Electric resistance heating devices – Heating devices – Continuous flow type fluid heater
Reexamination Certificate
1999-06-16
2001-08-28
Leung, Philip H. (Department: 3742)
Electric resistance heating devices
Heating devices
Continuous flow type fluid heater
C392S466000, C392S485000, C392S498000
Reexamination Certificate
active
06282370
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to control systems for bathing systems such as portable spas.
BACKGROUND OF THE INVENTION
A bathing system such as a spa typically includes a vessel for holding water, pumps, a blower, a light, a heater and a control for managing these features. The control usually includes a control panel and a series of switches which connect to the various components with electrical wire. Sensors then detect water temperature and water flow parameters, and feed this information into a microprocessor which operates the pumps and heater in accordance with programming. U.S. Pat. Nos. 5,361,215, 5,559,720 and 5,550,753 show various methods of implementing a microprocessor based spa control system.
For a properly designed system, the safety of the user and the equipment is important, and is typically concerned with the elimination of shock hazard through effective insulation and isolated circuity, which prevents normal supply voltage from reaching the user. Examples of isolation systems for spa side electronic control panels are described in U.S. Pat. Nos. 4,618,797 and 5,332,944.
The design of a system to control spas is complicated by the fact that there are electrical components in direct contact with the spa water. These electrical components, such as the heater, pumps, lights and blower are required to operate with precision and safety. If a malfunction occurs, it should be detected immediately and the spa shut down to protect the safety of the bather.
The accuracy of the temperature of the spa water is also important to the safety and comfort of the spa users. This temperature can vary depending on the number of bathers, the amount of insulation which is used in the construction of the spa, the operation of the pumps and blowers, and the outside temperature surrounding the spa.
When in continuous use, the spa temperature is controlled by temperature sensors which measure the temperature of the water, and selectively activate a pump to circulate water, and a heater which raises the water to the temperature set by the user at the control panel. There has not in the past been an effective method of accurately measuring and displaying the temperature of the spa if at least one of the various temperature sensors are not located at the spa, in direct contact with the water in the bathing vessel. The consequence of this is that the assembly of the control system into the spa is complicated and expensive, and requires special attention to the location, insulation and protection of the temperature sensors to achieve satisfactory results.
In normal service, a spa is kept continuously energized, and energy utilization is high during this time. However, bathers are typically in the spa water less than 5% of the daily time the spa is in place. At times when the spa is not in continuous use, the user may want to maintain a temperature close to use temperature, i.e. in an “almost ready” condition, so the spa may be quickly prepared for use by the bather. During this “almost ready” time, and while the owner is away from the spa site, e.g. on vacation, there is a need to maintain the water sanitation quality, and the temperature may be maintained at a lower level to conserve heat energy and therefore electrical energy. It would be advantageous if the spa computer system could record and predict the habits of the bather, and provide an optimum temperature maintenance based on the frequency of high and low usage. It would further be advantageous for the computer system to be able to predict the rate at which heat is lost and manage the pump and heater operations for optimum energy conservation, also reducing mechanical wear and tear on these components. These features are unknown and unavailable in known spa systems.
Because of the potentially corrosive nature of the spa water, and the possibility of the loss of the pump function due to pump failure, the system should have redundant systems to prevent damage to the heating element in the case of pump failure or water flow blockage. The use of mechanical devices such as pressure switches which respond to the pressure developed by pump outlet when the pump is activated, are prone to mechanical failure, corrosion failure and leaks. Flow switches which respond to the flow of water through a pipe or tube tend to be expensive, and subject to failure due to hair and foreign materials wrapping around the activating system, requiring frequent service. Pressure switches, currently the most popular method of water flow detection, can give false readings, are subject to damage and deterioration and often require calibration.
An additional hazard represented by the close proximity of electrical energy to the bathers, is a significant safety hazard to the user if the spa is not properly constructed and installed. The integrity of the ground earth system, which protects the spa user in case of an electrical failure of the heater element insulation system is important. Additionally, the control system preferably has an ability to detect and respond to a failure of the insulation system, and actively protect the user by disconnecting the device which has failed.
As systems controlled by microprocessors or other electronic controls can break down, be damaged by voltage surges, or fail through various component malfunctions, it would be highly desirable to have a redundant mechanism to protect from an overtemperature condition and shut down the system completely. This hardware high limit preferably would have the characteristic of tripping only once, and remaining in the off position, even after power down and repowering, but be resettable conveniently by the user without exposure to the high voltage wiring of the spa electrical system.
The control method of some conventional systems is subject to short cycling or rapid on-off pump activations because the location of the temperature sensors can cool off more quickly than the spa water.
Typical known spa control systems have employed a mechanical pressure switch or a mechanical flow switch which are subject to calibration failure, or mechanical breakdown. These random failures are difficult to repair, and present a considerable inconvenience to the user, since a spa is too large to move and must be repaired by a spa service technician.
Known spa control systems do not teach or use a method or technique of protecting the user from electric shock when the insulation of the electrical heater element is damaged and breached and the live electrical current is exposed to the bather's water and the ground line is absent.
A ground fault circuit interrupter (GFCI) is employed in typical spa systems which is remotely mounted in the power supply line to the spa. This GFCI must be tested by the user before each use to insure that it is functional, presenting an inconvenience.
SUMMARY OF THE INVENTION
In accordance with an aspect of this invention, techniques of improving the reliability and safety of the spa or hot tub are described, whereby the user is protected from the possible overheating of a spa through the use of a multiple sensor array which automatically responds to the failure of a component and covers the shutdown of the spa heating system before equipment is damaged or personnel are injured. Additionally, a more effective way of managing the set temperature of the spa is described, and a far more versatile and reliable method of heater overtemperature mode is provided.
A further aspect of this invention is a bather's control system which uses a plurality of temperature sensors to provide temperature measurement and other data to a microprocessor, each sensor additionally feeding temperature information to an individual manually resettable hardware high limit circuit, which operates separately from the computer temperature control system. The temperature sensors are proximately located with respect to the heater, and a computer algorithm prevents short cycling and provides highly accurate spa temperature control.
A further aspect of this invention is a control sy
Cline David J.
Daystrom Stefan
Otto Cindy
Balboa Instruments Inc.
Campbell Thor
Leung Philip H.
Roberts Larry K.
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