Optimal orientation for housing with low energy profile in a semi arid climate.

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1 121 Optimal orientation for housing with low energy profile in a semi arid climate. S. Bellara, S. Abdou, Université Mentouri de Constantine, Algeria SUMMARY Heating and cooling buildings needs too much energy consumption; thing that is becoming rare and more expensive. Internal thermal comfort is essentially evaluated according to bioclimatic conditions and energy consumption. So the aim of the study is to reach optimum thermal comfort conditions with less energy consumption according orientation factor in semi arid climate. In order to point out the relationship between orientation and energy consumption a site investigation is undertaken in Constantine new urban extension called Ali Mendjeli new town. It concerns readings of air and surface temperatures and relative humidity that are compared to thermal comfort limits for such climatic conditions. Moreover, a simulation using TRNSYS (Version 14.1) is done to validate site findings and to search the optimal building orientation which improve internal thermal conditions with economy in energy. The results confirm that taking into consideration the orientation factor make the building participating in the optic of new conception: Energy conservation buildings. Key word: Orientation, Thermal comfort, Energy consumption, Energy conservation. sunning, protection against the bad weather, prevailing winds (B.GIVONI, 1978). Present research is interested in internal thermal quality of the contemporary building in Algeria according to the various orientations. It aims to appreciate the impact of the orientation on the internal air temperature and to seek the optimal orientation. 2. SITE INVESTIGATION Summer investigation is carried out in the town of Constantine; North-east of Algeria. (36.17 Nord and Est, On an Altitude of approximately 687m from the sea Level.It is characterized by a semi arid climate, hot and dry in summer with a maximum temperature of 36 C and a humidity of about 25% with strong solar radiation. Cold and wet in winter, with a minimum temperature of -1 C. Prevailing winds are relatively from north and North West direction (figure 1.) 1. INTRODUCTION Art to build considering the influence of the climatic factors is not an invention of the 20éme century. Bioclimatic architecture is distinguished from conventional architecture by the fact that the exploitation of solar energy is integrated in the design of the building; this design makes it possible to decrease considerably heating and cooling needs. The contemporary multistory buildings not only failed to answer housing needs, but it also showed insufficiencies on the quality level, which causes climatic problems of integration and implies a considerable power consumption. The crisis of energy brutally stressed the importance of the volume of fuel used for the heating and cooling needs, because of this consumption that influences the running cost of the buildings and the whole of the economy of the country (Bernard château &Bruno lapillone, 1977). For that, the against consideration of the climatic aspect depends on the respect of the factors of the site, which can be useful: orientation, Fig 1. Mean monthly air temperature and relative humidity for Constantine city. On the basis of Humphrey s methodology of comfort evaluation, the bioclimatic analysis for the town of Constantine, retained two comfort zones, lying respectively between 22,04 C and 18,04 C for winter and C and C for summer limits (Abdou.S, 2004). Located in the new urban extension of Constantine, the monitored dwellings are selected according to various orientation factors. Site urban fabric is sparse that exposes external surfaces to solar rays and increases surfaces heat absorption during daytime. (fig.2) and (fig.3) Many research noted that difference in external air tem- PALENC Vol 1.indd 121 3/9/2007 1:23:44 µµ

2 122 2nd PALENC Conference and 28th AIVC Conference on Building Low Energy Cooling and perature going until 5 C can exist between the temperature of a space with burst structure and a space with dense structure (Akbari H, 1987) comfort zone while the two others are under lower comfort limit and this inspite of use of gas heating system. Fig 2. Orientation of the three stations Fig. 4 : Comparison internal and external temperatures with the limits of comfort Fig 3. Plan of the flat model investigation. 3. RESULTS 3.1 Thermal performance evaluation of the three stays (investigation) From the graph in (fig.4) the North East orientation is distinguished from two other as it gives the best results although it remains very close to higher comfort limits during the day. The results selected of the investigation determined the origin of the heat flow towards the internal space, the variation in the internal air temperature is due to the variation to the incidental power of solar radiations on the vertical wall and its transmission through the window. When comparing internal temperature and comfort limits for the summer period (fig.4) we notice that the Northeastern orientation is the most comfortable. Moreover, that the Southwestern orientation remains most uncomfortable. It can be avoided for such climatic conditions. Winter evaluation (fig.4) shows that southeast orientation gives the best result as its curve remains within 3.2 Simulation Comparison of the three orientations The results of simulation (figure 5) and (figure 6) show the relation between the quantity of energy received and absorbed by the wall and internal air temperature according to the orientation. In summer, the South-east wall absorbs a quantity of less significant heat which is explained by the fact that the sun at this time is high in the sky of 35 with 76. In winter, the South-east wall receives the most significant quantities of energy compared to other orientations. The density of the flow of the direct solar radiation on the level of an envelope is a function of the orientation of various surfaces of the envelope (Alain Liébard and Andre De Herde, 2003) PALENC Vol 1.indd 122 3/9/2007 1:23:44 µµ

3 123 OLGYAY, 1967, of GIVONI, 1978 and of MARTIN EVANS, According to (fig.8), winter evaluations mention that south orientation absorbs the greatest amount of solar radiations; these gains are favorable for winter period. Southeast and southwest orientations are less important for such cold situations. Fig.5 : Comparison of the internal air temperature of the three orientations and quantity of energy absorbed by the external wall [summer period]. Fig. 8 : Effect of the orientation on the internal temperature [winter period ] Fig.6 : Comparison of the internal air temperature of the three orientations and the radiation received by external wall (winter period) Effect of the orientation on the internal air temperature Optimal orientation According to the theoretical study of the climatic and thermal analysis, the most favorable orientation for the town of Constantine is that where the buildings would be exposed along the Southern Northern axis (ENAG, 1993) However simulation program TRNSYS allows to find optimal orientation when swiveling North south axe according to 15 angle from North; taking into consideration winter solar gains and minimizing summer overheating. As mentioned by (IZARD. J.L,2003) the Southern orientation offers the weakest solar contributions in summer, after full North, (fig.9) confirms that as it points out that south orientation with 15 azimuth towards east and west gets the smallest quantities of solar energy. Fig. 7 : Effect of the orientation on the internal temperature [ period of summer ] The study of orientation effects on the interior temperatures using TRNSYS program shows the effects of solar radiation on external exposed walls and its consequence on internal environment during summer time. Several possibilities were tested; the results on (fig.7), show the impact of orientation changes on internal air temperatures: - South and north orientation give the best internal temperatures - For semi-cardinal Northeast Southwest orientation, the south- east direction seems to be the most comfortable and favorable one. - While east and west orientations are to be avoided as they register the highest values of its temperatures during 24 hour on summer time - The difference of internal air temperature between the best and the worst orientation is about 2.20 C These conclusions confirm once more results of Fig. 9: Total radiation absorbed by the wall according to the orientation [summer period] (Fig.10) shows solar radiations for fairly enlightened days (sky has average release) absorbed by the wall for various orientations, the Southern orientation, the orientation with 15 azimuth towards West and the orientation with 30 azimuth towards East receive the greatest amount of solar energy. PALENC Vol 1.indd 123 3/9/2007 1:23:45 µµ

4 124 2nd PALENC Conference and 28th AIVC Conference on Building Low Energy Cooling and Adapted housing to the local climate makes it possible to benefit from the solar contributions as well as possible, to reduce the requirements in heating and air-conditioning (Oliver Sidler, 2000), a compromise has to be made between the two situations. Fig. 10 : Total radiation absorbed by the wall according to the orientation [ period of winter ] Energy consumption 3.2.4a Requirements in energy for the heating according to the orientation Simulations are carried out with heating in order to test the need for the stay in energy. According to ( fig.11) it appears that the energy consumption is a function of the orientation and that during the winter period the consumption of gas (demand for significant energy) is especially higher for the north orientations which has to be avoided. Remain the southern orientation and the orientation with 30 azimuth towards east and 15 azimuth towards West present much reduced consumption compared to other orientations. For that, we can deduce that during the winter period the best orientation is that which does not consume enough energy and is concretized by the Southern orientation. This orientation (Southern) presents the 1/10 of consumption compared to the northern orientation and 1/8 of consumption compared to the orientation East and West b Requirement in energy for cooling according to the orientation Simulations are carried out with air-conditioning in order to test the need for the stay in energy for cooling. Figure 12 shows that during the summer period the consumption of electricity (demand for significant energy) is especially higher for East and West orientations, which are to be avoided. Then South, North, south east (30 ) and south west(15 ) orientations present a muchreduced consumption compared to other orientations. The consumption of air-conditioning is appreciable especially for the west orientation, which are higher than that of the east what explains the coincidence of solar radiations with the high temperatures. Western orientations are to be avoided during the summer period. For that we can deduce that during the summer period the best orientation is that which does not consume enough energy and is concretized by south orientation. Fig.12: The need for air-conditioning according to the orientation (en kj). 4. CONCLUSION The study points out the thermal impact of orientation on internal thermal conditions; as far as the reduction of internal air temperatures is concerned the site and simulation result confirms that south orientation with 15 azimuth west and 30 azimuth east provide the best results for summer period as well as winter one in such climate. Therefore, a good control of building orientation makes the building performs well; it gives housing with low energy profile and less energy consumption. REFERENCES Fig.11: The requirement in heating following the orientation (en kj). Abdou.S Investigation sur l intégration climatique de l habitat traditionnel en région aride et semi aride d Algérie -cas de Constantine et Ouargla Université de Constantine thèse de doctorat d état 2004 Akbari H, Kurn DM, Bretz SE and Hanford JW Peak power and cooling energy savings of shade trees. Energy and Buildings. 997;25; Alain Liébard and Andre De Herde, Guide de l architecture bioclimatique. Tome 3 construire en climats chauds. Edition Système solaires- Paris PALENC Vol 1.indd 124 3/9/2007 1:23:45 µµ

5 125 B.GIVONI L homme, l architecture et le climat- Edition : le Moniteur Paris 1978 Bernard château &Bruno lapillone La prévision à long terme de la demande d énergie- énergie et société. Centre national de la recherche scientifique -CNR Paris IZARD. J.L - Architecture D été - construire pour le confort d été. EDISUD, Aix-en-Provence, 1993 La maison Bioclimatique : [enligne] dossiers de biorespect sur l énergie, l environnement.htm (page consulted on 20 mars 2005) Oliver Sidler, - Logement a faible besoin en énergie- Guide de recommandations et d aide à la conception. Mars, Recommendations Architecturales- ENAG /Editons ALGER 1993 Yakubu.G.S & Sharples.S Bioclimatic design studies for passive and low enenergy building design in hot dray/semi arid climates- world renewable pergamon press 1992 PALENC Vol 1.indd 125 3/9/2007 1:23:45 µµ