GB1351009A - Controlling electric thermal storage heaters - Google Patents

Abstract

1351009 Control systems for electrical storage heaters LANDIS & GYR AG 9 Aug 1971 [17 Aug 1970] 37327/71 Heading H2H [Also in Division G3] An electric storage heater is controlled in dependence upon the heat requirement of a space or 'object to be heated and on the supply network loading. Thus the heater may be charged during the night and also in certain periods during the day when the network is lightly loaded. In Fig. 3, a control device 16 including pulse generator 18 controlled by a device 17 (e.g. a time switch set according to normal network loading or a receiver which receives ripple control signals from the supply authority mains 1, 2 signifying a light load period) produces a first series of pulses having a mark-space ratio # S . A thermostat 8, responsive to the room temperature, produces a second series of pulses at a much lower frequency than the first pulses and having a mark-space ratio # T (by opening and closing switch arm 10) dependent upon deviation of room temperature from a desired temperature. The pulses with mark/space ratios # S and # T are in effect multiplied to give a resultant control signal having a mark/space ratio # R . This signal is applied via a switch 14 to a heater of a bi-metal strip 13 which in effect averages the signal and operates a switch arm 6 in series with storage heater element 4. Thus if the ratio # R is greater than a predetermined value # R *, e.g. 0À1, the switch 6 closes and charging of storage heater 3 is effected. If # R is less than the value # R * the switch 6 is continuously opened and closed. For the room temp. to be properly controlled when charging it is desirable that the uncontrolled heat loss of the storage heater due to radiation therefrom, should be less than the heat loss of the room. Thus a switch 21 controlled by a time clock 22 connects a heater resistor R20 to the A.C. supply. This resistor R20 influences thermostat 8 so that charging will be interrupted at a room temp. which is a given amount below the desired room temperature. Discharging of the storage heater is initiated by the clock controlled switch 21 connecting a discharging device 19 across the supply via thermostat switch arm 11 and disconnecting R20. The device 19 may operate an adjustable ventilator or air flap (not shown), to provide heat discharge in addition to the normal uncontrolled heat discharge by radiation and convection from the heater surface. A resistor 15 in the thermostat 8 is energized when 19 is operating and the greater the ON periods of 19 the more the influence of R15 on the thermostat. Control of room temperature is now effected by the continual cutting in and out of discharging device 19 under control of the thermostat, and the continual switching ON and OFF of storage heating element 4 under the control of the thermostat 8 and control device 16. Switch 14 is provided merely to prevent overheating of bimetal element 13. Switch 12 is an anti-freezing thermostat. Switch 5 opens to an upper limit of heater temperature. Alternatively, instead of the device 19 there may be an additional electric heater. Suitable circuit arrangements of control device 16 which converts the ripple control programme or time switch programme into pulses of mark/space ratio # S , are illustrated in Figs. 4, 5 (not shown). Influence of heat radiation upon the room thermostat 8 from the storage heater, may have the effect that the desired room temp. pre-set on the thermostat is too high. This may be compensated for by the provision of a thermal coupling (not shown) between the thermostat 8 and the storage heater or heat accumulator 3.