Regenerators

Field

[0001] The present disclosure relates to heat pumps that operate on a thermal- compression cycle.

Background

[0002] Some thermal-compression heat pumps 100 employ three chambers that are delimited by two reciprocating displacers, such as that shown in Figure 1. A hot chamber 112 is between a hot heat exchanger 122 and one of the two displacers, a hot displacer 102. A cold chamber 116 is located between a cold heat exchanger 126 and the other of the two displacers, a cold displacer 106. And, a warm chamber 114 is located between the two displacers 102 ad 106. Volumes within the chambers depend on the position of the displacers within the cylinder 130. Motion of displacers 102 and 106 are synchronized by a crank 110.

[0003] In a commonly-assigned patent, U.S. 9,677,794, actuation of the displacers via a mechatronics system provides independent control of the displacers. It is desirable to exploit opportunities that independent control of the displacers affords in changing the cycle employed and the configuration of the heat pump.

Summary

[0004] A four-process cycle is disclosed that demonstrates a higher coefficient of performance than the previously known Vuilleumier heat pumps. The warm chamber is broken into two chambers that communicate via a temperature barrier chamber. The two chambers: warm-hot and warm-cold each communicates with a dedicated heat exchanger, warm-hot and warm-cold, respectively. The temperature in the warm-hot and warm-cold chambers is controlled by the amount of liquid provided to each of their respective heat exchangers. This facilitates keeping the temperature in the warm-hot and warm-cold chambers different As a consequence, the heating capacity and temperature in each of the coolant loops in the warm-hot and warm-cold heat exchangers can be controlled separately to meet the demands of the particular application. [0005] A heat pump is disclosed that has: a hot cylinder with a hot displacer disposed therein; a cold cylinder with a cold displacer disposed therein; a mechatronics section located between the hot and cold cylinders; a dome disposed on one end of the hot cylinder; a cap disposed on one end of the cold cylinder; a hot chamber delimited by the dome, the hot cylinder, and the hot displacer; a warm-hot chamber delimited by the mechatronics section, the hot cylinder, and the hot displacer; a cold chamber delimited by the cap, the cold cylinder, and the cold displacer and a warm-cold chamber delimited by the mechatronics section, the cold cylinder, and the cold displacer. The warm-cold chamber and the warm-hot chamber are fluidly coupled via a temperature barrier chamber. The temperature barrier chamber, at least in some embodiments, can be considered a warm regenerator.

[0006] The heat pump further includes: a hot heat exchanger fluidly coupled to the hot chamber; a hot regenerator fluidly coupled to the hot heat exchanger; and a warm-hot heat exchanger fluidly coupled to the hot regenerator. The warm-hot heat exchanger is also fluidly coupled to the temperature barrier chamber.

[0007] The heat pump further includes: a cold heat exchanger fluidly coupled to the cold chamber; a cold regenerator fluidly coupled to the cold heat exchanger; and a warm-cold heat exchanger fluidly coupled to the cold regenerator. The warm-cold heat exchanger is also fluidly coupled to the temperature barrier chamber.

[0008] Two fluids flow through the warm-hot heat exchanger: a working fluid and a liquid coolant The working fluid is a gas that is disposed within the heat pump. The liquid coolant enters the warm-hot heat exchanger via an inlet port that pierces a housing of the heat pump and the liquid coolant exits the warm-hot heat exchanger via an outlet port that pierces the housing of the heat pump.

[0009] Two fluids flow through the warm-cold heat exchanger: a working fluid and a liquid coolant The working fluid is a gas that is disposed within the heat pump. The liquid coolant enters the warm-cold heat exchanger via an inlet port that pierces a housing of the heat pump and the liquid coolant exits the warm-cold heat exchanger via an outlet port that pierces the housing of the heat pump.

[0010] The temperature barrier chamber is made up a plurality of passages, in one embodiment. In some embodiments, the passages have a thermally-insulating coating on the inside Alternatively, the temperature barrier chamber has a regenerator chamber with a porous media disposed therein. In some embodiments, the temperature barrier chamber has a tube with a free-floating piston therein. In some embodiments, the piston is of a lightweight material.

[0011] The heat pump also has a warm-hot heat exchanger. The warm-hot heat exchanger and the temperature barrier chamber are both fluidly coupled to the warm- hot chamber.

[0012] The heat pump also has a warm-cold heat exchanger. The warm-cold heat exchanger wherein the warm-cold heat exchanger and the temperature barrier chamber are both fluidly coupled to the warm-cold chamber.

[0013] Also disclosed is a heat pump that includes: a housing; a hot cylinder and a cold cylinder disposed within the housing; a hot displacer disposed within the hot cylinder; a cold displacer disposed within the cold cylinder; a mechatronics section disposed in the housing between the hot cylinder and the cold cylinder; a dome coupled to the hot cylinder on an end of the hot cylinder away from the mechatronics section; a cap coupled to the cold cylinder on an end of the cold cylinder away from the mechatronics section; an annular space delimited by the housing, the hot cylinder, the cold cylinder, and the mechatronics section; a hot chamber delimited by the dome, the hot cylinder, and the hot displacer; a warm-hot chamber delimited by the mechatronics section, the hot cylinder, and the hot displacer; a cold chamber delimited by the cap, the cold cylinder, and the cold displacer; a warm-cold chamber delimited by the

mechatronics section, the cold cylinder, and the cold displacer. The warm-cold chamber and the warm-hot chamber are fluidly coupled via a temperature barrier chamber located in the annular space.

[0014] The temperature barrier chamber has a plurality of passages.

[0015] The temperature barrier chamber has a regenerator chamber with a porous media inside.

[0016] The temperature barrier chamber is a tube with a free-floating piston disposed therein.

[0017] The heat pump also has: a hot heat exchanger; a warm-hot heat exchanger; warm-cold heat exchanger; a cold heat exchanger; a hot regenerator; and a cold regenerator. The hot heat exchanger is fluidly coupled to both the hot chamber and the hot regenerator. The hot regenerator is fluidly coupled to both the hot heat exchanger and the warm-hot heat exchanger. The warm-hot heat exchanger is fluidly coupled to: the hot regenerator, the warm-hot chamber, and the temperature barrier chamber. The temperature barrier chamber is fluidly coupled to: the warm-hot heat exchanger, the warm-hot chamber, the warm-cold heat exchanger, and the warm-cold chamber. The warm-cold heat exchanger is fluidly coupled to: the temperature barrier chamber, the warm-cold chamber, and the cold regenerator. The cold regenerator is fluidly coupled to both the warm-cold heat exchanger and the cold heat exchanger. The cold heat exchanger is fluidly coupled to both the cold regenerator and the cold chamber.

[0018] The hot regenerator, the warm-hot heat exchanger, the warm-cold heat exchanger, and the cold regenerator are disposed in the annular space.

[0019] A working fluid is disposed in the hot chamber, the warm-hot chamber, the warm-cold chamber, the cold chamber, the hot regenerator, the temperature barrier chamber, the cold regenerator, the hot heat exchanger, the warm-hot heat exchanger, the warm-cold heat exchanger, and the cold heat exchanger. The working fluid is one of helium, neon, and hydrogen.

[0020] The warm-hot heat exchanger is provided two fluids: the working fluid and a warm-hot liquid coolant The warm-cold heat exchanger is provided two fluids: the working fluid and a warm-cold liquid coolant

[0021] The warm-hot liquid coolant has a warm-hot liquid coolant inlet and a warm-hot liquid coolant outlet that access the warm-hot heat exchanger via first and second orifices, respectively, that pierce the housing; and

[0022] The warm-cold liquid coolant has a warm-cold liquid coolant inlet and a warm-cold liquid coolant outlet that access the warm-cold heat exchanger via third and fourth orifices, respectively, that pierce the housing.

[0023] The hot heat exchanger is provided two fluids: the working fluid and combustion gases. The cold heat exchanger is provided two fluids: the working fluid and a cold liquid coolant.

[0024] Also disclosed is heat pump that includes: a warm-hot chamber delimited within the heat pump; a warm-cold chamber delimited within the heat pump; a warm- hot heat exchanger; a warm-cold heat exchanger; and a temperature barrier chamber having a hot end and a cold end. The hot end is fluidly coupled to both the warm-hot chamber and the warm-hot heat exchanger. The cold end is fluidly coupled to both the warm-cold chamber and the warm-cold heat exchanger. [0025] The temperature barrier chamber is one of: a regenerator chamber with a porous media disposed therein, a plurality of passages, a tube with a free-floating, impermeable piston disposed therein, and a tube with a free-floating, porous piston disposed there.

[0026] The heat pump further includes: a hot cylinder with a hot displacer disposed therein; a cold cylinder with a cold displacer disposed therein; a mechatronics section located between the hot and cold cylinders; a hot displacer rod coupled between the hot displacer and the mechatronics section; and a cold displacer rod coupled between the cold displacer and the mechatronics section. The warm-hot chamber is delimited by the mechatronics section, the hot cylinder, and the hot displacer. The warm-cold chamber is delimited by the mechatronics section, the cold cylinder, and the cold displacer.

[0027] There are a variety of applications in which having four chambers in the heat pump provide advantageous operating conditions. The heat pump may further include: a first external heat exchanger accepting a first fluid stream from the warm-hot heat exchanger and returning the first fluid stream to the warm-hot heat exchanger and a second external heat exchanger accepting a second fluid stream from the warm-cold heat exchanger and returning the second fluid stream to the warm-cold heat exchanger. The first heat exchanger may be operated at a higher temperature than the second heat exchanger to provide the desired temperatures for two draws within the house or building.

[0028] In another example, the heat pump includes: a valve accepting a fluid stream from the warm-hot heat exchanger, a first external heat exchanger fluidly coupled to the valve, a second external heat exchanger fluidly coupled to the valve, and a bypass pipe coupling an outlet pipe of the warm-cold heat exchanger to an inlet pipe of the warm-hot heat exchanger. The valve directs flow to one or both of the first and second external heat exchangers based on demands for heating.

[0029] In some embodiments, the heat pump also includes: a second valve accepting a fluid stream from the cold heat exchanger, a third external heat exchanger fluidly coupled to the second valve, and a fourth external heat exchanger fluidly coupled to the second valve. [0030] The heat pump is located within a building. The first and third heat exchangers are located within the building. The second and fourth heat exchangers are located outside the building.

Brief Description of Drawings

[0031] Figure 1 is a schematic of a prior art Vuilleumier heat pump;

[0032] Figure 2 is a cross-sectional drawing of a thermal-compression heat pump;

[0033] Figure 3 is a schematic representation of a thermal-compression heat pump shown at ends points of the cycle, A, B, C, D, A;

[0034] Figure 4 shows idealized thermodynamic cycles in each of the chambers of four-chamber heat pump showing the ends points of the cycles A, B, C, and D related to the end points of Figure 3;

[0035] Figures 5-7 show alternatives for a thermal barrier chamber;

[0036] Figures 8-11 show alternative configurations of how the heat pump is plumbed to external heat exchangers for a range of applications; and

[0037] Figure 12 shows a configuration of a building in which a heatpump is situated.

Detailed Description

[0038] As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.

[0039] A compression-expansion heat pump 200 is shown in Figure 2 in which the displacers are not crank synchronized and are actuated independently. Such heat pump 200 provides greater flexibility in controlling the output of the heat pump and in the arrangements of the chambers. Heat pump 200 has a hot heat exchanger 202, a cylinder 204 in which a hot displacer 206 reciprocates and a cylinder 208 in which a cold displacer 210 reciprocates. Mechatronics actuators, in mechatronics section 220, are coupled to hot and cold displacers 206 and 210 and drive the displacers between ends of travel. Hot displacer 206 and cold displacer 210 are coupled to the

mechatronics section 220 via rods 290 and 292, respectively. A working fluid, such as helium, that is contained within cylinders 204 and 208.

[0040] When displacers 206 and 210 reciprocate, the working gas moves among chambers (above and below each of displacers 206 and 210] A hot chamber 280 is located above hot displacer 206. A warm-hot chamber 282 is located below hot displacer 206. When hot chamber 280 moves upward, working gas moves from hot chamber 280 into hot heat exchanger 202 into a hot regenerator 230, into a hot-warm heat exchanger 230 and warm-hot chamber 282. When hot displacer 206 moves in the other direction, flow is reversed compared to that described above.

[0041] A warm-cold chamber 284 is within cylinder 208 between mechatronics section 220 and cold displacer 210. A cold chamber 286 is defined by cold displacer 210, cylinder 208, and a bottom end of a housing of heat pump 200. When cold displacer moves downward, working gas moves from cold chamber 286 into cold heat exchanger 260 in cold regenerator 270 into warm-cold heat exchanger 250, and into warm-cold chamber 284. When cold displacers moves upward, the flow is reversed in regard to that described immediately above.

[0042] One of the fluids passing through heat exchangers 240, 250, and 260 is the working fluid. The other fluid in the present example is a liquid coolant In regard to warm-hot heat exchanger 240, coolant accesses passageways of warm-hot heat exchanger 240 through inlet 242 and exits through outlet 244. Similarly, passages of warm-cold heat exchanger 250 are coupled to an inlet 252 and an outlet 254; and passages of cold heat exchanger 260 are coupled to an inlet 262 and an outlet 264.

[0043] A schematic representation of four positions of displacers in a thermal- compression heat pump is shown in Figure 3, positions A, B, C, D, and then back to the original position A to complete the cycle. Within the present disclosure, the term heat exchanger refers to a device for transferring heat between two or more fluids. The term regenerator, herein, refers to a heat exchange system in which heat from a single fluid is exchanged cyclically with a heat sink, the heat sink being a non-fluid, such as a metallic, fiber glass, ceramic mesh a solid piece of metal, or any other suitable material.

[0044] Referring to Figure 3, heat pump 10 has a cold displacer 16 and a hot displacer 12 that reciprocate within respective cylinders. The working fluid within heat pump 10 is a gas, such as helium or hydrogen. In positions A and B, hot displacer 12 is in its upper position. A hot chamber 22 has almost no fluid therein when hot displacer 12 is in its upper position. Below hot displacer 12 is a warm-hot chamber 24. Such warm- hot chamber 24 has very little fluid within when heat pump is in positions C or D.

Analogously, a cold displacer 16 delimits a warm-cold chamber 26 and cold chamber 28. When cold displacer 16 is in its upper position (positions A and D], there is almost no fluid in warm-cold chamber 26; and when cold displacer 16 is in its lower position (positions B and C], there is almost no fluid in cold chamber 28.

[0045] Hot chamber 22 is fluidly coupled to a hot heat exchanger 32. Exhaust gases enter at inlet 52 and leave at exit 53. Exhaust gases exchange heat with working fluid within hot heat exchanger 32. In one alternative, a solar heater is used to heat working fluid in place of hot heat exchanger 32. Cold chamber 28 is fluidly coupled to a cold heat exchanger 38. A cold liquid coolant loop (only partially shown in Figure 3] is provided to cold heat exchanger 38. A cold coolant is provided at inlet 58 and exits via outlet 59 of cold heat exchanger 38.

[0046] The working fluid within hot heat exchanger 32 is fluidly coupled with a hot regenerator 42. Hot regenerator 42 is fluidly coupled to a warm-hot heat exchanger 34. Warm-hot heat exchanger 34 is provided a warm-hot coolant through pipe 55 with the warm-hot coolant exiting at pipe 54.

[0047] The working fluid within cold heat exchanger 38 is fluidly coupled with a cold regenerator 46. Cold regenerator 46 is fluidly coupled to a warm-cold heat exchanger 36. Warm-cold heat exchanger 36 is provided a warm-cold coolant at pipe 57 and exits at outlet 56.

[0048] Warm-hot heat exchanger 34 is fluidly coupled to both warm-cold chamber 34 and a temperature barrier chamber 44. Analogously, warm-cold heat exchanger 36 is fluidly coupled to both warm-cold heat exchanger 36 and warm-cold chamber 26. As will be discussed below, there are several embodiments for the temperature barrier chamber envisioned. In one embodiment, the temperature barrier chamber is a warm regenerator. In other embodiments, the temperature barrier chamber provides much of the same function as a warm regenerator.

[0049] In a process that starts at position A and ends at position B, cold displacer 16 moves downward displacing working fluid out of cold chamber 28 into cold heat exchanger 38. Working fluid in cold heat exchanger 38 moves into cold regenerator 46. Working fluid in cold regenerator 46 is pushed into warm-cold heat exchanger 36.

Some of the working fluid in warm-cold heat exchanger moves into temperature barrier chamber 44 and most of it into warm-cold chamber 26.

[0050] In a process from position B to position C, the hot displacer moves downward, pushing fluid out of warm-hot chamber 24 into warm-hot heat exchanger 34 and into temperature barrier chamber 44. Working fluid in warm-hot exchanger 34 moves into hot regenerator 42. Working fluid in hot regenerator 42 moves into hot heat exchanger 32. Working fluid in hot heat exchanger 32 moves into hot chamber 22.

[0051] In a process from position C to position D, the working fluid is pushed out of warm-cold chamber 26. Working fluid moves into both temperature barrier chamber 44 and into warm-cold heat exchanger 36. Fluid from warm-cold heat exchanger 36 moves in cold regenerator 46, fluid from which moves into cold heat exchanger 38, and fluid from which moves into cold chamber 28.

[0052] In Figure 3, a rod 13 is shown that couples between hot displacer 12 and mechatronics section 20. Details of mechatronics section 20 are not shown in Figure 3. Referring back to Figure 2, it can be seen how the rod couples between the

mechatronics and the displacer. Analogously, a rod 17 couples cold displacer 16 with mechatronics section 20. Note that rod 17 is of a greater diameter than rod 13. Rod 17 impacts the volume that is contained within chamber 26 and rod 13 impacts the volume contained within chamber 24. In contrast, the outer chambers: hot chamber 22 and cold chamber 28, do not have a rod or other element that takes up some of the volume of the chamber. The effects of the volume of rods 13 and 17 are evident in a P-V diagram of Figure 4, which is discussed below. The rod diameters are selected to provide desirable forces on the displacers during the cycle to supplant at least a fraction of the electrical energy expended in the mechatronics section to drive the displacers.

[0053] Idealized thermodynamic cycles for the four chambers are shown on a P- V diagram in Figure 4. Essentially, the heat pump is the resultant of four cycles: hot chamber cycle 80, warm-hot chamber cycle 82, warm-cold chamber 84, and cold chamber 86. The volume in the cold and warm-cold chambers is related via the cold displacer. The reason that the volume in the cold chamber from point A to point B (cycle 86] is not inversely related to the volume in the warm-cold chamber from its point A to point B is due to rod 292 (shown in Figure 2] There is no rod that passes through cold chamber 286. Thus, volume within cold chamber 286 is related to position of the cold displacer and the cross-sectional area of the cylinder in which the cold displacer is reciprocating. The volume within the warm-cold chamber, however, is impacted by the rod that takes up volume in the center of the warm-cold chamber.

Thus, the ratio of the volume in the cold chamber at points A to B, VA:VB for cycle 86, is greater than the ratio of the volume in the warm-cold chamber, VB:VA for cycle 84.

[0054] In Figure 5, one embodiment of a temperature barrier chamber 300 has a chamber 302 that has a plurality of wire meshes inside chamber 302. Fluid enters and exits through openings 306, 308. In an alternative embodiment shown in Figure 6, a temperature barrier chamber 310 includes a plurality of narrow passages 316 that are inserted into orifices 314 in cylinder 312. To minimize heat transfer between passages 316 and cylinder 312 a thermally-insulating coating 320 is placed on outer surfaces of passages 316 and/or a thermally-insulating coating 318 on the interior surface of orifices 314, in some embodiments. In Figure 7, an alternative for a temperature barrier 330 includes a tube 332 with a free-floating piston 334 disposed therein. The piston shuttles between stops 326 at one end and stops 328 at the other end in response to pressure fluctuations that promote flow through temperature barrier 330. A thermally- insulated coating 340 is provided on the inner surface of tube 332.

[0055] Referring to Figure 3, when displacer 12 moves, the majority of the flow is between hot chamber 22 and warm-hot chamber 24. Analogously, when displacer 16 moves, the majority of the flow is between cold chamber 28 and warm-cold chamber 26. With either movement, there is a modest flow between warm-cold chamber 26 and warm-hot chamber 24 due to the fact that the pressure changes throughout the heat pump, as can be seen in Figure 4. The masses in the chambers adjust in response to the pressure changes. Temperature barrier chamber 44 that is located between warm-hot chamber 24 and warm-cold chamber 26 has a modest amount of flow therethrough, particularly compared to hot regenerator 42 in which the fluid in warm-hot chamber 24 pass through hot regenerator 42 when the heat pump undergoes a process from positions B to C or from D to A. Similarly, a lot of flow goes through cold regenerator 46 when the heat pump undergoes a process from position A to B or C to D. Because the flow through temperature barrier chamber 44 is small, it affords alternatives to the typical design of a regenerator that would be employed for regenerators 42 and 46, i.e., such as temperature barrier chambers 300, 310, and 330, as shown in Figures 5, 6, and 7, respectively.

[0056] Figure 5 shows temperature barrier chamber 300 to be very similar to regenerators 42 and 46 of Figure 3. Temperature barrier chamber 300 could alternatively be called a warm regenerator. Figures 6 and 7, as described above, are alternatives which also perform the function of preventing heat transfer between warm-hot chamber 24 and warm-cold chamber 26. By preventing such heat transfer, it is possible to maintain a temperature difference between the two chambers.

[0057] Figure 8 shows one configuration of heatpump 10 coupled to external heat exchangers 60 and 62. Pipe 54 that exits warm-hot heat exchanger 34 is an inlet to heat exchanger 60, which could be a hot water heater or in fluidic communication with a hot water heater. Fluid returns from heat exchanger 60 through pipe 55 to warm-hot heat exchanger 34 located within heatpump 10. Similarly, pipe 56 that exits warm-cold heat exchanger 36 is an inlet to heat exchanger 62. Fluid returns from heat exchanger 62 through pipe 57 to warm-cold heat exchanger 36. Heat exchanger 62 can be used for space heating. It could be a floor heating system, a water-based system using radiators, and a forced air system. Hot water heaters typically operate at higher temperature than space heating; thus, the hot water heater receives the higher temperature fluid from the warm-hot heat exchanger 36. Also shown in Figure 8 is an ambient heat exchanger 70 that is located in the environment, i.e., outside the home or building in which heat pump 10 is installed. Ambient heat exchanger 70 extracts energy from the ambient and providing that to heat pump 10 to improve its efficiency over conventional heating systems. Pumps furnished to cause liquids to circulate through the heat exchangers are not illustrated in Figures 8-10.

[0058] In Figure 9, heat exchanger 60 for hot water heating and heat exchanger 62 for space heating are receiving flow from pipe 54, i.e., the outlet from warm-hot heat exchanger 34. A valve 64 directs the flow to heat exchanger 60, heat exchanger 62, or some combination of heat exchangers 60 and 62, i.e., directing more or less flow depending on the demand for hot water and for space heating. Valve 64 can be a three- way valve, a two-way valve, and/or a variable valve. The outlet flow from heat exchangers 60 and 62 is directed to pipe 57 which is coupled to warm-cold heat exchanger 36. As shown in Figure 9, pipes 55 and 56 are coupled via a pipe 66 so that warm-cold heat exchanger 36 and warm-hot heat exchanger 34 are directly fluidly coupled. Such a heat pump configuration as shown in Figure 9 delivers high efficiency.

[0059] In Figure 10, as in Figure 9, warm warm-cold heat exchanger 36 and warm-hot heat exchanger 34 are directly fluidly coupled together by connecting pipes 55 and 56 via pipe 66. Fluid from warm-hot heat exchanger 34 is provided to a heat exchanger 68. Flow from warm-hot heat exchanger 34 is directed to valve 64 that can direct flow to either heat exchanger 60 that is providing space heating or to a heat exchanger 68, which is external to the building in which heat pump is located. Outlet pipe 59 of cold heat exchanger 38 is coupled to a valve 74 that selectively directs the flow to heat exchanger 70 and or a heat exchanger 72 used for space cooling. Figure 10 illustrates a configuration that has the option of heating and cooling modes of operation. In the heating mode, valve 64 directs flow to heat exchanger 60, which is for space heating; and valve 74 directs flow to heat exchanger 70, which is external to the building in which heat pump 10 is located. In the cooling mode, valve 64 directs from warm-hot heat exchanger 34 to heat exchanger 68, which is located external to the building. Heat exchanger 68 is rejecting heat to the environment in this mode of operation. In cooling, valve 74 directs flow to heat exchanger 72 that is located within the building to provide space cooling via any suitable method.

[0060] Figure 11 is yet one more alternative that may give higher COP than, for example, a system in which the flow out of warm-cold heat exchanger 36 leaves through pipe 57 to valve 65 in which the flow is directed to heat exchanger 60, heat exchanger 62, or a combination of the two heat exchangers. The flow returns to the warm-hot heat exchanger through pipe 54. Outlet pipe 55 from warm-hot heat exchanger 34 is coupled to inletpipe 56 to warm-cold heat exchanger 36 via a coupling pipe 66.

[0061] Figure 12 is a simplistic graphic showing heat pump 10 installed in a house or other building 74 with two heat exchangers 68 and 72 located in the environment external to house 74. Two other heat exchanger 60 and 70 are located external with respect to heat pump 10, but are within house 74. Pipes connecting heat pump to heat exchangers 60, 68, 70, and 72 are not shown in the interest of clarity. For more detail, refer to Figure 10. [0062] While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and

implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.