WoodCFD

Several new national strategies points out the importance of bioenergy in the future energy supply for Norway. Wood log combustion has long traditions in Norway and currently constitutes as much as 50% of the current use of biomass for energy purposes. The national target is a doubling of the use in 2020.

Three central documents are defining the current national bioenergy strategy: Klimameldingen, Energi21 and Strategy for increased expansion of bioenergy - 2008. The latter states that Norway shall double the bioenergy production from 14 to 28 TWh by 2020 and that the major single contributor of new bioenergy production shall come from bioenergy use in small-scale heating appliances for space heating, meaning in practise the use of wood log combustion in wood stoves and fireplaces (~50% of the increase, which equals 7 new TWh).

Using wood logs is important as a part of security of supply in Norway, where we today rely heavily on the electricity grid to deliver the needed heating for our houses. Close to 80% of the domestic heating is by electricity and 15-20% by wood log combustion, while district heating accounts for only about 2% and heating with gas is close to zero. This makes Norway quite special compared with other European countries.

Wood log combustion has long traditions in Norway, constituting almost 50% of the use of biomass for energy purposes. Increasing electricity prices, colder winters and increasing renewable energy awareness are factors that contribute to an increased use of wood log combustion. However, this is not enough and new solutions and technologies that enable a more widespread and extensive use of wood log combustion are clearly necessary to reach these ambitious targets. New houses, as well as retrofit/upgrading of old houses, have increasingly focused on improved insulation (e.g. the Norwegian passive house standard, the future TEK15 regulation and nearly-zero energy buildings in 2020). The space-heating effect (power) required for these highly-insulated buildings is drastically reduced, which means that wood stoves should be able to deliver a constant heating effect to the building as low as ~1 kW.

Norwegian houses are mainly wooden houses, which have two important implications; they cannot support large heat storing stoves (due to weight restrictions on the wooden floors) and the building itself is not able to store much heat compared to a concrete/brick building. The consequence of the above is that we need to develop new solutions and technologies that, while giving a stable heat release and distribution at a heat release effect as low as 1 kW, also reduce the emission levels and improves the thermal efficiency.

Combining heat production, storage and distribution in an optimum way makes it possible to achieve a substantially more stable heat release and distribution in wooden houses than the current solutions and technologies can offer. It opens up for a groundbreaking shift; enabling a substantially longer wood log heating season due to solutions that can operate at low and more stable effect early and late in the heating season, and thereby also increasing the total wood log use through the heating season due to the increased heat comfort. This will result in an increased number of operational hours per unit and also more units in active operation.

Low load wood stoves and fireplaces in buildings with new insulation standards demand new technologies and solutions with an increased focus on the combustion process and its control, the combustion quality and optimum design to ensure low emissions and high energy efficiency. To minimize the negative effects of the batch combustion process (compared to a continuous combustion process), a more stable heat generation and heat release is needed. This was the focus of the KMB StableWood project (2011-14), the predecessor to the proposed KPN WoodCFD, where a number of studies were carried out in a broad range. These studies confirmed that wood stoves have a place in future's buildings. However, it also clearly showed the need for a more concentrated effort on the development of improved models and the use of advanced modelling approaches to be able to further improve wood stoves and especially low load wood stoves with respect to emissions and energy efficiency, as well as combustion stability and optimum room and building integration.

WoodCFD therefore focuses on clean and efficient wood stoves through improved batch combustion models and CFD modelling approaches. Improved models and modelling approaches, in combination with targeted experiments, are keys in the development of future's downscaled clean burning and energy efficient wood stoves. This will have a potentially huge impact on the most important bioenergy value chain in Norway today, targeting key bottlenecks in the value chain, i.e. reducing today's still relatively high emissions from wood stoves and improving their energy efficiency, especially in low load wood stoves, as well as ensuring optimum room and building integration.