Wood energy options - schools & commercial buildings
Wood energy can be a good choice for schools and commercial buildings as it is a renewable energy option with relatively low running costs. These benefits make it a popular option in European and North American organisations.
Wood energy is a cheaper long-run option, and it is relatively easy to convert to energy if your organisation has an existing hot water heating system. Wood provides a safe, clean, reliable and economical alternative to other forms of energy. In the past, fuel for heating for schools and other commercial buildings came from non-renewable sources like coal, gas or oil and was used in hot water heating systems. However, energy sources like coal have a much higher rate of particle emissions (particle emissions from wood fuel are between 1/3 and 1/5 of those from coal).
The main two wood fuel types for school/commercial use are wood chips and wood pellets. The most appropriate fuel type for an organisation will depend on factors like location, energy requirements, existing wood burning technology and site issues such as fuel storage capacity. Monitoring fuel quality is important to maximise system efficiency.
Wood chips are available all over New Zealand, are relatively cheap as they are a wood residue product (in some cases prices are competitive with coal) and burn efficiently (at up to 55% moisture levels). Quality of wood chips can vary but the wood fuel quality guidelines set the standards for this.
Wood pellets produce heat quickly, take up less space when used as fuel, are consistent in quality, easy to handle and burn very cleanly, but they are also more limited in supply, more expensive per unit of energy and need a specific type of burner to be most efficient.
There are several types of wood chip boilers available with varying combustion and feed mechanisms. Most modern wood chip boilers are fully automated. Wood chip boilers use heat exchange surfaces to heat water and are, therefore, a good option for hot water heating systems and for large users of hot water (e.g. hotels, prisons, etc.).
There are also a range of wood pellet boilers available. Wood pellet boilers operate in a similar way to wood chip boilers but they are specially designed to burn pellets efficiently. The wood pellets are fed in automatically and the feed rate varies with the required heat output. Wood pellet fuel is very consistent in quality so that a pellet fire can adjust the air to match the fuel, making sure that the wood is completely combusted even on low settings. This leads to an increase in efficiency and lower emissions.
Converting to wood energy use
The cost effectiveness and ease of converting to using wood energy depends on the existing heating system.
- Coal burners are the easiest to convert, the main requirement is to build a steel bunker and feed system and then adjust the combustion characteristics. The addition of safety features may be needed to complete the conversion.
- Gas and oil burners require a different approach as they are simpler in design, the combustion head must be changed and storage capacity must be considered to allow for the additional storage requirements of wood fuel.
- New boiler installation can be a viable option if the existing boiler is old and in need of full replacement, the existing heating network can still be used.
- Heat pumps usually make it uneconomical to move to a wood energy system as the old heating network may have been removed and would then be expensive to reinstall. It is best to upgrade the network rather than remove it if you want to keep your future options open.