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Thermal Performance of Bamboo as a Multilayer Insulation Wall
J. Bonivento1, G. Vieira1 and I. Togo1
1 Peter the Great St. Petersburg Polytechnic University, 29 Politechnicheskaya St., St. Petersburg, 195251,
Russia
Email: ing.boniventob@gmail.com , gabriel.vieira@poli.ufrj.br
Abstract.
Bamboo is a woody giant herbage used for furniture, fences and constructions. Even though, this vegetal does
not present mechanical or thermal homogeneity, its high sustainability (CO2 reducer, highness and fast speed
of growth), strength and hollowed cylindric morphology make it an option in the construction sector. As an
insulation material, it can have a positive thermal performance due to the presence of air cavities, however when
many culms of Bamboo are aligned to make a wall, the contact surfaces in the joins, because of its rounded
nature, are few allowing thermal bridges. Therefore, the aim of this research is to analyse the thermal
performance in this type of walls, placing a second and third line to mitigate the heat leaking and improving the
thermal resistance of the wall developed in THERM 7.5 Finite Element Simulator. Besides the guadua can be
used as insulation material in the city of Guayaquil, it has some variables, which can lead to a different approach
and suggests further analysis for different parameters.
Key words.
bamboo; guadua; thermal resistance; insulation material; heat flow; energy efficient
Introduction.
The construction industry is one of the major source of
pollution in the air -around 4% of particulate emission-,
water, noise and soil [1]. Therefore, the use of
sustainable materials in construction is a decisive factor
to reduce this negative environmental impact. The
bamboo is a renewable material, well known as a giant
grass, belongs to the family Graminace (Poaceae) [4]
and is spread around the world according to Figure 1.
Some remarkable benefits of this vegetal are the
capability of CO2 sequestration (Bamboo – Guadua
fixing capacity of 76 t CO2/ha) [3], rapidly rate growth, 6
moths to have its height and 4 – 6 years [4] and high
mechanical performances along its fibres ¡Error! No se
encuentra el origen de la referencia.[10]. International standardizations and codifications from China, Colombia,
Ecuador, India, Peru and USA promote this sustainable material for construction of complex projects [8]. Moreover,
it has high resistant in seismic events. [13]
A cylindrical and hollowed shape governs the morphology of
the bamboo stick. Normally, the separation of internodes
varies between 10 cm and 40cm (Figure 2). Depending on
the specimens the culm can reach height upper 18m with
diameters from 5cm to 25cm and wall thickness from 0.9 to
1.3cm.[5]
Regarding its thermal characteristic, it has a cavity filled with
air entrapped, low thermal-conductor element, enveloped by
a porous woody material with fibre and vascular bundles.
However, the bamboo stick as an insulation material presents
two noticeable withdraws: firstly, due to its vegetable nature,
its physical, mechanical and geometrical properties change
between species, moreover, [6][22] demonstrated that in the
wall of Guadua-Bamboo, after 15% of its thickness measured
from the cortex the aggrupation of vascular bundles are more
Figure 1 Distribution of Bamboo around the world. I - Asia-Pacific
region, II - America region and III - African region. (INBAR 2010
[2])
Figure 2 Morphology of Bamboo [5]
separated (Figure 2), changing its properties. Thus, it is considered a heterogeneous material with physical,
mechanical and thermal variations, making this raw product difficult for being industrialized in mass, like industrial
woods panels or commercial wood elements [8][11]. Because of this variability, many researches about bamboo are
focused on making glued or pressed composites or mixing its fibres with another elements in order to improve the
resistance of the bamboo and generate mechanical and thermal properties predictable for calculation [5][8][11][12].
The second withdraw is related to its cylindrical geometry, Huang, P [6] researched the thermal properties of a stik
(culm) of Asian family “Moso-Bamboo” (Phyllostachys edulis) and found that the thermo-diffusivity and thermo-
resistance of this specimen vary in different transversal points, due to its rounded shape and heterogeneous density
in its wall. He registered an average thermo-conductivity of 0,226 W/m*K. Mata, M [7] obtained values of 0.15758
W/m*K for Bamboo-Guadua.
Nevertheless, the industrial process of lamination of Bamboo
changes the style of façade and costs, the design of a house
contemplates walls with the natural bamboo appearance, the
Colombian Standard NSR 10 [13] stablishes parameters of
constructability of this type of walls for the specimen Bamboo-
Guadua. In this case, one line of bamboo, as shown in Figure 3,
creates joins where the thermal bridges, where the heat leaks due
to the rounded shape of the culms which create reduced contact
area [14].
It was previously mentioned the benefit of using bamboo, in its raw
state, in the construction site and its thermal difficulties due to its
heterogenous nature. This paper studies the thermal performance
of a wall made by bamboo, and the possible mitigation of thermal bridges by adding further layers of this material and
decreasing the U-Value of the wall, evaluating its behaviour with THERM 7.5 Finite Element Simulator. The analysis
is done in a residential house located in the city of Guayaquil, Ecuador.
Methods
One of the facts of the thermodynamic law is the transference of the energy by the interaction (work and heat) of a
system with its surrounding. The transfer used in this document is heat transfer, which is the thermal energy in transit
due to a spatial temperature difference ¡Error! No se encuentra el origen de la referencia.. There are three modes
of heat transfer: Conduction, Convection and Radiation.
This article pays more attention on the heat transfer that will occur through a medium (solid or stationary fluid), in this
case, this medium is the bamboo layers. Therefore, it is necessary to calculate the capacity of the materials to conduct
heat, in other words, the thermal resistance, which is estimated primarily by the Fourier Law.
The Fourier law is the pillar of heat transfer by conduction and the heat transfer is a measurement of this heat transfer
of an area across the layers composites of a wall ¡Error! No se encuentra el origen de la referencia.. Thus, the
formula (1) represents the amount of heat during certain time through an area which emulate a resistance.
Where:
λ – coefficient of thermal resistance (W/m ºC)
δ – thickness of the material (m);
T1 – indoor temperature (or outdoor if it is hotter that indoor);
T2 – Outdoor temperature;
A – Area of the surface of layer (m2);
t – Time (s);
Figure 3 Thermal Bridges in Bamboo Wall
In order to analyse the thermal resistance of the Bamboo layers, it will be calculated according to ¡Error! No se
encuentra el origen de la referencia., which give the formulas (2) (3):
Where:
R – thermal resistance (m² ºC/ W)
int – inner surface heat transfer coefficient;
ext – outer surface heat transfer coefficient.
According ¡Error! No se encuentra el origen de la referencia., the internal/external heat transfer coefficient
represents the ability of the material to absorb heat when the temperature oscillates on its surface. It is calculated by
the formula (4):
(4)
Where:
cp – specific heat (J/kg ºC);
to – fluctuation period of a thermal steam (s);
p – density (kg/m³);
According to ¡Error! No se encuentra el origen de la referencia., in contemplation of the standards, the minimum
value of thermal resistance for India is set as 1,60 m² ºC/W.
The U-Value, which is a measure of the rate at which a building transmit heat ¡Error! No se encuentra el origen de
la referencia., is expressed in terms of thermal resistance. Therefore, it is given by (5).
U – thermal transmittance (W/ m² K);
Consequently, the maximum value for the thermal transmittance is 1,8 W/ m² K (IRAM 11.605).
Furthermore, it is relevant to calculate the thermostability of the layer. According to ¡Error! No se encuentra el origen
de la referencia., thermal stability is one of the most important topics in the building design, as it measures how
quickly a material gains or loses heat to the environment and it is determined by (6).
(6)
Where, b – Thermal stability (J/ m².K.c0,5).
According to World Meteorological Organization, Guayaquil has the following climate characteristics:
Dew Point: 20,4 ºC
Hottest Month of the year: January 37.2 ºC
For the simulations developed in this paper, the design temperature adopted will be 22,0 ºC.
The software simulation performed had the objective of analysing how the addition of more layers of Bamboo can
improve the thermal characteristics of a wall and analyse the heat flux when using it as a single, double and triple
insulation layer, as illustrated in Figure 4.
Figure 4 : Proposed multi-layered bamboo façade: One layer, two layers and three layers, respectively. The first and second line for all cases
are fixed at 10 cm
The specimen of Bamboo to use for calculation is Guadua - Angustifolia-Kunth. The diameter of the first line of
bamboo is 10 cm, in accordance to the chapter E.7.6 of NSR 10 [21]. The elements of the second line was set at 10
cm also. According to [4] the thickness of the Guadua culms varies from 1,00 cm to 1,50 cm and regarding to the
physical - thermal properties, it is adopted in accordance to the work of [23][6][7]. However, for this work the thickness
adopted will be 10cm.
The Figure 5 presents an aerial view of the bamboo wall and shows the axis in which will be considered the path of
the heat through both layers.
Figure 5 Cross sectional scheme for vertical orientation.
The software simulation initial data for THERM 7.5 it is shown below:
Outside Temperature: 37,2 ºC;
Inside Design Temperature: 22,0 ºC;
Relative Humidity: 79%;
The wall length which underwent through thermal simulation has 1,00m;
The interior part of the bamboo was considered as a Frame Cavity – CEN Simplified;
The thermal characteristics of the bamboo was set as
;
λ
α
ρ
c
0,157
1000 ± 20
0,11±0,01
0,6±0,07
1491
Table 1:hermal-physics Parameters: Thermal Conductivity (λ), Thermal Effusivity (e), Thermal Diffusivity (α), density (ρ) and Specific Heat (c)
of Guadua According to Delgado, F. [23]
Results and Discussions
The results obtained in the software simulation are presented below (Figure 6-8). For all three simulations (single-
layer, double-layer and triple-layer) it is displayed the temperature gradient through the bamboo and its heat flux.
Figure 6: Temperature Gradient (OC) and Heat Flux Gradient (W/m²) for Single Layer Bamboo Wall
Figure 7: Temperature Gradient (OC) and Heat Flux Gradient (W/m²) for Double-Layer Bamboo Wall
λ
α
ρ
c
0,157
1000 ± 20
0,11±0,01
0,6±0,07
1491
Figure 8: Temperature Gradient (OC) and Heat Flux Gradient (W/m²) for Triple-Layer Bamboo Wall
When analyzing the Temperature Gradient above, for all three simulations, a linear isotherm is obtained in the middle
of the 2 and 3 layer wall, while the 1-layer wall illustrates a nonlinear patron. This is a result due to the rounded shape
of the bamboo and as long as the walls with more layers get more stable, this variation tends to reduce. Furthermore,
the heat flow gradient shows that adding a second and further a third layer of bamboo interspersed, the thermal
bridges effect get reduced.
The ¡Error! No se encuentra el origen de la referencia. shows the values obtained after the Thermal Simulation.
As expected, the U-Value decreased as the number of layers increased. In comparison with the standards (IRAM
11.605), both double and triple layer have a U-Value lower than the maximum recommended (1,8W/m².K).
Moreover, the amount of heat flow through the bamboos’ layer decreased drastically when adding one layer as
insulation material.
Table 2: Results obtained for U-Value and Heat Flow
Layers
U-Value (W/m².K)
Heat Flow (W) *
Single-Layer
2,0657
34,204
Double-Layer
1,3996
16,094
Triple-Layer
0,6563
9,660
*Per meter
Conclusion
Thus, this paper concludes that the bamboo is an appropriate insulation material, for the city of Guayaquil, when using
it in two or three layers in terms of U-Value standard. Nevertheless, this paper recommends the utilization of three
layers of bamboo as the thermal bridges got a significantly reduction, which will lead to an energy saving in the
building. Moreover, its applicability must be evaluated from city to city, as the maximum U-Value for this city is much
higher than European standards, for example. Therefore, it is important to mention that this investigation was carried
out through computational simulation and, as long as the bamboo is a heterogeneous material, it can lead to diverse
results. Finally yet importantly, according to norms, it is necessary to submit the bamboo through some treatments in
order to increase its waterproof, fire resistance and to avoid the presence of animals that can damage it. Future
studies will evaluate the behavior of the bamboo as insulation material with different orientations in the second layer
(horizontal and inclined - 45%) in laboratory trials.
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