Modern Wood burning

Wood burning has always played a central role in our lives and even more so now when the energy prices are rising. Step by step the wood burning technology has improved, more and more of the heat value of the fuel mer or if we instead say the energy content of the wood has today been able to be utilized better with today's combustion technology combined with modern accumulator technology. Today we even see environmentaly certified wood boilers on the market that in most cases provide oxygen with help of a fan that makes the combustion more even and stable compared to the old natural draught principle. With today's technology wood burning is a very comfortable and profitable heating form for our homes. Many people think that modern wood boilers with a fan require electricity to work. If there is a power cut you can with advantage still even fire these boilers anyway. You simply open the door that shall provide the boiler with combustion air and fire these boilers exactly like you do with natural draught boilers. This is worth thinking about.

With a good wood burning installation you mean, a modern boiler that has a small water volume and is provided with fan and has a after combustion chamber of ceramics or similar and is installed by a professional installer to an accumulator tank that contains a big enough water volume to meet the function requirements to keep the heat for 24h at the coldest temperature. The fact that the water volume in the boiler should be as little as possible makes the boiler get up to the right temperature faster than in old boilers with a larger water content and that the efficiency becomes optimal, even radiation and standstill losses are eliminated. Calculate so that the accumulator tank is at least 15 times bigger than the volume of the hearth of the boiler and professionally installed.

The accumulator tank has not only one function for the wood burning, but several.
·  First of all the water volume of the accumulator tank be dimensioned so that it can handle to store the energy the house uses during 24h at the coldest outside temperature. The tank also works as an effect equalizer. When the effect demands are high during the winter.
·  The accumulator tank shall also be able to receive the energy from a full wood insert in the boiler without boiling. You might want to be able to fill the boiler with wood two times, maybe three while it is already burning and heat up the volume of the right installed accumulator tank, ignite again with a too small or wrong dimensioned accumulator tank.
·  The accumulator tank also makes a good impact on the environment which means you fire once a week during the summer and once a day in the winter. The amount of ignitions of the wood installation decreases radically if you fire wood against an accumulator tank.

In a normal sized house you then need approx. 1500 to 2 000 litres accumulator volume to handle this demand. With the right dimension on the water vaolume of the accumulator tank it is then enough to fire once per day in the winter, maybe with the exeption during the coldest days during the winter period when you might have to fire two times, but with right dimensioned accumulator tank this should be very rare.   

To have your own wood always gives the cheapest heat. But even if you buy e.g. pulpwood to fire, you end at an energy price of 15- 25 öre per kWh which correspondes to about half the pellet price or a quarter of the electricity price.

Charging equipment

To charge an accumulator tank with a "right choice" wood boiler you need to install a charging equipment that controls the charging adjustment between the boiler and the tank. What charging equipment you then choose depends on chosen boiler and chosen connection alternative. Note, different charging equipments have different functions, for example Laddomat 21, does so that when you ignite the boiler, the water is just being pumped around internally inside the boiler and in the charging equipment until a temperature of approx. 80°C is received. Then the thermostat opens and the equipment starts to charge the tank or tanks, if you have more than one, with 80 degree charging temperature from the boiler. The return temperature from the bottom of the accumulator tank, is then approx. 25 degrees if the tank is relatively discharged then the bottom temperature in the accumulator tank is blended with the charging temperature from the boiler in the charging equipment that is approx. 80 degrees. Then the cooling, or we can say mixture temperature, from the charging equipment to the boiler approx. 70 degrees. When the water temperature of the accumulator tank is close to 80 degrees on the bottom, then the charging of the tank is done. You shall not fire more than 80 degrees as cooling to the charging equipment from the bottom temperature of the tank if for example the bottom temperature of the accumulator tank exceeds 90 degrees, then the charging equipment will be completely open until the temperature goes down to 80 degrees before it closes the flow between the boiler and the accumulator tank. Then a lot of Kwh will be pumped around through the boiler and the charging equipment is of no use before it closes the internal flow. The boiler then operates like a reversed heat exchanger. With a flue-gas thermostat you can easilly solve this circulation that only creates a lot of energy losses.

Flue-gas thermostat

Can briefly be described that it controls the charging pump between the boiler and the accumulator tank via the flue-gas temperature from the boiler instead of controling it with the water temperature of the boiler. The difference between these two is that on a flue-gas thermostat the giver of the thermostat is placed inside the föue pipe from the boiler. With a normal thermostat the giver is placed inside the boiler with a so called diving pipe that is controled by the water temperature of the boiler.
The flue-gas thermostat is a better solution, it is much faster than a normal thermostat that is controlled by the water temperature of the boiler. When you ignite a wood boiler the flue-gas thermostat feels the flue-gas temperature almost immediately and starts the pump. That does not a giver do that is placed in the water of the boiler it is a lot slower in feeling temperature changes.

It is the same when the boiler has finished to burn, the charging pump stops faster when the flue-gas temperature is sinking compared to a thermostat that is placed in the water of the boiler. Even if you have a flue-gas thermostat it is important that you plan the wood insert so that there is glow in the boiler when the bottom temperature from the accumulator tank is 80-85 degrees. Then it is all about making sure that there is glow in the boiler when the charging equipment stands completely open, and set the flue-gas thermostat so that it turns off the charging pump at the right point after ended firing. 

It is very important that the flue-gas thermostat that shall start and stop the charging pump, is correctly adjusted. A suggestion is to provide the thermostat with an indicating light so that you can see when th pump is operating. This setting is different from different installations.

A short summary of wood burning is that, if you choose the right products and right boiler, and right installation method it is probably the cheapest heating form when it comes to bioenergy today. If you then have access to your own wood it is even better. You can also buy cheap pulpwood to very good prices.

Faster ignition of wood boilers with pressing fan.

Most wood boilers with pressing fans have some kind of bypass damper that is being used when igniting the boiler to fast get the temperature up in the chimney and to create a good under pressure. But there are also disadvantages with these dampers. One example is that when you fire too long with this damper open a very high flue-gas temperature will be created. Most modern wood boilers on the market today have hearth volumes that hold between 100 to 150 litres of wood. If you then fire too long with the bypass damper open, there will be very high flue-gas temperatures that can damage brick chimneys and even the isolation on steel pipe chimneys can be damaged. It can also create overheatings in joist floors with fire incidents as consequence.

Another thing that happens if you fire with the bypass damper open too long with over combustion, is that it creates heavy smoke emission in the chimney which is not necessary when doing it right when it comes to fast ignition of a modern wood installation. This goes for all lightings of wood boilers. It is often here there becomes trouble with neighbours and people living near by when the wood fireman does not have the correct knowledge to light the boiler in the right way despite the fact that the boiler is certified and environmentally approved.