AU2014268261A1 - Improvements relating to water heaters - Google Patents

Abstract

Disclosed herein is a sub-assembly for a water heater 10, comprising a water tank 1 having a cylindrical wall 2 formed from material having heat transfer properties. A heat exchanger tube 5 adapted to carry a refrigerant fluid is wrapped around the external surface of the tank wall 2 to heat water inside the tank. A barrier 7 extends around the tank 1 and covers the heat exchanger tube 5 to inhibit insulation material applied outwardly of the barrier from squeezing between the heat exchanger tube 5 and the tank 1. 1 3 17 1 1 41 3 7 1 1 12 18 12 18 10--r20 10 .2 ___. _ _-_-__-I- ------ 4 -4 : 6 40 - Fig. 2 Fig. 2B Fig. 2A

Description

1 AUSTRALIA Patents Act 1990 INFINITY ENERGY TECHNOLOGIES PTY LTD COMPLETE SPECIFICATION STANDARD PATENT Title: Improvements relating to water heaters The following statement is a full description of this invention including the best method of performing it known to us:- 2 Cross-Reference to Related Applications [0001] The present application claims priority from Australian Provisional Patent Application No 2013904626 filed on 29 November 2013, the content of which is incorporated herein by reference. Technical Field [0002] The present disclosure relates to improvements to water heaters. Disclosed herein is a heat pump water heater, and more particularly an ambient air heat pump water heater, a sub assembly therefor, and methods of manufacturing such a water heater and sub-assembly. The presently disclosed water heater has been developed primarily for use in generating domestic hot water and will described hereinafter with reference to this application. However, it will be appreciated that it may also be used in commercial or industrial applications for heating water or other fluids. Background [0003] Known ambient air heat pump water heaters have a limited operation range, and high failure rate, due to: 1) overheating of the compressor if forced to heat water to relatively high temperature, such as the 60'C temperature required under Australian standards and the standards of other industrial countries for sanitary/potable water; 2) failure of the water pump, 3) leakage of the heat exchanger coil inside the tank. [0004] Moreover, in most conventional ambient air heat pump water heaters, the heat pump cannot operate below 7'C ambient air temperature. As a result, conventional ambient air heat pump water heaters usually rely on a back-up electrical element to heat water when ambient air temperature drops below 7'C. Some conventional heat pump water heaters do not have a double wall heat exchange effect between refrigerant and water, which is required by standards in Australia and other industrial countries. Another problem with conventional heat pumps is that de-frosting of the evaporator is realised by reversing the refrigeration cycle. This reversing cycle de-frosting method is problematic, firstly as it takes heat from the water being heated, which reduces efficiency, secondly because when the water is hot, the suction pressure in the de- 3 frosting period is too high for the compressor, and thirdly because in the short de-frosting time, the return of oil to the compressor is often a problem, which can cause the compressor to lack oil and fail. [0005] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application. Summary [0006] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. [0007] In a first aspect, there is provided a sub-assembly for a water heater, said sub-assembly comprising: a water tank having a wall formed from material having heat transfer properties; a heat exchanger tube adapted to carry a refrigerant fluid, the tube being wound externally around the wall of said tank to heat water inside said tank; a barrier extending around the tank and covering the heat exchanger tube to inhibit insulation material applied outwardly of the barrier from squeezing between the heat exchanger tube and the tank. [0008] In a second aspect, there is provided a water heater comprising: a water tank having a wall formed from material having heat transfer properties; a heat pump circuit comprising: an evaporator for exposure to ambient air, a compressor downstream of the evaporator, a condenser downstream of the compressor, the condenser comprising a heat exchanger tube adapted to carry a refrigerant fluid, the tube being wound externally around the wall of said tank to heat water inside said tank, and an expansion device downstream of the condenser; 4 a barrier extending around the tank and covering the heat exchanger tube; a housing encasing the tank, the heat exchanger tube and the barrier; thermal insulation between the barrier and the housing, wherein the barrier inhibits the insulation from squeezing between the heat exchanger tube and the tank. [0009] The insulation may be injectable foam insulation. [0010] The barrier may comprise a film or tape applied over the heat exchanger tube. The barrier may be formed from plastic, such as PVC, or may be formed from metal, such as aluminium. The barrier may be adapted to withstand temperatures up to 150'C or at least up to 100'C. The barrier may be adapted to withstand temperatures up to 150'C or at least up to 100'C without emitting a toxic gas/smell. [0011] The tank wall may be cylindrical and the heat exchanger tube may be helically coiled around the cylindrical tank wall. The heat exchanger tube may be wound around the external surface of the tank under tension. The heat exchanger tube may be fastened at one or more locations to the wall of the tank. Two or more of the heat exchanger tubes may be wound around the tank. [0012] The heat exchanger tube may be formed from heat conductive metal, such as copper, steel, aluminium or a metal alloy. [0013] At least part of an outer surface of the heat exchanger tube may have a profile that substantially conforms to a profile of the outer surface of the tank. To facilitate same, the heat exchanger tube may be, for example, oval, "D" shaped, rectangular or kidney shaped in transverse cross-section. [0014] A heat transfer facilitating material may be provided between the heat exchanger tube and the tank. The heat transfer material may be substantially coextensive with the length of the heat exchanger tube. The heat exchanger material may comprise a heat transfer paste. [0015] In a third aspect, there is provided a method of manufacturing a sub assembly for a water heater, said method comprising: 5 providing a water tank having a wall formed from material having heat transfer properties; winding a heat exchanger tube externally around the wall of said tank, the heat exchanger tube being adapted to carry a refrigerant fluid to heat water inside said tank, and forming a barrier around the tank and covering the heat exchanger tube to inhibit insulation material applied outwardly of the barrier from squeezing between the heat exchanger tube and the tank. [0016] In a fourth aspect, there is provided a method of manufacturing a water heater, comprising: providing a water tank having a wall formed from material having heat transfer properties; providing a heat pump circuit comprising: an evaporator for exposure to ambient air, a compressor downstream of the evaporator, a condenser downstream of the compressor, the condenser comprising a heat exchanger tube adapted to carry a refrigerant fluid, the tube being wound externally around the wall of said tank to heat water inside said tank, and an expansion device downstream of the condenser; forming a barrier around the tank and covering the heat exchanger tube; encasing the tank, the heat exchanger tube and the barrier in a housing and providing a space between the barrier and the housing; and installing thermal insulation into the space between the barrier and the housing, wherein the barrier inhibits the insulation from squeezing between the heat exchanger tube and the tank during installation of the insulation. [0017] The insulation may be injectable foam insulation. [0018] The barrier may comprise a film or tape applied over the heat exchanger tube. The barrier may be formed from plastic, such as PVC, or may be formed from metal, such as aluminium. The barrier may be adapted to withstand temperatures up to 150'C or at least up to 100'C. The barrier may be adapted to withstand temperatures up to 150'C or at least up to 100'C without emitting a toxic gas/smell.

6 [0019] The tank wall may be cylindrical and the heat exchanger tube may be helically coiled around the cylindrical tank wall. The heat exchanger tube may be wound around the external surface of the tank under tension. The heat exchanger tube may be fastened at one or more locations to the wall of the tank. Two or more of the heat exchanger tubes may be wound around the tank. [0020] The heat exchanger tube may be formed from heat conductive metal, such as copper, steel, aluminium or a metal alloy. [0021] The heat exchanger tube may be oval or "D" shaped in transverse cross-section. [0022] A heat transfer facilitating material may be provided between the heat exchanger tube and the tank. The heat transfer material may be substantially coextensive with the length of the heat exchanger tube. The heat exchanger material may comprise a heat transfer paste. [0023] The outer surface of the tank may be cleaned, prior to winding the heat exchanger tube therearound, to remove surface contamination, such as rust or scales. The outer surface of the tank may be cleaned abrasively, such as by sandblasting, or chemically. Brief Description of Drawings [0024] Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic front view of an embodiment of a water heater according to the present disclosure; Fig. 1A is a schematic front view of the water heater of Fig. 1 in a defrost cycle; Fig. 2 is a fragmentary sectional elevation of a water tank incorporating a heat exchanger suitable for use with the water heater of Fig. 1; Fig. 2A is an enlarged fragmentary sectional elevation of portion of the tank of Fig. 2, showing the position of the heat exchanger tube; and Fig. 2B is an enlarged fragmentary sectional elevation of portion of the tank showing the film wrapped around the tube.

7 Description of Embodiments [0025] Referring to the drawings, there is shown a heat pump water heater 10. The water heater 10 comprises a water tank 1 having a cylindrical wall 2, a cold water inlet 3 and a hot water outlet 4. A heat exchanger tube 5 is wrapped around the external surface of the tank wall 2. The tube 5 is manufactured from copper, steel, aluminium or a metal alloy. The tube 5 is preferably flattened as shown in Fig. 2A, so that it is substantially D-shaped in transverse cross section to conform to the profile of the tank wall 2, with the flattened face of the tube located against the tank wall 2 to increase the surface contact area available for heat transfer. In the embodiment shown in Fig. 2A and 2B, the tube 5 comprises a single channel for carrying a refrigerant. A heat transfer paste 6 is applied to the flattened surface of the tube 5 prior to the tube being wound around the tank 1. Accordingly, with the tube 5 wrapped around the tank 1, the heat transfer paste 6 is located between the tube 5 and the tank wall 2 to facilitate heat transfer therebetween. Preferably the heat transfer paste 6 is located along the entire length of the interface between the tube 5 and the tank wall 2. [0026] To ensure the best possible contact of the tube 5 and tank wall 2, the tube 5 is wound around the tank 1 under tension and is mechanically or chemically fastened to the tank wall while to maintain the tension. Ideally, the tube 5 is fixed to the tank wall 2 by spot welding the lower end of the tube to the bottom of the tank wall 2, followed by winding the tube 5 around the tank 1 under tension, and then spot welding the upper end of the tube 5 to the top of the tank wall 2 to maintain the tube 5 under tension. [0027] Whilst it is preferable for the tube 5 to be helically wound around the external surface of the tank wall 2, it should be noted that alternative placings of the tube 5 on the external wall 2 of the tank may be possible. For example, the tube 5 may be formed in a concertina or zig-zag configuration and arranged on the external wall 2 of the tank so that the tube extends up and down the external wall of the tank. [0028] The heat transfer paste 6 may or may not need to be cured. If curing is required, it is preferable for the curing to occur under ambient conditions. A suitable heat transfer paste is "HTSP Silicone Heat Transfer Compound Plus", marketed in Australia by Electrolube. Another suitable heat transfer paste is "Bostik 1128 Heat Transfer Sealer", marketed in Australia by Bostik.

8 [0029] The exterior of the tank wall 2 is preferably cleaned prior to the tube 5 being wound therearound. The cleaning may be performed by an abrasive process such as sandblasting or by a chemical process. [0030] After the tube 5 is wrapped around and affixed to the tank 1, a barrier 7 is applied over the tube 5 and the tank assembly, as shown in Fig. 2B. The barrier 7 may be formed from plastic, such as PVC, or may be formed from metal, such as aluminium, and is adapted to withstand temperatures up to 100'C without emitting a toxic gas/smell. A housing 30 encases the tank 1, the heat exchanger tube 5 and the barrier 7. Foam insulation 40 is injected into a space between the barrier 7 and the housing 30 to thermally insulate the water heater 10. The barrier 7 acts to inhibit the foam insulation 40 squeezing between the tube 5 and the tank wall 2 and reducing the heat transfer efficiency between the tube 5 and tank wall 2. [0031] Referring again to Figs. 1 and 1A, the ambient air heat pump water 10 includes a heat pump circuit including an evaporator 11 exposed to ambient air, a compressor 12 downstream of the evaporator, a condenser comprising heat exchanger tube 5 downstream of the compressor, and an expansion device 13 downstream of the condenser 5. [0032] The expansion device 13 comprises a throttling restriction or an expansion valve or other means to drop the pressure and temperature of the refrigerant carried by the heat pump circuit. The evaporator 11 is in the form of a finned coil. A fan 14 is associated with the evaporator 11 to blow ambient air toward the evaporator. [0033] As best seen in Fig. 1A, a bypass circuit is provided and has a first end 15 connected to the heat pump circuit between the compressor 12 and the condenser 5 and a second end 16 connected to the heat pump circuit between the expansion device 13 and the evaporator 11. The bypass circuit includes a solenoid valve 17 for selectively diverting a portion of relatively hot refrigerant output from the compressor 12 to the evaporator 11. [0034] A controller 18 and associated timer are provided for controlling actuation of the compressor 12, fan 11, and valve 17. [0035] A filter/drier 19 is provided in the heat pump circuit between the condenser tube 5 and the expansion device 13 to clean and dry the refrigerant prior to its passing to the expansion device 13.

9 [0036] In use, the compressor 12 circulates refrigerant through the heat pump circuit. The compressor 12 draws refrigerant vapour from the evaporator 11, and compresses the low pressure, low temperature refrigerant vapour to a high pressure and high temperature superheated state, before exhausting the refrigerant vapour to the condenser tube 5. Heat from the high temperature refrigerant vapour is transferred via the condenser tube 5 and the tank wall 2 to the water in the tank 1. Accordingly, the refrigerant is de-superheated, condensed, and sub-cooled to sub-cooled liquid state. The sub-cooled refrigerant from the condenser tube 5 then passes through the filter/drier 19 and into the expansion device 13. After expansion, the temperature of the refrigerant is below the temperature of the surrounding ambient air, such that heat is transferred from the ambient air to the refrigerant in the evaporator 11 to vaporise the refrigerant. Actuation of the fan 14 facilitates heat transfer between the ambient air and the refrigerant in the evaporator 11. The cycle is continued until the water temperature in the tank 1 reaches a desired temperature. [0037] In one embodiment, the controller 18 opens the valve 17 to divert a small portion of hot refrigerant gas through the bypass circuit 15 to defrost the evaporator 18 under certain conditions. In the embodiment illustrated in Fig. 1, the controller 18 is responsive to the temperature of the suction gas, the heat pump circuit between the evaporator 11 and the compressor 12. The controller 18 opens the valve if sensor 20 between the evaporator 11 and the compressor 12 detects a temperature less than 5 0 C. The controller 18 also deactivates the fan 14 when the valve 17 is opened and reactivates the fan 14 before the valve 17 is closed to blow any melted frost off the evaporator 11. The controller 18 closes the valve 17 if the sensor 20 detects the temperature has increased to 13'C or after the valve has been open for 10 minutes. The controller 18 prevents the valve 17 being reopened for 45 minutes. [0038] When the suction temperature falls to below a certain level, such as 5 0 C as mentioned above, the density of the suction gas may be too thin to carry lubricant oil from the evaporator 11 or the compressor suction line returning to the compressor 12, which could cause failure of the compressor 11. Accordingly, if the suction temperature falls to 5 0 C, the valve 17 is opened to divert some of the hot refrigerant vapour discharged from the compressor 12 to the evaporator 11, which facilitates the oil returning to the compressor 12. [0039] As illustrated in Fig. 1, the controller 18 is also responsive to a compressor temperature sensor 21 for detecting the temperature of the compressor 12 and opens the valve 17 if the compressor temperature sensor 21 detects that the compressor temperature is higher than a 10 predetermined value, for example 90'C. The controller 18 closes the valve 17 when the compressor temperature sensor 21 detects that the compressor temperature has fallen to another predetermined value, for example 75 0 C. In the illustrated embodiment, the compressor temperature sensor 21 is shown attached to the heat pump circuit between the compressor 12 and the condenser tube 5. However, sensor 21 could alternatively be attached to the compression unit of the compressor 12. [0040] A water heater including a heat pump circuit as described above is disclosed in co pending Australian Patent Application No. 2013245437. [0041] It will be appreciated that the illustrated heat pump water heater provides the following benefits: * a double wall is provided between the refrigerant in the heat exchanger tube(s) and water in the tank 1, which protects the water against being polluted by the refrigerant; e providing barrier 7 over the heat exchanger tube 5 prior to installing the insulation 40 inhibits the insulation squeezing between the tube 5 and the tank wall 2 and reducing the heat transfer efficiency between the tube 5 and tank wall 2; e providing the bypass circuit 15 allows the water heater to operate at temperatures as low as -10 C without an electrical or other booster. [0042] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Examples of possible variations and/or modifications include, but are not limited to: * using a plurality of heat exchanger tubes in parallel instead of a single tube; and/or * the heat exchanger tube(s) 5 comprising micro channels for carrying a refrigerant.

Claims (15)

1. A sub-assembly for a water heater, said sub-assembly comprising: a water tank having a wall formed from material having heat transfer properties; a heat exchanger tube adapted to carry a refrigerant fluid, the tube being wound externally around the wall of said tank to heat water inside said tank; a barrier extending around the tank and covering the heat exchanger tube to inhibit insulation material applied outwardly of the barrier from squeezing between the heat exchanger tube and the tank.

2. A sub-assembly according to claim 1, wherein the barrier comprises a film or tape applied over the heat exchanger tube.

3. A sub-assembly according to claim 1 or claim 2, wherein the barrier is adapted to withstand temperatures up to 150'C.

4. A sub-assembly according to any one of the preceding claims, wherein the tank wall is cylindrical and the heat exchanger tube is helically coiled around the cylindrical tank wall.

5. A sub-assembly according to any one of the preceding claims, wherein at least part of an outer surface of the heat exchanger tube has a profile that substantially conforms to a profile of the outer surface of the tank

6. A sub-assembly according to any one of the preceding claims, wherein the heat exchanger tube comprises a plurality of channels in parallel.

7. A sub-assembly according to any one of the preceding claims, comprising a heat transfer facilitating material between the heat exchanger tube and the tank.

8. A water heater comprising: a sub-assembly according to any one of the preceding claims; a heat pump circuit comprising: an evaporator for exposure to ambient air, a compressor downstream of the evaporator, 12 a condenser downstream of the compressor, the condenser comprising said heat exchanger tube, and an expansion device downstream of the condenser; a housing encasing the tank, the heat exchanger tube and the barrier; thermal insulation between the barrier and the housing, wherein the barrier inhibits the thermal insulation from squeezing between the heat exchanger tube and the tank.

9. A water heater according to claim 8, wherein the insulation is injectable foam insulation.

10. A method of manufacturing a sub-assembly for a water heater, said method comprising: providing a water tank having a wall formed from material having heat transfer properties; winding a heat exchanger tube externally around the wall of said tank, the heat exchanger tube being adapted to carry a refrigerant fluid to heat water inside said tank, and forming a barrier around the tank and covering the heat exchanger tube to inhibit insulation material applied outwardly of the barrier from squeezing between the heat exchanger tube and the tank.

11. A method according to claim 10, comprising maintaining the tube under tension during its being wound around the tank and maintaining the tube under tension on completion of said winding by securing the tube to the tank.

12. A method according to claim 11, comprising fastening the tube to the tank at a plurality of locations along the length of the tube.

13. A method according to any one of claims 10 to 12, comprising providing a heat transfer facilitating material between the heat exchanger tube and the tank.

14. A method of manufacturing a water heater, comprising: performing the method of any one of claims 10 to 13; providing a heat pump circuit comprising: an evaporator for exposure to ambient air, a compressor downstream of the evaporator, 13 a condenser downstream of the compressor, the condenser comprising said heat exchanger tube, and an expansion device downstream of the condenser; encasing the tank, the heat exchanger tube and the barrier in a housing and providing a space between the barrier and the housing; and installing thermal insulation into the space between the barrier and the housing, wherein the barrier inhibits the thermal insulation from squeezing between the heat exchanger tube and the tank during installation of the insulation.

15. A method according to claim 14, wherein the thermal insulation is injected into the space between the barrier and the housing.