Electric resistance heating devices – Heating devices – Tank or container type liquid heater
Reexamination Certificate
1999-06-15
2001-01-09
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Tank or container type liquid heater
C392S481000, C392S496000, C126S344000
Reexamination Certificate
active
06173118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to electric water heaters for domestic use. More particularly, this invention relates to a compact electric water heater for domestic uses which is pressureless and continuously self-cleaning. The water heater preferably includes one or more of an automatic fill switch, an inlet temperature sensor block and top-nesting container for mounting the electric heating element and thermostat.
2. Background Art
The typical electric domestic water heater consists of a steel tank, insulated by fiberglass encased in a metal jacket. Cold water runs into the steel tank, is heated by lower and upper heating elements, and exits through a pipe. As hot water is drained off, cold water mixes with the remaining hot water, reducing the temperature of the remaining water.
Also, in a conventional electric water heater, minerals typically settle out from the water to form sediments, eventually reducing the heater's efficiency and causing corrosion and leaks. In addition, pressure is generated in the tightly sealed tank from heat and from occasional excessive water pressure entering the system from the cold water source. This pressure occasionally results in property damage and personal injury from steam and water leaving the pressure relief valve or from explosion from a failed valve.
The heating elements in conventional electric water heaters often fail before the tank and must be replaced. Because of the design of prior art domestic electric water heaters, replacement of the elements is a difficult task, usually requiring that the water supply be shut off and the tank drained prior to replacing the element.
SUMMARY OF THE INVENTION
One object of the electric water heater of this invention is to eliminate pressure inside the tank. This is accomplished by running the pressurized cold water that is to be heated through a copper coil. The copper coil which carries the cold water is immersed in a pressureless tank filled with a non-recirculating heat transfer fluid such as water. The water in the tank is heated by, for example, an electric heating element. The heated tank water heats the copper coils which are thermally conductive. The pressurized cold water, i.e., tap water from a water supply, is heated as it circulates through the coils by thermal conductivity. Thus, cold water enters the coils, indirectly absorbs heat from the heated tank water, and exits the coils as hot water.
In the pressureless tank of this invention, new sediment is rarely added to the tank because the tank water is rarely replaced. Thus, sediment buildup is reduced. The coil is continuously cleaned by the pressurized water running through it.
Because the tank of the water heater of this invention is not pressurized, the interior of the tank can be accessed without shutting off the water supply and draining the tank. Such access is required to replace a failed element.
In a preferred embodiment of the invention, the water heater comprises a double-walled cylindrical tank formed of plastic. The space between the inner and outer walls of the tank is insulated with foam. Water is heated in the tank by means of an electric heating element. Continuous copper coils are placed in the tank through which cold water enters and hot water exits. An optional overflow pipe, if present, the cold water inlet, and the hot water outlet are located above the water level of the tank in an air space below the top of the tank so that there are no holes in the tank to develop leaks. A float valve admits tank make-up water to the tank from the cold water inlet when the level of water in the tank falls below a minimum tank fill level. The float valve discontinues the flow of water into the tank from the cold water outlet when the level of water in the tank reaches a full level. The heating element is mounted on a heating element mount which is inserted through a hole in the tank's top. The mount extends and protrudes down into the water located in the tank. The heating element is controlled by a thermostat in contact with a sensor block placed in the incoming cold water line. The sensor block detects the circulation of cold water and triggers the thermostat, activating the heating element whenever water is added to the coil.
The continuously cleaned hot water heater of this invention will further provide increased hot water more efficiently in a smaller and lighter tank. This will reduce energy usage, material costs, shipping and storage cost.
REFERENCES:
patent: 1560528 (1925-11-01), Baum
patent: 2748249 (1956-05-01), Collerati
patent: 5228413 (1993-07-01), Tam
patent: 5438642 (1995-08-01), Posen
patent: 5485879 (1996-01-01), Lannes
patent: 5626287 (1997-05-01), Krause et al.
patent: 5838879 (1998-11-01), Harris
Campbell Thor
Howard Harris Building Inc.
Shanks & Herbert
Walberg Teresa
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