, an input stream 171 may be fed into the heat-sink heat exchanger 162, producing an output stream 172, which is at a higher temperature and / or a different phase than the input stream 171. For example, the heat-sink heat exchanger 162 may be used as a water heater, a steam generator, and the like. In some examples, the output stream 172 may be passed through a compressor 174 (e.g., a steam compressor) to produce an elevated output stream 175. Specifically, the elevated output stream 175 is elevated in pressure and temperature relative to the output stream 172

[0121] In some embodiments, a flash tank is used in the output stream 172. Specifically, hot pressurized water is generated in the heat-sink heat exchanger 162 and passed through an expansion valve that "flashes" the water into a two-phase mixture. The gas phase (steam) is directed to the compressor 174 (if present), while the liquid phase (water) may be reused in the input stream 171 (or used for other uses in the facility).FIG. 2: Gravitational Drain / Different Elevations of Components

[0122] FIG. 2 is a block diagram of another example of a cascading heat pump system 100, showing relative elevations of different system components. The cascading heat pump system 100 comprises a bottom heat pump cycle 120 and a top heat pump cycle 140, thermally coupled to each other by a cascading heat exchanger 142. The bottom heat pump cycle 120 comprises a bottom-cycle compressor set 130 and a bottom-cycle receiver 121. The bottom heat pump cycle 120 is configured to receive heat from a bottom-cycle heat exchanger 122. The top heat pump cycle 140 comprises a top-cycle compressor set 150 and a top-cycle receiver 141. The top heat pump cycle 140 is configured to release heat to the heat-sink heat exchanger 162.

[0123] The receivers, such as a bottom-cycle receiver 121 and a top-cycle receiver 141, are configured to passively store working fluid during periods when the cascading heat pump system 100 is inactive (and the compressors don't push corresponding working fluids through heat exchangers). The receivers are positioned at lower elevation points than the corresponding compressors and upstream heat exchangers within their respective cycles (relative to aPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 26 of 59PCT Application corresponding compressor set and an upstream heat exchanger, positioned between the compressor set and the receiver). This lower elevation position facilitates gravity-driven drainage of working fluid from a corresponding compressor set and an upstream heat exchanger (which may be referred to as elevated components).

[0124] In some examples, the bottom-cycle receiver 121 may be configured to serve multiple functions within the bottom heat pump cycle 120. For instance, the bottom-cycle receiver 121 may be operable as a bottom-cycle economizer 128 and may include an integrated bottom- cycle-economizer expansion valve 126. This configuration enables the receiver to act as both a fluid reservoir and a thermal control unit for enhancing the efficiency of the bottom-cycle 189. In further examples, the bottom-cycle receiver 121 may be sized to facilitate improved charge management, such as having a volume that is greater than or equal to about 110-140%, 115- 130%, or, more specifically, 120-125% of the volume of the cascading heat exchanger 142. In other examples, the bottom-cycle receiver 121 may have a volume that is greater than or equal to about 10-40%, 15%-35, or even 20%-30%, 35% of the total internal volume of the bottom heat pump cycle 120. Such sizing helps ensure sufficient liquid working fluid storage to completely drain heat exchanger 142 of liquid during idle conditions and supports effective passive draining of high-temperature refrigerant. In some examples, the bottom-cycle receiver 121 may be in the form of a sufficiently large pipe section connecting other components.Additionally, the bottom-cycle receiver 121 may comprise a drain plug or other serviceable port for removing bottom-cycle working fluid 189 from the bottom heat pump cycle 120 for maintenance, system shutdown, or refrigerant recovery operations. It should be noted that the above-referenced features are also applicable to the top heat pump cycle 140.

[0125] For example, the top heat pump cycle 140 is defined by a top-cycle drain level 163, e.g., positioned below the outlet of the heat-sink heat exchanger 162 that is directed to the topcycle receiver 141. The top-cycle compressor set 150, the top-cycle discharge line 193 (connecting the top-cycle compressor set 150 to the heat-sink heat exchanger 162), and the internal fluid-carrying components of the heat-sink heat exchanger 162 are positioned above this top-cycle drain level 163, while the top-cycle receiver 141 is positioned below this top-cycle drain level 163. Furthermore, the top-cycle compressor set 150 may be positioned at an elevation higher than the heat-sink heat exchanger 162 to ensure drainage from the top-cycle compressor set 150 through the heat-sink heat exchanger 162 into the top-cycle receiver 141. Furthermore, the top-cycle discharge line 193 may be sloped down toward the heat-sink heatPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 27 of 59PCT Application exchanger 162. Similarly, the heat-sink heat exchanger exit line 194, connecting the heat-sink heat exchanger 162 to the top-cycle receiver 141, may be sloped toward the top-cycle receiver 141 to ensure that the top-cycle working fluid 199 drains into the top-cycle receiver 141. It should be noted that when the top heat pump cycle 140 is inactive (e.g., the top-cycle compressor set 150 is not operational), the flow of the top-cycle working fluid 199 past the topcycle receiver 141 may be limited by the top-cycle expansion valve 149 (which may be shut during this inactive stage). Furthermore, the top-cycle return line 196 (connecting the top-cycle receiver 141 and the top-cycle expansion valve 149) may have a trap (an extension that is positioned above the top-cycle drain level 163).

[0126] Similarly, the bottom heat pump cycle 120 is defined by a bottom-cycle drain level 143, e.g., positioned below the outlet of the cascading heat exchanger 142 that is directed to the bottom-cycle receiver 121. The bottom-cycle compressor set 130 and the internal fluidcarrying components of the cascading heat exchanger 142 are positioned above this bottomcycle drain level 143, while the bottom-cycle receiver 121 is positioned below this bottom-cycle drain level 143. Likewise, the bottom-cycle discharge line 183 and the bottom-cycle cascading heat exchanger exit line 184 may be sloped. The bottom-cycle compressor set 130 may be positioned at an elevation higher than the cascading heat exchanger 142 to ensure drainage from the bottom-cycle compressor set 130 through the cascading heat exchanger 142 into the bottom-cycle receiver 121. When the bottom heat pump cycle 120 is inactive (e.g., the bottomcycle compressor set 130 is not operational), the flow of the bottom-cycle working fluid 189 past the bottom-cycle receiver 121 may be limited by the bottom-cycle expansion valve 129 (which may be shut during this inactive stage). Furthermore, the bottom-cycle return line 186 (connecting the bottom-cycle receiver 121 and the bottom-cycle expansion valve 129) may have a trap (an extension that is positioned above the bottom-cycle drain level 143).

[0127] Overall, when the cascading heat pump system 100 is in an inactive state, the elevation of the highest fluid-holding points within each heat pump cycle is lower than the corresponding condensers and / or heat exchangers. These elevation differences allow gravity to passively drive the working fluid out of the compressors and heat exchangers and into the receivers during shutdown. This configuration helps ensure that the working fluid does not remain within the heat exchangers while the system is inactive, reducing the risk of pressure buildup, unwanted refrigerant boiling, or compressor damage.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 28 of 59PCT Application

[0128] Each heat pump cycle may have two low points to collect the working fluid from this cycle. For example, in a bottom heat pump cycle 120, the bottom-cycle working fluid 189 to the right of the bottom-cycle compressor set 130 will drain into the bottom-cycle receiver 121. The fluid to the left of the bottom-cycle compressor set 130 will drain into the bottom-cycle heat exchanger 122. By having the elevated pipe / trap in the bottom-cycle return line 186 or by closing the bottom-cycle expansion valve 129, the bottom-cycle working fluid 189 is limited to the bottom-cycle receiver 121 and the bottom-cycle heat exchanger 122 (and no bottom-cycle working fluid 189 is present in the bottom-cycle compressor set 130 or the cascading heat exchanger 142). Having more than one low point (e.g., a low point in the bottom-cycle receiver 121 and another low point in the bottom-cycle heat exchanger 122) allows for faster charging of the bottom-cycle working fluid 189 and draining the bottom-cycle working fluid 189 for maintenance.

[0129] Furthermore, in some configurations, the piping between the top receiver and the cascading heat exchanger includes a section that is elevated above the highest fluid-holding point in the top cycle. This arrangement creates two gravitational low points within the top heat pump cycle, enhancing fluid drainage and charge stability. Similarly, the piping between the bottom receiver and the bottom-cycle heat exchanger may include a section positioned higher than the highest fluid-holding point in the bottom cycle, creating two low points in that cycle as well. These multi-low-point designs improve charge management and help ensure full drainage of refrigerant to the designated receiver locations during periods of system inactivity.

[0130] Overall, this elevation-based arrangement allows the working fluids to drain naturally from components that retain residual thermal energy after shutdown. For example, hot water in the heat-sink heat exchanger 162 can continue to transfer heat to any working fluid (e.g., refrigerant) in the heat-sink heat exchanger 162, causing undesired boiling and pressure buildup (e.g., while a top-cycle compressor set 150 is turned off). By enabling the working fluid (e.g., refrigerant) to drain into the top-cycle receiver 141, such thermal contact is minimized. The same principle applies to the bottom heat pump cycle 120, where its working fluid (e.g., refrigerant) remaining in the cascading heat exchanger 142 may otherwise continue to absorb heat or interfere with compressor suction conditions. Positioning the bottom-cycle receiver 121 below the cascading heat exchanger 142 ensures that the residual working fluid (e.g., refrigerant) is directed to the bottom-cycle receiver 121. In other words, draining the working fluids from the corresponding heat exchangers (i.e., the heat-sink heat exchanger 162 in the topPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 29 of 59PCT Application heat pump cycle 140 and the cascading heat exchanger 142 in the bottom heat pump cycle 120) allows to thermally isolate these cycles from the upstream cycles (i.e., thermally isolate the top heat pump cycle 140 from the steam generating / processing level and, separately, thermally isolate the bottom heat pump cycle 120 from the top heat pump cycle 140).

[0131] In addition to improving safety and reliability during shutdown, the receivers serve an important role during startup. The stored working fluid in each receiver can be used to prime suction lines and supply refrigerant to components such as motor windings or bearings in centrifugal compressors, which may require an immediate supply of liquid refrigerant for cooling and / or lubrication. This ensures that the cascading heat pump system 100 can be restarted reliably and efficiently without vapor lock or compressor damage due to inadequate lubrication or excessive thermal loading.

[0132] Because the system relies on passive gravitational flow into the receivers, no active control valves or refrigerant pumps are required to manage fluid relocation during mode transitions. This reduces system complexity and improves overall reliability by eliminating potential points of failure. Moreover, by placing portions of the piping between the heat exchangers and the receivers at higher elevations, fluid column height can be used to ensure that the refrigerant drains fully from critical components, further enhancing the effectiveness of the elevation-based charge management strategy.

[0133] In some examples, a receiver and a corresponding compressor set are connected by a line to route the working fluid into the compressor during the startup (for cooling, lubrication), e.g., as schematically shown in FIG 2. Specifically, the working fluid may be directed to one or more compressor components (e.g., bearings, motors, or windings) after the system has been in an inactive state. For example, the fluid is directed to the compressor components when the system is transitioning from an inactive state to an active state (e.g., before or during startup). This fluid directing may cool the compressor components while they are starting up, as the fluid in the receiver may not yet be warmed. In some examples, the working fluid may be pulled at this point for cooling, e.g., even in the active state. Furthermore, the working fluid is available for lubrication on the bearings before starting the compressors.

[0134] Furthermore, in some examples, the first working fluid and / or the second working fluid may be drained from one or more of the receivers. The draining may enable servicing ofPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 30 of 59PCT Application components of the system. Overall, without receivers, determining the location of the working fluid in each cycle may be challenging.FIG. 3A and 3B: Heat Output Control

[0135] As noted above, a cascading heat pump system 100 delivers heat output through its heat-sink heat exchanger 162 to an input stream 171 to form an output stream 172, such as a water stream passing through this heat-sink heat exchanger 162 and converted into steam. In some examples, this heat output is further boosted by directing the output stream 172 through a downstream compressor 174, which produces an elevated output stream 175 (e.g., a higher temperature steam).

[0136] However, in some examples, the heat output needs to be reduced or at least controlled once the output stream 172 leaves the heat-sink heat exchanger 162. It should be noted that this downstream heat control may be performed in addition to controls at the top heat pump cycle 140, the bottom heat pump cycle 120, and / or heat-source cycle 110. For example, the controls of the top heat pump cycle 140 may involve the power delivered to each compressor in the top-cycle compressor set 150 (e.g., changing power, shutting down / bypassing some of the compressors) and / or control over the top-cycle expansion valve 149 (and other components). Similarly, the controls of the bottom heat pump cycle 120 may involve the power delivered to each compressor in the bottom-cycle compressor set 130 (e.g., changing power, shutting down / bypassing some of the compressors) and / or control over the bottom-cycle expansion valve 129 (and other components).

[0137] The downstream control of the heat output may be achieved by (a) passing the output stream 172 and / or the elevated output stream 175 through a downstream heat exchanger 177, thereby forming a controlled output stream 176, e.g., as shown in FIG. 3A, and / or (b) by injecting a liquid (e.g., of the same composition as the output stream 172) into output stream 172, the compressor 174, and / or the elevated output stream 175, e.g., as shown in FIG. 3B. Each of these examples will now be described in more detail.

[0138] FIG. 3A is a diagram of a cascading heat pump system 100 that comprises a downstream heat exchanger 177 connected in series and positioned downstream from the compressor 174. The downstream heat exchanger 177 may use various types of input fluid 178,PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 31 of 59PCT Application e.g., water (to produce hot water as a heated fluid 178a), working fluid from one of the bottom heat pump cycle 120 or the top heat pump cycle 140, a working fluid from the heat source cycle 110, any other heat transfer fluid, or even an air heat exchanger (e.g., a radiator). When the input fluid 178 is water, the downstream heat exchanger 177 may be referred to as a hot water heat exchanger. In some examples, the input fluid 178 is a top-cycle working fluid in the portion between the top-cycle expansion valve 149 and the top-cycle compressor set 150 (e.g., before or after the cascading heat exchanger 142). Similarly, the input fluid 178 may be a bottom-cycle working fluid in the portion between the bottom-cycle expansion valve 129 and the bottomcycle compressor set 130 (e.g., before or after the bottom-cycle heat exchanger 122). As such, the heat removed from the elevated output stream 175 (to form the controlled output stream 176) is recycled back into the cascading heat pump system 100.

[0139] When water is used in an input stream 171, the elevated output stream 175 may be superheated steam. In the downstream heat exchanger 177, the superheated steam is cooled down to, e.g., de-superheated steam or, more specifically, saturated steam (forming the controlled output stream 176). For purposes of this disclosure, the term "superheated steam" is defined as steam that exists at a temperature higher than the saturation temperature corresponding to its pressure, such that no condensation occurs unless the steam is first cooled to at least the saturation temperature. The term "de-superheated steam" is defined as steam that has been cooled from a superheated condition to a temperature near or at the saturation temperature at a given pressure, but which remains entirely in the vapor phase without undergoing condensation. The term "saturated steam" is defined as steam that exists in thermal equilibrium with liquid water at a given pressure, such that its temperature corresponds to the saturation temperature and any heat removal results in condensation.

[0140] In some examples, the downstream heat exchanger 177 may be a standalone unit, connected to the compressor 174. Alternatively, the downstream heat exchanger 177 may be thermally coupled to the compressor 174, e.g., as active cooling around the compressor 174 or in the housing of the compressor 174. Any type of downstream heat exchanger 177 is within the scope, e.g., concurrent pipes. In further examples, passive cooling methods, such as having an uninsulated pipe downstream of the compressor designed to reject heat to the ambient air, may be used. Furthermore, a radiator-style heat exchanger or a finned pipe may be used as the downstream heat exchanger 177, for passive cooling (e.g., to the environment).PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 32 of 59PCT Application

[0141] FIG. 3A also illustrates a downstream controller 179 that is used to monitor the controlled output stream 176 (e.g., the temperature of the stream) and to control various operating parameters of the cascading heat pump system 100. Specifically, the downstream controller 179 may receive temperature and flow rate data associated with the output stream 172 and / or elevated output stream 175 and use this data to modulate one or more components within the downstream cycle 170. For example, the downstream controller 179 may regulate a valve that controls the flow of an input fluid 178 into a downstream heat exchanger 177, thereby adjusting the temperature of the controlled output stream 176. In some examples, the downstream controller 179 may adjust the valve position based on real-time temperature feedback, maintaining the output temperature within a defined range to match process demand.

[0142] The downstream controller 179 may also send control signals to other elements of the system based on downstream thermal demand. For instance, it may increase the speed of the downstream compressor 174 if the heat sink load rises, or signal to the top heat pump cycle 140 to modify its discharge temperature via compressor speed adjustment or expansion valve modulation. In some examples, the controller 179 may be configured to operate autonomously, or may be integrated into a centralized system controller that also receives data from the heatsource cycle 110, bottom heat pump cycle 120, and top heat pump cycle 140. This architecture enables closed-loop regulation of the full cascading heat pump system 100, ensuring stable, efficient delivery of steam or hot water across a range of output conditions. The downstream controller 179 may be used in various examples of the downstream cycle 170 described below with reference to FIG. 3B and FIGS. 4A-4C.

[0143] In some examples, the downstream controller 179 may be configured to implement predictive control strategies that adjust compressor speed setpoints or discharge temperature targets based on historical data trends. Industrial processes often follow repeatable thermal demand patterns, even when the downstream controller 179 has no direct insight into the internal details of the process. By analyzing time-stamped data (e.g., suction / discharge temperatures, compressor duty cycles, ambient conditions, or steam draw patterns), the downstream controller 179 can anticipate future heat sink loads and proactively adjust operational parameters. This predictive capability may reduce thermal lag, improve efficiency, and minimize overshooting or undershooting of target conditions.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 33 of 59PCT Application

[0144] For instance, in systems where steam or hot water is used for batch processing, the downstream controller 179 may detect cyclic demand intervals and begin ramping the compressor 174 ahead of a predicted thermal spike. Similarly, during known low-demand intervals, the downstream controller 179 may preemptively reduce compressor speed or initiate compressor cycling to avoid unnecessary energy use. These predictive adjustments may be implemented using statistical trend analysis, machine learning algorithms, or predefined demand profiles uploaded into the control logic.

[0145] The downstream controller 179 may also operate in conjunction with centralized or cloud-based data systems that aggregate performance trends across multiple installations. This aggregated data may be used to refine control rules or generate updated control maps tailored to specific user applications or seasonal conditions. Importantly, the predictive strategies described herein may operate independently of real-time process inputs and may be implemented with minimal or no additional instrumentation, enabling deployment in retrofit settings or opaque industrial environments.

[0146] FIG. 3B is a block diagram of another example of a cascading heat pump system 100, showing various examples of a fluid injector 165. The water injector 165 is configured to inject an additional fluid 173 in one or more locations downstream, past the heat-sink heat exchanger 162. In some examples, one or more locations are selectable (e.g., an input from a system controller to the water injector 165 may be used to select one or more locations for the injection of the additional fluid 173. These locations may include an output stream 172 (between the heat-sink heat exchanger 162 and the compressor 174), the compressor 174, and the elevated output stream 175 (downstream from the compressor 174). For example, the injections of the additional fluid 173 upstream of or into the compressor 174 may enable the use of more commercial equipment (e.g., steam compressors, valves around the steam compressors, or seals) as the compressor 174 will operate at a lower temperature.

[0147] For example, when the input stream 171 is water, the heat-sink heat exchanger 162 may convert water into steam (forming the output stream 172). This steam may then be passed into the compressor 174 to increase the pressure / temperature of the steam (now forming the elevated output stream 175). The water injector 165 may be configured to inject one or more water streams into the steam (at one or more locations), thereby reducing the steam temperature.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 34 of 59PCT ApplicationFIGS. 4A-4C: Downstream Compressor Integration

[0148] In some examples, one or more downstream compressors are parts of the same cascading heat pump system 100, e.g., integrated into the downstream cycle 170 (e.g., to increase the heat output). These downstream compressors are positioned downstream of the heat-sink heat exchanger 162. For example, when the output stream 172 comprises steam, these downstream compressors may be configured to compress superheated or saturated steam to a desired delivery pressure. This integration allows the cascading heat pump system 100 to provide higher heat output, e.g., higher-grade steam, without requiring elevated pressures in the top heat pump cycle 140, thereby improving system safety, efficiency, and component longevity of the overall cascading heat pump system 100.

[0149] Specifically, FIGS. 4A and 4B illustrate two downstream compressors, such as compressor 174 and an additional compressor 174a. However, any number of downstream compressors may be used (e.g., three, four, or more). In some examples, multiple compressors are driven by the same motor (thereby operating at the same rotational speed or different speeds due to different gearing of the compressors). In further examples, the compressors (e.g., the compressors' speeds) may be independently controlled. When multiple downstream compressors are used, these compressors may be deployed in series (e.g., as shown in FIG. 4A) or in parallel (e.g., as shown in FIG. 4B) depending on process requirements.

[0150] Referring to FIG. 4A, in a series configuration, two or more downstream compressors are fluidly connected such that the outlet of one compressor (a compressor 174) feeds the inlet of the next compressor (e.g., additional compressor 174a). This enables the downstream cycle 170 to achieve higher overall pressure ratios in a staged manner, which is advantageous when the target delivery pressure exceeds the design capability of a single-stage compressor. In series configurations also facilitate the delivery of fluid output (e.g., steam) at multiple pressure / temperature levels. For example, one output may be provided by diverting a portion of the output stream 172 before sending the output stream 172 to the compressor 174.Another output may be used directly at the intermediate pressure after the first compression stage, e.g., as an elevated output stream 175. The remainder continues to a second compression stage (provided by the additional compressor 174a) for use at a higher pressure as a controlled output stream 176. It should be noted that various input fluids may be delivered atPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 35 of 59PCT Application different locations to control the heat output. For example, FIG. 4A illustrates an input fluid 178 fed into the elevated output stream 175 and also illustrates an additional input fluid 178a fed into the controlled output stream 176.

[0151] Referring to FIG. 4B, two or more downstream compressors may be configured in parallel, such that each compressor receives steam from the same source (e.g., heat-sink heat exchanger 162 rather than from another compressor) and discharges either to a common manifold or to separate pressure levels depending on demand. Parallel operation enables higher aggregate output flow rates and provides improved turndown flexibility. Specifically, compressors can be selectively activated or deactivated in response to changes in process demand, allowing the system to operate efficiently across a wide range of flow conditions. In some examples, each parallel compressor may be tuned or selected for a different discharge pressure, further extending the range of deliverable steam conditions.

[0152] Referring to FIG. 4C, in some examples, a single downstream compressor may be shared across multiple heat pump units / systems, e.g., a first heat pump system 101 and a second heat pump system 102. For example, two or more heat pump cycles can be configured to feed steam into a common suction manifold (e.g., an output stream 172), from which a single larger-capacity downstream compressor draws and produces a controlled output stream 176. This architecture enables centralized boosting of the output pressure while simplifying overall system footprint and reducing component redundancy. It may be especially useful in large-scale installations where multiple heat pumps operate in tandem to meet variable demand profiles.

[0153] These various methods of integrating downstream compressors provide flexible and scalable options for tailoring steam output to specific industrial use cases. Whether deployed in series, in parallel, or in shared configurations across multiple heat pumps, the downstream compressor integration strategies enhance the capability of the system to deliver steam at multiple pressures and flow rates while preserving the thermodynamic efficiency and modularity of the overall heat pump architecture.FIGS. 5A and 5B: Speed modulation and compressor cycling (on / off)

[0154] A cascading heat pump system 100 may be configured to maintain a stable operating envelope (e.g., providing a stable steam output within a desired temperature range) over aPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 36 of 59PCT Application range of heat-source conditions. For example, the heat source may be ambient air, with the temperature variations ranging, e.g., -20°C to +40°C, depending on the season and time of the day. The heat-source conditions, which are experienced by the heat-source cycle 110, impact the heat transfer rate in the bottom-cycle heat exchanger 122 and the temperature of the bottom-cycle working fluid 189, entering the bottom-cycle compressor set 130 from the bottom-cycle suction line 180. While some of these temperature variations (of the bottom-cycle working fluid 189 received by the bottom-cycle compressor set 130) may be overcome by changing the speed of one or more stages of bottom-cycle compressor set 130, compressors are typically designed to operate within a relatively narrow speed range (e.g., varying less than 50% or even less than 35%). To address such variations while maintaining compressors within their operation range, one or more compressor stages may be turned off as the heat source temperature increases, as will now be described with reference to FIGS. 5A and 5B.

[0155] Specifically, FIG. 5A is a simplified diagram of a cascading heat pump system 100 comprising a bottom heat pump cycle 120 and a top heat pump cycle 140. The bottom heat pump cycle 120 comprises a bottom-cycle compressor set 130 formed by four compressors, such as a first bottom-cycle compressor 131, a second bottom-cycle compressor 132, a third bottom-cycle compressor 133, and a fourth bottom-cycle compressor 134. In some examples, each compressor may be referred to as a compressor stage, while two compressor stages (e.g., connected to the same motor) may be referred to as a compressor. Specifically, the first bottom-cycle compressor 131 and second bottom-cycle compressor 132 define a bottom low- pressure group 135a, while the third bottom-cycle compressor 133 and fourth bottom-cycle compressor 134 define a bottom high-pressure group 135b. It should be noted that any number of compressors (e.g., one, two, three, four, or more) may define each stage. Similarly, the top heat pump cycle 140 comprises a top-cycle compressor set 150 formed by four compressors, such as a first top-cycle compressor 151, a second top-cycle compressor 152, a third top-cycle compressor 153, and a fourth top-cycle compressor 154. Specifically, the first top-cycle compressor 151 and second top-cycle compressor 152 define a top low-pressure group 155a, while the third top-cycle compressor 153 and fourth top-cycle compressor 154 define a top high-pressure group 155b. Each of these bottom low-pressure group 135a, bottom high- pressure group 135b, top low-pressure group 155a, and top high-pressure group 155b may be operated independently, e.g., at different speeds, be shut down, etc.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 37 of 59PCT Application

[0156] The bottom heat pump cycle 120 also comprises a bypass valve 123 that controls the distribution of the bottom-cycle working fluid 189 between the bottom-cycle suction line 180 and the additional bottom-cycle suction line 181. Specifically, the bottom-cycle suction line 180 is connected to the bottom low-pressure group 135a (sending the bottom-cycle working fluid 189 from the bottom-cycle heat exchanger 122 to the bottom low-pressure group 135a), while the additional bottom-cycle suction line 181 is connected to the bottom high-pressure group 135b (sending the bottom-cycle working fluid 189 from the bottom-cycle heat exchanger 122 to the bottom high-pressure group 135b and bypassing the bottom low-pressure group 135a). The bypass valve 123 allows shutting down the bottom low-pressure group 135a and sending all bottom-cycle working fluid 189 to the bottom high-pressure group 135b, thereby reducing the heat added to the bottom-cycle working fluid 189 by the bottom-cycle compressor set 130. While FIG. 5A illustrates a bypass valve as a part of the bottom heat pump cycle 120, a similar bypass valve may be used in the top heat pump cycle 140. Furthermore, a bypass valve may be used to bypass the bottom high-pressure group 135b instead of the bottom low-pressure group 135a or even bypass both the bottom low-pressure group 135a and the bottom high-pressure group 135b.

[0157] FIG. 5B illustrates one example of operating the cascading heat pump system 100 in this FIG. 5A across different heat source temperatures. In this example, the top heat pump cycle 140 is assumed to operate a relatively narrow and fixed temperature range (e.g. approximately +60°C to +150°C) to keep the associated compressors within optimal performance zones. This allows the top cycle to efficiently deliver high-quality heat (through the heat-sink heat exchanger 162, e.g., in the form of steam or hot water) over a wide range of system demands while avoiding frequent speed changes or off-design operation of the top compressors. It should be noted that because the heat input into the top heat pump cycle 140 is from the bottom heat pump cycle 120, while the bottom heat pump cycle 120 receives its heat from a variable-temperature heat source (in this example), it may be functionally simpler to accommodate the temperature variability at the bottom heat pump cycle 120. However, other examples are also within the scope, e.g., when the top heat pump cycle 140 is configured to accommodate heat variability added to the cascading heat pump system 100 and, more specifically, from the bottom heat pump cycle 120 to the top heat pump cycle 140. In further examples, both the bottom heat pump cycle 120 and top heat pump cycle 140 are configured to accommodate heat variability added to the cascading heat pump system 100.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 38 of 59PCT Application

[0158] Specifically, different heat temperature ranges correspond to different operating zones. In Zone 1, when the heat source temperature is low (e.g., below -10°C), all four stages (e.g., bottom low-pressure group 135a, bottom high-pressure group 135b, top low-pressure group 155a, and top high-pressure group 155b) may be operational. In fact, the bottom high- pressure group 135b may be operated at a higher speed (than the nominal speed) to accommodate the higher pressure (or temperature) lift required in that cycle. It should be noted that the neat added to the cycle is actually decreasing because more energy is coming from the compressors instead of the heat source heat exchanger. The speed / power of the bottom high-pressure group 135b may gradually decrease as the temperature increases. In some examples, the speed / power of the bottom low-pressure group 135a may also be decreased in Mode 1 (e.g., at a lower rate than that of the bottom high-pressure group 135b). The bottom high-pressure group 135b may be the primary control at this Mode 1 because of upper speed / power limits of various compressors used. Furthermore, Mode 1 is optional and / or can be combined with Mode 2. The top low-pressure group 155a and top high-pressure group 155b may be operated at a substantially constant output in Mode 1.

[0159] In Mode 2 (e.g., -10°C to +12°C in this example), the speed / power of the bottom low- pressure group 135a may also be decreased. This decrease may be in addition to the speed / power of the bottom low-pressure group 135a, which may be at a lower rate in Mode 2 than the decrease of the speed / power of the bottom high-pressure group 135b. In other words, the rates of decrease may switch as the heat source temperature increases (from Mode 1 to Mode 2). The top low-pressure group 155a and top high-pressure group 155b may be operated at a substantially constant output in Mode 2.

[0160] In Mode 3 (e.g., +12°C to 18°C in this example), the bottom low-pressure group 135a may be shut down, while the speed / power of the bottom high-pressure group 135b may be increased in a step fashion to compensate for the loss of the power previously provided by the bottom low-pressure group 135a. In some examples, the speed / power of the top low-pressure group 155a and top high-pressure group 155b may also be increased in Mode 3 to further compensation. For example, the temperature of the top-cycle working fluid 199 fed into the top-cycle compressor set 150 may decrease when the bottom low-pressure group 135a is shut down. It should be also noted that the increase in speed on the top cycle during Mode 3 is optional.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 39 of 59PCT Application

[0161] In Mode 4, the speed / power of the bottom high-pressure group 135b gradually decreases (as the temperature increases). The bottom low-pressure group 135a remains non- operational. The top low-pressure group 155a and top high-pressure group 155b may be operated at a substantially constant output in Mode 4. It should be noted that these described operating modes are just one example, and other modes are within the scope.

[0162] It should be noted that similar operating modes may be applied to the top-cycle compressor set 150, e.g., shutting off one or more compressors. Furthermore, the rate of change of the compressor speeds / powers do not have to be linear but can change in the steplike fashion.

[0163] Overall, the cascading heat pump system 100 may utilize one or more control strategies to allow the bottom heat pump cycle 120 to float in response to changing heat source temperature (e.g., environmental conditions) while maintaining a target saturation temperature in the cascading heat exchanger 142. In some configurations, the saturation temperature on the bottom-cycle working fluid 189 at the inlet of the cascading heat exchanger 142 is maintained at +55°C to +75°C or, more specifically, +60°C to +70°C, such as about +65°C under typical operating conditions (e.g., +20°C to +25°C of the heat source). By allowing the bottom heat pump cycle 120 to handle temperature swings, the overall cascading heat pump system 100 can accommodate a wide temperature range of the heat source (e.g., ambient air) while maintaining stable output conditions at the heat-sink heat exchanger 162.

[0164] As noted above, the bottom heat pump cycle 120 may be configured to operate according to distinct operation modes (described above) based on heat source temperature (as described above), expansion valves' positions, suction pressures / temperatures for each compressor, working fluid temperatures at various locations, and temperature / heat output requirements at the heat-sink heat exchanger 162. For example, the speed of the bottom-cycle compressor set 130 may be controlled to maintain a saturation pressure in the cascading heat exchanger 142. This way, whenever just that bottom-cycle compressor set 130 is operating, the speed would increase or decrease as the heat source temperature decreases or increases, to maintain the saturation pressure in the cascading heat exchanger 142. A similar approach may be used with the suction temperature / pressure or heat source temperature as the control point for the speed of the bottom-cycle compressor set 130.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 40 of 59PCT Application

[0165] Furthermore, when the bottom low-pressure compressor (in the bottom-cycle compressor set 130) is operational, this compressor may be controlled to maintain a saturation pressure at its discharge (the suction pressure of the bottom high pressure compressor). In some examples, the bottom low-pressure compressor may be controlled based on its suction saturation pressure / temperature (or heat source temperature) such that the compressor's speed increases when its suction is lower or decreases when its suction is higher. As such, the discharge saturation pressure (which is the saturation pressure of the cascading heat exchanger 142 for the bottom high pressure compressor), suction saturation pressure, and heat source temperature, and / or the expansion valve position / opening may be used.

[0166] Furthermore, in addition to various operating modes, the cascading heat pump system 100 may have various transition modes (or transition zones). For example, switching between two operating modes may be performed at different temperatures depending on whether the heat source temperature increases or decreases. This approach prevents frequent switching between operating modes when the heat source temperature fluctuates. Specifically, the cascading heat pump system 100 may switch from operating the four compressor stages to operating the two compressor stages when the heat source temperature increases and reaches a set temperature (e.g., +15°C), which may be referred to as a heating set temperature. The same cascading heat pump system 100 may not switch from operating the two compressor stages to operating the four compressor stages when the heat source temperature decreases and reaches the heating set temperature. Instead, this switch occurs when the heat source temperature decreases and reaches a cooling set temperature, which is lower than the heating set temperature (e.g., by at least 2°C, at least 5°C, or even at least 10°C). This difference between the heating set temperature and the cooling set temperature may be set based on the expected fluctuations of the heat source temperatures (around the heating set temperature and the cooling set temperature) and difficulties associated with switching between different operating modes.FIG. 5C: Add-On Compressors

[0167] FIG. 5C is a block diagram of another example of a cascading heat pump system 100, in which the bottom-cycle compressor set 130 comprises an add-on compressor 139. For example, when a saturation temperature / heat delivery temperature of a top and / or bottom cycle dropsPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 41 of 59PCT Application due to cold weather or other operational changes, an add-on compressor 139 may be integrated into the cycle to maintain the cycle's main compressors at relatively constant operating conditions.

[0168] Specifically, the bottom-cycle compressor set 130 may comprise one or more main compressors, which may be centrifugal compressors (e.g., a first bottom-cycle compressor 131 and a second bottom-cycle compressor 132). These one or more main compressors are configured to compress / heat the bottom-cycle working fluid before sending this bottom-cycle working fluid to the cascading heat exchanger 142 (as described above with reference to FIG. 1). The add-on compressor 139 may be positioned upstream from the one or more main compressors and may help maintain suction pressure in the main compressors. The add-on compressor 139 can be the same type as other compressors in the same set (e.g., all compressors may be centrifugal) or they can be a different type of compressor.

[0169] The bottom-cycle compressor set 130 may also comprise valves controlling the flow of the bottom-cycle working fluid through the add-on compressor 139, e.g., a first add-on valve 137a and a second add-on valve 137b. Specifically, the first add-on valve 137a and the second add-on valve 137b may isolate the add-on compressor 139 (when no further lift is required) or may direct the working fluid to the add-on compressor 139 (when the main compressors are not providing sufficient lift to the working fluid). While FIG. 1 illustrates the add-on compressor 139 being a part of the bottom-cycle compressor set 130, a top-cycle compressor set 150 may also similarly utilize an add-on compressor 139.FIGS. 5D and 5E: Passive Compressor Control / Check Valves

[0170] In some examples, a compressor set may use passive control methods (e.g., check valves) to regulate refrigerant flow paths to different compressor stages. For example, two check valves with different crack pressures may be used as shown in FIGS. 5D and 5E, thereby eliminating the need for electronically actuated valves and reducing system complexity, cost, and failure points. The passive approach enables automatic flow switching based on the operating state of a given compressor / compressor stage (e.g., whether the compressor is running or idle) without requiring active feedback or external control logic. Specifically, FIGS. 5D and 5E illustrate two examples of a bottom-cycle compressor set 130, comprising four compressors formed by a couple of two-stage compressors. However, one having ordinary skillPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 42 of 59PCT Application in art would appreciate that this approach can also be used for a top-cycle compressor set 150 and / or for different configurations of compressor set (e.g., with two compressors only, with three compressors, and so on).

[0171] Referring to FIG. 5D, in some examples, the bottom-cycle suction line 180 coming from the bottom-cycle heat exchanger 122 is split and directed into the first bottom-cycle compressor 131 and a first check valve 138a. The first bottom-cycle compressor 131 is staged with the second bottom-cycle compressor 132, with the output of the second bottom-cycle compressor 132 connected to a second check valve 138b. In other words, a single bottom-cycle suction line 180 (the outlet of the bottom-cycle heat exchanger 122) branches into two parallel paths: (1) one leading to the suction inlet of a low-pressure compressor stage (i.e., the first bottom-cycle compressor 131 and then to the second bottom-cycle compressor 132) and the other bypassing the low-pressure compressor stage entirely. Each path includes a check valve that enforces unidirectional flow. The second bottom-cycle compressor 132 on the discharge of the low-pressure compressor stage is configured with a higher crack pressure than the first check valve 138a in the bypass line. For example, the first check valve 138a may have a crack pressure of 0.05 psi - 80 psi or, more specifically, 0.12 - 5 psi. The second check valve 138b may have a crack pressure of 0.05 psi - 80 psi or, more specifically, 0.25 - 10 psi. In the same of other examples, the difference between the crack pressure of the second check valve 138b and the crack pressure of the first check valve 138a may be 0.05 psi - 20 psi or, more specifically, 0.05 psi - 5 psi.

[0172] Accordingly, when the low-pressure compressor stage is inactive, the bottom-cycle working fluid (e.g., refrigerant) flows through the bypass path due to the lower resistance, and the second check valve 138b (i.e., the higher-crack-pressure valve) remains closed. When the low-pressure compressor stage becomes active, this low-pressure compressor stage creates a sufficient pressure differential to open the second check valve 138b and close the first check valve 138a (in the bypass valve), thereby directing flow through the low-pressure compressor stage. It should be noted that while the low-pressure compressor stage is shown to have two compressors (i.e., the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132), this approach, comprising a bypass line with the two check valves, may be used to bypass a single compressor. Furthermore, once the line from the two check valves merges, the downstream may be directed to a high-pressure compressor stage (e.g., as shown in FIG. 5D) or some other components (e.g., the cascading heat exchanger 142).PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 43 of 59PCT Application

[0173] Referring to FIG. 5E, in some examples, the bottom-cycle heat exchanger 122 (e.g., the evaporator) comprises two separate outlet ports, each connected to a separate suction line (e.g., a bottom-cycle suction line 180 that is also connected to a low-pressure compressor stage and an additional bottom-cycle suction line 181 that is also connected to a second check valve 138b and operable as a bypass line (bypassing the low-pressure compressor stage). Similar to the example described above with reference to FIG. 5D, the second check valve 138b has a higher crack pressure and remains closed when the low-pressure compressor stage is not operational. This architecture simplifies piping by avoiding the need for a tee connection downstream of the additional bottom-cycle suction line 181 (the evaporator). For example, this architecture may be used for shell-and-tube types of heat exchangers (used as the bottom-cycle heat exchanger 122) that support multiple outlet ports. Overall, this design offers an efficient and compact solution for integrating passive control with minimal system footprint.

[0174] These passive control architectures are particularly advantageous for applications involving variable compressor operation, where certain stages are cycled on or off in response to ambient temperature or suction pressure conditions. By leveraging pressure-driven actuation of check valves, the system maintains safe and efficient refrigerant routing across different operating modes without relying on sensor feedback or actuator reliability. The approach also supports rapid transitions between modes, ensuring refrigerant does not stagnate or enter an inactive compressor during shutdown or partial-load conditions.

[0175] In addition to improving system reliability, the passive bypass strategy supports flexible scaling across multiple compressor configurations, including bottom-cycle compressors, top-cycle compressors, and even steam compressors used to boost discharge pressure. By tuning the crack pressures appropriately, the same general approach can be applied to manage flow across a range of cycle types, fluid densities, and refrigerant charge conditions, thereby enabling a standardized, modular control solution across multiple product platforms.FIG. 6: Methods of Operating Cascading Steam-Generating Heat Pump System

[0176] FIG. 6 is a process flowchart corresponding to method 600 of operating a cascading steam-generating heat pump system 100, including coordinated control of multiple compressor stages and auxiliary subsystems, in accordance with some examples. Various features of the cascading heat pump system 100 are described above. In some examples, the cascading heatPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 44 of 59PCT Application pump system 100 may be used to generate one or more high-temperature heat, steam, or hot water. In particular, the cascading steam-generating heat pump system 100 may be used for generating medium- to high-pressure steam for industrial processes, including those in the food and beverage, pharmaceutical, and chemical manufacturing sectors. The cascading heat pump system 100 generates this heat out by receiving the heat from the heat source (e.g., ambient air, solar-heated glycol, river water, geothermal energy, and low-grade waste heat) and supplementing this heat with the energy controllably delivered using at least two sets of compressors, arranged into a bottom heat pump cycle 120 and a top heat pump cycle 140. For example, the cascading heat pump system 100 may operate across a wide range of ambient conditions and output temperatures.

[0177] In some examples, the cascading heat pump system 100 may generate pressurized hot water, e.g., for industrial plants as well as hot water supply in commercial buildings, such as hotels, hospitals, or multi-unit residential complexes. Additional applications include those involving energy recovery and load shifting. For example, the cascading heat pump system 100 may be coupled to waste heat streams or refrigeration equipment to recover low-grade thermal energy and upcycle it into usable steam or hot water. It may also be integrated with combined heat and power (CHP) systems or deployed in microgrid environments to provide flexible, demand-responsive heating solutions. In some examples, the cascading heat pump system 100 may be used for steam recompression in loop-based steam systems, thereby improving overall thermal efficiency and reducing the need for fresh steam generation.

[0178] Method 600 may comprise (block 610) determining one or more operating parameters for the cascading heat pump system 100 based on a combination of measured input parameters and predefined target parameters. In some examples, input parameters may include the heat source temperature (e.g., ambient air temperature at the inlet of the heat-source heat exchanger 112), while the target parameters may include the desired temperature and flow rate at the heat-sink heat exchanger 162 (e.g., to generate saturated or superheated steam), and the required heat flux at the heat sink. Based on these inputs, the system controller determines operating parameters such as which compressor stages are active (e.g., within the bottom-cycle compressor set 130 or top-cycle compressor set 150), their respective speed setpoints, expansion valve openings (e.g., bottom-cycle expansion valve 129), and flow settings for intermediate circuits such as the glycol loop in the heat-source cycle 110. These operatingPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 45 of 59PCT Application parameters are selected to ensure that the system delivers the required thermal output while maintaining efficient and stable operation within compressor operating envelopes.

[0179] For example, if the ambient heat source temperature is measured at +5°C and the target steam temperature is +150°C, the controller may activate all stages of the bottom-cycle compressor set 130 at elevated speeds to achieve a sufficiently high intermediate temperature at the cascading heat exchanger 142. Simultaneously, the top-cycle compressor set 150 may be configured to operate at a speed that achieves the desired saturation pressure at the heat-sink heat exchanger 162. If the required heat flux at the heat sink is relatively high (such as during process startup or high demand periods), the cascading heat pump system 100 may increase mass flow rates through both cycles, adjust superheat levels in the economizers 128 and 148, and open bypass paths through the first check valve 138a or second check valve 138b to engage additional compression stages (e.g., the add-on compressor 139). Conversely, if the heat flux requirement drops, one or more compressors may be automatically disabled or slowed to reduce energy consumption without overshooting the steam output target.

[0180] In other examples, determining operating parameters may include setting buffer zones and control logic around transition points where compressor stages switch on or off. For instance, if the system is operating near a crossover ambient temperature (e.g., +12°C), the control system may prepare for a transition between two-compressor and one-compressor operation in the bottom heat pump cycle 120 by adjusting glycol pump speed and airflow through the heat-source heat exchanger 112 to avoid abrupt shifts in system performance. Additionally, in systems configured with a downstream cycle 170, operating parameters may include the decision to engage a downstream compressor 174, e.g., based on a detected shortfall between the current steam pressure and the target elevated output stream 175, or to inject additional fluid 173 into the output stream 172 to fine-tune steam quality or temperature. These strategies allow the system to respond in real time to changing thermal loads, ambient conditions, and process demands, while preserving optimal compressor operation and energy efficiency.

[0181] Method 600 may comprise (block 620) receiving heat from a heat-source cycle 110, e.g., using a heat-source heat exchanger 112. Specifically, the heat-source heat exchanger 112 may be a radiator through which a heat-source working fluid is circulated, e.g., using a pump 114. The temperature of the heat-source working fluid may be less than that of the ambient airPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 46 of 59PCT Application that is blown through the heat-source heat exchanger 112 (e.g., using a fan). The heat-source working fluid is heated in the heat-source heat exchanger 112 and then delivered to the bottom-cycle heat exchanger 122, where the heat is transferred to the bottom-cycle working fluid 189. The heat-source cycle 110 provides multiple benefits that enhance the overall flexibility, performance, and integration capabilities of the cascading heat pump system 100. In some examples, the heat-source cycle 110 comprises a heat-source heat exchanger 112 configured to extract heat from an ambient air stream and transfer it to a working fluid (e.g., glycol), which is then pumped using a pump 114 to a bottom-cycle heat exchanger 122. This separation of the heat-source cycle 110 as a dedicated fluid loop allows for physical and functional decoupling from the bottom heat pump cycle 120. For example, the heat-source heat exchanger 112 may be located remotely, e.g., outdoors for ambient air exposure, while the bottom heat pump cycle 120 and associated components remain housed indoors or closer to the steam end-user (e.g., downstream cycle 170). In other examples, the heat may be received directly by the bottom-cycle heat exchanger 122.

[0182] Method 600 may comprise (block 630) operating the bottom heat pump cycle 120 and the top heat pump cycle 140 in accordance with the determined operating parameters. These parameters may include specific compressor speed setpoints, stage engagement combinations, expansion valve positions, and economizer flow rates. The bottom-cycle compressor set 130 receives the bottom-cycle working fluid 189 from the bottom-cycle heat exchanger 122 via a bottom-cycle suction line 180 and compresses it to a higher pressure and temperature. This compressed working fluid is delivered to the cascading heat exchanger 142 to transfer heat to the top-cycle working fluid 199. Similarly, the top-cycle compressor set 150 compresses the topcycle working fluid 199 received from the cascading heat exchanger 142 and delivers it to the heat-sink heat exchanger 162, where heat is transferred to an input stream 171 (e.g., water to be converted into steam or hot water). Each cycle operates dynamically to track variations in ambient temperature, steam demand, and system load.

[0183] For example, when operating under cold ambient conditions (e.g., below 0°C), the bottom heat pump cycle 120 may engage all four compressors (e.g., first bottom-cycle compressor 131 through fourth bottom-cycle compressor 134) to lift the temperature of the bottom-cycle working fluid 189 to an adequate level for transfer in the cascading heat exchanger 142. The compressor speeds may be increased to maximize intermediate temperature and avoid suction temperature or pressure limits. At the same time, the top heatPCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 47 of 59PCT Application pump cycle 140 may be operated in a high-lift mode, with the top-cycle compressor set 150 running at high speed to produce saturated or superheated steam at the desired temperature and pressure in the heat-sink heat exchanger 162. In contrast, during mild ambient conditions or reduced process heat demand, the cascading heat pump system 100 may operate with only one or two compressors active in the bottom-cycle compressor set 130, while the top-cycle compressor set 150 may reduce its speed to match a lower steam setpoint.

[0184] In some examples, operating the cycles may also include real-time adjustments based on monitored conditions. For instance, if a compressor in the bottom heat pump cycle 120 approaches a limiting condition (e.g., minimum speed, maximum suction pressure), the controller may reduce the fan speed or glycol flow rate in the heat-source cycle 110 to maintain discharge temperature without triggering shutdown. Similarly, if the top-cycle suction superheat drops below a safe threshold, the top-cycle expansion valve 149 may be modulated, or the top-line suction line heat exchanger 144 may be engaged to ensure vapor-only entry into the top-cycle compressor set 150. Operating parameters may also dictate whether economizer loops (e.g., bottom-cycle economizer 128 or top-cycle economizer 148) are engaged and whether intermediate injection lines (e.g., bottom-cycle economizer return line 185) are utilized to balance load across compressor stages. This coordinated operation across both cycles ensures stable, efficient delivery of high-quality steam or hot water under variable ambient and process conditions.

[0185] Method 600 may comprise (block 640) delivering heat using the heat-sink heat exchanger 162. In some examples, the heat-sink heat exchanger 162 is thermally coupled to the top heat pump cycle 140 and receives compressed top-cycle working fluid 199 from the topcycle discharge line 193. As the top-cycle working fluid 199 passes through the heat-sink heat exchanger 162, it releases heat to an input stream 171, which may comprise water, process fluid, or another heat-receiving medium. The output stream 172 exiting the heat-sink heat exchanger 162 may be a high-temperature water stream or steam, depending on the temperature and pressure achieved by the top-cycle compressor set 150. For example, the heat-sink heat exchanger 162 may be configured to produce saturated steam at +100°C to +180°C, superheated steam at temperatures exceeding +180°C, or hot water (or other liquids) at a temperature over +40°C, over+ 60°C, over +80°C, and even over +100°C. The form and quality of the output stream 172 may be adjusted based on target system requirements or process demands.PCT / US25 / 40920 06 August 2025 (06.08.2025)Docket No. ATMOP706WO Page 48 of 59PCT Application

[0186] In some embodiments, the heat-sink heat exchanger 162 is configured as a steam generator, and the output stream 172 may be routed to downstream equipment such as a steam compressor 174, flash tank, or industrial process. The heat delivery may be regulated by controlling the mass flow rate and superheat of the top-cycle working fluid 199, as well as the flow and preheat level of the input stream 171. For example, the top-cycle compressor set 150 may be operated at a higher speed to increase the discharge temperature when high-pressure steam is required. Alternatively, when the process requires only hot water, the compressor speed may be reduced and the system may operate at a lower lift. In some cases, the heat-sink heat exchanger 162 is also configured to accept fluid injection (e.g., via a water injector 165) to regulate the outlet temperature, adjust steam dryness, or enable staged delivery of heat.

[0187] In further examples, the delivery of heat via the heat-sink heat exchanger 162 may be coordinated with downstream control strategies. For instance, if the system includes a downstream compressor 174, the heat-sink heat exchanger 162 may be operated to produce slightly superheated steam, which is then compressed to higher pressures in the downstream cycle 170. This enables a multi-stage steam delivery strategy in which a portion of the steam is used as-is, while another portion is boosted to serve higher-pressure applications. Additionally, the system may monitor the output stream 172 temperature and pressure in real time and adjust the top-cycle expansion valve 149 or compressor staging accordingly to ensure consistent thermal output. In this way, block 640 enables precise, flexible, and application-specific heat delivery from the cascading heat pump system 100.Conclusion

[0188] Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing processes, systems, and apparatuses. Accordingly, the present examples are to be considered illustrative and not restrictive.

Claims

Docket No. ATMOP706WO Page 49 of 59 PCT ApplicationCLAIMS1. A cascading heat pump system 100 for receiving heat from a heat source and providing heat to an input stream 171, the cascading heat pump system 100 comprising: a bottom heat pump cycle 120 comprising a bottom-cycle compressor set 130, a bottom-cycle receiver 121, a bottom-cycle expansion valve 129, and a bottom-cycle heat exchanger 122, utilizing a bottom-cycle working fluid 189 and configured to receive the heat from the heat source; a top heat pump cycle 140 comprising a top-cycle compressor set 150, a top-cycle expansion valve 149, and a heat-sink heat exchanger 162, utilizing a top-cycle working fluid 199 and configured to receive the input stream 171 and to transfer heat from the top-cycle working fluid 199 to the input stream 171, thereby generating an output stream 172; and a cascading heat exchanger 142 thermally coupling the bottom heat pump cycle 120 and the top heat pump cycle 140 and configured to transfer heat from the bottom-cycle working fluid 189, discharged from the bottom-cycle compressor set 130, to the top-cycle working fluid 199 received from the top-cycle expansion valve 149 and directed to the top-cycle compressor set 150, wherein: the bottom-cycle receiver 121 is positioned downstream from the cascading heat exchanger 142 and configured to hold the bottom-cycle working fluid 189 received from the cascading heat exchanger 142, and the bottom-cycle receiver 121 is positioned at a lower elevation relative to the cascading heat exchanger 142, such that the bottom-cycle working fluid 189 drains from the cascading heat exchanger 142 into the bottom-cycle receiver 121 when the bottomcycle compressor set 130 is not operational.

2. The cascading heat pump system 100 of claim 1, wherein the cascading heat exchanger 142 is positioned at a lower elevation relative to the bottom-cycle compressor set 130 such that the bottom-cycle working fluid 189 drains from the bottom-cycle compressor set 130 and through the cascading heat exchanger 142 into the bottom-cycle receiver 121 when the bottom-cycle compressor set 130 is not operational.

3. The cascading heat pump system 100 of claim 1, wherein the top heat pump cycle 140 further comprises a top-cycle receiver 141, wherein:Docket No. ATMOP706WO Page 50 of 59 PCT Application the top-cycle receiver 141 is positioned downstream from the heat-sink heat exchanger 162 and configured to hold the top-cycle working fluid 199 received from the heatsink heat exchanger 162, and the top-cycle receiver 141 is positioned at a lower elevation relative to the heat-sink heat exchanger 162, such that the top-cycle working fluid 199 drains from the heat-sink heat exchanger 162 into the top-cycle receiver 141 when the top-cycle compressor set 150 is not operational.

4. The cascading heat pump system 100 of claim 3, wherein the top-cycle compressor set 150 is positioned at a higher elevation than the heat-sink heat exchanger 162 such that the top-cycle working fluid drains from the top-cycle compressor set 150 through the heat-sink heat exchanger 162 and into the top-cycle receiver 141 when the top-cycle compressor set 150 is not operational.

5. The cascading heat pump system 100 of claim 1, wherein the bottom-cycle receiver 121 is operable as a bottom-cycle economizer 128 and comprises a bottom-cycle-economizer expansion valve 126.

6. The cascading heat pump system 100 of claim 1, wherein the bottom-cycle receiver 121 has a volume of at least 125% of the cascading heat exchanger 142.

7. The cascading heat pump system 100 of claim 1, wherein the bottom-cycle receiver 121 has a volume of at least 30% of the bottom heat pump cycle 120.

8. The cascading heat pump system 100 of claim 1, wherein the bottom-cycle receiver 121 comprises a drain plug for removing the bottom-cycle working fluid 189 from the bottom heat pump cycle 120.

9. The cascading heat pump system 100 of claim 1, wherein the bottom-cycle receiver 121 is fluidically coupled to the bottom-cycle compressor set 130 for pumping the bottom-cycle working fluid 189 in a liquid form into the bottom-cycle compressor set 130 for lubricating the bottom-cycle compressor set 130 when the cascading heat pump system 100 is starting up.Docket No. ATMOP706WO Page 51 of 59 PCT Application10. The cascading heat pump system 100 of claim 1, wherein the heat-sink heat exchanger 162 and the top-cycle receiver 141 are f luidica lly connected by a heat-sink heat exchanger exit line 194 that is sloped toward the top-cycle receiver 141.

11. The cascading heat pump system 100 of claim 1, wherein the top-cycle compressor set 150 and the heat-sink heat exchanger 162 are fluidically connected by a top-cycle discharge line 193 that is sloped toward the heat-sink heat exchanger 162.

12. The cascading heat pump system 100 of claim 1, wherein the bottom-cycle receiver 121 is positioned between the cascading heat exchanger 142 and the bottom-cycle expansion valve 129 and is configured to shut down when the bottom-cycle compressor set 130 is not operational, thereby maintaining the bottom-cycle working fluid 189 in the bottom-cycle receiver 121.

13. The cascading heat pump system 100 of claim 1, wherein the bottom-cycle receiver 121 is connected with the bottom-cycle expansion valve 129 by a bottom-cycle return line 186, forming a trap, thereby maintaining the bottom-cycle working fluid 189 in the bottom-cycle receiver 121.

14. The cascading heat pump system 100 of claim 1, wherein each of the bottom-cycle working fluid 189 and the top-cycle working fluid 199 is selected from the group consisting of water, steam, glycol, air, a fluorocarbon, a hydrofluoroolefin, a hydrofluoroether, a hydrochlorofluoroolefins, a hydrocarbon, ammonia (NH3), water (H2O), carbon dioxide (CO2), pentane (C5H12), butane (C4H10), isobutane (HCfCHsh), propane (CsHs), and propene (CsHe), or a combination thereof.

15. The cascading heat pump system 100 of claim 1, wherein each of the bottom-cycle compressor set 130 and the top-cycle compressor set 150 comprises a centrifugal compressor.Docket No. ATMOP706WO Page 52 of 59 PCT Application16. The cascading heat pump system 100 of claim 1, wherein each of the bottom-cycle compressor set 130 and the top-cycle compressor set 150 comprises a set of four compressors connected in series.

17. The cascading heat pump system 100 of claim 1, wherein at least the bottom heat pump cycle 120 comprises a bottom-cycle suction line 180 and an additional bottom-cycle suction line 181 extending from the bottom-cycle heat exchanger 122 to different compressors in the bottom-cycle compressor set 130.

18. The cascading heat pump system 100 of claim 17, wherein at least one of the bottom-cycle suction line 180 and the additional bottom-cycle suction line 181 comprises a control valve for controlling distribution of the bottom-cycle working fluid 189 between the bottom-cycle suction line 180 and the additional bottom-cycle suction line 181.

19. The cascading heat pump system 100 of claim 1, further comprising a heat-source cycle 110 comprising a heat-source heat exchanger 112, configured to transfer heat from ambient air into a heat-source working fluid, and a pump 114, configured to pump the heat-source working fluid to the bottom-cycle heat exchanger 122.

20. The cascading heat pump system 100 of claim 1, further comprising a downstream cycle 170 comprising a compressor 174 such that the input stream 171 passes through the heat-sink heat exchanger 162 and forms an output stream 172, which is directed to the compressor 174 to form an elevated output stream 175.

21. A cascading heat pump system 100 comprising: a bottom heat pump cycle 120; a top heat pump cycle 140 thermally coupled to the bottom heat pump cycle 120 via a cascading heat exchanger 142; a heat-sink heat exchanger 162 configured to receive compressed top-cycle working fluid 199 from the top heat pump cycle 140 and generate an output stream 172; a downstream cycle 170 comprising a downstream controller 179 and a downstream compressor 174 configured to receive the output stream 172 and generate an elevated outputDocket No. ATMOP706WO Page 53 of 59 PCT Application stream 175, wherein the downstream controller 179 is configured to regulate thermal output of the cascading heat pump system 100 by modifying at least an output of the compressor 174.

22. The cascading heat pump system 100 of claim 21, wherein: the downstream cycle 170 further comprises a downstream heat exchanger 177 configured to receive the elevated output stream 175 and form a controlled output stream 176, the downstream heat exchanger 177 is further configured to receive an input fluid 178 and form a heated fluid 178a by transferring heat from the elevated output stream 175 to the input fluid 178.

23. The cascading heat pump system 100 of claim 22, wherein the downstream controller 179 is configured to control a flow rate of the input fluid 178 through the downstream heat exchanger 177.

24. The cascading heat pump system 100 of claim 22, wherein the input fluid 178 received by the downstream heat exchanger 177 is selected from the group consisting of water, a bottomcycle working fluid 189 used in the bottom heat pump cycle 120, a top-cycle working fluid 199 used in the top heat pump cycle 140, or ambient air.

25. The cascading heat pump system 100 of claim 21, further comprising a water injector 165 configured to introduce an additional fluid 173 into one or more of the output stream 172 and the elevated output stream 175.

26. The cascading heat pump system 100 of claim 25, wherein: the output stream 172 is steam; and the additional fluid 173 is water injected to control a superheating level in the elevated output stream 175.

27. The cascading heat pump system 100 of claim 21, wherein the downstream controller 179 is configured to maintain the output stream 172 within a target pressure and temperature band by modulating speed or flow rate through the downstream compressor 174.Docket No. ATMOP706WO Page 54 of 59 PCT Application28. The cascading heat pump system 100 of claim 21, wherein the downstream cycle 170 further comprises an additional compressor 174a connected in series with the downstream compressors 174.

29. The cascading heat pump system 100 of claim 28, wherein the additional compressor 174a is controlled independently of the downstream compressor 174 to provide a staged pressure increase across the downstream cycle 170.

30. The cascading heat pump system 100 of claim 28, wherein the downstream compressor 174 and the additional compressor 174a are mounted on a shared shaft and operate at coordinated rotational speeds.

31. The cascading heat pump system 100 of claim 28, wherein the additional compressor 174a is configured to activate only when the elevated output stream 175 requires a pressure greater than a defined threshold.

32. The cascading heat pump system 100 of claim 21, wherein the downstream cycle 170 further comprises an additional compressor 174a connected in parallel with the downstream compressor 174.

33. The cascading heat pump system 100 of claim 32, wherein each of the downstream compressor 174 and the additional compressor 174a is configured to receive a portion of the output stream 172 simultaneously.

34. The cascading heat pump system 100 of claim 32, wherein the output of the downstream compressor 174 and the additional compressor 174a is merged into a common elevated output stream 175.

35. The cascading heat pump system 100 of claim 32, wherein the downstream controller 179 is configured to selectively enable or disable the additional compressor 174a based on one or more of steam demand and temperature of a heat-source cycle 110.Docket No. ATMOP706WO Page 55 of 59 PCT Application36. The cascading heat pump system 100 of claim 21, wherein the downstream compressor 174 is a steam compressor selected from the group consisting of a centrifugal compressor, a positive-displacement compressor, and a rotary compressor.

37. The cascading heat pump system 100 of claim 21, wherein the downstream compressor 174 is a high-speed centrifugal compressor configured to operate at speeds greater than 30,000 rpm.

38. The cascading heat pump system 100 of claim 21, wherein the bottom heat pump cycle 120 comprises a bottom-cycle compressor set 130 having at least two compressors configured to operate in series.

39. The cascading heat pump system 100 of claim 21, further comprising a top-cycle compressor set 150 comprising two or more compressors arranged in series.

40. The cascading heat pump system 100 of claim 21, wherein the top heat pump cycle 140 is configured to maintain a discharge temperature between approximately +120°C and +185°C.

41. A cascading heat pump system 100 comprising: a bottom heat pump cycle 120 comprising a bottom-cycle compressor set 130, wherein the bottom-cycle compressor set 130 comprises a first bottom-cycle compressor 131 and a second bottom-cycle compressor 132 defining a bottom low-pressure group 135a, and a third bottom-cycle compressor 133 and a fourth bottom-cycle compressor 134 defining a bottom high-pressure group 135b, wherein the cascading heat pump system 100 is configured such that:(i) during a first operating condition, a bottom-cycle working fluid 189 flows through the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132 prior to entering the third bottom-cycle compressor 133 and the fourth bottomcycle compressor 134, and(ii) during a second operating condition, the bottom-cycle working fluid 189 bypasses the first bottom-cycle compressor 131 and the second bottom-cycleDocket No. ATMOP706WO Page 56 of 59 PCT Application compressor 132 and flows directly to the third bottom-cycle compressor 133 and the fourth bottom-cycle compressor 134.

42. The cascading heat pump system 100 of claim 41, further comprising a bypass valve 123 positioned between a bottom-cycle heat exchanger 122 and the bottom-cycle compressor set 130, wherein the bypass valve 123 selectively directs the bottom-cycle working fluid 189 through a bottom-cycle suction line 180 or an additional bottom-cycle suction line 181.

43. The cascading heat pump system 100 of claim 41, wherein the bottom-cycle compressor set 130 comprises an add-on compressor 139 disposed upstream of the first bottom-cycle compressor 131.

44. The cascading heat pump system 100 of claim 43, wherein the add-on compressor 139 is configured to increase suction pressure to the bottom low-pressure group 135a.

45. The cascading heat pump system 100 of claim 43, further comprising a first add-on valve 137a and a second add-on valve 137b configured to isolate or engage the add-on compressor 139.

46. The cascading heat pump system 100 of claim 41, wherein the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132 are staged in series.

47. The cascading heat pump system 100 of claim 46, further comprising a first check valve 138a positioned in a bypass line configured to bypass the first bottom-cycle compressor 131 and the second bottom-cycle compressor 132.

48. The cascading heat pump system 100 of claim 47, further comprising a second check valve 138b disposed at a discharge of the second bottom-cycle compressor 132.

49. The cascading heat pump system 100 of claim 48, wherein the second check valve 138b has a higher crack pressure than the first check valve 138a.Docket No. ATMOP706WO Page 57 of 59 PCT Application50. The cascading heat pump system 100 of claim 48, wherein the first check valve 138a is configured to open and permit fluid flow when the low-pressure compressor stage 135a is inactive.

51. The cascading heat pump system 100 of claim 48, wherein the second check valve 138b is configured to open and the first check valve 138a is configured to close when the low-pressure compressor stage 135a becomes active.

52. The cascading heat pump system 100 of claim 41, further comprising a bottom-cycle suction line 180, connected to the low-pressure compressor stage 135a, and an additional bottom-cycle suction line 181, bypassing the low-pressure compressor stage 135a and connected to the bottom high-pressure group 135b.

53. The cascading heat pump system 100 of claim 52, further comprising a bottom-cycle heat exchanger 122 comprising multiple outlet ports, each coupled to a separate suction line, comprising the bottom-cycle suction line 180 and the additional bottom-cycle suction line 181.

54. The cascading heat pump system 100 of claim 53, wherein the bottom-cycle heat exchanger 122 is a shell-and-tube heat exchanger.

55. The cascading heat pump system 100 of claim 41, wherein each of the first bottom-cycle compressor 131, the second bottom-cycle compressor 132, the third bottom-cycle compressor 133, and the fourth bottom-cycle compressor 134 is a centrifugal compressor.

56. The cascading heat pump system 100 of claim 41, wherein the third bottom-cycle compressor 133 and the fourth bottom-cycle compressor 134 are configured to operate independently of the low-pressure group 135a.

57. The cascading heat pump system 100 of claim 41, wherein operation switches from a four- stage configuration to a two-stage configuration based on heat source temperature.Docket No. ATMOP706WO Page 58 of 59 PCT Application58. The cascading heat pump system 100 of claim 57, wherein the switch occurs when the heat source temperature exceeds a heating set temperature.

59. The cascading heat pump system 100 of claim 57, wherein the system reverts to the four- stage configuration when the heat source temperature falls below a cooling set.

60. The cascading heat pump system 100 of claim 59, wherein a difference between the heating and cooling set temperatures is at least 5°C.

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