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Buhar difüzyonunun dış duvarların nem ile ilgili ve ısıl performansına etkilerinin değerlendirilmesinde kullanılabilecek bir yaklaşım

Başlık çevirisi mevcut değil.

  1. Tez No: 66393
  2. Yazar: M.CEM ALTUN
  3. Danışmanlar: PROF. DR. İMER SUNGUROĞLU
  4. Tez Türü: Doktora
  5. Konular: Mimarlık, Şehircilik ve Bölge Planlama, Architecture, Urban and Regional Planning
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1997
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Mimarlık Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 167

Özet

ÖZET Binalarda, dış ortam ile iç ortamı birbirinden ayıran dış duvarlarda, iki ortam arasındaki kısmi buhar basınç farklarından dolayı, normal şartlar altında, sürekli olarak bir buhar difüzyonu meydana gelmektedir. Böylece buhar difüzyonu, dış duvarlarda nemliliğin en önemli etkeni olarak ortaya çıkmaktadır. Farklı malzeme özelliklerine sahip katmanlardan oluşan dış duvarlarda, buhar geçirgenlik direnci düşük olan katmanlardan“rahat”bir biçimde geçebilen su buharı, buhar geçirgenlik direnci yüksek katmanlar önünde birikebilmektedir. Malzeme nemliliğinin, bazı malzeme özelliklerini değişime uğratması nedeni ile önemli yapısal sorunlara neden olduğu bilinmektedir. Özellikle, buhar difüzyonu sonucu oluşan malzeme nemliliğinin, malzemelerin ısı iletkenlik katsayıları ve buhar geçirgenlik özelliklerinde meydana gelen artışlar ve bozulmalar sonucu, dış duvarların kendilerinden beklenilen ısıl ve nem ile ilgili performansı yerine getirememeleri sözkonusu olabilmektedir. Bina yapımı tamamlandıktan sonra, duvarın kendisinden beklenilen performansı yerine getirememesi durumunda, bu tür sorunların ortadan kaldırılmasının çok zor, hatta bazı durumlarda olanaksız, olduğu, açıktır. Bu nedenden ötürü bu tür sorunların ortaya çıkıp çıkmayacağının tasarım aşamasında belirlenip, yine bu aşamada gerekli önlemlerin alınması, dış duvarın kendisinden beklenilen performansı sürekli olarak karşılayabilmesi açısından, önemlidir. Bu çalışmada; tasarım aşamasında, farklı dış duvar seçenekleri arasında ısıl ve nem ile ilgili performanslanna bağlı olarak bir değerlendirme ve bunun sonucunda bir seçim yapma olanağı veren veya mevcut binaların dış duvarlarının ısıl ve nem ile ilgili performanslarının değerlendirilmesinde ve karşılaştırılmasında kullanılabilecek bir yaklaşım ortaya koyulmuştur. Yaklaşım ile gerçekçi sonuçlar elde edebilmek amacı ile; hesaplamalarda, gerçeği en iyi yansıtacak dış ve iç iklimsel verilerin kullanılması ve dış duvarı oluşturan malzemelerin fiziksel özelliklerinde, zamana ve duvar içinde, çevresel etmenlerden kaynaklanarak, oluşan olaylara bağlı olarak meydana gelen değişimlerin ve bunların buhar difüzyonu ile ısı geçişi üzerindeki etkilerinin göz önünde bulundurulması, ilkelerinden yola çıkılmıştır. Yaklaşımdaki zamana bağlı ve tek boyutlu ısı geçişi ve buhar difüzyonu bağıntılarının çözümünde sonlu farklar yöntemi kullanılmış ve hesaplamalar için bir bilgisayar programı geliştirilmiştir. Ortaya koyulan yaklaşım ile dış duvar seçeneklerinin; istenilen zaman aralığındaki, duvar içindeki ve yüzeylerindeki, sıcaklık dağılımı, doymuş buhar basıncı dağılımı, kısmi buhar basıncı dağılımı, buhar difüzyon direnç faktörü dağılımı, bağıl nem oranı dağılımı, malzeme nemliliği oranı dağılımı, ısı iletkenlik katsayılarının değişimi ve duvarda meydana gelen saatlik ısı geçiş miktarı gibi ısıl ve nem ile ilgili performans ölçütlerinden yararlanarak karşılaştırıp, seçim yapmak olanaklıdır. Çalışmanın kapsamında, geliştirilen yaklaşım kullanılarak, ısı yalıtım malzemesinin yeri ve malzemesine bağlı olarak geliştirilen dış duvar seçeneklerinin, Türkiye' nin farklı iklim bölgelerindeki çevresel etmenlere bağlı olarak gösterdikleri ısıl ve nem ile ilgili performanslannı ortaya koyan bir uygulama çalışması da yapılmıştır. XV

Özet (Çeviri)

SUMMARY AN APPROACH FOR APPRAISING THE EFFECTS OF WATER VAPOR DIFFUSION ON THE THERMAL AND MOISTURE PERFORMANCE OF EXTERIOR WALLS Chapter 1 : Introduction Today the built environment became a complex system fulfilling the user's physiological, psychological, social - cultural requirements and the requirements related to the activities of the user, influenced by the natural - artificial, social, cultural environmental factors. Considering the built environment at the building level; it is a system, consisting of subsystems with various functions. Those subsystems are; the structural system, the service systems and the functional building elements. The functional elements, on the other hand, are; the external envelope, floors, stairs, windows and doors and indoor walls. The external envelope consists of external walls, roofs and floors in relation to the external environment. As the most important reason for erecting buildings is 'environmental control', the external envelope, is the most important one among the building elements, from this point of view. The most important external environmental factors are the climatic elements. The external envelope acts in some respects as a physical barrier and in some respects as a filter. In this way some external environmental factors are excluded and others are admitted selectively. Sometimes it is not possible, for the external envelope, with its barrier and filter functions, to keep the internal volume at the conditions that are required and supplementary climatisation is needed. In this relation the external envelope has also the function of preventing energy losses. The behavior shown by the external envelope under those changing internal and external environmental conditions, is the performance of the external envelope. Since the beginning of the 20th century new building and structural systems are used in building production. In time it has been seen that they had not only advantages but also some disadvantages from the point of view of building physics. Especially external walls, an important part of the external envelope, in steel or reinforced concrete frame buildings, became partitions between external environment and internal volume, without of their earlier load bearing function. Because of this it is an important design criterion that the external wall should be as 'light and thin' as possible for transmitting less load to the structural system. So it is necessary to design an external wall consisting of different layers of various materials, fulfilling different functions. Nearly all building materials may be exposed to moisture during construction and the subsequent life of the external wall, i.e. building. This moisture is transferred through the wall in the form of water or water vapor. The different layers resist the moisture transfer due to their different material properties i.e., resistance factors. Moisture is accumulated in front of XVIlayers with high resistance factors or extraordinary amounts of moisture is captured in the wall due to design or construction failures. As moisture is affecting the thermal and moisture performance of walls, it can cause important defects. After the building is erected it's very expensive or sometimes impossible to remove those defects. So it is very important to prevent those defects in the design stage. Since defects caused by water vapor diffusion, a kind of moisture transfer, appeared in building construction, many steady state and transient methods have been developed to predict the effects of water vapor diffusion. The most popular among them is the steady state, Glaser graphical method. As the steady state methods assume that there are no daily or seasonal changes in the climatic conditions outdoors it is difficult to obtain actual results from the predictions. There is no such problem in transient methods. Both the steady state and transient prediction methods assume that there are no effects of moisture, caused by damp diffusion, on the properties of materials used in the wall construction. This is another reason for difficulties in obtaining actual results from the predictions. It is possible to design various alternatives of wall construction with different materials. Another problem is the selection of the alternatives from the point of view of thermal and moisture performance. The aim of this study is to develop an approach in order to appraisal the effects of vapor diffusion on the thermal and moisture performance of external walls for decision making among the designed alternatives, during the design stage or in existing walls. Two important criteria have been used in evaluating the approach : 1. To take into consideration the hourly, daily and seasonal fluctuations of climatic element values, 2. To take into consideration the effects of vapor diffusion on the material properties. Chapter 2: Effects of Vapor Diffusion on the Thermal and Moisture Performance of External Walls The thermal performance requirements for external walls are as follows:. Low heat losses ( during the season when heating is needed ),. Low heat gains ( during the season when cooling is needed ),. Ability of heat storage,. Internal surface temperature should be at a desired level,. Durability against high or low temperatures,. Durability against thermal movements. The moisture performance requirements for external walls are as follows:. To prevent from physical, chemical, electrochemical, biological defects caused by accumulated moisture,. To prevent from esthetic deterioration caused by accumulated moisture on the wall surfaces. The thermal and moisture performance of external walls is affected by moisture accumulated in the wall. Moisture comes from different sources into the wall construction:. Moisture in the air. Construction moisture. Precipitation. Ground water. Leakage XVIIMoisture is transferred by;. Diffusion,. Molecular movement,. Water movement due to capillary, pressure differences, gravity or thermo- osmosis. Moisture is fixed in the wall construction either by sorption or as free water. The main effects of moisture on the wall construction are: Decreasing mechanical durability, Corrosion of metals. Efflorescence, Mould and decay, Frost damages, Increasing heat transfer, Decreasing vapor diffusion resistance. Under normal conditions the main cause of moisture accumulation in the wall construction is water vapor diffusion. The moisture is fixed in the wall mainly by sorption and its most important effects on the external wall performance are increasing heat transfer and decreasing vapor diffusion resistance. Chapter 3: Factors Causing the Effects of Vapor Diffusion on the Thermal and Moisture Performance of External Walls : Environmental Factors, Wall Properties The most important environmental factors affecting vapor diffusion are the outdoor and indoor climatic elements:. Air temperature. Relative air humidity. Solar radiation. Winds Properties of the external wall are also affecting the vapor diffusion and on the other hand they are affected themselves by the accumulated moisture due to vapor diffusion. Those hygrothermal and optical wall properties are : Water vapor diffusion factor Capillary suction factor Sorption isotherms Heat conduction factor Specific heat Absorptivity ratio for solar radiation As vapor diffusion is mainly affected by climatic elements and hygrothermal and optical material properties it is important to consider the hourly, daily and seasonal fluctuations of the climatic elements and the interaction between water vapor diffusion and material properties in order to obtain actual results from any simulation method. Chapter 4: Methods for Prediction of the Effects of Vapor Diffusion on the Thermal and Moisture Performance of External Walls The water vapor diffusion methods consist of three parts: prediction modeling, environmental conditions, i.e. climatic elements and material properties. XVIIIThe methods, developed for predicting the effects of water vapor diffusion can be classified under two different types, due to the climatic elements used for prediction. In steady state prediction methods climatic elements like temperature or relative humidity are considered to be constant. Unsteady state or transient methods take daily and seasonal fluctuations of the climatic elements outdoors, into consideration. There are analytical steady state methods like the“Allgemeine Former method and the ”Glaser“ analytical method and graphical steady state methods like the ”Glaser“ graphical method and the ”Kieper“ graphical method. Transient methods for predicting the water vapor diffusion are the ”Husseini“ method and the ”Husseini- Ricken“ method. The most important effect of water vapor diffusion on material properties is the changes in the heat conduction factor value due to moisture content. There are mainly two methods for determination of the heat conduction factor of moist materials: The ”Cammerer“ method that is also used in DIN 4108 and the ”Künzel“ method. As the steady state methods assume that there are no hourly, daily or seasonal fluctuations in the climatic conditions outdoors it is difficult to obtain actual results from those predictions. There is no such problem in transient methods. Both; the steady state and transient prediction methods listed above, assume that there are no effects of moisture, caused by water vapor diffusion, on the properties of materials used in the wall construction. With the ”Künzel" method, which uses the moisture content and an additional coefficient together with the thermal conductivity coefficient in dry state, it is possible to calculate the actual thermal conductivity coefficient of moist material. Chapter 5: An Approach for Appraising the Effects of Water Vapor Diffusion on the Thermal and Moisture Performance of Exterior Walls The approach consists of three steps: 1. The choice of the climatic conditions outdoors and indoors and the external wall properties, 2. Calculation of the heat and water vapor flux in the wall and its effects on thermal and moisture performance of walls, 3. The choice of one solution from the designed external wall construction alternatives, due to their thermal and moisture performance. The following properties of each designed external wall construction are needed for appraising the effects of vapor diffusion on the thermal and moisture performance: The thickness and arrangement of the layers, the hygrothermal properties of each layer material, optical properties of the surfaces and orientation of the wall. Also needed for determination are; the hourly outdoor temperatures, relative humidity and solar radiation values of the climatic region where the building, i.e. the external wall is considered to be The main calculation steps of the approach are as follows:. Choice of the layer thickness Ax and time interval At,. Determination of the temperatures of the surfaces and Ax - layers,. Determination of the saturated vapor pressure of the surfaces and Ax - layers,. Determination of the partial vapor pressure of the surfaces and Ax - layers, XIXDetermination of the partial vapor pressure of the surfaces and Ax - layers, Determination of the vapor diffusion resistance factor of each Ax - layer, Determination of the vapor flux between the air and the surfaces and between each Ax - layer, Determination of the moisture content as a function of vapor diffusion of the surfaces and Ax - layers, Distribution of the moisture content above the critical value due to capillary suction coefficient Determination of the relative humidity values as a function of moisture content of the surfaces and Ax - layers, Determination of the thermal conductivity coefficient of each material layer depending on the moisture content, Determination of the heat diffusivity coefficient, Determination of the heat flux, After the effects of water vapor diffusion on thermal and moisture performance have been calculated the external wall construction alternatives can be appraised according to the following performance criteria: Water vapor diffusion resistance factor distribution in the wall, Moisture distribution in the wall, Temperature distribution in the wall, Inner surface temperature, Thermal conductivity coefficients, Heat flux, Time lag of the wall construction, Reduction of the amplitude of the surface temperatures. Related to the appraising of alternatives a decision making during the design phase is possible. Chapter 6: Conclusion An approach for appraising the effects of water vapor diffusion on the thermal and moisture performance of external walls has been developed. Different from other methods, it takes into consideration; the hourly fluctuations of outdoor climatic elements, i.e. temperature, relative humidity and solar radiation, as well as the interaction between the moisture content, due to water vapor diffusion, and the material properties, i.e. thermal conductivity and water vapor diffusion resistance. A simulation computer program was also developed for the calculations of the approach. It is possible to use the approach for appraising wall construction alternatives during the design stage as well as for appraising existing external walls. Chapter 7: Application of the Approach for Appraising the Effects of Water Vapor Diffusion on the Thermal and Moisture Performance on Various Wall Types under Different Climatic Conditions of Turkey For the application of the approach; climatic conditions of the five different climate zones of Turkey have been chosen. The indoor climatic conditions were chosen as constant. Three different wall constructions with various placements of the polystrol xxthermal insulation and common building materials have been used for the appraisal. The simulation has been carried out, for a time interval of one year. The main results obtained from the application are as follows: There is mainly a moisture accumulation on the warm side of the polystrol thermal insulation due to its high water vapor diffusion resistance. Only in the dry - cold climate zone there is a moisture accumulation above the critical moisture content value in the wall construction with a thermal insulation located on the outer surface. The highest heat gains or losses are in walls with a thermal insulation located on the outer surface. There are no significant fluctuations in the thermal conductivity factors due to moisture content. XXI

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