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Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh
Alexandria Engineering Journal (2019) xxx, xxx–xxx
H O S T E D BY
Alexandria University
Alexandria Engineering Journal www.elsevier.com/locate/aej www.sciencedirect.com
ORIGINAL ARTICLE
Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh Farah Eddib *,1, Moulay Abdellah Lamrani 2 Department of Physics, Cadi Ayyad University, Marrakesh, Morocco Received 28 February 2019; revised 20 August 2019; accepted 22 August 2019
KEYWORDS Thermal comfort; Energy consumption; Thermal insulation; Thermal dynamic simulation; TRNSYS
Abstract Thermal insulation has become essential, firstly to ensure the thermal comfort of the occupants and secondly to save energy and that’s why we find more and more varieties of insulators (organic, inorganic and synthetic) in the Moroccan market, depending on the need when to make the right choice. This paper presents the theoretical part of a thermal and an energetic study of the envelop of a house located in the city of Marrakesh (Morocco), by using four types of insulators, that are mostly used in Moroccan markets, for different thicknesses to determine the most suitable insulator for Marrakech climate and its optimal thickness. The insulators studied are: Expanded Polystyrene, glass wool, rock wool and wood fiber. The numerical simulations were realized using the software of thermal dynamic simulation TRNSYS. The results show that for a thickness of 8 cm of the wood fiber insulator saves about 7% for heating and 14% for cooling loads. For temperatures, in January temperatures are higher by 0.26 °C, and in July are lower by 0.49 °C.
Ó 2019 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Morocco is a country that depends on more than 96% of imports for its supply of energy resources ADEREE [1]. In this perspective, the government has launched an energy efficiency * Corresponding author. E-mail addresses: [email protected] (F. Eddib), [email protected] (M.A. Lamrani). 1 Phd. Candidate, Laboratory of Fluid Mechanics and Energetics, Faculty of Sciences Semlalia, Marrakesh, Morocco. 2 Professor, Laboratory of Fluid Mechanics and Energetics, Faculty of Sciences Semlalia, Marrakesh, Morocco. Peer review under responsibility of Faculty of Engineering, Alexandria University.
program. The energy saving expected by 2020 will be between 12% and 15% of primary energy consumption compared to the year 2011 ADEREE [1]. This economy aims to optimize the energy consumption and improve the quality of energy. Internal atmosphere promotes users comfort in the residential sector which is considered to be the most energy consuming sector. Good insulation saves energy and therefore less energy will be needed for cooling the premises in summer and less heat to keep the room warm in winter. Building insulation is a simple technique but a high energy efficiency that can be applied to the residential, commercial and industrial sectors Xu et al. [2]. Thermal insulator is composed of a material or composite materials which is characterized by a high thermal resistance, which allows to reduce the flow of heat Al-Homoud [3]. Then, the
https://doi.org/10.1016/j.aej.2019.08.008 1110-0168 Ó 2019 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
2
F. Eddib, M.A. Lamrani
Nomenclature e Cp k P
thickness (cm) thermal capacity (kJ/kg K) thermal conductivity (W/m K) density (kg/m3)
insulation of buildings is able to keep the heat/cold in the house and to avoid heat flows with the external environment. Al-Sallal [4] proved that the most efficient improvement system is thermal insulation. Hamdani.[5] and Mokhtari et al. [6] have made an experimental study for the evaluation of the global thermal comfort of the buildings located in the city Be´char in Algeria by studying the notions of bioclimatic design (orientation, thermal insulation and thermal inertia). Kaynakli et al. [7] have studied the thickness of the thermal insulation used in the external walls of buildings, with the aim of optimizing it by considering condensation. They have found that the optimum thickness of the insulation is generally increased with increasing temperature, indoor and outdoor relative humidity, and have found that the use of extra-insulated walls gives better results. Several studies have been done to optimize the consumption, and allow maximum energy savings. Among these studies, we can find the paper of Guechchati et al. [8] that used the TRNSYS16 software for the thermal and energy study of educational center ‘‘SAFAA” in the city of Oujda. Their results revealed that the insulation of the roof coupled to the external insulation of the walls with 6 cm of expanded polystyrene 035 has been chosen as a solution to save the maximum of energy. Mousa et al. [9] studied the energy saving in buildings in Jordan and found that energy savings of up to 76.8% can be achieved by using polystyrene as insulation materials for walls and roofs. Bolatturk [10] used polystyrene for insulation in the hottest area of Turkey and concluded that the optimal thickness of the insulation varies between 3.2 and 3.8 cm, and energy savings range from $ 8.47 to $ 12.19/m2. On the other hand, for heat load, the thickness of the insulation varies between 1.6 cm and 2.7 cm, and the energy savings between 2.2 and 6.6 $/m2. Schiavoni et al. [11] did a review of the main commercialized insulation materials (conventional, alternative and advanced) for the building sector through a holistic and multidisciplinary approach. In each case study, thermal transmittance, periodic thermal transmittance and the thermal wave shift were evaluated considering a 10 cm layer of insulating material. Aditya et al. [12] collected the most common developments in thermal insulation of buildings and also studied life cycle analysis and emission reductions using appropriate insulation materials. Al-Senea et al. [13] concluded that the optimum insulation thickness is found to increase with the cost of electricity, building lifetime and inflation rate; and decrease with increasing cost of insulation material, coefficient of performance of air-conditioning equipment. Afif et al. [14] used life-cycle cost analysis to determine optimum insulation thickness for rock wool and polystyrene insulation. Mousa et al. [9] have used three different insulators which are polystyrene, Rock wool and air gap. Their results show that the insulation with the highest performance is polystyrene with a saving of 36% followed by Rockwool with an energy saving of 34%,
Vi Qi Ti As
volume of studied area (m3) net heat gain W/(m2K) temperature of the zone (K) inside area of surface S (m)
and the least efficient is air gap with a saving of 5,4%. Aktacir et al. [15] worked on the influence of different insulation thickness on the air conditioning load and on the energy consumption of the air conditioning system in a sample building located in Adana in the Mediterranean Region (hot and humid summer and warm winter). They found that the load of cooling decreased by 33%, and the capacity of equipment used in the air-conditioning system of insulated buildings is lower than that for non-insulated buildings. They have also found that the initial cost of the cooling for both variable volume and constant volume systems has decreased by 25% while the operating cost is 25% less for variable volume and 33% less for constant volume. In this study, the authors did not ignored the economic analysis for which results revealed that the thickness of the thermal insulation material of the buildings in coastal provinces of the Mediterranean countries should be determined according to the degree-day of air conditioning. Khoukhi et al. [16] evaluated the effect of the changes in the conductivity of the polystyrene insulating material as a function of the operating temperature, and found that the percentage of the increase of the values of k with respect to k24 for the wall and the roof can reach 9.4% and 20% respectively, which affects the calculation of cooling when the temperature exceeds 24°. Mangematin et al. [17] have developed a method to quickly measure the energy efficiency of buildings. They have shown that by measuring the transient states during the heating and cooling of an empty low-energy house, they have access to the thermal leakage coefficient K and the apparent heat capacity of the building, and these measurements can be obtained in one or two days. The aim of this work is to determine the best thermal insulation material and its optimal thickness to have the right compromise between thermal comfort of occupants and energy consumption in the case of Marrakech climate. For that, we had studied the effect of insulating the envelope of a typical house located in the city of Marrakech by using four types of thermal insulators: expanded polystyrene, glass wool, rock wool and wood fiber. The thermal and energetic behavior of the building is simulated by using the software of thermal dynamic simulation TRNSYS. 2. Building characteristics The house studied is consisting of 10 areas with four facades exposed outside. A fac¸ade is facing south and receives a continuous sunshine all day, and the others are oriented respectively East, North and West. The house is built on a surface of 117 m2 (Fig. 1), and located in the city of Marrakesh. It is on one floor, the ground floor, and deposited directly on the floor.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
Effect of the thermal insulators on the thermal and energetic performance Table 2 Room
Wall
Garage Living room Room1 Bath Room3 Room2 Hall WC Kitchen
Window
Orientation
Dimension (m)
East South South West West West North North West North North
8 2.8 3.53 3 1.3 4.77 1.7 1.66 1.2 0.4 4
3 Thermo-physical Properties of Insulation Materials.
Materials
Expanded Polystyrene
Rockwool
Glasswool
Wood fiber
1.45
0.92
0.84
1.950
0.159
0.15
0.15
0.138
0.4
Thermal capacity (kJ/kg K) Thermal conductivity (W/m K) Density (kg/m3)
20
300
12
180
1.2 1.2 Door (1.6) 0.4 1
Table 3 roof.
Dimension (m2) 0.6 0.8
The thermal behavior of the studied house is simulated through multi-zone transient modeling (type56a) with a time step of one hour. The TRNBUILD is used to enter all the information concerning the building envelope (materials, layer thickness, thermo-physical properties), windows, heating/cooling, infiltration . . .the thermo-physical properties of walls, roof, and insulators are given in the tables below (see Tables 1–3). For the simulations performed in this study, the thermophysical properties of these materials were taken from the TRNSYS library and Schiavoni et al. and Aditya et al. [11,12]. 2.1. Meteorological data The simulation of the building was carried out with actual meteorological data taken from the Agdal Marrakech station
The layers and thermo-physical properties of the
Materials
Plaster
Hourdis
Concrete
Mortar
Floor tile
Thickness (cm) Thermal capacity (kJ/kg K) Thermal conductivity (W/m K) Density (kg/m3)
1 1
16 0.65
4 0.653
10 1
1 0.7
0.351
1.23
1.75
1.15
1.75
1500
1300
2100
1700
2300
in 2014. These data are: the relative humidity at 3.2 m, global radiation, temperature at 3.2 m and the speed and wind direction at 3 m (TERMA 2014) [18]. Fig. 2 shows the temperature evolution of the city of Marrakech over a period of one year. 2.2. Calculation hypotheses The infiltration rate is equal to: 0.6 ACH (air change per hour), The temperature of the soil is taken from the meteorological file of the city of Marrakech, For all the cases of insulation studied, we consider that the roof is insulated with 4 cm polystyrene,
Fig. 1
Architectural plan of the house.
Table 1 Layers and thermo-physical properties of simple exterior walls. Materials
Cement mortar
Red brick terracotta
Thickness (cm) Thermal capacity (kJ/kg K) Thermal conductivity (W/m K) Density (kg/m3)
2.5 1 1.15 1700
10 0.878 1.15 1800
Fig. 2 Temperature evolution simulation of the city of Marrakesh over a year.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
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F. Eddib, M.A. Lamrani
All the thermo-physical properties of the materials used are taken from the TRNSYS16 library, The four facades are exposed outside, The windows have a single glazing, The house is placed directly on the ground and the roof is exposed outside, The internal generation is zero (unoccupied house), Thermal bridges are not taken into account.
where As : is the inside area of surface S. For an internal wall both sides are considered internal surfaces and must be held twice in the calculations. The energy balance of the star node* shows that
2.3. Mathematical modelling
1
The temperature of a zone is calculated from the rate of variation of the internal energy of the studied floating zone, which is equal to the net heat gained: Where Ci is the thermal capacity of the area, [Ci ¼ Vi qCp , Vi : volume of the studied area]. And Qi is the net heat gain, which can be calculated by calculating the heat gain of the sur_ , the heat gain by _ , the heat gain by infiltration Qinf;i faces Qsurf;i _ , and the heat gain by convective ventilationQvent;i _ . couplingQcplg;i
The net heat gain Q_ i_is a function of the temperature Ti ; and the temperatures of the other adjacent zones of the zone i. To simplify the calculation, Qi_ is considered constant during each time step. In this case, the solution of the differential equation for a given time step is equal to: _ Qi;Dt Ci
ð2Þ
The temperature variation is linear, and the average is given by: Ti ¼
Ti;s þ Ti;sDt 2
By solving the Eq. (3) for Ti,t and replacing the result obtained in Eq. (2) by introducing the individual expression representing the net heat gain, we obtain:
þ
knownbound X
surfaces Xi to j
_ C p Ta _ Cp T þ minf;i mcplg;s
d micplg;s Cp Tb;s dt surfaces Xi to j
adj zones X surfaces i to j
X
j¼1
i¼1
þ þ
exterior Xsurfaces
þ
As Bs Ta þ
known Xbound
As Bs Tb;s
As ðCs Tstar;i Ds Ss;i
As B s þ
surf:in Xi
X
As Bs ÞTa þ
As Cc ÞTstar;i !
As Bs Tstar;j
known X bounderies
1 Ti RStar;i
As Bs Tb;s
!
surfaceX in zone i
ð7Þ
As ðDs þ Ss;i
The energy balances obtained with Eqs. (4) and (7) for all the zones give the results in a linear set of equations in mean zone and star-shaped temperature equations. Where the star temperature given by Seem [19] uses an artificial temperature node (Tstar) to consider the parallel energy flow from a convective wall surface to the air node and radiation to other wall and window elements. ½X
½T ¼ ½Z
½X ¼ " ½T ¼ ½Z ¼
X1;2 X2;2
X1;1 X2;1 T1 T2 Z1 Z2
ð8Þ
#
" ¼
T Tstar
#
Surfaces Xi to j
mcplg;s C _for i–jp
! _ m_v;i Ti _ þ minf;i mcplg;s
X11;ij ¼
Surfaces Xi to j
mcplg;s C _for i–jp
ð4Þ
As Bs Tstar;j
intX walls
inter:walls X
where
The total gain to the studied zone i from all surfaces is the sum of the combined heat transfers:
Ext X surfaces
¼
adj:zone X walls i to j
X11;ii ¼
known X bounderies 1 _ þ mcplg;i Rstar X þ m_v;k cp Tv;k þ Q_gc;i
Q_ surf;i ¼
RStar;i
ð3Þ
X 2Ci ðTi Ti;sDt Þ zones ¼ Dt j¼1
ð6Þ
Equalizing Eqs. (5) and (6) gives the balance sheet:
2.3.1. Calculation of temperature
Ti;s ¼ Ti;sDt þ
1 ðTstar;i Ti Þ Rstar;i
Q_ surf;i ¼
X12;ii ¼¼
Rstar;i
X12;ij ¼ 0 for i–j X21;ii ¼
As Bs Tstar
surfaceX in zone i
1
1 Rstar;i
X21;ij ¼ 0 X22;ii ¼
intX walls
As B s þ
surf X in zone i
As Cs
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
Effect of the thermal insulators on the thermal and energetic performance X22;ij ¼
adj:zones i to j X wallsX
Z1;i ¼ minf;i Cp Ta þ
Xsurfaces
i to j
ext:surf X
Z2;i ¼
As B s Xnvent _ _ Cp Tb;s þ _ CP Tv;k mcplg;s mv;k;i k
5
þ
! As Bs Ta þ
surf:in zone i X
known X boundaries
As Bs Tb;s
As ðDs þ Ss;i Þ
By calculating and solving the equations, the final temperature of zone i is equal to Ti;s ¼ 2Ti Ti;sDt
ð9Þ
2.3.2. Heating and cooling Fig. 3 shows the output power versus the temperature. For areas with floating temperatures, the solution for average zone temperatures and star temperatures is in the form of: 1
0
½T ¼ ½X0 ½Z
Fig. 3 [20].
Output power versus temperature (TRNSYS16 volume 6)
4cm of thickness
ð10Þ
The coefficients of the matrix X0 and of the vector Z0 depend on the temperatures of the zones relative to the set point temperature, and are determined as when calculating
6cm of thickness
(a)
(b)
8cm of thickness
10cm of thickness
(c)
(d)
Fig. 4
January temperatures with different insulation materials thickness.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
6
F. Eddib, M.A. Lamrani
the factor coefficients of the matrix for calculating the temperatures of the zones with: Ci
d T ¼ Q_ i Pi dt
ð11Þ
Pi and Qi are considered constant over time and Q_ i is evaluated at the average temperature of the zone (TRNSYS16 volume 6) [20]. 3. Results and discussions 3.1. Internal temperature The simulations are run over a period of 48 h for the coldest temperatures in January and the hottest temperatures in July, using the simulation software TRNSYS16. The house studied as shown in Fig. 1 consists of 10 zones but for clarity in the figures, we chose to represent only the variation of temperatures of the room1.
4cm of thickness
Fig. 4 shows the evolution of temperatures for the four different types of insulation of the house studied. In January and on a simulation of 48 h for 4 cm thick (Fig. 4-a), the temperatures recorded for the wood fiber are higher than those recorded for the other three insulators of 0.03 °C. For 6 cm of thickness of insulation (Fig. 4-b), all temperatures for the three insulators are around 15 °C and with wood fiber temperatures are 0.04 °C higher than the three insulators. For a thickness of 8 cm (Fig. 4-c), the temperatures with the wood fiber are 0.06 °C greater than those recorded with the polystyrene, glass wool and rock wool insulation. Finally, for a thickness of 10 cm of insulation (Fig. 4-d), temperatures with wood fiber are 0.13 °C higher than those recorded with other insulators. This is due to its low thermal conductivity compared to other insulators. The temperatures noted with the wood fiber insulation are higher compared to those noted for the other insulators, and this for the four thicknesses studied. For the month of July, simulations were carried out for four different thicknesses 4, 6, 8, 10 cm for a duration of 48 h. For this month, we note the hottest temperatures.
6cm of thickness
(a)
(b)
8cm of thickness
10cm of thickness
(c)
(d)
Fig. 5
July temperatures with different insulation thickness of insulators.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
Effect of the thermal insulators on the thermal and energetic performance For insulation thickness 4 cm (Fig. 5-a), the temperatures recorded for the wood fiber insulation are 0.14 °C lower than polystyrene, 0.13 °C lower than glass wool and 0.09 °C lower than rock wool. Compared to rockwool, for 6 cm thickness of insulation (Fig. 5-b) the temperatures of the wood fiber are 0.17 °C lower than those recorded for polystyrene, glass wool and rockwool. For 8 cm of thickness (Fig. 5-c) the temperatures are lower of 0.19 °C compared to the other insulators. Finally for a thickness of 10 cm (Fig. 5-d) with the wood fiber the temperatures are lower of 0.19 °C compared to the polystyrene and 0.2 °C compared to rock wool and glass wool. The temperatures noted with the wood fiber insulation are lower than temperatures noted for the other insulators, and this for the four thicknesses studied.
Table 4 Heating demand for the four insulators with different thicknesses. Thermal load of heating in KWH Thickness (cm)
4
6
8
10
Polystyrene Glass wool Rock wool Wood fiber
3063 3058 3053 3023
2929 2925 2925 2898
2850 2847 2847 2824
2798 2796 2796 2796
Table 5 Demand for air conditioning for the four insulators with different thicknesses.
3.2. Demand for heating and air conditioning: With the beginning of the energetic study of the insulators, we will show the effect of the orientation on the energy load of heating and air conditioning of two rooms the one directed south (Ch1) and the other which is oriented north (Ch3) in Fig. 1. Fig. 6 shows the demands for heating and cooling in the case of south facing room and the other facing north. It was found that with just the change of orientation from north to south we note that we save for heating 25.516% and 13.18% for air conditioning. Regarding the energetic study of insulation study, the annual demand for heating and cooling is shown in the tables below in KWH. The heating demand for four insulators with four different thicknesses 4, 6, 8, 10 cm. Tables 4 and 5 give us the heating and cooling loads respectively for the different insulators and the four different thicknesses considered in our study. It is noted that for an insulation thickness of 4 and 6 cm (Table 4), the wood fiber allows a reduction of the thermal load of heating of almost 3% compared to polystyrene and 2% compared to the glass wool and the rockwool. For the air conditioning load (Table 5), we can observe that the wood fiber allows a reduction of almost 2% compared to polystyrene and 1% compared to glass wool and rockwool. For a thickness of 8 and 10 cm, and from Table 4, we can deduce that the wood fiber allows
Demand for heating and air conditioning 250
200
150
100
50
0
Hea ng KWH
Air condi oning KWH
Ch1 Fig. 6
Ch3
Demand for heating and air conditioning.
7
Thermal load of cooling in KWH Thickness (cm)
4
6
8
10
Polystyrene Glass wool Rock wool Wood fiber
1134 1130 1127 1108
1033 1030 1030 1009
973,5 971,2 971,2 952,3
934,2 932,4 932,4 915,6
a reduction of almost 2% on the thermal load of heating compared to the three insulators studied (polystyrene, rockwool and glass wool). For air conditioning (Table 5) and for a thickness of 10 cm we get almost the same results obtained for the thermal load of heating. Hence, the wood fiber insulation gives the most satisfactory results in terms of internal temperature, heating and air conditioning, In addition, for the four insulators, not to use a large thickness of insulation, we opt to use 8 cm thick. By changing the thickness of wood fiber insulation from 4 cm to 8 cm, we saved 7% on the heating load and 14% on the cooling load. Finally and according to all the results cited above, we can justify our choice to adopt the 8 cm thick wood fiber insulation. 4. Conclusion In this paper, we presented the theoretical part of a thermal and an energetic study of a house located in the city of Marrakech. We were interested in this work to improve the thermal quality of the building envelop by using a thermal insulation. For that, we used four types of insulators, which are expanded polystyrene, rockwool, glass wool and wood fiber. The thickness of these insulators was taken equal to 4, 6, 8 and 10 cm. The numerical simulations were carried out with TRNSYS software using the multizone model type56. The thermal and the energetic behaviour of the building, for the different insulators studied, showed that the wood fiber is the most adequate for the climate of Marrakech. We noticed that for 8 cm of wood fiber we obtained the optimal results for both the hot and the cold periods. Otherwise a reduction in energy consumption of about 7% for heating and 14% for air conditioning is obtained by using 8 cm of wood fiber comparing to polystyrene, glass wool and rockwool. And For temperatures in January the temperatures are higher by 0.26 °C, and in July the temperatures are lower by 0.49 °C. Currently, we are working on the experimental part of this study (Prototypes Laboratory Tests) to validate the numerical results found.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
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Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
H O S T E D BY
Alexandria University
Alexandria Engineering Journal www.elsevier.com/locate/aej www.sciencedirect.com
ORIGINAL ARTICLE
Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh Farah Eddib *,1, Moulay Abdellah Lamrani 2 Department of Physics, Cadi Ayyad University, Marrakesh, Morocco Received 28 February 2019; revised 20 August 2019; accepted 22 August 2019
KEYWORDS Thermal comfort; Energy consumption; Thermal insulation; Thermal dynamic simulation; TRNSYS
Abstract Thermal insulation has become essential, firstly to ensure the thermal comfort of the occupants and secondly to save energy and that’s why we find more and more varieties of insulators (organic, inorganic and synthetic) in the Moroccan market, depending on the need when to make the right choice. This paper presents the theoretical part of a thermal and an energetic study of the envelop of a house located in the city of Marrakesh (Morocco), by using four types of insulators, that are mostly used in Moroccan markets, for different thicknesses to determine the most suitable insulator for Marrakech climate and its optimal thickness. The insulators studied are: Expanded Polystyrene, glass wool, rock wool and wood fiber. The numerical simulations were realized using the software of thermal dynamic simulation TRNSYS. The results show that for a thickness of 8 cm of the wood fiber insulator saves about 7% for heating and 14% for cooling loads. For temperatures, in January temperatures are higher by 0.26 °C, and in July are lower by 0.49 °C.
Ó 2019 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Morocco is a country that depends on more than 96% of imports for its supply of energy resources ADEREE [1]. In this perspective, the government has launched an energy efficiency * Corresponding author. E-mail addresses: [email protected] (F. Eddib), [email protected] (M.A. Lamrani). 1 Phd. Candidate, Laboratory of Fluid Mechanics and Energetics, Faculty of Sciences Semlalia, Marrakesh, Morocco. 2 Professor, Laboratory of Fluid Mechanics and Energetics, Faculty of Sciences Semlalia, Marrakesh, Morocco. Peer review under responsibility of Faculty of Engineering, Alexandria University.
program. The energy saving expected by 2020 will be between 12% and 15% of primary energy consumption compared to the year 2011 ADEREE [1]. This economy aims to optimize the energy consumption and improve the quality of energy. Internal atmosphere promotes users comfort in the residential sector which is considered to be the most energy consuming sector. Good insulation saves energy and therefore less energy will be needed for cooling the premises in summer and less heat to keep the room warm in winter. Building insulation is a simple technique but a high energy efficiency that can be applied to the residential, commercial and industrial sectors Xu et al. [2]. Thermal insulator is composed of a material or composite materials which is characterized by a high thermal resistance, which allows to reduce the flow of heat Al-Homoud [3]. Then, the
https://doi.org/10.1016/j.aej.2019.08.008 1110-0168 Ó 2019 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
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F. Eddib, M.A. Lamrani
Nomenclature e Cp k P
thickness (cm) thermal capacity (kJ/kg K) thermal conductivity (W/m K) density (kg/m3)
insulation of buildings is able to keep the heat/cold in the house and to avoid heat flows with the external environment. Al-Sallal [4] proved that the most efficient improvement system is thermal insulation. Hamdani.[5] and Mokhtari et al. [6] have made an experimental study for the evaluation of the global thermal comfort of the buildings located in the city Be´char in Algeria by studying the notions of bioclimatic design (orientation, thermal insulation and thermal inertia). Kaynakli et al. [7] have studied the thickness of the thermal insulation used in the external walls of buildings, with the aim of optimizing it by considering condensation. They have found that the optimum thickness of the insulation is generally increased with increasing temperature, indoor and outdoor relative humidity, and have found that the use of extra-insulated walls gives better results. Several studies have been done to optimize the consumption, and allow maximum energy savings. Among these studies, we can find the paper of Guechchati et al. [8] that used the TRNSYS16 software for the thermal and energy study of educational center ‘‘SAFAA” in the city of Oujda. Their results revealed that the insulation of the roof coupled to the external insulation of the walls with 6 cm of expanded polystyrene 035 has been chosen as a solution to save the maximum of energy. Mousa et al. [9] studied the energy saving in buildings in Jordan and found that energy savings of up to 76.8% can be achieved by using polystyrene as insulation materials for walls and roofs. Bolatturk [10] used polystyrene for insulation in the hottest area of Turkey and concluded that the optimal thickness of the insulation varies between 3.2 and 3.8 cm, and energy savings range from $ 8.47 to $ 12.19/m2. On the other hand, for heat load, the thickness of the insulation varies between 1.6 cm and 2.7 cm, and the energy savings between 2.2 and 6.6 $/m2. Schiavoni et al. [11] did a review of the main commercialized insulation materials (conventional, alternative and advanced) for the building sector through a holistic and multidisciplinary approach. In each case study, thermal transmittance, periodic thermal transmittance and the thermal wave shift were evaluated considering a 10 cm layer of insulating material. Aditya et al. [12] collected the most common developments in thermal insulation of buildings and also studied life cycle analysis and emission reductions using appropriate insulation materials. Al-Senea et al. [13] concluded that the optimum insulation thickness is found to increase with the cost of electricity, building lifetime and inflation rate; and decrease with increasing cost of insulation material, coefficient of performance of air-conditioning equipment. Afif et al. [14] used life-cycle cost analysis to determine optimum insulation thickness for rock wool and polystyrene insulation. Mousa et al. [9] have used three different insulators which are polystyrene, Rock wool and air gap. Their results show that the insulation with the highest performance is polystyrene with a saving of 36% followed by Rockwool with an energy saving of 34%,
Vi Qi Ti As
volume of studied area (m3) net heat gain W/(m2K) temperature of the zone (K) inside area of surface S (m)
and the least efficient is air gap with a saving of 5,4%. Aktacir et al. [15] worked on the influence of different insulation thickness on the air conditioning load and on the energy consumption of the air conditioning system in a sample building located in Adana in the Mediterranean Region (hot and humid summer and warm winter). They found that the load of cooling decreased by 33%, and the capacity of equipment used in the air-conditioning system of insulated buildings is lower than that for non-insulated buildings. They have also found that the initial cost of the cooling for both variable volume and constant volume systems has decreased by 25% while the operating cost is 25% less for variable volume and 33% less for constant volume. In this study, the authors did not ignored the economic analysis for which results revealed that the thickness of the thermal insulation material of the buildings in coastal provinces of the Mediterranean countries should be determined according to the degree-day of air conditioning. Khoukhi et al. [16] evaluated the effect of the changes in the conductivity of the polystyrene insulating material as a function of the operating temperature, and found that the percentage of the increase of the values of k with respect to k24 for the wall and the roof can reach 9.4% and 20% respectively, which affects the calculation of cooling when the temperature exceeds 24°. Mangematin et al. [17] have developed a method to quickly measure the energy efficiency of buildings. They have shown that by measuring the transient states during the heating and cooling of an empty low-energy house, they have access to the thermal leakage coefficient K and the apparent heat capacity of the building, and these measurements can be obtained in one or two days. The aim of this work is to determine the best thermal insulation material and its optimal thickness to have the right compromise between thermal comfort of occupants and energy consumption in the case of Marrakech climate. For that, we had studied the effect of insulating the envelope of a typical house located in the city of Marrakech by using four types of thermal insulators: expanded polystyrene, glass wool, rock wool and wood fiber. The thermal and energetic behavior of the building is simulated by using the software of thermal dynamic simulation TRNSYS. 2. Building characteristics The house studied is consisting of 10 areas with four facades exposed outside. A fac¸ade is facing south and receives a continuous sunshine all day, and the others are oriented respectively East, North and West. The house is built on a surface of 117 m2 (Fig. 1), and located in the city of Marrakesh. It is on one floor, the ground floor, and deposited directly on the floor.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
Effect of the thermal insulators on the thermal and energetic performance Table 2 Room
Wall
Garage Living room Room1 Bath Room3 Room2 Hall WC Kitchen
Window
Orientation
Dimension (m)
East South South West West West North North West North North
8 2.8 3.53 3 1.3 4.77 1.7 1.66 1.2 0.4 4
3 Thermo-physical Properties of Insulation Materials.
Materials
Expanded Polystyrene
Rockwool
Glasswool
Wood fiber
1.45
0.92
0.84
1.950
0.159
0.15
0.15
0.138
0.4
Thermal capacity (kJ/kg K) Thermal conductivity (W/m K) Density (kg/m3)
20
300
12
180
1.2 1.2 Door (1.6) 0.4 1
Table 3 roof.
Dimension (m2) 0.6 0.8
The thermal behavior of the studied house is simulated through multi-zone transient modeling (type56a) with a time step of one hour. The TRNBUILD is used to enter all the information concerning the building envelope (materials, layer thickness, thermo-physical properties), windows, heating/cooling, infiltration . . .the thermo-physical properties of walls, roof, and insulators are given in the tables below (see Tables 1–3). For the simulations performed in this study, the thermophysical properties of these materials were taken from the TRNSYS library and Schiavoni et al. and Aditya et al. [11,12]. 2.1. Meteorological data The simulation of the building was carried out with actual meteorological data taken from the Agdal Marrakech station
The layers and thermo-physical properties of the
Materials
Plaster
Hourdis
Concrete
Mortar
Floor tile
Thickness (cm) Thermal capacity (kJ/kg K) Thermal conductivity (W/m K) Density (kg/m3)
1 1
16 0.65
4 0.653
10 1
1 0.7
0.351
1.23
1.75
1.15
1.75
1500
1300
2100
1700
2300
in 2014. These data are: the relative humidity at 3.2 m, global radiation, temperature at 3.2 m and the speed and wind direction at 3 m (TERMA 2014) [18]. Fig. 2 shows the temperature evolution of the city of Marrakech over a period of one year. 2.2. Calculation hypotheses The infiltration rate is equal to: 0.6 ACH (air change per hour), The temperature of the soil is taken from the meteorological file of the city of Marrakech, For all the cases of insulation studied, we consider that the roof is insulated with 4 cm polystyrene,
Fig. 1
Architectural plan of the house.
Table 1 Layers and thermo-physical properties of simple exterior walls. Materials
Cement mortar
Red brick terracotta
Thickness (cm) Thermal capacity (kJ/kg K) Thermal conductivity (W/m K) Density (kg/m3)
2.5 1 1.15 1700
10 0.878 1.15 1800
Fig. 2 Temperature evolution simulation of the city of Marrakesh over a year.
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F. Eddib, M.A. Lamrani
All the thermo-physical properties of the materials used are taken from the TRNSYS16 library, The four facades are exposed outside, The windows have a single glazing, The house is placed directly on the ground and the roof is exposed outside, The internal generation is zero (unoccupied house), Thermal bridges are not taken into account.
where As : is the inside area of surface S. For an internal wall both sides are considered internal surfaces and must be held twice in the calculations. The energy balance of the star node* shows that
2.3. Mathematical modelling
1
The temperature of a zone is calculated from the rate of variation of the internal energy of the studied floating zone, which is equal to the net heat gained: Where Ci is the thermal capacity of the area, [Ci ¼ Vi qCp , Vi : volume of the studied area]. And Qi is the net heat gain, which can be calculated by calculating the heat gain of the sur_ , the heat gain by _ , the heat gain by infiltration Qinf;i faces Qsurf;i _ , and the heat gain by convective ventilationQvent;i _ . couplingQcplg;i
The net heat gain Q_ i_is a function of the temperature Ti ; and the temperatures of the other adjacent zones of the zone i. To simplify the calculation, Qi_ is considered constant during each time step. In this case, the solution of the differential equation for a given time step is equal to: _ Qi;Dt Ci
ð2Þ
The temperature variation is linear, and the average is given by: Ti ¼
Ti;s þ Ti;sDt 2
By solving the Eq. (3) for Ti,t and replacing the result obtained in Eq. (2) by introducing the individual expression representing the net heat gain, we obtain:
þ
knownbound X
surfaces Xi to j
_ C p Ta _ Cp T þ minf;i mcplg;s
d micplg;s Cp Tb;s dt surfaces Xi to j
adj zones X surfaces i to j
X
j¼1
i¼1
þ þ
exterior Xsurfaces
þ
As Bs Ta þ
known Xbound
As Bs Tb;s
As ðCs Tstar;i Ds Ss;i
As B s þ
surf:in Xi
X
As Bs ÞTa þ
As Cc ÞTstar;i !
As Bs Tstar;j
known X bounderies
1 Ti RStar;i
As Bs Tb;s
!
surfaceX in zone i
ð7Þ
As ðDs þ Ss;i
The energy balances obtained with Eqs. (4) and (7) for all the zones give the results in a linear set of equations in mean zone and star-shaped temperature equations. Where the star temperature given by Seem [19] uses an artificial temperature node (Tstar) to consider the parallel energy flow from a convective wall surface to the air node and radiation to other wall and window elements. ½X
½T ¼ ½Z
½X ¼ " ½T ¼ ½Z ¼
X1;2 X2;2
X1;1 X2;1 T1 T2 Z1 Z2
ð8Þ
#
" ¼
T Tstar
#
Surfaces Xi to j
mcplg;s C _for i–jp
! _ m_v;i Ti _ þ minf;i mcplg;s
X11;ij ¼
Surfaces Xi to j
mcplg;s C _for i–jp
ð4Þ
As Bs Tstar;j
intX walls
inter:walls X
where
The total gain to the studied zone i from all surfaces is the sum of the combined heat transfers:
Ext X surfaces
¼
adj:zone X walls i to j
X11;ii ¼
known X bounderies 1 _ þ mcplg;i Rstar X þ m_v;k cp Tv;k þ Q_gc;i
Q_ surf;i ¼
RStar;i
ð3Þ
X 2Ci ðTi Ti;sDt Þ zones ¼ Dt j¼1
ð6Þ
Equalizing Eqs. (5) and (6) gives the balance sheet:
2.3.1. Calculation of temperature
Ti;s ¼ Ti;sDt þ
1 ðTstar;i Ti Þ Rstar;i
Q_ surf;i ¼
X12;ii ¼¼
Rstar;i
X12;ij ¼ 0 for i–j X21;ii ¼
As Bs Tstar
surfaceX in zone i
1
1 Rstar;i
X21;ij ¼ 0 X22;ii ¼
intX walls
As B s þ
surf X in zone i
As Cs
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
Effect of the thermal insulators on the thermal and energetic performance X22;ij ¼
adj:zones i to j X wallsX
Z1;i ¼ minf;i Cp Ta þ
Xsurfaces
i to j
ext:surf X
Z2;i ¼
As B s Xnvent _ _ Cp Tb;s þ _ CP Tv;k mcplg;s mv;k;i k
5
þ
! As Bs Ta þ
surf:in zone i X
known X boundaries
As Bs Tb;s
As ðDs þ Ss;i Þ
By calculating and solving the equations, the final temperature of zone i is equal to Ti;s ¼ 2Ti Ti;sDt
ð9Þ
2.3.2. Heating and cooling Fig. 3 shows the output power versus the temperature. For areas with floating temperatures, the solution for average zone temperatures and star temperatures is in the form of: 1
0
½T ¼ ½X0 ½Z
Fig. 3 [20].
Output power versus temperature (TRNSYS16 volume 6)
4cm of thickness
ð10Þ
The coefficients of the matrix X0 and of the vector Z0 depend on the temperatures of the zones relative to the set point temperature, and are determined as when calculating
6cm of thickness
(a)
(b)
8cm of thickness
10cm of thickness
(c)
(d)
Fig. 4
January temperatures with different insulation materials thickness.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
6
F. Eddib, M.A. Lamrani
the factor coefficients of the matrix for calculating the temperatures of the zones with: Ci
d T ¼ Q_ i Pi dt
ð11Þ
Pi and Qi are considered constant over time and Q_ i is evaluated at the average temperature of the zone (TRNSYS16 volume 6) [20]. 3. Results and discussions 3.1. Internal temperature The simulations are run over a period of 48 h for the coldest temperatures in January and the hottest temperatures in July, using the simulation software TRNSYS16. The house studied as shown in Fig. 1 consists of 10 zones but for clarity in the figures, we chose to represent only the variation of temperatures of the room1.
4cm of thickness
Fig. 4 shows the evolution of temperatures for the four different types of insulation of the house studied. In January and on a simulation of 48 h for 4 cm thick (Fig. 4-a), the temperatures recorded for the wood fiber are higher than those recorded for the other three insulators of 0.03 °C. For 6 cm of thickness of insulation (Fig. 4-b), all temperatures for the three insulators are around 15 °C and with wood fiber temperatures are 0.04 °C higher than the three insulators. For a thickness of 8 cm (Fig. 4-c), the temperatures with the wood fiber are 0.06 °C greater than those recorded with the polystyrene, glass wool and rock wool insulation. Finally, for a thickness of 10 cm of insulation (Fig. 4-d), temperatures with wood fiber are 0.13 °C higher than those recorded with other insulators. This is due to its low thermal conductivity compared to other insulators. The temperatures noted with the wood fiber insulation are higher compared to those noted for the other insulators, and this for the four thicknesses studied. For the month of July, simulations were carried out for four different thicknesses 4, 6, 8, 10 cm for a duration of 48 h. For this month, we note the hottest temperatures.
6cm of thickness
(a)
(b)
8cm of thickness
10cm of thickness
(c)
(d)
Fig. 5
July temperatures with different insulation thickness of insulators.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
Effect of the thermal insulators on the thermal and energetic performance For insulation thickness 4 cm (Fig. 5-a), the temperatures recorded for the wood fiber insulation are 0.14 °C lower than polystyrene, 0.13 °C lower than glass wool and 0.09 °C lower than rock wool. Compared to rockwool, for 6 cm thickness of insulation (Fig. 5-b) the temperatures of the wood fiber are 0.17 °C lower than those recorded for polystyrene, glass wool and rockwool. For 8 cm of thickness (Fig. 5-c) the temperatures are lower of 0.19 °C compared to the other insulators. Finally for a thickness of 10 cm (Fig. 5-d) with the wood fiber the temperatures are lower of 0.19 °C compared to the polystyrene and 0.2 °C compared to rock wool and glass wool. The temperatures noted with the wood fiber insulation are lower than temperatures noted for the other insulators, and this for the four thicknesses studied.
Table 4 Heating demand for the four insulators with different thicknesses. Thermal load of heating in KWH Thickness (cm)
4
6
8
10
Polystyrene Glass wool Rock wool Wood fiber
3063 3058 3053 3023
2929 2925 2925 2898
2850 2847 2847 2824
2798 2796 2796 2796
Table 5 Demand for air conditioning for the four insulators with different thicknesses.
3.2. Demand for heating and air conditioning: With the beginning of the energetic study of the insulators, we will show the effect of the orientation on the energy load of heating and air conditioning of two rooms the one directed south (Ch1) and the other which is oriented north (Ch3) in Fig. 1. Fig. 6 shows the demands for heating and cooling in the case of south facing room and the other facing north. It was found that with just the change of orientation from north to south we note that we save for heating 25.516% and 13.18% for air conditioning. Regarding the energetic study of insulation study, the annual demand for heating and cooling is shown in the tables below in KWH. The heating demand for four insulators with four different thicknesses 4, 6, 8, 10 cm. Tables 4 and 5 give us the heating and cooling loads respectively for the different insulators and the four different thicknesses considered in our study. It is noted that for an insulation thickness of 4 and 6 cm (Table 4), the wood fiber allows a reduction of the thermal load of heating of almost 3% compared to polystyrene and 2% compared to the glass wool and the rockwool. For the air conditioning load (Table 5), we can observe that the wood fiber allows a reduction of almost 2% compared to polystyrene and 1% compared to glass wool and rockwool. For a thickness of 8 and 10 cm, and from Table 4, we can deduce that the wood fiber allows
Demand for heating and air conditioning 250
200
150
100
50
0
Hea ng KWH
Air condi oning KWH
Ch1 Fig. 6
Ch3
Demand for heating and air conditioning.
7
Thermal load of cooling in KWH Thickness (cm)
4
6
8
10
Polystyrene Glass wool Rock wool Wood fiber
1134 1130 1127 1108
1033 1030 1030 1009
973,5 971,2 971,2 952,3
934,2 932,4 932,4 915,6
a reduction of almost 2% on the thermal load of heating compared to the three insulators studied (polystyrene, rockwool and glass wool). For air conditioning (Table 5) and for a thickness of 10 cm we get almost the same results obtained for the thermal load of heating. Hence, the wood fiber insulation gives the most satisfactory results in terms of internal temperature, heating and air conditioning, In addition, for the four insulators, not to use a large thickness of insulation, we opt to use 8 cm thick. By changing the thickness of wood fiber insulation from 4 cm to 8 cm, we saved 7% on the heating load and 14% on the cooling load. Finally and according to all the results cited above, we can justify our choice to adopt the 8 cm thick wood fiber insulation. 4. Conclusion In this paper, we presented the theoretical part of a thermal and an energetic study of a house located in the city of Marrakech. We were interested in this work to improve the thermal quality of the building envelop by using a thermal insulation. For that, we used four types of insulators, which are expanded polystyrene, rockwool, glass wool and wood fiber. The thickness of these insulators was taken equal to 4, 6, 8 and 10 cm. The numerical simulations were carried out with TRNSYS software using the multizone model type56. The thermal and the energetic behaviour of the building, for the different insulators studied, showed that the wood fiber is the most adequate for the climate of Marrakech. We noticed that for 8 cm of wood fiber we obtained the optimal results for both the hot and the cold periods. Otherwise a reduction in energy consumption of about 7% for heating and 14% for air conditioning is obtained by using 8 cm of wood fiber comparing to polystyrene, glass wool and rockwool. And For temperatures in January the temperatures are higher by 0.26 °C, and in July the temperatures are lower by 0.49 °C. Currently, we are working on the experimental part of this study (Prototypes Laboratory Tests) to validate the numerical results found.
Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008
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Please cite this article in press as: F. Eddib, M.A. Lamrani, Effect of the thermal insulators on the thermal and energetic performance of the envelope of a house located in Marrakesh, Alexandria Eng. J. (2019), https://doi.org/10.1016/j.aej.2019.08.008