AU649863B2 - Gas fuelled water heater with water entry diffuser - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATIOf FOR A STANDARD PATENT

ORIGINAL

FOR OFFICE USE P/00/011 Regulation 3.2 AK--3 Name of Applicant: Address of Applicant: Actual Inventors: Address for Service: *o oo TO BE COMPLETED BY APPLICANT Rheem Australia Limited Brodie Street Rydalmere NSW 2116 Jim JENSEN Stewart Henry WICKS Mr A W Tilley Rheem Australia Limited Brodie Street Rydalmere NSW 2116 Invention title: "GAS FUELLED WATER HEATER WITH WATER ENTRY DIFFUSER Details of associated provisional applications: PK7719 12 August 1991 The following statement is a full description of this invention, including the best method of performing it known to us: 052492. <13> This invention relates to the storage water heaters and In particular gas fuelled storage water heaters. Storage water heaters, irrespective of the means of heating, are most efficient when operating on the displacement principle. This principle requires the hot water outlet departing the storage tank being located near the top of the tank which takes advantage of the lower density hottest water in the tank tending to thermally stratify at the top of the tank. The incoming colder water by contrast is of higher density than the hottest water and so is admitted into the body of the stored water at a point low in the storage volume, so displacing upwardly the hotter water already in the tank. In commonly known water heaters, the cold water entry is horizontally directed through a hole formed In the lower vertical wall of the storage tank near the bottom. The invention applies to the conventional type of gas-fuelled storage water heater fitted with an automatic temperature control.

The storage tanks of known water heaters are generally cylindrical. In use, the cylindrical axis of the tank is vertical. Types using gas to heat the tank most frequently have a flue passing centrally through the tank. Usually the flue and •o tank are coaxial. In such gas fuelled water heaters, the above described temperature stratification tendency can be disadvantageous if steps are not taken to avoid excessive locallsed temperature that can arise In use close to the top of the S•tank. In the type of gas water heater with a central flue about half the total heat input from the bottom mounted gas burner transfers to the tank through the bottom wall. The remaining half enters through the area of contact between the stored water and the external circumferential area of the flue where it passes through the stored water in the tank. Normally such a water heater Includes a thermostat controlling the water temperature and for a number of design performance criteria, the thermostat is located on the tank side wall relatively closer to the bottom end than the top end of the tank. Thus it is Inevitable that some heat is transferred Into the stored water from the portion of the flue above the thermostat and this portion of the heat Input therefore is not controlled by the thermostat. Such a type of water heater can have the present invention advantageously applied and the type will hereinafter be referred to as being "of the type described".

Providing there is no draw-off of heated water from the tank during the heating up of a tank full of cold water in a heater of the type described, the temperature of the stored water throughout the tank equilibrates at approximately a uniform temperature. However, with the normal pattern of incremental usage of hot water from a storage tank with consequential displacement flow of incremental volumes of cold water into the tank, thermally stratified water layers are stored throughout the tank, each layer Increasing In temperature from the cold water Inlet at the bottom to the top of the tank. With each draw-off of hot water and entry of cold water, it Is possible for the water adjacent to the top of the tank to reach a temperature significantly higher than the water adjacent to the thermostat that is automatically controlled to the thermostat set point temperature, resulting in a process often referred to as "stacking". This results in difficulties in establishing a practicable thermostat setting that precludes the possibility of unsafe excessively hot water departing the storage tank through the hot water outlet from time to time.

Not only is user safety a factor but also excessively high temperature water near the top of the cylinder Is detrimental to the life of the most commonly employed S•vitreous enamel lining In the tank. A further disadvantage of excess water 15 temperature Is that the temperature may become high enough to activate the temperature relief valve situated near the top of the tank, resulting In the energy wasteful discharge of the entire contents of the tank.

Whilst promotion of the achievement of thermal stratification of stored water is desirable to maximise the effective capacity of a given volume of tank in storage •water heaters In general, there have ben a number of proposals developed to overcome the problem of stacking particularly associated with thermal stratification in centrally flued gas heated water heaters of the type described. One design has avoided "he use of a central flue entirely replacing It instead by a flue surrounding the tank. In at least one such version the external flue path is arranged so that all heat transfer takes place at a level below the height of the thermostat. In this way the thermostat has complete control of the water temperature and no thermal stratification takes place. However, this approach results in a water heater which Is more expensive to construct. An alternative approach, in some very large storage water heaters having tank capacities larger than for example 280 litres, is a second thermostat installed adjacent to the upper part of the tank. Whilst this does not prevent desirable thermal stratification frcmn occurrng, it does limit stacking near the top of the tank but still leaves room for improvement.

Another approach is typified in the applicant's Australian patent number 500476 that discloses a diffuser element Inserted into the cold water inlet entering the side of the tank toward the lower end. The diffuser directs some of the horizontally directed Incoming water upwards to mix with the hot water above. If such diffusing is excessive it leads to an unsatisfactory compromise between avoiding the possibility of there being dangerously hot water at the top of the tank ar' a reduction In the usable hot water that can be delivered from the heater under normal conditions of use.

There remains room for improvement In limiting very high temperature in the very localised region on the water side of the flue-to-top junction. It Is an object of the present invention to provide a more significant temperature reduction In the very locallised region on the water side of the flue-to-top junction without, by excessive diffusing or de-stratifying, detracting from the hot water delivery capacity regarded as acceptable for that particular total capacity of tank.

The Invention consists of a water heater of the type described having a long cylindrical storage tank installable for use with its longitudinal axis vertical and 15 having an inlet opening for cold water at a point low In the cylindrical wall of the tank and further being provided with an extended water discharge means passing through the irlet opening and extending therefrom towards the central axis of the tank; there being further provided outlet means In the discharge tube operative In use to direct all the water flowing Into the tank In one or more upwardly directed streams that emerge from at least one hole having a locus lying substantially at the same level of the tank as said Inlet opening and wherein said locus Includes only points as lie Inside the water storage volume of the tank radially inwardly of a point P1 lying at the outer extremrra' of a radius R1 where R1 Is equal to 90% of the Inside radius of the tank; and at least half of the cross sectional area of said outlet means is distributed radially inwardly of a point P2 lying at the outward extremity of a radius R2 where F2 Is equal to 50% of the inside radius of the tank and where radii R1 and R2 have their central origins coincident with the central longitudinal axis of the tank; and wherein the total cross-sectional area of the outlet means Is not less than 70% and not more 150% of the cross-sectional area of the inlet opening.

In a paticularly preferred form the water heater Is further characterised in that all the water flowing into the tank Is directed upwardly from the outlet means distributed radially Inwardly of the point P2.

In other preferred forms the water heater has outlet means that comprise only openings located radially inwardly of a further point P3 lying at the outward extremity of a radius R3 where R3 is equal to 35% of the Inside radius of the tank and in one particular form where the outlet means is a single rectangular hole.

For convenient assembly the water heater may have the extended water discharge means in the form of a substantially straight pipe adapted to be nserted through saJ Inlet opening and sealed thereto.

The Invention Is described by reference to a particularly preferred example and some variations thereof as shown in the accompanying illustrations in which: Figure 1 depicts in schematic cross-sectional elevation to a reduced scale a gas heated mains pressure storage type water heater according to the invention.

Figure 2 is an enlargement of the outlined portion as Indicated in Figure 1.

Figure 3 is an enlargement of the outlined portion as indirated in Figure 1 showing an alternative embodiment of the invention.

SWith reference to Figure 1 the water heater 10 comprises a tank 11 that in turn comprises a steel cylindrical body 12, an inwardly curved bottom end wall 14, an outwardly curved top end wall 16, a gas burner 18 situated below the tank to heat S* it, a cylindrical coaxial flue 20, a cold water Inlet 22 leading to the tank, a hot 25 .vater outlet 24 leading from the tank and a riser tube 26 connecting the highest region inside the tank to the outlet. Inserted in the cold water Inlet is a diffuser 30 significant to the present Invention and described in more detail below with reference to two alternative embodiments shown in Figure 2 and Figure 3. The tank 11 is surrounded by a layer of insulation 28, a jacket 29, and Is fitted with an automatic thermostat 27 in the conventional manner.

With reference to Figure 2, the diffuser 30 In the form of an extension to the water Inlet tube 22 Is Inserted Into the tank through the externally threaded annular boss 32 attached to the tank wall. The diffuser 30 has a flanged end which enables it to mate to the end of the boss 32 and is sealed thereto ./ith the inlet water pipe 22 using a flexible sealing washer 36, the connection being assembled with the aid of a retaining nut 34. The dlffuser 30 extends into the tank so that its innermost end almost touches the wall of the central flue 20. In the end of the water Inlet tube closest to the flue, there Is a hole 38 which, upon assembly of the diffuser to the tank, points upwardly into the tank. The upward pointing direction of the hole can be ensured by a polarising means not shown such as a flat on one side of the Inlet tube 30 to enable only one possible direction of polarisation with respect to the boss 32 provided with a corresponding flat located in a predetermined correct position. The hole 38, as Illustrated in Figure 2, is a single rectangular opening in the end of the tube. It does not extend into the closed end of the tube closest to the flue. Thus all incoming water is directed upwardly into the tank. The radial extent of the hole, with respect to where it lies upon assembly into the water heater tank, is significant in the optimal functioning of the invention. In the Illustrated preferred embodiment, the hole 38 does not extend radially outwardly 'beyond the imaginary point P3 which lies at the outward end of a radius R3 measured 15 from the tank's central longitudinal axis 40. Expressing the internal radius of the tank R as being equal to 100%, the ratio between R3 and R is equal to S. With reference to Figure 3, showing an alternative embodiment of diffuser 40, all features correspond to those described In Figure 2 with the exception that in the diffuser 40 a row of holes 42 is employed. Figure 3 shows 8 holes In the tube but there may be up to about 12, all pointing upwardly into the tank, the holes being from 5 to 7.6mm diameter and arranged on a pitch of about 10mm extending from a point close to the inward end of the tube to a point P1 at radius R1 where R1 equals 90% of R. The spacing, diameter and number of holes is such that all water entering 25 the tank in use is directed upwardly radially inwardly of point P1 and at )east of the incoming water is directed upwardly radially inwardly of a further point P2 S" which lies at the end of radius R2 where R2 equals 50% of R. The effectiverness of the illustrated embodiments and further embodiments which, although not illustrated, can be implied within the scope of the Invention, is shown in Table 1 below. In regard to the results shown in Table 1, it is explained that the effect ims of the arrangement of the hole 38 or holes 42 in Figures 2 znck 3 resper tivelv car be confirmed in terms of the thermal stratification performanm. of the sterage tank and In terms of the reduction in peak temperature measurable in the tank during use. As stated in the preamble to this specification, thermal stratification is important to achieve in a storage tank since it enables a substantial percentage of the storage tank volume to be delivered in the form of acceptably hot water at a sufficiently uniform temperature.

With reference again to Figure 1, the hot water removed from the tank is withdrawn through riser tube 26 which is directed upwardly into the heater to take maximum advantage of the hottest water being stored in the highest regions of the tank.

This hot water is withdrawn from the tank through riser tube 26 then outlet 24. The disadvantage with excessive stratification is that excessively high peak temperatures are recorded In a very locallsed region at the extreme top of the tank, particularly where the top end meets the flue In a small crevice 28. Although not far above the upper, inlet end of the outlet tube 26, temperatures measurable in the crevice 28 using a small thermocouple positioned In the crevice tend to be significantly higher than the average temperatures recorded passing out through the outlet 24. The lifetime of any corrosion protective coating on the wetted surfaces of the tank and flue, such as vitreous enamel, is very much shortened in the crevice region by the existence of the very high peak temperatures which are from time to time recorded In the crevice 28. Table 1 summarlses experiments embodying various :i 15 arrangements of directing the incoming cold water through hole 38 Figure 2 or holes 42 Figure 3. These have been explored in relation to the cross-sectional area of the discharge and hence the Incoming flow velocity for a given water usage rate together with the relative spatial diffusion of that Incoming flow in terms of where it is directed into the tank. The effectiveness of each arrangement has been assessed by the resulting peak temperature measured In the crevice 28 at the top of the heater, and In relation to the stratification test performance achieved.

i* 9 9* 99 TABLE 1.

Exp Inlet Opening(s) No. Holes, circular no. dia.mm Flow Distribution of total 0-P3 P3-P2 P2-P1 Pea, Crevice Temp °C 69 73.5 74 Stratification Test 35.9 50.1 58.0 65.8 67 72.4 5.7 6.25 4 4. 4* 4 83 85.5 80.5 83.5 84.5 12 7.6 12 7.6 Hole, rectangular Length Width mm mm 40 12 13 9 14 15 14 72.8 73.2 74.8 73 79.4 74,2 57.3 69.2 70.5 71.6 69.4 70.4 71.3 .4 4 445* The stratification test is as specified in a joint publication of the Australian Gas Association and the Australian Liquefied Petroleum Gas Association Ltd, entitled AGA102-1989, Approval Requirements for Gas Water Heaters. The revision available at the time of preparation of this specification is dated October 1989 and later amendments include those up to December 1990. In this publication the method of test 5.3.3 1989, Stratification Test Storage Water Heaters is described at pages 108 to 109.

The test requires that the heater be operated In a specified way involving heating under automatic control and drawing off hot water. For heaters to which the present Invention is directed having capacities exceeding 25 litres tank capacity, hot water is drawn off continuously at a flow rate of 9.0 0.5 litres/minute. Withdrawal Is stopped when the temperature of hot water emerging has fallen to a value 60°C below the temperature of the hot water that emerged at the end of the fourth litre withdrawn. The volume of water thus withdrawn is expressed as a percentage of the nominal capacity of the water heater. The heater complies with the requirements if the volume of water withdrawn is not less than 70% of that nominal capacity.

So long as any stratification test result exceeds 70%, the temperature shown in the column headed peak crevice temperature is regarded as good if it is below 850C, since this represents a significant and important reduction below that achieved in conventional tanks of the type described. Such temperatures if below 800°C are regarded as excellent. It can be seen in particular by referring to experiments 16 S' to 21, the advantages of having an Inlet area of 280 sq mm together with 100% of the 15 distribution of Incoming water Inside R3. Experiment 1 indicates the disadvantage of having too small an inlet area, despite being directed Inside R3, in that the stratification test result is only about half of that required. The experiments numbered 2 to 5 Inclusive Indicate that gradual Improvement as the inlet flow area is progressively Increased. Experiment 14, like Experiment 1, indicates that even where all the water Is ejected into the tank inside R3, too small a surface area (126 sq mm) results In a stratification test result of only 57.3%. Given that the Inlet opening generally used for hot water tanks, namely 20mm diameter, has an area of 314.2 sq mm then the effective inlet areas of the hole or holes in the discharge ""tube 30 may be expressed in terms of that Inlet area normally usable If no Inlet water diffuser were used. This is done In order to provide a dimensionless range of inlet parameters which limits the invention to forms that achieve the desired outcome. Thus the cross-sectional area of the outlet from the tube Into the tank should be not less ideally than 70% of the cross-sectional area of the inlet opening and ideally not more than 150% of it. Al;o, at least half tho Inflowing water that enters the tank should flow in upwardly from an cutlet that Is radially Inward of point P2 as depicted in Figure 3. Point P2 is at the extremity of radius R2 and is equal to 50% of the inside radius of the tank R. Even better results tend to be achieved where all the inflowing water is directed upwardly into the tank from an outlet radially inwardly of point P3 lying at the extremity of radius R3 where R3 is equal to 35% of the inside radius of the tank.

Whilst ki is important in the invention that no water be admitted into the tank in the outer 10% of its radial extremity, it is appareti that where a single hole is pc;itioned as close as possible to the inward end of th9 tube, consistently better results are obtained as compared with the somewhat more diffuse entry obtained with 12 holes arranged along the inlet tube. The scope of the invention includes all arrangements having openings pointing upwardly and positioned Inwardly of 90% of the tank radius, but the most preferred results are achieved where all the water is admitted inside of 35% of the tank radius. This must be qualified by the proviso that the incoming water velocity must neither be too high nor too low, that Is to say, that the inlet area should fall within the above specified range, namely 70 to 150% of the cross-sectional area of the Inlet opening. Of course, this Implies that the inlet area opening is one that Is likely to be in normal use. Thus, consistent with conventional plumbing practice, which would generally provide that for a water heater In the range of 60 to 200 litre capacity (a significant range for both 15 domestic and comme'cial use) Inlet water would be delivered through a nominal diameter opening into tic tank.

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Claims (6)

1. A water heater of the type described having a long cylindrlcal storage tank installable for use with Its longitudinal axis vertical and having an inlet opening for cold water at a point low in the cylindrical wall of the tank and further being provided with an extended water discharge means passing through the Inlet opening and extending therefrom towards the central axis of the tank; there being further provided outlet means In the discharge tube operative in use to direct all the water flowing into the tank in one or more upwardly directed streams that emerge from at least one hole having a locus lying substantially at the same level of the tank as said inlet opening and wherein said locus Includes only points as lie Inside the water storage volume of the tank radially inwardly of a point P1 lying at the outer extremity of a radius RI where R1 is equal to 90% of the inside radius of the tank; and at least half of the cross sectional area of said outlet means is distributed radially inwardly of a point P2 lying at the outward extremity of a radius R2 where R2 is equal to 50% of the inside radius of the tank and where radii R1 and R2 have their central origins coincident with the central longitudinal axis of the tank; and wherein the total cross-sectional area of the outlet means is not less than 70% and not more 150% of the cross-sectional area of the Inlet opening.

2. A water heater as claimed in claim 1 further characterlsed In that all the water flowing into the tank is directed upwardly from the outlet means distributed radially inwardly of the poini P2.

3. A water heater as claimed in claim 1 in which the outlet means comprise only S• *openings located radially Inwardly of a further point P3 lying at the outward extremity of a radius R3 where R3 Is equal to 35% of the Inside radius of the tank.

4. A water heater as claimed In claim 3 in which the outlet means Is a single rectangular hole.

A water heater as claimed In any preceding claim in which the extended water discharge means Is a substantially straight pipe adapted to be inserted through said inlet opening and sealed thereto.

6. A water heater substantially as described herein with reference to the accompanying Illustrations. DATED this 11th day of August 1992 RHEEM AUSTRALIA LIMITED 052492 u r r r s S4 S ABSTRACT. GAS FUELLED WATER HEAVER WITH WATER ENTRY DIFFUSER. A storage water heater (10) of the type heated by a gas burner (18) in a combustion region below the tank, with a flue (20) passing from the combusion region through lower and upper end walls (14,16) of the tank to exhaust. The gas burner is controlled by a thermostat (27) mounted In thermal contact with a mounting location partway up a vertical wall of the tank. The flue intersects with the top end of the tank creating a small Ibcallsed crevice region in which the water In presently used water heaters becomes excessively hot approximately 100°C) in relation to a normal operating temperature approximately 750C) for such a water heater during usual operating conditions. The excessive temperature Is moderated In a water heater of the invention by having in the tank a diffuser arrangement (30) in the form of an extended tube inserted through the cold water Inlet opening (22) and having a specified hole (38) or pattern of holes (42) to direct Incoming cold water in a way effective to reduce the high temperatures in the crevice region without appreciably reducing the hot water delivery performance as measurable in a S stratification test.. Figure 1.