Woodchips are a simple, cost-effective automated wood fuel which is commonly available in Vermont. Cost per delivered million Btu is typically lower than pellets, but capital cost of installations is often higher making them a better choice for larger facilities. Woodchip heating systems will function and perform better with a high-quality fuel. Using consistent, uniform-sized woodchips results in fewer mechanical jams of the fuel feeding equipment. Feeding lower moisture content woodchips to the system typically requires less fuel to produce the same amount of heat. Cleaner woodchips (free of excess bark, needle, dirt, and debris) produce less ash and can burn longer without maintenance and removal of ash. Not all woodchip heating systems will require the same quality of fuel, so matching the right fuel source and quality to the right system and application is extremely important. If possible, larger woodchip systems should be designed for a range of fuel quality. Larger woodchip systems can be equipped with fuel feeding systems designed to remove oversized materials.
High-quality wood chips are consistent in shape and size. Typical high-quality chips vary in size from 1” x 1” x 1/8” thick to 2 ¼” x 2 ¼” x ¼” thick. Conveying and feeding chips that are relatively square and flat into the system is easier and goes more smoothly. While the majority of wood chip heating systems can handle some oversized material, long “stringers” (i.e. small branches and long fibers) can present a risk for jamming feed augers and shutting the system down. Long stringy wood can also often “bridge” in hoppers and bins, meaning it can form hollow cavities as the material below is removed. Material bridging can cause some systems to shut down due to the perception that the bin is out of fuel when it is not.
Similarly, while most wood chip heating systems are designed to handle some amount of wood “fines” (i.e. sawdust), a high fines content can present problems when moisture content is either too low or too high.
Read about Wood Chip Boilers
District heating system at Norwich University