Outdoor Wood Boilers
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Outdoor Wood Boilers & Chip/Pellet-fired Boilers
Date introduced on the Market:
Commonly available since the early 1990's.
Maturity of the technology:
Both are mature technologies in different stages of technical evolution. Outdoor boilers are in the first generation of technological development, with generally poor combustion, high emissions and low overall efficiency. Chip/pellet boilers are in the second stage of technological development.
Expertise required for installation and operation:
Installation requires plumbing and electrical abilities, which may be beyond the abilities of the owner. Outdoor boilers are sometimes installed by the purchaser, whereas chip and pellet systems typically are installed by the vendor. Operation by the owner typically requires limited training.
Range of Operational & Maintenance requirements:
Outdoor boilers typically require twice daily to daily refuelling. Maintenance is seasonal plus periodic ash removal. Pellet/chip systems typically require refuelling daily to every few days, normally will need brief daily inspection of operation and periodic ash disposal. Occasional servicing of motors & moving parts
Range of size:
Outdoor boilers typically range in size from that of a prefab garden shed to a small outbuilding. Chip and pellet systems normally range in size from that of a single car garage to a machine shed, depending mainly on how much fuel storage is incorporated. A dedicated storage area is also required to keep firewood, chips and pellets from becoming contaminated with dirt and to control moisture content.
Range of heat outputs:
Outdoor boilers range in output from around 80MJ/h to over 250 MJ/h
Chip and pellet boilers range upward in output from around 80 MJ/h.
Type of energy produced:
Units provide hot water as heat transfer medium.
Range of current capital cost per unit of delivered energy:
Outdoor boilers start at around $100/MJ
Pellet systems start at around $120/MJ
Chip systems start at around $200/MJ
System advantages:
Outdoor boilers can reduce in-house dirt as well as risks of fire since they are located away from the buildings being heated. Chip and pellet systems share this advantage, as well as potentially long intervals between refuelling, and high efficiency combined with low emissions.
Limitation of the system:
Outdoor boilers may be restricted or prohibited in some areas. They may produce excessive smoke, particularly at low output rates. Emissions may be high and delivered efficiency low, due to unsophisticated combustion chamber design, losses from the boiler itself, and heat transfer losses associated with moving the heat to the remote buildings and recovering it there.
Chip systems are likely to require occasional removal of jammed chips and daily maintenance such as removal of clinkers in the firebox, plus periodic servicing of the various motors and moving parts associated with the unit.
Pellet systems are likely to need periodic removal of clinker from the combustion chamber as well as ash removal and occasional servicing of various motors and other moving parts. Corn fired systems often require more frequent removal of clinker and coke deposits.
All systems may require occasional replacement of insulation and baffles in high temperature areas.
Range of life expectancy:
All these units should have a virtually unlimited life expectancy, with occasional replacement of components as they reach their design life.
Modified: 03-31-2008
