EP2122261B1

EP2122261B1 - Boiler for a heating system, in particular for domestic use

Info

Publication number: EP2122261B1
Application number: EP08709798A
Authority: EP
Inventors: Flavio Chiavetti; Alessandro Zampetti
Original assignee: Merloni Termosanitari SpA; Ariston Thermo SpA
Current assignee: Merloni Termosanitari SpA; Ariston SpA
Priority date: 2007-02-16
Filing date: 2008-02-12
Publication date: 2012-12-19
Anticipated expiration: 2028-02-12
Also published as: ITTO20070115A1; WO2008099259A2; EP2122261A2; WO2008099259A3

Description

The present invention relates to a heating system gas boiler, particularly for domestic use, of the type intended to supply hot water to radiators or similar heating devices in a heating system.
Systems of this type comprise a heat generator, typically composed of a gas boiler, connected to a water circuit along which heating devices are foreseen, installed in the various rooms of the home, such as wall-mounted radiators or under-floor heat exchangers. The boiler is intended to heat the water and activate the circulation through the heating devices, through which the heat from the water is transferred into the room. The water is heated to a working temperature by a gas burner combined with a heat exchanger connected to the aforesaid circuit, and a control system on the boiler that performs the start-up for burner and water circulation pump. The boiler can also be possibly conceived to vary the water flow to be sent to the heating circuit. In the more simple solutions the boiler operation control is a standard ON/OFF switch type. In this case, the water is heated to a temperature level programmed by the user on the boiler control panel using a switch for this purpose, and the correct temperature is detected by a sensor inside the boiler. Successively, when the water temperature drops below the set temperature, the burner is started up again. When the temperature of the room heated by the system needs to be increased or reduced, the variations in the water temperature level, must be regulated manually using a switch-on the control panel.
In order to increase the comfort level of the heating system and improve its performance, the boiler can be equipped with external sensors, conceived to supply the boiler control system with room temperature and climatic information.
On the most common systems the sensors are composed of ON/OFF type thermostats, installed in a relevant room inside the home. In this case the water will be heated by the boiler and circulated in the system until the room temperature programmed on the thermostat by the user has been reached. Boiler start-up times are determined by the combination of the level set on the thermostat and the level of the water temperature set on the control panel. Any variations in the room temperature can be regulated manually by using the thermostat. Careful adjustment regulation of the boiler aimed at ensuring adequate comfort without wasting energy also requires accurate regulating of the water temperature level.
Programmable room thermostats, or chronothermostats also exist, where the room temperature can be set at two different levels for the same daily period, typically at "normal" rate and at "reduced" rate, for example the latter being programmed for periods when the house if not occupied or during the night.
With other known solutions, external temperature sensors are connected to the boiler. The room temperature sensors are used as an alternative to the use of ON/OFF thermostats, while sensors for external temperatures outdoors can be used as an alternative or in combination with the thermostats and room temperature sensors. The use of the aforesaid sensors permits the possibility of automatic water heating control according to the external conditions of the boiler, also keeping in mind the settings programmed by the user on the control panel or on the room temperature thermostat, in cases where these are installed.
Some of these solutions are described, as an example, in documents US 5 779 143 , DE 19613021 and FR 2 723 176 .
In particular, document US 5 779 143 describes a control unit operating an oil or gas fired boiler to maintain boiler water temperature at a selected value and to allow for zoned heating operation, controlling selectively the flow of heated water to each individual heating zone through the room thermostats and zone valves. Therefore the control unit includes, at least, a priority terminal which can be connected to a priority heating zone (to which divert exclusively the flow of heated water upon receiving a demand for heat), a terminal for connection of an outdoor air sensor (to relate the boiler water temperature to the outside air temperature), a terminal for connection of a hot water sensor which is also connected to a safety terminal (providing a safety switch should the water in the boiler exceed an upper limit) and further a connection for a low water cut-off probe that interrupts the power of the control unit should the amount of water heated by the boiler fall below a minimum value.
Even in the document DE 196 13 021 a domestic heating installation controller, in which thermoregulation programmes to achieve maximum comfort and to maintain the desired water temperature are memorized, is disclosed. In particular, inputs to the controller are supplied from an outdoor temperature sensor and counterparts on the hot water storage and inlet and return pipes of said domestic heating installation so as to provide control signals for its circulation pump and for its gaseous fuel supply valve.
Finally, document FR 2 723 176 discloses a controller (and respective method) for a heating equipment including, at least, sensors for measurement of variables and actuators acting on detected and preset conditions.
It's clear as the cost of the heating system, understood as the boiler and the relative means of control and sensor reading, will increase according to the complexity and precision level of the required thermoregulation. Learning the operating functions of a boiler equipped with sophisticated thermoregulation and the relative methods for correct programming is often complicated, to the point that the end user is often not able to take full advantage of the performance and benefits that the product is able to provide, both in terms of user comfort and in energy saving.
In the light of the observations described above, the general aim of the invention is to provide a boiler able to supply users with a system that has good comfort level and is easier to operate, while reducing energy consumption at the same time, but without a great cost increase in relation to existing boilers.
Another aim of the invention is to provide a boiler that is easy to operate for the end user, but able to supply high performance level as regards thermoregulation precision and efficiency.
Yet another aim of the invention is to provide a boiler of the type described whose performance and operating functions can be increased successively by installing external sensor devices at a later date.
These and other aims which will be made clearer further on, are provided according to the present invention, by a heating system gas boiler having the characteristics described in the appended claims which form an integrated part of the technical explanations provided herein, in relation to the invention.
In short, the boiler according to the invention is equipped with an automatic thermoregulation function that provides for the operation of between one and several possible thermoregulation strategies directed at optimising boiler function, performance, and consumption according to the availability or not of room and/or climatic information. For this purpose, the boiler is designed to be connected to one or more external sensor devices, while being able to maintain its capacity to operate in intelligent mode even when said external sensor devices are not present.
When the aforesaid automatic thermoregulation function is operating, the boiler control system selects one of the possible thermoregulation strategies, in an independent manner, according to the potential presence of and type of the connected external device/s. Preferably the boiler control system is equipped to recognise in an independent manner the potential presence of and type of the connected external sensor device/s. Again, preferably, the automatic thermoregulation function can be activated and deactivated using a switch to provide the user with the possibility of programming the boiler function manually.
Further aims, characteristics, and advantages of the invention will be provided in the following description, with reference to the appended drawings provided as non limiting examples wherein:

figure 1 shows a schematic diagram of a domestic heating system using a boiler according to the invention;
figure 2 shows a schematic diagram of the boiler in figure 1;
figure 3 shows a schematic diagram of possible thermoregulation curves used to control boiler operation according to the invention.

In figure 1 numeral 1 refers to a standard domestic house, in which is installed a heating system that includes a boiler according to the invention. The boiler, identified throughout by the numeral 10, is connected to the delivery 2 and return 3 branches of a heating system circuit, along which are foreseen heating devices 4, which in this case are supposedly wall mounted radiators. For the sake of simplicity, we will consider that house 1 is composed of a single room identified by numeral 5 in which the radiators 4 are installed.
The boiler 10 comprises all the known elements required to perform the operations traditionally foreseen, also according to prior art, and therefore the general composition and structure will not be described herein. As will be explained more clearly further on, the object of the invention is in fact, a specific configuration of the control system of the boiler 10, arranged to permit the particular operations of automatic thermoregulation to be performed.
With reference to figure 2, the boiler 10 is composed of a casing 11, inside which are housed heating means for the water which must be delivered to flow in the circuit 2-4. These heating means are of a conventional type and can be represented by a heat exchanger 12, for example, near a central zone installed with a gas burner 13. An outlet 12a and an inlet 12b of the exchanger 12 are intended to be connected to the delivery 2 and return 3 branches of the heating circuit, respectively. As occurs also in prior art, the outlet 12a and the inlet 12b can be possibly connected to respective manifolds that act as headers for the branches of several separate heating circuits, each section able to heat different rooms in the same home, or several homes in the same building.
The boiler 10 comprises a water pump 14 that in the non limiting example shown in figure 2, operates near the outlet 12a. The numeral 15 identifies a sensor destined to detect the temperature of the water delivered from the exchanger 12. The boiler 10 can also be equipped with a sensor 16 if necessary, to detect the temperature of the water that, after having passed through the circuit 2-4 returns to the exchanger 12.
The boiler 10 also comprises an electronic control system identified throughout by the numeral 15 in figure 1. As shown in figure 2, the control system comprises a microprocessor unit 20 that includes, or to which are operationally connected, non volatile memory means such as ROM and/or EPROM and/or EEPROM or Flash, for example, identified by numeral 21. The control system also comprises a control panel 22 equipped with display means 22a (such as an LCD display for example) and programming means, including at least a switching device 22b, to program the setting of the required temperature of the water when it leaves the boiler 10, at least when the boiler is operating in what we will define here as "normal" or standard conditions. Naturally the temperature can be selected within a predefined range, such as between 40 and 82°C for example.
The control system 15 also include an interfacing means of a conventional type, identified throughout by numeral 23, which is provided to permit the connection of one or more thermosensitive sensor devices external to the boiler 10. In the embodiment herein, the interfacing means 23 are foreseen to permit at least the connection of a room thermostat, RT, of the ON/OFF type, a room temperature sensor RS and a sensor for the temperature outside the house 1, identified by OS, according to the possible combinations described further on.
The sensor device means described herein are also conventional types known to prior art. The RS and OS sensors can be composed of thermoresistors for example (such as NTC resistors). The RT room thermostat is the type comprising a switch - identified by S - for the manual setting of a required room temperature, as well as an ON/OFF contact switch, sensitive to the temperature, identified by C, the trigger threshold of the contact switch C depends on the setting programmed by the user on the switch S. Naturally, the boiler 10 also includes all the other components normally known to prior art for boiler operation (hydraulic valves, gas valves, safety devices, fume evacuation flue, air ventilator for combustion air if necessary, etc) but which are not necessary in order to understand the context of the present invention.
Using any type of known programming method, the memory means 21 contains the coded information of the program used by the unit 20 to control the general boiler 10 operations, according to the selections performed manually on the panel 22, the parameters supplied by the sensors 15, 16, and the information provided by one or more of the external devices RT, RS, OS, when these are installed.
According to a preferred embodiment of the invention, the control panel 22 foresees a specific selection means (such as a push-button), identified throughout by numeral 24 in figure 2, which allow the user to enable a particular mode for a special boiler operation, hereafter defined as "AUTO".
Using the operating mode AUTO, the control unit 20 of the boiler 10 is able to select a predefined operating strategy in an independent manner, chosen from among a plurality of possible strategies, coded in program form in the memory means 21. More in particular, according to the invention, the control unit 20 is configured to choose a given thermoregulation strategy according to the type of environmental or climatic information that may be made available through one or more of the sensor devices RT, RS and OS. In the preferred embodiment, the control unit 20 appropriately preset to independently recognise whether the interfacing means 23 are connected or not to the aforesaid external sensor devices, and in the case where these devices are connected, which type is connected among those foreseen.
As stated previously, the AUTO mode can be activated using the specific key 24 on the control panel 22, while maintaining the possibility of deactivating this function if the user prefers, in order to program preferred boiler regulation parameters on the boiler 10 in manual mode, and in this case the boiler will operate according to its normal function mode. Start-up of the AUTO mode, represented by the operating mode described above, and defined as special mode, is preferably signalled on the display 22a, which will also show the possible presence of the external devices RT and/or RS and/or OS.
In the embodiment described herein, the AUTO mode basically foresees the following five possible cases of external device presence/absence, as well as the same number of corresponding thermoregulation strategies, coded in program mode in the control system of the boiler:

i) absence of external sensor devices: in these conditions, the unit 20 performs a first control strategy, hereafter called "Low power modulation";
ii) Room thermostat RT connected: in these conditions, the unit 20 performs a second control strategy hereafter called " Basic thermoregulation";
iii) OS sensor connected: in these conditions the unit 20 performs a third control strategy hereafter called "Climatic thermoregulation ";
iv) RS sensor connected: in these conditions the unit 20 performs a fourth control strategy, hereafter called "room temperature thermoregulation";
v) Simultaneous OS sensor OS and RS sensor connected: in these conditions the unit 20 performs a fifth control strategy hereafter called "Total thermoregulation".

The aforesaid strategies are basically directed at determining:

self-settings of the temperature of the delivery water from the boiler, and
choice of the best possible power modulation rules for water heating , in the general context of adapting the boiler operation to the external or internal environmental conditions, while taking into consideration the various thermal effects on the building and on the heating system as a whole. Naturally, the more information is provided from external sources, the more accurate the water heating strategy will be in terms of energy saving and comfort for the end user.

"Intelligent" control of the water temperature on delivery from the boiler and the rules for power modulation have an extremely positive effect on increasing boiler efficiency, the reduction of heat loss in the heating circuit, reduction in boiler switch-on/switch-off cycles (with increase work periods at low power), and reducing undesirable excess of temperatures programmed by the user.
Below are several non limiting descriptions of the aforesaid control strategies.

1. Low power modulation

This strategy is chosen by the control unit in cases where the boiler is not connected to any external sensor devices and whenever the AUTO mode is activated. In these conditions, the boiler will operate in automatic mode according to the following basic criteria:

1.1 Slow modulation

The control unit controls the boiler operation to obtain a slow increase in the delivery water temperature as far as the level hereafter defined as "Tset", set by the user with the switch 22b on the control panel 22. In this operating mode, the burner is used at reduced power, and in any case, never at its maximum power (except in the case described in point 1.3 below).
When the Tset temperature has been reached in this mode, it is comparatively slower than the condition where the AUTO mode is not active, in other words, when the boiler is running in conditions that can be defined as normal or standard. However, the slow increase in the water temperature permits the room temperature to stabilise gradually, and consequently, this reduces the switch-on/switch-off cycles of the burner (eliminating sudden switch-on action followed by the relative burner switch-off a short time later). Therefore, the burner is used at lower power and with a reduced number of switch-on/switch-off operations: this contributes towards considerable energy saving as well as reducing undesirable exceeding of Tset temperatures.
The control logic independently excludes slow modulation mode whenever the environment is not in working condition, and therefore, presumably requires a more rapid response. This recognition occurs by means of the memorising of the duration of the previous ON/OFF cycles performed by the control system.

1.2 Low power forced start-up

After burner switch-off, and when the sensor 15 successively identifies a drop in the water temperature under the Tset level, the burner is started up again (with a certain delay, described in the following point 1.4). When the switch-on occurs again, the control logic ensures that the burner operates at its minimum calorific power for a determined period. In the example considered herein, this period is approximately between 2 and 5 minutes, preferably about 3 minutes. When the aforesaid period has elapsed, the burner returns to normal operating mode according to the logic described above in point 1.1.
It should be noted that the burner switch-off action occurs in basically stabilised room temperature conditions, and therefore, the successive forced switch-on action of the burner at low power, not only does not penalize the user-comfort of system operation, but also contributes towards reducing energy consumption even further (longer work period at low power and fewer switch-on/switch-off cycles).

1.3 Power increase for long transitory periods

The control logic is set so that in order to carry out the low power modulation strategy in question herein, the burner is programmed to deliver maximum calorific power, which is a fraction, such as 70% for example, of the rated maximum power of the burner. However, if the quantity of heat supplied by the burner during the start-up stages according to the logic expressed in point 1.1 is not sufficient to reach the Tset temperature within a predetermined period, such as 40 minutes for example, the control unit will activate the burner at its maximum effective power (100%), until the Tset temperature has been reached.

1.4 Self adapting restart delay

Following each burner switch-off action as a result of reaching the Tset temperature, the burner will be started up by the control unit with a certain delay according to the Tset temperature programmed by the user. This possibility reduces the transitory periods of boiler switch-on/switch-off, and adapts the operating function to the actual heating requirements.
As a non-limiting example, the table below shows the preferred delay periods for restart, expressed in minutes, according to the Tset temperature programmed by the user using the switch 22b.

Tset Temperature Restart delay (minutes)

< 45°C 7

45 - 51°C 6

52 - 58°C 5

59 - 65°C 4

66 - 72°C 3

73 - 80°C 2

> 80°C 1

2. Basic thermoregulation

This strategy is performed by the control unit in cases where the boiler is connected to an RT room thermostat, and when the AUTO mode has been activated. The boiler control unit is able to identify, by means of the RT, when the room temperature has reached its correct level, hereafter defined as "Trset", set on the thermostat in question.
In AUTO mode, the control unit sets the temperature at which the water must be delivered from the boiler at a fixed level, and independent of the Tset level programmed on the control panel 22.
The aforesaid fixed level can be equal to 58°C, for example, in the case where the boiler 10 is condensation type, or equal to 62°C in the case where the boiler is a conventional type. These levels are central values in relation to those of the programming range (40-82°C) foreseen by the switch 22b of the control panel 22.
In these operating conditions, following a request for heat transmitted by the RT thermostat, the burner will be operated so that the boiler will deliver the water at a temperature equal to the aforesaid fixed level (58 or 62°C). However, if the required Trset room temperature is not reached within the predetermined period, such as 16 minutes for example, which can be modified if necessary, the aforesaid fixed temperature level will be increased step by step, such as by 4°C for example, with a preferably fixed maximum number of increases. Therefore, in the example provided, each 16 minutes, the delivery water temperature will be increased by a further 4°C, as far as a maximum of three increases, until the Trset room temperature has been reached.
Once the Trset room temperature has been reached, this will be communicated to the control unit 20 by the trigger action of the C contact switch on the RT thermostat, which will determine the burner switch-off action. The temperature of the delivered water from the boiler at successive start-ups will be automatically reduced according to the previous logic, in other words, in step mode for determined periods (4°C each 16 minutes, in the example described herein) until it returns to the aforesaid fixed level (58 or 62°C).
Using this strategy, the transitory cycles that are started up in cold domestic home conditions (such as in the morning after a long heating system shut-down period for example, in particularly cold climatic conditions) the boiler is able to react by increasing the water temperature, to prevent disadvantages in attempting to reach the desired Trset room temperature. On the other hand, most of the time during boiler operation, when the house is in basically stable conditions, the aforesaid fixed or central level is sufficient to reach the Trset room temperature in a relatively short time, less than 16 minutes.
Using these operation the boiler can therefore work with a lower water temperature for a long period, limiting the aforesaid disadvantages during the transitory periods, providing increased efficiency and comfort conditions. The main advantage to be gained is during the mid-season period, when domestic housing heating requirements are less excessive because of climatic conditions.

3. Climatic thermoregulation

This strategy is performed by the control unit in cases where the boiler is connected to an OS sensor measuring the outdoor temperature outside the house, and when the AUTO mode has been activated.
The control unit 20 independently establishes the temperature at which the water must be delivered from the boiler, herein defined as "Taut", according to a plurality of predefined thermoregulation curves chosen by the installer.
A preferred algorithm for calculation of the Taut temperature is shown below: $Taut = A + P 5 * (B - Tout) + P 6$

Where

A is a parameter that the boiler installer can program alternatively at 30 or 20 according to the type of heating system or the type of heating devices installed, such as wall mounted radiators or under-floor heating (in the former case, in fact, the heating devices must be supplied with warmer water than that required for the latter);
P5 is a parameter that expresses the slope of the thermoregulation curve, which varies between 0.2 and 3.5;
B is a fixed parameter, equal to 20;
Tout is the outdoor temperature;
P6 is an offset parameter that varies between +18 and -18.

A schematic diagram showing the thermoregulation curves expressed by the previous algorithm is shown in figure 3.
As stated above, the P5 parameter expresses the slope of the thermoregulation curve which is chosen by the boiler installer according to the climatic conditions of the area where the house is located and/or the thermal insulation in the house. Basically, if the house is poorly insulated and/or is located in an area with particularly severe climatic conditions, a curve will be chosen with a stronger slope in relation to an example with conditions to the contrary (favourable climatic conditions and/or a house with good thermal insulation).
When performing the strategy in question, the boiler decides the Taut temperature and therefore also the room temperature, independently, according to the algorithm shown above. It should also be stated that the value of the P6 parameter will be according to the original setting made on switch 22b of the panel 22, which we are taking into consideration herein only for the purpose of correcting the thermoregulation curve with higher precision.
In the case where the automatic boiler operation does not satisfy user's requirements, the user can intervene by modifying the P6 parameter, using switch 22b: this has the effect of moving the total thermoregulation curve either upwards or downwards. If this regulation is not sufficient to satisfy requirements - for example, because the user needs to raise the room temperature considerably in a short time - the AUTO function can be disabled, so that the boiler returns to operate in "manual" mode in order to reach the water temperature programmed by the user on switch 22b.
In cases where, as well as the OS outdoor temperature sensor, the boiler control unit is interfaced with the RT thermostat, the unit will organise the temperature increase according to logics similar to that described in point 2 (basic thermoregulation). Basically speaking, when a request for heating is made by the RT thermostat, the boiler will heat the water to the Taut temperature established by the aforesaid thermoregulation curve. However, if the Trset room temperature setting established by the RT thermostat is not reached within a predefined period, such as 16 minutes for example, which can be modified if necessary, the Taut level established by the curve will be increased step by step, such as by 4°C in the example under consideration herein.
Also in these operating conditions, when the required Trset room temperature is reached the triggered RT thermostat will provoke the switch-off action of the burner. The temperature of the delivered water from the boiler at successive start-ups will be automatically reduced according to the previous logic, in other words, in step mode for determined periods (4°C each 16 minutes, in the example described herein) until it returns to the Taut level established by the thermoregulation curve.
The climatic thermoregulation strategy permits the system to adapt the boiler function to the external climatic conditions. Self-regulation of the temperature of the delivery water and modulation of the heating power which is considered optimal in relation to the outdoor conditions provide a considerable increase in boiler efficiency as well as the relative energy saving as a result.

4. Room temperature thermoregulation

This strategy is performed by the control unit in case where the boiler is connected to an RS sensor measuring the room temperature in a correct reading position, and when the AUTO mode has been activated.
In this case, the boiler control unit independently establishes the temperature of the Taut delivery water basically according to the difference between the required room temperature and the room temperature measured by the RS sensor.
A possible algorithm used for this purpose is shown below: $Taut = Min CHsetTemp + P 4 * (Trset - Trmeas)$

where

Min CHsetTemp is the minimum temperature that can be programmed for the delivery water from the boiler;
P4 is an influence parameter of the room temperature that varies between 0 and 20;
Trset is the required room temperature set by using a switch on the RS sensor, for example;
Trmeas is the room temperature measured by the RS sensor.

The P4 parameter expresses the influence of the room temperature on the regulation of the delivery temperature of the water.
The strategy of the thermoregulation in question permits the system to adapt the boiler function according to the internal conditions. Also in this case, self-regulation of the temperature of the delivery water and modulation of the heating power which is considered optimal in relation to the internal conditions provide a considerable increase in boiler efficiency as well as the relative energy saving as a result.

5. Total thermoregulation

This strategy is performed by the control unit in cases where the boiler is connected to an OS outdoor temperature sensor as well as an RS sensor measuring the room temperature in a correct reading position, and when the AUTO mode has been activated.
In this case, the boiler control unit automatically establishes the temperature of the Taut delivery water from the boiler according to the difference between the required room temperature and the room temperature measured, the outdoor temperature and the thermoregulation curve chosen by the installer.
A possible algorithm used for this purpose is shown below: $Taut = [Trset + P 5 * (Trset - Tout) + P 6] + [P 5 * P 4 * (Trset - Tmeas) + P 6]$

where

Trset is the required room temperature;
P5 is the parameter that expresses the slope of the thermoregulation curve, that varied between 0.2 and 3.5;
Tout is the outdoor temperature read by the OS sensor ;
P6 is the offset parameter that varies between +18 and - 18.
P4 is the influence parameter of the room temperature, that varies between 0 and 20;
Trmeas is the room temperature measured by the RS sensor.

The total thermoregulation strategy combines the advantages of the climatic and room temperature thermoregulation strategies, with a further increase in boiler efficiency.
It was explained previously in a preferred embodiment of the invention, that the control system 15 of the boiler is programmed to recognise the connection of one or more external sensor devices in an independent manner, regardless of their type, through an interfacing means 23.
As explained above, in the example described, the basic configurations that the boiler control system must be able to recognise are as follows:

A) no external device connected (Low power modulation);
B) room temperature thermostat connected (Basic thermoregulation);
C) outdoor temperature sensor connected (Climatic thermoregulation);
D) internal temperature sensor connected (Room temperature thermoregulation); to which other possible combinations can be added as follows:
E) simultaneous connection of an outdoor temperature sensor and thermostat (particular case of basic thermoregulation), and
F) simultaneous connection of an outdoor temperature sensor and an internal temperature sensor (Total thermoregulation).

The control unit 20 and the interfacing means 23 are programmed to control up to an N number (for example N=3) of different rooms or areas in the house, with different room temperature devices, such as three RT thermostats, or three RS sensors, for example, or further still, a combination of two types of device whatsoever (such as two thermostats and a sensor).
Configuration A (no device connected) is performed by simply short-circuiting the connection terminals of the RS thermostat/s to the interface 23 (that includes connection terminals for the thermostat/s). Short-circuiting to the interface 23 is identified by the control unit microprocessor in a conventional manner.
On the other hand, recognition between the A and B configurations results as a little more complex, because it requires continuous auto-learning (the short-circuit in A configuration does not need to be interpreted by the control unit as a request for heat from the thermostat). This auto-learning process can be performed by means of a control logic that counts the heat requests (closure of the thermostat RT contact switch) and measures the time duration of each request, calculating an RTm average/mean duration each time. In the case where the RTm value is lower than a given threshold (such as 90 minutes for example) the control unit detects the presence of the RT thermostat. Viceversa, if the RTm value is higher than the aforesaid threshold, the control unit 20 detects that the connection terminals to the interface 23 are electrically short-circuited (configuration A) or that the thermostat RT is in an incorrect position, and therefore should not be taken into consideration (this occurs frequently in old installations): in both cases the basic thermoregulation is not performed, but the low power modulation strategy is applied. The self-recognition (in other words, the calculation of the mean duration of heat requests and the comparison with the 90-minute threshold) is a process that is performed continuously by the control logic.
As far as the C and D configurations are concerned (and the E and F configurations as well), the control system performs recognition of the type of hardware, to control that the RS and OS sensors are connected through the interface 23 to the respective dedicated inlets to the unit 20.
Naturally the method used for self-recognition can differ from that described above, and can be any conventional type known to prior art, according to the type and characteristics of the detection means to be applied for interfacing with the boiler control system.
The invention also includes the case where the type of external detection device or devices can be set directly by boiler installation or maintenance personnel, for example, on the user interface of the boiler. In this case, it is not strictly necessary that the control system be equipped with a auto-learning function of the type on the possible external devices.
The aforesaid auto-learning function is however advisable to permit the control system 15 - programmed in a conventional manner for this purpose - to compensate any faults or malfunction in external detection devices. For example, in the case where one of the internal or outdoor temperature sensors is broken, in the place of the Total thermoregulation strategy, the control system 15 could activate the Climatic thermoregulation strategy (in the case of a faulty internal sensor) or the Room thermoregulation strategy (in the case of a faulty outdoor sensor).
Furthermore, the recognition logic used to identify the A and B configurations described previously can also result as efficient in order to permit the boiler control system to perform the Basic thermoregulation strategy or the Climatic thermoregulation strategy in a more precise manner when an RT thermostat is foreseen. In this context, the aforesaid given RTm mean duration of the heat request can be processed by the control unit 20 to detect certain characteristics in the room (dispersion, temperature variation dynamics) and can adapt the duration of the delivery water temperature increase/reduction periods accordingly (the 4°C steps every 16 minutes, described in the examples above).
In addition or as an alternative to the RTm value calculation, processing performed by the control unit can be used for comparison between the duration of two or more successive heat requests, or for memorising the timing of a plurality of successive heat requests in order to obtain a relative room temperature trend curve, always with the aim of varying the aforesaid delivery water temperature increase/reduction periods.
The characteristics and advantages of the present invention result as clear from the description above.
The AUTO function foreseen according to the invention provides users with a far easier boiler operating method and improved operating function. This improved functionality is mainly provided by a software type program on the control system, and therefore does not increase the cost of the product to a large extent. The proposed boiler provides benefits in terms of a reduction in gas consumption, while guaranteeing that the required room temperature is provided for the user. Furthermore, as explained previously, the AUTO function can be disabled independently. The sophisticated boiler operation control does not create any particular difficulties for the user, since, when the AUTO function has been selected by the user the best possible strategy will be chosen independently by the boiler control system. The boiler according to the invention also has the advantage that it can be installed in its basic version, and then equipped with one or more external devices at a later date if necessary, in order to increase performance and facilitate operating functions.
Naturally, agreed that the principle of the invention remains the same, all construction details and forms of actuation can vary in relation to the description above illustrated simply as an example while remaining within the context of the invention as defined in the appended claims.

Claims

A heating system gas boiler intended for hydraulic connection to a heating circuit (2-4) and having:
- heating means (12-13), to heat the water destined to flow through the heating circuit (2-4),

- a control system (15), comprising at least one electronic control unit (20), a memory means (21), a manual control panel (22) and interface means (23),
wherein the control system (15) is adapted to be connected, through said interface means (23), to one or more predefined external temperature sensitive devices, such as at least one room thermostat (RT), at least one room temperature sensor (RS), at least one outdoor temperature sensor (OS),
and wherein the program information used by the control unit (20) is stored in said memory means (21), to control the operation of the heating means (12-13) in order to heat the water up to a water delivery temperature, the manual control panel (22) including:
- at least a switching device (22b) to set a desired value of the water delivery temperature, said setting being operative at least when the boiler (10) is in a first operation mode

- a selection means (24) allowing the user to enable a second operation mode on the boiler (10), the control system (15) being conceived in such a manner that, in said second operation mode, the control unit (20) selects a water heating strategy out of a plurality of water heating strategies stored in said memory means (21)
the boiler (10) being characterized in that the type of the heating strategy, selected and performed by the control unit (20), depending upon:
- whether one or more of said external devices (RT, RS, OS) is/are connected to said interface means (23) or not, and

- the type of the external device or devices (RT, RS, OS), if any, connected to said interface means (23).
The boiler according to claim 1, wherein the control system (15) is conceived to perform self-detecting action:
- whether one or more of said external devices (RT, RS, OS) is/are connected to said interface means (23) or not, and/or

- the type of connected external device or devices (RT, RS, OS), if any.
The boiler according to claim 1 or claim 2, wherein said plurality of heating strategies comprises at least two or more of the following strategies:
- a strategy designed to control the operation of the heating means (12-14) in cases where no external devices (RT, RS, OS) are connected to the interface means (23), hereinafter referred to as low power modulation strategy,

- a strategy designed to control operation of the heating means (12-14) in cases where at least one room thermostat (RT) is connected to the interface means (23), said strategy being hereinafter referred to as basic thermoregulation strategy,

- a strategy designed to control operation of the heating means (12-14) in cases where at least one outdoor temperature sensor (OS) is connected to the interface means (23), said strategy being hereinafter referred to as climatic thermoregulation strategy,

- a strategy designed to control operation of the heating means (12-14) in cases where at least one internal temperature sensor (RS) is connected to the interface means (23), said strategy being hereinafter referred to as ambient thermoregulation strategy, and

- a strategy designed to control operation of the heating means (12-14) in cases where either at least one internal temperature sensor (RS) and at least one outdoor temperature sensor (OS) are connected to the interface means (23), said strategy being hereinafter referred to as total thermoregulation strategy.
The boiler according to claim 3, wherein at least one of said strategies includes instructions followed by the control unit (20) to adjust the water delivery temperature in an independent manner ignoring a selection performed using said switching device (22b).
The boiler according to claim 3, wherein at least one of said strategies includes rules followed by the control unit (20) to modulate the water heating power.
The boiler according to claim 5, wherein said low power modulation strategy is designed so that the control unit (20) controls said heating means (12-13) to obtain a slow increase in the water delivery temperature up to a desired value set by said switching device (22b), using a heating power that is reduced in comparison to the heating power used when the boiler (10) is in said normal operation mode.
The boiler according to claim 6, wherein said low power modulation strategy is designed so that the control unit (20) activates said heating means (12-13) to operate at a minimal heating power for a predetermined period of time, following any restart operations by the heating means (12-13) when the water delivery temperature has dropped below said desired value.
The boiler according to claim 6, wherein said low power modulation strategy is designed so that the control unit (20) activates said heating means (12-13) to operate at a maxim power, if the desired value is not reached within a given period.
The boiler according to claim 6, wherein said low power modulation strategy is designed so that the control unit (20) activates said heating means (12-13) restart operation, when the water temperature drops below the desired value, with a delay which is variable according to said desired value, where in particular, the higher is the desired value, the shorter the delay.
The boiler according to claim 4 and/or 5, wherein said basic thermoregulation strategy is designed so that the control unit (20) automatically chooses a predefined water delivery temperature, said predefined temperature preferably contained within the range 55 - 65°C.
The boiler according to claim 10, wherein said basic thermoregulation strategy is designed so that the control unit (20) increases said predefined water delivery temperature according to predefined steps for given periods of time, if a desired room temperature set by means of said room thermostat (RT) has not been reached within a predetermined time, where in particular a predetermined maximum number of steps is foreseen.
The boiler according to claim 11, wherein said basic thermoregulation strategy is designed so that the control unit (20), once the desired room temperature has been reached, reduces the water delivery temperature by predefined steps for given periods of time, until said predefined water delivery temperature has been reached.
The boiler according to claim 4 and/or 5, wherein said climatic thermoregulation strategy is designed so that the control unit (20) independently calculates a given water delivery temperature according to an outdoor temperature detected by means of said outdoor sensor (OS).
The boiler according to claim 13, wherein said given water delivery temperature is calculated using the following algorithm: $Taut = A + P 5 * (B - Tout)$

where:
- Taut is the given water delivery temperature;

- A is a parameter depending upon the type of the heating system;

- P5 is a parameter expressing the slope of a given thermoregulation curve;

- B is a fixed parameter;

- Tout is an outdoor temperature detected by means of said outdoor temperature sensor (OS).
The boiler according to claim 14, wherein said algorithm further includes an offset parameter as follows: $Taut = A + P 5 * (B - Tout) + P 6$
where P6 is said offset parameter, according to a setting position of said switching device (22b).
The boiler according to one or more of claims from 13 to 15, wherein said climatic thermoregulation strategy is designed so that the control unit (20) increases said given water delivery temperature by predefined steps for given periods of time, on condition that
- a room thermostat (RT) is also connected to the interface means (23) and

- a desired room temperature set by means of said room thermostat (RT) has not been reached within a prefixed time.
The boiler according to claim 16, wherein said basic thermoregulation strategy is designed so that, once the desired room temperature has been reached, the control unit (20) reduces the water delivery temperature by predefined steps for given periods of time down to said predefined water delivery temperature.
The boiler according to claim 4 and/or 5, wherein said ambient thermoregulation strategy is designed so that the control unit (20) independently calculates a given water delivery temperature according to a difference between a desired room temperature and a room temperature detected by said room temperature sensor (RS).
The boiler according to claim 18, wherein said given water delivery temperature is calculated using the following algorithm: $Taut = Min CHsetTemp + P 4 * (Trset - Trmeas)$

where
- Taut is the given water delivery temperature;

- Min CHsetTemp is a minimal water temperature that can be selected using said switching device (22b);

- P4 is an influence parameter of the room temperature on the regulation;

- Trset is the desired room temperature;

- Trmeas is the room temperature detected by said room temperature sensor (RS).
The boiler according to claim 4 and/or 5, wherein said total thermoregulation strategy is designed so that the control unit (20) automatically calculates a given water delivery temperature according to:
- a difference between a desired room temperature and a room temperature detected by said room temperature sensor (RS), and

- the outdoor temperature detected by said outdoor temperature sensor (OS).
The boiler according to claim 20, wherein said given water delivery temperature is calculated using the following algorithm: $Taut = [Trset + P 5 * (Trset - Tout)] + [P 5 * P 4 * (Trset - Tmeas)]$
where
- Taut is the given water delivery temperature;

- Trset is the desired room temperature;

- P5 is a parameter expressing the slope of a given thermoregulation curve;

- Tout is an outdoor temperature detected by means of said outdoor temperature sensor (OS);

- P4 is an influence parameter of the room temperature on the regulation;

- Trmeas is the room temperature detected by said room temperature sensor (RS).
The boiler according to claim 21, wherein said algorithm further includes an offset parameter as follows: $Taut = [Trset + P 5 * (Trset - Tout) + P 6] + [P 5 * P 4 * (Trset - Tmeas) + P 6]$

where P6 is said offset parameter, according to a setting position of said switching device (22b).
The boiler according to claim 2, wherein said interface means (23) includes connection terminals for at least one room thermostat (RT) and the control system (15) is programmed to perform a auto-learning phase that includes calculating a mean value of the duration of terminal short-circuit periods.
The boiler according to claim 23, wherein the control system (15) is programmed to detect the presence of said room thermostat (RT) if said mean value is below a given threshold.
The boiler according to one or more of the preceding claims, wherein at least one room thermostat (RT) is connected to said interface means (23) and the control system (15) is programmed to perform at least one of the following:
- a calculation of a mean value of the duration of closure periods of an ON/OFF contact switch of said thermostat (RT),

- a comparison of the duration of two or more closure periods of an ON/OFF contact switch of said thermostat (RT), and

- a calculation of a trend curve based on the duration of two or more closure periods of an ON/OFF contact switch of said thermostat (RT).
The boiler according to claims 11 and 25 and/or claims 16 and 25, wherein the control system (15) is programmed to regulate said predetermined periods of time according to the result of said calculation or comparison.