Czech Technical University in Prague

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1 Czech Technical University in Prague WORKSHOP 2011 Project carried out within the framework of the CTU Student grant competition in 2010 This research has been supported by SGS grant No. SGS10/009/OHK1/1T/11 Conceptual Design and Life Cycle Assessment of Light Precast RC Frame from High Performance Concrete in Combination with Building Envelope from Wood, Recycled Materials and Biomaterials Case Study Ctislav Fiala, Tereza Pavlů, Martin Volf, Petr Hájek Faculty of Civil Engineering, Department of Building Structures, Czech Technical University in Prague Abstract The main aim of the research was conceptual design of light precast RC frame from high performance concrete. The load-bearing structure was combined with building envelope made of renewable or recycled materials. There were designed five constructional and material alternatives of building envelope. There was processed Life Cycle Assessment case study for three different building types and compared with standard constructional solutions. 1. Introduction Optimization of consumption of construction materials, their mixture aimed at reducing the consumption of primary non-renewable raw materials and energy sources, while the increased use of recycled materials is one of the basic requirements for development of new progressive building designs that respect the requirements of sustainable construction. New composite high performance silicate materials could be used for construction of more strong, more durable and at the same time slender structures. The optimized lightened shape of structural elements demands less material and consequently it can lead to improved environmental parameters of the entire structure. The application of HPC and UHPC is more frequent in engineering structures, such as bridges. However, in building structures there is also a good 1

2 chance to reduce environmental impacts and simultaneously to increase structural reliability and safety by the use of new types of high performance concretes. 2. Conceptual design of light precast RC frame for energy efficiency buildings There were made conceptual designs for three building types the family house, residential building and office building. For the subtle load-bearing column structure of residential or office building, the high performance fibre concretes HPC 105 and HPC 140 have been used. The family house was designed using ordinary C35/45 concrete. The framework consists of 150/200mm columns, rod girders and peripheral bracings 150/400mm. The floor structure was designed as filigree concrete structure with thickness of 210mm after solidification. There were made two design alternatives for both, residential and office buildings. The precast RC frame consisted of: a) Subtle rectangle column 150/200mm b) Squared 200/200mm column with longitudinal lightening cavity 140mm in diameter The columns are designed from fibre concrete HPC 140 with steel microfibers Stratec 0.15/13. The columns are reinforced only by longitudinal reinforcement; column s hoops are replaced by using tensile features of HPC 140. Horizontal load-bearing structures girders and floor panels are designed from high performance fibre-concrete HPC 105. There were designed chamber floor panels with recycled plastic mixture fillers with thickness 160 and 200mm, girders and peripheral bracings were designed in dimensions of 150/450mm and 200/450mm after solidification, according to the type of column and structure. Structure conceptual design also includes detailed selected precast RC elements connections solution - connections: floor panel/column, column/girder and floor panel/girder. The connections are designed as welded. 3. Variants of building envelope The precast RC frames of all three buildings were amended with several variants of light building envelope systems. We have designed 4 different variants (V4-V7) using renewable and recycled materials and two other variants (V2, V3) of standard solution were taken in account. A basis for comparison was set to standard masonry wall (V1) meeting the recommended thermal insulation qualities with U=0.24W/m 2 K. 2

3 All other variants (V2-V7) were designed in same standards to ensure meeting the requirements for low-energy buildings. Total U-value of these variants was set to 0.12W/m 2 K, which determined the final thickness of required insulation layers. Also, there have been used both variants of diffusion-opened and closed layer compositions to encompass main streams in light envelope structures. The basic variant V1 was standard masonry wall of thickness 0.44m with plasters on both sides. It is one of the most wide-spread external wall compositions in the Czech Republic with thermal qualities above valid regulations and it is appropriate reference level for our comparison. Variants V2 and V3 have proceeded from V1 variant, but these are meeting the requirements as they were set in the beginning. Both variants were designed to get U=0.12W/m 2 K, so there was used additional thermal insulation on the basic masonry wall. V2 variant uses 300mm of mineral wool insulation on 240mm ceramic masonry wall whereas V3 was designed from 300mm light-weight concrete blocks with mineral wool insulation layer at the thickness of 240mm. Both variants are finished by thin plaster. The first suggested alternative of light envelope system (V4) was common, diffusion closed composition using wooden columns 40/60mm in two half-module shifted lines. The space between columns was filled with mineral wool insulation and closed up with oriented-strain boards (OSB) and vapour-barrier from inner side. There were designed additional layers of thermal insulation from both sides placed in between wooden laths. Variant V5 has its origin in V4 variant but is designed as diffusion-opened. The vapour barrier is not present and the outer insulation layer is made from fiberwood boards. Details are shown in the Figure 1. 3

4 Figure 1: Variants V4 and V5, plans and sections. Figure 2: Variants V6 and V7, plans and sections. For the variant V6, there were introduced precast modules made of glued beams together with OSBs and blown cellulose fibres at the thickness of 300mm. The diffusion factor of the inner OSB must be significantly higher than diffusion factor of the outer one to ensure proper 4

5 moisture transport away from construction. The composition is again followed up with horizontal interior lathing with air gap for possible placement of HVAC pipes and electric conductors. From the exterior side is composition closed up by hemp fibre boards again with thin-layer plaster. The module system was described and registered under utility model application no. PUV The last V7 alternative uses a sandwich of boards with compressed beverage cartons and polystyrene in combination with supporting wooden studs 80/140mm. Structure is also furnished with a horizontal lathing with a space filled by 60mm of mineral wool insulation and plasterboard. From the exterior side is wall completed with 140mm of additional PS insulation with plaster. Material types used and its environmental performance comparison between all variants is show in the Figure 3. Figure 3: Comparison of material variants 4. Integration of solar systems Reduction of building energy demand, increase of the share of renewable energy sources and desire of higher energy independence lead to still more often usage of building envelope for active solar applications. Especially, higher residential buildings face the situation that the roof is no large enough, which means photovoltaics (PV) and solar thermal collectors (PT) are still often seen also integrated on or in the façade. Searching for not only well detailed and energetically optimal solutions but also aesthetical managed examples is the actually live topic. The exterior wall layer designs presented above are very similar from structural point of view. However they might notably differ in terms of water vapour transportation, when solar 5

6 modules or collectors are integrated in the façade. The integration of PV or PT is riskless, when a ventilated gap from the back side is introduced. It is necessary for PV applications to avoid overheating of the cells. Raising cell temperature decreases the conversion of the incident solar energy to the gained electrical energy of the product significantly. For solar thermal collector on the other hand it is advantageous to be integrated to the thermal insulation of the exterior wall without any gap. A collector integrated in the façade shows a lower coefficient of heat transport to the back and side wards, compared to the one in the stand alone position. This brings better efficiency in solar energy transformation and significantly lower heat loses when a higher temperature difference between the collector and exterior air temperature occurs [1]. On the other hand the outer layer of sealed water proof collectors forms a barrier in winter water vapour transportation from the interior to the exterior. As a result condensation on the back side of the collectors might occur. Therefore for these applications a wall design with a well performing moisture stop from the interior side with high diffusion factor is needed. As a result of this analysis two examples of active solar application integration is introduced: PV modules in the wall V5 with a ventilated gap and PT collectors in the wall V4 without any ventilation gap. Figure 4: Integration of PV modules with a ventilated gap to the wall V5 6

7 Figure 5: Integration of PT collectors without a ventilated gap to the wall V4 Another example of façade integration of solar systems offers an area of balcony railing. The drawback of this application is usually a limitation in both orientation and inclination. Generally, when comparing the vertically installed applications to the optimal inclination to ones, the former (suggesting south orientation) have only some 70% of the yearly incident solar radiation. On the other hand the higher inclination might be an advantage for a larger PT system because of the more balanced energy yield during the year. Stagnation time in the summer period is naturally reduced and the system performs more effectively in spring and autumn. Higher inclination for PT is thus more appropriate for a combination of hot water preparation and solar heating support. Balcony integration might also be advantageous for decentralized alternative. Then the piping is shorter and the resident has his own system under visual control. Figure 6: Example of PT collectors integrated in the balcony handrail 7

8 5. LCA of light precast RC frame in combination with building envelope from wood, recycled materials and biomaterials case study 5.1 Family house The family house [2] selected is designed with the effort for lowest possible environmental impact. To ensure this, the building is designed as passive house with the presumed demand of heating up to 20kWh/(m 2.a) with considerable number of renewable energy sources used (heat recuperation from used air, wood pellets combustion, photo-thermic and photo-voltaic systems). This led to designed building form, which minimizes heat loses and simplifies building s HVAC solution. Building has one underground and two elevated floors. The structure uses mostly naturalbased materials or primary waste materials. Concrete structures are optimized with respect to the weight of the materials. The vertical structure of the basement is formed by precast concrete blocks, structural system of the ground floor is subtle RC frame. Ceiling structure above these floors is composite monolithic concrete plate, filigree type. The second floor is designed as a wooden structure. Only the first floor was taken in the comparison. Figure 7: Family passive house ground plan and south view Figure 8: Basic layout of structural system 8

9 5.2 Residential building A simple four-storey residential house with the ground plan of approx x 22.3 m (design: Atelier KUBUS, J. Růžička) was chosen for environmental assessment of light precast RC frame in combination with building envelope from wood, recycled materials and biomaterials. The residential house is designed with a very universal layout enabling design of many feasible structural and material alternatives. The layout of the building is the following: the 2 nd and 4 th floor are divided into 3 flats - 2x 4+kt (95.9 m 2 ) and 1+kt (27.5 m 2 ), on the 1 st floor there are two flats 4+kt and technical facilities (Figure 9 and 10). Figure 9: Four-storey residential building grand plan and western view Figure 10: Basic layout of structural system 5.3 Office building Office building is a simple four-storey office building with the ground plan of approx. 94 x 28 m. The office building The Oregon House at Zličín, Prague was taken as a draft. This building was chosen for its simple shape. Construction system is designed as a light precast RC frame in combination with building envelope designed from wood, recycled materials and 9

10 biomaterials. The office building is designed with a very universal layout enabling design of many feasible structural and material alternatives. The layout of the building is regularly the central area is 6 x 6m and border area is 4 x 6m (Figure 12 and 13). Figure 12: Basic layout of structural system Figure 13: Basic layout of structural system 5.4 Methodology of the environmental comparison of alternatives for construction of individual building assessment There was applied computer-research model for defined construction variants and individual type of the buildings. This, according to the masses of load bearing structure and building envelope materials provides various environmental parameters. The basic model is formed by a database of materials and construction, which contains assessed specific values of environmental criteria of structures (such as various types of building enveloped, structural materials, etc.). Data [3], [4], [5] to quantify the embodied energy and embodied emissions were taken from the catalogues of building structures mentioned above. 6. Conclusion In term of the assessment criteria, there were reached approximately same results for different types of objects for the corresponding design solutions alternatives. In term of embodied emissions of CO 2, the family house and the office building have the lowest results for 10

11 reference variant V1, for the residential house it is the variant V2. We got unsatisfactory results due to a combination of light precast RC frame in and building envelope made from ceramic blocks with thermal insulation. On the other hand, the best option for all types of buildings is the V6 variant with building envelope made of panels with a blown cellulose. In term of embodied energy and emissions of SO 2, the family house with wall system got the best rating whereas the worst was combination of RC frame with variant V4. For residential building and office building have better scores variants with light precast RC frame in combination with building envelope from wood, recycled materials and biomaterials. Figure 14: Family house alternative comparison results Figure 15: Residential house alternatives comparison results 11

12 Figure 16: Office building alternatives comparison results Increasing production of concrete is associated with increasing environmental impacts caused by high energy consumption and high non-renewable material use. It has been already shown that utilization of optimized light subtle concrete structures can result in reduction of concrete consumption up to 50 70%. This could be achieved e.g. by the use of high performance concrete with significantly better mechanical properties and higher durability in combination with shape optimization. The case study presented in the paper showed, that it is effective to combine light precast RC frame from High Performance Concrete with building envelope made of wood and biomaterials. Application of this approach can lead to environmental savings and represents important contribution to sustainable building. Acknowledgments This work was supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS10/009/OHK1/1T/11. The support is gratefully acknowledged. References: [1] MATUŠKA, T., ŠOUREK B. Solární tepelné soustavy Ústav techniky prostředí, Fakulta strojní 2008 prezentace. [2] HÁJEK, P., FIALA, C., TYWONIAK, J., BÍLEK, V.: Lehký prefabrikovaný skelet pro energeticky efektivní budovy 16. Betonářské dny 2009, Hradec Králové, ČBS ČSSI, 2009, pp , ISBN [3] WALTJEN, T.: Passivhaus-Bauteilkatalog Ökologisch bewertete Konstruktionen, Springer-Verlag, Wien, 2008, ISBN [4] SCHIEßL, P., STENGEL, T.: Der kumulierte Energieaufwand ausgewählter Baustoffe für die ökologische Bewetung von Betonbauteilen, Wissenschatl. Kurzbericht Nr.13,

13 [5] [6] FIALA, C., HÁJEK, P., KYNČLOVÁ, M.: Energeticky a environmentálně efektivní konstrukce s použitím HPC 7. konference Speciální betony, Skalský dvůr (Lísek), Sekurkon s.r.o., 2010, pp , ISBN