Electric resistance heating devices – Heating devices – Tank or container type liquid heater
Reexamination Certificate
1999-12-30
2001-03-06
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Tank or container type liquid heater
Reexamination Certificate
active
06198879
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 that 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 tile 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.
Conventional electric water heaters are typically constructed of metal, a design that provides for hazardous conditions when a person comes in contact with the unit due to repairs or through casual contact. Conventional electric water heating units may also have electrical wires positioned near the metal surface, which if contacted by a frayed or loose live wire could cause electric shock and significant injury to an individual.
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, however other heat transfer fluids may be used in the present invention. The water in the tank is heated by, for example, at least one 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 reducing sediment buildup. In addition, the coil is continuously cleaned by the flow of 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 spaces between the inner and outer walls of the tank and the top are insulated such as with an amount of thermal insulation, such as foam or glass fiber. Water, or another applicable heat transfer fluid, 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 or a second open space region existing above the water in the tank and below the tank's insulated top. This arrangement ensures that there are no holes that could develop leaks. A float valve or automatic fill 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 inlet when the level of water in the tank reaches a full level. The heating element or a plurality of heating elements may be mounted on a heating element mount that is inserted through a hole in the tank's top. The mount extends and protrudes down into the water located in the tank. A thermostat, located on the inside of the mount, in contact with a sensor block placed within the tank, in the incoming cold water line, controls the heating element. 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, while maintaining a hot water output rate that is consistent with other types of water heaters within the industry. This will reduce energy usage, material costs, shipping and storage costs.
In another embodiment of the present invention, the cylindrical tank is comprised of two walls, an inner wall and an outer wall, along with a double-walled tank top, wherein the top and the tank each have at least a single open region of space that exists between the walls. In this embodiment, the layers of thermal insulation and the particular open regions of space exist between the walls of the cylindrical tank and the walls of the top. The spaces which exist between the inner and outer walls of the tank and between the upper and lower walls of the top are insulated with an amount of thermal insulation, whose acceptable thickness may vary to give the desired insulation, leaving a volume of open space between the insulation lining the inner and outer walls. This embodiment, incorporating the plurality of open spaces lined with thermal insulation, allows for a substantial reduction in the escape of heat through thermal conductive transfer. A larger portion of heat retained by the water heater provides for greater energy efficiency. Further, the open space regions substantially prevent the atmospheric temperature from adversely affecting the internal temperature of the tank.
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patent: 89 10 932 U (1989-12-01), None
patent: 0 323 942 A1 (1989-07-01), None
patent: 1 255 719 (1961-06-01), None
Campbell Thor
Howard Harris Builders, Inc.
Shanks & Herbert
Walberg Teresa
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