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  • 1.
    Eliasson, Lars
    et al.
    Skogforsk.
    Nilsson, Bengt
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Hyggeslagring av grot2015Other (Other academic)
  • 2.
    Lars, Eliasson
    et al.
    Skogforsk.
    Nilsson, Bengt
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Skotning av grot direkt efteravverkning eller efter hyggeslagring: Effekter på näringsuttag, barravfall och fukthalt2015Report (Other academic)
    Abstract [en]

    Tops and branches from final felling (logging residues) have been harvested for use as a fuel in heating and combined heat and power plants since the 1970s. It has been recommended that the residues be stored in small piles on the clear-cut for a summer to facilitate drying and shedding of needles. Drying increases the effective heating value of the biomass and thereby the economic value as a fuel. Another perception is that future forest growth is positively affected by nutrients that are released from the biomass through leaching and as needles and fi ne twigs loosen from the residues during the storage period.

    However, there are also drawbacks when residues are stored on the clear-cut. Costs are increased, as the same forwarder that extracted the roundwood cannot be used to extract the logging residues, so another forwarder has to be transported to the area. Furthermore, extraction of residues becomes a seasonal work concentrated to late summer and autumn, so areas with soft soil harvested during frozen winter conditions have to be trafficked in unfrozen conditions, thereby increasing the risk of ruts. Finally, the establishment of new forest is delayed, as the clear-cut is filled with residue piles and not available for scarification and planting the first summer after the harvest.

     To avoid these drawbacks, interest is growing in extracting the residues at the same time as the other assortments and drying them in a stack on the landing instead. A literature survey was carried out to obtain an overview of the effects of these two strategies for residue extraction.

     The survey showed that:

    - More than 20 per cent of the top and branch biomass is left on the clear-cut, regardless of extraction strategy.

    - Storing residues on the clear-cut does not necessarily lead to nutrient release and shedding of needles in residue piles.

    - The moisture content of the biomass at time of delivery to the customers is not affected by the extraction strategy.

    - The possible effects on future forest yield should be smaller than the relatively small effects found in studies of full-tree extraction, as biomass is left on the clear-cut.

    - The economic effect on the future yield is reduced, as replanting can be done at least one year earlier if the residues are extracted at the time of roundwood extraction, thereby reducing the time to next harvest.

  • 3.
    Nilsson, Bengt
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Extraction of logging residues for bioenergy: effects of operational methods on fuel quality and biomass losses in the forest2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wood products play a key role in the transformation to a more sustainable society based on renewable bio-based resources, together with the positive effects on climate mitigation by replacing fossil fuels. However, to increase the use of forest fuel in practice it is important to understand the effects of handling and storage on its quality and removal of nutrients from the forest. This thesis addresses these effects with special focus on a comparative evaluation of the traditional dried-stacked with “new” and to some extent more controversial fresh-stacked methods for extraction of logging residues from Norway spruce (Picea abies (L.) Karst).

    The results indicate that a normal extraction of logging residues will leave at least 20% of logging residues at the clear-felled area, in accordance with Swedish Forest Agency recommendations. However, the results also indicate that the ambition of the dried-stacked method to leave the majority of the needles well spread over the clear-felled area does not meet these recommendations. In fact, the harvesting operation is more important than the extraction method, with respect to how much logging residues (nutrients) being left in the forest. The results also show that the quality of fuel yielded by the two handling methods differs only to minor extent, indicating that other factors have stronger effects, where “dried-stacked” and “fresh-stacked” logging residues from different clear-felling areas is often similar. Generally, logging residues stored over summer (regardless method), seem to provide sufficiently dry forest fuel, with a needle content of about 5–10%. There is a clear correlation between drying and effective loss of needles from twigs, but the loss does not necessarily mean that the needles will remain in the forest.  However, needle color (green or brown) is not a strong indicator for a reduction in needle content.

    Acceptance of the fresh-stacked method would provide opportunities for the development of new technologies, more efficient use of machinery throughout the whole year, reduced costs, shorter lead times and increased amounts of logging residues extracted from each clear-felled area. This is mainly because it would enable extraction at optimal times from a logistical, financial and/or forestry perspectives.

    Written in English with summary and conclusion in Swedish.

  • 4.
    Nilsson, Bengt
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Skogsenergi: Framtiden och hoppet?2009Conference paper (Other (popular science, discussion, etc.))
  • 5.
    Nilsson, Bengt
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blom, Åsa
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Hanteringens inverkan på skogsbränslets barrandel och fukthalt: – en jämförande studie mellan grönrisskotning och traditionell brunrisskotning av grot2011Report (Other academic)
    Abstract [sv]

    I föreliggande studie har vi analyserat hur grotens barrandel påverkas av grönrisskotning jämfört med traditionell brunrisskotning. En hypotes har varit att den traditionella brunrisskotningen inte medför så stort barravfall som man tidigare trott. Om grönrisskotning skulle accepteras skulle det öppna möjligheter för nya tekniker, minskade kostnader, kortare ledtider samt ett större totalt uttag från den enskilda avverkningstrakten. Observera att även grönrisskotning ger ett torkat bränsle och inte skall förväxlas med färsk grot. Bestämning av fraktionsfördelning och fukthalt har genomförts i det material som levereras till den energiomvandlande industrin i anslutning till flisning av groten.

    Resultaten visar att grönrisskotning medför en kraftig avbarrning och innehåller betydligt mindre andel barr än färsk grot. Resultatet visar även att traditionellt brunrisskotad grot innehåller en hel del barr. I praktiken innebär det att grönrisskotad grot innehåller dubbelt så mycket barr (ca 8 % av grotens total torrmassa) som den traditionellt brunrisskotade (ca 4 % av grotens total torrmassa) vid leverans till den energiomvandlande industrin. Både grönrisskotning och brunrisskotning ger en tillfredsställande torkning och resultatet visar att det endast skiljer 5 procentenheter i medelfukthalt mellan grönrisskotad (36 %) för och brunrisskotad (31 %) grot.

    Det har även kunnat konstaterats att groten behöver ligga större delen av sommaren i små processorhögar för att uppnå den rekommenderade avbarrningen. All grot som skotas ihop tidigare än augusti månad är därmed att betrakta som mer eller mindre grönrisskotad. Slutsatsen blir att en stor del av den grot som idag levereras till den energiomvandlande industrin snarare är grönrisskotad än brunrisskotad och innehåller ca 5–10 % barr.

  • 6.
    Nilsson, Bengt
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Blom, Åsa
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    The influence of two different handling methods on the moisture content and composition of logging residuals2013In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 52, p. 34-42Article in journal (Refereed)
    Abstract [en]

    The most frequently used handling method in Sweden for the extraction of forest fuels is one in which logging residues are piled in harvester heaps to dry within the clear-cutting area before stacking into larger windrows. This handling method, however, requires multiple stages and the amount of handling involved results in a significant loss of biomass that could have been used for energy. This study compares two handling methods for the extraction of logging residues in stands dominated by Norway spruce. The traditional “dried-stacked” method was compared to the “fresh-stacked” method in which logging residues are collected simultaneously during normal logging operations and stacked in windrows at or near the roadside to dry. Determination of fraction composition and moisture content was carried out on the biomass provided to the energy-converting industry shortly after comminuting the logging residues. The results show that the fresh-stacked logging residues contained a higher amount of needles (8%), compared to 4% for the dried-stacked logging residues. However, the amount of needles was considered to be low in both handling methods. Both handling methods were proven to provide adequate drying with moisture content levels at approximately 36% for fresh-stacked and 31% for dried-stacked logging residues. These results indicate that weather and forest conditions have a greater impact on the moisture content than handling method. An acceptance of fresh-stacked logging residues, preferably connected to ash recycling, would afford the energy-converting industries the opportunity to use new technologies, reduce costs and extract a greater biomass total.

  • 7.
    Nilsson, Bengt
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Nilsson, Daniel
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Distribution of logging residues at the clear-felled site after fuel adapted logging operations2015In: Papers of the 23rd European Biomass Conference: Setting the course for a biobased economyExtracted from the Proceedings of the International Conference held in Viennna, Asutria1-4 June 2015 / [ed] Obernberger I, Baxter D, Grassi A, Helm P, ETA-Florence Renewable Energies , 2015, p. 270-272Conference paper (Refereed)
    Abstract [en]

    During extraction of logging residues previous studies in Sweden have shown that up to 50% of the available logging residues will not reach the energy-conversion site. The remaining potential of the logging residues are therefore lost by handling either at the clear-felled site, during transportation or due to decomposition. An outtake of 100% is not possible or desired, since the Swedish Forest Agency recommends that at least 20% of the logging residues should be left at the clear-felled site after a fuel adapted logging operation. In this study the losses at the clear-felled area is examined by studying the distribution of the remaining logging residues under and between the harvester heaps as well amount of logging residues that are left at the roadside landing after comminution. The results show that most of the reaming logging residues are well distributed at the clear-felled area between the harvester heaps. Additional logging residues are left at the clear-felled area since the forwarder cannot gather all logging residues from under the harvester heaps. In addition to this a not insignificant amount of logging residues are left at the roadside landing.

  • 8.
    Nilsson, Bengt
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Nilsson, Daniel
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Distributions and Losses of Logging Residues at Clear-Felled Areas during Extraction for Bioenergy: Comparing Dried- and Fresh-Stacked Method2015In: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 6, no 11, p. 4212-4227Article in journal (Refereed)
    Abstract [en]

    It is well known that a large proportion of available logging residues intended for extraction will not reach the energy-conversion industry, because some are lost during transportation or left on the clear-felled area. However, there is little understanding of where logging residue losses occur in the supply chain. In this study, the distribution of logging residues for two methods (dried- and fresh-stacked method) to extract logging residues were studied in one clear-felled area. In addition, residue fractions were examined in a detailed comparison. Even though the fresh-stacked method left somewhat more logging residues at the clear-felled area, the differences are small between the methods. Approximately 30% of the total amount of logging residues was left behind between the harvester heaps, with an additional 10%-15% under these heaps and approximately 2%-3% beneath the windrows. The final product that was delivered to the energy-conversion industry was very similar, regardless of the extraction method used. The delivered chipped logging residues had moisture contents of 37% and 36% following fresh- and dried-stacked methods respectively, and in both cases the needle content in the processed logging residues was approximately 10%. However, the total amount of fine fractions (needles and fines) was slightly higher following dried-stacking.

  • 9.
    Nilsson, Bengt
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Potential of forest fuel in the county of Småland: the woodshed of Sweden2012In: World Bioenergy 2012, 29-31 May, Jönköping, Sweden, 2012Conference paper (Other academic)
    Abstract [en]

    The county of Småland in southern Sweden is often labeled the woodshed of Sweden. The largest potential to increase has forest fuel from final fellings, in the form of logging residuals (branches and tops) and stumps. This study shows that logging residuals, stumps and by-products from sawmills have the potential to contribute with 5.9 TWh per year, equivalent to 88% of the total use of wood fuel in Småland today. The results also show distribution of forest fuel on municipality level.

  • 10.
    Nilsson, Bengt
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Thörnqvist, Thomas
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Regional Amount of Forest Fuel in Sweden2008Report (Other academic)
    Abstract [en]

    The present report is a subproject in Work Package 5 in CHRISGAS (Clean Hydrogen-RIchSynthesis GAS). CHRISGAS is financed by the European Union and The Swedish EnergyAgency. The aim of the project is to demonstrate the production of hydrogen rich syntheticgas in the manufacturing of vehicle fuel. The production takes place through gasification ofbiomass in a pilot plant, VVBGC (Växjö Värnamo Biomass Gasification Centre) inVärnamo. The aim of this study is to illustrate how much biomass, suitable for energyutilization, Swedish forestry can contribute with at the regional level in the form of loggingresiduals, stumps and by-products from sawmills. The regional distribution is partly done atthe county level in Sweden, and a deepening regarding reception area for the gasification centre VVBGC (100 km radius from Värnamo).

    According to the Swedish Energy Agency (2007), Sweden’s total energy supply during 2005was 640 TWh, of which 109 TWh was comprised of biofuel, including peat and waste. TheCommission on oil independence (2006) has even compiled the assessments of variousactors on how large the potential increase is for the production of bioenergy raw material. They then estimated that Sweden will use 154 TWh of bioenergy up to the year 2020, and upto 228 TWh of bioenergy up to the year 2050, of which forest fuel will comprise asubstantial portion.

    The need for renewable energy is increasing throughout the world, as the release of greenhouse gases will reduce and energy sources of fossil fuel will not be sufficient all the time. With the increased need for green energy, Sweden’s forests get an ever more significantrole in the future’s energy supply. Efficiency in the withdrawal must be better to manage inthe best way what raw materials there are and thus get out more energy at a low cost.According to the Swedish Statistical Yearbook of Forestry (2007), the actual land use offorest land is ca. 23 million hectares, 55% of Sweden’s total land mass. The Swedish ForestryAct §1 establishes that: “The forest is a National resource. It shall be managed in such a wayas to provide a valuable yield and at the same time preserve biodiversity. Forest managementshall also take into account other public interests.” This law lays the foundation for how theSwedish forest shall be used and how Swedish forest fuel should be handled. What is mostevident for forest fuel withdrawal is the part stating that the forest will be managed so that itcontinually provides a good yield. A withdrawal of forest fuel should therefore not risk theforest’s resistance in the form of nutritional losses.

    To estimate the potential quantity of logging residuals and stumps per hectare, the biomassfunctions developed by Marklund (1988) for the tree types pine, spruce and birch are used.The estimated potential is the biomass in a growing tree, followed by any handling andstorage losses of biomass. How much logging residuals can be delivered to the energyconverting industry is affected by how efficient the various handling methods are during thegathering and handling of forest fuel in the forest to industry. Depending on which handlingmethod is used, 30 – 50% dry mass of the potential amount in a final felling during logging disappears (Nilsson 2007). Besides logging residuals, there is also much forest fuel to becollected from the sawmill’s by-products. According to the Sawmill inventory (2002), thesawmills produce slightly more than 16 million m3 of sawed products annually, with thesawed products comprising almost half of the total volume timber supplied to production.However, the sawmills sell a large part of this to other industries, foremost to the pulpindustry. The biomass that will be accessible to other actors on the energy market is thusonly about 12% of the incoming biomass.

    When totalling the biomass that can be accessible for energy utilization from loggingresiduals, stumps and sawmill by-products, the total biomass is ca. 6.7 million tonnes drymass per year in all of Sweden. This is equivalent ca. 32 TWh per year, distributed as 18.3TWh logging residuals, 6.5 TWh stumps and 7.6 TWh by-products from industry. Toestimate the potential increase of accessible forest fuel, the total potential must be placed inrelation to how much forest fuel of different types is already used today. According to theBioenergy investigation (2004), 8.4 TWh logging residuals are used annually in Sweden. Themeans that the potential increase is ca. 10 TWh from logging residuals, if the needles areallowed to be included in the withdrawal. If a needle-free logging residuals is preferred, theaccessible biomass and potential increase from logging residuals is halved and becomes onlyca. 5 TWh. Such a reduction of the total supply is not to be lessened, but it is also unlikelythat all logging residuals withdrawal will always include the needles. A reasonable assumptionis probably that half of all logging residuals withdrawal would be able to include the needles,and that the total would give ca. 16 TWh logging residuals. The actual potential increase forlogging residuals would therefore be slightly more than 7 TWh. Regarding stumps clearingtoday is marginal. This makes it so that all future stump clearing in principle constitutes apotential increase equal to a little more than 6 TWh, for all of Sweden. The greatest limitingfactor in potential increase from stump clearing is composed of how large areas that canactually be current. Regarding the sawmills, all by-products are in principle used today. Whatis not turned into chips or used for board production is burned for internal usage or soldfurther to heating plants or pellet manufacturers. This means that if new actors on themarket want to use the sawmills’ by-products, they have to compete with already existing actors.

    The regional distribution in the present report shows clearly which part of Sweden have themost access to forest fuel, which should probably be interesting if building new gasificationcentres is wished for. The areas with most accessible forest fuel are comprised ofJönköpings, Kalmar and Kronoberg counties. Another area that could be interesting isSvealand, where there is a distinct area with much forest fuel in relation to the total area (see Figure 10).

    Most heating plants often want a needle-free forest fuel, limiting the total supply and leadingto expensive ‘processing costs’ as the needles are left in the forest. CHRISGAS should, as apioneer within gasification technology, examine the possibilities to even gasify loggingresiduals with needles, not only because the accessibility to forest fuel would increase, butalso to keep costs down. Through some form of bundling, the costs would be reduced by 25– 30% (Nilsson 2007).

  • 11.
    Nilsson, Bengt
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Trublins, Renats
    SLU Alnarp.
    Sallnäs, Ola
    SLU Alnarp.
    Dahlin, Bo
    University of Helsinki, Finland.
    Estimating potential stump harvest from multiple data sources: an example from a county in southern Sweden2014In: Proceedings of the Precision Forestry Symposium 2014: The anchor of your value chain, Stellenbosch: Stellenbosch University , 2014, p. 33-34Conference paper (Other academic)
  • 12.
    Nilsson, Daniel
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Nilsson, Bengt
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Nutrient removal after whole-tree harvesting with the traditional Swedish dried-stacked method for removal of logging residues2015In: Papers of the 23rd European Biomass Conference: Setting the course for a biobased economyExtracted from the Proceedings of the International Conference held in Viennna, Asutria1-4 June 2015 / [ed] Obernberger I, Baxter D, Grassi A, Helm P, ETA-Florence Renewable Energies , 2015, p. 9-13Conference paper (Refereed)
    Abstract [en]

    Bioenergy from logging residues is an important contributor to Swedish energy supplies. Logging residues where long defined and regarded as the unmerchantable aboveground biomass left behind in the clear-felled area, consisting of branches, tops and small trees that are gathered after the round wood harvest, but logging residues are nowadays regarded as a third assortment next to timber and pulpwood with high economic value. However long-term experiments on removal of logging residues from Norway spruce (Picea abies (L.)Karst) stands have shown both growth reductions and growth increase in the next generation, because of decreasing amounts of nutrients. So an increased removal of logging residues requires some sort of compensation of nutrients. Therefore it is of importance to investigate how much nutrients that is removed from the stand after whole-tree harvesting.

    In this study the removal of the nutrients nitrogen (N), phosphorus (P), calcium (Ca), potassium (K) and magnesium (Mg) have been investigated by laboratory analysis of the nutrients together with the actual removal of stemwood, bark and logging residues. The study has also investigated the distribution of nutrients at the clear-felled area.

    The results show that approximately half of the total nutrient removed in whole tree harvesting is done with the removal of stemwood and bark. The results also show that approximately 30% of the total amount of nutrients is left at the clear-felled area.

  • 13.
    Nilsson, Daniel
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Nilsson, Bengt
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Bergh, Johan
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Amount of nutrients extracted and left behind at a clear-felled area using the fresh-stacked and dried-stacked methods of logging residue extraction2018In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 33, no 5, p. 437-445Article in journal (Refereed)
    Abstract [en]

    Nutrient removal has been one of the key issues since the harvesting of logging residues started in Sweden. This study examined the actual removal of nutrients by measuring the amounts of biomass removed (from a forest products perspective) combined with their respective nutrient concentrations (N, P, Ca, K and Mg), from a clear-felled area when using the dried-stacked and fresh-stacked methods. The most important finding is that the two methods were very similar regarding nutrients remaining at the clear-felled area. Of the nutrients remaining there, most were found to be well distributed between the harvester heaps. Both methods fulfilled the requirements of the Swedish Forest Agency. A sensitivity analysis showed that even if the dried-stacked method left more needles, or the fresh-stacked method extracted more logging residues, there would only be a small impact on the levels of nutrients removed. The sensitivity analysis also showed that the amount of logging residues remaining between the harvester heaps seems to be much more important for nutrients left behind, regardless of extraction method. With this in mind, it is highly probable that improvements to the extraction of logging residues, without increasing nutrient removal, can be made.

  • 14.
    Sandberg, Dick
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Azoulay, Michel
    Baudin, Anders
    Blom, Åsa
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Carlsson, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Eliasson, Lars
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Jimmy
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Kifetew, Girma
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Nilsson, Bengt
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Nilsson, Daniel
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Nilsson, Jonaz
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Nordvall, Hans-Olof
    Thörnqvist, Thomas
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Utvändiga träfasader: Inverkan av materialval, konstruktion och ytbehandling på beständigheten hos fasader av gran och tall2011Report (Other academic)
    Abstract [en]

    The external façade must give expression to a building through both design and colour, and it must also protect the insulating layers in the wall from external influences. These functions can be fulfilled by almost all materials. If wood is to be competitive in this context, the wood material, the façade design and the surface treatment system must be chosen and interact in such a way that the façade is given a long life with little need for maintenance. A wooden façade will then in a broad sense be both economically and aesthetically attractive for the user.

    This study illustrates the state of knowledge regarding the outdoor use of pine (Pinus sylvestris L.) and spruce (Picea abies L. Karst.) facings above ground. Specifically, it deals with the use of wooden facings with regard to the choice of material, façade design, surface treatment and recycling. The market demands wooden facing systems, and the requirements emphasized by the actors on the market, e.g. the builders, real estate administrators, architects, designers, frame suppliers, contractors and representatives for the single-family timber housing industry can be summed up as follows:

    • There must be a specified life-time and given time intervals for maintenance of the wooden facings. (Shall be similar to those of competitive materials)
    • The supplier of the facing system should shoulder the long-term responsibility for its maintenance.
    • Flexibility, the supplier shall be able to replace or renovate the facings when necessary.
    • Building requirements, the wooden facing materials must be able to interact with other, specially fire-classified, materials.
    • The facing system shall have an attractive appearance.

    The primary market for the new facing systems should be multi-family houses but not necessarily multi-family houses of wood. The focus shall lie in the flexibility of the facing system in architectural expression, and in relation to other materials and systems. New building is important, but the million program, renovation and additions (ROT) and greater energy efficiency are also important spheres.

    The Swedish market is small (currently ca. 70 000 m3 wood for façades), but it should nevertheless be given priority before the Nordic countries, and thereafter Switzerland, Austria and Germany. The literature describes more or less well-founded recommendations for prolonging the life of wooden facing materials and extending their maintenance intervals, although some of the recommendations are directly conflicting.

    Many details relating to materials choice, façade design and surface treatment are important for the durability of wooden facings. It is difficult to separate the most important factors, but without taking into consideration aspects such as costs, availability and other factors of a practical nature, the following key factors can be identified as important for an environmentally correct and durable façade of pinewood or spruce:

    Choice of material

    • The wood shall have a high proportion of heartwood, preferably exclusively heartwood
    • The wood shall have vertical annual rings.

    Handling from forest to the façade

    • The wood shall be handled so that it does not suffer mechanical damage or microbial attack, or become wet or soiled, i.e. a rapid and correct handling with good packaging.

    Design

    • The façade shall start at least 30 cm above the ground level.
    • The façade shall be ventilated so that moisture can rapidly dry out. Ventilation of the space behind the facing is an easy way of achieving this.
    • Water run-off – no horizontal surfaces.
    • Flexibility –both in the construction and in the architectural design. There is a demand for facing systems which can be simply “hung onto” existing buildings.

    Surface treatment

    • Sealed end-grain sections – sealing of the end-grain surface to prevent moisture absorption into the wood is decisive for the life-time of the wood material. Nailing can open up new end-grain surfaces and should thus be carried out carefully and only after due consideration.
    • Rounded edges – increase the covering ability of paint and reduce the risk of mechanical damage to the facing boards.
    • Choice of surface treatment – vital for the performance of the facings. The wooden facings shall be delivered as part of the complete maintenance package.

    Nowadays there are many types of surface treatment where nano-technology is used to create an added value in a surface compared with what the more traditional products can offer. Nano-based surface-treatment products are already on the market, and they are said to make the surfaces dirt- and water-repellent, to prevent the growth of algae, fungi and moss, to improve UV- and temperature-resistance and colour permanence, to improve scratch- and abrasion-resistance, and to have anti-graffiti qualities etc. However, most of these products are new and for some of them there are still question marks with regard to their long-term performance and technical life-time, as well as their serviceability and thereto related economy seen from a life-cycle perspective for the product or system for which the surface treatment constitutes only a part.

    A cost analysis carried out as a part of the study makes the assessment that the new nano-technology-based surface-treatment systems could lead at most to a reduction of 15 %. in maintenance costs. The assumption is then that the façade needs to be cleaned every fifth or seventh year when a traditional painting system is used.

    According to the Swedish Standard, recovered wood from a wooden façade is defined as tree fuel and is generally designated recycled wood or, when the material is in a disintegrated form, as recycled chips,

    There is a major problem in recovering energy from recycled wood when a part of the material has been treated in some way, e.g. impregnated with a wood-protection agent or surface-treated, or when it contains other design components of e.g. plastic or metal. Recycled chips are a very good fuel for energy recovery provided the plant has adequate flue-gas cleaning and the ash is handled in a correct manner. Contaminated ash constitutes a problem, since it is classified as dangerous waste and cannot therefore be returned to the forest. If the content of heavy metals is not too high, the ash can be used as a covering and filling material. Otherwise, the ash must be deposited as landfill. A better sorting of household waste and an overhaul of the regulations would mean that the cleaned recycled wood could be burned in conventional biofuel boilers and that the contaminated portion could be burned separately.

     

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