EP0085466A1

EP0085466A1 - Central heating system

Info

Publication number: EP0085466A1
Application number: EP83200161A
Authority: EP
Inventors: Ronand Anthony Dogger
Original assignee: DOGGER LAM WILLEMPJE JOHANNA
Current assignee: DOGGER LAM WILLEMPJE JOHANNA
Priority date: 1982-01-28
Filing date: 1983-01-26
Publication date: 1983-08-10
Also published as: NL8200316A

Abstract

A heating system for heating a number of spaces (1a,1 b), provided with a boiler for supplying hot water through a pipeline-network to the radiators placed in the spaces to be heated. At least in a number of spaces temperature sensors (3a,3b) are provided for measuring the temperature in the related space. A temperature sensor is provided for measuring the boiler water temperature and means are provided for indicating a desired boiler water temperature. A central control unit (6) is further provided, to which the signals of the temperature sensors and of said temperature indication means are supplied.

The central control unit is provided with input means (7) by which a user can previously feed in the desired temperature for a predetermined period of time for each space individually.

in each of the spaces at least one valve (2a,2b) is provided for controlling the warm water supply to the related space. The central conrol unit on the one hand controls the valves provided in the related spaces dependent on the signals from the temperature sensors in said spaces such that for each individual space the desired fed in momentaneous temperature is maintained and on the other hand controls the means for indicating the desired boiler water temperature dependent on the total need for heat, such that the temperature of the boiler water is controlled at such a level, that the energy consumption of the boiler is minimized.

Description

The invention relates to a heating system for heating a number of spaces, comprising a boiler for supplying warm water through a pipeline-network to the radiators placed in the spaces to be heated, whereby at least in a number of spaces temperature sensors are provided for measuring the temperatue in the related space, a temperature sensor is provided for measuring the boiler water temperature, means are provided for indicating a desired boiler water temperature, and furthermore a central control unit is provided, to which the signals of the temperature sensors and of said boiler water temperature indication means are supplied, said central control unit is provided with input means, by which the user can previously feed in a desired temperature for a predetermined period of time.
In simple central heating systems a room thermostat is provided in one of the spaces to be heated by the heating system, which thermostat supplies a signal through which the burner of the boiler is switched on if the temperature in said room, watched by the room thermostat, drops under a temperature at which the room thermostat switches on, after which the burner is switched off if the temperature has risen to a level at which the room thermostat switches off. Between the point of switching on and the point of switching off the room thermostat exhibits a considerable hysteresis and because of that such a simple on-off control is fairly coarse. The temperature in the space in which the room thermostat is provided, can yet vary considerably with this type of control.
A further drawback of this type of control is that the temperature in other rooms is directly dependent on the temperature in the space watched by the room thermostat. Assuming a constant outside temperature it is theoretically possible to set the radiator valves of the radiators in the other spaces such that also these spaces are kept at a constant temperature. However, because the outside temperature is not constant and because moreover the heat loss from the space to outside through windows and doors and through the outer walls and the heat transport through the inner walls of one space to the other is a very complex physical system, it will be practically impossible to adjust a central heating system of the simple on-off control type such that every space to be heated by the heating system has exactly the desired constant temperature.
A futher known central heating system uses so-called ther. mostatic valves. Thereby in every space at least one of the radiators, but preferably all radiators, are provided with a thermostatic valve, which opens completely if the temperature drops below a predetermined temperature and closes completely if the temperature rises above a predetermined level. If the temperature in a space drops under the level set at the thermostatic valve, the valve will open, such that hot water can be supplied to the associated radiator by the boiler. As soon as the temperature in a space is sufficiently increased, the valve will close.
A drawback of such thermostatic valves is that they are very near the associated radiator and therefore are rapidly influenced by the heat dissipated by the radiators. Therefore also the application of thermostatic valves does not result into a smooth optimal temperature control in a space.
A system of the type indicated in the first paragraph is known from the British Patent Application 2040080A. In this system the temperatures measured by the temperature sensors are averaged in the control unit after which the mean value is used to control the entire heating system. In this system the spaces are not controlled individual. The mean signal of the temperature sensors is only used for controlling the burner and the pump. That implies that at a drop of the mean temperature below a preset value the burner as well as the pump are activated and are switched off at reaching the desired temperature.
Because of the averaging of the temperature signals from various spaces, the temperature in each space can considerably diverge from the desired temperature which might be different for the various spaces. Furthermore the outside temperature has a strong influence on the temperature in the various spaces, which is not taken into account. Also the location of the space in a building is of importance because of influences from the strength and direction of the wind, sunshine and so on.
In both above described types of heating systems further a boiler is used of which the capacity is calculated in a known way dependent on the total radiator surface to be installed, the lowest outside temperature, the transmission losses from inside to outside of the several rooms, and so on. Based on such a calculation the capacity of the boiler to be installed is determined, said boiler being in any case sufficiently large to be able to supply sufficient heat even under extreme circumstances, i.e. at very low outside temperatures, very large heat losses and so on. Therefore, generally the capacity of the boiler will in fact be too large.
The invention now aims to avoid above mentioned drawbacks and to provide a central heating system in which the temperature can be maintained at a predetermined level in every space to be heated by the heating system in an efficient and economic way, in which the capacity of the boiler is set at a value dependent on the momentaneous situation that the energy consumption of the entire system is minimized.
This objective is met in a central heating system of the type mentioned in the preamble, which is according to the invention characterized in that in each of said number of spaces at least one valve is provided for controlling the warm water supply to the related space, the input means are appropriate for feeding in a desired temperature for a predetermined period of time for each space individually, and the central control unit on the one hand controls the valves provided in the related spaces dependent on the signals from the temperature sensors in said spaces, such that for each individual space the desired fed in momentaneous temperature is maintained and on the other hand controls the means for indicating the desired boiler water temperature dependent on the totale need for heat, such that the temperature of the boiler water is controlled at such a level, that the energy consumption of the boiler is minimized.
It is known to change the temperature set in the boiler thermostat dependent on the outside temperature. The lower the outside temperature drops, the higher the boiler thermostat temperature is set. Also with such control the capacity of the boiler should be provided sufficiently large to be able to deliver the water within an acceptable period of time if at some moment warm water has to be supplied to all radiators simultaneously. Such a situation which is inherent to the way of controlling with the system of the first described type, can also occur in a system with thermostatic valves. With such a control only the outside temperature is taken into account. If a number of spaces is not used and radiators in said spaces are closed, such that said spaces cannot be heated, the boiler output will be too large in spite of this outside temperature dependent control.
The fact that the boiler capacity is too large causes the boiler to consume more energy, for instance in the form of gas or oil, than should be necessary in the optimum situation.
According to the invention this drawback is eleminated in that the outside temperature, measured by an outside temperature sensor is taken into account by the central control means controlling the means for indicating the. desired boiler water temperature such, that the energy consumption of the boiler is further minimized.
According to a preferred embodiment of the invention at least one valve provided in each space is embodied as a servo valve, which can proportionally be adjusted by the central control unit.
Preferably the energy consumption of the boiler is minimized, by each time measuring the length of the periods in which the bur. ner of the boiler is switched on, storing said measured periods of time in the central control unit, which controls the boiler water temperature based on a calculated mean time period such that the mean time period is minimized.
Now further advantages and characteristics of the invention will be explained more detailed with reference to the enclosed Figure in which schematically a number of parts of a central heating system being of interest for the invention, are illustrated.
In the enclosed Figure two spaces la and lb to be heated by the central heating system are schematically shown. In each of said spaces one or more radiators are provided for heating said space and these radiators are connected to the pipeline-network by a . valve 2a, 2b, said pipeline-network transporting warm water supplied by a boiler. In each of the spaces la, lb a temperature sensor 3a, 3b is provided, for measuring the temperature of the related space la, lb.
The boiler, the pipeline-network and the radiators are not shown in the Figure because details of it are supposed to be known for a person skilled in the art.
It will also be clear that the number of spaces is not limited to two, but that any number of spaces can be connected to the central heating system according to the invention.
The boiler of the central heating system comprises a boiler thermostat 4, which switches the burner of the boiler off if the boiler temperature set at the thermostat is reached. This thermostat is of the type which can be adjusted to a varying temperature by an external signal. Furthermore a temperature sensor is mounted outside the spaces to be heated for measuring the outside temperature. Temperature sensors 3 and 5 can for instance comprise temperature dependent resistors in a known way.
All temperature sensors 3a, 3b ..... and 5 as well as the valves 2a, 2b, ..... and the boiler thermostat 4 are connected to the central control unit 6. This central control unit 6 is also connected to input means, for instance a keyboard 7 as shown, and to output means, for instance a multidigit display 8.
The central control unit 6 comprises a memory, from which a part is accessible for the user through the keyboard 7. By means of this keyboard 7 the operator can set the desired temperatures for a predetermined period of time for each of the spaces 1, for instance
space la: temperature 21° C between 8.00 and 23.00 temperature 15° C between 23.00 and 8.00 If the central control unit is provided with such a clock unit that different days of the week can be distinguished, then it is possible to program the temperature for each day individually by an adjusted keyboard, for instance space lb: Mo to Fr between 8.00 and 18.00: temperature 21° C between 0.00 and 8.00 and between 18.00 and 24.00: temperature 15° C
Sa and Su between 0.00 and 24.00 temperature 15° C During the programming the user receives for instance every time a return signal from the central control unit through the display 8, on which the programmed values are visualized. Furthermore it is possible to visualize indications on this panel to assist the operator during the programming of the central control unit 6. During operation the display unit 8 can for instance be used to continuously indicate the present time in hours and minutes.
If the central control unit is programmed by the user the heating system functions during operation as follows.
In each of the spaces la, lb the temperature is measured by the temperature sensors 3a, 3b, .... provided therein. In the illustrated example each of these temperature sensors is individually connected with the central control unit. If a larger number of spaces with accordingly a larger number of temperature sensors is heated, then a multiplexer can for instance be applied by means of which the temperature sensors are cyclically sensed by the cen. tral control unit 6.
The temperature measured by a temperature sensor is compared with the temperature programmed in the central control unit 6 for said space and for the present moment (eventually taking into account the day of the week). If the measured temperature is too low, the valve 2 in the related space 1 is opened by the control unit 6, such that hot water is supplied from the boiler to the radiators in the related space through the pipeline-network, so that the temperature in the related space will rise. If the tempe* rature has reached the programmed value, the valve 2 will be closed by the central control unit.
For each space a separate control loop is created in this way by the central control unit 6, which causes the temperature in the related space to be maintained as good as possible on the desired programmed value.
If valves of the on-off type are applied, yet a variation of the temperature will occur, although within a small range. A more exact and more defined control is obtained if servo valves are applied, which can be controlled continuously between completely opened and completely closed.
The water which has to be fed to the radiators in the several spaces under control of the central control unit, is heated in a boiler provided with a burner and a boiler thermostat 4. This boiler thermostat 4 causes the burner to be switched off if the boiler water has reached the maximum temperature set at the boiler thermostat.
According to the invention now a boiler thermostat is applied of which the temperature can be adjusted by a suitable signal. For instance a thermostat can be used which is adjustable in steps, to for instance at 55° C, 65° C, 75° C, 85° C or 95° C. However, it is also possible to apply a thermostat of which the temperature is continuously adjustable, between for instance 55° C and 95° C, for instance by a servo mechanism. If necessary a return signal about the adjusted temperature can be transmitted from the thermostat 4 to the central control unit 6, as is shown in the Figure.
- The central control unit 6 continuously calculates the need for heat in each space based on the measured temperature and the programmed temperature for the related space. All these, for each space individually calculated values together provide the total need for heat in the entire system. This calculated needed total quantity of heat will be supplied to the boiler water by the boiler, such that the heat can be transported to the various radiators by the water.
It will be clear that the temperature of the boiler water has to increase if the total need for heat momentaneously increases, and that the boiler water temperature can drop if the total need for heat momentaneously decreases. The control unit 6 now controls the maximum boiler temperature set on the boiler thermostat such that on the one hand the momentaneous need for heat can be satisfied while on the other hand the needed energy for producing said heat is minimized.
By calculating methods, known per se, it is possible to determine for each value of the total need for heat a maximum economic boiler temperature. The relation between need for heat and boiler temperature can for instance fed in for a number of ranges by input means 7 or can be preprogrammed, after which thermostat 4 is controlled based on said values in the above-described way.
It is also possible to measure the power consumption of the boiler, for instance by each time measuring the length of time during which the burner is switched on. Based on the mean ratio between the periods of time during which the burner is switched on, and the periods of time during which the burner is switched off, it is possible in a per se known way to adjust the boiler temperature at such a value that said ratio approaches a minimum. As is described above a thermostat, adjustable in steps, can be used, however, preferably a continuously controllable, for instance servo controlled thermostat is used.
Because the central control unit 6 is previously programmed with time values and temperature values, the control unit can take measures anticipating the future need to energy. If for instance the temperature in a space has to be increased from 15° C to 21° C at a predetermined moment, for instance at 8.00, then such a rise in temperature needs time. The central control unit now can continuously "look ahead" for instance 15 minutes and seek in the memory if a temperature in one of the space has to rise after 15 minutes. In this case the central control unit can open the valve 2 in the related space earlier than at the programmed moment, dependent on the temperature difference to be bridged, with the result that on the programmed moment the desired temperature is al. ready reached or at least approached. The larger the temperature difference to be abridged the earlier the central control unit has to open the related valve. In relation therewith this the boiler thermostat should of course be adjusted to a suitable temperature in accordance with this temperature elevation through the boiler thermostat-control loop.
If a considerable temperature rise should occur in all spaced at the same or nearly the same moment, then the boiler has to pro. duce a very large quantity of heat in a very short time period. This means that the boiler must have a relatively high maximum heating capacity. To avoid this, it is now possible with the system according to the invention to introduce a waiting period for a predetermined number of spaces if such a situation threatens to occur, which can be determined previously by the central control unit 6, with the result that said rooms are brought to the desired temperature at a somewhat later moment, or that a predetermined number of rooms is heated earlier. By spreading the several temperature increases within an acceptable period of time it is achieved that the quantity of heat to be supplied by the boiler per unit of time will be reduced.
Although not presented in the Figure it will be clear that the control unit 6 can also deliver signals to a pump provided in the system for circulating the water through the pipeline-network. Said pump can be controlled by the control unit 6 in a per se known way such, that the pump is in any case switched on during the periods in which the burner is switched on and is furthermore switched off at the end of a predetermined time period after the burner is switched off.
Although in the description above special attention is paid to central heating systems using water as heat transport medium, it will be clear that the invention can with comparable results be applied to central heating systems using air as heat transport medium.

Claims

1. A heating system for heating a number of spaces, comprising a boiler for supplying warm water through a pipeline-network to the radiators placed in the spaces to be heated, whereby at least in a number of spaces temperature sensors are provided for measuring the temperatue in the related space, a temperature sensor is provided for measuring the boiler water temperature, means are provided for indicating a desired boiler water temperature, and furthermore a central control unit is provided, to which the signals of the temperature sensors and of said boiler water temperature indication means are supplied, said central control unit is provided with input means, by which the user can previously feed in a desired temperature for a predetermined period of time, characterized in that in each of said number of spaces at least one valve is provid. ed for controlling the warm water supply to the related space, the input means are appropriate for feeding in a desired temperature for a predetermined period of time for each space individually, and the central control unit on the one hand controls the valves provided in the related spaces dependent on the signals from the temperature sensors in said spaces, such that for each individual space the desired fed in momentaneous temperature is maintained and on the other hand controls the means for indicating the desired boiler water temperature dependent on the totale need for heat, such that the temperature of the boiler water is controlled at such a level, that the energy consumption of the boiler is minimized.

2. A heating system according to claim 1, characterized in that the outside temperature, measured by an outside temperature sensor is taken into account by the central control means controlling the means for indicating the desired boiler water temperature such, that the energy consumption of the boiler is further minimized.

3. A heating system according to claim 1, characterized in that at least one valve provided in each space is embodied as servo valve, which can proportionally be adjusted by the central control unit.

4. A heating system according to claims 1 or 2, characterized in that every time the length is measured of the time periods in which the burner of the boiler is switched on, said measured periods of time are stored in the central control unit, which con. trols the boiler water temperature, based on a calculated mean time period such that this mean time period is minimized.