AU2003200337A1 - Improvement in indirect heated hot water systems - Google Patents

Description

31-JAN-2003(FRI) 16:51 M A Martin and Associates (FAX)61 2 9818 4900 P. 005/036

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: THERMAL-ZERO PTY LTD Actual Inventor. ALBERT E MERRYFULL Address for Service: M A Martin Associates Locked Bag 290 Banmain 2041 Sydney NSW Australia Invention Title: Improvement In Indirect Heated Hot Water Systems The following statement is a full description of this invention, including the best method of performing it known to me/us: 2823-raujesLdoc 31-JAN-2003(FRI) 16:51 M A Martin and Associates (FAX)61 2 9818 4900 P.006/036 2823-i .doc 1

TITLE

FIELD OF INVENIMON This invention relates to indirect water heating systems and more particulariy to improvements in efficiency, longevity and usability of such systems.

s BACKGROUND Indirect water heating systems do not heat the potable water directly but utilise one or more intermedi ate fluids to transfer heat from a heat source to the potable water.

Typical heat sources include heat pumps and solar panels, although gas burners are also used. Typical intermediate fluids include refrigerant gases, water and glycol.

in A typical installation may utilise a heat pump to both cool air and provide hot water.

Normal indirect water heating systems include an open topped tank that contains a body of static fluid, usually water. Located in the tank are two coils, one carying potable water to be heated and the other carrying a heating fluid heated by the heat 1c pump. The heated fluid transfers some of its heat to the static fluid and in turn the static fluid transfers some of its heat to the potable water.

When providing hot water, the static fluid is usually heated to a temperature in the range of 65 0 C to 85 0 C. This means the heating fluid leaves the tank at about this temperature and so, without additional cooling, the difference in temperature between the inlets and outlets of the heat pump is low. The temperature drop of the heating fluid within the water tankc is also relatively low, so the amnount of heat transferred also from the heating fluid to the static fluid is quite low.

In addition, where the system provides a cooling fuinction as well as a heating function, it is desirable to reduce the temperature of the refrigerant fluid to as low a temperature as practicable before expanding it to cool air or water. A high temperature of the fluid at entry to an expansion valve results in a higher 31-JAN-2003(FRI) 16:52 M A Martin and Associates (FAX)B1 2 9318 4900 P.007/036 28n3-I1,nc 2 temperature after expansion and correspondingly less cooling effect. This can be overcome by cooling the refrigerant between the water tank and the expansion valve, but this results in heat being discharged to the environment and wasted.

Existing indirect water heating tanks typically utilise plastics pipes for the potable s, water heat exchanger without anything to hold and separate adjacent windings of the coils. The lack of separation and the use of plastics reduce heat transfer rates.

The coils usually have no permanent support and so a loose and unwieldy coil of plastics pipe in the tank complicates any maintenance. Copper pipes have been used but typically with spacers welded to the tube walls. Over time, the thermally generated expansion and contraction of the tubing and spacers causes the wall of the tubing to fail.

Indirect water heating systems heat the potable water as it flows through the heat exchanger. Low rates of heat transfer limit the maximum flow rate of the potable water. Lowering the temperature of the refigerant more than otherwise using the is potable waterr results in more heat transferfed to the potable water and more heat transfent~d, so raising the overall efficiency of the system; lIess heat is wasted by being transferred to the ambient environment.

Existing open topped indirect hot water heating tanks have a lid that is sealed against the tank. A gasket is provided to aid in sealing and this is attached to the 2a tank. The current sealing arrangements are not satisfactory as when raising the lid, the gasket frequently adheres to the lid and detaches from the tank. Attachment of the gasket to the tank is not easy.

SUNMIARY OF INVENTON In one broad trm the invention provides a heat exchange system that transfers heat between a first fluid and a second fluid, the system including: a first heat exchanger including: 31-JAN-2003(FRI) 16:52 MI A Mar±in and Associates (FAX)61 2 8818 4906 P.008/036 1 2823- I.oc 3 a first inlet for the first fluid; a second inlet for the second fluid; a first outlet for the firt fluid; a second outlet for the second fluid; and a second heat exchanger including: a third inlet for the first fluid; a fourth inlet for the second fluid; a third outlet for the first fluid; a fourth outlet for the second fluid, Wherein, the third inlet receives first -fluid from the first outlet and the second inlet receives second fluid fromn the fourth outlet.

The first heat exchanger may be an indirect heat exchanger utilising an intermediate fluid.

The second heat exchanger may be a reverse flow heat exchanger.

The first heat exchanger may include: a tank; a third fluid within the tanl-, at least one first pipe extending between the first inlet and first outlet and extending at least partially within the third fluid, and at lecast one second pipe extending between the second inlet and second outlet and extending at least partially within the third fluid.

31 -JAN-2003 (FR I) 16:52 M A Martin and Associates (FAX) 61 2 9818 4900 P. 009/036 2823-1 .doc 4 Preferably the at least one first pipe is coiled. The at least one second pipe is arranged in an elongate helix, The systemn may include at least one spacer clip attached to the coils of the at least one second pipe, the or each said at least one spacer clip attaching to at least one a pair of coils to separate the coils from each other.

The at least one second pipe may include at least two concentric elongate coils and the at least one spacer clip includes at least one spacer clip attached to at least one coil of at least two of said at least two concentric coils to separate the coils from each other.

in The at least one spacer clip may include a body having at least two recesses adapted to receive a pipe and to grip the pipe.

Preferably each recess has an interior portion and an opening, the opening sized to require deformation of the recess to receive a pipe within the recess. The reces may be generally circular or rectangular. The recess may be rectangular and have a 18 back wall and two, generally opposed side walls extending from the back wall The sidewalls may be substantially parallel or may diverge away from the back wall.

The clips may be comprised of bent wire or rod.

The system may also including at least one hollow reservoir within the first tank, the interior of at least one reservoir being in fluid communication with at least one of the second in let and the second outlet.

In a second broad form the invention provides an indirect hot water heating apparatus including: an tank having an opening; a l id that engages the opening of the tank and a gasket sandwiched between the tank and the lid, 31 -JAN-2003 (FRI) 16:52 M A Martin and Associates (FAX) 61 2 9818 4900 P. 010/038 1 283-I.doc wherein the opening is defined by at least one wall of the tank, the wall defining part of an annualar groove that extends outwardly from adjacent the opening, the gasket having a complementary annular tongue that engages the annular groove.

Pretbrably the annular groove extends outwardly.

s The tank may have an inner wall and an outer wall surrounding the inner wall and wherein the inner wall has a first annular portion extending outwardly from a free end portion and the outer wall has a second annular portion extending inwardly toward the inner wa~l adjacent the first annular portion, said first and second annular portions defining opposing walls of the groove.

'to The tank may have inner wall has a first annular portion extending outwardly from a free end portion and a second annular portion extending outwardly adjacent the first annular portion, said first and second annular portions defning opposing walls of the groove.

In a third broad form the invention provides a clip for separating windings of a is heat exchanger coil, the clip having a series of spaced apart recesses, each adapted to engage part of each winding and to maintain adjacent windings separated.

Preferably at least one of the recesses is generally part circular and preferably at least one of the recesses has an arcuate surface that extends for more than 180 degrees. Most preferably at least one of the recesses has an arcuate surface that extends for more than 300 degrees.

At least one of t recesses may have a general ly rectangular shape.

At least one of the recesses may be defined by a rear surface, two spaced apart and opposed side surfaces and an opening, the side surfaces extending from the rear surface to the opening. The side surfaces may be parallel or may diverge from each 2s other away from the rear surface.

3l-JAN-2003(FRI) 16:53 M A Martin and Associates (FAX)61 2 9818 4900 P.011/036 282- 1-4cr 6 The invention will be better understood ftom the following non-limiting description of preferred embodiments of the invention and the drawings.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a side view of a typical prior art indirect water-heating tank; Figure 2 is a schematic diagram showing an indirect hot water heating system according to a first embodiment of the invention; Figure 3 is a side view of a first spacer for use with tubing, such as in an indirect hot water heating tank; Figure 4 is a side view of a second spacer for use with tubing such as in an lo indirect hot water heating tank; Figure 5 is a side view of a third spacer for use with tubing such as in an indirect hot water heating tank; Figure 6 is a side view of a fourth spacer for use with tubing, such as in an indirect hot water heating tank; Figure 7 is a plan view from above of an indirect hot water heating tank with its lid removed showing the arrangement of the coils; Figure 8 is an axial cross-sectioned view of a part of the tank of figure 7.

Figure 9 is a cross sectional view of an indirect hot water heating tank according to another aspect of the invention; 2o Figure 10 is a plan view from above of the tank of figure 9.

Figure 11I is a cross sectional view of the top edge of the tank of figure 9 according to a first embodiment.

Figure 12 is a cross sectional view of the top edge of the tank of figure 9 according to a second embodiment.

31-JAN-2003(ERI) 16:53 M A Martin and Associates (FAX)61 2 9813 4900 P.012/038 1 283-) .doc 7 DETAI1LED DESCRIPTION OF PREFERRED AND OTHER

EMBODIMENTS

Referring to figure 1 there is shown a typical indirect hot water heating tank The tank 10 is normally cylindrical, but may the square, rectangular or oval when s vieowed froam above. The tank is not permanently sealed but is provided wit a removable lid 14. The lid 14 is attached to tile body 12 of the tank 10 with fasteners (not shown), with the joint therebetween sealed with a gasket 16.

Locrated within the tank 10 are a body of static fluid 18, usually water, coils carrying potable water and a coil 22 carrying a heating fluid. The heating fluid io passes through the coil 22, heating the static fluid 18, which in turn heats potable water as it flows through the coil The coil 20 is typically made of polyethylene or polypropylene plastics materials and, as can be seen, is typically not provided with any support structure. This results in the spirals of the coil resting on each other and so reducing the effective is area for heat transfer and movement of water past the coils. The tank 10 may also include an electric heater 19 that is used to boost the heating of the static water.

Referring to figures 3 to 6 there are shown a number of coil spacers that may be utilised to support and separate the coils of a heat exchanger, such as used in an indict water-heating tank.

2o The spacers 40 and 42 of figures 3 and 4 respectively are intended for use with either copper or plastics pipe. The spacers comprise a piece of stiff wire or rod bent, preferably formed of stainless steel, into the shapes shown. Each spacer has a series of part circular holding portions 44 separated by a spacing portion 46 between adjacent spacing portions. The holding portions are for receiving the a tubing of a heat exchanger coils and extend about an arc for approximately 300 degrees. This leaves a throat or opening 48 that is slightly smaller than the outside dimeter of the pipe 49 used. The length of the spacing portion is such to give a suitable separation 51 between the tube centres. When used with 19.05mm outside 31-JAN-2003(FRJ) 16:53 M A Martin and Associates (FAX)61 2 9818 4900 R.0i3/038 8 diameter pipe, a spacing 51 between centres of 30 mm~ may be used. Closer or wider spacings may be used. With 19 rnu outside diameter pipe the opening 48 is about 18.5mnm.

The pipe 49 is easily inserted into the holding portions. The wire is chosen of a s material and diameter so that it will flex and expand the opening 48 to allow a relatively rigid pipe, such as copper pipe, to be placed within the holding portion.

When a relatively flexible pipe, such as a plastics pipe is used, the pipe may flex rather than the spacer or both the spacer and the pipe may flex.

The first spacer 40 is designed to be attached verticay to the coils to space the lo windings vertically. Typically a circular coiled heat exchanger will have four spacers attached, arranged at 900 to each other round the circumference. More than four vertical spacers may be used, particularly for an oval shaped coil. When a heat exchanger has three or more such spacers attached to the coils, relative movement of the coils to each other is effectively prevented in both the vertical and horizontal directions and a single coil heat exchanged may easily be manipulated. Where the heat exchanger is oval it will be appreciated that extra spacers 40 may be used. It will be noted that the lower end 50 of the spacer includes a horizontal foot 52 that in use rests on the base of the beating tank. The foot 52 extends underneath the tubing and so does not increase the horizontal space 2o require for the coil. The feet of the spacers thus provide some extra stability to the coil.

The second spacer 42 is designed where the exchanger has multiple, concentric windings. In such a situation each coil will have its own set of vertical spacers The concentric coils are then separated from each other by sets of horizontal 2B spacers 42 attached to the upper-most and lowermost portions of the coils. This holds the concentric coils away from each other in a relatively rigid manner.

Figures 5 and 6 show a second set of' spacers, 60 and 62, respectively. The spacer is a vertical spacer and functions in a similar manner to the spacer 40 of figuire 31-JAN-2003(FRI) 18:53 MI A Martin and Associates (FAX)61 2 9818 4900 R.014/036 28123-1 .o 9 3. Spacer 62 is a horizontal spacer and functions similarly to the spacer 42 of Figure 4.

The spacer 60 is formed with a generally rectangular holding portion 64 separated by spacing portions 66 between adjacent holding portions. Each holding portion includes two generally opposed sections 68 and a generally transverse section therebetween. The two opposed sections 68 extend at substantially 9f0* to the transvere section 70 anid are substantially parallel to each other. The length of the transverse section 70 is such that the separation 72 of the two opposed sections is less than the diameter of the tubing being used. If copper tubing is being used, the spacing is only slightly less, than the outside diameter of the tubing. To mount the spacer on the coil one merely pushes the tubing into the opening.74, causing each of the two horizontal sections to flex and/or bend at the junction with the vertical portion. The separation 72 is chosen to allow easy insertion of the tubing Whilst providing sufficient grip due to compressive forces on the tube to hold it in the is spacer.

When used with tubing of plastics materials, the opening 74 may need to be appreciably les than the outside diameter of the tube to provide sufficient grip, due to the greater flexibility of the tubing.

The spacer 62 shown in figure 6 differs slightly from the spacer 60 of figure 5. The spacer includes holding portions 75, each of which includes opposed side arms 76 between the back section 78 and the spacing portions 80. The two side arms 76 are angled toward each other so the opening 82 is smaller than the back portion 78.

This aids in retaining a tube in the holding portion 75, as removal of the tube from the opening requires the two anns 76 to be bent away from each other to increase the size of the opening 82. This configuration is relatively easier to manufacture tha the arrangement of figures 3 and 4 whilst providing a similar functionality.

It will be appreciated that the arrangement of the holding portions of the spacers and 62 may be applied to the other device.

31-JAN-2003(FRI) 16:54 M A Martin and Associates (FAX)61 2 9818 4900 P.015/036 1 Z2CZ-1 .doc It will be appreciated that the number of holding portions on each spacer will be chosen to suit the heat exchanger and are not limited to the numbers shown in the drawings. It will be appreciated that the spacers may be made of materials other than metal and that a wire configuration is not necessary. For example, the spacers may be made of a relatively stiff sheet of plastics material with the holding reesses formed in an edge of the sheet.

Referring to figure 7 there is shown a plan view of an oval shaped open topped hot water tank 80. The tank has five heat exchanger coils 82 arranged concentrically about the outside portion within the tank. The five coils may be for a single heat lo exchanger, such as the potable water heat exchanger or the refrigerant heat exchanger or may be for both heat exchangers. The coils are secured together by horizontal clips 84 and vertical clips 86. For clarity only one set of vertical clips 86 is shown. There are a series of clips 86 located round the sets of coils. The horizontal clips 84 may be of the types atf figures 3 or 5 and the vertical clips 86 may be of the type of -figures 4 or 6.

Figure 7 also shows a two potable water storage tanks 88 located within the tank The tanks are cylindrical and extend the height of the tank 80. The tanks may be made of a suitable metal, such as a heavy grade of copper. A suitable size of tank 88 in a tank 80 that has internal dimensions of about 1200 mmn by 800 mm 2o in plan view is about 100 mm diameter. The tanks 8 8 are connected to the potable water supply by suitable valves and controls (not shown) and are provided as a backup supply for peak periods. Figure 8 shows a axial cross-sectioned view of one of these tanks 88. each tank has a diameter 89 ranging from about 50 to 150 mm and a height 91 ranging from about 800 to 1500 mm. An inlet pipe 93 has an a exit 95 near the base 97 of the tank through which potable water enters the tank 88.

An outlet 99, located in the top 10 1 of the tank is provided to remove hot water.

Indirect hot water systems have a maximum continuous flow rate, which is the maximum flow of potable water that can be passed through the system without the outlet temperature -falling below a set value. This is dependent on a number of 31-JAN-2003(FRI) 16:54 M A Martin and Associates (FAX)61 2 9818 4900 P.016/038 I factors, including the rate at which heat is transferred from the static water in the tank to the potablIe water in the heat exchanger, the rate at which heat is transferred from the refrigerant to the static water and the inlet temperature of the potable water.

s Once the water flow exceeds the maximum continuos flow rate, the temperature will fall below the set value. If the maximum heat flow to the potale water from the static water exceeds the maximum heat flow into the static water from the refrigerant then the static water will slowly cool. If the maximum heat flow to the potable water from the static water is less than the maximum heat flow into the lo static water from the refrigerant then the static water will remain at its maximum temperature. This is, obviously a mater of choice as to the design of the heat exchangers.

Where the potable water heat exchanger or the potable water inlet temperature limits the maximum water flow, increasing the beat transfer rate of the potable i s water heat exchanger or the inlet temperature will increase the maximum continuous flow rate possible.

When the demand for hot water is low, the static water is maintained at its maximum temperature and the water in the storage tanks is heated to and maintained at that temperature. In the event that the demand for hot water is such that the water flowing though the heat exchanger cannot be heated to the required temperature, water may be taken from the tanks 88, either totally or together with water flowing through the heat exchanger. Over a short period of "excess" flow, the static water will not cool greatly and so will not cool the water in the storage tanks 88 greatly. Obviously potable water will flow into the storage tanks 88 and 2e after most of the hot water in the tanks has been removed, the water in the tanks 8 8 will be relatively cold. By monitoring the temperatures of the potable water at the outlet of the heat exchanger and the storage tanks 8B, the system can cease'takcing water from the storage tanks 88 when the temnperature of water from the storage tanks 88 is less than the temperature of water fr-om the outlet of the heat exchanger.

81-JAN-2003(FRI) 16:54 H A Ma-tin and Associates (FAX)61 2 9818 4900 P. 017/036 1 2823.o 12 Once the demrand for hot water falls below the maximum continuous sustainable flow, the temperature of the static water and the water in the storage tanks 88 will return to the set maximum, An alternative arrangement is that the storage tanks 88 are in series with the potable water heat exchanger. Potable water will flow into the s heat exchanger and then into the storage tanks 88 before exiting the system. Thus there will always be a quantity of hot water that maybe extracted at that steady state temperature, irrespective of the flow rate.

Referring to figure 2 there is shown an indirect hot water heating system 100 according to an embodiment of the invention, The system 100 acts as an add-on to io an existing refrigeration system and replaces or supplements the heat dissipation side of the refrigeration system. Accordingly the system 100 receives a refrigerant gas 103 to a high pressure and temperature from a conventional refrigeration system at 104. The hot refrigerant gas flows into an inlet 106 of a heat exchanger 108 of an indirect water heating tank 110. The heat exchanger 108 has a series of windings, not shown, and is similar to the heat exchanger 22 of figure 1. The refrigerant typically arrives at the inlet 106 at a temperature of about 21 0 F (about 98.9 0

C).

The tank 1 10 contains a body of static fluid 112, usually water, that is heated by the refrigerant as it passes through the heat exchanger 108. The refrigerant leaves 2o the heat exchanger at outlet 114 at about 9 5 QC. The temperature of the static fluid varies depending of potable water flow but is usually held in a range of 65 0 IC to about 85 0 C. Potable water passes through a second heat exchanger 116 that is immersed in the static fluid 112. The potable water first passes through the secondary heat exchanger 130 and then enters the inlet 118 of the heat exchanger 116 at a lower temperature than the static fluid, is heated as it passes through the heat exchanger 116 and leaves at a higher temperature at outlet 120 usually in the range of about 65 0 C to about 85 0 C. If one or more storage tanks 88 of figure 7 are in series with the heat exchanger 116, the water passe s through these tanks 88 before arriving at the outlet 120.

31-JAN-2003(FRI) 16:55 M A Martin and Associates (FAX)61 2 9818 4900 P.018/036 2323-I.dac 13 The heat exchanger 116 may be a multi- coil heat exchanger such as shown in figures 1. Preferably the coils of heat exchanger 116 are supported and separated by the spacer clips shown in figures 3 to 6. The coils of the heat exchanger 116 may be copper or a plastics material. Polyethylene and polypropylene are suitable materials,, being rated to about 120CC and 1 50'C respectively.

The refrigerant leaves the tank 1 10 and passes to a secondary heat exchanger 130 for heating of potable water upstream of the inlet 118 of the tank 1 10. Mains pressure potable water enters at 135 and flows through the core of the heat exchanger. The secondary heat exchanger is a reverse flow jacket type heat exchanger in which a jacket 132 surrounds a section of the potable water supply pipe 134. The flow of potable water in the pipe 134 is opposite to that of the refrigerant in the jacket 132. Whilst the drawing shows a single potable water pipe 134 within the jacket 132, it will be appreciated that more than one pipe or tube for the potable water may pass through the jacket 132. The potable water pipe(s) may 1s be straight pipe(s) or they may be coiled. The inlet temperature of the potable water in Australia usually ranges from about 15 0 C in winter to about 20CC jn summer. The refrigerant enters the heat exchanger 130 at inlet 136 at a temperature from about 85 0 C to about 9500 and heats the water. The potable water leaves the heat exchanger 130 at exit 137 a temperature firom about 10%O to I 5 0 C higher than at entry, i.e. at about 259C to 35C2. The refrigerant leaves the beat exchanger at outlet 138 at a temperature from about 50OC to about 6000 and returns to the refrigeration system. Typically the refrigerant is then cooled to dissipate excess heat to the environment and is then expanded through an expansion valve before being used to cool air, such as for air conditioning, before returning to the compressor. Since the system 100 is, in effect, an alternate heat dissipation apparatus, it may be used with any heat pump systems that generate a heated fluid at a sufficiently high temrperature. It will be appreciated that the source of hot fluid is not limited to a heat pump and other source, such as solar cells or panels may be used.

31-JAN-2003(FRI) 16:55 M A Martin and Associates (FAX)61 2 9818 4900 P.0619/036 2823 I .doc 14 The use of the two heat exchange subsystems 110 (the indirect water heating tank) and the secondary heat exchanger 130 significantly increase the amount of heat transferred to the potable water.

In prior art systems the refrigerant only transfers heat to the potable water in the s tank 1 10 and so the heat transferred is small, due to the high temperature of the static water. An electric heater, such as item 19 in figure 1 is th-us needed to provide additional heat when the refrigerant cannot supply sufficient heat to the potable water. In prior art systems the refrigerant typically only transfers about of the total heat load and the electric boater supplies additional heat to the potable water. In this context the heat load is the heat extracted by the compression and expansion cycle plus the heat input (by the compressor) to drive the cycle.

hn the present invention additional heat is transferred to the potable water from the secondary heat exchanger 130 so that significantly less electrical energy is required. It is calculated that with suitable heat exchangers, the secondary heat exchanger 130 is capable of transferring more heat to the potable water than the indirect heating tank apparatus. It is estimated that a system according to the invention may transfer 50% or mare of the total heat load to the potable water.

Because of the increased overall efficiency of the two heat exchanger apparatus, where an electric heater is provided to heat the static water, it is preferable that this is only operational when the refrigeration system is not active. This mnay be achieved by a simple relay that disconnects the electric heater whenever the compressor(s) of the refrigeration or air conditioning plant are operating.

Referring to figures 9 to 12 there is shown a tank 200 according to embodiments of the invention. The tank has an inner wail 202 and an outer wall 204. The walls 2s have a thickness of about 6 mm and a separation of about 50 mm. The walls are shaped at their upper end 203 to define a sideways extending slot 210 to receive a gasket. Figure I11 shows a first embodiment in which the inner wall 202 extends vertically and at its upper end has an outwardly extending annular wall portion 206. The outer wa~l 204 also extends vertically and at its upper end has an 31 -JAN-2003(FRJ) 18:55 MI A Matin and Associates (FAX)61 2 9818 4900 P. 020/036 .2823AIdoc inwardly extending annular wall portion 208 preferably the wall portion is integrally formed with the inner wall. The outer wall 204 does not extend upwards as much as the inner wall 202 and so the portion 208 lies beneath the portion 206, defining a horizontal annular slot 210 therebetween. In use, a ring shaped gasket 212 is provided that has a sealing portion 214 and a retaining portion 21.6. The retaining portion includes a two horizontally extending annular walls 218 and 220 that define slot 222 therebetween. The gasket is a single piece moulding. The lower wall 218 is sized to fit snugly in the slot 2 10. The slot 222 between walls 218 220 is sized to snugly receive the annular wall portion 206. The gasket is io sized so that it is in tension and so pulls itself tightly into the annular slot 210. The wall portion 208 is also provided with apertures 224 in which nuts or the like are located for securing the lid to the tank. Preferably the wall is moulded until the nuts in position during manufacture. In use, the lid is tightened against the gasket, deforrning the sealing portion 214. When it is necessary to remove the lid for 1s inspection or the like, the fasteners are removed and the lid is raised. Because the gasket is firmly secured to the horizontal tongue and groove arrangement, the gasket is less likely to become detached from the tank.

Figure 12 shows a second embodiment of the top of the tank that provides similar fumctionality. The inner wall 250 is formed with two outwardly extending annular 2a wall portions 252 and 254 at its upper end. The two wall portions 252 and 254 are spaced vertically from each other and so define a horizontal slot 256 for receiving the gasket 212 as shown in figure 11. Referring to figures 9 and 10, the tank 200 is provided with vertically extending ribs 230 on the inner surface of the inner wall 2 02. The ribs 23 0 may be integrally formed with the inner wall 202 or may be separate items secured to the inner wall 202 by glue or fbsteners, not shown. In the preferred fbrm. the inner wall and ribs are roto-moulded simultaneously to form an integral unit. YIn the embodiment shown four ribs 230 are provided, each at 900 to each other. The ribs 230 extend ftrm adjacent the base 232 to adjacent the upper end 203.

31-JAN-2003(FRI) 18:56 M A Martin and Associates (FAX)61 2 9818 4900 P.021/036 2823-Idoc The base 232 is also provided with four ribs 234 that extend horizontally from adjacent the centre of the base to near the inner wall 202. The central portion 236 is sized to provide clearance for a circle of about 100 mm and aids in water flow around the heat exchangers.

The ribs 234 are also arranged at 90 to each other and in the embodiment shown extend adjacent the vertical ribs 230. This is not essential and the horizonta ribs need not align with the vertical ribs 230.

The ribs 230 and 234 serve to space the heat exchanger coils away from the base and side wall of the tank and so aid movement of the static water past the w indings ia of the two coils. This increases the maximum heat flow possible. The horizontal ribs 234 also reinforce the base of the tank.

The outer wall of the tank also includes an annular groove 238 to aid in grasping the tank when installing or otherwise moving the tank.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in allI respccts to be illustrative and not restrictive.

Claims (2)

1. 31-JAN-2003(FRI) 16:56 Md A Martin and Associates (FAX)61 2 9818 4900 P. 022/036
2. 2923-1 .doc 17 CLAIMS 1. A heat exchange systemn that transfers heat between a first fluid and a second fluid, the system including: a first heat exchanger including: a first inlet for the first fluid; a second inlet for the second fluid; a first outlet for the first fluid; a second outlet for the second fluid; and a second heat exchanger including: a third inlet for the first fluid; a fourth inlet for the second fluid; a thid outlet for the -first fluid; a fourth outlet for the second fluid, wherein, the third inlet receives first fluid from the first outlet and the second inlet receives second -fluid from the fourth outlet. 2. The system of claim 1 wherein the first heat exchanger is an indirect heat exchanger utilising an intermediate fluid. 2o 3. The system of any one of the preceding claims wherein the second heat exchanger is a reverse flow heat exchanger. 4. The system of any one of the preceding claims wherein the first hea exchanger includes: a tank;, 31-JAN-2008(FRI) 18:56 M A Martin and Associates (FAX)61 2 9818 4900 P.023/036 1 18 a third fluid within the tank, at least one first pipe extending between the first inlet and first outlet and e-xtending at least partially within the third fluid, and at least one second pipe extending between the second inlet and second 6 outlet and extending at least partially within the third fluid. The system of claim 4 wherein the at least one first pipe is coiled. 6. The system of claim 4 or claim 5 wherein the at least one second pipe is arranged in an elongate helix. 7. The system of any one of claims 4 to 6 including at least one spacer clip lo attached to the coils of the at least one second pipe, the or each said at least one spacer clip attaching to at least one pair of coilis to separate the coils from each other. 8. The system of claim 7 wherein the at least one second pipe includes at least two concentric elongate coils and the at least one spacer clip includes at least one is spacer clip attached to at least one coil of at least two of said at least two concentric coils to separate the coils from each other. 9. The system of claim 7 or claim 8 wherein the at least one spacer clip includes a body having at least two recesses adapted to receive a pipe and to grip the pipe. 10. The system of claim 9 wherein each recess has an interior portion and an opening, the opening sized to require deformation of the recess to receive a pipe within the recess. 11. The system of claim 9 or claim 10 wherein the recess is generally circular. 12. The system of claim 9 or claim 10 wherein the recess is rectagular. 31-JAN-2003(FRI) 16:57 M A Martin and Associates (FAX)61 2 9818 4900 P. 024/036 ZSL3-I AMc 19 13. The system of claim 9 or claim 10 wherein the recess is rectangular and has a back wall and two, generally opposed side walls extending from the back wall. 14. The system of claim 13 wherein the sidewails ar substantially parallel. The system of claim 13 wherein the sidewalls diverge away from the back wal. 16. The system of claim 1 wherein the clip is comprised of bent wire or rod. 17. The system of claim I further including at least one hollow reservoir within the first tank, the interior of at least one reservoir being in fluid communication wit at least one of the second inlet and the second outlet. 18. An indirect hot water heating apparatus including: an tank having an opening; alEd that engages the opening of the tank and a gasket sandwiched between the tank and the lid, wherein the opening is defined by at least one wall of the tank, the wall defining part of an annular groove that extends outwardly from adjacent the opening, the gasket having a complementary annular tongue that engages the annular groove. 19. The apparatus of claim 18 wherein the annular groove exends outwardly. The apparatus of claim 18 or claim 19 wherein the tank has an inner wall and an outer wall surrounding the inner wall and wherein the inner wall has a first 2a annular portion extending outwardly from a frece end portion and the outer wail has a second annular portion extending inwardly toward the inner wail adacent the first annular portion, said first and second annular portions defining opposing walls of the groove. 31-JAN--2003(FRI) 16:5? M A Martin and Associates (FAX)61 2 9818 4900 P.025/036 2823-1 .doc 21. The apparatus of anyone of claims 18 to 20 wherein the inner wallI has a first annular portion extending outwardly from a free end portion and a second annular portion extending outwardly adjacent the first annular portion, said first and second annular portions defining opposing walls of the groove. s 22. A clip for separating windings of a heat exchanger coil, -the clip having a series of spaced apart recesses, each adapted to engage part of each winding and to maintain adjacent windings separated. 22. The clip of claim 21 wherein at least one of the recesses is generally part circular. in 23. The clip of claim 21 wherein at least one of the recesses has an arcuate surface that extends for more than 180 degrees. 24. The clip of any one of claims 21 to 23 wherein at least one of the rcesses has an arcuate surface that extends for more than 300 degrees. The clip of claim 21 wherein at least one of the recesses has a generally rectangular shape. 26. The clip of claim 21 wherein at least one of the recesses is defined by a rear surface, two spaced apart opposed side surfaces and an opening, the side surfaces extending from the rear surface to the opening. 27. The clip of claim 26 wherein the side surfaces are parallel. 2o 28. The clip of claim 26 wherein the side surfaces diverge from each other away from the rear surface. 29. A beat exchange system, substantially as herein described with reference to figures 2to 12. An indirect hot water heating apparatus, substantially as herein described with reference to the figures. 31-JAN-2003(FRI) 16:57 M A Martin and Associates (FAX)61 2 9818 4900 P. 026/036 2523-Idoc 21 29. A clip, substantially as herein described with reference to the figures. Dated this 310 day of January 2003 Thermal-Zero Pty Ltd by its Patent Attorneys SM A Martin Associates