Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-10-25
2001-05-22
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S589000, C340S592000, C340S573600, C126S11600A, C126S11600A, C126S351100
Reexamination Certificate
active
06236321
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention deals generally with liquid heating systems typified by water heating systems. More particularly, the invention involves a clean out alerting system for scale buildup in water heating systems which derives from changes in recovery heating efficiencies in such systems. A decrease in efficiency, it has been learned, may be noted based on a percentage increase in the average time required to heat the water from the temperature at which the system calls for heat to the set point temperature, i.e., the duration of the ON portion of the cycle.
II. Related Art
Hot water tanks, boilers and the like have long provided sources of commercial hot water for a variety of purposes. These devices may be tankless but typically include a vessel for containing a volume of water to be heated and contained within a metal outer tank structure. Heating may be electrical, using one or more heating elements geometrically arranged and immersed within the volume of water, or gas heated, including a burner system and one or more heat exchangers. The tank or similar device is suitably attached to a source of make up water and one or more external devices for using the heated water such as faucets, radiators or other heat exchangers or the like.
The systems are thermostatically controlled about a manually adjustable set point calling for heat when the sensed water temperature falls a preset amount below the set point temperature and shutting off the energy input when the set point temperature is regained. This sequence is known as a heating cycle and is repeated many thousands of times over the life of the heating vessel.
Regardless of the type of heating unit involved, tank, tankless, boiler, etc., mineral deposits called scale form during the water heating process. These deposits form on the hot heat exchanger surfaces of the unit and create an insulating layer which builds and reduces heat transfer efficiency or decreases dissipation of input energy which also causes the temperature of the outside metal surface to increase. Continued buildup further reduces heat transfer and further increases the metal heat level. In this manner operating costs increase due to the lower heat transfer efficiency and the life of the heating unit decreases due to overheating. In some high duty applications which require large amounts of hot water such as restaurants, laundries, hotels and motels, etc., water heaters develop deposits quickly, causing short product life and thus frequent heater replacement.
The problem of scale buildup has been traditionally addressed by either of two approaches, i.e., by carrying out periodic cleaning on a regular basis or by adding water treatment equipment to the system. The first approach probably will not mimic or reflect properly the actual cleaning needs of the system and relies on guesswork. If the time between cleanings is too short, cleaning will be undertaken too often and thus not be cost effective. If the interval is too long, appliance life and efficiency are again sacrificed. The time variable nature of water use also works to thwart the desirability of this approach. The second solution is even more impractical for all but the largest industrial applications owing to the high cost of water treatment solutions.
In the past commercial water heater controls were rather unsophisticated ON-OFF electromechanical devices that turned a burner or other energy source on when a thermostat called for heat following a drop in temperature and turned the energy source off when the water temperature reached the set point temperature. More recently, the introduction of microprocessor based electronically controlled technology has enabled the sophistication of such control systems to be greatly expanded. This includes the sensing and the integrating of information pertaining to additional operating characteristics. It would be desirable if this potential could be harnessed to provide a more accurate estimate of the amount of accumulated scale in a water heater, boiler, or other such vessel.
It is known from U.S. Pat. No. 4,445,638 to measure the rate of rise of the temperature of boiler water to identify the existence of a low water condition perceived as an abnormally rapid rate of water temperature rise. This information is used to insure that the system operates in a proper rust-inhibiting mode and can be used to shut the system down if a preset minimum heating or recovery time limit is not reached. It is further known to incorporate a microprocessor in water heater control systems for a variety of reasons, for example, U.S. Pat. No. 5,797,358 depicts microprocessor control of temperature set point programming and burner control that prevents operation in the presence of detected unsafe conditions.
SUMMARY OF THE INVENTION
The present invention provides a needed solution to the long-standing problems associated with scale buildup in water heaters that provides an accurate measure of scale buildup effects on heat transfer in liquid heating vessels and alerts the operator of a need for scale clean out. The concept involves monitoring the average time rate of temperature change during the recovery or reheat phase of each heating cycle of the apparatus, i.e., from the time the control system calls for heat until the temperature reaches the control set point temperature and the heat input is turned off. An increase in the average time required to reheat or for the unit to recover to a given temperature of course indicates lower efficiency and scale buildup. A selected percentage increase may be used to trigger a clean out alert to those interested.
For the purposes of this application, the term “heating cycle” or “cycle” refers to a heating/cooling cycle consisting of a heat or reheat phase in which the associated source of heat is on and a use or cool-down phase during which the temperature drops a sufficient amount to trigger another reheat phase due to hot liquid usage and consequent make up by cooler liquid or from system heat loss. Also, the term “reheat” as used herein may also refer to a startup cycle or initial heating phase.
Since the rate of rise is affected by factors other than just scale it is necessary to use an averaging technique to neutralize the effects (water temperature, gas pressure, water usage, rate, etc.) based on a set of reheat rates based on monitoring a number of reheat rates as the system cycles a source of heat on and off based on thermostat or similar control. Thus, a number of consecutive or intermittent cycles are monitored to determine a set which becomes the then current effective average reheat time. Any suitable number of 2 or more reheat phases which allows accurate tracking of a particular system and application can be used to define a set. As indicated, these may be consecutive or intermittent (i.e., based on any desired dedicated function stored in memory such as every other or every third cycle, or even a random selection process). Considerations including application experience, make up water hardness and types of minerals in the water (for water heaters), types and composition of vessel heat exchangers may also be considered. Consistencies between cycles or heating phases can also be noted by the microprocessor and stored in memory and considered in determining what constitutes a proper set of reheat phases allowing the system to learn and become a “smart” system based on past history. In addition, the functions determining the sampling of heating phases for a set may be one that is programmed and stored in a programmable memory of a microprocessor associated with the alerting system of the invention.
Thus the system is preferably microprocessor controlled with the ability to utilize sensor data in a variety of ways. Generally, in one mode the system is utilized to measure and store the rate of rise for a number of successive heating cycles and when a preselected empirically determined sufficient, such as to constitute a representative average number of such cycles are stored,
Honeywell International , Inc.
Nguyen Tai T.
Rubow Charles L.
Wu Daniel J.
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