ATINER's Conference Paper Series CIV

Transcription

1 ATINER CONFERENCE PAPER SERIES No: CIV-975 Athens Institute for Education and Research ATINER ATINER's Conference Paper Series CIV-975 Numerical and Economical Study of Thermal Insulation in Multi-layer Wall Exposed to Real Climatic Conditions Youcef Tamene Lecturer University of Batna Algeria Said Abboudi Professor University of Technology of Belfort-Montbeliard France Cherif Bougriou Professor University of Batna Algeria

2 ATINER CONFERENCE PAPER SERIES No: CIV-975 An Introduction to ATINER's Conference Paper Series ATINER started to publish this conference papers series in. It includes only the papers submitted for publication after they were presented at one of the conferences organized by our Institute every year. The papers published in the series have not been refereed and are published as they were submitted by the author. The series serves two purposes. First, we want to disseminate the information as fast as possible. Second, by doing so, the authors can receive comments useful to revise their papers before they are considered for publication in one of ATINER's books, following our standard procedures of a blind review. Dr. Gregory T. Papanikos President Athens Institute for Education and Research This paper should be cited as follows: Tamene, Y., Bougriou, C. and Abboudi, S., () "Numerical and Economical Study of Thermal Insulation in Multi-layer Wall Exposed to Real Climatic Conditions" Athens: ATINER'S Conference Paper Series, No: CIV-975. Athens Institute for Education and Research 8 Valaoritou Street, Kolonaki, 7 Athens, Greece Tel: Fax: info@atiner.gr URL: URL Conference Papers Series: Printed in Athens, Greece by the Athens Institute for Education and Research. All rights reserved. Reproduction is allowed for non-commercial purposes if the source is fully acknowledged. ISSN: -89 5//

3 ATINER CONFERENCE PAPER SERIES No: CIV-975 Numerical and Economical Study of Thermal Insulation in Multi-layer Wall Exposed to Real Climatic Conditions Youcef Tamene Lecturer University of Batna Algeria Said Abboudi Professor University of Technology of Belfort-Montbeliard France Cherif Bougriou Professor University of Batna Algeria Abstract In this work a numerical study of the thermal behavior of a multi-layer building wall (3 and 5 layers) is presented. The external side of the wall is subjected to the local atmospheric conditions of Algeria. The finite differences method is used to solve the transient heat transfer equations through the building wall, which is submitted to a solar heat flux, and a convective heat transfer with the environment. A sinusoidal forms of the external temperature and the solar flux were used to approach the measured data of Ouargla city (Algeria) (attitude 3 57' N, longitude: 5 'E, altitude 3-35 m), during summer and winter seasons. An economic study is presented and a solution for a good thermal insulation at a lower cost is proposed. Keywords: Heat transfer, solar flux, transient regime, economical study, multilayer wall. 3

4 Introduction ATINER CONFERENCE PAPER SERIES No: CIV-975 Global warming is not currently disputed by the scientific community, according to forecasts; Earth may suffer from a global warming of.8 C to C, if no serious measures are taken to reduce greenhouse gas emissions (Kaemmerlen 9). One area that consumes a lot of energy and contributes significantly to the proliferation of greenhouse gas emissions is the building sector. A decrease of the energy consummation in buildings, through improved insulation of walls will have consistent economical and environmental benefits. The building sector is not the only concerned by the thermal insulation optimization, it appears in all domains where energy consumption is important in volume and cost: example the cold rooms (Al-Radaedeh et al 3), transportation (road, rail, etc.), and in the conservation of foods and medical products. The insulation also has an environmental interest because the reduction of energy consumption remains a priority in the context of sustainable development. Unfortunately, in Algeria and in many other third world countries, little importance is given to the thermal insulation; the price is the most important. In the current paper, the research of the optimal configuration for a good thermal insulation at a lower cost is presented. For this, we have developed a numerical program in FORTRAN to study the heat transfer in a multi-layer building wall under extreme atmospheric conditions of Ouargla city in the south of Algeria, during the months of January and of July. Formulation of the Problem We will be interested to external walls of buildings, in order to find the best configuration for a good thermal insulation, for this we have studied the case of a wall composed of three layers Figure and another composed of five layers Figure. Figure. Wall Composed of Three Layers Internal side h,t ƒ External side φ (t) h,t ƒ (t) e e e 3 x

5 ATINER CONFERENCE PAPER SERIES No: CIV-975 Figure. Wall Composed of Five Layers Internal side External side φ (t) h,t ƒ h,t ƒ (t) e e e 3 e e 5 x For the solar flux and the external air temperatures, we have chosen to use the climatic data of the region of Ouargla, south of Algeria (attitude 3 57' N, longitude 5 ' E, altitude 3 to 35 m), during the month of July for its high temperatures and the month of January for its low temperatures. The measured solar heat fluxes (Capderou 98), is presented, for the two mentioned months (Table ). Table. Measured Solar Heat Fluxes January Flux φ (w/m²) July Flux φ (w/m²)

6 Flux (W/m²) ATINER CONFERENCE PAPER SERIES No: CIV-975 An interpolation of these data leads to the following relationships: For January month: For July month: () Were and Figures 3 and, show a good agreement between the proposed relationships and the measured heat flux. Figure 3. Solar Heat Flux for July () () (3) calculated flux measured flux

7 Temperature (C) Flux (W/m²) ATINER CONFERENCE PAPER SERIES No: CIV-975 Figure. Solar Hear Flux for January 5 3 calculated flux measured flux The values of the average maximum temperature and average minimum temperature are used to find the relationship below. Were A 7,5 and B,95 for January And A 8, and B 3,8 for July Representing this relation, we have obtained the figures 5 and. This corresponds to the measured values, obtained from the international website of meteorology, (Table ). Figure 5. Evolution of the Temperature for July (5)

8 Temperature (C) ATINER CONFERENCE PAPER SERIES No: CIV-975 Figure. Evolution of the Temperature for January Table. Measured Temperatures January July January July Day T M 9,, 7,5 9, 7,8 8, 8 7,,5,,5 9,5 T m,5, 5,,, T M 5,8 3, 7 8,3 8, 8,3 8,3 8, T m 9 8, 3 8, 3,8 3, 3 3,5 33 3, 3 9, 9,9 3, Day T M, 3,5 5,5, 3,,7, 9,3,8 5,3 T m 9 7,5 7, 7,5,7,3,3 7,,5 T M, 38,9, 3,8 37,5 37,7, 5,5 5,8 T m 9,5 8,7 5,8,,,5 5, 9 5 8,5 9, 5,5, 9, 3 3 7,8, ,5 3, T M : Maximal temperature ( C) T m : Minimal temperature ( C) Monthly means 8 3,9,9 8,7 8

9 ATINER CONFERENCE PAPER SERIES No: CIV-975 Numerical Resolution Assumptions Heat transfer in the wall is one dimensional and unsteady. - Physical properties are constants. - No heat sources in the wall. So, the heat transfer in the multilayer wall is governed by the following equations: T T i i i, l i x li, t, i,..., 5 x t () Where: i i, C, li li ei, L l5 i i And this initial and boundary conditions Boundary conditions T h ( Tf T) x x (7) Ti Ti i i, T i T i x l, i, i x x (8) T3 3 h ( T3 Tf ) ( t) x x l 5 (9) where.3 Initial conditions: T i T for t and x l5 () The resolution of the system of equations () with boundary conditions (7), (8), (9) and initial conditions () is performed by finite differences method according to the Cranck-Nicolson scheme (Gerald 978). At each time, the Tri Diagonal Matrix Algorithm (TDMA) (Boumahrat and Gourdi.993) is used to solve the obtained algebraic system. The simulated results are performed for commonly materials used in building constructions. Their physical properties (the specific heat C p, the mass density and the thermal conductivity ) are presented in Table 3, (Tamene et al ), (Bekkouche et al 3). Table 3. Physical Characteristics Brick Mortar Plaster Air Polystyrene (kg/m³) C p (j/kg.k) (w/km)

10 Temperature (C) ATINER CONFERENCE PAPER SERIES No: CIV-975 The initial and boundary conditions used are: h 5 W m C, h W m C, T 5 C, T =T m / / f Results and Discussion To verify the program we have compared the results obtained by calculating the temperatures at the interfaces in the steady state with those calculated by the program in the case of a wall composed with five layers (configuration ). The solar flux is made zero, the indoor and outdoor air temperature are taken constants. Numerically, the number of steps used in each layer is as follows: At steady state, and based on the relationship of the flux we have: Tƒ Tƒ = with T ƒ=5 C and T ƒ =5 C R R R R R 3 R T T R were i i i R 5 R R 7 h e e e3 e 3 e5 h The interface temperatures obtained at steady state are the same as predicted analytically, figure 7. Figure 7. Evolution of the Temperature through the Multilayer Wall Temperatures calculated by the program after 9 h Temperatures calculated theoretically at interfaces Nodes Several configurations of multi-layer materials (Table ) were analyzed to find the best material providing better thermal insulation with a lower cost.

11 Temperature (C) ATINER CONFERENCE PAPER SERIES No: CIV-975 Table. Different Configurations Thickness Configuration Configuration Configuration3 Configuration cm plaster cm plaster cm plaster cm plaster cm brick cm brick 3 cm brick 5 cm brick cm air cm polys cm mortar cm mortar 5 cm brick 5 cm brick cm mortar cm mortar For all cases, the internal temperatures calculated for July month are presented in figures 8 and 9. For each configuration, the domain variation of the temperature is: Configuration :.75 C < T< 7.5 C Configuration : 7.5 C < T< 8.5 C Configuration 3: 3.75 C < T< 33 C Configuration : 7.5 C < T< 35 C Figure 8.The Temperature of the Internal Side ( st and nd Configuration) 8,5 8, 7,75 7,5 7,5 7,,75,5,5 first configuration second configuration

12 Temperature (C) Temperature (C) ATINER CONFERENCE PAPER SERIES No: CIV-975 Figure 9.The Temperature of the Internal Side (3 rd and th Configuration) third configuration fourth configuration Since, in summer the internal temperature must be as low as possible relative to the external, so we note that for a good thermal insulation, in summer the first configuration is better than the second, the third and the fourth. Similarly, the results of January are presented in figures and However, we see that the temperature change is as follows: Configuration : 3.75 C < T<.5 C Configuration : 3.5 C < T< C Configuration 3:.5 C < T<.75 C Configuration : 9 C < T<.75 C Figure.The Temperature of the Internal Side ( st and nd Configuration) 8 8 first configuration second configuration

13 Temperature (C) ATINER CONFERENCE PAPER SERIES No: CIV-975 Figure.The Temperature of the Internal (3 rd and th Configuration) 8 third configuration fourth configuration In winter the internal temperature must be as high as possible relative to the external, so we note that for a good thermal insulation, in winter the first configuration is better than the second, the third and the fourth. Economical Study From the thermal analysis presented above, we propose an economic analysis in terms of cost of the four configurations. The materials used are brick and polystyrene their prices are shown in Table 5, for the internal and external layers it is the same for the four configurations. Table 5. Material Prices ( DA = Euro). Materials Dimensions (cm) Price (DA) Brick 3xx5.5 Brick 8 3xx Polystyrene xx 3 The number of brick required, for a surface wall ( m x 3 m), is: Then the cost is: And the cost of a double wall of brick is: For a wall thickness of cm, the number of bricks required is: Then the cost is: 3

14 ATINER CONFERENCE PAPER SERIES No: CIV-975 The number of the polystyrene plate required is: And the price of polystyrene is: So, the cost of double wall of 5 cm and cm of brick spaced a cm layer of polystyrene is: And the cost of double wall of 5 cm and cm of brick spaced a cm layer of air is: A summary of the prices of the four configurations in euro is shown in Table. Table. Configurations Prices Configuration First second third fourth Price (Euro) Price per m² (Euro) From a viewpoint of heat insulation and price, the first configuration is better than the second and third. Note that the fourth configuration is the cheaper but it ensures the poor thermal insulation. Conclusion A numerical study of the thermal behavior of multi-layer wall for four configuration used in buildings is presented. The real climatic conditions (the measured solar flux and the temperature of external air) of Ouargla town are used to find the better thermal insulation in winter and summer, with the lower cost. An economic study has been presented and shown that it is possible to have a good thermal insulation with a lower price. Therefore and to have a good thermal insulation with a cheaper cost we recommend to use the first configuration, the economy is made also in long-term on energy consumption and the environment protection. References A. Kaemmerlen.9. Transfert de chaleur à travers les isolants thermiques du bâtiment. Thèse de doctorat, Université Henri-Poincaré, Nancy C. F. Gerald. Applied Numerical Analysis Addison Wesley publishing Company. J. Al-Radaedeh, B. Al-Zgoul, M. Frehat. 3. Selection of Thermal Insulation Thickness of Cold Store Enclosures.Innovative Systems Design and Engineering. (). M. Boumahrat, A. Gourdin Méthodes Numériques Appliqués. Office des Publications Universitaires, Algérie. M. Capderou.98. Atlas solaire de l Algérie, Tome. Office des Publications Universitaires, Algérie. S.M.E. Bekkouche, T. Benouaz, A. Cheknane. 3. A Modelling approach of thermal insulation applied to a Saharan building.thermal Science

15 ATINER CONFERENCE PAPER SERIES No: CIV-975 Y. Tamene, S. Abboudi, C. Bougriou.. Study of heat and moisture diffusion through a wall exposed to solar heat flux.journal of Engineering Science and Technology. Vol., No