Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1980-12-20
1983-09-20
Paschall, M. H.
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219494, 219507, 219328, 219331, H05B 102
Patent
active
044058551
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for regulating the temperature of a heating element in a water heater, preferably a reservoir water heater containing water which is to be heated to a certain temperature, the supplied power being regulated as a function of the temperature of the water.
The invention also relates to an apparatus for carrying out the method.
It is known that although modern water heaters usually have a lifetime of approximately 20 years at normal temperatures and pressures, it is unrealistic to envisage an average lifetime of the heating element of more than approximately 5 years. With today's prices on craftmanship the cost of replacements of elements may rapidly amount to more than what a new water heater would cost. It is also known that it is the element proper which is most influenced in an unfavourable direction when the water in the heater deviates fron the normal, i.e. becomes more acid, more calcareous, etc.
Further, it is known that all chemical processes are speeded up when the temperature increases. This is also true for the phenomenons which are particularly related to the heating element, i.e. corrosion, calcareous deposits and formation of fissures.
From DE-AS No. 1 565 134 there is known a through-flow heater, wherein the heating elements are switched on and off by current gates. The gates are trigged indirectly by a direct voltage which is proportional to the temperature of the water, a large power being supplied at low temperature of the water, whereas reduced power being supplied at high water temperature. The main purpose of this known power control arrangement is to bring the temperature of the water to a desired value irrespective of the maximum temperature to which the heating element will be subjected during maximum load. Thus, this publication does not give instructions for how the lifetime of the heating elements in a water heater can be increased by simple expediences, i.e. no instructions are given for how the effects of the processes which shorten the lifetime of the heating element, can be reduced to a minimum. Further, DE-AS No. 1 565 134 only deals with a through-flow heating in which the heating element during operation is continuously in contact with a flow of fresh water, a fact which involves that no local boiling phenomenons will occur in the area of the heating element. Such conditions will, however, often occur in reservoir water heaters which are controlled by conventional "on-off" thermostats which only senses whether the water temperature is above or below the rated value.
It is true that from DE-AS No. 1 565 134 there is known stepless regulation of power by antiparallel connection of thyristors, but such a regulation is not suggested to be used in a control system for reducing the maximum temperature of the heating element so as to reduce the development of calcareous deposits and fissure formations which aid in reducing the lifetime of the heating element, let alone for making the heating time of the water under these circumstances as short as possible.
From SCR Manual, 4th Edition 1967, General Electric Company, page 278-281 there are known systems for precision temperature control, but no instructions are given therein for how such control systems must be modified and interconnected to give a solution to the task underlying the present invention.
Thus, an object of the present invention is to give instructions for a dynamic control of the power which is supplied to a reservoir water heater, the dynamic control being designed so as to keep the temperature of the heating element below a certain limit for minimizing the effects of the processes which shorten the lifetime of the heating element, the supplied power nevertheless being kept at such a high value that the heating time is reduced to a minimum.
As stated in the preamble the present invention relates to a method for regulating the power which is supplied to the heating element in a water heater, preferably a reservoir water heater holding water which is to be heated to a given temp
REFERENCES:
patent: 3845274 (1974-10-01), Krenke et al.
patent: 4010412 (1977-03-01), Forman
patent: 4192992 (1980-03-01), Stevens et al.
Johannessen Svein
Kolle Kjell
FerroFil A/S
Paschall M. H.
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