An innovative straw bale wall package for sustainable buildings: experimental characterization, energy and environmental performance assessment

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AN INNOVATIVE STRAW BALE WALL PACKAGE FOR SUSTAINABLE BUILDINGS: EXPERIMENTAL CHARACTERIZATION, ENERGY AND ENVIRONMENTAL PERFORMANCE ASSESSMENT C. Cornaro , V. Zanella , P. Robazza , E. Belloni , C. Buratti PII: DOI: Reference:

S0378-7788(19)31910-3 https://doi.org/10.1016/j.enbuild.2019.109636 ENB 109636

To appear in:

Energy & Buildings

Received date: Revised date: Accepted date:

18 June 2019 11 November 2019 24 November 2019

Please cite this article as: C. Cornaro , V. Zanella , P. Robazza , E. Belloni , C. Buratti , AN INNOVATIVE STRAW BALE WALL PACKAGE FOR SUSTAINABLE BUILDINGS: EXPERIMENTAL CHARACTERIZATION, ENERGY AND ENVIRONMENTAL PERFORMANCE ASSESSMENT, Energy & Buildings (2019), doi: https://doi.org/10.1016/j.enbuild.2019.109636

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1

AN INNOVATIVE STRAW BALE WALL PACKAGE FOR SUSTAINABLE BUILDINGS:

2

EXPERIMENTAL CHARACTERIZATION, ENERGY AND ENVIRONMENTAL PERFORMANCE

3

ASSESSMENT

4 5

C. Cornaro1*, V. Zanella1, P. Robazza2, E. Belloni3, C. Buratti3

6

1

7

00133 Rome, Italy

8

2

BAG - Beyond Architecture Group, Via Macerata, 22 A, 00176 Rome, Italy

9

3

University of Perugia, Department of Enigineering, Via G. Duranti 93, 06125, Perugia, Italy

University of Rome ‗Tor Vergata‘, Department of Enterprise Engineering, Via del Politecnico, 1,

10 11

*Corresponding author

12

Keywords: Natural materials, straw bale, sustainability, LCA, energy performance, dynamic

13

simulation.

14 15 16

ABSTRACT

17

Natural materials, such as straw bale and earth, have substantially less embodied energy than

18

processed materials, so that their use in building construction can give a valuable contribution to

19

sustainability.

20

This paper presents a natural multi-sheet wall package (named straw wall, SW) consisting of straw

21

bale layer and innovative natural plasters, giving a rational evaluation of its potential of use in the

22

sustainable building construction. The new building component was investigated by analyzing its

23

environmental impact through the Life Cycle Assessment (LCA) from ―Cradle to Gate‖ and its

24

energy performance using dynamic simulation of a building case study; the energy saving potential

25

of SW was assessed in different climate conditions in Italy. The innovative package highlighted

26

excellent energy performance with respect to the NZEB reference, as prescribed by the Italian

27

regulation, for all climates.

28

Considering only the production and construction phases, the Embodied Energy associated to the

29

innovative wall system is about the half of the value related to a traditional wall package and the

30

CO2 equivalent emissions differ by more than 40%(Pescara site).

31 32

1. INTRODUCTION

33

Sustainability is a broad concept firstly applied to economy, in order to conjugate profit with

34

environmental and social aspects [1].This concept, applied to the building industry, should address

35

the effects of buildings on the environment and define limits for consumption of resources, while

36

simultaneously considering the needs of the future [2].The new building design process, driven by

37

a sustainable approach, should touch upon economic decisions related to life-cycle and matrix

38

costing, functionality via the building energy use and efficiency, and architectural scheduling,

39

promoting integrated building design. In other words the sustainable design should drive

40

architectural designer to a holistic approach to buildings. In this regard, these actors can give a

41

great contribution, being able to influence decisions in construction strategies [3].

42

Natural materials, such as straw bale and earth, have substantially less embodied energy than

43

processed materials, so that their use in building construction can give a valuable contribution to

44

sustainability [4–6]. Straw is a waste material from cereal harvest, made up of dead stalks of cereal

45

plants. This by-product of cereal farming can be re-grown annually and it is available every year in

46

large amounts; for this reason it can be regarded as a renewable building material since its primary

47

energy input is solar. In 2013 the global amount of straw produced worldwide summed up to

48

3.6×109 and this number is rising according to the increase of the production growth of these

49

cereals, as reported by FAOSTAT [7]. More recent data from [7] indicate an increasing trend of

50

production of wheat and rice paddy up to 2016, as shown in figure 1 for wheat case.

51 52

The use of straw bales in the building sector is mainly related to the invention of the baling

53

machine, at the end of the 19th century. In Nebraska, USA, around 1880, the modern construction

54

with straw bales got a foothold [8] and the Burke house built in 1903 in Alliance, Nebraska is one of

55

the first examples of straw bale house [9]. In 1921 Émile Feuillette built the first European straw

56

bale building in Montargis, France. The spread of cement, during 40s, stopped the diffusion of this

57

construction technique, then rediscovered in the 70s, due to the energy crisis [10]. Since the 80s,

58

Northern Europe and United Kingdom witnessed to the spread of many straw bale constructions,

59

while in Italy their diffusion is relatively recent, gaining significant attention among ―self-builders‖,

60

technicians, and scientists. In spite of this success, there is still a lack of information about a

61

rational definition and comprehensive characterization of straw bales building envelopes, that

62

includes also energy and environmental performance assessment.

63

This paper aims to develop a multi-sheet wall package, consisting of a straw bale layer and

64

innovative natural plasters, giving a quantitative evaluation of its potential use in the sustainable

65

building construction. The new building component was investigated by analyzing its environmental

66

impact through Life Cycle Assessment (LCA) from ―Cradle to Gate‖ and its energy performance

67

using dynamic building simulations of a building case study in different climate conditions. A

68

preliminary thermal characterization of the package was essential to get the right inputs to the

69

building model. The experimental activity was carried out at laboratory scale, evaluating the

70

thermal conductivity of each wall layer by means of the Small Hot Box technique [11].The total

71

thermal transmittance of the wall was calculated by combining the results and considering the real

72

scale thickness of each layer. After a brief Introduction presented in Section 1, Section 2 gives an

73

overview of the straw bale construction diffusion in Italy and in the world, together with a state of

74

the art of the material characterization. Section 3 presents the new wall package and briefly

75

describes the experimental facility and the software tools used for the investigation. Section 4

76

presents the results in terms of thermal measurements, energy performance assessment, and LCA

77

by comparing the behavior of the straw bale wall package with respect to a baseline wall package

78

and with respect to the requirements of the most recent Italian Legislation. A discussion of the

79

results is presented in section 5.

80 81

2. OVERVIEW

82

Quantitative data on the chemical and physical properties of straw are scarce and there is a lack of

83

regulations, nevertheless, a considerable spread of this kind of constructions can be observed in

84

several countries. In particular, the ease of the construction technology and the absence of rules

85

gave impulse to the ―auto construction‖, so that it is not easy to sketch a map of the real diffusion

86

of straw bales buildings in the world. The need of exchange of views regarding construction

87

techniques and maintenance encouraged the development of national and international networks,

88

that started collecting data about straw bale building typology and diffusion. Among them it is worth

89

mentioning the International Straw Bale Registry in USA [12] and the European Straw Bale

90

Association (ESBA) in Europe [13]. In Italy, Promopaglia [14] and Case in Paglia [15] are the main

91

associations that collect information about straw bale construction spread.

92

During last decades, with the growing of interest, some books were published on such topic

93

[9][16].Furthermore, associations like the Ecological Building Network EBNet [17], the California

94

Straw Building Association CASBA [18], and the German Straw Bale Association FASBA [19],

95

together with Universities and research centers, started producing high quality research, testing,

96

and certifying straw bale constructions.

97 98

2.1 Straw as building material

99

Various construction techniques were developed for straw bale buildings. It is mainly due to the

100

lack of regulations and to the availability of different traditional building materials, such as wood

101

and stones, in different geographical areas. Indeed, there are two basic types of construction using

102

straw bales: ―load bearing‖ and ―post and beam‖, although in recent years other building systems

103

are being investigated.

104

The first straw bale structures were all load-bearing of necessity because they were erected after

105

the invention of baling machines in western Nebraska, USA, characterized by scarcity of wood

106

[9].For this reason the ―load-bearing‖ system is also known as Nebraska Style. In the Nebraska

107

structure,

108

staggering the joints, as bricks. The ―load-bearing‖ walls in straw bales support the wooden

109

structure of the roof and transmit the loads to the foundation. Straw bale houses built according to

110

this technology cannot have openings that exceed 50% of the wall surface. This would cause the

111

instability of the wall system. The rigidity of Nebraska technique does not allow the construction of

straw

bales

are

structural

elements

and

they

are

stacked

and

laid

by

112

more than four floors. Nowadays, this system is regulated by legislation only in some countries,

113

such as USA and France.

114

The other main method of construction is ―post and beam‖. The straw bales are used as insulating

115

material and the load-bearing is usually a timber frame structure. The dwellings are made by

116

placing bales in a column in the frame. This construction system allows a greater flexibility of the

117

plan and also does not provide limits in the number of floors.

118

Alternative building systems were developed starting from the previous techniques. As an

119

example, the cell under tension (CUT) [20] and the Gagnè [21] techniques are a mix of the

120

Nebraska Style and the ―post and beam‖ technologies. In both the systems the straw bale walls are

121

semi-carrier. However, they have fallen in disuse, owing to their siting complexity.

122

Another technique was developed in 1995 by the Quebec Research Group of the Bay, Canada,

123

named GREB. This building system is based on the construction of a double timber frame structure

124

and straw bale in-filled walls, a very simple technology because the filling steps are methodical.

125

The double frame forms a case were straw bales are inserted. In fact, the dwellings made using

126

this technique spread rapidly, thanks to the publication of a practical manual by the French

127

association ACCROCHE-Paille, which was later translated into several languages [22].

128

Recently, prefabrication was introduced also for construction elements with straw bales; in this

129

case the wood frame and the bales are preassembled. This technique allows to save costs and

130

time in the construction site, providing, in the meantime, more accurate elements. The main

131

producers of these prefabricated walls are Mod-Cell® in UK, Paille Tech in France, and Ecocon in

132

Lithuania.

133

Pre-compressed straw boards are also available on the market. In this case straw is not

134

assembled in a bale, but it is used as raw material for the panel construction. It presents higher

135

thermal performance than common prefabricated elements, such as gypsum board or Oriented

136

Strand Board (OSB). This product is spreading especially in USA and Europe. In particular, in UK

137

the Stramit International company produces a straw board that is compliant with the British

138

Standard BS4046 [23].

139 140

2.2 Characterization of straw bales

141

Despite the recognized advantage of straw bale as efficient thermal and acoustic insulation

142

material and straw buildings are constantly developing in Europe and elsewhere, the definition of

143

its mechanical and physical properties is fundamental to allow this natural material to become

144

widespread in the construction sector. Straw bale is a mix of pressed straw and air and the mixture

145

characteristics depend on the compression given by the straw pressing machine. Therefore the

146

baling process produces large range of densities and can influence the orientation of the fibers

147

inside the straw bale [24]. Moreover, also the internal porosity and the water content of the fibers

148

can change its own density [25].

149

Besides, straw bales have a larger thickness than most of other insulating materials that can be

150

found in the building industry; the most commonly used format has indeed dimensions of

151

approximately 40x50x100 cm. For this reason, samples of straw bales are usually resized to be

152

housed in the most common measurement devices at laboratory scale. During this resizing

153

process, it is difficult to preserve the original physical characteristics of the material, such as its

154

density and stalk orientation [24].

155

All these issues contribute to a large variation in mechanical and thermal properties of straw bale,

156

as found in the literature(Table 1).

157 158 159

In particular, focusing on the thermal characteristics of the material, a detailed literature review

160

showed that the thermal conductivity of straw bales depends both on the density of the bale and

161

on the thermal flux orientation with respect to the stalks position. This orientation can be parallel to

162

the straw stalks (in this case the bale positioning is named ―on flat‖) or perpendicular to them (the

163

bale positioning is named ―on edge‖). Data reported in Table 1 refer only to straw of wheat and

164

most of the presented results come from laboratory measurements, with the Hot Guarded Plate

165

(HGP). It can be observed thatvalues vary in the 0.038-0.08 W/mK range, depending on the

166

density and stalks orientation. As regard density, it has to be remarked that the straw bale, as

167

construction material, requires a density ranging from 80 to 120 kg/m 3; nevertheless, for some

168

experiments, this value is not distinctively defined or is out of this range.

169

The major differences among data are mainly related to the different orientations at fixed density.

170

In particular, the orientation ―on edge‖ presents lower values of thermal conductivity than ―flat‖

171

orientation. Grelat [32] considered also the effect of relative humidity (RH). The results show that

172

the thermal conductivity increases from 0.064 W/mk to 0.069 W/mK passing from 0% RH to 22%

173

RH. This increase, however, is not significant considering that for a brick wall a variation of 10% in

174

RH produces an increase in thermal conductivity of 0.2 W/mK, passing from 0.6 W/mK to 0.8

175

W/mK[39]. The box plot graph in Figure 2 shows a synthetic representation of the distribution of 

176

values reported in Table 1 as a function of the stalks orientations. The values distribution is not

177

symmetrical for all cases and this asymmetry is more evident when the orientation is not specified.

178

For this type, also the maximum values are strongly asymmetric. The medians also show that the

179

configuration ―on edge‖ is preferable, while the ―flat‖ and ―not specified‖ categories show almost the

180

same value.

181 182

Figure 3 resumes the trend of thermal conductivity with respect to density of the straw bales as

183

found in the literature (Table 1). The strong dependence on the bale positioning is still evident; a

184

light increasing of thermal conductivity with density is observed, as expected.

185

.

186 187 188

3. MATERIALS AND METHODS

189

3.1 Straw buildings geographical diffusion

190

In order to have a systematic overview of the straw building spread worldwide and at national level,

191

a research was carried out gathering information from various sources. Apart from the legal

192

organizations, such as the ones mentioned above, also independent networks work on the census

193

of straw buildings all over the world. As an example, the organization Natural Homes built an

194

Ecohouse map at global level -[40] and its chart is upgraded by users, sending technical and

195

photographic documentation about their projects. However, in this case, the accuracy of

196

information is strictly related to the volunteer participation of the users, so that some discrepancies

197

with respect to national and official networks results can emerge. For this reason, in order to give

198

an accurate evaluation of the ―state of the art‖ of straw building geographical diffusion, a

199

crosscheck between various sources at international and national level was carried out for all the

200

countries[12,14,15,40–44]. In the process, the temporal update of the database, the geographical

201

proximity of the sources, and their reputation were taken into account. A vision at a glance of the

202

results is shown in Figure 4. To date, to the author knowledge, the registered straw buildings at

203

global level amount to approximately 3400 units. This number does not take into account buildings

204

provided with pre-compressed straw boards.

205 206

It can be observed that the majority of straw buildings are concentrated in the countries where a

207

regulation on this kind of construction exists. The country with the largest amount is USA, with 784

208

buildings, followed by France with 700. In these countries also the census at national level is more

209

accurate and the numbers are surely more realistic. Also China presents a large number of straw

210

buildings, owing to the huge amount of rice paddy in the area. In Europe, apart from France, we

211

observed large quantity of straw buildings in Germany, Norway, Austria, and Belarus. The most

212

concentration of buildings is also located in countries where there is an intensive cultivation of

213

wheat and corn, such as USA and Canada. Also in Europe, France and Italy are the major

214

producers of wheat.

215

Focusing on the Italian scenario, Promopaglia association claims the presence of 635 straw

216

buildings on the Italian territory; however the actual registered value amounts to 176. Their

217

distribution in the various regions, updated to 2018, is shown in Figure 5.

218 219

The regions in the North part of Italy where the maximum concentration of wheat production is

220

present (Lombardia, Piemonte, Veneto, Emilia Romagna, and Toscana) are the ones with the

221

largest number of straw buildings. Also Marche and Abruzzo show large diffusion, indeed straw

222

bales are used for post-seismic reconstruction.

223 224

3.1 The wall package

225

The wall considered for this study is completely made of natural and renewable materials. Itis

226

composed of an outer layer of cocciopesto plaster, a core made of straw bales contained within

227

continuous fir boards, an interspace bounded by uninterrupted planks of wood, and a final raw

228

earth plaster applied on the plywood (total thickness 0.523 m). The layers of the wall are shown in

229

Figure 6: the final stratigraphy originates from surveys and evaluations that take into account the

230

sustainability of the wall and its energy and mechanical efficiency. The external plaster of

231

cocciopesto is about 0.029 m thick, useful to resist to external atmospheric agents, to maintain the

232

straw in dry conditions with low humidity values, and to guarantee good breathability of the wall.

233

The cocciopesto plaster, based on natural hydraulic lime and fragments of bricks, consists of three

234

cohesive layers. The adhesion is guaranteed through the application of a layer of wickers,

235

anchored to the wooden plank with metal staples. The straw bales (0.35 m-thick) are positioned

236

with the fibers in vertical direction and they are contained within two layers of fir wood (0.021 m-

237

thick). In order to guarantee the bracing function, this boarding is fixed to the wooden supporting

238

structure in an oblique position with nails.

239 240

The internal air gap (total thickness 0.05 m) is necessary for the passage of the wires and plants

241

installations. Finally, the raw clay plaster consists of two layers: the plaster body made of selected

242

raw earth, sand (granule sizes and dosage controlled), and vegetable fibers, and the finishing

243

made of raw earth and very fine sand (total thickness 0.031 m). The clay quickly adsorbs moisture

244

from the air and releases it as quickly as necessary: this aspect is important in order to make the

245

indoor climate healthier. Moreover, the raw earth, thanks to the high thermal inertia, heats up very

246

slowly and just as slowly cools. In principle, in winter it has the ability to accumulate heat, in

247

summer it manages to keep a cool temperature. However, in the specific case, the thickness of the

248

plaster would not probably be enough to bring these benefits.

249 250

3.2 Thermal measurements

251

The apparatus for thermal tests is named Small Hot – Box [45] (Figure 7); it was developed and

252

calibrated by several preliminary measurements at the University of Perugia (Laboratory of

253

Environmental Control, Department of Engineering), following some of the prescriptions of EN ISO

254

8990 [46]. A detailed description of the new developed apparatus can be found in [11]. The thermal

255

conductivity can be obtained thanks to the thermal flux meter methodology and it is calculated as

256

reported in (1) considering the mean surface temperatures of the hot and cold sides (T sH and TsC,

257

respectively) during the tests, the heat flux through the sample (q) and the total thickness of the

258

specimen (s):

259

260

(1)

261 262

Considering the composition of the panels, it was necessary to use support layers (support layer 1

263

and support layer 2) for the more fragile materials: in these cases it was calculated the thermal

264

contribution of only one layer (Rsample) from the total thermal resistance of the composed samples

265

(Rtot),as shown in equation (2):

266 267

(2)

268 269 270

where: -

271 272

(m) and the thermal conductivity (W/mK) of the first support panel; -

273 274 275

Rsupport 1, ssupport 1 and λsupport 1 are respectively the thermal resistance (m2K/W), the thickness Rsupport 2, ssupport 2 and λsupport 2 are respectively the thermal resistance (m2K/W), the thickness (m) and the thermal conductivity (W/mK) of the second support panel;

-

Rsample, ssample and λsample are respectively the thermal resistance (m2K/W), the thickness (m) and the thermal conductivity (W/mK) of the sample layer to be tested.

276 277

Considering equal to ± 5 % the precision of the thermal flux meter and ± 0.10 °C the one of the

278

thermo-resistances, the measurement accuracy is 4-6% for all the tests. Finally the relative

279

uncertainties (type B) can be calculated in compliance with JCGM 100:2008 [47]: the values are

280

related to the fluctuation of the measured quantities during the test.

281 282

3.3 Energy simulation and case study

283

The potentiality of the straw bale wall package in terms of energy efficiency was assessed

284

introducing the construction element in an existing project of a building whose envelope was

285

designed according to the ―post and beam‖ technique. The building will be built in the area of

286

Pescara, a city located in central Italy.

287

The analysis of energy saving potential of the building provided with the new wall package was

288

carried out comparing its energy performance to the correspondent reference building provided by

289

the current Italian legislation [48] for the climate zone of Pescara (Lat. 42.433 N, Long. 14.2 E, D

290

zone). Additionally, the same building was located in Bolzano and Palermo, representing climate

291

zones F and B respectively [49],in order to investigate the impact of the climate variation. Also in

292

this case results were compared to the reference building provided by the Italian norm for each

293

climate condition. The simulations were carried out in the IDA ICE 4.8 software environment [50].

294

IDA ICE is a tool for building simulation of energy performance, indoor air quality, and thermal

295

comfort in dynamic conditions. It was developed by the Swedish Company EQUA Simulation AB in

296

collaboration with The Division of Building Services Engineering, the Royal Institute of Technology

297

in Stockholm (KTH), and the Swedish Institute of Applied Mathematics (ITM). It covers a large

298

range of phenomena, such as the integrated airflow network and thermal models, CO 2 and

299

moisture calculation, and vertical temperature gradients. A key issue in building simulation is the

300

treatment of direct and diffuse solar radiation. The Perez model [51] is used in this tool, to compute

301

by default the distribution of diffuse radiation in the sky. A single large simultaneous system of

302

equations is solved by the tool with numerical methods, for all processes in the building. It adapts

303

the time step to the frequency content of the solution.

304

Neutral Model Format (NMF) [52] is the language used to write the library of the mathematical

305

models of the building components that was developed and tested against measurements and

306

other programs in the scope of IEA Task22 ―Building Energy Analysis Tools‖ [53]. The tool was

307

also validated according to prEN 13791 defined test cases [54] and to Envelope BESTEST in the

308

scope of IEA Task 12 [55].

309

3.3.1 Case study

310

A render of the investigated building, called SBB from now on, is shown in figure 8.

311

The single family house consists of three floors, a basement, a ground floor and a first floor. The

312

basement envelope, such as the foundations, are made of concrete, the other external walls are

313

made of straw bales. The pitched roof is made of wood, with a layer of OSB insulating board.

314

Triple glazing system filled with argon is used for the windows. The south facade is provided with a

315

shading system, made of wood. The basement consists of a laundry, two storages, a toilet and a

316

garage that can host agricultural vehicles. The ground floor is divided in a large living area and a

317

night area provided with two bedrooms, two bathrooms, and one technical room. The first floor is

318

smaller than the ground one and consists of an office that overlooks the living underlying and a

319

storage. The floors are connected by a spiral staircase.

320 321

3.3.2 Model construction

322

The SBB model was built referring to the original project. The shading system in the south wall was

323

not taken into account, in order to reduce the model complexity considering the most heavy

324

thermal loads during summer (figure 8).

325 326 327

The properties of the materials used for the envelope and for the internal walls are listed in Table

328

2.

329

In Table 3 the U values of the different wall packages and glazing are shown, while Table 4 reports

330

the characteristics of the windows.

331 332

333 334

The buildings used as reference (NZEB) were built for the three locations (Pescara, Bolzano, and

335

Palermo) considering the U value as prescribed by the norm (Table 5, 6) and preserving the same

336

thicknesses as SBB and also the same heat capacities for each element of construction, so that

337

the internal volume of the NZEB and SBB were the same.

338 339 340

Each thermal zone corresponds to each room, for a total of 17 zones. A constant infiltration rate of

341

0.6 Air Change Hours (ACH) was considered while no equipment, lighting, and occupancy were

342

taken into account. Thermal bridges were set as ―typical‖, as provided by the software (Table 7).

343

Ψ-value represents the length-related thermal bridge loss coefficient of each building component.

344 345

Ideal heaters and ideal coolers were put into each zone, in order to evaluate the heating and

346

cooling demand. The indoor temperature set points were 20°C and 26°C, for winter and summer

347

respectively, considering a turn-on time for winter as defined by the Italian norm for the different

348

climate zones. The heating and cooling periods for the three cities are shown in Table 8. For

349

heating a continuous period corresponding to the prescribed hours was chosen for all the

350

locations. Since for the cooling period no regulations are enforced, we decided to consider the

351

period of the year that is complementary to the heating, however assuring that the starting and

352

ending time is regulated by the set points. Moreover, six hours per day were considered for cooling

353

and the time period was chosen to maximize the cooling load for all the locations. All these

354

conditions were applied to both SBB and NZEB.

355

The climate files used for Pescara, Bolzano, and Palermo were available in the software database

356

as ASHRAE IWEC2 weather files. Wind speed and direction were set as typical of suburban site.

357 358

3.4 Life Cycle Assessment

359

Life Cycle Assessment (LCA) is one of the most used methods for evaluating a product's impact on

360

the environment over its entire lifespan. The LCA method was developed to analyze the resources

361

extracted and to quantify the emissions related to a product over its entire life cycle [56]. LCA

362

provides valuable information that allows managers to make decisions aimed at improving the

363

environmental performance of their products. In life cycle assessment analysis it is important to

364

follow the international standard ISO 14040-series, very useful for the goal and scope definition

365

and for the inventory step. It involves the collection of all data necessary for the calculation of the

366

environmental impact, that can be retrieved from relevant studies, public databases, scientific

367

publications, as well as from established local and global databases of the employed LCA

368

software[57,58].

369

In order to assess the life cycle impacts of the proposed innovative wall (SW) and to perform a

370

comparison with conventional solutions, a LCA analysis was carried out based on ISO 14040

371

standard series [59]. Energy and mass flows were evaluated from the supply of the raw materials

372

to the final products, the installation of all the components in a reference building (SBB) located in

373

the center of Italy, and the maintenance during the use of the building.

374

The innovative system (SW) was compared to a traditional wall (TW) (Figure 9), whose

375

characteristics are shown in Table 9. TW has the same total thermal transmittance as SW.

376

Furthermore the functional unit of the LCA analysis is the area (m2) of the wall package installed in

377

the reference building. The LCA calculations were performed only for Pescara, which is the real

378

site where the building is under contruction. It allows a significant evaluation because it is in the

379

center of Italy, located far enough from Palermo, where are positioned all the manufacturing

380

companies of the SW layers: the authors would not benefit the emission results of the innovative

381

solution. The chosen site can be considered in favor of safety both for the Traditional Wall case

382

and for the Straw Wall one.

383

The analyzed impact categories were the Global Warming Potential (IPCC 2013, 100-years) and

384

the Cumulative Energy Demand (CED), that give information about greenhouse gas emissions and

385

energy consumption related to the production of the walls.

386

IPCC 100-years Global Warming Potential (GWP) characterization factors were applied to convert

387

greenhouse gas emissions into carbon dioxide equivalent (CO2eq) emissions: the characterization

388

factors used were 1, 25, and 298 for carbon dioxide, methane, and nitrous oxide, respectively.

389

Both the impact indexes were calculated considering the external surface of the walls of the

390

analyzed building (244 m2).

391 392

Part of the inventory data were directly collected at individual process level (primary data) at the

393

manufacturing company, such as the consumption of the production process (energy, water, etc.)

394

and the distances from the suppliers of the raw materials. Other secondary data were derived from

395

international databases (Ecoinvent) or calculated with suitable models (IPCC). It is necessary to

396

take into account that for the innovative system with straw, all the data were given from the

397

manufacturers, whereas for the traditional solutions some materials data were assumed from the

398

Literature [60].

399

For the construction phase, the impacts of transport, assembly, and production were calculated,

400

also taking into account the impacts of the re-production of materials that turn into waste. The

401

impact of transport from manufacturing plant to building site was calculated on the average

402

distances from the effective positions of the producers (Catania, South of Italy, for the cocciopesto

403

and Raw Earth plasters).

404

Finally, the impact of assembly phases in the building site in terms of electrical and water

405

consumptions were assumed to be equal to 5% of the embodied energy of all the building

406

materials, both for the straw wall and for the traditional one, in compliance with the Literature

407

recommendations [61–63].As concerning the Use Phase, the natural gas consumptions and

408

emissions of the case study with the two different wall configurations were estimated in a typical

409

year. For the use phase, energy consumptions (heating, domestic hot water, cooling, lighting, and

410

electrical appliances) were considered and data were taken from the simulation results. The end of

411

life step was deliberately overlooked, because of the lack of the data of this phase. A ―cradle to

412

gate‖ approach was therefore applied because the proposed wall is only a prototype and no data

413

are available concerning the end-of- life stages.

414

In Table 10 the inventory analysis of the different layers of the package is reported for the

415

innovative wall; in Table 11 they are referred to the traditional solution.

416

Figure 10a) and Figure 10b) show the flow chart of the LCA analysis for the two considered

417

scenarios. In both cases, the 3 steps of analysis are schematically represented (Production Phase,

418

Construction Phase in the building site, and the Use Phase (projection period of 50 years)). In

419

particular for the straw wall, the Production phase of the 5 layers, the transport of the raw materials

420

to the production site, and the consumptions for manufacturing are considered (Fig. 10(a)). For the

421

traditional one, the layers were associated to Ecoinvent categories and they include in this

422

processes the manufacturing and the transport of the raw materials (Fig. 10(b)).

423 424 425 426 427

4. RESULTS

428

4.1 Thermal measurements

429

In the Small Hot Box several tests were conducted for the samples, but the most significant results

430

were related to the measurements with a temperature of the hot chamber set at 45°C. In order to

431

evaluate the thermal conductivity of the only investigated materials that compose the final package,

432

the contribution of the support elements were deducted by eq. (2). Table 12 shows the description

433

of the tested samples and Table 13 shows the thermal conductivity values obtained in the Small

434

Hot-Box apparatus.

435 436

The plywood panel was used in the packages in order to have a support for the other materials: its

437

conductivity value (0.152 W/mK) was used in the subsequent tests for the conductivity

438

extrapolation of the straw, the cocciopesto, and the earth – based plasters. The polystyrene used

439

as support in some tests has a known certified value of λ, equal to 0.038 W/mK, but it was anyway

440

measured in order to confirm this value. Both the plywood and the polystyrene are not present in

441

the final composition of the wall.

442

The measured conductivity of the straw layer is 0.065 W/mK and it is in agreement with the values

443

present in Literature [24,27,33,64,65], with comparable densities (about 100 kg/m3), and a parallel

444

disposition of the fibers; on the contrary, considering a perpendicular orientation, the λ- values are

445

slightly lower. For the cocciopesto plaster the λ-value that can be considered significant is 0.92

446

W/mK; the second value should be discarded because of the too high uncertainty type B obtained

447

(about 10%). The Raw Earth plaster layer has a value variable in the range 0.95 – 0.98 W/mK,

448

close to the indicative value provided by the manufacturer, that was 0.91 W/mK. Also in this case

449

the λ obtained from the first test (45°C) is the most significant (0.98 W/mK). Finally the wooden

450

planking (W) tested at the end (total thickness 0.021 m) has a thermal conductivity equal to 0.089

451

W/mK, the same for both the tests. Also this value is in agreement with the Literature [4].

452

The type B uncertainties were calculated for each test. In general the uncertainty u – values varied

453

in 4.5 – 7.8 % range: only for one test a value of about 10% was obtained and the corresponding

454

result was discarded (cocciopesto plaster). For the test on the wooden planking, the uncertainty

455

values were higher than the ones obtained for the other materials (about 8%); this is due to the

456

total thickness of this sample, that is very low (about 2 cm): the heat flux was not very steady

457

during the test.

458

Finally, the total transmittance of the composed wall was calculated: the thermal resistances of

459

each layer Ri obtained from the previous tests are shown in Table 14, considering the effective

460

thicknesses of each material. For the air gap inside the wall, a thermal resistance of 0.18 m2K/W

461

was assumed, in compliance with UNI 10351 [66] (air gap of about 5 cm with a horizontal thermal

462

flux). The total thermal transmittance was evaluated by considering inside and outside surface

463

thermal resistances equal to 0.13 and 0.04 m2K/W respectively, in compliance with EN 6946 [67].

464

The final value of H is equal to 0.154 W/(m2K): it complies the limited values of the thermal

465

transmittances fixed by the DM 26/06/2015[48] for all the climate zones and also the stringent

466

limits imposed for the years 2019-2021 (0.43 – 0.24 W/m2K), passing from climate zone A to F.

467 468 469

4.2 Energy simulation results

470

Figure 11 shows the results in terms of delivered energy for heating and cooling for NZEB and

471

SBB, located in the three cities of Bolzano, Pescara, and Palermo for each month of the year.

472 473 474

The delivered energy for heating is higher than cooling in all cities, also in Palermo, where the

475

energy for cooling is usually higher than in the other locations. This is probably due to the

476

characteristic of this project in which the small window to wall ratio (3.5%) reduces the passive

477

gains due to solar radiation both in Winter and Summer. Moreover, SBB performs better than

478

NZEB in the three cases. On the contrary, cooling delivered energy for SBB is higher than NZEB.

479

Indeed, the higher insulating performance of straw with respect to the reference causes a certain

480

overheating effect during the night as shown, for example, in figure 12 for Pescara, during a week

481

in August.

482

483 484

In Table 15 the total amount of energy consumption of the two models and for the three locations is

485

shown, together with the percentage difference between NZEB and SBB (). It can be observed

486

that the major advantage of SBB is obtained in Palermo ( = 27%) where, however, the total

487

delivered energy is low with respect to the other two locations (approximately half of Pescara and

488

one third of Bolzano). Overall, SBB showed excellent energy performance with respect to NZEB.

489

In order to compare the Straw Wall (SW) with the Traditional Wall (TW) in terms of embodied

490

Energy and CO2 emissions, a building model substituting SW with TW has been built and run only

491

for the city of Pescara. The results in terms of Heating and Cooling delivered energy are very

492

similar (difference lower than 1%), considering that both SW and TW are characterized by the

493

same transmittance (Table 16).

494

4.3 LCA results

495

Table 17 gives the embodied energies and CO2eq emissions required to produce the two wall

496

systems for the specific case study (considering a total wall surface of 244 m2).

497 498

It is possible to observe that the impact of the Straw layer (S) is very low, despite its large

499

thickness, and the high amount of this material (about 3600 kg).

500

The production phase of this material and also the impacts of the transport are very low, because

501

of the wheat field closeness (Pescara surrounding areas, at about 10 km). The cocciopesto

502

(CPplaster) and the Raw Earth Plasters (REplaster) are also promising plaster solutions, thanks to

503

the good thermal insulation properties and to the low impact contribution, but the transports affect

504

very much the total results of the Embodied Energy and the CO2 emissions: the transports are

505

responsible for about the 70% of the GWP and for about the 35%of the total Embodied Energy.

506

The site of the case study is about 800 km far from the manufacturer factory. Obviously the choice

507

of a closer site can strongly reduce the impacts of these solutions.

508

As concerning the comparison with the traditional solution (TW), it can be observed a reduction of

509

about the 50% both for the EE (MJ) and the CO2 emissions (GWP in kg of CO2) (Table 18). This

510

behavior was observed both in the production phase and in the construction one. The maximum

511

impacts in terms of energy are related to the thermo-blocks and the faced clay bricks (both these

512

layers correspond to the 34% of the total Embodied Energy of the production phase); also the

513

foamed polyurethane has a high impact, despite the small thickness (27% of the total EE). As

514

expected, the maximum CO2 equivalent emissions are due to the clay bricks (about 52% of the

515

total emissions) and to the polyurethane (about 30%).

516

The consumptions during the Use Phase are due to the heat production of a natural gas

517

condensing modulating boiler (total efficiency equal to 0.9) and to the electricity consumptions of

518

the cooling system. The referring period is 50 year. The Embodied Energies related to the fuel are

519

very similar for the Straw Wall and the Traditional one, and this is due to the very similar delivered

520

energy consumptions (about 38˙000 MJ/year for both the systems): the total thermal transmittance

521

of the two walls is the same and this is the reason why the consumptions are not very different (as

522

shown in paragraph 4.2). The total emissions in terms of GWP and the EE of the electric

523

consumptions for the cooling are negligible, due to the low cooling energy demand for the

524

investigated building (2 and 4% of the total CO2 emissions for the Traditional Wall and the Straw

525

Wall, respectively).Considering only the production and construction phases, the Embodied Energy

526

associated to the innovative wall system is about half of the value related to the traditional wall.

527

Also the CO2 equivalent emissions differ by more than 40%.

528

Finally, from the Life Cycle Assessment analysis it can be observed that the Use phase is

529

responsible for about 91% and 85% of the total EE for the SW for the TW, respectively. In terms of

530

GWP, the Use phase represents the 93% and the 88% of the total CO2eq. emissions for the SW

531 532

and the TW, respectively (Figure13 a) and b)).

533

5. CONCLUSIONS

534

Nowadays natural materials are gaining more and more attention as building materials, due to their

535

thermal characteristics and sustainability. In this framework a novel wall layer made of straw bales

536

and natural plasters was characterized by evaluating its thermal behavior and environmental

537

impact.

538

A preliminary analysis of straw bale buildings spreading worldwide highlighted a scarce systematic

539

census of this kind of buildings. The certain sources analyzed showed the largest amount is USA,

540

with 784 buildings, followed by France with 700. In Italy, Promopaglia association claims the

541

presence of 635 straw buildings, however the actual registered value amounts to 176, mostly

542

concentrated in the North.

543

In this contest the new wall layer demonstrated relevant thermal characteristics, with an U-value

544

equal to 0.154 W/(m2K). It complies the limited values of the thermal transmittances fixed by the

545

DM 26/06/2015 for all the climate zones and also the stringent limits imposed for the years 2019-

546

2021 (0.43 – 0.24 W/m2K), passing from climate zone A to F.

547

The wall layer was used as building material of a design case study and dynamic simulation

548

highlighted high energy performance, lower than the reference building as defined in the

549

abovementioned DM for the sites of Pescara, Palermo, and Bolzano.

550

As regards sustainability, LCA assessment applied to the new wall (SW) and to a traditional wall

551

(TW) showed that for the production and construction phases, the Embodied Energy (EE) of SW is

552

about half of the value related to TW, while the CO2 equivalent emissions differ by more than 40%.

553

Life Cycle Assessment analysis also showed that the use phase is responsible for about 91% and

554

85% of the total EE for the SW for the TW, respectively.

555

represents the 93% and the 88% of the total CO2 eq. emissions for the SW and the TW,

556

respectively.

In terms of GWP, the Use phase

557

The proposed innovative wall package seems promising for building applications, both from energy

558

saving and environmental impact points of view.

559 560 561

AUTHOR DECLARATION

562 563 564 565 566 567 568

We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us.

569

this work and that there are no impediments to publication, including the timing of publication, with respect

570

to intellectual property. In so doing we confirm that we have followed the regulations of our institutions

571

concerning intellectual property.

572

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Figure 1: Trend of world production of wheat [7].

706 707 708 709

710 711 712 713

Figure 2: Box plot of the thermal conductivity data distribution for straw bales as retrieved by the literature survey.

714 715

Figure 3: Thermal conductivity vs density for straw bales on edge and flat.

716

717 718 719 720 721 722

Figure 4: Map of the global diffusion of straw bale buildings around the world.

723 724 725 726 727 728 729 730 731 732 733 734 735

Figure 5: Italian distribution of straw bale buildings.

736 737 738 739 740 741

Figure 6:The straw wall package layers.

742 743

Figure 7: The Small Hot Box apparatus: section views, list of the components and a picture with a

744

sample installed above (plywood box with straw inside).

745 746

Figure 8: The case study: render and IDA ICE model.

747 748

749 750 751 752 753 754

Figure 9: Traditional wall solution considered for the comparison with the innovative system in terms of environmental impact.

755

756 757 758 759 760 761 762 763

Figure 10: LCA analysis: flow charts of the straw wall – SW (a) and of the traditional wall - TW

Bolzano 20 NZEB Cooling

Delivered energy (kWh/m2)

18

NZEB Heating

SBB Cooling

SBB Heating

16 14 12 10 8 6 4 2 0 1

2

3

4

5

6

7

8

9

10

11

12

11

12

11

12

Pescara

14 NZEB Cooling

NZEB Heating

SBB Cooling

SBB Heating

Delivered energy (kWh/m2)

12 10 8 6 4 2 0 1

2

3

4

5

6

7

8

9

10

Palermo 7 NZEB Cooling

NZEB Heating

SBB Cooling

SBB Heating

Delivered energy (kWh/m2)

6 5 4 3 2 1 0 1

764 765 766 767 768

2

3

4

5

6

7

8

9

10

Month

Figure 11: Monthly delivered energy for heating and cooling, calculated per unit of floor area for NZEB and SBB at the three locations.

769 770

Figure 12: Temperature trend of indoor air for SBB and NZEB during a week of August. 100% 90%

80% 70%

EE (MJ)

Use Phase 60%

Construction phase

50%

40%

Production Phase

30% 20% 10%

0%

771

Straw Wall

Traditional Wall

(a)

Traditional Wall

(b)

100% 90% 80% 70%

GWP (kg CO2)

Use Phase 60% 50%

Construction phase

40%

Production Phase

30% 20% 10% 0%

772

Straw Wall

773

Figure 13: Focus on the contributions of the different phases for the SW (straw wall) and the

774

traditional wall TW buildings in terms of EE (a) and GWP (b).

775 776 777

Table 1: Literature review about straw bales features. Reference

Density (ρ)

Orientation

3

(λ) [W/mK]

[kg/m ] 130

on edge

0.048

130

flat

0.061

75

on edge

0.052

75

flat

0.056

90

on edge

0.056

90

flat

0.060

63

n.s.

*

0.059

123

n.s.

0.064

90-110

on edge

0.045

90-110

on edge

0.052

90-110

flat

0.080

75

flat

0.066

77

n.s.

0.064

77

n.s.

0.069

80

on edge

0.051

80

flat

0.072

n.a.

flat

0.060

n.a.

on edge

0.045

80

flat

0.060

80

on edge

0.040

120

on edge

0.055

120

flat

0.075

ForschungsinstitutfürWärmeschutz[36]

90

n.s.

0.038

GruppeAngepassteTechnologie[37]

90

n.s.

0.038

Goodhew and Griffiths[38]

60

n.s.

0.067

McCabe [26]

Danish Technological Institute[27]

Shea[28] FASBA[29] DIBt[30] Conti[31] Grelat[32]

Douzane[33]

Minke e Mahlke[34]

Oliva e Courgey[35]

778 779 780 781 782 783 784 785

Thermal conductivity

*

n.s. = not specified

786 787 788

Table 2: Thermal properties of construction materials (SBB). [W/mK]

Material

3 [kg/m ] c [J/kgK]

Render Perforated brick partition wall

0.800

1800

790

0.215

1633

840

Floor coating

0.180

1100

920

L/W concrete

0.150

500

1050

Concrete

1.700

2300

880

Light insulation

0.036

20

750

Wood

0.120

500

2300

Gypsum

0.220

970

1090

Chipboard Raw earth plaster

0.130 0.982

1000 1700

1300 1000

Fir wood planks

0.089

520

2300

Straw bale "on edge"

0.066

105.69

1900

Cocciopesto plaster

0.920

1600

1000

Air gap

0.170

1.2

1006

789 790 791

Table 3: U values of the various wall packages (SBB). Elements Internal walls

Internal floor

Roof

Basement wall and slab towards ground

3 pane glazing, clear 4-12-4-12-4

792 793 794 795 796

Layers

s (m)

Render

0.015

Brick forato

0.12

Render

0.15

Floor coating

0.005

L/W concrete

0.02

Brick forato

0.012

Concrete

0.05

Light insulation

0.04

wood

0.264

Gypsum

0.02

Chipboard Light insulation

0.016 0.04

Concrete

0.1

Light insulation

0.1

2

U [W/m K] 1.308

1.090

0.280

0.236

1.900

797 798 799

Table 4: Characteristics of the glazing system (SBB). 3 pane glazing, clear, 4-12-4-12-4 Parameter

Value

G, Solar Heat Gain Coef

0.68

T, solar Trasmittance

0.60

Tvis, Visible Trasmittance

0.74

Emissivity (int./ext.)

0.84

800 801 802 803

Table 5: U values for NZEB at the three locations. Pescara Elements of construction

2

Bolzano 2

Palermo 2

U [W/m K]

U [W/m K]

U [W/m K]

External walls

0.29

0.26

0.43

Internal walls

1.03

1.03

1.03

Internal floors

2.39

2.39

2.39

Roof

0.26

0.22

0.35

External floor

0.29

0.26

0.44

0.29 0.29

0.26

0.43 0.43

Basement wall towards ground Slab towards ground

0.26

804 805 806 807 808 809

Table 6: Characteristics of the glazing system for NZEB. Pescara

Bolzano

Palermo

G, Solar Heat Gain Coef

0.35

0.35

0.35

T, Solar Trasmittance

0.349

0.349

0.349

T vis, Visible Trasmittance

0.641

0.641

0.641

Emissivity (int./ext.)

0.837

0.837

0.837

1.8

1.1

3

Parameter

2

U [W/m K]

810 811 812 813 814 815

816 817 818

Table 7: Thermal bridges for the building model. Length (m) 111.54 62.98 45.93 73.16 5.60 52.78 52.92 27.58 13.70 8.26 -

Thermal bridges External wall / internal slab External wall / internal wall External wall / external wall External windows perimeter External doors perimeter Roof / external walls External slab / external walls Roof / Internal walls External walls, inner corner Roof / external walls, inner corner Extra losses Sum

Total (W/K) 3.826 2.16 3.675 7.316 0.56 9.401 26.459 1.007 -1.370 -1.096 1.121 52.372

Ψ (W/mK) 0.034 0.034 0.080 0.100 0.100 0.178 0.500 0.037 -0.100 -0.133 -

819 820 821 822 823

Table 8: Schedules for heating and cooling period in the three locations. Heating City

824 825 826 827 828 829 830 831 832 833 834 835 836 837 838

Cooling *

period

time

period

time

Palermo

01/12-31/03

14:00-22:00

01/04-30/11

12:00-18:00

Pescara

01/11-15/04

09:00-21:00

16/04-31/10

12:00-18:00

Bolzano

15/10- 15/04

08:00-22:00

16/04-14/10

12:00-18:00

*It is considered as complementary to the heating period, assuring that the plant is on only when the set point values of the inside temperature are not achieved.

839 840 841 842 843 844 845 846

Table 9: The traditional wall features. 2

Layer (from outside to inside)

s(m)

λ (W/mK)

Ri (m K/W)

Outdoor

-

-

0.04

Faced Clay Brick

0.12

-

0.340

Foamed Polyurethane

0.12

0.023

5.210

Thermoblock

0.20

0.210

0.950

Plaster

0.02

0.870

0.023

Indoor

-

-

stot (m)

0.46

0.130 2

Rtot(m K/W) 2

Utot (W/m K)

6.520 0.150

847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865

Table 10: Straw Wall (SW): data inventory for components production and supplying stage (referring to 1 m2 of produced material).

Material and energy inputs

Unit

Amount

Data source

CocciopestoBody Plaster Lime‘s production

kg

6

Primary Data

Silica Sand production

kg

18

Primary Data

tkm

15.5

Ecoinvent

tkm

0.54

Ecoinvent

tkm

48

Ecoinvent

kWh

0.61

Primary Data

Lime‘s production

kg

1.8

Primary Data

Silica Sand production

kg

4.5

Primary Data

tkm

4.7

Ecoinvent

tkm

0.135

Ecoinvent

tkm

0.06

Ecoinvent

tkm

48

Ecoinvent

kWh

0.61

Primary Data

Straw (rye production)

kg

14.8

Primary Data

Transport of the straw from a wheat field in Abruzzo in the building site (freight, lorry 3.5-7.5 metric ton, EURO4) – distance 10 km

tkm

0.74

Ecoinvent

0.06

Ecoinvent

Lime‘s Transport(freight, lorry 16-32 metric ton, EURO4) – distance 1290 km Sand‘s Transport from the quarry(freight, lorry 3.57.5 metric ton, EURO4) – distance 15 km Transport of the Cocciopesto plasters in the building site(freight, lorry 16-32 metric ton, EURO4) – distance 800 km Electricity (Mill + Rotary Mixer) Cocciopesto Finishing

Lime‘s Transport(freight, lorry 16-32 metric ton, EURO4) – distance 1290 km Sand‘s Transport from the quarry(freight, lorry 3.57.5 metric ton, EURO4) – distance 15 km Transport of the red wattle(freight, lorry 3.5-7.5 metric ton, EURO4) – distance 15 km Transport of the cocciopesto plasters in the building site(freight, lorry 16-32 metric ton, EURO4) – distance 800 km Electricity (Mill + Rotary Mixer) Straw

Wood 3

Fiberboard‘s production

m

Transport of the fiberboards from a local manufacturer in the building site (freight, lorry 3.57.5 metric ton, EURO4) – distance 15 km

tkm

0.54

Ecoinvent

Silica Sand production

kg

22.41

Primary Data

Straw

kg

0.27

Primary Data

Clay

kg

6.00

Primary Data

tkm

0.67

Ecoinvent

tkm

0.0054

Ecoinvent

tkm

0.18

Ecoinvent

Raw Earth plaster

Sand‘s Transport from the quarry(freight, lorry 3.57.5 metric ton, EURO4) – distance 15 km Straw‘s Transport from wheat field(freight, lorry 3.57.5 metric ton, EURO4) – distance 10 km Transport of the clay(freight, lorry 3.5-7.5 metric ton, EURO4) – distance 15 km

Transport of the red wattle (freight, lorry 3.5-7.5 metric ton, EURO4) – distance 15 km Transport of the Raw Earth plasters components in the building site(freight, lorry 16-32 metric ton, EURO4) – distance 800 km Electricity (Mill + Rotary Mixer + Land‘s sieving)

tkm

0.06

Ecoinvent

tkm

48

Ecoinvent

kWh

0.62

Primary Data

866 867 868 869 870 871 872 873 874

Table 11: Traditional Wall (TW): data inventory for components production and supplying stage (referring to 1 m2 of produced material). Material and energy inputs

Unit

Amount

Data source

Traditional Plaster Base Plaster production

kg

27.6

Ecoinvent

Transport in the building site (freight, lorry 16-32 metric ton, EURO4) – distance 70 km

tkm

3.9

Ecoinvent

Clay brick production

kg

107.8

Ecoinvent

Transport in the building site (freight, lorry 16-32 metric ton, EURO4) – distance 250 km

tkm

54

Ecoinvent

Polyurethane foam slab

kg

4.2

Ecoinvent

Transport in the building site (freight, lorry 16-32 metric ton, EURO4) – distance 400 km

tkm

3.4

Ecoinvent

Sand – lime brick production

kg

195

Ecoinvent

Transport in the building site (freight, lorry 16-32 metric ton, EURO4) – distance 250 km

tkm

97

Ecoinvent

Thermo-block

Foamed polyurethane

Faced clay brick

875 876 877 878 879 880

881 882 883 884 885

Table 12: Description of the tested samples. Samples

Description

sTOT(m)

composition pW+P

Layer to be analyzed

plywood panel (0.010 m) + polystyrene

0.064

plywood panel (pW)

0.100

Straw (S)

0.051

cocciopesto plaster

panel (0.054 m) pW+S+pW

A box composed by plywood panels (0.010 m) with straw inside (0.08 m thick) (fibers with parallel disposition)

pW+CPplaster+P

plywood panel (0.010 m) + cocciopesto

layer (CPplaster)

plaster layer (0.031 m) + polystyrene panel (0.010 m) pW+REplaster+P

plywood panel (0.010 m) + earth-based

0.049

Raw Earth plaster layer (REplaster)

plaster layer (0.029m) + polystyrene panel (0.010 m) Wood

two fir wooden planking elements joined by

0.021

Wood planking

nails in order to obtain a panel 30 x 30 cm

886 887 888 889

Table 13: Thermal results of the investigated samples: thermal flux meter methodology (Small Hot

890

Box). Samples

Hot Side Test

sTOT(m)

Condition (°C)

891 892 893 894 895 896

ΔTs

λTOT

q 2

(°C)

(W/m K)

(W/mK)

̇

pW+P

45

0.064

20.06

13.49

0.043

4.53

pW+S+pW

45

0.100

19.66

14.37

0.073

6.26

pW+CPplaster+P

45

0.051

17.03

46.85

0.140

4.66

pW+REplaster+P

45

0.049

15.12

42.08

0.136

5.50

Wood

45

0.021

13.07

55.37

0.089

7.67

897

Table 14: Thermal resistances of the layers that compose the innovative wall (SW). 2

Layer

s(m)

λ (W/mK)

Ri (m K/W)

Outdoor

-

-

0.04

Cocciopesto Plaster (CPplaster)

0.031

0.920

0.033

Wood (W)

0.021

0.089

0.23

Straw (S)

0.350

0.065

5.38

Wood (W)

0.021

0.089

0.23

Air gap

0.050

-

0.18

Wood (W)

0.021

0.089

0.23

Raw Earth plaster (REplaster)

0.029

0.982

0.029

Indoor

-

-

stot(m)

0.523

0.13 2

Rtot(m K/W) 2

Utot(W/m K)

6.482 0.154

898 899 900

Table 15: Annual delivered energy for NZEB and SBB at the three locations.

Bolzano Pescara Palermo

NZEB [kWh/m2year] 78.0 52.4 24.8

 [%] 18.3 17.2 27.4

SBB [kWh/m2year] 63.7 43.4 18.0

901 902 903 904 905 906 907

Table 16: Delivered energy calculated for the model with SW and TW. Cooling

Heating

Total

2

3.3

40.1

43.4

2

3.2

39.8

43.1

SW [kWh/m ] TW [kWh/m ]

908 909 910 911 912 913 914 915

916 917 918 919

Table 17: Materials, embodied energy and equivalent carbon emission of the Straw Wall (SW) and the Traditional Wall (TW). Items

PHASES

EE(MJ)

GWP (kg CO2)

64˙312

4˙280

13˙100

378

64˙134

2˙550

40˙750

2˙009

26˙464

1˙474

2˙165˙000

134˙500

496˙000

27˙000

2˙869˙760

172˙191

17˙370

2˙108

141˙860

2˙290

111˙543

4˙443

138˙125

9˙590

48˙122

2˙680

2˙150˙000

133˙000

492˙500

26˙850

3˙099˙520

180˙961

STRAW WALL Cocciopesto plaster and finishing Straw

Production and transport

Wood Raw Earth based plaster

Construction at the yard

Electricity + Water Fuel

Usage

Electricity Total TRADITIONAL WALL Traditional plaster Thermo-block

Production and transport

Foamed Polyurethane Faced Clay Brick

Construction at the yard

Electricity + Water Fuel

Usage

Electricity Total

920 921

Table 18: Global Warming Potential and Embodied Energy calculated for the three phases both for

922

the SW (straw wall) and the traditional wall TW buildings. GWP (kg CO2eq) TW

SW

Δ(%)

TW

SW

Δ(%)

Production

18˙434

9˙215

- 50%

408˙896

207˙940

- 49%

Construction

2˙681

1˙474

- 45%

48˙123

26˙464

- 45%

Use

159˙850

161˙500

+ 1%

2˙642˙500 2˙661˙000 + 0.7%

Total

180˙964

172˙189

- 4.8%

3˙099˙519 2˙895˙404

Phases

923 924

EE (MJ)

- 6.6%