High temperature dual rail heat pump cycle for high temperature rise and high performance in high temperature range

Abstract

The dual-rail heat pump cycle includes a low-temperature heat source, a two-stage high-temperature heat exchange process through which heat is exchanged with a heat transfer medium during operation, and a working fluid circuit. The working fluid circuit includes an expansion process, a compression process, a recuperation process, and a pair of parallel flow paths. The recuperation process is interposed between the expansion and compression processes and has a high-pressure side defined by the compression process and a low-pressure side defined by the expansion process. There is a pair of parallel flow paths between the recuperator process and a high temperature heat exchange process on the high pressure side of the recuperator process.

Description

[Technical Field]

[0001] This application claims priority to co-pending U.S. Non-Provisional Patent Application No. 17 / 974,913, filed October 27, 2022, in the name of Timothy Held, which is incorporated herein by reference in its entirety for all purposes, including priority, as if set forth verbatim herein. [Background technology]

[0002] Technical Field The present disclosure relates to heat pump cycles, and more particularly to heat pump cycles for high temperature rise and high performance in the high temperature range.

[0003] 2. Description of Related Art In several industrial processes, heat must be applied to one or more raw materials at relatively high temperatures. The most common way to generate this heat is through the combustion of fossil fuels. However, as the world shifts toward a carbon-free energy system, alternative technologies for providing industrial heat will be desirable. Direct electrical heating with devices such as electric resistance heaters, electric arc heaters, or electric induction heaters can achieve the required temperatures, but the coefficient of performance ("COP") of these processes can never exceed 1. As used in this context, COP is defined as the amount of heat transferred to a process divided by the power input. Summary of the Invention [Problem to be solved by the invention]

[0004] These forms of direct electric heating discussed in the immediately preceding paragraph are also potentially utilized in converting electrical power into thermal power, which can be stored for later use in so-called "electrical thermal energy storage" systems. In these cases, the round-trip efficiency of such systems is the mathematical product of the COP and the power generation cycle efficiency. Due to the characteristics of the heating systems described above, the round-trip efficiency ("RTE") of the overall storage process is lower than the efficiency of the power cycle used to convert thermal energy back into electricity, typically below 40% at temperatures ranging from 550°C to 600°C. [Means for solving the problem]

[0005] summary In a first aspect, a dual-rail heat pump cycle includes a low-temperature heat source, a two-stage high-temperature heat exchange process through which heat is exchanged with a heat medium during operation, and a working fluid circuit. The working fluid circuit includes an expansion process, a compression process, a recuperation process, and a pair of parallel flow paths. The recuperation process is interposed between the expansion process and the compression process and has a high-pressure side defined by the compression process and a low-pressure side defined by the expansion process. The pair of parallel flow paths between the recuperation process and the high-temperature heat exchange process is the high-pressure side of the recuperation process.

[0006] In another aspect, a dual-rail heat pump cycle includes a low-temperature heat source and a working fluid circuit through which a working fluid circulates during operation. The working fluid circuit includes a recuperator, a compression device, an expansion device, a pair of high-temperature heat exchangers, and a pair of parallel flow paths. The expansion device is downstream from the high-pressure side of the first recuperator and upstream from the low-temperature heat source, and defines the low-pressure side of the recuperator. The pair of parallel flow paths extend between the recuperator and the high-temperature heat exchanger on the high-pressure side of the recuperator.

[0007] The foregoing presents a simplified summary in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the disclosure or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form before the more detailed description that is presented below. [Brief explanation of the drawings]

[0008] BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to standard industry practice, various features have not been drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or decreased for clarity of discussion.

[0009] [Figure 1] FIG. 1 shows a prior art heat pump that uses a conventional heat pump cycle, which may be characterized as a simple heat pump cycle. [Figure 2] FIG. 2 is a pressure-enthalpy ("PH") diagram of the heat pump cycle of the heat pump of FIG. [Figure 3] FIG. 3 shows the coefficient of performance ("COP") and required compressor pressure ratio ("CPR") as a function of the maximum temperature of the heated heat transfer medium (Th2). [Figure 4] FIG. 4 shows a prior art heat pump that uses a simple recuperative heat pump cycle. [Figure 5] FIG. 5 plots the coefficient of performance and compressor pressure ratio for the simple recuperative cycle of FIG. 4 as a function of heat transfer medium temperature. [Figure 6A] FIG. 6A is a TQ plot of temperature versus heat load for the simple recuperation cycle, the high temperature heat exchanger, and the recuperator of the heat pump of FIG. [Figure 6B]FIG. 6B is a TQ plot of temperature versus heat load for the simple recuperation cycle, the high temperature heat exchanger, and the recuperator of the heat pump of FIG. [Figure 7] FIG. 7 is a process flow diagram of a first embodiment of a dual rail heat pump cycle in accordance with one or more embodiments of the below claimed subject matter. [Figure 8] FIG. 8 is a pressure-enthalpy ("PH") diagram of the heat pump cycle for the dual rail heat pump cycle of FIG. 7 at Th2=565°C and Trange=545°C. [Figure 9A] FIG. 9A is a TQ plot of the heat exchanger and recuperator of the dual rail heat pump cycle of FIG. [Figure 9B] FIG. 9B is a TQ plot of the heat exchanger and recuperator of the dual rail heat pump cycle of FIG. [Figure 10] FIG. 10 is a process flow diagram of a second embodiment of a dual rail heat pump cycle in accordance with one or more embodiments of the below claimed subject matter. [Figure 11] FIG. 11 is a process flow diagram of a first embodiment of a dual rail heat pump cycle in accordance with one or more embodiments of the below claimed subject matter. [Figure 12] FIG. 12 is a block diagram of a control system including a programmed controller that may be used to control the fluid flow of a working fluid in some embodiments. [Figure 13] Figure 13 compares the COP of the dual-rail heat pump cycle with the COP of the single recuperation heat pump cycle as a function of Trange at Th2 = 565°C.

[0010] While the disclosed technology is susceptible to various modifications and alternative forms, the drawings show by way of example specific embodiments described in detail herein. It is to be understood, however, that the description of specific embodiments herein is not intended to limit what is claimed to the particular forms disclosed, but on the contrary, to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[0011] Detailed Description In contrast to direct electrical heating, thermodynamic heat pump cycles can achieve COP values ​​well above 1.0. However, cycle and working fluid limitations typically allow only modest heating temperatures in the heat pump. FIG. 1 shows a prior art heat pump 100 using a conventional heat pump cycle. The heat pump 100 circulates a working fluid (not shown) through a working fluid circuit 105. The heat pump 100 uses several well-known components to compress, expand, heat, cool, etc. the working fluid to place it in various states defined by properties such as temperature and pressure. The state of the working fluid at various points in the working fluid circuit 105 is indicated using the convention well known in the art, where numbers are shown within circles.

[0012] In a conventional heat pump cycle 100, a working fluid is compressed using a compression device 110, such as a compressor, from a first, relatively low temperature, low pressure state 1 to one of higher temperature and pressure states 2. The heat introduced into the working fluid by the compression is then transferred to a heat transfer medium, which receives the heat so that it can be used or stored. In FIG. 1, this transfer occurs in a heat exchanger ("HTX") 115. The heat transfer medium is transferred from an initial temperature T h1 Low-temperature heating media start at a higher temperature, T h2 and is sometimes called a "high temperature" heating medium.

[0013] During the process of heating the heat transfer medium, the working fluid cools to state 3. The fluid is then expanded to state 4 using expansion device 120. Expansion device 120 may be an expander, such as an adiabatic expansion valve or a hydrodynamic expander, that also extracts thermodynamic work from the fluid. The temperature and pressure of the working fluid are reduced to state 4 within expansion device 120. Low temperature heat is then added to the working fluid from an external low temperature source 125 to return the working fluid to state 1. Often, the low temperature heat source can be ambient heat from the environment in which heat pump 100 is operating.

[0014] The thermodynamic process of the heat pump cycle of Figure 1 can also be illustrated in the pressure-enthalpy diagram of Figure 2. For some applications, conventional heat pump cycles offer a good combination of performance and simplicity. For example, CO2 heat pumps are frequently used to heat water from ambient temperature to domestic hot water heating temperatures.

[0015] The net specific work required to transfer the heat can be represented by the enthalpy increase during the compression process (State 1 to State 2) minus the enthalpy decrease during the expansion process (State 3 to State 4). The amount of heat transferred to the heat carrier is represented by the enthalpy change in the high-temperature heat exchanger 115 (State 2 to State 3). One performance parameter of the heat pump cycle introduced previously is the coefficient of performance (“COP”), which in this context is the heat transferred divided by the net specific work. Consistent with the previous definition of COP, the COP can be expressed by the following equation:

number

[0016] In the above equation, Q h is the heat transferred, W net is the net specific work, and h1 through h4 are the specific enthalpies of the working fluid in states 1 through 4 in Figure 1, respectively.

[0017] Another performance parameter is the temperature to which the heat transfer medium is heated (Th2 ) and the temperature "range." The temperature range is the difference between the final temperature of the heat transfer medium and its initial temperature (T range =T h2 -T h1 ). Another parameter is "lift", where lift = T h2 -T source It can be mathematically expressed as T source is the temperature of the heat source. Based on basic thermodynamics and heat transfer principles, to transfer heat to the heat carrier, the working fluid temperature at state 2 (T2) is T h2 The working fluid temperature in state 3 (T3) must be higher than T h1 must be higher than

[0018] To achieve this combination of performance parameters, the baseline heat pump cycle described above must use an extremely high compressor pressure ratio ("CPR"). This significantly increases the cost of the system, and above a certain pressure ratio (typically about 10:1), the solution becomes impractical. In the case shown in Figure 3, heat is extracted from a 15°C environment and T h1 = 20 °C. In practice, the maximum T achievable in a simple heat pump cycle is h2 is approximately 200°C.

[0019] The heat pump cycle shown in Figures 1-2 is sometimes referred to as a "simple heat pump cycle." Figure 4 shows a prior art heat pump 400 that uses what is known as a simple recuperated heat pump cycle. The heat pump 400 includes a recuperator ("RCX") 405. The recuperator 405 transfers heat from a first portion of the working fluid circulating in a working fluid circuit to another portion of the working fluid.

[0020] T h2 The value is approximately T h2= 200°C to 250°C, the performance of the recuperated heat pump cycle is superior to that of the simple heat pump cycle. For these simulations used to generate Figure 5, the compressor pressure ratio was limited to 10:1 or less. Figure 5 plots the coefficient of performance and compressor pressure ratio of the simple recuperated cycle 400 of Figure 4 as a function of heat transfer medium temperature.

[0021] However, another factor in heat pump performance is the combined high T range and T h2 and COP at 1000 kJ / s. Note that simple recuperative cycles are limited in their ability to provide this combination of properties. Figure 6A is a TQ plot for heat exchanger 115, and Figure 6B is a TQ plot for recuperator 405 of Figure 4. The TQ plots are the temperature vs. heat load Q / Q tot is graphed.

[0022] As Figures 6A-6B show, a simple recuperator system can achieve a high range, but is limited by the recuperation process itself to the relatively high working fluid temperature exiting heat exchanger 115 shown in Figure 1. As a result, the TQ curves have significantly different slopes, representing exergy losses in the recuperator and heat exchanger 115. In addition, the large discrepancy in specific heat capacity values ​​at different pressures in the system also results in a large slope difference in the recuperator TQ plot of Figure 6B, further adding exergy destruction to the cycle and reducing its performance.

[0023] Illustrative examples of the claimed subject matter are now disclosed. For clarity, not all features of an actual implementation are described herein. It will be understood that in the development of any such actual implementation, numerous implementation-specific decisions may be made to achieve the developer's particular goals, including compliance with system-related constraints and compliance with business-related constraints, which vary from implementation to implementation. Moreover, it will be understood that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0024] This disclosure describes a "dual rail" heat pump cycle that allows the flowing heat medium to be heated over a wide range of temperatures, flexibly achieving excellent heat pump performance values. h2 While increasing the range and still maintain a good COP. Next, a second embodiment, which is a variation of the first embodiment, is disclosed. In this more complex heat pump cycle, two internal heat exchangers, each called a "recuperator," are used to transfer some of the excess heat to the downstream side of the heat exchanger, preheating the working fluid before it enters the compressor.

[0025] FIG. 7 is a process flow diagram of a first embodiment of a dual-rail heat pump cycle 700 in accordance with one or more embodiments of the claimed subject matter. The dual-rail heat pump cycle 700 is so named because of the parallel recuperator and HTX flow paths 705, 706. Note that parallel flow paths, or "rails," 705, 706 run between the recuperator process 733 and the heat exchanger process 720. More specifically, the first rail 705 includes a flow path from a split at point 755 where the working fluid is at states 3A and 4A, as well as a second high-temperature heat exchanger 711. The second rail 706 includes a flow path from a split at point 755 where the working fluid is at states 3B and 4B, as well as a second recuperator 716. Thus, "parallel paths" or "parallel rails" can be thought of as flow paths that begin at a point in the cycle in which the working fluid flow splits into multiple conduits and then recombines at another point in the cycle.

[0026] Figure 8 shows the T h2 = 565℃, T range8 is a pressure-enthalpy ("PH") diagram of the heat pump cycle of the dual-rail heat pump cycle 700 of FIG. 7 at Θ = 545°C. FIGS. 9A-9B are TQ plots of the high-temperature heat exchangers 710, 711 and recuperators 715, 716 of the dual-rail heat pump cycle of FIG. 7. Those skilled in the art, having the benefit of this disclosure, will note that in FIG. 8, states 7 and 8 occupy approximately the same point in the graph. That is, states 7 and 8 are "overlapping" one another. This fact implies that the presence of recuperator 715 ("RCX1") provides little performance benefit over recuperator 716 ("RCX2"), but the performance benefit provided by recuperator 715 is not zero. Thus, some embodiments may omit recuperator 716.

[0027] As used herein, the terms "low temperature" and "high temperature" in the context of heat exchange are defined relative to each other and relative to the temperature of the circulating working fluid. In embodiments disclosed herein, "low temperature" can mean a temperature ranging from -25°C to 50°C, and "high temperature" can mean 80°C to 600°C. However, in other embodiments, these numbers may be different. For example, in some embodiments, the heat source may be the ambient environment. In other embodiments, the low temperature heat source may be a waste heat source rather than the ambient environment, in which case the low temperature and high temperature may be higher than in the embodiments disclosed herein. Nevertheless, the waste heat source may be a target heat sink temperature (T h2 ), however, this is generally a higher temperature than the ambient environment.

[0028] Thus, as used herein, a "cold" heat exchanger (if used) transfers heat from a heat source to a circulating working fluid. Thus, heat is transferred from a "higher" temperature heat source to a "lower" temperature working fluid. Conversely, a "hot" heat exchanger transfers heat from a "hotter" circulating working fluid to a relatively "colder" heat carrier. The temperature at which heat exchange occurs in a "hot" heat exchanger occurs at a higher temperature than the temperature at which heat exchange occurs in a "cold" heat exchanger.

[0029] The terms "high pressure" and "low pressure" are similarly defined relative to one another. For example, recuperator process 733 can be said to have a "high pressure side" and a "low pressure side" defined by expansion process 725 and compression process 730. The working fluid in states 7 through 8 and 1 is at a lower pressure than the pressure of the working fluid in states 3B, 4B, and 4 through 5. (This is due to the action of expansion process 725 and compression process 730, respectively.) Thus, the "side" of recuperation process 733 where the working fluid is in states 7 to 8 and 1 can be referred to as the "low-pressure side," and the "side" where the working fluid is in states 3B, 4B, and 4 to 5 can be referred to as the "high-pressure side."

[0030] Thus, the precise numerical quantification of the terms "high temperature," "low temperature," "high pressure," and "low pressure" in the context of heat exchange will depend on the implementation of the specific details of any given embodiment. While representative numerical quantifications may be provided herein for the illustrated embodiments, other embodiments not illustrated may likely use other numerical quantifications. One of ordinary skill in the art with the benefit of this disclosure will be readily able to determine the numerical quantifications appropriate for a particular embodiment.

[0031] The dual-rail heat pump cycle 700 includes a heat exchange process (“HTX”) 720, an expansion process 725, a compression process 730, a recuperation process 733, and a low-temperature heat source 735. A working fluid circulates through the heat exchange process 720, the expansion process 725, the compression process 730, and the low-temperature heat source 735, and through a working fluid circuit 740. The working fluid in this particular embodiment is carbon dioxide (CO2). Alternative embodiments may use other working fluids. The heat medium heated by the heat exchange process 720 may be any flowing heat medium, such as, but not limited to, air, water, a heat transfer fluid, or a molten salt. The working fluid circuit 740 also includes, in this particular embodiment, a generator 745 driven by the expansion process 725 and a motor 750 that drives the compression process 730.

[0032] The expansion process 725 and the compression process 730 each use at least one expansion device 726 and at least one compression device 731. The compression device 731 may be a compressor, such as a hermetic reciprocating compressor, a scroll compressor, or a centrifugal compressor. The expansion device may be an expander, such as an adiabatic expansion valve or a fluid expander. The fluid expander may be, for example, a turbine, a reciprocating expander, or a scroll expander. Those skilled in the art, given the benefit of this disclosure, will appreciate still other implementations.

[0033] 7 and 8, a dual-rail heat pump cycle 700 exchanges heat between a heat carrier and a working fluid in a heat exchange process 720. In this first embodiment of a dual-rail heat pump cycle, the heat exchange process 720 is divided into two stages, each represented by a respective one of the high-temperature heat exchangers 710 ("HTX1"), 711 ("HTX2").

[0034] In the first stage, the working fluid transfers heat to the heat carrier in heat exchanger 710, heating the heat carrier and cooling the working fluid. The working fluid enters heat exchanger 710 at state 2, where heat is exchanged between the working fluid and the heat carrier. This heat exchange heats the heat carrier and cools the working fluid.

[0035] Upon exiting the first stage of the heat exchange process 720 in State 3, the working fluid is then split into two portions at point 755. The first portion, in State 3A, enters the second stage of the heat exchange process 720. In the second stage, represented by heat exchanger 711, the working fluid is further cooled and preheats the heat carrier. Note that the terms "first" and "second" with respect to the heat exchange process 720 are in terms of the working fluid circulation. The heat carrier flows in the opposite direction to the working fluid. Thus, from the heat carrier perspective, the heat carrier is preheated in the second heat exchanger 711 prior to the second heat heating in the first heat exchanger 710, and the working fluid is cooled in both exchanges. The second portion of the working fluid, in State 3B, enters the second recuperator 716 ("RCX2"), where the second portion is cooled and preheats the working fluid on the low-pressure side of the system (State 8 to State 1).

[0036] Upon exiting the second stage of the heat exchange process 720, represented by heat exchanger 711 at State 4A and second recuperator 716 at State 4B, the flow recombines the first and second portions at point 760. The recombined working fluid at State 4 then enters an additional first recuperator ("RCX1") 715 to further cool the high-pressure working fluid (State 4 to State 5) and preheat the low-pressure working fluid (State 7 to State 8). The high-pressure working fluid then enters expansion device 726 at State 5, where work can be extracted, and the pressure and temperature of the working fluid are reduced to State 6. Heat is then added from an environmental or similar source (i.e., low-temperature heat source 735) as the working fluid is brought from State 6 to State 7.

[0037] Splitting the working fluid into two portions allows for better matching of the heat capacity, defined as the mathematical product of mass flow rate and specific heat capacity, on the two sides of the second recuperator (716): the high-pressure side (State 3B to State 4B) and the low-pressure side (State 8 to State 1). In addition, the working fluid can be cooled to a lower temperature than would be possible in a single recuperation cycle, which also allows its TQ gradient to better match the heat carrier thermal gradient, as shown in Figures 9A and 9B. Both effects reduce the exergy destruction of the cycle and improve its performance.

[0038] FIG. 10 illustrates a second embodiment of a dual-rail heat pump cycle, which may be referred to as an "extended" dual-rail heat pump cycle. The dual-rail heat pump cycle of FIG. 10 shares several common parts with the dual-rail heat pump cycle of FIG. 7. These common parts are similarly numbered and will not be described again here. This discussion will instead focus on the differences between the dual-rail heat pump cycles of FIG. 7 and FIG. 10.

[0039] In the extended dual-rail heat pump cycle 1000, the working fluid may be additionally split at State 4, with a first portion (State 4C) entering an additional low-temperature stage of the heat exchange process 1005 ("HTX"), represented by high-temperature heat exchanger 1010 ("HTX3"). The working fluid is then further cooled while further preheating the heat carrier in a third high-temperature heat exchanger. A second portion (State 4D) of the working fluid enters the first recuperator 1015 ("RCX1"), where it is cooled while heating the low-pressure working fluid (State 7 to State 8).

[0040] Note the presence of third and fourth parallel flow paths 1020, 1021. The third parallel flow path 1020, more particularly, the third rail 1020 includes a flow path from the split at point 1030 where the working fluid is in states 4C and 4D, and the third high-temperature heat exchanger 1010. The fourth rail 1021 includes a flow path from the split at point 1030 where the working fluid is in states 4D and 5D, and the recuperator 1015. Those skilled in the art having the benefit of this disclosure will understand that additional configurations can be envisioned that repeat the flow split and parallel HTX and RCX flow paths any number of times to further match the heat capacity of the fluid on each side of the heat exchanger.

[0041] As noted above in the discussion of Figure 7, some embodiments may omit one of the recuperators 715, 716 in the recuperation process 733. Figure 11 shows a heat pump cycle 1100 in which the recuperation process 1133 uses only a single recuperator 716. The design of the heat pump cycle 1100 is a variation of the heat pump cycle 700 of Figure 7, and like parts have like numbers. Note that the number of working fluid states is reduced from eight to six, while rails 705, 706 remain unchanged.

[0042] As one of ordinary skill in the art with the benefit of this disclosure will understand, the heat pump cycles of Figures 7, 10, and 11, as well as other embodiments, can include thermal reservoirs, other heat exchangers, piping, pumps, valves, and other controllers not separately shown. For example, the flow of working fluid through the working fluid circuit is generally a function of the programmable control of fluid flow valves. These other components are not shown in Figures 7, 10, and 11 for clarity and so as not to obscure what is claimed below in this discussion.

[0043] Such control systems are readily known to those skilled in the art, but for completeness, one such control system 1200 is shown in Figure 12. Control system 1200 may include a plurality of fluid flow valves 1205 and a controller 1210 that sends control signals over power lines 1215. A controller such as controller 1210 may send control signals to fluid flow valves 1205 to control the flow of working fluid as described above.

[0044] Controller 1210 includes processor-based resources 1220, which may be, for example, without limitation, a microcontroller, a microprocessor, an application-specific integrated circuit (“ASIC”), an electrically erasable programmable read-only memory (“EEPROM”), etc. Depending on the implementation of the processor-based resources, controller 1210 may also include memory 1225 encoded with instructions (not shown) executable by processor-based resources 1220 to implement the functions of controller 1210. Also, depending on the implementation of processor-based resources 1220, memory 1225 may be part of processor-based resources 1220 or a standalone device. For example, the instructions may be firmware stored in a memory portion of a microprocessor or may be routines stored in a standalone read-only or random-access memory chip. Similarly, in some implementations of processor-based resources 1220 (e.g., ASICs), memory 1235 may be omitted entirely.

[0045] A flow control system may be used to more particularly control the flow of working fluid between two parallel paths or rails. For example, with reference to FIG. 7 , a flow control system may control the flow of working fluid between first rail 705 and second rail 706. A programmable fluid control system, such as fluid control system 1200 of FIG. 12 , may be particularly useful in implementing variable flow between / among parallel flow paths to accommodate variations in operating conditions or changes in design parameters. However, in some embodiments, a programmable flow control system may be used to implement fixed flow of working fluid between / among parallel flow paths. Still other embodiments may use a non-programmable flow control system. For example, valves may be manually set or controlled.

[0046] Figure 13 illustrates the effectiveness of the techniques of the present disclosure. The relative performance of the single recuperative heat pump of Figure 4 and the dual rail heat pump of Figure 7 is shown in Figure 13. h2 = 565℃, T range The results for T = 265°C to 545°C are shown in Figure 11. range At relatively small values ​​of T (below 350°C), there is no clear advantage to a dual-rail heat pump cycle over a single recuperation cycle. range At higher values ​​of , the dual-rail cycle has a clear performance advantage as assessed by COP.

[0047] As used herein, the article "a" is intended to have its ordinary meaning in the patent art, i.e., "one or more." As used herein, the term "about," when applied to a value, generally means within the tolerance of the device used to generate that value, or in some instances, ±10%, ±5%, or ±1%, unless otherwise specified. Furthermore, as used herein, the term "substantially" means most, or nearly all, or all, or an amount, for example, ranging from about 51% to about 100%. Furthermore, the examples herein are intended to be exemplary only and are presented for purposes of illustration and not limitation.

[0048] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that specific details are not required to practice the systems and methods described herein. The foregoing descriptions of specific embodiments have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the disclosure to the precise forms described. Obviously, many modifications and variations are possible in light of the above teachings. The embodiments have been shown and described to best explain the principles and practical application of the present disclosure, so as to enable others skilled in the art to best utilize the present disclosure and various embodiments with various modifications suited to the particular uses contemplated. It is intended that the scope of the present disclosure be defined by the following claims and their equivalents.

Claims

1. A dual rail heat pump cycle, a low-temperature heat source; a two-stage high temperature heat exchange process through which heat is exchanged with a heat transfer medium during operation; A working fluid circuit, the working fluid circuit comprising: The expansion process and A compression process; a recuperation process interposed between the expansion process and the compression process, the recuperation process comprising: a high-pressure side defined by the compression process; and a low-pressure side defined by the expansion process; a pair of parallel flow paths between the recuperative process and the high-temperature heat exchange process on the high-pressure side of the recuperative process; a working fluid circuit including: A dual rail heat pump cycle.

2. The dual rail heat pump cycle is an extended dual rail heat pump cycle, the two-stage heat exchange process includes an extension stage that exchanges heat with a heat transfer medium during operation; The dual-rail heat pump cycle of claim 1 , wherein the working fluid circuit includes a third parallel flow path between the extension stage and a recuperator.

3. The dual-rail heat pump cycle of claim 1 , wherein the heat transfer medium flows through the heat exchange process.

4. the dual rail heat pump cycle is an extended dual rail heat pump cycle, The dual rail heat pump cycle of claim 1 , further comprising a third stage in a high temperature heat exchange process and a second pair of parallel flow paths between the recuperation process and the high temperature heat exchange process.

5. The dual-rail heat pump cycle of claim 1 , wherein the recuperation process includes a pair of recuperators.

6. a generator driven by the expansion process; a motor that drives the compression process; The dual rail heat pump cycle of claim 1 , further comprising:

7. The dual-rail heat pump cycle of claim 1 , wherein the compression process includes at least one compression device.

8. The dual rail heat pump cycle of claim 7 , wherein the compression device comprises a compressor.

9. The dual-rail heat pump cycle according to claim 8, wherein the compressor is a fully hermetic reciprocating compressor, a scroll compressor, or a centrifugal compressor.

10. The dual-rail heat pump cycle of claim 1 , wherein the expansion process includes at least one expansion device.

11. The dual rail heat pump cycle of claim 10 , wherein the expansion device comprises an expander.

12. The dual-rail heat pump cycle according to claim 11 , wherein the expander is an adiabatic expansion valve or a fluid expander.

13. The dual rail heat pump cycle of claim 12 , wherein the fluid expander is a turbine, a reciprocating expander, or a scroll expander.

14. A dual rail heat pump cycle, a low-temperature heat source; a working fluid circuit through which, during operation, a working fluid circulates; A recuperator, a compression device defining a high pressure side of the recuperator; an expansion device downstream from the high pressure side of the recuperator and upstream from the low temperature heat source, the expansion device defining the low pressure side of the recuperator; a pair of high-temperature heat exchangers through which the heat medium flows; a pair of parallel flow paths between the recuperator and a high-pressure side high-temperature heat exchanger of the recuperator; a working fluid circuit including: A dual rail heat pump cycle.

15. The dual rail heat pump cycle is an extended dual rail heat pump cycle, The extended dual rail heat pump cycle a third high-temperature heat exchanger through which the heat medium flows; a second pair of parallel flow paths between the third high-temperature heat exchanger and the recuperator; The dual rail heat pump cycle of claim 14 further comprising:

16. a generator driven by the expansion device; a motor that drives the compression device; The dual rail heat pump cycle of claim 14, comprising:

17. The dual rail heat pump cycle of claim 14 , wherein the compression device comprises a compressor.

18. 18. The dual-rail heat pump cycle according to claim 17, wherein the compressor is a fully hermetic reciprocating compressor, a scroll compressor, or a centrifugal compressor.

19. The dual rail heat pump cycle of claim 14 , wherein the expansion device comprises an expander.

20. 20. The dual-rail heat pump cycle of claim 19, wherein the expander is an adiabatic expansion valve or a fluid expander.

21. 21. The dual rail heat pump cycle of claim 20, wherein the fluid expander is a turbine, a reciprocating expander, or a scroll expander.

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