GB2340965A

GB2340965A - Controlling a central heating boiler

Info

Publication number: GB2340965A
Application number: GB9818282A
Authority: GB
Inventors: John Montgomery; Michael Dawson; Davey Mcroberts
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-08-22
Filing date: 1998-08-22
Publication date: 2000-03-01
Also published as: GB9818282D0

Abstract

To minimise 'dry cycling' where the boiler thermostat fires the boiler regardless of whether space heating or water heating is required, firing is delayed by a control timer circuit where the period of the delay is dependent on the temperature in at least the return pipe to the boiler which is sensed by a thermistor. In addition the boiler operates in two temperature ranges or bands depending on whether water heating (high) or space heating (low) is required as demanded by a hot water thermostat and run temperature calibration setting.

Description

J 2340.965 HEATING CONTROLLER This invention relates to a controller for a

heating system.

The unit has been named by the Applicants as '5ENSOR100" (Domestic unit) and "SENSOR500" (Industrial unit) and utilises their unique "REAL TIME ENERGY CONTROL" (RTEC) system and TWO HEATING BAND system.

A problem exists in the prior art - namely that of dry cycling. Dry cycling occurs when a thermostat controlling a boiler fires the boiler to keep its temperature up, even when a thermostat in a space to be heated, e.g. a house, is not demanding heat from it. This burns fuel not required to heat the space and, therefore, wastes energy and money.

A second problem exists in the prior art - namely the boiler thermostat cannot automatically adjust its temperature setting based on the different heating requirements for space heating and domestic hot water. The temperature of the boiler must be set at a fixed value to satisfy the demands of the domestic hot water. However, it is usually satisfactory to operate the boiler at a lower temperature to satisfy the needs of space heating. Operating the boiler at a reduced temperature for space heating purposes saves fuel, lowers exhaust emissions, reduces temperature overshoot and maintains comfort temperatures more constant.

It is an object of the present invention to obviate or mitigate the aforementioned problems in the prior art by the incorporation of the RTEC and Double Heat Band systems.

1. UNIQUE FEATURES 1.1 REAL TIME ENERGY CONTROL (RTEC) system According to this first aspect of the present invention there is provided a heating control unit characterised in that the unit utilises four thermistors, or sensors, to measure the heat generated in different parts of the boiler. The first sensor measures the temperature of the water in the boiler for operation of the Two Heat Band circuit (see 1.2) and for the operation of a temperature indicator comprising a ten element illuminated display. A second sensor measures the temperature of the water in the boiler to ensure that any delay in boiler firing imposed by the 1 1 RTEC is removed when the boiler temperature falls below a temperature that is preset by the RTEC. A third sensor is attached to the boiler's flow pipe for the purposes of monitoring the temperature of the water leaving the boiler. A fourth sensor is attached to the boiler's return pipe for the purposes of monitoring the temperature of the water returning to the boiler after passing through the heat circuit, i.e. radiators etc. The temperature readings from the four sensors act so as to enable the unit to controllably adjust the firing pattern of a burner for said boiler so as to maximise the efficiency of heating the water. Once the heating controller is fitted it requires no manual adjustment whatsoever.

Unlike the presently available fixed or variable delay system, the unit of the present invention constantly monitors the boilers thermostat, the actual temperature of the fluid (water) inside the boiler itself, and the temperatures of the flow and return pipes. This enables the unit to continually adjust the firing pattern of the burner to maximise its efficiency. This combination of the 4 sensor system and the delay circuit which has been designed to charge and discharge exponentially and so produce a more accurate representation of the boilers natural response; and the inclusion of an internal electronic thermostat in the SENSOR1 00 / 500 (see TWO HEATING BAND system below) allows the boiler to switch to a lower operating temperature range once the demands of the hot water are satisfied, resulting in significant energy savings. This is unique to the SENSOR system.

For example, if there is a period of low demand on the boiler, the unit holds off firing the burner for an extended time based on the boiler thermostat off period, as does the standard variable delay system. During the delay period the unit monitors the boiler temperature and that of the flow and return pipe continually. If at any point there is a sudden change in demand, the delay time is instantly adjusted. The standard variable delay cannot make instant changes in delay time during the delay period and can result in the boiler, and in turn, the room and tap water temperature, cooling too far. Not only is this inconvenient but is also wasteful in that, if the boiler is allowed to cool too much, a greater amount of fuel would be needed to bring it back up to the required temperature.

2 1.2 TWO HEATING BAND system According to the second aspect of the present invention the SENSOR has the ability to differentiate the the separate heating requirements for space heating and domestic hot water.

The heating requirements for domestic hot water are normally higher than for central heating. A boiler temperature of 70 deg. C may be required to produce a temperature of 65 deg. C in the hot water tank whilst a boiler temperature of 60 deg. C may be entirely adequate for space heating. The higher the operating temperature of a boiler the greater the fuel costs, as it takes greater energy to cause a certain temperature increase at higher operating temperature bands than it does at lower. The SENSOR ensures that the boiler switches to a lower operating temperature range (low band) once the demands of the domestic hot water are satisfied. Operating the boiler at a reduced temperature for space heating purposes saves fuel, lowers exhaust emissions, reduces temperature overshoot and maintains comfort temperatures more constantly.

The SENSOR can be fitted with an optional external dual function switch Central Heating Boost - that can return the central heating temperature control to the boiler thermostat setting for periods of colder weather or raise the low band temperature by 10 deg. C. The fitting of this Central Heating Boost switch allows for maximum fuel savings to be achieved as the low band temperature for space heating can be set to a low value suitable for mild weather conditions pertaining for the majority of the year. The RTEC circuits are fully functioning when the central heating boost switch is on.

An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings which are:

Fig I A simplified block diagram of the SENSOR100 / 500.

Fig 2 Function of SENSOR controls and indicators 3 Fig 3 A simplified diagram of boiler firing and two heat band circuits.

Fig 4 Circuit diagram of the SENSOR100/ 500.

2. BLOCK DIAGRAM EXPLANATION OF SENSOR100/500. See Figures 1 and 2 2.1 High band operation - D.H.W. calls for heat.

The boiler firing signal (usually 240v from the boiler thermostat) energises REL 2 which causes the Thermostat lamp to light. REL 2 also connects resistance across the capacitance in the Control Timer Circuit. The capacitance will quickly discharge, causing the lights to step down to the bottom of the Control Time indicator and REL I to go off. REL I contact connects the Burner lamp to +12v (lit) and removes +12v from REL 1 (on PSB) causing it to go off and connect the boiler thermostat to the burner (enabled). The burner fires and starts to raise the temperature of the water in the boiler. Whilst the D.H.W. thermostat is unsatisfied the two heat band circuit allows the boiler thermostat to govern the maximum temperature of the boiler. When the D.H.W. thermostat is satisfied the two heat band circuit will be switched to low temperature band operation.

2.2 Low band operation. - central heating demand only.

Assume the lower temperature band has been set to 60 deg. C by the preset Run Temp. Cal. The two heat band circuit compares this temperature to the actual temperature of the boiler fed in from the boiler thermistor installed on the flow pipe. If the flow pipe temperature is below 57 deg. C (dead band of PET electronic thermostat = 3 deg. Q REL 2 and the Thermostat lamp will come on. The circuit action will be the same as 1 above but the time taken for the capacitance to discharge will depend on the actual temperatures of the flow and return pipes e.g. if both pipes are hot the resistance across the capacitance will be high and the discharge time will be long producing a long hold-off (Control time) on burner firing. Conversely, if the both or one pipe (i.e. return) is cool the Control time will be shorter. Thus the SENSOR constantly monitors, moment by moment, the temperature of the flow and return pipes and calculates a suitable delay, if any, on 4 the firing of the boiler. When the boiler temperature reaches 60 deg. C REL 2 deenergises and the Thermostat lamp goes off. The capacitance in the Control Timer Circuit is reconnected to the +10v and quickly charges to +10v. This rising voltage drives the Control Time indicator lights up the ladder and also energises REL 1. The Burner lamp goes out and the Control lamp lights. REL 1 (on PSB) contact opens and inhibits burner control by the boiler thermostat.

N.B. Due to the exponential heating and cooling curves of all boiler plant the delay circuit has been designed to charge and discharge exponentially and so produce a more accurate representation of the boilers natural response.

The information produced by the above sensing system is used to maximise the efficiency of the burner by sensing changes in heat demand during the boiler's cooling cycle and adjusting this cooling cycle in such a way as to meet demand for heat without affecting comfort levels which remain more constant with the heating controller fitted.

This reduction in boiler operating temperature reduces burner running time and hence, fuel consumption and emissions.

This system of control not only reduces fuel costs, but also the electrical consumption of boiler plant. A reduction in running time is good for the boiler in that it reduces the number of hours the boiler is operating and hence extends the required service intervals further reducing plant running costs. Also, lower gas consumption means an equivalent reduction of emissions into the atmosphere.

The circuits that the Applicants have disclosed herein requires far fewer components than any of the alternative energy systems available. This system operates using analogue technology whereas all others use digital control. This has the advantage of allowing the system to operate in real time. Due to the reduction in component count this system will be more reliable.

3. BOILER FIRING AND DOUBLE HEAT BAND CIRCUITS See Figure 3 3.1 CHOICE OF BOILER FIRING SIGNALS 3.1.1 Mains operated boiler thermostat connected to J5[21.

This voltage is reduced and fed to switches 1 and 2. 3.1.2 +10V via link on J7 [1&2J. R6 is adjusted to give +10v to switches 1 and 2. 3.1.3 Low voltage boiler firing signal fed to SEN on J7[21.

R6 is adjusted to give the required voltage to switches 1 and 2.

3.2 DOUBLE BAND OPERATION (for a mains operated boiler thermostat) 3.2.1 High band. If the D.H.W. thermostat is unsatisfied switch 1 will be closed and the boiler firing signal will energise REL 2 and the Thermostat lamp will light. REL 2A contact will discharge the timing capacitance whereupon REL 1 will de-energise. REL 1A contact will enable the boiler thermostat signal to fire the boiler. The boiler temperature will rise to the setting on the boiler thermostat. Using a link between J7 1&2 produces a constant thermostat signal preventing the SENSOR introducing any delays whilst the D.H.W. is brought up to temperature (R6 is set fully anti-clockwise).

3.2.2 Low band. When the D.H.W. thermostat is satisfied, switch 1 will open and pass control of the selected boiler firing signal to switch 2, which is controlled by the double band circuit. If the temperature of the boiler (as sensed by the boiler thermistor) is below the setting of Run Temp Cal (e.g. 60 deg. Q switch 2 will be closed and will pass the boiler firing signal. REL 2 will energise and the Thermostat lamp will light. REL 2A contact will discharge the timing capacitance. This discharge (Control) time will depend on the temperature of the flow and return pipes as sensed by the flow and return thermistors. The hotter the pipes the slower the discharge time. When the capacitance is discharged REL 1 will deenergise. REL 1A contact will enable the boiler thermostat signal to fire the boiler. If the temperature of the boiler is above the setting of Run Temp Cal, switch 2 will be open and inhibit the selected boiler firing signal.

6 4. TECHNICAL DESCRIPTION OF SENSOR1001500. See Figure 4

It should be appreciated that the embodiment of the invention described here by way of giving an example only and is not meant to limit the scope of the invention in any way.

4.1 POWER SUPPLY The 240v mains input, derived from the boiler supply, is stepped down to 12v by Ll, full wave rectified by Cl and smoothed by Cl. This voltage (+ 17v) is used to feed the 12v voltage regulator U2 and the reset switch (if fitted) for the burner time and cycle counters. The +12v feeds the circuits on both pcbs.

The zener diode D2 and R9 provide a stabilised +12V for the heat band selection circuits.

4.2 THERMOSTAT CONTROL 4.2.1 Mains Thermostat (conventional boiler) When the boiler calls for heat the boiler thermostat will be closed (unsatisfied) and 240v will be connected to J5(2). LP1 will light to warn that mains is still present on the power supply board in the event of Fl blowing. This voltage is stepped down by the potential divider Rl and R2 and the positive half cycles are fed through D1 to energise the optical transistor Ul. Ul conducts heavily, connecting nearly +12v to the double heat band circuit as the thermostat on signal. C6 shunts any mains born high frequencies passed through the suppressor C3. This prevents the burner from continuing to fire after the control relay deenergises with the boiler thermostat unsatisfied.

4.2.2 AUX Thermostat The SENSOR power supply board contains a 3 terminal junction block (J7) which allows for different types of stat on/off switching signals to be received. This has been incorporated due to the trend of boiler manufacturers to dispense with boiler thermostats and rely on sensing the temperature of the boiler using thermistors.

7 The SENSOR can accept the following switching signals:

A low voltage ac or low +ve dc stat on/off switching signal. The range of voltage input allowed is 1.5v to 24v dc (30v ac). When there is a call for heat a suitable signal must be located in the boiler circuit and connected to the SENSE terminal. If the input is ac D4 will rectify it and R3 and C2 will act as smoothing. R6 adjusts the amplitude of the input voltage to a level suitable for operating the 2 heat band circuit. Terminal 3 on J7 provides a ground connection for the boiler supply.

FAST REHEAT OF D.H.W. TANK. If thermostat control is achieved by using methods 1 or 2 above some delay will be introduced into bringing the temperature of the D.H.W. tank up to its thermostat setting as hold-off delays in boiler firing will be introduced when the boiler thermostat calls for heat. However, maximum fuel savings will be achieved with these methods of connection. If this delay is unacceptable the following method is used instead.

Connect a link across the J7 1&2. R6 is adjusted to pass the full 1OV to the double band circuit. During high band operation this constant +10v ensures that the control relay REL 1A on the power supply board is kept in the off position thus allowing the boiler thermostat full control of boiler firing ensuring a fast reheat of the D.H.M During low band operation this permanent thermostat signal will allow the boiler to fire until it reaches the low band temperature setting, as adjusted by Run. Temp.Cal. At this temperature the double band circuit inhibits this signal causing the control relay REL 1A on the power supply board to go on, thus stopping the boiler firing.

4.3 HEAT BAND SELECTOR AND TWO HEAT BAND CIRCUIT 4.3.1 Heat Band Selector If the temperature of the DHW is below the value set by the D.H.W. thermostat, 240v will be present at 1ISL(1). LP2 will light to warn that mains is still present on the power supply board in the event of F1 blowing. This voltage is stepped down by R10 and R11 and the positive half cycles are fed through D5 to energise the optical transistor U3. U3 will conduct heavily with each positive half cycle of input. This 25Hz signal is smoothed by C4. The low collector voltage of U3 ensures T2 is cut off (High Band operation).

1 When the D.H.W. stat is satisfied the voltage at HSL(I) falls to Ov causing U3 to cut off. The voltage at the collector of U3 rises and biases Tl on. The low conducting resistance of Tl acts as a closed switch connecting the voltage at the junction of the boiler thermistor and RS to Run.Temp.Cal (Low Band operation).

4.3.2 Two Heat Band Circuit This description assumes the optional Heat Boost switch is not fitted and that links J9 l&2 and J9 3&4 are connected.

A - Operation of circuit with the D.H.W. stat closed (unsatisfied - High Band) Tl is biased off resulting in R12's wiper going to Ov causing T8 to cut off. A positive stat ON signal via R8 to the base of T9 will forward bias its emitter base junction and feed base current to T10 which will conduct and energise REL 2A. REL 2C contact will change over and connect +12v to the Thermostat lamp which will light. REL 2B contact will connect the timing capacitors to the Control Discharge circuit. CS prevents ripple voltage on the thermostat signal causing the relays to buzz when they change state.

B - Operation of circuit with the D.H.M Override stat open (satisfied Low Band) When the D.H.W. is at the correct temperature the D.H.W. stat switch will open, Tl will conduct and connect the voltage from the potential divider R5 and the boiler thermistor to R12 (Run Temp. Cal.). R12 is adjusted such that T8 is on until the temperature of the boiler has fallen below the maximum temperature required for low band operation (e.g. 60 deg. Q.

Whilst T8 is conducting, T9 is inhibited owing to the low voltage on its base. Any stat ON signal that is present at R8 is therefore ignored and REL 2A remains de-energised. As the boiler temperature falls the voltage fed to R12 also falls due to the increase of resistance of the boiler thermistor. Eventually, according to the setting of R12, the voltage on the base of T8 is insufficient to make it conduct and it cuts off enabling T9. The stat ON signal will now be experienced at the base of T9 and REL 2A will energise and the Thermostat lamp will light. The control capacitors (Cl etc) will discharge at a rate depending on the temperatures of the flow and return pipes and eventually the burner will fire (see 4.4). The boiler will try to reach its maximum temperature, but when its temperature reaches the lower band setting T8 will 9 conduct and inhibit T9 and 10, REL 2A will go off, the Thermostat light will go out and the timing circuit will recharge causing the boiler to stop firing (see 4.4). Thus, whilst there is no demand for D.H.W. heating, the boiler is forced to operate at a lower temperature (set by R12) suitable for central heating requirements.

4.4 CONTROL The Control hold off time is set by resistance values in the Control Discharge circuit and the number of the timing capacitors, The SENSOR 100 is fitted with two 100 micro Farad capacitors (Cl and C2), whilst the SENSOR 500 is fitted with four (Cl,C2,C3 and C4). Longer hold-off times are needed in commercial and industrial applications where the SENSOR 500 needs to be installed. The larger the values of resistance and capacitance the longer the hold-off time before the boiler is allowed to fire. The resistance value is governed by the values of R13 (CONTROL CAL), R19 and the flow and return thermistors. The resistance of both thermistors will increase as temperature decreases (they have a negative temperature coefficient).

When REL 2-A is OFF, its contact 2B connects the timing capacitors (Cl etc) to +10v via D10. When there is a call for heat from the Two Heat Band circuit REL 2A will energise and its contact 2B will connect the charged (+10v) timing capacitors to the collector of T2 via Dll. T2 will now conduct at a rate depending on the amplitude of the base current being fed to it by T4. The emitter current of T4 is set by the bias voltage on its base which is governed by the potential divider chain of R13 (CONTROL CAL), R19 and the flow and return thermistors. The colder the thermistors the higher their resistance and the greater the voltage fed to T4 base.

This will produce a lower conducting resistance for T2 and therefore a faster discharge time for the timing capacitors. Conversely, when the thermistors are hot and a longer hold-off time is required, the voltage to T4 base will fall, resulting in a higher conducting resistance in T2 and a slower discharge rate of the timing capacitors.

The voltage across the timing capacitors is fed to the Control LED Driver circuit via D8 and R14. TI and T3 provide power amplification to the indicator driver U2 which causes the light bar on the LED to climb as the voltage across the timing capacitors increases. The voltage across the timing capacitors is also fed to the Burner Control circuit (see 4.5).

4.5 BURNER CONTROL When the voltage across the tin-dng capacitors rises above about two volts T7 and T6 will conduct and energise REL 1A (on top pcb). Its contact REL IC will disconnect the +12v from the BURNER lamp and feed it instead to the CONTROL lamp and REL 1A (on the lower power supply pcb). This relay will energise and its contact REL 1C will open and break the mains supply to the burner fuel valve (or interrupt the output of the programmer to the boiler).

4.6 COUNTERS The SENSOR 500 is fitted with two counters which enable its performance to be monitored. (The counters are an optional extra on the SENSOR 100.) One counter (DD1) measures the total time the burner is on, whilst the other (DD2) counts the number of burner cycles. The switching signal is identical to both counters (they are different ICs). For the counters to operate correctly a suitable voltage must be present at J10 1&2 only when the burner is firing. This voltage must be between 240v and 1OV, ac or dc. The circuit is not polarity- or phaseconscious. If the SENSOR is connected to a conventional boiler with a mains operated thermostat, J5 1&3 are linked to J10 1&2. R13 and R14 are current limiters and G2 provides full wave rectification for ac inputs. U4, an optical isolator, will conduct for positive voltage inputs. The output from U4 is smoothed by C5 and passed via J1(10) to the switching terminals of both counters.

If the power is disconnected from the SENSOR the counters have an 8-year memory, ensuring that their count is not lost. To reset both counters to zero the Reset button on the front panel is pressed.

A measurement of SENSOR performance can be achieved by running the boiler system with the SENSOR switched on for a period of time and noting the counter readings. Then switch off the SENSOR timing capacitors are shortcircuited by the System switch) and run the boiler for the same period of time and compare the new readings with the previous ones.

4.7 BOILER TEMPERATURE INDICATOR The resistance of the boiler thermistor S1 varies inversely with temperature. As the boiler temperatures increases the voltage on the base of T5 will rise proportionately. The emitter voltage of T5 will follow its base and is stepped down by R1 and R2, to a level suitable to feed the indicator driver Ul which drives the LED temperature ladder. R3 is adjusted to calibrate the ladder readout to the boiler temperature.

4.8 MIN. TEMP. CAL The purpose of this circuit is to ensure that the temperature of the flow pipe does not fall below a preset temperature. A thermistor (M Temp. Sense) is connected to the flow pipe and forms part of a potential divider chain with R25 and R26 (Min.Temp.Cal). If the temperature of the flow pipe is below that set by R26, T12 and T11 are biased off. REL 3A is therefore off and its contact 3B is closed, ensuring the timing capacitors C1 to C4 are discharged. Thus there will be no hold-off time imposed on boiler firing.

4.9 CENTRAL HEATING BOOST SWITCH (OPTIONAL) The SENSOR can be fitted with an optional external dual function switch - Central Heating Boost - that can return the central heating temperature control to the boiler thermostat setting for periods of colder weather. This will be required if the low band setting (e.g. 60 deg. Q is insufficient for central heating purposes in particularly cold weather. Operation of the boost switch puts the SENSOR into single band mode when J9 1&2 are connected to 1&2 inside the boost switch. The setting of Run Temp. Cal (low band temperature) will now have no effect as T8 collector is open circuit when the boost switch is set to on. The customer can now control the boiler temperature to suit the central heating requirements.

12 If the boiler is not fitted with a conventional thermostatic control of the boiler's central heating temperature, the boost switch can be connected to J9 3&4 instead. Operation of the boost switch will connect R17 in series with R7 and alter the voltage fed to R12 as to raise the low band temperature by 10 deg. C (e.g. from 60 to 70 deg. Q.

J8 1&2 supply a current limited 12V dc supply to power the boost LED. The LED will light when the boost switch is closed.

When the boost switch is operated the SENSOR will continue to achieve fuel savings but not as high as before.

If the SENSOR is wired for single band operation, due to the absence of a D.H.W. thermostat, a boost switch is not required as boiler temperature can be adjusted by the customer.

To ensure single band operation the power supply board must be configured as follows:

I - Connect 240v Live to HSL1 (J4) and the Neutral to HSN2 (J4) on the power supply board.

2 - Remove any link between Sense (J7 - 2) and 10v Aux (J7 - 1).

Run Temp. Cal has no affect on operation as the SENSOR can no longer switch between two heat bands. The temperature of the boiler is now controlled by its own thermostat.

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Claims

1. The present invention constantly monitors the boiler's thermostat, the actual temperature of the fluid (water) inside the boiler itself, and the temperatures of the flow and return pipes, and differentiates between the needs of domestic hot water and space heating, allowing the boiler to work at a lower temperature when there is only a demand for space heating. This enables the unit to continually adjust the firing pattern of the burner and the temperature of the boiler to maximise its efficiency.

2. The RTEC circuit has been designed to charge and discharge exponentially and so produce a more accurate representation of the boiler's natural response. Another unique aspect of the present invention is that it is able to monitor the total load on any boiler plant from moment to moment.

3. The Two Heat Band circuit has a unique adjusting system that enables the boiler temperature to shift to a presetable higher or lower temperature depending on the state of the domestic hot water thermostat.

4 The said heating controller has been designed to be used in conjunction with a Central Heating Boost switch to maximise fuel savings.

5. The circuits disclosed herein require far fewer components than any of the alternative energy systems available. This system operates using analogue technology. This has the advantage of allowing the system to operate in real time.

Due to the reduction in component count this system will be more reliable and costs less to produce.

6. The heating controller does not affect comfort temperatures, in fact they are more constant.

7 The SENSOR can be fitted to all makes of boiler including those not fitted with a conventional mains-fed thermostat.

8 The SENSOR can be directly incorporated into the design of the boiler's control circuits.

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