Wood pellets and chips are the two most suitable fuels for automatically fired heating systems in large buildings. The bio-fuels to be used in this programme should comply with I.S. CEN / TS 14961:2005 or equivalent. Post consumer wood waste is not acceptable as a fuel for this programme.
The following table includes the typical characteristics of pellets and chips.
Moisture content of wood has a significant impact on the calorific or energy value of the fuel. The diagram below shows the relationship between moisture content and energy content.
It is important that the moisture content of the wood chip is compatible with the boiler in which it is being used.
Pellets and chips have various advantages and disadvantages that have to be weighed up. Which fuel is used will depend very much on local conditions. Preferably systems should be installed, that can use both fuels and can therefore respond flexibly to the future market situation. Such boilers have an electronic control system that adjusts the combustion parameters to the selected fuel. It is important that the feed system is suitable for handling both fuels. As chips (unlike pellets) are not generally blown in, the store should be designed to enable the fuel to be delivered by tipper truck if chips are expected to be used. The advantage of above ground silos for pellets is their lower cost. The following table highlights the advantages of the two fuels and compares them.
|Local availability||Availability generally is not local|
|Favourable effect on the local job market||Less favourable for the local economy|
|Cheaper than pellets||Higher fuel costs|
|Large storage space required||Smaller fuel store|
|Uniform fuel quality not standardised||Standardised fuel, greater reliability|
|More work required for system maintenance||Less work for service and maintenance|