AU2008271930B2

AU2008271930B2 - Water heating apparatus, especially for pools

Info

Publication number: AU2008271930B2
Application number: AU2008271930A
Authority: AU
Inventors: Darren William Ford; Peter Ronald Wallace
Original assignee: Astral Pool Australia Pty Ltd
Current assignee: Astral Pool Australia Pty Ltd
Priority date: 2007-07-04
Filing date: 2008-07-04
Publication date: 2012-03-22
Anticipated expiration: 2028-07-04
Also published as: US20100170452A1; WO2009003244A1; NZ582223A; AU2008271930A1; NZ616544A; NZ601752A

Abstract

A water heater for heating water includes a burner assembly (54) for generating a flow of hot gas. The burner assembly (54) includes a gas burner (52) and means (64) adjustable to determine a heat output of the burner assembly (54). The water heater further includes a heat exchanger assembly (20) for transferring heat from gas to water flowing therein. The heat exchanger assembly (20) has a higher temperature zone (110) and a lower temperature zone (100). The water heater is arranged to convey the flow of hot gas to the higher temperature zone (110) and in turn to the lower temperature zone (100). The water heater further includes ducting (22, 23) to conduct said flowing water to and from said heat exchanger assembly (20), means (40) to monitor the temperature of the hot gas intermediate the higher temperature zone (110) and the lower temperature zone (100), and control means (70) responsive to the temperature monitoring means (40) to modulate the heat output of the burner assembly (54) whereby to maintain the monitored temperature within a predetermined range so as to substantially prevent or minimise condensation of vapour from the hot gas in the higher temperature zone (110). There is also disclosed a modular heat exchanger apparatus (20) including like headers (34) for redirecting fluid within respective modules (24) and for interconnecting modules (24). There is also disclosed a water heater having a condensate duct (84) to direct condensate into the water for chemically treating the water.

Description

1 Water heating apparatus, especially for pools Field of the invention This invention relates generally to heating equipment, but has particularly useful application to pool and spa heaters. Respective aspects of the invention are concerned 5 with a novel configuration of water heater, with a heat exchanger arrangement some embodiments of which are useful in pool and spa heaters, and with a practical use for the condensate that is a by-product of certain types of water heaters. Throughout this specification, the term "pool" includes in its ambit any kind of confined water body in which humans can be immersed, including spas, swim spas and Japanese 0 style immersion tubs. Background of the invention Pool heating is conventionally effected either by circulating the pool water through solar panels, typically roof-mounted, or by means of gas-fired water heaters. Water heaters for this purpose are designed to heat a continuous flow of water circulated from the pool to a 5 target temperature in a range comfortable for swimming, and so the requirements differ considerably from, for example, hot water services, where a static body of water is heated in a tank to a relatively high temperature, and hydronic central heating systems, where a flow of water is heated but the total volume of water is much less and the target temperature significantly higher. 20 Conventional pool heaters typically have a gas burner assembly that generates a hot gas flow employed to heat the water as it traverses multiple tubes in a heat exchanger. Because of the relatively high water volume and relatively low water temperature, these systems must address the problem of condensation in the gas stream as it passes among the heat exchanger tubes: the condensate is slightly acidic because of the uptake of 25 combustion products, and is therefore a corrosive by-product. A popular material for the heat exchanger tubes is cupronickel, which is especially susceptible to corrosion by the condensate. Modern pool heater controllers advantageously receive a measurement of the pool water temperature, and thermostatically control the operation of the heater, and as the pool 30 water temperature approaches a desired temperature, modulate the heater down to a very 2 low power level to maintain the pool water temperature without noticeable stopping and starting of the heater. It has been discovered that operation at this very low power level results in low flue temperatures such that condensation and corrosion is particularly problematic. 5 The common approach to corrosion prevention is to design the heater so that at the maximum water flow condition, minimum water temperature and a predetermined gas flow rate the temperature in the heat exchanger remains above the dew point temperature at which condensation begins to occur. Water flow is typically reduced through the heat exchanger by diverting a proportion of the flow via a bypass. This approach places limits [0 on the efficiency achievable with the overall heater configuration. Two publications that illustrate known approaches to corrosion prevention are European patent publication 0226534 and Japanese published (Kokai) application 11351559. It is an object of the invention, at least in one or more aspects or applications, to improve the efficiency of pool heater systems. [5 Summary of the invention Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a 20 person skilled in the art. The invention involves a different approach to temperature management in the heat exchanger. The invention accordingly provides a water heater for heating water, including: a burner assembly for generating a flow of hot gas, which burner assembly includes 25 a gas burner and means adjustable to determine a heat output of the bumer assembly; a heat exchanger assembly for transferring heat from gas to water flowing therein, wherein the heat exchanger assembly has a higher temperature zone and a lower temperature zone, the water heater being arranged to convey the flow of hot gas to the higher temperature zone and in turn to the lower temperature zone; 3 ducting to conduct said flowing water to and from said heat exchanger assembly; means to monitor the temperature of the hot gas intermediate the higher temperature zone and the lower temperature zone; and control means responsive to said temperature monitoring means to modulate the 5 heat output of the burner assembly whereby to maintain the monitored temperature within a predetermined range so as to substantially prevent or minimise condensation of vapour from the hot gas in the higher temperature zone. By modulating the heat output of the burner the monitored temperature can be maintained within a pre-determined range without reducing the volume of water flowing through the [0 heat exchanger thereby improving efficiency. It is desirable to minimise said monitored temperature in order to maximise efficiency. Preferably said means to monitor the temperature of the hot gas is mounted closer to the lower temperature zone than to the higher temperature zone. The configuration is preferably such that the hot gas is directed downwardly from the 15 burner assembly through the heat exchanger assembly to traverse the higher temperature zone and then the lower temperature zone. Means is advantageously provided under the heat exchanger assembly for collecting condensate that forms in said lower temperature zone. 20 Brief description of the drawings The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a pool heater according to an embodiment of the invention, as viewed without its exterior decorative housing; 25 Figure 2 is a rear view of the pool heater depicted in Figure 1 with some parts omitted for a better view and with the condensate venturi additionally shown in place; 4 Figure 3 is a vertical, generally central cross-section of the pool heater depicted in Figures 1 and 2, with most of the heat exchanger tubes omitted for the purpose of illustration; Figures 4 and 5 are different perspective views of the heat exchanger assembly; 5 Figure 6 is a view of the heat exchanger assembly, and with many of the upper bank of tubes omitted; Figure 7 is a plan view of the heat exchanger assembly; Figure 8 is a cross-section on the line 8-8 in Figure 7; Figure 9 is a simplified schematic diagram of the burner control loop incorporating a .0 temperature sensor in the heat exchanger assembly; 5 5 10 THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK 6 5 L0 THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK WO 2009/003244 PCT/AU2008/000987 7 Figures 10 and 11 are respectively a perspective view and an end elevation of a larger heat exchanger assembly with four banks of tubes; Figure 12 is a rear view one embodiment of the third aspect of the invention entailing recycling of condensate collected from the heat exchanger assembly; 5 Figure 13 is a fragmentary axial cross-section view of the condensate venturi forming part of the embodiment of Figure 12; Figure 14 is a rear view of an alternative embodiment of the condensate recycling concept; Figure 15A is a perspective view of an embodiment of the return header; 10 Figures 15B and 15C are perspective cut away views of the header of Figure 15A; Figure 16 is a perspective view an embodiment of the tray; Figure 17 is a rear view of a further alternative embodiment of the condensate recycling concept; and 15 Figure 18 is a rear view of a further alternative embodiment of the condensate recycling concept. Detailed description of the embodiments of the invention The illustrated pool heater 10 is a stacked assembly of four principal components: a tray 80 over which is fitted a heat exchanger assembly 20 on which is mounted a firebox 50, 20 which is in turn capped by a fan unit 60 that includes a controller 70 with an external interface 72 and a lid 62 that is removable for access. Tray 80 sits in plastic base 12. Tray 80 is a unitary casting and, as will be further explained below, serves as a condensate collection tray. Tray 80 sealingly communicates with a flue 82 that extends WO 2009/003244 PCT/AU2008/000987 8 upwardly behind the heat exchanger assembly 20, firebox 50 and fan unit 60 to a flue outlet 83. In situ and in operation, pool water is circulated by a separate pump installation to a water intake port 22 and recovered from outlet 23. A fan 64 within fan unit 60 draws in a 5 correctly proportioned combustible mixture of gas (delivered via line 65) and air, and delivers the mixture to a gas burner 52 at the top of firebox 50. The gas burner 52 and the fan unit 60 together form a burner assembly 54 (Figure 3) that generates a downwardly directed flow of hot gas. This flow is received by the heat exchanger assembly 20 where heat is transferred from the hot gas to pool water flowing therein. 10 The burner 52 is of the premix type and includes a knitted mesh. Below the heat exchanger 20, the hot gas is guided laterally by the shaped tray 80 to the base of flue 82 and thence up the flue. Fan 64 constitutes a means that is adjustable to vary the volume of gas and air directed to the burner 52 and so determines the heat output of the burner. The fan 64 and gas 15 burner 52 together constitute a burner assembly for generating a flow of hot gas. The construction of heat exchanger assembly 20 is detailed in Figures 4 to 8. A simple box 24 of front, rear and side flanged plates 24a, 24b, 24c provides a suitable chassis. Side plates 24b, 24c have two rows of apertures 25a and 25b that communicate with the interior of heat exchange tubes 27, 29 arrange in respective lower and upper banks 20 26, 28. At one side plate 24b, there are fitted respective inlet and outlet headers 30, 32 that define a manifold space respectively communicating the lower and upper apertures 25 and therefore the lower tubes 27 and upper tubes 29 to water inlet ports 22, 23. At the other side plate 24c, there is a return header 34, a suitably profiled moulding that defines a manifold space for communicating the lower of apertures 25a with the upper 25 row 25b. Vanes 31 are placed between the tubes 27, 29 to deflect the gas flow and improve the heat transference to tubes 27, 29. A convenient method for assembling the module like box 24 involves forming side plates 24b and 24c with apertures 25a, 25b being slightly oversized, e.g. 0.1mm, to receive the tubes 27, 29. Tubes 27, 29 are inserted into apertures 25a, 25b and a 9 rotary swage used to expand the tubes to form an interference with sideplates 24b, 24c. An advantage of certain embodiments of the second aspect of the invention is that large heat exchangers can be economically built up of several modules each having two rows. The tubes of a two row module are easily gripped to prevent rotation during the rotary 5 swaging operation. Although modules having two rows defining U-shaped flow paths are illustrated, other arrangements are possible. For example, a module having three rows defining an S-shape flow path is an option. Return header 34 is shown in more detail in Figures 15A to 15C. Apertures 35 are 10 connected by cavity 37 and include a recess to receive a sealing washer (not shown) to sealingly engage with individual tubes 27, 29. The regular spacing of bolt locations 36 allows the header to securely press the sealing washers with less risk of leakage due to warping of the header. This advantageously allows for a cheaper moulded plastic (instead of cast metal) construction. 15 It will be seen that because the cooler water traverses the lower bank of tubes 27 and then the upper bank of tubes 29, the lower bank 26 constitutes a lower temperature zone 100 of the heat exchanger assembly and the upper bank 28 constitutes a higher temperature zone 110. Accordingly, the respective banks of tubes are formed of differing materials: the lower tubes 27 are aluminium-sheathed stainless steel tubes, while the upper tubes 29 are 20 of cupronickel alloy. It will be seen that the descending flow of hot gas will pass through and about tubes 29 first and then, in a cooler state, through and about tubes 27. The cupronickel tubes 29 are effective heat exchange elements at higher temperatures but are highly susceptible to corrosion by any condensate that forms on them in the gas flow, while the aluminium/stainless steel tubes 27 are resistant to condensate corrosion 25 but degrade at relatively low elevated temperatures. Accordingly, the temperature profile in the gas stream across the heat exchanger is managed to accommodate these characteristics. Temperature sensor 40 (Figure 8) is located on the vertically centred plane of the heat exchanger WO 2009/003244 PCT/AU2008/000987 10 assembly inwardly from side panel 24c between the respective banks 26, 28 of heat exchange tubes. The sensor output is delivered to controller 70 which adjusts the fan 64 to determine the heat output of burner 52 in response to various inputs including sensor 40. Other inputs may include a desired water temperature manually entered at 5 interface 72, and actual water temperature measured by sensor 73 on inlet header 32. A suitable controller is a Genus PCB controller. A diagram of the main elements of the burner control loop is presented in Figure 9. In particular, controller 70 is responsive to temperature sensor 40 (monitoring the temperature at its location in the heat exchanger assembly), to operate fan 64 so as to 10 modulate the heat output of burner 52, whereby to maintain the monitored temperature at sensor 40 within a predetermined set point range. This range is between a minimum selected so that the gas temperature in the higher temperature zone 110 remains above the dew point condensation temperature, and a maximum is determined so that, inter alia, the temperature of the gas delivered into the lower temperature zone 100 is not so 15 high as to damage aluminium/stainless steel tubes 27. In the former case, condensation of vapour from the gas is substantially prevented or minimised in the higher temperature zone 110 of the heat exchanger assembly. Figures 10 and 11 illustrate the manner in which the heat exchanger construction is readily adaptable to provide higher capacity heat exchangers. In the heat exchanger of 20 Figures 4 to 8, the side plates 24b, 24c and tubes 27, 29 constitute a heat exchange module 105. By forming the box chassis 24 from two of these modules 105a, 105b fixed between front and rear plates 24a of double height, comprising four banks 126, 128 of tubes 127, 129 can be provided. In this case, the lower and higher temperature zones are defined by the respective modules 105a, 105b. 25 This modular approach to enlarging the capacity of the heat exchanger means that three identical return headers 34 can be utilised as illustrated to direct water between the tubes of the two lower banks and between the tubes of the two upper banks, and also, on the other side of the box chassis 24, from the tubes of the lower, 11 aluminium/stainless steel tubes to the upper cupronickel tubes. The inlet and outlet headers 30, 32 are identical to the inlet headers 30, 32 depicted in Figures 4 to 6. The illustrated configuration of water heater, including the two-stage heat exchanger configuration and the control of burner heat output in response to monitoring of the 5 temperature in the heat exchanger, together result in a pool heater system of significantly higher efficiency than the earlier described conventional arrangements. Full volume water flow, say up to 400 [/min is maintained without periodic bypassing and burner output is matched with the desired set point gas temperature range in the heat exchanger. Condensation is accepted and properly managed by employing a two-stage L0 heat exchanger in which the materials of the heat exchange elements are selected to suit the respective higher and lower temperature zones. A further preferred aspect of the invention is concerned with the novel usage for the condensate collected in tray 80 which is depicted in more detail in Figure 16. The concept is that this condensate, which contains traces of combustion by-products and is thereby 15 slightly acidic, is recycled to the pool water as an effective chemical treatment. There are various ways in which this can be done. In the first (illustrated in Figures 12 and 13), a suitably dimensioned conduit 84 communicates the sump 81 via outlet 89 of tray 80 (see Figure 16) with the feed port 86 of a venturi suction device 87 fitted within water outlet port 23. Conduit 84 includes solenoid valve 85 for selectively determining when condensate 20 can flow to the venturi. The solenoid valve 85 is used to close conduit 84 when the heater 10 and pump are not in use to prevent water flowing through conduit 84 to tray 80. A suitable construction for the venturi 87 is illustrated in Figure 13: it will be seen that the feed port 86 at the end of conduit 84 communicates with a chamber 87 from which an aperture 88 opens into the neck of the venturi. 25 A float sensor (not shown) may be associated with the sump 81 to detect blockage of the outlet 89 or conduit 84. In the alternative condensate recycling arrangement depicted in Figure 14, a drain hose 90 from sump 81 conveys the condensate to a storage reservoir 92 from which WO 2009/003244 PCT/AU2008/000987 12 condensate is selectively drawn via a tube 93 by a dosing unit 94 for delivery at an insertion point 98 in the pool water return pipe 96 downstream of water heater 10. In a further alternative embodiment illustrated in Figure 17 the drain hose 90 is selectively closed by the solenoid valve 201. Downstream along the drain hose 90 from 5 the solenoid valve 201 is the condensate pump 202. The condensate pump 202 may be activated and the solenoid valve 201 opened to drive condensate collected in the tray 80 through the pump discharge line 203. The pump discharge line 203 extends from the pump 202 to a suction tee 204 positioned along the return pipe 96 downstream of water heater 10. The use of the solenoid valve 201 prevents water back feeding from the 10 return pipe 96 to the tray 80. Figure 18 illustrates a further alternative embodiment which includes a collector reservoir 210 interposed between the tray 80 and the solenoid valve 201 along the drain hose 90 to store condensate. A condensate suction line 211 extends from the solenoid valve 201 to a suction tee 212. The suction tee 212 is fitted to an inlet line 214 for 15 supplying water to the water intake port 22. A pump 213 is positioned along the inlet line 214 to draw water from the swimming pool and drive the water through the heat exchanger 20 (the water is in turn returned to the pool via the return pipe 96). The suction tee 212 is thereby in a low pressure region upstream of the pump 213 and in addition is configured to create some venturi effect so that condensate may be drawn 20 into the inlet pipe 214 when the solenoid valve 201 is open. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A water heater for heating water, including: a burner assembly for generating a flow of hot gas, which burner assembly includes a gas burner and means adjustable to determine a heat output of the burner 5 assembly; a heat exchanger assembly for transferring heat from gas to water flowing therein, wherein the heat exchanger assembly has a higher temperature zone and a lower temperature zone, the water heater being arranged to convey the flow of hot gas to the higher temperature zone and in turn to the lower temperature zone; 10 ducting to conduct said flowing water to and from said heat exchanger assembly; means to monitor the temperature of the hot gas intermediate the higher temperature zone and the lower temperature zone; and control means responsive to said temperature monitoring means to modulate the heat output of the burner assembly whereby to maintain the monitored temperature 15 within a predetermined range so as to substantially prevent or minimise condensation of vapour from the hot gas in the higher temperature zone.

2. A water heater according to claim 1 wherein use the monitored temperature is maintained within a pre-determined range without reducing the volume of water flowing through the heat exchanger. 20

3. A water heater according to claim 1 or 2 wherein said control means is operable to minimize said monitored temperature.

4. A water heater according to any one of claims 1 to 3 wherein said means to monitor the temperature of the hot gas is mounted closer to the lower temperature zone than to the higher temperature zone. WO 2009/003244 PCT/AU2008/000987 14

5. A water heater according to any one of claims 1 to 4 wherein the lower temperature zone and the higher temperature zone each have tubes for carrying water through the flow of hot gas, the tubes of the lower temperature zone and the higher temperature zone being formed of materials that respectively suit lower temperature 5 operation and higher temperature operation.

6. A water heater according to claim 5 wherein the tubes of the lower temperature zone are formed of aluminium sheathed stainless steel and the tubes of the higher temperature zone are formed of cupronickel.

7. A water heater according to claim 5 wherein the tubes of the higher temperature 10 zone are formed of copper.

8. A water heater according to any one of claims 1 to 7 configured for the flow of hot gas to travel downwardly from the burner assembly through the higher temperature zone and in turn through the lower temperature zone.

9. A water heater according to any one of claims 1 to 8 having means to collect 15 condensate produced from condensation of gas in said lower temperature zone.

10. A water heater according to claim 9 including a condensate duct arranged to direct said condensate into the water for chemically treating the water.

11. A water heater according to claim 10 wherein the condensate duct is arranged to direct said condensate into the ducting from the heat exchanger assembly. 20

12. A water heater according to claim 10 wherein the condensate duct is arranged to direct condensate into the water upstream of a pump arranged to drive water through the water heater.

13. A water heater according to claim 10, 11 or 12 including a venturi to draw said condensate into the water. 15

14. A water heater according to claim 10, 11 or 12 including a suction tee to draw the condensate into the water.

15. A water heater according to any one of claims 9 to 14 including a pump arranged to receive condensate from said means to collect condensate and drive said condensate 5 through said condensate duct.

16. A water heater according to claim 9 including a dosing apparatus for storing and selectively directing metered amounts of condensate into the water at any suitable location.