NO144182B - PROCEDURE FOR LOW FUEL FIREPLACE IN A CLOSED FIREPLACE ROOM, AND STOVE FOR EXECUTION OF THE PROCEDURE - Google Patents

Description

The invention relates to a method for firing with solid fuel in a closed fireplace room which has a supply air duct for combustion air and is designed for heating circulation air in a circulation air duct arranged around the fireplace, the supply of combustion air being regulated by means of at least one damper arranged in the supply air duct, the movement of which is controlled of at least one thermostat, while limiting the temperature of the circulating air so that it does not exceed a predetermined maximum temperature.

When firing with wood and similar solid fuels, the fireplace's effect cannot, as with coke firing, be regulated by a continuous throttling of the air supply, as there is then a great danger that the incomplete combustion results partly in an uneconomic surplus of unburned carbon-oxide and partly in the formation of tar and soot, which entails a risk of pipe fire and reduces the effectiveness of existing heat exchangers due to insulating coatings.

The purpose of the invention is to provide a method for burning a fire of the above-mentioned kind, by which the stated serious disadvantages are eliminated and which also makes it possible to feed the hearth with a larger amount of fuel at a time without this amount of fuel being burned faster than what is required to maintain a certain set temperature in a heated room, a water heater or similar.

In the Swedish patent document 110 379, a heating boiler for heating with wood is described and which has an impulse regulator for closing or opening a draft hatch belonging to the boiler. The arrangement is relatively complicated and does not meet modern requirements for safety and reliability.

Other similar, previously known arrangements are described in the German patent documents 235 019, 311 494,

352 252, 498 226, 647 750 and 1 230 957. Neither of these, however, describes a satisfactory solution from all points of view. For example, none of these can be used in such cases as you cannot rely on access to electricity for thermostat regulation.

The method according to the invention is characterized by the fact that the movement of the damper is controlled by means of one or more control devices, such as a thermostat, time relay or the like, between either a mainly fully open or a mainly fully closed position, in such a way that the combustion periodically ceases, ensuring so that the fuel temperature after a cessation of combustion is sufficiently high for the combustion process to start again when the damper is opened again, while at the same time the combustion is controlled to maintain a desired predetermined temperature in a room heated by means of circulating ionized air or in one of the flue gases heated object, such as an oven, hob, water heater or similar.

When the damper is open, combustion will take place with the best possible efficiency, so that the fuel is burned without soot and tar formation. Meanwhile, the combustion process in the hearth is interrupted, so that only very little heat is developed in it. The hearth can then be fed with a large quantity of fuel which allows an optimal combustion process for a long time.

At the same time, the greatest possible safety is achieved as the prescribed maximum temperature in the hearth will not be exceeded. When the damper has taken up the closed position, the temperature in the fireplace room will gradually drop, which will happen with a certain delay as a result of residual heat. The damper will then be opened again and a new combustion process with the highest degree of efficiency will begin, etc. In tests carried out, it has been found that even with fairly long regulation periods (10 - 60 min.) with the damper closed, the temperature of the fuel does not drop below that of re-ignition will quickly occur when the damper is opened again. Thereby, the described combustion process begins again with a high degree of efficiency. If the intervals should become too long with room thermostats of the usual type, special mechanical or electrical time relays can ensure that the damper is opened so that the combustion process starts.

During the periods when the damper assumes a closed position, the temperature of the fuel to allow re-ignition can be maintained by limiting the heat output from the hearth. This can happen by restricting the air circulation around the fireplace. At the same time as an impulse for closing the damper, an impulse for closing a is then appropriately given

circulation fan.

In practice, it is preferred that at least one thermostat,

which is conveniently located in the flue gas duct, at a temperature that exceeds a predetermined value, produces or via electric drive means controls a mechanical movement that quickly and essentially completely closes the damper.

This allows full safety against overheating in the flue gas duct, also in such cases when, for example, the normal thermostat function should fail as a result of a power cut. The method can be of particularly valuable use when heating premises and other rooms that are not connected to the electricity distribution network.

To ensure the best possible function, it is preferred that a mechanical or electric drive opens the damper and holds,

this open during time intervals of sufficient duration for the fire in the hearth to generate maintenance heat.

The mechanical body can e.g. consist of a timer.

The electrical device can e.g. is constituted by a delay circuit of conventional type containing a capacitor and a resistor. The aforementioned body can contribute to ensuring that the combustion process will, under all occurring conditions, occur discontinuously in the manner described above.

Special advantages can be achieved if, according to a preferred embodiment, a thermoelectric generator which affects

ked by the hot flue gases from the hearth, are brought together

operate with one or more electric thermostats in such a way that the damper is kept open when the thermoelectric generator

tor at a cold hearth does not emit energy, while the generator,

when the flue gas temperature and thus the power output from the generator reaches a certain desired value, via setting devices the damper closes unless at least one thermostat does not call for heat.

A thermogenerator of this type can be arranged between a hearth-limiting, hot surface and e.g. a surface in the supply air duct for combustion air. By using such a thermogenerator, one can under all conditions ensure automatic regulation of the discontinuous combustion process, which is of great value in many different application cases.

Further advantages Can be achieved if a thermostat is placed in the hearth, in the heated, circulating air or in a flue belonging to the hearth and arranged so that the damper opens automatically when the temperature falls below a predetermined value, so that the fire is re-ignited only for a short time, with unless another thermostat calls for heat.

In order to adapt the combustion process to different relevant fuels, it is appropriate that, in addition to the automatic control of the damper's movements, one also has one or another type of manual regulation by means of which the aforementioned adaptation to different fuels can be achieved manually. Of particular interest in this connection is allowing the setting of the amount of excess air which is appropriate for different fuels present.

The invention also relates to a stove for firing with solid fuel in accordance with the above-mentioned method, which stove's essential characteristics are stated in the patent claims.

A stove according to the invention has a very high degree of efficiency while at the same time achieving good controllability and safety against overheating. The stove is primarily intended for burning with fuel in solid form, e.g. wood, peat, coal, coke and the like. The stove also allows easy connection of additional devices for both direct and accumulative electric heating. The stove can therefore be used both as a back-up heat source and stove in the event of a power outage and/or as the only heat source in sports cabins, villas and terraced houses. The stove is also suitable as an additional heat source for heat pump and solar heating systems that utilize one or another type of heat accumulation.

According to the invention, regulation of the stove's effect takes place by regulating the supplied combustion air by means of the damper present in the supply air channel between fully closed and fully open positions. In this way, significantly increased efficiency and significantly increased safety against carbon monoxide poisoning is achieved compared to conventional regulation using a damper in the smoke pipe.

To further increase the efficiency, it can

according to one preferred embodiment, so-called balanced draft is used, whereby the temperature of the combustion air is increased by heat exchange with the flue gases. The limit for the degree of efficiency that can be achieved is set by the flue gas temperature. In order for the chimney effect to be achieved, this temperature must exceed the temperature of the combustion air by approx. 50 - 80° C if you want to avoid a special flue gas fan.

By means of simple mechanical or electrical wood

with the help of thermostats or manually regulated dampers, an embodiment of the stove can either quickly heat circulating room air or accumulate heat energy in a stone reservoir connected to its circulation air duct, so-called heating ground. A fan is required for charging and discharging such an accumulator. However, this stove works by direct rapid heating of the room air - even if it is with somewhat lower power and poorer efficiency - also without a fan. This ensures that the stove can be used as a reserve energy source, e.g. in the event of a power cut.

The ability to accumulate heat facilitates the application

to a significant extent and increases the well-being value. One can e.g. during the evening light several fires one after the other without the temperature becoming too high in the rooms, after which the heat added to the accumulator is utilized in a known manner during the following night.

The above-mentioned, intermittent, thermostatically controlled firing sequence according to the invention means that the stove can be supplied with a large fuel magazine which can be filled completely so that one filling is sufficient for 8-10 hours of firing. Firing with wood is therefore not particularly complicated and time-consuming, and due to the high degree of efficiency, wood consumption is significantly limited compared to what is the case with the previously known, conventional heating devices.

For use e.g. in sports cabins or the like, where electricity is lacking, the stove according to the invention can be supplied with a water heater with a volume of e.g. 50 - 100 litres. Overheating is prevented by means of a thermostat in combination with the damper control system described above. By efficient heat exchange with the flue gases, such a water heater* can further reduce the risk of the stove overheating. A desired accumulation according to the same principle as a tiled stove can also be easily achieved if the space between the heat exchanger and the outer casing is filled with heat-accumulating material, e.g. sandy.

Parts that are vital to the function of the stove, such as hearth, heat exchanger and damper devices, can be marketed as a unit for installation in e.g. a brick, open stove. In this connection, balanced draft can be arranged, e.g. by means of a flue gas channel inserted in the masonry, possibly a circular flue, preferably made of stainless material, the combustion air being led down through the space around the flue. Instead of a conventional, externally brick chimney, you can use the same chimney and heat exchanger that is used in a combi fireplace according to the invention, whereby the corrosion problems at the low flue gas temperature disappear.

Tests carried out have shown that even in a large house, good heat distribution can be achieved by all heat being emitted at roof level. Distribution to adjacent rooms can then be ensured using openings equipped with sound traps at ceiling and floor level. The combi stove can also be supplied with a special additional unit for electric heating, which preferably happens by inserting electric heating elements with protective thermostats in the upper part of the stove. Circulation fan and filter are preferably arranged in the lower part of the stove. In this way, the risk of fire in the filter is also significantly reduced, which risk is relatively great with conventional devices.

The invention shall be described in more detail below

in connection with an exemplary embodiment with reference to the schematic drawings, where fig. 1 shows a partially cut-through front view of a stove according to the invention, fig. 2 shows

a side section through the stove according to fig. 1, and fig. 3 illustrates the fire's combustion process with different heat needs,

as fig. 3a shows little and fig. 3b shows a large heat demand.

A stove 1 for intermittent burning with fuel in solid form consists of a hearth 2. The upper part 5 of the hearth 2 is designed as the inside of a heat exchanger that passes into a chimney 6. The hearth 2 with the upper part 5 is surrounded by this heat exchanger with a circulation air channel 7 through which circulating air is led with the help of a fan 10 arranged below the hearth, driven by a motor 10a. Also the upper part of the smoke pipe 5a present in the chimney 6 is surrounded by a heat exchanger 12 for combustion air whose inlet opens approximately in the area of the chimney's 6 outlets during provision of so-called balanced draft. The stove's supply air duct is designated 13.

The fireplace room 2 is delimited on the front of the stove by a closable hatch 15 made of tempered glass. As can be seen from the drawing, the hatch 15 has relatively large dimensions, so that the comfort effect of seeing the fire and of radiant heat is maintained.

The hatch 15 is arranged to allow precise closure and delimitation of the hearth space from the surrounding space, so that the course of combustion in the stove will depend on pressure variations both outdoors and indoors, e.g. wind or opening windows or similar.

The circulating air is sucked in by the fan 10 via a grid 17 or a slit at the lower part of the stove and then passes a filter 18 before heat exchange takes place by passage of the fireplace room 2 through a channel 19. The circulating air is then released via a grid 20 in the upper part of the stove, at the shown embodiment in the area of the ceiling in the room where the stove is located. The grid 20 forms an outer limitation of a module 21 which surrounds the upper part of the stove and which may possibly accommodate organs for the stove's electrical functions, which will be described in more detail below. A protective plate 23 can be placed between the module 21 and the ceiling 22 of the room to reduce the risk of overheating.

A damper 29 is arranged in the supply air channel 13, with the help of which the combustion rate is regulated. This

>. damper is designed to via a number of control bodies, e.g. 50,

51, and drive means (not shown), such as thermostats and time relays, to be controlled between either fully open or fully closed position. In the latter position, the supply is shut off

supply air to the fireplace 2. Combustion will then periodically cease completely. However, the control devices simultaneously ensure that the fuel maintains a sufficiently high temperature for the combustion process to begin again when the damper 29 on

in new opens. The control bodies also automatically ensure that the desired predetermined temperature is maintained in the heated room or in a hotplate 8 arranged above the hearth 2. Furthermore, it is automatically ensured that the gas emitted by the stove

effect or the temperature of the heated circulation air

) is limited to a maximum value desired or prescribed by the authorities.

During periods when the damper 29 takes a closed position, the temperature of the fuel is maintained by limiting the heat output from the hearth. In the first place, this happens by turning off the fan 10 for circulation air. Alternatively or in addition, the air circulation around the fireplace can be limited by means of a damper (not shown) placed in a suitable way in the circulation air channel 7, e.g. at the grid 20.

The damper 29 is controlled by one or more thermostats 50, in 51. Of these, a thermostat designated 50 can be a flue gas temperature-sensing safety thermostat which is designed to, at a temperature that exceeds a predetermined value, produce or via electric drive means control a mechanical movement which quickly and essentially completely closes the damper 29 or another similar damper 29'.

Another thermostat designated 51 is a room thermostat which closes the damper 29 when a predetermined room temperature is reached.

Moreover, the same or an additional mechanical or electrical drive (not shown) can open the damper 29 and keep it open for time intervals of sufficient duration for the fire in the hearth to generate maintenance heat.

The combustion process of the fire at different heat requirements is illustrated by fig. 3. Fig. 3a illustrates here little and fig. 3b large heat demand, as the width of the vertical bars shows the duration of the periods when combustion takes place at full effect. The spaces between these bars illustrate periods of time when combustion in the stove essentially ceases completely.

The thermostat 50 or additional thermostat (not shown) present in the fireplace room 2 or the smoke pipe 5a is arranged to automatically open the damper 29 when the flue gas temperature drops below a predetermined value even though the room thermostat 51 will keep the damper 29 closed. In this way, the fire is only rekindled momentarily in the manner illustrated by the narrow bars in fig. 3a.

32 denotes a thermoelectric generator, one side of which is coated by the hot flue gases in the hearth's upper part 5, while the cold side is cooled by combustion air coming from outside. The generator cooperates with one or more electric thermostats in such a way that the damper 29 is held fully open when the thermoelectric generator at a cold hearth does not emit energy, while this, via setting devices, closes the damper when the hearth temperature and thus the output power from the generator 32 reaches a certain maximum value. The room thermostat 51 can close the damper before this time via setting devices (not shown). In this way, reliable operation of the stove is ensured, even when a separate electricity supply is missing or randomly stops. In certain cases, the generator 3 2 can exclusively work as an energy source and drive the thermostat 51 in the manner indicated above.

In the module 21 which surrounds the upper part of the stove, in connection with the grate 20 there can be electric heating elements 24. Thus it is also possible to heat the circulating air electrically, i.e. the stove becomes a combi-air between solid fuel and electric energy.

The space 40 between the circulation air duct 7 and the stove's outer casing can optionally be filled with heavy material, e.g. sand, to allow short-term accumulation of heat.

The hob 8 can be surrounded by a cladding part la belonging to the stove with a hatch lb forming an oven chamber whose bottom is formed by the hob 8. Even temperature for the hob or the furnace is achieved by means of thermostats (not shown) which control the combustion process via the damper 29.

The fan 10 is arranged to cooperate with the filter 18 in such a way that when the fan is working, the air is sucked in via the filter, while the filter automatically folds to the side when the fan has stopped, so that air can be supplied to the circulation air channel 19, 7 without passing the filter.

In connection with the module 21, there can be a further damper 27, suitably made of bimetal, which automatically opens when the temperature of the preheated combustion air coming from outside exceeds a certain value, e.g. 50° C, so that room air with a temperature of approx. 20° C is instead drawn in as combustion air to the hearth. If the building is so dense that a negative pressure is then achieved, the air drawn in from outside is automatically replaced during heat exchange with incoming, preheated outside air.

In certain cases, it is appropriate to arrange the stove's electrical functions in a different place than in the module 21, e.g. in the lower part of the stove.

In certain cases, the flue gas thermostat 50 can be replaced with another thermostat (not shown) which is placed outside the flue pipe and senses a temperature which is dependent on the flue gas temperature.

The maximum temperature of the circulating air may not exceed a value that depends on the applicable fire protection regulations at the relevant location. In many cases, the maximum temperature of the circulating air must not exceed 200 - 210° C. If this safety value were to be achieved, the damper 29 or another similar damper is immediately affected so that the air supply to the fireplace is interrupted.

Claims (9)

1. Procedure for firing with solid fuel in a closed fireplace room (2) which has a supply air duct (13) for combustion air and is designed for heating circulation air in a circulation air duct (7) arranged around the fireplace, the supply of combustion air being regulated using at least a damper (29) arranged in the supply air duct (13) whose movement is controlled by at least one thermostat, while limiting the temperature of the circulating air so that it does not exceed a predetermined maximum temperature, characteri*- characterized by the movement of the damper (29) using one or more control devices, such as a thermostat (50, 51), time relay or the like, is controlled between either a mainly fully open or a mainly fully closed position, in such a way that combustion periodically ceases , whereby it is ensured that the fuel temperature after a cessation of combustion is sufficiently high for the combustion process to start again when the damper (29) is opened again, at the same time that the combustion is controlled to maintain a desired predetermined temperature in a room heated by means of the circulating air or object heated in one of the flue gases, such as an oven, hob, water heater or similar. 2. Method according to claim 1, characterized in that the temperature reduction of the fuel during the periods when the damper (29) is closed is limited by the air circulation around the hearth (2) being limited. 3. Method according to claim 1 or 2, characterized in that the damper (29) is kept open in time intervals of sufficient duration for the hearth (2) to generate maintenance heat. 4. Method according to claim 1, characterized in that a thermoelectric generator (32), which is affected by the hot flue gases from the hearth (2), is made to cooperate with one or more electric thermostats in such a way that the damper (29) is kept open when the thermoelectric generator at a cold hearth (2) does not emit energy, while it closes the damper when the flue gas temperature and thus the emitted power from the generator reaches a certain desired value, unless at least éh thermostat does not call for heat. 5. Stove for firing with solid fuel in accordance with the method according to claim 1, comprising a closed hearth space (2) with a hatch (15) arranged for fuel filling, which is designed to precisely shut off the hearth space from the surroundings, one with at least one damper (29 ) provided supply air duct (13) for supplying combustion air to the fireplace room (2), a circulation air duct (7) arranged around the fireplace, organs (5, 10) for heat exchange with circulating air, and at least one thermostat for controlling the damper (29 ) movement, characterized in that it comprises control elements (50, 51) which are arranged to control the movement of the damper (29) between a fully open position in the main case and a fully closed position in the main case, so that the combustion in the hearth (2) either takes place at full effect or periodically ceases, and organs that ensure that the fuel temperature after a cessation of combustion is sufficiently high for the combustion process to start again when the damper is opened again, as control the organs are further arranged to maintain a desired predetermined temperature in a room heated by means of the circulating air or in an object heated by the flue gases, such as an oven, hob, water heater or the like. 6. Stove according to claim 5, characterized in that the organs (10a, 17) which ensure a sufficiently high fuel temperature are arranged to limit the heat output emitted from the hearth (2) by limiting the air circulation around the hearth when the damper (29) assumes closed score. 7. Stove according to claim 5 or 6, characterized in that the control means comprise one or more electric thermostats (51) which are arranged to cooperate with a thermoelectric generator (32) which is affected by the hot flue gases from the hearth (2), on such a way that the damper (29) is kept fully open when the thermoelectric generator (32) at a cold hearth (2) does not emit energy, while the generator, when the hearth temperature and thus the emitted power from the generator achieves a certain desired value, via setting devices closes the damper (29) unless at least one thermostat does not call for heat. 8. Stove according to one of claims 5-7, characterized in that the supply air duct (13) during heat exchange with a flue gas duct (5a) departing from the hearth (2) is arranged for so-called balanced draft. 9. A stove according to one of claims 5-8, in which the circulating air is arranged to be drawn in at the lower part of the stove and after heat exchange leave in the area of the upper part of the stove, characterized in that the circulating air is drawn in by means of a in the area of the stove lower part arranged fan (10) which is designed to cooperate with a filter (18) in such a way that the air is sucked in via the filter when the fan (10) is working, while the filter automatically folds to the side when the fan is stopped, so that air can be supplied without passing the filter.