Study on the possibility of obtaining higher levels of ...

ECOTERRA - Journal of Environmental Research and Protection

www.ecoterra-online.ro 2019, Volume 16, Issue 2

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Study on the possibility of obtaining higher levels of energy efficiency using natural materials Marian Pruteanu, Fabian Tiba, Nadejda Calancea, Laura Cozmiuc

Faculty of Civil Engineering and Building Services, “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania. Corresponding author: M. Pruteanu, [email protected]

Abstract. The project aims to explore the possibility of implementing the passive house concept using natural materials, but also using modern technologies (solar panels) to achieve the desired energy efficiency while trying to reduce costs as much as possible. Climate changes, observed worldwide, are caused mostly by the impact of human activities. Nowadays, it is necessary to adopt solutions to considerably reduce the carbon footprint. In the field of civil engineering, the negative impact on the environment is generated by both the energy consumption required for building constructions and the energy consumption required to operate them. Therefore, the ideal execution solutions are buildings with high energy efficiency levels and low embodied energy. This also means constructing energy-efficient buildings, have minimum values. The paper presents a study meant to determine the maximum energy efficiency level that a residential building can achieve using as much as possible natural materials. Thereby, a case study was realised regarding energy efficiency, with the modelling of thermal bridges in the RDM 6 pro software. Determination of the annual heat ratio is made based on the simplified method presented by C107 – 2005 Norm, respectively by using the value of the global thermal insulation coefficient „G”. Also, for the calculus of the R-value, thermal proprieties of the materials used in the study are extracted from the C107 Norm and published literature. In the end, several conclusions and recommendations are pointed out in order to complete technical solutions to reach the level of passive house. Key Words: stabilized earth bricks, straw bales insulation, RDM modelling, passive house, embodied energy.

Introduction. In the current context, the existence of three main issues has been pointed out worldwide: the issue of preserving natural resources and of environment protection, the economic issue and the vernacular issue (UNEnvironment 2018). A challenge in this respect is to design constructions in balance with the nature. Therefore, starting from nature and then applying technology, working with the nature, striving to highlight it, is a noble but attainable ambition. However, the true challenge is to try and change the way we live with the environment (Searle 2011). The future of our civilisation depends on restoring the balance between the natural world and the urban jungle (Nullis 2019). When designing this residential building, we have tried to use as much as possible natural materials, thus adopting at the same time current technical solutions (solar panels, Canadian well/air to air heat exchanger, functional fireplace) in order to manage to integrate the passive house concept and to obtain the desired energetic efficiency (Mlecnik et al 2008). Through the intelligent use and combination of the natural materials in the construction of a residential building, one may achieve a healthy indoor setting and with maximum energy economy for indoor heating. Because Romania is rich in terms of resources, our purpose is to exploit and use them in an intelligent and constructive manner (MADR 2015; MAP 2018). This type of residential building is meant for persons who want to live in a healthy environment and who understand that an intelligent step for our evolution is getting closer to nature. Worldwide, the field of constructions made of ecological materials is in full bloom (Sutton et al 2011; Wall et al 2012). In many countries, governments encourage their use in the field of constructions; the local authorities are among the most important beneficiaries (Jones et al 2016). In Romania, the natural, ecological houses have become increasingly popular; more and more specialists are interested in this type of buildings (Tugui et al 2018). It has been proven that, by using the natural materials as building materials, energy is saved due to the low level of embodied energy which results to a reduced level of carbon dioxide emissions (Lee et al 2011). From the perspective of civil engineering, one of the possible solutions would be the construction of energy-efficient buildings involving annual energy consumption for heating that does not exceed 15 kWh/m2 per year, according to the Passivhaus Institute in Darmstadt. At the same time, the total primary conventional energy consumption



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obtained directly or indirectly from fossil fuels should not exceed 120 kWh/m2 per year (Passive House Institute 2015). The authors intended to check whether the "Passive house" energy efficiency level can be achieved for a residential building, built with traditional technologies specific to our country. For this purpose, a case study was carried out, in which the annual heat ratio was determined, for a ground floor height building, with the structure made of structural masonry walls from clay blocks stabilized with straw. The building was completely isolated with straw bales. In order to be able to have such thermal insulation on the inferior slab, it was chosen for it’s a ventilated solution. The upper slab under unheated attic was considered made of wood beams. The calculation of the annual heat ratio was performed using the simplified method of Norm C 107/2005, based on the value of the global thermal insulation coefficient "G". In order to reduce the energy consumption for heating caused by the ventilation of the building, a Canadian well was chosen, the allowed air temperature being considered 5oC.

Finally, a series of conclusions were drawn regarding the calculation made and recommendations were presented for obtaining the higher energy efficiency levels for the residential buildings, built in traditional technical solutions. Overview of the analyzed building. The building (the theoretical study was conducted between November 2018 - May 2019) was designed in such a way as to meet the needs and comfort of a modern family and it was made to test the efficiency of the natural materials by using a natural thermal insulation system of straw bales on the entire envelope of the building and adobe bricks masonry. The ventilation of the residential building will be ensured by a Canadian well assisted by air to air heat exchanger connected to air quality monitoring sensors. In order to reduce annual energy consumptions and to make the renewable energy use process more efficient, photovoltaic panels and solar panels are also part of the project. Furthermore, for the cold periods, a pellet-based functional fireplace must be installed.

The individual family residential building proposed for the theoretical study hereto is situated in the municipality of Iași, Romania. The conventional indoor temperature taken into account during the winter (Ti): 20oC; the conventional outdoor temperature taken into account during the cold periods of the year (Te): -18oC (in agreement with the climatic zoning map of the Romanian territory, for the winter period, for the municipality of Iaşi, the climatic area is III) (C 107/2005). The building is moderately sheltered; it is included in the medium permeability class, reason for which the number of air exchanges per hour will be considered to be equivalent with 0.6 [h-1]. To calculate the annual heating ratio, the following are taken into consideration: the annual number of degree-days calculated (N12

20): 3510 [K x days]; the conventional duration of the heating period (D12): 201 [days] (C 107/2005). The height regime of the building is the ground floor, with a rectangular shape in plane, with maximum dimensions of 11.8 m x 10.8 m. Net height is +2.60 m, while at eaves level +3.50 m The structural frame is made of resinous wooden planks with rectangular shape, with adobe brick walls masonry (Figure 1). The walls covering the outside will be thermally insulated on the outside using straw bales with a thickness of 35 cm that will be attached to the adobe brick walls using metal rods, with a plastic protection against condensation. The walls will be plastered on the inside and on the outside using clay-based plaster (Straube 2019). The floor above the ground level is made of wooden beams; on the upper and the lower side, there are wooden planks measuring 2 cm in thickness. On top of the floor, there will be a thermal insulation system made of 5 cm clay, covered by straw bales with a thickness of 35 cm. Between the clay level and the straw bales, a vapour barrier will be placed.



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Figure 1. Corner detail of the lower floor/outside wall. The building will have a continuous surface foundation layer comprising reinforced concrete beam networks in elevation, with wings on the outer outline to support the straw bale thermal insulation. The floor slab will be made of weakly reinforced concrete with a thickness of 10 cm (for further protection of straw bales thermal insulation) on a layer of gravel measuring 15 cm (Figure 2). Between the concrete slab and the gravel, a type of hydro-insulation will be installed. The thermal insulation of the floor slab will be executed within a ventilated system, using straw bales with a thickness of 35 cm within a rectangular system made of wooden planks (20 x 5). On the upper side, the floor will have a wooden finish. As for windows, three-layer stratified wooden frames windows will be used, the three layers comprising three special window layers designed with a triple fitting system for increased tightness.

Figure 2. Construction composition of the residential building studied.



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Physical characteristics. Buildings based on straw bales and/or unfired clay bricks have benefited lately from a constant development in Europe, but on a general note, the interest for this building solution (used together or separately) may be seen throughout the entire world, though the nature of materials is heterogeneous (Sutton et al 2011). The main advantage that comes with the use of such building techniques is related however to the energetic benefits and to environment protection (Lertwattanaruk & Choksiriwanna 2011). Certain aspects must be taken into account in this respect. Thermal conductivity Thermal conductivity of straw bales. The literature available on this topic comprises two distinct values which may be found for thermal conductivity of straw bales: perpendicular on the fibre orientation and parallel on it. Subsequent developments have taken into account the influence of density and the effect of the relative humidity of straws (the increase in thermal conductivity is linear when relative humidity ranges from 10 to 90%). The Table 1 features a synthesis of the findings obtained by various authors.

Table 1

Thermal conductivity of straw bales

It is worth noting a decrease in thermal conductivity when shifting from the parallel to the perpendicular direction. Nonetheless, it is impossible to state beyond any doubt the direction of straws inside the ballot, given that their direction is actually quite chaotic, as reported by the study of Shea et al (2013); this is why another value is given by the density of the straw ballot (Costes et al 2017). The measurements made within this project have shown similar values for the perpendicular and parallel direction with the direction of straws (λparallel=0.0557 [W/mK] and λperpendicular=0.0561 [W/mK]). This study will use the value of 0.06 [W/mK]. Thermal conductivity of adobe bricks. Regarding the conductivity of adobe bricks, we considered it necessary to study a certain composition, given the diversity hereof encountered in the scientific literature (Călătan 2018). Thus, the optimal mixture was determined to be the one featuring the following composition: 63% clay + 35% sand + 2% paste lime and the replacement of water by a 1.25 % solution of bone glue. This mixture has a density of 1.900 kg/m3, downward strength of 4.1 N/mm2 and a bending stress of 1.4 N/mm2. The lime was preserved because it improves mechanical strengths over time, as well as water resistance. Because the goal was to have a density as close as possible to the value within the scientific literature, axial contractions as low as possible, lower thermal conductivity, it has been assessed that the recommended amount of straws introduced into the mixture ranges between 30 and 40% volume percentages;

Author Density [kg/m3] Fibre orientation Thermal conductivity [W/mK]

perpendicular 0.0487 McCabe (1993)

130 parallel 0.0605

63 0.0594 76 0.0621 85 0.0619 107 0.0642 114 0.0642

Shea et al (2013)

123

unspecified

0.0636 perpendicular 0.052 DIB 90-110

parallel 0.08 51 0.061 Pruteanu

(2010) 76 unspecified

0.053 perpendicular 0.0561 Personal

measurements -

parallel 0.0557



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this area also records the highest increase in bending tensile stress, as well as the lowest reduction of downward strength. The determination of this interval was also supported by the effective workability of the mixture in various experiments. Hence, a value of the thermal conductivity coefficient of 0.32 [W/mK] may be considered acceptable (Călătan 2018). The adobe brick walls have the ability to store heat and to release it when necessary. Fire resistance and water vapour permeability. The discussions emerging when it comes to fire resistance are a logical consequence of the fact that straw bales are used as thermal insulation material. The fire resistance condition is one of the most important requirements that constructions must meet. The fire tests of straw bale structures or insulations using this material are scarce in the scientific literature, but their findings are satisfactory, thus recommending the use of straw bales (Marković & Milić 2018; 1-HR 2007). This is far from surprising: given the high degree of compression, inside the ballots there is no air facilitating burn (an analogy thereof would be the fire resistance of a book compared to the one of a piece of paper). Furthermore, the dirt and clay within the plaster exposed to fire turn into a ceramic mass through which it is very difficult for flames to penetrate. Concerning clay, it may be stated that it does not entail fire resistance issues. Scientific literature is poor in information and studies concerning the permeability to water vapours of straw bales, reason for which an estimate may be made by comparison to the permeability to vapours of the natural materials with high porosity; hence, the value we can expect is µ = 110-210 ng/Pa s m2, for a thickness of approximately 450 mm. Special attention will be paid to protection against moisture, through the types of plaster and finishing elements used; hence, the water vapours can cross insulation, not stationing in it. Therefore, interior plaster will be based on lime, sand and clay, while for the exterior a porous plaster will be used with impermeable elements in the mounting area. Generally, liquid transfer by straw insulation has no practical importance because liquid water must be preventing from reaching the straw insulation. The nutritional value of the straws is insignificant, but the value increases in contact with the water (mineral sources) (Reiter et al 2015). Concerning the adobe bricks, the main advantage, besides allowing the water vapours to circulate, have a very important role for health, having the property of regulating humidity from the inside, maintaining it between 40 and 60% (Lertwattanaruk & Choksiriwanna 2011). Various studies have reported that water vapour permeability is closely connected to the straw percentage within the composition and to the porosity of adobe bricks. It is apparent that adobe bricks, as well as the clay and lime-based plaster, must be protected by the direct contact with the water. To this end, wider eaves will be used, while the most exposed areas may be treated using flax oil (regarding which the studies have demonstrated very good results) (Călătan 2018). Thermal insulation Determination of the unidirectional specific thermal resistances of the envelope elements “R”. It could be seen in the Tables 2-4 and equations 1-3.

Table 2 Exterior wall stratification

Composition dj [m] λj [W/mK] Interior plaster 0.03 0.6 Adobe bricks 0.25 0.32

Straw insulation 0.35 0.060 Exterior plaster 0.04 0.6



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Table 3

Upper floor stratification

Composition dj [m] λj [W/mK] Straw insulation 0.35 0.060 Vapour barrier - - Clay protection 0.05 0.5

Wood 0.02 0.17 Air layer 0.10 - Wood 0.02 0.17

Table 4

Lower floor stratification

Composition dj [m] λj [W/mK] Floor 0.025 0.24

Air layer 0.025 - Straw insulation 0.35 0.060

Air layer 0.05 - WR concrete slab 0.1 - Hydro-insulation - -

Gravel 0.15 - Soil 2 -

Concerning thermal bridges, it has been theoretically determined, using a modelling software (RDM 6.17), that the residential building studied does not have thermal bridges. Nonetheless, unidirectional specific thermal resistance for the lower floor was corrected by 15% due to the thermal bridges created by the wooden structure:

R`=6.176 x 15%=5.2496 [m2K/W] Determination of the thermal characteristics of the building and calculation of the global thermal insulation coefficient “G”. Is presented in Table 5 and equation 4.

Vinc = 120 x 2.60 = 312 m3 ; n = 0.6 h-1



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Table 5 Thermal characteristics of the building

Envelope element Area [m2] R’ [m2K/W] τ (A x τ) / R’ Exterior walls N 33.6 6.617 1 5.078 Exterior walls S 33.6 6.617 1 5.078 Exterior walls E 36.6 6.617 1 5.531 Exterior walls W 36.6 6.617 1 5.531

Exterior carpentry N 3.15 0.770 1 4.091 Exterior carpentry S 6.15 0.770 1 7.987 Exterior carpentry E 6.54 0.770 1 8.493 Exterior carpentry W 2.76 0.770 1 3.584

Upper floor underneath a non-heated attic 120 6.439 0.868 16.175 Floor slab 120 5.250 0.473 10.811

TOTAL 72.362 The C 107/2005 Norm, updated in 2011, and the Methodology calculated MC 001/2006 mention that the losses in normal conditions of refreshing the air indoors, as well as the additional heat losses, due to excess infiltration of air from the outside, which may penetrate the of the carpentry (Pruteanu 2010; Bouasker et al 2014; Sluser et al 2017), in correlation with the building volume V and temperature difference T = Tj -Te, have the value 0.34·n [W/m3K], where: - n – the natural ventilation speed of the building, namely the number of air exchanges per hour[h-1]; - 0.34 represents the product between mass heat capacity (ca = 1000 W. s/(kg.K)) and the apparent air density (ρa = 1.23 kg/m3), values characteristic to air at a temperature of 10°C. In order to take into consideration the lower temperature difference between the indoor air and the air let in for refreshing, it is necessary to determine a correction coefficient for the value 0.34, with the following relation:

Hence,

0.34 · C · n = 0.34 · 0.394 · n = 0.13396 · n [W/m3K] (6) Annual heat ratio. The following formula is used for calculating the annual heat ratio:

where: G = 0.312 [W/m3K] (the global thermal insulation coefficient of the building); N12

Өi = N1220 = 3510 [k x days] (N12

Өi = N1220 – (20-Өi) x D12 – for Iaşi, climatic area III, the annual number of degree-days calculated N1220 = 3510. And the conventional duration of the heating period, corresponding to the outside temperature that marks the onset and the cessation of heat (12oC), D12 = 201); C = 0.867 (the correction coefficient corresponding to an installation featuring an automated thermal regulation device in the area of Iaşi); Qi = 7 [kWh/m3 x an] (internal heat contribution, resulting by the building being inhabited, corresponding to a m3 of heated volume); Qs = the heat contribution due to sun radiation, corresponding to a m3 of heated volume, is calculated using data from Table 6 and the formula below:



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Table 6 Calculation heat contribution due to sun radiation (Qs)

Orientation D12 ITj IGj gi Volume [m3] Area [m2] Subtotal

North 19.4 93.5856 3.15 0.425 South 82.1 396.0504 6.15 3.513 East 44 212.256 6.54

2.002

West

201

44 212.256

0.45 312

2.76 0.845 Total (Qs/0.40) 6.785

Qs = 2.714 [kWh/m3 • an] Therefore, Q = 13.073 [kWh/m3 • year]. Multiplying this with 2.60, the heated height of the studied house, the result is: Q = 33.99 [kWh/m2 • year]. Therefore, the efficiency level for passive house, as required by the Passive House Institute (2015) cannot be attained in these conditions. Energy embodied in the superstructure. The following values of the materials of interest for the study hereto have been taken into account for the calculations (Table 7):

Table 7

Characteristics of the materials used

Name of the material Density [kg/m3] Energy embodied per mass unit [MJ/kg] Straw bales 100 0.5 Adobe bricks 1900 0.3

Clay-based plaster 2000 0.4 Wood 400 0.7

With these values, the approximate level of the energy embodied in the superstructure is 228.864 MJ, a value lower than the one of a similar residential building built using classic materials. Conclusions and development perspectives. The use of thermal insulation with natural materials (straw bales) and adapted building techniques leads to high energetic efficiency levels. By using masonry comprising adobe bricks, the indoor comfort increases for the beneficiaries of the residential building. Clay, straws and wood, without excessive processing, show a natural combination with promising results, worth of subsequent developments and studies. It is mandatory to use the latest technologies and techniques (modern ventilation systems with heat retrievers, photovoltaic and thermal panels, effective heating devices). The use of natural materials has led to a decrease by 5 to 10 times of the embodied energy, which stands to prove the reliability and necessity of getting a better insight into the findings of this study. The subsequent development directions will focus on experimental analysis, costs and structural calculations. References Bouasker M., Belayachi N., Hoxha D., Al-Mukhtar M., 2014 Physical characterization of

natural straw fibers as aggregates for construction materials applications. Materials 7(4):3034-3048.

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2017 Thermal conductivity of straw bales: full size measurements considering the direction of the heat flow. Buildings 7(11), doi:10.3390/buildings7010011.



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Received: 12 April 2019. Accepted: 28 May 2019. Published online: 30 June 2019. Authors: Marian Pruteanu, Department of Civil and Industrial Engineering, Faculty of Civil Engineering and Building Services, “Gheorghe Asachi” Technical University of Iasi, Blvd. Prof. D. Mnageron no. 67, 700050 Iasi, Romania, e-mail: [email protected] Fabian Tiba, Faculty of Civil Engineering and Building Services, “Gheorghe Asachi” Technical University of Iasi, Blvd. Prof. D. Mnageron no. 67, 700050 Iasi, Romania, e-mail: [email protected] Nadejda Calancea, Faculty of Civil Engineering and Building Services, “Gheorghe Asachi” Technical University of Iasi, Blvd. Prof. D. Mnageron no. 67, 700050 Iasi, Romania, e-mail: [email protected] Laura Cozmiuc, Faculty of Civil Engineering and Building Services, “Gheorghe Asachi” Technical University of Iasi, Blvd. Prof. D. Mnageron no. 67, 700050 Iasi, Romania, e-mail: [email protected] This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited. How to cite this article: Pruteanu M., Tiba F., Calancea N., Cozmiuc L., 2019 Study on the possibility of obtaining higher levels of energy efficiency using natural materials. Ecoterra 16(2):29-38.

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