Liquid heaters and vaporizers – Stand boiler – And condition responsive feature
Reexamination Certificate
1997-07-15
2001-05-29
Gravini, Stephen (Department: 3749)
Liquid heaters and vaporizers
Stand boiler
And condition responsive feature
C122S018100, C122S019200
Reexamination Certificate
active
06237544
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improvements in water heaters (and gas burners for water heaters) in which combustion products are caused to flow past a tank to heat water in the tank.
BACKGROUND TO THE INVENTION
There are many designs of water heaters in which combustion products from a burner are directed to flow in heat exchange relationship to a water tank. One example is shown in U.S. Pat. No. 5,361,729 owned by the present applicants in which combustion products from a burner below the tank are directed to flow up one side of the tank, across the top, and down the other side(s) and thence to an external balanced flue. Although very effective in operation, this water heater requires relatively complex sheet metal components particularly to define the flow paths for the combustion products up one side and down the other side of the tank.
Another water heater is shown in patent specification AU-38573/93 in which combustion products are directed up through a central flue extending centrally through the height of the tank. Complex baffle arrangements are used to try to increase the efficiency of extraction of heat from the combustion products. Also there are problems with sealing the flue at the top and bottom of the tank.
In water heaters where water is heated in a storage vessel or tank and from which water is to be drawn at a temperature within a predetermined range, it is usual to provide a thermostat probe which extends into the tank to sense the temperature of the water in the tank. If the temperature of the water in the tank falls, e.g. due to progressive loss of heat through the tank to the ambient surroundings, or due to tapping of water from the tank and the consequent introduction of replacement cold water into the tank, the temperature probe senses the fall in temperature and initiates operation of heating means associated with the tank. In the case of a water heater where the heating means comprises a burner for burning of fuel, the heat from which is used to raise the temperature of water in the tank, the sensing of the temperature drop by the temperature probe initiates ignition of the burner. When the water temperature in the tank is raised to a predetermined level as sensed by the temperature probe, the burner is extinguished, by discontinuing supply of fuel.
The lower temperature at which the burner is ignited to heat water in the tank, and the upper temperature at which the burner is extinguished is a function of the construction and operation of the temperature probe. A known and conventional temperature probe used in gas water heaters for domestic and commercial hot water supply comprises a bimetallic rod made of the alloy Invar, a stainless steel alloy. The rod is manufactured to a close tolerance in length and is mounted in association with a gas supply valve so that the outer end of the rod pushes on an operative component of the gas valve to cause it to open when the temperature of water into which the inner end of the rod extends falls to a predetermined level. When the temperature of the water in the tank rises to an upper limit the rod causes the gas valve to close off supply of gas to the burner. The difference between the lower temperature at which the valve is opened and the upper temperature at which the valve is closed is called the “differential” for the particular temperature probe. Commonly available temperature probes for operating gas valves of commercial or domestic water heaters have a differential of 14° C. and this value is prescribed as the maximum differential allowable in regulations of the Australian Gas Association (the regulatory body for setting down and monitoring compliance with standards for gas appliances for the Australian market).
A water heater with a temperature probe and gas valve operating at the maximum allowed differential of 14° C. may be intended to supply hot water at a maximum of, say, 70° C. (which may be diluted to, say, 50° C. by mixing with cold water from the mains supply after the water at 70° C. is drawn from the tank). However with a differential of 14° C., water in the tank can fall to 56° C. before the burner is operated to raise the temperature again. This means that a consumer can find that the domestic hot water supply system when called upon to supply hot water, may do so at a temperature as low as 56° C. (which the downstream dilution may reduce to a temperature in the low 40° C. range)—an unacceptably low temperature for domestic requirements such as showering, bathing, washing dishes, or clothes, washing machines.
Therefore in use it is desirable to have a temperature differential substantially less than 14° C. However it is difficult to obtain commercially temperature probes for use with gas valves for hot water services having temperature differentials substantially less than 14° C. The present applicant sources a special thermostat with a guaranteed differential of 11° C. for use in its domestic and commercial gas hot water systems and this differential of 11° C. is about the best that is being offered in the market. However even a guaranteed differential of 11° C. can produce markedly different temperatures of water being supplied to the user of the hot water system depending on whether the water in the tank happened to be towards the lower end of the temperature range or towards the upper end of the temperature range determined by the differential of the temperature probe being used.
OBJECTS OF THE INVENTION
It is an object of one aspect of the present invention to provide a water heater which can effectively utilise heat from combustion of fuel to heat water in a tank.
It is a further preferred object to provide a water heater which has constructional features enabling advantages in manufacture, assembly or operation to be achieved.
It is a further object of another aspect of the present invention to provide an improved gas burner construction.
It is an object a further aspect of the present invention to provide a water beater having a burner for burning of fuel to heat water in a tank and in which it is possible to substantially improve the temperature differential between the lower temperature limit at which the burner is switched on and an upper temperature limit at which the burner is extinguished.
It is a further and preferred object of the present invention to provide a hot water heater achieving in use a lower differential between the burner ignition and burner extinguishing temperatures than the rated differential of the temperature probe being used in the water heater.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a water heater comprising: a tank for storage of water to be heated, the tank having a top, bottom and upright side walls, a casing surrounding the side walls and top of the tank and leaving a heat exchange zone entirely around the side walls of the tank, a burner below the tank for burning of fuel, the burner being spaced below the tank and arranged so that combustion products rise and flow up through the heat exchange zone along the side walls of the tank to heat the water in the tank, and support means arranged so that the tank is located and supported within the casing by the support means, the support means being located a substantial distance above the bottom of the tank so that combustion products flow up the side walls around the entire circumference of the tank for a substantial distance before encountering the support means. This provides an uninterrupted large surface area at the bottom and lower part of the tank for heat transfer from the combustion products.
The support means may be located at a plurality of points around the circumference of the tank, the support means bridging across the heat exchange zone and supporting the upright side walls of the tank. For example, there may be three support means arranged at 120° C. to each other around an upright central axis of the tank. Preferably, each support means provides a point or edge contact at which the weight of the tank is supported, the point
Croxford Bernard
Rees Richard
Zuccon Agostino
Aqua Max Pty LTD
Gravini Stephen
Lu Jiping
Ramsey William S.
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