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Evaluation of energy efficient design strategies for different climatic zones: Comparison of thermal performance of buildings in temperate-humid and hot-dry climate
Energy and Buildings 39 (2007) 306–316 www.elsevier.com/locate/enbuild
Evaluation of energy efficient design strategies for different climatic zones: Comparison of thermal performance of buildings in temperate-humid and hot-dry climate Z. Yılmaz * Faculty of Architecture, Istanbul Technical University, Taskisla, Taksim, Turkey Received 30 May 2006; received in revised form 27 July 2006; accepted 1 August 2006
Abstract Since the Kyoto protocol signed in December 1997 the majority of governments around the world have committed themselves to reducing the emission of the greenhouse gases. Thus, efficient use of energy and sustainability has become a key issue for the most energy policies. Sustainability and energy saving terms take place in building construction industry too since buildings are one of the most significant energy consumers. It is known that heating energy demand of a building has a great rate in building total energy consumption. In addition to that, the most of the heating energy has been lost from building envelope. TS 825, Heating Energy Conservation Standard for Buildings in Turkey, aims the reducing of heat loss in buildings through the envelope. But within buildings, one of the fastest growing sources of new energy demand is cooling and especially in hot-humid and hot-dry climatic parts of Turkey cooling season is much longer than the heating season. Moreover in hot-dry climate heat storage capacity of the envelope becomes more important issue than heat insulation for energy efficiency of the building. Since the Turkish standard is considering only heating energy conservation by using degree-day concept, Istanbul and Mardin are considered in the same zone, however those are in temperate-humid and hot-dry climatic zones, respectively. In this study energy efficient design strategies for these climatic zones have been explained and thermal performance of two buildings, which are constructed according to the TS 825 in Mardin and Istanbul cities were evaluated to show the importance of thermal mass in hot-dry climates. # 2006 Elsevier B.V. All rights reserved.
1. Introduction Energy issue is becoming more and more important in today’s world because of a possible energy shortage in the future and also global warming. Since the Kyoto protocol signed in December 1997, the majority of governments around the world have committed themselves to reducing the emission of the greenhouse gases. Efficient use of energy has become a key issue for the most energy policies. Buildings are one of the most significant energy consumers. Across the IEA countries, buildings consume over half of all electricity and one-third of natural gas, and are responsible for more than one-third of all greenhouse gas emissions [1]. Therefore, sustainable design and construction strategies are of great importance nowadays. Anyhow, one may say that sustainability was already a driving force in the past, showing its validity in those days in different
* Tel.: +90 212 293 1300; fax: +90 212 251 4895. E-mail address: [email protected]. 0378-7788/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2006.08.004
forms and techniques. Therefore, from Vitrivius till today, problems and precautions in design and construction did not change fundamentally, although a lot of development was seen in materials and technology [2]. Of course, these developments may have had some negative effects. Since the Turkish standard is considering only heating energy conservation by using degree-day concept, Istanbul and Mardin are considered in the same zone, however those are in temperatehumid and hot-dry climatic zones, respectively. Energy efficient design strategies for these zones are significantly different from each other as it can be easily seen in the traditional design. In this study thermal performance of two buildings, which are constructed according to the TS 825 in Mardin and Istanbul cities were evaluated to show the difference in climatic effects of two regions on building energy performance and importance of thermal mass of building envelope in hot-dry climate. The results are supported by a student workshop, which is carried out for of a traditional house and a contemporary house in Mardin area, to compare their thermal behavior via both measurements and questionnaires.
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2. Energy efficient design strategies in temperatehumid and hot-dry climates The most important design parameters affecting indoor thermal comfort and energy conservation in building scale are site and orientation of the building, distance between buildings, building form, optical and thermo-physical properties of the building envelope. Among these parameters building envelope, as it separates the outdoor and indoor environment, is the most important parameter. The climate of the Eastern Anatolian Plateau is relatively similar to desert climate. This region represents the hot-dry climate zones with a great temperature difference between day and night. Mardin displays the typical aspects of deserts where summers are quite hot. The city is located in southeastern Anatolia about 50 km from the Syrian boarder, lying between eastern longitudes 39–428 and northern latitudes 36–388. Istanbul is the representative city for temperatehumid climate of Turkey, locating on two continents, Europe and Asia with 418 north longitude and 298 east latitude. The both of the cities Istanbul and Mardin are considered in the same zone in TS 825-Turkish standards for building thermal insulation. When evaluating traditional architectural examples, it can be seen that designers were more sensitive and they presented the most suitable design and settlement examples for each climatic region. In hot and dry climatic zone in Turkey where the continental climate is effective, in traditional architecture examples, to benefit the time lag of the building envelope, materials with greater thermal mass have been chosen. These kinds of thermally massed envelope details are very convenient for continental climates, where the summers are very severe with high swings in daily temperature variations. This big thermal mass will slow down the heat transfer through the envelope and thus higher day-time temperatures will be reached
Fig. 1. The plan of the building.
indoors when outdoor air temperature is much lower and consequently more stable indoor thermal conditions will be provided. On the other hand this thermal mass, which has higher surface temperature on outer side will rapidly lose heating energy to the atmosphere via thermal radiation at night to start the next day from a cooler level [3]. When observing traditional examples, it can be seen that the transparency ratio of the building envelope is chosen as low as possible and the opaque parts of building envelope were constructed by the materials with a high heat capacity as thick as possible. The high heat capacity of the opaque component provides a high time lag for the transmission of the outside temperature to the internal area while the low transparency ratio minimizes the direct solar radiation gained through the windows.
Table 1 Details for external wall alternatives for the considered building Materials
d (m)
U (W/m2 K)
Concrete wall insulated inside
Plaster Concrete Insulation Plaster
0.02 0.12 0.06 0.02
0.55
Gas concrete wall insulated inside
Plaster Gas concrete Insulation Plaster
0.02 0.02 0.06 0.02
0.55
Masonary wall
Stone
1.20
1.42
Wall alternatives
308
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Table 2 Details for ceiling and floor the considered building Materials
d (m)
Internal wall
Plaster Concrete Plaster
0.02 0.08 0.02
Floor-ceiling
Glass mosaic Mortar Concrete Plaster
0.02 0.02 0.16 0.02
In temperate-humid climate it is not necessary to have a big thermal mass on the envelope, but thermal insulation is necessary since winter period is longer in this zone. For traditional architecture in this climate, bigger windows on the south fac¸ade are observed to get more direct solar radiation in winter. The north facades of the buildings are usually protected cooler winter wind by trees or other buildings. The distance between buildings should be arranged such that they should not obstruct their south direct solar radiation. In this study the same building has been thermally evaluated in case of it has been constructed in temperate-humid and hotdry zones to show the missing strategy of Turkish Standard taking those two climatic regions in one zone basing on the degree-day concept.
Fig. 2. Temperature variations for Istanbul in January.
Fig. 3. Temperature variations for Mardin in January.
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Fig. 4. Temperature variations for Istanbul in July.
3. Evaluation of thermal performance of the same building in Istanbul and Mardin The living room of a typical residential building has been considered for thermal evaluation in case of the building is constructed in Istanbul and Mardin with same envelope oriented to south as it is instructed in the Standard [4]. The living room is located in the intermediate floor of the building, so it is assumed that there is no heat flow through the ceiling and floor. The height and the floor area of the room are 2.80 m and 32 m2, respectively. The plan of the building is shown in Fig. 1. The external surface solar absorption coefficient is assumed as 0.7 and transparency ratio of the fac¸ade is 34%. Windows are double glass wooden frame. It has been assumed that heat
transfer coefficient of the external wall is 0.55 W/m2 K which is providing Standard’s requirement for Istanbul and Mardin. Different external wall details, which are providing this required U-value, have been examined to see the effect of the other thermo-physical properties of the envelope. One of the wall alternatives for Mardin is masonry wall with a high thermal mass of 1.2 m thickness, which is traditional wall type for this area. The U-value of the masonry wall is 1.42 W/m2 K, which is much higher than the Standard’s value. The ceiling and floor details are same for all alternatives. The details for external wall alternatives, ceiling and floor are given in Tables 1 and 2 [2]. Inner surface temperature of the external wall and indoor air temperature have been calculated by using finite difference
Fig. 5. Temperature variations for Mardin in July.
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Fig. 6. Heat flow through the south wall for Istanbul in January.
method [5,6] to see the thermal behavior of different wall details having same U-value and stone wall having higher Uvalue, but higher thermal mass at the same time. Thermal performance of wall types 1 and 2 in Istanbul and Mardin for January is shown in Figs. 2 and 3. As it can be seen in these figures, thermal performance of two wall details are significantly different from each other in the same city however the both of them are having same U-value. Moreover the same wall is showing very different thermal behavior in Istanbul and Mardin. In Figs. 4 and 5 July performance of wall types 1 and 2 is shown for Istanbul and Mardin. In addition to two wall types with 0.55 W/m2 K Uvalue, temperature variations for masonry wall with 1.42 W/ m2 K U-value is also shown in Fig. 5.
Significance of the temperature difference for the same wall in these cities can be easily observed in these figures. The inner surface and indoor air temperature are almost 10 8C lower for the masonry wall in July, however its U-value is almost three times higher than the other walls constructed according to the Standard. That means that thermal mass is more important than the U-value in hot-dry climate and energy conservation standards should certainly consider this property of the envelope in this climatic zone where cooling energy conservation is more important than the heating energy conservation. In Figs. 6–9 the heat flow through the total area of south wall of the room is seen for Istanbul and Mardin to keep the indoor air temperature at 19 and 24 8C, respectively, in the average day
Fig. 7. Heat flow through the south wall for Mardin in January.
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Fig. 8. Heat flow through the south wall for Istanbul in July.
of January and July. As parallel to the temperature variations, the amount of heat flow changes also significantly for the same wall in Istanbul and Mardin and walls 1 and 2 are providing different amounts of heat flow in the same city. The amount of heat loss for walls 1 and 2 is significantly different for the both cities as it can be seen in Figs. 6 and 7, however both of the walls have the same U-value. Moreover, in the comparison of Figs. 6 and 7 it is seen that there is heat loss through the both of walls 1 and 2 in Istanbul, but for the certain hours wall 1 is providing heat gain in Mardin in January. These results show that heating energy consumptions will be significantly different for the different walls in the same city and for the same wall in the different cities representing temperate-humid and hot-dry climates, however degree-days are similar for these cities. The similar results are observed for summer period as it is illustrated in Figs. 8 and 9. For the summer heat flow calculations, the traditional masonry wall is also examined for Mardin in July. As it can be seen in Fig. 9, masonry wall with higher U-value is providing the least heat gain in Mardin for the average day of July. Therefore, for Mardin, where the summer
conditions are severe and hot period is long, the masonry wall with big thermal mass is recommended in this climate. Wall 1 is having better thermal performance in the both cities in January, but in July wall 2 is better than wall 1 as it is observed in Figs. 6–9. The heating and cooling loads of the whole flat with wall types 1 and 2 in Istanbul and Mardin are given in Fig. 10. The heating and cooling loads for masonry wall in Mardin are also included in the figure. The heating and cooling loads have been calculated for the flat, which plan is given in Fig. 1, for the heating and cooling periods of Istanbul and Mardin. The heating and cooling periods for these cities are determined basing on the meterolgical data of 10 years [7,8]. Temperature data for 10 years between 1993 and 2003 for these cities is given in Fig. 11. As it can be easily seen in Fig. 10, the walls 1 and 2 are providing different heating and cooling loads in the same building in Istanbul and Mardin however their U-values are same. The masonry wall is proving the least cooling load in Mardin repesenting the hot and dry climate, in spite of its much bigger U-value. Considering the heating and cooling loads together, wall 1 is better for Istanbul for
Fig. 9. Heat flow through the south wall for Mardin in July.
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Fig. 10. Heating and cooling loads of the flat for the selected wall types.
the considered case and masonry wall is the best for Mardin area for energy conservation. In order to support these results a case study has been carried out in Mardin to take measurements in a traditional and a modern house at the end of may in 2004 which is in the cooling period for this hot-dry area. The traditional house has been constructed in the middle of the 17th century with masonry walls in the old settlement in Mardin where all energy eficiency strategies of hot-dry climate have been apllied. The modern house is located in the new part of the city and this building has been constructed according to the above mentioned Turkish Standard, TS 825 [9]. The details of the case study buildings are given below. 4. Case study for thermal evaluation of a traditional and a modern residential building in Mardin This case study is a part of a research project in which, design strategies in modern and traditional houses in hot and dry climate were examined at the end of May 2004. Since the design concepts of traditional and modern house are completely different, comfort conditions in these houses are also different. The objective is to demonstrate this difference by means of measurements and questionnaires. In this paper the study was simplified by using only measurements data
Fig. 12. View from exterior of Mungan House.
derived from the sample rooms chosen from modern and traditional houses. The traditional building, Mungan House, chosen for the measurements, is built in the middle of the 17th century. This building is a two story (with a ground floor) detached and terraced one-family house. The courtyard at the ground floor is surrounded by high walls and isolated from the street [10]. Mungan House is oriented to south-east (Figs. 12 and 13). Eyvan and revak; semi-open spaces, are used to create shady and cool places in open areas. The building envelope is masonry wall. Being located in a volcanic area, the basic material used in the local architecture is easily workable calcareous rock. Thermal properties of these materials are given in Table 3. The thickness of the walls is 0.8 m. Double-wooden frame windows have been divided into two parts. The upper parts of the windows provide lights in the room whereas the lower parts were closed with wooden shutters. Single glazed wooden window frame realize a U-value of 4.5 W/m2 K for windows. The modern building, Demir House, is situated in the new part of the city. It was built after 1990. This building is a two
Fig. 11. Temperature data for Istanbul (Go¨ztepe station) and Mardin between 1993 and 2003.
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Fig. 13. Plan of Mungan House.
story (with a ground floor) detached building. First and second floors are used as separate residential (Figs. 14 and 15). The building envelope is reinforced concrete structure with brick walls. No shading device was used on the facades. The thickness of the walls is 0.25 m. Thermal properties of the wall
materials are given in Table 3. Double glazed PVC window frame with a U-value of 2.6 W/m2 K is used in this building. The building was constructed by contemporary techniques in compliance with the instructions of Energy Conservation Standard of Turkey (TSE 825-1998). This regulation gives the
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Table 3 Thermal properties of the wall materials for traditional and modern houses Walls
Main wall material
Thickness (m)
l (W/m K)
Cp (kJ/kg 8C)
r (kg/m3)
Stone wall Brick wall
Mardin stone Brick
1.2 0.19
2.33 0.46
0.88 0.92
2200 1000
limit values of overall heat transfer coefficient of building envelope (U-value) independently from orientation and building form and consequently specifies the upper limit values of annual heat loss through the buildings. Although this new regulation is an important step to achieve energy conservation, its methodology is inadequate and incomplete for hot and dry climatic region from the thermal comfort point of view. Another weakness of the regulation is to assume and evaluate different cities, which have different climatic conditions, in the same climatic region as it is mentioned above. In order to evaluate indoor comfort level and the thermal performance of the building envelope, four rooms (two from the modern house and two from the traditional house) were chosen. All of the main facades of buildings in the old town are oriented to south, south-east or south-west. Therefore similarly oriented rooms are selected to enable the comparison of construction type of modern and traditional buildings for this study. During the field study the measurements have been taken in more rooms in these buildings and in another traditional building for thermal, visual and indoor air quality purposes. The results of all temperature measurements are similar and therefore, in this study the results are given only for the certain similarly oriented rooms as sample. These rooms with flat roof are all situated in the upper floor of the both houses. For the first part of the measurements room number 1 in modern and traditional houses were chosen [11,12]. These rooms have also additional windows on north-west side in modern house and in southeast and north-east sides in traditional house. To understand the spatial variation of the comfort conditions in the rooms of modern and traditional houses, nine different points were chosen and the indoor air temperature at those points were measured every hour simultaneously. The height of
the measurement points is 1.20 m. Measurements’ points and the distance from surrounding walls were shown in Fig. 16. Some values measured in the afternoon were shown as examples in Table 4. Even the transparency ratio of the northern fac¸ade is much bigger, temperatures measured in the room remained over the comfort level whereas the range of the measured inside temperature in the room of traditional house were much smaller. From Table 4, the difference of temperature level between the modern and traditional houses and the importance of the overheating problem due to the construction strategies in hot and dry climate can be seen easily. For the second part of the measurements, room number 3 in modern and traditional houses were chosen. In order to evaluate the heat capacity and the time lag of the wall, surface temperatures, the air temperatures and the humidity were measured in the rooms simultaneously for 24 h. Measurement results were given in Figs. 17 and 18. As it can be seen in these figures, air and wall surface temperatures are much lower in the traditional building and they are almost always constant because of the big thermal mass of masonry wall. As parallel to the measurements, questionnaires have been carried out for 68 traditional and 32 modern buildings to determine the users’ perception for indoor environment. The questionnaire includes 34 questions about users’ thermal, visual and air quality perceptions. The questionnaire asks users how they feel in their room, living room, eyvan, and courtyard and identify their feelings by selecting a point between ‘‘cold’’, ‘‘cool’’, ‘‘normal’’, ‘‘warm’’ and ‘‘hot’’ alternatives. Users were asked to express their feelings both for winter and summer. In this study, only for summer, results for indoor air
Fig. 14. View from exterior of Demir House.
Fig. 15. Plan of Demir House.
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Fig. 16. Measurement points in Mungan (traditional) and Demir (modern) Houses. Table 4 Temperature measured at nine points at different hours Measurement points
Hours 15:00
A B C D E F G H I
16:00
17:00
Modern
Traditional
Modern
Traditional
Modern
Traditional
28.7 28.6 28.2 28.9 28.8 28.8 28.7 28.7 28.8
24.8 24.8 24.8 25.0 24.9 24.7 25.1 25.1 24.8
30.1 29.5 29.3 30.2 30.2 30.2 30.0 30.1 30.2
24.4 24.4 24.4 24.6 24.6 24.6 24.5 24.6 24.6
30.0 29.1 28.9 30.6 30.9 30.1 30.3 30.3 30.2
24.2 24.2 24.2 24.2 24.2 24.2 24.1 24.2 24.2
thermal perception of users for their rooms are given to make a thermal comparison between traditional and modern buildings in hot and dry climate (Fig. 19). The results of this questionnaire support the results of the measurements. As it can be seen in Figs. 17–19, under hot summer conditions, traditional house can provide cooler indoor
environment than the modern one. That means that masonry wall with big thermal mass will provide less cooling load for the traditional building in comparison to the modern building which has been built according to TS 825 in this hot-dry climate.
Fig. 17. Temperature results in Mungan House.
Fig. 18. Temperature results in Demir House.
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Fig. 19. User’s perception of indoor temperature in summer.
5. Conclusion As it can be concluded from the results of the theoretical and field studies, the heat transfer coefficient of the building envelope and the heat transfer amount calculated in steady state conditions are not sufficient to determine the real thermal performance of buildings. These, observed especially on the traditional construction technology, have a very important role in hot and dry climatic zone where the continental climatic effects are dominant. The Energy Conservation Standard of Turkey (TS 825) has made a significant mistake by neglecting the heat storage capacity of the building envelope especially for hot-dry climate. Since the heat capacity of the building envelope has an important role on the energy conscious design, it should certainly be taken into consideration in the south-east Anatolia region, in which the hot and dry climatic conditions prevail. As the current standard is based on degree-day concept to determine the climatic zones of Turkey, it delivers another important mistake by proposing the same design strategies for both Istanbul and Mardin. Therefore, theoretical and field studies are carried out for traditional and modern houses in these cities. Theoretical study has been carried out for a residential building constructed with different wall details providing required U-value of the standard in Istanbul and Mardin and with also traditional masonry wall in Mardin. The most important conclusion of this study is: the masonry wall is providing the least energy consumption for heating and cooling of residential buildings in Mardin, however its U-value is almost three times higher than the other walls. On the other hand, dynamic thermal evaluation shows that energy consumption of the building with different wall details are different in the same city in spite of their equal U-values. Moreover it has
been concluded that the same wall detail is providing different heating and cooling loads for residential buildings in Istanbul and Mardin. Therefore, we can say that the modern buildings in south-eastern Anatolia, which are constructed according to this standard, cannot correctly respond to the climate of the region and these two cities should not be considered in the same zone as the standard did by using degree-day concept. The results of the theoretical study are also confirmed by the results of the field study including the both of measurements and the users’ perception in questionnaires, which have been done in both traditional and modern houses in Mardin. The measurements have been carried out for different rooms in the selected residential buildings, but in this study only one sample is given. As a conclusion it is possible to say that, especially on the regions, where the continental climate is experienced thermal performance of buildings should be evaluated by a dynamic model of heat transfer calculations during the design stage, taking into account also the heat capacity of the building envelope as the function of its thermal mass to provide heating and cooling energy conservation in buildings in these regions. References [1] International Energy Agency, Online Source, http://www.iea.org. [2] Vitivius, The Ten Books on Architecture, Dover Publication, New York, 1960. [3] Z. Yılmaz, The effect of thermal mass on energy efficient design, in: Proceedings of the Sixth International Symposium on HVAC+R Technology, May, 2004. [4] I. Osanmaz, The Evaluation of Heating Energy Conservation Standard for Buildings for Hot-dry Climatic Zone of Turkey, Master Thesis, Istanbul Technical University, 2005 (advisor: Z. Yilmaz). [5] J.P. Holman, Heat Transfer, 4th ed., Mc-Graw Hill Book Co., New York, 1976. [6] Z. Yilmaz, Evaluation of built environment from thermal comfort point of view, ASHRAE Transactions, Part I 93 (1987). [7] Turkish State Meteorology Headquarter Publications, Ankara, 2004. [8] Turkish HVAC Engineers Handbook, Istanbul, 2004. [9] Turkish Standards-TS 825: Rules of Heat Insulation in Building, 1998. [10] F. Alioglu, Mardin urban texture and houses, History Foundation of Turkey (1988). [11] Conference and Exhibition of Workshop on Energy Efficient Design in South East Turkey (Mardin Case), ITU Faculty of Architecture, Istanbul, October 2004. [12] Z. Yılmaz, Studies on energy efficient design in ITU Sustainable Energy Research Group, in: Proceedings of the Energy Conservation and Insulation Congress and Exhibition for Sustainable Environment, Istanbul, October, 2004.
Evaluation of energy efficient design strategies for different climatic zones: Comparison of thermal performance of buildings in temperate-humid and hot-dry climate Z. Yılmaz * Faculty of Architecture, Istanbul Technical University, Taskisla, Taksim, Turkey Received 30 May 2006; received in revised form 27 July 2006; accepted 1 August 2006
Abstract Since the Kyoto protocol signed in December 1997 the majority of governments around the world have committed themselves to reducing the emission of the greenhouse gases. Thus, efficient use of energy and sustainability has become a key issue for the most energy policies. Sustainability and energy saving terms take place in building construction industry too since buildings are one of the most significant energy consumers. It is known that heating energy demand of a building has a great rate in building total energy consumption. In addition to that, the most of the heating energy has been lost from building envelope. TS 825, Heating Energy Conservation Standard for Buildings in Turkey, aims the reducing of heat loss in buildings through the envelope. But within buildings, one of the fastest growing sources of new energy demand is cooling and especially in hot-humid and hot-dry climatic parts of Turkey cooling season is much longer than the heating season. Moreover in hot-dry climate heat storage capacity of the envelope becomes more important issue than heat insulation for energy efficiency of the building. Since the Turkish standard is considering only heating energy conservation by using degree-day concept, Istanbul and Mardin are considered in the same zone, however those are in temperate-humid and hot-dry climatic zones, respectively. In this study energy efficient design strategies for these climatic zones have been explained and thermal performance of two buildings, which are constructed according to the TS 825 in Mardin and Istanbul cities were evaluated to show the importance of thermal mass in hot-dry climates. # 2006 Elsevier B.V. All rights reserved.
1. Introduction Energy issue is becoming more and more important in today’s world because of a possible energy shortage in the future and also global warming. Since the Kyoto protocol signed in December 1997, the majority of governments around the world have committed themselves to reducing the emission of the greenhouse gases. Efficient use of energy has become a key issue for the most energy policies. Buildings are one of the most significant energy consumers. Across the IEA countries, buildings consume over half of all electricity and one-third of natural gas, and are responsible for more than one-third of all greenhouse gas emissions [1]. Therefore, sustainable design and construction strategies are of great importance nowadays. Anyhow, one may say that sustainability was already a driving force in the past, showing its validity in those days in different
* Tel.: +90 212 293 1300; fax: +90 212 251 4895. E-mail address: [email protected]. 0378-7788/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2006.08.004
forms and techniques. Therefore, from Vitrivius till today, problems and precautions in design and construction did not change fundamentally, although a lot of development was seen in materials and technology [2]. Of course, these developments may have had some negative effects. Since the Turkish standard is considering only heating energy conservation by using degree-day concept, Istanbul and Mardin are considered in the same zone, however those are in temperatehumid and hot-dry climatic zones, respectively. Energy efficient design strategies for these zones are significantly different from each other as it can be easily seen in the traditional design. In this study thermal performance of two buildings, which are constructed according to the TS 825 in Mardin and Istanbul cities were evaluated to show the difference in climatic effects of two regions on building energy performance and importance of thermal mass of building envelope in hot-dry climate. The results are supported by a student workshop, which is carried out for of a traditional house and a contemporary house in Mardin area, to compare their thermal behavior via both measurements and questionnaires.
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307
2. Energy efficient design strategies in temperatehumid and hot-dry climates The most important design parameters affecting indoor thermal comfort and energy conservation in building scale are site and orientation of the building, distance between buildings, building form, optical and thermo-physical properties of the building envelope. Among these parameters building envelope, as it separates the outdoor and indoor environment, is the most important parameter. The climate of the Eastern Anatolian Plateau is relatively similar to desert climate. This region represents the hot-dry climate zones with a great temperature difference between day and night. Mardin displays the typical aspects of deserts where summers are quite hot. The city is located in southeastern Anatolia about 50 km from the Syrian boarder, lying between eastern longitudes 39–428 and northern latitudes 36–388. Istanbul is the representative city for temperatehumid climate of Turkey, locating on two continents, Europe and Asia with 418 north longitude and 298 east latitude. The both of the cities Istanbul and Mardin are considered in the same zone in TS 825-Turkish standards for building thermal insulation. When evaluating traditional architectural examples, it can be seen that designers were more sensitive and they presented the most suitable design and settlement examples for each climatic region. In hot and dry climatic zone in Turkey where the continental climate is effective, in traditional architecture examples, to benefit the time lag of the building envelope, materials with greater thermal mass have been chosen. These kinds of thermally massed envelope details are very convenient for continental climates, where the summers are very severe with high swings in daily temperature variations. This big thermal mass will slow down the heat transfer through the envelope and thus higher day-time temperatures will be reached
Fig. 1. The plan of the building.
indoors when outdoor air temperature is much lower and consequently more stable indoor thermal conditions will be provided. On the other hand this thermal mass, which has higher surface temperature on outer side will rapidly lose heating energy to the atmosphere via thermal radiation at night to start the next day from a cooler level [3]. When observing traditional examples, it can be seen that the transparency ratio of the building envelope is chosen as low as possible and the opaque parts of building envelope were constructed by the materials with a high heat capacity as thick as possible. The high heat capacity of the opaque component provides a high time lag for the transmission of the outside temperature to the internal area while the low transparency ratio minimizes the direct solar radiation gained through the windows.
Table 1 Details for external wall alternatives for the considered building Materials
d (m)
U (W/m2 K)
Concrete wall insulated inside
Plaster Concrete Insulation Plaster
0.02 0.12 0.06 0.02
0.55
Gas concrete wall insulated inside
Plaster Gas concrete Insulation Plaster
0.02 0.02 0.06 0.02
0.55
Masonary wall
Stone
1.20
1.42
Wall alternatives
308
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Table 2 Details for ceiling and floor the considered building Materials
d (m)
Internal wall
Plaster Concrete Plaster
0.02 0.08 0.02
Floor-ceiling
Glass mosaic Mortar Concrete Plaster
0.02 0.02 0.16 0.02
In temperate-humid climate it is not necessary to have a big thermal mass on the envelope, but thermal insulation is necessary since winter period is longer in this zone. For traditional architecture in this climate, bigger windows on the south fac¸ade are observed to get more direct solar radiation in winter. The north facades of the buildings are usually protected cooler winter wind by trees or other buildings. The distance between buildings should be arranged such that they should not obstruct their south direct solar radiation. In this study the same building has been thermally evaluated in case of it has been constructed in temperate-humid and hotdry zones to show the missing strategy of Turkish Standard taking those two climatic regions in one zone basing on the degree-day concept.
Fig. 2. Temperature variations for Istanbul in January.
Fig. 3. Temperature variations for Mardin in January.
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Fig. 4. Temperature variations for Istanbul in July.
3. Evaluation of thermal performance of the same building in Istanbul and Mardin The living room of a typical residential building has been considered for thermal evaluation in case of the building is constructed in Istanbul and Mardin with same envelope oriented to south as it is instructed in the Standard [4]. The living room is located in the intermediate floor of the building, so it is assumed that there is no heat flow through the ceiling and floor. The height and the floor area of the room are 2.80 m and 32 m2, respectively. The plan of the building is shown in Fig. 1. The external surface solar absorption coefficient is assumed as 0.7 and transparency ratio of the fac¸ade is 34%. Windows are double glass wooden frame. It has been assumed that heat
transfer coefficient of the external wall is 0.55 W/m2 K which is providing Standard’s requirement for Istanbul and Mardin. Different external wall details, which are providing this required U-value, have been examined to see the effect of the other thermo-physical properties of the envelope. One of the wall alternatives for Mardin is masonry wall with a high thermal mass of 1.2 m thickness, which is traditional wall type for this area. The U-value of the masonry wall is 1.42 W/m2 K, which is much higher than the Standard’s value. The ceiling and floor details are same for all alternatives. The details for external wall alternatives, ceiling and floor are given in Tables 1 and 2 [2]. Inner surface temperature of the external wall and indoor air temperature have been calculated by using finite difference
Fig. 5. Temperature variations for Mardin in July.
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Fig. 6. Heat flow through the south wall for Istanbul in January.
method [5,6] to see the thermal behavior of different wall details having same U-value and stone wall having higher Uvalue, but higher thermal mass at the same time. Thermal performance of wall types 1 and 2 in Istanbul and Mardin for January is shown in Figs. 2 and 3. As it can be seen in these figures, thermal performance of two wall details are significantly different from each other in the same city however the both of them are having same U-value. Moreover the same wall is showing very different thermal behavior in Istanbul and Mardin. In Figs. 4 and 5 July performance of wall types 1 and 2 is shown for Istanbul and Mardin. In addition to two wall types with 0.55 W/m2 K Uvalue, temperature variations for masonry wall with 1.42 W/ m2 K U-value is also shown in Fig. 5.
Significance of the temperature difference for the same wall in these cities can be easily observed in these figures. The inner surface and indoor air temperature are almost 10 8C lower for the masonry wall in July, however its U-value is almost three times higher than the other walls constructed according to the Standard. That means that thermal mass is more important than the U-value in hot-dry climate and energy conservation standards should certainly consider this property of the envelope in this climatic zone where cooling energy conservation is more important than the heating energy conservation. In Figs. 6–9 the heat flow through the total area of south wall of the room is seen for Istanbul and Mardin to keep the indoor air temperature at 19 and 24 8C, respectively, in the average day
Fig. 7. Heat flow through the south wall for Mardin in January.
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Fig. 8. Heat flow through the south wall for Istanbul in July.
of January and July. As parallel to the temperature variations, the amount of heat flow changes also significantly for the same wall in Istanbul and Mardin and walls 1 and 2 are providing different amounts of heat flow in the same city. The amount of heat loss for walls 1 and 2 is significantly different for the both cities as it can be seen in Figs. 6 and 7, however both of the walls have the same U-value. Moreover, in the comparison of Figs. 6 and 7 it is seen that there is heat loss through the both of walls 1 and 2 in Istanbul, but for the certain hours wall 1 is providing heat gain in Mardin in January. These results show that heating energy consumptions will be significantly different for the different walls in the same city and for the same wall in the different cities representing temperate-humid and hot-dry climates, however degree-days are similar for these cities. The similar results are observed for summer period as it is illustrated in Figs. 8 and 9. For the summer heat flow calculations, the traditional masonry wall is also examined for Mardin in July. As it can be seen in Fig. 9, masonry wall with higher U-value is providing the least heat gain in Mardin for the average day of July. Therefore, for Mardin, where the summer
conditions are severe and hot period is long, the masonry wall with big thermal mass is recommended in this climate. Wall 1 is having better thermal performance in the both cities in January, but in July wall 2 is better than wall 1 as it is observed in Figs. 6–9. The heating and cooling loads of the whole flat with wall types 1 and 2 in Istanbul and Mardin are given in Fig. 10. The heating and cooling loads for masonry wall in Mardin are also included in the figure. The heating and cooling loads have been calculated for the flat, which plan is given in Fig. 1, for the heating and cooling periods of Istanbul and Mardin. The heating and cooling periods for these cities are determined basing on the meterolgical data of 10 years [7,8]. Temperature data for 10 years between 1993 and 2003 for these cities is given in Fig. 11. As it can be easily seen in Fig. 10, the walls 1 and 2 are providing different heating and cooling loads in the same building in Istanbul and Mardin however their U-values are same. The masonry wall is proving the least cooling load in Mardin repesenting the hot and dry climate, in spite of its much bigger U-value. Considering the heating and cooling loads together, wall 1 is better for Istanbul for
Fig. 9. Heat flow through the south wall for Mardin in July.
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Fig. 10. Heating and cooling loads of the flat for the selected wall types.
the considered case and masonry wall is the best for Mardin area for energy conservation. In order to support these results a case study has been carried out in Mardin to take measurements in a traditional and a modern house at the end of may in 2004 which is in the cooling period for this hot-dry area. The traditional house has been constructed in the middle of the 17th century with masonry walls in the old settlement in Mardin where all energy eficiency strategies of hot-dry climate have been apllied. The modern house is located in the new part of the city and this building has been constructed according to the above mentioned Turkish Standard, TS 825 [9]. The details of the case study buildings are given below. 4. Case study for thermal evaluation of a traditional and a modern residential building in Mardin This case study is a part of a research project in which, design strategies in modern and traditional houses in hot and dry climate were examined at the end of May 2004. Since the design concepts of traditional and modern house are completely different, comfort conditions in these houses are also different. The objective is to demonstrate this difference by means of measurements and questionnaires. In this paper the study was simplified by using only measurements data
Fig. 12. View from exterior of Mungan House.
derived from the sample rooms chosen from modern and traditional houses. The traditional building, Mungan House, chosen for the measurements, is built in the middle of the 17th century. This building is a two story (with a ground floor) detached and terraced one-family house. The courtyard at the ground floor is surrounded by high walls and isolated from the street [10]. Mungan House is oriented to south-east (Figs. 12 and 13). Eyvan and revak; semi-open spaces, are used to create shady and cool places in open areas. The building envelope is masonry wall. Being located in a volcanic area, the basic material used in the local architecture is easily workable calcareous rock. Thermal properties of these materials are given in Table 3. The thickness of the walls is 0.8 m. Double-wooden frame windows have been divided into two parts. The upper parts of the windows provide lights in the room whereas the lower parts were closed with wooden shutters. Single glazed wooden window frame realize a U-value of 4.5 W/m2 K for windows. The modern building, Demir House, is situated in the new part of the city. It was built after 1990. This building is a two
Fig. 11. Temperature data for Istanbul (Go¨ztepe station) and Mardin between 1993 and 2003.
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Fig. 13. Plan of Mungan House.
story (with a ground floor) detached building. First and second floors are used as separate residential (Figs. 14 and 15). The building envelope is reinforced concrete structure with brick walls. No shading device was used on the facades. The thickness of the walls is 0.25 m. Thermal properties of the wall
materials are given in Table 3. Double glazed PVC window frame with a U-value of 2.6 W/m2 K is used in this building. The building was constructed by contemporary techniques in compliance with the instructions of Energy Conservation Standard of Turkey (TSE 825-1998). This regulation gives the
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Table 3 Thermal properties of the wall materials for traditional and modern houses Walls
Main wall material
Thickness (m)
l (W/m K)
Cp (kJ/kg 8C)
r (kg/m3)
Stone wall Brick wall
Mardin stone Brick
1.2 0.19
2.33 0.46
0.88 0.92
2200 1000
limit values of overall heat transfer coefficient of building envelope (U-value) independently from orientation and building form and consequently specifies the upper limit values of annual heat loss through the buildings. Although this new regulation is an important step to achieve energy conservation, its methodology is inadequate and incomplete for hot and dry climatic region from the thermal comfort point of view. Another weakness of the regulation is to assume and evaluate different cities, which have different climatic conditions, in the same climatic region as it is mentioned above. In order to evaluate indoor comfort level and the thermal performance of the building envelope, four rooms (two from the modern house and two from the traditional house) were chosen. All of the main facades of buildings in the old town are oriented to south, south-east or south-west. Therefore similarly oriented rooms are selected to enable the comparison of construction type of modern and traditional buildings for this study. During the field study the measurements have been taken in more rooms in these buildings and in another traditional building for thermal, visual and indoor air quality purposes. The results of all temperature measurements are similar and therefore, in this study the results are given only for the certain similarly oriented rooms as sample. These rooms with flat roof are all situated in the upper floor of the both houses. For the first part of the measurements room number 1 in modern and traditional houses were chosen [11,12]. These rooms have also additional windows on north-west side in modern house and in southeast and north-east sides in traditional house. To understand the spatial variation of the comfort conditions in the rooms of modern and traditional houses, nine different points were chosen and the indoor air temperature at those points were measured every hour simultaneously. The height of
the measurement points is 1.20 m. Measurements’ points and the distance from surrounding walls were shown in Fig. 16. Some values measured in the afternoon were shown as examples in Table 4. Even the transparency ratio of the northern fac¸ade is much bigger, temperatures measured in the room remained over the comfort level whereas the range of the measured inside temperature in the room of traditional house were much smaller. From Table 4, the difference of temperature level between the modern and traditional houses and the importance of the overheating problem due to the construction strategies in hot and dry climate can be seen easily. For the second part of the measurements, room number 3 in modern and traditional houses were chosen. In order to evaluate the heat capacity and the time lag of the wall, surface temperatures, the air temperatures and the humidity were measured in the rooms simultaneously for 24 h. Measurement results were given in Figs. 17 and 18. As it can be seen in these figures, air and wall surface temperatures are much lower in the traditional building and they are almost always constant because of the big thermal mass of masonry wall. As parallel to the measurements, questionnaires have been carried out for 68 traditional and 32 modern buildings to determine the users’ perception for indoor environment. The questionnaire includes 34 questions about users’ thermal, visual and air quality perceptions. The questionnaire asks users how they feel in their room, living room, eyvan, and courtyard and identify their feelings by selecting a point between ‘‘cold’’, ‘‘cool’’, ‘‘normal’’, ‘‘warm’’ and ‘‘hot’’ alternatives. Users were asked to express their feelings both for winter and summer. In this study, only for summer, results for indoor air
Fig. 14. View from exterior of Demir House.
Fig. 15. Plan of Demir House.
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Fig. 16. Measurement points in Mungan (traditional) and Demir (modern) Houses. Table 4 Temperature measured at nine points at different hours Measurement points
Hours 15:00
A B C D E F G H I
16:00
17:00
Modern
Traditional
Modern
Traditional
Modern
Traditional
28.7 28.6 28.2 28.9 28.8 28.8 28.7 28.7 28.8
24.8 24.8 24.8 25.0 24.9 24.7 25.1 25.1 24.8
30.1 29.5 29.3 30.2 30.2 30.2 30.0 30.1 30.2
24.4 24.4 24.4 24.6 24.6 24.6 24.5 24.6 24.6
30.0 29.1 28.9 30.6 30.9 30.1 30.3 30.3 30.2
24.2 24.2 24.2 24.2 24.2 24.2 24.1 24.2 24.2
thermal perception of users for their rooms are given to make a thermal comparison between traditional and modern buildings in hot and dry climate (Fig. 19). The results of this questionnaire support the results of the measurements. As it can be seen in Figs. 17–19, under hot summer conditions, traditional house can provide cooler indoor
environment than the modern one. That means that masonry wall with big thermal mass will provide less cooling load for the traditional building in comparison to the modern building which has been built according to TS 825 in this hot-dry climate.
Fig. 17. Temperature results in Mungan House.
Fig. 18. Temperature results in Demir House.
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Fig. 19. User’s perception of indoor temperature in summer.
5. Conclusion As it can be concluded from the results of the theoretical and field studies, the heat transfer coefficient of the building envelope and the heat transfer amount calculated in steady state conditions are not sufficient to determine the real thermal performance of buildings. These, observed especially on the traditional construction technology, have a very important role in hot and dry climatic zone where the continental climatic effects are dominant. The Energy Conservation Standard of Turkey (TS 825) has made a significant mistake by neglecting the heat storage capacity of the building envelope especially for hot-dry climate. Since the heat capacity of the building envelope has an important role on the energy conscious design, it should certainly be taken into consideration in the south-east Anatolia region, in which the hot and dry climatic conditions prevail. As the current standard is based on degree-day concept to determine the climatic zones of Turkey, it delivers another important mistake by proposing the same design strategies for both Istanbul and Mardin. Therefore, theoretical and field studies are carried out for traditional and modern houses in these cities. Theoretical study has been carried out for a residential building constructed with different wall details providing required U-value of the standard in Istanbul and Mardin and with also traditional masonry wall in Mardin. The most important conclusion of this study is: the masonry wall is providing the least energy consumption for heating and cooling of residential buildings in Mardin, however its U-value is almost three times higher than the other walls. On the other hand, dynamic thermal evaluation shows that energy consumption of the building with different wall details are different in the same city in spite of their equal U-values. Moreover it has
been concluded that the same wall detail is providing different heating and cooling loads for residential buildings in Istanbul and Mardin. Therefore, we can say that the modern buildings in south-eastern Anatolia, which are constructed according to this standard, cannot correctly respond to the climate of the region and these two cities should not be considered in the same zone as the standard did by using degree-day concept. The results of the theoretical study are also confirmed by the results of the field study including the both of measurements and the users’ perception in questionnaires, which have been done in both traditional and modern houses in Mardin. The measurements have been carried out for different rooms in the selected residential buildings, but in this study only one sample is given. As a conclusion it is possible to say that, especially on the regions, where the continental climate is experienced thermal performance of buildings should be evaluated by a dynamic model of heat transfer calculations during the design stage, taking into account also the heat capacity of the building envelope as the function of its thermal mass to provide heating and cooling energy conservation in buildings in these regions. References [1] International Energy Agency, Online Source, http://www.iea.org. [2] Vitivius, The Ten Books on Architecture, Dover Publication, New York, 1960. [3] Z. Yılmaz, The effect of thermal mass on energy efficient design, in: Proceedings of the Sixth International Symposium on HVAC+R Technology, May, 2004. [4] I. Osanmaz, The Evaluation of Heating Energy Conservation Standard for Buildings for Hot-dry Climatic Zone of Turkey, Master Thesis, Istanbul Technical University, 2005 (advisor: Z. Yilmaz). [5] J.P. Holman, Heat Transfer, 4th ed., Mc-Graw Hill Book Co., New York, 1976. [6] Z. Yilmaz, Evaluation of built environment from thermal comfort point of view, ASHRAE Transactions, Part I 93 (1987). [7] Turkish State Meteorology Headquarter Publications, Ankara, 2004. [8] Turkish HVAC Engineers Handbook, Istanbul, 2004. [9] Turkish Standards-TS 825: Rules of Heat Insulation in Building, 1998. [10] F. Alioglu, Mardin urban texture and houses, History Foundation of Turkey (1988). [11] Conference and Exhibition of Workshop on Energy Efficient Design in South East Turkey (Mardin Case), ITU Faculty of Architecture, Istanbul, October 2004. [12] Z. Yılmaz, Studies on energy efficient design in ITU Sustainable Energy Research Group, in: Proceedings of the Energy Conservation and Insulation Congress and Exhibition for Sustainable Environment, Istanbul, October, 2004.