AU2008291678A1

AU2008291678A1 - Improvements in air intakes for water heaters

Info

Publication number: AU2008291678A1
Application number: AU2008291678A
Authority: AU
Inventors: Philip Guilfoyle
Original assignee: Rheem Australia Pty Ltd
Current assignee: Rheem Australia Pty Ltd
Priority date: 2007-08-24
Filing date: 2008-08-22
Publication date: 2009-03-05
Anticipated expiration: 2028-08-22
Also published as: NZ582508A; AU2008291678B2; WO2009026618A1

Description

WO 2009/026618 PCT/AU2008/001241 1 Improvements in Air Intakes for Water Heaters Field of the invention [001] This invention relates to water heaters having an air intake. Such water heaters can include a fan driven air intake. [002] The invention will be described in the context of an air-sourced heat pump. system. Background of the invention [003] An air-sourced heat pump water heater uses the waste heat from a refrigeration cycle to heat water. A refrigeration system such as a refrigerator or air conditioning system, uses gas to liquid compression to raise the temperature of the working fluid substantially above the ambient temperature, so heat energy can be removed from the working fluid by the ambient air due to the temperature differential. This heat energy can be thought of as waste heat in the refrigeration cycle. The working fluid is then permitted to expand through an expansion valve, during which the temperature of the working fluid falls below the ambient temperature. In refrigeration and air conditioning applications, this cooled working fluid absorbs heat from the surrounding space to be cooled. [004] In a heat pump water heater, the waste heat is used to heat water. [005] The elements of the air sourced heat pump refrigeration cycle system include a compressor to raise the temperature and pressure of the gaseous working fluid, a working fluid / water heat exchanger (condenser) transfers the heat from the compressed high pressure gaseous working fluid to the water to be heated, thus cooling and condensing the working fluid, an expansion device which reduces the pressure of the liquefied working fluid, an air / working fluid heat exchanger (evaporator) transfers heat from the ambient air to the low pressure liquefied working fluid, thus heating and vaporising the working fluid. A fan can be provided to increase the air flow through the air/working fluid heat exchanger. [006] Prior art air sourced heat pump water heaters have used split system air conditioners with the air/working fluid heat exchanger and compressor providing heat input into the heat pump refrigeration system. The working fluid/water heat WO 2009/026618 PCT/AU2008/001241 2 exchanger is located at the tank which may be remote from the compressor and air/working fluid heat exchanger. The working fluid in these systems is thus connected to the working fluid/water heat exchanger by lengths of pipe during installation. [007] Air-sourced heat pump water heaters are known in which the compressor and condenser are mounted on the top of the water tank. In analysing the performance of such equipment, we have found that such arrangements have been found to generate significant levels of noise because working components such as compressors and fans are located at a significant height above the ground, assisting the transmission of the noise. These units also have a high centre of gravity, which makes handling them difficult. [008] Figure 1A shows a prior art split system heat pump water heater having working fluid/water heat exchanger in the form of a coiled tube 111 carrying the working fluid located in the tank 102 wrapped around the cylinder or inside the cylinder. The tank is remote from the air/working fluid heat exchanger and compressor 112 and connected there-to by working fluid pipes 108, 110. A fan 114 is also provided to increase air flow through the air/working fluid heat exchanger. [009] The pipes 108, 110 must be connected when the equipment is being installed. The installation requires a refrigeration connection to be made in the field. The working fluid needs to be under pressure, so the connexions are critical and require high quality joints, and the system may need to be charged with refrigerant after the connexions have been made. Thus installation of such equipment can require two tradesmen, one having plumber's qualifications and another having refrigeration mechanic's qualifications. [010] Figure lB shows another prior art system in which a unit 106 including the compressor, air heat exchanger (evaporator) and fan 114, is installed on the top of the water tank 102. Again the water heat exchanger (condenser) 111 is located in the tank 102, either wrapped around the cylinder or immersed in the cylinder, and refrigerant connexions must be made to pipes 108, 110. [011] Figure IC shows a further prior art system in which the heat pump elements are contained in a unit 106 mounted on the top of the water tank 102. In this arrangement, the water heat exchanger is also contained in the unit 106.

WO 2009/026618 PCT/AU2008/001241 3 [012] Various types of split and integrated heat pumps have the compressor located on a substantially similar plane to the evaporator and fan, thereby allowing mechanical and fluid noise to escape due to the requirement that the fan air intake and outlet be substantially open. [013] In some instances, air intakes for water heaters can be a source of unwanted noise. Summary of the invention [014] It is desirable to produce a heat pump water heater which that overcomes or mitigates one or more of the problems of the prior art equipment. [015] According to a first embodiment of the invention, there is provided an air intake assembly for a water heater including a housing with one or more air intake apertures located proximate the side of the housing to be installed adjacent to the wall of the tank. [016] The invention also provides an air supply arrangement for a water heater including an air draft assembly providing one or more air apertures and a fan within the housing adapted to cause air or other gas to flow through the apertures. [017] In another embodiment of the invention there is provided a heat pump unit assembly for a heat pump water heater in which the components of the working fluid circuit of the heat pump assembly are assembled as a single unit contained in a housing, the housing having air intake apertures positioned to be proximate or adjacent the water tank of a water heater when installed. [018] The apertures can be formed by a cut-out of portion of the housing wall adjacent to the water tank wall. [019] The housing can have a lower compartment and an upper compartment. [020] The lower compartment can be in communication with the upper compartment via an air flow aperture. [021] The tank can be insulated and include a tank housing in which the apertures can be formed to provide the air intake for the air flow housing.

WO 2009/026618 PCT/AU2008/001241 4 [022] The upper compartment can include an air heat exchanger and a fan adapted to cause air flow through the air heat exchanger. [023] The lower compartment can include a compressor. [024] The lower compartment can include a water pump. [025] The air intake apertures can be formed in a pair of opposed panel inclined at an angle whereby the panels form a taper. [026] The panels can be angled to be substantially radial to the surface of a cylindrical water tank when installed. [027] The components of the heat pump assembly can be assembled in a single module, whereby only water connexions are required during installation of a water heater heated by the heat pump unit. [028] The invention also provides a heat pump water heater which incorporates a water storage tank and an air sourced heat pump unit integrated into a single close coupled appliance. [029] The working fluid circuit can include an air heat exchanger, a compressor, a water heat exchanger, and an expansion device, forming a closed fluid circuit. [030] The heat pump unit assembly can be adapted to be mounted proximate to the side surface of lower portion of the a storage tank. [031] The air heat exchanger can include a fan, the heat pump unit including an air inlet arrangement adapted to enable the fan to draw air across a curved wall of the storage tank. [032] The compressor can be located in a first chamber of the housing there being an air pathway from the first part of the housing to the air intake side of the air heat exchanger. [033] The heat pump unit can be attached proximate to the lower portion of the water tank with its evaporator and fan located above its compressor. [034] An air passage can be provided between a lower chamber containing, at least a compressor, and a lower pressure area above said chamber and before an WO 2009/026618 PCT/AU2008/001241 5 evaporator, enabling the fan to draw air from said lower pressure area across an evaporator. [035] The invention also provides a heat pump water heater which arranges the evaporator and fan substantially above the compressor in order to enclose the compressor to suppress noise. [036] The invention also provides a heat pump water heater which scavenges rising warm air heated by the compressor and various other heat loss sources by drawing it through an air passage between the lower area containing the compressor and an upper air intake area to be drawn across the evaporator by the fan. [037] The water heater can include an auxiliary heater. [038] The heat pump water heater can include a water pump adapted to circulate water from the tank through the water heat exchanger of the heat pump unit. [039] The mains and house water connexions between the heat pump unit and the tank and the fan air exhaust can be on one the same side of the tank. [040] The water heater can be adapted to be installed beside a wall in any orientation other than the fan air exhausting predominately towards the wall. [041] The invention also provides a modular heat pump unit adapted for use in a heat pump water heater. [042] The invention also provides an air-sourced heat pump water heater including a heat pump unit closely mounted to the exterior of a water tank, the heat pump unit being contained in a housing. [043] The heat pump unit can include a closed heat transfer fluid circuit. [044] The invention also provides a method of heating a heat pump water heater including the steps of: enclosing at least some of the heat generating components of the heat pump in an enclosure having an outlet air path; and drawing air from the enclosure through the evaporator. [045] The invention also provides a method of heating a heat pump water heater closely coupled with a side of a water tank, the method including the steps of: WO 2009/026618 PCT/AU2008/001241 6 mounting the evaporator in a housing having air inlets proximate the wall of the tank; and drawing air through the evaporator via the air inlets. [046] In one embodiment of the invention, the compressor is substantially enclosed in a first housing. [047] The first housing can be substantially sound proofed. [048] The first housing can enclose the water pump. [049] The first housing can enclose the condenser. [050] The invention also provides a heat pump water heater which arranges the evaporator and fan outside the first housing. [051] The invention also provides a heat pump water heater which scavenges rising warm air heated by the compressor by drawing it through a communicating air passage or path between the first housing containing the compressor and an upper housing section through which the air is drawn through the evaporator by the fan. [052] The cold water intake can be located on the inlet side of the water heat exchanger. [053] The cold water intake can be located on the intake side of the water pump. [054] The water connections between the heat pump water heater and the mains can be on the same side as the fan air exhaust. [055] The invention also provides an air-sourced heat pump water heater including a close coupled heat pump unit having a housing, the housing defining an air passage proximate the wall of the tank. [056] The invention further provides an air-sourced heat pump water heater including a close coupled heat pump unit having a housing, the tank including a casing having one or more recesses which, in combination with the housing, define an air passage proximate the wall of the tank.

WO 2009/026618 PCT/AU2008/001241 7 Brief description of the drawings [057] An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings. [058] Figures lA, lB and 1C show heat pump water heaters of prior art. [059] Figure 2 shows the structure of a heat pump water heater according to an embodiment of the invention. [060] Figure 3 shows detail of the heat pump arrangement of Figure 2. [061] Figure 4 represents airflow through the air heat exchanger. [062] Figure 5 is a schematic diagram showing the fluid paths of a heat pump water heater according to an embodiment of the invention. [063] Figure 6 is a schematic illustration of airflow within the heat pump housing. [064] Figure 7 shows an embodiment of the invention applied to a forced draft water heater. [065] Figure 8 is an illustration of a further embodiment of the invention in which the air aperture is formed in the outer casing of the tank. [066] Figure 9 is a section view of the arrangement of Figure 8 along line A A. Detailed description of the embodiments [067] In one embodiment of the invention as illustrated in Figure 2, a water heater 200 has a heat pump unit 220 mounted against the side of the tank with its base on the same level as the base of the tank. Thus the heat pump unit does not need to be lifted onto the top of the tank during assembly or installation. [068] The refrigeration circuit of the heat pump water heater assembly can be manufactured as a single modular unit so that only water connexions need to be made between the heat pump unit and the water tank at installation. This overcomes the need to connect the refrigeration circuit in the field and also averts the requirement for a refrigeration mechanic during installation.

WO 2009/026618 PCT/AU2008/001241 8 [069] Figure 2 shows the heat pump water heater 200 according to an embodiment of the invention. A heat pump assembly 220 is connected to the tank 202, preferably at the bottom end of the tank. This avoids the need to lift the heat pump module on to the top of the water tank, or to manoeuvre a tank with the heat pump assembly on top of the tank. In addition, most noise generated by the equipment during operation is at a low elevation. [070] Also, mechanical noise from the compressor can be confined in an enclosed space below the substantially open evaporator and fan assembly. [071] Air is drawn into the air/working fluid heat exchanger via slots 246 and matching slots on the other side (not shown) in the heat pump assembly housing. [072] The hot water from the heat pump arrangement is delivered to the tank via pipe 266. The pipe 266 is shown entering the tank in the upper third of the tank. A riser pipe and a diffuser can be provided inside the tank and connected to the pipe 266 to deliver the heated water to the upper portion of the tank. The diffuser can assist in reducing stirring and mixing of the heated and cooler water in the tank. Hot water can be drawn off via an outlet pipe (not shown) which draws water from the upper portion of the tank. [073] Preferably all the water connexions for delivering cold water to the tank 248, for drawing off hot water from the tank, 250, and pipes 266 and 364 (Figure 3), for connecting between the water/working fluid heat exchanger and the tank 202 are all on the same side of the tank. The water connexions can be in a vertical line. Preferably, the fan 234 is also on this side. [074] A fan outlet 235 is also provided to permit discharge of the air from the fan. Preferably the fan air exhaust is located on the same side of the tank as the mains and house water connection. [075] The housing can be removable or it can include an access door (not shown) to permit access to the components of the heat pump assembly. [076] The heat pump unit 220 can be manufactured as a modular, pre assembled unit with the working fluid circuit forming a sealed unit, so that only water connexions between the tank and the heat pump unit need to be made during assembly or installation.

WO 2009/026618 PCT/AU2008/001241 9 [077] Assembly of the heat pump against the side of the tank in a close coupled arrangement means that the tank effectively blocks a major portion of the sound radiation from the heat pump unit. [078] Figure 3 shows details of the modular heat pump unit 320. [079] In this description, a first heat exchanger 332 is an air/working fluid heat exchanger and will be referred to herein as the air heat exchanger. This heat exchanger is sometimes referred to as the evaporator. Similarly the second heat exchanger 340/360, which is a water/working fluid heat exchanger, sometimes referred to as a condenser, will be referred to as the water heat exchanger. [080] The working fluid circuit includes the compressor 336 to compress the working fluid, the working fluid side 340 of the water heat exchanger, the working fluid expansion valve 342, and the air heat exchanger 332, together with the interconnection plumbing. The air heat exchanger 332 is connected to the compressor 336 by pipe 352. The compressor 336 is connected to the water heat exchanger 340 by pipe 354. Pipe 356 connects the working fluid side of the water heat exchanger to the expansion nozzle evaporator 342. Pipe 358 connects the expansion nozzle evaporator 342 to the air heat exchanger. [081] Fan 334 draws ambient air from between the tank and the air heat exchanger 332 through the air heat exchanger 332. A cowling 372 ensures that the air drawn by fan 334 flows via the air heat exchanger 332. The cowling can be in the form of a truncated pyramid, but preferably has curved wall transitions to improve streamlining. [082] The working fluid circuit, also referred to herein as the refrigeration circuit, together with fan 334 can be pre-assembled into a modular unit with housing 370 and can be charged with working fluid in the factory so it does not need to be charged in the field. [083] The housing 370 includes a pair of air inlet grills 346 through which air is drawn by fan 334 to transfer heat energy from the ambient air to the working fluid in its gaseous form in the air heat exchanger 332. This heat energy is used to heat the water in the water heat exchanger 340/360, where 360 is the water side of the water heat exchanger.

WO 2009/026618 PCT/AU2008/001241 10 [084] The air inlets 346 are arranged in a panel 345 which is tapered towards the tank, and the top panel has a curved or arcuate profile 347 to conform to the tank. This feature is also shown in the plan view of Figure 4. The panel 345 can be arranged to be aligned radially with respect to the tank periphery. [085] The lower housing 370 encloses many of the noise generating components, such as the compressor and water pump, but has a communicating vent (best illustrated in Figure 4) to the air intake side of the air heat exchanger 332 to permit the air from the housing 370 to be drawn through the air heat exchanger 332 by the fan 334. Thus noise from the components in housing 370 does not have a direct route to the outside of the housing. [086] The water circuit includes a first pipe 364 connecting the lower part of the water tank to the water inlet of the water side 360 of the water heat exchanger 340/360. Pipe 361 connects the water heat exchanger 360 to a water pump 362. Pipe 366 connects the pump outlet to the tank. This pipe 366 is equivalent to pipe 266 in Figure 2. While the pump 362 in Figure 3 is shown on the outlet side of the water heat exchanger 360, in practice it can be located in pipe 364 on the inlet side of the water heat exchanger 360, as shown at 532 in Figure 5. [087] In operation, when the compressor 336 is running, the working fluid is heated due to the pressure increase and the heated working fluid is delivered to the water heat exchanger 340. Heat absorbed by the working fluid in the air heat exchanger 332 is also available in the water heat exchanger 340. The water pump 362 circulates water from lower portion of the tank via pipe 364 through the water side 360 of the water heat exchanger, and delivers the heated water to the tank via pipe 366. [088] Because the heat pump unit is located at the lower end of the tank, in an alternative embodiment, thermosyphoning can be used to circulate the water through the water heat exchanger, and the water pump can be omitted. [089] Having a two tiered assembly with the air heat exchanger and fan above the compressor and other components of the heat pump reduces the footprint of the heat pump unit. [090] Figure 4 shows a tank 402 with an insulating jacket 403 and a close coupled heat pump unit. Figure 4 is a plan view which illustrates airflow around the WO 2009/026618 PCT/AU2008/001241 11 periphery of the tank 402 and through the air heat exchanger 432. The dotted arrows 435 illustrate the air flow from outside the heat pump unit, while the dash-double dot arrows indicate the air flow from the lower portion of housing 470 which contains many of the heat generating components of the heat pump unit, such as the compressor and water pump. The air inlet slots 446 in the housing 470 are located proximate to the curved wall of the tank 402. This is consonant with the air flowing smoothly along the wall of the tank as illustrated at 437. In this embodiment, the air flow can be approximately tangential at the point of entry to the housing 470. The circled dots at the origins of the dash-double dot arrows indicate the upward airflow from the lower compartment of the housing. Dashed line 474 represents the edge of the aperture between the lower compartment of housing 470. This aperture is on the intake side of the air heat exchanger 432, so the warmed air from the lower compartment is drawn through the air heat exchanger 432 by the fan 434. [091] The close coupling of the heat pump unit and the water tank assists in reducing noise dispersion, as the tank acts as a buffer for a substantial part of the noise from the fan, and the housing and cowl also reduce the amount of noise radiated from the fan. Similarly noise from the compressor and pump is buffered by the tank on one side, and the housing also reduces the amount of noise radiated from the housing. The housing walls an be adapted to reduce re-propagation of noise from the housing walls by lagging and/or stiffening or by other suitable sound reducing techniques. [092] The footprint of the heat pump unit is also compact because of the two tier arrangement. [093] Figure 6 illustrates schematically the airflow within the heat pump housing 670. The housing is divided into upper and lower chambers by plate 674 provides has an air passage adjacent the wall of the tank 602. The compressor 636, pump 662 and water heat exchanger (condenser) 640 are located in the lower chamber, while the air heat exchanger (evaporator) 632 and fan 634 are located in the upper chamber. Some of the components in the lower chamber produce heat. The air passage between the dividing plate 674 and the tank wall is located on the intake side of the air heat exchanger 632, and the fan 634 draws air from the lower chamber through the air heat exchanger 634, as indicated by the dash-double dot line 676. A cowling formed in part by the upper portion of the housing 670 and cowling plate 676 can be used to provide smooth air flow from the air heat exchanger to the fan. An WO 2009/026618 PCT/AU2008/001241 12 air inlet aperture can be provided in the lower portion of the lower chamber to improve air flow. [094] The air intake slots 446 are formed in a panel which is angled to create a recess between the remainder of the housing 470 and the side of the tank, and this assists in preventing the inadvertent obstruction of the air inlets. In one embodiment, the panel carrying the air intake slots is radial in relation to the tank. However, the panel can be formed to meet the side of the tank at other angles. Preferably, the angle is selected to be compatible with the minimization of noise. [095] A booster heater 401 can also be provided to raise the temperature of the water delivered from the heat pump to the tank. The booster heater can be internal to the tank or external thereto. The booster heater can be an electric element 401. Alternatively, other forms of booster heater, such a gas can be used. [096] Figure 5 shows a schematic diagram of a modular heat pump unit 500 installed with a water tank 502. Figure 5 shows the fluid paths of a heat pump water heater. In the working fluid circuit, the compressor 536 delivers the hot compressed working fluid via pipe 554 to the water heat exchanger 540/560 where heat energy from the working fluid side 540 is transferred to the water side 560. The working fluid then flows through pipe 556 to expansion valve 542, the lowering of pressure and expansion of the working fluid causing the working fluid to cool. The cooled working fluid then flows to the evaporator/air heat exchanger 532 via pipe 558. The cooled working fluid in the evaporator/air heat exchanger 532 absorbs heat energy from the air, and is then delivered to inlet of the compressor 536. [097] The water circuit includes a pump 562 which, when the pump is in operation, pumps water through the water heat exchanger 560 via pipe 561 and delivers it to the upper portion of tank 502 via pipe 566 and riser 567. The water from the lower portion of the tank is drawn through the pump 562 via pipe 564. [098] As indicated by the dashed line representing the heat pump unit housing and the water pipes 564, 566, the modular heat pump unit 500 is installed on the tank using only water pipe connexions. The cold water inlet 548 connects into the pipe which is the intake pipe for the water pump 562. Hot water can be drawn off via pipe 550.

WO 2009/026618 PCT/AU2008/001241 13 [099] The control of the operation of the water heater can be performed using a programmable controller or processor and associated sensors (not shown). [0100] Close coupling of the air-supplied heat pump to the tank assists by providing a noise buffer on one side of the heat pump unit to reduce fan and compressor noise. Enclosure of the chamber containing the compressor reduces compressor noise. One side of the fan is masked by the tank thereby reducing fan noise, while the apertures allow relatively unimpeded air-flow with a largely enclosed layout. Heat from the lower chamber can be scavenged drawing it through the. The two-tiered structure provides a compact footprint. [0101] Figure 7 shows a forced draft gas water heater having a tank 702 with a central flue 706 connecting with a combustion chamber heated by gas burner 710 at the base of the tank. Gas is fed to the burner via pipe 716. A fan 712 is mounted in housing 720 to the side of the tank. A forced draft from fan 712 feeds a gas/air mixture to the burner. The combustion gasses rise up the flue and the walls of the flue act as a heat exchanger to heat the water in the tank. [0102] Cowling 772 separates the air intake side from the air outlet of the fan. The fan draws air from adjacent the wall of the tank 702 via apertures 746. The air is blown along radiused duct 773 to burner 710. Air is drawn from adjacent the wall of the tank and through duct 773 to burner 710, entraining gas from gas inlet 716. [0103] Figure 8 illustrates another embodiment in which the tank has an outer casing 803. The heat pump unit housing 820 and fan 812 are shown. The air apertures 880 are formed in the outer casing. In this embodiment, the mating edges 833 of the housing can be a straight edge and pass across the apertures 880 so part of the aperture 880 is open to external atmosphere, while the other part of the aperture is open to the interior of the housing 820. As seen in Figure 9, the aperture 980 is recessed into the casing 903. The space between the tank 902 and the casing 903 can be filled with insulation 990. [0104] Further variations can be implemented without departing from the inventive concept. For example, part of the edge 833 of the housing can be cut away, and a recess 880 can also be formed in the casing 803, the cut away and the recess forming the air passage.

WO 2009/026618 PCT/AU2008/001241 14 [0105] In this specification, reference to a document, disclosure, prior art heat pumps, or other publication or use is not an admission that the document, disclosure, prior art heat pumps, publication or use forms part of the common general knowledge of the skilled worker in the field of this invention at the priority date of this specification, unless otherwise stated. [0106] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of'. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [0107] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention. [0108] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. An air draft assembly for a water heater including a housing adapted to be installed adjacent to a hot water tank, a portion of the housing to be installed adjacent to the wall of the tank providing apertures located proximate or adjacent the side of the tank.

2. An air supply arrangement for a water heater including an air draft assembly as claimed in claim 1, and a fan within the housing adapted to cause air or other gas to flow through the apertures.

3. A heat pump assembly for a heat pump water heater in which the components of the working fluid circuit of the heat pump assembly are contained in a housing, the housing having air intake apertures positioned to be proximate or adjacent the water tank of a water heater when installed.

4. A heat pump assembly as claimed in claim 3, wherein the housing has an lower compartment and an upper compartment.

5. A heat pump assembly as claimed in claim 4, wherein the upper compartment includes an air heat exchanger and a fan adapted to cause air flow through the air heat exchanger.

6. A heat pump assembly as claimed in claim 4 or claim 5, wherein the lower compartment includes one or more of: a compressor; a water pump.

7. A heat pump assembly as claimed in any one of the claims 3 to 6, wherein the air intake apertures are formed in a pair of opposed panel which are inclined at an angle whereby the panels form a taper.

8. A heat pump assembly as claimed in claim 7, wherein the panels are angled to be substantially radial to the surface of a cylindrical water tank when installed.

9. A heat pump assembly as claimed in any one of claims 3 to 9, wherein the components of the heat pump assembly are assembled in a single module, whereby only water connexions are required during installation of a water heater heated by the modular heat pump unit. WO 2009/026618 PCT/AU2008/001241 16

10. A heat pump assembly as claimed in any one of claims 3 to 9, wherein the heat pump assembly is adapted to be mounted proximate to the side surface of a storage tank.

11. A heat pump assembly as claimed in any one of claims 3 to 10, wherein the air heat exchanger includes a fan, the heat pump unit including an air inlet arrangement adapted to enable the fan to draw air from a proximate wall of the storage tank.

12. A heat pump assembly as claimed in any one of claims 3 to 11, wherein the compressor is located in a first portion of the housing there being an air pathway from the first part of the housing to the air intake side of the air heat exchanger.

13. A heat pump assembly as claimed in any one of claims 3 to 12, wherein a working fluid circuit includes an air heat exchanger, a compressor, a water heat exchanger, and an expansion device, forming a closed fluid circuit.

14. A heat pump water heater including a heat pump unit as claimed any one of claims 3 to 13 and a water tank, wherein the heat pump unit is installed proximate to the lower portion of the water tank with the evaporator and fan are located above its compressor.

15. A heat pump water heater as claimed in claim 13 or claim 14, including an auxiliary heater.

16. A heat pump water heater as claimed in any one of claims 13 to 15, including a water pump adapted to circulate water from the tank through the water heat exchanger of the modular heat pump unit.

17. A water heater as claimed in any one of claims 13 to 16, wherein the mains and house water connexions are on the same side of the tank.

18. A water heater as claimed in any one of claims 13 to 17, wherein the water heater is adapted to be installed beside a wall in any orientation other than the fan air exhausting predominately towards the wall.

19. A heat pump water heater which incorporates a water storage tank and an air sourced heat pump unit integrated into a single close coupled appliance.

20. A water heater system including a water storage tank and a close coupled air draft assembly, the tank including an external casing having an air draft WO 2009/026618 PCT/AU2008/001241 17 housing, the interface between the air draft housing and the casing providing an air passage.

21. An air-sourced heat pump water heater including a heat pump unit closely mounted to the exterior of a water tank, the heat pump unit being contained in a housing.

22. A water heater as claimed in claim 21, wherein the heat pump unit is mounted proximate the lower part of the tank.

23. A water heater as claimed in claim 21 or claim 22, wherein the heat pump unit includes two or more compartments arranged one on top of the other.

24. A water heater as claimed in any one of claims 21 to 23, including air inlet adjacent or proximate the tank.

25. A water heater as claimed in any one of claims 21 to 24, the heat pump unit including a closed heat transfer fluid circuit.

26. A water heater as claimed in any one of claims 21 to 24, wherein an evaporator and fan are mounted in an upper compartment of the housing, the fan being adapted to draw air through the evaporator from proximate the tank.

27. A modular heat pump unit adapted for use in a heat pump water heater substantially as herein described with reference to the accompanying drawings.

28. A heat pump water heater substantially as herein described with reference to the accompanying drawings.

29. A method of heating a heat pump water heater including the steps of: enclosing at least some of the heat generating components of the heat pump in an enclosure having an outlet air path; and drawing air from the enclosure through the evaporator.

30. A method of heating a heat pump water heater closely coupled with a side of a water tank, the method including the steps of: mounting an evaporator in a housing having an air inlet proximate the wall of the tank; and drawing air through the evaporator via the air inlets.