Biomass Energy

What is biomass?

 

Biomass is a fuel that is produced by organic means. It is derived from burning of trees or plants which have absorbed CO2 during their lifetime. So, the CO2 that is absorbed during the life of the tree or plant, is then re-released when it is burnt. It is considered to be nearly carbon neutral, which is arguable as it still requires transportation and processing. It is argued that timber is better used a building material, where the CO2 will take longer to be released back into the atmosphere. 

 

There are many forms of biomass fuel, including logs, waste wood, chippings and woodchips. There are also sustainably grown short rotation crops such as willow that grow fast and can be made into wood pellets. 

Research suggests that burning biomass fuel is at least five times cleaner than burning gas. It can be burned in a biomass boiler or gasified in a CHP system (Combined heat and power). 

 

In countries such as Denmark, nearly 80% of the primary domestic energy needs are provided by a mixture of biofuel and waste powered CHP, plus extensive coastal wind farms. 

 

As reserves of oil, gas and coal become depleted there will be a growing pressure for countries to convert to biofuels and sustainable methods. Since timber is a renewable source and returns oxygen to the atmosphere during the growing phase it is safe to say it is a good sustainable option. 

Design requirements and recommendations

 
A biomass boiler is similar to a conventional boiler in that is is connected to the central heating system. The biomass boiler burns wood pellets, logs or chips instead of gas, which are fed into the boiler from the fuel storage area as required. 
 
Wood chips tend to be more available in the UK as a by product but these are more suited to larger schemes. The wood pellets which work better for single dwelling applications are sometimes imported from abroad so it is important to consider the environmental impact when specifying.
 
It is best to specify a biomass boiler option in well insulated efficient buildings, that are to a zero carbon standard or better. It is also important to ensure there is a fuel supply locally, in order to avoid long transportation issues and carbon footprint. 
 
Although a biomass boiler can provide for the hot water needs, it is worth considering a solar thermal approach for the summer months which will allow the boiler to be switched off throughout the warmer months. 
 
At design stage it is also important to consider the spacial requirements for the boiler and fuel storage. Delivery vehicles will require good access to the storage facility, a maximum of 15-30m from the road. 

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Advantages of Biomass Boiler Systems

  • Sustainable energy option (as long as fuel is sourced responsibly)
  • A positive step to replacing coal and gas
  • Biomass has stable prices when compared to traditional fuels
  • Biomass boilers qualify for the Renewable Heat Incentive scheme (RHI) [at time of writing]
 

Disadvantages Biomass Boiler Systems

  • Biomass boilers require relatively high user input
  • Sourcing spare parts can be difficult 
  • Biomass requires more space than standard systems for the boiler and fuel storage
  • Fuel storage conditions must be carefully designed as the fuel must remain dry
  • Require regular cleaning (depending on model)
 

Further reading:

 
www.greenspec.co.uk
Environmental Design Pocketbook – Sofie Pelsmakers
 

Image Credits:

Log boiler
 
Hoval biomass pellet boiler
 
Biomass wood chip from Dunster Energy

Make sure you check out all of the “Architecture and the Environment” series.

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