IN DEGREE PROJECT MECHANICAL ENGINEERING, SECOND CYCLE, 30 CREDITS , STOCKHOLM SWEDEN 2021 Evaluation of natural materials in Sustainable Buildings: A potential solution to the European 2050 long- term strategy. VÍCTOR DE LAS HERAS REVERTE KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF INDUSTRIAL ENGINEERING AND MANAGEMENT
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IN DEGREE PROJECT MECHANICAL ENGINEERING,SECOND CYCLE, 30 CREDITS
, STOCKHOLM SWEDEN 2021
Evaluation of natural materials in Sustainable Buildings: A potential solution to the European 2050 long-term strategy.
VÍCTOR DE LAS HERAS REVERTE
KTH ROYAL INSTITUTE OF TECHNOLOGYSCHOOL OF INDUSTRIAL ENGINEERING AND MANAGEMENT
Master of Science Thesis
Department of Energy Technology
KTH 2020
Evaluation of natural materials in Sustainable
Buildings: A potential solution to the
European 2050 long-term strategy.
TRITA: TRITA-ITM-EX 2021:299
Víctor de las Heras Reverte
Approved
2021-06-14
Examiner
Jaime Arias Hurtado
Supervisor
Jaime Arias Hurtado
Industrial Supervisor
Ximo Masip and Carlos Prades
Contact person
Ximo Masip
Evaluation of natural materials in Sustainable Buildings: A potential solution to the European 2050 long-term strategy.
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Abstract Today, buildings consume 40% of total energy demand in the EU and are responsible for 36% of GHG emissions. For this reason, and due to the delicate situation of climate change that planet Earth is experiencing, solutions are being sought to make the building sector more sustainable. In the current project, the use of natural materials has been chosen as a solution in line with the EU 2050 long-term strategy. This research broadens the knowledge on sustainable building with natural materials as an alternative to conventional construction. To this end, first, an extensive state of the art has been carried out to gather information and identify research gaps on natural building materials and energy efficiency, proving the suitability of natural construction materials. Special emphasis has been put on straw bale construction and rammed earth construction, which have been studied individually. In addition, geometrically identical building models of both building techniques have been developed and simulated in Stockholm and Valencia in order to see how they would perform in different climates. Total energy demand for the straw-bale building of 140.22 kWh/(m2·year) in the case of Stockholm and 37.05 kWh/(m2·year) in the case of Valencia has been obtained. For the rammed earth building, a total demand of 301.82 kWh/(m2·year) has been obtained in Stockholm and 78.66 kWh/(m2·year) in Valencia. Once passive measures are applied in the different models, a reduction in demand for the straw bale building of 77.8% and 36.3% has been achieved for Stockholm and Valencia, respectively. In the rammed earth building, in contrast, the demand has been reduced by 86.3% in Stockholm and 73.9% in Valencia. Heat recovery ventilation and high insulation level have been identified as imperative needs in Stockholm, in contrast to Valencia. Other improvement strategies such as windows substitution, air permeability improvement, or natural ventilation for cooling have been implemented. Apart from that, better performance of the straw-bale buildings has been identified for both climates. Additionally, focusing on thermal inertia, its influence has been identified as not completely significant in terms of annual demand in the simulated climates.
Keywords
Straw-bale building, Rammed earth building, Sustainable construction, Natural Building Materials, Energy performance analysis, Energy performance optimization
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Acknowledgements First of all, I wish to give my sincere gratitude to my supervisor and examiner Jaime Arias Hurtado, a great
teacher and a great person, who has supported the project with his knowledge. Furthermore, I would like
to thank the guys from Catenerg, Ximo, and Carlos, and the whole team for their technical and motivational
support. I am also grateful for the assistance given by Joan, from Okambuva, whose knowledge about
bioconstruction has facilitated the definition of constructive characteristics.
Leaving aside the professional aspect, I would like especially to express my deepest gratefulness to my family
for trusting me during my whole student period and giving me this opportunity, which will change the
course of the rest of my life. To my sister Aida, I would like to give special mention to her for being a
“friend by blood”, who has brought to the world the most beautiful thing that my eyes have been able to
see in these difficult times, my nephew Dani.
Of course, my friends, from the first to the last, for the laughs, for the adventures, for the trips, for their
affection, for their unconditional support, and for being there even when they are not.
I dedicate this space to show my heartfelt and sincere gratitude to her, who in the hardest time of my life,
has been the one who has kept me going, fighting for my physical and mental health, and also my dreams.
Her name is Luci, and she is "home".
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Acronyms
BBR Boverket’s Building Regulations
BEST Building Energy Software Tool
BIM Building Information Modelling
CEB Compressed Earth Blocks
COP Conference of Parties
COP Coefficient of Performance
CSV Comma-Separated Values
CTE Spanish Technical Building Code
DB HE Documento Básico de Ahorro de Energía (CTE)
DB HS Documento Básico de Salubridad (CTE)
DNI Direct Normal Irradiation
EIFS Exterior Insulation Finishing System
EPBD Energy Performance Building Directive
EPDM Ethylene Propylene Diene Monomer
EPS Expanded Polystyrene
ESBA European Straw Building Association
ETICS External Thermal Insulation Composite System
EU European Union
FASBA Fachverband Strohballenbau Deutschland
GHG Greenhouse gases
GHI Global Horizontal Irradiation
GREB Ecology Research Group of la Baie
HRV Heat Recovery Ventilation
HVAC Heating Ventilating and Air Conditioning
IDF Intermediate Data Format
IEA International Energy Agency
IFC Industry Foundation Classes
IPCC Intergovernmental Panel on Climate Change
IPS Infinite Power System (ideal system)
ISH Integrated Surface Hourly
IWEC International Weather for Energy Calculations
LCA Life Cycle Assessment
LCC Life Cycle Cost
MEP Mechanical Electrical and Plumbing
NZEB Nearly Zero Energy Buildings
OSB Oriented Strand Board
PHI Passive House Institute
PP Polypropylene
PS Polystyrene
RFCP Réseau Français de la Construction Paille
SBUK Strawbale Building United Kingdom
UNFCCC United Nations Framework Convention on Climate Change
VOC Air Volatile Compound
XPS Extruded Polystyrene
Evaluation of natural materials in Sustainable Buildings: A potential solution to the European 2050 long-term strategy.
2 Literature Survey ................................................................................................................................................10
2.1 Energy efficiency .......................................................................................................................................10
2.2 Natural Building Materials .......................................................................................................................11
2.2.1 Straw-bale construction ..................................................................................................................12
2.2.2 Earthen construction .......................................................................................................................17
3 Building and Modelling .....................................................................................................................................20
3.3 Technical and Constructive characteristics ...........................................................................................22
3.4 Data acquisition .........................................................................................................................................23
3.5 Building modelling ....................................................................................................................................23
3.5.1 Software selection and description ................................................................................................24
3.5.2 Geometric modelling in IFC Builder ............................................................................................25
3.5.3 Energy modelling in Cypetherm EPlus ........................................................................................27
3.6 Energy simulation .....................................................................................................................................35
4 Results and Discussion ......................................................................................................................................42
4.1 Energy simulation .....................................................................................................................................42
4.1.1 Straw-bale building ..........................................................................................................................42
4.1.2 Rammed earth building ...................................................................................................................47
4.2 Energy performance optimization – Measures ....................................................................................53
4.2.1 Straw-bale Building ..........................................................................................................................53
4.2.2 Rammed earth building ...................................................................................................................58
4.3 Energy performance optimization - Results .........................................................................................63
4.3.1 Straw-bale building ..........................................................................................................................63
4.3.2 Rammed earth building ...................................................................................................................66
5.1 Future work ................................................................................................................................................75
In a conclusion, in this case, it would be ineffective to apply this measure for the improvement of the
building, since it already has a high level of insulation, and upgrading any of the enclosures would not make
sense from an economic and energy perspective. Therefore, this measure is not applied in the optimisation
process of the straw-bale building located in Stockholm.
4.2.1.2 Valencia
The initial model simulation results (Section 4.1.1) indicate that no large efforts are needed to achieve Passive
House requirements since the starting point is close to it already. However, as there is room for
improvement, some measures are adopted to reduce even more the energy demand. To do this, results,
climate conditions and the identification of weak points have been considered to develop the following
strategies:
• Double-glazed windows – Argon gas
One of the negatively influencing factors identified in the results (Section 4.1.1) is windows. Initially, in the
building, as indicated in the construction characteristics (Section 3.3), old double-glazed windows with air
chamber have been selected, which correspond to a U-value of 2.9 W/(m2·K). Since the climate in Valencia
is not as extreme as in Stockholm, triple-glazed windows will not be necessary. However, it has been decided
to select a double-glazed window with an argon gas-tight chamber, which has better thermal properties than
air. This type of window has a thermal transmittance coefficient of 1.2 W/(m2·K) [164].
Apart from the glazed surface, frames have been also improved, since in the initial model they had 3.2
W/(m2·K). The frames selected are the same as for the building located in Stockholm; wooden frames with
a U-value of 2 W/(m2·K).
• Air permeability improvement
The results (Section 4.1.1) show that the influence of infiltration is high. This is due to the fact that outside
air, which is at a different temperature than the comfort temperature, enters the building in an uncontrolled
way. To achieve thermal comfort, HVAC systems consume energy to increase or decrease the air
temperature, depending on the operating mode.
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Thus, as an improvement measure, air infiltration has been reduced through an iterative process of
simulations in Cypetherm EPlus. In this way, the aim is to meet the Passive House requirements for the air
permeability of the building. Passive House Institute defines that the infiltrations must be, as maximum, 0.6
renovations per hour. After the iterative process, the improved infiltrations for each building element are
gathered in Table 4.1, while the initial ones are indicated in Table 3.16.
• Natural ventilation for cooling
In order to reduce the demand for cooling in the summer months, which is required due to the climatic
conditions in Valencia, it has been decided to implement what is known as natural cooling. Natural cooling
is based on the use of outside air during the summer nights, which is at a low temperature. In this way, using
this air as night ventilation, a cooling of the cooling demand is consequently achieved, improving the
building performance.
In Figure 4.20, the hourly temperature evolution in Valencia in the summer months could be observed. As
it can be seen, the lowest temperature each day, which is achieved during the night and early morning,
usually corresponds to comfort conditions (20ºC-26ºC). Given this outdoor temperature, it is interesting to
increase the ventilation rate in order to reduce the cooling demand this way.
Figure 4.20 Hourly dry temperature evolution in Valencia in summer months.
By means of an iterative process, it has been defined a maximum natural ventilation (windows opening) rate
of 4 l/(s·m2). Thus, the ventilation profile is the one represented in Figure 4.21, where maximum ventilation
occurs from 0 to 8 hours, which corresponds to night. After 8, natural ventilation is reduced until the usual
level, 0.8 l/(s·m2), which was the ventilation rate in the initial model to comply with legislation. In this case,
“summer” comprises from June to September, both included, in which this schedule (Figure 4.21) is applied.
Those months have been chosen according to the results obtained in the initial simulation (Section 4.1.1),
as these were the months when there was a demand for cooling. The rest of the months keep the original
constant ventilation rate of 0.8 l/(s·m2).
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Figure 4.21 Improved ventilation schedule for summer months. Natural cooling.
4.2.2 Rammed earth building
4.2.2.1 Stockholm
The initial rammed earth building located in Stockholm is not energy efficient as is shown in the results
(Section 4.1.2). For that reason, once results are analysed and weak points are identified, the following
improvement measures have been selected to be applied:
• Cork insulation (ETICS)
The rammed earth building, although external walls have high thermal inertia that could be useful in warmer
climates, do not have any insulation, so the conduction losses through the walls are significant. In addition,
as indicated in Section 3.3, in this type of construction technique, ETICS or an insulation layer inside the
wall is added in order to reduce the U-value of the enclosure.
In this case, to be consistent with bioconstruction principles and the use of natural building materials, a 10
cm cork panel is included as ETICS. The conductivity of this panel is 0.038 W/(m·K).
Figure 4.22 ETICS configuration for cork. Layers. [190]
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Figure 2 shows the layout of how the ETICS would be executed on the compacted earth wall. The layers
correspond to the following:
1. Support (Compacted earth)
2. Bonding mortar
3. Cork thermal Panel
4. Mechanical fixing
5. Regularisation mortar
6. Reinforcement mesh
7. Finishing mortar
8. Silicate paint
Notwithstanding, in Cypetherm EPlus, simplifications are made, since not all the layers have influence from
a thermal point of view. Thus, the external walls have been defined in the simulation software as follows
(Table 4.2 and Figure 4.23):
Table 4.2 Layers’ characteristics and thermal properties. Improved external wall. Rammed earth building in Stockholm.
Layers Thickness
(cm) Conductivity (W/(m·K))
Thermal resistance ((m²·K)/W)
Density (kg/m³)
Specific heat (J/(kg·K))
Finishing mortar 2 0.8 0.03 1525 1000
Cork panel 10 0.038 2.63 400 1500
Bonding mortar 1 0.41 0.02 1000 1000
Compacted earth 45 1.5 0.3 1855 2085
Figure 4.23 Layer’s configuration and thermal properties. Improved external wall. Rammed earth building in Stockholm.
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The thickness optimization has been carried out through a parametric study as explained in Section 4.2.1.
The optimization results are the following (Figure 4.24):
Figure 4.24 Cork panel thickness optimisation. Parametric study in Stockholm.
Logically, the greater the insulation, the better the performance of the building and the lower the heating
demand, as can be seen in Figure 4.24. However, above a certain insulation thickness, the reduction in
demand in relation to the increase in thickness is not cost-effective. Without a full technical and economic
study, it is difficult to determine the ideal value. However, a thickness of 10 cm of cork panel has been
determined, since, from that point on, the slope of the curve is close to 0.
• Heat Recovery Ventilation (HRV) (Eff. 85%)
Ventilation has been identified as one of the weaknesses of the rammed earth building in Stockholm, as
explained in Section 4.1.2. For that reason, a highly efficient (85%) latent HRV without outdoor bypass has
been determined as a solution not to lose such a great amount of energy. The HRV characteristics are
defined and explained in more detail in Section 4.2.1.
• Air permeability improvement
Air infiltrations suppose high heat losses in the building due to climate conditions in Stockholm. Outdoor
temperature is low, so these uncontrolled infiltrations are negative since there is only heating demand in this
scenario.
Therefore, the building air tightness is improved according to Passive House criteria through a simulation
iterative process, obtaining the results shown in Table 4.1 in Section 4.2.1.
• Triple-glazed windows – Argon gas
Initially, windows were double-glazed windows with air chamber, as detailed in Section 3.3. In order to
improve them, they are substituted by triple-glazed windows with argon gas chamber, which have a heat
transfer coefficient of 0.9 W/(m2·K). Windows carpentry is also improved by using wooden frames with 2
W/(m2·K). For more details, Section 4.2.1.
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4.2.2.2 Valencia
As explained in results (Section 4.1.2), the rammed earth building’s performance in Valencia in the winter
months is not as good as the straw-bale building. But, in summer, energy demand is low. Therefore, the
improvement measures shown below are, most of them, oriented towards the reduction of heating demand:
• Cork insulation (ETICS)
The weakest point of the earth building is the insulation, as the exterior walls lack insulating material.
Valencia is a city with moderate temperatures, so it will not need as much insulation as in Stockholm. In
order to be in line with the use of natural materials, it has been decided to use 4 cm cork panels (k=0.038
W/m/K) as ETICS. For more information about constructive characteristics of ETICS with cork panels
and about this measure, Section 4.1.2.1.
Therefore, the external walls have been defined in Cypetherm EPlus as indicated in Table 4.3 and Figure
4.25.
Table 4.3 Layers’ characteristics and thermal properties. Improved external wall. Rammed earth building in Valencia.
Layers Thickness
(cm) Conductivity (W/(m·K))
Thermal resistance ((m²·K)/W)
Density (kg/m³)
Specific heat (J/(kg·K))
Finishing mortar 2 0.8 0.03 1525 1000
Cork panel 4 0.038 2.63 400 1500
Bonding mortar 1 0.41 0.02 1000 1000
Compacted earth 45 1.5 0.3 1855 2085
Figure 4.25 Layer’s configuration and thermal properties. Improved external wall. Rammed earth building in Valencia.
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The thickness of the cork panel has been determined by means of a parametric study by means of the
Parametric Preprocessor of EnergyPlus, which is explained in Section 4.2.1. The thickness has been
modified from 2 cm to 20 cm, with 2 cm step simulations. The results obtained are represented in Figure
4.26:
Figure 4.26 Cork panel thickness optimisation. Parametric study in Valencia.
As it could be seen in Figure 4.26, the higher the thickness, the lower the total demand. However, increasing
thickness until a certain point could be not cost-effective, as this improvement measure is material
demanding. In addition, the initial building, as it is in Valencia (warm climate), resulted to have an acceptable
energy performance (Section 4.1.2) that can be reduced applying different measures. For that reason,
through an iterative simulation process carried out together with the other measures, a 4 cm thick cork panel
has been selected for the optimized model in the rammed earth building located in Valencia.
• Heat Recovery Ventilation (HRV) (Eff. 60%)
The ventilation initially defined in the building according to the standard is a problem in the winter months
as cold air from outside enters into the dwellings. However, the outdoor air temperature in Valencia is not
as low as in Stockholm. For this reason, it has been decided to incorporate a latent HRV in the building,
but with low efficiency (60%) in this case.
Cypetherm EPlus does not allow to have mechanical and natural ventilation at the same time. Since natural
ventilation for cooling is going to be applied, a solution to the software limitation has been adopted. An
outdoor bypass has been incorporated to be able to carry out natural ventilation at night in the summer
months so that the air does not pass through the HRV and can impair the performance of the building.
This outdoor bypass is activated when the temperature is between 18 ºC and 26ºC. These setpoint
temperatures have been defined by means of an iterative process. In this way, it is possible to avoid the
problem arising from the limitation of Cypetherm EPlus, since it interprets that in this temperature range,
the airflow has the same response as natural ventilation.
More information about the working principle of the HRV is detailed in Section 4.2.1.
• Air permeability improvement
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Air infiltrations are substantial from an energy point of view. For that reason, it has been decided to reduce
them until the Passive House value of 0.6 renovations per hour by means of an iterative process. Results
are shown in Table 4.1 in Section 4.2.1.
• Natural ventilation for cooling
In summer, natural ventilation (windows opening) could be positive when the outdoor temperature is close
to comfort conditions. For that reason, natural cooling through ventilation has been selected as an
improvement measure to include in the rammed earth building model. In this case, since HRV is also in
operation, an outdoor bypass (18ºC-26ºC) is included to allow it (This is the only way to define it in
Cypetherm EPlus, as explained before).
More detailed information about natural cooling through ventilation can be found in Section 4.2.1.
• Double-glazed windows – Argon gas
Windows are also placed for the rammed earth building in Valencia, by double-glazed windows with argon
gas chamber with a U-value of 1.2 W/(m2·K). Carpentry is substituted by wooden frames with 2 W/(m2·K).
More detailed information about windows substitution is in Section 4.2.1.
4.3 Energy performance optimization - Results
Building models have been optimized according to improvement measures applied, as indicated in Section
4.2. In the following sections, results about the energy performance of optimized buildings are shown and
analysed. The optimisation has been carried out with the aim, if possible, of achieving the Passive House
criteria of 15 kWh/(m2·K) for heating and cooling, respectively. However, this should be achieved without
changing the shape of the building and/or the distribution of the glazed surface, which has not been possible
in all scenarios.
4.3.1 Straw-bale building
4.3.1.1 Stockholm
Once the appropriate improvement measures have been applied to the straw bale building model at the
Stockholm location, the annual energy and power demand results are as shown in Figure 4.27.
Figure 4.27 Annual energy and capacity of the improved straw-bale building in Stockholm.
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In annual terms, the following results for demand per unit of air-conditioned building area are obtained for
the improved straw-bale building located in Stockholm:
Heating demand = 21.71 kWh/(m2·year)
Cooling demand = 9.42 kWh/(m2·year)
As can be seen, despite having implemented all the improvement measures specified in Section 2, the target
of 15 kWh/(m2·K) for heating and cooling has not been achieved. Given the climatic conditions in
Stockholm, it is not trivial to reduce the energy demand to such demanding values. Therefore, in order to
further reduce the demand, geometrical modifications (building shape, glazing surface, etc.) would be
needed.
Nonetheless, heating demand has been reduced by 118.29 kWh/(m2·K), while cooling demand has been
consequently increased by 9.22 kWh/(m2·K). This results in a total demand reduction of 77.8% thanks to
the improvement measures implementation.
In Figure 4.28, the annual energy balance of the improved straw-bale building located in Stockholm is
represented. Heat flow related to opaque enclosures and ventilation and infiltrations is still significant.
Nevertheless, insulation in walls, roof, or floors could be hardly improved since thicknesses of straw-bales
and floor insulation are already optimized. On the other hand, concerning ventilation, a highly efficient
HRV has been implemented, and not much more can be done in this respect since ventilation is compulsory
from a health perspective. Infiltrations have been highly minimized, until Passive House air renovations per
hour requirement.
Apart from that, cooling demand could be reduced by implementing shadowing in windows or through
natural ventilation in the summer months. However, since cooling demand is already low, it has been
reconsidered not to apply those passive measures in this scenario.
Figure 4.28 Annual energy balance of the improved straw-bale building in Stockholm.
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4.3.1.2 Valencia
Once the improvement measures have been applied to the straw-bale building model of Valencia, simulation
can be carried out. The results related to demanded energy and capacity are obtained, as shown in Figure
4.29.
Figure 4.29 Annual energy and capacity of the improved straw-bale building in Valencia.
In annual terms, the following results for demand per unit of air-conditioned building area are obtained for
the improved straw-bale building located in Valencia:
Heating demand = 14.04 kWh/(m2·year)
Cooling demand = 9.57 kWh/(m2·year)
As predicted, given the results of the energy simulation of the initial model and given the climatic conditions
of the Spanish city, the values required by Passive House in terms of heating and cooling demand have been
achieved. Efforts in terms of passive measures, to reduce the demand to this level, have been limited,
considering the starting point of the initial building performance. This indicates that further reductions in
demand could be achieved if desired through the application of other passive strategies.
Notwithstanding, heating and cooling demand have been reduced by 6.06 kWh/(m2·year) and by 7.38
kWh/(m2·year), respectively. This results in a total demand reduction of 36.3% after applying the different
improvement measures.
Figure 4.30 shows the thermal balance obtained after the simulation of the improved model. Despite the
reduction of air infiltration in the building, ventilation is still important in terms of energy balance. To
further improve the model, an HRV could be incorporated to operate in the winter months, thereby
reducing the heating demand. In summer, natural ventilation is already taking place at night, so the HRV
could be switched off during these times as the ventilation ratio would already be met non-mechanically.
As for the cooling demand, shading of the windows during the critical hours of the summer months would
be chosen in this case to further reduce consumption. Figure 4.30 shows the importance of heat flow
through the windows, which could be avoided if desired by means of blinds, awnings, overhangs, or other
shadowing elements.
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Figure 4.30 Annual energy balance of the improved straw-bale building in Valencia.
4.3.2 Rammed earth building
4.3.2.1 Stockholm
After several optimization measures included in the initial model of the rammed earth building in
Stockholm, the results concerning energy and power demand throughout the year are represented in the
graphs in Figure 4.31. At first glance, it can be seen that the demand for heating and cooling is unbalanced,
with the former being much higher, comprising the period from October to April. There is no demand for
air conditioning in May, June, and September, which is one of the big differences with respect to the straw-
bale building, being the thermal transmittance of the walls higher in the earthen house. Therefore, the earth
building, with its higher inertia, would perform much better in climates with an average temperature close
to comfort conditions.
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Figure 4.31 Annual energy and capacity of the improved rammed earth building in Stockholm.
In annual terms, the following results for demand per unit of air-conditioned building area are obtained for
the improved rammed earth building located in Stockholm:
Heating demand = 38.15 kWh/(m2·year)
Cooling demand = 3.22 kWh/(m2·year)
However, looking at the normalized annual values, it can be observed that, in spite of applying several
improvement strategies, the Passive House requirements, which are 15 kWh/(m2·year) for cooling and
heating, have not been achieved. This could be probably solved by changing the whole design of the building
in terms of geometry and window distribution, but it is not allowed in this study, as already explained.
Nevertheless, despite not having achieved the demand reduction target, the demand has been reduced to a
large extent, as initially, the heating demand was more than 300 kWh/(m2·year). Thus, the heating demand
has been reduced by 263 kWh/(m2·year), with a slight increase in cooling demand, which was initially zero.
This translates into a reduction of the total demand of the HVAC systems by 86.3% compared to the initial
model.
Analysing the annual energy balance of the rammed earth building in Stockholm (Figure 4.32), it can be
concluded that the heat flow released by conduction through opaque enclosures is still high. However, the
insulation thickness has been optimized and further improvement does not make sense from a techno-
economic perspective. The main reason why this heat flow is so high is the temperature difference between
indoor and outdoor the building, which is in certain moments over 30ºC.
The most important possible improvement measures for the reduction of heating demand have been
considered, analysed and, if necessary, applied to the model, but even so, it has not been possible to further
reduce consumption. Therefore, it can be concluded that, for a climate like Stockholm, in order to have a
building that meets the Passive House criteria and has the current constructive characteristics, it must have
a geometry that favours solar gain through the glazed surfaces in the winter months, and also have a high
level of thermal insulation in the envelope.
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Figure 4.32 Annual energy balance of the improved rammed earth building in Stockholm.
4.3.2.2 Valencia
Once applied the improvement strategies in the initial model of the rammed earth building in Valencia,
simulations are carried out in Cypetherm EPlus. Results, as in previous sections, are shown in terms of
demanded energy and capacity in Figure 4.33. As in the earth house in Stockholm, there are certain months
when there is no demand for heating and cooling, again showing that in the months when the temperature
is neither high nor low, thermal inertia has an appreciable advantage. However, if temperatures are not ideal
during the rest of the year, insulation is required to ensure a good performance of the building in terms of
comfort and demand.
Figure 4.33 Annual energy and capacity of the improved rammed earth building in Valencia
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In annual terms, the following results for demand per unit of air-conditioned building area are obtained for
the improved rammed earth building located in Valencia:
Heating demand = 5.99 kWh/(m2·year)
Cooling demand = 14.51 kWh/(m2·year)
The normalized values show that after applying some measures (more than in the straw-bale house in
Valencia), the Passive House criteria referred to as energy demand is achieved. The heating and cooling
demand have been reduced by 55.6 kWh/(m2·year) and by 2.56 kWh/(m2·year), respectively. As regards the
total demand, by applying the passive strategies, it has been reduced by 73.9%.
In this case, the main heat flow, as could be seen in Figure 4.34, corresponds to the heat released through
the opaque enclosures, but it does not suppose any problem since the highest demand is for cooling. For
that reason, a further improvement that has not been implemented is the windows shadowing in summer
when solar gains through them result in an important heat flow in the energy balance. This could be done
either by blinds, overhangs, or similar solutions.
Figure 4.34 Annual energy balance of the improved rammed earth building in Valencia.
4.4 Results Comparison
Throughout Chapter 4, the results obtained from the energy simulations of the different models have been
shown and analysed. In total, the results of 8 different simulations have been analysed: 4 simulations of the
initial models of both the straw-bale and rammed earth buildings, for the two selected climates, Stockholm
and Valencia, and 4 simulations corresponding to the optimizations of the initial models. The summary of
the results obtained for each of the scenarios, in terms of energy demand (heating and cooling) and demand
reduction once the improvement measures have been applied, is presented in Table 4.4.
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Table 4.4. Energy demand summary. Initial and optimized models.
Scenario Straw-bale Building Rammed earth building
Stockholm Valencia Stockholm Valencia
Initial Model
Heating demand (kWh/(m2·year))
140.00 20.10 301.82 61.59
Cooling demand (kWh/(m2·year))
0.22 16.95 0.00 17.07
Total demand (kWh/(m2·year))
140.22 37.05 301.82 78.66
Optimized Model
Heating demand (kWh/(m2·year))
21.71 14.04 38.15 5.99
Cooling demand (kWh/(m2·year))
9.42 9.57 3.22 14.51
Total demand (kWh/(m2·year))
31.13 23.61 41.37 20.5
Total Demand Reduction 77.8% 36.3% 86.3% 73.9%
Overall, as can be seen in Table 4.4, the straw bale building is more efficient than the earth building in both
climates. In the winter months, when the outside temperature is below the comfort temperature, the straw
bale building, which is more insulated than the earth building, performs substantially better. In fact, the
heating demand in the earth building is 2 times higher than that of the thatched building in both Stockholm
and Valencia, as can be seen in row 1 of Table 4.4.
On the other hand, as for the cooling demand of the initial models, it is almost identical for the two
buildings. In the case of Stockholm, since temperatures are low throughout the year, there is hardly any
need for the operation of the cooling equipment throughout the year. If one looks, in contrast, at the
buildings located in Valencia, it can be seen that the demand is very similar, which leads to the conclusion
that the insulation of the building envelope does not play such an important role as it does in winter. The
total demand of the two buildings clearly shows the predominance of the thatched building over the earth
building in terms of thermal behaviour in both climates.
Regarding the energy optimization of the scenarios, the results that have been obtained, in the case of
Stockholm, do not meet the Passive House criteria in the heating demand department, both for the straw-
bale building and the earth building, the latter being further away from the target of 15 kWh/(m2·year).
Further reduction in demand has not been achieved, due to the restrictions imposed on the modification of
the building geometry and windows to maintain consistency with the initial building. On the other hand,
the models of both buildings, simulated in Valencia, once optimized, comply with the requirements
established by Passive House in terms of energy demand, with just over 20 kWh/(m2·year) of total demand.
In any case, the efforts made in the earth building have been much greater, from the point of view of
optimisation. In the earthen models, a larger number of passive measures have been applied to achieve the
energy reduction that can be seen in Table 4.4. This factor must be taken into account in the comparison
of the results.
Apart from that, after the application of the improvement measures explained in Section 4.2, a large
reduction of the total demand has been achieved for all models. The reduction of the total demand is above
70% in all scenarios except for the straw-bale building located in Valencia. The reason why this reduction
in consumption is only 36.3% is that the starting point was favourable, and it was not necessary to reduce
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the demand very much to reach the demanding values imposed by Passive House. However, greater efforts
could have been made to reduce demand even further if this had been desired.
Regardless of whether the Passive House criteria have been met, it can be concluded that these buildings,
modelled and simulated with the use of natural materials, are highly efficient from a thermal and energy
point of view, with the correct application of improvement measures depending on the constructive
characteristics of the buildings and the climatic conditions.
But the analysis must go beyond the annual demand values. Since one of the objectives of this project is the
evaluation of the thermal inertia as a decisive parameter for the thermal aspect and the functioning of the
building, its influence needs to be assessed. It has already been shown that, in annual terms, the earth
building (high inertia) performs worse than the straw building (low inertia). However, by analysing the
evolution of the energy demand in all scenarios (Section 4.1 and Section 4.3) a pattern can be observed in
the spring and autumn months (warm temperature), especially in the optimised models, where the heating
and cooling consumption is zero for the high inertia building and not for the low inertia building. Through
an iterative process of simulations, acting on the density and specific heat of the earth, increasing and
decreasing the thermal inertia, it has been seen to have an influence in those months when the average
temperature is close to comfort conditions. Thermal inertia in these months is beneficial as the walls absorb
the heat by retaining it and dampening the heatwave due to the daily temperature change. However, at least
in the simulated climates, it does not make a big change to the overall performance of the building. The
results of the inertia study show that only a change of at most 5 kWh/(m2·year) is experienced, for the
climates studied. Nevertheless, the potential of thermal inertia has been observed, and its study in other
climates, where the temperature is constant throughout the year, and varying daily temperatures averaging
around comfort temperatures, could be of great interest. However, a more in-depth study should be carried
out given the complexity of this thermal property of materials. Thermal inertia can be defined in different
ways [191], but thermal effusivity is the one adopted in the current research.
4.4.1 Environmental and Economic assessment
In addition to the results related to energy demand, the environmental and economic aspect has also been
assessed, in terms of GHG emissions in ton CO2 and energy costs in €, respectively on an annual basis.
The price of electricity in Sweden and Spain are 0.1718 €/kWh and 0.2298 €/kWh, respectively, according
to the European Commission [192], as represented in Figure 4.35. Also, according to the IEA [160], the
GHG emissions attached to the Spanish energy mix is 1.9 ton CO2/toe (Figure 4.36), and in Sweden, it is
0.7 ton CO2/toe (Figure 4.37).
Figure 4.35. Electricity prices (including taxes) for household consumers in different countries. Second half 2020 [192].
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Figure 4.36 CO2 intensity of energy mix in Spain 1990-2019 [160].
Figure 4.37 CO2 intensity of energy mix in Sweden 1990-2019 [160].
Taking into account the total demand values obtained above, which are listed in Table 4.4, as well as the
economic and environmental factors, the following annual energy cost and GHG emission values have been
obtained for each of the buildings, on an absolute non-normalised basis (Table 4.5). Also, the HVAC system
technology considered is a heat pump with an annual coefficient of performance (COP1) of 3 for heating
and COP2 of 2 for cooling, respectively:
Table 4.5 Total energy cost and GHG emissions of the buildings and reduction after optimization.
Scenario Straw-bale Building Rammed earth building
Stockholm Valencia Stockholm Valencia
Initial Model
Total Energy Cost (€/year)
8,946 3,882 19,241 7,435
GHG Emissions (ton CO2/ year)
3.13 2.76 6.74 5.29
Optimized Model
Total Energy Cost (€/year)
2,284 2,421 2,740 2,366
GHG Emissions (ton CO2/ year)
0.80 1.72 0.96 1.68
Energy Cost Reduction (€/year) 6,661 1,460 16,501 5,068
GHG Emissions Reduction (ton CO2/ year)
2.33 1.04 5.78 3.60
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Electricity prices and emissions attached to electricity in Sweden are lower than in Spain. Notwithstanding,
Energy demand in Stockholm is higher. Therefore, in the initial models, where the difference in energy
demand between both countries is larger, the economic and environmental performances of the buildings
located in Stockholm are worse. However, after optimization is applied, for the straw-bale building, the
economic expense is higher in Valencia than in Stockholm. In regard to GHG emissions, in the optimized
models, the buildings located in Stockholm are less emitting than the ones located in Valencia since the
energy mix in Sweden is more environmentally responsible.
Energy cost reduction is also calculated for all the scenarios. The greatest reduction in energy costs and
emissions was achieved in the rammed earth building in Stockholm, which was, after all, the scenario where
the greatest reduction in total demand was obtained.
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5 Conclusions
The purpose of the current project is to provide information on construction with natural materials and to
demonstrate their suitability for the construction sector, as a solution in line with the long-term strategy of
the EU 2050. Thus, the research aims to conduct a literature review on sustainable construction with natural
materials and to evaluate individual case studies. These case studies correspond to two buildings, using straw
bales and compacted earth, respectively, as main materials, which are simulated in Stockholm and Valencia.
The reason why these two materials have been selected is that they have been identified as suitable for
construction due to their technical characteristics and their resource availability over a large part of the
Earth's surface. On the other hand, straw and earth have different thermal properties that are intended to
be evaluated from an energy point of view, since straw has low conductivity and thermal inertia, while earth
has high conductivity and thermal inertia. Therefore, through the current study, the influence of thermal
inertia on the thermal performance of buildings in the studied climates is evaluated. Valencia and Stockholm
have been selected because the aim is to demonstrate how high energy efficiency can be achieved by using
these natural materials in different climates through the optimisation of buildings.
This has been done by means of extensive state of the art study on energy efficiency and natural materials,
gathering valuable information from other studies, and identifying research gaps. The assessment of the
energy performance of the buildings has been carried out for each of the four scenarios, corresponding to
the buildings with the different materials and the two climates (deeply analysed), using Cypetherm EPlus.
Additionally, these models have been energy optimised by implementing improvement measures, taking the
Passive House criteria as a reference, depending on their initial construction characteristics and climatic
conditions. In the process of optimising the buildings, the imperative need for the use of heat recovery
ventilation, as well as the use of a high level of insulation in opaque enclosures, has been identified in
Stockholm. In Valencia, the use of insulation is necessary, at a lower level, but the use of a heat recovery
unit for ventilation is not.
Total energy demand to maintain thermal comfort inside the building has been obtained for the straw-bale
building of 140.22 kWh/(m2·year) in the case of Stockholm and 37.05 kWh/(m2·year) in the case of
Valencia. On the other hand, for the earth building, a total demand of 301.82 kWh/(m2·year) has been
obtained in Stockholm and 78.66 kWh/(m2·year) in Valencia. Clearly, the buildings located in Valencia have
a better thermal performance than those in Stockholm. This is mainly due to the climatic conditions of both
locations, as Valencia has more moderate temperatures. Furthermore, the straw bale building, having a lower
heat transfer coefficient in the building envelope, performs better in both climates, especially in terms of
cooling demand. Once improvement measures are applied, a reduction in demand for the straw bale building
of 77.8% and 36.3% has been achieved for Stockholm and Valencia, respectively. In the earth building, after
the application of the improvement measures, the demand has been reduced by 86.3% in Stockholm and
73.9% in Valencia. Other improvement measures, not involving modification of the building geometry, such
as improving the permeability of the building, replacement of windows, or night ventilation for cooling,
have been applied in the models according to their needs.
In Stockholm, despite the application of appropriate passive measures and the energy efficiency achieved,
the demand values required by Passive House have not been met. It has been concluded that in order to
achieve these values, a different geometrical design of the building should be adopted, as well as an optimised
distribution of the windows. However, the national legislation from Sweden and Spain has not been
assessed, whose criteria may be accomplished.
Apart from that, better performance of the straw bale building compared to the rammed earth building has
been observed, due to the low conductivity of the straw. This partly demonstrates that in the climates
studied, the influence of thermal inertia is not important from an energy efficiency point of view. This has
also been demonstrated by iterative simulations, modifying the thermal inertia, and observing its slight
influence on the overall demand of the buildings in the climates studied. However, a variation in the thermal
behaviour of the building has been observed from month to month, showing that inertia could be interesting
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in climates with a more constant annual temperature and varying daily temperatures close to comfort
conditions.
This study proves that, from an energy perspective, natural materials can be used in high-efficiency buildings
in different climates. In order to do this, buildings must be designed adapting to the environment in
accordance with the corresponding climatic conditions and with the natural materials used and their
characteristics.
5.1 Future work
Apart from the present energy study, an environmental impact study (such as an LCA) of buildings
constructed with these natural materials would have been of great interest. In this way, not only the great
thermal characteristics of these materials would have been demonstrated, but also the environmental
impacts, in terms of GHG or other pollutants emissions, over the whole life of the building would have
been assessed. This, if it were included in the thesis, would show how environmentally beneficial the use of
natural materials would be compared to conventional materials. However, to carry out this study, a wealth
of information would be needed, such as the location of the raw materials, the amount of each material, the
lifetime of the building, the end of life of the building, construction practices, and energy used on it…
In accordance with this, a Life Cycle Cost (LCC) could be included in a further stage of the project, detailing
the price of each stage of the project, including the construction and the materials. Notwithstanding, this
would require information about the production process which was not possible to obtain in this master
thesis.
In addition, a larger number of climates could be simulated with the two building typologies. Furthermore,
a more in-depth study on the thermal inertia of the earth could be the subject of a future study, where its
influence could be seen in a climate with more constant temperatures throughout the year. Better
performance of the rammed earth building is expected despite the lack of insulation.
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1.1.3. Description of the construction element.......................................................... 4
1.1.4. Calculation of the internal surface temperature required to avoid the criticalsurface humidity.......................................................................................... 4
1.2.3. Description of the construction element.......................................................... 7
1.2.4. Calculation of the internal surface temperature required to avoid the criticalsurface humidity.......................................................................................... 8
1.3.3. Description of the construction element.......................................................... 11
1.3.4. Calculation of the internal surface temperature required to avoid the criticalsurface humidity.......................................................................................... 12
The psychrometric diagram associated with the location, with a height above sea level of 0 m, is displayedbelow. Represented using straight line segments are the transitions from each external design condition toits corresponding internal condition.
Hum
idity
ratio
, w(g
/kg)
Temperature, T(°C)
-15 -10 -5 0 5 10 15 20 25 30 35 40 450
2
4
6
8
10
12
14
16
18
20
22
24
Condensation
Page 3 - 14
1.1.3. Description of the construction element
Below is the section diagram of the composition of the construction element:
1 2 3 4 5
Exte
rnal
Inte
rnal
The thermal properties and water vapour diffusion properties of the homogenous layers of the parallel sidesmaking up the design model of the construction element are as follows:
External wall e(cm)
λ(W/m·K)
R(m²·K/W)
μ Sd
(m)
Rse 0.04
1 Pine Wood C24 3.0 0.130 0.23077 20 0.6
2 Air gap 2.5 0.09000 0.01
3 Wood Fiber TOP220 2.5 0.050 0.50000 20 0.5
4 Straw bale 25.0 0.071 3.51124 1 0.25
5 Ecoclay 4.0 0.240 0.16667 10 0.4
Rsi 0.13where:
e: Thickness, cm.
λ: Thermal conductivity of the material, W/(m·K).
R: Thermal resistance of the material, m²·K/W.
μ: Water vapour diffusion resistance factor of the material.
Sd: Equivalent air thickness against the water vapour diffusion, m.
Rse: External surface thermal resistance of the element, m²·K/W.
Rsi: Internal surface thermal resistance of the element, m²·K/W.
The design information regarding the hygrothermal parameters of the complete element, derived from thehomogenous layer model, is the following:
RT: Total thermal resistance of the element, sum of the thermal resistance of each layer, including surface resistances Rse and Rsi,m²·K/W.
SdT: Total equivalent air thickness, sum of the equivalent thickness of each layer of the element, m.
U: Thermal transmittance of the element, calculated as the inverse of the total thermal resistance, W/(m²·K).
fRsi: Internal surface resistance factor, calculated as (1 - U·Rsi), where U = 0.214 W/m²·K and Rsi = 0.25 m²·K/W.
1.1.4. Calculation of the internal surface temperature required to avoid the critical surfacehumidity
With the aim to prevent the adverse affects of the critical surface humidity, the maximum relative humidityon the internal surface has been limited to a value of φsi,cr ≤ 0.8.
Condensation
Page 4 - 14
Given the external and internal hygrothermal conditions, fRsi,min is calculated as follows:
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:
θe: External air temperature, °C.
φe: Relative humidity of the external air, %.
θi: Internal air temperature, °C.
φi: Relative humidity of the internal air, increased by a safety coefficient 5%, %.
Pi: Vapour pressure in the internal air, Pa.
Psat(θsi): Minimum acceptable water vapour saturation pressure for the internal surface, Pa.
θsi,min: Minimum acceptable internal surface temperature, calculated based on the minimum acceptable saturation pressure, °C.
Given that fRsi = 0.946 > fRsi,min = 0.338, no surface condensation occurs in the construction element.
1.1.5. Interstitial condensation calculation
Displayed below are the results obtained in the analysis of the temperatures and pressures at eachinterface of the homogenous layers making up the design model of the construction element.
Calculation of the interstitial condensation in the month of January.
The psychrometric diagram associated with the location, with a height above sea level of 0 m, is displayedbelow. Represented using straight line segments are the transitions from each external design condition toits corresponding internal condition.
Hum
idity
ratio
, w(g
/kg)
Temperature, T(°C)
-15 -10 -5 0 5 10 15 20 25 30 35 40 450
2
4
6
8
10
12
14
16
18
20
22
24
1.2.3. Description of the construction element
Below is the section diagram of the composition of the construction element:
1 23 4 5 6 7
Exte
rnal
Inte
rnal
The thermal properties and water vapour diffusion properties of the homogenous layers of the parallel sidesmaking up the design model of the construction element are as follows:
RT: Total thermal resistance of the element, sum of the thermal resistance of each layer, including surface resistances Rse and Rsi,m²·K/W.
SdT: Total equivalent air thickness, sum of the equivalent thickness of each layer of the element, m.
U: Thermal transmittance of the element, calculated as the inverse of the total thermal resistance, W/(m²·K).
fRsi: Internal surface resistance factor, calculated as (1 - U·Rsi), where U = 0.226 W/m²·K and Rsi = 0.25 m²·K/W.
1.2.4. Calculation of the internal surface temperature required to avoid the critical surfacehumidity
With the aim to prevent the adverse affects of the critical surface humidity, the maximum relative humidityon the internal surface has been limited to a value of φsi,cr ≤ 0.8.
Given the external and internal hygrothermal conditions, fRsi,min is calculated as follows:
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
Condensation
Page 8 - 14
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:
θe: External air temperature, °C.
φe: Relative humidity of the external air, %.
θi: Internal air temperature, °C.
φi: Relative humidity of the internal air, increased by a safety coefficient 5%, %.
Pi: Vapour pressure in the internal air, Pa.
Psat(θsi): Minimum acceptable water vapour saturation pressure for the internal surface, Pa.
θsi,min: Minimum acceptable internal surface temperature, calculated based on the minimum acceptable saturation pressure, °C.
Given that fRsi = 0.944 > fRsi,min = 0.338, no surface condensation occurs in the construction element.
1.2.5. Interstitial condensation calculation
Displayed below are the results obtained in the analysis of the temperatures and pressures at eachinterface of the homogenous layers making up the design model of the construction element.
Calculation of the interstitial condensation in the month of January.
The psychrometric diagram associated with the location, with a height above sea level of 0 m, is displayedbelow. Represented using straight line segments are the transitions from each external design condition toits corresponding internal condition.
Hum
idity
ratio
, w(g
/kg)
Temperature, T(°C)
-15 -10 -5 0 5 10 15 20 25 30 35 40 450
2
4
6
8
10
12
14
16
18
20
22
24
1.3.3. Description of the construction element
Below is the section diagram of the composition of the construction element:
1 2 3 4 5 6
Exte
rnal
Inte
rnal
The thermal properties and water vapour diffusion properties of the homogenous layers of the parallel sidesmaking up the design model of the construction element are as follows:
RT: Total thermal resistance of the element, sum of the thermal resistance of each layer, including surface resistances Rse and Rsi,m²·K/W.
SdT: Total equivalent air thickness, sum of the equivalent thickness of each layer of the element, m.
U: Thermal transmittance of the element, calculated as the inverse of the total thermal resistance, W/(m²·K).
fRsi: Internal surface resistance factor, calculated as (1 - U·Rsi), where U = 0.357 W/m²·K and Rsi = 0.25 m²·K/W.
1.3.4. Calculation of the internal surface temperature required to avoid the critical surfacehumidity
With the aim to prevent the adverse affects of the critical surface humidity, the maximum relative humidityon the internal surface has been limited to a value of φsi,cr ≤ 0.8.
Given the external and internal hygrothermal conditions, fRsi,min is calculated as follows:
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
Condensation
Page 12 - 14
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:
θe: External air temperature, °C.
φe: Relative humidity of the external air, %.
θi: Internal air temperature, °C.
φi: Relative humidity of the internal air, increased by a safety coefficient 5%, %.
Pi: Vapour pressure in the internal air, Pa.
Psat(θsi): Minimum acceptable water vapour saturation pressure for the internal surface, Pa.
θsi,min: Minimum acceptable internal surface temperature, calculated based on the minimum acceptable saturation pressure, °C.
Given that fRsi = 0.911 > fRsi,min = 0.338, no surface condensation occurs in the construction element.
1.3.5. Interstitial condensation calculation
Displayed below are the results obtained in the analysis of the temperatures and pressures at eachinterface of the homogenous layers making up the design model of the construction element.
Calculation of the interstitial condensation in the month of January.
1.1.3. Description of the construction element.......................................................... 4
1.1.4. Calculation of the internal surface temperature required to avoid the criticalsurface humidity.......................................................................................... 4
1.2.3. Description of the construction element.......................................................... 7
1.2.4. Calculation of the internal surface temperature required to avoid the criticalsurface humidity.......................................................................................... 8
1.3.3. Description of the construction element.......................................................... 11
1.3.4. Calculation of the internal surface temperature required to avoid the criticalsurface humidity.......................................................................................... 12
The psychrometric diagram associated with the location, with a height above sea level of 0 m, is displayedbelow. Represented using straight line segments are the transitions from each external design condition toits corresponding internal condition.
Hum
idity
ratio
, w(g
/kg)
Temperature, T(°C)
-15 -10 -5 0 5 10 15 20 25 30 35 40 450
2
4
6
8
10
12
14
16
18
20
22
24
Condensation
Page 3 - 14
1.1.3. Description of the construction element
Below is the section diagram of the composition of the construction element:
1 2 3 4 5
Exte
rnal
Inte
rnal
The thermal properties and water vapour diffusion properties of the homogenous layers of the parallel sidesmaking up the design model of the construction element are as follows:
External wall e(cm)
λ(W/m·K)
R(m²·K/W)
μ Sd
(m)
Rse 0.04
1 Pine Wood C24 3.0 0.130 0.23077 20 0.6
2 Air gap 2.5 0.09000 0.01
3 Wood Fiber TOP220 2.5 0.050 0.50000 20 0.5
4 Straw bale 25.0 0.071 3.51124 1 0.25
5 Ecoclay 4.0 0.240 0.16667 10 0.4
Rsi 0.13where:
e: Thickness, cm.
λ: Thermal conductivity of the material, W/(m·K).
R: Thermal resistance of the material, m²·K/W.
μ: Water vapour diffusion resistance factor of the material.
Sd: Equivalent air thickness against the water vapour diffusion, m.
Rse: External surface thermal resistance of the element, m²·K/W.
Rsi: Internal surface thermal resistance of the element, m²·K/W.
The design information regarding the hygrothermal parameters of the complete element, derived from thehomogenous layer model, is the following:
RT: Total thermal resistance of the element, sum of the thermal resistance of each layer, including surface resistances Rse and Rsi,m²·K/W.
SdT: Total equivalent air thickness, sum of the equivalent thickness of each layer of the element, m.
U: Thermal transmittance of the element, calculated as the inverse of the total thermal resistance, W/(m²·K).
fRsi: Internal surface resistance factor, calculated as (1 - U·Rsi), where U = 0.214 W/m²·K and Rsi = 0.25 m²·K/W.
1.1.4. Calculation of the internal surface temperature required to avoid the critical surfacehumidity
With the aim to prevent the adverse affects of the critical surface humidity, the maximum relative humidityon the internal surface has been limited to a value of φsi,cr ≤ 0.8.
Condensation
Page 4 - 14
Given the external and internal hygrothermal conditions, fRsi,min is calculated as follows:
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:
θe: External air temperature, °C.
φe: Relative humidity of the external air, %.
θi: Internal air temperature, °C.
φi: Relative humidity of the internal air, increased by a safety coefficient 5%, %.
Pi: Vapour pressure in the internal air, Pa.
Psat(θsi): Minimum acceptable water vapour saturation pressure for the internal surface, Pa.
θsi,min: Minimum acceptable internal surface temperature, calculated based on the minimum acceptable saturation pressure, °C.
Given that fRsi = 0.946 > fRsi,min = 0.338, no surface condensation occurs in the construction element.
1.1.5. Interstitial condensation calculation
Displayed below are the results obtained in the analysis of the temperatures and pressures at eachinterface of the homogenous layers making up the design model of the construction element.
Calculation of the interstitial condensation in the month of January.
The psychrometric diagram associated with the location, with a height above sea level of 0 m, is displayedbelow. Represented using straight line segments are the transitions from each external design condition toits corresponding internal condition.
Hum
idity
ratio
, w(g
/kg)
Temperature, T(°C)
-15 -10 -5 0 5 10 15 20 25 30 35 40 450
2
4
6
8
10
12
14
16
18
20
22
24
1.2.3. Description of the construction element
Below is the section diagram of the composition of the construction element:
1 23 4 5 6 7
Exte
rnal
Inte
rnal
The thermal properties and water vapour diffusion properties of the homogenous layers of the parallel sidesmaking up the design model of the construction element are as follows:
RT: Total thermal resistance of the element, sum of the thermal resistance of each layer, including surface resistances Rse and Rsi,m²·K/W.
SdT: Total equivalent air thickness, sum of the equivalent thickness of each layer of the element, m.
U: Thermal transmittance of the element, calculated as the inverse of the total thermal resistance, W/(m²·K).
fRsi: Internal surface resistance factor, calculated as (1 - U·Rsi), where U = 0.226 W/m²·K and Rsi = 0.25 m²·K/W.
1.2.4. Calculation of the internal surface temperature required to avoid the critical surfacehumidity
With the aim to prevent the adverse affects of the critical surface humidity, the maximum relative humidityon the internal surface has been limited to a value of φsi,cr ≤ 0.8.
Given the external and internal hygrothermal conditions, fRsi,min is calculated as follows:
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
Condensation
Page 8 - 14
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:
θe: External air temperature, °C.
φe: Relative humidity of the external air, %.
θi: Internal air temperature, °C.
φi: Relative humidity of the internal air, increased by a safety coefficient 5%, %.
Pi: Vapour pressure in the internal air, Pa.
Psat(θsi): Minimum acceptable water vapour saturation pressure for the internal surface, Pa.
θsi,min: Minimum acceptable internal surface temperature, calculated based on the minimum acceptable saturation pressure, °C.
Given that fRsi = 0.944 > fRsi,min = 0.338, no surface condensation occurs in the construction element.
1.2.5. Interstitial condensation calculation
Displayed below are the results obtained in the analysis of the temperatures and pressures at eachinterface of the homogenous layers making up the design model of the construction element.
Calculation of the interstitial condensation in the month of January.
The psychrometric diagram associated with the location, with a height above sea level of 0 m, is displayedbelow. Represented using straight line segments are the transitions from each external design condition toits corresponding internal condition.
Hum
idity
ratio
, w(g
/kg)
Temperature, T(°C)
-15 -10 -5 0 5 10 15 20 25 30 35 40 450
2
4
6
8
10
12
14
16
18
20
22
24
1.3.3. Description of the construction element
Below is the section diagram of the composition of the construction element:
1 2 3 4 5 6
Exte
rnal
Inte
rnal
The thermal properties and water vapour diffusion properties of the homogenous layers of the parallel sidesmaking up the design model of the construction element are as follows:
RT: Total thermal resistance of the element, sum of the thermal resistance of each layer, including surface resistances Rse and Rsi,m²·K/W.
SdT: Total equivalent air thickness, sum of the equivalent thickness of each layer of the element, m.
U: Thermal transmittance of the element, calculated as the inverse of the total thermal resistance, W/(m²·K).
fRsi: Internal surface resistance factor, calculated as (1 - U·Rsi), where U = 0.357 W/m²·K and Rsi = 0.25 m²·K/W.
1.3.4. Calculation of the internal surface temperature required to avoid the critical surfacehumidity
With the aim to prevent the adverse affects of the critical surface humidity, the maximum relative humidityon the internal surface has been limited to a value of φsi,cr ≤ 0.8.
Given the external and internal hygrothermal conditions, fRsi,min is calculated as follows:
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338
Condensation
Page 12 - 14
θe
(°C)φe
(%)θi
(°C)φi
(%)Pi
(Pa)Psat (θsi)
(Pa)θsi,min
(°C)fRsi,min
December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:
θe: External air temperature, °C.
φe: Relative humidity of the external air, %.
θi: Internal air temperature, °C.
φi: Relative humidity of the internal air, increased by a safety coefficient 5%, %.
Pi: Vapour pressure in the internal air, Pa.
Psat(θsi): Minimum acceptable water vapour saturation pressure for the internal surface, Pa.
θsi,min: Minimum acceptable internal surface temperature, calculated based on the minimum acceptable saturation pressure, °C.
Given that fRsi = 0.911 > fRsi,min = 0.338, no surface condensation occurs in the construction element.
1.3.5. Interstitial condensation calculation
Displayed below are the results obtained in the analysis of the temperatures and pressures at eachinterface of the homogenous layers making up the design model of the construction element.
Calculation of the interstitial condensation in the month of January.
Ma: Accumulated humidity content per unit area, g/m².>> Graphical representation (January)
Condensation
Page 13 - 14
1.3.6. Graphical representation of the foreseen interstitial condensation
January
1 2 3 4 5 6-200
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
-2
0
2
4
6
8
10
12
14
16
18
20
22
Pressure (Pa) Temperature (°C)
-0.05 0.00 0.05 0.10 0.15 0.20
Thickness (m)Theoretical vapour pressure Real vapour pressure
Saturation pressure Temperature
Condensation
Page 14 - 14
Condensation
UNE EN ISO 13788
FreeText
Annex III
Rectangle
FreeText
Parametric study. Parametric Preprocessor and Python.
Rectangle
2
• Straw bale thickness:
By means of the EnergyPlus Parametric Preprocessor the following code has been added to the text file:
Parametric:FileNameSuffix, Names, !- Name E_straw_0.05, !- Suffix for File Name in Run 1 E_straw_0.10, !- Suffix for File Name in Run 2 E_straw_0.15, !- Suffix for File Name in Run 3 E_straw_0.20, !- Suffix for File Name in Run 4 E_straw_0.25, !- Suffix for File Name in Run 5 E_straw_0.30, !- Suffix for File Name in Run 6 E_straw_0.35, !- Suffix for File Name in Run 7 E_straw_0.40, !- Suffix for File Name in Run 8 E_straw_0.45, !- Suffix for File Name in Run 9 E_straw_0.50; !- Suffix for File Name in Run 10 Parametric:SetValueForRun, $e_straw, !- Name 0.05, !- Value for Run 1 0.10, !- Value for Run 2 0.15, !- Value for Run 3 0.20, !- Value for Run 4 0.25, !- Value for Run 5 0.30, !- Value for Run 6 0.35, !- Value for Run 7 0.40, !- Value for Run 8 0.45, !- Value for Run 9 0.50; !- Value for Run 10 Material, M15_Straw_bale (250mm), !- Name Rough, !- Roughness =$e_straw, !- Thickness {m} 0.0712, !- Conductivity {W/m-K} 130, !- Density {kg/m3} 1000, !- Specific Heat {J/kg-K} 0.9, !- Thermal Absorptance 0, !- Solar Absorptance 0.6; !- Visible Absorptance
3
• Floor insulation thickness:
For the floor insulation parametric study, the following code has been added to the file text of the model
in EnergyPlus Parametric Preprocessor:
Parametric:FileNameSuffix,
Names, !- Name
E_floor_ins_0.02, !- Suffix for File Name in Run 1
E_floor_ins_0.04, !- Suffix for File Name in Run 2
E_floor_ins_0.06, !- Suffix for File Name in Run 3
E_floor_ins_0.08, !- Suffix for File Name in Run 4
E_floor_ins_0.10, !- Suffix for File Name in Run 5
E_floor_ins_0.12, !- Suffix for File Name in Run 6
E_floor_ins_0.14, !- Suffix for File Name in Run 7
E_floor_ins_0.16, !- Suffix for File Name in Run 8
E_floor_ins_0.18, !- Suffix for File Name in Run 9
E_floor_ins_0.20; !- Suffix for File Name in Run 10
Parametric:SetValueForRun,
$e_floor_ins, !- Name
0.02, !- Value for Run 1
0.04, !- Value for Run 2
0.06, !- Value for Run 3
0.08, !- Value for Run 4
0.10, !- Value for Run 5
0.12, !- Value for Run 6
0.14, !- Value for Run 7
0.16, !- Value for Run 8
0.18, !- Value for Run 9
0.20; !- Value for Run 10
Material,
M07_Floor_insulation (80mm), !- Name
Rough, !- Roughness
=$e_floor_ins, !- Thickness {m}
0.038, !- Conductivity {W/m-K}
160, !- Density {kg/m3}
1000, !- Specific Heat {J/kg-K}
0.9, !- Thermal Absorptance
0, !- Solar Absorptance
0.6; !- Visible Absorptance
4
• Cork panel thickness:
For the cork panel thickness study in the rammed earth building, the following code has been added: