Storage of pellets and necessary volume of the silo

Heating with wood pellets: the question to ask before choosing this method of heating?

1) What are the conditions for good storage of pellets?

a) Close the boiler as we just said. If you do not have an adjacent room: nothing prevents you from building, if possible, an external annex next to your boiler room.

b) Humidity minimized: the pellets are, as you know, seasoned wood (RH <8% according to the Standard). Disadvantage: the pellets are therefore hydrophilic, in other words: they capture ambient humidity. Their high calorific value for wood (4,5 to 5 kWh / kg compared to log wood at approximately 2,5 kWH / kg) would drop in the event of humidity. In addition, this would clog your boiler and considerably increase your pellet consumption and therefore your heating budget. Limiting humidity is therefore an essential criterion for the proper functioning of your wood pellet heating. Remember to treat the room you want to use as a moisture silo before anything else!

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c) Air evacuation during filling: provide a vent.

automatic feed pellet boiler

The 3 types of automatic feed of a pellet boiler: worm, suction and bag (manual)

2) What is the required storage volume?

The storage volume should be sufficient to have about a year of heating and hot water. This obviously because of the price of delivery!

If you replace your boiler, calculation of the mass required per year is simple: energy 2 kg of pellets = oil 1L. (1 kg pellets = almost 5 kWh). So if you consume 2500L of oil, you will 5 tons of pellets.

German and Austrian standards require a pellet density of 1.200 Kg / m3 (yes, the pellet flows: it is heavier than water) which represents approximately 650 to 750Kg / m3 for bulk pellets.

So let's take 700 kg / m3 or the equivalent of 350L of fuel oil in a volume of 1000 Liter. You therefore need a volume 3 times greater than that of your annual fuel oil consumption, i.e. for an equivalent of 2500L of fuel oil, a volume of 7,5 m3.

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However, it is also necessary to provide for a “safety” volume of 10 to 15%, ie in our case: 9 m3 for 2500 L of fuel oil equivalent.

Therefore at final a pellet volume 3,5 times greater than the storage volume of oil equivalent energy and a tonnage 2 times higher than that of oil (or gas m3).

Read more: Financial aid and tax credit for pellets?

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