In the interest of full disclosure, the author is a Director of Maine Energy Systems, in Bethel, Maine.
As one of the leading developers of the residential biomass heating industry in the United States, we’ve learned a lot of lessons along the way. As the owner and operator of a residential pellet boiler system, I’ve learned a lot of lessons along the way as well. Following are a few of the lessons we’ve learned.
Sizing of boilers is still a bit mysterious, but the picture is clarifying somewhat. It is the American practice to oversize boilers because cost differentials between boiler sizes are relatively small and contractors don’t want to risk “I don’t have enough heat” phone calls. We have been told by Europeans since we began this venture to size boilers smaller than heat loss calculations would suggest are necessary. That’s a hard sell. However, we are routinely seeing boilers sized to match calculated heat loss running on shorter cycles than are ideal suggesting that smaller sizing was, in fact, in order. We will try to quantify the size reduction that would lead to most efficient use of this technology. In my own case, a purposefully undersized boiler (51,000 BTU/hr vs heat loss calculations of 106,000 BTU/hr) carries the house’s heat and DHW needs until the temperature gets down to 0 fahrenheit. When that point is reached, I can either accept a boost from my old oil boiler or accept the fact that 65 Fahrenheit is the best I can do in my kitchen. One of these days I’ll change my pellet boiler to a 25KW unit (85,000 BTU/hr)
Pellet durability is fundamentally important to the success of bulk pellet installations. The pellet mills with which we’ve worked along the way have been very good about ensuring durability of wood pellets in excess of 98%. This improvement has made a tremendous difference in fuel system dependability.
Ash removal cycles result from the complex relationship among boiler efficiency, pellet ash content, and quantity of pellets consumed. Different pellet burner types also create different amounts of waste. Whether ashes are removed from the boiler directly, as with more basic systems, or from ash storage containers, as with more modern systems, the remove cycle calculus must include all of those elements to be at all predictive.
Burner system modulation results in reasonably stable boiler temperatures and reduces fuel consumption. The well-established pattern of having burner output follow heat demand provides the same efficiencies that “highway driving” affords automobiles. Cold starts are not part of the picture with modern pellet boilers.
Pellet deliveries smell good!