WO2021116538A1

WO2021116538A1 - A fireplace, an arrangement for a fireplace and a method for the secondary air supply of a fireplace

Info

Publication number: WO2021116538A1
Application number: PCT/FI2020/050838
Authority: WO
Inventors: Pertti Harjaluoma
Original assignee: Harvia Finland Oy
Priority date: 2019-12-13
Filing date: 2020-12-14
Publication date: 2021-06-17
Also published as: FI20196083A1; EP4073434A1; EP4073434B1; EP4073434C0; FI130332B

Abstract

The invention relates to a fireplace (10), which includes a firebox (12) for a fuel charge (60), an intake air duct (17) for leading primary air to the firebox (12), a grate (20) for supporting the fuel charge (60), wherein the grate (20) includes intake air openings (21) for leading primary air from the intake air duct (17) to the firebox (12), a secondary air duct (30) for leading secondary air to the firebox (12) from a second end (32) to a first end (31) of the secondary air duct (30), and a secondary air limiter (22) arranged to form a regulating element (18) in the firebox (12) for regulating the flow of secondary air that leaves the secondary air duct (30). In addition, the secondary air limiter (22) is arranged to be mobile as a result of the effect of the mass of the fuel charge (60) placed on the grate (20) and arranged to use the regulating element (18) in such a way that when the mass of the fuel charge (60) placed on the grate (20) is reduced, the secondary air limiter (22) closes limiting the flow of secondary air to the firebox (12). The invention also relates to an arrangement for a fireplace and a method for the supply of secondary air of a fireplace.

Description

A FIREPLACE, AN ARRANGEMENT FOR A FIREPLACE AND A METHOD FOR THE SECONDARY AIR SUPPLY OF A FIREPLACE

The invention relates to a fireplace, which includes a firebox for a fuel charge, an intake air duct for leading intake air to the firebox, a grate for supporting the fuel charge. The grate includes intake air openings for leading primary air from the intake air duct to the firebox. In addition, the fireplace includes a secondary air duct for leading secondary air to the firebox from a second end to a first end of the secondary air duct, and a secondary air limiter arranged to form a regulating element in the firebox for regulating the flow of secondary air that leaves the secondary air duct. The invention also relates to an arrangement for a fireplace and a method for the secondary air supply of a fireplace. Air supply of a charge-heated fireplace is a compromise between different factors, such as, for example, easy ignitability, efficiency of combustion and emissions produced from combustion. Often, primary intake air is led to the firebox through a grate. It is known that by feeding secondary air in addition to primary air onto the burning substance, it is possible to achieve cleaner combustion. Secondary air is often fed through openings in the door of the firebox. However, when the combustion event moves to the ember combustion phase, secondary air supply should be markedly limited and air should only be fed via the primary duct through the ember bed in order that pieces of charcoal would quickly burn out and the total emissions would remain as small as possible. In addition, reducing the ember combustion phase standardises the efficiency of the fireplace. In the ember combustion phase, air flowing through the fireplace cools the fireplace and takes heat away from the room to be heated. By reducing the ember combustion phase, the efficiency of combustion can be kept closer to a constant, charge combustion therefore operating more uniformly. In addition, once the ember combustion phase of the last fuel charge has ended quickly, it is possible to close the damper and/or the air supply flaps of the fireplace earlier without the risk of carbon monoxide, thus blocking the air flow through the fireplace to prevent heat from escaping from the room to be heated.

In many fireplaces, both primary and secondary air supplies can be regulated manually, but such a method is awkward to use and requires continuous monitoring. To be workable, regulation of supply air must be automatic.

Patent publication FI119077 discloses a fireplace, wherein primary and secondary air supplies to the firebox are controlled in a self-sustained manner with a solution based on thermal expansion of the fireplace frame. However, a solution based on thermal expansion cannot influence the combustion of successive fuel charges because the temperature differences are not sufficiently big in the fireplace during the charge combustion. A hot frame remains thermally expanded between different charges. With thermal expansion, sufficient accuracy cannot be achieved for intake air supply, but the air supply is mainly regulated during the combustion of the first charge and while the fireplace cools down at the end of the heating cycle. Thus, control of the combustion event is far from optimal, for example, in a situation where, between the additions of fuel charges, the combustion event proceeds to the ember combustion phase once or several times. This solution is also mechanically very complex and thus difficult to utilise commercially.

The object of the invention is to provide an improved fireplace, which is equipped with an automatic regulation mechanism for intake air supply, the purpose of which is to control the combustion event for each fuel charge and reduce total emissions of the fireplace as well as improve the total efficiency ratio of the fireplace by equalising variations of charge combustion. The characteristic features of this invention are set forth in the accompanying Claim 1. Another object of the invention is to provide an improved arrangement for a fireplace including an automatic regulation mechanism for intake air supply, the purpose of which is to control the combustion event for each fuel charge and reduce total emissions of the fireplace as well as improve the total efficiency ratio of the fireplace by equalising variations of charge combustion. The characteristic features of this invention are set forth in the accompanying Claim 16. Still another object of the invention is to provide an improved method for the secondary air supply of a fireplace, the purpose of which is to control the combustion event for each fuel charge and reduce total emissions of the fireplace as well as improve the total efficiency ratio of the fireplace by equalising variations of charge combustion. The characteristic features of this invention are set forth in the accompanying Claim 17.

The fireplace according to the invention includes a firebox for a fuel charge, an intake air duct for leading intake air to the firebox, a grate for supporting the fuel charge. The grate includes intake air openings for leading primary air from the intake air duct to the firebox. In addition, the fireplace includes a secondary air duct for leading secondary air to the firebox from a second end to a first end of the secondary air duct, and a secondary air limiter arranged to form a regulating element in the firebox for regulating the flow of secondary air that leaves the secondary air duct. The secondary air limiter is arranged to be mobile as a result of the effect of the mass of a fuel charge placed on the grate and arranged to use the regulating element in such a way that when the mass of the fuel charge placed on the grate is reduced, the secondary air limiter closes limiting the flow of secondary air to the firebox.

In this way, the secondary air duct opens thanks to the mass of the fuel charge, thus permitting intake air to be led along the secondary air duct beyond the charge even upper in the firebox for combustion. Thus, the charge burns calmly and cleanly as oxygen is carried along with intake air above the fire. In the final phase of the combustion event, once the charge on the grate has mainly changed into a lighter ember, the secondary air duct closes resulting in that the flow of intake air is led through the grate and the ember bed covering it, accelerating burning of the ember. Rapid combustion in the ember phase is desirable and it influences the emissions of charge combustion and the efficiency ratio. Easily measurable typical emissions of charge combustion include carbon monoxide (CO) and carbon dioxide (CO₂)· Leading oxygen of intake air through the ember bed reduces the generation of carbon monoxide emissions extremely efficiently. It is known that the amount of generating carbon monoxide correlates well with small- particle emissions. Reduction of secondary air supply decreases the amount of excess air and keeps the combustion temperature higher, the temperature of the combustion process thus being sufficiently high for the carbon monoxide to burn until it forms carbon dioxide. When combustion air is led as primary air only through the ember bed, unburnt gases are not cooled by secondary air. Combustion air led through the ember bed also contributes to mixing, while a smaller burning substance (ember) burns out. By accelerating combustion of the ember, the efficiency of combustion can be kept more uniform, which remarkably improves the efficiency ratio of the fireplace. A five minutes' reduction in the ember combustion phase improves the efficiency ratio by one percentage point and the computational efficiency increases by about 9%. A ten minutes' reduction in the ember combustion phase improves the efficiency ratio by 1.8 percentage points and the computational efficiency increases by about 20%.

Here, the grate means the part comprising intake air openings that separates the intake air duct and the firebox. The grate supports the fuel charge, and in this context, the grate is also used to refer to other structures for supporting fuel.

The grate is preferably a slotted grate. Thus, the substance to be combusted is more tightly packed on the grate, compared to a wave-shaped grate, for example, and thus the fuel charge regulates the flow of primary air from the intake air duct to the firebox.

The surface area of the grate openings can be 10 - 60%, preferably 20 - 40% of the entire surface area of the grate.

The grate and the secondary air limiter can be formed as an integrated whole, for example, from an individual cast iron component, ceramics or other fire-resistant substance. The grate can also be assembled using several parts connected to each other. In an embodiment of the invention, the fireplace includes only one intake air duct, via which primary air is arranged to flow to the firebox through the grate and via which secondary air is arranged to flow to the firebox beyond the grate. In this way, the total air supply of the fireplace can be regulated by regulating the flow of one intake air duct.

In an embodiment of the invention, secondary air is arranged to flow to the firebox via separate intake air ducts, which can be located on the sides of the fireplace, for example. In this way, it is possible to regulate the flows of primary air and secondary air independently of each other.

Preferably, the secondary air limiter is arranged as an extension of the grate to limit a secondary air duct from the firebox for leading secondary air from the intake air duct to the firebox, and the regulating element is included in the first end included in the secondary air duct. In this way, the supply of secondary air to the firebox can be automatically regulated for each fuel charge.

Preferably, the fireplace includes a support joint arranged at the edge included in the secondary air limiter, between the grate and the secondary air limiter, for supporting the grate to the firebox, permitting at least the secondary air limiter to turn around the support joint for moving the regulating element relative to the firebox for automatically regulating the amount of secondary air in each combustion situation according to the combined mass of the fuel charge on the grate and the grate. Preferably, a secondary air opening is formed in the second end included in the secondary air duct, between the support joint and the firebox, for leading secondary air from the intake air duct to the secondary air duct. In this way, the supply of secondary air to the firebox can be automatically regulated for each fuel charge.

According to a first embodiment, the secondary air limiter and the support joint are fixedly connected to the grate forming a secondary air regulation mechanism. Thus, a low-cost and simple entity is achieved. The regulation mechanism can be manufactured, for example, as an individual component from cast iron or ceramics, which are known as materials with a good thermal resistance. The fireplace according to the first embodiment preferably includes two secondary air regulation mechanisms, each of which has a grate, a secondary air limiter and a support joint. Thus, regulation of secondary air operates mechanically well and regulation mechanisms can be easily fitted through the fireplace door and installed in a typical existing fireplace. In addition, a two-piece embodiment leads secondary air more uniformly from both sides of the firebox.

Preferably, the grate has a first level and the secondary air limiter has a second level and the first level and the second level are divergent, the secondary air limiter forming an inclined surface relative to the horizontal plane in the position of use for guiding the fuel charge onto the grate. In this way, it is easier for the user to place the fuel charge in the designated position. In other words, the regulating element preferably forms a structure that tapers downwards enabling the fuel charge to be guided onto the grate. Thus, the fuel charge on the intake air openings of the grate partly also limits the flow of primary air making it possible to regulate the total air supply to the firebox.

The width of the grate between the grate edge and the support point can be 25 - 100%, preferably 30 - 70% of the width of the secondary air limiter between the edge of the secondary air limiter and the support point. Thus, the regulation mechanism suits well as a whole to typical fireplaces and secondary air can be guided preferably sufficiently high.

The mass and length of the grate relative to the mass and length of the secondary air limiter can be such that the moment generated by the secondary air limiter relative to the support joint is equal to the moment generated jointly by the grate and the fuel amount, the mass of which is 5 - 30%, preferably 8 -

20% of the mass of the fuel charge placed in the firebox, opposite relative to the moment generated by the secondary air limiter relative to the support joint. Thus, the secondary air duct preferably closes at the right time as the combustion event proceeds to the ember combustion phase.

The secondary air regulation mechanisms can be identical with each other. This simplifies the structure of the regulation mechanism and decreases manufacturing costs.

Preferably, the support joint is formed of two separate support joints placed at a distance from each other, between which there is the secondary air opening of the second end and between which the axis of rotation of each secondary air regulation mechanism is formed. With such a construction, the regulation mechanism is provided with a robust structure and a large surface area is achieved for the intake opening of the secondary air duct. Preferably, the secondary air limiter, together with the secondary air opening, is arranged to form the secondary air duct leading from the intake air duct to the firebox. With such a construction, it is not necessary to build a separate secondary air duct in the fireplace and the fireplace can have a simple construction.

The fireplace can be a sauna stove. Sauna stoves are very commonly used fireplaces, with which achievement of the maximum heating efficiency is particularly aimed at. The invention can have a remarkable influence on emissions and the efficiency ratio of sauna stoves.

In this context, a sauna stove means a furnace-like heater of a sauna, in the upper part of which there is a stone arrangement capable of storing heat and onto the heated stones of which it is possible to throw water during use to provide water steam in the room functioning as the sauna.

The fuel charge can be wood. In the final phase of wood burning, there is a large ember in the firebox. The invention can remarkably accelerate combustion of an ember and thus reduce generation of carbon monoxide.

According to a second embodiment, the secondary air limiter and the support joint compose a secondary air regulation mechanism, separate from the grate, which further includes an arm, upon which the grate is arranged, on the other side of the support joint as an extension of the secondary air limiter. Thus, the secondary air regulation mechanism according to the invention can also be applied in existing fireplaces and grates.

There are preferably two regulation mechanisms according to the second embodiment, arranged on the opposite sides of the grate relative to each other. Thus, regulation of secondary air operates mechanically well and regulation mechanisms can be easily fitted through the fireplace door and installed in a typical existing fireplace. Moreover, a two-piece embodiment leads secondary air more uniformly from both sides of the firebox .

The minimum cross-sectional area of a completely open secondary air duct relative to the cross-sectional area of the primary air duct can be 40 - 100%, preferably 50 - 80%. Thus, secondary air can be fed to the firebox with an optimal ratio relative to primary air.

According to a third embodiment, the grate and the regulating element are supported by a spring or a counterweight or a combination of these. Thus, a force contrary to the force of gravity exerted on the grate and the fuel charge is provided enabling regulation of the secondary air supply.

The grate and regulating element supported by a spring or a counterforce or a combination of these can move in its entirety in an elevator-type manner or the grate can be hinged or articulated in such a way that the grate inclines as the fuel mass changes, the secondary air regulator thus being arranged to regulate the supply of secondary air when the grate inclines.

Preferably, the fireplace also includes equipment for regulating primary air for keeping the total air amount constant. Thus, both the primary air supply and the secondary air supply of the fireplace can be regulated to enable better control of the combustion event and to keep the efficiency of combustion constant. For regulating primary air, it is possible to use, for example, the fuel charge on the intake air openings of the grate.

The fuel power of the fireplace can be 5 - 80 kW. Typically, sauna stoves and other fireplaces of a similar size operate in this efficiency range.

The invention also relates to an arrangement for a fireplace. The fireplace subject of the arrangement includes a firebox for a fuel charge and an intake air duct for leading intake air to the firebox. The arrangement includes a grate, which includes intake air openings for leading primary air from the intake air duct to the firebox, for supporting a fuel charge, and a secondary air limiter arranged to form a regulating element for regulating secondary air that enters the firebox. In the arrangement, the secondary air limiter is arranged to be mobile as a result of the effect of the mass of the fuel charge placed on the grate and arranged to use the regulating element in such a way that when the mass of the fuel charge placed on the grate is reduced, the secondary air limiter closes limiting the flow of the secondary air to the firebox. With this arrangement, the regulation mechanism can be fitted in existing fireplaces. A conventional grate can be replaced with the arrangement, the benefits of which correspond to the benefits of the fireplace described above.

The invention also relates to a method for secondary air supply of a fireplace. In the method, for supplying secondary air to a fireplace with a fuel power of 5 to 80 kW, in which fireplace solid fuel is burnt on the grate in the firebox and primary air is led to the firebox through the grate and secondary air is led to the firebox above the grate, the flow of secondary air is regulated based on the force of gravity exerted on the fuel charge placed on the grate in such a way that when the mass of the fuel charge placed on the grate is reduced, the secondary air limiter included in the fireplace closes limiting the flow of secondary air to the firebox.

With this method, the secondary air supply of a fireplace can be regulated during the combustion event as the mass of the fuel charge changes, which can reduce emissions of the fireplace and improve the efficiency ratio of the fireplace. Wood is preferably burnt in the fireplace. In the final phase of wood burning, there is a large ember in the firebox. The invention can remarkably accelerate combustion of an ember and thus reduce generation of carbon monoxide.

Preferably, the flow of secondary air is only regulated by the effect of the mass that changes during the combustion process of the fuel charge. In this way, regulation of the flow of secondary air takes place automatically independently of the user. The regulation of the flow of secondary air operates in the same way for each fuel charge. Preferably, primary air and secondary air are led to the firebox from a common intake air duct. In this way, the total air supply of the fireplace can be regulated by regulating the flow of one intake air duct.

Preferably, the flow of secondary air to the firebox is limited when the mass of the fuel charge has been reduced to 5 - 30 percent, preferably to 8 - 20 percent of the mass of the fuel charge placed in the firebox. In this way, the flow of intake air can be regulated in a desired way in the ember combustion phase. The invention is described below in detail with reference to the accompanying drawings that illustrate some of the embodiments of the invention, in which

Figure la is a front view of a fireplace according to the invention without a front panel in a situation, in which the moment generated by the fuel charge relative to the support joint has opened the secondary air duct,

Figure lb is a front view of a fireplace according to the invention without a front panel in a situation, in which the mass of charcoals on the grate is so small that the secondary air duct is closed,

Figure 2a is a right diagonal front view and a top view of a fireplace according to the invention without a front panel with the secondary air duct open,

Figure 2b is a right diagonal front view and a top view of a fireplace according to the invention without a front panel with the secondary air duct closed,

Figure 3a isa right diagonal front view and a bottom view of a fireplace according to the invention without a front panel with the secondary air duct open,

Figure 3b isa right diagonal front view and a bottom view of a fireplace according to the invention without a front panel with the secondary air duct closed, Figure 4a is a basic view of a second fireplace according to the invention in a situation, in which the secondary air duct is open, Figure 4b is a basic view of a second fireplace according to the invention in a situation, in which the secondary air duct is closed,

Figure 5a depicts a third fireplace according to the invention without a front panel in a situation, in which the secondary air duct is open, and

Figure 5b depicts a third fireplace according to the invention without a front panel in a situation, in which the secondary air duct is closed. Figures la - 3b depict the first embodiment of a fireplace 10 according to the invention, in this case a sauna stove. The firebox 12 of a sauna stove is limited by the sides 141, the rear panel 142 and the front panel (not shown in figures) of the frame 14 of the fireplace 10. Below the firebox 12, there is an ash space 16, which forms the intake air duct 17. Between the firebox 12 and the ash space 16, there is a grate 20 comprising intake air openings 21 (Figure 2a) for leading primary air from the intake air duct 17 to the firebox 12. The grate 20 extends from the rear panel 142 of the fireplace 10 to the front panel of the fireplace 10 in the depth direction of the fireplace 10, which is illustrated in Figures 2a and 2b. The upper part of the firebox 12 is limited by a panel component 49, by going around of which combustion gases can enter the side ducts 50, wherein combustion gases indirectly heat stones in a stone space 180. The stone space 180 shown in Figures la - 2a is also equipped with sweeping openings covered with lids 191 as well as a connection to a chimney 192.

As an extension of the grate 20, there is a secondary air limiter 22, which functions as a regulating element 18 for regulating secondary air that enters the firebox 12 from the intake air duct 17. The entity formed by the grate 20, the secondary air limiter 22 and the support joint 26 between these is formed as a continuous integral part, of which there are two identical items, each of which forms a regulation mechanism 19. The regulation mechanisms 19 are arranged relative to each other as mirror images relative to the vertical centre line of the fireplace 10. The secondary air duct 30 shown in Figures 3a and 3b, formed between the secondary air limiter 22 and the side 141 of the fireplace 10 is limited to a so-called first end 31, which is located between the edge of the secondary air limiter 22 and the side 141 of the fireplace 10 (Figures 3a and 3b), and to a second end 32, which is located between the support joint 26 and the side 141 of the frame 14 of the fireplace 10. Identical secondary air ducts 30 are formed on both sides of the fireplace 10.

Both primary air and secondary air flow to the firebox 12 and to the burning substance via the intake air duct 17 formed by the ash space 16 below the grate 20. Thus, by regulating the door of the ash space 16, the user can regulate the flow of both primary air and secondary air.

In Figure la, a fuel charge, the mass of which can be about 3 kg, for example, has been loaded to the firebox 12 on the grate 20. Secondary air limiters 22 form a surface that is inclined relative to the horizontal plane in the position of use, a second level 202, which guides the fuel charge 60 onto the grate 20 to the first level 201, the fuel charge 60 thus at least partly blocking the intake air openings 21 of the grate 20 limiting the supply of primary air. In this situation, the force of gravity exerted on the fuel charge 60 and the grate 20 causes the turning of the regulation mechanism 19 around the support joint 26 in such a way that the secondary air limiter 22 moves towards the centre of the firebox 12. As a consequence, the first end 31 of the secondary air duct 30 opens thus permitting air coming from the second end 32 of the secondary air duct 30 to flow to the firebox 12 between the secondary air limiter 22 and the secondary air deflector 24. When the secondary air ducts 30 are fully open, the grate 20 can lean on the support component 144 of the frame 14 of the fireplace 10 by its bottom surface. Alternatively, the secondary air limiter 22 can lean on the support component 241 of the secondary air deflector 24. The purpose of the secondary air deflector 24 is to lead air coming from the secondary air duct 30 towards the combustion event. Figures 2a and 3a illustrate an opening 242 that remains between the support parts 241 of the secondary air deflector 24, via which secondary air is fed to the firebox 12 when the secondary air duct 30 is open. In the initial phase of the combustion event, air is fed to the firebox 12 both from the primary duct through the intake air openings 21 of the grate 20 below the burning substance and through the secondary air ducts 30 on the sides of the firebox 12 above the burning substance.

When the combustion event proceeds, the mass of the fuel charge 60 is reduced and, in the final phase of the combustion event, an ember bed 60', illustrated in Figure lb, remains from the charge. When the combustion process moves to the ember combustion phase and the mass of the remaining charge is below the limit of about 0.5 kg, the moment exerted by the secondary air limiter 22 on the regulation mechanism 19 relative to the support joint 26 exceeds the moment generated jointly by the grate 20 and the ember 60'. Thus, the regulation mechanism 19 turns around the support joint 26 in such a way that the secondary air limiter 22 moves towards the side 141 of the frame 14 of the fireplace 10 and limits access of secondary air to the firebox 12 by closing the first end 31 of the secondary air duct 30. In the ember combustion phase illustrated in Figure lb, air flows mainly via the primary air duct formed by the intake air openings 21 of the grate 20, through the ember bed 60'.

In a standby status, without a fuel charge, the secondary air limiter 22 leans on the side 141 of the frame 14 of the fireplace 10, thus the first end 31 of the secondary air duct 30 being closed.

Here, the closing of the first end 31 of the secondary air duct 30 does not mean complete air-tightness but a notable restriction of secondary air supply (more than 95%). It is advantageous that there remains a small clearance between the secondary air limiter 22 and the side 141 of the frame 14 of the fireplace 10 even when the secondary air duct 30 is closed for guaranteeing the reliability of operation of the regulation mechanism 19. Similarly, it is advantageous that a clearance remains on the sides of the grate 20, which extends from the rear panel 142 of the frame 14 of the fireplace 10 to the front wall of the frame 14 of the fireplace 10 in the depth direction of the fireplace 10, in order that the operation of the regulation mechanism 19 is not disturbed due to, for example, thermal expansion and/or charcoals or ash entering between the grate 20 and the support component 144 of the frame 14 of the fireplace 10.

Air can also be led to the fireplace 12 through the openings in the door of the firebox 12 achieving in this way clean combustion in the immediate vicinity of the door, which reduces soot formation on the transparent glass door. However, the amount of secondary air obtained through this is small relative to air fed via the secondary air duct 30.

In this embodiment, the fireplace has a fuel power ranging between 20 and 30 kW. The length of the grate 20 in the depth direction of the fireplace 10 can be, for example, 20 - 40 cm, preferably 25 - 35 cm, and the width between the edge of the grate 20 and the support joint 26 can be 5 - 20 cm, preferably 8 - 15 cm. The width of the secondary air limiter 22 between the secondary air limiter 22 and the support joint 26 can be, for example, 10 - 30 cm, preferably 15 - 25 cm. The distance of the connection point between the secondary air limiter 22 and the grate 20 from the side 141 of the frame 14 of the fireplace 10 can be, for example, 1 - 5 cm, preferably 2 - 4 cm. The length of the firebox 12 in the depth direction can be, for example, 20 - 50 cm, preferably 30 - 45 cm, the width can be, for example, 20 - 50 cm, preferably 25 - 40 cm, and the height can be, for example, 20 - 80 cm, preferably 30 - 70 cm.

Figures 4a - 4b illustrate a basic view of a second embodiment of the fireplace 10 according to the invention, comprising a one-part grate 20. By its first end, the grate 20 rests on the support part 148 of the frame 14 of the fireplace 10 and, by its first end, on the arm 29 of the regulation mechanism 19. Alternatively, there can be two regulation mechanisms 19 and the grate 20 can rest on separate regulation mechanisms 19 by both of its ends. When a fuel charge 60 is loaded on the grate 20, the arm 29 is moved downwards by the force of gravity exerted on the grate 20 and the fuel charge 60. Thus, the regulation mechanism 19 turns relative to the support joint 26 in such a way that the secondary air limiter 22 moves away from the side 141 of the frame 14 of the fireplace 10 opening the secondary air duct 30 (Figure 4a). When the combustion event proceeds to the ember combustion phase and the remaining mass of the fuel charge goes below a selected limit, the moment exerted by the secondary air limiter 22 on the system relative to the support joint 26 exceeds the moment generated jointly by the grate 20 and the ember 60'. Thus, the regulation mechanism 19 turns around the support joint 26 in such a way that the secondary air limiter 22 moves towards the side 141 of the fireplace 10 and limits access of secondary air to the firebox 12 by closing the secondary air duct 30. In the ember combustion phase, air thus flows mainly via the intake air duct formed by the intake air openings 21 of the grate 20 through the ember bed 60' (Figure 4b).

Figures 5a - 5b illustrate a basic view of a third embodiment of the fireplace 10 according to the invention, comprising a grate 20 supported by springs 200 and a regulation mechanism 19 formed by a regulating element 18. When a fuel charge 60 is loaded on the grate 20, the force of gravity exerted on the grate 20 and the fuel charge 60 compresses the springs 200 resulting in a downward movement of the grate 20 and the secondary air deflector 22. Thus, the secondary air ducts 30 on the sides 141 of the frame 14 of the fireplace 10 open and the fuel charge 60 on the grate 20 simultaneously limits the supply of primary air (Figure 5a). As the combustion event proceeds to the ember combustion phase and the remaining mass of the fuel charge 60 is reduced, the force exerted by the springs 200 on the grate 20, opposite in direction relative to the force of gravity, lifts the grate 20 and the secondary air limiter 22 upwards resulting in the closure of the secondary air ducts 30. Thus, air flows to the firebox 12 mainly via the intake air openings 21 of the grate 20 through the ember bed 60' (Figure 5b).

Correspondingly, instead of springs 200, a counterweight or a combination of springs 200 and a counterweight can be used, producing a force contrary to the force of gravity exerted on the grate 20 and the regulating element 18, where the regulation mechanism 19 operates otherwise in the same way as in the embodiment illustrated in Figures 5a - 5b.

In addition to an elevator-type grate 20 illustrated in Figures 5a - 5b, the grate can also be hinged or articulated in such a way that the grate inclines as the fuel mass changes, where the regulation mechanism 19 operates in a corresponding way.

In a fourth embodiment of the fireplace according to the invention, the grate is fixedly arranged to the fireplace and the secondary air limiter has pins coming through the intake air openings of the grate connected thereto, the mass of the fuel charge placed on top of these pins moving the secondary air limiter via the pins. More precisely, the force of gravity exerted on the fuel charge placed on the pins generates a moment in the regulation mechanism relative to the support joint, which moves the pins downwards resulting in the movement of the secondary air limiter arranged in the pins and the opening of the secondary air duct. As the combustion event proceeds to the ember combustion phase and the mass of the fuel charge goes below a pre-set limit, the moment exerted by the secondary air limiter on the regulation mechanism relative to the support joint exceeds the moment generated by the force of gravity exerted on the fuel charge. Thus, the regulation mechanism turns around the support joint in such a way that the pins are lifted up and the secondary air limiter closes the secondary air duct limiting access of secondary air to the firebox.

Besides a sauna stove, the fireplace can also be, for example, a furnace, stove, hearth, baking oven, or other similar fireplace suitable for the purpose of use.

Claims

1. A fireplace (10), which includes a firebox (12) for a fuel charge (60), - an intake air duct (17) for leading intake air to the firebox (12), a grate (20) for supporting the fuel charge (60), wherein the grate (20) includes intake air openings (21) for leading primary air from the intake air duct (17) to the firebox (12), a secondary air duct (30) for leading secondary air to the firebox (12) from a second end (32) to a first end (31) of the secondary air duct (30), and a secondary air limiter (22) arranged to form a regulating element (18) in the firebox (12) for regulating secondary air that leaves the secondary air duct (30), characterised in that said secondary air limiter (22) is arranged to be mobile as a result of the effect of the mass of the fuel charge (60) placed on the grate (20) and arranged to use the regulating element (18) in such a way that when the mass of the fuel charge (60) placed on the grate (20) is reduced, the secondary air limiter (22) closes limiting the flow of secondary air to the firebox (12).

2. A fireplace (10) according to Claim 1, characterised in that the fireplace (10) includes only one intake air duct (17), via which primary air is arranged to flow to the firebox (12) through the grate (20) and via which secondary air is arranged to flow to the firebox (12) beyond the grate (20).

3. A fireplace (10) according to Claim 1 or 2, characterised in that said secondary air limiter (22) is arranged as an extension of the grate (20) to limit said secondary air duct (30) from the firebox (12) for leading secondary air from the intake air duct (17) to the firebox (12) and said regulating element (18) is included in the first end (31) included in the secondary air duct (30).

4. A fireplace (10) according to any of Claims 1 to 3, characterised in that the fireplace (10) includes a support joint (26) arranged at the edge included in the secondary air limiter (22) between said grate (20) and secondary air limiter (22) for supporting the grate (20) to the firebox (12) enabling the turning of at least the secondary air limiter (22) around the support joint (26) for moving said regulating element (18) relative to the firebox (12) for automatically regulating the amount of secondary air in each combustion situation according to the combined mass of the fuel charge (60) on the grate (20) and the grate (20), wherein a secondary air opening is formed between the support joint (26) and the firebox (12) in the second end (32) included in the secondary air duct (30) for leading secondary air from the intake air duct (17) to the secondary air duct (30).

5. A fireplace (10) according to Claim 4, characterised in that said secondary air limiter (22) and support joint (26) are fixedly connected to the grate (20) forming a secondary air regulation mechanism (19).

6. A fireplace (10) according to Claim 4 or 5, characterised in that the fireplace (10) includes two secondary air regulation mechanisms (19), of which each regulation mechanism (19) has said grate (20), secondary air limiter (22) and support joint (26).

7. A fireplace (10) according to any of Claims 1 to 6, characterised in that said grate (20) has a first level (201) and the secondary air limiter (22) has a second level (202) and said first level (201) and second level (202) are divergent, the secondary air limiter (22) forming an inclined surface relative to the horizontal plane in the position of use for guiding the fuel charge (60) onto the grate (20).

8. A fireplace (10) according to any of Claims 4 to 7, characterised in that the mass and length of the grate (20) of each part relative to the mass and length of the secondary air limiter (22) is such that the moment generated by the secondary air limiter (22) relative to the support joint (26) is equal to the moment generated jointly by the grate (20) and the fuel amount, the mass of which is 5 - 30%, preferably 8 - 20% of the mass of the fuel charge (60) placed in the firebox (12), opposite relative to the moment generated by the secondary air limiter (22) relative to the support joint (26).

9. A fireplace (10) according to any of Claims 4 to 8, characterised in that in each part, the support joint (26) is formed of two separate support joints (26) placed at a distance from each other, with said secondary air opening of the second end (32) disposed between these, and between which the axis of rotation of each secondary air regulation mechanism (19) is formed.

10. A fireplace (10) according to any of Claims 4 to 9, characterised in that said secondary air limiter (22), together with the secondary air opening, is arranged to form the secondary air duct (30) leading from the intake air duct (17) to the firebox (12).

11. A fireplace (10) according to any of Claims 1 to 10, characterised in that the fireplace (10) is a sauna stove.

12. A fireplace (10) according to Claim 4, characterised in that said secondary air limiter (22) and support joint (20) compose a secondary air regulation mechanism (19), separate from the grate (20), which further includes an arm (29), upon which said grate (20) is arranged, on the other side of the support joint (26) as an extension of the secondary air limiter (26).

13. A fireplace (10) according to any of Claims 1 to 3, characterised in that the grate (20) and the regulating element (18) are supported by a spring (200) or a counterweight or a combination of these.

14. A fireplace (10) according to any of Claims 1 to 13, characterised in that the fireplace (10) also includes equipment for regulating primary air for keeping the total air amount constant.

15. A fireplace (10) according to any of Claims 1 to 14, characterised in that the fuel power of the fireplace (10) is between 5 and 80 kW.

16. An arrangement for a fireplace (10), which fireplace (10) includes a firebox (12) for a fuel charge (60) and an intake air duct (17) for leading intake air to the firebox (12) and said arrangement includes a grate (20) for supporting the fuel charge (60), wherein the grate (20) includes intake air openings (21) for leading primary air from the intake air duct (17) to the firebox (12), a secondary air limiter (22) arranged to form a regulating element (18) for regulating secondary air that enters the firebox (12), characterised in that said secondary air limiter (22) is arranged to be mobile as a result of the effect of the mass of the fuel charge (60) placed on the grate (20) and arranged to use the regulating element (18) in such a way that when the mass of the fuel charge (60) placed on the grate (20) is reduced, the secondary air limiter (22) closes limiting the flow of secondary air to the firebox (12).

17. A method for supplying secondary air to a fireplace

(10) with a fuel power of 5 to 80 kW, in which fireplace (10) solid fuel is burnt on a grate (20) in a firebox (12) and primary air is led to the firebox (12) through the grate (20) and secondary air is led to the firebox (12) above the grate (20), characterised in that the flow of secondary air is regulated based on the force of gravity exerted on the fuel charge (60) placed on the grate (20) in such a way that when the mass of the fuel charge (60) placed on the grate (20) is reduced, the secondary air limiter (22) included in the fireplace (10) closes limiting the flow of secondary air to the firebox (12).

18. A method according to Claim 17, characterised in that wood is burnt in the fireplace (10).

19. A method according to Claim 17 or 18, characterised in that the flow of secondary air is only regulated by the effect of the mass that changes during the combustion process of the fuel charge (60).

20. A method according to any of Claims 17 to 19, characterised in that primary air and secondary air are led to the firebox (12) from a common intake air duct (17).

21. A method according to any of Claims 17 to 20, characterised in that the flow of secondary air to the firebox (12) is limited when the mass of the fuel charge (60) has been reduced to 5 - 30 percent, preferably to 8 - 20 percent of the mass of the fuel charge (60) placed in the firebox (12).