Electric resistance heating devices – Heating devices – Continuous flow type fluid heater
Reexamination Certificate
2001-03-20
2003-07-08
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Continuous flow type fluid heater
C392S488000
Reexamination Certificate
active
06591063
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to heaters for maintaining the temperature of a personal jetted bath, and particularly to an assembly of a heating control unit and a bath temperature maintenance heater element.
BACKGROUND OF THE INVENTION
Many consumers have installed jetted bath tubs in their residences for relaxation. Hotels often also provide their guest rooms with jetted tubs, and likewise the same may be provided by therapeutic facilities. Jetted baths are typically filled with hot water from a tap. The hot water is drawn from the tub, passed through a pump, and reintroduced into the tub through jets to provide a soaking user with therapeutic and invigorating jets of water. As the tub is used during a soaking session, the temperature of the water in the tub gradually cools due to heat loss through the tub wall and to the ambient air. To avoid this cooling, some jetted tubs may be provided with a heater installed in the water circulation system. The heater is used to maintain the bath temperature at near its original temperature.
Early jetted bathtub heaters evolved from spa heaters. A spa heater must not only maintain the temperature of the large water volume contained in the spa, but also must initially raise the temperature of the water from ambient to the desired elevated temperature. Spa heaters having heating capacities of 1500 watts to 3000 watts have been used to maintain the temperature of much smaller jetted tubs, even though those outputs were excessive in relationship to the reason for providing a bathtub heater in the first place, i.e.: to maintain the water temperature of the bathtub to the bathers individual comfort level. A secondary heat source (other than the domestic hot water tank) is required only to rectify the loss of heat due to the cooling of the bath water below the bather's comfort level. Such cooling may be caused by the induction of air into the bath water, or the cooling effect of the bath water over time, or the inability to add additional water to the bath water from a domestic hot water tank that had been exhausted in the initial filling of the tub. While bath heaters must have an output sufficient to maintain the bath temperature during use for these reasons, such heaters need not initially heat the bath water from ambient, and thus have much lower actual power requirements than for a heater used in a spa.
Conventional bath maintenance heaters are larger in heat capacity than strictly needed to maintain bath temperature, as noted above. Therefor, conventional heaters must be regulated to assure they do not heat the bath water to above a safe upper limit. In designing a bath heater, there is also a need to limit the function of such conventional high-output heating devices when abnormal conditions are encountered that would produce an unsafe condition, due to excessively heating the water. The anticipated unsafe conditions include, (based upon the heaters ability to produce unsafe heating levels): dry fire, low flow, restricted flow, interrupted power (allowing for residual heat build-up in the heater vessel), and temperature-regulating control failure. Therefore, a temperature-regulating controller and high level limiting device have been required to avoid a heater operating in an unsafe condition, such as those noted above.
SUMMARY OF THE INVENTION
The present invention provides a temperature maintenance heater assembly that maintains temperature within a control range by selecting a heater element with a maximum power rating such that it is not capable of heating the water to a point where the water temperature at the outlet exceeds a specified temperature when running continuously. Further, temperature control is also maintained by one or more pressure switches, which will shut off the heater element when it senses low flow or no flow of fluid in the piping. In a first embodiment (referred to herein as the “dual pressure switch embodiment”), two pressure switches are provided, one for each leg of the power supply to the heating element. This meets certain industry standards (UL Standards) that all ungrounded power supply conductors to a heater element be opened when abnormal conditions occur. The invention is also workable with only a single pressure switch (referred to herein as the “single pressure switch embodiment”).
In the single pressure switch embodiment of the present invention, the temperature maintenance heater assembly for maintaining the temperature of a heated fluid circulating through piping of a jetted bath, includes a heating element having a first and second electrical contact, and a specified power rating. The predetermined maximum power rating of the heating element is selected such that the temperature maintenance heater will maintain the fluid immediately up stream of the heating element within a specified safe temperature range with the heating element operating continuously at its maximum power rating. The control assembly includes a pressure switch having first and second electrical terminals, a pressure sensor, and a switch mechanism activated by the pressure sensor. The control assembly is electrically connected between a power supply and at least one electrical contact of the heating element. The pressure switch of the control assembly may act to interrupt the supply of electricity from the power supply to the heating element when a threshold limit for the flow of fluid through the piping is not met, with the control assembly continuing the supply of electricity to the heating element whenever the threshold limit of fluid flow is met.
In the dual pressure switch embodiment of the present invention, a second pressure switch is also provided. The second pressure switch may be installed in parallel or in series with the first pressure switch. The first pressure switch may be normally open while the second pressure switch may be normally closed. For example, the first pressure switch may be set to actuate to the closed position when the sensed pressure exceeds a predetermined minimum threshold pressure, e.g., 2 pounds per square inch (PSI), to complete the circuit for normal fluid flow, while the second pressure switch may be set to actuate to the open position when the sensed pressure exceeds a predetermined maximum threshold pressure, e.g., 15 PSI, to break the circuit for pressure surges (such as outlet blockage or closure).
In a further aspect of the present invention, the temperature maintenance heater assembly further includes a base plate having an upper surface and a lower surface, a first aperture passing from the upper surface to the lower surface, wherein the control assembly may be attached to the upper surface of the base plate and the pressure sensor placed inside the first aperture.
In a further aspect of the present invention, the temperature maintenance heater assembly further includes a pipe section. The pipe section has an outer wall, an inlet, and an outlet. The control device assembly is attached to the upper surface of the base plate, and the base plate is attached to the outer wall of the pipe section. The heating element has a first and second electrical contact, wherein the heating element is housed mainly in the pipe section, the electrical contacts pass through the pipe section outer wall and pass from the lower base plate surface to the upper base plate surface, and at least one of the electrical contacts is conductively connected to the control device assembly.
In a further aspect of the present invention, the temperature maintenance heater assembly further includes a base plate cover. The base plate cover is removably attached to the base plate, and encloses the control device assembly.
The present invention thus provides a low wattage temperature maintenance heater assembly that, by virtue of its limited maximum power rating heating element, is unable to overcome the heat loss present during bathing. As low-flow and dry-fire conditions may be protected by the control device assembly, the temperature maintenance heater assembly is called upon to also protect
Alpha-Western Corporation
Campbell Thor
Christensen O'Connor Johnson & Kindness PLLC
Walberg Teresa
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