GB2065334A - Energy Conservation in a Central Heating System - Google Patents

Abstract

An energy conservation system for controlling, in particular, the heat energy supplied to a number of rooms in a building. The system senses the temperature at each location and provides an actuator to control the application of heat energy to that location. A processor having storage and data modification units is included in the system and stores data received from the sensors over a period between supplying heat to a location and stopping the supply at a predetermined time before the location reaches a set temperature. Each time a location is heated the stored data is modified by the new sensed temperature data which is averaged out over each period of heating.

Description

SPECIFICATION Energy Conservation System This invention relates to a system for energy conservation and in one particular aspect relates to a system for controlling heat energy supplied to or withdrawn from a number of zones or rooms in a building in accordance with a programme stored within a controller forming part of the system.

With the ever increasing costs of basic fuels, such as oil, natural gas and coal, and the uncertainty of their continuing availability it is becoming more and more important to obtain the maximum possible efficiency of utilisation.

Many forms of control are available to provide required levels of heating throughout a building but many of these do not anticipate and provide for factors which affect the quantity of heat required to maintain a room at a desired temperature. For example, rooms may be occupied for different periods each day and the occupancy may vary for each period. Furthermore the heat absorbtivity of the structure affects the rate at which heat has to be supplied to achieve the required temperature in a predetermined time.

Thermostatic control over heating appliances whilst being effective to control temperature within fairly narrow limits does not provide the most efficient form of heat utilisation.

Many of the problems associated with achieving optimum efficiency in central heating systems arise in the design of air conditioning systems. Also in large scale horticultural complexes it is often necessary not only to control the amount of energy supplied in the form of heat to individual buildings which may be located over a wide geographical area, but also to control the humidity of precipitation produced by different types of irrigation, spray, or mist systems. Also in the control of reactions in various chemical plants and the monitoring and control of nuclear reactors, it is essential to anticipate the effect that the control over the supply of energy is going to have not only to prevent overshoot of the required controlled condition but to optimise the supply of energy to achieve that condition or to optimise the energy produced by the controlled reaction.

Common to all the above forms of energy control is the need to anticipate the effect of that control by taking into account numerous factors that will affect the achievement of the desired result.

In accordance with this invention therefore we provide a system for controlling the energy supplied to a plurality of locations to control one or more physical conditions at each location comprising; a sensor for each location responsive to a physical condition thereat to provide a signal representative thereof; an actuator for each location to control the physical condition thereat; and a controller responsive to such signals to control said actuators to maintain each location at a predetermined set physical condition, said controller comprising, storage means to store the signals received from said sensors, input means to enter data into said storage means relating to the physical condition required at each location for different periods, a clock providing signals representative of time, processing means responsive to said clock signals, and the signals received from said sensors to control said actuators in accordance with the data stored in said storage means, and means for modifying the data stored in said storage means in accordance with information derived from the signals received from each sensor at predetermined times from the time at which a period commences until the location is within a predetermined amount of the set condition.

By physical condition we mean the temperature, humidity, pressure, radiation or other parameter to be controlled.

In order that the invention may be fully understood a preferred embodiment thereof will now be described with reference to the accompanying drawings in which: Figure 1 shows a system for controlling the energy supplied to a plurality of locations in accordance with this invention; Figure 2 is a table showing the temperature readings obtained from the different locations indicated in Figure 1; Figure 3 is a table showing the control windows during which control over a location is exercised; Figure 4 is a graph of temperatures projected towards a set temperature; Figure 5 is a graph showing the projected rate of change of temperature; Figures 6 and 7 are graphs of the temperature of a location during warm-up and repeat warm-up periods respectively, and Figure 8 is a table of occupancy for each day.

In the following description a preferred embodiment of the present invention will be described as relating to a central heating system, although it will be appreciated that the form of control disclosed herein is also applicable to air conditioning systems and to the other systems referred to above.

The system now to be described is designed to effectively divide a building into a number of controlled zones that may or may not correspond to actual rooms. Control is undertaken with respect to time co-ordinates set by the user. The main requirement is for the control of heating within each zone although other facets of the building systems may be included.

Control is effected on two levels. Firstly the user sets exact time co-ordinates when operations are to start and finish within a weekly cycle and in which of the zones this is to take place. Secondly the control unit automatically adjusts the process under control to provide optimum efficient working, or carrying out several consecutive control programmes at one and the same time.

The complete system includes a central control unit housing a microprocessor and user controls, a station control unit (of which there is one in each zone), a sensor or sensors depending how many of the buildings services are to be controlled by the system, a number of actuator devices to effect the control as determined by the central control unit, and lastly inter-connecting wiring, as shown in Figure 1.

The elements and primary functions that make up the central control unit and the system as a whole are separated out under the following headings; Room Identification Temperature Sensing Control Actuation Control Algorithm-General Control Algorithm-Method User Controls and Information Display Time Keeping Boiler Control and Energy Readout Other Facilities Additional Units Appendices: A-Programming Information B-Additional Information.

Room Identification Each room is identified by a number, or room index. For all control and programme operations the room or zone is referred to by this number.

The actual number of each room is determined by the order in which they are connected for each particular installation. Thus each detector station has a dedicated identification number.

During the programming of information and during display the room number always pre-fixes the operation or information. The actual method of control varies slightly depending on the type of control being exercised and the system that the controller has to interact with. In the case of heating control a difference occurs between conventional piped systems and micro-bore installations. In the latter case control is exercised at the manifold. For the more common types of radiator systems the actuating device at the radiator acts as the centre of each control station also housing the necessary electronic components and with an output to the zone sensor. Each station is connected to the control unit in a 'daisy chain' network. Smaller installations may consist of between 4 and 20 stations and larger systems require in the order of 250.

Temperature Sensing: A temperature sensor is fitted in each room or zone that is to be controlled. Its actual position is determined by the situation at each installation and is based on conventional parameters of sensor positioning. Air temperature is detected by a transducer (preferably a silicon transducer) fitted within a lightweight case that protects the device, allows relatively free air movement across it and is as visually unobtrusive as possible.

Absolute accuracy is not required in relation to a temperature standard, however sensors must have a matched performance in terms of linear recovery and stability. This relative accuracy has a preferred maximum of within 1 OC or better over a range of OOC to 300C.

The user sets the temperature desired irrespective of the actual temperature indicated until comfort conditions are achieved. However by increasing the efficiency of the method of control, comfort conditions can be present at a setting 10 or even 2 0C below that of other control systems.

The temperature sensor and other sensors for the same zone are connected to the zone's station.

Here the signal carrying the temperature information is sent back to the central control unit. Each sensor station is connected in a 'daisy chain' network. The user is able to programme temperatures required for each room on each day of the week in degrees centigrade over a range of OOC to 300C in increments of 1 OC.

Control Actuation: To provide the actual control of hot water at the radiator an electronically controlled valve is used in place of the normal hand or motorised valve. The control algorithm is designed for an on/off mode of control, the thermal capacity of the radiator being used to provide the effective modulation in the heating response. In new installations the pipework may be of either 1 5 mm or 22 mm diameter or microbore. In retro-fit installations pipe sizes may vary and in particular larger sizes of pipe will be encountered. The type of valve that is used in the main is a compound solenoid variety. This is a relatively low cost electronically controlled valve with the characteristic of minimising 'hammer' within the hydraulic system. These valves have a manual override and are relatively resistent to scaling.The valves have an actuating voltage of 240 volts A.C.

connected directly to the mains via a relay. The relay is activated by the central control unit via the appropriate station. The valves of up to 31 mm port size consume in the order of 7 to 14 watts taking 25 va on inrush and 15 VA on holding, and are of the normally closed type. In systems where inhibitors are not used it may be - required to fit strainers in series with each valve to ensure long term efficient operation.

Control Algorithm-General The main function of the central control unit is to accept programme data from the user and provide control in the zones set by the user in the manner set out in the control algorithm. The building services to be controlled are heating, lighting, security, fire, and some specialised situations although the control algorithms described herein are concerned with general time keeping, user programming, and heating control.

In relation to heating control the unit is primarily intended to be used in conjunction with wet systems using some form of radiator as the heat emitter. In the majority of cases the radiator will be sized in accordance to the standard method of sizing. This results in a near constant relationship between the room volume and the radiator size.

This results in most rooms being heated from start to a design temperature within 30 minutes.

From cold the radiator fills with hot water and begins to give up heat to the room. Heat is absorbed both by the room fabric and the air contained within the volume. In the main the radiant component feeds the mass of the room and the convective component feeds the air within the room. As the room heats up the energy emitted from the radiator produces a steady state temperature through the walls. Less and less energy is used for raising temperature as more is lost in direct transmittance to the outside. Losses caused by ventilation are direct losses which have to be replaced by cold air from outside. This air has to be heated from ambient and in consequence ventilation losses can have a rapid and dramatic effect on the rooms' requirement for heating.The relative time constants of the radiator and that of heat being gained or lost from particularly the mass is in the order of at least one order of magnitude. Increasing ventilation by opening doors or windows will of course increase the time required to heat the room particularly if the mass of the room is cold. Most separating walls between rooms have a U-value of at least 2.5 W/COM and some down to 0.4 W/COM.

Rarely is the temperature difference between two adjacent rooms greater than 100C due in the main to air infiltration.

The actual workings of the room, radiator, environment system is a very complex situation.

However the above statements hold true in the majority of cases. The form of control is very important due to the latest moves towards higher insulation standards and the use of constructlon methods employing lower thermal diffusion materials. This has the effect of causing very rapid changes in room temperature.

Control Algoritm--Method To describe the path of operation of the heating control algorithm the following section is a running account of the key actions from the point when the unit is switched on. Each action is presented with a straight forward description.

After commission the central control unit is switched on. This action results in the activation of all electronic circuits. Stations then begin to receive information from the sensors and the memories will begin to be filled with this data.

Power to the whole control system (except the solenoid valves) comes from a local mains 240 volt A.C. supply. Power to the electronics of the system comes from a fully stabilised power supply designed for the U.K. and European supplies. Preferably an integral emergency power supply is provided to sustain the operation of the clock and programmable memory circuits on loss of the local supply.

The user then proceeds to programme the central control unit. The programming sequence is started; in the description below this has been abbreviated however a full description is given in Appendix A. Programming is carried out using the 0--9 keyboard and other dedicated buttons.

Information is tapped out and is then displayed on a display unit which may comprise an output printer, a punched card unit, a cathode ray tubetype readout, or an L.C.D. or L.E.D. display. This allows the user to check the information and if necessary amend it before feeding it to the memory. The user then starts feeding in information after activating the display unit which initially displays time.

The user first synchronises the units own internal clock with real time. This is done using the clock cycle button and making reference to a known accurate clock. The clock cycles at a fast and then a slow rate, as controlled by the cycle switch. When set the clock stays at that setting until changed. All data is referenced to this clock so as to enable easy adjustment for different time zones and B.S.T. -- G.M.T. changes. The correct day is also fed in the same manner as real time.

When the time is set general programming begins. Displays on the video display unit may be arranged to self cancel 30 seconds after the last interaction.

Data is then fed in for each room in turn with respect to the day on which the programme is to run, the times at which heating is required, (the latter includes both on and off times) and the temperature at which the heating is to be set. The procedure for this information input consists of engaging the particular function button and tapping out the numerical quantity required. This procedure is then repeated for each day of the week unless a repeat is required on other days.

Each room or zone is then programmed in the same manner. After programming the unit is left to itself to carry out the programme that has been set.

The unit once fully programmed begins heating the various zones according to the times set.

While programming is in progress the unit accesses the temperature in the controlled spaces. From the point the clock is set the central control unit sends out control pulses to the room stations. Two pulses are required one to request that present temperature be sent to the central unit and another to change the mode of the valve, (the latter depends on the state of the valve before control is activated). A normalising pulse may be used to set all valves to a known state.

The central control unit then counts the number of stations. The unit sends out pulses that signal return information from the room stations and when these stop the unit then registers the total number of stations. This number is then used to ensure that the user programmes all rooms under control but does not try to programme any twice.

If this happens the video display unit indicates 'error'. Temperature readings from each room are fed to dedicated registers, one for each room under control. At any one time up to 12 temperature readings are retained within the register. Each room also requires memory for the storage of data concerning warm up, cool down, last relative performance, and search data.

Temperature readings are received from the stations in sequence. Each station sends out one reading each minute. Between each third and fourth temperature reading control is effected over the particular room valve. Thus if readings take place a 1, 2, 3, 4, 5 etc., minutes the control windows are set at T and 33 from reference time (see Figures 2 to 5).

During the initial phase of each heating cycle the central control unit 'normalises' all valves to a known state (off). Overriding all other control functions is a frost protection function. This activates the heating if the temperature in any zone is detected as falling below 50C, Six consecutive readings of 50C or below results in boiler activation and the respective valves are activated. Heating continues until fOOC is reached. The cycle then resets after six readings at 100C or over. When heat is programmed for a particular zone three stages are defined for the purposes of control. These are warm up, steady state, and cool down. During the warm up cycle two operations are carried out using the same data.One is so that the next warm up period can be based on the performance of the last cycle, the other is to control heating within the space. The basic principle is that the control unit takes its last performance and using the data in the memory improves on it the next time. After the boiler start sequence and the valves are opened, temperatures are retained in the memory register.

(Initial start temperature and time are also retained). As the temperature rises readings for time taken to heat through 40C increments are retained in the memory. This continues until the temperature reaches the set level less 20C (the latter is to allow for any flywheel effects). Data that is used in the next warm up cycle is now known and retained in memory. This is used for all times except after first switch on when obviously, there is no data to base performance on and therefore heating starts a programmed set time.

The data recorded is: Start temperature, Start time, Time to heat from start to 40C, to 80C, to 1 20C, to 1 60C, to 200C (if required) and Time taken to heat to set temperature less 2 0C. From this data the average rate of rise is determined for a particular start temperature. On the next cycle the rate of rise is used together with the new start temperature to determine the pre-heat time that is required to enable the room to reach the set temperature by the set time (see Figures 6 and 7).

On the next cycles this is repeated and the central control unit revises the data based on the last cycle's performance. The initial objective is to be within 4"C of the set temperature at the set time or better and then improve on this. To help in determining the warm-up period the unit takes into account variation in room or zone occupancy (see Figure 8). Before each heating cycle times, when heating is required, are averaged for weekdays and weekend. Heating time per day relates to occupancy. A bias is applied to the calculated pre-heat period if the previous heating cycle was longer or shorter then average. The bias lengthens the pre-heat period if occupancy was lower than average in the previous 24 hours and shortens it if the reverse is the case. Each warm up cycle is checked for error.If the room is not within 40C by the set time then a small factor is added. If the set temperature less 20C is reached before the set time then a small factor is taken off.

These biasing effects are always added to the basic period calculated on each cycle. After the warm-up or pre-heat period the room then enters the steady state period. This is deemed to be when the room or zone is within 20C of the set temperature. From the outset the temperature readings of the zone have been retained in a register taking a maximum of 12 readings. Thus at any one moment the temperature over 12 minutes is known for each room. See appendix B for the operation of this register. These are recorded in the form of difference readings relative to the set temperature when used in this mode, thus they verge towards zero as the temperature approaches the set level. The temperature is brought up to the set level less 20C as fast as possible, after this point temperature is controlled with more care to maintain a consistent response.This may not be noticeable directly by the user, however, a dependable temperature control enables thermostat levels to be slightly reduced with consequent savings in energy. The 12 readings are used to provide an average rise or fall determination on the first determination six are used and then all 1 2 to enable a comparison process to be carried out. The readings are used to determine three rates of change continuously for each room. The latest six temperature readings are firstly used to determine how close is the set temperature. These are averaged and a rate of rise calculated. This is projected to the next control window. If this results in a plus value before the next control window the valve is turned off. If this is negative the whole 12 values are used and if this shows negative the valve remains on if not the valve is turned off.When the actual temperature is within 1 C+ 2 C then the 12 readings are used to project past the next control window and the valve is turned on or off to keep the rate of change as low as possible. Current rates of change are projected to up to have the number of readings ahead i.e. with 12 reading projected change is up to 6 minutes ahead.

The third function of the readings is to allow a continuous comparison of the rate of temperature change over a relatively long period. This is used to check the operation of the total system and to determine if there are any external effects taking place such as a window or a cooker door being open. If a fauit occurs, the rate of change alters and remains different from previous readings.

Further if rate of change over a much shorter period goes either positive or negative relative to projected rate then an external influence is affecting the heating. This results in heating being turned off until the temperature reaches a consistent value for six readings then heating resumes and the cycle repeats.

The control unit also provides an optimum stop programme for heated rooms which follows the logic used for the warm up period and uses the same reassessment procedure. On the first cool down period the central control unit records the time taken for the temperature to fali to 40C below the set temperature. On the next cycle this time is deducted from the heating on period. The performance is accessed and a bias applied to increase or decrease time deducted from the heating programme. The performance of the stop programme is not as critical as for warm up as there is less energy to be saved in this area.

User Controls and Information Display The user controls are designed to be easily read and relatively simple to use. Controls are tailored to specific operations using a number of dedicated keys and a numeric keyboard.

Information for the user is provided by a display unit associated with the central control unit or an output may provide for an 'off unit' display such as a punched card unit.

The controller has the following controls: On the central control unit an on/off button interlocked to prevent accidental use.

The internal clock has a two position cycle button to provide a fast and slow mode of adjustment. All numerical quantities such as times, temperature, room numbers, etc., are fed in to the,controller using a numerical keyboard. This has keys 0--9, cancel entry and memory enter.

Information is first displayed after entry and the user may then either amend the data or feed it directly to the memory. A number of function buttons specify the quantities fed in to the unit using the numeric keyboard. The user selects the appropriate function to be specified before feeding in the quantity. Primary function buttons are time, temperature, readout, over-ride, and sleep. Additional function button may be included to provide for hot water, solar pre-heating and other particular areas of control that the controller may cover. To provide for an independent programme on each day of the week there are seven day buttons. These enable any programme to be set for one or a number of days. Thus weekends may be part of the controls standard pattern of operation.Preferably, a miniature video display unit is used to display information during programming, to recall programmed information and to access a current situation. This v.d.u. has a screen size of 50 mm and is capable of displaying 32 characters on 9 lines. A simple video output may provide a feed to a large v.d.u. if required.

Time Keeping All control functions are defined in relation to real time. The control unit has a 24 hour seven day cycle clock regulated by an off-chip crystal. It is important that the clock keeps accurate time as the user may leave the unit to function without change for some time. All time is referenced to the clock. This enables overall time adjustments to be made to allow for British Summer Time or clock adjustments. The clock is synchronised with real time by means of a two position switch. This switch enables the user to cycle the clock at a fast speed of one hour every ten seconds and a slow speed of one hour every minute. The clock provides a direct readout of real time, time coordinates for all programme functions, and timing of sensing and algorithm functions. Programme times are entered by the user in terms of startstop function in increments of 1 5 minutes.There is provision for up to four start-stop periods that the user can programme for any one zone in any 24 hour period. When the central control unit is supplied with the number of a programmed room and a day of the week the programmed times are displayed to enable the user to confirm data.

Boiler Control and Energy Readout The unit is capable of controlling the boiler much in the way a conventional programmer performs. However the central control unit operates so as to stop the boiler modulating and only turn on the boiler when a positive heating demand is determined. The controller is supplied with signals from a temperature sensor on the flow and return pipework adjacent to the boiler. It compares the water temperatures at the boiler with the total heating demand around the building. When heating is required the central control unit first switches on the pump. If the boiler flow sensor registers a temperature below the operating level, the boiler is turned on. When the flow temperature reaches the operating level the boiler is turned off and the pump allowed to run until the return temperature falls below a lower operating level.These operating levels are set to match the heating system by an adjustment on each sensor. Each sensor is adjustable through a range of 500C to 1 000C and provides an output when the set temperature is present. Generally the controller maintains a temperature difference across the boiler of not less than 80C and not more than 1 70C. If the temperature difference falls below 8 C then the heat output of the boiler is not being absorbed by the building and therefore the boiler is turned off. While heating is required the pump continues to turn until the return temperature falls below a set value, normally 600 C. When this value is reached the boiler is turned back on.Most boiler systems use a by-pass to feed water around a closed loop to maintain a minimum flow of water through the boiler. This will not be required in most cases using an electronic monitor but a by-pass may be retained as a safety measure. The controller has within the memory a statement of the total hours that heating is required for every moment during the week. This may be used to predict to a certain degree the boiler load. For example if a hot water requirement exists this load may be catered for when heating demand is low assuming that storage facilities are well insulated.

Other Facilities In many installations there is a requirement for hot water. This is an optional facility built in to the system. A sensor is fixed to the hot water tank to provide temperature readings. This is fixed one third from the bottom and according to standard practice. The times when hot water is required are programmed into the controller in the same manner as heating for a room. The tank supply is fitted with a valve (if it is not pump fed) and this is used to regulate the hot water flow to the tank. If hot water is programmed then the boiler is activated or remains on. Once the tank temperature is within 100C of the boiler output temperature the valve is closed (or pump switched off). If hot water is drawn off while hot water is programmed then supply is activated when total heating demand allows.

It may be necessary for the user to change the programme for a short time. This may be carried out using an override control. This is a short term master control that has priority time control functions. The user can select up to four zones or all zones on various programmes to be heated immediately. The selected zones will then be heated from the time the override is engaged until the end of their next programmed off times. This results in the facility of self-cancelling.

The user may require the system to be shut down for a predetermined period for a holiday or some other stoppage. This is carried out using 'sleep control'. Once sleep has been engaged by pressing the sleep function button the user feeds in the number of 24 hour periods that sleep is to be maintained. The sleep facility requires a controlled shut down sequence of boiler, pump, and then each valve in order to control priority.

A combination of sleep and override may be used automatically to provide heating after a long pause. This can be used to provide preheating of the building after a holiday and then self-cancel with the resumption of normal heating programme. Overriding all other controls is a frost protection facility. This automatically activates the system to provide heating to a maximum of 1 00 C if the temperature sensors detect an internal temperature of 50C or less. This facility is compietely automatic and there are no user controls. However, there is an external wiring link that can be disconnected to shut off the frost protection.

An important part of the strategy of the controller is to look ahead from the outset and therefore control of solar panels to pre-heat water may be provided. This facility, if required, consists of a sensor on the panel output, another on the solar storage tank, and a third on the panel input.

The controller acts as a comparator if the panel is hotter than the storage tank then a relay is activated on the pump. When the panels cool off the situation is reversed and the pump switches off. The control range may be varied to allow for different sensitivities in collection systems.

Additional Units Several other additional units may be used to supplement the basic controller and sensor stations that can increase both the range of control and scope of operation. For certain installations it may be desirable to use a larger type of video display unit. An output can then be provided to provide a standard video specification. All control functions and programmed information are fed to an output which may in turn be coupled to a monitor. This enables a recording of data to be collected periodically and analysed later.

Other areas of control can be added to the basic system and utilise the basic timekeeping, logic monitor, and station systems of the heating control system. Additional sensors and hardware at the central control may be required. Fire, security, and lighting control can be brought within the scope of the system as well as automatic monitoring of boiler efficiency and more accurate definition of hot water provisions.

Appendix B shows the basic elements of the preferred system described above and the functions carried out by each element.

Claims (4)

Claims

1. A system for controlling the energy supplied to a plurality of locations to control one or more physical conditions at each location comprising; a sensor for each location responsive to a physical condition thereat to provide a signal representative thereof; an actuator for each location to control the physical condition thereat; and a controller responsive to such signals to control said actuators to maintain each location at a predetermined set physical condition, said controller comprising, storage means to store the signals received from said sensors, input means to enter data into said storage means relating to the physical condition required at each location for different periods, a clock providing signals representative of time, processing means responsive to said clock signals, and the signals received from said sensors to control said actuators in accordance with the data stored in said storage means, and means for modifying the data stored in said storage means in accordance with information derived from the signals received from each sensor at predetermined times from the time at which a period commences until the location is within a predetermined amount of the set condition.

2. A system as claimed in Ciaim 1 wherein said modifying means averages the data derived from said signals received from a sensor at said predetermined times between commencement of one period and the time at which the location is within a predetermined amount of the set condition, said storage means storing signals representing said averaged data, and said processing means controls said actuators in accordance with the averaged data stored in said storage means.

3. A system as claimed in Claim 2 wherein each sensor senses temperature and each actuator actuates means to heat said location; said storage means storing period data relating to the time each location takes to reach said set condition from a starting temperature and said modifying means modifies said stored period and average data by the new period and average data derived during the next period a location is heated to said predetermined set condition.

4. A system as claimed in Claim 3 wherein said storage means stores data relating to location occupancy, and said processing means biases the period of control of said actuator in accordance with the location occupancy data.