Fire with the right technology

You need to fire enough to fulfill the energy demands of your house. How much you load the wood log boiler will often determine your firing results. To fire with wood without adding an accumulator tank directly to the effect demands of the house then requires a certain technology that not too many products can do. To fire to a small effect demand is also very difficult. To get a fairly good function you have to make a log fire which means adjusting the amount of wood logs used dependent on the actual heat demand required. You can rarely fill up the wood hopper with wood in the evening and with the help of the draught regulator have enough fuel to make it through the night. Such a firing makes the draught regulator strangle the oxygen within the combustion process and prevent a boiling, and then the combustion temperature sinks. With this way of firing you have destroyed both the temperature and the oxygen supply and then smoulder firing typically occurs. This type of activity can then lead to heavy carbon (soot) production which not only makes the efficiency lower, but can also seriously increase the risk of soot fire and harmful emissions. The worst case is obviously that this activity could also lead to a fire incident. To avoid this occurring it is up to the owner of a double boiler or an over combustion boiler to watch out for too high flue-gas temperatures. You can, to a certain degree, lower the flue-gas temperature by lowering the flue-gas damper of the boiler, so that the boiler is not over loaded compared to what the convection part within the boiler can actually receive. Dry wood and a good under pressure can increase the risk of an overload and produce very high flue-gas temperatures.
Below you can see listed the different boilers available on the mark and find further explanations on each to hopefully avoid any confusion:
There are at least four groups of boilers:
1. Simple boilers
2. Combination boilers
3. Double boilers
4. Kitchen boilers
Simple boiler:
These are typically boilers which have a hearth and are adjusted specifically to the fuel type, e.g: oil or pellets.
Combination boilers
These are all boilers which have the same type of hearth allowing several different types of fuel to be used. Examples include wood burning, oil and/or pellets. The same hearth is then combined for two or several different types of fuel and the boiler is then called a combination boiler.
Double boilers
These are boilers which have separate hearths for oil/pellets and/or wood. Within these boilers oil/pellet burners can be mounted even if you mainly want to fire with wood.
Kitchen boilers
These boilers are typically water jacketed hearths that are commonly installed in kitchens. These are often complemented with a hob or oven for cooking purposes. Over the past years these boilers have become increasingly common and today they exist with different combustion systems. The boilers can then be divided into separate groups based upon their different combustion principles.
Here these combustion principles are further explained:
Over combustion
This means that following combustion of the wood you take out the flue-gases within the upper part of the hearth and then use these gases to ignite the total wood content of the hearth with these very high flue-gas temperatures. By doing this, the firing cycle becomes at its most intense during the initial firing after the ignition. Gradually less and less people are using this firing principle as it makes it difficult to maintain the right amount of oxygen within the combustion and hold a stable combustion result.
Under combustion
This means that you take out the flue gases above the grate, but instead from the lower part of the hearth. As a result you are then igniting only a smaller part of the wood content within the hearth and mainly burning the wood fuel within the bottom of the boiler. This then allows new wood to fall down into the combustion zone with a relatively low flue gas temperature when compared with the over combustion principle. If the hearth is cone shaped with the bigger part facing upwards, it then means that the risk of the wood getting jammed decreases. More and more of the modern under combustion boilers have their ceramics insulated after the combustion chamber where the gases from the wood start to finish burning, before the convection then starts.
Reversed combustion
This principle basically works similar to that of under combustion, but with the difference that the primary air is added above the surface of the grate (or ceramic hearth), instead of under, and the flue gases are found within the ash space. With this principle the gases will, in comparison to under combustion, travel the opposite way and pass down through the surface of the grate, instead of from above.
Blue flame combustion
This is the best technology if you are thinking about choosing wood burning as your heat alternative. The principle is quite new within wood combustion although built on an old technology, being the wood-gas principle. The technology started in Sweden during the beginning of the 1980's. Briefly the combustion principle can be explained that you are using both the excess air and the moisture content within the wood (in other words the water vapour within the wood), to actually break down the pyrolysis gases into shorter hydrocarbon chains during combustion. Often boilers which use the reverse combustion principle are used and complemented with a fan in the boiler which provides both the primary and secondary combustion air. The air feed is constructed in such a way that the fan creates a jet effect, sucking down the pyrolysis gases from the wood hopper and down into the combustion chamber. As a result, both a more stable combustion result and faster combustion process are obtained which give a much better control over the end result. This method of firing and combustion technology can then put less pressure on the fireman and are not so sensitive to outside temperatures and weather conditions which natural draught boilers can be. The blue flame technology is distinguished by the fact that the flame is no longer white or yellow and glowing, but more transparent and blue in its formation. To a person who has not seen a blue flame boiler in operation, it is easiest to compare the flame to the flame you see when you fire with LP-gas. This combustion principle normally gives the best efficiency and the best environmental result and the lowest wood consumption.

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