WO1994002787A1

WO1994002787A1 - Device for controlling heating boilers

Info

Publication number: WO1994002787A1
Application number: PCT/SE1993/000627
Authority: WO
Inventors: Göran MÅRTENSSON
Original assignee: HALLSTRÖM, Peter
Priority date: 1992-07-16
Filing date: 1993-07-14
Publication date: 1994-02-03
Also published as: ATE160624T1; SE9202181D0; SE9202181L

Abstract

A device for heating boilers (1) in heating plants comprises a means (2) for heating a heat carrying medium present in the boiler and circulating out thereof in the heating plant as well as a means (11) adapted to detect the temperature of the heat carrying medium present in the boiler and send signals to the heating means (2) to start and stop the heating of the medium when a first lower temperature level is underpassed and a second higher temperature level is exceeded, respectively, by the medium in the heating boiler (1). The device comprises further means (12) adapted to delay the start of the heating means (2) when the first temperature level is reached by the medium and this is detected by the detecting means (11).

Description

Device for controlling heating boilers

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a device for heating boilers in heating plants having a means for heating a heat carrying medium present in the boiler and circulating out thereof in the heating plant as well as a means adapted to detect the temperature of the heat carrying medium present in the boiler and send signals to the heat¬ ing means to start and stop the heating of the medium when a first lower temperature level is underpassed and a second higher tem¬ perature level is exceeded, respectively, by the medium in the heating boiler.

The invention is in particular directed to devices for oil and gas boil- ers, and it will as a consequence thereof be discussed below for this application for exemplifying but non-limitative purpose. A disadvan¬ tage in common to all heating boilers for heating the rooms of a building and provide tap hot-water consists in that they are dimen¬ sioned so that they are able to manage conditions, in which an ex- tremely high heating demand exists, i.e. during the coldest winter days. This means that the capacity of the heating boilers is utilised to the greatest extent during cold periods, but the heating boilers get over-dimensioned with respect to the rest of the year, when the heating demand generally is only a fraction of the amount of heat which may be supplied by the boilers, so that the efficiency some¬ times will be comparatively low. It would therefor be desired to improve the efficiency of a heating boiler, so that it may comply with the heating demand when this is extremely high but nevertheless requires a considerably lower amount of supplied energy, in the oil boiler case fuel in the form of oil, for obtaining the heating comfort aimed at during periods of both high and low heat demands, and especially in the latter case, in which the heating boiler must be considered to be strongly over-di¬ mensioned.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a de¬ vice according to the type mentioned in the introduction, which finds a remedy to the inconveniences mentioned above by making it pos- sible to increase the efficiency of a heating boiler, especially when the heat demand is low, i.e. during warm seasons.

This object is obtained by the invention by providing a device of the type mentioned in the introduction with means adapted to delay the start of the heating means when the first temperature level is reached by the medium and this is detected by the detecting means.

Thus, by the invention it has been realized that it is possible to in¬ crease the efficiency of a heating boiler by modifying the heating cycles thereof. The detecting means of the device according to the invention has the task to keep the temperature of the heat carrying means present in the heating boiler, i.e. usually the water, between said first and second levels and by that almost static, for what rea¬ son the detecting means for the sake of simplicity will be called thermal relay in the following. By the fact that the device according to the invention delays the start of the heating means commanded by the thermal relay the temperature of the heat carrying medium present in the heating boiler will fall slightly, but this will not detri¬ mentally influence the heating capacity of the heating plant, since the medium circulating in the heating system of the building in ques¬ tion has a considerably lower temperature than the medium present in the boiler, and the shunt valve co-ordinated with the boiler is able to compensate this small lowering of the temperature of the heat carrying medium of the heating boiler. It has been found that a pro¬ longation of the off time of the heating boiler by a certain ratio with respect to the normal off time commanded by the thermal relay does not require a prolongation of the heating time of the heating means of a ratio being just as high should said means in the heating in both cases deliver the same power. Expressed in another way this means that the device according to the invention leads to a requirement of a smaller amount of heat energy, i.e. fuel for obtaining the same heating result as before, which means that the efficiency of the heating plant increases.

In a heating means in the form of an oil burner an additional fuel saving is also obtained by the lower number of starts of the burner per time unit, since a small amount of oil disappears at each start without giving any real heat energy, and these small amounts of oil constitute a considerable part of the total fuel consumption when the heating demand is low.

By the combustion cycles of the heating boiler prolonged by the de¬ vice according to the invention the boiler temperature is slightly low¬ ered, whereby reduced energy losses are obtained, but this does not lead to any higher risk of corrosion or hot well.

According to a particularly preferred embodiment of the invention the delay means comprises a first member adapted to measure the time between exceeding of the second temperature level and under- passing of the first temperature level following thereupon detected by the detecting means, and the delay means is adapted to deter- mine the length of the delay time on the basis of this time informa¬ tion and after this time has elapsed send signals starting the heating means. Thanks to the completely new method within this technique to measure the off time of the heating boiler, i.e. the time between switching off and on of the heating means commanded by the ther- mal relay, and utilise the result of this time measurement to deter¬ mine the length of the delay time for the start of the heating boiler, an automatic adaption of the delay time to the heating demand pre- vailing for the moment is obtained, i.e. the delay time becomes automatically longer in warmer seasons and shorter in colder sea¬ sons or when the heating demand suddenly increases in the form of tapping great amounts of hot-water for bath, shower and the like. Thus, an optimum prolongation of the heating cycles of the heating boiler is always obtained in every moment, so that the heating time thereof, i.e. the burning time of the oil burner, per time unit, for in¬ stance per day, gets so low that the conditions on the whole admit. This involves in its turn maximum improvement of the efficiency of the heating boiler - independently of how the heating demand varies - while utilising the principle to prolong the heating cycles.

According to another preferred embodiment of the invention the de¬ lay means is adapted to determine the length of the delay time to be a pre-determined ratio of the time measured by the time means. The length of the delay time is by that chosen to be for example 80% of the time measured by the time means, i.e. the time it takes for the temperature of the heat carrying medium present in the heating boiler to sink from the second to the first temperature level. Thus, the length of the delay time may be several times lower during warmer than during colder seasons.

According to a further preferred embodiment of the invention the delay means comprises a microprocessor which may be pro- grammed and is adapted to control the heating means, so that it be¬ comes possible to change the data being the basis of the length of the delay time according to desire and adapt the device to certain parameters of a certain heating boiler, the heating plant in question and special wishes of the user.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specific description of a preferred embodiment of the invention cited as an example,

In the drawings: Fig 1 is a schematic view of a heating plant and illustrates a de¬ vice according to a preferred embodiment of the invention, and

Fig 2-5 are diagrams in which the temperature of the heat carrying medium present in the heating boiler measured by the ther¬ mal relay of the device according to Fig 1 is plotted versus time for illustrating the function of the device according to the invention in some certain situations.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE IN¬ VENTION

Fig 1 illustrates schematically a device according to the invention applied on an oil boiler 1 having a burner 2 and a water tank 3 with water heated by the burner 2. The heating plant comprises further a tap hot-water system 4 schematically indicated by a tap and a room heating system 5 with a conventional shunt valve 6, circulation pump 7 and radiators 8. The heating plant comprises further an incoming conduit 9 for supply of cold water as well as a chimney 10 for dis¬ charging fluid gases resulting from the combustion of oil.

Furthermore, a thermal relay 11 is arranged to detect and react upon the temperature of the water present in the water tank 3 and heated by the burner 2. When the temperature of this water in the immediate proximity of the thermal relay when the burner is switched off falls below a fist temperature level, for instance 75° C, the thermal relay sends a signal in the direction of the burner so as to start this. However, the means 12 of the device according to the invention for delaying the start of the burner 2 is connected in series to the thermal relay 11 between the latter and the burner 2. The de¬ lay means 12 comprises a microprocessor having a first member adapted to measure the time elapsing between an exceeding of a second temperature level, recognised by the thermal relay, at which level the thermal relay sends signal in the direction of the burner so as to turn it off, and the falling below said first temperature level following thereupon. The microprocessor is adapted to multiply the time delivered by said first time measuring member by a given fac¬ tor, preferably between 0,6 and 1 ,0, particularly preferred about 0,8. On receiving a signal from the thermal relay 11 indicating that the first temperature level has been underpassed by the water in the water tank the microprocessor starts a count-down of the time re¬ sulting from the multiplication by said factor in a second time meas¬ uring member being a part thereof and the microprocessor is adapted to send the signal activating the burner 2 on to the burner 2 for starting it when said time is counted down.

Thus, an extension of the off-time of the heating boiler is obtained in this way, and the length of this extension is determined by a time measurement, more exactly by measuring the time elapsing between an exceeding of the second temperature level detected by the ther¬ mal relay and the underpassing of said first temperature level fol¬ lowing thereupon. This means that the extension of the off time of the heating boiler will at a low energy consumption of the heating plant be longer than at a high heat demand of the heating plant.

The device comprises further a sensor 13 adapted to detect the temperature of the tap hot-water of the heating plant and when the latter falls below a pre-determined temperature level, for instance 45°C, being lower than the first temperature level send signals to the delay means 12 for stopping the delay and immediately starting the burner 2. The heating boiler may thereby deliver a sufficient amount of heat also if the time measured by the thermal relay would be long and the delay means by that determines a long delay time, but shortly after this determination a strongly increased tapping of tap hot-water, is commenced, for instance for a shower, bath or the like.

With reference to Fig 2-5, the result obtained by the function of the device according to the invention will now be explained and com- pared with a device without the delay discussed above. It is shown in Fig 2 how the temperature T measured by a thermal relay 11 may vary over the time t when said delay is not there. This is for the rest possible to achieve in the device according to the in¬ vention by programme the multiplying factor being zero in the mi- croprocessor of the delay means 12. This means a certain numbers of starts of the burner 2 per time unit and at each start a certain op¬ erating time of the burner before it is turned off again. The burner is started at the themperature To of the hot-water of the boiler de¬ tected by the thermal relay 11 in the immediate proximity of the thermal relay. To is in this case 75°C and the second temperature level 80°C, but also another setting of the thermal relay, for instance 70° and 75°C, respectively, would be conceivable. The temperature T of the water in the water tank 3 measured by the thermal relay 11 is shown in Fig 3 plotted versus time under exactly the same heat demand conditions as in Fig 2, but the delay means is here adapted to prolong the off time by 80% of the time, which elapses from the detection of the second temperature level by the thermal relay and to the detection of the first one, so that the off time t-| will be 1 ,8 x to- this means in this case that the temperature of the water in the water tank has time to fall a little bit more before the burner is re¬ started, so that the operating time of the burner necessary for the heating to the second temperature level gets longer, but this longer operating time is not directly proportional to the prolongation of the off time of the boiler, but it has turned out that it is considerably shorter. Experiments have shown that for instance at 8 starts within four hours having each an operating time of 10 minutes in the func¬ tion according to Fig 2, will correspond to five starts having an op¬ erating time of about 12,4 minutes each in the function according to Fig 3. Since the total burning time of the oil burner, which has a constant burning power is directly proportional to the fuel consump¬ tion, a reduction of the fuel consumption by (80-62)/80=22% is ac¬ cordingly contained. A further saving of oil is added thereto since at each starting moment a certain amount oil gets lost without any ap¬ preciable delivery of heat energy. It appears from Fig 3 that the tem- perature of the hot-water at the thermal relay in practice falls very slowly during said off time extension, and this is due to that the thermal relay is located on the heating boiler at a considerable dis- tance from the burner, usually in the upper part of the boiler, and it will therefor after the switching off of the burner as a consequence of the hot-water tapping from this part of the boiler detect a tempera¬ ture fall being more rapid than actually is the case for the average temperature of the water present in the heating boiler, so that the thermal relay is "cheated" and sends signals activating the burner at the temperature level To, although this is not at all reached by said average temperature. However the heat is after by degrees trans¬ ferred from the water tank regions near the bottom to those located in the region of the thermal relay, so that the temperature fall in the proximity thereof is strongly slowed down. For this reason it is pos¬ sible to extend the off time as much as mentioned above without that the temperature of the water in the water tank of the heating boiler falls appreciable below the temperature TQ set by the thermal relay.

It is illustrated in Fig 4 what happens when the heat demand of the heating plant gets higher. A second off period 14 shown in this dia¬ gram is thought to be there during the time in which the heat de¬ mand of the device is comparatively high, while the off periods 15 shown before and after this are there when the heat demand of the heating plant is low. The periods shown in Fig 4 are in the reality not successive, although this would be possible. It appears from Fig 4 how the delay means of the device according to the invention thanks to the measuring of the time Δt between the second and the first temperature level procure a delay of the start of the burner 2, which is adapted to the heat demand prevailing at that moment, i.e. a long delay at a long off time between the two levels, i.e. a long Δt, and a short delay at a shorter off time between said levels.

It is illustrated in Fig 5 how the device manages the situation when after a long off time between said levels and by that a long delay time commanded suddenly shortly after the start of this delay time the hot-water tapping of the heating plant increases dramatically. Said first temperature level of the water in the heating boiler has been reached at the time t-| as a consequence of which the micro¬ processor starts a count-down of the delay time, which is intended to be terminated at t2- However, as a consequence of the compara- tively long time between t<| and t2 and the great tapping of hot water the sensor 13 will already at the time t3 detect that the temperature of the tap hot-water has fallen to 45°C whereupon it sends signals to the delay means to stop the delay and immediately start the burner. It would otherwise without the arrangement of the sensor 13 be possible that the heating boiler would be totally drained of hot-water before the start of the next combustion cycle with the inconven¬ iences connected thereto.

The microprocessor is preferably designed to store data concerning burning times of the burner, off times between said second and first temperature level and delay times in a memory, so that it is possible for the sake of comparison to run tests for the heating plant with the delay function of the device turned on and turned off, respectively. It may also be of interest to study information about off and burning times stored by the microprocessor so as to determine the optimum extension of the off time as a ratio of off times between said first and second temperature level so as to programme this ratio in the microprocessor. It is also conceivable that there is a wish to change this ratio with the seasons, it would especially be suitable to in¬ crease this ratio a little bit in the case that the thermal relay is set at somewhat lower temperature levels in warmer seasons.

The invention is of course not in any way restricted to the preferred embodiment described above, but several possibilities to modifica¬ tions thereof would be apparent to a man skilled in the art without departing from the basic idea of the invention.

The patent claim definition "means adapted to detect the tempera- ture of the heat carrying medium present in the boiler" is to be inter¬ preted in its broadest sense, which means that it is also intended to comprise the case in which the heating boiler is connected to a res¬ ervoir for accumulating hot-water and the thermal relay is arranged in connection to this reservoir.

It would also be possible to programme the microprocessor so that this does not make the delay of the off time directly proportional to the off time between said second and first temperature levels, but introduces this off time in any special mathematical formula for cal¬ culating and determining the delay of the off time, although it has turned out to function very well with a direct proportionality.

Furthermore, the first and second time measuring means could be constituted by one and the same clock. The time measuring means have for the rest not necessary to indicate time, as a conventional chronometer, but they may be any means being influenced by the time and are able to obtain the delay of the off time aimed at in de¬ pendence of the time between the detection of the exceeding and the underpassing of said temperature levels by the thermal relay.

Claims

1. A device for heating boilers (1) in heating plants having a means (2) for heating a heat carrying medium present in the boiler and cir- culating out thereof in the heating plant as well as a means (11) adapted to detect the temperature of the heat carrying medium pre¬ sent in the boiler and send signals to the heating means (2) to start and stop the heating of the medium when a first lower temperature level is underpassed and a second higher temperature level is ex- ceeded, respectively by the medium in the heating boiler (1 ), char¬ acterised in that it comprises means (12) adapted to delay the start of the heating means (2) when the first temperature level is reached by the medium and this is detected by the detecting means (11).

2. A device according to claim 1 , characterised in that the delay means (12) comprises a first member arranged to measure the time between exceeding of the second temperature level and underpass¬ ing of the first temperature level following thereupon detected by the detecting means (11), and that the delay means is adapted to de- termine the length of the delay time on the basis of this time infor¬ mation and after this time has elapsed send signals starting the heating means (2).

3. A device according to claim 1 or 2, characterised in that the delay means (12) is connected in series to the detecting means (11) and connected between this means and the heating means (2) and adapted to receive a signal indicating underpassing of said first temperature level of the medium and transmit it to the heating means (2) with delay.

4. A device according to claims 2 and 3, characterised in that the time measuring member is adapted to be started to measure time and terminate the time measuring by receiving signals emitted by the detecting means (11) for exceeding of a second temperature level and underpassing the first temperature level of the medium, respectively.

5. A device according to at least claim 2, characterised in that the delay means (12) is adapted to determine the length of the delay time to be a predetermined ratio of the time measured by the time member.

6. A device according to claim 5, characterised in that the delay means (12) is adapted to delay the start of the heating means by a time being 60-100% preferably 70-90%, of the time measured by the time measuring member.

7. A device according to any of the preceding claims, characterised in that the delay means (12) comprises a second time measuring member adapted to receive and be started by the signal for under¬ passing said first temperature level emitted by the temperature de- tecting means (11).

8. A device according to claim 7, characterised in that the delay means comprises a means adapted to multiply the time measured by the first time measuring member by a pre-determined factor, and that the second time measuring member is adapted to count down the time remaining until the start of the heating means from the time obtained by this multiplication.

9. A device according to claims 2 and 7, characterised in that a de- lay means (12) comprises a means adapted to compare the time measured by the second time measuring member and said time in¬ formation from the first time measuring member and at a certain time measured by the time measuring member and resulting from this comparison emit signals starting the heating means (12).

10. A device according to any of the preceding claims, characterised in that the delay means comprises a microprocessor which may be programmed and is adapted to control the heating means (2).

11. A device according to claim 10, characterised in that the micro¬ processor is designed to allow input of new data therein so as to change said delay time.

12. A device according to any of the preceding claims, characterised in that it comprises a means (13) adapted to detect the temperature of the tap hot-water of the heating plant and upon underpassing a pre-determined temperature level thereof being lower than said first temperature level interrupt said delay and start the heating means (2).

13. A device according to any of the preceding claims, characterised in that the heating means is an oil burner (2).