Heat pump apparatus

Abstract

A heat pump apparatus 10 comprises a first heat exchanger 100, a second heat exchanger 200, a compressor 300 and a turbine 400 (e.g. as a turbocharger) that each define a portion of a first fluid flow path. The first heat exchanger, second heat exchanger, compressor and turbine are mounted adjacent to one another such that a first region 102 of the first heat exchanger faces, and is adjacent to, a first region (202, figure 3) of the second heat exchanger. The compressor and turbine are located adjacent the first region of the first heat exchanger and a second region 204 of the second heat exchanger which extends in a direction away from the first region of the first heat exchanger. A first working fluid, such as air, is passed along the first fluid flow path and compressed by the compressor to heat it before exchanging heat with a second working fluid (e.g. water) in the second heat exchanger. The apparatus is compact in form, e.g. small enough to fit within a housing having dimensions equivalent to a domestic washing machine.

Description

The present disclosure relates to a heat pump apparatus. Background Air source heat pumps are commonly used for heating air and / or water, for example in buildings. Typically they comprise a number of units, at least one of which are provided outside of the building and others which are provided inside the building. Hence air source heat pumps which are able to deliver an adequate heat output are significantly larger than the equivalent gas or oil fuelled boiler and / or comprise more units which need to be installed. This results in heat pump installation in many properties being problematic as the heat pump units take up more space than is desirable and / or available. Additionally, to achieve the desired heat output the heat exchangers of conventional heat pumps are required to be large enough to achieve the desired heat transfer at stages of the working cycle. Pipework and ducting which define a working fluid flow path through the heat exchanger, needing to link heat exchangers, pumps and expanders, inherently occupy a large volume. A conventional heat pump apparatus can be made smaller to fit into a desired volume, but this will result in its heat output dramatically falling also, making the heat pump inadequate for the task for which it is provided. Hence a heat pump apparatus operable to deliver a desired heat output, and which can be provided in a compact unit, is highly desirable. Summary According to the present disclosure there is provided an apparatus as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows. Accordingly there may be provided a heat pump apparatus (10) which comprises a first heat exchanger unit (100), a second heat exchanger unit (200), a compressor module (300) and a turbine module (400) which each define a portion of a first working fluid flow path (900). The first heat exchanger unit (100), the second heat exchanger unit (200), the compressor module (300) and the turbine module (400) may be mounted adjacent to one another such that a first region (102) of the first heat exchanger unit (100) faces, and is adjacent to, a first region (202) of the second heat exchanger unit (200). The first heat exchanger unit (100), the second heat exchanger unit (200), the compressor module (300) and the turbine module (400) may be mounted adjacent to one another such that the compressor module (300) and the turbine module (400) are located adjacent to the first region (102) of the first heat exchanger unit (100) and adjacent to a second region (204) of the second heat exchanger unit (200). The second region (204) of the second heat exchanger unit (200) may extend in a direction away from the first region (102) of the first heat exchanger unit (100). The heat pump apparatus (10) may further comprise a flow inlet port (12) and a flow outlet port (14) which each define a portion of the working fluid flow path (900). The first heat exchanger unit (100) may comprise a first heat transfer path (110) and a second heat transfer path (112), the first heat exchanger unit first heat transfer path (110) being fluidly isolated from, and in heat transfer communication with, the first heat exchanger unit second heat transfer path (112). The second heat exchanger unit (200) may comprise a third heat transfer path (210) for heat transfer communication with a second working fluid (1200) contained within the second heat exchanger unit (200). The compressor module (300) may have a compressor module inlet (302) and a compressor module outlet (304). The turbine module (400) may have a turbine module inlet (402) and a turbine module outlet (404). The first working fluid flow path (900) may extend, in series, through: the flow inlet port (12), the first heat exchanger unit first heat transfer path (110), the compressor module inlet (302), the compressor module outlet (304), the second heat exchanger unit third heat transfer path (210), the first heat exchanger unit second heat transfer path (112), the turbine module inlet (402), the turbine module outlet (404) and the flow outlet port (14). The second heat exchanger unit (200) may comprise a fourth heat transfer path (212) for the second working fluid (1200), the second heat exchanger unit third heat transfer path (210) being fluidly isolated from, and in heat transfer communication with, the second heat exchanger unit fourth heat transfer path (212). The first heat exchanger unit (100) may comprise a first heat transfer path inlet (120) and a first heat transfer path outlet (122); a second heat transfer path inlet (124) and a second heat transfer path outlet (126). The first heat exchanger unit (100) may comprise a plurality of heat transfer plates (130), each of the heat transfer plates (130) being spaced apart from one another to define flow paths (132,134) therebetween. The heat transfer plates (130) may define flow paths (132) that define the first heat transfer path (110) between the first heat transfer path inlet (120) and the first heat transfer path outlet (122). The heat transfer plates (130) may define flow paths (134) that define the second heat transfer path (112) between the second heat transfer path inlet (124) and the second heat transfer path outlet (126). The first heat transfer flow paths (132) may be interdigitated with the second heat transfer flow paths (134). The first heat transfer flow paths (132) may be fluidly isolated from the second heat transfer flow paths (134). A first heat transfer path inlet duct (170) may extend between the first heat transfer path inlet (120) and inlets of each of the flow paths (132) of the first heat transfer path (110). A first heat transfer path outlet duct (172) may extend between the first heat transfer path outlet (122) and outlets of each of the flow paths (134) of the first heat transfer path (110). A second heat transfer path inlet duct (180) may extend between the second heat transfer path inlet (124) and inlets of each of the flow paths (134) of the second heat transfer path (112). A second heat transfer path outlet duct (182) may extend between the second heat transfer path outlet (126) and outlets of each of the flow paths (134) of the second heat transfer path (112). The first heat transfer path inlet duct (170), the first heat transfer path outlet duct (172), the second heat transfer path inlet duct (180) and the second heat transfer path outlet duct (182) may be defined by the same heat transfer plates (130). Each of the heat transfer plates (130) may comprise stainless steel, aluminium, aluminium alloy, titanium, titanium alloy, molybdenum, molybdenum alloy, nickel, nickel alloy, copper plated steel, copper and / or copper alloy. Each of the heat transfer plates (130) may be spaced apart from one another by at least 2mm but no more than 8mm. Each of the heat transfer plates (130) may be spaced apart from one another by at least 4mm but no more than 6mm. The first heat transfer path inlet (120), the first heat transfer path outlet (122), the second heat transfer path inlet (124) and the second heat transfer path outlet (126) may be located on the first region (102) of the first heat exchanger unit (100). The first heat transfer path inlet (120) and second heat transfer path outlet (126) may be located at a first end (150) of the first heat exchanger unit flow paths (132, 134). The first heat transfer path outlet (122) and second heat transfer path inlet (124) may be located at a second end (152) of the first heat exchanger unit flow paths (132, 134). The flow direction between the first heat transfer path inlet (120) and the first heat transfer path outlet (122) may be opposite to the flow direction between the second heat transfer path inlet (124) and the second heat transfer path outlet (126). The flow paths (132, 134) defined by the heat transfer plates (130) may first extend from their respective flow inlet (120, 124) in a first direction (D1, D1 ’) to a first turning point (160,160’), then extend in a second direction (D2, D2’) at an angle to the first direction (D1) to a second turning point (162, 162’), and then extend in a third direction (D3, D3’), wherein the third direction (D3, D3’) is opposite to the first direction (D1, D1 ’). The flow paths (132, 134) defined by the heat transfer plates (130) may extend in the third direction (D3, D3’) to a third turning point (164, 164’), then extend in the second direction (D2, D2’) to a fourth turning point (166, 166’) and then extend in the first direction (D1, D1’) to their respective flow outlets (122, 126). The flow paths (132, 134) defined by the heat transfer plates (130) may extend in the third direction (D3, D3’) to a third turning point (164, 164’), then extend in a fourth direction (D4, D4’) to a fourth turning point (166, 166’) and then extend in the first direction (D1, D1’) to their respective flow outlets (122, 126). The first heat exchanger unit flow paths (132) defined by the heat transfer plates (130) may extend in the third direction (D3) to a third turning point (164), then extend in the second direction (D2) to a fourth turning point (166) and then extend in the first direction (D1) to a fifth turning point (168, 168’), and then extend in a fourth direction (D4) to their respective flow outlets (122). The second heat exchanger unit flow paths (134) defined by the heat transfer plates (130) may extend in the third direction (D3’) to a third turning point (164’), then extend in a fourth direction (D4’) to a fourth turning point (166, 166’) and then extend in the third direction (D3’) to a fifth turning point (168, 168’), and then extend in the second direction (D2’) to their respective flow outlets (122, 126). The flow paths (132, 134) defined by the heat transfer plates (130) may extend in the third direction (D3, D3’) to a third turning point (164, 164’), then extend in a fourth direction (D4, D4’) to a fourth turning point (166, 166’) and then extend in the first direction (D1, D1 ’) to a fifth turning point (168, 168’), and then extend in the second direction (D2, D2’)to their respective flow outlets (122, 126). A flow guide (140) may be provided at one or more of the turning points (160, 160’; 162, 162’; 164, 164’; 166, 166’, 168, 168’). The flow guide (140) may be positioned to define a control flow path (142, 142’) between the flow guide (140) and the edge of the flow paths (132, 134) which define the smallest radius of the respective turning point (160, 160’; 162, 162’; 164, 164’; 166, 166’). The second heat exchanger unit third heat transfer path (210) may have an inlet (220) and an outlet (222). The second heat exchanger unit third heat transfer path inlet (220) and second heat exchanger unit third heat transfer path outlet (222) may extend between a plurality of spaced apart flow conduits (230). The second heat exchanger unit fourth heat transfer path (212) has an inlet (224) and an outlet (226) which may be in fluid communication with a heat sink (1100) such that the second working fluid (1200) passes through the fourth heat transfer path inlet (224), through the fourth heat transfer path (212), through the fourth heat transfer path outlet (226), into the heat sink (1100) and back to fourth heat transfer path the inlet (224). The second heat exchanger unit fourth heat transfer path inlet (224) and a fourth heat transfer path outlet (226) may be located so that flow between the fourth heat transfer path inlet (224) and a fourth heat transfer path outlet (226) goes between the spaced apart flow conduits (230). The second heat exchanger unit fourth heat transfer path inlet (224) and a fourth heat transfer path outlet (226) may be located so that flow between the second heat exchanger unit third heat transfer path inlet (220) and third heat transfer path outlet (222) and flow between the fourth heat transfer path inlet (224) and a fourth heat transfer path outlet (226) are in different directions. A fourth heat transfer path inlet (224) maybe provided proximate to the second heat exchanger unit third heat transfer path inlet (220). The fourth heat transfer path outlet (226) may be provided proximate to the third heat transfer path outlet (222). The fourth heat transfer path inlet (224) may be closer to the second heat exchanger unit third heat transfer path inlet (220) than it is to the second heat exchanger unit third heat transfer path outlet (222). The fourth heat transfer path outlet (226) may be closer to the second heat exchanger unit third heat transfer path outlet (222) than it is to the second heat exchanger unit third heat transfer path inlet (220). The heat sink (1100) may comprise a heat radiator, a heat radiator flow circuit, a hot water tank or a thermal energy storage unit containing phase change material. The second heat exchanger unit (200) may be configured as a thermal energy storage tank. The first working fluid (902) may be air. The second working fluid may comprise water, antifreeze and / or glycol. The heat pump apparatus (10) may further comprise a housing assembly (600) provided with a hollow polygonal prism section shape or a hollow cylindrical section shape which define the housing volume (500). The first heat exchanger unit (100), the second heat exchanger unit (200), the compressor module (300) and the turbine module (400) may be located within the housing volume (500). The housing volume (500) may be divided into a first sub-volume (502), a second sub-volume (504) and a third sub-volume (506). The first heat exchanger unit (100) may be located in the first sub-volume (502). The second heat exchanger unit (200) may be located in the second subvolume (504). The compressor module (300) and the turbine module (400) may be located the third sub-volume (506). Each of the first sub-volume (502), second sub-volume (504) and third sub-volume (506) may be shaped as polygonal prisms. Each of the first sub-volume (502), second sub-volume (504) and third sub-volume (506) may be shaped as segments of a cylinder. The first sub-volume (502) may provide / occupy at least 35% but no more than 70% of the housing volume (500). The second sub-volume (504) may provide / occupy at least 20% but no more than 40% of the housing volume (500). The third sub-volume (506) may provide / occupy the remainder of the housing volume (500). The first sub-volume (502) may be greater than the sum of the second sub-volume (504) and the third sub-volume (506). The second sub-volume (504) may be greater than the third sub-volume (506). The second sub-volume (504) and the third sub-volume (506) may be adjacent one another and extend from the first region (102) of the first heat exchanger unit (100). The compressor module (300) may comprise a compressor rotor (310) and the turbine module (400) may comprise a turbine rotor (410). The heat pump apparatus (10) may further comprise a motor unit (700). A rotatable shaft (800) may extend between the compressor rotor (310) and the turbine rotor (410), the compressor rotor (310) and the turbine rotor (410) being carried on, and rotatable with, the rotatable shaft (800). The motor unit (700) may be coupled to the rotatable shaft (800) and operable to drive the rotatable shaft (800). The rotatable shaft (800) and motor unit (700) may be located in the third sub-volume (506). The compressor module outlet (304) may be defined by a compressor volute (308) which defines the flow path between the compressor rotor (310) and compressor module outlet (304), the compressor module outlet (304) being coupled to the second heat exchanger unit third heat transfer path inlet (220). The turbine module inlet (402) may be defined by a turbine volute (406) which defines the flow path between the turbine rotor (410) and turbine module inlet (402), the turbine module inlet (402) being coupled to first heat transfer path outlet (126). The first heat exchanger unit first heat transfer path outlet (122) may be located in the first subvolume (502), and a compressor inlet duct (306) may extend from the first heat transfer path outlet (122) to the compressor inlet (302) in the third sub-volume (506). The first heat exchanger unit second heat transfer path inlet (124) may be located in the first subvolume (502). The second heat exchanger unit third heat transfer path outlet (222) may be located in the second sub-volume (504). A heat exchanger flow duct (206) may extend from the third heat transfer path outlet (222) to the second heat transfer path inlet (124). The turbine volute (406) may extend from the first heat transfer path outlet (126) in the first sub-volume (502) to the turbine module (400) in the third sub-volume (504). The motor unit (700) may be provided in the compressor inlet duct (306). The housing assembly (600) may be 75 to 85cm high, 59.5 to 60cm wide and 50 to 60cm deep. The housing assembly (600) may be 80cm high, 50cm wide and 45cm deep. The housing assembly (600) may be 45cm to 90cm high, 45cm to 65cm wide and 45 to 80cm deep. There may also be provided a facility defined at least in part by a wall (16) which defines a space in which a heat pump apparatus (10) according to the present disclosure is located, wherein the flow inlet port (12) and the flow outlet port (14) are provided in and / or extend through the wall (16). Hence there is provided a heat pump apparatus operable for heat output with a compact and unitary configuration. The features of the heat pump apparatus of the present disclosure (i.e. the components and relative positioning of the components) enable a compact and unitary configuration. The compact and unitary configuration results in a heat pump apparatus which is easier and quicker to install than examples of the related art. The configuration, efficiency and ease of installation enable a heat pump apparatus of the present disclosure to be provided which has a similar cost-through-life as a conventional gas fuelled boiler or oil fuelled boiler, thus making it an attractive alternative to conventional fossil fuel hating solutions. Brief Description of the Drawings Examples of the present disclosure will now be described with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic representation of a heat pump apparatus according to the present disclosure installed in an example structure; Figure 2 is a perspective view of part of a heat pump apparatus according to the present disclosure; Figure 3 illustrates a first side view of the arrangement shown in figure 2, with working fluid flow directions indicated; Figure 4 illustrates a second side view of the arrangement shown in figures 3, 4; Figure 5 illustrates an enlarged sectional view of part of the first heat exchanger of the heat pump apparatus according to the present disclosure; Figure 6 illustrates a side sectional view of the arrangement shown in figure 5; Figure 7 illustrates a side view of an alternative example of part of the first heat exchanger of the heat pump apparatus according to the present disclosure; Figure 8 illustrates a first example of the first heat exchanger which defines a first flow path configuration; Figure 9 illustrates a second example of the first heat exchanger which defines a second flow path configuration; Figure 10 illustrates a third example of the first heat exchanger which defines a third flow path configuration; Figure 11 illustrates a fourth example of the first heat exchanger which defines a fourth flow path configuration; Figure 12 illustrates an internal view of a flow interface between a compressor module and second heat exchanger unit according to the present disclosure; Figure 13 illustrates an example installation of the heat pump apparatus of the present disclosure; Figure 14 illustrates a perspective view of an example housing volume of the heat exchanger apparatus of the present disclosure; Figure 15 illustrates a plan view of the example housing volume shown in figure 14; Figure 16 illustrates a first example of an arrangement of a compressor rotor, motor and turbine rotor which form part of the heat exchanger apparatus of the present disclosure; and Figure 17 illustrates a second example of an arrangement of a compressor rotor, motor and turbine rotor which form part of the heat exchanger apparatus of the present disclosure. Detailed Description The present disclosure relates to a heat pump apparatus. The present disclosure also relates to a facility which comprises a heat pump apparatus. The heat pump apparatus may be an air source heat pump apparatus. Figure 1 shows a diagrammatic representation of a facility which comprises a heat pump apparatus according to the present disclosure. In the example shown in figure 1 the facility is a building (for example a house), but it may be provided as any building or structure, for example a vehicle, a building, or part of a vehicle or building. The heat pump apparatus may also be provided as a part of a substructure within a vehicle or building, for example a kitchen unit (as shown in figure 13). The structure may be defined at least in part by a wall 16 which defines a space in which a heat pump apparatus 10 is located. The relative positions of the components of the apparatus shown in figure 1 are purely diagrammatic, provided to illustrate how the different components are functionally linked, as will be described below. As illustrated in figure 1, the heat pump apparatus 10 of the present disclosure comprises a first heat exchanger unit 100, a second heat exchanger unit 200, a compressor module 300 configured to compress a first working fluid 902 and a turbine module 400 configured to expand the first working fluid 902. Each of the first heat exchanger unit 100, the second heat exchanger unit 200, the compressor module 300 the turbine module 400 define a portion of a first working fluid flow path 900 through which, in operation, the first working fluid 902 flow. Each of the first heat exchanger unit 100, the second heat exchanger unit 200, the compressor module 300 and the turbine module 400 may each be provided with a cover or housing. The first working fluid 902 may be air. Figure 2 is a perspective view of part of a heat pump apparatus according to the present disclosure. The first heat exchanger unit 100, the second heat exchanger unit 200, the compressor module 300 and the turbine module 400 are mounted adjacent to one another such that a first region (or first side) 102 of the first heat exchanger unit 100 faces, and is adjacent to, a first region (or first side) 202 of the second heat exchanger unit 200. The compressor module 300 and the turbine module 400 are located adjacent the first region 102 of the first heat exchanger unit 100 and a second region (or first side) 204 of the second heat exchanger unit 200. The second region 204 extends in a direction away from the first region 102 of the first heat exchanger unit 100. In the example shown the first region 102 of the first heat exchanger unit 100 is flat, the first region 204 of the second heat exchanger unit 200 is flat, and the second region 204 extends in a direction perpendicular to the first region 102. In the example shown in figure 2 the compressor module 300 and the turbine module 400 are located in a volume defined on two sides by the first region 102 of the first heat exchanger unit 100 and the first region 204 of the second heat exchanger unit 200. As illustrated in figures 16,17, the compressor module 300 may comprise a compressor rotor 310, the turbine module 400 may comprise a turbine rotor 410 and / or the heat pump apparatus 10 may further comprise a motor unit 700. Figures 16,17 illustrate different possible arrangement of these components. A rotatable shaft 800 may extend between the compressor rotor 310 and the turbine rotor 410. The compressor rotor 310 and the turbine rotor 410 may be carried on, and rotatable with, the rotatable shaft 800. The motor unit 700 may be coupled to the rotatable shaft 800. The motor unit 700 may be operable to drive the rotatable shaft 800, and hence rotate / drive the compressor rotor 310 and the turbine rotor 410. As illustrated in the figures, the rotatable shaft 800 may be mounted vertically with the compressor module 300 mounted above the turbine module 400. There may also be provided a control system 1000 to control the operation of the motor 700. As illustrated in figure 16, the motor unit 700 may be provided between the compressor rotor 310 and the turbine rotor 410 along the rotatable shaft 800. As illustrated in figure 17, the compressor rotor 310 may be provided between the motor unit 700 and the turbine rotor 410 rotatable shaft 800. A housing or housing assembly 600 may be provided around the assembly of the first heat exchanger unit 100, the second heat exchanger unit 200, the compressor module 300 and the turbine module 400. The housing 600 is not shown in figures 2, 3, 4 in order that the arrangement of the first heat exchanger unit 100, the second heat exchanger unit 200, the compressor module 300 and the turbine module 400 may be illustrated. A diagrammatic representation of a housing assembly 600 is illustrated in figures 14, 15. The housing assembly 600 may be provided as a hollow polygonal (e.g. rectangular) prism section shape which defines the housing volume 500. Hence the housing assembly 600 may have height (H), width (W) and depth (D) as illustrated in figures 14, 15. In one example, the housing assembly 600 may be 75 to 85cm high, 59.5 to 60cm wide and 50 to 60cm deep. In an alternative example, the housing assembly 600 may be 80cm high, 50cm wide and 45cm deep. In a further example, the housing assembly 600 may be 45cm to 90cm high, 45cm to 65cm wide and 45 to 80cm deep. In another example the housing assembly may be 84-85cm high, 59.5-60cm wide and 50-60cm deep. In an alternative example (not shown) the housing assembly 600 may be provided as a hollow cylindrical section shape which defines the housing volume 500. The first heat exchanger unit 100, the second heat exchanger unit 200, the compressor module 300 and the turbine module 400 are located within the housing volume 500. Hence the first heat exchanger unit 100, the second heat exchanger unit 200, the compressor module 300 and the turbine module 400 are located within the housing or housing assembly 600. As illustrated in figures 14, 15, the housing volume 500 may be divided into a first sub-volume 502, a second sub-volume 504 and a third sub-volume 506. Each of the first sub-volume 502, the second sub-volume 504 and the third sub-volume 506 may extend along at least part of the height of the housing volume 500. The first heat exchanger unit 100 may be located in the first sub-volume 502. The second heat exchanger unit 200 may be located in the second sub-volume 504. The compressor module 300 and the turbine module 400 may be located the third sub-volume 506. Each of the first sub-volume 502, second sub-volume 504 and third sub-volume 506 may be shaped as polygonal prisms. In an alternative example, not shown, each of the first sub-volume 502, second sub-volume 504 and third sub-volume 506 may be shaped as segments of a cylinder. The first sub-volume 502 may provide at least 35% but no more than 70% of the housing volume 500. The second sub-volume 504 may occupy at least 20% but no more than 40% of the housing volume 500. The third sub-volume 506 may occupy the remainder of the housing volume 500. The first sub-volume 502 may be greater than the sum of the second sub-volume 504 and the third sub-volume 506. The second sub-volume 504 may be greater than the third sub-volume 506. The second sub-volume 504 and the third sub-volume 506 may be adjacent one another and extend from the first region 102 of the first heat exchanger unit 100. As illustrated in figure 1, the heat pump apparatus may further comprise a flow inlet port 12 and a flow outlet port 14 which each define a portion of the working fluid flow path 900. The first heat exchanger unit 100 comprises (i.e. defines) a first heat transfer path 110 and a second heat transfer path 112. The first heat exchanger unit first heat transfer path 110 may be fluidly isolated from, and in heat transfer communication with, the first heat exchanger unit second heat transfer path 112. The second heat exchanger unit 200 comprises (i.e. defines) a third heat transfer path 210 for heat transfer communication with a second working fluid 1200 contained withing the second heat exchanger unit 200. The second heat exchanger unit 200 may comprise a tank (for example defined by its housing) which retains the second working fluid 1200. The second working fluid 1200 may comprise water, antifreeze and / or glycol. The compressor module 300 may have a compressor module inlet 302 and a compressor module outlet 304. The turbine module 400 may have a turbine module inlet 402 and a turbine module outlet 404. The first working fluid flow path 900 may extend, in series, through the flow inlet port 12, the first heat exchanger unit first heat transfer path 110, the compressor module inlet 302, the compressor module outlet 304, the second heat exchanger unit third heat transfer path 210, the first heat exchanger unit second heat transfer path 112, the turbine module inlet 402, the turbine module outlet 404 and the flow outlet port 14. The flow inlet port 12 and the flow outlet port 14 may be provided in fluid communication with a source of the first working fluid 902. The source may be the environment around the heat pump apparatus. In an example in which the heat pump apparatus 10 is located in a structure comprising a wall 16 or other structural element, the flow inlet port 12 and the flow outlet port 14 may be provided in and / or extend through the wall 16 and / or other structural element. Hence the flow inlet port 12 and the flow outlet port 14 may provide a flow route between the space outside of the structure and the heat pump apparatus. The second heat exchanger unit 200 may comprise (i.e. define) a fourth heat transfer path 212 for the second working fluid 1200. The second heat exchanger unit third heat transfer path 210 may be fluidly isolated from, and in heat transfer communication with, the second heat exchanger unit fourth heat transfer path 212. As illustrated in figure 1, the first heat exchanger unit 100 may comprise a first heat transfer path inlet 120 and a first heat transfer path outlet 122, as well as a second heat transfer path inlet 124 and a second heat transfer path outlet 126. Figures 8 to 11 illustrate a sectional view through the first heat exchanger unit 100, as well as example locations of the first heat transfer path inlet 120, first heat transfer path outlet 122, a second heat transfer path inlet 124 and a second heat transfer path outlet 126. As illustrated in figures 5 to 7, the first heat exchanger unit 100 may comprise a plurality of heat transfer plates 130, each of the heat transfer plates 130 being spaced apart from one another to define flow paths 132,134 therebetween. That is to say, the heat transfer plates 130 are provided side by side (i.e. layers) and spaced apart from one another to define flow paths 132, 134 therebetween. Hence the same plates 130 define the flow paths 132 of the first heat transfer path 110 and the flow paths 134 of the second heat transfer path 112. The heat transfer plates 130 define flow paths 132 that define (i.e. provide) the first heat transfer path 110 between the first heat transfer path inlet 120 and the first heat transfer path outlet 122. The heat transfer plates 130 define flow paths 134 that define (i.e. provide) the second heat transfer path 112 between the second heat transfer path inlet 124 and the second heat transfer path outlet 126. The first heat transfer flow paths 132 are interdigitated with the second heat transfer flow paths 134. The first heat transfer flow paths 132 being fluidly isolated from the second heat transfer flow paths 134. A first heat transfer path inlet duct 170 extends between the first heat transfer path inlet 120 and inlets of each of the flow paths 132 of the first heat transfer path 110. A first heat transfer path outlet duct 172 extends between the first heat transfer path outlet 122 and outlets of each of the flow paths 134 of the first heat transfer path 110. As illustrated in figures 3, 5 to 8, a second heat transfer path inlet duct 180 extends between the second heat transfer path inlet 124 and inlets of each of the flow paths 134 of the second heat transfer path 112. As illustrated in figure4, a second heat transfer path outlet duct 182 extends between the second heat transfer path outlet 126 and outlets of each of the flow paths 134 of the second heat transfer path 112. Although the first heat transfer path duct 170 and the first heat transfer outlet duct 172 are not illustrated in the figures, they may take the same form as the second heat transfer path inlet duct 180 and the second heat transfer path outlet duct 182. The ducts 170, 172, 180, 182 may have a constant flow area along their length (as illustrated in figures 5, 6). Alternatively, as shown in figure 7, the ducts 170, 172, 180, 182 may reduce in flow area along their length from the their inlet. Such an arrangement may provide a more even flow delivery to the respective flow passages 132, 134. As illustrated in figures 3 to 7, the first heat transfer path inlet duct 170, the first heat transfer path outlet duct 172, the second heat transfer path inlet duct 180 and the second heat transfer path outlet duct 182 are defined by the same heat transfer plates 130. Apertures are provided in the heat transfer plates 130 to form the first heat transfer path inlet duct 170, the first heat transfer path outlet duct 172, the second heat transfer path inlet duct 180 and the second heat transfer path outlet duct 182. A first set of aligned apertures are provided in the heat transfer plates 130 to form the first heat transfer path inlet duct 170. A second set of aligned apertures are provided in the heat transfer plates 130 to form the first heat transfer path outlet duct 172. A third set of aligned apertures are provided in the heat transfer plates 130 to form the second heat transfer path inlet duct 180. A fourth set of aligned apertures are provided in the heat transfer plates 130 to form the second heat transfer path outlet duct 182. As illustrated in figures 5 to 7, gaskets or seals 138 may be provided between alternate pairs of heat transfer plates 130 to isolate the flow paths 132 of the first heat transfer path 110 from the flow paths 134 of the second heat transfer path 112. Hence gaskets / seals 138 are provided between a different alternate pairs of heat transfer plates 130 in the first heat transfer path 110 and second heat transfer path 112. The gaskets / seals 138 may be provided around the aligned apertures which define the first heat transfer path inlet duct 170, the first heat transfer path outlet duct 172, the second heat transfer path inlet duct 180 and the second heat transfer path outlet duct 182. Each of the heat transfer plates 130 may comprise stainless steel, aluminium, aluminium alloy, titanium, titanium alloy, molybdenum, molybdenum alloy, nickel, nickel alloy, copper plated steel, copper and / or copper alloy. Each of the heat transfer plates 130 may be spaced apart from one another by at least 2mm but no more than 8mm. Each of the heat transfer plates 130 may be spaced apart from one another by at least 4mm but no more than 6mm. The first heat transfer path inlet 120, the first heat transfer path outlet 122, the second heat transfer path inlet 124 and the second heat transfer path outlet 126 may located on the first region (e.g. first side) 102 of the first heat exchanger unit 100. The first heat transfer path inlet 120 and second heat transfer path outlet 126 may be located at a first end 150 of the first heat exchanger unit flow paths 132, 134. The first heat transfer path outlet 122 and second heat transfer path inlet 124 may be located at a second end 152 of the first heat exchanger unit flow paths 132, 134. Consequently, the flow direction between the first heat transfer path inlet 120 and the first heat transfer path outlet 122 along the flow paths 132 of the first heat transfer path 110 is opposite to the flow direction between the second heat transfer path inlet 124 and the second heat transfer path outlet 126 along the flow paths 134 of the second heat transfer path 112. The contra-flow paths are illustrated in figures 5 to 11, where the solid arrows indicate the flow direction along the flow paths 132 of the first heat transfer path 110 and the arrows shown in broken lines indicate the flow direction along the flow paths 134 of the second heat transfer path 112. Flow from the compressor may be delivered such that the first working fluid 902 passes along the flow paths 132, 134 at a speed of at least 4 m / s but no more than 9 m / s. Flow from the compressor may be delivered such that the first working fluid 902 passes along the flow paths 132, 134 at a speed of at least 4 m / s but no more than 20 m / s. As illustrated in the examples of figures 8 to 11, the flow path between the ends 150, 152 of the first heat exchanger unit 100 may be convoluted, spiralled, boustrophedonic and / or serpentine. The directions of flow through the flow paths 132 of the first heat transfer path 110 and flow paths 134 of the second heat transfer path 112 are explained below with reference to figures 8 to 11. Features of the flow path 134 are indicated with an apostrophe (‘), for example directions D1 ’, D2’, D3’ and flow turning points (corners) 160’, 162’, 164’ to distinguish them from features of the flow path 132 which are not annotated with an apostrophe (‘). Common to all of the examples shown, the flow paths 132, 134 defined by the heat transfer plates 130 may first extend from their respective flow inlet 120, 124 in a first direction D1, D1 ’ to a first turning point 160, 160’, then extend in a second direction D2, D2’ at an angle to the first direction D1 to a second turning point 162, 162’, and then extend in a third direction D3, D3’, wherein the third direction D3, D3’ is opposite to the first direction D1, D1 As illustrated in the example of figure 8, the flow paths 132,134 defined by the heat transfer plates 130 extend in the third direction D3, D3’ to a third turning point 164, 164’, then extend in the second direction D2, D2’ at an angle to the third direction D3, D3’ to a fourth turning point 166, 166’ and then extend in the first direction D1, D1’ to their respective flow outlets 122, 126. As illustrated in the example of figure 9, the flow paths 132,134 defined by the heat transfer plates 130 may extend in the third direction D3, D3’ to a third turning point 164, 164’, then extend in a fourth direction D4, D4’ at an angle to the third direction D3, D3’ to a fourth turning point 166,166’ and then extend in the first direction D1, D1’ to their respective flow outlets 122, 126. As illustrated in the example of figure 10, the first heat exchanger unit flow paths 132 defined by the heat transfer plates 130 may extend in the third direction D3 to a third turning point 164, then extend in the second direction D2 to a fourth turning point 166 and then extend in the first direction D1 to a fifth turning point 168, 168’, and then extends in a fourth direction D4 at an angle to the third direction D3 to their respective flow outlets 122. The second heat exchanger unit flow paths 134 defined by the heat transfer plates 130 extend in the third direction D3’ to a third turning point 164’, then extend in a fourth direction D4’ at an angle to the third direction D3’ to a fourth turning point 166,166’ and then extend in the third direction D3’ to a fifth turning point 168,168’, and then extends in the second direction D2’ to their respective flow outlets 122, 126. As illustrated in the example of figure 11, the flow paths 132, 134 defined by the heat transfer plates 130 extend in the third direction D3, D3’ to a third turning point 164, 164’, then extend in a fourth direction D4, D4’ at an angle to the third direction D3, D3’ to a fourth turning point 166,166’ and then extends in the first direction D1, D1’ to a fifth turning point 168, 168’, and then extends in the second direction D2, D2’to their respective flow outlets 122,126. As illustrated in the example of figure 9, but which may be present in any of the examples, a flow guide 140 may be provided at one or more of the turning points 160, 160’; 162, 162’; 164, 164’; 166, 166’, 168, 168’, the flow guide being positioned to define a control flow path 142, 142’ between the flow guide 140 and the edge of the flow paths 132, 134 which define the smallest (e.g. inner) radius of the respective turning point 160, 160’; 162, 162’; 164, 164’; 166, 166’. Put another way, a flow guide 140 may be provided at one or more of the turning points 160, 160’; 162, 162’; 164, 164’; 166, 166’, 168, 168’, positioned to define a control flow path 142, 142’ between the flow guide 140 and inner corner of the flow paths 132, 134. The flow guides 140 may be simple inserts which are tack welded or glued onto the plates or may be pressed into the shape of the heat transfer plates 130. The flow guides 140 are used to promote even flow across the surface area of the heat transfer plates 130. That is to say, the flow guides 140 are configured to redirect flow towards the corners (i.e. turning points 160, 160’; 162, 162’; 164, 164’; 166, 166’, 168, 168’) to maximise use of the heat exchanger surface to increase efficiency. As illustrated in figures 1, 3, the second heat exchanger unit third heat transfer path 210 may have an inlet 220 and an outlet 222. As illustrated in figure 3, the second heat exchanger unit third heat transfer path inlet 220 and second heat exchanger unit third heat transfer path outlet 222 extend between a plurality of spaced apart flow conduits 230. Hence the flow conduits 230 define part of the working fluid flow path 900. The flow conduit to 30 may be provided as tubes. The flow conduits 230 may comprise metal or plastic. The flow conduits 230 may have a diameter of at least 5mm but no more than 15mm. As illustrated in figures 1,3, the second heat exchanger unit fourth heat transfer path 212 has an inlet 224 and an outlet 226. As illustrated in figure 1, the inlet 224 and an outlet 226 may be provided in fluid communication with a heat sink 1100 such that the second working fluid 1200 passes through the fourth heat transfer path inlet 224, through the fourth heat transfer path 212, through the fourth heat transfer path outlet 226, into the heat sink 1100 and back to the fourth heat transfer path the inlet 224. As illustrated in figure 3, the second heat exchanger unit fourth heat transfer path inlet 224 and a fourth heat transfer path outlet 226 may be located so that flow between the fourth heat transfer path inlet 224 and a fourth heat transfer path outlet 226 goes between the spaced apart flow conduits 230. As illustrated in figure 3, the second heat exchanger unit fourth heat transfer path 212 may in part be defined by a flow guide (or baffle) 260 provided in the housing / tank of the second heat exchanger unit 200 which in part defines the second heat exchanger unit fourth heat transfer path 212. The second heat exchanger unit fourth heat transfer path inlet 224 and a fourth heat transfer path outlet 226 may be located flow between the second heat exchanger unit third heat transfer path inlet 220 and third heat transfer path outlet 222 and flow between the fourth heat transfer path inlet 224 and a fourth heat transfer path outlet 226 are in different (for example, opposite) directions. As illustrated in figure 12, which shows a cut away sectional view of the heat exchanger apparatus, the fourth heat transfer path inlet 224 may be provided proximate to the second heat exchanger unit third heat transfer path inlet 220, and the fourth heat transfer path outlet 226 may be provided proximate to the third heat transfer path outlet 222. In the arrangement shown, the fourth heat transfer path inlet 224 is closer to the second heat exchanger unit third heat transfer path inlet 220 than it is to the second heat exchanger unit third heat transfer path outlet 222. Additionally, in this arrangement, the fourth heat transfer path outlet 226 is closer to the second heat exchanger unit third heat transfer path outlet 222 than it is to the second heat exchanger unit third heat transfer path inlet 220. This enables the maximum amount of time in the second heat exchanger for heat transfer between the second heat exchanger unit third heat transfer path 210 and the second heat exchanger unit fourth heat transfer path 212. The heat sink 1100 may comprise a heat radiator, a heat radiator flow circuit, a hot water tank or a thermal energy storage unit containing phase change material. The second heat exchanger unit 200 may be configured as a thermal energy storage tank. The thermal energy tank may comprise thermal energy storage material comprising hydrated salts, organic phase change materials e.g. paraffin wax type ~30-40C. As illustrated in figures 2, 4 the compressor module outlet 304 is defined by a compressor volute 308 which defines the flow path between the compressor rotor 310 and compressor module outlet 304. The compressor module outlet 304 (and hence the compressor volute 308) may be coupled to the second heat exchanger unit third heat transfer path inlet 220. That is to say, the compressor module outlet 304 (and hence the compressor volute 308) may be coupled directly to the second heat exchanger unit third heat transfer path inlet 220. That is to say, there is no intermediate duct or pipework provided between the compressor volute 308 and the second heat exchanger unit 200. A gasket or seal or the like may be provided between the compressor module outlet 304 (and hence the compressor volute 308) and the second heat exchanger unit third heat transfer path inlet 220, however this would still be considered to be a direct coupling. As illustrated in figures 2, 4, the turbine module inlet 402 may be defined by a turbine volute 406 which defines the flow path between the turbine rotor 410 and turbine module inlet 402. The turbine module inlet 402 (and hence the turbine volute 406) is coupled to first heat transfer path outlet 126. That is to say, the turbine module inlet 402 (and hence the turbine volute 406) may be coupled directly to first heat transfer path outlet 126. That is to say, there is no intermediate duct between the turbine volute 406 and the first heat exchanger unit 100. A gasket or seal or the like may be provided between the turbine module inlet 402 (and hence the turbine volute 406) and the first heat transfer path outlet 126, however this would still be considered to be a direct coupling. The direct connection between the compressor volute 308 and the second heat exchanger unit 200 and the direct connection between the turbine volute 406 and the first heat exchanger unit 100 (and hence avoidance of additional duct and pipe work) enables a compact assembly, meaning that the housing volume 500 may be smaller than for heat pump apparatus with equivalent heat outputs of the related art. As illustrated in figures 2, 3, 4, the first heat exchanger unit first heat transfer path outlet 122 may be located in the first sub-volume 502, and a compressor inlet duct 306 extends from the first heat transfer path outlet 122 to the compressor inlet 302 in the third sub-volume 506. The first heat exchanger unit second heat transfer path inlet 124 may be located in the first sub-volume 502. The second heat exchanger unit third heat transfer path outlet 222 may be located in the second sub-volume 504. A heat exchanger flow duct 206 may extend from the third heat transfer path outlet 222 to the second heat transfer path inlet 124. The turbine volute 406 may extend from the first heat transfer path outlet 126 in the first sub-volume 502 to the turbine module 400 in the third sub-volume 504. The rotatable shaft 800 and motor unit 700 may be located in the third subvolume 506. The motor unit 700 may be provided in the compressor inlet duct 306 such that the motor unit is directly above the compressor module (for example as shown in figure 17). This may be advantageous as the motor unit 700 would be cooled by air being delivered to the compressor 300, and would add heat from motor unit 700 to air entering the compressor module 300. By virtue of the structure of the first heat exchanger, second heat exchanger, their relative positioning and the flow couplings between the first heat exchanger, second heat exchanger, compressor and / or turbine, a heat pump apparatus according to the present disclosure may be provided with a compact and unitary configuration (e.g. within a single housing). The compact and unitary configuration results in a heat pump apparatus which is easier and quicker to install than examples of the related art. For example, a heat pump apparatus according to the present disclosure may be provided in a housing volume having size and dimensions equivalent to a domestic washing machine, boiler, dishwasher or fridge (for example 84-85cm high, 59.5-60cm wide and 50-60cm deep). Such an arrangement may therefore be provided with a housing having size and dimensions equivalent to a domestic washing machine, boiler, dishwasher or fridge. Put another way, the heat pump apparatus according to the present disclosure may be provided as a compact and unitary (e.g. single) unit. It may thus be conveniently installed and located where conventional heat pump apparatus, gas fuelled boilers and / or oil fuelled boilers cannot (for example, in a kitchen unit assembly 1300, as illustrated in figure 13). Since the heat pump apparatus of the present disclosure may be provided as a unitary and compact unit, and operable within a building without the need for any units external to the building it is quick, easy and inexpensive to install. Additionally, to operate, all the heat pump apparatus needs to operate is an electricity supply, and does not require any gas or oil supply, nor exhaust ducts, as are required with gas and oil fuelled boilers. This enables the installation cost of the heat pump apparatus of the present disclosure to be competitive with gas and oil boilers on through life costs, thus making it an attractive alternative to conventional fossil fuel hating solutions. The multi-layered heat exchanger flow paths 132, 134 of the first heat exchanger of the present disclosure provide highly efficient heat transfer between different stages of the first working fluid flow path 900. The defined paths increase the length of heat transfer flow paths possible in a compact space, which enables more effective heat transfer process. Additionally the flow guides 140 aid the control of flow around the flow paths of the first heat exchanger, ensuring as much of the heat flow path as possible is used for heat transfer. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract 5 and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and 10 drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention 15 extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1 A heat pump apparatus (10) which comprises a first heat exchanger unit (100), a second heat exchanger unit (200), a compressor module (300) and a turbine module (400) which each define a portion of a first working fluid flow path (900); andthe first heat exchanger unit (100), the second heat exchanger unit (200), the compressor module (300) and the turbine module (400) are mounted adjacent to one another such that:a first region (102) of the first heat exchanger unit (100) faces, and is adjacent to, a first region (202) of the second heat exchanger unit (200); andthe compressor module (300) and the turbine module (400) are located adjacent to the first region (102) of the first heat exchanger unit (100) and adjacent to a second region (204) of the second heat exchanger unit (200), wherein the second region (204) of the second heat exchanger unit (200) extends in a direction away from the first region (102) of the first heat exchanger unit (100);the first heat exchanger unit (100) comprises a first heat transfer path outlet (122); a second heat transfer path inlet (124) and a second heat transfer path outlet (126);the first heat transfer path outlet (122), the second heat transfer path inlet (124) and the second heat transfer path outlet (126) are located on the first region (102) of the first heat exchanger unit (100).2 A heat pump apparatus (10) as claimed in claim 1 which further comprises a flow inlet port (12) and a flow outlet port (14) which each define a portion of the working fluid flow path (900); andthe first heat exchanger unit (100) comprises a first heat transfer path (110) and a second heat transfer path (112), the first heat exchanger unit first heat transfer path (110) being fluidly isolated from, and in heat transfer communication with, the first heat exchanger unit second heat transfer path (112);the second heat exchanger unit (200) comprises a third heat transfer path (210) for heat transfer communication with a second working fluid (1200) contained within the second heat exchanger unit (200);the compressor module (300) having a compressor module inlet (302) and a compressor module outlet (304);the turbine module (400) having a turbine module inlet (402) and a turbine module outlet (404);the first working fluid flow path (900) extending, in series, through: the flow inlet port (12), the first heat exchanger unit first heat transfer path (110), the compressor module inlet (302), the compressor module outlet (304), the second heat exchanger unit third heat transfer path (210), the first heat exchanger unit second heat transfer path (112), the turbine module inlet (402), the turbine module outlet (404) and the flow outlet port (14).3 A heat pump apparatus (10) as claimed in claim 2 wherein:the second heat exchanger unit (200) comprises a fourth heat transfer path (212) for the second working fluid (1200), the second heat exchanger unit third heat transfer path (210) being fluidly isolated from, and in heat transfer communication with, the second heat exchanger unit fourth heat transfer path (212).4 A heat pump apparatus (10) as claimed in any one of claims 1,2,3 wherein:the first heat exchanger unit (100) comprises a first heat transfer path inlet (120);a plurality of heat transfer plates (130), each of the heat transfer plates (130) being spaced apart from one another to define flow paths (132, 134) therebetween;the heat transfer plates (130) defining flow paths (132) that define the first heat transfer path (110) between the first heat transfer path inlet (120) and the first heat transfer path outlet (122);the heat transfer plates (130) defining flow paths (134) that define the second heat transfer path (112) between the second heat transfer path inlet (124) and the second heat transfer path outlet (126);the first heat transfer flow paths (132) being interdigitated with the second heat transfer flow paths (134); andthe first heat transfer flow paths (132) being fluidly isolated from the second heat transfer flow paths (134).5 A heat pump apparatus (10) as claimed in claim 4 wherein:a first heat transfer path inlet duct (170) extends between the first heat transfer path inlet (120) and inlets of each of the flow paths (132) of the first heat transfer path (110);a first heat transfer path outlet duct (172) extends between the first heat transfer path outlet (122) and outlets of each of the flow paths (134) of the first heat transfer path (110);a second heat transfer path inlet duct (180) extends between the second heat transfer path inlet (124) and inlets of each of the flow paths (134) of the second heat transfer path (112); anda second heat transfer path outlet duct (182) extends between the second heat transfer path outlet (126) and outlets of each of the flow paths (134) of the second heat transfer path (112).6 A heat pump apparatus (10) as claimed in claim 5 wherein the first heat transfer path inlet duct (170), the first heat transfer path outlet duct (172), the second heat transfer path inlet duct (180) and the second heat transfer path outlet duct (182) are defined by the same heat transfer plates (130).7 A heat pump apparatus (10) as claimed in any one of claims 3 to 6 wherein each of the heat transfer plates (130) comprise stainless steel, aluminium, aluminium alloy, titanium, titanium alloy, molybdenum, molybdenum alloy, nickel, nickel alloy, copper plated steel, copper and / or copper alloy, and are spaced apart from one another by:at least 2mm but no more than 8mm; orat least 4mm but no more than 6mm.8 A heat pump apparatus (10) as claimed in any one of claims 1 to 7 wherein:the first heat transfer path inlet (120) is located on the first region (102) of the first heat exchanger unit (100);the first heat transfer path inlet (120) and second heat transfer path outlet (126) are located at a first end (150) of the first heat exchanger unit flow paths (132, 134); andthe first heat transfer path outlet (122) and second heat transfer path inlet (124) are located at a second end (152) of the first heat exchanger unit flow paths (132, 134);such that the flow direction between the first heat transfer path inlet (120) and the first heat transfer path outlet (122) is opposite to the flow direction between the second heat transfer path inlet (124) and the second heat transfer path outlet (126).9 A heat pump apparatus (10) as claimed in claim 4 when dependent on claim 3 wherein:the flow paths (132, 134) defined by the heat transfer plates (130) first extend from their respective flow inlet (120, 124) in a first direction (D1, D1’) to a first turning point (160,160’), then extend in a second direction (D2, D2’) at an angle to the first direction (D1) to a second turning point (162, 162’), and then extend in a third direction (D3, D3’), wherein the third direction (D3, D3’) is opposite to the first direction (D1, D1 ’).10 A heat pump apparatus (10) as claimed in claim 9 wherein:the flow paths (132, 134) defined by the heat transfer plates (130) extend in the third direction (D3, D3’) to a third turning point (164, 164’), then extend in the second direction (D2, D2’) to a fourth turning point (166, 166’) and then extend in the first direction (D1, D1’) to their respective flow outlets (122, 126).11 A heat pump apparatus (10) as claimed in claim 9 wherein:the flow paths (132, 134) defined by the heat transfer plates (130) extend in the third direction (D3, D3’) to a third turning point (164, 164’), then extend in a fourth direction (D4, D4’) to a fourth turning point (166, 166’) and then extend in the first direction (D1, D1’) to their respective flow outlets (122, 126).12 A heat pump apparatus (10) as claimed in claim 9 wherein:the first heat exchanger unit flow paths (132) defined by the heat transfer plates (130) extend in the third direction (D3) to a third turning point (164), then extend in the second direction (D2) to a fourth turning point (166) and then extend in the first direction (D1) to a fifth turning point (168, 168’), and then extend in a fourth direction (D4) to their respective flow outlets (122); andthe second heat exchanger unit flow paths (134) defined by the heat transfer plates (130) extend in the third direction (D3’) to a third turning point (164’), then extend in a fourth direction (D4’) to a fourth turning point (166, 166’) and then extend in the third direction (D3’) to a fifth turning point (168, 168’), and then extend in the second direction (D2’) to their respective flow outlets (122, 126).13 A heat pump apparatus (10) as claimed in claim 9 wherein:the flow paths (132, 134) defined by the heat transfer plates (130) extend in the third direction (D3, D3’) to a third turning point (164, 164’), then extend in a fourth direction (D4, D4’) to a fourth turning point (166, 166’) and then extend in the first direction (D1, D1’) to a fifth turning point (168, 168’), and then extend in the second direction (D2, D2’) to their respective flow outlets (122, 126).14 A heat pump apparatus (10) as claimed in any one of claims 9 to 13 wherein a flow guide (140) is provided at one or more of the turning points (160, 160’; 162, 162’; 164, 164’; 166, 166’, 168, 168’), the flow guide being positioned to define a control flow path (142, 142’) between the flow guide (140) and the edge of the flow paths (132, 134) which define the smallest radius of the respective turning point (160, 160’; 162, 162’; 164, 164’; 166, 166’).15 A heat pump apparatus (10) as claimed in any one of claims 2 to 14 wherein:the second heat exchanger unit third heat transfer path (210) has an inlet (220) and an outlet (222);the second heat exchanger unit third heat transfer path inlet (220) and second heat exchanger unit third heat transfer path outlet (222) extend between a plurality of spaced apart flow conduits (230).16 A heat pump apparatus (10) as claimed in claim 15 wherein: the second heat exchanger unit fourth heat transfer path (212) has an inlet (224) and an outlet (226) which are in fluid communication with a heat sink (1100) such that the second working fluid (1200) passes through the fourth heat transfer path inlet (224), through the fourth heat transfer path (212), through the fourth heat transfer path outlet (226), into the heat sink (1100) and back to fourth heat transfer path the inlet (224);the second heat exchanger unit fourth heat transfer path inlet (224) and a fourth heat transfer path outlet (226) are located so that:flow between the fourth heat transfer path inlet (224) and a fourth heat transfer path outlet (226) goes between the spaced apart flow conduits (230); andflow between the second heat exchanger unit third heat transfer path inlet (220) and third heat transfer path outlet (222) and flow between the fourth heat transfer path inlet (224) and a fourth heat transfer path outlet (226) are in different directions.17 A heat pump apparatus (10) as claimed in claim 16 wherein:the fourth heat transfer path inlet (224) is provided proximate to the second heat exchanger unit third heat transfer path inlet (220); andthe fourth heat transfer path outlet (226) is provided proximate to the third heat transfer path outlet (222);such that the fourth heat transfer path inlet (224) is closer to the second heat exchanger unit third heat transfer path inlet (220) than it is to the second heat exchanger unit third heat transfer path outlet (222), andsuch that fourth heat transfer path outlet (226) is closer to the second heat exchanger unit third heat transfer path outlet (222) than it is to the second heat exchanger unit third heat transfer path inlet (220).18 A heat pump apparatus (10) as claimed in claim 15 or claim 16 wherein the heat sink (1100) comprises a heat radiator, a heat radiator flow circuit, a hot water tank or a thermal energy storage unit containing phase change material.19 A heat pump apparatus (10) as claimed in any one of claims 2 to 18 wherein the second heat exchanger unit (200) is configured as a thermal energy storage tank.20 A heat pump apparatus (10) as claimed in any one of claims 2 to 19 wherein:the first working fluid (902) is air, and / orthe second working fluid comprises water, antifreeze and / or glycol.21 A heat pump apparatus (10) as claimed in any one of claims 1 to 20 further comprising a housing assembly (600) provided with a hollow polygonal prism section shape or a hollow cylindrical section shape which define the housing volume (500),the first heat exchanger unit (100), the second heat exchanger unit (200), the compressor module (300) and the turbine module (400) being located within the housing volume (500).22 A heat pump apparatus (10) as claimed in claim 21 wherein:the housing volume (500) is divided into a first sub-volume (502), a second sub-volume (504) and a third sub-volume (506);andthe first heat exchanger unit (100) is located in the first sub-volume (502);the second heat exchanger unit (200) is located in the second sub-volume (504);the compressor module (300) and the turbine module (400) are located the third subvolume (506).23 A heat pump apparatus (10) as claimed in claim 22 wherein each of the first sub-volume (502), second sub-volume (504) and third sub-volume (506) are shaped as polygonal prisms.24 A heat pump apparatus (10) as claimed in claim 22 wherein each of the first sub-volume (502), second sub-volume (504) and third sub-volume (506) are shaped as segments of a cylinder.25 A heat pump apparatus (10) as claimed in any one of claims 22 to 24 wherein:the first sub-volume (502) provides at least 35% but no more than 70% of the housing volume (500);the second sub-volume (504) occupies at least 20% but no more than 40% of the housing volume (500);the third sub-volume (506) occupies the remainder of the housing volume (500).26 A heat pump apparatus (10) as claimed in any one of claims 22 to 25 wherein the first sub-volume (502) is greater than the sum of the second sub-volume (504) and the third sub-volume (506).27 A heat pump apparatus (10) as claimed in any one of claims 22 to 26 wherein the second sub-volume (504) is greater than the third sub-volume (506).28 A heat pump apparatus (10) as claimed in any one of claims 22 to 27 wherein the second sub-volume (504) and the third sub-volume (506) are adjacent one another and extend from the first region (102) of the first heat exchanger unit (100).29 A heat pump apparatus (10) as claimed in any one of claims 22 to 28 wherein:the compressor module (300) comprises a compressor rotor (310) and the turbine module (400) comprises a turbine rotor (410); and the heat pump apparatus (10) further comprises a motor unit (700);a rotatable shaft (800) extends between the compressor rotor (310) and the turbine rotor (410), the compressor rotor (310) and the turbine rotor (410) being carried on, and rotatable with, the rotatable shaft (800);the motor unit (700) being coupled to the rotatable shaft (800) and operable to drive the rotatable shaft (800);the rotatable shaft (800) and motor unit (700) being located in the third sub-volume (506).30 A heat pump apparatus (10) as claimed in claim 29 wherein the compressor module outlet (304) is defined by a compressor volute (308) which defines the flow path between the compressor rotor (310) and compressor module outlet (304), the compressor module outlet (304) being coupled to the second heat exchanger unit third heat transfer path inlet (220).31 A heat pump apparatus (10) as claimed in claim 29 or claim 30 wherein the turbine module inlet (402) is defined by a turbine volute (406) which defines the flow path between the turbine rotor (410) and turbine module inlet (402), the turbine module inlet (402) being coupled to first heat transfer path outlet (126).32 A heat pump apparatus (10) as claimed in any one of claims 22 to 29 wherein:the first heat exchanger unit first heat transfer path outlet (122) is located in the first subvolume (502), and a compressor inlet duct (306) extends from the first heat transfer path outlet (122) to the compressor inlet (302) in the third sub-volume (506);the first heat exchanger unit second heat transfer path inlet (124) is located in the first sub-volume (502), the second heat exchanger unit third heat transfer path outlet (222) is located in the second sub-volume (504), and a heat exchanger flow duct (206) extends from the third heat transfer path outlet (222) to the second heat transfer path inlet (124); andthe turbine volute (406) extends from the first heat transfer path outlet (126) in the first sub-volume (502) to the turbine module (400) in the third sub-volume (504).33 A heat pump apparatus (10) as claimed in claim 32 wherein the motor unit (700) is provided in the compressor inlet duct (306).34 A heat pump apparatus (10) as claimed in any one of claims 22 to 33 wherein:the housing assembly (600) is 75 to 85cm high, 59.5 to 60cm wide and 50 to 60cm deep;the housing assembly (600) is 80cm high, 50cm wide and 45cm deep;the housing assembly (600) is 45cm to 90cm high, 45cm to 65cm wide and 45 to 80cm deep.535 A facility defined at least in part by a wall (16) which defines a space in which a heat pump apparatus (10) as claimed in any one of claims 2 to 34 is located, wherein the flow inlet port (12) and the flow outlet port (14) are provided in and / or extend through the wall (16).10

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