AU647886B2 - Storage water heater with top inlet - Google Patents

Description

~IOPC~i~FEI* i

I

i L P/00/Oil-~

Z

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

FOR OFFICE USE P/00/011 Regulation 3.2 647886

I

Name of Applicant: Address of Applicant: Actual Inventors: Address for Service: TO BE COMPLETED BY APPLICANT Rheem Australia Limited Brodie Street Rydalmere NSW 2116 Alan Raymond LAW Mr A W Tilley Rheem Australia Limited Brodie Street Rydalmere NSW 2116 Invention title: "STORAGE WATER HEATER WITH TOP INLET" Details of associated provisional applications: PK5147, 15 March 1991 The following statement is a full description of this invention, including the best method of performing it known to us: 052145 i i, i

A

This invention relates to storage water heaters and in particular gas fired storage water heaters. Storage water heaters, irrespective of the means of heating, are most efficient when operating on the displacement principle. This requires the hot water outlet departing the storage tank being located near the top of the tank which takes advantage of the lower density of the hottest water in the tank tending to thermally stratify at the top of th" tank. The incoming cold 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. In commonly known water heaters, this cold water entry is through a hole formed in the lower vertical wall of the storage tank nearthe bottom.

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 frequently have a flue passing centrally through the tank. Usually the flue and tank are coaxial. In such gas fuelled water heaters, the above described temperature stratification tendency can be disadvantageous. In the type of gas water heater with a central flue about half the total heat input from the bottom 1mounted gas burner enters the tank through the bottom wall. The remaining half enters through the area of contact of the stored water and the external circumference of the flue where it passes through the body of 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. Such types 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, the temperature of the stored water throughout the tank equilibrates at approximately a uniform temperature. However, with the normal pattern of usage of hot water from a storage tank, with consequential flow into the tank of cold water, 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 layers adjacent to the top of the tank to reach a temperature significantly higher than the water layers adjacent to the thermostat, and controlled to the thermostat set point temperature, resulting in difficulties in establishing a suitable thermostat setting which 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 vitreous enamel liningS in the tank. A further disadvantage of excess water 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 discharge of the entire contents of the tank.

Whilst some promotion of the concept 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 been a number of proposals developed to overcome the problem of excessive thermal strat;,ication particularly associated with centrally flued gas heated water heaters. One design has avoided the use of a central flue entireiy 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. In some very large storage water heaters having tank capacities larger than for example 280 litres, a second thermostat is installed adjacent to the upper part of the tank. Whilst this does not prevent thermal stratification from occurring, it does limit the maximum temperature achieved in the stored water near the top of the tank.

2 The applicant's Australian patent number 500476 discloses a diffuser elenimont inserted into the cold water Inlet positioned toward the lower end and enterirg the side of the tank. The diffuser directs some of the horizontally directed incoming water upwards to mix with the hot water above. If this diffusing is excessive, it leads to a compromise between avoiding dangerously hot water at the top of the tank and a reduction in the usable hot water which can be delivered from the heater under normal conditions of use.

Storage water heaters have a thermal insulating layer surrounding the tank on at least its vertical and top walls. Insulation comprises a layer which is in turn surrounded by a outer protective sheath usually made of relatively light gauge metal and referred to hereinafter as a "jacket". In the manufacture of water heaters of the type described in this specification, the assembly of the insulating layer and jacket around the tank results in manufacturing complications in respect of the known design where the cold water Inlet Is positioned in the side wall at a low level of the tank. It is thus an advantage to introduce the incoming cold water to the tank at an entry point in one of the ends of the tank rather than in the side wall. In view of the basic requirement for optimal efficiency that the hot -3- L water outlet be at the top, it is convenient for manufacture and installation that the cold water inlet to be also in the top end but extended inside the tank by a pipe to take the cold water vertically downwards to discharge into the body of water near the bottom of the tank.

The present invention offers the benefit of providing a simplified manufacture of water heaters of the type described together with an amelioration of the undesirable effects of the excessive temperature build-up problem referred to above.

The invention consists of a gas heated storage water heater of the displacement type having a flue extending through a tank, the tank having a cold water entry opening in a top wall thereof that is extended downwardly inside the tank by an elongate delivery tube to enable admission of cold water at a point near the bottom of the tank and wherein the delivery tube has a small outlet located towards the top end of the tube to be effective in admitting a minor proportion of the incoming cold water close to the top of the tank.

Preferably the small outlet is positioned to be effective in directing said minor proportion of cold water towards the flue and even more preferably to direct it towards the flue in the region of the junction of the flue with the top wall.

Preferably where the incoming cold water entry and delivery tube extending downward therefrom is nominally of diameter 12mm the hole positioned towards th3 top of the tube is 3 to 5mm diameter.

The invention is further described by reference 'ro a presently preferred example as shown in the accompanying illustration in which:- Figure 1 is a schematic cross-sectional elevation to a reduced scale of a tank of a gas fired mains pressure storage type water heater according to the invention.

With reference to Figure 1, the water heater tank 10 comprises a steel cylindrical body 12, a bottom end wall 14, outwardly dished top end wall 16, a burner (not illustrated) situated in the region bounded by the wall 14 and the base 18, a cylindrical coaxial flue 20, a hot water outlet 22 from the tank, a cold water inlet 24 to the tank and an extension or delivery tube 26 extending from the cold water inlet to a point low in the volume of water stored within the tank.

-4iL A small hole 30 is formed in the delivery tube at a point close to the top end just inside where it enters the tank. The hole may be aligned so as to direct a minor portion of the incoming cold water into the tank towards the flue at its top end.

With the aid of a small extension to the hole (not illustrated) the incoming cold water emerging from the hole may be directed advantageously towards the potentially hottest point in the tank, namely the region of water in the vicinity of the intersection between the flue and the highest point of the top wall of the tank.

The top end of the tank 16 is welded to the body, the line of intersection being as indicated by line 32-32. Because both the inlet and outlet holes are formed in the top end wall 16, before welding this relatively smaller part, the top end, can be handled in and out of a hole forming press more easily than can the larger body 12.

Also, it enables easier automation of the hole forming ano. subsequent socket welding operations associated with the hot water outlet and the cold water inlet points as compared to the earlier design requiring a side entry for the cold water inlet passing through both the jacket, the insulation and the side wall. Other assembly operations including the fitting of the jacket to the outer cylinder and the subsequent introduction of foam-In-place insulation into the space between the cylindrical wall and the jacket and the top end can be more efficiently completed when both holes for water flow are in the top end.

The major outlet 34 of the cold water inlet tube may alternatively be shaped to direct the incoming cold water near the bottom end of the cylinder in a generally more horizontal direction than illustrated In order to limit the amount of undesirable destratification caused by the turbulence associated with the major proportion of the incoming water stream issuing there. On the other hand, the smaller hole near the top end of the cylinder may be so formed as to provide a vertical or near vertical issuance of the cold water emerging into the hot wa. r space to promote a desirable mixing and destratification around that upper region.

In this way the efficiency advantage inherent In thermal stratification combined with the minimum risk of over-heating associated with the hot water in the top end of the storage tank can be optimised.

Claims (4)

1. A gas heated storage water heater of the displacement type having a flue extending through a tank, the tank having a cold water entry opening in a top wall thereof that is extended downwardly inside the tank by an elongate delivery tube to enable admission of cold water at a point near the bottom of the tank and wherein the delivery tube has a small outlet located towards the "op end of the tube to be effective in admitting a minor proportion of the incoming cold water close to the top of the tank.

2. A heater as claimed in claim 1 in which the small outlet is positioned to be effective in directing said minor proportion of cold water towards the flue.

3. A heater as claimed in claim 2 in which the small outlet is positioned to direct said minor proportion towards the flue in the region of the junction of the flue wij the top wall,

4. A heater as claimed in any one of the preceding claims in which the incoming cold water entry and delivery tube extending downward therefrom is nominally of diameter 12mm and the hole positioned towards the top of the tube is 3 to diameter. A heater substantially as described with reference to the accompanying illustration. DATED this 5th day of March 1992 RHEEM AUSTRALIA LIMITED 052145 -6- ABSTRACT 4i A gas heated storage water heater (10) of the displacement type having a flue extending through a tank the tank having a cold water entry opening (24) in its top wall (16) that extends downwardly inside the tank by an elongate delivery tube (26) to enable admission of cold water at a point near the bottom of the tank. A. The major proportion of incoming cold water is admitted from the bottom end (34) of the delivery tube but the delivery tube also has a small outlet (30) located towards j its top end to admit a minor proportion of the incoming cold water close to the top Sof the tank. Preferably the small outlet is positioned to direct the minor proportion of cold water towards the flue (20) and more preferably towards the region of the junction of the flue with the top wall; the heater thereby has a reduced tendency to excessive temperature build-up in the top end of the tank and the inlet (24) and outlet (22) being in the top wall (rather than the cylindrical body of the tank) makes the heater easier to manufacture. i4 t i