- Email: [email protected]
Hygrothermal Assessment of a Prefabricated Timber-frame Construction Based in Hemp
Available online at www.sciencedirect.com
ScienceDirect Procedia Environmental Sciences 38 (2017) 729 – 736
International Conference on Sustainable Synergies from Buildings to the Urban Scale, SBE16
Hygrothermal Assessment of a Prefabricated Timber-Frame Construction based in Hemp Roberto Garay Martineza,* a
Sustainable Construction Division, Tecnalia,c/ Geldo, Edificio 700, 48160, Derio, Spain
Abstract In this paper, an assessment is made on a pre-fabricated timber framed hemp-based building envelope system. The hemp-lime mixture within the envelope is produced by mixing the hemp shiv with a lime formulated solution, which acts as a binder, and provides thermal insulating and moisture buffering capacity to the resulting construction. Hemp, by its natural origin, is a fixative of CO2 and can result in a negative carbon footprint helping to reduce the global impact of a building. In addition the hemp- lime layer absorbs and expels heat and humidity in relation to the environment and acts as a thermal storage by reducing the flow of energy through the wall. The presented system targets at the generation of an innovative building system focused on the expansion of the market for structural products, sustainable, ecological and low carbon footprint. As part of its development its thermal insulation and moisture buffering properties have been assessed, and case studies and outcomes of full scale experimental studies are presented. © Published by Elsevier B.V. This © 2017 2017The TheAuthors. Authors. Published by Elsevier B.V.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. Peer-review under responsibility of the organizing committee of SBE16. Keywords: Hemp; Thermal performance; Low embodied energy; Experimental Assessment; Certification; Prefabrication
1. Introduction 1.1. The construction market in the 21st Century Within the last decades of the 20th century, and the beginning of the 21st century, the construction sector has evolved along with increasingly complex and demanding Building codes. A clear case for this is the Energy
* Corresponding author. Tel.: +34 667 178 958; fax: +34 946 460 900 E-mail address: [email protected]
1878-0296 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. doi:10.1016/j.proenv.2017.03.155
730
Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
Performance of Buildings Directive (EPBD)1 in Europe. At the same time, construction practices that incorporate materials with reduced embodied carbon footprint have steadily increased in popularity. It is estimate that globally, about 40% of all final energy consumption is performed in buildings. In order to ensure the sustainability of the energy system in Europe, the Europe 2020 2 strategy for a sustainable energy growth was created, which is the main initiative to promote the reduction of energy consumption, by addressing several action lines such as the reduction of greenhouse gas emissions, the promotion of renewable energy and energy efficiency measures. Also, design and commissioning codes and procedures such as the Passive House Standard 3, address building envelopes, along with building ventilation towards the optimization of the energy performance of buildings. In the evolution in design and construction of buildings envelopes, with the introduction of sustainable materials, it has been proved that they perform similarly to standard materials, with a substantially reduced environmental and carbon footprint. 1.2. Barriers in the implementation of construction systems with sustainable materials Prior to their introduction in the mainstream market, novel materials are commonly installed in small scale selfbuilt constructions for demonstration purposes. However, due to the size of the construction market, the atomization of the stakeholders, risks associated with material failure, need for insurance and warranty, along with many other historical and regulatory reasons, the construction sector is a highly regulated environment. Upon the escalation of production, manufacturers need to face the certification of their products. In the process for the introduction of novel materials in the building envelope, designers, manufacturers, installers and final users need to address the characterization and certification of the product performance. The regulatory environment provides many already available product standards which define the suitable testing and certification schemes for already established product categories (e.g. mineral wool insulation for buildings…), but new products are commonly out of the scope of these standards and lack a recognized procedure for its characterization and certification. In order to address the lack of standardized procedures, these need to be developed, and a consensus reached on their validity within assessment committees, commonly on a case-by-case basis. The uncertainty and time requirements for these procedures to be developed are a heavy burden to the development and commercialization of novel materials. In some cases an existing harmonized standard where the product can be placed within its scope, is available. In these cases, performance tests allow for a straightforward way to obtain the CE mark of a product. This label allows for the commercialization of the product in the EU. When such harmonized standards are not available, alternative certification procedures need to be activated. The most common procedure requires the drafting and approval of a European Assessment Document (EAD) within the European Organization for Technical Approvals (EOTA) 4, in order to obtain a European Technical Approval (ETA). Other alternatives are the declaration product conformity by means of National Assessment Bodies. Generally, these procedures need to be activated for each member states. In some cases, one of such approvals, if correctly targeted at a later use, may pave the way to a CE marking with the previously mentioned EAD+ETA process. All these alternative processes, when compared with CE marking according to harmonized standard, commonly impose a relevant delay in the time to market of construction products.
Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
1.3. A new prefabricated envelope system, based in hemp In this paper, a novel prefabricated hemp-based, timber-frame load bearing wall system is presented. The procedure followed for the correct commercialization of this well-proven system in the EU is presented, including the assessment of the hygrothermal performance of the wall system, and the definition of a product certification roadmap. Ultimately, the correct design of this system, along with the previously mentioned experimental campaigns and assessment procedures will achieve a high-performance system, for the new construction sector set by the EPBD, with minimal carbon footprint.
2. Hemp-based envelope system The Hempcell®5 system is composed by a set of natural materials, among which, the most innovative one is a hemp-lime mixture which serves as thermal insulation and hygrothermal buffering layer. It is estimated that the carbon footprint of this system is about 80% lower than in traditional construction systems.
Fig. 1. HempCell ® system5, and, several experimental setups with HempCell ®6
3. Hemp and bio-based building insulation materials The Hempcell panel incorporates a bio-based insulation material composed by a Hemp and lime mixture. Hemp fibre has been used as a basic construction material since ancient times, as it can be used to create a mortar with many possibilities for the construction sector, when combined with hydraulic lime. With a specific ratio between both materials, it is possible to obtain an optimal performance for pre-dried prefabricated timber frame façades, with outmost thermal and hygrothermal performance. Being hemp a renewable and sustainable material, and duet to the abundancy of lime in nature, the Hemp-lime mixture has a negative carbon footprint. The hemp-lime mixture also provides excellent hygrothermal performance figures, with thermal conductivity in the range 0.06-0.12 W/mK 7, 8, 9, and specific heat of 1300 to 1700 J/kgK 10, within a relatively dense (700kg/m3) compound (resulting heat capacity of 1-2 MJ/m3K).
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Furthermore previous experience shows that the thermal performance of this material is comparatively better than others with equivalent U-value11. As external (and also internal) boundary conditions are heavily variable, the thermal capacity of Hemp-lime façades store heat in such a way that they substantially reduce the overall building energy consumption. This is common to heavy construction methods (e.g. masonry), but hemp allows to achieve similar characteristics within a lightweight prefabricated envelope elements. 3.1. Advances in Hemp insulation Within the development of Hempcell, material development has been focused at obtaining a highly productive drying method in order to allow for an economic manufacturing process for this high performance envelope. This was achieved by a correct binder formulation, for a fast and reliable pouring, along with an ambient drying process. The final formulation allowed for panel manufacture-drying cycle of 24h, avoiding large stacking/storage areas, and reducing the lead time of the panel manufacture. 4. Prefabricated timber-frame panels, with hemp and natural insulation materials The prefabricated timber frame panels in the Hempcell® system are composed by two main layers: A Hemp-lime core, with an additional external wood-fibre insulation layer, where additional moisture control and weather proofing membranes are fixed. The timber frame construction, which can be adapted to any geometry on a project-by-project basis, provides a robust backbone where various render and lining systems can be applied. The composing materials provide a very interesting moisture buffering potential for the internal ambience, as well as thermal inertia- when compared to other lightweight solutions. The final result is a heavily insulated assembly (U~0.15W/m2K within 300mm thickness), with minimal carbon footprint. 5. Full scale assessment A full scale setup was constructed in order to obtain a high quality technical assessment of the thermal and hygrothermal performance of the hemp-lime based system. This setup was constructed at the Kubik by Tecnalia test facility12. KUBIK is a full scale experimental R&D infrastructure to demonstrate energy efficient technologies, focused on the development of new products and systems. The main distinctive feature of KUBIK is its capacity to create realistic scenarios for the quantitative determination of energy efficiency/ energy savings resulting from the interplay of constructive solutions, intelligent management of HVAC and lighting systems as well as non-renewable and renewable energy sources. The infrastructure is a building with a total floor area of 500 m2 distributed over basement, ground floor and two upper levels. The test set-up was constructed in a portion of the East-facing wall at second floor level. In this area, a specific support structure was generated in order to adapt the structure of the building to the Hempcell panels, in such a way were its integration into the building was made similarly to its implementation in real buildings. 3 panels were installed to integrate vertical and horizontal junctions in the test set-up. The particular dimensions of the installed Hempcell panels resulted in a Design U-value of 0.15W/m2K.
Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
a
b
c
Fig. 2. General view of the KUBIK facility (a), External view of the Hempcell system (b), internal view of the Hempcell system (c).
Along with temperature and relative humidity sensors embedded in the prefabricated elements, the set-up was consolidated with generic data acquisition capacities in the building, and specific surface and room sensors installed for this project. Internal surface measurements were performed at 5 different locations allowing for the mapping of the heat transfer at different heights ant locations of the panel.
Fig. 3. Layout of Heat flux sensors on the inner side of the test
U-value calculation was performed by means of averaging. For this process, 30-day moving averaged night-time data was taken from an 80-day period, from the 2015 summer-autumn period. Overall, data from the 5 internal measurement locations were found to reach to similar U-value results. However, Heat flux 5 was found to result in an approximately 0.04W/m2K increase in the calculated U-value. In Table 1, the calculated U-value is provided for each heat flux sensor. As it can be seen, the mean value of the calculated Uvalues matches well the expected/design value. Analysis on data from heat flux sensors 1 to 4 resulted on mean U-
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values in the range 0.14 to 0.17 W/m2K, only slightly deviated from the design value (0.15W/m2K). For each case, minimum-to-maximum variation of U-value is in the range 0.08-0.10 W/m2K, with 50% of the values (variation from quartile 1 to 3) in the range of 0.02W/m2K. Table 1. Experimentally-obtained U-value calculations. Results of 30-day averaged data for each heat flux meter U-value [W/m2K] 1
2
3
4
5
Minimum
0.10
0.13
0.14
0.12
0.15
Quartile 1
0.12
0.14
0.15
0.13
0.18
Quartile 2
0.14
0.15
0.17
0.15
0.19
Quartile 3
0.14
0.16
0.18
0.15
0.20
Maximum
0.19
0.21
0.23
0.20
0.25
In table 2, and figure, 4, a Gaussian a quartile representation is performed over the aggregated data from all 5 heat flux sensors. Given that the aggregated dataset contains all the information from each of the individual analysis per heat flow sensor, the total minimum-to-maximum variation is increased; however, the analysis on this data provides a better insight on the robustness of the calculated U-value, considering that more information is fed into the calculation of the mean value and confidence intervals. The calculated mean U-value is 0.16W/m2K, with 68% of the values within 0.03W/m2K of the mean value.
Fig. 4. Boxplot of averaged night-time U-value of the Hempsec Wall. Aggregated output of axes 1 to 4 Table 2. Statistical analysis of averaged night-time U-values of the Hempsec Wall. Aggregated output of axes 1 to 5 U-value [W/m2K] Gaussian
Quartile
MAX
0.25
100%
0.25
+1std dev
0.19
75%
0.18
Mean
0.16
50%
0.16
-1std dev
0.13
25%
0.15
MIN
0.10
0%
0.10
These results match well with similar experiences with full scale energy assessment in buildings, and test mockups in the UK, where temperature, relative humidity and heat flux are monitored have shown promising results.
Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
Also a good match is achieved with previous research has showed that the integration of natural and bio-based materials in a sustainable system can achieve performance levels of conventional materials 11. The outcome of the experiment will provide additional information on the full scale performance of the materials, and its relation on thermal assessments in13. 6. Certification process of HEMPCELL The growth of construction with hemp in the European market has been hampered by the lack of a consolidated constructive approach, supported by a product certification in Europe and at national level, which would provide a secure path to place hemp-based final products on the market. These certification processes would allow for the recognition of the systems by insurance, warranty and mortgage providers. At the same time, in order to promote the creation of self-sufficient regional supply chains, incorporating hemp growers, processors and manufacturers of building systems, the development of business plans, and market development of this system among Europe needs to be rooted in strong certificates, with proven insurance, warranty and finance schemes. Considering all these issues, common to many construction systems, the Construction Products Regulation14 aims to overcome technical barriers to enable the free movement of construction products within the European Economic Area. For this reason, a harmonized framework is designed in order to achieve a proper labelling of innovative products. When related to the certification process of the HEMPCELL systems, it has been assessed out of the scope of any harmonized standard. There are, however, draft harmonized standards15, 16, which could be used for the certification the prefabricated timber frame assembly, if all composing materials were CE labelled or had achieved an ETA. While most of the materials in Hempcell have their own CE mark, the Hemp-Lime does not have a harmonized standard upon which a CE mark could be obtained. However, Hemp-lime is defined within the scope of an alreadydeveloped EAD [17], which will be used to achieve the European Technical Approval of the Hemp-lime, allowing for the CE marking of this material, for its later use on the pre-fabricated assembly.
6.1. Next Steps A National Technical Assessment Body has been selected in the UK, where the ETA of the hemp-lime compound will be developed within 2016. When related to the CE marking of the full envelope panel, contacts with the relevant CEN committee are made regularly to monitorize the approval probability of 15, which would substantially facilitate market development in EU. Should this standard not be approved in a near future, Approval would be sought at National level, for key markets of Hempcell. 7. Conclusions The capacity of a pre-fabricated hemp-based timber-frame envelope system to achieve high insulation levels has been provided. To the authors’ belief, good agreement between design and measured U-values has been achieved for a highly insulated assembly. This positions the Hempcell system as a suitable candidate within the market for highly insulated constructions with low embodied-impact constructions. However, the certification path needs still to be paved out prior to the full scale deployment of this technology at wider scale. A certification route has been identified for this product, which adds on to the knowledge of the satisfactory results from real-life performance of this system in pilot housing projects with this system. Under such a scheme it should be expected that the Hemp-lime mixture within Hempcell should obtain an ETA within the next 12 months, which would allow for its installation in construction projects. Once the ETA of the hemp-lime is achieved, the prefabricated timber frame component containing this material should not face any differential trouble in achieving the required certifications when compared to any other pre-fabricated timber structure.
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Acknowledgements The research leading to the results reported in this work has received funding from the Eco-Innovation Initiative of the European Union, under the following project: Pre-fabricated, pre-dried panelised system of hemp-lime construction (HEMPSEC, ECO/12/332972). References 1. Energy Performance of Buildings Directive, EPBD, Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings, OJ L 153, 18.6.2010, p. 13–35 2. EUROPE 2020, A strategy for smart, sustainable and inclusive growth, http://ec.europa.eu/europe2020/index_en.htm, (10th December 2015) 3. Passipedia, The Passive House – definition, http://www.passipedia.org/basics/the_passive_house_-_definition (22th December 2015) 4. EOTA, European Organization for Technical Assessment, http://www.eota.eu/ (10th December 2015) 5. Hempsec, Hempcell system, http://www.hempsec.eu, (22th November 2015) 6. Hempsec, Wroughton test building presentation, http://www.greencoreconstruction.co.uk/downloads/Wroughton_presentation_REV_3_22_08_2014.pdf (10th December 2015) 7. Daly P, Ronchetti P, Woolley T. Hemp Lime Bio-composite as a Building Material Irish Construction. Ireland: Environmental Protection Agency; 2012. 8. Hirst E, A, J, Walker P, Paine K, A, Yates T. Characterization of Low Density Hemp-Lime Composite Building Materials under Compression Loading. Second International Conference on Sustainable Materials and Technologies. Università Politecnica delle Marche, 2010. 9. Lawrence M, Fodde E, Paine K, Walker P. Hygrothermal performance of an experimental hemp- lime building. Key Engineering Materials 2012, 517, 413-421. 10. Sutton A, Black D, Walker P. Hemp lime: An introduction to low impact building materials. In: Establishment BR, editor. Garston, Watford: IHS BRE Press; 2011. 11. Latif, E., Ciupala, M. A. and Wijeyesekera, D. C., 2014. The comparative in situ hygrothermal performance of Hemp and Stone Wool insulations in vapour open timber frame wall panels. Construction and Building Materials 2014, 73, 205-213. 12. Garay, R et Al, Energy efficiency achievements in 5 years through experimental research in KUBIK, 6th International Building Physics Conference IBPC 2015, Energy Procedia 2015, 78, 865-870 13. Latif E, Lawrence M, Shea A, Walker P, Moisture buffer potential of experimental wall assemblies incorporating formulated hemp-lime, Building and Environment 2015, 93, 199-209 14. Construction Products Regulation, REGULATION (EU) No 305/2011 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 9 March 2011 lying down harmonized conditions for the marketing of construction products and repealing Council Directive 89/106/EEC 15. CEN, prEN 14732:2014. Timber structures. Prefabricated wall, floor and roof elements. Requirements 16. Commission mandate M/112 to cen/cenelec concerning the execution of standardization work for harmonized standards on structural timber products and ancillaries, Ref. Ares(2012)1503269 - 17/12/2012 17. EOTA, EAD 040138-00-1201, In-Situ Formed Loose Fill Thermal and/or Acoustic Insulation Products Made of Vegetable Fibres (2015)
ScienceDirect Procedia Environmental Sciences 38 (2017) 729 – 736
International Conference on Sustainable Synergies from Buildings to the Urban Scale, SBE16
Hygrothermal Assessment of a Prefabricated Timber-Frame Construction based in Hemp Roberto Garay Martineza,* a
Sustainable Construction Division, Tecnalia,c/ Geldo, Edificio 700, 48160, Derio, Spain
Abstract In this paper, an assessment is made on a pre-fabricated timber framed hemp-based building envelope system. The hemp-lime mixture within the envelope is produced by mixing the hemp shiv with a lime formulated solution, which acts as a binder, and provides thermal insulating and moisture buffering capacity to the resulting construction. Hemp, by its natural origin, is a fixative of CO2 and can result in a negative carbon footprint helping to reduce the global impact of a building. In addition the hemp- lime layer absorbs and expels heat and humidity in relation to the environment and acts as a thermal storage by reducing the flow of energy through the wall. The presented system targets at the generation of an innovative building system focused on the expansion of the market for structural products, sustainable, ecological and low carbon footprint. As part of its development its thermal insulation and moisture buffering properties have been assessed, and case studies and outcomes of full scale experimental studies are presented. © Published by Elsevier B.V. This © 2017 2017The TheAuthors. Authors. Published by Elsevier B.V.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. Peer-review under responsibility of the organizing committee of SBE16. Keywords: Hemp; Thermal performance; Low embodied energy; Experimental Assessment; Certification; Prefabrication
1. Introduction 1.1. The construction market in the 21st Century Within the last decades of the 20th century, and the beginning of the 21st century, the construction sector has evolved along with increasingly complex and demanding Building codes. A clear case for this is the Energy
* Corresponding author. Tel.: +34 667 178 958; fax: +34 946 460 900 E-mail address: [email protected]
1878-0296 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. doi:10.1016/j.proenv.2017.03.155
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Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
Performance of Buildings Directive (EPBD)1 in Europe. At the same time, construction practices that incorporate materials with reduced embodied carbon footprint have steadily increased in popularity. It is estimate that globally, about 40% of all final energy consumption is performed in buildings. In order to ensure the sustainability of the energy system in Europe, the Europe 2020 2 strategy for a sustainable energy growth was created, which is the main initiative to promote the reduction of energy consumption, by addressing several action lines such as the reduction of greenhouse gas emissions, the promotion of renewable energy and energy efficiency measures. Also, design and commissioning codes and procedures such as the Passive House Standard 3, address building envelopes, along with building ventilation towards the optimization of the energy performance of buildings. In the evolution in design and construction of buildings envelopes, with the introduction of sustainable materials, it has been proved that they perform similarly to standard materials, with a substantially reduced environmental and carbon footprint. 1.2. Barriers in the implementation of construction systems with sustainable materials Prior to their introduction in the mainstream market, novel materials are commonly installed in small scale selfbuilt constructions for demonstration purposes. However, due to the size of the construction market, the atomization of the stakeholders, risks associated with material failure, need for insurance and warranty, along with many other historical and regulatory reasons, the construction sector is a highly regulated environment. Upon the escalation of production, manufacturers need to face the certification of their products. In the process for the introduction of novel materials in the building envelope, designers, manufacturers, installers and final users need to address the characterization and certification of the product performance. The regulatory environment provides many already available product standards which define the suitable testing and certification schemes for already established product categories (e.g. mineral wool insulation for buildings…), but new products are commonly out of the scope of these standards and lack a recognized procedure for its characterization and certification. In order to address the lack of standardized procedures, these need to be developed, and a consensus reached on their validity within assessment committees, commonly on a case-by-case basis. The uncertainty and time requirements for these procedures to be developed are a heavy burden to the development and commercialization of novel materials. In some cases an existing harmonized standard where the product can be placed within its scope, is available. In these cases, performance tests allow for a straightforward way to obtain the CE mark of a product. This label allows for the commercialization of the product in the EU. When such harmonized standards are not available, alternative certification procedures need to be activated. The most common procedure requires the drafting and approval of a European Assessment Document (EAD) within the European Organization for Technical Approvals (EOTA) 4, in order to obtain a European Technical Approval (ETA). Other alternatives are the declaration product conformity by means of National Assessment Bodies. Generally, these procedures need to be activated for each member states. In some cases, one of such approvals, if correctly targeted at a later use, may pave the way to a CE marking with the previously mentioned EAD+ETA process. All these alternative processes, when compared with CE marking according to harmonized standard, commonly impose a relevant delay in the time to market of construction products.
Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
1.3. A new prefabricated envelope system, based in hemp In this paper, a novel prefabricated hemp-based, timber-frame load bearing wall system is presented. The procedure followed for the correct commercialization of this well-proven system in the EU is presented, including the assessment of the hygrothermal performance of the wall system, and the definition of a product certification roadmap. Ultimately, the correct design of this system, along with the previously mentioned experimental campaigns and assessment procedures will achieve a high-performance system, for the new construction sector set by the EPBD, with minimal carbon footprint.
2. Hemp-based envelope system The Hempcell®5 system is composed by a set of natural materials, among which, the most innovative one is a hemp-lime mixture which serves as thermal insulation and hygrothermal buffering layer. It is estimated that the carbon footprint of this system is about 80% lower than in traditional construction systems.
Fig. 1. HempCell ® system5, and, several experimental setups with HempCell ®6
3. Hemp and bio-based building insulation materials The Hempcell panel incorporates a bio-based insulation material composed by a Hemp and lime mixture. Hemp fibre has been used as a basic construction material since ancient times, as it can be used to create a mortar with many possibilities for the construction sector, when combined with hydraulic lime. With a specific ratio between both materials, it is possible to obtain an optimal performance for pre-dried prefabricated timber frame façades, with outmost thermal and hygrothermal performance. Being hemp a renewable and sustainable material, and duet to the abundancy of lime in nature, the Hemp-lime mixture has a negative carbon footprint. The hemp-lime mixture also provides excellent hygrothermal performance figures, with thermal conductivity in the range 0.06-0.12 W/mK 7, 8, 9, and specific heat of 1300 to 1700 J/kgK 10, within a relatively dense (700kg/m3) compound (resulting heat capacity of 1-2 MJ/m3K).
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Furthermore previous experience shows that the thermal performance of this material is comparatively better than others with equivalent U-value11. As external (and also internal) boundary conditions are heavily variable, the thermal capacity of Hemp-lime façades store heat in such a way that they substantially reduce the overall building energy consumption. This is common to heavy construction methods (e.g. masonry), but hemp allows to achieve similar characteristics within a lightweight prefabricated envelope elements. 3.1. Advances in Hemp insulation Within the development of Hempcell, material development has been focused at obtaining a highly productive drying method in order to allow for an economic manufacturing process for this high performance envelope. This was achieved by a correct binder formulation, for a fast and reliable pouring, along with an ambient drying process. The final formulation allowed for panel manufacture-drying cycle of 24h, avoiding large stacking/storage areas, and reducing the lead time of the panel manufacture. 4. Prefabricated timber-frame panels, with hemp and natural insulation materials The prefabricated timber frame panels in the Hempcell® system are composed by two main layers: A Hemp-lime core, with an additional external wood-fibre insulation layer, where additional moisture control and weather proofing membranes are fixed. The timber frame construction, which can be adapted to any geometry on a project-by-project basis, provides a robust backbone where various render and lining systems can be applied. The composing materials provide a very interesting moisture buffering potential for the internal ambience, as well as thermal inertia- when compared to other lightweight solutions. The final result is a heavily insulated assembly (U~0.15W/m2K within 300mm thickness), with minimal carbon footprint. 5. Full scale assessment A full scale setup was constructed in order to obtain a high quality technical assessment of the thermal and hygrothermal performance of the hemp-lime based system. This setup was constructed at the Kubik by Tecnalia test facility12. KUBIK is a full scale experimental R&D infrastructure to demonstrate energy efficient technologies, focused on the development of new products and systems. The main distinctive feature of KUBIK is its capacity to create realistic scenarios for the quantitative determination of energy efficiency/ energy savings resulting from the interplay of constructive solutions, intelligent management of HVAC and lighting systems as well as non-renewable and renewable energy sources. The infrastructure is a building with a total floor area of 500 m2 distributed over basement, ground floor and two upper levels. The test set-up was constructed in a portion of the East-facing wall at second floor level. In this area, a specific support structure was generated in order to adapt the structure of the building to the Hempcell panels, in such a way were its integration into the building was made similarly to its implementation in real buildings. 3 panels were installed to integrate vertical and horizontal junctions in the test set-up. The particular dimensions of the installed Hempcell panels resulted in a Design U-value of 0.15W/m2K.
Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
a
b
c
Fig. 2. General view of the KUBIK facility (a), External view of the Hempcell system (b), internal view of the Hempcell system (c).
Along with temperature and relative humidity sensors embedded in the prefabricated elements, the set-up was consolidated with generic data acquisition capacities in the building, and specific surface and room sensors installed for this project. Internal surface measurements were performed at 5 different locations allowing for the mapping of the heat transfer at different heights ant locations of the panel.
Fig. 3. Layout of Heat flux sensors on the inner side of the test
U-value calculation was performed by means of averaging. For this process, 30-day moving averaged night-time data was taken from an 80-day period, from the 2015 summer-autumn period. Overall, data from the 5 internal measurement locations were found to reach to similar U-value results. However, Heat flux 5 was found to result in an approximately 0.04W/m2K increase in the calculated U-value. In Table 1, the calculated U-value is provided for each heat flux sensor. As it can be seen, the mean value of the calculated Uvalues matches well the expected/design value. Analysis on data from heat flux sensors 1 to 4 resulted on mean U-
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values in the range 0.14 to 0.17 W/m2K, only slightly deviated from the design value (0.15W/m2K). For each case, minimum-to-maximum variation of U-value is in the range 0.08-0.10 W/m2K, with 50% of the values (variation from quartile 1 to 3) in the range of 0.02W/m2K. Table 1. Experimentally-obtained U-value calculations. Results of 30-day averaged data for each heat flux meter U-value [W/m2K] 1
2
3
4
5
Minimum
0.10
0.13
0.14
0.12
0.15
Quartile 1
0.12
0.14
0.15
0.13
0.18
Quartile 2
0.14
0.15
0.17
0.15
0.19
Quartile 3
0.14
0.16
0.18
0.15
0.20
Maximum
0.19
0.21
0.23
0.20
0.25
In table 2, and figure, 4, a Gaussian a quartile representation is performed over the aggregated data from all 5 heat flux sensors. Given that the aggregated dataset contains all the information from each of the individual analysis per heat flow sensor, the total minimum-to-maximum variation is increased; however, the analysis on this data provides a better insight on the robustness of the calculated U-value, considering that more information is fed into the calculation of the mean value and confidence intervals. The calculated mean U-value is 0.16W/m2K, with 68% of the values within 0.03W/m2K of the mean value.
Fig. 4. Boxplot of averaged night-time U-value of the Hempsec Wall. Aggregated output of axes 1 to 4 Table 2. Statistical analysis of averaged night-time U-values of the Hempsec Wall. Aggregated output of axes 1 to 5 U-value [W/m2K] Gaussian
Quartile
MAX
0.25
100%
0.25
+1std dev
0.19
75%
0.18
Mean
0.16
50%
0.16
-1std dev
0.13
25%
0.15
MIN
0.10
0%
0.10
These results match well with similar experiences with full scale energy assessment in buildings, and test mockups in the UK, where temperature, relative humidity and heat flux are monitored have shown promising results.
Roberto Garay Martinez / Procedia Environmental Sciences 38 (2017) 729 – 736
Also a good match is achieved with previous research has showed that the integration of natural and bio-based materials in a sustainable system can achieve performance levels of conventional materials 11. The outcome of the experiment will provide additional information on the full scale performance of the materials, and its relation on thermal assessments in13. 6. Certification process of HEMPCELL The growth of construction with hemp in the European market has been hampered by the lack of a consolidated constructive approach, supported by a product certification in Europe and at national level, which would provide a secure path to place hemp-based final products on the market. These certification processes would allow for the recognition of the systems by insurance, warranty and mortgage providers. At the same time, in order to promote the creation of self-sufficient regional supply chains, incorporating hemp growers, processors and manufacturers of building systems, the development of business plans, and market development of this system among Europe needs to be rooted in strong certificates, with proven insurance, warranty and finance schemes. Considering all these issues, common to many construction systems, the Construction Products Regulation14 aims to overcome technical barriers to enable the free movement of construction products within the European Economic Area. For this reason, a harmonized framework is designed in order to achieve a proper labelling of innovative products. When related to the certification process of the HEMPCELL systems, it has been assessed out of the scope of any harmonized standard. There are, however, draft harmonized standards15, 16, which could be used for the certification the prefabricated timber frame assembly, if all composing materials were CE labelled or had achieved an ETA. While most of the materials in Hempcell have their own CE mark, the Hemp-Lime does not have a harmonized standard upon which a CE mark could be obtained. However, Hemp-lime is defined within the scope of an alreadydeveloped EAD [17], which will be used to achieve the European Technical Approval of the Hemp-lime, allowing for the CE marking of this material, for its later use on the pre-fabricated assembly.
6.1. Next Steps A National Technical Assessment Body has been selected in the UK, where the ETA of the hemp-lime compound will be developed within 2016. When related to the CE marking of the full envelope panel, contacts with the relevant CEN committee are made regularly to monitorize the approval probability of 15, which would substantially facilitate market development in EU. Should this standard not be approved in a near future, Approval would be sought at National level, for key markets of Hempcell. 7. Conclusions The capacity of a pre-fabricated hemp-based timber-frame envelope system to achieve high insulation levels has been provided. To the authors’ belief, good agreement between design and measured U-values has been achieved for a highly insulated assembly. This positions the Hempcell system as a suitable candidate within the market for highly insulated constructions with low embodied-impact constructions. However, the certification path needs still to be paved out prior to the full scale deployment of this technology at wider scale. A certification route has been identified for this product, which adds on to the knowledge of the satisfactory results from real-life performance of this system in pilot housing projects with this system. Under such a scheme it should be expected that the Hemp-lime mixture within Hempcell should obtain an ETA within the next 12 months, which would allow for its installation in construction projects. Once the ETA of the hemp-lime is achieved, the prefabricated timber frame component containing this material should not face any differential trouble in achieving the required certifications when compared to any other pre-fabricated timber structure.
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Acknowledgements The research leading to the results reported in this work has received funding from the Eco-Innovation Initiative of the European Union, under the following project: Pre-fabricated, pre-dried panelised system of hemp-lime construction (HEMPSEC, ECO/12/332972). References 1. Energy Performance of Buildings Directive, EPBD, Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings, OJ L 153, 18.6.2010, p. 13–35 2. EUROPE 2020, A strategy for smart, sustainable and inclusive growth, http://ec.europa.eu/europe2020/index_en.htm, (10th December 2015) 3. Passipedia, The Passive House – definition, http://www.passipedia.org/basics/the_passive_house_-_definition (22th December 2015) 4. EOTA, European Organization for Technical Assessment, http://www.eota.eu/ (10th December 2015) 5. Hempsec, Hempcell system, http://www.hempsec.eu, (22th November 2015) 6. Hempsec, Wroughton test building presentation, http://www.greencoreconstruction.co.uk/downloads/Wroughton_presentation_REV_3_22_08_2014.pdf (10th December 2015) 7. Daly P, Ronchetti P, Woolley T. Hemp Lime Bio-composite as a Building Material Irish Construction. Ireland: Environmental Protection Agency; 2012. 8. Hirst E, A, J, Walker P, Paine K, A, Yates T. Characterization of Low Density Hemp-Lime Composite Building Materials under Compression Loading. Second International Conference on Sustainable Materials and Technologies. Università Politecnica delle Marche, 2010. 9. Lawrence M, Fodde E, Paine K, Walker P. Hygrothermal performance of an experimental hemp- lime building. Key Engineering Materials 2012, 517, 413-421. 10. Sutton A, Black D, Walker P. Hemp lime: An introduction to low impact building materials. In: Establishment BR, editor. Garston, Watford: IHS BRE Press; 2011. 11. Latif, E., Ciupala, M. A. and Wijeyesekera, D. C., 2014. The comparative in situ hygrothermal performance of Hemp and Stone Wool insulations in vapour open timber frame wall panels. Construction and Building Materials 2014, 73, 205-213. 12. Garay, R et Al, Energy efficiency achievements in 5 years through experimental research in KUBIK, 6th International Building Physics Conference IBPC 2015, Energy Procedia 2015, 78, 865-870 13. Latif E, Lawrence M, Shea A, Walker P, Moisture buffer potential of experimental wall assemblies incorporating formulated hemp-lime, Building and Environment 2015, 93, 199-209 14. Construction Products Regulation, REGULATION (EU) No 305/2011 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 9 March 2011 lying down harmonized conditions for the marketing of construction products and repealing Council Directive 89/106/EEC 15. CEN, prEN 14732:2014. Timber structures. Prefabricated wall, floor and roof elements. Requirements 16. Commission mandate M/112 to cen/cenelec concerning the execution of standardization work for harmonized standards on structural timber products and ancillaries, Ref. Ares(2012)1503269 - 17/12/2012 17. EOTA, EAD 040138-00-1201, In-Situ Formed Loose Fill Thermal and/or Acoustic Insulation Products Made of Vegetable Fibres (2015)