Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1990-11-09
1994-02-08
Paschall, Mark H.
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219485, 219486, 219494, 219501, 307 38, 307 40, H05B 102
Patent
active
052850528
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the control of electrically operated heating systems.
PRIOR ART
Conventional arrangements for space heating by electrically operated heaters require some means of control so as to maintain the temperature within the space at or within defined temperature limits. Desirably the control means should ensure that economical use is made of the available power. The better the temperature control the closer the upper and lower temperature limits can be and hence the smaller the power consumption.
It is conventional to employ thermostats as a means of control, but this is not entirely satisfactory even with very accurate thermostats. This is because the accuracy of the thermostat can only make a limited contribution to the overall accuracy of the control system since its operation is influenced by other factors such as:
(1) The thermal lag of the heater/room combination.
(2) Local cooling due to, for example, draughts in the vicinity of a thermostat.
(3) The siting of the thermostat. The thermostat may not give a true reading of the space temperature. This can happen where, for example, the thermostat is mounted at a very low level and there is no simple relationship between the temperature at that level and the temperature at a higher level.
(4) The relationship between the heater capacity and the heat requirement. This relationship can vary according to the prevailing weather and any discrepancy aggravates particularly the affect "(1)" described above.
All the above factors tend to make conventional control of electrically operated heating systems inefficient.
SUMMARY OF INVENTION
The present invention proposes a control for an electrically operated heating system in which the control operates on the basis of two adjustable input parameters, one of which represents the maximum proportion P of the power of a heater or group of heaters which can be made available under any circumstances and the other of which represents the fraction F of that proportion which is to be used at any particular time. By using a control of this form, it is possible to match more precisely the heat input for a space to the heat losses of that space.
Another aspect of the present invention is concerned with a safety feature in which if a communication link to the control of a heater is sensed to be faulty, the control assumes a state in which heat output is reduced to a predefined acceptable level or cut off completely. In addition an alarm signal may be generated.
A still further aspect of the present invention concerns the timing of the switching on and off of the electrically operated heaters which make up the system. The control system makes use of free running oscillators which control the switching on and off of the individual heaters. Each heater has its own oscillator which produces an output whose timing is independent of the other oscillator so that the switching on and off of the various heaters will not be synchronised. This has the effect of reducing the probability of large fluctuations in loading of the electrical supply.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings:
FIG. 1 is a block schematic diagram showing a control circuit for use in a system in accordance with the present invention, and
FIG. 2 is a schematic diagram similar to FIG. 1 showing a modified form of control circuit.
DESCRIPTION OF PREFERRED EMBODIMENTS
In FIG. 1, the circuit has an input, shown generally at (10), for data supplied from a remote central control unit. This data represents a parameter (F) which is the fraction of the heater capacity required at a particular time. The fraction is based upon some sensed parameter or parameters such as, for example, the sensed temperature external to the space being heated and previously collected data. The circuit shown in the drawing also includes an output (11) which is connected to an electrically operated heater forming part of the space h
REFERENCES:
patent: 4160153 (1979-07-01), Melander
patent: 4168491 (1979-09-01), Phillips et al.
patent: 4216384 (1980-08-01), Hurley
patent: 4920252 (1990-04-01), Yoshino
British Technology Group Limited
Paschall Mark H.
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