GB2148015A - Calculating fuel costs - Google Patents

Abstract

A programmable controller for a heating system, such as for controlling hot water and hot water central heating, incorporates a microcomputer 21 which can be set by means of a keyboard 24 to operate relays 25 and 26 for switching the central heating and the hot water on and off at preset time intervals. A water heater has a gas valve 27 which is controlled by a thermostat 27A so as to provide the necessary hot water. The valve 27 provides the micro computer 21 with signals on a line 28B representing the length of each time for which the valve is open. The microcomputer pre-stores values representing the time rate of consumption of units of fuel by the particular water heater used and the cost of each such unit of fuel. From these values, the microcomputer 21 calculates the cost of fuel consumed for each "ON" period of the system, or the total cost of fuel used since previous resetting, and this cost figure is displayed on a cost display 29. The heating system may use other fuels such as electricity or oil. <IMAGE>

Description

SPECIFICATION Heating systems and controllers therefor The invention relates to heating systems, that is, systems which provide a heat output such as for water heating and space heating, and to control systems therefor.

It is known to provide heating systems with so-called programmable controllers which incorporate some form of time clock and enable the user to select particular times at which the system will switch itself on and off. Many such programmable controllers are known, usually of electro-mechanical form. GB-A2 094 503 shows a programmable controller which incorporates a micro processor.

In view of the high cost of heating fuel, its economical use is highiy desirable. One way in which economical use of heating fuel can be facilitated is by displaying to the user the actual cost of the fuel being used. This constant reminder of the cost of the fuel being used helps to ensure that the user uses only the amount of fuel which is strictly necessary for his current needs. GB-A-2010498 describes a system for providing a direct read out of the cost of electricity consumed since a datum time. This system involves relatively complex electrical circuitry which actually measures the load current in a supply line, converts this into a pulse train having a frequency directly proportional to the load current, and then counts the frequency to provide a digital display in terms of cost.Such a system is unduly complicated and, by definition, requires direct connection (even if merely inductive coupling) to, and therefor physical access to, the electrical supply line. Furthermore, it is only suitable for measuring consumption of fuel in the form of electricity.

The invention is concerned with the problem of providing a programmable controller for a heating system which can also in a simple manner and without involving complex interconnections with the fuel supply, provide the user with a continuous indication of the cost of the fuel being used-and without restriction on the type of fuel.

Accordingly, control apparatus for controlling a heating system comprising control means selectively settable to determine periods of time for which the heating system is operative is characterized by pre-settable means for storing the cost of fuel as a function of time, and output means responsive to the operation of the control means and in dependence on the pre-stored value to calculate the cost of fuel used.

In a more specific sense, a programmable controller for a heating system, comprising timing means for measuring clock time, setting means for storing particular clock times at which the system is to be switched on and off, and output means operative at the said particular times to produce on and off signals for switching the heating system on and off, is characterised by means providing a first input signal representing the length of each time period for which the heating system is switched on, pre-set means providing a second input signal having a selectively constant value representing the cost of fuel per unit time, and calculating and display means responsive to the first and second input signals for calculating and displaying the cost of the fuel used by the system.

A heating system and a controller therefor which embody the invention will now be described by way of example only and with reference to the accompanying diagrammatic drawings in which: Figure 1 is a block circuit diagram of one form of the system in broad outline; Figure 2 is a more detailed block circuit diagram of another form of the system; and Figure 3 is a front perspective view of the control panel of the controller.

The system shown in Fig. 1 has a heater 10 which can be any desired form of heater, for example a water heater or boiler. The fuel used by the heater 10 may be electricity, gas or fuel oil, or other suitable form of fuel, but whichever form of fuel is used, the heater is arranged to be electrically controllable; that is, it is arranged so that it may be switched on and off by means of an electrical control signal.

The electrical control signal is derived from a digital programmer unit 11. This may be of any suitable form and produces "ON" and "OFF" signals on a line 1 1a which is connected to control the heater 1 0. The programmer unit 11 may simply incorporate "ON" and "OFF" switches which are manually controllable by the user. Instead, however, it may be of more sophisticated form incorporating some form of time clock which can be set by the user so as to produce "ON" and "OFF signals on the line 11 a at variable times as set by the operator.

As shown, the programmer 11 has an electrical supply input.

A digital cost unit 1 2 is also connected to be controlled by the digital programmer, by means of a line 13.

The digital cost unit 1 2 incorporates a tim ing unit 14. The programmer unit :1 1 swit- ches the timer unit 14 on, by means of a signal on line 13, each time it switches the heater 10 on, and then switches the timer 1 4 off when it switches the heater 10 off. The unit 14 produces an output on a line 1 5 whose value represents the time for which the unit 1 4 is on (and thus the time for which the heater 10 is on). This signal is fed to a processing unit 16. The processing unit 16 operates by multiplying the time for which the unit 14 is on, represented by the value of the signal on the line 15, with a value represent ing the fuel cost per unit time.The output produced by the unit 1 6 on a line 1 7 therefore represents the cost of the fuel consumed (since the unit 1 6 was last reset) and this output is displayed by a display unit 1 8.

The unit 16 has to be preset with the unit cost of the fuel, and the operator may be provided with means for adjusting this to take account of fuel cost changes.

It is also possible for the unit 1 6 to be controlled by a continuously running time clock so as to be able to take account of changes in fuel cost at different times of the day.

In this way, therefore, the system is able to provide a continuous display to the user of the cost of fuel consumed in the heating system but without there being any necessity for direct measurement of actual fuel consumption.

Fig. 2 shows a more sophisticated version of the system shown in Fig. 1. Here, the heating system being controlled is for water heating and for hot water central heating, the water being heated by a gas water heater.

The controller incorporates a microprocessor or microcomputer 21 which receives electrical power from a mains supply unit 22 incorporating a rechargeable battery for maintaining continuity of supply in the event of mains failure.

The microcomputer 21 is arranged to produce a continuous output representing clock time and this is fed to a time display unit 23 by means of a line 23a.

By means of a keyboard 24, the operator can input signals into the microcomputer by means of which he can set the times at which the central heating is to be switched on and off and the times at which the hot water is to be switched on and off. When so set, the microcomputer 21 therefore produces central heating "ON" and "OFF" Signals to a central heating control relay 25, and produces hot water "ON" and "OFF" signals to a hot water control relay 26. Relay 25 thus switches the central heating on and off, as by operating a central heating water supply pump or supply valve (not shown). The relay 26 switches the hot water supply on and off as by switching a hot water supply valve (also not shown).

A gas valve 27 for the gas water heater is subject to control by a thermostat 27A which switches it on and off so as to control the temperature of the hot water. The gas valve 27 is connected to the microcomputer 21 so as to feed to the micro computer signals indicating the lengths of each time for which the valve is open.

Interconnections may be provided to prevent the gas valve 27 from being switched on when neither of the relays 25 and 26 is on.

The microcomputer 21 may be pre-programmed by means of preset switches 28 according to the rating of the particular water heater being used, that is, its gas consumption in BTu/hour or MJ/hour (1 BTu = 105.5 MJ). The preset switches 28 would normally be set up upon installation of the system and thereafter left unchanged.

By means of the keyboard 24, the operator can also feed into the microcomputer 21 the unit cost (cost per unit of energy) of the fuel being used, and this is stored in the microcomputer.

A cost display unit 29 is provided for displaying the cost of fuel actually used.

In operation, the user ensures that the up to date unit cost of the fuel is always stored in the microcomputer 21. By means of the keyboard 24 he can select one or more particular time periods during each day for which he requires the central heating and the hot water to be on. At the appropriate times, therefore, the microcomputer 21 will switch the control relays 25 and 26 on and off. The thermostat 27A controls the gas valve 27 so as to ensure that the temperature of the water is at the desired level. The microcomputer 21 receives signals indicating the length of each time for which the gas valve is on and is therefore able to calculate the cost of the gas being consumed, from the stored date representing the rate of consumption of fuel by the boiler and the cost of the gas per unit time. This cost is displayed by means of the display 29.

The display 29 can be set (by means of the keyboard 24) so as to display the cost incurred during the last 24 hour period (say) or the cost incurred since the system was last reset.

The time display 23 can be set (again by means of the keyboard 24) either to display clock time or (for example) to display, when required, the current "ON" and "OFF" times for the central heating or hot water.

Fig. 3 shows one form which the keyboard 24 can take. As shown, it is divided into two parts, a heating control part 30 and a "check cost" part 32. The part 30 incorporates the time display 23 (Fig. 2) and has seventeen (in this example) "keys" which may be in the form of touch switches or buttons which may be covered by a membrane.

The time clock provided within the microcomputer 21 is set to the correct local time by means of switch M1. Switches M2 to M7 are used, in conjunction with certain ones of the switches M8 to Ml 7 to set the "ON" and "OFF" times for the central heating and hot water. Thus, if the central heating is required to come on twice during a 24 hour period, switch M10 is operated in conjunction with, in sequence, switches M2,M3,M4 and M5.

While each of the latter four switches is held on in turn, the desired time is set into the microcomputer by means of the switches M6 and M7 which respectively advance and retard the time; during this setting process, the time being set is shown on the display 23.

A similar operation can be used to set the "ON" and "OFF" times for the hot water, but using switch M15 instead of M10.

Switches M9 and M14 are used (instead of switches Ml 0 and My 5) if the central heating and hot water are only required to be switched on once during a 24 hour period.

Switches Ml 1 and Ml 6 are used if it is desired to have the central heating and hot water on for the whole of each 24 hour period. Switches Ml 2 and M17 switch the central heating and hot water off, respectively.

The part 32 of the keyboard incorporates the cost display 29 (Fig. 2), together with five further switches M18 to M22 which are of course of the same type as the switches M1 to M17. Switches M18 to M20 are used by the user to set in the current cost per unit of the fuel being used. The cost display is normally in terms of the total cost since the system was last reset. Switch M21 may be used to convert the display temporarily to a display of the cost of the fuel used in the last 24 hour period. Switch M22 is used to reset the system.

It will be appreciated that many modifications may be made to the system.

For example, there could be a single display only, instead of the two displays 23 and 29.

The single display would then be used, selectively, to display the clock time, the "ON" and "OFF" times, or the fuel cost.

It is also possible for the microcomputer 21 to be programmed to display comparative costs over different time periods, for example to compare the cost for a current period with the corresponding period in previous years.

The system may be designed so as to enable a cost limit to be set in, applicable for a particular time period, for example 24 hours.

The system would then operate so as to switch the heating off if and when this cost limit was reached.

The system can also be arranged to record the total time for which heating is operative so as to indicate, in accordance with pre-stored data, when servicing becomes necessary or advisable.

If an outside temperature sensor is incorporated into the system, microcomputer may be programmed to measure and display the cost of the energy used as a function of the average outside temperature, so as to indicate the relative efficiency of the heating system.

The system may be used with more complex temperature control systems which enable (for example) the temperature for the hot water and the central heating to be controlled independently of each other and/or for the set temperatures to be changed automatically for different periods during the day. The temperature for the central heating may be controlled by means of a room temperature sensor. The sensors may be thermistors. The analogue electrical outputs of the sensors may be converted into digital form by a suitable converter and fed to the microcomputer which then digitally compares their digital values with digital values representing the desired temperatures. When the actual temperature falls below the desired temperature, the microcomputer produces a control output for operating the appropriate control relay.

Claims (11)

1. Control apparatus for controlling a heating system, comprising control means selectively settable to determine periods of time for which the heating system is operative, setting means for storing a predetermined cost value representing the cost of fuel as a function of time, and output means responsive to the operation of the control means and in dependence on the pre-stored value to calculate the cost of fuel used.

2. Apparatus according to claim 1, in which the setting means for setting the predetermined cost value comprises first-setting means for setting a value representing the rate of consumption of units of fuel when the heating system is operative and second setting means for setting the cost of each said unit of fuel.

3. Apparatus according to claim 1 or 2, including storage means for storing the calculated costs.

4. Apparatus according to any preceding claim, including display means for displaying the total calculated cost corresponding to a selectable period of clock time.

5. Apparatus according to any preceding claim, in which the control means comprises timing means which is manually settable to determine particular clock times at which the heating system is to be switched on and off.

6. A programmable controller for a heating system, comprising timing means for measuring clock time, setting means for storing particular clock times at which the system is to be switched on and off, output means operative at the said particular times to produce on and off signals for switching the heating system on and off, pre-set means providing a first input signal representing the length of each time period for which the heating system is switched on, pre-set means providing a second input signal having a selectively constant value representing the cost of fuel per unit time, and calculating and display means responsive to the first and second input signals for calculating and displaying the cost of the fuel used by the system.

7. A controller according to claim 6, including storage means for storing the calculated and displayed costs for each of a succession of said time periods, and means for totalising the costs for all the time periods within a selectable period of clock time and for displaying the totalised costs.

8. A controller according to claim 5 or 6, incorporating a microprocessor.

9. A controller according to any one of claims 6 to 8, in which the pre-set means providing the first input signal comprises presettable means for setting the value of a first intermediate signal representing the time rate of use of predetermined units of fuel when the heating system is on and for setting the value of a second intermediate signal representing the cost of each such unit of fuel, and including means responsive to the two intermediate signals for setting the value of the first input signal accordingly.

10. A controller according to any one of claims 6 to 9, in which the heating system provides two separately controllable heat outputs.

11. A controllable heating system, substantially as described with reference to Fig. 1 of the accompanying drawings.

1 2. A controllable heating system, substantially as described with reference to Fig. 2 of the accompanying drawings.

1 3. A programmable controller for a heating system, substantially as described with reference to Fig. 3 of the accompanying drawings.