Energy and Buildings

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1 Energy and Buildings 43 (2011) Contents lists available at ScienceDirect Energy and Buildings j our na l ho me p age: Development and performance evaluation of natural thermal-insulation materials composed of renewable resources Azra Korjenic a,, Vít Petránek b, Jiří Zach b, Jitka Hroudová b a Vienna University of Technology, Institute for Building Construction and Technology, Research Centre of Building Physics and Sound Protection, Karlsplatz 13/206-2, A Vienna, Austria b Brno University of Technology, Faculty of Civil Engineering, Technology Institute of Building Materials and Components, Veverí 95, Brno, Czech Republic a r t i c l e i n f o Article history: Received 14 January 2011 Received in revised form 5 May 2011 Accepted 12 June 2011 Keywords: Thermal insulating material Jute Flax Hemp a b s t r a c t Because energy efficiency in buildings will be evaluated not only based upon heating demand, but also according to the primary energy demand, the ecological properties of the building materials for the whole assessment has become essential. The demand for green building materials is rising sharply, especially insulating materials from renewable resources. The application of natural materials has become increasingly important as a consequence of the increasing need to conserve energy, use natural materials, incorporate architecture and construction into sustainable development processes, and the recently promulgated discussions on appropriate disposal of used insulation materials such as polystyrene (EPS). Due to the fact that natural materials are more sensitive to moisture, decomposition factors such as temperature, material moisture content, attacks by microorganisms, and possible decomposition of the material or shorter durability, it is necessary to evaluate the degradation rate of built-in materials and also determine their real in situ hygrothermal properties according to their moisture content, and volume changes. This paper describes the results of a research project carried out at the Vienna University of Technology and Brno University of Technology. The objective is to use jute, flax, and hemp to develop a new insulating material from renewable resources with comparable building physics and mechanical properties to commonly used insulations materials. All input components are varied in the tests. The impact of moisture content changes in relation to the rate of change of other properties was the focus of the investigation. The tests results show that the correct combination of natural materials is absolutely comparable with convectional materials Elsevier B.V. All rights reserved. 1. Introduction In the near future, all new buildings will be built to the passive house level and existing buildings will be renovated to meet the low energy building standard. The new approaches to energyefficient design are not only moving in the direction of lower and lower U-values to achieve lower energy consumption, but also the development and use of natural and local building materials. In recent years, the field of thermal protection in buildings are focusing more upon ecological properties. Environmental awareness is now not only limited to energy savings, but also contained within ecologically sound construction, i.e. minimum energy input, resource consumption, and pollution production should be a part of the production, installation, and use of insulation materials [1]. Corresponding author. Tel.: ; fax: address: azra.korjenic@tuwien.ac.at (A. Korjenic). In general, the principles of sustainable development are closely adhered to within the trends of existing development. Fears of raw material and energy resource depletion, and concerns about excessive air pollution are rising to a far greater extent now than in the past. Far more emphasis is placed upon non-toxic materials and recyclability. The indicated trends are also evident within innovation of buildings. Consideration is shifted away from energy demanding technologies towards organic materials, i.e. the natural raw materials that meet the majority of requirements for sustainable development. In the last time, some investigations are carried out with natural materials and have shown that they are comparable with standard building materials. In [2] an environment-friendly thermal insulation material binderless cotton stalk fiberboard was developed from cotton stalk fibres without resins and other chemical additives and exposed that it can successfully compete with other insulation materials. The research article of Agoudjil et al. shows that the date palm wood is a good candidate for the development of efficient and safe insulating materials when compared to the other natural materials [3]. In [4] was shown that /$ see front matter 2011 Elsevier B.V. All rights reserved. doi: /j.enbuild

2 A. Korjenic et al. / Energy and Buildings 43 (2011) hemp concrete can decrease the daily indoor relative humidity variations and reduction of 45% in energy consumption can be reached compared to cellular concrete. Also, systematic measurements of several important variables in a built house with straw bale walls in Germany shows excellent properties to provide excellent living conditions [5]. By using natural building materials in structures, human health can also be positively influenced [6]. Natural building materials regulate internal air humidity well and their characteristic odor acts on the human psyche beneficially. International research focusing on studying the effects of buildings on human health studies the relationship between psyche and building material odors. It takes several trends; we rank the following among the most important ones: - IAP (Indoor Air Pollution) deals with negative health effects of harmful physical, chemical and biological substances, - SBS (Sick Building Syndrome)- deals with the negative influence of the indoor environment on human health without demonstrable origin and continuity, BRI (Building Related Illness) deals with illnesses having their demonstrable origin in the building itself. The objective of the joint project between VUT in Brno and TU Vienna is namely the development, optimization, and observation of the behaviour of thermally insulating materials composed of easily renewable raw material resources originating from agricultural sources which could be used in new building structures and for renovation the existing engineering structures. Subsequently the possible applications of these materials should be precisely defined and measured, using simulation to verify functionality and durability [7]. 2. Thermal insulation materials composed of easily renewable raw material resources originating from agricultural sources The low thermal conductivity and fibrous character of the majority of organic materials contribute to a significant improvement of the thermal-insulation properties after incorporation in the structure of the exterior building envelope. Natural organic materials also show other different physical properties to ordinary silicate materials; they usually contain a higher specific heat capacity and higher moisture sensitivity. Organic materials are generally water vapour permeable and can accumulate moisture by adsorption from the air. Favourable properties of organic materials are the capabilities of absorbing moisture into the internal porous system at increased air humidities, and conversely, gradual moisture release into the surroundings with decreasing air humidity [8]. This mechanism favourably influences the indoor air humidity, primarily in winter when prolonged periods of low indoor air humidity may be experienced. Organic materials provide good sound insulation properties. This is mainly due to high sound absorption. However, the particular properties of each material depend on the structure and the density of a particular material. As mentioned above, natural materials mostly show higher moisture sensitivity, which is problematic if the material is exposed on a long term basis to an environment with high humidity or if is in contact with liquid water. Excessive exposure to humidity may cause biological corrosion, i.e. degradation by bacteria, mildew and fungi acting on the material. For this reason, the manufactured organic materials should always be separated from the sources of moisture, and/or a possibility of rapid drying must be ensured when materials get wet. Problems with moisture in walls should not occur if the building is properly designed. Thermal insulating properties deteriorate due to humidity and moisture. The thermal conductivity coefficient of a damp material is defined by the thermal conductivity of the fixed matrix, fluid phases, gas phases and their quantities, phase variations and spatial arrangement of the individual phases. The thermal conductivity coefficient is generally increasing with higher humidity. A very high open porosity value has a dominant influence on thermal and moisture behaviour of organic insulating materials, and is a very important factor of natural thermal insulating materials. Finally, poor fire resistance ranks among the negative properties of natural building materials. However, fire resistance can be effectively improved by fire retardants and by building these natural materials into structures with fireproof finishings (plaster or facing). 3. Heat and moisture transfer in a porous environment The thermal and moisture behaviour of building materials, and subsequently the building envelope, is a significant aspect of whole building performance [9]. Currently, hygrothermal transport through a building envelope exposed to standard climate conditions is well understood and a number of simulation models and computer codes have been developed and validated worldwide. The changes in temperature, moisture, and air pressure have a most important influence on the physical situation and functioning of the building components. To reproduce all this processes in the building using simulation programs, accurate input data for all materials are needed. Modelling of the different physical aspects of buildings (Heat, Air and Moisture) as well as the compilation of the absolutely necessary material data has been investigated in detail in Annex 41 of the International Energy Agency s (IEA) Energy Conservation in Buildings and Community Systems program (ECBCS) [10]. The exact knowledge of the material properties is central to identify the physical performance of building constructions. Especially the moisture-dependent physical structure material data are essential for natural materials because they respond to temperature and humidity changes. Mainly building materials are porous and can be considered as a solid medium with pores filled with air. Moisture is present in porous materials as bulk water in the coarse pores, as capillary condensed liquid water in the fine pores, water vapour in the airfilled pores, as adsorbed layers of water molecules on the internal pore wall surfaces, and as water physio-chemically bounded in the material that represents the solid matrix. The moisture content of a building material is presented as the relation of the weight of absorbed moisture to the dry weight of the material, u [kg kg 1 ]. Other units to indicate the moisture content could be volume specific units. Depending on the moisture content in the material, a partial pressure of water vapour exists in the pore. Likewise, the liquid moisture that is present in the capillaries of the material will exert a certain liquid pressure depending on how much moisture is absorbed in the materials. In general, equilibria exist between these pressures and moisture content, and the equilibria are described by two types of moisture retention curves: the sorption curve gives the equilibrium relation between the moisture content of the material and relative humidity of air in contact with or entrapped within the material. The suction curve gives the equilibrium between moisture content of the material and liquid pressure of pore water in the material. Therefore, it is very important to assess all moisture transport processes (Vapour-Diffusion, Liquid-Capillary suction, Darcy flow, Surface diffusion, Convective moisture flow) and all prop-

3 2520 A. Korjenic et al. / Energy and Buildings 43 (2011) erties depending on moisture content, to be able to evaluate the building material and its possible use. The fact is that this new developed material is a thermal-insulating material; the thermal conductivity is one of the most important dimensions. Because the thermal conductivity factor changes with the amount of moisture, the moisture influence on other properties was investigated. Within this research, the possibilities of using technical hemp fibres (type of hemp where amount of tetrahydrocannabinol-thc in hemp fibres is less than 0,3%), flax and jute for manufacturing insulating mats or boards for insulation of floating floors, interior walls, roofs, and facades was studied. Concurrently running simulations of various constructions by use of these plates and the results are described in the next paper. 4. Preparation and composition of the specimens Research of a new organic thermo insulating material and enduse properties has been ongoing within a joint research project between TU Vienna and TU Brno. Owing to ever-increasing trends to use natural insulating materials in the building industry, three different natural materials as input raw materials were selected and investigated for this research work. These were jute, flax and hemp. The objective was to monitor and compare the resulting characteristics of different compositions of input materials reciprocally and also to compare the materials with today s commonly used thermal insulating materials such as mineral wool, EPS and others. The next part of the project was to examine the influence of surroundings on thermal-engineering properties of these natural materials and on their function in the structure. Six sets of specimens made of thermal insulating materials were chosen from the natural raw materials for study. Three different organic input raw materials were selected for the comparison of resulting physical, mechanical and thermal insulating properties, i.e. jute, flax and hemp. As to hemp, specimen sets with the percentage composition of input raw materials (hemp fibres, chaff) similar to the first two specimen sets were selected, these specimen sets were denoted as 4 and 6 and with a different composition, specimen sets 3 and 5. Another comparative criterion was represented by the thickness of each specimen, in specimen sets marked as 1 to 4, the specimen thickness ranged from 77.4 to 81.2 mm; the specimen thickness in sets 5 and 6 were within the range of mm. The test specimens were composed of certain proportions of the following materials: natural fibres (jute, flax, technical hemp), shives, binder (bicomponent fibres). In Fig. 1, the hemp fibres with bicomponent fibres is pictured. Table 1 indicates individual percentages of individual components in the six specimen sets. The dosing of different materials was controlled by volume with a given density. Fig. 1. Photo of hemp fibres with bicomponent fibres. The technology of production of thermal-insulating carpets from technical hemp is implemented in practice according to the following procedure: preparation (application of additives to fibres, drying of the fibres, pneumatic mixing of hemp and bi-component fibres), homogenization of fibres mix and formation of insulation carpet, pressing down of insulation carpet to define thickness under and caking of boards under increased pressure and temperature, cooling and cutting insulation boards in the required format. Based on the above mentioned formulas, large format test specimens were made on a production line. Test specimens were prepared in plates sized 300 mm 300 mm, 200 mm 200 mm and 100 mm diameter circular specimens for determining bulk density, thermal insulating, and absorption properties. A set of analyzed samples is shown in Fig Operating method In order to study the behaviour of the organic thermal insulating materials, it was necessary to carry out the following test procedures according to relevant standards for insulation products applicable in building industry: The determination of bulk density was carried out on test specimens dried at 105 C by the gravimetric method. Exact dimensions of test specimens were measured with accuracy to 0.1 mm. The weight was determined using a laboratory balance with 0.01 g accuracy. The determination of bulk density was carried out according to EN 1602 [11]. Determination of mechanical properties Table 1 Percentages of various components in the test sets. Set of samples Material source Composition [hm. %] Natural fibres Binder Shives 1 Jute Flax Technical hemp Technical hemp Technical hemp Technical hemp Fig. 2. Testing samples.

4 A. Korjenic et al. / Energy and Buildings 43 (2011) Fig. 4. Measuring the diffusion resistance factor. Fig. 3. Device for measuring the thermal conductivity, Holometrix Lambda The stress at 10% deformation was determined on test specimens 200 mm 200 mm slabs. The test was carried out according to EN 826 Thermal insulating products for building applications Compression test. During the determination of mechanical properties, the test specimens were loaded by test equipment (a pressing machine). The applied pressure and related proportional deformation of the test specimen was read at specific intervals for the purpose of plotting the stress strain diagram. 10 = 10 3 F10 (1) A 0 F 10 is the force corresponding to 10% of compressive strain [N]; A 0 is the initial cross-section of test specimen [mm 2 ]. The tensile strength perpendicular to the plane of the slab was determined on 200 mm 200 mm slab test specimens. The test was conducted conforming to EN 1607 Thermal insulating products for building applications determination of tensile strength perpendicular to faces. The test specimens were fixed between two stiff boards and installed in the test equipment to determine the tensile test and they were subsequently pulled apart from each other with a given velocity. The maximum tensile force was registered and the tensile strength of the test sample was calculated. mt = F m A = F m (2) l b F m is the maximum tensile force [kn]; A is the sectional area [m 2 ]; l, b is the length, test specimen width [m] The determination of the thermal conductivity coefficient was carried out in a steady state using the slab method. Measurements were made using the Lambda 2300 measuring device, by Holometrix Micromet Inc., USA, operating on the principle of the stationary slab method at a mean temperature of +10 C and temperature gradient of 10 K. The measuring instrument is presented in Fig. 3. Test specimens 300 mm 300 mm slabs were dried at 65 C prior to testing and were then tested at 105 C. The thermal conductivity coefficient was determined according to ISO 8301 [12]. Measurements were taken using the device operating on the stationary slab principle at the mean temperature of +10 C and temperature gradient of 10 K [13]. q = T (3) x q is the heat flux density [W m 2 ]; is the thermal conductivity [W m 1 K 1 ]; T/x is the temperature gradient [K m 1 ]. The water vapour permeability was determined using 100 mm diameter circular test specimens (Fig. 4). The test was carried out in the climatic chamber at Faculty of Building in Brno at a temperature of 23 C and relative humidity of 93% and in compliance with EN Thermal insulating products for application on building industry determination of water vapour transmission properties [14]. The absorption properties were determined using test specimens at an ambient temperature of 23 C and relative humidity in the range from 0% to 92%. The values measured were used for plotting the absorption isotherms represented in Diagram 3. Knowledge of the absorption properties is crucial for determining the moisture content in the material after its used for building. 6. Measurement results and discussion Test specimens of organic thermal insulating materials were subject to individual tests as presented in Section Determination of physical and mechanical properties The resulting measurements of physical and mechanical properties of individual test specimen sets are presented in Table 2. The data acquired from the measurements were used as a resource for a part of further research work, i.e. the assessment of heat and moisture propagation in engineering structures and materials using calculation software. Bulk density values of individual test specimen sets were within the range of kg m 3. The value of 82.1 kg m 3, which is significantly higher for test specimens in set 6, was caused by stronger consolidation of input raw materials. The most favourable thermal conductivity coefficient was determined in specimen set 6 from hemp, the average thickness of which was 40.2 mm and the average bulk volume was 82.1 mm. The diffusion resistance factor in individual sets varied in the range of The minimum diffusion resistance was determined in specimen set 1 made of flax. As it is apparent from the above given tabular values, the stress at 10% deformation and the tensile stress perpendicular to slab faces that the hemp insulation made obtain very good mechanical properties relative to their bulk densities. The test specimen sets made of natural raw material resources (jute, flax) reached significantly lower values of tensile strength perpendicular to the faces of the slab Determination of balanced humidity absorption The moisture behaviour of newly developed materials was assessed based on the test results. Frequent moisture formation in buildings may result in faults; the increased moisture on wall and

5 2522 A. Korjenic et al. / Energy and Buildings 43 (2011) Table 2 Physical and mechanical properties of investigated samples. Set of samples Thickness [mm] Density [kg m 3 ] Thermal conductivity, dry [W m 1 K 1 ] Factor of diffuse resistance [ ] Tension at 10% deformation [kpa] Tensile strength [kpa] ceiling surfaces of interior rooms may lead to hygienic problems and health risks caused by mildew formation. The determination of balanced absorption moisture was carried out at an ambient temperature of 23 C (average value) and relative humidity in the range from 0% to 92%. The samples were placed into the exsiccators with different solutions to simulate different relative humidity values. The values measured were used for plotting absorption isotherms represented in Fig. 5. Knowledge of absorption properties is crucial for determining the moisture content in the material after it is incorporated into a building. It is evident from the test results that the investigated natural thermal insulating materials are sensitive to moisture in the surroundings into which they are built. Nevertheless, in comparison to other natural materials (wood, wool, etc.) the moisture sensitivity of hemp, flax and jute is lower. The maximum moisture sensitivity to the surroundings was observed in the flax set, specimen 2, conversely the lowest sensitivity was registered in the hemp set, specimens Determination of the moisture dependence of thermal-moisture characteristics In order to determine the moisture dependence of thermal conductivity coefficient values for individual test specimens, test specimens were measured with different moisture contents within the range of detected absorption moistures (see above). The defined amount of moisture was always installed in the test specimens before the measurement. Particularly, there were several moisture levels, from 0% to 14%. The specimens got desiccated or moistened so that their moisture approximates to the values of the selected moisture as much as possible. Subsequently, the specimens were wrapped in foil in order to prevent the moisture from escaping. The specimens were weighed before and after the measurements in order to compute the change of moisture during the measurement. The test results are presented in Fig. 6. Table 3 Conversion factor for mass moisture of six investigated samples. Set of samples f u [kg kg 1 ] As apparent from the above given behaviours of thermal conductivity coefficient versus moisture, a similar trend was observed in all cases: an increase in the thermal conductivity value was registered in specimens with higher moisture sensitivity (specimens 1 3). Based on EN ISO 10456, it is possible to convert the thermal values determined at certain boundary conditions ( 1, R 1 ) into values corresponding to different conditions ( 2, R 2 ). The following equation is applicable to convert a value into another material moisture value: 2 = 1. F m (4) whereas F m represents the moisture conversion factor: F m = e fu(u 1 u 2 ) (5) where u is the mass moisture [kg kg 1 ]; f u is the conversion factor for mass moisture [kg kg 1 ], According to EN ISO 10456, Tab. 4, the conversion coefficient for mass moistures f u = 0.5 kg kg 1 is also tabulated. Based on the measured values a back-calculation of coefficient for mass moistures f u for function was performed (6). The results are presented in Table 3 and Fig. 7. The comparison of moisture dependence of thermal conductivity for Set of samples 1 between measured, simulated, and standard values is shown in Fig. 8. Fig. 5. Illustration of stable balanced moisture absorption properties behaviour for individual test specimens at 23 C. Fig. 6. The moisture dependence of thermal conductivity coefficient values in individual test specimens.

6 A. Korjenic et al. / Energy and Buildings 43 (2011) Fig. 7. Conversion factor. For the implementation of the thermal protection which takes into account both comfort and hygiene, as well as energy and environmental savings, currently there are no better measures than the insulation of the shell of a building. The demand for new ecologically friendly materials based on fast-renewable natural sources is currently a growing topic. In addition to conventional insulating materials such as mineral wool, EPS, etc., natural alternative materials such as those from jute, flax and hemp are available. The latter is not a substitute for the previous, but an improvement of the product range. The use of these substances is dependent on specific advantages and disadvantages and depends on the given structural situation. Thermal, humidity, fire and sound protection are considered. In this investigation, different insulation plates from jute, flax and hemp are manufactured, diverse material characteristics measured and compared with conventional insulation materials. The selection of determining parameters was based on the relevant building physical processes, particularly moisture absorption and transport, as well as other moisture content dependent state properties. With respect to the development of science and technology, it can be said that thermal insulations made from natural raw materials are likely to become a suitable alternative to commonly used boards made from different materials (mineral wool, polystyrene or polyurethane). Measurements showed that properties of insulating board from organic fibres are fully comparable to common insulating boards made from other materials. Based on the measured values, a back-calculation of coefficient for mass moistures f u for function was performed. As you can see in Table 3 above, all calculated values are times higher compared to normalised value according to EN ISO It is apparent from the measured data that with increasing moisture content of samples there is higher rise of the measured thermal conductivity value than counted values according to EN ISO And thus it is very important to consider these measured values for designing composition of building structure and computing simulation. The next step of our investigation is to define all measured material properties in the database of the simulation program and to integrate using means of simulation calculations, the damage free application of these plates. The results of this part of the study are presented in the next paper. Acknowledgements This project was supported by the project MSM and project Studium der Verhaltung von Wärmeisolierungen aus einfach erneuerbaren Landwirtschaftsrohstoffquellen from program AKTION 2010/11. References Fig. 8. comparison of moisture dependence of thermal conductivity between measured, simulated, and standard values (Set of samples 1). 7. Conclusion [1] B. Berge, The Ecology of Building Materials, Second ed., 2009, ISBN [2] X. Zhou, F. Zheng, H. Li, C. Lu, An environment-friendly thermal insulation material from cotton stalk fibers, Energy and Buildings 42 (2010) [3] B. Agoudjil, A. Benchabane, A. Boudenne, L. Ibos, M. Fois, Renewable materials to reduce building heat loss: characterization of date palm wood, Energy and Buildings 43 (2011) [4] A.D. Tran Le, C. Maalouf, T.H. Mai, E. Wurtz, F. Collet, Transient hygrothermal behaviour of a hemp concrete building envelope, Energy and Buildings 42 (2010) [5] T. Ashour, H. Georg, W. Wu, Performance of straw bale wall: a case of study, Energy and Buildings (2010), doi: /j.enbuild [6] T. Torring, In Proceedings for the International Symposium of Integrated Life- Cycle Design of Materials and Structures, May 22-24, Helsinki, Finland, 2000, pp [7] J. Chybik, Natural Building materials, Grada Publishing, a.s., 2009, ISBN [8] A. Korjenic, H. Teblick, T. Bednar, Increasing the indoor humidity levels in buildings with ventilation systems: simulation aided design in case of passive houses, Building Simulation 3 (4) (2010) [9] T. Bednar, Baukonstruktionslehre 4, Wissen ist MANZ, 2010, ISBN [10] Annex 41, Whole Building Heat Air, Moisture Response: Modelling Principles and Common Exercises, International Energy Agency Energy Conservation in Buildings & Community Systems, [11] EN 1602, Thermal Insulating Products for Building Applications. Determination of the apparent density, 1997, Brussels. [12] ISO 8301, Thermal Insulation Determination of Steady-state Thermal Resistance and Related Properties Heat Flow Meter Apparatus, International Organization for Standardization (ISO), Switzerland, [13] S. Stastnik, J. Zach, Testing of Insulating Materials, CERM Publishing, 2002, ISBN X. [14] EN 12086, Thermal Insulating Products for Building Applications. Determination of Water Vapour Transmission Properties, 1997, Brussels.