WOOD CHIP/PELLET STOVES/BOILERS
Keeping the home fires burning is a concept that is making a big comeback, and these days we have it down to a fine art. Instead of burning wood in an inefficient open fireplace that gives out about a quarter of its potential heat, we can now burn wood in enclosed stoves or boilers that, by some reckonings, are as good as it gets when it comes to combustion efficiency – up to 85%.
Wood, in fact, is still the largest biomass energy resource we have today – and it is entirely renewable (albeit at a slow rate). As a heating system, wood chip or pellet stoves/boilers get the full support of the government through attractive grants under the Greener Homes Scheme. However, it has to be said that pellet appliances are more complex than traditional home-heating systems and they have expensive components that can (rarely) break down. In addition, users of the system who have taken shortcuts by using inferior quality pellets – always a temptation in the interest of reducing costs – have learned the hard way that quality is of the utmost importance.
There are two main elements to this system:
1. The burner: a stove or boiler.
2. The pellets: a compressed mix of sawdust and wood shavings.
1. The stove or boiler is fired automatically and continues to operate with little or no human involvement in the process. Not only is the system practically self-cleaning but the ashes seldom need to be emptied – generally speaking after several weeks in the case of a boiler, a month in the case of a stove. Pellet/chip stoves, which can be free-standing or fireplace inserts, fit in well with both modern and traditional decor in the home, apartment or office; they are also available with back boilers for feeding into central heating systems.
For both stove and boiler, it is now possible to adjust the heating from a distance by contacting the system via a mobile phone so that you arrive home to a warm house.
For both, an ample air supply is exceptionally important. Best practise, recommended by the Department of the Environment, is to have a controlled, dedicated air supply feeding in to the appliance rather than relying on air infiltration and/or leakage into the room.
Boiler installations must have bulk storage for the pellets, capable of storing a minimum of 3 tonnes of pellets, which is the equivalent of 80% of the requirement for a typical house for one year. It is also recommended by the Department that a pellet/chip boiler system have a buffer or accumulator tank. This is a primary heat storage/distribution cylinder heated by the boiler to store water at high temperature, which helps the boiler to run for longer at top efficiency.
2. Wood pellets are a high-energy, smoke-free fuel made from a sawdust/wood shavings mix. Unlike other solid fuels, they are easy to handle and they leave almost no ash. However, there is a wide range of quality on the market. However, there is a wide range of quality on the market. It is important for consumers to look carefully at all the characteristics of the pellets they buy, e.g. ash content, moisture content, fines.Customers are advised to buy pellets that come in bags with a quality mark and with a complete fuel analysis printed on the side. Note that pellets have to be manufactured, whereas wood chips are available locally – but they are less efficient and by some calculations you need three times as many wood chips as pellets in order to deliver the same heat.
Another consideration is that an adequate storage area is absolutely essential if you are using pellets in bulk. The storage must also be secure form wet and damp because the more moisture that gets into the pellets the more you need to burn to obtain the required amount of heat.
By the way, in case you get the wrong impression, pellet/chip stoves are far safer than the traditional old-style stoves. In the case of the traditional stove, the appliance itself got hot and radiated heat. In contrast, the pellet/chip stove does not heat up but ventilates warm air into the room/system.
Cost (initial)
Varies enormously due to the availability of so many different sizes and capacities of systems. Capital grants of up to 30% are available for commercial installations through the SEI under the ReHeat programme. Domestic users can get up to €1,400 to install a wood chip/pellet stove or up to €2,500 for a wood chip/pellet boiler under the Greener Homes Scheme.
Cost (running)
Before the recent hike in oil prices, wood pellets were costing around half the amount that fossil fuels cost. Wood chips are even cheaper.
Cost (maintenance)
Although pellets are smokeless and leave hardly any ash, the modern boiler system is highly sophisticated, with an automatic feed and augurs. It is very important to follow the manufacturer’s instructions for operation and maintenance.
Efficiency
Pellet stoves have been calculated to have a combustion efficiency of 78%-85%. And that’s high!
Payback
Payback periods of 4-5 years have been mentioned in relation to individual projects.
Glossary
Fines
The dust to be found in a bag of pellets (from the fine particles caused by the break-up of the pellets). Fines should be less than 1%.