(619p) Residential Wood Pellet Heating System Optimization Using Process Dynamic Simulation

As a growing part in biomass energy utilization, the use of wood pellet boilers for residential space heating have been increased over the past decades in EU and North America. A typical wood pellet heating system has three major components: the boiler, thermal storage tank, and heat consumption unit. Considerable effort has been applied to the design of the boiler to build high efficiency and low emissions (HELE) boilers. However, currently there is no systematic process optimization in terms of the system efficiency, especially the optimization of the operation of the thermal storage tank with the heating system.

In this study, a 25 kW nominal output wood pellet boiler was installed and monitored through the past two heating seasons (from February 2015 to May 2016). Two 120 gallon tanks were connected in parallel with the boiler as the thermal storage unit. Field data were collected for boiler thermal efficiency calculation. Meanwhile, several runs of CTM-039 stack sampling were performed to evaluate the emissions from the boiler. In the end, a process dynamic simulation using VMGSim^TM was built for the residential wood pellet heating system. The boiler simulation is based on wood combustion modeling of the boiler and tuned with field data.

The whole system was optimized for a better combustion and a higher system efficiency from the following aspects. Firstly, optimize the combustion efficiency through control of excess air ratio, pellet quality, etc. Secondly, optimize boiler thermal efficiency by running the boiler at maximum load and employing more efficient cleaning mechanisms. Thirdly, optimize of the tank sizing with respect to boiler nominal output and heat consumption from the building for a higher tank efficiency and better use of water stratification in the tank. And lastly, a sensitivity analysis was performed for the validation of the model.

This work can substantially improve future residential space heating system designs based on wood pellet heating technology.