Fully automated woodchip heating systems, which feed the chips from the storage bin automatically to the boiler, can be very expensive. A more cost-effective alternative for smaller facilities with lower heating loads is the semi-automated system.
The semi-automated system is typically installed in an on-grade slab building that includes both a boiler room and chip storage (a chip pile on the slab floor). The system also includes a day bin fuel hopper of sufficient capacity to supply the boiler automatically for one-to-two days without reloading. In the fully automated system, fuel is delivered to the boiler with augers and conveyors. The day bin of a semi-automated woodchip system is loaded by an operator using a small tractor with a front end bucket or skid steer. Semi-automated systems have automated controls to manage fuel supply and combustion air, although the controls are simpler than those in a fully automated system. Semi-automated systems can range in capacity from 0.5 MMBtu/hour to 2.0 MMBtu/hour.
The attraction of a semi-automated system is that both the building that houses the system and the vendor equipment are less expensive than a fully automated system. The system takes the operator an estimated additional 30-minutes per day over the typical operation and maintenance time required for a fully automated system; this additional time is for loading the day bin. The semi-automated woodchip system is a good match for a smaller rural school or office building where the additional time in fuel handling is not a significant burden to maintenance staff.
Vendor supplied equipment includes the day bin and the automated fuel-handling system from the day bin to the boiler, the boiler and combustion chamber with combustion air fans, connection from the boiler to the chimney, and controls. No emission controls are needed for these small-scale systems.
Green woodchips (mill or forest residue, 25-50% moisture content)
Hot water or steam (boiler system)
Size (Boiler Output)
0.5 - 2.0 Million Btu/hour (or larger)
Slab-on-grade building (overhead door for delivery)
Tractor with front-end bucket, from pile to day bin (performed by operator, once or twice daily)
Automated from day bin to combustion chamber (no operator labor)
Operator Work Load
Operator Word Load up to 1 hour daily
Electronic control panel (minimum)
On-off single firing rate (minimum)
Automated, tuned control of fuel and combustion air
"Idle" or flame maintenance mode
Stack Emission Control Device
None required (unless required by state regulations)
Must meet applicable state regulations, if any
Manual or automated
Boiler with standard controls
Day bin with automated fuel reclaim in bottom
Automated fuel handling system (day bin to boiler)
Wood system wiring (from system control panel)
Breaching (from boiler to stack)
Coordination with General Contractor
Service Capability (limited)
(Plumbing connection by others)
(Building construction by others)
(Tractor by others)
(Bonding generally not required)