Biomass Boiler Performance Evaluation Study
Woody biomass has been burned for heat for millennia. However, recent advances in wood heat technology have made it more efficient, cleaner burning, and therefore more sustainable. Wood heat is now seen as a viable long-term alternative to expensive heating fuel, especially in rural Alaska, where heating fuel is imported at great cost.
This project seeks to examine performance of wood-fired hydronic boiler systems in three different Alaskan communities. The operational principle behind these boiler systems is that instead of building a smoldering fire to sustain itself, as home wood stove users do, a very hot, clean fire is built and used to heat water instead, which circulates to heat the building. In most cases, the heat is further transferred to glycol using heat exchangers, and the glycol is circulated instead, retaining more heat and heating a larger area. In addition to burning hotter, hydronic systems are also cleaner because they utilize venting and appropriate channel geometry to reclaim some of the exhaust gases and combust them a second time, which also increases the efficiency of the boiler.
Performance of the boilers will be monitored using an energy metering system comprised of an in-line flow meter, and two temperature-sensors, one on the hot water supply side and the other on the return side. By tracking the water flow rate and the temperature at both sides, the amount of heat input to the water can be measured. By correlating this against wood consumption and wood moisture content, a rough assessment of boiler efficiency may be obtained.
In addition, an emissions probe will be brought to each site during an extremely cold time, and a moderately cold time, and stack emissions will be measured for both climate points.
Gulkana is an Ahtna Athabascan village located in the Copper Valley near Glenallen. The boiler system we are testing is comprised of two series-connected Garn boilers, each rated at 425,000 Btu/hr, burning cordwood harvested from local lands.
Tanana is a Koyukon Athabascan village located at the confluence of the Tanana and Yukon Rivers, about 100 air miles west of Fairbanks. The boiler system we are testing is comprised of a Garn boiler, rated at 425,000 Btu/hr, burning cordwood that is pulled from the Yukon River as driftwood.
Delta Junction is an agricultural community on the Alaska Highway. The boiler system we are testing is a Messersmith chip-fired boiler rated at 5,000,000 btu/hr. They will burn exceptionally high-quality chips, made from scrap wood from Dry Creek Lumber, a local lumber mill.
The Tanana Btu metering system was installed on October 2nd, 2013. The Gulkana installation was completed November 2013. The Delta Junction system will be installed in summer of 2014.
Photo 1: The GARN system and cordwood storage in Gulkana, Alaska. Photo courtesy of D. Huang, ACEP/UAF.
Photo 2: The GARN system and cordwood storage in Tanana, Alaska. Photo courtesy of Tanana Fire Department.
Photo 3: Driftwood logs pulled from the Yukon River for the Tanana biomass heating systems. Photo courtesy of D Huang UAF/ACEP.