Yapı malzemelerinin güneş enerjisi karşısındaki termodinamik davranışı

Abstract

ÖZET Bu çalışmada, binaların ısıtılması amacıyla güneş enerjisinden faydalanma konusu pasif sistem çerçevesinde ele alınmıştır. Bu amaçla, opak bina kabuğundan emilebi lecek radyan enerji (güneş enerjisi) ve bu enerjinin iç mekâna iletilmesi konuları daha önce yapılmış yayınlara ve bu çalışmada gerçekleştirilen deneylere dayanılarak incelenmiştir. Deneylerde incelenen malzemeler, gelenek sel sıva malzemeleri (çimento, kireç, alçı); sıvasız kul lanılabilen duvar malzemeleri (tuğla, kerpiç, beton); po limer esaslı boya ve kaplama malzemeleri olmak üzere üç grupta toplanmıştır. Bu malzemeler üzerinde monokromatik yönlenmiş emme oranları, renk, pürüzlülük, kompasite deneyleri yapılmış, optik mikroskopla 25 defa büyütülmüş yüzey filmleri çe kilmiştir. Çimento numuneler üzerinde X-ışını analizleri de yapılmıştır. Yüzeylerin gerçek atmosfer şartlarındaki davranışlarını incelemek üzere, katkılı portland çimento su, beyaz çimento, alçı katkılı kerpiç, fabrika tuğlası, harman tuğlası, polimer katkılı-kireç esaslı kaplama mal zemesi ve PVA esaslı beyaz ve siyah boyalar üzerinde albedo deneyleri yapılmıştır. Çimento numuneler ile alçı katkılı kerpiç ve fabri ka tuğlasından hazırlanmış numuneler üzerinde laboratu varda simüle edilen periyodik rejim şartlarında ortam, yüzey ve kesit sıcaklıkları ölçülmüştür. Ayrıca bu mal zemelerin birim ağırlıkları, özgül ısıları ve ısı ilet kenlik katsayıları da deneyle bulunmuştur. Teorik ve deneysel incelemelerin sonucunda yüzeyle rin monokromatik yönlenmiş emme oranlarının yüzey rengin den, pürüzlülüğünden, sıcaklığından, rutubetinden ve yüze yi meydana getiren malzemenin iç yapısından farklı biçim ve derecelerde etkilendiği belirlenmiştir. Ayrıca ışınla rın geliş açısı da bazı yüzeyler için etkili olmaktadır. Gelen enerjinin dalga boyu dağılımı, tüm yüzeyler için etkili bir büyüklüktür. Isı iletimi açısından ise, hafif ve ağır malzemelerin birlikte kullanıldığı birden fazla tabakalı kompozit elemanlar daha uygun olmaktadır. Son olarak, yüzeyden emilen radyan enerji ve bu e nerjinin iç yüze iletilmesi açılarından etkili olabilecek ideal iklim tipleri belirlenmiştir. Daha sonra ülkemizin coğrafi bölgeleri için geçerli olan iklim özellikleri, Meteoroloji Bülten' ler inden faydalanarak belirlenmiş ve her bölge için uygun olabilecek opak bina kabuğu kesitle ri teklif edilmiştir. -viii-

SUMMARY THE THERMODYNAMIC BEHAVIOUR OF BUILDING MATERIALS SUBJECTED TO SOLAR ENERGY The increase of energy consumption and prices force men to find new energy sources. As clean and renewable, the solar energy. drew enthusiasm in the past. However, today, a more conservative approach is taken due to problem arising from the amount of this energy being changeable and the storage for a long period being very difficult. Nevertheless, the use of solar energy in heating the buildings is still interesting. The main systems for this purpose are divided into two groups: active and passive. For architect and materials scientists, the passive systems are more attractive. The main principle in this system is to let the solar energy (into the building) through the transparent portions of building envelope in the direction where is abundantly available solar energy and to prevent the escape of this energy to outside by means of the opaque parts of the building envelope. Taking the opaque building envelope exposed to solar energy throughout the day as having only an insulating function is considered a deficient view. It is necessary to take into consideration also the energy absorbed by the opaque surfaces and to investigate the possibilities of transfering this energy inside. For this purpose, firstly all relevant properties of solar energy reaching the earth should be defined and the factors affecting these properties should be known. Then, the radiative characteristics of opaque surfaces and the variables which influence these charac teristics must be determined. Lastly, it is necessary to examine in detail the transfer of this absorbed energy through the building materials (to inside). The present study is based on these principles and the solar energy gain through the opaque building envelope is examined on the basis of former researches by others and test results obtained in this study. From a review of the former investigations, the following points attract attention. - The amount and the spectral distribution of the solar energy reaching the building envelopes are depen dent on the atmospheric, geographical and meteorological -ix-and settlements properties of the region. Different re gions have different properties and amount of energy- gain. - The energy absorbed by opaque surfaces is affect ed by the angle of incidence and the spectral distribu tion of solar energy. The colour, texture, temperature and internal structure of the surface also influence the energy absorbed by the surface. - The solar energy absorbed by surface increases the sol-air temperature which is an important property as it determines the heat transfer through the material. - When the heat transfer occurs in the periodic regime, the variations of outer surface temperature are transmitted to the interiour surface with a certain phase lag ( t) and a decrease in amplitude, (8=(8)x/(8)o ). These characteristics are calculated approximately by the following equations. x / 1 At = / 2 sj D-7t-n (8)x = (8)0 -exp(-xYmc/D') where, x : thickness of material n : frequency. D : thermal heat diffusion coef f icient = A/O-C X : thermal conductivity ^ p : density c : specific heat (8)0 : amplitude of temperature changes of outer surface (8 )x : amplitude of temperature changes at a distance x from outer surface -In the periodic -regime, the most important mate rial constant is the thermal diffusion coefficient. Tests and testing materials are summarized below. The opaque building materials used may be classified in three main groups: - The exterior coatings for walls, cement, lime and gypsum based (traditional plastering materials) - Traditional wall materials without plaster (brick, adobe, concrete) The exterior polymeric coatings and paints (polyvinil acetate, polyacrylics, alkid) -x-i' The cements used in the production of samples are puzzolana Portland cement and white portland cement. Series of cement, gypsum and lime samples were produced with different water/binder ratios. Three sub-series were also produced with the same water-cement ratio but having different surface roughness and using another puzzolona portland cement purchased from a different factory. Adobe and adobe stabilized with lime and/or gypsum were also produced in the laboratory. On the other hand two kinds of brick were used: one produced in a brick-factory ; the other produced in countryside in a brick pile. The surface of the puzzolana portland cement samples series were covered by polyvinil acetate, polyacrylics paints and polyacrylics, alkid ready-made plaster. The monochromatic hemispherical reflectances, roughnesses, colours, compactnesses of the above surfaces have been determined experimentally. The 25 times magni fied surface films have been obtained using an optical microscope. X-ray analysis have been also, made on puzzolona and white portland cement samples. The above mentioned tests were aimed at determining directly the behaviour of opaque surface in response to radiant energy. On the other hand, albedo measurements were made on the following square surfaces of lxl m. : Puzzolona portland cement, white portland cement, adobe stabilized gypsum, factory brick, country brick, white and black painted surface (polyvinil acetate), white coated surface with a mixture of lime and polymer. On these surfaces, incident and reflected global solar energy and the surface temperatures were measured under real atmospheric conditions. The cloudiness was noted based on visual observation in addition to the meas urements of temperature and relative humidity. The sun angles were calculated theoretically. Unfortunately the spectral disribution of solar energy could not be meas ured, because the instrument needed for the measurement was not available. In the second part of the research the environment, surface and section temperatures were measured in period ic regime simulated in the laboratory on the puzzolona and white cement, adobe stabilized with gypsum and manu factured brick. These are traditional wall materials which may be used without plaster. Density, specific heat and thermal conductivity of these materials were deter mined experimentally. In this way, traditional building materials were compared with one another from the point of view of transfer of absorbed energy. In this investi gation it is accepted that there is no energy source in side. So only the behaviour of materials have been con sidered in heat transfer phenomena. -xi-The following general conclusions are drawn from the results theoretical and experimental investigation carried out in this work. - Albedo (reflectance) of PVA black paint and country brick with mm magnitute roughness surfaces are not effected by the angle of incident beam. The surfaces that were influenced in increasing order are: the lime and polymer based exterior white coatings, factory brick, puzzolana portland cement, adobe stabilized with gypsum, PVA white paint and white portland cement. A simple rule relating material properties to their behaviours is not available. - The surfaces investigated are evaluated as follows from the suitability point of view with respect to seasons considering the absolute values and the variations of their albedo. winter summer albedo, albedo, in the morning in the evening *... undesirable surface 100-70 0-10 **.. inconvenient surface 70-50 10-50 ***. convenient surface 50-10 50-70 **** the most convenient surface 10-0 10-100 -xii-- The monochromotic directional emittance (mde) in creases approximately 10% as the roughness of surface reaches a mm level. - Hue, the first component of the surface colour, defines the changing of the spectral distribution of mde; value, the second component, defines the amount of mde; chroma, the third component, defines the level of influence of hue. The evaluation related to the colour of surface must be taken into consideration with the structure of materials. Chemical composition of materials (electron configuration), a structural feature, influences the mde as it can change colour and/or texture of the surface. On the other hand, the type of interatomic bonding influ ences the mde significantly and independently. The increase of the crystallization ratio for the same material caused an increase in mde of about 10 %. - A general and simple relationship is not avail able between the porosity of the surface material and mde. - When the surface is wetted, if a larger of water film forms on the surface, its albedo decreases signifi cantly. But if no layer of water film forms, the albedo of the surface does not change by wetting. - the temperature of all surfaces decreases much more when the surface gets wet. - Cement based materials (o.c bigger) are more con venient than soil based materials (^smaller) in periodic regime heat flow. However soil materials (Asmaller) are superior to cement materials (o.c bigger) with regard to energy economy and in steady-state regime approach. - The heat storage which is an important parameter in periodic regime, is greater in the materials, with high. c.X and the surfaces with high sol-air temperature. ^ But in summer, of course the sol-air temperature must be lower for thermal comfort. - It is unsuitable to use o.ne layer element of o- paque envelopes unless the amplitude of outer environment temperatures is very small. It is necessary to use composite building elements made of heavy and light materials. - To design a composite section it is necessary to -xiii-define the dominating seasons and predicted function of building. In the last section of the present thesis, idealized types of climate are described with respect to the gain of radiant energy (solar energy) by opaque surfaces. Then the design of composite elements are given for both the energy absorbed by the surface and the energy tranfered to inside for the above idealized climates. The idealized climates which are valid for geographical regions of Turkey are determined in general making use of the long-term data in the bulletins of meteorology. Then an approximate correspondence between the geographical regions and these idealized climates have been established, and the convenient composite elements for the geographical regions of Turkey have been proposed in general. -xiv-