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Building incorporated bio-based materials: Experimental and numerical study
Journal Pre-proof Building incorporated bio-based materials: Experimental and numerical study Faiza Mnasri, Sofiane Bahria, Mohamed El-Amine Slimani, Ouhsaine Lahoucine, Mohammed El Ganaoui PII:
S2352-7102(19)30253-0
DOI:
https://doi.org/10.1016/j.jobe.2019.101088
Reference:
JOBE 101088
To appear in:
Journal of Building Engineering
Received Date: 1 December 2018 Revised Date:
11 October 2019
Accepted Date: 21 November 2019
Please cite this article as: F. Mnasri, S. Bahria, M. El-Amine Slimani, O. Lahoucine, M. El Ganaoui, Building incorporated bio-based materials: Experimental and numerical study, Journal of Building Engineering (2019), doi: https://doi.org/10.1016/j.jobe.2019.101088. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
Building Incorporated Bio-Based Materials: Experimental and Numerical Study Faiza Mnasri a,*, Sofiane Bahria a, Mohamed El-Amine Slimani b, c, Lahoucine Ouhsaine a, Mohammed El Ganaoui a a
Laboratory of Energetic, LERMAB, IUT Henri Poincaré, University of Lorraine, 186 route
de Lorraine, 54400 Cosnes-et-Romain, France b
Department of Energetic and Fluid Mechanics, University of Science and Technology
Houari Boumediene (USTHB), 16111 Algiers, Algeria c
Unité de Développement des Equipements Solaires (UDES), Centre de Développement des
Energies Renouvelables (CDER), 42415 Tipaza, Algeria
Abstract In building environments, several research on dynamic moisture storage in hygroscopic building materials has improved interest in moisture buffering capacity of bio-based materials and demonstrated the potential of these materials to improve thermal comfort and buildings energy consumption. This paper presents an investigation, which aims to compare the hygroscopic behavior of different bio-based materials to identify their hygric proprieties. For this, an experimental facility is used to measure the moisture buffer value (MBV) for different categories of building materials. Thereafter, a dynamic simulation has been carried out by using TRNSYS software in order to evaluate heating and cooling loads. The results showed that the wood-cement composite still has excellent moisture regulator when compared to wood panels or fibrous materials. It has a buffer capacity superior to 3 [g/m2.% RH] very close to that of wood fiber panels. The simulation results of the different cases showed that the insulation reduces significantly total energy demand, but it does not lead heat evacuation in the summer season. Thus, from this study, it can be concluded that a natural ventilation mechanism is recommended to improve energy efficiency in the building.
* Corresponding author E-mail address: [email protected] (F. MNASRI), [email protected] (S. BAHRIA), [email protected] (M.E.A. SLIMANI), [email protected] (L. OUHSAINE), [email protected] (M. EL GANAOUI)
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Keywords: Bio-based materials, Moisture Buffer Value, Dynamic simulation, Energy efficiency. Nomenclature Symbol
Explanation
Unit
A
Exchange area
m²
RH
Relative humidity
%
ρ0
Dry apparent density
Kg.m-3
w
Water content
kg.m-3
∆m
Mass variation during the absorption/desorption phase
g
MBV
Moisture buffer value
g/(m2. % RH)
mwater, cal
Water value of the calorimeter
g
mi
Mass capacity
g
C
Thermal capacity
J.kg-1K-1
Q
Heat capacity
J.K-1
1. Introduction Bio-based building materials were used since several years and had been improved over that the last decades. There are characterized by high environmental performance and a good hygrothermal behavior in the wall [1,2]. In areas with cold climates, most buildings require a good insulation level (specified by R-Value). Thus, higher the R-Value, better is the thermal insulation performance [3]. In the construction industry, we do not need materials with high thermal conductivity. Indeed, this property is the key property for thermal diffusivity and effusivity, two terms that represent the heat diffusion and the thermal inertia of building [4,5]. The heat transfer through the building materials depends mainly on the constituents forming the materials and their microstructure. Material configurations for the building envelope can be modified and improved by appropriately arranging the materials to achieve the required performance. The building materials properties that are easily modifiable, such as the density, 2
composition, and proportions of the mixture, are different from those who are unalterable, such as geometry and the size of the micropores and the inherent mineral properties [6,7]. In the study of Amel et al. [8], the thermal properties of wood-cork sandwich panels with different thicknesses were investigated. The measurement of the thermal conductivity, thermal resistance, specific heat, and thermal diffusivity indicated that increasing the density of the samples leads to an increase of the value of the thermal conductivity and a decrease in thermal resistance of sandwich structures. Several researches have been carried out around the world to develop bio-based materials for building construction. Ramesh et al. [9] presented a review on plant fiber-based biocomposites for material construction. While focusing on composite materials, the main points to consider are environment friendliness and lightness, with high specific properties. This century has seen remarkable progress in the field of green technologies in the field of materials science through the development of high-performance materials made from natural resources around the world. Préneron et al. [10] proposed a simple and efficient experimental method, useful for building materials laboratories; this method is adapted through the methods proposed in the literature. For this, fungal growth has been studied and analyzed under different environmental conditions on earth-based materials with or without the addition of hemp ship or straw. Some other studies are examining such growth deal with paper-based or wood-based materials, as well as inorganic materials such as gypsum plasterboard or cement [11–13]. However, the hygric characterization can be based on the exploitation of steady-state measurements [14] or measured under dynamic conditions such as the measurement of the Moisture Buffer value (MBV) [15]. In the study of Mnasri et al. [16], an example of the feasibility of eco-materials production chain in a European project context is presented. The analysis based on a hygric characterization of different eco-materials, which are selected as candidate materials in the great cross-border region (Belgium, France, Luxembourg). Collet et al. [17] have proposed a study where they compared the hygroscopic behavior of three hemps concretes by measuring their sorption curve, water vapor permeability,and moisture buffer value. These measurements allow to identify the hygric storage capacity of each material and to classify them as excellent or not hygric regulators us a function to MBV value.
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Indeed, this test of MBV indicates the amount of water vapor that is transported in or out of material, during a certain period, when the vapor concentration of the surrounding air varies [18]. It requires an experimental procedure, and its value permits a direct comparison of the building materials moisture performance. The protocol of the MBV investigation has been created by the NORDTEST Project, which is defined as the practical measurement of the hygric performance of materials under dynamic conditions [19]. A similar experimental methodology to evaluate the hygroscopic buffering capacity of porous materials has been proposed by the Japanese Industrial Standard (JIS) [20]. This experimental procedure is also based on an evaluation of weight changes of a specimen when its surrounding climate is subjected to relative humidity variation but differs from the NORDTEST Project, as regards for the time scheme, the imposed signal and the thickness of specimen [21]. Rahim et al. [22] have investigated the effect of the temperature, which depended to the sorption isothermal, on the hygrothermal behavior of a two bio-based building envelope. Thus, the effect of moisture buffering capacity of these materials on hygric indoor comfort in a room has been studied. Belakroum et al. [23] have proposed an experimental investigation, where the sound absorption coefficient and moisture buffer value (MBV) of new insulation materials are evaluated. The studied composites are aggregates of date palm fiber and lime or starch. Two types of date palm fiber were tested: trunk surface fiber and rachis fiber. In order to find out the most efficient specimens, we analyzed several samples of different composition. The measurements of the Moisture Buffer Value (MBV) have shown that the composite made from 50% of trunk fiber and lime had an average MBV of 3.73 g/(m2%RH). For samples based on petioles fiber and lime, the greatest MBV measured was 2.58 g/(m2%RH) for samples of 50% of fibers. Using starch as a binder, we recorded a moisture buffer value of 4.05 g/(m2%RH) with only 20% of trunk fibers. Thus, all MBV measured classify these new materials as an excellent hygric regulator. Thus, hygroscopic materials research has marked more consideration to the development of new materials [24–26] by using biodegradable and natural materials. However, in construction, for similar environments, users use the same materials, the effects often being different due to the use of air conditioning in the building, the ventilation strategy, thickness of materials and differences in the initial moisture content of hygroscopic materials [21]. In order to analyze the problem of space heating demand reducing, heat losses can be reduced by improving building performance with increased insulation levels [27]. This is the most effective way to significantly reduce heating demand, taking into account, dependence on 4
climatic conditions variations [28–30]. However, in the existing building stock, this measure can be, sometimes, more expensive than the substitution of boilers in heating systems [31,32]. Abahri et al. [33] analyzed the heat and mass transfers combined to the convective and diffusive driving potentials in hygroscopic materials and demonstrated the availability of the sub-models by numerical simulation. The results showed that when the hygric state between the environment and the wall was stable, convection was a significant driving potential. Shui Yu et al. [34] have simulated three terms: indoor humidity conditions, energy consumption, and economy at the room level in order to analyze the moisture buffering performance of different hygroscopic materials.They have examined moisture-buffering materials across three aspects: indoor humidity conditions, the building’s energy consumption, and the building’s life-cycle cost. The results showed that hygroscopic materials could control indoor air humidity changes and improve human comfort but they needed to be used together with central air conditioning because of their limited humidity controlling performance. Kuznik et al. [35] developed a new TRNSYS model to evaluate the thermal behavior of an external wall with PCM. Asadi et al. [36] have investigated a multi-objective optimization scheme (a combination of TRNSYS, GenOpt, and MATLAB) in order to optimize the retrofit cost, energy savings and thermal comfort of a residential building. In this work, a study has been achieved to compare thermal performances of building materials. Our paper is organized as fellow: the first part represents an experimental hygrothermal study, where, we propose a hygric water comparison of different biobased materials. The second part, a methodology to optimize and calculate the thermal loads within dynamic constraints and for different insulations types is proposed. Thus, a developed model has been used to study the different cases and finally, results have also been analyzed and discussed.
2. Materials and Methods 2.1.Composition and Manufacturing In this paper, we propose to study a new structure distributed by a Belgian company SYSTEM'BAT. It is based on a formwork system, named ISOL+ST, which is a monolithic technology of construction where the walls and slabs are concreted in prepared casing panels of wood chips. The basic element of ISOL + ST construction systems, IBS is a wood-cement panel. The basic raw material used for its manufacture is coniferous wood chips, which form 89% of the 5
total volume of the panel. The other components are the cement, which ensures the strength of panels, a water glass solution that stabilizes the panels against moisture and increases their resistance against fungi, rodents, insects, and water. Its proprieties are related to water and thermal characteristics of raw materials. The manufacture of this product is made through several steps, which are as follows (fig.1).
Fig.1. Production steps of the IBS wood panel
2.2. Hygrothermal Study In this study, we propose a hygric comparison of different biobased materials. These materials were the result of an identification study of an eco-materials sector in the Greater Region (Belgium, France, Luxembourg) as part of an ECOTRANSFAIRE project [37]. These materials can be categorized into two families; one for fibrous panels and the other for woodbased panels. The two families of different materials are presented in table 1. Tabel.1. Classification of study materials Wood panels
Fibrous materials
Placo panel
Hemp fiber panel
Waterproof placo panel
Wood fiber panel
Chipboard panel
Cellulose wadding panel
OSB Panel
Recycled Textile Fiber Panel
In front of these two categories, the IBS composite panel, which represents a mixture of wood and cement is compared with these different types of materials by a hygric characterization in a dynamic mode that is the Moisture Buffer Value (MBV) test. This characterization method gives access to the hygric regulator quality of the material. •
Moisture Buffer Value (MBV)
The term "Moisture buffer value (MBV)" was set up by the NORDTEST project to determine the hygric buffering capacity value of materials. It indicates the amount of water absorbed or
6
desorbed when the material is subjected to a change in the external relative humidity for a given time [18]. The NORDTEST project defines a dynamic cycle of 24 hours in which the relative humidity is set at 75% for 8 hours, and then at 33% for the following 16 hours [38]. When the thickness of the material is greater than the depth of water penetration under the diurnal conditions, the hygric buffering capacity value is independent of the material thickness and the amplitude of the relative humidity variation. Classification of materials has been proposed by the NORDTEST Project which is shown in fig. 2 and which makes it possible to evaluate the performance of a material according to its MBV value.
Fig.2.Moisture Buffer Values (MBV) classification according to Project NORDTEST [21]
The classification of MBV is evaluated according to the hygric response of a material. According to Rode, 2005 [39], the buffering effect of building materials can be considered very important for the hygrothermal performance of a building. However, there are materials whose MBV is very negligible, others which have water buffering values greater than 2 [g/m2.% RH] are classified for an excellent hygric response. •
Experimental Protocol
The Characterization by the MBV test according to the NORDTEST experimental protocol [40] consists of measuring the capacity of a material, moderating the relative humidity variations of the surrounding air. The moisture buffer value characterizes the ability of a material, or a multi-layer component, to moderate the variations in relative humidity of the surrounding air. Thus, this value is defined by: MBV =
∆m A( RH haute − RH basse )
(1)
7
Where:
∆m: mass variation during the absorption/desorption phase (g) A: Exchange area (m²) RHhigh/low: relative humidity high and low during the cycle (%) The principle of the associated test protocol proposes to focus samples in square format to well-defined relative humidity cycles that generally have meteorological data in order to be representative of the cycles imposed on the walls of buildings. The temperature is set constant. Thus, several pairs of relative humidity can be considered to present cycles of humidification and drying. The reference torque is 75% RH for an exposure time of 8 hours in absorption and 33% RH for a period of 16 hours in desorption. The mass tracking by weighing at each cycle of the samples, which are subjected to periodic variations of humidity, then makes it possible to determine the water buffering value of the materials. The test bench used consists of a Memmert HCP climatic cabinet (Fig.3) in which the temperature can be regulated between 30 and 90 °C and the relative humidity between 30 and 95%.
Fig.3. Climate chamber controlled in temperature and relative humidity (LERMAB Longwy)
The mass tracking of the samples is based on weighing during the absorption phase and weighing during the desorption phase. The cycles are repeated for two weeks. •
Specimens
The study was performed on samples of two lists of materials mentioned in Table.1 and on the composite wood cement material. They are all isolated on five sides with aluminum tape 8
so that the moisture circulates vertically as shown in Fig.4. The samples are cut according to the capacities of the balance (210 grams accuracy 0.01 gram) and their mass per unit area.
Chipboard panel
Hemp fiber panel Recycled Textile Fiber Pane
Placo panel Waterproof placo panel OSB Panel wood cement panel
Wood fiber panel
(a)
Cellulose wadding panel
wood cement panel
(b)
Fig.4. Samples of different materials: (a) wood panels, (b) fibrous materials
The samples are cut out according to the balance of capacities and their surface density. In order to perform the MBV test in the oven, we have created the cycle on Celsius software as shown in table 2.
Table.2. MBV cycle Hours
Duration
Temperature
Relative
Type
hh:mm
hh:mm
°C
humidity
1
0:01
0:01
40
33
next
2
16:00
15:59
40
33
next
3
16:01
0:01
40
75
next
4
24:00
7:59
40
75
loop
The first ramp lasts one minute. It can increase or decrease the indoor temperature to 40 °C and set the relative humidity to 33%. The second ramp maintains the temperature at 40 °C and 33% relative humidity for 16 hours, in order to achieve the desorption cycle. The third ramp is again a ramp of one minute. It allows going from a relative humidity of 33% to 75%. Finally, the fourth ramp maintains the temperature at 40 °C and 75% relative humidity for 8 hours, to achieve the absorption cycle. During the test, we can see that the average value of relative humidity drops at 10:00 from 75% to 19%. This drop is due to the opening of the door during weighing. On the other hand, during changes of instructions, the passage from 33% to 75% takes place in about a minute.
9
2.3. Heat Capacity The specific heat capacity of a substance is defined as the amount of heat energy required to raise the temperature of a unit mass of a substance through 1°C. According to the law of energy conservation or calorimeter principle, in a closed system, the heat lost by a hot body is equal to the heat gained by a cold body. In this method, a bit of solid is heated at high temperature and is quickly transferred to a calorimeter containing cold water. The solid loses thermal energy while the cold water gains it. After sometimes, the solidwater and calorimeter attain the same temperature. Then, the liquid should also be stirred to allow an even distribution of the heat energy throughout its volume. Fig. 5 shows the main materials used for the determination of heat capacity by a Dewar silt calorimeter.
Fig.5. Determination of heat capacity by a Dewar silt calorimeter
The calorimeter is composed by various materials. It is therefore difficult to determine its thermal capacity. That is why it can be modeled as follows: n
mcal C cal = ∑ mi Ci = mmer C mer + malu C alu + m glas C glas
(2)
i
We replace this calculation by its water equivalent. We thus have:
mcal Ccal = mwater,cal Cwater
(3)
10
Where mwater, cal is called the water value of the calorimeter, and Cwater= 4185 J / kg / K is the thermal capacity of the water, mi and Ci are the mass and thermal capacities of the different components of the calorimeter. The water value is a characteristic of the calorimeter; it must be determined experimentally and will be kept for all manipulations. The first step is to determine the mass of water (m
water, cal)
of the calorimeter. For this, we
introduce into the calorimeter a mass of water m1(500g) at room temperature T1, where the calorimeter is itself at the temperature T1. After that, we added to it the second mass of water m2(200g) previously heated to the temperature T2=80°C. After stirring the mixture, thermal equilibrium is expected, and the final temperature Tf is recorded in the calorimeter. According to the principle of energy conservation, in an isolated system, there is no heat exchange with the outside. There must be heat preservation inside the system: Heat loss = heat gain: Q1 + Q 2 + Q cal = 0
(4)
With: Q1 = m 1C water (T f − T1 )
(5)
Q 2 = m 2 C water (T f − T2 ) Q cal = m water
, cal
(6)
C water (T f − T1 )
(7)
m 2 C water (T f − T 2 ) + ( m 1 + m water ,cal )C water (T f − T1 ) = 0
mwater,cal =
(8)
m2 (Tf − T2 ) − m1 (Tf − T1 )
(9)
(Tf − T1 )
The second step is the determination of the thermal capacity of different materials constituting the envelope of an eco-cottage, which will be the subject of the following part of this study. Then, to be prepared, a mass of water m1 = 300 g is introduced into the calorimeter at room temperature T1, the calorimeter is itself at the same temperature T1.The mass sample (msample) is added to this. The sample will have been previously heated to T2 on a water bath, by taking care to isolate the sample from the bottom of the kettle to avoid conduction between the electrical resistance and the sample. The water is continuously agitated in the calorimeter, and the system is expected to be at thermal equilibrium. Finally, the final temperature Tf measured in the calorimeter is recorded. From the measurement of Tf and the measurement of the mass of the sample (m sample), one will determine the experimental value of Csample (J/kg.K).
11
By writing the first principle of thermodynamics applied to the system {calorimeter + mass of water + sample} by assuming that the calorimeter is perfectly adiabatic. The analytical expression of the heat capacity of the sample Csample: Q water + Q sample + Q cal = 0
(10)
With: Q water = m water C water (T f − T1 )
(11)
Q sample = m sample C sampler (T f − T 2 ) Q cal = m water
, cal
(12)
C water (T f − T1 )
(13)
m water C water (T f − T1 ) + m sample C sample (T f − T 2 ) + ( m water ,cal C water (T f − T1 ) = 0
Csample =
Cwater (mwater + mwater,cal )(T1 − Tf )
(14) (15)
msample(Tf − T2 )
The investigation aim is to measure the heat capacity of building materials. We show that the heat capacity of the calorimeter with the plastic protective cover is 32.05 J/°C.
Fig.6. Temperature profile in the calorimeter
Fig. 6 shows the temperature evolution in the calorimeter for the different samples. It should be noted that the temperature decreased over time to finally attain thermal equilibrium. Table 3 shows the calculated thermal capacities for the different samples using the equation (Eq.15).
Table 3.Thermal capacity for different samples 12
Initial temperature
Final temperature Tf
Thermal capacity
T2 (°C)
(°C)
kJ/ (kg K)]
86
71,9
1,4
Concrete
85,2
70,3
0,92
Panel OSB
82,9
68
2,45
Panel IBS
82
68,5
2,1
GPS insulation
We can note that between 85 and 72 °C, the decrease in temperature is 1.8 °C per minute, on an average. Below 70°C, the decrease remains almost constant at 0.27 °C per minute over the entire measuring range. Therefore, the loss of heat remains low considering the experimental parameters: -
We are located more than 20 °C above the ambient temperature
-
The volume of water represents only 1/5th of the calorimeter’s effective volume.
3. Dynamic simulation Residential buildings account for about 40% of total energy use; there is therefore great interest in improving building performance [41]. In this context, an eco-cottage is being built in Longwy University Institute of Technology (UIT Longwy). The first step is the process of research on energy efficiency field. This first construction was created by a partnership between IUT and IsolHABITAT (Belgian company- based in Liege). The eco-cottage is built with IzoLox system, insulating shuttering blocks composed by Graphite Polystyrene (GPS) and the ISB panel (Fig.7), which is the wood-cement composite, presented in the first part of this study.
Fig.7. Bloc of wall composed by GPS insulation and ISB panel
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In Table 4, the description of construction materials is given for floor, external walls, and roof.
Table 4. Description of the construction materials Layer type
Density
Floor
External Walls
Roof
[Kg/m3]
Thermal
Heat capacity
conductivity [kJ/h
kJ/kg.K
mK]
OSB panel
620
0.468
2.1
Wood wool
50
0.1404
2.1
Air gap
1
0.325
1.227
Plasterboard
790
1.155
0.801
ISB panel
675
0.396
2.45
Neopor
15
0.1224
1.4
Concrete
2300
6.318
0.92
ISB panel
675
0.396
2.45
Concrete slab
2300
6.318
0.92
25
0.142
1.38
2300
6.137
0.7
EPS Expanded polystyrene Floor tile
3.1.Geometrical description The eco-cottage area is 24.75m²; it’s composed by a single room with a door on the north side of 1.5m² (double glazed) and three windows with the same area (0.42m²). The first is in the east, and the two others are on the south side. The roof is slanted by 5° to the south for the evacuation of waters rain Fig.8. The eco-cottage is located in the Longwy city (Lorraine, north-east of France). The altitude of the city is 300 m. The latitude and longitude of Longwy are respectively 49.52 °N and 5.769° E. 14
Fig.8. The eco-cottage geometry
The average monthly temperature ranges from 0.1°C in January to 17.5°C in July. The average temperature during the year is 9.3 °C. The data of minimum and maximum temperature are presented in Fig.9.
Fig. 9. Data of the minimum and maximum temperature in Longwy city
3.2.Cases studies In this party, we propose to study seven studies cases. These investigated cases were the same dimensions as the reference case, except it differs in external wall composition, thermal insulation, and window glazing; they are as follows: Case1: In the external walls, the GPS insulation material is replaced by an air gap of 5 cm. Case2: In the external walls, the concrete material is replaced by a hollow brick of 15 cm. Case3: In the external walls, the GPS insulation material is replaced by a wood wool insulation of 15 cm. Case4: Single glazing is used for all window and door.
15
Case5: Double glazing is used for all window and door. Case6: On the floor, polystyrene material is replaced by a mortar layer (2 cm). Case7: Floor without insulation Fig.10. shows the simulation diagram made on the numerical environment of TRNSYS for dynamic simulation.
Fig.10.TRNSYS diagram for dynamic simulation
TRNSYS is a transient system simulation program used to simulate the behavior of building components [4]. In this study the following data are introduced into the simulation program structure:
-
Air Flows: The infiltration rate is fixed at 0.6 air changes per hour during all the times.
-
Earnings: in this study, we don’t take into account gains from people and lights.
-
Heating: The room is maintained at 20 degrees Celsius during occupied hours and at 15 degrees other times. The storage area is unheated.
-
Cooling: the air conditioner is which turns on if the temperature rises above 26 degrees Celsius.
-
Ground temperature: Type 77 is used to calculate the mean ground surface temperature for the year. 16
4. Results and Discussion 4.1. Moisture buffer value (MBV) After carrying out the successive humidification-drying cycles, regular weightings were carried out for each cycle as noted above. Thus, the MBV values are calculated for each tested material according to the formula defined by the NORDTEST project. The two lists of materials presented below are analyzed, and the results are presented in Figs. 11-13. The Moisture buffer values for different tested wood panels (Waterproof placo panel, Placo panel, wood-cement panel, Chipboard panel, and OSB Panel) are given in Fig. 11. Fig.12. shows mass evolutions of samples during the absorption and desorption cycles for fibrous materials. Fig. 13 gives the MBV measurements for both wood-based panel and fibrous materials.
3,6
waterproof placo panel Placo panel
3,2
wood-cement panel chipboard panel
OSB panel
2
MBV[g/(m ,HR)]
2,8 2,4 2,0 1,6 1,2 0,8 0,4 0,0 MBV 1
MBV 2
MBV 3
MBV 4
Wood panels
Fig.11.Moisture buffer values of different tested materials
17
MBV 5
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Hemp fiber panel
Wood fiber panel
Cellulose wadding panel Recycled Textile Fiber Panel wood-cement panel 0
1
2
3
4
5
6
MBV [g/m^2.%]
Fig.12.Mass evolutions of samples during the absorption and desorption cycles
3.5 3 2.5 2 1.5 1 0.5 0
(a)
(b)
Fig.13.MBV measurements of different materials; (a) wood-based panel, (b) fibrous materials
According to the classification of materials in table1, it is noted that the moisture buffer value varies from one list to another and from one material to another. In fact, for the first list concerning wood panels, it is found that it has lower values than the list of fibrous materials. However, the IBS composite panel still has excellent hygric regulator compared to wood panels or fibrous materials. It has a buffer capacity greater than 3 [g/m2.% RH] very close to that of wood fiber panels. It is also noted that placo panels have moderate responses (MBV <1 [g/(m2.% RH)]), according to the classification of Rode [39]. Agglomerated panels and OSB gave MBV values between 1 and 2 [g/(m2. % RH)] which allows us to classify them as good hygric regulators. Concerning fibrous materials are all considered excellent hygric regulators
18
since their MBV is greater than 2 [g/(m2. % RH)] except recycled textiles fiber panels that have a lower response to this value. This is what interests us, in our study, it is the IBS composite material, which is a heterogeneous material whose composition is at the base of a mixture of vegetable particles with mineral particles. This composition offers it an excellent absorption and desorption of the water content. Its hygric response is very similar to that of fibrous materials than that of wood panels. 4.2. Energy load The following results are obtained using the TRNSYS dynamic model presented in section §3 for the considered cases study. Heating, Ventilation and Air Conditioning (HVAC) needs evaluation has been conducted for an eco-cottage prototype (within wood-cement composite material) situated in the region of Lorraine (France). Thus, a numerical analysis is carried out, through the TRNSYS software, based on different materials of construction and in different climatic zones in order to improve the building performances. For all cases, yearly heating and cooling energy requirements are reported in Fig.14. For the reference case presented in table 4, the total heating and cooling achieve 1842 kWh per year, correspond to 74kWh/m². We can regroup the seven studied cases into two main categories.
Fig.14.Total energy requirements for all studies cases
The first one represents all cases that are close to the reference case, while the second one regroups the case that has low building envelop performances and it represents high energy demands relative to the reference case. Then, in the first category, we found four cases (2, 3, 5 and 6). We note that case 2 can reduce the construction costs significantly by replacing the concrete wall with hollow brick, while case 3 shows fewer improvements by using wood wool insulation (2.6%). 19
However, in the second case where GPS was used as an insulating material, the environmental impact remains significant. On the other hand, the use of double-glazing is sufficient to limit heat loss. Although triple glazing is the best, but it costs more, that's why case 5 is better than sixth.On the other hand, the use of double glazing is sufficient to limit heat losses. Although the triple glazing is the best one,but it is more expensive, that’s why case 5 is preferable that the sixth case. The second category contains case 1, 4 and 7. Case 1 represents 41% of the energy demands increasing without insulation. The fourth case has 22% of supplement energy demands as regards to the referring case. The seventh case represents floor without insulation and caused 44% of energy demands.
Fig. 15.Monthly cooling load
Figure 15 represents the monthly cooling load, computed by numerical simulation according to the input data of the model mentioned in the Fig.10 and the metrological data presented in Fig. 9. We can observe that the first category for these figures, 4 and 5 cases could be almost
beneficial in winter as approved in figure 15, but they could not be a suitable scenario in the summer season (Fig. 16). While the second category shows the inverse behavior of the first one.
20
Fig. 16.Monthly heating load
In regards to monthly heating load, the floor insulation has a good effect in winter while in summer could not be preferred because it limits the ground freezing effect. We notice from figure 15 and 16 that the insulation of the soil has a good effect in winter because it will be able to maintain a suitable interior atmosphere, whereas in summer season, this insulation will come overheating because it limits the effect of soil gel. As for the insulation of the walls, it is noted that the thermal insulation allows reducing heat losses to the environment in the winter season, but it limits heat evacuation in summer, which is due to high thermal inertia of the inner wall. The same effect can be observed in the windows when it comes to double and triple glazing.
5. Conclusions In this paper, a study by characterization of the hygric behavior of materials for different categories, in dynamic regime was made, at first. The MBV method was thus used for this experimental study. It was noted that fiber-based materials have good hygric responses to compressed wood panels. However, the wood-cement composite, characterized by a heterogeneous composition, has marked a very important MBV value 3.301[g/m2.% RH], a value which is very close to that of wood fiber panels. After that, a dynamic simulation of a simple cottage building based on the wood wall has been carried out using TRNSYS software. Different cases have been investigated in eco-building materials. However, the insulation reduces significantly total energy demand, but it doesn’t lead heat evacuation in the summer season, thus from this study, it can be concluded that a natural ventilation mechanism is recommended in order to enhance energy efficiency in the building. Furthermore, towards low material costs, we conclude that the double glazing window should be more reliable than triple glass and using hallow brick instead of concrete wall. In other side wood wool is 21
recommended to be used rather than GPS insulation material that can contribute to environmental damages.
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26
Highlights
Potential of biobased materials to improve thermal comfort in buildings was demonstrated. An experimental facility is used to measure the moisture buffer value (MBV) for different categories of building materials and their hygroscopic behaviors were performed. The wood-cement composite has excellent moisture regulator when compared to wood panels or fibrous materials. A dynamic simulation has been carried out by using TRNSYS software in order to evaluate heating and cooling loads in an eco cottage example of building. The simulation results of the different cases showed that the insulation reduces significantly total energy demand, but it doesn’t lead heat evacuation in the summer season.
Conflict of interest
On behalf of the co-authors, i hereby certify that: (i) The manuscript, or its contents in some other form, has not been published previously by any of the authors and is not under consideration for publication in another journal at the time of submission; (ii) Its publication is approved by all authors and tacitly or explicitly by the responsible
authorities where the work was carried out; (iii) If accepted, it will not be published elsewhere in the same form, in English or in any other language, including electronically without the written consent of the copyright-holder. Faiza MNASRI Doctor of Process Engineering and Products Energetic Engineering University of Lorraine
S2352-7102(19)30253-0
DOI:
https://doi.org/10.1016/j.jobe.2019.101088
Reference:
JOBE 101088
To appear in:
Journal of Building Engineering
Received Date: 1 December 2018 Revised Date:
11 October 2019
Accepted Date: 21 November 2019
Please cite this article as: F. Mnasri, S. Bahria, M. El-Amine Slimani, O. Lahoucine, M. El Ganaoui, Building incorporated bio-based materials: Experimental and numerical study, Journal of Building Engineering (2019), doi: https://doi.org/10.1016/j.jobe.2019.101088. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
Building Incorporated Bio-Based Materials: Experimental and Numerical Study Faiza Mnasri a,*, Sofiane Bahria a, Mohamed El-Amine Slimani b, c, Lahoucine Ouhsaine a, Mohammed El Ganaoui a a
Laboratory of Energetic, LERMAB, IUT Henri Poincaré, University of Lorraine, 186 route
de Lorraine, 54400 Cosnes-et-Romain, France b
Department of Energetic and Fluid Mechanics, University of Science and Technology
Houari Boumediene (USTHB), 16111 Algiers, Algeria c
Unité de Développement des Equipements Solaires (UDES), Centre de Développement des
Energies Renouvelables (CDER), 42415 Tipaza, Algeria
Abstract In building environments, several research on dynamic moisture storage in hygroscopic building materials has improved interest in moisture buffering capacity of bio-based materials and demonstrated the potential of these materials to improve thermal comfort and buildings energy consumption. This paper presents an investigation, which aims to compare the hygroscopic behavior of different bio-based materials to identify their hygric proprieties. For this, an experimental facility is used to measure the moisture buffer value (MBV) for different categories of building materials. Thereafter, a dynamic simulation has been carried out by using TRNSYS software in order to evaluate heating and cooling loads. The results showed that the wood-cement composite still has excellent moisture regulator when compared to wood panels or fibrous materials. It has a buffer capacity superior to 3 [g/m2.% RH] very close to that of wood fiber panels. The simulation results of the different cases showed that the insulation reduces significantly total energy demand, but it does not lead heat evacuation in the summer season. Thus, from this study, it can be concluded that a natural ventilation mechanism is recommended to improve energy efficiency in the building.
* Corresponding author E-mail address: [email protected] (F. MNASRI), [email protected] (S. BAHRIA), [email protected] (M.E.A. SLIMANI), [email protected] (L. OUHSAINE), [email protected] (M. EL GANAOUI)
1
Keywords: Bio-based materials, Moisture Buffer Value, Dynamic simulation, Energy efficiency. Nomenclature Symbol
Explanation
Unit
A
Exchange area
m²
RH
Relative humidity
%
ρ0
Dry apparent density
Kg.m-3
w
Water content
kg.m-3
∆m
Mass variation during the absorption/desorption phase
g
MBV
Moisture buffer value
g/(m2. % RH)
mwater, cal
Water value of the calorimeter
g
mi
Mass capacity
g
C
Thermal capacity
J.kg-1K-1
Q
Heat capacity
J.K-1
1. Introduction Bio-based building materials were used since several years and had been improved over that the last decades. There are characterized by high environmental performance and a good hygrothermal behavior in the wall [1,2]. In areas with cold climates, most buildings require a good insulation level (specified by R-Value). Thus, higher the R-Value, better is the thermal insulation performance [3]. In the construction industry, we do not need materials with high thermal conductivity. Indeed, this property is the key property for thermal diffusivity and effusivity, two terms that represent the heat diffusion and the thermal inertia of building [4,5]. The heat transfer through the building materials depends mainly on the constituents forming the materials and their microstructure. Material configurations for the building envelope can be modified and improved by appropriately arranging the materials to achieve the required performance. The building materials properties that are easily modifiable, such as the density, 2
composition, and proportions of the mixture, are different from those who are unalterable, such as geometry and the size of the micropores and the inherent mineral properties [6,7]. In the study of Amel et al. [8], the thermal properties of wood-cork sandwich panels with different thicknesses were investigated. The measurement of the thermal conductivity, thermal resistance, specific heat, and thermal diffusivity indicated that increasing the density of the samples leads to an increase of the value of the thermal conductivity and a decrease in thermal resistance of sandwich structures. Several researches have been carried out around the world to develop bio-based materials for building construction. Ramesh et al. [9] presented a review on plant fiber-based biocomposites for material construction. While focusing on composite materials, the main points to consider are environment friendliness and lightness, with high specific properties. This century has seen remarkable progress in the field of green technologies in the field of materials science through the development of high-performance materials made from natural resources around the world. Préneron et al. [10] proposed a simple and efficient experimental method, useful for building materials laboratories; this method is adapted through the methods proposed in the literature. For this, fungal growth has been studied and analyzed under different environmental conditions on earth-based materials with or without the addition of hemp ship or straw. Some other studies are examining such growth deal with paper-based or wood-based materials, as well as inorganic materials such as gypsum plasterboard or cement [11–13]. However, the hygric characterization can be based on the exploitation of steady-state measurements [14] or measured under dynamic conditions such as the measurement of the Moisture Buffer value (MBV) [15]. In the study of Mnasri et al. [16], an example of the feasibility of eco-materials production chain in a European project context is presented. The analysis based on a hygric characterization of different eco-materials, which are selected as candidate materials in the great cross-border region (Belgium, France, Luxembourg). Collet et al. [17] have proposed a study where they compared the hygroscopic behavior of three hemps concretes by measuring their sorption curve, water vapor permeability,and moisture buffer value. These measurements allow to identify the hygric storage capacity of each material and to classify them as excellent or not hygric regulators us a function to MBV value.
3
Indeed, this test of MBV indicates the amount of water vapor that is transported in or out of material, during a certain period, when the vapor concentration of the surrounding air varies [18]. It requires an experimental procedure, and its value permits a direct comparison of the building materials moisture performance. The protocol of the MBV investigation has been created by the NORDTEST Project, which is defined as the practical measurement of the hygric performance of materials under dynamic conditions [19]. A similar experimental methodology to evaluate the hygroscopic buffering capacity of porous materials has been proposed by the Japanese Industrial Standard (JIS) [20]. This experimental procedure is also based on an evaluation of weight changes of a specimen when its surrounding climate is subjected to relative humidity variation but differs from the NORDTEST Project, as regards for the time scheme, the imposed signal and the thickness of specimen [21]. Rahim et al. [22] have investigated the effect of the temperature, which depended to the sorption isothermal, on the hygrothermal behavior of a two bio-based building envelope. Thus, the effect of moisture buffering capacity of these materials on hygric indoor comfort in a room has been studied. Belakroum et al. [23] have proposed an experimental investigation, where the sound absorption coefficient and moisture buffer value (MBV) of new insulation materials are evaluated. The studied composites are aggregates of date palm fiber and lime or starch. Two types of date palm fiber were tested: trunk surface fiber and rachis fiber. In order to find out the most efficient specimens, we analyzed several samples of different composition. The measurements of the Moisture Buffer Value (MBV) have shown that the composite made from 50% of trunk fiber and lime had an average MBV of 3.73 g/(m2%RH). For samples based on petioles fiber and lime, the greatest MBV measured was 2.58 g/(m2%RH) for samples of 50% of fibers. Using starch as a binder, we recorded a moisture buffer value of 4.05 g/(m2%RH) with only 20% of trunk fibers. Thus, all MBV measured classify these new materials as an excellent hygric regulator. Thus, hygroscopic materials research has marked more consideration to the development of new materials [24–26] by using biodegradable and natural materials. However, in construction, for similar environments, users use the same materials, the effects often being different due to the use of air conditioning in the building, the ventilation strategy, thickness of materials and differences in the initial moisture content of hygroscopic materials [21]. In order to analyze the problem of space heating demand reducing, heat losses can be reduced by improving building performance with increased insulation levels [27]. This is the most effective way to significantly reduce heating demand, taking into account, dependence on 4
climatic conditions variations [28–30]. However, in the existing building stock, this measure can be, sometimes, more expensive than the substitution of boilers in heating systems [31,32]. Abahri et al. [33] analyzed the heat and mass transfers combined to the convective and diffusive driving potentials in hygroscopic materials and demonstrated the availability of the sub-models by numerical simulation. The results showed that when the hygric state between the environment and the wall was stable, convection was a significant driving potential. Shui Yu et al. [34] have simulated three terms: indoor humidity conditions, energy consumption, and economy at the room level in order to analyze the moisture buffering performance of different hygroscopic materials.They have examined moisture-buffering materials across three aspects: indoor humidity conditions, the building’s energy consumption, and the building’s life-cycle cost. The results showed that hygroscopic materials could control indoor air humidity changes and improve human comfort but they needed to be used together with central air conditioning because of their limited humidity controlling performance. Kuznik et al. [35] developed a new TRNSYS model to evaluate the thermal behavior of an external wall with PCM. Asadi et al. [36] have investigated a multi-objective optimization scheme (a combination of TRNSYS, GenOpt, and MATLAB) in order to optimize the retrofit cost, energy savings and thermal comfort of a residential building. In this work, a study has been achieved to compare thermal performances of building materials. Our paper is organized as fellow: the first part represents an experimental hygrothermal study, where, we propose a hygric water comparison of different biobased materials. The second part, a methodology to optimize and calculate the thermal loads within dynamic constraints and for different insulations types is proposed. Thus, a developed model has been used to study the different cases and finally, results have also been analyzed and discussed.
2. Materials and Methods 2.1.Composition and Manufacturing In this paper, we propose to study a new structure distributed by a Belgian company SYSTEM'BAT. It is based on a formwork system, named ISOL+ST, which is a monolithic technology of construction where the walls and slabs are concreted in prepared casing panels of wood chips. The basic element of ISOL + ST construction systems, IBS is a wood-cement panel. The basic raw material used for its manufacture is coniferous wood chips, which form 89% of the 5
total volume of the panel. The other components are the cement, which ensures the strength of panels, a water glass solution that stabilizes the panels against moisture and increases their resistance against fungi, rodents, insects, and water. Its proprieties are related to water and thermal characteristics of raw materials. The manufacture of this product is made through several steps, which are as follows (fig.1).
Fig.1. Production steps of the IBS wood panel
2.2. Hygrothermal Study In this study, we propose a hygric comparison of different biobased materials. These materials were the result of an identification study of an eco-materials sector in the Greater Region (Belgium, France, Luxembourg) as part of an ECOTRANSFAIRE project [37]. These materials can be categorized into two families; one for fibrous panels and the other for woodbased panels. The two families of different materials are presented in table 1. Tabel.1. Classification of study materials Wood panels
Fibrous materials
Placo panel
Hemp fiber panel
Waterproof placo panel
Wood fiber panel
Chipboard panel
Cellulose wadding panel
OSB Panel
Recycled Textile Fiber Panel
In front of these two categories, the IBS composite panel, which represents a mixture of wood and cement is compared with these different types of materials by a hygric characterization in a dynamic mode that is the Moisture Buffer Value (MBV) test. This characterization method gives access to the hygric regulator quality of the material. •
Moisture Buffer Value (MBV)
The term "Moisture buffer value (MBV)" was set up by the NORDTEST project to determine the hygric buffering capacity value of materials. It indicates the amount of water absorbed or
6
desorbed when the material is subjected to a change in the external relative humidity for a given time [18]. The NORDTEST project defines a dynamic cycle of 24 hours in which the relative humidity is set at 75% for 8 hours, and then at 33% for the following 16 hours [38]. When the thickness of the material is greater than the depth of water penetration under the diurnal conditions, the hygric buffering capacity value is independent of the material thickness and the amplitude of the relative humidity variation. Classification of materials has been proposed by the NORDTEST Project which is shown in fig. 2 and which makes it possible to evaluate the performance of a material according to its MBV value.
Fig.2.Moisture Buffer Values (MBV) classification according to Project NORDTEST [21]
The classification of MBV is evaluated according to the hygric response of a material. According to Rode, 2005 [39], the buffering effect of building materials can be considered very important for the hygrothermal performance of a building. However, there are materials whose MBV is very negligible, others which have water buffering values greater than 2 [g/m2.% RH] are classified for an excellent hygric response. •
Experimental Protocol
The Characterization by the MBV test according to the NORDTEST experimental protocol [40] consists of measuring the capacity of a material, moderating the relative humidity variations of the surrounding air. The moisture buffer value characterizes the ability of a material, or a multi-layer component, to moderate the variations in relative humidity of the surrounding air. Thus, this value is defined by: MBV =
∆m A( RH haute − RH basse )
(1)
7
Where:
∆m: mass variation during the absorption/desorption phase (g) A: Exchange area (m²) RHhigh/low: relative humidity high and low during the cycle (%) The principle of the associated test protocol proposes to focus samples in square format to well-defined relative humidity cycles that generally have meteorological data in order to be representative of the cycles imposed on the walls of buildings. The temperature is set constant. Thus, several pairs of relative humidity can be considered to present cycles of humidification and drying. The reference torque is 75% RH for an exposure time of 8 hours in absorption and 33% RH for a period of 16 hours in desorption. The mass tracking by weighing at each cycle of the samples, which are subjected to periodic variations of humidity, then makes it possible to determine the water buffering value of the materials. The test bench used consists of a Memmert HCP climatic cabinet (Fig.3) in which the temperature can be regulated between 30 and 90 °C and the relative humidity between 30 and 95%.
Fig.3. Climate chamber controlled in temperature and relative humidity (LERMAB Longwy)
The mass tracking of the samples is based on weighing during the absorption phase and weighing during the desorption phase. The cycles are repeated for two weeks. •
Specimens
The study was performed on samples of two lists of materials mentioned in Table.1 and on the composite wood cement material. They are all isolated on five sides with aluminum tape 8
so that the moisture circulates vertically as shown in Fig.4. The samples are cut according to the capacities of the balance (210 grams accuracy 0.01 gram) and their mass per unit area.
Chipboard panel
Hemp fiber panel Recycled Textile Fiber Pane
Placo panel Waterproof placo panel OSB Panel wood cement panel
Wood fiber panel
(a)
Cellulose wadding panel
wood cement panel
(b)
Fig.4. Samples of different materials: (a) wood panels, (b) fibrous materials
The samples are cut out according to the balance of capacities and their surface density. In order to perform the MBV test in the oven, we have created the cycle on Celsius software as shown in table 2.
Table.2. MBV cycle Hours
Duration
Temperature
Relative
Type
hh:mm
hh:mm
°C
humidity
1
0:01
0:01
40
33
next
2
16:00
15:59
40
33
next
3
16:01
0:01
40
75
next
4
24:00
7:59
40
75
loop
The first ramp lasts one minute. It can increase or decrease the indoor temperature to 40 °C and set the relative humidity to 33%. The second ramp maintains the temperature at 40 °C and 33% relative humidity for 16 hours, in order to achieve the desorption cycle. The third ramp is again a ramp of one minute. It allows going from a relative humidity of 33% to 75%. Finally, the fourth ramp maintains the temperature at 40 °C and 75% relative humidity for 8 hours, to achieve the absorption cycle. During the test, we can see that the average value of relative humidity drops at 10:00 from 75% to 19%. This drop is due to the opening of the door during weighing. On the other hand, during changes of instructions, the passage from 33% to 75% takes place in about a minute.
9
2.3. Heat Capacity The specific heat capacity of a substance is defined as the amount of heat energy required to raise the temperature of a unit mass of a substance through 1°C. According to the law of energy conservation or calorimeter principle, in a closed system, the heat lost by a hot body is equal to the heat gained by a cold body. In this method, a bit of solid is heated at high temperature and is quickly transferred to a calorimeter containing cold water. The solid loses thermal energy while the cold water gains it. After sometimes, the solidwater and calorimeter attain the same temperature. Then, the liquid should also be stirred to allow an even distribution of the heat energy throughout its volume. Fig. 5 shows the main materials used for the determination of heat capacity by a Dewar silt calorimeter.
Fig.5. Determination of heat capacity by a Dewar silt calorimeter
The calorimeter is composed by various materials. It is therefore difficult to determine its thermal capacity. That is why it can be modeled as follows: n
mcal C cal = ∑ mi Ci = mmer C mer + malu C alu + m glas C glas
(2)
i
We replace this calculation by its water equivalent. We thus have:
mcal Ccal = mwater,cal Cwater
(3)
10
Where mwater, cal is called the water value of the calorimeter, and Cwater= 4185 J / kg / K is the thermal capacity of the water, mi and Ci are the mass and thermal capacities of the different components of the calorimeter. The water value is a characteristic of the calorimeter; it must be determined experimentally and will be kept for all manipulations. The first step is to determine the mass of water (m
water, cal)
of the calorimeter. For this, we
introduce into the calorimeter a mass of water m1(500g) at room temperature T1, where the calorimeter is itself at the temperature T1. After that, we added to it the second mass of water m2(200g) previously heated to the temperature T2=80°C. After stirring the mixture, thermal equilibrium is expected, and the final temperature Tf is recorded in the calorimeter. According to the principle of energy conservation, in an isolated system, there is no heat exchange with the outside. There must be heat preservation inside the system: Heat loss = heat gain: Q1 + Q 2 + Q cal = 0
(4)
With: Q1 = m 1C water (T f − T1 )
(5)
Q 2 = m 2 C water (T f − T2 ) Q cal = m water
, cal
(6)
C water (T f − T1 )
(7)
m 2 C water (T f − T 2 ) + ( m 1 + m water ,cal )C water (T f − T1 ) = 0
mwater,cal =
(8)
m2 (Tf − T2 ) − m1 (Tf − T1 )
(9)
(Tf − T1 )
The second step is the determination of the thermal capacity of different materials constituting the envelope of an eco-cottage, which will be the subject of the following part of this study. Then, to be prepared, a mass of water m1 = 300 g is introduced into the calorimeter at room temperature T1, the calorimeter is itself at the same temperature T1.The mass sample (msample) is added to this. The sample will have been previously heated to T2 on a water bath, by taking care to isolate the sample from the bottom of the kettle to avoid conduction between the electrical resistance and the sample. The water is continuously agitated in the calorimeter, and the system is expected to be at thermal equilibrium. Finally, the final temperature Tf measured in the calorimeter is recorded. From the measurement of Tf and the measurement of the mass of the sample (m sample), one will determine the experimental value of Csample (J/kg.K).
11
By writing the first principle of thermodynamics applied to the system {calorimeter + mass of water + sample} by assuming that the calorimeter is perfectly adiabatic. The analytical expression of the heat capacity of the sample Csample: Q water + Q sample + Q cal = 0
(10)
With: Q water = m water C water (T f − T1 )
(11)
Q sample = m sample C sampler (T f − T 2 ) Q cal = m water
, cal
(12)
C water (T f − T1 )
(13)
m water C water (T f − T1 ) + m sample C sample (T f − T 2 ) + ( m water ,cal C water (T f − T1 ) = 0
Csample =
Cwater (mwater + mwater,cal )(T1 − Tf )
(14) (15)
msample(Tf − T2 )
The investigation aim is to measure the heat capacity of building materials. We show that the heat capacity of the calorimeter with the plastic protective cover is 32.05 J/°C.
Fig.6. Temperature profile in the calorimeter
Fig. 6 shows the temperature evolution in the calorimeter for the different samples. It should be noted that the temperature decreased over time to finally attain thermal equilibrium. Table 3 shows the calculated thermal capacities for the different samples using the equation (Eq.15).
Table 3.Thermal capacity for different samples 12
Initial temperature
Final temperature Tf
Thermal capacity
T2 (°C)
(°C)
kJ/ (kg K)]
86
71,9
1,4
Concrete
85,2
70,3
0,92
Panel OSB
82,9
68
2,45
Panel IBS
82
68,5
2,1
GPS insulation
We can note that between 85 and 72 °C, the decrease in temperature is 1.8 °C per minute, on an average. Below 70°C, the decrease remains almost constant at 0.27 °C per minute over the entire measuring range. Therefore, the loss of heat remains low considering the experimental parameters: -
We are located more than 20 °C above the ambient temperature
-
The volume of water represents only 1/5th of the calorimeter’s effective volume.
3. Dynamic simulation Residential buildings account for about 40% of total energy use; there is therefore great interest in improving building performance [41]. In this context, an eco-cottage is being built in Longwy University Institute of Technology (UIT Longwy). The first step is the process of research on energy efficiency field. This first construction was created by a partnership between IUT and IsolHABITAT (Belgian company- based in Liege). The eco-cottage is built with IzoLox system, insulating shuttering blocks composed by Graphite Polystyrene (GPS) and the ISB panel (Fig.7), which is the wood-cement composite, presented in the first part of this study.
Fig.7. Bloc of wall composed by GPS insulation and ISB panel
13
In Table 4, the description of construction materials is given for floor, external walls, and roof.
Table 4. Description of the construction materials Layer type
Density
Floor
External Walls
Roof
[Kg/m3]
Thermal
Heat capacity
conductivity [kJ/h
kJ/kg.K
mK]
OSB panel
620
0.468
2.1
Wood wool
50
0.1404
2.1
Air gap
1
0.325
1.227
Plasterboard
790
1.155
0.801
ISB panel
675
0.396
2.45
Neopor
15
0.1224
1.4
Concrete
2300
6.318
0.92
ISB panel
675
0.396
2.45
Concrete slab
2300
6.318
0.92
25
0.142
1.38
2300
6.137
0.7
EPS Expanded polystyrene Floor tile
3.1.Geometrical description The eco-cottage area is 24.75m²; it’s composed by a single room with a door on the north side of 1.5m² (double glazed) and three windows with the same area (0.42m²). The first is in the east, and the two others are on the south side. The roof is slanted by 5° to the south for the evacuation of waters rain Fig.8. The eco-cottage is located in the Longwy city (Lorraine, north-east of France). The altitude of the city is 300 m. The latitude and longitude of Longwy are respectively 49.52 °N and 5.769° E. 14
Fig.8. The eco-cottage geometry
The average monthly temperature ranges from 0.1°C in January to 17.5°C in July. The average temperature during the year is 9.3 °C. The data of minimum and maximum temperature are presented in Fig.9.
Fig. 9. Data of the minimum and maximum temperature in Longwy city
3.2.Cases studies In this party, we propose to study seven studies cases. These investigated cases were the same dimensions as the reference case, except it differs in external wall composition, thermal insulation, and window glazing; they are as follows: Case1: In the external walls, the GPS insulation material is replaced by an air gap of 5 cm. Case2: In the external walls, the concrete material is replaced by a hollow brick of 15 cm. Case3: In the external walls, the GPS insulation material is replaced by a wood wool insulation of 15 cm. Case4: Single glazing is used for all window and door.
15
Case5: Double glazing is used for all window and door. Case6: On the floor, polystyrene material is replaced by a mortar layer (2 cm). Case7: Floor without insulation Fig.10. shows the simulation diagram made on the numerical environment of TRNSYS for dynamic simulation.
Fig.10.TRNSYS diagram for dynamic simulation
TRNSYS is a transient system simulation program used to simulate the behavior of building components [4]. In this study the following data are introduced into the simulation program structure:
-
Air Flows: The infiltration rate is fixed at 0.6 air changes per hour during all the times.
-
Earnings: in this study, we don’t take into account gains from people and lights.
-
Heating: The room is maintained at 20 degrees Celsius during occupied hours and at 15 degrees other times. The storage area is unheated.
-
Cooling: the air conditioner is which turns on if the temperature rises above 26 degrees Celsius.
-
Ground temperature: Type 77 is used to calculate the mean ground surface temperature for the year. 16
4. Results and Discussion 4.1. Moisture buffer value (MBV) After carrying out the successive humidification-drying cycles, regular weightings were carried out for each cycle as noted above. Thus, the MBV values are calculated for each tested material according to the formula defined by the NORDTEST project. The two lists of materials presented below are analyzed, and the results are presented in Figs. 11-13. The Moisture buffer values for different tested wood panels (Waterproof placo panel, Placo panel, wood-cement panel, Chipboard panel, and OSB Panel) are given in Fig. 11. Fig.12. shows mass evolutions of samples during the absorption and desorption cycles for fibrous materials. Fig. 13 gives the MBV measurements for both wood-based panel and fibrous materials.
3,6
waterproof placo panel Placo panel
3,2
wood-cement panel chipboard panel
OSB panel
2
MBV[g/(m ,HR)]
2,8 2,4 2,0 1,6 1,2 0,8 0,4 0,0 MBV 1
MBV 2
MBV 3
MBV 4
Wood panels
Fig.11.Moisture buffer values of different tested materials
17
MBV 5
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Hemp fiber panel
Wood fiber panel
Cellulose wadding panel Recycled Textile Fiber Panel wood-cement panel 0
1
2
3
4
5
6
MBV [g/m^2.%]
Fig.12.Mass evolutions of samples during the absorption and desorption cycles
3.5 3 2.5 2 1.5 1 0.5 0
(a)
(b)
Fig.13.MBV measurements of different materials; (a) wood-based panel, (b) fibrous materials
According to the classification of materials in table1, it is noted that the moisture buffer value varies from one list to another and from one material to another. In fact, for the first list concerning wood panels, it is found that it has lower values than the list of fibrous materials. However, the IBS composite panel still has excellent hygric regulator compared to wood panels or fibrous materials. It has a buffer capacity greater than 3 [g/m2.% RH] very close to that of wood fiber panels. It is also noted that placo panels have moderate responses (MBV <1 [g/(m2.% RH)]), according to the classification of Rode [39]. Agglomerated panels and OSB gave MBV values between 1 and 2 [g/(m2. % RH)] which allows us to classify them as good hygric regulators. Concerning fibrous materials are all considered excellent hygric regulators
18
since their MBV is greater than 2 [g/(m2. % RH)] except recycled textiles fiber panels that have a lower response to this value. This is what interests us, in our study, it is the IBS composite material, which is a heterogeneous material whose composition is at the base of a mixture of vegetable particles with mineral particles. This composition offers it an excellent absorption and desorption of the water content. Its hygric response is very similar to that of fibrous materials than that of wood panels. 4.2. Energy load The following results are obtained using the TRNSYS dynamic model presented in section §3 for the considered cases study. Heating, Ventilation and Air Conditioning (HVAC) needs evaluation has been conducted for an eco-cottage prototype (within wood-cement composite material) situated in the region of Lorraine (France). Thus, a numerical analysis is carried out, through the TRNSYS software, based on different materials of construction and in different climatic zones in order to improve the building performances. For all cases, yearly heating and cooling energy requirements are reported in Fig.14. For the reference case presented in table 4, the total heating and cooling achieve 1842 kWh per year, correspond to 74kWh/m². We can regroup the seven studied cases into two main categories.
Fig.14.Total energy requirements for all studies cases
The first one represents all cases that are close to the reference case, while the second one regroups the case that has low building envelop performances and it represents high energy demands relative to the reference case. Then, in the first category, we found four cases (2, 3, 5 and 6). We note that case 2 can reduce the construction costs significantly by replacing the concrete wall with hollow brick, while case 3 shows fewer improvements by using wood wool insulation (2.6%). 19
However, in the second case where GPS was used as an insulating material, the environmental impact remains significant. On the other hand, the use of double-glazing is sufficient to limit heat loss. Although triple glazing is the best, but it costs more, that's why case 5 is better than sixth.On the other hand, the use of double glazing is sufficient to limit heat losses. Although the triple glazing is the best one,but it is more expensive, that’s why case 5 is preferable that the sixth case. The second category contains case 1, 4 and 7. Case 1 represents 41% of the energy demands increasing without insulation. The fourth case has 22% of supplement energy demands as regards to the referring case. The seventh case represents floor without insulation and caused 44% of energy demands.
Fig. 15.Monthly cooling load
Figure 15 represents the monthly cooling load, computed by numerical simulation according to the input data of the model mentioned in the Fig.10 and the metrological data presented in Fig. 9. We can observe that the first category for these figures, 4 and 5 cases could be almost
beneficial in winter as approved in figure 15, but they could not be a suitable scenario in the summer season (Fig. 16). While the second category shows the inverse behavior of the first one.
20
Fig. 16.Monthly heating load
In regards to monthly heating load, the floor insulation has a good effect in winter while in summer could not be preferred because it limits the ground freezing effect. We notice from figure 15 and 16 that the insulation of the soil has a good effect in winter because it will be able to maintain a suitable interior atmosphere, whereas in summer season, this insulation will come overheating because it limits the effect of soil gel. As for the insulation of the walls, it is noted that the thermal insulation allows reducing heat losses to the environment in the winter season, but it limits heat evacuation in summer, which is due to high thermal inertia of the inner wall. The same effect can be observed in the windows when it comes to double and triple glazing.
5. Conclusions In this paper, a study by characterization of the hygric behavior of materials for different categories, in dynamic regime was made, at first. The MBV method was thus used for this experimental study. It was noted that fiber-based materials have good hygric responses to compressed wood panels. However, the wood-cement composite, characterized by a heterogeneous composition, has marked a very important MBV value 3.301[g/m2.% RH], a value which is very close to that of wood fiber panels. After that, a dynamic simulation of a simple cottage building based on the wood wall has been carried out using TRNSYS software. Different cases have been investigated in eco-building materials. However, the insulation reduces significantly total energy demand, but it doesn’t lead heat evacuation in the summer season, thus from this study, it can be concluded that a natural ventilation mechanism is recommended in order to enhance energy efficiency in the building. Furthermore, towards low material costs, we conclude that the double glazing window should be more reliable than triple glass and using hallow brick instead of concrete wall. In other side wood wool is 21
recommended to be used rather than GPS insulation material that can contribute to environmental damages.
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26
Highlights
Potential of biobased materials to improve thermal comfort in buildings was demonstrated. An experimental facility is used to measure the moisture buffer value (MBV) for different categories of building materials and their hygroscopic behaviors were performed. The wood-cement composite has excellent moisture regulator when compared to wood panels or fibrous materials. A dynamic simulation has been carried out by using TRNSYS software in order to evaluate heating and cooling loads in an eco cottage example of building. The simulation results of the different cases showed that the insulation reduces significantly total energy demand, but it doesn’t lead heat evacuation in the summer season.
Conflict of interest
On behalf of the co-authors, i hereby certify that: (i) The manuscript, or its contents in some other form, has not been published previously by any of the authors and is not under consideration for publication in another journal at the time of submission; (ii) Its publication is approved by all authors and tacitly or explicitly by the responsible
authorities where the work was carried out; (iii) If accepted, it will not be published elsewhere in the same form, in English or in any other language, including electronically without the written consent of the copyright-holder. Faiza MNASRI Doctor of Process Engineering and Products Energetic Engineering University of Lorraine