IE54734B1

IE54734B1 - A progressively switched electrical apparatus for storing heat

Info

Publication number: IE54734B1
Application number: IE224283A
Authority: IE
Original assignee: Electricite De France
Priority date: 1982-09-24
Filing date: 1983-09-23
Publication date: 1990-01-17
Also published as: IE832242L; FR2533792A1; DK159358B; DK437283D0; FR2533792B1; DK159358C; DK437283A; EP0104979A1; EP0104979B1; DE3378457D1

Abstract

1. Electrical apparatus with heat storage of the type comprising at least one set of heating elements supplied by the electrical distribution system and switched over to it at a defined time (T0) of day, this apparatus comprising : - means for increasing, gradually and independently of the level of residual heat stored, the power (P) delivered by the heating elements from a minimum value to a maximum value, as a function of a time parameter during the period of operation thereof, the minimum value of the power (P) delivered being substantially zero, said means for increasing the power comprising, in series with the heating elements (10), a triggered solid-state circuit (20) which is phase-controlled by a circuit (32) in response to the signals issuing from a ramp generator (31) which is put into operation at the defined switching over time so as to increase the power delivered, continuously from the minimum value, throughout the operating period, - a triggered solid-state circuit (20, 21, 22) which puts each set of heating elements into operation, - a circuit (30) which receives remote-control pulses transmitted over the distribution system and effects the switching over operation at the defined time of day.

Description

The present invention relates to an electrical apparatus that stores heat.

Such devices, e.g. water heaters or domestic storage heaters, are generally switched on at a particular time of day - e.g. at 10 pa - so that they draw electrical power from the electricity mains during off-peak hours. Like all heaters, such devices generally consume relatively large amounts of power. Their use is therefore encouraged by the electricity supplier since switching them off during the day when overall power demand is high, and switching them on during the night when excess power production capacity is available, has the beneficial effect of evening out the demand for power over a 24 hour period. In return, the user enjoys a reduced tariff during off-peak hours.

These devices are generally switched on by a relay under the remote control of pulses applied to the mains at the appointed time. They may also be controlled by a timer device set to operate the relay at the same time.

This type of switching causes all such devices in the same region to be turned on simultaneously or nearly simultaneously, resulting in a surge in power demand which is undesirable both from the distribution and from the production points of view. Preferred embodiments of the present invention remedy this drawback by drawing increasing levels of power during the course of the 547 3 off-peak period, while still drawing the same total energy as is drawn by conventional devices.

In particular, the present invention provides an electrical apparatus for storing heat, the device being of the type comprising at least one group of heater elements powered from the electricity supply mains and switched thereto at a defined time of day, said apparatus comprising: means for increasing, gradually and independently of the level of residual heat stored, the power delivered by the heater elements from a minimum value to a maximum value, as a function of a time parameter during the period of operation thereof, the minimum value of the power delivered being substantially zero, said means for increasing the power comprising, in series with the heater elements, a triggerable semiconductor circuit which is phase controlled by a circuit in response to the signals issuing from a ramp generator which is put into operation at the defined swtiching time so as to Increase the power delivered, continuously from the minimum value, throughout the operating period; - a triggerable semi-conductor circuit which puts each set of heater elements into operation; and a circuit which receives remote-control pulses transmitted over the distribution system and effects the switching operation at the defined time of day.

In a first embodiment, the slope issuing from the slope generator is linear and the maximum value of power drawn is substantially double the power drawn by a heater element operating at constant power and storing the same total amount of heat.

In a second embodiment, the apparatus includes two different groups of heater elements, the first group being switched on at the defined switching time, and the second group being switched on later after a predetermined delay.

Two embodiments of the invention are described by way of example with reference to the accompanying drawing, in which: Figure 1 is a graph showing power demand as a io function of time for the first embodiment; Figure 2 is a block diagram of apparatus made in accordance with the first embodiment; and Figures 3 and 4 are similar to Figures 1 and 2, but for the second embodiment.

The power P demanded by the first embodiment follows the curve shown in Figure l. Between an instant TQ corresponding to the defined switching time (e.g. 10 pm) and an instant Τχ corresponding to the end of the off-peak period (e.g. 6 am), the power drawn by the apparatus rises linearly from a value of zero to a maximum value. To ensure that the energy supplied causes the same amount of energy to be stored as with a heater element that operates in conventional manner at constant power, it can easily be shown that the maximum power demand must be twice the power demand Ρθ of a conventional heater element; the energy supplied is the same provided that the triangular areas and S2 above and below the average power level are equal.

Naturally, the Figure 1 graph corresponds to supplying the necessary energy In full, which corresponds for example to a water heater which was completely full of cold water to begin with. Xn the event that only a portion of the volume of hot water had been drawn off during the day, operation would stop earlier on (dashed line in Figure 1). Nonetheless, in such an event, energy supply would still have been spread over several hours, whereas in the conventional situation the energy would have been supplied by operating at full power for a relatively short period of time beginning at the instant Τθ.

Figure 2 shows an example of this first embodiment, in which a heater element 10 is connected in series with a triggerable semiconductor 20 such as a thyristor or a triac, the semiconductor being phase controlled by a circuit 32 in response to signals delivered by a slope generator 31 which is started by a circuit 30 for receiving the remote control pulses transmitted over the mains.

In the second embodiment, shown in Figures 3 and 4, the power is varied in stages by successively switching on two different groups of heater elements with a low power group being switched on first. It can be seen from Figure 3 that, if the delay r before the high power group is switched on is chosen to be substantially equal to half the duration Τ^-Τθ, then the first heater group should draw 0.5 Ρθ and the second heater group should draw Ρθ (where Ρθ is defined in the same manner as for the first embodiment) in order for the rectangular areas S'x and S'j on either side of the average to be equal.

Under such conditions, the apparatus will draw only half power at the instant Τθ, and may subsequently draw one-and-a-half times the nominal power of a conventional device by switching on the second group of heater elements at instant T2, but the second heater group is only switched on if more than one third of the water heater capacity has been used during the previous day.

Figure 4 shows an example of a circuit for performing this function: the heater element 11 of power 0.5 PQ ie switched on by a relay, e.g. a static triggerable semiconductor relay 21 (although a conventional electromechanical relay could also be used), and the second heater element 12 is switched by a static semiconductor relay 22.

The static relay 21 is switched on as soon as the circuit 30 receives the remote control pulses from the mains; the static relay 22 is switched on after a delay τ has been applied by a timing circuit 33. After the relay 22 has switched on, the total power drawn by the apparatus is PQ.

This may be achieved by the second heater element having a power of Ρθ and by leaving the first heater element switched on at the same time as the second. In such a case the first element comprises a first group on its own and the first and second elements together comprise a second group. Clearly numerous other groupings of two or more heater elements could be devised to achieve the same end of low initial power consumption followed by high power consumption later on and if required.

It is advantageous to use a timer circuit of poor accuracy (e.g. to within + quarter of an hour), since as well as costing less, such a timer will give a wide spread of device characteristics and will consequently spread out the switch-on instants of the second heater elements of all the devices connected to a given sector of the mains.

Claims

1. CLAIMS;

1. An electrical apparatus for Btoring heat, the device being of the type comprising at least one group of heater elements powered from the electricity supply 5 mains and switched thereto at a defined time of day, said apparatus comprising: means for increasing, gradually and independently of the level of residual heat stored, the power delivered by the heater elements from a minimum 10 value to a maximum value, as a function of a time parameter during the period of operation thereof, the minimum value of the power delivered being substantially zero, said means for increasing the power comprising, in series with the heater 15 elements, a triggerable semi-conductor circuit which is phase-controlled by a circuit in response to the signals issuing from a ramp generator which is put into operation at the defined swtiching time so as to increase the power delivered, continuously 20 from the minimum value, throughout the operating period; a triggerable semi-conductor circuit which puts each set of heater elements into operation; and - a circuit which receives remote-control pulses 25 transmitted over the distribution system and effects the switching operation at the defined time of day.

2. An apparatus according to Claim 1, wherein the slope issuing from the slope generator is linear and wherein 30 the maximum value of power drawn is substantially double the power drawn by a heater element operating at constant power and storing the same total amount of heat. 9 547 3 4

3. An apparatus according to Claim 1, comprising two distinct groupe of heater elements, a first group which is switched on at the defined switching time, and a second group which is switched on after a determined 5 delay has elapsed.

4. An apparatus according to Claim 3, wherein the power drawn by the first group is substantially half the power that would be drawn by a single element operating at constant power during the same period of operation and lo storing the same total amount of heat, the power drawn by the eecond group being substantially twice the power drawn by the first group, and the delay being about half the maximum duration of device operation for full heat storage. 15

5. An electrical apparatus according to Claim 1 for storing heat, substantially as hereinbefore described with reference to the accompanying drawings.