Energy performance and environmental and economic assessment of the platform frame system with compressed straw

Accepted Manuscript

ENERGY PERFORMANCE AND ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF THE PLATFORM FRAME SYSTEM WITH COMPRESSED STRAW Stefano Cascone , Federico Catania , Antonio Gagliano , Gaetano Sciuto PII: DOI: Reference:

S0378-7788(17)32681-6 10.1016/j.enbuild.2018.01.035 ENB 8295

To appear in:

Energy & Buildings

Received date: Revised date: Accepted date:

4 August 2017 6 December 2017 6 January 2018

Please cite this article as: Stefano Cascone , Federico Catania , Antonio Gagliano , Gaetano Sciuto , ENERGY PERFORMANCE AND ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF THE PLATFORM FRAME SYSTEM WITH COMPRESSED STRAW, Energy & Buildings (2018), doi: 10.1016/j.enbuild.2018.01.035

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ACCEPTED MANUSCRIPT Highlights Platform frame system with a filling in compressed straw as insulating material

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Use of natural materials derived from agricultural waste in the construction process

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Performance comparison between XLAM system and platform frame system

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The thermo-physical properties of the proposed construction system were assessed

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Comparative environmental and economic analyses

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ENERGY PERFORMANCE AND ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF THE PLATFORM FRAME SYSTEM WITH COMPRESSED STRAW a,

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Stefano Cascone *, Federico Catania , Antonio Gagliano , Gaetano Sciuto a

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Department Civil Engineering and Architecture, University of Catania, Via Santa Sofia 64, 95123, Catania,

Italy b

Department of Electrical, Electronics and Computer Engineering, University of Catania, Viale Andrea Doria

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6, 95125, Catania, Italy

* Corresponding author. E-mail address: [email protected] (S. Cascone) Abstract

In recent years there have been considerable improvements in the energy and environmental performance

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of buildings, due not only to the creation of building envelopes with a low level of thermal transmittance but also to the use of natural (“green”) materials. Construction systems combining a wooden framework with eco-compatible materials represent solutions for a building envelope, which prove effective in reducing both energy needs and the discharge of polluting substances. The principal aim of the present research is to

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investigate the use of natural waste materials from farm products in the creation of building envelopes. The system described here proposes the use of compressed straw to obtain a layer of insulating material, that

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may be combined with the use of a wooden shell known as platform frame. The thermo-physical characteristics, energy performance as well as the hygrometric features of the proposed

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system were tested in various sites. As regard the formation of condensation, the thermo-hygrometric

observed.

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analysis proved the absence of such threat over a period of a whole year in all the different climates

A comparison with a similar XLAM system evidenced that the platform frame system lined internally with

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compressed straw offers a 12% reduction in U thermal transmittance, a 22% improvement in YIE periodic thermal transmittance, and a comparable thermal lag. Moreover, the platform frame system filled with compressed straw allows a cost reduction by 38% compared to the XLAM system. On the whole, the outcomes obtained indicate that the platform frame system with compressed straw offers a suitable alternative to the XLAM system, above all in the case of buildings of two or three stories.

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Keywords: compressed straw, wooden envelope, XLAM, platform frame, hygrometric assessment, energy consumption

1. Introduction Recent studies [1] have shown that over 35% of the total energy production is used for the air-conditioning of

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buildings. Thereby building energy consumptions are imputable of over 19% of the Greenhouse Gases into the atmosphere. The forecasts indicate that these values may be doubled over the next thirty years. A priority for all energy policies is therefore a reduction in energy consumption for the heating and/or cooling of buildings, in order to mitigate those environmental impacts linked above all to climate change. To reduce energy consumption in this field, it is essential to improve the energy performance of building envelopes,

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reducing the loss of heat during the winter months and avoiding overheating in the summer period.

In recent years, attempts have been made to improve the energy efficiency of buildings, not only through the creation of building envelopes with a low coefficient of thermal transmittance, but also with the use of natural materials with a low intrinsic energy content, (embodied energy), nontoxic and with notable environmental-

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friendly characteristics, which discharge a minimum of polluting substances into the air during their entire lifecycle. The environmental impact of construction can be greatly reduced by the use of eco-compatible

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materials instead of traditional ones [2]. Such materials may be used both for the realization of natural thermal insulators of the building envelope as well as like vertical component of the building shell [3]. The

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use of construction systems in wood combined with other natural materials represents an effective strategy to reduce both the consumption of primary energy produced from fossil sources and the discharge of

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polluting substances. Tests performed in order to determine life-cycle (LCA) have proved the benefits in terms of a mitigation in climate change thanks to the use of wood-based construction materials [4]. The

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energy consumed for the extraction, transport, transformation and assembly of raw materials represents in fact a significant part of the energy consumption involved in the total life-cycle of buildings, together with the production of polluting substances and CO 2[5][6]. A number of studies [7][8][9] have demonstrated that buildings realized in wood preserve a high level of eco-performance for their entire life-cycle. Over the last decades, above all in Europe, technologies known as CLT (Cross Laminated Timber) or XLAM (Cross Laminated) have become widespread. These, unlike the light framework system (timber framing), make use of massive structural walls realized entirely in wood. The XLAM system may be used effectively for the realization of multi-storey buildings, while for those of a single floor the timber framing system may be

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used as an alternative to XLAM. In order to optimize thermo-physical performance, the massive system in XLAM is prevalently used in climates like the Mediterranean one. As well known, the Mediterranean climate is characterized by hot summers and mild winters, as well as by wide daily temperature ranges. In winter, when the principal aim is to reduce heat loss from inside to outside, it is necessary to increase the thickness of the insulating materials used. On the other hand, during the hot season, it is necessary to reduce solar gains during the hottest central hours, while at night the aim is to

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disperse the heat accumulated during the day. It is therefore advisable that the elements of the shell should possess is thermal inertia [10][11], which may interact in a dynamic manner with the external climatic conditions [12][13][14] and allow a reduction in energy consumption for the use of air-conditioning systems. The improvement of thermal resistance in the building envelope of wooden buildings has become a priority

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requirement at the project stage, where wood-fiber based insulating materials are used as much as possible [15].

Recently, the construction sector has shown growing interest in the developing of new insulating panels capable of combining both excellent thermo-physical performance and low costs during the entire life-cycle

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of the building. Between those, the promotion of product recovered from discarded agricultural waste is particularly attractive being environmentally appropriate and economically viable.

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It has been estimated that the replacement of common insulating panels present on the market (e.g. stone wool, glass wool or expanded polystyrene) with others created from cellulose fiber allows to reduce by 39%

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fossil fuels, and by 6-8% in CO2 emissions [16].

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A number of studies have been carried out to assess the thermo-physical properties of insulating materials obtained from natural fibers. It has been demonstrated that an insulating panel produced from cotton stalk

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fibers has an energy performance comparable to the materials commonly used in insulating panels [17]. Agoudjil et al. [18] and Ali [19] have shown that wood and superficial date-palm fibers may be used in the production of high-performance insulating panels. Moreover, natural fibers may be added to the concrete mix, in order to reduce energy consumption by as much as 45% compared to concrete realized with the traditional mix and also to regulate relative humidity in the interior rooms [20]. Recent studies performed in Hungary [21] propose the realization of insulating panels in material derived from the bark of the black cedar, obtaining levels of heat conductivity around 0.6 W/(m K), with a discharge of formaldehyde lower than that of the other panels at present on the market. Kangcheng et al. [22] have produced a thermal insulator obtained with the high-temperature compression of rice straw, achieving a rate

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of heat conduction of 0.051 - 0.053 W/(m K) with a density di 250 kg/m , resulting in excellent thermophysical and mechanical properties. In Germany, meticulous studies carried out on a building entirely realized in straw bales [23] have established the excellent qualities of energy and environmental comfort of such a material. Further studies on the use of insulating materials realized with linen fibers, hemp and jute, have been performed by Korjenic et al. [24], demonstrating the comparability, in terms of thermo-physical qualities, between these natural fibers and conventional insulating materials. Given the greater sensitivity of

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natural fibers to factors of decomposition, such as humidity content, temperature and the attack of microorganisms, particular attention was paid in order to estimate the durability of building components realized with natural materials.

Straw is a product of natural origin obtained from the cultivation of cereals: it is economical, easy to work and

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to transport, and readily available, especially in those regions where the cultivation of cereals is widespread. Being a by-product of cereal farming, its production is in surplus compared to market requirements. This material is used, in the form of compressed bales, to realize the envelope of buildings with a high level of energy performance and durability [23]. Moreover, as a result of specific interventions at the project stage,

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bales of straw prove also to possess excellent fire-resistant qualities [25].

There is a lack of studies in the literature which combine the use of straw as a thermal insulator with wooden

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frameworks of the platform frame type.

The present work aims to assess the performance of a technological solution consisting of a vertical closure,

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combining the platform frame (PF) system with a filling in compressed straw as an insulating material.

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In addition, the energy performances of the proposed construction system were compared to that of an

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analogous system realized with the XLAM technology under different meteorological climates.

2. Material and Method In the first stage of the research, the performance of two different wooden envelopes were analyzed: the first one constituted with XLAM and the second with a platform frame system, which is a framework filled with natural fibers of compressed straw. Following this, energy consumptions were estimated in different climatic conditions, for a building chosen as reference case, both in the case with a structure in XLAM and in the case where the platform frame system

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filled with compressed straw is used. Finally, comparative analyses were carried out in order to assess whether the platform frame system with compressed straw might be preferable to the XLAM system regarding both the environmental and economic performance.

2.1. Compressed straw As demonstrated by literature experimental studies [17][22] aimed at determining the features of insulating

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materials derived from compressed natural fibers, density is a fundamental parameter to determine both the mechanical and the thermo-physical properties. Specifically, the straw is compressed sufficiently in order to obtain the required density. These studies, have proven that the ratio between the density of the straw and its thermal conductivity, in fact thermal transmittance and therefore thermal conductivity increase as density

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increases. This occurs because the empty spaces between the fibers have a lower thermal conductivity than the fibers themselves, therefore with a high density of the straw there are fewer empty spaces and the heat conduction throughout the material is greater.

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The densities generally used for compressed straw vary from 150 to 450 kg/m . In the case of cotton stalk fibers, according to the density chosen, the values of thermal conductivity “k” vary from 0.06 to 0.08 W/mK,

varies less according to density.

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while in the case of rice straw, k remains between 0.047 and 0.06 W/mK, therefore thermal conductivity

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The values of density and thermal conductivity of compressed straw used for the present research were those established experimentally in previous studies [17]. Variations in density, at a constant thickness, lead

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to different values of thermal lag, measured according to the standards of the regulation EN ISO 13786 [26]. The values of density, thermal conductivity, thermal transmittance and thermal lag are set out in Table 1.

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These values are referred to compressed straw thickness of 80 mm that is the same as the gap width in the platform frame system proposed. In this study, it was adopted a compressed straw with a density of 300 3

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kg/m and thermal conductivity λ = 0.075 W/mK. This choice could represent a compromise in terms of both thermal insulation and thermal inertia performance. Straw is a natural material requiring little energy to be transformed, so it has a low value of embodied energy. The embodied energy can be defined as the energy consumed during the construction of the building and its components, from extraction and processing of natural resources to manufacturing, transport and delivery. Embodied energy does not include energy consumed during the building operational phase. Previous studies [27] have made detailed calculations on the possible built-in energy within straw used as building material. This value depends on many local variables such as transport vehicles used, use of

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herbicides and fertilizers, human labor, distance travelled. In study [27] it has been proved that one kg of cereal straw incorporates about 1.2 MJ, including transport. This value is very low when compared to high embodied energy values reached by the most common building materials, ranging from 2.0 MJ/kg to more than 200 MJ/kg [28].

2.2. Description of the two technological systems

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Globally, the two technological systems have the same thickness, 21.3 cm, as reported in Table 4. Figure 1 shows the horizontal section of the two panels representing the constructive systems examined. The platform frame system consists of 80 x 80 mm vertical posts in coniferous wood, braced on both sides with 10 mm boards in OSB/3. The distance between one vertical wooden post and the other is 625 mm.

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In the Platform frame system, the gap between the vertical posts is entirely filled with compressed straw. This combines the advantages deriving from the use of a construction system in light wooden framework with the use of low-cost natural insulating materials derived from agricultural waste with very low embodied energy.

In order to ensure both a high level of quality control during the assembly stage of the vertical closure and a

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speedy assembly process on site, these panels may be pre-assembled in advance in the workshop where the framework is created and the internal gap filled with compressed straw.

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The thermo-physical properties of XLAM panels are not univocal since there are a number of variables associated with each area of production and installation. For example, each producer of panels uses

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different thicknesses and adhesives, moreover, the number of layers of wood used to create the panels, their homogeneity and arrangement, are all important factors.

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For these reasons, the values of the thermo-physical features used within the present study were those supplied by the producers of the XLAM panels in the building chosen as case study ( see Table 2.)

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The stratigraphy of the vertical platform frame system is shown in Table 3. The thermo-physical values of the panels in OSB were taken from the European international regulation EN 13986 [29]. The thermo-physical parameters that characterize the performance of a vertical facade, besides transmittance, are the thermal lag and periodic thermal transmittance. These parameters were calculated according to the guidelines set down in the norms ISO 13786 [26]. With reference only to the panels with a structural function (100 mm thick), the XLAM system showed a value 2

of thermal transmittance of 1.06 W/m K, while the platform frame panels with compressed straw had a 2

thermal transmittance of 0.72 W/m K.

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The difference in these two values indicates that the introduction of compressed straw in the platform frame panels provide a clear plus in terms of thermal transmittance, that is by 32% lower than the XLAM system. Subsequently, the thermo-physical parameters were assessed for the entire vertical cladding, including both the panels defined above and the remaining layers completing the facade. Table 7 shows the thermo-physical parameters of the two vertical facades, which have the same total thickness.

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As predictable, the two systems have fairly comparable features, although the thermo-physical properties of the platform frame system filled with compressed straw prove slightly superior to those of the XLAM system. Indeed, the XLAM system presents lower values for both thermal (22%) and periodic transmittance (12%) and a higher value of thermal lag (30’).

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Both system presents excellent thermo-physical properties, especially during the cooling season, when the thermal flow from outside is transmitted to the interior with a delay of over 12 hours. Moreover, the envelope realized with the platform frame system has lower surface mass density which is not so far compared to XLAM system, that is about 13%.

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2.3. Hygrometric test

The platform frame system with compressed straw contains no anti-steam barriers and therefore guarantees

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permeability to water vapor. Moreover, the insulating material used to enhance thermal insulation is realized in wood fibers, which are more permeable to steam than the insulating materials in EPS commonly used in

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Europe. As specified in a number of studies [30], insulating layers realized in non-synthetic and breathable

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materials play an important part in improving the hygrometric characteristics of building envelopes. In addition, R. McClung et al. [31] maintain that materials with a low level of permeability, such as

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polyethylene and steam-resistant barriers, may result in a slow drying-out of the wooden material constituting the vertical cladding system, and therefore should be used with attention. In particular, when a source of vapor is present internally, steam-resistant barriers may slow down the elimination process, resulting in a phenomenon of decay of the wood fibers and consequently a reduction in both thermo-physical performance and durability. The findings of L. Wang, H. Ge [32] have shown that building envelopes realized in XLAM and assembled with low-permeability steam barriers present a greater risk of problems arising from damp compared to envelopes without steam barriers. This finding underlines the importance of the breathability of the vertical cladding, allowing the passage of steam and avoiding localized patches of damp.

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The purpose of the hygrometric tests is to assess the efficiency of the platform frame system with compressed straw, the performance of which may vary according to the presence of damp and the contact with water. This implies that the use of straw as a construction material must be evaluated on the basis of parameters related to the migration of steam, because if there should be the presence of interstitial condensed water vapor, this would jeopardize the energy performance of the entire vertical envelope, risking the decomposition of the straw and the formation of mildew and fungi.

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In order to verify the formation of superficial and interstitial condensation in the proposed system, reference was made to the regulation ISO 13788 [33]. The tests were performed using the DesignBuilder software, inserting values of temperature and humidity characteristic of the climatic area.

The efficiency of the system was tested under different typical climatic conditions, in order to identify any

vapor, to apply the construction system proposed.

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geographic areas in which it might be potentially inadvisable, owing to the risk of formation of condensed

The climatic areas considered are representative of the typical conditions present on the European continent

envelope proposed at different latitudes.

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and therefore make it possible to assess the variations in thermo-hygrometric performance of the types of

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Specifically, the following areas were selected: Catania, representing the Mediterranean climate with dry summers (according to the Köppen classification Csa); Amsterdam-Schiphol, representing the mild humid

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oceanic climate with warm summers (defined as Cfb) and Stockholm-Arlanda, for the boreal climate, defined as Dfb in the Köppen classification.

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The class of humidity adopted according to the existing regulations is number 2, which establishes the

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internal supply of water vapor for areas destined for use as offices.

2.4. Reference Building The building chosen for the case study is situated in Giarre (latitude 37°43′27″ N, longitude 15°10′53″ E), Catania (Italy). This building uses a construction system in XLAM, with a single storey (Fig. 2) and its destined use is as the offices of a large hospital.

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The modeling of the building was carried out by means of the software DesignBuilder 5.0.3[34], graphic interface of the open source calculation code EnergyPlus 8.5[35]. During the modelingstage, it was necessary to know both the climatic features of the geographic area where the building is situated and the thermo-physical properties of the opaque and transparent envelope of the building, as well as those of the air conditioning system installed for both the heating and cooling of the interior.

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Two different analyses were performed, the first using the stratigraphy of the existing building envelope realized in XLAM, the second on the hypothesis of adopting the platform frame construction system, of the same thickness, with the gap between the two OSB boards filled with compressed straw.

For the modeling of the components of the opaque envelope of the building, the stratigraphies of the

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dispersing elements were inserted. Besides the system in XLAM described above, the vertical cladding also contains a series of layers for the purpose of thermal insulation and the superficial finishing. The characteristics of the opaque building envelope are shown in Table 4, 5 and 6. Some of the data reported in those are provided by manufacturers, other values are obtained from international manuals and regulations [36][37][38][39].

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The transparent building envelope consists of double glazing, with a transmittance of Ug=1.94 W/m K and an 2

aluminum frame with thermal break, 50 mm thick. The transmittance of the frame is equal to U F=2.47 W/m K.

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The total transmittance of the window was calculated using the formula provided by the UNI ISO 10077-1

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[40],

(1)

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For the existing standard openings, 1.00 m high and 2.75 m wide, the global transmittance of the window, 2

results to 2.15 W/m K. The thermal breaks were evaluated assuming a linear coefficient of transmittance

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by 0.06, with a length, between glass and frame, by 7.18 m. With regard to the air conditioning system, the existing heating system is fueled by natural gas, with a seasonal yield of 0.85. Hot water for domestic use is also provided by natural gas fuel, by means of a specific boiler. The cooling system uses electricity from the mains while the thermal unit consists of a chiller, with a seasonal COP of /1.80. For the endogenous loads due to human activity and to electrical and electronic appliances, the templates adopted were those for use in office buildings. In particular, a metabolic rate of 123 W per person and an

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average density of 0.111 people per m were considered. Regarding the presence of office equipment in use, 2

a value of 11.77 W/m was considered, with a daily use compatible with office hours. The results of the simulation for both the systems of vertical cladding gave the monthly energy consumption for both heating and cooling.

3. Results and discussion

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The energy consumption of the case study building have been calculated with reference to the three different climatic conditions investigated. The adoption of one construction system rather than the other results in different energy requirements.

Fig. 3, 4 and 5 depict the energy consumption in kWh required to heat and cool the interior of the building, in

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both summer and winter, using the platform frame system and the XLAM system.

It is possible to observe that the energy required for the heating and the cooling of the building is comparable for the two constructive systems.

The annual energy requirements for heating and cooling are shown in Table 8. In colder climates, heating costs are higher than those for cooling. The platform frame system provides better

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performance during winter, resulting in lower energy consumption around 1% compared to the XLAM system. During the summer season, the platform frame system entails an increase in energy consumption, in

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spite of this, as annual consumption is concerned, there is still energy saving, which is more pronounced in colder climates. The energy-saving values of the platform frame system with compressed straw and the

saving performance.

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XLAM system proved to be comparable, with the platform frame system showing a slightly better energy-

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Further advantages of the system proposed derive from the use of high-density straw panels, especially during the summer period: owing to the increased thermal inertia compared to lighter shells, energy

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consumption may be reduced and therefore also lowering the CO2 emission into the atmosphere [41]. In Table 9 the platform frame system reduces thermal dispersion through the opaque vertical envelope in all three climatic conditions considered, compared to the XLAM system. The platform frame system implies an 2

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improvement in the total thermal transmittance of vertical walls by 12% (from 0.25 W/m K to 0.22 W/m K). This improvement is quantifiable with a reduction of approximately 9-10% of the thermal dispersions through the vertical walls.

3.1. Hygrometric tests

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In order to compare the thermo-hygrometric performance of structures with different stratigraphies, it is possible to apply the equivalent air (layer) thickness sd defined as the thickness of the air layer, in meters, which has a resistance to the passage of water vapor equal to that of the wall under study. sd=µ∆x

(2)

Where µ is the factor of permeability to water vapor, ∆x represents the thickness in meters of the layer considered.

thicknesses.

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If a material is very permeable it will have a very low value of µ and this will result in equivalently reduced air

Figure 6 shows Glaser Diagrams, obtained according to the directives of the regulation ISO 13788 [38], of the two construction systems in the three different climatic conditions. These diagrams were derived with the

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use of the border conditions indicated in Table 10.

Although the thickness of both systems (platform frame and XLAM) is the same, 213 mm, it may be observed that the XLAM system presents an air thickness equal to around 6 m, while the PF system has an air thickness equivalent to 2.33 m. This indicates that the XLAM system offers a greater resistance to the passage of water vapor and it is less breathable.

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The Glaser diagrams (Fig. 6) show that for both the layered systems there are no interstitial condensation problems in the layer containing compressed straw, even during the coldest months of the climates studied,

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when there is a greater risk of condensation and stagnation. The system with compressed straw is therefore applicable in all three of the climatic areas considered, since it has been demonstrated that there is no risk of

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water stagnating inside the insulating cavity, causing its rapid decay. In the platform frame system, for the Mediterranean climate of Catania, there is always a considerable

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distance, up to the most external layer, between the partial pressure curve of the water vapor and the saturation curve of the same. Otherwise, when the climatic conditions become colder, (e.g. Stockholm) the

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distance between the partial pressure curve of the water vapor and the saturation curve is severely reduced, thus the two curves are almost equal in such climatic area. Anyway, the most critical area falls in the more external layer, while in the gap filled with compressed straw, which is the zone presenting the highest risk of condensation problems, the partial pressure of the water vapor is sufficiently far from saturation conditions, thus there are not risks of the formation of condensation in this zone.

3.2 Economic and environmental considerations

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The results of the tests to assess thermal and hygrometric performance show that the two construction systems are almost equivalent, though with some advantages for the platform frame system. The elements to be considered in the choice of one constructive system rather than another are therefore more generally of an environmental and economic nature. The aim is to demonstrate the advantages of one technical solution which proposes the use of products derived from farm waste, which would normally be wasted. Moreover, farm waste material is often subject to

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incineration, which results in the discharge into the atmosphere of a further unknown quantity of greenhouse gas.

3.3. Costs of the XLAM system

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The prices of massive wood used as a construction material vary considerably according to the geographic area, the wood veneer considered and the volume of timber required. Red pinewood, very common in Alpine Italy and Austria, is used as a raw material for wooden constructions and for the production of XLAM. The unit price, derived as a result of market research carried out among local producers of XLAM panels, is 3

equal to 800 €/m . The price includes the processing of the boards of red pinewood, the cutting, the

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longitudinal and transversal joining and the hot adhesive gluing of the strips.

A basic modular panel has standard dimensions of 1.25 x 3.0 m x 0.10 mm. The wood is arranged in three 2

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layers of equal size, each 33 mm thick. The surface of a standard-dimension module is of 3.75 m . The total volume of red pinewood used for a panel with this standard surface area, together with the cost of

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each module, are set out in Table 11.

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3.4. Costs of the platform frame system

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The assembly of a platform frame panel requires a greater investment in manpower as well as the use of metal joints to connect vertical posts and horizontal crossbeams and to fix the frame to the OSB panels. Moreover, particular tilting pallets and cranes are required to allow the insertion of the compressed straw in 3

the interstices. Therefore, although the price of the materials used is about 500 €/m , the total cost of the 3

preparation and assembly of the wooden framework amounts to about 3000 €/m . A single panel of the platform frame system of the same dimensions as the panel in XLAM, 1.25meters long, consists of two 2.84 m high posts, 80 x 80 mm and two 80 x 80 mm cross beams. The total volume V of wood required is 0.052 m

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With regard to the paneling in 10 mm OSB/3, 2 × 3.75 m of panels are required, with a cost on the Italian 2

market of about 4 €/m . 3

About 75 kg of compressed straw, at a density of 300 kg/m , are required to fill the 80 mm. interstices. The average price, calculated over the last 12 months in Italy, is about 1.1 €/ton, that is 0.11 €cent/kg.

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Table 12 shows a breakdown of the costs to produce a modular panel in platform frame.

3.5. Costs comparison

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The case study building presents an external surface of about 450 m , that requires 45 m of timber, since the XLAM envelope consists entirely of wood. Using the costs quantified above, the XLAM system has a

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total cost of 36,000€.

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For the platform frame system, the total volume of timber used is equal to 0.052 m for each 125 cm wide 2

module thus the quantity of timber required is 0.014 kg/m . Therefore, the quantity of timber required is 6.4 3

m , which is about a seventh of the quantity required for the XLAM system, with an evident saving in terms of consumption of raw materials and deforestation. The cost of the envelope for the platform frame system is

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22,446€.

Following the above considerations, it is evident that the platform frame system has a lower cost, about 38%

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lessthan the XLAM system, as a result of the smaller quantity of timber required. A further advantage in the use of the platform frame system derives from the diminished weight of the 3

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panels: a framed element weighs about 200 kg/m less than the corresponding model in XLAM. This not only

system.

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reduces transport costs but also permits a greater ease of assembly of the elements of the platform frame

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3.6. Environmental analysis With regard to the use of raw materials, a panel in XLAM of the dimensions 3.00 x 1.00 x 0.10 requires 0.3 3

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m of timber, compared to the 0.043 m of timber required for the construction of a similar panel using the platform frame system, that is for the realization of posts and crossbeams. To this sum, however, it is 3

necessary to add the cost of the paneling in OSB, equal to about 0.038 m . These panels are created from the transformation of high-quality wood-shavings and other timber waste, the use of which increases the sustainability of the entire platform frame system.

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Moreover, the use of high density compressed straw derived principally from agricultural waste, which constitutes a natural insulator, contributes to increasing the sustainability of the envelope, compared to the use of traditional insulating materials of synthetic or mineral origin, such as stone wool, fiberglass or polystyrene, all of which incorporate a considerable amount of primary energy. It is useful comparing the embodied energy of both construction systems analyzed to understand the environmental benefits with the same thermal performance but different embodied energy. Table 13 shows

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the embodied energy comparison between the two constructive systems. The unitary embodied energy values are given by M. K. Dixit [42], taking into account the difference between the solid timber used for the platform frame system and the timber used in the XLAM system, which has a manufacturing process comparable to softwood plywood. The embodied energy included in the straw material is given by the

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aforementioned study [27].

Platform system results in volume reduction of the wood used, in addition pressed straw has a significant reduction in embodied energy, reaching around 60%, compared to the XLAM system. The findings above indicate a preference for the platform frame system with compressed straw, in both

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economic and environmental terms.

4. Conclusion

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The aim of this study was to assess the possibilities of using suistanable materials derived from agricultural waste in the construction process.

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The idea proposed is the use of a system of high-density compression of straw to obtain an insulating material that may be suitably combined with a wooden framework, the platform frame system.

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The presence of high-density compressed straw enhances the thermal efficiency of the external walls by acting as a further layer of insulating material.

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This solution in the project design stage was compared with a more widespread technology using Cross Laminated Timber (XLAM). The thermo-physical properties, thermal transmittance, periodic transmittance and time-lag of both systems were assessed, with the result that the two construction systems present very similar characteristics. However, the platform frame system allows to reach a lower thermal transmittance, U, around by 12%, a higher periodic thermal transmittance, YIE, around by 12%, as well as the increase thermal lag of about half an hour in comparison with the XLAM stratigraphy

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Extending the comparison to observe energy consumption in the case study building, similar performances were again noted, with a reduction in energy consumption in favor of the platform frame system. These results certainly prove the effective comparability among the platform frame and XLAM systems. The hygrometric analysis, conducted without membranes resistant to the passage of water vapor, proved the total absence of interstitial condensation phenomena over an entire year in the different climatic conditions studied. In particular, the platform frame allows to obtain a very breathable vertical cladding and therefore

mildew.

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avoiding the increase of water vapor accumulated in the interior, leading to the well-known formation of

Moreover, it was demonstrated the absence of any risk of formation of interstitial condensation in correspondence with the gaps filled with compressed straw.

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While the two systems are similar in energy performance, the platform frame system with compressed straw yields a superior environmental performance and a higher level of eco-sustainability during its entire life cycle by consuming less raw material, in fact, it requires the use of less than a fifth of the volume of timber required by XLAM and approximately 40% of the embodied energy included in the XLAM system. Moreover, the platform frame system incurs costs which are about 38% lower than those of the XLAM

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system, owing above all to the smaller quantity of timber required.

In conclusion, the platform frame system represents a valid alternative to the XLAM system, from the point of

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view of energy, environmental and economic performance. Further experimental analyses need to be performed to assess the thermo-physical parameters of

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compressed straw when the vegetable composition is varied according to the different geographic areas. Moreover, LCA analyses should be carried out to quantify the improvement in eco-performance of the

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platform frame system compared to the XLAM system.

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Acknowledgements

This research is funded by “the Notice 5/2016 for financing the Ph.D. regional grant in Sicily” as part of Operational Programme of European Social Funding 2014-2020 (PO FSE 2014-2020).

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Fig. 1. Horizontal section

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a. XLAM, 1 plaster, 2 Mineralized wood wool, 3 Wood fiber, 4 XLAM, 5 Gypsum board

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CE

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b. Platform frame, 6 OSB/3, 7 Pressed straw, 8 wooden post

Fig. 2. Construction stage of the building realized in XLAM, chosen for the case study

21

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Fig. 3. Energy consumption of the case study building in Catania (heating from December until March –

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cooling from April until November)

Fig. 4. Energy consumption of the case study building in Amsterdam

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Fig. 5. Energy consumption of the case study building in Stockholm

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Fig. 6. Hygrometric testing of the XLAM and Platform frame systems in different climatic conditions

23

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Table 1. Ratios between density and thermal conductivity in compressed straw Thermal Conductivity [W/mK] 0.06 0.07 0.075 0.080

Thermal lag for 80 mm [h] 2.27 2.49 2.80 3.08

Thermal Transmittance 2 [W/m K] 0.665 0.762 0.809 0.855

Table 2. Thermal Properties of the XLAM

XLAM with 3 layers

Thickness

Dry Density

[mm]

[kg/m ]

100

500

3

Thermal Conductivity

Specific Heat

[W/mK]

[J/kgK]

Coefficient of diffusion resistance [-]

0.13

1600

50

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Material

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Oven Dry Density 3 [kg/m ] 200 250 300 350

Ref.

Producer data

Thickness

Ref.

[J/kg K]

Coefficient of diffusion resistance [-]

0.13

1700

50

[29]

300

0.075

1900

4

[17]

650

0.13

1700

50

[29]

Dry Density

Thermal Conductivity

Specific Heat

[mm]

[kg/m3]

[W/m K]

10

650

80 10

OSB

2

Pressed straw

3

OSB

AC

CE

1

PT

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Material

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Table 3. Thermal properties of the layers of the platform frame

Table 4. Stratigraphy of the existing vertical cladding in the case study building Material

Thickness

Thermal Conductivity [W/mK]

Specific Heat [J/kgK]

Thermal transmittance 2 [W/m K]

Ref.

[mm]

Dry Density 3 [kg/m ]

1

Plaster

10

1760

0.72

840

72.00

[36]

2

Mineralized wood wool

25

460

0.065

1810

2.60

producer

3

Wood fiber

60

150

0.039

2100

0.65

producer

4

XLAM

100

500

0.13

1600

1.30

producer

5

Gypsum board

18

680

0.20

1000

11.11

producer

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Table 5. Stratigraphy of the existing base horizontal cladding in the case study building Material

Thickness

Thermal Conductivity [W/mK]

Specific Heat [J/kgK]

Thermal transmittance 2 [W/m K]

Ref.

[mm]

Dry Density 3 [kg/m ]

1

Clay tile

10

2000

1.0

800

100.00

[37]

2

Cement mortar

15

1800

1.0

1000

66.67

[37]

3

Concrete

40

1800

1.35

1000

4

Reinforced Concrete

300

2300

2.3

1000

[37]

33.75

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7.67

[37]

Table 6. Stratigraphy of the existing roof horizontal cladding in the case study building Thickness [mm]

Dry Density 3 [kg/m ]

Waterproof sheet PVC

1

1200

2

OSB

22

650

3

Air gap

400

5.55

4

Wood fiber

120

150

5

Vapor seal membrane Fire-wood boards

1

4.76

High-density gypsum board

9

Air gap

10

Gypsum plasterboard

Ref.

0.14

1000

140.00

[37]

0.13

1700

5.91

[29]

2100

0.325

producer

[38]

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XLAM

8

CE

7

Thermal transmittance 2 [W/m K]

0.039 [39]

20

510

0.12

1380

6.00

[36]

100

500

0.13

1600

1.30

producer

18

680

0.20

1000

11.11

producer

800

5.55

12

900

1000

20.83

[37]

PT

6

Specific Heat [J/kgK]

M

1

Thermal Conductivity [W/mK]

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Material

[38] 0.25

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Table 7. Thermo-physical parameters of the envelope Thickness [m]

Thermal transmittance 2 [W/m K]

Periodic thermal transmittance 2 [W/m K]

Thermal lag [h]

Surface mass density 2 [kg/m ]

XLAM

0.10

0.25

0.055

13.12

100.34

PLATFORM FRAME

0.10

0.22

0.043

13.76

87.34

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Table 8. Energy consumption and percent variations between the two constructive system TOTAL CONSUMPTION [kWh] Platform XLAM Δ% Frame 27355.81 27238.80 -0.43

AMSTERDAM

54492.91 53903.69 -1.08 1941.14

1979.05

+1.95

56434.05

55882.74

-0.98

STOCKHOLM

82121.35 81298.01 -1.00 1951.21

1985.81

+1.77

84072.56

83283.82

-0.94

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CATANIA

ANNUAL HEATING ANNUAL COOLING [kWh] [kWh] Platform Platform XLAM Δ% XLAM Δ% Frame Frame 12168.71 12011.23 -1.29 15187.10 15227.57 +0.27

Table 9. Annual thermal dispersion through vertical opaque envelope [kWh]

-8008.12

STOCKHOLM

-10563.50

Δ% [-] -9.62

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AMSTERDAM

Platform Frame [kWh] -2406.72 -7214.87

-9.91

-9512.21

-9.95

M

CATANIA

XLAM [kWh] -2662.84

Table 10. Boundary climatic conditions for Catania, Amsterdam and Stockholm Amsterdam-Schiphol TOUT UROUT TIN URIN [°C] [%] [°C] [%] 4 87 20 49 4 87 20 49 5 83 20 49 8 87 20 55 13 74 20 55 15 75 18 69 17 85 18 84 17 79 18 79 14 85 20 65 11 83 20 57 6 89 20 53 4 89 20 50

ED

PT

CE

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January February March April May June July August September October November December

Catania-Fontanarossa TOUT UROUT TIN URIN [°C] [%] [°C] [%] 10 73 20 51 10 78 20 54 12 76 20 54 14 74 18 66 18 76 18 80 22 72 22 72 25 64 25 64 25 70 25 70 23 69 23 69 18 74 18 79 15 74 18 68 12 74 20 55

Stockholm-Arlanda TOUT UROUT TIN URIN [°C] [%] [°C] [%] -4 91 20 41 -1 79 20 42 0 84 20 45 4 65 20 41 12 64 20 47 14 68 18 61 17 73 18 73 16 72 18 69 11 82 20 57 7 86 20 53 2 88 20 47 -2 89 20 43

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Table 11. Cost of an XLAM module

XLAM 3S

Width

Length

Thickness

Volume

[m] 1.25

[m] 3.00

[m] 0.10

[m ] 0.375

3

Price 3 per m [€] 800

Table 12. Costs of a module in Platform Frame Quantity

Posts C24 80x80 Crossbeams C24 80x80 OSB boards 10 mm Pressed Straw

Density 3 [kg/m ]

Width [m]

Height [m]

Thickness [m]

U.m. [-]

2

0.08

2.84

0.08

m

2

1.25

2

1.25 1.09

Total Cost

[€/module] 300

Unit price 3 [€/m ]

Total cost [€/module]

3

3000.0

109.00

0.08

0.08

m

3

3000.0

48.00

3.00

0.010

m

2

4.00

30.00

2.84

0.08

kg

0.0011

0.082

M

300

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Material

Unit price thickness of 10 cm 2 [€/m ] 80

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Material

TOTALE

2

ED

Unit price for a thickness of 10 cm (€/m )

187.08 € 49.88

Table 13. Embodied energy comparison for a constructive system module Quantity

Density

PT

Material

3

CE

[kg/m ]

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Posts C24 80x80 Crossbeams C24 80x80 OSB boards 10 mm Pressed Straw

XLAM 3 layers

Width.

Height

Thickness

[m] [m] [m] PLATFORM FRAME

Mass [kg]

Embodied energy [MJ/kg]

Embodied energy [MJ]

2

420

0.08

2.84

0.08

15.27

6.5

99.26

2

420

1.25

0.08

0.08

6.72

6.5

43.68

2

650

1.25

3.00

0.010

48.75

9.2

448.50

300

1.09

2.84

0.08

74.29

1.2

89.15

TOTAL

680.59

1.25

XLAM 3.00

500

0.10

187.50

9.2 TOTAL

1725.00