GB2171539A

GB2171539A - Storage heater control apparatus

Info

Publication number: GB2171539A
Application number: GB08602476A
Authority: GB
Inventors: Allan Edward Clark
Original assignee: Diamond H Controls Ltd
Current assignee: Diamond H Controls Ltd
Priority date: 1985-02-22
Filing date: 1986-01-31
Publication date: 1986-08-28
Also published as: GB8504627D0; GB8602476D0

Abstract

Control apparatus controls the supply of electrical energy to a storage heater during a charge period which represents part of a 24 hour period, has a manually operable variable resistor (14), for setting a desired temperature. A thermistor 12 senses an ambient temperature. A control circuit (11, 12, 15, 16, 17, 22 and 23) is connected to receive the outputs of the variable resistor (14) and the thermistor (13) and controls a relay (25) through which electrical energy is supplied to the storage heater. The control circuit is arranged to begin the supply of energy to the storage heater when a time period after the beginning of the charge period has elapsed so that the energisation of the storage heater from the end of the time period until the end of the charge period stores a quantity of energy in the storage heater approximately equal to that required to maintain the temperature at the desired temperature. <IMAGE>

Description

SPECIFICATION Storage heater control apparatus This invention relates to storage heater control apparatus.

In recent years, off peak electric power (known as Economy 7 tarriff in the U.K.) has become much more popular for domestic users, due mainly to the rise in price of natural gas and solid fuels. On an Economy 7 tarriff, cheap electricity is available to the user for a seven hour period, usually from 12.30 am until 7.30 am (regions may vary these times).

During this time it is in the interest of the user to use and also store power for use during the following day when electricity prices rise back to normal levels. The power is most conveniently stored as heat with two main applications: 1. Storage radiators for space heating.

2. Hot water storage for day time use.

This invention relates to storage heater control apparatus for use in these applications, the purpose being to provide a composite control giving: 1. Control of the heat stored by a thermostat to ensure the system is operating efficiently.

2. Economy of operation by ensuring that only the correct amount of heat is stored at the end of the charging period for the control setting and operating conditions required.

Conventional control apparatus for heat storage devices generally control the maximum temperature of the storage medium. In order to provide control for varying conditions, the maximum temperature of the storage medium is adjusted. This system takes no account of the varying condition from day to day. At intermediate settings the control apparatus will bring the storage temperature up to the control level quite quickly after the seven hour charge period has started. (See Section A of Figure 1 which illustrates the conventional control technique). Then for the remainder of the off peak period (Section B of Figure 1) the thermostat will cycle the load on and off until the end of the seven hour charging period.

Each time the control cycles "ON" this represents wasted power due to bringing the temperature up to the control temperature far too early. Similarly, if there had been any residual charge in the storage medium at the beginning of the charging period, Section A on Figure 1 would have been even shorter and the time cycling, B, even longer.

Some modern storage radiators have a control which adjusts the energy stored according to the ambient temperature in the room. This control gives a much improved comfort level in the room since it will automatically adjust the charge stored for weather conditions. The room will however still be heated prematurely, to the required temperature, during the charging period.

In an effort to save energy the switch on time of the radiator can be delayed. Thus in Figure 2 the radiator is not switched on until after a delay. Energy is saved since the storage medium temperature only reaches the desired level at the end of the charging period, removing the wasteful cycling period B in Figure 1. The level of charge in the storage medium at the end of the charge period can then be adjusted by varying the lengths of the delayed switch on time. With the arrangement of Figure 2 there is no thermostatic control of the level of charge in the storage medium at the end of the charge period.

According to this invention there is provided storage heater control apparatus for supplying electrical energy during a charge period which represents part of a 24 hour period, comprising manually operable setting means for setting a desired temperature, sensing means for sensing an ambient temperature, switching means for switching electrical energy to a storage heater, control means connected to the setting means, the sensing means, and the switching means and arranged, in use, to operate the switching means to begin the supply of energy to the storage heater when a time period after the beginning of the charge period has elapsed so that the energisation of the storage heater from the end of said time period until the end of the charge period stores a quantity of energy in the storage heater approximately equal to that required to maintain the temperature at the desired temperature.

The energy stored in the storage heater will decline from the end of the charge period and, for example, in the case of space heating, the storage heater will give out its energy to a room or the like in which the storage heater is located. The ambient temperature in that room may fall slowly but it will be held at a desired level of comfort.

This invention provides a storage heater control apparatus which incorporates the automatic control provided by an ambient temperature control together with the economical operation obtainable using a temperature dependent delayed start.

Embodiments of this invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figures 1 and 2 are graphical illustrations of the control methods of known storage heater control apparatus: Figure 3 is a block diagram of a first storage heater control apparatus according to this invention; Figure 4 is a graphical illustration of the control method of the storage heater control apparatus shown in Figure 3.

Figure 5 is a circuit diagram showing details of the storage heater control apparatus shown in Figure 5: and Figure 6 is a block diagram of a second storage control apparatus according to this invention.

Referring now to Figure 3, the storage heater control apparatus shown therein comprises a time delay circuit 1 and a thermostat 2 each connected to receive the output of a sensor 3 and a manually operating setting device 4; the sensor 3 is responsive to an ambient temperature. A power on reset circuit S is connected to the time delay circuit 1. The output of the time delay circuit 1 and of the thermostat 2 are connected to an AND gate 6 which controls the energisation of the storage heater via a buffer 7. Both the time delay circuit 1 and the thermostat 2 are variable by means of either the sensor 3 or the manual control 4. The detailed description which follows shows how this embodiment of the invention would operate when controlling a storage radiator.In the case of space heating the sensor 3 senses room temperature and in the case of a water heater the sensor 3 senses water temperature.

When power is first applied to the radiator the power-on reset circuit 5 will initiate the time delay. Whilst the time delay circuit is running it will hold the current supply to the storage radiator OFF via the AND gate 6 and the output buffer 7. The operation of the thermostat 2 will thus be inhibited. When the time delay of circuit 1 expires the output will no longer be inhibited and the thermostat 2 will control the output storage device according to the control setting and the ambient temperature being measured. The thermostat 2 receives the outputs of the sensor 3 and the control 4 and, when the sensed temperature is below the set or control temperature, energises the storage device.

The sequence of operation is shown in Figure 4. At the beginning of the seven hour charging period the radiator will not be switched on but the time delay will be initiated. The length of the time delay (Section A) is dependent on both the ambient temperature measured by the sensor 3 and the setting of the control 4. The delay will be longer for higher temperature measured and longer for lower control settings. Hence, if the ambient temperature of the room is high the charge required for the following day will be less and the start of the charge can be delayed longer, thus saving energy but not warming the room early in the morning.

Likewise, if a lower setting has been selected by the user the time delay can be longer, saving energy under certain conditions.

At the end of the delay, the radiator is switched on and begins to store energy (Section B). The amount of energy stored is controlled by the thermostat 2 (Section C) which adjusts the stored energy according to the ambient temperature conditions and the control setting.

The time delay length is calculated to ensure that the thermostat 2 will cycle a few times at the end of the charge period (Section C) to ensure that adequate energy is stored for the following day.

The control thus described will automatically compensate for weather changes and store the appropriate amount of energy required for the following day. In order to conserve energy the control will automatically delay the start of the charging period to prevent heating the room prematurely.

In the event that there is residual charge in the storage medium at the beginning of the charging period, then in the case of space heating the room temperature will be relatively high with the result that the time delay will be increased. Moreover, the difference between the control output and the sensor output will be relatively small so that the period during which the thermostat 2 allows energy to be supplied to the storage medium will be relatively short.

The same control can be used to control a hot water storage system. If the water is for domestic hot water use the temperature of the water itself and not the ambient temperature, would be measured. Otherwise the control would be the same.

In order to reduce the cost of the control, the thermostat 2 can be omitted. In this version the time delay alone will control the final charge of energy in a radiator. (Hot water controls would not normally be operated without a thermostat for safety reasons.) In a particular embodiment of the control, the flexibility of electronics has been used to achieve the required function. Figure 5 shows a schematic of the circuit employed.

Oscillators 11 and 12 have their frequencies controlled by the voltages derived from the thermistor 13 the sensor 3) and a manually settable variable resistor 14 (the manual con troi 4). The thermistor 13 and variable resistor 14 are, respectively, connected in series with fixed resistors 18 and 19 between a positive supply terminal and a negative supply terminal.

The junction of the thermistor 13 and the resistor 18 is connected from an input of the oscillator 11 whereas the junction of the resistors 14 and 19 is connected to an input of the oscillator 12. Another input of each of the oscillators 11 and 12 is connected to earth through a capacitor, the capacitors being denoted at 20 and 21 respectively. As the temperature increases the output frequency of the oscillator 11 will decrease, also as the control setting is increased, the output frequency of the oscillator 12 will increase The outputs of the oscillator 11 and 12 are applied through an OR gate 15 to a 12 but counter whose Q12 output is converted to the clock input of a bistable 17. The Q12 output of the counter 16 and the Q output of the bistable 17 are connected through an OR gate 22 to one input of a NOR Gate 23.The other input of the NOR gate 23 receives the output of a thermostat 24. The thermostat 24 has one input connected to the junction of the thermistor 13 and the resistor 18 and another input connected to the junction of the resistors 14 and 19. The output of the NOR Gate 23 is connected through a relay 25 to the negative supply terminal.

When power is first applied to the control the power on reset circuit 5 will reset the bistable 17 and the 12 bit counter 16. Output 012 of the counter 16 will be low and will inhibit operation of oscillator 12. The 0 output of the bistable 17 which is conmected to the oscillator 11 will be high so that oscillator 11 will be operating and will cause via OR gate 3 the counter 16 to count. The Q high signal of the bistable 17 will also hold off the output relay 25 via OR gate 22 and NOR gate 23.

Following a delay, determined by the frequency of oscillator 11 frequency, output 012 of the counter 16 will go high and the bistable 27 will charge state. The Q output of the bistable 1 7 will go low inhibiting oscillator 11.

The output Q12, which is high, of the counter 16 will continue to inhibit the output relay 25 via OR gate 22 and NOR gate 23 but will enable oscillator 12 to run. Counter 16 will thus then continue to count but at a different frequency.

Following a further delay during which the counter 16 counts the output of the oscillator 12, output Q12 to the counter 16 will go low inhibiting oscillator 12 but this has no effect on the bistable 17. Output 012 of the counter 16 and output 0 of the bistable will now remain low until reset by a further power on reset.

The two low signals on 012 of the counter 16 and output 0 of the bistable 17 will remove the output inhibitor of the relay 25 (OR gate 22) via and NOR gate 23 and the thermostat 24 will be able to control the output relay 25 via NOR gate 23 according to the control setting and temperature of the thermistor 13.

Thus the initial time delay from power on to thermostatic control will be dependent on both the control setting and the temperature measured.

In a modification of the embodiment of Figures 3 and 4, there is no connection between the setting device 4 and the time delay circuit 1 shown in Figure 3. In detail, as shown in Figure 5, the oscillator 12, the capacitor 21 and the OR gate 15 are all omitted, the junction of the variable resistor 14 and fixed resistor 19 only being connected to the thermostat 24. Further, the bistable 17 and the OR gate 23 are omitted, the output of the counter 16 being connected to the NOR gate 23 via an inverter. With the modification, in use, the counter 16 only counts the output of the oscillator 11 and the time delay is only dependent on the temperature sensed by the thermistor 13. This has been found satisfactory for space heating applications.

In another example of the control, the main controlling function is performed by a small microprocessor 30. (Figure 6.) The microprocessor is fitted with a power on reset circuit 15 which ensures correct initialisation of the programme at the beginning of the charging period or following a short break in the supply. Thermistor 3 and a manually operable variable resistor 32 are connected via an analogue-to-digital converter 33 to the microprocessor 30; the analogue-to-digital converter 33 includes astables 34 and 35 for the thermistor 31 and variable resistor 32 respectively. A time reference is supplied from the time reference circuit 36 to the microprocessor 30. The output of the microprocessor 30 is used to control a relay 30 via a transistor 38.

The thermistor 31 and variable resistor 32 signals are converted to digital signals by the digital to analogue converter 33 before being passed to the MPU (microprocessor 30). In the circuit shown the conversion is achieved by converting the analogue input into a series of pulses, the number of these pulses being measured within a fixed period by the internal timing system of the microprocessor 30. The converter 33 may be any type of analogue to digital integrated circuit available for use with microprocessors.

Having measured the control setting and temperature the microprocessor 30 computes the required time delay and waits the required time before switching on the relay output to the heating element. Once the time delay has expired the microprocessor 30 will switch the heating element on and off as required to achieve and maintain the required set temperature at the thermistor 31.

The timing reference for the microprocessor 30 will be derived either from the main supply 50Hz or an oscillator external to the microprocessor.

The fact the current supply begins after a delay, which will vary from unit to unit and from application to application, reduces the sudden load on the electricity supply which is desirable.

Claims

1. Storage heater control apparatus for supplying electrical energy during a charge period which represents part of a 24 hour period, comprising manually operable setting means for setting a desired temperature, sensing means for sensing an ambient temperature, switching means for switching electrical energy to a storage heater, control means connected to the setting means, the sensing means, and the switching means and arranged, in use, to operate the switching means to begin the supply of energy to the storage heater when a time period after the beginning of the charge period has elapsed so that the energisation of the storage heater from the end of said time period until the end of the charge period stores a quantity of energy in the storage heater approximately equal to that required to maintain the temperature at the desired temperature.

2. Storage heater control apparatus according to claim 1, which comprises a thermostat arranged to control the switching means.

3. Storage heater control apparatus according to claim 2, wherein the thermostat receives an output signal of the setting means and an output signal of the sensing means.

4. Storage heater control apparatus according to any of claims 1 to 3, wherein the control means includes a first oscillator arranged to oscillate at a frequency set by an output signal of the sensing means, a second oscillator arranged to oscillate at a frequency by an output signal of the setting means, and a counter arranged to counter a first predetermined number from the output of the first oscillator and a second predetermined number from the output of the second oscillator, the output of the first oscillator being counted prior to that of the second oscillator or vice versa.

5. Storage heater control apparatus according to Claim 4, wherein the counter is arranged to inhibit the second oscillator until it has counted the output of the first oscillator up to the first predetermined number.

6. Storage heater control apparatus according to Claim 5, as dependent on claim 3 which comprises a gate which receives the output of the counter and the output of the thermostat and is arranged to control the switching means.

7. Storage heater control apparatus according to any of claims 1 to 3, wherein the control means includes an oscillator arranged to oscillate at a frequency set by an output signal of the sensing means, and a counter arranged to counter a predetermined number from the output of the oscillator.

8. Storage heater control apparatus according to claim 7, as dependent on claim 3 which comprises a gate which receives the output of the counter and the output of the thermostat and is arranged to control the switching means.

9. Storage heater control apparatus according to Claim 1, wherein said control means comprises a microprocessor arranged to receive an output signal of the setting means and an output signal of the sensing means, and arranged to control the switching means.

10. Storage heater control apparatus according to Claim 9, wherein the setting means and the sensing means are connected to the microprocessor through analogue to digital conversion means.

11. Storage heater control apparatus substantially as hereinbefore described with reference to Figures 3 to 6 of the accompanying drawings.